Mechanisms of hemorrhage-induced hepatic insulin resistance: role of tumor necrosis factor-alpha

Apoptosis of hematopoietic progenitor-derived adipose tissue-resident macrophages contributes to insulin resistance after myocardial infarction

Patients with insulin resistance have high risk of cardiovascular disease such as myocardial infarction (MI). However, it is not known whether MI can initiate or aggravate insulin resistance. We observed that patients with ST-elevation MI and mice with MI had de novo hyperglycemia and features of insulin resistance, respectively. In mouse models of both myocardial and skeletal muscle injury, we observed that the number of visceral adipose tissue (VAT)-resident macrophages decreased because of apoptosis after these distant organ injuries. Patients displayed a similar decrease in VAT-resident macrophage numbers and developed systemic insulin resistance after ST-elevation MI. Loss of VAT-resident macrophages after MI injury led to systemic insulin resistance in non-diabetic mice. Danger signaling-associated protein high mobility group box 1 was released by the dead myocardium after MI in rodents and triggered macrophage apoptosis via Toll-like receptor 4. The VAT-resident macrophage population in the steady state in mice was transcriptomically distinct from macrophages in the brain, skin, kidney, bone marrow, lungs, and liver and was derived from hematopoietic progenitor cells just after birth. Mechanistically, VAT-resident macrophage apoptosis and de novo insulin resistance in mouse models of MI were linked to diminished concentrations of macrophage colony-stimulating factor and adiponectin. Collectively, these findings demonstrate a previously unappreciated role of adipose tissue-resident macrophages in sensing remote organ injury and promoting MI pathogenesis.

Diabetes mellitus after injury in burn and non-burned patients: A population based retrospective cohort study

OBJECTIVE

To compare hospitalisations for diabetes mellitus (DM) after injury experienced by burn patients, non-burn trauma patients and people with no record of injury admission, adjusting for socio-demographic, health and injury factors.

METHODS

Linked hospital and death data for a burn patient cohort (n=30,997) in Western Australia during the period 1980-2012 and two age and gender frequency matched comparison cohorts: non-burn trauma patients (n=28,647); non-injured people (n=123,399). The number of DM admissions and length of stay were used as outcome measures. Multivariate negative binomial regression was used to derive adjusted incidence rate ratios and 95% confidence intervals (IRR, 95%CI) for overall post-injury DM admission rates. Multivariate Cox regression models and hazard ratios (HR) were used to examine time to first DM admission and incident admission rates after injury discharge.

RESULTS

The burn cohort (IRR, 95%: 2.21, 1.80-2.72) and other non-burn trauma cohort (IRR, 95%CI: 1.63, 1.24-2.14) experienced significantly higher post-discharge admission rates for DM than non-injured people. Compared with the non-burn trauma cohort, the burn cohort experienced a higher rate of post-discharge DM admissions (IRR, 95%CI: 1.40, 1.07-1.84). First-time DM admissions were significantly higher during first 5-years after-injury for the burn cohort compared with the non-burn trauma cohort (HR, 95%CI: 2.00, 1.31-3.05) and non-injured cohort (HR, 95%CI: 1.96, 1.46-2.64); no difference was found >5years (burn vs. non-burn trauma: HR, 95%CI: 0.88, 0.70-1.12; burn vs non-injured: 95%CI: 1.08 0.82-1.41). No significant difference was found when comparing the non-burn trauma and non-injured cohorts (0-5 years: HR, 95%CI: 1.03, 0.71-1.48; >5years: HR. 95%CI: 1.11, 0.93-1.33).

CONCLUSIONS

Burn and non-burn trauma patients experienced elevated rates of DM admissions after injury compared to the non-injured cohort over the duration of the study. While burn patients were at increased risk of incident DM admissions during the first 5-years after the injury this was not the case for non-burn trauma patients. Sub-group analyses showed elevated risk in both adult and pediatric patients in the burn and non-burn trauma. Detailed clinical data are required to help understand the underlying pathogenic pathways triggered by burn and non-burn trauma. This study identified treatment needs for patients after burn and non-burn trauma for a prolonged period after discharge.

Animal models of insulin resistance: A review

Insulin resistance can be seen as a molecular and genetic mystery, with a role in the pathophysiology of type 2 diabetes mellitus. It is a basis for a number of chronic diseases like hypertension, dyslipidemia, glucose intolerance, coronary heart disease, cerebral vascular disease along with T2DM, thus the key is to cure and prevent insulin resistance. Critical perspicacity into the etiology of insulin resistance have been gained by the use of animal models where insulin action has been modulated by various transgenic and non-transgenic models which is not possible in human studies. The following review comprises the pathophysiology involved in insulin resistance, various factors causing insulin resistance, their screening and various genetic and non-genetic animal models highlighting the pathological and metabolic characteristics of each.

Resveratrol ameliorates mitochondrial dysfunction but increases the risk of hypoglycemia following hemorrhagic shock

BACKGROUND

Hemorrhagic shock (HS) may contribute to organ failure, by profoundly altering mitochondrial function. Resveratrol (RSV), a naturally occurring polyphenol, has been shown to promote mitochondrial function and regulate glucose homeostasis in diabetes. We hypothesized that RSV during resuscitation would ameliorate HS-induced mitochondrial dysfunction and improve hyperglycemia following acute blood loss.

METHODS

With the use a decompensated HS model, male Long-Evans rats (n = 6 per group) were resuscitated with lactated Ringer's solution with or without RSV (30 mg/kg) and were killed before hemorrhage (sham), at severe shock, following resuscitation, and 18 hours after resuscitation. At each time point, the liver and kidney mitochondria were isolated to assess individual respiratory complexes (CI, CII, and CIV) and the production of reactive oxygen species (ROS). Blood samples were assayed for glucose, insulin, corticosterone, total glucagon-like peptide (GLP-1), glucagon, and serum cytokine levels. The Homeostatic Model Assessment-Insulin Resistance index was used to quantify insulin resistance.

RESULTS

RSV supplementation following HS significantly improved mitochondrial function and decreased mitochondrial ROS production in both liver and kidney. RSV-treated animals had significantly lower blood glucose levels following resuscitation when compared with sham animals (116.0 ± 20.2 mg/dL vs. 227.7 ± 8.3 mg/dL, p < 0.05) or those resuscitated with lactated Ringer's solution (116.0 ± 20.2 mg/dL vs. 359.0 ± 79.5 mg/dL, p < 0.05). RSV supplementation was associated with significantly decreased plasma insulin levels (1.0 ± 0.4 ng/mL vs. 6.5 ± 3.7 ng/mL, p < 0.05), increased total GLP-1 levels (385.8 ± 56.6 ng/mL vs. 187.3 ± 11.1 ng/mL, p < 0.05), and a lower natural Log Homeostatic Model Assessment-Insulin Resistance index (1.30 ± 0.42 vs. 4.18 ± 0.68, p < 0.05) but had minimal effect on plasma corticosterone, glucagon, or cytokine levels.

CONCLUSION

Resuscitation with RSV restores mitochondrial function and decreases insulin resistance but may be associated with increased hypoglycemia. The observed antiglycemic effects of RSV may be mediated by decreased mitochondrial ROS and increased GLP-1 secretion.

Relationship between tyrosine phosphorylation and protein expression of insulin receptor and insulin resistance in gestational diabetes mellitus

The relationship between tyrosine phosphorylation (TP) and protein expression of insulin receptor (InsR) and insulin resistance (IR) in patients with gestational diabetes mellitus (GDM) was investigated. The InsR expression and TP in skeleton muscle tissue were determined by Western blotting and immunoprecipitation in women with GDM (GDM group, n=22), normal pregnant women (normal pregnancy group, n=22) and normal non-pregnant women (normal non-pregnant group, n=13). Fasting plasma glucose (FPG) and fasting insulin (FINS) were measured by oxidase assay and immunoradioassay. The results showed that the levels of FPG (5.61±0.78 mmol/L), FINS (15.42±5.13 mU/L) and Homeostasis model assessment-IR (HOMA-IR) (1.21±0.52) in GDM group were significantly higher than those in normal pregnancy group (4.43±0.46 mmol/L, 10.56±3.07 mU/L and 0.80±0.31 respectively) (P<0.01). The levels of FINS and HOMA-IR in normal pregnancy group were significantly higher than those in normal non-pregnant group (7.56±2.31 mU/L and 0.47±0.26 respectively) (P<0.01). There was no significant difference in the InsR expression level among the three groups (P>0.05). TP of InsR with insulin stimulation was significantly decreased in GDM group (0.20±0.05) as compared with normal pregnancy group (0.26±0.06) (P<0.01). TP of InsR with insulin stimulation in normal pregnancy group was lower than that in normal non-pregnant group (0.31±0.06) (P<0.01). TP of InsR with insulin stimulation was negatively related with HOMA-IR in GDM group (r=-0.525, P<0.01). There was no correlation between the protein expression of InsR and HOMA-IR in GDM group (r=-0.236, P>0.05). It was suggested that there is no significant correlation between the protein expression of InsR in skeletal muscle and IR in GDM, but changes in TP of InsR are associated with IR in GDM.

Monitoring systems and quantitative measurement of biomolecules for the management of trauma

Continued high morbidity and complications due to trauma related hemorrhage underscores the fact that our understanding of the detailed molecular events of trauma are inadequate to bring life-saving changes to practice. The current state of efficacy and advances in biomedical microdevice technology for trauma diagnostics concerning hemorrhage and hemorrhagic shock was considered with respect to vital signs and metabolic biomarkers. Tachycardia and hypotension are markers of hemorrhagic shock in decompensated trauma patients. Base deficit has been predicative of injury severity at hospital admission. Tissue oxygen saturation has been predicative of onset of multiple organ dysfunction syndrome. Blood potassium levels increase with onset of hemorrhagic shock. Lactate is a surrogate for tissue hypoxia and its clearance predicts mortality. Triage glucose measurements have been shown to be specific in predicting major injuries. No vital sign has yet to be proven effective as an independent predictor of trauma severity. Point of care (POC) devices allow for rapid results, easy sample preparation and processing, small sample volumes, small footprint, multifunctional analysis, and low cost. Advances in the field of in-vivo biosensors has provided a much needed platform by which trauma related metabolites can be monitored easily, rapidly and continuously. Multi-analyte monitoring biosensors have the potential to explore areas still undiscovered in the realm of trauma physiology.

Endocrinopathies in the cardiac ICU

The past several years have seen an increased appreciation of the potential role of the endocrine system in the recovery process following surgery for congenital heart disease. Many of the hormonal changes following cardiac surgery are adaptive and necessary, whereas activation of proinflammatory cytokine and chemokine responses and some of the metabolic changes following surgery are likely mediators leading to detrimental outcomes. Additionally, other hormonal perturbations may contribute to adverse outcomes. This review examines the pain and the stress response, thyroid function and hyperglycemia following cardiopulmonary bypass (CPB), and the potential role of corticosteroids in the pediatric cardiac critical care unit.

Hepatic growth hormone resistance after acute injury

Severe injury and infection are often followed by accelerated protein catabolism and acute insulin resistance. This results in several effects that complicate and prolong recovery, including weakness, immobility, impaired wound healing, and organ dysfunction. Recent studies have demonstrated the development of GH resistance during severe inflammation, providing a potential mechanism for the protein loss that follows injury and infection. To understand this GH resistance, we recently developed a murine model of acute injury. Mice were subjected to soft-tissue injury, alone or combined with hemorrhage, and injected iv with GH 30, 60, or 90 minutes later. Hepatic GH signaling was measured via Western analysis. GH-induced signal transducer and activator of transcription 5 phosphorylation was decreased immediately after completion of the trauma procedure, and at 30 and 60 minutes, but further decreased by 90 minutes after trauma. Combined trauma and hemorrhage resulted in severely decreased GH-induced signal transducer and activator of transcription 5 phosphorylation compared with trauma alone, and this was true at all time points studied. Western analysis revealed an apparent decrease in the molecular weight of the hepatic GH receptor (GHR) after trauma and hemorrhage, but not trauma alone. Additional studies determined that the hemorrhage-induced decrease in receptor size was not due to changes in GHR N-linked glycosylation. These results suggest that GH sensitivity is rapidly impaired after acute injury and that trauma combined with hemorrhage results in a more severe form of GH resistance resulting from alteration or inactivation of hepatic GHR.

Amperometric glucose biosensor based on electroconductive hydrogels

Fabrication of an enzyme amperometric biosensor for glucose via electropolymerization of pyrrole in the presence of glucose oxidase onto a hydrogel coated platinum electrode is hereby established as a viable biotransducer fabrication method. Platinum micro- (φ=25 μm) and macro- (φ=100 μm) electrodes were electrochemically activated and chemically modified with 3-aminopropyl-trimethoxysilane (APTMS), functionalized with acryloyl(polyethyleneglycol)-N-hydroxysuccinamide (ACRL-PEG-NHS), dipped into a polyHEMA based hydrogel cocktail and UV cross-linked. Electropolymerization of Py in the presence of GOx produced glucose responsive biotransducers that showed; (i) a 4-fold reduction in sensitivity compared with directly electropolymerized PPy films, (ii) an electropolymerization charge density dependence of biotransducer sensitivity and enzyme activity that was maximal at 1.0 mC/cm(2) with an apparent K(M) of 33 mM, (iii) interference screening of ascorbic acid and (iv) a temporal increase in sensitivity with storage over a 17 days period. This method has the ability to precisely and quantitatively add enzyme catalytic bioactivity to metal or semiconductor biointerfaces for applications in biosensors, bioelectronics and bionics.

Early insulin resistance in severe trauma without head injury as outcome predictor? A prospective, monocentric pilot study

Background

Hyperglycemia following major trauma is a well know phenomenon related to stress-induced systemic reaction. Reports on glucose level management in patients with head trauma have been published, but the development of insulin resistance in trauma patients without head injury has not been extensively studied. The aim of this study was therefore to investigate the prognostic role of acute insulin-resistance, assessed by the HOMA model, in patients with severe trauma without head injury.

Methods

All patients consecutively admitted to the Intensive Care Unit (ICU) of a tertiary referral center (Careggi Teaching Hospital, Florence, IT) for major trauma without head injury (Jan-Dec 2010) were enrolled. Patients with a previous diagnosis of diabetes mellitus requiring insulin therapy or metabolism alteration were excluded from the analysis. Patients were divided into “insulin resistant” and “non-insulin resistant” based on the Homeostasis Model Assessment index (HOMA IR). Results are expressed as medians.

Results

Out of 175 trauma patients admitted to the ICU during the study period, a total of 54 patients without head trauma were considered for the study, 37 of whom met the inclusion criteria. In total, 23 patients (62.2%) resulted insulin resistant, whereas 14 patients (37.8%) were non-insulin resistant. Groups were comparable in demographic, clinical/laboratory characteristics, and severity of injury. Insulin resistant patients had a significantly higher BMI (P=0.0416), C-reactive protein (P=0.0265), and leukocytes count (0.0301), compared to non-insulin resistant patients. Also ICU length of stay was longer in insulin resistant patients (P=0.0381).

Conclusions

Our data suggest that admission insulin resistance might be used as an early outcome predictor.

Role of tissue macrophages in the development of critical illness diabetes

Macrophage-derived factors, including TNF-α, are known as important inducers of insulin resistance. However, the role of macrophages in insulin resistance in the liver is unclear. Hyperglycemia and insulin resistance commonly occur following acute injuries or critical illness, referred to as "critical illness diabetes." In the present studies, the roles of macrophages in hepatic insulin resistance following surgical trauma and hemorrhage were investigated. Intravenous administration of gadolinium chloride or clodronate-liposome resulted in depletion of macrophages in both liver and spleen of rats. Macrophage depletion by either gadolinium chloride or clodronate-liposome did not prevent the development of trauma and hemorrhage-induced insulin resistance in the liver of rats, as indicated by impaired hepatic insulin signaling following a 90-minute hemorrhage period. Similarly, hepatic insulin resistance still developed in rats after removal of the spleen (splenectomy). In contrast, macrophage depletion significantly reversed the hepatic insulin resistance several hours later, following resuscitation. As a comparison, splenectomy resulted in improvement in hepatic insulin signaling following resuscitation, but to a lesser extent, suggesting that both liver and spleen resident macrophages have a role in the continuation of hepatic insulin resistance following resuscitation. These studies demonstrated that the initial development of insulin resistance in liver is macrophage-independent in a rodent model of critical illness diabetes, whereas both liver and spleen macrophages have a role in the later maintenance of the insulin-resistant state, following resuscitation.

Injury-induced insulin resistance in adipose tissue

Hyperglycemia and insulin resistance are common findings in critical illness. Patients in the surgical ICU are frequently treated for this 'critical illness diabetes' with intensive insulin therapy, resulting in a substantial reduction in morbidity and mortality. Adipose tissue is an important insulin target tissue, but it is not known whether adipose tissue is affected by critical illness diabetes. In the present study, a rodent model of critical illness diabetes was used to determine whether adipose tissue becomes acutely insulin resistant and how insulin signaling pathways are being affected. There was a reduction in insulin-induced phosphorylation of IR, IRS-1, Akt and GSK-3β. Since insulin resistance occurs rapidly in adipose tissue, but before the insulin resistance in skeletal muscle, it may play a role in the initial development of critical illness diabetes.

Role of inhibitory κB kinase and c-Jun NH2-terminal kinase in the development of hepatic insulin resistance in critical illness diabetes

Hyperglycemia and insulin resistance induced by acute injuries or critical illness are associated with increased mortality and morbidity, as well as later development of type 2 diabetes. The molecular mechanisms underlying the acute onset of insulin resistance following critical illness remain poorly understood. In the present studies, the roles of serine kinases, inhibitory κB kinase (IKK) and c-Jun NH(2)-terminal kinase (JNK), in the acute development of hepatic insulin resistance were investigated. In our animal model of critical illness diabetes, activation of hepatic IKK and JNK was observed as early as 15 min, concomitant with the rapid impairment of hepatic insulin signaling and increased serine phosphorylation of insulin receptor substrate 1. Inhibition of IKKα or IKKβ, or both, by adenovirus vector-mediated expression of dominant-negative IKKα or IKKβ in liver partially restored insulin signaling. Similarly, inhibition of JNK1 kinase by expression of dominant-negative JNK1 also resulted in improved hepatic insulin signaling, indicating that IKK and JNK1 kinases contribute to critical illness-induced insulin resistance in liver.

p38 mitogen-activated protein kinase-dependent transactivation of ErbB receptor family: a novel common mechanism for stress-induced IRS-1 serine phosphorylation and insulin resistance

OBJECTIVE

Stress stimuli such as tumor necrosis factor (TNF) have been shown to induce insulin receptor substrate (IRS)-1 serine phosphorylation and insulin resistance by transactivation of ErbB receptors. We aimed at elucidating the potential role of p38 mitogen-activated protein kinase (p38MAPK) in mediating stress-induced ErbB receptors activation.

RESEARCH DESIGN AND METHODS

p38MAPK effect on ErbBs transactivation and insulin signaling was assessed in Fao or HepG2 cells, exposed to stress stimuli, and on metabolic parameters in ob/ob and C57/BL6 mice.

RESULTS

High-fat diet-fed mice and ob/ob mice exhibited elevated hepatic p38MAPK activation associated with glucose intolerance and hyperinsulinemia. Liver expression of dominant-negative (DN)-p38MAPKα in ob/ob mice reduced fasting insulin levels and improved glucose tolerance, whereas C57/BL6 mice overexpressing wild-type p38MAPKα exhibited enhanced IRS-1 serine phosphorylation and reduced insulin-stimulated IRS-1 tyrosine phosphorylation. Fao or HepG2 cells exposed to TNF, anisomycin, or sphingomyelinase demonstrated rapid transactivation of ErbB receptors leading to PI3-kinase/Akt activation and IRS-1 serine phosphorylation. p38MAPK inhibition either by SB203580, by small interfering RNA, or by DN-p38MAPKα decreased ErbB receptors transactivation and IRS-1 serine phosphorylation and partially restored insulin-stimulated IRS-1 tyrosine phosphorylation. When cells were incubated with specific ErbB receptors antagonists or in cells lacking ErbB receptors, anisomycin- and TNF-induced IRS-1 serine phosphorylation was attenuated, despite intact p38MAPK activation. The stress-induced p38MAPK activation leading to ErbB receptors transactivation was associated with intracellular reactive oxygen species generation and was attenuated by treatment with antioxidants.

CONCLUSIONS

Hepatic p38MAPK is activated following various stress stimuli. This event is upstream to ErbB receptors transactivation and plays an important role in stress-induced IRS-1 serine phosphorylation and insulin resistance.

Failure to achieve euglycemia despite aggressive insulin control signals abnormal physiologic response to trauma

PURPOSE

We hypothesize that a failure to normalize a patient's glucose on an automated euglycemia protocol signals an adverse response after trauma and that this response can identify patients with an increased mortality.

MATERIALS AND METHODS

There were 1246 ventilated, critically ill trauma patients who were placed on an automated euglycemia. All glucose values collected both by laboratory serum measurements and by bedside arterial samples were included in the analysis.

RESULTS

Forty six thousand two hundred eighteen data entries for glucose (mg/dL) were analyzed. Time to normalization, defined as the first value in the goal range of 80 to 110 mg/dL, was different between the 2 groups, survivors correcting significantly faster (396 vs 487 minutes; P = .003). Mortality in patients who normalized (80-110 mg/dL) in the first 6 hours of admission was 13.6% vs 18.3% in patients requiring greater than 6 hours (P = .02). Patients who never normalized also required significantly greater insulin doses despite there being no significant difference in demographic data between the 2 groups.

CONCLUSIONS

A posttraumatic patient's response to tight glycemic control revealed important prognostic information about the patients' physiologic status. Patients who failed to reach euglycemia in the first 6 hours of admission had an increased hospital mortality. The time to normalization is significantly longer in those patients who died. Patients who did not correct rapidly required significantly higher insulin doses, suggesting insulin resistance.

Role of reactive oxygen species in injury-induced insulin resistance

Acute insulin resistance is common after injury, infection, and critical illness. To investigate the role of reactive oxygen species (ROS) in critical illness diabetes, we measured hepatic ROS, which rapidly increased in mouse liver. Overexpression of superoxide dismutase 2, which decreased mitochondrial ROS levels, protected mice from the development of acute hepatic insulin resistance. Insulin-induced intracellular signaling was dramatically decreased, and cellular stress signaling was rapidly increased after injury, resulting in the hyperglycemia of critical illness diabetes. Insulin-induced intracellular signaling, activation of stress (c-Jun N-terminal kinase) signaling, and glucose metabolism were all normalized by superoxide dismutase 2 overexpression or by pretreatment with antioxidants. Thus, ROS play an important role in the development of acute hepatic insulin resistance and activation of stress signaling after injury.

Bench-to-bedside review: Glucose and stress conditions in the intensive care unit

The physiological response to blood glucose elevation is the pancreatic release of insulin, which blocks hepatic glucose production and release, and stimulates glucose uptake and storage in insulin-dependent tissues. When this first regulatory level is overwhelmed (that is, by exogenous glucose supplementation), persistent hyperglycaemia occurs with intricate consequences related to the glucose acting as a metabolic substrate and as an intracellular mediator. It is thus very important to unravel the glucose metabolic pathways that come into play during stress as well as the consequences of these on cellular functions. During acute injuries, activation of serial hormonal and humoral responses inducing hyperglycaemia is called the 'stress response'. Central activation of the nervous system and of the neuroendocrine axes is involved, releasing hormones that in most cases act to worsen the hyperglycaemia. These hormones in turn induce profound modifications of the inflammatory response, such as cytokine and mediator profiles. The hallmarks of stress-induced hyperglycaemia include 'insulin resistance' associated with an increase in hepatic glucose output and insufficient release of insulin with regard to glycaemia. Although both acute and chronic hyperglycaemia may induce deleterious effects on cells and organs, the initial acute endogenous hyperglycaemia appears to be adaptive. This acute hyperglycaemia participates in the maintenance of an adequate inflammatory response and consequently should not be treated aggressively. Hyperglycaemia induced by an exogenous glucose supply may, in turn, amplify the inflammatory response such that it becomes a disproportionate response. Since chronic exposure to glucose metabolites, as encountered in diabetes, induces adverse effects, the proper roles of these metabolites during acute conditions need further elucidation.

Adenovirus infection results in alterations of insulin signaling and glucose homeostasis

Recombinant adenovirus (Ad) vectors can initiate an inflammatory response, limiting its use in gene therapy and basic research. Despite increased efforts to better understand Ad infection, little is known about how it affects cellular metabolic responses. In the current studies, we explored the effects of Ad vectors on insulin signaling molecules and glucose homeostasis. Nonreplicative Ad vectors were injected into rats through the tail vein, and at 4-13 days postinjection insulin signaling and glucose tolerance were examined. Ad vector infection significantly reduced total levels of the insulin receptor (IR), and insulin receptor substrates 1 and 2 (IRS-1, IRS-2) in the liver of rats, resulting in decreased insulin-induced tyrosine phosphorylation of IR, IRS-1, and IRS-2, and decreased interaction of IRS-1 and IRS-2 with phosphoinositide 3-kinase (PI3K). In addition, Ad infection resulted in impaired systemic glucose homeostasis, which recovered by 13 days, after the protein levels of IR, IRS-1, and IRS-2 had started to normalize. Expression of a TNF inhibitor or Kupffer cell depletion attenuated the Ad vector-induced decreases of insulin signaling molecules, indicating a potential role of Kupffer cell activation in this process. These studies provide evidence that systemic administration of Ad vectors can impair insulin signaling in liver, resulting in altered systemic glucose metabolism. Thus, effects of Ad vector infection on insulin action and glucose metabolism need to be considered when Ad vectors are used in research or gene therapy and may be more broadly applicable to other viral agents.

Age and tissue specific differences in the development of acute insulin resistance following injury

Injuries, hemorrhage, sepsis, burn, and critical illnesses all induce insulin resistance, and insulin resistance is strongly associated with advancing age. However, the effect of age on injury induced insulin resistance is not well studied. We performed surgical trauma in male rats of three different ages (3-, 6-, and 10-weeks old). Rats were either hemorrhaged to a mean arterial pressure of 35-40 mmHg and subsequently maintained at that pressure for up to 90 min, or maintained without hemorrhage as controls. Results indicate that insulin-induced intracellular signaling was diminished in liver and skeletal muscle of 6- and 10-week old rats following trauma and hemorrhage. In even younger rats, immediately post-weaning ( approximately 3 weeks of age), insulin signaling was lost in liver, but not in skeletal muscle. Glucocorticoids can play a role in the chronic development of insulin resistance. Our results demonstrate that corticosterone levels were increased in 6- and 10-week old animals following hemorrhage, but little change was measured in 3-week old animals. Blockade of glucocorticoid synthesis prevented the development of insulin resistance in skeletal muscle, but not in liver of 6- and 10-week old rats. Moreover, skeletal muscle glucocorticoid receptor levels increased dramatically between 3 and 6 weeks of age. These results indicate that trauma and hemorrhage-induced hepatic insulin resistance occurs at all ages tested. However, there is no development of insulin resistance following trauma and hemorrhage in skeletal muscle of post-weaning rats. In skeletal muscle of 6- and 10-week old rats, inhibition of glucocorticoid levels prevents the development of insulin resistance.

Acute insulin resistance following injury

Hyperglycemia and insulin resistance often occur following injury and/or critical illness. Whereas intensive insulin treatment reduces hyperglycemia, mortality and morbidity in certain patients, little is known regarding the pathophysiology of acute insulin resistance following injury and infection. Studies suggest that acute insulin resistance is complex and might differ in a tissue-specific manner, involving multiple causative factors and intracellular signaling pathways. Therefore, the advantages of intensive insulin therapy might not be uniform to all injuries or critical illnesses. Clearly, the increased incidence of hypoglycemic incidents following intensive insulin therapy indicates a need for understanding the underlying molecular mechanisms of the acute development of insulin resistance, which will allow a more targeted approach to treat altered glucose metabolism of critically ill patients.

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.

Insulin resistance despite tight glucose control is associated with mortality in critically ill surgical patients

BACKGROUND

The hyperglycemic state following trauma and surgery is related partially to insulin resistance (IR). The objective is to determine if critically ill surgical patients vary in their extent of IR and is IR associated with mortality.

METHODS

Prospective observational study in trauma and surgical intensive care units. There were 925 ventilated, critically ill surgical patients who were placed on an automated euglycemia protocol. A mathematic multiplier (M) employed by the protocol was used as a measure of IR. Outcome, phenotypic, laboratory, and treatment variables were analyzed.

RESULTS

54,141 entries for glucose (mg/dl) and M were analyzed. Median glucose was 118mg/dL, with 45% of values between 80-110mg/dL, 81% between 80-150 mg/dL, and 0.2% less than 40 mg/ dL. M varied by 42 fold over the entire population, and by an average of 11-fold among individual patients. The median blood glucose was not different between groups (118 mg/dl for survivors and 118 mg/dl for non-survivors, P = 0.36). The median insulin dose and M were significantly higher in non-survivors (4.1 U/hr versus 3.4 U/hr, P = 0.005; 0.061 versus 0.058, P = 0.02).

CONCLUSIONS

There was a large amount of variation in insulin resistance, as measured by an adapting multiplier, both across the population and within patients. In the setting of tight glucose control measures of glucose control (median blood glucose and percent in range) do not differentiate between patients who lived and died while measures of insulin resistance (median insulin dose and multiplier) do, suggesting that the insulin resistance is a better predictor of outcome.

Tissue-specific difference in the molecular mechanisms for the development of acute insulin resistance after injury

Acute insulin resistance occurs after injury, hemorrhage, infection, and critical illness. However, little is known about the development of this acute insulin-resistant state. In the current study, we found that insulin resistance develops rapidly in skeletal muscle, with the earliest insulin signaling defects at 60 min. However, defects in insulin signaling were measurable even earlier in liver, by as soon as 15 min after hemorrhage. To begin to understand the mechanisms for the development of acute insulin resistance, serine phosphorylation of insulin receptor substrate (IRS)-1 and c-Jun N-terminal kinase phosphorylation/activation was investigated. These markers (and possible contributors) of insulin resistance were increased in the liver after hemorrhage but not measurable in skeletal muscle. Because glucocorticoids are important counterregulatory hormones responsible for glucose homeostasis, a glucocorticoid synthesis inhibitor, metyrapone, and a glucocorticoid receptor antagonist, RU486, were administered to adult rats prior to hemorrhage. In the liver, the defects of insulin signaling after hemorrhage, including reduced tyrosine phosphorylation of the insulin receptor and IRS-1, association between IRS-1 and phosphatidylinositol 3-kinase and serine phosphorylation of Akt in response to insulin were not altered by pretreatment of rats with metyrapone or RU486. In contrast, hemorrhage-induced defects in insulin signaling were dramatically reversed in skeletal muscle, indicating a prevention of insulin resistance in muscle. These results suggest that distinct mechanisms for hemorrhage-induced acute insulin resistance are present in these two tissues and that glucocorticoids are involved in the rapid development of insulin resistance in skeletal muscle, but not in the liver, after hemorrhage.

Glycemic control in the ICU

Glycemic control clearly improves outcome in critically ill patients. Remaining questions are how tight the control must be to obtain the most benefit without increasing the risk for severe hypoglycemia, and whether an acuity level exists in which this benefit is not clearly visualized. In other words, is this benefit only seen in severely ill patients? The authors believe that clinical trials with ICU lengths of stay of 3 days or less make showing a clinical benefit difficult. Rather, they believe that clinical benefit is seen in higher acuity patients whose ICU length of stay is directly related to the reversal of the inflammatory systemic response rather than the disease or injury alone. Finally, the issue remains of how to obtain a TGC in the 80 to 110 mg/dL range without achieving a less-than-acceptable incidence of hypoglycemia. The answer may well lie with the introduction of continuous glucose monitors that will allow measurements to be obtained every 15 to 30 minutes without introducing an increased workload to the nursing staff. Many of these devices, such as the Optiscanner, which measures plasma glucose continuously, are on the horizon and should be approved by the FDA in 2008.

Effect of periodontitis on insulin resistance and the onset of type 2 diabetes mellitus in Zucker diabetic fatty rats

BACKGROUND

Studies indicate that an association exists between periodontitis and type 2 diabetes mellitus (T2DM) and/or obesity, with chronic inflammation hypothesized as the common denominator. The purpose of this study was to determine the causal effect of periodontitis and the concomitant impact of diet on the onset of insulin resistance (IR) and T2DM using a rat model system that simulates human obesity and T2DM.

METHODS

Twenty-eight, 5-week-old female Zucker diabetic fatty (ZDF, fa/fa) rats were divided into four groups of seven animals: high-fat fed-periodontitis (HF/P), high-fat fed-no periodontitis (HF/C), low-fat fed-periodontitis (LF/P), and low-fat fed-no periodontitis (LF/C). Periodontitis was induced by ligature placement. Fasting plasma insulin and glucose levels were measured, and glucose tolerance tests were performed to assess glucose homeostasis, IR, and the onset of T2DM. The level of tumor necrosis factor-alpha (TNF-alpha), leptin, triglycerides, and free fatty acids were determined in week 13 at sacrifice.

RESULTS

HF/P rats developed more severe IR compared to HF/C rats (P <0.01) and LF/P or LF/C rats (P <0.001) as measured by fasting insulin levels and homeostasis model assessment analysis. The onset of severe IR occurred approximately 3 weeks earlier in HF/P rats compared to HF/C rats. HF/P rats developed impaired (110 to 125 mg/dl) and frank fasting hyperglycemia (>125 mg/dl) 2 weeks earlier than HF/C rats. There was no difference in the severity and onset of IR and T2DM between LF/P and LF/C rats. The level of TNF-alpha was significantly higher in HF/P rats compared to HF/C rats (P <0.01).

CONCLUSION

Periodontitis accelerated the onset of severe IR and impaired glucose homeostasis in high-fat fed ZDF rats.

Acute, muscle-type specific insulin resistance following injury

Acute insulin resistance can develop following critical illness and severe injury, and the mortality of critically ill patients can be reduced by intensive insulin therapy. Thus, compensating for the insulin resistance in the clinical care setting is important. However, the molecular mechanisms that lead to the development of acute injury/infection-associated insulin resistance are unknown, and the development of acute insulin resistance is much less studied than chronic disease-associated insulin resistance. An animal model of injury and blood loss was utilized to determine whether acute skeletal muscle insulin resistance develops following injury, and surgical trauma in the absence of hemorrhage had little effect on insulin-mediated signaling. However, following hemorrhage, there was an almost complete loss of insulin-induced Akt phosphorylation in triceps, and severely decreased tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-1. The severity of insulin resistance was similar in triceps and extensor digitorum longus muscles, but was more modest in diaphragm, and there was little change in insulin signaling in cardiac muscle following hemorrhage. Since skeletal muscle is an important insulin target tissue and accounts for much of insulin-induced glucose disposal, it is important to determine its role in injury/infection-induced hyperglycemia. This is the first report of an acute development of skeletal muscle insulin signaling defects. The presented data indicates that the defects in insulin signaling occurred rapidly, were reversible and more severe in some skeletal muscles, and did not occur in cardiac muscle.

Activation of endoplasmic reticulum stress response following trauma-hemorrhage

Hemorrhagic trauma leads to organ dysfunction, sepsis and death. There is abnormal production of proinflammatory cytokines by Kupffer cells, tissue hypoxia and liver injury following trauma-hemorrhage. The physiological conditions consequent to trauma-hemorrhage are consistent with factors necessary to initiate endoplasmic reticulum (ER) stress and unfolded protein response. However, the contribution of ER stress to apoptosis and liver injury after trauma-hemorrhage is not known. In the present study ER stress was investigated in mice that underwent trauma-hemorrhage or sham operation. Expressions of endoplasmic reticulum stress proteins Bip, ATF6, PERK, IRE1alpha, and PDI were significantly elevated in the liver after trauma-hemorrhage compared to the controls. The ER stress associated proapoptotic transcription factor CHOP protein expression was also significantly elevated in trauma-hemorrhage group. Consistent with this, enhanced DNA fragmentation was observed, confirming apoptosis, in the liver following trauma-hemorrhage. These results demonstrate the initiation of ER stress and its role in apoptosis and liver injury, subsequent to hemorrhagic trauma.

Trauma and hemorrhage-induced acute hepatic insulin resistance: dominant role of tumor necrosis factor-alpha

It has long been known that injury, infections, and other critical illnesses are often associated with hyperglycemia and hyperinsulinemia. Mortality of critically ill patients is greatly reduced by intensive insulin therapy, suggesting the significance of reversing or compensating for the development of acute insulin resistance. However, the development of acute injury/infection-induced insulin resistance is poorly studied, much less than the chronic diseases associated with insulin resistance, such as type 2 diabetes and obesity. We previously found that insulin resistance develops acutely in the liver after trauma and hemorrhage. The present study was designed to begin to understand the first steps in the development of trauma and hemorrhage-induced acute hepatic insulin resistance in an animal model of injury and blood loss similar to traumatic or surgical injury and hemorrhage. We present novel data that indicate that hepatic insulin resistance increased dramatically with an increasing extent of hemorrhage. With increasing extent of blood loss, there were increases in serum TNF-alpha levels, phosphorylation of liver insulin receptor substrate-1 on serine 307, and liver c-Jun N-terminal kinase activation/phosphorylation. Exogenous TNF-alpha infusion increased c-Jun N-terminal kinase phosphorylation and insulin receptor substrate-1 serine 307 phosphorylation, and inhibited insulin-induced signaling in liver. Conversely, neutralizing TNF-alpha antibody treatment reversed many of the hemorrhage-induced changes in hepatic insulin signaling. Our data indicate that the acute development of insulin resistance after trauma and hemorrhage may have some similarities to the insulin resistance that occurs in chronic diseases. However, because so little is known about this acute insulin-resistant state, much more needs to be done before we can attain a level of understanding similar to that of chronic states of insulin resistance.

Improvement of hyperlipidemia by indomethacin in Min mice

Apc gene-deficient Min and Apc(1309) mice feature a hyperlipidemic state with a markedly low expression level of lipoprotein lipase (LPL) compared to their wild-type counterparts. We previously showed that induction of LPL mRNA by peroxisome proliferator-activated receptor (PPAR) alpha and gamma agonists or an LPL selective inducer suppresses both high serum lipid levels and intestinal polyp formation in these model animals. Since the general cyclooxygenase inhibitor, indomethacin, is known to suppress intestinal tumor development, but not to affect serum lipids, its influence in Min mice was here investigated. Treatment with 2.5, 5 and 10 ppm indomethacin in the diet for 14 weeks from 6 weeks of age caused significant dose-dependent reduction in serum triglycerides, along with a reduction in the numbers of intestinal polyps to 25% of the untreated control value. LPL mRNA levels in the liver were slightly increased by indomethacin treatment. We further performed oligonucleotide microarray analysis and quantitative PCR analysis and found 8 lipid metabolism-related genes, regulated by sterol regulatory element binding protein-1c, to be modulated by indomethacin-treatment in the Min mouse liver. Furthermore, TNFalpha was downregulated. These results indicate that indomethacin might suppress intestinal tumor formation together with a hyperlipidemic state by regulating LPL and other lipid metabolic factors.

Diabetes and hyperglycemia: strict glycemic control

OBJECTIVE

To critically review recent evidence on pathophysiology, diagnosis, and control of acute and chronic hyperglycemia in medical and surgical intensive care unit (ICU) patients.

DATA SOURCE AND STUDY SELECTION

A MEDLINE/PubMed search (1966 through February 2006) with manual cross-referencing was conducted, including all relevant articles published on blood glucose control in intensive care patients. An emphasis was placed on more recent clinical trials investigating the effects of tight glycemic control in ICU patients and on basic science studies investigating the pathophysiology and systemic effects of transient hyperglycemia in nondiabetic patients.

DATA EXTRACTION AND SYNTHESIS

Original articles, selected reviews, letters to the editor, and chapters of selected textbooks were extracted. The reviewed information was then analyzed with respect to the prevalence of hyperglycemia in ICU patients, the pathophysiology of hyperglycemia in nondiabetics, and evidence on glycemic control in various subgroups of ICU patients. The risk of iatrogenic hypoglycemia in the ICU and potential future research directions are discussed at the end of the review.

CONCLUSIONS

Recent evidence shows direct improvements in patient mortality and in-hospital morbidity with strict control of even short-term elevations of glucose levels in certain subgroups of ICU patients. However, precisely defined target glucose levels, subgroup analyses of different patient populations and treatment interventions, and the avoidance of hypoglycemic episodes during insulin therapy remain incompletely resolved and warrant future investigation.

Adverse effects of reactive oxygen species on vascular reactivity in insulin resistance

Insulin resistance (IR) has adverse effects on the reactivity of arteries and arterioles and promotes arterial hypertension and vascular occlusive diseases. Altered reactivity of resistance vessels occurs at both the endothelium and smooth-muscle levels. One major mechanism of vascular dysfunction with IR involves the augmented generation, availability, and/or actions of reactive oxygen species (ROS). Scavengers of ROS are able immediately to restore normal dilator responsiveness in arteries from IR animals. Other factors, such as increased importance of constrictor agents such as endothelin, also restrict normal dilator responses. The basis of ROS-mediated vascular dysfunction in IR may be secondary to underlying inflammatory processes throughout the arterial wall. Although ROS scavengers may be beneficial in the short term, prolonged treatments involving behavioral approaches, such as changes in diet, weight loss, and regular exercise, and pharmacological approaches, involving the use of insulin-sensitizing agents, inhibitors of the renin-angiotensin system, or administration of statins, appear to offer benefits against the detrimental vascular effects of IR. Nonetheless, the most effective approach appears to involve prevention of IR via adoption of a healthy lifestyle by young people.

Human progenitor cells from bone marrow or adipose tissue produce VEGF, HGF, and IGF-I in response to TNF by a p38 MAPK-dependent mechanism

Accumulating evidence suggests that progenitor cells may decrease destructive inflammation and reduce tissue loss by antiapoptotic mechanisms. However, they remain poorly characterized, and many questions remain regarding the mechanisms by which they may positively affect wound healing, tissue remodeling, or tissue regeneration. It has been speculated that various growth factors are responsible, but what components of the wound milieu stimulate progenitor cell production of growth factors and by what mechanisms? We hypothesized that tumor necrosis factor-alpha (TNF-alpha) stimulated progenitor cell secretion of vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), and insulin-like growth factor I (IGF-I) by a p38 mitogen-activated protein kinase (MAPK)-dependent mechanism. Human mesenchymal stem cells (hMSCs) and human adipose progenitor cells (hAPCs) were divided into four groups: control, p38 MAPK inhibitor (p38MKI), TNF, and TNF + p38MKI. After 24 h of incubation, supernatants were harvested for ELISA of VEGF, HGF, and IGF-I. Cells were collected for Western blot analysis of p38 MAPK activation. Secretion of VEGF, HGF, and IGF-I in hMSCs and hAPCs was significantly increased by stimulation with TNF and was associated with increased activation of p38 MAPK. The p38 MAPK inhibitor decreased production of TNF-stimulated VEGF, HGF, and IGF-I in hMSCs and hAPCs. However, p38 MAPK inhibitor alone had no effect on production of growth factors. These data demonstrate that progenitor cells are potent sources of VEGF, HGF, and IGF-I. TNF, a prominent tissue cytokine, strongly stimulated production of growth factors by hMSCs and hAPCs via a p38 MAPK-dependent mechanism.

Metformin prevents endotoxin-induced liver injury after partial hepatectomy

Metformin [2-(N,N-dimethylcarbamimidoyl)guanidine] is a drug used in the treatment of type 2 diabetes. Recent studies have suggested that metformin may have effects in addition to lowering serum glucose concentrations (e.g., anti-inflammatory). The aim of the present study was to determine whether metformin prevents the inflammatory reaction and liver damage in a model of postsurgical sepsis. Accordingly, rats underwent 2/3 partial hepatectomy (PH; or sham surgery); 48 h after surgery, animals were administered endotoxin (LPS; 1.5 mg/kg i.v.). Both PH and LPS alone caused some minor liver damage. However, their combined effect (PH/LPS) was synergistic, leading to robust hepatic damage, as indicated by plasma enzymes and histological assessment. Although metformin treatment did not alter changes caused by PH alone, it almost completely blunted the effects of LPS in the PH/LPS group. Increases in biomarkers of inflammation (e.g., interleukin 6, interferon gamma, and neutrophil number) were also blunted by metformin treatment. Furthermore, PH/LPS caused a >200x increase in hepatic plasminogen activator inhibitor 1 (PAI-1) mRNA expression and plasma PAI-1 protein. These increases were associated with inhibition of hepatic urokinase plasminogen activator activity and an increase in fibrin deposition, indicative of local thrombosis. These effects were markedly reduced by metformin treatment. In conclusion, these data demonstrate that metformin prevents liver damage in a model of postsurgical sepsis in rats by decreasing proinflammatory and hemostatic responses.