Human gastrointestinal metabolism of the anti-rheumatic fraction of Dianbaizhu (Gaultheria leucocarpa var. yunnanensis) in vitro: Elucidation of the metabolic analysis in gastric juice, intestinal juice and human intestinal bacteria by UPLC-LTQ-Orbitrap-MSn and HPLC-DAD.

The anti-rheumatic fraction (ARF), is responsible for the anti-inflammatory and analgesic effects of Dianbaizhu derived from the aerial part of Gaultheria leucocarpa var. yunnanensis (Ericaceae). The gastrointestinal metabolism of ARF was investigated in vitro through simulating a series of models-gastric juice, intestinal juice, and human intestinal bacteria, analyzed by HPLC-DAD and UPLC-LTQ-Orbitrap-MSⁿ. ARF includes three categories: methyl salicylate glycosides, organic acids and the others. The primordial and metabolic components of ARF bio-transformed by simulated gastric fluid (36 and 13), intestinal fluid (29 and 7) and two human fecal bacteria (34 and 34, 40 and 25) were characterized, respectively. The methyl salicylate glycosides, MSTG-B, MSTG-A and gaultherin, with terminal-xylosyl-moiety in sugar chain were always being found in the whole gastrointestinal incubation processing. The metabolites were formed through hydrolysis of ester and glucosidic bond, as well as methylation, hydroxylation, acetylation, sulfation, reduction, decarboxylation, deglycosylation and glucuronidation. The metabolic conversion effect of the four index compounds, MSTG-B, MSTG-A, gaultherin, and chlorogenic acid by human intestinal bacteria exhibited much stronger. Those markers' variation in content-time curve in volunteer A gut flora were faster than that in volunteer B's. These results indicate that ARF is relatively stable in the gastrointestinal tract.