Relationship Between Insulin Secretion and Insulin Sensitivity and its Role in Development of Type 2 Diabetes Mellitus: Beyond the Disposition Index

Effects of the ABCC8 R1420H loss-of-function variant on beta-cell function, diabetes incidence, and retinopathy

INTRODUCTION

The ABCC8 gene regulates insulin secretion and plays a critical role in glucose homeostasis. The effects of an ABCC8 R1420H loss-of-function variant on beta-cell function, incidence of type 2 diabetes, and age-at-onset, prevalence, and progression of diabetes complications were assessed in a longitudinal study in American Indians.

RESEARCH DESIGN AND METHODS

We analyzed beta-cell function through the relationship between insulin secretion and insulin sensitivity in members of this population without diabetes aged ≥5 years using standard major axis regression. We used hierarchical logistic regression models to study cross-sectional associations with diabetes complications including increased albuminuria (albumin-to-creatinine ratio (ACR) ≥30 mg/g), severe albuminuria (ACR ≥300 mg/g), reduced estimated glomerular filtration rate (eGFR <60 mL/min/1.73 m2), and retinopathy. This study included 7675 individuals (254 variant carriers) previously genotyped for the R1420H with available phenotypic data and with a median follow-up time of 13.5 years (IQR 4.5-26.8).

RESULTS

Variant carriers had worse beta-cell function than non-carriers (p=0.0004; on average estimated secretion was 22% lower, in carriers), in children and adults, with no difference in insulin sensitivity (p=0.50). At any body mass index and age before 35 years, carriers had higher type 2 diabetes incidence. This variant did not associate with prevalence of increased albuminuria (OR 0.87, 95% CI 0.66 to 1.16), severe albuminuria (OR 0.96, 95% CI 0.55 to 1.68), or reduced eGFR (OR 0.44, 95% CI 0.18 to 1.06). By contrast, the variant significantly associated with higher retinopathy prevalence (OR 1.74, 95% CI 1.19 to 2.53) and this association was only partially mediated (<11%) by glycemia, duration of diabetes, risk factors of retinopathy, or insulin use. Retinopathy prevalence in carriers was higher regardless of diabetes presence.

CONCLUSIONS

The ABCC8 R1420H variant is associated with increased risks of diabetes and of retinopathy, which may be partially explained by higher glycemia levels and worse beta-cell function.

Effects of different doses of exercise and diet-induced weight loss on beta-cell function in type 2 diabetes (DOSE-EX): a randomized clinical trial

Diet-induced weight loss is associated with improved beta-cell function in people with type 2 diabetes (T2D) with remaining secretory capacity. It is unknown if adding exercise to diet-induced weight loss improves beta-cell function and if exercise volume is important for improving beta-cell function in this context. Here, we carried out a four-armed randomized trial with a total of 82 persons (35% females, mean age (s.d.) of 58.2 years (9.8)) with newly diagnosed T2D (<7 years). Participants were randomly allocated to standard care (n = 20), calorie restriction (25% energy reduction; n = 21), calorie restriction and exercise three times per week (n = 20), or calorie restriction and exercise six times per week (n = 21) for 16 weeks. The primary outcome was beta-cell function as indicated by the late-phase disposition index (insulin secretion multiplied by insulin sensitivity) at steady-state hyperglycemia during a hyperglycemic clamp. Secondary outcomes included glucose-stimulated insulin secretion and sensitivity as well as the disposition, insulin sensitivity, and secretion indices derived from a liquid mixed meal tolerance test. We show that the late-phase disposition index during the clamp increases more in all three intervention groups than in standard care (diet control group, 58%; 95% confidence interval (CI), 16 to 116; moderate exercise dose group, 105%; 95% CI, 49 to 182; high exercise dose group, 137%; 95% CI, 73 to 225) and follows a linear dose-response relationship (P > 0.001 for trend). We report three serious adverse events (two in the control group and one in the diet control group), as well as adverse events in two participants in the diet control group, and five participants each in the moderate and high exercise dose groups. Overall, adding an exercise intervention to diet-induced weight loss improves glucose-stimulated beta-cell function in people with newly diagnosed T2D in an exercise dose-dependent manner (NCT03769883).

Weight Loss, Lifestyle Intervention, and Metformin Affect Longitudinal Relationship of Insulin Secretion and Sensitivity

CONTEXT

Insulin secretion and sensitivity regulate glycemia, with inadequately compensated deficiencies leading to diabetes.

OBJECTIVE

We investigated effects of weight loss, an intensive lifestyle intervention (ILS), and metformin on the relationship between insulin secretion and sensitivity using repository data from 2931 participants in the Diabetes Prevention Program clinical trial in adults at high risk of developing type 2 diabetes.

METHODS

Insulin secretion and sensitivity were estimated from insulin and glucose concentrations in fasting and 30-minute postload serum samples at baseline and 1, 2, and 3 years after randomization, during the active intervention phase. The nonlinear relationship of secretion and sensitivity was evaluated by standardized major axis regression to account for variability in both variables. Insulin secretory demand and compensatory insulin secretion were characterized by distances along and away from the regression line, respectively.

RESULTS

ILS and metformin decreased secretory demand while increasing compensatory insulin secretion, with greater effects of ILS. Improvements were directly related to weight loss; decreased weight significantly reduced secretory demand (b=-0.144 SD; 95% CI (-0.162, -0.125)/5 kg loss) and increased compensatory insulin secretion (b = 0.287 SD, 95% CI (0.261, 0.314)/5 kg loss). In time-dependent hazard models, increasing compensatory insulin secretion (hazard ratio [HR] = 0.166 per baseline SD, 95% CI 0.133, 0.206) and weight loss (HR = 0.710 per 5 kg loss, 95% CI 0.613, 0.819) predicted lower diabetes risk.

CONCLUSION

Diabetes risk reduction was directly related to the amount of weight loss, an effect mediated by lowered insulin secretory demand (due to increased insulin sensitivity) coupled with improved compensatory insulin secretion.