In vitro interaction of clopidogrel and its hydrolysate with OCT1, OCT2 and OAT1

Clopidogrel (CP) is metabolized by CYPs to the active metabolite, or hydrolyzed by esterase to clopidogrel carboxylate (CPC) in liver, and CPC is partly excreted from urine. Therefore, the objective of the present study was to evaluate the interactions of CP and CPC with organic cation transporter 1 (OCT1) (in liver), and CPC with organic cation transporter 2 (OCT2) and organic anion transporter 1 (OAT1) (in kidney). Both CP and CPC inhibited the uptake of 1-methyl-4-phenylpyridinium (MPP(+)) and metformin, typical substrates of OCT1, in MDCK-hOCT1 cells with low IC₅₀ (0.307-14.0 μM). CPC (100 μM) reduced the uptake of MPP(+) and metformin mediated by OCT2 in MDCK-hOCT2 cells to 60.8% and 33.6% of the control, CPC (500 μM) decreased the uptake of 6-carboxyfluorescein (6-CFL) and para-aminohippuric acid (PAH), substrates of OAT1, in MDCK-hOAT1 cells to 64.6% and 79.4% of the control. CP and CPC were also found to inhibit other drugs of OCT1 substrates, such as lamivudine and amantadine, in MDCK-hOCT1 cells with the IC₅₀ of 1.97-4.15μM, except CPC on amantadine (IC₅₀>100 μM). The inhibition of CP and CPC on lamivudine uptake in primary rat hepatocytes was also confirmed with the IC₅₀ of 2.91 and 1.25μM, respectively. Additionally, CP and CPC were not substrates of OCT1 and OCT2, whereas CPC was a substrate of OAT1 with the Km of 5.61 μM. In conclusion, CP and CPC are strong inhibitors of OCT1, but weak inhibitors of OCT2 and OAT1, and CPC is a high affinity substrate of OAT1.