Isoeicosanoids are free radical-catalyzed isomers of the enzymatic products of arachidonic acid. They are formed in situ in cell membranes, are cleaved, circulate, and are excreted in urine. Isomers of prostaglandin F 2␣ , the F 2 -isoprostanes, have emerged as sensitive indices of lipid peroxidation in vivo. Analogous compounds formed from docosahexaenoic acid (DHA) are termed neuroprostanes and are more abundant than isoprostanes (iPs) in brain. Isofurans are another class of isoeicosanoids characterized by a substituted tetrahydrofuran ring. They are preferentially formed, relative to iPs, under conditions of elevated oxygen tension. Here, we report the discovery of neurofurans (nFs), the analogous family of compounds formed from DHA. Isoprostanes (iPs) 2 are prostaglandin isomers derived by free radical attack on esterified arachidonic acid (AA) in cell membranes (1). They are then cleaved, presumably by phospholipases, circulate in plasma, and are excreted in urine, where they can be quantified by immunologic methods or by mass spectrometry. Isomers of PGF 2␣ , F 2 -iPs, have been measured in urine as indices of in vivo lipid peroxidation (2). Compounds analogous to the F 2 -iPs may be formed from other fatty acid substrates. For example, neuroprostanes (nPs) are iPs derived from the -3 fatty acid, docosahexaenoic acid (DHA) (3). Given that DHA is more abundant than AA in brain, the nPs may prove to be a more attractive biomarker of neurodegeneration than are the iPs (4). Consequently, there is considerable interest in the use of these compounds as indices of progression in neurodegeneration, such as in Alzheimer disease (AD) (5).The isofurans (iFs) are a family of free radical-induced peroxidation products of AA (6). They are even more abundant than iPs in tissues as diverse as kidney and hippocampus in the rat and may offer an adjunctive approach to the assessment of oxidant stress in vivo (6, 7). They are formed preferentially under conditions of elevated oxygen tension (6).Here we report the characterization of the analogous compounds derived from DHA: the neurofurans (nFs). Quantitative assessment of nFs in vivo reveals modulated formation under conditions of elevated and diminished oxidant stress. Given the abundance of DHA in the brain, analysis of nFs may have particular value in the quantitative assessment of lipid peroxidation in neurodegenerative disease.
EXPERIMENTAL PROCEDURES
In Vivo Oxidation: Analysis of Liver from CCl 4 -treated MiceTreatment of mice with CCl 4 was used to induce oxidant injury to the liver as previously described (8). Three-month-old C57/BL6 male mice were fasted overnight and then administered intraperitoneal injections of CCl 4 (4 g/kg of body weight). CCl 4 was mixed with canola oil (1:1 by volume). The mice were anesthetized with CO 2 prior to sacrifice at 0, 1, 2.5, 7.5, and 20 h after CCl 4 administration, and their livers were removed and rapidly frozen in liquid nitrogen prior to storage at Ϫ80°C. Total lipids were extracted using a modified Folch procedure (9). Br...