Sulphite enhances peroxynitrite-dependent alpha1-antiproteinase inactivation. A mechanism of lung injury by sulphur dioxide?

Sulphite is toxic to the lung and can cause allergic reactions, the most common of which is bronchoconstriction in asthmatics. We show that sulphite can considerably potentiate the inactivation of alpha1-antiproteinase caused by peroxynitrite. Addition of peroxynitrite to sulphite generated inactivating species that persisted at pH 7.4 and 37 degrees C for at least 30 min. We propose that formation of protein-modifying sulphite radicals from SO3(2-) exposed to ONOO- is a mechanism by which SO2 could cause lung injury, both by enhancing proteolysis and by creating new antigens that could provoke an immune response.