Genistein decreases basal hepatic cytochrome P450 1A1 protein expression and activity in Swiss Webster mice.

Soy consumption has been associated with risk reduction for chronic diseases such as cancer. One proposed mechanism for cancer prevention by soy is through decreasing cytochrome P450 1A1 (Cyp1a1) activity. However, it is not known with certainty which soy components modulate Cyp1a1, or the characteristics or mechanisms involved in the responses after short-term (<20 days) dietary treatment without concomitant carcinogen-mediated induction. Therefore, the objective was to test the hypothesis that physiologic concentrations of dietary genistein and/or daidzein will decrease basal hepatic Cyp1a1 protein expression and activity in male and female Swiss Webster mice via inhibiting the bindings of aryl hydrocarbon receptor (AhR)-AhR nuclear translocator (ARNT) and estrogen receptor-α to the Cyp1a1 promoter region xenobiotic response element. The mice were fed the AIN-93G diet supplemented with 1500 mg/kg of genistein or daidzein for up to 1 week. Genistein, but not daidzein, significantly decreased basal hepatic microsomal Cyp1a1 protein expression and activity. AhR protein expression was not altered. Molecular mechanisms were investigated in Hepa-1c1c7 cells treated with 5 µmol/L purified aglycones genistein, daidzein, or equol. Cells treated with genistein exhibited inhibitions in ARNT and estrogen receptor-α bindings to the Cyp1a1 promoter region. This study demonstrated that genistein consumption reduced constitutive hepatic Cyp1a1 protein expression and activity, thereby contributing to the understanding of how soy isoflavone aglycones modulate cytochrome P450 biotransformation enzymes.

Soy isoflavones increase quinone reductase in hepa-1c1c7 cells via estrogen receptor beta and nuclear factor erythroid 2-related factor 2 binding to the antioxidant response element.

Soy protein and isoflavones (genistein and daidzein) have been demonstrated to increase quinone reductase (QR) activity, protein, and mRNA in animal and cell culture models. However, their mechanism of action has not been completely characterized. Additionally, it has not been determined if equol, a daidzein metabolite, can modulate QR activity and expression. Estrogen receptor beta (ERß) is thought to be involved in stimulating QR gene transcription by anti-estrogens and phytoestrogens, along with nuclear factor erythroid 2-related factor 2 (Nrf2). This study tested the hypothesis that genistein, daidzein and equol increase quinone reductase activity, protein and mRNA via ERß and Nrf2 binding to the QR antioxidant response element (ARE). QR expression and activity were determined using TaqMan polymerase chain reaction, protein immunoblots and activity assays. Molecular events were investigated using luciferase reporter gene assays and chromatin immunoprecipitation (ChIP). Hepa-1c1c7 cells were treated with control [0.1% (v:v) dimethyl sulfoxide (DMSO)]; 1 µmol/L ß-naphthoflavone (positive control); 5 µmol/L resveratrol (ChIP positive control for ERß binding) and 1, 5 and 25 µmol/L genistein, daidzein or equol. Treatment durations were 1 h (ChIP), 24 h (mRNA and luciferase assays) and 24 and 48 h (protein and activity). Genistein, daidzein and equol increased QR activity, protein and mRNA, with daidzein and equol having more of an impact at physiologic concentrations (1 and 5 µmol/L) compared to genistein. Furthermore, the study results demonstrate that genistein, daidzein and equol interact with the QR ARE and that daidzein and equol act via both ERß and Nrf2 binding strongly to the QR ARE.

Regulation of phase II enzymes by genistein and daidzein in male and female Swiss Webster mice.

The consumption of soy and soy isoflavones has been associated with a decreased risk of certain cancers. A factor contributing to this dietary chemoprevention is the activity of phase I and II biotransformation enzymes. This study evaluated the hypothesis that dietary soy isoflavones will increase hepatic and extrahepatic quinone reductase (QR), UDP-glucuronosyltransferase (UGT), and glutathione S-transferase (GST) phase II enzyme activities, under short-term feeding and basal (non-pharmacologic-induced) conditions. Male and female Swiss Webster mice were fed for 1, 3, 5, or 7 days of one of four treatments: control (casein AIN-93G) or control supplemented with flavone (positive control), genistein, or daidzein aglycones at 1,500 mg/kg of diet. QR activity was increased by daidzein in the liver, by both isoflavones in the kidney and small intestine, and by genistein in the heart. Genistein and daidzein slightly decreased UGT activities in some tissues. Liver GST activity was decreased by genistein in females. In contrast, genistein and daidzein increased kidney GST activity. In general, the greatest effects of isoflavones on phase II enzymes were observed in liver and kidney tissues, occurring at day 3, and peaking at day 5. Sex effects in the liver and kidney included females exhibiting higher QR activities and males exhibiting higher UGT and GST activities. In conclusion, individual soy isoflavones modulate phase II enzymes in mice under short-term feeding and basal conditions. This study provides insights into the actions of isolated isoflavones in mice.