Studies of Metabolism and Disposition of Natural Products using Mass Spectrometry

The studies of metabolism and disposition of natural products and active compounds in botanical dietary supplements are essential for evaluating their efficacy and safety. In this dissertation, several in vitro and in vivo models were used to evaluate metabolism and disposition of various natural products using high performance liquid chromatography-mass spectrometry (HPLC-MS).;The hepatic metabolism of zapotin was investigated using human liver microsomes and human hepatocytes. Metabolites were characterized using LC-MS and LC-MS-MS. The data indicated that zapotin undergoes extensive phase I and phase II metabolism via hydroxylation, O-demethylation, and conjugation. Pathways for the hepatic metabolism of zapotin were proposed. The in vivo biotransformation and bioavailability of zapotin were investigated in rats using LC-MS and LC-MS-MS. Low levels of zapotin were detected and extensive in vivo metabolism of zapotin was observed in serum and tissue samples. In addition, in vitro hepatic metabolism of drug candidate, MAR-I-54 (2,4-dibromo-1-hydroxyphenazine) was conducted with human liver microsomes. Metabolites were characterized using LC-MS and LC-MS-MS. Pathways for the hepatic metabolism of MAR-I-54 were proposed.;Chemical standardization of a hop (Humulus lupulus L.) extract for use in a phase I clinical trial at the UIC/NIH Center for Botanical Dietary Supplements was carried out using LC-MS-MS. The metabolic fate of the hop marker compounds was also investigated in women. Glucuronides of isoxanthohumol, xanthohumol and 8-prenylnaringenin, but no sulfate conjugates, were detected. Cis- and trans- isoxanthohumol alcohols were also detected. Interestingly, mildly estrogenic IX was metabolically converted to the potent estrogen 8-PN.;The inhibition of human liver cytochrome P450 enzymes by the standardized black cohosh (Cimicifuga racemosa L.) extracts and isolated black cohosh triterpenes was investigated for possible herb-drug interactions. Crude ethanolic extract of black cohosh inhibited CYP3A4 with an IC50 value of 16.5 mug/mL. Eight black cohosh triterpenoids showed IC 50 values of 2-5 muM against CYP3A4. In addition, inhibition of tamoxifen metabolism by black cohosh extracts was also conducted. Crude ethanolic extract of black cohosh showed 66.3% and 74.6% inhibition of 4-hydroxy-TAM and N-desmethyl-TAM formation, respectively, at 50 mug/mL.