Granulocyte elastase-mediated proteolysis of alpha 1-antitrypsin in cystic fibrosis bronchopulmonary secretions.
Airway secretions of patients with cystic fibrosis (CF) contain large amounts of alpha 1-antitrypsin (alpha 1-AT), yet elastase activity is also often detectable, suggesting that airway alpha 1-AT may not be functional in some CF patients. It is unknown whether in CF sputum alpha 1-AT is inactivated by oxidants, neutrophil metalloproteinases, bacterial elastase, or neutrophil elastase. To investigate the mechanism(s) by which alpha 1-AT may be inactivated in CF airway secretions, sputum samples were obtained from nine patients during respiratory physiotherapy. alpha 1-AT was measured by radial immunodiffusion. Sputum-alpha 1-AT was purified by antibody affinity chromatography. Electrophoresis of alpha 1-AT from seven patients with acute infectious exacerbations revealed two distinct components: a minor band corresponding to an elastase/alpha 1-AT complex and a major band typical of proteolysed alpha 1-AT (Mr = 48 kD). Each patient had large amounts of sputum elastase activity. In contrast, two patients without free sputum elastase activity had intact sputum alpha 1-AT; however, alpha 1-AT was partially truncated by porcine pancreatic elastase suggesting that the alpha 1-AT may have been partially oxidized. Adding alpha 1-AT purified from normal serum to alpha 1-AT-depleted sputum containing elastase activity resulted in a small alpha 1-AT/elastase complex with most alpha 1-AT being truncated. The serine proteinase inhibitor phenylmethylsulfonyl fluoride but not the metalloproteinase inhibitor EDTA prevented alpha 1-AT proteolysis, thus granulocyte elastase can mediate alpha 1-AT degradation in CF. Apparently, the large granulocyte elastase burden in some acutely ill patients with cystic fibrosis can proteolytically inactivate alpha 1-AT.
Cantin
A
A
Unité de Recherche Pulmonaire, Centre Hospitalier Universitaire de Sherbrooke, Quebec, Canada.
Bilodeau
G
G
Bégin
R
R
D000293:Adolescent; D000818:Animals; D001980:Bronchi / Q000378:metabolism; D003550:Cystic Fibrosis / Q000378:metabolism*; D006098:Granulocytes / Q000201:enzymology*; D006801:Humans; D010196:Pancreatic Elastase / Q000378:metabolism*; D013183:Sputum / Q000032:analysis* / Q000201:enzymology; D000515:alpha 1-Antitrypsin / Q000378:metabolism*
D000515:alpha 1-Antitrypsin; D010196:Pancreatic Elastase