We investigated oxidative stress in human postmortem frontal cortex from individuals characterized as mild-cognitive impairment (n = 8), mild/moderate Alzheimer disease (AD) (n = 4), and late stage AD (n = 9). Samples from subjects with no cognitive impairment (n = 10) that were age- and postmortem interval-matched with these cases were used as controls. The short postmortem interval brain samples were processed for postmitochondrial supernatant (PMS), non-synaptic mitochondria, and synaptosome fractions. Samples were analyzed for several antioxidants (glutathione [GSH], glutathione peroxidase [GPx], glutathione reductase, glutathione-S-transferase [GST] glucose-6-phosphate dehydrogenase, superoxide dismutase [SOD], catalase) and the oxidative marker, thiobarbituric acid reactive substances. The tissue was also analyzed for possible changes in protein damage using neurochemical markers for protein carbonyls, 3-nitrotyrosine, 4-hydroxynonenal, and acrolein. All 3 neuropil fractions (PMS, mitochondrial, and synaptosomal) demonstrated significant disease-dependent increases in oxidative markers. The highest changes were observed in the synaptosomal fraction. Both mitochondrial and synaptosomal fractions had significant declines in antioxidants (GSH, GPx, GST, and SOD). Levels of oxidative markers significantly correlated with Mini-Mental Status Examination scores. Oxidative stress was more localized to the synapses, with levels increasing in a disease-dependent fashion. These correlations implicate an involvement of oxidative stress in AD-related synaptic loss.

Oxidative stress, an imbalance between oxidants and antioxidants, contributes to the pathogenesis of traumatic brain injury (TBI). Oxidative neurodegeneration is a key mediator of exacerbated morphological responses and deficits in behavioral recoveries. The present study assessed early hippocampal sequential imbalance to possibly enhance antioxidant therapy. Young adult male Sprague-Dawley rats were subjected to a unilateral moderate cortical contusion. At various times post TBI, animals were killed and the hippocampus analyzed for antioxidants (GSH, GSSG, glutathione peroxidase, glutathione reductase, glutathione-S-transferase, glucose-6-phosphate dehydrogenase, superoxide dismutase and catalase), and oxidants (acrolein,, protein carbonyl [PC] and 3-nitrotyrosine. Synaptic markers (synapsin-I, post synaptic density-95 [PSD-95], synapse associated protein-97 [SAP-97], growth associated protein-43 were also analyzed. All values were compared to sham operated animals. Significant time-dependent changes in antioxidants were observed as early as 3 h post trauma and paralleled increases in oxidants (4-HNE, acrolein and PC) with peak values obtained at 24-48 h. Time dependent changes in synaptic proteins (synapsin-I, PSD-95 and SAP-97) occurred well after levels of oxidants peaked. These results indicate that depletion of antioxidant systems following trauma could adversely affect synaptic function and plasticity. Early onset of oxidative stress suggests that the initial therapeutic window following TBI appears to be relatively short and it may be necessary to stagger selective types of anti-oxidant therapy to target specific oxidative components.

Quercetin, a flavonoid found in various foodstuffs, has antioxidant properties, increases glutathione (GSH) levels and antioxidant enzyme function. Considerable attention has been focused on increasing the intracellular GSH levels in many diseases, including Alzheimer's disease (AD). Amyloid beta-peptide [Abeta(1-42)], elevated in AD brain, is associated with oxidative stress and neurotoxicity. The present study was aimed to investigate the protective effects of quercetin on Abeta (1-42)-induced oxidative cell toxicity in cultured neurons. Decreased cell survival in neuronal cultures treated with Abeta(1-42) correlated with increased free radical production measured by dichlorofluorescein fluorescence and an increase in protein oxidation (protein carbonyl, 3-nitrotyrosine) and lipid peroxidation (protein bound 4-hydroxy-2-nonenal). Pretreatment of primary hippocampal cultures with quercetin significantly attenuated Abeta(1-42)-induced cytotoxicity, protein oxidation, lipid peroxidation and apoptosis. A dose-response study suggested that quercetin showed protective effects against Abeta(1-42) toxicity by modulating oxidative stress at lower doses, but higher doses not only were non-neuroprotective, but were toxic. These findings provide motivation to test the hypothesis, that quercetin may provide a promising approach for the treatment of AD and other oxidative stress-related neurodegenerative diseases.

Proteolytic processing and phosphorylation of amyloid precursor protein (APP), and hyperphosphorylation of tau protein, have been shown to be increased in Alzheimer's disease (AD) brains, leading to increased production of b-amyloid (Ab) peptides and neurofibrillary tangles, respectively. These observations suggest that phosphorylation events are critical to the understanding of the pathogenesis and treatment of this devastating disease. Pin-1, one of the peptidyl-prolyl isomerases (PPIase), catalyzes the isomerization of the peptide bond between pSer/Thr-Pro in proteins, thereby regulating their biological functions which include protein assembly, folding, intracellular transport, intracellular signaling, transcription, cell cycle progression and apoptosis. A number of previous studies have shown that Pin1 is co-localized with phosphorylated tau in AD brain, and shows an inverse relationship to the expression of tau. Pin1 protects neurons under in vitro conditions. Moreover, recent studies demonstrate that APP is a target for Pin1 and thus, in Ab production. Furthermore, Pin1 was found to be oxidatively modified and to have reduced activity in the hippocampus in mild cognitive impairment (MCI) and AD. Because of the diverse functions of Pin1, and the discovery that this protein is one of the oxidized proteins common to both MCI and AD brain, the question arises as to whether Pin1 is one of the driving forces for the initiation or progression of AD pathogenesis, finally leading to neurodegeneration and neuronal apoptosis. In the present review, we discuss the role of Pin1 with respect to Alzheimer's disease.

An imbalance between oxidants and antioxidants has been postulated to lead to oxidative damage in traumatic brain injury (TBI). Oxidative neurodegeneration is a key mediator of exacerbated morphological responses and deficits in behavioral recoveries. The present study was designed to delineate the early temporal sequence of this imbalance in order to enhance possible antioxidant therapy. Young adult male Sprague-Dawley rats were subjected to a unilateral moderate cortical contusion. At various times post-trauma (3, 6, 12, 24, 48, 72, and 96 h), animals were killed and the cortex analyzed for enzymatic and non-enzymatic oxidative stress markers. Fresh tissues were prepared for biochemical analysis of several antioxidants (glutathione [GSH], glutathione peroxidase [GPx], glutathione reductase [GR], glutathione-S-transferase [GST], and thiobarbituric acid reactive substances [TBARS]). Synaptic markers Synapsin-I, PSD-95, SAP-97 and GAP-43 were analyzed by Western blot with antibodies directed against them. All activity levels were compared to sham-operated animals. Activity of antioxidant enzymes and GSH clearly demonstrate a significant time-dependent increase in oxidative stress. Changes in pre- and post-synaptic proteins (Synapsin-I and PSD-95) occur early (24 h), whereas SAP-97 levels demonstrate a protracted reduction. These results indicate that depletion of antioxidant systems following trauma could adversely affect synaptic function and plasticity. Because of the observed differences in the time-course of various markers, it may be necessary to stagger selective types of anti-oxidant therapy to target specific oxidative components. The initial therapeutic window following TBI appears relatively short since oxidative damage occurs as early as 3 h.