Cellular response to cigarette smoke and oxidants: adapting to survive.

The gaseous and soluble phases of cigarette smoke are sources of oxidants that contribute to the pathogenesis of chronic obstructive pulmonary disease (COPD). Chronic oxidative stress of cigarette smoking induces mucus secretion and inhibits cystic fibrosis transmembrane conductance regulator function. The increased mucus viscosity renders the airways susceptible to bacterial infections, a hallmark of chronic bronchitis. Furthermore, lungs chronically exposed to the toxic mixture of oxidants in cigarette smoke show signs of endoplasmic reticulum stress, unfolded protein response, altered ceramide metabolism, and apoptosis. Fortunately, the respiratory tract has developed effective adaptive cellular mechanisms to limit oxidant damage. Numerous antioxidant enzymes and glutathione-dependent detoxification systems are increased in healthy smokers. The regulation of the antioxidant response is largely dependent on the nuclear factor erythroid 2-related factor-2 (Nrf2) pathway. However, patients with COPD have defective Nrf2 responses. Novel therapies such as 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) to correct defective Nrf2-dependent cellular response may hold promise for patients with COPD.