Chemical Mechanisms of Lipid Peroxidation

The chemical framework for free radical chain oxidation of naturally-occurring lipids, commonly referred to as peroxidation, has provided a basis for understanding important processes in biology. H-atom transfer to peroxyl free radicals and olefin addition of those radicals are the primary rate-determining steps in peroxidation, but the lipid carbon radicals generated in these primary steps have multiple mechanistic pathways available. Oxygen addition, homolytic intramolecular substitution (s _H i) and various cyclization reactions of intermediate peroxyl and alkoxyl radicals leads to a diverse set of products from polyunsaturated fatty acids and phospholipid esters. 5,7-Diene sterols are particularly reactive H-atom donors and give rise to complex product mixtures. The mechanistic guidelines for the important transformations of lipid peroxidation are summarized here and the connection between these fundamental chemical conversions and important enzymatic and non-enzymatic biological processes are outlined.