Acid-induced cell injury and death in lung epithelial cells is associated with the activation of mitogen-activated protein kinases

Abstract

Abstract. Gastric hydrochloric acid (HCl) has been regarded as a causative factor of acute lung injury (ALI). The activation of mitogen-activated protein kinases (MAPKs) has been suggested to be a mechanism involved in the pathogenesis of ALI in vivo. However, the effects of HCl on MAPK activation in lung epithelial cells remain to be fully elucidated. Further investigation into the role of MAPK activation in acid-induced cell injury and death is also needed. In the present study, BEAS-2B cells were treated with HCl (pH 4.0 medium) for 5, 15 and 30 min, and the acidified medium was then removed. Cell viability and death were detected by MTT assay and trypan blue exclusion staining, respectively. The activation of MAPKs [c-Jun N-terminal kinase (JNK), p38 MAPK and extracellular signal-regulated kinase (ERK) 1/2] was analyzed by western blot analysis. Cytotoxicity was assessed by lactate dehydrogenase (LDH) release, and IL-8 levels in culture supernatants were measured by enzyme-linked immunosorbent assay (ELISA). Cell apoptosis was detected as changes in the levels of capase-3, Bad and fas by western blot analysis and the number of apoptotic cells by using Annexin V/propidium iodide (PI) staining. Following pre-treatment with the JNK inhibitor II (10 µmol/l), the p38 inhibitor SB202190 (10 µmol/l) or the ERK inhibitor U0126 (10 µmol/l) for 30 min, BEAS-2B cells were exposed to HCl for 30 min. Cell viability, cytotoxicity, IL-8 levels and apoptosis were detected 4 h following acid stimulation. The viability of BEAS-2B cells was inhibited and cell death was increased in the presence of HCl. HCl stimulation induced activation of MAPKs in a time-dependent manner. HCl exposure increased the levels of IL-8 and the release of LDH, and induced apoptosis in BEAS-2B cells. JNK and p38 inhibitors increased cell viability and decreased cytotoxicity and cell apoptosis, while ERK inhibitor had no effect on cell viability, cytotoxicity or apoptosis. These results indicate that acid exposure induced epithelial cell injury and death. The activation of JNK and p38 is involved in HCl-induced epithelial lung cell injury and death. IntroductionAcute respiratory distress syndrome (ARDS) is a multifactorial, heterogeneous disease associated with high rates of mortality and disability in critically ill patients (1-3). Acid aspiration-induced lung injury accounts for ~11% of all clinical ARDS cases and is a major cause of morbidity in cases of critical illness (4,5). Acid aspiration-induced ARDS is characterized by pulmonary edema from increased vascular and epithelial permeability, as well as alveolar and interstitial inflammation with leukocyte infiltration (6). Cell death has been demonstrated in the lung during the pathogenesis of acute lung injury (ALI)/ARDS. However, the mechanism of acid-induced cell injury and death in ALI has yet to be fully elucidated.Mitogen-activated protein kinases (MAPKs), including the c-Jun NH2-terminal kinase (JNK), p38 MAPK and extracellular signal-regulated kinase (ERK) 1/2, are commonly involved in th...

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