Environmental Engineering Reference
In-Depth Information
Korach.2006,.Phillips.and.Foster.2008a,b)..According.to.the.2001.WHO.report,.
at. least. 80. million. worldwide. were. estimated. to. be. affected. by. infertility..
Among.those,.more.than.10%.of.infertility.cases.cannot.be.explained.medi-
cally,. which. is. probably. attributed. to. the. chronic. exposure. to. low. level. of.
environmental.pollutants,.as.early.as.
in utero
..Therefore,.research.is.needed.
to. elucidate. the. role. and. the. mechanistic. actions. of. pollutants. in. wildlife.
and.humans,.for.the.protection.of.our.future.generations.from.reproductive.
problems.
EndocrineDisruptorsandTheirEffectsonEmbryo
DevelopmentandEpigenomicModification
There.is.increasing.epidemiological.evidence.to.suggest.that.environmental.
exposure.to.EDs.early.in.the.fetal.development.has.a.role.in.susceptibility.to.
reproductive.dysfunction.and.disease.in.later.life.(Jirtle.and.Skinner.2007)..
Interestingly,.numerous.protection.strategies.have.been.identiied.in.animal.
embryos.to.provide.robustness.for.buffering.the.developmental.processes.in.
response.to.changing.stress.conditions.(Hamdoun.and.Epel.2007)..Although.
cellular. mechanisms. in. embryos. can. buffer. the. stress. encountered,. expo-
sure. to. highly. bioactive. chemicals/pollutants. may. overwhelm. this. intrin-
sic. robustness.. We. have. learned. the. lesson. from. human. exposure. to. the.
synthetic. estrogen,. diethylstilbestrol,. and. thalidomide;. these. can. induce.
changes. in. the. development. of. reproductive. tract. in. male. and. female. off-
spring,.lower.sperm.counts,.increase.incidence.of.vaginal.cancer,.and.cause.
severe.developmental.malformations.(Finnell.et.al..2002,.Rubin.2007)..In.ani-
mal. study. that. used. rodents. reported. the. link. between. prenatal. exposure.
to.several.phthalates.and.a.shortening.of.the.anogenital.index.(Swan.et.al..
2005)..These.examples.illustrate.that.the.placenta.cannot.provide.complete.
protection. to. the. developmental. fetus.. The. leakage. of. environmental. tox-
ins.via.placenta.barriers.to.developmental.fetus.has.been.reported.(Couture.
et.al..1990,.Safe.1990).
Using.
in utero
.exposure.studies.in.rodent.models.as.well,.transient.expo-
sure. of. gestating. female. rats. to. a. fungicide. (i.e.,. vinclozolin). or. a. pesticide.
(methoxychlor,.a.substitute.for.DDT),.between.E8.and.E15,.decreased.sper-
matogenic.capacity.and.increased.infertility.in.male.offspring..These.effects.
were.found.to.be.manifested.via.an.alternation.of.DNA.methylation.patterns.
in.germ. line,.leading. to. changes.in.embryonic.testis. transcriptome.in. sub-
sequent.generations.(Anway.et.al..2005,.Anway.and.Skinner.2008,.Jirtle.and.
Skinner.2007)..Other.reports.demonstrated.that.the.exposure.of.preimplanta-
tion.embryo.to.dioxin. caused.an.increase.in.the.cellular. methyltransferase.
activity.(Wu.et.al..2004),.establishing.a.possible.link.between.EDs.and.epi-
genetic.modiication..More.recently,.Jirtle's.group.demonstrated.that.rodents'.
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