Neonatal Hyperoxic Lung Injury Research Articles

Timing of umbilical cord blood derived mesenchymal stem cells transplantation determines therapeutic efficacy in the neonatal hyperoxic lung injury.

Intratracheal transplantation of human umbilical cord blood (UCB)-derived mesenchymal stem cells (MSCs) attenuates the hyperoxia-induced neonatal lung injury. The aim of this study was to optimize the timing of MSCs transplantation. Newborn Sprague-Dawley rats were randomly exposed to hyperoxia (90% for 2 weeks and 60% for 1 week) or normoxia after birth for 21 days. Human UCB-derived MSCs (5×105 cells) were delivered intratracheally early at postnatal day (P) 3 (HT3), late at P10 (HT10) or combined early+late at P3+10 (HT3+10). Hyperoxia-induced increase in mortality, TUNEL positive cells, ED1 positive alveolar macrophages, myeloperoxidase activity and collagen levels, retarded growth and reduced alveolarization as evidenced by increased mean linear intercept and mean alveolar volume were significantly better attenuated in both HT3 and HT3+10 than in HT10. Hyperoxia-induced up-regulation of both cytosolic and membrane p47phox indicative of oxidative stress, and increased inflammatory markers such as tumor necrosis factor-α, interleukin (IL) -1α, IL-1β, IL-6, and transforming growth factor-β measured by ELISA, and tissue inhibitor of metalloproteinase-1, CXCL7, RANTES, L-selectin and soluble intercellular adhesion molecule-1 measured by protein array were consistently more attenuated in both HT3 and HT3+10 than in HT10. Hyperoxia-induced decrease in hepatocyte growth factor and vascular endothelial growth factor was significantly up-regulated in both HT3 and HT3+10, but not in HT10. In summary, intratracheal transplantation of human UCB derived MSCs time-dependently attenuated hyperoxia-induced lung injury in neonatal rats, showing significant protection only in the early but not in the late phase of inflammation. There were no synergies with combined early+late MSCs transplantation.

Long-Term (Postnatal Day 70) Outcome and Safety of Intratracheal Transplantation of Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells in Neonatal Hyperoxic Lung Injury

PurposeThis study was performed to evaluate the long-term effects and safety of intratracheal (IT) transplantation of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) in neonatal hyperoxic lung injury at postnatal day (P)70 in a rat model.Materials and MethodsNewborn Sprague Dawley rat pups were subjected to 14 days of hyperoxia (90% oxygen) within 10 hours after birth and allowed to recover at room air until sacrificed at P70. In the transplantation groups, hUCB-MSCs (5×105) were administered intratracheally at P5. At P70, various organs including the heart, lung, liver, and spleen were histologically examined, and the harvested lungs were assessed for morphometric analyses of alveolarization. ED-1, von Willebrand factor, and human-specific nuclear mitotic apparatus protein (NuMA) staining in the lungs and the hematologic profile of blood were evaluated.ResultsImpaired alveolar and vascular growth, which evidenced by an increased mean linear intercept and decreased amount of von Willebrand factor, respectively, and the hyperoxia-induced inflammatory responses, as evidenced by inflammatory foci and ED-1 positive alveolar macrophages, were attenuated in the P70 rat lungs by IT transplantation of hUCB-MSCs. Although rare, donor cells with human specific NuMA staining were persistently present in the P70 rat lungs. There were no gross or microscopic abnormal findings in the heart, liver, or spleen, related to the MSCs transplantation.ConclusionThe protective and beneficial effects of IT transplantation of hUCB-MSCs in neonatal hyperoxic lung injuries were sustained for a prolonged recovery period without any long-term adverse effects up to P70.

Heme oxygenase-1 regulates postnatal lung repair after hyperoxia: Role of β-catenin/hnRNPK signaling

In the newborn, alveolarization continues postnatally and can be disrupted by hyperoxia, leading to long-lasting consequences on lung function. We wanted to better understand the role of heme oxygenase (HO)-1, the inducible form of the rate-limiting enzyme in heme degradation, in neonatal hyperoxic lung injury and repair. Although it was not observed after 3 days of hyperoxia alone, when exposed to hyperoxia and allowed to recover in air (O2/air recovered), neonatal HO-1 knockout (KO) mice had enlarged alveolar spaces and increased lung apoptosis as well as decreased lung protein translation and dysregulated gene expression in the recovery phase of the injury. Associated with these changes, KO had sustained low levels of active β-catenin and lesser lung nuclear heterogeneous nuclear ribonucleoprotein K (hnRNPK) protein levels, whereas lung nuclear hnRNPK was increased in transgenic mice over-expressing nuclear HO-1. Disruption of HO-1 may enhance hnRNPK-mediated inhibition of protein translation and subsequently impair the β-catenin/hnRNPK regulated gene expression required for coordinated lung repair and regeneration.

In pursuit of scientific excellence: sex matters

In pursuit of scientific excellence: sex matters

Apelin Attenuates Hyperoxic Lung and Heart Injury in Neonatal Rats

Apelin, a potent vasodilator and angiogenic factor, may be a novel therapeutic agent in neonatal chronic lung disease, including bronchopulmonary dysplasia. To determine the beneficial effect of apelin in neonatal rats with hyperoxia-induced lung injury, a model for premature infants with bronchopulmonary dysplasia. The cardiopulmonary effects of apelin treatment (62 μg/kg/d) were studied in neonatal rats by exposure to 100% oxygen, using two treatment strategies: early concurrent treatment during continuous exposure to hyperoxia for 10 days and late treatment and recovery in which treatment was started on Day 6 after hyperoxic injury for 9 days and continued during the 9-day recovery period. We investigated in both models the role of the nitric oxide-cyclic guanosine monophosphate (cGMP) pathway in apelin treatment by specific inhibition of the nitric oxide synthase activity with N(ω)-nitro-L-arginine methyl ester (L-NAME, 25 mg/kg/d). Parameters investigated include survival, lung and heart histopathology, pulmonary fibrin deposition and inflammation, alveolar vascular leakage, lung cGMP levels, right ventricular hypertrophy, and differential mRNA expression in lung and heart tissue. Prophylactic treatment with apelin improved alveolarization and angiogenesis, increased lung cGMP levels, and reduced pulmonary fibrin deposition, inflammation, septum thickness, arteriolar wall thickness, and right ventricular hypertrophy. These beneficial effects were completely absent in the presence of L-NAME. In the injury-recovery model apelin also improved alveolarization and angiogenesis, reduced arteriolar wall thickness, and attenuated right ventricular hypertrophy. Apelin reduces pulmonary inflammation, fibrin deposition, and right ventricular hypertrophy, and partially restores alveolarization in rat pups with neonatal hyperoxic lung injury via a nitric oxide synthase-dependent mechanism.

Vitamin A and Retinoic Acid Act Synergistically to Increase Lung Retinyl Esters During Normoxia and Reduce Hyperoxic Lung Injury in Newborn Mice

We have shown that vitamin A (VA) and retinoic acid (RA) synergistically increase lung retinyl ester content in neonatal rats. To confirm whether this biochemical synergism attenuates early neonatal hyperoxic lung injury in mice, we exposed newborn C57BL/6 mice to 95% O2 or air from birth to 4 d. The agent [vehicle, VA, RA, or the combination vitamin A+retinoic acid (VARA)] was given orally daily. Lung and liver retinyl ester content was measured, and lung injury and development were evaluated. We observed that lung, but not liver, retinyl ester levels were increased more by VARA than by VA or RA alone. Hyperoxic lung injury was reduced by VA and RA, and more so by VARA. VARA attenuated the hyperoxia-induced increases in macrophage inflammatory protein (MIP)-2 mRNA and protein expression, but did not alter hyperoxia-induced effects on peptide growth factors (PDGF, VEGF, and TGF-beta1). The 4-d exposure to hyperoxia or retinoids did not lead to observable differences in lung development. We conclude that the VARA combination has synergistic effects on lung retinyl ester concentrations and on the attenuation of hyperoxia-induced lung injury in newborn mice, possibly by modulation of inflammatory mediators.

Sildenafil attenuates pulmonary inflammation and fibrin deposition, mortality and right ventricular hypertrophy in neonatal hyperoxic lung injury

BackgroundPhosphodiesterase-5 inhibition with sildenafil has been used to treat severe pulmonary hypertension and bronchopulmonary dysplasia (BPD), a chronic lung disease in very preterm infants who were mechanically ventilated for respiratory distress syndrome.MethodsSildenafil treatment was investigated in 2 models of experimental BPD: a lethal neonatal model, in which rat pups were continuously exposed to hyperoxia and treated daily with sildenafil (50–150 mg/kg body weight/day; injected subcutaneously) and a neonatal lung injury-recovery model in which rat pups were exposed to hyperoxia for 9 days, followed by 9 days of recovery in room air and started sildenafil treatment on day 6 of hyperoxia exposure. Parameters investigated include survival, histopathology, fibrin deposition, alveolar vascular leakage, right ventricular hypertrophy, and differential mRNA expression in lung and heart tissue.ResultsProphylactic treatment with an optimal dose of sildenafil (2 × 50 mg/kg/day) significantly increased lung cGMP levels, prolonged median survival, reduced fibrin deposition, total protein content in bronchoalveolar lavage fluid, inflammation and septum thickness. Treatment with sildenafil partially corrected the differential mRNA expression of amphiregulin, plasminogen activator inhibitor-1, fibroblast growth factor receptor-4 and vascular endothelial growth factor receptor-2 in the lung and of brain and c-type natriuretic peptides and the natriuretic peptide receptors NPR-A, -B, and -C in the right ventricle. In the lethal and injury-recovery model we demonstrated improved alveolarization and angiogenesis by attenuating mean linear intercept and arteriolar wall thickness and increasing pulmonary blood vessel density, and right ventricular hypertrophy (RVH).ConclusionSildenafil treatment, started simultaneously with exposure to hyperoxia after birth, prolongs survival, increases pulmonary cGMP levels, reduces the pulmonary inflammatory response, fibrin deposition and RVH, and stimulates alveolarization. Initiation of sildenafil treatment after hyperoxic lung injury and continued during room air recovery improves alveolarization and restores pulmonary angiogenesis and RVH in experimental BPD.

Phosphodiesterase‐5 inhibition attenuates pulmonary inflammation and fibrin deposition, and prolongs survival in neonatal hyperoxic lung injury

Phosphodiesterase‐5 inhibition attenuates pulmonary inflammation and fibrin deposition, and prolongs survival in neonatal hyperoxic lung injury

A new population of bone marrow cells restores lung growth in a model of Bronchopulmonary Dysplasia (BPD)

BPD is characterized by impaired lung growth that persists in adulthood. We have shown neonatal hyperoxia reduces bone marrow progenitor cells & causes abnormal lung structure in mice. The role of progenitor cells in lung growth is controversial. We isolated a new population of bone marrow derived angiogenic cells (BMDAC). We hypothesize that BMDACs can home & engraft in the lung, & promote vascular & alveolar growth after neonatal hyperoxic lung injury.Methods: BMDACs from transgenic Tie2‐GFP mice, were cultured on a feeder cell layer, & characterized by FACS. Neonatal mice were exposed to hyperoxia (FiO2=0.8) X 10 days. BMDAC (10^5 cells) were injected into the right ventricle prior to room air recovery X 10 days. Lung morphometry & immunofluorescence was done.Results: BMDAC displayed a phenotype of a myeloid progenitor: CD45+/CD34‐/CD38+/CD11b‐/CXCR4+/Ly6c‐/F4/80+. Hyperoxia impaired lung structure, which persisted in room air recovery in controls. BMDAC treatment improved septation by 78% & vessel density by 134%(p<0.01), equal to room air raised mice. BMDAC engraftment was 12%, & localized to vessel wall & interstitium, in association with Type II cells. BMADCs did not co‐express smooth muscle, endothelial, epithelial or pericyte markers. We conclude BMDACs are a novel cell population that home to sites of injury in the infant lung & stimulate alveolar & vascular growth after neonatal hyperoxia.

Clarithromycin, montelukast, and pentoxifylline combination treatment ameliorates experimental neonatal hyperoxic lung injury

Objective. We aimed to assess the efficiency of clarithromycin, montelukast, and pentoxifylline treatments, alone and in combination, in reducing hyperoxic lung injury at the histopathologic level.Methods. The experiment was carried out with 47 newborn rat pups divided into six groups during postnatal days 3 to 13. The rats belonging to group 1 were designated as the control group and kept in room air without exposure to hyperoxia. Group 2 (clarithromycin), group 3 (montelukast), group 4 (pentoxifylline), group 5 (clarithromycin + montelukast + pentoxifylline combination), and group 6 (placebo) were kept in plexiglass chamber and exposed to hyperoxia (88–92%) throughout the experiment. Alveolar surface area percentage, fibrosis, and smooth muscle actin expression were assessed in the lungs, which were resected by thoracotomy on postnatal day 14.Results. Drug treatments, when used separately, were not detected to be superior to placebo with regard to mean alveolar surface area, fibrosis, and smooth muscle actin expression. Combination treatment resulted in significantly higher mean lung area percentages and lower actin scores with respect to the placebo treatment group (64.0% vs. 50.2%, p=0.002; 0 (0–1) vs. 7 (2–12), p=0.005, respectively).Conclusions. It was determined that clarithromycin, montelukast, and pentoxifylline combination treatment is superior to placebo treatment in the newborn rat hyperoxic lung injury model. The present study indicates that combination therapy might be successful in bronchopulmonary dysplasia, which has complex pathophysiologic processes and lacks established efficient treatment strategies.

Phosphodiesterase-4 inhibition attenuates pulmonary inflammation in neonatal lung injury

Phosphodiesterase-4 (PDE4) inhibitors may offer novel therapeutic strategies in respiratory diseases, including asthma and chronic obstructive pulmonary disease. Therefore, selective PDE4 inhibitors may also provide a therapeutic option for very pre-term infants with bronchopulmonary dysplasia (BPD). The anti-inflammatory effect of two PDE4 inhibitors was investigated in a pre-term rat model of hyperoxia-induced lung injury. Pre-term rat pups were exposed to room air, hyperoxia, or hyperoxia and one of two PDE4 inhibitors: rolipram and piclamilast. The anti-inflammatory effects of prolonged PDE4 inhibitor therapy were investigated by studying survival, histopathology, fibrin deposition, alveolar vascular leakage and differential mRNA expression (real-time RT-PCR) of key genes involved in inflammation, alveolar enlargement, coagulation and fibrinolysis. PDE4 inhibitor therapy prolonged median survival by up to 7 days and reduced alveolar fibrin deposition, lung inflammation and vascular leakage by decreasing the influx of monocytes and macrophages and protein efflux in bronchoalveolar lavage fluid. Analysis of mRNA expression of key genes involved in experimental BPD revealed a significant PDE4 inhibitor-induced improvement of genes involved in inflammation, fibrin deposition and alveolarisation. In conclusion, phosphodiesterase-4 inhibition prolongs survival by inhibiting inflammation and reducing alveolar fibrin deposition in pre-term rat pups with neonatal hyperoxic lung injury, whereby piclamilast outperformed rolipram.

Inhaled nitric oxide attenuates pulmonary inflammation and fibrin deposition and prolongs survival in neonatal hyperoxic lung injury

Administration of inhaled nitric oxide (iNO) is a potential therapeutic strategy to prevent bronchopulmonary dysplasia (BPD) in premature newborns with respiratory distress syndrome. We evaluated this approach in a rat model, in which premature pups were exposed to room air, hyperoxia, or a combination of hyperoxia and NO (8.5 and 17 ppm). We investigated the anti-inflammatory effects of prolonged iNO therapy by studying survival, histopathology, fibrin deposition, and differential mRNA expression (real-time RT-PCR) of key genes involved in the development of BPD. iNO therapy prolonged median survival 1.5 days (P = 0.0003), reduced fibrin deposition in a dosage-dependent way up to 4.3-fold (P < 0.001), improved alveolar development by reducing septal thickness, and reduced the influx of leukocytes. Analysis of mRNA expression revealed an iNO-induced downregulation of genes involved in inflammation (IL-6, cytokine-induced neutrophilic chemoattractant-1, and amphiregulin), coagulation, fibrinolysis (plasminogen activator inhibitor 1 and urokinase-type plasminogen activator receptor), cell cycle regulation (p21), and an upregulation of fibroblast growth factor receptor-4 (alveolar formation). We conclude that iNO therapy improves lung pathology and prolongs survival by reducing septum thickness, inhibiting inflammation, and reducing alveolar fibrin deposition in premature rat pups with neonatal hyperoxic lung injury.

Recombinant human VEGF treatment transiently increases lung edema but enhances lung structure after neonatal hyperoxia

Recent studies suggest that VEGF may worsen pulmonary edema during acute lung injury (ALI), but, paradoxically, impaired VEGF signaling contributes to decreased lung growth during recovery from ALI due to neonatal hyperoxia. To examine the diverse roles of VEGF in the pathogenesis of and recovery from hyperoxia-induced ALI, we hypothesized that exogenous recombinant human VEGF (rhVEGF) treatment during early neonatal hyperoxic lung injury may increase pulmonary edema but would improve late lung structure during recovery. Sprague-Dawley rat pups were placed in a hyperoxia chamber (inspired O(2) fraction 0.9) for postnatal days 2-14. Pups were randomized to daily intramuscular injections of rhVEGF(165) (20 microg/kg) or saline (controls). On postnatal day 14, rats were placed in room air for a 7-day recovery period. At postnatal days 3, 14, and 21, rats were killed for studies, which included body weight and wet-to-dry lung weight ratio, morphometric analysis [including radial alveolar counts (RAC), mean linear intercepts (MLI), and vessel density], and lung endothelial NO synthase (eNOS) protein content by Western blot analysis. Compared with room air controls, hyperoxia increased pulmonary edema by histology and wet-to-dry lung weight ratios at postnatal day 3, which resolved by day 14. Although treatment with rhVEGF did not increase edema in control rats, rhVEGF increased wet-to-dry weight ratios in hyperoxia-exposed rats at postnatal days 3 and 14 (P < 0.01). Compared with room air controls, hyperoxia decreased RAC and increased MLI at postnatal days 14 and 21. Treatment with VEGF resulted in increased RAC by 181% and decreased MLI by 55% on postnatal day 14 in the hyperoxia group (P < 0.01). On postnatal day 21, RAC was increased by 176% and MLI was decreased by 58% in the hyperoxia group treated with VEGF. rhVEGF treatment during hyperoxia increased eNOS protein on postnatal day 3 by threefold (P < 0.05). We conclude that rhVEGF treatment during hyperoxia-induced ALI transiently increases pulmonary edema but improves lung structure during late recovery. We speculate that VEGF has diverse roles in hyperoxia-induced neonatal lung injury, contributing to lung edema during the acute stage of ALI but promoting repair of the lung during recovery.

Synergistic Effect of Vitamin a and Retinoic Acid in Reducing Neonatal Hyperoxic Lung Injury

Synergistic Effect of Vitamin a and Retinoic Acid in Reducing Neonatal Hyperoxic Lung Injury

Commentary

HIGHLIGHTED TOPICSLung Growth and RepairCommentaryGary C. SieckGary C. SieckJournal of Applied Physiology November 2004, Volume 97Published Online:01 Nov 2004https://doi.org/10.1152/japplphysiol.00920.2004MoreSectionsPDF (9 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat In the first featured article, entitled “Redistribution of pulmonary EC-SOD after exposure to asbestos,” Drs. R. Tan and C. Fattman and colleagues (1) examine the role of extracellular superoxide dismutase (EC-SOD) in asbestos-mediated lung injury. EC-SOD is the predominant antioxidant enzyme in the extracellular matrix of the lung. These investigators found that exposure to asbestos causes EC-SOD to be redistributed in the mouse lung, leading to depleted supplies in the lung parenchyma and accumulation in the bronchoalveolar lavage fluid. The mechanism for redistribution appears to be proteolytic cleavage of the heparin-binding domain of EC-SOD, as most of the EC-SOD found in the bronchoalveolar lavage fluid is the proteolyzed form lacking this domain. This redistribution of EC-SOD from the lung parenchyma to the bronchoalveolar lavage fluid was associated with development of pulmonary fibrosis (asbestosis) 14 days after exposure to asbestos. Such redistribution of EC-SOD after asbestos-induced lung injury may contribute to the development of pulmonary fibrosis by intensifying the oxidant/antioxidant imbalance in the extracellular matrix of the lung, resulting in greater injury and impaired repair.In the second featured article, entitled “Pentoxifylline reduces fibrin deposition and prolongs survival in neonatal hyperoxic lung injury,” Dr. S. ter Horst and colleagues (2) explore the efficacy of pentoxifylline, a xanthine derivative and phosphodiesterase inhibitor, to suppress production of early mediators of inflammation and stimulate fibrinolysis in the lung. Ventilated preterm infants frequently develop bronchopulmonary dysplasia, a multifactorial, chronic lung disease characterized by arrested alveolarization and vascularization. Treating hyperoxia-exposed preterm rat pups with pentoxifylline diminished the severity of tissue damage by reducing capillary leakage of proteins, deposition of fibrin in the lung alveoli, expression of monocyte chemoattractant protein-1 in the lungs, and white blood cell counts in the bronchoalveolar lavage fluid. Most importantly, treatment with pentoxifylline prolonged survival. Pentoxifylline did not affect expression of tumor necrosis factor-α (TNF-α) or interleukin-6, its key proinflammatory targets in endotoxemia, suggesting that TNF-α does not play the same pivotal role in the inflammatory response in neonatal hyperoxia-induced lung injury as it does in endotoxemia. These observations are exciting because inflammation and coagulation are pivotal events not only in the lungs of ventilated preterm infants but also in the lungs of children and adults with acute respiratory distress syndrome.REFERENCES1 Tan RJ, Fattman CL, Watkins SC, and Oury TD. Redistribution of pulmonary EC-SOD after exposure to asbestos. J Appl Physiol 97: 2006–2013, 2004.Link | ISI | Google Scholar2 Ter Horst SAJ, Wagenaar GTM, deBoer E, van Gastelen MA, Meijers JCM, Poorthuis BJHM, and Walther FJ. Pentoxifylline reduces fibrin deposition and prolongs survival in neonatal hyperoxic lung injury. J Appl Physiol 97: 2014–2019, 2004.Link | ISI | Google Scholar Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 97Issue 5November 2004Pages 2005-2005 Copyright & PermissionsCopyright © 2004 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00920.2004History Published online 1 November 2004 Published in print 1 November 2004 Metrics

Pentoxifylline reduces fibrin deposition and prolongs survival in neonatal hyperoxic lung injury

Bronchopulmonary dysplasia is a leading cause of mortality and morbidity in preterm infants despite improved treatment modalities. Pentoxifylline, a phosphodiesterase inhibitor, inhibits multiple processes that lead to neonatal hyperoxic lung injury, including inflammation, coagulation, and edema. Using a preterm rat model, we investigated the effects of pentoxifylline on hyperoxia-induced lung injury and survival. Preterm rat pups were exposed to 100% oxygen and injected subcutaneously with 0.9% saline or 75 mg/kg pentoxifylline twice a day. On day 10, lung tissue was harvested for histology, fibrin deposition, and mRNA expression, and bronchoalveolar lavage fluid was collected for total protein concentration. Pentoxifylline treatment increased mean survival by 3 days (P = 0.0018) and reduced fibrin deposition by 66% (P < 0.001) in lung homogenates compared with untreated hyperoxia-exposed controls. Monocyte chemoattractant protein-1 expression in lung homogenates was decreased, but the expressions of TNF-alpha, IL-6, matrix metalloproteinase-12, tissue factor, and plasminogen activator inhibitor-1 were similar in both groups. Total protein concentration in bronchoalveolar lavage fluid was decreased by 33% (P = 0.029) in the pentoxifylline group. Pentoxifylline treatment attenuates alveolar fibrin deposition and prolongs survival in preterm rat pups with neonatal hyperoxic lung injury, probably by reducing capillary-alveolar protein leakage.

Changes in gene expression in hyperoxia-induced neonatal lung injury

Exposure to high concentrations of oxygen (hyperoxia) can result in lung injury. The biochemical basis of this injury is poorly understood, but it is likely to include alterations in gene expression. Hyperoxia-induced (H-I) cDNAs have been molecularly cloned (Horowitz et al. J. Biol. Chem. 264: 7092-7095, 1989) from the lungs of an adult rabbit exposed to toxic levels of oxygen. One of them (H-I 1) was identified as encoding the tissue inhibitor of metalloproteinases (TIMP), a key regulatory protein of extracellular matrix turnover. Here we identify another clone (H-I 3) as encoding pulmonary surfactant apoprotein A (SP-A). We also show that in neonatal rabbits exposed to 100% oxygen for 96 h, the mRNAs corresponding to TIMP, SP-A, and another H-I gene are increased. These studies have begun to explore specific changes in gene expression associated with neonatal hyperoxic lung injury.