Role of caspases in the regulation of apoptotic pancreatic islet beta-cells death

Cellular and transcriptomic response to pathogenic and non-pathogenic Vibrio parahaemolyticus strains causing acute hepatopancreatic necrosis disease (AHPND) in Litopenaeus vannamei

The shrimp industry has historically been affected by viral and bacterial diseases. One of the most recent emerging diseases is Acute Hepatopancreatic Necrosis Disease (AHPND), which causes severe mortality. Despite its significance to sanitation and economics, little is known about the molecular response of shrimp to this disease. Here, we present the cellular and transcriptomic responses of Litopenaeus vannamei exposed to two Vibrio parahaemolyticus strains for 98 h, wherein one is non-pathogenic (VpN) and the other causes AHPND (VpP). Exposure to the VpN strain resulted in minor alterations in hepatopancreas morphology, including reductions in the size of R and B cells and detachments of small epithelial cells from 72 h onwards. On the other hand, exposure to the VpP strain is characterized by acute detachment of epithelial cells from the hepatopancreatic tubules and infiltration of hemocytes in the inter-tubular spaces. At the end of exposure, RNA-Seq analysis revealed functional enrichment in biological processes, such as the toll3 receptor signaling pathway, apoptotic processes, and production of molecular mediators involved in the inflammatory response of shrimp exposed to VpN treatment. The biological processes identified in the VpP treatment include superoxide anion metabolism, innate immune response, antimicrobial humoral response, and toll3 receptor signaling pathway. Furthermore, KEGG enrichment analysis revealed metabolic pathways associated with survival, cell adhesion, and reactive oxygen species, among others, for shrimp exposed to VpP. Our study proves the differential immune responses to two strains of V. parahaemolyticus, one pathogenic and the other nonpathogenic, enlarges our knowledge on the evolution of AHPND in L. vannamei, and uncovers unique perspectives on establishing genomic resources that may function as a groundwork for detecting probable molecular markers linked to the immune system in shrimp.

An overview of programmed cell death: Apoptosis and pyroptosis-Mechanisms, differences, and significance in organism physiology and pathophysiology

Regulated cell death is an essential and heterogeneous process occurring in the life cycle of organisms, from embryonic development and aging to the regulation of homeostasis and organ maintenance. Under this term, we can distinguish many distinct pathways, including apoptosis and pyroptosis. Recently, there has been an increasing comprehension of the mechanisms governing these phenomena and their characteristic features. The coexistence of different types of cell death and the differences and similarities between them has been the subject of many studies. This review aims to present the latest literature in the field of pyroptosis and apoptosis and compare their molecular pathway's elements and significance in the physiology and pathophysiology of the organism.

The Role of Galectin 3 in the Pathogenesis of Diabetes Mellitus: Focus on Β-Cell Function and Survival

Galectin 3 is a lectin expressed in many tissues with a significant biological role in physiological and pathological processes. Our review aims to sublimate the effects of galectin 3 on the β-cells function and survival. Data about the effect of galectin 3 on β- cells are scarce and contradictory. Several studies have shown that reduced activity of the galectin 3 gene reduces the risk of developing type 1 diabetes in an experimental model of diabetes in galectin 3 deficient mice. On the other side, in an experimental model of type 1 diabetes with mice with selectively enhanced expression of galectin 3 in β-cells, was shown that increased expression of this lectin has a protective role. Unlike type 1 diabetes where the autoimmune process plays a dominant role in pathogenesis, the pathogenesis of type 2 diabetes is multifactorial. One of the main factors which contribute to type 2 diabetes, the insulin resistance, is related to the concentration of soluble galectin 3. The effect of galectin 3 is very important for β-cell function. When a harmful factor acts on a β-cell, its intracellular concentration increases to preserve the function of β-cells and prevent their apoptosis, by blocking the internal path of apoptosis. However, excessive accumulation of galectin 3 inside the cell leads to its secretion, which encourages tissue inflammation. Based on all the above, galectin 3 has a double effect on β-cells.

Oxidative stress-mediated beta cell death and dysfunction as a target for diabetes management

The biggest drawback of a current diabetes therapy is the treatment of the consequences not the cause of the disease. Regardless of the diabetes type, preservation and recovery of functional pancreatic beta cells stands as the biggest challenge in the treatment of diabetes. Free radicals and oxidative stress are among the major mediators of autoimmune destruction of beta cells in type 1 diabetes (T1D) or beta cell malfunction and death provoked by glucotoxicity and insulin resistance in type 2 diabetes (T2D). Additionally, oxidative stress reduces functionality of beta cells in T2D by stimulating their de-/trans-differentiation through the loss of transcription factors critical for beta cell development, maturity and regeneration. This review summarizes up to date clarified redox-related mechanisms involved in regulating beta cell identity and death, underlining similarities and differences between T1D and T2D. The protective effects of natural antioxidants on the oxidative stress-induced beta cell failure were also discussed. Considering that oxidative stress affects epigenetic regulatory mechanisms involved in the regulation of pancreatic beta cell survival and insulin secretion, this review highlighted huge potential of epigenetic therapy. Special attention was paid on application of the state-of-the-art CRISPR/Cas9 technology, based on targeted epigenome editing with the purpose of changing the differentiation state of different cell types, making them insulin-producing with ability to attenuate diabetes. Clarification of the above-mentioned mechanisms could provide better insight into diabetes etiology and pathogenesis, which would allow development of novel, potentially more efficient therapeutic strategies for the prevention or reversion of beta cell loss.

β-Cell Death in Diabetes: Past Discoveries, Present Understanding, and Potential Future Advances

β-cell death is regarded as a major event driving loss of insulin secretion and hyperglycemia in both type 1 and type 2 diabetes mellitus. In this review, we explore past, present, and potential future advances in our understanding of the mechanisms that promote β-cell death in diabetes, with a focus on the primary literature. We first review discoveries of insulin insufficiency, β-cell loss, and β-cell death in human diabetes. We discuss findings in humans and mouse models of diabetes related to autoimmune-associated β-cell loss and the roles of autoreactive T cells, B cells, and the β cell itself in this process. We review discoveries of the molecular mechanisms that underlie β-cell death-inducing stimuli, including proinflammatory cytokines, islet amyloid formation, ER stress, oxidative stress, glucotoxicity, and lipotoxicity. Finally, we explore recent perspectives on β-cell death in diabetes, including: (1) the role of the β cell in its own demise, (2) methods and terminology for identifying diverse mechanisms of β-cell death, and (3) whether non-canonical forms of β-cell death, such as regulated necrosis, contribute to islet inflammation and β-cell loss in diabetes. We believe new perspectives on the mechanisms of β-cell death in diabetes will provide a better understanding of this pathological process and may lead to new therapeutic strategies to protect β cells in the setting of diabetes.

The long-term failure of RYGB surgery in improving T2DM is related to hyperinsulinism

BACKGROUND

Roux-en-Y gastric bypass (RYGB) is the gold standard method for bariatric surgery and leads to substantial improvements in Type 2 Diabetes mellitus. However, many patients experience relapses in diabetes five years after undergoing this aggressive surgical procedure. We focus on beta-cell population changes and absorptive intestinal consequences after RYGB in a healthy nonobese animal model after a long survival period.

METHODS

For our purpose, we use three groups of Wistar rats: RYGB-operated, surgical control (Sham) and fasting control. We measure alpha-, beta-cell mass; transcription (Arx, and Pdx-1) and proliferation (Ki67) factors; glucose tolerance and insulin release after oral glucose tests; histological adaptive changes in the jejunum; and intestinal glucose transporters.

RESULTS

Our results showed an early increase in insulin secretion after surgery, that decrease at the end of the study. The beta-cell mass reduces twenty-four weeks after RYGB, which coincides with decrease of Pdx-1 transcription promoter factor. These was coincident with an increase in alpha-mass and a high expression of Arx in RYGB group.

CONCLUSIONS

The analysis of all data showed beta-cell mass transdifferentiation into alpha-cell mass in RYGB rats. Due to long-term exhaustion of the beta-cell population by hyperinsulinism derived from digestive tract adaptation to surgery.

Toxicity Induced by Cytokines, Glucose, and Lipids Increase Apoptosis and Hamper Insulin Secretion in the 1.1E7 Beta Cell-Line

Basic research on types 1 and 2 diabetes mellitus require early stage studies using beta cells or cell lines, ideally of human origin and with preserved insulin secretion in response to glucose. The 1.1E7 cells are a hybrid cell line resulting from the electrofusion of dispersed human islets and PANC-1 cells, capable of secreting insulin in response to glucose, but their survival and function under toxic conditions remains untested. This characterization is the purpose of the present study. We treated these cells with a cytokine mix, high glucose, palmitate, and the latter two combined. Under these conditions, we measured cell viability and apoptosis (MTT, Caspase Glo and TUNEL assays, as well as caspase-8 and -9 levels by Western blotting), endoplasmic reticulum stress markers (EIF2AK3, HSPA4, EIF2a, and HSPA5) by real-time PCR, and insulin secretion with a glucose challenge. All of these stimuli (i) induce apoptosis and ER stress markers expression, (ii) reduce mRNA amounts of 2–5 components of genes involved in the insulin secretory pathway, and (iii) abrogate the insulin release capability of 1.1E7 cells in response to glucose. The most pronounced effects were observed with cytokines and with palmitate and high glucose combined. This characterization may well serve as the starting point for those choosing this cell line for future basic research on certain aspects of diabetes.

Exposure to maternal obesity programs sex differences in pancreatic islets of the offspring in mice

AIMS/HYPOTHESIS

Obesity during pregnancy increases offspring type 2 diabetes risk. Given that nearly half of women of child-bearing age in many populations are currently overweight/obese, it is key that we improve our understanding of the impact of the in utero/early life environment on offspring islet function. Whilst a number of experimental studies have examined the effect of maternal obesity on offspring islet architecture and/or function, it has not previously been delineated whether these changes are independent of other confounding risk factors such as obesity, postnatal high-fat-feeding and ageing. Thus, we aimed to study the impact of exposure to maternal obesity on offspring islets in young, glucose-tolerant male and female offspring.

METHODS

Female C57BL/6J mice were fed ad libitum either chow or obesogenic diet prior to and throughout pregnancy and lactation. Offspring were weaned onto a chow diet and remained on this diet until the end of the study. An IPGTT was performed on male and female offspring at 7 weeks of age. At 8 weeks of age, pancreatic islets were isolated from offspring for measurement of insulin secretion and content, mitochondrial respiration, ATP content, reactive oxygen species levels, beta and alpha cell mass, granule and mitochondrial density (by transmission electron microscopy), and mRNA and protein expression by real-time RT-PCR and Western blotting, respectively.

RESULTS

Glucose tolerance was similar irrespective of maternal diet and offspring sex. However, blood glucose was lower (p < 0.001) and plasma insulin higher (p < 0.05) in female offspring of obese dams 15 min after glucose administration. This was associated with higher glucose- (p < 0.01) and leucine/glutamine-stimulated (p < 0.05) insulin secretion in these offspring. Furthermore, there was increased mitochondrial respiration (p < 0.01) and density (p < 0.05) in female offspring of obese dams compared with same-sex controls. Expression of mitochondrial and nuclear-encoded components of the electron transport chain, L-type Ca²⁺ channel subtypes that play a key role in stimulus-secretion coupling [Cacna1d (p < 0.05)], and oestrogen receptor α (p < 0.05) was also increased in islets from these female offspring of obese dams. Moreover, cleaved caspase-3 expression and BAX:Bcl-2 were decreased (p < 0.05) reflecting reduced susceptibility to apoptosis. In contrast, in male offspring, glucose and leucine/glutamine-stimulated insulin secretion was comparable between treatment groups. There was, however, compromised mitochondrial respiration characterised by decreased ATP synthesis-driven respiration (p < 0.05) and increased uncoupled respiration (p < 0.01), reduced docked insulin granules (p < 0.001), decreased Cacna1c (p < 0.001) and Cacna1d (p < 0.001) and increased cleaved caspase-3 expression (p < 0.05).

CONCLUSIONS/INTERPRETATION

Maternal obesity programs sex differences in offspring islet function. Islets of female but not male offspring appear to be primed to cope with a nutritionally-rich postnatal environment, which may reflect differences in future type 2 diabetes risk.

Regulated hAAT Expression from a Novel rAAV Vector and Its Application in the Prevention of Type 1 Diabetes

We, and others, have previously achieved high and sustained levels of transgene expression from viral vectors, such as recombinant adeno-associated virus (rAAV). However, regulatable transgene expression may be preferred in gene therapy for diseases, such as type 1 diabetes (T1D) and rheumatoid arthritis (RA), in which the timing and dosing of the therapeutic gene product play critical roles. In the present study, we generated a positive feedback regulation system for human alpha 1 antitrypsin (hAAT) expression in the rAAV vector. We performed quantitative kinetics studies in vitro and in vivo demonstrating that this vector system can mediate high levels of inducible transgene expression. Transgene induction could be tailored to occur rapidly or gradually, depending on the dose of the inducing drug, doxycycline (Dox). Conversely, after withdrawal of Dox, the silencing of transgene expression occurred slowly over the course of several weeks. Importantly, rAAV delivery of inducible hAAT significantly prevented T1D development in non-obese diabetic (NOD) mice. These results indicate that this Dox-inducible vector system may facilitate the fine-tuning of transgene expression, particularly for hAAT treatment of human autoimmune diseases, including T1D.

Boolean network modeling of β-cell apoptosis and insulin resistance in type 2 diabetes mellitus

BACKGROUND

Major alteration in lifestyle of human population has promoted Type 2 diabetes mellitus (T2DM) to the level of an epidemic. This metabolic disorder is characterized by insulin resistance and pancreatic β-cell dysfunction and apoptosis, triggered by endoplasmic reticulum (ER) stress, oxidative stress and cytokines. Computational modeling is necessary to consolidate information from various sources in order to obtain a comprehensive understanding of the pathogenesis of T2DM and to investigate possible interventions by performing in silico simulations.

RESULTS

In this paper, we propose a Boolean network model integrating the insulin resistance pathway with pancreatic β-cell apoptosis pathway which are responsible for T2DM. The model has five input signals, i.e. ER stress, oxidative stress, tumor necrosis factor α (TNF α), Fas ligand (FasL), and interleukin-6 (IL-6). We performed dynamical simulations using random order asynchronous update and with different combinations of the input signals. From the results, we observed that the proposed model made predictions that closely resemble the expression levels of genes in T2DM as reported in the literature.

CONCLUSION

The proposed model can make predictions about expression levels of genes in T2DM that are in concordance with literature. Although experimental validation of the model is beyond the scope of this study, the model can be useful for understanding the aetiology of T2DM and discovery of therapeutic intervention for this prevalent complex disease. The files of our model and results are available at https://github.com/JieZheng-ShanghaiTech/boolean-t2dm .

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.

Pancreatic Beta Cell Death: Novel Potential Mechanisms in Diabetes Therapy

PURPOSE OF REVIEW

Describing the diverse molecular mechanisms (particularly immunological) involved in the death of the pancreatic beta cell in type 1 and type 2 diabetes mellitus.

RECENT FINDINGS

Beta cell death is the final event in a series of mechanisms that, up to date, have not been entirely clarified; it represents the pathophysiological mechanism in the natural history of diabetes mellitus. These mechanisms are not limited to an apoptotic process only, which is characteristic of the immune-mediated insulitis in type 1 diabetes mellitus. They also include the action of proinflammatory cytokines, the production of reactive oxygen species, DNA fragmentation (typical of necroptosis in type 1 diabetic patients), excessive production of islet amyloid polypeptide with the consequent endoplasmic reticulum stress, disruption in autophagy mechanisms, and protein complex formation, such as the inflammasome, capable of increasing oxidative stress produced by mitochondrial damage.

SUMMARY

Necroptosis, autophagy, and pyroptosis are molecular mechanisms that modulate the survival of the pancreatic beta cell, demonstrating the importance of the immune system in glucolipotoxicity processes and the potential role for immunometabolism as another component of what once known as the "ominous octet."

Genetic and clinic predictors of new onset diabetes mellitus after transplantation

New Onset Diabetes after Transplantation (NODAT) is a frequent complication after solid organ transplantation, with higher incidence during the first year. Several clinical and genetic factors have been described as risk factors of Type 2 Diabetes (T2DM). Additionally, T2DM shares some genetic factors with NODAT. We investigated if three genetic risk scores (w-GRS) and clinical factors were associated with NODAT and how they predicted NODAT development 1 year after transplantation. In both main (n = 725) and replication (n = 156) samples the clinical risk score was significantly associated with NODAT (OR_main: 1.60 [1.36-1.90], p = 3.72*10^-8 and OR_replication: 2.14 [1.39-3.41], p = 0.0008, respectively). Two w-GRS were significantly associated with NODAT in the main sample (OR_{w-GRS 2}:1.09 [1.04-1.15], p = 0.001 and OR_{w-GRS 3}:1.14 [1.01-1.29], p = 0.03) and a similar OR_{w-GRS 2} was found in the replication sample, although it did not reach significance probably due to a power issue. Despite the low OR of w-GRS on NODAT compared to clinical covariates, when integrating w-GRS 2 and w-GRS 3 in the clinical model, the Area under the Receiver Operating Characteristics curve (AUROC), specificity, sensitivity and accuracy were 0.69, 0.71, 0.58 and 0.68, respectively, with significant Likelihood Ratio test discrimination index (p-value 0.0004), performing better in NODAT discrimination than the clinical model alone. Twenty-five patients needed to be genotyped in order to detect one misclassified case that would have developed NODAT 1 year after transplantation if using only clinical covariates. To our knowledge, this is the first study extensively examining genetic risk scores contributing to NODAT development.

Genomic determinants of long-term cardiometabolic complications in childhood acute lymphoblastic leukemia survivors

BACKGROUND

While cure rates for childhood acute lymphoblastic leukemia (cALL) now exceed 80%, over 60% of survivors will face treatment-related long-term sequelae, including cardiometabolic complications such as obesity, insulin resistance, dyslipidemia and hypertension. Although genetic susceptibility contributes to the development of these problems, there are very few studies that have so far addressed this issue in a cALL survivorship context.

METHODS

In this study, we aimed at evaluating the associations between common and rare genetic variants and long-term cardiometabolic complications in survivors of cALL. We examined the cardiometabolic profile and performed whole-exome sequencing in 209 cALL survivors from the PETALE cohort. Variants associated with cardiometabolic outcomes were identified using PLINK (common) or SKAT (common and rare) and a logistic regression was used to evaluate their impact in multivariate models.

RESULTS

Our results showed that rare and common variants in the BAD and FCRL3 genes were associated (p<0.05) with an extreme cardiometabolic phenotype (3 or more cardiometabolic risk factors). Common variants in OGFOD3 and APOB as well as rare and common BAD variants were significantly (p<0.05) associated with dyslipidemia. Common BAD and SERPINA6 variants were associated (p<0.05) with obesity and insulin resistance, respectively.

CONCLUSIONS

In summary, we identified genetic susceptibility loci as contributing factors to the development of late treatment-related cardiometabolic complications in cALL survivors. These biomarkers could be used as early detection strategies to identify susceptible individuals and implement appropriate measures and follow-up to prevent the development of risk factors in this high-risk population.

Pancreatic-β-cell survival and proliferation are promoted by protein kinase G type Iα and downstream regulation of AKT/FOXO1

Early studies showed nitric oxide as a pro-inflammatory-cytokine-induced toxin involved in pancreatic β-cell destruction during pathogenesis of type-1 diabetes. However, nitric oxide has both cytotoxic and cytoprotective effects on mammalian cells, depending on concentration and micro-environmental surroundings. Our studies have shown that low/physiological-level nitric oxide selectively activates protein kinase G type Iα isoform, promoting cytoprotective/pro-cell-survival effects in many cell types. In bone marrow-derived stromal/mesenchymal stem cells, protein kinase G type Iα mediates autocrine effects of nitric oxide and atrial natriuretic peptide, promoting DNA-synthesis/proliferation and cell survival. In this study, endothelial nitric oxide synthase/neuronal nitric oxide synthase inhibitor L-NIO (L-N(5)-(1-iminoethyl)ornithine), soluble guanylyl cyclase inhibitor ODQ (1H-[1,2,4]oxadiazolo[4,3,-a] quinoxalin-1-one), atrial natriuretic peptide-receptor inhibitor A71915 and protein kinase G type Iα kinase activity inhibitor DT-2 all increased apoptosis and decreased insulin secretion in RINm5F pancreatic β-cells, suggesting autocrine regulatory role for endogenous nitric oxide- and atrial natriuretic peptide-induced activation of protein kinase G type Iα. In four pancreatic β-cell lines, Beta-TC-6, RINm5F, INS-1 and 1.1B4, protein kinase G type Iα small-interfering RNA decreased phospho-serine-239-VASP (indicator of endogenous protein kinase G type Iα kinase activity), increased apoptosis and decreased proliferation. In protein kinase G type Iα-knockdown β-cell lines, expressions of phospho-protein kinase B (PKB/AKT) (AKT), phospho-Forkhead box protein O1 (FOXO1) (transcriptional repressor of pancreas duodenum homobox-1) and pancreas duodenum homobox-1 were decreased, suppressing proliferation and survival in pancreatic β-cells. The data suggest autocrine nitric oxide/atrial natriuretic peptide-induced activation of protein kinase G type Iα/p-AKT/p-FOXO1 promotes survival and proliferation in pancreatic β-cells, providing therapeutic implications for development of new therapeutic agents for diabetes.

Apoptosis of pancreatic β-cells in Type 1 diabetes

Type 1 diabetes mellitus (T1DM) results from autoimmune destruction of pancreatic β-cells after an asymptomatic period over years. Insulitis activates antigen presenting cells, which trigger activating CD4+ helper-T cells, releasing chemokines/cytokines. Cytokines activate CD8+ cytotoxic-T cells, which lead to β-cell destruction. Apoptosis pathway consists of extrinsic (receptor-mediated) and intrinsic (mitochondria-driven) pathway. Extrinsic pathway includes Fas pathway to CD4+-CD8+ interaction, whereas intrinsic pathway includes mitochondria-driven pathway at a balance between anti-apoptotic B-cell lymphoma (Bcl)-2 and Bcl-xL and pro-apoptotic Bad, Bid, and Bik proteins. Activated cleaved caspse-3 is the converging point between extrinsic and intrinsic pathway. Apoptosis takes place only when pro-apoptotic proteins exceed anti-apoptotic proteins. Since the concordance rate of T1DM in identical twins is about 50%, environmental factors are involved in the development of T1DM, opening a door to find means to detect and prevent further development of autoimmune β-cell destruction for a therapeutic application.

An optimized protocol for purification of functional islets of Langerhans

Islets of Langerhans and β-cell isolation constitute routinely used cell models for diabetic research, and refining islet isolation protocols and cell quality assessment is a high priority. Numerous protocols have been published describing isolate of islets, but often rigorous and systematic assessment of their integrity is lacking. Herein, we propose a new protocol for optimal generation of islets. Pancreases from mice and rats were excised and digested using a low-activity collagenase solution and islets were then purified by a series of sedimentations and a Percoll gradient. Islets were maintained in culture for 5 days, during which viability, pro/antiapoptotic, and islet-specific genes, glucose-stimulated calcium entry, glucose uptake, and insulin secretion were assessed. The commonly used islet isolation technique by collagenase injection through the common bile duct (CBD) was also performed and compared with the present approach. This new protocol produced islets that retained a healthy status as demonstrated by the yield of stable living cells. Furthermore, calcium oscillation, glucose uptake, and insulin secretion remained intact in the islet cultures. This was reproducible when many rodent species were used, and neither sex nor age affected the cells behavior. When compared with the CBD technique, islet physiology was similar. Finally, this approach was used to uncover new ion channel candidates implicated in insulin secretion. In conclusion, this study outlines an efficient protocol for islet preparation that may support research into new therapeutic targets in diabetes research.

Apoptosis in pancreatic β-islet cells in Type 2 diabetes

Apoptosis plays important roles in the pathophysiology of Type 2 diabetes mellitus (T2DM). The etiology of T2DM is multifactorial, including obesity-associated insulin resistance, defective insulin secretion, and loss of β-cell mass through β-cell apoptosis. β-cell apoptosis is mediated through a milliard of caspase family cascade machinery in T2DM. The glucose-induced insulin secretion is the principle pathophysiology of diabetes and insufficient insulin secretion results in chronic hyperglycemia, diabetes. Recently, hyperglycemia-induced β-cell apoptosis has been extensively studied on the balance of pro-apoptotic Bcl-2 proteins (Bad, Bid, Bik, and Bax) and anti-apoptotic Bcl family (Bcl-2 and Bcl-xL) toward apoptosis in vitro isolated islets and insulinoma cell culture. Apoptosis can only occur when the concentration of pro-apoptotic Bcl-2 exceeds that of anti-apoptotic proteins at the mitochondrial membrane of the intrinsic pathway. A bulk of recent research on hyperglycemia-induced apoptosis on β-cells unveiled complex details on glucose toxicity on β-cells in molecular levels coupled with cell membrane potential by adenosine triphosphate generation through K+ channel closure, opening Ca2+ channel and plasma membrane depolarization. Furthermore, animal models using knockout mice will shed light on the basic understanding of the pathophysiology of diabetes as a glucose metabolic disease complex, on the balance of anti-apoptotic Bcl family and pro-apoptotic genes. The cumulative knowledge will provide a better understanding of glucose metabolism at a molecular level and will lead to eventual prevention and therapeutic application for T2DM with improving medications.

Antiaging Gene Klotho Attenuates Pancreatic β-Cell Apoptosis in Type 1 Diabetes

Apoptosis is the major cause of death of insulin-producing β-cells in type 1 diabetes mellitus (T1DM). Klotho is a recently discovered antiaging gene. We found that the Klotho gene is expressed in pancreatic β-cells. Interestingly, halplodeficiency of Klotho (KL(+/-)) exacerbated streptozotocin (STZ)-induced diabetes (a model of T1DM), including hyperglycemia, glucose intolerance, diminished islet insulin storage, and increased apoptotic β-cells. Conversely, in vivo β-cell-specific expression of mouse Klotho gene (mKL) attenuated β-cell apoptosis and prevented STZ-induced diabetes. mKL promoted cell adhesion to collagen IV, increased FAK and Akt phosphorylation, and inhibited caspase 3 cleavage in cultured MIN6 β-cells. mKL abolished STZ- and TNFα-induced inhibition of FAK and Akt phosphorylation, caspase 3 cleavage, and β-cell apoptosis. These promoting effects of Klotho can be abolished by blocking integrin β1. Therefore, these cell-based studies indicated that Klotho protected β-cells by inhibiting β-cell apoptosis through activation of the integrin β1-FAK/Akt pathway, leading to inhibition of caspase 3 cleavage. In an autoimmune T1DM model (NOD), we showed that in vivo β-cell-specific expression of mKL improved glucose tolerance, attenuated β-cell apoptosis, enhanced insulin storage in β-cells, and increased plasma insulin levels. The beneficial effect of Klotho gene delivery is likely due to attenuation of T-cell infiltration in pancreatic islets in NOD mice. Overall, our results demonstrate for the first time that Klotho protected β-cells in T1DM via attenuating apoptosis.

Can CD44 Be a Mediator of Cell Destruction? The Challenge of Type 1 Diabetes

CD44 is a multi-functional receptor with multiple of isoforms engaged in modulation of cell trafficking and transmission of apoptotic signals. We have previously shown that injection of anti-CD44 antibody into NOD mice induced resistance to type 1 diabetes (T1D). In this communication we describe our efforts to understand the mechanism underlying this effect. We found that CD44-deficient NOD mice develop stronger resistance to T1D than wild-type littermates. This effect is not explained by the involvement of CD44 in cell migration, because CD44-deficient inflammatory cells surprisingly had greater invasive potential than the corresponding wild type cells, probably owing to molecular redundancy. We have previously reported and we show here again that CD44 expression and hyaluronic acid (HA, the principal ligand for CD44) accumulation are detected in pancreatic islets of diabetic NOD mice, but not of non-diabetic DBA/1 mice. Expression of CD44 on insulin-secreting β cells renders them susceptible to the autoimmune attack, and is associated with a diminution in β-cells function (e.g., less insulin production and/or insulin secretion) and possibly also with an enhanced apoptosis rate. The diabetes-supportive effect of CD44 expression on β cells was assessed by the TUNEL assay and further strengthened by functional assays exhibiting increased nitric oxide release, reduced insulin secretion after glucose stimulation and decreased insulin content in β cells. All these parameters could not be detected in CD44-deficient islets. We further suggest that HA-binding to CD44-expressing β cells is implicated in β-cell demise. Altogether, these data agree with the concept that CD44 is a receptor capable of modulating cell fate. This finding is important for other pathologies (e.g., cancer, neurodegenerative diseases) in which CD44 and HA appear to be implicated.

Implications of ghrelin and hexarelin in diabetes and diabetes-associated heart diseases

Ghrelin and its synthetic analog hexarelin are specific ligands of growth hormone secretagogue (GHS) receptor. GHS have strong growth hormone-releasing effect and other neuroendocrine activities such as stimulatory effects on prolactin and adrenocorticotropic hormone secretion. Recently, several studies have reported other beneficial functions of GHS that are independent of GH. Ghrelin and hexarelin, for examples, have been shown to exert GH-independent cardiovascular activity. Hexarelin has been reported to regulate peroxisome proliferator-activated receptor gamma (PPAR-γ) in macrophages and adipocytes. PPAR-γ is an important regulator of adipogenesis, lipid metabolism, and insulin sensitization. Ghrelin also shows protective effects on beta cells against lipotoxicity through activation of phosphatidylinositol-3 kinase/protein kinase B, c-Jun N-terminal kinase (JNK) inhibition, and nuclear exclusion of forkhead box protein O1. Acylated ghrelin (AG) and unacylated ghrelin (UAG) administration reduces glucose levels and increases insulin-producing beta cell number, and insulin secretion in pancreatectomized rats and in newborn rats treated with streptozotocin, suggesting a possible role of GHS in pancreatic regeneration. Therefore, the discovery of GHS has opened many new perspectives in endocrine, metabolic, and cardiovascular research areas, suggesting the possible therapeutic application in diabetes and diabetic complications especially diabetic cardiomyopathy. Here, we review the physiological roles of ghrelin and hexarelin in the protection and regeneration of beta cells and their roles in the regulation of insulin release, glucose, and fat metabolism and present their potential therapeutic effects in the treatment of diabetes and diabetic-associated heart diseases.

Dietary supplementation with a low dose of (-)-epigallocatechin-3-gallate reduces pro-inflammatory responses in peripheral leukocytes of non-obese type 2 diabetic GK rats

(-)-Epigallocatechin-3-gallate (EGCG), which is largely found in green tea, is known to eliminate reactive oxygen species and associated inflammatory responses in vitro and in cells. However, the in vivo mechanisms underlying the effects of EGCG on the amelioration of metabolic disorders are not fully understood. In this study, we examined whether dietary supplementation with EGCG reduces inflammatory responses in peripheral leukocytes of a non-obese type 2 diabetes animal model, Goto-Kakizaki (GK) rats. GK rats at 9 wk of age were fed a control high-fat diet (46 energy % from lard and corn oil) or a high-fat diet containing 0.1%, 0.2%, or 0.5% EGCG (w/w) for 25 wk. The oxidative stress markers 8-hydroxydeoxyguanosine (OHdG) and total malondialdehyde (MDA) were reduced by supplementation with EGCG at 0.1%, but not at 0.2% or more. Significant reductions in the mRNA levels of genes related to inflammatory responses (TNF-α, IFN-γ, IL-1β, IL-6, IL-18, MCP-1, CD11b, and S100a6), 8-OHdG, and total MDA were induced in peripheral leukocytes of GK rats by EGCG supplementation at 0.1%, but not at 0.2% or more, compared with rats fed the control diet. The present results suggest that supplementation with a low dose of EGCG reduces oxidative stress and the expressions of genes involved in inflammation in peripheral leukocytes of GK rats.

Effect of nanostructured TiO₂ crystal phase on photoinduced apoptosis of breast cancer epithelial cells

Purpose

The use of nanoparticles has seen exponential growth in the area of health care, due to the unique physicochemical properties of nanomaterials that make them desirable for medical applications. The aim of this study was to examine the effects of crystal phase-nanostructured titanium dioxide particles on bioactivity/cytotoxicity in breast cancer epithelial cells.

Materials and methods

Cultured Michigan Cancer Foundation (MCF)-7 and human breast adenocarcinoma (MDA-MB-468) breast cancer epithelial cells were exposed to ultraviolet A light (wavelength 350 nm) for 20 minutes in the presence of aqueous dispersions of two different nanostructured titanium dioxide (TiO₂) crystal phases: anatase and an anatase–rutile mixture. Detailed characterization of each titanium dispersion was performed by dynamic light scattering. A 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) colorimetric assay was employed to estimate the percentage of viable cells after each treatment. Western blot analysis of protein expression and characterization, as well as a deoxyribonucleic acid (DNA)-laddering assay, were used to detect cell apoptosis.

Results

Our results documented that 100% anatase TiO₂ nanoparticles (110–130 nm) exhibited significantly higher cytotoxicity in the highly malignant MDA-MB-468 cancer cells than anatase– rutile mixtures (75%/25%) with the same size. On the contrary, MCF-7 cells (characterized by low invasive properties) were not considerably affected. Exposure of MDA-MB-468 cells to pure anatase nanoparticles or anatase–rutile mixtures for 48 hours resulted in increased proapoptotic Bax expression, caspase-mediated poly(adenosine diphosphate ribose) polymerase (PARP) cleavage, DNA fragmentation, and programmed cell death/apoptosis.

Conclusion

The obtained results indicated that pure anatase TiO₂ nanoparticles exhibit superior cytotoxic effects compared to anatase–rutile mixtures of the same size. The molecular mechanism of TiO₂ nanoparticle cytotoxicity involved increased Bax expression and caspase-mediated PARP inactivation, thus resulting in DNA fragmentation and cell apoptosis.

The protective effects and genetic pathways of thorn grape seeds oil against high glucose-induced apoptosis in pancreatic β-cells

Background

Excessive apoptosis of β-cell is closely related to diabetes mellitus. Chronic exposure to high glucose causes β-cell dysfunction and apoptosis in diabetes. Thorn grape (Vitis davidii Foex.) has been used to treat diabetes in Traditional Chinese medicine for many years. In our previous research, thorn grape seeds oil (TGSO) showed promising anti-diabetic effects in animal models. However, it is unknown whether TGSO played an anti-apoptotic role in the anti-diabetic effects and the mechanism regarding signal transduction pathway is unclear either.

Methods

The rattus pancreatic β-cell line RIN-m5F was treated with/without TGSO which was extracted by supercritical carbon dioxide (CO₂) fluid extraction and analyzed by Gas Chromatography/Mass Spectrometry (GC/MS). Cell apoptosis was detected by fluorescence activated cell sorting (FACS), insulin secretion was assayed by Enzyme-Linked Immunosorbent Assay (ELISA), and the apoptosis-related genes expressions were evaluated by quantitative Reverse Transcription Polymerase Chain Reaction (qRT-PCR).

Results

TGSO, containing 87.02% unsaturated fatty acids (UFAs), significantly reduced pancreatic β-cell apoptosis and protected the insulin secretion impaired by high glucose. The expressions of pro-apoptotic genes such as iNOS, Caspase-3, ATF-3, JNK, p38 and Fas were down-regulated while the anti-apoptotic genes Akt and Bcl-2/Bax were up-regulated.

Conclusions

The results indicated that TGSO protected β-cells from high glucose-induced apoptosis and its protective activity may be linked to mitochondrial pathway, endoplasmic reticulum (ER) stress pathway and Fas signal pathway, which implied that TGSO might be an effective complementary or alternative medicine to reduce β-cell apoptosis and dysfunction.

Genetics of new-onset diabetes after transplantation

New-onset diabetes after transplantation is a common complication that reduces recipient survival. Research in renal transplant recipients has suggested that pancreatic β-cell dysfunction, as opposed to insulin resistance, may be the key pathologic process. In this study, clinical and genetic factors associated with new-onset diabetes after transplantation were identified in a white population. A joint analysis approach, with an initial genome-wide association study in a subset of cases followed by de novo genotyping in the complete case cohort, was implemented to identify single-nucleotide polymorphisms (SNPs) associated with the development of new-onset diabetes after transplantation. Clinical variables associated with the development of diabetes after renal transplantation included older recipient age, female sex, and percentage weight gain within 12 months of transplantation. The genome-wide association study identified 26 SNPs associated with new-onset diabetes after transplantation; this association was validated for eight SNPs (rs10484821, rs7533125, rs2861484, rs11580170, rs2020902, rs1836882, rs198372, and rs4394754) by de novo genotyping. These associations remained significant after multivariate adjustment for clinical variables. Seven of these SNPs are associated with genes implicated in β-cell apoptosis. These results corroborate recent clinical evidence implicating β-cell dysfunction in the pathophysiology of new-onset diabetes after transplantation and support the pursuit of therapeutic strategies to protect β cells in the post-transplant period.

Inhibition of postprandial hyperglycemia by either an insulin-dependent or -independent drug reduces the expression of genes related to inflammation in peripheral leukocytes of OLETF rats

Treatment with the dipeptidyl peptidase-4 inhibitor, anagliptin, or with the α-glucosidase inhibitor, miglitol, reduced the oral sucrose load-inducible expression of interleukin (IL)-1β, IL-18, tumor necrosis factor-α, S100a8, S100a9, S100a11, IL-1R2, IL-1Rn and tumor necrosis factor receptor 2 genes in peripheral leukocytes of Otsuka Long-Evans Tokushima fatty (OLETF) rats at the stage of impaired glucose tolerance. Inhibiting postprandial hyperglycemia reduced the expression of genes related to inflammation in peripheral leukocytes of OLETF rats.

Possible involvement of A₂A and A₃ receptors in modulation of insulin secretion and β-cell survival in mouse pancreatic islets

Adenosine A1, A₂A, A₂B and A₃ receptor mRNAs were found to be expressed in mouse pancreatic islets and Beta-TC6 cells but their physiological or pharmacological actions are not fully clarified. We showed that adenosine (100 μM) augmented insulin secretion by islets in the presence of either normal (5.5 mM) or a high concentration of glucose (20 mM). The augmentation of insulin secretion in the presence of high glucose was blocked by an A₂A antagonist, but not by A₂B and A₃ antagonists, while an A₁ antagonist potentiated the adenosine effect. An adenosine analogue 5'-N-ethylcarboxamidoadenosine (NECA) as well as A₁, A₂A and A₃ receptor agonists also produced stimulation. On the other hand, an A₃ agonist markedly reduced Beta-TC6 cell proliferation and the islet cell viability, while adenosine and NECA did not. The effect of A₃ agonist was partially blocked by the A₃ antagonist. In addition, treatment with the A₃ agonist produced a small but significant extent of apoptosis in Beta-TC6 cells as judged by terminal transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) assay. These results combined together suggested that like the A₁ receptor, activation of A₂A receptors by adenosine results in augmented insulin secretion, while the A₃ receptor is involved in modulation of the survival of pancreatic β-cells.

Thiazolidinediones protect mouse pancreatic β-cells directly from cytokine-induced cytotoxicity through PPARγ-dependent mechanisms

Since most of the current studies of thiazolidinediones (TZDs) are only focused on improving glycemic control, increasing insulin sensitivity, and regulating inflammatory states in Type 2 Diabetes, it is still controversial whether TZDs have direct, protective effects on pancreatic β-cells in autoimmune diabetes. Here, we show the protective effects of TZDs on mouse pancreatic β-cell line cells (NIT-1) impaired by exposure to inflammatory cytokines (IL-1β and IFN-γ) and explore the potential mechanisms for this. The apoptosis rate and caspase-3 activity were remarkably increased, and insulin secretion response to glucose was impaired severely by exposure to IL-1β/IFN-γ for 48 h compared to control cells, whereas apoptosis rate and caspase-3 activity were significantly decreased in cells with treatment of rosiglitazone (RGZ) or pioglitazone (PIG), and the capacity for insulin secretion response to glucose was recovered. TZDs protect pancreatic β-cells from cytokine-induced cytotoxicity through PPARγ activation. The protective effects of the TZDs on NIT-1 cells disappeared when PPARγ was blocked with PPARγ-siRNA interference or treatment with GW9662, the PPARγ antagonist. Additionally, the enhancement of PPARγ expression by treatment with TZDs inhibited the expression of caspase 3 in IL-1β/IFN-γ-induced NIT-cells. Also, the inhibition of caspase 3 expression by TZDs was blocked by co-treatment with GW9662 or infection with PPARγ-siRNA. Taken together, our data suggest that TZDs might serve to protect pancreatic β-cells directly from cytokine-induced cytotoxicity through a PPARγ-dependent pathway, and caspase-3 may play an important role in the mechanisms involved.

Comparison of the killing effects between nitrogen-doped and pure TiO2 on HeLa cells with visible light irradiation

The killing effect of nitrogen-doped titanium dioxide (N-TiO2) nanoparticles on human cervical carcinoma (HeLa) cells by visible light photodynamic therapy (PDT) was higher than that of TiO2 nanoparticles. To study the mechanism of the killing effect, the reactive oxygen species produced by the visible-light-activated N-TiO2 and pure-TiO2 were evaluated and compared. The changes of the cellular parameters, such as the mitochondrial membrane potential (MMP), intracellular Ca2+, and nitrogen monoxide (NO) concentrations after PDT were measured and compared for N-TiO2- and TiO2-treated HeLa cells. The N-TiO2 resulted in more loss of MMP and higher increase of Ca2+ and NO in HeLa cells than pure TiO2. The cell morphology changes with time were also examined by a confocal microscope. The cells incubated with N-TiO2 exhibited serious distortion and membrane breakage at 60 min after the PDT.

Alpha-1-antitrypsin for the improvement of autoimmunity and allograft rejection in beta cell transplantation

Islet transplantation offers hope for patients with type 1 diabetes, which is an autoimmune disease. However, islet transplant recipients must overcome two obstacles in both allograft rejection and autoimmune reaction. Alpha-1-antitrypsin (a1-proteinase inhibitor, AAT) possesses anti-inflammatory properties, reduces cytokine-mediated islet damage, and induces specific immune tolerance. In this study, an insulinoma cell line, NIT-1, was transfected with human AAT (hAAT), named NIT-hAAT, and was transplanted to the left renal subcapsular spaces of 7-week-old female non-obese diabetic (NOD) mice (n=22). Cyclophosphamide(CY) was administered to synchronize and accelerate the development of diabetes. Thus, the immunosuppressive and cytoprotective activity of hAAT in β-cell transplantation was investigated. NIT-hAAT has immunomodulatory properties, which delay the onset of autoimmune diabetes, reduce diabetes incidence, inhibit insulitis and β-cell apoptosis, and dampen transplant site inflammation. We propose that NIT-hAAT has a dual function by improving islet autoimmunity and protecting transplanted β-cells from allograft rejection. However, the low expression of hAAT in vivo results in the inability of NIT-hAAT to induce long-term specific immune tolerance and to completely block allograft rejection.

BCDO2 acts as a carotenoid scavenger and gatekeeper for the mitochondrial apoptotic pathway

Carotenoids and their metabolites are widespread and exert key biological functions in living organisms. In vertebrates, the carotenoid oxygenase BCMO1 converts carotenoids such as β,β-carotene to retinoids, which are required for embryonic pattern formation and cell differentiation. Vertebrate genomes encode a structurally related protein named BCDO2 but its physiological function remains undefined. Here, we show that BCDO2 is expressed as an oxidative stress-regulated protein during zebrafish development. Targeted knockdown of this mitochondrial enzyme resulted in anemia at larval stages. Marker gene analysis and staining for hemoglobin revealed that erythropoiesis was not impaired but that erythrocytes underwent apoptosis in BCDO2-deficient larvae. To define the mechanism of this defect, we have analyzed the role of BCDO2 in human cell lines. We found that carotenoids caused oxidative stress in mitochondria that eventually led to cytochrome c release, proteolytic activation of caspase 3 and PARP1, and execution of the apoptotic pathway. Moreover, BCDO2 prevented this induction of the apoptotic pathway by carotenoids. Thus, our study identifying BCDO2 as a crucial protective component against oxidative stress establishes this enzyme as mitochondrial carotenoid scavenger and a gatekeeper of the intrinsic apoptotic pathway.

Effects of melatonin on islet neogenesis and beta cell apoptosis in streptozotocin-induced diabetic rats: an immunohistochemical study

This investigation was carried out to explore the antidiabetic, antiapoptotic and neogenetic effects of melatonin (MLT) in streptozotocin-induced diabetic rats. Sixty-four male rats were assigned randomly to one of four groups for periods of 21 and 42 d as follows; i) control, ii) MLT, iii) diabetic (DM), and iv) DM + MLT. Immunohistochemical methods were used -with pancreatic tissue to determine the intensity of insulin, caspase-3 and Bcl-x(L) immune reactivities, and new islet formation. In untreated DM rats, BW loss, increased plasma glucose and MLT concentrations, as well as cytoplasmic degranulation and vacuolization were observed. We also observed a marked increase in the number of apoptotic caspase-3 positive cells and a few insulin- positive cells, but not antiapoptotic Bcl-x(L) positive cells. Observations in the DM + MLT-treated group revealed a high intensity of insulin- and antiapoptotic Bcl-x(L) immune reactivities at 21 and 42 d. Moreover, data indicated that MLT may cause beta cell proliferation and that new small islets originate from cells associated with ductal epithelium and from centroacinar cells by day 21. These data indicate that; i) MLT treatment may stimulate neogenesis in the pancreas of diabetic rats, and ii) MLT's antiapoptotic action may increase beta cell differentiation and caspase-3 inactivation or Bcl-x(L) activation.

Nodal induces apoptosis through activation of the ALK7 signaling pathway in pancreatic INS-1 β-cells

We demonstrated previously that the activation of ALK7 (activin receptor-like kinase-7), a member of the type I receptor serine/threonine kinases of the TGF-β superfamily, resulted in increased apoptosis and reduced proliferation through suppression of Akt signaling and the activation of Smad2-dependent signaling pathway in pancreatic β-cells. Here, we show that Nodal activates ALK7 signaling and regulates β-cell apoptosis. We detected Nodal expression in the clonal β-cell lines and rodent islet β-cells. Induction of β-cell apoptosis by treatment with high glucose, palmitate, or cytokines significantly increased Nodal expression in clonal INS-1 β-cells and isolated rat islets. The stimuli induced upregulation of Nodal expression levels were associated with elevation of ALK7 protein and enhanced phosphorylated Smad3 protein. Nodal treatment or overexpression of Nodal dose- or time-dependently increased active caspase-3 levels in INS-1 cells. Nodal-induced apoptosis was associated with decreased Akt phosphorylation and reduced expression level of X-linked inhibitor of apoptosis (XIAP). Remarkably, overexpression of XIAP or constitutively active Akt, or ablation of Smad2/3 activity partially blocked Nodal-induced apoptosis. Furthermore, siRNA-mediated ALK7 knockdown significantly attenuated Nodal-induced apoptosis of INS-1 cells. We suggest that Nodal-induced apoptosis in β-cells is mediated through ALK7 signaling involving the activation of Smad2/3-caspase-3 and the suppression of Akt and XIAP pathways and that Nodal may exert its biological effects on the modulation of β-cell survival and β-cell mass in an autocrine fashion.

Treatment with the α-glucosidase inhibitor miglitol from the preonset stage in Otsuka Long-Evans Tokushima Fatty rats improves glycemic control and reduces the expression of inflammatory cytokine genes in peripheral leukocytes

Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an animal model of type 2 diabetes mellitus, exhibit chronic and slowly progressive hyperglycemia with obesity. In this study, we examined whether dietary supplementation with the α-glucosidase inhibitor miglitol from the preonset stage improves glycemic control and reduces the gene expression of inflammatory cytokines in peripheral leukocytes. The OLETF rats were fed a control diet or a diet containing 800 ppm miglitol (miglitol diet) for 40 weeks from 5 weeks of age (preonset stage). We determined nonfasting blood glucose, blood 1,5-anhydroglucitol, and messenger RNA levels of inflammatory cytokines in peripheral leukocytes in these rats. Nonfasting blood glucose concentrations gradually increased in OLETF rats fed the control diet, with significant increases at weeks 28 and 40 compared with week 0. In contrast, nonfasting blood glucose levels did not increase in miglitol-treated rats during the experimental period. Miglitol-treated rats had lower nonfasting blood glucose levels and higher 1,5-anhydroglucitol levels, a marker for glucose fluctuations, at week 40 than control rats. The gene expression of inflammatory cytokines including interleukin-6, tumor necrosis factor-α, and interferon-γ in peripheral leukocytes gradually increased during the development of diabetes in control rats, but not in miglitol-treated rats. Our results suggest that dietary supplementation with miglitol from the preonset stage in OLETF rats improves glycemic control and reduces gene expression of cytokines related to inflammation in peripheral leukocytes.

Mechanism of action of natural products used in the treatment of diabetes mellitus

Diabetes mellitus (DM) is a metabolic disorder caused by insufficient or inefficient insulin secretary response and it is characterized by increased blood glucose levels (hyperglycemia). DM is a heterogonous group of syndromes. Glucose is the main energy source for the body, and in the case of DM, management of glucose becomes irregular. There are three key defects in the onset of hyperglycemia in DM, namely increased hepatic glucose production, diminished insulin secretion, and impaired insulin action. Conventional drugs treat diabetes by improving insulin sensitivity, increasing insulin production and/or decreasing the amount of glucose in blood. This article provides a comprehensive review of the mode of action of most popular hypoglycemic herbs, such as ginseng, bitter melon, fenugreek, banaba, Gymnema sylvestre and Coptis chinensis. The herbs act by increasing insulin secretion, enhancing glucose uptake by adipose and skeletal muscle tissues, inhibiting intestinal glucose absorption and inhibiting hepatic glucose production. Although evidence from animals and humans consistently supports the therapeutic effect of these phytomedicines, multicenter large-scale clinical trials have not been conducted to evaluate the safety and efficacy of these herbal medicines and their interaction with conventional drugs when administered simultaneously.

Induction of the intrinsic apoptosis pathway in insulin-secreting cells is dependent on oxidative damage of mitochondria but independent of caspase-12 activation

Pro-inflammatory cytokine-mediated beta cell apoptosis is activated through multiple signaling pathways involving mitochondria and endoplasmic reticulum. Activation of organelle-specific caspases has been implicated in the progression and execution of cell death. This study was therefore performed to elucidate the effects of pro-inflammatory cytokines on a possible cross-talk between the compartment-specific caspases 9 and 12 and their differential contribution to beta cell apoptosis. Moreover, the occurrence of ROS-mediated mitochondrial damage in response to beta cell toxic cytokines has been quantified. ER-specific caspase-12 was strongly activated in response to pro-inflammatory cytokines; however, its inhibition did not abolish cytokine-induced mitochondrial caspase-9 activation and loss of cell viability. In addition, there was a significant induction of oxidative mitochondrial DNA damage and elevated cardiolipin peroxidation in insulin-producing RINm5F cells and rat islet cells. Overexpression of the H(2)O(2) detoxifying enzyme catalase effectively reduced the observed cytokine-induced oxidative damage of mitochondrial structures. Taken together, the results strongly indicate that mitochondrial caspase-9 is not a downstream substrate of ER-specific caspase-12 and that pro-inflammatory cytokines cause apoptotic beta cell death through activation of caspase-9 primarily by hydroxyl radical-mediated mitochondrial damage.

AMP-activated protein kinase regulates glucagon secretion from mouse pancreatic alpha cells

AIM/HYPOTHESIS

AMP-activated protein kinase (AMPK), encoded by Prkaa genes, is emerging as a key regulator of overall energy homeostasis and the control of insulin secretion and action. We sought here to investigate the role of AMPK in controlling glucagon secretion from pancreatic islet alpha cells.

METHODS

AMPK activity was modulated in vitro in clonal alphaTC1-9 cells and isolated mouse pancreatic islets using pharmacological agents and adenoviruses encoding constitutively active or dominant negative forms of AMPK. Glucagon secretion was measured during static incubation by radioimmunoassay. AMPK activity was assessed by both direct phosphotransfer assay and by western (immuno-)blotting of the phosphorylated AMPK α subunits and the downstream target acetyl-CoA carboxylase 1. Intracellular free [Ca²(+)] was measured using Fura-Red.

RESULTS

Increasing glucose concentrations strongly inhibited AMPK activity in clonal pancreatic alpha cells. Forced increases in AMPK activity in alphaTC1-9 cells, achieved through the use of pharmacological agents including metformin, phenformin and A-769662, or via adenoviral transduction, resulted in stimulation of glucagon secretion at both low and high glucose concentrations, whereas AMPK inactivation inhibited both [Ca²(+)](i) increases and glucagon secretion at low glucose. Transduction of isolated mouse islets with an adenovirus encoding AMPK-CA under the control of the preproglucagon promoter increased glucagon secretion selectively at elevated glucose concentrations.

CONCLUSIONS/INTERPRETATION

AMPK is strongly regulated by glucose in pancreatic alpha cells, and increases in AMPK activity are sufficient and necessary for the stimulation of glucagon release in vitro. Modulation of AMPK activity in alpha cells may therefore provide a novel approach to controlling blood glucose concentrations.

Effects of caloric restriction on SIRT1 expression and apoptosis of islet beta cells in type 2 diabetic rats

Increasing evidence suggests that a restricted caloric intake extends the life span of mammals, and SIRT1 may play a key role in this process. To study the effects of caloric restriction on SIRT1 expression and apoptosis of islet beta cells in type 2 diabetic rats, we first induced a model of type 2 diabetes in rats with a low-dose of streptozotocin. Then, the rats were fed with a normal diet, high-fat diet or 60% caloric restriction, respectively. As a result, the apoptosis ratio of islet beta cells in diabetic rats was dramatically increased compared to the control group, and mRNA and protein expression of SIRT1 in islet beta cells were much lower than those of the control group. After caloric restriction for 1 month, the blood glucose and serum insulin of rats decreased. The mRNA and protein expression of SIRT1 in islet beta cells significantly increased; however, the apoptosis ratio of islet beta cells decreased remarkably. These data show that caloric restriction notably improves the sensitivity to insulin and significantly increases mRNA and protein expression of SIRT1 while decreasing the apoptosis ratio of islet beta cells in diabetic rats. Therefore, SIRT1 may play an important role in the apoptosis of islet beta cells of type 2 diabetes.

Glucose intolerance and reduced proliferation of pancreatic beta-cells in transgenic pigs with impaired glucose-dependent insulinotropic polypeptide function

OBJECTIVE

The insulinotropic action of the incretin glucose-dependent insulinotropic polypeptide (GIP) is impaired in type 2 diabetes, while the effect of glucagon-like peptide-1 (GLP-1) is preserved. To evaluate the role of impaired GIP function in glucose homeostasis and development of the endocrine pancreas in a large animal model, we generated transgenic pigs expressing a dominant-negative GIP receptor (GIPR(dn)) in pancreatic islets.

RESEARCH DESIGN AND METHODS

GIPR(dn) transgenic pigs were generated using lentiviral transgenesis. Metabolic tests and quantitative stereological analyses of the different endocrine islet cell populations were performed, and beta-cell proliferation and apoptosis were quantified to characterize this novel animal model.

RESULTS

Eleven-week-old GIPR(dn) transgenic pigs exhibited significantly reduced oral glucose tolerance due to delayed insulin secretion, whereas intravenous glucose tolerance and pancreatic beta-cell mass were not different from controls. The insulinotropic effect of GIP was significantly reduced, whereas insulin secretion in response to the GLP-1 receptor agonist exendin-4 was enhanced in GIPR(dn) transgenic versus control pigs. With increasing age, glucose control deteriorated in GIPR(dn) transgenic pigs, as shown by reduced oral and intravenous glucose tolerance due to impaired insulin secretion. Importantly, beta-cell proliferation was reduced by 60% in 11-week-old GIPR(dn) transgenic pigs, leading to a reduction of beta-cell mass by 35% and 58% in 5-month-old and 1- to 1.4-year-old transgenic pigs compared with age-matched controls, respectively.

CONCLUSIONS

The first large animal model with impaired incretin function demonstrates an essential role of GIP for insulin secretion, proliferation of beta-cells, and physiological expansion of beta-cell mass.

Apoptotic, regenerative, and immune-related signaling in human islets from type 2 diabetes individuals

Islet dysfunction is a primary cause of developing type 2 diabetes mellitus (T2DM). Events leading to islet failure are still poorly defined due to the complexity of the disease and scarcity of human T2DM islets. The aim of the present study was to identify cellular mechanisms involved in the T2DM pathophysiology by protein profiling islets obtained from T2DM individuals and age- and weight-matched controls using liquid chromatography Fourier transform ion cyclotron resonance mass spectrometry and surface enhanced laser desorption/ionization time-of-flight mass spectrometry. In T2DM islets, multiple differentially expressed proteins correlated with insulin secretion. When these T2DM islet proteins were analyzed for differential pathway activation, three of the five most activated pathways were pathways of cell arrest and apoptosis (p53, caspase, stress-activated), one represented immune-response (Fas), and the most activated pathway was connected with proliferation and regeneration (E2F). Among the inactivated pathways, three out of five were pathways of proliferation and regeneration (insulin, PRL, PDGF). The present study is the first to report differential activation of specific pathways during T2DM islet deterioration. The information about alterations in pathway signaling patterns may open new ways to develop strategies aimed at restoring islet cell function and survival.