Metabolism of benzo[a]pyrene and (-)-trans-benzo[a]pyrene-7,8-dihydrodiol by freshly isolated hepatocytes of brown bullheads.
The metabolism of [3H]benzo[a]pyrene (BP) and (-)-trans-[14C]7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol) was studied in freshly isolated hepatocytes of the wild benthic fish, brown bullhead (Ictalurus nebulosus). Bullhead hepatocytes incubated with 40 microM [3H]BP for 1 h metabolized BP to water soluble metabolites which were separated on silica gel t.l.c. plates to reveal conjugates with glucuronic acid, glutathione, and sulfate (51%, 14% and 4% of total metabolites, respectively). Additional metabolites that were extractable with ethyl acetate were separated by reversed phase HPLC to reveal only two major metabolites: BP-9,10-dihydrodiol and BP-7,8-diol (13% and 2.6% of total metabolites, respectively). Hepatocytes isolated from individual fish displayed an 11-fold variability in the rates at which they metabolized BP (756 +/- 167 pmol x mg dry wt-1 x h-1), which correlated negatively (r = -0.7, P less than 0.01) with an 18-fold variability in the glycogen content of the cells. Hepatocytes isolated from the same fish, in parallel incubations under the same optimum conditions, metabolized BP-7,8-diol 4.5-fold faster than they metabolized BP. The variability in the rate of BP-7,8-diol metabolism was about 7-fold. Major metabolites included glutathione conjugates, glucuronides and sulfates (35%, 25% and 30% of total metabolites, respectively). These conjugates, like those formed from BP, were degradable with gamma-glutamyltransferase, beta-glucuronidase and arylsulfatase, respectively. Ethyl acetate extractable metabolites were predominantly isomeric benzo-ring tetrahydrotetrols (9% of total metabolites). In summary, this study indicates that during short-term incubations bull-head hepatocytes metabolize BP and BP-7,8-diol primarily to conjugated derivatives. The usefulness of thin-layer chromatography for the convenient determination of the rate of BP-7,8-diol metabolism is demonstrated.
Steward
A R
AR
Great Lakes Laboratory, State University, New York College, Buffalo 14222.
Zaleski
J
J
Sikka
H C
HC
D000818:Animals; D001564:Benzo(a)pyrene / Q000378:metabolism*; D001711:Biotransformation; D002250:Carbon Radioisotopes; D002478:Cells, Cultured; D004101:Dihydroxydihydrobenzopyrenes / Q000378:metabolism*; D005260:Female; D005399:Fishes; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008297:Male; D012621:Seasons; D014316:Tritium
D002250:Carbon Radioisotopes; D004101:Dihydroxydihydrobenzopyrenes; D014316:Tritium; C017228:benzo(a)pyrene 7,8-dihydrodiol; D001564:Benzo(a)pyrene