SGLT2 deletion improves glucose homeostasis and preserves pancreatic beta-cell function

OBJECTIVE

Inhibition of the Na⁺-glucose cotransporter type 2 (SGLT2) is currently being pursued as an insulin-independent treatment for diabetes; however, the behavioral and metabolic consequences of SGLT2 deletion are unknown. Here, we used a SGLT2 knockout mouse to investigate the effect of increased renal glucose excretion on glucose homeostasis, insulin sensitivity, and pancreatic β-cell function.

RESEARCH DESIGN AND METHODS

SGLT2 knockout mice were fed regular chow or a high-fat diet (HFD) for 4 weeks, or backcrossed onto the db/db background. The analysis used metabolic cages, glucose tolerance tests, euglycemic and hyperglycemic clamps, as well as isolated islet and perifusion studies.

RESULTS

SGLT2 deletion resulted in a threefold increase in urine output and a 500-fold increase in glucosuria, as well as compensatory increases in feeding, drinking, and activity. SGLT2 knockout mice were protected from HFD-induced hyperglycemia and glucose intolerance and had reduced plasma insulin concentrations compared with controls. On the db/db background, SGLT2 deletion prevented fasting hyperglycemia, and plasma insulin levels were also dramatically improved. Strikingly, prevention of hyperglycemia by SGLT2 knockout in db/db mice preserved pancreatic β-cell function in vivo, which was associated with a 60% increase in β-cell mass and reduced incidence of β-cell death.

CONCLUSIONS

Prevention of renal glucose reabsorption by SGLT2 deletion reduced HFD- and obesity-associated hyperglycemia, improved glucose intolerance, and increased glucose-stimulated insulin secretion in vivo. Taken together, these data support SGLT2 inhibition as a viable insulin-independent treatment of type 2 diabetes.Treatments of type 2 diabetes must balance the prevention of microvascular complications with the minimization of clinically significant hypoglycemia. The difficulty in safely achieving these goals, combined with epidemic increases in diabetes worldwide, has spurred the search for novel therapeutic strategies. Among these, inhibition of the Na⁺-glucose cotransporter type 2 (SGLT2) has emerged as a promising therapy (1,2). SGLT2 is a member of the SLC5 gene family and transports glucose across cells using the Na⁺ gradient established by Na⁺-K⁺-ATPases (3). SGLT2 is a low-affinity, high-capacity transporter expressed predominantly in the early proximal tubule of the kidney and accounts for about 90% of renal glucose reabsorption (4–6). Given that the kidney filters approximately 180 g of glucose daily, SGLT2 inhibition may not just reduce hyperglycemia but may also promote negative energy balance and weight loss.Type 2 diabetes is characterized by fasting hyperglycemia as a result of insulin resistance, but is often preceded by hyperinsulinemia and normal blood glucose levels, a state that is maintained by compensatory insulin secretion by the pancreatic β-cell (7). The ability of the β-cell to counteract an increased glucose load is short-lived, however, and eventually pancreatic islets fail, giving rise to hyperglycemia. Rodent and human studies have both shown that glucose toxicity is implicated in β-cell failure by increasing the rate of β-cell death by the induction of proapoptotic genes (8–10). Inhibition of SGLT2 therefore has the potential to not only acutely lower hyperglycemia but to also improve glucose homeostasis by reducing glucose toxicity and preventing islet failure.Despite recent interest in SGLT2 as a potential target for diabetes treatment, relatively few long-term models of SGLT2 deficiency have been characterized. Previously, nonselective inhibition of both SGLT1 and SGLT2 for 4 weeks in partially pancreatomized diabetic rats by injection of phlorizin led to increases in insulin sensitivity and insulin secretion (11,12). More recently, improvements in glucose homeostasis were demonstrated in diabetic rodent models after treatment with SGLT2-specific inhibitors for periods of 2 to 9 weeks (13–16). As many as seven different SGLT2 inhibitors designed for use in humans have been characterized in cell culture and animal studies, and many of these have moved on to clinical trials (2,17–22). Here, we describe the first in vivo characterization of glucose homeostasis in a SGLT2 knockout mouse model. We investigated the behavioral and metabolic consequences of SGLT2 deletion, and furthermore, we determined the effect of renal glucose excretion on glucose homeostasis, insulin sensitivity, and β-cell function in the context of both high-fat feeding and genetically determined obesity (db/db) and diabetes.     

The efficacy and safety of dipeptidyl peptidase-4 inhibitors for treatment of type 2 diabetes mellitus patients with severe renal impairment: a meta-analysis

Aims/introduction Dipeptidyl peptidase-4 (DPP-4) inhibitors are a new class of oral antidiabetic agents, and have been increasingly and widely used in the treatment of diabetes mellitus (DM). However, information of DPP-4 inhibitors in type 2?DM patients with severe renal impairment (RI) is limited. Our study aimed to assess the efficacy and safety of DPP-4 inhibitors as compared to placebos or other hypoglycemic drugs in type 2?DM patients with severe RI. Materials and methods A meta-analysis was conducted to examine the literature comparing the effects of DPP-4 inhibitors on hemoglobin A1c (HbA1c) and fasting blood glucose (FBG). Randomized control trials (RCTs) including adults with type 2?DM and severe RI were analyzed. Safety was evaluated based on the percentage of patients who developed hypoglycemia and the occurrence of adverse events (AEs) as well as the incidence of peripheral edema, urinary tract infection, diarrhea, and death. Results Five RCTs including 503 patients were analyzed. Compared with a placebo or no treatment, DPP-4 inhibitors were associated with a larger decline in HbA1c (mean difference (MD)?=??0.57, 95% confidence interval (CI): ?0.73 to ?0.41; p?0.01) but not with FBG (MD?=??0.26, 95% CI: ?1.40 to 0.8; p?= 0.66). Compared with glipizide monotherapy, no significant differences in HbA1c (MD?=?0.15, 95% CI: ?0.19 to 0.49; p?= 0.38) or FBG (MD?=??0.26, 95% CI: ?1.16 to 0.64; p?= 0.57) were found. Similar odds of experiencing an AE were found in both the DPP-4 inhibitor groups and comparison groups. Conclusions In type 2?DM patients with severe RI, treatment with DPP-4 inhibitors is safe and it effectively lowers HbA1c.     

Chronic methylglyoxal infusion by minipump causes pancreatic beta-cell dysfunction and induces type 2 diabetes in Sprague-Dawley rats

OBJECTIVE

The incidence of high dietary carbohydrate-induced type 2 diabetes is increasing worldwide. Methylglyoxal (MG) is a reactive glucose metabolite and a major precursor of advanced glycation end products (AGEs). MG levels are elevated in diabetic patients. We investigated the effects of chronic administration of MG on glucose tolerance and β-cell insulin secreting mechanism in 12-week-old male Sprague-Dawley rats.

RESEARCH DESIGN AND METHODS

MG (60 mg/kg/day) or 0.9% saline was administered by continuous infusion with a minipump for 28 days. We performed glucose and insulin tolerance tests and measured adipose tissue glucose uptake and insulin secretion from isolated pancreatic islets. We also used cultured INS-1E cells, a pancreatic β-cell line, for molecular studies. Western blotting, quantitative PCR, immunohistochemistry, and transferase-mediated dUTP nick-end labeling (TUNEL) assay were performed.

RESULTS

In rats treated with MG and MG + l-buthionine sulfoximine (BSO), MG levels were significantly elevated in plasma, pancreas, adipose tissue, and skeletal muscle; fasting plasma glucose was elevated, whereas insulin and glutathione were reduced. These two groups also had impaired glucose tolerance, reduced GLUT-4, phosphoinositide-3-kinase activity, and insulin-stimulated glucose uptake in adipose tissue. In the pancreatic β-cells, MG and MG + BSO reduced insulin secretion, pancreatic duodenal homeobox-1, MafA, GLUT-2, and glucokinase expression; increased C/EBPβ, nuclear factor-κB, MG-induced AGE, N^ε-carboxymeythyllysine, and receptor for AGEs expression; and caused apoptosis. Alagebrium, an MG scavenger and an AGE-breaking compound, attenuated the effects of MG.

CONCLUSIONS

Chronic MG induces biochemical and molecular abnormalities characteristic of type 2 diabetes and is a possible mediator of high carbohydrate-induced type 2 diabetes.Type 2 diabetes is characterized by hyperglycemia, insulin resistance, and progressive decrease in insulin secretion from the pancreas (1). A genetic predisposition has been found in many patients. More recently there has been a staggering increasing in the incidence of type 2 diabetes, many of the cases being reported in children. This explosive increase is attributed to a diet high in carbohydrates, fat, and a sedentary lifestyle (2–6). Oxidative stress is associated with diabetes and has been proposed as one of the causative factors (7,8). An increase in oxidative stress caused the insulin resistance of Zucker obese rats to progress to type 2 diabetes in 1 week (9).Methylglyoxal (MG) is a reactive dicarbonyl metabolite of mainly glucose metabolism (10). MG reacts with proteins to form advanced glycation end products (AGEs) (10,11), which are implicated in the pathogenesis of vascular complications of diabetes (11,12). Plasma MG levels in healthy humans are 1 μmol/L or less and are elevated two- to fourfold in diabetic patients (13,14). Under physiological conditions, the glyoxalase system degrades MG into d-lactate with the help of reduced glutathione (GSH) (10,14) and keeps plasma MG levels at approximately 1 μmol/L or less (13,14). Incubation of vascular smooth muscle cells with 25 mmol/L glucose or fructose for 3 h significantly increases MG production and oxidative stress (15). In vitro incubation of MG with insulin modifies the insulin molecule and impairs insulin-mediated glucose uptake in adipocytes (16). Incubation of cultured L6 muscle cells with MG (2.5 mmol/L) for 30 min impaired insulin signaling (17). However, the in vitro studies cannot establish whether MG is the cause of diabetes or an effect of diabetes.The molecular mechanisms of high dietary carbohydrate-induced type 2 diabetes are not clear. It is possible that high carbohydrate-induced chronic elevation of MG causes cumulative pathologic changes that contribute to the development of insulin resistance and type 2 diabetes. We have recently shown that acute MG (50 mg/kg iv) administered to 12-week-old male Sprague-Dawley (SD) rats caused glucose intolerance and reduced adipose tissue insulin-stimulated glucose uptake (18). Here we report the results of a comprehensive study on the effects of chronically administered MG on in vivo glucose tolerance, adipose tissue glucose uptake and insulin secretion from isolated pancreatic islets, and the underlying molecular mechanisms. We administered MG by continuous infusion with minipump for 28 days, a method used for the first time to administer MG.     

Angiotensin II type 1 receptor blockade improves beta-cell function and glucose tolerance in a mouse model of type 2 diabetes

We identified an angiotensin-generating system in pancreatic islets and found that exogenously administered angiotensin II, after binding to its receptors (angiotensin II type 1 receptor [AT1R]), inhibits insulin release in a manner associated with decreased islet blood flow and (pro)insulin biosynthesis. The present study tested the hypothesis that there is a change in AT1R expression in the pancreatic islets of the obesity-induced type 2 diabetes model, the db/db mouse, which enables endogenous levels of angiotensin II to impair islet function. Islets from 10-week-old db/db and control mice were isolated and investigated. In addition, the AT1R antagonist losartan was administered orally to 4-week-old db/db mice for an 8-week period. We found that AT1R mRNA was upregulated markedly in db/db islets and double immunolabeling confirmed that the AT1R was localized to beta-cells. Losartan selectively improved glucose-induced insulin release and (pro)insulin biosynthesis in db/db islets. Oral losartan treatment delayed the onset of diabetes, and reduced hyperglycemia and glucose intolerance in db/db mice, but did not affect the insulin sensitivity of peripheral tissues. The present findings indicate that AT1R antagonism improves beta-cell function and glucose tolerance in young type 2 diabetic mice. Whether islet AT1R activation plays a role in the pathogenesis of human type 2 diabetes remains to be determined.     

Prevention of type 2 diabetes: insulin resistance and beta-cell function

Type 2 diabetes is increasing worldwide in epidemic proportions. Its associated morbidity and mortality is imposing a major burden on the health care system. Based on a better understanding of the pathophysiology of glucose intolerance, clinical trials on the prevention of diabetes have been performed. It has now been demonstrated that diet and exercise, metformin, acarbose, and troglitazone can prevent or at least delay the development of diabetes in subjects with impaired glucose tolerance (IGT). It is now generally accepted that insulin resistance and beta-cell dysfunction are major factors involved in the development of diabetes. The relative contribution of insulin resistance versus beta-cell dysfunction on the pathogenesis of diabetes has aroused much debate. These two processes should be studied in relation to one another: their relationship is best described as hyperbolic in nature. When this relationship is taken into consideration, it becomes evident that subjects at risk of developing type 2 diabetes have beta-cell dysfunction before they develop glucose intolerance. Insulin resistance may be mostly explained by the presence of obesity and accelerate the progression to diabetes in subjects with the propensity to beta-cell failure. By the time hyperglycemia occurs, impairment in both insulin sensitivity and insulin secretion are present. There are still few data on insulin sensitivity and insulin secretion from the trials on the prevention of diabetes. The few data that we do have suggest that most interventions mostly have an effect on insulin resistance. By reducing insulin resistance, they protect and preserve the beta-cell function. No intervention has yet shown any direct effect on beta-cell function.     

Correlations of in vivo beta-cell function tests with beta-cell mass and pancreatic insulin content in streptozocin-administered baboons

In vivo beta-cell function tests are used increasingly in humans during the preclinical phase of insulin-dependent diabetes mellitus (IDDM), but the severity of the beta-cell loss responsible for the abnormalities seen in these tests is unknown. We have measured several physiological beta-cell function tests--fasting plasma glucose, glucose disappearance constant, fasting insulin, acute insulin responses to arginine (AIRarginine) and glucose (AIRglucose), and glucose potentiation of AIRarginine (delta AIRarginine/delta G) and two direct objective measurements (pancreatic insulin content [PIC] and quantitative beta-cell mass)--in adolescent male baboons (Papio anubis/cyanocephalus). We have correlated in vivo measurements obtained within 3 days after the animals were killed with in vitro estimates of PIC and beta-cell mass in 15 animals, (2 nondiabetic requiring insulin treatment and 13 after varying doses of streptozocin to induce degrees of beta-cell damage ranging from normoglycemia to severe hyperglycemia). There was a strong linear correlation between beta-cell mass and PIC (r = 0.79, P less than 0.001). Physiological measures of beta-cell function were significantly correlated with both PIC and beta-cell mass. The correlations between physiological measures and beta-cell mass were linear and intercepted the beta-cell mass axis at 0.15-0.2 g, suggesting that in vivo measures of beta-cell function approach 0 when there is still approximately 40-50% of the beta-cell mass detectable histologically. With PIC, the linear correlations intercepted the axes close to 0. These findings provide considerable validity to the measurements of beta-cell function used in preclinical IDDM in humans.(ABSTRACT TRUNCATED AT 250 WORDS)     

Coordinate changes in plasma glucose and pancreatic beta-cell function in Latino women at high risk for type 2 diabetes

The purpose of this study was to examine longitudinally the relationship among glucose levels, pancreatic beta-cell function, and insulin resistance in women at high risk for type 2 diabetes. Oral glucose tolerance tests (OGTTs) and intravenous glucose tolerance tests (IVGTTs) were performed at 15-month intervals for up to 5 years or until fasting plasma glucose exceeded 140 mg/dl in Hispanic women with recent gestational diabetes. Data were analyzed 1) to compare changes in insulin sensitivity, beta-cell function, and glucose levels between women who had diabetes at one or more visits and women who remained diabetes free and 2) to determine longitudinal patterns of change in glucose levels and acute beta-cell compensation for insulin resistance. Seventy-one women provided data from a total of 280 paired OGTTs and IVGTTs during a median follow-up of 46 months. Compared with the 47 women who remained free of diabetes, the 24 who either had diabetes (n = 9) or developed it during follow-up (n = 15) had higher baseline glucose levels and lower acute beta-cell compensation for insulin resistance. Baseline insulin sensitivity was low in both groups and did not change significantly during follow-up. Fasting and 2-h glucose levels increased more rapidly in the diabetic group despite a decline in acute beta-cell compensation that was significantly slower than the decline in women who did not develop diabetes. This paradox was explained by an accelerated rise in glucose levels for any decline in beta-cell compensation when beta-cell compensation reached approximately 10% of normal, a level that was reached in the women who had or developed diabetes but not in the women who remained diabetes free. These findings define a pathogenesis for type 2 diabetes in one high-risk group that is characterized by a relatively long-term decline in acute beta-cell compensation for chronic insulin resistance that is attended by slowly rising glucose levels. Only relatively late in this process do glucose levels rise rapidly and into the diabetic range.     

Altered homeostatic adaptation of first- and second-phase beta-cell secretion in the offspring of patients with type 2 diabetes: studies with a minimal model to assess beta-cell function

We adapted a minimal model to assess beta-cell function during a hyperglycemic glucose clamp and to uncover peculiar aspects of the relationship among beta-cell function, plasma glucose, and insulin sensitivity (IS) in offspring of Caucasian patients with type 2 diabetes (OfT2D). We pooled two data sets of OfT2D (n = 69) and control subjects (n = 45) with normal glucose regulation. Plasma C-peptide was measured during a hyperglycemic clamp ( approximately 10 mmol/l) to quantify model-based first-phase secretion and glucose sensitivity of second-phase secretion (beta). IS was quantified during the hyperglycemic clamp. In the pooled data, first-phase secretion was linearly and negatively related to fasting plasma glucose, but not IS; OfT2D lay on a distinct line shifted to the left of the control subjects. In contrast, beta was negatively related to IS, and OfT2D lay on a distinct line shifted more and more to the left of the control subjects, as IS was worse. Thus, in OfT2D lower beta-cell adaptive responses exist between ambient glycemia and first-phase insulin secretion and between IS and second-phase secretion. Under conditions leading to decreased insulin sensitivity, these disturbed relationships may lead to progression to diabetes in OfT2D.     

Natural history of beta-cell function in type 1 diabetes

Despite extensive and ongoing investigations of the immune mechanisms of autoimmune diabetes in humans and animal models, there is much less information about the natural history of insulin secretion before and after the clinical presentation of type 1 diabetes and the factors that may affect its course. Studies of insulin production previously published and from the Diabetes Prevention Trial (DPT)-1 suggest that there is progressive impairment in insulin secretory responses but the reserve in response to physiological stimuli may be significant at the time of diagnosis, although maximal responses are more significantly impaired. Other factors, including insulin resistance, may play a role in the timing of clinical presentation along this continuum. The factors that predict the occurrence and rapidity of decline in beta-cell function are still largely unknown, but most studies have identified islet cell autoantibodies as predictors of future decline and age as a determinant of residual insulin production at diagnosis. Historical as well as recent clinical experience has emphasized the importance of residual insulin production for glycemic control and prevention of end-organ complications. Understanding the modifiers and predictors of beta-cell function would allow targeting immunological approaches to those individuals most likely to benefit from therapy.     

Preservation of pancreatic beta-cell function and prevention of type 2 diabetes by pharmacological treatment of insulin resistance in high-risk hispanic women

Type 2 diabetes frequently results from progressive failure of pancreatic beta-cell function in the presence of chronic insulin resistance. We tested whether chronic amelioration of insulin resistance would preserve pancreatic beta-cell function and delay or prevent the onset of type 2 diabetes in high-risk Hispanic women. Women with previous gestational diabetes were randomized to placebo (n = 133) or the insulin-sensitizing drug troglitazone (400 mg/day; n = 133) administered in double-blind fashion. Fasting plasma glucose was measured every 3 months, and oral glucose tolerance tests (OGTTs) were performed annually to detect diabetes. Intravenous glucose tolerance tests (IVGTTs) were performed at baseline and 3 months later to identify early metabolic changes associated with any protection from diabetes. Women who did not develop diabetes during the trial returned for OGTTs and IVGTTs 8 months after study medications were stopped. During a median follow-up of 30 months on blinded medication, average annual diabetes incidence rates in the 236 women who returned for at least one follow-up visit were 12.1 and 5.4% in women assigned to placebo and troglitazone, respectively (P < 0.01). Protection from diabetes in the troglitazone group 1) was closely related to the degree of reduction in endogenous insulin requirements 3 months after randomization, 2) persisted 8 months after study medications were stopped, and 3) was associated with preservation of beta-cell compensation for insulin resistance. Treatment with troglitazone delayed or prevented the onset of type 2 diabetes in high-risk Hispanic women. The protective effect was associated with the preservation of pancreatic beta-cell function and appeared to be mediated by a reduction in the secretory demands placed on beta-cells by chronic insulin resistance.     

Effect of pioglitazone on pancreatic beta-cell function and diabetes risk in Hispanic women with prior gestational diabetes

The Pioglitazone In Prevention Of Diabetes (PIPOD) study was conducted to evaluate beta-cell function, insulin resistance, and the incidence of diabetes during treatment with pioglitazone in Hispanic women with prior gestational diabetes who had completed participation in the Troglitazone In Prevention Of Diabetes (TRIPOD) study. Women who completed the TRIPOD study were offered participation in the PIPOD study for a planned 3 years of drug treatment and 6 months of postdrug washout. Oral glucose tolerance tests were performed annually on pioglitazone and at the end of the postdrug washout. Intravenous glucose tolerance tests (IVGTTs) for assessment of insulin sensitivity and beta-cell function were conducted at baseline, after 1 year on pioglitazone, and at the end of the postdrug washout. Of 95 women who were not diabetic at the end of the TRIPOD study, 89 enrolled in the PIPOD study, 86 completed at least one follow-up visit, and 65 completed all study visits, including the postdrug tests. Comparison of changes in beta-cell compensation for insulin resistance across the TRIPOD and PIPOD studies revealed that pioglitazone stopped the decline in beta-cell function that occurred during placebo treatment in the TRIPOD study and maintained the stability of beta-cell function that had occurred during troglitazone treatment in the TRIPOD study. The risk of diabetes, which occurred at an average rate of 4.6% per year, was lowest in women with the largest reduction in total IVGTT insulin area after 1 year of treatment. The similarity of findings between the PIPOD and TRIPOD studies support a class effect of thiazolidinedione drugs to enhance insulin sensitivity, reduce insulin secretory demands, and preserve pancreatic beta-cell function, all in association with a relatively low rate of type 2 diabetes, in Hispanic women with prior gestational diabetes.     

Mechanisms of beta-cell death in type 2 diabetes

A decrease in the number of functional insulin-producing beta-cells contributes to the pathophysiology of type 2 diabetes. Opinions diverge regarding the relative contribution of a decrease in beta-cell mass versus an intrinsic defect in the secretory machinery. Here we review the evidence that glucose, dyslipidemia, cytokines, leptin, autoimmunity, and some sulfonylureas may contribute to the maladaptation of beta-cells. With respect to these causal factors, we focus on Fas, the ATP-sensitive K+ channel, insulin receptor substrate 2, oxidative stress, nuclear factor-kappaB, endoplasmic reticulum stress, and mitochondrial dysfunction as their respective mechanisms of action. Interestingly, most of these factors are involved in inflammatory processes in addition to playing a role in both the regulation of beta-cell secretory function and cell turnover. Thus, the mechanisms regulating beta-cell proliferation, apoptosis, and function are inseparable processes.     

Prolonged elevation of plasma free fatty acids impairs pancreatic beta-cell function in obese nondiabetic humans but not in individuals with type 2 diabetes

Our recent in vivo observations in healthy nonobese humans have demonstrated that prolonged elevation of plasma free fatty acids (FFAs) results in diminished glucose-stimulated insulin secretion (GSIS) when the FFA-mediated decrease in insulin sensitivity is taken into account. In the present study, we investigated whether obese individuals and patients with type 2 diabetes are more sensitive than healthy control subjects to the inhibitory effect of prolonged elevation of plasma FFAs on GSIS. In seven patients with type 2 diabetes and seven healthy nondiabetic obese individuals, we assessed GSIS with a programmed graded intravenous glucose infusion on two occasions, 6-8 weeks apart, with and without a prior 48-h infusion of heparin and Intralipid, which was designed to raise plasma FFA concentration approximately twofold over basal. The nondiabetic obese subjects had a significant 21% decrease in GSIS (P = 0.0008) with the heparin and Intralipid infusion, associated with a decrease in whole body insulin clearance. The impairment in GSIS was evident at low (<11 mmol/l) but not at higher plasma glucose concentrations. In contrast, the patients with type 2 diabetes had a slight increase in GSIS (P = 0.027) and no change in insulin clearance, although there was marked interindividual variability in response. Plasma proinsulin concentrations measured in a subset of subjects were not altered in either group by the infusion of heparin and Intralipid. In summary, 1) obese nondiabetic individuals are susceptible to a desensitization of GSIS with heparin and Intralipid infusion, and 2) patients with type 2 diabetes do not demonstrate such susceptibility when FFAs are elevated approximately twofold above basal with heparin and Intralipid. Our results suggest that FFAs could play an important role in the development of beta-cell failure in obese individuals who are at risk for developing type 2 diabetes. They do not, however, seem to further deteriorate the beta-cell function of patients who already have established type 2 diabetes and may even result in a slight increase in GSIS in this latter group.