Effect of TCF7L2 polymorphism on pancreatic hormones after exenatide in type 2 diabetes

BACKGROUND: Glucagon-like peptide 1 (GLP-1) stimulates insulin secretion and reduces blood glucose in type 2 diabetes mellitus (T2DM). TCF7L2 rs7903146 polymorphism has been associated with decreased insulin secretion, reduced GLP-1 action, and possible impaired peripheral insulin sensitivity. OBJECTIVES: To evaluate the postprandial pancreatic hormone response in patients with T2DM carriers of the TCF7L2 variant rs7903146 (CT/TT) compared with noncarriers of this variant (CC) after treatment with the GLP-1 agonist exenatide. METHODS: Intervention study. Patients with T2DM (n = 162) were genotyped for the TCF7L2 rs7903146 single nucleotide polymorphism (SNP). Individuals with CT/TT and CC genotypes were compared regarding basal serum levels of glucose, glycosylated hemoglobin A1C (HbA1c), HDL, uric acid, insulin, and C-peptide. A subset of 56 individuals was evaluated during a 500-calorie mixed-meal test with measurements of glucose, insulin, proinsulin, C-peptide and glucagon before and after treatment with exenatide for 8 weeks. RESULTS: Patients with genotypes CC and CT/TT presented similar glucose area under the curve (AUC) 0–180 min before treatment and a similar decrease after treatment (p < 0.001). Before exenatide, insulin levels at 30–120 min were higher in CT/TT versus CC subjects (p < 0.05). After treatment with exenatide, only CT/TT individuals demonstrated insulin reduction at 30–180 min during the meal test (p < 0.05). Patients with the CC genotype presented no differences in insulin concentrations before and after treatment. The areas under the glucagon curve between 0 and 180 min were similar before treatment and reduced after treatment in both groups (p < 0.001). CONCLUSIONS: The presence of the TCF7L2 rs7903146 T allele in patients with T2DM was associated with increased secretion of insulin response to a mixed-meal test. Furthermore, after treatment with exenatide, only the carriers of the T allele showed significantly decreased postprandial plasma insulin peak levels comparing with non carriers.