Selegeline suppressed cigarette smoke medium (CSM)-induced oxidative stress, inflammation and apoptosis via monoamine oxidase-B inhibition in airway epithelial cells

Abstract

Background: Cigarette smoking is the major risk factor for the development of chronic obstructive pulmonary disease (COPD). Cigarette smoke (CS) is a rich source of oxidants, and is thought to disrupt the oxidantantioxidant balance in the lung, thus inducing inflammation and apoptosis. Selegiline, an inhibitor of monoamine oxidase (MAO)-B, has long been used as an adjuvant to the levodopa therapy for Parkinson’s disease. The aim of this study was to explore the effect of selegiline on cigarette smoke medium (CSM)–induced oxidative stress, inflammation, and apoptosis in human airway epithelial cells (AECs) and the underlying mechanisms involved. Methods: BEAS-2B cells were treated with 2% CSM following a 30-minute pretreatment of 100 nM selegiline. After treatment, medium was collected for the measurement of interleukin 8 (IL-8) release by ELISA; cells were reserved for flow cytometry as a measurement of apoptosis and reactive oxygen species (ROS); cell lysate was extracted for measurement of antioxidant enzymes activities and Western blot analysis. Results: CSM (2%) treatment increased MAO-B activity, ROS levels, and pro-inflammatory marker IL-8 release in AECs. Pretreatment with selegiline inhibited the CSM-induced elevation of MAO-B activity, attenuated CSMinduced ROS levels and IL-8 release. In addition, CSM treatment elevated anti-oxidant enzyme superoxide dismutase (SOD) activity, but inhibited catalase (CAT) activity and decreased GSH/GSSG ratio. Pretreatment of selegiline normalised CSM-mediated SOD and CAT activities and GSH/GSSG ratio. Selegiline suppressed CSMinduced nuclear translocation of nuclear factor erythroid 2–related factor 2 (Nrf2) and cytosol translocation of its negative regulator, BTB and CNC homolog 1 (Bach1), thus decreased protein expression of heme oxygenase-1 (HO-1) and NAD(P)H quinone dehydrogenase 1 (NQO1). In addition, selegiline also reversed CSM-induced phosphorylation of IKK, reduction of cytoplasmic I kappa B expression and nuclear translocation of nuclear factor-kappa B p65 subunit, leading to attenuation of IL-8 release. CSM also increased apoptotic cells, cytochrome c, cleaved caspased-3, and pro-apoptotic protein bax expression. Pretreatment of selegiline suppressed CSM-induced apoptosis and apoptosis-associated protein expression. Conclusion: These findings confirmed that MAO-B inhibitor is capable of reversing CSM-induced oxidative stress, inflammation, and apoptosis via Nrf2/NF-κB pathways for the first time in human bronchial epithelial cells, which may provide a promising therapeutic strategy for COPD.