Influence of SLC22A1 gene polymorphisms on gastrointestinal adverse effects with metformin therapy in South Indian type 2 diabetes mellitus patients

Abstract

Background: Metformin, a first-line agent in Type 2 diabetes mellitus, causes gastrointestinal adverse effects in 20-30% of patients, leading to discontinuation in 5-10% of them. Organic cation transporter 1 (OCT1) encoded by SLC22A1, transports metformin from the enterocytes into the bloodstream. Reduced function OCT1 variants could lead to increased luminal concentration of metformin leading to gastrointestinal adverse effects. Two single nucleotide polymorphisms in the SLC22A1 gene were studied in this cross-sectional study with cases and controls. Objective was to determine the association between genetic polymorphisms rs628031 (1222A>G) and rs622342 (1386C>A) in SLC22A1 gene and gastrointestinal adverse effects to metformin therapy in South Indian type 2 diabetes mellitus patients. Methods: The study was conducted in JIPMER, Puducherry, India in T2DM patients (n=300) of South Indian origin, who were categorized into case (N=100) and control (N=200) groups, based on their gastrointestinal tolerance to metformin. DNA was extracted from the patients using whole blood by phenol-chloroform method and genotyping was done using real-time PCR. Results: Minor allele frequency of rs628031 (A allele) and rs622342 (C allele) were 33.8% and 26.5% respectively. Genotype frequencies did not differ significantly between the case and control groups (rs628031, p=0.45, rs622342, p=0.28). Female gender (AOR 3.77; 95% CI 2.07, 6.85; p<0.001) and proton pump inhibitor usage (AOR 7.66; 95% CI 3.01, 19.47; p<0.001) had higher association with metformin intolerance. Conclusions: No significant association was found between the genotypes of single nucleotide polymorphisms (rs628031 and rs622342) in the SLC22A1 gene and gastrointestinal adverse effects to metformin therapy in South Indian type 2 diabetes mellitus patients.