Effect of inhaled chromium on pulmonary A1AT

A major health hazard to coal miners is development of emphysema following long-term exposure to coal dust. One mechanism underlying development of emphysema is the oxidation of critical methionine (Met) residues in antiproteolytic factor, alpha1-antitrypsin (A1AT) resulting in a protease-antiprotease imbalance in the lung. Several studies have documented an association between the incidence and severity of emphysema among miners and their exposure to crystalline silica (i.e., SiO2). However, what remains unclear is the role of other co-inhaled nonemphysematogenic nonoxidant inorganic constituent in disease pathogenesis. We hypothesize that in miners, inhaled trivalent chromium (Cr3+, the only form of Cr in coal) may potentially affect lung A 1,AT activity in situ via Cr complexing with Met residues, and thereby exacerbate any SiO2-induced imbalance. To ascertain if Cr3+ could, in fact, affect A1AT activity, in vitro studies were done to assess elastase inhibitory activity following A1AT incubation with soluble Cr3+. In addition, to determine if Cr3+ found in the lungs as detoxification products of inhaled hexavalent Cr (Cr6-) could affect A1AT in situ, lavages from the lungs of chromate-exposed rats were also analyzed for elastase inhibitory activity The in vitro results indicate that Cr3+ ions clearly inhibited A1AT function, with an IC50 of 1.1 mM being estimated under the experimental conditions used. The in vivo results indicate that long-term inhalation (12 wk or longer) of chromate-bearing atmospheres also gave rise to significant (i.e., 50-70%) inhibition of the antielastase activity of A1AT. Together, these results clearly suggest that the Cr3- present in coal dusts could potentially act to inhibit A1AT activity in the lungs of miners and thereby promote the emphysema togenicity of SiO2 or of other emphysematogens present as coconstituents in these dusts.