50-Hz electromagnetic fields enhance cell proliferation and(4)

Fromapathogeneticviewpoint,itcanbehypothesizedthatshort-termexposurestoELF-EMF,andconsequentformationofROS,inducegrowthstimulationandincreasethenumberofDNAsynthesizingcells.Long-termexpo-surestoELF-EMFandcontinuousgenerationofROSeventuallycauseaccumulationofDNAdamage,whichslowsdowntheprogressionofthecellcycle.Collectively,thepercentageofcellsintheSphasewasinverselyrelatedtoDNAdamageanddirectlyrelatedtoDNArepair(cf.Table1andFig.3).TheseresultsareconsistentwiththerecentevidenceforarelationshipbetweencellcycledistributionandsusceptibilitytooxidativeDNAdamage[34].AccordingtothisinterpretationcellcyclearrestinG1protectsagainstoxidativeDNAdamage,demonstratinganinverserelationshipbetweencellproliferationandoxidativeDNAdamage.ReactiveoxygenspecieshavebeententativelyproposedtomediatetheeffectsofELF-EMF[35].WehaveextendedandvalidatedthisconceptbydemonstratingthatasizableincreaseofROSoccurredshortlyafterexposuretoELF-EMFandprecededactivationofmoleculareventsabletoinducecellproliferation(cf.Figs.6–8).Inaddition,wehaveshownthatanantioxidantlikea-tocopherolbluntedtheincreaseofROSandconsistentlypreventedproliferationandDNAdamageinducedbyELF-EMF(cf.Table2andFigs.4–7).Itisworthnotingthattheeffectofa-tocopherolwasmorepersistentinWI-38cellsthaninHL-60cells,andexhibitedanintermediatedurationinRat-1cells(cf.Table2andFig.4).Thismightbeattributedtocell-specificratesofincorporationandmetabolismofa-tocopherol,asshowninpreviousstudiesofotherantioxidants[36].

WealsoprovidenovelinformationaboutthemechanismwherebyROScanmediatetheeffectsofELF-EMFoncellproliferation.Infact,ourdatademonstratethatELF-EMFincreasethelevelsofNFnB-relatedproteins,mostnotablyp65,whilealsodecreasingthelevelsofInBa(cf.Figs7and8).Theincreasedlevelsofp65,inconjunctionwiththereducedlevelsoftotalInBa,haveafunctionalroleinregulatingtranscriptionprocesses,asp65-p65[37]homo-dimersorp50-p65heterodimers[26]areknowntoactivatetranscription.Antioxidantpretreatmentwitha-tocopheroldoesnotinterferewiththeeffectsofELF-EMFonp65orp50butincreasesthelevelsofInBainsuchamanner

that

128F.I.Wolfetal./BiochimicaetBiophysicaActa1743(2005)120–129

theratioofp65toInBareturnstoessentiallythesamelevelsofuntreatedcells.Bydoingso,a-tocopherolprecludesnucleartranslocationofp65-p50activecom-plexes[38].

TheprecisemechanismsthroughwhichELF-EMFincreasecellularROSproductionremainunknown.Like-wise,wecannotspeculatewhichparticularreactivespeciesmediatedtheproliferativeandDNA-damagingeffectsandhowsuchreactivespeciescouldbescavengedbya-tocopherol.DichlorofluoresceiniswidelyusedfordetectingcellularROS,andreportedlyexhibitsapeculiarspecificityforhydrogenperoxide[39];however,chemicalstudiesshowthatDCFactuallydetectsamuchbroaderarrayofreactiveintermediates[40].Alpha-tocopherolisoneofthemosteffectivelipid-solubleantioxidantsand,assuch,wouldbeexpectedtoscavengelipidcenteredradicalsratherthanhydrogenperoxideorthehydroxylradicalsthateventuallyform8-OHdGadductssuchasthosedetectedinourstudy.Nonetheless,previousstudiesshowedthata-tocopherolinhibitedtheformationofDCF-detectableROSincells[41],andwasabletodiminishDNAstrandbreaksinducedbyhydrogenperoxide[42].Ourfindingsthata-tocopheroldecreasestheyieldofDCF-detectableROSincellsexposedtoELF-EMF,whilealsodiminishingproliferationandDNAoxidativedamage,mustthereforebeappreciatedwithinthecontextofanoxidizingtoneinwhichmorethanoneoxidantwasinvolvedanda-tocopherolprobablyactedonmorethanonefreeradicalspecies.

ThebiologicaleffectsofELF-EMFremainamatterofdebate,asindicatedbyrecentpaperssupporting[8,43–46]ordisproving[47–49]aneffectofELF-EMFoncellgrowthandDNAdamage.Thesediscrepanciesmightatleastinpartbeattributedtoexperimentalfactorslikeintensityanddurationofexposureorthecelltypesusedinthedifferentstudies.HerewehaveshownthatELF-EMFfirstincreaseproliferationandtheninducereversibleDNAdamageinnormalandleukemiccellculturescharacterizedbydifferentgrowthrates.Thus,ourmodelshowsthatbothcellgrowthandDNAdamagecanbeobservedincellpopulationsthatareexposedtoELF-EMFforasufficientlylongtimeandthenareallowedtorecoveraftertreatment.Theconsequen-cesofthesedualandtime-dependenteffectswoulddependontheDNArepaircapacityofcells,ortheaccumulationofpotentiallycarcinogenicmutations,orthecouplingofDNAdamagewithapoptosis.HavingoneconsequenceortheotherwillalsodependonenvironmentalornutritionalfactorsthatmodulatetheimpactofELF-EMFonthecell.Theseresultsmaythereforebeofvaluetodevelopresearchandnewinvestigationalmodelsonthepotentiallydelete-riouseffectsofELF-EMF.

Inconclusion,thedatareportedinthispaperconfirmthatELF-EMFinfluencecellproliferationandsusceptibilitytoDNAdamage,anduncovermechanismsthroughwhichROSmaybeimportantinthesesettings.Sucheffectsareseeninnormalortransformedcellswithverydifferentproliferationrates,andthushighlighttheimportanceof

characterizingtheroleofELF-EMFinthecomplexprocessofcarcinogenesisortumorprogression.

Acknowledgements

ThisworkwassupportedbyCOFINnos.2001064293and2003067599toF.I.Wolfand2002064819toC.G.byISPESL(IstitutoSuperioreperlaPrevenzioneelaSicurezzadelLavoro)andUCSC.

References

[1]N.Wertheimer,E.Leeper,Am.J.Epidemiol.109(1979)273–284.[2]M.S.Linet,E.E.Hatch,R.A.Kleinerman,L.L.Robison,W.T.Kaune,

D.R.Friedman,R.K.Severson,C.M.Haines,C.T.Hartsock,S.Niwa,S.Wacholder,R.E.Tarone,NewEngl.J.Med.337(1997)1–7.[3]L.M.Green,A.B.Miller,P.J.Villeneuve,D.A.Agnew,M.L.

Greenberg,J.Li,K.E.Donnely,Int.J.Cancer82(1999)161–170.[4]UKChildhoodCancerStudyInvestigators,Lancet354(1999)

1925–1931.

[5]A.Ahlbom,E.Cardis,A.Green,M.Linet,D.Savitz,A.Swerdlow,

Environ.HealthPerspect.109(2001)911–933.

[6]W.Z.Fam,E.L.Mikhail,CancerLett.105(1996)257–269.

[7]G.A.Boorman,D.L.McCormick,J.M.Ward,J.K.Haserman,R.C.

Sills,Radiat.Res.153(2000)617–626.

[8]M.DeMattei,A.Caruso,G.C.Traina,F.Pezzetti,T.Baroni,V.

Sollazzo,Bioelectromagnetics20(1999)177–182.

[9]M.J.RuizGomez,L.DelaPena,J.M.Pastor,M.MartineMorill,L.

Gil,Bioelectrochemistry53(2001)13 …… 此处隐藏：5831字，全部文档内容请下载后查看。喜欢就下载吧 ……