Youth type 2 diabetes: insulin resistance, beta-cell failure, or both?

Abstract

Objective: This study evaluates insulin sensitivity, pancreatic beta-cell function (BCF), and the balance between the two in youth with type 2 diabetes and assesses the relationship of diabetes duration and HbA(1c) to insulin sensitivity and BCF.

Research design and methods: The subjects were 14 adolescents with type 2 diabetes and 20 obese control subjects of comparable age, BMI, body composition, and puberty. Insulin sensitivity was evaluated with a 3-h hyperinsulinemic (80 mU . m(-2) . min(-1)) euglycemic clamp. First-phase insulin secretion (FPIS) and second-phase insulin secretion (SPIS) were evaluated with a 2-h hyperglycemic (12.5 mmol/l) clamp. Fasting glucose rate of appearance was determined with the use of [6,6-(2)H(2)]glucose.

Results: Fasting glucose rate of appearance was higher in type 2 diabetic patients than in obese control subjects (16.5 +/- 1.1 vs. 12.3 +/- 0.5 micromol . kg(-1) . min(-1); P = 0.002). Insulin sensitivity was lower in type 2 diabetic patients than in obese control subjects (1.0 +/- 0.1 vs. 2.0 +/- 0.2 micromol . kg(-1) . min(-1) per pmol/l; P = 0.001). Fasting insulin was higher in type 2 diabetic patients than in obese control subjects (289.8 +/- 24.6 vs. 220.2 +/- 18.0 pmol/l; P = 0.007), and FPIS and SPIS were lower (FPIS: 357.6 +/- 42.0 vs. 1,365.0 +/- 111.0 pmol/l; SPIS: 652.2 +/- 88.8 vs. 1,376.4 +/- 88.8 pmol/l; P < 0.001 for both). The glucose disposition index (GDI = insulin sensitivity x FPIS) was approximately 86% lower in type 2 diabetic patients than in obese control subjects. HbA(1c) correlated with FPIS (r = -0.61, P = 0.025) with no relationship to insulin sensitivity.

Conclusions: Despite the impairment in both insulin sensitivity and BCF in youth with type 2 diabetes, the magnitude of the derangement is greater in BCF than insulin sensitivity when compared with that in obese control subjects. The inverse relationship between BCF and HbA(1c) may either reflect the impact of deteriorating BCF on glycemic control or be a manifestation of a glucotoxic phenomenon on BCF. Future studies in youth type 2 diabetes should target the natural course of beta-cell failure and means of retarding and/or preventing it.

Figure 1

Insulin-stimulated total, oxidative, and nonoxidative glucose disposal (A) and insulin sensitivity (B) during a 3-h hyperinsulinemic (80 mU · m⁻² · min⁻¹)-euglycemic clamp in adolescents with type 2 diabetes (T2DM) versus obese control subjects. C: GDI in adolescents with type 2 diabetes and obese control subjects.

Figure 2

Insulin levels during the hyperglycemic clamp (A), mean of fasting, first-phase, and second-phase insulin levels (B), and mean of fasting, first-phase, and second-phase C-peptide levels (C) during the hyperglycemic (12.5 mmol/l) clamp in type 2 diabetes (T2DM) patients versus obese control (OBC) subjects.