RELATIONSHIP BETWEEN BENZO(A)PYRENE-INDUCED DNA-BASE MODIFICATION AND FREQUENCY OF REVERSE MUTATIONS IN MUTANT STRAINS OF SALMONELLA-TYPHIMURIUM

  • 1 January 1981
    • journal article
    • research article
    • Vol. 41  (9) , 3400-3406
Abstract
Salmonella typhimurium cells (TA98 and TA100) were incubated with [3H]benzo(a)pyrene ([3H]BP) and induced rat liver microsomes. The BP-induced cytotoxicity and His+ reverse-mutation frequencies were determined and bacterial DNA hydrolysates chromatographed on Sephadex LH-20. Analysis indicated 3 principal DNA adducts formed from the 2 diastereoisomeric BP diol-epoxides and a 9-hydroxybenzo(a)pyrene metabolite. An 8.6-fold increase in TA100 cell concentration in the microsome incubation was paralleled by a 7.2-fold decrease in total adducts per cell and a 7.4-fold decrease in mutation frequency. Separate TA98 incubations were titrated with increasing concentrations of [3H](.+-.)-7.beta.,8.alpha.-dihydroxy-9.alpha.,10.alpha.-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene ([3H]anti BP diol-epoxide),[3H](.+-.)-7.beta.,8.alpha.-dihydroxy-9.beta.,10.beta.-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene [3H]syn BP diol-epoxide), or [3H)9-hydroxybenzo(a)pyrene. Linear, nonsaturated increases in DNA adduct levels were seen up to the highest observed concentrations of 4.00 .mu.M BP diol-epoxide or 6.00 .mu.M 9-hydroxybenzo(a)pyrene in TA98 and TA100 cells. The increasing adduct levels were accompanied by linearly increasing mutation frequencies. At equivalent concentrations of the 2 BP diol-epoxides, an average of 8.2-fold more base substitution mutations (TA100) were seen than frameshift mutations (TA98). Significant differences appeared in absolute mutagenic efficiency (mutation frequency/unit modified DNA) between these 3 covalent DNA ligands (TA98, syn BP diol-epoxide > 9-hydroxy-4,5-epoxy-benzo(a)pyrene > anti BP diol-epoxide; TA100, 9-hydroxy-4,5-epoxy-benzo(a)pyrene > syn BP diol-epoxide > anti BP diol-epoxide).