beta-Amyloid 25-35 activates nitric oxide synthase in a neuronal clone

Amyloid-beta(25-35) impairs memory and increases NO in the temporal cortex of rats

beta-Amyloid plays an important role in the neurodegeneration process of Alzheimer's disease (AD), but its neurotoxic mechanisms are not clear. It has been associated with the increase of oxidative stress and cognitive impairment because the beta-amyloid peptide 25-35 (Abeta((25-35))) has the critical neurotoxic properties of the full-length Abeta(1-42). Our present study shows the role of Abeta((25-35)) when injected into the temporal cortex on the nitric oxide pathways, 3-nitrotyrosine, neuronal death, and the spatial memory of rats 1 month after the injection. Our data showed that Abeta((25-35)) increases oxidative stress, causes neuronal damage, and decreases spatial memory in rats. Notably, the injection of the fraction Abeta((25-35)) caused an increase of nNOS and iNOS immunoreactivity in the temporal cortex and hippocampus. We demonstrated a significant increase of reactive astrocytosis, which was accompanied by neuronal damage in the temporal cortex and hippocampus of rats injected with Abeta((25-35)). These data suggest that the fraction Abeta((25-35)) injected into the temporal cortex might contribute to understanding the role of nitric oxide on the biological changes related to the neuropathological progression and the memory impairment in AD.

Beta-amyloid toxicity and reversal in embryonic rat septal neurons

Alzheimer's disease is characterized mainly by loss of neurons from the septal nucleus. In this study, neurons from the septal nucleus of the embryonic day 16 (E16) rat were grown in culture with a plane of astrocytes from the embryonic rat and in a defined medium in the absence of serum. Neurons were treated with beta-amyloid (Abeta: 0.1, 1 and 10 microM) on day in vitro (DIV) 1 and DIV 4 and fluorescent microscopy was used to measure survival and apoptosis following exposure of the treated cells on DIV 7. Reversal of neurotoxicity was studied using the potentially neuroprotective agents nerve growth factor (NGF, 100 ng/ml), basic fibroblast growth factor (bFGF, 5 ng/ml), insulin-like growth factors (IGF1 and IGF2, 10 ng/ml) and estrogen (10 nM), administered on DIV 4 and DIV 5, that is, subsequent to the Abeta (10 microM)-induced neurotoxicity. Abeta caused a significant decrease in survival at 10 microM, and a significant increase in apoptosis at 0.1 and 10 microM. IGF1, IGF2 and bFGF all caused a reversal of the Abeta-induced neurotoxic effect on survival while NGF and estrogen did not under these experimental conditions.

Beta-amyloid toxicity in embryonic rat astrocytes

The senile plaques of Alzheimer's disease contain a high concentration of beta-amyloid (betaA) protein, which may affect the glial population in the septal nucleus, an area of increased risk in AD. BetaA toxicity was measured in septal glia, via a dose-response experiment, by quantifying the effects of three different doses (0.1, 1, and 10 microM) of betaA on cell survival. Astrocytes from embryonic day-16 rats were grown in serum-free media in a single layer culture. Cells were treated on day in vitro (DIV)1 and survival was determined on DIV3 to ascertain which concentration was most toxic. In a separate set of experiments, an attempt was made to protect glial cells from the degenerative effects of betaA, with treatments of growth factors and estrogen. BetaA (10 microM) treatment was administered on DIV1, on DIV2 the cells were treated with estrogen (EST, 10 nM), insulin-like growth factors (IGF1 and IGF2, each 10 ng/ml), basic fibroblast growth factor (bFGF, 5 ng/ml) or nerve growth factor (NGF, 100 ng/ml), and on DIV3 the cells were visualized and quantified by fluorescence microscopy with DAPI (4,6-diamidino-2-phenylindole). In addition to dose-response and glial protection, experiments were also conducted to determine whether toxic effects were due to apoptosis. Our results suggest that the survival of glial populations is significantly affected in all three concentrations (0.1, 1.0, and 10 microM) of betaA. Glial protection was evident in the presence of NGF, for it showed the significantly highest survival rate relative to the betaA treatment alone. Furthermore, toxic effects of betaA appear to be due primarily to apoptosis. Significant reversal of betaA-induced apoptosis was seen with bFGF and IGF1.

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.

Expression of nitric oxide system in clinically evaluated cases of Alzheimer's disease

The expression of neuronal nitric oxide (nNOS) and inducible nitric oxide (iNOS) as isoforms of the nitric oxide synthase (NOS) as well as nitrotyrosine as an end product of protein nitration was analyzed in sections of temporal cortex taken from postmortem brains of patients with Alzheimer's disease (AD). The patients were evaluated by the Clinical Dementia Rating scale (CDR0-CDR3) and studied in the Memory and Aging Project (MAP) of the Washington University Alzheimer Disease Research Center (ADCR). With the use of immunocytochemical procedures, neurons immunoreactive to nNOS were found to show large and small multipolar and pyramidal morphologies over the entire chronic AD evolution. The iNOS and nitrotyrosine immunoreactivities were also found in pyramidal-like cortical neurons and glial cells. Here, we speculate on the interaction among all specific neurodegenerative changes in AD and nitric oxide as an additional contribution to neuronal death in AD.

Nitric oxide in the cerebral cortex of amyloid-precursor protein (SW) Tg2576 transgenic mice

Changes in the amyloid-peptide (Abeta), neuronal and inducible nitric oxide (NO)synthase (nNOS, iNOS), nitrotyrosine, glial fibrillary acidic protein, and lectin from Lycopersicon esculentum (tomato) were investigated in the cerebral cortex of transgenic mice (Tg2576) to amyloid precursor protein (APP), by immunohistochemistry (bright light, confocal, and electron microscopy). The expression of nitrergic proteins and synthesis of nitric oxide were analyzed by immunoblotting and NOS activity assays, respectively. The cerebral cortex of these transgenic mice showed an age-dependent progressive increase in intraneuronal aggregates of Abeta-peptide and extracellular formation of senile plaques surrounded by numerous microglial and reactive astrocytes. Basically, no changes to nNOS reactivity or expression were found in the cortical mantle of either wild or transgenic mice. This reactivity in wild mice corresponded to numerous large type I and small type II neurons. The transgenic mice showed swollen, twisted, and hypertrophic preterminal and terminal processes of type I neurons, and an increase of the type II neurons. The calcium-dependent NOS enzymatic activity was higher in wild than in the transgenic mice. The iNOS reactivity, expression and calcium-independent enzymatic activity increased in transgenic mice with respect to wild mice, and were related to cortical neurons and microglial cells. The progressive elevation of NO production resulted in a specific pattern of protein nitration in reactive astrocytes. The ultrastructural study carried out in the cortical mantle showed that the neurons contained intracellular aggregates of Abeta-peptide associated with the endoplasmic reticulum, mitochondria, and Golgi apparatus. The endothelial vascular cells also contained Abeta-peptide deposits. This transgenic model might contribute to understand the role of the nitrergic system in the biological changes related to neuropathological progression of Alzheimer's disease.

Potential roles of Alzheimer precursor protein A4 and beta-amyloid in survival and function of aged spinal motor neurons after axonal injury

To study the potential role of Alzheimer precursor protein A4 (APP) and beta-amyloid (A/beta) on aging motor neuron survival, expression of APP, A/beta, and choline acetyltransferase (ChaT) were investigated in aged rats after either distal axotomy or root avulsion injury. Approximately 45% in number of total aged spinal motor neuron were normally APP-positive. A/beta-positive neurites were observed normally in the spinal ventral horn of aged rats. After distal axotomy, without apparent neurodegeneration such as cell loss and decreased ChaT-immunoreactivity, increased levels of APP expression were observed in the spinal cords of aged rats post-injury. In contrast, after avulsion, expression of APP and A/beta were downregulated in the spinal ventral horn of aged rats, and marked loss of spinal motor neurons and downregulated ChaT expression were observed. Our data indicate that APP and A/beta might play beneficial roles in neuronal survival of aged spinal motor neurons after axonal injury.

Aberrant expression of NOS isoforms in Alzheimer's disease is structurally related to nitrotyrosine formation

Various isoforms of the nitric oxide (NO) producing enzyme nitric oxide synthase (NOS) are elevated in Alzheimer's disease (AD) indicating a critical role for NO in the pathomechanism. NO can react with superoxide to generate peroxynitrite, a process referred to as oxidative stress, which is likely to play a role in AD. Peroxynitrite in turn, nitrates tyrosine residues to form nitrotyrosine which can be identified immunohistochemically. To study the potential structural link between the increased synthesis of NO and the deposition of nitrotyrosine in AD, we analyzed the expression of neuronal NOS (nNOS), inducible NOS (iNOS) and endothelial NOS (eNOS) in AD and control brain, and compared the localization with the distribution of nitrotyrosine. Nitrotyrosine was detected in neurons, astrocytes and blood vessels in AD cases. Aberrant expression of nNOS in cortical pyramidal cells was highly co-localized with nitrotyrosine. Furthermore, iNOS and eNOS were highly expressed in astrocytes in AD. In addition, double immunolabeling studies revealed that in these glial cells iNOS and eNOS are co-localized with nitrotyrosine. Therefore, it is suggested that increased expression of all NOS isoforms in astrocytes and neurons contributes to the synthesis of peroxynitrite which leads to generation of nitrotyrosine. In view of the wide range of isoform-specific NOS inhibitors, the determination of the most responsible isoform of NOS for the formation of peroxynitrite in AD could be of therapeutic importance in the treatment of Alzheimer's disease.

Expression of endothelial and inducible NOS-isoforms is increased in Alzheimer's disease, in APP23 transgenic mice and after experimental brain lesion in rat: evidence for an induction by amyloid pathology

The nitric oxide-synthesizing enzyme nitric oxide synthase (NOS) is present in the mammalian brain in three different isoforms, two constitutive enzymes (i.e., neuronal, nNOS, and endothelial eNOS) and one inducible enzyme (iNOS). All three isoforms are aberrantly expressed in Alzheimer's disease giving rise to elevated levels of nitric oxide apparently involved in the pathogenesis of this disease by various different mechanisms including oxidative stress and activation of intracellular signalling mechanisms. It still is a matter of debate, however, whether the abnormal expression of NOS isoforms has some primary importance in the pathogenetic chain and might thus be a potential therapeutic target or only reflects a secondary effect that occurs at more advanced stages of the disease process. To tackle this question, we analysed the expression of both eNOS and iNOS in patients with sporadic AD, in transgenic mice expressing human amyloid precursor protein (APP) with the Swedish double mutation under control of the Thy1 promotor (APP23 mice), and after electrolytic cortical lesion in rat, an experimental paradigm associated with elevated expression of APP. In all three conditions, an astrocytosis was induced accompanied by a strong increase of both iNOS and eNOS. Both NOS isoforms were frequently though not always colocalized. Thus, based on the expression pattern of NOS isoforms three types of astrocytes, expressing only one of the two isoforms or both together could be distinguished. In both AD and transgenic mice eNOS-expressing astrocytes exceeded iNOS-expressing astrocytes in number. Astrocytes with elevated levels of iNOS or eNOS were constantly seen in direct association with Abeta-deposits in AD and transgenic mice and were found in the vicinity of the lesion site in the rat cortex. The results of the present study show that expression of both iNOS and eNOS is increased in activated astrocytes under experimental conditions associated with elevated expression of APP (electrolytic brain lesion) or Abeta-deposition (APP23 transgenic mice). Therefore, it is suggested that altered expression of these NOS isoforms being part of AD pathology is secondary to the amyloid pathology and might not be primarily involved in the pathogenetic chain though it might contribute to the maintenance, self-perpetuation and progression of the neurodegenerative process.

Mechanisms of amyloid beta protein-induced modification in ion transport systems: implications for neurodegenerative diseases

1. Alzheimer's disease (AD) is a neurodegenerative disorder that affects the cognitive function of the brain. Pathological changes in AD are characterized by the formation of amyloid plaques and neurofibrillary tangles as well as extensive neuronal loss. Abnormal proteolytic processing of amyloid precursor protein (APP) is the central step that leads to formation of amyloid plaque, neurofibrillary tangles, and neuronal loss. 2. The plaques, which accumulate extracellularly in the brain, are composed of aggregates and cause direct neurotoxic effects and/or increase neuronal vulnerability to excitotoxic insults. The aggregates consist of soluble pathologic amyloid beta peptides AbetaP[1-42] and AbetaP[1-43] and soluble nonpathologic AbetaP[1-40]. Both APP and AbetaP interact with ion transport systems. AbetaP induces a wide range of effects as the result of activating a cascade of mechanisms. 3. The major mechanisms proposed for AbetaP-induced cytotoxicity involve the loss of Ca2+ homeostasis and the generation of reactive oxygen species (ROS). The changes in Ca2+ homeostasis could be the result of (1) changes in endogenous ion transport systems, e.g. Ca2+ and K+ channels and Na+/K+-ATPase, and membrane receptor proteins, such as ligand-driven ion channels and G-protein-driven releases of second messengers, and (2) formation of heterogeneous ion channels. 4. The consequences of changes in Ca2+-homeostasis-induced generation of ROS are (a) direct modification of intrinsic ion transport systems and their regulatory mechanisms, and (b) indirect effects on ion transport systems via peroxidation of phospholipids in the membrane, inhibition of phosphorylation, and reduction of ATP levels and cytoplasmic pH. 5. We propose that in AD, AbetaP with its different conformations alters cell regulation by modifying several ion transport systems and also by forming heterogeneous ion channels. The changes in membrane transport systems are proposed as early steps in impairing neuronal function preceding plaque formation. We conclude that these changes damage the membrane by compromising its integrity and increasing its ion permeability. This mechanism of membrane damage is not only central for AD but also may explain other malfunctioned protein-processing-related pathologies.

Beta-amyloid plaques induce neuritic dystrophy of nitric oxide-producing neurons in a transgenic mouse model of Alzheimer's disease

A causative role for nitric oxide has been postulated in a number of neurodegenerative diseases. Using histochemical and immunohistochemical methods, we examined the effect of beta-amyloid plaques on nitric oxide-producing cells in transgenic mice which overexpress a mutant human amyloid precursor protein (APP). In 14-month-old animals, nitric oxide synthase (NOS)-positive dystrophic neurites were observed frequently in the cerebral cortex and hippocampus of all of 16 plaque-bearing transgenic animals and in none of 16 wild-type animals. Double labeling of NOS and beta-amyloid revealed that 90% of beta-amyloid plaques were associated with NOS-containing dystrophic neurites. In 7-month-old animals, beta-amyloid plaques were very rare, but those present were frequently associated with NOS-positive neuritic dystrophy. We conclude that beta-amyloid plaques induce neuritic dystrophy in cortical neurons containing NOS in this model of AD, and hypothesize that this finding may be relevant to the mechanism of beta-amyloid neurotoxicity in human AD.

Vinpocetine attenuates the metabolic dysfunction induced by amyloid beta-peptides in PC12 cells

The cytoprotective effect of vinpocetine [14-ethoxycarbonyl-(3alpha, 16alpha-ethyl)-14,15-eburnamine] was investigated on PC12 cells treated with the amyloid beta-peptides (Abeta) for 24 hours. Vinpocetine was shown to protect cells from the inhibition in redox status induced by exposure to Abeta25-35 and Abeta1-40, the maximal protection being achieved at a vinpocetine concentration of 40 microM. At this concentration, vinpocetine blocked the inhibition of the mitochondrial respiratory chain complexes II-III and IV and completely abolished the depletion of pyruvate levels induced by toxic concentrations of Abeta peptides. Furthermore, the accumulation of ROS in cells exposed to Abeta25-35 and Abeta1-40 evaluated using the fluorescent probe 2',7'-dichlorofluorescin (DCF), was reduced in the presence of 40 microM vinpocetine. Taken together, the data presented herein demonstrate that vinpocetine protects cells from Abeta toxicity, preventing the generation of oxidative stress due to the excessive accumulation of ROS. This study suggests that vinpocetine can exert neuroprotective properties which might be of importance and contribute to its clinical efficacy in the treatment of Alzheimer's disease or other neurodegenerative disorders in which oxidative stress is involved.

nNOS expression in reactive astrocytes correlates with increased cell death related DNA damage in the hippocampus and entorhinal cortex in Alzheimer's disease

The immunocytochemical distribution of the neuronal form of nitric oxide synthase (nNOS) was compared with neuropathological changes and with cell death related DNA damage (as revealed by in situ end labeling, ISEL) in the hippocampal formation and entorhinal cortex of 12 age-matched control subjects and 12 Alzheimer's disease (AD) patients. Unlike controls, numerous nNOS-positive reactive astrocytes were found in AD patients around beta-amyloid plaques in CA1 and subiculum and at the places of clear and overt neuron loss, particularly in the entorhinal cortex layer II and CA4. This is the first evidence of nNOS-like immunoreactivity in reactive astrocytes in AD. In contrast to controls, in all but one AD subject, large numbers of ISEL-positive neuronal nuclei and microglial cells were found in the CA1 and CA4 regions and subiculum. Semiquantitative analysis showed that neuronal DNA fragmentation in AD match with the distribution of nNOS-expressing reactive astroglial cells in CA1 (r = 0.74, P < 0.01) and CA4 (r = 0.58, P < 0.05). A portion of the nNOS-positive CA2/CA3 pyramidal neurons was found to be spared even in the most affected hippocampi. A significant inverse correlation between nNOS expression and immunoreactivity to abnormally phosphorylated tau proteins (as revealed by AT8 monoclonal antibody) in perikarya of these CA2/3 neurons (r = -0.85, P < 0.01) suggests that nNOS expression may provide selective resistance to neuronal degeneration in AD. In conclusion, our results imply that an upregulated production of NO by reactive astrocytes may play a key role in the pathogenesis of AD.

A beta peptides and calcium influence secretion of the amyloid protein precursor from chick sympathetic neurons in culture

The major constituent of amyloid plaques in the Alzheimer disease (AD) brain is the amyloid protein (A beta). A beta has been shown to be neurotoxic to cells, but the exact mechanism of its effects are still not known. Most studies have focussed on A beta neurotoxicity, but little is known about the effect of A beta peptides on cellular protein metabolism and secretion. To examine the effect of A beta peptides on APP secretion, chick sympathetic neurons were metabolically labeled with [(35)S]methionine and the amounts of radiolabeled APP and A beta quantitated. Several A beta peptides (A beta(25-35), [pyroglu(3)]A beta(3-40), and [pyroglu(11)]A beta(11-40)) inhibited secretion of [(35)S]APP and increased cell-associated [(35)S]APP. There was also a 2-2.5-fold increase in secretion of several other proteins when cells were incubated with A beta(25-35). However, the amount of A beta secreted into the medium was decreased. Treatment of cells with the calcium ionophore A23187 caused a 1.5-fold increase in secreted [(35)S]APP and a decrease in cell-associated [(35)S]APP. Although L-type voltage-dependent calcium channels (VDCC) have been implicated in A beta toxicity, the effect of L-type VDCC on APP secretion has not previously been examined. The L-type VDCC antagonists nifedipine and diltiazem both increased [(35)S]APP secretion into the medium but did not influence the effect of A beta on [(35)S]APP secretion. These studies suggest that A beta interferes with the secretory pathway of APP. Insofar as secreted APP has been proposed to have a neuroprotective function, the accumulation of A beta in the AD brain could decrease secreted APP and thereby indirectly increase A beta toxicity.

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

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

Survival of motor neurons and expression of beta-amyloid protein in the aged rat spinal cord

The present study investigated expression of beta-amyloid protein (AP) and Amyloid precursor protein (APP) in spinal motor neurons of young adult (3 month old) and aged (26-30 month old) rats. The total number of spinal motor neurons in the seventh cervical (C7) spinal segment was also examined in both young adult and aged rats. There was an approximately 21% (p<0.001) decrease in the number of motor neurons of the C7 spinal segment in aged rats compared with young ones. Immunoreactivity (IR) of AP and APP was not observed in spinal motor neurons of young adult rats. In contrast, approximately 50% of the spinal motor neurons of the aged rats were APP positive. Furthermore, extensive immunoreactivity was found in the processes of spinal motor neurons of aged rats. These results have shown that AP and APP is coincident with the loss of motor neurons in the spinal cord of aged rats, and might be associated with the degenerative processes of ageing motor neurons.

Increased vulnerability of hippocampal neurons from presenilin-1 mutant knock-in mice to amyloid beta-peptide toxicity: central roles of superoxide production and caspase activation

Many cases of early-onset inherited Alzheimer's disease (AD) are caused by mutations in the presenilin-1 (PS1) gene. Overexpression of PS1 mutations in cultured PC12 cells increases their vulnerability to apoptosis-induced trophic factor withdrawal and oxidative insults. We now report that primary hippocampal neurons from PS1 mutant knock-in mice, which express the human PS1M146V mutation at normal levels, exhibit increased vulnerability to amyloid beta-peptide toxicity. The endangering action of mutant PS1 was associated with increased superoxide production, mitochondrial membrane depolarization, and caspase activation. The peroxynitrite-scavenging antioxidant uric acid and the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone protected hippocampal neurons expressing mutant PS1 against cell death induced by amyloid beta-peptide. Increased oxidative stress may contribute to the pathogenic action of PS1 mutations, and antioxidants may counteract the adverse property of such AD-linked mutations.

Catecholamines potentiate amyloid beta-peptide neurotoxicity: involvement of oxidative stress, mitochondrial dysfunction, and perturbed calcium homeostasis

Oxidative stress and mitochondrial dysfunction are implicated in the neuronal cell death that occurs in physiological settings and in neurodegenerative disorders. In Alzheimer's disease (AD) degenerating neurons are associated with deposits of amyloid beta-peptide (A beta), and there is evidence for increased membrane lipid peroxidation and protein oxidation in the degenerating neurons. Cell culture studies have shown that A beta can disrupt calcium homeostasis and induce apoptosis in neurons by a mechanism involving oxidative stress. We now report that catecholamines (norepinephrine, epinephrine, and dopamine) increase the vulnerability of cultured hippocampal neurons to A beta toxicity. The catecholamines were effective in potentiating A beta toxicity at concentrations of 10-200 microM, with the higher concentrations (100-200 microM) themselves inducing cell death. Serotonin and acetylcholine were not neurotoxic and did not modify A beta toxicity. Levels of membrane lipid peroxidation, and cytoplasmic and mitochondrial reactive oxygen species, were increased following exposure to neurons to A beta, and catecholamines exacerbated the oxidative stress. Subtoxic concentrations of catecholamines exacerbated decreases in mitochondrial energy charge and transmembrane potential caused by A beta, and higher concentrations of catecholamines alone induced mitochondrial dysfunction. Antioxidants (vitamin E, glutathione, and propyl gallate) protected neurons against the damaging effects of A beta and catecholamines, whereas the beta-adrenergic receptor antagonist propanolol and the dopamine (D1) receptor antagonist SCH23390 were ineffective. Measurements of intracellular free Ca2+ ([Ca2+]i) showed that A beta induced a slow elevation of [Ca2+]i which was greatly enhanced in cultures cotreated with catecholamines. Collectively, these data indicate a role for catecholamines in exacerbating A beta-mediated neuronal degeneration in AD and, when taken together with previous findings, suggest roles for oxidative stress induced by catecholamines in several different neurodegenerative conditions.

Possible causes of Alzheimer's disease: amyloid fragments, free radicals, and calcium homeostasis

Alzheimer's disease (AD) is a form of dementia in which patients develop neurodegeneration and complete loss of cognitive abilities and die prematurely. No treatment is known for this condition. Evidence points toward beta-amyloid as one of the main causes for cytotoxic processes. The cascade of biochemical events that lead to neuronal death appears to be interference with intracellular calcium homeostasis via activation of calcium channels, intracellular calcium stores, and subsequent production of free radicals by calcium-sensitive enzymes. The glutamatergic system seems to be implicated in mediating the toxic processes. Several strategies promise amelioration of neurodegenerative developments as judging from in vitro experiments. Glutamate receptor-selective drugs, antioxidants, inhibitors of nitric oxide synthase, calcium channel antagonists, receptor or enzyme inhibitors, and growth factors promise help. Especially combinations of drugs that act at different levels might prolong patients' health.

Activation of NF-kappaB protects hippocampal neurons against oxidative stress-induced apoptosis: evidence for induction of manganese superoxide dismutase and suppression of peroxynitrite production and protein tyrosine nitration

The transcription factor NF-kappaB is expressed in neurons wherein it is activated in response to a variety of stress- and injury-related stimuli including exposure to cytokines such as tumor necrosis factor-alpha (TNFalpha), and excitotoxic and oxidative insults. NF-kappaB may play a role in the anti-death actions of TNFalpha in cultured hippocampal neurons exposed to metabolic and oxidative insults. We now report that pretreatment of hippocampal cell cultures with agents that activate NF-kappaB (TNFalpha and C2-ceramide) confers resistance of neurons to apoptosis induced by the oxidative insults FeSO4 and amyloid beta-peptide (Abeta25-35). The neuroprotective actions of TNFalpha and ceramide were abolished in cultures cotreated with kappaB decoy DNA demonstrating a requirement for NF-kappaB activation for prevention of cell death. Levels of manganese superoxide dismutase (Mn-SOD) in neurons were increased following exposure of cultures to TNFalpha and ceramide in control cultures, but not in cultures cotreated with kappaB decoy DNA. FeSO4 and Abeta25-35 induced accumulation of mitochondrial peroxynitrite, and membrane lipid peroxidation, in neurons. Peroxynitrite accumulation and lipid peroxidation were largely prevented in neurons pretreated with TNFalpha and ceramide prior to exposure to FeSO4 and Abeta25-35, an effect blocked by kappaB decoy DNA. Immunoreactivity of neurons with an anti-nitrotyrosine antibody was increased following exposure to FeSO4 and Abeta25-35; TNFalpha and C2-ceramide suppressed protein tyrosine nitration, and kappaB decoy DNA blocked the effects of TNFalpha and C2-ceramide. Finally, the peroxynitrite scavenger uric acid protected neurons against apoptosis induced by FeSO4 and Abeta, and suppressed peroxynitrite accumulation. We conclude that, by inducing production of Mn-SOD and suppressing peroxynitrite formation and membrane lipid peroxidation, NF-kappaB plays an anti-apoptotic role in neurodegenerative conditions that involve oxidative stress. The data further suggest important roles for peroxynitrite and NF-kappaB in the pathogenesis of neuronal degeneration in Alzheimer's disease.

Nicotinic receptor stimulation protects neurons against beta-amyloid toxicity

beta-Amyloid (A beta), a major constituent of senile plaques in Alzheimer's disease (AD), is thought to contribute to the neurodegeneration. We examined the effects of nicotinic receptor agonists on A beta cytotoxicity in cultured rat cortical neurons. The number of viable neurons decreased significantly when cultures were exposed to synthetic A beta peptides (25-35). Concomitant administration of nicotine with A beta markedly reduced the number of dead cells. This nicotine-induced neuroprotection was dependent on the concentration. When hexamethonium or mecamylamine, nicotinic antagonist, was added, neuroprotective effect of nicotine was blocked, which indicates that effect of nicotine was mediated by nicotinic receptors. In addition, a selective alpha7-receptor antagonist, alpha-bungarotoxin (alpha-BTX), blocked the neuroprotective effect of nicotine. Furthermore, incubation with 3-(2,4)-dimethoxybenzylidene anabaseine (DMXB), a selective alpha7-receptor agonist, protected against A beta-induced neuronal death. These results suggest that alpha7-receptor activation plays an important role in neuroprotection against A beta cytotoxicity. This study suggests that nicotinic receptor stimulation, especially alpha7-receptor activation, may be able to protect neurons from degeneration induced by A beta and may have effects that counter the progress of AD.

Control of nitric oxide production by transforming growth factor-beta1: mechanistic insights and potential relevance to human disease

Studies on the multifunctional nature of the transforming growth factor-beta (TGF-beta) family of cytokines and the enzyme nitric oxide synthase (NOS) have suggested that they mediate a wide variety of vital processes in evolutionarily divergent organisms. Numerous mechanistic studies have investigated the consequences of the regulation of NO by the TGF-beta's for mammalian physiology. Studies with several cell types in vitro indicate that TGF-beta1 negatively controls the expression of the enzyme responsible for the prolonged production of large amounts NO, the inducible nitric oxide synthase (NOS2; iNOS), by reducing the expression and activity of NOS2 at multiple levels. Recent studies with TGF-beta1 null mice or mice which overexpress TGF-beta1 suggest that this cytokine may be a primary negative regulator of NOS2 in vivo. The interaction between NOS2 and TGF-beta1 may represent a central homeostatic mechanism in mammalian physiology with implications for a variety of human diseases.

Increase of nitric oxide synthases and nitrotyrosine in inclusion-body myositis

To investigate the possible role of nitric oxide (NO)-induced 'oxidative stress' in the pathogenesis of inclusion-body myositis (IBM), we immunostained muscle biopsies of 12 patients with IBM with isoform-specific antibodies against the neuronal and inducible forms of nitric oxide synthase and with antibodies against nitrotyrosine. Between 70 and 80% of IBM vacuolated muscle fibers contained inclusions strongly immunoreactive with all three antibodies, which by immuno-electronmicroscopy co-localized mainly to cytoplasmic paired-helical filaments, and also to amorphous structures and floccular material. Excess intracellular NO can combine with superoxide to produce highly reactive peroxynitrite which can nitrate tyrosines of proteins. The presence of nitrotyrosine is indicative of NO-induced "oxidative stress'. Our data suggest that this mechanism may play a pathogenic role in IBM.

Inducible nitric oxide synthase in tangle-bearing neurons of patients with Alzheimer's disease

In Alzheimer's disease (AD), affected neurons accumulate beta amyloid protein, components of which can induce mouse microglia to express the high-output isoform of nitric oxide synthase (NOS2) in vitro. Products of NOS2 can be neurotoxic. In mice, NOS2 is normally suppressed by transforming growth factor beta 1 (TGF-beta 1). Expression of TGF-beta 1 is decreased in brains from AD patients, a situation that might be permissive for accumulation of NOS2. Accordingly, we investigated the expression of NOS2 in patients with AD, using three monospecific antibodies: a previously described polyclonal and two new monoclonal antibodies. Neurofibrillary tangle-bearing neurons and neuropil threads contained NOS2 in brains from each of 11 AD patients ranging in age from 47 to 81 years. NOS2 was undetectable in brains from 6 control subjects aged 23-72 years, but was expressed in small amounts in 3 control subjects aged 77-87 years. Thus, human neurons can express NOS2 in vivo. The high-output pathway of NO production may contribute to pathogenesis in AD.

Amyloid beta-peptide and oxidative cellular injury in Alzheimer's disease

Alzheimer's disease is a progressive neurodegenerative disorder that affects primarily learning and memory functions. There is significant neuronal loss and impairment of metabolic functioning in the temporal lobe, an area believed to be crucial for learning and memory tasks. Aggregated deposits of amyloid beta-peptide may have a causative role in the development and progression of AD. We review the cellular actions of A beta and how they can contribute to the cytotoxicity observed in AD. A beta causes plasma membrane lipid peroxidation, impairment of ion-motive ATPases, glutamate uptake, uncoupling of a G-protein linked receptor, and generation of reactive oxygen species. These effects contribute to the loss of intracellular calcium homeostasis reported in cultured neurons. Many cell types other than neurons show alterations in the Alzheimer's brain. The effects of A beta on these cell types is also reviewed.

Cytokine-stimulated astrocytes damage human neurons via a nitric oxide mechanism

Astrocytes have been reported to play a neuropathogenic role within the brain, although little is known about the mechanism underlying astrocyte-mediated neuronal injury. We investigated the hypothesis that cytokine-stimulated astrocytes adversely affect neuronal cell survival via generation of the free radical nitric oxide (NO). Primary human astrocytes produced substantial amounts of NO in response to interleukin (IL)-1 alpha or IL-1 beta, which was blocked by the NO synthase inhibitor NG-mono-methyl-L-arginine (NMMA). IL-1 beta-induced NO production was markedly potentiated by interferon (IFN)-gamma. IL-1 receptor agonist protein (IRAP) totally blocked NO generation by cytokine-stimulated astrocytes. Using reverse transcription-polymerase chain reaction and sequencing analyses of the astrocyte NO synthase gene, we found a single band encoding for a 615 bp product that was identical to the corresponding sequence reported for human hepatocytes. Treatment of human fetal brain cell cultures with IL-1 beta plus IFN-gamma resulted in marked neuronal loss, as assessed by microscopic analysis and measurement of lactate dehydrogenase release. This cytokine-induced neuronal damage was blocked by simultaneous treatment of the brain cell cultures with NMMA or IRAP, suggesting a critical role of IL-1. These findings indicate that cytokine-stimulated astrocytes are neurotoxic via a NO-mediated mechanism and point to potential new therapies for neurodegenerative disorders that involve cytokines and reactive astrocytes.

Cell death induced by beta-amyloid 1-40 in MES 23.5 hybrid clone: the role of nitric oxide and NMDA-gated channel activation leading to apoptosis

The molecular events associated with beta-amyloid-induced neuronal injury remain incompletely characterized. Using a substantia nigra/neuroblastoma hybrid cell line (MES 23.5) synthetic beta-amyloid 1-40 induced a time and dose-dependent apoptotic cell death which was characterized by cell shrinkage and fragmentation of DNA, and was inhibited by aurintricarboxylic acid (ATA), and cycloheximide (CHX). Following beta-amyloid 1-40 treatment, cyclic GMP, an index of NO synthesis, was increased in MES 23.5 cells. The NO scavenger hemoglobin, as well as the NO synthase inhibitors NG-monomethyl-L-arginine acetate (L-NMMA) and L-N5-(1-iminoethyl)ornithine hydrochloride (L-NI0) attenuated such increases. These same inhibitors and scavengers also significantly prevented cytotoxicity. beta-Amyloid also induced an early and transient increase in intracellular calcium as monitored with laser scanning confocal microscopy and Fluo-3 imaging. These induced calcium transients could be significantly blocked by the N-methyl-D-aspartic acid (NMDA) receptor antagonist MK-801. Pretreatment with MK-801 or removal of extracellular Ca2+ also reduced beta-amyloid-induced NO production and neurotoxicity. Furthermore, beta-amyloid neurotoxicity was greatly enhanced in the absence of Mg2+ or in the presence of glutamate or NMDA. These data suggest that beta-amyloid can lead to apoptotic cell death through a NO mediated process possibly triggered by Ca2+ entry through activated NMDA-gated channels.

Inhibitors of free radical formation fail to attenuate direct beta-amyloid25-35 peptide-mediated neurotoxicity in rat hippocampal cultures

The direct neurotoxic action of the beta-amyloid protein, the major constituent of senile plaques, may represent the underlying cause of neuronal degeneration observed in Alzheimer's disease. The apoptotic-mediated neuronal death induced by beta-amyloid appears to reside in its ability to form Ca(2+)-permeable pores in neuronal membranes resulting in an excessive influx of Ca2+ and the induction of neurotoxic cascades. It is possible that during beta-amyloid exposure a Ca(2+)-mediated increase in free radical generation may exceed the defensive capacity of cells and thus lead to cell death. Consequently, in the present study we have investigated the effect of a panoply of antioxidants and inhibitors of free radical formation on the development of beta-amyloid neurotoxicity. Acute exposure of rat hippocampal neurons to "aged" beta-amyloid25-35 peptide (5-50 microM) induced a slow, concentration-dependent apoptotic neurotoxicity (25-85%) during a 6 day exposure. Co-incubation of cultures with beta-amyloid25-35 peptide (25 microM) and inhibitors of nitric oxide synthase and/or xanthine oxidase (NG-monomethyl-L-arginine [1 mM), N omega-nitro-L-arginine [1 mM], oxypurinol [100 microM], allopurinol [100 microM]), important mediators of nitric oxide, superoxide, and hydroxyl radical formation, did not attenuate beta-amyloid neurotoxicity. Similarly, a reduction in free radical generation by selective inhibition of phospholipase-A2 cyclooxygenase, and lipoxygenase activities with quinacrine (0.5 microM), indomethacin (50 microM), and nor-dihydroguaiaretic acid (0.5 microM), respectively, did not reduce the proclivity of beta-amyloid to induce cell death. Exposure of cultures to catalase (25 U/ml) and/or superoxide dismutase (10 U/ml) as well as the free radical scavengers vitamin E (100 microM), vitamin C (100 microM), glutathione (100 microM), L-cysteine (100 microM), N-acetyl-cysteine (100 microM), deferoxamine (5 microM), or haemoglobin (35 micrograms/ml) failed to attenuate the neurotoxic action of beta-amyloid. On the other hand, pre-treatment of cultures with subtoxic concentrations of beta-amyloid peptide significantly increased the vulnerability of neurons to H2O2 exposure and suggest that beta-amyloid peptide renders neurons more sensitive to free radical attack. However, a potential beta-amyloid-mediated increase in free radical formation is not a proximate cause of the neurotoxic mechanism of beta-amyloid in vitro.