Mass spectrometry-based analysis for investigating drug metabolism and drug-microbiota interactions

This thesis presents three research projects that show the application of liquid chromatography coupled with mass spectrometry (LC-MS) in pharmaceutical analysis, with a particular focus on drug metabolism and drug-microbiota interactions. The first study used a chronic stress model in male rats to explore the relationship among the endocannabinoid system, the gut microbiota, and faecal lipid metabolism. The results of this project showed that inhibiting FAAH supports stress-resilient behaviour and helps preserve gut microbiota composition and faecal lipid content. The second project investigated the metabolic transformations of orally administered glucocorticoids carried out by artificial gut microbiota (AGM) communities. Using a combined LC-HRMS and metagenomic workflow, the study uncovered distinct microbial biotransformation patterns and revealed how corticosteroids can reshape microbial populations, offering new insights into the bidirectional interactions between microorganisms and drugs. The final study focused on developing and validating a sensitive LC-MS/MS method to quantify idarubicin and its active metabolite, idarubicinol, in human plasma. This method was subsequently applied in a pharmacokinetic study involving patients with hepatocellular carcinoma undergoing cTACE treatment, revealing differences in the clearance of the two compounds. Collectively, these projects highlight the power and versatility of mass spectrometry, for both targeted measurements and untargeted analyses. They demonstrate how this technology can elucidate complex biological and pharmacological processes at the intersection of analytical chemistry, microbiology, and clinical pharmacology.