Beta-cells in type 2 diabetes: a loss of function and mass

Approximate estimation of cell-type resolution transcriptome in bulk tissue through matrix completion

Single-cell RNA sequencing (scRNA-seq) has emerged as a powerful tool for uncovering cellular heterogeneity. However, the high costs associated with this technique have rendered it impractical for studying large patient cohorts. We introduce ENIGMA (Deconvolution based on Regularized Matrix Completion), a method that addresses this limitation through accurately deconvoluting bulk tissue RNA-seq data into a readout with cell-type resolution by leveraging information from scRNA-seq data. By employing a matrix completion strategy, ENIGMA minimizes the distance between the mixture transcriptome obtained with bulk sequencing and a weighted combination of cell-type-specific expression. This allows the quantification of cell-type proportions and reconstruction of cell-type-specific transcriptomes. To validate its performance, ENIGMA was tested on both simulated and real datasets, including disease-related tissues, demonstrating its ability in uncovering novel biological insights.

NMDA receptors - regulatory function and pathophysiological significance for pancreatic beta cells

Due to its unique features amongst ionotropic glutamate receptors, the NMDA receptor is of special interest in the physiological context but even more as a drug target. In the pathophysiology of metabolic disorders, particularly type 2 diabetes mellitus, there is evidence that NMDA receptor activation contributes to disease progression by impairing beta cell function. Consequently, channel inhibitors are suggested for treatment, but up to now there are many unanswered questions about the signaling pathways NMDA receptors are interfering with in the islets of Langerhans. In this review we give an overview about channel structure and function with special regard to the pancreatic beta cells and the regulation of insulin secretion. We sum up which signaling pathways from brain research have already been transferred to the beta cell, and what still needs to be proven. The main focus is on the relationship between an over-stimulated NMDA receptor and the production of reactive oxygen species, the amount of which is crucial for beta cell function. Finally, pilot studies using NMDA receptor blockers to protect the islet from dysfunction are reviewed and future perspectives for the use of such compounds in the context of impaired glucose homeostasis are discussed.

Second Sphere Interactions in Amyloidogenic Diseases

Amyloids are protein aggregates bearing a highly ordered cross β structural motif, which may be functional but are mostly pathogenic. Their formation, deposition in tissues and consequent organ dysfunction is the central event in amyloidogenic diseases. Such protein aggregation may be brought about by conformational changes, and much attention has been directed toward factors like metal binding, post-translational modifications, mutations of protein etc., which eventually affect the reactivity and cytotoxicity of the associated proteins. Over the past decade, a global effort from different groups working on these misfolded/unfolded proteins/peptides has revealed that the amino acid residues in the second coordination sphere of the active sites of amyloidogenic proteins/peptides cause changes in H-bonding pattern or protein-protein interactions, which dramatically alter the structure and reactivity of these proteins/peptides. These second sphere effects not only determine the binding of transition metals and cofactors, which define the pathology of some of these diseases, but also change the mechanism of redox reactions catalyzed by these proteins/peptides and form the basis of oxidative damage associated with these amyloidogenic diseases. The present review seeks to discuss such second sphere modifications and their ramifications in the etiopathology of some representative amyloidogenic diseases like Alzheimer's disease (AD), type 2 diabetes mellitus (T2Dm), Parkinson's disease (PD), Huntington's disease (HD), and prion diseases.

AdRoit is an accurate and robust method to infer complex transcriptome composition

Bulk RNA sequencing provides the opportunity to understand biology at the whole transcriptome level without the prohibitive cost of single cell profiling. Advances in spatial transcriptomics enable to dissect tissue organization and function by genome-wide gene expressions. However, the readout of both technologies is the overall gene expression across potentially many cell types without directly providing the information of cell type constitution. Although several in-silico approaches have been proposed to deconvolute RNA-Seq data composed of multiple cell types, many suffer a deterioration of performance in complex tissues. Here we present AdRoit, an accurate and robust method to infer the cell composition from transcriptome data of mixed cell types. AdRoit uses gene expression profiles obtained from single cell RNA sequencing as a reference. It employs an adaptive learning approach to alleviate the sequencing technique difference between the single cell and the bulk (or spatial) transcriptome data, enhancing cross-platform readout comparability. Our systematic benchmarking and applications, which include deconvoluting complex mixtures that encompass 30 cell types, demonstrate its preferable sensitivity and specificity compared to many existing methods as well as its utilities. In addition, AdRoit is computationally efficient and runs orders of magnitude faster than most methods.

Treatment Patterns, Effectiveness, and Satisfaction Among Patients with Type 2 Diabetes Treated with Insulin in Saudi Arabia: Results of the RIMODIS Study

INTRODUCTION

The alarming increase in type 2 diabetes mellitus (T2DM) in Saudi Arabia is aggravated by increasing obesity, sedentary lifestyle, and population aging. The RIMODIS study aimed at describing the practices in the therapeutic management of patients with T2DM treated with different insulin regimens.

METHODS

This national, multicenter, non-interventional, cross-sectional disease registry on the real-life therapeutic management of insulin-treated patients with T2DM in Saudi Arabia enrolled 3010 patients. It primarily aimed at describing treatment patterns, complications, and glycemia levels. Patients completed the diabetes treatment satisfaction questionnaire (DTSQ). Data on different treatment patterns were analyzed using chi-square or Fisher's exact test. Outcomes were analyzed according to the different insulin regimen subgroups (basal versus premixed).

RESULTS

Over 60% of patients were treated with premixed insulin and most patients were also prescribed oral antidiabetics (OADs). Patients on insulin alone seemed to achieve better glycated hemoglobin (HbA1c) control. Adding OADs to insulin slightly increased treatment satisfaction scores, with scores higher in patients on basal insulin compared to premixed insulin. Hypoglycemia was lower when adding OADs to insulin. Most patients showed high treatment adherence; however, two-thirds of study patients failed to achieve glycemic target levels.

CONCLUSION

Most patients are treated with a combination of insulin and OADs, associated with glycemic control and low incidence of hypoglycemia. However, we highlight suboptimal glycemic target achievement, underscoring the need to improve T2DM clinical management and promote healthier lifestyle among patients in Saudi Arabia.

Adenosine kinase: An epigenetic modulator in development and disease

Adenosine kinase (ADK) is the key regulator of adenosine and catalyzes the metabolism of adenosine to 5'-adenosine monophosphate. The enzyme exists in two isoforms: a long isoform (ADK-long, ADK-L) and a short isoform (ADK-short, ADK-S). The two isoforms are developmentally regulated and are differentially expressed in distinct subcellular compartments with ADK-L localized in the nucleus and ADK-S localized in the cytoplasm. The nuclear localization of ADK-L and its biochemical link to the transmethylation pathway suggest a specific role for gene regulation via epigenetic mechanisms. Recent evidence reveals an adenosine receptor-independent role of ADK in determining the global methylation status of DNA and thereby contributing to epigenomic regulation. Here we summarize recent progress in understanding the biochemical interactions between adenosine metabolism by ADK-L and epigenetic modifications linked to transmethylation reactions. This review will provide a comprehensive overview of ADK-associated changes in DNA methylation in developmental, as well as in pathological conditions including brain injury, epilepsy, vascular diseases, cancer, and diabetes. Challenges in investigating the epigenetic role of ADK for therapeutic gains are briefly discussed.

Diminished Sphingolipid Metabolism, a Hallmark of Future Type 2 Diabetes Pathogenesis, Is Linked to Pancreatic β Cell Dysfunction

Gestational diabetes mellitus (GDM) is the top risk factor for future type 2 diabetes (T2D) development. Ethnicity profoundly influences who will transition from GDM to T2D, with high risk observed in Hispanic women. To better understand this risk, a nested 1:1 pair-matched, Hispanic-specific, case-control design was applied to a prospective cohort with GDM history. Women who were non-diabetic 6-9 weeks postpartum (baseline) were monitored for the development of T2D. Metabolomics were performed on baseline plasma to identify metabolic pathways associated with T2D risk. Notably, diminished sphingolipid metabolism was highly associated with future T2D. Defects in sphingolipid metabolism were further implicated by integrating metabolomics and genome-wide association data, which identified two significantly enriched T2D-linked genes, CERS2 and CERS4. Follow-up experiments in mice and cells demonstrated that inhibiting sphingolipid metabolism impaired pancreatic β cell function. These data suggest early postpartum alterations in sphingolipid biosynthesis contribute to β cell dysfunction and T2D risk.

Glycemic Response to Oral Dexamethasone Predicts Incident Prediabetes in Normoglycemic Subjects With Parental Diabetes

Background

Prediabetes, an often unrecognized precursor of type 2 diabetes (T2DM), is associated with cardiometabolic complications. Here, we investigated the utility of dexamethasone challenge in predicting incident prediabetes among normoglycemic subjects with parental T2DM enrolled in the prospective Pathobiology of Prediabetes in a Biracial Cohort study.

Design and Methods

After documenting normoglycemic status with an oral glucose tolerance test (OGTT), participants ingested dexamethasone (2 mg) at 10:00 pm, and fasting plasma glucose (FPG-Dex) and cortisol were measured at 8:00 am the next day. Subjects were followed quarterly for 5 years, the primary outcome being incident prediabetes. Serial assessments included body composition, blood chemistry, OGTT, insulin sensitivity, and secretion.

Results

We analyzed data from 190 participants (107 Black, 83 white; mean age 44.7 ± 10.0 years; body mass index [BMI] 29.8 ± 6.8 kg/m²; fasting plasma glucose [FPG] 90.9 ± 5.7 mg/dL). Following dexamethasone ingestion, plasma cortisol was < 5 µg/dL; FPG-Dex levels displayed marked variability (81-145 mg/dL) as did delta FPG (–7 to +48 mg/dL). During 5 years of follow-up, 58 of 190 subjects (30.5%) progressed to prediabetes. FPG-Dex (116.8 ± 10.9 vs 106.9 ± 10.8 mg/dL, P < 0.0001) and delta FPG (23.4 ± 10.1 vs 17.0 ± 10.2 mg/dL, P < 0.0001) were higher in progressors than nonprogressors. FPG-Dex (P = 0.007) was an independent predictor of incident prediabetes in a multivariate model that included age, race, gender, BMI, waist circumference, FPG, insulin sensitivity, and secretion. In further analyses, an FPG-Dex level ≥ 107 mg/dL predicted incident prediabetes with 88% sensitivity and 49% specificity.

Conclusions

The glycemic response to dexamethasone significantly predicted incident prediabetes among offspring of parents with T2DM, and may be a tool for uncovering latent risk of dysglycemia.

Pyrroloquinoline quinone protected autophagy-dependent apoptosis induced by mono(2-ethylhexyl) phthalate in INS-1 cells

Mono(2-ethylhexyl) phthalate (MEHP) is the main metabolite of di(2-ethylhexyl) phthalate (DEHP) in organisms and is commonly used as a plasticizer. Exposure to DEHP impairs the function of islet beta cells (INS-1 cells), which is related to insulin resistance and type 2 diabetes. At present, some research data have also confirmed that MEHP has a certain damage effect on INS-1 cells. In our experiment, we found that MEHP would lead to the increase of reactive oxygen species (ROS) and the upregulation of autophagy. And downregulated ROS production by N-acetyl-L-cysteine could also reduce autophagy. In addition, MEHP-induced lysosomal membrane permeability (LMP) subsequently released cathepsin D. Additionally, MEHP induced the collapse of mitochondrial transmembrane potential and release of cytochrome c. Addition of autophagy inhibitor 3-methyladenine relieved MEHP-induced apoptosis as assessed by the expression of cleaved caspase 3, cleaved caspase 9, and terminal deoxynucleotidyl transferase dUTP nick end labeling assay, indicating that MEHP-induced apoptosis was autophagy dependent. Cathepsin D inhibitor, pepstatin A, suppressed MEHP-induced mitochondria release of cytochrome c and apoptosis as well. Meanwhile, pyrroloquinoline quinone (PQQ), a new B vitamin, improved the above phenomenon. Taken together, our results indicate that MEHP induces autophagy-dependent apoptosis in INS-1 cells by lysosomal-mitochondrial axis. PQQ improved this process by downregulating ROS and provided a degree of protection. Our study provides a new perspective for MEHP on the cytotoxic mechanism and PQQ protection in INS-1 cells.

Molecular mechanisms by which GLP-1 RA and DPP-4i induce insulin sensitivity

Glucagon-like peptide-1 is a peptide of incretin family which is used in the management of diabetes as glucagon-like peptide-1 receptor agonist (GLP-1RA). Dipeptidyl peptidase-4 enzyme metabolizes glucagon-like peptide-1 and various dipeptidyl peptidase-4 enzyme inhibitors (DPP-4i) are also used in the management of diabetes. These antidiabetic agents provide anti-hyperglycemic effects via several molecular mechanisms including promoting insulin secretion, suppression of glucagon secretion and slowing the gastric emptying. There is some research suggesting that they can induce insulin sensitivity in peripheral tissues. In this study, we review the possible molecular mechanisms by which GLP-1RA and DPP-4i can improve insulin resistance and increase insulin sensitivity in insulin-dependent peripheral tissues.

Is miRNA-375 a promising biomarker for early detection and monitoring of patients with type 2 diabetes?

miRNAs are small, non-coding RNAs, functioning as negative suppressors of target gene expression. A significant proportion of the transcriptome is subject to miRNA modulation. A single miRNA determines the expression of hundreds of genes, while miRNAs are relatively stable in biological fluids. Thus, they have attracted scientific interest regarding their use as biomarkers for several diseases. miRNA-375 mainly influences β-cell function and insulin secretion. Several studies, primarily experimental, have assessed its role as a biomarker in type 2 diabetes, while recently obtained human evidence supports this potential role. Besides its diagnostic potential, miRNA-375 may also have therapeutic implications. In view of the growing epidemic of type 2 diabetes, there is an unmet need for identification of biomarkers for early recognition and monitoring of these patients. Long-term, prospective human studies are required to elucidate whether miRNA-375 can evolve as a key player in diagnosis and prognosis of type 2 diabetes.

Clinical inertia in insulin prescription for patients with type 2 diabetes mellitus at a primary health care institution of Cartagena, Colombia

Introduction: Evidence has demonstrated clinical or prescriptive inertia along with an increased prescription of insulin, causing a delay in the change of prescription.Objective: To determine the prescription pattern and clinical inertia of insulin use in the treatment of patients with type 2 diabetes mellitus (DM2) enrolled in a diabetes program at a primary health care institution of Cartagena, Colombia.Materials and methods: Pharmacoepidemiology study that addresses drug utilization based on data collected through a review of medical records of 331 patients with DM2, aged 18 and older, who had at least 6 months of control.Results: 64.4% of patients were treated with long-acting insulin analogues and 18.4% used insulin; 52.7% of the patients in which insuline use was required did not have a prescription of this drug.Conclusions: There is clinical inertia related to insulin prescription. Strategies should be implemented to overcome prescriptive inertia for people with DM2 in order to achieve therapeutic goals earlier and effectively prevent the development and progression of chronic complications.

The role of orexin in controlling the activity of the adipo-pancreatic axis

Orexin A and B are two neuropeptides, which regulate a variety of physiological functions by interacting with central nervous system and peripheral tissues. Biological effects of orexins are mediated through two G-protein-coupled receptors (OXR1 and OXR2). In addition to their strong influence on the sleep-wake cycle, there is growing evidence that orexins regulate body weight, glucose homeostasis and insulin sensitivity. Furthermore, orexins promote energy expenditure and protect against obesity by interacting with brown adipocytes. Fat tissue and the endocrine pancreas play pivotal roles in maintaining energy homeostasis. Since both organs are crucially important in the context of pathophysiology of obesity and diabetes, we summarize the current knowledge regarding the role of orexins and their receptors in controlling adipocytes as well as the endocrine pancreatic functions. Particularly, we discuss studies evaluating the effects of orexins in controlling brown and white adipocytes as well as pancreatic alpha and beta cell functions.

miR-494 protects pancreatic β-cell function by targeting PTEN in gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is one of the most common pregnancy complications characterized by insulin resistance and pancreatic β-cell dysfunction. Increasing evidence suggests that microRNAs (miRNAs) play key roles in the diverse types of diabetes, including GDM. However, the underlying mechanisms remain largely unknown. The purpose of this study is to investigate the role of microRNAs in GDM. The microarray data of dysregulated miRNAs in blood and placenta was retrieved in the GEO dataset under the accession number GSE19649. Quantitative reverse transcription PCR (qRT-PCR) was performed to analyze the expression levels of miR-494 in peripheral blood from twenty pairs of gestational diabetes (GDM) women and healthy women. Then, we investigated the effects of miR-494 on the insulin secretion of pancreatic β-cells. Moreover, the role of this miR-494 in regulating the proliferation and apoptosis of pancreatic β-cells were determined by MTT assay and flow cytometry, respectively in INS1 cells transfected with a miR-494 mimic or inhibitor. In addition, the direct target of miR-494 was confirmed using 3' untranslated region (UTR) luciferase reporter assay. Our data demonstrated that the miR-494 level was significantly decreased in the blood of GDM patients, and the low level was associated with a high concentration of blood glucose. Furthermore, overexpression of miR-494 improved pancreatic β-cell dysfunction by enhancing insulin secretion and total insulin content, inducing cell proliferation, and inhibiting cell apoptosis, whereas miR-494 knockdown exhibited decreased insulin secretion and proliferation, as well as stimulated apoptosis. In addition, phosphatase and tensin homolog (PTEN) which has been shown to play a pivotal role in apoptosis, was proved to be a direct target of miR-494 in pancreatic β-cells. More importantly, siRNA-induced downregulation of PTEN reversed the effects of miR-494 knockdown on insulin secretion, cell proliferation, and apoptosis of pancreatic β-cells.

Geniposide accelerates proteasome degradation of Txnip to inhibit insulin secretion in pancreatic β-cells

PURPOSE

To analyze the role of geniposide in the protein degradation of Txnip and to determine the impact of Txnip on geniposide-regulated GSIS in pancreatic INS-1 cells.

METHODS

The content of Txnip protein was measured by western blot; insulin content and glucose uptake were determined by ELISA; and knockdown of Txnip was the method of RNA interference.

RESULTS

Glucose induces a rapid increase in Txnip protein, and geniposide accelerates the degradation of Txnip via proteasome pathway in the presence of high glucose (25 mM) in INS-1 pancreatic β-cells. And MG132, a proteasomal inhibitor, potentiates glucose uptake, metabolism (ATP production) and glucose-stimulated insulin secretion (GSIS) in high-glucose (25 mM)-treated INS-1 cells, but geniposide significantly prevents these effects. Furthermore, the combination of geniposide and Txnip knockdown shows substantial synergistic effects to reduce glucose uptake, metabolism and GSIS in high-glucose (25 mM)-treated INS-1 cells.

CONCLUSIONS

Txnip protein played an essential role in glucose uptake, metabolism and GSIS, and geniposide could accelerate the degradation via proteasome pathway in high-glucose-treated pancreatic INS-1 cells.

Endoplasmic Reticulum Stress Links Oxidative Stress to Impaired Pancreatic Beta-Cell Function Caused by Human Oxidized LDL

Elevated plasma concentration of the pro-atherogenic oxidized low density lipoprotein cholesterol (LDL) triggers adverse effects in pancreatic beta-cells and is associated with type 2 diabetes. Here, we investigated whether the endoplasmic reticulum (ER) stress is a key player coupling oxidative stress to beta-cell dysfunction and death elicited by human oxidized LDL. We found that human oxidized LDL activates ER stress as evidenced by the activation of the inositol requiring 1α, and the elevated expression of both DDIT3 (also called CHOP) and DNAJC3 (also called P58IPK) ER stress markers in isolated human islets and the mouse insulin secreting MIN6 cells. Silencing of Chop and inhibition of ER stress markers by the chemical chaperone phenyl butyric acid (PBA) prevented cell death caused by oxidized LDL. Finally, we found that oxidative stress accounts for activation of ER stress markers induced by oxidized LDL. Induction of Chop/CHOP and p58IPK/P58IPK by oxidized LDL was mimicked by hydrogen peroxide and was blocked by co-treatment with the N-acetylcystein antioxidant. As a conclusion, the harmful effects of oxidized LDL in beta-cells requires ER stress activation in a manner that involves oxidative stress. This mechanism may account for impaired beta-cell function in diabetes and can be reversed by antioxidant treatment.

Proteasome regulates turnover of toxic human amylin in pancreatic cells

Toxic human amylin (hA) oligomers and aggregates are implicated in the pathogenesis of type 2 diabetes mellitus (T2DM). Although recent studies demonstrated a causal connection between hA uptake and toxicity in pancreatic cells, the mechanism of amylin's clearance following its internalization and its relationship to toxicity is yet to be determined, and hence was investigated here. Using pancreatic rat insulinoma β-cells and human islets as model systems, we show that hA, following its internalization, first accumulates in the cytosol followed by its translocation into nucleus, and to a lesser extent lysosomes, keeping the net cytosolic amylin content low. An increase in hA accumulation in the nucleus of pancreatic cells correlated with its cytotoxicity, suggesting that its excessive accumulation in the nucleus is detrimental. hA interacted with 20S core and 19S lid subunits of the β-cell proteasomal complex, as suggested by immunoprecipitation and confocal microscopy studies, which subsequently resulted in a decrease in the proteasome's proteolytic activity in these cells. In vitro binding and activity assays confirmed an intrinsic and potent ability of amylin to interact with the 20S core complex thereby modulating its proteolytic activity. Interestingly, less toxic and aggregation incapable rat amylin (rA) showed a comparable inhibitory effect on proteasome activity and protein ubiquitination, decoupling amylin aggregation/ toxicity and amylin-induced protein stress. In agreement with these studies, inhibition of proteasomal proteolytic activity significantly increased intracellular amylin content and toxicity. Taken together, our results suggest a pivotal role of proteasomes in amylin's turnover and detoxification in pancreatic cells.

Protein Modifications as Manifestations of Hyperglycemic Glucotoxicity in Diabetes and Its Complications

Diabetes and its complications are hyperglycemic toxicity diseases. Many metabolic pathways in this array of diseases become aberrant, which is accompanied with a variety of posttranslational protein modifications that in turn reflect diabetic glucotoxicity. In this review, we summarize some of the most widely studied protein modifications in diabetes and its complications. These modifications include glycation, carbonylation, nitration, cysteine S-nitrosylation, acetylation, sumoylation, ADP-ribosylation, O-GlcNAcylation, and succination. All these posttranslational modifications can be significantly attributed to oxidative stress and/or carbon stress induced by diabetic redox imbalance that is driven by activation of pathways, such as the polyol pathway and the ADP-ribosylation pathway. Exploring the nature of these modifications should facilitate our understanding of the pathological mechanisms of diabetes and its associated complications.

Hyperglycemic Stress and Carbon Stress in Diabetic Glucotoxicity

Diabetes and its complications are caused by chronic glucotoxicity driven by persistent hyperglycemia. In this article, we review the mechanisms of diabetic glucotoxicity by focusing mainly on hyperglycemic stress and carbon stress. Mechanisms of hyperglycemic stress include reductive stress or pseudohypoxic stress caused by redox imbalance between NADH and NAD(+) driven by activation of both the polyol pathway and poly ADP ribose polymerase; the hexosamine pathway; the advanced glycation end products pathway; the protein kinase C activation pathway; and the enediol formation pathway. Mechanisms of carbon stress include excess production of acetyl-CoA that can over-acetylate a proteome and excess production of fumarate that can over-succinate a proteome; both of which can increase glucotoxicity in diabetes. For hyperglycemia stress, we also discuss the possible role of mitochondrial complex I in diabetes as this complex, in charge of NAD(+) regeneration, can make more reactive oxygen species (ROS) in the presence of excess NADH. For carbon stress, we also discuss the role of sirtuins in diabetes as they are deacetylases that can reverse protein acetylation thereby attenuating diabetic glucotoxicity and improving glucose metabolism. It is our belief that targeting some of the stress pathways discussed in this article may provide new therapeutic strategies for treatment of diabetes and its complications.

E2F1 and E2F2 prevent replicative stress and subsequent p53-dependent organ involution

Tissue homeostasis requires tight regulation of cellular proliferation, differentiation and apoptosis. E2F1 and E2F2 transcription factors share a critical role in tissue homeostasis, since their combined inactivation results in overall organ involution, specially affecting the pancreatic gland, which subsequently triggers diabetes. We have examined the mechanism by which these E2Fs regulate tissue homeostasis. We show that pancreas atrophy in E2F1/E2F2 double-knockout (DKO) mice is associated with mitochondrial apoptosis and activation of the p53 pathway in young animals, before the development of diabetes. A deregulated expression of E2F target genes was detected in pancreatic cells of young DKO animals, along with unscheduled DNA replication and activation of a DNA damage response. Importantly, suppression of DNA replication in vivo with aphidicolin led to a significant inhibition of the p53 pathway in DKO pancreas, implying a causal link between DNA replication stress and p53 activation in this model. We further show that activation of the p53 pathway has a key role in the aberrant phenotype of DKO mice, since targeted inactivation of p53 gene abrogated cellular apoptosis and prevented organ involution and insulin-dependent diabetes in mice lacking E2F1/E2F2. Unexpectedly, p53 inactivation unmasked oncogenic features of E2F1/E2F2-depleted cells, as evidenced by an accelerated tumor development in triple-knockout mice compared with p53(-/-) mice. Collectively, our data reveal a role for E2F1 and E2F2 as suppressors of replicative stress in differentiating cells, and uncover the existence of a robust E2F-p53 regulatory axis to enable tissue homeostasis and prevent tumorigenesis. These findings have implications in the design of approaches targeting E2F for cancer therapy.

Cathepsin inhibition-induced lysosomal dysfunction enhances pancreatic beta-cell apoptosis in high glucose

Autophagy is a lysosomal degradative pathway that plays an important role in maintaining cellular homeostasis. We previously showed that the inhibition of autophagy causes pancreatic β-cell apoptosis, suggesting that autophagy is a protective mechanism for the survival of pancreatic β-cells. The current study demonstrates that treatment with inhibitors and knockdown of the lysosomal cysteine proteases such as cathepsins B and L impair autophagy, enhancing the caspase-dependent apoptosis of INS-1 cells and islets upon exposure to high concentration of glucose. Interestingly, treatment with cathepsin B and L inhibitors prevented the proteolytic processing of cathepsins B, D and L, as evidenced by gradual accumulation of the respective pro-forms. Of note, inhibition of aspartic cathepsins had no effect on autophagy and cell viability, suggesting the selective role of cathepsins B and L in the regulation of β-cell autophagy and apoptosis. Lysosomal localization of accumulated pro-cathepsins in the presence of cathepsin B and L inhibitors was verified via immunocytochemistry and lysosomal fractionation. Lysotracker staining indicated that cathepsin B and L inhibitors led to the formation of severely enlarged lysosomes in a time-dependent manner. The abnormal accumulation of pro-cathepsins following treatment with inhibitors of cathepsins B and L suppressed normal lysosomal degradation and the processing of lysosomal enzymes, leading to lysosomal dysfunction. Collectively, our findings suggest that cathepsin defects following the inhibition of cathepsin B and L result in lysosomal dysfunction and consequent cell death in pancreatic β-cells.

Anti-apoptotic Effects of Bone Marrow on Human Islets: A Preliminary Report

Apoptosis is one of the major factors contributing to the failure of human islet transplantation. Contributors to islet apoptosis exist in both the pre-transplantation and post transplantation stages. Factors include the islet isolation process, deterioration in vitro prior to transplantation, and immune rejection post transplantation. Previous studies have demonstrated that co-cultured bone marrow cells with human islets not only significantly enhanced the longevity of human islets but also maintained function. We hypothesized that the protective effects of bone marrow cells on human islets are through mechanisms related to preventing apoptosis. This study observed the levels of inflammatory factors such as interleukin-1β (IL-1β), the release of extracellular ATP in vitro, and expression levels of P2X7 ATP receptor (P2X7R), all of which lead to the occurrence of apoptosis in human islets. When human islets were co-cultured with human bone marrow, there was a reduction in the rate of apoptosis correlated with the reduction in inflammatory factors, extra cellular ATP accumulation, and ATP receptor P2X7R expression versus human islets cultured alone. These results suggest that co-culturing bone marrow cells with human islets inhibits inflammation and reduces apoptosis, thus protecting islets from self-deterioration.

Synopsis on the linkage of Alzheimer's and Parkinson's disease with chronic diseases

Neurodegeneration is the progressive loss of neuronal structure and function, which ultimately leads to neurological disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis, and Huntington's disease. Even after the recent significant advances in neurobiology, the above-mentioned disorders continue to haunt the global population. Several studies have suggested the role of specific environmental and genetic risk factors associated with these disorders. However, the exact mechanism associated with the progression of these disorders still needs to be elucidated. In the recent years, sophisticated research has revealed interesting association of prominent neurodegenerative disorders such as AD and PD with chronic diseases such as cancer, diabetes, and cardiovascular diseases. Several common molecular mechanisms such as generation of free radicals, oxidative DNA damage, aberrations in mitochondrial DNA, and dysregulation of apoptosis have been highlighted as possible points of connection. The present review summarizes the possible mechanism of coexistence of AD and PD with other chronic diseases.

The pathogenic mechanism of diabetes varies with the degree of overexpression and oligomerization of human amylin in the pancreatic islet β cells

The aggregation of human amylin (hA) to form cytotoxic structures has been closely associated with the causation of type 2 diabetes. We sought to advance understanding of how altered expression and aggregation of hA might link β-cell degeneration with diabetes onset and progression, by comparing phenotypes between homozygous and hemizygous hA-transgenic mice. The homozygous mice displayed elevated islet hA that correlated positively with measures of oligomer formation (r=0.91; P<0.0001). They also developed hyperinsulinemia with transient insulin resistance during the prediabetes stage and then underwent rapid β-cell loss, culminating in severe juvenile-onset diabetes. The prediabetes stage was prolonged in the hemizygous mice, wherein β-cell dysfunction and extensive oligomer formation occurred in adulthood at a much later stage, when hA levels were lower (r=-0.60; P<0.0001). This is the first report to show that hA-evoked diabetes is associated with age, insulin resistance, progressive islet dysfunction, and β-cell apoptosis, which interact variably to cause the different diabetes syndromes. The various levels of hA elevation cause different extents of oligomer formation in the disease stages, thus eliciting early- or adult-onset diabetes syndromes, reminiscent of type 1 and 2 diabetes, respectively. Thus, the hA-evoked diabetes phenotypes differ substantively according to degree of amylin overproduction. These findings are relevant to the understanding of the pathogenesis and the development of experimental therapeutics for diabetes.

Differences in physician and patient perceptions about insulin therapy for management of type 2 diabetes: the DAWN Japan study

OBJECTIVE

To better understand patient resistance to initiation of insulin therapy, this study examined the perception gap concerning initiation of insulin therapy between individuals with type 2 diabetes and their physicians by using data from the DAWN Japan study.

METHODS

The DAWN Japan study is a multi-center, questionnaire-based survey, conducted between 2004-2005. Patients recommended to start insulin therapy (n = 148) answered a questionnaire by rating degree of agreement with 16 statements concerning insulin therapy on a 5-point scale (1: strongly disagree to 5: strongly agree). Ratings of 1 and 2 were categorized as 'disagree' with a statement, and 3, 4, and 5 as 'agree'. Their attending physicians (n = 68) selected statements which could be associated with patient's concerns about insulin therapy.

RESULTS

Nearly all the patients agreed with the statements 'I don't want to inject myself for the rest of my life' (95%), and 'I don't want to be bothered with doing injections' (90%); fewer than half agreed with 'My friendships may suffer' (46%), and 'I don't understand why insulin is necessary for me' (45%). Estimation by the physicians and the actual perceptions patients reported differed significantly for 13 statements. Physicians seemed to particularly under-estimate the impact associated with social aspects of insulin use (e.g., 'I don't want to be different from others', 55% patients vs 7% physicians). On the contrary, the statement 'Injections are painful' was the only concern over-estimated by the physicians.

CONCLUSIONS

It was demonstrated that differences in perceptions regarding insulin therapy exist between physicians and patients, particularly in terms of social impacts. The data, obtained in 2004, may not precisely reflect the present situation, but still represents a barrier to insulin therapy widely held by patients and physicians. These results suggest that appropriate understanding of patients' concerns about insulin therapy is important to encourage timely insulin initiation.

High glucose aggravates the detrimental effects of pancreatic stellate cells on Beta-cell function

Background and Aims. We here assess the effects of PSCs on β-cell function and apoptosis in vivo and in vitro. Materials and Methods. PSCs were transplanted into Wistar and Goto-Kakizaki (GK) rats. Sixteen weeks after transplantation, β-cell function, apoptosis, and islet fibrosis were assessed. In vitro the effects of PSCs conditioned medium (PSCs-CM) and/or high concentration of glucose on INS-1 cell function was assessed by measuring insulin secretion, INS-1 cell survival, apoptosis, and endoplasmic reticulum stress (ER stress) associated CHOP expression. Results. PSCs transplantation exacerbated the impaired β-cell function in GK rats, but had no significant effects in Wistar rats. In vitro, PSCs-CM caused impaired INS-1 cell viability and insulin secretion and increased apoptosis, which were more pronounced in the presence of high glucose. Conclusion. Our study demonstrates that PSCs induce β-cell failure in vitro and in vivo.

Role of microRNAs in islet beta-cell compensation and failure during diabetes

Pancreatic beta-cell function and mass are markedly adaptive to compensate for the changes in insulin requirement observed during several situations such as pregnancy, obesity, glucocorticoids excess, or administration. This requires a beta-cell compensation which is achieved through a gain of beta-cell mass and function. Elucidating the physiological mechanisms that promote functional beta-cell mass expansion and that protect cells against death, is a key therapeutic target for diabetes. In this respect, several recent studies have emphasized the instrumental role of microRNAs in the control of beta-cell function. MicroRNAs are negative regulators of gene expression, and are pivotal for the control of beta-cell proliferation, function, and survival. On the one hand, changes in specific microRNA levels have been associated with beta-cell compensation and are triggered by hormones or bioactive peptides that promote beta-cell survival and function. Conversely, modifications in the expression of other specific microRNAs contribute to beta-cell dysfunction and death elicited by diabetogenic factors including, cytokines, chronic hyperlipidemia, hyperglycemia, and oxidized LDL. This review underlines the importance of targeting the microRNA network for future innovative therapies aiming at preventing the beta-cell decline in diabetes.

Serum Fructosamine, Total Cholesterol, and High-Density Lipoprotein in Children with Asthma during Glucocorticoid Treatment

Background/Aims. Glucocorticoids may have adverse effects on carbohydrate and lipid metabolism. The present study was conducted to investigate possible effects on carbohydrate and lipid metabolism of inhaled and oral glucocorticoids in children with asthma. Methods. Two randomised controlled trials with blinded crossover designs were performed. Active treatment was 400  μ g inhaled budesonide or 5 mg prednisolone orally daily during one week. The budesonide trial included 17 and the prednisolone trial 20 school children. Serum fructosamine, total cholesterol and high-density lipoprotein were assessed. Results. Serum fructosamine was increased during active treatment (prednisolone 252.3  μ M versus placebo 247.3  μ M; P = 0.03 and budesonide 228.1  μ M versus no treatment 223.1  μ M; P = 0.02). Total cholesterol and high-density lipoprotein were not statistically significantly increased. Conclusion. Short-term treatment with oral prednisolone and inhaled budesonide may adversely affect mean blood glucose concentration. Possible long-term consequences require further investigations.

Combinations of insulin and oral hypoglycemic agents in diabetes mellitus type 2

Insulin therapy is considered to be the most effective therapy for the reduction of high glucose levels. In patients who cannot be regulated with the combination of oral hypoglycemic agents, insulin should be administrated. The first step is the combination of insulin together with the already administrated oral hypoglycemic agents. The fear for hypoglycemia, the refusal and weakness that patients face when dealing with insulin, constitute reasons for many doctors to deal with insulin therapy in a more skeptical way. As a result, the initiation of insulin therapy is delayed for those patients who need it for hyperglycemia adjustments. This article provides useful practical instructions for initiating insulin therapy.

Circulating interleukin-1β and interleukin-6 concentrations are closely associated with γ-glutamyltranspeptidase activity in middle-aged Japanese men without obvious cardiovascular diseases

Interleukin (IL)-1β and IL-6 expressions are known to be induced by oxidant stress. In the present study, we examined the relationships between these interleukins and the activity of γ-glutamyltranspeptidase (γ-GTP), which was recently reported as a source of oxidant stress production, in the circulating blood of middle-aged Japanese men without obvious cardiovascular diseases. We conducted a cross-sectional study of 317 Japanese men without obvious cardiovascular diseases aged 40 to 69 years (mean ± SD, 58.6 ± 7.6 years) who participated in health checkups in Japan. We analyzed their clinical parameters in serum, lifestyle factors, and plasma IL-1β and IL-6 concentrations. We compared the relationships between these interleukin concentrations and the clinical parameters and lifestyle factors by Spearman correlation coefficients. Stepwise multiple linear regression analyses for interleukins based on the other parameters and γ-GTP, which were classified into 3 groups according to the concentrations, were performed. Interleukin-1β and IL-6 concentrations were closely associated with γ-GTP activity but less associated with alanine aminotransferase and aspartate aminotransferase activities by Spearman correlation coefficients. Stepwise multiple linear regression analyses showed that γ-GTP activity was the explanatory variable for elevated IL-1β and IL-6 concentrations. As natural logarithms, the IL-1β and IL-6 concentrations were estimated to be 1.734- and 1.157-fold higher, respectively, in subjects with high γ-GTP activity ranges than in subjects with a low γ-GTP activity range. The present results show that circulating IL-1β and IL-6 concentrations are strongly and independently associated with γ-GTP activity in middle-aged Japanese men without obvious cardiovascular diseases.

Blocking interleukin-1β in acute and chronic autoinflammatory diseases

An expanding spectrum of acute and chronic inflammatory diseases is considered 'autoinflammatory' diseases. This review considers autoinflammatory diseases as being distinct from 'autoimmune' diseases. Autoimmune diseases are associated with dysfunctional T cells and treated with 'biologicals', including antitumour necrosis factorα, CTLA-Ig, anti-IL-12/23, anti-CD20, anti-IL-17 and anti-IL-6 receptor. In contrast, autoinflammatory diseases are uniquely attributed to a dysfunctional monocyte caspase 1 activity and secretion of IL-1β; indeed, blocking IL-1β results in a rapid and sustained reduction in the severity of most autoinflammatory diseases. Flares of gout, type 2 diabetes, heart failure and smouldering multiple myeloma are examples of seemingly unrelated diseases, which are uniquely responsive to IL 1β neutralization.

The roles of ATF3, an adaptive-response gene, in high-fat-diet-induced diabetes and pancreatic beta-cell dysfunction

Most people with type 2 diabetes (T2D) have reduced beta-cell mass, and apoptosis is a key factor for this reduction. Previously, we showed that ATF3, an adaptive-response gene, is induced by various stress signals relevant to T2D, such as high glucose and high fatty acid. Because ATF3 is proapoptotic in beta-cells, we tested the hypothesis that ATF3 plays a detrimental role and contributes to the development of T2D. We compared wild-type (WT) and ATF3 knockout (KO) mice in an animal model for T2D, high-fat diet-induced diabetes. We also used INS-1 beta-cells and primary islets to analyze the roles of ATF3 in beta-cell function, including insulin gene expression and glucose-induced insulin secretion. Surprisingly, WT mice performed better in glucose tolerance test than KO mice, suggesting a protective, rather than detrimental, role of ATF3. At 12 wk on high-fat diet, no beta-cell apoptosis was observed, and the WT and KO mice had comparable beta-cell areas. However, ATF3 deficiency significantly reduced serum insulin levels in the KO mice without affecting insulin sensitivity, suggesting reduced beta-cell function in the KO mice. Analyses using INS-1 cells and primary islets support the notion that this defect is due, at least partly, to reduced insulin gene transcription in the KO islets without detectable reduction in glucose-induced calcium influx, a critical step for insulin secretion. In conclusion, our results support a model in which, before apoptosis becomes obvious, expression of ATF3 can be beneficial by helping beta-cells to cope with higher metabolic demand.

Activation of G protein-coupled receptor 30 modulates hormone secretion and counteracts cytokine-induced apoptosis in pancreatic islets of female mice

The role of the newly discovered estrogen receptor GPR30 in islet physiology and pathophysiology is unclear. We examined GPR30 expression in relation to hormone secretion and possible anti-apoptotic effects in isolated mouse islets using the synthetic GPR30 ligand G-1. The mRNA and protein expression of GPR30 was analyzed by qPCR, Western blot and confocal microscopy. Hormone secretion and cAMP content were determined with RIA and apoptosis in islet cells with the Annexin-V method. GPR30 mRNA and protein expression was markedly higher in islets from females compared to male. This gender difference was not found for the genomic estrogen receptors ER alpha and ER beta, the ER alpha expression being 10-fold higher than ER beta in both genders. Confocal microscopy revealed abounden GPR30 expression in insulin, glucagon and somatostatin cells. Dose-response studies of G-1 vs 17beta-estradiol in isolated islets at 1 or 12 mM glucose showed an almost identical pattern in that both compounds increased insulin and inhibited glucagon and somatostatin secretion. ICI-182,780 and EM-652, potent antagonists of the 17beta-estradiol receptors (ER alpha and ER beta) did not influence the amplifying effect of G-1 or 17beta-estradiol on cAMP content or insulin secretion from isolated islets. Cytokine-induced (IL-1 beta+TNFalpha+INF gamma) apoptosis in islets, cultured for 24h at 5mM glucose, was almost abolished by G-1 or 17beta-estradiol treatment. Addition of ICI-182,780 or EM-652 did not affect this beneficial effect of G-1 or 17beta-estradiol. Taken together, our findings show that GPR30 is expressed in most islet endocrine cells. The synthetic GPR30 ligand G-1 mimics the non-genomic effects of 17beta-estradiol on islet hormone secretion, cAMP content in islets and its anti-apoptotic effects. G-1 or analogs thereof might be new potential candidates in the therapeutic strategy for type 2 diabetes in women.

Sarcopoterium spinosum extract as an antidiabetic agent: in vitro and in vivo study

ETHNOPHARMACOLOGICAL RELEVANCE

Sarcopoterium spinosum (L.) sp., a common plant in the Mediterranean region, is widely used as an antidiabetic drug by Bedouin healers. However, the antidiabetic properties of Sarcopoterium spinosum had not been fully validated using scientific tools.

AIM OF THE STUDY

To determine the effectiveness of Sarcopoterium spinosum extract as an antidiabetic agent in vitro and in vivo.

MATERIALS AND METHODS

RINm pancreatic beta-cells, L6 myotubes, 3T3-L1 adipocytes and AML-12 hepatocytes were treated with an aqueous Sarcopoterium spinosum extract (0.001-10mg/ml). The effect of the extract on specific physiological functions, including insulin secretion, pancreatic beta-cell viability, GSK3 beta phosphorylation, lipolysis and glucose uptake was measured. In vivo studies were performed using KK-A(y) mice, given the extract for several weeks. IPGTT was performed, and plasma insulin, FFA, food consumption and body weight were measured. In addition, diabetic KK-A(y) mice were given a single dose of the extract, and IPGTT was performed.

RESULTS

Sarcopoterium spinosum extract increased basal and glucose/forskolin-induced insulin secretion in RINm cells, and increased cell viability. The extract inhibited lipolysis in 3T3-L1 adipocytes, and induced glucose uptake in these cells as well as in AML-12 hepatocytes and L6 myotubes. GSK3 beta phosphorylation was also induced in L6 myotubes, suggesting increased glycogen synthesis. Sarcopoterium spinosum extract had a preventive effect on the progression of diabetes in KK-A(y) mice. Catechin and epicatechin were detected in Sarcopoterium spinosum extract using hyphenated LC-MS/MS.

CONCLUSIONS

Sarcopoterium spinosum extract has effects that mimic those of insulin and provide the basis for antidiabetic activity of the extract.

Regulation of beta-cell viability and gene expression by distinct agonist fragments of adiponectin

Obesity is an established risk factor for type 2 diabetes. Activation of the adiponectin receptors has a clear role in improving insulin resistance although conflicting evidence exists for its effects on pancreatic beta-cells. Previous reports have identified both adiponectin receptors (ADR-1 and ADR-2) in the beta-cell. Recent evidence has suggested that two distinct regions of the adiponectin molecule, the globular domain and a small N-terminal region, have agonist properties. This study investigates the effects of two agonist regions of adiponectin on insulin secretion, gene expression, cell viability and cell signalling in the rat beta-cell line BRIN-BD11, as well as investigating the expression levels of adiponectin receptors (ADRs) in these cells. Cells were treated with globular adiponectin and adiponectin (15-36) +/-leptin to investigate cell viability, expression of key beta-cell genes and ERK1/2 activation. Both globular adiponectin and adiponectin (15-36) caused significant ERK1/2 dependent increases in cell viability. Leptin co-incubation attenuated adiponectin (15-36) but not globular adiponectin induced cell viability. Globular adiponectin, but not adiponectin (15-36), caused a significant 450% increase in PDX-1 expression and a 45% decrease in LPL expression. ADR-1 was expressed at a higher level than ADR-2, and ADR mRNA levels were differentially regulated by non-esterified fatty acids and peroxisome-proliferator-activated receptor agonists. These data provide evidence of roles for two distinct adiponectin agonist domains in the beta-cell and confirm the potentially important role of adiponectin receptor agonism in maintaining beta-cell mass.

Mechanisms of pancreatic beta-cell apoptosis in diabetes and its therapies

Diabetes occurs when beta-cells no longer function properly or have been destroyed. Pancreatic beta-cell death by apoptosis contributes significantly in both autoimmune type 1 diabetes and type 2 diabetes. Pancreatic beta-cell death can be induced by multiple stresses in both major types of diabetes. There are also several rare forms of diabetes, including Wolcott-Rallison syndrome, Wolfram syndrome, as well as some forms of maturity onset diabetes of the young that are caused by mutations in genes that may play important roles in beta-cell survival. The use of islet transplantation as a treatment for diabetes is also limited by excessive beta-cell apoptosis. Mechanistic insights into the control of pancreatic beta-cell apoptosis are therefore important for the prevention and treatment of diabetes. Indeed, a substantial quantity of research has been dedicated to this area over the past decade. In this chapter, we review the factors that influence the propensity of beta-cells to undergo apoptosis and the mechanisms of this programmed cell death in the initiation and progression of diabetes.

Expression of the NH(2)-terminal fragment of RasGAP in pancreatic beta-cells increases their resistance to stresses and protects mice from diabetes

OBJECTIVE

Our laboratory has previously established in vitro that a caspase-generated RasGAP NH(2)-terminal moiety, called fragment N, potently protects cells, including insulinomas, from apoptotic stress. We aimed to determine whether fragment N can increase the resistance of pancreatic beta-cells in a physiological setting.

RESEARCH DESIGN AND METHODS

A mouse line, called rat insulin promoter (RIP)-N, was generated that bears a transgene containing the rat insulin promoter followed by the cDNA-encoding fragment N. The histology, functionality, and resistance to stress of RIP-N islets were then assessed.

RESULTS

Pancreatic beta-cells of RIP-N mice express fragment N, activate Akt, and block nuclear factor kappaB activity without affecting islet cell proliferation or the morphology and cellular composition of islets. Intraperitoneal glucose tolerance tests revealed that RIP-N mice control their glycemia similarly as wild-type mice throughout their lifespan. Moreover, islets isolated from RIP-N mice showed normal glucose-induced insulin secretory capacities. They, however, displayed increased resistance to apoptosis induced by a series of stresses including inflammatory cytokines, fatty acids, and hyperglycemia. RIP-N mice were also protected from multiple low-dose streptozotocin-induced diabetes, and this was associated with reduced in vivo beta-cell apoptosis.

CONCLUSIONS

Fragment N efficiently increases the overall resistance of beta-cells to noxious stimuli without interfering with the physiological functions of the cells. Fragment N and the pathway it regulates represent, therefore, a potential target for the development of antidiabetes tools.

The honeymoon phase: intersection of metabolism and immunology

PURPOSE OF REVIEW

Even though the honeymoon phase in type 1 diabetes mellitus has been well known, its underlying pathogenic mechanisms remain poorly described. The common explanation that it occurs due to 'beta-cell rest' on initiation of insulin therapy seems inadequate based on recent observations and studies and its underlying immunological aspects overlooked.

RECENT FINDINGS

In this article, we will review the metabolic and immunological aspects of the honeymoon phase and we will present our current model of the pathophysiology of this phase. Our view is that it is one of many phases of remission occurring basically due to development of adaptive immune tolerance along the course of type 1 diabetes. We will also review new findings of the interplay between metabolic factors (ambient glucose level) and immune function.

SUMMARY

The honeymoon phase provides a unique model to understand the pathogenesis of type 1 diabetes. Research to unravel its immune pathogenesis is needed. It may turn out that the optimum form of intervention in type 1 diabetes is one that combines enhancement of antigen-specific adaptive immune tolerance with optimized metabolic control in order to keep cytotoxic T cells anergic.

Insulin glulisine in the management of diabetes

Insulin glulisine is appealing in principle, but the advantages of this drug over the other rapid-acting insulin analogs are still relatively unknown. The frequency of hypoglycemia, convenience in the timing of administration, and improvements in terms of HbA(1c) seem similar among the rapid-acting insulin analogs, including insulin glulisine. Only properly randomized long-term clinical studies with insulin glulisine will reveal the true value of this novel insulin analog.

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

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

Resolving the conundrum of islet transplantation by linking metabolic dysregulation, inflammation, and immune regulation

Although type 1 diabetes cannot be prevented or reversed, replacement of insulin production by transplantation of the pancreas or pancreatic islets represents a definitive solution. At present, transplantation can restore euglycemia, but this restoration is short-lived, requires islets from multiple donors, and necessitates lifelong immunosuppression. An emerging paradigm in transplantation and autoimmunity indicates that systemic inflammation contributes to tissue injury while disrupting immune tolerance. We identify multiple barriers to successful islet transplantation, each of which either contributes to the inflammatory state or is augmented by it. To optimize islet transplantation for diabetes reversal, we suggest that targeting these interacting barriers and the accompanying inflammation may represent an improved approach to achieve successful clinical islet transplantation by enhancing islet survival, regeneration or neogenesis potential, and tolerance induction. Overall, we consider the proinflammatory effects of important technical, immunological, and metabolic barriers including: 1) islet isolation and transplantation, including selection of implantation site; 2) recurrent autoimmunity, alloimmune rejection, and unique features of the autoimmune-prone immune system; and 3) the deranged metabolism of the islet transplant recipient. Consideration of these themes reveals that each is interrelated to and exacerbated by the other and that this connection is mediated by a systemic inflammatory state. This inflammatory state may form the central barrier to successful islet transplantation. Overall, there remains substantial promise in islet transplantation with several avenues of ongoing promising research. This review focuses on interactions between the technical, immunological, and metabolic barriers that must be overcome to optimize the success of this important therapeutic approach.

A Biophysical Characterization of the Peptide Drug Pramlintide (AC137) Using Empirical Phase Diagrams

AC137 (pramlintide) is a 37-residue peptide analogue of the hormone amylin. Pramlintide has been studied as an adjunct antihyperglycemic treatment for patients with type 2 or type 1 diabetes who use insulin. This study took an empirical phase diagram (EPD) approach to obtain information about the structural stability of this peptide by compiling thermal perturbation data acquired from multiple spectroscopic methods, including high-resolution second-derivative UV absorbance spectroscopy, optical density, fluorescence, and circular dichroism. This approach enabled us to accomplish two major goals: (1) characterize the structure and physical stability of AC137 and (2) assess the application of EPDs to a small peptide. Results obtained at low concentration of AC137 revealed a peptide with ill-defined structure and insensitivity to pH. Use of isotope exchange NMR confirmed this lack of structure. At the current formulation of pH 4, AC137 exhibited stability at concentrations of 1.8 to 8.8 mg/mL. High concentrations of the peptide showed a tendency to aggregate at pH 6-7.5. Construction of EPDs under the various experimental conditions examined manifested color changes that correlated well with the raw data. The utility and limitations of the EPD approach when applied to weakly structured peptides are discussed.

Exendin-4 protects beta-cells from interleukin-1 beta-induced apoptosis by interfering with the c-Jun NH2-terminal kinase pathway

OBJECTIVE

The pro-inflammatory cytokine interleukin-1 beta (IL-1 beta) generates pancreatic beta-cells apoptosis mainly through activation of the c-Jun NH(2)-terminal kinase (JNK) pathway. This study was designed to investigate whether the long-acting agonist of the hormone glucagon-like peptide 1 (GLP-1) receptor exendin-4 (ex-4), which mediates protective effects against cytokine-induced beta-cell apoptosis, could interfere with the JNK pathway.

RESEARCH DESIGN AND METHODS

Isolated human, rat, and mouse islets and the rat insulin-secreting INS-1E cells were incubated with ex-4 in the presence or absence of IL-1 beta. JNK activity was assessed by solid-phase JNK kinase assay and quantification of c-Jun expression. Cell apoptosis was determined by scoring cells displaying pycnotic nuclei.

RESULTS

Ex-4 inhibited induction of the JNK pathway elicited by IL-1 beta. This effect was mimicked with the use of cAMP-raising agents isobutylmethylxanthine and forskolin and required activation of the protein kinase A. Inhibition of the JNK pathway by ex-4 or IBMX and forskolin was concomitant with a rise in the levels of islet-brain 1 (IB1), a potent blocker of the stress-induced JNK pathway. In fact, ex-4 as well as IBMX and forskolin induced expression of IB1 at the promoter level through cAMP response element binding transcription factor 1. Suppression of IB1 levels with the use of RNA interference strategy impaired the protective effects of ex-4 against apoptosis induced by IL-1 beta.

CONCLUSIONS

The data establish the requirement of IB1 in the protective action of ex-4 against apoptosis elicited by IL-1 beta and highlight the GLP-1 mimetics as new potent inhibitors of the JNK signaling induced by cytokines.

Structural requirements for the cytoprotective actions of mono-unsaturated fatty acids in the pancreatic beta-cell line, BRIN-BD11

BACKGROUND AND PURPOSE

Exposure of pancreatic beta-cells to long-chain free fatty acids leads to differential responses according to the chain length and degree of unsaturation. In particular, long-chain saturated molecules such as palmitate (C16:0) cause apoptosis, whereas equivalent mono-unsaturated species (for example, palmitoleate (C16:1)) are not overtly toxic. Moreover, mono-unsaturates exert a powerful cytoprotective response against a range of proapoptotic stimuli. However, the structural requirements that determine cytoprotection have not been determined and form the basis of the present study.

EXPERIMENTAL APPROACH

BRIN-BD11 and INS-1 beta-cells were exposed either to the saturated fatty acid palmitate, or to serum withdrawal, to mediate cytotoxicity. The protective effects of a wide range of mono-unsaturated fatty acid derivatives were tested in cytotoxicity assays. Effector caspase activity was also measured and correlated with viability.

KEY RESULTS

The cytotoxic actions of palmitate were inhibited dose-dependently by long-chain mono-unsaturated fatty acids with a defined potency order C18:1>C16:1>>C14:1. The configuration of the double bond was also important with cis forms being more potent than trans forms. Alkylated mono-unsaturated fatty-acid derivates were also cytoprotective, although their efficacy declined as the alkyl chain length increased. Cytoprotection was achieved rapidly on addition of mono-unsaturates and correlated with a rapid and dramatic inhibition of caspase-3/7 activity in palmitate-treated cells.

CONCLUSIONS AND IMPLICATIONS

The data reveal the structural requirements that dictate the cytoprotective actions of mono-unsaturated fatty acids in pancreatic beta-cells. Metabolic activation is not required and the data point at the potential involvement of a fatty acid receptor in mediating cytoprotection.

Gender-based dimorphic pattern for interleukin-1 receptor antagonist in type 2 diabetes mellitus

Adipose tissue secretes a variety of cytokines, some of which are increased in the serum of obese patients. The anti-inflammatory interleukin-1 receptor antagonist (IL-1Ra) is the most highly elevated known cytokine in human obesity, and its serum levels are strongly associated with the degree of insulin resistance in non-diabetic patients.

AIM

The present study examined serum levels of IL-1Ra in type 2 diabetic patients (T2DM) and their relationships with three other adipokines (leptin, interleukin-6 [IL-6], adiponectin). Their correlation with anthropometric and biochemical variables was examined, as well as their intraindividual fluctuations.

METHODS

Fifty T2DM patients, aged 58+/-13 years, were consecutively recruited among those electively hospitalized for a one-week intensive training course with our Diabetes Education Service. Anthropometric measurements and blood samples were taken after an overnight fast on admission (baseline) and after four days.

RESULTS

Mean serum levels of IL-1Ra and leptin, but not of IL-6 and adiponectin, were significantly higher in women than in men (P<0.0006), and this difference persisted after correction for body mass index (BMI) (P<0.0004). In addition, IL-1Ra and leptin were strongly correlated with the BMI (P<0.0004). By contrast, no significant correlations were observed between IL-1Ra and glucose-control parameters. Finally, all four adipokines exhibited wide interindividual variability, but with limited intraindividual fluctuations over the short time period.

CONCLUSION

IL-1Ra, leptin and adiponectin serum levels exhibit marked interindividual variation with high intraindividual consistency. A gender-based dimorphic pattern for IL-1Ra, independent of the degree of adiposity and glucose control, was also found.

Fas-associated death receptor signaling evoked by human amylin in islet beta-cells

OBJECTIVE

Aggregation of human amylin (hA) into beta-sheet-containing oligomers is linked to islet beta-cell dysfunction and the pathogenesis of type 2 diabetes. Here, we investigated possible contributions of Fas-associated death-receptor signaling to the mechanism of hA-evoked beta-cell apoptosis.

RESEARCH DESIGN AND METHODS

We measured responses to hA in isolated mouse islets and two insulinoma cell lines, wherein we measured Fas/Fas ligand (FasL) and Fas-associated death domain (FADD) expression by quantitative RT-PCR, Western blotting, and immunofluorescence staining. We used two anti-Fas/FasL blocking antibodies and the Fas/FasL antagonist Kp7-6 to probe roles of Fas interactions in the regulation of apoptosis in hA-treated beta-cells and measured Kp7-6-mediated effects on beta-sheet formation and aggregation using circular dichroism and thioflavin-T binding.

RESULTS

hA treatment stimulated Fas and FADD expression in beta-cells. Both blocking antibodies suppressed hA-evoked apoptosis but did not modify its aggregation. Therefore, Fas receptor interactions played a critical role in induction of this pathway. Interestingly, hA-evoked beta-cell apoptosis was suppressed and rescued by Kp7-6, which also impaired hA beta-sheet formation.

CONCLUSIONS

This is the first report linking hA-evoked induction and activation of Fas and FADD to beta-cell apoptosis. We have identified a Fas/FasL antagonist, Kp7-6, as a potent inhibitor of hA aggregation and related beta-cell death. These results also support an interaction between hA and Fas on the surface of apoptotic beta-cells. Increased expression and activation of Fas in beta-cells could constitute a molecular event common to the pathogenesis of both type 1 and type 2 diabetes, although the mode of pathway activation may differ between these common forms of diabetes.