Cigarette smoke stimulates cathepsin B activity in alveolar macrophages of rats

Cathepsin B activity was determined in alveolar macrophages and cell-free bronchoalveolar lavage fluid from Sprague-Dawley rats exposed only through the nose to fresh mainstream smoke from University of Kentucky high-tar, high-nicotine reference cigarettes, and in cells and fluid from room control and sham control animals. Increased levels of blood carboxyhemoglobin and pulmonary aryl hydrocarbon hydroxylase activity in smoke-exposed animals indicated effective exposure of animals to cigarette smoke. Cathepsin B activity was quantitated with alpha-N-benzyloxycarbonyl-leucine-leucine-arginine-2-naphthylamide as substrate. Specific activity (nanomoles of substrate cleaved per milligram of protein per hour) in alveolar macrophages was increased by 43% at both 4- and 10-week exposure points in animals exposed twice daily to 10 puffs of cigarette smoke. These data indicate that maximal stimulation of the enzyme occurs within 4 weeks of the initiation of smoke exposure. When the activity was expressed on a per-cell basis, cathepsin B activity was also increased in the smoke-exposed group at both exposure points. Activity in bronchoalveolar lavage fluid of smoke-exposed animals was increased by approximately 50% at 4 and 10 weeks, but the differences were not statistically significant. These findings demonstrate that cigarette smoke is a potent inducer of cathepsin B activity in alveolar macrophages of rats.