Role of neutrophils and alpha(1)-antitrypsin in coal- and silica-induced connective tissue breakdown

Mineral dusts produce emphysema, and administration of dust to rats results in the rapid appearance of desmosine and hydroxyproline in lavage fluid, c onfirming that dusts directly induce connective tissue breakdown. To examin e the role of neutrophils and alpha(1)-antitrypsin (alpha(1)-AT) in this pr ocess, we instilled silica or coal into normal rats or rats that had been p retreated with antiserum against neutrophils. One day after dust exposure, lavage fluid neutrophils and desmosine and hydroxyproline levels were all e levated; treatment with antiserum against neutrophils reduced neutrophils b y 75%, desmosine by 40-50%, and hydroxyproline by 25%. By 7 days, lavage fl uid neutrophils and desmosine level had decreased, whereas macrophages and hydroxyproline level had increased. By ELISA analysis, lavage fluid al-AT l evels were increased four- to eightfold at both times. On Western blot, som e of the alpha(1)-AT appeared as degraded fragments, and by HPLC analysis, 5-10% of the methionine residues were oxidized. At both times, lavage fluid exhibited considerably elevated serine elastase inhibitory capacity and al so showed elevations in metalloelastase activity. We conclude that, in this model, connective tissue breakdown is initially driven largely by neutroph il-derived proteases and that markedly elevated levels of functional alpha( 1)-AT do not prevent breakdown, thus providing in vivo support for the conc ept of quantum proteolysis proposed by Lieu and Campbell (T. G. Liou and E. J. Campbell. Biochemistry 34: 16171-16177, 1995). Macrophage-derived prote ases may be of increasing importance over time, especially in coal-treated animals.