The antiinflammatory cytokine interleukin-1 receptor antagonist protects from high-fat diet-induced hyperglycemia

MECHANISMS IN ENDOCRINOLOGY: Metabolic and inflammatory pathways on the pathogenesis of type 2 diabetes

Obesity is the main risk factor for type 2 diabetes (T2D). Studies performed over the last 20 years have identified inflammation as the most important link between these two diseases. During the development of obesity, there is activation of subclinical inflammatory activity in tissues involved in metabolism and energy homeostasis. Intracellular serine/threonine kinases activated in response to inflammatory factors can catalyse the inhibitory phosphorylation of key proteins of the insulin-signalling pathway, leading to insulin resistance. Moreover, during the progression of obesity and insulin resistance, the pancreatic islets are also affected by inflammation, contributing to β-cell failure and leading to the onset of T2D. In this review, we will present the main mechanisms involved in the activation of obesity-associated metabolic inflammation and discuss potential therapeutic opportunities that can be developed to treat obesity-associated metabolic diseases.

Colchicine to decrease NLRP3-activated inflammation and improve obesity-related metabolic dysregulation

Obesity is a major risk-factor for the development of insulin resistance, type 2 diabetes, and cardiovascular disease. Circulating molecules associated with obesity, such as saturated fatty acids and cholesterol crystals, stimulate the innate immune system to incite a chronic inflammatory state. Studies in mouse models suggest that suppressing the obesity-induced chronic inflammatory state may prevent or reverse obesity-associated metabolic dysregulation. Human studies, however, have been far less positive, possibly because targeted interventions were too far downstream of the inciting inflammatory events. Recently, it has been shown that, within adipose tissue macrophages, assembly of a multi-protein member of the innate immune system, the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, is essential for the induction of this inflammatory state. Microtubules enable the necessary spatial arrangement of the components of the NLRP3 inflammasome in the cell, leading to its activation and propagation of the inflammatory cascade. Colchicine, a medication classically used for gout, mediates its anti-inflammatory effect by inhibiting tubulin polymerization, and has been shown to attenuate macrophage NLRP3 inflammasome arrangement and activation in vitro and in vivo. Given these findings, we hypothesize that, in at-risk individuals (those with obesity-induced inflammation and metabolic dysregulation), long-term colchicine use will lead to suppression of inflammation and thus cause improvements in insulin sensitivity and other obesity-related metabolic impairments.

IL-1β at the crossroad between rheumatoid arthritis and type 2 diabetes: may we kill two birds with one stone?

Although in the past the prevention of joint destruction in rheumatoid arthritis (RA) was strongly emphasized, now a great interest is focused on associated comorbidities in these patients. Multiple data suggest that a large percentage of RA patients are affected by Type 2 Diabetes (T2D), whose incidence has reached epidemic levels in recent years, thus increasing the health care costs. A better knowledge about the pathogenesis of these diseases as well as the mechanisms of action of drugs may allow both policy designers and physicians to choose the most effective treatments, thus lowering the costs. This review will focus on the role of Interleukin (IL)-1β in the pathogenesis of both the diseases, the efficacy of IL-1 blocking molecules in controlling these diseases, and will provide information suggesting that targeting IL-1β, in patients affected by both RA and T2D, may be a promising therapeutic choice.

Interleukin-1 signaling contributes to acute islet compensation

IL-1β is a well-established inducer of both insulin resistance and impaired pancreatic islet function. Despite this, findings examining IL-1 receptor deficiency or antagonism in in vivo animal models, as well as in clinical studies of type 2 diabetic (T2D) patients, have led to conflicting results, suggesting that the actions of IL-1β on glycemic control may be pleiotropic in nature. In the present work, we find that the ability of IL-1β to amplify glucose-stimulated insulin secretion from human islets correlates with donor BMI. Islets from obese donors are sensitized to the insulinotropic effects of this cytokine, whereas the stimulatory effects of IL-1β are lost in islets from obese T2D patients, suggesting a role for IL-1 signaling in islet compensation. Indeed, mice deficient in IL-1 receptor type I become glucose intolerant more rapidly than their WT littermates and have impaired secretory responses during the acute stages of inflammatory and metabolic stress induced by LPS and high-fat diet, respectively. IL-1β directly enhances β cell insulin secretion by increasing granule docking and soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) complex formation at the plasma membrane. Together, our study highlights the importance of IL-1β signaling in islet compensation to metabolic and inflammatory stress.

Distinct functions of the dual leucine zipper kinase depending on its subcellular localization

The dual leucine zipper kinase DLK induces β-cell apoptosis by inhibiting the transcriptional activity conferred by the β-cell protective transcription factor cAMP response element binding protein CREB. This action might contribute to β-cell loss and ultimately diabetes. Within its kinase domain DLK shares high homology with the mixed lineage kinase (MLK) 3, which is activated by tumor necrosis factor (TNF) α and interleukin (IL)-1β, known prediabetic signals. In the present study, the regulation of DLK in β-cells by these cytokines was investigated. Both, TNFα and IL-1β induced the nuclear translocation of DLK. Mutations within a putative nuclear localization signal (NLS) prevented basal and cytokine-induced nuclear localization of DLK and binding to the importin receptor importin α, thereby demonstrating a functional NLS within DLK. DLK NLS mutants were catalytically active as they phosphorylated their down-stream kinase c-Jun N-terminal kinase to the same extent as DLK wild-type but did neither inhibit CREB-dependent gene transcription nor transcription conferred by the promoter of the anti-apoptotic protein BCL-xL. In addition, the β-cell apoptosis-inducing effect of DLK was severely diminished by mutation of its NLS. In a murine model of prediabetes, enhanced nuclear DLK was found. These data demonstrate that DLK exerts distinct functions, depending on its subcellular localization and thus provide a novel level of regulating DLK action. Furthermore, the prevention of the nuclear localization of DLK as induced by prediabetic signals with consecutive suppression of β-cell apoptosis might constitute a novel target in the therapy of diabetes mellitus.

Increased T cell immunoglobulin and mucin domain containing 4 (TIM-4) is negatively correlated with serum concentrations of interleukin-1β in type 2 diabetes

BACKGROUND

T cell immunoglobulin and mucin domain containing 4 (TIM-4), a novel immune regulator, is selectively expressed on antigen-presenting cells, especially macrophages and mature dendritic cells. Although TIM-4 plays key roles in mutiple immune diseases, whether it is involved in type 2 diabetes mellitus (T2D) remains unknown. The aim of the present study was to investigate the expression of TIM-4 in T2D and determine its significance in disease progression.

METHODS

Peripheral blood mononuclear cells (PBMC) were isolated from T2D patients and healthy controls to measure TIM-4 mRNA expression by real-time polymerase chain reaction (PCR), and sera were collected to determine interleukin (IL)-1β concentrations and other clinical indicators (high-sensitivity C-reactive protein [hsCRP], total cholesterol, low-density lipoprotein cholesterol [LDL-C], high-density lipoprotein cholesterol, triglyceride, fasting glucose, HbA1c, aspartate aminotransferase, and alanine aminotransferase).

RESULTS

Expression of TIM-4 mRNA was increased significantly in PBMCs from T2D patients compared with healthy controls. There was a positive correlation between TIM-4 mRNA expression and serum concentrations of hsCRP. However, there was a negative correlation between TIM-4 mRNA expression and IL-1β concentrations, indicating the potential role for TIM-4 to negatively regulate IL-1β production. In addition, TIM-4 mRNA expression was negatively correlated with lowLDL-C, and there was a tendency for a negative relationship between TIM-4 mRNA expression and HbA1c.

CONCLUSIONS

The results of the present study indicate that TIM-4 contributes, at least in part, to the pathogenesis of T2D, possibly by regulating IL-1β.

Puerarin Protects Pancreatic β-Cells in Obese Diabetic Mice via Activation of GLP-1R Signaling

Diabetes is characterized by a loss and dysfunction of the β-cell. Glucagon-like peptide 1 receptor (GLP-1R) signaling plays an important role in β-cell survival and function. It is meaningful to identify promising agents from natural products which might activate GLP-1R signaling. In this study, puerarin, a diet isoflavone, was evaluated its beneficial effects on β-cell survival and GLP-1R pathway. We showed that puerarin reduced the body weight gain, normalized blood glucose, and improved glucose tolerance in high-fat diet-induced and db/db diabetic mice. Most importantly, increased β-cell mass and β-cell proliferation but decreased β-cell apoptosis were observed in puerarin-treated diabetic mice as examined by immunostaining of mice pancreatic sections. The protective effect of puerarin on β-cell survival was confirmed in isolated mouse islets treated with high glucose. Further mechanism studies showed that the circulating level of GLP-1 in mice was unaffected by puerarin. However, puerarin enhanced GLP-1R signaling by up-regulating expressions of GLP-1R and pancreatic and duodenal homeobox 1, which subsequently led to protein kinase B (Akt) activation but forkhead box O1 inactivation, and promoted β-cell survival. The protective effect of puerarin was remarkably suppressed by Exendin(9-39), an antagonist of GLP-1R. Our study demonstrated puerarin improved glucose homeostasis in obese diabetic mice and identified a novel role of puerarin in protecting β-cell survival by mechanisms involving activation of GLP-1R signaling and downstream targets.

Regulation of metabolism by the innate immune system

Low-grade tissue inflammation induced by obesity can result in insulin resistance, which in turn is a key cause of type 2 diabetes mellitus. Cells of the innate immune system produce cytokines and other factors that impair insulin signalling, which contributes to the connection between obesity and the onset of type 2 diabetes mellitus. Here, we review the innate immune cells involved in secreting inflammatory factors in the obese state. In the adipose tissue, these cells include proinflammatory adipose tissue macrophages and natural killer cells. We also discuss the role of innate immune cells, such as anti-inflammatory adipose tissue macrophages, eosinophils, group 2 innate lymphoid cells and invariant natural killer T cells, in maintaining an anti-inflammatory and insulin-sensitive environment in the lean state. In the liver, both Kupffer cells and recruited hepatic macrophages can contribute to decreased hepatic insulin sensitivity. Proinflammatory macrophages might also adversely affect insulin sensitivity in the skeletal muscle and pancreatic β-cell function. Finally, this Review provides an overview of the mechanisms for regulating proinflammatory immune responses that could lead to future therapeutic opportunities to improve insulin sensitivity.

The IL-1β Receptor Antagonist SER140 Postpones the Onset of Diabetes in Female Nonobese Diabetic Mice

The cytokine interleukin-1β (IL-1β) is known to stimulate proinflammatory immune responses and impair β-cell function and viability, all critical events in the pathogenesis of type 1 diabetes (T1D). Here we evaluate the effect of SER140, a small peptide IL-1β receptor antagonist, on diabetes progression and cellular pancreatic changes in female nonobese diabetic (NOD) mice. Eight weeks of treatment with SER140 reduced the incidence of diabetes by more than 50% compared with vehicle, decreased blood glucose, and increased plasma insulin. Additionally, SER140 changed the endocrine and immune cells dynamics in the NOD mouse pancreas. Together, the data suggest that SER140 treatment postpones the onset of diabetes in female NOD mice by interfering with IL-1β activated pathways.

Considerations for Defining Cytokine Dose, Duration, and Milieu That Are Appropriate for Modeling Chronic Low-Grade Inflammation in Type 2 Diabetes

Proinflammatory cytokines have been implicated in the pathophysiology of both type 1 diabetes (T1D) and type 2 diabetes (T2D). T1D is an autoimmune disease involving the adaptive immune system responding to pancreatic beta-cells as antigen-presenting cells. This attracts immune cells that surround pancreatic islets (insulitis) and secrete cytokines, such as IL-1beta, IFN-gamma, and TNF-alpha, in close proximity to pancreatic beta-cells. In contrast, there is little evidence for such a focused autoimmune response in T2D. Instead, the innate immune system, which responds to cellular damage and pathogens, appears to play a key role. There are three major sources of proinflammatory cytokines that may impact islet/beta-cell function in T2D: (1) from islet cells, (2) from increased numbers of intraislet macrophages/immune cells, and (3) from increased circulating levels of proinflammatory cytokines due to obesity, presumably coming from inflamed adipose tissue. These differences between T1D and T2D are reflected by significant differences in the cytokine concentration, duration, and milieu. This review focuses on chronic versus acute cytokine action, cytokine concentrations, and cytokine milieu from the perspective of the pancreatic islet in T2D. We conclude that new cytokine models may be needed to reflect the pathophysiology of T2D more effectively than what are currently employed.

Hypothalamic inflammation in the control of metabolic function

Diet-induced obesity leads to devastating and common chronic diseases, fueling ongoing interest in determining new mechanisms underlying both obesity and its consequences. It is now well known that chronic overnutrition produces a unique form of inflammation in peripheral insulin target tissues, and efforts to limit this inflammation have met with some success in preserving insulin sensitivity in obese individuals. Recently, the activation of inflammatory pathways by dietary excess has also been observed among cells located in the mediobasal hypothalamus, a brain area that exerts central control over peripheral glucose, fat, and energy metabolism. Here we review progress in the field of diet-induced hypothalamic inflammation, drawing key distinctions between metabolic inflammation in the hypothalamus and that occurring in peripheral tissues. We focus on specific stimuli of the inflammatory response, the roles of individual hypothalamic cell types, and the links between hypothalamic inflammation and metabolic function under normal and pathophysiological circumstances. Finally, we explore the concept of controlling hypothalamic inflammation to mitigate metabolic disease.

Damage-associated molecular patterns and their pathological relevance in diabetes mellitus

Diabetes, a group of metabolic and age-related diseases, is a major global health problem, the incidence of which has increased dramatically in recent decades. Type 1 diabetes mellitus (T1DM) is a complex, T cell-mediated autoimmune disease characterized by immune cell infiltration and chronic inflammation in the islets of Langerhans. Type 2 diabetes mellitus (T2DM) is a complex metabolic disease characterized by hyperglycemia (high blood sugar) resulting from insulin resistance and β-cell dysfunction. The involvement of inflammatory processes, such as immune cell infiltration, and chronic inflammation in the pathogenesis of diabetes is less well understood in T2DM than in T1DM. However, studies conducted in the past decade have shown a strong link between inflammation and metabolic dysfunction. They have also shown that chronic inflammation plays a key role in the pathogenesis of both T1DM and T2DM. Two immunological factors commonly contribute to the pathogenesis of diabetes: the activation of inflammasomes and the release of proinflammatory cytokines in response to damage-associated molecular patterns (DAMPs). Inflammasomes are intracellular multiprotein molecular platforms. DAMPs act as endogenous danger signals. Here, we review current research on the function(s) of inflammasomes and DAMPs and discuss their pathological relevance and therapeutic implications in diabetes.

Moderate calorie restriction to achieve normal weight reverses β-cell dysfunction in diet-induced obese mice: involvement of autophagy

Background

Severe calorie restriction (CR) is shown to improve or even reverse β-cell dysfunction in patients with obesity and type 2 diabetes mellitus. However, whether mild to moderate CR can reverse β-cell dysfunction induced by obesity and the underlying mechanism remain unclear. Autophagy plays an important role in maintaining mass, architecture and function of β-cells. While the impact of CR on β-cell autophagy is unknown. This study aims to investigate the effects of moderate CR on β-cell function and autophagy activity in diet-induced obese (DIO) mice.

Methods

DIO C57BL/6 mice were subjected to 3 weeks of switching to normal chow (HF → NC group) or normal chow with 40 % CR (HF → NC CR group). Then hematoxylin-eosin and immunohistochemistry staining were performed to observe β-cell morphology. β-cell function was evaluated by intraperitoneal glucose tolerance test in vivo and static GSIS (glucose-stimulated insulin secretion) in isolated islets. β-cell autophagy activity was determined by transmission electron microscope and western blot.

Results

In the HF → NC CR group, CR normalized body weights, completely restored glucose tolerance, early-phase and second-phase insulin secretion, insulin sensitivity, and islet size. CR also normalized insulin content and glucose-stimulated insulin secretion in isolated islets in vitro. Furthermore, β-cell autophagy level was increased in the HF → NC CR group, but AMPK phosphorylation remained unchanged. Although HF → NC mice achieved moderate weight loss and normal glucose tolerance, their insulin secretion was not improved compared with obese control mice, and additionally, β-cell autophagy was not activated in these mice.

Conclusions

Moderate (40 %) CR to achieve normal weight reversed β-cell dysfunction and insulin resistance, and restored glucose homeostasis in DIO mice. Furthermore, the up-regulation of β-cell autophagy may play a role in this process, independent of AMPK activation.

IL-1 family members in the pathogenesis and treatment of metabolic disease: Focus on adipose tissue inflammation and insulin resistance

Obesity is characterized by a chronic, low-grade inflammation that contributes to the development of insulin resistance and type 2 diabetes. Cytokines and chemokines produced by immunocompetent cells influence local as well as systemic inflammation and are therefore critical contributors to the pathogenesis of type 2 diabetes. Hence, cytokines that modulate inflammatory responses are emerging as potential targets for intervention and treatment of the metabolic consequences of obesity. The interleukin-1 (IL-1) family of cytokines and receptors are key mediators of innate inflammatory responses and exhibit both pro- and anti-inflammatory functions. During the last decades, mechanistic insights into how the IL-1 family affects the initiation and progression of obesity-induced insulin resistance have increased significantly. Here, we review the current knowledge and understanding, with emphasis on the therapeutic potential of individual members of the IL-1 family of cytokines for improving insulin sensitivity in patients with diabetes.

Early initiation of low-level parenteral dextrose induces an accelerated diabetic phenotype in septic C57BL/6J mice

Development of hyperglycemia during sepsis is associated with increased morbidity and mortality. Nutritional support is common practice in the intensive care unit, but the metabolic effects are not well understood. The purpose of this study is to determine the effect of early low-level calorie provision on the development of hyperglycemia in a clinically relevant murine model of sepsis. C57BL/6J mice underwent femoral arterial and venous catheterization followed by cecal ligation and puncture (CLP) or sham surgery and low-dose intravenous dextrose or saline infusion. Blood glucose, plasma insulin, and cytokines were measured after 24 h. Additional septic mice underwent hyperinsulinemic-euglycemic clamps or received intravenous insulin concurrent with dextrose to determine whole-body insulin sensitivity and test the efficacy of insulin to reverse hyperglycemia. Neither dextrose infusion nor CLP alone induced hyperglycemia. Early initiation of low-level dextrose in septic mice produced a variable glycemic response: 49% maintained euglycemia (blood glucose < 200) and 27% developed severe hyperglycemia (blood glucose ≥ 600). Hyperglycemia was associated with increased inflammation and reduced insulin secretion and sensitivity compared with control mice or CLP mice maintaining euglycemia. Insulin prevented the progression to severe hyperglycemia but was ineffective in reestablishing glycemic control once hyperglycemia had developed. In conclusion, early initiation of clinically relevant low-level dextrose (∼ 20% daily caloric requirements) precipitated hyperglycemia akin to an acute diabetic phenotype in septic mice characterized by decreased insulin sensitivity, decreased insulin secretion, and an increased inflammatory response.

Monocytes from patients with rheumatoid arthritis and type 2 diabetes mellitus display an increased production of interleukin (IL)-1β via the nucleotide-binding domain and leucine-rich repeat containing family pyrin 3(NLRP3)-inflammasome activation: a possible implication for therapeutic decision in these patients

A better understanding about the mechanisms involved in the pathogenesis of type 2 diabetes mellitus (T2D) showed that inflammatory cytokines such as tumour necrosis factor (TNF) and interleukin (IL)-1β play a pivotal role, mirroring data largely reported in rheumatoid arthritis (RA). IL-1β is produced mainly by monocytes (MO), and hyperglycaemia may be able to modulate, in the cytoplasm of these cells, the assembly of a nucleotide-binding domain and leucine-rich repeat containing family pyrin (NLRP3)-inflammosome, a cytosolic multi-protein platform where the inactive pro-IL-1β is cleaved into active form, via caspase-1 activity. In this paper, we evaluated the production of IL-1 β and TNF, in peripheral blood MO of patients affected by RA or T2D or both diseases, in order to understand if an alteration of the glucose metabolism may influence their proinflammatory status. Our data showed, after 24 h of incubation with different glucose concentrations, a significantly increased production of IL-1β and TNF in all evaluated groups when compared with healthy controls. However, a significant increase of IL-1β secretion by T2D/RA was observed when compared with other groups. The analysis of relative mRNA expression confirmed these data. After 24 h of incubation with different concentrations of glucose, our results showed a significant increase in NLRP3 expression. In this work, an increased production of IL-1β by MO obtained from patients affected by both RA and T2D via NLRP3-inflammasome activation may suggest a potential IL-1β targeted therapy in these patients.

Manganese-mediated MRI signals correlate with functional β-cell mass during diabetes progression

Diabetes diagnostic therapy and research would strongly benefit from noninvasive accurate imaging of the functional β-cells in the pancreas. Here, we developed an analysis of functional β-cell mass (BCM) by measuring manganese (Mn(2+)) uptake kinetics into glucose-stimulated β-cells by T1-weighted in vivo Mn(2+)-mediated MRI (MnMRI) in C57Bl/6J mice. Weekly MRI analysis during the diabetes progression in mice fed a high-fat/high-sucrose diet (HFD) showed increased Mn(2+)-signals in the pancreas of the HFD-fed mice during the compensation phase, when glucose tolerance and glucose-stimulated insulin secretion (GSIS) were improved and BCM was increased compared with normal diet-fed mice. The increased signal was only transient; from the 4th week on, MRI signals decreased significantly in the HFD group, and the reduced MRI signal in HFD mice persisted over the whole 12-week experimental period, which again correlated with both impaired glucose tolerance and GSIS, although BCM remained unchanged. Rapid and significantly decreased MRI signals were confirmed in diabetic mice after streptozotocin (STZ) injection. No long-term effects of Mn(2+) on glucose tolerance were observed. Our optimized MnMRI protocol fulfills the requirements of noninvasive MRI analysis and detects already small changes in the functional BCM.

Is interleukin-1β a culprit in macrophage-adipocyte crosstalk in obesity?

Adipose tissue remodeling occurs in obesity, characterized by adipocyte hypertrophy and increased infiltration of macrophages which also shift to a proinflammatory phenotype. Factors derived from these macrophages significantly alter adipocyte function, such as repressing adipogenesis, inducing inflammatory response and desensitizing insulin action. As macrophages produce a cocktail of inflammatory signals, identifying the key factors that mediate the detrimental effects may offer effective therapeutic targets. IL-1β, a major cytokine produced largely by macrophages, is implicated in the development of obesity-associated insulin resistance. In this article, we discuss recent advances in our understanding of the role of IL-1β in macrophage-adipocyte crosstalk in obesity. IL-1β impairs insulin sensitivity in adipose tissue by inhibition of insulin signal transduction. Blocking the activity of IL-1β, its receptor binding or production improves insulin signaling and action in human adipocytes. This is in parallel with a reduction in macrophage-stimulated proinflammatory profile and lipolysis. Targeting IL-1β may be beneficial for protecting against obesity-related insulin resistance at the tissue and systemic levels.

IL-1 mediates amyloid-associated islet dysfunction and inflammation in human islet amyloid polypeptide transgenic mice

AIMS/HYPOTHESIS

Aggregation of islet amyloid polypeptide (IAPP) to form amyloid contributes to beta cell dysfunction in type 2 diabetes. Human but not non-amyloidogenic rodent IAPP induces islet macrophage proIL-1β synthesis. We evaluated the effect of IL-1 receptor antagonist (IL-1Ra) on islet inflammation and dysfunction in a mouse model of type 2 diabetes with amyloid formation.

METHODS

Lean and obese male mice (A/a or A(vy)/A at the agouti locus, respectively) with or without beta cell human IAPP expression (hIAPP(Tg/0)) were treated with PBS or IL-1Ra (50 mg kg(-1) day(-1)) from 16 weeks of age. Intraperitoneal glucose and insulin tolerance tests were performed after 8 weeks. Pancreases were harvested for histology and gene expression analysis.

RESULTS

Aggregation of human IAPP was associated with marked upregulation of proinflammatory gene expression in islets of obese hIAPP(Tg/0) mice, together with amyloid deposition and fasting hyperglycaemia. IL-1Ra improved glucose tolerance and reduced plasma proinsulin:insulin in both lean and obese hIAPP(Tg/0) mice with no effect on insulin sensitivity. The severity and prevalence of islet amyloid was reduced by IL-1Ra in lean hIAPP (Tg/0) mice, suggesting a feed-forward mechanism by which islet inflammation promotes islet amyloid at the early stages of disease. IL-1Ra limited Il1a, Il1b, Tnf and Ccl2 expression in islets from obese hIAPP(Tg/0) mice, suggesting an altered islet inflammatory milieu.

CONCLUSIONS/INTERPRETATION

These data provide the first in vivo evidence—using a transgenic mouse model with amyloid deposits resembling those found in human islets—that IAPP-induced beta cell dysfunction in type 2 diabetes may be mediated by IL-1. Anti-IL-1 therapies may limit islet inflammation and dysfunction associated with amyloid formation.

Interactions between differential fatty acids and inflammatory stressors-impact on metabolic health

Current interest in obesity has established a clear link between diets high in fat and metabolic complications such as Type 2 Diabetes. Dietary fats and their metabolites act as stressors to induce a pro-inflammatory immune response which dysregulates many essential metabolic functions. Recent research suggests that different dietary fats may have varying inflammatory potentials. However the molecular mechanisms involved in the cross talk between dietary fat composition and the 'immuno-metabolism' remain enigmatic. It is probable that lipids, and their derivatives, differentially regulate IL-1β activation and inflammatory signaling via the NLRP3 inflammasome complex. Also from the translational perspective, certain nutrient sensitive genotypes and potential gene nutrient interactions offer the possibility to reduce inflammation through personalized nutrition approaches.

Natural history of β-cell adaptation and failure in type 2 diabetes

Type 2 diabetes mellitus (T2D) is a complex disease characterized by β-cell failure in the setting of insulin resistance. The current evidence suggests that genetic predisposition, and environmental factors can impair the capacity of the β-cells to respond to insulin resistance and ultimately lead to their failure. However, genetic studies have demonstrated that known variants account for less than 10% of the overall estimated T2D risk, suggesting that additional unidentified factors contribute to susceptibility of this disease. In this review, we will discuss the different stages that contribute to the development of β-cell failure in T2D. We divide the natural history of this process in three major stages: susceptibility, β-cell adaptation and β-cell failure, and provide an overview of the molecular mechanisms involved. Further research into mechanisms will reveal key modulators of β-cell failure and thus identify possible novel therapeutic targets and potential interventions to protect against β-cell failure.

The interleukin-1 receptor antagonist anakinra improves endothelial dysfunction in streptozotocin-induced diabetic rats

Background

Endothelial dysfunction is a crucial early phenomenon in vascular diseases linked to diabetes mellitus and associated to enhanced oxidative stress. There is increasing evidence about the role for pro-inflammatory cytokines, like interleukin-1β (IL-1β), in developing diabetic vasculopathy. We aimed to determine the possible involvement of this cytokine in the development of diabetic endothelial dysfunction, analysing whether anakinra, an antagonist of IL-1 receptors, could reduce this endothelial alteration by interfering with pro-oxidant and pro-inflammatory pathways into the vascular wall.

Results

In control and two weeks evolution streptozotocin-induced diabetic rats, either untreated or receiving anakinra, vascular reactivity and NADPH oxidase activity were measured, respectively, in isolated rings and homogenates from mesenteric microvessels, while nuclear factor (NF)-κB activation was determined in aortas. Plasma levels of IL-1β and tumor necrosis factor (TNF)-α were measured by ELISA. In isolated mesenteric microvessels from control rats, two hours incubation with IL-1β (1 to 10 ng/mL) produced a concentration-dependent impairment of endothelium-dependent relaxations, which were mediated by enhanced NADPH oxidase activity via IL-1 receptors. In diabetic rats treated with anakinra (100 or 160 mg/Kg/day for 3 or 7 days before sacrifice) a partial improvement of diabetic endothelial dysfunction occurred, together with a reduction of vascular NADPH oxidase and NF-κB activation. Endothelial dysfunction in diabetic animals was also associated to higher activities of the pro-inflammatory enzymes cyclooxygenase (COX) and the inducible isoform of nitric oxide synthase (iNOS), which were markedly reduced after anakinra treatment. Circulating IL-1β and TNF-α levels did not change in diabetic rats, but they were lowered by anakinra treatment.

Conclusions

In this short-term model of type 1 diabetes, endothelial dysfunction is associated to an IL-1 receptor-mediated activation of vascular NADPH oxidase and NF-κB, as well as to vascular inflammation. Moreover, endothelial dysfunction, vascular oxidative stress and inflammation were reduced after anakinra treatment. Whether this mechanism can be extrapolated to a chronic situation or whether it may apply to diabetic patients remain to be established. However, it may provide new insights to further investigate the therapeutic use of IL-1 receptor antagonists to obtain vascular benefits in patients with diabetes mellitus and/or atherosclerosis.

NR4A1 is associated with chronic low-grade inflammation in patients with type 2 diabetes

Type 2 diabetes (T2D) is a common disorder characterized by chronic low-grade inflammation. In the present study, the expression levels of nuclear receptor subfamily 4 group A member 1 (NR4A1) and the correlation with inflammatory cytokine production and free fatty acids (FFAs) in patients with T2D and healthy participants were investigated. NR4A1 expression levels in peripheral blood mononuclear cells (PBMCs) from patients with T2D (n=30) and healthy controls (n=34) were analyzed. In addition, the levels of fasting blood glucose (FBG), fasting plasma insulin (FIN), FFAs, total cholesterol (TC), triglyceride (TG), high-density lipoprotein-cholesterol (HDL-C) and low-density lipoprotein-cholesterol (LDL-C) were analyzed, and the homeostasis model assessment (HOMA) was used to estimate the insulin resistance (IR). Additionally, PBMCs from healthy subjects were cultured with or without 250 μM palmitic acid (PA). Levels of NR4A1, tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the PBMCs were also analyzed. The basal expression levels of NR4A1, TNF-α and IL-6 were higher in the T2D patients when compared with the controls. In addition, the levels of FFAs, TG and LDL-C, as well as the HOMA-IR, were higher in T2D patients. Furthermore, NR4A1 expression was demonstrated to positively correlate with the HOMA-IR and the levels of FFAs, TNF-α, IL-6, FIN and FBG. Furthermore, 250 μM PA stimulation was shown to increase NR4A1 expression and the secretion of inflammatory cytokines in the cultured PBMCs. Therefore, increased NR4A1 expression levels are correlated with a chronic low-grade inflammatory state and the disorder of lipid metabolism in patients with T2D.

Preclinical efficacy and safety of an anti-IL-1β vaccine for the treatment of type 2 diabetes

Neutralization of the inflammatory cytokine interleukin-1β (IL-1β) is a promising new strategy to prevent the β-cell destruction, which leads to type 2 diabetes. Here, we describe the preclinical development of a therapeutic vaccine against IL-1β consisting of a detoxified version of IL-1β chemically cross-linked to virus-like particles of the bacteriophage Qβ. The vaccine was well tolerated and induced robust antibody responses in mice, which neutralized the biological activity of IL-1β, as shown both in cellular assays and in challenge experiments in vivo. Antibody titers were long lasting but reversible over time and not associated with the development of potentially harmful T cell responses against IL-1β. Neutralization of IL-1β by vaccine-induced antibodies had no influence on the immune responses of mice to Listeria monocytogenes and Mycobacterium tuberculosis. In a diet-induced model of type 2 diabetes, immunized mice showed improved glucose tolerance, which was mediated by improved insulin secretion by pancreatic β-cells. Hence, immunization with IL-1β conjugated to virus-like particles has the potential to become a safe, efficacious, and cost-effective therapy for the prevention and long-term treatment of type 2 diabetes.

Knock-down of IL-1Ra in obese mice decreases liver inflammation and improves insulin sensitivity

Interleukin 1 Receptor antagonist (IL-1Ra) is highly elevated in obesity and is widely recognized as an anti-inflammatory cytokine. While the anti-inflammatory role of IL-1Ra in the pancreas is well established, the role of IL-1Ra in other insulin target tissues and the contribution of systemic IL-1Ra levels to the development of insulin resistance remains to be defined. Using antisense knock down of IL-1Ra in vivo, we show that normalization of IL-1Ra improved insulin sensitivity due to decreased inflammation in the liver and improved hepatic insulin sensitivity and these effects were independent of changes in body weight. A similar effect was observed in IL1-R1 KO mice, suggesting that at high concentrations of IL-1Ra typically observed in obesity, IL-1Ra can contribute to the development of insulin resistance in a mechanism independent of IL-1Ra binding to IL-1R1. These results demonstrate that normalization of plasma IL-1Ra concentration improves insulin sensitivity in diet- induced obese mice.

IL-1 signaling in obesity-induced hepatic lipogenesis and steatosis

Non-alcoholic fatty liver disease is prevalent in human obesity and type 2 diabetes, and is characterized by increases in both hepatic triglyceride accumulation (denoted as steatosis) and expression of pro-inflammatory cytokines such as IL-1β. We report here that the development of hepatic steatosis requires IL-1 signaling, which upregulates Fatty acid synthase to promote hepatic lipogenesis. Using clodronate liposomes to selectively deplete liver Kupffer cells in ob/ob mice, we observed remarkable amelioration of obesity-induced hepatic steatosis and reductions in liver weight, triglyceride content and lipogenic enzyme expressions. Similar results were obtained with diet-induced obese mice, although visceral adipose tissue macrophage depletion also occurred in response to clodronate liposomes in this model. There were no differences in the food intake, whole body metabolic parameters, serum β-hydroxybutyrate levels or lipid profiles due to clodronate-treatment, but hepatic cytokine gene expressions including IL-1β were decreased. Conversely, treatment of primary mouse hepatocytes with IL-1β significantly increased triglyceride accumulation and Fatty acid synthase expression. Furthermore, the administration of IL-1 receptor antagonist to obese mice markedly reduced obesity-induced steatosis and hepatic lipogenic gene expression. Collectively, our findings suggest that IL-1β signaling upregulates hepatic lipogenesis in obesity, and is essential for the induction of pathogenic hepatic steatosis in obese mice.

NR4A1 is associated with chronic low-grade inflammation in patients with type 2 diabetes

Type 2 diabetes (T2D) is a common disorder characterized by chronic low-grade inflammation. In the present study, the expression levels of nuclear receptor subfamily 4 group A member 1 (NR4A1) and the correlation with inflammatory cytokine production and free fatty acids (FFAs) in patients with T2D and healthy participants were investigated. NR4A1 expression levels in peripheral blood mononuclear cells (PBMCs) from patients with T2D (n=30) and healthy controls (n=34) were analyzed. In addition, the levels of fasting blood glucose (FBG), fasting plasma insulin (FIN), FFAs, total cholesterol (TC), triglyceride (TG), high-density lipoprotein-cholesterol (HDL-C) and low-density lipoprotein-cholesterol (LDL-C) were analyzed, and the homeostasis model assessment (HOMA) was used to estimate the insulin resistance (IR). Additionally, PBMCs from healthy subjects were cultured with or without 250 μM palmitic acid (PA). Levels of NR4A1, tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the PBMCs were also analyzed. The basal expression levels of NR4A1, TNF-α and IL-6 were higher in the T2D patients when compared with the controls. In addition, the levels of FFAs, TG and LDL-C, as well as the HOMA-IR, were higher in T2D patients. Furthermore, NR4A1 expression was demonstrated to positively correlate with the HOMA-IR and the levels of FFAs, TNF-α, IL-6, FIN and FBG. Furthermore, 250 μM PA stimulation was shown to increase NR4A1 expression and the secretion of inflammatory cytokines in the cultured PBMCs. Therefore, increased NR4A1 expression levels are correlated with a chronic low-grade inflammatory state and the disorder of lipid metabolism in patients with T2D.

Interleukin-1β mediates macrophage-induced impairment of insulin signaling in human primary adipocytes

Adipose tissue expansion during obesity is associated with increased macrophage infiltration. Macrophage-derived factors significantly alter adipocyte function, inducing inflammatory responses and decreasing insulin sensitivity. Identification of the major factors that mediate detrimental effects of macrophages on adipocytes may offer potential therapeutic targets. IL-1β, a proinflammatory cytokine, is suggested to be involved in the development of insulin resistance. This study investigated the role of IL-1β in macrophage-adipocyte cross-talk, which affects insulin signaling in human adipocytes. Using macrophage-conditioned (MC) medium and human primary adipocytes, we examined the effect of IL-1β antagonism on the insulin signaling pathway. Gene expression profile and protein abundance of insulin signaling molecules were determined, as was the production of proinflammatory cytokine/chemokines. We also examined whether IL-1β mediates MC medium-induced alteration in adipocyte lipid storage. MC medium and IL-1β significantly reduced gene expression and protein abundance of insulin signaling molecules, including insulin receptor substrate-1, phosphoinositide 3-kinase p85α, and glucose transporter 4 and phosphorylation of Akt. In contrast, the expression and release of the proinflammatory markers, including IL-6, IL-8, monocyte chemotactic protein-1, and chemokine (C-C motif) ligand 5 by adipocytes were markedly increased. These changes were significantly reduced by blocking IL-1β activity, its receptor binding, or its production by macrophages. MC medium-inhibited expression of the adipogenic factors and -stimulated lipolysis was also blunted with IL-1β neutralization. We conclude that IL-1β mediates, at least in part, the effect of macrophages on insulin signaling and proinflammatory response in human adipocytes. Blocking IL-1β could be beneficial for preventing obesity-associated insulin resistance and inflammation in human adipose tissue.

How does high-fat diet induce adipose tissue fibrosis?

Obesity is one of the most serious pandemic health problems in modern society and the predisposing factor for the type 2 diabetes mellitus. Chronic low-grade inflammation mediates the pathogenesis of insulin resistance in obese humans and rodents, and white adipose tissue is one of major tissues to modulate inflammation. Obese humans and rodents show dynamic changes of immunocellular compositions in white adipose tissue to induce inflammatory responses. Innate and adaptive immune responses mainly mediated by macrophages and T cells contribute insulin resistance. Recently, it has been shown that adipose tissue fibrosis is also enhanced in obese humans and rodents along with inflammatory responses, and suppression of adipose tissue fibrosis shows improved insulin sensitivity in rodent models, suggesting that adipose tissue fibrosis is involved in insulin resistance.

MST1 is a key regulator of beta cell apoptosis and dysfunction in diabetes

Apoptotic cell death is a hallmark of the loss of insulin producing beta-cells in all forms of diabetes mellitus. Current treatment fails to halt the decline in functional beta-cell mass. Strategies to prevent beta-cell apoptosis and dysfunction are urgently needed. Here, we identified Mammalian Sterile 20-like kinase 1 (MST1) as a critical regulator of apoptotic beta-cell death and function. MST1 was strongly activated in beta-cells under diabetogenic conditions and correlated with beta-cell apoptosis. MST1 specifically induced the mitochondrial-dependent pathway of apoptosis in beta-cells through up-regulation of the BH3-only protein Bim. MST1 directly phosphorylated PDX1 at Thr11, resulting in its ubiquitination, degradation and impaired insulin secretion. Mst1 deficiency completely restored normoglycemia, beta-cell function and survival in vitro and in vivo. We show MST1 as novel pro-apoptotic kinase and key mediator of apoptotic signaling and beta-cell dysfunction, which may serve as target for the development of novel therapies for diabetes.

Toll-like receptors and NLRP3 as central regulators of pancreatic islet inflammation in type 2 diabetes

The global health and economic burden of type 2 diabetes (T2D) has reached staggering proportions. Current projections estimate that 592 million people will have diabetes by 2035. T2D-which comprises 90% of cases-is a complex disease, in most cases resulting from a combination of predisposing genes and an unhealthy environment. Clinical onset of the disease occurs when pancreatic β cells fail in the face of insulin resistance. It has long been appreciated that chronic activation of the innate immune system is associated with T2D, and many organs critical to the regulation of glucose homeostasis show signs of a chronic inflammatory process, including the pancreatic islets of Langerhans. Recent clinical trials using IL-1-targeting agents have confirmed that inflammation contributes to β-cell failure in humans with T2D. However, little is known about the nature of the pro-inflammatory response within the islet, and there is considerable debate about the triggers for islet inflammation, which may be systemically derived and/or tissue-specific. In this review, we present evidence that Toll-like receptors 2 and 4 and the NLRP3 (Nucleotide-binding oligomerization domain, Leucine-rich Repeat and Pyrin domain containing 3) inflammasome are triggers for islet inflammation in T2D and propose that the activation of macrophages by these triggers mediates islet endocrine cell dysfunction. Therapeutically targeting these receptors may improve hyperglycemia and protect the β cell in T2D.

Metabolic syndrome and insulin resistance: underlying causes and modification by exercise training

Metabolic syndrome (MS) is a collection of cardiometabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia. Although there has been significant debate regarding the criteria and concept of the syndrome, this clustering of risk factors is unequivocally linked to an increased risk of developing type 2 diabetes and cardiovascular disease. Regardless of the true definition, based on current population estimates, nearly 100 million have MS. It is often characterized by insulin resistance, which some have suggested is a major underpinning link between physical inactivity and MS. The purpose of this review is to: (i) provide an overview of the history, causes and clinical aspects of MS, (ii) review the molecular mechanisms of insulin action and the causes of insulin resistance, and (iii) discuss the epidemiological and intervention data on the effects of exercise on MS and insulin sensitivity.

Immune cells and metabolic dysfunction

Throughout evolution, effective nutrient sensing and control of systemic energy homeostasis have relied on a close physical and functional interaction between immune and metabolically active cells. However, in today's obesogenic environment, this fine-tuned immunometabolic interface is perturbed. As a consequence, chronic inflammatory conditions and aberrant activation of immune cells have emerged as key features of obesity-related metabolic disorders, including insulin resistance, cardiovascular complications, and type 2 diabetes, whereas a major research focus has been placed on the adipocyte-macrophage interaction in the context of metabolic dysfunction; recent studies have not only expanded the scope of relevant immune cells in this setting but also highlight the impact of distinct metabolic organs, including the liver, on immunometabolic control, metabolic disease development, and potential anti-inflammatory therapeutic options in obesity-driven pathologies. This review will thus summarize recent progress in this emerging area of metabolic research.

Macrophages and islet inflammation in type 2 diabetes

Type 2 diabetes (T2D) is characterized by insulin resistance and impaired insulin secretion from pancreatic β-cells. Inflammatory cytokines, including tumour necrosis factor-α (TNF-α), have been shown to promote insulin resistance, and altered expression of cytokines (adipokines) in obese adipose tissue is thought to be an important link between obesity and insulin resistance. It is also becoming clear that inflammation plays a key role in the development of β-cell dysfunction. Inflammatory changes, including accumulation of macrophages, have been documented in T2D islets. Moreover, therapeutic inhibition of interleukin-1β (IL-1β) ameliorates β-cell dysfunction in humans. This review summarizes current understanding of the molecular mechanisms underlying inflammation within islets and its relation to β-cell dysfunction in T2D. A particular focus is on the physiological and pathological functions of macrophages within islets.

NLRP3 and IL-1β in macrophages as critical regulators of metabolic diseases

The activation of the NLRP3 inflammasome leads to the autocleavage and activation of caspase-1. Caspase-1 cleaves several substrates, including the pro-inflammatory cytokine IL-1β. Inflammation, in particular IL-1β, has long been associated with the progression of metabolic disorders, and recent evidence suggests that the NLRP3 inflammasome plays a critical role in this inflammation. This review concentrates on the activation of NLRP3 during the development of metabolic disorders and the effect this activation has on the inflammatory state as well as the metabolic state of the cell.

Circulating levels of IL-1B+IL-6 cause ER stress and dysfunction in islets from prediabetic male mice

Elevated levels of circulating proinflammatory cytokines are associated with obesity and increased risk of type 2 diabetes, but the mechanism is unknown. We tested whether proinflammatory cytokines IL-1B+IL-6 at low picogram per milliliter concentrations (consistent with serum levels) could directly trigger pancreatic islet dysfunction. Overnight exposure to IL-1B+IL-6 in islets isolated from normal mice and humans disrupted glucose-stimulated intracellular calcium responses; cytokine-induced effects were more severe among islets from prediabetic db/db mice that otherwise showed no signs of dysfunction. IL-1B+IL-6 exposure reduced endoplasmic reticulum (ER) calcium storage, activated ER stress responses (Nos2, Bip, Atf4, and Ddit3 [CHOP]), impaired glucose-stimulated insulin secretion, and increased cell death only in islets from prediabetic db/db mice. Furthermore, we found increased serum levels of IL-1B and IL-6 in diabetes-prone mice at an age before hyperglycemia was exhibited, suggesting that low-grade systemic inflammation develops early in the disease process. In addition, we implanted normal outbred and inbred mice with subcutaneous osmotic mini-pumps containing IL-1B+IL-6 to mimic the serum increases found in prediabetic db/db mice. Both IL-1B and IL-6 were elevated in serum from cytokine-pump mice, but glucose tolerance and blood glucose levels did not differ from controls. However, when compared with controls, isolated islets from cytokine-pump mice showed deficiencies in calcium handling and insulin secretion that were similar to observations with islets exposed to cytokines in vitro. These findings provide proof of principle that low-grade systemic inflammation is present early in the development of type 2 diabetes and can trigger ER stress-mediated islet dysfunction that can lead to islet failure.

Connecting type 1 and type 2 diabetes through innate immunity

The escalating epidemic of obesity has driven the prevalence of both type 1 and 2 diabetes mellitus to historically high levels. Chronic low-grade inflammation, which is present in both type 1 and type 2 diabetics, contributes to the pathogenesis of insulin resistance. The accumulation of activated innate immune cells in metabolic tissues results in release of inflammatory mediators, in particular, IL-1β and TNFα, which promote systemic insulin resistance and β-cell damage. In this article, we discuss the central role of innate immunity and, in particular, the macrophage in insulin sensitivity and resistance, β-cell damage, and autoimmune insulitis. We conclude with a discussion of the therapeutic implications of this integrated understanding of diabetic pathology.

The DPP-4 inhibitor linagliptin restores β-cell function and survival in human isolated islets through GLP-1 stabilization

CONTEXT

Inhibition of dipeptidyl peptidase-4 (DPP-4) is a potent strategy to increase glucose-dependent insulinotropic polypeptide and glucagon like peptide 1 (GLP-1) induced insulin secretion in diabetes. It is important to know whether new drugs approved for the treatment of type 2 diabetes have direct effects on the β-cell.

OBJECTIVE

Herein we investigated the effect of linagliptin, a novel DPP-4 inhibitor, on β-cell function and survival.

DESIGN

Human islets were exposed to a diabetic milieu (11.1-33.3 mM glucose, 0.5 mM palmitate, the mixture of 2 ng/mL IL-1β+1000 U/mL interferon-γ, or 50 μM H₂O₂) with or without 500 ng/mL IL-1 receptor antagonist (IL-1Ra) or 30-50 nM linagliptin.

RESULTS

Linagliptin restored β-cell function and turnover, which was impaired when islets were exposed to elevated glucose, palmitate, cytokines, or H₂O₂. Pretreatment with IL-1Ra was similarly effective, except against H₂O₂ treatment. Nitrotyrosine concentrations in islet lysates, an indicator of oxidative stress, were highly elevated under diabetic conditions but not in islets treated with linagliptin or IL-1Ra. Linagliptin also reduced cytokine secretion and stabilized GLP-1 in islet supernatants.

CONCLUSIONS

We show that the novel DPP-4 inhibitor linagliptin protected from gluco-, lipo-, and cytokine-toxicity and stabilized active GLP-1 secreted from human islets. This provides a direct GLP-1 mediated protective effect of linagliptin on β-cell function and survival.

Exogenous glucose administration impairs glucose tolerance and pancreatic insulin secretion during acute sepsis in non-diabetic mice

Objectives

The development of hyperglycemia and the use of early parenteral feeding are associated with poor outcomes in critically ill patients. We therefore examined the impact of exogenous glucose administration on the integrated metabolic function of endotoxemic mice using our recently developed frequently sampled intravenous glucose tolerance test (FSIVGTT). We next extended our findings using a cecal ligation and puncture (CLP) sepsis model administered early parenteral glucose support.

Methods

Male C57BL/6J mice, 8-12 weeks, were instrumented with chronic indwelling arterial and venous catheters. Endotoxemia was initiated with intra-arterial lipopolysaccharide (LPS; 1 mg/kg) in the presence of saline or glucose infusion (100 µL/hr), and an FSIVGTT was performed after five hours. In a second experiment, catheterized mice underwent CLP and the impact of early parenteral glucose administration on glucose homeostasis and mortality was assessed over 24 hrs.

Measurements

And MAIN RESULTS: Administration of LPS alone did not impair metabolic function, whereas glucose administration alone induced an insulin sensitive state. In contrast, LPS and glucose combined caused marked glucose intolerance and insulin resistance and significantly impaired pancreatic insulin secretion. Similarly, CLP mice receiving parenteral glucose developed fulminant hyperglycemia within 18 hrs (all > 600 mg/dl) associated with increased systemic cytokine release and 40% mortality, whereas CLP alone (85 ± 2 mg/dL) or sham mice receiving parenteral glucose (113 ± 3 mg/dL) all survived and were not hyperglycemic. Despite profound hyperglycemia, plasma insulin in the CLP glucose-infused mice (3.7 ± 1.2 ng/ml) was not higher than sham glucose infused mice (2.1 ± 0.3 ng/ml).

Conclusions

The combination of parenteral glucose support and the systemic inflammatory response in the acute phase of sepsis induces profound insulin resistance and impairs compensatory pancreatic insulin secretion, leading to the development of fulminant hyperglycemia.

IL-1Ra and its delivery strategies: inserting the association in perspective

Interleukin-1 receptor antagonist (IL-1Ra) is a naturally occurring anti-inflammatory antagonist of interleukin-1 family of pro-inflammatory cytokines. The broad spectrum anti-inflammatory effects of IL-1Ra have been investigated against various auto-immune diseases such as diabetes mellitus, rheumatoid arthritis. Despite of its outstanding broad spectrum anti-inflammatory effects, IL-1Ra has short biological half-life (4-6 h) and to cope with this problem, up till now, many delivery strategies have been applied either to extend the half-life and/or prolong the steady-state sustained release of IL-1Ra from its target site. Here in our present paper, we have provided an overview of all approaches attempted to prolong the duration of therapeutic effects of IL-1Ra either by fusing IL-1Ra using fusion protein technology to extend the half-life and/or development of new dosage forms using various biodegradable polymers to prolong its steady-state sustained release at the site of administration. These approaches have been characterized by their intended impact on either in vitro release characteristics and/or pharmacokinetic and pharmacodynamic parameters of IL-1Ra. We have also compared these delivery strategies with each other on the basis of bioactivity of IL-1Ra after fusion with fusion protein partner and/or encapsulation with biodegradable polymer.

Mechanisms of obesity-induced inflammation and insulin resistance: insights into the emerging role of nutritional strategies

Obesity and associated chronic inflammation initiate a state of insulin resistance (IR). The secretion of chemoattractants such as MCP-1 and MIF and of cytokines IL-6, TNF-α, and IL-1β, draw immune cells including dendritic cells, T cells, and macrophages into adipose tissue (AT). Dysfunctional AT lipid metabolism leads to increased circulating free fatty acids, initiating inflammatory signaling cascades in the population of infiltrating cells. A feedback loop of pro-inflammatory cytokines exacerbates this pathological state, driving further immune cell infiltration and cytokine secretion and disrupts the insulin signaling cascade. Disruption of normal AT function is causative of defects in hepatic and skeletal muscle glucose homeostasis, resulting in systemic IR and ultimately the development of type 2 diabetes. Pharmaceutical strategies that target the inflammatory milieu may have some potential; however there are a number of safety concerns surrounding such pharmaceutical approaches. Nutritional anti-inflammatory interventions could offer a more suitable long-term alternative; whilst they may be less potent than some pharmaceutical anti-inflammatory agents, this may be advantageous for long-term therapy. This review will investigate obese AT biology, initiation of the inflammatory, and insulin resistant environment; and the mechanisms through which dietary anti-inflammatory components/functional nutrients may be beneficial.

Insulin signalling mechanisms for triacylglycerol storage

Insulin signalling is uniquely required for storing energy as fat in humans. While de novo synthesis of fatty acids and triacylglycerol occurs mostly in liver, adipose tissue is the primary site for triacylglycerol storage. Insulin signalling mechanisms in adipose tissue that stimulate hydrolysis of circulating triacylglycerol, uptake of the released fatty acids and their conversion to triacylglycerol are poorly understood. New findings include (1) activation of DNA-dependent protein kinase to stimulate upstream stimulatory factor (USF)1/USF2 heterodimers, enhancing the lipogenic transcription factor sterol regulatory element binding protein 1c (SREBP1c); (2) stimulation of fatty acid synthase through AMP kinase modulation; (3) mobilisation of lipid droplet proteins to promote retention of triacylglycerol; and (4) upregulation of a novel carbohydrate response element binding protein β isoform that potently stimulates transcription of lipogenic enzymes. Additionally, insulin signalling through mammalian target of rapamycin to activate transcription and processing of SREBP1c described in liver may apply to adipose tissue. Paradoxically, insulin resistance in obesity and type 2 diabetes is associated with increased triacylglycerol synthesis in liver, while it is decreased in adipose tissue. This and other mysteries about insulin signalling and insulin resistance in adipose tissue make this topic especially fertile for future research.

The hydrolase DDAH2 enhances pancreatic insulin secretion by transcriptional regulation of secretagogin through a Sirt1-dependent mechanism in mice

The role of dimethylarginine dimethylaminohydrolase 2 (DDAH2) in glucose metabolism is unknown. Here, we generated DDAH2 transgenic (Tg) mice. These mice had lower plasma glucose levels (60 min: 298±32 vs. 418±35 mg/dl; 120 min: 205±15 vs. 284±20 mg/dl) and higher insulin levels (15 min: 2.1±0.2 vs. 1.5±0.1 ng/ml; 30 min: 1.8±0.1 vs. 1.5±0.1 ng/ml) during intraperitoneal glucose tolerance tests when fed a high-fat diet (HFD) compared with HFD-fed wild-type (WT) mice. Glucose-stimulated insulin secretion (GSIS) was increased in Tg islets by 33%. Pancreatic asymmetrical dimethylarginine, nitric oxide, and oxidative stress levels were not correlated with improvements in insulin secretion in Tg mice. Secretagogin, an insulin vesicle docking protein, was up-regulated by 2.7-fold in Tg mice and in pancreatic MIN-6 cells overexpressing DDAH2. GSIS in MIN-6 cells was dependent on DDAH2-induced secretagogin expression. Pancreatic Sirt1, DDAH2, and secretagogin were down-regulated in HFD-fed WT mice by 70, 75, and 85%, respectively. Overexpression of Sirt1 overexpression by 3.9-fold increased DDAH2 and secretagogin expression in MIN-6 cells by 3.2- and 2.5-fold, respectively. DDAH2 overexpression improved GSIS in pancreas-specific Sirt1-deficient mice. In summary, the Sirt1/DDAH2/secretagogin pathway is a novel regulator of GSIS.

Sustained delivery of IL-1Ra from PF127-gel reduces hyperglycemia in diabetic GK-rats

Interleukin-1beta (IL-1β) is a major cause for induction of various inflammatory mechanisms that are decisively involved to provoke pathogenesis of type 2 diabetes mellitus (T2DM). Interleukin-1 receptor antagonist (IL-1Ra) a naturally occurring anti-inflammatory antagonist of IL-1β has been recently approved for treatment of T2DM but due to its short half-life, higher doses and frequent dosing intervals are required. Pluronic F-127 (PF127) has previously shown to prolong the release of various proteinous drugs and their serum half-lives. Subsequently, in our previous work, we developed a new dosage form of IL-1Ra using PF127 and investigated its in-vitro and in-vivo effects. Here in present work, we have extended this approach using diabetic Goto-kakizaki (GK) rats. We administered IL-1Ra loaded in PF127 gel subcutaneously for one month into GK rats. IL-1Ra loaded in PF127 gel exhibited a sustained and prolonged hypoglycemic effects on treated animals. Intraperitoneal glucose tolerance test (IPGTT) results showed that IL-1Ra loaded in PF127 gel increased glucose tolerance along with increased insulin sensitivity and β-cell’s secretory function in treated rats. Moreover, significant reduction in pro-insulin/insulin ratio, lipid profiles and interleukin 6 (IL-6) were also observed. Immunohistochemical analysis showed slight macrophages infiltration in pancreatic islets. Histochemical analysis revealed no PF127-induced alteration in the normal physiology of skin and kidney of treated animals. Hence, we concluded that IL-1Ra loaded in PF127 gel has potential to exhibit broad spectrum anti-inflammatory effects alleviating the symptoms of T2DM.

The adipocytokine Nampt and its product NMN have no effect on beta-cell survival but potentiate glucose stimulated insulin secretion

AIMS/HYPOTHESIS

Obesity is associated with a dysregulation of beta-cell and adipocyte function. The molecular interactions between adipose tissue and beta-cells are not yet fully elucidated. We investigated, whether or not the adipocytokine Nicotinamide phosphoribosyltransferase (Nampt) and its enzymatic product Nicotinamide mononucleotide (NMN), which has been associated with obesity and type 2 diabetes mellitus (T2DM) directly influence beta-cell survival and function.

METHODS

The effect of Nampt and NMN on viability of INS-1E cells was assessed by WST-1 assay. Apoptosis was measured by Annexin V/PI and TUNEL assay. Activation of apoptosis signaling pathways was evaluated. Adenylate kinase release was determined to assess cytotoxicity. Chronic and acute effects of the adipocytokine Nampt and its enzymatic product NMN on insulin secretion were assessed by glucose stimulated insulin secretion in human islets.

RESULTS

While stimulation of beta-cells with the cytokines IL-1β, TNFα and IFN-γ or palmitate significantly decreased viability, Nampt and NMN showed no direct effect on viability in INS-1E cells or in human islets, neither alone nor in the presence of pro-diabetic conditions (elevated glucose concentrations and palmitate or cytokines). At chronic conditions over 3 days of culture, Nampt and its product NMN had no effects on insulin secretion. In contrast, both Nampt and NMN potentiated glucose stimulated insulin secretion acutely during 1 h incubation of human islets.

CONCLUSION/INTERPRETATION

Nampt and NMN neither influenced beta-cell viability nor apoptosis but acutely potentiated glucose stimulated insulin secretion.

Metabolic syndrome and insulin resistance: underlying causes and modification by exercise training

Metabolic syndrome (MS) is a collection of cardiometabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia. Although there has been significant debate regarding the criteria and concept of the syndrome, this clustering of risk factors is unequivocally linked to an increased risk of developing type 2 diabetes and cardiovascular disease. Regardless of the true definition, based on current population estimates, nearly 100 million have MS. It is often characterized by insulin resistance, which some have suggested is a major underpinning link between physical inactivity and MS. The purpose of this review is to: (i) provide an overview of the history, causes and clinical aspects of MS, (ii) review the molecular mechanisms of insulin action and the causes of insulin resistance, and (iii) discuss the epidemiological and intervention data on the effects of exercise on MS and insulin sensitivity.

Adipokines mediate inflammation and insulin resistance

For many years, adipose tissue was considered as an inert energy storage organ that accumulates and stores triacylglycerols during energy excess and releases fatty acids in times of systemic energy need. However, over the last two decades adipose tissue depots have been established as highly active endocrine and metabolically important organs that modulate energy expenditure and glucose homeostasis. In rodents, brown adipose tissue plays an essential role in non-shivering thermogenesis and in energy dissipation that can serve to protect against diet-induced obesity. White adipose tissue collectively referred too as either subcutaneous or visceral adipose tissue is responsible for the secretion of an array of signaling molecules, termed adipokines. These adipokines function as classic circulating hormones to communicate with other organs including brain, liver, muscle, the immune system, and adipose tissue itself. The dysregulation of adipokines has been implicated in obesity, type 2 diabetes, and cardiovascular disease. Recently, inflammatory responses in adipose tissue have been shown as a major mechanism to induce peripheral tissue insulin resistance. Although leptin and adiponectin regulate feeding behavior and energy expenditure, these adipokines are also involved in the regulation of inflammatory responses. Adipose tissue secretes various pro- and anti-inflammatory adipokines to modulate inflammation and insulin resistance. In obese humans and rodent models, the expression of pro-inflammatory adipokines is enhanced to induce insulin resistance. Collectively, these findings have suggested that obesity-induced insulin resistance may result, at least in part, from an imbalance in the expression of pro- and anti-inflammatory adipokines. Thus we will review the recent progress regarding the physiological and molecular functions of adipokines in the obesity-induced inflammation and insulin resistance with perspectives on future directions.