Sulphur dioxide suppresses inflammatory response by sulphenylating NF-κB p65 at Cys³⁸ in a rat model of acute lung injury

The present study was designed to investigate whether endogenous sulphur dioxide (SO₂) controlled pulmonary inflammation in a rat model of oleic acid (OA)-induced acute lung injury (ALI). In this model, adenovirus expressing aspartate aminotransferase (AAT) 1 was delivered to the lungs, and the levels of SO₂ and proinflammatory cytokines in rat lung tissues were measured. In the human alveolar epithelial cell line A549, the nuclear translocation and DNA binding activities of wild-type (wt) and C38S (cysteine-to-serine mutation at p65 Cys³⁸) NF-κB p65 were detected. GFP-tagged C38S p65 was purified from HEK 293 cells and the sulphenylation of NF-κB p65 was studied. OA caused a reduction in SO₂/AAT pathway activity but increased pulmonary inflammation and ALI. However, either the presence of SO₂ donor, a combination of Na₂SO₃ and NaHSO₃, or AAT1 overexpression in vivo successfully blocked OA-induced pulmonary NF-κB p65 phosphorylation and consequent inflammation and ALI. Either treatment with an SO₂ donor or overexpression of AAT1 down-regulated OA-induced p65 activity, but AAT1 knockdown in alveolar epithelial cells mimicked OA-induced p65 phosphorylation and inflammation in vitro. Mechanistically, OA promoted NF-κB nuclear translocation, DNA binding activity, recruitment to the intercellular cell adhesion molecule (ICAM)-1 promoter, and consequent inflammation in epithelial cells; these activities were reduced in the presence of an SO₂ donor. Furthermore, SO₂ induced sulphenylation of p65, which was blocked by the C38S mutation on p65 in epithelial cells. Hence, down-regulation of SO₂/AAT is involved in pulmonary inflammation during ALI. Furthermore, SO₂ suppressed inflammation by sulphenylating NF-κB p65 at Cys³⁸.