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Glucuronidation of carcinogen metabolites by complementary DNA-expressed uridine 5'-diphosphate
P I Mackenzie1, L Rodbourn, T Iyanagi
1Department of Clinical Pharmacology, Flinders University School of Medicine, Bedford Park South Australia.
Abstract:
Five UDP glucuronosyltransferases (UGT) were synthesized from complementary DNAs expressed in COS 7 cells and were tested for their capacities to glucuronidate a range of 2-acetylaminofluorene and benzo(a)pyrene-hydroxylated metabolites. Three forms, UGT1*06, UGT2B1, and UGT2B2 [names of UGT forms follow recommended nomenclature (B. B. Burchell et al., DNA Cell Biol., 10: 487-494, 1991)], had similar capacities to glucuronidate the reactive metabolite, N-hydroxy-2-acetylaminofluorene. The less reactive 1-, 3-, 5-, and 8-hydroxy derivatives of this aromatic amine were glucuronidated by UGT1*06 and UGT2B2 to varying degrees, but these were not substrates of UGT2B1. The three isozymes also glucuronidated phenolic metabolites of benzo(a)pyrene. UGT1*06 was more active toward 2- and 5-hydroxybenzo(a)pyrene, whereas UGT2B1 preferentially glucuronidated the 4- and 11-hydroxy derivatives and UGT2B2 preferentially glucuronidated the 1-, 2-, 8-, and 9-hydroxy metabolites. Two other UDP glucuronosyltransferases, UGT2B3 and UGT2B6, that glucuronidated testosterone when expressed in COS 7 cells were both inactive toward all the carcinogen metabolites tested. These results demonstrate that the glucuronidation of metabolites of 2-acetylaminofluorene and benzo(a)pyrene is mediated by at least three UDP glucuronosyltransferases and that each form glucuronidates a unique spectrum of metabolites.
Insights
Three UDP glucuronosyltransferases (UGTs) mediate the glucuronidation of 2-acetylaminofluorene and benzo(a)pyrene metabolites. Each UGT form processes a distinct set of these carcinogenic compound metabolites.
Area of Science:
- Biochemistry
- Pharmacology
- Toxicology
Background:
- UDP glucuronosyltransferases (UGTs) are crucial enzymes in xenobiotic metabolism.
- Metabolism of carcinogens like 2-acetylaminofluorene and benzo(a)pyrene involves complex pathways, including glucuronidation.
- Understanding UGT activity is vital for assessing carcinogenic risk and drug interactions.
Purpose of the Study:
- To characterize the substrate specificity of different UDP glucuronosyltransferase (UGT) forms.
- To investigate the glucuronidation capacities of UGT1*06, UGT2B1, UGT2B2, UGT2B3, and UGT2B6 towards hydroxylated carcinogen metabolites.
Main Methods:
- Synthesis of five UDP glucuronosyltransferase (UGT) forms via complementary DNA expression in COS 7 cells.
- Incubation of UGTs with hydroxylated metabolites of 2-acetylaminofluorene and benzo(a)pyrene.
- Analysis of glucuronidation activity using a range of carcinogen-derived substrates.
Main Results:
- UGT1*06, UGT2B1, and UGT2B2 showed similar activity towards N-hydroxy-2-acetylaminofluorene.
- UGT1*06 and UGT2B2 glucuronidated other 2-acetylaminofluorene metabolites, while UGT2B1 had limited activity.
- Differential substrate specificities were observed for benzo(a)pyrene metabolites among UGT1*06, UGT2B1, and UGT2B2.
- UGT2B3 and UGT2B6 were inactive towards tested carcinogen metabolites but glucuronidated testosterone.
Conclusions:
- At least three UDP glucuronosyltransferase (UGT) forms (UGT1*06, UGT2B1, UGT2B2) are involved in the glucuronidation of 2-acetylaminofluorene and benzo(a)pyrene metabolites.
- Each identified UGT isoform exhibits a unique substrate preference for these carcinogen metabolites.
- UGT2B3 and UGT2B6 do not contribute to the glucuronidation of these specific carcinogen metabolites.