Search

World COPD Day raises awareness about chronic obstructive pulmonary disease (COPD). COPD accounts for over 150,000 US deaths per year. A major challenge is that COPD receives only a fraction of the research funding provided to other major diseases. Control of COPD is dependent on developing new approaches to diagnose the disease earlier with a recognition of either pre-COPD or established COPD based on symptoms, lung structural change and/or loss of lung function that occurs before meeting long established criteria for a population-based definition of obstruction. Optimization of current therapies improves lung function, exercise capacity, quality of life, and survival. New pathways of disease progression are being identified creating new opportunities for development of therapies that could stop or cure this disease.

Nitric oxide (NO) serves multiple functions in the developing lung, and pulmonary NO production is decreased in a baboon model of chronic lung disease (CLD) after premature birth at 125 days (d) gestation (term = 185d). To determine whether postnatal NO administration alters the genesis of CLD, the effects of inhaled NO (iNO, 5 ppm) were assessed in the baboon model over 14d. iNO caused a decrease in pulmonary artery pressure in the first 2d and a greater rate of spontaneous closure of the ductus arteriosus, and lung compliance was greater and expiratory resistance was improved during the first week. With iNO, postmortem pressure-volume curves were shifted upward, lung DNA content and cell proliferation were increased, and lung growth was preserved to equal that which occurs during the same period in utero. In addition, the excessive elastin deposition characteristic of CLD was normalized by iNO, and there was evidence of stimulation of secondary crest development. Thus, in the baboon model of CLD, iNO improves early pulmonary function and alters lung growth and extracellular matrix deposition. As such, NO biosynthetic pathway dysfunction may contribute to the pathogenesis of CLD.

Hemorrhage results in excessive production of superoxide that is associated with severe lung injury. We examined whether the superoxide dismutase (SOD) mimetic manganese(III) mesotetrakis (di- N-ethylimidazole) porphyrin (AEOL 10150) could attenuate this lung injury and whether extracellular (EC)-SOD-deficient mice would have increased hemorrhage-induced lung injury. Compared with wild-type mice, EC-SOD-deficient mice had increased lung neutrophil accumulation, a 3.9-fold increase in myeloperoxidase activity, a 1.5-fold increase in nuclear factor (NF)-κB activation, and a 1.5-fold increase in lipid peroxidation 1 h after hemorrhage. Pretreatment with AEOL 10150 did not attenuate neutrophil accumulation but significantly reduced NF-κB activation and lipid peroxidation in both wild-type and EC-SOD-deficient mice. The increase in hemorrhage-induced neutrophil accumulation in the lungs of EC-SOD-deficient mice suggests that EC-SOD might play a role in mediating neutrophil recruitment to the lung.

Bleomycin administration results in well-described intracellular oxidative stress that can lead to pulmonary fibrosis. The role of alveolar interstitial antioxidants in this model is unknown. Extracellular superoxide dismutase (EC-SOD) is the primary endogenous extracellular antioxidant enzyme and is abundant in the lung. We hypothesized that EC-SOD plays an important role in attenuating bleomycin-induced lung injury. Two weeks after intratracheal bleomycin administration, we found that wild-type mice induced a 106 ± 25% increase in lung EC-SOD. Immunohistochemical staining revealed that a large increase in EC-SOD occurred in injured lung. Using mice that overexpress EC-SOD specifically in the lung, we found a 53 ± 14% reduction in bleomycin-induced lung injury assessed histologically and a 17 ± 6% reduction in lung collagen content 2 wk after bleomycin administration. We conclude that EC-SOD plays an important role in reducing the magnitude of lung injury from extracellular free radicals after bleomycin administration.

The initial pulmonary vasodilation that occurs during nitric oxide (⋅ NO) inhalation does not appear to be maintained chronically in many cases. ⋅ NO may acutely relax vascular smooth muscle by increasing levels of guanosine 3′,5′-cyclic monophosphate (cGMP), tumor necrosis factor (TNF)-α, and inducible nitric oxide synthase (iNOS) while decreasing levels of lipid peroxidation. It was hypothesized that the acute ⋅ NO-induced changes in cGMP, TNF-α, iNOS, and lipid peroxidation, all of which may mediate vasodilation, are transient rather than sustained. Lungs from rats kept in chambers containing 6 parts/million ⋅ NO for 1 h, 1 day, or 1 wk were analyzed for levels of ⋅ NO-induced vasodilatory mediators. Pulmonary cGMP, iNOS mRNA, and TNF-α were increased 1 h after ⋅ NO exposure but decreased to control values at later times. Levels of malonyl dialdehyde, an indicator of lipid peroxidation, were decreased at all times during ⋅ NO inhalation. As a whole, the data suggest that in lungs the vasodilatory mediators cGMP, iNOS, and TNF-α are only acutely and transiently elevated during inhalation of ⋅ NO, consistent with the initially positive clinical response to inhaled ⋅ NO that deteriorates over time.

Inflammatory cytokines have been shown to upregulate secretion of the antioxidant enzyme extracellular superoxide dismutase (EC-SOD) in dermal fibroblasts and, in other cells, to stimulate production of nitric oxide (⋅ NO). Because superoxide rapidly scavenges ⋅ NO, forming the injurious peroxynitrite anion (OONO−), we hypothesize that stimulated cells upregulate EC-SOD expression concurrently with ⋅ NO release. To test for coregulation of EC-SOD and ⋅ NO within the same cell, the timing of inducible nitric oxide synthase (iNOS) and EC-SOD transcription was measured after exposure of a rat type II pneumocyte analog, the L2 cell line, to a combination of interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α). Upregulation of iNOS and EC-SOD transcription occurred after 6 h of exposure, and transcription of both genes was linked by activation of the transcription factor nuclear factor-κB. Both EC-SOD and iNOS were elevated in rat lung homogenates 24 h after intratracheal instillation with IFN-γ and TNF-α. The observation that EC-SOD and iNOS are temporally coregulated after cytokine exposure suggests the possibility of a critical mechanism by which cells might protect ⋅ NO and avoid the formation of OONO−during inflammation.

A calcium-independent type II nitric oxide (NO) synthase has been localized in lung epithelial cells; however, the function of NO. released by epithelial cells is unclear. We hypothesized that epithelial-derived NO may affect the interactions between polymorphonuclear neutrophils (PMN) and the alveolar epithelium and studied PMN adhesion and cytotoxicity to lung epithelial cells. A dose- and time-dependent production of NO. by L2 cells can be induced by a mixture of inflammatory mediators (cytomix) containing lipopolysaccharide, tumor necrosis factor-alpha, and interferon-gamma. Increased NO. production by L2 cells was associated with decreased 51Cr release by the epithelial cells after they were incubated with activated PMN. Addition of NG-monomethyl-L-arginine or oxyhemoglobin reversed the protective effects of cytomix, suggesting that increased NO. production by L2 cells was responsible for the decreased 51Cr release. However, PMN adhesion and intercellular adhesion molecule-1, a major adhesion molecule involved in PMN adhesion to epithelium, were increased by cytomix. We conclude that NO. released by lung epithelial cells was involved in protecting epithelial cells from PMN-mediated cytotoxicity. NO.-mediated protection of lung epithelial cells occurred in spite of PMN adhesion being increased, suggesting that reduced adhesion is not required for NO.-mediated inhibition of PMN cytotoxicity.

To understand the molecular mechanisms that upregulate the activities of pulmonary antioxidant enzymes in adult rats during exposure to 85% oxygen, the relative contents of corresponding mRNA in normal and hyperoxic lungs were determined. Hyperoxic exposure drastically induced the expression of lung manganese-containing superoxide dismutase (MnSOD) mRNA. Maximal induction of MnSOD mRNA occurred at days 3 and 5 of exposure to hyperoxia, reaching a 600 and a 340% increase over the levels of air-exposed rats, respectively. In addition, hyperoxia induced lung mRNA for glucose-6-phosphate dehydrogenase, glutathione peroxidase, glyceraldehyde-3-phosphate dehydrogenase, alpha-tubulin, and gamma-actin to different extends at various days of exposure. Hyperoxia had little or no effect on the levels of mRNA for copper/zinc-containing superoxide dismutase (CuZnSOD), catalase, heat shock protein (HSP70), and creatine kinase. Nuclear run-on experiments showed that the transcriptional rate of the MnSOD gene is enhanced in hyperoxic rat lungs by approximately 400% at day 3 of exposure compared with that of controls. The specific activities of CuZnSOD and MnSOD in these lung samples per unit of lung protein or DNA were also determined. The activity of CuZnSOD in hyperoxic lungs was found to be unchanged compared with controls, except a 20% decrease at day 7 of exposure when standardized against protein content of lung homogenate. Changes of CuZnSOD activity were more dramatic in hyperoxic lungs (a 40% increase at days 3, 5, 7, and 14 of exposure) when enzyme activity was normalized using lung DNA content. Surprisingly, no proportional increase of lung MnSOD enzyme activity was observed at days 3 and 5 of oxygen exposure. The increase of MnSOD activity per unit of lung protein also did not parallel the increase in MnSOD protein content at days 5, 7, and 14 of exposure. These data suggest that, in addition to transcriptional activation, translational and/or posttranslational regulation of the MnSOD gene expression may play a critical role in controlling lung MnSOD activity on hyperoxic exposure.

We have analyzed the magnitude and uniformity of the expression of manganese superoxide dismutase (Mn SOD) protein in alveolar type II cells of rats exposed to hyperoxia using quantitative colloidal gold immunocytochemistry and morphometric techniques. Sprague-Dawley rats were exposed continuously to normal air or to 85% oxygen for 7 and 14 days. The lungs were fixed by intratracheal instillation of a paraformaldehyde-glutaraldehyde fixative. Lung samples were dehydrated in ethanol and embedded in LR-White. Thin sections for electron microscopy were labeled with anti-rat Mn SOD rabbit antiserum followed by protein-A gold. The labeling density (gold particles/micron 2) over subcellular compartments was determined, and relative organelle volumes were measured using a random point overlay. The results confirm that alveolar type II cells are a locus of Mn SOD response in the lungs of hyperoxic rats and contribute to this response through a combination of changes: an increase of Mn SOD concentration in the mitochondrial matrix, an increase of mitochondrial volume per cell, and type II cell hyperplasia.