Bacterial priming increases lung injury in gram-negative sepsis

Nonhuman primate species as models of human bacterial sepsis

Sepsis involves a disordered host response to systemic infection leading to high morbidity and mortality. Despite intense research, targeted sepsis therapies beyond antibiotics have remained elusive. The cornerstone of sepsis research is the development of animal models to mimic human bacterial infections and test novel pharmacologic targets. Nonhuman primates (NHPs) have served as an attractive, but expensive, animal to model human bacterial infections due to their nearly identical cardiopulmonary anatomy and physiology, as well as host response to infection. Several NHP species have provided substantial insight into sepsis-mediated inflammation, endothelial dysfunction, acute lung injury, and multi-organ failure. The use of NHPs has usually focused on translating therapies from early preclinical models to human clinical trials. However, despite successful sepsis interventions in NHP models, there are still no FDA-approved sepsis therapies. This review highlights major NHP models of bacterial sepsis and their relevance to clinical medicine.

Treatment for bacterial sepsis remains limited beyond the use of antibiotics. Lingye Chen, Karen Welty-Wolf, and Bryan Kraft review nonhuman primate models of sepsis and highlight their advantages and limitations compared to other preclinical models.

Invited review: Compartmentalization of the inflammatory response in sepsis and SIRS

Sepsis and systemic inflammatory response syndrome (SIRS) are associated with an exacerbated production of both pro- and anti-inflammatory mediators that are mainly produced within tissues. Although a systemic process, the pathophysiological events differ from organ to organ, and from organ to peripheral blood, leading to the concept of compartmentalization. The nature of the insult ( e.g. burn, hemorrhage, trauma, peritonitis), the cellular composition of each compartment ( e.g . nature of phagocytes, nature of endothelial cells), and its micro-environment ( e.g. local presence of granulocyte-macrophage colony stimulating factor [GM-CSF] in the lungs, low levels of arginine in the liver, release of endotoxin from the gut), and leukocyte recruitment, have a great influence on local inflammation and on tissue injury. High levels of pro-inflammatory mediators ( e.g. interleukin-1 [IL-1], tumor necrosis factor [TNF], gamma interferon [IFN-γ], high mobility group protein-1 [HMGB1], macrophage migration inhibitory factor [MIF]) produced locally and released into the blood stream initiate remote organ injury as a consequence of an organ cross-talk. The inflammatory response within the tissues is greatly influenced by the local delivery of neuromediators by the cholinergic and sympathetic neurons. Acetylcholine and epinephrine contribute with IL-10 and other mediators to the anti-inflammatory compensatory response initiated to dampen the inflammatory process. Unfortunately, this regulatory response leads to an altered immune status of leukocytes that can increase the susceptibility to further infection. Again, the nature of the insult, the nature of the leukocytes, the presence of circulating microbial components, and the nature of the triggering agent employed to trigger cells, greatly influence the immune status of the leukocytes that may differ from one compartment to another. While anti-inflammatory mediators predominate within the blood stream to avoid igniting new inflammatory foci, their presence within tissues may not always be sufficient to prevent the initiation of a deleterious inflammatory response in the different compartments.

Integrative "omic" analysis of experimental bacteremia identifies a metabolic signature that distinguishes human sepsis from systemic inflammatory response syndromes

RATIONALE

Sepsis is a leading cause of morbidity and mortality. Currently, early diagnosis and the progression of the disease are difficult to make. The integration of metabolomic and transcriptomic data in a primate model of sepsis may provide a novel molecular signature of clinical sepsis.

OBJECTIVES

To develop a biomarker panel to characterize sepsis in primates and ascertain its relevance to early diagnosis and progression of human sepsis.

METHODS

Intravenous inoculation of Macaca fascicularis with Escherichia coli produced mild to severe sepsis, lung injury, and death. Plasma samples were obtained before and after 1, 3, and 5 days of E. coli challenge and at the time of killing. At necropsy, blood, lung, kidney, and spleen samples were collected. An integrative analysis of the metabolomic and transcriptomic datasets was performed to identify a panel of sepsis biomarkers.

MEASUREMENTS AND MAIN RESULTS

The extent of E. coli invasion, respiratory distress, lethargy, and mortality was dependent on the bacterial dose. Metabolomic and transcriptomic changes characterized severe infections and death, and indicated impaired mitochondrial, peroxisomal, and liver functions. Analysis of the pulmonary transcriptome and plasma metabolome suggested impaired fatty acid catabolism regulated by peroxisome-proliferator activated receptor signaling. A representative four-metabolite model effectively diagnosed sepsis in primates (area under the curve, 0.966) and in two human sepsis cohorts (area under the curve, 0.78 and 0.82).

CONCLUSIONS

A model of sepsis based on reciprocal metabolomic and transcriptomic data was developed in primates and validated in two human patient cohorts. It is anticipated that the identified parameters will facilitate early diagnosis and management of sepsis.

Development of a novel preclinical model of pneumococcal pneumonia in nonhuman primates

Pneumococcal pneumonia is a leading cause of bacterial infection and death worldwide. Current diagnostic tests for detecting Streptococcus pneumoniae can be unreliable and can mislead clinical decision-making and treatment. To address this concern, we developed a preclinical model of pneumococcal pneumonia in nonhuman primates useful for identifying novel biomarkers, diagnostic tests, and therapies for human S. pneumoniae infection. Adult colony-bred baboons (n = 15) were infected with escalating doses of S. pneumoniae (Serotype 19A-7). We characterized the pathophysiological and serological profiles of healthy and infected animals over 7 days. Pneumonia was prospectively defined by the presence of three criteria: (1) change in white blood cell count, (2) isolation of S. pneumoniae from bronchoalveolar lavage fluid (BALF) or blood, and (3) concurrent signs/symptoms of infection. Animals given 10(9) CFU consistently met our definition and developed a phenotype of tachypnea, tachycardia, fever, hypoxemia, and radiographic lobar infiltrates at 48 hours. BALF and plasma cytokines, including granulocyte colony-stimulating factor, IL-6, IL-10, and IL-1ra, peaked at 24 to 48 hours. At necropsy, there was lobar consolidation with frequent pleural involvement. Lung histopathology showed alveolar edema and macrophage influx in areas of organizing pneumonia. Hierarchical clustering of peripheral blood RNA data at 48 hours correctly identified animals with and without pneumonia. Dose-dependent inoculation of baboons with S. pneumoniae produces a host response ranging from spontaneous clearance (10(6) CFU) to severe pneumonia (10(9) CFU). Selected BALF and plasma cytokine levels and RNA profiles were associated with severe pneumonia and may provide clinically useful parameters after validation.

Lung microenvironment contributes to the resistance of alveolar macrophages to develop tolerance to endotoxin*

OBJECTIVE

Endotoxin tolerance corresponds to reprogramming of mononuclear phagocytes after iterative encounters with toll-like receptor agonists aimed to dampen the inflammatory response. We investigated why this phenomenon cannot be observed with murine alveolar macrophages.

DESIGN

Animal study.

SETTING

Research institution laboratory.

SUBJECTS

rag2-/-, rag2γc-/-, cd3ε-/-, µ-/-, il-15-/-, Jα18-/-, ifnγr-/-, il-18r-/-, and wild-type mice.

INTERVENTIONS

Alveolar macrophages were harvested from untreated mice or after injection of endotoxin. Alveolar macrophages were activated in vitro with endotoxin (lipopolysaccharide), and tumor necrosis factor production was monitored.

MEASUREMENTS AND MAIN RESULTS

In contrast to monocytes or peritoneal macrophages, alveolar macrophages did not display endotoxin tolerance in an ex vivo model after injection of endotoxin. An in vivo systemic inhibition of granulocyte-macrophage colony-stimulating factor or interferon-γ allowed the induction of alveolar macrophage endotoxin tolerance, which was also observed in interferon-γ receptor-deficient mice. Using mice missing different leukocyte subsets and adoptive cell transfers, we demonstrated the involvement of B lymphocytes in interferon-γ production within the lung microenvironment and in the prevention of alveolar macrophage endotoxin tolerance. Furthermore, we demonstrated the importance of interleukin-18 in preventing alveolar macrophage endotoxin tolerance through studies of interleukin-18 messenger RNA expression in il-18r-/- mice and injection of interleukin-18 in rag2-/- and µ-/- mice.

CONCLUSIONS

Our results support the conclusion that at homeostasis in the lungs, constitutive expression of granulocyte-macrophage colony-stimulating factor, interleukin-18, interferon-γ and possibly interleukin-15, and a cross-talk between B lymphocytes and alveolar macrophages create a microenvironment specific to the lungs that prevents alveolar macrophages from becoming tolerant to endotoxin.

Intestinal epithelium is more susceptible to cytopathic injury and altered permeability than the lung epithelium in the context of acute sepsis

Mitochondrial morphology and function are altered in intestinal epithelia during endotoxemia. However, it is unclear whether mitochondrial abnormalities occur in lung epithelial cells during acute sepsis or whether mitochondrial dysfunction corresponds with altered epithelial barrier function. Thus, we hypothesized that the intestinal epithelium is more susceptible to mitochondrial injury than the lung epithelium during acute sepsis and that mitochondrial dysfunction precedes impaired barrier function. Using a resuscitated feline model of Escherichia coli-induced sepsis, lung and ileal tissues were harvested after 6 h for histological and mitochondrial ultrastructural analyses in septic (n = 6) and time-matched controls (n = 6). Human lung epithelial cells (HLEC) and Caco-2 monolayers (n = 5) were exposed to 'cytomix' (TNFα: 40 ng/ml, IL-1β: 20 ng/ml, IFNγ: 10 ng/ml) for 24-72 h, and measurements of transepithelial electrical resistance (TER), epithelial permeability and mitochondrial membrane potential (ΔΨ) were taken. Lung epithelial morphology, mitochondrial ultrastructure and pulmonary gas exchange were unaltered in septic animals compared to matching controls. While histologically intact, ileal epithelia demonstrated marked mitochondrial ultrastructural damage during sepsis. Caco-2 monolayers treated with cytomix showed a significant decrease in mitochondrial ΔΨ within 24 h, which was associated with a progressive reduction in TER and increased epithelial permeability over the subsequent 48 h. In contrast, mitochondrial ΔΨ and epithelial barrier functions were preserved in HLEC following cytomix. These findings indicate that intestinal epithelium is more susceptible to mitochondrial damage and dysfunction than the lung epithelium in the context of sepsis. Early alterations in mitochondrial function portend subsequent epithelial barrier dysfunction.

Nitric oxide synthase-2 induction optimizes cardiac mitochondrial biogenesis after endotoxemia

Mitochondrial biogenesis protects metabolism from mitochondrial dysfunction produced by activation of innate immunity by lipopolysaccharide (LPS) or other bacterial products. Here we tested the hypothesis in mouse heart that activation of toll-like receptor-4 (TLR4), which induces early-phase genes that damage mitochondria, also activates mitochondrial biogenesis through induction of nitric oxide synthase (NOS2). We compared three strains of mice: wild type (Wt) C57BL/6J, TLR4(-/-), and NOS2(-/-)for cardiac mitochondrial damage and mitochondrial biogenesis by real-time RT-PCR, Western analysis, immunochemistry, and isoform analysis of myosin heavy chain (MHC) after sublethal heat-killed Escherichia coli (HkEC). After HkEC, Wt mice displayed significant myocardial mtDNA depletion along with enhanced TLR4 and NOS2 gene and protein expression that normalized in 72 h. HkEC generated less cytokine stress in TLR4(-/-)and NOS2(-/-)than Wt mice, NOS2(-/-)mice had mtDNA damage comparable to Wt, and both knockout strains failed to restore mtDNA copy number because of mitochondrial transcriptosome dysfunction. Wt mice also showed the largest beta-MHC isoform switch, but MHC recovery lagged in the NOS2(-/-)and TLR4(-/-)strains. The NOS2(-/-)mice also unexpectedly revealed the codependency of TLR4 expression on NOS2. These findings demonstrate the decisive participation of NOS2 induction by TLR4 in optimization of mitochondrial biogenesis and MHC expression after gram-negative challenge.

Post-transcriptional regulation of urokinase-type plasminogen activator receptor expression in lipopolysaccharide-induced acute lung injury

RATIONALE

Urokinase-type plasminogen activator (uPA) receptor (uPAR) is required for the recruitment of neutrophils in response to infection. uPA induces its own expression in lung epithelial cells, which involves its interaction with cell surface uPAR. Regulation of uPAR expression is therefore crucial for uPA-mediated signaling in infectious acute lung injury (ALI).

OBJECTIVES

To determine the role of uPA in uPAR expression during ALI caused by sepsis.

METHODS

We used Western blot, Northern blot, Northwestern assay, and immunohistochemistry. Phosphate-buffered saline- and lipopolysaccharide (LPS)-treated wild-type and uPA(-/-) mice were used.

MEASUREMENTS AND MAIN RESULTS

Biological activities of uPA, including proteolysis, cell adhesion, migration, proliferation, and differentiation, are dependent on its association with uPAR. Bacterial endotoxin (LPS) is a major cause of pulmonary dysfunction and infection-associated mortality. The present study shows that LPS induces uPAR expression both in vitro and in vivo, and that the mechanism involves post-transcriptional stabilization of uPAR mRNA by reciprocal interaction of phosphoglycerate kinase (PGK) and heterogeneous nuclear ribonucleoprotein C (hnRNPC) with uPAR mRNA coding region and 3' untranslated region determinants, respectively. The process involves tyrosine phosphorylation of PGK and hnRNPC. uPA(-/-) mice failed to induce uPAR expression after LPS treatment. In these mice, LPS treatment failed to alter the binding of PGK and hnRNPC protein with uPAR mRNA due to lack of tyrosine phosphorylation.

CONCLUSIONS

Our study shows that induction of LPS-mediated uPAR expression is mediated through tyrosine phosphorylation of PGK and hnRNPC. This involves expression of uPA as an obligate intermediary.

Large animal models: baboons for trauma, shock, and sepsis studies

A few limited examples of large animal models are outlined, with the main emphasis on baboon models. The baboon offers all the advantages of a large animal and is comparable with humans in nearly all physiological and immunological aspects. In addition, cross-reactivity with human therapeutic and diagnostic reagents allows testing of new species-specific therapies such as antihuman antibodies, on the one hand, and monitoring with available human analytical procedures, on the other.

Hypoxia aggravates lipopolysaccharide-induced lung injury

The animal model of inflammatory response induced by intratracheal application of lipopolysaccharide includes many typical features of acute lung injury or the acute respiratory distress syndrome. A number of experimental investigations have been performed to characterize the nature of this injury more effectively. In inflammatory conditions, hypoxia occurs frequently before and in parallel with pulmonary and non-pulmonary pathological events. This current study was designed to examine the in vivo effect of hypoxia as a potentially aggravating condition in endotoxin-induced lung injury. Lipopolysaccharide, 150 microg, was instilled intratracheally into rat lungs, and thereafter animals were exposed to either normoxia or hypoxia (10% oxygen). Lungs were collected 2, 4, 6 and 8 h later. Inflammatory response and tissue damage were evaluated by quantitative analysis of inflammatory cells and mediators, surfactant protein and vascular permeability. A significantly enhanced neutrophil recruitment was seen in lipopolysaccharide-animals exposed to hypoxia compared to lipopolysaccharide-animals under normoxia. This increased neutrophil accumulation was triggered by inflammatory mediators such as tumour necrosis factor-alpha and macrophage inflammatory protein-1beta, secreted by alveolar macrophages. Determination of vascular permeability and surfactant protein-B showed enhanced concentrations in lipopolysaccharide-lungs exposed to hypoxia, which was absent in animals previously alveolar macrophage-depleted. This study demonstrates that hypoxia aggravates lipopolysaccharide injury and therefore represents a second hit injury. The additional hypoxia-induced inflammatory reaction seems to be predominantly localized in the respiratory compartment, underlining the compartmentalized nature of the inflammatory response.

Blockade of tissue factor-factor X binding attenuates sepsis-induced respiratory and renal failure

Tissue factor expression in sepsis activates coagulation in the lung, which potentiates inflammation and leads to fibrin deposition. We hypothesized that blockade of factor X binding to the tissue factor-factor VIIa complex would prevent sepsis-induced damage to the lungs and other organs. Acute lung injury was produced in 15 adult baboons primed with killed Escherichia coli [1 x 10(9) colony-forming units (CFU)/kg], and then 12 h later, they were given 1 x 10(10) CFU/kg live E. coli by infusion. Two hours after live E. coli, animals received antibiotics with or without monoclonal antibody to tissue factor intravenously to block tissue factor-factor X binding. The animals were monitored physiologically for 34 h before being killed and their tissue harvested. The antibody treatment attenuated abnormalities in gas exchange and lung compliance, preserved renal function, and prevented tissue neutrophil influx and bowel edema relative to antibiotics alone (all P < 0.05). It also attenuated fibrinogen depletion (P < 0.01) and decreased proinflammatory cytokines, e.g., IL-6 and -8 (P < 0.01), in systemic and alveolar compartments. Similar protective effects of the antibody on IL-6 and -8 expression and permeability were found in lipopolysaccharide-stimulated endothelial cells. Blockade of factor X binding to the tissue factor-factor VIIa complex attenuates lung and organ injuries in established E. coli sepsis by attenuating the neutrophilic response and inflammatory pathways.

Toll-like receptor 4 mediates mitochondrial DNA damage and biogenic responses after heat-inactivated E. coli

An important site of cellular damage in bacterial sepsis is mitochondrial DNA (mtDNA), which we proposed is caused by reactive oxygen and nitrogen species generated by activation of signaling through specific toll-like receptors (TLR). In wild-type (Wt) mice injected with heat-inactivated E. coli, hepatic TLR4 and TLR2 proteins were up-regulated with TLR-dependent increases in transcript levels for tumor necrosis factor (TNF-alpha), interleukin 6, nitric oxide synthase-II (iNOS), and NADPH oxidase 2 (Nox2). The accompanying stress significantly depleted hepatic mtDNA despite eight- and fourfold increases in manganese superoxide dismutase (MnSOD) and mitochondrial transcription factor A (Tfam) expression, respectively. The identical E. coli dose generated significantly less TNF-alpha, NO, and Nox2 in TLR4-/- and TLR2/4-/- but not in TLR2-/- mice. TLR4-/- and TLR2/4-/- compared with Wt mice were protected from mtDNA oxidation but showed no Tfam up-regulation and little copy number restoration. A critical role in the mtDNA damage was determined for TLR4-mediated iNOS transcription through the MyD88 pathway. In Wt mice, mtDNA depletion was avoided by selective iNOS blockade, and residual mtDNA loss was linked to NF-kappaB-dependent TNF-alpha expression. These data disclose the dual role of TLR4 in mtDNA damage and compensatory mitochondrial biogenic responses after innate immune activation.

Efeitos da castração pós-natal sobre o tecido pulmonar após sepse experimental de origem abdominal em ratos

OBJETIVO: Avaliar os efeitos da castração pós-natal sobre o tecido pulmonar na sepse de origem abdominal induzida em ratos. MÉTODOS: Foram utilizados 33 ratos Wistar distribuídos em dois grupos: Grupo Controle (GC) = 5 machos adultos normais sem desafio séptico. Grupo Experimento (GE): 28 ratos submetidos a sepse por ligadura e perfuração de ceco (LPC) e distribuídos em três subgrupos: Subgrupo Macho (SgM): nove ratos machos adultos, sem castracão e submetidos a sepse por LPC. Subgrupo Fêmea (SgF): nove ratos fêmeas adultos normais submetidas a sepse por LPC. Subgrupo Castrado (SgC): dez ratos machos que no quarto dia de vida foram submetidos a orquiectomia bilateral e quando adultos à sepse por LPC. Após a LPC os animais foram observados até o óbito, realizada análise histomorfométrica do pulmão, observando-se o número de polimorfonucleares e mononucleares. RESULTADOS: 50% dos animais do SgC sobreviveram 24 horas, contra 33% do SgF e 0% do SgM, mostrando uma nítida influência da castração na resposta ao desafio séptico. O número de polimorfonucleares e mononucleares não foi diferente estatisticamente entre o SgC e CG, estando estatisticamente aumentados no SgM e SgF. CONCLUSÃO: Os animais castrados apresentaram uma maior tendência à sobrevida e menor alteração pulmonar.

Blockade of tissue factor: treatment for organ injury in established sepsis

Blockade of tissue factor before lethal sepsis prevents acute lung injury and renal failure in baboons, indicating that activation of coagulation by tissue factor is an early event in the pathogenesis of acute lung injury and organ dysfunction. We hypothesized that blockade of tissue factor would also attenuate these injuries in established sepsis by prevention of further fibrin deposition and inflammation. Twelve male baboons received heat-killed Escherichia coli intravenously followed 12 hours later by live E. coli infusion. Six animals were treated 2 hours after the live bacteria with site-inactivated Factor VIIa, a competitive tissue factor inhibitor, and six animals were vehicle-treated sepsis control subjects. Animals were ventilated and monitored for 48 hours. Physiologic and hematologic parameters were measured every 6 hours, and pathologic evaluation was performed after 48 hours. Animals treated with site inactivated Factor VIIa had less severe lung injury, with preserved gas exchange, better lung compliance and histology scores, and decreased lung wet/dry weight. In treated animals, urine output was higher, metabolic acidosis was attenuated, and renal tubular architecture was protected. Coagulopathy was attenuated, and plasma interleukin-6, interleukin-8, and soluble tumor necrosis factor receptor-1 levels were significantly lower in the treated animals. These results show that blockade of coagulation attenuates acute lung and renal injury in established Gram-negative sepsis accompanied by antiinflammatory effects of therapy.

Future research directions in acute lung injury: summary of a National Heart, Lung, and Blood Institute working group

Acute lung injury (ALI) and its more severe form, the acute respiratory distress syndrome (ARDS), are syndromes of acute respiratory failure that result from acute pulmonary edema and inflammation. The development of ALI/ARDS is associated with several clinical disorders including direct pulmonary injury from pneumonia and aspiration as well as indirect pulmonary injury from trauma, sepsis, and other disorders such as acute pancreatitis and drug overdose. Although mortality from ALI/ARDS has decreased in the last decade, it remains high. Despite two major advances in treatment, low VT ventilation for ALI/ARDS and activated protein C for severe sepsis (the leading cause of ALI/ARDS), additional research is needed to develop specific treatments and improve understanding of the pathogenesis of these syndromes. The NHLBI convened a working group to develop specific recommendations for future ALI/ARDS research. Improved understanding of disease heterogeneity through use of evolving biologic, genomic, and genetic approaches should provide major new insights into pathogenesis of ALI. Cellular and molecular methods combined with animal and clinical studies should lead to further progress in the detection and treatment of this complex disease.

Hemodynamic effects of metalloporphyrin catalytic antioxidants: structure-activity relationships and species specificity

Superoxide plays a role in blood pressure regulation in certain vascular diseases, however, its involvement in regulating basal blood pressure is uncertain. Vascular superoxide concentrations are limited by extracellular superoxide dismutase (EC-SOD), which is highly expressed in the vasculature of most animal species. Metalloporphyrins are low molecular weight, synthetic, redox-active, catalytic antioxidants that act as SOD mimetics. We evaluated the effects of metalloporphyrins on blood pressure in different animal species. The metalloporphyrin AEOL10113 (5-10 micro /kg iv), but not native or polyethylene glycol-CuZnSOD, caused a dose-dependent reduction in blood pressure in anesthetized rats. AEOL10113 had no effect on blood pressure in mice (wild-type or EC-SOD knockouts), guinea pigs, dogs, or baboons at doses up to 5 mg/kg iv Structure-activity studies indicated that metalloporphyrins with high SOD activity were more effective in lowering rat blood pressure than low-activity analogs. The blood pressure effect of AEOL10113 was not attributable to the release of manganese, nor was it affected by inhibitors of nitric oxide synthase (L-NAME) and guanylate cyclase (ODQ, 8-bromo-cGMP, and methylene blue) or nitric oxide scavengers (HbAo). Chlorpheniramine attenuated the effect, suggesting that the blood pressure response in rats is related to histamine release rather than the protection of nitric oxide.

Heterogeneous expression of cell adhesion molecules by endothelial cells in ARDS

ARDS (acute respiratory distress syndrome) can be associated with septic shock and multiple organ failure caused by an uncontrolled systemic inflammatory response to Gram-negative bacterial infection. While in animal models the key role of the endothelial adhesion molecules ICAM-1, E-selectin, and VCAM in ARDS has been extensively studied, there are scarcely any corresponding pathomorphological studies of human lung tissue. Hence, little is known about whether there is a comparable, or even heterogeneous, expression pattern of these molecules in the human pulmonary vasculature. This study was therefore undertaken to investigate the immunohistochemical expression of the constitutively expressed PECAM (CD31) and the inducible molecules ICAM-1, E-selectin, and VCAM in ARDS lungs from patients who had died in septic shock induced by Gram-negative bacteria. While in all specimens (ARDS and normal lungs) there was homogeneous strong expression of PECAM in all vessels, ICAM-1 was clearly up-regulated in ARDS lungs. E-selectin and VCAM were not expressed by endothelial cells (ECs) in normal lungs, but in ARDS lungs there was strong expression of both molecules in larger vessels, while in the capillaries there was only mosaic-like weak expression of a few ECs. This immunohistochemical investigation demonstrates the induction and up-regulation of adhesion molecules in human ARDS lungs, comparable to that described in animal models. There is also markedly heterogeneous expression of E-selectin and VCAM, indicating toporegional differences in the function of pulmonary ECs.

Disseminated intravascular coagulation in association with pig-to-primate pulmonary xenotransplantation

BACKGROUND

Profound coagulopathy has been proposed as a barrier to xenotransplantation. Disseminated intravascular coagulation (DIC) has been observed with the rejection of renal and bone marrow xenografts but has not yet been described in pulmonary xenografts.

METHODS

This study examined the coagulation parameters in five baboons that received pulmonary xenografts and one baboon that was exposed to porcine lung during an extracorporeal perfusion. Platelet counts, prothrombin times (PT), and levels of fibrinogen, D-dimers, and thrombin-antithrombin III complex (TAT) were analyzed. In addition, serum levels of plasminogen activator inhibitor-1 (PAI-1), thrombomodulin (TM), tissue plasminogen activator (tPA), and tissue factor (TF) were determined.

RESULTS

Hyperacute pulmonary xenograft dysfunction, which occurred within 0-9 hr of graft reperfusion, was associated with clinically evident DIC. This coagulopathy was characterized by thrombocytopenia, decreased fibrinogen levels, elevations in PT, and increases in D-dimers and TAT. Furthermore, transient increases in PAI-1, increases in TM, and increases in tPA were observed in the serum of some but not all recipients. None of the baboons demonstrated measurable increases in soluble TF.

CONCLUSIONS

Although DIC in renal or bone marrow xenotransplantation develops over a period of days, DIC associated with hyperacute pulmonary xenograft dysfunction develops within hours of graft reperfusion. Thus, the DIC in pulmonary xenotransplantation may represent a unique and/or accelerated version of the coagulopathy observed with renal and bone marrow xenotransplantation.

Coagulation blockade prevents sepsis-induced respiratory and renal failure in baboons

Sepsis-induced tissue factor (TF) expression activates coagulation in the lung and leads to a procoagulant environment, which results in fibrin deposition and potentiates inflammation. We hypothesized that preventing initiation of coagulation at TF-Factor VIIa (FVIIa) complex would block fibrin deposition and control inflammation in sepsis, thereby limiting acute lung injury (ALI) and other organ damage in baboons. A model of ALI was used in which adult baboons were primed with killed Escherichia coli (1 x 10(9) CFU/kg), and bacteremic sepsis was induced 12 h later by infusion of live E. coli at 1 x 10(10) CFU/kg. Animals in the treatment group were given a competitive inhibitor of TF, site-inactivated FVIIa (FVIIai), intravenously at the time of the infusion of live bacteria and monitored physiologically for another 36 h. FVIIai dramatically protected gas exchange and lung compliance, prevented lung edema and pulmonary hypertension, and preserved renal function relative to vehicle (all p < 0.05). Treatment attenuated sepsis-induced fibrinogen depletion (p < 0.01) and decreased systemic proinflammatory cytokine responses, for example, interleukin 6 (p < 0.01). The protective effects of TF blockade in sepsis-induced ALI were confirmed by using tissue factor pathway inhibitor. The results show that TF-FVIIa complex contributes to organ injury in septic primates in part through selective stimulation of proinflammatory cytokine release and fibrin deposition.

Antibody to intercellular adhesion molecule 1 (CD54) decreases survival and not lung injury in baboons with sepsis

Neutrophil influx into the lung is an important event in the pathogenesis of acute lung injury in gram-negative sepsis. We hypothesized that administration of a monoclonal antibody to intercellular adhesion molecule 1 (ICAM-1, CD54), a molecule mediating neutrophil adhesion to endothelial cells, would decrease neutrophil sequestration and transmigration in the lung and attenuate lung injury in Escherichia coli sepsis. Sepsis was induced in 12 baboons primed with heat-killed E. coli (1 x 10(9) CFU/kg) 12 h before infusion of live bacteria (1 x 10(10) CFU/kg). Six animals received monoclonal antibody to CD54 (1 mg/kg) intravenously at the time of live E. coli infusion. After 48 h or when blood pressure could not be maintained, tissues were harvested and bronchoalveolar lavage (BAL) samples were obtained. Median survival time was decreased in anti-CD54-treated animals. This group also had decreased mean arterial pressure, increased metabolic acidosis, and decreased urine output. Measures of lung injury including gas exchange, lung lavage protein and lactate dehydrogenase (LDH), lung thiobarbituric acid-reactive species, and lung histology, including alveolar neutrophil volumes, were unaffected by treatment. The effect of anti-CD54 on neutrophil influx into tissues as measured by myeloperoxidase was organ specific. These data show that monoclonal antibody to CD54 does not ameliorate acute lung injury in E. coli sepsis, and septic primates given anti-CD54 have worsened metabolic parameters and decreased survival.

E. coli hemolysin-induced lipid mediator metabolism in alveolar macrophages: impact of eicosapentaenoic acid

Escherichia coli hemolysin (HlyA) is a prototype of a large family of pore-forming proteinaceous exotoxins that have been implicated in the pathogenetic sequelae of severe infection and sepsis, including development of acute lung injury. In the present study in rabbit alveolar macrophages (AMs), subcytolytic concentrations of purified HlyA evoked rapid synthesis of platelet-activating factor, with quantities approaching those in response to maximum calcium ionophore challenge. In parallel, large quantities of leukotriene (LT) B(4) and 5-, 8-, 9-, 12-, and 15-hydroxyeicosatetraenoic acid (HETE) were liberated from HlyA-exposed AMs depending on exogenous arachidonic acid (AA) supply. Coadministration of eicosapentaenoic acid (EPA) dose dependently suppressed generation of the proinflammatory lipoxygenase products LTB(4) and 5-, 8-, 9-, and 12-HETE in parallel with the appearance of the corresponding EPA-derived metabolites LTB(5) and 5-, 8-, 9-, and 12-hydroxyeicosapentaenoic acid (HEPE). At equimolar concentrations, EPA turned out to be the preferred substrate over AA for these AM lipoxygenase pathways, with the sum of LTB(5) and 5-, 8-, 9-, and 12-HEPE surpassing the sum of LTB(4) and 5-, 8-, 9-, and 12-HETE by >80-fold. In contrast, coadminstration of EPA did not significantly reduce HlyA-elicited generation of the anti-inflammatory AA lipoxygenase product 15-HETE. We conclude that AMs are sensitive target cells for HlyA attack, resulting in marked proinflammatory lipid mediator synthesis. In the presence of EPA, lipoxygenase product formation is shifted from a pro- to an anti-inflammatory profile.

Administration of endotoxin associated with lipopolysaccharide tolerance protects mice against fungal infection

Lipopolysaccharide (LPS) pretreatment of mice resulted in a significantly enhanced survival after disseminated Cryptococcus neoformans infection. The survival was associated with reduced fungal burden in tissues. LPS-pretreated mice had lower levels of cytokines in blood, spleen, and lungs and higher levels in brain. Pentoxifylline abolished the beneficial effect of LPS pretreatment.

Platelet-activating factor and bacteremia-induced pulmonary hypertension

BACKGROUND

Acute lung injury is a common complication of gram-negative sepsis. Pulmonary hypertension and increased lung vascular permeability are central features of lung injury following experimental bacteremia. Platelet-activating factor is a prominent proinflammatory mediator during bacterial sepsis. Our previous studies have demonstrated that exogenous administration of platelet-activating factor (PAF) induces pulmonary edema without causing pulmonary hypertension. Interestingly, inhibition of PAF activity during Escherichia coli bacteremia prevents the development of both pulmonary hypertension and pulmonary edema. These data suggest that PAF contributes to pulmonary hypertension during sepsis, but that this is unlikely to be a direct vascular effect of PAF. The goal of the present study was to investigate the mechanism by which acute E. coli bacteremia induces pulmonary injury and to define the role that PAF plays in this injury. We hypothesized that the effects of PAF on pulmonary hypertension during bacteremia are due to the effects of PAF on other vascular mediators. Several studies suggest that PAF induces the expression of endothelin-1 (ET), a potent peptide vasoconstrictor. Further, our previous studies have implicated ET as a central mediator of systemic vasoconstriction during bacteremia. We therefore sought to assess whether ET is modulated by PAF. E. coli has also been demonstrated to increase endothelial production of nitric oxide (NO), which contributes to maintenance of basal vascular tone in the pulmonary circulation. We hypothesized that PAF might increase pulmonary vascular resistance during bacteremia by activating neutrophils, increasing expression of ET, and decreasing the tonic release of NO. Furthermore, we hypothesized that hypoxic vasoconstriction did not contribute to pulmonary vasoconstriction during the first 120 min of E. coli bacteremia.

METHODS

Pulmonary artery pressure (PAP), blood pressure (BP), heart rate (HR), and arterial blood gases (ABG) were measured in anesthetized spontaneously breathing adult male Sprague-Dawley rats. E. coli (10(9) CFU/100 g body wt) was injected at t = 0, and hemodynamic data were obtained at 10-min intervals and ABG data at 30-min intervals for a total of 120 min. Sham animals were treated equally but received normal saline in place of E. coli. In treatment groups, a 2.5 mg/kg dose of WEB 2086, a PAF receptor antagonist, was administered intravenously 15 min prior to the onset of sepsis or sham sepsis. The groups were (1) intravenous E. coli (n = 5); (2) intravenous WEB 2086 pretreatment + intravenous E. coli (n = 5); (3) intravenous WEB 2086 alone (n = 5); and (4) intravenous normal saline (n = 6). Nitric oxide metabolites (NOx) and ET concentrations were assayed from arterial serum samples obtained at the end of the protocol. Lung tissue was harvested for measurement of myeloperoxidase (MPO) activity and pulmonary histology.

RESULTS

E. coli bacteremia increased HR, PAP, and respiratory rate early during sepsis (within 20 min), while hypoxemia, hypotension, and hemoconcentration were not manifest until the second hour. Pretreatment with WEB 2086 completely abrogated all of these changes. E. coli bacteremia increased the activity of serum ET, lung MPO, and neutrophil sequestration in the lung parenchyma via a PAF-dependent mechanism. However, the mechanism of increased production of NO appears to be PAF independent.

CONCLUSIONS

These data support the hypothesis that E. coli bacteremia rapidly induces pulmonary hypertension stimulated by PAF and mediated at least in part by endothelin-1 and neutrophil activation and sequestration in the lung. Microvascular injury with leak is also mediated by PAF during E. coli bacteremia, but the time course of resultant hypoxemia and hemoconcentration is slower than that of pulmonary hypertension. The contribution of hypoxic vasoconstriction in exacerbating pulmonary hypertension in gram-negative sepsis is probably a late