Aspirin inhibits serine phosphorylation of IRS-1 in muscle and adipose tissue of septic rats

Aspirin-Mediated Acetylation Protects Against Multiple Neurodegenerative Pathologies by Impeding Protein Aggregation

AIMS

Many progressive neurological disorders, including Alzheimer's disease (AD), Huntington's disease, and Parkinson's disease (PD), are characterized by accumulation of insoluble protein aggregates. In prospective trials, the cyclooxygenase inhibitor aspirin (acetylsalicylic acid) reduced the risk of AD and PD, as well as cardiovascular events and many late-onset cancers. Considering the role played by protein hyperphosphorylation in aggregation and neurodegenerative diseases, and aspirin's known ability to donate acetyl groups, we asked whether aspirin might reduce both phosphorylation and aggregation by acetylating protein targets.

RESULTS

Aspirin was substantially more effective than salicylate in reducing or delaying aggregation in human neuroblastoma cells grown in vitro, and in Caenorhabditis elegans models of human neurodegenerative diseases in vivo. Aspirin acetylates many proteins, while reducing phosphorylation, suggesting that acetylation may oppose phosphorylation. Surprisingly, acetylated proteins were largely excluded from compact aggregates. Molecular-dynamic simulations indicate that acetylation of amyloid peptide energetically disfavors its association into dimers and octamers, and oligomers that do form are less compact and stable than those comprising unacetylated peptides.

INNOVATION

Hyperphosphorylation predisposes certain proteins to aggregate (e.g., tau, α-synuclein, and transactive response DNA-binding protein 43 [TDP-43]), and it is a critical pathogenic marker in both cardiovascular and neurodegenerative diseases. We present novel evidence that acetylated proteins are underrepresented in protein aggregates, and that aggregation varies inversely with acetylation propensity after diverse genetic and pharmacologic interventions.

CONCLUSIONS

These results are consistent with the hypothesis that aspirin inhibits protein aggregation and the ensuing toxicity of aggregates through its acetyl-donating activity. This mechanism may contribute to the neuro-protective, cardio-protective, and life-prolonging effects of aspirin. Antioxid. Redox Signal. 27, 1383-1396.

Skeletal muscle atrogene expression and insulin resistance in a rat model of polytrauma

Polytrauma is a combination of injuries to more than one body part or organ system. Polytrauma is common in warfare, and in automobile and industrial accidents. The combination of injuries can include burn, fracture, hemorrhage, and trauma to the extremities or specific organ systems. Resistance to anabolic hormones, loss of muscle mass, and metabolic dysfunction can occur following injury. To investigate the effects of combined injuries, we have developed a highly reproducible rodent model of polytrauma. This model combines burn injury, soft tissue trauma, and penetrating injury to the gastrointestinal (GI) tract. Adult, male Sprague–Dawley rats were anesthetized with pentobarbital and subjected to a 15–20% total body surface area scald burn, or laparotomy and a single puncture of the cecum with a G30 needle, or the combination of both injuries (polytrauma). In the current studies, the inflammatory response to polytrauma was examined in skeletal muscle. Changes in skeletal muscle mRNA levels of the proinflammatory cytokines TNF‐α, IL‐1β, and IL‐6 were observed following single injuries and polytrauma. Increased expression of the E3 ubiquitin ligases Atrogin‐1/FBX032 and TRIM63/MuRF‐1 were measured following injury, as was skeletal muscle insulin resistance, as evidenced by decreased insulin‐inducible insulin receptor (IR) and AKT/PKB (Protein Kinase B) phosphorylation. Changes in the abundance of IR and insulin receptor substrate‐1 (IRS‐1) were observed at the protein and mRNA levels. Additionally, increased TRIB3 mRNA levels were observed 24 h following polytrauma, the same time when insulin resistance was observed. This may suggest a role for TRIB3 in the development of acute insulin resistance following injury.

Profiles of serum amino acids to screen for catabolic and inflammation status in calves with Mycoplasma bronchopneumonia

The aim of the present study was to investigate the relationships between serum amino acid profiles in normal and calves with Mycoplasma bronchopneumonia. Serum free amino acid concentrations in serum obtained from 34 calves with or without Mycoplasma bronchopneumonia were determined by high-performance liquid chromatography. The calves with Mycoplasma were characterized by significantly lower total amino acid and total essential amino acid concentrations and molar ratios of branched-chain amino acid (BCAA) to aromatic amino acid (BCAA/AAA) and BCAA to tyrosine (BTR), and by a significantly higher molar ratio of serine phosphorylation (SPR). The proposed diagnostic cutoffs for BCAA/AAA, BTR and SPR in serum based on ROC analysis for detection of catabolic states associated with Mycoplasma bronchopneumonia were set at <1.75, <2.86 and >0.85, respectively. Our results suggest that determining the profiles of amino acids, especially BTR and SPR, could provide useful diagnostic information in terms of predicting protein catabolism in Mycoplasma bronchopneumonia.

Fraction from wax apple [Syzygium samarangense (Blume) Merrill and Perry] fruit extract ameliorates insulin resistance via modulating insulin signaling and inflammation pathway in tumor necrosis factor α-treated FL83B mouse hepatocytes

Inflammation is associated with the development of insulin resistance in Type 2 diabetes mellitus. In the present study, mouse FL83B cells were treated with tumor necrosis factor-alpha (TNF-α) to induce insulin resistance, and then co-incubated with a fraction from wax apple fruit extract (FWFE). This fraction significantly increased the uptake of the nonradioactive fluorescent indicator 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino]-2-deoxy-d-glucose (2-NBDG) in insulin resistant cells. Western blot analysis revealed that, compared with the TNF-α-treated control group, FWFE increased the expression of the insulin receptor (IR), insulin receptor substrate-1 (IRS-1), protein kinase B (Akt/PKB), phosphatidylinositol-3 kinase (PI3K), and glucose transporter 2 (GLUT-2), and increased IR tyrosyl phosporylation, in insulin resistant FL83B cells. However, FWFE decreased phosphorylation of c-Jun N-terminal kinases (JNK), but not the expression of the intercellular signal-regulated kinases (ERK), in the same cells. These results suggest that FWFE might alleviate insulin resistance in TNF-α-treated FL83B cells by activating PI3K-Akt/PKB signaling and inhibiting inflammatory response via suppression of JNK, rather than ERK, activation.

Salicylate downregulates 11β-HSD1 expression in adipose tissue in obese mice and in humans, mediating insulin sensitization

Recent trials show salicylates improve glycemic control in type 2 diabetes, but the mechanism is poorly understood. Expression of the glucocorticoid-generating enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in adipose tissue is increased in vitro by proinflammatory cytokines and upregulated in obesity. 11β-HSD1 inhibition enhances insulin sensitivity. We hypothesized that salicylates downregulate 11β-HSD1 expression, contributing to their metabolic efficacy. We treated diet-induced obese (DIO) 11β-HSD1-deficient mice and C57Bl/6 mice with sodium salicylate for 4 weeks. Glucose tolerance was assessed in vivo. Tissue transcript levels were assessed by quantitative PCR and enzyme activity by incubation with (3)H-steroid. Two weeks' administration of salsalate was also investigated in a randomized double-blind placebo-controlled crossover study in 16 men, with measurement of liver 11β-HSD1 activity in vivo and adipose tissue 11β-HSD1 transcript levels ex vivo. In C57Bl/6 DIO mice, salicylate improved glucose tolerance and downregulated 11β-HSD1 mRNA and activity selectively in visceral adipose. DIO 11β-HSD1-deficient mice were resistant to these metabolic effects of salicylate. In men, salsalate reduced 11β-HSD1 expression in subcutaneous adipose, and in vitro salicylate treatment reduced adipocyte 11β-HSD1 expression and induced adiponectin expression only in the presence of 11β-HSD1 substrate. Reduced intra-adipose glucocorticoid regeneration by 11β-HSD1 is a novel mechanism that contributes to the metabolic efficacy of salicylates.

Aspirin attenuates insulin resistance in muscle of diet-induced obese rats by inhibiting inducible nitric oxide synthase production and S-nitrosylation of IRbeta/IRS-1 and Akt

AIM/HYPOTHESIS

High-dose aspirin treatment improves fasting and postprandial hyperglycaemia in patients with type 2 diabetes, as well as in animal models of insulin resistance associated with obesity and sepsis. In this study, we investigated the effects of aspirin treatment on inducible nitric oxide synthase (iNOS)-mediated insulin resistance and on S-nitrosylation of insulin receptor (IR)-beta, IRS-1 and protein kinase B (Akt) in the muscle of diet-induced obese rats and also in iNos (also known as Nos2)-/- mice on high fat diet.

METHODS

Aspirin (120 mg kg-1 day-1 for 2 days) or iNOS inhibitor (L-NIL; 80 mg/kg body weight) were administered to diet-induced obese rats or mice and iNOS production and insulin signalling were investigated. S-nitrosylation of IRbeta/IRS-1 and Akt was investigated using the biotin switch method.

RESULTS

iNOS protein levels increased in the muscle of diet-induced obese rats, associated with an increase in S-nitrosylation of IRbeta, IRS-1 and Akt. These alterations were reversed by aspirin treatment, in parallel with an improvement in insulin signalling and sensitivity, as measured by insulin tolerance test and glucose clamp. Conversely, while aspirin reversed the increased phosphorylation of IkappaB kinase beta and c-Jun amino-terminal kinase, as well as IRS-1 serine phosphorylation in diet-induced obese rats and iNos -/- mice on high-fat diet, these alterations were not associated with the improvement of insulin action induced by this drug.

CONCLUSIONS/INTERPRETATION

Our data demonstrate that aspirin treatment not only reduces iNOS protein levels, but also S-nitrosylation of IRbeta, IRS-1 and Akt. These changes are associated with improved insulin resistance and signalling, suggesting a novel mechanism of insulin sensitisation evoked by aspirin treatment.

Hyperglycemia in critical illness: a review

Hyperglycemia is commonplace in the critically ill patient and is associated with worse outcomes. It occurs after severe stress (e.g., infection or injury) and results from a combination of increased secretion of catabolic hormones, increased hepatic gluconeogenesis, and resistance to the peripheral and hepatic actions of insulin. The use of carbohydrate-based feeds, glucose containing solutions, and drugs such as epinephrine may exacerbate the hyperglycemia. Mechanisms by which hyperglycemia cause harm are uncertain. Deranged osmolality and blood flow, intracellular acidosis, and enhanced superoxide production have all been implicated. The net result is derangement of endothelial, immune and coagulation function and an association with neuropathy and myopathy. These changes can be prevented, at least in part, by the use of insulin to maintain normoglycemia.

Targeted disruption of iNOS prevents LPS-induced S-nitrosation of IRbeta/IRS-1 and Akt and insulin resistance in muscle of mice

We have previously demonstrated that the insulin resistance associated with inducible nitric oxide synthase (iNOS) induction in two different models of obesity, diet-induced obesity and the ob/ob mice, is mediated by S-nitrosation of proteins involved in insulin signal transduction: insulin receptor beta-subunit (IRbeta), insulin receptor substrate 1(IRS-1), and Akt. S-nitrosation of IRbeta and Akt impairs their kinase activities, and S-nitrosation of IRS-1 reduces its tissue expression. In this study, we observed that LPS-induced insulin resistance in the muscle of wild-type mice, as demonstrated by reduced insulin-induced tyrosine phosphorylation of IRbeta and IRS-1, reduced IRS-1 expression and reduced insulin-induced serine phosphorylation of Akt. This resistance occurred in parallel with enhanced iNOS expression, which was accompanied by S-nitrosation of IRbeta/IRS-1 and Akt. In the muscle of iNOS(-/-) mice, we did not observe enhanced iNOS expression or any S-nitrosation of IRbeta/IRS-1 and Akt after LPS treatment. Moreover, insulin resistance was not present. The preservation of insulin-induced tyrosine phosphorylation of IRbeta and IRS-1, of IRS-1 protein expression, and of insulin-induced serine phosphorylation of Akt observed in LPS-treated iNOS(-/-) mice strongly suggests that the insulin resistance induced by LPS is iNOS mediated, probably through S-nitrosation of proteins of early steps of insulin signaling.

Aspirin resistance: moving forward with multiple definitions, different assays, and a clinical imperative

Many patients are treated with aspirin to prevent a serious vascular event, most notably myocardial infarction and stroke. A growing number of studies have been appearing in the literature that indicate a significant fraction of aspirin-treated patients may be resistant to the antiplatelet effects of the drug. Resistance to aspirin may be related to the concomitant ingestion of aspirin and nonsteroidal anti-inflammatory drugs, which impairs the aspirin effect, or to more complex situations, such as metabolic defects that diminish the therapeutic effect of aspirin. The incidence of aspirin resistance is unknown, but it may approach 20% to 30%. The diagnosis of aspirin resistance has been evaluated using multiple assays, and because there are multiple assays, this has resulted in multiple definitions for aspirin resistance. This review considers aspirin resistance at a time when there is confusion about the definition, and the clinical assay to best assess it, because there is a clinical imperative to know now which patients taking aspirin are not receiving a therapeutic effect.

Modulation of insulin signalling by insulin sensitizers

Insulin resistance is a hallmark of Type II diabetes. It is well documented that insulin sensitizers such as peroxisome-proliferator-activated receptor gamma agonists and aspirin improve insulin action in vivo. The detailed mechanisms by which the insulin sensitizers promote insulin signalling, however, are not completely understood and remain somewhat controversial. In the present review, we summarize our studies attempting to explore the molecular mechanisms underlying the effects of insulin sensitizers in cells and in animal models of insulin resistance. In 3T3-L1 adipocytes and/or in HEK-293 cells stably expressing recombinant IRS1 protein (insulin receptor substrate protein 1), the peroxisome-proliferator-activated receptor gamma agonist rosiglitazone and aspirin promote insulin signalling by decreasing inhibitory IRS1 serine phosphorylation. Increased IRS1 Ser-307 phosphorylation and concomitant decreased insulin signalling as measured by insulin-stimulated IRS1 tyrosine phosphorylation and Akt threonine phosphorylation were observed in adipose tissues of Zucker obese rats compared with lean control rats. Treatment with rosiglitazone for 24 and 48 h increased insulin signalling and decreased IRS1 Ser-307 phosphorylation concomitantly. Treatment of the Zucker obese rats with rosiglitazone for 24 h also reversed the high circulating levels of free fatty acids, which have been shown to correlate with increased IRS1 serine phosphorylation. Taken together, the results suggest that IRS1 inhibitory serine phosphorylation is a key component of insulin resistance and its reversal may be physiologically relevant to insulin sensitization in vivo.

Retracted: Aspirin inhibits serine phosphorylation of insulin receptor substrate 1 in growth hormone treated animals

In this study, we demonstrate that pretreatment with aspirin inhibits GH-induced insulin resistance. GH was observed to lead to serine phosphorylation of IRS-1, a phenomenon which was reversed by aspirin in liver, muscle and WAT in parallel with a reduction in JNK activity. In addition, our data show an impairment of insulin activation in the IR/IRS/PI(3)kinase pathway and a reduction in IRS-1 protein levels in rats treated with GH, which was also reversed in the animals pretreated with aspirin. Overall, these results provide new insights into the mechanism of GH-induced insulin resistance.