Metabolite identification of crude extract from Ganoderma lucidum in rats using ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry

The metabolism of traditional Chinese medicine is very complicated and has been a great challenge. In the present paper, a new strategy was established to study the metabolism of crude extract from Ganoderma lucidum using the highly separative and sensitive ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry. Based on the investigation of the metabolism of five representative single compounds (ganoderic acid), a total of 90 metabolites were identified from the bile sample after oral administration of the crude extract. Among them, 21 compounds were identified by comparison with the reference standards, the other unknown metabolites were tentatively characterized by interpretation of the high resolution low collision energy and high collision energy mass spectra using the fragmentation rules. The metabolic characteristics and "soft spots" of the ganoderic acids were revealed. After being absorbed, the ganoderic acids from the extract could undergo extensive phases I and II metabolism in rat before excreted into the bile. The main ganoderic acids could transform from one to another through reduction, oxidation, deacetylation and desaturation reactions. Other metabolic transformation included hydroxylation, sulfation and glucuronidation. The total tendency was that the low polar ganoderic acids were transformed into the high polar metabolites to eliminate from the organism. The metabolic "soft spots" of the ganoderic acids were 3,7,15,23-carbonyl groups (or hydroxyl groups), angular methyl groups, 20(22)-double bond, 12-acetoxyl group and 26-carboxylic acid moiety. These results are considered to be important for the further investigation of G. lucidum.