Toralactone glycoside in Cassia obtusifolia mediates hepatoprotection via an Nrf2-dependent anti-oxidative mechanism.

Cassia obtusifolia L. (Leguminosae) seeds are a well-known medicinal food in East Asia and are used to clear liver heat, sharpen vision, lubricate the intestines, and promote bowel movement. The aims of the present study were to identify the hepatoprotective components of C. obtusifolia seeds by bioactivity-guided isolation and to elucidate their mechanisms of action. Ten phenolic glycosides were isolated from the most active ethyl acetate fraction, and their chemical structures were elucidated by spectroscopic analyses. Among the isolated compounds, toralactone 9-O-gentiobioside (5) had the highest hepatoprotective efficacy against tert-butylhydroperoxide-induced cell death in HepG2 cells. Immunoblotting and real-time polymerase chain reaction analyses revealed that the hepatoprotective effects were exerted through nuclear factor erythroid-2-related factor 2 (Nrf2)-dependent antioxidative signaling. Together, these results provide insights into the effects of this medicinal plant as well as a basis for developing hepatoprotective agents as pharmaceuticals and/or nutraceuticals.