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The body of evidence indicating that oligomers of amyloid β1−42 (Aβ1−42) produce toxicity to neurons, together with our demonstration that prostaglandin H2 (PGH2) oligomerizes amyloid β1−42, led to the examination of the neurotoxicity of amyloid β1−42 treated with PGH2. The neurotoxic effects of Aβ1−42 incubated with PGH2 was examined in primary cultures of cerebral neurons of mice, monitoring the reduction of 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) as an indicator of cell toxicity. Whereas Aβ1−42 itself, incubated for 24 h, has little or no effect on MTT reduction, Aβ1−42 24 h after exposure to PGH2 produced a marked inhibition of MTT reduction, comparable with the inhibition resulting from Aβ1−42 that has been oligomerized by incubation for 6 days. Similar results were obtained when Aβ1−42 was incubated with levuglandin E2 (LGE2), a reactive aldehyde formed by spontaneous rearrangement of PGH2. The oligomers formed from reaction of Aβ1−42 with LGE2 exhibit immunochemical similarity with amyloid-derived diffusible ligands (ADDLs), as determined by analysis of the products of reaction of Aβ1−42 with LGE2 using western blotting with an antibody that is selective for ADDLs. [ABSTRACT FROM AUTHOR]

The formation of cyclooxygenase-derived lipid adducts of protein in brains of patients who had Alzheimer's disease has been investigated. The enzymatic product of the cyclooxygenases, prostaglandin H2, rearranges in part to highly reactive γ-ketoaldehydes, levuglandin (LG) E2 and LGD2. These γ-ketoaldehydes react with free amines on proteins to yield a covalent adduct. Utilizing analysis of the levuglandinyl-lysine adducts by liquid chromatography-tandem mass spectrometry, we now find that this post-translational modification is increased significantly in the hippocampus in Alzheimer's disease. The magnitude of the increase correlates with the pathological evidence of severity. [ABSTRACT FROM AUTHOR]

Aging and apolipoprotein E ( APOE) isoform are among the most consistent risks for the development of Alzheimer's disease (AD). Metabolic factors that modulate risk have been elusive, though oxidative reactions and their by-products have been implicated in human AD and in transgenic mice with overt histological amyloidosis. We investigated the relationship between the levels of endogenous murine amyloid β (Aβ) peptides and the levels of a marker of oxidation in mice that never develop histological amyloidosis [i.e. APOE knockout (KO) mice with or without transgenic human APOEℇ3 or human APOEℇ4 alleles]. Aging-, gender-, and APOE-genotype-dependent changes were observed for endogenous mouse brain Aβ40 and Aβ42 peptides. Levels of the oxidized lipid F2-isoprostane (F2- isoPs) in the brains of the same animals as those used for the Aβ analyses revealed aging- and gender-dependent changes in APOE KO and in human APOEℇ4 transgenic KO mice. Human APOEℇ3 transgenic KO mice did not exhibit aging- or gender-dependent increases in F2- isoPs. In general, the changes in the levels of brain F2- isoPs in mice according to age, gender, and APOE genotype mirrored the changes in brain Aβ levels, which, in turn, paralleled known trends in the risk for human AD. These data indicate that there exists an aging-dependent, APOE-genotype-sensitive rise in murine brain Aβ levels despite the apparent inability of the peptide to form histologically detectable amyloid. Human APOEℇ3, but not human APOEℇ4, can apparently prevent the aging-dependent rise in murine brain Aβ levels, consistent with the relative risk for AD associated with these genotypes. The fidelity of the brain Aβ/F2- isoP relationship across multiple relevant variables supports the hypothesis that oxidized lipids play a role in AD pathogenesis, as has been suggested by recent evidence that F2- isoPs can stimulate Aβ generation and aggregation. [ABSTRACT FROM AUTHOR]

Epidemiologic evidence implicates cyclooxygenase activity in the pathogenesis of Alzheimer's disease, in which amyloid plaques have been found to contain increased levels of dimers and higher multimers of the amyloid β peptide. The product of the oxygenation of arachidonic acid by the cyclooxygenases, prostaglandin H[sub 2] (PGH[sub 2]), rearranges non-enzymatically to several prostaglandins, including the highly reactive γ-keto aldehydes, levuglandins E[sub 2] and D[sub 2]. We demonstrate that PGH[sub 2] markedly accelerates the formation of dimers and higher oligomers of amyloid β[sub 1]-42- This is associated with the formation of levuglandin adducts of the peptide. These findings provide the molecular basis for a hypothesis linking cyclooxygenase activity to the formation of oligomers of amyloid β. [ABSTRACT FROM AUTHOR]

Elevated production of 4-hydroxy-trans-2-nonenal (HNE) occurs in numerous neurological disorders involving oxidative damage. HNE is metabolized to the non-toxic 4-hydroxy-trans-2-nonenoic acid (HNEAcid) by aldehyde dehydrogenases in the rat cerebral cortex. Based upon the structural similarity of HNEAcid to ligands of the gamma-hydroxybutyrate (GHB) receptor, we hypothesized that HNEAcid is an endogenous ligand for the GHB receptor. HNEAcid displaced the specific binding of the GHB receptor ligand (3)H-NCS382 (30 nm) in membrane preparations of human frontal cerebral cortex and whole rat cerebral cortex with IC(50s) of 3.9 +/- 1.1 and 5.6 +/- 1.2 micro m, respectively. Inhibition was attenuated when the carboxyl group of HNEAcid was replaced with an aldehyde or an alcohol. HNEAcid (300 micro m) did not displace the binding of beta-adrenergic receptor and GABA(B) receptor antagonists, demonstrating the selectivity of HNEAcid for the GHB receptor. HNEAcid is formed in homogenates of human frontal cortical gray matter in an NAD(+)-dependent (V(Max), 0.71 nmol/min/mg) and NADP(+)-dependent (V(Max), 0.12 nmol/min/mg) manner. Lastly, (3)H-NCS382 binding is elevated 2.7-fold with age in the cerebral cortex of rats. Our data demonstrate that an HNE metabolite, formed in rat and human brain, is a signaling molecule analogous to other bioactive lipid peroxidation products.

Epidemiologic evidence implicates cyclooxygenase activity in the pathogenesis of Alzheimer's disease, in which amyloid plaques have been found to contain increased levels of dimers and higher multimers of the amyloid beta peptide. The product of the oxygenation of arachidonic acid by the cyclooxygenases, prostaglandin H2 (PGH2), rearranges non-enzymatically to several prostaglandins, including the highly reactive gamma-keto aldehydes, levuglandins E2 and D2. We demonstrate that PGH2 markedly accelerates the formation of dimers and higher oligomers of amyloid beta1-42. This is associated with the formation of levuglandin adducts of the peptide. These findings provide the molecular basis for a hypothesis linking cyclooxygenase activity to the formation of oligomers of amyloid beta.