Metabolism of the phytoestrogens by sulfate and glucuronic acid conjugation reactions

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 14572072
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Biological pharmacy
• Research Institution: Tokyo University of Pharmacy and Life Science
• Principal Investigator: OGURA Kenichiro Tokyo University of Pharmacy and Life Science, School of Pharmacy, associate professor, 薬学部, 助教授 (10185564)
• Project Period (FY): 2002 – 2004
• Keywords: phytoestrogen / genistein / daidzein / sulfate conjugation / glucuronic acid conjugation / metabolism / excretion / conjugation reaction

Research Abstract

Regioselective glucuronidation and formation of sulfoglucuronides of the phytoestrogen genistein (GS,5,7,4'-trihydroxyisoflavone) was investigated using human liver cytosol, microsomes, purified recombinant human sulfotransferase(SULT) isoforms, SULT1A1,SULT1A3,SULT2A1, and SULT1E1, and recombinant human glucuronosyltransferases (UGT) isoforms, UGT1A1,UGT1A3,UGT1A4,UGT1A6,UGT1A9,UGT2B7 and UGT2B15. 7-Position-preferential glucuronidation of GS was observed in human hepatic microsomes from 7 female and 3 male subjects. Average ratios for 7- to 4'-glucuronide formation were 26:1 from GS in these human liver microsomes. Apparent Km value for the 7- and 4'-glucuronidation of GS by the microsomes from a male subject was 12.3 and 84.2 μM, respectively. Recombinant human UGTs, UGT1A1,UGT1A3,UGT1A6,UGT1A9, and UGT2B7 had activity for 7-glucuronidation of GS. However, no isoform showed catalytic activity of 4'-glucuronidation of GS. UGT1A1 and UGT1A9 exhibited much higher catalytic efficiency, kcat/Km, for 7-glucuronidation than did the other isoforms. UGT1A9 showed a Km value of 9.5 for the mono-glucuronidation of GS, which were very similar to that of human microsomes. The observed kcat/Km indicated that UGT1A1 and UGT1A9 catalyzed 7-glucuronidation of GS in the human liver microsomes. The results of enzymatic study using synthetic GS 7- and 4'-glucuronides as substrates for sulfation by recombinant SULTs showed that SULT1E1 most efficiently catalyzed the formation of sulfoglucuronides from GS mono-glucuronides. On the other hand, only UGT1A1 showed a catalytic activity of the sulfoglucuronide formation from GS 4'-sulfate. No isoform had activity to form sulfoglucuronide from GS 7-sulfate.