The effect of reducing agents on proteolytic enzymes and oxidation of alpha 1-proteinase inhibitor.
We have studied the effect of the mucolytic agent N-acetylcysteine and dithiothreitol on the oxidation of alpha 1-PI by hydrogen peroxide, and their effect on porcine pancreatic elastase and leukocyte elastase. In addition, the effect of S-(carboxymethyl)cysteine (= carbocisteine, a mucolytic agent which does not have reducing properties) was studied in vitro and in patients with chronic obstructive bronchitis. Following addition of 59.6mM N-acetylcysteine, the amidolytic activity of leukocyte elastase was decreased by 55.3% and that of porcine pancreatic elastase by 57.0%. Dithiothreitol (5.7 mM) caused the loss of 97.4% and 67.6% of amidolytic activity of leukocyte elastase and porcine pancreatic elastase respectively whereas S-(carboxymethyl)cysteine had no effect. Similar results were found for the effect on elastolytic activity. Oxidation of alpha 1-PI by 8.6mM H2O2 resulted in partial loss of inhibitory function (mean 68.7% activity of native alpha 1-PI). N-Acetylcysteine and dithiothreitol prevented oxidation of alpha 1-PI when pre-incubated with H2O2 or incubated with alpha 1-PI and H2O2 simultaneously (94.5% and 94.4% activity of native alpha 1-PI for N-acetylcysteine; 78.3% and 87.6% activity for dithiothreitol - p less than 0.025). S-(Carboxymethyl)cysteine, when pre-incubated with H2O2 or incubated concurrently with alpha 1-PI and H2O2, caused a further decrease in the porcine pancreatic elastase inhibitory capacity of alpha 1-PI (53.1% and 63.0% respectively - p less than 0.025). None of the agents reversed oxidative inactivation once it had occurred. S-(Carboxymethyl)cysteine had no effect on alpha 1-PI function in sputum at the dose used.
D000111:Acetylcysteine / Q000494:pharmacology*; D001798:Blood Proteins / Q000378:metabolism*; D001991:Bronchitis / Q000201:enzymology; D004229:Dithiothreitol / Q000494:pharmacology*; D005541:Forced Expiratory Volume; D006801:Humans; D007700:Kinetics; D010084:Oxidation-Reduction; D010447:Peptide Hydrolases / Q000378:metabolism*; D011480:Protease Inhibitors / Q000378:metabolism*; D013183:Sputum / Q000201:enzymology; D000515:alpha 1-Antitrypsin
D001798:Blood Proteins; D011480:Protease Inhibitors; D000515:alpha 1-Antitrypsin; D010447:Peptide Hydrolases; D004229:Dithiothreitol; D000111:Acetylcysteine