Gram-negative sepsis. Background, clinical features, and intervention

The toll-like receptor-4 (TLR-4) pathway and its possible role in the pathogenesis of Escherichia coli mastitis in dairy cattle

Mastitis is one of the most costly production diseases in the dairy industry that is caused by a wide array of microorganisms. In this review, we focus on the Gram-negative Escherichia coli infections that often occur at periods when the innate immune defence mechanisms are impaired (i.e., parturition through the first 60 days of lactation). There is substantial evidence demonstrating that at these periods, the expected influx of polymorphonuclear neutrophil leukocytes (PMN) into the mammary gland is delayed during inflammation after intramammary infection with E. coli. Here, we provide some hypotheses on the potential mechanisms of action on how the disease may develop under circumstances of immunosuppression, and describe the potential involvement of the toll-like receptor-4 signal transduction pathway in the pathogenesis of E. coli mastitis. In addition, some ideas are proposed to help prevent E. coli mastitis and potentially other diseases caused by Gram-negative infections in general.

Lipopolysaccharide primes macrophages to increase nitric oxide production in response to Staphylococcus Aureus

Sepsis, the leading cause of death in intensive care units, is associated with overproduction of nitric oxide (NO). The mechanism concerning the NO production in the sepsis caused by both Gram-negative and Gram-positive bacteria is largely unknown. The present study examines the effect of lipopolysaccharide (LPS) on Staphylococcus aureus-induced NO production in macrophages. In the naïve murine macrophage cell line RAW264.7, heat-killed Staphylococcus aureus (HKSa) induced a significant NO production at a high concentration (100 microg/ml). However, pretreatment of the cells with increasing concentration of LPS (10-50 ng/ml) resulted in induction of NO production by HKSa even at the doses of 1 and 10 microg/ml. The expression of inducible NO synthase (iNOS) in response to HKSa was also enhanced by LPS pretreatment, suggesting that LPS priming NO production is due to the enhancement of iNOS expression. We examined whether protein kinase C (PKC), mitogen-activated protein kinases (MAPKs) and calcineurin signaling pathways are involved in the priming effects of LPS. It was found that the PKC inhibitor Gö6976, the p38 inhibitor SB203580 and the calcineurin inhibitor cyclosporine A significantly reversed the priming effects of LPS on HKSa-induced NO production and iNOS expression. In contrast, the ERK1/2 inhibitor PD98059 did not block the induction of priming by LPS. These data support the hypothesis that LPS primes macrophages for enhancement of HKSa-induced NO production, and indicate that PKC, p38 and calcineurin might be involved in the LPS-induced priming.

Sepsis and the heart

Sepsis is generally viewed as a disease aggravated by an inappropriate immune response encountered in the afflicted individual. As an important organ system frequently compromised by sepsis and always affected by septic shock, the cardiovascular system and its dysfunction during sepsis have been studied in clinical and basic research for more than 5 decades. Although a number of mediators and pathways have been shown to be associated with myocardial depression in sepsis, the precise cause remains unclear to date. There is currently no evidence supporting global ischemia as an underlying cause of myocardial dysfunction in sepsis; however, in septic patients with coexistent and possibly undiagnosed coronary artery disease, regional myocardial ischemia or infarction secondary to coronary artery disease may certainly occur. A circulating myocardial depressant factor in septic shock has long been proposed, and potential candidates for a myocardial depressant factor include cytokines, prostanoids, and nitric oxide, among others. Endothelial activation and induction of the coagulatory system also contribute to the pathophysiology in sepsis. Prompt and adequate antibiotic therapy accompanied by surgical removal of the infectious focus, if indicated and feasible, is the mainstay and also the only strictly causal line of therapy. In the presence of severe sepsis and septic shock, supportive treatment in addition to causal therapy is mandatory. The purpose of this review is to delineate some characteristics of septic myocardial dysfunction, to assess the most commonly cited and reported underlying mechanisms of cardiac dysfunction in sepsis, and to briefly outline current therapeutic strategies and possible future approaches.

Lipopolysaccharide reduces electrical coupling in microvascular endothelial cells by targeting connexin40 in a tyrosine-, ERK1/2-, PKA-, and PKC-dependent manner

Electrical coupling along the endothelium is central in the arteriolar conducted response and in control of vascular resistance. It has been shown that exposure of endothelium to lipopolysaccharide (LPS, an initiating factor in sepsis) reduces intercellular communication in vitro and in vivo. The molecular basis for this reduction is not known. We examined the effect of LPS on electrical coupling in monolayers of cultured mouse microvascular endothelial cells (MMEC) derived from the mouse hindlimb skeletal muscle. To assess coupling, we measured the spread of electrical current injected into the monolayer and computed the monolayer intercellular resistance (inverse measure of coupling). LPS (10 microg/ml, 1 h) reduced coupling (i.e., increased resistance) in MMEC isolated from wild-type, connexin37 (Cx37) null and Cx43(G60S) (nonfunctional mutant) mice, but not in MMEC derived from Cx40 null mice. LPS also activated JNK1/2, p38 and ERK1/2 MAP kinases. Pretreatment of WT monolayers with ERK1/2 inhibitor U0126 (20 microM, 1 h) prevented the LPS-induced decrease in coupling, while inhibition of JNK1/2 with SP600125 (20 microM, 1 h) and p38 with a p38 inhibitor (10 nM, 1 h) had no effect. Furthermore, inhibition of tyrosine kinases with PP-2 (10 nM, 1 h), activation of PKA by 8-bromo-cAMP (1 mM, 5 min), and activation of PKC by bryostatin-2 (10 nM, 1 h) also prevented the reduction in coupling. We propose that LPS reduces inter-endothelial electrical coupling via tyrosine-, ERK1/2-, PKA-, and PKC-dependent signaling that targets Cx40. We suggest that this mechanism contributes to compromised arteriolar function following LPS exposure.

The role of tumour necrosis factor in the kinetics of lipopolysaccharide-mediated neutrophil priming in whole blood

Neutrophils can be primed by bacterial lipopolysaccharide (LPS) for an enhanced oxidative burst, which is a key element in the pathogenesis of Gram-negative sepsis. Some serum proteins (e.g. lipopolysaccharide-binding protein) avidly bind LPS and markedly enhance receptor binding and cellular activation while other serum factors (lipoproteins, bactericidal/permeability-increasing protein) neutralize LPS and prevent neutrophil activation. In this paper we examined the kinetics of this priming reaction in whole blood. To study the balance between neutrophil activation and LPS neutralization a sensitive chemiluminescence assay was used in a whole blood system. LPS was able to prime neutrophils for enhanced oxidative burst in whole blood with an optimum incubation time of 25 min. However, LPS was neutralized very rapidly with a t(1/2) of 10 min. After 20 min a second priming factor was already generated, which was shown to be monocyte-derived tumour necrosis factor (TNF).

Inhibition of glucocorticoid receptor binding by nitric oxide in endotoxemic rats

OBJECTIVE

Nitric oxide is an important participant in septic shock. For example, it causes profound vasodilation and hypotension. Despite their potent antiinflammatory properties, glucocorticoids are not routinely used in septic shock. Some studies show that antiinflammatory doses of glucocorticoids can be beneficial, but other studies do not indicate their use in this situation. We have previously shown the inhibitory effect of nitric oxide on glucocorticoid receptor binding in vitro. Nitric oxide donors decreased the binding of immunoprecipitated glucocorticoid receptor obtained from mouse L929 fibroblasts. These in vitro findings prompted us to study whether in vivo manipulations of the nitric oxide system would interfere with the glucocorticoid receptor binding.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a university.

SUBJECTS

Female Wistar rats.

INTERVENTIONS

Injection of bacterial lipopolysaccharide, anesthesia, cardiovascular perfusion, and organ removal for biochemical assays.

MEASUREMENTS AND MAIN RESULTS

Following lipopolysaccharide injection, plasma nitrate + nitrite increased and inducible nitric oxide synthase activity was stimulated in several organs, the highest rates being in the lung and spleen. If dexamethasone was injected before lipopolysaccharide, it completely blocked inducible nitric oxide synthase induction and the increase in plasma nitrate + nitrite. On the other hand, if dexamethasone was injected after lipopolysaccharide, it failed to affect both inducible nitric oxide synthase induction and increased plasma nitrate + nitrite levels. Lipopolysaccharide also caused an inhibition of glucocorticoid receptor binding in lung and spleen. Previous administration of a nitric oxide synthase inhibitor prevented both lipopolysaccharide-induced decrease in glucocorticoid receptor binding and the increase in plasma nitrate + nitrite. Injection of a nitric oxide donor into naive animals significantly decreased glucocorticoid receptor binding activity and prevented dexamethasone-induced increase in liver tyrosine aminotransferase activity.

CONCLUSIONS

The results indicate that the failure of glucocorticoids to exhibit their antiinflammatory effects when administered to endotoxemic rats may be explained, at least in part, by the nitric oxide-induced inhibition of glucocorticoid receptor binding ability, thus precluding the expression of the antiinflammatory effects of both exogenous and endogenous corticosteroids.

Glutamine attenuates endotoxin-induced lung metabolic dysfunction: Potential role of enhanced heat shock protein 70

OBJECTIVE

Septic shock leads to derangement of cellular metabolism. Enhanced heat shock protein 70 (HSP-70) can preserve cellular metabolism after other forms of cellular stress. Glutamine (GLN) can enhance lung HSP-70 expression after lethal endotoxemia. However, it is unknown whether GLN can enhance HSP-70 expression and attenuate lung metabolic dysfunction after sublethal endotoxemia. Our aim was to determine whether GLN could upregulate HSP-70 and attenuate metabolic dysfunction in lung tissue after sublethal endotoxemia.

METHODS

Sprague-Dawley rats were assigned to one of five groups. The first two groups were treated with Escherichia coli lipopolysaccharide (LPS; 1 mg/kg intravenously). GLN (0.75 g/kg intravenously) or balanced salt solution as a control was administered 5 min after LPS administration. The next two groups of rats were treated with quercetin (HSP-70 inhibitor; 400 mg/kg intraperitoneally) 6 h before LPS administration. The final group received no treatment. Lung tissue was harvested 24-h after LPS and analyzed with immunofluorescence and western blot for HSP-70. Tissue metabolites were quantified by 1H and 31P nuclear magnetic resonance spectroscopy.

RESULTS

GLN compared with balanced salt solution (BSS) administration in LPS-treated animals led to significant increases in lung HSP-70. Increased HSP-70 expression was observed in lung epithelial cells and macrophages. GLN significantly improved the ratio of adenosine triphosphate to adenosine diphosphate in the lung after LPS. Quercetin inhibited a GLN-mediated increase in lung HSP-70 and blocked a beneficial effect of GLN on the ratio of adenosine triphosphate to adenosine diphosphate after LPS.

CONCLUSIONS

A single dose of GLN can enhance HSP-70 in pulmonary epithelial cells and macrophages after sublethal endotoxemia. Further, GLN can attenuate endotoxin-induced lung metabolic dysfunction. GLN's beneficial effect on lung tissue after metabolic dysfunction caused by sublethal endotoxemia may be mediated in part by enhanced HSP-70.

Rapid infectious killers

Central to the practice of emergency medicine is the ability to identify patients in whom immediate intervention is needed to prevent long-term morbidity and mortality. This article has highlighted some of the characteristics of several infectious diseases that may become fatal quickly if not treated quickly and appropriately by physicians. Bacterial meningitis,necrotizing soft tissue infections, invasive gram-negative disease, pneumo-coccal pneumonia, and West Nile encephalitis all require prompt recognition and treatment by emergency care providers.

Optimum treatment of severe sepsis and septic shock: evidence in support of the recommendations

Severe sepsis and septic shock are among the most common causes of death in noncoronary intensive care units. The incidence of sepsis has been increasing over the past two decades, and is predicted to continue to rise over the next 20 years. While our understanding of the complex pathophysiologic alterations that occur in severe sepsis and septic shock has increased greatly asa result of recent clinical and preclinical studies, mortality associated with the disorder remains unacceptably high. Despite these new insights, the cornerstone of therapy continues to be early recognition, prompt initiation of effective antibiotic therapy, and source control, and goal-directed hemodynamic, ventilatory,and metabolic support as necessary. To date, attempts to reduce mortality with innovative, predominantly anti-inflammatory therapeutic strategies have been extremely disappointing. Observations of improved outcomes with physiologic doses of corticosteroid replacement therapy and activated protein C (drotrecogin alfa[activated]) have provided new adjuvant therapies for severe sepsis and septic shock in selected patients. This article reviews the components of sepsis management and discusses the available evidence in support of these recommendations. In addition, there is a discussion of some promising new strategies.

Septic mice are susceptible to pulmonary aspergillosis

Clinical data underscores the fact that subsequent high mortality rates occur in patients who survive acute septic episodes. Herein, we described a clinically relevant model of experimental sepsis that we believe will allow further investigation of the manner in which the pulmonary innate immune response is modulated after sepsis. C57BL/6 mice were subjected to cecal ligation and puncture (CLP) model, whereby the cecum was partially ligated and punctured nine times with a 21-gauge needle. This procedure was associated with 100% mortality at 3 days after surgery. In contrast, when mice subjected to CLP were treated with antibiotic beginning at 8 hours after surgery, and every 12 hours thereafter until 3 days, approximately 60% of the mice survived. Interestingly, CLP survivors quickly succumbed (100% mortality) to pulmonary infection when intratracheally challenged, at day 3 after CLP, with viable Aspergillus fumigatus conidia. No mortality was observed in conidia-challenged sham-operated mice. The defective innate immune response against A. fumigatus in CLP mice could not be explained by a failure of neutrophils to infiltrate the lungs. Instead, gene array analysis revealed that several components of the innate immune response, including the nuclear factor-kappaB signaling pathway, were down-regulated. Thus, we describe a system of sepsis-induced innate immune failure in the lungs of C57BL/6 mice.

Modulation of the Lipopolysaccharide Receptor Complex (CD14, TLR4, MD-2) and Toll-Like Receptor 2 in Systemic Inflammatory Response Syndrome-Positive Patients With and Without Infection: Relationship to Tolerance

The lipopolysaccharide (LPS) receptor complex consists of two interacting receptors (CD14 and TLR4) and an associated protein (MD-2). When engaged by LPS, as in gram-negative infection, this complex transduces a signal detected by MyD88 and passed onward by a cascade of the IRAKs, TRAF6, and NIK, resulting in activation of NF-kappaB. A similar cascade, mediated by TLR2, occurs with ligands derived from gram-positive bacteria. In vitro studies of human monocytes have shown that TLR4 mRNA is paradoxically upregulated in response to "tolerizing" doses of LPS. This study evaluated changes in vivo of blood monocyte CD14, TLR4, TLR2, and MD-2 mRNA by reverse transcription followed by real-time polymerase chain reaction in surgical intensive care unit patients and in normal controls. In addition cell-surface receptor expression of TLR2, TLR4, and CD14 was assessed by flow cytometry in patients and normal controls. Inflammation-induced acute tolerance to LPS was evaluated by ex vivo whole blood tumor necrosis factor alpha production and was significantly reduced in patients compared with controls, confirming LPS hyporesponsiveness. Monocyte mRNA and cell-surface receptor expression of TLR4 were increased 2.4-fold (P < 0.05) and 1.7-fold (P <.002), respectively, in patients compared with normal controls. Monocyte TLR2 mRNA, MD-2 mRNA and CD14 and TLR2 cell-surface expression were not significantly changed compared with controls. The present study suggests that the acute inflammatory condition associated with peripheral cellular LPS hyporesponsiveness is neither specific to prior infectious challenge nor can be ascribed to significant alterations in expression of the cell-surface LPS binding complex proteins.

Association of the endotoxin antagonist E5564 with high-density lipoproteins in vitro: dependence on low-density and triglyceride-rich lipoprotein concentrations

The objective of this study was to determine the distribution profile of the novel endotoxin antagonist E5564 in plasma obtained from fasted human subjects with various lipid concentrations. Radiolabeled E5564 at 1 microM was incubated in fasted plasma from seven human subjects with various total cholesterol (TC) and triglyceride (TG) concentrations for 0.5 to 6 h at 37 degrees C. Following these incubations, plasma samples were separated into their lipoprotein and lipoprotein-deficient fractions by ultracentrifugation and were assayed for E5564 radioactivity. TC, TG, and protein concentrations in each fraction were determined by enzymatic assays. Lipoprotein surface charge within control and phosphatidylinositol-treated plasma and E5564's influence on cholesteryl ester transfer protein (CETP) transfer activity were also determined. We observed that the majority of E5564 was recovered in the high-density lipoprotein (HDL) fraction. We further observed that incubation in plasma with increased levels of TG-rich lipoprotein (TRL) lipid (TC and TG) concentrations resulted in a significant increase in the percentage of E5564 recovered in the TRL fraction. In further experiments, E5564 was preincubated in human TRL. Then, these mixtures were incubated in hypolipidemic human plasma for 0.5 and 6 h at 37 degrees C. Preincubation of E5564 in purified TRL prior to incubation in human plasma resulted in a significant decrease in the percentage of drug recovered in the HDL fraction and an increase in the percentage of drug recovered in the TRL and low-density lipoprotein fractions. These findings suggest that the majority of the drug binds to HDLs. Preincubation of E5564 in TRL prior to incubation in normolipidemic plasma significantly decreased the percentage of drug recovered in the HDL fraction. Modifications to the lipoprotein negative charge did not alter the E5564 concentration in the HDL fraction. In addition, E5564 does not influence CETP-mediated transfer activity. Information from these studies could be used to help identify the possible components of lipoproteins which influence the interaction of E5564 with specific lipoprotein particles.

Beta-arrestin-2 regulates the development of allergic asthma

Asthma is a chronic inflammatory disorder of the airways that is coordinated by Th2 cells in both human asthmatics and animal models of allergic asthma. Migration of Th2 cells to the lung is key to their inflammatory function and is regulated in large part by chemokine receptors, members of the seven-membrane-spanning receptor family. It has been reported recently that T cells lacking beta-arrestin-2, a G protein-coupled receptor regulatory protein, demonstrate impaired migration in vitro. Here we show that allergen-sensitized mice having a targeted deletion of the beta-arrestin-2 gene do not accumulate T lymphocytes in their airways, nor do they demonstrate other physiological and inflammatory features characteristic of asthma. In contrast, the airway inflammatory response to LPS, an event not coordinated by Th2 cells, is fully functional in mice lacking beta-arrestin-2. beta-arrestin-2-deficient mice demonstrate OVA-specific IgE responses, but have defective macrophage-derived chemokine-mediated CD4+ T cell migration to the lung. This report provides the first evidence that beta-arrestin-2 is required for the manifestation of allergic asthma. Because beta-arrestin-2 regulates the development of allergic inflammation at a proximal step in the inflammatory cascade, novel therapies focused on this protein may prove useful in the treatment of asthma.

The influence of inadequate empirical antimicrobial treatment on patients with bloodstream infections in an intensive care unit

OBJECTIVE

To determine the occurrence of inadequate antimicrobial therapy among critically ill patients with bacteremia and the factors associated with it, to identify the microorganisms that received inadequate antimicrobial treatment, and to determine the relationship between inadequate treatment and patients outcome.

METHODS

From June 1995 to January 1999 we collected data on all clinically significant ICU-bacteremias in our teaching hospital. Clinical and microbiological characteristics were recorded and the adequacy of empirical antimicrobial treatment in each case was determined. We defined inappropriate empirical antimicrobial treatment as applying to infection that was not being effectively treated at the time the causative microorganism and its antibiotic susceptibility were known. Multivariate analysis was used to determine the variables associated with inappropriate empirical antimicrobial treatment and to evaluate the influence of this on the related mortality to bacteremia, using the SPSS package (9.0).

RESULTS

Among 166 intensive care unit patients with bacteremia, 39 (23.5%) received inadequate antimicrobial treatment. In this last group the mean age of patients was 64.1 +/- 13.2 years, and 64% were men. Bacteremia was hospital-acquired in 92% of these cases. Eleven percent developed septic shock and 37.7% severe sepsis, and ultimately fatal underlying disease was present in 28.2% of patients given inadequate empirical antimicrobial treatment. The main sources of bacteremias in this group were: a vascular catheter (15.3%), respiratory (7.6%) or unknown (53.8%). The microorganisms most frequently isolated in the group with inadequate empirical antimicrobial treatment were: coagulase-negative staphylococci (29.5%), Acinetobacter baumannii (27.3%), Enterococcus faecalis, Pseudomonas aeruginosa, Enterobacter cloacae, Proteus mirabilis, Escherichia coli, and Candida species (4.5% each). The frequency of coagulase-negative staphylococci in the cases with inappropriate treatment was higher than in the group with appropriate treatment (OR 2.62; 95% CI: 1.10-6.21; P = 0.015). The global mortality rate was 56% and the related mortality was 30% in the group with inadequate empirical antimicrobial treatment. The only factor associated with inappropriate empirical antibiotic treatment was the absence of abdominal or respiratory focus (P = 0.04; OR = 0.35; 95% CI: 0.12-0.97). Septic shock was related to attributable mortality (P = 0.03; OR = 3.19; 95% CI: 1.08-9.40), but not inappropriate empirical antibiotic treatment (P = 0.24; OR = 1.71; 95% CI: 0.66-4.78).

CONCLUSION

Almost a quarter of critically ill patients with bloodstream infections were given inadequate empirical antibiotic treatment, but mortality was not higher in the group with inadequate treatment than in the group with adequate treatment. This fact was probably due to microbiological factors and clinical features, such as the type of microorganism most frequently isolated and the source of the bacteremia.

Inhibition of endotoxin response by e5564, a novel Toll-like receptor 4-directed endotoxin antagonist

Alpha-D-glucopyranose,3-O-decyl-2-deoxy-6-O-[2-deoxy-3-O-[(3R)-3-methoxydecyl]-6-O-methyl-2-[[(11Z)-1-oxo-11-octadecenyl]amino]-4-O-phosphono-beta-D-glucopyranosyl]-2-[(1,3-dioxotetradecyl)amino]-1-(dihydrogen phosphate), tetrasodium salt (E5564) is a second-generation synthetic lipodisaccharide designed to antagonize the toxic effects of endotoxin, a major immunostimulatory component of the outer cell membrane of Gram negative bacteria. In vitro, E5564 dose dependently (nanomolar concentrations) inhibited lipopolysaccharide (LPS)-mediated activation of primary cultures of human myeloid cells and mouse tissue culture macrophage cell lines as well as human or animal whole blood as measured by production of tumor necrosis factor-alpha and other cytokines. E5564 also blocked the ability of Gram negative bacteria to stimulate human cytokine production in whole blood. In vivo, E5564 blocked induction of LPS-induced cytokines and LPS or bacterial-induced lethality in primed mice. E5564 was devoid of agonistic activity when tested both in vitro and in vivo and has no antagonistic activity against Gram positive-mediated cellular activation at concentrations up to 1 microM. E5564 blocked LPS-mediated activation of nuclear factor-kappaB in toll-like receptor 4/MD-2-transfected cells. In a mouse macrophage cell line, activity of E5564 was independent of serum, suggesting that E5564 exerts its activity through the cell surface receptor(s) for LPS, without the need for serum LPS transfer proteins. Similar to (6-O-[2-deoxy-6-O-methyl-4-O-phosphono-3-O-[(R)-3-Z-dodec-5-endoyloxydecl]-2-[3-oxo-tetradecanoylamino]-beta-O-phosphono-alpha-D-glucopyranose tetrasodium salt (E5531), another lipid A-like antagonist, E5564 associates with plasma lipoproteins, causing low concentrations of E5564 to be quantitatively inactivated in a dose- and time-dependent manner. However, compared with E5531, E5564 is a more potent inhibitor of cytokine generation, and higher doses retain activity for durations likely sufficient to permit clinical application. These results indicate that E5564 is a potent antagonist of LPS and lacks agonistic activity in human and animal model systems, making it a potentially effective therapeutic agent for treatment of disease states caused by endotoxin.

First-generation adenovirus vectors shorten survival time in a murine model of sepsis

Adverse immunological reactions to adenoviral vectors have significantly impacted the utility of this virus for treating genetic and environmentally induced diseases. In this study, we evaluate the effect of adenoviral vectors on an animal model of sepsis. Systemic delivery of first-generation adenoviral vectors to septic mice (cecal ligation and puncture) resulted in a shortened survival time. This effect was not observed with second-generation or inactivated first-generation vectors. The accelerated death was accompanied by a number of important changes in the disease. These changes included increased liver cell apoptosis (including Kupffer cells) and a marked increase in liver bacterial load. In the lung, the combination induced an increase in bacterial load, as well as greater lung injury. In the serum, the combination was associated with decreased TNF-alpha levels and an increase in bacterial load. Finally, a profound degree of lymphocyte apoptosis was observed in these animals. These observations suggest that prior exposure to first-generation adenovirus gene therapy vectors may worsen the outcome of some forms of sepsis.

Endotoxemia in critically ill patients: why a reliable test could be beneficial

The detection of endotoxemia may provide a clue to the cause of sepsis or may indicate translocation of endotoxin from the gastrointestinal tract. A reliable endotoxin activity assay (EAA) offers the potential to determine Gram-negative infections in critically ill patients. In addition, a reliable EAA may indicate the adequacy of gastrointestinal tract perfusion, as well as potentially help to predict morbidity and mortality. A recent study by Marshall and colleagues, published in the present issue of Critical Care, evaluated the use of a whole blood EAA in a medical–surgical intensive care unit and found that 58% of the patients had positive endotoxin assays. However, only 13.5% of the population had a documented Gram-negative infection. This discrepancy and the observation that translocation and other causes of endotoxemia may not reflect true Gram-negative infection might severely limit the clinical utility of this EAA. Further study may better define the potential role of this technique in the diagnostic evaluation of the critically ill patient.

Genes other than TLR4 are involved in the response to inhaled LPS

For several decades, the mouse strains C3H/HeJ and C57BL/10ScNCr have been known to be hyporesponsive to endotoxin or lipopolysaccharide (LPS). Recently, mutations in Toll-like receptor (TLR) 4 have been shown to underlie this aberrant response to LPS. To further determine the relationship between TLR4 and responsiveness to LPS, we genotyped 18 strains of mice for TLR4 and evaluated the physiological and biological responses of these strains to inhaled LPS. Of the 18 strains tested, 6 were wild type for TLR4 and 12 had mutations in TLR4. Of those strains with TLR4 mutations, nine had mutations in highly conserved residues. Among the strains wild type for TLR4, the inflammatory response in the airway induced by inhalation of LPS showed a phenotype ranging from very sensitive (DBA/2) to hyporesponsive (C57BL/6). A broad spectrum of airway hyperreactivity after inhalation of LPS was also observed among strains wild type for TLR4. Although the TLR4 mutant strains C3H/HeJ and C57BL/10ScNCr were phenotypically distinct from the other strains with mutations in the TLR4 gene, the other strains with mutations for TLR4 demonstrated a broad distribution in their physiological and biological responses to inhaled LPS. The results of our study indicate that although certain TLR4 mutations can be linked to a change in the LPS response phenotype, additional genes are clearly involved in determining the physiological and biological responses to inhaled LPS in mammals.

Lipopolysaccharide induces Rac1-dependent reactive oxygen species formation and coordinates tumor necrosis factor-alpha secretion through IKK regulation of NF-kappa B

Reactive oxygen species (ROS) are important second messengers generated in response to many types of environmental stress. In this setting, changes in intracellular ROS can activate signal transduction pathways that influence how cells react to their environment. In sepsis, a dynamic proinflammatory cellular response to bacterial toxins (e.g. lipopolysaccharide or LPS) leads to widespread organ damage and death. The present study demonstrates for the first time that the activation of Rac1 (a GTP-binding protein), and the subsequent production of ROS, constitutes a major pathway involved in NFkappaB-mediated tumor necrosis factor-alpha (TNFalpha) secretion following LPS challenge in macrophages. Expression of a dominant negative mutant of Rac1 (N17Rac1) reduced Rac1 activation, ROS formation, NFkappaB activation, and TNFalpha secretion following LPS stimulation. In contrast, expression of a dominant active form of Rac1 (V12Rac1) mimicked these effects in the absence of LPS stimulation. IKKalpha and IKKbeta were both required downstream modulators of LPS-activated Rac1, since the expression of either of the IKK dominant mutants (IKKalphaKM or IKKbetaKA) drastically reduced NFkappaB-dependent TNFalpha secretion. Moreover, studies using CD14 blocking antibodies suggest that Rac1 induces TNFalpha secretion through a pathway independent of CD14. However, a maximum therapeutic inhibition of LPS-induced TNFalpha secretion occurred when both CD14 and Rac1 pathways were inhibited. Our results suggest that targeting both Rac1- and CD14-dependent pathways could be a useful therapeutic strategy for attenuating the proinflammatory cytokine response during the course of sepsis.

Glutamine induces heat shock protein and protects against endotoxin shock in the rat

Enhanced expression of heat shock protein (HSP) has been shown to be protective against laboratory models of septic shock. Induction of HSPs to improve outcome in human disease has not been exploited because laboratory induction agents are themselves toxic and not clinically relevant. In this study, we demonstrate that a single dose of intravenous glutamine causes a rapid and significant increase in HSP25 and HSP72 expression in multiple organs of the unstressed Sprague-Dawley rat. With the utilization of a fluid-resuscitated rat model of endotoxemia, mortality was dramatically reduced by glutamine administration concomitant with the endotoxin injury. Endotoxin-treated animals given glutamine exhibited dramatic increases in tissue HSP expression and marked reduction of end-organ damage. These data suggest glutamine may protect against mortality and attenuate end-organ injury in endotoxemic shock via enhanced HSP expression. Furthermore, glutamine confers protection when administered at the initiation of sepsis, rather than as pretreatment. Thus glutamine appears to be a clinically viable enhancer of HSP expression and may prove beneficial in the therapy of sepsis and sepsis-induced organ injury.

Protective effects of n-acetylcysteine on lung injury and red blood cell modification induced by carrageenan in the rat

Oxidative stress has been suggested as a potential mechanism in the pathogenesis of lung inflammation. The pharmacological profile of n-acetylcysteine (NAC), a free radical scavenger, was evaluated in an experimental model of lung injury (carrageenan-induced pleurisy). Injection of carrageenan into the pleural cavity of rats elicited an acute inflammatory response characterized by fluid accumulation in the pleural cavity that contained many neutrophils (PMNs), an infiltration of PMNs in lung tissues and subsequent lipid peroxidation, and increased production of nitrite/nitrate, tumor necrosis factor alpha, and interleukin 1beta. All parameters of inflammation were attenuated by NAC treatment. Furthermore, carrageenan induced an up-regulation of the adhesion molecules ICAM-1 and P-selectin, as well as nitrotyrosine and poly (ADP-ribose) synthetase (PARS), as determined by immunohistochemical analysis of lung tissues. The degree of staining for the ICAM-1, P-selectin, nitrotyrosine, and PARS was reduced by NAC. In vivo NAC treatment significantly reduced peroxynitrite formation as measured by the oxidation of the fluorescent dihydrorhodamine-123, prevented the appearance of DNA damage, an decrease in mitochondrial respiration, and partially restored the cellular level of NAD+ in ex vivo macrophages harvested from the pleural cavity of rats subjected to carrageenan-induced pleurisy. A significant alteration in the morphology of red blood cells was observed 24 h after carrageenan administration. NAC treatment has the ability to significantly diminish the red blood cell alteration. Our results clearly demonstrate that NAC treatment exerts a protective effect and clearly indicate that NAC offers a novel therapeutic approach for the management of lung injury where radicals have been postulated to play a role.

Expression of MHC class II molecules contributes to lipopolysaccharide responsiveness

Activation of phagocytes by lipopolysaccharide (LPS) causes synthesis and secretion of various mediators of inflammation. CD14, a glycosylphosphatidylinositol-anchored monocytic antigen serving as receptor for LPS, and members of the family of Toll-like receptors mediate cellular activation in response to LPS. Here we investigated whether expression of MHC class II molecules modified the response to LPS. Comparing LPS responsiveness of human and murine cells differing for expression of MHC class II molecules, we found that lack or a low level of expression of MHC class II molecules resulted in diminished secretion of pro-inflammatory cytokines following stimulation with LPS. Thus, expression of MHC class II molecules modifies LPS responsiveness, a finding suggesting that these molecules contribute to the pathogenesis not only of exotoxin-triggered toxic shock but also of endotoxin-triggered septic shock. Additionally to their role in antigen-specific immunity MHC class II molecules may influence the inflammatory response triggered by microbial constituents.

Influence of amrinone on intestinal villus blood flow during endotoxemia

PURPOSE

The objective of this study was to determine the effects of a continuous infusion of the phosphodiesterase (PDE) inhibitor amrinone on mucosal villus blood flow in a normotensive model of endotoxemia.

MATERIALS AND METHODS

Twenty-four anesthetized and ventilated rats underwent laparotomy, and an ileal portion was exteriorized and opened by an antimesenteric incision. The ileal segment was fixed on a plexiglass stage with the mucosal surface upward. Microcirculatory parameters were assessed by intravital videomicroscopy. The animals were randomly assigned to receive one of three treatments: infusion of Escherichia coli lipopolysaccharides (LPS, 2 mg/kg/h) without phosphodiesterase inhibitor pretreatment (LPS group); or infusion of LPS with amrinone pretreatment (40 microg/kg/min, start 30 minutes before LPS infusion) (amrinone group), or infusion of equivalent volumes of NaCl 0.9% (control group). Macrohemodynamic parameters (MAP, HR) and microhemodynamic parameters of ileal mucosa (mean diameter of central arterioles = D(A) and mean erythrocyte velocity within the arterioles = VE) were measured 30 minutes before and at 0, 60, and 120 minutes after induction of endotoxemia. Mucosal villus blood flow was calculated from D(A) and VE.

RESULTS

In this normotensive endotoxemia model, MAP remained stable in the control and the LPS group but significantly decreased in the amrinone group.The endotoxin-induced decrease of V(E) and D(A) of central arterioles of mucosal villi could be attenuated and prevented, respectively. Thus, the endotoxin-induced decrease of mucosal villus blood flow was diminished but not fully restored by amrinone infusion.

CONCLUSION

Our results indicate that amrinone during an early stage of sepsis is of limited value. It attenuates mucosal hypoperfusion but contributes to systemic hypotension.

Influence of amrinone on tissue oxygenation of jejunal mucosa during endotoxemia

BACKGROUND

The intestinal mucosa is the portion of the gut most susceptible to impaired perfusion and oxygen delivery. The phosphodiesterase (PDE) inhibitor amrinone has been proposed to improve oxygen delivery and tissue perfusion during sepsis. The objective of this study was to investigate the effects of amrinone on arterial oxygenation (Pao(2)) and tissue oxygenation (Ptio(2)) of jejunal mucosa during endotoxemia.

MATERIALS AND METHODS

Forty anesthetized and ventilated rats were laparotomized and a jejunal portion was exteriorized and fixed on a plexiglass stage. The jejunum was punctured and a Clark-type microcatheter Po(2) probe and a microthermocouple were placed on the mucosa to measure Ptio(2). The animals were randomly assigned to receive one of the four treatments: infusion of Escherichia coli lipopolysaccharides (LPS, 2 mg/kg/h) without amrinone pretreatment (LPS group); infusion of LPS with amrinone pretreatment (40 microg/kg/min, start 30 min before LPS infusion, amrinone + LPS group); no treatment with either amrinone or LPS (control group); treatment with amrinone without LPS infusion (amrinone group). Mean arterial pressure (MAP), heart rate (HR), Pao(2), and Ptio(2) were measured 30 min before and 0, 60, and 120 min after induction of endotoxemia.

RESULTS

MAP remained stable in the control and LPS groups. In the amrinone + LPS group MAP decreased within the first 30 min of amrinone infusion and decreased further during endotoxemia. Pao(2) remained stable in the control group and decreased in the LPS group. This endotoxin-induced decrease in Pao(2) was attenuated in the amrinone + LPS group. The mucosal Ptio(2) decreased in the LPS group but remained stable in both the control and amrinone + LPS groups.

CONCLUSIONS

Pretreatment with amrinone was able to diminish a decrease in Pao(2) during endotoxemia, indicating that pulmonary dysfunction was attenuated. Endotoxin-induced tissue hypoxia of the intestinal mucosa, however, could be fully prevented, indicating that an additional improvement in compromised tissue perfusion had occurred.

Tissue-specific gene expression of heme oxygenase-1 (HO-1) and non-specific delta-aminolevulinate synthase (ALAS-N) in a rat model of septic multiple organ dysfunction syndrome

Reactive oxygen species are thought to be involved in the pathogenesis of septic multiple organ dysfunction syndrome (MODS). It has been reported that heme oxygenase-1 (HO-1) (EC 1.14.99.3) is induced in septic animal models and is thought to confer protection against oxidative tissue injury. In this study, we examined changes in gene expression of HO-1 and non-specific delta-aminolevulinate synthase (ALAS-N) (EC 2.3.1.37), the rate-limiting enzymes in heme catabolism and heme synthesis, respectively, after intraperitoneal administration of bacterial lipopolysaccharide (LPS) to rats. LPS treatment caused the elevation of body temperature, increases in white blood cell counts, and marked elevation of serum interleukin-6 levels associated with liver, lung, and kidney injuries, characteristic of septic MODS. LPS administration significantly induced HO-1 mRNA, protein, and enzyme activity in the liver, lung, and kidney. In contrast, ALAS-N mRNA was decreased rapidly in the liver, followed by an oscillating recovery pattern. Induction of hepatic HO-1 mRNA and rapid suppression of ALAS-N mRNA were likely the result of a rapid increase in hepatic free heme concentration as judged by the increase in heme saturation of tryptophan pyrrolase. In contrast to that in the liver, the ALAS-N mRNA level in the lung and kidney was increased significantly after LPS administration, suggesting a novel mechanism of ALAS-N regulation in these tissues. These findings suggest that HO-1 and ALAS-N mRNA are regulated in a tissue-specific manner in a rat model of septic MODS.

Milrinone improves intestinal villus blood flow during endotoxemia

PURPOSE

To determine whether the compromised intestinal villus blood flow in a rat model of endotoxemia could be improved by continuous infusion of the phosphodiesterase (PDE) inhibitor milrinone.

METHODS

Twenty-four anesthetized and ventilated rats were laparotomized and an ileal portion was exteriorized and opened by an antimesenteric incision. The ileal segment was fixed with the mucosal surface upward. Microcirculatory parameters were assessed by intravital videomicroscopy. The animals were randomly assigned to receive one of three treatments: infusion of Escherichia coli lipopolysaccharides without phosphodiesterase inhibitor pretreatment (=LPS group); or infusion of LPS with milrinone pretreatment (= milrinone group), or without infusion of LPS or milrinone (=control group). Macrohemodynamic parameters (MAP, HR) and microhemodynamic parameters of ileal mucosa (mean diameter of central arterioles = D(A) and mean erythrocyte velocity within the arterioles= V(E)) were measured 30 min before and at 0, 60, and 120 min after induction of endotoxemia. Mucosal villus blood flow was calculated from D(A) and V(E).

RESULTS

In the milrinone group MAP decreased 60 min after induction of endotoxemia whereas it remained stable in the control and the LPS group. In both groups given endotoxin V(E) decreased after start of LPS infusion. In contrast, D(A) decreased in the LPS group, but increased in the milrinone group after 120 min of endotoxemia. Thus, the endotoxin-induced decrease of intestinal villus blood flow was diminished but not fully restored by milrinone infusion.

CONCLUSION

Our results indicate that milrinone has some beneficial microcirculatory effects during endotoxemia. Although it contributed to systemic hypotension, it attenuated intestinal mucosal hypoperfusion.

Changes in circulating lymphocyte subpopulations and mitogen-stimulated response in a rat infusion model of intra-abdominal infection

OBJECTIVE

To describe the alterations in circulating concentrations of immune cells as well as in in vitro mitogen-stimulated response in a recently developed rat model of intra-abdominal infection.

DESIGN

Randomized, controlled study.

SETTING

Government research facility.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Infected animals received an intraperitoneal infusion of 6.0 x 10(8) colony forming units of Escherichia coli during 12 hrs, whereas control rats received a sterile inoculum. All experimental animals underwent laparotomy and peritoneal lavage at the end of the infusion period. Blood samples were obtained 12 hrs, 36 hrs, or 7 days after the onset of infusion. Splenocytes were concomitantly harvested and assayed for response to the mitogens phytohemagglutinin (PHA), concanavalin A (Con A), and lipopolysaccharides, as well as for production of interleukin (IL)-2.

MEASUREMENTS AND MAIN RESULTS

Infected rats showed a marked leukopenia (-82% for 36 hrs), with leukocyte counts returning to normal at 7 days. They also developed a marked lymphocytopenia throughout the study; this was achieved through comparable reductions in circulating T and B cells. Con A responses in both groups were similar for 7 days. In contrast, splenocytes from infected animals showed reduced responses to lipopolysaccharides (-64%) and PHA (-30%) for 36 hrs compared with control splenocytes. IL-2 production from mitogen-stimulated splenocytes was suppressed in infected rats to 66% of that of control rats for 7 days. Suppressed PHA responses were not restored to control values in the presence of IL-2. For all of the parameters assessed, control animals showed either no significant changes or relatively fewer changes than infected rats.

CONCLUSIONS

This model of intra-abdominal infection is associated with changes in circulating concentrations of immune cells as well as with temporary functional defects in B and T cells, consistent with those often observed in patients with peritonitis. However, the role of IL-2 in limiting the adverse effects of infection in this experimental model seems to be limited. This model may be a useful tool in furthering our understanding of the pathophysiology of intra-abdominal infections and in assessing the efficacy of new therapeutic modalities.

Severe sepsis and septic shock. Definitions, epidemiology, and clinical manifestations

Severe sepsis and septic shock are frequently encountered conditions in today's hospital environment. The incidence appears to be increasing despite our growing armamentarium of antibiotics and our enhanced knowledge of the pathophysiologic processes at play. The clinical presentation may take a variety of forms, especially in patients at the extremes of age and in the immunocompromised population. A high index of suspicion and prompt institution of appropriate antimicrobial treatment is mandatory for a successful outcome. It is hoped that adoption of uniform definitions will aid in research and in effective communication concerning sepsis and its adverse sequelae.

Lipoteichoic Acid inhibits Lipopolysaccharide-Induced Adhesion Molecule Expression and IL-8 Release in Human Lung Microvascular Endothelial Cells

Cell adhesion molecule expression (CAM) and IL-8 release in lung microvascular endothelium facilitate neutrophil accumulation in the lung. This study investigated the effects of lipoteichoic acid (LTA), a cell wall component of Gram-positive bacteria, alone and with LPS or TNF-α, on CAM expression and IL-8 release in human lung microvascular endothelial cells (HLMVEC). The concentration-dependent effects of Staphylococcus aureus (S. aureus) LTA (0.3–30 μg/ml) on ICAM-1 and E-selectin expression and IL-8 release were bell shaped. Streptococcus pyogenes (S. pyogenes) LTA had no effect on CAM expression, but caused a concentration-dependent increase in IL-8 release. S. aureus and S. pyogenes LTA (30 μg/ml) abolished LPS-induced CAM expression, and S. aureus LTA reduced LPS-induced IL-8 release. In contrast, the effects of S. aureus LTA with TNF-α on CAM expression and IL-8 release were additive. Inhibitory effects of LTA were not due to decreased HLMVEC viability, as assessed by ethidium homodimer-1 uptake. Changes in neutrophil adhesion to HLMVEC paralleled changes in CAM expression. Using RT-PCR to assess mRNA levels, S. aureus LTA (3 μg/ml) caused a protein synthesis-dependent reduction (75%) in LPS-induced IL-8 mRNA and decreased the IL-8 mRNA half-life from &gt;6 h with LPS to ∼2 h. These results suggest that mechanisms exist to prevent excessive endothelial cell activation in the presence of high concentrations of bacterial products. However, inhibition of HLMVEC CAM expression and IL-8 release ultimately may contribute to decreased neutrophil accumulation, persistence of bacteria in the lung, and increased severity of infection.

Bacteremia in HIV-infected patients: short-term predictors of mortality

To identify characteristics associated with mortality in HIV-infected patients with bacteremia, 88 bacteremic episodes in 80 HIV-infected patients were prospectively identified over a 5-month period and observed for 30 days. Demographic, clinical, laboratory, and radiologic data were collected. Mean and median age was 41 years. Most study subjects were homosexual men. Median CD4 count was 20 cells/mm3. Gram-positive organisms predominated (65%). The most common source of bacteremia was intravascular catheters (45%). Overall mortality was 30%. A history of malignancy, three or more opportunistic infections, shock, low hemoglobin, source of bacteremia other than an intravascular catheter, resistance to therapy, and a second bacteremic episode during the study period, were all found to be independent predictors of mortality. In this cohort of HIV-infected patients, most of whom were severely immunosuppressed, several factors were found to be significantly and independently associated with mortality.

Signaling Events Induced by Lipopolysaccharide-Activated Toll-Like Receptor 2

Human Toll-like receptor 2 (TLR2) is a signaling receptor that responds to LPS and activates NF-κB. Here, we investigate further the events triggered by TLR2 in response to LPS. We show that TLR2 associates with the high-affinity LPS binding protein membrane CD14 to serve as an LPS receptor complex, and that LPS treatment enhances the oligomerization of TLR2. Concomitant with receptor oligomerization, the IL-1R-associated kinase (IRAK) is recruited to the TLR2 complex. Intracellular deletion variants of TLR2 lacking C-terminal 13 or 141 aa fail to recruit IRAK, which is consistent with the inability of these mutants to transmit LPS cellular signaling. Moreover, both deletion mutants could still form complexes with wild-type TLR2 and act in a dominant-negative (DN) fashion to block TLR2-mediated signal transduction. DN constructs of myeloid differentiation protein, IRAK, TNF receptor-associated factor 6, and NF-κB-inducing kinase, when coexpressed with TLR2, abrogate TLR2-mediated NF-κB activation. These results reveal a conserved signaling pathway for TLR2 and IL-1Rs and suggest a molecular mechanism for the inhibition of TLR2 by DN variants.

Influence of epinephrine and norepinephrine on intestinal villous blood flow during endotoxemia

PURPOSE

The objective of this study was to determine the effects of epinephrine and norepinephrine on mucosal villous blood flow in a normotensive model of endotoxemia.

MATERIALS AND METHODS

Thirty-two anesthetized rats were laparotomized, and a jejunal portion was exteriorized and opened by an antimesenteric incision. The jejunal segment was fixed on a plexiglass stage with the mucosal surface upward. Microcirculatory parameters were assessed by intravital videomicroscopy. The animals were randomly assigned to receive one of four treatments: infusion of Escherichia coli lipopolysaccharides (LPS, 2 mg/kg/h) without catecholamine pretreatment (LPS group); or infusion of LPS with epinephrine pretreatment (0.2 microg/kg/min, start 30 minutes before LPS infusion) (E group), or infusion of LPS with norepinephrine pretreatment (0.2 microg/kg/min, start 30 minutes before LPS infusion) (NE group). The control group did not receive either catecholamines or LPS. Mean diameter of central arterioles (D(A)) and mean erythrocyte velocity within the arterioles (V(E)) were measured 30 minutes before and at 0, 60, and 120 minutes after induction of endotoxemia. Mucosal villous blood flow was calculated from D(A) and V(E).

RESULTS

LPS infusion alone and norepinephrine plus LPS infusion led to a significant vasoconstriction of central arterioles, which was associated with a similar decrease in mucosal villous blood flow. Epinephrine infusion alone led to a vasodilation and an increase in villous blood flow within the first 30 minutes. After induction of endotoxemia, D(A) returned to baseline values and villous blood flow was as low as in the LPS and the norepinephrine group after 120 minutes.

CONCLUSION

In this experimental rat model, the catecholamines epinephrine and norepinephrine in a dosage of 0.2 microg.kg(-1).min(-1) neither diminish nor improve mucosal villous blood flow during the early phase of endotoxemia.

Human neutrophils secrete gelatinase B in vitro and in vivo in response to endotoxin and proinflammatory mediators

Bacterial sepsis is characterized by a systemic inflammatory state, with activation of numerous cell types. Phagocytes participate in this phenomenon by secreting various proinflammatory cytokines and enzymes. Matrix metalloproteinases (MMPs) such as gelatinases are produced by phagocytes and are thought to play an important role in processes of cell transmigration and tissue remodeling. In this work, we show that endotoxin (lipopolysaccharide [LPS]) and other inflammatory mediators, such as tumor necrosis factor (TNF), interleukin-8, and granulocyte colony-stimulating factor, induce a rapid (within 20 min) release of gelatinase-B (MMP-9) zymogen in whole human blood, as determined by gelatin zymography. The polymorphonuclear neutrophil was identified as the cell responsible for this rapid secretion, as a result of the release of preformed enzymes stored in granules. Normal human subjects given LPS intravenously showed a similar pattern of proMMP-9 secretion, with maximum plasma levels reached 1.5 to 3 h after LPS administration (P = 0.0009). Prior administration of TNF receptor:Fc, a potent TNF antagonist, to subjects given LPS, only partially blunted the release of proMMP-9 (P = 0.033). Ibuprofen, a cyclooxygenase inhibitor, did not alter this pattern of release. Increased levels of proMMP-9 and proMMP-2, as well as activated forms of MMP-9, were found in plasma from two patients with gram-negative sepsis. The levels of MMPs paralleled the severity of clinical condition and a marker of the severity of sepsis, plasma procalcitonin. These data indicate that MMPs are released in whole blood in response to various inflammatory mediators and that they could serve as sensitive and early markers for cell activation during the course of bacterial sepsis.

Isolation of highly enriched human monocytes from ten ml samples of heparinised whole blood

A detailed study of the immune dysregulation involved in systemic inflammation requires the analysis of the main inflammatory cells in the circulation - the monocytes. Blood samples available from patients are necessarily restricted so that a rapid and efficient method is required to isolate these cells. Here we present a protocol to isolate blood monocytes in high yield from small samples of heparinised blood. The method yields monocyte preparations with a purity greater than 96%.

Inhibition of glucocorticoid receptor binding by nitric oxide

Septic shock is a dangerous condition with high mortality rates. In sepsis, the inducible form of nitric oxide (NO) synthase is induced, releasing high amounts of NO. Glucocorticoids have potent anti-inflammatory properties and are very effective in inhibiting the induction of this enzyme if administered before the shock onset. It is known that glucocorticoid receptor (GR) has critical cysteine residues for steroid binding in its hormone-binding and DNA-binding domains. It has also been reported that NO reacts with ---SH groups, forming S-nitrosothiols. Therefore, we examined the potential effect of NO on the ligand-binding ability of GR. NO donors (S-nitroso-acetyl-DL-penicillamine, S-nitroso-DL-penicillamine, or S-nitroso-glutathione) decreased, in a time- and dose-dependent manner, the binding of [3H]triamcinolone to immunoprecipitated GR from mouse L929 fibroblasts. The nonnitrosylated parent molecules, N-acetyl-DL-penicillamine, and reduced gluthatione were without effect. Scatchard plots revealed that the number of ligand binding sites and Kd were reduced (50%) by NO donors. Western blot analysis ruled out the possibility that dissociation of GR/heat shock protein 90 heterocomplex or decrease in GR protein would account for the inhibitory effect of NO. Decreased ligand binding to GR was found when NO donors were incubated with intact fibroblasts. Incubation with NO donors also decreased the steroid-induced reduction in [3H]uridine incorporation into RNA. All of these NO effects were inhibited by the thiol-protecting agent dithiothreitol. Therefore, S-nitrosylation of critical ---SH groups in GR by NO with consequent decreases in binding and affinity may be the mechanisms which explain the failure of glucocorticoids to exert their anti-inflammatory effects in septic shock.

Anti-CD14 mAb treatment provides therapeutic benefit after in vivo exposure to endotoxin

The presence of endotoxin from Gram-negative bacteria signals the innate immune system to up-regulate bacterial clearance and/or killing mechanisms. Paradoxically, such responses also contribute to septic shock, a clinical problem occurring with high frequency in Gram-negative septicemia. CD14 is a receptor for endotoxin (lipopolysaccharide, LPS) and is thought to have an essential role in innate immune responses to infection and thereby in the development of septic shock. Using a novel rabbit model of endotoxic shock produced by multiple exposures to endotoxin, we show that anti-rabbit CD14 mAb, which blocks LPS-CD14 binding, protects against organ injury and death even when the antibody is administered after initial exposures to LPS. In contrast, anti-rabbit tumor necrosis factor mAb treatment fails to protect when administered after LPS injections. These results support the concept that anti-CD14 treatment provides a new therapeutic window for the prevention of pathophysiologic changes that result from cumulative exposures to LPS during septic shock in man.

Evidence that aminoguanidine inhibits endotoxin-induced bacterial translocation

BACKGROUND

The role of inducible nitric oxide synthase (iNOS) in endotoxin-induced bacterial translocation was investigated by using its specific blocker aminoguanidine in 46 albino mice (25-35 g) allocated into four groups.

METHODS

The first group received intraperitoneal saline (control; 0.9 per cent w v(-1) sodium chloride 1 ml kg(-1); n=6), the second group intraperitoneal endotoxin (Escherichia coli lipopolysaccharide 055:B5 20 mg kg(-1); n=19), the third group intraperitoneal aminoguanidine (20 mg kg(-1), 20 min before and 12 h after saline; n=6) and the fourth group both endotoxin and aminoguanidine intraperitoneally (n=15). Some 24 h later, the animals were anaesthetized with ether and blood samples were collected by cardiac puncture together with mesenteric lymph node (MLN), spleen and liver specimens under aseptic conditions. Specimens were then cultured to determine the presence of colony-forming units as an index of bacterial translocation.

RESULTS

No bacterial growth was detected in samples from the first and third groups. Colony-forming bacteria were found in ten of 14 MLN samples, eight of 14 spleens, four of 14 livers and three of 14 peripheral blood samples in the second group, with E. coli being the predominant pathogen. In contrast, in the fourth group, colony-forming bacteria were found in only three of 14 MLN samples (P=0.02 versus the second group), three of 14 spleens and one of 14 liver specimens. None of the values in the fourth group was significantly different from those in the saline control group.

CONCLUSION

The inhibition of iNOS during endotoxaemia by its specific blocker aminoguanidine attenuates the incidence of bacterial translocation in mice. These results may be exploited clinically for the prophylaxis and treatment of septic states.

Capillary and arteriolar responses to local vasodilators are impaired in a rat model of sepsis

Although sepsis is known to affect vascular function, little is known about changes at the capillary level. We hypothesized that sepsis attenuates the "upstream" arteriolar response to vasoactive agents applied locally to capillaries. Sepsis in rats was induced by cecal ligation and perforation. After 24 h, extensor digitorum longus muscle was prepared for intravital microscopy. Phenylephrine (PE, 10 mM) and acetylcholine (ACh, 10 mM) were applied iontophoretically on terminal arterioles and on their downstream daughter capillaries (300 micron from arteriole). There was no significant difference between control and septic rats in baseline arteriolar diameters [8.0 +/- 0.6 vs. 9.8 +/- 0.8 (SE) micron- or baseline red blood cell velocity (VRBC) in perfused daughter capillaries (255 +/- 10 vs. 264 +/- 13 micron/s). Application of PE onto arterioles resulted in comparable constrictions (i.e., -22% diameter change) and VRBC reductions (-100%) in control and septic rats. In contrast, arteriolar diameter and VRBC increases after application of ACh were attenuated in sepsis (diameter: from 41 to 14%; VRBC: from 67 to 24%). Application of PE onto the capillary reduced VRBC to the same level (-100%) in both groups, whereas application of ACh increased VRBC less in septic than in control rats (20 vs. 73%). On the basis of arteriolar-capillary pair stimulations, sepsis affected VRBC responses to ACh more in the capillary than in the arteriole. When the adenosine analog 5'-N-ethylcarboxamidoadenosine (0.1 mM) was used instead of ACh, similar effects of sepsis were seen. To test for a possible involvement of inducible NO synthase (iNOS) in sepsis-induced attenuated ACh responses, arterioles and capillaries in septic animals were locally pretreated with the iNOS blocker aminoguanidine (10 mM). In both microvessels, aminoguanidine restored the ACh response to the control level. We conclude that impaired capillary VRBC and arteriolar diameter responses to vasodilators applied to capillaries in septic rat skeletal muscle were due to dysfunction at arteriolar and capillary levels. The study underscores the significant role iNOS/NO may play in sepsis-induced alteration of vascular reactivity in vivo.

Chronic ethanol ingestion impairs alveolar type II cell glutathione homeostasis and function and predisposes to endotoxin-mediated acute edematous lung injury in rats

Chronic alcohol abuse increases the incidence and mortality of the acute respiratory distress syndrome (ARDS) in septic patients. To examine a potential mechanism, we hypothesized that ethanol ingestion predisposes to sepsis-mediated acute lung injury by decreasing alveolar type II cell glutathione homeostasis and function. Lungs isolated from rats fed ethanol (20% in water for >/= 3 wk), compared with lungs from control-fed rats, had greater (P < 0. 05) edematous injury (reflected by nonhydrostatic weight gain) after endotoxin (2 mg/kg intraperitoneally) and subsequent perfusion ex vivo with n-formylmethionylleucylphenylalanine (fMLP, 10(-7) M). Ethanol ingestion decreased (P < 0.05) glutathione levels in the plasma, lung tissue, and lung lavage fluid, and increased (P < 0.05) oxidized glutathione levels in the lung lavage fluid. Furthermore, ethanol ingestion decreased type II cell glutathione content by 95% (P < 0.05), decreased (P < 0.05) type II cell surfactant synthesis and secretion, and decreased (P < 0.05) type II cell viability, in vitro. Finally, treatment with the glutathione precursors S-adenosyl-L-methionine and N-acetylcysteine in the final week of ethanol ingestion significantly reduced lung edema during perfusion ex vivo. We conclude that ethanol ingestion in rats alters alveolar type II cell glutathione levels and function, thereby predisposing the lung to acute edematous injury after endotoxemia. We speculate that chronic alcohol abuse in humans predisposes to ARDS through similar mechanisms.

Heat stress increases survival rates in lipopolysaccharide-stimulated rats

OBJECTIVE

To examine the hypothesis that heat stress applied after the administration of bacterial endotoxin is protective.

DESIGN

Prospective, randomized, laboratory study.

SETTING

University research laboratory.

SUBJECTS

One hundred eleven adult male Sprague-Dawley rats (weight range 250 to 400 g).

INTERVENTIONS

Production of endotoxemia by the administration of a bacterial endotoxin and exposure to heat stress by heating animals in a neonatal incubator until their rectal temperatures reached 105.8 degrees F (41 degrees C).

MEASUREMENTS AND MAIN RESULTS

The rats (n = 111) were anesthetized and were injected with 15 mg/kg of Escherichia coli endotoxin (lipopolysaccharide, LPS) intravenously to produce septic shock. Immediately thereafter, a set of 50 rats were randomly assigned to one of two treatment groups: a) LPS-treated (control); or b) LPS-treated and heated to 105.8 degrees F (41 degrees C). The animals were then observed for the development of fever, and survival rates were monitored for 72 hrs. In another set of 40 animals, the same experimental protocol was used to determine plasma cytokine concentrations in heated and nonheated groups. Blood samples were obtained at 0, 2, 4, or 6 hrs after LPS injection for tumor necrosis factor-alpha and interleukin (IL)-1 beta detection. In a third set of animals, the same experimental protocol was applied to nine animals for the detection of heat-shock proteins of 72-kilodalton molecular weight. LPS injection in the control group did not produce fever. Heat stress increased the abundance of heat-shock proteins of 72-kilodalton molecular weight in the rats' lungs (analysis of variance, p = .016). Twelve hours after the initiation of sepsis, the survival rates of the control group injected with LPS alone and the group heated to 105.8 degrees F (41 degrees C) were 48% and 80%, respectively (p = .039). The peak plasma IL-1 beta concentrations occurring at 2 hrs after LPS injection were significantly reduced in rats heated to 105.8 degrees F (41 degrees C) when compared with nonheated rats (p = .003).

CONCLUSION

We conclude that heat stress applied after the initiation of endotoxemia can provide protection against an otherwise lethal stimulus and that the mechanism of protection may be related to the attenuation of plasma IL-1 beta concentrations.

Central amygdala Fos expression during hypotensive or febrile, nonhypotensive endotoxemia in conscious rats

The distribution and time course of Fos expression in neurons in the central nucleus of the amygdala (CeA) were studied in endotoxemic rats in two separate experiments. In each case, the severity of the endotoxin (lipopolysaccharide; LPS) challenge was characterized by using physiological outcome variables, including blood pressure and heart rate. Throughout the rostrocaudal extent of the CeA, extensive Fos staining was found 3 hours after injection with a hypotensive dose of Salmonella enteritidis LPS. Hypotension alone has been reported to induce Fos in the CeA; therefore, the remaining experiments were performed by using a lower dose of Escherichia coli LPS that did not cause hypotension. The nonhypotensive dose of E. coli LPS also induced Fos in large numbers of neurons of the CeA, with peak staining at 2 hours and Fos staining persisting for 6 hours after LPS injection. Tachycardia and fever after LPS also persisted for at least 6 hours. CeA Fos staining during nonhypotensive endotoxemia was predominantly located in the lateral subnucleus, although Fos-stained medial sub-nucleus neurons were also present. Additional forebrain regions that showed persistent Fos staining 6 hours after LPS included the parvocellular paraventricular nucleus of the hypothalamus, the bed nucleus of the stria terminalis, and the medial preoptic area. Forebrain regions that contained Fos-stained nuclei at earlier time points, but not at 6 hours, included the supraoptic nucleus, magnocellular regions of the paraventricular nucleus of the hypothalamus, the subfornical organ, and the organum vasculosum of the lamina terminalis. Few CeA neurons showed Fos staining in rats that were restrained in a ventilated plastic tube. Neurons in the lateral septal nucleus and the medial amygdaloid nucleus, which have numerous Fos-stained nuclei after stressors such as footshock or restraint, did not show Fos staining above control levels after LPS administration. Activation of CeA neurons after intravenous LPS may indicate persistent drive from vagal afferents and may implicate the CeA in the autonomic, neuroendocrine, and/or behavioral responses to this treatment.

Urinary pyridinium cross-link excretion is increased in critically ill surgical patients

OBJECTIVES

To determine: a) the rate of pyridinium cross-links of collagen excretion, breakdown products of bone, in critically ill surgical patients in the intensive care unit (ICU); and b) the relationship between cross-link excretion and nitrogen excretion and balance to ascertain whether collagen breakdown products contribute to protein losses during a hypercatabolic state.

DESIGN

Observational study starting on the first postoperative day to 20 days or until discharge.

SETTING

A surgical ICU in a University hospital.

PATIENTS

Nine mechanically ventilated, postoperative surgical patients (73 +/- 3 [SD] yrs), receiving routine parenteral nutrition (18% protein) and 17 age-matched healthy subjects.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Resting energy expenditure was determined daily for < or = 5 days after admission, and energy intake was set at 1.04 times the initial energy expenditure; thereafter, values of intake were reset weekly. Daily 24-hr urine samples were analyzed for cross-links, total and urea nitrogen, calcium, and creatinine for 20 days or until discharge. Two urine samples were also analyzed for cross-links in the healthy subjects. The excretion of cross-links from the surgical patients was markedly higher (p < .001) than in the healthy subjects, and calcium balance was significantly negative (p < .05). Patients who were discharged from the ICU within 5 days showed a lower rate of cross-link excretion (p < .02) and less day-to-day variability, compared with those patients who stayed longer, whether calculated over the course of the study or over the first 2 days in the ICU. There was no correlation between cross-links and energy expenditure, nitrogen excretion, or balance.

CONCLUSIONS

The rate of cross-link excretion in critically ill patients: a) is markedly increased; b) is greater within the first two postoperative days in those patients who have an extended stay (> 5 days) in the ICU; and c) is independent of the rate of nitrogen excretion. These findings suggest that critically ill postoperative patients experience an acute breakdown of collagen, which is likely due to resorption of bone or possibly comes from other collagen sources.

Dopexamine maintains intestinal villus blood flow during endotoxemia in rats

OBJECTIVE

To determine the influence of dopexamine, a synthetic catecholamine ligand for dopaminergic and beta 2-adrenergic receptors, on alterations of the intestinal villus microcirculation in a model of normotensive endotoxemia.

DESIGN

Randomized, controlled trial.

SETTING

Experimental laboratory.

SUBJECTS

Twenty-one male Wistar rats.

INTERVENTIONS

Rats were treated with a continuous infusion of dopexamine (2.5 micrograms/kg/min; N = 7; group A) or 0.9% saline (n = 7; group B) during a study period of 120 mins. Both groups were given endotoxin (Escherichia coli lipopolysaccharide; 1.5 mg/kg Iv) over 60 mins. Animals in the control group (n = 7; group C) received a volume-equivalent infusion of 0.9% saline. Total volume substitution in all groups was 15 mL/kg/hr.

MEASUREMENTS AND MAIN RESULTS

Blood flow in the intestinal villi of the distal ileum was determined using in vivo videomicroscopy at baseline, and 60 and 120 mins after the endotoxin challenge. These blood flow determinations were done by an observer who was unaware of the previous treatment of the animals. In addition, mean arterial pressure was monitored at baseline, and 15, 30, 45, 60, 75, 90, 105, and 120 mins later. The administration of 1.5 mg/kg endotoxin alone (group B) resulted in a reduction of the intestinal villus blood flow to 74.8 +/- 9.5% of baseline after 60 mins, and to 61.1 +/- 8.5% of baseline after 120 mins (baseline: 7.4 +/- 0.6 nL/min; 60 mins: 5.3 +/- 0.8 nL/min; 120 mins: 4.4 +/- 0.5 nL/min; p < .05). This reduction of blood flow was associated with a decrease in the arteriolar diameters by 13.8 +/- 2.5% after 60 mins, and by 17.1 +/- 4.3% after 120 mins (p < .05 vs. baseline). In contrast, villus blood flow in the dopexamine group (group A) did not show statistically significant changes during the entire study period, despite the administration of endotoxin (baseline: 8.2 +/- 0.6 nL/min; 60 mins: 7.3 +/- 0.8 nL/min; 120 mins: 7.8 +/- 0.5 nL/min). No vasoconstriction of the villus arterioles was noted in this group. In control animals (group C), the blood flow (baseline: 8.1 +/- 1.6 nL/min; 60 mins: 7.6 +/- 1.4 nL/min: 120 mins: 7.8 +/- 1.4 nL/min) and the arteriolar diameters remained unchanged throughout the observation period. Mean arterial pressure did not differ between groups: it remained unaltered in all groups during the entire study period.

CONCLUSIONS

Dopexamine maintains intestinal villus arterial perfusion and prevents the vasoconstriction in villus arterioles during early normotensive endotoxemia. Therefore, further studies in critically ill patients will have to determine whether the early prophylactic use of dopexamine can limit ischemia and prevent the development of multiple organ failure.