Nobiletin, a citrus flavonoid, improves memory impairment and Abeta pathology in a transgenic mouse model of Alzheimer's disease

Increasing evidence suggests that the elevation of beta-amyloid (Abeta) peptides in the brain is central to the pathogenesis of Alzheimer's disease (AD). Our recent studies have demonstrated that nobiletin, a polymethoxylated flavone from citrus peels, enhances cAMP/protein kinase A/extracellular signal-regulated kinase/cAMP response element-binding protein signaling in cultured hippocampal neurons and ameliorates Abeta-induced memory impairment in AD model rats. For the first time, we report that this natural compound improves memory deficits in amyloid precursor protein (APP) transgenic mice that overexpress human APP695 harboring the double Swedish and London mutations [APP-SL 7-5 transgenic (Tg) mice]. Our enzyme-linked immunosorbent assay (ELISA) also showed that administration of nobiletin to the transgenic mice for 4 months markedly reduced quantity of guanidine-soluble Abeta(1-40) and Abeta(1-42) in the brain. Furthermore, consistent with the results of ELISA, by immunohistochemistry with anti-Abeta antibody, it was evidently shown that the administration of nobiletin decreased the Abeta burden and plaques in the hippocampus of APP-SL 7-5 Tg mice. These findings suggest that this natural compound has potential to become a novel drug for fundamental treatment of AD.     

Modulation of amyloid beta-protein clearance and Alzheimer's disease susceptibility by the LDL receptor-related protein pathway

Susceptibility to Alzheimer's disease (AD) is governed by multiple genetic factors. Remarkably, the LDL receptor-related protein (LRP) and its ligands, apoE and alpha2M, are all genetically associated with AD. In this study, we provide evidence for the involvement of the LRP pathway in amyloid deposition through sequestration and removal of soluble amyloid beta-protein (Abeta). We demonstrate in vitro that LRP mediates the clearance of both Abeta40 and Abeta42 through a bona fide receptor-mediated uptake mechanism. In vivo, reduced LRP expression is associated with LRP genotypes and is correlated with enhanced soluble Abeta levels and amyloid deposition. Although LRP has been proposed to be a clearance pathway for Abeta, this work provides the first in vivo evidence that the LRP pathway may modulate Abeta deposition and AD susceptibility by regulating the removal of soluble Abeta.     

The experimental Alzheimer's disease drug posiphen [(+)-phenserine] lowers amyloid-beta peptide levels in cell culture and mice

Major characteristics of Alzheimer's disease (AD) are synaptic loss, cholinergic dysfunction, and abnormal protein depositions in the brain. The amyloid beta-peptide (Abeta), a proteolytic fragment of amyloid beta precursor protein (APP), aggregates to form neuritic plaques and has a causative role in AD. A present focus of AD research is to develop safe Abeta-lowering drugs. A selective acetylcholinesterase inhibitor, phenserine, in current human trials lowers both APP and Abeta. Phenserine is dose-limited in animals by its cholinergic actions; its cholinergically inactive enantiomer, posiphen (+)-[phenserine], was assessed. In cultured human neuroblastoma cells, posiphen, like phenserine, dose- and time-dependently lowered APP and Abeta levels by reducing the APP synthesis rate. This action translated to an in vivo system. Posiphen administration to mice (7.5-75 mg/kg daily, 21 consecutive days) significantly decreased levels of total APP (tissue mass-adjusted) in a dose-dependent manner. Abeta40 and Abeta42 levels were significantly lowered by posiphen (> or =15 mg/kg) compared with controls. The activities of alpha-, beta-, and gamma-secretases were assessed in the same brain samples, and beta-secretase activity was significantly reduced. Posiphen, like phenserine, can lower Abeta via multiple mechanisms and represents an interesting drug candidate for AD treatment.     

Adenovirus-mediated delivery and expression of a cAMP-dependent protein kinase inhibitor gene to BEAS-2B epithelial cells abolishes the anti-inflammatory effects of rolipram, salbutamol, and prostaglandin E2: a comparison with H-89

cAMP-elevating drugs are thought to mediate their biological effects by activating the cAMP/cAMP-dependent protein kinase (PKA) cascade. However, this hypothesis is difficult to confirm due to a lack of selective inhibitors. Here, we have probed the role of PKA in mediating inhibitory effects of several cAMP-elevating drugs in BEAS-2B epithelial cells using an adenovirus vector encoding a PKA inhibitor protein (PKIalpha) and have compared it to H-89, a commonly used small molecule PKA inhibitor. Initial studies established efficient gene transfer and confirmed functionality of PKIalpha 48 h after virus infection. All cAMP-elevating drugs tested promoted the phosphorylation of cAMP response element-binding protein (CREB), activated a cAMP response element (CRE)-driven luciferase reporter gene, and suppressed both granulocyte/macrophage colony-stimulating factor (GM-CSF) generation and [(3)H]arachidonic acid (AA) release in response to interleukin-1beta and monocyte chemotactic protein (MCP)-1, respectively. These effects were abolished by PKIalpha. In contrast, H-89 behaved unpredictably under the same conditions. Thus, although CREB phosphorylation evoked by a range of cAMP-elevating drugs was abolished by H-89, neither activation of the CRE-dependent luciferase reporter gene construct nor the inhibition of GM-CSF generation was inhibited. Paradoxically, H-89 antagonized MCP-1-induced [(3)H]AA release and enhanced the inhibitory effect of submaximal concentrations of rolipram and 8-bromo-cAMP. We suggest that expression of PKIalpha in susceptible cells provides a simple and unambiguous way to assess the role of PKA in cAMP signaling and to probe the mechanism of action of other drugs and cAMP-dependent responses where the participation of PKA is equivocal. Furthermore, these data suggest that H-89 is not a selective inhibitor of PKA and should be avoided.     

Peripheral transgene expression of plasma gelsolin reduces amyloid in transgenic mouse models of Alzheimer's disease.

The accumulation and deposition of the 40-42-amino acid peptide amyloid beta (Abeta) is thought to be a critical event in the pathology of Alzheimer's disease (AD). Both passive and active immunizations against Abeta in amyloid-depositing transgenic mice have reduced Abeta pathology and improved memory-related behavior. Peripheral treatments with other amyloid-binding agents have also reduced Abeta pathology. The present study demonstrates that peripheral delivery of plasmid DNA coding for the amyloid-binding protein plasma gelsolin reduces brain Abeta in two separate amyloid-depositing transgenic mouse models of AD when inter-litter variability is accounted for. The reduction in Abeta pathology observed is accompanied by an apparent increase in activated and reactive microglia and soluble oligomeric forms of amyloid. These findings demonstrate that peripheral expression of plasma gelsolin may be a suitable gene-therapeutic approach for the prevention or treatment of AD.     

Factors influencing the processing and function of the amyloid beta precursor protein--a potential therapeutic target in Alzheimer's disease?

The amyloid beta precursor protein (AbetaPP), which plays a pivotal role in Alzheimer's disease (AD), can exist as either a membrane-bound or soluble protein. The former is cleaved at the level of the plasma membrane to generate the soluble form of the protein (AbetaPP(s)). An alternative pathway exists, however, for the cleavage of AbetaPP to generate a 40-42 amino acid peptide termed amyloid beta (Abeta), either within the lysosomal or the endoplasmic reticulum/Golgi compartments of the cell. In AD, there is an increase in the ratio of the 42 amino acid form of the Abeta peptide (Abeta(42)) to Abeta(40). The Abeta(42) form is the more amyloidogenic form and has an increased potential to form the insoluble amyloid deposits characteristic of AD pathology. Studies on the familial form of the disease, with mutations in AbetaPP or in the presenilin proteins, have confirmed an increase in Abeta(42) generation associated with the early stages of the disease. This review will examine the factors that influence AbetaPP processing, how they may act to modulate the biological effects of AbetaPP(s) and Abeta, and if they provide a viable target for therapeutic intervention to modify the rate of progression of the disease.     

NSAIDs and enantiomers of flurbiprofen target gamma-secretase and lower Abeta 42 in vivo

Epidemiologic studies demonstrate that long-term use of NSAIDs is associated with a reduced risk for the development of Alzheimer disease (AD). In this study, 20 commonly used NSAIDs, dapsone, and enantiomers of flurbiprofen were analyzed for their ability to lower the level of the 42-amino-acid form of amyloid beta protein (Abeta42) in a human H4 cell line. Thirteen of the NSAIDs and the enantiomers of flurbiprofen were then tested in acute dosing studies in amyloid beta protein precursor (APP) transgenic mice, and plasma and brain levels of Abeta and the drug were evaluated. These studies show that (a). eight FDA-approved NSAIDs lower Abeta42 in vivo, (b). the ability of an NSAID to lower Abeta42 levels in cell culture is highly predicative of its in vivo activity, (c). in vivo Abeta42 lowering in mice occurs at drug levels achievable in humans, and (d). there is a significant correlation between Abeta42 lowering and levels of ibuprofen. Importantly, flurbiprofen and its enantiomers selectively lower Abeta42 levels in broken cell gamma-secretase assays, indicating that these compounds directly target the gamma-secretase complex that generates Abeta from APP. Of the compounds tested, meclofenamic acid, racemic flurbiprofen, and the purified R and S enantiomers of flurbiprofen lowered Abeta42 levels to the greatest extent. Because R-flurbiprofen reduces Abeta42 levels by targeting gamma-secretase and has reduced side effects related to inhibition of cyclooxygenase (COX), it is an excellent candidate for clinical testing as an Abeta42 lowering agent.     

Caspase-cleavage of tau is an early event in Alzheimer disease tangle pathology

Neurofibrillary tangles (NFTs) are composed of abnormal aggregates of the cytoskeletal protein tau. Together with amyloid beta (Abeta) plaques and neuronal and synaptic loss, NFTs constitute the primary pathological hallmarks of Alzheimer disease (AD). Recent evidence also suggests that caspases are activated early in the progression of AD and may play a role in neuronal loss and NFT pathology. Here we demonstrate that tau is cleaved at D421 (DeltaTau) by executioner caspases. Following caspase-cleavage, DeltaTau facilitates nucleation-dependent filament formation and readily adopts a conformational change recognized by the early pathological tau marker MC1. DeltaTau can be phosphorylated by glycogen synthase kinase-3beta and subsequently recognized by the NFT antibody PHF-1. In transgenic mice and AD brains, DeltaTau associates with both early and late markers of NFTs and is correlated with cognitive decline. Additionally, DeltaTau colocalizes with Abeta(1-42) and is induced by Abeta(1-42) in vitro. Collectively, our data imply that Abeta accumulation triggers caspase activation, leading to caspase-cleavage of tau, and that this is an early event that may precede hyperphosphorylation in the evolution of AD tangle pathology. These results suggest that therapeutics aimed at inhibiting tau caspase-cleavage may prove beneficial not only in preventing NFT formation, but also in slowing cognitive decline.     

Regulation of Aβ pathology by beclin 1: a protective role for autophagy?

The amyloid beta (Abeta) peptide is thought to be a major culprit in Alzheimer disease (AD), and its production and degradation have been intensely investigated. Nevertheless, it remains largely unknown how Abeta pathology is modulated by the autophagy pathway. The study by Pickford and colleagues in this issue of the JCI shows that beclin 1, a multifunctional protein that also plays an important role in the autophagy pathway, affects some aspects of Abeta pathology in aged but not young transgenic mice expressing amyloid precursor protein (APP) (see the related article beginning on page 2190). These findings further support the notion that modulation of autophagy, in this case through beclin 1, may represent a novel therapeutic strategy for AD.     

CNI-1493 inhibits Abeta production, plaque formation, and cognitive deterioration in an animal model of Alzheimer's disease

Alzheimer's disease (AD) is characterized by neuronal atrophy caused by soluble amyloid beta protein (Abeta) peptide "oligomers" and a microglial-mediated inflammatory response elicited by extensive amyloid deposition in the brain. We show that CNI-1493, a tetravalent guanylhydrazone with established antiinflammatory properties, interferes with Abeta assembly and protects neuronal cells from the toxic effect of soluble Abeta oligomers. Administration of CNI-1493 to TgCRND8 mice overexpressing human amyloid precursor protein (APP) for a treatment period of 8 wk significantly reduced Abeta deposition. CNI-1493 treatment resulted in 70% reduction of amyloid plaque area in the cortex and 87% reduction in the hippocampus of these animals. Administration of CNI-1493 significantly improved memory performance in a cognition task compared with vehicle-treated mice. In vitro analysis of CNI-1493 on APP processing in an APP-overexpressing cell line revealed a significant dose-dependent decrease of total Abeta accumulation. This study indicates that the antiinflammatory agent CNI-1493 can ameliorate the pathophysiology and cognitive defects in a murine model of AD.     

The role of amyloid beta peptide 42 in Alzheimer's disease

During the last 20 years, an expanding body of research has elucidated the central role of amyloid precursor protein (APP) processing and amyloid beta peptide (Abeta) production in the risk, onset, and progression of the neurodegenerative disorder Alzheimer's disease (AD), the most common form of dementia. Ongoing research is establishing a greater level of detail for our understanding of the normal functions of APP, its proteolysis products, and the mechanisms by which this processing occurs. The importance of this processing machinery in normal cellular function, such as Notch processing, has revealed specific concerns about targeting APP processing for therapeutic purposes. Aspects of AD that are now well studied include direct and indirect genetic and other risk factors for AD, APP processing, and Abeta production. Emerging from these studies is the particular importance of the long form of Abeta, Abeta42. Elevated Abeta42 levels, as well as particularly the elevation of the ratio of Abeta42 to the shorter major form Abeta40, has been identified as important in early events in the pathogenesis of AD. The specific pathological importance of Abeta42 has drawn attention to seeking drugs that will selectively lower the levels of this peptide through reduced production or increased clearance while allowing normal protein processing to remain substantially intact. An increasing variety of compounds that modulate APP processing to reduce Abeta levels are being identified, some with Abeta42 selectivity. Such compounds are now reaching clinical evaluation to determine how they may be of benefit in the treatment of AD.     

The autophagy-related protein beclin 1 shows reduced expression in early Alzheimer disease and regulates amyloid beta accumulation in mice

Autophagy is the principal cellular pathway for degradation of long-lived proteins and organelles and regulates cell fate in response to stress. Recently, autophagy has been implicated in neurodegeneration, but whether it is detrimental or protective remains unclear. Here we report that beclin 1, a protein with a key role in autophagy, was decreased in affected brain regions of patients with Alzheimer disease (AD) early in the disease process. Heterozygous deletion of beclin 1 (Becn1) in mice decreased neuronal autophagy and resulted in neurodegeneration and disruption of lysosomes. In transgenic mice that express human amyloid precursor protein (APP), a model for AD, genetic reduction of Becn1 expression increased intraneuronal amyloid beta (Abeta) accumulation, extracellular Abeta deposition, and neurodegeneration and caused microglial changes and profound neuronal ultrastructural abnormalities. Administration of a lentiviral vector expressing beclin 1 reduced both intracellular and extracellular amyloid pathology in APP transgenic mice. We conclude that beclin 1 deficiency disrupts neuronal autophagy, modulates APP metabolism, and promotes neurodegeneration in mice and that increasing beclin 1 levels may have therapeutic potential in AD.     

P-glycoprotein deficiency at the blood-brain barrier increases amyloid-beta deposition in an Alzheimer disease mouse model

Accumulation of amyloid-beta (Abeta) within extracellular spaces of the brain is a hallmark of Alzheimer disease (AD). In sporadic, late-onset AD, there is little evidence for increased Abeta production, suggesting that decreased elimination from the brain may contribute to elevated levels of Abeta and plaque formation. Efflux transport of Abeta across the blood-brain barrier (BBB) contributes to Abeta removal from the brain. P-glycoprotein (Pgp) is highly expressed on the luminal surface of brain capillary endothelial cells and contributes to the BBB. In Pgp-null mice, we show that [I]Abeta40 and [I]Abeta42 microinjected into the CNS clear at half the rate that they do in WT mice. When amyloid precursor protein-transgenic (APP-transgenic) mice were administered a Pgp inhibitor, Abeta levels within the brain interstitial fluid significantly increased within hours of treatment. Furthermore, APP-transgenic, Pgp-null mice had increased levels of brain Abeta and enhanced Abeta deposition compared with APP-transgenic, Pgp WT mice. These data establish a direct link between Pgp and Abeta metabolism in vivo and suggest that Pgp activity at the BBB could affect risk for developing AD as well as provide a novel diagnostic and therapeutic target.     

电针对Aβ25—35致阿尔茨海默病模型大鼠cAMP／PKA／CREB信号转导通路的影响

目的探讨电针对Aβ25-35导致的阿尔茨海默病模型大鼠应用电针刺激后cAMP／PKA／CREB信号转导通路的变化。方法48只健康雌性SD大鼠随机分为AD模型组、电针组、假手术组和正常对照组各12只。模型组与电针组采用Aβ25-35建立AD模型后电针组给予电针刺激,模型组未给予电针刺激;假手术组双侧海马注射等量生理盐水;正常对照组不做任何处理。4组均采用Morris水迷宫实验检测大鼠记忆与空间探索能力,采用分光光度计法检测脑组织超氧化物歧化酶与丙二醛水平,采用放射免疫法检测海马cAMP水平,采用免疫组织化学法检测海马5-羟色胺1A受体、蛋白激酶A与p-CREB蛋白表达水平,采用Westernblot检测海马总Tau蛋白表达水平及Tau蛋白Ser396位点磷酸化情况。结果与模型组比较,电针组、假手术组与对照组逃避潜伏期缩短、跨越平台次数增多、目标象限停留时间延长（P〈0．05）,脑组织中超氧化物歧化酶、5-羟色胺1A受体、蛋白激酶A及p-CREB水平增高（P〈0．05）,丙二醛、总Tau蛋白、pTau—Ser396、c—los蛋白水平降低（P〈0．05）;电针组总Tau蛋白、c—los及PKA水平高于假手术组（P〈0．05）,与对照组比较差异无统计学意义（P〉0．05）。结论电针可明显提高阿尔茨海默病大鼠学习记忆功能和空间探索能力,可能是通过拮抗cAMP／PKA／CREB信号转导通路相关蛋白的异常改变起作用。     

The novel gamma secretase inhibitor N-[cis-4-[(4-chlorophenyl)sulfonyl]-4-(2,5-difluorophenyl)cyclohexyl]-1,1,1-trifluoromethanesulfonamide (MRK-560) reduces amyloid plaque deposition without evidence of notch-related pathology in the Tg2576 mouse

There is a substantial body of evidence indicating that beta-amyloid peptides (Abeta) are critical factors in the onset and development of Alzheimer's disease (AD). One strategy for combating AD is to reduce or eliminate the production of Abeta through inhibition of the gamma-secretase enzyme, which cleaves Abeta from the amyloid precursor protein (APP). We demonstrate here that chronic treatment for 3 months with 3 mg/kg of the potent, orally bioavailable and brain-penetrant gamma-secretase inhibitor N-[cis-4-[(4-chlorophenyl)-sulfonyl]-4-(2,5-difluorophenyl)cyclohexyl]-1,1,1-trifluoromethanesulfonamide (MRK-560) attenuates the appearance of amyloid plaques in the Tg2576 mouse. These reductions in plaques were also accompanied by a decrease in the level of reactive gliosis. The morphometric and histological measures agreed with biochemical analysis of Abeta(40) and Abeta(42) in the cortex. Interestingly, the volume of the plaques across treatment groups did not change, indicating that reducing Abeta levels does not significantly alter deposit growth once initiated. Furthermore, we demonstrate that these beneficial effects can be achieved without causing histopathological changes in the ileum, spleen, or thymus as a consequence of blockade of the processing of alternative substrates, such as the Notch family of receptors. This indicates that in vivo a therapeutic window between these substrates seems possible--a key concern in the development of this approach to AD. An understanding of the mechanisms whereby MRK-560 shows differentiation between the APP and Notch proteolytic pathway of gamma-secretase should provide the basis for the next generation of gamma-secretase inhibitors.     

Increased T cell reactivity to amyloid beta protein in older humans and patients with Alzheimer disease

Alzheimer disease (AD) is characterized by the progressive deposition of the 42-residue amyloid beta protein (Abeta) in brain regions serving memory and cognition. In animal models of AD, immunization with Abeta results in the clearance of Abeta deposits from the brain. However, a trial of vaccination with synthetic human Abeta1-42 in AD resulted in the development of meningoencephalitis in some patients. We measured cellular immune responses to Abeta in middle-aged and elderly healthy subjects and in patients with AD. A significantly higher proportion of healthy elderly subjects and patients with AD had strong Abeta-reactive T cell responses than occurred in middle-aged adults. The immunodominant Abeta epitopes in humans resided in amino acids 16-33. Epitope mapping enabled the identification of MHC/T cell receptor (TCR) contact residues. The occurrence of intrinsic T cell reactivity to the self-antigen Abeta in humans has implications for the design of Abeta vaccines, may itself be linked to AD susceptibility and course, and appears to be associated with the aging process.     

Amyloid beta and Alzheimer disease therapeutics: the devil may be in the details

Alzheimer disease (AD) is characterized by the progressive accumulation of amyloid beta protein (Abeta) in areas of the brain serving cognitive functions such as memory and language. The first of two separate reports (see the related articles beginning on pages 415 and 440) reveals that intrinsic T cell reactivity to the self-antigen Abeta exists in many humans and increases with age. This finding has implications for the design of Abeta vaccines. The second report demonstrates that a number of FDA- approved nonsteroidal anti-inflammatory drugs are capable of lowering Abeta levels in mice. The work suggests that further testing of the therapeutic utility of these types of compounds for the potential treatment of AD is warranted.     

Gene therapy for Alzheimer' s disease

One of the keys to successful gene therapy is the selection of the appropriate therapeutic gene and its molecular vehicle. A recombinant adeno-associated virus (rAAV) vector offers the advantage of the ability to infect non-dividing cells, affording a non-pathogenic, long-term transgene expression without a substantial inflammatory response. In Alzheimer's disease (AD), accumulation of amyloid-beta peptide (Abeta) in the brain is a triggering event leading to the long-term pathological cascade. Therefore, it is necessary for therapy and prevention of AD to promote the degradation and clearance of Abeta . Neprilysin is a rate-limiting peptidase in Abeta degradation in the brain and a reduction in neprilysin activity will contribute to Abeta deposition and thus to AD development. As an experimental gene therapy for AD, neprilysin gene was introduced in the hippocampus of mice using rAAV vector. The neprilysin gene transfer increased the reduced neprilysin activity, abolished the increase of Abeta levels in the hippocampus of neprilysin-deficient mice, and also remarkably decelerated amyloid deposition in aged AD model mice. Thus, introduction of this Abeta--degrader gene into the brain would have therapeutic potential for AD.     

P-glycoprotein efflux and other factors limit brain amyloid beta reduction by beta-site amyloid precursor protein-cleaving enzyme 1 inhibitors in mice

Alzheimer's disease (AD) is a progressive neurodegenerative disease. Amyloid beta (Abeta) peptides are hypothesized to cause the initiation and progression of AD based on pathologic data from AD patients, genetic analysis of mutations that cause early onset forms of AD, and preclinical studies. Based on this hypothesis, beta-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1) inhibitors are an attractive therapeutic approach for AD because cleavage of the APP by BACE1 is required to form Abeta. In this study, three potent BACE1 inhibitors are characterized. All three inhibitors decrease Abeta formation in cultured cells with IC(50) values less than 10 nM. Analysis of APP C-terminal fragments by immunoblotting and Abeta peptides by mass spectrometry showed that these inhibitors decreased Abeta by inhibiting BACE1. An assay for Abeta1-40 in mice was developed and used to show that these BACE1 inhibitors decreased plasma Abeta1-40, but not brain Abeta1-40, in wild-type mice. Because these BACE1 inhibitors were substrates for P-glycoprotein (P-gp), a member of the ATP-binding cassette superfamily of efflux transporters, these inhibitors were administered to P-gp knockout (KO) mice. These studies showed that all three BACE1 inhibitors decreased brain Abeta1-40 in P-gp KO mice, demonstrating that P-gp is a major limitation for development of BACE1 inhibitors to test the amyloid hypothesis. A comparison of plasma Abeta1-40 and brain Abeta1-40 dose responses for these three compounds revealed differences in relative ED(50) values, indicating that factors other than P-gp can also contribute to poor brain activity by BACE1 inhibitors.