beta-cell failure in diabetes and preservation by clinical treatment

Impact of glycemic treatment choices on cardiovascular complications in type 2 diabetes

As the diabetic population has significant morbidity and mortality from cardiovascular disease (CVD), much of its medical care focuses on CVD prevention and treatment. Some medications used to treat hyperglycemia may have beneficial effects on CV outcomes, others may have negative effects, while still others seem to have no direct effect. Although past epidemiological studies have shown a relationship between glycated hemoglobin levels and CV events in patients with type 2 diabetes, recent large randomized clinical trials (ACCORD, ADVANCE, and VADT) lasting 3.5 to 5.6 years have found that intensive glycemic control either has no impact on CV outcomes or even worsens them. Results of the 10-year follow-up of the UKPDS suggest that tight glycemic control of younger, newly diagnosed patients with type 2 diabetes may have CV benefits many years later. Because the pathogenesis of atherosclerosis spans decades, it may be that beneficial effects of tight glycemic control on CV outcomes are mainly in younger patients without established macrovascular disease. There is an emerging notion that tight glycemic control may be beneficial in primary prevention of CVD in younger patients with diabetes, but may become deleterious in older patients with established or subclinical CVD. Thus, while tight control may lessen microvascular disease, it may increase the risk of hypoglycemia and possibly of adverse CV events. In each patient, the goals of glycemic control need to be individualized based on age, overall prognosis, presence of macrovascular disease, and risk of hypoglycemia.

Unusually rapid beta-cell failure in a patient newly diagnosed with type 2 diabetes presenting acutely with unprovoked severe hyperglycaemic hyperosmolar state: a case report

Pancreatic β-cell failure on a background of insulin resistance results in the inability to compensate for fasting hyperglycaemia and eventually produces type 2 diabetes mellitus. We describe an interesting case of a patient who presented acutely with unprovoked severe hyperglycaemic hyperosmolar state and was subsequently diagnosed with type 2 diabetes mellitus on a background of only impaired first phase insulin secretion 4 months prior. Glucagon stimulation test detected significant β-cell failure necessitating long term exogenous insulin therapy which is highly unusual by virtue of the rapid apparent deterioration.

Medical versus surgical interventions for the metabolic complications of obesity in children

The global epidemic of obesity has not spared children. Although prevention of obesity is commendable, we cannot hide from the pressing need to identify, assess, and actively manage children seriously afflicted by obesity and its associated conditions. Sustained weight loss (or, for children, lowering of body mass index standard deviation score) delivers major health benefit, but in children has been difficult to achieve. In adults, the success of the diabetes prevention programs using practical lifestyle interventions is indisputable. Medical therapy, although currently limited in it scope, provides some promise for older children. There is now accumulating evidence, generally of poor quality that surgical interventions (laparoscopic adjustable gastric banding and Roux-en-Y gastric bypass) provide excellent sustained weight loss and improvement in comorbidity and quality of life in selected older children. Their benefits in adults are well demonstrated. Surgery comes with risk, both immediate and in the future, as does severe obesity. Carefully weighing risk and benefit is challenging for the individual and for health service providers. Careful health outcomes research with registries and well-conducted trials will provide better direction in the future. In the meantime, we should move forward ethically and cautiously in providing more intensive obesity management in children.

Impact of plasmatic lipids in glycemic control and its influence in the cardiometabolic risk in morbidly obese subjects

OBJECTIVES: To evaluate whether biochemical parameters are associated with a good glycemic control and to identify the occurrence of cardiometabolic risk variables. MATERIAL AND METHODS: One hundred forty Brazilians were evaluated. The subjects were characterized with regard to glycemic control as good, fair and poor and were divided into tertiles by TG and HbA1c. We use the ROC curve to determine which variables were predicted of poor glycemic control and the factor analyses to identify the domains that segregated among the risk variables. RESULTS: Fasting glucose and insulin levels, TG level, VLDL-C and HOMA-IR increased significantly across HbA1c tertiles. The best marker for identification of poor glycemic control was triglycerides. The presence of cardiometabolic abnormalities did not alter the glycemic control, but HOMA-IR was significantly higher in subjects with abnormalities. CONCLUSION: The use of TG levels offers a reasonable degree of clinical utility. In morbidly obese subjects insulin resistance is associated with individual cardiometabolic factors.

Long-term treatment with sergliflozin etabonate improves disturbed glucose metabolism in KK-A(y) mice

Sergliflozin etabonate, a novel oral selective low-affinity sodium glucose cotransporter (SGLT2) inhibitor, improves hyperglycemia by suppressing renal glucose reabsorption, in which SGLT2 participates as a dominant transporter. In the present study, we examined the antidiabetic profile of sergliflozin etabonate in a diabetic model, KK-A(y) mice, with symptoms of obesity and hyperinsulinemia. The blood glucose level was monitored in non-fasted female KK-A(y) mice after a single oral administration of sergliflozin etabonate. The non-fasting blood glucose level was reduced in a dose-dependent manner after a single oral administration of sergliflozin etabonate (39% reduction at 2 h after a dose of 30 mg/kg). The effects of long-term administration of sergliflozin etabonate on the blood glucose level were assessed in female KK-A(y) mice in several studies (4-day, 8-week, and 9-week administration study), in which sergliflozin etabonate was administered in the diet. The non-fasting blood glucose and plasma insulin were both lowered dose-dependently in the 4-day administration study. Long-term treatment with sergliflozin etabonate dose-dependently improved the hyperglycemia and prevented body weight gain in the 8-week study. In addition to the improvement in glycemic control, fatty liver and pancreatic beta-cell abnormalities were ameliorated in mice fed sergliflozin etabonate in the 9-week study. These data indicate that SGLT2 inhibitors could be useful to improve hyperglycemia resulting from insulin resistance without pancreatic beta-cell abuse or body weight gain. SGLT2 inhibitors may simultaneously realize both a systemic negative energy balance and correction of hyperglycemia.

Unraveling the science of incretin biology

Type 2 diabetes mellitus has become an enormous and worldwide healthcare problem that is almost certain to worsen. Current therapies, which address glycemia and insulin resistance, have not adequately addressed the complications and treatment failures associated with this disease. New treatments based on the incretin hormones provide a novel approach to address some components of the complex pathophysiology of type 2 diabetes. The purpose of this review is to elucidate the science of the incretin hormones and describe the incretin effect and its regulatory role in beta-cell function, insulin secretion, and glucose metabolism. The key endogenous hormones of incretin system are glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1); a key enzymatic regulator of these hormones is dipeptidyl peptidase-4, which rapidly inactivates/degrades the incretin hormones. The roles of the incretin hormones in the regulation of glucose metabolism and other related physiologic processes such as gut motility and food intake are disturbed in type 2 diabetes. These disturbances--defects in the incretin system--contribute to the pathophysiology of type 2 diabetes in manifold ways. Consequently, therapies designed to address impairments to the effects of the incretin hormones have the potential to improve glucose regulation and other abnormalities (e.g., weight gain, loss of beta-cell function) associated with type 2 diabetes.

Impact of sitagliptin on markers of beta-cell function: a meta-analysis

BACKGROUND

Progressive beta-cell dysfunction and beta-cell failure are fundamental pathogenic consequences of type 2 diabetes. Dipeptidyl peptidase-IV inhibitors may exhibit improvement on preclinical measures of both beta-cell function, homeostasis model assessment of beta-cell (HOMA-beta) index, and beta-cell dysfunction, proinsulin/insulin ratio (PI/IR), correlating to beta-cell survival.

RESEARCH DESIGN AND METHODS

A systematic literature search through July 2008 was conducted to extract a consensus of randomized, controlled trials of sitagliptin therapy on measures of beta-cell function. A random-effects model meta-analysis evaluated effects on HOMA-beta and PI/IR versus placebo. Several subgroup analyses, including active control, were conducted. Studies were included if they met the following criteria: (1) randomized trials on sitagliptin; (2) placebo or active control; and (3) data reported on HOMA-beta or PI/IR.

RESULTS

A total of 11 trials (n = 3039) reported effects on HOMA-beta and 8 trials (n = 2325) on PI/IR versus placebo. Four trials (n = 1425) were included in the active control subgroup analysis. Sitagliptin significantly improved HOMA-beta index by 12.03% [95% confidence interval (CI), 9.45-14.60] versus placebo. Sitagliptin also significantly decreased PI/IR -0.06 (95% CI, -0.08 to -0.04). Sitagliptin was inferior to active control for HOMA-beta index [5.64% (95% CI, 0.38-10.90)], but not different in terms of PI/IR [0.01 (95% CI, -0.04 to 0.06)].

CONCLUSIONS

Despite significant improvement in HOMA-beta index and PI/IR from placebo, there does not seem to be a benefit of dipeptidyl peptidase-IV inhibitors over other agents with respect to beta-cell function/activity. Long-term prevention of beta-cell dysfunction cannot be ruled out.

Initiation of insulin therapy in elderly patients taking oral antidiabetes drugs

BACKGROUND

We sought to estimate the rate of initiation of insulin therapy among elderly patients using oral anti-diabetes drugs and to identify the factors associated with this initiation.

METHODS

We conducted a population-based cohort study involving people aged 66 or more years who were newly dispensed an oral antidiabetes drug. Individuals who had received acarbose or a thiazolidinedione were excluded. The rate of insulin initiation was calculated by use of the Kaplan-Meier method. Factors associated with insulin initiation were identified by multivariable Cox regression analyses.

RESULTS

In this cohort of 69,674 new users of oral antidiabetes drugs, insulin was initiated at rate of 9.7 cases per 1000 patient-years. Patients who had initially received an insulin secretagogue (rather than metformin), who were prescribed an oral antidiabetes drug by an endocrinologist or an internist, who received higher initial doses of an oral antidiabetes drug, who received oral corticosteroids, used glucometer strips, or were admitted to hospital in the year before initiation of oral antidiabetes therapy, or who received 16 or more medications were more likely than those without these characteristics to have insulin therapy initiated. In contrast, patients who received thiazides or who used up to 12 medications (v. none) were less likely to have insulin therapy initiated.

INTERPRETATION

Several factors related to drugs and health services are associated with the initiation of insulin therapy in elderly patients receiving oral antidiabetes drugs. It is unclear whether these factors predict secondary failure of oral antidiabetes drugs or instead reflect better management of type 2 diabetes.

Insights from the Liraglutide Clinical Development Program--the Liraglutide Effect and Action in Diabetes (LEAD) studies

Standard therapies for type 2 diabetes often fail to maintain glycemic control over the long term, in part because they do not target the underlying cause. Current treatments may also be associated with weight gain, hypoglycemia, and other adverse effects, and can be difficult to use. Disease progression is accompanied by a progressive decline in beta-cell function, which begins early in the disease course, and an impaired incretin response. The recently developed glucagon-like peptide-1 (GLP-1) receptor agonists overcome some of the limitations of conventional treatments. This article summarizes the key results of the new GLP-1 receptor agonist (liraglutide) phase 3 Liraglutide Effect and Action in Diabetes (LEAD) studies. This series of 6 randomized controlled studies involved > 4400 patients with type 2 diabetes who were unable to maintain glycemic control with diet and exercise alone or with oral treatment, approximately 2700 of whom received liraglutide. The studies demonstrated the efficacy and safety of liraglutide both as monotherapy and as combination therapy with 1 or 2 oral agents. In addition to providing robust glycemic control in these studies, liraglutide reduced weight in most patients, improved beta-cell function, lowered blood pressure and triglycerides, and was well tolerated with minimal risk of hypoglycemia.

Analysis of beta cell proliferation dynamics in zebrafish

Among the different mechanisms invoked to explain the beta cell mass expansion during postnatal stages and adulthood, self-replication is being considered the major cellular event occurring both under physiological conditions and in regenerating pancreas after partial pancreactomy. Neogenesis, i.e. differentiation from pancreatic progenitors, has been demonstrated to act concurrently with beta cell replication during pancreatic regeneration. Both phenomena have been largely elucidated in higher vertebrates (mouse, rat and guinea pig), but an extensive description of beta cell dynamics in other animal models is currently lacking. We, therefore, explored in zebrafish the cellular origins of new beta cells in both adult and larval stages. By integrating the results from in vivo time lapse analysis and immunostaining, we provide a detailed reconstruction of the major processes involved in fish beta cell genesis and maintenance. Moreover, by establishing the selective ablation of proliferating beta cells, through the ganciclovir-HSVTK system, we could show that in larval stages self-replication is the main mechanism of beta cells expansion. Since the same mechanism of proliferation has been observed to occur during early and late life stages, we suggest that zebrafish larvae can be used as an alternative tool for an in vivo exploration and screening of new potential mitogens specifically targeting beta cells.

Unraveling the science of incretin biology

Type 2 diabetes mellitus has become an enormous and worldwide healthcare problem that is almost certain to worsen. Current therapies, which address glycemia and insulin resistance, have not adequately addressed the complications and treatment failures associated with this disease. New treatments based on the incretin hormones provide a novel approach to address some components of the complex pathophysiology of type 2 diabetes. The purpose of this review is to elucidate the science of the incretin hormones and describe the incretin effect and its regulatory role in beta-cell function, insulin secretion, and glucose metabolism. The key endogenous hormones of incretin system are glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1); a key enzymatic regulator of these hormones is dipeptidyl peptidase-4, which rapidly inactivates/degrades the incretin hormones. The roles of the incretin hormones in the regulation of glucose metabolism and other related physiologic processes such as gut motility and food intake are disturbed in type 2 diabetes. These disturbances--defects in the incretin system--contribute to the pathophysiology of type 2 diabetes in manifold ways. Consequently, therapies designed to address impairments to the effects of the incretin hormones have the potential to improve glucose regulation and other abnormalities (e.g., weight gain, loss of beta-cell function) associated with type 2 diabetes.

Comparison of continual insulin or secretagogue treatment in type 2 diabetic patients with alternate insulin-secretagogue administration

BACKGROUND

To compare the compliance and efficacy among three treatment modalities in patients of type 2 diabetes with fairly good islet function.

METHODS

This 38-month open, randomized, prospective study enrolled 536 subjects (HbA1c 9.4+/-0.8%). Patients were divided into three groups including continual insulin injection (I), continual secretagogue administration (S) and alternation of two-month insulin injection and four-month secretagogue treatment (A). At baseline and every three months, HbA1c was measured and a standard bread meal test (100g) was performed.

RESULTS

HbA1c were better controlled in both groups I and A than in S (6.9+/-0.3%, 6.8+/-0.3% vs. 7.6+/-0.5%). Hypoglycemia incidence was much lower in group A than that in I (0.8 times/patient/month vs. 2.4 times/patient/month) also with less weight gain (1.6 kg vs. 2.8 kg/patient/year). From the standard bread meal test, patients in group A got the greatest increment of 2-h C-peptide. Inquiry from all subjects showed that alternate strategy was welcomed by most of them considering for convenience and efficacy.

CONCLUSIONS

Alternate insulin-secretagogue treatment can effectively reduce HbA1c and help to improve islet function with reduced risk of hypoglycemia and weight gain under good compliance.

Islet G protein-coupled receptors as potential targets for treatment of type 2 diabetes

Islet dysfunction - characterized by a combination of defective insulin secretion, inappropriately high glucagon secretion and reduced beta-cell mass - has a central role in the pathophysiology of type 2 diabetes. Several G protein-coupled receptors (GPCRs) expressed in islet beta-cells are known to be involved in the regulation of islet function, and therefore are potential therapeutic targets. This is evident from the recent success of glucagon-like peptide 1 (GLP1) mimetics and dipeptidyl peptidase 4 (DPP4) inhibitors, which promote activation of the GLP1 receptor to stimulate insulin secretion and inhibit glucagon secretion, and also have the potential to increase beta-cell mass. Other islet beta-cell GPCRs that are involved in the regulation of islet function include the glucose-dependent insulinotropic peptide (GIP) receptor, lipid GPCRs, pleiotropic peptide GPCRs and islet biogenic amine GPCRs. This Review summarizes islet GPCR expression, signalling and function, and highlights their potential as targets for the treatment of type 2 diabetes.

Inhibition of human insulin gene transcription by peroxisome proliferator-activated receptor gamma and thiazolidinedione oral antidiabetic drugs

BACKGROUND AND PURPOSE

The transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma) is essential for glucose homeostasis. PPARgamma ligands reducing insulin levels in vivo are used as drugs to treat type 2 diabetes mellitus. Genes regulated by PPARgamma have been found in several tissues including insulin-producing pancreatic islet beta-cells. However, the role of PPARgamma at the insulin gene was unknown. Therefore, the effect of PPARgamma and PPARgamma ligands like rosiglitazone on insulin gene transcription was investigated.

EXPERIMENTAL APPROACH

Reporter gene assays were used in the beta-cell line HIT and in primary mature pancreatic islets of transgenic mice. Mapping studies and internal mutations were carried out to locate PPARgamma-responsive promoter regions.

KEY RESULTS

Rosiglitazone caused a PPARgamma-dependent inhibition of insulin gene transcription in a beta-cell line. This inhibition was concentration-dependent and had an EC(50) similar to that for the activation of a reporter gene under the control of multimerized PPAR binding sites. Also in normal primary pancreatic islets of transgenic mice, known to express high levels of PPARgamma, rosiglitazone inhibited glucose-stimulated insulin gene transcription. Transactivation and mapping experiments suggest that, in contrast to the rat glucagon gene, the inhibition of the human insulin gene promoter by PPARgamma/rosiglitazone does not depend on promoter-bound Pax6 and is attributable to the proximal insulin gene promoter region around the transcription start site from -56 to +18.

CONCLUSIONS AND IMPLICATIONS

The human insulin gene represents a novel PPARgamma target that may contribute to the action of thiazolidinediones in type 2 diabetes mellitus.

Noncanonical activation of Akt/protein kinase B in {beta}-cells by the incretin hormone glucose-dependent insulinotropic polypeptide

Therapeutics based on the actions of the incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), have recently been introduced for the treatment of type 2 diabetes mellitus. The serine/threonine kinase Akt is a major mediator of incretin action on the pancreatic islet, increasing beta-cell mass and function and promoting beta-cell survival. The mechanisms underlying incretin activation of Akt are thought to involve an essential phosphoinositide 3-kinase-mediated phosphorylation of threonine 308, similar to the prototypical Akt activator, insulin-like growth factor-I (IGF-I). In this study, using activity assays on immunoprecipitated Akt, we discovered that GIP and GLP-1 were capable of stimulating Akt in the INS-1 beta-cell line and isolated mouse islets via a mechanism that did not require phosphoinositide 3-kinase or phosphorylation of Thr(308) and Ser(473), and this pathway involved the production of cAMP. Furthermore, we found that GIP stimulated anti-apoptotic signaling via this alternate mode of Akt activation. We conclude that incretins can activate Akt via a novel noncanonical mechanism that may provide an alternative therapeutic target for the treatment of type 2 diabetes mellitus and have broader implications for Akt physiology in human health and disease.

Genetic determinants and molecular pathways in the pathogenesis of Type 2 diabetes

T2DM (Type 2 diabetes mellitus) has reached epidemic proportions worldwide, exerting major health consequences at an individual and public health level alike. Unfortunately, the molecular pathophysiology of diabetes remains incompletely understood, impairing progress towards more effective prevention and treatment strategies. Although the rapid increase in the prevalence of insulin resistance and T2DM over the past several decades highlights a major environmental contribution related to overnutrition, obesity and inactivity, susceptibility is likely to reflect individual differences in complex gene-environment interactions. In the present review, we focus on mediators of genetic and environmental risk for T2DM at a molecular level.

11C-dihydrotetrabenazine PET of the pancreas in subjects with long-standing type 1 diabetes and in healthy controls

Type 2 vesicular monoamine transporter (VMAT2), found in the brain, is also expressed by beta-cells of the pancreas in association with insulin. Preclinical experiments suggested that (11)C-dihydrotetrabenazine PET-measured VMAT2 binding might serve as a biomarker of beta-cell mass. We evaluated the feasibility of (11)C-dihydrotetrabenazine PET quantification of pancreatic VMAT2 binding in healthy subjects and patients with long-standing type 1 diabetes.

METHODS

(11)C-Dihydrotetrabenazine PET was performed on 6 patients and 9 controls. VMAT2 binding potential (BP(ND)) was estimated voxelwise by using the renal cortex as reference tissue. As an index of total pancreatic VMAT2, the functional binding capacity (the sum of voxel BP(ND) x voxel volume) was calculated. Pancreatic BP(ND), functional binding capacity, and stimulated insulin secretion measurements were compared between groups.

RESULTS

The pancreatic mean BP(ND) was decreased in patients (1.86 +/- 0.05) to 86% of control values (2.14 +/- 0.08) (P = 0.01). In controls, but not in patients, BP(ND) correlated with stimulated insulin secretion (r(2) = 0.50, P = 0.03). The average functional binding capacity was decreased by at least 40% in patients (P = 0.001). The changes in functional binding capacity and BP(ND) were less than the near-complete loss of stimulated insulin secretion observed in patients (P = 0.001).

CONCLUSION

These results suggest that (11)C-dihydrotetrabenazine PET allows quantification of VMAT2 binding in the human pancreas. However, BP(ND) and functional binding capacity appear to overestimate beta-cell mass given the near-complete depletion of beta-cell mass in long-standing type 1 diabetes, which may be due to higher nonspecific binding in the pancreas than in the renal cortex.

Emerging dipeptidyl peptidase-4 inhibitors for the treatment of diabetes

Inhibition of dipeptidyl peptidase-4 (DPP-4) prevents the inactivation of glucagon-like peptide-1 (GLP-1). This increases circulating levels of active GLP-1, stimulates insulin secretion and inhibits glucagon secretion, resulting in lowering of glucose levels and improvement of glycemic control in patients with type 2 diabetes. Several DPP-4 inhibitors are emerging for therapeutic use. Most experience exists for sitagliptin, vildagliptin, saxagliptin and alogliptin. They all improve metabolic control in type 2 diabetes in monotherapy and in combination therapy with metformin, sulfonylurea and thiazolidinediones. Vildagliptin and alogliptin have also been shown to improve glycemic control when added to insulin therapy, and sitagliptin improves glycemic control in triple therapy with metformin plus thiazolidinedione. DPP-4 inhibition also shows a favorable safety profile, high tolerability, only a minimal risk of hypoglycemia, and body-weight neutrality. The main clinical indication for DPP-4 inhibitors will be in the early stage of type 2 diabetes, in combination with metformin or other treatments in subjects with inadequate glycemic control on these treatments alone. The durability and long-term safety of DPP-4 inhibition, as well as clinical positioning in relation to GLP-1 mimetics, remain now to be established.

Importance of postprandial glucose levels as a target for glycemic control in type 2 diabetes

Increasing evidence supports the importance of postprandial glucose (PPG) in glycemic control with regard to the development of complications in patients with diabetes. PPG plays a critical role in determining overall glycemic control, particularly in patients who are close to their glycemic goals. Data also indicate that postprandial hyperglycemia may have a greater effect on the development of cardiovascular complications compared with elevated fasting plasma glucose. Several antidiabetic agents that specifically target PPG are currently available, including glinides, glucagon-like peptide-1 mimetics, dipeptidyl peptidase-4 inhibitors, and rapid-acting insulin analogs. A more intensive approach to managing PPG may improve the care of patients with diabetes and, ultimately, the outcome of these patients.

Incretin-based therapies in type 2 diabetes: a review of clinical results

GLP-1 analogues (incretin mimetics) and DPP-4 inhibitors (incretin enhancers) represent new classes of anti-diabetic agents for the treatment of type 2 diabetes. The efficacy and safety of the incretin mimetic exenatide and of the DPP-4 inhibitors, sitagliptin and vildagliptin, have been clearly demonstrated by a very large number of clinical trials. Efficacy was demonstrated in terms of reduction of HbA1c, fasting and postprandial glucose. Moreover, exenatide showed a favourable effect on weight, while DPP-4 inhibitors were neutral with respect to this outcome. The low rate of hypoglycemic events seen in all studies confirms the glucose dependent action of incretins.

Synaptotagmins bind calcium to release insulin

Plasma insulin levels are determined mainly by the rate of exocytosis of the insulin-containing large dense core vesicles (LDCVs) of pancreatic islet beta-cells. This process involves the recruitment of LDCVs to the plasma membrane, where they are docked by the assembly of multiprotein SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes. However, fusion of the two membranes will proceed only in the presence of Ca(2+) ions, implicating a Ca(2+) sensor protein. The synaptotagmin gene family, comprising 15 members, was proposed to act as such Ca(2+) sensor in regulated exocytosis in neurons and neuroendocrine and endocrine cells. Herein, we review the physiological function of the various synaptotagmins with reference to their impact on insulin exocytosis. Cumulating evidence emphasizes the crucial role of synaptotagmin VII and IX as mediators of glucose-induced insulin secretion.

Beta-cell failure as a complication of diabetes

Type 2 diabetes mellitus is a complex disease characterized by beta-cell failure in the setting of insulin resistance. In early stages of the disease, pancreatic beta-cells adapt to insulin resistance by increasing mass and function. As nutrient excess persists, hyperglycemia and elevated free fatty acids negatively impact beta-cell function. This happens by numerous mechanisms, including the generation of reactive oxygen species, alterations in metabolic pathways, increases in intracellular calcium and the activation of endoplasmic reticulum stress. These processes adversely affect beta-cells by impairing insulin secretion, decreasing insulin gene expression and ultimately causing apoptosis. In this review, we will first discuss the regulation of beta-cell mass during normal conditions. Then, we will discuss the mechanisms of beta-cell failure, including glucotoxicity, lipotoxicity and endoplasmic reticulum stress. Further research into mechanisms will reveal the key modulators of beta-cell failure and thus identify possible novel therapeutic targets. Type 2 diabetes mellitus is a multifactorial disease that has greatly risen in prevalence in part due to the obesity and inactivity that characterize the modern Western lifestyle. Pancreatic beta-cells possess the potential to greatly expand their function and mass in both physiologic and pathologic states of nutrient excess and increased insulin demand. beta-cell response to nutrient excess occurs by several mechanisms, including hypertrophy and proliferation of existing beta-cells, increased insulin production and secretion, and formation of new beta-cells from progenitor cells [1, 2]. Failure of pancreatic beta-cells to adequately expand in settings of increased insulin demand results in hyperglycemia and diabetes. In this review, we will first discuss the factors involved in beta-cell growth and then discuss the mechanisms by which beta-cell expansion fails and leads to beta-cell failure and diabetes (Fig. 1).

Switching from NPH insulin to once-daily insulin detemir in basal-bolus-treated patients with diabetes mellitus: data from the European cohort of the PREDICTIVE study

BACKGROUND

The PREDICTIVE study is a multinational observational study designed to follow up patients with diabetes who started insulin detemir (IDet) in routine care. Recruitment started in June 2004 and is ongoing in some countries.

METHODS

We report 12-week follow-up data for patients with type 1 (T1D) or type 2 diabetes (T2D) in the European cohort who, as part of basal-bolus therapy, switched from once- (qd) or twice-daily (bid) neutral protamine Hagedorn insulin (NPH) to qd IDet. End-points - evaluated from patients' records and diaries - were incidence of serious adverse drug reactions, glycaemic parameters, hypoglycaemia and weight change.

RESULTS

A total of 3637 patients were included, n = 1500 T1D [mean age 40.9 years, body mass index (BMI) 25.0 kg/m(2), glycosylated haemoglobin (HbA(1c)) 7.9%] and n = 2137 T2D (mean age 60.5 years, BMI 31.9 kg/m(2), HbA(1c) 8.0%). IDet was well tolerated. Lower overall, major and nocturnal rates of hypoglycaemia were observed in T1D and T2D patients switching from NPH to IDet (overall, T1D: 38.2-18.56 episodes/patient year, p < 0.001; T2D: 13.8-3.3 [corrected] episodes/patient year, p < 0.001). Switching from bid NPH to qd IDet resulted in significant 12-week reductions in HbA(1c) (T1D: -0.40%; T2D: -0.56%; both p < 0.001). Switching from qd NPH to qd IDet, resulted in HbA(1c) reductions of: T1D -0.52%; T2D -0.56%; both p < 0.001. Fasting blood glucose levels were also significantly reduced in patients with T1D or T2D. Overall mean weight changes were: T1D: 0.0 kg, T2D: -0.2 kg after 12 weeks.

CONCLUSION

In routine care, patients with T1D or T2D may be switched from NPH to IDet qd as part of a basal-bolus regimen.

The metabolic syndrome

The "metabolic syndrome" (MetS) is a clustering of components that reflect overnutrition, sedentary lifestyles, and resultant excess adiposity. The MetS includes the clustering of abdominal obesity, insulin resistance, dyslipidemia, and elevated blood pressure and is associated with other comorbidities including the prothrombotic state, proinflammatory state, nonalcoholic fatty liver disease, and reproductive disorders. Because the MetS is a cluster of different conditions, and not a single disease, the development of multiple concurrent definitions has resulted. The prevalence of the MetS is increasing to epidemic proportions not only in the United States and the remainder of the urbanized world but also in developing nations. Most studies show that the MetS is associated with an approximate doubling of cardiovascular disease risk and a 5-fold increased risk for incident type 2 diabetes mellitus. Although it is unclear whether there is a unifying pathophysiological mechanism resulting in the MetS, abdominal adiposity and insulin resistance appear to be central to the MetS and its individual components. Lifestyle modification and weight loss should, therefore, be at the core of treating or preventing the MetS and its components. In addition, there is a general consensus that other cardiac risk factors should be aggressively managed in individuals with the MetS. Finally, in 2008 the MetS is an evolving concept that continues to be data driven and evidence based with revisions forthcoming.

Chop deletion reduces oxidative stress, improves beta cell function, and promotes cell survival in multiple mouse models of diabetes

The progression from insulin resistance to type 2 diabetes is caused by the failure of pancreatic beta cells to produce sufficient levels of insulin to meet the metabolic demand. Recent studies indicate that nutrient fluctuations and insulin resistance increase proinsulin synthesis in beta cells beyond the capacity for folding of nascent polypeptides within the endoplasmic reticulum (ER) lumen, thereby disrupting ER homeostasis and triggering the unfolded protein response (UPR). Chronic ER stress promotes apoptosis, at least in part through the UPR-induced transcription factor C/EBP homologous protein (CHOP). We assessed the effect of Chop deletion in multiple mouse models of type 2 diabetes and found that Chop-/- mice had improved glycemic control and expanded beta cell mass in all conditions analyzed. In both genetic and diet-induced models of insulin resistance, CHOP deficiency improved beta cell ultrastructure and promoted cell survival. In addition, we found that isolated islets from Chop-/- mice displayed increased expression of UPR and oxidative stress response genes and reduced levels of oxidative damage. These findings suggest that CHOP is a fundamental factor that links protein misfolding in the ER to oxidative stress and apoptosis in beta cells under conditions of increased insulin demand.

The dipeptidyl peptidase-4 inhibitor alogliptin in combination with pioglitazone improves glycemic control, lipid profiles, and increases pancreatic insulin content in ob/ob mice

The combination of two agents with different but complementary mechanisms of action is a logical approach for treating patients with type 2 diabetes. Thus, we evaluated chronic combination therapy with alogliptin, a highly selective dipeptidyl peptidase-4 inhibitor that enhances the action of incretins, and pioglitazone, a thiazolidinedione that improves peripheral and hepatic insulin sensitivity. Studies were designed to investigate the chronic metabolic and pancreatic effects of alogliptin (0.03%) plus pioglitazone (0.003%) combination treatment in obese ob/ob mice. After 4-5 weeks of treatment, alogliptin significantly increased plasma active glucagon-like peptide-1 levels up to 4.1-fold and decreased plasma glucagon up to 25%, whereas pioglitazone significantly increased plasma adiponectin up to 1.3-fold. Combination treatment exhibited a complementary effect, increasing plasma insulin levels by 3.2-fold (alogliptin alone, 1.6-fold; pioglitazone alone, 1.5-fold) and decreasing glycosylated hemoglobin by 2.3% (alogliptin alone, 1.0%; pioglitazone alone, 1.5%), and non-fasting and fasting plasma glucose by 37% and 62% (alogliptin alone, 17% and 24%; pioglitazone alone, 30% and 45%), respectively. Combination treatment also decreased plasma triglycerides by 67% and non-esterified fatty acids by 25% (alogliptin alone, 24% and 11%; pioglitazone alone, 54% and 8%). Moreover, combination treatment increased pancreatic insulin content by 2.2-fold (alogliptin alone, 1.3-fold; pioglitazone alone, 1.6-fold), with no significant changes in body weight. These results indicate that combination treatment with alogliptin and pioglitazone improved glycemic control, lipid profiles and increased pancreatic insulin content in ob/ob mice by preventing incretin inactivation and improving insulin resistance. These results provide a strong argument for using alogliptin in combination with pioglitazone.

Prevention and management of hyperglycemia after pancreas transplantation

PURPOSE OF REVIEW

Pancreas transplantation is considered the optimal therapy for patients with insulin-dependent diabetes. Successful pancreas transplantation achieves euglycemia and allows freedom from insulin therapy. Long-term allograft success may be limited by the development of impaired glucose metabolism. The objectives of the present review are to summarize the possible reasons for endocrine pancreatic dysfunction and to focus on its prevention and management and emphasize the role of immunosuppression.

RECENT FINDINGS

The diabetogenic effects of current immunosuppressive agents have been well established. Regimens without corticosteroids and calcineurin-inhibitor minimization or avoidance have been promoted. Recent studies have revisited the pathogenesis of type I and type II diabetes and demonstrated common pathways, including apoptosis induction, for the exhaustion and destruction of the pancreatic islets.

SUMMARY

The immunosuppressive regimens in pancreatic transplantation should be designed and appropriately modified according to the graft immunological and metabolic conditions. New molecules that are able to preserve islet function and maintain optimal insulin secretion should be considered for pancreas transplant recipients.

The diabetogenic effects of excessive ethanol: reducing beta-cell mass, decreasing phosphatidylinositol 3-kinase activity and GLUT-4 expression in rats

The diabetogenic impact of ethanol remains as a focal point of basic and clinical investigations. In this study, Wistar rats were subjected to daily intragastric ethanol administration (10 ml/kg body weight injection with 0 (control), 10, 20 and 33 % (v/v) ethanol in the injections, respectively) for 19 weeks. At the end of the administration, we found that the fasting plasma glucose level of the 33 % (v/v) ethanol-loaded group was 18 % higher than the control. Insulin sensitivity was decreased in a dose-dependent manner in all the ethanol-loaded groups (r - 0.842, P < 0.001) during intraperitoneal insulin tolerance test. Necrotic/haemorrhagic injury was detected in the pancreas and islet beta-cell mass was significantly reduced in the 33 % (v/v) ethanol-loaded rats by immunohistochemical and morphometric analysis. At the molecular level, we detected a dose-dependent attenuation of phosphatidylinositol 3-kinase activity (r - 0.956, P < 0.001) and GLUT-4 expression (GLUT-4 mRNA, r - 0.899, P < 0.001; GLUT-4 protein, r - 0.964, P < 0.001) in skeletal muscle. These results demonstrated that drinking is a conditional aetiological factor for diabetes and excessive ethanol intake is negatively associated with both insulin sensitivity and beta-cell mass. The whole-body insulin resistance might result from the ethanol-induced insulin signalling defects in muscle.

Overexpression of pre-pro-cholecystokinin stimulates beta-cell proliferation in mouse and human islets with retention of islet function

Type 1 and type 2 diabetes result from a deficit in insulin production and beta-cell mass. Methods to expand beta-cell mass are under intensive investigation for the treatment of type 1 and type 2 diabetes. We tested the hypothesis that cholecystokinin (CCK) can promote beta-cell proliferation. We treated isolated mouse and human islets with an adenovirus containing the CCK cDNA (AdCMV-CCK). We measured [(3)H]thymidine and BrdU incorporation into DNA and additionally, performed flow cytometry analysis to determine whether CCK overexpression stimulates beta-cell proliferation. We studied islet function by measuring glucose-stimulated insulin secretion and investigated the cell cycle regulation of proliferating beta-cells by quantitative RT-PCR and Western blot analysis. Overexpression of CCK stimulated [(3)H]thymidine incorporation into DNA 5.0-fold and 15.8-fold in mouse and human islets, respectively. AdCMV-CCK treatment also stimulated BrdU incorporation into DNA 10-fold and 21-fold in mouse and human beta-cells, respectively. Glucose-stimulated insulin secretion was unaffected by CCK expression. Analysis of cyclin and cdk mRNA and protein abundance revealed that CCK overexpression increased cyclin A, cyclin B, cyclin E, cdk1, and cdk2 with no change in cyclin D1, cyclin D2, cyclin D3, cdk4, or cdk6 in mouse and human islets. Additionally, AdCMV-CCK treatment of CCK receptor knockout and wild-type mice resulted in equal [(3)H]thymidine incorporation. CCK is a beta-cell proliferative factor that is effective in both mouse and human islets. CCK triggers beta-cell proliferation without disrupting islet function, up-regulates a distinct set of cell cycle regulators in islets, and signals independently of the CCK receptors.

Beneficial effects of insulin on glycemic control and beta-cell function in newly diagnosed type 2 diabetes with severe hyperglycemia after short-term intensive insulin therapy

OBJECTIVE

To evaluate whether treatment with insulin is advantageous compared with oral antidiabetes agents in newly diagnosed type 2 diabetes with severe hyperglycemia after short-term intensive insulin therapy.

RESEARCH DESIGN AND METHODS

Newly diagnosed type 2 diabetic patients with severe hyperglycemia were hospitalized and treated with intensive insulin injections for 10-14 days. The oral glucose tolerance test (OGTT) was performed after intensive insulin treatment. After discharge, the patients were randomized to receive either insulin injections or oral antidiabetes drugs (OADs) for further management. The OGTT was repeated 6 months later, and beta-cell function and insulin sensitivity were evaluated again. These subjects were continually followed up for another 6 months to evaluate their long-term glycemic control.

RESULTS

At the 6th month of the study, the A1C level was significantly lower in the insulin group than in the OAD group (6.33 +/- 0.70% vs. 7.50 +/- 1.50%; P = 0.002). During the follow-up visit, the A1C level was still better in the insulin group (6.78 +/- 1.21% vs. 7.84 +/- 1.74%; P = 0.009). All parameters regarding beta-cell function measured in the OGTT were improved significantly in both groups after 6 months of treatment. Compared with the OAD group, the homeostasis model assessment of beta-cell function index, insulin area under the curve, and insulinogenic index were better in the insulin group.

CONCLUSIONS

A 6-month course of insulin therapy, compared with OAD treatment, could more effectively achieve adequate glycemic control and significant improvement of beta-cell function in new-onset type 2 diabetic patients with severe hyperglycemia.

Efficacy of the dipeptidyl peptidase IV inhibitor isoleucine thiazolidide (P32/98) in fatty Zucker rats with incipient and manifest impaired glucose tolerance

AIM

Incretin enhancers are a new class of antidiabetic drugs with promising therapeutic potential for type 2 diabetes. Therapeutic intervention in prediabetes is an attractive strategy for preventing or delaying diabetes onset. The aim of the present study was to investigate the therapeutic effects of incretin enhancement on incipient impaired glucose tolerance (iIGT) and manifest IGT (mIGT) using the dipeptidyl peptidase IV (DPP-4) inhibitor P32/98- and fatty Zucker rat (ZR, fa/fa) as a model.

METHODS

ZRs were classified into groups with iIGT and mIGT (n = 10 per group). P32/98 (21.61 mg/kg body weight) was administered orally to ZR with iIGT and mIGT once daily for 6 and 3 weeks respectively. Assessments included body weight, morning blood glucose and insulin, oral glucose tolerance test (oGTT; 2 g glucose/kg), plasma parameters and blood glucose day-night profile (DNP). In addition, glucose responsiveness of isolated islets and islet morphology were analysed.

RESULTS

P32/98 decreased non-fasting morning blood glucose more effectively in ZR with iIGT than in ZR with mIGT. Compared with study entry, P32/98 improved DNP of blood glucose in ZR with mIGT and nearly normalized DNP in ZR with iIGT. An acute bolus of inhibitor reduced glucose load during oGTT in rats chronically treated with placebo or P32/98. In contrast to placebo-treated rats, rats receiving long-term treatment with P32/98 required less insulin during oGTT. This effect was larger in rats with iIGT vs. rats with mIGT. In isolated pancreatic islets of ZR with mIGT, treatment with P32/98 decreased pancreatic insulin content and increased glucose responsiveness, while the beta-cell volume density was unaffected. P32/98 significantly reduced triglycerides and non-esterified fatty acids. Intestinal growth was comparable between inhibitor- and placebo-treated fatty rats.

CONCLUSIONS

Enhancement of incretin with the DPP-4 inhibitor P32/98 has therapeutic effects in hyperinsulinaemia, hyperglycaemia and IGT in ZR with iIGT and mIGT. Apparently, administration of P32/98 in ZR with iIGT results in more efficient beta-cell function, which is associated with less need for insulin to cope with deterioration of glucose tolerance. Importantly, P32/98 has a strong effect on dyslipidaemia in mIGT. P32/98 has no side effect on intestinal growth. Daily intake of P32/98 is a promising strategy for treatment of glucose intolerance and has the potential to prevent type 2 diabetes.

Beta-cell apoptosis in type 2 diabetes: quantitative and functional consequences

Type 2 diabetes, the most common form of diabetes in humans, is characterized by impaired insulin secretion paralleled by a progressive decline in beta-cell function and chronic insulin resistance. Several authors have showed that in type 2 diabetes there is a reduction of islet and/or insulin-containing cell mass or volume. Regulation of the beta-cell mass appears to involve a balance of beta-cell replication and apoptosis but, at the molecular level, pancreatic beta-cell loss by apoptosis appears to play an important role in the development of insulin deficiency and the onset and/or progression of the disease. The mechanisms favoring apoptosis in type 2 diabetic pancreatic islets and new potential therapeutic approaches to prevent beta-cell death and maintain beta-cell mass are discussed.

Selective small-molecule agonists of G protein-coupled receptor 40 promote glucose-dependent insulin secretion and reduce blood glucose in mice

OBJECTIVE

Acute activation of G protein-coupled receptor 40 (GPR40) by free fatty acids (FFAs) or synthetic GPR40 agonists enhances insulin secretion. However, it is still a matter of debate whether activation of GPR40 would be beneficial for the treatment of type 2 diabetes, since chronic exposure to FFAs impairs islet function. We sought to evaluate the specific role of GPR40 in islets and its potential as a therapeutic target using compounds that specifically activate GPR40.

RESEARCH DESIGN AND METHODS

We developed a series of GPR40-selective small-molecule agonists and studied their acute and chronic effects on glucose-dependent insulin secretion (GDIS) in isolated islets, as well as effects on blood glucose levels during intraperitoneal glucose tolerance tests in wild-type and GPR40 knockout mice (GPR40(-/-)).

RESULTS

Small-molecule GPR40 agonists significantly enhanced GDIS in isolated islets and improved glucose tolerance in wild-type mice but not in GPR40(-/-) mice. While a 72-h exposure to FFAs in tissue culture significantly impaired GDIS in islets from both wild-type and GPR40(-/-) mice, similar exposure to the GPR40 agonist did not impair GDIS in islets from wild-type mice. Furthermore, the GPR40 agonist enhanced insulin secretion in perfused pancreata from neonatal streptozotocin-induced diabetic rats and improved glucose levels in mice with high-fat diet-induced obesity acutely and chronically.

CONCLUSIONS

GPR40 does not mediate the chronic toxic effects of FFAs on islet function. Pharmacological activation of GPR40 may potentiate GDIS in humans and be beneficial for overall glucose control in patients with type 2 diabetes.

Incretin mimetics and dipeptidyl peptidase-4 inhibitors: innovative treatment therapies for type 2 diabetes

The prevalence of diabetes and impaired glucose tolerance is predicted to dramatically increase over the next two decades. Clinical therapies for type 2 diabetes mellitus (T2DM) have traditionally included lifestyle modification, oral anti-diabetic agents, and ultimately insulin initiation. In this report, we review the clinical trial results of two innovative T2DM treatment therapies that are based on the glucoregulatory effects of incretin hormones. Incretin mimetics are peptide drugs that mimic several of the actions of glucagon-like peptide-1 (GLP-1) and have been shown to lower glycated hemoglobin (A1C) levels in patients with T2DM. Additionally, incretin mimetics lower postprandial and fasting glucose, suppress elevated glucagon release, and are associated with progressive weight reduction. Dipeptidyl peptidase-4 (DPP-4) inhibitors increase endogenous GLP-1 levels by inhibiting the enzymatic degradation of GLP-1. Clinical studies in patients with T2DM have shown that DPP-4 inhibitors reduce elevated A1C, lower postprandial and fasting glucose, suppress glucagon release, and are weight neutral. Collectively, these new drugs, given in combination with other antidiabetic agents, such as metformin, sulfonylureas, and/or thiazolidinediones, can help restore glucose homeostasis in poorly controlled patients with T2DM.

Effect of intensive insulin therapy on beta-cell function and glycaemic control in patients with newly diagnosed type 2 diabetes: a multicentre randomised parallel-group trial

BACKGROUND

Early intensive insulin therapy in patients with newly diagnosed type 2 diabetes might improve beta-cell function and result in extended glycaemic remissions. We did a multicentre, randomised trial to compare the effects of transient intensive insulin therapy (continuous subcutaneous insulin infusion [CSII] or multiple daily insulin injections [MDI]) with oral hypoglycaemic agents on beta-cell function and diabetes remission rate.

METHODS

382 patients, aged 25-70 years, were enrolled from nine centres in China between September, 2004, and October, 2006. The patients, with fasting plasma glucose of 7.0-16.7 mmol/L, were randomly assigned to therapy with insulin (CSII or MDI) or oral hypoglycaemic agents for initial rapid correction of hyperglycaemia. Treatment was stopped after normoglycaemia was maintained for 2 weeks. Patients were then followed-up on diet and exercise alone. Intravenous glucose tolerance tests were done and blood glucose, insulin, and proinsulin were measured before and after therapy withdrawal and at 1-year follow-up. Primary endpoint was time of glycaemic remission and remission rate at 1 year after short-term intensive therapy. Analysis was per protocol. This study was registered with ClinicalTrials.gov, number NCT00147836.

FINDINGS

More patients achieved target glycaemic control in the insulin groups (97.1% [133 of 137] in CSII and 95.2% [118 of 124] in MDI) in less time (4.0 days [SD 2.5] in CSII and 5.6 days [SD 3.8] in MDI) than those treated with oral hypoglycaemic agents (83.5% [101 of 121] and 9.3 days [SD 5.3]). Remission rates after 1 year were significantly higher in the insulin groups (51.1% in CSII and 44.9% in MDI) than in the oral hypoglycaemic agents group (26.7%; p=0.0012). beta-cell function represented by HOMA B and acute insulin response improved significantly after intensive interventions. The increase in acute insulin response was sustained in the insulin groups but significantly declined in the oral hypoglycaemic agents group at 1 year in all patients in the remission group.

INTERPRETATION

Early intensive insulin therapy in patients with newly diagnosed type 2 diabetes has favourable outcomes on recovery and maintenance of beta-cell function and protracted glycaemic remission compared with treatment with oral hypoglycaemic agents.

Combination of the insulin sensitizer, pioglitazone, and the long-acting GLP-1 human analog, liraglutide, exerts potent synergistic glucose-lowering efficacy in severely diabetic ZDF rats

OBJECTIVE

Severe insulin resistance and impaired pancreatic beta-cell function are pathophysiological contributors to type 2 diabetes, and ideally, antihyperglycaemic strategies should address both.

RESEARCH DESIGN AND METHODS

Therapeutic benefits of combining the long-acting human glucagon-like peptide-1 (GLP-1) analog, liraglutide (0.4 mg/kg/day), with insulin sensitizer, pioglitazone (10 mg/kg/day), were assessed in severely diabetic Zucker diabetic fatty rats for 42 days. Impact on glycaemic control was assessed by glycated haemoglobin (HbA(1C)) at day 28 and by oral glucose tolerance test at day 42.

RESULTS

Liraglutide and pioglitazone synergistically improved glycaemic control as reflected by a marked decrease in HbA(1C) (liraglutide + pioglitazone: 4.8 +/- 0.3%; liraglutide: 8.8 +/- 0.6%; pioglitazone: 7.9 +/- 0.4%; vehicle: 9.7 +/- 0.3%) and improved oral glucose tolerance at day 42 (area under the curve; liraglutide + pioglitazone: 4244 +/- 445 mmol/l x min; liraglutide: 7164 +/- 187 mmol/l x min; pioglitazone: 7430 +/- 446 mmol/l x min; vehicle: 8093 +/- 139 mmol/l x min). A 24-h plasma glucose profile at day 38 was significantly decreased only in the liraglutide + pioglitazone group. In addition, 24-h insulin profile was significantly elevated only in the liraglutide + pioglitazone group. Liraglutide significantly decreased food intake alone and in combination with pioglitazone, while pioglitazone alone increased cumulated food intake. As a result, rats on liraglutide alone gained significantly less weight than vehicle-treated rats, whereas rats on pioglitazone alone gained significantly more body weight than vehicle-treated rats. However, combination therapy with liraglutide and pioglitazone caused the largest weight gain, probably reflecting marked improvement of energy balance because of reduction of glucosuria.

CONCLUSIONS

Combination therapy with insulinotropic GLP-1 agonist liraglutide and insulin sensitizer, pioglitazone, improves glycaemic control above and beyond what would be expected from additive effects of the two antidiabetic agents.

Inducible nitric oxide synthase-nitric oxide plays an important role in acute and severe hypoxic injury to pancreatic beta cells

BACKGROUND

Islet transplantation is a potential strategy to cure type 1 diabetes mellitus. However, a substantial part of the islet graft becomes nonfunctional due to several factors including hypoxia. However, the precise mechanism of cell damage is largely unknown in hypoxic exposure to pancreatic beta cells. The aim of the present study was to investigate whether acute and severe hypoxic injury could involve inducible nitric oxide synthase (iNOS)-nitric oxide (NO) signaling in beta cells.

METHODS

The rat beta cell line (INS-1) and primary rat islets were incubated in an anoxic chamber. Cell viability was determined by propium iodide staining or cell counting kit. The expression of iNOS mRNA and protein was examined using reverse-transcription polymerase chain reaction and Western blot analysis. NO production was measured as nitrite accumulation by Griess reagent method.

RESULTS

After hypoxic exposure, marked cell death occurred in INS-1 cells and rat islets, accompanied by increase in activated caspase-3 expression. NO production was increased in the culture medium in a time-dependent manner. Increase in expression of iNOS mRNA and protein was found. Pretreatment with a selective iNOS inhibitor, 1400W, significantly prevented cell death during hypoxia. In addition, hypoxia activated c-Jun N-terminal kinase (JNK) significantly, but the addition of 1400W inhibited hypoxia-induced JNK phosphorylation.

CONCLUSIONS

Our data suggest that iNOS-NO plays an important role in acute and severe hypoxic injury to pancreatic beta cells. Therefore, iNOS-NO might be a potential therapeutic target for preserving beta cell survival in islet transplantation through prevention of hypoxia-mediated cell death.

Noninvasive in vivo imaging of pancreatic islet cell biology

Advanced imaging techniques have become a valuable tool in the study of complex biological processes at the cellular level in biomedical research. Here, we introduce a new technical platform for noninvasive in vivo fluorescence imaging of pancreatic islets using the anterior chamber of the eye as a natural body window. Islets transplanted into the mouse eye engrafted on the iris, became vascularized, retained cellular composition, responded to stimulation and reverted diabetes. Laser-scanning microscopy allowed repetitive in vivo imaging of islet vascularization, beta cell function and death at cellular resolution. Our results thus establish the basis for noninvasive in vivo investigations of complex cellular processes, like beta cell stimulus-response coupling, which can be performed longitudinally under both physiological and pathological conditions.