β-Cell dysfunction is a core defect in T2DM, and chronic, sustained hyperglycemia has been implicated in progressive β-cell failure, ie, glucotoxicity. The aim of the present study was to examine the effect of lowering the plasma glucose concentration with dapagliflozin, a glucosuric agent, on β-cell function in T2DM individuals.

Twenty-four subjects with T2DM received dapagliflozin (n = 16) or placebo (n = 8) for 2 weeks, and a 75-g oral glucose tolerance test (OGTT) and insulin clamp were performed before and after treatment. Plasma glucose, insulin, and C-peptide concentrations were measured during the OGTT.

Dapagliflozin significantly lowered both the fasting and 2-hour plasma glucose concentrations and the incremental area under the plasma glucose concentration curve (ΔG_0–120) during OGTT by −33 ± 5 mg/dL, −73 ± 9 mg/dL, and −60 ± 12 mg/dL · min, respectively, compared to −13 ± 9, −33 ± 13, and −18 ± 9 reductions in placebo-treated subjects (both P < .01). The incremental area under the plasma C-peptide concentration curve tended to increase in dapagliflozin-treated subjects, whereas it did not change in placebo-treated subjects. Thus, ΔC-Pep_0–120/ΔG_0–120 increased significantly in dapagliflozin-treated subjects, whereas it did not change in placebo-treated subjects (0.019 ± 0.005 vs 0.002 ± 0.006; P < .01). Dapagliflozin significantly improved whole-body insulin sensitivity (insulin clamp). Thus, β-cell function, measured as ΔC-Pep_0–120/ ΔG_0–120 ÷ insulin resistance, increased by 2-fold (P < .01) in dapagliflozin-treated vs placebo-treated subjects.

Lowering the plasma glucose concentration with dapagliflozin markedly improves β-cell function, providing strong support in man for the glucotoxic effect of hyperglycemia on β-cell function.