Lung vascular injury after administration of viable hemolysin-forming Escherichia coli in isolated rabbit lungs

Escherichia coli hemolysin, a transmembrane pore-forming exotoxin, is considered an important virulence factor. In the present study, the possible significance of hemolysin production was investigated in a model of septic lung failure through infusion of viable bacteria in isolated rabbit lungs; 10(4) to 10(7) E. coli/ml perfusate caused a dose- and time-dependent appearance of hemolysin, accompanied by release of potassium, thromboxane A2, and PGI2 into the perfusate. Concomitantly, marked pulmonary hypertension developed. Inhibitor studies suggested that the pressor response was predominantly mediated by pulmonary thromboxane generation. Administration of hemolysin-forming E. coli additionally caused a protracted, dose-dependent increase in the lung capillary filtration coefficient, followed by severe edema formation. The permeability increase was independent of lung prostanoid generation. An E. coli strain that releases an inactive form of hemolysin completely failed to provoke the described biophysical and biochemical responses. Preapplication of 2 x 10(8) human granulocytes was without effect in the present experimental model. We conclude that the hemolysin produced by low numbers of E. coli organisms can provoke thromboxane-mediated pulmonary hypertension and severe vascular leakage. E. coli hemolysin and, possibly, other related cytolysins may thus contribute directly to the pathogenesis of acute respiratory failure under conditions of sepsis or pneumonia.

Induction of vascular injury by Pseudomonas aeruginosa cytotoxin in rabbit lungs is associated with the generation of different leukotrienes and hydroxyeicosatetraenoic acids

Pseudomonas aeruginosa cytotoxin, a transmembrane pore-forming protein, causes an increase in pulmonary microvascular permeability with subsequent lung edema formation, possibly related to the induction of arachidonic acid (AA) lipoxygenase products. To investigate this, isolated rabbit lungs were perfused with cytotoxin-containing buffer (6.5 and 13 micrograms of toxin/ml). A severalfold increase in the capillary filtration coefficient was induced, both preceded and accompanied by a marked time- (15-60 min) and dose-dependent release of cysteinyl leukotrienes (LT), LTB4, and 5-, 12-, and 15-hydroxyeicosatetraenoic acids (HETEs) into the lung perfusate. In the bronchoalveolar lavage fluid, corresponding AA-derived products were detected; the total sum of HETEs surpassed that of cysteinyl LTs in this compartment. The lipoxygenase inhibitors AA861 (10 microM) and nordihydroguaiaretic acid (100 microM) and EGTA (5 mM) suppressed the intravascular and alveolar liberation of all 5-lipoxygenase-derived AA metabolites, paralleled by a marked reduction and retardation of microvascular permeability increase (AA861). It thus seems that Pseudomonas cytotoxin induces generation of LTs and HETEs in rabbit lungs that may contribute to the development of pulmonary microvascular injury evoked by this bacterial agent.

Human leukoagglutinating antibody evokes cooperative leukotriene synthesis in pulmonary microvasculature. Model of transfusion-related acute lung injury

Leukoagglutinating antibodies have been implicated in the development of transfusion-related acute lung injury. In the present study, human neutrophil leukotriene generation was provoked by an anti-5b immunoglobulin G, isolated from a multiparous donor plasma that caused noncardiogenic lung edema during transfusion therapy. In 5b-positive polymorphonuclear neutrophils (PMNs), the antibody stimulated marked arachidonic acid metabolism, dependent on the presence of plasma as the complement source. Quantity and profile of lipid mediators (leukotriene B4 and its omega-oxidation products, 5-hydroxyeicosatetraenoic acid, and nonenzymatic hydrolysis products of leukotriene A4) corresponded to those repeatedly described after PMN in vitro stimulation with the artificial calcium ionophore A23187. Anti-5b challenge of PMNs sequestered in the microvasculature of perfused rabbit lungs did, however, induce a markedly modified metabolite profile. Nonenzymatic hydrolysis products of leukotriene A4 were not detected, and 5-hydroxyeicosatetraenoic acid was markedly reduced. In contrast, cysteinyl leukotrienes were measured as predominant compounds, with rapid appearance of leukotriene C4 and more protracted generation of leukotriene E4. Leukotriene B4 and its omega-oxidation products were released with similar kinetics, but in lower amounts, as compared with the isolated PMN stimulation. Anti-5b challenge of PMNs coincubated with pulmonary artery endothelial cells in vitro, but not stimulation of either cell type alone, provoked marked generation of cysteinyl leukotrienes. These findings suggest modulation of PMN 5-lipoxygenase metabolism in favor of leukotriene A4 transfer to adjacent acceptor cells with subsequent enzymatic conversion to cysteinyl leukotrienes under conditions of lung vascular sequestration. Endothelial cells appear to serve as predominant cooperative cells under circumstances of blood-free lung perfusion. PMN-related transcellular eicosanoid synthesis may be involved in the pathogenesis of transfusion-evoked acute lung injury.

Omega-oxidized leukotriene B4 detected in the broncho-alveolar lavage fluid of patients with non-cardiogenic pulmonary edema, but not in those with cardiogenic edema

Leukotriene (LT) generation has been implicated in the pathogenesis of the acute respiratory distress syndrome, ARDS. In the present study, we analysed broncho-alveolar lavage fluids of patients on mechanical ventilation because of ARDS (17 samples taken from 9 patients) or because of cardiogenic edema (8 samples taken from 6 patients) and of healthy volunteers (10 samples from different donors). LTs were separated as methylated and non-methylated compounds using different HPLC procedures, and were identified by chromatographic mobility, on-line UV-spectrum analysis and post HPLC immunoreactivity. In the lavage samples of the healthy volunteers and the patients with cardiogenic edema, no LTs were detected by these techniques (detection limit congruent to 0.1-0.2 ng/ml lavage fluid). By contrast, in 15 out of 17 samples from patients with ARDS LTB4 or its metabolites 20-OH-LTB4 and 20-COOH-LTB4 were detected. The endproduct of omega-oxidation, 20-COOH-LTB4, represented the quantitatively predominant compound, detected in the range of 0.3-2.6 ng/ml perfusate. We conclude that the chemotactic agent LTB4 may be involved in the amplification of inflammatory events encountered in ARDS, and that the oxidized metabolites of LTB4 are particularly suitable for monitoring lung leukotriene generation under conditions of neutrophil efflux and oxidative stress.

Reproduction of transfusion-related acute lung injury in an ex vivo lung model

Leukoagglutinins are implicated in transfusion-related acute lung injury (TRALI). In the present study, severe lung vascular leakage was reproduced by application of a leukoagglutinating antibody of anti-5b specificity in an ex vivo lung model. The antibody originated from a multiparous donor-plasma, observed to cause noncardiogenic edema during transfusion therapy. Heated full plasma (anti-5b-titer 1/128) or purified immunoglobulin G fraction was used for the studies. Ex vivo isolated rabbit lungs were perfused with albumin buffer, and human granulocytes (PMN) were admixed to the recirculating perfusate. In presence of anti-5b antibody plus 5b-positive PMN plus rabbit plasma as complement-source, severe lung edema occurred after a latent period of 3 to 6 hours. Pulmonary artery pressure was only transiently and moderately increased, and the leakage reaction could be traced back to a several-fold increase in lung vascular permeability. In contrast, no vascular leakage was noted in lungs perfused in the absence of anti-5b antibody, PMN, or rabbit plasma. Moreover, no permeability increase occurred on use of 5b-negative PMN. This reproduction of TRALI in an ex vivo lung model corroborates the role of leukoagglutinating antibodies in initiating PMN-dependent respiratory distress and suggests a contribution of concomitant complement activation.

Inflammatory lipid mediator generation elicited by viable hemolysin-forming Escherichia coli in lung vasculature

Escherichia coli hemolysin, a transmembrane pore-forming exotoxin, is considered an important virulence factor for E. coli-related extraintestinal infections and sepsis. The possible significance of hemolysin liberation for induction of inflammatory lipid mediators was investigated in isolated rabbit lungs infused with viable bacteria (concentration range, 10(4)-10(7)/ml). Hemolysin-secreting E. coli (E. coli-Hly+), but not an E. coli strain that releases an inactive form of the exotoxin, induced marked lung leukotriene (LT) generation with predominance of cysteinyl LTs. Eicosanoid synthesis was not inhibited in the presence of plasma with toxin-neutralizing capacity. Pre-application of 2 x 10(8) human granulocytes, which sequestered in the lung microvasculature, caused a severalfold increase in leukotriene generation in response to E. coli-Hly+ challenge both in the absence and presence of plasma. Data are presented indicating neutrophil-endothelial cell cooperation in arachidonic acid lipoxygenase metabolism as an underlying mechanism. We conclude that liberation of hemolysin from viable E. coli induces marked lipid mediator generation in lung vasculature, which is potentiated in the presence of neutrophil sequestration and may contribute to microcirculatory disturbances during the course of severe infections.

Leukotriene and hydroxyeicosatetraenoic acid generation elicited by low doses of Escherichia coli hemolysin in rabbit lungs

Low doses of Escherichia coli hemolysin cause thromboxane-mediated hypertension and vascular leakage in blood-free perfused rabbit lungs (W. Seeger, H. Walter, N. Suttorp, M. Muhly, and S. Bhakdi, J. Clin. Invest. 84:220-227, 1989). The recirculating buffer medium and bronchoalveolar lavage fluid from lungs exposed to hemolysin (2.5 hemolytic units per ml) in the presence of cyclooxygenase inhibitor were analyzed for leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs) by reverse-phase and straight-phase high-pressure liquid chromatographic techniques combined with UV spectrum analysis and post-high-pressure liquid chromatography radioimmunoassay. A rapid release of large amounts of cysteinyl-LTs and leukotriene B4 (LTB4) into the intravascular space was noted (total sum, approximately 4 to 5 micrograms). Similar quantities have hitherto been elicited only by high concentrations of the artificial calcium ionophore A 23187. Moreover, a marked liberation of 5-HETE and 12-hydroxyheptadecatrienoic acid into the buffer medium occurred, whereas LTB4 represented the predominant compound in the lavage fluid. The hemolysin-induced burst of LT and HETE generation preceded the onset of vascular leakage. The outstanding capacity of E. coli hemolysin to produce the liberation of potent lipid mediators is probably relevant to the pathways of vascular injury and amplification of inflammatory events during severe infection with hemolytic E. coli strains.

Influence of microvascular adherence on neutrophil leukotriene generation. Evidence for cooperative eicosanoid synthesis

Profile and quantity of leukotriene (LT) and hydroxyeicosatetraenoic acid (HETE) generation upon selective stimulation of isolated polymorphonuclear neutrophils (PMN) compared with neutrophils in a model of pulmonary leukostasis were investigated. Freshly prepared human PMN (2 x 10(8) were injected into the pulmonary artery of isolated, ventilated, and bloodfree perfused rabbit lungs, resulting in nearly quantitative sticking in the microvasculature. The sequestered neutrophils and, in parallel, aliquots of isolated PMN were stimulated with mAb in the presence of C, known to activate PMN arachidonate metabolism via formation of membrane attack complexes. In the isolated cells, a typical LT profile including LTB4 and its omega-oxidation products, 5-HETE and nonenzymatic hydrolysis products of LTA4 was evoked. The latter indicate secretion of LTA4 in considerable amounts. In the model of pulmonary leukostasis, no nonenzymatic LTA4-derivatives were detected, coincident with a predominance of cysteinyl-LT. This finding gives indirect evidence for an efficient LTA4-transfer between PMN feeder cells and vascular acceptor cells with glutathione-S-transferase activity. Moreover, a threefold increase in the total amount of LTA4-derived products was noted in the model of leukostasis, paralleled by a marked decrease in 5-HETE liberation. This effect was further enhanced by inhibition of lung cyclooxygenase. These findings were corroborated in a homologous system, in which rabbit PMN, sticking in the rabbit lung microvasculature, were stimulated with calcium-ionophore A23187. Collectively, these data suggest a complex interaction between microvascular tissue and adhering neutrophils in LT synthesis, involving transcellular LTA4-shift, modulation of the PMN 5-lipoxygenase pathway, and amplification of LT generation. These findings may be relevant for inflammatory events with neutrophils involved.

Influence of microvascular adherence on neutrophil leukotriene generation. Evidence for cooperative eicosanoid synthesis

Profile and quantity of leukotriene (LT) and hydroxyeicosatetraenoic acid (HETE) generation upon selective stimulation of isolated polymorphonuclear neutrophils (PMN) compared with neutrophils in a model of pulmonary leukostasis were investigated. Freshly prepared human PMN (2 x 10(8) were injected into the pulmonary artery of isolated, ventilated, and bloodfree perfused rabbit lungs, resulting in nearly quantitative sticking in the microvasculature. The sequestered neutrophils and, in parallel, aliquots of isolated PMN were stimulated with mAb in the presence of C, known to activate PMN arachidonate metabolism via formation of membrane attack complexes. In the isolated cells, a typical LT profile including LTB4 and its omega-oxidation products, 5-HETE and nonenzymatic hydrolysis products of LTA4 was evoked. The latter indicate secretion of LTA4 in considerable amounts. In the model of pulmonary leukostasis, no nonenzymatic LTA4-derivatives were detected, coincident with a predominance of cysteinyl-LT. This finding gives indirect evidence for an efficient LTA4-transfer between PMN feeder cells and vascular acceptor cells with glutathione-S-transferase activity. Moreover, a threefold increase in the total amount of LTA4-derived products was noted in the model of leukostasis, paralleled by a marked decrease in 5-HETE liberation. This effect was further enhanced by inhibition of lung cyclooxygenase. These findings were corroborated in a homologous system, in which rabbit PMN, sticking in the rabbit lung microvasculature, were stimulated with calcium-ionophore A23187. Collectively, these data suggest a complex interaction between microvascular tissue and adhering neutrophils in LT synthesis, involving transcellular LTA4-shift, modulation of the PMN 5-lipoxygenase pathway, and amplification of LT generation. These findings may be relevant for inflammatory events with neutrophils involved.

Potentiation of leukotriene production following sequestration of neutrophils in isolated lungs: indirect evidence for intercellular leukotriene A4 transfer

Granulocyte (polymorphonuclear leukocyte, PMN) sequestration in the microvascular bed with release of different mediators has been implicated in the pathogenesis of inflammatory and allergic disorders in many organs including the lung. In the present study, we investigated the profile and quantity of leukotriene (LT) generation in isolated blood-free perfused rabbit lungs, in isolated PMNs in vitro and in rabbit lungs, following administration of PMNs, mimicking pulmonary leukostasis. Following stimulation with increasing concentrations of the calcium ionophore A 23137 (0.1 to 2 mumol/L), LTs were detected in the buffer fluid by their chromatographic mobility in different high-performance liquid chromatography (HPLC) systems, by on-line peak spectrum analysis, and by post-HPLC radioimmunoassay (RIA). In isolated lungs, a dose-dependent generation of cysteinyl LTs greater than LTB4, in the complete absence of omega-oxidation products of LTB4 as well as nonenzymatic hydrolysis products of LTA4, was evoked. PMNs in vitro showed a typical profile of LT liberation (LTB4, 20-OH-, and COOH-LTB4, nonenzymatic LTA4 metabolites). In the model of pulmonary leukostasis, the presence of omega-oxidation products of LTB4 indicated metabolic integrity of the trapped PMNs. Nonenzymatic hydrolysis products of LTA4 were, however, not detected in the combined system, whereas the cysteinyl LTs increased markedly. This profile suggests intercellular transfer of PMN-derived LTA4 to lung cells in the microenvironment. In addition, at 2 mumol/L A23187, the sum of all LTA4-derived products surpassed the arithmetic sum of the isolated preparations more than threefold. This potentiation of an LT generation under conditions of pulmonary leukostasis may be of biologic significance for amplification of inflammatory events.

High yield enzymatic conversion of intravascular leukotriene A4 in blood-free perfused lungs

Experiments to investigate the fate of intravascularly administered leukotriene (LT) A4, an unstable intermediate of LT generation, were performed in isolated, ventilated, and blood-free perfused rabbit lungs. LT extracted from the lung effluent were separated by different reverse phase and straight phase HPLC procedures as methylated and nonmethylated compounds. Identity of eluting LT was confirmed by UV spectrum analysis and immunoreactivity. Pulmonary artery injection of 75 to 300 nmol of LTA4 resulted in the rapid appearance of cysteinyl-LT as well as LTB4 in the recirculating perfusate. The yield of these enzymatically generated LTA4 metabolites vs non-enzymatic hydrolysis products (6-trans-LTB4, 5-trans-epi-LTB4, 5,6-dihydroxyeicosatetraenoic acids) ranged above 90%. Experiments with application of tritiated LTA4 showed exclusive origin of the detected LT from the exogenously applied precursor. The time course of cysteinyl-LT appearance in the perfusate suggested metabolism of LTC4 via LTD4 to LTE4, whereas there was no evidence for LTB4 omega-oxidation. In the dose range of LTA4 used, the enzymatic conversion of this LT precursor did not approach saturation. Collectively, these data indicate that the intact pulmonary vasculature contains a hitherto not described capacity for enzymatic conversion of intravascularly offered LTA4 to both cysteinyl-LT and LTB4. This may be of biological significance for a putative transcellular biosynthesis of LT in the pulmonary microcirculation upon contact with LTA4 feeder cells, such as activated granulocytes.

High yield enzymatic conversion of intravascular leukotriene A4 in blood-free perfused lungs

Experiments to investigate the fate of intravascularly administered leukotriene (LT) A4, an unstable intermediate of LT generation, were performed in isolated, ventilated, and blood-free perfused rabbit lungs. LT extracted from the lung effluent were separated by different reverse phase and straight phase HPLC procedures as methylated and nonmethylated compounds. Identity of eluting LT was confirmed by UV spectrum analysis and immunoreactivity. Pulmonary artery injection of 75 to 300 nmol of LTA4 resulted in the rapid appearance of cysteinyl-LT as well as LTB4 in the recirculating perfusate. The yield of these enzymatically generated LTA4 metabolites vs non-enzymatic hydrolysis products (6-trans-LTB4, 5-trans-epi-LTB4, 5,6-dihydroxyeicosatetraenoic acids) ranged above 90%. Experiments with application of tritiated LTA4 showed exclusive origin of the detected LT from the exogenously applied precursor. The time course of cysteinyl-LT appearance in the perfusate suggested metabolism of LTC4 via LTD4 to LTE4, whereas there was no evidence for LTB4 omega-oxidation. In the dose range of LTA4 used, the enzymatic conversion of this LT precursor did not approach saturation. Collectively, these data indicate that the intact pulmonary vasculature contains a hitherto not described capacity for enzymatic conversion of intravascularly offered LTA4 to both cysteinyl-LT and LTB4. This may be of biological significance for a putative transcellular biosynthesis of LT in the pulmonary microcirculation upon contact with LTA4 feeder cells, such as activated granulocytes.

Arachidonic acid lipoxygenase pathways and increased vascular permeability in isolated rabbit lungs

Products of arachidonic acid (AA) pathways have repeatedly been implicated in acute lung vascular injury with respiratory distress. In blood-free perfused isolated rabbit lungs, AA endogenously released or exogenously applied causes an acute pressor response, mediated by metabolites of the cyclooxygenase pathway including thromboxane A2. Moreover, bolus application of AA (final concentration, 100 microM in the recirculating buffer) during an acute hydrostatic challenge was recently noted to cause a rapid, severalfold increase in the capillary filtration coefficient (Kf,c), though any significant rise in pulmonary vascular pressure was inhibited by indomethacin. In the present study, we showed that during this mode of AA bolus application in cell-free perfused rabbit lungs, microgram amounts of peptidoleukotrienes (LTE4 greater than LTC4 greater than LTD4) and LTB4 were released into the recirculating buffer within 5 min and continued to be released even after 2 exchanges of the perfusion fluid. In the presence of 2 structurally unrelated lipoxygenase inhibitors (nordihydroguaiaretic acid and AA-861), the leukotriene release was nearly completely inhibited and the AA-induced severe increase in vascular permeability was significantly reduced (2.5- to 3-fold rise in Kf,c, compared to a greater than 10-fold increase in Kf,c in the absence of lipoxygenase inhibition). Exogenous LTC4 caused a dose-dependent, sustained pressure rise in protein-free perfused lungs, apparently mediated via the pulmonary generation of AA cyclooxygenase products. Bolus application of 10 micrograms LTC4 or LTD4 or 7.5 micrograms LTB4 in protein-free perfused lungs during an acute hydrostatic challenge did not, however, mimic the AA bolus-induced severalfold increase in vascular permeability.(ABSTRACT TRUNCATED AT 250 WORDS)