Retraction Note to: L-glutamine supplementation induces insulin resistance in adipose tissue and improves insulin signalling in liver and muscle of rats with diet-induced obesity

In light of forensic evidence indicating duplication and/or manipulation of western blot images the Editor-in-Chief is retracting the article cited above.

TLR4 at the Crossroads of Nutrients, Gut Microbiota, and Metabolic Inflammation

Obesity is accompanied by the activation of low-grade inflammatory activity in metabolically relevant tissues. Studies have shown that obesity-associated insulin resistance results from the inflammatory targeting and inhibition of key proteins of the insulin-signaling pathway. At least three apparently distinct mechanisms-endoplasmic reticulum stress, toll-like receptor (TLR) 4 activation, and changes in gut microbiota-have been identified as triggers of obesity-associated metabolic inflammation; thus, they are expected to represent potential targets for the treatment of obesity and its comorbidities. Here, we review the data that place TLR4 in the center of the events that connect the consumption of dietary fats with metabolic inflammation and insulin resistance. Changes in the gut microbiota can lead to reduced integrity of the intestinal barrier, leading to increased leakage of lipopolysaccharides and fatty acids, which can act upon TLR4 to activate systemic inflammation. Fatty acids can also trigger endoplasmic reticulum stress, which can be further stimulated by cross talk with active TLR4. Thus, the current data support a connection among the three main triggers of metabolic inflammation, and TLR4 emerges as a link among all of these mechanisms.

Alzheimer-associated Aβ oligomers impact the central nervous system to induce peripheral metabolic deregulation

Alzheimer's disease (AD) is associated with peripheral metabolic disorders. Clinical/epidemiological data indicate increased risk of diabetes in AD patients. Here, we show that intracerebroventricular infusion of AD-associated Aβ oligomers (AβOs) in mice triggered peripheral glucose intolerance, a phenomenon further verified in two transgenic mouse models of AD. Systemically injected AβOs failed to induce glucose intolerance, suggesting AβOs target brain regions involved in peripheral metabolic control. Accordingly, we show that AβOs affected hypothalamic neurons in culture, inducing eukaryotic translation initiation factor 2α phosphorylation (eIF2α-P). AβOs further induced eIF2α-P and activated pro-inflammatory IKKβ/NF-κB signaling in the hypothalamus of mice and macaques. AβOs failed to trigger peripheral glucose intolerance in tumor necrosis factor-α (TNF-α) receptor 1 knockout mice. Pharmacological inhibition of brain inflammation and endoplasmic reticulum stress prevented glucose intolerance in mice, indicating that AβOs act via a central route to affect peripheral glucose homeostasis. While the hypothalamus has been largely ignored in the AD field, our findings indicate that AβOs affect this brain region and reveal novel shared molecular mechanisms between hypothalamic dysfunction in metabolic disorders and AD.

Fractalkine (CX3CL1) is involved in the early activation of hypothalamic inflammation in experimental obesity

Hypothalamic inflammation is a common feature of experimental obesity. Dietary fats are important triggers of this process, inducing the activation of toll-like receptor-4 (TLR4) signaling and endoplasmic reticulum stress. Microglia cells, which are the cellular components of the innate immune system in the brain, are expected to play a role in the early activation of diet-induced hypothalamic inflammation. Here, we use bone marrow transplants to generate mice chimeras that express a functional TLR4 in the entire body except in bone marrow-derived cells or only in bone marrow-derived cells. We show that a functional TLR4 in bone marrow-derived cells is required for the complete expression of the diet-induced obese phenotype and for the perpetuation of inflammation in the hypothalamus. In an obesity-prone mouse strain, the chemokine CX3CL1 (fractalkine) is rapidly induced in the neurons of the hypothalamus after the introduction of a high-fat diet. The inhibition of hypothalamic fractalkine reduces diet-induced hypothalamic inflammation and the recruitment of bone marrow-derived monocytic cells to the hypothalamus; in addition, this inhibition reduces obesity and protects against diet-induced glucose intolerance. Thus, fractalkine is an important player in the early induction of diet-induced hypothalamic inflammation, and its inhibition impairs the induction of the obese and glucose intolerance phenotypes.

Abstract 413: Hypothalamic Leptin Signaling And Blood Pressure Regulation In Obese Rats

The main function of Leptin is to inform the individual's nutritional status to hypothalamus, which in turn regulate food intake and energy expenditure. Such actions are orchestrated by phosphorylation of ObRb receptor on tyrosine 985 and 1138, the latter is related to metabolism and Stat3 pathway. Recently, it was demonstrated that high serum levels of leptin, which is seen in DIO, correlates strongly with hypertension. On the other hand, obese individuals have resistance to metabolic actions of leptin (satiety and thermogenesis).

To investigate the molecular hypothalamic pathways that characterize the selective activity of leptin on the effect of blood pressure (BP) increase, adults Sprague Dawley rats were fed with standard diet (SD) or HFD for three months and were submitted to chronic ICV injection of leptin (2μg/day) or saline (2μl) for 10 days. BP, food intake and energy expenditure were assessed before and after treatment.

SD+leptin group had reduced food intake from 109,48±8,48 to 57,3±7,04 kcal / day, increased energy expenditure from 85,6±1,87 to 94,4±0,58 kcal/day/kg^0,75 and consequently weight reduction of 15,25±3,54 g (P <0.001 all) which did not occur in HFD+leptin. However, both SD and HFD group, leptin increased BP of 10.44±0.12% (from 103,7±0,7 to 114,8±0,8 mmHg) and 14.22±1.9% (from 118,6±1,3 to 132,2±1,5 mmHg), respectively.

As expected, obese animals had elevated levels of serum leptin when compared to SD group (SD: 2,24±0,38 ng/dl and HFD: 9,88±1,82 ng/dl, p<0,05). Additionally, we evaluate the main activated signal pathways by leptin in hypothalamus. SD+leptin group showed a significant increase in activity of Stat3, Akt and in MAPK expression. However, HFD+leptin group manifested an increase only on the expression of MAPK pathway. Both SD and HFD leptin-treated groups had higher ObRb tyr985 phosphorylation, which was not observed with the pObRb tyr1138. It was possible to see that ObRb tyr985 dependent pathway is responsive to leptin in SD and HFD, and ObRb tyr1138 as well as the related protein Stat3 and Akt are reduced in obese animals. Therefore, it may be suggested that in HFD-induced obesity hypothalamic pathway ObRb tyr985 / MAPK, unlike the other pathways, is not resistent and can be related to cardiovascular actions of leptin.

Inhibition of 72 kDa inositol polyphosphate 5-phosphatase E improves insulin signal transduction in diet-induced obesity

The 72 kDa inositol polyphosphate 5-phosphatase E (72k-5ptase) controls signal transduction through the catalytic dephosphorylation of the 5-position of membrane-bound phosphoinositides. The reduction of 72k-5ptase expression in the hypothalamus results in improved hypothalamic insulin signal transduction and reduction of food intake and body mass. Here, we evaluated the tissue distribution and the impact of obesity on the expression of 72k-5ptase in peripheral tissues of experimental animals. In addition, insulin signal transduction and action were determined in an animal model of obesity and insulin resistance treated with an antisense (AS) oligonucleotide that reduces 72k-5ptase expression. In lean Wistar rats, 72k-5ptase mRNA and protein are found in highest levels in heart, skeletal muscle, and white adipose tissue. In three distinct models of obesity, Wistar rats, Swiss mice fed on high-fat diet, and leptin-deficient ob/ob mice, the expression of 72k-5ptase is increased in skeletal muscle and adipose tissue. The treatment of obese Wistar rats with an anti-72k-5ptase AS oligonucleotide results in significant reduction of 72k-5ptase catalytic activity, which is accompanied by reduced food intake and body mass and improved insulin signal transduction and action as determined by immunoblotting and clamp studies respectively. 72k-5ptase expression is increased in obesity and its AS inhibition resulted in a significant improvement in insulin signal transduction and restoration of glucose homeostasis.

Diacerhein attenuates the inflammatory response and improves survival in a model of severe sepsis

Introduction

Hyperglycemia and insulin resistance have been associated with a worse outcome in sepsis. Although tight glycemic control through insulin therapy has been shown to reduce morbidity and mortality rates, the effect of intensive insulin therapy in patients with severe sepsis is controversial because of the increased risk of serious adverse events related to hypoglycemia. Recently, knowledge about diacerhein, an anthraquinone drug with powerful antiinflammatory properties, revealed that this drug improves insulin sensitivity, mediated by the reversal of chronic subclinical inflammation. The aim of the present study was to evaluate whether the antiinflammatory effects of diacerhein after onset of sepsis-induced glycemic alterations is beneficial and whether the survival rate is prolonged in this situation.

Methods

Diffuse sepsis was induced by cecal ligation and puncture surgery (CLP) in male Wistar rats. Blood glucose and inflammatory cytokine levels were assessed 24 hours after CLP. The effect of diacerhein on survival of septic animals was investigated in parallel with insulin signaling and its modulators in liver, muscle, and adipose tissue.

Results

Here we demonstrated that diacerhein treatment improves survival during peritoneal-induced sepsis and inhibits sepsis-induced insulin resistance by improving insulin signaling via increased insulin-receptor substrate-1-associated phosphatidylinositol 3-kinase activity and Akt phosphorylation. Diacerhein also decreases the activation of endoplasmic reticulum stress signaling that involves upregulation of proinflammatory pathways, such as the I kappa B kinase and c-Jun NH₂-terminal kinase, which blunts insulin-induced insulin signaling in liver, muscle, and adipose tissue. Additionally, our data show that this drug promoted downregulation of proinflammatory signaling cascades that culminate in transcription of immunomodulatory factors such interleukin (IL)-1β, IL-6, and tumor necrosis factor-α.

Conclusions

This study demonstrated that diacerhein treatment increases survival and attenuates the inflammatory response with a significant effect on insulin sensitivity. On the basis of efficacy and safety profile, diacerhein represents a novel antiinflammatory therapy for management of insulin resistance in sepsis and a potential approach for future clinical trials.

Inhibition of hypothalamic inflammation reverses diet-induced insulin resistance in the liver

Defective liver gluconeogenesis is the main mechanism leading to fasting hyperglycemia in type 2 diabetes, and, in concert with steatosis, it is the hallmark of hepatic insulin resistance. Experimental obesity results, at least in part, from hypothalamic inflammation, which leads to leptin resistance and defective regulation of energy homeostasis. Pharmacological or genetic disruption of hypothalamic inflammation restores leptin sensitivity and reduces adiposity. Here, we evaluate the effect of a hypothalamic anti-inflammatory approach to regulating hepatic responsiveness to insulin. Obese rodents were treated by intracerebroventricular injections, with immunoneutralizing antibodies against Toll-like receptor (TLR)4 or tumor necrosis factor (TNF)α, and insulin signal transduction, hepatic steatosis, and gluconeogenesis were evaluated. The inhibition of either TLR4 or TNFα reduced hypothalamic inflammation, which was accompanied by the reduction of hypothalamic resistance to leptin and improved insulin signal transduction in the liver. This was accompanied by reduced liver steatosis and reduced hepatic expression of markers of steatosis. Furthermore, the inhibition of hypothalamic inflammation restored defective liver glucose production. All these beneficial effects were abrogated by vagotomy. Thus, the inhibition of hypothalamic inflammation in obesity results in improved hepatic insulin signal transduction, leading to reduced steatosis and reduced gluconeogenesis. All these effects are mediated by parasympathetic signals delivered by the vagus nerve.

Unsaturated fatty acids revert diet-induced hypothalamic inflammation in obesity

BACKGROUND

In experimental models, hypothalamic inflammation is an early and determining factor in the installation and progression of obesity. Pharmacological and gene-based approaches have proven efficient in restraining inflammation and correcting the obese phenotypes. However, the role of nutrients in the modulation of hypothalamic inflammation is unknown.

METHODOLOGY/PRINCIPAL FINDINGS

Here we show that, in a mouse model of diet-induced obesity, partial substitution of the fatty acid component of the diet by flax seed oil (rich in C18:3) or olive oil (rich in C18:1) corrects hypothalamic inflammation, hypothalamic and whole body insulin resistance, and body adiposity. In addition, upon icv injection in obese rats, both ω3 and ω9 pure fatty acids reduce spontaneous food intake and body mass gain. These effects are accompanied by the reversal of functional and molecular hypothalamic resistance to leptin/insulin and increased POMC and CART expressions. In addition, both, ω3 and ω9 fatty acids inhibit the AMPK/ACC pathway and increase CPT1 and SCD1 expression in the hypothalamus. Finally, acute hypothalamic injection of ω3 and ω9 fatty acids activate signal transduction through the recently identified GPR120 unsaturated fatty acid receptor.

CONCLUSIONS/SIGNIFICANCE

Unsaturated fatty acids can act either as nutrients or directly in the hypothalamus, reverting diet-induced inflammation and reducing body adiposity. These data show that, in addition to pharmacological and genetic approaches, nutrients can also be attractive candidates for controlling hypothalamic inflammation in obesity.

The immunosuppressant drug, thalidomide, improves hepatic alterations induced by a high-fat diet in mice

BACKGROUND

Pro-inflammatory cytokines, such as tumour necrosis factor (TNF)-alpha, are known to be involved in the establishment of insulin resistance. Insulin resistance plays a key role in the development of obesity-related pathologies, such as type 2 diabetes and non-alcoholic fatty liver disease (NAFLD). The state of chronic inflammation associated with obesity led us to hypothesize that TNF-alpha blockade may have an effect on experimentally obese animals.

AIMS

We studied the effects of thalidomide, an immunosuppressant and anti-TNF-alpha drug, on hepatic alterations that were induced by a high-fat diet (HFD) in mice.

METHODS

Obesity was induced in Swiss mice using a HFD for 12 weeks. Thalidomide-treated animals received thalidomide i.p. (100 mg/kg/day, 10 days). Glucose, aspartate aminotransferases and alanine aminotransferases levels were assessed in the blood. Insulin and glucose tolerance tests were performed. The liver was excised for histological, triglyceride, gene and protein expression analyses.

RESULTS

We found improvements in both the basal glucose blood levels and the response to insulin administration in the treated animals. The molecular analysis of insulin signalling revealed a restoration of the hepatic insulin receptor substrate (IRS)-1 and AKT phosphorylation. The hepatic expression of TNF-alpha was inhibited and the levels correlated with a significant reduction in the steatosis area. Other hepatic inflammatory markers, such as iNOS and suppressor of cytokine signalling (SOCS-3), were also reduced.

CONCLUSIONS

We suggest that immunosuppressant drugs that target TNF-alpha and that may also contribute to reductions in the inflammatory markers that are associated with obesity could be a therapeutic option in NAFLD and type 2 diabetes.

Obesity enhances eosinophilic inflammation in a murine model of allergic asthma

BACKGROUND AND PURPOSE

Obesity is associated with deterioration in asthma outcomes. Although airways eosinophil accumulation is characteristic of lung allergic diseases, little is known about the influence of obesity on the allergic eosinophil trafficking from bone marrow to lung tissues, and recruitment to airways lumen. Here, we have assessed the effects of diet-induced obesity on allergic eosinophilic inflammation in mice, examining eosinophil trafficking from bone marrow to airways, and production of T(H)1/T(H)2 cytokines.

EXPERIMENTAL APPROACH

C57BL/6 mice fed for 10 weeks with standard chow or high-fat diet were sensitized and challenged with ovalbumin. At 24-96 h post-ovalbumin challenge, bronchoalveolar lavage (BAL) fluid, lung tissue and bone marrow were examined.

KEY RESULTS

The high-fat-fed mice exhibited increased body weight and epididymal fat, glucose intolerance and alterations in lipid profile compared with the lean mice. Obesity markedly elevated serum leptin and lowered adiponectin levels. Ovalbumin challenge in obese mice promoted a markedly higher eosinophil accumulation in bone marrow and connective tissue surrounding the bronchial and bronchiolar segments. Eosinophil number in BAL fluid of obese mice was lower at 24 and 48 h. Levels of interleukin (IL)-5, eotaxin, tumour necrosis factor-alpha and IL-10 in BAL fluid of obese mice were significantly higher than in lean mice.

CONCLUSIONS AND IMPLICATIONS

Diet-induced obesity enhanced eosinophil trafficking from bone marrow to lung tissues, and delayed their transit through the airway epithelium into the airway lumen. Consequently, eosinophils remain longer in lung peribronchiolar segments due to overproduction of T(H)1/T(H)2 cytokines and chemokines.

Antiobesity effects of yerba maté extract (Ilex paraguariensis) in high-fat diet-induced obese mice

Because the potential of yerba maté (Ilex paraguariensis) has been suggested in the management of obesity, the aim of the present study was to evaluate the effects of yerba maté extract on weight loss, obesity-related biochemical parameters, and the regulation of adipose tissue gene expression in high-fat diet-induced obesity in mice. Thirty animals were randomly assigned to three groups. The mice were introduced to standard or high-fat diets. After 12 weeks on a high-fat diet, mice were randomly assigned according to the treatment (water or yerba maté extract 1.0 g/kg). After treatment intervention, plasma concentrations of total cholesterol, high-density lipoprotein cholesterol, triglyceride, low-density lipoprotein (LDL) cholesterol, and glucose were evaluated. Adipose tissue was examined to determine the mRNA levels of several genes such as tumor necrosis factor-alpha (TNF-alpha), leptin, interleukin-6 (IL-6), C-C motif chemokine ligand-2 (CCL2), CCL receptor-2 (CCR2), angiotensinogen, plasminogen activator inhibitor-1 (PAI-1), adiponectin, resistin, peroxisome proliferator-activated receptor-gamma(2) (PPAR-gamma(2)), uncoupling protein-1 (UCP1), and PPAR-gamma coactivator-1 alpha (PGC-1 alpha). The F4/80 levels were determined by immunoblotting. We found that obese mice treated with yerba maté exhibited marked attenuation of weight gain, adiposity, a decrease in epididymal fat-pad weight, and restoration of the serum levels of cholesterol, triglycerides, LDL cholesterol, and glucose. The gene and protein expression levels were directly regulated by the high-fat diet. After treatment with yerba maté extract, we observed a recovery of the expression levels. In conclusion, our data show that yerba maté extract has potent antiobesity activity in vivo. Additionally, we observed that the treatment had a modulatory effect on the expression of several genes related to obesity.

High-fat diet induces apoptosis of hypothalamic neurons

Consumption of dietary fats is amongst the most important environmental factors leading to obesity. In rodents, the consumption of fat-rich diets blunts leptin and insulin anorexigenic signaling in the hypothalamus by a mechanism dependent on the in situ activation of inflammation. Since inflammatory signal transduction can lead to the activation of apoptotic signaling pathways, we evaluated the effect of high-fat feeding on the induction of apoptosis of hypothalamic cells. Here, we show that consumption of dietary fats induce apoptosis of neurons and a reduction of synaptic inputs in the arcuate nucleus and lateral hypothalamus. This effect is dependent upon diet composition, and not on caloric intake, since pair-feeding is not sufficient to reduce the expression of apoptotic markers. The presence of an intact TLR4 receptor, protects cells from further apoptotic signals. In diet-induced inflammation of the hypothalamus, TLR4 exerts a dual function, on one side activating pro-inflammatory pathways that play a central role in the development of resistance to leptin and insulin, and on the other side restraining further damage by controlling the apoptotic activity.

The crosstalk between insulin and renin-angiotensin-aldosterone signaling systems and its effect on glucose metabolism and diabetes prevention

Essential hypertension is an insulin resistant state. Early insulin signaling steps are impaired in essential hypertension and a large body of data suggests that there is a crosstalk at multiple levels between the signal transduction pathways that mediate insulin and angiotensin II actions. At the extracellular level the angiotensin converting enzyme (ACE) regulates the synthesis of angiotensin II and bradykinin that is a powerful vasodilator. At early intracellular level angiotensin II acts on JAK-2/IRS1-IRS2/PI3-kinase, JNK and ERK to phosphorylate serine residues of key elements of insulin signaling pathway therefore inhibiting signaling by the insulin receptor. On another level angiotensin II inhibits the insulin signaling inducing the regulatory protein SOCS 3. Angiotensin II acting through the AT1 receptor can inhibit insulin-induced nitric oxide (NO) production by activating ERK 1/2 and JNK and enhances the activity of NADPH oxidase that leads to an increased reactive oxygen species generation. From the clinical standpoint, the inhibition of the renin angiotensin system improves insulin sensitivity and decreases the incidence of Type 2 Diabetes Mellitus (T2DM). This might represent an alternative approach to prevent type 2 diabetes in patients with hypertension and metabolic syndrome, (i.e. insulin resistant patients). This review will discuss: a) the molecular mechanisms of the crosstalk between the insulin and angiotensin II signaling systems b) the results of clinical studies employing drugs targeting the renin-angiotensin II-aldosterone systems and their role in glucose metabolism and diabetes prevention.

Intracerebroventricular injection of citrate inhibits hypothalamic AMPK and modulates feeding behavior and peripheral insulin signaling

We hypothesized that citrate might modulate the AMP-activated protein kinase/acetyl-CoA carboxylase (AMPK)/(ACC) pathway and participate in neuronal feeding control and glucose homeostasis. To address this issue, we injected citrate into the lateral ventricle of rats. Intracerebroventricular (ICV) injection of citrate diminished the phosphorylation of hypothalamic AMPK/ACC, increased the expression of anorexigenic neuropeptide (pro-opiomelanocortin and corticotropin-releasing hormone), elevated the level of malonyl-CoA in the hypothalamus, and reduced food intake. No change was observed in the concentration of blood insulin after the injection of citrate. With a euglycemic-hyperinsulinemic clamp, the glucose infusion rate was higher in the citrate group than in the control group (28.6+/-0.8 vs 19.3+/-0.2 mU/kg body weight/min respectively), and so was glucose uptake in skeletal muscle and the epididymal fat pad. Concordantly, insulin receptor (IR), IR substrate type 1 (IRS1), IRS2, and protein kinase B (AKT) phosphorylation in adipose tissue and skeletal muscle was improved by citrate ICV treatment. Moreover, the treatment with citrate for 7 days promoted body weight loss and decreased the adipose tissue. Our results suggest that citrate and glucose may serve as signals of energy and nutrient availability to hypothalamic cells.

Distinct subsets of hypothalamic genes are modulated by two different thermogenesis-inducing stimuli

Obesity results from an imbalance between food intake and energy expenditure, two vital functions that are tightly controlled by specialized neurons of the hypothalamus. The complex mechanisms that integrate these two functions are only beginning to be deciphered. The objective of this study was to determine the effect of two thermogenesis-inducing conditions, i.e., ingestion of a high-fat (HF) diet and exposure to cold environment, on the expression of 1,176 genes in the hypothalamus of Wistar rats. Hypothalamic gene expression was evaluated using a cDNA macroarray approach. mRNA and protein expressions were determined by reverse-transcription PCR (RT-PCR) and immunoblot. Cold exposure led to an increased expression of 43 genes and to a reduced expression of four genes. HF diet promoted an increased expression of 90 genes and a reduced expression of 78 genes. Only two genes (N-methyl-D-aspartate (NMDA) receptor 2B and guanosine triphosphate (GTP)-binding protein G-alpha-i1) were similarly affected by both thermogenesis-inducing conditions, undergoing an increment of expression. RT-PCR and immunoblot evaluations confirmed the modulation of NMDA receptor 2B and GTP-binding protein G-alpha-i1, only. This corresponds to 0.93% of all the responsive genes and 0.17% of the analyzed genes. These results indicate that distinct environmental thermogenic stimuli can modulate predominantly distinct profiles of genes reinforcing the complexity and multiplicity of the hypothalamic mechanisms that regulate energy conservation and expenditure.

Differential expression of pro-inflammatory cytokines and a pro-apoptotic protein in pelvic ileal pouches for ulcerative colitis and familial adenomatous polyposis

BACKGROUND

Pouchitis after total rectocolectomy is among the most common complications of patients with ulcerative colitis (UC). However, its frequency is quite rare in patients with familial adenomatous polyposis (FAP). We evaluated the inflammatory and pro-apoptotic activity in endoscopically normal mucosa of the ileal pouch in patients with UC and FAP.

METHODS

Twenty patients (10 with UC and 10 with FAP) with "J" pouch after total proctocolectomy were studied as were 10 normal controls. Biopsies were obtained from the mucosa of the pouch of UC and FAP patients and from the normal ileum of controls. The expression levels of TNF-alpha, IL-1beta, IL-6, IL-8 and phospho-BAD were determined by immunoblotting. Activated NFkappaB was evaluated by immuno-precipitation and immunoblotting for IkappaB kinase beta.

RESULTS

Patients with UC had higher levels of IL-1beta, IL-6, IL-8 and TNF-alpha than patients with FAP. The level of TNF-alpha was higher in patients with UC than in patients with FAP; both patient groups had TNF-alpha levels higher than controls. Activation of NFkappaB was similar in all three groups. The expression of phospho-BAD was significantly lower in patients with FAP than in patients with UC.

CONCLUSIONS

As compared with patients with FAP, patients with UC presented increased levels of some pro-inflammatory cytokines, even in the absence of clinical or endoscopic signs of pouchitis. Patients with FAP presented lower levels of pro-inflammatory proteins and of phospho-BAD. These findings may explain the higher rates of progression to pouchitis in UC patients, which could correlate with mucosal atrophy that occurs in inflamed tissue.

L-glutamine supplementation induces insulin resistance in adipose tissue and improves insulin signalling in liver and muscle of rats with diet-induced obesity

AIMS/HYPOTHESIS

Diet-induced obesity (DIO) is associated with insulin resistance in liver and muscle, but not in adipose tissue. Mice with fat-specific disruption of the gene encoding the insulin receptor are protected against DIO and glucose intolerance. In cell culture, glutamine induces insulin resistance in adipocytes, but has no effect in muscle cells. We investigated whether supplementation of a high-fat diet with glutamine induces insulin resistance in adipose tissue in the rat, improving insulin sensitivity in the whole animal.

MATERIALS AND METHODS

Male Wistar rats received standard rodent chow or a high-fat diet (HF) or an HF supplemented with alanine or glutamine (HFGln) for 2 months. Light microscopy and morphometry, oxygen consumption, hyperinsulinaemic-euglycaemic clamp and immunoprecipitation/immunoblotting were performed.

RESULTS

HFGln rats showed reductions in adipose mass and adipocyte size, a decrease in the activity of the insulin-induced IRS-phosphatidylinositol 3-kinase (PI3-K)-protein kinase B-forkhead transcription factor box 01 pathway in adipose tissue, and an increase in adiponectin levels. These results were associated with increases in insulin-stimulated glucose uptake in skeletal muscle and insulin-induced suppression of hepatic glucose output, and were accompanied by an increase in the activity of the insulin-induced IRS-PI3-K-Akt pathway in these tissues. In parallel, there were decreases in TNFalpha and IL-6 levels and reductions in c-jun N-terminal kinase (JNK), IkappaB kinase subunit beta (IKKbeta) and mammalian target of rapamycin (mTOR) activity in the liver, muscle and adipose tissue. There was also an increase in oxygen consumption and a decrease in the respiratory exchange rate in HFGln rats.

CONCLUSIONS/INTERPRETATION

Glutamine supplementation induces insulin resistance in adipose tissue, and this is accompanied by an increase in the activity of the hexosamine pathway. It also reduces adipose mass, consequently attenuating insulin resistance and activation of JNK and IKKbeta, while improving insulin signalling in liver and muscle.

Hepatic morphological alterations, glycogen content and cytochrome P450 activities in rats treated chronically with N(omega)-nitro-L-arginine methyl ester (L-NAME)

Chronic treatment of rats with N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) biosynthesis, results in hypertension mediated partly by enhanced angiotensin-I-converting enzyme (ACE) activity. We examined the influence of L-NAME on rat liver morphology, on hepatic glycogen, cholesterol, and triglyceride content, and on the activities of the cytochrome P450 isoforms CYP1A1/2, CYP2B1/2, CYP2C11, and CYP2E1. Male Wistar rats were treated with L-NAME (20 mg/rat per day via drinking water) for 2, 4, and 8 weeks, and their livers were then removed for analysis. Enzymatic induction was produced by treating rats with phenobarbital (to induce CYP2B1/2), beta-naphthoflavone (to induce CYP1A1/2), or pyrazole (to induce CYP2E1). L-NAME significantly elevated blood pressure; this was reversed by concomitant treatment with enalapril (ACE inhibitor) or losartan (angiotensin II AT(1) receptor antagonist). L-NAME caused vascular hypertrophy in hepatic arteries, with perivascular and interstitial fibrosis involving collagen deposition. Hepatic glycogen content also significantly increased. L-NAME did not affect fasting glucose levels but significantly reduced insulin levels and increased the insulin sensitivity of rats, based on an intraperitoneal glucose tolerance test. Immunoblotting experiments indicated enhanced phosphorylation of protein kinase B and of glycogen synthase kinase 3. All these changes were reversed by concomitant treatment with enalapril or losartan. L-NAME had no effect on hepatic cholesterol or triglyceride content or on the basal or drug-induced activities and protein expression of the cytochrome P450 isoforms. Thus, the chronic inhibition of NO biosynthesis produced hepatic morphological alterations and changes in glycogen metabolism mediated by the renin-angiotensin system. The increase in hepatic glycogen content probably resulted from enhanced glycogen synthase activity following the inhibition of glycogen synthase kinase 3 by phosphorylation.

Inducible-NOS but not neuronal-NOS participate in the acute effect of TNF-α on hypothalamic insulin-dependent inhibition of food intake

TNF-alpha acts on the hypothalamus modulating food intake and energy expenditure through mechanisms incompletely elucidated. Here, we explore the hypothesis that, to modulate insulin-induced anorexigenic signaling in hypothalamus, TNF-alpha requires the synthesis of NO. TNF-alpha activates signal transduction through JNK and p38 in hypothalamus, peaking at 10(-8) M. This is accompanied by the induction of expression of the inducible and neuronal forms of NOS, in both cases peaking at 10(-12) M. In addition, TNF-alpha stimulates NOS catalytic activity. Pre-treatment with TNF-alpha at a low dose (10(-12) M) inhibits insulin-dependent anorexigenic signaling, and this effect is abolished in iNOS but not in nNOS knockout mice.

The phosphatidylinositol/AKT/atypical PKC pathway is involved in the improved insulin sensitivity by DHEA in muscle and liver of rats in vivo

DHEA improves insulin sensitivity and has anti-obesity effect in animal models and men. However, the molecular mechanisms by which DHEA improves insulin action have not been clearly understood. In the present study, we examined the protein levels and phosphorylation state of insulin receptor (IR), IRS-1 and IRS-2, the association between IRSs and PI3K and SHP2, the insulin-induced IRSs associated PI 3-kinase activities, and the phosphorylation status of AKT and atypical PKCzeta/lambda in the liver and the muscle of 6 month-old Wistar rats treated with DHEA. There was no change in IR, IRS-1 and IRS-2 protein levels in both tissues of treated rats analysed by immunoblotting. On the other hand, insulin-induced IRS-1 tyrosine phosphorylation was increased in both tissues while IRS-2 tyrosyl phosphorylation was increased in liver of DHEA treated group. The PI3-kinase/AKT pathway was increased in the liver and the PI3K/atypical PKCzeta/lambda pathway was increased in the muscle of DHEA treated rats. These data indicate that these regulations of early steps of insulin action may play a role in the intracellular mechanism for the improved insulin sensitivity observed in this animal model.

Prolactin-signal transduction in neonatal rat pancreatic islets and interaction with the insulin-signaling pathway

During pregnancy, pancreatic islets undergo structural and functional changes in response to an increased demand for insulin. Different hormones, especially placental lactogens, mediate these adaptive changes. Prolactin (PRL) mainly exerts its biological effects by activation of the JAK2/STAT5 pathway. PRL also stimulates some biological effects via activation of IRS-1, IRS-2, PI 3-kinase, and MAPK in different cell lines. Since IRS-2 is important for the maintenance of pancreatic islet cell mass, we investigated whether PRL affects insulin-signaling pathways in neonatal rat islets. PRL significantly potentiated glucose-induced insulin secretion in islets cultured for 7 days. This effect was blocked by the specific PI 3-kinase inhibitor wortmannin. To determine possible effects of PRL on insulin-signaling pathways, fresh islets were incubated with or without the hormone for 5 or 15 min. Immunoprecipitation and immunoblotting with specific antibodies showed that PRL induced a dose-dependent IRS-1 and IRS-2 phosphorylation compared to control islets. PRL-induced increase in IRS-1/-2 phosphorylation was accompanied by an increase in the association with and activation of PI 3-kinase. PRL-induced IRS-2 phosphorylation and its association with PI 3-kinase did not add to the effect of insulin. PRL also induced JAK2, SHC, ERK1 and ERK2 phosphorylation in neonatal islets, demonstrating that PRL can activate MAPK. These data indicate that PRL can stimulate the IRSs/PI 3-kinase and SHC/ERK pathways in islets from neonatal rats.

Effects of age on elements of insulin-signaling pathway in central nervous system of rats

Insulin resistance is known to play a pivotal role in type 2 diabetes. Senile individuals, besides being prone to insulin resistance and, consequently, to type 2 diabetes, manifest diseases of the central nervous system (CNS) that may be influenced by disturbances of insulin signaling in the brain, such as memory impairment, Parkinson disease, and Alzheimer disease. We investigated the expression and response to insulin of elements involved in the insulin-signaling pathway in the forebrain cortex and cerebellum of rats ages 1 d to 60 wk. The protein content of insulin receptors and SRC homology adaptor protein (SHC) did not change significantly along the time frame analyzed. However, insulin-induced tyrosine phosphorylation of the insulin receptor and SHC, and the association of SHC/growth factor receptor binding protein-2 (GRB2) decreased significantly from d 1 to wk 60 of life in both types of tissues. Moreover, the expression of SH protein tyrosine phosphatase-2 (SHP2), a tyrosine phosphatase involved in insulin signal transduction and regulation of the insulin signal, decreased significantly with age progression, in both the forebrain cortex and the cerebellum of rats. Thus, elements involved in the insulin-signaling pathway are regulated at the expression and/or functional level in the CNS, and this regulation may play a role in insulin resistance in the brain.

Regulation of IRS-2 tyrosine phosphorylation in fasting and diabetes

Intracellular insulin signaling involves a series of alternative and complementary pathways created by the multiple substrates of the insulin receptor (IRS) and the various isoforms of the SH2 domain signaling molecules that can interact with substrate. In this study we investigated IRS-1 and IRS-2 tyrosine phosphorylation, their association with PI3-kinase and the phosphorylation of Akt, a serine-threonine kinase situated downstream to PI 3-kinase, in liver and muscle of two animal models of insulin resistance: 72 h of fasting and STZ-diabetic rats. There was an upregulation in insulin-induced IRS-1 and IRS-2 tyrosine phosphorylation and association with PI3-kinase in liver and muscle of both animal models of insulin resistance. However, Akt phosphorylation showed different regulation, increasing in fasting and decreasing in STZ-diabetic rats. Since an important difference between these two animal models of insulin resistance is the plasma glucose levels, we can suggest that in STZ diabetic rats, the reduction in Akt phosphorylation is probably related to hyperglycemia and may certainly contribute to the molecular mechanism of insulin resistance observed in these animals.

Early steps of insulin action in the skin of intact rats

Insulin is an important regulator of growth and initiates its action by binding to its receptor, which undergoes tyrosyl autophosphorylation and further enhances its tyrosine kinase activity towards other intermediate molecules, including insulin receptor substrate 1, insulin receptor substrate 2, and Shc. Insulin receptor substrate proteins can dock various src-homology-2-domain-containing signaling proteins, such as the 85 kDa subunit of phosphatidylinositol 3 kinase and growth-factor-receptor-bound protein 2. The serine-threonine kinase is activated downstream to phosphatidylinositol 3 kinase. Shc protein has been shown to directly induce the association with growth-factor-receptor-bound protein 2 and downstream the activation of the mitogen-activated protein kinase. In this study we investigated insulin signal transduction pathways in skin of intact rats by immunoprecipitation and immunoblotting with specific antibodies, and also by immunohistochemistry with anti-insulin-receptor antibody. Our results showed that skin fragments clearly demonstrated the presence of insulin receptor in cell bodies of the epidermis and hair follicles and some faint staining was also detected in fibroblasts of the dermis. It was also observed that acute stimulation with insulin can induce tyrosyl phosphorylation of insulin receptor, that the insulin receptor substrates and Shc proteins serve as signaling molecules for insulin in skin of rats, and that insulin is able to induce association of insulin receptor substrate 1/phosphatidylinositol 3 kinase and Shc/growth-factor-receptor-bound protein 2 in this tissue, as well as phosphorylation of mitogen-activated protein kinase and serine-threonine kinase, demonstrating that proteins involved in early steps of insulin action are expressed in skin of intact rats and are quickly activated after insulin stimulation.

Tissue-specific regulation of early steps in insulin action in septic rats

Sepsis is known to induce insulin resistance, but the exact molecular mechanism involved is unknown. In the present study we have examined the levels and phosphorylation state of the insulin receptor and of insulin receptor substrate 1 (IRS-1), as well as the association between IRS-1 and phosphatidylinositol 3-kinase (PI 3-kinase) in the liver and muscle of septic rats by immunoprecipitation and immunoblotting with anti-insulin receptor, anti-IRS-1, anti-PI 3-kinase and anti-phosphotyrosine antibodies. There were no changes in the insulin receptor concentration and phosphorylation levels in the liver and muscle of septic rats. IRS-1 protein levels were decreased by 40+/-3% (p < 0.01) in muscle but not in liver of septic rats. In samples previously immunoprecipitated with anti-IRS-1 antibody and blotted with antiphosphotyrosine antibody, the insulin-stimulated IRS-1 phosphorylation levels in the muscle of septic rats decreased by 38+/-5% (p < 0.01) and insulin-stimulated IRS-1 association with PI 3-kinase decreased by 44+/-7% in muscle (p < 0.01) but no changes were seen in liver. These data suggest that there is a tissue-specific regulation of early steps of insulin signal transduction in septic rats, and the changes observed in muscle may have a role in the insulin resistance of these animals.

A high-fructose diet induces insulin resistance but not blood pressure changes in normotensive rats

Rats fed a high-fructose diet represent an animal model for insulin resistance and hypertension. We recently showed that a high-fructose diet containing vegetable oil but a normal sodium/potassium ratio induced mild insulin resistance with decreased insulin receptor substrate-1 tyrosine phosphorylation in the liver and muscle of normal rats. In the present study, we examined the mean blood pressure, serum lipid levels and insulin sensitivity by estimating in vivo insulin activity using the 15-min intravenous insulin tolerance test (ITT, 0.5 ml of 6 microg insulin, iv) followed by calculation of the rate constant for plasma glucose disappearance (Kitt) in male Wistar-Hannover rats (110-130 g) randomly divided into four diet groups: control, 1:3 sodium/potassium ratio (R Na:K) diet (C 1:3 R Na:K); control, 1:1 sodium/potassium ratio diet (CNa 1:1 R Na:K); high-fructose, 1:3 sodium/potassium ratio diet (F 1:3 R Na:K), and high-fructose, 1:1 sodium/potassium ratio diet (FNa 1:1 R Na:K) for 28 days. The change in R Na:K for the control and high-fructose diets had no effect on insulin sensitivity measured by ITT. In contrast, the 1:1 R Na:K increased blood pressure in rats receiving the control and high-fructose diets from 117 +/- 3 and 118 +/- 3 mmHg to 141 +/- 4 and 132 +/- 4 mmHg (P < 0.05), respectively. Triacylglycerol levels were higher in both groups treated with a high-fructose diet when compared to controls (C 1:3 R Na:K: 1.2 +/- 0.1 mmol/l vs F 1:3 R Na:K: 2.3 +/- 0.4 mmol/l and CNa 1:1 R Na:K: 1.2 +/- 0.2 mmol/l vs FNa 1:1 R Na:K: 2.6 +/- 0.4 mmol/l, P < 0.05). These data suggest that fructose alone does not induce hyperinsulinemia or hypertension in rats fed a normal R Na:K diet, whereas an elevation of sodium in the diet may contribute to the elevated blood pressure in this animal model.

Insulin modulates leptin-induced STAT3 activation in rat hypothalamus

Insulin and leptin have overlapping effects in the control of energy homeostasis, but the molecular basis of this synergism is unknown. Insulin signals through a receptor tyrosine kinase that phosphorylates and activates the docking proteins IRSs (insulin receptor substrates), whereas the leptin receptor and its associated protein tyrosine kinase JAK2 (Janus kinase 2) mediate phosphorylation and activation of the transcription factor STAT3 (signal transducer and activator of transcription). Here, we present evidence for the integration of leptin and insulin signals in the hypothalamus. Insulin induced JAK2 tyrosine phosphorylation, leptin receptor phosphorylation which, in the presence of leptin, augmented the interaction between STAT3 and this receptor. Insulin also increased the leptin-induced phosphorylation of STAT3 and its activation. These results indicate that insulin modulates the leptin signal transduction pathway, and may provide a molecular basis for the coordinated effects of insulin and leptin in feeding behavior and weight control.

[Study of renal glucose release in rabbits submitted to total functional hepatectomy and norepinephrine infusion]

AIM

To study the possible endogenous sources of glucose in the absence of the liver (equivalent to the anhepatic period of liver transplantation).

MATERIAL AND METHODS

A experimental model of total functional hepatectomy in anesthetized rabbits was developed. The aorta and the right renal vein were catheterised in order to collect blood samples to measure glucose contents. The animals were divided into two groups: group 1, 5 animals underwent only norepinephrine infusion; group 2, 15 animals underwent norepinephrine infusion and submitted to total functional hepatectomy.

RESULTS

In group 2, before the hepatectomy, arterial glucose levels were higher than venous ones and after the liver removal, the venous levels became higher than the arterial ones. This pattern showed an inversion in the glycemic curves. In group 1 this pattern was not observed.

CONCLUSION

The glycemic curves behavior observed in group 2 its not due to norepinephrine infusion, but represents renal glucose release after total functional hepatectomy.

Lack of insulin inhibition on insulin secretion in non-diabetic morbidly obese patients

OBJECTIVE

Insulin inhibition of insulin secretion has been described in normal lean subjects. In this study, we examined whether this phenomenon also occurs in the morbidly obese who often have severe peripheral insulin resistance.

SUBJECTS

Twelve obese patients, normotolerant to glucose (8 F/4 M, body mass index (BMI)=54.8+/-2.5 kg/m(2), 39 y) and 16 lean control subjects (10 F/6 M, BMI=22.0+/-0.5 kg/m(2), 31 y).

DESIGN AND MEASUREMENTS

An experimental study using various parameters, including an euglycemic hyperinsulinemic clamp (280 pmol/min/m(2) of body surface), an oral glucose tolerance test (OGTT), electrical bioimpedance and indirect calorimetry.

RESULTS

The obese subjects were insulin resistant (M=19.8+/-1.6 vs 48.7+/-2.6 micromol/min kg FFM, P<0.0001) and hyperinsulinemic in the fasted state and after glucose ingestion. Fasting plasma C-peptide levels (obese 1425+/-131 pmol/l vs lean 550+/-63 pmol/l; P<0.0001) decreased less during the clamp in the obese groups (-16.9+/-6.9% vs -43.0+/-5.6% relative to fasting values; P=0.007). In the lean group, the C-peptide decrease during the clamp (percentage variation) was related to insulin sensitivity, M/FFM (r=0.56, P=0.03), even after adjustment for the clamp glucose variation.

CONCLUSION

We conclude that, in lean subjects, insulin inhibits its own secretion, and this may be related to insulin sensibility. This response is blunted in morbidly obese patients and may have a role in the pathogenesis of fasting hyperinsulinemia in these patients.

Expression and distribution of NOS1 and NOS3 in the myocardium of angiotensin II-infused rats

Studies have indicated a complex functional interaction between angiotensin (Ang) II and NO in the heart. The purpose of the present study was to examine the protein expression and tissue distribution of NO synthases 1 (NOS1) and 3 (NOS3) in the myocardium of rats that underwent continuous infusion of Ang II at 2 different rates (10 and 40 ng. kg(-1). min(-1)) for 6 days. Mean arterial pressure increased by approximately 15 mm Hg in rats infused with Ang II at 40 ng. kg(-1). min(-1), but it remained close to the values observed in saline-infused rats ( approximately 110 mm Hg) when Ang II was infused at 10 ng. kg(-1). min(-1). The protein expression of a 160-kDa NOS1 and a 135-kDa NOS3 were found to increase ( approximately 200%) in the myocardium of rats infused with both subpressor and pressor doses of Ang II. Immunohistochemistry studies showed that NOS1 and NOS3 are differentially expressed in myocardial cells. NOS1 was detected in cardiac myocytes and in smooth muscle cells of small and large coronary arteries, whereas NOS3 was detected in the endothelium and in perivascular and interstitial tissues, but NOS3 was not detected in cardiac or smooth muscle cells. Ang II infusion enhanced the tissue immunoreactivity of both isoforms in their specific locations but did not change the distribution throughout the myocardium. Myocardium staining with anti-angiotensin type 1 (AT(1)) receptor antibody indicated that AT(1) receptor is expressed in cardiac myocytes, coronary smooth muscle cells, and interstitial and perivascular tissues. Ang II infusion did not change the protein expression and distribution of AT(1) receptor in the myocardium. These results indicate that long-term increases in the circulating levels of Ang II modulate the protein expression of NOS1 and NOS3 and, consequently, the function of the local myocardial NO system.

Magnesium deficiency improves glucose homeostasis in the rat: studies in vivo and in isolated islets in vitro

The serum mineral levels, glucose disappearance rate (kg), total area under the glucose (DeltaG) and insulin (DeltaI) curves, and static insulin secretion were compared among rats fed a Mg-deficient diet for 6 (DF-6) or 11 (DF-11) weeks, and rats fed a control diet for the same periods (CO-6 and CO-11 groups). No change in glucose homeostasis was observed among DF-6, CO-6 and CO-11 rats. DF-11 rats showed an elevated kg and a reduced DeltaG and DeltaI. For evaluating the effect of supplementation, rats fed a control or Mg-deficient diet for 6 weeks were then fed a Mg- supplemented diet for 5 weeks (SCO and SDF groups respectively). The serum Mg levels in SDF rats were similar to those in CO-11 and SCO rats, but higher than in the DF-11 group. SDF rats showed similar kg, DeltaG and DeltaI compared with the CO-11 and SCO groups. However, a significantly lower kg and higher DeltaG and DeltaI were observed in SDF compared with DF-11 rats. Basal and 8.3 mmol glucose/l-stimulated insulin secretion by islets from DF-11 rats were higher than by islets from CO-11 rats. These results indicate that moderate Mg depletion for a long period may increase the secretion and sensitivity to insulin, while Mg supplementation in formerly Mg-deficient rats may prevent the increase in sensitivity and secretion of insulin.

Regulation of insulin-stimulated tyrosine phosphorylation of Shc and Shc/Grb2 association in liver, muscle, and adipose tissue of epinephrine- and streptozotocin-treated rats

Shc protein phosphorylation has been extensively characterized as the initial step that activates a complex mitogenic pathway through its association with Grb2. In the present study, we investigated the adrenergic control of insulin-induced Shc phosphorylation and Shc-Grb2 association, and the modulating effect of streptozotocin-induced diabetes mellitus on Shc phosphorylation and Shc/Grb2 association. Acute treatment with epinephrine, which leads to a normoglycemic insulin-resistant state, does not affect insulin-induced Shc tyrosine phosphorylation or Shc-Grb2 association in liver, muscle, or fat. By contrast, a significant increase in insulin-induced Shc phosphorylation is observed in liver and muscle of rats treated with streptozotocin. The association of Shc/Grb2 is also increased in both tissues following insulin treatment. These data suggest that while epinephrine preserves the insulin-induced phosphorylation of Shc and the mitogenic pathway stimulated by Shc-Grb2 association, treatment with streptozotocin leads to a tissue-specific increase in the activity of the initial step that ultimately results in the activation of the Shc/Grb2 mitogenic pathway.

A high-fructose diet induces changes in pp185 phosphorylation in muscle and liver of rats

Insulin stimulates the tyrosine kinase activity of its receptor resulting in the tyrosine phosphorylation of pp185, which contains insulin receptor substrates IRS-1 and IRS-2. These early steps in insulin action are essential for the metabolic effects of insulin. Feeding animals a high-fructose diet results in insulin resistance. However, the exact molecular mechanism underlying this effect is unknown. In the present study, we determined the levels and phosphorylation status of the insulin receptor and pp185 (IRS-(1/2)) in liver and muscle of rats submitted to a high-fructose diet evaluated by immunoblotting with specific antibodies. Feeding fructose (28 days) induced a discrete insulin resistance, as demonstrated by the insulin tolerance test. Plasma glucose and serum insulin and cholesterol levels of the two groups of rats, fructose-fed and control, were similar, whereas plasma triacylglycerol concentration was significantly increased in the rats submitted to the fructose diet (P<0.05). There were no changes in insulin receptor concentration in the liver or muscle of either group. However, insulin-stimulated receptor autophosphorylation was reduced to 72 +/- 4% (P<0.05) in the liver of high-fructose rats. The IRS-1 protein levels were similar in both liver and muscle of the two groups of rats. In contrast, there was a significant decrease in insulin-induced pp185 (IRS-(1/2)) phosphorylation, to 83 +/- 5% (P<0.05) in liver and to 77 +/- 4% (P<0.05) in muscle of the high-fructose rats. These data suggest that changes in the early steps of insulin signal transduction may have an important role in the insulin resistance induced by high-fructose feeding.

Characterization of the insulin-signaling pathway in lacrimal and salivary glands of rats

PURPOSE

Insulin has been acknowledged as a mediator of several physiological events in lacrimal and salivary glands. We investigated the presence of insulin receptors and of insulin-induced autophosphorylation of the insulin receptor and activation of elements involved in the early steps of insulin signaling in lacrimal and salivary glands of rats.

METHODS

Lacrimal and salivary glands of Wistar rats were removed and processed for immunohistochemistry using anti-insulin receptor and anti-IGF-1 receptor antibodies. The activation of insulin receptors following insulin treatment, and the involvement of insulin receptor substrates-1 and -2, Shc, JAK-2 and STAT-1, were analyzed by immunoprecipitation, followed by SDS-PAGE and immunoblotting of rat lacrimal and salivary glands after exposure to insulin.

RESULTS

Insulin and IGF-1 receptors were present in rat lacrimal and salivary glands and were located predominantly in the cytoplasm and plasma membrane. Functional studies demonstrated that insulin induced a dose-dependent phosphorylation of the insulin receptor, IGF-1R, insulin receptor substrates-1 and -2, Shc, and STAT-1. In rats with streptozotocin-induced diabetes mellitus there was a significant reduction in insulin-induced insulin receptor and STAT-1 phosphorylation in the lacrimal gland but not in the salivary gland; there was no influence on Shc phosphorylation in either tissue.

CONCLUSIONS

The present results indicate that insulin and IGF-1 receptors are expressed in lacrimal and salivary glands, and that insulin can induce the phosphorylation of its receptor and activate elements involved in the early steps of insulin signaling in both tissues.

Early activation of the multicomponent signaling complex associated with focal adhesion kinase induced by pressure overload in the rat heart

Mechanical overload elicits functional and structural adaptive mechanisms in cardiac muscle. Signaling pathways linked to integrin/cytoskeleton complexes may have a function in mediation of the effects of mechanical stimulus in myocardial cells. We investigated the tyrosine phosphorylation and the assembly of the multicomponent signaling complex associated with focal adhesion kinase (Fak) and the actin cytoskeleton in the overloaded myocardium of rats. Pressure overload induced a 3-fold increase in Fak tyrosine phosphorylation within 3 minutes after a 60-mm Hg rise in aortic pressure. A pressure stimulus that lasted for 60 minutes was accompanied by a 5-fold increase in the amount of tyrosine-phosphorylated Fak, and a stimulus as low as 10 mm Hg doubled the amount of tyrosine-phosphorylated Fak in the myocardium within 10 minutes. Pressure overload also induced a time-dependent association of actin with Fak and an increase in the amount of Fak detected in the cytoskeletal fraction of the myocardium. These events were paralleled by c-Src activation and binding to Fak and by an association of Grb2 and p85 subunit of phosphatidylinositol 3-kinase with Fak. Erk1/2 and Akt, two possible downstream effectors of Fak via Grb2 and phosphatidylinositol 3-kinase, were also shown to be activated in parallel with Fak. These findings show that pressure overload induced a rapid activation of the Fak multiple signaling complex in the myocardium of rats, which suggests that this mechanism may have a role in mechanotransduction in the myocardium.

Effect of vitamin E supplementation on antibody levels against malondialdehyde modified LDL in hyperlipidemic hamsters

OBJECTIVE

The aim of this work was to investigate the effect of vitamin E (VE) supplementation on the formation of autoantibodies against oxidized low density lipoproteins (LDL) in a hyperlipidemic animal model.

METHODS

Thirty-four male hamsters (Mesocricetus auratus), (4 weeks old) were divided into three groups: Group A (n=9) was fed with standard rodent chow; group B (n=13) was fed with a standard rodent chow plus 2% cholesterol and 10% butter and group C (n=12) was fed with the same diet plus 0.2% (w/w) VE. Blood samples were collected by intracardiac puncture and antibody levels were determined in each animal at 4 weeks of age and after 20 weeks of experimental diet. A modified ELISA technique was used to analyze the modulation of autoantibody titers against an epitope of oxidized LDL in serum samples. Antigens prepared for the ELISA tests were characterized using spectrofluorimetry. Serum VE levels were determined in the lipidic fractions by HPLC.

RESULTS

The groups fed with cholesterol-fat enriched diet presented a three-fold increase in total serum cholesterol and two-fold increase in serum triglycerides compared to the control group. VE supplementation played no role in serum cholesterol and serum triglyceride concentrations but led to a decreased autoantibody (anti-LDL-malondialdehyde) formation (P<0.05).

CONCLUSIONS

Our results show that VE supplementation leads to a lower production of autoantibodies against oxidized LDL, suggesting a protective effect of VE against in vivo oxidation of LDL particles, in a dose-dependent manner.

A high fructose diet affects the early steps of insulin action in muscle and liver of rats

A high fructose diet induces insulin resistance in rats, although the exact molecular mechanism involved is unknown. In this study, we used immunoprecipitation and immunoblotting to examine the levels and phosphorylation status of the insulin receptor (IR) and insulin receptor substrate-1 (IRS-1), as well as the association of the IRS-1 with phosphatidylinositol 3-kinase (PI 3-kinase), and phosphotyrosine phosphatase (SHP2) in the liver and muscle of rats fed a control or high fructose diet for 28 d. There were no differences in IR and the IRS-1 protein levels in the liver and muscle of rats fed the control and high fructose diets. However, tyrosine-phosphorylation of the insulin receptor after insulin stimulation was reduced to 71 +/- 2% (P < 0.05) of control in the liver of the fructose-fed rats. In samples previously immunoprecipitated with anti-IRS-1 antibody and blotted with antiphosphotyrosine antibody, the insulin-stimulated IRS-1 phosphorylation levels in the liver and muscle of the fructose-fed group were only 70 +/- 6% (P < 0.05) and 76 +/- 5% (P < 0.05) of those of control rats, respectively. The insulin-stimulated IRS-1 association with PI 3-kinase was reduced to 84 +/- 3% (P < 0.05) in the liver and to 84 +/- 4% (P < 0.05) in the muscle of the fructose-fed group compared with control rats. Insulin-stimulated IRS-1 association with SHP2 was reduced to 79 +/- 5% (P < 0.05) in liver of the fructose-fed rats. These data suggest that changes in the early steps of insulin signal transduction may have an important role in the insulin resistance observed in these rats.

Regulation of cardiac Jak-2 in animal models of insulin resistance

Insulin induces phosphorylation and activation of JAK2 tyrosine, as well as its association with STAT1 and SHP2 in insulin-sensitive tissues of intact rats, thus demonstrating a new pathway in transduction of insulin signals. We investigated this pathway in hearts of rats in three situations of insulin resistance: 72 h of fasting, chronic treatment with dexamethasone, and acute treatment with epinephrine. The acute treatment with epinephrine showed no difference in insulin-induced JAK2 tyrosine phosphorylation or JAK2/STAT1 and JAK2/SHP2 association in comparison with the control. In fasted rats the JAK2 protein concentration decreased, accompanied by a decrease in the stoichiometry of the phosphorylation to 70%, an increase in association of JAK2/STAT1 to 160%, and a decrease in JAK2/SHP2 association to 85%. In the dexamethasone-treated group, the JAK2 protein concentrations increased but the stoichiometry of its phosphorylation decreased to 20%, whereas the JAK2/STAT1 and JAK2/SHP2 associations changed by 70% and 170%, respectively. In fasting and dexamethasone-treated rats, therefore, insulin-induced JAK2 tyrosine phosphorylation decreases, and the JAK2 protein expression is differentially regulated such that the insulin-induced JAK2 association with SHP2 and STAT1 shows opposite interactions with the kinase.

Myocardial contractile response to an oral glucose load in normal subjects evaluated by echocardiography

There is a paucity of experimental data on the actual mechanism of insulin-induced changes on the myocardial function. In the present study we investigated the myocardial contractile, response to an oral glucose load using echocardiography. Fifteen healthy volunteers were studied after overnight fast and 150 minutes after the oral load of 75 g glucose. Oral glucose load caused an increase in plasma glucose and insulin levels, which was accompanied by a significant increase in left ventricular shortening (from 35.2 +/- 0.7% at baseline, to 38.5 +/- 0.6% and 39 +/- 0.9% at 30 and 60 minutes post glucose load, respectively [P < 0.05 vs baseline]; ejection fraction rose from 0.73% +/- 0.01 to 0.77% +/- 0.01 (P < 0.05); pressure rate product increased from 7.29 +/- 0.2 to 8.31 +/- 0.3 mmHg x beats per min (P < 0.007) and heart rate enhanced from 68.3 +/- 1.9 to 74 +/- 1.6 (P < 0.034) and 75.3 +/- 1.5 beats per min (P < 0.008) at 60 and 90 minutes after glucose, respectively. Meanwhile, mean arterial pressure decreased significantly (10 +/- 1.5%, P < 0.018) when compared to basal values. These results indicate a significant change in the myocardial contractile response to an oral glucose load, probably related to baroreceptor reflex response as well as an overridden by a potent vasodilator action of insulin. Nevertheless, we could not rule out that the cardiac effects may also be due an insulin-induced sympathetic activation or a direct myocardial effect.

Magnesium deficiency modulates the insulin signaling pathway in liver but not muscle of rats

Altered insulin secretion and sensitivity have been observed in Mg-deficient animals. However, the effects of Mg deficiency and supplementation on intracellular signaling events triggered by insulin are unknown. Therefore, we studied the early steps of insulin action in muscle and liver of rats fed Mg-deficient (DF-6, DF-11) or control (CO-6, CO-11) diets for 6 or 11 wk, respectively, and Mg-deficient or control diets for 6 wk, followed by Mg supplementation for 5 wk (SDF and SCO groups, respectively). There were no differences in the glucose disappearance rate (K(itt)) or insulin signaling between CO-6 and DF-6 rats. Between the two groups of rats fed for 11 wk, the DF-11 group had a significantly greater K(itt). SDF and SCO rats had K(itt) that did not differ from CO-11 rats, but that were significantly lower than in DF-11 rats. In the latter rats, insulin receptor and insulin receptor substrate-1 protein and phosphorylation levels were elevated in liver and there was a greater association between the insulin receptor substrate-1 and p85 subunit of phosphatidyl-inositol 3-kinase compared with CO-11 rats. There were no differences in the early steps of insulin action in SDF and control rats. These results suggest that the normal insulin sensitivity maintained by Mg supplementation and the increased insulin sensitivity produced by a long period of Mg deprivation may result, at least in part, from alterations in or maintenance of the early molecular steps of insulin action in hepatic tissue.

Tissue-specific regulation of IRS-2/PI 3-kinase association in aged rats

We have examined the insulin-stimulated IRS-2 association with PI 3-kinase and the phosphorylation of AKT/PKB, which is functionally located downstream of the PI 3-kinase, in aged (obese) rats. The IRS-2 protein levels were similar in 2 and 20 month-old rats in both tissues, liver and muscle. There were reductions in insulin-induced IRS-2 tyrosine phosphorylation in liver and muscle, accompanied by a decrease in IRS-2/PI 3-kinase association and in AKT/PKB phosphorylation only in muscle tissue of aged rats. This regulation may be important in the altered glucose metabolism observed in aged (obese) rats.

Insulin-induced tyrosine phosphorylation of Shc in liver, muscle and adipose tissue of insulin resistant rats

Insulin stimulates rapid tyrosine phosphorylation of the protein Shc, which subsequently binds to Grb2, resulting in the activation of a complex mitogenic signaling network. In this study, we examined the levels of Shc protein, its phosphorylation state and Shc-Grb2 association in liver, muscle and adipose tissue before and after insulin administration in three animal models of insulin resistance (chronic dexamethasone treatment, 72-h starvation and aging). There were no differences in Shc protein expression between tissues from control and insulin resistant animals. In fasted hypoinsulinemic rats, there was a decrease in insulin-induced Shc phosphorylation in liver and adipose tissue. However, a significant increase in Shc phosphorylation was observed in liver and muscle from dexamethasone-treated hyperinsulinemic rats and in liver, muscle and adipose tissue of hyperinsulinemic 20-month-old rats. Alterations in Shc phosphorylation correlated well with the level of Shc-Grb2 association. These results indicate that Shc tyrosyl phosphorylation and Shc-Grb2 association are regulated in the different types of insulin resistance and that this regulation is apparently related to the animals' plasma insulin levels. The Shc-Grb2 association is directly related to the insulin-induced tyrosyl phosphorylation of Shc.

Crosstalk between insulin and angiotensin II signalling systems

Insulin resistance and hypertension commonly occur together. Pharmacological inhibition of the renin-angiotensin system has been found to reduce not only hypertension, but also insulin resistance. This raises the possibility that the renin-angiotensin system may interact with insulin signalling. We have investigated the relationship between insulin and angiotensin II (AII) intracellular signalling in vivo using an intact rat heart model, and in vitro using rat aorta smooth muscle cells (RASMC). Results generated in the in vivo studies indicate that, like insulin, AII stimulates tyrosine phosphorylation of the insulin receptor substrates IRS-1 and IRS-2. This leads to binding of IRS-1 and IRS-2 to PI3-kinase. However, in contrast to the effect of insulin. IRS-1- and IRS-2-associated PI3-kinase activity is inhibited by AII in a dose-dependent manner. Moreover, AII inhibits insulin-stimulated IRS-1/IRS-2-associated PI3-kinase activity. The in vivo effects of AII are mediated via the AT1 receptor. The results of the in vitro studies indicate that AII inhibits insulin-stimulated, IRS-1-associated PI3-kinase activity by interfering with the docking of IRS-1 with the p85 regulatory subunit of PI3-kinase. It appears that AII achieves this effect by stimulating serine phosphorylation of the insulin receptor beta-subunit IRS-1, and the p85 regulatory subunit of PI3-kinase. These actions result in the inhibition of normal interactions between the insulin signalling pathway components. Thus, we believe that AII negatively modulates insulin signalling by stimulating multiple serine phosphorylation events in the early components of the insulin signalling cascade. Overactivity of the renin-angiotensin system is likely to impair insulin signalling and contribute to insulin resistance observed in essential hypertension.

Insulin induces tyrosine phosphorylation of the insulin receptor and SHC, and SHC/GRB2 association in cerebellum but not in forebrain cortex of rats

A growth-related branch of the insulin-signaling pathway was studied in the forebrain cortex and cerebellum of Wistar rats. Anesthetized rats received a bolus injection of saline or insulin through the cava vein after which fragments of cerebellum and forebrain cortex were excised and immediately homogenized. Insulin receptor and p46SHCA phosphorylation, and p46SHCA/GRB2 association were detected by immunoprecipitation and blotting with specific antibodies. Insulin stimulated the rapid phosphorylation of its receptor in cerebellum, followed by p46SHCA phosphorylation and GRB2 recruitment. The optimal insulin dose for the induction of p46SHCA/GRB2 binding was 60 microg, and time-course experiments showed that maximum phosphorylation/binding occurred 2-3 min after stimulation. Although insulin receptors and SHC were present in forebrain cortex, there was no increase in their phosphorylation, nor was there any recruitment of GRB2 following stimulation with insulin. Thus, although elements involved in the early intracellular response to insulin are present in the central nervous system, differences in their activation/regulation may account for the functional roles of insulin in these tissues.