%0 Journal Article
%T Hydroxyl Radical and Its Scavengers in Health and Disease
%A Boguslaw Lipinski
%J Oxidative Medicine and Cellular Longevity
%D 2011
%I Hindawi Publishing Corporation
%R 10.1155/2011/809696
%X It is generally believed that diseases caused by oxidative stress should be treated with antioxidants. However, clinical trials with such antioxidants as ascorbic acid and vitamin E, failed to produce the expected beneficial results. On the other hand, important biomolecules can be modified by the introduction of oxygen atoms by means of non-oxidative hydroxyl radicals. In addition, hydroxyl radicals can reduce disulfide bonds in proteins, specifically fibrinogen, resulting in their unfolding and scrambled refolding into abnormal spatial configurations. Consequences of this reaction are observed in many diseases such as atherosclerosis, cancer and neurological disorders, and can be prevented by the action of non-reducing substances. Moreover, many therapeutic substances, traditionally classified as antioxidants, accept electrons and thus are effective oxidants. It is described in this paper that hydroxyl radicals can be generated by ferric ions without any oxidizing agent. In view of the well-known damaging effect of poorly chelated iron in the human body, numerous natural products containing iron binding agents can be essential in the maintenance of human health. However, beneficial effects of the great number of phytochemicals that are endowed with hydroxyl radical scavenging and/or iron chelating activities should not be considered as a proof for oxidative stress. 1. Introduction It is commonly believed that the in vivo damage of biomolecules is initiated by reactive oxygen species (ROS) in a process known as oxidative stress. However, oxidation reaction in biological systems may also occur via a nonradical pathway, for example, by hydrogen peroxide. In such cases, the products of its action are molecules that are enriched in one or more oxygen atoms that are generally considered to be markers of oxidative stress. Yet mere presence of extra oxygen does not tell us whether a given product is generated by a single- (free radical) or two-electron oxidation reaction. It should be emphasized that, according to the concept of oxidative stress, peroxidation and degradation of vulnerable biological molecules is caused by oxygen-centered radicals generated, in turn, by excessive blood oxygenation. However, this conclusion is based on studies of ischemia/reperfusion cases in which periods of prolonged hypoxia are followed by a sudden supply of oxygen. For example, in patients with extracorporeal circulation the appearance of lipid and/or nucleic acids oxidation products is accepted as signs of oxidative stress. However, a very important fact is being
%U http://www.hindawi.com/journals/omcl/2011/809696/