Potent and Specific Inhibition of mMate1-Mediated Efflux of Type I Organic Cations in the Liver and Kidney by Pyrimethamine

Abstract

This report describes a potent and selective inhibitor of multidrug and toxin extrusion (MATE) protein, pyrimethamine (PYR), and examines its effect on the urinary and biliary excretion of typical Mate1 substrates in mice. In vitro inhibition studies demonstrated that PYR is a potent inhibitor of mouse (m)Mate1 (K i ϭ 145 nM) among renal organic cation transporters mOctn1 and mOctn2 (K i Ͼ 30 M), mOct1 (K i ϭ 3.6 M), and mOct2 (K i ϭ 6.0 M). PYR inhibited the uptake of metformin by kidney brush-border membrane vesicles (BBMVs) (K i ϭ 41 nM) and canalicular membrane vesicles in the presence of outward gradient of H ϩ . PYR treatment significantly increased the kidneyto-plasma ratio of tetraethylammonium, and both the liver-and kidney-to-plasma ratios of metformin in mice, whereas it did not affect their plasma concentrations and urinary excretion rates. Furthermore, the plasma lactate concentration, a biomarker for inhibition of gluconeogenesis by metformin, was significantly higher in the PYR-treated group than in the control group. These results not only suggest the importance of mMate1 in the efflux of organic cations into the urine and bile in mice but also the importance of canalicular efflux mediated by MATE proteins for the therapeutic efficacy of metformin. PYR is a potent inhibitor of human (h)MATE1 and hMATE2-K (K i ϭ 77 and 46 nM, respectively) and H ϩ and organic cation exchanger in human kidney BBMVs (K i ϭ 31 nM) in the presence of outward gradient of H ϩ . Taken together, PYR can be used as a potent probe inhibitor of human MATE transporters.

[11C]-Labeled Metformin Distribution in the Liver and Small Intestine Using Dynamic Positron Emission Tomography in Mice Demonstrates Tissue-Specific Transporter Dependency

“…Although the number of animals was insufficient to draw firm conclusions, we did not observe further reduction in hepatic uptake under these conditions, indicating an insignificant role of MATE1 in hepatic uptake of metformin. Instead, inhibition of MATE1 profoundly affected hepatic elimination of metformin, which supports previous reports from pyrimethamine-treated mice (24). These prominent effects open the possibility to potentiate metformin action by cotreatment with MATE1 inhibitors.…”

Metformin Sinusoidal Efflux from the Liver Is Consistent with Negligible Biliary Excretion and Absence of Enterohepatic Cycling

“…Since metformin intravenous dose was completely recovered as parent in urine, and because drug-related material was not detected in feces, it has been broadly assumed that biliary excretion does not contribute to systemic clearance (Tucker et al, 1981;Glucophage, 2009;Graham et al, 2011). This assumption was confirmed in biliary excretion studies, in which #0.3% of the intravenous dose was recovered in bile (Maeda et al, 2007;Ito et al, 2010). Nonetheless, metformin distribution to the kidney is only approximately 3-fold higher than metformin distribution to the liver (kidney/plasma ratio = 6-25; liver/plasma ratio = 2-7) (Maeda et al, 2007;Ito et al, 2010;Higgins et al, 2012), which raises the question why is the drug wholly eliminated in urine with negligible biliary excretion?…”

Effect of Ondansetron on Metformin Pharmacokinetics and Response in Healthy Subjects

“…Metformin has been reported to be not metabolized in the liver, so only a small fraction is excreted into the bile (Ito et al, 2010;Shingaki et al, 2015). Consistently, the effect of ondansetron treatment on metformin clearance was mainly explained by its effect on renal clearance (Table 1).…”