First 11 pages of thesis. - OPUS - Universität Würzburg

1.3 Oxidative Stress
Oxidative stress results from increased production of reactive oxygen
species (ROS) in biological systems. ROS include “free radicals” and “non-free
radicals” which are produced during electron transfer reactions in oxygen (O2)
metabolism. Molecular O2 is essential for the survival of all aerobic organisms
and acts as the electron acceptor during various metabolic reactions. The
partially reduced, highly reactive metabolites formed during these reactions
react more avidly compared to molecular O2. ROS are generally considered to
be by-products of metabolism with a potential to cause cellular injury 25 . During
evolution organisms have developed several strategies to potentially detoxify
ROS. However, under physiological condition ROS are also important signalling
molecules 26 and there exists a balance between production and detoxification of
ROS. Diseases may cause an imbalance between the production and
neutralization of ROS, resulting in altered cell signalling and oxidative stress.
Superoxide anion formation generates a chain of reactions which result
in the formation of various highly reactive free radicals and non radicals. In
atherosclerosis and other vascular diseases ROS are potent pathological
mediators 27 , as they cause lipid peroxidation, smooth muscle cell proliferation,
protein oxidation, inflammatory cell recruitment and vascular inflammation. For
example, oxidative modification of lipoproteins initiates foam cell formation 23
and vascular oxidative stress is a major cause of cardiovascular diseases 28 .
ROS are implicated in the process of initiation of foam cell formation until
ultimate plaque rupture. Increased oxidative stress results in reduced
endothelial dysfunction 29 .
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