RT Journal Article
SR Electronic
T1 UDP-Glucuronosyltransferase 1A6 Is the Major Isozyme Responsible for Protocatechuic Aldehyde Glucuronidation in Human Liver Microsomes
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 1562
OP 1569
DO 10.1124/dmd.108.020560
VO 36
IS 8
A1 Hui-Xin Liu
A1 Yong Liu
A1 Jiang-Wei Zhang
A1 Wei Li
A1 Hong-Tao Liu
A1 Ling Yang
YR 2008
UL http://dmd.aspetjournals.org/content/36/8/1562.abstract
AB 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 Km 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 μM for M-1 and 336.7 ± 15.3, 494.3 ± 48.7, 211.4 ± 13.4, and 238.5 ± 26.2 μM 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 IC50 for phenylbutazone inhibition of PAL glucuronidation was similar in HLMs (61.9 ± 7.9 μM) compared with rUGT1A6 (45.3 ± 7.7 μM). In contrast, androsterone inhibited rUGT1A9-catalyzed and HLM-catalyzed PAL glucuronidation with IC50 values of 27.1 ± 3.8 and >500 μM, respectively. In combination, we identified UGT1A6 as the major isozyme responsible for PAL glucuronidation in HLMs. The American Society for Pharmacology and Experimental Therapeutics