Structural transformation of saikosaponins by gastric juice and intestinal flora.

Structural transformation of saikosaponin a and saikosaponin d, main components of Bupleuri Radix, were investigated using rat gastric juice (pH 1.5) and mouse intestinal flora in vitro and the excretion of saikosaponin derivatives in rat feces was also studied. Quantitative analysis of saikosaponins and their derivatives was carried out by high performance liquid chromatography. By the incubation of saikosaponins in rat gastric juice, saikosaponin a decreased with time dependently. After 3 h, saikosaponin a disappeared completely and saikosaponin b1 which possessed heteroannular diene moiety at C-11,13(18) and saikosaponin g which possessed homoannular diene moiety at C-9(11),12 were detected with the ratio of 3:1. On the other hand, saikosaponin d rapidly changed to only saikosaponin b2 (heteroannular diene structure) completely 30 min after the incubation. Next, by the anaerobic incubation of saikosaponin a with mouse intestinal flora, the formation of saikogenin F, a genuine aglycone of saikosaponin a, reached to the maximum 1 h after the incubation and its yield was 80%. A minor peak of prosaikogenen F, a monofucoside of saikogenin F, was also detected at 15 min. By the same procedures, saikosaponin b1, g, d and b2 also changed to the corresponded prosaikogenin A, H, G and D and saikogenin A, H, G and D with the almost similar pattern to that of saikosaponin a. Finally, the contents of nine excreted metabolites from saikosaponin a, 5 and 20 mg/kg, in feces after its oral administration was investigated using fasted or non-fasted rats.(ABSTRACT TRUNCATED AT 250 WORDS)