Increased peroxidation and reduced antioxidant enzyme activity in Alzheimer's disease

Nuclear factor erythroid 2-related factor 2 protects against beta amyloid

Nuclear factor erythroid 2-related factor 2 (Nrf2) coordinates the up-regulation of cytoprotective genes via the antioxidant response element (ARE). In the pathogenesis of Alzheimer's disease (AD) current evidence supports the role of oxidative stress. Considering the protective role of Nrf2 against oxidative injury, we studied Nrf2 and Nrf2-ARE target genes in transgenic AD mice and tested whether Nrf2 could confer neuroprotection against amyloid-beta peptides (Abeta). Nrf2-ARE pathway was attenuated in APP/PS1 transgenic mouse brain at the time of Abeta deposition. Boosting the activity of the Nrf2-ARE pathway by tert-butylhydroquinone treatment or adenoviral Nrf2 gene transfer protected against Abeta toxicity. This neuroprotection was associated with increased expression of Nrf2 target genes and reduced phosphorylation of p66Shc, a marker of increased susceptibility for oxidative stress. The findings suggest that the Nrf2-ARE pathway may be impaired in AD and that induction of the Nrf2-ARE defence mechanism may prevent or delay AD-like pathology.

Vitamin E for Alzheimer's disease and mild cognitive impairment

BACKGROUND

Vitamin E is a dietary compound that functions as an antioxidant scavenging toxic free radicals. Evidence that free radicals may contribute to the pathological processes of cognitive impairment including Alzheimer's disease (AD) has led to interest in the use of Vitamin E in the treatment of Alzheimer's disease and Mild Cognitivie Impairment (MCI).

OBJECTIVES

To assess the efficacy of Vitamin E in the treatment of Alzheimer's disease and prevention of progression of Mild Cognitive Impairment to Alzheimer's disease.

SEARCH STRATEGY

The Cochrane Dementia and Cognitive Improvement's Specialized Register was searched on 8 January 2007 using the following terms: "Vitamin E", vitamin-E, alpha-tocopherol. The CDCIG Registers contains records from major health care databases and ongoing trial databases and is updated regularly.

SELECTION CRITERIA

All unconfounded, double blind, randomized trials in which treatment with Vitamin E at any dose was compared with placebo for patients with Alzheimer's disease or Mild Cognitive Impairment.

DATA COLLECTION AND ANALYSIS

Two reviewers independently applied the selection criteria and assessed study quality and extracted and analysed the data. For each outcome measure data were sought on every patient randomized. Where such data were not available an analysis of patients who completed treatment was conducted.

MAIN RESULTS

Only 2 studies met the inclusion criteria. The primary outcome used in the AD study was survival time to the first of 4 endpoints: death, institutionalisation, loss of 2 out of 3 basic activities of daily living and severe dementia (defined as a global Clinical Dementia Rating of 3). The investigators reported the total numbers in each group who reached the primary endpoint within two years for participants completing the study ("completers"). There appeared to be some benefit from Vitamin E with fewer participants reaching endpoint - 58% (45/77) of completers compared with 74% (58/78) - a Peto odds ratio of 0.49, 95% confidence interval 0.25 to 0.96.However, more participants taking Vitamin E suffered a fall (12/77 compared with 4/78; odds ratio 3.07, 95% CI 1.09 to 8.62). It was not possible to interpret the reported results for specific endpoints or for secondary outcomes of cognition, dependence, behavioural disturbance and activities of daily living.The primary outcome used in the MCI study which had 769 participants (257 in the Vitamin E group and 259 in the placebo group; a third Donepezil group of 253 was not included in this review) was the time to progression from MCI to possible or probable AD. A total of 214 of the 769 participants had progression to dementia, with 212 being classified as having possible or probable AD. There was no significant difference in the probability of progression from MCI to AD between the Vitamin E group and the placebo group. There was no significant difference between the placebo group and the Vitamin E group in adverse events. Five subjects died in each group and 72 discontinued treatment in the Vitamin E group and 66 in the placebo group.

AUTHORS' CONCLUSIONS

There is no evidence of efficacy of Vitamin E in the prevention or treatment of people with AD or MCI. More research is needed to identify the role of Vitamin E, if any, in the management of cognitive impairment.

Association between enzymatic and non-enzymatic antioxidant defense mechanism with apolipoprotein E genotypes in Alzheimer disease

OBJECTIVE

There are evidence suggesting that APOE-varepsilon4 allele play an important role in the pathogenesis of Alzheimer's disease (AD) by reducing peripheral levels and activities of a broad spectrum of nonenzymatic and enzymatic antioxidants systems. However, the link between APOE genotype, oxidative stress, and AD has yet to be established. In this study we examined whether antioxidant defense mechanism exacerbates the risk of AD in individual carrying APOE-varepsilon4 allele in a population from Tehran, Iran.

METHOD

We determined the enzymatic activities of the erythrocyte Cu-Zn superoxide dismutase (Cu-Zn SOD), glutathione peroxidase (GSH-Px), catalase (CAT) and serum level of total antioxidant status(TAS) in various APOE genotypes in 91 patients with AD and 91 healthy subjects as control group (age and sex-matched).

RESULT

The results showed that the TAS level and the activities of enzymatic antioxidants CAT and GSH-Px were significantly lower and the SOD activity was significantly higher in AD patients compared to controls. The AD patients with APOE-varepsilon4 allele genotype had significantly lower serum TAS concentration and lower erythrocytes GSH-Px and CAT activities (p=0.001) but significantly higher erythrocytes Cu-Zn SOD activity (p=0.001) than the non-APOE-varepsilon4 carrier AD and the control group. In addition, the association observed between the factors involved in an antioxidant defense mechanism and APOE-varepsilon4 allele in AD increased with age of the subjects.

CONCLUSION

These data indicate that the reduced serum level of TAS and activity of CAT, GSH-Px and increased SOD exacerbate the risk of AD in individuals carrying APOE-varepsilon4 allele. The reduced antioxidants defense in APOE-varepsilon4 allele carrier may contribute to beta-amyloidosis. This effect, however, is more pronounced in the AD patients older than 75 years of age. This suggests that a therapeutic modality should be considered for these subjects.

Clair DK. A neuronal model of Alzheimer's disease: an insight into the mechanisms of oxidative stress-mediated mitochondrial injury

Alzheimer's disease (AD) is associated with beta-amyloid accumulation, oxidative stress and mitochondrial dysfunction. However, the effects of genetic mutation of AD on oxidative status and mitochondrial manganese superoxide dismutase (MnSOD) production during neuronal development are unclear. To investigate the consequences of genetic mutation of AD on oxidative damages and production of MnSOD during neuronal development, we used primary neurons from new born wild-type (WT/WT) and amyloid precursor protein (APP) (NLh/NLh) and presenilin 1 (PS1) (P264L) knock-in mice (APP/PS1) which incorporated humanized mutations in the genome. Increasing levels of oxidative damages, including protein carbonyl, 4-hydroxynonenal (4-HNE) and 3-nitrotyrosine (3-NT), were accompanied by a reduction in mitochondrial membrane potential in both developing and mature APP/PS1 neurons compared with WT/WT neurons suggesting mitochondrial dysfunction under oxidative stress. Interestingly, developing APP/PS1 neurons were significantly more resistant to beta-amyloid 1-42 treatment, whereas mature APP/PS1 neurons were more vulnerable than WT/WT neurons of the same age. Consistent with the protective function of MnSOD, developing APP/PS1 neurons have increased MnSOD protein and activity, indicating an adaptive response to oxidative stress in developing neurons. In contrast, mature APP/PS1 neurons exhibited lower MnSOD levels compared with mature WT/WT neurons indicating that mature APP/PS1 neurons lost the adaptive response. Moreover, mature APP/PS1 neurons had more co-localization of MnSOD with nitrotyrosine indicating a greater inhibition of MnSOD by nitrotyrosine. Overexpression of MnSOD or addition of MnTE-2-PyP(5+) (SOD mimetic) protected against beta-amyloid-induced neuronal death and improved mitochondrial respiratory function. Together, the results demonstrate that compensatory induction of MnSOD in response to an early increase in oxidative stress protects developing neurons against beta-amyloid toxicity. However, continuing development of neurons under oxidative damage conditions may suppress the expression of MnSOD and enhance cell death in mature neurons.

Cellular responses to reactive oxygen species-induced DNA damage and aging

Oxidative stress in cells and tissues can occur during pathophysiological developments, e.g., during inflammatory and allergic diseases or during ischemic or toxic and hyperglycemic conditions via the generation of reactive oxygen species (ROS). Moreover, ROS can be generated by radiation (UV, X-rays) and pharmacologically, e.g., by anthracyclins as chemotherapeutic compounds for treatment of a variety of tumors to induce 'stress or aberrant signaling-inducing senescence' (STASIS). Although STASIS is distinguished from intracellular replicative senescence, a variety of cellular mechanisms appear similar in both aging pathways. It is generally accepted that oxidative stress and ROS eventually cause DNA damage, whereby insufficient cellular repair mechanisms may contribute to premature aging and apoptosis. Conversely, ROS-induced imbalances of the signaling pathways for metabolic protein turnover may also result in opposite effects to recruit malfunctioning aberrant proteins and compounds that trigger tumorigenic processes. Consequently, DNA damage plays a role in the development of carcinogenesis, but is also associated with an aging process in cells and organisms.

Is antioxidant therapy a viable alternative for mild cognitive impairment? Examination of the evidence

Therapeutic interventions for the prodromal stages of dementia are currently being sought with a view to delaying if not preventing disease onset. Uncertainty as to whether cognitive disorder in a given individual will progress towards dementia and adverse drug side effects has led to hesitancy on the part of drug regulators to instigate preventive pharmacotherapies. In this context, antioxidant therapies may provide a low-risk alternative, targeting very early biological changes. While a growing body of knowledge demonstrates both the importance of oxidative stress in the aetiology of dementia and the efficacy of antioxidant treatment in animal and cellular models, studies in humans are presently inconclusive. While some antioxidants, notably flavonoid- or vitamin-rich diets, appear to lower the relative risk for Alzheimer's disease in humans in observational studies, these results must be interpreted in the light of the biological complexity of the relationship between oxidative stress and neurodegeneration, and the methodological and theoretical shortcomings of studies conducted to date. A clearer understanding of these factors will assist in the interpretation of the results of the intervention studies which are now being undertaken; these studies being the only current means of establishing efficacy for preventive drug treatment of Alzheimer's disease.

Treating neurodegeneration by modifying mitochondria: potential solutions to a "complex" problem

Mitochondria function differently in aged brains than they do in young brains. Consistently reported changes include reduced electron transport chain (ETC) enzyme activities, reduced phosphorylation of ADP, and increased reactive oxygen species (ROS) production. Various neurodegenerative diseases are also associated with changes in mitochondrial function, and these changes both recapitulate and extend those seen in "normal" aging. Unfortunately, attempts to treat neurodegenerative diseases by treating mitochondria-related pathology have thus far minimally impacted affected patients. A better understanding of how mitochondrial function changes in aging and neurodegenerative diseases, though, now suggests new approaches to mitochondrial therapy may prove more efficacious. Increasing ETC capacity, increasing oxidative phosphorylation, or decreasing mitochondrial ROS may yet prove useful for the treatment of brain aging and neurodegenerative diseases, and accomplishing this seems increasingly feasible. This review will discuss the role of mitochondrial function and dysfunction in aging and neurodegenerative diseases, and will focus on potential treatment strategies.

Oxidative stress and transcriptional regulation in Alzheimer disease

Alzheimer disease (AD) is defined by progressive impairments in memory and cognition and by the presence of extracellular neuritic plaques and intracellular neurofibrillary tangles. However, oxidative stress and impaired mitochondrial function always accompany AD. Mitochondria are a major site of production of free radicals [ie, reactive oxygen species (ROS)] and primary targets of ROS. ROS are cytotoxic, and evidence of ROS-induced damage to cell membranes, proteins, and DNA in AD is overwhelming. Nevertheless, therapies based on antioxidants have been disappointing. Thus, alternative strategies are necessary. ROS also act as signaling molecules including for transcription. Thus, chronic exposure to ROS in AD could activate cascades of genes. Although initially protective, prolonged activation may be damaging. Thus, therapeutic approaches based on modulation of these gene cascades may lead to effective therapies. Genes involved in several pathways including antioxidant defense, detoxification, inflammation, etc, are induced in response to oxidative stress and in AD. However, genes that are associated with energy metabolism, which is necessary for normal brain function, are mostly down-regulated. Redox-sensitive transcription factors such as activator protein-1, nuclear factor-kappaB, specificity protein-1, and hypoxia-inducible factor are important in redox-dependent gene regulation. Peroxisome proliferators-activated receptor-gamma coactivator (PGC-1alpha) is a coactivator of several transcription factors and is a potent stimulator of mitochondrial biogenesis and respiration. Down-regulated expression of PGC-1alpha has been implicated in Huntington disease and in several Huntington disease animal models. PGC-1alpha role in regulation of ROS metabolism makes it a potential candidate player between ROS, mitochondria, and neurodegenerative diseases. This review summarizes the current progress on how oxidative stress regulates the expression of genes that might contribute to AD pathophysiology and the implications of the transcriptional modifications for AD. Finally, potential therapeutic strategies based on the updated understandings of redox state-dependent gene regulation in AD are proposed to overcome the lack of efficacy of antioxidant therapies.

Effect of gender on mitochondrial toxicity of Alzheimer's Abeta peptide

The aim of this article is to review the role of mitochondria in the pathogenesis of Alzheimer's disease. Additionally, the effect of gender on the incidence of Alzheimer's disease and the pathophysiological mechanisms involved will be discussed. Mitochondria, in the presence of Alzheimer's amyloid-beta peptide, increase the formation of reactive oxygen species which act both as damaging agents and also as signaling molecules. These radicals, in fact, unleash a mechanism involving the liberation of cytochrome c that leads to neuronal apoptosis. Notably, young females appear protected against the mitochondrial toxicity of amyloid-beta, likely due to the upregulation of antioxidant enzymes which occur in females. Estrogens are responsible for this effect. Overall, the findings support the notion that amyloid-beta causes intracellular toxicity via the increased production of oxidant species. Reactive oxygen species generated by mitochondria act as a signal to start the mitochondrial apoptotic pathway. There is a possibility of prevention, and indirect evidence shows that estrogenic compounds (either endogenous estradiol or phytoestrogens such as genistein) may increase the expression of antioxidant enzymes, leading to a lowering of oxidative stress and thus protection against intracellular toxicity of amyloid-beta peptide. These ideas open up the possibility of using phytoestrogens to prevent the onset of Alzheimer's disease. More studies are required to determine whether estrogens and/or phytoestrogens fulfill these expectations.

Redox reactions of copper complexes formed with different beta-amyloid peptides and their neuropathological [correction of neuropathalogical] relevance

The binding stoichiometry between Cu(II) and the full-length beta-amyloid Abeta(1-42) and the oxidation state of copper in the resultant complex were determined by electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) and cyclic voltammetry. The same approach was extended to the copper complexes of Abeta(1-16) and Abeta(1-28). A stoichiometric ratio of 1:1 was directly observed, and the oxidation state of copper was deduced to be 2+ for all of the complexes, and residues tyrosine-10 and methionine-35 are not oxidized in the Abeta(1-42)-Cu(II) complex. The stoichiometric ratio remains the same in the presence of more than a 10-fold excess of Cu(II). Redox potentials of the sole tyrosine residue and the Cu(II) center were determined to be ca. 0.75 and 0.08 V vs Ag/AgCl [or 0.95 and 0.28 V vs normal hydrogen electrode (NHE)], respectively. More importantly, for the first time, the Abeta-Cu(I) complex has been generated electrochemically and was found to catalyze the reduction of oxygen to produce hydrogen peroxide. The voltammetric behaviors of the three Abeta segments suggest that diffusion of oxygen to the metal center can be affected by the length and hydrophobicity of the Abeta peptide. The determination and assignment of the redox potentials clarify some misconceptions in the redox reactions involving Abeta and provide new insight into the possible roles of redox metal ions in the Alzheimer's disease (AD) pathogenesis. In cellular environments, the reduction potential of the Abeta-Cu(II) complex is sufficiently high to react with antioxidants (e.g., ascorbic acid) and cellular redox buffers (e.g., glutathione), and the Abeta-Cu(I) complex produced could subsequently reduce oxygen to form hydrogen peroxide via a catalytic cycle. Using voltammetry, the Abeta-Cu(II) complex formed in solution was found to be readily reduced by ascorbic acid. Hydrogen peroxide produced, in addition to its role in damaging DNA, protein, and lipid molecules, can also be involved in the further consumption of antioxidants, causing their depletion in neurons and eventually damaging the neuronal defense system. Another possibility is that Abeta-Cu(II) could react with species involved in the cascade of electron transfer events of mitochondria and might potentially sidetrack the electron transfer processes in the respiratory chain, leading to mitochondrial dysfunction.

Neuronal apoptosis in neurodegeneration

Apoptosis mediates the precise and programmed natural death of neurons and is a physiologically important process in neurogenesis during maturation of the central nervous system. However, premature apoptosis and/or an aberration in apoptosis regulation is implicated in the pathogenesis of neurodegeneration, a multifaceted process that leads to various chronic disease states, such as Alzheimer's (AD), Parkinson's (PD), Huntington's (HD) diseases, amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), and diabetic encephalopathy. The current review focuses on two major areas (a) the fundamentals of apoptosis, which includes elements of the apoptotic machinery, apoptosis inducers, and emerging concepts in apoptosis research, and (b) apoptotic involvement in neurodegenerative disorders, neuroprotective treatment strategies/modalities, and the mechanisms of, and signaling in, neuronal apoptosis. Current and new experimental models for apoptosis research in neurodegenerative diseases are also discussed.

Fruit polyphenols and their effects on neuronal signaling and behavior in senescence

The onset of age-related neurodegenerative diseases superimposed on a declining nervous system could exacerbate the motor and cognitive behavioral deficits that normally occur in senescence. It is likely that, in cases of severe deficits in memory or motor function, hospitalization and/or custodial care would be a likely outcome. This means that unless some way is found to reduce these age-related decrements in neuronal function, healthcare costs will continue to rise exponentially. Thus, it is extremely important to explore methods to retard or reverse the age-related neuronal deficits as well as their subsequent, behavioral manifestations. Applying molecular biological approaches to slow aging in the human condition may be years away. So it is important to determine what methods can be used today to increase healthy aging, forestall the onset of these diseases, and create conditions favorable to obtaining a "longevity dividend" in both financial and human terms. In this regard, epidemiological studies indicate that consumption of diets rich in antioxidants and anti-inflammatory compounds, such as those found in fruits and vegetables, may lower the risk of developing age-related neurodegenerative diseases, such as Alzheimer's or Parkinson's diseases (AD and PD). Research suggests that the polyphenolic compounds found in fruits, such as blueberries, may exert their beneficial effects by altering stress signaling and neuronal communication, suggesting that interventions may exert protection against age-related deficits in cognitive and motor function. The purpose of this article is to discuss the benefits of these interventions in rodent models and to describe the putative molecular mechanisms involved in their benefits.

Iron: the Redox-active center of oxidative stress in Alzheimer disease

Although iron is essential in maintaining the function of the central nervous system, it is a potent source of reactive oxygen species. Excessive iron accumulation occurs in many neurodegenerative diseases including Alzheimer disease (AD), Parkinson's disease, and Creutzfeldt-Jakob disease, raising the possibility that oxidative stress is intimately involved in the neurodegenerative process. AD in particular is associated with accumulation of numerous markers of oxidative stress; moreover, oxidative stress has been shown to precede hallmark neuropathological lesions early in the disease process, and such lesions, once present, further accumulate iron, among other markers of oxidative stress. In this review, we discuss the role of iron in the progression of AD.

Oxidative stress: A bridge between Down's syndrome and Alzheimer's disease

Besides the genetic, biochemical and neuropathological analogies between Down's syndrome (DS) and Alzheimer's disease (AD), there is ample evidence of the involvement of oxidative stress (OS) in the pathogenesis of both disorders. The present paper reviews the publications on DS and AD in the past 10 years in light of the "gene dosage" and "two-hit" hypotheses, with regard to the alterations caused by OS in both the central nervous system and the periphery, and the main pipeline of antioxidant therapeutic strategies. OS occurs decades prior to the signature pathology and manifests as lipid, protein and DNA oxidation, and mitochondrial abnormalities. In clinical settings, the assessment of OS has traditionally been hampered by the use of assays that suffer from inherent problems related to specificity and/or sensitivity, which explains some of the conflicting results presented in this work. For DS, no scientifically proven diet or drug is yet available, and AD trials have not provided a satisfactory approach for the prevention of and therapy against OS, although most of them still need evidence-based confirmation. In the future, a balanced up-regulation of endogenous antioxidants, together with multiple exogenous antioxidant supplementation, may be expected to be one of the most promising treatment methods.

Determination of malondialdehyde, reduced glutathione levels and APOE4 allele frequency in late-onset Alzheimer's disease in Denizli, Turkey

OBJECTIVES

The aim of the present study was to determine the Apolipoprotein E (APOE) 4 allele frequency of patients with late-onset Alzheimer's disease (AD) and to determine the effects of oxidant-antioxidant balance on AD.

DESIGN AND METHODS

PCR-RFLP was undertaken in 62 cases with AD and 56 aged-matched controls. Activities of reduced glutathione (GSH) and malondialdehyde (MDA) concentration were measured in same groups.

RESULTS

Patients with at least one E4 allele genotype were significantly different in patients with AD (21%) than controls (9%) (p=0.01). Serum MDA levels were significantly different between AD patients and Control group (p=0.0001). There was no significant difference in serum GSH levels between AD patients and C groups.

CONCLUSION

These results confirmed that the APOE4 allele occurs frequently in late onset AD compared with normal controls. Also elevated MDA levels are likely an essential factor in the pathogenesis and neuronal damage of AD.

Effect of pseudophosphorylation and cross-linking by lipid peroxidation and advanced glycation end product precursors on tau aggregation and filament formation

Accumulation of hyperphosphorylated Tau protein as paired helical filaments in pyramidal neurons is a major hallmark of Alzheimer disease. Besides hyperphosphorylation, other modifications of the Tau protein, such as cross-linking, are likely to contribute to the characteristic features of paired helical filaments, including their insolubility and resistance against proteolytic degradation. In this study, we have investigated whether the four reactive carbonyl compounds acrolein, malondialdehyde, glyoxal, and methylglyoxal accelerate the formation of Tau oligomers, thioflavin T-positive aggregates, and fibrils using wild-type and seven pseudophosphorylated mutant Tau proteins. Acrolein and methylglyoxal were the most reactive compounds followed by glyoxal and malondialdehyde in terms of formation of Tau dimers and higher molecular weight oligomers. Furthermore, acrolein and methylglyoxal induced the formation of thioflavin T-fluorescent aggregates in a triple pseudophosphorylation-mimicking mutant to a slightly higher degree than wild-type Tau. Analysis of the Tau aggregates by electron microscopy study showed that formation of fibrils using wild-type Tau and several Tau mutants could be observed with acrolein and methylglyoxal but not with glyoxal and malondialdehyde. Our results suggest that reactive carbonyl compounds, particularly methylglyoxal and acrolein, could accelerate tangle formation in vivo and that this process could be slightly accelerated, at least in the case of methylglyoxal and acrolein, by hyperphosphorylation. Interference with the formation or the reaction of these reactive carbonyl compounds could be a promising way of inhibiting tangle formation and neuronal dysfunction in Alzheimer disease and other tauopathies.

Overstimulation of PrPC signaling pathways by prion peptide 106-126 causes oxidative injury of bioaminergic neuronal cells

Transmissible spongiform encephalopathies, also called prion diseases, are characterized by neuronal loss linked to the accumulation of PrP(Sc), a pathologic variant of the cellular prion protein (PrP(C)). Although the molecular and cellular bases of PrP(Sc)-induced neuropathogenesis are not yet fully understood, increasing evidence supports the view that PrP(Sc) accumulation interferes with PrP(C) normal function(s) in neurons. In the present work, we exploit the properties of PrP-(106-126), a synthetic peptide encompassing residues 106-126 of PrP, to investigate into the mechanisms sustaining prion-associated neuronal damage. This peptide shares many physicochemical properties with PrP(Sc) and is neurotoxic in vitro and in vivo. We examined the impact of PrP-(106-126) exposure on 1C11 neuroepithelial cells, their neuronal progenies, and GT1-7 hypothalamic cells. This peptide triggers reactive oxygen species overflow, mitogen-activated protein kinase (ERK1/2), and SAPK (p38 and JNK1/2) sustained activation, and apoptotic signals in 1C11-derived serotonergic and noradrenergic neuronal cells, while having no effect on 1C11 precursor and GT1-7 cells. The neurotoxic action of PrP-(106-126) relies on cell surface expression of PrP(C), recruitment of a PrP(C)-Caveolin-Fyn signaling platform, and overstimulation of NADPH-oxidase activity. Altogether, these findings provide actual evidence that PrP-(106-126)-induced neuronal injury is caused by an amplification of PrP(C)-associated signaling responses, which notably promotes oxidative stress conditions. Distorsion of PrP(C) signaling in neuronal cells could hence represent a causal event in transmissible spongiform encephalopathy pathogenesis.

Lipid peroxidation in brain during aging in the senescence-accelerated mouse (SAM)

Accumulation of toxic amyloid-beta (Abeta)-peptide is suggested to cause oxidative stress in Alzheimer's disease (AD) brain, and decrease the content of polyunsaturated fatty acids (PUFA) in neuronal membrane lipids. The senescence accelerated prone mice (SAMP8) have age-related increases in the level of hippocampal Abeta-peptide, learning and memory deficits, and a shorter lifespan than their controls. The effects of age-related oxidative damage on PUFA content in membrane phospholipids (PL), and alpha-tocopherol concentration were investigated in hippocampus and amygdala of 2-, 4-, 12-, and 18-month-old SAMP8 mice. In comparison to the younger SAMP8 mice, the hippocampus of the 12-month-old mice contained lower proportions of docosahexaenoic acid (DHA) in phosphatidylserine (PS) and phosphatidylinositol (PI), and higher proportions of arachidonic acid (AA) in PS. Their amygdala contained a lower proportion of AA in phosphatidylcholine (PC). In the hippocampus of the oldest age group, the proportions of DHA in PS, and AA in PC and PI were higher than in the younger age groups. At 2 months of age, the amygdala contained a higher concentration of alpha-tocopherol than the hippocampus, but this difference between the two brain regions was lost with aging. The oldest age group contained the highest concentration of alpha-tocopherol, indicating a protection against oxidative damage of PUFA in brain membrane phospholipids.

Mitoenergetic failure in Alzheimer disease

Brain cells are highly energy dependent for maintaining ion homeostasis during high metabolic activity. During active periods, full mitochondrial function is essential to generate ATP from electrons that originate with the oxidation of NADH. Decreasing brain metabolism is a significant cause of cognitive abnormalities of Alzheimer disease (AD), but it remains uncertain whether this is the cause of further pathology or whether synaptic loss results in a lower energy demand. Synapses are the first to show pathological symptoms in AD before the onset of clinical symptoms. Because synaptic function has high energy demands, interruption in mitochondrial energy supply could be the major factor in synaptic failure in AD. A newly discovered age-related decline in neuronal NADH and redox ratio may jeopardize this function. Mitochondrial dehydrogenases and several mutations affecting energy transfer are frequently altered in aging and AD. Thus, with the accumulation of genetic defects in mitochondria at the level of energy transfer, the issue of neuronal susceptibility to damage as a function of age and age-related disease becomes important. In an aging rat neuron model, mitochondria are both chronically depolarized and produce more reactive oxygen species with age. These concepts suggest that multiple treatment targets may be needed to reverse this multifactorial disease. This review summarizes new insights based on the interaction of mitoenergetic failure, glutamate excitotoxicity, and amyloid toxicity in the exacerbation of AD.

Emerging role of polyphenolic compounds in the treatment of neurodegenerative diseases: a review of their intracellular targets

Aging is the major risk factor for neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. A large body of evidence indicates that oxidative stress is involved in the pathophysiology of these diseases. Oxidative stress can induce neuronal damages, modulate intracellular signaling, ultimately leading to neuronal death by apoptosis or necrosis. Thus antioxidants have been studied for their effectiveness in reducing these deleterious effects and neuronal death in many in vitro and in vivo studies. Increasing number of studies demonstrated the efficacy of polyphenolic antioxidants from fruits and vegetables to reduce or to block neuronal death occurring in the pathophysiology of these disorders. These studies revealed that other mechanisms than the antioxidant activities could be involved in the neuroprotective effect of these phenolic compounds. We will review some of these mechanisms and particular emphasis will be given to polyphenolic compounds from green tea, the Ginkgo biloba extract EGb 761, blueberries extracts, wine components and curcumin.

Increased susceptibility to amyloid toxicity in familial Alzheimer's fibroblasts

Much experimental evidence suggests that an imbalance in cellular redox status is a major factor in the pathogenesis of Alzheimer's disease (AD). Our previous data showed a marked increase in membrane lipoperoxidation in primary fibroblasts from familial AD (FAD) patients. In the present study, we demonstrate that when oligomeric structures of Abeta 1-40 and Abeta 1-42 are added to the culture media, they accumulate quicker near the plasma membrane, and are internalized faster and mostly in APPV717I fibroblasts than in age-matched healthy cells; this results in an earlier and sharper increase in the production of reactive oxygen species (ROS). Higher ROS production leads in turn to an increase in membrane oxidative-injury and significant impairment of cellular antioxidant capacity, giving rise to apoptotic cascade activation and finally to a necrotic outcome. In contrast, healthy fibroblasts appear more resistant to amyloid oxidative-attack, possibly as a result of their plasma membrane integrity and powerful antioxidant capacity. Our data are consistent with increasing evidence that prefibrillar aggregates, compared to mature fibrils, are likely the more toxic species of the peptides. These findings provide compelling evidence that cells bearing increased membrane lipoperoxidation are more susceptible to aggregate toxicity as a result of their reduced ability to counteract amyloid oligomeric attack.

Role of fibrillar Abeta25-35 in the inflammation induced rat model with respect to oxidative vulnerability

The major pathological ramification of Alzheimer's disease (AD) is accumulation of beta-Amyloid (Abeta) peptides in the brain. An emerging therapeutic approach for AD is elimination of excessive Ass peptides and preventing its re-accumulation. Immunization is the most effective strategy in removing preexisting cerebral Abetas and improving the cognitive capacity as shown in transgenic mice model of AD. However, active immunization is associated with adverse effect such as encephalitis with perivascular inflammation and hemorrhage. Details about the mechanistic aspects of propagation of these toxic effects are matter of intense enquiry as this knowledge is essential for the understanding of the AD pathophysiology. The present work aimed to study the oxidative vulnerability in the plasma, liver and brain of the inflammation-induced rats subjected to Ass immunization. Induction of inflammation was performed by subcutaneous injection of 0.5?ml of 2% silver nitrate. Our present result shows that the proinflammatory cytokines such as IL1alpha and TNFalpha are increased significantly in the inflammation-induced, Abeta1-42, Abeta25-35 treated groups and inflammation with Abeta25-35 treated group when compared to control, complete Freund's adjuvant and Abeta35-25 treated groups. These increased proinflammatory cytokines concurrently releases significant amount of free radicals in the astrocytes of respected groups. The present result shows that nitric oxide (NO) level was significantly higher (P<0.001) in plasma, liver and brain of the rat subjected to inflammation, Abeta1-42, Abeta25-35 and inflammation with Abeta25-35 injected groups when compared to control. The increased level of lipid peroxides (LPO) (P<0.001) and decreased antioxidant status (P<0.05) were observed in the plasma, liver and brain of inflammation-induced group when compared to control. Our result shows that significant oxidative vulnerability was observed in the inflammation with Ass treated rats when compared to other groups. Based on our results, we suggest that immunization of AD patients with Ass should be done with caution as the increase in Ass could trigger the brain inflammation in uncontrollable level.

Gender and genetic background effects on brain metal levels in APP transgenic and normal mice: Implications for Alzheimer β-amyloid pathology

The incidence of Alzheimer's disease (AD) is greater in women than men at any age, as is the development of amyloid pathology in several transgenic mouse models of AD. Due to the involvement of metals in AD pathogenesis, variations between the sexes in metal metabolism may contribute to the sex difference in AD risk. In this study, we investigated sex differences in brain metal levels across the lifespan in mice of two different background strains, as well as in mice overexpressing the human amyloid precursor protein (APP) and amyloid-beta protein (Abeta). We demonstrate consistently lower Cu and higher Mn levels in females compared with males at any age studied. The sex differences in Cu and Mn levels are independent of APP/Abeta expression. AD brain exhibits decreased Cu and increased Mn levels, as do transgenic mice overexpressing APP or Abeta. The age-dependent elevations of Cu, Fe and Co levels were found to be significantly greater in mice of B6/SJL background compared with B6/DBA. If depleting Cu and/or rising Mn levels contribute to AD pathogenesis, natural sex differences in these brain metal levels may contribute to the increased propensity of females to develop AD.

Circulating biomarkers of cognitive decline and dementia

Plasma and serum biochemical markers proposed for cognitive decline of degenerative (Alzheimer's disease, AD) or vascular origin and predementia syndromes (mild cognitive impairment and other related entities) are based on pathophysiologic processes such as lipoprotein metabolism (total cholesterol, apolipoprotein E, 24S-hydroxy-cholesterol), and vascular disease (homocysteine, lipoprotein(a)); SP formation (amyloid beta(Abeta)-protein, Abeta autoantibodies, platelet APP isoforms), oxidative stress (isoprostanes, vitamin E), and inflammation (cytokines). This review will focus on the current knowledge on circulating serum and plasma biomarkers of cognitive decline and dementia that are linked to cholesterol homeostasis and lipoprotein abnormalities, senile plaque formation and amyloid precursor protein (APP) metabolism, oxidative stress, and inflammatory reactions. Special emphasis will, however, be placed on biomarkers related to lipoprotein metabolism and vascular disease. Analytically, most plasma and serum proteins or metabolites lack reproducibility, sensitivity, or specificity for the diagnosis, risk and progression assessment, or therapeutic monitoring of AD and other dementing disorders. Measures linked to lipoprotein metabolism and vascular disease, APP metabolism, oxidative stress, or inflammation appear altered in AD relative to controls, but lack sufficient discriminatory power. Measures combining several biomarkers or incorporating a range of proteins in plasma and small molecule metabolites are promising approaches for the development of plasma or serum-based diagnostic tests for AD and other dementing disorders, as well as for predementia syndromes.

Antioxidant capacity in postmortem brain tissues of Parkinson's and Alzheimer's diseases

Oxidative stress has been associated with damage and progressive cell death that occurs in neurodegenerative disorders such as Parkinson's disease (PD) and Alzheimer's disease (AD). The aim of this study was to investigate the antioxidant capacity in postmortem motor cortex (MC), nucleus caudatus (NC), gyrus temporalis (GT) and substantia nigra (SN) from controls (C) and patients with PD and AD. The initial samples consisted of 68 subjects of PD, AD and C. Brains were matched for age, sex and postmortem time. Brain tissue was homogenized in a phosphate buffer pH 7.3 and separated with two-step centrifugation at 15,000rpm for 30 min and 15,000 rpm for 10 min at 4 degrees C. Antioxidant capacity in the supernatants was measured using the oxygen radical absorbance assay (ORAC). The results showed that in the SN of parkinsonian's brain the balance between production of free radicals and the neutralization by a complex antioxidant system is disturbed. No changes in the antioxidant capacity of postmortem MC and NC of parkinsonian's brain in comparison with C were found. In the SN of parkinsonian's brain, antioxidant capacity seems to be lower in comparison with C (p < 0.05). Antioxidant capacity against peroxyl radical showed that MC of AD patients was lower than in the MC of C (p < 0.005). In NC of AD patients the antioxidant capacity against hydroxyl radical was increased in comparison with C (p < 0.04). No changes in the antioxidant capacity were found in brain tissues of AD in comparison with C, when CuSO4 was used as a free radical generator.

Peripheral-type benzodiazepine receptor in neurosteroid biosynthesis, neuropathology and neurological disorders

The peripheral-type benzodiazepine receptor is a mitochondrial protein expressed at high levels in steroid synthesizing tissues, including the glial cells of the brain. Peripheral-type benzodiazepine receptor binds cholesterol with high affinity and is a key element of the cholesterol mitochondrial import machinery responsible for supplying the substrate cholesterol to the first steroidogenic enzyme, thus initiating and maintaining neurosteroid biosynthesis. Neurosteroid formation and metabolism of steroid intermediates are critical components of normal brain function. Peripheral-type benzodiazepine receptor also binds with high affinity various classes of compounds. Upon ligand activation peripheral-type benzodiazepine receptor-dependent cholesterol transport into mitochondria is accelerated leading in increased formation of neuroactive steroids. These steroids, such as allopregnanolone, have been shown to be involved in various neurological disorders, such as anxiety and mood disorders. Thus, peripheral-type benzodiazepine receptor drug ligand-induced neuroactive steroid formation offers a means to regulate brain dysfunction. Peripheral-type benzodiazepine receptor basal expression is upregulated in a number of neuropathologies, including gliomas and neurodegenerative disorders, as well as in various forms of brain injury and inflammation. In Alzheimer's disease pathology neurosteroid biosynthesis is altered and a decrease in the intermediate 22R-hydroxycholesterol levels is observed. This steroid was found to exert neuroprotective properties against beta-amyloid neurotoxicity. Based on this observation, a stable spirostenol derivative showing to display neuroprotective properties was identified, suggesting that compounds developed based on critical intermediates of neurosteroid biosynthesis could offer novel means for neuroprotection. In conclusion, changes in peripheral-type benzodiazepine receptor and neurosteroid levels are part of the phenotype seen in neuropathology and neurological disorders and offer potential targets for new therapies.

Involvement of glutaredoxin-1 and thioredoxin-1 in beta-amyloid toxicity and Alzheimer's disease

Strong evidence indicates oxidative stress in the pathogenesis of Alzheimer's disease (AD). Amyloid beta (Abeta) has been implicated in both oxidative stress mechanisms and in neuronal apoptosis. Glutaredoxin-1 (GRX1) and thioredoxin-1 (TRX1) are antioxidants that can inhibit apoptosis signal-regulating kinase (ASK1). We examined levels of GRX1 and TRX1 in AD brain as well as their effects on Abeta neurotoxicity. We show an increase in GRX1 and a decrease in neuronal TRX1 in AD brains. Using SH-SY5Y cells, we demonstrate that Abeta causes an oxidation of both GRX1 and TRX1, and nuclear export of Daxx, a protein downstream of ASK1. Abeta toxicity was inhibited by insulin-like growth factor-I (IGF-I) and by overexpressing GRX1 or TRX1. Thus, Abeta neurotoxicity might be mediated by oxidation of GRX1 or TRX1 and subsequent activation of the ASK1 cascade. Deregulation of GRX1 and TRX1 antioxidant systems could be important events in AD pathogenesis.

Antioxidative and steroid systems in neurological and psychiatric disorders

A large number of neurological and psychiatric diseases like Morbus Parkinson, amyotrophic lateral sclerosis, dementia, schizophrenia and probably also affective disorders show an enhanced production of reactive oxygen species. Moreover, alterations of antioxidative systems and beneficial effects of antioxidative substances including steroid compounds such as estrogens have been described in several of these diseases. This review focuses on alterations of antioxidative systems in the course of neurological diseases and psychiatric disorders and on the differential effects of steroids on these systems in the central nervous system. Moreover, a possible clinical relevance of alterations of circulating steroids and of steroid treatment under these conditions is discussed.

Promotion of oxidative lipid membrane damage by amyloid beta proteins

Senile plaques in the cerebral parenchyma are a pathognomonic feature of Alzheimer's disease (AD) and are mainly composed of aggregated fibrillar amyloid beta (Abeta) proteins. The plaques are associated with neuronal degeneration, lipid membrane abnormalities, and chemical evidence of oxidative stress. The view that Abeta proteins cause these pathological changes has been challenged by suggestions that they have a protective function or that they are merely byproducts of the pathological process. This investigation was conducted to determine whether Abeta proteins promote or inhibit oxidative damage to lipid membranes. Using a mass spectrometric assay of oxidative lipid damage, the 42-residue form of Abeta (Abeta42) was found to accelerate the oxidative lipid damage caused by physiological concentrations of ascorbate and submicromolar concentrations of copper(II) ion. Under these conditions, Abeta42 was aggregated, but nonfibrillar. Ascorbate and copper produced H(2)O(2), but Abeta42 reduced H(2)O(2) concentrations, and its ability to accelerate oxidative damage was not affected by catalase. Lipids could be oxidized by H(2)O(2) and copper(II) in the absence of ascorbate, but only at significantly higher concentrations, and Abeta42 inhibited this reaction. These results indicate that the ability of Abeta42 to promote oxidative damage is more potent and more likely to be manifest in vivo than its ability to inhibit oxidative damage. In conjunction with prior results demonstrating that oxidatively damaged membranes cause Abeta42 to misfold and form fibrils, these results suggest a specific chemical mechanism linking Abeta42-promoted oxidative lipid damage to amyloid fibril formation.

Bitterness and toxicity in wild yam (Dioscorea spp.) tubers of Nepal

Wild yams make a significant contribution to diets of tribal people in Nepal. However, these wild tubers are unpalatable, taste bitter, produce inflammation and show occasional toxicity. Four wild yam species, which are eaten after primary treatment by Nepali aborigines, were analyzed for bitter and toxic principles. Bitter components were identified as furanoid norditerpenes (diosbulbins A and B). Diosbulbins A and B were found in the range of 0.023-0.046 and 0.151-0.442 g kg(-1), respectively. Results demonstrated that diosbulbin B, with an average value of 0.314 g kg(-1), was the principal bitter compound as compared to diosbulbin A (0.037 g kg(-1)). The toxic alkaloid, dioscorine and histamine (an allergen) were not detected in these tubers, whereas cyanogens (as HCN equivalent) content were found ranging from 3.2 to 6.0 ppm. Our results revealed that Nepali wild yam tubers are not toxic varieties, as they do not contain either toxic dioscorine or histamine and cyanogens contents were satisfactorily below the safety limits. The inflammation and occasional toxicity observed could possibly be due to the presence of high level of oxalate in these tubers. Domestic cooking methods were found to be very efficient in removing bitterness, thus making the bitter yams palatable.

Increased glutathione levels in cortical and striatal mitochondria of the R6/2 Huntington's disease mouse model

Huntington's disease (HD) is a progressive neurodegenerative disease characterized by a severe neuronal loss that occurs primarily in the neostriatum. It has been postulated that mitochondria dysfunction and oxidative stress may play significant roles in the etiology of the disease. Indeed, markers of oxidative stress damage have been detected in the brains of HD patients and in mouse models of HD. In this study, we evaluate the changes in the levels of the potent, endogenous antioxidant glutathione and enzymes involved in its metabolism or recycling in the cortex and striatum of an extensively studied HD mouse model (R6/2). In both cortex and striatum, the levels of cellular glutathione were not significantly different in the R6/2 mice when compared with littermate wild type controls. Remarkably, the levels of glutathione were significantly increased in mitochondria isolated from the cortex and striatum of R6/2 mice when compared with wild type control mice. This specific increase in the levels of glutathione in mitochondria suggests that a compensatory mechanism is induced in the R6/2 mice to protect against an increase in oxidative stress in mitochondria.

Increased oxidative damage in nuclear and mitochondrial DNA in Alzheimer's disease

Increasing evidence suggests that oxidative stress is associated with normal aging and several neurodegenerative diseases, including Alzheimer's disease (AD). Here we quantified multiple oxidized bases in nuclear and mitochondrial DNA of frontal, parietal, and temporal lobes and cerebellum from short postmortem interval AD brain and age-matched control subjects using gas chromatography/mass spectrometry with selective ion monitoring (GC/MS-SIM) and stable labeled internal standards. Nuclear and mitochondrial DNA were extracted from eight AD and eight age-matched control subjects. We found that levels of multiple oxidized bases in AD brain specimens were significantly (p < 0.05) higher in frontal, parietal, and temporal lobes compared to control subjects and that mitochondrial DNA had approximately 10-fold higher levels of oxidized bases than nuclear DNA. These data are consistent with higher levels of oxidative stress in mitochondria. Eight-hydroxyguanine, a widely studied biomarker of DNA damage, was approximately 10-fold higher than other oxidized base adducts in both AD and control subjects. DNA from temporal lobe showed the most oxidative damage, whereas cerebellum was only slightly affected in AD brains. These results suggest that oxidative damage to mitochondrial DNA may contribute to the neurodegeneration of AD.

Oxidative state in platelets and erythrocytes in aging and Alzheimer's disease

Several studies have shown involvement of peroxynitrite anion, a potent oxidative agent, in Alzheimer's disease (AD) neuropathology. Herein, we assessed in platelets and erythrocytes of AD patients, age-matched and young adults controls: thiobarbituric acid-reactive substances (TBARS) production; superoxide dismutase (SOD), nitric oxide synthase (NOS) and Na,K-ATPase activities; cyclic GMP (cGMP) content, both basal and after sodium nitroprusside (SNP) stimulation. Aging was associated with an increase in TBARS production and NOS activity, a decrease in basal cGMP content and no change in SOD and Na,K-ATPase activities. AD patients, compared to aged controls, have: increase in TBARS production and in NOS, SOD and Na,K-ATPase activities but no alteration in basal cGMP content. SNP increased cGMP platelets production in all groups. In conclusion, we demonstrated in platelets and erythrocytes a disruption in systemic modulation of oxidative stress in aging and with more intensity in AD.

Proteomic and functional analyses reveal a mitochondrial dysfunction in P301L tau transgenic mice

Transgenic mice overexpressing the P301L mutant human tau protein exhibit an accumulation of hyperphosphorylated tau and develop neurofibrillary tangles. The consequences of tau pathology were investigated here by proteomics followed by functional analysis. Mainly metabolism-related proteins including mitochondrial respiratory chain complex components, antioxidant enzymes, and synaptic proteins were identified as modified in the proteome pattern of P301L tau mice. Significantly, the reduction in mitochondrial complex V levels in the P301L tau mice revealed using proteomics was also confirmed as decreased in human P301L FTDP-17 (frontotemporal dementia with parkinsonism linked to chromosome 17) brains. Functional analysis demonstrated a mitochondrial dysfunction in P301L tau mice together with reduced NADH-ubiquinone oxidoreductase activity and, with age, impaired mitochondrial respiration and ATP synthesis. Mitochondrial dys-function was associated with higher levels of reactive oxygen species in aged transgenic mice. Increased tau pathology as in aged homozygous P301L tau mice revealed modified lipid peroxidation levels and the up-regulation of antioxidant enzymes in response to oxidative stress. Furthermore, P301L tau mitochondria displayed increased vulnerability toward beta-amyloid (Abeta) peptide insult, suggesting a synergistic action of tau and Abeta pathology on the mitochondria. Taken together, we conclude that tau pathology involves a mitochondrial and oxidative stress disorder possibly distinct from that caused by Abeta.

Oxidative stress related markers in the “VITA” and the centenarian projects

Oxidative stress seems to play an important role in the pathophysiology of Alzheimer's disease (AD). At present there are no easily accessible biochemical markers for AD. We performed activity assays for platelet MAO-B and erythrocyte Cu/Zn-SOD as well as Western blotting for these two proteins. Moreover, we assessed plasma lactoferrin and performed RFLP-analysis for the MAO-B-intron-13-polymorphism in patients from the Vienna-Transdanube Aging (VITA) and from the so called centenarian project. The first one, VITA, is a community-based cohort study of all 75 years old inhabitants of a geographical region of Vienna. The centenarian project investigates chronic care in-old patients suffering from AD. In both sexes platelet MAO-B activity increased significantly in the AD group, and Cu/Zn-SOD activity decreased, but the latter effect was significant only in females. No significant difference was found regarding plasma lactoferrin. No correlation was found between MAO-Bi13 and MAO-B platelet activity or allele MAO-Bi13 and disease frequency. These results point to the possibility that a combination of MAO-B and SOD activity levels might be useful tools for an early diagnosis of AD.

Effects of steroid hormones on catalase activity in neuronal and glial cell systems

The aim of the present study was to determine short- (1 and 3 h) and long-term (24 h) effects of glucocorticoids [GCs; corticosterone (CORT), dexamethasone (DEX) and 6-methylprednisolone (6-MP)] and gonadal steroids [GSs; 17beta-estradiol (E2), progesterone (PROG) and testosterone (TEST)] on the activity of the hydrogen-peroxide-detoxifying enzyme catalase (CAT) in neural hippocampal HT22 cells and glial C6 cells because such effects have been described in peripheral organ systems. In HT22 cells, only long-term treatment with glucocorticoids (10(-5) M) induced effects on catalase activity, whereas gonadal steroids (10(-5) M) affected catalase activity after both short- and long-term incubations. At a lower concentration of 10(-7) M, glucocorticoids exerted only short-term treatment effects on catalase activity, while gonadal steroids (10(-7) M) affected the enzyme activity after short- and long-term treatments. In C6 glial cells, both glucocorticoids (10(-7) M) and gonadal steroids (10(-7) M) induced short- and long-term treatment effects. Thereby, our data show that steroid hormones differentially regulate catalase activity in models of the central nervous system (CNS) in a time- and steroid-dependent manner.

A chronic Alzheimer's model evoked by mitochondrial poison sodium azide for pharmacological investigations

Alzheimer's disease (AD) is a neurodegenerative disorder and accounts for 50-70% of all dementia cases affecting more than 12 million people worldwide. The primary cause of the disease is presently unknown; however, much evidence suggests the involvement of mitochondrial damage. Selective reduction of complex IV activity is present in post-mortem AD brains. Inhibition of this complex could be evoked by chronic sodium azide (NaN(3)) administration in animals. Partial inhibition of the mitochondrial respiratory chain produces free radicals, diminishes aerobic energy metabolism and causes excitotoxic damage creating a deleterious spiral causing neurodegeneration, a pathological process considered to underlie AD. In the present study SPRD rats were treated by various doses of NaN(3) (24-51 mg/kg per day) for 31 days via subcutaneously implanted osmotic minipumps. We have found the proper dose and duration of NaN(3) treatment which was able to cause easily detectable and reproducible cognitive changes. Animals receiving Na-azide doses under 45 mg/kg daily did not show cognitive deficits, but minor histopathological changes were already present. Doses above 45 mg/kg per day proved to be toxic in 4-week-long application causing mortality. NaN(3) dose of 45 mg/kg per day caused cognitive deficit in Morris water maze and passive avoidance tests and a decrease of spontaneous exploratory activity in open field. Histopathological but not biochemical changes were present: dendritic thickening, nerve cell loss, corkscrew-like dendrites and pycnotic nerve cells. The cognitive, behavioural and histopathological features were reproducible. The chronic Na-azide-induced mitochondrial poisoning is suitable for producing AD-like symptoms in rats and testing neuroprotective drug candidates by preventive or curative applications.

Antioxidant treatment in Alzheimer's disease: current state

Accumulating data from experimental and human studies indicate that oxidative stress (OS) plays a major role in the pathogenesis of Alzheimer's disease (AD). The production of reactive oxygen species (ROS), which leads to OS, can occur very early, even before the appearance of symptoms and molecular events (beta-amyloid plaques and neurofibrillary tangles), leading to tissue damage via several different cellular molecular pathways. ROS can cause damage to cardinal cellular components such as lipids, proteins, and nucleic acids (e.g., RNA, DNA), causing cell death by modes of necrosis or apoptosis. The damage can become more widespread because of the weakened cellular antioxidant defense systems. Therefore, treatment with antioxidants might theoretically act to prevent propagation of tissue damage and improve both survival and neurological outcome. Indeed, several studies preformed to date examined whether dietary intake of several antioxidants, mainly vitamins, might prevent or reduce the progression of AD. Although a few of the antioxidants showed some efficacy in these trials, no answer is yet available as to whether antioxidants are truly protective against AD. Reasons for these results might include, in part, blood-brain barrier (BBB) permeability, inappropriate timing of administration, or suboptimal drug levels at the target site in the central nervous system. Thus, antioxidant cocktails or antioxidants combined with other drugs may have more successful synergistic effects. Further, well-designed intervention, as well as observational investigations based on large cohorts studied over a long period of time with several methods for assessing antioxidant exposure, including relation to BBB penetration, are needed to test this hypothesis.

Antisense directed at the Abeta region of APP decreases brain oxidative markers in aged senescence accelerated mice

Amyloid beta-peptide (Abeta) is known to induce free radical-mediated oxidative stress in the brain. Free radical-mediated damage to the neuronal membrane components has been implicated in the etiology of Alzheimer's disease (AD). Abeta is produced by proteolytic processing of the amyloid precursor protein (APP). The senescence accelerated mouse prone 8 (SAMP8) strain was developed by phenotypic selection from a common genetic pool. The SAMP8 strain exhibits age-related deterioration in memory and learning as well as Abeta accumulation, and it is considered an effective model for studying brain aging in accelerated senescence. Previous research has shown that a phosphorothiolated antisense oligonucleotide directed against the Abeta region of APP decreases the expression of APP and reverses deficits in learning and memory in aged SAMP8 mice. Consistent with other reports, our previous study showed that 12-month-old SAMP8 mice have increased levels of oxidative stress markers in the brain compared with that in brains from 4-month-old SAMP8 mice. In the current study, 12-month-old SAMP8 mice were treated with antisense oligonucleotide directed against the Abeta region of APP, and the oxidative markers in brain were decreased significantly. Therefore, we conclude that Abeta may contribute to the oxidative stress found in aged SAMP8 mice that have learning and memory impairments. These results are discussed in reference to AD.

Oxidative stress impairs glutamate uptake in fibroblasts from patients with Alzheimer's disease

Oxidative stress has been demonstrated in Alzheimer's disease (AD) brain and may affect glutamate transport (GT), thereby leading to excitotoxic neuronal death. Since oxidative stress markers have been shown also in peripheral tissues, we investigated possible GT alterations in fibroblast cultures obtained from 18 patients with AD and 15 control patients and analyzed the effects of the lipoperoxidation product 4-hydroxynonenal (4-HNE) and antioxidants. Basal GT was decreased by 60% in fibroblasts from patients with AD versus control patients. Exposure to HNE did not affect GT in control patients, but it reduced GT by 50% in patients with AD, without any concomitant change in cell viability; conversely, HNE exposure induced a larger increase in ROS intracellular levels in AD than in control fibroblasts. Glutathione and N-acetylcysteine completely blocked 4-HNE effects and also increased basal uptake in AD cells. Moreover, inhibition of glutathione synthesis in control fibroblasts by pretreatment with buthionine sulfoximine resulted in GT reduction (40%) and an increase in ROS levels after exposure to 4-HNE. Nevertheless, since there are no differences between GSH basal level in controls and patients with AD, the alteration of other antioxidant systems cannot be excluded. Our study supports the hypothesis of a systemic impairment of GT in AD, possibly linked to oxidative stress and to reduced antioxidant defenses, which may be partially reversed by antioxidant treatment. Therefore, we suggest fibroblast cultures as a tool for exploring pathogenetic mechanisms and possible therapeutic strategies in patients with AD.

The Catalase -262C/T Promoter Polymorphism and Aging Phenotypes

A low level of the central antioxidant enzyme catalase has been suggested to be a risk factor for diseases influenced by oxidative stress. In this study, we investigated the possible association of the catalase -262C/T polymorphism with survival, physical and cognitive functioning, and a number of oxidative stress-mediated disorders. The study population was 2223 Danish individuals, aged 45-93 years, drawn from three population-based surveys. The results suggest that the catalase -262C/T polymorphism is not associated with either survival, or the majority of the age-related phenotypes investigated. However, our data indicate a statistical significant association of TT homozygosity with improved physical functioning as well as a trend of the T allele conferring an improved general cognitive functioning, although these results did not remain significant after correcting for multiple testing. The results raise the hypothesis that the catalase -262T allele serves as protection against neurodegenerative and physical decline, although replication in other studies is warranted for confirmation of these findings.

Hypericum perforatum extract demonstrates antioxidant properties against elevated rat brain oxidative status induced by amnestic dose of scopolamine

This study was designed to investigate if the impairment of learning and memory induced by acute administration of scopolamine (1.4 mg/kg ip) in rats is associated with altered brain oxidative stress status. The passive avoidance paradigm was used to assess retrieval memory of rats after scopolamine treatment. Following retrieval testing, biochemical assessments of malondialdehyde (MDA), glutathione peroxidase (GSHPx), glutathione (GSH), and superoxide dismutase (SOD) levels/activities as oxidative stress indices were performed. This study also investigated the effect of acute administration of Hypericum perforatum extract (4.0, 8.0, 12.0, and 25.0 mg/kg ip), containing flavonoids with documented antioxidant activity, on brain oxidative status of nai;ve rats treated with amnestic dose of scopolamine. Results showed that administration of 1.4 mg/kg of scopolamine impaired retrieval memory of rats and that such amnesia was associated with elevated MDA and reduced GSH brain levels. In nai;ve rats, which have not been exposed to conditioned fear, scopolamine administration also increased MDA and reduced GSH levels, although with an increase in brain GSHPx activity. Pretreatment of the animals with Hypericum extract (4, 8, and 12 mg/kg) resulted in an antioxidant effect through altering brain MDA, GSHPx, and/or GSH level/activity. Since oxidative stress is implicated in the pathophysiology of dementia, the findings of this study may substantiate the value of scopolamine-induced amnesia in rats as a valid animal model to screen for drugs with potential therapeutic benefit in dementia. Exposure of animals to conditioned fear may be suggested to impair the balance between the rate of lipid peroxidation and the activation of GSHPx as a compensatory antioxidant protective mechanism. It is also concluded that low doses of Hypericum extract, demonstrating antioxidant activity, may be of value for demented patients exhibiting elevated brain oxidative status. Since depression commonly coexists with dementia, Hypericum extract as a drug with documented antidepressant action may also be a better alternative than several other antidepressant medications that have not been evaluated to test their effect on brain oxidative status during amnesia.

Important role of striatal catalase in aging- and reserpine-induced oral dyskinesia

Tardive dyskinesia, the most serious iatrogenic movement disorder, has been tentatively associated with nigrostriatal dopaminergic supersensitivity and with oxidative stress. It is also suggested that long-term neuroleptic treatment does not cause oral dyskinesia (OD), but interacts with some substrate of brain aging, resulting in the premature emergence of OD, that can occur spontaneously with aging. In order to investigate a possible role of nigrostriatal dopaminergic supersensitivity and of oxidative stress in aging- and reserpine-induced OD, the stereotyped behavior induced by dopaminergic agonists, a functional index of dopaminergic striatal activity, as well as the striatal antioxidant enzymes glutathione peroxidase and catalase were assessed. We demonstrate that, opposite to normotensive Wistar rats (NWR), spontaneously hypertensive rats (SHR) do not develop aging- or reserpine-OD. There were no differences between NWR and SHR in stereotyped behavior or in striatal glutathione peroxidase activity. Adult and old SHR presented higher striatal catalase activity relative to NWR, and aging increased it only in SHR. The catalase inhibitor aminotriazole reverted the absence of aging- and reserpine-induced OD in SHR. Our results suggest an important role of striatal catalase in the development of reserpine- and aging-induced OD.