CATHEPSIN-L ACTIVITY IS INCREASED IN ALVEOLAR MACROPHAGES AND BRONCHOALVEOLAR LAVAGE FLUID OF SMOKERS

Elastinolytic enzymes derived from alveolar macrophages (AM) are consi dered to play an important role in the development of emphysema associ ated with cigarette smoking. In this study, the enzyme activity and mR NA expression of cathepsin L were quantitated in AM and bronchoalveola r lavage (BAL) fluid obtained from current smokers and compared with t hose from nonsmokers. Activity was measured with the synthetic substra te Z-Phe-Arg-MCA combined with a novel cathepsin B inhibitor, CA-074. We found that the specific activity of cathepsin L was significantly e levated in BAL cells from smokers (7.1 +/- 0.7 mumol/mg protein/h, mea n +/- SEM) compared with cells from nonsmokers (2.9 +/- 0.3) (p < 0.01 ). The expression of cathepsin L mRNA in BAL cells as determined by do t-blot analysis was also higher in BAL cells from smokers, which was c omparable to the increase in the enzyme activity. About 5 to 6% of the specific activity of cathepsin L in BAL cell lysates was detected in unconcentrated BAL fluid; specific activity was also significantly hig her in samples from smokers (0.38 +/- 0.04 mumol/mg protein/h) than fr om nonsmokers (0.14 +/-0.02). In addition, procathepsin L (42 kD) and the mature form of cathepsin L (33 kD) were demonstrated in BAL fluid by immunoblot analyses. These data suggest that cigarette smoking indu ces mRNA expression and the synthesis of cathepsin L in AM and the rel ease of procathepsin from AM into extracellular milieu. Furthermore, i ncreased activity levels of cathepsin L in extracellular compartments may contribute to the proteolysis of elastin in the process of lung de struction associated with cigarette smoking.