Interactions between apolipoprotein E gene and dietary alpha-tocopherol influence cerebral oxidative damage in aged mice.

Cerebral oxidative damage is a feature of aging and is increased in a number of neurodegenerative diseases. We pursued the gene-environment interaction of lack of apolipoprotein E (apoE) and modulation of dietary alpha-tocopherol on cerebral oxidative damage in aged male and female mice by quantifying the major isomers of cerebral isoprostanes, derived from arachidonic acid (AA) oxidation, and neuroprostanes, derived from docosahexaenoic acid (DHA) oxidation. Mice fed alpha-tocopherol-deficient, normal, or -supplemented diet had undetectable, 4486 +/- 215, or 6406 +/- 254 ng of alpha-tocopherol per gram of brain tissue (p < 0.0001), respectively. Two factors, male gender and lack of apoE, combined to increase cerebral AA oxidation by 28%, whereas three factors, male gender, lack of apoE, and deficiency in alpha-tocopherol, combined to increase cerebral DHA oxidation by 81%. alpha-Tocopherol supplementation decreased cerebral isoprostanes but not neuroprostanes and enhanced DHA, but not AA, endoperoxide reduction in vivo and in vitro. These results demonstrated that the interaction of gender, inherited susceptibilities, and dietary alpha-tocopherol contributed differently to oxidative damage to cerebral AA and DHA in aged mice.

Brain regional quantification of F-ring and D-/E-ring isoprostanes and neuroprostanes in Alzheimer's disease.

Isoprostanes (IsoP) are produced exclusively from free radical damage to arachidonic acid, a fatty acid that is evenly distributed throughout white matter and gray matter, whereas neuroprostanes (NPs) are generated analogously from docosahexaenoic acid (DHA), a fatty acid enriched in gray matter where it is concentrated in neurons. IsoP and NPs derive from endoperoxide intermediates that isomerize to D/E-ring forms or that are reduced to F-ring compounds. We quantified F-ring and D/E-ring IsoP and NPs in temporal and parietal cortex, hippocampus, and cerebellum of nine definite Alzheimer's disease (AD) patients and 11 age-matched controls. Total NP levels (F-ring plus D/E-ring), but not total IsoP, were significantly greater in AD than controls (P: < 0.0001); only cerebral regions in AD patients had NPs greater than controls (P: < 0.05). The F-ring to D/E-ring ratio for NPs, but not IsoP, was 40 to 70% lower in all brain regions of AD patients compared to controls (P: < 0.005). These data extend results from in situ techniques, that have localized reactive products of lipid peroxidation primarily to neurons, by quantifying significantly greater free radical damage to the DHA-containing compartments in cerebrum in AD patients than controls, and suggest that one mechanism of increased oxidative stress may be diminished reducing capacity in DHA-containing compartments.

Formation of novel D-ring and E-ring isoprostane-like compounds (D4/E4-neuroprostanes) in vivo from docosahexaenoic acid.

Free radical-mediated oxidant injury and lipid peroxidation have been implicated in a number of neural disorders. We have reported that bioactive prostaglandin D2/E2-like compounds, termed D2/E2-isoprostanes, are produced in vivo by the free radical-catalyzed peroxidation of arachidonic acid. Docosahexaenoic acid, in contrast to arachidonic acid, is the most abundant unsaturated fatty acid in brain. We therefore questioned whether D/E-isoprostane-like compounds (D4/E4-neuroprostanes) are formed from the oxidation of docosahexaenoic acid. Levels of putative D4/E4-neuroprostanes increased 380-fold after oxidation of docosahexaenoic acid in vitro from 15.2 +/- 6.3 to 5773 +/- 1024 ng/mg of docosahexaenoic acid. Subsequently, chemical approaches and liquid chromatography electrospray ionization tandem mass spectrometry definitively identified these compounds as D4/E4-neuroprostanes. We then explored the formation of D4/E4-neuroprostanes from a biological source, rat brain synaptosomes. Basal levels of D4/E4-neuroprostanes were 3.8 +/- 0.6 ng/mg of protein and increased 54-fold after oxidation (n = 4). We also detected these compounds in fresh brain tissue from rats at levels of 12.1 +/- 2.4 ng/g of brain tissue (n = 3) and in human brain tissue at levels of 9.2 +/- 4.1 ng/g of brain tissue (n = 4). Thus, these studies have identified novel D/E-ring isoprostane-like compounds that are derived from docosahexaenoic acid and that are formed in brain in vivo. The fact that they are readily detectable suggests that ongoing oxidative stress is present in the central nervous system of humans and animals. Further, identification of these compounds provides a rationale for examining their role in neurological disorders associated with oxidant stress.