Characteristics of pemetrexed transport by renal basolateral organic anion transporter hOAT3.

PURPOSE: Pemetrexed transport by human organic anion transporters, hOAT1 (SLC22A6) and hOAT3 (SLC22A8), were characterized in comparison with methotrexate. METHODS: Accumulation of pemetrexed and methotrexate in hOAT1- and hOAT3-expressing cells were evaluated. Pemetrexed and methotrexate were determined by HPLC. Kinetic parameters were calculated by Eadie-Hofstee plot. RESULTS: When HEK-hOAT3 and -hOAT1 cells were incubated with 100 µM pemetrexed for 30 min, pemetrexed was accumulated at 14- and 1.7-fold greater than that in control cells, respectively. Pemetrexed and methotrexate transport by hOAT3 was saturated at high concentrations with apparent Km values 28.2 µM and 76.6 µM, respectively. In addition, intrinsic activity (Vmax/Km) of pemetrexed and methotrexate transport by hOAT3 was 4.82 and 0.42 µl/min/mg protein, respectively, suggesting 11-fold higher transport of pemetrexed than methotrexate by hOAT3. Furthermore, loxoprofen, ibuprofen, pravastatin, and cefazolin, transport substrates of hOAT3, inhibited pemetrexed transport by hOAT3 with IC50 values, 34.2, 27.9, 76.3 and 650 µM, respectively. CONCLUSIONS: Pemetrexed is a superior substrate to methotrexate for hOAT3. Loxoprofen, ibuprofen, and cefazolin could cause drug-drug interactions when attaining high blood concentrations.

Altered pharmacokinetics of cimetidine caused by down-regulation of renal rat organic cation transporter 2 (rOCT2) after liver ischemia-reperfusion injury.

The renal tubular secretion of cationic drugs is dominated by basolateral organic cation transporter 2 (rOCT2/SLC22A2) and luminal multidrug and toxin extrusion 1 (rMATE1/SLC47A1). Little is known about the variation in the expression of these renal transporters after liver ischemia-reperfusion (I/R) injury. Here, we examined the pharmacokinetics of a cationic drug, cimetidine, and renal rOCT2 and rMATE1 levels as well as their regulation after liver I/R. Rats were subjected to 60 min of liver ischemia followed by 12 h of reperfusion. The antioxidant Trolox was administered intravenously 5 min before reperfusion. The systemic and tubular secretory clearances of cimetidine (78% and 55%) as well as renal rOCT2 and rMATE1 levels (67% and 61%) in I/R rats were decreased compared with those in sham-operated rats, respectively. However, the renal tissue-to-plasma concentration ratio but not the renal tissue-to-urine clearance ratio of cimetidine was decreased after liver I/R. Moreover, Trolox prevented the decreases in renal rOCT2 levels and systemic clearance of cimetidine after liver I/R. These results demonstrate that liver I/R decreases the tubular secretion of cimetidine, mainly because of the decreased rOCT2 level in the kidney, and that oxidative stress should be responsible in part for decreased renal rOCT2 after liver I/R injury.

Elevated systemic elimination of cimetidine in rats with acute biliary obstruction: the role of renal organic cation transporter OCT2.

Renal tubular secretion of cationic drugs is dominated by two classes of organic cation transporters, OCT2/SLC22A2 and MATE1/SLC47A1, localized to the basolateral and brush-border membranes of the renal tubular epithelial cells, respectively. However, little is known about the expression and function of these transporters in acute cholestasis. Systemic clearance of cimetidine was significantly higher in rats with bile duct ligation (BDL) for 24 hours than in sham-operated rats, with no significant changes in the volume of distribution between the groups. In addition, net tubular secretory clearance of cimetidine was significantly higher in the BDL rats compared with the sham rats, with no significant changes in the glomerular filtration rate. Moreover, the renal tissue-to-plasma concentration ratio of cimetidine was elevated in BDL rats, although the renal tissue-to-urine clearance ratio of cimetidine was not different between the two groups. The expression level of basolateral organic cation transporter rOCT2 protein in the kidney cortex was markedly higher in BDL rats than that in the sham rats, but that of H+/organic cation antiporter rMATE1 protein in the brush-border membranes was not significantly different between the two groups. These results demonstrate that the renal tubular secretion of cimetidine was increased by acute cholestasis, and this increase was attributable to elevated expression levels of rOCT2 but not of rMATE1 in the rat.