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Identification of a new metabolite of astilbin, 3'-O-methylastilbin, and its immunosuppressive activity against contact dermatitis.

BACKGROUND
Astilbin is a flavonoid isolated from the rhizome of Smilax glabra. In a previous study, we revealed its unique immunosuppressive activity, a selective inhibition against activated T lymphocytes. This characteristic of astilbin is beneficial for the treatment of human immune diseases.


METHODS
We incubated astilbin with rat liver microsomal/cytosolic fractions and isolated the metabolite of astilbin, which was fully characterized by mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. We administered astilbin orally via a gastric tube to rats at 0.22 mmol/kg and collected whole blood samples after 30 min and urine samples after 0 to 12 h. We applied HPLC and liquid chromatography/MS to measure the metabolite in the samples, and we assayed cytokine expression by reverse-transcription PCR.


RESULTS
After incubation of astilbin with rat liver microsomal/cytosolic fractions, we detected a new metabolite of astilbin and isolated it from the culture solution. We characterized this metabolite by MS and NMR techniques as 3'-O-methylated astilbin. We detected the metabolite in both blood and urine samples after oral administration of astilbin, and the metabolite inhibited picryl chloride-induced ear swelling in mice and suppressed the expression of tumor necrosis factor-alpha and interferon-gamma, similarly to astilbin.


CONCLUSION
This is the first identification of 3'-O-methylastilbin as a new flavonoid, as well as an active metabolite of astilbin in vivo, and is helpful for studying the kinetics of astilbin and its clinical applications.