Mutation induction and DNA adduct formation in Chinese hamster ovary cells treated with 6-nitrochrysene, 6-aminochrysene and their metabolites.
6-Nitrochrysene, 6-aminochrysene and several of their metabolites were assayed for mutagenic activity at the hypoxanthine-guanine phosphoribosyl transferase (hprt) locus in DNA-repair-proficient Chinese hamster ovary (CHO-K1) cells and excision-repair-deficient CHO-UV5 cells. Mutagen-DNA adducts were analyzed by 32P-postlabeling in cells treated under the conditions of the mutagenicity assay and compared with the adduct patterns produced from the in vitro reaction of metabolites of 6-nitrochrysene and 6-aminochrysene with calf-thymus DNA. The mutagenic activities of the test compounds in the presence of a liver homogenate (S9) fraction from Aroclor 1254-pretreated rats, expressed as the number of mutants per 10(6) cells per nmole test compound per ml, in CHO-K1 and CHO-UV5 cells, respectively, were as follows: 6-nitrochrysene, 0.3 and 4; 6-aminochrysene, 35 and 117; 6-nitrochrysene-1,2-dihydrodiol, 1 and 6; 6-aminochrysene-1,2-dihydrodiol, 488 and 644; chrysene (run as a positive control), 12 and 28. 6-Nitrosochrysene was a direct-acting mutagen, yielding 127 and 618 mutants per 10(6) cells per nmole per ml in CHO-K1 and CHO-UV5 cells, respectively. Mutagen-DNA adduct analysis indicated that cells treated with 6-aminochrysene in the presence of S9 or 6-nitrosochrysene in the absence of S9 contained an adduct pattern identical to that derived from the in vitro reaction of N-hydroxy-6-aminochrysene with calf-thymus DNA. Cells treated with 6-aminochrysene-1,2-dihydrodiol plus S9 contained a single mutagen-DNA adduct that was distinct from those derived from N-hydroxy-6-aminochrysene. Based on comparison with previous studies, this adduct is presumed to be derived from 1,2-dihydroxy-3,4-epoxy-1,2,3,4-tetrahydro-6-aminochrysene. Cells treated with 6-nitrochrysene plus S9 and 6-nitrochrysene-1,2-dihydrodiol plus S9 contained a single major chromatographically identical adduct that was apparently derived from N-hydroxy-6-aminochrysene-1,2-dihydrodiol. The results indicate that 6-nitrochrysene, 6-aminochrysene and their metabolites are mutagenic in CHO cells, but that the major activation pathway for 6-nitrochrysene and 6-nitrochrysene-1,2-dihydrodiol in this system differs from previously described pathways.
Delclos
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KB
Food and Drug Administration, National Center for Toxicological Research, Jefferson, AR 72079.
Heflich
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RH
D000818:Animals; D016466:CHO Cells; D002911:Chrysenes / Q000378:metabolism / Q000633:toxicity*; D006224:Cricetinae; D004247:DNA / Q000378:metabolism*; D009152:Mutagenicity Tests; D009153:Mutagens / Q000378:metabolism*
D002911:Chrysenes; D009153:Mutagens; C035986:6-nitrochrysene; D004247:DNA; C100101:6-chrysenamine