Amyloid beta-peptide (1-40)-mediated oxidative stress in cultured hippocampal neurons. Protein carbonyl formation, CK BB expression, and the level of Cu, Zn, and Mn SOD mRNA

Restoration of energy homeostasis under oxidative stress: Duo synergistic AMPK pathways regulating arginine kinases

Rapid depletion of cellular ATP can occur by oxidative stress induced by reactive oxygen species (ROS). Maintaining energy homeostasis requires the key molecular components AMP-activated protein kinase (AMPK) and arginine kinase (AK), an invertebrate orthologue of the mammalian creatine kinase (CK). Here, we deciphered two independent and synergistic pathways of AMPK acting on AK by using the beetle Tribolium castaneum as a model system. First, AMPK acts on transcriptional factor forkhead box O (FOXO) leading to phosphorylation and nuclear translocation of the FOXO. The phospho-FOXO directly promotes the expression of AK upon oxidative stress. Concomitantly, AMPK directly phosphorylates the AK to switch the direction of enzymatic catalysis for rapid production of ATP from the phosphoarginine-arginine pool. Further in vitro assays revealed that Sf9 cells expressing phospho-deficient AK mutants displayed the lower ATP/ADP ratio and cell viability under paraquat-induced oxidative stress conditions when compared with Sf9 cells expressing wild-type AKs. Additionally, the AMPK-FOXO-CK pathway is also involved in the restoration of ATP homeostasis under oxidative stress in mammalian HEK293 cells. Overall, we provide evidence that two distinct AMPK-AK pathways, transcriptional and post-translational regulations, are coherent responders to acute oxidative stresses and distinguished from classical AMPK-mediated long-term metabolic adaptations to energy challenge.

Oxidative Stress in Brain in Amnestic Mild Cognitive Impairment

Amnestic mild cognitive impairment (MCI), arguably the earliest clinical stage of Alzheimer disease (AD), is characterized by normal activities of daily living but with memory issues but no dementia. Oxidative stress, with consequent damaged key proteins and lipids, are prominent even in this early state of AD. This review article outlines oxidative stress in MCI and how this can account for neuronal loss and potential therapeutic strategies to slow progression to AD.

Modifiable, Non-Modifiable, and Clinical Factors Associated with Progression of Alzheimer's Disease

There is an extensive literature relating to factors associated with the development of Alzheimer's disease (AD), but less is known about factors which may contribute to its progression. This review examined the literature with regard to 15 factors which were suggested by PubMed search to be positively associated with the cognitive and/or neuropathological progression of AD. The factors were grouped as potentially modifiable (vascular risk factors, comorbidities, malnutrition, educational level, inflammation, and oxidative stress), non-modifiable (age at clinical onset, family history of dementia, gender, Apolipoprotein E ɛ4, genetic variants, and altered gene regulation), and clinical (baseline cognitive level, neuropsychiatric symptoms, and extrapyramidal signs). Although conflicting results were found for the majority of factors, a positive association was found in nearly all studies which investigated the relationship of six factors to AD progression: malnutrition, genetic variants, altered gene regulation, baseline cognitive level, neuropsychiatric symptoms, and extrapyramidal signs. Whether these or other factors which have been suggested to be associated with AD progression actually influence the rate of decline of AD patients is unclear. Therapeutic approaches which include addressing of modifiable factors associated with AD progression should be considered.

Role of Catalase in Oxidative Stress- and Age-Associated Degenerative Diseases

Reactive species produced in the cell during normal cellular metabolism can chemically react with cellular biomolecules such as nucleic acids, proteins, and lipids, thereby causing their oxidative modifications leading to alterations in their compositions and potential damage to their cellular activities. Fortunately, cells have evolved several antioxidant defense mechanisms (as metabolites, vitamins, and enzymes) to neutralize or mitigate the harmful effect of reactive species and/or their byproducts. Any perturbation in the balance in the level of antioxidants and the reactive species results in a physiological condition called “oxidative stress.” A catalase is one of the crucial antioxidant enzymes that mitigates oxidative stress to a considerable extent by destroying cellular hydrogen peroxide to produce water and oxygen. Deficiency or malfunction of catalase is postulated to be related to the pathogenesis of many age-associated degenerative diseases like diabetes mellitus, hypertension, anemia, vitiligo, Alzheimer's disease, Parkinson's disease, bipolar disorder, cancer, and schizophrenia. Therefore, efforts are being undertaken in many laboratories to explore its use as a potential drug for the treatment of such diseases. This paper describes the direct and indirect involvement of deficiency and/or modification of catalase in the pathogenesis of some important diseases such as diabetes mellitus, Alzheimer's disease, Parkinson's disease, vitiligo, and acatalasemia. Details on the efforts exploring the potential treatment of these diseases using a catalase as a protein therapeutic agent have also been described.

Trigonelline protects hippocampus against intracerebral Aβ(1-40) as a model of Alzheimer's disease in the rat: insights into underlying mechanisms

Alzheimer's disease (AD) is a chronic neurodegenerative disorder and the most common phenotype of dementia. Trigonelline is an alkaloid found in medicinal plants such as fenugreek seeds and coffee beans with neuroprotective potential and according to existing evidences, a favorable agent for treatment of neurodegenerative disorders. In this study, the possible protective effect of trigonelline against intracerebral Aβ(1-40) as a model of AD in the rat was investigated. For induction of AD, aggregated A(1-40) (10 μg/2 휇l for each side) was bilaterally microinjected into the hippocampal CA1 area. Trigonelline was administered p.o. at a dose of 100 mg/kg. The results showed that trigonelline pretreatment of Aβ-microinjected rats significantly improves spatial recognition memory in Y maze and performance in novel object recognition (NOR) task, mitigates hippocampal malondialdehyde (MDA), protein carbonyl, lactate dehydrogenase (LDH), and improves mitochondrial membrane potential (MMP), glutathione (GSH), and superoxide dismutase (SOD) with no significant change of catalase activity, nitrite level, caspase 3 activity, and DNA fragmentation. Additionally, trigonelline ameliorated hippocampal levels of glial fibrillary acidic protein (GFAP), S100b, cyclooxygenase 2 (Cox2), tumor necrosis factor α (TNFα), and interleukin 6 (IL-6) with no significant alteration of inducible nitric oxide synthase (iNOS). In addition, trigonelline pretreatment prevented loss of hippocampal CA1 neurons in Aβ-microinjected group. Therefore, our results suggest that trigonelline pretreatment in Aβ model of AD could improve cognition and is capable to alleviate neuronal loss through suppressing oxidative stress, astrocyte activity, and inflammation and also through preservation of mitochondrial integrity.

Involvement of calpain in the neuropathogenesis of Alzheimer's disease

Alzheimer’s disease (AD) is the most common (60% to 80%) age‐related disease associated with dementia and is characterized by a deterioration of behavioral and cognitive capacities leading to death in few years after diagnosis, mainly due to complications from chronic illness. The characteristic hallmarks of the disease are extracellular senile plaques (SPs) and intracellular neurofibrillary tangles (NFTs) with neuropil threads, which are a direct result of amyloid precursor protein (APP) processing to Aβ, and τ hyperphosphorylation. However, many indirect underlying processes play a role in this event. One of these underlying mechanisms leading to these histological hallmarks is the uncontrolled hyperactivation of a family of cysteine proteases called calpains. Under normal physiological condition calpains participate in many processes of cells’ life and their activation is tightly controlled. However, with an increase in age, increased oxidative stress and other excitotoxicity assaults, this regulatory system becomes impaired and result in increased activation of these proteases involving them in the pathogenesis of various diseases including neurodegeneration like AD. Reviewed here is a pool of data on the implication of calpains in the pathogenesis of AD, the underlying molecular mechanism, and the potential of targeting these enzymes for AD therapeutics.

Oxidative Stress, Amyloid-β Peptide, and Altered Key Molecular Pathways in the Pathogenesis and Progression of Alzheimer's Disease

Oxidative stress is implicated in the pathogenesis and progression of Alzheimer's disease (AD) and its earlier stage, amnestic mild cognitive impairment (aMCI). One source of oxidative stress in AD and aMCI brains is that associated with amyloid-β peptide, Aβ1-42 oligomers. Our laboratory first showed in AD elevated oxidative stress occurred in brain regions rich in Aβ1-42, but not in Aβ1-42-poor regions, and was among the first to demonstrate Aβ peptides led to lipid peroxidation (indexed by HNE) in AD and aMCI brains. Oxidatively modified proteins have decreased function and contribute to damaged key biochemical and metabolic pathways in which these proteins normally play a role. Identification of oxidatively modified brain proteins by the methods of redox proteomics was pioneered in the Butterfield laboratory. Four recurring altered pathways secondary to oxidative damage in brain from persons with AD, aMCI, or Down syndrome with AD are interrelated and contribute to neuronal death. This "Quadrilateral of Neuronal Death" includes altered: glucose metabolism, mTOR activation, proteostasis network, and protein phosphorylation. Some of these pathways are altered even in brains of persons with preclinical AD. We opine that targeting these pathways pharmacologically and with lifestyle changes potentially may provide strategies to slow or perhaps one day, prevent, progression or development of this devastating dementing disorder. This invited review outlines both in vitro and in vivo studies from the Butterfield laboratory related to Aβ1-42 and AD and discusses the importance and implications of some of the major achievements of the Butterfield laboratory in AD research.

A Novel Genetic Screen Identifies Modifiers of Age-Dependent Amyloid β Toxicity in the Drosophila Brain

The accumulation of amyloid β peptide (Aβ) in the brain of Alzheimer's disease (AD) patients begins many years before clinical onset. Such process has been proposed to be pathogenic through the toxicity of Aβ soluble oligomers leading to synaptic dysfunction, phospho-tau aggregation and neuronal loss. Yet, a massive accumulation of Aβ can be found in approximately 30% of aged individuals with preserved cognitive function. Therefore, within the frame of the "amyloid hypothesis", compensatory mechanisms and/or additional neurotoxic or protective factors need to be considered and investigated. Here we describe a modifier genetic screen in Drosophila designed to identify genes that modulate toxicity of Aβ42 in the CNS. The expression of Aβ42 led to its accumulation in the brain and a moderate impairment of negative geotaxis at 18 days post-eclosion (d.p.e) as compared with genetic or parental controls. These flies were mated with a collection of lines carrying chromosomal deletions and negative geotaxis was assessed at 5 and 18 d.p.e. Our screen is the first to take into account all of the following features, relevant to sporadic AD: (1) pan-neuronal expression of wild-type Aβ42; (2) a quantifiable complex behavior; (3) Aβ neurotoxicity associated with progressive accumulation of the peptide; and (4) improvement or worsening of climbing ability only evident in aged animals. One hundred and ninety-nine deficiency (Df) lines accounting for ~6300 genes were analyzed. Six lines, including the deletion of 52 Drosophila genes with human orthologs, significantly modified Aβ42 neurotoxicity in 18-day-old flies. So far, we have validated CG11796 and identified CG17249 as a strong candidate (whose human orthologs are HPD and PRCC, respectively) by using RNAi or mutant hemizygous lines. PRCC encodes proline-rich protein PRCC (ppPRCC) of unknown function associated with papillary renal cell carcinoma. HPD encodes 4-hydroxyphenylpyruvate dioxygenase (HPPD), a key enzyme in tyrosine degradation whose Df causes autosomal recessive Tyrosinemia type 3, characterized by mental retardation. Interestingly, lines with a partial Df of HPD ortholog showed increased intraneuronal accumulation of Aβ42 that coincided with geotaxis impairment. These previously undetected modifiers of Aβ42 neurotoxicity in Drosophila warrant further study to validate their possible role and significance in the pathogenesis of sporadic AD.

The 2013 SFRBM discovery award: selected discoveries from the butterfield laboratory of oxidative stress and its sequela in brain in cognitive disorders exemplified by Alzheimer disease and chemotherapy induced cognitive impairment

This retrospective review on discoveries of the roles of oxidative stress in brain of subjects with Alzheimer disease (AD) and animal models thereof as well as brain from animal models of chemotherapy-induced cognitive impairment (CICI) results from the author receiving the 2013 Discovery Award from the Society for Free Radical Biology and Medicine. The paper reviews our laboratory's discovery of protein oxidation and lipid peroxidation in AD brain regions rich in amyloid β-peptide (Aβ) but not in Aβ-poor cerebellum; redox proteomics as a means to identify oxidatively modified brain proteins in AD and its earlier forms that are consistent with the pathology, biochemistry, and clinical presentation of these disorders; how Aβ in in vivo, ex vivo, and in vitro studies can lead to oxidative modification of key proteins that also are oxidatively modified in AD brain; the role of the single methionine residue of Aβ(1-42) in these processes; and some of the potential mechanisms in the pathogenesis and progression of AD. CICI affects a significant fraction of the 14 million American cancer survivors, and due to diminished cognitive function, reduced quality of life of the persons with CICI (called "chemobrain" by patients) often results. A proposed mechanism for CICI employed the prototypical ROS-generating and non-blood brain barrier (BBB)-penetrating chemotherapeutic agent doxorubicin (Dox, also called adriamycin, ADR). Because of the quinone moiety within the structure of Dox, this agent undergoes redox cycling to produce superoxide free radical peripherally. This, in turn, leads to oxidative modification of the key plasma protein, apolipoprotein A1 (ApoA1). Oxidized ApoA1 leads to elevated peripheral TNFα, a proinflammatory cytokine that crosses the BBB to induce oxidative stress in brain parenchyma that affects negatively brain mitochondria. This subsequently leads to apoptotic cell death resulting in CICI. This review outlines aspects of CICI consistent with the clinical presentation, biochemistry, and pathology of this disorder. To the author's knowledge this is the only plausible and self-consistent mechanism to explain CICI. These two different disorders of the CNS affect millions of persons worldwide. Both AD and CICI share free radical-mediated oxidative stress in brain, but the source of oxidative stress is not the same. Continued research is necessary to better understand both AD and CICI. The discoveries about these disorders from the Butterfield Laboratory that led to the 2013 Discovery Award from the Society of Free Radical and Medicine provide a significant foundation from which this future research can be launched.

Oxidative stress in Alzheimer's disease: Primary villain or physiological by-product?

The prevalence of Alzheimer's disease (AD) is increasing rapidly worldwide due to an ageing population and largely ineffective treatments. In AD cognitive decline is due to progressive neuron loss that begins in the medial temporal lobe and spreads through many brain regions. Despite intense research the pathogenesis of the common sporadic form of AD remains largely unknown. The popular amyloid cascade hypothesis suggests that the accumulation of soluble oligomers of beta amyloid peptides (Aβ) initiates a series of events that cause neuronal loss. Among their putative toxic effects, Aβ oligomers are thought to act as pro-oxidants combining with redox-active metals to produce excessive reactive oxygen and nitrogen species. However, to date the experimental therapies that reduce Aβ load in AD have failed to halt cognitive decline. Another hypothesis proposed by the late Mark Smith and colleagues is that oxidative stress, rather than Aβ, precipitates the pathogenesis of AD. That is, Aβ and microtubule-associated protein tau are upregulated to address the redox imbalance in the AD brain. As the disease progresses, excess Aβ and tau oligomerise to further accelerate the disease process. Here, we discuss redox balance in the human brain and how this balance is affected by ageing. We then discuss where oxidative stress is most likely to act in the disease process and the potential for intervention to reduce its effects.

Extracellular superoxide dismutase in cultured astrocytes: decrease in cell-surface activity and increase in medium activity by lipopolysaccharide-stimulation

Under pathological conditions such as ischemia/reperfusion, a large amount of superoxide anion (O(2) (-)) is produced and released in brain. Among three isozymes of superoxide dismutase (SOD), extracellular (EC)-SOD, known to be excreted outside cells and bound to extracellular matrix, should play a role to detoxify O(2) (-) in extracellular space; however, a little is known about EC-SOD in brain. In order to evaluate the SOD activity in extracellular space of CNS as direct as possible, we attempted to measure the cell-surface SOD activity on primary cultured rat brain cells by the inhibition of color development of a water-soluble tetrazolium due to O(2) (-) generation by xanthine oxidase/hypoxanthine added into extracellular medium of intact cells. The cell-surface SOD activity on cultured neuron and microglia was below the detection limit; however, that on cultured astrocyte was high enough to measure. By means of RT-PCR, all mRNA of three isozymes of SOD could be detected in the three types of the cells examined; however, the semi-quantitative analysis revealed that the level of EC-SOD mRNA in astrocytes was significantly higher than that in neurons and microglia. When astrocytes were stimulated with lipopolysaccharide (LPS) for 12-24 h, the cell-surface SOD activity decreased to a half, whereas the activity recovered after 36-48 h. The decrease in the activity was dependent on the LPS concentration. On the other hand, the SOD activity in the medium increased by the LPS-stimulation in a dose dependent manner; suggesting that the SOD protein localized on cell-surface, probably EC-SOD, was released into the medium. These results suggest that EC-SOD of astrocyte play a role for detoxification of extracellular O(2) (-) and the regulation of EC-SOD in astrocytes may contribute to the defensive mechanism against oxidative stress in brain.

Early changes in cerebral oxidative stress and apoptotic neuronal injury after various flows for selective cerebral perfusion in piglets

BACKGROUND

The impact of various flows for selective cerebral perfusion (SCP) on cerebral oxidative stress in the immature brain is unknown. We examined early changes in cerebral markers of oxidative damage, apoptotic protein activation and histological outcome after different flows for SCP in a piglet model of deep hypothermic circulatory arrest (DHCA).

METHODS

Twenty piglets, randomly divided into four groups (each n = 5), were placed on cardiopulmonary bypass (CPB) at 20°C, then underwent DHCA for 60 minutes. SCP was conducted at flow rates of 0, 25, 50 and 80 ml·kg(-1)·min(-1) through the innominate artery in the DHCA, SCP 25, SCP 50, and SCP 80 groups, respectively. The animals were killed at 2 hours off CPB. Brain tissues were examined for the activity of SOD, MDA and caspase-3, and histological damage was quantitatively assayed by light microscopic examinations.

RESULTS

There were no significant differences in the activities of SOD, MDA and the SOD/MDA index between the groups. Caspase-3 activity significantly decreased in the SCP 25, SCP 50 and SCP 80 groups compared with the DHCA group. However, the caspase-3 level was higher in the SCP 80 group than in the SCP 25 and SCP 50 group. There were no significant correlations between MDA, SOD, SOD/MDA index and caspase-3.

CONCLUSIONS

In this acute model, under different flows for SCP, cerebral MDA and SOD activities show no change, whereas activated caspase-3 has a marked change. There was no relationship between oxidative stress, indicated by MDA and SOD, and apoptotic protein activation in the early phase after DHCA.

Association between frontal cortex oxidative damage and beta-amyloid as a function of age in Down syndrome

Down syndrome (DS) is the most common genetic cause of intellectual disability in children, and the number of adults with DS reaching old age is increasing. By the age of 40 years, virtually all people with DS have sufficient neuropathology for a postmortem diagnosis of Alzheimer disease (AD). Trisomy 21 in DS leads to an overexpression of many proteins, of which at least two are involved in oxidative stress and AD: superoxide dismutase 1 (SOD1) and amyloid precursor protein (APP). In this study, we tested the hypothesis that DS brains with neuropathological hallmarks of AD have more oxidative and nitrosative stress than those with DS but without significant AD pathology, as compared with similarly aged-matched non-DS controls. The frontal cortex was examined in 70 autopsy cases (n=29 control and n=41 DS). By ELISA, we quantified soluble and insoluble Aβ40 and Aβ42, as well as oligomers. Oxidative and nitrosative stress levels (protein carbonyls, 4-hydroxy-2-trans-nonenal (HNE)-bound proteins, and 3-nitrotyrosine) were measured by slot-blot. We found that soluble and insoluble amyloid beta peptide (Aβ) and oligomers increase as a function of age in DS frontal cortex. Of the oxidative stress markers, HNE-bound proteins were increased overall in DS. Protein carbonyls were correlated with Aβ40 levels. These results suggest that oxidative damage, but not nitrosative stress, may contribute to the onset and progression of AD pathogenesis in DS. Conceivably, treatment with antioxidants may provide a point of intervention to slow pathological alterations in DS.

Subcellular and metabolic examination of amyloid-beta peptides in Alzheimer disease pathogenesis: evidence for Abeta(25-35)

Amyloid-beta peptide (Abeta) is a central player in the pathogenesis and diagnosis of Alzheimer disease. It aggregates to form the core of Alzheimer disease-associated plaques found in coordination with tau deposits in diseased individuals. Despite this clinical relevance, no single hypothesis satisfies and explicates the role of Abeta in toxicity and progression of the disease. To explore this area, investigators have focused on mechanisms of cellular dysfunction, aggregation, and maladaptive responses. Extensive research has been conducted using various methodologies to investigate Abeta peptides and oligomers, and these multiple facets have provided a wealth of data from specific models. Notably, the utility of each experiment must be considered in regards to the brain environment. The use of Abeta(25-35) in studies of cellular dysfunction has provided data indicating that the peptide is indeed responsible for multiple disturbances to cellular integrity. We will review how Abeta peptide induces oxidative stress and calcium homeostasis, and how multiple enzymes are deleteriously impacted by Abeta(25-35). Understanding and discussing the origin and properties of Abeta peptides is essential to evaluating their effects on various intracellular metabolic processes. Attention will also be specifically directed to metabolic compartmentation in affected brain cells, including mitochondrial, cytosolic, nuclear, and lysosomal enzymes.

Amyloid toxicity in skeletal myoblasts: Implications for inclusion-body myositis

Skeletal muscle disorder, inclusion-body myositis (IBM) has been known for accumulation of amyloid characteristic proteins in muscle. To understand the biophysical basis of IBM, the interaction of amyloid fibrils with skeletal myoblast cells (SMC) has been studied in vitro. Synthetic insulin fibrils and Abeta(25-35) fibrils were used for this investigation. From the saturation binding analysis, the calculated dissociation constant (K(d)) for insulin fibril and Abeta(25-35) fibrils were 69.37+/-11.17nM and 115.60+/-12.17nM, respectively. The fibrillar insulin comparatively has higher affinity binding to SMC than Abeta fibrils. The competitive binding studies with native insulin showed that the amount of bound insulin fibril was significantly decreased due to displacement of native insulin. However, the presence of native insulin is not altered the binding of beta-amyloid fibril. The cytotoxicity of insulin amyloid intermediates was measured. The pre-fibrillar intermediates of insulin showed significant toxicity (35%) as compared to matured fibrils. Myoblast treated with beta-amyloid fibrils showed more oxidative damage than the insulin fibril. Cell differentiating action of amyloidic insulin was assayed by creatine kinase activity. The insulin fibril treated cells differentiated more slowly compared to native insulin. However, beta-amyloid fibrils do not show cell differentiation property. These findings reinforce the hypothesis that accumulation of amyloid related proteins is significant for the pathological events that could lead to muscle degeneration and weakness in IBM.

Increase in Expression Levels and Resistance to Sulfhydryl Oxidation of Peroxiredoxin Isoforms in Amyloid β-Resistant Nerve Cells

Peroxiredoxins (Prxs) are a ubiquitously expressed family of thiol peroxidases that reduce hydrogen peroxide, peroxynitrite, and hydroperoxides using a highly conserved cysteine. There is substantial evidence that oxidative stress elicited by amyloid beta (Abeta) accumulation is a causative factor in the pathogenesis of Alzheimer disease (AD). Here we show that Abeta-resistant PC12 cell lines exhibit increased expression of multiple Prx isoforms with reduced cysteine oxidation. Abeta-resistant PC12 cells also display higher levels of thioredoxin and thioredoxin reductase, two enzymes critical for maintaining Prx activity. PC12 cells and rat primary hippocampal neurons transfected with wild type Prx1 exhibit increased Abeta resistance, whereas mutant Prx1, lacking a catalytic cysteine, confers no protection. Using an antibody that specifically recognizes sulfinylated and sulfonylated Prxs, it is demonstrated that primary rat cortical nerve cells exposed to Abeta display a time-dependent increase in cysteine oxidation of the catalytic site of Prxs that can be blocked by the addition of the thiol-antioxidant N-acetylcysteine. In support of previous findings, expression of Prx1 is higher in post-mortem human AD cortex tissues than in age-matched controls. In addition, two-dimensional gel electrophoresis and mass spectrometry analysis revealed that Prx2 exists in a more oxidized state in AD brains than in control brains. These findings suggest that increased Prx expression and resistance to sulfhydryl oxidation in Abeta-resistant nerve cells is a compensatory response to the oxidative stress initiated by chronic pro-oxidant Abeta exposure.

Proteomic identification of brain proteins in the canine model of human aging following a long-term treatment with antioxidants and a program of behavioral enrichment: relevance to Alzheimer's disease

Aging and age-related disorders such as Alzheimer's disease (AD) are usually accompanied by oxidative stress as one of the main mechanisms contributing to neurodegeneration and cognitive decline. Aging canines develop cognitive dysfunction and neuropathology similar to those seen in humans, and the use of antioxidants results in reductions in oxidative damage and in improvement in cognitive function in this canine model of human aging. In the present study, the effect of a long-term treatment with an antioxidant-fortified diet and a program of behavioral enrichment on oxidative damage was studied in aged canines. To identify the neurobiological mechanisms underlying these treatment effects, the parietal cortex from 23 beagle dogs (8.1-12.4 years) were treated for 2.8 years in one of four treatment groups: i.e., control food-control behavioral enrichment (CC); control food-behavioral enrichment (CE); antioxidant food-control behavioral enrichment (CA); enriched environment-antioxidant-fortified food (EA). We analyzed the levels of the oxidative stress biomarkers, i.e., protein carbonyls, 3-nitrotyrosine (3-NT), and the lipid peroxidation product, 4-hydroxynonenal (HNE), and observed a decrease in their levels on all treatments when compared to control, with the most significant effects found in the combined treatment, EA. Since EA treatment was most effective, we also carried out a comparative proteomics study to identify specific brain proteins that were differentially expressed and used a parallel redox proteomics approach to identify specific brain proteins that were less oxidized following EA. The specific protein carbonyl levels of glutamate dehydrogenase [NAD (P)], glyceraldehyde-3-phosphate dehydrogenase (GAPDH), alpha-enolase, neurofilament triplet L protein, glutathione-S-transferase (GST) and fascin actin bundling protein were significantly reduced in brain of EA-treated dogs compared to control. We also observed significant increases in expression of Cu/Zn superoxide dismutase, fructose-bisphosphate aldolase C, creatine kinase, glutamate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase. The increased expression of these proteins and in particular Cu/Zn SOD correlated with improved cognitive function. In addition, there was a significant increase in the enzymatic activities of glutathione-S-transferase (GST) and total superoxide dismutase (SOD), and significant increase in the protein levels of heme oxygenase (HO-1) in EA treated dogs compared to control. These findings suggest that the combined treatment reduces the levels of oxidative damage and improves the antioxidant reserve systems in the aging canine brain, and may contribute to improvements in learning and memory. These observations provide insights into a possible neurobiological mechanism underlying the effects of the combined treatment. These results support the combination treatments as a possible therapeutic approach that could be translated to the aging human population who are at risk for age-related neurodegenerative disorders, including Alzheimer's disease.

Melatonin in Alzheimer's disease and other neurodegenerative disorders

Increased oxidative stress and mitochondrial dysfunction have been identified as common pathophysiological phenomena associated with neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). As the age-related decline in the production of melatonin may contribute to increased levels of oxidative stress in the elderly, the role of this neuroprotective agent is attracting increasing attention. Melatonin has multiple actions as a regulator of antioxidant and prooxidant enzymes, radical scavenger and antagonist of mitochondrial radical formation. The ability of melatonin and its kynuramine metabolites to interact directly with the electron transport chain by increasing the electron flow and reducing electron leakage are unique features by which melatonin is able to increase the survival of neurons under enhanced oxidative stress. Moreover, antifibrillogenic actions have been demonstrated in vitro, also in the presence of profibrillogenic apoE4 or apoE3, and in vivo, in a transgenic mouse model. Amyloid-β toxicity is antagonized by melatonin and one of its kynuramine metabolites. Cytoskeletal disorganization and protein hyperphosphorylation, as induced in several cell-line models, have been attenuated by melatonin, effects comprising stress kinase downregulation and extending to neurotrophin expression. Various experimental models of AD, PD and HD indicate the usefulness of melatonin in antagonizing disease progression and/or mitigating some of the symptoms. Melatonin secretion has been found to be altered in AD and PD. Attempts to compensate for age- and disease-dependent melatonin deficiency have shown that administration of this compound can improve sleep efficiency in AD and PD and, to some extent, cognitive function in AD patients. Exogenous melatonin has also been reported to alleviate behavioral symptoms such as sundowning. Taken together, these findings suggest that melatonin, its analogues and kynuric metabolites may have potential value in prevention and treatment of AD and other neurodegenerative disorders.

Focally elevated creatine detected in amyloid precursor protein (APP) transgenic mice and Alzheimer disease brain tissue

The creatine/phosphocreatine system, regulated by creatine kinase, plays an important role in maintaining energy balance in the brain. Energy metabolism and the function of creatine kinase are known to be affected in Alzheimer diseased brain and in cells exposed to the beta-amyloid peptide. We used infrared microspectroscopy to examine hippocampal, cortical, and caudal tissue from 21-89-week-old transgenic mice expressing doubly mutant (K670N/M671L and V717F) amyloid precursor protein and displaying robust pathology from an early age. Microcrystalline deposits of creatine, suggestive of perturbed energetic status, were detected by infrared microspectroscopy in all animals with advanced plaque pathology. Relatively large creatine deposits were also found in hippocampal sections from post-mortem Alzheimer diseased human brain, compared with hippocampus from non-demented brain. We therefore speculate that this molecule is a marker of the disease process.

Aging-related increase in oxidative stress correlates with developmental pattern of beta-secretase activity and beta-amyloid plaque formation in transgenic Tg2576 mice with Alzheimer-like pathology

The molecular mechanisms of beta-amyloidogenesis in sporadic Alzheimer's disease are still poorly understood. To reveal whether aging-associated increases in brain oxidative stress and inflammation may trigger onset or progression of beta-amyloid deposition, a transgenic mouse (Tg2576) that express the Swedish double mutation of human amyloid precursor protein (APP) was used as animal model to study the developmental pattern of markers of oxidative stress and APP processing. In Tg2576 mouse brain, cortical levels of soluble beta-amyloid (1-40) and (1-42) steadily increased with age, but significant deposition of fibrillary beta-amyloid in cortical areas did not occur before postnatal age of 10 months. The slope of increase in cerebral cortical beta-secretase (BACE1) activities in Tg2576 mice between ages of 9 and 13 months was significantly higher as compared to that of the alpha-secretase, while the expression level of BACE1 protein and mRNA did not change with age. The activities of superoxide dismutase and glutathione peroxidase in cortical tissue from Tg2576 mice steadily increased from postnatal age 9-12 months. The levels of cortical nitric oxide, and reactive nitrogen species demonstrated peak values around 9 months of age, while the level of interleukin-1beta steadily increased from postnatal month 13 onwards. The developmental temporal coincidence of increased levels of reactive nitrogen species and antioxidative enzymes with the onset of beta-amyloid plaque deposition provides further evidence that developmentally and aging-induced alterations in brain oxidative status exhibit a major factor in triggering enhanced production and deposition of beta-amyloid, and potentially predispose to Alzheimer's disease.

The glutamatergic system and Alzheimer's disease: therapeutic implications

Alzheimer's disease affects nearly 5 million Americans currently and, as a result of the baby boomer cohort, is predicted to affect 14 million Americans and 22 million persons totally worldwide in just a few decades. Alzheimer's disease is present in nearly half of individuals aged 85 years. The main symptom of Alzheimer's disease is a gradual loss of cognitive function. Glutamatergic neurotransmission, an important process in learning and memory, is severely disrupted in patients with Alzheimer's disease. Loss of glutamatergic function in Alzheimer's disease may be related to the increase in oxidative stress associated with the amyloid beta-peptide that is found in the brains of individuals who have the disease. Therefore, therapeutic strategies directed at the glutamatergic system may hold promise. Therapies addressing oxidative stress induced by hyperactivity of glutamate receptors include supplementation with estrogen and antioxidants such as tocopherol (vitamin E) and acetylcysteine (N-acetylcysteine). Therapy for hypoactivity of glutamate receptors is aimed at inducing the NMDA receptor with glycine and cycloserine (D-cycloserine). Recently, memantine, an NMDA receptor antagonist that addresses the hyperactivity of these receptors, has been approved in some countries for use in Alzheimer's disease.

Ethanol and oxidative mechanisms in the brain

There is strong evidence showing that chronic and excessive ethanol consumption may enhance oxidative damage to neurons and result in cell death. Although not yet well understood, ethanol may enhance ROS production in brain through a number of pathways including increased generation of hydroxyethyl radicals, induction of CYP2E1, alteration of the cytokine signaling pathways for induction of iNOS and sPLA(2), and production of prostanoids through the PLA(2)/COX pathways. Since many neurodegenerative diseases are also associated with oxidative and inflammatory mechanisms in the brain, it would be important to find out whether chronic and excessive ethanol consumption may exacerbate the progression of these diseases. There is evidence that the polyphenolic antioxidants, especially those extracted from grape skin and seed, may protect the brain from neuronal damage due to chronic ethanol administration. Among the polyphenols from grapes, resveratrol seems to have unique antioxidant properties. The possible use of this compound as a therapeutic agent to ameliorate neurodegenerative processes should be further explored.

Neuronal plasticity and stressor toxicity during aging

Brain aging, Alzheimer disease and stroke share common elements of deficits in calcium regulation, declines in mitochondrial function, increases in generation of reactive oxygen species (ROS), accumulated damage from ROS and immune system dysfunction. The problem is to distinguish less significant side reactions, such as gray hair, from aspects of aging that contribute to disease. Toward establishing cause and effect relationships, a neuron cell culture system is described that allows comparisons with age under uniform environmental conditions. This neuron culture model indicates that susceptibility to death by apoptosis and consequences of the inflammatory response from beta-amyloid are age-related and an inherent characteristic of the neurons. Further mechanistic investigations are possible. New therapeutic approaches are suggested that combine inhibition of calcium overloads (calcium channel blockers), reduced ROS damage (melatonin, N-acetyl-cysteine), and bolstered mitochondrial function and energy generation (creatine). Together with newly demonstrated capabilities for adult and aged neuron regeneration and multiplication, i.e. plasticity, these approaches offer new hope toward reversing age-related decrements and damage from neurodegenerative disease.

Review: Alzheimer's amyloid beta-peptide-associated free radical oxidative stress and neurotoxicity

Alzheimer's disease, the major dementing disorder of the elderly that affects over 4 million Americans, is related to amyloid beta-peptide, the principal component of senile plaques in Alzheimer's disease brain. Oxidative stress, manifested by protein oxidation and lipid peroxidation, among other alterations, is a characteristic of Alzheimer's disease brain. Our laboratory united these two observations in a model to account for neurodegeneration in Alzheimer's disease brain, the amyloid beta-peptide-associated oxidative stress model for neurotoxicity in Alzheimer's disease. Under this model, the aggregated peptide, perhaps in concert with bound redox metal ions, initiates free radical processes resulting in protein oxidation, lipid peroxidation, reactive oxygen species formation, cellular dysfunction leading to calcium ion accumulation, and subsequent neuronal death. Free radical antioxidants abrogate these findings. This review outlines the substantial evidence from multiidisciplinary approaches for amyloid beta-peptide-associated free radical oxidative stress and neurotoxicity and protection against these oxidative processes and cell death by free radical scavengers. In addition, we review the strong evidence supporting the notion that the single methionine residue of amyloid beta-peptide is vital to the oxidative stress and neurotoxicological properties of this peptide. Further, we discuss studies that support the hypothesis that aggregated soluble amyloid beta-peptide and not fibrils per se are necessary for oxidative stress and neurotoxicity associated with amyloid beta-peptide.

Oxidative modification of creatine kinase BB in Alzheimer's disease brain

Creatine kinase (CK) BB, a member of the CK gene family, is a predominantly cytosolic CK isoform in the brain and plays a key role in regulation of the ATP level in neural cells. CK BB levels are reduced in brain regions affected by neurodegeneration in Alzheimer's disease (AD), Pick's disease, and Lewy body dementia, and this reduction is not a result of decreased mRNA levels. This study demonstrates that posttranslational modification of CK BB plays a role in the decrease of CK activity in AD brain. The specific CK BB activity and protein carbonyl content were determined in brain extracts of six AD and six age-matched control subjects. CK BB activity per microgram of immunoreactive CK BB protein was lower in AD than in control brain extracts, indicating the presence of inactive CK BB molecules. The analysis of specific protein carbonyl levels in CK BB, performed by two-dimensional fingerprinting of oxidatively modified proteins, identified CK BB as one of the targets of protein oxidation in the AD brain. The increase of protein carbonyl content in CK BB provides evidence that oxidative posttranslational modification of CK BB plays a role in the loss of CK BB activity in AD.

Protective effect of the energy precursor creatine against toxicity of glutamate and beta-amyloid in rat hippocampal neurons

The loss of ATP, which is needed for ionic homeostasis, is an early event in the neurotoxicity of glutamate and beta-amyloid (A(beta)). We hypothesize that cells supplemented with the precursor creatine make more phosphocreatine (PCr) and create larger energy reserves with consequent neuroprotection against stressors. In serum-free cultures, glutamate at 0.5-1 mM was toxic to embryonic hippocampal neurons. Creatine at >0.1 mM greatly reduced glutamate toxicity. Creatine (1 mM) could be added as late as 2 h after glutamate to achieve protection at 24 h. In association with neurotoxic protection by creatine during the first 4 h, PCr levels remained constant, and PCr/ATP ratios increased. Morphologically, creatine protected against glutamate-induced dendritic pruning. Toxicity in embryonic neurons exposed to A(beta) (25-35) for 48 h was partially prevented by creatine as well. During the first 6 h of treatment with A(beta) plus creatine, the molar ratio of PCr/ATP in neurons increased from 15 to 60. Neurons from adult rats were also partially protected from a 24-h exposure to A(beta) (25-35) by creatine, but protection was reduced in neurons from old animals. These results suggest that fortified energy reserves are able to protect neurons against important cytotoxic agents. The oral availability of creatine may benefit patients with neurodegenerative diseases.

Laminin 1 attenuates beta-amyloid peptide Abeta(1-40) neurotoxicity of cultured fetal rat cortical neurons

A growing amount of evidence indicates the involvement of extracellular matrix components, especially laminins, in the development of Alzheimer's disease, although their role remains unclear. In this study, we clearly demonstrate that laminin 1 inhibits beta-amyloid peptide (Abeta)-induced neuronal cell death by preventing the fibril formation and interaction of the Abeta peptide with cell membranes. The presence of laminin at a laminin/Abeta peptide molar ratio of 1:800 significantly inhibits the Abeta-induced apoptotic events, together with inhibition of amyloid fibril formation. The inhibitory effects of laminin 1 were time- and dose-dependent, whereas laminin 2 had less effect on Abeta neurotoxicity. A preincubation of laminin and Abeta was not required to observe the protective effect of laminin, suggesting a direct interaction between laminin 1 and Abeta. Moreover, laminin had no effect on the toxicity of the fibrillar Abeta peptide, suggesting an interaction of laminin with nonfibrillar species of the Abeta peptide, sequestering the peptide in a soluble form. These data extend our understanding of laminin-dependent binding of Abeta and highlight the possible modulation role of laminin regarding Abeta aggregation and neurotoxicity in vivo.

Potent neuroprotective properties against the Alzheimer beta-amyloid by an endogenous melatonin-related indole structure, indole-3-propionic acid

Widespread cerebral deposition of a 40-43-amino acid peptide called the amyloid beta-protein (Abeta) in the form of amyloid fibrils is one of the most prominent neuropathologic features of Alzheimer's disease. Numerous studies suggest that Abeta is toxic to neurons by free radical-mediated mechanisms. We have previously reported that melatonin prevents oxidative stress and death of neurons exposed to Abeta. In the process of screening indole compounds for neuroprotection against Abeta, potent neuroprotective properties were uncovered for an endogenous related species, indole-3-propionic acid (IPA). This compound has previously been identified in the plasma and cerebrospinal fluid of humans, but its functions are not known. IPA completely protected primary neurons and neuroblastoma cells against oxidative damage and death caused by exposure to Abeta, by inhibition of superoxide dismutase, or by treatment with hydrogen peroxide. In kinetic competition experiments using free radical-trapping agents, the capacity of IPA to scavenge hydroxyl radicals exceeded that of melatonin, an indoleamine considered to be the most potent naturally occurring scavenger of free radicals. In contrast with other antioxidants, IPA was not converted to reactive intermediates with pro-oxidant activity. These findings may have therapeutic applications in a broad range of clinical situations.