Designation:E1398–91(Reapproved2003)StandardPracticeforInVivoRatHepatocyteDNARepairAssay1ThisstandardisissuedunderthefixeddesignationE1398;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(e)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1ThispracticecoversatypicalprocedureandguidelinesforconductingtheratinvivohepatocyteDNArepairassay.Theprocedurespresentedherearebasedonsimilarprotocolsthathavebeenshowntobereliable(1,2,3,4,5).21.2Mentionoftradenamesorcommercialproductsaremeantonlyasexamplesandnotasendorsements.Othersuppliersormanufacturersofequivalentproductsareaccept-able.1.3Thisstandarddoesnotpurporttoaddressallofthesafetyconcernsassociatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappropriatesafetyandhealthpracticesanddeterminetheapplicabilityofregulatorylimitationspriortouse.2.SignificanceandUse2.1MeasurementofchemicallyinducedDNArepairisameansofassessingtheabilityofachemicaltoreachandaltertheDNA.DNArepairisanenzymaticprocessthatinvolvesrecognitionandexcisionofDNA-chemicaladducts,followedbyDNAstrandpolymerizationandligationtorestoretheoriginalprimarystructureoftheDNA(6).ThisprocesscanbequantitatedbymeasuringtheamountoflabeledthymidineincorporatedintothenuclearDNAofcellsthatarenotinS-phaseandisoftencalledunscheduledDNAsynthesis(UDS)(7).Numerousassayshavebeendevelopedforthemeasure-mentofchemicallyinducedDNArepairinvariouscelllinesandprimarycellculturesfrombothrodentandhumanorigin(4).TheprimaryculturerathepatocyteDNArepairassayhasproventobeparticularlyvaluableinassessingthegenotoxicactivityofchemicals(8).Genotoxicactivityoftenresultsfrommetabolitesofachemical.Theinvitrorathepatocyteassayprovidesasysteminwhichametabolicallycompetentcellisalsothetargetcell.Mostotherinvitroshort-termtestsforgenotoxicityemployaratliverhomogenate(S-9)formetabolicactivation,whichdiffersmarkedlyinma...
