The role of human neutrophil elastase in the development of human emphysema

It has been proposed that the development of human emphysema is related to an imbalance between elastase and its inhibitors in the lung. This report describes the immunolocalization of human neutrophil elastase (HNE) in the alveolar interstitium of 6 patients with emphysema by using immunohistochemical, ultrastructure technique. The results showed that HNE is localized in the azurophil granules of neutrophils, and extracellularly on the elastic fibers of alveolar interstitium and basement membranes of epithelium and endothelium in four emphysematous lungs with chronic bronchitis. The damage of elastic fibers and basement membranes can also be observed. The HNE level of the alveolar interstitium is obviously elevated and closely related to the severity of emphysematous lesions by measuring mean linear intercept (MLI), with the correlation coefficient r = 0.84. This suggests HNE can bind to elastic fibers and basement membranes in the emphysematous lung, and damage these tissues, which might play an important role in the development of human emphysema. These findings support the elastase-antielastase imbalance hypothesis concerning the pathogenesis of human emphysema.     

The beige mouse: role of neutrophil elastase in the development of pulmonary emphysema

Mutant beige mice and normal C57 black mice were given endotoxin intratracheally (IT) once a week for 10 weeks. The objective was to establish whether repeated recruitment of neutrophils to the lung, at levels that induced lung injury to normal mice, would be ineffective in producing lung lesions in neutrophil elastase-deficient beige mice. Endotoxin (25 mg) given IT causes a rapid influx of neutrophils into the lungs of both the C57 black and beige mice, reaching a maximum after 18 h and remaining elevated for at least another 30 h. After 10 weeks of endotoxin instillation the normal C57 black mouse lungs showed evidence of lung injury. There were histological signs of alveolar wall damage, and the mean linear intercepts (Lm) were increased 30% in the endotoxin-treated group. The specific compliance of the lungs from the endotoxin-treated mice was slightly increased. Beige mice, on the other hand, showed no histological or morphological evidence that the neutrophil influx produced lung injury. There was, however, a notable difference in the histological appearance of the control beige lungs compared to control C57 blacks. Beige lungs appeared normal at birth but apparently do not undergo normal alveolarization during neonatal development. Adult lungs have fewer alveoli with smooth terminal air ducts lacking the normal complement of alveolar struts. There was not indication of copper deficiency or problems in elastin synthesis or structure in the beige mice. The results of these studies support a preeminent role for elastase in neutrophil-induced lung lesions.     

The role of NETT in emphysema research

Lung volume reduction surgery (LVRS) is one of a long lineage of surgical approaches to emphysema. The reintroduction of this operation in the mid-1990s led to great controversy over the value of the procedure and its long-term outcomes. The National Emphysema Treatment Trial (NETT) represented an historical scientific collaboration of the National Institutes of Health (NIH), the Centers for Medicare and Medicaid Services (CMS), and the Agency for Health Research and Quality (AHRQ). NETT was designed primarily as a pivotal surgical clinical trial, but also incorporated data collection to inform health policy and cost-benefit analyses. NETT faced challenges that included practical and ethical matters, statistical design and analysis issues, and intense public and political scrutiny. The study design required the development of methods for pulmonary rehabilitation, lung imaging, and exercise testing that have become templates for current clinical and research practice. During the course of the trial, the confidential deliberations of the Data and Safety Monitoring Board (DSMB) played an important role in the ultimate success of the trial and protection of research participants. Because of the importance of the NETT outcomes, the results were disseminated to the medical community and transformed into health policy in a rapid and efficient manner. In many ways, the story of NETT serves as a model for evaluation of new surgical approaches to chronic diseases.     

The role of oxidative processes in emphysema

Elastase/elastase inhibitor imbalance in the lung has been implicated in the pathogenesis of pulmonary emphysema. In light of this, it may be significant that the activity of two major elastase inhibitors, alpha 1-proteinase inhibitor (alpha 1-antitrypsin, alpha 1Pi) and bronchial mucous proteinase inhibitor, can be decreased by oxidizing agents. The effect can be observed with ozone, substances present in cigarette smoke, and oxygen metabolites generated by lung macrophages as well as peroxidative systems released by other phagocytic cells. Thus alpha 1Pi recovered from lung washings of cigarette smokers has only half the predicted normal activity per mg inhibitor and contains 4 moles of methionine sulfoxide (oxidized methionine) per mole of inactive inhibitor. By contrast, alpha 1Pi purified from nonsmokers' lung washings is fully active and contains only native methionine. At the same time, lung washes from some smokers show significantly greater hydrolytic activity against a specific synthetic elastase substrate than do lung washes of nonsmokers. These findings suggest that some smokers may develop an acquired imbalance between elastase and elastase inhibitor in their lungs, favoring activity of the enzyme. In addition to the potential effect of cigarette smoking on lung elastase/elastase inhibitor balance, smoking also may interfere with elastin repair mechanisms. Specifically, acidic water-soluble gas phase components of cigarette smoke prevent synthesis of desmosine cross-links during elastinogenesis in vitro. This report will attempt to correlate the foregoing information on biochemical changes in the lung induced by cigarette smoking with the development of emphysema in the smoker.     

The role of free radicals and neutrophil elastase in development of pulmonary emphysema.

Extracellular proteolysis is hypothesized to be the major cause of pulmonary emphysema and oxygen-derived free radicals and neutrophil elastase are thought to play an important role in its pathogenesis. In this study, peripheral polymorphonuclear leukocytes (PMNs) obtained from 16 patients with emphysema generated a significantly larger amount of superoxide and elastase activity than those obtained from normal controls. A significant correlation was observed between elastase activity and superoxide release. In addition, the superoxide release showed a negative correlation with the disease duration. The superoxide release appeared to correlated with a decline of FEV1.0 over the course of several years in 8 patients. It seems likely that activated PMNs play an important role in the development of pulmonary emphysema.     

The role of nicotine in the pathogenesis of pulmonary emphysema

An investigation was undertaken to evaluate the potential role of nicotine in the pathogenesis of pulmonary emphysema. The acute lethality and the pulmonary toxicity of a single endotracheally administered dose of nicotine were studied in Long-Evans rats. The 24-h LD50 of nicotine was established at 19.3 +/- SD 5.4 mg/kg. Subsequently, rats were treated with either nicotine alone (3 or 7.5 mg/kg), porcine pancreatic elastase (PPE) alone (200 IU/kg) or PPE (200 IU/kg) followed 5 days later by nicotine (3 mg/kg). The selected dose of PPE was below the threshold dose for induction of emphysematous lesions. Cage and sham-treated control groups also were included in the investigation. Four weeks after treatment, extensive physiologic tests were conducted to evaluate the ventilatory, mechanical, and gas exchange functions of the lungs. Lung tissue specimens also were taken for estimation of tissue volume density. Although a few isolated incidents of significant intergroup differences were observed, no distinctive pattern of functional or structural change reminiscent of emphysema was noted in any of the experimental groups. It is concluded that endotracheal instillation of a single, relatively high, dose of nicotine neither induces nor augments the development of pulmonary emphysema in the rat.     

The development of emphysema in cigarette smoke-exposed mice is strain dependent

Only 20% of smokers develop chronic obstructive pulmonary disease. An important determinant of susceptibility is genomic variation. We undertook this study to define strains of mice with different susceptibilities for the development of smoking-induced emphysema because they could help identify genetic factors of susceptibility. NZWLac/J, C57BL6/J, A/J, SJ/L, and AKR/J strains were exposed to cigarette smoke for 6 months. Elastance (Htis), the extent of emphysema (mean linear intercept [Lm]), and the inflammatory cell and cytokine response were measured. NZWLac/J had no change in Lm or Htis (resistant). C57BL6/J, A/J, and SJ/L increased Lm, but not Htis (mildly susceptible). AKR/J increased Lm and Htis (super-susceptible). Only AKR/J had significant inflammation comprising macrophages, neutrophils, and T cells. The AKR/J showed an upregulation of Th1 cytokines whereas in the C57BL/6/J and NZWlac/J, cytokines did not change or were downregulated. We conclude that Lm, elastance, and inflammation are features that are needed to phenotype emphysema in mice. The inflammatory cell and cytokine profile may be an important determinant of the phenotype in response to cigarette smoke exposure. The identification of resistant and susceptible strains for the development of emphysema could be useful for genomic studies of emphysema susceptibility in mice and eventually in humans.     

Morphological mechanism of the development of pulmonary emphysema in klotho mice

The concept of fractal geometry is useful for the analysis of irregular and complex structures often seen in nature. Here we apply this concept to investigate the structural mechanism of the development of pulmonary emphysema in the klotho mouse, which, after milk feeding, exhibits characteristics resembling aging and develops emphysema. We calculated the relationships between perimeter and size characterizing shape and between cumulative frequency and size of the terminal air spaces identified from histologic slides and found that both relations followed a power law with fractal properties. However, the fractal dimensions related to the shape and size (Dsn) in the klotho mice were significantly lower than in controls. Additionally, in the klotho mice, Dsn decreased with age without significant change in mean linear intercept. These abnormal morphological changes were restored when the klotho mice were fed with a vitamin D-deficient diet. Previously undescribed morphological model simulations showed that a random destruction, in which the destruction process occurs homogeneously in the lungs, was more consistent with the data than a correlated destruction that is usually seen in smoking-related human emphysema. These results suggest that the pathological changes in the lungs of the klotho mice are derived not from localized causes, but from systemic causes that are related to abnormal activation of vitamin D. The morphogenesis of emphysema in the klotho mice and morphological analyses using fractal geometry may contribute to the understanding of the progressive nature and cause of parenchymal destruction in human emphysema.     

The heart in emphysema

From these observations it appears (1) that the heart is affected in the majority of patients with emphysema; (2) that the lesion, cardiac hypertrophy, with dilatation of the right ventricle when advanced, may produce symptoms, but probably has no clinical reflection in its earlier stages; (3) that the cause of the left ventricular hypertrophy remains, as yet, undetermined; (4) that there is experimental evidence which indicates that the right ventricular dilatation and hypertrophy occur chiefly in the earlier stage of emphysema, when the lungs are in the process of distention, rather than later as generally believed.