The isoprostanes: unique products of arachidonic acid oxidation-a review.

The isoprostanes are a unique series of prostaglandin-like compounds formed in vivo from the free radical-catalyzed peroxidation of arachidonic acid independent of the cyclooxygenase enzyme. The purpose of this article is to summarize our knowledge regarding the isoprostanes and discuss what are avenues for future research. Novel aspects related to the biochemistry of isoprostane formation and methods by which these compounds are analyzed, including potential pitfalls that may occur during the analysis, are discussed first. The isoprostanes possess potent biological activity, and their potential role in mediating certain aspects of the detrimental effects of oxidant stress is then examined. A considerable portion of this review deals with the utility of measuring isoprostanes as markers of oxidant injury both in vitro and in vivo. A number of studies have shown these compounds to be extremely accurate markers of lipid peroxidation in animal models of oxidative stress and have illuminated the role of oxidant injury in association with a number of human diseases.

Formation of highly reactive A-ring and J-ring isoprostane-like compounds (A4/J4-neuroprostanes) in vivo from docosahexaenoic acid.

Free radical-initiated oxidant injury and lipid peroxidation have been implicated in a number of neural disorders. Docosahexaenoic acid is the most abundant unsaturated fatty acid in the central nervous system. We have shown previously that this 22-carbon fatty acid can yield, upon oxidation, isoprostane-like compounds termed neuroprostanes, with E/D-type prostane rings (E(4)/D(4)-neuroprostanes). Eicosanoids with E/D-type prostane rings are unstable and dehydrate to cyclopentenone-containing compounds possessing A-type and J-type prostane rings, respectively. We thus explored whether cyclopentenone neuroprostanes (A(4)/J(4)-neuroprostanes) are formed from the dehydration of E(4)/D(4)-neuroprostanes. Indeed, oxidation of docosahexaenoic acid in vitro increased levels of putative A(4)/J(4)-neuroprostanes 64-fold from 88 +/- 43 to 5463 +/- 2579 ng/mg docosahexaenoic acid. Chemical approaches and liquid chromatography/electrospray ionization tandem mass spectrometry definitively identified them as A(4)/J(4)-neuroprostanes. We subsequently showed these compounds are formed in significant amounts from a biological source, rat brain synaptosomes. A(4)/J(4)-neuroprostanes increased 13-fold, from a basal level of 89 +/- 72 ng/mg protein to 1187 +/- 217 ng/mg (n = 4), upon oxidation. We also detected these compounds in very large amounts in fresh brain tissue from rats at levels of 97 +/- 25 ng/g brain tissue (n = 3) and from humans at levels of 98 +/- 26 ng/g brain tissue (n = 5), quantities that are nearly an order of magnitude higher than other classes of neuroprostanes. Because of the fact that A(4)/J(4)-neuroprostanes contain highly reactive cyclopentenone ring structures, it would be predicted that they readily undergo Michael addition with glutathione and adduct covalently to proteins. Indeed, incubation of A(4)/J(4)-neuroprostanes in vitro with excess glutathione resulted in the formation of large amounts of adducts. Thus, these studies have identified novel, highly reactive A/J-ring isoprostane-like compounds that are derived from docosahexaenoic acid in vivo.