Lysosomal enzymes from polymorphonuclear leukocytes and proteinase inhibitors in patients with cystic fibrosis

Abstract

In serum and sputum samples from 15 patients with cystic fibrosis (CF) suffering from chronic Pseudomonas aeruginosa lung infections, concentrations and/or activities of elastase derived from polymorphonuclear leukocytes (PMN), cathepsin G, myeloperoxidase (MPO), and superoxide dismutase (SOD), as well as concentrations of the proteinase inhibitors alpha 1-proteinase inhibitor (alpha 1-PI) and alpha 2-macroglobulin (alpha 2-M), were determined. High enzyme concentrations compared with those in normal control subjects were found for PMN elastase (mean, 96.1 +/- 91.7 micrograms/ml), cathepsin G (mean, 5.9 +/- 6.0 micrograms/ml), and MPO (mean, 138.0 +/- 177 micrograms/ml) in patients' sputum samples. Superoxide dismutase was not detectable in any of the sputum specimens (below 1 ng/ml). Proteinase inhibitor concentrations were elevated in serum samples (alpha 1-PI: mean, 3,457 +/- 1,084 micrograms/ml; alpha 2-M: mean, 4,835 +/- 1,334 micrograms/ml). Means of 61 +/- 38 micrograms/ml alpha 1-PI and 29 +/- 31 micrograms/ml alpha 2-M were present in the sputum specimens. Both proteinase inhibitors were functional in the serum samples. However, sputum alpha 1-PI was proteolytically degraded, as shown by western blot technique, and was not able to bind 125I-labeled PMN elastase, as shown by autoradiography. Only 10.9 +/- 8.5% of the total alpha 1-PI in the sputum samples was complexed to PMN elastase and 3.6 +/- 3.2% to cathepsin G. On the other hand, 96.2 +/- 96.8% of the total PMN elastase and 78.0 +/- 100% of cathepsin G were unbound in the sputum samples. The study suggests that the imbalance between PMN proteinases and their inhibitors is due to inactivation of alpha 1-PI in the sputum caused by proteolytic or oxidative attack from PMN enzymes.