Beta cell mass in diabetes: a realistic therapeutic target?

Do statins cause diabetes?

A wealth of evidence has established that cholesterol-lowering statin drugs, widely used for the prevention of cardiovascular disease, do increase the risk of new-onset diabetes, possibly by impairing pancreatic beta cell function and decreasing peripheral insulin sensitivity. Groups at particular risk include the elderly, women, and Asians. The diabetogenic effect of statins appear directly related to statin dose and the degree of attained cholesterol lowering. Statins can cause hyperinsulinemia even in the absence of hyperglycemia and the potential mitogenic effects and implications of prolonged hyperinsulinemia are discussed. Suggestions are made as to how physicians might avert the hyperinsulinemic and diabetogenic effects of statin therapy in clinical practice, and modulate the detrimental effects of these drugs on exercise performance. Finally, long-term studies are needed to determine if the deleterious hyperinsulinemic and diabetogenic effects of statin therapy undermine the beneficial cardiovascular disease risk outcomes in various segments of the population.

Addition of exenatide or sitagliptin to insulin in new onset type 1 diabetes: a randomized, open label study

Incretin based therapies are known to have pleotropic benefits in type 2 diabetes but have not been studied in new onset type 1 diabetes. In this randomized, open label study, we investigated the effect of the addition of exenatide or sitagliptin to insulin in patients with new onset type 1 diabetes. Our data suggest that the addition of exenatide and sitagliptin decreases insulin requirements without increasing endogenous insulin production and hypoglycemic events.

Microarray analysis of isolated human islet transcriptome in type 2 diabetes and the role of the ubiquitin-proteasome system in pancreatic beta cell dysfunction

To shed light on islet cell molecular phenotype in human type 2 diabetes (T2D), we studied the transcriptome of non-diabetic (ND) and T2D islets to then focus on the ubiquitin-proteasome system (UPS), the major protein degradation pathway. We assessed gene expression, amount of ubiquitinated proteins, proteasome activity, and the effects of proteasome inhibition and prolonged exposure to palmitate. Microarray analysis identified more than one thousand genes differently expressed in T2D islets, involved in many structures and functions, with consistent alterations of the UPS. Quantitative RT-PCR demonstrated downregulation of selected UPS genes in T2D islets and beta cell fractions, with greater ubiquitin accumulation and reduced proteasome activity. Chemically induced reduction of proteasome activity was associated with lower glucose-stimulated insulin secretion, which was partly reproduced by palmitate exposure. These results show the presence of many changes in islet transcriptome in T2D islets and underline the importance of the association between UPS alterations and beta cell dysfunction in human T2D.

The novel GLP-1-gastrin dual agonist, ZP3022, increases β-cell mass and prevents diabetes in db/db mice

AIM

Diabetes is characterized by β-cell deficiency, and therefore restoration of β-cell function has been suggested as a potential therapy. We hypothesized that a novel glucagon-like peptide-1 (GLP-1)-gastrin dual agonist, ZP3022, improves glycaemic control via improvement of β-cell status in db/db mice.

METHODS

Diabetic mice were studied following short- or long-term treatment with either the GLP-1-gastrin dual agonist or the commercially available GLP-1 agonists (exendin-4 and liraglutide). The effects on glycaemic control were addressed by repeated glucose tolerance tests and/or measurements of HbA1c levels, and pancreatic islet and β-cell masses were determined by stereology.

RESULTS

ZP3022 and the pure GLP-1 agonists improved glycaemic control after both short- and long-term treatment compared with vehicle. Interestingly, the effect was sustainable only in mice treated with ZP3022. Stereology data displayed a dose-dependent increase of β-cell mass (p < 0.05) following treatment with ZP3022, whereas no significant effect of liraglutide was observed (β-cell mass: vehicle 3.7 ± 0.2 mg; liraglutide (30 nmol/kg) 3.4 ± 0.5 mg; ZP3022 (30 nmol/kg) 4.3 ± 0.4 mg and ZP3022 (100 nmol/kg) 5.2 ± 0.4 mg).

CONCLUSION

The novel GLP-1-gastrin dual agonist, ZP3022, improved glycaemic control in db/db mice, and pancreatic islet and β-cell mass increased significantly following treatment with ZP3022 compared with vehicle.

Noninvasive monitoring of β-cell mass and fetal β-cell genesis in mice using bioluminescence imaging

Bioluminescence imaging (BLI) has been applied in gene therapy and research to screen for transgene expression, progression of infection, tumor growth and metastasis, and transplantation. It enables real-time and relatively noninvasive localization and serial quantification of biological processes in experimental animals. In diabetes research, BLI has been employed for the quantification of β-cell mass, monitoring of islet graft survival after transplantation, and detection of reporter gene expression. Here, we explore the use of BLI in a transgenic mouse expressing luciferase under the control of the mouse insulin 1 promoter (MIP-Luc-VU). A previous report on MIP-Luc-VU mice showed luminescence intensities emitted from the islets correlated well with the number of islets in vitro and in vivo. In this study, we showed MIP-Luc-VU mice fed a high fat diet for 8 weeks gave rise to a greater bioluminescent signal than mice fed a regular diet for the same period of time. Conversely, there was a strong reduction in the signal observed in diabetic Mafa-deficient/Mafk-transgenic mutant mice and streptozotocin-treated mice, reflecting the loss of β-cells. Furthermore, we were able to monitor fetal β-cell genesis in MIP-Luc-VU mice during the late gestational stage in a noninvasive and repetitive manner. In summary, we show that bioluminescence imaging of mice expressing a β-cell specific reporter allows detection of changes in β-cell mass and visualization of fetal β-cell neogenesis in uteri.

Possible role of GLP-1 and its agonists in the treatment of type 1 diabetes mellitus

Unfortunately, the only approved medical treatment for type 1 diabetes mellitus (DM) is insulin, despite the fact that tight control cannot be reached without some serious side effects such as hypoglycemia and weight gain. More and more importance is now shifted towards developing new drugs that can reach a better glycemic control with lesser side effects. Some of these promising drugs are the glucagon-like peptides 1 (GLP-1) and their agonists, which have been FDA approved for the treatment of type 2 DM. The purpose of this article is to review all of the relevant literature on the potential role of GLP-1 in the treatment of type 1 DM. The major source of data acquisition included Medline search strategies, using the words "type 1 diabetes mellitus" and "GLP-1." Articles published in the last 20 years were screened. GLP-1 increases insulin secretion in humans with existing beta cells; it also decreases glucagon secretion, and blunts appetite. Of note, new animal studies demonstrate a role in beta cell-proliferation and decreased apoptosis. Because of all the effects mentioned above, GLP-1 seems to be a promising drug for type 1 DM treatment, but more studies are still needed before solid conclusions can be drawn.

Role of stereotaxically injected IgG from db/db mice in the phosphorylation of the microtubule-associated protein tau in hippocampus

People with type 2 diabetes (T2DM) mellitus are high risk for dementia and Alzheimer's disease (AD) via several plausible pathways. However, the underlying mechanisms have been still unclear, and the relation of immune injury to the pathogenesis of T2DM-related AD is not yet completely understood. Our present study aimed to elucidate the possible role of immunoglobulin IgG in the immune process of AD associated with T2DM in db/db mice. Hippocampi of 20 db/db mice and 20 C57BL/6 mice were subjected to immunohistochemistry and immunofluorescence assays. The phosphorylation of tau, glycogen synthase kinase (GSK)-3β and AKT activity was examined by Western blot analysis. IgG purified from the sera of IgG deposit-positive db/db mice was stereotaxically injected into the hippocampi of another 12 db/db mice and 12 C57BL/6 mice. The phosphorylation of tau, Abeta, GSK-3β and AKT activity was analyzed. Compared with the C57BL/6 control, 13 of the 20 db/db mice exhibited high levels of IgG deposits in the hippocampus. Treatment with IgG triggered tau hyperphosphorylations and Abeta deposition, which are likely major factors in AD. Meanwhile, IgG inhibited AKT phosphorylation and promoted GSK-3β activity. The IgG deposits observed in some db/db mice were possibly related to the impairment of T2DM-related AD development. Some autoimmune processes may be involved in AD in type 2 diabetes mellitus development at the level of the hippocampus.

Transient overexpression of cyclin D2/CDK4/GLP1 genes induces proliferation and differentiation of adult pancreatic progenitors and mediates islet regeneration

The molecular mechanism of β-cell regeneration remains poorly understood. Cyclin D2/CDK4 expresses in normal β cells and maintains adult β-cell growth. We hypothesized that gene therapy with cyclin D2/CDK4/GLP-1 plasmids targeted to the pancreas of STZ-treated rats by ultrasound-targeted microbubble destruction (UTMD) would force cell cycle re-entry of residual G(0)-phase islet cells into G(1)/S phase to regenerate β cells. A single UTMD treatment induced β-cell regeneration with reversal of diabetes for 6 mo without evidence of toxicity. We observed that this β-cell regeneration was not mediated by self-replication of pre-existing β cells. Instead, cyclin D2/CDK4/GLP-1 initiated robust proliferation of adult pancreatic progenitor cells that exist within islets and terminally differentiate to mature islets with β cells and α cells.

Diabetes mellitus: Exploring the challenges in the drug development process

Diabetes mellitus has reached epidemic proportions and continues to be a major burden on society globally. The International Diabetes Federation (IDF) estimated the global burden of diabetes to be 366 million in 2011 and predicted that by 2030 this will have risen to 552 million. In spite of newer and effective treatment options, newer delivery and diagnostic devices, stricter glycaemic targets, better treatment guidelines and increased awareness of the disease, baseline glycosylated hemoglobin remains relatively high in subjects diagnosed and treated with type 2 diabetes. The search continues for an ideal anti diabetic drug that will not only normalize blood glucose but also provide beta cell rest and possibly restoration of beta cell function. The development of anti diabetic drugs is riddled with fundamental challenges. The concept of beta cell rest and restoration is yet to be completely understood and proven on a long term. The ideal therapeutic approach to treating type 2 diabetes is not yet determined. Our understanding of drug safety in early clinical development is primarily limited to "Type A" reactions. Until marketing authorization most drugs are approved based on the principle of confirming non-inferiority with an existing gold standard or determining superiority to a placebo. The need to obtain robust pharmaco-economic data prior to marketing authorization in order to determine appropriate pricing of a new drug remains a major challenge. The present review outlines some of the challenges in drug development of anti-diabetic drugs citing examples of pulmonary insulin, insulin analogues, thiazolidinediones and the GLP1 analogues.

The pancreatic beta cell surface proteome

The pancreatic beta cell is responsible for maintaining normoglycaemia by secreting an appropriate amount of insulin according to blood glucose levels. The accurate sensing of the beta cell extracellular environment is therefore crucial to this endocrine function and is transmitted via its cell surface proteome. Various surface proteins that mediate or affect beta cell endocrine function have been identified, including growth factor and cytokine receptors, transporters, ion channels and proteases, attributing important roles to surface proteins in the adaptive behaviour of beta cells in response to acute and chronic environmental changes. However, the largely unknown composition of the beta cell surface proteome is likely to harbour yet more information about these mechanisms and provide novel points of therapeutic intervention and diagnostic tools. This article will provide an overview of the functional complexity of the beta cell surface proteome and selected surface proteins, outline the mechanisms by which their activity may be modulated, discuss the methods and challenges of comprehensively mapping and studying the beta cell surface proteome, and address the potential of this interesting subproteome for diagnostic and therapeutic applications in human disease.

The protective effect of peroxiredoxin II on oxidative stress induced apoptosis in pancreatic β-cells

Excessive loss of pancreatic β-cells, mainly through apoptosis, contributes to the development of diabetic hyperglycemia. Oxidative stress plays a major role in the process of β-cell apoptosis due to low expression level of endogenous antioxidants in the β-cells. Peroxiredoxins (PRDX) are a family of peroxide reductases which uses thioredoxin to clear peroxides. Several members of PRDX have been found in β-cells and recent studies suggested that these antioxidant enzymes possess protective effects in β-cells against oxidative stress mediated apoptosis. In this study, we aimed to investigate the role of PRDX2 in modulating β-cell functions. We detected the expression of PRDX2 both at the transcript and protein levels in the clonal β-cells INS-1 and MIN6 as well as rodent islets. Western blot showed that treatment of MIN6 β-cell line with proinflammatory cytokines, palmitic acid or streptozotocin dose- or time-dependently increased apoptosis, which was associated with reduced endogenous expression levels of PRDX2. To examine the role for PRDX2 in the apoptotic stimuli-induced β-cell apoptosis, we used plasmid overexpression and siRNA knockdown strategies to investigate whether the elevation or knockdown of PRDX2 affects stimuli-induced apoptosis in the β-cells. Remarkably, overexpression of PRDX2 in MIN6 cells significantly attenuated the oxidative stresses mediated apoptosis, as evaluated by cleaved caspase 3 expression, nuclear condensation and fragmentation, as well as FACS analysis. Conversely, attenuation of PRDX2 protein expression using siRNA knockdown exaggerated the cell death induced by proinflammatory cytokines and palmitic acid in the MIN6 cells. These results suggest that PRDX2 may play a protective role in pancreatic β-cells under oxidative stress.

The ghrelin gene products and exendin-4 promote survival of human pancreatic islet endothelial cells in hyperglycaemic conditions, through phosphoinositide 3-kinase/Akt, extracellular signal-related kinase (ERK)1/2 and cAMP/protein kinase A (PKA) signalling pathways

AIMS/HYPOTHESIS

Pancreatic islet microendothelium exhibits unique features in interdependent relationship with beta cells. Gastrointestinal products of the ghrelin gene, acylated ghrelin (AG), unacylated ghrelin (UAG) and obestatin (Ob), and the incretin, glucagon-like peptide-1 (GLP-1), prevent apoptosis of pancreatic beta cells. We investigated whether the ghrelin gene products and the GLP-1 receptor agonist exendin-4 (Ex-4) display survival effects in human pancreatic islet microendothelial cells (MECs) exposed to chronic hyperglycaemia.

METHODS

Islet MECs were cultured in high glucose concentration and treated with AG, UAG, Ob or Ex-4. Apoptosis was assessed by DNA fragmentation, Hoechst staining of the nuclei and caspase-3 activity. Western blot analyses and pharmacological inhibition of protein kinase B (Akt) and extracellular signal-related kinase (ERK)1/2 pathways, detection of intracellular cAMP levels and blockade of adenylyl cyclase (AC)/cAMP/protein kinase A (PKA) signalling were performed. Levels of NO, IL-1β and vascular endothelial growth factor (VEGF)-A in cell culture supernatant fractions were measured.

RESULTS

Islet MECs express the ghrelin receptor GHS-R1A as well as GLP-1R. Treatment with AG, UAG, Ob and Ex-4 promoted cell survival and significantly inhibited glucose-induced apoptosis, through activation of PI3K/Akt, ERK1/2 phosphorylation and intracellular cAMP increase. Moreover, peptides upregulated B cell lymphoma 2 (BCL-2) and downregulated BCL-2-associated X protein (BAX) and CD40 ligand (CD40L) production, and significantly reduced the secretion of NO, IL-1β and VEGF-A.

CONCLUSIONS/INTERPRETATION

The ghrelin gene-derived peptides and Ex-4 exert cytoprotective effects in islet MECs. The anti-apoptotic effects involve phosphoinositide 3-kinase (PI3K)/Akt, ERK1/2 and cAMP/PKA pathways. These peptides could therefore represent a potential tool to improve islet vascularisation and, indirectly, islet cell function.

Incretin-based therapies--review of the physiology, pharmacology and emerging clinical experience

Diabetes therapies based on manipulation of the incretin system are now widely available, with millions of people receiving treatment. The incretin hormones, glucose-dependent insulinotropic peptide and glucagon-like peptide-1 are released from endocrine cells in the small intestinal mucosa primarily in response to oral nutrient ingestion. They have various effects, but those most relevant to metabolic dysfunction include stimulation of insulin and suppression of glucagon secretion, with resultant reduction in fasting and postprandial glucose. Incretin secretion and/or action is impaired in type 2 diabetes, leading to development of strategies aimed at redressing this abnormality. These strategies include pharmacological inhibition of dipeptidyl peptidase-4, the enzyme responsible for the short half-life of endogenous incretins, and administration of long-acting dipeptidyl peptidase-4-resistant peptides that bind to and activate the glucagon-like peptide-1 receptor. In this review, we address aspects of incretin biology and pharmacotherapy with a view to highlighting potentially clinically relevant issues and areas of basic research that may impinge on these.

Evaluation of antidiabetic potential of selected traditional Chinese medicines in STZ-induced diabetic mice

AIMS

Traditional Chinese medicine (TCM) has been used for treating complex chronic diseases owing to their fewer side-effects, better patient tolerance and relatively less cost. The present work was carried out to study the anti-diabetic efficacy and mechanisms of 34 TCMs.

MATERIALS AND METHODS

Streptozotocin (STZ)-diabetic mice were orally administrated with corresponding herbal solution once a day for 4 weeks. At the end of experiment, the level of plasma glucose, malondialdehyde (MDA), the activity of superoxide dismutase (SOD) and the serum aldose reductase (AR) were determined, the effects of TCM extract on α-glucosidase and angiotensin-converting enzyme (ACE) in vitro were also evaluated.

RESULTS

13 out of the 34 herbs showed a statistically significant plasma glucose lowering action compared with the diabetic control group. Biochemical analysis revealed that Atractylodes macrocephala, Codonopsis pilosula, Dioscorea opposite, Flos lonicerae and Pueraria lobata may retard the progression of diabetes via reduce the blood glucose level and prevent the increase of AR activity. Other tested herbs, such as Ramulus cinnamomi, Cinnamomum cassia, and Eucommia ulmoides, showed the antidiabetic ability by either prevent the decrease in SOD activity or suppress the increase of MDA. Zymologic assay reveals that Pueraria lobata and Anemarrhena asphodeloides showed the highest inhibition against α-glucosidase and ACE respectively. Interestingly, the post-treatment glucose levels and AR activity were positively correlated with kidney/body weight of 34 herbs treated diabetic mice (p = 0.02, 0.04 respectively).

CONCLUSIONS

Several potential antidiabetic herbs derived from Chinese traditional pharmacopeia such as Dioscorea opposite, Pueraria lobata, Codonopsis pilosula and Ramulus cinnamomi, have been found to exert a beneficial action on diabetes and diabetic complications via multi-mechanisms.

Diabetes in Danish bank voles (M. glareolus): survivorship, influence on weight, and evaluation of polydipsia as a screening tool for hyperglycaemia

Background

Previous studies have concluded that the development of polydipsia (PD, a daily water intake ≥21 ml) among captive Danish bank voles, is associated with the development of a type 1 diabetes (T1D), based on findings of hyperglycaemia, glucosuria, ketonuria/-emia, lipemia, destroyed beta cells, and presence of autoantibodies against GAD65, IA-2, and insulin.

Aim and Methods

We retrospectively analysed data from two separate colonies of Danish bank voles in order to 1) estimate survivorship after onset of PD, 2) evaluate whether the weight of PD voles differed from non-PD voles, and, 3), evaluate a state of PD as a practical and non-invasive tool to screen for voles with a high probability of hypeglycaemia. In addition, we discuss regional differences related to the development of diabetes in Scandinavian bank voles and the relevance of the Ljungan virus as proposed etiological agent.

Results

We found that median survival after onset of PD is at least 91 days (lower/upper quartiles = 57/134 days) with a maximum recording of at least 404 days survivorship. The development of PD did not influence the weight of Danish bank voles. The measures of accuracy when using PD as predictor of hyperglycaemia, i.e. sensitivity, specificity, positive predictive value, and negative predictive value, equalled 69%, 97%, 89%, and 89%, respectively.

Conclusion

The relatively long survival of Danish PD bank voles suggests potentials for this model in future studies of the long-term complications of diabetes, of which some observations are mentioned. Data also indicates that diabetes in Danish bank is not associated with a higher body weight. Finally, the method of using measurements of daily water intake to screen for voles with a high probability of hyperglycaemia constitutes a considerable refinement when compared to the usual, invasive, methods.

The antioxidant HDL-associated paraoxonase-1 (PON1) attenuates diabetes development and stimulates β-cell insulin release

OBJECTIVE

To analyze the direct effects of paraoxonase-1 (PON1) on diabetes development and on β-cell insulin release.

METHODS AND RESULTS

Injection of rePON1 to mice, prior to STZ-induced diabetes, resulted in reduced incidence of diabetes, as well as, in higher serum insulin levels. Incubation of β-cells with PON1 also dose-dependently increased insulin secretion and its cellular content. PON1 increased cell survival under high glucose levels, but not under high STZ concentrations. The addition of the PON1 carrier in the circulation - HDL, to βTC3 cell line, had an additive effect on PON1-induced insulin secretion. PON1 administration to mice or incubation with β-cells was associated with a substantial decreased oxidative stress. Just like PON1, the dietary anti-oxidants, pomegranate juice, punicalagin (major polyphenol in pomegranate) or vitamin E, also increased insulin release from βTC3, but unlike PON1, failed to increase insulin cellular content, suggesting a possible role for PON1 in insulin biosynthesis, separately from PON1 antioxidative effect. Both, PON1 catalytic activity and PON1 association to HDL, were not required for PON1 stimulation of insulin release from β-cells. However, the PON1 free sulfhydryl group was shown to be essential for insulin release by PON1, as blocking the PON1 SH group, abolished PON1 stimulatory effect on insulin secretion.

CONCLUSION

PON1 is a potent anti-diabetic enzyme that exerts this protection against diabetes through its antioxidative, as well as via its insulin stimulation properties on β-cells.

Isolation of genes involved in pancreas regeneration by subtractive hybridization

The deterioration of β cells in the pancreas is a crucial factor in the progression of diabetes mellitus; therefore, the recovery of β cells is of vital importance for effective diabetic therapeutic strategies. Partially pancreatectomized rats have been used for the investigation of pancreatic regeneration. Because it was determined that tissue extract from the partially-dissected pancreas induces pancreatic differentiation in embryonic stem cells, paracrine factors were thought to be involved in the regeneration. In this study, we screened for genes that had higher mRNA levels 2 days after 60%-pancreatectomy. The genes were isolated using subtractive hybridization and DNA sequencing. Twelve genes (adipsin, Aplp2, Clu, Col1a2, Glul, Krt8, Lgmn, LOC299907, LOC502894, Pla2g1b, Reg3α and Xbp1) were identified, and RT-PCR and real-time PCR analyses were performed to validate their expression levels. Among the genes identified, three genes (Glul, Lgmn and Reg3a) were selected for further analyses. Assays revealed that Glul and Reg3α enhance cell growth. Glul, Lgmn and Reg3α change the expression level of islet marker genes, where NEUROD, NKX2.2, PAX4 and PAX6 are up-regulated and somatostatin is down-regulated. Thus, we believe that Glul, Lgmn and Reg3a can serve as novel targets in diabetes mellitus genetic therapy.

Cell proliferation in visceral organs induced by ventromedial hypothalamic (VMH) lesions: Development of electrical VMH lesions in mice and resulting pathophysiological profiles

We have found that ventromedial hypothalamic (VMH) lesions produced by electrocoagulation induce cell proliferation in visceral organs through vagal hyperactivity, and also stimulate regeneration of partially resected liver in rats. To facilitate identification of proliferative and/or regenerative factors at the gene level, we developed electrical production of VMH lesions in mice, for which more genetic information is available compared to rats, and examined the pathophysiological profiles in these mice. Using ddy mice, we produced VMH lesions with reference to the previously reported method in rats. We then examined the pathophysiological profiles of the VMH-lesioned mice. Electrical VMH lesions in mice were produced using the following coordinates: 1.6 mm posterior to the bregma, anteriorly; 0.5 mm lateral to the midsagittal line, transversely; and 0.2 mm above the base of the skull, vertically, with 1 mA of current intensity and 10 s duration. The VMH-lesioned mice showed similar metabolic characteristics to those of VMH-lesioned rats, including body weight gain, increased food intake, increased percentage body fat, and elevated serum insulin and leptin. However, there were some differences in short period of hyperphagia, and in normal serum lipids compared to those of VMH-lesioned rats. The mice showed a similar cell proliferation in visceral organs, including stomach, small intestine, liver, and, exocrine and endocrine pancreas. In conclusion, procedures for development of VMH lesions in mice by electrocoagulation were developed and the VMH-lesioned mice showed pathophysiological profiles similar to those of VMH-lesioned rats, particularly in cell proliferation in visceral organs. These findings have not been observed previously in gold thioglucose-induced VMH-lesioned mice. This model may be a new tool for identifying factors involved in cell proliferation or regeneration in visceral organs.

Effect of alogliptin, pioglitazone and glargine on pancreatic β-cells in diabetic db/db mice

OBJECTIVE

Progressive β-cell dysfunction and loss of β-cell mass are fundamental pathogenic features of type 2 diabetes. To examine if anti-diabetic reagents, such as insulin, pioglitazone (pio), and alogliptin (alo), have protective effects on β-cell mass and function in vivo, we treated obese diabetic db/db mice with these reagents.

METHODS

Male db/db mice were treated with a chow including pio, alo, or both of them from 8 to 16 weeks of age. Insulin glargine (gla) was daily injected subcutaneously during the same period.

RESULTS

At 16 weeks of age, untreated db/db mice revealed marked increase of HbA1c level, whereas those treated with pio, pio+alo, or insulin revealed the almost same HbA1c levels as non-diabetic db/m mice. Islet mass evaluated by direct counting in the whole pancreas and insulin content in isolated islets were preserved in pio, pio+alo and gla groups compared with untreated or alo groups, and there was no difference among pio, pio+alo and gla groups. To precisely evaluate islet β-cell functions, islet perifusion analysis was performed. In pio, pio+alo and gla groups, biphasic insulin secretion was preserved compared with untreated or alo groups. In particular, pio+alo as well as gla therapy preserved almost normal insulin secretion, although pio therapy improved partially. To examine the mechanism how these reagents exerted beneficial effects on β-cells, we evaluated expression levels of various factors which are potentially important for β-cell functions by real-time RT-PCR and immunohistochemistry. The results showed that expression levels of MafA and GLP-1 receptor were markedly decreased in untreated and alo groups, but not in pio, pio+alo and gla groups.

CONCLUSION

Combination therapy with pio and alo almost completely normalized β-cell functions in vivo, which was comparable with gla treatment.

Proinsulin levels in patients with pancreatic diabetes are associated with functional changes in insulin secretion rather than pancreatic beta-cell area

INTRODUCTION

Hyperproinsulinaemia has been reported in patients with type 2 diabetes. It is unclear whether this is due to an intrinsic defect in β-cell function or secondary to the increased demand on the β-cells. We investigated whether hyperproinsulinaemia is also present in patients with secondary diabetes, and whether proinsulin levels are associated with impaired β-cell area or function.

PATIENTS AND METHODS

Thirty-three patients with and without diabetes secondary to pancreatic diseases were studied prior to pancreatic surgery. Intact and total proinsulin levels were compared with the pancreatic β-cell area and measures of insulin secretion and action.

RESULTS

Fasting concentrations of total and intact proinsulin were similar in patients with normal, impaired (including two cases of impaired fasting glucose) and diabetic glucose tolerance (P=0.58 and P=0.98 respectively). There were no differences in the total proinsulin/insulin or intact proinsulin/insulin ratio between the groups (P=0.23 and P=0.71 respectively). There was a weak inverse association between the total proinsulin/insulin ratio and pancreatic β-cell area (r(2)=0.14, P=0.032), whereas the intact proinsulin/insulin ratio and the intact and total proinsulin levels were unrelated to β-cell area. However, a strong inverse relationship between homeostasis model assessment index of β-cell function and both the total and the intact proinsulin/insulin ratio was found (r(2)=0.55 and r(2)=0.48 respectively). The association of insulin resistance (IR) with intact proinsulin was much weaker than the correlation with fasting insulin.

CONCLUSIONS

Hyperproinsulinaemia is associated with defects in insulin secretion rather than a reduction in β-cell area. The weak association between intact proinsulin and IR argues against the usefulness of this parameter in clinical practice.

Endogenous hyperinsulinaemia in insulinoma patients is not associated with changes in beta-cell area and turnover in the tumor-adjacent pancreas

INTRODUCTION

Insulin therapy has been suggested to preserve beta-cell mass in patients with diabetes through the mechanisms of beta-cell rest as well as direct effects on beta-cell proliferation. However, data about the effects of hyperinsulinism on beta-cell mass and turnover in humans are sparse.

PATIENTS AND METHODS

Pancreatic tissue specimens from five patients with pancreatic insulinomas and ten non-diabetic control subjects were examined. Pancreatic sections were stained for insulin, Ki67 (replication) and TUNEL (apoptosis), and quantitative morphometric analyses were performed.

RESULTS

Fractional beta-cell area was 1.11%±0.67% in the tumor-free pancreatic tissue of the insulinoma patients and 0.78%±0.26% in the control group (p=0.19). There also were no differences in islet size (p=0.62) or beta-cell nuclear diameter (p=0.20). Beta-cell replication and apoptosis were infrequently detected, without any measurable differences between the groups. There were also no differences in percentage of duct cells expressing insulin (p=0.47), a surrogate marker for islet neogenesis.

CONCLUSIONS

Beta-cell area and turnover are not significantly altered in the proximity of intra-pancreatic insulinomas. Future in vivo studies, ideally employing larger animal models, are warranted to further evaluate the impact of exogenous insulin on beta-cell turnover.

Beta-cell replication is increased in donor organs from young patients after prolonged life support

OBJECTIVE

This study assesses beta-cell replication in human donor organs and examines possible influences of the preterminal clinical conditions.

RESEARCH DESIGN AND METHODS

beta-Cell replication was quantified in a consecutive series of n = 363 human organ donors using double immunohistochemistry for Ki67 and insulin. Uni- and multivariate analysis was used to correlate replication levels to clinical donor characteristics and histopathologic findings.

RESULTS

beta-Cell replication was virtually absent in most donors, with < or =0.1% Ki67-positive beta-cells in 72% of donors. A subpopulation of donors, however, showed markedly elevated levels of replication of up to 7.0% Ki67-positive beta-cells. beta-Cell replication was accompanied by the increased replication of glucagon-, somatostatin-, and CA19.9-positive cells. Prolonged life support, kidney dysfunction, relatively young donor age, inflammatory infiltration, and prolonged brain death before organ retrieval were all found to be significantly associated with an increased level (> or =90th percentile) of beta-cell replication, with the first three risk factors being independent predictors. Increased beta-cell replication was most often noted in relatively young donors (< or =25 years) who received prolonged (> or =3 days) life support (68%); in contrast, it was rare in donors with a short duration of life support regardless of age (1%). Prolonged life support was accompanied by increased levels of CD68(+) and LCA/CD45(+) infiltration in the pancreatic parenchyma.

CONCLUSION

These results indicate that preterminal clinical conditions in (young) organ donors can lead to increased inflammatory infiltration of the pancreas and to increased beta-cell replication.

Determinants of glucose control in patients with chronic pancreatitis

AIMS/HYPOTHESIS

Diabetes frequently develops in patients with chronic pancreatitis (CP). Partial pancreatectomy has emerged as a treatment option for such patients. We addressed whether the development of diabetes in CP patients is related to pancreatic beta cell area or clinical variables, and which factors predict the diabetes risk after partial pancreatectomy.

METHODS

Fractional beta cell area was determined in pancreatic tissue samples obtained from 114 CP patients undergoing pancreatic surgery and related to measures of glucose control, as well as clinical and anthropometric data. Seventy-four patients without diabetes at the time of surgery were contacted again 2.5 +/- 1.0 years after partial pancreatectomy in order to obtain information about the post-operative development of diabetes.

RESULTS

In the surgical samples in the whole cohort, pancreatic beta cell area was 0.40 +/- 0.06% in patients with and 0.64 +/- 0.06% in those without previously known diabetes (p = 0.039). There was an inverse non-linear relationship between pancreatic beta cell area and fasting glucose concentrations (r = 0.29) as well as HbA(1c) levels (r = 0.36). Nineteen out of 74 previously normoglycaemic patients (26%) developed diabetes over an average period of 2.5 years of follow-up. Pre-operative fasting glucose levels, HbA(1c) and BMI were identified as predictors of diabetes after partial pancreatectomy. However, pancreatic beta cell area did not differ in those who subsequently developed diabetes (0.66 +/- 0.15%) and those who did not (0.62 +/- 0.08%, p = 0.45).

CONCLUSIONS/INTERPRETATION

Hyperglycaemia in CP patients is associated with reduced beta cell area. However, reduced beta cell area does not predict the development of diabetes, suggesting that other factors are more important determinants of alterations in glucose metabolism in patients with CP.

Effects of high-density lipoproteins on pancreatic beta-cell insulin secretion

OBJECTIVE

Type 2 diabetes is characterized by impaired beta-cell secretory function, insulin resistance, reduced high-density lipoprotein (HDL) levels, and increased cardiovascular risk. Given the current interest in therapeutic interventions that raise HDLs levels, this study investigates the effects of HDLs on insulin secretion from beta-cells.

METHODS AND RESULTS

Incubation of Min6 cells and primary islets under basal or high-glucose conditions with either apolipoprotein (apo) A-I or apoA-II in the lipid-free form, as a constituent of discoidal reconstituted HDLs (rHDLs), or with HDLs isolated from human plasma increased insulin secretion up to 5-fold in a calcium-dependent manner. The increase was time and concentration dependent. It was also K(ATP) channel and glucose metabolism dependent under high-glucose, but not low-glucose, conditions. The lipid-free apolipoprotein-mediated increase in insulin secretion was ATP binding cassette (ABC) transporter A1 and scavenger receptor-B1 dependent. The rHDL-mediated increase in insulin secretion was ABCG1 dependent. Exposure of beta-cells to lipid-free apolipoproteins also increased insulin mRNA expression and insulin secretion without significantly depleting intracellular insulin or cholesterol levels.

CONCLUSIONS

These results establish that lipid-free and lipid-associated apoA-I and apoA-II increase beta-cell insulin secretion and indicate that interventions that raise HDLs levels may be beneficial in type 2 diabetes.

Combination treatment with alogliptin and voglibose increases active GLP-1 circulation, prevents the development of diabetes and preserves pancreatic beta-cells in prediabetic db/db mice

AIM

Alogliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, and voglibose, an alpha-glucosidase inhibitor, have different but complementary mechanisms of action on glucagon-like peptide-1 (GLP-1) regulation and glucose-lowering effects. The present study evaluated the chronic effects of combination treatment with alogliptin and voglibose in prediabetic db/db mice.

METHODS

Alogliptin (0.03%) and voglibose (0.001%) alone or in combination were administered in the diet to prediabetic db/db mice.

RESULTS

After 3 weeks, voglibose treatment increased GLP-1 secretion (voglibose alone, 1.6-fold; alogliptin plus voglibose, 1.5-fold), while it decreased plasma glucose-dependent insulinotropic polypeptide (GIP) (voglibose alone, -30%; alogliptin plus voglibose, -29%). Alogliptin, voglibose and combination treatment decreased plasma DPP-4 activity by 72, 15 and additively by 80%, respectively, and increased plasma active GLP-1 levels by 4.5-, 1.8- and synergistically by 9.1-fold respectively. Combination treatment increased plasma insulin by 3.6-fold (alogliptin alone, 1.3-fold; voglibose alone, 1.8-fold), decreased plasma glucagon by 30% (alogliptin alone, 11%; voglibose alone, 8%), and prevented the development of diabetes, much more effectively than either agent alone. After 4 weeks, alogliptin, voglibose and combination treatment increased pancreatic insulin content by 1.6-, 3.4- and synergistically by 8.5-fold respectively. Furthermore, combination treatment resulted in an increased expression of insulin, pancreatic and duodenal homeobox 1 (PDX1) and glucose transporter 2 (GLUT2), and maintenance of normal beta/alpha-cell distribution in the pancreatic islet.

CONCLUSIONS

Chronic treatment with alogliptin in combination with voglibose concurrently increased active GLP-1 circulation, increased insulin secretion, decreased glucagon secretion, prevented the onset of the disease, and preserved pancreatic beta-cells and islet structure in prediabetic db/db mice.

Benefit-risk assessment of exenatide in the therapy of type 2 diabetes mellitus

Exenatide is the first incretin mimetic, introduced into type 2 diabetes mellitus therapy in 2005, with first approval in the US. It is a glucagon-like peptide-1 (GLP-1) receptor agonist that can be used for treatment by twice-daily injection. A long-acting release formulation for once-weekly injection is in clinical development. Clinical studies and postmarketing experience with exenatide have shown a significant and sustained reduction in glycosylated haemoglobin (HbA(1c)) by approximately 1% together with other gylcaemic parameters without an intrinsic risk for hypoglycaemias, and a reduction in bodyweight by 5.3 kg in 82 weeks. Blood pressure and lipids are also favourably affected, but hard cardiovascular endpoints are not yet available. Animal studies show an improvement of beta-cell function and an increase in beta-cell mass after exenatide treatment. The most frequent adverse events associated with exenatide therapy are nausea and antibody formation (both approximately 40%). Nausea, mostly mild and transient, was responsible for a 6% dropout rate in clinical studies. A recent review on the association of acute pancreatitis with exenatide treatment showed no increased risk (relative risk 1.0; 95% CI 0.6, 1.7). This review gives a benefit-risk assessment of exenatide.

The effects of glucagon-like peptide-1 on the beta cell

Type 2 diabetes is a progressive disease characterized by insulin resistance and impaired beta-cell function. Treatments that prevent further beta-cell decline are therefore essential for the management of type 2 diabetes. Glucagon-like peptide-1 (GLP-1) is an incretin hormone that is known to stimulate glucose-dependent insulin secretion. Furthermore, GLP-1 appears to have multiple positive effects on beta cells. However, GLP-1 is rapidly degraded by dipeptidyl peptidase-4 (DPP-4), which limits the clinical relevance of GLP-1 for the treatment of type 2 diabetes. Two main classes of GLP-1-based therapies have now been developed: DPP-4 inhibitors and GLP-1 receptor agonists. Liraglutide and exenatide are examples of GLP-1 receptor agonists that have been developed to mimic the insulinotropic characteristics of endogenous GLP-1. Both have demonstrated improved beta-cell function in patients with type 2 diabetes, as assessed by homoeostasis model assessment-B analysis and proinsulin : insulin ratio. Additionally, liraglutide and exenatide are able to enhance first- and second-phase insulin secretion and are able to restore beta-cell sensitivity to glucose. Preclinical studies have shown that both liraglutide and exenatide treatment can increase beta-cell mass, stimulate beta-cell proliferation, increase beta-cell neogenesis and inhibit beta-cell apoptosis. Clinical studies are needed to confirm these findings in humans. Replication of these data in humans could have important clinical implications for the treatment of type 2 diabetes.

Treating type 2 diabetes: incretin mimetics and enhancers

As a consequence of excess abdominal adiposity and genetic predisposition, type 2 diabetes is a progressive disease, often diagnosed after metabolic dysfunction has taken hold of multiple organ systems. Insulin deficiency, insulin resistance and impaired glucose homeostasis resulting from beta-cell dysfunction characterize the disease. Current treatment goals are often unmet due to insufficient treatment modalities. Even when combined, these treatment modalities are frequently limited by safety, tolerability, weight gain, edema and gastrointestinal intolerance. Recently, new therapeutic classes have become available for treatment. This review will examine the new therapeutic classes of incretin mimetics and enhancers in the treatment of type 2 diabetes.

Inhibitor selectivity in the clinical application of dipeptidyl peptidase-4 inhibition

DPP-4 (dipeptidyl peptidase-4) degrades the incretin hormones GLP-1 (glucagon-like peptide-1) and GIP (gastric inhibitory polypeptide), decreasing their stimulatory effects on beta-cell insulin secretion. In patients with Type 2 diabetes, meal-related GLP-1 secretion is reduced. DPP-4 inhibitors (alogliptin, saxagliptin, sitagliptin and vildagliptin) correct the GLP-1 deficiency by blocking this degradation, prolonging the incretin effect and enhancing glucose homoeostasis. DPP-4 is a member of a family of ubiquitous atypical serine proteases with many physiological functions beyond incretin degradation, including effects on the endocrine and immune systems. The role of DPP-4 on the immune system relates to its extra-enzymatic activities. The intracytosolic enzymes DPP-8 and DPP-9 are recently discovered DPP-4 family members. Although specific functions of DPP-8 and DPP-9 are unclear, a potential for adverse effects associated with DPP-8 and DPP-9 inhibition by non-selective DPP inhibitors has been posed based on a single adverse preclinical study. However, the preponderance of data suggests that such DPP-8 and DPP-9 enzyme inhibition is probably without clinical consequence. This review examines the structure and function of the DPP-4 family, associated DPP-4 inhibitor selectivity and the implications of DPP-4 inhibition in the treatment of Type 2 diabetes.

The contribution of incretin hormones to the pathogenesis of type 2 diabetes

The incretin effect, that is, the postprandial augmentation of insulin secretion by gastrointestinal hormones, mediates approximately 50-70% of the overall insulin responses after a mixed meal or glucose ingestion in healthy subjects. In patients with type 2 diabetes, the incretin effect is markedly reduced, and this has been attributed to defects in the secretion and insulinotropic action of the two main incretin hormones, namely gastric inhibitory polypeptide (GIP) and glucagon-like peptide 1 (GLP-1). It has been speculated that a reduced incretin effect might precede the onset of hyperglycaemia in patients with type 2 diabetes. However, the secretion and action of GIP and GLP-1 is relatively unaltered in normal glucose-tolerant individuals at high risk for type 2 diabetes (e.g., first-degree relatives) and a diminished incretin effect is also detectable in other types of diabetes, thereby arguing against such reasoning. This article will describe the defects in the incretin system in patients with type 2 diabetes, summarise their relevance in the development of hyperglycaemia and discuss the potential individual roles of GIP and GLP-1 in the pathogenesis of type 2 diabetes.

The pancreas in human type 1 diabetes: providing new answers to age-old questions

PURPOSE OF REVIEW

Although studies of pancreata from type 1 diabetes (T1D) patients largely fell dormant for a period of decades, research efforts have recently been 'rekindled' in this area to address, using modern techniques, many unanswered questions related to the pathogenesis of this disease.

RECENT FINDINGS

As historically noted, a pancreatic infiltrate commonly referred to as 'insulitis' is present at the symptomatic onset of T1D. Recent studies have further characterized this infiltrate both in terms of its cellular composition as well as the mechanisms that likely underlie beta cell death in T1D. In addition, the notion that the pancreas from T1D patients is completely devoid of insulin producing cells years after the onset of disease has been challenged, whereas the concepts of whether beta cell regeneration or replication are present have also been subject to much debate. Novel concepts regarding the rate and degree of beta cell loss throughout the natural history of the disease have also been put forward to aid in explaining the disorder's pathogenesis.

SUMMARY

Although answers to many long-standing questions in T1D have recently been addressed, perhaps the main finding has been one supporting a disease of remarkable heterogeneity. However, additional lessons remain to be learned from the pancreas in T1D. Hence, attempts aimed at organizing the scientific community to address these issues are ongoing, particularly those from collaborative efforts, including the Belgium Organ Donor Consortium and the Network for Pancreatic Organ Donors with Diabetes (nPOD).

Functional assessment of pancreatic beta-cell area in humans

OBJECTIVE

beta-Cell mass declines progressively during the course of diabetes, and various antidiabetic treatment regimens have been suggested to modulate beta-cell mass. However, imaging methods allowing the monitoring of changes in beta-cell mass in vivo have not yet become available. We address whether pancreatic beta-cell area can be assessed by functional test of insulin secretion in humans.

RESEARCH DESIGN AND METHODS

A total of 33 patients with chronic pancreatitis (n = 17), benign pancreatic adenomas (n = 13), and tumors of the ampulla of Vater (n = 3) at various stages of glucose tolerance were examined with an oral glucose load before undergoing pancreatic surgery. Indexes of insulin secretion were calculated and compared with the fractional beta-cell area of the pancreas.

RESULTS

beta-Cell area was related to fasting glucose concentrations in an inverse linear fashion (r = -0.53, P = 0.0014) and to 120-min postchallenge glycemia in an inverse exponential fashion (r = -0.89). beta-Cell area was best predicted by a C-peptide-to-glucose ratio determined 15 min after the glucose drink (r = 0.72, P < 0.0001). However, a fasting C-peptide-to-glucose ratio already yielded a reasonably close correlation (r = 0.63, P < 0.0001). Homeostasis model assessment (HOMA) beta-cell function was unrelated to beta-cell area.

CONCLUSIONS

Glucose control is closely related to pancreatic beta-cell area in humans. A C-peptide-to-glucose ratio after oral glucose ingestion appears to better predict beta-cell area than fasting measures, such as the HOMA index.

Association of highly compact type II diabetes related islet amyloid polypeptide intermediate species at physiological temperature revealed by diffusion NMR spectroscopy

Self-association of human islet amyloid polypeptide (hIAPP) is correlated with the development of type II diabetes by the disruption of cellular homeostasis in islet cells through the formation of membrane-active oligomers. The toxic species of hIAPP responsible for membrane damage has not been identified. In this study, we show by pulsed field gradient NMR spectroscopy that the monomeric form of the toxic, amyloidogenic human variant of IAPP (hIAPP) adopts a temperature dependent compact folded conformation that is absent in both the nontoxic and nonamyloidogenic rat variant of IAPP and absent in hIAPP at low temperatures, suggesting this compact form of monomeric hIAPP may be linked to its later aggregation and cytotoxicity. In addition to the monomeric form of hIAPP, a large oligomeric species greater than 100 nm in diameter is also present but does not trigger the nucleation-dependent aggregation of IAPP at 4 degrees C, indicating the large oligomeric species may be an off-pathway intermediate that has been predicted by kinetic models of IAPP fiber formation. Furthermore, analysis of the polydispersity of the calculated diffusion values indicates small oligomeric species of hIAPP are absent in agreement with a recent ultracentrifugation study. The absence of small oligomeric species in solution suggests the formation of small, well-defined ion channels by hIAPP may proceed by aggregation of monomeric IAPP on the membrane, rather than by the insertion of preformed structured oligomers from the solution state as has been proposed for other amyloidogenic proteins.

Autophagy in human type 2 diabetes pancreatic beta cells

AIMS/HYPOTHESIS

Beta cell loss contributes to type 2 diabetes, with increased apoptosis representing an underlying mechanism. Autophagy, i.e. the physiological degradation of damaged organelles and proteins, may, if altered, be associated with a distinct form of cell death. We studied several features of autophagy in beta cells from type 2 diabetic patients and assessed the role of metabolic perturbation and pharmacological intervention.

METHODS

Pancreatic samples were obtained from organ donors and isolated islets prepared both by collagenase digestion and density gradient centrifugation. Beta cell morphology and morphometry were studied by electron microscopy. Gene expression studies were performed by quantitative RT-PCR.

RESULTS

Using electron microscopy, we observed more dead beta cells in diabetic (2.24 +/- 0.53%) than control (0.66 +/- 0.52%) samples (p < 0.01). Massive vacuole overload (suggesting altered autophagy) was associated with 1.18 +/- 0.54% dead beta cells in type 2 diabetic samples and with 0.36 +/- 0.26% in control samples (p < 0.05). Density volume of autophagic vacuoles and autophagosomes was significantly higher in diabetic beta cells. Unchanged gene expression of beclin-1 and ATG1 (also known as ULK1), and reduced transcription of LAMP2 and cathepsin B and D was observed in type 2 diabetic islets. Exposure of non-diabetic islets to increased NEFA concentration led to a marked increase of vacuole accumulation, together with enhanced beta cell death, which was associated with decreased LAMP2 expression. Metformin ameliorated autophagy alterations in diabetic beta cells and beta cells exposed to NEFA, a process associated with normalisation of LAMP2 expression.

CONCLUSIONS/INTERPRETATION

Beta cells in human type 2 diabetes have signs of altered autophagy, which may contribute to loss of beta cell mass. To preserve beta cell mass in diabetic patients, it may be necessary to target multiple cell-death pathways.

Adaptive beta-cell proliferation is severely restricted with advanced age

OBJECTIVE

Regeneration of the insulin-secreting beta-cells is a fundamental research goal that could benefit patients with either type 1 or type 2 diabetes. beta-Cell proliferation can be acutely stimulated by a variety of stimuli in young rodents. However, it is unknown whether this adaptive beta-cell regeneration capacity is retained into old age.

RESEARCH DESIGN AND METHODS

We assessed adaptive beta-cell proliferation capacity in adult mice across a wide range of ages with a variety of stimuli: partial pancreatectomy, low-dose administration of the beta-cell toxin streptozotocin, and exendin-4, a glucagon-like peptide 1 (GLP-1) agonist. beta-Cell proliferation was measured by administration of 5-bromo-2'-deoxyuridine (BrdU) in the drinking water.

RESULTS

Basal beta-cell proliferation was severely decreased with advanced age. Partial pancreatectomy greatly stimulated beta-cell proliferation in young mice but failed to increase beta-cell replication in old mice. Streptozotocin stimulated beta-cell replication in young mice but had little effect in old mice. Moreover, administration of GLP-1 agonist exendin-4 stimulated beta-cell proliferation in young but not in old mice. Surprisingly, adaptive beta-cell proliferation capacity was minimal after 12 months of age, which is early middle age for the adult mouse life span.

CONCLUSIONS

Adaptive beta-cell proliferation is severely restricted with advanced age in mice, whether stimulated by partial pancreatectomy, low-dose streptozotocin, or exendin-4. Thus, beta-cells in middle-aged mice appear to be largely postmitotic. Young rodents may not faithfully model the regenerative capacity of beta-cells in mature adult mice.

Exploring functional beta-cell heterogeneity in vivo using PSA-NCAM as a specific marker

Background

The mass of pancreatic β-cells varies according to increases in insulin demand. It is hypothesized that functionally heterogeneous β-cell subpopulations take part in this process. Here we characterized two functionally distinct groups of β-cells and investigated their physiological relevance in increased insulin demand conditions in rats.

Methods

Two rat β-cell populations were sorted by FACS according to their PSA-NCAM surface expression, i.e. β^high and β^low-cells. Insulin release, Ca²⁺ movements, ATP and cAMP contents in response to various secretagogues were analyzed. Gene expression profiles and exocytosis machinery were also investigated. In a second part, β^high and β^low-cell distribution and functionality were investigated in animal models with decreased or increased β-cell function: the Zucker Diabetic Fatty rat and the 48 h glucose-infused rat.

Results

We show that β-cells are heterogeneous for PSA-NCAM in rat pancreas. Unlike β^low-cells, β^high-cells express functional β-cell markers and are highly responsive to various insulin secretagogues. Whereas β^low-cells represent the main population in diabetic pancreas, an increase in β^high-cells is associated with gain of function that follows sustained glucose overload.

Conclusion

Our data show that a functional heterogeneity of β-cells, assessed by PSA-NCAM surface expression, exists in vivo. These findings pinpoint new target populations involved in endocrine pancreas plasticity and in β-cell defects in type 2 diabetes.

Oral antidiabetic drug metabolism: pharmacogenomics and drug interactions

BACKGROUND

Type 2 diabetes is progressive in nature and so to control cardiovascular risk, most patients need combinations of oral antidiabetic drugs (OADs) plus or minus insulin. Thus, drug-drug interactions may substantially contribute to harmful effects of intensive glucose lowering therapy.

METHODS

A PubMed literature search was performed to select the most recent and relevant publications examining OAD metabolism and the effects of concomitant use of OADs.

RESULTS/CONCLUSION

Considering the individual sensitivity to OADs, pharmacogenetic factors could be of critical importance. The therapeutic range and efficacy as well as adverse effects of OADs may be significantly affected by genetic polymorphisms of cytochrome P450 drug metabolising enzymes, organic cation transporters or organic anion transporting polypeptides. Although current data suggest that modest pharmacokinetics interferences among some OAD combinations exist, they do not seem to have substantial clinical consequences. As long-term adherence to multi-drug treatment is poor in diabetic patients, the future will show a strong move towards earlier treatment with combination therapies. As metformin is cardiovascular protective and is not metabolised through the hepatic cytochrome P450 system, it is a key compound for any OAD combination. There is an overwhelming amount of small-sized in vitro studies and investigations mostly including healthy volunteers dealing with short-term effects and surrogate parameters of concomitant OAD use. Further evidence from large-scale studies including typical subjects with type 2 diabetes, in particular multimorbid and geriatric patients with polypharmacy, is needed. Postmarketing surveillance using large patients' registries could be helpful to improve the early detection of clinically relevant drug-drug interactions.

Phosphodiesterase 5 inhibition improves beta-cell function in metabolic syndrome

OBJECTIVE

This study tested the hypothesis that phosphodiesterase 5 inhibition alone or in combination with ACE inhibition improves glucose homeostasis and fibrinolysis in individuals with metabolic syndrome.

RESEARCH DESIGN AND METHODS

Insulin sensitivity, beta-cell function, and fibrinolytic parameters were measured in 18 adults with metabolic syndrome on 4 separate days after a randomized, crossover, double-blind, 3-week treatment with placebo, ramipril (10 mg/day), tadalafil (10 mg o.d.), and ramipril plus tadalafil.

RESULTS

Ramipril decreased systolic and diastolic blood pressure, ACE activity, and angiotensin II and increased plasma renin activity. Ramipril did not affect insulin sensitivity or beta-cell function. In contrast, tadalafil improved beta-cell function (P = 0.01). This effect was observed in women (331.9 +/- 209.3 vs. 154.4 +/- 48.0 32 micro x mmol(-1) x l(-1), respectively, for tadalafil treatment vs. placebo; P = 0.01) but not in men. There was no effect of any treatment on fibrinolysis. CONCLUSIONS Phosphodiesterase 5 inhibition may represent a novel strategy for improving beta-cell function in metabolic syndrome.

Impact of incretin therapy on islet dysfunction: an underlying defect in the pathophysiology of type 2 diabetes

Glucose homeostasis is governed by a complex interplay of hormonal signaling and modulation. Insulin, glucagon, amylin, the incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), and other hormones and enzymes interact to maintain glucose homeostasis and normal cellular metabolism. Derangements in these hormonal interactions, particularly insulin deficits and impaired insulin action, result in the development of type 2 diabetes-but only in individuals who have experienced significant dysfunction or loss of beta-cells, located in the pancreatic islets of Langerhans. Much less is known about the impact of alpha-cell dysregulation on glucose homeostasis, although it has been demonstrated that glucagon-secreting alpha-cells, also located in the pancreatic islets, play an important role in glucose metabolism. Because beta-cell dysfunction occurs early in the course of type 2 diabetes and is progressive, early intervention with therapies that improve beta-cell function is desirable. In addition to reducing HbA1c and fasting plasma glucose, the recently developed diabetes therapies GLP-1 receptor agonists (eg, exenatide, liraglutide) and dipeptidyl peptidase-4 (DPP-4) inhibitors (eg, sitagliptin, vildagliptin) appear to have beneficial effects on beta-cell dysfunction and, possibly, on alpha-cell dysregulation.

Metabolic consequences of a 50% partial pancreatectomy in humans

AIMS/HYPOTHESIS

Partial pancreatectomy is frequently performed in patients with pancreatic tumours or chronic pancreatitis, but little is known about the metabolic impact of this intervention. We examined the effects of approximately 50% partial pancreatectomy on glucose homeostasis and insulin secretion.

METHODS

Fourteen patients with chronic pancreatitis, ten patients with pancreatic carcinoma and 13 patients with benign pancreatic tumours or extra-pancreatic masses (control group) underwent 240 min oral glucose tolerance tests before and after pancreatic tail-resection (n = 12), duodenopancreatectomy (n = 19) or duodenum-preserving pancreatic-head resection (n = 6).

RESULTS

Partial pancreatectomy led to a reduction in post-challenge insulin excursions by 49% in chronic pancreatitis patients, 52% in carcinoma patients and 55% in controls (p < 0.05). Nevertheless, post-challenge glucose concentrations were transiently ameliorated after surgery (p < 0.001). In the control participants, pancreatic-head resection caused a transient reduction of post-challenge glycaemia, whereas pancreatic-tail resection increased both fasting and post-challenge glycaemia (p < 0.05). Insulin sensitivity was highest in chronic pancreatitis patients before surgery (p < 0.01), but remained unchanged by the partial pancreatectomy. High pre-operative body weight and elevated fasting glucose levels were associated with poor glycaemic control after surgery.

CONCLUSIONS/INTERPRETATION

Insulin secretion is diminished after pancreatic-head and -tail resection, but post-challenge glucose concentrations can be ameliorated after pancreatic-head resection. These data highlight the unequal impact of different surgical procedures on glucose control and suggest that obesity and high pre-operative glucose levels should be considered as risk factors for the development of hyperglycaemia after pancreatic surgery.

An update on preventive and regenerative therapies in diabetes mellitus

Type 1A (immune-mediated) and type 2 diabetes mellitus are two of the most common severe chronic illnesses, affecting over 230 million people worldwide with an estimated global prevalence of 5.1%. Although type 1 and type 2 diabetes differ greatly in modes of pathogenesis, these illnesses share a common pathology and consequences characterized by loss of functional beta-cell mass and subsequent dysregulation of carbohydrate and lipid metabolism. Since therapy for diabetes and the associated complications poses enormous public health and economic burdens, novel preventive and regenerative therapies have emerged in the past decade with the aim to preserve beta-cell mass and delay the onset of diabetes. The goal of this review is to provide a comprehensive overview of current efforts in the fight against diabetes, and attempts to document all strategies that have emerged in clinical studies within the past 25 years. First, strategies to identify individuals at risk, ranging from whole-genome scans to autoantibody screening, will be discussed. Second, novel approaches to prevent or delay the onset of disease will be covered. Particular focus is given on emerging strategies for individuals at risk for type 1 diabetes that target T-cell regulation and induction of tolerance, while new pharmaceutical concepts in combination with lifestyle interventions are discussed within the scope of type 2 diabetes prevention. Lastly, important efforts to halt disease progression with emphasis on beta-cell regeneration are presented.