ABSTRACT
Oxidative stress has been implicated in the pathogenesis of many chronic inflammatory disorders, including respiratory diseases. In healthy individuals the production of damaging reactive oxygen species (ROS) and reactive nitrogen species (RNS) is balanced by the presence of endogenous and exogenous anti-oxidants. Oxidative stress occurs when there is an imbalance towards excessive levels of ROS and RNS when antioxidant defences are defective. However, the presence of increased ROS and RNS is not always detrimental as both are used within normal physiological processes in healthy tissues. These can be as diverse as acting as second messengers and modulating redox-sensitive intracellular signalling pathways, to regulating blood pressure and acting as defence mechanisms against pathogens. Mild and acute levels of oxidative stress can be tolerated and even adapted to. It is, however, when individuals are exposed to chronic episodes of oxidative stress that cellular damage can occur leading to pathology.
