P-selectin is upregulated early in the course of hyperoxic lung injury in mice

Antioxidant strategies in respiratory medicine

Pulmonary oxidant stress plays an important pathogenetic role in disease conditions including acute lung injury/adult respiratory distress syndrome (ALI/ARDS), hyperoxia, ischemia-reperfusion, sepsis, radiation injury, lung transplantation, COPD, and inflammation. Reactive oxygen species (ROS), released from activated macrophages and leukocytes or formed in the pulmonary epithelial and endothelial cells, damage the lungs and initiate cascades of pro-inflammatory reactions propagating pulmonary and systemic stress. Diverse molecules including small organic compounds (e.g. gluthatione, tocopherol (vitamin E), flavonoids) serve as natural antioxidants that reduce oxidized cellular components, decompose ROS and detoxify toxic oxidation products. Antioxidant enzymes can either facilitate these antioxidant reactions (e.g. peroxidases using glutathione as a reducing agent) or directly decompose ROS (e.g. superoxide dismutases [SOD] and catalase). Many antioxidant agents are being tested for treatment of pulmonary oxidant stress. The administration of small antioxidants via the oral, intratracheal and vascular routes for the treatment of short- and long-term oxidant stress showed rather modest protective effects in animal and human studies. Intratracheal and intravascular administration of antioxidant enzymes are being currently tested for the treatment of acute oxidant stress. For example, intratracheal administration of recombinant human SOD is protective in premature infants exposed to hyperoxia. However, animal and human studies show that more effective delivery of drugs to cells experiencing oxidant stress is needed to improve protection. Diverse delivery systems for antioxidants including liposomes, chemical modifications (e.g. attachment of masking pegylated [PEG]-groups) and coupling to affinity carriers (e.g. antibodies against cellular adhesion molecules) are being employed and currently tested, mostly in animal and, to a limited extent, in humans, for the treatment of oxidant stress. Further studies are needed, however, in order to develop and establish effective applications of pulmonary antioxidant interventions useful in clinical practice. Although beyond the scope of this review, antioxidant gene therapies may eventually provide a strategy for the management of subacute and chronic pulmonary oxidant stress.

Inflammatory mediators in the immunobiology of bronchopulmonary dysplasia

Inflammation is important in the development of bronchopulmonary dysplasia (BPD). Polymorphonuclear cells and macrophages and proinflammatory cytokines/chemokines denote early inflammation in clinical scenarios such as in utero inflammation with chorioamnionitis or initial lung injury associated with respiratory distress syndrome or ventilator-induced lung injury. The persistence and non-resolution of lung inflammation contributes greatly to BPD, including altering the lung's ability to repair, contributing to fibrosis, and inhibiting secondary septation, alveolarization, and normal vascular development. Further understanding of the role of inflammation in the pathogenesis of BPD, in particular, during the chronic inflammatory period, offers us the opportunity to develop inflammation-related prevention and treatment strategies of this disease that has long-standing consequences for very premature infants.

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.

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.

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.

Reduction of inflammatory response in composite flap transfer by local stress conditioning-induced heat-shock protein 32

BACKGROUND

The failure of composite flaps despite anastomotic patency is thought to be mediated by the inflammatory response within the microvasculature, which results from unavoidable surgical trauma and transfer-related ischemia-reperfusion. Evidence suggests that stress conditioning may improve flap survival; however, the molecular mechanisms of protection are far from being clear. Therefore, we analyzed whether stress conditioning-induced heat-shock protein 32 is effective to prevent the inflammatory response in transferred osteomyocutaneous flaps.

METHODS

In a rat model, leukocyte-endothelial cell interaction and endothelial integrity disruption as early indicators of the inflammatory response were quantitatively analyzed in muscle, subcuticular tissue, and periosteum of microvascularly transferred osteomyocutaneous flaps by using intravital fluorescence microscopy. Twenty-four hours before flap transfer, stress conditioning was induced by local heating of the left hindlimb up to 42.5 degrees C for 30 minutes. In additional animals, stress conditioning-induced activity of heat-shock protein 32 was inhibited by tin protoporphyrin-IX. Unconditioned flaps served as controls.

RESULTS

In all tissues analyzed, control flaps showed significant leukocyte adherence in postcapillary venules, increased intercellular adhesion molecule-1 (ICAM-1) expression, and endothelial integrity disruption, but a lack of heat-shock protein 32. In contrast, stress conditioning induced marked heat-shock protein 32 expression, which was associated with a significant reduction (P <.05) of leukocyte adherence, ICAM-1 expression, and endothelial hyperpermeability. The inhibition of heat-shock protein 32 by tin protoporphyrin-IX completely abolished the stress conditioning-induced amelioration of the inflammatory response in all tissues analyzed.

CONCLUSIONS

Stress conditioning by local heat-shock priming reduces the inflammatory response in osteomyocutaneous flaps. The protective effect is predominantly mediated by the induction of heat-shock protein 32.

Early clinical markers for the development of bronchopulmonary dysplasia: soluble E-Selectin and ICAM-1

OBJECTIVE

To test the hypothesis that in infants born at </=29 weeks' gestation soluble adhesion molecule concentrations would be higher in the first week of life in infants that subsequently develop bronchopulmonary dysplasia than in infants that do not.

DESIGN AND METHODS

In cord blood and on days of life 1, 3, and 7, we measured serum concentrations of soluble P-Selectin, E-Selectin, and intercellular adhesion molecule-1 in samples obtained from infants </=29 weeks' gestational age. At 1 month of age we assessed the infants' clinical courses to determine whether the infants met the criteria for the diagnosis of bronchopulmonary dysplasia (BPD) and evaluated the infants' radiographic studies to stage the level of BPD. On discharge, the duration of oxygen therapy, the requirement for home oxygen therapy, and length of hospital stay were determined.

RESULTS

Concentrations of soluble P-Selectin were greatest in cord blood samples obtained from all infants and were markedly reduced on day of life 1, regardless of the subsequent development of BPD. In serum samples obtained from cord blood and on days of life 1 and 3, soluble E-Selectin levels were higher in infants that developed BPD than in infants that did not develop BPD. In addition, the highest concentrations of soluble E-Selectin in serum samples from cord blood and on day of life 1 were associated with the development of stage 3 or 4 BPD. Soluble intercellular adhesion molecule-1 concentrations were higher on days of life 3 and 7 in the infants that went on to develop BPD than in those that did not.

CONCLUSIONS

Because neutrophil attachment to endothelial cell adhesion molecules is a key event in the initiation of an inflammatory response, the association of higher early concentrations of soluble E-Selectin with the development of BPD suggests that E-Selectin may play a key role in the pathogenesis of lung inflammation and the development of BPD. This association also suggests that inflammatory events or effects leading to inflammatory responses occurring in the prenatal and/or very early perinatal periods contribute significantly to the pathogenesis of BPD.

Increased endothelial cell expression of platelet-endothelial cell adhesion molecule-1 during hyperoxic lung injury

Lung injury is a frequent consequence of oxygen (O2) therapy administered to newborns and adults with respiratory distress. Acute exposure to hyperoxia results in a well-described pathophysiologic response in the lungs. Because inflammation is an important component of pulmonary O2 toxicity, we have an interest in identifying the inflammatory mediators that increase during hyperoxia. Platelet-endothelial cell adhesion molecule-1 (PECAM-1), a member of the immunoglobulin superfamily that is expressed at the junctions between endothelial cells, is essential to the transendothelial migration of leukocytes. We hypothesized that increased expression of PECAM-1 occurs in pulmonary endothelial cells during hyperoxic lung injury. Adult mice were exposed to 100% O2 for up to 96 h. We analyzed PECAM-1 expression by RNA blot hybridization, in situ hybridization, and immunohistochemistry. A increase in PECAM-1 mRNA was seen as soon as 2 d of hyperoxia relative to unexposed control mice. PECAM-1 mRNA and protein were found in endothelial cells of both large and small arteries. The expression of PECAM-1 in capillary vessels was further confirmed using in situ hybridization at the electron microscope level. This increase in PECAM-1 expression coincided with the appearance of leukocytes in lung tissue. These observations suggest that PECAM-1 expression is a relatively early step in the inflammation cascade, and intervention at this phase may be critical to the prevention of further damage.

Dexamethasone enhancement of hyperoxic lung inflammation in rats independent of adhesion molecule expression

Infants and adults on oxygen often are treated with glucocorticoids in an attempt to reduce lung inflammatory injury. However, glucocorticoids hasten the development of hyperoxic lung injury in some animal models. The purpose of this study was to test the hypothesis that dexamethasone alters the lung inflammatory responses to hyperoxia exposure. We studied male Sprague-Dawley rats, placing them in >95% oxygen immediately after administration of 0, 0.1, 1, or 10 mg/kg of dexamethasone. At 0, 24, or 48 hr of exposure to hyperoxia, extravascular lung water contents were measured, and lung inflammatory responses were assessed by lung myeloperoxidase activities, lung neutrophil counts, and lung expression of E-Selectin and intercellular adhesions molecule-1 (ICAM-1). Dexamethasone, independent of exposure to hyperoxia, led to marked increases in lung neutrophil counts, without increases in lung myeloperoxidase activities or increases in the expression of the adhesion molecules. Hyperoxia exposure also enhanced lung neutrophil accumulation, and extravascular lung water increased earlier in animals exposed to hyperoxia and dexamethasone than in those exposed to hyperoxia alone. In conclusion, the increase in lung neutrophils in dexamethasone-treated rats without enhanced expression of E-Selectin or intracellular adhesions molecule-1 suggests that dexamethasone leads to lung neutrophil accumulation by its effect on neutrophils. The more rapid development of hyperoxic lung injury associated with earlier lung neutrophil accumulation suggests that dexamethasone-induced lung neutrophil sequestration primes the lung for the development of hyperoxic lung injury and supports further the conclusion that lung inflammation contributes significantly to the development of hyperoxic lung injury.