Hepatoprotective Activity of Reduohanxiao-tang (Yuldahanso-tang) is Related to the Inhibition of β-Glucuronidase

β-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 β-glucuronidases. Serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactic acid dehydrogenase (LDH) levels of the CCl₄ group orally treated with Reduohanxiao-tang (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 it Scutellaria baicalensis potently inhibited β-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 β-glucuronidase. However, daidzein, which is produced from puerarin by human intestinal bacteria, potently inhibited β-glucuronidase. These results suggest that β-glucuronidase inhibition by herbal medicines may protect a gainst CCl₄-induced liver injury.