Oxidative in Vitro Metabolism of the Soy Phytoestrogens Daidzein and Genistein

Abstract

The oxidative metabolism of the major soy isoflavones daidzein and genistein was investigated using liver microsomes from Aroclor-treated male Wistar rats. Both daidzein and genistein were extensively metabolized and are therefore excellent substrates for cytochrome P450 enzymes. The identity of the metabolites was elucidated using high-performance liquid chromatography (HPLC) with diode array detection, gas chromatography-mass spectrometry (GC/MS), and HPLC/atmospheric pressure ionization electrospray mass spectrometry (API-ES MS) as well as reference substances. Daidzein was converted to nine metabolites, comprising four monohydroxylated, four dihydroxylated, and one trihydroxylated metabolite. Genistein was metabolized to four monohydroxylated and two dihydroxylated products. With both isoflavones the additional hydroxy groups are exclusively introduced into the ortho positions of existing phenolic hydroxy groups. The major metabolites of daidzein were identified as 6,7,4'-trihydroxyisoflavone, 6,7,3',4'-tetrahydroxyisoflavone, 7,8, 4'-trihydroxyisoflavone, and 5,6,7,4'-tetrahydroxyisoflavone. The main microsomal metabolites of genistein were 5,6,7, 4'-tetrahydroxyisoflavone and 5,7,8,4'-tetrahydroxyisoflavone. Furthermore, the GC/MS and HPLC/API-ES MS analysis support the conclusion that one monohydroxylated metabolite of daidzein and genistein is hydroxylated at the aliphatic position C-2 of the C-ring. The UV-vis, GC/MS, and HPLC/MS data of all detected metabolites as well as the derived chemical structure of the metabolites are presented. Most metabolites are reported in this paper for the first time. On the basis of these findings it is suggested that hydroxylation reactions may also play an important role in the in vivo metabolism of the soy isoflavones daidzein and genistein.

Identification of Cyp1a2 as the Main Isoform for the Phase I Hydroxylated Metabolism of Genistein and a Prodrug Converting Enzyme of Methylated Isoflavones

“…1). This pattern is similar to those reported by earlier studies (Roberts-Kirchhoff et al, 1999;Kulling et al, 2000;. Additional hydroxylated metabolites of genistein, which elutes earlier than genistein, have been previously reported (Kulling et al, 2000(Kulling et al, , 2001.…”

“…Thus, identifying phase I metabolites of genistein, characterizing its metabolic pathways, and determining the biological activity of metabolites are of great importance for understanding the biological functions of isoflavones. Recently, several phase I metabolites of genistein, which are mainly hydroxylated metabolites, have been identified in vitro and in vivo (Kulling et al, 2000(Kulling et al, , 2001(Kulling et al, , 2002. Additionally, formononetin and biochanin A were shown to be converted to daidzein and genistein following oral administration to humans (Setchell et al, 2001).…”

Isoflavones: Chemistry, Analysis, Functions and Effects on Health and Cancer

“…In addition to bacterial metabolism, isoflavone metabolized by phase-I and II isoenzymes in liver. Genistein and daidzein undergo hydroxylation catalyzed by Phase-I enzymes (cyptochrome P450) and glycetin is metabolized to mono-or dihydrozylated glycetin metabolites (Kulling et al, 2000). And conjugated metabolites by phase-II enzymes such as Uridine 5'-diphospho-glucuronosyl transferase and sulfotransferase were synthesized (Kulling et al, 2001).…”

7,3′,4′-Trihydroxyisoflavone Inhibits Epidermal Growth Factor-induced Proliferation and Transformation of JB6 P+ Mouse Epidermal Cells by Suppressing Cyclin-dependent Kinases and Phosphatidylinositol 3-Kinase

“…In rats (28) and humans (25), isoflavones are subject to oxidative biotransformation through hepatic metabolism. One of the major products of the hepatic metabolism of daidzein is 7,3Ј,4Ј-THIF (29).…”