Boosting with intranasal dendrimeric Abeta1-15 but not Abeta1-15 peptide leads to an effective immune response following a single injection of Abeta1-40/42 in APP-tg mice

Exposure to Lead in Drinking Water Causes Cognitive Impairment via an Alzheimer's Disease Gene-Dependent Mechanism in Adult Mice

Background

Exposure to lead (Pb) is a major public health problem that could occur through contaminated soil, air, food, or water, either during the course of everyday life, or while working in hazardous occupations. Although Pb has long been known as a neurodevelopmental toxicant in children, a recent and growing body of epidemiological research indicates that cumulative, low-level Pb exposure likely drives age-related neurologic dysfunction in adults. Environmental Pb exposure in adulthood has been linked to risk of late-onset Alzheimer's disease (AD) and dementia.

Objective

Although the biological mechanism underlying this link is unknown, it has been proposed that Pb exposure may increase the risk of AD via altering the expression of AD-related genes and, possibly, by activating the molecular pathways underlying AD-related pathology.

Methods

We investigated Pb exposure using a line of genetically modified mice with AD-causing knock-in mutations in the amyloid precursor protein and presenilin 1 (APPΔNL/ΔNL x PS1P264L/P264L) that had been crossed with Leprdb/db mice to impart vulnerability to vascular pathology.

Results

Our data show that although Pb exposure in adult mice impairs cognitive function, this effect is not related to either an increase in amyloid pathology or to changes in the expression of common AD-related genes. Pb exposure also caused a significant increase in blood pressure, a well known effect of Pb. Interestingly, although the increase in blood pressure was unrelated to genotype, only mice that carried AD-related mutations developed cognitive dysfunction, in spite of showing no significant change in cerebrovascular pathology.

Conclusions

These results raise the possibility that the increased risk of dementia associated with Pb exposure in adults may be tied to its subsequent interaction with either pre-existing or developing AD-related neuropathology.

Dendrimers: A Neuroprotective Lead in Alzheimer Disease: A Review on its Synthetic approach and Applications

Alzheimer disease is a neurodegenerative disease that is signified by cognitive decline, memory loss, and erratic behavior. Dendrimers are a type of polymer that has a well-defined structure, a high degree of molecular uniformity, and a low polydispersity which have shown to be effective intracellular drug carriers for bring down the in numerous cases. The data reported by the clinical trials and chemical bonds of dendrimers loading and biological properties that may be used in the bringing out the treatment of nano formulation for Alzheimer disease. Below-range dendrimers have an unlocked figure, but higher-range dendrimers have a more globular and dense structure so handling is difficult. Dendrimers are similar in size to a variety of biological structures; for example, fifth-generation polyamidoamine (PAMAM) dendrimers are similar in size and shape to haemoglobin (5.5 nm diameter). Each generation of dendrimer is described in terms of size, shape, molecular weight, and the number of surface functional groups, with increasing growth specified in terms of 'generation number.' In contrast, Hawker and Frechet were the first to report the convergent approach. A stepwise repeating reaction strategy is used to synthesize dendrimers radically from a central core. The value of dendrimers as drug carriers is discussed in this paper. The information presented in this article can provide useful references for further studies on making dendrimers and applications.

Lactoferrin Coupled Lower Generation PAMAM Dendrimers for Brain Targeted Delivery of Memantine in Aluminum-Chloride-Induced Alzheimer's Disease in Mice

Lower generation PAMAM dendrimers have an immense potential for drug delivery with lower toxicity, but these dendrimers yet need certain basic ameliorations. In this study, the brain delivery potential of the synthesized PAMAM-Lf (lower generation PAMAM and lactoferrin conjugate) loaded with memantine (MEM) was explored and evaluated in vitro and in vivo in the disease-induced mouse model. The developed nanoscaffolds were characterized for size, zeta potential and in vitro release. Increase in the average size from 11.54 ± 0.91 to 131.72 ± 4.73 nm, respectively, was observed for drug-loaded PAMAM (i.e., PAMAM-MEM) and PAMAM-Lf (i.e., MEM-PAMAM-Lf).  Release profile of MEM from MEM-PAMAM-Lf was slow and sustained up to 48 h. In vivo biodistribution in the Sprague-Dawley rat model revealed that the brain uptake of MEM-PAMAM-Lf was significantly higher than that of MEM alone. The behavioral response study in the healthy rats did not result in any significant changes. The in vivo study in an AlCl₃-induced Alzheimer's (AD) mice model showed a significant improvement in behavioral responses. Optical density, which reflects the acetylcholinesterase (AChE) activity, was highest in the AL group 0.16 ± 0.01 (higher than the CON group, 0.09 ± 0.02; p < 0.05). No significant suppression of AChE activity was recorded in all the other treated groups. Similarly, the DOPAmine and 3,4 dihydroxyphenylacetic acid (DOPAC) levels were unaffected by the developed formulations. The study reported improved brain bioavailability of MEM in AlCl₃-induced Alzheimer's mice leading to improved memory, with the resultant mechanism behind in a descriptive manner. This study is among the preliminary studies reporting the memory improvement aspect of PAMAM-Lf conjugates for MEM in AlCl₃-AD induced mice. The formulation developed was beneficial in AD-induced mice and had a significant impact on the memory aspects.

Expand classical drug administration ways by emerging routes using dendrimer drug delivery systems: a concise overview

Drugs are introduced into the body by numerous routes such as enteral (oral, sublingual and rectum administration), parenteral (intravascular, intramuscular, subcutaneous and inhalation administration), or topical (skin and mucosal membranes). Each route has specific purposes, advantages and disadvantages. Today, the oral route remains the preferred one for different reasons such as ease and compliance by patients. Several nanoformulated drugs have been already approved by the FDA, such as Abelcet®, Doxil®, Abraxane® or Vivagel®(Starpharma) which is an anionic G4-poly(L-lysine)-type dendrimer showing potent topical vaginal microbicide activity. Numerous biochemical studies, as well as biological and pharmacological applications of both dendrimer based products (dendrimers as therapeutic compounds per se, like Vivagel®) and dendrimers as drug carriers (covalent conjugation or noncovalent encapsulation of drugs) were described. It is widely known that due to their outstanding physical and chemical properties, dendrimers afforded improvement of corresponding carried-drugs as dendrimer-drug complexes or conjugates (versus plain drug) such as biodistribution and pharmacokinetic behaviors. The purpose of this manuscript is to review the recent progresses of dendrimers as nanoscale drug delivery systems for the delivery of drugs using enteral, parenteral and topical routes. In particular, we focus our attention on the emerging and promising routes such as oral, transdermal, ocular and transmucosal routes using dendrimers as delivery systems.

MER5101, a novel Aβ1-15:DT conjugate vaccine, generates a robust anti-Aβ antibody response and attenuates Aβ pathology and cognitive deficits in APPswe/PS1ΔE9 transgenic mice

Active amyloid-β (Aβ) immunotherapy is under investigation to prevent or treat early Alzheimer's disease (AD). In 2002, a Phase II clinical trial (AN1792) was halted due to meningoencephalitis in ∼6% of the AD patients, possibly caused by a T-cell-mediated immunological response. Thus, generating a vaccine that safely generates high anti-Aβ antibody levels in the elderly is required. In this study, MER5101, a novel conjugate of Aβ1-15 peptide (a B-cell epitope fragment) conjugated to an immunogenic carrier protein, diphtheria toxoid (DT), and formulated in a nanoparticular emulsion-based adjuvant, was administered to 10-month-old APPswe/PS1ΔE9 transgenic (Tg) and wild-type (Wt) mice. High anti-Aβ antibody levels were observed in both vaccinated APPswe/PS1ΔE9 Tg and Wt mice. Antibody isotypes were mainly IgG1 and IgG2b, suggesting a Th2-biased response. Restimulation of splenocytes with the Aβ1-15:DT conjugate resulted in a strong proliferative response, whereas proliferation was absent after restimulation with Aβ1-15 or Aβ1-40/42 peptides, indicating a cellular immune response against DT while avoiding an Aβ-specific T-cell response. Moreover, significant reductions in cerebral Aβ plaque burden, accompanied by attenuated microglial activation and increased synaptic density, were observed in MER5101-vaccinated APPswe/PS1ΔE9 Tg mice compared with Tg adjuvant controls. Last, MER5101-immunized APPswe/PS1ΔE9 Tg mice showed improvement of cognitive deficits in both contextual fear conditioning and the Morris water maze. Our novel, highly immunogenic Aβ conjugate vaccine, MER5101, shows promise for improving Aβ vaccine safety and efficacy and therefore, may be useful for preventing and/or treating early AD.

Cucumber mosaic virus as the expression system for a potential vaccine against Alzheimer's disease

A primary therapeutic goal in Alzheimer's disease (AD) is to reduce the quantity of amyloid β protein (Aβ) present in the brain. To develop an effective, safe system for vaccination against Alzheimer's disease, the plant virus Cucumber mosaic virus (CMV) was engineered genetically to express Aβ-derived fragments that stimulate mainly humoral immune responses. Six chimeric constructs, bearing the Aβ1-15 or the Aβ4-15 sequence in positions 248, 392 or 529 of the CMV coat protein (CP) gene, were created. Viral products proved to be able to replicate in their natural host. However, only chimeric Aβ1-15-CMVs were detected by Aβ1-42 antiserum in Western blot analysis. Experimental evidence of Immunoelectron microscopy revealed a complete decoration of Aβ1-15-CMV(248) and Aβ1-15-CMV(392) following incubation with either anti-Aβ1-15 or anti-Aβ1-42 polyclonal antibodies. These two chimeric CMVs appear to be endowed with features making them possible candidates for vaccination against Alzheimer's disease.

Diminished amyloid-beta burden in Tg2576 mice following a prophylactic oral immunization with a salmonella-based amyloid-beta derivative vaccine

Immunotherapy holds great promise for Alzheimer's disease (AD) and other conformational disorders but certain adverse reactions need to be overcome. Prior to the side effects in the first Elan/Wyeth AD vaccine trial, we proposed using amyloid-beta (Abeta) derivatives as a safer approach. The route of administration may also affect vaccine safety. To assess the feasibility of oral immunization that promotes mucosal immunity, Tg2576 AD model mice were treated prophylactically three times over 6 weeks starting at 3-5 months of age with a Salmonella vaccine expressing K6Abeta(1-30). At 22-24 months of age, cortical Abeta plaque burden and total Abeta(40/42) levels were reduced by 48-75% in the immunized mice compared to controls, which received unmodified Salmonella. Plaque clearance was not associated with increased microglial activation, which may be explained by the long treatment period. Furthermore, cerebral microhemorrhages were not increased in the treated mice in contrast to several passive Abeta antibody studies. These results further support our findings with this immunogen delivered subcutaneously and demonstrate its efficacy when given orally, which may provide added benefits for human use.

Magnetic resonance imaging detection and time course of cerebral microhemorrhages during passive immunotherapy in living amyloid precursor protein transgenic mice

In recent years immunotherapy-based approaches for treating Alzheimer's disease have become the subject of intensive research. However, an important mechanistic-related safety concern is exacerbation of the risk of microhemorrhage that may be associated with fast removal of amyloid-β (Aβ) deposits found in blood vessels or brain parenchyma. Rapid in vivo detection of microhemorrhages in living amyloid precursor protein transgenic mice has not been described, and histological analysis can take several months before this risk is assessed. Aged transgenic mice were divided into two groups that would undergo longitudinal passive immunotherapy for 12 or 18 weeks. 6G1, a nonselective anti-Aβ monoclonal antibody, and 8F5, a more selective antioligomeric Aβ monoclonal antibody, were examined in both longitudinal studies. High-resolution T2*-weighted magnetic resonance microscopy (100 × 100 × 400 μm) was used for microhemorrhage detection in vivo. Cerebral microhemorrhages by magnetic resonance imaging were compared with histological hemosiderin staining in each animal; results showed that T2*-weighted magnetic resonance microscopy can reliably detect microhemorrhages of ≥60 μm in diameter at baseline and after 12 to 18 weeks of treatment in the same animals in vivo. This correlated significantly with histological readings. This new imaging safety biomarker can be readily applied to preclinical antibody screening in a longitudinal manner. 6G1 and 8F5, however, both increased microhemorrhage incidence in aged amyloid precursor protein transgenic mice compared with their baseline and vehicle treatment. A highly selective antibody for soluble Aβ is needed to address the question of whether antibodies that do not bind to deposited Aβ have microhemorrhage liability.

Amyloid-beta immunotherapy for Alzheimer's disease

Alzheimer's disease (AD) is a progressive, degenerative disorder of the brain and the most common form of dementia among the elderly. As the population grows and lifespan is extended, the number of AD patients will continue to rise. Current clinical therapies for AD provide partial symptomatic benefits for some patients; however, none of them modify disease progression. Amyloid-beta (Abeta) peptide, the major component of senile plaques in AD patients, is considered to play a crucial role in the pathogenesis of AD thereby leading to Abeta as a target for treatment. Abeta immunotherapy has been shown to induce a marked reduction in amyloid burden and an improvement in cognitive function in animal models. Although preclinical studies were successful, the initial human clinical trial of an active Abeta vaccine was halted due to the development of meningoencephalitis in approximately 6% of the vaccinated AD patients. Some encouraging outcomes, including signs of cognitive stabilization and apparent plaque clearance, were obtained in subset of patients who generated antibody titers. These promising preliminary data support further efforts to refine Abeta immunotherapy to produce highly effective and safer active and passive vaccines for AD. Furthermore, some new human clinical trials for both active and passive Abeta immunotherapy are underway. In this review, we will provide an update of Abeta immunotherapy in animal models and in human beings, as well as discuss the possible mechanisms underlying Abeta immunotherapy for AD.

Antibody response and plasma Abeta1-40 levels in young Microcebus murinus primates immunized with Abeta1-42 and its derivatives

We have been developing Abeta derivative vaccines with the objective to improve the safety of Abeta targeting immunotherapy. Our Abeta homologs are designed to have less direct toxicity and to produce a modified immune response compared to Abeta. In extensive mouse studies, all our vaccines have improved cognition in transgenic mice while eliciting different immune responses and reducing brain amyloid burden to a variable degree. While we are continuing to characterize these vaccines in mice, in preparation for studies in old primates and for human trials we assessed their effect in young lemur primates (n=25) that with age develop Abeta plaques and tau aggregates as seen in Alzheimer's disease. In the primates, all the peptides administered with alum adjuvant elicited a moderate to robust anti-Abeta IgM response. Abeta1-42, K6Abeta1-30 and K6Abeta1-30[E(18)E(19)] resulted in a high anti-Abeta IgG response, whereas Abeta1-30[E(18)E(19)] produced a weaker more variable IgG titer. Notably, 22 weeks after the 3rd immunization, IgM and IgG levels in derivative-vaccinated primates were similar to preimmune values whereas Abeta1-42 treated primates maintained a moderate IgG titer. The increase in antibodies that recognized Abeta1-40 often correlated with increase in Abeta1-40 in plasma, which suggests that the antibodies were binding to Abeta in vivo. Interestingly, significant transient weight gain was observed (K6Abeta1-30-, Abeta1-30[E(18)E(19)]- and Abeta1-42-treated) or a trend in the same direction (K6Abeta1-30[E(18)E(19)]-treated, adjuvant controls) following the injections. Based on these findings, we have chosen K6Abeta1-30 for immunizations in old primates as the antibody response to this vaccine was less variable compared to other Abeta derivatives. Our present findings indicate that most of our Abeta derivatives elicit a substantial antibody response in primates, and importantly this effect is reversible which enhances the safety profile of our approach.

Maximizing the potential of plasma amyloid-beta as a diagnostic biomarker for Alzheimer's disease

Amyloid plaques are composed primarily of amyloid-beta (Abeta) peptides derived from proteolytic cleavage of amyloid precursor protein (APP) and are considered to play a pivotal role in Alzheimer's disease (AD) pathogenesis. Presently, AD is diagnosed after the onset of clinical manifestations. With the arrival of novel therapeutic agents for treatment of AD, there is an urgent need for biomarkers to detect early stages of AD. Measurement of plasma Abeta has been suggested as an inexpensive and non-invasive tool to diagnose AD and to monitor Abeta modifying therapies. However, the majority of cross-sectional studies on plasma Abeta levels in humans have not shown differences between individuals with AD compared to controls. Similarly, cross-sectional studies of mouse plasma Abeta have yielded inconsistent trends in different mouse models. However, longitudinal studies appear to be more promising in humans. Recently, efforts to modify plasma Abeta levels using modulators have shown some promise. In this review, we will summarize the present data on plasma Abeta in humans and mouse models of AD. We will discuss the potential of modulators of Abeta levels in plasma, including antibodies and insulin, and the challenges associated with measuring plasma Abeta. Modulators of plasma Abeta may provide an important tool to optimize plasma Abeta levels and may improve the diagnostic potential of this approach.

Immunotherapy as treatment for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is characterized pathologically by the deposition of beta-amyloid (A beta)-containing extracellular neuritic plaques, intracellular neurofibrillary tangles and neuronal loss. Much evidence supports the hypothesis that A beta peptide aggregation contributes to AD pathogenesis, however, currently approved therapeutic treatments do nothing to stop or reverse A beta deposition. The success of active and passive anti-A beta immunotherapies in both preventing and clearing parenchymal amyloid in transgenic mouse models led to the initiation of an active anti-A beta vaccination (AN1792) trial in human patients with mild-to-moderate AD, but was prematurely halted when 6% of inoculated patients developed aseptic meningoencephalitis. Autopsy results from the brains of four individuals treated with AN1792 revealed decreased plaque burden in select brain areas, as well as T-cell lymphocytes in three of the patients. Furthermore, antibody responders showed some improvement in memory task measures. These findings indicated that anti-A beta therapy might still be a viable option for the treatment of AD, if potentially harmful proinflammatory processes can be avoided. Over the past 6 years, this target has led to the development of novel experimental immunization strategies, including selective A beta epitope targeting, antibody and adjuvant modifications, as well as alternative routes and mechanisms of vaccine delivery, to generate anti-A beta antibodies that selectively target and remove specific A beta species without evoking autoimmunity. Results from the passive vaccination AD clinical trials that are currently underway will provide invaluable information about both the effectiveness of newly improved anti-A beta vaccines in clinical treatment, as well as the role of the A beta peptide in the pathogenesis of the disease.

Antibody-mediated clearance of amyloid-beta peptide from cerebral amyloid angiopathy revealed by quantitative in vivo imaging

Cerebral amyloid angiopathy (CAA) is the accumulation of amyloid-beta peptide (Abeta) in the vessel wall of arteries in the brain. Because CAA is commonly associated with Alzheimer's disease (AD), characterized by parenchymal deposition of the same peptide in the form of senile plaques, there is considerable interest in the relationship of the two deposits in generating human disease. The study of CAA is of particular importance for immunotherapeutic approaches to AD, because reports of anti-Abeta immunotherapy in mice and humans have suggested that, whereas CAA appeared resistant to clearance, its response to this treatment promoted potential adverse effects, including meningoencephalitis. We used multiphoton microscopy and longitudinal imaging to monitor CAA in a mouse model of amyloid deposition to evaluate the effects of anti-Abeta passive immunotherapy. We found detectable clearance of CAA deposits within 1 week after a single administration of antibody directly to the brain, an effect that was short-lived. Chronic administration of antibody over 2 weeks led to more robust clearance without evidence of hemorrhage or other destructive changes. We found that the progressive clearance of Abeta from vessels follows distinct kinetics from what has been previously reported for clearance of plaques (parenchymal deposits of Abeta). This quantitative in vivo imaging approach directly demonstrates that CAA in a transgenic mouse model can be cleared with an optimized immunotherapy.

Amyloid-beta vaccination, but not nitro-nonsteroidal anti-inflammatory drug treatment, increases vascular amyloid and microhemorrhage while both reduce parenchymal amyloid

Vaccination with Abeta(1-42) and treatment with NCX-2216, a novel nitric oxide releasing flurbiprofen derivative, have each been shown separately to reduce amyloid deposition in transgenic mice and have been suggested as potential therapies for Alzheimer's disease. In the current study we treated doubly transgenic amyloid precursor protein and presenilin-1 (APP+PS1) mice with Abeta(1-42) vaccination, NCX-2216 or both drugs simultaneously for 9 months. We found that all treatments reduced amyloid deposition, both compact and diffuse, to the same extent while only vaccinated animals, with or without nonsteroidal anti-inflammatory drug (NSAID) treatment, showed increased microglial activation associated with the remaining amyloid deposits. We also found that active Abeta vaccination resulted in significantly increased cerebral amyloid angiopathy and associated microhemorrhages, while NCX-2216 did not, in spite of similar reductions in parenchymal amyloid. Co-administration of NCX-2216 did not attenuate this effect of the vaccine. This is the first report showing that active immunization can result in increased vascular amyloid and microhemorrhage, as has been observed with passive immunization. Co-administration of an NSAID agent with Abeta vaccination does not substantially modify the effects of Abeta immunotherapy. The difference between these treatments with respect to vascular amyloid development may reflect the clearance-promoting actions of the vaccine as opposed to the production-modifying effects proposed for flurbiprofen.

Effects of prolonged angiotensin-converting enzyme inhibitor treatment on amyloid beta-protein metabolism in mouse models of Alzheimer disease

Genetic and pathologic studies have associated angiotensin-converting enzyme (ACE) with Alzheimer disease. Previously, we and others have reported that ACE degrades in vitro the amyloid beta-protein (Abeta), a putative upstream initiator of Alzheimer disease. These studies support the hypothesis that deficiency in ACE-mediated Abeta proteolysis could increase Alzheimer disease risk and raise the question of whether ACE inhibitors, a commonly prescribed class of anti-hypertensive medications, can elevate Abeta levels in vivo. To test this hypothesis, we administered the ACE inhibitor captopril to two lines of APP transgenic mice harboring either low levels of Abeta or high levels of Abeta with associated plaque deposition. In both models, we show that captopril does not affect cerebral Abeta levels in either soluble or insoluble pools. Furthermore, we find no change in plaque deposition or in peripheral Abeta levels. Data from these Alzheimer models suggest that captopril and similar ACE inhibitors do not cause Abeta accumulation in vivo.