Hepatoprotective activity of Reduohanxiao-tang (Yuldahanso-tang) is related to the inhibition of β-glucuronidase

beta-Glucuronidase-inhibitory and hepatoprotective effects of Reduohanxiao-tang (Yuldahanso-tang), which has been used for liver diseases and stroke, on carbon tetrachloride (CCl4)-induced hepatotoxicity of rats were investigated. Reduohanxiao-tang potently inhibited beta-glucuronidases. Serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactic acid dehydrogenase (LDH) levels of the CCl4 group orally treated with Reduohanxiaotang (100 mg/kg) were lowered to 54%, 71.5% and 66.1% of the CCl4-treated control group, respectively. Among the ingredients of the Reduohanxiao-tang, the rhizomes of Pueraria thunbergiana and Scutellaria baicalensis potently inhibited beta-glucuronidases and protected against CCl4-induced liver injury. Orally administered puerarin, which is a main component of Pueraria thunbergiana, showed potent hepatoprotective activity, but did not inhibit beta-glucuronidase. However, daidzein, which is produced from puerarin by human intestinal bacteria, potently inhibited beta-glucuronidase. These results suggest that beta-glucuronidase inhibition by herbal medicines may protect against CCl4-induced liver injury.