Increased sheep lung vascular permeability caused by Escherichia coli endotoxin

Pediatric Chronic Pulmonary Aspiration Is Associated With Low Molecular Weight Hyaluronic Acid in the Bronchoalveolar Lavage

OBJECTIVES

Low molecular-weight hyaluronic acid (LMW-HA) is produced by the degradation of high-molecular-weight hyaluronic acid at the pulmonary interstitium and alveolar epithelium by reactive intermediates following lung injury. We aimed to investigate the role of bronchoalveolar lavage (BAL) LMW-HA as a biomarker of pediatric chronic pulmonary aspiration (CPA).

METHODS

Single-center prospective comparison of LMW-HA presence in BAL in pediatric Aerodigestive patients with and without CPA undergoing clinically indicated bronchoscopy. Pediatric pulmonologists diagnosed CPA based on video-fluoroscopic swallowing evaluation.

RESULTS

Fifteen children (mean age 6.1 years, male predominance at 73%, and 53% with CPA) were enrolled. Children with CPA have comparable baseline characteristics (age, sex, and race), but their BAL had higher white blood cell count, higher neutrophil percentages, higher bacterial culture positivity rates, and lower macrophage percentages than those without CPA. The two groups were comparable in sex, BAL lymphocyte percentages, eosinophil percentages, red blood cell counts, and lipid-laden macrophage positivity. Detection of BAL LMW-HA in the BAL had a 100% specificity and 88% sensitivity for CPA diagnosis. BAL protein levels were higher in the CPA group and in participants with positive LMW-HA.

CONCLUSIONS

We suggest BAL LMW-HA as a potential novel biomarker of pediatric CPA with high specificity and sensitivity. BAL LMW-HA is not detectable in subjects without CPA and is associated with increased BAL protein levels.

Biomarkers of Acute Respiratory Distress Syndrome: Current State and Future Prospects

Biomarkers are an important tool aiding researchers in the study of acute respiratory distress syndrome (ARDS). Mechanisms involving injury to the alveolar-capillary membrane, endothelium and epithelium resulting in lung inflammation and alterations in coagulation pathways have been validated in human trials and have been used to discover promising phenotypes that share similar characteristics and differential treatment responses. The emergence of powerful point-of-care technologies will enable the prospective study of biomarkers for future enrichment trials with the goal of transforming biomarkers into the clinical realm to inform delivery of personalized medicine at the bedside.

Targeting EB3-IP3R3 Interface with Cognate Peptide Protects from Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a lung disease characterized by acute onset of noncardiogenic pulmonary edema, hypoxemia, and respiratory insufficiency. The current treatment for ARDS is mainly supportive in nature, providing a critical need for targeted pharmacological management. We addressed this medical problem by developing a pharmacological treatment for pulmonary vascular leakage, a culprit of alveolar damage and lung inflammation. Our novel therapeutic target is the microtubule accessory factor EB3 (end binding protein 3), which contributes to pulmonary vascular leakage by amplifying pathological calcium signaling in endothelial cells in response to inflammatory stimuli. EB3 interacts with IP3R3 (inositol 1,4,5-trisphosphate receptor 3) and orchestrates calcium release from endoplasmic reticulum stores. Here, we designed and tested the therapeutic benefits of a 14-aa peptide named CIPRI (cognate IP3 receptor inhibitor), which disrupted EB3-IP3R3 interaction in vitro and in lungs of mice challenged with endotoxin. Treatment with CIPRI or depletion of IP3R3 in lung microvascular endothelial monolayers mitigated calcium release from endoplasmic reticulum stores and prevented a disassembly of vascular endothelial cadherin junctions in response to the proinflammatory mediator α-thrombin. Furthermore, intravenous administration of CIPRI in mice mitigated inflammation-induced lung injury, blocked pulmonary microvascular leakage, prevented activation of NFAT (nuclear factor of activated T cells) signaling, and reduced production of proinflammatory cytokines in the lung tissue. CIPRI also improved survival of mice from endotoxemia and polymicrobial sepsis. Together, these data demonstrate that targeting EB3-IP3R3 interaction with a cognate peptide is a promising strategy to address hyperpermeability of microvessels in inflammatory lung diseases.

Crucial role of carbon monoxide as a regulator of diarrhea caused by cholera toxin: Evidence of direct interaction with toxin

The present study evaluated the role of heme oxygenase 1 (HO-1)/carbon monoxide (CO) pathway in the cholera toxin-induced diarrhea and its possible action mechanism. The pharmacological modulation with CORM-2 (a CO donor) or Hemin (a HO-1 inducer) decreased the intestinal fluid secretion and Cl- efflux, altered by cholera toxin. In contrast, ZnPP (a HO-1 inhibitor) reversed the antisecretory effect of Hemin and potentiated cholera toxin-induced intestinal secretion. Moreover, CORM-2 also prevented the alteration of intestinal epithelial architecture and local vascular permeability promoted by cholera toxin. The intestinal absorption was not altered by any of the pharmacological modulators. Cholera toxin inoculation also increased HO-1 immunoreactivity and bilirubin levels, a possible protective physiological response. Finally, using fluorometric technique, ELISA assay and molecular docking simulations, we show evidence that CO directly interacts with cholera toxin, forming a complex that affects its binding to GM1 receptor, which help explain the antisecretory effect. Thus, CO is an essential molecule for protection against choleric diarrhea and suggests its use as a possible therapeutic tool.

Cardiovascular Responses During Sepsis

Sepsis is the life-threatening organ dysfunction arising from a dysregulated host response to infection. Although the specific mechanisms leading to organ dysfunction are still debated, impaired tissue oxygenation appears to play a major role, and concomitant hemodynamic alterations are invariably present. The hemodynamic phenotype of affected individuals is highly variable for reasons that have been partially elucidated. Indeed, each patient's circulatory condition is shaped by the complex interplay between the medical history, the volemic status, the interval from disease onset, the pathogen, the site of infection, and the attempted resuscitation. Moreover, the same hemodynamic pattern can be generated by different combinations of various pathophysiological processes, so the presence of a given hemodynamic pattern cannot be directly related to a unique cluster of alterations. Research based on endotoxin administration to healthy volunteers and animal models compensate, to an extent, for the scarcity of clinical studies on the evolution of sepsis hemodynamics. Their results, however, cannot be directly extrapolated to the clinical setting, due to fundamental differences between the septic patient, the healthy volunteer, and the experimental model. Numerous microcirculatory derangements might exist in the septic host, even in the presence of a preserved macrocirculation. This dissociation between the macro- and the microcirculation might account for the limited success of therapeutic interventions targeting typical hemodynamic parameters, such as arterial and cardiac filling pressures, and cardiac output. Finally, physiological studies point to an early contribution of cardiac dysfunction to the septic phenotype, however, our defective diagnostic tools preclude its clinical recognition. © 2021 American Physiological Society. Compr Physiol 11:1605-1652, 2021.

The novel N-methyl-d-aspartate receptor antagonist MN-08 ameliorates lipopolysaccharide-induced acute lung injury in mice

Acute lung injury (ALI) is a clinically severe respiratory disorder, and effective therapy is urgently needed. MN-08, a novel synthetic N-methyl-d-aspartate receptor (NMDAR) antagonist, was investigated for its effect on lipopolysaccharide (LPS)-induced ALI. In vitro, the protective effect of MN-08 on inflammatory response, oxidative stress, and tight junctions (TJs) structure was explored in LPS-induced RAW 264.7 cells and A549 cells. MN-08 markedly decreased (p < 0.001) the levels of pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), and reactive oxygen species (ROS), whereas it moderately upregulated (p < 0.05) heme oxygenase (HO)-1 protein expression in LPS-induced RAW 264.7 cells. Moreover, MN-08 significantly inhibited (p < 0.001) cell apoptosis and improved (p < 0.001) protein expression of TJs in LPS-induced A549 cells. In vivo, the therapeutic effect of MN-08 was evaluated in the LPS-induced ALI model through intratracheal instillation in BALB/c mice. MN-08 administration dramatically attenuated (p < 0.001) pulmonary pathological changes and reduced (p < 0.001) the levels of glutamate, myeloperoxidase (MPO), malondialdehyde (MDA), and number of cells in BALF, whereas it increased (p < 0.05) superoxide dismutase (SOD) and glutathione (GSH) activities in ALI mice. Furthermore, MN-08 markedly blocked the mitogen-activated protein kinases (MAPKs)/nuclear translocation of nuclear factor-κB (NF-κB) signaling pathways in RAW 264.7 cells and lung tissues. These results indicate that MN-08 exhibits lung protection in an LPS-induced ALI model via anti-inflammatory and anti-oxidative activities.

Fluid flux and clearance in acute lung injury

Acute lung injury (ALI) and its most severe form, acute respiratory distress syndrome (ARDS), were presciently described nearly two centuries ago by René Laennec, later to be described clinically in the 1950s and 1960s. Substantial advances have been made in understanding the pathogenesis of these forms of permeability pulmonary edema, including Starling forces and cellular transport mechanisms involved in the generation and resolution of this form of lung injury. Functional animal models and clinically applicable case definitions for ALI and ARDS were instrumental in gaining these new insights. Although no specific pharmacological therapies for ALI and ARDS yet exist, outcomes have improved with advancements in respiratory and fluid-based supportive therapies, and methods to prevent the development or exacerbation of lung injury. Newer targeted therapies continue to be tested for efficacy in this condition where mortality rates frequently exceed 30%. In this article, we review the history of the pathophysiology of lung fluid and solute movement and the seminal clinical observations that brought that history to clinical relevance. We review the relevant lung structure and function and the dynamics of edema formation and resolution, and we describe the related clinical syndromes and the current treatment modalities.

Cecal ligation and puncture-induced murine sepsis does not cause lung injury

OBJECTIVE

The cause of death in murine models of sepsis remains unclear. The primary purpose of this study was to determine if significant lung injury develops in mice predicted to die after cecal ligation and puncture-induced sepsis compared with those predicted to live.

DESIGN

Prospective, laboratory controlled experiments.

SETTING

University research laboratory.

SUBJECTS

Adult, female, outbred Institute of Cancer Research mice.

INTERVENTIONS

Mice underwent cecal ligation and puncture to induce sepsis. Two groups of mice were euthanized at 24 and 48 hrs postcecal ligation and puncture and samples were collected. These mice were further stratified into groups predicted to die (Die-P) and predicted to live (Live-P) based on plasma interleukin-6 levels obtained 24 hrs postcecal ligation and puncture. Multiple measures of lung inflammation and lung injury were quantified in these two groups. Results from a group of mice receiving intratracheal normal saline without surgical intervention were also included as a negative control. As a positive control, bacterial pneumonia was induced with Pseudomonas aeruginosa to cause definitive lung injury. Separate mice were followed for survival until Day 28 postcecal ligation and puncture. These mice were used to verify the interleukin-6 cutoffs for survival prediction.

MEASUREMENTS AND MAIN RESULTS

After sepsis, both the Die-P and Live-P mice had significantly suppressed measures of respiratory physiology but maintained normal levels of arterial oxygen saturation. Bronchoalveolar lavage levels of pro- and anti-inflammatory cytokines were not elevated in the Die-P mice compared with the Live-P. In addition, there was no increase in the recruitment of neutrophils to the lung, pulmonary vascular permeability, or histological evidence of damage. In contrast, all of these pulmonary injury and inflammatory parameters were increased in mice with Pseudomonas pneumonia.

CONCLUSIONS

These data demonstrate that mice predicted to die during sepsis have no significant lung injury. In murine intra-abdominal sepsis, pulmonary injury cannot be considered the etiology of death in the acute phase.

An official American Thoracic Society workshop report: features and measurements of experimental acute lung injury in animals

Acute lung injury (ALI) is well defined in humans, but there is no agreement as to the main features of acute lung injury in animal models. A Committee was organized to determine the main features that characterize ALI in animal models and to identify the most relevant methods to assess these features. We used a Delphi approach in which a series of questionnaires were distributed to a panel of experts in experimental lung injury. The Committee concluded that the main features of experimental ALI include histological evidence of tissue injury, alteration of the alveolar capillary barrier, presence of an inflammatory response, and evidence of physiological dysfunction; they recommended that, to determine if ALI has occurred, at least three of these four main features of ALI should be present. The Committee also identified key "very relevant" and "somewhat relevant" measurements for each of the main features of ALI and recommended the use of least one "very relevant" measurement and preferably one or two additional separate measurements to determine if a main feature of ALI is present. Finally, the Committee emphasized that not all of the measurements listed can or should be performed in every study, and that measurements not included in the list are by no means "irrelevant." Our list of features and measurements of ALI is intended as a guide for investigators, and ultimately investigators should choose the particular measurements that best suit the experimental questions being addressed as well as take into consideration any unique aspects of the experimental design.

[Burn: An inflammatory process]

Thermal injury induce a two-phase inflammatory response: first, a pro-inflammatory status, resulting in a systemic inflammatory response syndrome, then an anti-inflammatory phase characterized by a profound defect in cellular-mediated immunity. This inflammatory reaction proceeds from complex phenomenons in whom many cellular elements are involved (macrophage is the central one) and very complex molecular products interact (especially cytokines). These phenomenons promote significant physiopathologic consequences, especially on cardiovascular homeostasis and endothelial permeability, that lower the prognosis. The inflammatory reaction can be modified, enhanced or maintained by adverse events (i.e. infection) resulting in degradation of clinical situation. Despite a better comprehension of the phenomenons underlying this inflammatory process, diagnosis or therapeutic applications are at that time disappointing.

Respiratory burst function of ovine neutrophils

BACKGROUND

Respiratory burst function resulting in the release of reactive oxygen species such as superoxide anion (O2-) from neutrophils is one of the key mechanisms of the innate immune system, and maladaptive control of this mechanism is thought to play a pivotal role in the development of pathologies such as acute lung injury and sepsis. Ovine models of these pathologies are limited by the poor understanding of ovine neutrophil respiratory burst function.

RESULTS

Aspects of ovine neutrophil respiratory burst function to be characterised were: i) the maximum rate of O2- generated (Vmax); ii) the time taken to reach Vmax; iii) the total amount of O2- generated during the reaction; and iv) the duration of the reaction. As well as for unstimulated neutrophils, these aspects were also characterised after incubation with a priming agonist (platelet activating factor [PAF], tumour necrosis factor alpha [TNF-alpha] and lipopolysaccharides [LPS]) activating agonists (N-formylmethionyl-leucyl-phenylalanine [fMLP] and phorbol 12-myristate 13-acetate [PMA]) or a combination of a priming and an activating agonist. In the absence of priming or activating agonists, ovine neutrophils displayed a low level of respiratory burst function which was not enhanced by either PAF, TNF-alpha, LPS or fMLP, but was significantly enhanced by PMA. The PMA-induced respiratory burst function was further enhanced by pre-incubation with PAF, but not with TNF-alpha or LPS. By varying the length of pre-incubation with PAF it was demonstrated that this effect decreased as the duration of pre-incubation with PAF increased, and that PAF was enhancing PMA's effects rather than PMA enhancing PAF's effects.

CONCLUSION

This study successfully adapted a commonly used method of measuring human neutrophil respiratory burst function to characterise different aspects of ovine neutrophil respiratory burst function. This improved understanding of ovine neutrophils will facilitate the validitation of ovine biomedical models of human pathologies in which neutrophils have been implicated.

Recombinant human activated protein C attenuates endotoxin-induced lung injury in awake sheep

Introduction

Acute lung injury often complicates severe sepsis. In Gram-negative sepsis, bacterial endotoxin activates both coagulation and inflammation. Enhanced lung vascular pressures and permeability, increased extravascular lung water content and deteriorated gas exchange characterize ovine endotoxin-induced lung injury, a frequently used model of acute lung injury. Recombinant human activated protein C (rhAPC), with its anticoagulant, anti-inflammatory, fibrinolytic and antiapoptotic effects, reportedly reduces the respirator-dependent days and the mortality of patients with severe sepsis. We speculate whether rhAPC antagonizes endotoxin-induced lung injury in sheep.

Methods

Two groups of sheep were exposed to Escherichia coli endotoxin (lipopolysaccharide) 15 ng/kg/minute intravenously from 0 to 24 hours; one group received only lipopolysaccharide throughout (n = 8), and the other group received lipopolysaccharide in combination with rhAPC 24 μg/kg/hour from 4 to 24 hours (n = 9). In addition, one group received rhAPC as above as the only intervention (n = 4), and four sham-operated sheep were used for determination of the α and ε isoforms of protein kinase C in pulmonary tissue. Data were assessed by one-way analysis of variance for repeated measurements. Biochemical data were analyzed using Student's t test, or using the Mann–Whitney U test when appropriate.

Results

Infusion of endotoxin caused lung injury, manifested by increments in pulmonary artery pressure, in pulmonary micro-occlusion pressure, in pulmonary vascular downstream resistance, in pulmonary vascular permeability index, in extravascular lung water index and in deterioration of oxygenation that were all attenuated by infusion of rhAPC. Endotoxemia led to changes in inflammation and coagulation, including pulmonary neutrophil accumulation paralleled by increased TNFα and decreased protein C and fibrinogen in animal plasma, which all improved following infusion of rhAPC. Moreover, rhAPC prevented the translocation of protein kinase C α and ε isoforms from the cytosolic fraction of lung tissue extracts.

Conclusion

In awake sheep, rhAPC alleviates endotoxin-induced lung injury – as characterized by improvements of oxygenation, coagulation and inflammation, as well as by reversal of pulmonary hemodynamic and volumetric changes.

Impact of extravascular lung water index on outcomes of severe sepsis patients in a medical intensive care unit

BACKGROUND

This study was designated to investigate whether extravascular lung water index (EVLI) is an independent predictor for mortality outcome in patients with severe sepsis.

METHODS

This study prospectively recruited patients with severe sepsis from a medical intensive care unit (ICU) at a university affiliated hospital. In each patient, transpulmonary thermodilution was used to measure cardiovascular hemodynamics and EVLI via an arterial catheter placed within 48h of the patient meeting the criteria for severe sepsis.

RESULTS

In total, 33 patients were studied. EVLI, Acute Physiology and Chronic Health Evaluation (APACHE) II score, development of acute respiratory distress syndrome, chest X-ray score, lung injury score, body mass index, prior 24h fluid balance, albumin, and white blood cell counts were shown to be predictors of in-hospital survival by a bivariate analysis. In multinominal logistic regression, EVLI (adjusted odds ratio, 6.21; p=0.01; 95% confidence interval, 1.05-1.44) acted as an independent predictor for in-hospital survival. A cut-off value for EVLI of 10ml/kg had good sensitivity (88.2%) and specificity (68.7%) by ROC curve analysis. Medical ICU patients with extremely severe sepsis and a high EVLI (> or =10ml/kg) had lower in-hospital survival rate than those with a low EVLI (<10ml/kg) (15% vs. 67.7%, respectively, p<0.001.

CONCLUSIONS

This investigation suggested that EVLI was an independent predictor for in-hospital survival in medical ICU patients with severe sepsis. Measurement of EVLI may be used for risk stratification among those patients.

MLCK210 gene knockout or kinase inhibition preserves lung function following endotoxin-induced lung injury in mice

Barrier dysfunction, involving the endothelium or epithelium, is implicated in the pathophysiology of many disease states, including acute and ventilator-associated lung injury. Evidence from cell culture, in vivo and clinical studies, has identified myosin light chain kinase as a drug discovery target for such diseases. Here, we measured disease-relevant end points to test the hypothesis that inhibition of myosin light chain kinase is a potential therapeutic target for treatment of barrier dysfunction resulting from acute lung injury. We used a combined gene knockout and chemical biology approach with an in vivo intact lung injury model. We showed that inhibition of myosin light chain kinase protects lung function, preserves oxygenation, prevents acidosis, and enhances survival after endotoxin exposure with subsequent mechanical ventilation. This protective effect provided by the small molecule inhibitor of myosin light chain kinase is present when the inhibitor is administered during a clinically relevant injury paradigm after endotoxin exposure. Treatment with inhibitor confers additional protection against acute lung injury to that provided by a standard protective mode of ventilation. These results support the hypothesis that myosin light chain kinase is a potential therapeutic target for acute lung injury and provide clinical end points of arterial blood gases and pulmonary compliance that facilitate the direct extrapolation of these studies to measures used in critical care medicine.

Influence of fructose-1,6-diphosphate on endotoxin-induced lung injuries in sheep

BACKGROUND

Fructose-1,6-diphosphate (FDP) is reported to have a salutary effect in endotoxin shock and sepsis. This investigation describes the effect of FDP on pulmonary and systemic hemodynamics, lung lymph protein clearance, and leukocyte count in sheep infused with Escherichia coli endotoxin.

MATERIALS AND METHODS

Anesthetized sheep (n = 18), some of which underwent thoracotomy to cannulate lymphatic nodes, were used in this study. After stabilization, all sheep received E. coli endotoxin, 5 microg/kg i.v. infusion over 30 min. Concomitant with the endotoxin infusion, half of the animals were randomly selected to receive an i.v. bolus of FDP (10%), 50 mg/kg, followed by a continuous infusion of 5 mg.kg(-1).min(-1) for 4 h; the rest were treated in the same manner with glucose (10%) in 0.9% NaCl.

RESULTS

Pulmonary artery pressure (PAP) and resistance in the glucose group increased from 20.8 +/- 1.6 to 36.7 +/- 3.2 mmHg (P < 0.007) and from 531 +/- 114 to 1137 +/- 80 dyn.s(-1).cm(-5), respectively (P < 0.005). Despite an increase during endotoxin infusion, these parameters in the FDP group returned to control values. There were no differences in left ventricular pressures, cardiac output, heart rate, and arterial oxygen tension between the groups. In the glucose group, lymph protein clearance was higher (P < 0.01) and blood leukocyte count was lower (P < 0.02). The wet/dry lung weight ratio (g/g) for the glucose group was 5.57 +/- 0.04 and for the FDP-treated group 4.76 +/- 0.06 (P < 0.0005).

CONCLUSION

FDP treatment attenuated significantly the characteristic pulmonary hypertension, lung lymph protein clearance, and pulmonary vascular leakage seen in sheep infused with endotoxin.

Experimental background--review of animal studies

Most of the research on the physiological effects of intramedullary nailing is technically difficult or ethically impossible to perform in humans. A substantial range of factors apply in clinical cases, which means that the data obtained from this source may lack the control needed to reveal the basic mechanisms of pathophysiology associated with this surgical procedure. Consequently, animal studies have been relied upon to provide answers that would otherwise be unavailable. This review manuscript summarizes the available literature on animal studies dealing with the local and systemic effects of intramedullary nailing. It focuses on whether these studies have contributed to our clinical knowledge of the procedure's impact on perfusion and fracture healing, as well as the medical relevance of coincident systemic effects.

DATA SOURCES

Medline, personal library of the first author and of the Department of Trauma Surgery, University of Pittsburgh Medical Center.

STUDY SELECTION

All animal studies on intramedullary stabilization published in English, German, and French.

CONCLUSIONS

The relevance of animal studies investigating the impact of a surgical procedure and its influence on concomitant injuries depends on the design and the type of the animal model. If this fact is considered, and if a model is selected that simulates a systemic impact comparable with the clinical situation, then animal studies may provide a valuable source of otherwise unobtainable information. Such an example is the study of fat embolization associated with intramedullary nailing. Animal subjects enable assessment of the intervention's additive surgical impact, measurement of side effects that may have adverse results, and influence of cofactors (eg, thoracic trauma, severe shock, polytrauma) that predispose the individual to postoperative complications.

Review article: Organ per fusion/permeabilityrelated effects of norepinephrine and vasopressin in sepsis

PURPOSE

One invariable hallmark of severe sepsis is generalized tissue "malperfusion" and hyperpermeability secondary to microcirculatory/capillary leakage. This review focuses on direct and/or indirect influences of norepinephrine, as a standard of care, and vasopressin, as an alternative vasoactive drug, on organ and tissue perfusion/permeability in severe sepsis.

SOURCE

English and French language articles and books published between 1966 and 2005 were identified through a computerized Medline search using the terms "sepsis, permeability, norepinephrine and vasopressin". Relevant publications were retrieved and scanned for additional sources.

PRINCIPAL FINDINGS

There are few randomized clinical trials comparing different vasopressors in sepsis; most available literature consists of clinical reports, animal experiments and occasional reviews. Based on the best current evidence from these sources, we describe the status of major organ perfusion/permeability in sepsis (i.e., the lung, the kidney, the heart, the intestine/gut) in the context of sepsis-induced organ dysfunction/failure. Potential and differential therapeutic effects of the vasopressors norepinephrine and arginine-vasopressin, in the setting of sepsis, are identified.

CONCLUSIONS

In the treatment of sepsis, arginine-vasopressin exhibits organ-specific heterogeneity in vascular responsiveness, compared to norepinephrine. While norepinephrine is a current standard of care in sepsis, arginine-vasopressin shows promise for the treatment of septic shock.

Effects of levosimendan in normodynamic endotoxaemia: a controlled experimental study

OBJECTIVES

Levosimendan is an inotropic and vasodilator drug that has proved to be useful in cardiogenic shock. Pretreatment with levosimendan in experimental hypodynamic septic shock in pigs has shown valuable effects in oxygen transport. Our goal was to assess the effects of levosimendan in a normodynamic model of endotoxaemia.

METHODS

Twelve sheep were anaesthetized and mechanically ventilated. After taking basal haemodynamic and oxygen transport measurements, sheep were assigned to two groups during 120 min: (1) endotoxin (5 microg/kg endotoxin); (2) levosimendan (5 microg/kg endotoxin plus levosimendan 200 microg/kg followed by 200 microg/kg/h). Both groups received hydration of 20 ml/kg/h of saline solution.

RESULTS

In the endotoxin group, cardiac output, intestinal blood flow and systemic and intestinal oxygen transports and consumptions (DO(2) and VO(2)) remained unchanged. In the levosimendan group, systemic and intestinal DO(2) were significantly higher than in the endotoxin group. Because stroke volume did not change (basal versus 120': 0.9+/-0.1 ml/kg versus 0.9+/-0.2 ml/kg, p=0.3749), the elevation in cardiac output by levosimendan (145+/-17 ml/min/kg versus 198+/-16 ml/min/kg, p=0.0096) was related to an increased heart rate (159+/-32 beats l/min versus 216+/-19 beats l/min, p=0.0037). Levosimendan precluded the development of gut intramucosal acidosis at 120' (endotoxin versus levosimendan, ileal intramucosal-arterial PCO(2) difference: 19+/-4 Torr versus 10+/-4 Torr, p=0.0025). However, levosimendan decreased mean arterial blood pressure (99+/-20 Torr versus 63+/-13 Torr, p=0.0235) and increased blood lactate levels (2.4+/-0.9 mmol/l versus 4.8+/-1.5 mmol/l, p=0.0479). All p-values are differences in specific points (paired or unpaired t-test with Bonferroni correction) after two-way repeated measures ANOVA. A p-value<0.05 was considered significant.

CONCLUSIONS

Levosimendan improved oxygen transport and prevented the development of intramucosal acidosis in this experimental model of endotoxaemia. However, systemic hypotension and lactic acidosis occurred. Additional studies are needed to show if different doses and timing of levosimendan administration in septic shock might improve gut perfusion without adverse effects.

Endotoxin-induced acute lung injury requires interaction with the liver

Clinical and laboratory data indicate that the liver plays an important role in the incidence, pathogenesis, and outcome of acute lung injury/acute respiratory distress syndrome. To distinguish direct effects of endotoxin on the lungs from liver-dependent effects during the early phase of the response to endotoxemia, we used an in situ perfused piglet preparation in which only the ventilated lung or both the lung and liver could be included in a blood perfused circuit. We monitored pulmonary vascular resistance, oxygenation, neutrophil count, lung edema as reflected by wet-dry weights of lung tissue, perfusate concentrations of TNF-alpha, IL-6, and 8-isoprostane (a marker of oxidative stress), and activation of the transcription factor (NF-kappaB) in lung tissue before and for 2 h after endotoxin. When only the lung was perfused, endotoxin caused pulmonary hypertension and neutropenia; but oxygenation was maintained; TNF-alpha, IL-6, and 8-isoprostane levels were minimally elevated; and there was no lung edema. When both the liver and lung were perfused, endotoxin caused marked hypoxemia, large increases in perfusate TNF-alpha, IL-6, and 8-isoprostane concentrations, and severe lung edema. NF-kappaB activation in the lung was greatest when the liver was in the perfusion circuit. We conclude that the direct effects of endotoxemia on the lungs include vasoconstriction and leukocyte sequestration, but not lung injury. Intense activation of the inflammatory response and oxidative injury that results in pulmonary edema and hypoxemia (acute lung injury) requires interaction of the lungs with the liver.

Vascular changes after intra-amniotic endotoxin in preterm lamb lungs

Chorioamnionitis is associated with preterm delivery and bronchopulmonary dysplasia (BPD), characterized by impaired alveolar and pulmonary vascular development and vascular dysfunction. To study the vascular effects in a model of chorioamnionitis, preterm lambs were exposed to 20 mg of intra-amniotic endotoxin or saline for 1, 2, 4, or 7 days and delivered at 122 days gestational age (term = 150 days). This intra-amniotic endotoxin dose was previously shown to induce lung maturation. The effect of intra-amniotic endotoxin on expression of endothelial proteins was evaluated. Muscularization of the media and collagen deposition in adventitia of small pulmonary arteries was used to assess vascular remodeling. Compared with controls, bronchoalveolar lavage fluid protein content was increased 2 days after intra-amniotic endotoxin exposure. Vascular endothelial growth factor (VEGF) 165 isoform mRNA decreased 2–4 days after intra-amniotic endotoxin. VEGF, VEGF receptor-2, endothelial nitric oxide synthase (eNOS), platelet endothelial cell adhesion molecule-1, and Tie-2 protein expression in the lung coordinately decreased 1–7 days after intra-amniotic endotoxin. Intra-amniotic endotoxin appeared to selectively decrease eNOS expression in small pulmonary vessels compared with large vessels. Medial smooth muscle hypertrophy and increased adventitial fibrosis were observed 4 and 7 days after intra-amniotic endotoxin. These results demonstrate that, in the preterm lamb lung, antenatal inflammation inhibits endothelial cell protein expression followed by vascular remodeling changes in small pulmonary arteries. Exposure to antenatal inflammation may cause vascular remodeling and contribute to the development of BPD.

Therapeutic effect of in vivo transfection of transcription factor decoy to NF-kappaB on septic lung in mice

Nuclear factor-kappaB (NF-kappaB) plays a key role in regulating expression of several genes involved in the pathophysiology of endotoxic shock. We investigated whether in vivo introduction of synthetic double-stranded DNA with high affinity for the NF-kappaB binding site could block expression of genes mediating pulmonary vascular permeation and thereby provide effective therapy for septic lung failure. Endotoxic shock was induced by an intravenous injection of 10 mg/kg Escherichia coli endotoxin in mice. We introduced NF-kappaB decoy oligodeoxynucleotide (ODN) in vivo 1 h after endotoxic shock by using a gene transfer kit. At 10 h, blood samples were collected for measurement of histamine and for blood-gas analysis. Gene and protein expression levels of target molecules were determined by means of Northern and Western blot analyses, respectively. The transpulmonary flux of (125)I-labeled albumin was used as an index of lung vascular permeability. Administration of endotoxin caused marked increases in plasma histamine and gene and protein expressions of histidine decarboxylase, histamine H(1) receptors, and inducible nitric oxide synthase in lung tissues. Elevated lung vascular permeability was also found. Blood-gas analysis showed concurrent decreases in arterial Po(2), Pco(2), and pH. All of these events induced by endotoxin were significantly inhibited by transfection of NF-kappaB decoy ODN but not by its mutated (scrambled) form (used as a control). Our results indicate for the first time the potential usefulness of NF-kappaB decoy ODN for gene therapy of endotoxic shock.

Hyperoxia-induced emphysematous changes in subacute phase of endotoxin-induced lung injury in rats

We examined the effects of prolonged hyperoxia (75% O2) on lung structure and collagen metabolism in the subacute phase of lung injury induced by continuous infusion of endotoxin (LPS) in a rat model. Experimental groups included control, endotoxin alone, endotoxin plus hyperoxia, and hyperoxia alone. Endotoxin-treated rats received a bolus of LPS (10 mg/kg iv) followed by 500 μg·kg−1·day−1in continuous infusion for 10 days. The bronchoalveolar lavage (BAL) fluid/plasma albumin concentration ratio, an index of capillary permeability, and neutrophil and macrophage counts in BAL fluid were highest in the endotoxin plus hyperoxia group. On pathological examination, prolonged hyperoxia exacerbated destruction of the alveolar wall and caused most prominent emphysematous changes in the endotoxin plus hyperoxia group. Lung tissue hydroxyproline concentration was significantly decreased in the hyperoxia group and increased in the endotoxin group. The latent forms of MMP-2 and MMP-9 increased in BAL fluid of the endotoxin- and/or hyperoxia-treated groups, whereas the activities of collagenase and gelatinase, and the active form of MMP-2 were all increased in the hyperoxia-treated groups. Added to endotoxin, prolonged hyperoxia degraded collagen, the major structural component of basement membranes, and caused emphysematous changes associated with activation of collagenase and MMP-2. Our observations suggest that, in the subacute phase of endotoxin-induced lung injury, prolonged hyperoxia causes pulmonary emphysematous changes with persistent injury to the alveolar capillary barrier. Collagenase and MMP-2 activated by hyperoxia, together with MMP-9, may play prominent roles in disruption of the alveolar basement membranes and degradation of collagen lining the alveolar walls.

Effective attenuation of endotoxin-induced acute lung injury by 2,3-diacetyloxybenzoic acid in two independent animal models

The pathology of acute lung injury (ALI) is often modeled in animal studies by the administration of lipopolysaccharide (LPS), which results in an endotoxemia with sequelae similar to that seen in acute respiratory distress syndrome (ARDS). Here we report the results of two studies designed to examine the efficacy of a novel agent, 2,3-diacetyloxybenzoic acid (2,3-DABA), in the treatment of LPS-induced ALI. In two separate animal models, 2,3-DABA was effective in significantly reducing lung microvascular permeability, a condition commonly seen in ARDS, which results in pulmonary edema and respiratory insufficiency. In each model, it is demonstrated that the mechanism by which 2,3-DABA exerts this effect occurs subsequent to the recruitment of neutrophils to the site of inflammation. Lung permeability was significantly decreased in both models by treatment with 2,3-DABA, suggesting that this agent, either alone or in combination therapy, may be useful in the treatment of ALI associated with ARDS.

Effects of acute hypoxia and lipopolysaccharide on nitric oxide synthase-2 expression in acute lung injury

The potential role of nitric oxide synthase-2 (NOS2) in acute lung injury (ALI) has gained increasing attention. This study evaluates the effects of hypoxia, an important feature of ALI, on NOS2 expression in a rat model of ALI caused by exposure to hypoxia and LPS. Exposure to hypoxia alone had no effect on the expression of NOS2 in rat lungs. LPS treatment resulted in a significant increase in NOS2 in the lungs, which was further enhanced by concomitant exposure to hypoxia. Immunohistochemical analysis and in situ hybridization showed no changes in the expression of NOS2 in lung resident cells under any conditions. The increase in NOS2 levels is mainly due to the influx of NOS2-expressing inflammatory cells. By morphologic analysis, these inflammatory cells were identified as neutrophils, lymphocytes, and monocytes. In vitro experiments of lung epithelial and endothelial cell lines showed no detectable expression of NOS2 with any of the treatments. In a macrophage cell line, LPS-induced NOS2 expression was not affected by the concomitant exposure to hypoxia. In conclusion, LPS increases NOS2 expression in rat lungs through the recruitment of NOS2-producing leukocytes. Simultaneous exposure to LPS and hypoxia results in a greater influx of inflammatory cells that further enhances NOS2 expression.

Inhibition of matrix metalloproteinases reduces local and distant organ injury following experimental acute pancreatitis

BACKGROUND

Pulmonary complications from pancreatitis involve parenchymal destruction via proteolytic enzymes. Matrix metalloproteinases (MMPs) may play an important role in pulmonary injury following acute severe pancreatitis. We hypothesized that local and distant organ injury would be decreased by the presence of an MMP inhibitor (Batimistat; BB-94) following severe acute pancreatitis (AP).

METHODS

Eighteen male rats were randomized into two groups: BB-94 (AP + 40 mg/kg/24 h BB-94 ip x three doses) or control (AP + 20 ml/kg/24 h normal saline ip x three doses). Necrotizing AP was induced by retrograde infusion of 5% sodium taurocholate (1.5 ml/kg) into the pancreatic duct. Twenty additional animals were randomized into BB-94 and control groups for the survival study. Serum was evaluated for amylase and MMP activity. Pancreatic sections were graded for edema, necrosis, neutrophil infiltrate, and hemorrhage. Myloperoxidase (MPO) activity was used to determine PMN infiltration in the lung. Evan's Blue dye extravasation was used to quantify vascular permeability.

RESULTS

Animals in the BB-94 group had decreased amylase levels (1086.0 +/- 61.7 U/L vs 2232.7 +/- 309.9 U/L; P < 0.05), decreased cellular infiltrate (1.4 +/- 0.2 vs 2.3 +/- 0.2; P < 0.02), and decreased necrosis (4.1 +/- 0.3 vs 6.1 +/- 0.4; P < 0.005) compared to the control group. Lung tissue following pancreatitis in the BB-94 group demonstrated decreased MPO activity (41.5 +/- 2.4 units vs 57.3 +/- 2.9 units; P < 0.05) and decreased vascular permeability (18.3 +/- 2.8 mg/100 g vs 30.1 +/- 4.6 mg/100 g; P < 0.05). Animals treated with BB-94 had 100% survival compared to 50% survival in control at 72 h.

CONCLUSIONS

Pancreatitis results in increased local and distant MMP activity. Pulmonary and pancreatic injury following AP can be abrogated by treatment with an MMP inhibitor (Batimistat; BB-94) which may result in decreased morbidity and mortality.

Effects of intramedullary femoral fracture fixation: what is the impact of experimental studies in regards to the clinical knowledge?

This review manuscript summarizes the available literature on animal studies dealing with the local and systemic effects of intramedullary (IM) reamed and unreamed nailing. It focuses on the question of whether the large numbers of studies have contributed to our clinical knowledge about its impact on perfusion, fracture healing, and about the clinical relevance of systemic side effects. The effects of IM contents that are squeezed out of the medullary canal into the venous and the systemic circulation due to reaming and nailing has been a major issue. In addition, the impact of the surgical procedure and the timing of such a major operation as femoral fractures surgery has been a major source of debate within the last decade. The compilation of relevant studies investigating the degree of impact of a surgical procedure and the influence of concomitant injuries depends on the design and the type of the animal model. If this fact is considered and if a model is selected that reflects the systemic impact comparable with the clinical situation, animal studies represent a valuable source of information. In this respect, fat embolization represents an additive surgical impact and can cause clinically relevant side effects if cofactors (e.g., thoracic trauma, severe shock, and polytrauma) are present that set the individual up for postoperative complications.

A new model for the continuous monitoring of polymorphonuclear leukocyte trapping in the pulmonary vasculature of the rabbit

INTRODUCTION

Accumulation of polymorphonuclear leukocytes (PMNs) within the pulmonary vasculature contributes to the pathophysiology of a number of diseases, including chronic obstructive pulmonary disease (COPD) and acute respiratory distress syndrome. The techniques available to study this have their limitations.

METHODS

We have developed a minimally invasive technique for the continuous monitoring of 111In-labelled PMNs (111In-PMNs) in the thoracic and groin regions of rabbits. The effects of intravenous injection of the chemoattractants, interleukin (IL)-8, leukotriene (LT) B(4), and lipopolysaccharide (LPS) were studied.

RESULTS

Intravenous injection of LTB(4), IL-8, or LPS caused an accumulation of 111In-PMNs in the lung and a concomitant decrease in counts in the leg and caused no significant change from baseline in counts in the lung or the leg after injection of 111In-labelled red blood cells (RBCs).

CONCLUSION

In conclusion, we have demonstrated a technique that is simple, reproducible, and robust, which can be used to investigate PMN trapping in the lung vasculature in response to well characterised PMN chemoattractants and that may be applied to the preclinical study of new drugs.

Growth hormone increases circulating neutrophil activation and provokes lung microvascular injury in septic peritonitis rats

BACKGROUND

Growth hormone (GH) has been shown to increase mortality in critical illness, illustrating the need for better understanding of GH treatment. The neutrophil is a key mediator in producing organ injury following shock and trauma and is regulated by GH. Therefore, the purpose of the present study was to examine the effects of GH on circulating neutrophil activation and subsequent lung injury induced by sepsis in rats.

MATERIALS AND METHODS

Sepsis was induced in male Wistar rats via cecal ligation and puncture (CLP). Recombinant human growth hormone (1 IU/kg) was given subcutaneously right after CLP with an additional injection at 12 h after CLP. CD11b expression and an oxidative burst of neutrophils were detected using flow cytometric analysis. Lung myeloperoxidase activity was determined as an index of tissue neutrophil accumulation. Lung microvascular injury was assessed by quantitating extravasation of Evan's blue dye into lung parenchyma.

RESULTS

Growth hormone significantly increased sepsis-induced expression of CD11b and sepsis-induced circulating neutrophil activation. Also growth hormone increased neutrophil accumulation in lungs induced by sepsis. Lung microvascular injury was aggravated by growth hormone treatment in septic rats.

CONCLUSIONS

It is worthwhile to rethink GH administration in critical illness and further studies are required to determine the safety and clinical benefits of GH administration in critical illness.

Effect of crystalloid resuscitation and inhalation injury on extravascular lung water: clinical implications

STUDY OBJECTIVE

Arterial thermal dilution with an integrated fiberoptic monitoring system (COLD Z-021; Pulsion Medical Systems; Munich, Germany) allows measurement of extravascular lung water (EVLW) and pulmonary permeability index (PPI). The aim of this study was to evaluate the widespread clinical assumption that early respiratory failure following burn and inhalation injury is due to interstitial fluid accumulation in the lung.

DESIGN

Clinical, prospective study.

SETTING

ICU of a university referral center of burn care.

PATIENTS

Thirty-five severely burned adults (> 20% of body surface area).

INTERVENTIONS

Resuscitation therapy was guided by the results of hemodynamic monitoring using the intrathoracic blood volume (ITBV) as a cardiac preload indicator. The resuscitation goals included a normalization of preload (ITBV > 850 mL/m(2)) and cardiac index (> 3.5 L/min/m(2)) within 24 h after ICU admission. Fluid loading was implemented to reach these goals.

MEASUREMENTS AND RESULTS

One hundred forty lung water measurements were performed at 0 h, 12 h, 24 h, and 48 h after admission to the ICU. Significant elevation of EVLW and PPI was found in three measurements (2%) at 48 h after ICU admission, and was in one patient associated with inhalation injury. EVLW and PPI were not significantly different between patients with and without inhalation injury. No correlation was found between resuscitation volume and EVLW (r(2) = 0.02) or between the alveolar-arterial oxygen pressure difference and EVLW (r(2) = 0.017). Chest radiograph abnormalities were found in 2 of 22 patients with inhalation injury; these were not associated with increased values of EVLW.

CONCLUSION

Early fluid accumulation in the lung in burned patients is very uncommon, even in the presence of inhalation injury. There is no evidence that thermal injury causes an increase in pulmonary capillary membrane permeability.

Effects of adenosine on extravascular lung water content in endotoxemic pigs

OBJECTIVE

To investigate whether adenosine protects against endotoxin-induced increments in extravascular lung water content.

DESIGN

Prospective, randomized, animal study.

SETTING

University research laboratory.

SUBJECTS

Twenty-one anesthetized juvenile pigs.

INTERVENTIONS

The animals were divided into two groups subjected to endotoxin infusion: Endotoxin alone (n = 7), or endotoxin combined with adenosine infusion (n = 7) administered during the whole experimental period. Two other groups were exposed to anesthesia alone (n = 4) or adenosine infusion alone (n = 3), respectively.

MEASUREMENTS AND MAIN RESULTS

Central hemodynamic variables and extravascular lung water, as assessed by the thermal dye dilution double indicator technique, were monitored. Plasma endothelin-1 concentrations were measured hourly. Extravascular lung water increased significantly in response to endotoxemia (p <.001) along with an increase in pulmonary microvascular pressure (P(mv) [p <.01]). Although the Pmv increased less in endotoxemic animals exposed to adenosine infusion, no intergroup difference was found. From 4 through 6 hrs, adenosine-treated pigs displayed only half of the extravascular lung water content of nontreated animals (p <.01). The latter did not differ from that of anesthetized controls receiving anesthesia or adenosine alone. Adenosine administered alone had no effect on P(mv). In pigs receiving adenosine alone, extravascular lung water content reached nadir after 3 hrs. In both endotoxin groups, plasma endothelin-1 concentration increased two-fold, peaking 4-6 hrs after the start of endotoxin infusion (p <.001).

CONCLUSIONS

The endotoxin-induced increase in lung extravascular water was hampered by intravenously infused adenosine in the presence of a nonsignificantly reduced microvascular pressure. This leaves reduced microvascular permeability the most likely reason for the beneficial effect of adenosine.

Lung albumin accumulation is spatially heterogeneous but not correlated with regional pulmonary perfusion

The contribution of pulmonary perfusion heterogeneity to the development of regional differences in lung injury and edema is unknown. To test whether regional differences in pulmonary perfusion are associated with regional differences in microvascular function during lung injury, pigs were mechanically ventilated in the prone position and infused with endotoxin (Escherichia coli 055:B5, 0.15 microg. kg(-1). h(-1); n = 8) or saline (n = 4) for 4 h. Extravascular albumin accumulation and perfusion were measured in multiple approximately 0.7-ml lung regions by injecting pigs with radiolabeled albumin and radioactive microspheres, respectively. Extravascular albumin accumulation was spatially heterogeneous but not correlated with regional perfusion. Extravascular albumin accumulation was greater in dorsal than ventral regions, and regions with similar albumin accumulation were spatially clustered. This spatial organization was less evident in endotoxemic than control pigs. We conclude that there are regional differences in lung albumin accumulation that are spatially organized but not mediated by regional differences in pulmonary perfusion. We speculate that regional differences in microvascular pressure or endothelial function may account for the observed distribution of extravascular albumin accumulation.

The role of interleukin-8 and its receptors in inflammatory lung disease: implications for therapy

Neutrophils have been implicated in the pathogenesis of many inflammatory lung diseases, including the acute respiratory distress syndrome, chronic obstructive pulmonary disease and asthma. The CXC chemokine interleukin (IL)-8, is a potent neutrophil recruiting and activating factor and the detection of IL-8 in clinical samples from patients with these diseases has led clinicians to believe that antagonism of IL-8 may be a practicable therapeutic strategy for disease management. Work over the last decade has concentrated on both the molecular mechanisms by which IL-8 is produced in the inflammatory setting and also on the manner in which IL-8 activates the neutrophil. Expression of the IL-8 gene appears to be controlled by several components of the inflammatory milieu. Whilst lipopolysaccharide, IL-1beta and tumor necrosis factor-alpha are capable of augmenting IL-8 production, IL-10 is a potent inhibitor of IL-8 synthesis and appears to play an auto-regulatory role. Regulation of the IL-8 gene is under the control of nuclear factor kappaB which appears to be a primary target for corticosteroid-mediated repression of IL-8 production. IL-8 exerts is effects on neutrophils by binding with high affinity to two receptors on its cell surface, the chemokine receptors CXCR1 and CXCR2. These closely related receptors belong to the superfamily of G-protein coupled receptors, proteins that historically have proved amenable to antagonism by small molecules. The recent descriptions in the literature of highly potent small molecule antagonists of CXCR2 and their success in blocking in vivo trafficking of neutrophils suggest that antagonism of IL-8 at the receptor level is a viable therapeutic strategy. Clinical trials of such compounds will ultimately provide crucial information currently lacking and will define whether or not IL-8 blockade provides future therapy in pulmonary disease.

Increased matrix metalloproteinase expression and activation following experimental acute pancreatitis

BACKGROUND

The observation that matrix metalloproteinases (MMPs) are central to tissue remodeling and may contribute to organ failure prompted us to investigate the role of MMPs in acute pancreatitis. We hypothesize that increased expression and activation of MMP-2 and MMP-9 will correlate with organ injury following acute pancreatitis.

METHODS

Acute pancreatitis was induced in five male rats by retrograde infusion of 5% sodium taurocholate into the pancreatic duct. Sham laparotomy was performed on five rats serving as a control. Pancreatitis was confirmed by histology and serum amylase levels. MMP-2 and MMP-9 activity and expression were assayed by gelatin zymography in the lungs and ascitic fluid of each animal. Lung permeability was assayed by Evans blue dye extravasation. Lung activity of MMP-2 and MMP-9 was confirmed by a specific fluorogenic MMP substrate assay.

RESULTS

Lung permeability increased twofold in the animals with severe pancreatitis compared with sham. Analysis of the zymograms from lung homogenate revealed a threefold increase in active MMP-2 in severe pancreatitis compared with sham and no change in MMP-9 activity. Gelatin zymograms of peritoneal fluid from severe pancreatitis animals demonstrated increased levels of active MMP-2 and MMP-9 compared with the sham group. Increases in MMP activity were confirmed by MMP activity assay using a fluorogenic substrate.

CONCLUSIONS

This study demonstrates a correlation between severity of acute pancreatitis and active MMP-2 and MMP-9 levels in the peritoneal fluid and MMP-2 activity in lung homogenate. The MMP-mediated degradation of the basement membrane offers a potential pharmacologic and therapeutic target for halting the final biologic outcome of severe pancreatitis.

Detergent inhibits 70-90% of responses to intravenous endotoxin in awake sheep

Sheep have reactive pulmonary intravascular macrophages, which are essential for the marked pulmonary vascular response to infusions of small quantities of endotoxin. In another species with reactive pulmonary intravascular macrophages, horses, our laboratory found that an intravenous biosafe detergent, tyloxapol, inhibited some systemic and pulmonary responses to endotoxin (Longworth KE, Smith BL, Staub NC, Steffey EP, and Serikov V. Am J Vet Res 57: 1063-1066, 1996). We determined whether the same detergent would inhibit endotoxin responses in awake sheep. In 10 awake, instrumented sheep with chronic lung lymph fistulas, we did a control experiment by intravenously infusing 1 microg/kg Escherichia coli endotoxin. One week later, we gave 40 micromol/kg tyloxapol intravenously 1-4 h before infusing the same dose of endotoxin. In these paired studies, we compared pulmonary hemodynamics, lung lymph dynamics, body temperature, circulating leukocyte concentrations, and circulating tumor necrosis factor for 6 h. In all 10 sheep, tyloxapol blocked 80-90% of the pulmonary responses and 70-90% of the systemic responses. Tyloxapol is safe, inexpensive, easy to use, and effective immediately. It may be a clinically useful approach to contravening many of the effects of endotoxemia, in humans as well as animals.

The lung is the major site that produces nitric oxide to induce acute pulmonary oedema in endotoxin shock

1. The present study was undertaken to determine the locus of nitric oxide (NO) production that is toxic to the lung and produces acute pulmonary oedema in endotoxin shock, to examine and compare the effects of changes in lung perfusate on endotoxin-induced pulmonary oedema (EPE) and to evaluate the involvement of constitutive and inducible NO synthase (cNOS and iNOS, respectively). 2. Experiments were designed to induce septic shock in anaesthetized rats with the administration of Escherichia coli lipopolysaccharide (LPS). Exhaled NO, lung weight (LW)/bodyweight (BW) ratio, LW gain (LWG) and lung histology were measured and observed to determine the degree of EPE 4 h following LPS. The EPE was compared between groups in which LPS had been injected either into the systemic circulation or into the isolated perfused lung. The lung perfusate was altered from whole blood to physiological saline solution (PSS) with 6% albumin to test whether different lung perfusions affected EPE. Pretreatment with various NOS inhibitors was undertaken 10 min before LPS to investigate the contribution of cNOS and iNOS to the observed effects. 3. Endotoxin caused profound systemic hypotension, but little change in pulmonary arterial pressure. The extent of EPE was not different between that induced by systemic injection and that following administration to isolated lungs preparations. Replacement of whole blood with PSS greatly attenuated (P < 0.05) EPE. In blood-perfused lungs, pretreatment with NOS inhibitors, such as Nomega-nitro-L-arginine methyl ester, aminoguanidine and dexamethasone, significantly prevented EPE (P < 0.05). 4. The major site of NO production through the whole blood is in the lung. The NO production mediated by the iNOS system is toxic to the endothelium in the pulmonary microvasculature. Inhalation of NO for patients with sepsis may be used with clinical caution. Therapeutic consideration of lung extracorporeal perfusion with PSS and pharmacological pretreatment with iNOS inhibitors may be warranted.

Methylene blue reduces lung fluid filtration during the early phase of endotoxemia in awake sheep

OBJECTIVE

To determine whether methylene blue (MB), an inhibitor of soluble guanylate cyclase and nitric oxide synthase, alters lung hemodynamics and fluid filtration after endotoxin in sheep.

DESIGN

Prospective, randomized, controlled experimental study with repeated measurements.

SETTING

University animal laboratory.

SUBJECTS

Eight yearling, awake sheep.

INTERVENTIONS

Sheep were instrumented for a chronic study with vascular and lung lymph catheters. In two experiments, separated by 1 wk of recovery, the animals received intravenously either an injection of MB 10 mg/kg or a corresponding volume of 0.9% sodium chloride as pretreatment. Thirty minutes later, sheep received a bolus injection of Escherichia coli endotoxin 1 microg/kg, followed by either an infusion of MB 2.5 mg/kg/hr or a corresponding volume of 0.9% sodium chloride for 5 hrs.

MEASUREMENTS AND MAIN RESULTS

MB decreased the early phase endotoxin-induced rises in pulmonary capillary pressure and pulmonary vascular resistance. MB also reduced the increments in lung lymph flow (QL) and protein clearance (CL) as well as the rightward shift of the permeability-surface area product (PS). In addition, MB diminished the decrease in cardiac output, stabilized mean arterial pressure, and precluded the rise in plasma and lung lymph cyclic guanosine 3'-5' monophosphate. However, during the late phase, MB-treated sheep presented with a faster rise in QL with no difference in CL and PS from the endotoxemic controls.

CONCLUSIONS

During the early phase of endotoxemia in sheep, MB attenuates lung injury by decreasing the enhanced lung fluid filtration as a result of reduced pulmonary capillary pressure and permeability. However, MB does not counteract the late phase increase in lung fluid filtration.

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.

Gut ischemia/reperfusion activates lung macrophages for tumor necrosis factor and hydrogen peroxide production

BACKGROUND

Gut ischemia followed by reperfusion (I/R) is implicated as a prime initiating event in the mechanism of multiple organ failure after trauma and hemorrhagic shock. Several lines of evidence indicate that macrophages are involved in this prime event. Our purpose was to evaluate hydrogen peroxide (H2O2) and tumor necrosis factor (TNF) production and phagocytosis by lung macrophages in a gut I/R model of multiple organ failure in rats.

METHODS

In the experimental group (I/R), Wistar rats (n = 35) were anesthetized and subjected to a median laparotomy, and the superior mesenteric artery was clamped for 45 minutes followed by 60 minutes of reperfusion. In the control group (LAP) (n = 37), animals underwent sham laparotomy. After the period of reperfusion, bronchoalveolar lavage (BAL) was performed and the resulting BAL cells were assayed for H2O2 production using the horseradish peroxidase-mediated red phenol oxidation method. TNF release was determined using the L929 cells bioassay. Zymosan phagocytosis by BAL macrophages was quantitated using phase microscopy.

RESULTS

H2O2 release in BAL cells of I/R rats (19.90 +/- 7.98 nmol/L/2 x 10(5) cells) is statistically higher than in the LAP group (10.92 +/- 5.01 nmol/L per 2 x 10(5) cells) (p = 0.0155), and the TNF production by BAL cells of the I/R group (38.09 +/- 20.79 units per 10(6) cells) was significantly higher than that of LAP rats (17.16 +/- 13.35 units per 10(6) cells) (p = 0.0281). Phagocytic activity of BAL mac. Macrophages of I/R rats was not statistically different from LAP animals.

CONCLUSION

These results suggest that BAL macrophage play a role in the mechanism of acute lung injury after trauma and hemorrhagic shock.

Triolein increases microvascular permeability in isolated perfused rabbit lungs: role of neutrophils

BACKGROUND

Pathophysiologic mechanisms of the fat embolism syndrome are poorly understood. Neutrophils are thought to play a role in the development of many forms of acute lung injury. The objective of this study was to examine the role of intrapulmonary neutrophils in lung injury resulting from fat infusion.

METHODS

Triolein (0.08 mL/kg) was infused into isolated rabbit lungs perfused with Krebs-Henseleit buffer. Pulmonary arterial pressure was monitored, and pulmonary vascular resistance and microvascular permeability (Kf) were measured at baseline and 60 minutes after triolein infusion.

RESULTS

Triolein produced increases in pulmonary arterial pressure, pulmonary vascular resistance, and Kf. Neutrophil depletion or inhibition of neutrophil elastase prevented the increase in Kf after triolein, and catalase partially blocked this Kf increase.

CONCLUSION

These results suggest that activated intrapulmonary neutrophils play a major role in developing triolein-induced lung injury, intrapulmonary neutrophils act chiefly via neutrophil elastase release, and reactive oxygen species are involved in the lung injury.

Effect of aminoguanidine on lung fluid filtration after endotoxin in awake sheep

It has been suggested that enhanced generation of nitric oxide by inducible nitric oxide synthase (iNOS) may contribute to acute lung injury. We hypothesized that aminoguanidine (AG), a proposed selective inhibitor of iNOS, would alter pulmonary hemodynamics, fluid filtration, and gas exchange after endotoxin in chronically instrumented awake sheep. Eighteen sheep were randomly assigned to receive either AG (10 mg/kg + 1 mg/kg/h), or NaCl 0.9% intravenously for 4 h, beginning 2 h after injection of Escherichia coli endotoxin (1 microgram/kg). After endotoxin, pulmonary artery pressure (Ppa), capillary pressure (Pc), and vascular resistance index (PVRI) rose concomitantly with six-fold increments in lung lymph flow (Q L) and protein clearance (CL). Extravascular lung water (EVLW) doubled, as assessed with the thermal dye dilution technique; Pa(O(2)) decreased, AaPO(2) and venous admixture (Q S/Q T) increased. After AG, Q L and CL increased further by approximately 30%, whereas EVLW remained unchanged, despite an additional increase in Pc. Ppa, PVRI, and systemic vascular resistance index rose, whereas cardiac index and pulmonary blood volume index declined. In addition, Pa(O(2)) rose, and AaPO(2) and Q S/Q T decreased. We conclude that in endotoxemic sheep, AG improves gas exchange and increases Q L and CL, whereas EVLW remains unchanged in spite of enhanced Pc. Apparently, increased lymphatic drainage prevents EVLW from rising after AG.

Transglutaminase-mediated fibronectin multimerization in lung endothelial matrix in response to TNF-alpha

Exposure of lung endothelial monolayers to tumor necrosis factor (TNF)-alpha causes a rearrangement of the fibrillar fibronectin (FN) extracellular matrix and an increase in protein permeability. Using calf pulmonary artery endothelial cell layers, we determined whether these changes were mediated by FN multimerization due to enhanced transglutaminase activity after TNF-alpha (200 U/ml) for 18 h. Western blot analysis indicated that TNF-alpha decreased the amount of monomeric FN detected under reducing conditions. Analysis of (125)I-FN incorporation into the extracellular matrix confirmed a twofold increase in high molecular mass (HMW) FN multimers stable under reducing conditions (P < 0.05). Enhanced formation of such HMW FN multimers was associated with increased cell surface transglutaminase activity (P < 0.05). Calf pulmonary artery endothelial cells pretreated with TNF-alpha also formed nonreducible HMW multimers of FN when layered on surfaces precoated with FN. Inhibitors of transglutaminase blocked the TNF-alpha-induced formation of nonreducible HMW multimers of FN but did not prevent either disruption of the FN matrix or the increase in monolayer permeability. Thus increased cell surface transglutaminase after TNF-alpha exposure initiates the enhanced formation of nonreducible HMW FN multimers but did not cause either the disruption of the FN matrix or the increase in endothelial monolayer permeability.

Spontaneous high systemic oxygen delivery increases survival rate in awake sheep during sustained endotoxemia

OBJECTIVE

To study the natural evolution of systemic oxygen delivery (Do2) and oxygen consumption (Vo2) in sheep infused with low or high doses of endotoxin.

DESIGN

Prospective, controlled experimental study.

SETTING

Animal research laboratory at a medical university.

SUBJECTS

Twenty-nine chronically instrumented awake sheep (25-35 kg).

INTERVENTIONS

Awake animals were continuously infused with saline (n = 8) or two doses of Escherichia coli endotoxin (20 or 40 ng/kg/min; n = 21) for 72 hrs. No attempt was made to increase Do2, but respiratory failure was treated by mechanical ventilation and metabolic acidosis was corrected.

MEASUREMENTS AND MAIN RESULTS

The mortality rate was 25% in the group infused with the low dose and 89% in the group infused with the high dose of endotoxin. During the first 12 hrs of endotoxemia, both surviving (S group; n = 10) and nonsurviving (NS group; n = 11) sheep developed similar pulmonary hypertension, left ventricular failure, and hypotension with low systemic vascular resistance. However, S sheep had less interstitial lung edema (pulmonary lymph protein clearance at 8 hrs was 13+/-3 mL/hr vs. 27+/-6 mL/hr in the NS group and 4+/-1 mL/hr in the control group). During this early phase of endotoxemia, Do2, Vo2, and oxygen extraction ratio did not change significantly in any group. After this phase, animals that ultimately survived had a persistent hyperdynamic syndrome with high cardiac output and hypotension. In this group, the Do2 increase was greater than the Do2 measured in controls and remained steady up to 48 hrs after the start of the endotoxin infusion. Because systemic Vo2 did not change significantly, oxygen extraction ratio decreased progressively to values less than those measured in controls. In contrast, animals that ultimately died had a hypotensive and normokinetic syndrome associated with pulmonary hypertension, persistent depressed left ventricular function, hypothermia, and a progressive deterioration of gas exchange. Systemic Do2 was not significantly different from that in the control group. In contrast, Vo2 decreased progressively to values significantly lower than those measured in controls and remained low until death.

CONCLUSIONS

Our results indicate that in the absence of treatment such as fluid challenge or inotropic drugs in sheep infused with endotoxin, the occurrence of spontaneous hyperdynamic syndrome and high Do2 improves the survival rate.