Targeting alzheimer amyloid plaques in vivo

The only definitive diagnosis for Alzheimer disease (AD) at present is postmortem observation of neuritic plaques and neurofibrillary tangles in brain sections. Radiolabeled amyloid-beta peptide (Abeta), which has been shown to label neuritic plaques in vitro, therefore could provide a diagnostic tool if it also labels neuritic plaques in vivo following intravenous injection. In this study, we show that the permeability of Abeta at the blood-brain barrier can be increased by at least twofold through covalent modification with the naturally occurring polyamine, putrescine. We also show that, following intravenous injection, radiolabeled, putrescine-modified Abeta labels amyloid deposits in vivo in a transgenic mouse model of AD, as well as in vitro in human AD brain sections. This technology, when applied to humans, may be used to detect plaques in vivo, allowing early diagnosis of the disease and therapeutic intervention before cognitive decline occurs.     

Abeta immunotherapy leads to clearance of early, but not late, hyperphosphorylated tau aggregates via the proteasome

Amyloid-beta (Abeta) plaques and neurofibrillary tangles are the hallmark neuropathological lesions of Alzheimer's disease (AD). Using a triple transgenic model (3xTg-AD) that develops both lesions in AD-relevant brain regions, we determined the consequence of Abeta clearance on the development of tau pathology. Here we show that Abeta immunotherapy reduces not only extracellular Abeta plaques but also intracellular Abeta accumulation and most notably leads to the clearance of early tau pathology. We find that Abeta deposits are cleared first and subsequently reemerge prior to the tau pathology, indicative of a hierarchical and direct relationship between Abeta and tau. The clearance of the tau pathology is mediated by the proteasome and is dependent on the phosphorylation state of tau, as hyperphosphorylated tau aggregates are unaffected by the Abeta antibody treatment. These findings indicate that Abeta immunization may be useful for clearing both hallmark lesions of AD, provided that intervention occurs early in the disease course.     

Ferulic acid ethyl ester protects neurons against amyloid beta- peptide(1-42)-induced oxidative stress and neurotoxicity: relationship to antioxidant activity

Alzheimer's disease (AD) is neuropathologically characterized by depositions of extracellular amyloid and intracellular neurofibrillary tangles, associated with loss of neurons in the brain. Amyloid beta-peptide (Abeta) is the major component of senile plaques and is considered to have a causal role in the development and progress of AD. Several lines of evidence suggest that enhanced oxidative stress and inflammation play important roles in the pathogenesis or progression of AD. The present study aimed to investigate the protective effects of ethyl-4-hydroxy-3-methoxycinnamic acid (FAEE), a phenolic compound which shows antioxidant and anti-inflammatory activity, on Abeta(1-42)-induced oxidative stress and neurotoxicity. We hypothesized that the structure of FAEE would facilitate radical scavenging and may induce protective proteins. Abeta(1-42) decreases cell viability, which was correlated with increased free radical formation, protein oxidation (protein carbonyl, 3-nitrotyrosine), lipid peroxidation (4-hydroxy-2-trans-nonenal) and inducible nitric oxide synthase. Pre-treatment of primary hippocampal cultures with FAEE significantly attenuated Abeta(1-42)-induced cytotoxicity, intracellular reactive oxygen species accumulation, protein oxidation, lipid peroxidation and induction of inducible nitric oxide synthase. Treatment of neurons with Abeta(1-42) increases levels of heme oxygenase-1 and heat shock protein 72. Consistent with a cellular stress response to the Abeta(1-42)-induced oxidative stress, FAEE treatment increases the levels of heme oxygenase-1 and heat shock protein 72, which may be regulated by oxidative stresses in a coordinated manner and play a pivotal role in the cytoprotection of neuronal cells against Abeta(1-42)-induced toxicity. These results suggest that FAEE exerts protective effects against Abeta(1-42) toxicity by modulating oxidative stress directly and by inducing protective genes. These findings suggest that FAEE could potentially be of importance for the treatment of AD and other oxidative stress-related diseases.     

An aluminum-based rat model for Alzheimer's disease exhibits oxidative damage, inhibition of PP2A activity, hyperphosphorylated tau, and granulovacuolar degeneration

In Alzheimer's disease (AD), oxidative damage leads to the formation of amyloid plaques while low PP2A activity results in hyperphosphorylated tau that polymerizes to form neurofibrillary tangles. We probed these early events, using brain tissue from a rat model for AD that develops memory deterioration and AD-like behaviors in old age after chronically ingesting 1.6 mg aluminum/kg bodyweight/day, equivalent to the high end of the human dietary aluminum range. A control group consumed 0.4 mg aluminum/kg/day. We stained brain sections from the cognitively-damaged rats for evidence of amyloid plaques, neurofibrillary tangles, aluminum, oxidative damage, and hyperphosphorylated tau. PP2A activity levels measured 238.71+/-17.56 pmol P(i)/microg protein and 580.67+/-111.70 pmol P(i)/microg protein (p<0.05) in neocortical/limbic homogenates prepared from cognitively-damaged and control rat brains, respectively. Thus, PP2A activity in cognitively-damaged brains was 41% of control value. Staining results showed: (1) aluminum-loading occurs in some aged rat neurons as in some aged human neurons; (2) aluminum-loading in rat neurons is accompanied by oxidative damage, hyperphosphorylated tau, neuropil threads, and granulovacuolar degeneration; and (3) amyloid plaques and neurofibrillary tangles were absent from all rat brain sections examined. Known species difference can reasonably explain why plaques and tangles are unable to form in brains of genetically-normal rats despite developing the same pathological changes that lead to their formation in human brain. As neuronal aluminum can account for early stages of plaque and tangle formation in an animal model for AD, neuronal aluminum could also initiate plaque and tangle formation in humans with AD.     

Oxidative stress in Alzheimer disease

Alzheimer disease (AD) is a progressive dementia affecting a large proportion of the aging population. The histopathological changes in AD include neuronal cell death, formation of amyloid plaques and neurofibrillary tangles. There is also evidence that brain tissue in patients with AD is exposed to oxidative stress (e.g., protein oxidation, lipid oxidation, DNA oxidation and glycoxidation) during the course of the disease. Advanced glycation endproducts (AGEs) are present in amyloid plaques in AD, and its extracellular accumulation may be caused by an accelerated oxidation of glycated proteins. AGEs participate in neuronal death causing direct (chemical) and indirect (cellular) free radical production and consequently increase oxidative stress. The development of drugs for the treatment of AD that breaks the vicious cycles of oxidative stress and neurodegeneration offer new opportunities. These approaches include AGE-inhibitors, antioxidants and anti-inflammatory substances, which prevent free radical production.     

Oxidative stress in Alzheimer disease

Alzheimer disease (AD) is a progressive dementia affecting a large proportion of the aging population. The histopathological changes in AD include neuronal cell death, formation of amyloid plaques and neurofibrillary tangles. There is also evidence that brain tissue in patients with AD is exposed to oxidative stress (e.g., protein oxidation, lipid oxidation, DNA oxidation and glycoxidation) during the course of the disease. Advanced glycation endproducts (AGEs) are present in amyloid plaques in AD, and its extracellular accumulation may be caused by an accelerated oxidation of glycated proteins. AGEs participate in neuronal death causing direct (chemical) and indirect (cellular) free radical production and consequently increase oxidative stress. The development of drugs for the treatment of AD that breaks the vicious cycles of oxidative stress and neurodegeneration offer new opportunities. These approaches include AGE-inhibitors, antioxidants and anti-inflammatory substances, which prevent free radical production.Key words: ageing, advanced glycation endproducts, Alzheimer disease, amyloid, oxidative stress     

Intravenous Administration of Human Umbilical Cord Mesenchymal Stem Cells Improves Cognitive Impairments and Reduces Amyloid-Beta Deposition in an AβPP/PS1 Transgenic Mouse Model

Alzheimer’s disease (AD) is characterized by Amyloid-β (Aβ) deposition in senile plaques in specific areas of the brain and by intraneuronal p-tau accumulation in neurofibrillary tangles. Cumulative evidence supports that oxidative stress is an important factor in the pathogenesis of AD and contributes to Aβ generation. However, there is no effective treatment for AD. Human umbilical cord mesenchymal stem cells (HUMSCs) have potential therapeutic value for the treatment of neurological disease. However, the therapeutic impact of systemic administration of HUMSCs and their mechanism of action in AD have not yet been determined. Here, we found that intravenous infusion of HUMSCs significantly improved spatial learning and alleviated memory decline in an AβPP/PS1 mouse model of AD. HUMSC treatment also increased glutathione (GSH) activity and ratio of GSH to oxidative glutathione as well as superoxide dismutase activity, while decreasing malondialdehyde activity and protein carbonyl level, which suggests that HUMSC infusion alleviated oxidative stress in AβPP/PS1 mice. In addition, HUMSC infusion reduced β-secretase 1 and CTFβ, thus reducing Aβ deposition in mice. HUMSCs may have beneficial effects in the prevention and treatment of AD.     

Decreasing oxidative stress and neuroinflammation with a multifunctional peptide rescues memory deficits in mice with Alzheimer disease

Alzheimer disease (AD) is characterized by extracellular senile plaques, intracellular neurofibrillary tangles, and memory loss. Aggregated amyloid-β (Aβ), oxidative stress, and inflammation have pivotal roles in the pathogenesis of AD. Therefore, the inhibition of Aβ-induced neurotoxicity, oxidative stress, and inflammation is a potential therapeutic strategy for the treatment of AD. In this study, a heptapeptide, isolated from a Ph.D.-C7C library by phage display, attenuated Aβ42-induced cytotoxicity in SH-SY5Y neuroblastoma cells and reduced Aβ42-induced oxidative stress by decreasing the production of reactive oxygen species and glutathione disulfide. As a result, glutathione level increased and superoxide dismutase and glutathione peroxidase activities were enhanced in vitro and in vivo. This peptide also suppressed the inflammatory response by decreasing the release of proinflammatory cytokines, such as tumor necrosis factor α and interleukin 1β, in microglia and by reducing microgliosis and astrogliosis in AD transgenic mice. This peptide was intracerebroventricularly administered to APPswe/PS1dE9 transgenic mice. We found that this peptide significantly improved spatial memory and reduced the amyloid plaque burden and soluble and insoluble Aβ levels. Our findings suggest that this multifunctional peptide has therapeutic potential for an Aβ-targeted treatment of AD.     

Oxidatively Modified GST and MRP1 in Alzheimer’s Disease Brain: Implications for Accumulation of Reactive Lipid Peroxidation Products

Alzheimer disease (AD) is a neurodegenerative disorder characterized pathologically by intracellular inclusions including neurofibrillary tangles (NFT) and senile plaques. Several lines of evidence implicate oxidative stress with the progression of AD. 4-hydroxy-2-trans-nonenal (HNE), an aldehydic product of membrane lipid peroxidation, is increased in AD brain. The alpha class of glutathione S-transferase (GST) can detoxify HNE and plays an important role in cellular protection against oxidative stress. The export of the glutathione conjugate of HNE is required to fully potentiate the GST-mediated protection. The multidrug resistance protein-1 (MRP1) and GST proteins may act in synergy to confer cellular protection. In the present study, we studied oxidative modification of GST and MRP1 in AD brain by immunoprecipitation of GST and MRP1 proteins followed by Western blot analysis using anti-HNE antibody. The results suggested that HNE is covalently bound to GST and MRP1 proteins in excess in AD brain. Collectively, the data suggest that HNE may be an important mediator of oxidative stress-induced impairment of this detoxifying system and may thereby play a role in promoting neuronal cell death. The results from this study also imply that augmenting endogenous oxidative defense capacity through dietary or pharmacological intake of antioxidants may slow down the progression of neurodegenerative processes in AD.     

Genetically augmenting tau levels does not modulate the onset or progression of Abeta pathology in transgenic mice

The two hallmark pathologies of Alzheimer's disease (AD) are amyloid plaques, composed of the small amyloid-beta (Abeta) peptide, and neurofibrillary tangles, comprised aggregates of the microtubule binding protein, tau. The molecular linkage between these two lesions, however, remains unknown. Based on human and mouse studies, it is clear that the development of Abeta pathology can trigger tau pathology, either directly or indirectly. However, it remains to be established if the interaction between Abeta and tau is bidirectional and whether the modulation of tau will influence Abeta pathology. To address this question, we used the 3xTg-AD mouse model, which is characterized by the age-dependent buildup of both plaques and tangles. Here we show that genetically augmenting tau levels and hyperphosphorylation in the 3xTg-AD mice has no effect on the onset and progression of Abeta pathology. These data suggest that the link between Abeta and tau is predominantly if not exclusively unidirectional, which is consistent with the Abeta cascade hypothesis and may explain why tauopathy-only disorders are devoid of any Abeta pathology.     

AD发病机制的新探索:轴浆运输障碍假说

阿尔采末病(Alzheimer's disease,AD)是一种以老年斑、神经纤维缠结、突触密度减少和神经元丢失为主要病理改变的神经退行性疾病.目前对该病发病机制解释普遍接受的是淀粉样沉淀假说.而最新研究发现,早在β淀粉样多肽(Aβ)沉积和神经纤维缠结出现之前就有另一种病理改变,即轴突肿胀的出现.并且这一病理改变是由轴浆运输障碍引起的,最终可以导致Aβ沉积、突触功能障碍等其它AD相关的病理变化.据此推测,各种原因引起的轴浆运输障碍导致了AD的发病.本文通过介绍轴浆运输假说及其相关实验依据,对近年来AD发病机制的最新研究进展和尚待解决的问题作一综述.     

Nutritional approaches to combat oxidative stress in Alzheimer's disease

Alzheimer's disease (AD) brains are characterized by extensive oxidative stress. Additionally, large depositions of amyloid beta-peptide (Abeta) are observed, and many researchers opine that Abeta is central to the pathogenesis of AD. Our laboratory combined these two observations in a comprehensive model for neurodegeneration in AD brains centered around Abeta-induced oxidative stress. Given the oxidative stress in AD and its potentially important role in neurodegeneration, considerable research has been conducted on the use of antioxidants to slow or reverse the pathology and course of AD. One source of antioxidants is the diet. This review examines the literature of the effects of endogenous and exogenous, nutritionally-derived antioxidants in relation to AD. In particular, studies of glutathione and other SH-containing antioxidants, vitamins, and polyphenolic compounds and their use in AD and modulation of Abeta-induced oxidative stress and neurotoxicity are reviewed.     

Compensatory responses induced by oxidative stress in Alzheimer disease

Oxidative stress occurs early in the progression of Alzheimer disease, significantly before the development of the pathologic hallmarks, neurofibrillary tangles and senile plaques. In the first stage of development of the disease, amyloid-beta deposition and hyperphosphorylated tau function as compensatory responses and downstream adaptations to ensure that neuronal cells do not succumb to oxidative damage. These findings suggest that Alzheimer disease is associated with a novel balance in oxidant homeostasis.     

Triple-transgenic model of Alzheimer's disease with plaques and tangles: intracellular Abeta and synaptic dysfunction

The neuropathological correlates of Alzheimer's disease (AD) include amyloid-beta (Abeta) plaques and neurofibrillary tangles. To study the interaction between Abeta and tau and their effect on synaptic function, we derived a triple-transgenic model (3xTg-AD) harboring PS1(M146V), APP(Swe), and tau(P301L) transgenes. Rather than crossing independent lines, we microinjected two transgenes into single-cell embryos from homozygous PS1(M146V) knockin mice, generating mice with the same genetic background. 3xTg-AD mice progressively develop plaques and tangles. Synaptic dysfunction, including LTP deficits, manifests in an age-related manner, but before plaque and tangle pathology. Deficits in long-term synaptic plasticity correlate with the accumulation of intraneuronal Abeta. These studies suggest a novel pathogenic role for intraneuronal Abeta with regards to synaptic plasticity. The recapitulation of salient features of AD in these mice clarifies the relationships between Abeta, synaptic dysfunction, and tangles and provides a valuable model for evaluating potential AD therapeutics as the impact on both lesions can be assessed.     

Reduction of soluble Abeta and tau, but not soluble Abeta alone, ameliorates cognitive decline in transgenic mice with plaques and tangles

Increasing evidence points to soluble assemblies of aggregating proteins as a major mediator of neuronal and synaptic dysfunction. In Alzheimer disease (AD), soluble amyloid-beta (Abeta) appears to be a key factor in inducing synaptic and cognitive abnormalities. Here we report the novel finding that soluble tau also plays a role in the cognitive decline in the presence of concomitant Abeta pathology. We describe improved cognitive function following a reduction in both soluble Abeta and tau levels after active or passive immunization in advanced aged 3xTg-AD mice that contain both amyloid plaques and neurofibrillary tangles (NFTs). Notably, reducing soluble Abeta alone did not improve the cognitive phenotype in mice with plaques and NFTs. Our results show that Abeta immunotherapy reduces soluble tau and ameliorates behavioral deficit in old transgenic mice.     

Protein-Bound Acrolein

Abstract : Several lines of evidence support the role of oxidative stress, including increased lipid peroxidation, in the pathogenesis of Alzheimer's disease (AD). Lipid peroxidation generates various reactive aldehydes, such as 4-hydroxynonenal (HNE), which have been detected immunochemically in AD, particularly in neurofibrillary tangels, one of the major diagnostic lesions in AD brains. A recent study demonstrated that acrolein, the most reactive among the α, β-unsaturated aldehyde products of lipid peroxidation, could be rapidly incorporated into proteins, generating a carbonyl derivative, a marker of oxidative stress to proteins. The current studies used an antibody raised against acrolein-modified keyhole limpet hemocyanin (KLH) to test whether acrolein modification of proteins occurs in AD. Double immunofluorescence revealed strong acrolein-KLH immunoreactivity in more than half of all paired helical filament (PHF)-1-labeled neurofibrillary tangles in AD cases. Acrolein-KLH immunoreactivity was also evident in a few neurons lacking PHF-1-positive neurofibrillary tangles. Light acrolein-KLH immunoreactivity occurred in dystrophic neurites surrounding the amyloid-β core, which itself lacked acrolein-KLH staining. The pattern of acrolein-KLH immunostaining was similar to that of HNE. Control brains did not contain any acrolein-KLH-immunoreactive structures. The current results suggest that protein-bound acrolein is a powerful marker of oxidative damage to protein and support the hypothesis that lipid peroxidation and oxidative damage to protein may play a crucial role in the formation of neurofibrillary tangles and to neuronal death in AD.     

Attenuated hippocampus-dependent learning and memory decline in transgenic TgAPPswe Fischer-344 rats

Alzheimer's disease (AD) is characterized by increased beta amyloid (Abeta) levels, extracellular Abeta deposits in senile plaques, neurofibrillary tangles, and neuronal loss. However, the physiological role of normal levels of Abeta and its parent protein, the amyloid precursor protein (APP) are unknown. Here we report that low-level transgenic (Tg) expression of the Swedish APP mutant gene (APPswe) in Fischer-344 rats results in attenuated age-dependent cognitive performance decline in 2 hippocampus-dependent learning and memory tasks compared with age-matched nontransgenic Fischer-344 controls. TgAPPswe rats exhibit mild increases in brain APP mRNA (56.8%), Abeta-42 (21%), and Abeta-40 (6.1%) peptide levels at 12 mo of age, with no extracellular Abeta deposits or senile plaques at 6, 12, and 18 mo of age, whereas 3- to 6-fold increases in Abeta levels are detected in plaque-positive human AD patients and transgenic mouse models. The data support the hypothesis that a threshold paradigm underlies Abeta-related pathology, below which APP expression may play a physiological role in specific hippocampus-dependent tasks, most likely related to its neurotrophic role.     

Oxidative regulation of fatty acid-induced tau polymerization

Alzheimer's disease (AD) is characterized by the presence of amyloid-positive senile plaques and tau-positive neurofibrillary tangles. Aside from these two pathological hallmarks, a growing body of evidence indicates that the amount of oxidative alteration of vulnerable molecules such as proteins, DNA, and fatty acids is elevated in the brains of AD patients. It has been hypothesized that the elevated amounts of protein oxidation could lead directly to the formation of neurofibrillary tangles through a cysteine-dependent mechanism. We have tested this hypothesis in an in vitro system in which tau assembly is induced by fatty acids. Using sulfhydryl protective agents and site-directed mutagenesis, we found that cysteine-dependent oxidation of the tau molecule is not required for its polymerization and may even be inhibitory. However, by adjusting the oxidative environment of the polymerization reaction through the addition of a strong antioxidant or through the addition of an oxidizing system consisting of iron, adenosine diphosphate, and ascorbate, we found that oxidation does play a major role in our in vitro paradigm. The results indicated that fatty acid oxidation, the amount of which is found to be elevated in AD patients, can facilitate the polymerization of tau. However, "overoxidation" of the fatty acids can inhibit the process. Therefore, we postulate that specific fatty acid oxidative products could provide a direct link between oxidative stress mechanisms and the formation of neurofibrillary tangles in AD.     

Beta-amyloid treatment of two complementary P301L tau-expressing Alzheimer's disease models reveals similar deregulated cellular processes

Alzheimer's disease (AD) is characterized by Abeta peptide-containing plaques and tau-containing neurofibrillary tangles (NFTs). Both pathologies have been combined by crossing Abeta plaque-forming APP mutant mice with NFT-forming P301L tau mutant mice or by stereotaxically injecting beta-amyloid peptide 1-42 (Abeta42) into brains of P301L tau mutant mice. In cell culture, Abeta42 induces filamentous tau aggregates. To understand which processes are disrupted by Abeta42 in the presence of tau aggregates, we applied comparative proteomics to Abeta42-treated P301L tau-expressing neuroblastoma cells and the amygdala of P301L tau transgenic mice stereotaxically injected with Abeta42. Remarkably, a significant fraction of proteins altered in both systems belonged to the same functional categories, i.e. stress response and metabolism. We also identified model-specific effects of Abeta42 treatment such as differences in cell signaling proteins in the cellular model and of cytoskeletal and synapse associated proteins in the amygdala. By Western blotting (WB) and immunohistochemistry (IHC), we were able to show that 72% of the tested candidates were altered in human AD brain with a major emphasis on stress-related unfolded protein responsive candidates. These data highlight these processes as potentially important initiators in the Abeta42-mediated pathogenic cascade in AD and further support the role of unfolded proteins in the course of AD.     

N epsilon-carboxymethyllysine in brain aging, diabetes mellitus, and Alzheimer's disease

Oxidative stress has been implicated in the pathophysiology of Alzheimer's disease (AD) and diabetes mellitus (DM). N epsilon-carboxymethyllysine (CML) is an advanced glycation end product (AGE) recently found to be associated with oxidative stress mechanisms. Using immunocytochemical methods we examined the distribution of CML in brain tissue from AD and DM subjects and aging controls. CML reactivity was present in the cytoplasm of neurons, but there were marked differences in the intensity of expression, number of cells, and topographical distribution. CML expression was higher in hippocampus than in frontal and temporal cortex. In the hippocampus, neuronal and, to an extent, glial expression was more marked in CA3 and CA4 than in CA1 and CA2. In AD, CML was found to be coexpressed with tau protein, showing the similar neurofibrillary tangle shape, as well as in neuritic plaques but not in the core of amyloid plaques. We noted an increasing degree of CML expression such that the highest reactivity was evident in those with both AD and DM, followed by AD, DM, and aging controls. There was an inverse relationship between Braak staging and topography of CML expression. Although DM cases did not show Abeta deposition or neurofibrillary tangles, these findings suggest increased CML expression is not limited to AD. Nonetheless, high CML expression in AD with coexistent DM suggests there are additive effects compared with AD alone. It is plausible that the microangiopathy also associated with DM could worsen AD pathogenesis.