Sulphite enhances peroxynitrite‐dependent α₁‐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 α 1 ‐antiproteinase caused by peroxynitrite. Addition of peroxynitrite to sulphite generated inactivating species that persisted at pH 7.4 and 37°C for at least 30 min. We propose that formation of protein‐modifying sulphite radicals from SO 2− 3 exposed to ONOO − is a mechanism by which SO 2 could cause lung injury, both by enhancing proteolysis and by creating new antigens that could provoke an immune response.