Reactive Oxygen Species (ROS) are produced during normal cellular function.
ROS include hydroxyl radicals, superoxide anion, hydrogen peroxide and nit
ric oxide. They are very transient species due to their high chemical react
ivity that leads to lipid peroxidation and oxidation of DNA and proteins. U
nder normal conditions, antioxidant systems of the cell minimize the pertur
bations caused by ROS. When ROS generation is increased to an extent that o
vercomes the cellular antioxidants the result is oxidative stress. It is no
w clear that several biological molecules, which are involved in cell signa
ling and gene regulation systems are very sensitive to redox statue of the
cell. Antioxidants are substances that delay or prevent the oxidation of ce
llular oxidizable substrates. The various antioxidants exert their effect b
y scavenging superoxide, or by activating of a battery of detoxifying/defen
sive proteins. The prevention of oxidation is an essential process in all t
he aerobic organisms, as decreased antioxidant protection may lead to cytot
oxicity, mutagenicity and/or carcinogenicity. This article also focuses on
the mechanisms by which antioxidants and xenobiotics induce the gene expres
sion of detoxifying enzymes. On the other hand, small molecules that mimic
antioxidant enzymes are becoming new tools for the treatment of many diseas
es. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.