an update on oxidative damage to spermatozoa and oocytes

8/19/2019 An Update on Oxidative Damage to Spermatozoa and Oocytes

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Review Article An Update on Oxidative Damage to Spermatozoa and Oocytes

Chinyerum S. Opuwari and Ralf R. Henkel

Department of Medical Biosciences, University of the Western Cape, Robert Sobukwe Road, Bellville , South Africa

Correspondence should be addressed to Ral R. Henkel; [email protected]

Received November ; Revised December ; Accepted January

Academic Editor: Monica Muratori

Copyright © C. S. Opuwari and R. R. Henkel. Tis 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.

On the one hand, reactive oxygen species (ROS) are mandatory mediators or essential cellular unctions including the unction o germ cells (oocytes and spermatozoa) and thereby the ertilization process. However, the exposure o these cells to excessive levelso oxidative stressby toohigh levelso ROS or toolow levelso antioxidativeprotectionwill renderthese cells dysunctional thereby ailing the ertilization process and causing couples to be inertile. Numerous causes are responsible or the delicate bodily redoxsystem being out o balance and causing disease and inertility. Many o these causes are modifiable such as liestyle actors likeobesity, poor nutrition, heat stress, smoking, or alcohol abuse. Possible correctable measures include oremost liestyle changes, butalso supplementation with antioxidants to scavenge excessive ROS. However, this should only be done afer careul examinationo the patient and establishment o the individual bodily antioxidant needs. In addition, other corrective measures include spermseparation or assisted reproductive techniques. However, these techniques have to be carried out very careully as they, i applied

wrongly, bear risks o generating ROS damaging the germ cells and preventing ertilization.

1. Introduction

One o the downalls o all assisted reproduction techniques(ARs), particularly intracytoplasmic sperm injection (ICSI),is thought to be the act that genetically and/or chromosoma-lly damaged spermatozoa may ertilize an oocyte by bypass-ing all the physiological selection barriers in place in theemale organism to prevent such event (or review see []).Te likelihood o using DNA-damaged spermatozoa in ICSI

is much higher since the DNA ragmentation rate is signifi-cantly higher in patients with poor semen quality [, ] andthe DNA damage cannot be recognized while selecting sper-matozoa or this process [] and since there is no practical,nonconsumptive test available that can successully excludeDNA-damaged spermatozoa rom being selected by the emb-ryologist or the injection procedure [, ]. Besides affectingertilization and the outcome o pregnancy, sperm DNAdamage has a negative impact on the health o the offspring asuncorrected sperm DNA damage ollowing zygote ormationhas the potential to create mutations/epimutations in the off-spring []. Tis has been shown or intrauterine insemination(IUI), in vitro ertilization (IVF), and ICSI, and increased

incidences o chromosomal abnormalities, minor and majorbirth deects, or early childhood cancers, particularly in themale offspring, have been linked to these procedures [–].Te level o sperm DNA ragmentation may give a sense o guidance as to the appropriate method o ARs to employ especially between IVF and ICSI [, ]. As a result, numer-ous authors have suggested an introduction o sperm DNAdamage testing into the andrological laboratory workup as anindependent tool as DNA ragmentation apart rom normal

sperm morphology appears to be a reliable and more robustparameterthan conventionalsemen analysis due to itslow bio-logical variability and thus is a useul biomarker that shouldbe implemented in any andrological diagnostic workup [–]. Furthermore, sperm DNA damage appears to be linkedto the most important checkpoints o ertility such as reducedertilization rates, lower embryo quality and pregnancy rates,higher miscarriage rates, malormations, and childhood dis-eases [].

Evidencecontinues to suggest that AR doesincrease risk o higher order pregnancy (with its inherent pre- and perina-tal risks), prematurity and low birth weight, congenital mal-ormations, in particular o the male urogenital system, and

Hindawi Publishing CorporationBioMed Research InternationalVolume 2016, Article ID 9540142, 11 pageshttp://dx.doi.org/10.1155/2016/9540142


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BioMed Research International

imprinting disorders [–]. Paternal sperm DNA damagehas negative effects on the integrity o early embryonic devel-opment as the percentage o good quality embryos as wellas implantation rates was significantly reduced in patientsexhibiting high DNA damage [] and it appears that thesecond and third mitoses are the sensitive periods [].

Ghaleno et al. () showed that the intracellular levels o hydrogen peroxide (H2O

2) and superoxide (O

2

−∙) correlatenegatively with impaired sperm mitochondrial membranepotential leading to poor-quality pronuclear embryos [].However, only H

2O

2 interered with pronuclear ormation.

Reassuringly, evidence points away rom an increased overallcancer risk or differences in neurodevelopmental outcomes.However, many unknowns remain, including uture ertility and cardiovascular risks and risk o cerebral palsy [].

On the other hand, very recent data suggest that the obse-rved increased requency o birth deects, congenital mal-ormations, and chromosomal abnormalities afer assistedreproduction might be due to conounders [, ]. It appearsthat the increase in birth deects because o increased sexchromosome abnormalities is due to the assisted reproduc-tion protocol per se rather than to the biological perturbations[]. Yet in the absence o indubitable evidence o no incre-ased risks it is mandatory to investigate the possible inuenceo the male genome on the health o the offspring with asuitable test.

Considering the inconsistent data situation, the existenceo a variety o different assays that test or different aspects o sperm DNA ragmentation [], anda lack o standardizationand clinical evaluation, which makes it difficult or cliniciansand scientists to decide which assay would be the best orclinical implementation [], it is mandatory in the bestinterest o both prospective parents and the uture offspringto implementa test to evaluate the extent o sperm DNA dam-age. Furthermore, there is still an urgent need or scientists tounderstand the principle on which the respective assays arebased and which aspects o DNA damage these tests measure[]. Te various tests employed or DNA damage, the level atwhich sperm DNA damage may occur, assay principles, andthe advantages and disadvantages thereo havebeen reviewed[].

In this context, numerous reports have been published onthe impact o oxidative stress on spermatozoa (or review see[–]) with its beneficial and detrimental effects o reactiveoxygen species (ROS) like H

2O

2, O

2

−, and/or the hydroxylradical (∙OH) [–]. Yet most literature on oxidative dam-

age to human gametes is ocussing on sperm and less on theoocytes or the oocyte-cumulus complex. Nevertheless, it canbe assumed that this point is not less important or the ertili-zation process, the onset o pregnancy, and the birth o healthy offspring.

2. Oxidative Stress andOocytes/Granulosa Cells

It is well-known that ROS have both beneficial and detri-mental effects in terms o important regulatory unctions andplaying a role in the origin and progression o diseases suchas cancer, neurodegenerative diseases or deleterious effects in

embryo development, respectively, not only on spermatozoa[–], but also on all other cells in the body including cellso the emale reproductive tract such as granulosa cells oroocytes [–].

In this context, not only are ROS levels in the ollicularuid significantly highly elevated in ollicles rom which

poor-quality embryos derived and can thereore be regardedas a marker to determine ovarian and ollicular metabolic age[], but also the antioxidant capacity correlates positively with pregnancy afer intracytoplasmic sperm injection inhealthy women with endometriosis [, ]. Similar relation-ships were ound in women with polycystic ovaries afer IVFand ICSI [, ]. Even the serum and ollicular uid contento vitamins C and E may be related to the success in assistedreproduction [].

On the other hand, in light o a proper redox balance bothROS and antioxidants transduce signals and trigger physio-logical events. It could be shown that ROSproduced by leuko-cytes in the ollicle at ovulation induce oocyte maturation,whereas antioxidants inhibit resumption o meiosis [], thussuggesting a close relationship in the ovary. Tus, or healthy oocyte development a proper interplay o ROS with rele-

vant enzymatic antioxidants such as superoxide dismutase,catalase, glutathione peroxidase, or glutathione reductasemaintains the levels o reduced glutathione (GSH) and thusinhibits atresia o antral ollicles and granulosa cell apoptosis[]. Afer the LH surge triggering ovulation, oocyte GSHconcentration increases rapidly as GSH is essential or ertili-zation events and early embryo development as GSH deple-tion prevents sperm chromatin decondensation and orma-tion o the male pronucleus [–] where GSH is importantor the reduction o the disulphide bridges o the protaminesin the sperm nucleus [, ].

Apart rom the direct inuence in the ertilization andoocyte maturation process and embryo development out-lined above, oxidative stress has been implicated in ovariansteroidogenesis and luteolysis and thereore indirectly affectsemale ertility [, , ].

3. Factors Causing Sperm DNA Damage

Factors that can cause DNA damage include apoptosis,improper DNApackaging and ligation during spermatogene-sis and sperm maturation, andoxidative stress [–]. Reac-tive oxygen species (ROS) can be produced in an ejaculate by the spermatozoa via the normal leakage o electrons rom the

mitochondrial electron transer chain rom Complex I or III[] or leukocytes [, , ]. Eventually, overavailability o these oxidants caused by either an overproduction o ROS orunderavailability o antioxidative protection by various scav-engers leads to an imbalance o the extremely sensitive redoxequilibrium and thus oxidative stress []. Te overavailabil-ity o ROS and the underavailability o antioxidants, respec-tively, can be caused by diseases such as genital tract inec-tions, by unhealthy liestyle, or by the laboratory handling o the gametes in course o an assisted reproduction treatment.

Most o the ocus in the literature is on the detrimentaleffects o ROS on spermatozoa. A target o direct ROS actionis the polyunsaturated atty acids in the plasma membrane


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[, ] leading to lipid peroxidation and direct loss o motil-ity. In addition, ROS can also directly damage the gametes’DNA. On the other hand, indirect action via end productso lipid peroxidation leads to the ormation o carbonyl-containing compounds such as malondialdehyde, various -hydroxy--alkenals suchas -hydroxynonenal and -alkenals

[] which are genotoxic and cancerogenic [, ], thusaffecting male ertility and thereby possibly contributing tohigher rates o malormations. Alternatively, ROS have theability not only to decrease the activity o antioxidative enzy-mes [], but also to damage mitochondrial DNA (mtDNA),which encodes polypeptides essential or the electrontranser chain on the inner mitochondrial membrane and is,thereore, intimately involved in oxidative phosphorylationand AP production in the mitochondria. Hence, mtDNAdeects will inevitably result in a decreased mitochondrialmembrane potential (ΔΨ) thereby throwing the redoxbalance into the direction o oxidative stress. Deective mito-chondrial unction is essential orsperm motility [] andhasbeen suggested as a sensitive sperm parameter [].

An association between male subertility and inertility with the presence o genital tract inection and an increasednumber o leukocytes exists even though other scholars haveon the contrary shown that seminal plasma leukocytes haveno impact on the sperm ertilizing capacity []. Te seminalplasmacontainsnatural antioxidant such as vitamins C andE,superoxide dismutase, glutathione, uric acid, and polyaminespermine which act as a ree radical scavenger. Spermatozoadepend on this scavenging system provided by the seminalplasma afer normal ejaculation in vivo [, , , –].Besides ertility, leukocytes negatively correlate with semenquality, PMN elastase, andROS by secreting cytokine. Leuko-cytes produce , times more ROS than spermatozoa [,], yet there is a stronger correlation between the percentageo ROS producing spermatozoa and sperm DNA damagethan those rom leukocyte derived ROS production []. Interms o the percentages o DNA damage, it was recom-mended that testicular sperm rather than ejaculated sperma-tozoa be used or ICSI [].

Other actors that contribute to DNA damage are spermstorage and sperm separation techniques. Fresh semen sam-ples were shownto have reduced levelso DNA ragmentationwhile the levels o DNA ragmentation increased afer storagesuch that wet-ice reezing andsnap-reezinghad similar effecto the damage in comparison to cryopreservation by ES-yolk buffer with glycerol (YBG) []. From a separation

technique point o view, density-gradient centriugation,swim-up, and density-gradient centriugation ollowed by aswim-up reduced the rate o DNA ragmentation comparedto the increasing effect in resh and washed semen samples,with density-gradient centriugation stepollowed by a swim-up having the most significant effect [].

4. Sperm Separation Techniques

Sperm separation rom seminal plasma is an essential step orany assisted reproduction technique. Even in vivo, sperm areseparated rom the protective seminal uid as the male germcells move out o this milieu and thereby gaining ertilizing

ability and the inhibiting decapacitation actors such asspermine or glycodelins, which are abundant in seminal uid,are removed rom the sperm plasma membrane [–].

Historically, the firstsperm separation technique includedup to two washing procedures in order to remove seminalplasma with subsequent resuspension o male germ cells [–

]. Tis was ollowed by the employment o more sophisti-cated methods using a swim-up procedure rom the washedcell pellet in order to obtain sufficient amount o motile,unctionally competent spermatozoa or IVF []. Followingthese first reports on human sperm separation, more sophis-ticated methods were developed to obtain sufficient amountso motile, unctionally competent spermatozoa or IVF.

Sperm selection or assisted reproduction should aim tominimize the risk o abnormal sperm participating in theprocess o ertilization with the ideal technique being ableto eliminate nonviable spermatozoa, leukocytes, bacteria, andother sources o contamination []. According to Henkel []criteria or a “good” sperm selection include the ollowing:elimination o seminal plasma, decapacitation actors anddebris, ROS producing sperm, leukocytes, and bacteria,enrichment o unctional sperm, cost-effectiveness, ease, andquickness to be perormed, and allowance or larger volumeso ejaculates to be processed.

In each case, care must be taken when employing any o the different methods, also taking the specific situation o the individual patient into account. Currently, the standardsperm processing techniques employed in assisted reproduc-tion programs include simple washing, swim-up, migrationand sedimentation, glass wool filtration, and density-gradientcentriugation (DGC). For the latter, different kinds o gra-dients such as PureSperm®, Percoll® gradients that produce

varying results are used. Te specific advantages and disadvantages have been reviewed []. Other more sophisticatedand more recently developed techniques are annexin V mag-netic activated cell separation which is based on the external-ization o phosphatidylserine [], hyaluronic acid- (HA-)mediated sperm selection based on the presence o HA recep-tors [], electrophoretic isolation [, ], and the zetamethod, which is based on sperm membrane electric charge[].

With respect to finding the most appropriate method toemploy in order to obtain a normal unctional sperm (i.e.,without damage), several studies had been conducted withno consensus reached as to which method between density-gradient centriugation and swim-up method can be rec-

ommended [–]. Te use o apoptotic or DNA-damagedsperm during assisted reproductive techniques (ARs) hasbeen linked to be one reason or suboptimal ertilizationresults. Particularly in cases with extremely poor semenquality, when intracytoplasmic sperm injection (ICSI) needsto be perormed to achieve ertilization, the demand or thesperm separation techniquelies in selecting notonly the mostmotile spermatozoa, but also the most competent ones. Teproblem is that unctional competence o individual spermcells including the quality o chromatin condensation andDNA integrity cannot be assessed using normal light micro-scopy without using individual spermatozoa or the test.Tereore, scientists tried to find physiologic associations


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between visible eatures and the DNA quality and relate theseassociations to sperm separation.

Ricci et al. [] aimed to compare the effects o density-gradient centriugation and swim-up methods on spermquality by the use o multiparameter ow cytometry. Teirfindings indicate that DGC significantly increased the mean

recovery rate o viable sperm (“quantity”), while swim-upsignificantly lowered the mean percentage o apoptotic andnecrotic sperm (“quality”). Furthermore, these authors alsosuggested that both preparatory methods led to obtaining asperm population with a low percentage o apoptotic sperm.Considering the unavailability o ow cytometry in mostAR laboratories, the choice o method o sperm preparationwill depend on whether the sperm will be used or IUI orIVF/ICSI techniques [].

Another study showed that resh and washed semen sam-ples hadthe highestlevels o sperm DNA ragmentation com-pared to swim-up, DGC, and DGC ollowed by a swim-up,with the latter having the most significant effect []. On theother hand, other authors demonstrated that elimination o apoptotic-like spermatozoa rom semen is not very effectiveafer DGC [–]. DGC and the swim-up technique havedifferent efficiencies in removing single- or double-strandedDNA breaks [], o which the ormer is quite effective inisolating spermatozoa with singular characteristics such aslarge size telomere [].

In a different study, DGC brought about a significantreduction in the baseline level o sperm DNA ragmentationbut is deleterious to the sperm DNA longevity afer reezingand thawing in comparison to neat semen samples [].Hence, these authors proposed a direct sperm wash using astandard semen extender and direct sperm isolation usingpolyvinyl pyrrolidone (PVP), thereby avoiding centriuga-tion. Tis principle was first described by Shekarriz et al. []who showed that centriugation time is an essential actorthat causes sublethal damage to spermatozoa due to oxidativestress.

ranslocation o phosphatidylserine (PS) rom the innerto theouterleaet o the plasmamembranetakesplace duringearly stages o apoptosis []. Considering that annexin Vhas a high affinity or PS and binds to externalized PS, thistest serves as an early marker o apoptosis []. Accordingto Hoogendijk et al. [] the use o uorescing conjugateannexin V and ow cytometry with a strict sperm morphol-ogy assessment is a noninvasive method that can be effec-tively used to separate annexin V-negative and V-positive

sperm subpopulations. Tese findings also suggested thatannexin V-negative spermatozoa have a morphologically superior quality compared to the annexin V-positive subpop-ulation [].

Bungum et al. [] recommended that sperm DNA anal-ysisby meanso the SCSAshouldbe perormed onraw semenaliquots, as elevated DFI identified in neat semen may reectchromatin abnormalities within an entire sperm populationand are not completely eliminated by density-gradient cen-triugation or swim-up []. Hence, the DFI in neat semenis regarded as predictive o the treatment outcome o ARwhereas the determination o thisparameter in DGC sampleswould not be predictive o pregnancy outcome [, –].

Similar to Jackson et al. [], oro and coworkers []showed a significant increase in DFI in samples incubated or– hours at room temperature in comparison to nonincu-bated (resh) semen samples. Te implication o this findingor AR is that the DFI can be higher in processed semensamples, that is, incubated at room temperature or cryopre-

served. In addition, in a fixed aliquot used or DNA ragmen-tation testing beore insemination the DNA damage as deter-mined by means o the SCSA can be different rom thatin the sample directly used or oocyte insemination [].Hence, unnecessary incubation o semen in the laboratory should be avoided, as increased sperm DNA ragmentationwas observed during aerobic incubation o semen and afersemen cryopreservation [].

Since the s, cryopreservation o human spermatozoahas been a routine practice in many assisted reproductivetechnology laboratories [] and has become an integralpart o ARs []. However, this technique poses the risk o oxidative stress with increased apoptotic DNA ragmentationregardless o the sperm concentration, yet the percentageo DNA-damaged sperm is higher in oligozoospermic men[]. It appears that particularly the thawing process o cry-opreserved sperm results in increased oxygenradical induceddamage that leads to sperm DNA ragmentation []. Teseeffects o ROS on DNA integrity include abasic sites, cross-linking, modification o nitrogenous bases, and DNA strandbreakages [, ].

Repeated reezing and thawing cycles are usually offeredto patients in order to maximize the use o the availablesperm or reasons that may include maximizing the usage o samples obtained or cryopreservation beore the treatmento cancer or other diseases, rom patients with severe oligo-zoospermia or intermittent azoospermia, sexual dysunction,or or the purpose o cost-effectiveness []. Several studieshave demonstrated the detrimental effects o repeated cycleso reezing and thawing to not only decrease the percentageo motile and viable sperm but also increase the percentageo sperm with DNA damage [–]. On the other hand,repeated reezing and thawing up to three cycles producedsimilar level o risk with respect to sperm DNA damagein comparison to a single cycle, provided the samples arererozen in their original cryoprotectant and not washed orhave undergone any urther treatment and are separated by DGC or swim-up beore use in AR [].

Most o the studies employed to test or DNA integrity are testing either potential (e.g., SCSA) or real (e.g., UNEL

assay) DNA ragmentation, with the relevant advantages ordisadvantages []. Even though in the absence o ragmenta-tion, significant DNA damage could still be detected in somegenome regions []. In order to use a molecularly healthy semen sample or insemination, Valcarce et al. [] recom-mended a quantitative PCR- (qPCR-) base technique that canbe used or DNA evaluation in specific genes (PRM, BIK,FSHB, PEG/MES, ADD, ARN, UBEA, and SNORD/PWSAS) that could assist in selecting and improving cryop-reservation protocols used in clinics []. In order to inves-tigate and compare commercially available cryoprotectantmedia in terms o DNA integrity o spermatozoa recoveredafer cryopreservation and separation using DGC, Tomson


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et al. [] ound no significant difference between each typeo cryoprotectant to preserve DNA integrity or in its ability topredict the percentage o ragmented DNA afer cryopreser-

vation, thawing, and DGC.Finally, considering that the current most requently used

sperm separation methods swim-up and density-gradient

centriugation are essentially limited in their selection o themost unctionally competent spermatozoa, particularly incases o poor and very poor semen quality, new proceduresthat could saely and efficiently select motile sperm are desir-able [] and are either in practical use such as motile spermorganelle morphological examination (MSOME) which, incombination with ICSI (IMSI) or afer HA-binding (PICSI),showed ability to select unctionally competent spermatozoaor in an experimental stage such as Raman spectrometry [] or polarization microscopy [] (or review see []). Inthe context o applying physiological criteria or the spermselection, chemotaxis, thermotaxis, and probable oviductalcontraction are also thought to be some o the physiologicmechanisms that successully guide the sperm along theemale genital tract []. A microchannel-based device thatmimics the mammalian emale reproductive tract and allowsor both motility screening and chemotaxis testing simulta-neously resulted in the selection o competent spermatozoawhich could possibly be used or IVF to improve ertilizationand pregnancy rates [].

5. Effects of Lifestyle

Te reproductive system has evolved over millions o years.Yet the human is unique as we are severely and rapidly notonly changing our own environment, but also changing ourbehaviour and habits in a negative way. In addition, humanspermatogenesis appears to be genetically impaired as com-pared to other animal species [] and a number o muta-tions in ertility genes considered important in other speciesare evident [, ] and apparently make the human speciesessentially subertile and more susceptible to negative envi-ronmental inuences [].

Among the liestyle actors negatively inuencing arecigarette smoking, drugs, alcohol abuse, heat exposure, orobesity. Te common eature o the exposure o a man’s body to these actors is the significant increase o reactive oxygenspecies causing oxidative stress leading to inertility as well ashaving significant effect on the offspring. Significant associ-ations exist between paternal smoking and increased sperm

DNA damage and elevated levels o -hydroxy--deoxygua-nosine (-OHdG) [, ] caused by the high cadmiumcontent o cigarette smoke which is known to trigger andpromote DNA damage [–]. Te DNA damage is urtherexacerbated by the presence o SerCys polymorphism inthe -oxoguanine DNA glycosylase (OGG) gene [].OGG is downregulated by cadmium []. In addition, pate-rnal, but not maternal, cigarette smoking is positively associ-ated with an increased risk o early childhood cancer in theprogeny [, , ]. Moreover, the risk o oxidative damageto sperm in smokers is even higher as this habit causes a %increase in seminal leukocyte concentration and ROS []as well as a decrease in antioxidant levels [, ].

Alcohol has also been described as a potent systemicstimulator o ROS [, ], which would then contributeto seminal oxidative stress. Tese studies also reveal thatalcoholicmen ofen suffer rom a lack o antioxidative deencedue to insufficient diets, a act which in turn worsens thesituation. Maneesh et al. [] reported that alcoholic men

had significantly reduced plasma testosterone concentrationsconfirming the disturbances in the hypothalamus-pituitary-gonadal axis []. It also seems that chronic alcohol abuseleads to a higher risk o XY chromosome aneuploidy as com-pared to nondrinkers [].

Another parameterthat is significantly changed as a resulto our modern liestyle is testicular temperature. Te ratio-nale behind thisthermosensitivity is that in most mammalianspecies, including man, the testicles are located extracorpo-rally in the scrotum resulting in scrotal temperatures o about∘C-∘C. In addition, it is notable that the scrotal skin has

very little hairs and numerous sweat glands, which ensurethat the evaporating moist is cooling down the scrotumincluding the testicles. Moreover, the pampiniorm plexusrepresents an effective heat exchanger by means o a counter-ow mechanism which cools down the arterial blood inow into the testes (or review see [, ]). Tese mechanisms,together with the actions o the dartosand cremaster muscles,lead to effective testicular thermoregulation (or review see[]). It is thought that lower scrotal temperatures reduceoxidative damage to the sperm DNA and lower the metabolicrate in the epididymis leading to less mutations and thereoreto less oxidative stress, respectively [, , ]. Numerousstudies revealed that both Sertoli cells and the process o spermatogenesis per se are sensitive to elevated temperatures,particularly the steps o the transition rom gonocytes tospermatogonia Adark , as well as rom primary to secondary spermatocytes [–].

Te act that many people have jobs with sedentary posi-tions such as office workers and taxi or long-distance driversor many men are occupationally exposed to high tempera-tures, or example, in the welding or metal manuacturingindustry or in bakeries, and, also, regular wet heat exposureo the testicles in Jacuzzis, saunas, or hot baths can have asignificant negative effect on semen quality []. Te latterexposure appears to be reversible as studies o Jung et al. [,] have shown that nocturnal scrotal cooling can improvesemen quality. Well-known pathologies which lead to ele-

vated testicular temperatures are cryptorchidism and varic-ocele o which both conditions have been shown to be a

cause o sperm DNA ragmentation due to induction o apo-ptosis with subsequent consequences or the developingemb-ryo [, ].

Last but not least, overweight, obesity, and metabolicsyndrome not only are increasing problems worldwide con-tributing to the overall burden o other chronic illnesses andcausing major conditions such as cardiovascular diseases,but also significantly affect male ertility via various possiblemechanisms. Particularly, obesity and the metabolic syn-drome are considered to cause a systemic inammatory con-dition with increased levels o C-reactive protein and inam-matory cytokines [] and ROS []. Several authors [–] could demonstrate the significant negative effect o


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obesity on sperm count, motility, and unction. Significantdifferences between metabolic syndrome patients and normalertile donors were ound not only orsperm motility or DNAragmentation, but also or serum and seminal inammatory cytokines such as NF, IL-, IL-, and IL- with valuesbeing significantly higher in seminal plasma (Leisegang et

al., unpublished). Tus, it appears that these inammatory cytokines per se stimulate lipid peroxidation [, ], aprocess which is triggered and propagated by ROS [], andin turn cause DNA damage. On the other hand, accordingto a recent small study including six obese men by Faureet al. [], it appears that obesity is a correctable liestyleactor as significant loss o abdominal at through a liestyleprogram led to significantly decreased sperm DNA ragmen-tation, increased serum testosteronelevels, decreased seminaloxidative stress by increased superoxide dismutase levels,and, most importantly, pregnancy in all spouses included inthe study.

6. ConclusionSince human liestyle and behaviour and environmentalpollution significantly affect male reproductive unctionsincluding the ertilizing ability o spermatozoa, more andmore couples are suffering rom male inertility posing anincreasing global problem. As a result, assisted reproductivetechniques had been developed in which scientists and clini-cians try to select the most competent spermatozoa to be usedorthe ertilization process. However, all these efforts are only dealing with the symptoms and consequences o the problemas many o the actors causing oxidative stress to the malegerm cells are modifiable either by avoidance o exposureto environmental toxicants or by behavioural changes (e.g.,stopping smoking and drinking, wearing loose underpants)or by loss o weight and ollowing a healthy diet [].Alternatively, oxidative stress can be reduced by taking clin-ically ormulated antioxidant supplements which i correctly administered to the patient can improve the success rate o reproduction. Yet uncontrolled intake o the so-called healthy supplements can also cause harm and significant adverseeffects [, , ]. Tereore, a complete evaluation, notonly o the individual patient, but also o the sperm nucleusquality, should be mandatory [].

Conflict of Interests

Te authors declare that there is no conict o interestsregarding the publication o this paper.

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