48] Iron redox reactions and lipid peroxidation

Abstract

This chapter discusses iron redox reactions and lipid peroxidation. Iron-catalyzed lipid peroxidation has been studied in many in vitro model systems. While the mechanism of iron-catalyzed lipid peroxidation is not completely understood, it is well established that the redox chemistry of iron influences both the occurrence and the rate of lipid peroxidation. For example, iron-catalyzed lipid peroxidation in systems comprises initially of Fe(II) and phospholipid liposomes requires some Fe(II) oxidation. Conversely, iron-catalyzed lipid peroxidation in systems containing Fe(III) and phospholipid liposomes requires some Fe(III) reduction. However, complete Fe(II) oxidation or complete Fe(III) reduction results in conditions that do not promote lipid peroxidation. Thus, measurements of the rate and extent of Fe(II) oxidation or Fe(III) reduction aid the interpretation of experimental lipid peroxidation data. While several methods are available, only methods pertinent to lipid peroxidation are discussed in the chapter. Two important factors that influence both the rates and extents of Fe(II) oxidation or Fe(III) reduction are chelation and pH. Chelators that preferentially bind Fe(II) tend to prevent or slow the rate of Fe(II) autoxidation as well as the rates of Fe(II) oxidation by peroxides. Chelators that bind Fe(III) with greater affinity than Fe(II), however, have the opposite effect—that is, they increase the rate of Fe(II) autoxidation as well as Fe(II) oxidation by peroxides. In addition, the rate of Fe(II) autoxidation, particularly unchelated Fe(II), increases with increasing pH.