Free radicals (synonyms: Free radicals; Free radikals; Free radicals (disease); Free radicals (oxidative stress); Oxidative stress (free radicals); ICD-10-GM E88.9: Metabolic disorder, unspecified) are reactive atoms or molecules with at least one unpaired electron in the outer orbital. They are highly reactive, very aggressive, chemical oxygen molecules or organic compounds. Major free reactive 02 species (ROS) [oxidative stress] and N species (RNS) [nitrostress; nitrosative stress] are:
- Superoxide anion (O2-.)
- Hydroxyl radical (OH.)
- Nitric oxide radical (NO-)
- Peroxynitrite anion (ONOO-)
As intermediates of metabolism, free radicals are constantly produced in every cell of the human body. The oxygen compounds with unpaired electrons are eager to snatch electrons from another atom or molecule. They react with these and form new radicals, which in turn also snatch electrons from other substances, and in a chain reaction there is a steady increase in the number of radicals in the body. As a result of this chain reaction, oxidative or nitrosative stress occurs when the cellular antioxidant defense (antioxidants) is too low to compensate for the reactive oxygen radicals or nitric oxide radicals.
Antioxidants counteract the oxidants. They are reducing agents (= reducing substances), i.e., they cancel the effect of oxidants and thus render them harmless.
