Intestinal bioavailability and biotransformation of 3-hydroxybenzo(a) pyrene in an isolated perfused preparation from channel catfish, Ictalurus punctatus
Mo. James et al., Intestinal bioavailability and biotransformation of 3-hydroxybenzo(a) pyrene in an isolated perfused preparation from channel catfish, Ictalurus punctatus, DRUG META D, 29(5), 2001, pp. 721-728
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.