Organic cation transporter 1 variants and gastrointestinal side effects of metformin in patients with Type 2 diabetes.

AIMS: Metformin is the most widely used oral anti-diabetes agent and has considerable benefits over other therapies, yet 20-30% of people develop gastrointestinal side effects, and 5% are unable to tolerate metformin due to the severity of these side effects. The mechanism for gastrointestinal side effects and their considerable inter-individual variability is unclear. We have recently shown the association between organic cation transporter 1 (OCT1) variants and severe intolerance to metformin in people with Type 2 diabetes. The aim of this study was to explore the association of OCT1 reduced-function polymorphisms with common metformin-induced gastrointestinal side effects in Type 2 diabetes. METHODS: This prospective observational cohort study included 92 patients with newly diagnosed Type 2 diabetes, incident users of metformin. Patients were genotyped for two common loss-of-function variants in the OCT1 gene (SLC22A1): R61C (rs12208357) and M420del (rs72552763). The association of OCT1 reduced-function alleles with gastrointestinal side effects was analysed using logistic regression. RESULTS: Forty-three patients (47%) experienced gastrointestinal adverse effects in the first 6 months of metformin treatment. Interestingly, the number of OCT1 reduced-function alleles was significantly associated with over two-fold higher odds of the common metformin-induced gastrointestinal side effects (odds ratio = 2.31, 95% confidence interval 1.07-5.01, P = 0.034). CONCLUSIONS: In conclusion, we showed for the first time the association between OCT1 variants and common metformin-induced gastrointestinal side effects. These results confirm recent findings related to the role of OCT1 in severe metformin intolerance, and suggest that high inter-individual variability in mild/moderate and severe gastrointestinal intolerance share a common underlying mechanism. These data could contribute to more personalized and safer metformin treatment.

Effects of melatonin receptor 1B gene variation on glucose control in population from Bosnia and Herzegovina.

Common variants in MTNR1B, encoding melatonin receptor 1B, have been recently associated with impaired glucose homeostasis and an increased risk for developing Type 2 diabetes (T2D). In this study we investigated the association of MTNR1B variant rs10830963 with T2D and related quantitative traits in a population from Bosnia and Herzegovina (BH). A total number of 268 subjects were recruited in the study (162 T2D patients and 106 nondiabetic controls). Subjects were genotyped for MTNR1B rs10830963 SNP by using hydrolysis probes. Our data showed that the prevalence of the MTNR1B rs10830963 risk G-allele in BH population was 26%. Furthermore, we demonstrated a significant association of MTNR1B rs10830963 variant with fasting plasma glucose (FPG) levels in nondiabetic subjects. Under the additive genetic model, each variant G-allele was associated with an increased FPG levels of 0.29 mmol/L (95% CI 0.12, 0.46, p = 0.001). Strikingly, our results also showed a significant association of this MTNR1B polymorphism with increased glycated hemoglobin (HbA1c) levels in nondiabetic subjects (p = 0.040, additive genetic model). An association of the MTNR1B variant rs10830963 with T2D risk was not detected in our cohort. In conclusion, here we have demonstrated the association between the common MTNR1B rs10830963 variation and fasting plasma glucose levels in BH population. Furthermore, the influence of this polymorphism on the HbA1c levels was also shown in this study, further strengthening its role in blood glucose control.