Excretion of tectoridin metabolites in rat urine and bile orally administrated at different dosages and their inhibitory activity against aldose reductase

This study investigated the urinary and biliary excretion of tectoridin, a major active isoflavonoid found in the flowers of Pueraria thomsonii Benth. and the rhizomes of Belamcanda chinensis (L.) DC. Using UHPLC/Q-TOFMS, seven glucuronides and/or sulfated metabolites and four Phase I metabolites were simultaneously quantified in rat urine after oral administration of tectoridin at 100 and 200 mg/kg. Over a 72-h period, 14.2% and 14.7% of the tectoridin were excreted as eleven metabolites in urine, among which, two major metabolites tectorigenin-7-O-β-D-glucuronide (Te-7G) and tectorigenin accounted for 5.5–5.5% and 4.3–4.4%. Furthermore, the cumulative excretion of four glucuronides and sulfated metabolites in bile accounted for 7.3% and 3.9% of the dose within 60 h, among which, Te-7G and tectorigenin-7-O-glucuronide-4′-O-sulfate (Te-7G-4′S) accounted for 2.3–3.0% and 1.4–3.9%, respectively. The results indicate that the urine was the primary elimination route, and glucuronidation after deglycosylation at C-7 position was the major metabolic pathway of tectoridin in vivo. Moreover, the inhibitory activities of tectoridin and its five metabolites on rat lens aldose reductase were confirmed (IC₅₀: 1.4–15.5 μM), whereas irisolidone-7-O-glucuronide (Ir-7G) and irisolidone showed little activity.