Metabolites and the pharmacokinetics of kobophenol A from Caragana sinica in rats

Abstract

This research aims to study the metabolism and pharmacokinetics of phytoestrogen kobophenol A (1), the main active compound of Caragana sinica (Buc’hoz) Rehd. (Fabaceae), in rats. Metabolites of 1 in rats’ feces were isolated and purified by multi-chromatograph techniques; three new metabolites of 1, named koboquinone A (M1), koboquinone B (M2) and koboquinone C (M3), were isolated, purified from rats’ feces after they being orally administered with 1. Structure identification of the metabolites was fulfilled by spectroscopic analysis. M1 and M2 are structurally different to those natural occurring stilbene tetramers, which also have para-quinone structure. M1 also showed the activity of stimulating the proliferation of cultured osteoblasts. The pharmacokinetics of 1 in rats could be described by a two-compartmental model (P < 0.05). The half-life was 0.68 h for i.v. administration and 5.78 h for oral administration. The oral bioavailability of 1 was calculated to be 2.0%; rats tissue distribution experiments show that 1 was prominently concentrated in livers. Both of the low oral bioavailability and the rapid reduction of 1 in blood indicated a suitable formulation is needed while it is developed as a new drug.

Introduction

Over the past 50 years, hormone replacement therapy (HRT) has been widely used to alleviate menopausal syndrome such as hot flashes, vaginal dryness, insomnia, etc. It can lower the occurrence of cardiovascular disease (CVD) to 40%, effectively prevent and cure osteoporosis especially. However, stoppage of HRT would lose therapy effects and long-term HRT introduce side effects (Karen and William, 1998). These side effects include weight put on, irregular vaginal discharge, the danger of breast cancer and endometrium cancer, etc. Recently, numerous research findings indicated that estrogen metabolites could stimulate or inhibit cancer growth (Lippert et al., 2000). These cause a big debate on HRT. Therefore, looking for effective phytoestrogen to replace HRT to prevent and cure the menopausal syndrome is now being the focus of research.

Caragana sinica (Buc’hoz) Rehd. (Fabaceae) is widely distributed in China. Its dried roots (Chinese name: Jinquegen) have been used in China as a folk medicine for the treatment of asthenia syndrome, vascular hypertension, leukorrhagia, bruises and contused wounds. In our previous study, we found that the major chemicals of the ethyl acetate extract of the roots were oligostilbenes, which have been found to have multi-faceted bioactivities (Luo et al., 2001). kobophenol A (1) (Fig. 1) is one of the leading chemicals. MTT assay showed that 1 is a phytoestrogen and can strongly stimulate the proliferation of osteoblasts cultured in vitro. Likely be developed as a new drug.

There were no research reports on the metabolites and the pharmacokinetics of 1. In the present investigation, metabolites of 1 in rats after orally treated were isolated and purified by multi-chromatography techniques. Three new metabolites of 1, were identified and named koboquinone A (M1), koboquinone B (M2) and koboquinone C (M3) (Fig. 2). The pharmacokinetic behavior of 1 in rats was characterized by HPLC assays. Following i.v. and oral administration of 1 to rats, the oral bioavailability and tissue distribution were evaluated.