Oxidative stress is a medical term for damage to animal or plant cells (and thereby the organs and tissues composed of those cells) caused by reactive oxygen species, which include (but are not limited to) superoxide, singlet oxygen, peroxynitrite or hydrogen peroxide. It is defined as an imbalance between pro-oxidants and anti-oxidants, with the former prevailing. Superoxide is produced deleteriously by 1-electron transfers in the mitochondrial electron transfer chain. Other enzymes capable of producing superoxide are xanthine oxidase, NADPH oxidases and cytochrome P450(s). Hydrogen peroxide is produced by a wide variety of enzymes including monoxygenases and oxidases. Reactive oxygen species may also play a role in cell signalling. Oxidative stress is known to contribute to tissue injury following irradiation and hyperoxia and is thought to be a cause of neurodegenerative diseases including Lou Gehrig's disease (aka MND or ALS), Parkinson's disease, Alzheimer's disease and Huntington's disease. Oxidative stress is thought to be linked to certain cardiovascular disease, since oxidation of LDL in the endothelium is a precursor to plaque formation. However treatment in this area of medicine is sometimes controversial, as clinical trials with the antioxidant vitamin E have failed to demonstrate a clear beneficial effect. It has been shown that vegetables rich in vitamin E are beneficial to neurodegenerative disease. Epidemiological evidence suggests that vitamin E supplementation decreases the incidence of ALS and Alzheimer's. Oxidative stress (as formulated in Harman's free radical theory of aging) is also thought to contribute to the aging process. While there is rather strong evidence to support this idea in the model organism Drosophila melanogaster, the evidence in mammals is contradictory.

Metal catalysts

Metals such as iron, copper, chromium, vanadium and cobalt are capable of redox cycling in which a single electron may be accepted or donated by the metal. This action catalyzes reactions that produce reactive radicals and can produce reactive oxygen species such as hydroxyl radical in reactions like Fenton's reaction. The hydroxyl radical then can lead to modifications of amino acids (e.g. meta-tyrosine and ortho-tyrosine formation from phenylalanine), carbohydrates, initiate lipid peroxidation. Most enzymes that produce reactive oxygen species contain one of these metals. The presence of such metals in biological systems in an unsequestered form (not in an enzyme or other protein) can significantly increase the level of oxidative stress.

See also

• Endothelium
• L-Arginine
• Nitric oxide

References

• Current Medicinal Chemistry, Volume 12, Number 10, May 2005, pp. 1161-1208(48) Metals, Toxicity and Oxidative Stress