Lipophilic fluorescent products of free radicals

BACKGROUND: Fluorescent pigments are the end-products of reactions involving free radical attack on biological molecules and can be formed, for example, in reactions between lipid peroxidation products, mainly unsaturated aldehydes, with free amino groups. Their characteristic emission maximum was found to be at 420-470 nm after being excited at 340-390 nm. The mechanism of their formation and chemical identity has been revealed in many in vitro studies, in which reactive aldehydes were incubated with amino group-containing molecules. Owing to their intrinsic fluorescent properties and molecular stability these products are easily measured by means of spectrofluorimetry and are used as biomarkers of oxidative stress caused by various triggers. It has been found that the fluorescent products are formed in excess in conditions linked with increased free radical production, such as atherosclerosis, Alzheimer's disease and multiple sclerosis. METHODS: We searched the literature using "MEDLINE" and "Web of Science" in order to get an overview of the state of knowledge about fluorescent products of free radicals, that is, their analysis from in vitro studies, animal and human studies and their use as markers of oxidative damage. CONCLUSIONS: Although their chemical structure may not have been elucidated, the fluorophores formed in this way have found application as markers of oxidative stress in many animal and human studies. In vitro experiments using model reactions have given some clues as to how certain fluorescent pigments arise during oxidative reactions in vivo. Advances in analytical techniques should lead the chemical characterization of pigments of different origin to completeness.