Identification of Sinensetin Metabolites in Rat Urine by an Isotope-Labeling Method and Ultrahigh-Performance Liquid Chromatography-Electrospray Ionization Mass Spectrometry

Sinensetin (SIN), one of the major polymethoxyflavones (PMFs) contained mainly in the citrus peels, has been reported to possess various bioactivities, including antifungal, antimutagenic, anticancer, and anti-inflammatory activities. Although the biotransformation of SIN in fungi and insects has been reported, the information about the metabolism of SIN in mammals is still unclear. In this study, formation of SIN metabolites in rats was investigated. Four isotope-labeled SINs ([4'-D-3]SIN, [3'-D-3]SIN, [5-D-3]SIN, and [6-D-3]SIN) were synthesized and administered to rat. The urine samples were collected and main metabolites were monitored by ultrahigh-performance liquid chromatography electrospray ionization mass spectrometry. The administered compound and four SIN metabolites were detected in rat urine. These metabolites were identified as 4'-hydroxy-5,6,7,3'-tetramethoxyflavone, 5-hydroxy-6,7,3',4'-tetramethoxyflavone, 6-hydroxy-5,7,3',4'-tetramethoxyflavone, and 7-hydroxy-5,6,3',4'-tetramethoxyflavone sulfate.