Aurora Merovci

Dapagliflozin improves muscle insulin sensitivity but enhances endogenous glucose production.

Chronic hyperglycemia impairs insulin action, resulting in glucotoxicity, which can be ameliorated in animal models by inducing glucosuria with renal glucose transport inhibitors. Here, we examined whether reduction of plasma glucose with a sodium-glucose cotransporter 2 (SGLT2) inhibitor could improve insulin-mediated tissue glucose disposal in patients with type 2 diabetes. Eighteen diabetic men were randomized to receive either dapagliflozin (n = 12) or placebo (n = 6) for 2 weeks. We measured insulin-mediated whole body glucose uptake and endogenous glucose production (EGP) at baseline and 2 weeks after treatment using the euglycemic hyperinsulinemic clamp technique. Dapagliflozin treatment induced glucosuria and markedly lowered fasting plasma glucose. Insulin-mediated tissue glucose disposal increased by approximately 18% after 2 weeks of dapagliflozin treatment, while placebo-treated subjects had no change in insulin sensitivity. Surprisingly, following dapagliflozin treatment, EGP increased substantially and was accompanied by an increase in fasting plasma glucagon concentration. Together, our data indicate that reduction of plasma glucose with an agent that works specifically on the kidney to induce glucosuria improves muscle insulin sensitivity. However, glucosuria induction following SGLT2 inhibition is associated with a paradoxical increase in EGP. These results provide support for the glucotoxicity hypothesis, which suggests that chronic hyperglycemia impairs insulin action in individuals with type 2 diabetes.

Dapagliflozin Lowers Plasma Glucose Concentration and Improves β-Cell Function

BACKGROUND 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. RESEARCH DESIGN AND METHODS 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. RESULTS Dapagliflozin significantly lowered both the fasting and 2-hour plasma glucose concentrations and the incremental area under the plasma glucose concentration curve (ΔG0-120) 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-Pep0-120/ΔG0-120 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-Pep0-120/ ΔG0-120 ÷ insulin resistance, increased by 2-fold (P < .01) in dapagliflozin-treated vs placebo-treated subjects. CONCLUSION 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.

Chronic reduction of plasma free fatty acid improves mitochondrial function and whole-body insulin sensitivity in obese and type 2 diabetic individuals.

Insulin resistance and dysregulation of free fatty acid (FFA) metabolism are core defects in type 2 diabetic (T2DM) and obese normal glucose tolerant (NGT) individuals. Impaired muscle mitochondrial function (reduced ATP synthesis) also has been described in insulin-resistant T2DM and obese subjects. We examined whether reduction in plasma FFA concentration with acipimox improved ATP synthesis rate and altered reactive oxygen species (ROS) production. Eleven NGT obese and 11 T2DM subjects received 1) OGTT, 2) euglycemic insulin clamp with muscle biopsy, and 3) 1H-magnetic resonance spectroscopy of tibialis anterior muscle before and after acipimox (250 mg every 6 h for 12 days). ATP synthesis rate and ROS generation were measured in mitochondria isolated from muscle tissue ex vivo with chemoluminescence and fluorescence techniques, respectively. Acipimox 1) markedly reduced the fasting plasma FFA concentration and enhanced suppression of plasma FFA during oral glucose tolerance tests and insulin clamp in obese NGT and T2DM subjects and 2) enhanced insulin-mediated muscle glucose disposal and suppression of hepatic glucose production. The improvement in insulin sensitivity was closely correlated with the decrease in plasma FFA in obese NGT (r = 0.81) and T2DM (r = 0.76) subjects (both P < 0.001). Mitochondrial ATP synthesis rate increased by >50% in both obese NGT and T2DM subjects and was strongly correlated with the decrease in plasma FFA and increase in insulin-mediated glucose disposal (both r > 0.70, P < 0.001). Production of ROS did not change after acipimox. Reduction in plasma FFA in obese NGT and T2DM individuals improves mitochondrial ATP synthesis rate, indicating that the mitochondrial defect in insulin-resistant individuals is, at least in part, reversible.

Dapagliflozin Enhances Fat Oxidation and Ketone Production in Patients With Type 2 Diabetes

OBJECTIVE Insulin resistance is associated with mitochondrial dysfunction and decreased ATP synthesis. Treatment of individuals with type 2 diabetes mellitus (T2DM) with sodium–glucose transporter 2 inhibitors (SGLT2i) improves insulin sensitivity. However, recent reports have demonstrated development of ketoacidosis in subjects with T2DM treated with SGLT2i. The current study examined the effect of improved insulin sensitivity with dapagliflozin on 1) mitochondrial ATP synthesis and 2) substrate oxidation rates and ketone production. RESEARCH DESIGN AND METHODS The study randomized 18 individuals with T2DM to dapagliflozin (n = 9) or placebo (n = 9). Before and after 2 weeks, subjects received an insulin clamp with tritiated glucose, indirect calorimetry, and muscle biopsies. RESULTS Dapagliflozin reduced fasting plasma glucose (167 ± 13 to 128 ± 6 mg/dL) and increased insulin-stimulated glucose disposal by 36% (P < 0.01). Glucose oxidation decreased (1.06 to 0.80 mg/kg ⋅ min, P < 0.05), whereas nonoxidative glucose disposal (glycogen synthesis) increased (2.74 to 4.74 mg/kg ⋅ min, P = 0.03). Dapagliflozin decreased basal glucose oxidation and increased lipid oxidation and plasma ketone concentration (0.05 to 0.19 mmol/L, P < 0.01) in association with an increase in fasting plasma glucagon (77 ± 8 to 94 ± 13, P < 0.01). Dapagliflozin reduced the ATP synthesis rate, which correlated with an increase in plasma ketone concentration. CONCLUSIONS Dapagliflozin improved insulin sensitivity and caused a shift from glucose to lipid oxidation, which, together with an increase in glucagon-to-insulin ratio, provide the metabolic basis for increased ketone production.

Effect of Dapagliflozin With and Without Acipimox on Insulin Sensitivity and Insulin Secretion in T2DM Males

AIM To investigate the effect of lowering the plasma glucose and free fatty acid (FFA) concentrations with dapagliflozin and acipimox, respectively, on insulin sensitivity and insulin secretion in T2DM individuals. METHODS Fourteen male T2DM patients received an oral glucose tolerance test and euglycemic hyperinsulinemic clamp at baseline and were treated for 3 weeks with dapagliflozin (10 mg per day). During week 3, acipimox (250 mg four times per day) treatment was added to dapagliflozin. The oral glucose tolerance test and insulin clamp were repeated at the end of weeks 2 and 3. RESULTS Dapagliflozin caused glucosuria and significantly lowered the plasma glucose concentration (by 35 mg/dL; P < .01), whereas the fasting plasma FFA concentration was unaffected. Acipimox caused a further decrease in the fasting plasma glucose concentration (by 20 mg/dL; P < .01) and a significant decrease in the fasting plasma FFA concentration. Compared to baseline, insulin-mediated glucose disposal increased significantly at week 2 (from 4.48 ± 0.50 to 5.30 ± 0.50 mg/kg · min; P < .05). However, insulin-mediated glucose disposal at week 3 (after the addition of acipimox) did not differ significantly from that at week 2. Glucose-stimulated insulin secretion at week 2 increased significantly compared to baseline, and it increased further and significantly at week 3 compared to week 2. CONCLUSION Lowering the plasma glucose concentration with dapagliflozin improves both insulin sensitivity and β-cell function, whereas lowering plasma FFA concentration by addition of acipimox to dapagliflozin improves β-cell function without significantly affecting insulin sensitivity.

Pioglitazone Improves Left Ventricular Diastolic Function in Subjects With Diabetes

OBJECTIVE To examine the effect of pioglitazone on myocardial insulin sensitivity and left ventricular (LV) function in patients with type 2 diabetes (T2D). RESEARCH DESIGN AND METHODS Twelve subjects with T2D and 12 with normal glucose tolerance received a euglycemic insulin clamp. Myocardial glucose uptake (MGU) and myocardial perfusion were measured with [18F]fluoro-2-deoxy-d-glucose and [15O]H2O positron emission tomography before and after 24 weeks of pioglitazone treatment. Myocardial function and transmitral early diastolic relation/atrial contraction (E/A) flow ratio were measured with magnetic resonance imaging. RESULTS Pioglitazone reduced HbA1c by 0.9%; decreased systolic and diastolic blood pressure by 7 ± 2 and 7 ± 2 mmHg, respectively (P < 0.05); and increased whole-body insulin-stimulated glucose uptake by 71% (3.4 ± 1.3 to 5.8 ± 2.1 mg/kg · min; P < 0.01) in subjects with T2D. Pioglitazone enhanced MGU by 75% (0.24 ± 0.14 to 0.42 ± 0.13 μmol/min · g; P < 0.01) and myocardial perfusion by 16% (0.95 ± 0.16 to 1.10 ± 0.25 mL/min · g; P < 0.05). Measures of diastolic function, E/A ratio (1.04 ± 0.3 to 1.25 ± 0.4) and peak LV filling rate (349 ± 107 to 433 ± 99 mL/min), both increased (P < 0.01). End-systolic volume, end-diastolic volume, peak LV ejection rate, and cardiac output trended to increase (P not significant), whereas the ejection fraction (61 ± 6 to 66 ± 7%) and stroke volume increased significantly (71 ± 20 to 80 ± 20 L/min; both P < 0.05). CONCLUSIONS Pioglitazone improves whole-body and myocardial insulin sensitivity, LV diastolic function, and systolic function in T2D. Improved myocardial insulin sensitivity and diastolic function are strongly correlated.

Effect of Chronic Hyperglycemia on Glucose Metabolism in Subjects with Normal Glucose Tolerance

Chronic hyperglycemia causes insulin resistance, but the inheritability of glucotoxicity and the underlying mechanisms are unclear. We examined the effect of 3 days of hyperglycemia on glucose disposal, enzyme activities, insulin signaling, and protein O-GlcNAcylation in skeletal muscle of individuals without (FH−) or with (FH+) family history of type 2 diabetes. Twenty-five subjects with normal glucose tolerance received a [3-3H]glucose euglycemic insulin clamp, indirect calorimetry, and vastus-lateralis biopsies before and after 3 days of saline (n = 5) or glucose (n = 10 FH− and 10 FH+) infusion to raise plasma glucose by ∼45 mg/dL. At baseline, FH+ had lower insulin-stimulated glucose oxidation and total glucose disposal (TGD) but similar nonoxidative glucose disposal and basal endogenous glucose production (bEGP) compared with FH−. After 3 days of glucose infusion, bEGP and glucose oxidation were markedly increased, whereas nonoxidative glucose disposal and TGD were lower versus baseline, with no differences between FH− and FH+ subjects. Hyperglycemia doubled skeletal muscle glycogen content and impaired activation of glycogen synthase (GS), pyruvate dehydrogenase, and Akt, but protein O-GlcNAcylation was unchanged. Insulin resistance develops to a similar extent in FH− and FH+ subjects after chronic hyperglycemia, without increased protein O-GlcNAcylation. Decreased nonoxidative glucose disposal due to impaired GS activation appears to be the primary deficit in skeletal muscle glucotoxicity.