Sulfur dioxide-induced exacerbation of airway inflammation via reactive oxygen species production and the toll-like receptor 4/nuclear factor-κB pathway in asthmatic mice

Abstract

Sulfur dioxide (SO₂) is a common air pollutant that can exacerbate asthmatic airway inflammation. The mechanisms underlying these effects are not yet fully understood. In this study, we investigated the effects of SO₂ exposure (10 mg/m³) on asthmatic airway inflammation in ovalbumin-induced asthmatic mice. Our results showed that SO₂ exposure alone induced slight airway injury, decreased superoxide dismutase activity, and increased nuclear factor-κB (NF-κB) expression in the lungs of mice. Moreover, SO₂ exposure in asthmatic mice induced marked pathological damage, significantly increased the counts of inflammatory cells (e.g., macrophages, lymphocytes, and eosinophils) in bronchoalveolar lavage fluid, and significantly enhanced malondialdehyde and glutathione levels in the lungs. Moreover, the expression of toll-like receptor 4 (TLR4), NF-κB, pro-inflammatory cytokines (e.g., tumor necrosis factor α and interleukin-6), and type II T-helper cell (Th2) cytokines was found to be elevated in the mice exposed to SO₂ and ovalbumin compared to those exposed to ovalbumin alone. These results suggest that SO₂ amplifies Th2-mediated inflammatory responses, which involve reactive oxygen species and TLR4/NF-κB pathway activation; these can further enhance Th2 cytokine expression and eosinophilic inflammation. Thus, our findings provide important evidence to understand a potential mechanism through which SO₂ may exacerbate airway asthmatic inflammation.