Evaluation of herb-drug interactions of xanthophylls and fermented Ginseng extract focused on inhibitory effects of human hepatic cytochrome P450s and UDP-glucuronyltransferases

Abstract

Herb-drug interactions have received more attention recently because of the wide popularity of herbal supplements or dietary supplements. The major xanthophylls, astaxanthin, β-cryptoxanthin, canthaxanthin, lutein, and zeaxanthin, are widely used and studied because of their activities as antioxidants, their roles in preventing cancer or age-related macular degeneration. BST204, a fermented ginseng extract, contains high concentrations of ginsenoside Rh2 (over 5.0%) and ginsenoside Rg3 (over 10.0%). The object of this thesis was to investigate the herb-drug interactions of five xanthophylls and BST204 on inhibition of human hepatic microsomal cytochrome P450s and UDP-gluronosyltransferases. Cocktails, test compounds and NADPH re-generating system were incubated 15min after 5 pre-incubation with human liver microsomes (HLMs) in vitro for competitive screening. Time-dependent inhibition (TDI) experiments were also executed. The xanthophlls, HLMs with/without NADPH were incubated at 37℃ for 30 min and then were partly shifted to substrates solutions for continued 15 min incubations. For UGT inhibition study, test compounds, HLMs, (0.25 mg/ml), 100 mM Tris-HCl buffer (pH 7.5), MgCl2 (5 mM), substrate, and alamethicin (25 μg/mL) were pre-incubated on ice to allow alamethicin pore formation in vitro for 30 min. Incubations were commenced with the addition of UDPGA (5 mM) to a final incubation volume of 0.1 ml and incubated at 37°C for 30 min or 60 min. The results showed that xanthophylls and fermented Ginseng extract play ignorable effects on the reversible and irreversible inhibitions of 9 CYPs. But, β-cryptoxanthin, canthaxanthin and zeaxanthin showed inhibitory effects on UGT1A1 with IC50 of 23.68, 36.74 and 42.57 μM, respectively. β-cryptoxanthin and lutein also played inhibitory effect on UGT1A4. BST204 inhibited UGT1A1, 1A9, 2B7 with IC50 values 13.80, 24.59 and 30.83 μg/mL, respectively. S-Rg3, not R-Rg3, showed inhibitory interaction toward UGT1A9 and 2B7. Kinetic constants (Ki) of BST204 on UGT1A1, 1A9, 2B7 enzymes were 27.38, 17.53, 32.51 μg/mL, respectively. The Ki of S-Rg3 inhibiting UGT1A9 and 2B7 were 8.33 and 24.89 μM, respectively. Based on the IC50 values of these five xanthophylls and BST204 on CYPs and UGTs were markedly greater than the Cmax values in human plasma, it is unlikely that these five xanthophylls and BST204 alter the pharmacokinetics of drugs metabolized by CYPs and UGTs. These findings provide some useful information for the safety use of these herbs in clinical practice.