Download - Oxidative Stress and Atherosclerosis
Oxidative Stress and Oxidative Stress and AtherosclerosisAtherosclerosis
ObjectivesObjectives
What is “free radicalfree radical” ? Reactive oxygen and nitrogen species (RONSRONS) Are the RONS always dangerous? Well known term “oxidative stressoxidative stress” - what is it? AntioxidantsAntioxidants - types DisordersDisorders Associated with Oxidative stress Oxidative stress and atherosclerosisatherosclerosis
TermTerm DefinitionDefinition
OxidationOxidation Gain in oxygenLoss of hydrogenLoss of electrons
ReductionReduction Loss of oxygenGain of hydrogenGain of electrons
OxidantOxidant Oxidizes another chemical by takingelectrons hydrogen or by adding oxygen
ReductantReductant Reduces another chemical by supplying electrons, hydrogen or by removing oxygen
Basics of Redox ChemistryBasics of Redox Chemistry
Free RadicalsFree Radicals A molecule with an unpaired electron in an
outer valence shell• Tend to reach equilibrium, plucks an electron plucks an electron
from the nearest intact molecule.• Most of biomoleculs are not radicals• Radicals are highly reactive species
R3C. Carbon-centered
R3N. Nitrogen-centered
R-O. Oxygen-centered
R-S. Sulfur-centered
Reactive SpeciesReactive Species
Non RadicalsNon Radicals Species that have strong oxidizing potentialoxidizing potential Species that favor the formation favor the formation of strong
oxidants (e.g. transition metals)
H2O2 Hydrogen peroxide
HOCl- Hypochlorous acid
O3 Ozone1O2 Singlet oxygen
ONOO- Peroxynitrite
Men+ Transition metals
Reactive Oxygen Species (ROS)Reactive Oxygen Species (ROS)
RadicalsRadicals
O2.- Superoxide
OH .- Hydroxyl
RO2. Peroxyl
RO. Alkoxyl
HO2. Hydroperoxyl
Non-RadicalsNon-Radicals
H2O2 Hydrogen peroxide
HOCl- Hypochlorous acid
Reactive Nitrogen Species (RNS)Reactive Nitrogen Species (RNS)
Radicals as:
NO. Nitric Oxide
NO2. Nitrogen dioxide
Non-Radicals as:Peroxynitrite
“An An imbalanceimbalance favoring (pro) oxidants and/or disfavoring favoring (pro) oxidants and/or disfavoring antioxidants, potentially leading to antioxidants, potentially leading to damagedamage” ”
AntioxidantsAntioxidants
OxidantsOxidants
Oxidative StressOxidative Stress
Oxidative StressOxidative Stress
• It is a state in the cells in which there is increased concentration of reactive species which is not counterbalanced by increased levels of antioxidants.
• This imbalance was implicated in production of different diseases as atherosclerosis
Endogenous sources of ROS & RNSEndogenous sources of ROS & RNS
MitochondriaMitochondria
LysosomesLysosomes
PeroxisomesPeroxisomes
Endoplasmic ReticulumEndoplasmic Reticulum
CytoplasmCytoplasm
Microsomal Oxidation, Microsomal Oxidation, Flavoproteins, CYP enzymesFlavoproteins, CYP enzymes MyeloperoxidaseMyeloperoxidase
(phagocytes) (phagocytes)
Electron transportElectron transport
Oxidases,Oxidases,FlavoproteinsFlavoproteins
Plasma MembranePlasma MembraneLipoxygenases,Lipoxygenases,
Prostaglandin synthaseProstaglandin synthaseNADPH oxidase
Xanthine Oxidase,Xanthine Oxidase,NOS isoformsNOS isoforms
FeCu
Transition Transition metalsmetals
Reactive Oxygen Species (ROS)Reactive Oxygen Species (ROS)
ROS are:ROS are:Free radicalsFree radicals: : e.g. Superoxide & hydroxyl radicalse.g. Superoxide & hydroxyl radicalsNon radicalsNon radicals: Hydrogen peroxide: Hydrogen peroxide
ROSROS are formed continuously by partial reduction of molecular oxygen in electron transport chain in mitochondria
For example:For example:Oxygen dependent pathway for microbial killingOxygen dependent pathway for microbial killing
In phagocytic cells (neutrophils & monocytes), In phagocytic cells (neutrophils & monocytes), microorganisms are phagocytosedmicroorganisms are phagocytosed
NADPH oxidase in these cells convertsNADPH oxidase in these cells convertsmolecular oxygen into superoxide (Respiratory molecular oxygen into superoxide (Respiratory Burst). Burst).
Superoxide + chloride ions are converted into Superoxide + chloride ions are converted into hypochlorous acid that kills bacteriahypochlorous acid that kills bacteria(by help of the lysosomal enzyme myeloperoxidsase(by help of the lysosomal enzyme myeloperoxidsaseMPO)MPO)
Sometimes, ROS is useful for humansSometimes, ROS is useful for humans
AntioxidantsAntioxidants
Enzymes that catalyze antioxidant Enzymes that catalyze antioxidant reactionsreactions::1- Superoxide dismutase 2- Catalase3- Glutathione system (glutathione, NADPH, reductase, peroxidase & selenium).
VitaminsVitamins1- Vitamin A & β-carotenes2- Vitamin C (ascorbic acid)3- Vitamin E
Trace elementsTrace elementsSelenium
Enzymatic Antioxidant MechanismsEnzymatic Antioxidant Mechanisms
Glutathione SystemGlutathione System
SeleniumSelenium
Glutathione system Glutathione system in RBCSin RBCS
Nitric Oxide (NO)Nitric Oxide (NO)Nitric oxide (NO):Nitric oxide (NO):Free radical gasVery short half-life (seconds)Metabolized into nitrates & nitrites & perooxynitrite
SynthesisSynthesis
Enzyme: NO synthasePrecursor: L-Arginine
EffectsEffectsRelaxes vascular smooth musclePrevents platelet aggregationBactricidal & tumoricidal effectsNeurotransmitter in brain
NNitric itric OOxide xide SSynthase ynthase (NOS)(NOS)
Two constitiutive NOSTwo constitiutive NOSs s
in endothelium = eNOSeNOS neural = nNOSnNOSconstantlyconstantly produce lowlow level of NOcalcium-calmodulin dependent
One inducible (iNOS)One inducible (iNOS)
Can be expressed in many cells including hepatocytes, macrophages & neutrophils.InducersInducers include bacterial toxins, tumor-necrosis factor & inflammatory cytokinesIt can produce largelarge amounts of NO over hours or even daysCalcium independent
Endotheilal Nitric Oxide Endotheilal Nitric Oxide Synthase (eNOS)Synthase (eNOS)
NO productionNO production
Diffuses to smooth muscles
Activates guanylate cyclase
production of cGMP from GTP
Activation of protein kinase G
Phosphorylstes myosin light-chain kinase (becomes inactive)
Decrease smooth muscular contraction
(RELAXATION)
NO effect on vascular endotheliumNO effect on vascular endothelium
Oxidative Stress: Role of Nitric Oxide (NO)
NO produced by endothelial NOS (eNOS) improving
vascular dilation and perfusion (i.e. beneficial).
Vasodilators such as nitroglycerin is metabolized into NO and
causes vasodilatation
Increased iNOS activity is generally associated with
inflammatory processes
LipidsLipids Proteins Proteins DNA DNA Oxidation of
vitamin E
Lipid peroxidationLipid peroxidation
Membrane damageMembrane damage
Thiol oxidationThiol oxidationCarbonyl formationCarbonyl formation
Damage to CaDamage to Ca2+2+ and andother ion transportother ion transport
systemssystems
DNA damageDNA damage
Cell InjuryCell Injury
Disruption of normalDisruption of normalion gradientsion gradients
Activation/deactivationActivation/deactivationof various enzyme systemsof various enzyme systems
MutationsMutations
Depletion of ATPand NAD(P)H
Adapted from: Kehrer JP, 1993
Cellular Damage Cellular Damage caused by Oxidative Stresscaused by Oxidative Stress
PathologicalPathological conditions that conditions that involve involve
oxidative stressoxidative stress•InflammationInflammation•AtherosclerosisAtherosclerosis•Ischemia/reperfusion injuryIschemia/reperfusion injury•CancerCancer•AgingAging•ObesityObesity
Oxidation of the Oxidation of the lipid components & apo B in LDLlipid components & apo B in LDL
Oxidized LDL Oxidized LDL
Injury of endothelium (inner lining of blood vessels)Injury of endothelium (inner lining of blood vessels)
Monocytes adhere to endothelial cells Monocytes adhere to endothelial cells
Move to (subendothelium) intimaMove to (subendothelium) intima
Monocytes are converted to Macrophages Monocytes are converted to Macrophages
Macrophages uptakes oxidized LDL through scavenger receptor Macrophages uptakes oxidized LDL through scavenger receptor class A (SR-A)class A (SR-A)
Macrophages are converted to Foam cells Macrophages are converted to Foam cells
Release cytokines Release cytokines & participates in formation of & participates in formation of
ATHEROSCLEROTIC PLAQUESATHEROSCLEROTIC PLAQUES
Oxidative stress & Oxidative stress & AtherosclerosisAtherosclerosis
Athersclerotic Plaque FormationAthersclerotic Plaque Formation