Background. Sodium-glucose cotransporter 2 (SGLT2) inhibitors lower glycemia by enhancing urinary glucose excretion. The physiologic response to pharmacologically induced acute or chronic glycosuria has not been investigated in human diabetes. Methods.We evaluated 66 patients with type 2 diabetes (62 ± 7 years, BMI = 31.6 ± 4.6 kg/m 2 , HbA 1c = 55 ± 8 mmol/mol, mean ± SD) at baseline, after a single dose, and following 4-week treatment with empagliflozin (25 mg). At each time point, patients received a mixed meal coupled with dual-tracer glucose administration and indirect calorimetry.

OBJECTIVE -Available insulin sensitivity (IS) methods based on the oral glucose tolerance test (OGTT) are empirical. We used a glucose-insulin model to derive an OGTT-based IS (oral glucose insulin sensitivity [OGIS]) index, which predicts glucose clearance in a glucose clamp. We validated OGIS against clamp data.RESEARCH DESIGN AND METHODS -OGIS requires glucose and insulin concentrations from a 75-g OGTT at 0, 2, and 3 h (3-h OGTT) or at 0, 1.5, and 2 h (2-h OGTT). The formula includes six constants optimized to match the clamp results. For this purpose, 15 lean nondiabetic subjects (BMI Ͻ 25 kg/m 2 ), 38 obese nondiabetic subjects (BMI Ͼ 25 kg/m 2 ), and 38 subjects with type 2 diabetes randomly underwent an OGTT and a 120 mU ⅐ min Ϫ1 ⅐ m Ϫ2insulin infusion euglycemic clamp. Glucose clearance (Cl CLAMP ), calculated as the ratio of glucose infusion to concentration during the last hour of the clamp, was compared with OGIS. OGIS was also tested on an independent group of 13 subjects with impaired glucose tolerance (IGT).RESULTS -OGIS and Cl CLAMP were correlated in the whole group (R ϭ 0.77, P Ͻ 0.0001), in the subgroups (lean: R ϭ 0.59; obese: R ϭ 0.73; type 2 diabetes: R ϭ 0.49; P Ͻ 0.02), and in the independent IGT group (R ϭ 0.65, P Ͻ 0.02). Reproducibility of OGIS and Cl CLAMP were similar (coefficients of variation: OGIS 7.1%, Cl CLAMP 6.4%). OGIS was as effective as Cl CLAMP in discriminating between groups (for OGIS, lean vs. obese: 440 Ϯ 16 vs. 362 Ϯ 11 ml ⅐ min Ϫ1⅐ m Ϫ2 , P Ͻ 0.001; lean vs. type 2 diabetes: 440 Ϯ 16 vs. 239 Ϯ 7, P Ͻ 0.0001; obese vs. type 2 diabetes: 362 Ϯ 11 vs. 239 Ϯ 7, P Ͻ 0.0001; results were similar for Cl CLAMP ). The relationships between IS and BMI, fasting plasma insulin, and insulin secretion (calculated from the OGTT insulin concentration) were examined. OGIS yielded results similar to Cl CLAMP and fully consistent with established physiological principles. The performance of the index for the 3-h and 2-h OGTT was similar.CONCLUSIONS -OGIS is an index of IS in good agreement with the clamp. Because of its simplicity (only three blood samples required), this method has potential use for clinical investigation including large-scale epidemiological studies. Diabetes Care 24:539 -548, 2001

Pharmacologically induced glycosuria elicits adaptive responses in glucose homeostasis and hormone release. In type 2 diabetes (T2D), along with decrements in plasma glucose and insulin levels and increments in glucagon release, sodium-glucose cotransporter 2 (SGLT2) inhibitors induce stimulation of endogenous glucose production (EGP) and a suppression of tissue glucose disposal (TGD). We measured fasting and postmeal glucose fluxes in 25 subjects without diabetes using a double glucose tracer technique; in these subjects and in 66 previously reported patients with T2D, we also estimated lipolysis (from [ 2 H 5 ]glycerol turnover rate and circulating free fatty acids, glycerol, and triglycerides), lipid oxidation (LOx; by indirect calorimetry), and ketogenesis (from circulating b-hydroxybutyrate concentrations). In both groups, empagliflozin administration raised EGP, lowered TGD, and stimulated lipolysis, LOx, and ketogenesis. The pattern of glycosuria-induced changes was similar in subjects without diabetes and in those with T2D but quantitatively smaller in the former. With chronic (4 weeks) versus acute (first dose) drug administration, glucose flux responses were attenuated, whereas lipid responses were enhanced; in patients with T2D, fasting b-hydroxybutyrate levels rose from 246 6 288 to 561 6 596 mmol/L (P < 0.01). We conclude that by shunting substantial amounts of carbohydrate into urine, SGLT2-mediated glycosuria results in a progressive shift in fuel utilization toward fatty substrates. The associated hormonal milieu (lower insulin-to-glucagon ratio) favors glucose release and ketogenesis.When large quantities of glucose are pharmacologically forced into urinary excretion, whole-body metabolism undergoes adaptive changes involving glucose fluxes, hormonal responses, fuel selection, and energy expenditure (1,2). In previous work (3), we used empagliflozin to investigate the physiological response to forced glycosuria in patients with type 2 diabetes (T2D). By combining a mixed meal with the double-tracer technique, we found that after acute or chronic empagliflozin administration endogenous glucose production (EGP) rose, tissue glucose disposal (TGD) decreased, and lipid utilization increased. The aims of the present work were to measure the full spectrum of changes in lipolysis, lipid levels, and substrate availability consequent upon empagliflozininduced glycosuria in patients with T2D and to test whether and to what extent these changes occur in subjects without diabetes. RESEARCH DESIGN AND METHODS PopulationSixty-six patients with T2D were recruited into the study; their inclusion criteria are detailed in Ferrannini et al. (3). Twenty-five subjects without diabetes (12 with normal glucose tolerance [NGT] and 13 with impaired glucose tolerance [IGT]) served as control subjects (Supplementary Table 1). The glucose and hormone data for the patients with T2D have been reported (3) and are repeated here for comparison purposes. The study (clinicaltrials.gov identifier NCT01248364; EudraCT number 2010-...

The nature of the progressive beta-cell failure occurring as normal glucose tolerant (NGT) individuals progress to type 2 diabetes (T2DM) is incompletely understood. We measured insulin sensitivity (by a euglycemic insulin clamp) and insulin secretion rate (by deconvolution of plasma C-peptide levels during an oral glucose tolerance test) in 188 subjects [19 lean NGT (body mass index [BMI]

OBJECTIVE -Insulin resistance, associated with increased lipolysis, results in a high exposure of nonadipose tissue to lipids. Experimental data indicate that fatty infiltration of pancreatic islets may also contribute to ␤-cell dysfunction, but whether this occurs in humans in vivo is unknown.RESEARCH DESIGN AND METHODS -Using proton magnetic resonance spectroscopy and oral glucose tolerance tests, we studied the association of pancreatic lipid accumulation in vivo and various aspects of ␤-cell function in 12 insulin-naive type 2 diabetic and 24 age-and BMI-matched nondiabetic men.RESULTS -Patients versus control subjects had higher A1C, fasting plasma glucose, and insulin and triglyceride levels and lower HDL cholesterol, but similar waist circumference. Median (interquartile range) pancreatic fat content in patients and control subjects was 20.4% (13.4 -43.6) and 9.7% (7.0 -20.2), respectively (P ϭ 0.032). Pancreatic fat correlated negatively with ␤-cell function parameters, including the insulinogenic index adjusted for insulin resistance, early glucose-stimulated insulin secretion, ␤-cell glucose sensitivity, and rate sensitivity (all P Ͻ 0.05), but not potentiation. However, these associations were significantly affected by the diabetic state, such that a significant association of pancreatic fat with ␤-cell dysfunction was only present in the nondiabetic group (all P Ͻ 0.01), suggesting that once diabetes occurs, factors additional to pancreatic fat account for further ␤-cell function decline. In control subjects, the association of pancreatic fat and ␤-cell function remained significant after correction for BMI, fasting plasma glucose, and triglycerides (P ϭ 0.006).CONCLUSIONS -These findings indicate that pancreatic lipid content may contribute to ␤-cell dysfunction and possibly to the subsequent development of type 2 diabetes in susceptible humans. Diabetes Care 30:2916-2921, 2007P rogressive ␤-cell dysfunction, in the context of insulin resistance, is a hallmark of type 2 diabetes (1). Glucose toxicity, ensuing from diabetesrelated hyperglycemia, has been regarded as a contributor to ␤-cell damage (2). In contrast, chronic exposure of the pancreatic islets to nonesterified fatty acids (NEFAs) is considered as a potential primary cause of ␤-cell dysfunction (3). In obese individuals, increased lipolysis contributes to high levels of circulating NEFAs, whereas liver insulin resistance leads to elevated hepatic output of triglyceriderich particles (4). When NEFA supply exceeds utilization, nonadipose tissues, including the pancreatic islets, start accumulating triglycerides (3), which is aggravated by the simultaneous presence of hyperglycemia (2,5,6). Subsequently, various mechanisms including the formation of reactive long-chain fatty acyl-CoAs and toxic metabolites, such as ceramide, the activation of protein kinase C-␦, and increased oxidative stress, may all contribute to apoptosis and the decline of ␤-cell mass (2,3,5-7). Finally, experimental and autopsy data indicate that fatty infiltration of th...

Meal and oral glucose tests for assessment of ␤-cell function: modeling analysis in normal subjects. Am J Physiol Endocrinol Metab 283: E1159-E1166, 2002. First published August 6, 2002 10.1152/ajpendo.00093.2002We investigated ␤-cell function and its relationship to insulin sensitivity in 17 normal volunteers. For insulin secretion (derived by C-peptide deconvolution), a mathematical model was applied to 24-h triple-meal tests (MT) as well as oral glucose tolerance tests (OGTT); insulin sensitivity was assessed by the euglycemic insulin clamp technique. The ␤-cell model featured a glucose concentration-insulin secretion dose response (characterized by secretion at 5 mM glucose and slope), a secretion component proportional to the glucose concentration derivative, and a time-dependent potentiation factor (modulating the dose response and accounting for effects of sustained hyperglycemia and incretins). The ␤-cell dose-response functions estimated from the whole 24-h MT, the first 2 h of the MT, and the OGTT differed systematically, because a different potentiation factor was involved. In fact, potentiation was higher than average during meals (1.6 Ϯ 0.1-fold during the first meal) and had a different time course in the MT and OGTT. However, if potentiation was accounted for, the 24-and 2-h MT and the OGTT yielded similar dose responses, and most ␤-cell function parameters were intercorrelated (r ϭ 0.50-0.86, P Յ 0.05). The potentiation factor was found to be related to plasma glucose-dependent insulin-releasing polypeptide concentrations (r ϭ 0.49, P Ͻ 0.0001). Among ␤-cell function parameters, only insulin secretion at 5 mM glucose from MT correlated inversely with insulin sensitivity (24-h MT: r ϭ Ϫ0.74, P Ͻ 0.001; 2-h MT: r ϭ Ϫ0.52, P Ͻ 0.05), whereas the dose-response slope and the OGTT parameters did not. In nine other subjects, reproducibility of model parameters was evaluated from repeated MTs. Coefficients of variation were generally ϳ20%, but the derivative component was less reproducible. We conclude that our model for the multiple MT yields useful information on ␤-cell function, particularly with regard to the role of potentiation. With cautious interpretation, a 2-h MT or a standard OGTT can be used as surrogates of 24-h tests in assessing spontaneous ␤-cell function. insulin secretion; glucose-induced insulin release; potentiation of glucose-induced insulin release; insulin sensitivity

OBJECTIVE-To quantitate the separate impact of obesity and hyperlycemia on the incretin effect (i.e., the gain in ␤-cell function after oral glucose versus intravenous glucose). (75 g) and intravenous glucose administration was performed in 51 subjects (24 with normal glucose tolerance [NGT], 17 with impaired glucose tolerance [IGT], and 10 with type 2 diabetes) with a wide range of BMI (20 -61 kg/m 2 ). C-peptide deconvolution was used to reconstruct insulin secretion rates, and ␤-cell glucose sensitivity (slope of the insulin secretion/glucose concentration dose-response curve) was determined by mathematical modeling. The incretin effect was defined as the oral-tointravenous ratio of responses. In 8 subjects with NGT and 10 with diabetes, oral glucose appearance was measured by the double-tracer technique. RESEARCH DESIGN AND METHODS-Isoglycemic oralRESULTS-The incretin effect on total insulin secretion and ␤-cell glucose sensitivity and the GLP-1 response to oral glucose were significantly reduced in diabetes compared with NGT or IGT (P Յ 0.05). The results were similar when subjects were stratified by BMI tertile (P Յ 0.05). In the whole dataset, each manifestation of the incretin effect was inversely related to both glucose tolerance (2-h plasma glucose levels) and BMI (partial r ϭ 0.27-0.59, P Յ 0.05) in an independent, additive manner. Oral glucose appearance did not differ between diabetes and NGT and was positively related to the GLP-1 response (r ϭ 0.53, P Ͻ 0.01). Glucagon suppression during the oral glucose tolerance test was blunted in diabetic patients.CONCLUSIONS-Potentiation of insulin secretion, glucose sensing, glucagon-like peptide-1 release, and glucagon suppression are physiological manifestations of the incretin effect. Glucose tolerance and obesity impair the incretin effect independently of one another.

Insulin resistance is common in the general population and tends to cluster with glucose intolerance, dyslipidaemia and high blood pressure. The importance of the insulin-resistant phenotype for the assessment of cardiovascular risk and response to intervention is increasingly being recognized. Therefore, there is a need for an accurate and reproducible method for measuring insulin resistance in vivo. The euglycaemic insulin clamp is currently the best available standard technique. It provides steady-state measures of insulin action and is easily combined with a number of other investigative methods (tracer dilution, limb catheterization, indirect calorimetry, positron emission tomography and nuclear magnetic resonance scans). Whereas homeostatic model assessment uses fasting plasma glucose and insulin concentrations to derive indices of insulin sensitivity and secretion from a mathematical model, other techniques are based on the exogenous infusion of glucose or insulin, or both, either under steady-state (the insulin suppression test) or under dynamic conditions (insulin tolerance test, intravenous glucose-tolerance test with minimal model analysis, and constant infusion of glucose with model assessment). This article recalls the principles of insulin action, with special reference to the concept of clearance and the equivalence of different approaches to estimating this function. Merits and disadvantages of the various techniques are then concisely reviewed, with emphasis on their relative feasibilities and reliabilities. Recent developments and future trends are mentioned. Criteria for choice and some reference data are given to aid the clinical investigator.