review article interaction of local anesthetics with biomembranes...

Hindawi Publishing CorporationAnesthesiology Research and PracticeVolume 2013 Article ID 297141 18 pageshttpdxdoiorg1011552013297141

Review ArticleInteraction of Local Anesthetics with BiomembranesConsisting of Phospholipids and Cholesterol Mechanistic andClinical Implications for Anesthetic and Cardiotoxic Effects

Hironori Tsuchiya1 and Maki Mizogami2

1 Department of Dental Basic Education Asahi University School of Dentistry 1851 Hozumi Mizuho Gifu 501-0296 Japan2Department of Anesthesiology and Reanimatology University of Fukui Faculty of Medical Sciences 23-3 MatsuokashimoaizukiEiheiji-cho Yoshida-gun Fukui 910-1193 Japan

Correspondence should be addressed to Hironori Tsuchiya hirodentasahi-uacjp

Received 5 June 2013 Revised 13 August 2013 Accepted 17 August 2013

Academic Editor Yukio Hayashi

Copyright copy 2013 H Tsuchiya and M Mizogami This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Despite a long history in medical and dental application the molecular mechanism and precise site of action are still arguablefor local anesthetics Their effects are considered to be induced by acting on functional proteins on membrane lipids or on bothLocal anesthetics primarily interact with sodium channels embedded in cell membranes to reduce the excitability of nerve cellsand cardiomyocytes or produce a malfunction of the cardiovascular system However the membrane protein-interacting theorycannot explain all of the pharmacological and toxicological features of local anesthetics The administered drug molecules mustdiffuse through the lipid barriers of nerve sheaths and penetrate into or across the lipid bilayers of cellmembranes to reach the actingsite on transmembrane proteins Amphiphilic local anesthetics interact hydrophobically and electrostatically with lipid bilayers andmodify their physicochemical property with the direct inhibition of membrane functions and with the resultant alteration of themembrane lipid environments surrounding transmembrane proteins and the subsequent protein conformational change leading tothe inhibition of channel functions We review recent studies on the interaction of local anesthetics with biomembranes consistingof phospholipids and cholesterol Understanding the membrane interactivity of local anesthetics would provide novel insights intotheir anesthetic and cardiotoxic effects

1 Introduction

Local anesthetics clinically used so far have the commonchemical structure that is composed of three portions thehydrophobic moiety consisting of an aromatic ring theintermediate chain and the hydrophilic moiety consistingof an amino terminus The aromatic residue confers lipidsolubility on a drug molecule whereas the ionizable aminogroup confers water solubility The intermediate portionprovides the spatial separation between hydrophobic andhydrophilic end and structurally classifies local anestheticsinto amide type and ester type (Figure 1)

Because of the presence of substituted amino groupslocal anesthetics are referred to as the bases with pKa valuesranging from 77 to 81 at 37∘C for the amide type and from 84to 89 at 37∘C for the ester type [1] so they exist in uncharged

and positively charged form After injected local anestheticsshow an in vivo equilibrium between the uncharged and thecharged fraction of molecules According to the Henderson-Hasselbalch equation the percentage of unchargedmoleculesdepends on the pKa and medium pH (Figure 2) The phar-macokinetics and the mode of action of local anestheticsare closely related to their interaction with membrane lipidsUncharged molecules can predominantly diffuse throughthe lipid barriers of nerve sheaths and penetrate into andacross the lipid bilayers of cell membranes to reach theacting sites The pH-dependent effects of local anestheticshave been discussed in association with the pH changes ininflammation ischemia and several diseases [2ndash4]

It is generally recognized that local anesthetics primarilyaffect sodium channels in sensory nerve fibers and car-diomyocytes [5] Blocking peripheral nerves to induce local

2 Anesthesiology Research and Practice

NH C

O

OC

O

C

O

O

NH C C

O

N

NH C C

O

NHH

H

NH C C

O

N

H

NH C C

O

N

H

NH C C

O

N

H

NH C C

O

NHH

S

C

O

O

H

N

Lidocaine

Mepivacaine

Ropivacaine

Bupivacaine

Procaine

Cocaine

Benzocaine

Tetracaine

Propoxycaine

Prilocaine

Etidocaine

Articaine

2-Chloroprocaine

Amide local anesthetics Ester local anesthetics

N

C

O

O N

Cl

C

O

N O NH

C

O

O N

N

CH2CH3

CH2CH2

CH2CH3

CH2CH3

CH3

CH2CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH2

CH3

CH3

CH2CH2CH3

CH2CH2CH2

CH2CH2

CH2CH3

CH2CH2

CH2CH2

CH2CH2

CH2CH3

CH2CH3

CH2CH3

CH2CH3

CH2CH3

CH3

CH2CH2CH2CH3

CH3

CH2CH2CH3

CH3

COOCH3

H2N

H2N

H2N

H2N

H3CH2CH2CH2C

CHCH2C

OCH2CH2CH3

COOCH3

Figure 1 Representative amide and ester local anesthetics

anesthesia is achieved at the relatively high concentrations ofdrugs in local areas At lower concentrations certain localanesthetics also showmore subtle effects on hearts which areclinically important as an antiarrhythmic agent In additionlidocaine administered systemically may be useful for reduc-ing the excitability of nociceptive sensory neurons [6]

Local anesthetics block the conduction of nerve impulsesby affecting the influx of ions through transmembrane chan-nels Proposed mechanistic theories include the action onmembrane-embedded ion channels membrane-associated

enzymes membrane lipids and water In the protein-interacting theory local anesthetics are presumed to inhibitthe generation and conduction of action potentials in nervecells and cardiomyocytes by binding to the intracellular siteof voltage-gated sodium channels embedded in membranelipid bilayers (Figure 3) Local anesthetics specifically bind totheD4-S6 region of the 120572-subunit of neural sodium channelsSince this site is intracellular or cell interior drug moleculesare absolutely required to be in uncharged hydrophobic formfor accessing there

Anesthesiology Research and Practice 3

Uncharged (nonionized) lidocaine

QX-314 (N-ethyl lidocaine)

NH C

O

N

Charged (ionized) cationic lidocaine

NH C

O

N H

NH C

O

N

For lidocaine with the pKa of 78 at tissue pH of 74[uncharged lidocaine molecule][charged lidocaine molecule] = 04

For procaine with the pKa of 89 at tissue pH of 74[uncharged lidocaine molecule][charged lidocaine molecule] = 003

CH2CH3

CH2CH3

CH2CH3 CH2

CH2

CH3

CH2CH3

CH3

CH3

CH2

CH2

CH3

CH3

CH3

CH2

CH2

CH3

CH3

CH3

Log10 [uncharged drug][charged drug]= pH minus pKa

Figure 2 Uncharged and charged local anesthetics and permanently charged derivative

Local anesthetic Local anesthetic

Cell interior

Lipid bilayercell membrane

Sodium channel Sodium channel

Figure 3 Channel protein-interacting and membrane lipid-interacting local anesthetics

Drugs acting on proteinous channels receptors andenzymes also have the ability to act on lipid bilayers andmodify membrane physicochemical properties [7] Localanesthetics interact with membrane lipids to change fluidityordermicroviscosity and permeability ofmembranes [8] andalso influence the electrostatic potential across lipid bilayerswhich may affect the functions of voltage-gated ion channels[7 9] They are presumed to act on lipid bilayers withthe resultant alteration of the membrane lipid environmentssurrounding transmembrane proteins and the subsequentchange of protein conformation thereby influencing thechannel activity (Figure 3) Considering the diversity in theirchemical structures a specific single acting site within ionchannels has been suggested to be unlikely for all of localanesthetics [10] Local anesthetics affect various functionalmembrane proteins such as potassium ion channel cal-cium ion channel acetylcholine receptor adrenergic recep-tor GABAA receptor 120574-aminobutyric acid receptor glycine

receptor adenylate cyclase phospholipase A2 and NaK-

ATPase [11ndash13] Such broad spectra are interpretable by thefundamental action on a target common to local anestheticsmembrane lipids [14] A wide range of pharmacologicaland toxicological properties of local anesthetics cannot beascribed to binding to a single protein target alone [7] so it isreasonable to assume that the interaction of local anestheticswith lipid bilayer biomembranes contributes at least partlybut significantly to their anesthetic and toxic effects It hasbeen recently suggested that the responsibility of membranelipids for and the role of specific membrane component(s) inanesthetic mechanisms should be reverified [15]

2 Drug and Membrane Interaction

21 Membrane Preparation Because biological membranesare a very complex system biomimetic model membranes


OO

OH

O OO

OH

O OO

OH

O

H

O

OOP

OO O

O O

HOOH

O O

OO P

O

OPOHOO

O

H

O OO

OOP

O

1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (PO

PC)

1-Palmitoyl-2-oleoyl- sn-glycero-3-phosphoethanolam

ine (POPE)

1-Palmitoyl-2-oleoyl- sn-glycero-3-[phospho-L-serine] (PO

PS)

Cardiolipin

OH

OHOHOHOH

H

H

H

H

Cholesterol

OHH

OO

O

OOP

H

O

O

12-Dipalm

itoyl-sn-glycero-3-phosphocholine (DPPC)

OHHO NH

H

OOP

O

Sphingomyelin (SM

)

1-Palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1 998400-m

yo-inositol) (POPI)

CH3

CH3

CH3

CH3

H3C

minusOminusO

minusOminusO

minusOminusO minusO

OOP

OminusO

OOP

OminusO

+H3N+H3N+H3N+H3N

NH3+

Figure 4 Membrane lipid components

consisting of lipids have been employedmore frequently thannatural biomembranes for studying the drug and membraneinteraction [16] The advantages of using protein-free lipidmembranes are that one can easily manipulate the reactioncondition and the membrane lipid composition focus onlyon the interaction between drugs and membrane lipidsavoid the interference from other membrane componentsand quantitatively evaluate the membrane response to drugsModel membranes with the lipid bilayer structure can beprepared tomimic cellular and plasmamembranes of interestby adjusting their lipid compositions One of biomimeticmodel membranes widely used is a liposome the vesiclewith concentric lipid layers in which an aqueous volume isentirely enclosed bymembranous lipids Aunilamellar vesicleis characterized by a single lipid bilayer consisting of innerand outer leaflet

The major phospholipids constituting biological mem-branes are glycerophospholipids with the content of 40ndash60mol in total lipid fraction They consist of a glycerolbackbone on which two fatty acids are commonly esterifiedat the stereospecifically numbered sn-1 and sn-2 positionThe third carbon atom of a glycerol backbone supports thepolar head group composed of choline ethanolamine serineinositol and so forth which are linked to a negatively chargedphosphate group Representative lipids used for preparingbiomimetic membranes are shown in Figure 4 The mostabundant steroid in biological membranes is cholesterol thatcomprises four fused cycles in the trans-configuration ahydroxyl group at the 3-position a double bond betweenthe carbon 5 and 6 and an iso-octyl lateral chain at the 17-position Liposomal membranes are prepared by the aqueousdispersion of these authentic lipids (either a single compo-nent or a mixture of several lipids) or lipids extracted fromcells

22 Membrane Interactivity Analysis The drug and mem-brane interaction can be analyzed by different techniquessuch as electron spin resonance differential scanningcalorimetry nuclear magnetic resonance X-ray diffraction

and fluorometry Of spectroscopic and biophysical methodsfluorescence polarization has been most frequently used todetermine the change in membrane fluidity which is usableas an index for quantitatively evaluating the membrane inter-activity of drugs The term ldquomembrane fluidityrdquo may meana combination of different kinds of membrane componentmobility like the flexibility of membrane phospholipid acylchains the lateral or transverse diffusion of molecules in lipidbilayers and the membrane lipid phase transition

The polarization of fluorescence emitted by a membrane-incorporated fluorophore reflects its mobility in the sur-roundingmembrane lipid environments Fluorescence polar-ization is measured by excitation performed with monochro-matic light that is vertically polarized and the emissionintensity detected through an analyzer oriented parallel orperpendicular to the direction of polarization of the exci-tation light A variety of fluorophores such as 16-diphenyl-135-hexatriene (DPH) 1-(4-trimethylammoniumphenyl)-6-phenyl-135-hexatriene (TMA-DPH) N-phenyl-1-naphthyl-amine (PNA) and n-(9-anthroyloxy)stearic acid (n = 26 9 and 12 n-AS) are usable for measuring fluorescencepolarization These probes penetrate into membranes toalign with phospholipid acyl chains and locate in differentmembrane regions based on their chemical structures andlipid-interacting properties indicating the fluidity of themembrane region specific to each individual probe Theyare subject to the rotational restriction imparted by lipidbilayer rigidity or order Drugs interact with lipid bilayersto produce more fluid (less rigid) or disordered membraneswhich facilitate the probe rotation to emit the absorbedlight in all directions resulting in a decrease in fluorescencepolarization On the contrary more rigid (less fluid) orordered membranes produced by drugs disturb the proberotation to emit the absorbed light in all directions resultingin an increase in fluorescence polarization Compared withcontrols decreased and increased polarization means anincrease of membrane fluidity (membrane fluidization) anda decrease in membrane fluidity (membrane rigidification)respectively


3 Local Anesthetic Membrane Interaction

Yun et al [17] investigated the effects of lidocaine bupi-vacaine prilocaine and procaine on synaptosomes isolatedfrom bovine cerebral cortex and liposomes prepared withextracted lipids by measuring the fluorescence polarizationwith 2-AS and 12-AS They showed that these local anes-thetics increased the membrane fluidity by preferentiallyacting on the hydrocarbon interior Tsuchiya et al [18 19]reported that lidocaine prilocaine bupivacaine ropivacaineand mepivacaine interacted with liposomal membranes toincrease the membrane fluidity by measuring DPH TMA-DPH and PNA fluorescence polarizationThey also revealedthat the interactivity with lipid bilayer membranes is to agreat extent consistent with the local anesthetic potency[20] Local anesthetics are speculated to interact with lipidbilayers to rearrange the intermolecular hydrogen-bondednetwork among phospholipid molecules in association withthe liberation of hydrated water molecules on membranesand also alter the orientation of the PndashN dipole of phos-pholipid molecules resulting in an increase in membranefluidity [17] However themembrane lipid-interacting theoryhas been criticized as to whether local anesthetics can affectbiomembranes at clinically relevant concentrations whetherlocal anesthetic molecules in charged form can interact withlipid bilayers and whether local anesthetics like bupivacaineand ropivacaine can stereostructure-specifically act on lipidmembranes to show the potency different between stereoiso-mers These subjects are discussed in Sections 4 5 6 and 8

4 Membrane Interaction at ClinicallyRelevant Concentrations

The concentrations of lidocaine typically used in the clinicalsetting for dentistry are 1ndash3 (wv) [14] At 003ndash008 timesthese concentrations Tsuchiya and Mizogami [20] appliedlidocaine to liposomal membranes consisting of 100molDPPC or POPC and found that lidocaine increases the mem-brane fluidity by determining DPH fluorescence polarizationdecreases At 003ndash025 times lower concentrations of usuallyadministered 0125ndash075 (wv) [21] Mizogami et al [19 20]revealed that bupivacaine and ropivacaine interact with nervecell-mimetic membranes to increase the membrane fluidityresulting in decreases in DPH PNA and TMA-DPH fluores-cence polarization The interaction of local anesthetics withnerve cell membranes at clinically relevant concentrationsis supported by the fact that membrane-interactive agentsincluding local anesthetics are more effective in modifyingthe physicochemical property of biological membranes thanartificial model membranes [17]

Onyuksel et al [22] reported that bupivacaine enhancedthe carboxyfluorescein release from liposomes withincreasing the cardiolipin content in liposomal membranesTsuchiya et al [23] found that bupivacaine increases thefluidity of 25ndash125mol cardiolipin-containing membranesto decrease DPH fluorescence polarization at 10ndash50120583Mwhich corresponded to the blood concentrations for freebupivacaine to produce the cardiac collapse and depress the

myocardial function When dogs were administered withbupivacaine of the cumulative dose of 217 plusmn 26mgkg themean plasma concentration of free and total bupivacaineat cardiovascular collapse was 20 and 63 120583M respectively[24] The dose of bupivacaine of 72ndash88mgkg caused thearrhythmias of dogs in which the mean concentrationof free and total bupivacaine in plasma reached 4 and17 120583M respectively [25] In the range of these cardiotoxicconcentrations bupivacaine is able to interact withcardiolipin-containing biomembranes and significantlychange the membrane fluidity

The membrane effects were frequently investigated bymeasuring fluorescence polarization with DPH in previ-ous studies [19 20 23] The degrees of local anesthetics-induced changes inDPHpolarization correspond to the func-tional changes of lipid bilayer membranes and membrane-embedded proteins [23 26 27] possibly producing thepharmacologic and toxic effects of local anesthetics

Membrane-acting drugs accumulate in lipid bilayers andtheir local membrane concentrations are much higher thantheir concentrations in the bulk aqueous phase to showthe intramembrane concentrations being hundreds of timeshigher than the aqueous concentrations [28] Their con-centrations in lipid bilayer membranes are consistent withthe properties of local anesthetics to interact with biomem-branes and modify the membrane fluidity at clinically rele-vant concentrations While general anesthetics interact withbiomembranes as well as local anesthetics do they showthe water-membrane interfacial concentrations much higherthan the concentrations in bulk hexane [29] Kopec et al[7] speculated that the drug dosage necessary to effect aprotein-mediated response may be higher than that neededfor amembrane-mediatedmechanism so clinical dosages fortargeting membranes may be lower They also suggested thatthe drugmembrane concentration is few orders ofmagnitudehigher than typically found in plasma

5 Membrane Interactivity Depending onLipid Components

51 Lidocaine Derivative QX-314 One reason the membranelipid-interacting theory is controversial is the generalrecognition that the pharmacological activity of chargeddrugs is negligible when they are applied extracellularlyQX-314 (N-(26-dimethylphenylcarbamoylmethyl)triethyl-ammonium chloride N-ethyl lidocaine) is a quaternaryderivative of lidocaine whose structural difference is only anN-ethyl group but renders its parent structure permanentlycharged andwater soluble (see Figure 2 forQX-314 structure)In contrast to lidocaine this cationic agent shows only veryslow penetration into membrane lipid bilayers and cannotreadily cross lipid barriers [30] In previous experimentsextracellularly applied QX-314 was not effective in blockingaction potentials whereas the intracellular application ofQX-314 exerted the significant effects Surprisingly howeverLim et al [31] recently reported that extracellularly appliedQX-314 produced the long-lasting local anesthesiawith a slowonset in guinea pigs and mice challenging the conventional


notion that charged molecular species are inactive whenadministered from the external side of cells [32]

Tsuchiya and Mizogami [20] compared the interactivityof lidocaine and QX-314 with biomimetic model membranesby measuring DPH fluorescence polarization Lidocaineincreased the membrane fluidity of liposomes consisting of100mol DPPC and POPC but not QX-314 These compar-ative results agree with previous reports that charged localanesthetics were ineffective on cell membranes when appliedextracellularly [32] On the other hand QX-314 was revealedto decrease the DPH polarization values of both nervecell-mimetic membranes and liposomal membranes consist-ing of POPS 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphate(POPA) 1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (POPG) or cardiolipin and to show almost thesame membrane-fluidizing effect as lidocaine [20] Mem-brane lipid components and their compositions are very likelyto determine whether the charged molecules of local anes-thetics can modify membrane physicochemical properties ornot

52 Interaction with Specific Phospholipids A zwitterion is aneutral molecule with positive and negative electrical chargewithin the molecule The major membrane phospholipidsare zwitterions with the polar head groups consisting ofanionic phosphate and cationic quaternary ammonium cen-ters (Figure 4) When comparing phospholipid species QX-314 was not effective in changing the fluidity of biomimeticmembranes consisting of zwitterionic phospholipids suchas DPPC POPC and POPE [20] POPS has an additionalcarboxyl group neither POPA nor POPC has an ammo-nium group and cardiolipin has two phosphate groupsQX-314 significantly decreased the DPH polarization valuesof biomimetic membranes containing these anionic phos-pholipids to produce the membrane fluidization as well aslidocaine [20] Amphiphilic drugs like local anesthetics causenot only the hydrophobic interaction with phospholipidaliphatic acyl chains but also the electrostatic interactionwith phospholipid polar head groupsThe difference betweenanionic and zwitterionic phospholipid membranes suggeststhe electrostatic interaction between positively charged anes-thetic molecules and negatively chargeable phospholipidhead groupsThe interaction of local anesthetics with specificmembrane phospholipids also provides a mechanistic clue toexplain their structure-dependent cardiotoxicity as describedin Section 72

6 Change of Membrane Interactivity

61 Anesthetic Efficacy Reduced by Inflammation Inflam-matory diseases alter the pharmacodynamics and pharma-cokinetics of various drugs resulting in a decrease in theirbeneficial effects andor an increase in their adverse effects[33 34] Such an alteration by inflammation is well knownin clinical dentistry where the local anesthetic failure or thedifficulty to obtain satisfactory analgesia commonly occursin the situations of pulpitis and apical periodontitis [2] Theanesthetic efficacy of lidocaine mepivacaine and articaine

injections is remarkably reduced in the teeth with pulpitis[35 36] The presence of inflammation in dental pulp wasreported to cause the inferior alveolar nerve block to fail inapproximately 30ndash45 of cases [37]

62 Verification of Conventional Acidosis Theory Acidicmetabolites like lactic acid are increasingly produced andconcentrated in inflamed tissues thereby inducing the aci-dosis that lowers the tissue pH at least the order of 05ndash10 pH unit [38 39] The pKa values of almost all of localanesthetics in dental use are larger than 75 at 37∘C [1] so agreater proportion of administered drugs exist as positivelychargedmolecules in and near inflammatory lesions Becausecationic molecules are much less in membrane permeabilityandmembrane interactivity under acidic conditions the localanesthetic effects should be remarkably decreased leadingto the mechanistic theory that the local anesthetic efficacyis reduced by inflammatory tissue acidosis This acidosistheory has been conventionally accepted due to its theoreticalsimplicity and understandability and most frequently citedfor explaining the reduction of local anesthetic efficacyHowever even the fundamental subject as to whether localanesthetics decreasingly interact with lipid bilayers underacidic conditions has not been experimentally confirmed

Tsuchiya et al [40 41] compared the membrane effectsof local anesthetics with lowering the reaction pH and vary-ing the composition of membrane lipids When liposomalmembranes consisting of 100mol DPPC were treated atpH 59ndash74 with lidocaine prilocaine and bupivacaine of005ndash02 (wv) all of the tested local anesthetics increasedthe membrane fluidity in 15 minutes almost correspondingto their onset time Compared with pH 74 however theirmembrane effects were significantly decreased at pH 64 thatis almost comparable to inflamed tissue conditions [38] Sucha pH dependence in DPPCmembranes supports the acidosistheory

On the other hand lidocaine prilocaine and bupivacaineof 005ndash02 (wv) were revealed to interact even at pH 64with nerve cell-mimetic membranes prepared with POPCPOPE POPS SM and cholesterol resulting in a significantincrease in the membrane fluidity [40 41] Their membrane-fluidizing effects under acidic conditions are in conflict withthe conventional acidosis theory Local anesthetics showedless fluidizing effects at pH 64 on liposomal membranesconsisting of DPPC POPC POPE and SM whereas theireffects on POPS liposomal membranes were significantlygreater at pH 64 contradicting the relative decrease ofuncharged molecules but correlating to the relative increaseof charged molecules Phospholipid DPPC POPC POPEand SM are zwitterionic but POPS is acidic Under acidicconditions the cationic moieties of local anesthetics arelikely to electrostatically interact with the anionic headgroups of acidic phospholipids resulting in the modificationof membrane fluidity Therefore the tissue acidosis is notnecessarily related to the local anesthetic efficacy reduced byinflammation

Punnia-Moorthy [38] revealed that inflamed tissueslower only the order of 05 pH unit In animal experiments


the tissues were found to rapidly buffer the excess acidity afteracidic solution infiltrations and such a pH-buffering abilitywas more potent in inflamed tissues [42] These pathophys-iological features are also unfavorable for the conventionalmechanism based on tissue acidosis

63 PossibleMechanismAlternative to Acidosis Peroxynitritehas been implicated in the pathogenesis of various diseasesincluding inflammation Inflammatory cells produce perox-ynitrite by the reaction between nitric oxide and superox-ide anion both of which are present in inflamed tissuesPeroxynitrite is also known to react with lidocaine andbupivacaine [43 44] Ueno et al [41] focused on inflam-matory peroxynitrite responsible for the local anestheticfailure of inflamed tissues They treated nerve cell-mimeticmembranes with lidocaine prilocaine and bupivacaine of005ndash02 (wv) together with 50120583M peroxynitrite at pH74 and 64 The following DPH fluorescence polarizationmeasurements showed that the membrane-fluidizing effectsof local anesthetics were inhibited by the peroxynitritetreatment Such inhibitions are causable by peroxynitritedirectly acting on anesthetic molecules [45] and indirectly onmembrane lipids [46]

Since local anesthetic solutions are injected relatively nearto acutely inflamed tissues in dental anesthesia [14] peroxyni-trite could interfere with the maxillary andmandibular nerveblock by local anesthetics Inflammation possibly produceshyperexcitability or hyperalgesia [47 48] The absorptionof local anesthetics into the circulatory system to removethem from the administered site is promoted in inflammatorylesions [42] In addition to these pathophysiological changesinflammatory peroxynitrite is responsible for reducing theefficacy of topical and infiltration anesthesia

7 Membrane InteractionAssociated with Cardiotoxicity

71 Adverse Effects of Local Anesthetics Theadministration oflocal anesthetics is accompanied by the potential risk that israre but could be fatal complication The adverse effects oflocal anesthetics include systemic and local toxic reactionsand allergic reactions mostly related to ester-type drugs Thesystemic toxicity occurs in the cardiovascular and centralnervous system while the local toxicity may lead to neuro-toxicity transient neurological symptom ormyotoxicity [49]The cardiovascular system toxicity of commonly used amidelocal anesthetics has been clinically of much interest sincethe report of cardiotoxic effects of bupivacaine and etidocaine[50]

Local anesthetics especially bupivacaine cause cardiacdisorders that consist of the initial depression of intraven-tricular conduction followed by reentrant arrhythmia Greatconcerns over their cardiotoxicity include profound brady-cardia arrhythmia myocardial depression and eventuallycardiovascular collapse which are induced when the drugconcentrations in blood are elevated by an accidental intra-venous injection and an absolute overdose Although bupiva-caine has beenwidely used for cutaneous infiltration regional

nerve block epidural anesthesia and spinal anesthesia insurgery and obstetrics this long-acting agent is greater in tox-icity compared with shorter-acting amide local anestheticsThe rank order of cardiotoxic potency has been estimatedto be bupivacainegt ropivacainegt lidocainegt prilocaine [51]However the detailed mechanism(s) for structure-specific orstructure-dependent cardiotoxicity has not been clear

72 Interaction with Membrane Cardiolipin Althoughmyocardial ion channels are referred to as the primarytarget of local anesthetics another site of toxic action isassumed to contribute to the cardiotoxicity discriminationbetween structurally different drugs Besides binding to ionchannels local anesthetics act on membrane lipids to modifypermeability fluidity lipid packing order and lipid phasetransition of biomembranes [22 23 52] The inhibitoryeffects of anesthetic agents on ionic current generations alsorequire the molecular interplay of ion channel proteins andmembrane lipids [53]

As cardiotoxic drugs affect the permeability of mito-chondrial membranes local anesthetics also act on lipidbilayers and increase the membrane permeability with thepotency correlating to the seriousness of cardiotoxicityOnyuksel et al [22] reported that bupivacaine concentration-dependently increased at 100ndash400120583M the release of car-boxyfluorescein from 75mol cardiolipin-containing lipo-somes composed of egg yolk phosphatidylcholine and choles-terol although it showed no significant effects on themembrane permeability of liposomes devoid of cardiolipinTsuchiya et al [23] found that bupivacaine ropivacainelidocaine and prilocaine increase at 10ndash300 120583Mthe fluidity ofbiomimetic membranes with the potency being cardiolipin-≫POPA-gtPOPG-gtPOPS-containing membranes and thattheir membrane effects were increased with elevating theanionic phospholipid content in membranes They alsorevealed that local anesthetics interact with biomimeticmembranes containing 25ndash125mol cardiolipin to showthe rank order of membrane fluidization being bupi-vacaine≫ ropivacainegt lidocainegt prilocaine which agreeswith their relative cardiotoxicity

Since local anesthetics predominantly exist as positivelycharged molecules at physiological pH they should electro-statically interact with anionic phospholipidsWith respect tothe polar head structure DOPG and POPA have one phos-phate group whereas cardiolipin has two phosphate groupsIn the comparative study of anionic phospholipidmembranes[23] the relative DPH polarization change induced by bupi-vacaine was 100 040 and 049 for 10mol cardiolipin-10molPOPG- and 10molPOPA-containingmembranesrespectively which is consistent with the structural constitu-tion of a cardiolipin polar head group Cardiolipin is localizedin the mitochondrial membranes of cardiomyocytes to playan important role in heart functions energymetabolism andmembrane dynamics [54] A relation is presumed betweenthe interaction with mitochondrial membrane cardiolipinand the induction of cardiotoxic effects

Groban et al [24] reported that when open-chest dogswere received the incremental infusions of local anesthetics


free and total plasma concentrations at the cardiovascularcollapse were 10ndash38 and 39ndash100 120583M for bupivacaine 36ndash142 and 64ndash163 120583M for ropivacaine and 162ndash754 and 276ndash847 120583M for lidocaine While dosing dogs with bupivacaine72ndash88mgkg caused cardiac arrhythmia the plasma concen-trations of free and total bupivacaine reached 4 and 17120583Mrespectively [25] In the range of cardiotoxic concentra-tions bupivacaine interacts with 25ndash125mol cardiolipin-containing membranes more intensively and induce thegreater membrane fluidization compared with other localanesthetics [23]

Bupivacaine is more hydrophobic than ropivacaine lido-caine and prilocaine [18] The high hydrophobicity of bupi-vacaine is linked to its strong attraction to myocardialsodium channels slow dissociation from sodium channelsand access to mitochondrial membranes [55] The rankorder of interactivity with cardiolipin-containingmembranesis also correlated to that of cardiotoxicity being bupi-vacainegt ropivacainegt lidocainegt prilocaine Since bupiva-caine can readily reachmitochondrialmembranes evenwhenapplied on the outside of cells the interaction with cardiomy-ocytemitochondrialmembraneswould be responsible for thestructure-specific cardiotoxic effects of local anesthetics Acrucial role of anionic phospholipids like cardiolipin in theinteraction between local anesthetics and membrane lipidsmay also lead to the therapeutic possibility for local anestheticcardiotoxicity [56] as described in Section 73

73 Treatment of Cardiotoxicity with Lipid EmulsionAlthough newly introduced ropivacaine and levobupivacaineare less toxic they still cause the life-threatening eventsso the cardiotoxicity of long-acting local anestheticsremains an important problem The property of localanesthetics to hydrophobically interact with or selectivelybind to membrane lipids may provide a novel strategy fortreating their cardiotoxicity Weinberg et al [57] reportedthat the treatment with a lipid infusion shifted the doseresponse to bupivacaine-induced asystole of rats and dogsto increase the bupivacaine lethal doses Since then therapid infusion of lipid emulsions has been performed totreat the local anesthetic systemic toxicity in animal modelsand humans [58ndash60] The successful resuscitation of localanesthetic-induced cardiovascular collapse was achievedby an intravenous lipid infusion [61] whereas the failureof a lipid emulsion to reverse local anesthetic-inducedneurotoxicity is found in the literature [62]

For entrapping cardiotoxic drug molecules the com-monly used lipid emulsions are composed mainly of soybean and egg phospholipids with triglycerides of varyingchain lengths There are several lipid emulsions availablesuch as Intralipid Medialipide Structolipid and so forth[63] Although many case reports support the use of anintravenous lipid infusion for the cardiotoxicity of bupiva-caine levobupivacaine and ropivacaine the mode of actionof this treatment is not fully apparent One of proposedmechanisms is the ldquolipid sinkrdquo theory in which the morehydrophobic (lipid soluble) are drug molecules the greaterare their bindings to lipid emulsions enabling the emulsions

to act like a sink that drains cardiotoxic local anesthetics fromplasma [60 63] This theory is supported by the comparativeemulsification degrees of bupivacaine levobupivacaine andropivacaine in the decreasing order which correlate to thecardiotoxic intensities [64] The Association of Anesthetistsof Great Britain and Ireland released the guidelines for usinga lipid rescue therapy [65]

74 Cardiotoxicity Enhanced by Ischemia Ischemia potenti-ates the cardiotoxic effects of local anesthetics and hastensthe onset of fibrillation induced by local anesthetics Theelectrical ventricular fibrillation thresholds of bupivacaineand ropivacaine were decreased during myocardial ischemia[66] Pacini et al [67] revealed that the effect of lidocaineon sheep Purkinje fibers is greater under simulated ischemiathan that in normal conditions Freysz et al [68] also reportedthat the risk of cardiac disorders in bupivacaine anesthesiawas increased by ischemia However the detailedmechanismremains unclear for the local anesthetic cardiotoxicity alteredby ischemia Myocardial ischemia is characterized by asignificant lowering of tissue pH to 65 or less [69] Since localanesthetics show greater cardiotoxic not anesthetic effects inthe presence of acidosis [70] their enhanced cardiotoxicitymay be related to ischemic acidic conditions While localanesthetics block sodium channels to decrease the excitabilityof myocardia and cause the cardiac malfunction it has beencontroversial whether their blocking potency is reduced orenhanced at acidic pH Tan and Saint [4] reported that theblock of cardiac sodium channels by lidocaine was decreasedby lowering the pH

In the comparative study of Tsuchiya et al [71] bupi-vacaine and lidocaine of cardiotoxically relevant concentra-tions interacted with liposomal membranes consisting of100mol DPPC and peripheral nerve cell-mimetic mem-branes to increase the membrane fluidity and their mem-brane effects were decreased by lowering the pH from 74to 59 In contrast the fluidizing effects of bupivacaineand lidocaine on mitochondria-mimetic membranes werereversely increased at pH 59ndash64 compared with those atpH 74 Such increases under acidic conditions were greaterin the biomimetic membranes that contained the substantialamounts of cardiolipin and phosphatidylserine Positivelycharged bupivacaine and lidocaine are presumed to interactwith the negatively charged head groups of phospholipidsthereby increasing their membrane effects at acidic pHThe interactivity with cardiolipin-containing mitochondrialmembranes which is enhanced by lowering the pH isassociated with the local anesthetic cardiotoxicity enhancedby cardiac ischemia-relating acidosis

Besides ischemic acidosis reactive oxygen species [72]and mitochondrial membrane cardiolipin [54] may be alsoresponsible for enhancing local anesthetic cardiotoxicityIschemic and reperfused myocardia produce nitric oxidesimultaneously with generating superoxide anion both ofwhich react to form peroxynitrite that pathologically con-tributes to the myocardial ischemia-reperfusion injury byperoxidizing membrane lipids [73] The peroxidation ofmembrane lipids is accompanied by a change in fluidity of


liposomal and biological membranes Cardiolipin constitutesa significant portion of total mitochondrial phospholipids inmammalian cardiomyocytes and plays an important physi-ological role for hearts Since hydrophobic local anestheticsreadily reach mitochondrial membranes even when appliedextracellularly they can interact with membrane cardiolipin

Tsuchiya et al [74] treated biomimetic model mem-branes of varying lipid compositions with peroxynitrite andlocal anesthetics separately or in combination They foundthat peroxynitrite reacts with the membranes to decreasethe membrane fluidity with the potency being cardiolipin-gt SAPC-gtDPPC-containingmembranes Biomimeticmem-branes treated with 01ndash10120583M peroxynitrite were more rigidby increasing the membrane cardiolipin content from 0 to30mol suggesting that cardiolipin is a possible target forperoxynitrite Cardiolipin in cardiomyocyte mitochondrialmembranes preferentially reacts with peroxynitrite [75]While the peroxidizability of membrane lipids is enhanced asa function of the number of double bonds in lipid moleculescardiolipin in mammalian cells predominantly containslinoleic acid (C18 2) as a side-chain fatty acid [76] Linoleicacid constitutes 80ndash90 acyl chains of cardiolipin and tetrali-noleoyl cardiolipin is the most common molecular speciesin cardiomyocyte mitochondrial membranes Because of itshigh unsaturation degree cardiolipin is more susceptible toperoxynitrite compared with other membrane-constitutingunsaturated phospholipids Bupivacaine and lidocaine ofeach 200 120583M were revealed to exert the greater fluidizingeffects on biomimetic membranes containing 10mol car-diolipin by pretreating the membranes with 01 and 1120583Mperoxynitrite [74] which is attributable to the membranerigidity enhanced by peroxynitrite The drug and membraneinteraction is essentially influenced by the inherent fluidity ofmembranes as bupivacaine and ropivacaine aremore effectivein fluidizing the membranes that contain a certain amountof membrane-rigidifying cholesterol [77] Local anestheticshave the property to exert greater membrane-fluidizingeffects on the relatively rigid (less fluid) membranes thanthose on the relatively fluid (less rigid) ones Peroxynitritepreferentially decreases the fluidity of cardiolipin-containingbiomembranes and the resulting membranes are susceptibleto the interaction with local anesthetics which may be partlyassociated with the local anesthetic cardiotoxicity enhancedby myocardial ischemia

One may interpret that the membrane effects of bupiva-caine and lidocaine lead to the protection against myocardialischemic insults not the cardiotoxicity The cardioprotectiveeffects of local anesthetics were recently revealed to bemediated by their antioxidant and antiapoptotic activities[78 79] Although membrane-fluidizing bupivacaine andlidocaine can counteract the membrane rigidification by per-oxynitrite their membrane interactivities are not correlatedto such activities [44 79] Membrane lipids are completelyperoxidized in a very short time by peroxynitrite resultingin the structural and functional changes of membrane-constituting cardiolipin [80] The interaction of local anes-thetics with peroxynitrite-treated membranes seems to relateto their cardiotoxic effects not cardioprotective ones Themembrane interactivity of lidocaine was enhanced when

mitochondria-mimetic membranes containing cardiolipinwere pretreated with ischemic peroxynitrite but reducedwhen nerve cell-mimetic membranes not containing cardi-olipin were treated with inflammatory peroxynitrite [46]suggesting that the presence or absence of cardiolipin deter-mines whether the membrane interaction of local anestheticsis increased or decreased

Myocardial ischemia decreases the content of cardiolipinin mitochondria The 20ndash25 depletion was indicated forcardiolipin in rabbit heart subsarcolemmal mitochondria[81]The effects of local anesthetics onmembrane fluidity andpermeability are influenced by the composition of cardiolipinin membranes [22 23] The responsibility of the membraneinteraction for local anesthetic cardiotoxicity may be influ-enced to some degree by varying cardiolipin membranecontent

8 Discrimination between Stereoisomers

81 Local Anesthetic Stereoisomers More than 50 of cur-rently used drugs are composed of chiral compounds about90 of which have been clinically administered as a racemate(racemic mixture) consisting of an equimolar mixture ofenantiomers [82] The chirality of drug molecules generallyarises due to the presence of an asymmetric carbon Enan-tiomers are a pair of stereoisomers that are mirror images ofeach other and not superimposable called chiral

Drug enantiomers are discriminable in qualitative andquantitative pharmacology Typically one enantiomer ismore active or more toxic than its enantiomeric counterpartantipode Stereoselectivity (selectivity to one stereoisomer) islinked to the clinical advantage of using a single enantiomerover its antipode and racemate which increases the beneficialeffect and decreases the adverse effect Since the clinical use inthe 1960s bupivacaine had beenwidelymarketed as a racemicmixture of bupivacaine (rac-bupivacaine) that consists ofequimolar enantiomers S(minus)-bupivacaine of the levorotatoryconfiguration and R(+)-bupivacaine of the dextrorotatoryconfiguration (Figure 5) In the 1990s however an urgentproblem of its cardiotoxic effects led to the first develop-ment of an S(minus)-enantiomeric local anesthetic less toxicropivacaine [83]This trend was followed by the introductionof levobupivacaine into clinical practice as a pure S(minus)-enantiomer of bupivacaine [84]

Vladimirov et al [85] indicated the inhibition ratio ofrat neuronal channels to be 1 13ndash3 for S(minus)-bupivacaine andR(+)-bupivacaine Lyons et al [86] also reported that the rel-ative analgesic effect of S(minus)-bupivacaine to rac-bupivacainewas 087 for epidural pain relief in labor Lim et al [87]found the stereoselectivity that the analgesic effect of rac-bupivacaine is greater than S(minus)-bupivacaine for patients inlabor while Vladimirov et al [85] showed that the in vivonerve block by bupivacaine was less enantioselective (selec-tive to one enantiomer) at clinically used concentrations

Compared with the analgesic potency local anesthet-ics show a greater difference in cardiotoxicity betweenstereoisomers [51] Graf et al [88] found that an R(+)-enantiomer prolongs the atrioventricular conduction time


R(+)-bupivacaine(dextrobupivacaine)

S(minus)-bupivacaine(levobupivacaine)

R(+)-ropivacaine(dextroropivacaine)(levoropivacaine)

Racemic bupivacaine(rac-bupivacaine bupivacaine)

lt

lt

lt

NHO

NH

NHO

NH

NHO

NH

NHO

NH

NHO

NH

lowastlowast

S(minus)-ropivacaine

CH3

CH3CH3CH3

CH3

H3C

H3CH3C

H3CH3C

H3CH2CH2CH2CH3CH2CH2CH2CH3CH2CH2CH2C

H3CH2CH2CH3CH2CH2C

lowast lowast

Figure 5 Local anesthetic stereoisomers and their relative cardiotoxicity

more significantly than a racemate and an S(minus)-enantiomerin isolated guinea pig hearts perfused with 05ndash10120583M bupi-vacaine stereoisomers The relative atrioventricular time was154 for R(+)-bupivacaine and 130 for rac-bupivacaine versus100 for S(minus)-bupivacaine in the perfusion of each 10 120583MGroban et al [24] carried out the incremental escalatinginfusions of local anesthetics on open-chest dogs to thepoint of cardiovascular collapse Consequently they foundthat themortality is lidocaine ropivacaine S(minus)-bupivacaineand rac-bupivacaine in the increasing order and that thecomparative cardiotoxicity is 17 for rac-bupivacaine versus10 for S(minus)-bupivacaine Morrison et al [89] determinedthe electrocardiographic cardiotoxic effects of bupivacainestereoisomers on swine injected with increasing anestheticdoses and showed that the relativemedian lethal dosewas 187for S(minus)-bupivacaine versus 100 for rac-bupivacaine

The major mode of action of local anesthetics is referredto as the block of sodium potassium and calcium channels inthe nervous and cardiovascular system Valenzuela et al [90]found that bupivacaine blocks the relevant sodium channelsso enantioselectively that R(+)-enantiomer is 12ndash17 timesmore potent than S(minus)-enantiomer in isolated guinea pigventricular myocytes Valenzuela et al [91] also reported thatthe relative potency to block cloned human cardiac potassiumchannels was 16 for R(+)-bupivacaine versus 10 for S(minus)-bupivacaine Pharmacological studies have been exclusivelyfocusing on the interactions of local anesthetics with pro-teinous ion channels receptors and enzymes This is mainlydue to the stereostructure-specific actions on functional pro-teins that can be understood by the enantioselective affinity ofdrugs for proteins [83] However the protein-interacting the-ory does not fully explain the pharmacodynamic difference

between bupivacaine stereoisomers requiring an alternativeor additional explanation for the discriminable effects of localanesthetic stereoisomers

82 Enantioselective Membrane Interactivity Tsuchiya andMizogami [20] reported that local anesthetic stereoisomersincreased the fluidity of nerve cell-mimetic membranes withthe potency being S(minus)-enantiomer lt racemate lt R(+)-enantiomer and also the fluidity of cardiomyocyte-mimeticmembranes with the potency being S(minus)-ropivacaine lt S(minus)-bupivacaine lt R(+)-bupivacaine However these stereoiso-mers were not discriminated in interactivity with the mem-branes devoid of cholesterol When 40mol and morecholesterol were contained in membranes the membraneinteractivity was S(minus)-bupivacaine lt rac-bupivacaine ltR(+)-bupivacaine and S(minus)-ropivacaine lt R(+)-ropivacainewhich agreed with the rank order of their cardiotoxic-ity [77] Mizogami et al [92] also reported that bupiva-caine stereostructure-specifically interacted with biomimeticmembranes containing cholesterol to show the relativepotency consistent with the clinical features of bupivacainestereoisomers Membrane cholesterol is essential to the enan-tiomeric discrimination of local anesthetics

The membrane lipid-interacting theory is still con-troversial as to whether local anesthetics actually act onbiomembranes at cardiotoxically relevant concentrationsAt 5ndash200120583M covering the free plasma concentrations forbupivacaine stereoisomers to cause cardiovascular collapse[24] Tsuchiya and Mizogami [93] proved that bupiva-caine stereoisomers are able to modify the fluidity ofcardiomyocyte-mimetic membranes even at low micromolar


concentrations with the potency being S(minus)-bupivacaine ltrac-bupivacaine lt R(+)-bupivacaine While the bupivacaine-induced changes in DPH fluorescence polarization are con-sidered relevant to the clinical effects [23] the differencebetween stereoisomers varied depending on their testedconcentrations [93] which may account for the inconsis-tent results of previous studies The comparative effectsof R(+)-bupivacaine rac-bupivacaine and S(minus)-bupivacaineto produce arrhythmia and cardiovascular collapse differedin experimental and clinical studies [24 51 89] An anal-gesic effect of rac-bupivacaine was greater than that ofS(minus)-bupivacaine in humans [87] whereas bupivacaine wasmuch less enantioselective in the in vivo rat nerve blockat clinically used concentrations [85] When comparingthe blocking effects on human nerves S(minus)-bupivacaineshowed an almost similar potency to rac-bupivacaine [84]These inconsistencies are attributable to the concentration-dependent enantiomeric discrimination that the difference inmembrane interactivity between R(+)-bupivacaine and S(minus)-bupivacaine steeply increases at concentrations lower than50120583M [93]

83 Chirality of LipidMembranes Because drug enantiomersabsolutely differ in spatial configuration they should behavedifferently when interacting with chiral systems while notbeing in achiral environments such as an aqueous solutionIn fact enantiomeric compounds of each other show thedifferent interaction with other compounds that are alsoenantiomers Almost all of substances in the body are com-posed of enantiomeric biocompounds therefore chiral drugscould interact enantioselectively with such chiral macro-molecular targets The conventional protein-interacting the-ory emphasizes the importance of proteinous acting sitesbecause proteins are entirely made up of L-amino acids notD-amino acids Drug enantiomers form the different spatialrelationship in the asymmetric environments of functionalproteins that are composed of only L-amino acids Howeverthe action of enantiomeric local anesthetics on ion channelsis not necessarily consistent with the stereoselectivity that anR(+)-enantiomer is more potent than an S(minus)-enantiomerPrevious comparisons showed that S(minus)-bupivacaine blockedion channels with the potency equal to or greater than rac-bupivacaine [94 95]

Considering that amphiphilic drugs pharmacodynami-cally and pharmacokinetically interact with lipid bilayers itis reasonable to presume that membrane lipids could playa significant role in the in vivo discriminative recognitionof such drug molecules Local anesthetics penetrate intomembrane lipid bilayers align between phospholipid acylchains and occupy the space to perturb the phospholipidacyl chain alignment If local anesthetics stereostructure-specifically interact with chiral components in lipid bilayerstheywouldmodifymembrane fluidity with the potency beingdifferent between stereoisomers Tsuchiya and Mizogami[96] hypothesized that drugs interact enantioselectively withchiral lipid membranes to induce membrane fluidity orderand permeability changes that were discriminable betweendrug enantiomers The enantioselective lipid environments

to discriminate stereoisomers may be provided by phospho-lipids andor cholesterol with the chirality

The enantiomeric discrimination arises from the directinteraction with chiral centers Based on the hypothesis thata chiral carbon in their glycerol backbone may allow phos-pholipids to behave as a chiral component in membranesphospholipids were speculated to interact preferentially withmolecules having the same chirality and exhibit the selectivityto one enantiomer over its counterpart [97] However anymembrane phospholipids were not found to produce the dis-crimination of local anesthetic S(minus)-enantiomers from theirantipodes [77] Compared with phospholipids cholesterolhasmuchmore chiral carbons It is very likely that cholesterolenhances the chirality of lipid bilayers and its absolute config-uration modulates the membrane stereoselectivity [98]

In comparisons of the membrane interactivity betweenbupivacaine stereoisomers [20 77 93] the used probe DPHpartitions into the center of lipid bilayers [92] the membranecomponent cholesterol is located in lipid bilayers with itsbackbone embedded in the hydrocarbon core [99] andbupivacaine is preferentially localized in the hydrophobicmembrane core [19] Different polarization changes areattributed to the enantioselective interaction of bupivacainenot to the differential affinity of bupivacaine enantiomersfor specific membrane regions The opposite configurationsare considered to allow drug enantiomers to be discrimi-nated by their interaction with another chiral molecule inbiomembranes Membrane cholesterol contributes to such anenantioselective interaction by increasing the chirality of lipidbilayers The stereostructure and membrane interactivityrelationship supports the clinical use of S(minus)-enantiomersto decrease the adverse effects of local anesthetics on thecardiovascular system

9 Interaction Preference for MembraneMicrodomain Lipid Rafts

In the late 1990s the fluid mosaic model of Singer andNicholson for biomembranes was evolved to a more sophis-ticated concept especially concerning the membrane lipidcomposition and molecular organization It has becomeclear that biomembranes are not the simple bilayer structurewith uniformly distributed lipids but organized into phase-separated microdomains called lipid rafts with specific lipidcomponents andmolecular dynamics that differ from the sur-rounding liquid crystalline phase and bulk membranes [100]In lipid rafts cholesterol and sphingolipids are packed in ahighly ordered structure (liquid ordered) distinct from therest of membranes (liquid disordered)There is accumulatingevidence to indicate that lipid rafts are the target of variousdrugs including general anesthetic agents [101] However theinteraction of local anesthetics withmembranemicrodomainlipid rafts is unclear

Ion channels 120573-adrenergic receptors and signalingproteins were discovered to be localized to membranemicrodomains within the cardiovascular system [102 103]Drugs and chemicals were also revealed to initiate and facili-tate their effects by interacting with membrane microdomain


lipid rafts [104 105] As one of possible pharmacologicalmechanisms it is of much interest to know whether localanesthetics more intensively or selectively interact with thelipid rafts surrounding ion channels compared with overalllipid bilayers Kamata et al [106] recently reported thatlidocaine disrupted the raft structures in human erythrocytemembranesThey also reported that lidocaine reversibly pre-vented the raft formation in human erythrocyte membranessuggesting the involvement of raft-related signal transductionin the mode of local anesthetic action [107]

In order to verify the hypothesis that local anestheticscould interact preferentially with lipid rafts over nonraftmembranes Tsuchiya et al [108] compared the effects of50ndash200120583M local anesthetics on raft model membranescardiolipin-containing biomimetic membranes and car-diomyocyte mitochondria-mimetic membranes Local anes-thetics interacted with nonraft membranes to increase themembrane fluidity with the potency being R(+)-bupivacainegt rac-bupivacaine gt S(minus)-bupivacaine gt ropivacaine gt lido-caine gt prilocaine which is consistent with the rank orderof cardiotoxic potency These local anesthetics also actedon raft-like liquid-ordered membranes but any raft modelmembranes showed neither drug structure dependence norstereoselectivity in membrane interaction leading to theconclusion that the mechanistic relevance of membranemicrodomain lipid rafts to local anesthetics is questionable atleast in their effects on raftmodelmembranes Bandeiras et al[109] also reported that lidocaine interacted with raft modelmembranes although its interactivity was weaker comparedwith nonraft membranes

10 Anesthetic and PhytochemicalMembrane Interaction

101 Drug Interaction with Phytochemicals While the con-comitant use of medicines with medicinal plants or herbshas been increasing in popularity it potentially causes thebeneficial or adverse drug interactionwith plant componentsUnlike the drug-drug interaction however the interactionbetween drugs and phytochemicals (bioactive chemical sub-stances in plants) has not been extensively investigateddespite the possibility of more frequent occurrence thanexpected [110] Various drugs appear to show the antagonisticadditive and synergistic interactions with phytochemicals[111]

102 Capsaicin Topical or systemic lidocaine therapy isexpected to provide a novel management of neuropathic painsymptoms together with enhancing the utility by combin-ing with capsaicin [112] Capsaicin 8-methyl-N-vanillyl-6-nonenamide is a pungent component of plants belongingto the genus Capsicum such as chili pepper On the initialapplication this phytochemical shows an excitatory effect toproduce burning pain and hyperalgesia whereas with therepeated or prolonged application it shows an inhibitoryeffect on the receptive terminals of nociceptors Capsaicinactivates a transient receptor potential vanilloid (TRPV1)receptor which belongs to a family of TRP channels to exert

an analgesic or algesic effect depending on its concentrations[113] Capsaicin-activating TRPV1 receptor is a nonselectivecation channel that plays an important role to modulatethe nociceptive and pain transmission in the peripheraland central nervous system [114 115] Besides the use as afood additive in spicy cuisines capsaicin is currently usedfor the therapy to treat painful conditions such as diabeticneuropathy and rheumatoid arthritis

Binshtok et al [116] suggested that capsaicin couldtransport a sodium channel blocker QX-314 to nociceptorsthrough the activation of TRPV1 channels and produce thenociceptive-selective analgesia In their whole-cell voltage-clamp recordings from rat dorsal root ganglion neuronsexternally applied QX-314 showed no effects on the sodiumchannel activity of small sensory neurons when it was appliedalone By applying together with capsaicin however QX-314blocked sodium channels to induce a long-lasting reductionof pain sensitivity Ries et al [117] found that a TRPV1receptor agonist capsaicin accelerates the onset kinetics ofQX-314 in a mouse tail-flick test whereas a TRPV1 receptorantagonist capsazepine decreases the nerve blocking efficacyof QX-314 Permanently charged cationic QX-314 cannot passthrough the lipid bilayers of cell membranes but can gain anaccess to the cell interior through TRPV1 channels that areopened by capsaicin (Figure 6) Once inside QX-314 is ableto bind to the acting site on sodium channels Shen et al [118]reported that the peripheral block of nociceptive afferents byQX-314 combined with capsaicin was effective in reducingneuropathic pain It was also suggested that capsaicin couldbe applied in combination with bupivacaine and lidocaineinstead of QX-314 [119] Because the transmembrane accessrout for QX-314 occurs only on nociceptors the combinationof QX-314 or local anesthetics with capsaicin is expected toproduce the ideal analgesia affecting pain alone or the pain-restricted local anesthesia preserving motor and autonomicresponses [120] Shin et al [121 122] found that capsaicinsignificantly potentiates at 50120583M the rat sciatic nerve blockby lidocaineThe cooperative drug interaction with capsaicinalso would be useful for increasing and prolonging localanesthetic effects

Capsaicin acts on lipid bilayers to modify the mem-brane fluidity as well as local anesthetics and QX-314 [123]Experimental data show that capsaicin interacts with nervecell-mimetic membranes to change the membrane fluidityand that the combined use with 50 120583M capsaicin additivelyincreases the membrane effects of lidocaine and bupivacaineof clinically relevant concentrations [124] Capsaicin mayinfluence the effects of local anesthetics by cooperativelyenhancing their interactivity with biomembranes

103 Phloretin Flavonoid phloretin is a polyphenol primarilycontained in apples and their products which has beensuggested to possess the antioxidant and cancer-preventiveactivity [125] Tsuchiya and Mizogami [124] reported themembrane interaction between phloretin and local anes-thetics They treated biomimetic model membranes withlidocaine bupivacaine or phloretin alone and in combinationand then determined the membrane fluidity changes by


Capsaicin

Cell interior

TRPV1 channel

Sodium channelLipid bilayercell membrane

QX-314

Figure 6 Combined use of QX-314 and capsaicin

measuring DPH fluorescence polarization Consequentlyphloretin was revealed to act on nerve cell-mimetic mem-branes and decrease the membrane fluidity in contrast tolocal anesthetics increasing the membrane fluidity The com-bined use with 25 120583Mphloretin antagonistically inhibited themembrane effects of lidocaine and bupivacaine of clinicallyrelevant concentrations Phloretin was also reported to affectthemembrane structure and the local anesthetic permeabilityof lipid monolayers and bilayers [126 127]

A phloretin derivative (polymeric mixture of polyestersof phloretin and phosphoric acid) was found to shorten theduration time of infiltration anesthesia of guinea pigs bylidocaine bupivacaine and prilocaine and to terminate theirlocal anesthetic effects [128] Its local anesthetic-inhibitoryeffect was also proved in the infiltration anesthesia of humanteeth [129] As a clinical utility of the drug and phytochemicalinteraction phloretin may be valuable to discontinue localanesthesia as soon as the treatment is completed

11 Conclusions

Membrane-embedded ion channels especially sodium chan-nels have been recognized to be primarily responsible for thepharmacologic and toxic effects of local anestheticsHoweverthe drug and lipid membrane interaction is not disregardableas themode of local anesthetic actionWhile channel proteinshave the affinity specific to individual ligand structures theycannot necessarily interact with all of structurally differentdrugs Membrane lipids also play an important role in thedifferential recognition of drug structures A substantialnumber of administered local anesthetic molecules must betransported to the target through the lipid barriers of nervesheaths and penetrate into or across the lipid bilayers of cellmembranes Amphiphilic local anesthetics hydrophobicallyand electrostatically interact with lipid bilayers to modify thefluidity of biomembranes with the potency correlating to theanesthetic activity and the cardiac toxicity Such interactionsresult in not only the direct influence onmembrane functionsbut also the influence on channel functions by changing the

conformation of transmembrane proteins Membrane com-ponents phospholipids and cholesterol rich in molecularspecies and chirality allow the membrane interaction of localanesthetics to be structure dependent and stereostructureselective

The interaction between local anesthetics and membranelipids would be associated with both the basic mechanismsfor anesthetic and cardiotoxic effects and the clinical featuressuch as the activity and toxicity altered by pathophysio-logical conditions the cardiotoxicity varying by structuraldifferences and discriminating between stereoisomers theutility of a lipid emulsion to treat cardiotoxicity and thecombination with phytochemicals The interaction with onlyfunctional proteins cannot explain all of the pharmacologicaland toxicological characteristics of local anesthetics nor canthe interaction with only membrane lipids Membrane lipid-interacting theory and membrane protein-interacting theoryare complimentary to each other suggesting the modifiedlipid-protein interaction mechanism for local anesthetics

Abbreviations

DPH 16-Diphenyl-135-hexatrieneDPPC 12-Dipalmitoyl-sn-glycero-3-phosphocholinen-AS n-(9-Anthroyloxy)stearic acid (n = 2 6 9 and 12)PNA N-Phenyl-1-naphthylaminePOPA 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphatePOPC 1-Palmitoyl-2-oleoyl-sn-glycero-3-

phosphocholinePOPE 1-Palmitoyl-2-oleoyl-sn-glycero-3-

phosphoethanolaminePOPG 1-Palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-

(1-glycerol)]POPI 1-Palmitoyl-2-oleoyl-sn-glycero-3-phospho-(11015840-

myo-inositol)POPS 1-Palmitoyl-2-oleoyl-sn-glycero-3-[phospho-L-

serine]QX-314 N-Ethyl lidocaineSM Sphingomyelin


TMA-DPH 1-(4-Trimethylammoniumphenyl)-6-phenyl-135-hexatriene

TRPV1 receptor Transient receptor potential vanilloidreceptor

Conflict of Interests

The authors (Hironori Tsuchiya andMakiMizogami) declarethere is no conflict of interests

Acknowledgments

This work was supported by grants-in-aid for ScientificResearch 20592381 and 23593005 from Japan Society forthe Promotion of Science and a grant from San-Ei GenFoundation for Food Chemical Research

References

[1] G R Strichartz V Sanchez G R Arthur R Chafetz andD Martin ldquoFundamental properties of local anesthetics IIMeasured octanol buffer partition coefficients and pKa valuesof clinically used drugsrdquoAnesthesia and Analgesia vol 71 no 2pp 158ndash170 1990

[2] A B Lopez andM P Diago ldquoFailure of locoregional anesthesiain dental practice Review of the literaturerdquo Medicina OralPatologıa Oral y Cirugıa Bucal vol 11 no 6 pp E510ndashE5132006

[3] D E Becker and K L Reed ldquoEssentials of local anestheticpharmacologyrdquo Anesthesia Progress vol 53 no 3 pp 98ndash1092006

[4] J H C Tan and D A Saint ldquoInteraction of lidocaine withthe cardiac sodium channel Effects of low extracellular pH areconsistent with an external blocking siterdquo Life Sciences vol 67no 22 pp 2759ndash2766 2000

[5] F Yanagidate and G R Strichartz ldquoLocal anestheticsrdquo inHandbook of Experimental Pharmacology vol 177 pp 95ndash127Springer Berlin Germany 2007

[6] G McCleane ldquoIntravenous lidocaine an outdated or underuti-lized treatment for painrdquo Journal of Palliative Medicine vol 10no 3 pp 798ndash805 2007

[7] W Kopec J Telenius and H Khandelia ldquoMolecular dynamicssimulations of the interactions of medicinal plant extracts anddrugs with lipid bilayer membranesrdquo FEBS Journal vol 280 no12 pp 2785ndash2805 2013

[8] J G Paiva P Paradiso A P Serro A Fernandes and BSaramago ldquoInteraction of local and general anaesthetics withliposomal membrane models a QCM-D and DSC studyrdquoColloids and Surfaces B vol 95 pp 65ndash74 2012

[9] CHogberg andA P Lyubartsev ldquoEffect of local anesthetic lido-caine on electrostatic properties of a lipid bilayerrdquo BiophysicalJournal vol 94 no 2 pp 525ndash531 2008

[10] M Pasenkiewicz-Gierula T Rog J Grochowski et al ldquoEffectsof a carane derivative local anesthetic on a phospholipid bilayerstudied bymolecular dynamics simulationrdquoBiophysical Journalvol 85 no 2 pp 1248ndash1258 2003

[11] A Alberola-Die J Martinez-Pinna J M Gonzalez-Ros IIvorra andAMorales ldquoMultiple inhibitory actions of lidocaineon Torpedo nicotinic acetylcholine receptors transplanted toXenopus oocytesrdquo Journal of Neurochemistry vol 117 no 6 pp1009ndash1019 2011

[12] K Hara and T Sata ldquoThe effects of the local anestheticslidocaine and procaine on glycine and 120574-aminobutyric acidreceptors expressed in Xenopus oocytesrdquo Anesthesia and Anal-gesia vol 104 no 6 pp 1434ndash1439 2007

[13] TW R Lee H P Grocott D Schwinn and E Jacobsohn ldquoHighspinal anesthesia for cardiac surgery effects on 120573-adrenergicreceptor function stress response and hemodynamicsrdquo Anes-thesiology vol 98 no 2 pp 499ndash510 2003

[14] J T Jastak J A Yagiela and D Donaldson Local Anesthesia ofthe Oral Cavity WB Saunders Philadelphia Pa USA 1995

[15] C Lynch III ldquoMeyer and Overton revisitedrdquo Anesthesia andAnalgesia vol 107 no 3 pp 864ndash867 2008

[16] M Eeman and M Deleu ldquoFrom biological membranes tobiomimetic model membranesrdquo Biotechnology Agronomy andSociety and Environment vol 14 no 4 pp 719ndash736 2010

[17] I Yun E Cho H Jang et al ldquoAmphiphilic effects of localanesthetics on rotational mobility in neuronal and modelmembranesrdquo Biochimica et Biophysica Acta vol 1564 no 1 pp123ndash132 2002

[18] H Tsuchiya M Mizogami and K Takakura ldquoReversed-phaseliquid chromatographic retention and membrane activity rela-tionships of local anestheticsrdquo Journal of Chromatography Avol 1073 no 1-2 pp 303ndash308 2005

[19] M Mizogami H Tsuchiya and J Harada ldquoMembrane effectsof ropivacaine compared with those of bupivacaine and mepi-vacainerdquo Fundamental and Clinical Pharmacology vol 16 no 4pp 325ndash330 2002

[20] H Tsuchiya and M Mizogami ldquoMembrane interactivity ofcharged local anesthetic derivative and stereoselectivity inmembrane interaction of local anesthetic enantiomersrdquo Localand Regional Anesthesia vol 1 pp 1ndash9 2008

[21] K J McClellan and D Faulds ldquoRopivacaine an update of itsuse in regional anaesthesiardquoDrugs vol 60 no 5 pp 1065ndash10932000

[22] H Onyuksel V Sethi G L Weinberg P K Dudejaand I Rubinstein ldquoBupivacaine but not lidocaine disruptscardiolipin-containing small biomimetic unilamellar lipo-somesrdquo Chemico-Biological Interactions vol 169 no 3 pp 154ndash159 2007

[23] H Tsuchiya T Ueno M Mizogami and K Takakura ldquoLocalanesthetics structure-dependently interact with anionic phos-pholipidmembranes tomodify the fluidityrdquoChemico-BiologicalInteractions vol 183 no 1 pp 19ndash24 2010

[24] L Groban D D Deal J C Vernon R L James and J But-terworth ldquoCardiac resuscitation after incremental overdosagewith lidocaine bupivacaine levobupivacaine and ropivacainein anesthetized dogsrdquo Anesthesia and Analgesia vol 92 no 1pp 37ndash43 2001

[25] L Groban D D Deal J C Vernon R L James and JButterworth ldquoVentricular arrhythmias with or without pro-grammed electrical stimulation after incremental overdosagewith lidocaine bupivacaine levobupivacaine and ropivacainerdquoAnesthesia and Analgesia vol 91 no 5 pp 1103ndash1111 2000

[26] J Wang and G Zhang ldquoInfluence of membrane physicalstate on lysosomal potassium ion permeabilityrdquo Cell BiologyInternational vol 29 no 6 pp 393ndash401 2005

[27] G Balogh I Horvath E Nagy et al ldquoThe hyperfluidizationof mammalian cell membranes acts as a signal to initiate theheat shock protein responserdquo FEBS Journal vol 272 no 23 pp6077ndash6086 2005


[28] S Schreier S V P Malheiros and E de Paula ldquoSurface activedrugs self-association and interaction with membranes andsurfactants Physicochemical and biological aspectsrdquo Biochim-ica et Biophysica Acta vol 1508 no 1-2 pp 210ndash234 2000

[29] A PohorilleMAWilsonMHNew andCChipot ldquoConcen-trations of anesthetics across the water-membrane interface theMeyer-Overton hypothesis revisitedrdquo Toxicology Letters vol100-101 pp 421ndash430 1998

[30] A Sunami I W Glaaser and H A Fozzard ldquoA critical residuefor isoform difference in tetrodotoxin affinity is a moleculardeterminant of the external access path for local anestheticsin the cardiac sodium channelrdquo Proceedings of the NationalAcademy of Sciences of the United States of America vol 97 no5 pp 2326ndash2331 2000

[31] T K Y Lim B A MacLeod C R Ries and S K W SchwarzldquoThe quaternary lidocaine derivative QX-314 produces long-lasting local anesthesia in animal models in vivordquo Anesthesiol-ogy vol 107 no 2 pp 305ndash311 2007

[32] G K Wang ldquoLocal anestheticsrdquo in Neural Mechanisms ofAnesthesia J F Antognini E E Carstens andD E Raines EdsHumana Press Totowa NJ USA 2003

[33] K A Slaviero S J Clarke and L P Rivory ldquoInflammatoryresponse an unrecognised source of variability in the phar-macokinetics and pharmacodynamics of cancer chemotherapyrdquoThe Lancet Oncology vol 4 no 4 pp 224ndash232 2003

[34] S Sattari W F Dryden L A Eliot and F Jamali ldquoDespiteincreased plasma concentration inflammation reduces potencyof calcium channel antagonists due to lower binding to the ratheartrdquo British Journal of Pharmacology vol 139 no 5 pp 945ndash954 2003

[35] E Claffey A Reader J Nusstein M Beck and JWeaver ldquoAnes-thetic efficacy of articaine for inferior alveolar nerve blocks inpatients with irreversible pulpitisrdquo Journal of Endodontics vol30 no 8 pp 568ndash571 2004

[36] N Srinivasan M Kavitha C S Loganathan and G PadminildquoComparison of anesthetic efficacy of 4 articaine and 2lidocaine for maxillary buccal infiltration in patients with irre-versible pulpitisrdquo Oral Surgery Oral Medicine Oral PathologyOral Radiology and Endodontology vol 107 no 1 pp 133ndash1362009

[37] I Potocnik and F Bajrovic ldquoFailure of inferior alveolar nerveblock in endodonticsrdquo Dental Traumatology vol 15 no 6 pp247ndash251 1999

[38] A Punnia-Moorthy ldquoEvaluation of pH changes in inflamma-tion of the subcutaneous air pouch lining in the rat inducedby carrageenan dextran and Staphylococcus aureusrdquo Journal ofOral Pathology vol 16 no 1 pp 36ndash44 1987

[39] D de Backer ldquoLactic acidosisrdquoMinerva Anestesiologica vol 69no 4 pp 281ndash284 2003

[40] H Tsuchiya M Mizogami T Ueno and K Takakura ldquoInterac-tion of local anaesthetics with lipid membranes under inflam-matory acidic conditionsrdquo Inflammopharmacology vol 15 no4 pp 164ndash170 2007

[41] T Ueno H Tsuchiya M Mizogami and K Takakura ldquoLocalanesthetic failure associated with inflammation verification ofthe acidosis mechanism and the hypothetic participation ofinflammatory peroxynitriterdquo Journal of Inflammation Researchvol 1 pp 41ndash48 2008

[42] A Punnia-Moorthy ldquoBuffering capacity of normal andinflamed tissues following the injection of local anaestheticsolutionsrdquo British Journal of Anaesthesia vol 61 no 2 pp154ndash159 1988

[43] B Gunaydin and A T Demiryurek ldquoInteraction of lidocainewith reactive oxygen and nitrogen speciesrdquo European Journal ofAnaesthesiology vol 18 no 12 pp 816ndash822 2001

[44] H Tsuchiya T Ueno M Mizogami and K Takakura ldquoAntiox-idant activity analysis by liposomal membrane system andapplication to anestheticsrdquo Analytical Sciences vol 24 no 12pp 1557ndash1562 2008

[45] T Ueno M Mizogami K Takakura and H Tsuchiya ldquoMem-brane effect of lidocaine is inhibited by interaction with perox-ynitriterdquo Journal of Anesthesia vol 22 no 1 pp 96ndash99 2008

[46] T Ueno M Mizogami K Takakura and H Tsuchiya ldquoPerox-ynitrite affects lidocaine by acting on membrane-constitutinglipidsrdquo Journal of Anesthesia vol 22 no 4 pp 475ndash478 2008

[47] N M Flake and M S Gold ldquoInflammation alters sodiumcurrents and excitability of temporomandibular joint afferentsrdquoNeuroscience Letters vol 384 no 3 pp 294ndash299 2005

[48] JWang J A StrongW Xie and J Zhang ldquoLocal inflammationin rat dorsal root ganglion alters excitability and ion currents insmall-diameter sensory neuronsrdquoAnesthesiology vol 107 no 2pp 322ndash332 2007

[49] J M Dippenaar ldquoLocal anaesthetic toxicityrdquo Southern AfricanJournal of Anaesthesia and Analgesia vol 13 no 3 pp 23ndash282007

[50] C Gevirtz ldquoLocal anesthetic systemic toxicity prevention andtreatmentrdquo Topics in Pain Management vol 27 no 12 pp 1ndash62012

[51] J E Heavner ldquoCardiac toxicity of local anesthetics in the intactisolated heart model a reviewrdquo Regional Anesthesia and PainMedicine vol 27 no 6 pp 545ndash555 2002

[52] L Pardo T J J Blanck and E Recio-Pinto ldquoThe neuronallipid membrane permeability was markedly increased by bupi-vacaine and mildly affected by lidocaine and ropivacainerdquoEuropean Journal of Pharmacology vol 455 no 2-3 pp 81ndash902002

[53] P Friederich ldquoBasic concepts of ion channel physiology andanaesthetic drug effectsrdquo European Journal of Anaesthesiologyvol 20 no 5 pp 343ndash353 2003

[54] R H Houtkooper and F M Vaz ldquoCardiolipin the heartof mitochondrial metabolismrdquo Cellular and Molecular LifeSciences vol 65 no 16 pp 2493ndash2506 2008

[55] K Felice and H Schumann ldquoIntravenous lipid emulsion forlocal anesthetic toxicity a review of the literaturerdquo Journal ofMedical Toxicology vol 4 no 3 pp 184ndash191 2008

[56] JMuhonen JMHolopainen and S KWiedmer ldquoInteractionsbetween local anesthetics and lipid dispersions studied withliposome electrokinetic capillary chromatographyrdquo Journal ofChromatography A vol 1216 no 15 pp 3392ndash3397 2009

[57] GWeinberg R Ripper D L Feinstein andWHoffman ldquoLipidemulsion infusion rescues dogs from bupivacaine-inducedcardiac toxicityrdquo Regional Anesthesia and PainMedicine vol 28no 3 pp 198ndash202 2003

[58] R J Litz M Popp S N Stehr and T Koch ldquoSuccessfulresuscitation of a patient with ropivacaine-induced asystoleafter axillary plexus block using lipid infusionrdquoAnaesthesia vol61 no 8 pp 800ndash801 2006

[59] G Foxall R McCahon J Lamb J G Hardman and N MBedforth ldquoLevobupivacaine-induced seizures and cardiovascu-lar collapse treated with Intralipidrdquo Anaesthesia vol 62 no 5pp 516ndash518 2007

[60] S Ciechanowicz and V Patil ldquoLipid emulsion for local anes-thetic systemic toxicityrdquo Anesthesiology Research and Practicevol 2012 Article ID 131784 11 pages 2012


[61] J A Warren R B Thoma A Georgescu and S J ShahldquoIntravenous lipid infusion in the successful resuscitation oflocal anesthetic-induced cardiovascular collapse after supra-clavicular brachial plexus blockrdquo Anesthesia and Analgesia vol106 no 5 pp 1578ndash1580 2008

[62] E Calenda and S A Dinescu ldquoFailure of lipid emulsion toreverse neurotoxicity after an ultrasound-guided axillary blockwith ropivacaine and mepivacainerdquo Journal of Anesthesia vol23 no 3 pp 472ndash473 2009

[63] E Bourne CWright andC Royse ldquoA review of local anestheticcardiotoxicity and treatment with lipid emulsionrdquo Local andRegional Anesthesia vol 3 no 1 pp 11ndash19 2010

[64] J Mazoit R Le Guen H Beloeil and D Benhamou ldquoBindingof long-lasting local anesthetics to lipid emulsionsrdquo Anesthesi-ology vol 110 no 2 pp 380ndash386 2009

[65] AAGBI Management of Severe Local Anaesthetic Toxicity 2(2010) AAGBI Guidelines 2010 httpwwwaagbiorgpubli-cationspublications-guidelinesMR

[66] P Tsibiribi C Bui-Xuan B Bui-Xuan et al ldquoThe effects ofropivacaine at clinically relevant doses on myocardial ischemiain pigsrdquo Journal of Anesthesia vol 20 no 4 pp 341ndash343 2006

[67] D J Pacini G Boachie-Ansah and K A Kane ldquoModificationby hypoxia hyperkalaemia and acidosis of the cardiac electro-physiological effects of a range of antiarrhythmic drugsrdquo BritishJournal of Pharmacology vol 107 no 3 pp 665ndash670 1992

[68] M Freysz Q Timour L Bertrix J Loufoua-Moundanga SOmar and G Faucon ldquoEnhancement by ischemia of the risk ofcardiac disorders especially fibrillation in regional anesthesiawith bupivacainerdquo Acta Anaesthesiologica Scandinavica vol 37no 4 pp 350ndash356 1993

[69] R Ferrari A Cargnoni P Bernocchi et al ldquoMetabolic adap-tation during a sequence of no-flow and low-flow ischemia apossible trigger for hibernationrdquo Circulation vol 94 no 10 pp2587ndash2596 1996

[70] Y Watanabe S Dohi H Iida and T Ishiyama ldquoThe effects ofbupivacaine and ropivacaine on baroreflex sensitivity with orwithout respiratory acidosis and alkalosis in ratsrdquo Anesthesiaand Analgesia vol 84 no 2 pp 398ndash404 1997

[71] H Tsuchiya M Mizogami T Ueno and K Shigemi ldquoCar-diotoxic local anesthetics increasingly interact with biomimeticmembranes under ischemia-like acidic conditionsrdquo Biologicaland Pharmaceutical Bulletin vol 35 no 6 pp 988ndash992 2012

[72] G Paradies G Petrosillo M Pistolese N Di Venosa A Fed-erici and F M Ruggiero ldquoDecrease in mitochondrial complexI activity in ischemicreperfused rat heart involvement ofreactive oxygen species and cardiolipinrdquo Circulation Researchvol 94 no 1 pp 53ndash59 2004

[73] M M Lalu W Wang and R Schulz ldquoPeroxynitrite in myocar-dial ischemia-reperfusion injuryrdquo Heart Failure Reviews vol 7no 4 pp 359ndash369 2002

[74] H Tsuchiya M Mizogami and K Shigemi ldquoIncreasingmembrane interactions of local anaesthetics as hypotheticmechanism for their cardiotoxicity enhanced by myocardialischaemiardquo Basic and Clinical Pharmacology and Toxicologyvol 111 no 5 pp 303ndash308 2012

[75] E J Lesnefsky and C L Hoppel ldquoCardiolipin as an oxidativetarget in cardiac mitochondria in the aged ratrdquo Biochimica etBiophysica Acta vol 1777 no 7-8 pp 1020ndash1027 2008

[76] G Paradies G Petrosillo V Paradies and F M RuggieroldquoRole of cardiolipin peroxidation and Ca2+ in mitochondrialdysfunction and diseaserdquo Cell Calcium vol 45 no 6 pp 643ndash650 2009

[77] H Tsuchiya T Ueno and M Mizogami ldquoStereostructure-based differences in the interactions of cardiotoxic local anes-thetics with cholesterol-containing biomimetic membranesrdquoBioorganic and Medicinal Chemistry vol 19 no 11 pp 3410ndash3415 2011

[78] D J Kaczmarek C Herzog J Larmann et al ldquoLidocaine pro-tects frommyocardial damage due to ischemia and reperfusionin mice by its antiapoptotic effectsrdquo Anesthesiology vol 110 no5 pp 1041ndash1049 2009

[79] F Lenfant J Lahet C Courderot-Masuyer M Freysz andL Rochette ldquoLidocaine has better antioxidant potential thanropivacaine and bupivacaine in vitro comparison in a modelof human erythrocytes submitted to an oxidative stressrdquoBiomedicine and Pharmacotherapy vol 58 no 4 pp 248ndash2542004

[80] S Pope J M Land and S J R Heales ldquoOxidative stress andmitochondrial dysfunction in neurodegeneration cardiolipin acritical targetrdquo Biochimica et Biophysica Acta vol 1777 no 7-8pp 794ndash799 2008

[81] E J Lesnefsky T J Slabe M S K Stoll P E Minkler and CLHoppel ldquoMyocardial ischemia selectively depletes cardiolipinin rabbit heart subsarcolemmal mitochondriardquo American Jour-nal of Physiology vol 280 no 6 pp H2770ndashH2778 2001

[82] K M Rentsch ldquoThe importance of stereoselective determina-tion of drugs in the clinical laboratoryrdquo Journal of Biochemicaland Biophysical Methods vol 54 no 1-3 pp 1ndash9 2002

[83] C Nau and G R Strichartz ldquoDrug chirality in anesthesiardquoAnesthesiology vol 97 no 2 pp 497ndash502 2002

[84] R H Foster and AMarkham ldquoLevobupivacaine a review of itspharmacology and use as a local anaestheticrdquoDrugs vol 59 no3 pp 551ndash579 2000

[85] M Vladimirov C NauWMMok and G Strichartz ldquoPotencyof bupivacaine stereoisomers tested in vitro and in vivo bio-chemical electrophysiological and neurobehavioral studiesrdquoAnesthesiology vol 93 no 3 pp 744ndash755 2000

[86] G Lyons M Columb R C Wilson and R V JohnsonldquoEpidural pain relief in labour potencies of levobupivacaineand racemic bupivacainerdquo British Journal of Anaesthesia vol81 no 6 pp 899ndash901 1998 Erratum in British Journal ofAnaesthesia vol 82 no 3 p 488 1998

[87] Y Lim C E Ocampo and A T Sia ldquoA comparison of durationof analgesia of intrathecal 25mg of bupivacaine ropivacaineand levobupivacaine in combined spinal epidural analgesia forpatients in laborrdquo Anesthesia and Analgesia vol 98 no 1 pp235ndash239 2004

[88] B M Graf E Martin Z J Bosnjak and D F Stowe ldquoStereospe-cific effect of bupivacaine isomers on atrioventricular conduc-tion in the isolated perfused guinea pig heartrdquo Anesthesiologyvol 86 no 2 pp 410ndash419 1997

[89] S G Morrison J J Dominguez P Frascarolo and S ReizldquoA comparison of the electrocardiographic cardiotoxic effectsof racemic bupivacaine levobupivacaine and ropivacaine inanesthetized swinerdquoAnesthesia and Analgesia vol 90 no 6 pp1308ndash1314 2000

[90] C Valenzuela D J Snyders P B Bennett J Tamargo and L MHondeghem ldquoStereoselective block of cardiac sodium channelsby bupivacaine in guinea pig ventricularmyocytesrdquoCirculationvol 92 no 10 pp 3014ndash3024 1995

[91] C Valenzuela E Delpon M M Tamkun J Tamargo and DJ Snyders ldquoStereoselective block of a human cardiac potassiumchannel (Kv15) by bupivacaine enantiomersrdquo Biophysical Jour-nal vol 69 no 2 pp 418ndash427 1995


[92] M Mizogami H Tsuchiya T Ueno M Kashimata andK Takakura ldquoStereospecific interaction of bupivacaine enan-tiomers with lipid membranesrdquo Regional Anesthesia and PainMedicine vol 33 no 4 pp 304ndash311 2008

[93] H Tsuchiya and M Mizogami ldquoR(+)- Rac- and S(minus)-bupivacaine stereostructure-specifically interact with mem-brane lipids at cardiotoxically relevant concentrationsrdquoAnesthe-sia and Analgesia vol 114 no 2 pp 310ndash312 2012

[94] T Gonzalez C Arias R Caballero et al ldquoEffects of levobupiva-caine ropivacaine and bupivacaine on HERG channels stere-oselective bupivacaine blockrdquo British Journal of Pharmacologyvol 137 no 8 pp 1269ndash1279 2002

[95] P Friederich A Solth S Schillemeit and D Isbrandt ldquoLocalanaesthetic sensitivities of cloned HERG channels from humanheart comparison with HERGMiRP1 and HERGMiRP1T8ArdquoBritish Journal of Anaesthesia vol 92 no 1 pp 93ndash101 2004

[96] H Tsuchiya and M Mizogami ldquoThe membrane interaction ofdrugs as one of mechanisms for their enantioselective effectsrdquoMedical Hypotheses vol 79 no 1 pp 65ndash67 2012

[97] N Nandi andD Vollhardt ldquoChiral discrimination and recogni-tion in Langmuir monolayersrdquo Current Opinion in Colloid andInterface Science vol 13 no 1-2 pp 40ndash46 2008

[98] S Lalitha A S Kumar K J Stine and D F Covey ldquoChiralityin membranes first evidence that enantioselective interac-tions between cholesterol and cell membrane lipids can bea determinant of membrane physical propertiesrdquo Journal ofSupramolecular Chemistry vol 1 no 2 pp 53ndash61 2001

[99] A Kessel N Ben-Tal and S May ldquoInteractions of cholesterolwith lipid bilayers the preferred configuration and fluctua-tionsrdquo Biophysical Journal vol 81 no 2 pp 643ndash658 2001

[100] K Simons andD Toomre ldquoLipid rafts and signal transductionrdquoNature Reviews Molecular Cell Biology vol 1 no 1 pp 31ndash392000

[101] M-O Parat ldquoCould endothelial caveolae be the target of generalanaestheticsrdquo British Journal of Anaesthesia vol 96 no 5 pp547ndash550 2006

[102] K M S OrsquoConnell J R Martens and M M TamkunldquoLocalization of ion channels to lipid raft domains within thecardiovascular systemrdquo Trends in Cardiovascular Medicine vol14 no 2 pp 37ndash42 2004

[103] Y Xiang V O Rybin S F Steinberg and B Kobilka ldquoCaveolarlocalization dictates physiologic signaling of 120573

2

-adrenoceptorsin neonatal cardiac myocytesrdquo The Journal of Biological Chem-istry vol 277 no 37 pp 34280ndash34286 2002

[104] Y Fujimura H Tachibana and K Yamada ldquoLipid raft-associated catechin suppresses the Fc120576RI expression byinhibiting phosphorylation of the extracellular signal-regulatedkinase12rdquo FEBS Letters vol 556 no 1-3 pp 204ndash210 2004

[105] A Ausuili A Torrecillas F J Aranda et al ldquoEdelfosine isincorporated into rafts and alters their organizationrdquo Journal ofPhysical Chemistry B vol 112 no 37 pp 11643ndash11654 2008

[106] K Kamata S Manno M Ozaki and Y Takakuwa ldquoFunctionalevidence for presence of lipid rafts in erythrocyte membranesGs120572 in rafts is essential for signal transductionrdquo AmericanJournal of Hematology vol 83 no 5 pp 371ndash375 2008

[107] K Kamata S Manno Y Takakuwa and M Ozaki ldquoReversibleeffect of lidocaine on raft formationrdquo International CongressSeries vol 1283 pp 281ndash282 2005

[108] H Tsuchiya T UenoMMizogami and K Takakura ldquoDo localanesthetics interact preferentially with membrane lipid raftsComparative interactivities with raft-like membranesrdquo Journalof Anesthesia vol 24 no 4 pp 639ndash642 2010

[109] C Bandeiras A P Serro K Luzyanin A Fernandes and BSaramago ldquoAnesthetics interacting with lipid raftsrdquo EuropeanJournal of Pharmaceutical Sciences vol 48 no 1-2 pp 153ndash1652013

[110] C Ioannides ldquoDrug-phytochemical interactionsrdquo Inflammo-pharmacology vol 11 no 1 pp 7ndash42 2003

[111] S Zhou Z Zhou C Li et al ldquoIdentification of drugs thatinteract with herbs in drug developmentrdquo Drug DiscoveryToday vol 12 no 15-16 pp 664ndash673 2007

[112] Y Vorobeychik V Gordin J Mao and L Chen ldquoCombinationtherapy for neuropathic pain a review of current evidencerdquoCNS Drugs vol 25 no 12 pp 1023ndash1034 2011

[113] D Spicarova and J Palecek ldquoThe role of spinal cord vanilloid(TRPV1) receptors in pain modulationrdquo Physiological Researchvol 57 supplement 3 pp S69ndashS77 2008

[114] M J Caterina M A Schumacher M Tominaga T A RosenJ D Levine and D Julius ldquoThe capsaicin receptor a heat-activated ion channel in the pain pathwayrdquoNature vol 389 no6653 pp 816ndash824 1997

[115] K Venkatachalam and C Montell ldquoTRP channelsrdquo AnnualReview of Biochemistry vol 76 pp 387ndash417 2007

[116] A M Binshtok B P Bean and C J Woolf ldquoInhibition ofnociceptors by TRPV1-mediated entry of impermeant sodiumchannel blockersrdquo Nature vol 449 no 7162 pp 607ndash610 2007

[117] C R Ries R Pillai C C Chung J TWang B AMacLeod andS K Schwarz ldquoQX-314 produces long-lasting local anesthesiamodulated by transient receptor potential vanilloid receptors inmicerdquo Anesthesiology vol 111 no 1 pp 122ndash126 2009

[118] J Shen L E Fox and J Cheng ldquoDifferential effects of peripheralversus central coadministration of QX-314 and capsaicin onneuropathic pain in ratsrdquoAnesthesiology vol 117 no 2 pp 365ndash380 2012

[119] P Gerner A M Binshtok C Wang et al ldquoCapsaicin combinedwith local anesthetics preferentially prolongs sensorynocicep-tive block in rat sciatic nerverdquoAnesthesiology vol 109 no 5 pp872ndash878 2008

[120] E W McCleskey ldquoNeuroscience a local route to pain reliefrdquoNature vol 449 no 7162 pp 545ndash546 2007

[121] H Shin H J Park S A Raymond and G R StrichartzldquoPotentiation by capsaicin of lidocainersquos tonic impulse block inisolated rat sciatic nerverdquoNeuroscience Letters vol 174 no 1 pp14ndash16 1994

[122] H Shin H J Park and S A Raymond ldquoPotentiation bycapsaicin of lidocainersquos phasic impulse block in isolated ratsciatic nerverdquo Pharmacological Research vol 30 no 1 pp 73ndash79 1994

[123] H Tsuchiya ldquoBiphasic membrane effects of capsaicin an activecomponent in Capsicum speciesrdquo Journal of Ethnopharmacol-ogy vol 75 no 2-3 pp 295ndash299 2001 Erratum in Journal ofEthnopharmacology vol 76 no 3 p 313 2001

[124] H Tsuchiya and M Mizogami ldquoPlant components exhibitpharmacological activities and drug interactions by acting onlipid membranesrdquo Pharmacognosy Communications vol 2 no4 pp 58ndash71 2012

[125] K Yang C Tsai Y Wang et al ldquoApple polyphenol phloretinpotentiates the anticancer actions of paclitaxel through induc-tion of apoptosis in human Hep G2 cellsrdquo Molecular Carcino-genesis vol 48 no 5 pp 420ndash431 2009

[126] R Cseh and R Benz ldquoInteraction of phloretin with lipidmonolayers relationship between structural changes and dipolepotential changerdquo Biophysical Journal vol 77 no 3 pp 1477ndash1488 1999


[127] B G Auner and C Valenta ldquoInfluence of phloretin on theskin permeation of lidocaine from semisolid preparationsrdquoEuropean Journal of Pharmaceutics and Biopharmaceutics vol57 no 2 pp 307ndash312 2004

[128] G Aberg and G Sydnes ldquoAn inhibitory effect of polyphloretinphosphate (PPP) on local anaesthesiardquo Acta AnaesthesiologicaScandinavica vol 19 no 5 pp 377ndash383 1975

[129] A Nordenram and K Danielsson ldquoThe effect of polyphloretinphosphate (PPP) on oral infiltration anaesthesia An experi-mental investigationrdquo Swedish Dental Journal vol 12 no 6 pp217ndash220 1988

Submit your manuscripts athttpwwwhindawicom

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


MEDIATORSINFLAMMATION

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Behavioural Neurology

EndocrinologyInternational Journal of



Disease Markers


BioMed Research International

OncologyJournal of



Oxidative Medicine and Cellular Longevity


PPAR Research

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Immunology ResearchHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

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OphthalmologyJournal of


Diabetes ResearchJournal of



Research and TreatmentAIDS


Gastroenterology Research and Practice


Parkinsonrsquos Disease

Evidence-Based Complementary and Alternative Medicine

Volume 2014Hindawi Publishing Corporationhttpwwwhindawicom


NH C

O

OC

O

C

O

O

NH C C

O

N

NH C C

O

NHH

H

NH C C

O

N

H

NH C C

O

N

H

NH C C

O

N

H

NH C C

O

NHH

S

C

O

O

H

N

Lidocaine

Mepivacaine

Ropivacaine

Bupivacaine

Procaine

Cocaine

Benzocaine

Tetracaine

Propoxycaine

Prilocaine

Etidocaine

Articaine

2-Chloroprocaine

Amide local anesthetics Ester local anesthetics

N

C

O

O N

Cl

C

O

N O NH

C

O

O N

N

CH2CH3

CH2CH2

CH2CH3

CH2CH3

CH3

CH2CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH2

CH3

CH3

CH2CH2CH3

CH2CH2CH2

CH2CH2

CH2CH3

CH2CH2

CH2CH2

CH2CH2

CH2CH3

CH2CH3

CH2CH3

CH2CH3

CH2CH3

CH3

CH2CH2CH2CH3

CH3

CH2CH2CH3

CH3

COOCH3

H2N

H2N

H2N

H2N

H3CH2CH2CH2C

CHCH2C

OCH2CH2CH3

COOCH3

Figure 1 Representative amide and ester local anesthetics

anesthesia is achieved at the relatively high concentrations ofdrugs in local areas At lower concentrations certain localanesthetics also showmore subtle effects on hearts which areclinically important as an antiarrhythmic agent In additionlidocaine administered systemically may be useful for reduc-ing the excitability of nociceptive sensory neurons [6]

Local anesthetics block the conduction of nerve impulsesby affecting the influx of ions through transmembrane chan-nels Proposed mechanistic theories include the action onmembrane-embedded ion channels membrane-associated

enzymes membrane lipids and water In the protein-interacting theory local anesthetics are presumed to inhibitthe generation and conduction of action potentials in nervecells and cardiomyocytes by binding to the intracellular siteof voltage-gated sodium channels embedded in membranelipid bilayers (Figure 3) Local anesthetics specifically bind totheD4-S6 region of the 120572-subunit of neural sodium channelsSince this site is intracellular or cell interior drug moleculesare absolutely required to be in uncharged hydrophobic formfor accessing there




NH C

O

N


NH C

O

N H

NH C

O

N



CH2CH3

CH2CH3

CH2CH3 CH2

CH2

CH3

CH2CH3

CH3

CH3

CH2

CH2

CH3

CH3

CH3

CH2

CH2

CH3

CH3

CH3




Cell interior










OO

OH

O OO

OH

O OO

OH

O

H

O

OOP

OO O

O O

HOOH

O O

OO P

O

OPOHOO

O

H

O OO

OOP

O


PC)


ine (POPE)


PS)

Cardiolipin

OH

OHOHOHOH

H

H

H

H

Cholesterol

OHH

OO

O

OOP

H

O

O

12-Dipalm


OHHO NH

H

OOP

O

Sphingomyelin (SM

)


yo-inositol) (POPI)

CH3

CH3

CH3

CH3

H3C

minusOminusO

minusOminusO

minusOminusO minusO

OOP

OminusO

OOP

OminusO

+H3N+H3N+H3N+H3N

NH3+


































































lt

lt

lt

NHO

NH

NHO

NH

NHO

NH

NHO

NH

NHO

NH

lowastlowast


CH3

CH3CH3CH3

CH3

H3C

H3CH3C

H3CH3C


H3CH2CH2CH3CH2CH2C

lowast lowast




























Capsaicin

Cell interior

TRPV1 channel


QX-314




11 Conclusions




Abbreviations












Acknowledgments


References











































































































2


































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of



















NH C

O

N


NH C

O

N H

NH C

O

N



CH2CH3

CH2CH3

CH2CH3 CH2

CH2

CH3

CH2CH3

CH3

CH3

CH2

CH2

CH3

CH3

CH3

CH2

CH2

CH3

CH3

CH3




Cell interior










OO

OH

O OO

OH

O OO

OH

O

H

O

OOP

OO O

O O

HOOH

O O

OO P

O

OPOHOO

O

H

O OO

OOP

O


PC)


ine (POPE)


PS)

Cardiolipin

OH

OHOHOHOH

H

H

H

H

Cholesterol

OHH

OO

O

OOP

H

O

O

12-Dipalm


OHHO NH

H

OOP

O

Sphingomyelin (SM

)


yo-inositol) (POPI)

CH3

CH3

CH3

CH3

H3C

minusOminusO

minusOminusO

minusOminusO minusO

OOP

OminusO

OOP

OminusO

+H3N+H3N+H3N+H3N

NH3+


































































lt

lt

lt

NHO

NH

NHO

NH

NHO

NH

NHO

NH

NHO

NH

lowastlowast


CH3

CH3CH3CH3

CH3

H3C

H3CH3C

H3CH3C


H3CH2CH2CH3CH2CH2C

lowast lowast




























Capsaicin

Cell interior

TRPV1 channel


QX-314




11 Conclusions




Abbreviations












Acknowledgments


References











































































































2


































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of

















OO

OH

O OO

OH

O OO

OH

O

H

O

OOP

OO O

O O

HOOH

O O

OO P

O

OPOHOO

O

H

O OO

OOP

O


PC)


ine (POPE)


PS)

Cardiolipin

OH

OHOHOHOH

H

H

H

H

Cholesterol

OHH

OO

O

OOP

H

O

O

12-Dipalm


OHHO NH

H

OOP

O

Sphingomyelin (SM

)


yo-inositol) (POPI)

CH3

CH3

CH3

CH3

H3C

minusOminusO

minusOminusO

minusOminusO minusO

OOP

OminusO

OOP

OminusO

+H3N+H3N+H3N+H3N

NH3+


































































lt

lt

lt

NHO

NH

NHO

NH

NHO

NH

NHO

NH

NHO

NH

lowastlowast


CH3

CH3CH3CH3

CH3

H3C

H3CH3C

H3CH3C


H3CH2CH2CH3CH2CH2C

lowast lowast




























Capsaicin

Cell interior

TRPV1 channel


QX-314




11 Conclusions




Abbreviations












Acknowledgments


References











































































































2


































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of











































































lt

lt

lt

NHO

NH

NHO

NH

NHO

NH

NHO

NH

NHO

NH

lowastlowast


CH3

CH3CH3CH3

CH3

H3C

H3CH3C

H3CH3C


H3CH2CH2CH3CH2CH2C

lowast lowast




























Capsaicin

Cell interior

TRPV1 channel


QX-314




11 Conclusions




Abbreviations












Acknowledgments


References











































































































2


































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of





































Capsaicin

Cell interior

TRPV1 channel


QX-314




11 Conclusions




Abbreviations












Acknowledgments


References











































































































2


































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of





















Acknowledgments


References











































































































2


































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of































































































2


































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of

























of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of
















review article interaction of local anesthetics with biomembranes...

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