Effect of hypoxia and dexamethasone on inflammation and ion transporter function in pulmonary cells

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SummaryDexamethasone has been found to reduce the incidence of high-altitude pulmonary oedema. Mechanisms explaining this effect still remain unclear. We assessed the effect of dexamethasone using established cell lines, including rat alveolar epithelial cells (AEC), pulmonary artery endothelial cells (RPAEC) and alveolar macrophages (MAC), in an environment of low oxygen, simulating a condition of alveolar hypoxia as found at high altitude. Inflammatory mediators and ion transporter expression were quantified. Based on earlier results, we hypothesized that hypoxic conditions trigger inflammation. AEC, RPAEC and MAC, pre-incubated for 1 h with or without dexamethasone (10−7 mol/l), were subsequently exposed to mild hypoxia (5% O2, or normoxia as control) for 24 h. mRNA and protein levels of cytokine-induced neutrophil chemoattractant-1, monocyte chemoattractant protein-1 and interleukin-6 were analysed. mRNA expression and functional activity of the apical epithelial sodium channel and basolateral Na+/K+-ATPase were determined using radioactive marker ions. In all three types of pulmonary cells hypoxic conditions led to an attenuated secretion of inflammatory mediators, which was even more pronounced in dexamethasone pretreated samples. Function of Na+/K+-ATPase was not significantly influenced by hypoxia or dexamethasone, while activity of epithelial sodium channels was decreased under hypoxic conditions. When pre-incubated with dexamethasone, however, transporter activity was partially maintained. These findings illustrate that long-term hypoxia does not trigger an inflammatory response. The ion transport across apical epithelial sodium channels under hypoxic conditions is ameliorated in cells treated with dexamethasone.

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