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UDP-glucuronosyltransferase 1A6 is the major isozyme responsible for protocatechuic aldehyde glucuronidation in human liver microsomes. 2008

Hui-Xin Liu, and Yong Liu, and Jiang-Wei Zhang, and Wei Li, and Hong-Tao Liu, and Ling Yang
Laboratory of Pharmaceutical Resource Discovery, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, No. 457 Zhongshan Rd., Dalian 116023 China.

Glucuronidation is an important pathway in the metabolism of protocatechuic aldehyde (3,4-dihydroxybenzaldehyde, PAL). However, the metabolites and primary UDP-glucuronosyltransferase (UGT) isozymes responsible for PAL glucuronidation remain to be determined in human. Here, we characterized PAL glucuronidation by human liver microsomes (HLMs), human intestine microsomes (HIMs), and 12 recombinant UGT (rUGT) isozymes to identify what kinds of metabolites are present and which human UGT isozymes are involved. Two metabolites (M-1 and M-2) were detected in reactions catalyzed by HLMs, HIMs, rUGT1A6, and rUGT1A9 and were identified as monoglucuronides by liquid chromatography-mass spectrometry. A kinetic study showed that PAL glucuronidation by rUGT1A6, rUGT1A9, HIMs, and HLMs followed Michaelis-Menten kinetics. The K(m) values of HLMs, HIMs, rUGT1A6, and rUGT1A9 for PAL glucuronidation were as follows: 432.7 +/- 24.5, 626.9 +/- 49.2, 367.5 +/- 25.1, and 379.9 +/- 42.5 microM for M-1 and 336.7 +/- 15.3, 494.3 +/- 48.7, 211.4 +/- 13.4, and 238.5 +/- 26.2 microM for M-2, respectively. The PAL glucuronidation activity was significantly correlated with UGT1A6 activity rather than with UGT1A9 activity from 15 individual HLMs. A chemical inhibition study showed that the IC(50) for phenylbutazone inhibition of PAL glucuronidation was similar in HLMs (61.9 +/- 7.9 microM) compared with rUGT1A6 (45.3 +/- 7.7 microM). In contrast, androsterone inhibited rUGT1A9-catalyzed and HLM-catalyzed PAL glucuronidation with IC(50) values of 27.1 +/- 3.8 and > 500 microM, respectively. In combination, we identified UGT1A6 as the major isozyme responsible for PAL glucuronidation in HLMs.

UI MeSH Term Description Entries
D007527 Isoenzymes Structurally related forms of an enzyme. Each isoenzyme has the same mechanism and classification, but differs in its chemical, physical, or immunological characteristics. Alloenzyme,Allozyme,Isoenzyme,Isozyme,Isozymes,Alloenzymes,Allozymes
D008862 Microsomes, Liver Closed vesicles of fragmented endoplasmic reticulum created when liver cells or tissue are disrupted by homogenization. They may be smooth or rough. Liver Microsomes,Liver Microsome,Microsome, Liver
D002396 Catechols A group of 1,2-benzenediols that contain the general formula R-C6H5O2. Pyrocatechols,o-Dihydroxybenzenes,ortho-Dihydroxybenzenes,o Dihydroxybenzenes,ortho Dihydroxybenzenes
D002851 Chromatography, High Pressure Liquid Liquid chromatographic techniques which feature high inlet pressures, high sensitivity, and high speed. Chromatography, High Performance Liquid,Chromatography, High Speed Liquid,Chromatography, Liquid, High Pressure,HPLC,High Performance Liquid Chromatography,High-Performance Liquid Chromatography,UPLC,Ultra Performance Liquid Chromatography,Chromatography, High-Performance Liquid,High-Performance Liquid Chromatographies,Liquid Chromatography, High-Performance
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D001547 Benzaldehydes Compounds that consist of a benzene ring with a formyl group. They occur naturally in the seeds of many fruits and are used as FLAVORING AGENTS and fragrances, as well as precursors in pharmaceutical and plastics manufacturing.
D001711 Biotransformation The chemical alteration of an exogenous substance by or in a biological system. The alteration may inactivate the compound or it may result in the production of an active metabolite of an inactive parent compound. The alterations may be divided into METABOLIC DETOXICATION, PHASE I and METABOLIC DETOXICATION, PHASE II.
D013056 Spectrophotometry, Ultraviolet Determination of the spectra of ultraviolet absorption by specific molecules in gases or liquids, for example Cl2, SO2, NO2, CS2, ozone, mercury vapor, and various unsaturated compounds. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed) Ultraviolet Spectrophotometry
D014453 Glucuronosyltransferase A family of enzymes accepting a wide range of substrates, including phenols, alcohols, amines, and fatty acids. They function as drug-metabolizing enzymes that catalyze the conjugation of UDPglucuronic acid to a variety of endogenous and exogenous compounds. EC 2.4.1.17. Glucuronyltransferase,UDP Glucuronosyltransferase,17 beta-Hydroxysteroid UDP-Glucuronosyltransferase,4-Nitrophenol-UDP-Glucuronosyltransferase,7-Hydroxycoumarin UDP Glucuronyltransferase,Androsterone UDP-Glucuronosyltransferase,Bilirubin UDP-Glucuronyltransferase,Estrogen UDP-Glucuronosyltransferase,Estrone Glucuronyltransferase,Glucuronic Transferase,Morphine Glucuronyltransferase,UDP Glucuronyl Transferase,UDP-Glucuronic Acid 3-O-beta-D-Galactosyl-D-Galactose Glucuronosyltransferase,p-Nitrophenyl UDP-Glucuronosyltransferase,17 beta Hydroxysteroid UDP Glucuronosyltransferase,4 Nitrophenol UDP Glucuronosyltransferase,7 Hydroxycoumarin UDP Glucuronyltransferase,Androsterone UDP Glucuronosyltransferase,Bilirubin UDP Glucuronyltransferase,Estrogen UDP Glucuronosyltransferase,Glucuronosyltransferase, UDP,Glucuronyl Transferase, UDP,Glucuronyltransferase, 7-Hydroxycoumarin UDP,Glucuronyltransferase, Estrone,Glucuronyltransferase, Morphine,Transferase, Glucuronic,Transferase, UDP Glucuronyl,UDP Glucuronic Acid 3 O beta D Galactosyl D Galactose Glucuronosyltransferase,UDP Glucuronyltransferase, 7-Hydroxycoumarin,UDP-Glucuronosyltransferase, 17 beta-Hydroxysteroid,UDP-Glucuronosyltransferase, Androsterone,UDP-Glucuronosyltransferase, Estrogen,UDP-Glucuronosyltransferase, p-Nitrophenyl,UDP-Glucuronyltransferase, Bilirubin,p Nitrophenyl UDP Glucuronosyltransferase
D020719 Glucuronides Glycosides of GLUCURONIC ACID formed by the reaction of URIDINE DIPHOSPHATE GLUCURONIC ACID with certain endogenous and exogenous substances. Their formation is important for the detoxification of drugs, steroid excretion and BILIRUBIN metabolism to a more water-soluble compound that can be eliminated in the URINE and BILE. Glucuronide

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