Generation of oxysterols formed by free radicals and enzymes by electrochemical oxidation

It is commonly accepted that cholesterol oxide derivatives, also named oxysterols, are 27 carbon-atom molecules deriving either from enzymatic and non-enzymatic oxidation of cholesterol. Most of these compounds can be synthesized by more or less difficult and time consuming chemical reactions, and some of them have been discovered before the identification of the enzymes [mainly cytochrome P450 enzymes (CYP enzymes)] involved in their biosynthesis. A wide range of biological activities depends on oxysterols. Some oxysterols are also involved in the synthesis of cholesterol metabolites which have various properties. The paper by Weber et al. in this issue of European Journal of Lipid Science and Technology is of interest because it reports that an electrochemical oxidation of cholesterol rapidly generates numerous oxysterols which are usually generated either by enzymatic processes in vivo or under the action of different chemical and physical agents (free radicals, sun light, ...) in vivo or not. This has a crucial importance and suggests that the border between enzymatic and non-enzymatic generation of oxysterols should be reconsidered, at least for some of these compounds. Consequently, these observations may have major chemical and physiopathological significance.