Effect of endotoxin on oleic acid lung injury does not depend on priming

The effect of agility exercise on eicosanoid excretion, oxidant status, and plasma lactate in dogs

Background

The objective was to determine the effects of agility exercise on dogs of different skill levels with respect to urinary eicosanoids, urinary 15F_2t-isoprostane (lipid peroxidation marker) and hematological/biochemical changes in plasma. Fifteen adult dogs had blood and urine samples obtained prior to, immediately and 4-hours following an agility exercise.

Results

Hematocrit, red blood cells (RBC), albumin, and hemoglobin increased following exercise, with greatest increases correlating to increased skill group (novice, intermediate, masters); at 4-hours post-exercise, hematocrit, RBC, and hemoglobin were decreased. Phosphorus increased following exercise with the greatest increase in novice and intermediates. Plasma lactate increased 3.6-fold in masters, 3.2-fold in intermediates, and 1.2-fold in novice dogs. Urine thromboxane B₂ (TXB2) more than tripled 4-hours post-exercise while 6-keto prostaglandin F_1α (PGF1α, prostacyclin metabolite), prostaglandin E₂ metabolites (13,14-dihydro-15-keto-prostaglandin A₂ and 13,14-dihydro-15-keto-prostaglandin E₂), and 13,14-dihydro-15-keto prostaglandin F_2α were unaffected as determined by a competitive enzyme immunoassay and standardized by division with urine creatinine. Urine 15F_2t-isoprostane increased insignificantly.

Conclusions

Alterations in the plasma post-exercise were likely due to hemoconcentration from insensible water loss, splenic contraction and sympathetic stimulation while 4-hours later autohemodilution reduced RBC parameters. Elevations in plasma lactate and urinary TXB2 correlated with advanced skill level/speed of the dogs.

Measurement of urinary F2-isoprostanes as markers of in vivo lipid peroxidation: a comparison of enzyme immunoassays with gas chromatography-mass spectrometry in domestic animal species

F(2)-isoprostanes are useful markers for assessing oxidant injury; however, the validity of measuring urinary 15-F(2t)-isoprostane concentration by enzyme-linked immunosorbent assay (ELISA) has not been evaluated in veterinary species. The current study assesses the agreement between 2 commercially available urinary isoprostane kits and gas chromatography and negative ion chemical ionization-mass spectrometry (GC/NICI-MS). The results indicate that only feline urinary isoprostane measurement by glucuronidase (GL)-ELISA has acceptable agreement with GC/NICI-MS. Urinary isoprostane concentration was highly variable in critically ill animals, but there were too many variations between healthy and critically ill animals to draw meaningful conclusions. Currently, GC/NICI-MS is the only method that can be recommended for the assessment of urinary isoprostanes in dogs, cattle, and horses. Feline urinary isoprostanes can be assessed by GL-ELISA, but caution is still warranted when comparing data from manuscripts using different methods given the relatively low Spearman rank correlation coefficient. Future studies may require large sample sizes or focused inclusion criteria to account for variability in isoprostane concentration.

Redistribution of pulmonary blood flow impacts thermodilution-based extravascular lung water measurements in a model of acute lung injury

BACKGROUND

Studies using transthoracic thermodilution have demonstrated increased extravascular lung water (EVLW) measurements attributed to progression of edema and flooding during sepsis and acute lung injury. The authors hypothesized that redistribution of pulmonary blood flow can cause increased apparent EVLW secondary to increased perfusion of thermally silent tissue, not increased lung edema.

METHODS

Anesthetized, mechanically ventilated canines were instrumented with PiCCO (Pulsion Medical, Munich, Germany) catheters and underwent lung injury by repetitive saline lavage. Hemodynamic and respiratory physiologic data were recorded. After stabilized lung injury, endotoxin was administered to inactivate hypoxic pulmonary vasoconstriction. Computed tomographic imaging was performed to quantify in vivo lung volume, total tissue (fluid) and air content, and regional distribution of blood flow.

RESULTS

Lavage injury caused an increase in airway pressures and decreased arterial oxygen content with minimal hemodynamic effects. EVLW and shunt fraction increased after injury and then markedly after endotoxin administration. Computed tomographic measurements quantified an endotoxin-induced increase in pulmonary blood flow to poorly aerated regions with no change in total lung tissue volume.

CONCLUSIONS

The abrupt increase in EVLW and shunt fraction after endotoxin administration is consistent with inactivation of hypoxic pulmonary vasoconstriction and increased perfusion to already flooded lung regions that were previously thermally silent. Computed tomographic studies further demonstrate in vivo alterations in regional blood flow (but not lung water) and account for these alterations in shunt fraction and EVLW.

Increased isoprostane levels in oleic acid-induced lung injury

The present study was performed to examine a role of oxidative stress in oleic acid-induced lung injury model. Fifteen anesthetized sheep were ventilated and instrumented with a lung lymph fistula and vascular catheters for blood gas analysis and measurement of isoprostanes (8-epi prostaglandin F2alpha). Following stable baseline measurements, oleic acid (0.08 ml/kg) was administered and observed 4 h. Isoprostane was measured by gas chromatography mass spectrometry with the isotope dilution method. Isoprostane levels in plasma and lung lymph were significantly increased 2 h after oleic acid administration and then decreased at 4 h. The percent increases in isoprostane levels in plasma and lung lymph at 2 h were significantly correlated with deteriorated oxygenation at the same time point, respectively. These findings suggest that oxidative stress is involved in the pathogenesis of the pulmonary fat embolism-induced acute lung injury model in sheep and that the increase relates with the deteriorated oxygenation.

Animal models of acute lung injury

Acute lung injury in humans is characterized histopathologically by neutrophilic alveolitis, injury of the alveolar epithelium and endothelium, hyaline membrane formation, and microvascular thrombi. Different animal models of experimental lung injury have been used to investigate mechanisms of lung injury. Most are based on reproducing in animals known risk factors for ARDS, such as sepsis, lipid embolism secondary to bone fracture, acid aspiration, ischemia-reperfusion of pulmonary or distal vascular beds, and other clinical risks. However, none of these models fully reproduces the features of human lung injury. The goal of this review is to summarize the strengths and weaknesses of existing models of lung injury. We review the specific features of human ARDS that should be modeled in experimental lung injury and then discuss specific characteristics of animal species that may affect the pulmonary host response to noxious stimuli. We emphasize those models of lung injury that are based on reproducing risk factors for human ARDS in animals and discuss the advantages and disadvantages of each model and the extent to which each model reproduces human ARDS. The present review will help guide investigators in the design and interpretation of animal studies of acute lung injury.

Mechanism of hypoxemia in acute lung injury evaluated by multidetector-row CT

RATIONALE AND OBJECTIVES

Hypoxic pulmonary vasoconstriction (HPV) is a homeostatic mechanism causing pulmonary arterial constriction in response to local hypoxia, redistributing blood flow to lung regions with better oxygenation and ventilation. We present the use of computed tomographic (CT) volume and perfusion imaging to show differences in the mechanisms of hypoxemia from alterations in blood flow distribution within different animal models of acute lung injury (ALI).

MATERIALS AND METHODS

Three anesthetized, instrumented, and ventilated sheep were studied, two with induced ALI and one with native pneumonia. One subject was injured by using intravenous infusion of lipopolysaccharide (LPS), and the other, by repetitive saline lavage. Subjects were imaged using multidetector-row CT (MDCT) before and after injury. Lung volume scans were gated to the respiratory cycle. Contrast injection perfusion images were electrocardiogram gated. Computer-based image analysis quantified regional blood flow and total lung, air, and tissue volumes.

RESULTS

Total lung air fraction was decreased in both ALI models. In lavage injury, there was a decrease in perfusion to dependent poorly aerated regions, with perfusion shifting to nondependent regions. Conversely, LPS injury greatly increased perfusion to dependent poorly aerated regions. In the subject with pneumonia, decreasing fraction of inspired oxygen redistributed blood flow into the injured regions.

CONCLUSIONS

MDCT techniques can be used to investigate regional lung perfusion and lung volume distributions to explain physiological mechanisms in ALI. Our findings suggest that after lavage injury, blood flow is redistributed, consistent with preserved HPV and resulting in better oxygenation despite greater lung volume loss compared with LPS injury. In native pneumonia, HPV inactivation can be localized to the injured regions.

Physiologic, biochemical, and imaging characterization of acute lung injury in mice

RATIONALE

Most models of acute lung injury in mice have yet to be fully characterized.

OBJECTIVES

To directly compare and contrast endotoxin and oleic acid models of acute lung injury in mice in terms of their physiologic, biochemical, histopathologic, and imaging manifestations.

METHODS

Survival studies, lung weights, x-ray computed tomographic scanning, light and electron microscopy, bronchoalveolar lavage, lung uptake of ((18)F)fluorodeoxyglucose, tissue myeloperoxidase, arterial blood gases, mean arterial pressure, and lung tissue prostanoids were measured in separate groups of C57Bl/6 mice (normal animals, endotoxin only [20 microg/g], oleic acid only [0.15 microl/g], or endotoxin + oleic acid).

RESULTS

Endotoxin alone caused only mild pulmonary neutrophilic inflammation with little functional or structural damage to the alveolar architecture. In contrast, oleic acid caused severe alveolar damage with the development of alveolar edema of the increased-permeability type with associated abnormalities in gas exchange. When given together, endotoxin and oleic acid acted synergistically to increase pulmonary edema and to worsen gas exchange and hemodynamics, thereby increasing mortality. This synergism was significantly attenuated by the prior administration of the endotoxin antagonist E5564 (eritoran).

CONCLUSIONS

Under the conditions of these studies, only mice exposed to oleic acid showed both structural and functional characteristics of acute lung injury. Nevertheless, endotoxin had potent synergistic physiologic effects that increased mortality. Overall, these models, which can be translated to genetically altered mice, are amenable to study with state-of-the-art imaging techniques, and with experimental interventions that can probe the underlying mechanisms of injury.

Sphingosine 1-Phosphate Reduces Vascular Leak in Murine and Canine Models of Acute Lung Injury

Excessive mechanical stress is a key component of ventilator-associated lung injury, resulting in profound vascular leak and an intense inflammatory response. To extend our in vitro observations concerning the barrier-protective effects of the lipid growth factor sphingosine 1-phosphate (Sph 1-P), we assessed the ability of Sph 1-P to prevent regional pulmonary edema accumulation in clinically relevant rodent and canine models of acute lung injury induced by combined intrabronchial endotoxin administration and high tidal volume mechanical ventilation. Intravenously delivered Sph 1-P significantly attenuated both alveolar and vascular barrier dysfunction while significantly reducing shunt formation associated with lung injury. Whole lung computed tomographic image analysis demonstrated the capability of Sph 1-P to abrogate significantly the accumulation of extravascular lung water evoked by 6-hour exposure to endotoxin. Axial density profiles and vertical density gradients localized the Sph 1-P response to transitional zones between aerated and consolidated lung regions. Together, these results indicate that Sph 1-P represents a novel therapeutic intervention for the prevention of pulmonary edema related to inflammatory injury and increased vascular permeability.

Neutrophils and neutrophil products do not mediate pulmonary hemodynamic effects of endotoxin on oleic acid-induced lung injury

Small-dose endotoxin (Etx) prevents pulmonary perfusion redistribution away from edematous dorsal lung regions after oleic acid (OA)-induced injury in dogs, causing a significant deterioration in oxygenation. We hypothesized that small-dose Etx might mediate this effect via polymorphonuclear neutrophil (PMN) priming with release of inflammatory mediators such as platelet activating factor (PAF) or secretory phospholipase A(2) (sPLA(2)). To test this hypothesis, we administered specific inhibitors directed against each mediator and used two strategies to generate neutropenia. PAF and sPLA(2) inhibitors were administered before OA injury, followed 2 h later by small-dose Etx (n = 4 each group). PMN depletion was achieved by hydroxyurea administration for 5 days before the study to achieve absolute neutrophil counts <1000/mm(3) (n = 4). Inhibition of PMN adherence to lung endothelium was achieved by the administration of an anti-CD18 monoclonal antibody immediately before lung injury (n = 5). Positron emission tomography was used to evaluate pulmonary perfusion distribution and lung water content. We observed no effect of these interventions on the perfusion pattern after Etx + OA. Thus, neither neutrophils nor PAF or sPLA(2) mediate the effects of Etx on the pattern of perfusion in this model of lung injury.

IMPLICATIONS

Acute respiratory failure is characterized by severe decreases in blood oxygen. The pattern of blood flow within the lungs can contribute to this problem. This study investigated the potential role of white blood cells and their products in mediating abnormal pulmonary blood flow patterns in an experimental animal model of respiratory failure.