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Context: Loss of the incretin effect (IE) in type 2 diabetes (T2D) contributes to hyperglycemia and the mechanisms underlying this impairment are unclear. Objective: To quantify the IE impairment in T2D and to investigate the factors associated with it using a meta-analytic approach. Methods: PubMed, Scopus, and Web-of-Science were searched. Studies measuring IE by the gold-standard protocol employing an oral glucose tolerance test (OGTT) and an intravenous glucose infusion at matched glucose levels were selected. We extracted IE, sex, age, body mass index (BMI), and hemoglobin A1c, fasting values, and area under curve (AUC) of glucose, insulin, C-peptide, glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide 1 (GLP-1). In subjects with T2D, we also recorded T2D duration, age at diagnosis, and the percentage of subjects taking antidiabetic medications. Results: The IE weighted mean difference between subjects with T2D and those with normal glucose tolerance (NGT) was -27.3% (CI -36.5% to -18.1%; P < .001; I2 = 86.6%) and was affected by age (P < .005). By meta-regression of combined NGT and T2D data, IE was inversely associated with glucose tolerance (lower IE in T2D), BMI, and fasting GIP (P < .05). By meta-regression of T2D studies only, IE was associated with the OGTT glucose dose (P < .0001). IE from insulin was larger than IE from C-peptide (weighted mean difference 11.2%, CI 9.2-13.2%; P < .0001; I2 = 28.1%); the IE difference was inversely associated with glucose tolerance and fasting glucose. Conclusion: The IE impairment in T2D vs NGT is consistent though considerably variable, age being a possible factor affecting the IE difference. Glucose tolerance, BMI, and fasting GIP are independently associated with IE; in subjects with T2D only, the OGTT dose is a significant covariate. [ABSTRACT FROM AUTHOR]

Aims/hypothesis: Studies in permanent neonatal diabetes suggest that sulphonylureas lower blood glucose without causing hypoglycemia, in part by augmenting the incretin effect. This mechanism has not previously been attributed to sulphonylureas in patients with type 2 diabetes (T2DM). We therefore aimed to evaluate the impact of low-dose gliclazide on beta-cell function and incretin action in patients with T2DM.Methods: Paired oral glucose tolerance tests and isoglycemic infusions were performed to evaluate the difference in the classical incretin effect in the presence and absence of low-dose gliclazide in 16 subjects with T2DM (hemoglobin A1c < 64 mmol/mol, 8.0%) treated with diet or metformin monotherapy. Beta-cell function modeling was undertaken to describe the relationship between insulin secretion and glucose concentration.Results: A single dose of 20 mg gliclazide reduced mean glucose during the oral glucose tolerance test from 12.01 ± 0.56 to 10.82 ± 0.5mmol/l [P = 0.0006; mean ± standard error of the mean (SEM)]. The classical incretin effect was augmented by 20 mg gliclazide, from 35.5% (lower quartile 27.3, upper quartile 61.2) to 54.99% (34.8, 72.8; P = 0.049). Gliclazide increased beta-cell glucose sensitivity by 46% [control 22.61 ± 3.94, gliclazide 33.11 ± 7.83 (P = 0.01)] as well as late-phase incretin potentiation [control 0.92 ± 0.05, gliclazide 1.285 ± 0.14 (P = 0.038)].Conclusions/interpretation: Low-dose gliclazide reduces plasma glucose in response to oral glucose load, with concomitant augmentation of the classical incretin effect. Beta-cell modeling shows that low plasma concentrations of gliclazide potentiate late-phase insulin secretion and increase glucose sensitivity by 50%. Further studies are merited to explore whether low-dose gliclazide, by enhancing incretin action, could effectively lower blood glucose without risk of hypoglycemia. [ABSTRACT FROM AUTHOR]

Context: Elevated heart rate has been associated with insulin resistance and incident type 2 diabetes but its relationship with β-cell function is not known. Our aim was to investigate whether baseline heart rate is associated with β-cell function and hyperglycaemia. Methods: We used the prospective RISC cohort with 1005 non-diabetic individuals who had an oral glucose tolerance test (OGTT) at baseline and after 3 years. Impaired glucose regulation was defined as a fasting plasma glucose ≥6.1 mmol/l or a 2-h plasma glucose ≥7.8 mmol/l. Insulin sensitivity was assessed by the OGIS index and insulin secretion and β-cell glucose sensitivity at both baseline and 3 years. Results: Baseline heart rate was positively related to both fasting (P<0.0001) and 2 h glucose levels (P=0.02) at year 3 and predicted the presence of impaired glucose regulation at year 3 in a logistic regression model adjusting for insulin sensitivity at inclusion (OR/10 beats per min: 1.31; 95% CI (1.07-1.61); P=0.01). Baseline heart rate was associated with lower insulin sensitivity (β= -0.11; P<.0001), a decrease in both β-cell glucose sensitivity (β= -0.11; P=0.003) and basal insulin secretion rate (β= -0.11; P=0.002) at 3 years in an adjusted multivariable regression model. Baseline heart rate predicted the 3-year decrease in β-cell glucose sensitivity (β= -0.10; P=0.007) and basal insulin secretion (β= -0.12; P=0.007). Conclusions: Heart rate predicts β-cell function and impaired glucose regulation at 3 years in non-diabetic individuals, independently of the level of insulin sensitivity. These findings suggest a possible effect of the sympathetic nervous system on β-cell dysfunction, which deserves further investigation. [ABSTRACT FROM AUTHOR]

Objective: Anti-inflammatory glucocorticoid (GC) therapy often induces hyperglycemia due to insulin resistance and islet-cell dysfunction. Incretin-based therapies may preserve glucose tolerance and pancreatic islet-cell function. In this study, we hypothesized that concomitant administration of the dipeptidyl peptidase-4 inhibitor sitagliptin and prednisolone in men at high risk to develop type 2 diabetes could protect against the GC-induced diabetogenic effects. Design and methods: Men with the metabolic syndrome but without diabetes received prednisolone 30 mg once daily plus sitagliptin 100 mg once daily (n=14), prednisolone (n=12) or sitagliptin alone (n=14) or placebo (n=12) for 14 days in a double-blind 2×2 randomized-controlled study. Glucose, insulin, C-peptide, and glucagon were measured in the fasted state and following a standardized mixed-meal test. β-cell function parameters were assessed both from a hyperglycemic-arginine clamp procedure and from the meal test. Insulin sensitivity (M-value) was measured by euglycemic clamp. Results: Prednisolone increased postprandial area under the curve (AUC)-glucose by 17% (P<0.001 vs placebo) and postprandial AUC-glucagon by 50% (P<0.001). Prednisolone reduced 1st and 2nd phase glucose-stimulated-and combined hyperglycemia-arginine-stimulated C-peptide secretion (all P≤0.001). When sitagliptin was added, both clamp-measured β-cell function (P=NS for 1st and 2nd phase vs placebo) and postprandial hyperglucagonemia (P=NS vs placebo) remained unaffected. However, administration of sitagliptin could not prevent prednisolone-induced increment in postprandial glucose concentrations (P<0.001 vs placebo). M-value was not altered by any treatment. Conclusion: Fourteen-day treatment with high-dose prednisolone impaired postprandial glucose metabolism in subjects with the metabolic syndrome. Concomitant treatment with sitagliptin improved various aspects of pancreatic islet-cell function, but did not prevent deterioration of glucose tolerance by GC treatment. [ABSTRACT FROM AUTHOR]