Investigation of the in vivo metabolism of harpagoside and distribution of its metabolites in rats by HPLC-IT-TOF-MS.

Harpagoside, an iridoid glycoside, is the major bioactive constituent of the traditional Chinese medicine Scrophulariae Radix. High-performance liquid chromatography with a diode array detector combined with electrospray ionization ion trap time-of-flight multistage mass spectrometry (HPLC-ESI-IT-TOF-MS ) was used to profile and identify the metabolites of harpagoside in rats in vivo and to study the distribution of these metabolites in rats for the first time. A total of 45 metabolites were identified, 37 of which were postulated to be new compounds. The number of detected metabolites in the heart, liver, spleen, lung, kidney, stomach and small intestine was 2, 9, 6, 16, 4, 16 and 6, respectively, which indicated that the target organs of harpagoside should be spleen, lung and stomach. The main types of metabolic reactions of harpagoside in rats are hydrolysis, reduction, sulfuric acid addition, hydroxylation, methoxylation, sulfate substitution, methylation, glucose conjugation and amino acid conjugation. Furthermore, 23 metabolites were determined to have bioactivities based on the literature and 'PharmMapper' analysis. These findings are useful for better comprehension of the effective forms, target organs and pharmacological effects of harpagoside. Moreover, these findings provide a reference for studying the metabolism and distribution of iridoid compounds.