Pharmacometabolomics Detects Various Unreported Metoprolol Metabolites in Urine of (Potential) Living Kidney Donors and Kidney Transplant Recipients

BACKGROUND AND OBJECTIVE: Metoprolol is primarily metabolized via the polymorphic cytochrome P450-2D6 (CYP2D6) enzyme, which underlies interindividual variation in conversion rates and may benefit from pharmacogenetics-driven therapy personalization. However, the field relies heavily on knowledge of a drug's metabolism, often originating from early-phase clinical trials with single-dose administration in small samples of healthy volunteers. Pharmacogenetics could thus benefit from real-world drug metabolism studies. METHODS: We conducted a real-world drug metabolism study for metoprolol in 18 (potential) living kidney donors and 374 kidney transplant recipients from the Transplant Lines Food and Nutrition Biobank and Cohort Study (NCT02811835) using existing liquid chromatography-high resolution mass spectrometry pharmacometabolomic data. RESULTS: In both groups, we confirmed the presence of seven expected metabolites, including the high-abundance substances metoprolol acid and hydroxymetoprolol. We were unable to detect deisopropylmetoprolol and a metabolite known as "H 119/68". However, we did find putative further oxidized forms, namely the expected variant of deisopropylmetoprolol in which the primary amine is removed and the leftover methyl group is oxidized into a carboxylic acid ("H 104/83") and an unknown/unreported metoprolol metabolite that we refer to as "metoprolol benzoic acid". Moreover, we found nine other previously unknown/unreported metabolites, putatively reflecting N-glucuronidated metoprolol, four glucuronidated versions of hydroxymetoprolol, and a formylated, a glucuronidated, and two hydroxylated versions of metoprolol acid. Interestingly, the same metabolites were detected in potential living kidney donors and kidney transplant recipients, and metabolite profiles did not differ between both groups in principal component analysis. CONCLUSION: We found more metoprolol metabolites than previously reported, calling for replication studies and evaluation of pharmacogenetic testing approaches to realize safer, more effective metoprolol therapy.