INTESTINAL TOXICITY OF ACRYLONITRILE - IN-VITRO METABOLISM BY INTESTINAL CYTOCHROME-P450 2E1

Acrylonitrile (VCN) is known to cause extensive gastrointestinal damag e and tumors in rats. In this study the metabolism of VCN to cyanide ( CN-) was characterized in the small intestinal mucosa. The majority of the metabolic reactivity was localized in the microsomal fraction and required reduced nicotinamide adenine dinucleotide phosphate for maxi mal activity, The intestinal metabolism of VCN to CN- was characterize d with respect to VCN concentration, time, pH, and microsomal protein concentration, VCN metabolism to CN- was enhanced significantly by the addition of sulfhydryl compounds such as glutathione, cysteine, and D -penicillamine (10 mM) to 142, 161, and 189% of control, respectively. The intestinal bioactivation of VCN to CN- was enhanced by microsomes obtained from intestinal mucosa of phenobarbital (455% of control), b eta-naphithoflavone (375% of control), 4-methylpyrazole (305% of contr ol), or ethanol (165% of control)-treated rats, Addition of ethanol (8 0 mM) to incubation mixtures containing control or ethanol-induced mic rosomes resulted in significant inhibition of microsomal metabolism of VCN to CN- to 20 and 34% of control, respectively. Addition of dimeth yl sulfoxide induced a similar inhibitory effect on VCN metabolism by control or ethanol-induced microsomes (8 and 26% of control, respectiv ely). Furthermore, antibody to cytochrome P450 2E1, but not antibody t o cyt P450 2B1, significantly inhibited VCN metabolism by ethanol-indu ced intestinal microsomes to about 25% of control, Mild inhibition (80 -85% of control) of VCN metabolism was detected when antibody to cyt P 450 2B1 or 2E1 was added to incubation mixtures containing Pb-induced intestinal microsomes, These findings indicate that extrahepatic tissu es such as the intestinal mucosa are capable of metabolizing VCN to CN - and establish a major role of intestinal cyt P450, particularly cyt P450 2E1, in the intestinal metabolism of VCN to CN-. (C) 1995 Academi c Press, Inc.