Free radicals are species containing one or more unpaired electrons, and for this reason they are highly reactive and can combine with a great variety of biomolecules, changing their physico-chemical characteristics. Oxygen free radicals are normally produced during cellular metabolism and aerobic cells are provided with antioxidant defense mechanisms able to counteract this physiological production. In conditions of increased production or decreased scavenging of free radicals, they can assume a fundamental importance in the pathogenesis of acute or chronic brain diseases
