Metabolism of aflatoxin B 1 in rhesus monkeys.

Abstract

J.I.DaleziosandG.N.WoganDepartmentofNutritionandFoodScience,MassachusettsInstituteofTechnology,Cambridge,Massachusetts02139SUMMARYThemetabolismofaflatoxinB,hasbeeninvestigatedinmalerhesusmonkeysgiveni.p.injectionsofamixtureofring-labeledaflatoxinB!-'4Candnonradioactivetoxin,atatotaldoseof0.4mg/kg.Thirty-five%oftheadministeredradioactivitywasexcretedinurinewithin96hr.Theexcretionratereachedamaximum1hrafterdosingandthenfellrapidly,buturineexcretedafter96hrstillcontaineddetectableradioactivity.Anewmethodforisolationandidentificationofurinaryaflatoxinmetaboliteswasdevised.Ofthetotalurinarymetabolites,only12to15%werechloroformextractable,includingatleast3fluorescentmetabolitesofunknownstructureinadditiontoaflatoxinsB!andMI.Chloroform-insolublemetaboliteswereisolatedonanAmberliteXAD-2columnandseparatedbyaDEAE-SephadexA-25columninto6subfractions.Themajorsubfraction(60%)washydrolyzedalmostquantitativelybyAŸ-glucuronidaseandtheliberatedmetabolitewasidentifiedasaflatoxinPj,the0-demethylationproductofaflatoxinB!.AflatoxinP,inurinerepresentedapproximately20%oftheadministereddose,17%asglucuronide,3%assulfate,and1%asunconjugated phenol.AflatoxinsM,andB,inurineaccountedfor2.3and0.01to0.1%ofthedose,respectively.Fourdaysafterinjection,5.6%oftheaflatoxindosewasstillretainedbyliverandwasmainlyboundtoliverproteins.Radioactivityinbloodattainedapeakat1hrafterinjection,andat96hritdecreasedto40%ofitsmaximumvalue.Gelelectrophoresis ofserumfollowedbyautoradiographyindicatedassociationoftheradioactivitywiththealbuminfraction.INTRODUCTIONVariousaspectsofthemetabolicfateofaflatoxinBhavebeeninvestigatedinanimals.AflatoxinM],ahydroxylatedderivative,hasbeenidentifiedbyfluorescencetechniquesasametaboliteappearinginthemilkandurineofcows,sheep,andratsdosedexperimentallywithB!(seeRef.21forreview).Ithasalsobeenfoundintheurineofhumansingestingaflatoxin-contaminateddiets(4).Inanimalsandhumans,onlyabout5%ofingestedB,appearstobeexcretedasMIinurine(4,21).ThekineticsofaflatoxindistributionandexcretioninratshasbeenquantitativelystudiedwiththeuseofradioactiveaflatoxinB!(22).ThesestudiesindicatedurinaryexcretionofsubstantiallylargeramountsofaflatoxinderivativesthancouldReceivedApril17,1972;acceptedJuly13,1972.beaccountedforbyaflatoxinM(andalsothat0-demethyla-tionconstitutedamajorpathwayofmetabolicconversion.Knowledgeofthemetabolismofthetoxinisimportanttoanunderstandingofthefactorsdeterminingresponseandalsoforextrapolationofanimaldatatoevaluatehumanrisk.WethereforeundertookinvestigationsofthepharmacokineticsofaflatoxinB!-I4Cinrhesusmonkeyswiththefollowingobjectives:developingmethodologyadequateforseparationandisolationofurinarymetabolites; determining thequantitativerelationshipsbetweenexcretionofmetabolitesandadministereddose;anddeterminingthedistributionofinjectedaflatoxinBjintissuesandblood.Monkeyswereselectedfortheseinvestigationsinordertoobtaininformationonurinaryexcretorypatternsinaprimatethatcouldsubsequentlybecomparedwithobservationsinotherspecies,ultimatelyincludingman.Developmentofmethodologyforquantitativerecoveryofurinarymetaboliteswasgreatlyfacilitatedbytheuseoftheseanimals.Inthecourseoftheseexperiments,aflatoxinP,wasisolatedandidentifiedasamajorurinarymetabolite,aswehavereportedelsewhere(7).Thispapersummarizedfindingsofotherphasesoftheinvestigation.MATERIALSANDMETHODSMalerhesusmonkeyswereprovidedbyandhousedattheNewEnglandRegionalPrimateResearchCenter,Southboro,Mass.Theyweighed2.5to4.0kgandweremaintainedonaPurinachowdietsupplementedwithfreshfruit.Duringmetabolismexperiments,theanimalswerekeptinarestrainingchair.Forfacilitationofquantitativetimedurinecollection,waterwaswithheldovernight;thenaccesstoitwasprovided2hrbeforeeachexperimentbegan.Theanimalsweregivenfoodthroughoutthecourseofthestudyperiod,andurinewasquantitativelycollected,withoutfecalcontamination,inavesselsubmergediniceandprotectedfromlight.AflatoxinBI,labeledwith'4Cintheringcarbons(1),waspreparedfromacetate-l-14CaccordingtothemethodofDonkerslootetal.(8), thespecificactivityof finalpreparationbeing29.6/nCi/^mole.Purityofthepreparationwasverifiedbythin-layerchromatographyonSilicaGelGHR(Brinkmann Instruments, Inc.,Westbury,N.Y.)platesdevelopedwithchlorofornracetone, 9:1(v/v).Autoradiographyandexposuretolong-waveUVlightshowednocontaminationbyothersubstanceswithinadetectionlimitof1.6X10~2nCi.NonradioactiveaflatoxinB,wasisolatedbyChromatographiefractionofcultureextracts.Dimethylsul-foxide(spectralgrade;BurdickandJacksonLaboratories,Muskegon,Mich.)wasusedastheaflatoxinvehicle.OtherNOVEMBER1972 2297