Beta- and alpha-cell dysfunction in type 2 diabetes

Modeling of Ultrasound Stimulation of Adolescent Pancreas for Insulin Release Therapy

OBJECTIVES

Our previous published studies have focused on safety and effectiveness of using therapeutic ultrasound (TUS) for treatment of type 2 diabetes mellitus (T2DM) in preclinical models. Here we present a set of simulation studies to explore potential ultrasound application schemes that would be feasible in a clinical setting.

METHODS

Using the multiphysics modeling tool OnScale, we created two-dimensional (2D) models of the human abdomen from CT images captured from one normal weight adolescent patient, and one obese adolescent patient. Based on our previous studies, the frequency of our TUS was 1 MHz delivered from a planar unfocused transducer. We tested five different insonation angles, as well as four ultrasound intensities combined with four different duty factors and five durations of application to explore how these variables effect the peak pressure and temperature delivered to the pancreas as well as surrounding tissue in the model.

RESULTS

We determined that ultrasound applied directly from the anterior of the patient abdomen at 5 W/cm2 delivered consistent acoustic pressures to the pancreas at the levels which we have previously found to be effective at inducing an insulin release from preclinical models.

CONCLUSIONS

Our modeling work indicates that it may be feasible to non-invasively apply TUS in clinical treatment of T2DM.

Diabetes mellitus: what the neurologists need to know

Diabetes mellitus is a common condition associated with numerous complications and comorbidities. The diabetes spectrum includes type 1, type 2 and other forms of diabetes, which may be associated with medical therapies and genetic factors. Type 2 diabetes is managed with lifestyle, oral therapies, non-insulin-based injectables and subsequently insulin. Type 1 diabetes requires insulin from the time of diagnosis. In recent years, there have been considerable developments in the therapies available to treat type 2 diabetes and some of these also afford cardiorenal protection. This review summarises the nature, complications and therapeutic advances in the field of diabetes and provides a concise review for neurologists. Managing diabetes optimally prevents complications and all medical specialties need a basic understanding of the principles involved in diabetes care.

Angiotensin(1-7) activates MAS-1 and upregulates CFTR to promote insulin secretion in pancreatic β-cells: the association with type 2 diabetes

OBJECTIVE

The beneficial effect of angiotensin(1-7) (Ang(1-7)), via the activation of its receptor, MAS-1, has been noted in diabetes treatment; however, how Ang(1-7) or MAS-1 affects insulin secretion remains elusive and whether the endogenous level of Ang(1-7) or MAS-1 is altered in diabetic individuals remains unexplored. We recently identified an important role of cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-activated Cl- channel, in the regulation of insulin secretion. Here, we tested the possible involvement of CFTR in mediating Ang(1-7)'s effect on insulin secretion and measured the level of Ang(1-7), MAS-1 as well as CFTR in the blood of individuals with or without type 2 diabetes.

METHODS

Ang(1-7)/MAS-1/CFTR pathway was determined by specific inhibitors, gene manipulation, Western blotting as well as insulin ELISA in a pancreatic β-cell line, RINm5F. Human blood samples were collected from 333 individuals with (n = 197) and without (n = 136) type 2 diabetes. Ang(1-7), MAS-1 and CFTR levels in the human blood were determined by ELISA.

RESULTS

In RINm5F cells, Ang(1-7) induced intracellular cAMP increase, cAMP-response element binding protein (CREB) activation, enhanced CFTR expression and potentiated glucose-stimulated insulin secretion, which were abolished by a selective CFTR inhibitor, RNAi-knockdown of CFTR, or inhibition of MAS-1. In human subjects, the blood levels of MAS-1 and CFTR, but not Ang(1-7), were significantly higher in individuals with type 2 diabetes as compared to those in non-diabetic healthy subjects. In addition, blood levels of MAS-1 and CFTR were in significant positive correlation in type-2 diabetic but not non-diabetic subjects.

CONCLUSION

These results suggested that MAS-1 and CFTR as key players in mediating Ang(1-7)-promoted insulin secretion in pancreatic β-cells; MAS-1 and CFTR are positively correlated and both upregulated in type 2 diabetes.

Personalized Type 2 Diabetes Management: An Update on Recent Advances and Recommendations

Previous guidelines for the treatment of people with type 2 diabetes mellitus (T2D) have relied heavily upon rigid algorithms for the sequential addition of pharmacotherapies to achieve target glycemic control. More recent guidelines advocate a personalized approach for diabetes treatment, to improve patient satisfaction, quality of life, medication adherence and overall health outcomes. Clinicians should work with patients to develop personalized goals for their treatment, including targeted glycemic control, weight management, prevention and treatment of associated comorbidities and avoidance of complications such as hypoglycemia. Factors that affect the intensity of treatment and choice of pharmacotherapy should include medical and patient influences. Medical considerations include the diabetes phenotype, biomarkers including genetic tests, and the presence of comorbidities such as cardiovascular, renal, or hepatic disease. Patient factors include their treatment preference, age and life expectancy, diabetes duration, hypoglycemia fear and unawareness, psychological and social circumstances. The use of a personalized approach in the management of people with T2D can reduce the cost and failure associated with the algorithmic "one-size-fits-all" approach, to anticipate disease progression, improve the response to diabetes pharmacotherapy and reduce the incidence of diabetes-associated complications. Ultimately, the use of personalized medicine in people with T2D should improve medication adherence, patient satisfaction and quality of life to reduce diabetes distress and improve physical health outcomes.

Live-cell imaging of glucose-induced metabolic coupling of β and α cell metabolism in health and type 2 diabetes

Type 2 diabetes is characterized by β and α cell dysfunction. We used phasor-FLIM (Fluorescence Lifetime Imaging Microscopy) to monitor oxidative phosphorylation and glycolysis in living islet cells before and after glucose stimulation. In healthy cells, glucose enhanced oxidative phosphorylation in β cells and suppressed oxidative phosphorylation in α cells. In Type 2 diabetes, glucose increased glycolysis in β cells, and only partially suppressed oxidative phosphorylation in α cells. FLIM uncovers key perturbations in glucose induced metabolism in living islet cells and provides a sensitive tool for drug discovery in diabetes.

A Review on Cellular and Molecular Mechanisms Linked to the Development of Diabetes Complications

Modern lifestyle, changing eating habits and reduced physical work have been known to culminate into making diabetes a global pandemic. Hyperglycemia during the course of diabetes is an important causative factor for the development of both microvascular (retinopathy, nephropathy and neuropathy) and macrovascular (coronary artery disease, stroke and peripheral artery disease) complications. In this article, we summarize several mechanisms accountable for the development of both microvascular and macrovascular complications of diabetes. Several metabolic and cellular events are linked to the augmentation of oxidative stress like the activation of advanced glycation end products (AGE) pathway, polyol pathway, Protein Kinase C (PKC) pathway, Poly-ADP Ribose Polymerase (PARP) and hexosamine pathway. Oxidative stress also leads to the production of reactive oxygen species (ROS) like hydroxyl radical, superoxide anion and peroxides. Enhanced levels of ROS rescind the anti-oxidant defence mechanisms associated with superoxide dismutase, glutathione and ascorbic acid. Moreover, ROS triggers oxidative damages at the level of DNA, protein and lipids, which eventually cause cell necrosis or apoptosis. These physiological insults may be related to the microvascular complications of diabetes by negatively impacting the eyes, kidneys and the brain. While underlying pathomechanism of the macrovascular complications is quite complex, hyperglycemia associated atherosclerotic abnormalities like changes in the coagulation system, thrombin formation, fibrinolysis, platelet and endothelial function and vascular smooth muscle are well proven. Since hyperglycemia also modulates the vascular inflammation, cytokines, macrophage activation and gene expression of growth factors, elevated blood glucose level may play a central role in the development of macrovascular complications of diabetes. Taken collectively, chronic hyperglycemia and increased production of ROS are the miscreants for the development of microvascular and macrovascular complications of diabetes.

Phoenixin: More than Reproductive Peptide

Phoenixin (PNX) neuropeptide is a cleaved product of the Smim20 protein. Its most common isoforms are the 14- and 20-amino acid peptides. The biological functions of PNX are mediated via the activation of the GPR173 receptor. PNX plays an important role in the central nervous system (CNS) and in the female reproductive system where it potentiates LH secretion and controls the estrus cycle. Moreover, it stimulates oocyte maturation and increases the number of ovulated oocytes. Nevertheless, PNX not only regulates the reproduction system but also exerts anxiolytic, anti-inflammatory, and cell-protective effects. Furthermore, it is involved in behavior, food intake, sensory perception, memory, and energy metabolism. Outside the CNS, PNX exerts its effects on the heart, ovaries, adipose tissue, and pancreatic islets. This review presents all the currently available studies demonstrating the pleiotropic effects of PNX.

Therapeutic Ultrasound-Induced Insulin Release in Vivo

The tolerability and efficacy of low-frequency, low-intensity therapeutic ultrasound-induced insulin release was investigated in a pre-clinical in vivo murine model. The treatment groups received a single 5-min continuous sonication at 1 MHz and 1.0 W/cm². Insulin and glucagon levels in the serum were determined using enzyme-linked immunosorbent assay. The pancreas was excised and sectioned for histologic analysis. In terminal studies, we observed a moderate (∼50 pM) but significant increase in blood insulin concentration in vivo immediately after sonication compared with a decrease of approximately 60 pM in sham animals (n < 6, p < 0.005). No difference was observed in the change in glucose or glucagon concentrations between groups. Comparisons of hematoxylin and eosin-stained terminal and survival pancreatic tissue revealed no visible differences or evidence of damage. This study is the first step in assessing the translational potential of therapeutic ultrasound as a treatment for early stages of type 2 diabetes.

Natural phenolic compounds potentiate hypoglycemia via inhibition of Dipeptidyl peptidase IV

Dipeptidyl peptidase IV (DPP IV) is a surface glycoprotein that can degrade glucagon like pepetide-1 (GLP-1) by decreasing blood sugar. Herbal medicines for diabetic therapy are widely used with acceptable efficacy but unsatisfied in advances. DPP IV was chosen as a template to employ molecular docking via Discovery Studio to search for natural phenolic compounds whether they have the inhibitory function of DPP IV. Then, docking candidates were validated and further performed signal pathway via Caco-2, C2C12, and AR42J cells. Lastly, a diet-induced diabetes in mice were applied to examine the efficacy and toxicity of hit natural phenolic products in long-term use (in vivo). After screening, curcumin, syringic acid, and resveratrol were found in high affinity with DPP IV enzymes. In enzymatic tests, curcumin and resveratrol showed potential inhibition of DPP IV. In vitro assays, curcumin inhibited of DPP IV activity in Caco-2 cells and ERK phosphorylation in C2C12 cells. Additionally, curcumin attenuated blood sugar in S961-treated C57BL/6 mice and in diet-induced diabetic ICR mice and long-term regulate HbA1c in diabetic mice. Curcumin targeted to DPP IV for reducing blood glucose, it possesses potential and alternative substitution of synthetic clinical drugs for the medication of diabetes.

Association of glucagon-to-insulin ratio and nonalcoholic fatty liver disease in patients with type 2 diabetes mellitus

OBJECTIVE

The aim of this study is to investigate the association between glucagon-to-insulin ratio and the presence of nonalcoholic fatty liver disease on ultrasonography in participants with type 2 diabetes mellitus.

RESEARCH DESIGN AND METHODS

This cross-sectional study was performed with data obtained from 172 participants with type 2 diabetes mellitus admitted to a University hospital of Korea. Participants were assessed for serum fasting and postprandial serum glucagon-to-insulin ratio and divided into tertiles. Nonalcoholic fatty liver disease was defined as ultrasonographically detected fatty liver.

RESULTS

Prevalence of nonalcoholic fatty liver disease was significantly decreased across tertile of fasting and postprandial glucagon-to-insulin ratio ( p = 0.009 for trend, p = 0.001 for trend, respectively). Lower glucagon-to-insulin ratio was significantly associated with the presence of nonalcoholic fatty liver disease even after adjustment for potential confounding variables [fasting glucagon-to-insulin ratio: odds ratio (95% confidence interval), 2.68 (1.08-6.86)], postprandial glucagon-to-insulin ratio: [2.72 (1.03-7.35)]. The participants in the lowest tertile of fasting glucagon-to-insulin ratio had higher body mass index, visceral fat thickness, subcutaneous fat thickness, homeostasis model assessment-insulin resistance and shorter duration of diabetes mellitus.

CONCLUSION

This study suggests that lower glucagon relative insulin may be independently associated with nonalcoholic fatty liver disease in participants with type 2 diabetes.

Ultrasound-Induced Insulin Release as a Potential Novel Treatmentfor Type 2 Diabetes Mellitus

Therapeutic ultrasound presents a potential novel treatment for type 2 diabetes mellitus that utilizes the non-invasive application of ultrasound energy to treat secretory defects in the earlier stages of the disease. Our previous studies have shown that ultrasound is capable of stimulating insulin release from pancreatic beta cells, safely and effectively. This study aims to both examine the calcium-dependent mechanisms of ultrasound-mediated insulin release from pancreatic beta cells using three complementary modalities - carbon fiber amperometry, ELISA studies, and Ca2+ fluorescence imaging - and to study the translational potential of therapeutic ultrasound using transgenic hyperglycemic mice for safety and efficacy studies.

Generation of Scaffold-free, Three-dimensional Insulin Expressing Pancreatoids from Mouse Pancreatic Progenitors In Vitro

The pancreas is a complex organ composed of many different cell types that work together to regulate blood glucose homeostasis and digestion. These cell types include enzyme-secreting acinar cells, an arborized ductal system responsible for the transportation of enzymes to the gut, and hormone-producing endocrine cells. Endocrine beta-cells are the sole cell type in the body that produce insulin to lower blood glucose levels. Diabetes, a disease characterized by a loss or the dysfunction of beta-cells, is reaching epidemic proportions. Thus, it is essential to establish protocols to investigate beta-cell development that can be used for screening purposes to derive the drug and cell-based therapeutics. While the experimental investigation of mouse development is essential, in vivo studies are laborious and time-consuming. Cultured cells provide a more convenient platform for screening; however, they are unable to maintain the cellular diversity, architectural organization, and cellular interactions found in vivo. Thus, it is essential to develop new tools to investigate pancreatic organogenesis and physiology. Pancreatic epithelial cells develop in the close association with mesenchyme from the onset of organogenesis as cells organize and differentiate into the complex, physiologically competent adult organ. The pancreatic mesenchyme provides important signals for the endocrine development, many of which are not well understood yet, thus difficult to recapitulate during the in vitro culture. Here, we describe a protocol to culture three-dimensional, cellular complex mouse organoids that retain mesenchyme, termed pancreatoids. The e10.5 murine pancreatic bud is dissected, dissociated, and cultured in a scaffold-free environment. These floating cells self-assemble with mesenchyme enveloping the developing pancreatoid and a robust number of endocrine beta-cells developing along with the acinar and the duct cells. This system can be used to study the cell fate determination, structural organization, and morphogenesis, cell-cell interactions during organogenesis, or for the drug, small molecule, or genetic screening.

Calcium-dependent ultrasound stimulation of secretory events from pancreatic beta cells

BACKGROUND

Our previous studies have indicated that ultrasound can stimulate the release of insulin from pancreatic beta cells, providing a potential novel treatment for type 2 diabetes. The purpose of this study was to explore the temporal dynamics and Ca2+-dependency of ultrasound-stimulated secretory events from dopamine-loaded pancreatic beta cells in an in vitro setup.

METHODS

Carbon fiber amperometry was used to detect secretion from INS-1832/13 beta cells in real time. The levels of released insulin were also measured in response to ultrasound treatment using insulin-specific ELISA kit. Beta cells were exposed to continuous wave 800 kHz ultrasound at intensities of 0.1 W/cm2, 0.5 W/cm2 and 1 W/cm2 for several seconds. Cell viability tests were done with trypan blue dye exclusion test and MTT analysis.

RESULTS

Carbon fiber amperometry experiments showed that application of 800 kHz ultrasound at intensities of 0.5 and 1 W/cm2 was capable of stimulating secretory events for durations lasting as long as the duration of the stimulus. Furthermore, the amplitude of the detected peaks was reduced by 64% (p < 0.01) when extracellular Ca2+ was chelated with 10 mM EGTA in cells exposed to ultrasound intensity of 0.5 W/cm2. Measurements of released insulin in response to ultrasound stimulation showed complete inhibition of insulin secretion by chelating extracellular Ca2+ with 10 mM EGTA (p < 0.01). Viability studies showed that 800 kHz, 0.5 W/cm2 ultrasound did not cause any significant effects on viability and metabolic activity in cells exposed to ultrasound as compared to sham-treated cells.

CONCLUSIONS

Our results demonstrated that application of ultrasound was capable of stimulating the release of insulin from pancreatic beta cells in a safe, controlled and Ca2+-dependent manner.

Encapsulation of 16-Hydroxycleroda-3,13-Dine-16,15-Olide in Mesoporous Silica Nanoparticles as a Natural Dipeptidyl Peptidase-4 Inhibitor Potentiated Hypoglycemia in Diabetic Mice

Natural supplements comprise good efficacy with less adverse effects as against diabetic therapy, but their advancement as anti-diabetic agents is unsatisfactory with regard to the delivery system. Dipeptidyl peptidase-4 (DPP4)/CD26) can degrade glucagon-like pepetide-1 (GLP-1) which renders a decrease of blood glucose levels. 16-hydroxycleroda-3,13-dine-16,15-olide (HCD) extracted from Polyalthia longifolia, exhibits numerous medicinal potentials including hypoglycemic potential. On consideration of HCD application, the bioavailability is affected by low solubility. Extended experiments of anti-diabetic efficacy confirmed HCD biocompatible with mesoporous silica nanoparticles (MSNs) encapsulation resulted in a sustained release property in delivering HCD for the inhibition of DPP4 via the activity and protein levels of DPP4 analysis. In the enzymatic activity assay, MSN-HCD directly changed DPP4 activity. Moreover, MSN-HCD nanoparticles were treated with Caco-2 cells and the protein levels of DPP4 determined within the cells. The results revealed that MSN-HCD caused reduction of DPP4 activity in a time- and dose-dependent fashion. Orally administered MSN-HCD in diet-induced diabetic mice alleviated blood glucose via an oral glucose tolerance test. In addition, administration of MSN-HCD for five weeks revealed that the biochemical cues such as pyruvate transaminase (GPT), glutamate oxaloacetate transaminase (GOT), triglycerides (TG), cholesterol (CHO), and glycated hemoglobin (HbA1c) in mice were commendable as further confirmation of MSN-HCD efficacy and less adverse effects in down-regulation of hyperglycemia. Furthermore, this formulation effectively controlled blood glucose and significantly decreased the body weight of mice, suggesting that MSN-HCD exerts natural DPP4 inhibitor as a potential clinical drug for the treatment of diabetes.

Bridging Type 2 Diabetes and Alzheimer's Disease: Assembling the Puzzle Pieces in the Quest for the Molecules With Therapeutic and Preventive Potential

Type 2 diabetes (T2D) and Alzheimer's disease (AD) are two age-related amyloid diseases that affect millions of people worldwide. Broadly supported by epidemiological data, the higher incidence of AD among type 2 diabetic patients led to the recognition of T2D as a tangible risk factor for the development of AD. Indeed, there is now growing evidence on brain structural and functional abnormalities arising from brain insulin resistance and deficiency, ultimately highlighting the need for new approaches capable of preventing the development of AD in type 2 diabetic patients. This review provides an update on overlapping pathophysiological mechanisms and pathways in T2D and AD, such as amyloidogenic events, oxidative stress, endothelial dysfunction, aberrant enzymatic activity, and even shared genetic background. These events will be presented as puzzle pieces put together, thus establishing potential therapeutic targets for drug discovery and development against T2D and diabetes-induced cognitive decline-a heavyweight contributor to the increasing incidence of dementia in developed countries. Hoping to pave the way in this direction, we will present some of the most promising and well-studied drug leads with potential against both pathologies, including their respective bioactivity reports, mechanisms of action, and structure-activity relationships.

Angiopoietin-like peptide 4 regulates insulin secretion and islet morphology

Insulin secretion from pancreatic islet β-cells is primarily regulated by the blood glucose level, and also modulated by a number of biological factors produced inside the islets or released from remote organs. Previous studies have shown that angiopoietin-like protein 4 (Angptl4) controls glucose and lipid metabolism through its actions in the liver, adipose tissue, and skeletal muscles. In this present study, we investigated the possible role of Angptl4 in the regulation of insulin secretion from pancreatic islets. Angptl4 was found to be highly expressed in the α-cells but not β-cells of rodent islets. Moreover, treatment of rodent islets with Angptl4 peptide potentiated glucose-stimulated insulin secretion through a protein kinase A-dependent mechanism. Consistently, Angptl4 knockout mice showed impaired glucose tolerance. In the cultured islets from Angptl4 knockout mice, glucose-stimulated insulin secretion was significantly lower than in islets from wild type mice. Angptl4 peptide replacement partially reversed this reduction. Moreover, Angptl4 knockout mice had dysmorphic islets with abnormally distributed α-cells. In contrast, the β-cell mass and distribution were not significantly altered in these knockout mice. Our current data collectively suggest that Angptl4 may play a critical role in the regulation of insulin secretion and islet morphogenesis.

Reduced islet function contributes to impaired glucose homeostasis in fructose-fed mice

Increased sugar consumption, particularly fructose, in the form of sweetened beverages and sweeteners in our diet adversely affects metabolic health. Because these effects are associated with features of the metabolic syndrome in humans, the direct effect of fructose on pancreatic islet function is unknown. Therefore, we examined the islet phenotype of mice fed excess fructose. Fructose-fed mice exhibited fasting hyperglycemia and glucose intolerance but not hyperinsulinemia, dyslipidemia, or hyperuricemia. Islet function was impaired, with decreased glucose-stimulated insulin secretion and increased glucagon secretion and high fructose consumption leading to α-cell proliferation and upregulation of the fructose transporter GLUT5, which was localized only in α-cells. Our studies demonstrate that excess fructose consumption contributes to hyperglycemia by affecting both β- and α-cells of islets in mice.

Hypoglycemic activity of Gleditsia caspica extract and its saponin-containing fraction in streptozotocin-induced diabetic rats

The fruits of Gleditsia species (Fabaceae) have been known in traditional medicine as a saponin-rich herbal medicine. The present study aimed to investigate the effects of the total methanolic extract of Gleditsia caspica (MEGC) and its saponin-containing fractions (SFGC) on hyperglycemia in streptozotocin (STZ)-induced diabetic rats. A single intraperitoneal injection of STZ (55 mg/kg body weight) was used to induce hyperglycemia in male albino rats. MEGC (15, 30 and 60 mg/kg, p.o.) and SFGC (15, 30 and 60 mg/kg, p.o.) were administered to the diabetic rats daily for 14 days. The anti-diabetic drug gliclazide (10 mg/kg, p.o.) was used as a positive control. Blood samples were collected from overnight fasted rats for the evaluation of the antihyperglycemic, antihyperlipidemic and antioxidant activities. The levels of glucose, triglycerides (TG), cholesterol (TC) and malondialdehyde (MDA) were increased significantly, whereas the levels of α-amylase, insulin and reduced glutathione (GSH) were decreased in the experimental diabetic rats. Pancreas and liver of the diabetic rats exhibited significant changes in the histopathology, morphology and DNA content. Administration of MEGC or SFGC led to a decrease in the levels of glucose, TG, TC and MDA. In addition, the levels of α-amylase, insulin and GSH were increased in MEGC and SFGC treated diabetic rats. Also, the histopathological and morphological changes, as well the changes in DNA were significantly reversed by the extracts. Thus, MEGC and SFGC exhibited potent hypoglycemic and hypolipidemic activities in STZ- induced diabetic rats.

Diabetes: Rationale for Dipeptidyl Peptidase 4 Inhibitors: A New Class of Oral Agents for the Treatment of Type 2 Diabetes Mellitus

Objective:

To review advances in understanding the pathophysiologic basis of type 2 diabetes mellitus and the pharmacology and mechanism of action of dipeptidyl peptidase 4 (DPP-4) inhibition in correcting the underlying defects in glycemic control.

Data Sources:

Articles were identified through MEDLINE for the period 1966 through November 2006. Abstracts and presentations from the American Diabetes Association Scientific Sessions and the European Association for the Study of Diabetes (2002–2006) were also searched for scientific reports on DPP-4 inhibitors.

Study Selection And Data Extraction:

Abstracts, original clinical and preclinical research reports, and review articles published in the English language were identified for review. Literature discussing glucose regulation, incretin hormones, type 2 diabetes pathophysiology, and DPP-4 inhibition were evaluated and selected based on consideration of their support for the proof of concept, mechanistic and in vivo findings, and timeliness.

Data Synthesis:

The search for new and effective therapies for type 2 diabetes has led to the identification of a novel therapeutic target, the incretin hormones, which play a role in mediating glucose homeostasis via effects on glucagon and insulin secretion from pancreatic islet α- and β-cells, respectively. The incretins' glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide are rapidly inactivated by the enzyme DPP-4. DPP-4 inhibitor agents act by blocking the active site of DPP-4, thereby preventing inactivation of and prolonging the duration of action of incretins, which in turn helps to correct the defective insulin and glucagon secretion that marks type 2 diabetes. Clinical studies to date indicate that DPP-4 inhibitors effectively stimulate insulin secretion, suppress glucagon release, and improve glucose control in patients with type 2 diabetes. These agents are well tolerated and have a low incidence of adverse effects.

Conclusions:

The DPP-4 inhibitors are novel agents for the treatment of type 2 diabetes. Compounds under development in this new class of oral antidiabetic drugs may be free of the limitations of current therapies.

Hyperglucagonemia in an animal model of insulin- deficient diabetes: what therapy can improve it?

Background

Intra-islet insulin contributes to alpha-cell suppression. Akita mice carry a toxic-gain-of- function Ins2 gene mutation encoding proinsulin-C(A7)Y, similar to that described in human Mutant Ins-gene induced Diabetes of Youth, which decreases intra-islet insulin. Herein, we examined Akita mice for examination of circulating insulin and circulating glucagon levels. The possibility that loss of intra-islet suppression of alpha-cells, with increased circulating glucagon, contributes to diabetes under conditions of intra-islet insulin deficiency, raises questions about effective treatments that may be available.

Methods

Blood glucose, plasma insulin, C-peptide I, C-peptide II, and glucagon were measured at various times during development of diabetes in Akita mice. We also used Akita- like hProC(A7)Y-CpepGFP transgenic mice in Ins2^+/+, Ins2^+/− and Ins2^−/− genetic backgrounds (providing animals with greater or lesser defects in islet insulin production, respectively) in order to examine the relative abundance of immunostainable intra-islet glucagon-positive and insulin-positive cells. Similar measurements were made in Akita mice. Finally, the effects of treatment with insulin, exendin-4, and leptin on blood glucose were then compared in Akita mice.

Results

Interestingly, total insulin levels in the circulation were not frankly low in Akita mice, although they did not rise appropriately with the onset of hyperglycemia. By contrast, in severely diabetic Akita mice at 6 weeks of age, circulating glucagon levels were significantly elevated. Additionally, in Ins2^+/− and Ins2^−/− mice bearing the Akita-like hProC(A7)Y-CpepGFP transgene, development of diabetes correlated with an increase in the relative intra-islet abundance of immunostainable glucagon-positive cells, and a similar observation was made in Akita islets. In Akita mice, whereas a brief treatment with exendin-4 resulted in no apparent improvement in hyperglycemia, leptin treatment resulted in restoration of normoglycemia. Curiously, leptin treatment also suppressed circulating glucagon levels.

Conclusions

Loss of insulin-mediated intra-islet suppression of glucagon production may be a contributor to hyperglycemia in Akita mice, and leptin treatment appears beneficial in such a circumstance. This treatment might also be considered in some human diabetes patients with diminished insulin reserve.

Clinical audit of patients using DPP4 inhibitors in longstanding type 2 diabetes

AIMS

Dipeptidyl peptidase-4 inhibitors (DPP 4i) are oral hypoglycemic agents and are supposed to be beneficial in the early stages of diabetes. In this study, we evaluated the role of DPP4i in long standing type 2 diabetes mellitus (T2DM).

MATERIALS AND METHODS

This retrospective data analysis was conducted from the patient records. All the patients (T2DM>5 years; Age>50 years; Gliptin use >12 months) were divided into 2 groups based on the duration of T2DM: Group A (<10 years) and Group B (>10 years). We excluded patients with type 1 diabetes and drug default of more than one month. Our primary objective was to study the change in HbA1c and secondary objectives were change in body weight and insulin requirement. Data are presented as mean ± S.D and comparison between the groups was done using Mann-Whitney and Fisher's exact tests.

RESULTS

The study participants (n=501) had a mean age (64.2 ± 8.2 yr), diabetes duration (10.1 ± 4.9 yr), body weight (65.3 ± 9.5 kg), BMI (23.4 ± 3.9 kg/m(2)) and HbA1c of 9.7 ± 1.3%. The use of gliptins resulted in similar HbA1c reduction between the groups (p=0.8405) and greater reduction of insulin requirement in group B (p=0.0433) at the end of one year. Body weight and hypoglycemia episodes did not differ between the groups.

CONCLUSION

DPP4 inhibitors give similar benefit irrespective of the duration of diabetes and our data gives reassurance about their role in long standing diabetes.

Short-term intensive insulin therapy at diagnosis in type 2 diabetes: plan for filling the gaps

Short-term intensive insulin therapy is unique amongst therapies for type 2 diabetes because it offers the potential to preserve and improve beta-cell function without additional pharmacological treatment. On the basis of clinical experience and the promising results of a series of studies in newly diagnosed patients, mostly in Asian populations, an expert workshop was convened to assess the available evidence and the potential application of short-term intensive insulin therapy should it be advocated for inclusion in clinical practice. Participants included primary care physicians and endocrinologists. We endorse the concept of short-term intensive insulin therapy as an option for some patients with type 2 diabetes at the time of diagnosis and have identified the following six areas where additional knowledge could help clarify optimal use in clinical practice: (1) generalizability to primary care, (2) target population and biomarkers, (3) follow-up treatment, (4) education of patients and providers, (5) relevance of ethnicity, and (6) health economics.

The FOXP1, FOXP2 and FOXP4 transcription factors are required for islet alpha cell proliferation and function in mice

AIMS/HYPOTHESIS

Several forkhead box (FOX) transcription factor family members have important roles in controlling pancreatic cell fates and maintaining beta cell mass and function, including FOXA1, FOXA2 and FOXM1. In this study we have examined the importance of FOXP1, FOXP2 and FOXP4 of the FOXP subfamily in islet cell development and function.

METHODS

Mice harbouring floxed alleles for Foxp1, Foxp2 and Foxp4 were crossed with pan-endocrine Pax6-Cre transgenic mice to generate single and compound Foxp mutant mice. Mice were monitored for changes in glucose tolerance by IPGTT, serum insulin and glucagon levels by radioimmunoassay, and endocrine cell development and proliferation by immunohistochemistry. Gene expression and glucose-stimulated hormone secretion experiments were performed with isolated islets.

RESULTS

Only the triple-compound Foxp1/2/4 conditional knockout (cKO) mutant had an overt islet phenotype, manifested physiologically by hypoglycaemia and hypoglucagonaemia. This resulted from the reduction in glucagon-secreting alpha cell mass and function. The proliferation of alpha cells was profoundly reduced in Foxp1/2/4 cKO islets through the effects on mediators of replication (i.e. decreased Ccna2, Ccnb1 and Ccnd2 activators, and increased Cdkn1a inhibitor). Adult islet Foxp1/2/4 cKO beta cells secrete insulin normally while the remaining alpha cells have impaired glucagon secretion.

CONCLUSIONS/INTERPRETATION

Collectively, these findings reveal an important role for the FOXP1, 2, and 4 proteins in governing postnatal alpha cell expansion and function.

Oxidative stress-related genes in type 2 diabetes: association analysis and their clinical impact

Worldwide prevalence of diabetes mellitus motivates a number of association studies to be conducted throughout the world. Eleven polymorphisms from nine candidate genes in oxidative stress pathway have been analyzed in eastern Indian type 2 diabetic patients (n = 145) and healthy controls (n = 100). Different biochemical parameters were also analyzed for their association with the disease. Significant associations were observed for rs2070424 A>G SOD1 (OR 3.91, 95% CI 2.265-8.142, P < 0.001), rs854573 A>G PON1 (OR 3.415, 95% CI 2.116-5.512, P < 0.001), rs6954345 G>C PON2 (OR 3.208, 95% CI 2.071-4.969, P < 0.001), RAGE rs1800624 -374 T>A (OR 3.58, 95% CI 2.218-5.766, P < 0.001), and NOS3 -786 T>C (OR 3.75, 95% CI 2.225-6.666, P < 0.001). Haplotype containing two risk alleles of PON1 and PON2 genes was significantly associated with disease (OR 8.34, 95% CI 1.554-44.804, P < 0.002). Our results suggest that carriers of major and efficient alleles of oxidative stress genes are more likely to survive the comorbid complications and single copy of risk allele is sufficient for developing the disease.

Acute glucagon induces postprandial peripheral insulin resistance

Glucagon levels are often moderately elevated in diabetes. It is known that glucagon leads to a decrease in hepatic glutathione (GSH) synthesis that in turn is associated with decreased postprandial insulin sensitivity. Given that cAMP pathway controls GSH levels we tested whether insulin sensitivity decreases after intraportal (ipv) administration of a cAMP analog (DBcAMP), and investigated whether glucagon promotes insulin resistance through decreasing hepatic GSH levels.Insulin sensitivity was determined in fed male Sprague-Dawley rats using a modified euglycemic hyperinsulinemic clamp in the postprandial state upon ipv administration of DBcAMP as well as glucagon infusion. Glucagon effects on insulin sensitivity was assessed in the presence or absence of postprandial insulin sensitivity inhibition by administration of L-NMMA. Hepatic GSH and NO content and plasma levels of NO were measured after acute ipv glucagon infusion. Insulin sensitivity was assessed in the fed state and after ipv glucagon infusion in the presence of GSH-E. We founf that DBcAMP and glucagon produce a decrease of insulin sensitivity, in a dose-dependent manner. Glucagon-induced decrease of postprandial insulin sensitivity correlated with decreased hepatic GSH content and was restored by administration of GSH-E. Furthermore, inhibition of postprandial decrease of insulin sensitivity L-NMMA was not overcome by glucagon, but glucagon did not affect hepatic and plasma levels of NO. These results show that glucagon decreases postprandial insulin sensitivity through reducing hepatic GSH levels, an effect that is mimicked by increasing cAMP hepatic levels and requires physiological NO levels. These observations support the hypothesis that glucagon acts via adenylate cyclase to decrease hepatic GSH levels and induce insulin resistance. We suggest that the glucagon-cAMP-GSH axis is a potential therapeutic target to address insulin resistance in pathological conditions.

Failure of hyperglycemia and hyperinsulinemia to compensate for impaired metabolic response to an oral glucose load

OBJECTIVE

To evaluate whether the augmented insulin and glucose response to a glucose challenge is sufficient to compensate for defects in glucose utilization in obesity and type 2 diabetes, using a breath test measurement of integrated glucose metabolism.

METHODS

Non-obese, obese normoglycemic and obese type 2 diabetic subjects were studied on 2 consecutive days. A 75g oral glucose load spiked with ¹³C-glucose was administered, measuring exhaled breath ¹³CO₂ as an integrated measure of glucose metabolism and oxidation. A hyperinsulinemic euglycemic clamp was performed, measuring whole body glucose disposal rate. Body composition was measured by DEXA. Multivariable analyses were performed to evaluate the determinants of the breath ¹³CO₂.

RESULTS

Breath ¹³CO₂ was reduced in obese and type 2 diabetic subjects despite hyperglycemia and hyperinsulinemia. The primary determinants of breath response were lean mass, fat mass, fasting FFA concentrations, and OGTT glucose excursion. Multiple approaches to analysis showed that hyperglycemia and hyperinsulinemia were not sufficient to compensate for the defect in glucose metabolism in obesity and diabetes.

CONCLUSIONS

Augmented insulin and glucose responses during an OGTT are not sufficient to overcome the underlying defects in glucose metabolism in obesity and diabetes.

Autocrine C-peptide mechanism underlying INS1 beta cell adaptation to oxidative stress

BACKGROUND

Excessive generation of reactive oxygen species (ROS) causing oxidative stress plays a major role in the pathogenesis of diabetes by inducing beta cell secretory dysfunction and apoptosis. Recent evidence has shown that C-peptide, produced by beta cells and co-secreted with insulin in the circulation of healthy individuals, decreases ROS and prevents apoptosis in dysfunctional vascular endothelial cells. In this study, we tested the hypothesis that an autocrine activity of C-peptide similarly decreases ROS when INS1 beta cells are exposed to stressful conditions of diabetes.

METHODS

Reactive oxygen species and apoptosis were induced in INS1 beta cells pretreated with C-peptide by either 22 mM glucose or 100 μM hydrogen peroxide (H2 O2 ). To test C-peptide's autocrine activity, endogenous C-peptide secretion was inhibited by the KATP channel opener diazoxide and H2 O2 -induced ROS assayed after addition of either exogenous C-peptide or the secretagogue glibenclamide. In similar experiments, extracellular potassium, which depolarizes the membrane otherwise hyperpolarized by diazoxide, was used to induce endogenous C-peptide secretion. ROS was measured using the cell-permeant dye chloromethyl-2',7'-dichlorodihydrofluorescein diacetate (CM-H2 -DCFDA). Insulin secretion and apoptosis were assayed by enzyme-linked immunosorbent assay.

RESULTS

C-peptide significantly decreased high glucose-induced and H2 O2 -induced ROS and prevented apoptosis of INS1 beta cells. Diazoxide significantly increased H2 O2 -induced ROS, which was reversed by exogenous C-peptide or glibenclamide or potassium chloride.

CONCLUSIONS

These findings demonstrate an autocrine C-peptide mechanism in which C-peptide is bioactive on INS1 beta cells exposed to stressful conditions and might function as a natural antioxidant to limit beta cell dysfunction and loss contributing to diabetes.

Fluoxetine-induced pancreatic beta cell dysfunction: New insight into the benefits of folic acid in the treatment of depression

BACKGROUND

Major depressive disorder is a common psychiatric illness with reported prevalence rates of 12-16% in persons aged 12 and over. Depression is also associated with a high risk of new onset of type 2 diabetes (T2D). This relationship between depression and diabetes may be related to depression itself and/or drugs prescribed. Importantly, the use of selective serotonin reuptake inhibitors (SSRIs), the most commonly prescribed class of antidepressants, increases the risk of developing T2D. However, the mechanism(s) underlying this association remains elusive.

METHODS

Here we examine the effects of the SSRI fluoxetine (Prozac®) on beta cell function utilizing INS-1E cells, a rat beta cell line, to elucidate the underlying molecular mechanisms.

RESULTS

Fluoxetine treatment significantly reduced glucose stimulated insulin secretion (GSIS). This decreased beta cell function was concomitant with an increased production of reactive oxygen species and oxidative damage which may contribute to decreased mitochondrial electron transport chain enzyme (ETC) activity. Importantly the fluoxetine-induced deficits in beta cell function were prevented by the addition of the antioxidant folic acid.

LIMITATIONS

These studies were conducted in vitro; the in vivo relevance remains to be determined.

CONCLUSIONS

These findings suggest that use of SSRI antidepressants may increase the risk of new-onset T2D by causing oxidative stress in pancreatic beta cells. However, folic acid supplementation in patients taking SSRIs may reduce the risk of new onset diabetes via protection of normal beta cell function.

A link between hepatic glucose production and peripheral energy metabolism via hepatokines

Type 2 diabetes is characterized by a deterioration of glucose tolerance, which associates insulin resistance of glucose uptake by peripheral tissues and increased endogenous glucose production. Here we report that the specific suppression of hepatic glucose production positively modulates whole-body glucose and energy metabolism. We used mice deficient in liver glucose-6 phosphatase that is mandatory for endogenous glucose production. When they were fed a high fat/high sucrose diet, they resisted the development of diabetes and obesity due to the activation of peripheral glucose metabolism and thermogenesis. This was linked to the secretion of hepatic hormones like fibroblast growth factor 21 and angiopoietin-like factor 6. Interestingly, the deletion of hepatic glucose-6 phosphatase in previously obese and insulin-resistant mice resulted in the rapid restoration of glucose and body weight controls. Therefore, hepatic glucose production is an essential lever for the control of whole-body energy metabolism during the development of obesity and diabetes.

Impact of three oral antidiabetic drugs on markers of β-cell function in patients with type 2 diabetes: a meta-analysis

Background

The effect of metformin, pioglitazone and sitagliptin on β-cell function in the treatment of type 2 diabetes is controversial. Therefore, we performed a systematic review and meta-analysis to obtain a better understanding in the β-cell effects of metformin, pioglitazone and sitagliptin.

Methods

We searched Pubmed and the Cochrane Center Register of Controlled Trials to identify relevant studies. Trials investigating effects of sitagliptin, metformin or pioglitazone on β-cell function were identified. The primary outcomes were homeostasis model assessment of β-cells (HOMA-β) and proinsulin/insulin ratio (PI/IR). Secondary outcome was hemoglobin A1c level. We used version 2 of the Comprehensive Meta Analysis software for all statistical analyses.

Results

Metformin monotherapy was more effective than sitagliptin in improving HOMA-β (18.01% (95% CI 11.09% to 24.94%) vs. 11.29% (95% CI 9.21% to 13.37%), P = 0.040) and more effective (−0.137 (95% CI −0.082 to −0.192)) than both sitagliptin (−0.064 (95% CI −0.036 to −0.092), P = 0.019) and pioglitazone (−0.068 (95% CI −0.044 to −0.093), P = 0.015) in decreasing PI/IR. Metformin and sitagliptin combined (40.23% (95%CI 32.30% to 48.16%)) were more effective than sitagliptin and pioglitazone (11.82% (95% CI 6.61% to 17.04%), P = 0.000) and pioglitazone and metformin(9.81% (95% CI 1.67% to 17.95%), P = 0.022) in improving HOMA-β and decreasing PI/IR (−0.177 (95% CI −0.118 to −0.237); −0.080 (95% CI −0.045 to −0.114), P = 0.007; −0.038 (95% CI, −0.005 to 0.071), P = 0.023).

Limitations

The included RCTs were of short duration (12–54 weeks). We could not determine long term effects on β-cells.

Conclusions

Metformin improves β-cell function more effectively than pioglitazone or sitagliptin in type 2 diabetes patients. Metformin and sitagliptin improved HOMA-β and PI/IR more than other combinations.

Short-term continuous subcutaneous insulin infusion combined with insulin sensitizers rosiglitazone, metformin, or antioxidant α-lipoic acid in patients with newly diagnosed type 2 diabetes mellitus

BACKGROUND

Short-term continuous subcutaneous insulin infusion (CSII) in patients with newly diagnosed type 2 diabetes has been proved effective in improving metabolic control and β-cell function, thus inducing long-term drug-free remission. A randomized controlled trial was conducted to investigate whether CSII in combination with rosiglitazone, metformin, or α-lipoic acid separately brings about extra benefits.

PATIENTS AND METHODS

One hundred sixty patients with newly diagnosed type 2 diabetes were randomized to one of four treatment groups: CSII alone, CSII in combination with rosiglitazone or metformin for 3 months, or CSII with α-lipoic acid intravenous infusion for 2 weeks. Duration of CSII treatment was identical in the four groups. Glucose and lipid profiles, homeostasis model assessment (HOMA) indices, acute insulin response (AIR), intramyocellular lipid (IMCL) level, and malondialdehyde level were compared before and after intervention.

RESULTS

The near-normoglycemia rate at the third month in CSII alone and that in combination with rosiglitazone, metformin, or α-lipoic acid was 72.5%, 87.5%, 90%, and 75%, respectively (metformin group vs. CSII alone, P=0.045). The metformin group achieved euglycemia in a shorter time (2.6 ± 1.3 vs. 3.7 ± 1.8 days, P=0.020) with less daily insulin dosage and was more powerful in lowering total cholesterol, increasing AIR and HOMA β-cell function, whereas reduction of IMCL in the soleus was more obvious in the rosiglitazone group but not in the metformin group. The efficacy of combination with α-lipoic acid was similar to that of CSII alone.

CONCLUSIONS

Short-term CSII in combination with rosiglitazone or metformin is superior to CSII alone, yet the efficacy of the two differs in some way, whereas that with α-lipoic acid might not have an additive effect.

A DPP-IV-resistant triple-acting agonist of GIP, GLP-1 and glucagon receptors with potent glucose-lowering and insulinotropic actions in high-fat-fed mice

AIMS/HYPOTHESIS

We designed a chemically modified, enzyme-resistant peptide with triple-acting properties based on human glucagon with amino acid substitutions aligned to strategic positions in the sequence of glucose-dependent insulinotropic polypeptide (GIP).

METHODS

Y(1)-dA(2)-I(12)-N(17)-V(18)-I(27)-G(28,29)-glucagon (termed YAG-glucagon) was incubated with dipeptidylpeptidase IV (DPP-IV) to assess stability, BRIN-BD11 cells to evaluate insulin secretion, and receptor-transfected cells to examine cAMP production. Acute glucose-lowering and insulinotropic properties of YAG-glucagon were assessed in National Institutes of Health (NIH) Swiss mice, while longer-term actions on glucose homeostasis, insulin secretion, food intake and body weight were examined in high-fat-fed mice.

RESULTS

YAG-glucagon was resistant to DPP-IV, increased in vitro insulin secretion (1.5-3-fold; p < 0.001) and stimulated cAMP production in GIP receptor-, glucagon-like peptide-1 (GLP-1) receptor- and glucagon receptor-transfected cells. Plasma glucose levels were significantly reduced (by 51%; p < 0.01) and insulin concentrations increased (1.2-fold; p < 0.01) after acute injection of YAG-glucagon in NIH Swiss mice. Acute actions were countered by established GIP, GLP-1 and glucagon antagonists. In high-fat-fed mice, twice-daily administration of YAG-glucagon for 14 days reduced plasma glucose (40% reduction; p < 0.01) and increased plasma insulin concentrations (1.8-fold; p < 0.05). Glycaemic responses were markedly improved (19-48% reduction; p < 0.05) and insulin secretion enhanced (1.5-fold; p < 0.05) after a glucose load, which were independent of changes in insulin sensitivity, food intake and body weight.

CONCLUSIONS/INTERPRETATION

YAG-glucagon is a DPP-IV-resistant triple agonist of GIP, GLP-1 and glucagon receptors and exhibits beneficial biological properties suggesting that it may hold promise for treatment of type 2 diabetes.

Imaging beta-cell mass and function in situ and in vivo

Glucose-stimulated insulin secretion (GSIS) from pancreatic beta-cells is critical to the maintenance of blood glucose homeostasis in animals. Both decrease in pancreatic beta-cell mass and defects in beta-cell function contribute to the onset of diabetes, although the underlying mechanisms remain largely unknown. Molecular imaging techniques can help beta-cell study in a number of ways. High-resolution fluorescence imaging techniques provide novel insights into the fundamental mechanisms underlying GSIS in isolated beta-cells or in situ in pancreatic islets, and dynamic changes of beta-cell mass and function can be noninvasively monitored in vivo by imaging techniques such as positron emission tomography and single-photon emission computed tomography. All these techniques will contribute to the better understanding of the progression of diabetes and the search for the optimized therapeutic measures that reverse deficits in beta-cell mass and function.

Stimulation of insulin secretion by large-dose oral arginine administration in healthy adults

The effects of large-dose oral arginine administration on the secretion of insulin by islet β-cells in healthy adults were determined. Eight non-obese healthy volunteers with normal glucose tolerance participated randomly in tests with four stages (with an interval of at least 3 days): the 300 ml purified water stage (PWS), the 75 g glucose stage (GSS), the 30 g arginine stage (ARS) and the 75 g glucose with 30 g arginine stage (GAS). Venous blood samples were collected to detect the concentrations of glucose and insulin at baseline (0) and at 15, 30, 45, 60 and 120 min after drug administration. The glucose and insulin levels were steady in the PWS. The remaining three stages had similarly shaped insulin concentration-time curves, which differed from that of the PWS. The peak concentration of blood insulin and the net incremental area under the curve of blood insulin in the GSS, ARS and GAS were significantly higher compared with those in the PWS (P<0.05). In the ARS, the glucose levels remained stable; however, the net incremental area under the curve for blood insulin in the ARS was much lower compared with that in the GSS or GAS (P<0.05). Large-dose oral arginine administration may slightly stimulate insulin secretion by islet β-cells in healthy adults with normal glucose tolerance in a manner that is independent of glucose concentration.

Logistic model of glucose-regulated C-peptide secretion: hysteresis pathway disruption in impaired fasting glycemia

The present analysis tests the hypothesis that quantifiable disruption of the glucose-stimulated insulin-secretion dose-response pathway mediates impaired fasting glycemia (IFG) and type 2 diabetes mellitus (DM). To this end, adults with normal and impaired fasting glycemia (NFG, n = 30), IFG (n = 32), and DM (n = 14) were given a mixed meal containing 75 g glucose. C-peptide and glucose were measured over 4 h, 13 times in NFG and IFG and 16 times in DM (age range 50-57 yr, body mass index 28-32 kg/m(2)). Wavelet-based deconvolution analysis was used to estimate time-varying C-peptide secretion rates. Logistic dose-response functions were constructed analytically of the sensitivity, potency, and efficacy (in the pharmacological sense of slope, one-half maximal stimulation, and maximal effect) of glucose's stimulation of prehepatic insulin (C-peptide) secretion. A hysteresis changepoint time, demarcating unequal glucose potencies for onset and recovery pathways, was estimated simultaneously. According to this methodology, NFG subjects exhibited distinct onset and recovery potencies of glucose in stimulating C-peptide secretion (6.5 and 8.5 mM), thereby defining in vivo hysteresis (potency shift -2.0 mM). IFG patients manifested reduced glucose onset potency (8.6 mM), and diminished C-peptide hysteretic shift (-0.80 mM). DM patients had markedly decreased glucose potency (18.8 mM), reversal of C-peptide's hysteretic shift (+4.5 mM), and 30% lower C-peptide sensitivity to glucose stimulation. From these data, we conclude that a dynamic dose-response model of glucose-dependent control of C-peptide secretion can identify disruption of in vivo hysteresis in patients with IFG and DM. Pathway-defined analytic models of this kind may aid in the search for prediabetes biomarkers.

Impaired incretin effect and fasting hyperglucagonaemia characterizing type 2 diabetic subjects are early signs of dysmetabolism in obesity

AIMS

People with type 2 diabetes mellitus (T2DM) are characterized by reduced incretin effect and inappropriate glucagon levels. We evaluated α and β-cell responses to oral glucose tolerance test (OGTT) and isoglycaemic intravenous glucose infusion (IIGI) in lean and obese persons with T2DM or normal glucose tolerance (NGT) to elucidate the impact of obesity on the incretin effect and incretin hormone and glucagon responses.

METHODS

Four hour 50-g OGTT and IIGI were performed in (i) Eight obese patients with T2DM [mean body mass index (BMI): 37 (range: 35-41) kg/m(2)]; (ii) Eight obese subjects with NGT [BMI: 33 (35-38) kg/m(2)]; (iii) Eight lean patients with T2DM [BMI: 24 (22-25) kg/m(2)]; and (iv) Eight lean healthy subjects [BMI: 23 (20-25) kg/m(2)].

RESULTS

The incretin effect was significantly (p < 0.05) reduced in patients with T2DM {obese: 7 ± 7% [mean ± standard error of the mean (SEM)]; lean: 29 ± 8%; p = 0.06)} and was lower in obese subjects (41 ± 4%) than in lean subjects with NGT (53 ± 4%; p < 0.05). Obese subjects with NGT were also characterized by elevated fasting plasma glucagon levels, but the inappropriate glucagon responses to OGTT found in the T2DM patients were not evident in these subjects.

CONCLUSIONS

Our findings suggest that reduced incretin effect and fasting hyperglucagonaemia constitute very early steps in the pathophysiology of T2DM detectable even in obese people who despite their insulin-resistant state have NGT.

Altered islet composition and disproportionate loss of large islets in patients with type 2 diabetes

Human islets exhibit distinct islet architecture with intermingled alpha- and beta-cells particularly in large islets. In this study, we quantitatively examined pathological changes of the pancreas in patients with type 2 diabetes (T2D). Specifically, we tested a hypothesis that changes in endocrine cell mass and composition are islet-size dependent. A large-scale analysis of cadaveric pancreatic sections from T2D patients (n = 12) and non-diabetic subjects (n = 14) was carried out combined with semi-automated analysis to quantify changes in islet architecture. The method provided the representative islet distribution in the whole pancreas section that allowed us to examine details of endocrine cell composition in individual islets. We observed a preferential loss of large islets (>60 µm in diameter) in T2D patients compared to non-diabetic subjects. Analysis of islet cell composition revealed that the beta-cell fraction in large islets was decreased in T2D patients. This change was accompanied by a reciprocal increase in alpha-cell fraction, however total alpha-cell area was decreased along with beta-cells in T2D. Delta-cell fraction and area remained unchanged. The computer-assisted quantification of morphological changes in islet structure minimizes sampling bias. Significant beta-cell loss was observed in large islets in T2D, in which alpha-cell ratio reciprocally increased. However, there was no alpha-cell expansion and the total alpha-cell area was also decreased. Changes in islet architecture were marked in large islets. Our method is widely applicable to various specimens using standard immunohistochemical analysis that may be particularly useful to study large animals including humans where large organ size precludes manual quantitation of organ morphology.

Role of beta-cell dysfunction, ectopic fat accumulation and insulin resistance in the pathogenesis of type 2 diabetes mellitus

In the natural history of type 2 diabetes (T2DM), individuals progress from normal glucose tolerance (NGT) to impaired glucose tolerance (IGT) to overt T2DM and this progression has been demonstrated in populations of diverse ethnic background. It is widely recognised that both insulin resistance and beta-cell dysfunction are important in the pathogenesis of glucose intolerance. In populations with a high prevalence of T2DM, insulin resistance is well established long before the development of any impairment in glucose homeostasis, particularly in subjects with ectopic fat accumulation. However, as long as the beta cell is able to secrete sufficient amounts of insulin to offset the severity of insulin resistance, glucose tolerance remains normal. This dynamic interaction between insulin secretion and insulin resistance is essential to the maintenance of NGT and interruption of this crosstalk between the beta cell and peripheral tissues results in the progressive deterioration of glucose homeostasis. In this paper the role of beta-cell function is reviewed, as well as the role of ectopic fat accumulation and insulin resistance in the development of type 2 diabetes.

Management of type 2 diabetes: new and future developments in treatment

The increasing prevalence, variable pathogenesis, progressive natural history, and complications of type 2 diabetes emphasise the urgent need for new treatment strategies. Longacting (eg, once weekly) agonists of the glucagon-like-peptide-1 receptor are advanced in development, and they improve prandial insulin secretion, reduce excess glucagon production, and promote satiety. Trials of inhibitors of dipeptidyl peptidase 4, which enhance the effect of endogenous incretin hormones, are also nearing completion. Novel approaches to glycaemic regulation include use of inhibitors of the sodium-glucose cotransporter 2, which increase renal glucose elimination, and inhibitors of 11β-hydroxysteroid dehydrogenase 1, which reduce the glucocorticoid effects in liver and fat. Insulin-releasing glucokinase activators and pancreatic-G-protein-coupled fatty-acid-receptor agonists, glucagon-receptor antagonists, and metabolic inhibitors of hepatic glucose output are being assessed. Early proof of principle has been shown for compounds that enhance and partly mimic insulin action and replicate some effects of bariatric surgery.

Advances in the treatment of type 2 diabetes mellitus

There is a rising worldwide prevalence of diabetes, especially type 2 diabetes mellitus (T2DM), which is one of the most challenging health problems in the 21st century. The associated complications of diabetes, such as cardiovascular disease, peripheral vascular disease, stroke, diabetic neuropathy, amputations, renal failure, and blindness result in increasing disability, reduced life expectancy, and enormous health costs. T2DM is a polygenic disease characterized by multiple defects in insulin action in tissues and defects in pancreatic insulin secretion, which eventually leads to loss of pancreatic insulin-secreting cells. The treatment goals for T2DM patients are effective control of blood glucose, blood pressure, and lipids (if elevated) and, ultimately, to avert the serious complications associated with sustained tissue exposure to excessively high glucose concentrations. Prevention and control of diabetes with diet, weight control, and physical activity has been difficult. Treatment of T2DM has centered on increasing insulin levels, either by direct insulin administration or oral agents that promote insulin secretion, improving sensitivity to insulin in tissues, or reducing the rate of carbohydrate absorption from the gastrointestinal tract. This review presents comprehensive and up-to-date information on the mechanism(s) of action, efficacy, pharmacokinetics, pleiotropic effects, drug interactions, and adverse effects of the newer antidiabetic drugs, including (1) peroxisome proliferator-activated-receptor-γ agonists (thiazolidinediones, pioglitazone, and rosiglitazone); (2) the incretin, glucagon-like peptide-) receptor agonists (incretin-mimetics, exenatide. and liraglutide), (3) inhibitors of dipeptidyl-peptidase-4 (incretin enhancers, sitagliptin, and vildagliptin), (4) short-acting, nonsulfonylurea secretagogue, meglitinides (repaglinide and nateglinide), (5) amylin anlog-pramlintide, (6) α-glucosidase inhibitors (miglitol and voglibose), and (7) colesevelam (a bile acid sequestrant). In addition, information is presented on drug candidates in clinical trials, experimental compounds, and some plants used in the traditional treatment of diabetes based on experimental evidence. In the opinion of this reviewer, therapy based on orally active incretins and incretin mimetics with long duration of action that will be efficacious, preserve the β-cell number/function, and block the progression of diabetes will be highly desirable. However, major changes in lifestyle factors such as diet and, especially, exercise will also be needed if the growing burden of diabetes is to be contained.

α-Synuclein binds the K(ATP) channel at insulin-secretory granules and inhibits insulin secretion

α-Synuclein has been studied in numerous cell types often associated with secretory processes. In pancreatic β-cells, α-synuclein might therefore play a similar role by interacting with organelles involved in insulin secretion. We tested for α-synuclein localizing to insulin-secretory granules and characterized its role in glucose-stimulated insulin secretion. Immunohistochemistry and fluorescent sulfonylureas were used to test for α-synuclein localization to insulin granules in β-cells, immunoprecipitation with Western blot analysis for interaction between α-synuclein and K(ATP) channels, and ELISA assays for the effect of altering α-synuclein expression up or down on insulin secretion in INS1 cells or mouse islets, respectively. Differences in cellular phenotype between α-synuclein knockout and wild-type β-cells were found by using confocal microscopy to image the fluorescent insulin biosensor Ins-C-emGFP and by using transmission electron microscopy. The results show that anti-α-synuclein antibodies labeled secretory organelles within β-cells. Anti-α-synuclein antibodies colocalized with K(ATP) channel, anti-insulin, and anti-C-peptide antibodies. α-Synuclein coimmunoprecipitated in complexes with K(ATP) channels. Expression of α-synuclein downregulated insulin secretion at 2.8 mM glucose with little effect following 16.7 mM glucose stimulation. α-Synuclein knockout islets upregulated insulin secretion at 2.8 and 8.4 mM but not 16.7 mM glucose, consistent with the depleted insulin granule density at the β-cell surface membranes observed in these islets. These findings demonstrate that α-synuclein interacts with K(ATP) channels and insulin-secretory granules and functionally acts as a brake on secretion that glucose stimulation can override. α-Synuclein might play similar roles in diabetes as it does in other degenerative diseases, including Alzheimer's and Parkinson's diseases.

Novel avenues of drug discovery and biomarkers for diabetes mellitus

Globally, developed nations spend a significant amount of their resources on health care initiatives that poorly translate into increased population life expectancy. As an example, the United States devotes 16% of its gross domestic product to health care, the highest level in the world, but falls behind other nations that enjoy greater individual life expectancy. These observations point to the need for pioneering avenues of drug discovery to increase life span with controlled costs. In particular, innovative drug development for metabolic disorders such as diabetes mellitus becomes increasingly critical given that the number of diabetic people will increase exponentially over the next 20 years. This article discusses the elucidation and targeting of novel cellular pathways that are intimately tied to oxidative stress in diabetes mellitus for new treatment strategies. Pathways that involve wingless, β-nicotinamide adenine dinucleotide (NAD(+)) precursors, and cytokines govern complex biological pathways that determine both cell survival and longevity during diabetes mellitus and its complications. Furthermore, the role of these entities as biomarkers for disease can further enhance their utility irrespective of their treatment potential. Greater understanding of the intricacies of these unique cellular mechanisms will shape future drug discovery for diabetes mellitus to provide focused clinical care with limited or absent long-term complications.

Role of lipoic acid on insulin resistance and leptin in experimentally diabetic rats

OBJECTIVE

We aimed to examine the changes in serum insulin and leptin levels in induced type 1 diabetes mellitus in relationship to glycemic state and lipid profiles and to clarify the role of lipoic acid (LA).

METHODS

Ninety-six male rats were equally divided into the following: a control group (normal, nondiabetic), a diabetic group induced by subcutaneous injection of alloxan (non-LA-treated), and an LA-treated diabetic group (for 4 weeks). Body weight, serum lipid profile, glucose, insulin, homeostasis model assessment-insulin resistance (HOMA-IR), and leptin were measured.

RESULTS

This study showed a significant increase in serum triacylglycerol (TG), total cholesterol, glucose levels, and HOMA-IR and a significant decrease in body weight gain, insulin, and leptin levels in the diabetic group compared to the control group. LA treatment induced a significant decrease in glucose, TG, and total cholesterol levels and significantly increased serum insulin and leptin levels in comparison with the diabetic group.

CONCLUSION

Induced diabetes resulted in insulin resistance, hyperlipidemia, and hypoleptinemia, while LA ameliorates these changes and improves insulin sensitivity.

Glucagon-like peptide-2, but not glucose-dependent insulinotropic polypeptide, stimulates glucagon release in patients with type 1 diabetes

This study investigated the glucagon-releasing properties of the hormones glucagon-like peptide-2 (GLP-2) and glucose-dependent insulinotropic polypeptide (GIP) in 8 patients with type 1 diabetes mellitus (T1DM) without paracrine intraislet influence of insulin (C-peptide negative following a 5 g intravenous arginine stimulation; on study days only treated with basal insulin substitution). On 3 study days, 180-minute two-step glucose clamps were performed. Plasma glucose (PG) was clamped at fasting values, with a mean of 7.4+/-0.5 mM in the first 90 min (period 1) and raised 1.5 times the fasting values to a mean of 11.1+/-0.1 mM in the last 90 min (period 2). In randomised order either GIP, GLP-2, or saline were infused intravenously during first 50 min in both periods at rates designed to mimic postprandial hormone responses. The resulting incremental area under curve values of glucagon were in period 1 -38+/-44 (GIP), 120+/-48 (GLP-2), and -16+/-61 (saline) pMx90 min (p=0.087), respectively; and in period 2 -157+/-76, 135+/-52, and -77+/-77pMx90 min (p=0.019), respectively. Post hoc analysis showed significant differences only between the GLP-2 days versus the GIP and saline days. In conclusion, GLP-2, but not GIP, was found to stimulate the release of glucagon in patients with T1DM, suggesting a role for GLP-2 in the postprandial hyperglucagonaemia characterising individuals with T1DM.

Fate of the beta-cell in the pathophysiology of type 2 diabetes

OBJECTIVE

To describe the progression of beta-cell dysfunction, now presumed to be the primary progenitor of type 2 diabetes, which appears early in the clinical course (perhaps antedating and even contributing to the development of insulin resistance) and progressively worsens even under treatment.

DATA SOURCES

Medline search of all relevant clinical and review articles.

STUDY SELECTION

By the author.

DATA EXTRACTION

By the author.

DATA SYNTHESIS

The physiology of glucose homeostasis requires the close cooperation of a number of organ systems, humoral secretions, and neural signaling complexes; disruption of any of these processes may lead to the development of type 2 diabetes. Predisposing risk factors for type 2 diabetes include overweight and obesity, poor diet, and lack of exercise. Genetic factors, many of which as yet require elucidation, may also elevate the risk of developing type 2 diabetes. Insulin resistance (IR) has long been recognized as a primary, if not the primary, cause of type 2 diabetes. Recent research in disease pathogenesis suggests that IR is neither a necessary nor sufficient condition for development and progression of type 2 diabetes. Although IR is highly correlated with type 2 diabetes, many individuals with IR will not go on to develop the disease; and the disease may be present in individuals not markedly insulin resistant. The primary progenitor of type 2 diabetes is now presumed to be progressive beta-cell dysfunction, which appears early in the clinical course (perhaps antedating and even contributing to the development of IR) and progressively worsens even under treatment. Among the mechanisms of beta-cell dysfunction in type 2 diabetes is the reduction or abrogation of the "incretin effect."

CONCLUSION

The incretins are gut hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), which in healthy individuals potentiate glucose-dependent insulin secretion. In addition, these hormones, and particularly GLP-1, have a number of protective effects on the beta-cell, including reduction in apoptosis and promotion of beta-cell proliferation and neogenesis. As these benefits are lost in diabetes, "repairing" the incretin effect has become an important treatment target. Treatments that maintain the beta-cell could offer durable glycemic control and potentially reduce the micro- and macrovascular complications 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.

Combining a dipeptidyl peptidase-4 inhibitor, alogliptin, with pioglitazone improves glycaemic control, lipid profiles and beta-cell function in db/db mice

BACKGROUND AND PURPOSE

Alogliptin, a highly selective dipeptidyl peptidase-4 (DPP-4) inhibitor, enhances incretin action and pioglitazone enhances hepatic and peripheral insulin actions. Here, we have evaluated the effects of combining these agents in diabetic mice.

EXPERIMENTAL APPROACH

Effects of short-term treatment with alogliptin alone (0.01%-0.1% in diet), and chronic combination treatment with alogliptin (0.03% in diet) and pioglitazone (0.0075% in diet) were evaluated in db/db mice exhibiting early stages of diabetes.

KEY RESULTS

Alogliptin inhibited plasma DPP-4 activity up to 84% and increased plasma active glucagon-like peptide-1 by 4.4- to 4.9-fold. Unexpectedly, alogliptin alone lacked clear efficacy for improving glucose levels. However, alogliptin in combination with pioglitazone clearly enhanced the effects of pioglitazone alone. After 3-4 weeks of treatment, combination treatment increased plasma insulin by 3.8-fold, decreased plasma glucagon by 41%, both of which were greater than each drug alone, and increased plasma adiponectin by 2.4-fold. In addition, combination treatment decreased glycosylated haemoglobin by 2.2%, plasma glucose by 52%, plasma triglycerides by 77% and non-esterified fatty acids by 48%, all of which were greater than each drug alone. Combination treatment also increased expression of insulin and pancreatic and duodenal homeobox 1 (PDX1), maintained normal beta-cell/alpha-cell distribution in islets and restored pancreatic insulin content to levels comparable to non-diabetic mice.

CONCLUSIONS AND IMPLICATIONS

These results indicate that combination treatment with alogliptin and pioglitazone at an early stage of diabetes improved metabolic profiles and indices that measure beta-cell function, and maintained islet structure in db/db mice, compared with either alogliptin or pioglitazone monotherapy.

Demographic and metabolic characteristics of individuals with progressive glucose tolerance

We evaluated changes in glucose tolerance of 17 progressors and 62 non-progressors for 9 years to improve our understanding of the pathogenesis of type 2 diabetes mellitus. Changes in anthropometric measurements and responses to an oral glucose tolerance test (OGTT) were analyzed. We identified 14 pairs of individuals, one from each group, who were initially normal glucose tolerant and were matched for gender, age, weight, and girth. We compared initial plasma glucose and insulin curves (from OGTT), insulin secretion (first and second phases) and insulin sensitivity indices (from hyperglycemic clamp assay) for both groups. In the normal glucose tolerant phase, progressors presented: 1) a higher OGTT blood glucose response with hyperglycemia in the second hour and a similar insulin response vs non-progressors; 2) a reduced first-phase insulin secretion (2.0 +/- 0.3 vs 2.3 +/- 0.3 pmol/L; P < 0.02) with a similar insulin sensitivity index and a lower disposition index (3.9 +/- 0.2 vs 4.1 +/- 0.2 micromol.kg-1.min-1 ; P < 0.05) vs non-progressors. After 9 years, both groups presented similar increases in weight and fasting blood glucose levels and progressors had an increased glycemic response at 120 min (P < 0.05) and reduced early insulin response to OGTT (progressors, 1st: 2.10 +/- 0.34 vs 2nd: 1.87 +/- 0.25 pmol/mmol; non-progressors, 1st: 2.15 +/- 0.28 vs 2nd: 2.03 +/- 0.39 pmol/mmol; P < 0.05). Theses data suggest that beta-cell dysfunction might be a risk factor for type 2 diabetes mellitus.