Divergent efficacy of antibody to tumor necrosis factor-alpha in intravascular and peritonitis models of sepsis

Animal and human models for sepsis

Several preclinical models for sepsis have been used in the last decades to successfully unravel the pathophysiologic processes during sepsis. Furthermore, these models for sepsis revealed promising immunomodulating agents for the treatment of sepsis. Nevertheless, several clinical trials evaluating the efficacy of these new anti-inflammatory agents in septic patients showed disappointing results. In this article the advantages and disadvantages of different models for sepsis are discussed. Most models for sepsis lack an infectious focus. Importantly, investigations studying the effects of several immunomodulating strategies have demonstrated strikingly opposite results when using models for sepsis lacking an infectious focus and when using models for sepsis with a more natural route of infection. These differences will be discussed in this article. In general, it is advised to use a combination of models to test a new therapeutic agent, before starting a clinical study evaluating this new therapy.

CXC chemokine redundancy ensures local neutrophil recruitment during acute inflammation

Previous publications demonstrated that elevated systemic levels of interleukin (IL)-8 decrease local neutrophil recruitment. We tested whether sustained, high plasma levels of IL-8 would prevent local inflammation after inflammatory insults. Mice carrying the transgene for human IL-8 were separated on the basis of their plasma levels of IL-8 into IL-8-positive (plasma levels >90 ng/ml) and IL-8-negative (IL-8 below detection). Presence of the IL-8 transgene did not improve survival or morbidity nor did it alter peritoneal neutrophil recruitment induced by the cecal ligation and puncture model of sepsis. In an acute lung injury model created by intratracheal injection of acid, IL-8-positive mice showed no reduction in alveolar neutrophil recruitment. There was no difference in the local recruitment of neutrophils when either thioglycollate or glycogen was injected intraperitoneally. We examined the chemotactic response to murine chemokines to test how neutrophil recruitment occurs in the setting of elevated plasma IL-8 and found that neutrophils from both IL-8-positive and -negative mice respond equally well to recombinant KC or macrophage inflammatory protein (MIP)-2. We measured KC and MIP-2 in the peritoneum after thioglycollate injection and demonstrated that IL-8-positive mice have significantly higher levels of the chemokines compared to the IL-8-negative mice. Antibody inhibition of KC and MIP-2 in the IL-8-positive mice significantly decreased peritoneal neutrophil recruitment in response to thioglycollate, clarifying their important role in the local neutrophil recruitment. Our data demonstrate that despite the presence of high plasma levels of IL-8, neutrophils may still be recruited to sites of local inflammation because of chemokine redundancy.

Intrahepatic nuclear factor-kappa B activity and alpha 1-acid glycoprotein transcription do not predict outcome after cecal ligation and puncture in the rat

OBJECTIVE

Sepsis is the leading cause of death in critically ill surgical patients. Septic hepatic dysfunction, an important determinant of outcome, is poorly understood but includes inappropriate transcriptional down-regulation. This may be modulated by proinflammatory cytokines. We hypothesized that intrahepatic changes in tumor necrosis factor (TNF)/interleukin (IL)-1-linked processes, such as the activation of the p50 homodimeric and the p65/p50 heterodimeric isoforms of the transcription factor nuclear factor (NF)-kappaB or transcription of the acute phase reactant alpha1-acid glycoprotein (AGP), would correlate with recovery from sepsis.

DESIGN

Prospective experimental comparison of sham operation and nonlethal and lethal sepsis in male Sprague-Dawley rats.

INTERVENTIONS

Nonlethal sepsis was induced by using single-puncture cecal ligation and puncture (CLP). Lethal sepsis was induced via double-puncture CLP. NF-kappaB DNA binding activity was determined by using electrophoretic mobility shift analysis with differentiation of p50/p50 and p50/p65 isoforms by using appropriate antibodies. AGP transcription was assessed with transcription elongation analysis, intrahepatic IL-1beta, and TNF-alpha abundance by using immunohistochemistry, and serum IL-1beta was assessed by using ELISA.

MAIN RESULTS

Overall NF-kappaB activity increased equivalently over time after both single- and double-puncture CLP, with a peak occurring 3 hrs after intervention. In single-puncture CLP, there was an increase in the binding of the p50 homodimer form over time. After double-puncture CLP, no such change was observed. AGP transcription was increased equivalently in both models. Intrahepatic IL-1beta was detected 16 and 24 hrs after single-puncture CLP and 6 hrs after double-puncture CLP. After double-puncture CLP, intrahepatic TNF-alpha was detected at 6, 16, and 24 hrs. Serum IL-1beta was undetectable after both single- and double-puncture CLP.

CONCLUSIONS

Although AGP transcription was similar in mild and fulminant sepsis, double-puncture CLP increased the binding activity of the p50 homodimer relative to binding of the p50/p65 NF-kappaB heterodimer. These results imply that transcriptional activity not linked to acute phase responses is an important determinant of outcome in sepsis.

Tumor necrosis factor-dependent adhesions as a major protective mechanism early in septic peritonitis in mice

The occurrence of peritoneal adhesions in surgical patients is positively correlated with tumor necrosis factor (TNF) levels. In a model of septic peritonitis-cecal ligation and puncture-TNF neutralization prevented formation of peritoneal adhesions and increased mortality, most likely because localization of the septic focus was prevented. To discriminate between the coagulation-independent protective TNF effect and a potential protective procoagulant TNF effect, formation of peritoneal adhesions after CLP was inhibited with heparin, hirudin, or urokinase. Each treatment increased mortality and increased the number of bacteria in the peritoneal lavage fluid, kidney, and liver to various degrees. Under these experimental conditions, antibiotics prevented death. In coagulation-compromised mice, lethality was further enhanced by additional TNF neutralization. These findings demonstrate that peritoneal adhesions early in septic peritonitis are an important mechanism of innate immunity that prevents increased spread of bacteria and reduces mortality.

IL-10-deficient mice demonstrate multiple organ failure and increased mortality during Escherichia coli peritonitis despite an accelerated bacterial clearance

To determine the role of endogenous IL-10 in local antibacterial host defense and in the development of a systemic inflammatory response syndrome during abdominal sepsis, IL-10 gene-deficient (IL-10(-/-)) and wild-type (IL-10(+/+)) mice received an i.p. injection with Escherichia coli. Peritonitis was associated with a bacterial dose-dependent increase in IL-10 concentrations in peritoneal fluid and plasma. The recovery of E. coli from the peritoneal fluid, blood, and lungs was diminished in IL-10(-/-) mice, indicating that endogenous IL-10 impaired bacterial clearance. Despite a lower bacterial load, IL-10(-/-) mice had higher concentrations of TNF, macrophage inflammatory protein-2 and keratinocyte in peritoneal fluid and plasma, and demonstrated more severe multiple organ damage as indicated by clinical chemistry and histopathology. Furthermore, IL-10(-/-) mice showed an increased neutrophil recruitment to the peritoneal cavity. To examine the role of elevated TNF levels in the altered host response in IL-10(-/-) mice, the effect of a neutralizing anti-TNF mAb was determined. Anti-TNF did not influence the clearance of E. coli in either IL-10(+/+) or IL-10(-/-) mice. Furthermore, anti-TNF did not affect leukocyte influx in the peritoneal fluid, multiple organ damage, or survival in IL-10(+/+) mice. In IL-10(-/-) mice, anti-TNF partially attenuated neutrophil recruitment and multiple organ damage, and prevented the increased lethality. These data suggest that although endogenous IL-10 facilitates the outgrowth and dissemination of bacteria during E. coli peritonitis, it protects mice from lethality by attenuating the development of a systemic inflammatory response syndrome by a mechanism that involves inhibition of TNF release.

Effects of soluble TNF receptor treatment on lipopolysaccharide-induced myocardial cytokine expression

Tumor necrosis factor (TNF)-alpha plays a key role in the pathogenesis of septic shock syndrome, and myocardial TNF-alpha expression may contribute to this pathophysiology. We examined the myocardial expression of TNF-alpha-related cytokines and chemokines in mice exposed to lipopolysaccharide (LPS) and tested the effects of anti-TNF therapy on myocardial cytokine expression. Cytokine mRNA levels were measured by RNase protection assay, and protein levels in the plasma and myocardium were assessed by enzyme-linked immunosorbent assays. LPS (4 microg/g body wt ip) induced marked cytokine expression, including TNF-alpha, interleukin (IL)-1beta, IL-6, and monocyte chemotactic protein (MCP)-1, in both the plasma and myocardium. Pretreatment with adenovirus-mediated TNF receptor fusion protein (AdTNFR1; 10(9) plaque-forming units iv) decreased plasma cytokine levels. In contrast, whereas myocardial IL-1beta expression was also suppressed, expression of IL-6 and MCP-1 was not inhibited by AdTNFR1. In summary, anti-TNF treatment differentially altered the cytokine expression in the plasma and myocardium during endotoxemia. Inability to block myocardial expression of IL-6 and MCP-1 suggests a possible mechanism for the failure of anti-TNF therapies in the treatment of endotoxin shock.

Experimental models of gram-negative sepsis

BACKGROUND

The mortality rate from sepsis has improved little over the past two decades. One reason for this has been the use of flawed or inappropriate experimental models in preclinical sepsis studies.

METHODS

A literature review of animal models of sepsis was performed following a Medline search based on the following medical subject headings: disease models, endotoxin, inflammation, peritonitis and sepsis. Additional references were identified from the papers identified in the search.

RESULTS AND CONCLUSION

Many animal models of sepsis have been described but none has proved to be superior. Extrapolation of results from endotoxicosis or bacterial infusion models should be regarded with caution. Peritonitis models should be accepted as the 'gold standard' but the use of appropriate virulent bacterial species needs to be ensured. A standardized panel of animal models for the preclinical assessment of immunomodulatory agents should be established, including at least one immuno- suppressed model to simulate the immunocompromised patient with sepsis. A uniform and valid definition of sepsis applicable to both small and large animal species is required.

Microspheres containing neutralizing antibodies to tumor necrosis factor-alpha and interleukin-1 beta protect rats from Staphylococcus aureus-induced peritonitis

Previous studies using microencapsulated neutralizing antibodies (NA) to tumor necrosis factor (TNF) and interleukin-1 (IL-1) in combination with gentamicin have demonstrated improved survival in a peritonitis model of gram-negative septic shock. Microencapsulation has been shown to improve the effectiveness of NA by delivering them intracellularly, taking advantage of the natural phagocytic activity of the macrophage. It is the purpose of this study to see if microencapsulated NA to TNF and IL-1 in combination with vancomycin can improve survival compared with NA in solution in Staphlococcus aureus-induced septic shock. Groups of 10 rats received the following treatments: (1) S. aureus plus no treatment, (2) S. aureus plus blank microspheres, (3) S. aureus plus vancomycin, (4) S. aureus plus a microsphere form of NA and vancomycin, (5) S. aureus plus a solution form of NA and vancomycin, (6) S. aureus plus a microsphere form of NA, and (7) S. aureus plus a solution form of NA. Survival was monitored for 5 days, and plasma TNF and IL-1 levels were measured for 48 h after S. aureus administration. All (100%) animals that received the microsphere form of NA plus vancomycin, 20%-70% of the animals that received the microsphere form of NA alone, and 20% of the animals that received antibiotics alone survived for 5 days or more. None of the animals in the no treatment group or blank microsphere treatment group and only 10% of the animals in the solution form of NA plus or minus vancomycin group survived for more than 5 days. Plasma TNF and IL-1 levels were significantly increased after S. aureus treatment. Simultaneous and delayed treatment with the microsphere form of NA plus or minus vancomycin significantly reduced TNF and IL-1 levels, and the solution form of NA significantly reduced only TNF levels after immediate treatment. The survival rate was higher in animals with lower TNF levels and IL-1 levels. The results demonstrate that the microsphere form of cytokine NA is 100% effective in combination with vancomycin in protecting rats from S. aureus-induced peritonitis. The microsphere form was also more efficient in attenuating both TNF and IL-1 levels.

Experimental study on the possibility of treatment of some hemorrhagic fevers

After intracerebral challenge with 100 PFU of Lassa virus (strain Josiah), all infected mice (CBA/calac) died (control group). Production of pro-inflammatory cytokines (IL-1beta, TNF-alpha) significantly increased in the blood of these mice during the infection. For neutralization of increasing concentrations of these cytokines recombinant IL-1RA was used intraperitonealy at a dose 100 microg kg(-1), everyday, within 5 days from the third day after the challenge. Injections of IL-1RA decreased the concentration of IL-1beta and TNF-alpha and resulted in survival of all infected mice (treatment group). Marburg fever (strain Popp) caused in guinea pigs by 5 LD(50) of virus lead to the significant increase of TNF-alpha in the animal's blood and caused a lethal outcome (control group). Treatment of infected guinea pigs by IL-1RA or anti-TNF serum decreased the concentration of TNF-alpha and resulted in survival of half of the animals (treatment group). For the treatment recombinant IL-1RA was used at a dose 100 microg kg(-1), intramuscularly, everyday, within 6 days from the third day after the challenge or anti-TNF serum, intramuscularly 0.5 ml (2000 U ml(-1); 1 U of the antiserum neutralises 0.03 ng of TNF-alpha), everyday, within 6 days from the third day after the challenge.

Tissue factor pathway of coagulation in sepsis

OBJECTIVE

To review the role of the tissue factor pathway of coagulation in experimental sepsis.

DATA SOURCES

Studies published in biomedical journals.

STUDY SELECTION

Studies on the role of the tissue factor pathway in animal or human models for sepsis.

DATA EXTRACTION AND SYNTHESIS

Variables reflecting tissue factor pathway activation in the various models are discussed; the effects of administration of tissue factor pathway inhibitors on these and inflammatory variables, as well as on the course and outcome, are analyzed.

CONCLUSION

Activation of coagulation during experimental sepsis occurs mainly, if not exclusively, via the tissue factor pathway; inhibitors of this pathway improve mortality, presumably by a combined attenuating effect on coagulative and inflammatory responses.

Anti-inflammatory therapies in sepsis and septic shock

Despite advances in supportive care, the morbidity and mortality rate resulting from sepsis and septic shock remain high (30 - 50%). A central hypothesis driving sepsis research in recent years is that this syndrome is the result of excessive inflammation. Therapies designed to inhibit the inflammatory response were first shown to be markedly beneficial in animal models of sepsis and then tested in numerous clinical trials involving thousands of patients. Three broad anti-inflammatory strategies have been investigated. First, glucocorticoids in high doses administered at the onset of sepsis were studied. This approach proved unsuccessful. More recently, however, glucocorticoids in lower doses have been found to have a beneficial effect in patients with septic shock. Whether the mechanism of this treatment benefit is through inhibition of inflammation, or by counteracting a relative steroid refractoriness occurring during sepsis, remains unknown. The next focus of research were agents active against the endotoxin molecule. However, as with the experience with glucocorticoids, this approach lacked a consistent pattern of efficacy. It is unclear if this lack of efficacy is the result of endotoxin being a poor therapeutic target, or from testing agents which lacked the appropriate biological activity. Most recently, clinical trials in sepsis have focused on inhibiting specific host pro-inflammatory mediators (e.g., TNF, interleukins). While individual trials of inhibitors of these pro-inflammatory mediators failed to show a convincing benefit, pooling the results of these trials suggest that this approach has a marginal effect, supporting a role for excessive inflammation in sepsis. An unanswered question is reconcilling the very favourable effects obtained with anti-inflammatory treatments in animal models with the marginal results in humans. Further clinical and laboratory research is needed and may provide insight into more effective ways to use the anti-inflammatory agents already tested, or to investigate other potentially more effective anti-inflammatory agents in this syndrome.

Peritoneal cytokine concentrations and survival outcome in an experimental bacterial infusion model of peritonitis

OBJECTIVE

To correlate the dynamics of peritoneal cytokines with systemic concentrations and survival outcome.

DESIGN

Randomized, controlled study using a recently developed rat model of peritonitis.

SETTING

Government research facility.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Infected animals (INF) received an intraperitoneal infusion of 6.5 x 10(8) colony-forming units of Escherichia coli over 12 hrs, whereas control rats (CON) received a sterile inoculum. Peritoneal fluid and plasma samples were obtained from all rats at the end of the 12-hr infusion period as well as from all animals that survived the 7-day study (SURV).

MEASUREMENTS AND MAIN RESULTS

Interleukin (IL)-1beta concentration in the peritoneal fluid at 12 hrs tended to be higher in nonsurvivors (NONSURV) than in SURV. Tumor necrosis factor-alpha and IL-6 peritoneal concentrations at 12 hrs were significantly greater in NONSURV than in SURV. There were no significant differences in IL-2 and IL-4 peritoneal concentrations at 12 hrs between SURV and NONSURV. Although the concentrations of IL-1beta and tumor necrosis factor-alpha in the peritoneal fluid of INF decreased gradually during the study, these concentrations remained significantly higher than those of CON at 7 days. In contrast, peritoneal IL-2 concentrations remained lower in INF than in CON for most of the experiment. Peritoneal IL-6 concentrations in INF were transiently elevated above those of CON for 12 hrs. Cytokine concentrations in the peritoneal fluid of INF were always higher than those in plasma, which remained relatively unchanged throughout the study. For most of the variables as. sessed, CON showed no significant changes compared with INF.

CONCLUSIONS

This model of peritonitis is associated with a significant and prolonged peritoneal inflammatory response that is adversely correlated with survival outcome. Our data would suggest that to be effective, novel immunotherapies should target mainly the peritoneal compartment.

Protection from septic shock by neutralization of macrophage migration inhibitory factor

Identification of new therapeutic targets for the management of septic shock remains imperative as all investigational therapies, including anti-tumor necrosis factor (TNF) and anti-interleukin (IL)-1 agents, have uniformly failed to lower the mortality of critically ill patients with severe sepsis. We report here that macrophage migration inhibitory factor (MIF) is a critical mediator of septic shock. High concentrations of MIF were detected in the peritoneal exudate fluid and in the systemic circulation of mice with bacterial peritonitis. Experiments performed in TNFalpha knockout mice allowed a direct evaluation of the part played by MIF in sepsis in the absence of this pivotal cytokine of inflammation. Anti-MIF antibody protected TNFalpha knockout from lethal peritonitis induced by cecal ligation and puncture (CLP), providing evidence of an intrinsic contribution of MIF to the pathogenesis of sepsis. Anti-MIF antibody also protected normal mice from lethal peritonitis induced by both CLP and Escherichia coli, even when treatment was started up to 8 hours after CLP. Conversely, co-injection of recombinant MIF and E. coli markedly increased the lethality of peritonitis. Finally, high concentrations of MIF were detected in the plasma of patients with severe sepsis or septic shock. These studies define a critical part for MIF in the pathogenesis of septic shock and identify a new target for therapeutic intervention.

Inflammatory cytokine response in patients with septic shock secondary to generalized peritonitis

OBJECTIVES

The aims of this study were the following: a) to assess the proinflammatory cytokine (tumor necrosis factor [TNF]-alpha, interleukin [IL]-1, and IL-6) response in patients with septic shock secondary to generalized peritonitis; and b) to evaluate the influence of bacteremic status, type of peritonitis (acute perforation or postoperative), and peritoneal microbial status (mono- or polymicrobial) on cytokine expression and mortality.

DESIGN

Prospective study.

SETTING

Surgical intensive care unit of a university hospital.

PATIENTS

Fifty-two consecutive patients with septic shock caused by generalized peritonitis.

INTERVENTIONS

Routine blood tests, blood cultures, and cytokine assays were performed during the first 3 days after onset of shock.

MEASUREMENTS AND MAIN RESULTS

Serum TNF-alpha and IL-6 concentrations were measured by using a radioimmunoassay, and IL-1 concentrations were measured by using ELISA. Median serum concentrations on day 1 were: TNF-alpha, 90 pg/mL; IL-1, 7 pg/mL; and IL-6, 5000 pg/mL. TNF-alpha and IL-6 concentrations decreased significantly between the first and third days of septic shock (p = .0001), whereas IL-1 concentrations remained low. The decrease in IL-6 tended to be more pronounced in the survivors group (p = .057). Median TNF-alpha serum concentrations were higher in bacteremic compared with nonbacteremic patients (151 vs. 73 pg/mL, p = .003). TNF-alpha, IL-1, and IL-6 serum concentrations and mortality were not different between acute perforation vs. postoperative peritonitis and mono- versus polymicrobial peritonitis.

CONCLUSIONS

The systemic release of TNF-alpha and IL-6 during septic shock caused by generalized peritonitis was maximal on day 1 and decreased rapidly during the next days. No systemic release of IL-1 was observed. IL-6 serum concentrations remained higher in patients who subsequently died. Among the different features of peritonitis studied, only bacteremia influenced the systemic cytokine response (higher TNF-alpha).

Temporal sequence of pulmonary and systemic inflammatory responses to graded polymicrobial peritonitis in mice

The lungs are the remote organ most commonly affected in human peritonitis. The major goals of this study were to define the dose- and time-dependent relationship between graded septic peritonitis and systemic and pulmonary inflammatory responses in mice. BALB/c mice were treated with intraperitoneal polymicrobial inoculi and sacrificed at 3, 12, and 24 h. The treatment protocol resulted in distinct groups of animals with respect to mortality rate, kinetics, and concentrations of a broad spectrum of pro- and anti-inflammatory endogenous mediators, intrapulmonary bacterial accumulation, and static lung compliance. In sublethally infected mice, pulmonary bacterial proliferation was controlled. Levels of monocyte chemoattractant protein-1 (MCP-1), interleukin-10, interleukin-6, granulocyte colony-stimulating factor (G-CSF), and tumor necrosis factor (TNF) in plasma were elevated 3 h after infection exclusively. At 3 h, MCP-1, gamma interferon, and TNF were detected in extracts of pulmonary tissue or in bronchoalveolar lavage (BAL) fluid. Static lung compliance (C(st)) was transiently decreased at 12 h. In contrast, in lethally infected mice pulmonary bacterial proliferation was not contained. Concentrations of MCP-1, G-CSF, and TNF in plasma were maximal at 24 h, as were pulmonary MCP-1 levels. Lung myeloperoxidase activity was increased at 3, 12, and 24 h. C(st) was reduced after 3 h and did not reach control values at 24 h. Pulmonary cyclooxygenase-2 mRNA and eicosanoids in BAL fluid and plasma were elevated at 3 and 24 h. This study shows that polymicrobial peritonitis in mice leads to dose-dependent systemic and pulmonary inflammation accompanied by a decrease in lung compliance.

Prevention of lethality and suppression of proinflammatory cytokines in experimental septic shock by microencapsulated CNI-1493

CNI-1493, a newly developed, water-soluble tetravalent guanylhydrazone, is a powerful inhibitor of tumor necrosis factor (TNF) and interleukin-1 (IL-1) synthesis. Microencapsulation of drugs into microcapsules that target macrophages has improved the effectiveness of both TNF and IL-1 neutralizing antibodies in experimental models of septic shock. It is the purpose of this study to determine if microencapsulation of CNI-1493 will improve cytokine inhibition. CNI-1493 was microencapsulated using albumin into 1 microm spheres. Comparable amounts of CNI-1493 in solution and in microencapsulated form were added to 1 ml aliquots of whole blood along with 100 ng of endotoxin. TNF and IL-1 were measured by ELISA. Microencapsulated CNI-1493 was also given to rats with endotoxic shock (15 mg/kg Escherichia coli endotoxin) and rats with peritonitis induced by peritoneally injecting 10(10) CFU E. coli. Equivalent amounts of encapsulated and solution CN I-493 were given intravenously. Endotoxin 15 mg/kg was also given to rats 6 and 24 h after a dose of encapsulated CNI-1493 to determine the duration of action of encapsulated drug. The microencapsulated CNI-1493 produced significantly greater inhibition of TNF and IL-1 at all doses in the whole blood model. There was significantly improved survival and cytokine inhibition in the endotoxic shock model as well as the peritonitis model in rats treated with microencapsulated CNI-1493. There was also 83% survival in rats given endotoxin 24 h after a dose of encapsulated CNI-1493. From these data, we conclude that CNI-1493 is a potent inhibitor of cytokine production and is greatly potentiated by microencapsulation, which transports the drug to macrophages.

The effective removal of proinflammatory cytokines by continuous hemofiltration with a polymethylmethacrylate membrane following severe burn injury: report of three cases

The serum levels of proinflammatory cytokines were investigated in three patients with severe burn injuries complicated by sepsis and pulmonary edema, who were treated with continuous hemofiltration (CHF) using a polymethylmethacrylate (PMMA) membrane. All patients had suffered burn injuries to more than 30% of their total body surface area (TBSA) and had burn indexes of 20 or more. Both interleukin (IL)-6 and tumor necrosis factor-alpha were detectable in one patient, while the serum IL-6 levels were elevated in the remaining two patients. The serum cytokines decreased 24 h after the initiation of CHF. Determinations of IL-6 in inflow and outflow blood samples as well as in the filtration fluid revealed that IL-6 was ultrafiltrated and/or adsorbed by the filter. Two of the three patients did not survive. Nevertheless, the results of this study indicate that since burn injuries are frequently associated with hypercytokinemia, the removal of cytokines by CHF with a PMMA membrane may be effective in the management of severe burn injuries.

New Frontiers in Cytokine Involvement during Experimental Sepsis

Despite significant advances in the antibiotic arsenal and in intensive care unit technology, including mechanical ventilation, sepsis-related morbidity and mortality remain unacceptably high. Ultimately, 25 to 50% of all septic episodes end in death. However, various subsets of septic patients, including those who experience septic peritonitis, and various secondary sequelae like the acute respiratory distress syndrome or nosocomial infections, demonstrate much higher mortality rates ranging from 60 to 95%. Although a number of strategies have been utilized to curb the progression of systemic inflammatory response syndrome with immune or inflammatory modulating therapies, none of these interventions has resulted in significant improvement in survival, and some have proven deleterious. The inability to utilize immune-modulating strategies effectively to treat septic patients likely reflects the inherent conflict that is illustrated by the two diagnostic criteria for the syndrome. The very immune/inflammatory response that has evolved to eliminate infection results in severe and life-threatening damage to host tissues. This review outlines the inflammatory pathways utilized by the host during a septic response. The basis of early immune-modulating therapies and possible reasons these approaches have failed in the treatment of sepsis are discussed. A picture of the ideal therapeutic approach for acute inflammatory diseases like sepsis is also created, and the reason therapies targeting chemokine pathways may more closely approximate the ideal therapy is proposed.

Effect of inflammation on prostatic protein synthesis and luminal secretion in vivo

PURPOSE

Inflammation of the prostate, or prostatitis, can be caused by an infectious process or can occur in a reportedly non-bacterial form, the etiology of which is largely unknown. The present study was undertaken to establish a method of studying prostatic protein synthesis and secretion in vivo and determine the effects of lipopolysaccharide (LPS)-induced prostatic inflammation on these processes.

MATERIALS AND METHODS

Sprague-Dawley rats were divided into three groups: control, 24 hours LPS-inflammation, and 24 hours LPS + antibody against tumor necrosis factor (anti-TNF). 35S-methionine was perifused in vivo around ventral prostate ducts for 3 hours. Ductal fluid (DF) was collected by micropuncture and ductal extract (DE) was collected by tissue homogenization. DE and DF were then subjected to SDS-PAGE and autoradiography. Densitometric analysis of gels and autoradiograms was used to compare protein synthesis (total DE 35S-proteins) and protein secretion (DF 35S-proteins) among the three groups.

RESULTS AND CONCLUSIONS

The method proved to be effective for studying prostatic protein synthesis and secretion in vivo. LPS-induced inflammation caused an increase in total 35S-proteins in both the DE and the DF when compared with controls. There were significant increases in both the total number of proteins produced as well as the densitometric quantity of protein in the inflamed group. Some specific prostatic proteins were also upregulated by inflammation. The addition of anti-TNF did not significantly alter inflammation-induced protein synthesis or secretion at the time/dose studied.

Endogenous cytokines during a lethal infection with Listeria monocytogenes in mice

It has been demonstrated that endogenous cytokines including gamma interferon (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) play protective roles but that IL-4 and IL-10 play detrimental roles in nonlethal Listeria monocytogenes infection in mice. In this paper, we studied the roles of endogenous cytokines in a lethal infection with L. monocytogenes in mice. TNF-alpha and IL-6 titres in the bloodstreams, spleens and livers paralleled bacterial numbers in the organs, and both these cytokines and the bacterial numbers peaked just before the mice died. The high titres of TNF-alpha notably detected in the circulation in lethal infection were different from those in nonlethal infection. The maximum production of IFN-gamma was observed before the peaks of TNF-alpha and IL-6, and IFN-gamma almost disappeared from the bloodstreams and organs just before the mice died. No notable difference of IFN-gamma titres between lethal infection and nonlethal infection in the specimens obtained from mice was observed. IL-10 was also detected in the bloodstreams earlier than the peaks of TNF-alpha and IL-6 during lethal infection, while IL-4 was never detected in the sera. The administration of monoclonal antibodies (mAbs) against TNF-alpha, IFN-gamma, IL-6, IL-4 or IL-10 failed to rescue mice from lethal L. monocytogenes infection, whereas anti-TNF-alpha mAb and anti-IFN-gamma mAb prevented mice from lethality by high-dose endotoxin shock. These results suggest that lethality in L. monocytogenes infection might not be determined solely by these cytokines.

Intrapulmonary tumor necrosis factor gene therapy increases bacterial clearance and survival in murine gram-negative pneumonia

Tumor necrosis factor alpha (TNF) has been shown to be an essential cytokine mediator of innate immunity in bacterial pneumonia. To augment the expression of TNF within the lung, a recombinant adenoviral vector containing the murine TNF cDNA (Ad5mTNF) has been developed, and the intratracheal administration of this vector resulted in the dose- and time-dependent expression of TNF in the lung, but not systemically. Administration of Ad5mTNF resulted in significant airspace and peribronchial inflammation, with a predominant neutrophil influx by 2 days, and mononuclear cell infiltrates by 4 to 7 days posttreatment. Importantly, the administration of Ad5mTNF at a dose of 1 x 10(8) PFU significantly improved the survival of animals challenged concomitantly with Klebsiella pneumoniae, which occurred in association with enhanced clearance of bacteria from the lung and decreased dissemination of K. pneumoniae to the bloodstream. However, the delivery of higher doses of Ad5mTNF (5 x 10(8) PFU) was not beneficial and in fact the intratracheal administration of a similar dose of control vector (Ad5LacZ) actually enhanced Klebsiella-induced lethality by impairing clearance of K. pneumoniae from the lung. Our studies suggests that the transient transgenic expression of TNF within the lung dose dependently augments antibacterial host defense in murine Klebsiella pneumonia.

Microbiological and inflammatory effects of murine recombinant interleukin-10 in two models of polymicrobial peritonitis in rats

A protective effect of interleukin-10 (IL-10) against the development of lethal shock has been demonstrated in various animal models. In contrast, the immunosuppressant properties of this mediator have been minimally evaluated in low-mortality models of infections. The clinical, microbiological, and inflammatory effects of murine recombinant IL-10 (mrIL-10) therapy were evaluated in two models of peritonitis in rats, which differed in the degree of severity of peritoneal inflammation 3 days after inoculation of Escherichia coli and Bacteroides fragilis with or without Enterococcus faecalis. The severity of the disease remained unchanged compared to that in control animals. A dose-related decrease in the peritoneal phagocyte count was observed in the treated groups compared to the counts in control animals. The subsequent experiments were performed exclusively in the mixed gram-positive-gram negative model, which exhibits an intense and prolonged inflammatory response with similar criteria. The early effects of mrIL-10 (evaluated 6 h after inoculation), repeated injections of mrIL-10 (four doses injected from 0 to 9 h after bacterial challenge), and pretreatment (two doses injected 6 and 3 h before inoculation) were evaluated. The clinical and microbiological parameters remained unchanged in the treated animals. Decreases in the peritoneal phagocyte count and the peritoneal concentration of tumor necrosis factor were observed following repeated injections of mrIL-10. In summary, our data suggest that mrIL-10 does not worsen the manifestations of sepsis. However, these results need to be confirmed in clinical practice.

Targeting macrophages with microspheres containing cytokine-neutralizing antibodies prevents lethality in gram-negative peritonitis

Macrophages release proinflammatory cytokines in response to infection that play a critical role in the pathophysiology of septic shock. We propose that targeting cytokine-neutralizing antibodies using albumin microspheres to macrophages will be more beneficial than the soluble form in reducing mortality related to peritonitis. In this study, we compared the distribution pattern of microspheres in infected and noninfected animals, evaluated the amount of microsphere taken up by peritoneal macrophages in vitro, and compared the efficacy of soluble and microsphere forms of cytokine-neutralizing antibodies in preventing lethality caused by Escherichia coli-induced peritonitis. The results indicate that twice the amount of microspheres accumulates near the site of infection (the peritoneal cavity), and 70% of the microspheres exposed to peritoneal macrophages were phagocytosed in 1 h. Treatment with the microsphere form of cytokine-neutralizing antibodies was more efficacious than using the soluble form in preventing lethality induced by E. coli. Immediate treatment was more efficacious than delayed treatment in the absence of gentamicin, whereas immediate and delayed treatment were equally efficacious in the presence of gentamicin. The combination of microspheres containing neutralizing antibodies to tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) protected 100% of the animals, whereas either one alone protected only 60%-90% of the animals from lethality caused by E. coli-induced peritonitis. In conclusion, the microsphere form of neutralizing antibodies to TNF-alpha IL-1beta may be an effective therapeutic agent in the treatment of septic shock caused by peritonitis.

Tumor necrosis factor-alpha in ischemia and reperfusion injury in rat lungs

The effects of both recombinant rat tumor necrosis factor-alpha (TNF-alpha) and an anti-TNF-alpha antibody were studied in isolated buffer-perfused rat lungs subjected to either 45 min of nonventilated [ischemia-reperfusion (I/R)] or air-ventilated (V/R) ischemia followed by 90 min of reperfusion and ventilation. In the I/R group, the vascular permeability, as measured by the filtration coefficient (Kfc), increased three- and fivefold above baseline after 30 and 90 min of reperfusion, respectively (P < 0.001). Over the same time intervals, the Kfc for the V/R group increased five- and tenfold above baseline values, respectively (P < 0.001). TNF-alpha measured in the perfusates of both ischemic models significantly increased after 30 min of reperfusion. Recombinant rat TNF-alpha (50,000 U), placed into perfusate after baseline measurements, produced no measurable change in microvascular permeability in control lungs perfused over the same time period (135 min), but I/R injury was significantly enhanced in the presence of TNF-alpha. An anti-TNF-alpha antibody (10 mg/rat) injected intraperitoneally into rats 2 h before the lung was isolated prevented the microvascular damage in lungs exposed to both I/R and V/R (P < 0.001). These results indicate that TNF-alpha is an essential component at the cascade of events that cause lung endothelial injury in short-term I/R and V/R models of lung ischemia.

Effect of interleukin-10 on gut-derived sepsis caused by Pseudomonas aeruginosa in mice

We evaluated the protective effect of interleukin-10 (IL-10) against murine gut-derived sepsis caused by Pseudomonas aeruginosa. Gut-derived sepsis was induced by administering cyclophosphamide and ampicillin while feeding P. aeruginosa to specific-pathogen-free mice. Treating mice with recombinant human IL-10 (rhIL-10) at 1.0 or 5.0 microg/mouse twice a day following the second cyclophosphamide administration significantly increased the survival rate compared to that of control mice treated with saline; however, treatment with rhIL-10 at 0.1 microg/mouse did not result in significant protection. Bacterial counts in the liver, spleen, and blood were all significantly lower in mice treated with rhIL-10 than in saline-treated control mice. Treatment with rhIL-10 significantly suppressed tumor necrosis factor alpha, interleukin-1beta, interleukin-6, and gamma interferon levels in the serum of mice following induction of gut-derived sepsis. We also studied the effect of IL-10 on leukocyte recovery after cyclophosphamide treatment of mice. Administration of rhIL-10 intraperitoneally at 1. 0 microg/mouse significantly accelerated the recovery of leukocytes in comparison with that of the group of saline-treated controls. These results indicate that IL-10 shows a protective effect against gut-derived P. aeruginosa sepsis. We suspect that the mechanism of this effect is that IL-10 regulates in vivo production of inflammatory cytokines. Furthermore, acceleration of leukocyte recovery by IL-10 after cyclophosphamide-induced depression may also play an important role in this protection.

Diaphragm sarcolemmal injury is induced by sepsis and alleviated by nitric oxide synthase inhibition

Endotoxemia is associated with impaired diaphragm contractility, and increased nitric oxide (NO) production has recently been implicated in this phenomenon. However, the precise nature of sepsis-related alterations in diaphragm myofiber function remains unclear. We tested the hypothesis that enhanced NO synthesis during sepsis produces diaphragm sarcolemmal injury with attendant abnormalities of myofiber membrane electrophysiology. Two different rat sepsis models were employed: acute (4 h) intraarterial endotoxin (LPS; 20 mg/kg) and subacute (24 h) peritonitis induced by cecal ligation and perforation (CLP). Diaphragm damage occurred after both LPS and CLP, as indicated by hyperpermeability of myofibers to a low molecular weight tracer dye, which is normally unable to penetrate the sarcolemma. Sarcolemmal injury was significantly correlated with reductions in the resting membrane potential (Em) of single diaphragm myofibers. Western analysis revealed increased diaphragmatic expression of the inducible isoform of NO synthase (iNOS) after LPS and CLP. An inhibitor of NOS activity, LNMMA, significantly decreased morphologic as well as electrophysiologic signs of myofiber membrane injury and dysfunction. Therefore, we conclude that both acute endotoxemia and subacute peritonitis models of sepsis lead to significant sarcolemmal damage and altered Em in diaphragm myofibers. These changes appear to be mediated, at least in part, through the pathway of increased nitric oxide production.

Bacterial lipopolysaccharide induces uncoupling protein-2 expression in hepatocytes by a tumor necrosis factor-alpha-dependent mechanism

The liver is a target for bacterial lipopolysaccharide (LPS) and participates in the metabolic response to endotoxemia. Recently published evidence indicates that LPS increases the expression of mitochondrial uncoupling protein-2 (UCP-2) mRNAs in several tissues, including the liver. Because hepatocytes in the healthy liver do not express UCP-2, LPS was thought to induce UCP-2 in liver macrophages, which express UCP-2 constitutively. However, the present studies of cultured peritoneal macrophages indicate that LPS reduces steady state levels of UCP-2 mRNAs in these cells. In contrast, UCP-2 mRNAs are induced in hepatocytes isolated from LPS treated rats and transfection of these hepatocytes with UCP-2 promoter-reporter constructs demonstrates substantial increases in UCP-2 promoter activity. LPS induction of hepatocyte UCP-2 expression is virtually abolished by prior treatment of rats with neutralizing antibodies to tumor necrosis factor alpha (TNF). Futhermore, TNFalpha treatment induces UCP-2 mRNA accumulation in primary cultures of hepatocytes from healthy rats. Thus, hepatocytes are likely to be important contributors to endotoxin-related increases in liver UCP-2 via a mechanism that involves the LPS-inducible cytokine, TNFalpha.

Human and rat neutrophils constitutively express neural nitric oxide synthase mRNA

Freshly isolated rat circulating neutrophils (PMN) constitutively expressed neural nitric oxide synthase (nNOS) mRNA and nNOS protein and exhibited spontaneous basal release of low concentrations of nitrate and nitrite anion (RNI). In contrast, rat peripheral monocytes and macrophages were devoid of nNOS mRNA and protein and did not exhibit basal or spontaneous release of RNI. Constitutive neural NOS mRNA was also found in human PMN. However, nNOS protein was not expressed and spontaneous generation of RNI was absent in the human PMN. Spontaneous release of RNI from rat PMN was inhibited by 7-nitroindazole but not by L-N-iminoethyllysine, which further supported the nNOS origin of the spontaneously produced RNI. Intravenous administration of Escherichia coli endotoxin (0.6 mg/kg) did not acutely affect the content of nNOS mRNA or protein but inhibited nNOS-derived production of RNI in PMN and up-regulated iNOS mRNA and iNOS protein in PMN, macrophages, and monocytes. This communication demonstrates the existence of nNOS mRNA in rat and human PMN and nNOS protein in rat PMN. Moreover, the data also show that the nNOS system in rat PMN is functional and is inhibitable by the nNOS inhibitor 7-nitroindazole. These findings offer an explanation for the spontaneous formation of the PMN-derived relaxing factor resembling nitric oxide (NO). Moreover, since basal production of NO can affect expression of adhesion molecules and cell-cell binding, the nNOS system within the rat may play an important role in PMN function in normal and disease states. Finally and speculatively, if constitutively expressed nNOS mRNA is subject to activation and translation into nNOS protein, nNOS may also play a role in the function of human PMN.

Intrapulmonary delivery of tumor necrosis factor agonist peptide augments host defense in murine gram-negative bacterial pneumonia

Tumor necrosis factor alpha (TNF) has been shown to be an essential cytokine mediator of innate immunity in Klebsiella pneumonia. Recently, a TNF agonist peptide consisting of the 11-amino-acid TNF binding site (TNF70-80) has been shown to possess many of the leukocyte-activating properties of TNF without the associated toxicity when administered locally or systemically. Given the beneficial effects of TNF in gram-negative pneumonia, we hypothesize that the intratracheal (i.t.) administration of TNF70-80 would augment lung innate immunity in mice challenged with intrapulmonary Klebsiella pneumoniae. The administration of TNF70-80 i.t. to CBA/J mice 7 days prior to, but not concomitantly with, the i.t. delivery of 3 x 10(3) CFU of K. pneumoniae resulted in a marked increase in survival compared to that of animals receiving a control peptide i.t. In addition, pretreatment with TNF70-80 resulted in improved bacterial clearance, which occurred in association with enhanced lung myeloperoxidase activity (as a measure of lung polymorphonuclear leukocyte influx), and increased expression of the important activating cytokines TNF, macrophage inflammatory protein-2, interleukin-12, and gamma interferon compared that for animals receiving control peptide. Finally, the administration of TNF70-80 intraperitoneally resulted in enhanced rather than decreased lethality of Klebsiella pneumonia compared to that for animals receiving either TNF70-80 or control peptide i.t. Our studies suggest that the intrapulmonary, but not systemic, administration of the TNF agonist peptide may serve as an important immunoadjuvant in the treatment of murine Klebsiella pneumonia.

Essential role of gamma interferon in survival of colon ascendens stent peritonitis, a novel murine model of abdominal sepsis

Despite considerable progress, peritonitis and sepsis remain life-threatening conditions. To improve the understanding of the pathophysiology encountered in sepsis, a new standardized and highly reproducible murine model of abdominal sepsis termed colon ascendens stent peritonitis (CASP) was developed. In CASP, a stent is inserted into the ascending colon, which generates a septic focus. CASP employing a stent of 14-gauge diameter (14G stent) results in a mortality of 100% within 18 to 48 h after surgery. By inserting stents of small diameters, mortality can be exactly controlled. Thus, CASP surgery with insertion of a 22G or 18G stent (22G or 18G CASP surgery) results in 38 or 68% mortality, respectively. 14G CASP surgery leads to a rapid invasion of bacteria into the peritoneum and the blood. As a consequence, endotoxemia occurs, inflammatory cells are recruited, and a systemic inflammatory response syndrome develops. Interestingly, the most pronounced upregulation of inflammatory cytokines (gamma interferon [IFN-gamma], tumor necrosis factor alpha [TNF-alpha] and interleukin-12) is observed in spleen and lungs. CASP surgery followed by stent removal at specific time intervals revealed that all animals survived if intervention was performed after 3 h, whereas removal of the septic focus after 9 h did not prevent death, suggesting induction of autonomous mechanisms of a lethal inflammatory response syndrome. 18G CASP surgery in IFN-gamma receptor-deficient (IFNgammaR-/-) mice revealed an essential role of IFN-gamma in survival of sepsis, whereas TNF receptor p55-deficient (TNFRp55-/-) mice did not show altered survival rates. In summary, this study describes a novel animal model that closely mimics human sepsis and appears to be highly suitable for the study of the pathophysiology of abdominal sepsis. Importantly, this model demonstrates a protective role of IFN-gamma in survival of bacterial sepsis.

Exogenous interleukin-10 fails to decrease the mortality or morbidity of sepsis

OBJECTIVE

To determine if exogenous interleukin (IL)-10 will decrease the morbidity or mortality of sepsis induced by cecal ligation and puncture.

DESIGN

Prospective, randomized, controlled study.

SETTING

University research laboratory.

SUBJECTS

Adult, female, Balb¿c mice.

INTERVENTIONS

Balb¿c mice were subjected to cecal ligation and puncture with an 18- or 23-gauge needle and treated with triple antibiotics. Mice were injected subcutaneously with recombinant human IL-10 (diluted in normal saline with 0.1% mouse serum albumin) and followed until death. In a separate experiment, IL-10 was also injected subcutaneously and lipopolysaccharide (LPS) injected intraperitoneally and plasma tumor necrosis factor concentrations measured 90 mins later.

MEASUREMENTS AND MAIN RESULTS

In the LPS experiments, IL-10 decreased tumor necrosis factor (TNF) production by nearly 90%. For the cecal ligation and puncture experiments, temperature and movement were recorded continuously via implanted transmitters. Studies on mortality indicated that exogenous IL-10 given at 0, +6 and +12 hrs after surgery failed to increase survival when using an 18-gauge needle (alive:total cecal ligation and puncture alone 4:21; IL-10 10 microg/mouse 2:12; 1 microg/mouse 8:25; 0.1 microg/mouse 1:12) or a 23-gauge needle (cecal ligation and puncture alone 13:29; IL-10 1 microg 18:30). There was no difference in the number of hours to death between the groups. IL-10 did not prevent the hypothermia after cecal ligation and puncture or increase the animals' activity. To examine parameters of inflammation, mice were killed 8 hrs after 18-gauge cecal ligation and puncture. IL-10 (1 microg/mL) failed to reduce pulmonary neutrophil sequestration (lung myeloperoxidase, cecal ligation and puncture 107 +/- 10 [SEM], IL-10 107 +/- 5) or recruitment of neutrophils to the peritoneum (neutrophils x 10(6), cecal ligation and puncture 3.72 +/- 0.62; IL-10 3.49 +/- 0.37). IL-10 also failed to reduce the appearance of TNF or IL-6 in the plasma or peritoneal fluid. The chemokine KC was reduced in the peritoneal fluid but not the plasma and endogenous IL-10 production was not reduced in the peritoneum.

CONCLUSION

Our data indicate that exogenous IL-10 fails to improve morbidity or mortality in the clinically relevant cecal ligation and puncture model of sepsis.

Anti-inflammatory cytokine profile and mortality in febrile patients

BACKGROUND

An anti-inflammatory cytokine profile on whole-blood stimulation in vitro is associated with fatal outcome of meningococcal disease. We investigated whether an anti-inflammatory cytokine profile in the circulation is associated with adverse outcome in other infectious diseases.

METHODS

We enrolled 464 consecutive patients (272 men, 192 women) who presented to hospital with fever (> or = 38.2 degrees C). On admission we measured plasma interleukin 10 (IL-10) and tumour necrosis factor alpha (TNF alpha), and collected clinical and microbiological data on the febrile illness, then followed up all patients for clinical outcome.

FINDINGS

In at least 399 of the 464 patients fever was caused by infection. 33 patients died after a median hospital stay of 11 days (interquartile range 3-20). Concentrations of IL-10 were significantly higher in non-survivors (median 169 pg/mL [IQR 83-530]) than in survivors (median 88 pg/mL [42-235], p=0.042). When dichotomised around the median, the mortality risk was two times higher in patients who had high concentrations of IL-10 than in those with low concentrations (relative risk 2.39 [95% CI 1.07-5.33]), in patients with low and high concentrations of TNF alpha. In the 406 patients without haemodynamic deterioration in the first 24 h, IL-10 was higher and TNF alpha lower in patients who died than in those who survived. The ratio of IL-10 to TNF alpha was higher in non-survivors (median 6.9 [3.0-21.0]) than in survivors (median 3.9 [2.0-7.0], p=0.040). This ratio was highest in patients who died without underlying disease (median 21.5 [5.0-25.0]). Age, sex, and duration of fever before admission did not explain the differences in IL-10 and TNF alpha.

INTERPRETATION

An anti-inflammatory cytokine profile of a high ratio of IL-10 to TNF alpha is associated with fatal outcome in febrile patients with community-acquired infection. Our findings caution against a widespread use of proinflammatory cytokine inhibition in patients with sepsis.

The significance of endotoxin release in experimental and clinical sepsis in surgical patients--evidence for antibiotic-induced endotoxin release?

Sepsis and peritonitis remain a serious challenge for surgical patients, despite improvement in surgical therapy and intensive care and the introduction of new powerful antibiotics. Recent in vitro studies revealed the potential of certain antibiotics, e.g. penicillin-binding protein (PBP) 3-specific antibiotics, to cause antibiotic-induced endotoxin release. Other types of antibiotics, e.g., PBP 2-specific antibiotics, were associated with no or less endotoxin release. Further in vitro experiments and investigations in animals support the hypothesis of antibiotic-induced endotoxin release, but there is little clinical evidence. The clinical significance of endotoxin is subject of open dispute with many pro's and contra's. Endotoxin, although an important trigger, may not be the only factor to induce cytokine release, e.g., peptidoglycans were able to stimulate cells to release cytokines. Gram-positive pathogens have gained more importance in clinical sepsis and may not be sufficiently reflected in current clinical studies. The hypothesis that neutralization of endotoxin and pro-inflammatory cytokines is beneficial in sepsis was seriously challenged by the results of recent clinical and experimental studies. The better understanding of mechanisms in endotoxin-induced cell activation and cell, cell-receptor and soluble receptor interactions led to new treatment options. Recent reports on the complex pathogenesis of peritonitis and the detection of pathogen-related factors with intraperitoneal immune response may have implications on clinical studies investigating the potential of new compounds and the effect of antibiotics on endotoxin release. However, only few reports are available on the clinical significance of antibiotic-induced endotoxin release, and association of endotoxin release with pathogens, mortality or alteration of physiological parameters were not observed. With regard to the particulars of these studies, e.g., a small study population or low mortality rate, mortality may not be an ideal outcome parameter for these studies. There is clinical evidence for antibiotic-induced endotoxin release. However, the need for well-designed and performed studies using newly developed monitoring devices in intensive care therapy is obvious.

Shedding kinetics of soluble tumor necrosis factor (TNF) receptors after systemic TNF leaking during isolated limb perfusion. Relevance to the pathophysiology of septic shock

We examined the kinetics of shedding of the soluble TNF receptors (TNF-Rs) in response to TNF leakage during isolated limb perfusion procedures and correlated them to the resulting hemodynamic effects. Shedding of the TNF-Rs started 7 min after TNF leakage into the systemic circulation. Three waves of shedding were observed peaking at 1, 8-12, and 48-72 h both in vivo and in cell cultures. The soluble receptors prolonged the half-life of TNF in the systemic circulation to 2.5-6 h. Excess shedding of the p75 compared with p55 TNF-Rs was noted during the first wave. The amount and speed of shedding of the p75 TNF-Rs were proportional to the serum TNF levels (P < 0.001). A maximal shedding capacity was attained only during the first wave of shedding, at TNF concentrations of approximately 1.5 ng/ml. Above this level, the linearity between TNF and its soluble receptors was lost. TNF-induced hypotension coincided with the initial imbalance between the concentrations of TNF and its soluble receptors. Despite the spontaneous correction of this imbalance at 8-12 h, the hemodynamic and biochemical alterations persisted and were further aggravated at 18 h, suggesting that other factors induced earlier by TNF are responsible for the perpetuation of the hemodynamic instability. This study may provide the basis for a more physiological therapeutic approach to TNF neutralization in septic shock patients.

Therapeutic effects of nitric oxide inhibition during experimental fecal peritonitis: role of interleukin-10 and monocyte chemoattractant protein 1

This study demonstrates that the therapeutic effect of a nitric oxide inhibitor in a murine model of fecal peritonitis is mediated in part by increased levels of interleukin-10 (IL-10) and monocyte chemoattractant protein 1 (MCP-1). Female CD1 mice were subjected to cecal ligation and puncture (CLP) with a 21-gauge needle and, immediately following surgery, were injected intraperitoneally with saline, N(G)-nitro-L-arginine methyl ester (L-NAME; 8 mg/kg), or N(G)-nitro-D-arginine methyl ester (D-NAME; 8 mg/kg). At 96 h after surgery and drug treatment, 20% of mice that received D-NAME had survived whereas 60% of mice that received L-NAME were alive. To elucidate the effect of L-NAME treatment on chemokine and cytokine production during fecal peritonitis, the levels of macrophage inflammatory protein 2 (MIP-2), IL-10, and MCP-1 were measured in peritoneal washings from additional groups of mice 24 h after the CLP surgery. Peritoneal fluids from L-NAME-treated mice contained significantly higher levels of IL-10 and MCP-1 than did those from D-NAME-treated mice. To elucidate the effect of nitric oxide inhibition on potential cellular sources of IL-10 and MCP-1 in the CLP model, cultured alveolar and peritoneal macrophages were activated with bacterial lipopolysaccharide in the presence of L-NAME; these macrophages produced significantly more MCP-1 than did similarly activated macrophages in the presence of D-NAME. In the CLP surgery model, immunoneutralization of IL-10 alone or IL-10 and MCP-1 together with polyclonal antibodies prior to surgery significantly reduced the survival rates in L-NAME-treated groups compared with L-NAME-treated groups that received preimmune serum. Taken together, these data demonstrate that the inhibition of nitric oxide following experimental CLP fecal peritonitis is therapeutic, in part through the modulatory effect of this treatment on the synthesis of IL-10 and MCP-1.

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.

The systemic inflammatory response in the development of ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) is the most frequent occurring infection among mechanically ventilated patients. The clinical presentation of VAP ranges from relatively benign to a severe illness with septic shock. The influence of VAP on patient outcome has not been elucidated and its effects on the inflammatory response of the host are unknown. In a case-control study, the systemic inflammatory response was investigated in patients developing VAP as compared with control patients matched on duration of mechanical ventilation and underlying diseases. Patients developing VAP (n = 42) were matched to a single control (without VAP), who was matched on seven variables. VAP was diagnosed with bronchoscopic techniques. The inflammatory response, reflected by circulating levels of interleukin-6 (IL-6) and interleukin-8 (IL-8), was determined on the day of diagnosis (or day of matching for controls), 4 and 2 d before diagnosis, and 2 d after diagnosis. The development of VAP was not associated with an increase in circulating levels of IL-6 or IL-8. Among patients in which VAP was associated with a clinical presentation of severe sepsis or septic shock (n = 10), IL-6 and IL-8 levels increased and were higher than in the corresponding controls. Moreover, 60% of cases with severe sepsis or septic shock died as compared with 20% of their matched controls (p = 0.06). Mortality rates were similar in patients with uncomplicated VAP and their matched controls (25% and 34%, respectively). High circulating levels of IL-6 and IL-8 were associated with higher mortality rates. The clinical picture of VAP can be subdivided into different types, ranging from uncomplicated to an infection associated with severe sepsis or septic shock, elevated circulating levels of IL-6 and IL-8, and an increased mortality rate.