Chronic Obstructive Pulmonary Disease

COPD is the fourth leading cause of death in the United States [16] and is set to become the third cause of mortality in 2020 worldwide [17]. COPD is as a common, preventable, and treatable disease, characterized by persistent airflow limitation that is usually progressive and associated with an

FigurE 1: Potential contribution of ROS to various lung disease development. ROS—reactive oxygen species; COPD—chronic obstructive pulmonary disease; ARDS—acute respiratory distress syndrome.

enhanced chronic inflammatory response in the airways and the lung to noxious particles or gases. The most commonly encountered risk factor for COPD is cigarette smoke [2]. Moreover, outdoor, occupational, and indoor air pollution may contribute to this disease development. COPD refers mainly to two types: chronic bronchitis and emphysema. Chronic bronchitis is defined as the presence of a cough and sputum production for at least three months in each of two consecutive years [16, 18]. Emphysema is characterized by the destruction of the alveoli, the tiny air sacs in the lung where the exchange of oxygen and carbon dioxide takes place, which results in a decreased level of oxygen in the blood (hypoxemia) combined with an increased level of carbon dioxide in the blood (hypercapnia). Tuder et al. [19, 20] indicated that cigarette smoke could induce alveolar wall destruction by the interaction of apoptosis, oxidative stress, and protease/antiprotease imbalance. This may cause emphysema, which leads to the progressive and relentless loss of lung function due to the destruction of lung parenchyma and chronic inflammation. Furthermore, studies from animal models indicate that 4- to 6-month exposure to cigarette smoke leads to emphysema development in mice, rats, and rabbits [21–23]. Exacerbations of COPD are of major global importance [24]. Exacerbations are defined as sustained worsening of the patient’s condition of the stable state and beyond normal day-to-day variations that is acute in onset and may warrant additional treatment in a patient with underlying COPD [25]. It has been reported that exacerbations are also involved in emphysema progression in patients with COPD [26]. Bacteria, viruses, and environmental agents account for the vast majority of episodes of exacerbation. Exacerbation, systemic inflammation, ROS generation, alterations of metabolism, cardiovascular events, and lung cancer contribute to the overall disease severity and untimely death [2, 20].