Overexpression of superoxide dismutase 1 protects against beta-amyloid peptide toxicity: effect of estrogen and copper chelators

Inescapable footshocks induce molecular changes in the prefrontal cortex of rats in an amyloid-beta-42 model of Alzheimer's disease

Alzheimer's disease (AD) affects several brain areas, including the prefrontal cortex (PFC) involved in execution, working memory, and fear extinction. Despite these critical roles, the PFC is understudied in AD pathology. People with post-traumatic stress disorder (PTSD) have twice the risk of developing AD, and the underlying mechanisms linking these two diseases are less understood. Here, we investigated the effect of footshock stress on behavioural vis-a-vis molecular changes in the PFC of an amyloid-beta (Aβ)-42 lesion rat model of AD. Trauma-like conditions were induced by exposing the animals to several footshocks. AD-like condition was induced via intra-hippocampal injection of Aβ-42 peptide. Following Aβ-42 injections, animals were tested for behavioural changes using the Open Field Test (OFT) and Y-maze test. The PFC was later harvested for neurochemical analyses. Our results showed an interactive effect of footshocks and Aβ-42 lesion on: reduced percentage alternation in the Y-maze test, suggesting memory impairment; reduced number of line crosses and time spent in the centre square of the OFT, indicating anxiogenic responses. Similarly, there was an interactive effect of footshocks and Aβ-42 lesion on: increased FK506 binding protein 51 (FKBP5) expression, which can be associated with stress-induced anxiogenic behaviours; and increased neuronal apoptosis in the PFC of the animals. In addition, footshocks, as well as Aβ-42 lesion, reduced superoxide dismutase levels and Bridging Integrator-1 (BIN1) expression in the PFC of the animals, which can be linked to the observed memory impairment. In conclusion, our findings indicate that footshocks exaggerate PFC-associated behavioural and molecular changes induced by an AD-like pathology.

From Menopause to Neurodegeneration-Molecular Basis and Potential Therapy

The impacts of menopause on neurodegenerative diseases, especially the changes in steroid hormones, have been well described in cell models, animal models, and humans. However, the therapeutic effects of hormone replacement therapy on postmenopausal women with neurodegenerative diseases remain controversial. The steroid hormones, steroid hormone receptors, and downstream signal pathways in the brain change with aging and contribute to disease progression. Estrogen and progesterone are two steroid hormones which decline in circulation and the brain during menopause. Insulin-like growth factor 1 (IGF-1), which plays an import role in neuroprotection, is rapidly decreased in serum after menopause. Here, we summarize the actions of estrogen, progesterone, and IGF-1 and their signaling pathways in the brain. Since the incidence of Alzheimer’s disease (AD) is higher in women than in men, the associations of steroid hormone changes and AD are emphasized. The signaling pathways and cellular mechanisms for how steroid hormones and IGF-1 provide neuroprotection are also addressed. Finally, the molecular mechanisms of potential estrogen modulation on N-methyl-d-aspartic acid receptors (NMDARs) are also addressed. We provide the viewpoint of why hormone therapy has inconclusive results based on signaling pathways considering their complex response to aging and hormone treatments. Nonetheless, while diagnosable AD may not be treatable by hormone therapy, its preceding stage of mild cognitive impairment may very well be treatable by hormone therapy.

Superoxide Dismutase 1 in Health and Disease: How a Frontline Antioxidant Becomes Neurotoxic

Cu/Zn superoxide dismutase (SOD1) is a frontline antioxidant enzyme catalysing superoxide breakdown and is important for most forms of eukaryotic life. The evolution of aerobic respiration by mitochondria increased cellular production of superoxide, resulting in an increased reliance upon SOD1. Consistent with the importance of SOD1 for cellular health, many human diseases of the central nervous system involve perturbations in SOD1 biology. But far from providing a simple demonstration of how disease arises from SOD1 loss-of-function, attempts to elucidate pathways by which atypical SOD1 biology leads to neurodegeneration have revealed unexpectedly complex molecular characteristics delineating healthy, functional SOD1 protein from that which likely contributes to central nervous system disease. This review summarises current understanding of SOD1 biology from SOD1 genetics through to protein function and stability.

N-3 PUFA Prevent Oxidative Stress in a Rat Model of Beta-Amyloid-Induced Toxicity

Polyunsaturated fatty acids (PUFA) are involved in brain disorders associated to amyloid beta (Aβ) toxicity for which oxidative stress, neurochemical dysfunctions, and neuroinflammation are underlying mechanisms. Here, mechanisms through which lifelong exposure to n-3 PUFA-enriched or n-6/n-3 balanced diets could elicit a protective role in a rat model of Aβ-induced toxicity were investigated. To this aim, we quantified hippocampal reactive oxygen species (ROS) amount, 8-hydroxy-2'-deoxyguanosine and interleukin-10 levels, NADPH oxidase (NOX) 1, NOX2, superoxide dismutase 1, and glutathione contents, as well as plasmatic malondialdehyde. Moreover, in the same experimental groups, we assessed tryptophan, serotonin, and its turnover, kynurenine, and noradrenaline amounts. Results showed increased hippocampal ROS and NOX2 levels, serotonin turnover, kynurenine, and noradrenaline contents in Aβ-treated rats. Both n-6/n-3 balanced and n-3 PUFA enriched diets reduced ROS production, NOX1 and malondialdehyde levels, serotonin turnover, and kynurenine amount in Aβ-injected rats, while increasing NOX2, superoxide dismutase 1, and serotonin contents. No differences in plasmatic coenzyme Q10, reduced glutathione (GSH) and tryptophan levels were detected among different experimental groups, whereas GSH + oxidized glutathione (GSSG) levels were increased in sham animals fed with n-3 PUFA enriched diet and in Aβ-treated rats exposed to both n-6/n-3 balanced and n-3 enriched diets. In addition, Aβ-induced decrease of interleukin-10 levels was prevented by n-6/n-3 PUFA balanced diet. N-3 PUFA enriched diet further increased interleukin-10 and 8-hydroxy-2'-deoxyguanosine levels. In conclusion, our data highlight the possible neuroprotective role of n-3 PUFA in perturbation of oxidative equilibrium induced by Aβ-administration.

Estrogen Protects Optic Nerve Head Astrocytes Against Oxidative Stress by Preventing Caspase-3 Activation, Tau Dephosphorylation at Ser422 and the Formation of Tau Protein Aggregates

Glaucoma is a neurodegenerative disorder that leads to the slow degeneration of retinal ganglion cells, and results in damage to the optic nerve and concomitant vision loss. As in other disorders affecting the viability of central nervous system neurons, neurons affected by glaucoma do not have the ability to regenerate after injury. Recent studies indicate a critical role for optic nerve head astrocytes (ONHAs) in this process of retinal ganglion cell degeneration. Cleavage of tau, a microtubule stabilizing protein and constituent of neurofibrillary tangles (NFT), plays a major part in the mechanisms that lead to toxicity in CNS neurons and astrocytes. Here, we tested the hypothesis that estrogen, a pleiotropic neuro- and cytoprotectant with high efficacy in the CNS, prevents tau cleavage, and hence, protects ONHAs against cell damage caused by oxidative stress. Our results indicate that estrogen prevents caspase-3 mediated tau cleavage, and thereby decreases the levels of the resulting form of proteolytically cleaved tau protein, which leads to a decrease in NFT formation, which requires proteolytically cleaved tau protein. Overall, our data propose that by stopping the reduction of estrogen levels involved with aging the sensitivity of the optic nerve to glaucomatous damage might be reduced. Furthermore, our data suggest that therapeutic use of estrogen may be beneficial in slowing or preventing the onset or severity of neurodegenerative diseases such as glaucoma and potentially also other degenerative diseases of the CNS through direct control of posttranslational modifications of tau protein.

Protective effects of Huang-Lian-Jie-Du-Tang against A25-35-induced memory deficits and oxidative stress in rats

Objective

Huang-Lian-Jie-Du-Tang (HLJDT), a traditional Chinese medicine, improves cognitive ability in rat models of Alzheimer’s disease (AD). The objective of this study was to evaluate the protective effects of HLJDT on learning and memory impairment that are caused by Aβ_25–35.

Methods

Rats were randomly assigned to the following groups: control (water), Aβ_25–35, donepezil hydrochloride 1.05 mg/kg, HLJDT 6 g/kg, HLJDT 3 g/kg, and HLJDT 1.5 g/kg and the corresponding drugs were administered for 28 days by oral gavage. HLJDT for the prevention of Aβ_25–35-induced injury in rats and the underlying mechanisms were assessed. Aβ_25–35 and amyloid precursor protein (APP) levels were measured in the hippocampal specimens. Total superoxide dismutase (T-SOD), glutathione (GSH), and malondialdehyde (MDA) levels in the hippocampus were also measured. The ultrastructure of CA1 hippocampal region was observed using electron microscopy.

Results

HLJDT treatment ameliorated impaired learning and memory significantly, decreased Aβ_25–35, and APP levels in the hippocampus, increased T-SOD and GSH activity and decreased the MDA concentration, and alleviated the nuclear and cytoplasmic abnormalities of the hippocampal CA 1 region that were induced by Aβ_25–35 injection.

Conclusions

HLJDT might decrease hippocampal vulnerability to Aβ_25–35, suggesting its potential neuroprotective effect in AD.

Brain Renin-Angiotensin System at the Intersect of Physical and Cognitive Frailty

The renin–angiotensin system (RAS) was initially considered to be part of the endocrine system regulating water and electrolyte balance, systemic vascular resistance, blood pressure, and cardiovascular homeostasis. It was later discovered that intracrine and local forms of RAS exist in the brain apart from the endocrine RAS. This brain-specific RAS plays essential roles in brain homeostasis by acting mainly through four angiotensin receptor subtypes; AT₁R, AT₂R, MasR, and AT₄R. These receptors have opposing effects; AT₁R promotes vasoconstriction, proliferation, inflammation, and oxidative stress while AT₂R and MasR counteract the effects of AT₁R. AT₄R is critical for dopamine and acetylcholine release and mediates learning and memory consolidation. Consequently, aging-associated dysregulation of the angiotensin receptor subtypes may lead to adverse clinical outcomes such as Alzheimer’s disease and frailty via excessive oxidative stress, neuroinflammation, endothelial dysfunction, microglial polarization, and alterations in neurotransmitter secretion. In this article, we review the brain RAS from this standpoint. After discussing the functions of individual brain RAS components and their intracellular and intracranial locations, we focus on the relationships among brain RAS, aging, frailty, and specific neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, and vascular cognitive impairment, through oxidative stress, neuroinflammation, and vascular dysfunction. Finally, we discuss the effects of RAS-modulating drugs on the brain RAS and their use in novel treatment approaches.

β-amyloid and Oxidative Stress: Perspectives in Drug Development

Alzheimer's Disease (AD) is a slow-developing neurodegenerative disorder in which the main pathogenic role has been assigned to β-amyloid protein (Aβ) that accumulates in extracellular plaques. The mechanism of action of Aβ has been deeply analyzed and several membrane structures have been identified as potential mediators of its effect. The ability of Aβ to modify neuronal activity, receptor expression, signaling pathways, mitochondrial function, and involvement of glial cells have been analyzed. In addition, extensive literature deals with the involvement of oxidative stress in Aβ effects. Herein we focus more specifically on the reciprocal regulation of Aβ, that causes oxidative stress, that favors Aβ aggregation and toxicity and negatively affects the peptide clearance. Analysis of this strict interaction may offer novel opportunities for therapeutic intervention. Both common and new molecules endowed with antioxidant properties deserve attention in this regard.

Accelerated aging and aging process in the brain

One of the approaches to the research of the problem of aging is the study of genetic pathologies leading to accelerated aging, such as the Hutchinson-Gilford progeria syndrome, Werner syndrome, and Down syndrome. Probably, this approach can be used in an attempt to understand the neuronal mechanisms underlying normal and pathological brain aging. The analysis of the current state of scientific knowledge about these pathologies shows that in the Hutchinson-Gilford progeria and Werner syndrome, the rate of brain aging is significantly lower than the rate of whole body aging, whereas in Down syndrome, the brain ages faster than other organs due to amyloid-beta accumulation and chronic oxidative stress in the brain tissue. The main point of a previously proposed hypothesis is that the aging of higher animals and humans is associated with an increased level of reactive oxygen species in mitochondria with age, which activates apoptosis, thus reducing the number of functioning cells.

Reduced expression of SIRT1 and SOD-1 and the correlation between these levels in various regions of the brains of patients with Alzheimer's disease

AIMS

This study was designed to explore the expression and distribution of silent information regulator 1 (SIRT1) and superoxide dismutase 1 (SOD-1) in various regions of the brains of patients with Alzheimer's disease (AD), as well as to assess potential correlations between the levels of these proteins and also between these proteins and the Braak stage of AD.

METHODS

In the temporal and frontal cortices, hippocampus and cerebellum of 10 patients with AD and 10 age-matched control subjects, expression of SIRT1 and SOD-1, together with histopathology, were assessed by immunohistochemical and immunofluorescent stainings. Relationships between variables were examined with the Pearson correlation test.

RESULTS

The numbers of both SIRT1-positive and SOD-1-positive neurons and integrated optical density of immunohistochemical staining for these proteins in the temporal and frontal cortices, and hippocampus of patients with AD were significantly decreased than those in corresponding controls. In the case of the cerebellum, very weak expression of SIRT1 and obvious expression of SOD-1 were observed in granule cells, with no significant difference between AD and the control group. Interestingly, the protein levels between SIRT1 and SOD-1, as well as the level of SIRT1 or SOD-1 and Braak stage, were significantly correlated in neurons in all regions of the AD brains investigated except for the cerebellum.

CONCLUSIONS

These findings indicate that the reduced level of SIRT1 in the brains of patients with AD may be related to the decline in SOD-1 and neuropathological changes of this disorder.

ALS-linked mutant SOD1 proteins promote Aβ aggregates in ALS through direct interaction with Aβ

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive degeneration of motor neurons. Aggregation of ALS-linked mutant Cu/Zn superoxide dismutase (SOD1) is a hallmark of a subset of familial ALS (fALS). Recently, intracellular amyloid-β (Aβ) is detected in motor neurons of both sporadic and familial ALS. We have previously shown that intracellular Aβ specifically interacts with G93A, an ALS-linked SOD1 mutant. However, little is known about the pathological and biological effect of this interaction in neurons. In this study, we have demonstrated that the Aβ-binding region is exposed on the SOD1 surface through the conformational changes due to misfolding of SOD1. Interestingly, we found that the intracellular aggregation of Aβ is enhanced through the direct interaction of Aβ with the Aβ-binding region exposed to misfolded SOD1. Ultimately, increased Aβ aggregation by this interaction promotes neuronal cell death. Consistent with this result, Aβ aggregates was three-fold higher in the brains of G93A transgenic mice than those of non Tg. Our study provides the first direct evidence that Aβ, an AD-linked factor, is associated to the pathogenesis of ALS and provides molecular clues to understand common aggregation mechanisms in the pathogenesis of neurodegenerative diseases. Furthermore, it will provide new insights into the development of therapeutic approaches for ALS.

4'-Chlorodiazepam is neuroprotective against amyloid-beta in organotypic hippocampal cultures

The translocator protein (TSPO) is an outer mitochondrial membrane protein involved in the transport of cholesterol into the mitochondria, which is the first step for the synthesis of steroid hormones, as well as in the regulation of mitochondrial permeability transition pore opening and apoptosis. Studies have shown that the activation of TSPO may promote neuroprotective actions in experimental models of neurodegeneration and brain injury. In a previous study, our group showed that 4'-chlorodiazepam (4'-CD), a TSPO ligand, was neuroprotective against amyloid-beta (Aβ) in SHSY-5Y neuroblastoma cells. The aim of this study was to evaluate if 4'-CD was also neuroprotective against Aβ in organotypic hippocampal cultures and to identify its mechanisms of action. Aβ decreased the cell viability of organotypic hippocampal cultures, while 4'-CD had a neuroprotective effect when administered at 100nM and 1000nM. The neuroprotective effects of 4'-CD against Aβ were associated with an increased expression of superoxide dismutase (SOD). No differences were found in the expression of catalase, glial fibrillary acidic protein, Akt and procaspase-3. In summary, our results show that 4'-CD is neuroprotective against Aβ by a mechanism involving the modulation of SOD protein expression.

Cross-interactions between the Alzheimer Disease Amyloid-β Peptide and Other Amyloid Proteins: A Further Aspect of the Amyloid Cascade Hypothesis

Many protein folding diseases are intimately associated with accumulation of amyloid aggregates. The amyloid materials formed by different proteins/peptides share many structural similarities, despite sometimes large amino acid sequence differences. Some amyloid diseases constitute risk factors for others, and the progression of one amyloid disease may affect the progression of another. These connections are arguably related to amyloid aggregates of one protein being able to directly nucleate amyloid formation of another, different protein: the amyloid cross-interaction. Here, we discuss such cross-interactions between the Alzheimer disease amyloid-β (Aβ) peptide and other amyloid proteins in the context of what is known from in vitro and in vivo experiments, and of what might be learned from clinical studies. The aim is to clarify potential molecular associations between different amyloid diseases. We argue that the amyloid cascade hypothesis in Alzheimer disease should be expanded to include cross-interactions between Aβ and other amyloid proteins.

Immunocytochemical staining of endogenous nuclear proteins with the HIS-1 anti-poly-histidine monoclonal antibody: a potential source of error in His-tagged protein detection

Histidine-tagged proteins are widely used in biochemical studies and frequently detected with antibodies specific for the histidine tag. Immunocytochemistry is widely used in studies with overexpressed proteins to determine cellular localization and in the case of histidine-tagged proteins can be carried out with anti-polyhistidine antibodies. Recent studies have suggested that polyhistidine sequences are present within a small number of human proteins and may direct expression to the nucleus and nuclear speckles compartments of the cell. In this study immunocytochemical staining of human SH-SY5Y neuroblastoma cell lines with the HIS-1 anti-polyhistidine monoclonal antibody were determined. Results showed that the HIS-1 anti-polyhistidine monoclonal antibody stained endogenous nuclear proteins in SH-SY5Y cells. The stained proteins were contained within the nuclear membrane, but were not directly linked to DNA. In a histidine-tagged catalase overexpressing cell line the HIS-1 anti-polyhistidine monoclonal antibody showed nuclear staining, whilst staining with the CAT-505 anti-catalase monoclonal antibody showed primarily cytoplasmic staining. These results suggest that anti-polyhistidine antibody staining shows significant cross-reactivity with endogenous nuclear proteins in SH-SY5Y neuroblastoma cells and may not be suitable for localization studies of histidine-tagged proteins. Immunocytochemical studies with anti-polyhistidine antibodies and localization of histidine-tagged proteins must be confirmed with protein specific antibodies or other methodology.

Oxidative stress, neurodegeneration, and the balance of protein degradation and protein synthesis

Oxidative stress occurs in a variety of disease settings and is strongly linked to the development of neuron death and neuronal dysfunction. Cells are equipped with numerous pathways to prevent the genesis, as well as the consequences, of oxidative stress in the brain. In this review we discuss the various forms and sources of oxidative stress in the brain and briefly discuss some of the complexities in detecting the presence of oxidative stress. We then focus the review on the interplay between the diverse cellular proteolytic pathways and their roles in regulating oxidative stress in the brain. Additionally, we discuss the involvement of protein synthesis in regulating the downstream effects of oxidative stress. Together, these components of the review demonstrate that the removal of damaged proteins by effective proteolysis and the synthesis of new and protective proteins are vital in the preservation of brain homeostasis during periods of increased levels of reactive oxygen species. Last, studies from our laboratory and others have demonstrated that protein synthesis is intricately linked to the rates of protein degradation, with impairment of protein degradation sufficient to decrease the rates of protein synthesis, which has important implications for successfully responding to periods of oxidative stress. Specific neurodegenerative diseases, including Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, and stroke, are discussed in this context. Taken together, these findings add to our understanding of how oxidative stress is effectively managed in the healthy brain and help elucidate how impairments in proteolysis and/or protein synthesis contribute to the development of neurodegeneration and neuronal dysfunction in a variety of clinical settings.

Therapeutic approach to neurodegenerative diseases by medical gases: focusing on redox signaling and related antioxidant enzymes

Oxidative stress in the central nervous system is strongly associated with neuronal cell death in the pathogenesis of several neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. In order to overcome the oxidative damage, there are some protective signaling pathways related to transcriptional upregulation of antioxidant enzymes, such as heme oxygenase-1 (HO-1) and superoxide dismutase (SOD)-1/-2. Their expression is regulated by several transcription factors and/or cofactors like nuclear factor-erythroid 2 (NF-E2) related factor 2 (Nrf2) and peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α). These antioxidant enzymes are associated with, and in some cases, prevent neuronal death in animal models of neurodegenerative diseases. They are activated by endogenous mediators and phytochemicals, and also by several gases such as carbon monoxide (CO), hydrogen sulphide (H₂S), and hydrogen (H₂). These might thereby protect the brain from severe oxidative damage and resultant neurodegenerative diseases. In this paper, we discuss how the expression levels of these antioxidant enzymes are regulated. We also introduce recent advances in the therapeutic uses of medical gases against neurodegenerative diseases.

Identification of [CuCl(acac)(tmed)], a copper(II) complex with mixed ligands, as a modulator of Cu,Zn superoxide dismutase (Sod1p) activity in yeast

Superoxide dismutases (SODs) stand in the prime line of enzymatic antioxidant defense in nearly all eukaryotic cells exposed to oxygen, catalyzing the breakdown of the superoxide anionic radical to O(2) and H(2)O(2). Overproduction of superoxide correlates with numerous pathophysiological conditions, and although the native enzyme can be used as a therapeutic agent in superoxide-associated conditions, synthetic low molecular weight mimetics are preferred in terms of cost, administration mode, and bioavailability. In this study we make use of the model eukaryote Saccharomyces cerevisiae to investigate the SOD-mimetic action of a mononuclear mixed-ligand copper(II) complex, [CuCl(acac)(tmed)] (where acac is acetylacetonate anion and tmed is N,N,N',N'-tetramethylethylenediamine). Taking advantage of an easily reproducible phenotype of yeast cells which lack Cu-Zn SOD (Sod1p), we found that the compound could act either as a superoxide scavenger in the absence of native Sod1p or as a Sod1p modulator which behaved differently under various genetic backgrounds.

Does physical activity reduce risk for Alzheimer's disease through interaction with the stress neuroendocrine system?

Lack of physical activity (PA) is a risk factor for Alzheimer's disease (AD), and PA interventions are believed to provide an effective non-pharmacological approach for attenuating the symptoms of this disease. However, the mechanism of action of these positive effects is currently unknown. It is possible that the benefits may be at least partially mediated by the effects on the neuroendocrine stress system. Chronic stress can lead to dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis, leading to aberrant basal and circadian patterns of cortisol secretion and a cascade of negative downstream events. These factors have been linked not only to reduced cognitive function but also increased levels of amyloid-β plaques and protein tau "tangles" (the neuropathological hallmarks of AD) in the non-demented mouse models of this disease. However, there is evidence that PA can have restorative effects on the stress neuroendocrine system and related risk factors relevant to AD. We explore the possibility that PA can positively impact upon AD by restoring normative HPA axis function, with consequent downstream effects upon underlying neuropathology and associated cognitive function. We conclude with suggestions for future research to test this hypothesis in patients with AD.

Rhinacanthus nasutus extracts prevent glutamate and amyloid-β neurotoxicity in HT-22 mouse hippocampal cells: possible active compounds include lupeol, stigmasterol and β-sitosterol

The Herb Rhinacanthus nasutus (L.) Kurz, which is native to Thailand and Southeast Asia, has become known for its antioxidant properties. Neuronal loss in a number of diseases including Alzheimer’s disease is thought to result, in part, from oxidative stress. Glutamate causes cell death in the mouse hippocampal cell line, HT-22, by unbalancing redox homeostasis, brought about by a reduction in glutathione levels, and amyloid-β has been shown to induce reactive oxygen species (ROS) production. Here in, we show that ethanol extracts of R. nasutus leaf and root are capable of dose dependently attenuating the neuron cell death caused by both glutamate and amyloid-β treatment. We used free radical scavenging assays to measure the extracts antioxidant activities and as well as quantifying phenolic, flavonoid and sterol content. Molecules found in R. nasutus, lupeol, stigmasterol and β-sitosterol are protective against glutamate toxicity.

eIF4A inhibition allows translational regulation of mRNAs encoding proteins involved in Alzheimer's disease

Alzheimer's disease (AD) is the main cause of dementia in our increasingly aging population. The debilitating cognitive and behavioral symptoms characteristic of AD make it an extremely distressing illness for patients and carers. Although drugs have been developed to treat AD symptoms and to slow disease progression, there is currently no cure. The incidence of AD is predicted to increase to over one hundred million by 2050, placing a heavy burden on communities and economies, and making the development of effective therapies an urgent priority. Two proteins are thought to have major contributory roles in AD: the microtubule associated protein tau, also known as MAPT; and the amyloid-beta peptide (A-beta), a cleavage product of amyloid precursor protein (APP). Oxidative stress is also implicated in AD pathology from an early stage. By targeting eIF4A, an RNA helicase involved in translation initiation, the synthesis of APP and tau, but not neuroprotective proteins, can be simultaneously and specifically reduced, representing a novel avenue for AD intervention. We also show that protection from oxidative stress is increased upon eIF4A inhibition. We demonstrate that the reduction of these proteins is not due to changes in mRNA levels or increased protein degradation, but is a consequence of translational repression conferred by inhibition of the helicase activity of eIF4A. Inhibition of eIF4A selectively and simultaneously modulates the synthesis of proteins involved in Alzheimer's disease: reducing A-beta and tau synthesis, while increasing proteins predicted to be neuroprotective.

Amyloid precursor protein and alpha synuclein translation, implications for iron and inflammation in neurodegenerative diseases

Recent studies that alleles in the hemochromatosis gene may accelerate the onset of Alzheimer's disease by five years have validated interest in the model in which metals (particularly iron) accelerate disease course. Biochemical and biophysical measurements demonstrated the presence of elevated levels of neurotoxic copper zinc and iron in the brains of AD patients. Intracellular levels of APP holoprotein were shown to be modulated by iron by a mechanism that is similar to the translation control of the ferritin L- and H mRNAs by iron-responsive element (IRE) RNA stem loops in their 5' untranslated regions (5'UTRs). More recently a putative IRE-like sequence was hypothesized present in the Parkinsons's alpha synuclein (ASYN) transcript (see [A.L. Friedlich, R.E. Tanzi, J.T. Rogers, The 5'-untranslated region of Parkinson's disease alpha-synuclein messenger RNA contains a predicted iron responsive element, Mol. Psychiatry 12 (2007) 222-223. [6]]). Together with the demonstration of metal dependent translation of APP mRNA, the involvement of metals in the plaque of AD patients and of increased iron in striatal neurons in the substantia nigra (SN) of Parkinson's disease patients have stimulated the development of metal attenuating agents and iron chelators as a major new therapeutic strategy for the treatment of these neurodegenerative diseases. In the case of AD, metal based therapeutics may ultimately prove more cost effective than the use of an amyloid vaccine as the preferred anti-amyloid therapeutic strategy to ameliorate the cognitive decline of AD patients.

Reduction of cerebral oxidative stress following environmental enrichment in mice with Alzheimer-like pathology

Oxidative stress is a key feature during progression of chronic neurodegenerative conditions such as Alzheimer's disease. In aging humans and animals, voluntary exercise lowers oxidative stress reactions. Additionally, recent work in our lab demonstrated that cognitive and physical stimulation (termed environmental enrichment) counteracts amyloid beta pathology, neurovascular dysfunction and behavioral symptoms in mice with Alzheimer-like disease. Based on these facts, we hypothesized that cognitive and physical activity can also protect against oxidative stress in Alzheimer-diseased brain. We, therefore, kept female TgCRND8 mice under standard and enriched housing from day 30 until 5 months of age. Environmental stimulation attenuated pro-oxidative processes and triggered anti-oxidative defense mechanisms as indicated by diminished biomarkers for reactive oxygen and nitrogen species, downregulation of pro-inflammatory and pro-oxidative mediators, decreased expression of pro-apoptotic caspases, and upregulation of SOD1 and SOD2. This study identifies a thus far undescribed antagonizing effect of environmental stimulation on Alzheimer's disease-related oxidative damage.

Altered calcium homeostasis in motor neurons following AMPA receptor but not voltage-dependent calcium channels' activation in a genetic model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a late-onset progressive neurodegenerative disease characterized by a substantial loss of motor neurons in the spinal cord, brain stem and motor cortex. By combining electrophysiological recordings with imaging techniques, clearance/buffering capacity of cultured spinal cord motor neurons after a calcium accumulation has been analyzed in response to AMPA receptors' (AMPARs') activation and to depolarizing stimuli in a genetic mouse model of ALS (G93A). Our studies demonstrate that the amplitude of the calcium signal in response to AMPARs' or voltage-dependent calcium channels' activation is not significantly different in controls and G93A motor neurons. On the contrary, in G93A motor neurons, the [Ca(2+)](i) recovery to basal level is significantly slower compared to control neurons following AMPARs but not voltage-dependent calcium channels' activation. This difference was not observed in G93A cultured cortical neurons. This observation is the first to indicate a specific alteration of the calcium clearance linked to AMPA receptors' activation in G93A motor neurons and the involvement of AMPA receptor regulatory proteins controlling both AMPA receptor functionality and the sequence of events connected to them.

Metal specificity of an iron-responsive element in Alzheimer's APP mRNA 5'untranslated region, tolerance of SH-SY5Y and H4 neural cells to desferrioxamine, clioquinol, VK-28, and a piperazine chelator

Iron closely regulates the expression of the Alzheimer's Amyloid Precursor Protein (APP) gene at the level of message translation by a pathway similar to iron control of the translation of the ferritin L- and H mRNAs by Iron-responsive Elements in their 5' untranslated regions (5'UTRs). Using transfection based assays in SH-SY5Y neuroblastoma cells we tested the relative efficiency by which iron, copper and zinc up-regulate IRE activity in the APP 5'UTR. Desferrioxamine (high affinity Fe3+ chelator), (ii) clioquinol (low affinity Fe/Cu/Zn chelator), (iii) piperazine-1 (oral Fe chelator), (iv) VK-28 (oral Fe chelator), were tested for their relative modulation of APP 5' UTR directed translation of a luciferase reporter gene. Iron chelation based therapeutic strategies for slowing the progression of Alzheimer's disease (and other neurological disorders that manifest iron imbalance) are discussed with regard to the relative neural toxic action of each chelator in SH-SY5Y cells and in H4 glioblastoma cells.

Caspase-3- and calpain-mediated tau cleavage are differentially prevented by estrogen and testosterone in beta-amyloid-treated hippocampal neurons

A growing body of evidence suggests that the proteolytic cleavage of the microtubule-associated protein tau, the main component of neurofibrillary tangles, might play a role in the molecular mechanisms underlying beta-amyloid (Abeta) -induced neurotoxicity in central neurons. In the present study, we analyzed whether sex hormones could prevent such tau cleavage, and hence, protect rat hippocampal neurons against Abeta toxicity. Our results indicated that estrogen and testosterone prevented caspase-3- and calpain-mediated tau cleavage, respectively. Thus, estrogen decreased the levels of caspase-3-cleaved 50-kDa truncated tau, while testosterone prevented the generation of a calpain-cleaved 17-kDa tau fragment. In addition, our results showed that the decrease in the levels of these tau proteolytic forms was accompanied by an increased cell survival in Abeta-treated neurons. Furthermore, our findings indicated that testosterone was more effective than estrogen in protecting hippocampal neurons against Abeta-induced cell death. Collectively, our data suggest that preventing the decline of estrogen and testosterone associated with normal aging might reduce the susceptibility of central neurons to Abeta-induced toxicity.

Oxidative stress in Alzheimer's disease

Oxidative damage is a major feature in the pathophysiology of Alzheimer's disease (AD). In this review, we discuss free radical-mediated damage to the biochemical components involved in the pathology and clinical symptoms of AD. We explain how amyloid beta-protein (Abeta), microtubule-associated protein tau, presenilins, apolipoprotein E, mitochondria and proteases play a role in increasing oxidative stress in AD. Abeta not only can induce oxidative stress, but its generation is also increased as a result of oxidative stress. Finally, a hypothetical model linking oxidative stress with beta-amyloid and neurofibrillary tangle pathology in AD is proposed.

Elevated oxidative stress in the brain of senescence-accelerated mice at 5 months of age

The senescence-accelerated mouse (SAM) is a useful animal model to study aging or age-associated disorder. In the present study, we have used a multidisciplinary approach to the characterization of changes that occur in aging and in the modelling of brain aging. The SAMP8 mouse at 5 months of age exhibited an increase in gliosis and molecular oxidative damage. Likewise, we found that superoxide dismutase activity decreased compared with age-matched SAMR1 while there were no differences in activity of catalase and glutathione reductase. These results indicate that the decrease of superoxide dismutase may be involved in the increase of oxidative stress in brain of SAMP8 at younger stages. This suggestion is supported by an increase in the expression of alpha-synuclein together with phosphorylated tau protein, which is concurrent with the decline of that antioxidant enzyme. Alpha-synuclein aggregates are invariably associated with tau pathologies and our results demonstrate that alpha-synuclein accumulation is a potent inducer of tau pathologies not only in neurodegenerative diseases but also in normal aging. These results also imply that SAMP8 are exposed to elevated levels of oxidative stress from an early age, and that could be a very important cause of the senescence-related impairments and degeneration in the brain seen in this strain.

beta-Amyloid infusion results in delayed and age-dependent learning deficits without role of inflammation or beta-amyloid deposits

beta-Amyloid (Abeta) polypeptide plays a critical role in the pathogenesis of Alzheimer's disease (AD), which is characterized by progressive decline of cognitive functions, formation of Abeta deposits and neurofibrillary tangles, and loss of neurons. Increased genetic production or direct intracerebral administration of Abeta in animal models results in Abeta deposition, gliosis, and impaired cognitive functions. Whether aging renders the brain prone to Abeta and whether inflammation is required for Abeta-induced learning deficits is unclear. We show that intraventricular infusion of Abeta1-42 results in learning deficits in 9-month-old but not 2.5-month-old mice. Deficits that become detectable 12 weeks after the infusion are associated with a slight reduction in Cu,Zn superoxide dismutase activity but do not correlate with Abeta deposition and are not associated with gliosis. In rats, Abeta infusion induced learning deficits that were detectable 6 months after the infusion. Approximately 20% of the Abeta immunoreactivity in rats was associated with astrocytes. NMR spectrum analysis of the animals cerebrospinal fluid revealed a strong reduction trend in several metabolites in Abeta-infused rats, including lactate and myo-inositol, supporting the idea of dysfunctional astrocytes. Even a subtle increase in brain Abeta1-42 concentration may disrupt normal metabolism of astrocytes, resulting in altered neuronal functions and age-related development of learning deficits independent of Abeta deposition and inflammation.

Differential effects and changes of ceruloplasmin in the hippocampal CA1 region between adult and aged gerbils after transient cerebral ischemia

In this study, we examined the differential effects and changes of ceruloplasmin between adult and aged gerbil hippocampus after transient forebrain ischemia. Ceruloplasmin in the hippocampal CA1 region of adult and aged gerbils was significantly changed after ischemia/reperfusion. Whereas, it was not significantly changed in the CA2/3 region compared to the CA1 region after ischemia. Ceruloplasmin immunoreactivity and its protein level in aged gerbil CA1 region were higher than those in adult gerbil CA1 region. Ceruloplasmin in the CA1 region was highest in adult gerbils and aged gerbils at 24h and 12h after transient ischemia, respectively. At these time points, strong ceruloplasmin immunoreactivity was observed in CA1 pyramidal cells. Thereafter, ceruloplasmin was decreased with time after ischemia. Four days after ischemia/reperfusion, ceruloplasmin immunoreactivity in both adult and aged gerbils was expressed in astrocytes in the CA1 region. Ceruloplasmin treatment in adult ischemic gerbils showed strong protective effect against ischemic damage in CA1 pyramidal cells compared to that in aged ischemic gerbils. We conclude that ceruloplasmin early increases in the aged gerbil CA1 region compared to that of the adult gerbil CA1 region may be associated with the earlier induction of reactive oxygen species, and ceruloplasmin shows strong neuroprotective effects in adults compared to those in aged gerbils.

Intracellular oxidative activity and respiratory burst of leukocytes isolated from multiple sclerosis patients

Oxidative damage induced by free radicals and reactive oxygen species (ROS) have been suggested to play an important role in the development of autoimmune diseases such as multiple sclerosis (MS) disease and it has been hypothesised that oxidative injury could mediate demyelination and axonal injury in MS subjects. In our study, we compared intracellular oxidative activity and the respiratory burst activity in MS patients (n=20) and healthy controls (n=15) using leukocytes as cellular model. At this purpose, intracellular ROS levels were evaluated by fluorometric assay using the 2'-7'-dichlorodihydrofluorescin diacetate probe (H(2)DCFDA) in untreated or in leukocytes stimulated with phorbol-12-myristate-13-acetate (PMA). Our results demonstrate that the intracellular spontaneous ROS production in leukocytes from MS patients was higher with respect to cells from control subjects (p<0.001). PMA addition induced a higher formation of ROS both in leukocytes from MS patients and controls (p<0.001). The PMA-induced production of ROS was significantly higher in leukocytes from MS with respect to controls (p<0.001). Significant positive correlations were established between intracellular spontaneous or PMA-induced production of ROS in leukocytes isolated from MS patients and the clinical parameters used to evaluate disease disability such as expanded disability status scale (EDSS), brain lesions evaluated by MRI and visual evoked potential (VEP) (p<0.001). In conclusion, our results demonstrate higher levels of intracellular ROS in untreated or in PMA-treated leukocytes isolated from MS patients with respect to healthy subjects confirming the role of oxidative stress in multiple sclerosis.

From clinical evidence to molecular mechanisms underlying neuroprotection afforded by estrogens

Recent studies have highlighted that female sex hormones represent potential neuroprotective agents against damage produced by acute and chronic injuries in the adult brain. Clinical reports have documented the effectiveness of estrogens to attenuate symptoms associated with Parkinson's disease, and to reduce the risk of Alzheimer's disease and cerebrovascular stroke. This evidence is corroborated by numerous experimental studies documenting the protective role of female sex hormones both in vitro and in vivo. Accordingly, estrogens have been shown to promote survival and differentiation of several neuronal populations maintained in culture, and to reduce cell death associated with excitotoxicity, oxidative stress, serum deprivation or exposure to beta-amyloid. The neuroprotective effects of estrogens have been widely documented in animal models of neurological disorders, such as Alzheimer's and Parkinson's diseases, as well as cerebral ischemia. Although estrogens are known to exert several direct effects on neurones, the cellular and molecular mechanisms implicated in their protective actions on the brain are not completely understood. Thus, on the basis of clinical and experimental evidence, in this review, we discuss recent findings concerning the neuronal effects of estrogens that may contribute to their neuroprotective actions. Both estrogen receptor-dependent and -independent mechanisms will be described. These include modulation of cell death regulators, such as Bcl-2, Akt and calpain, as well as interaction with growth factors, such as BDNF, NGF, IGF-I and their receptors. The anti-inflammatory effects of estrogens will also be described, namely their ability to reduce brain levels of inflammatory mediators, cytokines and chemokines. Finally, a brief overview about receptor-independent mechanisms of neuroprotection will aim at describing the antioxidant effects of estrogens, as well as their ability to modulate neurotransmission.

Expression of nicotinic receptors on primary cultures of rat astrocytes and up-regulation of the α7, α4 and β2 subunits in response to nanomolar concentrations of the β-amyloid peptide1–42

Neuronal nicotinic acetylcholine receptors (nAChRs) are thought to be involved in the pathogenesis of Alzheimer's disease (AD). Interestingly, in the brains of patients with this disease, losses of several subtypes of nAChRs on neurons have been reported, while an increase in alpha7 nAChRs was recently detected in the astrocytes. However, little is presently known about the expressions of individual subunits of nAChR on rat astrocytes in primary culture or the possible influence of exposure to beta-amyloid peptide (Abeta), a neuropathological hallmark of AD, on this expression. Thus, in the present investigation the levels of individual nAChR subunits on primary rat astrocytes and the possible direct influence of Abetas on the receptors were examined by RT-PCR, Western blotting, monitoring intracellular free calcium and immunohistochemistry. The alpha4, alpha7, beta2 and beta3 subunits and related calcium channel responses were found in these cells, whereas neither alpha2 nor alpha3 could be detected. Elevation in the levels of alpha7, alpha4 and beta2 mRNAs and proteins were observed in astrocytes exposed to 0.1-100nM Abeta(1-42). In contrast, incubation with 1muM Abeta(1-42) or Abeta(35-25) did not affect these levels. We propose that the enhanced expression of alpha7, alpha4 and beta2 nAChRs by astrocytes stimulated directly by nanomolar concentrations of Abeta(1-42) might be related to ongoing defensive or compensative mechanisms.

Impaired Cu/Zn-SOD activity contributes to increased oxidative damage in APP transgenic mice

Oxidative stress plays an important role in the pathogenesis of Alzheimer's disease. To determine which mechanisms cause the origin of oxidative damage, we analyzed enzymatic antioxidant defense (Cu/Zn-superoxide dismutase Cu/Zn-SOD, glutathione peroxidase GPx and glutathione reductase GR) and lipid peroxidation products malondialdehyde MDA and 4-hydroxynonenal HNE in two different APP transgenic mouse models at 3-4 and 12-15 months of age. No changes in any parameter were observed in brains from PDGF-APP695(SDL) mice, which have low levels of Abeta and no plaque load. In contrast, Thy1-APP751(SL) mice show high Abeta accumulation with aging and plaques from an age of 6 months. In brains of these mice, HNE levels were increased at 3 months (female transgenic mice) and at 12 months (both gender), that is, before and after plaque deposition, and the activity of Cu/Zn-SOD was reduced. Interestingly, beta-amyloidogenic cleavage of APP was increased in female Thy1-APP751(SL) mice, which also showed increased HNE levels with simultaneously reduced Cu/Zn-SOD activity earlier than male Thy1-APP751(SL) mice. Our results demonstrate that impaired Cu/Zn-SOD activity contributes to oxidative damage in Thy1-APP751(SL) transgenic mice, and these findings are closely linked to increased beta-amyloidogenic cleavage of APP.

SOD-1 inhibits FAS expression in cortex of APP transgenic mice

Peptides derived from proteolytic processing of the amyloid precursor protein (APP) are important for the pathogenesis of Alzheimer's disease (AD). In the present study, we found that transgenic mice overexpressing wild-type human APP gene (hAPP/+) displayed a much higher expression of FAS, one of the death receptor subfamily. This FAS overexpression was significantly reduced in the cortex of mice overexpressing both wild-type hAPP gene and wild-type human superoxide dismutase-1 gene (hSOD-1). Moreover hSOD-1 transgenic expression was associated with an increase of Glial fibrillary acidic protein (GFAP) production. This study indicates that SOD-1 overexpression can inhibit FAS expression, which may be beneficial in AD.

The effects of moderate-, strenuous- and over-training on oxidative stress markers, DNA repair, and memory, in rat brain

We have tested the hypothesis that training with moderate- (MT), strenuous- (ST), or over- (OT) load can cause alterations in memory, lipid peroxidation, protein oxidation, DNA damage, activity of 8-oxoG-DNA glycosylase (OGG1) and brain-derived neurotrophic factor (BDNF), in rat brain. Rat memory was assessed by a passive avoidance test and the ST and OT group demonstrated improved memory. The content of BDNF was increased only in the OT group. The oxidative damage of lipids and DNA, as measured by thiobarbituric acid reactive substances (TBARS), and 8-hydroxydeoxyguanosine (8-OHdG), did not change significantly with exercise. Similarly, the activity of DNA repair enzyme, 8-oxoguanine DNA glycosylase (OGG1), was not altered with exercise training. On the other hand, the content of reactive carbonyl derivatives (RCDs) decreased in all groups and the decrease reached significance levels in the ST and OT groups. The activity of the proteasome complex increased in the brain of OT. The findings of this study imply that over-training does not induce oxidative stress in the brain and does not cause loss of memory. The improved memory was associated with enhanced BDNF content.

Overexpressed Sod1p acts either to reduce or to increase the lifespans and stress resistance of yeast, depending on whether it is Cu(2+)-deficient or an active Cu,Zn-superoxide dismutase

Yeast overexpressing SOD1, the gene for Cu,Zn-superoxide dismutase (Cu,Zn-Sod), was used to determine how Sod1p overexpression influences the chronological lifespan [the survival of non-dividing stationary (G0) phase cells over time], the replicative lifespan (the number of buds produced by actively dividing yeast cells) and stress resistance. Increasing the level of active Cu,Zn-Sod in yeast was found to require either growth in the presence of high copper, or the simultaneous overexpression of both SOD1 and CCS1 (the latter being the gene that encodes the chaperone dedicated to Cu(2+)-loading of Sod1p in vivo). Dual SOD1 + CCS1 overexpression elevated the levels of Cu,Zn-Sod activity six- to eight-fold in vegetative cultures. It also increased the optimized survival of stationary cells up to two-fold, showing this chronological lifespan is ultimately limited by oxidative stress. In contrast, several detrimental effects resulted when the SOD1 gene was overexpressed in the absence of either high copper or a simultaneous overexpression of CCS1. Both the chronological and the replicative lifespans were shortened; the cells displayed an abnormally high level of endogenous oxidative stress, resulting in a high rate of spontaneous mutation. Such harmful effects were all reversed through the overexpression of CCS1. It is apparent therefore that they relate to the incomplete Cu(2+)-loading of the overexpressed Sod1p, most probably accumulation of a Cu(2+)-deficient Sod1p to appreciable levels in vivo. The same events may generate the detrimental effects that are frequently, though not universally, observed when Cu,Zn-Sod overexpression is attempted in metazoans.

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.

Role of the metabotropic P2Y(4) receptor during hypoglycemia: cross talk with the ionotropic NMDAR1 receptor

It is well established that both extracellular ATP and glutamate exert a critical role during metabolic impairment, that several P2 receptor subunits are directly involved in this action and that a strong relationship exists between glutamatergic and purinergic signals. Therefore, here we studied the molecular behavior of the purinergic metabotropic P2Y(4) and the glutamatergic ionotropic NMDAR1 receptors during hypoglycemic cell death. We find that these proteins are oppositely modulated during glucose starvation (P2Y(4) is induced, whereas NMDAR1 is inhibited) and that both P2 and NMDA antagonists can restore basal protein expression levels. Moreover, double immunofluorescence experiments with confocal laser microscopy reveal co-localization at the membrane level between the P2Y(4) and NMDAR1 receptors, in both homologous (cerebellar granule neurons) and heterologous (Hek-293) cellular systems. This is furthermore confirmed by co-immunoprecipitation experiments. Finally, when we express the P2Y(4) receptor in the heterologous SH-SY5Y neuronal cell line, hypoglycemia then causes severe cell death and simultaneous downregulation of the NMDAR1 protein. In summary, our work establishes a potential molecular interplay between P2Y(4) and NMDAR1 receptors during glucose deprivation and the causative role of the P2Y(4) during cell death.

Brain ?-Amyloid Accumulation in Transgenic Mice Expressing Mutant Superoxide Dismutase 1

Oxidative stress is implicated in both the deposition and pathogenesis of beta-amyloid (Abeta) protein in Alzheimer's disease (AD). Accordingly, overexpression of the antioxidant enzyme superoxide dismutase 1 (SOD1) in neuronal cells and transgenic AD mice reduces Abeta toxicity and accumulation. In contrast, mutations in SOD1 associated with amyotrophic lateral sclerosis (ALS) confer enhanced pro-oxidative enzyme activities. We therefore examined whether ALS-linked mutant SOD1 overexpression in motor neuronal cells or transgenic ALS mice modulates Abeta toxicity or its accumulation in the brain. Aggregated, but not freshly solubilised, substrate-bound Abeta peptides induced degenerative morphology and cytotoxicity in motor neuron-like NSC-34 cells. Transfection of NSC-34 cells with human wild-type SOD1 attenuated Abeta-induced toxicity, however this neuroprotective effect was also observed for ALS-linked mutant SOD1. Analysis of the cerebral cortex, brainstem, cerebellum and olfactory bulb from transgenic SOD1G93A mice using enzyme-linked immunosorbent assay of acid-guanidine extracts revealed age-dependent elevations in Abeta levels, although not significantly different from wild-type mouse brain. In addition, brain amyloid protein precursor (APP) levels remained unaltered as a consequence of mutant SOD1 expression. We therefore conclude that mutant SOD1 overexpression promotes neither Abeta toxicity nor brain accumulation in these ALS models.

S-Allylcysteine prevents amyloid-β peptide-induced oxidative stress in rat hippocampus and ameliorates learning deficits

The effects of S-allylcysteine on oxidative damage and spatial learning and memory deficits produced by an intrahippocampal injection of amyloid-beta peptide 25-35 (Abeta(25-35)) in rats were investigated. The formation of reactive oxygen species, lipid peroxidation and the activities of the antioxidant enzymes superoxide dismutase and glutathione peroxidase were all measured in hippocampus 120 min after Abeta(25-35) injection (1 microl of 100 microM solution), while learning and memory skills were evaluated 2 and 35 days after the infusion of Abeta(25-35) to rats, respectively. Abeta(25-35) increased both reactive oxygen species and lipid peroxidation, whereas pretreatment with S-allylcysteine (300 mg/kg, i.p.) 30 min before peptide injection decreased both of these markers. In addition, Abeta(25-35)-induced incorrect learning responses were prevented in most of trials by S-allylcysteine. In contrast, enzyme activities were found unchanged in all groups tested. Findings of this work: (i) support the participation of reactive oxygen species in Abeta(25-35)-induced hippocampal toxicity and learning deficits; and (ii) suggest that the protective effects of S-allylcysteine were related to its ability to scavenge reactive oxygen species.