Involvement of free oxygen radicals in beta-amyloidosis: an hypothesis

Indian Medicinal Herbs and Formulations for Alzheimer's Disease, from Traditional Knowledge to Scientific Assessment

Cognitive impairment, associated with ageing, stress, hypertension and various neurodegenerative disorders including Parkinson's disease and epilepsy, is a major health issue. The present review focuses on Alzheimer's disease (AD), since it is the most important cause of cognitive impairment. It is characterized by progressive memory loss, language deficits, depression, agitation, mood disturbances and psychosis. Although the hallmarks of AD are cholinergic dysfunction, β-amyloid plaques and neurofibrillary tangle formation, it is also associated with derangement of other neurotransmitters, elevated levels of advanced glycation end products, oxidative damage, neuroinflammation, genetic and environmental factors. On one hand, this complex etiopathology makes a response to commonly used drugs such as donepezil, rivastigmine, galantamine and memantine less predictable and often unsatisfactory. On the other hand, it supports the use of herbal medicines due to their nonspecific antioxidant and anti-inflammatory activity and specific cholinesterase inhibitory activity. The popularity of herbal medicines is also increasing due to their perceived effectiveness, safety and affordability. In the present article, the experimental and clinical evidence have been reviewed for various Indian herbal medicines such as Centella asiatica, Bacopa monnieri, Curcuma longa, Clitoria ternatea, Withania somnifera, Celastrus paniculatus, Evolvulus alsinoides, Desmodium gangeticum, Eclipta alba, Moringa oleifera and Convolvulus pluricaulis, which have shown potential in cognitive impairment. Some commonly available herbal formulations for memory impairment in India have also been reviewed.

Liposome delivery systems for the treatment of Alzheimer's disease

Alzheimer's disease (AD) will affect around 115 million people worldwide by the year 2050. It is associated with the accumulation of misfolded and aggregated proteins (β-amyloid and tau) in the senile plaques and neurofibrillary tangles found in the brain. Currently available drugs for AD only temporarily alleviate symptoms and do not slow the inevitable progression of this disease. New drugs are required that act on key pathologies in order to arrest or reverse cognitive decline. However, there has been a spectacular failure rate in clinical trials of conventional small molecule drugs or biological agents. Targeted nanoliposomes represent a viable and promising drug delivery system for AD that have not yet reached clinical trials. They are biocompatible, highly flexible, and have the potential to carry many different types of therapeutic molecules across the blood-brain barrier (BBB) and into brain cells. They can be tailored to extend blood circulation time and can be directed against individual or multiple pathological targets. Modifications so far have included the use of brain-penetrating peptides, together with Aβ-targeting ligands, such as phosphatidic acid, curcumin, and a retro-inverted peptide that inhibits Aβ aggregation. Combining several modifications together into multifunctional liposomes is currently a research area of great interest. This review focuses on recent liposomal approaches to AD therapy, including mechanisms involved in facilitating their passage across the BBB, and the evaluation of new therapeutic agents for blocking Aβ and/or tau aggregation.

Ginkgo biloba: A Cognitive Enhancer?

Ginkgo biloba is an herb often used as an alternative treatment to improve cognitive functions. Like most herbal treatments, the use of ginkgo is poorly regulated by government agencies, on the basis of either its efficacy or its health risks. This article reviews the experimental evidence available regarding efficacy, neurobiological actions, and health risks. Findings obtained in studies of humans often include demonstrations of rather mild cognitive enhancement. Interpretation of these findings is complicated by somewhat inconsistent findings, by experimental designs that do not permit identification of cognitive functions susceptible to the influence of ginkgo, and by the paucity of direct comparisons with other treatments. The number of peer-reviewed reports of studies in nonhuman animals is surprisingly small. In this small set, the findings reveal mild behavioral effects that might be attributable to actions on cognitive functions. However, these experiments in rodents, like those in humans, do not involve the use of designs to assess ginkgo's effects on particular cognitive attributes, and generally do not include direct comparisons with other treatments. Interpretation of the findings is further complicated by evidence, obtained in studies of both humans and rats, showing that a single administration of the treatment enhances performance on cognitive measures.

If ginkgo has effects on cognition, there should be effects evident on biological processes as well. Neurobiological studies have largely examined the effects of chronic ginkgo administration, mirroring the most common design in behavioral studies. However, the addition of findings that single administration of ginkgo may influence behavior directs biological investigations to short-term actions of the treatment. Biological effects of ginkgo include vasodilation, protection of neurons from oxidative stress, and actions mediated by effects via neurotransmitters. Adverse reactions to ginkgo consumption have been observed but are relatively rare.

Collectively, the behavioral literature reviewed cannot be used conclusively to document or to refute the efficacy of ginkgo in improving cognitive functions. At best, the effects seem quite modest. In particular, it is questionable whether effects of ginkgo, if present, are equal to those obtained by administration of acetylcholinesterase inhibitors, hearing an arousing story, or ingesting glucose.

Therapeutic advantage of pro-electrophilic drugs to activate the Nrf2/ARE pathway in Alzheimer's disease models

Alzheimer's disease (AD) is characterized by synaptic and neuronal loss, which occurs at least partially through oxidative stress induced by oligomeric amyloid-β (Aβ)-peptide. Carnosic acid (CA), a chemical found in rosemary and sage, is a pro-electrophilic compound that is converted to its active form by oxidative stress. The active form stimulates the Keap1/Nrf2 transcriptional pathway and thus production of phase 2 antioxidant enzymes. We used both in vitro and in vivo models. For in vitro studies, we evaluated protective effects of CA on primary neurons exposed to oligomeric Aβ. For in vivo studies, we used two transgenic mouse models of AD, human amyloid precursor protein (hAPP)-J20 mice and triple transgenic (3xTg AD) mice. We treated these mice trans-nasally with CA twice weekly for 3 months. Subsequently, we performed neurobehavioral tests and quantitative immunohistochemistry to assess effects on AD-related phenotypes, including learning and memory, and synaptic damage. In vitro, CA reduced dendritic spine loss in rat neurons exposed to oligomeric Aβ. In vivo, CA treatment of hAPP-J20 mice improved learning and memory in the Morris water maze test. Histologically, CA increased dendritic and synaptic markers, and decreased astrogliosis, Aβ plaque number, and phospho-tau staining in the hippocampus. We conclude that CA exhibits therapeutic benefits in rodent AD models and since the FDA has placed CA on the 'generally regarded as safe' (GRAS) list, thus obviating the need for safety studies, human clinical trials will be greatly expedited.

Oxidative Stress in Alzheimer's Disease: Should We Keep Trying Antioxidant Therapies?

The risk of chronic diseases such as Alzheimer's disease is growing as a result of the continuous increasing average life span of the world population, a syndrome characterized by the presence of intraneural neurofibrillary tangles and senile plaques composed mainly by beta-amyloid protein, changes that may cause a number of progressive disorders in the elderly, causing, in its most advanced stage, difficulty in performing normal daily activities, among other manifestations. Therefore, it is important to understand the underlying pathogenic mechanisms of this syndrome. Nevertheless, despite intensive effort to access the physiopathological pathways of the disease, it remains poorly understood. In that context, some hypotheses have arisen, including the recent oxidative stress hypothesis, theory supported by the involvement of oxidative stress in aging, and the vulnerability of neurons to oxidative attack. In the present revision, oxidative changes and redox mechanisms in Alzheimer's disease will be further stressed, as well as the grounds for antioxidant supplementation as adjuvant therapy for the disease will be addressed.

Inflammation and the pathophysiology of Alzheimer's disease

There is increasing evidence that a chronic inflammatory response in the brain in Alzheimer's disease (AD) ultimately leads to neuronal injury and cognitive decline. Microglia, the primary immune effector cells of the brain, are thought to be key to this process. This paper discusses the evidence for inflammation in AD, and describes the mechanism whereby microglia generate neurotoxic cytokines, reactive oxygen species, and nitric oxide. Evidence that the cytokine macrophage colony-stimulating factor (M-CSF) is an important cofactor in microglial activation in AD is presented. Ongoing work using organotypic hippocampal expiant cultures to model the inflammatory process in the AD brain is also discussed. Potential avenues for therapeutic intervention are outlined.

Beneficial effect of Toona sinensis Roemor on improving cognitive performance and brain degeneration in senescence-accelerated mice

The purpose of the present study was to examine the effects of Toona sinensis Roemor extracts on antioxidative activities, brain morphological changes and cognitive ability. In an in vitro study, the antioxidant capacities of water extracts from Toona sinensis Roemor leaf (TSL), root (TSR) and bark (TSB) were evaluated by an alpha,alpha-diphenyl-beta-pricryl-hydrazyl radical-scavenging test. The results showed that the scavenging activities of all Toona sinensis Roemor extracts were over 80% at a concentration of 0.625 mg/ml. In an in vivo study, 3-month-old male senescence-accelerated-prone 8 mice were used as the tested subjects and fed four different diets: casein diet or casein diet supplemented with 1% TSL, TSR or TSB extract for 12 weeks. The results showed that the mice supplemented with Toona sinensis Roemor extracts demonstrated significantly less amyloid beta-protein deposition and lower levels of thiobarbituric acid-reactive substances than the control group. All Toona sinensis Roemor diet groups also showed better active shuttle avoidance responses, and higher superoxide dismutase, catalase and glutathione peroxidase activities, than the control group. It can thus be concluded that supplementation with either TSL, TSR or TSB extract could not only reduce the incidence of ss-amyloid plaques, but also improve learning and memory ability in senescence-accelerated-prone 8 mice. This might be due to the beneficial effects of Toona sinensis Roemor extracts on promoting the antioxidative defence system.

In vivo protective effects of ferulic acid ethyl ester against amyloid-beta peptide 1-42-induced oxidative stress

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the deposition of amyloid-beta peptide (Abeta), a peptide that as both oligomers and fibrils is believed to play a central role in the development and progress of AD by inducing oxidative stress in brain. Therefore, treatment with antioxidants might, in principle, prevent propagation of tissue damage and neurological dysfunction. The aim of the present study was to investigate the in vivo protective effect of the antioxidant compound ferulic acid ethyl ester (FAEE) against Abeta-induced oxidative damage on isolated synaptosomes. Gerbils were injected intraperitoneally (i.p.) with FAEE or with dimethylsulfoxide, and synaptosomes were isolated from the brain. Synaptosomes isolated from FAEE-injected gerbils and then treated ex vivo with Abeta(1-42) showed a significant decrease in oxidative stress parameters: reactive oxygen species levels, protein oxidation (protein carbonyl and 3-nitrotyrosine levels), and lipid peroxidation (4-hydroxy-2-nonenal levels). Consistent with these results, both FAEE and Abeta(1-42) increased levels of antioxidant defense systems, evidenced by increased levels of heme oxygenase 1 and heat shock protein 72. FAEE led to decreased levels of inducible nitric oxide synthase. These results are discussed with potential therapeutic implications of FAEE, a brain accessible, multifunctional antioxidant compound, for AD involving modulation of free radicals generated by Abeta.

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 oxidative stress in neurodegeneration: recent developments in assay methods for oxidative stress and nutraceutical antioxidants

Reactive oxygen species (ROS) are produced in the course of normal metabolism and they serve important physiological functions. However, because of their high reactivity, accumulation of ROS beyond the immediate needs of the cell may affect cellular structure and functional integrity, by bringing about oxidative degradation of critical molecules, such as the DNA, proteins, and lipids. Although cells possess an intricate network of defense mechanisms to neutralize excess ROS and reduce oxidative stress, some tissues, especially the brain, are much more vulnerable to oxidative stress because of their elevated consumption of oxygen and the consequent generation of large amounts of ROS. For the same reason, the mitochondrial DNA (mtDNA) of brain cells is highly susceptible to structural alterations resulting in mitochondrial dysfunction. Several lines of evidence strongly suggest that these effects of ROS may be etiologically related to a number of neurodegenerative disorders. Nutraceutical antioxidants are dietary supplements that can exert positive pharmacological effects on specific human diseases by neutralizing the negative effects of ROS. The present communication concentrates on a review of recent concepts and methodological developments, some of them based on the results of work from our own laboratory, on the following aspects: (1) the complex interactions and complementary interrelationships between oxidative stress, mitochondrial dysfunction, and various forms of neural degeneration; (2) fractionation and isolation of substances with antioxidant properties from plant materials, which are extensively used in the human diet and, therefore, can be expected to be less toxic in any pharmacological intervention; (3) recent developments in methodologies that can be used for the assay of oxidative stress and determination of biological activities of exogenous and endogenous antioxidants; and (4) presentation of simple procedures based on polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) of the resulting amplicon for investigations of structural alterations in mtDNA.

Attenuation of chronic neuroinflammation by a nitric oxide-releasing derivative of the antioxidant ferulic acid

Chronic neuroinflammation and oxidative stress contribute to the neurodegeneration associated with Alzheimer's disease and represent targets for therapy. Ferulic acid is a natural compound that expresses antioxidant and anti-inflammatory activities. Nitric oxide is also a key modulator of inflammatory responses. Grafting a nitric oxide-releasing moiety onto anti-inflammatory drugs results in enhanced anti-inflammatory activity. We compared the effectiveness of ferulic acid with a novel nitric oxide-releasing derivative of ferulic acid in an animal model of chronic neuroinflammation that reproduces many interesting features of Alzheimer's disease. Lipopolysaccharide was infused into the 4th ventricle of young rats for 14 days. Various doses of ferulic acid or its nitric oxide-releasing derivative were administered daily. Both drugs produced a dose-dependent reduction in microglia activation within the temporal lobe. However, the nitric oxide-releasing ferulic acid derivative was significantly more potent. If we delayed the initiation of therapy for 14 days, we found no reduction in microglial activation. In addition, both drugs demonstrated antioxidant and hydroxyl radical scavenging abilities in in vitro studies. Overall, our results predict that a treatment using nitric oxide-releasing ferulic acid may attenuate the processes that drive the pathology associated with Alzheimer's disease if the treatment is initiated before the neuroinflammatory processes can develop.

Ammonia and Alzheimer's disease

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder. Behavioural, cognitive and memory dysfunctions are characteristic symptoms of AD. The formation of amyloid plaques is currently considered as the key event of AD. Other histological hallmarks of the disease are the formation of fibrillary tangles, astrocytosis, and loss of certain neuronal systems in cortical areas of the brain. A great number of possible aetiologic and pathogenetic factors of AD have been published in the course of the last two decades. Among the toxic factors, which have been considered to contribute to the symptoms and progression of AD, ammonia deserves special interest for the following reasons: (a) Ammonia is formed in nearly all tissues and organs of the vertebrate organism; it is the most common endogenous neurotoxic compounds. Its effects on glutamatergic and GABAergic neuronal systems, the two prevailing neuronal systems of the cortical structures, are known for many years. (b) The impairment of ammonia detoxification invariably leads to severe pathology. Several symptoms and histologic aberrations of hepatic encephalopathy (HE), of which ammonia has been recognised as a pathogenetic factor, resemble those of AD. (c) The excessive formation of ammonia in the brains of AD patients has been demonstrated, and it has been shown that some AD patients exhibit elevated blood ammonia concentrations. (d) There is evidence for the involvement of aberrant lysosomal processing of beta-amyloid precursor protein (beta-APP) in the formation of amyloid deposits. Ammonia is the most important natural modulator of lysosomal protein processing. (e) Inflammatory processes and activation of microglia are widely believed to be implicated in the pathology of AD. Ammonia is able to affect the characteristic functions of microglia, such as endocytosis, and cytokine production. Based on these facts, an ammonia hypothesis of AD has first been suggested in 1993. In the present review old and new observations are discussed, which are in support of the notion that ammonia is a factor able to produce symptoms of AD and to affect the progression of the disease.

The brain in Down syndrome

Down syndrome (trisomy 21) is a genetic disease with developmental brain abnormalities resulting in early mental retardation and precocious, age dependent Alzheimer-type neurodegeneration. We tried to discuss the role of neurodevelopmental abnormalities in connection with aberrant expression of genes on chromosome 21 including amyloid precursor protein (APP), CuZn superoxide dismutase (SOD1) and glial-derived S100 beta protein for neurodegeneration in DS. In this model, alterations in developmental pathways due to aberrant gene expression can impair cellular homeostasis and predispose to neurodegeneration of certain brain regions and types of nerve cells, involving cholinergic, serotonergic and catecholaminergic transmission, by shifting balance toward a pro-apoptotic state.

The curry spice curcumin reduces oxidative damage and amyloid pathology in an Alzheimer transgenic mouse

Inflammation in Alzheimer's disease (AD) patients is characterized by increased cytokines and activated microglia. Epidemiological studies suggest reduced AD risk associates with long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs). Whereas chronic ibuprofen suppressed inflammation and plaque-related pathology in an Alzheimer transgenic APPSw mouse model (Tg2576), excessive use of NSAIDs targeting cyclooxygenase I can cause gastrointestinal, liver, and renal toxicity. One alternative NSAID is curcumin, derived from the curry spice turmeric. Curcumin has an extensive history as a food additive and herbal medicine in India and is also a potent polyphenolic antioxidant. To evaluate whether it could affect Alzheimer-like pathology in the APPSw mice, we tested a low (160 ppm) and a high dose of dietary curcumin (5000 ppm) on inflammation, oxidative damage, and plaque pathology. Low and high doses of curcumin significantly lowered oxidized proteins and interleukin-1beta, a proinflammatory cytokine elevated in the brains of these mice. With low-dose but not high-dose curcumin treatment, the astrocytic marker GFAP was reduced, and insoluble beta-amyloid (Abeta), soluble Abeta, and plaque burden were significantly decreased by 43-50%. However, levels of amyloid precursor (APP) in the membrane fraction were not reduced. Microgliosis was also suppressed in neuronal layers but not adjacent to plaques. In view of its efficacy and apparent low toxicity, this Indian spice component shows promise for the prevention of Alzheimer's disease.

Long-term estrogen replacement is associated with improved nonverbal memory and attentional measures in postmenopausal women

OBJECTIVE

To determine the cognitive domains improved or preserved by long-term hormone replacement therapy (HRT).

DESIGN

A comprehensive neuropsychological test battery was administered to healthy postmenopausal women who had been treated or not treated with long-term HRT without interruption since menopause.

SETTING

Women were recruited by advertisement from a university town and surrounding areas.

PATIENT(S)

Women 60 years or older were studied who were treated (n = 16) or not treated (n = 13) with HRT.

INTERVENTION(S)

Neuropsychological testing included tests of memory, verbal fluency, executive functions, attention and concentration, and psychomotor function. Tests of intellectual function, depressive symptoms, and emotional functioning assessed general functions and comparability of the groups.

MAIN OUTCOME MEASURE(S)

Neuropsychological testing scores were compared between groups.

RESULT(S)

No statistically significant differences between the groups were found for general demographic, intellectual, and psychological measures. Scores from both the Weschler Memory Scale Visual Reproduction (delayed recall) and the Digit Vigilance Test (attention) showed statistically significant better performance and fewer errors in the group of women on HRT.

CONCLUSION(S)

Long-term postmenopausal HRT is associated with higher scores in tests of nonverbal memory and attention.

Intracellular mechanisms of amyloid accumulation and pathogenesis in Alzheimer's disease

Cell-culture studies have revealed some of the fundamental features of the interaction of amyloid Abeta with cells and the mechanism of amyloid accumulation and pathogenesis in vitro. A(beta)1-42, the longer isoform of amyloid that is preferentially concentrated in senile plaque (SP) amyloid deposits in Alzheimer's disease (AD), is resistant to degradation and accumulates as insoluble aggregates in late endosomes or lysosomes. Once these aggregates have nucleated inside the cell, they grow by the addition of aberrantly folded APP and amyloidgenic fragments of APP, that would otherwise be degraded, onto the amyloid lattice in a fashion analogous to prion replication. This accumulation of heterogeneous aggregated APP fragments and Abeta appears to mimic the pathophysiologyof dystrophic neurites, where the same spectrum of components has been identified by immunohistochemistry. In the brain, this residue appears to be released into the extracellular space, possibly by a partially apoptotic mechanism that is restricted to the distal compartments of the neuron. Ultimately, this insoluble residue may be further digested to the protease-resistant A(beta)n-42 core, perhaps by microglia, where it accumulates as senile plaques. Thus, the dystrophic neurites are likely to be the source of the immediate precursors of amyloid in the senile plaques. This is the opposite of the commonly held view that extracellular accumulation of amyloid induces dystrophic neurites. Many of the key pathological events of AD may also be directly related to the intracellular accumulation of this insoluble amyloid. The aggregated, intracellular amyloid induces the production of reactive oxygen species (ROS) and lipid peroxidation products and ultimately results in the leakage of the lysosomal membrane. The breakdown of the lysosomal membrane may be a key pathogenic event, leading to the release of heparan sulfate and lysosomal hydrolases into the cytosol. Together, these observations provide the novel view that amyloid deposits and some of the early events of amyloid pathogenesis initiate randomly within single cells in AD. This pathogenic mechanism can explain some of the more enigmatic features of Alzheimer's pathogenesis, like the focal nature of amyloid plaques, the relationship between amyloid, dystrophic neurites and neurofibrillary-tangle pathology, and the miscompartmentalization of extracellular and cytosolic components observed in AD brain.

Neuroimaging of aging and estrogen effects on central nervous system physiology

OBJECTIVE

To review the literature on neuroimaging studies focusing on gender differences in the aging process and on the effects of postmenopausal estrogen use on the brain.

DESIGN

Pertinent studies were identified through a computer MEDLINE search. References of selected articles were hand-searched for additional citations.

CONCLUSION(S)

The current literature suggests that estrogen replacement may decrease brain white matter lesions, increase cerebral blood flow, alter regional brain activation patterns during cognitive processing, and have modulatory effects on various neurotransmitter systems. Overall, this points to a functional plasticity in higher order brain processing that can be altered by gonadal steroids.

Increased mitochondrial superoxide generation in neurons from trisomy 16 mice: a model of Down's syndrome

Increased neuronal cell death in neurodegenerative diseases has been suggested to result from an increased mitochondrial generation of radical oxygen species (ROS). To test this hypothesis, we investigated superoxide formation in cultured hippocampal neurons from diploid and trisomy 16 mice (Ts16), a model of Down's syndrome. Microflurometric techniques were used to measure superoxide-induced oxidation rate of hydroethidine (HEt) to ethidium and reduced nicotinamide adenine dinucleotide (NADH) and reduced nicotinamide adenine dinucleotide phosphate (NADPH) autofluorescence signal to monitor changes in neuronal energy metabolism. We found an increase in superoxide formation by more than 50% in Ts16 neurons in comparison with diploid control neurons. In the presence of the mitochondrial respiratory chain complex I inhibitor rotenone superoxide production was blocked in diploid neurons, but the increased superoxide generation in Ts16 neurons remained. Uncoupling of mitochondrial oxidative phosphorylation using carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) caused irreversible deficiency in the energy metabolism, monitored by NAD(P)H autofluorescence in Ts16 neurons, but not in diploid control neurons. These results suggest an increased basal generation of superoxide in Ts16 neurons, probably caused by a deficient complex I of mitochondrial electron transport chain, which leads to an impaired mitochondrial energy metabolism and finally neuronal cell death.

Hydroxylamine attenuates the effects of simulated subarachnoid hemorrhage in the rat brain and improves neurological outcome

Some of the neurological deficits that emerge after aneurysmal subarachnoid hemorrhage (SAH) in humans are presumably caused by ischemic brain damage consequential to SAH-induced delayed cerebral vasospasm. This vasospasm probably results from an imbalance among vasoactive factors released from both the clot formed by extravasated blood and adjacent tissues, and in particular from a decrease in the endothelium-derived relaxing factor nitric oxide (NO). Brain ischemia is also known to elevate brain production and deposition of beta-amyloid, and to induce a delayed increase in total NO synthase (NOS) activity due to induction of expression of so-called induced NOS isoform, phenomena that may secondarily contribute to SAH-related brain damage. The aim of this study was to investigate the effects of treatment with the intracellular NO donor hydroxylamine on: (i) basilar arterial wall that remained in a direct contact with the clot, (ii) formation of the beta-amyloid precursor protein (beta-APP), (iii) total brain NOS activity, and (iv) neurological outcome in a 'two-hemorrhage' rat SAH model. Intraperitoneal (i.p.) administration of 0.18 mmol/kg hydroxylamine hydrochloride (12.5 mg/kg) twice daily for 7 days beginning immediately after the first 'hemorrhage' (intracisternal blood injection) reduced basilar arterial wall damage and attenuated post-SAH neurological deficit. It also reduced the SAH-related increases in hippocampal and cortical beta-APP immunoreactivities and hippocampal NOS activity measured 24 h after commencement of the treatment. These results indicate that intracellular NO donors that yield NO through the action of widely distributed enzymes in brain cells (cytochromes, catalase) can attenuate detrimental effects of SAH.

Alzheimer's disease and oxidative stress: implications for novel therapeutic approaches

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with a deadly outcome. AD is the leading cause of senile dementia and although the pathogenesis of this disorder is not known, various hypotheses have been developed based on experimental data accumulated since the initial description of this disease by Alois Alzheimer about 90 years ago. Most approaches to explain the pathogenesis of AD focus on its two histopathological hallmarks, the amyloid beta protein- (A(beta)-) loaded senile plaques and the neurofibrillary tangles, which consist of the filament protein tau. Various lines of genetic evidence support a central role of A(beta) in the pathogenesis of AD and an increasing number of studies show that oxidation reactions occur in AD and that A(beta) may be one molecular link between oxidative stress and AD-associated neuronal cell death. A(beta) itself can be neurotoxic and can induce oxidative stress in cultivated neurons. A(beta) is, therefore, one player in the concert of oxidative reactions that challenge neurons besides inflammatory reactions which are also associated with the AD pathology. Consequently, antioxidant approaches for the prevention and therapy of AD are of central interest. Experimental as well as clinical data show that lipophilic antioxidants, such as vitamin E and estrogens, are neuroprotective and may help patients suffering from AD. While an additional intensive elucidation of the cellular and molecular events of neuronal cell death in AD will, ultimately, lead to novel drug targets, various antioxidants are already available for a further exploitation of their preventive and therapeutic potential. reserved

Low plasma vitamin C in Alzheimer patients despite an adequate diet

OBJECTIVE

To compare the vitamin C and E plasma levels in patients with Alzheimer's disease (AD) and to assess the vitamin C intake and nutritional status.

DESIGN

Case-control study. Four groups of sex- and age-matched subjects were compared: severe AD and moderate AD, in patients with moderate AD and controls.

SETTING

Community and hospitalized patients in the region of Toulouse, France.

PARTICIPANTS

Patients with dementia who fulfilled criteria for Alzheimer's disease: severe Alzheimer group (N = 20), Mini-Mental State Examination (MMSE) score range 0-9; moderate Alzheimer group (N = 24), MMSE 10-23; hospitalized Alzheimer group (N = 9), MMSE 10-23. Control group (N = 19), MMSE 24-30.

MEASURES

Plasma vitamin E and C were quantified by HPLC-fluorescence. Consumption of raw and cooked fruit and vegetables was evaluated in order to determine the mean vitamin C intakes. Mini Nutritional Assessment (MNA) and plasma albumin were used to measure nutritional status.

RESULTS

Institutionalized and community subjects were analysed separately. MNA scores were normal in home-living Alzheimer subjects with moderate dementia and significantly lower in those with severe disease, despite normal plasma albumin levels. In the home-living Alzheimer subjects, vitamin C plasma levels decreased in proportion to the severity of the cognitive impairment despite similar vitamin C intakes, whereas vitamin E remained stable. The hospitalized Alzheimer subjects had lower MNA scores and albumin levels but normal vitamin C intakes, but their plasma vitamin C was lower than that of community-living subjects. Institutionalized Alzheimer subjects had significantly lower MNA scores but normal vitamin C and albumin levels and vitamin C intakes compared with community-dwelling subjects of similar degree of cognitive impairment.

CONCLUSION

Plasma vitamin C is lower in AD in proportion to the degree of cognitive impairment and is not explained by lower vitamin C intake. These results support the hypothesis that oxygen-free radicals may cause damage.

Glutathione depletion exacerbates impairment by oxidative stress of phosphoinositide hydrolysis, AP-1, and NF-kappaB activation by cholinergic stimulation

Oxidative stress appears to contribute to neuronal dysfunction associated with Alzheimer's disease and other CNS neurodegenerative disorders. This investigation examined if oxidative stress might contribute to impairments in cholinergic receptor-linked signaling systems and if intracellular glutathione levels modulated responses to oxidative stress. To do this the activation of the AP-1 and NF-kappaB transcription factors and of the phosphoinositide second-messenger system was measured in human neuroblastoma SH-SY5Y cells after exposure to the oxidants H2O2 or diamide, with or without prior depletion of cellular glutathione. H2O2 concentration-dependently inhibited carbachol-stimulated AP-1 activation and this inhibition was potentiated in glutathione-depleted cells. Carbachol-stimulated NF-kappaB activation was unaffected by H2O2 unless glutathione was depleted, in which case there was a H2O2 concentration-dependent inhibition. Glutathione depletion also potentiated the inhibition by H2O2 of carbachol- or G-protein (NaF)-stimulated phosphoinositide hydrolysis, whereas phospholipase C activated by the calcium ionophore ionomycin was not inhibited. The thiol-oxidizing agent diamide also inhibited phosphoinositide hydrolysis stimulated by carbachol or NaF, and glutathione depletion potentiated the diamide concentration-dependent inhibition. Unlike H2O2, diamide also inhibited ionomycin-stimulated phosphoinositide hydrolysis. Activation of both AP-1 and NF-kappaB stimulated by carbachol was inhibited by diamide, and glutathione depletion potentiated the inhibitory effects of diamide. Thus, diamide inhibited a wider range of signaling processes than did H2O2, but glutathione depletion increased the susceptibility of phosphoinositide hydrolysis and of transcription factor activation to inhibition by both H2O2 and diamide. These results demonstrate that the vulnerability of signaling systems to oxidative stress is influenced by intracellular glutathione levels, indicating that cell-selective susceptibility to inhibition of signal transduction systems by oxidative stress can arise from cellular variations in antioxidant capacity.

Mechanisms of resistance to oxidative stress in Alzheimer's disease

It is likely that amyloid beta-protein (A beta) mediates nerve cell death in Alzheimer's disease (AD). Some nerve cell populations, however, remain undamaged in AD brain. To understand the biochemical basis for resistance to A beta toxicity, a series of cell lines were isolated which are resistant to A beta toxicity. It is shown that a major component of the resistance mechanism is the transcriptional elevation of two H2O2 degrading enzymes, glutathione peroxidase and catalase. These data support other evidence for the role of oxidative damage in A beta toxicity, and suggest strategies for clinical approaches to the disease.

Oxidative modification of glutamine synthetase by amyloid beta peptide

beta-Amyloid peptide (A beta), the main constituent of senile plaques and diffuse amyloid deposits in Alzheimer's diseased brain, was shown to initiate the development of oxidative stress in neuronal cell cultures. Toxic lots of A beta form free radical species in aqueous solution. It was proposed that A beta-derived free radicals can directly damage cell proteins via oxidative modification. Recently we reported that synthetic A beta can interact with glutamine synthetase (GS) and induce inactivation of this enzyme. In the present study we present the evidence that toxic A beta(25-35) induces the oxidation of pure GS in vitro. It was found that inactivation of GS by A beta, as well as the oxidation of GS by metal-catalyzed oxidation system, is accompanied by an increase of protein carbonyl content. As it was reported previously by our laboratory, radicalization of A beta is not iron or peroxide-dependent. Our present observations consistently show that toxic A beta does not need iron or peroxide to oxidize GS. However, treatment of GS with the peptide, iron and peroxide together significantly stimulates the protein carbonyl formation. Here we report also that A beta(25-35) induces carbonyl formation in BSA. Our results demonstrate that beta-peptide, as well as other free radical generators, induces carbonyl formation when brought into contact with different proteins.

Evidence against increased glycoxidation in patients with Alzheimer's disease

Neuropathological findings of Alzheimer's disease (AD) are intracellular (neurofibrillary tangles) and extracellular (senile plaques) filamentous protein aggregates. Non-enzymatic glycation has been proposed as a primary factor in this pathogenesis, leading to increased insolubility of tau protein and beta-amyloid. The aim of our study was to test the hypothesis that increased glycoxidation, i.e. increased levels of oxidized products from non-enzymatic glycation could be found in brains of patients with AD and of aged Down syndrome (DS) subjects with abundant AD-like neuropathological lesions. Frontal cortex specimens were assayed for pentosidine (Pent) and N-epsilon-carboxymethyl-lysine (CML) by reversed phase high performance liquid chromatographical methods. Pent and CML levels in AD (n = 10; Pent, 35.5 +/- 4.84 mumol/g wet-weight tissue; CML, 135.2 +/- 5.0 mumol/g wet-weight tissue) were comparable to DS (n = 9; Pent, 36.4 +/- 3.21; CML, 133.5 +/- 4.7) and controls (n = 10; Pent, 35.2 +/- 3.55; CML, 136.9 +/- 3.3). We conclude that the results are not compatible with the concept of increased glycoxidation in AD compared to normal aging.

Zinc and Alzheimer's disease: is there a direct link?

Zinc is an essential trace element in human biology, but is neurotoxic at high concentrations. Several studies show that zinc promotes aggregations of beta-amyloid protein, the main component of the senile plaques typically found in Alzheimer's disease brains. In other neurological disorders where neurons appear to be dying by apoptosis (gene-directed cell death), chelatable zinc accumulates in the perikarya of neurons before, or during degeneration. As there is evidence for apoptotic death of neurons in Alzheimer's disease, an involvement of zinc in this process needs to be investigated. Zinc interacts with enzymes and proteins, including transcription factors, which are critical for cell survival and could be linked to apoptotic processes. While controversial, some studies indicate that total tissue zinc is markedly reduced in several brain regions of Alzheimer's patients. At face value, it seems that a paradox exists between reports of a decrease in zinc in the Alzheimer's brain and the putative link to aberrant high zinc levels promoting plaque formation. An hypothesis to explain this inconsistency is presented. Neuropathological changes mediated by endogenous or exogenous stressors may be relevant factors affecting abnormal zinc metabolism. This paper reviews current investigations that suggest a role of zinc in the etiology of Alzheimer's disease.

Dexamethasone attenuates NF-kappa B DNA binding activity without inducing I kappa B levels in rat brain in vivo

This investigation tested if glucocorticoid hormones modulate activation of the NF-kappa B transcription factor in rat brain in vivo. Dexamethasone (2 mg/kg) administration decreased NF-kappa B DNA binding in cerebral cortex and hippocampus nuclear extracts, maximally at 3-6 h after dexamethasone, followed by recovery at 24 h. Dexamethasone did not inhibit NF-kappa B by increasing the level of the inhibitory protein I kappa B alpha, as occurs in some peripheral cells, but instead lowered I kappa B alpha levels. Direct protein-protein inhibition by glucocorticoids was indicated by co-precipitation of glucocorticoid receptors with the p65 NF-kappa B subunit. Thus, glucocorticoids inhibit NF-kappa B DNA binding in rat brain, apparently by complexing with NF-kappa B subunits, which may contribute to the detrimental effects of glucocorticoids on neuronal function associated with oxidative stress and excitotoxicity.

Cholinergic stimulation of AP-1 and NF kappa B transcription factors is differentially sensitive to oxidative stress in SH-SY5Y neuroblastoma: relationship to phosphoinositide hydrolysis

Oxidative stress appears to contribute to neuronal dysfunction in a number of neurodegenerative conditions, notably including Alzheimer's disease, in which cholinergic receptor-linked signal transduction activity is severely impaired. To test whether oxidative stress could contribute to deficits in cholinergic signaling, responses to carbachol were measured in human neuroblastoma SH-SY5Y cells exposed to H2O2. DNA binding activities of two transcription factors that are respondent to oxidative conditions, AP-1 and NF kappa B, were measured in nuclear extracts. H2O2 and carbachol individually induced dose- and time-dependent increases in AP-1 and NF kappa B. In contrast, when given together, H2O2 concentration dependently (30-300 microM) inhibited the increase after carbachol in AP-1. Carbachol's stimulation of NF kappa B was not inhibited except with a high concentration (300 microM) of H2O2, which was associated with impaired activation of protein kinase C. Lower concentrations of H2O2 (30-300 microM) inhibited carbachol-induced [3H]phosphoinositide hydrolysis, and this inhibition correlated (r = 0.95) with the inhibition of carbachol-induced AP-1. Activation [3H]phosphoinositide hydrolysis by the calcium ionophore ionomycin was unaffected by H2O2, indicating that phospholipase C and phosphoinositides were impervious to this treatment. In contrast, activation with NaF of G-proteins coupled to phospholipase C was concentration dependently inhibited by H2O2, indicating impaired G-protein function. These effects of H2O2 are similar to signaling impairments reported in Alzheimer's disease brain, which involve deficits in receptor- and G-protein-stimulated phosphoinositide hydrolysis, but not phospholipase C activity. Thus, these findings indicate that oxidative stress may contribute to impaired phosphoinositide signaling in neurological disorders in which oxidative stress occurs, and that oxidative stress can differentially influence transcription factors activated by cholinergic stimulation.

Increased regional brain concentrations of ceruloplasmin in neurodegenerative disorders

Ceruloplasmin (CP), the major plasma anti-oxidant and copper transport protein, is synthesized in several tissues, including the brain. We compared regional brain concentrations of CP and copper between subjects with Alzheimer's disease (AD, n = 12), Parkinson's disease (PD, n = 14), Huntington's disease (HD, n = 11), progressive supranuclear palsy (PSP, n = 11), young adult normal controls (YC, n = 6) and elderly normal controls (EC, n = 7). Mean CP concentrations were significantly increased vs. EC (P < 0.05) in AD hippocampus, entorhinal cortex, frontal cortex, and putamen. PD hippocampus, frontal, temporal, and parietal cortices, and HD hippocampus, parietal cortex, and substantia nigra. Immunocytochemical staining for CP in AD hippocampus revealed marked staining within neurons, astrocytes, and neuritic plaques. Increased CP concentrations in brain in these disorders may indicate a localized acute phase-type response and/or a compensatory increase to oxidative stress.

8OHdG levels in brain do not indicate oxidative DNA damage in Alzheimer's disease

Accumulation of oxidative DNA damage has been proposed to underlie aging and neurodegenerative diseases such as Alzheimer's Disease (AD). The DNA adduct 8-hydroxy-2'-deoxyguanosine (8OHdG) is considered a good indicator of oxidative DNA damage. To investigate whether this type of DNA damage is involved in AD etiology, 8OHdG levels were determined in postmortem human brain tissue of controls and AD patients (in frontal, occipital, and temporal cortex and in hippocampal tissue). Parametric studies in rat revealed no influences of postmortem delay, repeated freezing/thawing or storage time. In human brain, approximately two 8OHdG molecules were present per 10(5) 2'-deoxyguanosines. In AD patients and controls, 8OHdG-levels were not related to age, sex, or brain region. Also, no differences were found between controls and AD patients. It was concluded that 8OHdG in nuclear DNA, although present throughout the brain in fairly high amounts, does not accumulate with age, nor does it appear to be involved in AD. More detailed studies are required to extend this conclusion to other types of oxidative damage.

Immunocytochemical localization of seleno-glutathione peroxidase in the adult mouse brain

Cytoplasmic seleno-glutathione peroxidase, by reducing hydrogen peroxide and fatty acid hydroperoxides, may be a major protective enzyme against oxidative damage in the brain. Oxidative damage is strongly suspected to contribute to normal aging and neurodegenerative process of Alzheimer's and Parkinson's diseases. We report here an immunocytochemical analysis of the localization of glutathione peroxidase in the adult mouse brain, carried out with an affinity-purified polyclonal antibody. Most of the brain areas analysed showed weak to strong glutathione peroxidase immunoreactivity, expressed in both neurons and glial cells. The strongest immunoreactivity was found in the reticular thalamic and red nuclei. Highly immunoreactive neurons were observed in the cerebral cortex (layer II), the CA1, dentate gyrus and pontine nucleus. Other regions, such as the caudate-putamen, septum nuclei, diagonal band of Broca, hippocampus, thalamus and hypothalamus, showed moderate staining. This study provides original information about the wide distribution of glutathione peroxidase in the mouse brain. Double-staining experiments indicated that specific subsets of cholinergic neurons in septal and diagonal band nuclei were negative for this antigen. Similarly, many dopaminergic neurons of the substantia nigra pars compacta expressed low levels of glutathione peroxidase antigen, in contrast to the ventral tegmental area, wherein most catecholaminergic cells were strongly positive. A lack of glutathione peroxidase in subsets of dopaminergic or cholinergic neurons may thus confer a relative sensitivity of these cells to oxidative injury of various origins, including catecholamine oxidation, neurotoxins and excitotoxicity.

Evidence against the involvement of reactive oxygen species in the pathogenesis of neuronal death in Down's syndrome and Alzheimer's disease

It has been proposed that the pathogenesis of Down's Syndrome (DS) involves reactive oxygen species (ROS) arising from a gene dosage effect that disproportionately elevates superoxide dismutase (SOD1) activity. It was also suggested that generation of ROS might be responsible for neuronal death in Alzheimer's Disease (AD). Little data on brain ROS in DS and AD exist; therefore, we determined activities of choline acetyltransferase (ChAT) and of the oxidative defense enzymes SOD1 and glutathione peroxidase (GSHPx) in frontal cortex of aged patients with DS and AD. We also measured levels of malondialdehyde, which reflects lipid peroxidation, and o-tyrosine, which represents the hydroxyl radical attack. ChAT was significantly reduced in cortex of patients with DS (-68%) and AD (-66%) as compared to controls. There were no statistically significant differences, however, between controls and both neurodegenerative disorders for SOD1, GSHPx, malondialdehyde and o-tyrosine. Our data contradict the only previous finding on increased SOD1 and ROS in brains of patients with DS: age as well as methodological differences might account for the discrepancy. In conclusion, no evidence for a pathogenetic role of SOD1, GSHPx, lipid peroxidation or hydroxyl radical attack in aged patients with DS and AD could be provided.

Deleterious network hypothesis of Alzheimer's disease

Numerous studies indicate that aberrant amyloid precursor protein metabolism, elevated peroxidative damage, depressed energy metabolism and altered calcium homeostasis are four pivotal deleterious factors in the pathogenesis of Alzheimer's disease. Cumulative evidence further suggests that these four factors are intimately interrelated, forming a deleterious network. Based on this new concept of 'deleterious network', a unifying hypothesis-the deleterious network hypothesis of Alzheimer's disease-is proposed. The main ideas of the hypothesis are delineated as follows: increases in free radical damage, alterations in amyloid precursor protein metabolism, impairment of energy metabolism and abnormalities of calcium homeostasis are four cornerstones of a deleterious network. Various risk factors of Alzheimer's disease can triger the network by promoting the occurrence of one of these key components, resulting in the biological abnormalities of Alzheimer's disease. Based on this new theory, a majority of the important observations about Alzheimer's disease can be explained consistently and succinctly.

beta-Amyloid toxicity in organotypic hippocampal cultures: protection by EUK-8, a synthetic catalytic free radical scavenger

Oxygen free radicals have been proposed to mediate amyloid peptide (beta-AP)-induced neurotoxicity. To test this hypothesis, we evaluated the effects of EUK-8, a synthetic catalytic superoxide and hydrogen peroxide scavenger, on neuronal injury produced by beta-AP in organotypic hippocampal slice cultures. Cultures of equivalent postnatal day 35 (defined as mature) and 14 (defined as immature) were exposed to various concentrations of beta-AP (1-42 or 1-40) in the absence or presence of 25 microM EUK-8 for up to 72 hours. Neuronal injury was assessed by lactate dehydrogenase release and semiquantitative analysis of propidium iodide uptake at various times after the initiation of beta-AP exposure. Free radical production was inferred from the relative increase in dichlorofluorescein fluorescence, and the degree of lipid peroxidation was determined by assaying thiobarbituric acid-reactive substances. Treatment of mature cultures with beta-AP (50-250 microg/ml) in serum-free conditions resulted in a reproducible pattern of damage, causing a time-dependent increase in neuronal injury accompanied with formation of reactive oxygen species. However, immature cultures were entirely resistant to beta-AP-induced neurotoxicity and also demonstrated no dichlorofluorescein fluorescence or increased lipid peroxidation after beta-AP treatment. Moreover, mature slices exposed to beta-AP in the presence of 25 microM EUK-8 were significantly protected from beta-AP-induced neurotoxicity. EUK-8 also completely blocked beta-AP-induced free radical accumulation and lipid peroxidation. These results not only support a role for oxygen free radicals in beta-AP toxicity but also highlight the therapeutic potential of synthetic radical scavengers in Alzheimer disease.

HWA 285 (propentofylline)--a new compound for the treatment of both vascular dementia and dementia of the Alzheimer type

The pharmacological profile of HWA 285 favors its use in patients with both Alzheimer's disease (PDD) and/or vascular dementia (MID). Clinical trials showed clinically relevant, statistically significant efficacy in the domains of cognitive function, global function and activities of daily living (ADL) in both PDD and MID. HWA 285 had a prolonged symptomatic effect for at least 12 months, although therapeutic effects were seen already after the first 3 months of treatment. HWA 285 was very well tolerated for at least 1 year.

The toxicity in vitro of beta-amyloid protein

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Future therapeutic developments of estrogen use

The potential long-term benefits of estrogen replacement therapy (ERT) in the prevention of osteoporosis and heart disease have been reasonably well established. However, the favorable effects of ERT on cognitive function and prevention of senile dementia in old age now represents a revitalized area of clinical research. A growing body of experimental evidence has recently provided the neurobiologic basis to support the hypothesis that gonadal hormones such as estrogen have psychologic effects on human brain function and behavior. Studies in women who have undergone surgical menopause have demonstrated that the menopause is associated with subclinical cognitive and affective dysfunction, which is improved by ERT. In addition, a growing body of evidence suggests that estrogen may be an effective therapy for senile dementia in some elderly women. Recent epidemiologic studies have indicated that long-term postmenopausal ERT may prevent late-life cognitive dysfunction in older women. Several clinical trials employing oral estrogen therapy have also observed that some aged women with senile dementia have improved cognitive and affective function after estrogen therapy. Estrogen loss resulting in cognitive disorders, including menopausal cognitive dysfunction and senile dementia in late life, may act via several mechanisms. Estrogen may be an important growth factor for estrogen-responsive neurons. Estrogen therapy may also have substantial neurochemical effects, direct effects on the vasculature, and effects on the generation of free radicals, which may be toxic to neurons. At this time, several important clinical questions need to be answered regarding the role of ERT in the cognitive and affective dysfunctions associated with menopause and senile dementia. Should estrogen be used for menopausal women whose sole complaint is cognitive or affective dysfunction? Does long-term ERT prevent cognitive decline in late life if initiated at the time of menopause? Can ERT improve cognition and affective function in postmenopausal women with Alzheimer's disease, and does estrogen therapy prevent the progression of Alzheimer's disease in these patients? Finally, do the vascular effects of estrogen play a role in the treatment or prevention of both Alzheimer's disease and vascular dementia?

Down's syndrome and the links with Alzheimer's disease

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Different amyloidogenic peptides share a similar mechanism of neurotoxicity involving reactive oxygen species and calcium

The amyloid beta-peptide (A beta) that accumulates as insoluble plaques in the brains of Alzheimer's victims can be neurotoxic, by a mechanism that may involve generation of reactive oxygen species (ROS) and destabilization of cellular calcium homeostasis. We now provide evidence that the mechanism of neurotoxicity of two other amyloidogenic peptides (APs), human amylin and beta 2-microglobulin, also involves induction of ROS and elevation of [Ca2+]i. Human amylin, beta 2-microglobulin and A beta 1-40 all caused significant death of neurons in rat hippocampal cell cultures during 24-48 h exposure periods. Rat amylin, a non-AP, was not neurotoxic. Each AP caused an elevation of rest [Ca2+]i during a 20 h exposure period, and promoted a sustained elevation of [Ca2+]i following exposure to glutamate which was significantly greater than controls. Each AP induced accumulation of ROS in neurons which preceded elevation of [Ca2+]i. Several antioxidants, including propyl gallate, vitamin E and the spin-trapping compound N-tert-butyl-alpha-phenylnitrone attenuated the elevation of [Ca2+]i and neurotoxicity induced by the peptides. The data indicate that different APs share a common mechanism of neurotoxicity involving free radical accumulation and destabilization of [Ca2+]i homeostasis.