Genetic variants of organic cation transporter 2 (OCT2) significantly reduce metformin uptake in oocytes.
1. The authors sought to evaluate the contribution of organic cation transporters (OCTs) to the renal tubular transport of metformin using LLC-PK1 cells as an in vitro model for the renal proximal tubule, and to investigate the effects of three non-synonymous genetic variants of OCT2 on the transport activity of metformin in vitro using an oocyte over-expression system. 2. The basolateral-to-apical transport of metformin was significantly greater than the apical-to-basolateral transport and showed concentration dependency with the kinetic parameters: maximum transport rate (V(max)), 922 pmol min(-1) per 5 x 10(5) cells; Michaelis-Menten constant (K(m)), 393 microM; intrinsic clearance (CL(int)), 2.35 microl min(-1) per 5 x 10(5) cells; and diffusion constant (K(d)), 0.33 microl min(-1) per 5 x 10(5) cells. The basolateral-to-apical transport of metformin was inhibited by phenoxybenzamine, an inhibitor of OCTs, but not by cyclosporine A, MK571, or fumitremorgin C, which are inhibitors of P-glycoprotein, multidrug resistance proteins (MRPs), and breast cancer resistance protein (BCRP), respectively, suggesting that OCTs play a role in renal tubular secretion of metformin. 3. Metformin uptake was much greater in oocytes expressing OCT2-wild type (OCT2-WT) than OCT1-WT compared with uptake in water-injected oocytes. Uptake was significantly decreased in oocytes expressing OCT2-T199I, -T201M, and -A270S compared with that in OCT2-WT, suggesting that metformin is a better substrate for OCT2 than for OCT1 and that the amino acid-substituted variants of OCT2 cause a functional decrease in metformin uptake. 4. In conclusion, the genetic variants of OCT2 (OCT2-T199I, -T201M, and -A270S) decreased the transport activity of metformin and thus may contribute to the inter-individual variation in metformin disposition as OCT2 plays a pivotal role in renal excretion, the major disposition route of metformin.
Song
I S
IS
Department of Pharmacology and Pharmacogenomics, Research Center, Inje University College of Medicine, Busan, Korea. issong@inje.ac.kr
Shin
H J
HJ
Shin
J G
JG
D019943:Amino Acid Substitution; D000818:Animals; D002460:Cell Line; D015870:Gene Expression; D007004:Hypoglycemic Agents / Q000378:metabolism*; D007684:Kidney Tubules / Q000378:metabolism; D008687:Metformin / Q000378:metabolism*; D009865:Oocytes; D027701:Organic Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D000075102:Organic Cation Transporter 2; D013552:Swine; D014981:Xenopus
D007004:Hypoglycemic Agents; D027701:Organic Cation Transport Proteins; D000075102:Organic Cation Transporter 2; C491013:SLC22A2 protein, human; D008687:Metformin