Toxicity of Antioxidants

Abstract

The fundament of toxicology is the risk-benefit analysis. This means that the positive as well as the negative health effects of all compounds, including antioxidants, have to be assessed and related to each other. Only in this way the rational for the use of a compound can be evaluated. The beneficial effects of antioxidants are due to their ability to protect against free radical damage. In the diseases and other pathological conditions where free radicals are implicated, the biochemistry may greatly vary, i.e. the radicals involved, their flux, the site where they are generated and the target they attack can differ.1 Thus for each type of radical damage specific criteria need to be fulfilled by an antioxidant in order to be active. Free radicals of biological interest are often divided into oxygen centred and nitrogen centred radicals. Reactive Oxygen Species (ROS) is a collective term that includes both oxygen centred radicals and certain oxygen containing non-radicals that are oxidizing agents or easily converted into radicals. In the Reactive Nitrogen Species (RNS) the reactivity of the species is located on or near a nitrogen atom. The adjective “reactive” is not always appropriate; H2O2, O2•- and NO• quickly react only with very few molecules. OH• reacts instantaneously with almost everything. RO2•, RO•, HOCl, NO2•, ONOOH, and O3 have a reactivity that lies in between these extremes.