Measurement of products of docosahexaenoic acid peroxidation, neuroprostanes, and neurofurans

Abstract

Free radicals derived primarily from oxygen have been implicated in the pathophysiology of a wide variety of human diseases. Quantification of products of free radical damage in biological systems is necessary to understand the role of free radicals in disease states. Measures of lipid peroxidation are often used to quantitate oxidative damage though many of these measures have inherent problems with sensitivity and specificity especially when used to quantitate in vivo oxidative injury. The discovery of the F(2)-isoprostanes (F(2)-IsoPs), prostaglandin F(2)-like compounds derived by the free radical peroxidation of arachidonic acid (AA, C20:4, omega-6) has largely overcome these limitations. The measurement of the F(2)-IsoPs has been shown to be one of the most accurate approaches to quantifying oxidative damage in vivo. We have extended our studies of lipid peroxidation and the F(2)-IsoPs to docosahexaenoic acid (DHA, C22:6, omega-3) and its peroxidation products. We have found that DHA oxidizes both in vitro and in vivo to form F(2)-IsoP-like compounds termed F(4)-neuroprostanes (F(4)-NPs). DHA is specifically enriched in neuronal membranes making the F(4)-NPs sensitive and specific markers of neuronal oxidative damage. Adapting the methodology used to quantitate the F(2)-IsoPs, we utilize stable isotope dilution, negative ion chemical ionization, gas chromatography mass spectrometry (GC/MS) to quantitate the F(4)-NPs with a limit of detection in the low picomolar range. Methods have been developed to quantitate both the F(4)-NPs and the neurofurans (NFs), DHA derived peroxidation products containing a substituted tetrahydrofuran ring, in brain tissue and cerebrospinal fluid. This review outlines in detail proper sample handling, extraction and hydrolysis of the F(4)-NPs and NFs from tissue membrane phospholipids or biological fluids, and purification and derivatization of the compounds for analysis by GC/MS.