Metabolism of Sennosides by Human Intestinal Bacteria

Species and numbers of intestinal bacteria have recently been investigated and the biochemical interaction between a host and its intestinal flora has become the object of research. It has been suggested that the purgative activities of Rhei rhizoma and Sennae folium are related to the intestinal bacterial action. The present study was undertaken to reveal the process of the metabolism of sennosides, the main effective components of these crude drugs, by human intestinal bacteria, to account for the relation between their defaecation effect and intestinal flora. Through a qualitative study of the ability of 20 species of anaerobes to metabolize sennoside A (A), species were classified into four types: Type I possessing ß-glucosidase activity to produce sennidin, Type II isomerizing A to sennoside B (B), Type III producing unknown glucosides, and Type IV possessing no metabolic activity. Quantitative analyses of intermediates and products clarified the process of the metabolism of A. Type I bacterium, using Clostridium sphenoides as a typical example, reductively cleaved A to produce 8-glucosylrheinanthrone (8GRA), which was then hydrolyzed by ß-glucosidase to produce rheinanthrone (RA), which was rapidly oxidized to sennidin. Type II bacterium, using Eubacte-rium rectale, reduced both A and B to 8GRA in the same way as Type I bacteria, followed by oxidation to the isomers B and A, because of deficiency of ß-glucosidase activity. The active principle is probably RA, which can be formed by Type I bacteria through the reduction and subsequent hydrolysis of sennosides. The individual differences of Type I bacteria in the purgative effect of sennosides may be due to the difference of Type I bacteria in the intestinal flora.