Metabolite profiling of astilbin in rat sera using UPLC/MS(E) and impact of its metabolites on immunosuppressive activity.

Astilbin, a natural flavonoid, has been shown to have a selective immunosuppressive activity on activated T lymphocytes. In our previous study, 3'-O-methylastilbin was identified as an active metabolite in vivo. However, more comprehensive information regarding the kinetics and metabolic characteristics of astilbin is yet unknown. Here, we isolated and identified 4 metabolites after incubating astilbin with rat liver microsomal/cytosolic fractions. Besides 3'-O-methylastilbin, 4'-O-methylastilbin was firstly identified and detected in the rat plasma after either oral or intravenous administration of astilbin. And phenotypic differences in the metabolic profile were observed between the two administration routes when using UPLC/MS(E) to measure the metabolites in the plasma. Moreover, 4'-O-methylastilbin decreased serum transaminases elevation in mice with concanavalin A-induced liver injury and reduced the mRNA expression of TNF-alpha and IFN-gamma in primed lymph cells upon antigen restimulation. The immunosuppressive activity of 4'-O-methylastilbin appears weaker than astilbin and 3'-O-methylastilbin. Taken together, the characterization of the comprehensive metabolic profile of astilbin confirmed 3'-O-methylastilbin as the major active form of astilbin metabolites, revealed 4'-O-methylastilbin as a minor active form, and helped us to evaluate the route of astilbin administration, which is beneficial for the treatment of human immune diseases.