Adding insulin glargine vs. NPH insulin to metformin results in a more efficient postprandial β-cell protection in individuals with type 2 diabetes

AIM: Postprandial release of intact proinsulin (IP) is an independent marker for β-cell dysfunction in patients with type 2 diabetes. This open-label, parallel-group, two-arm, pilot study compared the β-cell protective effect of adding insulin glargine (GLA) vs. NPH insulin to ongoing metformin. MATERIAL AND METHODS: Overall, 28 insulin-naive type 2 diabetes subjects (mean ± SD age, 61.5 ± 6.7 years; diabetes duration, 9.8 ± 6.5 years; HbA1c, 7.1 ± 0.5%; BMI, 30.7 ± 4.3 kg/m(2)) treated with metformin and sulfonylurea were randomized to add once-daily GLA or NPH at bedtime. At baseline and after 3 months, subjects received a standardized breakfast, lunch and dinner, with pre- and postprandial blood sampling to measure plasma IP, total insulin and blood glucose (BG). RESULTS: Insulin dose after 3 months was comparable in both groups (GLA vs. NPH: 23.6 ± 13.4 vs. 23.3 ± 12.7; p = NS ). Both treatments significantly reduced fasting BG levels (GLA: 158 ± 19 to 121 ± 23 mg/dl; NPH: 156 ± 34 to 119 ± 29 mg/dl; both p < 0.01 vs. baseline). Fasting and postprandial BG levels did not differ between groups. IP levels decreased in both groups (p < 0.05 at all timepoints). Although IP release after breakfast did not differ between treatments, GLA induced a greater reduction in IP release after lunch (p = 0.08) and dinner (p = 0.04). Total plasma insulin levels did not differ between groups. CONCLUSIONS: Adding basal insulin to metformin reduces postprandial β-cell load. While GLA and NPH had comparable effects at breakfast, GLA reduces β-cell stress more effectively at dinner, and with a trend at lunch, most probably because of its longer lasting pharmacodynamic profile.