Dietary Isosaponarin is Intestinally Metabolized to Isovitexin, Most of Which are Excreted in Feces without Being Absorbed

Abstract

Objective: The metabolism of isosaponarin was investigated using a Caco-2 intestinal epithelial model and animal experiment. Background: Isosaponarin is a flavonoid in wasabi (Wasabia japonica) leaves and has unique structure, in which two glucose molecules bind to apigenin through O-glycosidic and C-glycosidic bonds. Materials and Methods: The absorption and metabolism of isosaponarin was investigated by a Caco-2 intestinal epithelial model in vitro and a single oral administration to mice in vivo. Results: These experiments showed that isosaponarin was hardly absorbed into the body. However, isosaponarin was metabolized to isovitexin (apigenin-6-C-glucoside) by hydrolysis of O-glycosidic bond. This hydrolysis was mainly caused at small intestine, and the gastric acid in the stomach might partially contribute to the hydrolysis. Both Caco-2 intestinal epithelial model and animal experiment indicated that isovitexin was also not absorbed into the body, and that half of the administered isosaponarin was excreted as isovitexin in feces. Conclusion: Half of the administered isosaponarin was metabolized to isovitexin in the intestinal tract and then excreted, and the rest was probably degraded by intestinal microflora. Therefore, it was suggested that the bioavailability of dietary isosaponarin is very low.