Oxidative stress in COPD: molecular background and clinical monitoring

Chronic obstructive pulmonary disease (COPD) is a major and rapidly increasing health problem associated with a chronic inflammatory response, predominantly in small airways and lung parenchyma. Oxidative stress induced by reactive oxygen and nitrogen species (ROS and RNS) plays a central role in the pathophysiology of COPD. There is evidence that several molecules formed during oxidative processes may have the potential to serve as biomarkers of oxidative stress in the airways of patients with COPD. Among these molecules carbon monoxide, ethane and pentane can be measured in the exhaled air, while 8-isoprostane, malondialdehyde, 4- hydroxyhexenal, 4-hyroxynonenal, acrolein, hydrogen peroxide, nitrogen oxides and 3-nitrotyrosine can be detected in exhaled breath condensate and/or sputum supernatant. In this review the molecular background of these processes including the formation of ROS and RNS, the biosynthesis of essential ω-3 and ω-6 polyunsaturated fatty acids as building blocks of lipids in the cellular membranes and their enzymatic and non-enzymatic metabolism to eicosanoids and related compounds have been summarized. Moreover, the formation of oxidative stress markers studied most commonly in the context of COPD has been briefly discussed. The associations between biomarkers and clinical variables have also been highlighted in an attempt to illustrate the potential clinical applicability of these biomarker measurements.