Intestinal bioavailability and biotransformation of 3-hydroxybenzo(a) pyrene in an isolated perfused preparation from channel catfish, Ictalurus punctatus

The intestinal bioavailability and biotransformation of 3-hydroxybenzo(a)py rene, a major metabolite of benzo(a)pyrene in many animal species, was inve stigated in an in situ isolated intestinal preparation from the channel cat fish, and in vitro with preparations of catfish intestine and blood. 3-Hydr oxybenzo(a)pyrene was a good substrate for adenosine 3'-phosphate 5'-phosph osulfate (PAPS)-sulfotransferase and UDP-glucuronosyltransferase in cytosol or microsomes prepared from intestinal mucosa. The benzo(a)pyrene-3-glucur onide and 3-sulfate conjugates were only very slowly hydrolyzed by intestin al beta -glucuronidase and sulfatase. The K-m values for PAPS-sulfotransfer ase and UDP-glucuronosyltransferase were 0.4 and 1 muM, respectively, and V -max were 1.61 +/- 1.08 nmol benzo(a)pyrene-3-sulfate/min/mg of cytosolic p rotein and 1.08 +/- 0.54 nmol benzo(a)pyrene-3-glucuronide/min/mg of micros omal protein. Hydrolytic enzyme activities were three orders of magnitude s lower. In the in situ intestinal preparation, [H-3]3-hydroxybenzo(a)pyrene was readily metabolized to the glucuronide and sulfate conjugates. After 1 h of incubation of 2 or 20 muM [H-3]3-hydroxybenzo(a)pyrene in the in situ preparation, the luminal contents contained 3-hydroxybenzo(a)pyrene, benzo( a)pyrene-3,6-dione, benzo(a)pyrene-3-sulfate, and benzo(a)pyrene-3-glucuron ide. Mucosal samples contained these components, as well as some unextracta ble material. The blood contained mainly benzo(a)pyrene-3-sulfate and an as yet unidentified metabolite of 3-hydroxybenzo(a) pyrene bound to hemoglobi n. Some, but not all, blood samples contained small amounts of 3-hydroxyben zo(a)pyrene, benzo(a)pyrene-3-glucuronide, and benzo(a)pyrene-3,6-dione. Th ese studies demonstrate the rapid phase 2 conjugation of a phenolic benzo(a ) pyrene metabolite in intestinal mucosa, and the transfer of the phase 2 s ulfate and glucuronide conjugates to blood.