Well-Known and Less Well-Known Functions of Alpha-1 Antitrypsin. Its Role in Chronic Obstructive Pulmonary Disease and Other Disease Developments

Abstract

Alpha-1 antitrypsin (A1AT) is an acute-phase protein, and is best known as an inhibitor of the serine proteases, specifically, neutrophil elastase, proteinase 3, and cathepsin G. The discovery of the connection between inherited A1AT deficiency and emphysema resulted in the concept of a proteinase-antiproteinase imbalance to explain the pathogenic mechanisms of chronic obstructive pulmonary disease, as well as the concomitant development of augmentation therapy with plasma-purified human A1AT. This proteinase-antiproteinase imbalance concept has been difficult to prove, as no single mechanism can account for the complex pathology of chronic obstructive pulmonary disease. New studies have begun to characterize A1AT as an antiinflammatory and an immunoregulatory protein, independent of its antiprotease activity. We recently found that A1AT binds to free fatty acids, and it is this form of A1AT that induces the expression and release of angiopoietin-like protein 4, a protein associated with dyslipidemia and inflammation. This latter finding further strengthens the idea that describing A1AT therapy as antiserine protease is perhaps an oversimplification. The preliminary findings suggest that A1AT could be used for the management of diseases not necessarily related to inherited A1ATD, and points toward a need for more detailed investigations into the relationships between the concentration, structure, and function of A1AT protein.

Keywords: alpha-1 antitrypsin; alpha-1 antitrypsin deficiency; augmentation therapy; molecular forms; proteases.