Characterization of Pleiotropic Activities of alpha1-Antitrypsin

Chronic Obstructive Pulmonary Disease (COPD) is a respiratory disease characterized by chronic inflammatory response in the airways and lung parenchyma that involves the influx of inflammatory, structural cells and mediators. The inflammatory process resulting in lung tissue destruction, emphysema, includes the excess of uninhibited proteases released from inflammatory cells. alpha1-antitrypsin (AAT), an acute phase protein, is the prototypic member of the serpin super family and a major inhibitor of serine proteases such as neutrophil elastase. The clinical importance of AAT is highlighted in individuals with inherited AAT deficiency who exhibits an increased susceptibility to develop chronic inflammatory conditions including COPD. Both native (inhibitory) and modified (non-inhibitory) molecular forms of AAT, such as oxidized, nitrated, polymerized, cleaved and complexed with other proteins, have been detected in vivo. Recently it has become apparent that various forms of AAT express biological properties which are independent of protease inhibition. Studies characterizing these new biological activities of AAT are incomplete, particularly with regard to understanding the involvement of signalling mechanisms. We hypothesize that novel biological activities of native AAT and its by-products may play an important role in the pathological processes characterized by chronic inflammation. We therefore examined; a) the effects of polymerized AAT on neutrophil activation, in vitro; b) the role of oxidized AAT on monocyte/macrophage activation both in vitro and in vivo; c) the effects of augmentation therapy on levels of plasma inflammatory markers and the properties of blood neutrophils obtained from a severe AAT-deficient COPD subject; d) the relationship between AAT levels and endotoxin receptor CD14 expression in young AAT-deficient subjects, and because low plasma AAT levels have been linked to diabetes type 1 we; e) measured plasma AAT levels in diabetes type 2 subjects. Our findings show that: 1. Some of the reported pro-inflammatory activities of polymerized AAT may be due to bacterial or other contaminants and that endotoxin-free polymerized AAT does not exhibit pro-inflammatory activity. 2. Oxidized AAT induces a pro-inflammatory activation of both structural and inflammatory cells and may be involved in the development of COPD. 3. Blood neutrophils from a COPD patient with severe PiZZ AAT deficiency isolated after augmentation therapy release significantly lower levels of IL-8 in response to zymosan as compared to neutrophils obtained before therapy. Our results support the idea that augmentation therapy with human AAT has anti-inflammatory effects. 4. Blood monocytes from clinically healthy subjects with severe AAT-deficiency show significantly higher expression of CD14, an endotoxin receptor, than age and gender matched non-deficient controls. This finding in part explains why reduced AAT levels are related to increased susceptibility to infections and the development of chronic inflammation. 5. A possible link may exist between low plasma levels of AAT and the development of diabetes type 2. To summarize, the findings from our studies further improve our understanding of the biological activities of AAT and highlight the potentially broader modulatory role of AAT in inflammatory diseases. (Less)