Current Alzheimer Research - Volume 4, Issue 3, 2007

Anesthesia and surgery have been reported to produce long-term cognitive problems, and to accelerate neurodegenerative disorders in the elderly. In previous work, we found that inhaled anesthetics enhance fibril formation and cytotoxicity of amyloid β peptide. In this work we show that the inhaled anesthetics halothane (2-bromo-2-chloro-1,1,1- trifluoroethane) and isoflurane (1-chloro-2,2,2-trifluoroethyl difluoromethyl ether) also favor intermediate oligomers of amyloid β1-40, and reduce solubility of amyloid β1-40 monomer. Size-exclusion chromatography, analytical ultracentrifugation and photo-induced cross-linking experiments indicate halothane enhancement of oligomeric species having molecular weight ∼44-100 kDa. Bis-ANS fluorescence experiments revealed that halothane stabilizes a population of diffusible oligomers relative to the monomer or the mature fibril. These data show that inhaled anesthetics lower the amyloid β1-40 concentration necessary to initiate oligomer formation, probably by preferential binding to intermediate oligomers en route to fibril formation.

Alzheimer's disease (AD) involves neuronal loss and reduction of synaptic density in specific brain region. Some of the neuronal deaths are associated with excitotoxicity. We previously reported that amyloid β-peptide (Aβ) induced release of N-methyl-D-aspartate receptor (NMDA-R) co-agonists, including glutamate and D-serine. The induction of D-serine production by Aβ involves transcriptional and/or translational regulation of serine racemase gene. Similarly, we report here that conditioned medium from microglia treated with secreted amyloid precursor protein (sAPP) contained elevated levels of D-serine. In microglia, sAPP increased the steady-state dimeric protein level of serine racemase. Promoter- reporter and mRNA analyses suggested that serine racemase is transcriptionally induced by sAPP. These data extend the link between excitotoxicity and neuroinflammation. D-serine may cooperate with glutamate to link neuroinflammation with excitotoxicity, suggesting a pathogenic mechanism applicable to neuronal death in AD and other neurodegenerative diseases.

For centuries, extracts from the leaves of the Ginkgo biloba tree have been used as Chinese herbal medicine to treat a variety of health disorders. The standardized Ginkgo biloba extract EGb 761 was marketed in France and Germany 30 years ago for various vascular and cerebral deficits and is now classified as a food supplement in the United States. EGb 761 is currently the focus of phase-III clinical trials, GEM and GuidAge studies, to evaluate its efficacy on the prevention of Alzheimer's disease (AD) in subjects over 70 years old. This review summarizes recent advancements in our understanding of the potential role of EGb 761 in the prevention of AD. Besides its well-known free radical scavenging properties, the ability of EGb 761 to protect neurons probably also involves other intracellular pathways. We will point out potential targets of EGb 761 in the amyloid cascade such as its antiamyloidogenic properties or the regulation of gene expression. Moreover we will discuss the complexity of the cellular and molecular mechanisms of EGb 761 and the significance of the synergic effect of different constituents of EGb 761.

One of the earliest manifestations of Alzheimer's disease (AD) is the characteristic inability of affected individuals to form new memories. Memory impairment appears to significantly predate the death of nerve cells, implying that neuronal dysfunction is responsible for the pathophysiology of early stage AD. Mounting evidence now indicates that soluble oligomers of the amyloid-β peptide (Aβ) are the main neurotoxins that lead to early neuronal dysfunction and memory deficits in AD. Cyclic AMP (cAMP) is a central component of intracellular signaling pathways that regulate a wide range of biological functions, including memory. Among other actions, cAMP triggers the phosphorylation and activation of the cAMP responsive element binding protein (CREB), a transcription factor that regulates the expression of genes that are important for long-term memory. Here, we discuss recent evidence suggesting that cAMP enhancing compounds may find applications as neurocognitive enhancers in AD and in other neurological disorders, as well as possible roles of cAMP in the regulation of neuronal regeneration. In particular, we review recent results showing that low concentrations of 2,4-dinitrophenol (DNP) upregulate neuronal cAMP and tau levels, promote neurite outgrowth and neuronal differentiation and block the oligomerization and neurotoxicity of Aβ. Possible implications of these findings in the development of novel therapeutic approaches in AD are discussed.

Previous research suggests separate neural networks for implicit (non-declarative) and explicit (declarative) memory processes. A core cognitive impairment in mild to moderate Alzheimer's disease (AD) is a pronounced declarative memory and learning deficit with relative preservation of non-declarative memory. Cholinesterase inhibitors has been purported to enhance cognitive function, and previous clinical trials consistently showed that donepezil, a reversible inhibitor of acetylcholinesterase (AChE), led to statistically significant improvements in cognition and patient function. This prospective pilot study is a randomized, double blind, placebo-controlled clinical trial investigating 10 patients with AD. Our purpose was to examine the relationship between declarative and non-declarative capability with particular emphasis on implicit sequence learning. Patients were assessed at baseline and again at 4-weeks. After participants' baseline data were obtained, each was double-blindly randomized to one of two groups: donepezil or placebo. At baseline participants were tested with two outcome measures (Serial Reaction Time Task, Alzheimer's Disease Assessment Scale-Cognitive Subscale). Participants were given either 5 mg donepezil or an identically appearing placebo to be taken nightly for 4 weeks (28 tablets), and then retested. The donepezil group demonstrated a greater likelihood of increases in both nondeclarative and declarative processes. The placebo group was mixed without clearly definable trends or patterns. When the data were examined for coincidental changes in the two outcome measures together they are suggestive of a benefit from donepezil treatment for non-declarative and declarative processes.

Executive functions describe a variety of cognitive processes responsible for structuring behaviors around goals, and developing plans to achieve those goals in relation to the environment. In addition to deficits in basal forebrain cholinergic neuronal input into the frontal cortex, impaired control of executive function has been associated with lesions to the frontal cortex and its basal ganglia-thalamic connections. In addition to executive dysfunction, features that imply fronto-subcortical pathology include profound slowing of cognition, attentional deficits, apathy and changes in mood. Fronto-subcortical systems are vulnerable to white matter change, atrophy, and certain forms of neurotransmitter depletion. The diffuse, and likely non-cholinergic, projections of acetylcholinesterase (AChE)-containing thalamic neurons innervate all cortical areas. Butyrylcholinesterase (BuChE) activity is relatively high in thalamic nuclei that project to frontal cortical structures involved in attention, executive function, and behavior. However, the largest pool of BuChE in the brain is found in the glia, particularly those in deeper cortical and subcortical structures. These findings suggest that Bu- ChE may also be an important therapeutic target in the management of symptoms due to subcortical pathology. Whereas ‘pure’ Alzheimer's disease (AD) may involve significant subcortical pathology in addition to cortical pathology, AD with cerebrovascular disease, vascular dementia (VaD), Parkinson's disease dementia (PDD) and dementia due to Lewy bodies (DLB) may involve a generally greater degree of subcortical, in addition to cortical, pathology. It may be hypothesized that these dementia types, which are characterized by executive dysfunction, might derive particular benefits from cholinesterase inhibitors such as rivastigmine that inhibit BuChE in addition to AChE.

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Transgenic mouse models of Alzheimer's disease (AD) are being utilized as models for elucidating AD etiology and potential therapeutic approaches. However, two major drawbacks of these models are: (1) transgenic animals often over-express amyloid beta (Aβ) to high levels compared to that seen in sporadic human AD and (2) the current intellectual property issues surrounding a number of these models make them difficult to utilize in a commercial setting. Our goal was to identify an appropriate non-transgenic mouse strain, devoid of these patent restrictions and test whether amyloid- modulating compounds will lower total brain and plasma Aβ. Plasma and brain samples were collected from eight commonly used mouse strains (C57BL/6, SJL, CF-1, DBA/2, CD-1, 129, FVB and B6D2F1; Charles River Labs) and total Aβ levels were validated and quantified with a rodent-specific monoclonal Aβ antibody. Plasma Aβ in SJL mice was the highest of the eight strains tested (213 pM ± 21 pM), but was not significantly different than the seven other strains. Total brain Aβ in SJL mice was also the greatest of the mouse strains tested (356 pM ± 73 pM). SJL, C57BL/6 and CF-1 mice had total brain Aβ levels that were significantly greater than Aβ levels in B6D2F1 mice (242 ± 20 pM). In vivo efficacy of an Aβ lowering agent was observed in CF-1 mice upon oral administration of the γ-secretase inhibitors, DAPT and LY-411575. The absolute levels of rodent brain Aβ detected and the efficacy of the γ-secretase treatment were dependent upon the antibodies used, as well as the extraction methodology. The measurement of total brain Aβ lowering in a common mouse strain could help accelerate drug discovery programs for Alzheimer's disease without relying on costly transgenic animals that overexpress APP in a manner that may not be predictive of the effects of these compounds in human AD.

Amyloid peptides (Aβ) are fragments of the Amyloid Precursor Protein (APP), an integral membrane protein. Aβ peptides are continuously generated by neurons and non-neuronal cells via sequential cleavage of APP by secretases. In particular, Aβ1-42 is the main component of the senile plaques associated with Alzheimer's disease (AD). Glial cells participate in the uptake of soluble extra-cellular Aβ and in the clearance of this material at localized sites where the Aβ are concentrated. It has been shown that clusterin (Apo J) and apolipoprotein E (ApoE) exert important additive effects in reducing Aβ deposition. In agreement with the fact that homocysteine (Hcy) potentiates Aβ peptide neurotoxicity, and Hcy brain levels increase with age, it has been demonstrated that high plasma levels of Hcy are a risk factor for AD. In the present paper, we used animals subjected to chronic intake of methionine (1 g/kg/day) in the drinking water, since this treatment can increase plasma Hcy levels by 30%. By means of this animal model, interactions between the Aβ β- sheet rich fibrils and clusterin, have been evaluated in striata of animals after Aβ injection. Furthermore, it has been demonstrated that Aβ peptides are not only signals capable of activating astrocytes but also capable of reducing tyrosinehydroxylase immunoreactivity in the basal ganglia probably leading to a reduction of volume transmission. These alterations in the neuroglial network morphology and function can, at least in part, explain the enhanced pain threshold observed in the Aβ intra-striatally injected animals.

The aggregation of tau protein into paired helical filaments is one of the hallmarks of Alzheimer's disease and related dementias. We therefore continue our search for non-toxic, cell penetrating inhibitors of tau aggregation, which hold potential for brain penetration. Pickhardt et al. (2005) have reported a high throughput screen for tau aggregation inhibitors previously, which resulted in the identification of several hit classes. Here we report the identification of novel inhibitors which were not present in the initial high throughput assay. This was achieved by transformation of the high throughput screen data into the 3D relationships of virtual pharmacophores The pharmacophore models were utilized in a virtual screen of a Maybridge database. The virtual screen provided 136 hits; 19 representative hits were selected and assayed, this resulted in two novel leads with an IC50 < 13 μM. These two leads feature a novel scaffold for tau aggregation inhibitors.

CATIE-AD was a multicenter effectiveness trial of atypical antipsychotics in patients with agitation and psychosis associated with AD who resided in the community. The study enrolled 421 participants. In this paper we present and discuss baseline characteristics of participants (demographics, cognitive, behavioral, and functional assessments), caregivers (demographics and caregiver burden) and settings at randomization. Those enrolled suffered from a wide range of cognitive impairment, were medically complex and experienced acute psychopathology requiring intervention with atypical antipsychotics. Family members providing the equivalent of institutional care experienced significant depression and caregiver burden. With the increasing prevalence of AD, clinicians and health care planners should look into future needs of those AD sufferers who are residing in community.