Molecular basis of Alzheimer's disease: From amyloid hypothesis to treatment in the foreseeable future

Alzheimer's disease (AD) is the most common dementing disorder in the elderly. It is clinically characterized by insidious onset of memory disturbance followed by slowly progressive global dementia. The patient's brain at autopsy shows diffuse cerebral atrophy, and microscopic findings are characterized by the presence of intraneuronal neurofibrillary tangle (NFT), senile plaques with extraneuronal β amyloid deposits, and dystrophic changes of neuronal processes with synaptic and neuronal loss. The pathological mechanism of these hallmarks are now well understood on the molecular basis, and new strategies to prevent and reverse these pathological changes are now being developed. Here I review some personal interest of the mechanism, and describe future strategies for prevention and treatment of AD.     

Study of Alzheimer's disease using transgenic mice: The mechanism of formation of brain Aβ amyloid and neurofibrillary tangles

Background:   The purpose of the present paper was to clarify the role of brain amyloid β protein (Aβ) in Alzheimer's disease (AD) with the eventual aim of developing new treatments.
Methods:   Three kinds of transgenic mice (Tg) were examined: those overexpressing βAPP695ΔNL (APPsw mice), those expressing the R406W mutant form of human 4-repeat tau (tauR406W mice), and those with both βAPP695ΔNL and R406W mutant tau (APPsw × tau R406 double Tg).
Results:   First, cored plaques, diffuse plaques and amyloid angiopathy were detected in the brains of APPsw mice. Loss of neurons and synapses was seen in the cored plaques, and accumulation of phosphorylated-tau in dystrophic neurites around the cored plaques. However, Neurofibrillary tangles were not seen. These mice displayed memory impairment and decreased levels of acetylcholine in the cortex and hippocampus. Second, tau R406W mice were produced. These mice developed motor disturbances and memory impairment, accompanied by gliosis and marked tau accumulation in neurons of the frontotemporal cortex, hippocampus and amygdala. No Aβ was detected. Third, APPsw × tauR406W double Tg were produced. The pattern of Aβ deposition was similar in these double Tg and the APPsw mice. Gallyas silver-staining showed greater levels of tauopathy in the hippocampus in these double Tg compared to the tauR406W mice.
Conclusion:   These findings suggest that deposition of brain Aβ is the initial event leading to subsequent disease such as accumulation of phosphorylated tau, neuronal loss and memory disturbance, and that the treatment of brain Aβ should be the first priority in finding a cure for AD.     

Current status of metals as therapeutic targets in Alzheimer's disease

There is accumulating evidence that interactions between beta-amyloid and copper, iron, and zinc are associated with the pathophysiology of Alzheimer's disease (AD). A significant dyshomeostasis of copper, iron, and zinc has been detected, and the mismanagement of these metals induces beta-amyloid precipitation and neurotoxicity. Chelating agents offer a potential therapeutic solution to the neurotoxicity induced by copper and iron dyshomeostasis. Currently, the copper and zinc chelating agent clioquinol represents a potential therapeutic route that may not only inhibit beta-amyloid neurotoxicity, but may also reverse the accumulation of neocortical beta-amyloid. A Phase II double-blind clinical trial of clioquinol with B12 supplementation will be published soon, and the results are promising. This article summarizes the role of transition metals in amyloidgenesis and reviews the potential promise of chelation therapy as a treatment for AD.     

阿尔茨海默病的发病机制及营养调节

阿尔茨海默病是一种进行性中枢神经系统退行性疾病,是威胁人类健康的重大疾病之一。目前,阿尔茨海默病的发病机制尚不明确,关于阿尔茨海默病的发病机制有很多学说,对于阿尔茨海默病的治疗效果不理想,但一些营养调节能起到改善的作用,本文即对阿尔茨海默病的发病机制及营养调节研究现状作一综述。     

Binding and safety profile of novel benzoxazole derivative for in vivo imaging of amyloid deposits in Alzheimer's disease

Background:   In vivo detection of amyloid deposits in the brain is potentially useful for early diagnosis of Alzheimer's disease (AD) and tracking the efficacy of anti-amyloid therapy.
Methods:   To develop an amyloid-binding agent for positron emission tomography, we screened over 2600 compounds.
Results:   We found benzoxazole derivatives as candidate compounds for in vivo amyloid imaging probes. One of these agents, 2-(2-[2-dimethylaminothiazol-5-yl]ethenyl)-6-(2-[fluoro]ethoxy)benzoxazole (BF-227), displays high binding affinity to Aβ fibrils. BF-227 binding increased linearly with increasing Aβ fibril formation. In temporal and hippocampal AD brain sections, BF-227 selectively bound to amyloid plaques. In contrast, no staining was evident in the cerebellum. Compared with the previously reported compound BF-168, ¹⁸F-labeled BF-227 displayed selective in vivo labeling of amyloid fibrils and rapid washout from white matter areas in an Aβ-injected rat model. An acute and subacute toxicity study of BF-227 indicated sufficient safety for clinical use as a positron emission tomography probe.
Conclusions:   These findings suggest that BF-227 is feasible as an in vivo imaging probe of amyloid deposits in AD patients.     

Vitamin A and Alzheimer's disease

The deposition of amyloid β‐protein (Aβ) in the brain is an invariant feature of Alzheimer's disease (AD). Vitamin A, which has been traditionally considered an anti‐oxidant compound, plays a role in maintaining higher function in the central nervous system. Plasma or cerebrospinal fluid concentrations of vitamin A and β‐carotene have been reported to be lower in AD patients, and these vitamins have been clinically shown to slow the progression of dementia. Vitamin A (retinol, retinal and retinoic acid) and β‐carotene have been shown in in vitro studies to inhibit the formation, extension and destabilizing effects of β‐amyloid fibrils. Recently, the inhibition of the oligomerization of Aβ has been suggested as a possible therapeutic target for the treatment of AD. We have recently shown the inhibitory effects of vitamin A and β‐carotene on the oligomerization of Aβ40 and Aβ42 in vitro. In previous in vivo studies, intraperitoneal injections of vitamin A decreased brain Aβ deposition and tau phosphorylation in transgenic mouse models of AD, attenuated neuronal degeneration, and improved spatial learning and memory. Thus, vitamin A and β‐carotene could be key molecules for the prevention and therapy of AD. Geriatr Gerontol Int 2012; 12: 180–188.     

CD147 is a regulatory subunit of the gamma-secretase complex in Alzheimer's disease amyloid beta-peptide production

gamma-Secretase is a membrane protein complex that cleaves the beta-amyloid precursor protein (APP) within the transmembrane region, after prior processing by beta-secretase, producing amyloid beta-peptides Abeta(40) and Abeta(42). Errant production of Abeta-peptides that substantially increases Abeta(42) production has been associated with the formation of amyloid plaques in Alzheimer's disease patients. Biophysical and genetic studies indicate that presenilin-1, which contains the proteolytic active site, and three other membrane proteins [nicastrin, anterior pharynx defective-1 (APH-1), and presenilin enhancer-2 (PEN-2)] are required to form the core of the active gamma-secretase complex. Here, we report the purification of the native gamma-secretase complexes from HeLa cell membranes and the identification of an additional gamma-secretase complex subunit, CD147, a transmembrane glycoprotein with two Ig-like domains. The presence of this subunit as an integral part of the complex itself was confirmed through coimmunoprecipitation studies of the purified protein from HeLa cells and of solubilized complexes from other cell lines such as neural cell HCN-1A and HEK293. Depletion of CD147 by RNA interference was found to increase the production of Abeta peptides without changing the expression level of the other gamma-secretase components or APP substrates whereas CD147 overexpression had no statistically significant effect on Abeta-peptide production, other gamma-secretase components or APP substrates, indicating that the presence of the CD147 subunit within the gamma-secretase complex down-modulates the production of Abeta-peptides.     

Polymorphisms of the Z protein protease inhibitor and risk of venous thromboembolism: a meta-analysis

Two nonsense polymorphisms of Z-dependent protease inhibitor (ZPI; Serpina10) have been identified. To assess the risk of venous thromboembolism (VTE) associated with W303x and R67X Serpina10 mutations, we performed a meta-analysis of studies comparing the prevalence of these two mutations in VTE patients and in controls Odds Ratios (ORs) and 95% confidence intervals (CIs) were calculated for each trial and pooled using a random-effects model. Five studies involving 5000 patients were included. R67X and W303X mutations of Serpina10 were not associated with increased VTE risk (OR 1.63; 95% CI 0.84, 3.16 and OR 1.21; 95% CI 0.29, 4.98 respectively).     

Inhibition of platelet activation by the Alzheimer's disease amyloid precursor protein

The amyloid precursor protein (APP) of Alzheimer's disease is abundantly expressed in the platelet α-granule where its role remains unclear. This study describes a novel function for APP in regulating human platelet activation. Preincubation of platelet-rich plasma with recombinant secreted APP (sAPP) isoforms dose-dependently inhibited platelet aggregation and secretion induced by ADP or adrenaline. Similarly, sAPP potently inhibited low-dose thrombin-induced activation in washed platelet suspensions, indicating that the activity does not require plasma cofactors. There were no functional differences between sAPP forms with or without the Kunitz protease inhibitor domain or derived from either α- or β-secretase cleavage. In fact, the N-terminal cysteine-rich region of APP (residues 18–194) was as effective as the entire sAPP region in the inhibition of platelet activation. The inhibitory activity of sAPP correlated with a significant reduction in the agonist-induced production of the arachidonic acid (AA) metabolites thromboxane B₂ and prostaglandin E₂. However, sAPP did not affect AA-induced platelet aggregation or secretion, indicating the enzymatic conversion of AA was not inhibited. The addition of a threshold dose of AA reversed the sAPP-inhibition of agonist-induced platelet activation. This suggests that sAPP decreases the availability of free AA, although the mechanism is not yet known. These data provide evidence that the release of sAPP upon platelet degranulation may result in negative feedback regulation during platelet activation.     

Structural differences between apoE3 and apoE4 may be useful in developing therapeutic agents for Alzheimer's disease

Apolipoproteins E3 and E4, proteins with a molecular mass of 34.15 kDa, differ by a single amino acid change. ApoE4 contains an arginine residue at position 112, whereas apoE3 has a cysteine at this position. ApoE4 is the major risk factor for late-onset Alzheimer's disease, whereas apoE3, the common isoform, is neutral with respect to this disease. Here, using literature data from both hydrogen-deuterium exchange and site-directed mutations, we suggest structural differences between these two isoforms that are distant from the site of the arginine-to-cysteine change. These structural differences involve sequences from both the N- and C-terminal domains, sequentially far apart but structurally close. In addition, these regions are close to regions that bind lipid and to a region involved in association of apoE monomers to higher molecular weight forms. We discuss the possibility that these regions could be targeted preferentially to affect the function of apoE4 relative to apoE3.     

Altered morphology and 3D architecture of brain vasculature in a mouse model for Alzheimer's disease

Substantial evidence from epidemiological, pathological, and clinical reports suggests that vascular factors are critical in the pathogenesis of Alzheimer's disease (AD), and changes in blood flow are currently the most reliable indicators of the disease. We previously reported that older APP23 transgenic (tg) mice have significant blood flow alterations correlated with structural modifications of blood vessels. For the present study, our objective was to analyze the age-dependent morphological and architectural changes of the cerebral vasculature of APP23 tg mice. To visualize the 3D arrangement of the entire brain vasculature, we used vascular corrosion casts. Already at young ages, when typically parenchymal amyloid plaques are not yet present, APP23 tg mice had significant alterations, particularly of the microvasculature, often accompanied by small deposits attached to the vessels. In older animals, vasculature abruptly ended at amyloid plaques, resulting in holes. Often, small deposits were sitting near or at the end of truncated vessels. Between such holes, the surrounding vascular array appeared more dense and showed features typical for angiogenesis. We propose that small amyloid aggregates associated with the microvasculature lead to morphological and architectural alterations of the vasculature, resulting in altered local blood flow. The characteristic early onset of vascular alterations suggests that imaging blood flow and/or vasculature architecture could be used as a tool for early diagnosis of the disease and to monitor therapies.     

血清淀粉样蛋白A与冠心病合并糖尿病患者高密度脂蛋白胆固醇外流能力的相关性

目的 探讨冠心病合并糖尿病患者血浆高密度脂蛋白(HDL)胆固醇外流能力的变化及其影响因素.方法 选取北京大学第三医院心内科住院并经冠状动脉造影证实的冠心病患者140例为研究对象,依据是否合并糖尿病分为两组,即冠心病合并糖尿病组70例,单纯冠心病组70例.选取同期入院且经冠状动脉造影证实的非冠心病非糖尿病患者25例作为对...     

Mechanisms of progression in native coronary artery disease: role of healed plaque disruption

OBJECTIVE—To determine the role of healed plaque disruption in the generation of chronic high grade coronary stenosis.
METHODS—Coronary arteries obtained at necropsy were perfuse fixed with formal saline for 24 hours at 100 mg Hg. The percentage lumen diameter stenosis was measured in each 3 mm segment containing a plaque, using the lumen size at the nearest histologically normal segment as the reference point. Each segment was prepared for histological examination and stained with Sirius red and immunohistochemistry for smooth muscle actin. Healed disruption was considered to be present when under polarised light there was a break in the yellow-white dense collagen of the cap filled in by more loosely arranged green collagen. Increased smooth muscle density in the green staining areas was required. Each section was read independently by two observers; any segment with discordant views was considered negative.
MATERIAL—31 men aged 51-69 dying suddenly of ischaemic heart disease. 39 coronary arteries were studied containing 256 separate plaques, after excluding coronary arteries with old total occlusions, an acute culprit thrombotic lesion, diffuse disease without normal arterial segments, and arteries related to old myocardial scars.
RESULTS—16 of 99 plaques causing < 20% diameter stenosis had prior disruption. In the 21-50% stenosis range 16 of 86 plaques showed healed disruption. Stenosis  51% by diameter was present in 71 plaques, 52 of which showed a healed disruption pattern. The difference between stenosis < 50% and stenosis  51% was significant by the χ² test (p < 0.001).
CONCLUSIONS—Subclinical episodes of plaque disruption followed by healing are a stimulus to plaque growth that occurs suddenly and is a major factor in causing chronic high grade coronary stenosis. This mechanism would explain the phasic rather than linear progression of coronary disease observed in angiograms carried out annually in patients with chronic ischaemic heart disease.


Keywords: atherosclerosis; stenosis; plaque disruption     

Melatonin alleviates behavioral deficits associated with apoptosis and cholinergic system dysfunction in the APP 695 transgenic mouse model of Alzheimer's disease

Melatonin is an endogenous antioxidant and free radical scavenger. A transgenic (Tg) mouse model for Alzheimer's disease mimics the accumulation of senile plaques, neuronal apoptosis and memory impairment. Previous studies indicated that melatonin reduced beta-amyloid (Abeta)-induced neurotoxicity. In this study, after giving melatonin at 10 mg/kg to APP 695 transgenic (APP 695 Tg) mice for 4 months, we evaluated the long-term influence of melatonin on behavior, biochemical and neuropathologic changes in APP 695 Tg mice. Step-down and step-through passive avoidance tests suggested that 8-month-old APP 695 Tg mice showed decreases in step-down latency and step-through latency and increases in count of error throughout the entire learning trial and memory session, which suggested learning and memory impairment. However, melatonin alleviated learning and memory deficits. Additionally, choline acetyltransferase (ChAT) activity also decreased in the frontal cortex and hippocampus of APP 695 Tg mice compared with non-Tg littermates. Melatonin supplementation increased ChAT activity in the frontal cortex and hippocampus. DNA fragmentation was present in the frontal cortex of the APP 695 Tg mice; melatonin reduced the number of apoptotic neurons. Congo Red staining and Bielschowsky silver impregnation both showed the apparent extracellular Abeta deposition in frontal cortex of APP 695 Tg mice. However, melatonin decreased the Abeta deposits. Our results indicate that neuroprotection by melatonin is partly related to modulation of apoptosis and protection of the cholinergic system. Early rational melatonin interventions may be one of the most promising strategies in the development of approaches to retard or prevent Abeta-mediated disease progression.     

Pathology and Pathways of Alzheimer's Disease with an Update on New Developments in Treatment

As our understanding of the complex pathology of Alzheimer's disease improves, more targets for therapy emerge. These include the actions of beta amyloid, the inflammatory cascade, pathobiology of tau proteins' conversion to neurofibrillary tangles, oxidative neuronal damage, and neurotransmitter depletion. Many agents now under investigation target the early stages of the disease process, aiming to prevent or slow the development of symptoms. This article reviews the current understanding of the course and pathology of Alzheimer's disease as it relates to emerging therapies, then summarizes some promising current research directions in primary prevention, secondary prevention, and treatment.     

胆固醇酯转运蛋白抑制剂对动脉粥样硬化性心血管疾病影响的研究进展

大量临床流行病学资料证实血浆低密度脂蛋白胆固醇水平升高及高密度脂蛋白胆固醇水平降低均是动脉粥样硬化性心血管疾病的独立危险因素。在生理过程中抑制胆固醇酯转运蛋白可以升高血浆高密度脂蛋白胆固醇水平,理论上可能具有抗动脉粥样硬化的作用。然而迄今为止,调节胆固醇酯转运蛋白的动物模型和临床研究结果不尽一致,以抑制胆固醇酯转运蛋白为基础的相关药物治疗选择带来了不确定性。文章从胆固醇酯转运蛋白在脂质代谢中的生理作用、部分动物研究中与动脉粥样硬化的关系以及临床应用对动脉粥样硬化性心血管疾病的影响等方面的最新研究进展进行综述。     

Atheroprotective immunity and cardiovascular disease: therapeutic opportunities and challenges

Emerging knowledge of the role of atheroprotective immune responses in modulating inflammation and tissue repair in atherosclerotic lesions has provided promising opportunities to develop novel therapies directly targeting the disease process in the artery wall. Regulatory T (Treg) cells have a protective role through release of anti‐inflammatory cytokines and suppression of autoreactive effector T cells. Studies in experimental animals have shown that blocking the generation or action of Treg cells is associated with more aggressive development of atherosclerosis. Conversely, cell transfer and other approaches to expand Treg cell populations in vivo result in reduced atherosclerosis. There have been relatively few clinical studies of Treg cells and cardiovascular disease, but the available evidence also supports a protective function. These observations have raised hope that it may be possible to develop therapies that act by enforcing the suppressive activities of Treg cells in atherosclerotic lesions. One approach to achieve this goal has been through development of vaccines that stimulate immunological tolerance for plaque antigens. Several pilot vaccines based on LDL‐derived antigens have demonstrated promising results in preclinical testing. If such therapies can be shown to be effective also in clinical trials, this could have an important impact on cardiovascular prevention and treatment. Here, we review the current knowledge of the mode of action of atheroprotective immunity and of the ways to stimulate such pathways in experimental settings. The challenges in translating this knowledge into the clinical setting are also discussed within the perspective of the experience of introducing immune‐based therapies for other chronic noninfectious diseases.     

Pathogenesis of metastatic disease: implications for current therapy and for the development of new therapeutic strategies

Different tumor cell subpopulations coexisting within the same tumor exhibit varied susceptibilities to antineoplastic agents. Tumor cell heterogeneity is now recognized as the principal cause of treatment failure in cancer, and is a formidable obstacle to effective therapy and to the development of drug delivery systems for selective targeting of antineoplastic agents to tumor cells. Recent insights into the genesis of tumor cell heterogeneity during progressive tumor growth reveal new complexities that raise challenging questions about the adequacy of certain approaches to the current therapy of metastatic disease and impose challenging criteria for the development of improved therapeutic strategies. Many of the experimental approaches used in the search for new antineoplastic agents and targeted drug delivery systems ignore the pathogenesis of metastasis and the problem of tumor cell heterogeneity. The adoption of more relevant assay systems is an urgent priority. These include the greater use of metastatic tumor models and the increased use of human tumor cells to replace rodent cell systems which have been of limited predictive value in identifying effective anticancer agents. In contrast to current strategies for the development of new antineoplastic drugs which seek to identify agents with activity against a broad range of histologically diverse tumors, greater success may be achieved by seeking agents active only against specific cell lineages. Many established human tumor cell lines may not be suitable for this purpose because of extensive phenotypic change produced by prolonged passage ex vivo. Development of histiotype-specific human tumor cell screens will require an extensive research effort to identify target cells that display demonstrable phenotypic relatedness to tumor cells in neoplastic lesions. Major advances in the therapy of metastatic disease are considered unlikely in the next few years, and progress will stem from improved use of existing agents in refined combination therapy protocols in which greater attention is given to the duration, frequency, and sequence of therapy with different agents to limit emergence of tumor cell variants resistant to one or more antineoplastic agents. Advances in molecular biology offer exciting prospects for the identification of new therapeutic targets in human tumor cells, for the induction of alterations in tumor cells that could serve as therapeutic targets, and for the elucidation of the mechanisms responsible for the rapid phenotypic diversification of tumor cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Mechanisms of drug resistance in colon cancer and its therapeutic strategies

Drug resistance develops in nearly all patients with colon cancer, leading to a decrease in the therapeutic efficacies of anticancer agents. This review provides an up-to-date summary on over-expression of ATPbinding cassette(ABC) transporters and evasion of apoptosis, two representatives of transport-based and non-transport-based mechanisms of drug resistance, as well as their therapeutic strategies. Different ABC transporters were found to be up-regulated in colon cancer, which can facilitate the efflux of anticancer drugs out of cancer cells and decrease their therapeutic effects. Inhibition of ABC transporters by suppressing their protein expressions or co-administration of modulators has been proven as an effective approach to sensitize drug-resistant cancer cells to anticancer drugs in vitro. On the other hand, evasion of apoptosis observed in drug-resistant cancers also results in drug resistance to anticancer agents, especially to apoptosis inducers. Restoration of apoptotic signals by BH3 mimetics or epidermal growth factor receptor inhibitors and inhibition of cancer cell growth by alternative cell death pathways, such as autophagy, are effective means to treat such resistant cancer types. Given that the drug resistance mechanisms are different among colon cancer patients and may change even in a single patient at different stages, personalized and specific combination therapy is proposed to be more effective and safer for the reversal of drug resistance in clinics.