N -glucuronidation is an important pathway for metabolism and disposition of tertiary amines in humans. This reaction is mainly catalyzed by the enzymes UGT1A4 and UGT2B10. However, the metabolic patterns of UGT1A4- and UGT2B10-mediated N -glucuronidation are not fully clear. In this study, we first optimized in vitro reaction conditions for N -glucuronidation by using specific substrates (i.e., trifluoperazine for UGT1A4, cotinine and amitriptyline for UGT2B10). Furthermore, we found that hepatic N -glucuronidation showed significant species differences. In addition, UGT1A4 and UGT2B10 were primarily responsible for N -glucuronidation of many tertiary amines, including asenapine, loxapine, clozapine, chlorpromazine, dothiepin, doxepin, mirtazapine, mianserin, chlorcyclizine, cyclizine, promethazine, cyclobenzaprine, imatinib, retrorsine, strychnine and brucine. In conclusion, this study provides an in vitro assay system for evaluating N -glucuronidation of amines. Also, UGT1A4- and UGT2B10-mediated N -glucuronidation might play significant roles in metabolism and detoxification of tertiary amines in humans.
Juan Chen,Lin Qin,Xingdong Wu,Daopeng Tan,Yanliu Lu,Yimei Du,Di Wu,Yuqi He
Gypensapogenin C (GPC) is one of the important aglycones ofGynostemma pentaphyllum(GP), which is structurally glucuronidated and is highly likely to bind to UGT enzymes in vivo. Due to the important role of glucuronidation in the metabolism of GPC, the UDP-glucuronosyltransferase metabolic pathway of GPC in human and other species’ liver microsomes is investigated in this study. In the present study, metabolites were detected using high-performance liquid chromatography–tandem mass spectrometry (LC–MS/MS). The results show that GPC could generate a metabolite through glucuronidation in the human liver microsomes (HLMs). Additionally, chemical inhibitors combined with recombinant human UGT enzymes clarified that UGT1A4 is the primary metabolic enzyme for GPC glucuronidation in HLMs according to the kinetic analysis of the enzyme. Metabolic differential analysis in seven other species indicated that rats exhibited the most similar metabolic rate to that of humans. In conclusion, UGT1A4 is a major enzyme responsible for the glucuronidation of GPC in HLMs, and rats may be an appropriate animal model to evaluate the GPC metabolism.Keywords:gypensapogenin C;glucuronidation;human liver microsomes;UGT1A4;species differences
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