Tumor necrosis factor alpha-induced pancreatic beta-cell insulin resistance is mediated by nitric oxide and prevented by 15-deoxy-Delta12,14-prostaglandin J2 and aminoguanidine. A role for peroxisome proliferator-activated receptor gamma activation and inos expression

Effects of the synbiotic composed of mangiferin and Lactobacillus reuteri 1-12 on type 2 diabetes mellitus rats

Many synbiotics are effective for the prevention and treatment of type 2 diabetes mellitus (T2DM). In the treatment of T2DM, synbiotics often regulate the composition of intestinal flora, which autoinducer-2 (AI-2) may play an important role. Whether the changes of intestinal flora are related to AI-2 during synbiotics treatment of T2DM is a topic worth studying. We elucidated the effects of synbiotic composed of mangiferin and Lactobacillus reuteri 1-12 (SML) on T2DM rats. Male Spraque-Dawley rats were injected intraperitoneally with streptozotocin (STZ) and randomly grouped. After that, biochemical parameters, intestinal flora, fecal AI-2, and intestinal colonization of L. reuteri were detected. The results showed that SML had a hypoglycemic effect and mitigated the organ lesions of the liver and pancreas. Also, SML regulated biochemical parameters such as short chain fatty acids (SCFAs), lipopolysaccharides (LPS), intercellular cell adhesion molecule-1 (ICAM-1), and tumor necrosis factor-α (TNF-α). On the other hand, the proportion of probiotics, such as Lactobacillus acidophilus, L. reuteri, Bifidobacterium pseudolongum, Lactobacillus murinus, and Lactobacillus johnsonii, were elevated by the treatment of SML. In addition, SML promoted the colonization and proliferation of L. reuteri in the gut. Another thing to consider was that AI-2 was positively correlated with the total number of OTUs sequences and SML boosted AI-2 in the gut. Taken together, these results supported that SML may modulate intestinal flora through AI-2 to treat T2DM. This study provided a novel alternative strategy for the treatment of T2DM in future.

Exercise tolls the bell for key mediators of low-grade inflammation in dysmetabolic conditions

Metabolic conditions share a common low-grade inflammatory milieu, which represents a key-factor for their ignition and maintenance. Exercise is instrumental for warranting systemic cardio-metabolic balance, owing to its regulatory effect on inflammation. This review explores the effect of physical activity in the modulation of sub-inflammatory framework characterizing dysmetabolic conditions. Regular exercise suppresses plasma levels of TNFα, IL-1β, FFAs and MCP-1, in dysmetabolic subjects. In addition, a single session of training increases the anti-inflammatory IL-10, IL-1 receptor antagonist (IL-1ra), and muscle-derived IL-6, mitigating low-grade inflammation. Resting IL-6 levels are decreased in trained-dysmetabolic subjects, compared to sedentary. On the other hand, the acute release of muscle-IL-6, after exercise, seems to exert a regulatory effect on the metabolic and inflammatory balance. In fact, muscle-released IL-6 is presumably implicated in fat loss and boosts plasma levels of IL-10 and IL-1ra. The improvement of adipose tissue functionality, following regular exercise, is also critical for the mitigation of sub-inflammation. This effect is likely mediated by muscle-released IL-15 and IL-6 and partly relies on the brown-shifting of white adipocytes, induced by exercise. In obese-dysmetabolic subjects, moderate training is shown to restore gut-microbiota health, and this mitigates the translocation of bacterial-LPS into bloodstream. Finally, regular exercise can lower plasma advanced glycated endproducts. The articulated physiology of circulating mediators and the modulating effect of the pathophysiological background, render the comprehension of the exercise-regulatory effect on sub-inflammation a key issue, in dysmetabolism.

Gut Microbiota as a Trigger for Metabolic Inflammation in Obesity and Type 2 Diabetes

The gut microbiota has been linked to the development of obesity and type 2 diabetes (T2D). The underlying mechanisms as to how intestinal microbiota may contribute to T2D are only partly understood. It becomes progressively clear that T2D is characterized by a chronic state of low-grade inflammation, which has been linked to the development of insulin resistance. Here, we review the current evidence that intestinal microbiota, and the metabolites they produce, could drive the development of insulin resistance in obesity and T2D, possibly by initiating an inflammatory response. First, we will summarize major findings about immunological and gut microbial changes in these metabolic diseases. Next, we will give a detailed view on how gut microbial changes have been implicated in low-grade inflammation. Lastly, we will critically discuss clinical studies that focus on the interaction between gut microbiota and the immune system in metabolic disease. Overall, there is strong evidence that the tripartite interaction between gut microbiota, host immune system and metabolism is a critical partaker in the pathophysiology of obesity and T2D.

Effects of Endurance Training on the Skeletal Muscle Nitric Oxide Metabolism in Insulin-Independent Type 2 Diabetic Men-A Pilot Study

BACKGROUND

Increases in the amount of inducible nitric oxide synthase (iNOS) protein and abnormal production of nitric oxide (NO) in skeletal muscle have been suggested to be associated with peripheral insulin resistance in patients with type 2 diabetes mellitus (T2DM). This pilot study analyzed whether a 3-month endurance training can affect iNOS protein and NO metabolite levels in the vastus lateralis muscle of insulin-independent T2DM men, thereby affecting the patients` glycemic control. Furthermore, serum molecules, which have been shown to activate iNOS protein expression in in vitro experiments, were quantified.

METHODS

Eight overweight/obese T2DM men (years = 61 ± 10) participated in the study. Muscle biopsies and venous blood collections were performed at T1 (6 weeks before training), T2 (1 week before training), and T3 (3 to 4 days after training). Protein contents (iNOS) were determined by Western blotting, nitrite concentrations by chemiluminescence, and serum molecule levels by enzyme-linked immunosorbent assay kits.

RESULTS

The training reduced iNOS protein contents significantly (T2-T3: approximately -31%, P = 0.018). Nitrite concentrations as well as fasting glucose and HbA1c decreased, but not significantly. Serum tumor necrosis factor-α, thiobarbituric acid-reactive substances (lipid peroxidation as an indirect measure of reactive oxygen species), lipopolysaccharide binding protein, interferon-γ, and interleukin-1β showed no significant changes.

CONCLUSIONS

The data indicate that the endurance training performed in the present study can reduce iNOS protein contents in insulin-independent T2DM men. Future studies should identify key molecules in iNOS regulation in vivo and fully clarify whether iNOS downregulation can help improve insulin sensitivity in T2DM patients in the long term.

Impaired glucose tolerance and metformin: clinical and mechanistic aspects

The Diabetes Prevention Program (DPP) showed that metformin reduced the incidence of diabetes in subjects with impaired glucose tolerance (IGT) who were at high risk of progression to type 2 diabetes. Metformin was not as efficient as intensive life style intervention, but had a clinically significant effect in obese individuals and in those with impaired fasting glucose (IFG). This review discusses the clinical implications and the mechanistic aspects of the effect of metformin in IGT and IFG. Acute actions of metformin on postprandial metabolism to improve hepatic glucose handling and improve the lipid profile could contribute to the lower incidence of diabetes. Longer term improvements in haemodynamic parameters and reduced oxidative stress are also implicated. Metformin offers a potential alternative or complement to lifestyle intervention for IGT, and deserves further evaluation in this respect.

Cytokines Regulate β-Cell Thioredoxin-interacting Protein (TXNIP) via Distinct Mechanisms and Pathways

Thioredoxin-interacting protein (TXNIP) is a key regulator of diabetic β-cell apoptosis and dysfunction, and TXNIP inhibition prevents diabetes in mouse models of type 1 and type 2 diabetes. Although we have previously shown that TXNIP is strongly induced by glucose, any regulation by the proinflammatory cytokines tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), and interferon γ (IFNγ) has remained largely unexplored. Moreover, even though this three-cytokine mixture is widely used to mimic type 1 diabetes in vitro, the mechanisms involved are not fully understood. Interestingly, we have now found that this cytokine mixture increases β-cell TXNIP expression; however, although TNFα had no effect, IL-1β surprisingly down-regulated TXNIP transcription, whereas IFNγ increased TXNIP levels in INS-1 β-cells and primary islets. Human TXNIP promoter analyses and chromatin immunoprecipitation studies revealed that the IL-1β effect was mediated by inhibition of carbohydrate response element binding protein activity. In contrast, IFNγ increased pro-apoptotic TXNIP post-transcriptionally via induction of endoplasmic reticulum stress, activation of inositol-requiring enzyme 1α (IRE1α), and suppression of miR-17, a microRNA that targets and down-regulates TXNIP. In fact, miR-17 knockdown was able to mimic the IFNγ effects on TXNIP, whereas miR-17 overexpression blunted the cytokine effect. Thus, our results demonstrate for the first time that the proinflammatory cytokines TNFα, IL-1β, and IFNγ each have distinct and in part opposing effects on β-cell TXNIP expression. These findings thereby provide new mechanistic insight into the regulation of TXNIP and β-cell biology and reveal novel links between proinflammatory cytokines, carbohydrate response element binding protein-mediated transcription, and microRNA signaling.

Unacylated ghrelin restores insulin and autophagic signaling in skeletal muscle of diabetic mice

Impairment of insulin signaling in skeletal muscle detrimentally affects insulin-stimulated disposal of glucose. Restoration of insulin signaling in skeletal muscle is important as muscle is one of the major sites for disposal of blood glucose. Recently, unacylated ghrelin (UnAG) has received attention in diabetic research due to its favorable actions on improving glucose tolerance, glycemic control, and insulin sensitivity. The investigation of UnAG has entered phase Ib clinical trial in type 2 diabetes and phase II clinical trial in hyperphagia in Prader-Willi syndrome. Nonetheless, the precise mechanisms responsible for the anti-diabetic actions of UnAG remain incompletely understood. In this study, we examined the effects of UnAG on restoring the impaired insulin signaling in skeletal muscle of db/db diabetic mice. Our results demonstrated that UnAG effectively restored the impaired insulin signaling in diabetic muscle. UnAG decreased insulin receptor substrate (IRS) phosphorylation, increased protein kinase B (Akt) phosphorylation, and, hence, suppressed mTOR signaling. Consequently, UnAG enhanced Glut4 localization and increased PDH activity in the diabetic skeletal muscle. Intriguingly, our data indicated that UnAG normalized the suppressed autophagic signaling in diabetic muscle. In conclusion, our findings illustrated that UnAG restored the impaired insulin and autophagic signaling in skeletal muscle of diabetic mice, which are valuable to understand the underlying mechanisms of the anti-diabetic action of UnAG at peripheral skeletal muscle level.

Fractalkine (CX3CL1), a new factor protecting β-cells against TNFα

Objective

We have previously shown the existence of a muscle–pancreas intercommunication axis in which CX3CL1 (fractalkine), a CX3C chemokine produced by skeletal muscle cells, could be implicated. It has recently been shown that the fractalkine system modulates murine β-cell function. However, the impact of CX3CL1 on human islet cells especially regarding a protective role against cytokine-induced apoptosis remains to be investigated.

Methods

Gene expression was determined using RNA sequencing in human islets, sorted β- and non-β-cells. Glucose-stimulated insulin secretion (GSIS) and glucagon secretion from human islets was measured following 24 h exposure to 1–50 ng/ml CX3CL1. GSIS and specific protein phosphorylation were measured in rat sorted β-cells exposed to CX3CL1 for 48 h alone or in the presence of TNFα (20 ng/ml). Rat and human β-cell apoptosis (TUNEL) and rat β-cell proliferation (BrdU incorporation) were assessed after 24 h treatment with increasing concentrations of CX3CL1.

Results

Both CX3CL1 and its receptor CX3CR1 are expressed in human islets. However, CX3CL1 is more expressed in non-β-cells than in β-cells while its receptor is more expressed in β-cells. CX3CL1 decreased human (but not rat) β-cell apoptosis. CX3CL1 inhibited human islet glucagon secretion stimulated by low glucose but did not impact human islet and rat sorted β-cell GSIS. However, CX3CL1 completely prevented the adverse effect of TNFα on GSIS and on molecular mechanisms involved in insulin granule trafficking by restoring the phosphorylation (Akt, AS160, paxillin) and expression (IRS2, ICAM-1, Sorcin, PCSK1) of key proteins involved in these processes.

Conclusions

We demonstrate for the first time that human islets express and secrete CX3CL1 and CX3CL1 impacts them by decreasing glucagon secretion without affecting insulin secretion. Moreover, CX3CL1 decreases basal apoptosis of human β-cells. We further demonstrate that CX3CL1 protects β-cells from the adverse effects of TNFα on their function by restoring the expression and phosphorylation of key proteins of the insulin secretion pathway.

An islet in distress: β cell failure in type 2 diabetes

Over 200 million people worldwide suffer from diabetes, a disorder of glucose homeostasis. The majority of these individuals are diagnosed with type 2 diabetes. It has traditionally been thought that tissue resistance to the action of insulin is the primary defect in type 2 diabetes. However, recent longitudinal and genome‐wide association studies have shown that insulin resistance is more likely to be a precondition, and that the failure of the pancreatic β cell to meet the increased insulin requirements is the triggering factor in the development of type 2 diabetes. A major emphasis in diabetes research has therefore shifted to understanding the causes of β cell failure. Collectively, these studies have implicated a complex network of triggers, which activate intersecting execution pathways leading to β cell dysfunction and death. In the present review, we discuss these triggers (glucotoxicity, lipotoxicity, amyloid and cytokines) with respect to the pathways they activate (oxidative stress, inflammation and endoplasmic reticulum stress) and propose a model for understanding β cell failure in type 2 diabetes. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00021.x, 2010)

Skeletal muscle nitric oxide (NO) synthases and NO-signaling in "diabesity"--what about the relevance of exercise training interventions?

Type 2 diabetes mellitus associated with obesity, or "diabesity", coincides with an altered nitric oxide (NO) metabolism in skeletal muscle. Three isoforms of nitric oxide synthase (NOS) exist in human skeletal muscle tissue. Both neuronal nitric oxide synthase (nNOS) and endothelial nitric oxide synthase (eNOS) are constitutively expressed under physiological conditions, producing low levels of NO, while the inducible nitric oxide synthase (iNOS) is strongly up-regulated only under pathophysiological conditions, excessively increasing NO concentrations. Due to chronic inflammation, overweight/obese type 2 diabetic patients exhibit up-regulated protein contents of iNOS and concomitant elevated amounts of NO in skeletal muscle. Low muscular NO levels are important for attaining an adequate cellular redox state--thereby maintaining metabolic integrity--while high NO levels are believed to destroy cellular components and to disturb metabolic processes, e.g., through strongly augmented posttranslational protein S-nitrosylation. Physical training with submaximal intensity has been shown to attenuate inflammatory profiles and iNOS protein contents in the long term. The present review summarizes signaling pathways which induce iNOS up-regulation under pathophysiological conditions and describes molecular mechanisms by which high NO concentrations are likely to contribute to triggering skeletal muscle insulin resistance and to reducing mitochondrial capacity during the development and progression of type 2 diabetes. Based on this information, it discusses the beneficial effects of regular physical exercise on the altered NO metabolism in the skeletal muscle of overweight/obese type 2 diabetic subjects, thus unearthing new perspectives on training strategies for this particular patient group.

CCCTC-binding factor mediates effects of glucose on beta cell survival

OBJECTIVES

Pancreatic islet β-cell survival is paramount for regulation of insulin activity and for maintaining glucose homeostasis. Recently, Pax6 has been shown to be essential for many vital functions in β-cells, although many molecular mechanisms of its homeostasis in β-cells remain unclear. The present study investigates novel effects of glucose- and insulin-induced CCCTC-binding factor (CTCF) activity on Pax6 gene expression as well as for subsequent effects of insulin-activated signalling pathways, on β-cell proliferation.

MATERIALS AND METHODS

Pancreatic β-TC-1-6 cells were cultured in DMEM and stimulated with high concentrations of glucose (5-125 mm); cell viability was assessed by MTT assay. Effects of CTCF on Pax6 were evaluated in the high glucose-induced environment and CTCF/Erk-suppressed cells, by promoter reporter and western blotting analyses.

RESULTS

Increases in glucose and insulin concentrations upregulated CTCF and consequently downregulated Pax6 in β-cell survival and proliferation. Knocking-down CTCF directly affected Pax6 transcription through CTCF binding and blocked the response to glucose. Altered Erk activity mediated effects of CTCF on controlling Pax6 expression, which partially regulated β-cell proliferation.

CONCLUSIONS

CTCF functioned as a molecular mediator between insulin-induced upstream Erk signalling and Pax6 expression in these pancreatic β-cells. This pathway may contribute to regulation of β-cell survival and proliferation.

Enhanced in vitro refolding of soluble human glucocorticoid-induced TNF receptor-related ligand

The glucocorticoid-induced tumor necrosis factor receptor (GITR) is a member of the tumor necrosis factor receptor superfamily. Attachment of GITR to its ligand (GITRL) regulates diverse biological functions, including cell proliferation, differentiation, and survival. In this study, the extracellular region of human GITRL (hGITRL) was cloned, expressed, and purified. The coding sequence of the extracellular region of hGITRL was isolated from human brain cDNA and inserted in pET20b vector. The hGITRL was expressed in Escherichia coli BL21 (DE3) Star at 37 and 25 °C. The majority of the protein was found in inclusion bodies. We identified three important factors for efficient refolding of hGITRL: a ratio of GSH/GSSG, pH, and addition of polyethylene glycol. The renaturated protein was purified by Ni-NTA chromatography. The overall yield of the expression and refolding was higher than 50 mg/l E. coli culture grown at 37 °C. Size exclusion chromatography showed that hGITRL exists as mixture of various multimeric forms in solution. We tested the association of recombinant hGITRL with THP-1 and U937 cell lines and its activity to promote extracellular signal-regulated protein kinase phosphorylation. The results showed that the recombinant protein was biologically active.

Endocrine and metabolic changes in human aging

Numerous alterations in hormonal secretion occur with aging. In general, these tend towards a disintegration of the normal cyclic secretory patterns resulting in lower total circulating levels. In addition, declines in receptors and postreceptor function further decreases the ability of the hormonal orchestra to maintain coordinated function throughout the organism. Clues to some of these age-related changes in humans may come from the study of simpler organisms where regulatory systems are known to modulate the aging process. In particular, the interactions among the environment, hormones, and insulin receptor genes have led to new insights into the genetic control of longevity and the development of syndrome X.

Bimodal impact of skeletal muscle on pancreatic β-cell function in health and disease

Diabetes is a complex disease that affects many organs directly or indirectly. Type 2 diabetes mellitus is characterized by insulin resistance with a relative deficiency in insulin secretion. It has become apparent that inter-organ communication is of great importance in the pathophysiology of diabetes. Far from being an inert tissue in terms of inter-organ communication, it is now recognized that skeletal muscle can secrete so-called myokines that can impact on the function of distant organs/tissues both favourably and unfavourably. We have proposed that communication between insulin-resistant skeletal muscle and β-cells occurs in diabetes. This is a novel route of communication that we further suggest is modified by the prevailing degree of insulin resistance of skeletal muscle. This review focuses on the various myokines [interleukin-6 (IL-6), tumor necrosis factor-α, CXCL10, follistatin and IL-8] which have been identified either after different types of exercise or in the secretome from control and insulin-resistant human skeletal myotubes. We will also summarize studies on the impact of several myokines on pancreatic β-cell proliferation, survival and function.

mRNA of the pro-apoptotic gene BBC3 serves as a molecular marker for TNF-α-induced islet damage in humans

AIMS/HYPOTHESIS

TNF-α plays important roles in the pathogenesis of type 1 and type 2 diabetes mellitus. In light of this, we examined the involvement of a pro-apoptotic gene, BBC3 (also known as PUMA), in TNF-α-mediated beta cell dysfunction and destruction in human islets.

METHODS

Human islets were exposed in vitro to TNF-α alone or in combination with IFN-γ. Gene expression was assessed by RT-PCR using a set of single islets. Protein abundance and cellular localisation of BBC3 were assessed by immunoblot and immunohistochemistry. A marginal number of islets were transplanted into diabetic NODscid mice to correlate in vivo islet function with BBC3 expression.

RESULTS

BBC3 and IL8 mRNA were upregulated in TNF-α-stimulated islets in a dose-dependent manner and enhanced through addition of IFN-γ, but not upregulated by IFN-γ alone. Immunohistochemistry revealed that TNF-α in combination with IFN-γ upregulated basal BBC3 abundance in the cytoplasm of beta cells along with the perinuclear clustering of mitochondria partially co-localised with BBC3. TNF-α alone did not induce beta cell death, but did abrogate preproinsulin precursor mRNA synthesis in response to high glucose stimulation, which was inversely associated with upregulation of BBC3 mRNA expression by TNF-α. Higher BBC3 mRNA expression in islets correlated with decreased graft function in vivo.

CONCLUSIONS/INTERPRETATION

These results suggest that BBC3 mRNA can serve as a molecular marker to detect early TNF-α-induced beta cell stress and may help identify islet-protective compounds for the treatment of diabetes.

Plasma Proteomic Signature in Overweight Girls Closely Correlates with Homeostasis Model Assessment (HOMA), an Objective Measure of Insulin Resistance

Obesity is known to be associated with a large number of long-term morbidities, and while in some cases the relationship of obesity and the consequences is clear (for example, excess weight and lower extremity orthopedic problems) in others the mechanism is not as clear. One common system of categorizing overweight in terms of the likelihood of negative consequences involves using the concept of “metabolic syndrome”. We hypothesized that the development of a plasma protein profile of overweight adolescents with and without the metabolic syndrome might give a more precise and informative picture of the disease process than the current clinical categorization and permit early targeted intervention. For this paper, we used antibody microarrays to analyze the plasma proteome of a group of 15 overweight female adolescent patients. Upon analysis of the proteome, the overweight patients diverged from the nonoverweight female controls. Furthermore, the overweight patients were divided by the analysis into two population clusters, each with distinctive protein expression patterns. Interestingly, the clusters were characterized by differences in insulin resistance, as measured by HOMA. Categorization according to the presence or absence of the metabolic syndrome did not yield such clusters.

Silencing mitogen-activated protein 4 kinase 4 (MAP4K4) protects beta cells from tumor necrosis factor-alpha-induced decrease of IRS-2 and inhibition of glucose-stimulated insulin secretion

Obesity and type 2 diabetes present partially overlapping phenotypes with systemic inflammation as a common feature, raising the hypothesis that elevated cytokine levels may contribute to peripheral insulin resistance as well as the decreased beta cell functional mass observed in type 2 diabetes. In healthy humans, TNF-alpha infusion induces skeletal muscle insulin resistance. We now explore the impact of TNF-alpha on primary beta cell function and the underlying signaling pathways. Human and rat primary beta cells were sorted by FACS and cultured for 24 h +/- 20 ng/ml TNF-alpha to explore the impact on apoptosis, proliferation, and short-term insulin secretion (1 h, 2.8 mm glucose followed by 1 h, 16.7 mm glucose at the end of the 24-h culture period) as well as key signaling protein phosphorylation and expression. Prior exposure to TNF-alpha for 24 h inhibits glucose-stimulated insulin secretion from primary beta cells. This is associated with a decrease in glucose-stimulated phosphorylation of key proteins in the insulin signaling pathway including Akt, AS160, and other Akt substrates, ERK as well as the insulin receptor. Strikingly, TNF-alpha treatment decreased IRS-2 protein level by 46 +/- 7% versus control, although mRNA expression was unchanged. While TNF-alpha treatment increased MAP4K4 mRNA expression by 33 +/- 5%, knockdown of MAP4K4 by siRNA-protected beta cells against the detrimental effects of TNF-alpha on both insulin secretion and signaling. We thus identify MAP4K4 as a key upstream mediator of TNF-alpha action on the beta cell, making it a potential therapeutic target for preservation of beta cell function in type 2 diabetes.

Diabetes mellitus and apoptosis: inflammatory cells

Since the early observation that similarities between thyroiditis and insulitis existed, the important role played by inflammation in the development of diabetes has been appreciated. More recently, experiments have shown that inflammation also plays a prominent role in the development of target organ damage arising as complications, with both elements of the innate and the adaptive immune system being involved, and that cytokines contributing to local tissue damage may arise from both infiltrating and resident cells. This review will discuss the experimental evidence that shows that inflammatory cell-mediated apoptosis contributes to target organ damage, from beta cell destruction to both micro- and macro-vascular disease complications, and also how alterations in leukocyte turnover affects immune function.

Rosiglitazone inhibits hypercholesterolaemia-induced myeloperoxidase upregulation--a novel mechanism for the cardioprotective effects of PPAR agonists

AIMS

Hypercholesterolaemia and myeloperoxidase (MPO) overexpression are two well-recognized risk factors for ischaemic heart disease. Peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists have recently been shown to reduce ischaemic heart injury in hypercholesterolaemic animals. However, whether PPARgamma agonists may exert their cardioprotective effects by eliminating those risk factors that increase ischaemic injury remains unknown.

METHODS AND RESULTS

Male New Zealand rabbits were fed with a normal or a high-cholesterol diet for 8 weeks, treated with vehicle or rosiglitazone (RSG, 3 mg/kg/day for the last 5 weeks) and subjected to myocardial ischaemia/reperfusion (1 h/4 h). MPO expression, activity, and distribution, cardiac caspase-3 activity, and myocardial infarct size were determined. Diet-induced hypercholesterolaemia caused a significant increase in neutrophil MPO expression/activity (7.2-/5.4-fold). Hypercholesterolaemia also tripled MPO activity in ischaemic/reperfused hearts when compared with rabbits fed with a normal diet. Surprisingly, MPO immunostaining was not only observed in perivascular and extracellular spaces in ischaemic/reperfused hearts, but also in cardiomyocytes. This intracardiomyocyte MPO staining was further intensified by hypercholesterolaemia. There is a strong positive correlation between cardiac MPO activity and caspase-3 activity, and treatment with an MPO inhibitor significantly reduced post-ischaemic caspase-3 activation. Treatment with RSG markedly inhibited hypercholesterolaemia-induced leucocyte MPO overexpression and activation, reduced MPO activity in ischaemic/reperfused hearts, decreased caspase-3 activity, and reduced myocardial infarct size (P < 0.01).

CONCLUSION

Our results demonstrated that hypercholesterolaemia and MPO overexpression are causally related and that PPARgamma agonists may have great therapeutic value in ischaemic heart disease patients with multiple complications such as hypercholesterolaemia and diabetes.

Resistin induces rat insulinoma cell RINm5F apoptosis

Beta-cell apoptosis induced by adipokines may result in beta-cell dysfunction in type 2 diabetes. Resistin, an adipokine-linked obesity with type 2 diabetes, impairs glucose-stimulated insulin secretion (GSIS) in beta-cells. Presently, the effects of resistin on rat insulinoma cells RINm5F were examined. Treatment of RINm5F with resistin induced cell damage. Tissue Inhibitor of Metalloproteinase-1 (TIMP-1) protected resistin-mediated cytotoxicity in RINm5F. Incubation with resistin up-regulated caspase-3 activity and induced the formation of a DNA ladder. TIMP-1 attenuated these effects. The molecular mechanism of TIMP-1 inhibition of resistin-mediated cytotoxicity appeared to involve Akt phosphorylation and activation of IkB-alpha phosphorylation. Resistin treatment suppressed Akt phosphorylation and activated IkB-alpha phosphorylation, which could be attenuated by TIMP-1. We conclude that resistin can induce beta-cell apoptosis and that resistin-related beta-cell apoptosis can be prevented by TIMP-1.

Does garlic have a role as an antidiabetic agent?

Diabetes affects a large segment of the population worldwide, and the prevalence of this disease is rapidly increasing. Despite the availability of medication for diabetes, traditional remedies are desirable and are currently being investigated. Garlic (Allium sativum), which is a common cooking spice and has a long history as a folk remedy, has been reported to have antidiabetic activity. However, there is no general agreement on the use of garlic for antidiabetic purposes, primarily because of a lack of scientific evidence from human studies and inconsistent data from animal studies. The validity of data from previous studies of the hypoglycemic effect of garlic in diabetic animals and the preventive effects of garlic on diabetes complications are discussed in this review. The role of garlic as both an insulin secretagogue and as an insulin sensitizer is reviewed. Evidence suggests that garlic's antioxidative, antiinflammatory, and antiglycative properties are responsible for garlic's role in preventing diabetes progression and the development of diabetes-related complications. Large-scale clinical studies with diabetic patients are warranted to confirm the usefulness of garlic in the treatment and prevention of diabetes.

Negative and positive feedback regulation of insulin in glucose-stimulated Ca2+ response in pancreatic beta cells

Secreted insulin from pancreatic beta cells exerts autocrine and paracrine effects within the islets. The present study has evaluated how exogenous insulin participates in cytosolic Ca(2+) response to high glucose, according to glucose concentration at which insulin is applied. When 100 nM insulin was pretreated to the bath solution containing islet cells in the presence of basal level of glucose, the elevation of cytosolic Ca(2+) concentration ([Ca(2+)](c)) by subsequently applied 10mM glucose was remarkably attenuated. In contrast, the glucose-stimulated [Ca(2+)](c) elevation was more potentiated when insulin was superimposed on the high glucose stimulation. These insulin actions were modestly inhibited by the application of LY294002, the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor, but not completely, suggesting that another mechanism is also involved. By 100 nM insulin, phosphorylated form of AMP-activated protein kinases (p-AMPK) was dramatically decreased in basal glucose but increased in high glucose, when compared with their reciprocal controls. These results may suggest that the extent of AMPK activation may be a tool for insulin receptors to monitor blood glucose level, with which insulin-induced insulin receptor activation determines the way to go negatively or positively toward [Ca(2+)](c).

Comparison of the alteration of the concentration of C-peptide in 24-h urine according to the combination patterns of hypoglycemic agents in type 2 diabetes patients

AIMS

Urinary C-peptide (UCP) has been considered as a simple method for monitoring beta-cell function in diabetic patients clinically. The aim of the study is to compare the changes of 24-h urinary C-peptide levels according to subgroups divided by therapeutic agents for subjects with type 2 diabetes.

METHODS

In 206 participants, under treatment for type 2 diabetes, 24-h urinary C-peptide levels were assessed yearly for 3 years. All participants were subdivided into four groups according to the therapeutic agents. Changes for the measured values during the follow-up were compared between groups.

RESULTS

Mean HbA1C was 7.1% and mean 24-h UCP was 61.7 microg/24h and mean duration of diabetes was 8.7 years in all subjects at baseline. Mean 24-h UCP levels increased significantly from a baseline to at 36 months in the insulin sensitizers (IS) only group, in the IS plus sulfonylurea combination group and in IS plus insulin combination group (p<0.001), whereas in the sulfonylurea only group, we could not find statistically significant changes (p=0.152). Treatment with only IS significantly reduced fasting plasma glucose (FPG) and HbA1C level (p=0.045, p<0.001). Differences between baseline and last 24-h UCP were significantly different between-groups and this difference was more significant after adjustment in FPG, HbA1C, and the duration of diabetes (p=0.024). Especially, IS plus sulfonylurea combination group resulted in greatest increase of 24-h UCP (DeltaC-peptide=51.19 microg/24h).

CONCLUSIONS

This study suggested that IS, in mono- or in combination, significantly improved pancreatic beta-cell function, especially when combined with sulfonylurea as evidenced by the increase of 24-h UCP.

Degree of obesity and glucose allostasis are major effectors of glucose tolerance dynamics in obese youth

OBJECTIVE

One of the signals for the beta-cell to maintain an adequate response to worsening insulin sensitivity is elevated ambient glycemia, namely the concept of "glucose allostasis." We examined whether glucose allostasis can be demonstrated using oral glucose tolerance tests (OGTTs) and the effects of the dynamics of beta-cell demand on longitudinal changes of glucose tolerance in obese youth.

RESEARCH DESIGN AND METHODS

A cross-sectional analysis of 784 OGTTs of obese youth was used to demonstrate the concept of allostasis, and a longitudinal assessment of 181 subjects was used to examine the effects of changes in beta-cell demand and the degree of obesity on glucose tolerance.

RESULTS

Glucose allostasis can be demonstrated using indexes derived from an OGTT. Increasing beta-cell demand and the degree of obesity at baseline were independently related to elevations in ambient glycemia over time. Baseline BMI Z score was a significant contributor to elevated glucose levels on the second OGTT, while the change in degree of obesity during follow-up was not.

CONCLUSIONS

Increasing beta-cell demand related to worsening insulin sensitivity and the degree of obesity per se have independent roles in the development of elevated glucose levels over time. This implicates that peripheral insulin sensitization and/or beta-cell enhancement alongside a significant reduction in obesity may be needed to prevent the development of altered glucose metabolism in obese youth.

The heterogeneity of diabetes: unraveling a dispute: is systemic inflammation related to islet autoimmunity?

Diabetes is an emblematic example of a heterogeneous disease. Systemic inflammation has emerged as a prominent factor in the type 2 diabetes pathoetiology, but it remains ill-defined in type 1 diabetes. There is a wide spectrum of associations between inflammatory responses and diabetic syndromes. At one end of this spectrum, there is type 1 diabetes for which there is convincing evidence that chronic inflammation of pancreatic islets is a central aspect of disease pathogenesis. At the opposite end, is type 2 diabetes that is clearly associated with systemic inflammation, which could be either the cause or simply mark the underlying pathology. Accumulating evidence has substantiated that a subgroup of adult patients clinically diagnosed with type 2 diabetes exhibit autoantibody responses to islet autoantigens. The presence of these immunologic abnormalities is associated with a severe insulin secretory defect and the absence of signs of systemic inflammation as documented by plasma C-reactive protein and fibrinogen levels that are comparable with those of control populations. Islet autoantibody evaluation should be part of the diagnostic assessment for clinically diagnosed type 2 diabetes not only because it might predict the rate of progression to insulin requirement in adult populations but also to identify a pathogenically distinct disease phenotype characterized by the absence of systemic inflammation and its related disorders. A more appropriate characterization of this subgroup of clinically diagnosed type 2 diabetes, diabetes of autoimmune pathogenesis, will promote future research into the etiology, natural history, and treatment.

Antidiabetic effect of garlic oil but not diallyl disulfide in rats with streptozotocin-induced diabetes

We investigated the effects of garlic oil and diallyl disulfide (DADS) on glycemic control and renal function in rats with streptozotocin-induced diabetes. Rats received by gavage garlic oil (100 mg/kg body wt) or DADS (40 or 80 mg/kg body wt) every other day until 16 weeks after the induction of diabetes. The control rats were treated with corn oil only. Neither garlic oil nor DADS significantly affected fasting blood glucose concentrations throughout the investigation period. Garlic oil did not affect oral glucose tolerance in diabetes acutely but significantly improved oral glucose tolerance at 4, 8, 12, and 16 weeks and significantly ameliorated proteinuria at the end of 16 weeks. DADS did not significantly affect oral glucose tolerance or renal function. Diabetic rats fed 80 mg DADS/kg body wt had a significantly lower rate of body weight gain and a significantly lower ratio of muscle weight to body weight than did vehicle-treated diabetic rats. In conclusion, long-term treatment of diabetes with garlic oil can improve oral glucose tolerance and renal function in diabetes but not through the action of DADS. High doses of DADS may further complicate the metabolic disturbances in diabetes.

Contribution of adipocyte-derived factors to beta-cell dysfunction in diabetes

In addition to serving as an energy reservoir, the adipocyte has been characterized as an endocrine cell, secreting many bioactive factors which influence energy homeostasis. Being overweight, with excessive adipose tissue, is considered to be part of the pathogenesis of type 2 diabetes. Insulin resistance and beta-cell dysfunction are two major pathophysiological changes seen in type 2 diabetes. In addition to inducing insulin resistance in insulin-responsive tissues, adipocyte-derived factors play an important role in the pathogenesis of beta-cell dysfunction. Leptin, free fatty acids, adiponectin, tumor necrosis factor-alpha and interleukin-6 are all produced and secreted by adipocytes, and may directly influence aspects of beta-cell function, including insulin synthesis and secretion, insulin cell survival and apoptosis. During the progression from normal weight to obesity and on to overt diabetes, the adipocyte-derived factors contribute to the occurrence and development of beta-cell dysfunction and type 2 diabetes.

Glucose-stimulated prehepatic insulin secretion is associated with circulating alanine, triglyceride, glucagon, lactate and TNF-alpha in patients with HIV-lipodystrophy

OBJECTIVES

We examined whether insulin-resistant lipodystrophic HIV-infected patients with known high fasting prehepatic insulin secretion rates (FISRs) displayed alterations in first-phase prehepatic insulin response to intravenous glucose (ISREG0-10 min).

METHODS

Eighteen normoglycaemic lipodystrophic HIV-infected (LIPO) patients and 25 normoglycaemic nonlipodystrophic HIV-infected patients (controls) were included in the study. The prehepatic insulin secretion rate was estimated by deconvolution of C-peptide concentrations, and insulin sensitivity (SIRd) was estimated by the glucose clamp technique. The disposition index (Di=ISREG0-10 min x SIRd) was calculated to estimate the beta-cell response relative to insulin sensitivity.

RESULTS

FISR was increased by 69% (P<0.001), whereas median Di was decreased by 75% (P<0.01), primarily as a result of a reduction of SI(Rd) by 60% (P<0.001) in LIPO patients compared with controls. Three LIPO groups were identified arbitrarily according to their FISR and ISREG0-10 min values relative to those of controls. Four LIPO patients displayed high FISR [+3 standard deviations (SD), P<0.001], high ISREG0-10 min (+3 SD, P<0.001) and low SIRd (P<0.01), suggesting an intact B-cell capacity to compensate insulin resistance; six LIPO patients exhibited high FISR (+3SD, P<0.001), low ISREG0-10min (-1 SD, P=0.01), and low SIRd (P<0.01), suggesting depletion of readily releasable insulin stores; the remaining eight LIPO patients and controls displayed identical FISR and ISREG0-10 min. Increased concentrations of the nonglucose insulin secretagogues triglyceride (+124%), alanine (+35%) and glucagon (+88%), and also lactate (+96%) and tumour necrosis factor (TNF)-alpha (+62%) were observed in the 10 LIPO patients with aberrations in FISR and ISREG0-10 min compared with the remaining HIV-infected patients (all P<0.05).

CONCLUSION

Plasma triglyceride, alanine, glucagon, lactate and TNF-alpha may be associated with alterations in the first-phase prehepatic insulin secretion response to intravenous glucose in normoglycaemic lipodystrophic HIV-infected patients.

Beta-cell preservation: a potential role for thiazolidinediones to improve clinical care in Type 2 diabetes

Type 2 diabetes is caused by progressively increasing insulin resistance coupled with deteriorating beta-cell function, and there is a growing body of evidence to suggest that both of these defects precede hyperglycaemia by many years. Several studies have demonstrated the importance of maintaining beta-cell function in patients with Type 2 diabetes. This review explores parameters used to indicate beta-cell dysfunction, in Type 2 diabetes and in individuals with a predisposition to the disease. A genetic element undoubtedly underlies beta-cell dysfunction; however, a number of modifiable components are also associated with beta-cell deterioration, such as chronic hyperglycaemia and elevated free fatty acids. There is also evidence for a link between pro-inflammatory cytokines and impairment of insulin-signalling pathways in the beta-cell, and the potential role of islet amyloid deposition in beta-cell deterioration continues to be a subject for debate. The thiazolidinediones are a class of agents that have demonstrated clinical improvements in indices of beta-cell dysfunction and have the potential to improve beta-cell function. Data are accumulating to show that this therapeutic group offers a number of advantages over traditionally employed oral agents, and these data demonstrate the growing importance of thiazolidinediones in Type 2 diabetes management.

Adiponectin and beta cell dysfunction in gestational diabetes: pathophysiological implications

AIMS/HYPOTHESIS

Gestational diabetes mellitus (GDM) identifies a population of young women at high risk of developing type 2 diabetes and thus provides an excellent model for studying early events in the natural history of this disease. Adiponectin, a novel adipocyte-derived protein with insulin-sensitising properties, has been proposed as a factor linking insulin resistance and beta cell dysfunction in the pathogenesis of type 2 diabetes. We conducted the current investigation to determine whether adiponectin is associated with beta cell dysfunction in GDM.

METHODS

We studied 180 women undergoing OGTT in late pregnancy. Based on the OGTT results, participants were stratified into three groups: (1) NGT (n=93); (2) IGT (n=39); and (3) GDM (n=48). First-phase insulin secretion was determined using a validated index previously proposed by Stumvoll. Insulin sensitivity was assessed using the validated OGTT insulin sensitivity index of Matsuda and DeFronzo (IS(OGTT)).

RESULTS

To evaluate beta cell function in relation to ambient insulin sensitivity, an insulin secretion-sensitivity index (ISSI) was derived from the product of the Stumvoll index and the IS(OGTT), based on the existence of the predicted hyperbolic relationship between these two measures. Mean ISSI was highest in the NGT group (6,731), followed by that in the IGT group (4,976) and then that in the GDM group (3,300) (overall p<0.0001), compatible with the notion of declining beta cell function across these glucose tolerance groups. Importantly, adiponectin was significantly correlated with ISSI (r=0.34, p<0.0001), with a stepwise increase in mean ISSI observed per tertile of adiponectin concentration (trend p<0.0001). In multivariate linear regression analysis, ISSI was positively correlated with adiponectin and negatively correlated with GDM, IGT and C-reactive protein (r(2)=0.54).

CONCLUSIONS/INTERPRETATION

Adiponectin concentration is an independent correlate of beta cell function in late pregnancy. As such, adiponectin may play a key role in mediating insulin resistance and beta cell dysfunction in the pathogenesis of diabetes.

S-nitrosation of the insulin receptor, insulin receptor substrate 1, and protein kinase B/Akt: a novel mechanism of insulin resistance

Evidence demonstrates that exogenous nitric oxide (NO) and the NO produced by inducible nitric oxide synthase (iNOS) can induce insulin resistance in muscle. Here, we investigated whether this insulin resistance could be mediated by S-nitrosation of proteins involved in early steps of the insulin signal transduction pathway. Exogenous NO donated by S-nitrosoglutathione (GSNO) induced in vitro and in vivo S-nitrosation of the insulin receptor beta subunit (IRbeta) and protein kinase B/Akt (Akt) and reduced their kinase activity in muscle. Insulin receptor substrate (IRS)-1 was also rapidly S-nitrosated, and its expression was reduced after chronic GSNO treatment. In two distinct models of insulin resistance associated with enhanced iNOS expression-diet-induced obesity and the ob/ob diabetic mice-we observed enhanced S-nitrosation of IRbeta/IRS-1 and Akt in muscle. Reversal of S-nitrosation of these proteins by reducing iNOS expression yielded an improvement in insulin action in both animal models. Thus, S-nitrosation of proteins involved in insulin signal transduction is a novel molecular mechanism of iNOS-induced insulin resistance.

The potential role of SOCS-3 in the interleukin-1beta-induced desensitization of insulin signaling in pancreatic beta-cells

Defects in insulin secretion, resulting from loss of function or destruction of pancreatic beta-cells, trigger diabetes. Interleukin (IL)-1beta is a proinflammatory cytokine that is involved in type 1 and type 2 diabetes development and impairs beta-cell survival and function. Because effective insulin signaling is required for the optimal beta-cell function, we assessed the effect of IL-1beta on the insulin pathway in a rat pancreatic beta-cell line. We show that IL-1beta decreases insulin-induced tyrosine phosphorylation of the insulin receptor (IR) and insulin receptor substrate (IRS) proteins as well as phosphatidylinositol 3-kinase (PI3K) activation, and that this action is not due to the IL-1beta-dependent nitric oxide (NO) production in RINm5F cells. We next analyzed if suppressor of cytokine signaling (SOCS)-3, which can be induced by multiple cytokines and which we identified as an insulin action inhibitor, was implicated in the IL-1beta inhibitory effect on insulin signaling in these cells. We show that IL-1beta increases SOCS-3 expression and induces SOCS-3/IR complex formation in RINm5F cells. Moreover, we find that ectopically expressed SOCS-3 associates with the IR and reduces insulin-dependent IR autophosphorylation and IRS/PI3K pathway in a way comparable to IL-1beta treatment in RINm5F cells. We propose that IL-1beta decreases insulin action in beta-cells through the induction of SOCS-3 expression, and that this effect potentially alters insulin-induced beta-cell survival.

Protein thiol modification by 15-deoxy-Delta12,14-prostaglandin J2 addition in mesangial cells: role in the inhibition of pro-inflammatory genes

The cyclopentenone prostaglandin and PPARgamma agonist 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) displays anti-inflammatory effects in several experimental models. Direct modification of protein thiols is arising as an important mechanism of cyclopentenone prostaglandin action. However, little is known about the extent or specificity of this process. Mesangial cells (MC) play a key role in glomerulonephritis. In this work, we have studied the selectivity of protein modification by 15d-PGJ(2) in MC, and the correlation with the modulation of several proinflammatory genes. MC incubation with biotinylated 15d-PGJ(2) results in the labeling of a distinct set of proteins as evidenced by two-dimensional electrophoresis. 15d-PGJ(2) binds to nuclear and cytosolic targets as detected by fluorescence microscopy and subcellular fractionation. The pattern of biotinylated 15d-PGJ(2)-modified polypeptides is readily distinguishable from that of total protein staining or labeling with biotinylated iodoacetamide. 15d-PGJ(2) addition requires the double bond in the cyclopentane ring. 9,10-Dihydro-15d-PGJ(2), a 15d-PGJ(2) analog that shows the same potency as peroxisome proliferator-activated receptor (PPAR) agonist in MC but lacks the cyclopentenone moiety, displays reduced ability to modify proteins and to block 15d-PGJ(2) binding. Micromolar concentrations of 15d-PGJ(2) inhibit cytokine-elicited levels of inducible nitricoxide synthase, cyclooxygenase-2, and intercellular adhesion molecule-1 in MC. In contrast, 9,10-dihydro-15d-PGJ(2) does not reproduce this inhibition. 15d-PGJ(2) effect is not blocked by the PPARgamma antagonist 2-chloro-5-nitro-N-phenylbenzamide (GW9662). Moreover, compounds possessing an alpha,beta-unsaturated carbonyl group, like 2-cyclopenten-1-one and 2-cyclohexen-1-one, reduce pro-inflammatory gene expression. These observations indicate that covalent modification of cellular thiols by 15d-PGJ(2) is a selective process that plays an important role in the inhibition of MC responses to pro-inflammatory stimuli.

Pioglitazone improves insulin secretory capacity and prevents the loss of beta-cell mass in obese diabetic db/db mice: Possible protection of beta cells from oxidative stress

In order to assess the beneficial effect of the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist pioglitazone on reduction of mass and alteration of function of pancreatic beta cells under diabetic conditions, diabetic C57BL/KsJ db/db mice were treated with pioglitazone for 6 weeks, and insulin secretory capacity and insulin content of isolated pancreatic islets were evaluated. In addition, the expression of oxidative stress markers, 4-hydroxy-2-nonenal (HNE)-modified proteins and heme oxygenase-1, in endocrine pancreas was examined to measure reduction of oxidative stress in pancreatic beta cells. The capacity for glucose-induced insulin secretion from isolated islets and their insulin content were improved by pioglitazone treatment (P <.01). When beta cells were stained with anti-insulin antibodies, those of db/db mice treated with pioglitazone exhibited strong staining, as also observed in their lean littermates. The density of immunostaining for oxidative stress markers was significantly reduced in pancreatic islets of pioglitazone-treated db/db mice (P <.05). This study clearly demonstrates the benefit of long-term treatment with pioglitazone in decreasing hyperglycemia and improving glucose-induced insulin secretory capacity in diabetic db/db mice. The results of immunocytochemical examination suggest that this treatment reduces oxidative stress and thereby preserves beta-cell mass. Treatment with pioglitazone thus protects against beta-cell damage and would be useful for restoration of insulin secretory capacity in obese diabetes individuals.

Inhibition of inducible nitric-oxide synthase by activators of AMP-activated protein kinase: a new mechanism of action of insulin-sensitizing drugs

AMP-activated protein kinase (AMPK), an energy-sensing enzyme that is activated in response to cellular stress, is a critical signaling molecule for the regulation of multiple metabolic processes. AMPK has recently emerged as an attractive novel target for the treatment of obesity and type 2 diabetes because its activation increases fatty acid oxidation and improves glucose homeostasis. Here we show that pharmacological activation of AMPK by insulin-sensitizing drugs markedly inhibits inducible nitric-oxide synthase (iNOS), a proinflammatory mediator in endotoxic shock and in chronic inflammatory states including obesity-linked diabetes. AMPK-mediated iNOS inhibition was observed in several cell types (myocytes, adipocytes, macrophages) and primarily resulted from post-transcriptional regulation of the iNOS protein. AMPK activation in vivo also blunted iNOS induction in muscle and adipose tissues of endotoxin-challenged rats. Reduction of AMPK expression by small interfering RNA reversed the inhibitory effects of AMPK activators on iNOS expression and nitric oxide production in myocytes. These results indicate that AMPK is a novel anti-inflammatory signaling pathway and thus represents a promising therapeutic target for immune-inflammatory disorders.

Anti-inflammatory and Anti-nociceptive Effects of the Methanol Extract of Fomes fomentarius

In an attempt to find bioactive natural products with an anti-inflammatory activity, we evaluated the effects of the methanol extract of Fomes fomentarius (MEFF) on in vivo anti-inflammatory and anti-nociceptive activities. MEFF (50, 100 mg/kg/d, p.o.) reduced acute paw edema induced by carrageenin in rats, and showed MEFF analgesic activity, as determined by an acetic acid-induced writhing test and a hot plate test in mice. To investigate the mechanism of the anti-inflammatory action of MEFF, we examined the effect of MEFF on lipopolysaccharide (LPS)-induced responses in murine macrophages cell line RAW 264.7. MEFF potently inhibited the production of nitric oxide (NO), prostaglandin E2 (PGE2), and tumor necrosis factor-alpha (TNF-alpha) in LPS-stimulated RAW 264.7 macrophages. Consistent with these observations, inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) levels were reduced by MEFF in a dose-dependent manner. Furthermore, MEFF suppressed nuclear factor-kappaB (NF-kappaB) activation in LPS-stimulated RAW 264.7 macrophages. These findings suggest that the anti-inflammatory and anti-nociceptive properties of the methanol extract of MEFF may result from the inhibition of iNOS and COX-2 expression through the down-regulation of NF-kappaB binding activity.

Insulin receptor substrate 1 regulation of sarco-endoplasmic reticulum calcium ATPase 3 in insulin-secreting beta-cells

We have previously characterized an insulin receptor substrate 1 (IRS-1)-overexpressing beta-cell line. These beta-cells demonstrated elevated fractional insulin secretion and elevated cytosolic Ca(2+) levels compared with wild-type and vector controls. This effect of IRS-1 may be mediated via an interaction with the sarco-endoplasmic reticulum calcium ATPase (SERCA). Here we demonstrate that IRS-1 and IRS-2 localize to an endoplasmic reticulum (ER)-enriched fraction in beta-cells using subcellular fractionation. We also observe co-localization of both IRS-1 and IRS-2 with ER marker proteins using immunofluorescent confocal microscopy. Furthermore, immuno-electron microscopy studies confirm that IRS-1 and SERCA3b localize to vesicles derived from the ER. In Chinese hamster ovary-T (CHO-T) cells transiently transfected with SERCA3b alone or together with IRS-1, SERCA3b co-immunoprecipitates with IRS-1. This interaction is enhanced with insulin treatment. SERCA3b also co-immunoprecipitates with IRS-1 in wild-type and IRS-1-overexpressing beta-cell lines. Ca(2+) uptake in ER-enriched fractions prepared from wild-type and IRS-1-overexpressing cell lines shows no significant difference, indicating that the previously observed decrease in Ca(2+) uptake by IRS-1-overexpressing cells is not the result of a defect in SERCA. Treatment of wild-type beta-cells with thapsigargin, an inhibitor of SERCA, resulted in an increase in glucose-stimulated fractional insulin secretion similar to that observed in IRS-1-overexpressing cells. The colocalization of IRS proteins and SERCA in the ER of beta-cells increases the likelihood that these proteins can interact with one another. Co-immunoprecipitation of IRS-1 and SERCA in CHO-T cells and beta-cells confirms that these proteins do indeed interact directly. Pharmacological inhibition of SERCA in beta-cells results in enhanced secretion of insulin. Taken together, our data suggest that interaction between IRS proteins and SERCA is an important regulatory step in insulin secretion.

Capsaicin exhibits anti-inflammatory property by inhibiting IkB-a degradation in LPS-stimulated peritoneal macrophages

Capsaicin, a major ingredient of hot pepper, was considered to exhibit an anti-inflammatory property. In order to clarify the signalling mechanism underlying the anti-inflammatory action of capsaicin, we investigated the effect of capsaicin on the production of inflammatory molecules in lipopolysaccharide (LPS)-stimulated murine peritoneal macrophages. The level of PGE2 was measured by EIA. The expression levels of COX-2, iNOS, IkB-a, and vanilloid receptor-1 (VR-1) were determined at the protein and mRNA levels. Significant inhibition of the production of LPS-induced PGE2 by capsaicin was observed in a dose-dependent manner. Capsaicin did not affect the COX-2 expression at either the protein or mRNA level, but inhibited the enzyme activity of COX-2 and the expression of the iNOS protein. Capsaicin completely blocked LPS-induced disappearance of IkB-a and therefore inactivated NF-kB. The inhibitory action of capsaicin on PGE2 production was not abolished by capsazepine, a specific antagonist to VR-1. A high expression level of the VR-1 like protein (VRL-1) was observed in peritoneal macrophages, while the expression of VR-1 was not detected. These findings suggest that the anti-inflammatory action of capsaicin may occur through a novel mechanism, not by a VR-1 receptor-mediated one. Both capsaicin and capsazepine may be a promising drug candidates for ameliorating inflammatory diseases and cancer.

Nitric Oxide Signalling with a Special Focus on Lipid-Derived Mediators

The ways in which cells communicate among each other concerns all aspects of biology, from developmental processes to diseases. Nitric oxide (NO) is one of the most remarkable and unusual regulatory molecules. It is a labile free radical gas that is not stored but generated on demand, and has been implicated in an extraordinarily diverse range of physiological and pathophysiological functions. The modulation of cell signalling by free radicals is an emerging area of research that provides insight into the orchestration of cell adaptation to a changing microenvironment. In a multicellular organism this serves to coordinate complex physiological responses, such as inflammation. Cell signalling is also accompanied by rapid remodelling of membrane lipids by activated lipases. The discovery that NO, which does not reversibly interact with membrane receptors like conventional hormones and growth factors, targets enzymes such as phospholipase A2, sphingomyelinases or ceramidases, has stimulated growing interest in the crosstalk between redox and lipid signalling.

Insulin feedback action on pancreatic beta-cell function

Pancreatic beta-cell function is essential for the regulation of glucose homeostasis and its impairment leads to diabetes mellitus. Besides glucose, the major nutrient factor, inputs from neural and humoral components and intraislet cell-cell communication act together to guarantee an appropriate pancreatic beta-cell function. Data obtained over the last 5 years in several laboratories have revitalized a controversial concept, namely the autocrine feedback action of secreted insulin on beta-cell function. While, historically, insulin was suggested to exert a negative effect on beta-cells, recent data provide evidence for a positive role of insulin in transcription, translation, ion flux, insulin secretion and beta-cell survival.

Phosphorylated inositol compounds in beta -cell stimulus-response coupling

Pancreatic beta-cell function is essential for the regulation of glucose homeostasis in humans, and its impairment leads to the development of type 2 diabetes. Inputs from glucose and cell surface receptors act together to initiate the beta-cell stimulus-response coupling that ultimately leads to the release of insulin. Phosphorylated inositol compounds have recently emerged as key players at all levels of the stimulus-secretion coupling process. In this current review, we seek to highlight recent advances in beta-cell phosphoinositide research by dividing our examination into two sections. The first involves the events that lead to insulin secretion. This includes both new roles for inositol polyphosphates, particularly inositol hexakisphosphate, and both conventional and 3-phosphorylated inositol lipids. In the second section, we deal with the more novel concept of the autocrine role of insulin. Here, released insulin initiates signal transduction cascades, principally through the activity of phosphatidylinositol 3-kinase. This new round of signal transduction has been established to activate key beta-cell genes, particularly the insulin gene itself. More controversially, this insulin feedback has also been suggested to either terminate or enhance insulin secretion events.

PPAR(gamma) and glucose homeostasis

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor involved in the control of metabolism. Research on PPARgamma is oriented towards understanding its role in insulin sensitization, which was inspired by the discovery that antidiabetic agents, the thiazolidinediones, were agonists for PPARgamma. PPARgamma stimulation improves glucose tolerance and insulin sensitivity in type 2 diabetic patients and in animal models of insulin resistance through mechanisms that are incompletely understood. Upon activation, PPARgamma heterodimerizes with retinoid X receptor, recruits specific cofactors, and binds to responsive DNA elements, thereby stimulating the transcription of target genes. Because PPARgamma is highly enriched in adipose tissue and because of its major role in adipocyte differentiation, it is thought that the effects of PPARgamma in adipose tissue are crucial to explain its role in insulin sensitization, but recent studies have highlighted the contribution of other tissues as well. Although relatively potent for their insulin-sensitizing action, currently marketed PPARgamma activators have some important undesirable side effects. These concerns led to the discovery of new ligands with potent antidiabetic properties but devoid of certain of these side effects. Data from human genetic studies and from PPARgamma heterozygous knockout mice indicate that a reduction in PPARgamma activity could paradoxically improve insulin sensitivity. These findings suggest that modulation of PPARgamma activity by partial agonists or compounds that affect cofactor recruitment might hold promise for the treatment of insulin resistance.

Biology and toxicology of PPARgamma ligands

The peroxisome proliferator activated receptor-gamma (PPARgamma) is an attractive target for therapeutic intervention, as modulation of PPARgamma-regulated pathways is potentially beneficial in a number of disease areas. This review provides an overview of what is known about the biology of PPARgamma, and an indication of what progress has been made towards drug development in several therapy areas. As well as efficacy, the safety of drugs is of course an important issue, and a substantial volume of preclinical and clinical information has already accumulated for PPARgamma agonists. Here we discuss some of the major toxicology issues with PPARgamma agonists, and give a perspective on likely issues concerning the development of PPARgamma modulators in the future.

Troglitazone improves GLUT4 expression in adipose tissue in an animal model of obese type 2 diabetes mellitus

Troglitazone has been shown to improve peripheral insulin resistance in type 2 diabetic patients and animal models. We examined the effect of troglitazone on the expression of glucose transporter 4 (GLUT4) in muscle and adipose tissue from Otsuka Long-Evans Tokushima Fatty (OLETF) rat, an animal model of obese type 2 diabetes mellitus. In addition, the effects of troglitazone on GLUT4 translocation and on glucose transport activity in adipocytes were also evaluated. Muscle and adipose tissues were isolated from 35-week-old male troglitazone-treated and untreated OLETF rats at a dose of 150 mg/kg per day for 14 days. In skeletal muscle, the protein and mRNA levels of GLUT4 were not significantly different between OLETF and control rats and they were not affected by troglitazone. On the other hand, GLUT4 protein and mRNA levels in adipose tissue from OLETF rats were significantly decreased (P<0.01) compared with control rats and they were significantly increased (1.5-fold, P<0.01) by troglitazone. Troglitazone had no major effect on GLUT4 translocation in adipocytes, but it significantly increased (1.4-fold, P<0.05) the basal and insulin-induced amounts of GLUT4 in plasma membrane (PM) in adipocytes from OLETF rats. Consistent with these results, the basal and insulin-induced glucose uptakes in adipocytes from troglitazone-treated OLETF rats were significantly increased (1.5-fold, P<0.05) compared with untreated OLETF rats. Our results suggest that troglitazone may exert beneficial effects on insulin resistance by increasing the expression of GLUT4 in adipose tissue.

Identifying the links between obesity, insulin resistance and beta-cell function: potential role of adipocyte-derived cytokines in the pathogenesis of type 2 diabetes

A combination of insulin resistance and pancreatic beta-cell dysfunction underlies most cases of type 2 diabetes. While the interplay of these two impairments is believed to be important in the development and progression of type 2 diabetes, the mechanisms involved are unclear. A number of factors have been suggested as possibly linking insulin resistance and beta-cell dysfunction in the pathogenesis of type 2 diabetes mellitus. Pro-inflammatory cytokines such as tumour necrosis factor-alpha (TNF-alpha) have deleterious effects on both glucose homeostasis and beta-cell function, and can disrupt insulin signalling pathways in both pancreatic beta cells and liver and adipose tissue. The anti-inflammatory activity of the thiazolidinedione anti-diabetic agents is potentially beneficial, given the possible role of pro-inflammatory cytokines in linking insulin resistance with beta-cell dysfunction.

Troglitazone does not protect rat pancreatic beta cells against free fatty acid-induced cytotoxicity

Thiazolidinediones are a novel class of antidiabetic drugs that reduce insulin resistance through interaction with nuclear peroxisome proliferator-activated receptor (PPAR)gamma. One of these agents, troglitazone, was also proposed to protect beta cells against FFA-induced toxicity, but this effect has not yet been directly demonstrated. We recently reported in vitro conditions under which free fatty acids (FFA) cause beta cell death by necrosis or apoptosis. The present study investigates whether troglitazone (10 microM) interferes with this FFA-induced toxicity. Addition of this compound did not protect against oleate- or palmitate-induced toxicity. On the contrary, it increased palmitate-induced necrosis during the first two days of culture, and elevated (increase by 10-20%, P<0.05) both oleate- and palmitate-induced apoptosis after 8 days. These results do not support the view that troglitazone exerts a direct protective effect on beta cells that are exposed to cytotoxic FFA concentrations. They instead indicate that the agent may sensitize pancreatic beta cells to FFA-induced damage, raising the possibility that its use facilitates the deleterious effect of increased FFA levels on the pancreatic beta cell mass.