Inhibition of the mutagenicity and metabolism of 6-methyl-benzo[a]pyrene and 6-hydroxymethyl-benzo[a]pyrene.

Previously reported inhibitors of benzo[a]pyrene (BaP) mutagenicity in Salmonella typhimurium strain TA98 were tested for their effectiveness against the mutagenicity of 6-methyl-benzo[a]pyrene (6-CH3-BaP), 6-hydroxymethyl-benzo[a]pyrene (6-CH2OH-BaP) and 6-acetoxymethyl-benzo[a]pyrene (6-CH3COOCH2-BaP). Dose-response curves obtained for phenothiazine (PTH), 2-chlorophenothiazine (2Cl-PTH), phenylisothiocyanate (PHN), phenethylisothiocyanate (PNE), trans-retinol (TR) and disulfiram (TETD) showed a variety of degrees of inhibition of mutagenicity. Additionally, glutathione (GSH) was found to inhibit the mutagenicity of 6-CH3COOCH2-BaP, and the mutagenicity of 6-CH2OH-BaP was enhanced by the addition of supplemental ATP, Na2SO4 and EDTA. Only 2Cl-PTH was equally as good an inhibitor of 6-CH3-BaP and BaP, reducing revertant colonies to less than 50% of control at 10 X BaP concentration. To probe the mechanism of inhibition, the effect of 2Cl-PTH on the binding of BaP and the 6-substituted benzo[a]pyrenes to cytochrome P-450 was investigated by difference spectroscopy. Also, the effect of 2Cl-PTH on the subsequent metabolism of 6-CH3-BaP and 6-CH2OH-BaP was investigated by rapid scan difference spectroscopy and high-performance liquid chromatographic separation of products. The results are consistent with a major mechanism of inhibition for 2Cl-PTH involving a competition for the cytochrome P-450 binding site.