Sulfation and glucuronidation of benzo[a]pyrene-7,8-dihydrodiol in intestinal mucosa of channel catfish (Ictalurus punctatus).
Intestinal metabolism plays a significant role in the bioavailability of ingested environmental toxicants. In this study, the potential for first pass, phase 2 biotransformation of benzo[a]pyrene-7,8-dihydrodiol (BaP-7,8-diol) in intestinal mucosa was examined. Sulfotransferase and Uridine 5'-Diphospho-Glucuronyl-transferase activity were measured in cytosol, and microsomes respectively. Radiolabeled conjugation products were analyzed by TLC and high-performance liquid chromatography (HPLC). The results indicated that BaP-7,8-diol was a poor substrate for intestinal sulfotransferase. Vmax for the sulfation of BaP-7,8-diol was 0.002 nmol mg-1 min-1, which is at least three orders of magnitudes lower than the Vmax for phenolic BaP metabolites. Studies with 3'phosphoadenosine-5' phosphosulfate (PAP)-35S as co-substrate showed that an unidentified compound in the reaction mixture was sulfated, dependent on the BaP-7,8-diol concentration. This could indicate that BaP-7,8-diol was interacting with a regulatory site on the enzyme and stimulated sulfation of an endogenous molecule in cytosol. Kinetic analysis of microsomal glucuronidation resulted in a Vmax of 0.30 nmol mg-1 min-1 (+/- 0.06 S.D., n = 4), with a Km of 23.39 microM (+/- 2.66 S.D.). The Km for the co-substrate UDP-glucuronic acid was approximately 43 microM. The slow rates for sulfation and glucuronidation of BaP-7,8-diol may explain its relatively high systemic availability when ingested or produced by intestinal phase 1 enzymes.
van den Hurk
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Department of Medicinal Chemistry, College of Pharmacy, University of Florida, PO Box 100485, Gainesville, FL 32610, USA. pvdhurk@ufl.edu
James
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D000818:Animals; D002397:Catfishes / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D004101:Dihydroxydihydrobenzopyrenes / Q000378:metabolism*; D020719:Glucuronides / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism*; D007700:Kinetics; D013431:Sulfates / Q000378:metabolism*
D004101:Dihydroxydihydrobenzopyrenes; D020719:Glucuronides; D013431:Sulfates; C017228:benzo(a)pyrene 7,8-dihydrodiol; D014453:Glucuronosyltransferase