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

Chronic consumption of imbalance diets high in sucrose or fat induces abdominal obesity with different pattern of metabolic disturbances and lost in Langerhans cells population

AIM

Obesity is a worldwide health issue, associated with development of type 2 Diabetes Mellitus. The aim of this study is to analyze the effect of consumption of two hypercaloric diets on metabolic disturbance and beta cells damage.

MAIN METHODS

Male Wistar rats were subjected to twelve months consumption of three diets: a Control balanced diet (CTD, carbohydrates 58 %, proteins 29 %, lipids 13 %) and two hypercaloric diets, high in sucrose (HSD, carbohydrates 68 %, proteins 22 %, lipids 10 %) or high in fat (HFD, carbohydrates 31 %, proteins 14 %, lipids 55 %). Serum levels of glucose, triglycerides and free fatty acids were measured after zoometric parameters determination. Antioxidant enzymes activity and oxidative stress-marker were measured in pancreas tissue among histological analysis of Langerhans islets.

KEY FINDINGS

Although diets were hypercaloric, the amount of food consumed by rats decreased, resulting in an equal caloric consumption. The HSD induced hypertriglyceridemia and hyperglycemia with higher levels in free fatty acids (FFA, lipotoxicity); whereas HFD did not increased neither the triglycerides nor FFA, nevertheless the loss of islets' cell was larger. Both diets induced obesity with hyperglycemia and significant reduction in Langerhans islets size.

SIGNIFICANCE

Our results demonstrate that consumption of HSD induces more significant metabolic disturbances that HFD, although both generated pancreas damage; as well hypercaloric diet consumption is not indispensable to becoming obese; the chronic consumption of unbalanced diets (rich in carbohydrates or lipids) may lead to abdominal obesity with metabolic and functional disturbances, although the total amount of calories are similar.

Identification of Potential Plant-Derived Pancreatic Beta-Cell-Directed Agents Using New Custom-Designed Screening Method: Gymnema sylvestre as an Example

BACKGROUND

Folk medicines are attractive therapeutic agents for treating type 2 diabetes mellitus (T2DM). Most plant extracts that have been suggested to restore β-cells function were tested in vivo. Some only have been tested in vitro to determine whether they have a direct effect on β-cells islets of Langerhans. Currently, there are no defined criteria for screening of β-cell-directed plant-based remedies as potential antidiabetic agents.

SUMMARY

In this review, we have identified certain criteria/characteristics that can be used to generate a "screening portfolio" to identify plant extracts as potential β-cell-directed agents for the treatment of T2DM. To validate our screening method, we studied the potential therapeutic efficacy of a Gymnema sylvestre (GS) extract using the screening criteria detailed in the review. Six criteria have been identified and validated using OSA®, a GS extract. By using this screening method, we show that OSA® fulfilled most of the criteria identified for an effective β-cell-directed antidiabetic therapy, being an effective insulin-releasing agent at nontoxic concentrations; maintaining β-cell insulin content by stimulating a concomitant increase in insulin gene transcription; maintaining β-cell mass by protecting against apoptosis; and being effective at maintaining normoglycemia in vivo in a mouse model and a human cohort with T2DM.

KEY MESSAGES

The present review has highlighted the importance of having a screening portfolio for plant extracts that have potential antidiabetic effects in the treatment of T2DM. We propose that this screening method should be adopted for future studies to identify new β-cell-directed antidiabetic plant derived agents.

HM-Chromanone Alleviates Hyperglycemia by Protecting Pancreatic Islet Cells in Streptozotocin-Induced Diabetic Mice

We examined the effects of HM-chromanone (HMC) on alleviating hyperglycemia and protecting pancreatic β-cells from streptozotocin (STZ)-induced damage in C57BL/6J mice. HMC was administered to STZ-induced diabetic mice at 10 or 30 mg/kg, for 14 days. Thereafter, changes in fasting blood glucose levels, insulin-secretion, histopathological examination of pancreas islet cell and apoptotic protein levels, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay were determined. The results revealed that HMC dose-dependently improved blood glucose concentrations and alleviated pancreatic islet cells damage. In diabetic mice, degeneration of the islet cells was observed wherein they appeared shrunken, with hyaline deterioration, nuclear dissolution, and condensation. However, morphology of the islet cell was restored, and nuclei were visibly rounded in the HMC (30 mg/kg)-administered diabetic mice. In addition, β-cell numbers were markedly increased in HMC mice compared to STZ-induced diabetic mice, and the number of cells stained with glucagon was decreased. HMC markedly decreased the expression of proapoptotic proteins and increased antiapoptotic proteins, and the number of apoptotic cells detected by TUNEL was elevated. HMC decreased expression of interleukin (IL)-1β, IL-6, and tumor necrosis factor-α in diabetic mice. Moreover, HMC increased antioxidant-enzymes activity, and decreased reactive oxygen species generation. In conclusion, the results demonstrate the potential of HMC to alleviate hyperglycemia by protecting the pancreatic β-cells in diabetic mice.

Rhein for treating diabetes mellitus: A pharmacological and mechanistic overview

With the extension of life expectancy and changes in lifestyle, the prevalence of diabetes mellitus is increasing worldwide. Rheum palmatum L. a natural botanical medicine, has been used for thousands of years to prevent and treat diabetes mellitus in Eastern countries. Rhein, the main active component of rhubarb, is a 1, 8-dihydroxy anthraquinone derivative. Previous studies have extensively explored the clinical application of rhein. However, a comprehensive review of the antidiabetic effects of rhein has not been conducted. This review summarizes studies published over the past decade on the antidiabetic effects of rhein, covering the biological characteristics of Rheum palmatum L. and the pharmacological effects and pharmacokinetic characteristics of rhein. The review demonstrates that rhein can prevent and treat diabetes mellitus by ameliorating insulin resistance, possess anti-inflammatory and anti-oxidative stress properties, and protect islet cells, thus providing a theoretical basis for the application of rhein as an antidiabetic agent.

Advanced Glycation End Products (AGEs) Inhibit Macrophage Efferocytosis of Apoptotic β Cells through Binding to the Receptor for AGEs

Pancreatic β cell apoptosis is important in the pathogenesis of type 2 diabetes mellitus (T2DM). Generally, apoptotic β cells are phagocytosed by macrophages in a process known as "efferocytosis." Efferocytosis is critical to the resolution of inflammation and is impaired in T2DM. Advanced glycation end products (AGEs), which are increased in T2DM, are known to suppress phagocytosis function in macrophages. In this study, we found that AGEs inhibited efferocytosis of apoptotic β cells by primary peritoneal macrophages in C57BL/6J mice or mouse macrophage cell line Raw264.7. Mechanistically, AGEs inhibit efferocytosis by blocking Ras-related C3 botulinum toxin substrate 1 activity and cytoskeletal rearrangement through receptor for advanced glycation end products/ras homolog family member A/Rho kinase signaling in macrophages. Furthermore, it was observed that AGEs decreased the secretion of anti-inflammatory factors and promoted the proinflammatory ones to modulate the inflammation function of efferocytosis. Taken together, our results indicate that AGEs inhibit efferocytosis through binding to receptor for advanced glycation end products and activating ras homolog family member A/Rho kinase signaling, thereby inhibiting the anti-inflammatory function of efferocytosis.

Beta-cell autophagy under the scope of hypoglycemic drugs; possible mechanism as a novel therapeutic target

Physiologically, autophagy is a major protective mechanism of β-cells from apoptosis, through can reserve normal β- cell mass and inhibit the progression of β-cells destruction. Beta-cell mass can be affected by differentiation from progenitors and de-differentiation as well as self-renewal and apoptosis. Shred evidence indicated that hypoglycemic drugs can induce β-cell proliferation capacity and neogenesis via autophagy stimulation. However, prolonged use of selective hypoglycemic drugs has induced pancreatitis besides several other factors that contribute to β-cell destruction and apoptosis initiation. Interestingly, some nonhypoglycemic medications possess the same effects on β-cells but depending on the combination of these drugs and the duration of exposure to β-cells. The paper comprehensively illustrates the role of the hypoglycemic drugs on the insulin-producing cells and the pathogeneses of β-cell destruction in type 2 diabetes mellitus, in addition to the regulation mechanisms of β-cells division in norm and pathology. The grasping of the hypoglycemic drug’s role in beta-cell is clinically crucial to evaluate novel therapeutic targets such as new signaling pathways. The present paper addresses a new strategy for diabetes mellitus management via targeting specific autophagy inducer factors (transcription factors, genes, lipid molecules, etc.).

Effect of free fatty acids on insulin secretion, insulin sensitivity and incretin effect - a narrative review

Deleterious effects of free fatty acids, FFAs, on insulin sensitivity are observed in vivo studies in humans. Mechanisms include impaired insulin signaling, oxidative stress, inflammation, and mitochondrial dysfunction, but the effects on insulin secretion are less well known. Our aim was to review the relationship of increased FFAs with insulin resistance, secretion and mainly with the incretin effect in humans. Narrative review. Increased endogenous or administered FFAs induce insulin resistance. FFAs effects on insulin secretion are debatable; inhibition and stimulation have been reported, depending on the type and duration of lipids exposition and the study subjects. Chronically elevated FFAs seem to decrease insulin biosynthesis, glucose-stimulated insulin secretion and β-cell glucose sensitivity. Lipids infusion decreases the response to incretins with unchanged incretin levels in volunteers with normal glucose tolerance. In contrast, FFAs reduction by acipimox did not restore the incretin effect in type-2 diabetes, probably due to the dysfunctional β-cell. Possible mechanisms of FFAs excess on incretin effect include reduction of the expression and levels of GLP-1 (glucagon like peptide-1) receptor, reduction of connexin-36 expression thus the coordinated secretory activity in response to GLP-1, and GIP (glucose-dependent insulinotropic polypeptide) receptors downregulation in islets cells. Increased circulating FFAs impair insulin sensitivity. Effects on insulin secretion are complex and controversial. Deleterious effects on the incretin-induced potentiation of insulin secretion were reported. More investigation is needed to better understand the extent and mechanisms of β-cell impairment and insulin resistance induced by increased FFAs and how to prevent them.

Beta-Cell Dysfunction Induced by Tacrolimus: A Way to Explain Type 2 Diabetes?

The combination of insulin resistance and β-cells dysfunction leads to the onset of type-2 diabetes mellitus (T2DM). This process can last for decades, as β-cells are able to compensate the demand for insulin and maintain normoglycemia. Understanding the adaptive capacity of β-cells during this process and the causes of its failure is essential to the limit onset of diabetes. Post-transplant diabetes mellitus (PTDM) is a common and serious disease that affects 30% of renal transplant recipients. With the exception of immunosuppressive therapy, the risk factors for T2D are the same as for PTDM: obesity, dyslipidaemia, insulin resistance and metabolic syndrome. Tacrolimus (TAC) is the immunosuppressant of choice after renal transplantation but it has the highest rates of PTDM. Our group has shown that insulin resistance and glucolipotoxicity, without favouring the appearance of apoptosis, modify key nuclear factors for the maintenance of identity and functionality of β-cells. In this context, TAC accelerates or enhances these changes. Our hypothesis is that the pathways that are affected in the progression from pre-diabetes to diabetes in the general population are the same pathways that are affected by TAC. So, TAC can be considered a tool to study the pathogenesis of T2DM. Here, we review the common pathways of β-cells dysfunction on T2DM and TAC-induced diabetes.

Obesity and Insulin Resistance: A Review of Molecular Interactions

The prevalence of insulin resistance and diabetes mellitus is rising globally in epidemic proportions. Diabetes and its complications contribute to significant morbidity and mortality. An increase in sedentary lifestyle and consumption of a more energydense diet increased the incidence of obesity which is a significant risk factor for type 2 diabetes. Obesity acts as a potent upstream event that promotes molecular mechanisms involved in insulin resistance and diabetes mellitus. However, the exact molecular mechanisms between obesity and diabetes are not clearly understood. In the current study, we have reviewed the molecular interactions between obesity and type 2 diabetes.

IRS-2/Akt/GSK-3β/Nrf2 Pathway Contributes to the Protective Effects of Chikusetsu Saponin IVa against Lipotoxicity

Chronic hyperlipidemia leads to pancreatic β-cell apoptosis and dysfunction through inducing oxidative stress. Chikusetsu saponin IVa (CHS) showed antioxidant and antidiabetic properties in our previous studies; however, its protective effects against lipotoxicity-induced β-cell oxidative stress and dysfunction are not clear. This study was designed to investigate the effects of CHS against lipotoxicity-induced β-cell injuries and its possible mechanism involved. High-fat (HF) diet and a low dose of streptozotocin- (STZ-) induced type 2 diabetes mellitus (T2DM) model in vivo and βTC3 cells subjected to 0.5 mM palmitate (PA) to imitate the lipotoxic model in vitro were performed. Pancreatic functions, ROS, and antioxidant protein measurements were performed to evaluate the effects of CHS on cell injuries. Protein expression levels were measured by Western blotting. Furthermore, siRNA-targeted Nrf2, PI3K/Akt inhibitor (LY294002), or GSK-3β inhibitor (LiCl) was used to investigate the crosstalk relationships between proteins. As the results showed, CHS treatment inhibited apoptosis, promoted insulin release, and reduced oxidative stress. CHS treatment significantly increased the expression of Nrf2 in the cytoplasm and nuclear protein. The antioxidative and benefit effects of CHS were inhibited by siNrf2. The phosphorylation of IRS-2, PI3K, Akt, and GSK-3β was markedly increased by CHS which were inhibited by PA. In addition, inhibition of PI3K/Akt or GSK-3β with specific inhibitors dramatically abrogated the protective effects of CHS, revealing that the IRS-2/Akt/GSK-3β signaling axis was involved in the protective effects of CHS. These results demonstrate that CHS protected βTC3 cells against PA-induced oxidative stress and cell dysfunction through Nrf2 by the IRS-2/Akt/GSK-3β-mediated pathway.

Chitosan Oligosaccharides Attenuate Amyloid Formation of hIAPP and Protect Pancreatic β-Cells from Cytotoxicity

The deposition of aggregated human islet amyloid polypeptide (hIAPP) in the pancreas, that has been associated with β-cell dysfunction, is one of the common pathological features of patients with type 2 diabetes (T2D). Therefore, hIAPP aggregation inhibitors hold a promising therapeutic schedule for T2D. Chitosan oligosaccharides (COS) have been reported to exhibit a potential antidiabetic effect, but the function of COS on hIAPP amyloid formation remains elusive. Here, we show that COS inhibited the aggregation of hIAPP and disassembled preformed hIAPP fibrils in a dose-dependent manner by thioflavin T fluorescence assay, circular dichroism spectroscopy, and transmission electron microscope. Furthermore, COS protected mouse β-cells from cytotoxicity of amyloidogenic hIAPP, as well as apoptosis and cycle arrest. There was no direct binding of COS and hIAPP, as revealed by surface plasmon resonance analysis. In addition, both chitin-oligosaccharide and the acetylated monosaccharide of COS and glucosamine had no inhibition effect on hIAPP amyloid formation. It is presumed that, mechanistically, COS regulate hIAPP amyloid formation relating to the positive charge and degree of polymerization. These findings highlight the potential role of COS as inhibitors of hIAPP amyloid formation and provide a new insight into the mechanism of COS against diabetes.

A novel Gymnema sylvestre extract protects pancreatic beta-cells from cytokine-induced apoptosis

Inflammatory cytokines such as interleukin-1β, TNF-α, and interferon-γ are known to be involved in mediating β-cells death in diabetes mellitus (DM). Thus, protecting from β-cells death in patients with DM may be a useful target in alleviating symptoms of hyperglycemia. Traditional plant-based remedies have been used to treat DM for many centuries and may play a role in protecting β-cell from death. An example of these remedies is Gymnema sylvestre (GS) extract. In this study, we investigated the effect of this plant extract on β-cells apoptosis. Om Santal Adivasi (OSA®) maintained cell membrane integrity in MIN6 cells and mouse islets. Om Santal Adivasi significantly protected MIN6 cells and mouse islets from cytokine-induced apoptosis. In the presence of cytokines, OSA® significantly reduced the expression and activity of caspase-3. The antiapoptotic effect of OSA® as shown by microarray analysis is largely mediated by activating pathways involved in cell survival (mainly casein kinase II pathway) and the free radical scavenger system (specifically superoxide dismutase and catalase). This study indicates that the GS isolate OSA® protects against cytokine-induced apoptosis of β-cells by increasing the expression of cell survival pathways and free radical scavenger system.

Danzhi Jiangtang Capsule Mediates NIT-1 Insulinoma Cell Proliferation and Apoptosis by GLP-1/Akt Signaling Pathway

Objective

This study aimed to investigate the effects of Danzhi Jiangtang Capsule (DJC) on the proliferation and apoptosis functions of NIT-1 pancreatic β-cells exposed to high-glucose load through GLP-1 activated Akt/ FoxO1 signaling pathway.

Methods

Cellular apoptosis of NIT-1 pancreatic β-cells was induced by culturing in medium with 33.3mmol/L high glucose (HG). Then low-dose DJC (HG +LD), high-dose DJC (HG +HD), high-dose DJC+ GLP-1 inhibition (HG +HD +GI), and high-dose DJC+AKT inhibition (HG +HD+AI) were added, respectively. Cellular proliferation was accessed by cell counting kit (CCK-8) and cellular apoptosis was measured by Annexin V-FITC/PI staining. The protein levels of phosphorylated phosphatidylinositol-3-kinase (p-PI3K), phosphorylated AKT (p-AKT), phosphorylated Forkhead box protein O1 (p-FoxO1), and cleaved caspase-3 were detected by Western blotting. The mRNA expression of pancreatic duodenal homeobox-1 (PDX-1), CyclinD1, Bcl-2, and insulin was tested by Q-PCR.

Results

Comparing to HG group, (HG+HD) group showed a significantly increased cellular proliferation. The apoptosis of NIT-1 cells also was obviously reduced, with downregulated cleaved caspase-3 protein level and upregulated PDX-1, CyclinD1, and Bcl-2 mRNA levels (P<0.05). Additionally, (HG+HD) group manifested increased insulin mRNA expression; the protein levels of p-PI3K and p-AKT were markedly increased and p-FoxO1 was decreased. All of the above therapeutic effects by DJC intervention had been reversed by GLP-1 inhibition in (HG+HD+GI) group or AKT inhibition in (HG+HD+AI) group.

Conclusion

DJC was able to attenuate the toxicity of high-glucose load in NIT-1 pancreatic β-cells, ascribed to the improvement of cellular proliferation and apoptosis by GLP-1/Akt signaling pathway. This study could supply a new mechanism of DJC effects on type 2 diabetes mellitus (T2DM) treatment.

A novel polysaccharide from Lentinus edodes mycelia protects MIN6 cells against high glucose-induced damage via the MAPKs and Nrf2 pathways

Background

Diabetes mellitus is one of the most widespread diseases in the world, high glucose can damage islet cells, it is important to discover new natural products to inhibit high glucose damage. The protective effects and mechanisms of a novel Lentinus edodes mycelia polysaccharide (LMP) against damage induced by high glucose in MIN6 cells were explored.

Methods

Cell viability, malondialdehyde (MDA) inhibition, lactate dehydrogenase (LDH) release and the activity of superoxide dismutase (SOD) were evaluated under 40 mM glucose with or without LMP for 48 h. Cell signaling pathway analysis was performed to investigate the possible mechanisms of the protective effects of LMP in MIN6 cells.

Results

The results showed that LMP could increase cell viability and the activity of SOD, decrease the reactive oxygen species ( ROS) production, and reduce the MDA content and LDH release in high glucose-induced MIN6 cells. Moreover, LMP prevented high glucose-induced apoptosis by decreasing the expression of Bax and the activation of caspase-1 and caspase-3. Cell signaling pathway analysis showed that p38 mitogen-activated protein kinase (MAPK) and JNK pathways were inhibited and the Nrf2 pathway was activated after treated with LMP.

Conclusion

The protective effects of LMP against MIN6 cells damage induced by high glucose might rely on the regulation of the MAPK and Nrf2 pathways. These results indicated that LMP had great potential as a therapeutic agent for the treatment of diabetes mellitus.

Mitigating effects of antioxidant properties of Artemisia herba alba aqueous extract on hyperlipidemia and oxidative damage in alloxan-induced diabetic rats

Chronic hyperglycemia and excess reactive oxygen species overproduced in diabetes were associated with oxidative stress, led to continuous injury and functions damage to different organs: eyes, kidneys, neural and cardiovascular system. The present study was undertaken to evaluate the protective effect of Artemisia herba alba (AHA) leaf powder against alloxane-induced oxidative damage in diabetic rats. Rats were randomly divided into four groups: Group I controls received saline solution 9%; Group II was treated with 150 mg alloxane/(kg body weight) administered by intraperitoneal. Rats of Group III have received saline solution and treated with 400 mg AHA/(kg body weight). Animals of Group IV were treated with alloxane and AHA. Alloxane exposure led to increased blood glucose, total cholesterol, triglycerides, malondialdehyde, and a decrease in the antioxidants enzymes activities (catalase, glutathione peroxidase and glutathione-S-transferase). Administration of AHA aqueous extract ameliorated these parameters. These results demonstrate that AHA ameliorates hyperglycemia, hyperlipidemia and oxidative damage in alloxan-induced diabetes in rats.

Wushenziye Formula Inhibits Pancreatic β Cell Apoptosis in Type 2 Diabetes Mellitus via MEK-ERK-Caspase-3 Signaling Pathway

Background

Wushenziye formula (WSZYF), composed of Radix Polygoni Multiflori Preparata, Mori fructus, Mori folium, and Cassiae semen, is effective in the treatment of type 2 diabetes mellitus (T2DM).

Aim

In this study, we aimed to explore the effects and the underlying mechanisms of WSZYF on inhibiting pancreatic β cell apoptosis and improving insulin resistance (IR) in T2DM.

Methods

A T2DM model was induced by Goto-Kakizaki diabetes prone rats. Cell apoptosis model was induced in MIN6 cells.

Results

In vivo, WSZYF decreased fasting blood glucose (FBG), insulin concentration, insulin resistance index, triglyceride (TG), total cholesterol (TC), and free fatty acids (FFA) in T2DM rats. Meanwhile, WSZYF ameliorated impairments in the morphology and structure of pancreatic tissues. In vitro, WSZYF enhanced cell viability and promoted insulin secretion in the apoptosis model of MIN6 cells. Furthermore, WSZYF modulated the expressions of apoptosis-related molecules by increasing the expressions of MEK1/2, p-MEK1/2, ERK1/2, and p-ERK1/2 and decreasing the cleaved-caspase-3 expression.

Conclusion

These findings indicate that WSZYF may become a new drug candidate in the treatment of T2DM and its antidiabetic mechanism is probably inhibiting pancreatic β cell apoptosis by modulating the MEK-ERK-Caspase-3 signaling pathway.

Possible ameliorative effect of aqueous extract of date (Phoenix dactylifera) pits in rats exposed to gamma radiation

PURPOSE

To evaluate the radioprotective efficacy of date (Phoenix dactylifera) pits extract (DPE) against γ-irradiation-induced liver damage in the male albino rats. For this study, 30-day survival, dose reduction factor (DRF), antioxidant status and some biochemical changes in the serum and hepatic tissue were evaluated.

MATERIALS AND METHODS

To calculate 30-day survival, median lethal dose of 30 days (LD50/30) and DRF, DPE was orally administered to rats for 21 days before irradiation with different doses (5, 6, 8, 10 and 12 Gy) of γ-rays and the rats were observed for 30 days post-irradiation. To evaluate the radioprotective efficacy of DPE against γ-irradiation induced-liver tissue damage, animals were divided into four groups (eight animals in each group). (i) Control: rats not subjected to any treatment; (ii) DPE: DPE was orally administrated (1000 mg/kg body weight) for 21 days; (iii) RAD: rats' whole body exposed to 5 Gy of γ-rays; (iv) DPE + RAD: rats received DPE treatment for 21 days before γ-irradiation. Animals were sacrificed on the seventh day postexposure to radiation.

RESULTS

The results showed that pretreatment prior to irradiation with DPE resulted in a significantly higher 30-day survival rate of rats after exposure to different doses of γ-irradiation. Furthermore, DPE treatment resulted in a significant improvement in the hepatic redox state, manifested by a marked increase of superoxide dismutase (SOD) and catalase (CAT) activities and glutathione content associated with a significant decrease of malondialdehyde (MDA) level. In addition, DPE exhibited hepatoprotective effect evidenced by a marked increase in serum levels of insulin, testosterone, high-density lipoprotein-cholesterol (HDL-c) and hepatic glucose 6 phosphate dehydrogenase (G6PHD) activity associated with a significant decrease in serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), γ-glutamyl transferase (γ-GT), glucose, total cholesterol (TC), triglycerides (TG), low density-lipoprotein cholesterol (LDL-c) and hepatic glucose 6 phosphatase (G6Pase) activity, compared with irradiated group. Moreover, DPE showed positive modulation in the levels of hepatic metals [(iron (Fe), zinc (Zn), copper (Cu) and manganese (Mn)].

CONCLUSIONS

DPE treatment prior to gamma irradiation produced biochemical changes that could lead to a reduction in radiation-induced oxidative stress. Hence, we suggest that DPE may be useful as a new natural radioprotective agent.

Chronic hyperglycemia mediated physiological alteration and metabolic distortion leads to organ dysfunction, infection, cancer progression and other pathophysiological consequences: An update on glucose toxicity

Chronic exposure of glucose rich environment creates several physiological and pathophysiological changes. There are several pathways by which hyperglycemia exacerbate its toxic effect on cells, tissues and organ systems. Hyperglycemia can induce oxidative stress, upsurge polyol pathway, activate protein kinase C (PKC), enhance hexosamine biosynthetic pathway (HBP), promote the formation of advanced glycation end-products (AGEs) and finally alters gene expressions. Prolonged hyperglycemic condition leads to severe diabetic condition by damaging the pancreatic β-cell and inducing insulin resistance. Numerous complications have been associated with diabetes, thus it has become a major health issue in the 21st century and has received serious attention. Dysregulation in the cardiovascular and reproductive systems along with nephropathy, retinopathy, neuropathy, diabetic foot ulcer may arise in the advanced stages of diabetes. High glucose level also encourages proliferation of cancer cells, development of osteoarthritis and potentiates a suitable environment for infections. This review culminates how elevated glucose level carries out its toxicity in cells, metabolic distortion along with organ dysfunction and elucidates the complications associated with chronic hyperglycemia.

Effect of gastric bypass combined with ileal transportation on type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a chronic progressive disease, which manifests as an endocrine disorder. Among the different methods of surgery available to treat patients with T2DM, Roux-en-Y gastric bypass (RYGBP) and ileal transposition (IT) are the most commonly performed. The aim of the present study was to investigate the effects of RYGBP combined with IT on rats with T2DM. A total of 8 healthy male rats were used as a control group and 40 GK rats were randomly divided into 5 groups: A diabetes mellitus (DM) group, a sham operative group (SO), a RYGBP group, an IT group and a RYGBP+IT group. The results demonstrated that fasting blood glucose, triglyceride, total cholesterol and gastric inhibitory polypeptide levels in all treatment groups were significantly lower than those of the SO and DM groups. Furthermore, levels TC and TG in the RYGBP+IT group were significantly lower than in the RYGBP and IT groups. Levels of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase mRNA and IRS-2 protein in all treatment groups were also significantly lower than those of the SO group; and they were significantly lower in the RYGBP+IT group compared with the RYGBP and IT groups. The expression of phosphorylated Akt in the treatment groups was significantly higher than the SO group and was significantly higher in the RYGBP+IT group compared with the RYGBP and IT groups. These results indicate that RYGBP and IT surgical treatment can induce T2DM remission by mediating the expression of insulin-related factors to reverse insulin resistance. The current study also indicated that the effect of RYGBP combined with IT may be developed as a novel first-line method of treating T2DM.

Five-Year Predictors of Insulin Initiation in People with Type 2 Diabetes under Real-Life Conditions

We performed a real-life analysis of clinical and laboratory parameters, in orally treated T2DM patients aiming at identifying predictors of insulin treatment initiation. Overall, 366955 patients (55.8% males, age 65 ± 11 years, diabetes duration 7 ± 8 years) were followed up between 2004 and 2011. Each patient was analyzed step-by-step until either eventually starting insulin treatment or getting to the end of the follow-up period. Patients switching to insulin showed a worse global risk profile, longer disease duration (10 ± 9 years vs. 6 ± 7 years, respectively; p < 0.001), higher HbA1c (8.0 ± 1.6% vs. 7.2 ± 1.5%, respectively; p < 0.001), higher triglycerides, a greater prevalence of arterial hypertension, antihypertensive, lipid-lowering and aspirin treatment, a higher rate of nonproliferative/proliferative retinopathy, and a nearly 4 times lower prevalence of the "diet alone." They also showed a higher prevalence of subjects with eGFR < 60 ml/min/1.73 m² (24.0% vs. 16.2%, respectively; p < 0.001). Multivariate analysis identified diabetes duration, HbA1c, triglyceride and low HDL-C values, presence of retinopathy or renal dysfunction, and sulphonylurea utilization (the risk being approximately 3 times greater in the latter case) as independent predictors of insulin treatment initiation. LDL-C, lipid-lowering treatment, and overweight/obese seem to be protective. Results of tree analysis showed that patients on sulphonylurea, with high HbA1c, eGFR below 50 ml/min/1.73 m², and at least 5-year disease duration, are at very high risk to start insulin treatment. We have to stick to this real-life picture, of course, until enough data are collected on patients treated with innovative medications which are expected to improve beta cell survival and further delay treatment-related insulin requirement.

Identification of islet-enriched long non-coding RNAs contributing to β-cell failure in type 2 diabetes

Objective

Non-coding RNAs constitute a major fraction of the β-cell transcriptome. While the involvement of microRNAs is well established, the contribution of long non-coding RNAs (lncRNAs) in the regulation of β-cell functions and in diabetes development remains poorly understood. The aim of this study was to identify novel islet lncRNAs differently expressed in type 2 diabetes models and to investigate their role in β-cell failure and in the development of the disease.

Methods

Novel transcripts dysregulated in the islets of diet-induced obese mice were identified by high throughput RNA-sequencing coupled with de novo annotation. Changes in the level of the lncRNAs were assessed by real-time PCR. The functional role of the selected lncRNAs was determined by modifying their expression in MIN6 cells and primary islet cells.

Results

We identified about 1500 novel lncRNAs, a number of which were differentially expressed in obese mice. The expression of two lncRNAs highly enriched in β-cells, βlinc2, and βlinc3, correlated to body weight gain and glycemia levels in obese mice and was also modified in diabetic db/db mice. The expression of both lncRNAs was also modulated in vitro in isolated islet cells by glucolipotoxic conditions. Moreover, the expression of the human orthologue of βlinc3 was altered in the islets of type 2 diabetic patients and was associated to the BMI of the donors. Modulation of the level of βlinc2 and βlinc3 by overexpression or downregulation in MIN6 and mouse islet cells did not affect insulin secretion but increased β-cell apoptosis.

Conclusions

Taken together, the data show that lncRNAs are modulated in a model of obesity-associated type 2 diabetes and that variations in the expression of some of them may contribute to β-cell failure during the development of the disease.

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Mouse pancreatic islets express a large number of novel long non-coding RNAs.

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Many long non-coding RNAs are differentially expressed in the islets of obese mice.

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The level of two islet long non-coding RNAs correlates to body weight and glycemia.

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The expression of these islet long non-coding RNAs is altered in Type 2 diabetes.

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Altered expression of these long non-coding RNAs sensitise β-cells to apoptosis.

Current Therapies for the Medical Management of Diabetes

Diabetes affects a large and diverse number of individuals who share in common its risks for complications but who differ greatly from one another in age, health, and a number of circumstances influential to successful treatment. Because type 2 diabetes comprises the majority of diabetes cases, a number of agents have been developed for its treatment. Their unique properties offer opportunities to overcome some of the treatment limitations of older medicines and enable a more individualized and flexible approach to glucose-lowering. At the same time, new medications are accompanied by greater costs and uncertainties about their long-term benefits or safety, and thus the present state of care for type 2 diabetes places focus on a process of shared decision-making between the clinician and patient as to which treatments can optimize health while minimizing harms. We review the major classes of diabetes agents and provide some guidance for how one might approach decision-making in choosing among them.

Curcumin improves high glucose-induced INS-1 cell insulin resistance via activation of insulin signaling

Curcumin is a yellow pigment isolated from Corcuma longan. This research investigates the improvement of curcumin on INS-1 cells with insulin resistance induced by high glucose. INS-1 cells were treated with high glucose (30 mmol L(-1)) for 48 h. Subsequently, the medium was replaced with curcumin for 24 h. Curcumin effectively increased insulin gene expression and glucose stimulated insulin secretion (GSIS) in a dose-dependent manner. Furthermore, the molecular mechanism of curcumin-induced insulin expression and secretion in high glucose-induced INS-1 cells was investigated in this study. Curcumin increased the expression of glucose transporter 2 (GLUT2) and phosphorylation of insulin receptor (IR), insulin receptor substrate-1 (IRS1), phosphatidylinositol-3-kinase (PI3K) and AKT in the INS-1 cells. Moreover, curcumin stimulation increased the expression of PDX-1 and GCK. This investigation suggests that curcumin prevented high glucose-reduced insulin expression and secretion through activation of the PI3K/Akt/GLUT2 pathway in INS-1 cells.

Delta cell death in the islet of Langerhans and the progression from normal glucose tolerance to type 2 diabetes in non-human primates (baboon, Papio hamadryas)

AIMS/HYPOTHESIS

The cellular composition of the islet of Langerhans is essential to ensure its physiological function. Morphophysiological islet abnormalities are present in type 2 diabetes but the relationship between fasting plasma glucose (FPG) and islet cell composition, particularly the role of delta cells, is unknown. We explored these questions in pancreases from baboons (Papio hamadryas) with FPG ranging from normal to type 2 diabetic values.

METHODS

We measured the volumes of alpha, beta and delta cells and amyloid in pancreatic islets of 40 baboons (Group 1 [G1]: FPG < 4.44 mmol/l [n = 10]; G2: FPG = 4.44-5.26 mmol/l [n = 9]; G3: FPG = 5.27-6.94 mmol/l [n = 9]; G4: FPG > 6.94 mmol/l [n = 12]) and correlated islet composition with metabolic and hormonal variables. We also performed confocal microscopy including TUNEL, caspase-3, and anti-caspase cleavage product of cytokeratin 18 (M30) immunostaining, electron microscopy, and immuno-electron microscopy with anti-somatostatin antibodies in baboon pancreases.

RESULTS

Amyloidosis preceded the decrease in beta cell volume. Alpha cell volume increased ∼ 50% in G3 and G4 (p < 0.05), while delta cell volume decreased in these groups by 31% and 39%, respectively (p < 0.05). In G4, glucagon levels were higher, while insulin and HOMA index of beta cell function were lower than in the other groups. Immunostaining of G4 pancreatic sections with TUNEL, caspase-3 and M30 showed apoptosis of beta and delta cells, which was also confirmed by immuno-electron microscopy with anti-somatostatin antibodies.

CONCLUSIONS/INTERPRETATION

In diabetic baboons, changes in islet composition correlate with amyloid deposition, with increased alpha cell and decreased beta and delta cell volume and number due to apoptosis. These data argue for an important role of delta cells in type 2 diabetes.

Dipeptidyl peptidase-4 inhibitor sitagliptin improves pancreatic β-cell function in hypertensive diabetic patients treated with angiotensin receptor blockers

INTRODUCTION

Dipeptidyl peptidase (DPP)-4 inhibitors, a novel oral anti-diabetic agents, exert a protective effect on pancreatic β-cell function in patients with type 2 diabetic mellitus (T2DM). However, their beneficial effect in hypertensive T2DM patients treated with angiotensin receptor blockers (ARBs) has not been investigated.

METHODS

In this open-label multicenter randomized study, a total of 55 hypertensive T2DM patients treated with ARBs were randomly assigned to receive the DPP-4 inhibitor sitagliptin or sulfonylurea (SU).

RESULTS

After 24 weeks of treatment, a significant reduction in fasting blood glucose was only observed in the sitagliptin group, while HbA1c was significantly reduced in both groups. Homeostasis model assessment of insulin resistance was not significantly improved in either group. Indicators of pancreatic β-cell function, including proinsulin to insulin ratio and homeostasis model assessment of β-cell function, were significantly improved in the sitagliptin group, but not in the SU group. The beneficial effects of sitagliptin were observed in hypoglycemic drug naïve patients, but not in patients who had received SU monotherapy prior to the study.

CONCLUSION

Treatment with the DPP-4 inhibitor sitagliptin might exert beneficial effects on pancreatic β-cell function in ARB-treated T2DM patients and its efficacy might be more pronounced in hypoglycemic drug naïve patients.

Targeting metabolic disorders by natural products

The most prevalent metabolic disorders are diabetes mellitus, obesity, dyslipidemia, osteoporosis and metabolic syndrome, which are developed when normal metabolic processes are disturbed. The most common pathophysiologies of the above disorders are oxidative stress, Nrf2 pathways, epigenetic, and change in miRNA expression. There is a challenge in the prevention and treatment of metabolic disorders due to severe adverse effects of some synthetic drugs, their high cost, lack of safety and poverty in some conditions, and insufficient accessibility for the general population in the world. With increasing interest in shifting from synthetic drugs to phytotherapy as an alternative treatment, there is still a gap in scientific evidences of plant-derived therapeutic benefits. One reason may be slow rate of translation of animal studies' findings into human clinical trials. Since metabolic disorders are multifactorial, it seems that poly-herbal medications, or drug-herbal combination are needed for their treatment. However, further researches to determine the most effective plant-derived metabolites, and their cellular mechanism in order to set priorities for well-designed animal and clinical trials, and also more studies with strong scientific evidences such as systematic review and meta-analysis of controlled studies are needed.

Assay development and multivariate scoring for high-content discovery of chemoprotectants of endoplasmic-reticulum-stress-mediated amylin-induced cytotoxicity in pancreatic beta cells

The underlying pathogenesis of type-II diabetes mellitus is in the dysfunction and selective loss of pancreatic islet β-cells, which ultimately leads to underproduction of endogenous insulin. Amylin, a 37-amino-acid human hormone that is cosecreted with insulin, helps regulate gastric emptying and maintain blood glucose homeostasis through improved postprandial satiety. It is hypothesized that amylin protofibrils cause selective loss of pancreatic β-cells in a manner similar to amyloid β aggregation in Alzheimer's disease. β-Cell death occurs in vitro when isolated human or rodent β-cells are exposed to micromolar concentrations of amylin, but the exact mechanism of selective β-cell loss in vivo remains unknown. Therefore, pursuing small-molecule drug discovery for chemoprotectants of amylin-induced β-cell toxicity is a viable phenotypic target that can lead to potential pharmacotherapies for the preservation of β-cell mass, delaying insulin dependence and allowing additional opportunities for lifestyle intervention. Additionally, chronic endoplasmic reticulum (ER) stress induced by chronic hyperglycemia and hyperlipidemia is a potentiating factor of amylin-induced β-cell loss. Herein, we describe a high-content/high-throughput screening (HTS) assay for the discovery of small molecules that are chemoprotective of amylin-induced, ER-stress-potentiated β-cell loss. We also put forth a general method for construction of a robust well-level multivariate scoring system using partial least squares regression analysis to improve high-content assay performance and to streamline the association of complex high-content data into HTS activity databases where univariate responses are typical.

Sesamin Ameliorates Advanced Glycation End Products-Induced Pancreatic β-Cell Dysfunction and Apoptosis

Advanced glycation end products (AGEs), the direct modulators of β-cells, have been shown to cause insulin-producing β-cell dysfunction and apoptosis through increase of intracellular reactive oxygen species (ROS) production. Sesamin has been demonstrated to possess antioxidative activity. This study was designed to investigate whether sesamin protects against AGEs-evoked β-cell damage via its antioxidant property. The effects of sesamin were examined in C57BL/6J mice and MIN6 cell line. In in vivo studies, mice were intraperitoneally injected with AGEs (120 mg/kg) and orally treated with sesamin (160 mg/kg) for four weeks. Intraperitoneal glucose tolerance and insulin releasing tests were performed. Insulin content, ROS generation and β-cell apoptosis in pancreatic islets were also measured. In in vitro studies, MIN6 cells were pretreated with sesamin (50 or 100 μM) and then exposed to AGEs (200 mg/L) for 24 h. Insulin secretion, β-cell death, ROS production as well as expression and activity of NADPH oxidase were determined. Sesamin treatment obviously ameliorated AGE-induced β-cell dysfunction and apoptosis both in vivo and in vitro. These effects were associated with decreased ROS production, down-regulated expression of p67^phox and p22^phox, and reduced NADPH oxidase activity. These results suggest that sesamin protects β-cells from damage caused by AGEs through suppressing NADPH oxidase-mediated oxidative stress.

Pancreatic β cell dedifferentiation in diabetes and redifferentiation following insulin therapy

Diabetes is characterized by "glucotoxic" loss of pancreatic β cell function and insulin content, but underlying mechanisms remain unclear. A mouse model of insulin-secretory deficiency induced by β cell inexcitability (K(ATP) gain of function) demonstrates development of diabetes and reiterates the features of human neonatal diabetes. In the diabetic state, β cells lose their mature identity and dedifferentiate to neurogenin3-positive and insulin-negative cells. Lineage-tracing experiments show that dedifferentiated cells can subsequently redifferentiate to mature neurogenin3-negative, insulin-positive β cells after lowering of blood glucose by insulin therapy. We demonstrate here that β cell dedifferentiation, rather than apoptosis, is the main mechanism of loss of insulin-positive cells, and redifferentiation accounts for restoration of insulin content and antidiabetic drug responsivity in these animals. These results may help explain gradual decrease in β cell mass in long-standing diabetes and recovery of β cell function and drug responsivity in type 2 diabetic patients following insulin therapy, and they suggest an approach to rescuing "exhausted" β cells in diabetes.

Identification of particular groups of microRNAs that positively or negatively impact on beta cell function in obese models of type 2 diabetes

AIMS/HYPOTHESIS

MicroRNAs are key regulators of gene expression involved in health and disease. The goal of our study was to investigate the global changes in beta cell microRNA expression occurring in two models of obesity-associated type 2 diabetes and to assess their potential contribution to the development of the disease.

METHODS

MicroRNA profiling of pancreatic islets isolated from prediabetic and diabetic db/db mice and from mice fed a high-fat diet was performed by microarray. The functional impact of the changes in microRNA expression was assessed by reproducing them in vitro in primary rat and human beta cells.

RESULTS

MicroRNAs differentially expressed in both models of obesity-associated type 2 diabetes fall into two distinct categories. A group including miR-132, miR-184 and miR-338-3p displays expression changes occurring long before the onset of diabetes. Functional studies indicate that these expression changes have positive effects on beta cell activities and mass. In contrast, modifications in the levels of miR-34a, miR-146a, miR-199a-3p, miR-203, miR-210 and miR-383 primarily occur in diabetic mice and result in increased beta cell apoptosis. These results indicate that obesity and insulin resistance trigger adaptations in the levels of particular microRNAs to allow sustained beta cell function, and that additional microRNA deregulation negatively impacting on insulin-secreting cells may cause beta cell demise and diabetes manifestation.

CONCLUSIONS/INTERPRETATION

We propose that maintenance of blood glucose homeostasis or progression toward glucose intolerance and type 2 diabetes may be determined by the balance between expression changes of particular microRNAs.

Investigational anti-hyperglycemic agents: the future of type 2 diabetes therapy?

As the pandemic of type 2 diabetes spreads globally, clinicians face many challenges in treating an increasingly diverse patient population varying in age, comorbidities, and socioeconomic status. Current therapies for type 2 diabetes are often unable to alter the natural course of the disease and provide durable glycemic control, and side effects in the context of individual patient characteristics often limit treatment choices. This often results in the progression to insulin use and complex regimens that are difficult to maintain. Therefore, a number of agents are being developed to better address the pathogenesis of type 2 diabetes and to overcome limitations of current therapies. The hope is to provide more options for glucose lowering and complication reduction with less risk for hypoglycemia and other adverse effects. These agents include newer incretin-based therapies and PPAR agonists, as well as new therapeutic classes such as sodium-coupled glucose cotransporter 2 inhibitors, free fatty acid receptor agonists, 11-β-hydroxysteroid dehydrogenase type 1 inhibitors, glucokinase activators, and several others that may enter clinical use over the next decade. Herein we review these agents that are advancing through clinical trials and describe the rationale behind their use, mechanisms of action, and potential for glucose lowering, as well as what is known of their limitations.

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

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

Inhibition of GPR40 protects MIN6 β cells from palmitate-induced ER stress and apoptosis

Chronic exposure to elevated concentration of free fatty acids (FFA) has been verified to induce endoplasmic reticulum (ER) stress, which leads to pancreatic β-cell apoptosis. As one of the medium and long chain FFA receptors, GPR40 is highly expressed in pancreatic β cells, mediates both acute and chronic effects of FFA on β-cell function, but the role of GPR40 in FFA-induced β-cell apoptosis remains unclear. In this study, we investigated the possible effects of GPR40 in palmitate-induced MIN6 β-cell apoptosis, and found that DC260126, a novel small molecular antagonist of GPR40, could protect MIN6 β cells from palmitate-induced ER stress and apoptosis. Similar results were observed in GPR40-deficient MIN6 cells, indicating that palmitate-induced β-cell apoptosis is at least partially dependent on ER stress pathway via GRP40.

Oxidative metabolism genes are not responsive to oxidative stress in rodent Beta cell lines

Altered expression of oxidative metabolism genes has been described in the skeletal muscle of individuals with type 2 diabetes. Pancreatic beta cells contain low levels of antioxidant enzymes and are particularly susceptible to oxidative stress. In this study, we explored the effect of hyperglycemia-induced oxidative stress on a panel of oxidative metabolism genes in a rodent beta cell line. We exposed INS-1 rodent beta cells to low (5.6 mmol/L), ambient (11 mmol/L), and high (28 mmol/L) glucose conditions for 48 hours. Increases in oxidative stress were measured using the fluorescent probe dihydrorhodamine 123. We then measured the expression levels of a panel of 90 oxidative metabolism genes by real-time PCR. Elevated reactive oxygen species (ROS) production was evident in INS-1 cells after 48 hours (P < 0.05). TLDA analysis revealed a significant (P < 0.05) upregulation of 16 of the 90 genes under hyperglycemic conditions, although these expression differences did not reflect differences in ROS. We conclude that although altered glycemia may influence the expression of some oxidative metabolism genes, this effect is probably not mediated by increased ROS production. The alterations to the expression of oxidative metabolism genes previously observed in human diabetic skeletal muscle do not appear to be mirrored in rodent pancreatic beta cells.

Nifedipine protects INS-1 β-cell from high glucose-induced ER stress and apoptosis

Sustained high concentration of glucose has been verified toxic to β-cells. Glucose augments Ca²⁺-stimulated insulin release in pancreatic β-cells, but chronic high concentration of glucose could induce a sustained level of Ca²⁺ in β-cells, which leads to cell apoptosis. However, the mechanism of high glucose-induced β-cell apoptosis remains unclear. In this study, we use a calcium channel blocker, nifedipine, to investigate whether the inhibition of intracellular Ca²⁺ concentration could protect β-cells from chronic high glucose-induced apoptosis. It was found that in a concentration of 33.3 mM, chronic stimulation of glucose could induce INS-1 β-cells apoptosis at least through the endoplasmic reticulum stress pathway and 10 μM nifedipine inhibited Ca²⁺ release to protect β-cells from high glucose-induced endoplasmic reticulum stress and apoptosis. These results indicated that inhibition of Ca²⁺ over-accumulation might provide benefit to attenuate islet β-cell decompensation in a high glucose environment.

Which is the eligible patient to be treated with pioglitazone? The expert view

Pioglitazone has an important role in the treatment of patients with Type 2 diabetes. The drug can help patients to achieve sustained glycemic control and may delay the requirement for insulin. Pioglitazone may provide benefits beyond its effects on glycemia, with data suggesting it may confer anti-atherosclerotic and cardioprotective properties. Attention should be given to possible side effects relating to class effects of TZD, and selection of appropriate patients to be prescribed pioglitazone will enable optimum benefits to be derived from pioglitazone treatment.

Ceramide formation as a target in beta-cell survival and function

INTRODUCTION

Ceramide may be synthesized de novo or generated by sphingomyelinase-dependent hydrolysis of sphingomyelin.

AREAS COVERED

The role of ceramide, ceramide-sensitive signaling and ion channels in β-cell apoptosis, lipotoxicity and amyloid-induced β-cell death.

EXPERT OPINION

Ceramide participates in β-cell dysfunction and apoptosis after exposure to TNFα, IL-1β and IFN-γ, excessive amyloid and islet amyloid polypeptide or non-esterified fatty acids (lipotoxicity). Knockout of sphingomyelin synthase 1, which converts ceramide to sphingomyelin, leads to impairment of insulin secretion. Increased ceramidase activity or pharmacological inhibition of ceramide synthetase, inhibits β-cell apoptosis. Ceramide contributes to endoplasmatic reticulum (ER) stress, decreased mitochondrial membrane potential in insulin-secreting cells and mitochondrial release of cytochrome c into the cytosol, which are all triggers of apoptotic cell death. Ceramide-dependent signaling involves activation of extracellularly regulated kinases 1 and 2 (ERK1/2), downregulation of Period (Per)-aryl hydrocarbon receptor nuclear translocator (Arnt)-single-minded (Sim) kinase (PASK), activation of okadaic-acid-sensitive protein phosphatase 2A (PP2A) and stimulation of NADPH-oxidase with generation of superoxides and lipid peroxides. Ceramide reduces the activity of voltage gated potassium (Kv)-channels in insulin-secreting cells. The role of ceramide in β-cell survival and function may be therapeutically relevant, because ceramide formation can be suppressed by pharmacological inhibition of ceramide synthetase and/or sphingomyelinase.

Are sulfonylureas less desirable than DPP-4 inhibitors as add-on to metformin in the treatment of type 2 diabetes?

Sulfonylureas (SUs) are commonly used as add-on to metformin in treatment of type 2 diabetes in patients who are insufficiently controlled by metformin alone. They have good efficacy and have been shown to prevent microvascular complications. However, treatment with SUs is also associated with a high frequency of hypoglycemia, increased body weight, and a high risk of secondary failure. During recent years, dipeptidyl peptidase-4 (DPP-4) inhibitors have emerged as alternatives to SUs. They show similar efficacy as SUs but with lower risk of hypoglycemia, and reduction or no change in body weight, and if confirmed in humans, they may preserve islet function and thereby minimize the risk for secondary failure. Their limitation at present is the lack of long-term (>5 years) experience on durability and safety. Overall, therefore, the conclusion emerges that SUs are less desirable than DPP-4 inhibitors in management of hyperglycemia in type 2 diabetes.

Abeta and human amylin share a common toxicity pathway via mitochondrial dysfunction

Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM) are leading causes of morbidity and mortality in the elderly. Both diseases are characterized by amyloid deposition in target tissues: aggregation of amylin in T2DM is associated with loss of insulin-secreting beta-cells, while amyloid beta (A beta) aggregation in AD brain is associated with neuronal loss. Here, we used quantitative iTRAQ proteomics as a discovery tool to show that both A beta and human amylin (HA) deregulate identical proteins, a quarter of which are mitochondrial, supporting the notion that mitochondrial dysfunction is a common target in these two amyloidoses. A functional validation revealed that mitochondrial complex IV activity was significantly reduced after treatment with either HA or A beta, as was mitochondrial respiration. In comparison, complex I activity was reduced only after treatment with HA. A beta and HA, but not the non-amyloidogenic rat amylin, induced significant increases in the generation of ROS. Co-incubation of HA and A beta did not produce an augmented effect in ROS production, again suggesting common toxicity mechanisms. In conclusion, our data suggest that A beta and HA both exert toxicity, at least in part, via mitochondrial dysfunction, thus restoring their function may be beneficial for both AD and T2DM.