Amelioration of Lipopolysaccharide-Induced Acute Lung Injury in Rats by Na-H Exchanger-1 Inhibitor Amiloride Is Associated with Reversal of ERK Mitogen-Activated Protein Kinase

BACKGROUND: Na-H exchanger-1 (NHE-1) is expressed in the lung of rats. Accumulating evidence shows that Na-H exchangers are involved in inflammation. Amiloride, an inhibitor of NHE-1, inhibits the activation of macrophages and endothelial cells and reduces their production of cytokines. Since these processes have been implicated in acute lung injury (ALI) induced by lipopolysaccharide (LPS), we examined the protective effect of amiloride on ALI induced by LPS in rats. MATERIAL AND METHODS: ALI in specific pathogen-free male Sprague-Dawley rats was induced by an intravenous injection of 6 mg/kg LPS. Amiloride pretreated rats received an intravenous injection of 10 mg/kg amiloride 30 min before the administration of LPS. Controls received normal saline in a similar manner. All animals were sacrificed 6 h after LPS or normal saline administration. The degree of ALI was assessed by wet-to-dry weight ratio (W/D) and lung histological examination. Neutrophilic infiltration was determined by myeloperoxidase (MPO) activity in lung tissue. Concentrations of total protein (TP), tumor necrosis factor-alpha (TNF-α), and macrophage inflammatory protein-2 (MIP-2) in bronchoalveolar lavage fluid (BALF) were also measured. Expression of NHE-1 and mitogen-activated protein kinase (MAPK) p38, p-p38, ERK, and p-ERK was evaluated by western blot analysis. RESULTS: Pretreatment with amiloride significantly reduced the increase in W/D, ALI score, lung tissue MPO activity, concentrations of TP, TNF-α, and MIP-2 in BALF, resulting in attenuation of ALI induced by LPS. Meanwhile, levels of NHE-1 and p-ERK proteins were reversed, whereas that of p-p38 was not. CONCLUSIONS: These findings suggest that NHE-1 inhibitor amiloride could attenuate ALI induced by LPS in rats. This effect is mediated through reversal of ERK.