Safety and Efficacy of Inhaled Alpha-1 Antitrypsin in Preventing Bronchiolitis Obliterable Syndrome in Lung Transplant Recipients

Plain-language summary

Bronchiolitis obliterable syndrome (BOS) is the most common cause of death in long-term survivors after lung transplantation and refractory to most interventions. Many risk factor for BOS were identified in previous studies such as acute cellular rejection, lymphocytic bronchiolitis, cytomegalovirus (CMV) and non-CMV respiratory infections, injury to the allograft or airways, Primary graft dysfunction, HLA mismatching, and organizing pneumonia. (Belperio JA. et al.). Neutrophils and their released products may be involved in the development of BOS. Neutrophilia was repeatedly observed in the bronchoalveolar lavage fluid of patients after lung transplantation. In addition, infiltration of neutrophils into the bronchial epithelium has been detected in patients with higher degrees of active airway damage. Neutrophils are capable of causing severe damage to the lung tissue by releasing toxic proteases and reactive oxygen species if not counterbalanced by the antiprotease/ antioxidant screen of the lung. Based on this background, a causal relationship between neutrophilia and the development of BOS has been proposed. (Hirsch J. et al.) Detection of unopposed Neutrophile elastase (NE) activity in BAL appears to correlate with poor outcome due to refractory BOS. Unopposed NE in these subjects may not only serve as a marker of evolving graft dysfunction but also participate in damaging the airways of the allograft and inhibit adequate bacterial clearance. Prevention of neutrophil sequestration or inhibition of NE may prevent or attenuate airway damage and improve bacterial clearance mechanisms. (Nutley D et al.) These data demonstrate the importance of neutrophils and unopposed NE in the pathogenesis of BOS and call for new approach to prevent or modulate BOS targeting this mechanism. AAT is the main inhibitor of neutrophil elastase in the lower airways and patients with AAT deficiency have low concentrations of the protein in this region of the lung. This explains the proteinase/antiproteinase theory of the development of emphysema in deficient patients in which the amount of elastase released in the lung exceeds the amount of AAT. The net result is persistence of elastase activity leading to lung destruction and the pathological changes of emphysema. (Abusriwil H. et al.) The administration of the AAT is to address proteinase/antiproteinase imbalance. Administration of AAT will help to prevent further destruction of the lung architecture and reduce the inflammatory dysregulation that causes pulmonary dysfunction. It is expected that by attacking a specific and previously untreated key component part of the pathophysiological cycle of BOS, AAT therapy would decrease the prevalence of BOS in lung transplant recipients and prolong life expectancy of these patients.

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