Received for publication November 16, 2005.
Revised February 21, 2006.
Accepted for publication February 22, 2006.

Absorption and metabolism of Astragali Radix decoction: in silico, in vitro and a case study in vivo

Abstract

To profile absorption of Astragali Radix decoction and identify its oral absorbable constituents and their metabolites, four complementary in silico, in vitro and in vivo methods, i.e., computational chemistry prediction method, Caco-2 cell monolayer model experiment, improved rat everted gut sac experiment and healthy human volunteer experiment were used. According to in silico computation result, 26 compounds of Astragali Radix could be regarded as oral available compounds, including 12 flavonoids. In the in vitro and in vivo experiments, 21 compounds were tentatively identified by high-performance liquid chromatography-diode array detection-electrospray ion trap tandem mass spectrometry data, which involved calycosin, formononetin, (6aR,11aR)-3-hydroxy-9,10-dimethoxypterocarpan, 7,2^'-dihydroxy-3^',4^'-dimethoxyisoflavan, calycosin-7-O--D-glucoside, formononetin-7-O--D-glucoside, 7,2^'-dihydroxy-3^',4^'-dimethoxyisoflavan-7-O--D-glucoside-6^''-O-malonate, (6aR,11aR)-3-hydroxy-9,10-dimethoxypterocarpan-3-O--D-glucoside and phase II metabolites calycosin-7-O--D-glucuronide, formononetin-7-O--D-glucuronide, (6aR,11aR)-3-hydroxy-9,10-dimethoxypterocarpan-3-O--D-glucuronide, 7,2^'-dihydroxy-3^',4^'-dimethoxyisoflavan-7-O--D-glucuronide and calycosin sulphate. Calycosin and formononetin were proved absorbable by four methods; (6aR,11aR)-3-hydroxy-9,10-dimethoxypterocarpan and 7,2^'-dihydroxy-3^',4^'-dimethoxyisoflavan were proved absorbable by three methods; formononetin-7-O--D-glucoside and (6aR,11aR)-3-hydroxy-9,10-dimethoxypterocarpane-3-O--D-glucoside were proved absorbable by two methods. The existence of calycosin-7-O--D-glucuronide, formononetin-7-O--D-glucuronide, (6aR,11aR)-3-hydroxy-9,10-dimethoxypterocarpan-3-O--D-glucuronide, 7,2^'-dihydroxy-3^',4^'-dimethoxyisoflavan-7-O--D-glucuronide and calycosin sulphate was proved by two or three methods. We found that besides isoflavones, pterocarpans and isoflavans also could be metabolized by the intestine during absorption, and the major metabolites were glucuronides. In conclusion, the present study demonstrated that the flavonoids in Astragali Radix decoction, including isoflavones, pterocarpans and isoflavans, could be absorbed and metabolized by intestine. These absorbable compounds, which were reported to have various bioactivities related to the curative effects of Astragali Radix decoction, could be regarded as an important component part of the effective constituents of Astragali Radix decoction.

Key words: analytical chemistry, computer modeling and simulation, drug absorption, glucuronidation, HPLC, intestinal bioavailability, mass spectrometry, membrane permeability, oral absorption, structure elucidation