HIGH MUTAGENIC ACTIVITY OF N-NITROSOBIS(2-OXOPROPYL)AMINE AND N-NITROSOBIS(2-HYDROXYPROPYL)AMINE IN THE HOST-MEDIATED ASSAY IN HAMSTERS - EVIDENCE FOR PREMUTAGENIC METHYL AND HYDROXYLPROPYL ADDUCTS

The carcinogenic nitrosamines N-nitrosobis(2-oxopropyl)-amine (BOP) an d N-nitrosobis(2-hydroxypropyl)amine (BHP) were tested in excision-rep air-deficient strains of hisG46 Salmonella mutants in the intrasanguin ous host-mediated mutagenesis assay (HMA) in male Syrian hamsters. The major adducts produced by BOP in the hamster are methylguanines, whil e BHP leads to hydroxypropylguanines as well as methylguanines. Both n itrosamines were potent mutagens in bacteria recovered from the liver. On a comparison of administered dose, BOP was more potent, but when c ompared at doses producing similar levels of O6-methylguanine (O6-MeG) in host liver DNA, or at equitoxic doses in the hamster, BHP was more potent. BHP was approximately 10 times less mutagenic in an excision- repair-proficient strain of Salmonella, but the mutagenicity of BOP wa s not reduced. The effects of excision repair on in vitro mutagenesis induced by the direct-acting analogs N-(2-oxopropyl)-N-nitrosourea (OP NU), a methylating agent, and N-(2-hydroxypropyl)-N-nitrosourea (HPNU) , a hydroxypropylating agent, were also examined. Mutagenesis by HPNU, but not OPNU was very sensitive to excision repair. Thus BOP appears to lead to mutagenesis via methylation, while mutagenesis by BHP appar ently proceeds via hydroxypropylation. BOP, BHP, OPNU and HPNU were se veral times less mutagenic in hisG428 than hisG46 strains. In contrast to hisG46 strains, which are reverted mainly by base-pair substitutio ns at G:C base pairs, hisG428 strains are generally more sensitive to mutagenesis at A:T base pairs. Taken together the above results and ob servations that > 90% of the adducts from BOP and BHP were alkylguanin es, suggest that the major premutagenic adducts produced from BOP and BHP are alkylguanines as opposed to other alkylated bases. BOP and BHP were weak mutagens in the Salmonella IS-9 mutagenesis assay using ham ster liver S-9 fraction. When compared with results in the HMA, BOP an d BHP were orders of magnitude less mutagenic in vitro. This observati on suggests: (i) the pathways or enzymes involved in the activation of these carcinogens (although uncertain) may be different in vivo and i n vitro; or (ii) the pathways for the in vitro and in vivo metabolism may be similar, but the conditions used for the in vitro activation of these nitrosamines are inadequate to generate significant levels of n itrosamine metabolites.