A novel receptor tyrosine kinase, Mer, inhibits TNF-alpha production and lipopolysaccharide-induced endotoxic shock.
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The regulation of monocyte function and the inhibition of TNF-alpha production during bacterial sepsis are critical in attenuating adverse host responses to endotoxemia. To study the function of a novel receptor tyrosine kinase, mer, that is expressed in monocytes, we generated mice (merkd) that lack the signaling tyrosine kinase domain. Upon LPS challenge, merkd animals died of endotoxic shock (15/17, 88.2%), whereas control wild-type mice survived (1/15, 6.7% died). Susceptible merkd mice exhibited edema, leukocyte infiltration, and signs of endotoxic shock that correlated with higher levels of TNF-alpha found in the serum of merkd mice as compared with wild-type control animals. Death due to LPS-induced endotoxic shock in merkd mice was blocked by administration of anti-TNF-alpha Ab, suggesting that overproduction of this cytokine was principally responsible for the heightened suseptibility. The increase in TNF-alpha production appeared to be the result of a substantial increase in the LPS-dependent activation of NF-kappa B nuclear translocation resulting in greater TNF-alpha production by macrophages from merkd mice. Thus, Mer receptor tyrosine kinase signaling participates in a novel inhibitory pathway in macrophages important for regulating TNF-alpha secretion and attenuating endotoxic shock. (+info)
Lipopolyamines: novel antiendotoxin compounds that reduce mortality in experimental sepsis caused by gram-negative bacteria.
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The interactions of lipopolyamines, a class of structurally unique compounds currently being used as transfection (lipofection) agents, with lipopolysaccharide (LPS) have been characterized. Our studies have demonstrated that 1,3-di-oleoyloxy-2-(6-carboxyspermyl)-propylamide), available commercially as DOSPER, binds to purified LPS with an affinity of about 1/10 that of polymyxin B. This essentially nontoxic compound inhibits, in a dose-dependent manner, LPS-induced activation of the Limulus clotting cascade and the production of tumor necrosis factor alpha (TNF-alpha) interleukin-6 (IL-6), and nitric oxide from LPS-stimulated J774.A1 cells, a murine macrophage-like cell line. Cytokine inhibition is paralleled by decreased steady-state levels of TNF-alpha and IL-6 mRNA and inhibits the nuclear translocation of nuclear factor kappa B. These findings suggest that the lipopolyamine compound sequesters LPS, thereby blocking downstream cellular activation events that lead to the production of proinflammatory mediators. Administration of DOSPER to D-galactosamine-sensitized mice challenged either with LPS or with Escherichia coli organisms provided significant protection against lethality both with and without antibiotic chemotherapy. Partial protection is evident in LPS-challenged mice treated with DOSPER as late as 2 to 4 h following the endotoxin challenge. A greater degree of protection is observed in E. coli-challenged animals receiving ceftazidime than in those receiving imipenem, which is probably attributable to the higher levels of LPS released in vivo by the former antibiotic. Potent antiendotoxic activity, low toxicity, and ease of synthesis render the lipopolyamines candidate endotoxin-sequestering agents of potential significant therapeutic value. (+info)
Inflammation, sepsis, and coagulation.
(19/5981)
The molecular links between inflammation and coagulation are unquestioned. Inflammation promotes coagulation by leading to intravascular tissue factor expression, eliciting the expression of leukocyte adhesion molecules on the intravascular cell surfaces, and down regulating the fibrinolytic and protein C anticoagulant pathways. Thrombin, in turn, can promote inflammatory responses. This creates a cycle that logically progresses to vascular injury as occurs in septic shock. Most complex systems are regulated by product inhibition. This inflammation-coagulation cycle seems to follow this same principle with the protein C pathway serving as the regulatory mechanism. The molecular basis by which the protein C pathway functions as an anticoagulant is relatively well established compared to the mechanisms involved in regulating inflammation. As one approach to identifying the mechanisms involved in regulating inflammation, we set out to identify novel receptors that could modulate the specificity of APC in a manner analogous to the mechanisms by which thrombomodulin modulates thrombin specificity. This approach led to the identification of an endothelial cell protein C receptor (EPCR). To understand the mechanism, we obtained a crystal structure of APC (lacking the Gla domain). The crystal structure reveals a deep groove in a location analogous to anion binding exosite 1 of thrombin, the location of interaction for thrombomodulin, platelet thrombin receptor and fibrinogen. Thrombomodulin blocks the activation of platelets and fibrinogen without blocking reactivity with chromogenic substrates or inhibitors. Similarly, in solution, EPCR blocks factor Va inactivation without modulating reactivity with protease inhibitors. Thus, these endothelial cell receptors for the protein C system share many properties in common including the ability to be modulated by inflammatory cytokines. Current studies seek to identify the substrate for the APC-EPCR complex as the next step in elucidating the mechanisms by which the protein C pathway modulates the response to injury and inflammation. (+info)
Serum leptin concentrations and their relation to metabolic abnormalities in human sepsis.
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Circulating leptin concentrations are raised in animal models of inflammation and sepsis. The purpose of this study was to determine the effect of sepsis on serum leptin concentration in humans and to examine the relationship between leptin and the metabolic consequences of sepsis. Resting energy expenditure, insulin sensitivity, and fasting serum leptin, plasma insulin, and cortisol concentrations were measured in 20 subjects with intra-abdominal sepsis and 20 healthy control subjects, before and during a 2-h period of euglycemic hyperinsulinemia. Fasting serum leptin concentrations were similar in septic and control subjects. In simple regression analysis, serum leptin concentrations correlated significantly with percent body fat in both septic patients (r = 0. 64, P < 0.005) and healthy subjects (r = 0.75, P < 0.0001). Multiple regression analyses additionally indicated that percent body fat, fasting plasma insulin, and plasma cortisol, but not sepsis, were significant and independent determinants of serum leptin concentration. No relationship between leptin and resting energy expenditure or insulin sensitivity was identifiable. A major metabolic role for leptin in human sepsis therefore appears unlikely. (+info)
Overexpression of Bcl-2 in transgenic mice decreases apoptosis and improves survival in sepsis.
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In sepsis there is extensive apoptosis of lymphocytes, which may be beneficial by down-regulating the accompanying inflammation. Alternatively, apoptosis may be detrimental by impairing host defense. We studied whether Bcl-2, a potent antiapoptotic protein, could prevent lymphocyte apoptosis in a clinically relevant model of sepsis. Transgenic mice in which Bcl-2 was overexpressed in T cells had complete protection against sepsis-induced T lymphocyte apoptosis in thymus and spleen. Surprisingly, there was also a decrease in splenic B cell apoptosis in septic Bcl-2 overexpressors compared with septic HeJ and HeOuJ mice. There were marked increases in TNF-alpha, IL-1beta, and IL-10 in thymic tissue in sepsis in the three species of mice, and the increase in TNF-alpha and IL-10 in HeOuJ mice was greater than that in Bcl-2 mice. Mitotracker, a mitochondrial membrane potential indicator, demonstrated a sepsis-induced loss of membrane potential in T cells in HeJ and HeOuJ mice but not in Bcl-2 mice. Importantly, Bcl-2 overexpressors also had improved survival in sepsis. To investigate the potential impact of loss of lymphocytes on survival in sepsis, Rag-1-/- mice, which are totally deficient in mature T and B cells, were also studied. Rag-1-/- mice had decreased survival compared with immunologically normal mice with sepsis. We conclude that overexpression of Bcl-2 provides protection against cell death in sepsis. Lymphocyte death may be detrimental in sepsis by compromising host defense. (+info)
Enteral nutritional supplementation with key nutrients in patients with critical illness and cancer: a meta-analysis of randomized controlled clinical trials.
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OBJECTIVE: To conduct a meta-analysis of 11 randomized controlled trials comparing enteral nutritional support supplemented with key nutrients versus standard enteral nutritional support to determine effects on morbidity and mortality rates and hospital stay. BACKGROUND DATA: Recent studies have shown that malnutrition occurs in up to 30% of patients undergoing gastrointestinal surgery, resulting in an increased risk of postoperative complications and death. With the realization that key nutrients can modulate inflammatory, metabolic, and immune processes, enteral nutritional regimens (supplemented with large amounts of key nutrients) have been developed for clinical use. METHODS: Eleven prospective, randomized controlled trials evaluating 1009 patients treated with combinations of key nutrients (Impact, Immun-Aid) were evaluated. Outcome measures examined were the incidences of pneumonia, infectious complications, and death, and length of hospital stay. Meta-analyses were undertaken to obtain the odds ratio and 95% confidence interval for incidences of infectious complications, pneumonia, and death, and the weighted mean difference and 95% confidence interval for length of hospital stay. RESULTS: The provision of nutritional support supplemented with key nutrients to patients with critical illness resulted in a decrease in infectious complications when compared with patients receiving standard nutritional support and a significant reduction in overall hospital stay. Similar results were documented in patients with gastrointestinal cancer. However, there were no differences between patient groups for either pneumonia or death. CONCLUSIONS: This meta-analysis has demonstrated that nutritional support supplemented with key nutrients results in a significant reduction in the risk of developing infectious complications and reduces the overall hospital stay in patients with critical illness and in patients with gastrointestinal cancer. However, there is no effect on death. These data have important implications for the management of such patients. (+info)
Pulmonary clearance of adrenomedullin is reduced during the late stage of sepsis.
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Polymicrobial sepsis is characterized by an early, hyperdynamic phase followed by a late, hypodynamic phase. Although upregulation of adrenomedullin (ADM), a novel potent vasodilatory peptide, plays an important role in producing cardiovascular responses during the progression of sepsis, it remains unknown whether the clearance of this peptide is altered under such conditions. To determine this, male adult rats were subjected to sepsis by cecal ligation and puncture (CLP) followed by fluid resuscitation. At 5 h (i.e., the hyperdynamic phase of sepsis) or 20 h (the hypodynamic phase) after CLP, the animals were injected with 125I-labeled ADM through the jugular vein. Blood and tissue samples (including the lungs, kidneys, gastrointestinal tract, pancreas, spleen, mesentery, liver, brain, skeletal muscle, heart, and skin) were harvested 30 min after the injection and the radioactivity was determined. The results indicate that there were no significant alterations in tissue [125I]ADM distribution at 5 h after CLP compared to shams. At 20 h after CLP, however, there was a significant decrease in radioactivity in the lungs. In contrast, a significant increase of radioactivity was observed in all other organs except the liver and kidneys. The pulmonary distribution of [125I]ADM was found to be far greater than in any other organs tested, irrespective of the effect of sepsis. In separate groups of animals, injection of [125I]ADM into the left ventricle resulted in a significant decrease in radioactivity in the lungs of both sham and septic animals at 20 h after surgery. These results suggest that the lungs are the primary site of ADM clearance, which is significantly diminished during the late stage of sepsis. The decreased clearance of ADM by the lungs may play an important role in maintaining the sustained levels of plasma ADM under such conditions. (+info)
Multiple roles for IL-12 in a model of acute septic peritonitis.
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The present study addressed the role of IL-12 in a murine model of septic peritonitis, induced by cecal ligation and puncture (CLP). Although CLP surgery induced IL-12 production at 6 and 24 h after surgery, IL-12 immunoneutralization was clearly deleterious in this model: 54% of CLP mice receiving preimmune serum survived, whereas mice administered IL-12 antisera prior to CLP experienced a 25% survival rate. IL-12 immunoneutralization not only led to increased mortality, but also appeared to promote a shift away from IL-12 and IFN-gamma, in favor of IL-10. This cytokine shift corresponded to changes in bacterial load, as CLP mice receiving IL-12 antiserum yielded more CFUs from the peritoneal cavity at 24 h after CLP. To address the role of bacterial infection in IL-12 antiserum-induced mortality following CLP, antibiotics were administered for 4 days after surgery. Despite regular antibiotic administration, IL-12 immunoneutralization still reduced survival in CLP mice. Furthermore, histology of the ceca revealed that mice administered IL-12 antisera failed to show typical organization of the damaged cecum wall. Accordingly, Gram staining revealed bacteria within peritoneal fluids from these mice, while peritoneal fluids from CLP mice that received preimmune serum and antibiotics were free of bacteria. Altogether, these data suggested multiple important roles for IL-12 in the evolution of murine septic peritonitis. (+info)