α1-Antitrypsin Suppresses TNF-α and MMP-12 Production by Cigarette Smoke–Stimulated Macrophages

Abstract

We have previously observed that mice exposed to cigarette smoke and treated with exogenous α₁-antitrypsin (A1AT) were protected against the development of emphysema and against smoke-induced increases in serum TNF-α. To investigate possible mechanisms behind this latter observation, we cultured alveolar macrophages lavaged from C57 mice. Smoke-conditioned medium caused alveolar macrophages to increase secretion of macrophage metalloelastase (MMP-12) and TNF-α, and this effect was suppressed in a dose–response fashion by addition of A1AT. Macrophages from animals exposed to smoke in vivo and then lavaged also failed to increase MMP-12 and TNF-α secretion when the animals were pretreated with A1AT. Because proteinase activated receptor-1 (PAR-1) is known to control MMP-12 release, macrophages were treated with the G protein–coupled receptor inhibitor, pertussis toxin; this suppressed both TNF-α and MMP-12 release, while a PAR-1 agonist (TRAP) increased TNF-α and MMP-12 release. Smoke-conditioned medium caused increased release of the prothrombin activator, tissue factor, from macrophages. Hirudin, a thrombin inhibitor, and aprotinin, an inhibitor of plasmin, reduced smoke-mediated TNF-α and MMP-12 release, and A1AT inhibited both plasmin and thrombin activity in a cell-free functional assay. These findings extend our previous suggestion that TNF-α production by alveolar macrophages is related to MMP-12 secretion. They also suggest that A1AT can inhibit thrombin and plasmin in blood constituents that leak into the lung after smoke exposure, thereby preventing PAR-1 activation and MMP-12/TNF-α release, and decreasing smoke-mediated inflammatory cell influx.