Inducible nitric oxide synthase plays a role in LPS-induced hyperglycemia and insulin resistance

Influence of gut microbiota on subclinical inflammation and insulin resistance

Obesity is the main condition that is correlated with the appearance of insulin resistance, which is the major link among its comorbidities, such as type 2 diabetes, nonalcoholic fatty liver disease, cardiovascular and neurodegenerative diseases, and several types of cancer. Obesity affects a large number of individuals worldwide; it degrades human health and quality of life. Here, we review the role of the gut microbiota in the pathophysiology of obesity and type 2 diabetes, which is promoted by a bacterial diversity shift mediated by overnutrition. Whole bacteria, their products, and metabolites undergo increased translocation through the gut epithelium to the circulation due to degraded tight junctions and the consequent increase in intestinal permeability that culminates in inflammation and insulin resistance. Several strategies focusing on modulation of the gut microbiota (antibiotics, probiotics, and prebiotics) are being experimentally employed in metabolic derangement in order to reduce intestinal permeability, increase the production of short chain fatty acids and anorectic gut hormones, and promote insulin sensitivity to counteract the inflammatory status and insulin resistance found in obese individuals.

Anesthesia with propofol induces insulin resistance systemically in skeletal and cardiac muscles and liver of rats

Hyperglycemia together with hepatic and muscle insulin resistance are common features in critically ill patients, and these changes are associated with enhanced inflammatory response, increased susceptibility to infection, muscle wasting, and worsened prognosis. Tight blood glucose control by intensive insulin treatment may reduce the morbidity and mortality in intensive care units. Although some anesthetics have been shown to cause insulin resistance, it remains unknown how and in which tissues insulin resistance is induced by anesthetics. Moreover, the effects of propofol, a clinically relevant intravenous anesthetic, also used in the intensive care unit for sedation, on insulin sensitivity have not yet been investigated. Euglycemic hyperinsulinemic clamp study was performed in rats anesthetized with propofol and conscious unrestrained rats. To evaluate glucose uptake in tissues and hepatic glucose output [(3)H]glucose and 2-deoxy[(14)C]glucose were infused during the clamp study. Anesthesia with propofol induced a marked whole-body insulin resistance compared with conscious rats, as reflected by significantly decreased glucose infusion rate to maintain euglycemia. Insulin-stimulated tissue glucose uptake was decreased in skeletal muscle and heart, and hepatic glucose output was increased in propofol anesthetized rats. Anesthesia with propofol induces systemic insulin resistance along with decreases in insulin-stimulated glucose uptake in skeletal and heart muscle and attenuation of the insulin-mediated suppression of hepatic glucose output in rats.

Insulin in the brain: there and back again

Insulin performs unique functions within the CNS. Produced nearly exclusively by the pancreas, insulin crosses the blood-brain barrier (BBB) using a saturable transporter, affecting feeding and cognition through CNS mechanisms largely independent of glucose utilization. Whereas peripheral insulin acts primarily as a metabolic regulatory hormone, CNS insulin has an array of effects on brain that may more closely resemble the actions of the ancestral insulin molecule. Brain endothelial cells (BECs), the cells that form the vascular BBB and contain the transporter that translocates insulin from blood to brain, are themselves regulated by insulin. The insulin transporter is altered by physiological and pathological factors including hyperglycemia and the diabetic state. The latter can lead to BBB disruption. Pericytes, pluripotent cells in intimate contact with the BECs, protect the integrity of the BBB and its ability to transport insulin. Most of insulin's known actions within the CNS are mediated through two canonical pathways, the phosphoinositide-3 kinase (PI3)/Akt and Ras/mitogen activated kinase (MAPK) cascades. Resistance to insulin action within the CNS, sometimes referred to as diabetes mellitus type III, is associated with peripheral insulin resistance, but it is possible that variable hormonal resistance syndromes exist so that resistance at one tissue bed may be independent of that at others. CNS insulin resistance is associated with Alzheimer's disease, depression, and impaired baroreceptor gain in pregnancy. These aspects of CNS insulin action and the control of its entry by the BBB are likely only a small part of the story of insulin within the brain.

Thiazolidinedione treatment decreases oxidative stress in spontaneously hypertensive heart failure rats through attenuation of inducible nitric oxide synthase-mediated lipid radical formation

The current study was designed to test the hypothesis that inducible nitric oxide synthase (iNOS)-mediated lipid free radical overproduction exists in an insulin-resistant rat model and that reducing the accumulation of toxic metabolites is associated with improved insulin signaling and metabolic response. Lipid radical formation was detected by electron paramagnetic resonance spectroscopy with in vivo spin trapping in an obese rat model, with or without thiazolidinedione treatment. Lipid radical formation was accompanied by accumulation of toxic end products in the liver, such as 4-hydroxynonenal and nitrotyrosine, and was inhibited by the administration of the selective iNOS inhibitor 1400 W. The model showed impaired phosphorylation of the insulin signaling pathway. Ten-day rosiglitazone injection not only improved the response to an oral glucose tolerance test and corrected insulin signaling but also decreased iNOS levels. Similar to the results with specific iNOS inhibition, thiazolidinedione dramatically decreased lipid radical formation. We demonstrate a novel mechanism where a thiazolidinedione treatment can reduce oxidative stress in this model through reducing iNOS-derived lipid radical formation. Our results suggest that hepatic iNOS expression may underlie the accumulation of lipid end products and that reducing the accumulation of toxic lipid metabolites contributes to a better redox status in insulin-sensitive tissues.

Inducible nitric oxide synthase deficiency ameliorates skeletal muscle insulin resistance but does not alter unexpected lower blood glucose levels after burn injury in C57BL/6 mice

Burn injury is associated with inflammatory responses and metabolic alterations including insulin resistance. Impaired insulin receptor substrate-1 (IRS-1)-mediated insulin signal transduction is a major component of insulin resistance in skeletal muscle following burn injury. To further investigate molecular mechanisms that underlie burn injury-induced insulin resistance, we study a role of inducible nitric oxide synthase (iNOS), a major mediator of inflammation, on burn-induced muscle insulin resistance in iNOS-deficient mice. Full-thickness third-degree burn injury comprising 12% of total body surface area was produced in wild-type and iNOS-deficient C57BL/6 mice. Insulin-stimulated activation (phosphorylation) of IR, IRS-1, and Akt was assessed by immunoblotting and immunoprecipitation. Insulin-stimulated glucose uptake by skeletal muscle was evaluated ex vivo. Burn injury caused induction of iNOS in skeletal muscle of wild-type mice. The increase of iNOS expression paralleled the increase of insulin resistance, as evidenced by decreased tyrosine phosphorylation of IR and IRS-1, IRS-1 expression, insulin-stimulated activation of phosphatidylinositol 3-kinase and Akt/PKB, and insulin-stimulated glucose uptake in mouse skeletal muscle. The absence of iNOS in genetically engineered mice significantly lessened burn injury-induced insulin resistance in skeletal muscle. In wild-type mice, insulin tolerance test revealed whole-body insulin resistance in burned mice compared with sham-burned controls. This effect was reversed by iNOS deficiency. Unexpectedly, however, blood glucose levels were depressed in both wild-type and iNOS-deficient mice after burn injury. Gene disruption of iNOS ameliorated the effect of burn on IRS-1-mediated insulin signaling in skeletal muscle of mice. These findings indicate that iNOS plays a significant role in burn injury-induced skeletal muscle insulin resistance.

Comparative analysis of the human hepatic and adipose tissue transcriptomes during LPS-induced inflammation leads to the identification of differential biological pathways and candidate biomarkers

BACKGROUND

Insulin resistance (IR) is accompanied by chronic low grade systemic inflammation, obesity, and deregulation of total body energy homeostasis. We induced inflammation in adipose and liver tissues in vitro in order to mimic inflammation in vivo with the aim to identify tissue-specific processes implicated in IR and to find biomarkers indicative for tissue-specific IR.

METHODS

Human adipose and liver tissues were cultured in the absence or presence of LPS and DNA Microarray Technology was applied for their transcriptome analysis. Gene Ontology (GO), gene functional analysis, and prediction of genes encoding for secretome were performed using publicly available bioinformatics tools (DAVID, STRING, SecretomeP). The transcriptome data were validated by proteomics analysis of the inflamed adipose tissue secretome.

RESULTS

LPS treatment significantly affected 667 and 483 genes in adipose and liver tissues respectively. The GO analysis revealed that during inflammation adipose tissue, compared to liver tissue, had more significantly upregulated genes, GO terms, and functional clusters related to inflammation and angiogenesis. The secretome prediction led to identification of 399 and 236 genes in adipose and liver tissue respectively. The secretomes of both tissues shared 66 genes and the remaining genes were the differential candidate biomarkers indicative for inflamed adipose or liver tissue. The transcriptome data of the inflamed adipose tissue secretome showed excellent correlation with the proteomics data.

CONCLUSIONS

The higher number of altered proinflammatory genes, GO processes, and genes encoding for secretome during inflammation in adipose tissue compared to liver tissue, suggests that adipose tissue is the major organ contributing to the development of systemic inflammation observed in IR. The identified tissue-specific functional clusters and biomarkers might be used in a strategy for the development of tissue-targeted treatment of insulin resistance in patients.

Liver-specific inducible nitric-oxide synthase expression is sufficient to cause hepatic insulin resistance and mild hyperglycemia in mice

Inducible nitric-oxide synthase (iNOS), a major mediator of inflammation, plays an important role in obesity-induced insulin resistance. Inhibition of iNOS by gene disruption or pharmacological inhibitors reverses or ameliorates obesity-induced insulin resistance in skeletal muscle and liver in mice. It is unknown, however, whether increased expression of iNOS is sufficient to cause insulin resistance in vivo. To address this issue, we generated liver-specific iNOS transgenic (L-iNOS-Tg) mice, where expression of the transgene, iNOS, is regulated under mouse albumin promoter. L-iNOS-Tg mice exhibited mild hyperglycemia, hyperinsulinemia, insulin resistance, and impaired insulin-induced suppression of hepatic glucose output, as compared with wild type (WT) littermates. Insulin-stimulated phosphorylation of insulin receptor substrate-1 (IRS-1) and -2, and Akt was significantly attenuated in liver, but not in skeletal muscle, of L-iNOS-Tg mice relative to WT mice without changes in insulin receptor phosphorylation. Moreover, liver-specific iNOS expression abrogated insulin-stimulated phosphorylation of glycogen synthase kinase-3β, forkhead box O1, and mTOR (mammalian target of rapamycin), endogenous substrates of Akt, along with increased S-nitrosylation of Akt relative to WT mice. However, the expression of insulin receptor, IRS-1, IRS-2, Akt, glycogen synthase kinase-3β, forkhead box O1, protein-tyrosine phosphatase-1B, PTEN (phosphatase and tensin homolog), and p85 phosphatidylinositol 3-kinase was not altered by iNOS transgene. Hyperglycemia was associated with elevated glycogen phosphorylase activity and decreased glycogen synthase activity in the liver of L-iNOS-Tg mice, whereas phosphoenolpyruvate carboxykinase, glucose-6-phosphatase, and proliferator-activated receptor γ coactivator-1α expression were not altered. These results clearly indicate that selective expression of iNOS in liver causes hepatic insulin resistance along with deranged insulin signaling, leading to hyperglycemia and hyperinsulinemia. Our data highlight a critical role for iNOS in the development of hepatic insulin resistance and hyperglycemia.

Regulation of Inducible Nitric Oxide Synthase (iNOS) and its Potential Role in Insulin Resistance, Diabetes and Heart Failure

Nitric oxide synthases (NOS) are the enzymes responsible for nitric oxide (NO) generation. NO is a reactive oxygen species as well as a reactive nitrogen species. It is a free radical which mediates several biological effects. It is clear that the generation and actions of NO under physiological and pathophysiological conditions are regulated and extend to almost every cell type and function within the circulation. In mammals 3 distinct isoforms of NOS have been identified: neuronal NOS (nNOS), inducible NOS (iNOS) and endothelial NOS (eNOS). The important isoform in the regulation of insulin resistance (IR) is iNOS. Understanding the molecular mechanisms regulating the iNOS pathway in normal and hyperglycemic conditions would help to explain some of vascular abnormalities observed in type 2 diabetes mellitus (T2DM). Previous studies have reported increased myocardial iNOS activity and expression in heart failure (HF). This review considers the recent animal studies which focus on the understanding of regulation of iNOS activity/expression and the role of iNOS agonists as potential therapeutic agents in treatment of IR, T2DM and HF.

Insulin alleviates degradation of skeletal muscle protein by inhibiting the ubiquitin-proteasome system in septic rats

Hypercatabolism is common under septic conditions. Skeletal muscle is the main target organ for hypercatabolism, and this phenomenon is a vital factor in the deterioration of recovery in septic patients. In skeletal muscle, activation of the ubiquitin-proteasome system plays an important role in hypercatabolism under septic status. Insulin is a vital anticatabolic hormone and previous evidence suggests that insulin administration inhibits various steps in the ubiquitin-proteasome system. However, whether insulin can alleviate the degradation of skeletal muscle protein by inhibiting the ubiquitin-proteasome system under septic condition is unclear. This paper confirmed that mRNA and protein levels of the ubiquitin-proteasome system were upregulated and molecular markers of skeletal muscle proteolysis (tyrosine and 3-methylhistidine) simultaneously increased in the skeletal muscle of septic rats. Septic rats were infused with insulin at a constant rate of 2.4 mU.kg^-1.min^-1 for 8 hours. Concentrations of mRNA and proteins of the ubiquitin-proteasome system and molecular markers of skeletal muscle proteolysis were mildly affected. When the insulin infusion dose increased to 4.8 mU.kg^-1.min^-1, mRNA for ubiquitin, E2-14 KDa, and the C2 subunit were all sharply downregulated. At the same time, the levels of ubiquitinated proteins, E2-14KDa, and the C2 subunit protein were significantly reduced. Tyrosine and 3-methylhistidine decreased significantly. We concluded that the ubiquitin-proteasome system is important skeletal muscle hypercatabolism in septic rats. Infusion of insulin can reverse the detrimental metabolism of skeletal muscle by inhibiting the ubiquitin-proteasome system, and the effect is proportional to the insulin infusion dose.

The ethanolamide metabolite of DHA, docosahexaenoylethanolamine, shows immunomodulating effects in mouse peritoneal and RAW264.7 macrophages: evidence for a new link between fish oil and inflammation

Several mechanisms have been proposed for the positive health effects associated with dietary consumption of long-chain n-3 PUFA (n-3 LC-PUFA) including DHA (22 : 6n-3) and EPA (20 : 5n-3). After dietary intake, LC-PUFA are incorporated into membranes and can be converted to their corresponding N-acylethanolamines (NAE). However, little is known on the biological role of these metabolites. In the present study, we tested a series of unsaturated NAE on the lipopolysaccharide (LPS)-induced NO production in RAW264.7 macrophages. Among the compounds tested, docosahexaenoylethanolamine (DHEA), the ethanolamide of DHA, was found to be the most potent inhibitor, inducing a dose-dependent inhibition of NO release. Immune-modulating properties of DHEA were further studied in the same cell line, demonstrating that DHEA significantly suppressed the production of monocyte chemotactic protein-1 (MCP-1), a cytokine playing a pivotal role in chronic inflammation. In LPS-stimulated mouse peritoneal macrophages, DHEA also reduced MCP-1 and NO production. Furthermore, inhibition was also found to take place at a transcriptional level, as gene expression of MCP-1 and inducible NO synthase was inhibited by DHEA. To summarise, in the present study, we showed that DHEA, a DHA-derived NAE metabolite, modulates inflammation by reducing MCP-1 and NO production and expression. These results provide new leads in molecular mechanisms by which DHA can modulate inflammatory processes.

Quantitative proteomic analysis of S-nitrosated proteins in diabetic mouse liver with ICAT switch method

In this study we developed a quantitative proteomic method named ICAT switch by introducing isotope-coded affinity tag (ICAT) reagents into the biotin-switch method, and used it to investigate S-nitrosation in the liver of normal control C57BL/6J mice and type 2 diabetic KK-Ay mice. We got fifty-eight S-nitrosated peptides with quantitative information in our research, among which thirty-seven had changed S-nitrosation levels in diabetic mouse liver. The S-nitrosated peptides belonged to forty-eight proteins (twenty-eight were new S-nitrosated proteins), some of which were new targets of S-nitrosation and known to be related with diabetes. S-nitrosation patterns were different between diabetic and normal mice. Gene ontology enrichment results suggested that S-nitrosated proteins are more abundant in amino acid metabolic processes. The network constructed for S-nitrosated proteins by text-mining technology provided clues about the relationship between S-nitrosation and type 2 diabetes. Our work provides a new approach for quantifying S-nitrosated proteins and suggests that the integrative functions of S-nitrosation may take part in pathophysiological processes of type 2 diabetes.

Impaired liver glucose production in a murine model of steatosis and endotoxemia: protection by inducible nitric oxide synthase

This study hypothesized that upregulation of inducible nitric oxide synthase (iNOS) would preserve the metabolic status of the liver under conditions of steatosis and acute inflammation. Wild-type C57BL/6J and C57BL/6 iNOS-knockout (-/-) mice were fed a choline-deficient ethionine-supplemented diet (CDE). Mice were also injected with 5 mg/kg lipopolysaccharide (LPS) to induce endotoxemia. Consumption of the CDE diet led to steatosis of the liver and decreased expression of the gluconeogenic genes compared with controls. LPS treatment exacerbated these effects because of inhibition of PGC-1alpha expression, which resulted in hypoglycemia. In steatotic livers, LPS-induced iNOS expression was enhanced. Comparison between wild-type and iNOS-knockout mice under these conditions demonstrated a protective role of iNOS against fatal hypoglycemia. Nitric oxide (NO) signaling effects were confirmed by treatment of hepatocytes in culture with an NO donor, which resulted in increased expression of PGC-1alpha and gluconeogenic genes. In conclusion, iNOS was found to act as a protective protein and provides a possible mechanism by which the liver preserves glucose homeostasis under stress.

Deletion of inducible nitric-oxide synthase in leptin-deficient mice improves brown adipose tissue function

Background

Leptin and nitric oxide (NO) on their own participate in the control of non-shivering thermogenesis. However, the functional interplay between both factors in this process has not been explored so far. Therefore, the aim of the present study was to analyze the impact of the absence of the inducible NO synthase (iNOS) gene in the regulation of energy balance in ob/ob mice.

Methods and Findings

Double knockout (DBKO) mice simultaneously lacking the ob and iNOS genes were generated, and the expression of molecules involved in the control of brown fat cell function was analyzed by real-time PCR, western-blot and immunohistochemistry. Twelve week-old DBKO mice exhibited reduced body weight (p<0.05), decreased amounts of total fat pads (p<0.05), lower food efficiency rates (p<0.05) and higher rectal temperature (p<0.05) than ob/ob mice. Ablation of iNOS also improved the carbohydrate and lipid metabolism of ob/ob mice. DBKO showed a marked reduction in the size of brown adipocytes compared to ob/ob mutants. In this sense, in comparison to ob/ob mice, DBKO rodents showed an increase in the expression of PR domain containing 16 (Prdm16), a transcriptional regulator of brown adipogenesis. Moreover, iNOS deletion enhanced the expression of mitochondria-related proteins, such as peroxisome proliferator-activated receptor γ coactivator-1 α (Pgc-1α), sirtuin-1 (Sirt-1) and sirtuin-3 (Sirt-3). Accordingly, mitochondrial uncoupling proteins 1 and 3 (Ucp-1 and Ucp-3) were upregulated in brown adipose tissue (BAT) of DBKO mice as compared to ob/ob rodents.

Conclusion

Ablation of iNOS improved the energy balance of ob/ob mice by decreasing food efficiency through an increase in thermogenesis. These effects may be mediated, in part, through the recovery of the BAT phenotype and brown fat cell function improvement.

Aminoguanidine inhibition of iNOS activity ameliorates cerebral vasospasm after subarachnoid hemorrhage in rabbits via restoration of dysfunctional endothelial cells

BACKGROUND

This study was to delineate the therapeutic efficacy and potential cellular and molecular mechanisms of aminoguanidine (AG), a relatively selective inhibitor of iNOS activity, in cerebral vasospasm after subarachnoid hemorrhage (SAH) in rabbits.

METHODS

SAH was induced by a single injection of autologous arterial blood into the cisterna magna of adult male rabbits. An intravenous bolus injection of AG (150 mg/kg) was administrated 1h after SAH, and this dosage was repeated on the following day. Vasospasm was verified by computed tomography angiography (CTA) day 2 after SAH. Rabbit basilar arteries were harvested for transmission electron microscopy (TEM), immunohistochemical examination, RT-PCR, and western blot analysis.

RESULTS

CTA data revealed that cerebral vasospasm of SAH rabbits was significantly prevented via AG treatment. TEM results demonstrated the ultrastructural morphological changes of endothelial cells of SAH rabbits were ameliorated by AG treatment. In parallel, AG treatment increased eNOS mRNA and protein levels along with the reduced immunoreactivity of nitrotyrosine in rabbit basilar arteries.

CONCLUSIONS

Our discovery suggested AG inhibition of iNOS activity could significantly reverse cerebral vasospasm after SAH via restoration of dysfunctional endothelial cells by the upregulation of eNOS, indicating a regulatory cross-talk between eNOS and iNOS in the pathogenesis of SAH.

Minimal penetration of lipopolysaccharide across the murine blood-brain barrier

LPS given peripherally or into the brain induces a neuroinflammatory response. How peripheral LPS induces its effects on brain is not clear, but one mechanism is that LPS crosses the blood-brain barrier (BBB). Alternatively, LPS acts outside the BBB by stimulating afferent nerves, acting at circumventricular organs, and altering BBB permeabilities and functions. Here, we labeled LPS with radioactive iodine (I-LPS) and coinjected it with radioactively labeled albumin (I-Alb) which acted as a vascular space marker. Measurable amounts of I-LPS associated with the BBB, most reversibly bound to brain endothelia. Brain endothelia also sequestered small amounts of I-LPS and about 0.025% of an intravenously injected dose of I-LPS crossed the BBB to enter the CNS. Disruption of the BBB with repeated injections of LPS did not enhance I-LPS uptake. Based on dose-response curves in the literature of the amounts of LPS needed to stimulate brain neuroimmune events, it is unlikely that enough peripherally administered LPS enters the CNS to invoke those events except possibly at the highest doses used and for the most sensitive brain functions. I-LPS injected into the lateral ventricle of the brain entered the circulation with the reabsorption of cerebrospinal fluid (bulk flow) as previously described. In conclusion, brain uptake of circulating I-LPS is so low that most effects of peripherally administered LPS are likely mediated through LPS receptors located outside the BBB.

Resistin is more abundant in liver than adipose tissue and is not up-regulated by lipopolysaccharide

CONTEXT

Resistin is an adipokine correlated with inflammatory markers and is predictive for cardiovascular diseases. There is evidence that serum resistin levels are elevated in obese patients; however, the role of resistin in insulin resistance and type 2 diabetes remains controversial.

OBJECTIVE

We addressed the question of whether inflammation may induce expression of resistin in organs involved in regulation of total body energy metabolism, such as liver and adipose tissue (AT).

METHODS

Human liver tissue, sc AT, and omentum were cultured in the absence/presence of lipopolysaccharide (LPS). The resistin and cytokine mRNA and protein expression levels were determined by real-time PCR, ELISA, and Multiplex Technology, respectively. The localization of resistin in human liver was analyzed by immunohistochemistry.

RESULTS

Resistin gene and protein expression was significantly higher in liver than in AT. Exposure of human AT and liver tissue in culture to LPS did not alter resistin concentration; however, concentrations of IL-1beta, IL-6, and TNFalpha were significantly increased in these tissues. In liver, resistin colocalizes with markers for Kupffer cells, for a subset of endothelial and fibroblast-like cells.

CONCLUSIONS

High level of resistin gene and protein expression in liver compared to AT implies that resistin should not be considered only as an adipokine in humans. LPS-induced inflammation does not affect resistin protein synthesis in human liver and AT. This suggests that elevated serum resistin levels are not indicative for inflammation of AT or liver in a manner similar to known inflammatory markers such as IL-1beta, IL-6, or TNFalpha.

Novos mecanismos pelos quais o exercício físico melhora a resistência à insulina no músculo esquelético

O prejuízo no transporte de glicose estimulada por insulina no músculo constitui um defeito crucial para o estabelecimento da intolerância à glicose e do diabetes tipo 2. Por outro lado, é notório o conhecimento de que tanto o exercício aeróbio agudo quanto o crônico podem ter efeitos benéficos na ação da insulina em estados de resistência à insulina. No entanto, pouco se sabe sobre os efeitos moleculares pós-exercício sobre a sinalização da insulina no músculo esquelético. Assim, esta revisãoapresenta novos entendimentos sobre os mecanismos por meio dos quais o exercício agudo restaura a sensibilidade à insulina, com destaque ao importante papel que proteínas inflamatórias e a S-nitrosação possuem sobre a regulação de proteínas da via de sinalização da insulina no músculo esquelético.

Impaired insulin-mediated vasorelaxation in diabetic Goto-Kakizaki rats is caused by impaired Akt phosphorylation

Insulin resistance associated with Type 2 diabetes contributes to impaired vasorelaxation. Previously, we showed the phosphorylation of myosin-bound phosphatase substrate MYPT1, a marker of the vascular smooth muscle cell (VSMC) contraction, was negatively regulated by Akt (protein kinase B) phosphorylation in response to insulin stimulation. In this study we examined the role of Akt phosphorylation on impaired insulin-induced vasodilation in the Goto-Kakizaki (GK) rat model of Type 2 diabetes. GK VSMCs had impaired basal and insulin-induced Akt phosphorylation as well as increases in basal MYPT1 phosphorylation, inducible nitric oxide synthase (iNOS) expression, and nitrite/nitrate production compared with Wistar-Kyoto controls. Both iNOS expression and the inhibition of angiotensin (ANG) II-induced MYPT1 phosphorylation were resistant to the effects of insulin in diabetic GK VSMC. We also measured the isometric tension of intact and denuded GK aorta using a myograph and observed significantly impaired insulin-induced vasodilation. Adenovirus-mediated overexpression of constitutively active Akt in GK VSMC led to significantly improved insulin sensitivity in terms of counteracting ANG II-induced contractile signaling via MYPT1, myosin light chain dephosphorylation, and reduced iNOS expression, S-nitrosylation and survivin expression. We demonstrated for the first time the presence of Akt-independent iNOS expression in the GK diabetic model and that the defective insulin-induced vasodilation observed in the diabetic vasculature can be restored by the overexpression of active Akt, which advocates a novel therapeutic strategy for treating diabetes.

Obesity-induced insulin resistance and hyperglycemia: etiologic factors and molecular mechanisms

Obesity is a major cause of type 2 diabetes, clinically evidenced as hyperglycemia. The altered glucose homeostasis is caused by faulty signal transduction via the insulin signaling proteins, which results in decreased glucose uptake by the muscle, altered lipogenesis, and increased glucose output by the liver. The etiology of this derangement in insulin signaling is related to a chronic inflammatory state, leading to the induction of inducible nitric oxide synthase and release of high levels of nitric oxide and reactive nitrogen species, which together cause posttranslational modifications in the signaling proteins. There are substantial differences in the molecular mechanisms of insulin resistance in muscle versus liver. Hormones and cytokines from adipocytes can enhance or inhibit both glycemic sensing and insulin signaling. The role of the central nervous system in glucose homeostasis also has been established. Multipronged therapies aimed at rectifying obesity-induced anomalies in both central nervous system and peripheral tissues may prove to be beneficial.

Hypermetabolic syndrome as a consequence of repeated psychological stress in mice

Stress is a powerful modulator of neuroendocrine, behavioral, and immunological functions. After 4.5-d repeated combined acoustic and restraint stress as a murine model of chronic psychological stress, severe metabolic dysregulations became detectable in female BALB/c mice. Stress-induced alterations of metabolic processes that were found in a hepatic mRNA expression profiling were verified by in vivo analyses. Repeatedly stressed mice developed a hypermetabolic syndrome with the severe loss of lean body mass, hyperglycemia, dyslipidemia, increased amino acid turnover, and acidosis. This was associated with hypercortisolism, hyperleptinemia, insulin resistance, and hypothyroidism. In contrast, after a single acute stress exposure, changes in expression of metabolic genes were much less pronounced and predominantly confined to gluconeogenesis, probably indicating that metabolic disturbances might be initiated already early but will only manifest in repeatedly stressed mice. Thus, in our murine model, repeated stress caused severe metabolic dysregulations, leading to a drastic reduction of the individual's energy reserves. Under such circumstances stress may further reduce the ability to cope with new stressors such as infection or cancer.

Nitric oxide isoenzymes regulate lipopolysaccharide-enhanced insulin transport across the blood-brain barrier

Insulin transported across the blood-brain barrier (BBB) has many effects within the central nervous system. Insulin transport is not static but altered by obesity and inflammation. Lipopolysaccharide (LPS), derived from the cell walls of Gram-negative bacteria, enhances insulin transport across the BBB but also releases nitric oxide (NO), which opposes LPS-enhanced insulin transport. Here we determined the role of NO synthase (NOS) in mediating the effects of LPS on insulin BBB transport. The activity of all three NOS isoenzymes was stimulated in vivo by LPS. Endothelial NOS and inducible NOS together mediated the LPS-enhanced transport of insulin, whereas neuronal NOS (nNOS) opposed LPS-enhanced insulin transport. This dual pattern of NOS action was found in most brain regions with the exception of the striatum, which did not respond to LPS, and the parietal cortex, hippocampus, and pons medulla, which did not respond to nNOS inhibition. In vitro studies of a brain endothelial cell (BEC) monolayer BBB model showed that LPS did not directly affect insulin transport, whereas NO inhibited insulin transport. This suggests that the stimulatory effect of LPS and NOS on insulin transport is mediated through cells of the neurovascular unit other than BECs. Protein and mRNA levels of the isoenzymes indicated that the effects of LPS are mainly posttranslational. In conclusion, LPS affects insulin transport across the BBB by modulating NOS isoenzyme activity. NO released by endothelial NOS and inducible NOS acts indirectly to stimulate insulin transport, whereas NO released by nNOS acts directly on BECs to inhibit insulin transport.

New role of resistin in lipopolysaccharide-induced liver damage in mice

Studies in rodents suggest that the adipocytokine resistin causes insulin resistance via impairing normal insulin signaling. However, in humans, resistin may play a more important role in inflammation than in insulin resistance. Whether resistin contributes to inflammation in rodents is unclear. Therefore, the purpose of the present study was to determine the effect of resistin exposure on the basal and stimulated [lipopolysaccharide (LPS)] inflammatory response in mouse liver in vivo. Resistin alone had no major effects on hepatic expression of insulin-responsive genes, either in the presence or absence of LPS. Although it had no effect alone, resistin significantly enhanced hepatic inflammation and necrosis caused by LPS. Resistin increased expression of proinflammatory genes, e.g., plasminogen activator inhibitor (PAI)-1, and activity of mitogen-activated protein (MAP) kinase, extracellular signal-regulated kinase 1/2, caused by LPS, but had little effect on anti-inflammatory gene expression. Resistin also enhanced fibrin deposition (an index of hemostasis) caused by LPS. The increase in PAI-1 expression, fibrin deposition, and liver damage caused by LPS + resistin was almost completely prevented either by inhibiting the coagulation cascade, hirudin, or by blocking MAP kinase signaling, U0126 [1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio) butadiene], indicating that these pathways play a causal role in observed enhanced liver damage caused by resistin. Taken together, the augmentation of LPS-induced liver damage caused by resistin seems to involve, at least in part, up-regulation of hepatic inflammation via mechanisms most likely involving the coagulation cascade and fibrin accumulation. These data also suggest that resistin may have proinflammatory roles in mouse liver independent of its effects on insulin signaling, analogous to previous work in humans.

Involvement of c-Jun NH2-terminal kinase and nitric oxide-mediated mitochondria-dependent intrinsic pathway signaling in cardiotoxin-induced muscle cell death: role of testosterone

To test the hypothesis that c-Jun NH2-terminal kinase (JNK) and nitric oxide (NO)-mediated signaling plays an important role in muscle cell apoptosis, we examined the contribution of these molecules in muscle cell apoptosis during cardiotoxin (ctx)-induced muscle injury in mice. Compared to controls, where no apoptosis was detected, the percent of muscle cell apoptosis rose significantly (P < 0.05) at 4 h (27%) after ctx-treatment and increased further progressively up to 16 h posttreatment (80%), before it fell again at 24 h posttreatment (38%). Initiation of apoptosis was preceded by JNK activation and elevated levels of B-cell lymphoma-2 (BCL-2) in the mitochondrial fractions (BAX levels remained unaffected). Ctx treatment also resulted in the inactivation of BCL-2 through phosphorylation at serine 70, thereby perturbing the BAX/BCL-2 rheostat, and the subsequent activation of the cytochrome c-mediated death pathway. Concomitant administration of SP600125, a selective JNK inhibitor, or aminoguanidine (AG), a selected inducible nitric oxide synthase (iNOS) inhibitor, effectively diminished BCL-2 phosphorylation, suppressed cytochrome c release from mitochondria and caspase activation, and significantly prevented ctx-induced muscle cell apoptosis. In additional studies, we examined the role of testosterone in preventing such ctx-induced muscle cell apoptosis. Collectively, the present study emphasizes the role of a new signal transduction pathway involving JNK and iNOS that promotes ctx-induced myocyte apoptosis by provoking BCL-2 phosphorylation, leading to its inactivation, and subsequent activation of the intrinsic pathway signaling. Testosterone therapy has no protective effect in acute muscle injury associated with increased muscle cell death after ctx-treatment.

Substrate utilization in sepsis and multiple organ failure

Sepsis and multiple organ failure are characterized by an excessive release of inflammatory mediators and a marked stimulation of stress hormones. These in turn have profound effects on energy and substrate metabolism: energy expenditure is generally increased, and increased lipolysis and fat oxidation are observed. Net protein breakdown occurs and leads to accelerated wasting. Most of these effects can be produced in healthy humans by administration of bacterial endotoxin or by tumor necrosis factor-alpha. Hyperlactatemia is a hallmark of sepsis and critical illness, and its severity is related to mortality. An increased lactate production, possibly secondary to activation of Na-K adenosine 5'-triphosphatase and to muscle mitochondrial dysfunction, is involved. Lactate production by immune cells and wound tissue may also play a role. Long-chain, n-3 polyunsaturated fatty acids have anti-inflammatory effects that may be beneficial in sepsis. They also decrease the stimulation of stress hormones induced by bacterial endotoxin, possibly through an effect exerted at the level of the central nervous sytem. Their use in patients with sepsis does not lead to adverse metabolic effects.

Farnesyltransferase Inhibitor, Manumycin A, Prevents Atherosclerosis Development and Reduces Oxidative Stress in Apolipoprotein E-Deficient Mice

OBJECTIVE

Statins are presumed to exert their antiatherogenic effects in part via lipid-lowering-independent mechanisms. Inhibition of protein farnesylation and/or geranylgeranylation by statins has been postulated to contribute to the lipid-lowering-independent effects. However, a role for protein farnesylation in atherogenesis has not yet been studied. Therefore, we examined the effects of farnesyltransferase inhibitor, manumycin A, on the development of atherosclerosis in apolipoprotein E (apoE)-deficient mice fed a high-fat diet.

METHODS AND RESULTS

Manumycin A treatment for 22 weeks decreased Ras activity, and reduced fatty streak lesion size at the aortic sinus to 43% of that in vehicle-treated apoE-deficient mice (P<0.05), while plasma total cholesterol was unaltered. Moreover, manumycin A reduced alpha-smooth muscle actin-positive area to 29% of that in vehicle-treated apoE-deficient mice (P<0.01). The prevention of atherogenesis by manumycin A was accompanied by amelioration of oxidative stress, as judged by reduced ex vivo superoxide production and nitrotyrosine immunoreactivity.

CONCLUSIONS

These results indicate that the inhibition of farnesyltransferase prevents the development of mature atherosclerosis with concomitant alleviation of oxidative stress in apoE-deficient mice. The present data highlight farnesyltransferase as a potential molecular target for preventive and/or therapeutic intervention against atherosclerosis.

Nitrosative stress and pathogenesis of insulin resistance

Insulin resistance is a major causative factor for type 2 diabetes and is associated with increased risk of cardiovascular disease. Despite intense investigation for a number of years, molecular mechanisms underlying insulin resistance remain to be determined. Recently, chronic inflammation has been highlighted as a culprit for obesity-induced insulin resistance. Nonetheless, upstream regulators and downstream effectors of chronic inflammation in insulin resistance remain unclarified. Inducible nitric oxide synthase (iNOS), a mediator of inflammation, has emerged as an important player in insulin resistance. Obesity is associated with increased iNOS expression in insulin-sensitive tissues in rodents and humans. Inhibition of iNOS ameliorates obesity-induced insulin resistance. However, molecular mechanisms by which iNOS mediates insulin resistance remain largely unknown. Protein S-nitrosylation, a covalent attachment of NO moiety to thiol sulfhydryls, has emerged as a major mediator of a broad array of NO actions. S-nitrosylation is elevated in patients with type 2 diabetes, and increased S-nitrosylation of insulin signaling molecules, including insulin receptor, insulin receptor substrate-1, and Akt/PKB, has been shown in skeletal muscle of obese, diabetic mice. Akt/PKB is reversibly inactivated by S-nitrosylation. Based on these findings, S-nitrosylation has recently been proposed to play an important role in the pathogenesis of insulin resistance.

Insulin sensitivity and resistin expression in nitric oxide-deficient rats

AIMS/HYPOTHESIS

The aim of this study was to investigate changes in insulin sensitivity and expression of the gene encoding resistin (Retn) in adipocytes from long-term nitric oxide (NO)-deficient rats.

METHODS

Male Sprague-Dawley rats received [Formula: see text]-nitro-L: -arginine methyl ester (L-NAME 0.5 mg/ml) in their drinking water for 4 weeks, while control rats received plain drinking water. During the experimental period, changes in plasma glucose, insulin and C-peptide levels were measured. After administration of L-NAME for 4 weeks, insulin sensitivity was evaluated in vivo and in vitro. An insulin binding assay was also performed to determine the number and binding affinity of insulin receptors in adipocytes. Adipocyte Retn mRNA levels were examined using northern blotting.

RESULTS

Successful induction of NO deficiency was demonstrated by an increase in systemic blood pressure. No difference in plasma glucose levels was found between the two groups. Compared with the control rats, plasma insulin and C-peptide levels were significantly decreased in the NO-deficient rats, and insulin sensitivity was significantly increased. Insulin-stimulated glucose uptake and insulin binding capacity, but not binding affinity, were significantly increased in adipocytes isolated from NO-deficient rats. In addition, adipocyte Retn mRNA levels, but not plasma resistin levels, were significantly decreased in NO-deficient rats, and the Retn mRNA levels were negatively correlated with insulin sensitivity.

CONCLUSIONS/INTERPRETATION

Insulin sensitivity was increased in NO-deficient rats and this was associated with insulin binding capacity and downregulated Retn expression. These findings suggest that NO plays a regulatory role in metabolism. Dysregulation of NO production may result in the development of metabolic disorders.

The blood-brain barrier as a regulatory interface in the gut-brain axes

The blood-brain barrier (BBB) prevents the unrestricted movement of peptides and proteins between the brain and blood. However, some peptides and regulatory proteins can cross the BBB by saturable and non-saturable mechanisms. Leptin and insulin each cross the BBB by their own transporters. Impaired transport of leptin occurs in obesity and accounts for peripheral resistance; that is, the condition wherein an obese animal loses weight when given leptin directly into the brain but not when given leptin peripherally. Leptin transport is also inhibited in starvation and by hypertriglyceridemia. Since hypertriglyceridemia occurs in both starvation and obesity, we have postulated that the peripheral resistance induced by hypertriglyceridemia may have evolved as an adaptive mechanism in response to starvation. Insulin transport is also regulated. For example, treatment of mice with lipopolysaccharide (LPS) increases insulin transport across the BBB by about threefold. Since many of the actions of CNS insulin oppose those of peripheral insulin and since LPS releases proinflammatory cytokines, enhanced transport of insulin across the BBB could be a mechanism which promotes insulin resistance in sepsis. The brain endothelial cells which comprise the BBB secrete many substances including cytokines. Such secretion can be stimulated from one side of the BBB with release into the other side. For example, it appears that adiponectin can inhibit release of interleukin-6 from brain endothelial cells. Overall, the BBB represents an important interface in mediating gut-brain axes.

Cytokine-induced metabolic effects in human adipocytes are independent of endogenous nitric oxide

Nitric oxide (NO) has been recognized as a potential mediator of inflammation-induced metabolic alterations, including insulin resistance. However, expression mechanisms and potential roles of endothelial and inducible NO synthases (eNOS and iNOS, respectively) in human adipocytes are poorly understood. In the present study, we aimed to analyze several aspects of NO-related gene expression and metabolite synthesis in basal and inflammation-activated human adipocyte models. eNOS mRNA was highly expressed in omental and to a lesser extent in human subcutaneous adipose tissue biopsies, but not in purified adipocytes, in mesenchymal stem cell (MSC)- and in preadipocyte-derived adipocytes, respectively. Trace amounts of iNOS mRNA were detected in adipose tissue samples of donors with abdominal infection, as opposed to noninfected subjects. Interferon-gamma, in combination with interleukin-1beta or lipopolysaccharide, evoked a transient (4 h < time < 24 h) iNOS mRNA expression in human MSC and preadipocyte-derived adipocytes, respectively. This induction was preceded by cytokine-specific mRNAs. In addition, it was accompanied by an activation of the tetrahydrobiopterin synthesis pathway and by inhibition of peroxisome proliferator-activated receptor-gamma2. In contrast to murine 3T3-L1-derived adipocytes, iNOS protein and NO oxidation products remained undetectable in iNOS mRNA-positive human adipocytes. Accordingly, coadministration of NOS inhibitors (i.e., Nomega-nitro-L-arginine methyl ester, Nomega-monomethyl-L-arginine, and 1400W) had no effects on insulin-mediated glucose uptake and lipolysis. We conclude that, in human adipocytes, endogenous NO is not involved in metabolic regulation during either basal or cytokine-activated conditions.

Gliotoxin non-selectively induces apoptosis in fibrotic and normal livers

BACKGROUND

Liver fibrosis is the common response to chronic liver injury, ultimately leading to cirrhosis. Several lines of evidence indicate that inducing apoptosis of hepatic stellate cells (HSC) may lead to regression of liver fibrosis. Recently, it was shown that gliotoxin (GTX) induces apoptosis of HSC. However, the clinical use of GTX may be limited because of the lack of cell and tissue specificity, causing a high risk of potentially severe adverse effects. The aim of this study, therefore, was to study the effect of GTX on different cells of the liver.

METHODS

We used normal and fibrotic precision-cut rat liver slices to study the effect of GTX on the various resident liver cell types. In these slices, the complex cell-cell interactions are preserved, which closely mimics the in vivo situation.

RESULTS

GTX exhibited a potent apoptosis-inducing activity in these slices. Both immunohistochemical stainings and real-time mRNA techniques showed that this apoptosis-inducing effect was seen in HSC. However, Kupffer cells and liver endothelial cells were also affected by GTX, whereas hepatocytes were only mildly affected.

CONCLUSIONS

This study indicates that the apoptosis-inducing strategy to treat liver fibrosis has high potential, but it will be necessary to develop an HSC-specific therapy to prevent adverse effects.

On the role and fate of LPS-dephosphorylating activity in the rat liver

Gut-derived lipopolysaccharide (LPS) plays a role in the pathogenesis of liver diseases like fibrosis. The enzyme alkaline phosphatase (AP) is present in, among others, the intestinal wall and liver and has been previously shown to dephosphorylate LPS. Therefore, we investigated the effect of LPS on hepatic AP expression and the effect of AP on LPS-induced hepatocyte responses. LPS-dephosphorylating activity was expressed at the hepatocyte canalicular membrane in normal and fibrotic animals. In addition to this, fibrotic animals also displayed high LPS-dephosphorylating activity around bile ducts. The enzyme was shown to dephosphorylate LPS from several bacterial species. LPS itself rapidly enhanced the intrahepatic mRNA levels for this enzyme within 2 h by a factor of seven. Furthermore, in vitro and in vivo studies showed that exogenous intestinal AP quickly bound to the asialoglycoprotein receptor on hepatocytes. This intestinal isoform significantly attenuated LPS-induced hepatic tumor necrosis factor-alpha and nitric oxide (nitrite and nitrate) responses in vitro. The enzyme also reduced LPS-induced hepatic glycogenolysis in vivo. This study shows that LPS enhances AP expression in hepatocytes and that intestinal AP is rapidly taken up by these same cells, leading to an attenuation of LPS-induced responses in vivo. Gut-derived LPS-dephosphorylating activity or enzyme upregulation within hepatocytes by LPS may therefore be a protective mechanism within the liver.

A role for iNOS in fasting hyperglycemia and impaired insulin signaling in the liver of obese diabetic mice

Chronic inflammation has been postulated to play an important role in the pathogenesis of insulin resistance. Inducible nitric oxide synthase (iNOS) has been implicated in many human diseases associated with inflammation. iNOS deficiency was shown to prevent high-fat diet-induced insulin resistance in skeletal muscle but not in the liver. A role for iNOS in fasting hyperglycemia and hepatic insulin resistance, however, remains to be investigated in obesity-related diabetes. To address this issue, we examined the effects of a specific inhibitor for iNOS, L-NIL, in obese diabetic (ob/ob) mice. iNOS expression was increased in the liver of ob/ob mice compared with wild-type mice. Treatment with iNOS inhibitor reversed fasting hyperglycemia with concomitant amelioration of hyperinsulinemia and improved insulin sensitivity in ob/ob mice. iNOS inhibitor also increased the protein expression of insulin receptor substrate (IRS)-1 and -2 1.5- and 2-fold, respectively, and enhanced IRS-1- and IRS-2-mediated insulin signaling in the liver of ob/ob mice. Exposure to NO donor and ectopically expressed iNOS decreased the protein expression of IRS-1 and -2 in cultured hepatocytes. These results suggest that iNOS plays a role in fasting hyperglycemia and contributes to hepatic insulin resistance in ob/ob mice.

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.

Burn injury impairs insulin-stimulated Akt/PKB activation in skeletal muscle

The molecular bases underlying burn- or critical illness-induced insulin resistance still remain unclarified. Muscle protein catabolism is a ubiquitous feature of critical illness. Akt/PKB plays a central role in the metabolic actions of insulin and is a pivotal regulator of hypertrophy and atrophy of skeletal muscle. We therefore examined the effects of burn injury on insulin-stimulated Akt/PKB activation in skeletal muscle. Insulin-stimulated phosphorylation of Akt/PKB was significantly attenuated in burned compared with sham-burned rats. Insulin-stimulated Akt/PKB kinase activity, as judged by immune complex kinase assay and phosphorylation status of the endogenous substrate of Akt/PKB, glycogen synthase kinase-3beta (GSK-3beta), was significantly impaired in burned rats. Furthermore, insulin consistently failed to increase the phosphorylation of p70 S6 kinase, another downstream effector of Akt/PKB, in rats with burn injury, whereas phosphorylation of p70 S6 kinase was increased by insulin in controls. The protein expression of Akt/PKB, GSK-3beta, and p70 S6 kinase was unaltered by burn injury. However, insulin-stimulated activation of ERK, a signaling pathway parallel to Akt/PKB, was not affected by burn injury. These results demonstrate that burn injury impairs insulin-stimulated Akt/PKB activation in skeletal muscle and suggest that attenuated Akt/PKB activation may be involved in deranged metabolism and muscle wasting observed after burn injury.

IKK-beta links inflammation to obesity-induced insulin resistance

Inflammation may underlie the metabolic disorders of insulin resistance and type 2 diabetes. IkappaB kinase beta (IKK-beta, encoded by Ikbkb) is a central coordinator of inflammatory responses through activation of NF-kappaB. To understand the role of IKK-beta in insulin resistance, we used mice lacking this enzyme in hepatocytes (Ikbkb(Deltahep)) or myeloid cells (Ikbkb(Deltamye)). Ikbkb(Deltahep) mice retain liver insulin responsiveness, but develop insulin resistance in muscle and fat in response to high fat diet, obesity or aging. In contrast, Ikbkb(Deltamye) mice retain global insulin sensitivity and are protected from insulin resistance. Thus, IKK-beta acts locally in liver and systemically in myeloid cells, where NF-kappaB activation induces inflammatory mediators that cause insulin resistance. These findings demonstrate the importance of liver cell IKK-beta in hepatic insulin resistance and the central role of myeloid cells in development of systemic insulin resistance. We suggest that inhibition of IKK-beta, especially in myeloid cells, may be used to treat insulin resistance.

Maldi-TOF analysis of portal sera of pancreatic cancer patients: identification of diabetogenic and antidiabetogenic peptides

BACKGROUND

Pancreatic cancer (PC) associated diabetes mellitus (DM) might be consequent to the diabetogenic effects of tumour products, possibly acting via nitric oxide (NO). Our aims were: (1) to verify whether PC associated DM determines an increased hepatic NO and (2) using MALDI-TOF analysis, to evaluate the peptide composition of PC cell conditioned media (CM) and of portal sera from patients with PC with (n=7) or without (n=4) DM.

METHODS

In liver tissue homogenates of 23 patients with PC (n=17) or chronic pancreatitis (n=6) GAPDH mRNA and activity, glucose, lactate, nitrite and nitrate were assayed. MALDI-TOF analysis was performed in three PC cell lines CM, and in portal sera from patients with PC.

RESULTS

Higher GAPDH mRNA and nitrite were found in patients with than in patients without DM. In PC cell CM, only 9 among a total of 75 fragments identified, were tumour specific. One hundred seventy-three fragments were identified in the portal sera of patients: one was positively and six fragments were negatively correlated with DM.

CONCLUSIONS

Unlike liver GAPDH, NO appears to be involved in PC associated DM. In portal sera, the absence, rather than the presence, of specific fragments, appears to be correlated with the development of DM.

Suppressor of cytokine signaling 1 (SOCS-1) and SOCS-3 cause insulin resistance through inhibition of tyrosine phosphorylation of insulin receptor substrate proteins by discrete mechanisms

Insulin resistance is a pathophysiological component of type 2 diabetes and obesity and also occurs in states of stress, infection, and inflammation associated with an upregulation of cytokines. Here we show that in both obesity and lipopolysaccharide (LPS)-induced endotoxemia there is an increase in suppressor of cytokine signaling (SOCS) proteins, SOCS-1 and SOCS-3, in liver, muscle, and, to a lesser extent, fat. In concordance with these increases by LPS, tyrosine phosphorylation of the insulin receptor (IR) is partially impaired and phosphorylation of the insulin receptor substrate (IRS) proteins is almost completely suppressed. Direct overexpression of SOCS-3 in liver by adenoviral-mediated gene transfer markedly decreases tyrosine phosphorylation of both IRS-1 and IRS-2, while SOCS-1 overexpression preferentially inhibits IRS-2 phosphorylation. Neither affects IR phosphorylation, although both SOCS-1 and SOCS-3 bind to the insulin receptor in vivo in an insulin-dependent fashion. Experiments with cultured cells expressing mutant insulin receptors reveal that SOCS-3 binds to Tyr960 of IR, a key residue for the recognition of IRS-1 and IRS-2, whereas SOCS-1 binds to the domain in the catalytic loop essential for IRS-2 recognition in vitro. Moreover, overexpression of either SOCS-1 or SOCS-3 attenuates insulin-induced glycogen synthesis in L6 myotubes and activation of glucose uptake in 3T3L1 adipocytes. By contrast, a reduction of SOCS-1 or SOCS-3 by antisense treatment partially restores tumor necrosis factor alpha-induced downregulation of tyrosine phosphorylation of IRS proteins in 3T3L1 adipocytes. These data indicate that SOCS-1 and SOCS-3 act as negative regulators in insulin signaling and serve as one of the missing links between insulin resistance and cytokine signaling.

Lipopolysaccharide increases resistin gene expression in vivo and in vitro

Although resistin has been thought to be an important link between obesity and diabetes, recent results do not support this hypothesis. We speculated that resistin may be involved in inflammatory processes and be induced by inflammatory stimuli. In this study, we tested whether lipopolysaccharide (LPS) induced resistin expression in rats. The results show that resistin mRNA levels in white adipose tissue and white blood cells were increased by LPS treatment. LPS also increased resistin mRNA levels in 3T3-L1 adipocytes and human peripheral blood monocytes. The results suggest that resistin is involved in insulin resistance and probably in other inflammatory responses.

Mediators of cytokine-induced insulin resistance in obesity and other inflammatory settings

Increased release and action of proinflammatory cytokines are thought to be responsible for the occurrence of insulin resistance in inflammatory and metabolic diseases including obesity-linked diabetes. Recent work has identified several signal transduction pathways activated by cytokines which can impede on insulin receptor signaling in skeletal muscle, liver, and adipose cells. A majority of these complex and interrelated pathways appear to converge at the level of insulin receptor substrate-1 by promoting its serine phosphorylation in order to mediate heterologous inhibition of insulin receptor substrate-1 signaling which, in turn, counterregulates the insulin response. Other possible mechanisms of insulin resistance in cytokine-treated cells include nitration of insulin receptor substrate-1 tyrosine residues by nitric oxide-derived reactive nitrogen species as well as direct interference with insulin signaling molecules further downstream such as protein kinase B/Akt. A detailed knowledge of the complex network of intracellular signaling pathways triggered by cytokines may be instrumental in the development of new approaches to prevent insulin resistance in acute and chronic inflammatory settings.