TY - JOUR T1 - Identification of the UDP-Glucuronosyltransferase Isozyme Involved in Senecionine Glucuronidation in Human Liver Microsomes JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 626 LP - 634 DO - 10.1124/dmd.109.030460 VL - 38 IS - 4 AU - Yu-Qi He AU - Yong Liu AU - Bin-Feng Zhang AU - Hui-Xin Liu AU - Yan-Liu Lu AU - Li Yang AU - Ai-zhen Xiong AU - Ling-Ling Xu AU - Chang-Hong Wang AU - Ling Yang AU - Zheng-Tao Wang Y1 - 2010/04/01 UR - http://dmd.aspetjournals.org/content/38/4/626.abstract N2 - Senecionine (SEN) is a representative of the hepatotoxic pyrrolizidine alkaloids. Although phase I metabolism for cytochrome P450-mediated metabolic activation of SEN was investigated extensively, phase II metabolism for glucuronidation of this compound has not been investigated until now. In our present study, one unique glucuronidation product of SEN in human liver microsomes (HLMs) was identified as SEN N-glucuronide using an authentically synthesized product for which the structure was identified via 1H and 13C NMR analysis. Subsequently, kinetics indicated that SEN N-glucuronidation followed the typical Michaelis-Menten model and only one major isozyme participated in it. Finally, this isozyme was demonstrated to be UDP-glucuronosyltransferase (UGT) 1A4, with the direct evidence that recombinant UGT1A4 exhibited predominant and exclusive activity on SEN N-glucuronidation. This result was confirmed by other experiments including chemical inhibition by selective inhibitors and a correlation study between activities of SEN N-glucuronidation and various UGT isozymes. The exclusive role of UGT1A4 on SEN N-glucuronidation was strengthened additionally by its inhibitory kinetic study in which the selective inhibitor of UGT1A4 showed a similar inhibition pattern and Ki values in both HLM and recombinant UGT1A4 systems. Because UGT2B10 activity failed to correlate with SEN N-glucuronidation in HLMs from 10 individuals, it was impossible for UGT2B10 to play an important role in this metabolism. Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics ER -