Lung injury induced by leukocytic proteases

Area of Science:

• Pulmonary Medicine
• Cell Biology
• Biochemistry

Background:

• Human polymorphonuclear neutrophilic leukocytes (PMNs) possess neutral proteases capable of degrading key lung matrix components like elastin and collagen.
• Pulmonary emphysema, a major human lung disease, is strongly linked to cigarette smoking.
• Alveolar antiproteases normally regulate protease activity, preventing excessive tissue degradation.

Purpose of the Study:

• To investigate the role of PMN and macrophage elastases in the pathogenesis of pulmonary emphysema.
• To explore the mechanisms by which cigarette smoke contributes to lung injury and emphysema.
• To present a unified hypothesis for lung injury in emphysema involving both cellular proteases and smoke exposure.

Main Methods:

• In vivo instillation of purified elastase into dog lungs to observe anatomical changes.
• In vitro studies on the effect of tobacco smoke oxidants on alpha 1-proteinase inhibitor.
• Short-term exposure of cultured mouse macrophages to cigarette smoke to assess elastase secretion.

Main Results:

• Elastase instillation in dogs induced anatomical changes mimicking human pulmonary emphysema.
• Tobacco smoke's oxidizing activity was shown to inactivate alpha 1-proteinase inhibitor in vitro.
• Cigarette smoke exposure augmented elastase secretion from mouse macrophages.
• Mouse macrophage elastase demonstrated resistance to inhibition by alpha 1-proteinase inhibitor and alpha 2-macroglobulin.

Conclusions:

• Both PMN and macrophage-derived elastases are implicated in the lung tissue degradation observed in emphysema.
• Cigarette smoke contributes to emphysema by inactivating protective antiproteases and stimulating protease release from macrophages.
• A unified hypothesis suggests a dual role for cellular elastases and cigarette smoke in the development of pulmonary emphysema.