MUTAGENICITY OF BENZO[A]PYRENE AND DIBENZOPYRENES IN THE SALMONELLA-TYPHIMURIUM TM677 AND THE MCL-5 HUMAN CELL FORWARD MUTATION ASSAYS

The mutagenicity of benzo[a]pyrene (B[a]P), dibenzo[ae]pyrene (DB[ae]P), dibenzo[nh]pyrene (DB[ah]P), dibenzo[ai]pyrene (DB[ai]P), and dibenzo[al]pyrene (DB[al]P) was measured in quantitative forward mutation assays with bacteria (Salmonella typhimurium TM677) and a metabolically competent cell line derived from human B-lymphoblastoid cells (MCL-5) that contained activity for five cytochrome P450s and microsomal epoxide hydrolase found in human liver. DB[al]P and B[a]P, both potent animal carcinogens, were the most mutagenic substances in both assays. DB[al]P was nearly 50-fold more potent than B[a]P in human cells, but only 60% more mutagenic in Salmonella. The carcinogenic isomer DB[ah]P, though nonmutagenic in bacteria, was active in human cells. The following mutagenic potency series, expressed as the minimum detectable mutagen concentration (MDMC) in nmol/ml, was obtained with Salmonella in the presence of rat liver postmitochondrial supernatant (PMS): DB[al]P (3.7), B[a]P (5.8), DB[ae]P (6.9), DB[ai]P (14.9), DB[ah]P (> 100). None of the compounds were mutagenic in the absence of PMS. In human MCL-5 cells the potency series was: DB[al]P (3.1 x 10(-4)), B[a]P (1.5 x 10(-2)), DB[ae]P (2.5 X 10(-2)), DB[ah]P (0.5), DB[ai]P (3.2). The human cell assay thus exhibited over a 10000-fold range between the most mutagenic and least mutagenic compound, whereas in the bacterial assay there was only a corresponding four-fold difference if the nonmutagenic DB[ah]P was excluded. The results were discussed in terms of their concordance with animal carcinogenicity studies.