Cholesterol-binding ability of saponin from Japanese starfish

Steroidal gylcosides are the predominant metabolites of starfish and are responsible for various biological activities. Some of these activities are recognized as a part of self-defense mechanism of starfish. Cholesterol-binding ability was evaluated with seven starfish crude extracts, where significantly ( p < 0.05) highest ability (34%) was observed in Asterias amurensis and the lowest (16%) was attributed in Distolasterias nippon. To characterize the active compound exists in crude saponin from A. amurensis , the extract was subjected to thin layer chromatography following silica gel column chromatography. As the results, seven fractions (fr. A-G) were separated and frs. D and F demonstrated the highest cholesterol-binding ability (32% and 33%, respectively), equivalent to that of the A. amurensis extract. The isolated component (fr. F) was further separated (fr. F1–F3) for structural analysis. Based on cholesterol-binding ability result (29%), fr. F2 was analysed by matrix-assisted laser desorption ionization–time-of-flight mass spectroscopy (MALDI-TOF MS) and then nuclear magnetic resonance spectroscopy (NMR). The compound was identified as thornasteroside A, one of the major bioactive compounds already found in A. amurensis . The discovery of a saponin with cholesterol-binding ability has important implications not only for the utilization of starfish but also for food and pharmaceutical research.