Beclomethasone dipropionate and formoterol reduce oxidative/nitrosative stress generated by cigarette smoke extracts and IL-17A in human bronchial epithelial cells

Interleukin-17A (IL-17A), cigarette smoke and oxidative/nitrosative stress are involved in inflammatory airway diseases, and the mechanisms behind these processes are still poorly understood. We investigated whether recombinant human IL-17A (rhIL-17A), in combination with cigarette smoke extracts (CSE), increases the levels of inducibile nitric oxide synthase (iNOS), reactive oxygen species, nitrotyrosine (NT) and the activation of signal transducer and activator of transcription 1 (STAT-1) in normal human bronchial epithelial cells (16HBE). The effect of beclomethasone dipropionate (BDP), formoterol and their combination was also evaluated. We demonstrated that rhIL-17A or CSE alone increases iNOS expression, reactive oxygen species and NT production and STAT-1 downstream signalling activation in terms of STAT-1ser727 and STAT-1tyr701 phosphorylation. The combination of both stimuli further increased iNOS, ROS, NT and STAT-1ser727 phosphorylation. The silencing of STAT-1 expression partially reduced the levels of iNOS, reactive oxygen species and NT generated by rhIL-17A and inhibited the effect of CSE alone in 16HBE cells. The treatment of the cells with the MEK1/2 inhibitor U0126 (1,4-diamino-2,3-dicyano-1,4-bis (o-aminophenylmercapto butadiene) abolished the expression of iNOS and STAT-1ser727 phosphorylation generated by rhIL-17A. 16HBE treated with BDP or formoterol alone partially suppressed the effect of IL-17A or CSE on ROS, NT, and STAT-1 activation. Furthermore the use of the drugs in combination showed an additive effect in 16HBE. Our findings demonstrate that IL-17A increases oxidative/nitrosative markers, likely via ERK1/2 downstream signalling and STAT-1 pathway activation in human bronchial epithelial cells. BDP and formoterol treatment reduces this effect showing an additive effect used in combination.