Abstract
The intestinal bioavailability and biotransformation of 3-hydroxybenzo(a)pyrene, a major metabolite of benzo(a)pyrene in many animal species, was investigated in an in situ isolated intestinal preparation from the channel catfish, and in vitro with preparations of catfish intestine and blood. 3-Hydroxybenzo(a)pyrene was a good substrate for adenosine 3′-phosphate 5′-phosphosulfate (PAPS)-sulfotransferase and UDP-glucuronosyltransferase in cytosol or microsomes prepared from intestinal mucosa. The benzo(a)pyrene-3-glucuronide and 3-sulfate conjugates were only very slowly hydrolyzed by intestinal β-glucuronidase and sulfatase. The Kmvalues for PAPS-sulfotransferase and UDP-glucuronosyltransferase were 0.4 and 1 μM, respectively, and Vmax were 1.61 ± 1.08 nmol benzo(a)pyrene-3-sulfate/min/mg of cytosolic protein and 1.08 ± 0.54 nmol benzo(a)pyrene-3-glucuronide/min/mg of microsomal protein. Hydrolytic enzyme activities were three orders of magnitude slower. In the in situ intestinal preparation, [3H]3-hydroxybenzo(a)pyrene was readily metabolized to the glucuronide and sulfate conjugates. After 1 h of incubation of 2 or 20 μM [3H]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-glucuronide. Mucosal samples contained these components, as well as some unextractable material. The blood contained mainly benzo(a)pyrene-3-sulfate and an as yet unidentified metabolite of 3-hydroxybenzo(a)pyrene bound to hemoglobin. Some, but not all, blood samples contained small amounts of 3-hydroxybenzo(a)pyrene, benzo(a)pyrene-3-glucuronide, and benzo(a)pyrene-3,6-dione. These studies demonstrate the rapid phase 2 conjugation of a phenolic benzo(a)pyrene metabolite in intestinal mucosa, and the transfer of the phase 2 sulfate and glucuronide conjugates to blood.
Footnotes
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Send reprint requests to: Dr. Margaret O. James, Department of Medicinal Chemistry, P.O. Box 100485, College of Pharmacy, University of Florida, Gainesville, FL 32610-0485. E-mail:mojames{at}ufl.edu
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↵1 Present address: Wyeth-Ayerst Research, Department of Biotransformation, CN 8000, Princeton, NJ 08543-8000.
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This work was supported by Grant ES 05781 from the U.S. Public Health Service. A preliminary report was presented at the Society of Toxicology annual meeting, Baltimore, MD, 1995.
- Abbreviations used are::
- PAH
- polycyclic aromatic hydrocarbons
- BaP
- benzo(a)pyrene
- 3-OH-BaP
- 3-hydroxybenzo(a)pyrene
- BaP-3-glucuronide
- benzo(a)pyrene-3-β-d-glucopyranosiduronic acid
- BaP-3-sulfate
- benzo(a)pyrene-3-sulfate
- BaP-3,6-dione
- benzo(a)pyrene-3,6-dione
- PAPS
- adenosine 3′-phosphate 5′-phosphosulfate
- SULT
- PAPS-sulfotransferase
- UGT
- UDP-glucuronosyltransferase
- BNF
- β-naphthoflavone
- HPLC
- high-performance liquid chromatography
- NCI
- National Cancer Institute
- Received November 7, 2000.
- Accepted February 1, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
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