Differential contribution of various adhesion molecules to leukocyte kinetics in pulmonary microvessels of hyperoxia-exposed rat lungs

Recruitment maneuvers modulate epithelial and endothelial cell response according to acute lung injury etiology

OBJECTIVE

To investigate the effects of the rate of increase in airway pressure and duration of lung recruitment maneuvers in experimental pulmonary and extrapulmonary acute lung injury.

DESIGN

Prospective, randomized, controlled experimental study.

SETTINGS

University research laboratory.

SUBJECTS

Fifty adult male Wistar rats.

INTERVENTIONS

Acute lung injury was induced by Escherichia coli lipopolysaccharide either intratracheally (pulmonary acute lung injury) or intraperitoneally (extrapulmonary acute lung injury). After 24 hours, animals were assigned to one of three different recruitment maneuvers, targeted to maximal airway pressure of 30 cm H2O: 1) continuous positive airway pressure for 30 seconds (CPAP-30); 2) stepwise airway pressure increase (5 cm H2O/step, 8.5 s at each step) over 51 seconds (STEP-51) to achieve a pressure-time product similar to that of CPAP-30; and 3) stepwise airway pressure increase (5 cm H2O/step, 5 s at each step) over 30 seconds with maximum pressure sustained for a further 30 seconds (STEP-30/30).

MEASUREMENTS AND MAIN RESULTS

All recruitment maneuvers reduced static lung elastance independent of acute lung injury etiology. In pulmonary acute lung injury, CPAP-30 yielded lower surfactant protein-B and higher type III procollagen expressions compared with STEP-30/30. In extrapulmonary acute lung injury, CPAP-30 and STEP-30/30 increased vascular cell adhesion molecule-1 expression, but the type of recruitment maneuver did not influence messenger ribonucleic acid expression of receptor for advanced glycation end products, surfactant protein-B, type III procollagen, and pro-caspase 3.

CONCLUSIONS

CPAP-30 worsened markers of potential epithelial cell damage in pulmonary acute lung injury, whereas both CPAP-30 and STEP-30/30 yielded endothelial injury in extrapulmonary acute lung injury. In both acute lung injury groups, recruitment maneuvers improved respiratory mechanics, but stepwise recruitment maneuver without sustained airway pressure appeared to associate with less biological impact on lungs.

Endothelial cell heterogeneity

The endothelial lining of blood vessels shows remarkable heterogeneity in structure and function, in time and space, and in health and disease. An understanding of the molecular basis for phenotypic heterogeneity may provide important insights into vascular bed-specific therapies. First, we review the scope of endothelial heterogeneity and discuss its proximate and evolutionary mechanisms. Second, we apply these principles, together with their therapeutic implications, to a representative vascular bed in disease, namely, tumor endothelium.

Exposure of human megakaryocytes to high shear rates accelerates platelet production

Platelets originate from megakaryocytes (MKs) by cytoplasmic elongation into proplatelets. Direct platelet release is not seen in bone marrow hematopoietic islands. It was suggested that proplatelet fragmentation into platelets can occur intravascularly, yet evidence of its dependence on hydrodynamic forces is missing. Therefore, we investigated whether platelet production from MKs could be up-regulated by circulatory forces. Human mature MKs were perfused at a high shear rate on von Willebrand factor. Cells were observed in real time by videomicroscopy, and by confocal and electron microscopy after fixation. Dramatic cellular modifications followed exposure to high shear rates: 30% to 45% adherent MKs were converted into proplatelets and released platelets within 20 minutes, contrary to static conditions that required several hours, often without platelet release. Tubulin was present in elongated proplatelets and platelets, thus ruling out membrane tethers. By using inhibitors, we demonstrated the fundamental roles of microtubule assembly and MK receptor GPIb. Secretory granules were present along the proplatelet shafts and in shed platelets, as shown by P-selectin labeling. Platelets generated in vitro were functional since they responded to thrombin by P-selectin expression and cytoskeletal reorganization. In conclusion, MK exposure to high shear rates promotes platelet production via GPIb, depending on microtubule assembly and elongation.

ICAM-1 depletion does not alter retinal vascular development in a model of oxygen-mediated neovascularization

ICAM-1 has been identified as a mediator of inflammatory and VEGF-dependent corneal neovascularization. Furthermore, ICAM-1 has been demonstrated to be involved in leukocyte-mediated endothelial injury in diabetic retinopathy. Here we investigated the role of ICAM-1 in retinal vaso-obliteration and vascularization. ICAM-1 deficient mice as well as their respective wild-type controls were exposed to 75% oxygen from postnatal day 7 to day 12. Retinal vascularization was investigated after lectin labeling of endothelial cells on day 14, 17, and 20 in flat mount preparations. Retinal mRNA expression of VEGF, Angiopoietin 1 and 2 as well as PDGFbeta was examined at day 14 and 20 by Real Time RT-PCR. ICAM-1(-/-) mice and their respective wild-type controls demonstrated similar retinal development and vascularization under normoxic conditions. Similarly, after oxygen challenge, the vascular area, the avascularized area as well as the area of neovascular tufts did not differ between ICAM-1(-/-) and the respective wild-type mice although the mRNA expression of VEGF, ang-1, ang-2, and PDGFbeta differed clearly. This study demonstrates that lack of ICAM-1 leads to an altered expression of angiogenic factors that in combination may neutralize each other and do not alter retinal development and angiogenesis in oxygen-induced retinopathy.

Effects of different peep levels on mesenteric leukocyte-endothelial interactions in rats during mechanical ventilation

INTRODUCTION

Mechanical ventilation with positive end expiratory pressure (PEEP) improves oxygenation and treats acute pulmonary failure. However, increased intrathoracic pressure may cause regional blood flow alterations that may contribute to mesenteric ischemia and gastrointestinal failure. We investigated the effects of different PEEP levels on mesenteric leukocyte-endothelial interactions.

METHODS

Forty-four male Wistar rats were initially anesthetized (Pentobarbital I.P. 50 mg/kg) and randomly assigned to one of the following groups: 1) NAIVE (only anesthesia; n=9), 2) PEEP 0 (PEEP of 0 cmH2O, n=13), 3) PEEP 5 (PEEP of 5 cmH2O, n=12), and 4) PEEP 10 (PEEP of 10 cmH2O, n=13). Positive end expiratory pressure groups were tracheostomized and mechanically ventilated with a tidal volume of 10 mL/kg, respiratory rate of 70 rpm, and inspired oxygen fraction of 1. Animals were maintained under isoflurane anesthesia. After two hours, laparotomy was performed, and leukocyte-endothelial interactions were evaluated by intravital microscopy.

RESULTS

No significant changes were observed in mean arterial blood pressure among groups during the study. Tracheal peak pressure was smaller in PEEP 5 compared with PEEP 0 and PEEP 10 groups (11, 15, and 16 cmH2O, respectively; p<0.05). After two hours of MV, there were no differences among NAIVE, PEEP 0 and PEEP 5 groups in the number of rollers (118+/-9,127+/-14 and 147+/-26 cells/10 minutes, respectively), adherent leukocytes (3+/-1,3+/-1 and 4+/-2 cells/100 microm venule length, respectively), and migrated leukocytes (2+/-1,2+/-1 and 2+/-1 cells/5,000 microm(2), respectively) at the mesentery. However, the PEEP 10 group exhibited an increase in the number of rolling, adherent and migrated leukocytes (188+/-15 cells / 10 min, 8+/-1 cells / 100 microm and 12+/-1 cells / 5,000 microm(2), respectively; p<0.05).

CONCLUSIONS

High intrathoracic pressure was harmful to mesenteric microcirculation in the experimental model of rats with normal lungs and stable systemic blood pressure, a finding that may have relevance for complications related to mechanical ventilation.

Tumour necrosis factor-alpha blockade suppresses murine allergic airways inflammation

Asthma is a heterogeneous disease that has been increasing in incidence throughout western societies and cytokines, including proinflammatory tumour necrosis factor alpha (TNF-alpha), have been implicated in the pathogenesis of asthma. Anti-TNF-alpha therapies have been established successfully in the clinic for diseases such as rheumatoid arthritis and Crohn's disease. TNF-alpha-blocking strategies are now being trialled in asthma; however, their mode of action is poorly understood. Based on the observation that TNF-alpha induces lymph node hypertrophy we have attempted to investigate this as a mechanism of action of TNF-alpha in airway inflammation by employing two models of murine airway inflammation, that we have termed short and long models, representing severe and mild/moderate asthma, respectively. The models differ by their immunization schedules. In the short model, characterized by eosinophilic and neutrophilic airway inflammation the effect of TNF-alpha blockade was a reduction in draining lymph node (DLN) hypertrophy, eosinophilia, interleukin (IL)-5 production and immunoglobulin E (IgE) production. In the long model, characterized by eosinophilic inflammation, TNF-alpha blockade produced a reduction in DLN hypertrophy and IL-5 production but had limited effects on eosinophilia and IgE production. These results indicate that anti-TNF-alpha can suppress DLN hypertrophy and decrease airway inflammation. Further investigations showed that anti-TNF-alpha-induced inhibition of DLN hypertrophy cannot be explained by preventing l-selectin-dependent capture of lymphocytes into the DLN. Given that overall TNF blockade was able to suppress the short model (severe) more effectively than the long model (mild/moderate), the results suggest that TNF-alpha blocking therapies may be more effective in the treatment of severe asthma.

Real-time lung microscopy

Although proinflammatory cell signaling in the alveolo-capillary region predisposes to acute lung injury, key cell-signaling mechanisms remain inadequately understood. Alveolo-capillary inflammation is likely to involve coordinated signaling among cells of different phenotypes. For example, migration of inflammatory cells into the alveolus might entail coordinated signaling between adjoining alveolar epithelial and microvascular endothelial cells. The popular cultured cell experimental strategy fails to replicate this multicellular environment. Cultured lung cells, both alveolar and endothelial, undergo phenotypic transformations; hence they might inadequately reflect innate responses of native cells. Consequently, new approaches are required for the investigation of cell signaling in the native setting. Here we summarize new developments in classical intravital microscopy and discuss real-time fluorescence imaging as a novel technique for studying second-messenger mechanisms in the alveolo-capillary region.

Phenotypic Heterogeneity of the Endothelium

Endothelial cells, which form the inner cellular lining of blood vessels and lymphatics, display remarkable heterogeneity in structure and function. This is the first of a 2-part review focused on phenotypic heterogeneity of blood vessel endothelium. This review provides an historical perspective of our understanding of endothelial heterogeneity, discusses the scope of phenotypic diversity across the vascular tree, and addresses proximate and evolutionary mechanisms of endothelial cell heterogeneity. The overall goal is to underscore the importance of phenotypic heterogeneity as a core property of the endothelium.

Impact of severity of local soft-tissue trauma on long-term manifestation of microcirculatory and microlymphatic dysfunctions

BACKGROUND

The present study aimed at quantitatively evaluating the impact of severity of local trauma on manifestation of soft-tissue injury-associated microcirculatory and microlymphatic dysfunctions in a chronic model that allowed repeated analyses by intravital fluorescence microscopy.

METHODS

C57BL/6 mice were chronically instrumented with dorsal skinfold chambers and subjected to mild (180 J/m2, n = 6), moderate (270 J/m2, n = 6), or severe trauma (450 J/m2, n = 6; 540 J/m2, n = 6). Nontraumatized animals served as controls (sham; n = 8). Intravital microscopy was performed before and at 5 minutes, 1 hour, 8 hours, 24 hours, 3 days, and 5 days after trauma, and included the analysis of (1) blood and lymph microvessel rupture, (2) hematoma formation and lymph leakage, (3) arteriolar and venular constriction, (4) capillary perfusion failure, (5) arteriolar and venular leukocyte adhesion, and (6) interstitial edema formation.

RESULTS

Mild trauma did not induce any changes of microcirculatory and microlymphatic functions. Moderate trauma did not affect lymphatics but provoked arteriolar constriction, capillary perfusion failure, leukocyte-endothelial cell interactions, and minor blood vessel ruptures with hematoma formation. These alterations, however, recovered within the first 24 hours after trauma. Severe trauma also did not affect the lymphatic microvasculature, but resulted in massive hematoma formation, arteriolar constriction, and capillary perfusion failure, which was associated with marked arteriolar and venular leukocyte recruitment and edema formation, and which did not recover to normal over a 5-day observation period.

CONCLUSION

Only severe trauma of > 450 J/m2 provokes irreversible microcirculatory dysfunction in soft tissue, however, without affecting the integrity of lymphatic microvessels. Of interest, trauma-induced microcirculatory alterations are neither dominated solely by microcirculatory dysfunction nor by leukocytic inflammation. Instead, both pathologies develop in parallel, generating a vicious circle, which may be responsible for the compromised healing of severely traumatized soft tissue frequently observed in clinical practice.

Dissociation between alveolar transmigration of neutrophils and lung injury in hyperoxia

The objective of this study was to quantitatively assess changes in cell adhesion molecule (CAM) expression on the pulmonary endothelial surface during hyperoxia and to assess the functional significance of those changes on cellular trafficking and development of oxygen-induced lung injury. Mice were placed in >95% O2 for 0–72 h, and pulmonary injury and neutrophil (PMN) sequestration were assessed. Specific pulmonary CAM expression was quantified with a dual-radiolabeled MAb technique. To test the role of CAMs in PMN trafficking during hyperoxia, blocking MAbs to murine P-selectin, ICAM-1, or platelet-endothelial cell adhesion molecule-1 (PECAM-1) were injected in wild-type mice. Mice genetically deficient in these CAMs and PMN-depleted mice were also evaluated. PMN sequestration occurred within 8 h of hyperoxia, although alveolar emigration occurred later (between 48 and 72 h), coincident with rapid escalation of the lung injury. Hyperoxia significantly increased pulmonary uptake of radiolabeled antibodies to P-selectin, ICAM-1, and PECAM-1, reflecting an increase in their level on pulmonary endothelium and possibly sequestered blood cells. Although both anti-PECAM-1 and anti-ICAM-1 antibodies suppressed PMN alveolar influx in wild-type mice, only mice genetically deficient in PECAM-1 showed PMN influx suppression. Neither CAM blockade, nor genetic deficiency, nor PMN depletion attenuated lung injury. We conclude that early pulmonary PMN retention during hyperoxia is not temporally associated with an increase in endothelial CAMs; however, subsequent PMN emigration into the alveolar space may be supported by PECAM-1 and ICAM-1. Blocking PMN recruitment did not prevent lung injury, supporting dissociation between PMN infiltration and lung injury during hyperoxia in mice.

Various adhesion molecules impair microvascular leukocyte kinetics in ventilator-induced lung injury

Although the endothelial expression of various adhesion molecules substantially differs between pulmonary microvessels, their importance for neutrophil and lymphocyte sequestration in ventilator-induced lung injury (VILI) has not been systematically analyzed. We investigated the kinetics of polymorphonuclear cells (PMN) and mononuclear cells (MN) in the acinar microcirculation of the isolated rat lung with VILI by real-time confocal laser fluorescence microscopy, with or without inhibition of ICAM-1, VCAM-1, or P-selectin by monoclonal antibodies (MAb). Adhesion molecules in each microvessel were estimated by intravital fluorescence microscopy or immunohistochemical staining. In high tidal volume-ventilated lungs, 1) ICAM-1, VCAM-1, and P-selectin were differently upregulated in venules, arterioles, and capillaries; 2) venular PMN rolling was improved by inhibition of ICAM-1, VCAM-1, or P-selectin, whereas arteriolar PMN rolling was improved by ICAM-1 or VCAM-1 inhibition; 3) capillary PMN entrapment was ameliorated only by anti-ICAM-1 MAb; and 4) MN rolling in venules and arterioles and MN entrapment in capillaries were improved by ICAM-1 and VCAM-1 inhibition. In conclusion, the contribution of endothelial adhesion molecules to abnormal leukocyte behavior in VILI-injured microcirculation is microvessel and leukocyte specific. ICAM-1- and VCAM-1-dependent, but P-selectin-independent, arteriolar PMN rolling, which is expected to reflect the initial stage of tissue injury, should be taken as a phenomenon unique to ventilator-associated lung injury.

Hyperoxia-induced reactive oxygen species formation in pulmonary capillary endothelial cells in situ

Lung capillary endothelial cells (ECs) are a critical target of oxygen toxicity and play a central role in the pathogenesis of hyperoxic lung injury. To determine mechanisms and time course of EC activation in normobaric hyperoxia, we measured endothelial concentration of reactive oxygen species (ROS) and cytosolic calcium ([Ca(2+)](i)) by in situ imaging of 2',7'-dichlorofluorescein (DCF) and fura 2 fluorescence, respectively, and translocation of the small GTPase Rac1 by immunofluorescence in isolated perfused rat lungs. Endothelial DCF fluorescence and [Ca(2+)](i) increased continuously yet reversibly during a 90-min interval of hyperoxic ventilation with 70% O(2), demonstrating progressive ROS generation and second messenger signaling. ROS formation increased exponentially with higher O(2) concentrations. ROS and [Ca(2+)](i) responses were blocked by the mitochondrial complex I inhibitor rotenone, whereas inhibitors of NAD(P)H oxidase and the intracellular Ca(2+) chelator BAPTA predominantly attenuated the late phase of the hyperoxia-induced DCF fluorescence increase after > 30 min. Rac1 translocation in lung capillary ECs was barely detectable at normoxia but was prominent after 60 min of hyperoxia and could be blocked by rotenone and BAPTA. We conclude that hyperoxia induces ROS formation in lung capillary ECs, which initially originates from the mitochondrial electron transport chain but subsequently involves activation of NAD(P)H oxidase by endothelial [Ca(2+)](i) signaling and Rac1 activation. Our findings demonstrate rapid activation of ECs by hyperoxia in situ and identify mechanisms that may be relevant in the initiation of hyperoxic lung injury.

The changing role of eosinophils in long-term hyperreactivity following a single ozone exposure

Ozone hyperreactivity over 24 h is mediated by blockade of inhibitory M2 muscarinic autoreceptors by eosinophil major basic protein. Because eosinophil populations in the lungs fluctuate following ozone, the contribution of eosinophils to M2 dysfunction and airway hyperreactivity was measured over several days. After one exposure to ozone, M2 function, vagal reactivity, smooth muscle responsiveness, and inflammation were measured in anesthetized guinea pigs. Ozone-induced hyperreactivity to vagal stimulation persisted over 3 days. Although hyperreactivity one day after ozone is mediated by eosinophils, AbVLA-4 did not inhibit either eosinophil accumulation in the lungs or around the nerves or prevent hyperreactivity at this time point. Two days after ozone, eosinophils in BAL, around airway nerves and in lungs, were decreased, and neuronal M2 receptor function was normal, although animals were still hyperreactive to vagal stimulation. Depleting eosinophils with AbIL-5 prevented hyperreactivity, thus eosinophils contribute to vagal hyperreactivity by mechanisms separate from M2 receptor blockade. Three days after ozone, vagal hyperreactivity persisted, eosinophils were again elevated in BAL in lungs and around nerves, and M2 receptors were again dysfunctional. At this point, airway smooth muscle was also hyperresponsive to methacholine. Eosinophil depletion with AbIL-5, AbVLA-4, or cyclophosphamide protected M2 function 3 days after ozone and prevented smooth muscle hyperreactivity. However, vagal hyperreactivity was significantly potentiated by eosinophil depletion. The site of hyperreactivity, muscle or nerve, changes over 3 days after a single exposure to ozone. Additionally, the role of eosinophils is complex; they mediate hyperreactivity acutely while chronically may be involved in repair.

Pressure-induced leukocyte margination in lung postcapillary venules

Although pressure elevation in lung postcapillary venules increases endothelial P-selectin expression, the extent to which P-selectin causes lung leukocyte margination remains controversial. To address this issue, we optically viewed postcapillary venules of the isolated blood-perfused rat lung by real-time fluorescence imaging. To determine leukocyte margination in single postcapillary venules, we quantified the fluorescence of leukocytes labeled in situ with rhodamine 6G (R6G). Although baseline fluorescence was sparse, a 10-min pressure elevation by 10 cmH(2)O markedly increased R6G fluorescence. Both stopping blood flow during pressure elevation and eliminating leukocytes from the perfusion blocked the fluorescence increase, affirming that these fluorescence responses were attributable to pressure-induced leukocyte margination. A P-selectin-blocking MAb and the L- and P-selectin blocker fucoidin each inhibited the fluorescence increase, indicating that P-selectin was critical for inducing margination. Time-dependent imaging of blood-borne fluorescent beads revealed reduction of plasma velocity during pressure elevation. After pressure returned to baseline, a similar reduction of plasma velocity, established by manually decreasing the perfusion rate, prolonged margination. Our findings show that in lung postcapillary venules, the decrease in plasma velocity critically determines pressure-induced leukocyte margination.

Mild hypothermia reduces expression of intercellular adhesion molecule-1 (ICAM-1) and the accumulation of neutrophils after acid-induced lung injury in the rat

BACKGROUND

The pathophysiology of the acute phase of acid-induced lung injury (AILI) has been elucidated. However, once acute respiratory distress syndrome (ARDS) develops, the mortality rate remains high and there is, as yet, no effective therapy. There are reports that application of mild hypothermia is an effective treatment for ARDS. In this study, we hypothesize that mild hypothermia inhibits activation of neutrophils and expression of intercellular adhesion molecule-1 (ICAM-1) in an injured lung. We studied the effects of mild hypothermia on the expression of ICAM-1 and the accumulation of neutrophils after AILI in the rat.

METHODS

Male Sprague-Dawley rats were randomly allocated to one of the four groups: control normothermic group, induced mild hypothermia group, acid-instilled normothermic group, and acid-instilled group with mild hypothermia. At 6 h after instillation of acid, lungs were removed to measure neutrophil activity and to detect the expression of ICAM-1 in each group.

RESULTS

Oxygenation in acid-instilled rats was significantly impaired as compared to that in non-instilled groups, but induction of mild hypothermia gradually improved oxygenation. Expression of ICAM-1 was enhanced in the acid-instilled normothermic group. By contrast, no overexpression of ICAM-1 and its mRNA was detected in the acid-instilled hypothermic group. In addition, accumulation of neutrophils was markedly inhibited after exposure to mild hypothermia irrespective of the instillation of acid.

CONCLUSION

Our data suggest mild hypothermia can inhibit the adhesion, activation, and accumulation of neutrophils during the acute phase of AILI in the rat and may have the potential to reduce ongoing inflammation of ALI or ARDS.

Activated leukocytes and endothelial cells enhance retention of ultrasound contrast microspheres containing perfluoropropane in inflamed venules

PURPOSE

To characterize the flow dynamics of albumin ultrasound contrast microspheres containing perfluoropropane (PFP) in normal and inflamed microvasculature.

MATERIALS AND METHODS

Mesenteric microvessels of rats were examined after an intravenous injection of fluorocein-labeled erythrocytes or PFP microspheres by fluorescence intravital microscopy with and without local application of 10(-8) M platelet activating factor (PAF) as an experimental form of inflammation.

RESULTS

All the microspheres passed freely through arterioles and capillaries. Mean velocities of the microspheres in each vessel were closely correlated with those of erythrocytes. Only a minor fraction of the microspheres was retained in the venules (> or =0.1 s stoppage) by attachment to endothelial cells. The frequency of microsphere retention in venules was significantly enhanced by PAF (2.6+/-2.1%, P<0.01 vs. control), especially in regions with leukocyte adhesion. Treatment with a monoclonal antibody to intercellular adhesion molecule-1, P-selectin or the common leukocyte antigen inhibited PAF-induced microsphere retention in venules (P<0.05). In the inflamed microcirculation, a small subgroup of microspheres becomes attached to venular endothelial cells in regions with leukocyte adhesion via interaction among microspheres, activated leukocytes and endothelial cells via adhesion molecules.

CONCLUSION

In inflamed microcirculation, a small subgroup of microspheres becomes attached to venular endothelial cells in regions with leukocyte adhesion via interaction among microspheres, activated leukocytes and endothelial cells via adhesion molecules. These results suggest that ultrasonography with microspheres has the potential to evaluate inflammatory site distribution as well as tissue perfusion.

CXCR2 is critical to hyperoxia-induced lung injury

Hyperoxia-induced lung injury is characterized by infiltration of activated neutrophils in conjunction with endothelial and epithelial cell injury, followed by fibrogenesis. Specific mechanisms recruiting neutrophils to the lung during hyperoxia-induced lung injury have not been fully elucidated. Because CXCL1 and CXCL2/3, acting through CXCR2, are potent neutrophil chemoattractants, we investigated their role in mediating hyperoxia-induced lung injury. Under variable concentrations of oxygen, murine survival during hyperoxia-induced lung injury was dose dependent. Eighty percent oxygen was associated with 50% mortality at 6 days, while greater oxygen concentrations were more lethal. Using 80% oxygen, we found that lungs harvested at day 6 demonstrated markedly increased neutrophil sequestration and lung injury. Expression of CXCR2 ligands paralleled neutrophil recruitment to the lung and CXCR2 mRNA expression. Inhibition of CXC chemokine ligands/CXCR2 interaction using CXCR2(-/-) mice exposed to hyperoxia significantly reduced neutrophil sequestration and lung injury, and led to a significant survival advantage as compared with CXCR2(+/+) mice. These findings demonstrate that CXC chemokine ligand/CXCR2 biological axis is critical during the pathogenesis of hyperoxia-induced lung injury.

Neutrophil adhesion molecule expression in the developing neonatal rat exposed to hyperoxia

Neonatal rats have an increased tolerance to hyperoxia, which is associated with a diminished pulmonary inflammatory response compared with adults. To investigate this differing response, expression of the neutrophil adhesion molecules, L-selectin and CD18, and levels of soluble L-selectin, were examined using flow cytometry and sandwich enzyme-linked immunosorbent assay on air-exposed neonatal rat neutrophils at 0-24 and 72 h and 7, 10, 14, and 21 d of age compared with the adult and after exposure to hyperoxia (>/= 98% O2) for 56 h in adults and for 72 h and 7 d in neonates. Expression of L-selectin in 0-24-h neonates was similar to adults, but was significantly lower than adults at 72 h and 7 d (P = 0.011). Soluble L-selectin levels were significantly higher than those in adults in the 0-24- and 72-h neonates (P < 0.001). CD18 expression in unstimulated and activated neutrophils of neonatal rats was higher at 0-24 h than in the adult (P < 0.001), but thereafter did not differ from adults. After hyperoxic exposure, L-selectin did not differ between the exposure groups but soluble L-selectin tended to increase in neonates after 7 d of O2 exposure Finally, CD18 was significantly higher after hyperoxic exposure of the adult (P = 0.008), but did not change with oxygen exposure in the neonate. Based on these findings, we speculate that differences between neonatal and adult rats in expression of L-selectin may contribute to delayed oxygen toxicity in neonatal rats.

Hypercapnic acidosis attenuates endotoxin-induced nuclear factor-[kappa]B activation

Although permissive hypercapnia improves the prognosis of patients with acute respiratory distress syndrome, it has not been conclusively determined whether hypercapnic acidosis (HA) is harmful or beneficial to sustained inflammation of the lung. The present study was designed to explore the molecular mechanism of HA in modifying lipopolysaccharide (LPS)-associated signals in pulmonary endothelial cells. LPS elicited degradation of inhibitory protein kappaB (IkappaB)-alpha, but not IkappaB-beta, resulting in activation of nuclear factor (NF)-kappaB in human pulmonary artery endothelial cells. Exposure to HA significantly attenuated LPS-induced NF-kappaB activation through suppressing IkappaB-alpha degradation. Isocapnic acidosis and buffered hypercapnia showed qualitatively similar but quantitatively smaller effects. HA did not attenuate the LPS-enhanced activation of activator protein-1. Following the reduced NF-kappaB activation, HA suppressed the mRNA and protein levels of intercellular adhesion molecule-1 and interleukin-8, resulting in a decrease in both lactate dehydrogenase release into the medium and neutrophil adherence to LPS-activated human pulmonary artery endothelial cells. In contrast, HA did not inhibit LPS-enhanced neutrophil expression of integrin, Mac-1. Based on these findings, we concluded that hypercapnic acidosis would have anti-inflammatory effects essentially through a mechanism inhibiting NF-kappaB activation, leading to downregulation of intercellular adhesion molecule-1 and interleukin-8, which in turn inhibits neutrophil adherence to pulmonary endothelial cells.

Deficiency in the c-Jun NH2-terminal kinase signaling pathway confers susceptibility to hyperoxic lung injury in mice

Hyperoxia generates an oxidative stress in the mouse lung, which activates the major stress-inducible kinase pathways, including c-Jun NH2-terminal kinase (JNK). We examined the effect of Jnk1 gene deletion on in vivo responses to hyperoxia in mice. The survival of Jnk1-/- mice was reduced relative to wild-type mice after exposure to continuous hyperoxia. Jnk1-/- mice displayed higher protein concentration in bronchoalveolar lavage (BAL) fluid and increased expression of heme oxygenase-1, a stress-inducible gene, after 65 h of hyperoxia. Contrary to other markers of injury, the leukocyte count in BAL fluid of Jnk1-/- mice was markedly diminished relative to that of wild-type mice. The decrease in BAL leukocyte count was not associated with any decrease in lung myeloperoxidase activity at baseline or after hyperoxia treatment. Pretreatment with inhaled lipopolysaccharide increased BAL neutrophil content and extended hyperoxia survival time to a similar extent in Jnk1-/- and wild-type mice. Associated with increased mortality, Jnk1-/- mice had increased pulmonary epithelial cell apoptosis after exposure to hyperoxia compared with wild-type mice. These results indicate that JNK pathways participate in adaptive responses to hyperoxia in mice.

Gene expression profiling of the early pulmonary response to hyperoxia in mice

To identify molecular events occurring during the early response to hyperoxia, we measured changes over time in total lung gene expression in C57BL/6 mice during prolonged exposure to > 95% O2. Specifically, differential gene expression of > 8,734 sequence-verified murine complementary DNAs was analyzed after 0, 8, 24, and 48 h of O2 exposure, with additional genes of interest analyzed at 24 h. Of the 385 genes differentially expressed, hyperoxia increased expression of 175 genes (2.0%) and decreased expression of 210 genes (2.3%). The majority of "classic" antioxidant enzymes, including catalase, MnSOD, and Cu-Zn SOD, showed no change in expression during hyperoxia, with a number of other antioxidant enzymes, including glutathione peroxidase, glutathione-S-Transferase (GST) Pi1, GST mu2, and heme oxygenase-1 showing relatively moderate increases. The exception was the heavy metal-binding protein metallothionein, which increased expression over 7-fold after 48 h of O2. We found no change in the expression of a number of known proinflammatory genes after 24 or 48 h of hyperoxia. A large increase in p21 expression was demonstrated, suggesting overall inhibition of cell cycle progression. Increases of the antiapoptotic gene Bcl-XL were counterbalanced by similar increases of the proapoptotic gene BAX. New findings included significant increases in expression of cysteine-rich protein 61(cyr61) at 48 h, suggesting a potential role for this factor in angiogenesis or remodeling of the extra cellular matrix during recovery from hyperoxia. In addition, downregulation of thrombomodulin expression occurred by 24 h and was further decreased at 48 h. Given the importance of thrombomodulin/thrombin interaction in regulating protein C activity, decreases in thrombomodulin may contribute to activation of the coagulation and inflammatory cascades and development of lung injury with hyperoxia.

Leukocytes mediate retinal vascular remodeling during development and vaso-obliteration in disease

Retinal ischemia can cause vision-threatening pathological neovascularization. The mechanisms of retinal ischemia are not fully understood, however. Here we have shown that leukocytes prune the retinal vasculature during normal development and obliterate it in disease. Beginning at postnatal day 5 (P5) in the normal rat, vascular pruning began centrally and extended peripherally, leaving behind a less dense, smaller-caliber vasculature. The pruning was correlated with retinal vascular expression of intercellular adhesion molecule-1 (ICAM-1) and coincided with an outward-moving wave of adherent leukocytes composed in part of cytotoxic T lymphocytes. The leukocytes adhered to the vasculature through CD18 and remodeled it through Fas ligand (FasL)-mediated endothelial cell apoptosis. In a model of oxygen-induced ischemic retinopathy, this process was exaggerated. Leukocytes used CD18 and FasL to obliterate the retinal vasculature, leaving behind large areas of ischemic retina. In vitro, T lymphocytes isolated from oxygen-exposed neonates induced a FasL-mediated apoptosis of hyperoxygenated endothelial cells. Targeting these pathways may prove useful in the treatment of retinal ischemia, a leading cause of vision loss and blindness.

High tidal volume ventilation induces proinflammatory signaling in rat lung endothelium

Alveolar overdistension during mechanical ventilation causes leukocyte sequestration, leading to lung injury. However, underlying endothelial cell (EC) mechanisms are undefined. In a new approach, we exposed isolated blood-perfused rat lungs to high tidal volume ventilation (HV) for 2 h, then obtained fresh lung endothelial cells (FLEC) by immunosorting at 4 degrees C. Immunoblotting experiments indicated that as compared with FLEC derived from lungs ventilated at low volume (LV), HV markedly enhanced tyrosine phosphorylation (TyrP). The tyrosine kinase blocker, genistein, inhibited this response. HV also induced focal adhesion (FA) formation in FLEC, as detected by immunofluorescent aggregates of the alpha(v)beta(3) integrin that co-localized with aggregations of focal adhesion kinase (FAK). Immunoprecipitation and blotting experiments revealed that HV increased TyrP of the FA protein, paxillin. In addition, HV induced a paxillin-associated P-selectin expression on FLEC that was also inhibited by genistein. However, HV did not increase lung water. These results indicate that in HV, EC signaling in situ causes FA formation and induces TyrP-dependent P-selectin expression. These signaling mechanisms may promote leukocyte-mediated responses in HV.

Endotoxin protection from oxygen toxicity: effect on pulmonary neutrophils and L-selectin

The mechanisms by which sublethal doses of endotoxin protect against hyperoxic lung injury are not completely understood. We hypothesized that endotoxin treatment would result in a decreased inflammatory response to hyperoxia and that this would be accompanied by activation of neutrophils (as evidenced by loss of L-selectin) in the peripheral circulation. Adult rats were injected with endotoxin 0.5 mg/kg prior to and 24 hr after onset of exposure to > or = 98% O2. After 56 hr of hyperoxia, pulmonary neutrophils were lower in the O2/endotoxin group compared to O2 controls as measured by myeloperoxidase in lung homogenates and neutrophil counts in bronchoalveolar lavage fluid. Circulating neutrophils were also significantly lower in the O2/endotoxin group compared to O2 controls at 56 hr. Expression of the neutrophil adhesion molecule, L-selectin, was lower at 4 and 24 hr in the endotoxin-treated rats compared to O2 controls. There were no differences at 48 hr. Expression of CD18 rose significantly in the O2/endotoxin group after 4 hr, but thereafter did not differ from O2 controls. In summary, endotoxin protection from O2 toxicity was associated with reduced neutrophils in the lung and a loss of L-selectin from peripheral blood neutrophils.

Soluble intercellular cell adhesion molecule-1 and L-selectin plasma concentrations and response to surfactant in preterm infants

OBJECTIVE

To investigate whether plasma concentrations of soluble intercellular cell adhesion molecule (ICAM)-1 and L-selectin at 24 hrs of life are related to good or poor response to exogenous surfactant in preterm infants.

DESIGN

Prospective study of markers of inflammation in circulating blood at 24 hrs of life.

SETTING

Level III neonatal intensive care unit.

PATIENTS

Twenty-nine preterm newborns suffering from severe respiratory distress syndrome (Fio(2) > 0.4) without signs of infection or fetal acidosis, and 17 healthy preterm newborns of similar gestational age serving as controls.

INTERVENTIONS

Infants with respiratory distress were treated with natural surfactant at 0.3-5 hrs of life. A response to surfactant, defined as a decrease of Fio(2) >50% within 6 hrs after surfactant, was seen in 21 infants.

MEASUREMENTS AND MAIN RESULTS

Soluble ICAM-1 and L-selectin concentrations were determined in plasma samples taken at 24 hrs of age. ICAM-1 was elevated (p <.001) in infants who responded poorly to surfactant (median, 392 ng/mL; range, 58.26-4884.24 ng/mL) compared with good responders (20.52 ng/mL, 2.32-138.58 ng/mL) or controls (21.91 ng/mL, 2.61-65.73 ng/mL), without differences between controls and good responders. L-selectin was lower (p =.004) in surfactant-treated infants (4.45 nmol/L, 2.0-10.4 ng/mL) than in controls (6.0/2.35-10.25 nmol/L) without differences between surfactant good and poor responders. However, infants requiring supplemental oxygen at 36 wks of gestational age had reduced L-selectin at 24 hrs of age (3.2/2.0-3.45 vs. 5.0/2.35-10.4 nmol/L, p =.004), whereas there was no difference in ICAM-1.

CONCLUSIONS

In preterm infants with respiratory distress, a poor response to surfactant within 6 hrs of administration is associated with elevated circulating ICAM-1 concentrations at 24 hrs of age. Low plasma L-selectin at 24 hrs of age predicts prolonged requirement for supplemental oxygen.

Protective effect of fucoidin (a neutrophil rolling inhibitor) on ischemia reperfusion injury: experimental study in rat epigastric island flaps

The objective of this study was to examine whether a decrease in neutrophil-mediated tissue injury using Fucoidin, a nontoxic neutrophil rolling inhibitor, would improve flap survival in an island flap model after ischemia-reperfusion. Myeloperoxidase activity (an indirect index of tissue neutrophil count) and malondialdehyde (an indicator of lipid peroxidation), the degree of neutrophil infiltration by direct counting, and macroscopic flap survival were assessed in the flap after arterial ischemia-reperfusion. Epigastric island skin flaps were elevated in 56 rats. The first group of 21 rats was subjected to 6 hours of arterial ischemia. The second group of 21 rats was subjected to 10 hours of arterial ischemia, and the rest of the rats were used as nonischemic controls (sham flaps). For inhibiting neutrophil rolling, a nontoxic polysaccharide agent-Fucoidin-was used. Each ischemic group was divided further into three subgroups: Subgroup I (control rats) received saline, subgroup II received 10 mg per kilogram Fucoidin, and subgroup III received 25 mg per kilogram Fucoidin before reperfusion. The results were evaluated as tissue neutrophil counts, tissue malondialdehyde content, tissue myeloperoxidase activity, and flap survival. Neutrophil counts and tissue myeloperoxidase activity were decreased significantly (p <0.001) in subgroup III, but lipid peroxidation by means of tissue malondialdehyde content was not affected by Fucoidin administration. The authors conclude that administration of Fucoidin before reperfusion can limit tissue injury apparently by inhibiting neutrophil rolling in a dose-dependent manner.

Important roles for L-selectin and ICAM-1 in the development of allergic airway inflammation in asthma

Airway inflammation and airway hyperresponsiveness (AHR) are fundamental features of asthma. Migration of inflammatory cells from the circulation into the lungs is dependent upon adhesion molecule interactions. The cell surface adhesion molecules L-selectin and intercellular adhesion molecule (ICAM)-1 have been demonstrated to mediate leukocyte rolling on inflamed pulmonary endothelium, and ICAM-1 has also been shown to mediate capillary sequestration in inflamed lung. However, their roles in the development of airway inflammation and AHR in asthma have not been directly examined. We have characterised the roles of L-selectin and ICAM-1 in the recruitment of inflammatory cells to the lung and in the development of airway hyperresponsiveness using an ovalbumin (OVA)-induced allergic airway disease model of asthma and adhesion molecule-deficient mice. OVA-sensitized/challenged ICAM-1-deficient mice have dramatically reduced inflammatory influx into the airway/lung and a corresponding attenuation of AHR as compared to wild-type controls. OVA-sensitized/challenged L-selectin-deficient mice demonstrate significantly reduced numbers of CD3(+)lymphocytes and increased numbers of B220(+)lymphocytes in BAL as compared to wild-type mice (P< 0.05). However, other parameters of airway/lung inflammation in OVA-sensitized/challenged L-selectin-deficient mice were equivalent to wild-type control mice. Remarkably, despite a fulminant inflammatory response in the airway/lung, AHR was completely abrogated in OVA-sensitized/challenged L-selectin-deficient mice. These findings suggest a crucial role for ICAM-1 in the development of airway inflammation and AHR in asthma. In contrast, L-selectin plays a more selective role in the development of airway hyperresponsiveness but not allergic inflammation in this animal model of asthma. Thus, L-selectin and ICAM-1 represent potential targets for novel asthma therapies specifically aimed at controlling airway inflammation and/or airway hyperresponsiveness.

Effects of dexamethasone on antigen-induced airway eosinophilia and M(2) receptor dysfunction

In antigen-challenged guinea pigs, airway hyperreactivity is due to recruitment of eosinophils to the airway nerves and dysfunction of M(2) muscarinic receptors. M(2) receptor dysfunction is caused by eosinophil major basic protein, which is an allosteric antagonist at the receptor. Because glucocorticoids inhibit airway hyperreactivity in humans and in animal models of asthma, we tested whether dexamethasone treatment (6 microg. kg(-)(1). d(-)(1) for 3 d, intraperitoneal) before antigen challenge prevents M(2) receptor dysfunction and airway hyperreactivity. Guinea pigs were sensitized to ovalbumin via intraperitoneal injections, and were challenged with ovalbumin via inhalation. Twenty-four hours later, hyperreactivity and M(2) receptor function were tested. Antigen-challenged animals were hyperreactive to vagal stimulation, and demonstrated loss of M(2) receptor function. Dexamethasone pretreatment prevented hyperreactivity and M(2) receptor dysfunction in antigen-challenged guinea pigs. Antigen challenge resulted in recruitment of eosinophils to the airways and to the airway nerves. Dexamethasone prevented recruitment of eosinophils to the airway nerves but did not affect total eosinophil influx into the airways. These results demonstrate that dexamethasone prevents antigen-induced hyperreactivity by protecting neuronal M(2) muscarinic receptors from antagonism by eosinophil major basic protein, and this protective mechanism appears to be by specifically inhibiting eosinophil recruitment to the airway nerves.

L-Selectin is required for the development of airway hyperresponsiveness but not airway inflammation in a murine model of asthma

BACKGROUND

Airway inflammation and airway hyperresponsiveness (AHR) are fundamental features of asthma. Migration of inflammatory cells from the circulation into the lungs is dependent on adhesion molecule interactions. The cell surface adhesion molecule L-selectin has been demonstrated to mediate leukocyte rolling on inflamed and noninflamed pulmonary endothelium. However, its role in the development of airway inflammation and AHR in asthma has not been examined.

OBJECTIVE

We sought to characterize the role of L-selectin in the recruitment of inflammatory cells to the airway-lung and the development of AHR in a murine model of asthma.

METHODS

An ovalbumin (OVA)-induced allergic airway disease model of asthma was applied to L-selectin-deficient (LKO) mice and C57BL/6 wild-type (WT) control mice. The development of airway inflammation was assessed by examining leukocyte influx into bronchoalveolar lavage (BAL) fluid and the lung. Total and differential BAL leukocyte counts were determined, and the immunophenotype of BAL lymphocytes was assessed by means of flow cytometry. The development of AHR was assessed by means of whole-body plethysmography.

RESULTS

Airway-lung inflammation was equivalent in LKO and WT mice sensitized-challenged with OVA, as measured by total and differential BAL cell counts and histologic analysis of lung tissue. Numbers of eosinophils, neutrophils, lymphocytes, and monocytes in BAL fluid were equivalent in LKO and WT mice. However, phenotypic analysis of BAL lymphocytes demonstrated significantly reduced CD3(+) populations and increased B220(+) populations in LKO compared with WT mice (P <.05). Remarkably, despite a fulminant inflammatory response in the airway-lung in LKO mice sensitized-challenged with OVA, AHR was completely abrogated.

CONCLUSION

L-selectin plays a crucial role in the development of AHR but not allergic inflammation in an animal model of asthma. L-selectin represents a potential target for novel asthma therapies specifically aimed at controlling AHR.

Oxidant stress and endothelial cell dysfunction

Reactive oxygen species (ROS) are generated at sites of inflammation and injury, and at low levels, ROS can function as signaling molecules participating as signaling intermediates in regulation of fundamental cell activities such as cell growth and cell adaptation responses, whereas at higher concentrations, ROS can cause cellular injury and death. The vascular endothelium, which regulates the passage of macromolecules and circulating cells from blood to tissues, is a major target of oxidant stress, playing a critical role in the pathophysiology of several vascular diseases and disorders. Specifically, oxidant stress increases vascular endothelial permeability and promotes leukocyte adhesion, which are coupled with alterations in endothelial signal transduction and redox-regulated transcription factors such as activator protein-1 and nuclear factor-kappaB. This review discusses recent findings on the cellular and molecular mechanisms by which ROS signal events leading to impairment of endothelial barrier function and promotion of leukocyte adhesion. Particular emphasis is placed on the regulation of cell-cell and cell-surface adhesion molecules, the actin cytoskeleton, key protein kinases, and signal transduction events.

L-selectin and intercellular adhesion molecule 1 mediate lymphocyte migration to the inflamed airway/lung during an allergic inflammatory response in an animal model of asthma

T lymphocytes play a critical role in the development of allergic inflammation in asthma. Early in the allergic response, T lymphocytes migrate from the circulation into the lung to initiate and propagate airway inflammation. The adhesion molecules that mediate lymphocyte entry into inflamed lung have not been defined. This study directly examined the roles of L-selectin and intercellular adhesion molecule 1 (ICAM-1) in lymphocyte migration to the lung during an allergic inflammatory response in an animal model of asthma. Short-term (1 hour) in vivo migration assays and various combinations of adhesion molecule-deficient and wild-type mice were used. Migration of in vivo activated lymphocytes into inflamed lung was significantly greater than entry of resting lymphocytes into noninflamed lung (24.5% +/- 2.7% vs 9.5% +/- 1.3%, P =.001). Migration of activated lymphocytes into inflamed lung was inhibited by 30% in the absence of L-selectin (17.3% +/- 1.3%, P =.04), 47% in the absence of cell surface ICAM-1 (13.0% +/- 2.5%, P =.01), and 47% in the absence of endothelial ICAM-1 (13.0% +/- 2.5%, P =.01). Loss of ICAM-1 on both lymphocytes and lung endothelium inhibited lymphocyte migration by 60% (9.8% +/- 1.8%, P =.002). These findings demonstrate clear roles for both L-selectin and ICAM-1 in lymphocyte migration to the lung during an allergic inflammatory response, with ICAM-1 playing a greater role.

Effect of ICAM-1 blockade on lung inflammation and physiology during acute viral bronchiolitis in rats

Viral respiratory infections cause acute bronchiolitis and physiologic dysfunction in human infants and in animals. It is possible that the pulmonary dysfunction is a consequence of the inflammatory cells that are recruited during viral illness. We hypothesized that blockade of intercellular adhesion molecule-1 (ICAM-1), a major cell adhesion molecule, would impede the ingress of leukocytes during viral infection and attenuate virus-induced pulmonary dysfunction. Adult male rats were inoculated with parainfluenza type 1 (Sendai) virus or sterile vehicle, and treated with blocking or nonblocking MAb specific for rat ICAM-1. Respiratory system resistance, oxygenation (PaO2), methacholine responsiveness, and bronchoalveolar lavage (BAL) leukocyte counts were measured in anesthetized, paralyzed, ventilated rats. Treatment with the blocking ICAM-1 antibody reduced virus-induced increases in BAL neutrophils and lymphocytes by 70% (p < 0.001), but did not affect BAL monocytes/macrophages. Peripheral blood leukocyte counts were elevated in anti-ICAM-1 blocking antibody-treated rats (p = 0.0003). Although virus-induced increases in resistance and decreases in PaO2 were not affected by anti-ICAM-1 treatment, there was a small but significant attenuation of virus-induced methacholine hyperresponsiveness (p = 0.02). We conclude that ICAM-1 has an important role in neutrophil and lymphocyte infiltration during respiratory viral illness, and that virus-induced changes in pulmonary physiology are not related directly to the numbers of neutrophils and lymphocytes that migrate to the air spaces during infection.

Roles of ICAM-1 for abnormal leukocyte recruitment in the microcirculation of bleomycin-induced fibrotic lung injury

To assess the importance of endothelial intercellular adhesion molecule-1 (ICAM-1) in microvascular leukocyte kinetics in diseased lungs, we investigated the transitional changes in ICAM-1 expression, vascular diameter, and leukocyte behavior in rat pulmonary microcirculation during the development of acute lung injury (ALI) and chronic fibrosis (FIB) evoked by bleomycin (BLM). Observations were made in the isolated perfused lung with a real-time confocal laser luminescence microscope. Microvascular cell kinetics were evaluated by measuring the behavior of fluorescence- labeled leukocytes and erythrocytes in the presence or absence of anti-ICAM-1 monoclonal antibody (1A29). Arteriolar ICAM-1 showed little change at any time after BLM treatment. Venular ICAM-1 was first enhanced at the initial phase of ALI followed by the second upregulation at the early phase of FIB. Capillary ICAM-1 showed a sustained increase at both ALI and FIB. Arteriolar and venular diameters were not altered but capillary diameter decreased during ALI and early FIB stages. Although firm adherence of leukocytes to arteriolar and venular walls was not observed, rolling leukocytes were increased in venules both at the initial phase of ALI and at the early phase of FIB. The leukocyte rolling in venules correlated well with transitional changes in ICAM-1 and was inhibited by 1A29. Sustained entrapment of leukocytes in capillaries was attributed to changes in vascular diameter as well as augmented ICAM-1. In conclusion, ICAM-1 plays an important role in microvascular leukocyte recruitment in both ALI and FIB in the BLM-injured lung.

L-selectin in trauma patients: a marker for organ dysfunction and outcome?

BACKGROUND

Systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction syndrome (MODS) are important factors affecting morbidity and mortality after trauma. Adhesion molecules, e.g. L-selectin (CD62 L), play crucial roles in both conditions.

PATIENTS AND METHODS

In 51 multiple trauma patients, CD62 L surface expression on granulocytes, monocytes, lymphocytes, as well as sCD62 L plasma concentrations were determined during the first 6 days after trauma, starting at the site of accident. Clinical parameters were severity of injury scores (ISS, APACHE II), requirement of red blood cell transfusion, acute lung or liver failure, development of MODS or SIRS, early (< or = 6 d) or late (> 6 d), and outcome.

RESULTS

CD62 L expression was reversibly elevated on granulocytes, T cells and monocytes in comparison with initial values. sCD62 L plasma concentrations did not show temporal variations but were depressed throughout observation period, in comparison with healthy controls. Lung failure within the first 6 days was associated with increased CD62 L expression on monocytes and B cells on admission and increased sCD62 L concentrations after 12 and 24 h. Patients with more severe injuries (APACHE II > 20 points) had higher sCD62 L concentrations after 24 h. Non-survivors had decreased sCD62 L (on admission) and T-cell CD62 L expression (after 4 h). Patients with early MODS or SIRS showed increased monocyte CD62 L expression after 6 days.

CONCLUSIONS

In multiple trauma patients, severe organ dysfunction is associated with altered CD62 L expression on leukocytes and circulating sCD62 L plasma concentrations. However, the obvious complexity of the pattern currently restricts use of CD62 L quantitation for clinical purposes.

Induction of heme oxygenase-1 suppresses venular leukocyte adhesion elicited by oxidative stress: role of bilirubin generated by the enzyme

This study aimed to examine whether an elevated activity of heme oxygenase (HO)-1 in the tissue attenuates endothelial cell-leukocyte interactions microvessels in vivo. When rats were pretreated with an intraperitoneal injection of hemin, an HO-1 inducer, mesenteric tissues, including their microvessels, displayed a marked induction of HO-1 concurrent with an increase in plasma concentrations of bilirubin-IXalpha, the product of HO-catalyzed degradation of protoheme IX. In these rats, oxidative stress such as superfusion with H(2)O(2) and ischemia-reperfusion of the tissues neither induced rolling nor exhibited adherent responses of leukocytes in venules. In contrast, the oxidative stresses evoked marked rolling and adhesion of leukocytes in the control rats without HO-1 induction. The HO-1 induction also downregulated leukocyte adhesion elicited by other pro-oxidant stimuli such as N(omega)-nitro-L-arginine methyl ester. The decreases in the oxidant-elicited leukocyte adhesive responses under HO-1-inducing conditions were restored by perfusion with zinc protoporphyrin-IX, an HO inhibitor, but not with copper protoporphyrin-IX, which did not inhibit the enzyme. Furthermore, the effects of zinc protoporphyrin-IX were repressed by superfusion with bilirubin or biliverdin at the micromolar level, but not by the same concentration of carbon monoxide, another product of HO. These results indicate that induction of the HO-1 activity serves as a potential stratagem to prevent oxidant-induced microvascular leukocyte adhesion through the action of bilirubin, a product of HO reaction.

Pressure is proinflammatory in lung venular capillaries

Endothelial responses may contribute importantly to the pathology of high vascular pressure. In lung venular capillaries, we determined endothelial [Ca(2+)](i) by the fura-2 ratioing method and fusion pore formation by quantifying the fluorescence of FM1-43. Pressure elevation increased endothelial [Ca(2+)](i). Concomitantly evoked exocytotic events were evident in a novel spatial-temporal pattern of fusion pore formation. Fusion pores formed predominantly at vascular branch points and colocalized with the expression of P-selectin. Blockade of mechanogated Ca(2+) channels inhibited these responses, identifying entry of external Ca(2+) as the critical triggering mechanism. These endothelial responses point to a proinflammatory effect of high vascular pressure that may be relevant in the pathogenesis of pressure-induced lung disease.

Effects of inflammatory cells on neuronal M2 muscarinic receptor function in the lung

In the lungs, acetylcholine released from the parasympathetic nerves stimulates M3 muscarinic receptors on airway smooth muscle inducing contraction and bronchoconstriction. The amount of acetylcholine released from these nerves is limited locally by neuronal M2 muscarinic receptors. These neuronal receptors are dysfunctional in asthma and in animal models of asthma. Decreased M2 muscarinic receptor function results in increased release of acetylcholine and in airway hyperreactivity. Inflammation has long been associated with hyperreactivity and the role of inflammatory cells in loss of neuronal M2 receptor function has been examined. There are several different mechanisms for loss of neuronal M2 receptor function. These include blockade by endogenous antagonists such as eosinophil major basic protein, decreased expression of M2 receptors following infection with viruses or exposure to pro inflammatory cytokines such as gamma interferon. Finally, the affinity of acetylcholine for these receptors can be decreased by exposure to neuraminidase.