Translational research on the way to effective therapy for Alzheimer disease

A Boron-Containing Compound Acting on Multiple Targets Against Alzheimer's Disease. Insights from Ab Initio and Molecular Dynamics Simulations

Given the multifactorial nature and pathogenesis of Alzheimer's disease, therapeutic strategies are addressed to combine the benefits of every single-target drug into a sole molecule. Quantum mechanics and molecular dynamics (MD) methods were employed here to investigate the multitarget action of a boron-containing compound against Alzheimer's disease. The antioxidant activity as a radical scavenger and metal chelator was explored by means of density functional theory. The most plausible radical scavenger mechanisms, which are hydrogen transfer, radical adduct formation, and single-electron transfer in aqueous and lipid environments, were fully examined. Metal chelation ability was investigated by considering the complexation of Cu(II) ion, one of the metals that in excess can even catalyze the β-amyloid (Aβ) aggregation. The most probable complexes in the physiological environment were identified by considering both the stabilization energy and the shift of the λ^max induced by the complexation. The excellent capability to counteract Aβ aggregation was explored by performing MD simulations on protein-ligand adducts, and the activity was compared with that of curcumin, chosen as a reference.

Tocotrienol Rich Fraction Supplementation Modulate Brain Hippocampal Gene Expression in APPswe/PS1dE9 Alzheimer's Disease Mouse Model

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by loss of memory and other cognitive abilities. AD is associated with aggregation of amyloid-β (Aβ) deposited in the hippocampal brain region. Our previous work has shown that tocotrienol rich fraction (TRF) supplementation was able to attenuate the blood oxidative status, improve behavior, and reduce fibrillary-type Aβ deposition in the hippocampus of an AD mouse model. In the present study, we investigate the effect of 6 months of TRF supplementation on transcriptome profile in the hippocampus of APPswe/PS1dE9 double transgenic mice. TRF supplementation can alleviate AD conditions by modulating several important genes in AD. Moreover, TRF supplementation attenuated the affected biological process and pathways that were upregulated in the AD mouse model. Our findings indicate that TRF supplementation can modulate hippocampal gene expression as well as biological processes that can potentially delay the progression of AD.

Amyloid Positivity Using [18F]Flutemetamol-PET and Cognitive Deficits in Nondemented Community-Dwelling Older Adults

Little research exists examining the relationship between beta-amyloid neuritic plaque density via [18F]flutemetamol binding and cognition; consequently, the purpose of the current study was to compare cognitive performances among individuals having either increased amyloid deposition (Flute+) or minimal amyloid deposition (Flute-). Twenty-seven nondemented community-dwelling adults over the age of 65 underwent [18F]flutemetamol amyloid-positron emission tomography imaging, along with cognitive testing using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and select behavioral measures. Analysis of variance was used to identify the differences among the cognitive and behavioral measures between Flute+/Flute- groups. Flute+ participants performed significantly worse than Flute- participants on RBANS indexes of immediate memory, language, delayed memory, and total scale score, but no significant group differences in the endorsed level of depression or subjective report of cognitive difficulties were observed. Although these results are preliminary, [18F]flutemetamol accurately tracks cognition in a nondemented elderly sample, which may allow for better prediction of cognitive decline in late life.

Identification of promethazine as an amyloid-binding molecule using a fluorescence high-throughput assay and MALDI imaging mass spectrometry

The identification of amyloid-binding compounds is a crucial step in the development of imaging probes and therapeutics for the detection and cure of Alzheimer's disease. Unfortunately, the process typically lags during the translation from in vitro to in vivo studies due to the impenetrable nature of the blood brain barrier (BBB). Here, we integrate fluorescence assay with MALDI imaging mass spectrometry to screen known compounds and repurpose their properties to enable the second function of binding to amyloid plaques. Through this approach, we identified an antihistamine compound, promethazine, that can bind to amyloid plaques. Finally, we demonstrate that promethazine is retained in the amyloid-burdened brain compared to a normal brain and that its distribution within the brain corroborates with that of amyloid plaques.

Bapineuzumab and solanezumab for Alzheimer's disease: is the 'amyloid cascade hypothesis' still alive?

INTRODUCTION

The 'amyloid cascade hypothesis' remains the leading hypothesis to explain the pathophysiology of Alzheimer's disease (AD). Immunotherapeutic agents have been developed to remove the neurotoxic amyloid β42 protein and prevent the hypothesized amyloid β42-induced neurotoxicity and neurodegeneration. The most notable of these immunotherapies are bapineuzumab and solanezumab.

AREAS COVERED

This article briefly reviews the experimental agents in development for treatment of AD and then discusses the results of bapineuzumab and solanezumab in AD patients, as reported in preclinical studies, clinical trials and press releases.

EXPERT OPINION

Phase III trials showed that bapineuzumab failed to improve cognitive and functional performances in AD patients, and was associated with a high incidence of amyloid-related imaging abnormalities (ARIA). Solanezumab's two Phase III trials in AD patients failed to meet endpoints when analyzed independently. However, analysis of pooled data from both trials showed a significant reduction in cognitive decline in mild AD patients. The improvement was associated with an increase in plasma amyloid-β (Aβ) levels and a low incidence of ARIA in solanezumab-treated patients. The marginal benefits of solanezumab are encouraging to support continued evaluation in future studies, and offer small support in favor of the ongoing viability of the 'amyloid cascade hypothesis' of AD.

Current advances in the treatment of Alzheimer's disease: focused on considerations targeting Aβ and tau

Alzheimer’s disease (AD) is a neurodegenerative disorder that impairs mainly the memory and cognitive function in elderly. Extracellular beta amyloid deposition and intracellular tau hyperphosphorylation are the two pathological events that are thought to cause neuronal dysfunction in AD. Since the detailed mechanisms that underlie the pathogenesis of AD are still not clear, the current treatments are those drugs that can alleviate the symptoms of AD patients. Recent studies have indicated that these symptom-reliving drugs also have the ability of regulating amyloid precursor protein processing and tau phosphorylation. Thus the pharmacological mechanism of these drugs may be too simply-evaluated. This review summarizes the current status of AD therapy and some potential preclinical considerations that target beta amyloid and tau protein are also discussed.

A peptide prime-DNA boost immunization protocol provides significant benefits as a new generation Aβ42 DNA vaccine for Alzheimer disease

Immunotherapy has the potential to provide a possible treatment therapy to prevent or delay Alzheimer disease. In a clinical trial (AN1792) in which patients received this immunotherapy and received active Aβ1-42 peptide immunizations, treatment was stopped when 6% of patients showed signs of meningoencephalitis. Follow up on these patients led to the conclusion that the antibody response was beneficial in removing Aβ1-42 from brain but an accompanying inflammatory Th1 T cell response was harmful. As a safe alternative treatment targeting the same self protein, Aβ1-42, in brain, we and others are working on a DNA Aβ1-42 immunization protocol as the immune response to DNA immunizations differs in many aspects from immunizations with peptide antigens. Because the immune response to DNA vaccination has different kinetics and has a significantly lower antibody production, we evaluated two different prime boost regimens, Aβ1-42 DNA prime/Aβ1-42 peptide boost and Aβ1-42 peptide prime/Aβ1-42 DNA boost for their effectiveness in antibody production and possible side effects due to inflammatory T cell responses. While both boost regimes significantly enhanced the specific antibody production with comparable antibody concentrations, the absence of the Aβ1-42 T cell response (no proliferation and no cytokine production) is consistent with our previous findings using this DNA Aβ1-42 trimer immunization and greatly enhances the safety aspect for possible clinical use.

Active DNA Aβ42 vaccination as immunotherapy for Alzheimer disease

As a neurodegenerative disorder, Alzheimer disease (AD) is the most common form of dementia found in the aging population. Immunotherapy with passive or active immunizations targeting amyloid beta (Aβ) build-up in the brain may provide a possible treatment option and may help prevent AD from progressing. A number of passive immunizations with anti-Aβ42 antibodies are in different phases of clinical trials. One active immunization approach, AN-1792, was stopped after the development of autoimmune encephalitis in 6% of patients and a second one, CAD106, in which a small Aβ epitope is used, is currently in safety and tolerability studies. Besides active immunizations with proteins or peptides, active immunizations using DNA which codes for the protein against which the immune response will be directed, so called genetic immunizations, provide additional safety as the immune response in DNA immunizations differs quantitatively and qualitatively from the response elicited by peptide immunizations. In this review, we summarize our data using DNA Aβ42 immunizations in mouse models and discuss the results together with the results presented by other groups working on a DNA vaccine as treatment option for AD.

Changing the course of Alzheimer's disease: anti-amyloid disease-modifying treatments on the horizon

OBJECTIVES

To review the amyloid hypothesis as the predominant mechanistic theory of Alzheimer's disease and update the status of new disease-modifying, anti-amyloid treatments in clinical development.

DATA SOURCES

Governmental Web sites and those of professional Alzheimer's disease associations and drug manufacturers were searched for new drugs in development. An English-language search of PubMed (January 2003-January 2006) was conducted using the search terms Alzheimer's disease and amyloid hypothesis and each of the drugs and immunotherapies from the 4 identified classes of anti-amyloid, disease-modifying therapies.

STUDY SELECTION AND DATA EXTRACTION

Studies and reports were selected on the basis of recent publication, adequate methodology, and completeness of data.

DATA SYNTHESIS

Immunotherapy, γ-secretase inhibitors, selective neurotoxic aggregated 42-amino acid peptide subspecies of amyloid β (Aβ₄₂)-lowering agents (tarenflurbil), inhibitors of amyloid aggregation (tramiprosate), and statins show promise in clinical trials. Safety remains an important factor. Disease-modifying drugs that specifically target the amyloid cascade and do not interact with essential biological pathways are expected to possess a lower rate of unintended adverse events.Agents that selectively target Aβ₄₂ production (e.g., tarenflurbil), block Aβ aggregation (e.g., tramiprosate), or enhance alpha-secretase activity (statins) offer hope for disease modification and prevention and do not appear to interfere with other biological pathways.

CONCLUSIONS

Discovery of safe and effective disease-modifying therapies will usher in a new age of Alzheimer's disease treatment.

DNA immunization against amyloid beta 42 has high potential as safe therapy for Alzheimer's disease as it diminishes antigen-specific Th1 and Th17 cell proliferation

The pathogenesis of Alzheimer's disease (AD) has been strongly associated with the accumulation of amyloid beta (Aβ) peptides in brain, and immunotherapy targeting Aβ provides potential for AD prevention. A clinical trial in which AD patients were immunized with Aβ42 peptide was stopped when 6% of participants showed meningoencephalitis, apparently due to an inflammatory Th1 immune response. Previously, we and other have shown that Aβ42 DNA vaccination via gene gun generates a Th2 cellular immune response, which was shown by analyses of the respective antibody isotype profiles. We also determined that in vitro T cell proliferation in response to Aβ42 peptide re-stimulation was absent in DNA Aβ42 trimer-immunized mice when compared to Aβ42 peptide-immunized mice. To further characterize this observation prospectively and longitudinally, we analyzed the immune response in wild-type mice after vaccination with Aβ42 trimer DNA and Aβ42 peptide with Quil A adjuvant. Wild-type mice were immunized with short-term (1-3× vaccinations) or long-term (6× vacinations) immunization strategies. Antibody titers and isotype profiles of the Aβ42 specific antibodies, as well as cytokine profiles and cell proliferation studies from this longitudinal study were determined. Sufficient antibody titers to effectively reduce Aβ42, but an absent T cell proliferative response and no IFNγ or IL-17 secretion after Aβ42 DNA trimer immunization minimizes the risk of inflammatory activities of the immune system towards the self antigen Aβ42 in brain. Therefore, Aβ42 DNA trimer immunization has a high probability to be effective and safe to treat patients with early AD.

Analysis of three plasmid systems for use in DNA A beta 42 immunization as therapy for Alzheimer's disease

In an effort to optimize DNA immunization-elicited antibody production responses against A beta 1-42 (A beta 42) as a therapy for Alzheimer's disease (AD), comparisons were made between three distinct plasmid systems using gene gun delivery. Plasmids encoding A beta 42 monomer and a novel A beta 42 trimeric fusion protein were evaluated in conjunction with CMV or Gal4/UAS promoter elements. It was found that vaccination A beta 42 trimer under the Gal4/UAS promoter elicited high levels of anti-A beta 42 antibody production. Serum antibody levels from Gal4/UAS-A beta 42 trimer immunized mice were found to be 16.6+/-5.5 microg/ml compared to 6.5+/-2.5 microg/ml with Gal4/UAS-A beta 42 monomer or even less with CMV-A beta 42 trimer. As compared to monomeric A beta 42 or A beta 42 trimer expressed under the CMV promoter, injection of the Gal4/UAS-A beta 42 trimer induced high levels of A beta 42 antigen expression in tissue suggesting a mechanism for the increase in anti-A beta 42 antibody. Antibodies were found to be primarily IgG1 suggesting a predominant Th2 response (IgG1/IgG2a ratio of 9). Serum from A beta 42 trimer-vaccinated mice was also found to identify amyloid plaques in the brains of APP/PS1 transgenic mice. These results demonstrate the potential therapeutic use of Gal4/UAS DNA A beta 42 trimer immunization in preventing Alzheimer's disease.

Memantine lowers amyloid-beta peptide levels in neuronal cultures and in APP/PS1 transgenic mice

Memantine is a moderate-affinity, uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist that stabilizes cognitive, functional, and behavioral decline in patients with moderate to severe Alzheimer's disease (AD). In AD, the extracellular deposition of fibrillogenic amyloid-beta peptides (Abeta) occurs as a result of aberrant processing of the full-length Abeta precursor protein (APP). Memantine protects neurons from the neurotoxic effects of Abeta and improves cognition in transgenic mice with high brain levels of Abeta. However, it is unknown how memantine protects cells against neurodegeneration and affects APP processing and Abeta production. We report the effects of memantine in three different systems. In human neuroblastoma cells, memantine, at therapeutically relevant concentrations (1-4 muM), decreased levels of secreted APP and Abeta(1-40). Levels of the potentially amylodogenic Abeta(1-42) were undetectable in these cells. In primary rat cortical neuronal cultures, memantine treatment lowered Abeta(1-42) secretion. At the concentrations used, memantine treatment was not toxic to neuroblastoma or primary cultures and increased cell viability and/or metabolic activity under certain conditions. In APP/presenilin-1 (PS1) transgenic mice exhibiting high brain levels of Abeta(1-42), oral dosing of memantine (20 mg/kg/day for 8 days) produced a plasma drug concentration of 0.96 microM and significantly reduced the cortical levels of soluble Abeta(1-42). The ratio of Abeta(1-40)/Abeta(1-42) increased in treated mice, suggesting effects on the gamma-secretase complex. Thus, memantine reduces the levels of Abeta peptides at therapeutic concentrations and may inhibit the accumulation of fibrillogenic Abeta in mammalian brains. Memantine's ability to preserve neuronal cells against neurodegeneration, to increase metabolic activity, and to lower Abeta level has therapeutic implications for neurodegenerative disorders.

DNA beta-amyloid(1-42) trimer immunization for Alzheimer disease in a wild-type mouse model

CONTEXT

DNA beta-amyloid(1-42) (Abeta42) trimer immunization was developed to produce specific T helper 2 cell (T(H)2)-type antibodies to provide an effective and safe therapy for Alzheimer disease (AD) by reducing elevated levels of Abeta42 peptide that occur in the brain of patients with AD.

OBJECTIVE

To compare the immune response in wild-type mice after immunization with DNA Abeta42 trimer and Abeta42 peptide.

DESIGN AND INTERVENTION

Wild-type mice received either 4 microg of DNA Abeta42 trimer immunization administered with gene gun (n = 8) or intraperitoneal injection of 100 microg of human Abeta42 peptide with the adjuvant Quil A (n = 8). Titers, epitope mapping, and isotypes of the Abeta42-specific antibodies were analyzed.

MAIN OUTCOME MEASURES

Antibody titers, mapping of binding sites (epitopes), isotype profiles of the Abeta42-specific antibodies, and T-cell activation.

RESULTS

DNA Abeta42 trimer immunization resulted in antibody titers with a mean of 15 microg per milliliter of plasma. The isotype profile of the antibodies differed markedly. A predominant IgG1 antibody response was found in the DNA-immunized mice, indicating a T(H)2 type of immune response (IgG1/IgG2a ratio of 10). The peptide-immunized mice showed a mixed T(H)1/T(H)2 immune response (IgG1/IgG2a ratio of 1) (P < .001). No increased T-cell proliferation was observed in the DNA-immunized mice (P = .03).

CONCLUSION

In this preliminary study in a wild-type mouse model, DNA Abeta42 trimer immunization protocol produced a T(H)2 immune response and appeared to have low potential to cause an inflammatory T-cell response.

Predicting dementia: role of dementia risk indices

There are currently more than 5 million people in the USA living with Alzheimer's disease and other forms of dementia, and prevalence is expected to triple over the next 40 years. As new strategies for prevention and treatment are developed, it will be critically important to be able to identify older adults who do not currently have dementia but have a high risk of developing symptoms within a few years so that they can be targeted for monitoring, prevention and early treatment. In other fields, prognostic models and risk indices are often used to identify high-risk individuals (e.g., Framingham Heart Index and Breast Cancer Risk Assessment Tool). The objective of this paper is to describe the development of Dementia Risk Indices and to discuss the potential for these tools to be incorporated into clinical and research settings for the identification of individuals with a high risk of dementia.

Endogenous Aβ causes cell death via early tau hyperphosphorylation

Alzheimer's disease (AD) is characterized by Aβ overproduction and tau hyperphosphorylation. We report that an early, transient and site-specific AD-like tau hyperphosphorylation at Ser262 and Thr231 epitopes is temporally and causally related with an activation of the endogenous amyloidogenic pathway that we previously reported in hippocampal neurons undergoing cell death upon NGF withdrawal [Matrone, C., Ciotti, M.T., Mercanti, D., Marolda, R., Calissano, P., 2008b. NGF and BDNF signaling control amyloidogenic route and Ab production in hippocampal neurons. Proc. Natl. Acad. Sci. 105, 13138-13143]. Such tau hyperphosphorylation, as well as apoptotic death, is (i) blocked by 4G8 and 6E10 Aβ antibodies or by specific β and/or γ-secretases inhibitors; (ii) temporally precedes tau cleavage mediated by a delayed (6-12h after NGF withdrawal) activation of caspase-3 and calpain-I; (iii) under control of Akt-GSK3β-mediated signaling. Finally, we show that such site-specific tau hyperphosphorylation causes tau detachment from microtubules and an impairment of mitochondrial trafficking. These results depict, for the first time, a rapid interplay between endogenous Aβ and tau post-translational modifications which act co-ordinately to compromise neuronal functions in the same neuronal system, under physiological conditions as seen in AD brain.

Abeta amyloid and glucose metabolism in three variants of primary progressive aphasia

OBJECTIVE

Alzheimer's disease (AD) is found at autopsy in up to one third of patients with primary progressive aphasia (PPA), but clinical features that predict AD pathology in PPA are not well defined. We studied the relationships between language presentation, Abeta amyloidosis, and glucose metabolism in three PPA variants using [11C]-Pittsburgh compound B ([11C]PIB) and [18F]-labeled fluorodeoxyglucose positron emission tomography ([18F]FDG-PET).

METHODS

Patients meeting PPA criteria (N = 15) were classified as logopenic aphasia (LPA), progressive nonfluent aphasia (PNFA), or semantic dementia (SD) based on language testing. [11C]PIB distribution volume ratios were calculated using Logan graphical analysis (cerebellar reference). [18F]FDG images were normalized to pons. Partial volume correction was applied.

RESULTS

Elevated cortical PIB (by visual inspection) was more common in LPA (4/4 patients) than in PNFA (1/6) and SD (1/5) (p < 0.02). In PIB-positive PPA, PIB uptake was diffuse and indistinguishable from the pattern in matched AD patients (n = 10). FDG patterns were focal and varied by PPA subtype, with left temporoparietal hypometabolism in LPA, left frontal hypometabolism in PNFA, and left anterior temporal hypometabolism in SD. FDG uptake was significant asymmetric (favoring left hypometabolism) in PPA (p < 0.005) but not in AD.

INTERPRETATION

LPA is associated with Abeta amyloidosis, suggesting that subclassification of PPA based on language features can help predict the likelihood of AD pathology. Language phenotype in PPA is closely related to metabolic changes that are focal and anatomically distinct between subtypes, but not to amyloid deposition patterns that are diffuse and similar to AD.

Developing new treatments for Alzheimer's disease: the who, what, when, and how of biomarker-guided therapies

This synthetic review presents an approach to the use of biomarkers for the development of new treatments for Alzheimer's disease (AD). After reviewing the process of translation as applied to AD, the paper provides a general update on what is known about the biology of the disease, and highlights currently available treatments. This is followed by a discussion of future drug development for AD emphasizing the roles that biomarkers are likely to play in this process: (1) define patients who are going to progress rapidly for the purpose of trial enrichment; (2) differentiate disease and therapeutically relevant AD subtypes; (3) assess the potential activity of specific therapies in vivo or ex vivo; and (4) measure the underlying disease state, so as to (a) detect disease and assess drug response in asymptomatic patients, (b) serve as a secondary outcome measure in clinical trials of symptomatic patients, and (c) decide if further development of a treatment should be stopped if not likely to be effective. Several examples are used to illustrate each biomarker utility in the AD context.

Alleviation of Abeta-induced cognitive impairment by ultrasound-mediated gene transfer of HGF in a mouse model

A new therapeutic approach to treat Alzheimer's disease (AD) is needed, and the use of growth factors is considered to be a candidate. Hepatocyte growth factor (HGF) is a unique multifunctional growth factor, which has the potential effect to exert neurotrophic action and induce angiogenesis. In this study, we examined the effects of overexpression of human HGF plasmid DNA using ultrasound-mediated gene transfer into the brain in an Abeta-infused cognitive dysfunction mouse model. We demonstrated that HGF gene transfer significantly alleviated Abeta-induced cognitive impairment in mice in behavioral tests. These beneficial effects of HGF might be due to (1) significant recovery of the vessel density in the dentate gyrus of the hippocampus, (2) upregulation of BDNF, (3) a significant decrease in oxidative stress and (4) synaptic enhancement. A pharmacological approach including gene therapy to increase the HGF level in combination with anti-Abeta therapy might be a new therapeutic option for the treatment of AD.

Pharmacogenomics in Alzheimer's disease

Pharmacological treatment in Alzheimer's disease (AD) accounts for 10-20% of direct costs, and fewer than 20% of AD patients are moderate responders to conventional drugs (donepezil, rivastigmine, galantamine, memantine), with doubtful cost-effectiveness. Both AD pathogenesis and drug metabolism are genetically regulated complex traits in which hundreds of genes cooperatively participate. Structural genomics studies demonstrated that more than 200 genes might be involved in AD pathogenesis regulating dysfunctional genetic networks leading to premature neuronal death. The AD population exhibits a higher genetic variation rate than the control population, with absolute and relative genetic variations of 40-60% and 0.85-1.89%, respectively. AD patients also differ in their genomic architecture from patients with other forms of dementia. Functional genomics studies in AD revealed that age of onset, brain atrophy, cerebrovascular hemodynamics, brain bioelectrical activity, cognitive decline, apoptosis, immune function, lipid metabolism dyshomeostasis, and amyloid deposition are associated with AD-related genes. Pioneering pharmacogenomics studies also demonstrated that the therapeutic response in AD is genotype-specific, with apolipoprotein E (APOE) 4/4 carriers the worst responders to conventional treatments. About 10-20% of Caucasians are carriers of defective cytochrome P450 (CYP) 2D6 polymorphic variants that alter the metabolism and effects of AD drugs and many psychotropic agents currently administered to patients with dementia. There is a moderate accumulation of AD-related genetic variants of risk in CYP2D6 poor metabolizers (PMs) and ultrarapid metabolizers (UMs), who are the worst responders to conventional drugs. The association of the APOE-4 allele with specific genetic variants of other genes (e.g., CYP2D6, angiotensin-converting enzyme [ACE]) negatively modulates the therapeutic response to multifactorial treatments affecting cognition, mood, and behavior. Pharmacogenetic and pharmacogenomic factors may account for 60-90% of drug variability in drug disposition and pharmacodynamics. The incorporation of pharmacogenetic/pharmacogenomic protocols to AD research and clinical practice can foster therapeutics optimization by helping to develop cost-effective pharmaceuticals and improving drug efficacy and safety.

Looking for novel ways to treat the hallmarks of Alzheimer's disease

Alzheimer's disease (AD) represents an increasing public health issue as demographic changes and generally improved medical care result in a larger aged population. Although significant advances have been made in the diagnosis and treatment of AD, the unmet medical need remains and few treatment options are available. This review focuses on emerging therapies that aim to treat the underlying causes of the disease rather than the symptoms. Such disease-modifying treatments, focused on the two main hallmarks of the disease (plaques and tangles), include new and old targets which have significant potential in the field and are on the cusp of providing new treatment paradigms within the coming years.

Possibilities for the prevention and treatment of cognitive impairment and dementia

The human brain has a remarkable capacity for plasticity, but does it have the capacity for repair and/or regeneration? On the basis of controversial new evidence we speculate that the answer may be ;yes', and suggest that clinicians should therefore approach cognitive impairment and dementia with a new, cautious optimism.

Alzheimer's disease: progress in the development of anti-amyloid disease-modifying therapies

The amyloid hypothesis--the leading mechanistic theory of Alzheimer's disease--states that an imbalance in production or clearance of amyloid beta (Abeta) results in accumulation of Abeta and triggers a cascade of events leading to neurodegeneration and dementia. The number of persons with Alzheimer's disease is expected to triple by mid-century. If steps are not taken to delay the onset or slow the progression of Alzheimer's disease, the economic and personal tolls will be immense. Different classes of potentially disease-modifying treatments that interrupt early pathological events (ie, decreasing production or aggregation of Abeta or increasing its clearance) and potentially prevent downstream events are in phase II or III clinical studies. These include immunotherapies; secretase inhibitors; selective Abeta42-lowering agents; statins; anti-Abeta aggregation agents; peroxisome proliferator-activated receptor-gamma agonists; and others. Safety and serious adverse events have been a concern with immunotherapy and gamma-secretase inhibitors, though both continue in clinical trials. Anti-amyloid disease-modifying drugs that seem promising and have reached phase III clinical trials include those that selectively target Abeta42 production (eg, tarenflurbil), enhance the activity of alpha-secretase (eg, statins), and block Abeta aggregation (eg, transiposate).

The pathogenesis of Alzheimer's disease and the role of Abeta42

We appear to be on the brink of a new epoch of treatment for Alzheimer's disease. Compelling evidence suggests that Aβ42 secretion is the triggering event in the pathogenesis of Alzheimer's disease, and that tau aggregation may be an important secondary event linked to neurodegeneration. Prophylactic administration of anti-amyloid agents designed to prevent Aβ accumulation in persons with subclinical disease is likely to be more effective than therapeutic interventions in established Alzheimer's disease. Drug development programs in Alzheimer's disease focus primarily on agents with anti-amyloid disease-modifying properties, and many different pharmacologic approaches to reducing amyloid pathology and tauopathy are being studied. Classes of therapeutic modalities currently in advanced-stage clinical trial testing include forms of immunotherapy (active β-amyloid immunoconjugate and human intravenous immunoglobulin), a γ-secretase inhibitor, the selective Aβ42-lowering agent R-flurbiprofen, and the anti-aggregation agent tramiprosate. Non-traditional dementia therapies such as the HMG-CoA reductase inhibitors (statins), valproate, and lithium are now being assessed for clinical benefit as anti-amyloid disease-modifying treatments. Positive findings of efficacy and safety from clinical studies are necessary but not sufficient to demonstrate that a drug has disease-modifying properties. Definitive proof of disease-modification requires evidence from validated animal models of Alzheimer's disease; rigorously controlled clinical trials showing a significantly improved, stabilized, or slowed rate of decline in cognitive and global function compared to placebo; and prospectively obtained evidence from surrogate biomarkers that the treatment resulted in measurable biological changes associated with the underlying disease process.

Disease modifying therapy for AD?

Alzheimer's disease (AD) is the most common form of dementia in industrialized nations. If more effective therapies are not developed that either prevent AD or block progression of the disease in its very early stages, the economic and societal cost of caring for AD patients will be devastating. Only two types of drugs are currently approved for the treatment of AD: inhibitors of acetyl cholinesterase, which symptomatically enhance cognitive state to some degree but are not disease modifying; and the adamantane derivative, memantine. Memantine preferentially blocks excessive NMDA receptor activity without disrupting normal receptor activity and is thought to be a neuroprotective agent that blocks excitotoxicty. Memantine therefore may have a potentially disease modifying effect in multiple neurodegenerative conditions. An improved understanding of the pathogeneses of AD has now led to the identification of numerous therapeutic targets designed to alter amyloid beta protein (Abeta) or tau accumulation. Therapies that alter Abeta and tau through these various targets are likely to have significant disease modifying effects. Many of these targets have been validated in proof of concept studies in preclinical animal models, and some potentially disease modifying therapies targeting Abeta or tau are being tested in the clinic. This review will highlight both the promise of and the obstacles to developing such disease modifying AD therapies.

Alzheimer's disease and frontotemporal dementia: prospects of a tailored therapy?

Alzheimer's disease (AD) is the most prevalent dementia (accounting for 50%-75% of cases of dementia in people aged over 65 years), followed by frontotemporal dementia (FTD) (10%-20% of cases). AD is characterised histopathologically by Abeta-containing amyloid plaques and tau-containing neurofibrillary tangles, whereas FTD exhibits neurofibrillary tangles alone. Current symptomatic treatments of AD are of limited benefit, as they are not directed at the underlying biological basis of the disease. The development of transgenic animal models has provided insight into disease mechanisms and helped define novel drug targets. More than 50 drugs are currently in clinical trials, and novel and more effective drugs targeting both AD and FTD are expected to become available within 5-10 years.

Abeta42 gene vaccination reduces brain amyloid plaque burden in transgenic mice

OBJECTIVE

To demonstrate that in APPswe/PS1DeltaE9 transgenic mice, gene gun mediated Abeta42 gene vaccination elicits a high titer of anti-Abeta42 antibodies causal of a significant reduction of Abeta42 deposition in brain.

METHODS

Gene gun immunization is conducted with transgenic mice using the Abeta42 gene in a bacterial plasmid with the pSP72-E3L-Abeta42 construct. Enzyme-linked immunoabsorbent assays (ELISA) and Western blots are used to monitor anti-Abeta42 antibody levels in serum and Abeta42 levels in brain tissues. Enzyme-linked immunospot (ELISPOT) assays are used for detection of peripheral blood T cells to release gamma-interferon. Immunofluorescence detection of Abeta42 plaques and quantification of amyloid burden of brain tissue were measured and sections were analyzed with Image J (NIH) software.

RESULTS

Gene gun vaccination with the Abeta42 gene resulted in high titers of anti-Abeta42 antibody production of the Th2-type. Levels of Abeta42 in treated transgenic mouse brain were reduced by 60-77.5%. The Mann-Whitney U-test P=0.0286.

INTERPRETATION

We have developed a gene gun mediated Abeta42 gene vaccination method that is efficient to break host Abeta42 tolerance without using adjuvant and induces a Th2 immune response. Abeta42 gene vaccination significantly reduces the Abeta42 burden of the brain in treated APPswe/PS1DeltaE9 transgenic mice with no overlap between treated and control mice.

Towards subtlety: understanding the role of Toll-like receptor signaling in susceptibility to human infections

Recent years have seen a dramatic improvement in our understanding of the role of innate immunity, and particularly Toll-like receptor (TLR) signaling, in human host defense. Appreciation of how defects in human TLR signaling enhance susceptibility to infection began with the identification of patients with monogenic immunodeficiencies, such as hypohydrotic ectodermal dysplasia with immunodeficiency and IRAK4 deficiency. Empowered by technological advances in genotyping and bioinformatics, we are now beginning to appreciate how common genetic variation in the genes controlling the innate immune response alters infectious susceptibility in a subtle but specific fashion. This review highlights the mechanisms of infectious susceptibility that result from complex interactions between the genetically variable host and microbe and explores how this new knowledge may ultimately translate into better care for our patients.