Investigation of endogenous compounds for assessing the drug interactions in the urinary excretion involving multidrug and toxin extrusion proteins.

PURPOSE: Multidrug and toxin extrusion proteins (MATEs) are multispecific organic cation transporters mediating the efflux of various cationic drugs into the urine. The present study aimed at identifying endogenous compounds in human plasma and urine specimens as biomarkers to evaluate drug interactions involving MATEs in the kidney without administration of their exogenous probe drugs. METHODS: An untargeted metabolomic analysis was performed using urine and plasma samples from healthy volunteers and mice treated with or without the potent MATE inhibitor, pyrimethamine. Plasma and urinary concentrations of candidate markers were measured using liquid chromatography-mass spectrometry. Transport activities were determined in MATE- or OCT2-expressing HEK293 cells. The deuterium-labeled compounds of candidates were administered to mice for pharmacokinetics study. RESULTS: Urinary excretion of eleven compounds including thiamine and carnitine was significantly lower in the pyrimethamine-treatment group in humans and mice, whereas no endogenous compound was noticeably accumulated in the plasma. The renal clearance of thiamine and carnitine was decreased by 70%-84% and 90%-94% (p < 0.05), respectively, in human. The specific uptake of thiamine was observed in MATE1-, MATE2-K- or OCT2-expressing HEK293 cells with Km of 3.5 ± 1.0, 3.9 ± 0.8 and 59.9 ± 6.7 µM, respectively. The renal clearance of carnitine-d 3 was decreased by 62% in mice treated with pyrimethamine. CONCLUSIONS: Our findings indicate that MATEs account for the efflux of thiamine and perhaps carnitine as well as drugs into the urine. The urinary excretion of thiamine is useful to detect drug interaction involving MATEs in the kidney.