Metabolism and pharmacokinetics of major polyphenol components in rat plasma after oral administration of total flavonoid tablet from Anemarrhenae Rhizoma

Total flavonoid tablet from Anemarrhenae Rhizoma (Zhimu tablet), which was made of total polyphenol components extracted from the dried rhizome of Anemarrhena asphodeloides Bge. (Zhimu in Chinese), is a novel traditional Chinese medicine prescribed for the treatment of diabetes. Mangiferin (MF) and neomangiferin (NMF) are the two main components detected and determined in Zhimu tablet, accounting for 8.9% of the total weight of each tablet. In the present study, high performance liquid chromatography (HPLC) coupled with time-of-flight (TOF) tandem mass spectrometry (MS) was applied to characterize the metabolites of MF and NMF in rat plasmas collected at different time points after oral administration of Zhimu tablet at a dose of 3.63 g/kg (corresponding to 270 mg/kg MF). Accurate mass measurement was used to determine the elemental composition of metabolites and thus to confirm the proposed structures of identified metabolites. Time points of appearance of some metabolites, such as isomers, were also taken into account during the structure confirmation. A total of 21 potential metabolites were found in rat plasma at different time points, and the metabolic pathways in vivo were involved in hydrolysis, methylation, glucuronide conjugation, glycoside conjugation, sulphation, dehydration and isomerisation. Furthermore, a selective and accurate LC–MS assay method was developed and validated for the quantification of MF in plasma. Semi-quantification of main conjugated metabolites was also performed in order to describe the dynamic metabolism profiles of polyphenol components in Zhimu tablet. MF concentration in plasma reached 1.36 ± 0.47 μg mL−1 about 5.0 h after oral administration of Zhimu tablet, which showed a 3.24- and 4.91-fold increase in plasma maximum concentration and area under the concentration-time curve (AUC) from 0 to 24 h of MF compared with those for rats administered with free MF, respectively. The results indicated that the pharmacokinetic processes and bioavailability of MF in rats would be affected by other components in Zhimu tablet.