title: Characterizing the effects of common UDP glucuronosyltransferase (UGT) 1A6 and UGT1A1 polymorphisms on cis- and trans-resveratrol glucuronidation.
abstract: The dietary polyphenol resveratrol (RES) exists as cis- and trans-isomers with known stereospecific and stereoselective glucuronidation at the 3 and 4' positions by distinct UGT1A isoforms. We examined cis-RES glucuronidation in various protein sources. UGT1A6 or UGT1A1 genotype-dependent cis-or trans-RES glucuronidation, respectively, was further determined. cis-RES exhibited partial substrate inhibition in UGT1A6 Supersomes and human embryonic kidney 293 cells overexpressing genetically variant UGT1A6 alleles. Cells expressing UGT1A6*4 had the highest activity with a V(max) of 612 +/- 27.36 nmol/min/mg, followed by UGT1A6*3. The *2 allozyme had a higher V(max) (1.6-fold) and K(m) (1.9-fold) than *1. In 51 human liver samples genotyped for UGT1A6, four alleles (frequencies) were identified as *1 (0.58), *2 (0.36), *3 (0.01), and *4 (0.05), leading to assignment of the following genotypes (frequencies): *1/*1 (0.29), *1/*2 (0.45), *1/*3 (0.02), *1/*4 (0.10), and *2/*2 (0.14). Up to 5-fold variability in trans-RES glucuronidation was observed in individual liver samples. In livers stratified by UGT1A6 genotype, a significant difference in cis-RES glucuronidation activity (p < 0.05) was seen between the *2 variants compared with homozygous *1 livers. The trans-RES glucuronidation was quantitated in a human liver bank genotyped for the UGT1A1 TATA box repeat polymorphism. There was no significant difference for formation of trans-RES 3-O-glucuronide. We were surprised to find that trans-RES 4'-O-glucuronide formation was higher in livers with the 7/7 genotype compared with 6/6 and 6/7 (p < 0.05). In conclusion, cis-RES glucuronidation exhibited atypical partial substrate inhibition kinetics in vitro. Whereas cis-RES glucuronidation varied with UGT1A6 genotypes, the UGT1A1*28 polymorphism did not explain variability in trans-RES glucuronidation.
authors.affiliation: Department of Pharmaceutical Sciences, Temple University School of Pharmacy, 3307 North Broad Street, Philadelphia, PA 19140, USA.
authors.forename: Otito Frances
authors.initials: OF
authors.lastname: Iwuchukwu
authors.forename: Jumoke
authors.initials: J
authors.lastname: Ajetunmobi
authors.forename: Din
authors.initials: D
authors.lastname: Ung
authors.forename: Swati
authors.initials: S
authors.lastname: Nagar
mesh_terms: D002460:Cell Line; D005787:Gene Frequency; D005838:Genotype; D020719:Glucuronides / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology; D010641:Phenotype; D011110:Polymorphism, Genetic; D000077185:Resveratrol; D013267:Stilbenes / Q000378:metabolism*; D016385:TATA Box; D014015:Tissue Banks; D014162:Transfection; D000099148:UGT1A1 Enzyme
chemical_list: D020719:Glucuronides; D014453:Glucuronosyltransferase; D000077185:Resveratrol; D013267:Stilbenes; D000099148:UGT1A1 Enzyme; C110655:UDP-glucuronosyltransferase, UGT1A6