Corticosteroid insensitivity in asthma associated with obstructive sleep apnoea: Role of oxidative stress and histone acetylation.

Background and purpose: Obstructive sleep apnoea (OSA) worsens asthma control. Oxygen desaturation increases oxidative stress, contributing to corticosteroid insensitivity, a hallmark of severe asthma. This study investigated the impact of hypoxaemia and reactive oxygen species on corticosteroid responsiveness in asthma with OSA.

Experimental approach: Asthmatic patients with apnoea-hypopnoea index (AHI) ≥ 5 h^-1 were classified as OSA. Interleukin (IL)-8 and IL-6 production by peripheral blood mononuclear cells (PBMCs), serum cytokines, oxidative stress markers and nuclear histone deacetylase 2 (HDAC2) were quantified by enzyme-linked immunosorbent assay. HDAC2 and hypoxia-inducible factor-1α (HIF-1α) expression were evaluated by Western blotting and flow cytometry.

Key results: Compared with non-OSA asthmatics, OSA patients used higher inhaled corticosteroid doses and had increased serum thiobarbituric acid-reactive substances and 8-hydroxy-2-deoxyguanosine, but lower superoxide dismutase and total antioxidant capacity. HDAC2 was lower in OSA PBMCs and in non-OSA PBMCs exposed to 5% O₂ than in normoxia. HDAC2 was correlated inversely with AHI, corticosteroid dose, serum IL-8, oxidative stress, baseline production of IL-8/IL-6 and dexamethasone-induced IL-8 suppression. Dexamethasone inhibited TNF-α-induced IL-8 and lipopolysaccharide (LPS)-induced IL-6 in non-OSA PBMCs, but not in OSA PBMCs. HDAC2 inhibitor CAY10683 impaired corticosteroid action, while N-acetylcysteine and inhibitors of HIF-1α (CAY10585) or phosphoinositide 3-kinase (LY294002) restored HDAC2 and corticosteroid sensitivity.

Conclusions and implications: OSA is associated with oxidative stress, reduced HDAC2, and corticosteroid insensitivity in asthma. Antioxidants may help restore corticosteroid efficacy.