Sequential Metabolism of Sesamin by Cytochrome P450 and UDP-Glucuronosyltransferase in Human Liver

Abstract

ABSTRACT:Our previous study revealed that CYP2C9 played a central role in sesamin monocatecholization. In this study, we focused on the metabolism of sesamin monocatechol that was further converted into the dicatechol form by cytochrome P450 (P450) or the glucuronide by UDP-glucuronosyltransferase (UGT). Catecholization of sesamin monocatechol enhances its antioxidant activity, whereas glucuronidation strongly reduces its antioxidant activity. In human liver microsomes, the glucuronidation activity was much higher than the catecholization activity toward sesamin monocatechol. In contrast, in rat liver microsomes, catecholization is predominant over glucuronidation. In addition, rat liver produced two isomers of the glucuronide, whereas human liver produced only one glucuronide. These results suggest a significant species-based difference in the metabolism of sesamin between humans and rats. Kinetic studies using recombinant human UGT isoforms identified UGT2B7 as the most important UGT isoform for glucuronidation of sesamin monocatechol. In addition, a good correlation was observed between the glucuronidation activity and UGT2B7-specific activity in in vitro studies using 10 individual human liver microsomes. These results strongly suggest that UGT2B7 plays an important role in glucuronidation of sesamin monocatechol. Interindividual difference among the 10 human liver microsomes is approximately 2-fold. These results, together with our previous results on the metabolism of sesamin by human P450, suggest a small interindividual difference in sesamin metabolism. We observed the methylation activity toward sesamin monocatechol by catechol O-methyl transferase (COMT) in human liver cytosol. On the basis of these results, we concluded that CYP2C9, UGT2B7, and COMT played essential roles in the metabolism of sesamin in the human liver.

Comparison of Metabolism of Sesamin and Episesamin by Drug-Metabolizing Enzymes in Human Liver

“…from three separate experiments. The values for sesamin were obtained in our previous study (Yasuda et al, 2010 dmd.aspetjournals.org metabolite was detected (data not shown), and metabolic enzymes of episesamin monocatechol were similar to those of sesamin monocatechol (Yasuda et al, 2011). These results strongly suggest that oxidation, glucuronidation, and methylation of episesamin monocatechol would occur simultaneously in human liver.…”

“…We demonstrated previously that sesamin was catecholized in human liver microsomes predominantly by CYP2C9, and sesamin was a mechanism-based inhibitor of CYP2C9 (Yasuda et al, 2010). Furthermore, we also demonstrated the speciesspecific differences in sesamin metabolism between humans and rats (Yasuda et al, 2011). In this article, we reveal P450 species responsible for episesamin metabolism and compared the sequential metabolism of episesamin by drug-metabolizing enzymes with that of sesamin in human and rat liver.…”

“…To compare the sequential metabolism of sesamin and episesamin in human liver, we performed kinetic analysis of P450-dependent metabolism of episesamin and then P450-, UGT-, or COMTdependent metabolism of episesamin monocatechol (Yasuda et al, 2011). In human liver microsomes, the V max /K m value of episesamin was 29% of that of sesamin, indicating that episesamin was a poorer substrate than sesamin in human liver (Table 3).…”

“…The 3Ј-azido-3Ј-deoxythymidine (AZT) glucuronidation activity in pooled human liver microsomes was analyzed as described in our previous study (Yasuda et al, 2011). In brief, the reaction mixture containing 0.5 mg protein/ml of human liver microsomes, 1 mM AZT, 2 mM UDP-GlcUA, and 1 mM MgCl 2 in 100 mM potassium-phosphate buffer (pH 7.4) was incubated for 15 min at 37°C.…”

“…Each of P450-dependent catecholization, UGT-dependent glucuronidation, and catechol-O-methyltransferase (COMT)-dependent methylation of M1 and M2 were analyzed by the same methods described in our previous study (Yasuda et al, 2011). In brief, the conditions of each reaction were described as follows.…”