Airway epithelial anion secretion and barrier function following exposure to fungal aeroallergens: role of oxidative stress

Abstract

Aeroallergens produced by <i>Alternaria alternata</i> can elicit life-threatening exacerbations of asthma in patients sensitized to this fungus. In this study, the effect of <i>Alternaria</i> on ion transport mechanisms underlying mucociliary clearance and airway epithelial barrier function was investigated in human airway epithelial cells. Apical exposure to <i>Alternaria</i> induced an increase in anion secretion that was inhibited by blockers of CFTR and Ca²⁺-activated Cl^- channels. Stimulation of anion secretion was dependent on Ca²⁺ uptake from the apical solution. <i>Alternaria</i> exposure also produced an increase in reactive oxygen species (ROS) that was blocked by pretreatment with the oxidant scavenger glutathione (GSH). GSH and the NADPH oxidase inhibitor/complex 1 electron transport inhibitor diphenylene iodonium chloride (DPI) blocked ATP release and the increase in intracellular [Ca²⁺] evoked by <i>Alternaria</i><i>Alternaria</i> also decreased transepithelial resistance, and a portion of this effect was dependent on the increase in ROS. However, the <i>Alternaria</i>-induced increase in unidirectional dextran (molecular mass = 4,000 Da) flux across the epithelium could not be accounted for by increased oxidative stress. These results support the conclusion that oxidative stress induced by <i>Alternaria</i> was responsible for regulating Ca²⁺-dependent anion secretion and tight junction electrical resistance that would be expected to affect mucociliary clearance.