MODULATIVE EFFECTS OF METABOLIC EFFECTORS ON BENZO(A)PYRENE-INDUCED CYTOTOXICITY AND MUTAGENICITY IN MAMMALIAN-CELLS

Conjugation and detoxification of mixed function oxidase (MFO)-mediate d benzo(a)pyrene [B(a)P] metabolites with glucuronic acid and glutathi one (GSH) are major pathways of B(a)P elimination and ultimately excre tion in vivo. We have studied the effects of uridine diphosphate alpha -D-glucuronic acid (UDPGA) and GSH, a cofactor for the synthesis of gl ucuronide and GSH conjugates, respectively, on B(a)P-induced cytotoxic ity and mutagenicity in mammalian cells. The S9-mix used in the Chines e hamster ovary cell/hypoxanthine-guanine phosphoribosyltransferase (C HO/HPRT) mutational assay was supplemented with either UDPGA, GSH or G SH plus purified GSH-S-transferases (GSHTs), to study modulation of gl ucuronide and GSH detoxification mechanisms on B(a)P-induced cytotoxic and mutagenic effects. We found that the addition of UDPGA to S9-mix reduces cytotoxicity induced by either B(a)P or B(a)P 6-OH but not by B(a)P 7,8-diol [B(a)P-diol]. The reduction of B(a)P and B(a)P 6-OH-ind uced cytotoxicity by glucuronide conjugation is likely due to eliminat ion of cytotoxic phenols and quinones. The addition of GSH to the S9-m ix resulted in a reduction of B(a)P- and B(a)P-diol-induced cytotoxici ty. GSH plus GSHT reduced B(a)P-induced cytotoxicity and mutagenicity. GSH inhibited the mutagenicity at low concentrations of B(a)P-diol. G SH plus GSHTs inhibited the cytotoxicity and mutagenicity of B(a)P-dio l at concentrations not affected by GSH alone. These studies demonstra te that mechanisms of detoxification can affect the biological activit y of B(a)P and B(a)P-diol as profoundly as bioactivation by the MFO sy stem. Future research should address studies of mutagenicity modulatio n by metabolic effecters at both the molecular (DNA sequence) and cell ular (quantitative mutagenesis) level.