Genetic Polymorphisms in Organic Cation Transporter 1 (OCT1) in Chinese and Japanese Populations Exhibit Altered Function

Abstract

Organic cation transporter 1 (OCT1; SLC22A1) seems to play a role in the efficacy and disposition of the widely used antidiabetic drug metformin. Genetic variants in OCT1 have been identified largely in European populations. Metformin is increasingly being used in Asian populations where the incidence of type 2 diabetes (T2D) is on the rise. The goal of this study is to identify genetic variants of OCT1 in Chinese and Japanese populations, which may potentially modulate response to metformin. We used recent data from the 1000 Genomes Project (Chinese and Japanese) and direct sequencing of selected amplicons of OCT1 in 66 DNA samples from Japanese patients with T2D. A total of six nonsynonymous variants were identified. Three of them (Q97K, P117L, and R206C) had not been functionally characterized previously and had allele frequencies of 0.017, 0.023 and 0.008, respectively. The uptake of metformin in cells expressing Q97K, P117L, and R206C was significantly reduced relative to the OCT1 reference (62 Ϯ 4.3, 55 Ϯ 6.8, and 22 Ϯ 1.5% for Q97K, P117L, and R206C, respectively). Kinetic studies indicated that P117L and R206C exhibited a reduced V max , whereas Q97K showed an increased K m . The green fluorescent protein (GFP)-tagged Q97K and P117L variants localized to the plasma membrane, whereas the GFP-tagged R206C was retained mainly in the endoplasmic reticulum. Replacement of the highly conserved R206 with different amino acids modulated the subcellular localization and function of the transporter. This study suggests that nonsynonymous variants of OCT1 in Chinese and Japanese populations may affect the differential response to metformin.

Influences of Organic Cation Transporter Polymorphisms on the Population Pharmacokinetics of Metformin in Healthy Subjects

“…The other allele frequencies were 0%. These were comparable to previously observed results (6,8,9,21,(27)(28)(29)(30)(31)(32)(33)(34). The observed frequencies were in Hardy-Weinberg equilibrium.…”

“…Shu et al (43) previously demonstrated that OCT1-1022C>T variants are not related to decreased metformin uptake in HEK-293 cells and our in vivo study showed similar results. Chen et al (6) reported that the uptake of metformin in cells expressing OCT1-289C>A, -350C>T, and -616C>T was significantly reduced relative to the OCT1 wild types. However, in the current study, the genetic polymorphisms of OCT1-289C>T, -350C>T, -616C>T display no significant impact on the pharmacokinetics of metformin because there was no subject carrying the variant in the Korean population (Table I).…”

“…However, those variants are quite rare in the Korean population (14). Recently, Chen et al (6) reported that genetic variants of OCT1 (289C>A, 350C>T, and 616C>T) also have reduced function in vitro. Song et al (12) found that the variants of OCT2 (596C>T, 602C>T, and 808 G>T) resulted in markedly higher values for area under the serum concentration-time curve (AUC), peak concentration (C max ) values, but lower volume of distribution (V d /F), apparent oral clearance (CL/F) values, compared to the wild types in the 26 Korean volunteer subjects.…”

“…07MK003B, Boehringer Ingelheim Korea Ltd, Seoul, Korea). Blood samples were collected in Vacutainer® tubes before dosing and at 0.5, 1, 1.5, 2, 2.5, 3,4,6,8,10,12, and 24 h after drug administration. After centrifugation (3,000×g, 20 min, 4°C), serum samples were transferred to polyethylene tubes and immediately stored at −70°C until analysis.…”

“…Organic cation transporters (OCTs) of the solute carrier (SLC) family 22 and multidrug and toxin extrusion (MATE) transporters of the SLC47 family have been identified as uptake and efflux transporters of metformin, respectively (6)(7)(8)(9)(10). Previous studies have shown that genetic polymorphisms in OCTs are associated with variations in the pharmacokinetics (PKs)/pharmacodynamics profiles of metformin (7,(11)(12)(13).…”