Icariin is one of the predominant flavonoids contained in Herba Epimedii (Yin-yang-huo in Chinese), a well-known Chinese\nmedicine for the treatment of cancers and immune system diseases. Although Herba Epimedii has been widely used in China and\nthere are so many and various research reports on the herbal drug and its main flavones, very limited data is available on the tissue\ndistribution and biotransformation of icariin. In the present study, a liquid chromatographic method combined with electrospray\nionization tandem mass spectrometry was developed to quantify the concentration of icariin in rat plasma and various tissues\ncollected at different time points after oral administration of the total flavonoid extract of Herba Epimedii at a dose of 0.69 g/kg\n(corresponding to 42mg/g icariin). Biological samples were processed by simple protein precipitation. Genistein was chosen as\ninternal standard. The method was successfully applied to plasma pharmacokinetic and tissue distribution studies of icariin in\nrat. As a result, it was worth noting that the tissue distribution characteristics of icariin exhibited a significant gender difference.\nMoreover, in vivo metabolism of icariin was also investigated. A total of 11 potential metabolites were found in rat feces collected in\ndifferent time periods after oral and intramuscular administration of icariin. In vivo metabolic pathwayswere involved in hydrolysis,\ndemethylation, oxidation, and conjugation.The preclinical data would be useful for fully understanding in vivo disposition of this\ncompound and interpreting the mechanism of its biological response.
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