The In Vivo Existence Forms of Engeletin and Their Anti-Hyperuricemia Activity

Smilacis Glabrae Rhizoma is a traditional Chinese medicine commonly used for hyperuricemia. Engeletin, one of its major flavonoids, exhibits various pharmacological activities, but its in vivo uric acid-lowering activity and metabolic processes remain unclear. This study aims to elucidate the in vivo existence forms of engeletin and the pharmacological basis underlying its uric acid-lowering effects. The in vivo metabolites of engeletin were identified by using UHPLC-Q-TOF-MS. The xanthine oxidase inhibitory activity was investigated using in vitro enzymatic assays. The in vivo uric acid-lowering effect was evaluated in hyperuricemic mice. A total of 11, 34, 7, 6, and 5 compounds were detected in urine, feces, serum, liver, and kidney samples, respectively. After removing duplicates, 52 compounds were preliminarily identified as in vivo existence forms of engeletin. The main metabolic reaction types were glucuronidation, sulfation, and hydrolysis. Engeletin exhibited no xanthine oxidase inhibitory activity in vitro but possessed uric acid-lowering activity in vivo. Neoisoastilbin and naringenin were metabolites with both xanthine oxidase inhibitory activity and uric acid-lowering activity. The in vivo uric acid-lowering activity of engeletin may be attributable to its two metabolites rather than itself. This study elucidated the pharmacological basis of engeletin and laid the foundation for developing potential therapeutics for hyperuricemia.