Effect of genetic variation in the organic cation transporter 1 (OCT1) on metformin action
Yan Shu, Steven A. Sheardown, Chaline Brown, Ryan P. Owen, Shuzhong Zhang, Richard A. Castro, Alexandra G. Ianculescu, Lin Yue, Joan C. Lo, Esteban G. Burchard, Claire M. Brett, Kathleen M. Giacomini
Yan Shu, Steven A. Sheardown, Chaline Brown, Ryan P. Owen, Shuzhong Zhang, Richard A. Castro, Alexandra G. Ianculescu, Lin Yue, Joan C. Lo, Esteban G. Burchard, Claire M. Brett, Kathleen M. Giacomini
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Research Article

Effect of genetic variation in the organic cation transporter 1 (OCT1) on metformin action

Abstract

Metformin is among the most widely prescribed drugs for the treatment of type 2 diabetes. Organic cation transporter 1 (OCT1) plays a role in the hepatic uptake of metformin, but its role in the therapeutic effects of the drug, which involve activation of AMP-activated protein kinase (AMPK), is unknown. Recent studies have shown that human OCT1 is highly polymorphic. We investigated whether OCT1 plays a role in the action of metformin and whether individuals with OCT1 polymorphisms have reduced response to the drug. In mouse hepatocytes, deletion of Oct1 resulted in a reduction in the effects of metformin on AMPK phosphorylation and gluconeogenesis. In Oct1-deficient mice the glucose-lowering effects of metformin were completely abolished. Seven nonsynonymous polymorphisms of OCT1 that exhibited reduced uptake of metformin were identified. Notably, OCT1-420del (allele frequency of about 20% in white Americans), previously shown to have normal activity for model substrates, had reduced activity for metformin. In clinical studies, the effects of metformin in glucose tolerance tests were significantly lower in individuals carrying reduced function polymorphisms of OCT1. Collectively, the data indicate that OCT1 is important for metformin therapeutic action and that genetic variation in OCT1 may contribute to variation in response to the drug.

Authors

Yan Shu, Steven A. Sheardown, Chaline Brown, Ryan P. Owen, Shuzhong Zhang, Richard A. Castro, Alexandra G. Ianculescu, Lin Yue, Joan C. Lo, Esteban G. Burchard, Claire M. Brett, Kathleen M. Giacomini

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Figure 4

Oct1 deletion results in reduced metformin uptake and response in primary hepatocytes from mice.

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Oct1 deletion results in reduced metformin uptake and response in primar...
(A) Metformin uptake was lower in the primary hepatocytes isolated from Oct1-knockout (Oct1–/–) mice than in those with a normal Oct1 allele (Oct1+/+ and Oct1+/–). The uptake of metformin (250 μM) was performed for 10 minutes in the presence or absence of 100 μM quinidine, where indicated. *P < 0.01 versus Oct1+/– without quinidine (ANOVA and Dunnett’s procedure). (B) Metformin resulted in less phosphorylation of AMPK and ACC in Oct1–/– hepatocytes than in Oct1+/+ hepatocytes. The cellular extracts from primary hepatocytes treated with or without metformin (250 μM) for 4.5 hours were detected with polyclonal antibodies against phospho-ACC (Ser 79), phospho-AMPKα (Thr172), AMPKα, and β-actin. (C) Treatment with the OCT inhibitor quinidine reduced the stimulation of AMPK phosphorylation and thus ACC phosphorylation by metformin in Oct1+/+ hepatocytes. Where indicated, 100 μM quinidine was added 30 minutes before metformin (250 μM) treatment (Met + quin). (D) Metformin suppressed glucagon-stimulated glucose production in Oct1+/+ hepatocytes, with no effect in Oct1–/– hepatocytes. Metformin (1 mM) was added 2 hours before glucose measurement. The primary hepatocytes were isolated and cultured as described in Methods. **P < 0.001 versus no treatment (2-tailed Student’s test).