Determination of primary and secondary lipid peroxidation products: Plasma lipid hydroperoxides and thiobarbituric acid reactive substances

Abstract

Lipid peroxidation is a complex process whereby unsaturated lipid undergoes reaction with molecular oxygen to yield lipid hydroperoxides. In most situations involving biological samples the lipid hydroperoxides are degraded to a variety of products including alkanals, alkenals, hydroxyalkenals, ketones, alkanes. Although attack by singlet oxygen on unsaturated lipid has been shown to give hydroperoxides by a nonradical process, the vast majority of situations involving lipid peroxidation proceeds through a free radicalmediated chain reaction initiated by the abstraction of a hydrogen atom from the unsaturated lipid by a reactive free radical, followed by a complex sequence of propagation reactions. The involvement of free oxygen radicals in the pathology, of certain diseases explains the growing interest in the assay of lipid peroxides. Assay of polyunsaturated fatty acid degradation products is currently performed by measuring the so-called thiobarbituric acid-reactive substances, of which malondialdehyde is the best known. Because this assay is controversial, a second index of free radical attack would be useful to confirm the peroxidative process.