Metabolism of swertiamarin from Swertia japonica by human intestinal bacteria.

The biotransformation of swertiamarin [1, a seco-iridoid glucoside isolated from Swertia japonica (Schult.) Makino] by human intestinal bacteria was investigated. Three metabolites were isolated and identified as erythrocentaurin (2), 5-hydroxymethylisochroman-1-one (3), and gentianine (4) by spectroscopic methods. Through screening of various defined strains of intestinal bacteria (25 species), it was found that all these species had the ability to metabolize 1 to 2 and 3, whereas only a few species had the ability to produce 4. This is the first report to show that one of the metabolic intermediates of the secoiridoid compound is further transformed to a nitrogen-containing compound through metabolic processes by human intestinal bacteria.