Quantitative analysis of the metabolism of 9,10-dihydrobenzo[ a]pyrene by induced rat liver microsomes

Abstract

The ability of reduced polycyclic aromatic hydrocarbons to be converted to their fully aromatic forms by the microsomal cytochrome P-450 mixed-function oxidases may assist in the explanation of the mutagenic and tumorigenic activities of these agents. The metabolic conversion of 9,10-dihydrobenzo[ a]pyrene (9,10-DHB[ a]P) to benzo[ a]pyrene (B[ a]P) and 9- and/or 10-hydroxy-9,10-DHB[ a]P (OH-9,10-DHB[ a]P) was quantitatively measured. In β-naphthoflavone-induced rat liver microsomes, 9,10-DHB[ a]P was metabolized to B[ a]P with a specific activity of 1.51 nmol B[ a]P formed/min/mg microsomal protein. The formation of B[ a]P was directly related to incubation time and microsomal protein concentration. Similarly, 9,10-DHB[ a]P was converted to OH-9,10-DHB[ a]P with a specific activity of 4.48 nmol OH-9,10-DHB[ a]P formed/min/mg microsomal protein. Its formation was directly related to incubation time and microsomal protein concentration. The possibility of OH-9,10-DHB[ a]P as a metabolic intermediate to B[ a]P is discussed.