Background: Eosinophils are important effector cells in the pathogenesis of allergic diseases such as bronchial asthma. Oxidative stress in the form of cellular reactive oxygen species (ROS) has been implicated in the pathogenesis of several allergic diseases. Recently, it has become evident that mitochondrial-derived ROS are important transducers of apoptosis and intracellular signaling. In this study, we investigated the role of mitochondrial ROS in the activation of extracellular signal-regulated kinases (ERK) 1 and 2–mitogen-activated protein kinase (MAPK) and caspase-3 in human eosinophils stimulated with H2O2.

Methods: Human eosinophils were purified using immunomagnetic negative selection and then stimulated with H2O2. H2O2-induced eosinophil apoptosis was measured by staining cells with annexin V. Activation of ERK1/2 MAPK and caspases was assessed by Western  blotting. Eosinophils were pretreated with rotenone, an inhibitor of the mitochondrial electron transport chain, before H2O2 was added.

Results: Treatment with 1 mM H2O2 induced externalization of phosphatidylserine (PS) and activation of caspases in eosinophils. H2O2-triggered PS externalization and cleavage of caspase-3 were markedly inhibited by pretreatment with the mitochondrial ROS scavenger N-acetyl-L-cysteine. In addition, H2O2 strongly induced phosphorylation of ERK1/2, but not ERK5, in eosinophils. Hydrogen peroxide-triggered activation of caspase-3 and ERK1/2 was attenuated by pretreatment with rotenone.

Conclusions: These results suggest that mitochondrial respiration is essential for activation of ERK1/2 and caspase-3 in human eosinophils stimulated with H2O2.

Key words: Eosinophil. Hydrogen peroxide. Mitochondria. ERK1/2. Caspase-3.