Daniel G. Remick

Role of tumor necrosis factor-alpha in the pathophysiologic alterations after hepatic ischemia/reperfusion injury in the rat.

Cytokines are recognized as critical early mediators of organ injury. We attempted to determine whether or not severe hepatic ischemia/reperfusion injury results in tumor necrosis factor-alpha (TNF-alpha) release with subsequent local and systemic tissue injury. After 90 min of lobar hepatic ischemia, TNF was measurable during the reperfusion period in the plasma of all 14 experimental animals, with levels peaking between 9 and 352 pg/ml. Endotoxin was undetectable in the plasma of these animals. Pulmonary injury, as evidenced by a neutrophilic infiltrate, edema and intra-alveolar hemorrhage developed after hepatic reperfusion. The neutrophilic infiltrate was quantitated using a myeloperoxidase (MPO) assay; this demonstrated a significant increase in MPO after only 1 h of reperfusion. Anti-TNF antiserum pretreatment significantly reduced the pulmonary MPO after hepatic reperfusion. After a 12-h reperfusion period, there was histologic evidence of intra-alveolar hemorrhage and pulmonary edema. Morphometric assessment showed that pretreatment with anti-TNF antiserum was able to completely inhibit the development of pulmonary edema. Liver injury was quantitated by measuring serum glutamic pyruvic transaminase which showed peaks at 3 and 24 h. Anti-TNF antiserum pretreatment was able to significantly reduce both of these peak elevations. These data show that hepatic ischemia/reperfusion results in TNF production, and that this TNF is intimately associated with pulmonary and hepatic injury.

Comparison of the mortality and inflammatory response of two models of sepsis: lipopolysaccharide vs. cecal ligation and puncture.

Sepsis remains a serious clinical problem despite intense efforts to improve survival. Experimental animal models of sepsis have responded dramatically to immunotherapy blocking the activity of cytokines. Despite these preclinical successes, human clinical trials have not demonstrated any improvement in survival. We directly compared the mortality, morbidity, and immunopathology in two models of sepsis, one due to lipopolysaccharide (LPS) and the other to cecal ligation and puncture (CLP). BALB/c mice were injected intraperitoneally with 250 microg of LPS or subjected to CLP with an 18-gauge needle. Both models yielded similar mortality (> 85%) and morbidity. Additionally, neutropenia and lymphopenia developed in both groups. Plasma and peritoneal levels of cytokines (TNF, IL-1, IL-6, and the chemokines KC and MIP-2) were measured at 1.5, 4, and 8 h after challenge. LPS induced substantially higher levels of cytokines in both compartments with peak levels between 1.5 and 4 h that began to decline at 8 h. In contrast, cytokine levels in the CLP model were continuing to increase at the 8 h-time point and often exceeded the LPS-induced values at this time. Our data demonstrate that the LPS and CLP models have similar mortality but significant differences in the kinetics and magnitude of cytokine production. Immunotherapy for sepsis based on cytokine production after LPS challenge is misdirected because the LPS model does not accurately reproduce the cytokine profile of sepsis.

Six at six: Interleukin-6 measured 6 H after the initiation of sepsis predicts mortality over 3 days

Virtually of the all recent therapeutic interventions for treating sepsis have failed to improve survival. One potential explanation is that the heterogeneity of the immune response to the septic challenge is such that only a portion of the patients die as a result of excessive inflammation. The clinical trials lacked power because traditional measurements do not accurately identify these patients. Previous work has shown that higher levels of interleukin (IL)-6 are found in those mice that die from septic peritonitis; therefore, we sought to determine whether IL-6 measured 6 h after surgery could predict outcome. Adult, female BALB/c mice (n = 79) were subjected to cecal ligation and puncture with a 21-gauge needle and treated with imipenem in D5W every 12 h for 5 days, resulting in a homogenous population at the outset. Six hours after surgery, 20 &mgr;L of blood was obtained from the tail vein to measure IL-6. Mortality was followed for 21 days. Overall 3-day survival was 77%, and 21-day mortality was 56%. Plasma IL-6 levels >2000 pg/mL were determined to predict mortality within the first 3 days with a sensitivity of 58% and specificity of 97%. To further refine the mortality prediction, body weight and a complete blood count were performed 24 hours after cecal ligation and puncture. Discriminate analysis indicated that a weighted formula combining body mass, lymphocyte, and platelet count would predict death with sensitivity of 83% and a specificity of 79%. We tested the value of the IL-6 prediction by surgically resecting the cecum in those animals with IL-6 > 2000 pg/mL, which resulted in a significant improvement in survival. These data demonstrate that IL-6 measured 6 h after injury accurately predicts mortality resulting from experimental sepsis. This measurement may be determined quickly so that therapy may be targeted only to those individuals at significant risk of dying and initiated within sufficient time to be effective.

Circulating Cytokine/Inhibitor Profiles Reshape the Understanding of the SIRS/CARS Continuum in Sepsis and Predict Mortality

Mortality in sepsis remains unacceptably high and attempts to modulate the inflammatory response failed to improve survival. Previous reports postulated that the sepsis-triggered immunological cascade is multimodal: initial systemic inflammatory response syndrome (SIRS; excessive pro-, but no/low anti-inflammatory plasma mediators), intermediate homeostasis with a mixed anti-inflammatory response syndrome (MARS; both pro- and anti-inflammatory mediators) and final compensatory anti-inflammatory response syndrome (CARS; excessive anti-, but no/low proinflammatory mediators). To verify this, we examined the evolution of the inflammatory response during the early phase of murine sepsis by repetitive blood sampling of septic animals. Increased plasma concentrations of proinflammatory (IL-6, TNF, IL-1β, KC, MIP-2, MCP-1, and eotaxin) and anti-inflammatory (TNF soluble receptors, IL-10, IL-1 receptor antagonist) cytokines were observed in early deaths (days 1–5). These elevations occurred simultaneously for both the pro- and anti-inflammatory mediators. Plasma levels of IL-6 (26 ng/ml), TNF-α (12 ng/ml), KC (33 ng/ml), MIP-2 (14 ng/ml), IL-1 receptor antagonist (65 ng/ml), TNF soluble receptor I (3 ng/ml), and TNF soluble receptor II (14 ng/ml) accurately predicted mortality within 24 h. In contrast, these parameters were not elevated in either the late-deaths (day 6–28) or survivors. Surprisingly, either pro- or anti-inflammatory cytokines were also reliable in predicting mortality up to 48 h before outcome. These data demonstrate that the initial inflammatory response directly correlates to early but not late sepsis mortality. This multifaceted response questions the use of a simple proinflammatory cytokine measurement for classifying the inflammatory status during sepsis.

The Pathogenesis of Sepsis

Sepsis is a serious clinical condition that represents a patients response to a severe infection and has a very high mortality rate. Normal immune and physiologic responses eradicate pathogens, and the pathophysiology of sepsis is due to the inappropriate regulation of these normal reactions. In an ideal scenario, the first pathogen contact with the inflammatory system should eliminate the microbe and quickly return the host to homeostasis. The septic response may accelerate due to continued activation of neutrophils and macrophages/monocytes. Upregulation of lymphocyte costimulatory molecules and rapid lymphocyte apoptosis, delayed apoptosis of neutrophils, and enhanced necrosis of cells/tissues also contribute to the pathogenesis of sepsis. The coagulation system is closely tied to the inflammatory response, with cross talk between the two systems driving the dysregulated response. Biomarkers may be used to help diagnose patients with sepsis, and they may also help to identify patients who would benefit from immunomodulatory therapies.

Evidence for tumor necrosis factor-induced pulmonary microvascular injury after intestinal ischemia-reperfusion injury

Acute lung injury characterized by increased microvascular permeability Is one feature of multiple-organ system failure and the adult respiratory distress syndrome. Intestinal ischemia–reperfusion injury has been linked to this type of acute lung injury. The purpose of these experiments was to examine the pathogenic mediators that link the two processes, with particular emphasis on the roles of endotoxln and tumor necrosis factor α (TNFα). Previously described characteristics of the acute lung Injury in this rat model of Intestinal ischemia-reperfusion include pulmonary neutrophil sequestration, depletion of lung tissue ATP, alveolar endotnelial cell disruption, and increased microvascular permeability. Plasma levels of TNF In the systemic circulation of sham-operated animals and those with intestinal ischemlc injury less than 60 minutes In duration were very low or undetectable. Intestinal ischemia for 120 minutes was associated with TNF elevation to 1.19 ± 0.50 U/mL. Reperfusion for periods of 15 and 30 minutes generated 5− to 10-fold Increases In circulating TNF levels (6.61 ± 3.11 U/mL, p > 0.05 and 10.41 ± 5.41 U/mL, p.= 0.004 compared to sham); however this increase in circulating TNF was transient and largely cleared within 60 minutes after Initiating reperfusion. Portal vein endotoxln levels were found to increase significantly before the appearance of TNF in systemic plasma, suggesting that gut-derived endotoxin may Induce TNF release from hepatic macrophages into the systemic circulation. Antl-TNF antibody attenuated the increase in pulmonary microvascular permeability In this preparation but did not prevent pulmonary, neutrophil sequestration. These observations suggest that endotoxin and TNF have pathogenic roles in this acute lung Injury, but that mechanisms of adherence of neutrophils to endotnelial cells Independent of TNF may be Involved. The accumulation of neutrophils in the lung but the prevention of a vascular permeability increase in the presence of antibody to TNF may imply an in vivo role for TNF in the process of neutrophil activation. These studies provide additional evidence of the Importance of the endogenous inflammatory mediators in the development of systemic injury in response to local tissue Injury.

Acute Inflammatory Response to Endotoxin in Mice and Humans

ABSTRACT Endotoxin injection has been widely used to study the acute inflammatory response. In this study, we directly compared the inflammatory responses to endotoxin in mice and humans. Escherichia coli type O113 endotoxin was prepared under identical conditions, verified to be of equal biological potency, and used for both mice and humans. The dose of endotoxin needed to induce an interleukin-6 (IL-6) concentration in plasma of ∼1,000 pg/ml 2 h after injection was 2 ng/kg of body weight in humans and 500 ng/kg in mice. Healthy adult volunteers were injected intravenously with endotoxin, and male C57BL/6 mice (n = 4 to 12) were injected intraperitoneally with endotoxin. Physiological, hematological, and cytokine responses were determined. Endotoxin induced a rapid physiological response in humans (fever, tachycardia, and slight hypotension) but not in mice. Both mice and humans exhibited lymphopenia with a nadir at 4 h and recovery by 24 h. The levels of tumor necrosis factor (TNF) and IL-6 in plasma peaked at 2 h and returned to baseline levels by 4 to 6 h. IL-1 receptor antagonist RA and TNF soluble receptor I were upregulated in both mice and humans but were upregulated more strongly in humans. Mice produced greater levels of CXC chemokines, and both mice and humans exhibited peak production at 2 h. These studies demonstrate that although differences exist and a higher endotoxin challenge is necessary in mice, there are several similarities in the inflammatory response to endotoxin in mice and humans.

Acute pancreatitis: models, markers, and mediators.

Acute pancreatitis has an incidence of approximately 40 cases per year per 100,000 adults. Although usually self-limiting, 10% to 20% of afflicted patients will progress to severe pancreatitis. The mortality rate among patients with severe pancreatitis may approach 30% when they progress to multisystem organ failure. The development of acute pancreatitis illustrates the requirement for understanding the basic mechanisms of disease progression to drive the exploration of therapeutic options. The pathogenesis of acute pancreatitis involves the interplay of local and systemic immune responses that are often difficult to characterize, particularly when results from animal models are used as a foundation for human trials. Experimental studies suggest that the prognosis for acute pancreatitis depends upon the degree of pancreatic necrosis and the intensity of multisystem organ failure generated by the systemic inflammatory response. This suggests an intricate balance between localized tissue damage with proinflammatory cytokine production and a systemic, anti-inflammatory response that restricts the inappropriate movement of proinflammatory agents into the circulation. The critical players of this interaction include the proinflammatory cytokines IL-1β, TNF-α, IL-6, IL-8, and platelet activating factor (PAF). The anti-inflammatory cytokines IL-10, as well as TNF-soluble receptors and IL-1 receptor antagonist, have also been shown to be intimately involved in the inflammatory response to acute pancreatitis. Other compounds implicated in disease pathogenesis in experimental models include complement, bradykinin, nitric oxide, reactive oxygen intermediates, substance P, and higher polyamines. Several of these mediators have been documented to be present at increased concentrations in the plasma of patients with severe, acute pancreatitis. Preclinical work has shown that some of these mediators are markers for disease activity, whereas other inflammatory components may actually drive the disease process as important mediators. Implication of such mediators suggests that interruption or blunting of an inappropriate immune response has the potential to improve outcome. Although the manipulations of specific mediators in animal models may be promising, they may not transition well to the human clinical setting. However, continued reliance on experimental animal models of acute pancreatitis may be necessary to determine the underlying causes of disease. Full understanding of these basic mechanisms involves determining not only which mediators are present, but also closely documenting the kinetics of their appearance. Measurement of the inflammatory response may also serve to identify diagnostic markers for the presence of acute pancreatitis and provide insight into prognosis. Understanding the models, documenting the markers, and deciphering the mediators have the potential to improve treatment of acute pancreatitis.

Neutralization of Groα and Macrophage Inflammatory Protein-2 Attenuates Renal Ischemia/Reperfusion Injury

Previous studies have provided strong evidence for a role for neutrophils in mediating pathology during reperfusion of ischemic tissues. CXC chemokines including interleukin-8, KC/Groα, and macrophage inflammatory protein (MIP)-2, direct neutrophils to tissue sites of inflammation. In the current study we tested the efficacy of antibodies to KC/Groα and MIP-2 in inhibiting neutrophil infiltration into kidneys during reperfusion after 1 hour of warm ischemia using a mouse model. KC mRNA and protein were produced within 3 hours after reperfusion of the ischemic kidneys. MIP-2 mRNA and protein were twofold to fourfold lower than KC and were at low levels until 9 hours after reperfusion. Only 60% of mice subjected to ischemia/reperfusion injury survived to day 3 after reperfusion. Treatment with rabbit neutralizing antibodies to both KC and MIP-2 inhibited neutrophil infiltration into ischemic kidneys during reperfusion, restored renal function as assessed by decreased serum creatinine and urea nitrogen levels to near normal levels, and resulted in complete survival of treated animals. Finally, treatment with both antibodies significantly reduced histologically graded pathology of kidneys subjected to ischemia/reperfusion injury. Collectively, the results indicate the efficacy of neutralizing the chemokines directing neutrophils into ischemic kidneys during reperfusion to inhibit this infiltration and attenuate the resulting pathology.

Tumor necrosis factor participates in the pathogenesis of acute immune complex alveolitis in the rat.

We have examined the role of intrapulmonary TNF in a rat model of acute immune complex-triggered alveolitis. Intratracheal instillation of IgG anti-bovine serum albumin (anti-BSA) followed by intravenous infusion of BSA results in acute alveolitis. Over the 4-h course of evolving lung injury, a 10-fold increase in TNF activity occurred in bronchoalveolar lavage (BAL) fluid. Immunohistochemical analysis of lung sections and BAL cells revealed that alveolar macrophages are the chief source of TNF. Antibodies that specifically neutralize rat TNF activity were raised in rabbits immunized with recombinant mouse TNF alpha. When administered into the lungs with anti-BSA, anti-TNF resulted in a marked reduction (up to 61%) in lung injury. Intratracheal instillation of exogenous TNF alone, or in combination with anti-BSA, resulted in an increase in lung injury compared to controls. Morphometric analysis and measurements of myeloperoxidase activities in whole lung extracts from rats treated with anti-TNF revealed a marked reduction in neutrophils compared to positive controls. The anti-TNF antibody preparation did not inhibit in vitro complement activation or diminish neutrophil chemotactic activity present in activated rat serum. These data indicate that intrapulmonary TNF activity is required for the full development of acute immune complex-triggered alveolitis, that alveolar macrophages are the primary source of this cytokine, and that TNF participates in the pathogenesis of immune complex alveolitis through a mechanism involving neutrophil recruitment.