Maniak, Peter J.

Aeroallergens produced by Alternaria alternata can elicit life-threatening exacerbations of asthma in patients sensitized to this fungus. In this study, the effect of Alternaria on ion transport mechanisms underlying mucociliary clearance and airway epithelial barrier function was investigated in human airway epithelial cells. Apical exposure to Alternaria 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. Alternaria 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 Alternaria. Alternaria also decreased transepithelial resistance, and a portion of this effect was dependent on the increase in ROS. However, the Alternaria-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 Alternaria was responsible for regulating Ca2+-dependent anion secretion and tight junction electrical resistance that would be expected to affect mucociliary clearance.

AbstractBackgroundInterleukin (IL)‐33 is implicated in the pathophysiology of asthma and allergic diseases. However, our knowledge is limited regarding how IL‐33 release is controlled. The transcription factor nuclear factor‐erythroid‐2‐related factor 2 (Nrf2) plays a key role in antioxidant response regulation.ObjectiveThe goal of this project was to investigate the role of cellular oxidative stress in controlling IL‐33 release in airway epithelium.MethodsComplementary approaches were used that included human bronchial epithelial cells and mouse models of airway type‐2 immunity that were exposed to fungus Alternaria extract. The clinically available Nrf2 activator 2‐cyano‐3,12‐dioxooleana‐1,9‐dien‐28‐oic acid methyl ester (CDDO‐Me) was used to evaluate the role of Nrf2‐induced antioxidant molecules.ResultsHuman bronchial epithelial cells produced reactive oxygen species (ROS) when they were exposed to Alternaria extract. ROS scavengers, such as glutathione (GSH) and N‐acetyl cysteine, prevented extracellular secretion of ATP and increases in intracellular calcium concentrations that precede IL‐33 release. Administration of CDDO‐Me to mice enhanced expression of a number of antioxidant molecules in the lungs and elevated lung levels of endogenous GSH. Importantly, CDDO‐Me treatment reduced allergen‐induced ATP secretion and IL‐33 release by airway epithelial cells in vitro and protected mice from IL‐33 release and asthma‐like pathological changes in the lungs.ConclusionsThe balance between oxidative stress and antioxidant responses plays a key role in controlling IL‐33 release in airway epithelium. The therapeutic potential of Nrf2 activators needs to be considered for asthma and allergic airway diseases.