RESEARCH ARTICLE Cigarette Smoke Causes Caspase- Independent Apoptosis of Bronchial

Background Epidemiologic studies have demonstrated important links between air pollution and asthma. Amongst these pollutants, environmental cigarette smoke is a risk factor both for asthma pathogenesis and exacerbation. As the barrier to the inhaled environment, the bronchial ep-ithelium is a key structure that is exposed to cigarette smoke. Objectives Since primary bronchial epithelial cells (PBECs) from asthmatic donors are more suscepti-ble to oxidant-induced apoptosis, we hypothesized that they would be susceptible to ciga-rette smoke-induced cell death. Methods PBECs from normal and asthmatic donors were exposed to cigarette smoke extract (CSE); cell survival and apoptosis were assessed by fluorescence-activated cell sorting, and pro-tective effects of antioxidants evaluated. The mechanism of cell death was evaluated using caspase inhibitors and immunofluorescent staining for apoptosis-inducing factor (AIF). Results Exposure of PBEC cultures to CSE resulted in a dose-dependent increase in cell death. At 20 % CSE, PBECs from asthmatic donors exhibited significantly more apoptosis than cells from non-asthmatic controls. Reduced glutathione (GSH), but not ascorbic acid (AA), pro-tected against CSE-induced apoptosis. To investigate mechanisms of CSE-induce