Targeted disruption of inducible nitric oxide synthase protects against obesity-linked insulin resistance in muscle

Skeletal muscle glucose metabolism and inflammation in the development of the metabolic syndrome

Insulin resistance and metabolic dysfunction in skeletal muscle play a major role in the development of the metabolic syndrome and type 2 diabetes. Numerous mechanisms have been proposed to explain the pathophysiology of obesity-linked metabolic dysfunction and this review will focus on the contributing role of adiponectin and inflammation. The beneficial effects of adiponectin on both insulin action and inflammation are now well documented and will be reviewed. More recent work provided new insights into adiponectin signaling mechanisms. The development of strategies to mimic adiponectin action holds promise that adiponectin-based compounds may translate into effective therapeutic applications. We will also discussed the novel role of long chain ω-3 PUFA-derived resolution mediators, which in addition to resolving inflammation, can also exert glucoregulatory effects in models of obesity and insulin resistance. We will focus on one resolution mediator, protectin DX (PDX), which was recently shown to act as a muscle interleukin-6 secretagogue. PDX and its isomer PD1 also enhance adiponectin expression and action. Ultimately, it is via a better understanding the molecular mechanisms of action via which inflammation, insulin resistance and metabolic dysfunction occur in skeletal muscle, and also how they crosstalk with each other, that we can generate new and improved therapies for obesity-linked metabolic complications.

Inflammatory stimuli induce inhibitory S-nitrosylation of the deacetylase SIRT1 to increase acetylation and activation of p53 and p65

Inflammation increases the abundance of inducible nitric oxide synthase (iNOS), leading to enhanced production of nitric oxide (NO), which can modify proteins by S-nitrosylation. Enhanced NO production increases the activities of the transcription factors p53 and nuclear factor κB (NF-κB) in several models of disease-associated inflammation. S-nitrosylation inhibits the activity of the protein deacetylase SIRT1. SIRT1 limits apoptosis and inflammation by deacetylating p53 and p65 (also known as RelA), a subunit of NF-κB. We showed in multiple cultured mammalian cell lines that NO donors or inflammatory stimuli induced S-nitrosylation of SIRT1 within CXXC motifs, which inhibited SIRT1 by disrupting its ability to bind zinc. Inhibition of SIRT1 reduced deacetylation and promoted activation of p53 and p65, leading to apoptosis and increased expression of proinflammatory genes. In rodent models of systemic inflammation, Parkinson's disease, or aging-related muscular atrophy, S-nitrosylation of SIRT1 correlated with increased acetylation of p53 and p65 and activation of p53 and NF-κB target genes, suggesting that S-nitrosylation of SIRT1 may represent a proinflammatory switch common to many diseases and aging.

Adipose tissue signaling by nuclear receptors in metabolic complications of obesity

In recent years white adipose tissue inflammation has been recognized to be associated with obesity. Adipocytes and adipose tissue associated macrophages (ATMs) secrete bioactive molecules, including adipokines, chemokines/cytokines and free fatty acids that modulate the development of low-grade inflammation and insulin resistance responsible for obesity-related metabolic and cardiovascular diseases. Nuclear receptors, notably peroxisome-proliferator-activated receptors, are sensors of dietary lipids and control transcriptional programs of key metabolic and inflammatory pathways in adipocytes and macrophages. This review focuses on mechanisms by which nuclear receptors maintain white adipose tissue homeostasis. The identification of ATMs as active players in the initiation of chronic inflammation and the links between inflammatory signaling and metabolic dysfunction will be presented, followed by discussion of recent evidence for nuclear receptors in ATM function, with an emphasis on the paracrine interaction between adipocytes and ATMs.

Macrophage HIF-2α ameliorates adipose tissue inflammation and insulin resistance in obesity

In obesity, adipose tissue macrophages (ATMs) play a key role in mediating proinflammatory responses in the adipose tissue, which are associated with obesity-related metabolic complications. Recently, adipose tissue hypoxia has been implicated in the regulation of ATMs in obesity. However, the role of hypoxia-inducible factor (HIF)-2α, one of the major transcription factors induced by hypoxia, has not been fully elucidated in ATMs. In this study, we demonstrate that elevation of macrophage HIF-2α would attenuate adipose tissue inflammation and improve insulin resistance in obesity. In macrophages, overexpression of HIF-2α decreased nitric oxide production and suppressed expression of proinflammatory cytokines through induction of arginase 1. HIF-2α-overexpressing macrophages alleviated proinflammatory responses and improved insulin resistance in adipocytes. In contrast, knockdown of macrophage HIF-2α augmented palmitate-induced proinflammatory gene expression in adipocytes. Furthermore, compared with wild-type mice, Hif-2α heterozygous-null mice aggravated insulin resistance and adipose tissue inflammation with more M1-like ATMs upon high-fat diet (HFD). Moreover, glucose intolerance in HFD-fed Hif-2α heterozygous-null mice was relieved by macrophage depletion with clodronate treatment, implying that increase of proinflammatory ATMs is responsible for insulin resistance by haplodeficiency of Hif-2α upon HFD. Taken together, these data suggest that macrophage HIF-2α would counteract the proinflammatory responses to relieve obesity-induced insulin resistance in adipose tissue.

Finger millet bran supplementation alleviates obesity-induced oxidative stress, inflammation and gut microbial derangements in high-fat diet-fed mice

Several epidemiological studies have shown that the consumption of finger millet (FM) alleviates diabetes-related complications. In the present study, the effect of finger millet whole grain (FM-WG) and bran (FM-BR) supplementation was evaluated in high-fat diet-fed LACA mice for 12 weeks. Mice were divided into four groups: control group fed a normal diet (10 % fat as energy); a group fed a high-fat diet; a group fed the same high-fat diet supplemented with FM-BR; a group fed the same high-fat diet supplemented with FM-WG. The inclusion of FM-BR at 10 % (w/w) in a high-fat diet had more beneficial effects than that of FM-WG. FM-BR supplementation prevented body weight gain, improved lipid profile and anti-inflammatory status, alleviated oxidative stress, regulated the expression levels of several obesity-related genes, increased the abundance of beneficial gut bacteria (Lactobacillus, Bifidobacteria and Roseburia) and suppressed the abundance of Enterobacter in caecal contents (P≤ 0·05). In conclusion, FM-BR supplementation could be an effective strategy for preventing high-fat diet-induced changes and developing FM-BR-enriched functional foods.

Macrophages inhibit insulin signalling in adipocytes: role of inducible nitric oxide synthase and nitric oxide

OBJECTIVES

The interaction of immune cells with adipocytes within the adipose tissues in obese persons with diabetes mellitus may play a role in insulin resistance. We examined in vitro whether nitric oxide (NO) and inducible nitric oxide synthase (iNOS) play a role in impaired insulin signalling in adipocytes exposed to activated macrophages.

METHODS

We used a co-culture system in which Raw264.7 macrophages were plated over differentiated, low passage 3T3-L1 cells (dif3T3) at a cell density ratio of 1:2. Inflammation was induced by a challenge with bacterial lipopolysaccharide.

RESULTS

Significantly (p<0.001) enhanced iNOS expression and NO synthesis was observed in activated co-cultures. In the co-cultures as compared with Raw264.7 cells alone, iNOS protein was induced up to 11-fold above background, and NO release was significantly (p<0.001) increased up to 2.8-fold. Co-culturing dif3T3 and Raw264.7 cells as compared to dif3T3 alone reduced insulin-induced Akt phosphorylation by 50% and AS160 phosphorylation by 42%. This was correlated with reduced glucose consumption when dif3T3 was exposed to 1,3-morpholinosydnonimine. Adiponectin, GLUT4 and AS160 mRNA were reduced by 4-fold, 5-fold and 2-fold, respectively, in co-cultures as compared to dif3T3 alone. On the contrary, GLUT1 mRNA levels were increased by 2-fold in co-cultures as compared to dif3T3. NG-monomethyl-L-arginine abolished NO production with modest reversal of Akt/AS160 phosphorylation.

CONCLUSIONS

This study demonstrated a potential association between iNOS/NO-mediated inflammation and insulin resistance.

Regulation of obesity and insulin resistance by nitric oxide

Obesity is a risk factor for developing type 2 diabetes and cardiovascular disease and has quickly become a worldwide pandemic with few tangible and safe treatment options. Although it is generally accepted that the primary cause of obesity is energy imbalance, i.e., the calories consumed are greater than are utilized, understanding how caloric balance is regulated has proven a challenge. Many "distal" causes of obesity, such as the structural environment, occupation, and social influences, are exceedingly difficult to change or manipulate. Hence, molecular processes and pathways more proximal to the origins of obesity-those that directly regulate energy metabolism or caloric intake-seem to be more feasible targets for therapy. In particular, nitric oxide (NO) is emerging as a central regulator of energy metabolism and body composition. NO bioavailability is decreased in animal models of diet-induced obesity and in obese and insulin-resistant patients, and increasing NO output has remarkable effects on obesity and insulin resistance. This review discusses the role of NO in regulating adiposity and insulin sensitivity and places its modes of action into context with the known causes and consequences of metabolic disease.

Oxidative stress and metabolic pathologies: from an adipocentric point of view

Oxidative stress plays a pathological role in the development of various diseases including diabetes, atherosclerosis, or cancer. Systemic oxidative stress results from an imbalance between oxidants derivatives production and antioxidants defenses. Reactive oxygen species (ROS) are generally considered to be detrimental for health. However, evidences have been provided that they can act as second messengers in adaptative responses to stress. Obesity represents a major risk factor for deleterious associated pathologies such as type 2 diabetes, liver, and coronary heart diseases. Many evidences regarding obesity-induced oxidative stress accumulated over the past few years based on established correlations of biomarkers or end-products of free-radical-mediated oxidative stress with body mass index. The hypothesis that oxidative stress plays a significant role in the development of metabolic disorders, especially insulin-resistance state, is supported by several studies where treatments reducing ROS production reverse metabolic alterations, notably through improvement of insulin sensitivity, hyperlipidemia, or hepatic steatosis. In this review, we will develop the mechanistic links between oxidative stress generated by adipose tissue in the context of obesity and its impact on metabolic complications development. We will also attempt to discuss potential therapeutic approaches targeting obesity-associated oxidative stress in order to prevent associated-metabolic complications.

The role of omega-3 fatty acid receptor GPR120 in insulin resistance

Obesity is the dominant cause of acquired insulin resistance, and it is the epidemic of obesity in the United States that is driving the markedly increasing incidence of type 2 diabetes. Adipocyte dysfunction and chronic low-grade adipose tissue (AT) inflammation are the major causes of insulin resistance. Abnormal accumulation and activation of AT macrophages (ATMs) and abnormal activation of the TLR4-mediated immune responses within ATMs are the key characters of the chronic low-grade AT inflammation associated with insulin resistance. We have recently shown that GPR120 acts as a physiological receptor of omega-3 fatty acid in macrophages and adipocytes, which mediate potent anti-inflammatory and insulin-sensitizing effects. The important role that GPR120 has in the control of inflammation raises the possibility that targeting this receptor could have therapeutic potential in many inflammatory diseases including obesity and type 2 diabetes. In this review paper, we discuss omega-3 fatty acid-sensing GPR120 and highlight the potential outcomes of targeting this receptor in ameliorating disease.

Increased adipocyte O2 consumption triggers HIF-1α, causing inflammation and insulin resistance in obesity

Adipose tissue hypoxia and inflammation have been causally implicated in obesity-induced insulin resistance. Here, we report that, early in the course of high-fat diet (HFD) feeding and obesity, adipocyte respiration becomes uncoupled, leading to increased oxygen consumption and a state of relative adipocyte hypoxia. These events are sufficient to trigger HIF-1α induction, setting off the chronic adipose tissue inflammatory response characteristic of obesity. At the molecular level, these events involve saturated fatty acid stimulation of the adenine nucleotide translocase 2 (ANT2), an inner mitochondrial membrane protein, which leads to the uncoupled respiratory state. Genetic or pharmacologic inhibition of either ANT2 or HIF-1α can prevent or reverse these pathophysiologic events, restoring a state of insulin sensitivity and glucose tolerance. These results reveal the sequential series of events in obesity-induced inflammation and insulin resistance.

A possible change process of inflammatory cytokines in the prolonged chronic stress and its ultimate implications for health

Sustained stress triggers series of changes in the brain and the body. At the early stage of stress, the activated hypothalamus-pituitary-adrenal (HPA) axis and sympathetic nervous system (SNS) axis can upregulate the levels of glucocorticoid (GCs) and catecholamines (CAs), respectively, and then they in turn inhibit the secretion of proinflammatory cytokines directly or indirectly while promoting the secretion of anti-inflammatory cytokines. At the prolonged stage, the sustained activated HPA demonstrates cortisol-resistance. At the same time, the inflammation related transcription pathway, such as nuclear-factor kappa-B (NF-κB) signaling, may be inhibited. Additionally, the inflammatory cytokines mediate a negative feedback regulation on themselves. Collectively, these regulations may increase the proinflammatory cytokines while decreasing the anti-inflammatory cytokines. This may further activate NF-κB and increase the proinflammation cytokines, which in turn reduce the inflammatory responses, contributing to various diseases.

Sexual dimorphism in white and brown adipose tissue with obesity and inflammation

This article is part of a Special Issue "Energy Balance". Obesity and its associated comorbidities remain at epidemic levels globally and show no signs of abatement in either adult or child populations. White adipose tissue has long been established as an endocrine signalling organ possessing both metabolic and immune functions. This role can become dysregulated following excess adiposity caused by adipocyte hypertrophy and hyperplasia. In contrast, brown adipose tissue (BAT) is only present in comparatively small amounts in the body but can significantly impact on heat production, and thus could prevent excess white adiposity. Obesity and associated risk factors for adverse metabolic health are not only linked with enlarged fat mass but also are dependent on its anatomical deposition. In addition, numerous studies have revealed a disparity in white adipose tissue deposition prior to and during the development of obesity between the sexes. Females therefore tend to develop a greater abundance of femoral and gluteal subcutaneous fat whereas males exhibit more central adiposity. In females, lower body subcutaneous adipose tissue depots appear to possess a greater capacity for lipid storage, enhanced lipolytic flux and hyperplastic tissue remodelling compared to visceral adipocytes. These differences are acknowledged to contribute to the poorer metabolic and inflammatory profiles observed in males. Importantly, the converse outcomes between sexes disappear after the menopause, suggesting a role for sex hormones within the onset of metabolic complications with obesity. This review further considers how BAT impacts upon on the relationship between excess adiposity, gender, inflammation and endocrine signalling and could thus ultimately be a target to prevent obesity.

CXCR3 modulates obesity-induced visceral adipose inflammation and systemic insulin resistance

OBJECTIVE

Chemokine (C-X-C motif) receptor 3 (CXCR3) is a chemokine receptor involved in the regulation of immune cell trafficking and activation. Increased CXCR3 expression in the visceral adipose of obese humans and mice was observed. A pathophysiologic role for CXCR3 in diet-induced obesity (DIO) was hypothesized.

METHODS

Wild-type (WT) C57B/L6J and chemokine receptor 3 knockout (CXCR3(-/-) ) mice were fed a high-fat diet (HFD) for 20 weeks followed by assessment of glucose metabolism and visceral adipose tissue (VAT) inflammation.

RESULTS

CXCR3(-/-) mice exhibited lower fasting glucose and improved glucose tolerance compared with WT-HFD mice, despite similar body mass. HFD-induced VAT innate and adaptive immune cell infiltration, including immature myeloid cells (CD11b(+) F4/80(lo) Ly6C(+) ), were markedly ameliorated in CXCR3(-/-) mice. In vitro IBIDI and in vivo migration assays demonstrated no CXCR3-mediated effect on macrophage or monocyte migration, respectively. CXCR3(-/-) macrophages, however, had a blunted response to interferon-γ, a TH 1 cytokine that induces macrophage activation.

CONCLUSIONS

A previously unreported role for CXCR3 in the development of HFD-induced insulin resistance (IR) and VAT macrophage infiltration in mice was demonstrated. Our results support pharmaceutical targeting of the CXCR3 receptor as a potential treatment for obesity/IR.

Screening native botanicals for bioactivity: an interdisciplinary approach

OBJECTIVE

Plant-based therapies have been used in medicine throughout recorded history. Information about the therapeutic properties of plants often can be found in local cultures as folk medicine is communicated from one generation to the next. The aim of this study was to identify native Louisiana plants from Creole folk medicine as a potential source of therapeutic compounds for the treatment of insulin resistance, type 2 diabetes, and related disorders.

METHODS

We used an interdisciplinary approach combining expertise in disciplines ranging from cultural anthropology and botany to biochemistry and endocrinology to screen native southwest Louisiana plants. Translation of accounts of Creole folk medicine yielded a list of plants with documented use in treating a variety of conditions, including inflammation. These plants were collected, vouchered, and catalogued before extraction of soluble components. Extracts were analyzed for bioactivity in regulating inflammatory responses in macrophages or fatty acid-induced insulin resistance in C2C12 skeletal muscle cells.

RESULTS

Several extracts altered gene expression of inflammatory markers in macrophages. Multiplex analysis of kinase activation in insulin-signaling pathways in skeletal muscle also identified a subset of extracts that alter insulin-stimulated protein kinase B phosphorylation in the presence of fatty-acid-induced insulin resistance.

CONCLUSION

An interdisciplinary approach to screening botanical sources of therapeutic agents can be successfully applied to identify native plants used in folk medicine as potential sources of therapeutic agents in treating insulin resistance in skeletal muscle or inflammatory processes associated with obesity-related insulin resistance.

Antioxidant and anti-inflammatory activities of berberine in the treatment of diabetes mellitus

Oxidative stress and inflammation are proved to be critical for the pathogenesis of diabetes mellitus. Berberine (BBR) is a natural compound isolated from plants such as Coptis chinensis and Hydrastis canadensis and with multiple pharmacological activities. Recent studies showed that BBR had antioxidant and anti-inflammatory activities, which contributed in part to its efficacy against diabetes mellitus. In this review, we summarized the antioxidant and anti-inflammatory activities of BBR as well as their molecular basis. The antioxidant and anti-inflammatory activities of BBR were noted with changes in oxidative stress markers, antioxidant enzymes, and proinflammatory cytokines after BBR administration in diabetic animals. BBR inhibited oxidative stress and inflammation in a variety of tissues including liver, adipose tissue, kidney and pancreas. Mechanisms of the antioxidant and anti-inflammatory activities of BBR were complex, which involved multiple cellular kinases and signaling pathways, such as AMP-activated protein kinase (AMPK), mitogen-activated protein kinases (MAPKs), nuclear factor erythroid-2-related factor-2 (Nrf2) pathway, and nuclear factor- κ B (NF- κ B) pathway. Detailed mechanisms and pathways for the antioxidant and anti-inflammatory activities of BBR still need further investigation. Clarification of these issues could help to understand the pharmacology of BBR in the treatment of diabetes mellitus and promote the development of antidiabetic natural products.

Differential regulation of adipose tissue and vascular inflammatory gene expression by chronic systemic inhibition of NOS in lean and obese rats

We tested the hypothesis that a decrease in bioavailability of nitric oxide (NO) would result in increased adipose tissue (AT) inflammation. In particular, we utilized the obese Otsuka Long Evans Tokushima Fatty rat model (n = 20) and lean Long Evans Tokushima Otsuka counterparts (n = 20) to determine the extent to which chronic inhibition of NO synthase (NOS) with N (ω) -nitro-l-arginine methyl ester (L-NAME) treatment (for 4 weeks) upregulates expression of inflammatory genes and markers of immune cell infiltration in retroperitoneal white AT, subscapular brown AT, periaortic AT as well as in its contiguous aorta free of perivascular AT. As expected, relative to lean rats (% body fat = 13.5 ± 0.7), obese rats (% body fat = 27.2 ± 0.8) were hyperlipidemic (total cholesterol 77.0 ± 2.1 vs. 101.0 ± 3.3 mg/dL), hyperleptinemic (5.3 ± 0.9 vs. 191.9 ± 59.9 pg/mL), and insulin-resistant (higher HOMA IR index [3.9 ± 0.8 vs. 25.2 ± 4.1]). Obese rats also exhibited increased expression of proinflammatory genes in perivascular, visceral, and brown ATs. L-NAME treatment produced a small but statistically significant decrease in percent body fat (24.6 ± 0.9 vs. 27.2 ± 0.8%) and HOMA IR index (16.9 ± 2.3 vs. 25.2 ± 4.1) in obese rats. Further, contrary to our hypothesis, we found that expression of inflammatory genes in all AT depots examined were generally unaltered with L-NAME treatment in both lean and obese rats. This was in contrast with the observation that L-NAME produced a significant upregulation of inflammatory and proatherogenic genes in the aorta. Collectively, these findings suggest that chronic NOS inhibition alters transcriptional regulation of proinflammatory genes to a greater extent in the aortic wall compared to its adjacent perivascular AT, or visceral white and subscapular brown AT depots.

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.

Targeting the Peroxisome Proliferator-Activated Receptor-γ to Counter the Inflammatory Milieu in Obesity

Adipose tissue, which was once viewed as a simple organ for storage of triglycerides, is now considered an important endocrine organ. Abnormal adipose tissue mass is associated with defects in endocrine and metabolic functions which are the underlying causes of the metabolic syndrome. Many adipokines, hormones secreted by adipose tissue, regulate cells from the immune system. Interestingly, most of these adipokines are proinflammatory mediators, which increase dramatically in the obese state and are believed to be involved in the pathogenesis of insulin resistance. Drugs that target peroxisome proliferator-activated receptor-γ have been shown to possess anti-inflammatory effects in animal models of diabetes. These findings, and the link between inflammation and the metabolic syndrome, will be reviewed here.

Type 2 diabetes mellitus--an autoimmune disease?

Inflammation-induced inhibition of the insulin signalling pathway can lead to insulin resistance and contribute to the development of type 2 diabetes mellitus (T2DM). Obesity and insulin resistance are associated with a chronic but subclinical inflammatory process that impairs insulin action in most tissues and could also hamper pancreatic β-cell function. The involvement of monocytic cells and the profiles of the chemokines and cytokines induced by this inflammation suggest an innate immune response. However, emerging data indicate that elements of the adaptive immune system could also be involved. As activation of an adaptive response requires antigen specificity, some researchers have hypothesized that T2DM evolves from an innate immune response to an autoimmune condition. In this Perspectives article, we present the arguments for and against this hypothesis and discuss which mechanisms could be involved in a putative switch from innate immunity to autoimmunity.

Effects of exercise and diet composition on expression of MCP-1 and oxidative stress-related mRNA of adipose tissue in diet-induced obese mice

The aim of the study was to analyze how the expression of MCP-1, HIF-1α, NOX2, ERK1, ERK2, and Mn-SOD mRNA, which are related to inflammation and oxidative stress and which can influence the accumulation of macrophage in obese adipose tissue, differed according to a high-fat diet, change of diet composition, and exercise. Obesity was induced using a high-fat diet (45% fat) for five weeks. This investigation analyzed how the change of diet composition for eight weeks and long-term exercise training affected the expression of mRNA in epididymal white adipose tissue. For the experiment, 56 four-week-old C57BL/6 mice were used. Their epididymal white adipose tissue was extracted and used in RT-PCR analysis to find the expression level of mRNA. A high-fat diet for 13 weeks showed a significant increase in the expression of MCP-1, HIF-1α, NOX2, and ERK1 mRNA in epididymal adipose tissue. Change in diet composition and exercise decreased the expression of MCP-1, HIF-1α, NOX2, and ERK1 mRNA. Particularly, the group combining a high-fat diet and exercise had a significant increase in the expression of Mn-SOD mRNA in epididymal adipose tissue; however, it showed a significant decrease in MCP-1, HIF-1α, and NOX2. These results suggest that the antioxidant effect and weight loss by exercise decreased inflammation and oxidative stress.

CEACAM1 loss links inflammation to insulin resistance in obesity and non-alcoholic steatohepatitis (NASH)

Mounting epidemiological evidence points to an association between metabolic syndrome and non-alcoholic steatohepatitis (NASH), an increasingly recognized new epidemic. NASH pathologies include hepatocellular ballooning, lobular inflammation, hepatocellular injury, apoptosis, and hepatic fibrosis. We will review the relationship between insulin resistance and inflammation in visceral obesity and NASH in an attempt to shed more light on the pathogenesis of these major metabolic diseases. Moreover, we will identify loss of the carcinoembryonic antigen-related cell adhesion molecule 1 as a unifying mechanism linking the immunological and metabolic abnormalities in NASH.

Metformin attenuates the exacerbation of the allergic eosinophilic inflammation in high fat-diet-induced obesity in mice

A positive relationship between obesity and asthma has been well documented. The AMP-activated protein kinase (AMPK) activator metformin reverses obesity-associated insulin resistance (IR) and inhibits different types of inflammatory responses. This study aimed to evaluate the effects of metformin on the exacerbation of allergic eosinophilic inflammation in obese mice. Male C57BL6/J mice were fed for 10 weeks with high-fat diet (HFD) to induce obesity. The cell infiltration and inflammatory markers in bronchoalveolar lavage (BAL) fluid and lung tissue were evaluated at 48 h after ovalbumin (OVA) challenge. HFD obese mice displayed peripheral IR that was fully reversed by metformin (300 mg/kg/day, two weeks). OVA-challenge resulted in higher influx of total cell and eosinophils in lung tissue of obese mice compared with lean group. As opposed, the cell number in BAL fluid of obese mice was reduced compared with lean group. Metformin significantly reduced the tissue eosinophil infiltration and prevented the reduction of cell counts in BAL fluid. In obese mice, greater levels of eotaxin, TNF-α and NOx, together with increased iNOS protein expression were observed, all of which were normalized by metformin. In addition, metformin nearly abrogated the binding of NF-κB subunit p65 to the iNOS promoter gene in lung tissue of obese mice. Lower levels of phosphorylated AMPK and its downstream target acetyl CoA carboxylase (ACC) were found in lung tissue of obese mice, which were restored by metformin. In separate experiments, the selective iNOS inhibitor aminoguanidine (20 mg/kg, 3 weeks) and the anti-TNF-α mAb (2 mg/kg) significantly attenuated the aggravation of eosinophilic inflammation in obese mice. In conclusion, metformin inhibits the TNF-α-induced inflammatory signaling and NF-κB-mediated iNOS expression in lung tissue of obese mice. Metformin may be a good pharmacological strategy to control the asthma exacerbation in obese individuals.

A journey in science: promise, purpose, privilege

Real innovations in medicine and science are historic and singular; the stories behind each occurrence are precious. At Molecular Medicine we have established the Anthony Cerami Award in Translational Medicine to document and preserve these histories. The monographs recount the seminal events as told in the voice of the original investigators who provided the crucial early insight. These essays capture the essence of discovery, chronicling the birth of ideas that created new fields of research; and launched trajectories that persisted and ultimately influenced how disease is prevented, diagnosed, and treated. In this volume, the first Cerami Award Monograph, by Carl Nathan, MD, chairman of the Department of Microbiology and Immunology at Weill Cornell Medical College, reflects towering genius and soaring inspiration.

Diet-induced obesity alters immune cell infiltration and expression of inflammatory cytokine genes in mouse ovarian and peri-ovarian adipose depot tissues

Dysregulation of immune cells and/or altered inflammatory signaling have been implicated with reproductive dysfunction. Physiological changes leading to perturbations in the profile of immune cells and/or pro-inflammatory cytokines in or around female reproductive tissue could potentially have profound effects on ovarian function. Obesity is associated with chronic low-grade inflammation due, in part, to increased immune cell infiltration and inflammation in visceral adipose depots. This study investigated the impact of diet-induced obesity on immune cell infiltration and inflammation in peri-ovarian adipose tissue and mRNA expression of key inflammatory markers and microRNAs (miRs) in ovarian tissue. Six-week-old female C57Bl/6J mice were fed a standard chow or high-fat diet (HFD; 60% kcal fat) for approximately 7 months, at which time peri-ovarian adipose tissue and ovarian tissues were collected. Histological analysis of peri-ovarian adipose tissue from obese mice revealed increased (P < 0.05) adipocyte size and the presence of crown-like structures, the morphological presentation of infiltrating immune cells in adipose tissue, along with increases (P < 0.05) in the mRNA levels of markers of T-cells, activated macrophages, inflammatory cytokines, and chemokines. Ovarian mRNA levels of Il1b, Il6, Tnfa, p55, p75, Ccl2, Ikbkb, and Rela were higher in obese tissue (P < 0.05), with a strong trend (P = 0.06) for an increase in Nos2 and RELA protein. Additionally, ovarian miR125b and miR143 levels were decreased (P = 0.1). These data demonstrate that diet-induced obesity elevates expression of inflammatory-mediator genes in both the ovary and surrounding adipose depot, potentially negatively affecting ovarian function.

Late-life enalapril administration induces nitric oxide-dependent and independent metabolic adaptations in the rat skeletal muscle

Recently, we showed that administration of the angiotensin-converting enzyme inhibitor enalapril to aged rats attenuated muscle strength decline and mitigated apoptosis in the gastrocnemius muscle. The aim of the present study was to investigate possible mechanisms underlying the muscle-protective effects of enalapril. We also sought to discern the effects of enalapril mediated by nitric oxide (NO) from those independent of this signaling molecule. Eighty-seven male Fischer 344 × Brown Norway rats were randomly assigned to receive enalapril (n = 23), the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; n = 22), enalapril + L-NAME (n = 19), or placebo (n = 23) from 24 to 27 months of age. Experiments were performed on the tibialis anterior muscle. Total NOS activity and the expression of neuronal, endothelial, and inducible NOS isoforms (nNOS, eNOS, and iNOS) were determined to investigate the effects of enalapril on NO signaling. Transcript levels of tumor necrosis factor-alpha (TNF-α) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) were assessed to explore actions of enalapril on inflammation and mitochondrial biogenesis, respectively. Protein expression of energy-sensing and insulin signaling mediators, including protein kinase B (Akt-1), phosphorylated Akt-1 (pAkt-1), mammalian target of rapamycin (mTOR), AMP-activated protein kinase subunit alpha (AMPKα), phosphorylated AMPKα (pAMPKα), and the glucose transporter GLUT-4, was also determined. Finally, the generation of hydrogen peroxide (H2O2) was quantified in subsarcolemmal (SSM) and intermyofibrillar (IFM) mitochondria. Enalapril increased total NOS activity, which was prevented by L-NAME co-administration. eNOS protein content was enhanced by enalapril, but not by enalapril + L-NAME. Gene expression of iNOS was down-regulated by enalapril either alone or in combination with L-NAME. In contrast, protein levels of nNOS were unaltered by treatments. The mRNA abundance of TNF-α was reduced by enalapril relative to placebo, with no differences among any other group. PCG-1α gene expression was unaffected by enalapril and lowered by enalapril + L-NAME. No differences in protein expression of Akt-1, pAkt-1, AMPKα, pAMPKα, or GLUT-4 were detected among groups. However, mTOR protein levels were increased by enalapril compared with placebo. Finally, all treatment groups displayed reduced SSM, but not IFM H2O2 production relative to placebo. Our data indicate that enalapril induces a number of metabolic adaptations in aged skeletal muscle. These effects result from the concerted modulation of NO and angiotensin II signaling, rather than from a dichotomous action of enalapril on the two pathways. Muscle protection by enalapril administered late in life appears to be primarily mediated by mitigation of oxidative stress and pro-inflammatory signaling.

The beneficial role of vitamin D in obesity: possible genetic and cell signaling mechanisms

The prevalence rates of overweight and obesity are considered an important public issue in the United States, and both of these conditions are increasing among both children and adults. There is evidence of aberrations in the vitamin D-endocrine system in obese subjects. Vitamin D deficiency is highly prevalent in patients with obesity, and many studies have demonstrated the significant effect of calcitriol on adipocytes. Genetic studies have provided an opportunity to determine which proteins link vitamin D to obesity pathology, including the vitamin D receptor, toll-like receptors, the renin-angiotensin system, apolipoprotein E, vascular endothelial growth factor, and poly (ADP-ribose) polymerase-1. Vitamin D also exerts its effect on obesity through cell-signaling mechanisms, including matrix metalloproteinases, mitogen-activated protein kinase pathways, the reduced form of nicotinamide adenine dinucleotide phosphate, prostaglandins, reactive oxygen species, and nitric oxide synthase.

In conclusion, vitamin D may have a role in obesity. The best form of vitamin D for use in the obese individuals is calcitriol because it is the active form of the vitamin D₃ metabolite, its receptors are present in adipocytes, and modulates inflammatory cytokine expression.

Increased plasma citrulline in mice marks diet-induced obesity and may predict the development of the metabolic syndrome

In humans, plasma amino acid concentrations of branched-chain amino acids (BCAA) and aromatic amino acids (AAA) increase in states of obesity, insulin resistance and diabetes. We here assessed whether these putative biomarkers can also be identified in two different obesity and diabetic mouse models. C57BL/6 mice with diet-induced obesity (DIO) mimic the metabolic impairments of obesity in humans characterized by hyperglycemia, hyperinsulinemia and hepatic triglyceride accumulation. Mice treated with streptozotocin (STZ) to induce insulin deficiency were used as a type 1 diabetes model. Plasma amino acid profiling of two high fat (HF) feeding trials revealed that citrulline and ornithine concentrations are elevated in obese mice, while systemic arginine bioavailability (ratio of plasma arginine to ornithine + citrulline) is reduced. In skeletal muscle, HF feeding induced a reduction of arginine levels while citrulline levels were elevated. However, arginine or citrulline remained unchanged in their key metabolic organs, intestine and kidney. Moreover, the intestinal conversion of labeled arginine to ornithine and citrulline in vitro remained unaffected by HF feeding excluding the intestine as prime site of these alterations. In liver, citrulline is mainly derived from ornithine in the urea cycle and DIO mice displayed reduced hepatic ornithine levels. Since both amino acids share an antiport mechanism for mitochondrial import and export, elevated plasma citrulline may indicate impaired hepatic amino acid handling in DIO mice. In the insulin deficient mice, plasma citrulline and ornithine levels also increased and additionally these animals displayed elevated BCAA and AAA levels like insulin resistant and diabetic patients. Therefore, type 1 diabetic mice but not DIO mice show the “diabetic fingerprint” of plasma amino acid changes observed in humans. Additionally, citrulline may serve as an early indicator of the obesity-dependent metabolic impairments.

Endothelial relaxation mechanisms and nitrative stress are partly restored by Vitamin D3 therapy in a rat model of polycystic ovary syndrome

AIMS

In polycystic ovary syndrome (PCOS), metabolic and cardiovascular dysfunction is related to hyperandrogenic status and insulin resistance, however, Vitamin D3 has a beneficial effect partly due to its anti-oxidant capacity. Nitrative stress is a major factor in the development of cardiovascular dysfunction and insulin resistance in various diseases. Our aim was to determine the effects of vitamin D3 in a rat model of PCOS, particularly the pathogenic role of nitrative stress.

MAIN METHODS

Female Wistar rats weighing 100-140g were administered vehicle (C), dihydrotestosterone (DHT) or dihydrotestosterone plus vitamin D3 (DHT+D) (n=10 per group). On the 10th week, acetylcholine (Ach) induced relaxation ability of the isolated thoracic aorta rings was determined. In order to examine the possible role of endothelial nitric oxide synthase (eNOS) and cyclooxygenase-2 (COX-2) pathways in the impaired endothelial function, immunohistochemical labeling of aortas with anti-eNOS and anti-COX-2 antibodies was performed. Leukocyte smears, aorta and ovary tissue sections were also immunostained with anti-nitrotyrosine antibody to determine nitrative stress.

KEY FINDINGS

Relaxation ability of aorta was reduced in group DHT, and vitamin D3 partly restored Ach induced relaxation. eNOS labeling was significantly lower in DHT rats compared to the other two groups, however COX-2 staining showed an increment. Nitrative stress showed a significant increase in response to dihydrotestosterone, while vitamin D3 treatment, in case of the ovaries, was able to reverse this effect.

SIGNIFICANCE

Nitrative stress may play a role in the pathogenesis of PCOS and in the development of the therapeutic effect of vitamin D3.

AMPK and insulin action--responses to ageing and high fat diet

The 5′-AMP-activated protein kinase (AMPK) is considered “a metabolic master-switch” in skeletal muscle reducing ATP- consuming processes whilst stimulating ATP regeneration. Within recent years, AMPK has also been proposed as a potential target to attenuate insulin resistance, although the exact role of AMPK is not well understood. Here we hypothesized that mice lacking α2AMPK activity in muscle would be more susceptible to develop insulin resistance associated with ageing alone or in combination with high fat diet. Young (∼4 month) or old (∼18 month) wild type and muscle specific α2AMPK kinase-dead mice on chow diet as well as old mice on 17 weeks of high fat diet were studied for whole body glucose homeostasis (OGTT, ITT and HOMA-IR), insulin signaling and insulin-stimulated glucose uptake in muscle. We demonstrate that high fat diet in old mice results in impaired glucose homeostasis and insulin stimulated glucose uptake in both the soleus and extensor digitorum longus muscle, coinciding with reduced insulin signaling at the level of Akt (pSer473 and pThr308), TBC1D1 (pThr590) and TBC1D4 (pThr642). In contrast to our hypothesis, the impact of ageing and high fat diet on insulin action was not worsened in mice lacking functional α2AMPK in muscle. It is concluded that α2AMPK deficiency in mouse skeletal muscle does not cause muscle insulin resistance in young and old mice and does not exacerbate obesity-induced insulin resistance in old mice suggesting that decreased α2AMPK activity does not increase susceptibility for insulin resistance in skeletal muscle.

Liver sinusoidal endothelial cells link hyperinsulinemia to hepatic insulin resistance

Insulin signaling in vascular endothelial cells (ECs) is critical to maintain endothelial function but also to mediate insulin action on peripheral glucose disposal. However, gene knockout studies have reached disparate conclusions. Thus, insulin receptor inactivation in ECs does not impair insulin action, whereas inactivation of Irs2 does. Previously, we have shown that endothelial ablation of the three Foxo genes protects mice from atherosclerosis. Interestingly, here we show that mice lacking FoxO isoforms in ECs develop hepatic insulin resistance through excessive generation of nitric oxide (NO) that impairs insulin action in hepatocytes via tyrosine nitration of insulin receptors. Coculture experiments demonstrate that NO produced in liver sinusoidal ECs impairs insulin's ability to suppress glucose production in hepatocytes. The effects of liver sinusoidal ECs can be mimicked by NO donors and can be reversed by NO inhibitors in vivo and ex vivo. The findings are consistent with a model in which excessive, rather than reduced, insulin signaling in ECs predisposes to systemic insulin resistance, prompting a reevaluation of current approaches to insulin sensitization.

Blood flow restriction enhances post-resistance exercise angiogenic gene expression

PURPOSE

The objective of this study is to evaluate the effects of blood flow restriction (BFR) on muscle oxygenation during low-intensity resistance exercise as well as postexercise expression of molecules related to physiological angiogenesis.

METHODS

Using a randomized cross-over design, six apparently healthy young adults (22 ± 1 yr) performed 120 unilateral knee extensions at 40% of 1 repetition maximum with and without BFR (CNTRL). Near-infrared spectroscopy was used to measure oxygenation of the vastus lateralis during exercise. Serum and muscle expression of Post-Resistance vascular endothelial growth factor (VEGF) were determined preexercise, 4 h postexercise, and 24 h postexercise. Transcript (mRNA) expression of VEGF and other angiogenic genes was also determined.

RESULTS

BFR increased muscle hemoglobin (Hb) concentrations during exercise (14.4 ± 1.6 vs. 0.9 ± 1.6, P = 0.002), driven largely by an increase in deoxygenated Hb (11.0 ± 2.5 vs. 0.5 ± 1.1, P = 0.030). BFR also increased (P < 0.05) transcript expression of VEGF, VEGF-R2, hypoxia-inducible factor 1 alpha, inducible nitric oxide synthase (NOS), and neuronal NOS. The most dramatic change in response to BFR was an increase in VEGF mRNA at 4 h postexercise (4.1 ± 0.6 vs. 0.6 ± 0.2-fold change, P = 0.028). Compared with control, transcript expression of endothelial NOS, serum VEGF, or muscle protein expression of VEGF was not altered in response to BFR (P > 0.05).

CONCLUSION

Acute BFR increases postexercise expression of mRNA related to skeletal muscle angiogenesis, plausibly in response to changes in muscle Hb concentrations.

iNOS inhibitor, L-NIL, reverses burn-induced glycogen synthase kinase-3β activation in skeletal muscle of rats

OBJECTIVES

Recent studies suggest that activation of glycogen synthase kinase (GSK)-3β may be involved in burn injury-induced metabolic derangements and protein breakdown in skeletal muscle. However, the mechanism for GSK-3β activation after burn injury is unknown. To investigate the role of inducible nitric oxide synthase (iNOS) in this scenario, a major mediator of inflammation, we examined the effects of a specific inhibitor for iNOS, L-NIL, on GSK-3β activity in skeletal muscle of burned rats.

MATERIALS/METHODS

Full-thickness third degree burn injury comprising 40% of total body surface area was produced under anesthesia in male Sprague-Dawley rats (160-190g) by immersing the back of the trunk for 15s and the abdomen for 8s in 80°C water. Burned and sham-burned rats were treated with L-NIL (60mg/kg BW, b.i.d., IP) or phosphate-buffered saline for three days. GSK-3β activity in skeletal muscle was evaluated by immune complex kinase assay, and by phosphorylation status of GSK-3β and its endogenous substrate, glycogen synthase.

RESULTS

GSK-3β activity was increased in a time-dependent manner in skeletal muscle after burn injury, concomitant with the induction of iNOS expression. iNOS inhibitor, L-NIL, reverted the elevated GSK-3β activity in skeletal muscle of burned rats, although L-NIL did not alter GSK-3β activity in sham-burned rats.

CONCLUSIONS

Our results clearly indicate that iNOS plays an important role in burn injury-induced GSK-3β activation in skeletal muscle. These findings suggest that iNOS may contribute to burn injury-induced metabolic derangements, in part, by activating GSK-3β.

AMP-activated protein kinase (AMPK)α2 plays a role in determining the cellular fate of glucose in insulin-resistant mouse skeletal muscle

AIMS/HYPOTHESIS

We determined whether: (1) an acute lipid infusion impairs skeletal muscle AMP-activated protein kinase (AMPK)α2 activity, increases inducible nitric oxide synthase (iNOS) and causes peripheral insulin resistance in conscious, unstressed, lean mice; and (2) restoration of AMPKα2 activity during the lipid infusion attenuates the increase in iNOS and reverses the defect in insulin sensitivity in vivo.

METHODS

Chow-fed, 18-week-old C57BL/6J male mice were surgically catheterised. After 5 days they received: (1) a 5 h infusion of 5 ml kg(-1) h(-1) Intralipid + 6 U/h heparin (Lipid treatment) or saline (Control); (2) Lipid treatment or Control, followed by a 2 h hyperinsulinaemic-euglycaemic clamp (insulin clamp; 4 mU kg(-1) min(-1)); and (3) infusion of the AMPK activator, 5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR) (1 mg kg(-1) min(-1)), or saline during Lipid treatment, followed by a 2 h insulin clamp. In a separate protocol, mice producing a muscle-specific kinase-dead AMPKα2 subunit (α2-KD) underwent an insulin clamp to determine the role of AMPKα2 in insulin-mediated muscle glucose metabolism.

RESULTS

Lipid treatment decreased AMPKα2 activity, increased iNOS abundance/activation and reduced whole-body insulin sensitivity in vivo. AICAR increased AMPKα2 activity twofold; this did not suppress iNOS or improve whole-body or tissue-specific rates of glucose uptake during Lipid treatment. AICAR caused a marked increase in insulin-mediated glycogen synthesis in skeletal muscle. Consistent with this latter result, lean α2-KD mice exhibited impaired insulin-stimulated glycogen synthesis even though muscle glucose uptake was not affected.

CONCLUSIONS/INTERPRETATION

Acute induction of insulin resistance via lipid infusion in healthy mice impairs AMPKα2, increases iNOS and causes insulin resistance in vivo. However, these changes do not appear to be interrelated. Rather, a functionally active AMPKα2 subunit is required for insulin-stimulated muscle glycogen synthesis.

Insulin resistance and atherosclerosis

Insulin resistance is a complex metabolic defect that has several causes dependent on an individual's genetic substrate and the underlying pathophysiologic state. Atherogenic dyslipidemia, hyperinsulinemia, dysglycemia, inflammation associated with obesity, and ectopic steatosis in liver and skeletal muscle all collude to facilitate endothelial dysfunction and predispose to the initiation and propagation of atherosclerosis. As aggressive management of the various risk factors does not seem to abrogate the so-called residual risk, more research is needed to define ways by which intervention can fundamentally alter the metabolic and vascular milieu and slow the pace of atherosclerosis, thus favorably affecting outcomes.

Mitochondrial dysfunction and activation of iNOS are responsible for the palmitate-induced decrease in adiponectin synthesis in 3T3L1 adipocytes

Mitochondrial dysfunction and endoplasmic reticulum (ER) stress are considered the key determinants of insulin resistance. Impaired mitochondrial function in obese animals was shown to induce the ER stress response, resulting in reduced adiponectin synthesis in adipocytes. The expression of inducible nitric oxide synthase (iNOS) is increased in adipose tissues in genetic and dietary models of obesity. In this study, we examined whether activation of iNOS is responsible for palmitate-induced mitochondrial dysfunction, ER stress, and decreased adiponectin synthesis in 3T3L1 adipocytes. As expected, palmitate increased the expression levels of iNOS and ER stress response markers, and decreased mitochondrial contents. Treatment with iNOS inhibitor increased adiponectin synthesis and reversed the palmitate-induced ER stress response. However, the iNOS inhibitor did not affect the palmitate-induced decrease in mitochondrial contents. Chemicals that inhibit mitochondrial function increased iNOS expression and the ER stress response, whereas measures that increase mitochondrial biogenesis (rosiglitazone and adenoviral overexpression of nuclear respiratory factor-1) reversed them. Inhibition of mitochondrial biogenesis prevented the rosiglitazone-induced decrease in iNOS expression and increase in adiponectin synthesis. These results suggest that palmitate-induced mitochondrial dysfunction is the primary event that leads to iNOS induction, ER stress, and decreased adiponectin synthesis in cultured adipocytes.

Targeted disruption of inducible nitric oxide synthase protects against aging, S-nitrosation, and insulin resistance in muscle of male mice

Accumulating evidence has demonstrated that S-nitrosation of proteins plays a critical role in several human diseases. Here, we explored the role of inducible nitric oxide synthase (iNOS) in the S-nitrosation of proteins involved in the early steps of the insulin-signaling pathway and insulin resistance in the skeletal muscle of aged mice. Aging increased iNOS expression and S-nitrosation of major proteins involved in insulin signaling, thereby reducing insulin sensitivity in skeletal muscle. Conversely, aged iNOS-null mice were protected from S-nitrosation-induced insulin resistance. Moreover, pharmacological treatment with an iNOS inhibitor and acute exercise reduced iNOS-induced S-nitrosation and increased insulin sensitivity in the muscle of aged animals. These findings indicate that the insulin resistance observed in aged mice is mainly mediated through the S-nitrosation of the insulin-signaling pathway.

Thioredoxin and thioredoxin reductase in relation to reversible S-nitrosylation

SIGNIFICANCE

Nitric oxide (NO) regulates a diverse range of cellular processes, including vasodilation, neurotransmission, and antimicrobial and anti-tumor activities. S-nitrosylation with the formation of S-nitrosothiols (RSNOs) is an important feature of NO signaling regulating protein function. In mammalian cells, glutathione (GSH), S-nitrosoglutathione reductase (GSNOR), and thioredoxin (Trx) have been identified as the major protein denitrosylases.

RECENT ADVANCES

Human cytosolic/nuclear Trx1 in the disulfide form can be nitrosylated at Cys73 and transnitrosylate target proteins, including caspase 3. Thus, similar to GSH, which by forming S-nitrosoglutathione (GSNO) can transnitrosylate proteins, Trx can either denitrosylate or nitrosylate proteins depending on its oxidation state.

CRITICAL ISSUES

In this review, we discuss the regulation of cellular processes by reversible S-nitrosylation and Trx-mediated cellular homeostasis of RSNOs and S-nitrosoproteins.

FUTURE DIRECTIONS

Functions of RSNOs in vivo and their pharmacological uses have not yet been fully studied. Further investigations on the role of Trx systems in relation to biologically relevant RSNOs, their functions, and the mechanisms of denitrosylation will facilitate the development of drugs and therapies. Antioxid. Redox Signal. 18, 259-269.

Sphingolipid metabolism and obesity-induced inflammation

Obesity is a metabolic disorder developed by overnutrition and a major cause for insulin resistance and cardiovascular events. Since adipose tissue is one of the major sites for the synthesis and secretion of cytokines, enlarged adipose tissue in obese condition alters inflammatory state leading to pathophysiological conditions such as type 2 diabetes and increased cardiovascular risk. A plausible theory for development of metabolic dysregulation is that obesity increases secretion of inflammatory cytokines from adipose tissue and causes a chronic inflammation in the whole body. Additionally accumulation of lipids in non-adipose tissues elevates the cellular levels of bioactive lipids that inhibit the signaling pathways implicated in metabolic regulation together with activated inflammatory response. Recent findings suggest that obesity-induced inflammatory response leads to modulation of sphingolipid metabolism and these bioactive lipids may function as mediators for increased risk of metabolic dysfunction. Importantly, elucidation of mechanism regarding sphingolipid metabolism and inflammatory disease will provide crucial information to development of new therapeutic strategies for the treatment of obesity-induced pathological inflammation.

Oxidative stress in diabetes

Oxidative stress and diabetes, both Type 1 and Type 2 as well as their related conditions have been extensively studied. As diabetes, obesity and metabolic syndrome have reached at epidemic levels, there is a huge need and effort to understand the detailed molecular mechanisms of the possible redox imbalance, underlying the cause of pathology and progression of the disease. These studies provide new insights at cellular and subcellular levels to design effective clinical interventions. This chapter is intended to emphasize the latest knowledge and current evidence on the role of oxidative stress in diabetes as well as to discuss some key questions that are currently under discussion.

Brd2 gene disruption causes "metabolically healthy" obesity: epigenetic and chromatin-based mechanisms that uncouple obesity from type 2 diabetes

Disturbed body energy balance can lead to obesity and obesity-driven diseases such as Type 2 diabetes, which have reached an epidemic level. Evidence indicates that obesity-induced inflammation is a major cause of insulin resistance and Type 2 diabetes. Environmental factors, such as nutrients, affect body energy balance through epigenetic or chromatin-based mechanisms. As a bromodomain and external domain family transcription regulator, Brd2 regulates expression of many genes through interpretation of chromatin codes and participates in the regulation of body energy balance and immune function. In the severely obese state, Brd2 knockdown in mice prevented obesity-induced inflammatory responses, protected animals from insulin resistance, glucose intolerance and pancreatic beta cell dysfunction, and thus uncoupled obesity from diabetes. Brd2 provides an important model for investigation of the function of transcription regulators and the development of obesity and diabetes; it also provides a possible, innovative target to treat obesity and diabetes through modulation of the function of a chromatin code reader.

Differential nitric oxide levels in the blood and skeletal muscle of type 2 diabetic subjects may be consequence of adiposity: a preliminary study

BACKGROUND AND AIMS

Nitric oxide (NO·) exerts key regulatory functions including vasodilation and glucose uptake. Thus reduced NO· levels are associated with insulin resistance and hypertension. In this preliminary work we aimed to measure the levels of NO· metabolites in serum and skeletal muscle of obese and non-obese subjects, with or without type 2 diabetes mellitus (T2DM).

METHODS

Fifteen sedentary male participants [7 obese controls (C) vs 5 obese and 3 non-obese T2DM; age 54±9 years] were selected according to their BMI (>30 kg/m(2) for obese and 23-27 kg/m(2) for non-obese participants) and evaluated for fasted values of blood glucose, HbA1c, lipid profile, serum CRP (C-reactive protein), erythrocyte glutathione (GSH) metabolism, plasma adiponectin, leptin and cytokines (TNF-α and INFγ), serum and skeletal muscle nitric oxide metabolites (nitrite and nitrates; tNOx) and skeletal muscle nNOS and iNOS expression. Body composition was measured by whole body DEXA and muscle microbiopsy was performed in the vastus lateralis.

RESULTS

We found that serum tNOx (total nitrite/nitrate; μmol/L) was lower in obese T2DM group (12.7±3.5) when compared with their controls (21.1±2.4), although the non-obese group presented higher concentration of tNOx (33.8±7.2). Skeletal muscle nNOS was higher in obese controls, lower in non-obese T2DM and undetected in obese T2DM. On the other hand, expression of iNOS had an inverse relationship with nNOS, showing higher expression in obese T2DM, decrease in non-obese T2DM and absence in obese control group. tNOx levels (μmol/mg protein) were decreased in the non-obese T2DM group (12.07±0.59) when compared with the obese control (21.68±6.2) and the obese T2DM group (26.3±7.26).

CONCLUSION

We conclude that the decreased serum NO∙ production in obese T2DM patients seems to be associated with adipose mass as lower adiposity was associated with normal NO∙ which was reduced in the skeletal muscle of the non-obese T2DM patients. We suggest that the lower adiposity (and higher adiponectin) in non-obese T2DM could be responsible for differential levels of NO∙ production and insulin resistance.

Double-stranded RNA-activated protein kinase is a key modulator of insulin sensitivity in physiological conditions and in obesity in mice

The molecular integration of nutrient- and pathogen-sensing pathways has become of great interest in understanding the mechanisms of insulin resistance in obesity. The double-stranded RNA-dependent protein kinase (PKR) is one candidate molecule that may provide cross talk between inflammatory and metabolic signaling. The present study was performed to determine, first, the role of PKR in modulating insulin action and glucose metabolism in physiological situations, and second, the role of PKR in insulin resistance in obese mice. We used Pkr(-/-) and Pkr(+/+) mice to investigate the role of PKR in modulating insulin sensitivity, glucose metabolism, and insulin signaling in liver, muscle, and adipose tissue in response to a high-fat diet. Our data show that in lean Pkr(-/-) mice, there is an improvement in insulin sensitivity, and in glucose tolerance, and a reduction in fasting blood glucose, probably related to a decrease in protein phosphatase 2A activity and a parallel increase in insulin-induced thymoma viral oncogene-1 (Akt) phosphorylation. PKR is activated in tissues of obese mice and can induce insulin resistance by directly binding to and inducing insulin receptor substrate (IRS)-1 serine307 phosphorylation or indirectly through modulation of c-Jun N-terminal kinase and inhibitor of κB kinase β. Pkr(-/-) mice were protected from high-fat diet-induced insulin resistance and glucose intolerance and showed improved insulin signaling associated with a reduction in c-Jun N-terminal kinase and inhibitor of κB kinase β phosphorylation in insulin-sensitive tissues. PKR may have a role in insulin sensitivity under normal physiological conditions, probably by modulating protein phosphatase 2A activity and serine-threonine kinase phosphorylation, and certainly, this kinase may represent a central mechanism for the integration of pathogen response and innate immunity with insulin action and metabolic pathways that are critical in obesity.

Obese rats exhibit high levels of fat necrosis and isoprostanes in taurocholate-induced acute pancreatitis

BACKGROUND

Obesity is a prognostic factor for severity in acute pancreatitis in humans. Our aim was to assess the role of oxidative stress and abdominal fat in the increased severity of acute pancreatitis in obese rats.

METHODOLOGY

Taurocholate-induced acute pancreatitis was performed in lean and obese Zucker rats. Levels of reduced glutathione, oxidized glutathione, L-cysteine, cystine, and S-adenosylmethionine were measured in pancreas as well as the activities of serine/threonine protein phosphatases PP1 and PP2A and tyrosin phosphatases. Isoprostane, malondialdehyde, triglyceride, and free fatty acid levels and lipase activity were measured in plasma and ascites. Lipase activity was measured in white adipose tissue with and without necrosis and confirmed by western blotting.

FINDINGS

Under basal conditions obese rats exhibited lower reduced glutathione levels in pancreas and higher triglyceride and free fatty acid levels in plasma than lean rats. S-adenosyl methionine levels were markedly increased in pancreas of obese rats. Acute pancreatitis in obese rats led to glutathione oxidation and lower reduced glutathione levels in pancreas together with decreased activities of redox-sensitive phosphatases PP1, and PP2A. S-adenosyl methionine levels decreased but cystine levels increased markedly in pancreas upon pancreatitis. Acute pancreatitis triggered an increase in isoprostane levels in plasma and ascites in obese rats. Free fatty acid levels were extremely high in pancreatitis-associated ascitic fluid from obese rats and lipase was bound with great affinity to white adipose tissue, especially to areas of necrosis.

CONCLUSIONS

Our results show that oxidative stress occurs locally and systemically in obese rats with pancreatitis favouring inactivation of protein phosphatases in pancreas, which would promote up-regulation of pro-inflammatory cytokines, and the increase of isoprostanes which might cause powerful pulmonary and renal vasoconstriction. Future studies are needed to confirm the translational relevance of the present findings obtained in a rat model of taurocholate-induced pancreatic damage and necrosis.

Skeletal muscle nitric oxide signaling and exercise: a focus on glucose metabolism

Nitric oxide (NO) is an important vasodilator and regulator in the cardiovascular system, and this link was the subject of a Nobel prize in 1998. However, NO also plays many other regulatory roles, including thrombosis, immune function, neural activity, and gastrointestinal function. Low concentrations of NO are thought to have important signaling effects. In contrast, high concentrations of NO can interact with reactive oxygen species, causing damage to cells and cellular components. A less-recognized site of NO production is within skeletal muscle, where small increases are thought to have beneficial effects such as regulating glucose uptake and possibly blood flow, but higher levels of production are thought to lead to deleterious effects such as an association with insulin resistance. This review will discuss the role of NO in skeletal muscle during and following exercise, including in mitochondrial biogenesis, muscle efficiency, and blood flow with a particular focus on its potential role in regulating skeletal muscle glucose uptake during exercise.

Protein carbonylation and adipocyte mitochondrial function

Carbonylation is the covalent, non-reversible modification of the side chains of cysteine, histidine, and lysine residues by lipid peroxidation end products such as 4-hydroxy- and 4-oxononenal. In adipose tissue the effects of such modifications are associated with increased oxidative stress and metabolic dysregulation centered on mitochondrial energy metabolism. To address the role of protein carbonylation in the pathogenesis of mitochondrial dysfunction, quantitative proteomics was employed to identify specific targets of carbonylation in GSTA4-silenced or overexpressing 3T3-L1 adipocytes. GSTA4-silenced adipocytes displayed elevated carbonylation of several key mitochondrial proteins including the phosphate carrier protein, NADH dehydrogenase 1α subcomplexes 2 and 3, translocase of inner mitochondrial membrane 50, and valyl-tRNA synthetase. Elevated protein carbonylation is accompanied by diminished complex I activity, impaired respiration, increased superoxide production, and a reduction in membrane potential without changes in mitochondrial number, area, or density. Silencing of the phosphate carrier or NADH dehydrogenase 1α subcomplexes 2 or 3 in 3T3-L1 cells results in decreased basal and maximal respiration. These results suggest that protein carbonylation plays a major instigating role in cytokine-dependent mitochondrial dysfunction and may be linked to the development of insulin resistance in the adipocyte.

Obesity, insulin resistance, and skeletal muscle nitric oxide synthase

The molecular mechanisms responsible for impaired insulin action have yet to be fully identified. Rodent models demonstrate a strong relationship between insulin resistance and an elevation in skeletal muscle inducible nitric oxide synthase (iNOS) expression; the purpose of this investigation was to explore this potential relationship in humans. Sedentary men and women were recruited to participate (means ± SE: nonobese, body mass index = 25.5 ± 0.3 kg/m(2), n = 13; obese, body mass index = 36.6 ± 0.4 kg/m(2), n = 14). Insulin sensitivity was measured using an intravenous glucose tolerance test with the subsequent modeling of an insulin sensitivity index (S(I)). Skeletal muscle was obtained from the vastus lateralis, and iNOS, endothelial nitric oxide synthase (eNOS), and neuronal nitric oxide synthase (nNOS) content were determined by Western blot. S(I) was significantly lower in the obese compared with the nonobese group (~43%; P < 0.05), yet skeletal muscle iNOS protein expression was not different between nonobese and obese groups. Skeletal muscle eNOS protein was significantly higher in the nonobese than the obese group, and skeletal muscle nNOS protein tended to be higher (P = 0.054) in the obese compared with the nonobese group. Alternative analysis based on S(I) (high and low tertile) indicated that the most insulin-resistant group did not have significantly more skeletal muscle iNOS protein than the most insulin-sensitive group. In conclusion, human insulin resistance does not appear to be associated with an elevation in skeletal muscle iNOS protein in middle-aged individuals under fasting conditions.

A role for sphingolipids in the pathophysiology of obesity-induced inflammation

Following the initial discovery that adipose tissue actively synthesizes and secretes cytokines, obesity-induced inflammation has been implicated in the etiology of a host of disease states related to obesity, including cardiovascular disease and type II diabetes. Interestingly, a growing body of evidence similarly implicates sphingolipids as prime instigators in these same diseases. From the recent discovery that obesity-related inflammatory pathways modulate sphingolipid metabolism comes a novel perspective—sphingolipids may act as the dominant mediators of deleterious events stemming from obesity-induced inflammation. This paradigm may identify sphingolipids as an effective target for future therapeutics aimed at ameliorating diseases associated with chronic inflammation.