Rat and human explant metabolism, binding studies, and DNA adduct analysis of benzo(a)pyrene and its 6-nitro derivative.

Human colon and bronchus tissue explants were incubated with either [3H]benzo(a)pyrene ([3H]BP) or [3H]-6-nitrobenzo(a)pyrene ([3H]-6-NBP). The total percentage of metabolism of BP and 6-NBP was, respectively, 8-59% and 18-41% in bronchus and 11-23% and 36-50% in colon. A product tentatively identified as 3-hydroxy-6-NBP was isolated from the 6-NBP incubation medium. BP and 6-NBP when incubated at equivalent concentrations were found to bind covalently to the DNA of human bronchi from 15 cases at means of 42 and 50.9 pmol/10 mg DNA, respectively, and to the DNA of human colon from 6 cases at means of 66.5 and 35 pmol/10 mg DNA, respectively. The range among individuals was within one order of magnitude. High pressure liquid chromatography (HPLC) of enzymic hydrolysates of human bronchus explant DNA revealed one adduct from the BP-incubated bronchus which cochromatographed with (+/-)-7,8-dihydroxy-9,10-epoxy-7,8,9, 10-tetrahydrobenzo(a)pyrene-deoxyguanosine and a possible two adducts from the 6-NBP-incubated bronchus which eluted earlier than did the BP adduct. DNA obtained from the lung or liver of rats given 2.0-mg/kg doses of either [3H]BP or [3H]-6-NBP by i.p. injection was also enzymically hydrolyzed and analyzed on HPLC. Three DNA adducts were observed in liver and two were observed in lung DNA hydrolysates from rats given injections of [3H]BP. One adduct from each organ cochromatographed with (+/-)-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene- deoxyguanosine; however, the major adduct in each case eluted earlier. Only one adduct was detected in liver and lung DNA hydrolysates from rats given [3H]-6-NBP, and this had the same retention time as did the major adduct isolated from human bronchus that had been incubated previously with [3H]-6-NBP. Salmonella typhimurium TA98 was incubated with [3H]-6-NBP and Aroclor-induced rat liver S9. Enzymically hydrolyzed DNA analyzed by HPLC revealed three adducts, two of which cochromatographed with the two DNA adducts isolated from human bronchus DNA adduct which had the same retention time as did the major liver and lung DNA adduct from rats given i.p. injections of [3H]-6-NBP. In each case the major adduct from DNA hydrolysates of rat liver and lung, human bronchus, and S. typhimurium, all treated with [3H]-6-NBP, cochromatographed with the major DNA adduct isolated from liver and lung DNA of rats given [3H]BP.(ABSTRACT TRUNCATED AT 400 WORDS)