Subacute meningoencephalitis in a subset of patients with AD after Abeta42 immunization

Positron emission tomography and single-photon emission computed tomography in central nervous system drug development

In this review, the value of functional imaging [positron emission tomography (PET)/single-photon emission computed tomography (SPECT)] in drug development is considered. Radionuclide imaging can help establish the diagnosis of neurodegenerative disorders where this is in doubt and provides a potential biomarker for following drug effects on disease progression. PET and SPECT can help understand mechanisms of disease and determine the functional effects of therapeutic approaches on neurotransmission and metabolism. Synthesizing radiotracer analogs of novel drugs can provide proof of principle that these agents reach their enzyme or receptor targets and delineate their regional brain distribution. If such radiotracers do not prove to have ideal properties for imaging, the concept of microdosing potentially allows multiple other drug analogs to be tested with less stringent regulatory requirements than for novel medicinals. Finally, PET tracers can provide receptor and enzyme active site dose occupancy profiles, thereby guiding dosage selection for phase 1 and phase 2 trials. The eventual hope is that radiotracer imaging will provide a surrogate marker for drug efficacy, although this has yet to be realized, and progress the concept of personalized medicine where receptor/enzyme binding profiles help predict therapeutic outcome.

Exacerbation of cerebral amyloid angiopathy-associated microhemorrhage in amyloid precursor protein transgenic mice by immunotherapy is dependent on antibody recognition of deposited forms of amyloid beta

Passive immunization with an antibody directed against the N terminus of amyloid beta (Abeta) has recently been reported to exacerbate cerebral amyloid angiopathy (CAA)-related microhemorrhage in a transgenic animal model. Although the mechanism responsible for the deleterious interaction is unclear, a direct binding event may be required. We characterized the binding properties of several monoclonal anti-Abeta antibodies to deposited Abeta in brain parenchyma and CAA. Biochemical analyses demonstrated that the 3D6 and 10D5, two N-terminally directed antibodies, bound with high affinity to deposited forms of Abeta, whereas 266, a central domain antibody, lacked affinity for deposited Abeta. To determine whether 266 or 3D6 would exacerbate CAA-associated microhemorrhage, we treated aged PDAPP mice with either antibody for 6 weeks. We observed an increase in both the incidence and severity of CAA-associated microhemorrhage when PDAPP transgenic mice were treated with the N-terminally directed 3D6 antibody, whereas mice treated with 266 were unaffected. These results may have important implications for future immune-based therapeutic strategies for Alzheimer's disease.

Nasal vaccination with a proteosome-based adjuvant and glatiramer acetate clears beta-amyloid in a mouse model of Alzheimer disease

Amyloid beta-peptide (Abeta) appears to play a key pathogenic role in Alzheimer disease (AD). Immune therapy in mouse models of AD via Abeta immunization or passive administration of Abeta antibodies markedly reduces Abeta levels and reverses behavioral impairment. However, a human trial of Abeta immunization led to meningoencephalitis in some patients and was discontinued. Here we show that nasal vaccination with a proteosome-based adjuvant that is well tolerated in humans plus glatiramer acetate, an FDA-approved synthetic copolymer used to treat multiple sclerosis, potently decreases Abeta plaques in an AD mouse model. This effect did not require the presence of antibody, as it was observed in B cell-deficient (Ig mu-null) mice. Vaccinated animals developed activated microglia that colocalized with Abeta fibrils, and the extent of microglial activation correlated strongly with the decrease in Abeta fibrils. Activation of microglia and clearing of Abeta occurred with the adjuvant alone, although to a lesser degree. Our results identify a novel approach to immune therapy for AD that involves clearing of Abeta through the utilization of compounds that have been safely tested on or are currently in use in humans.

‘Nature-inspired’ drug–protein complexes as inhibitors of Aβ aggregation

Protein–protein interactions are a regulatory mechanism for a number of physiological and pathological cellular processes. Neurodegenerative diseases, such as AD (Alzheimer's disease), are associated with the accelerated production or delayed clearance of protein aggregates. Hence, inhibition of pathologic protein–protein interactions is a very attractive mechanism for drug development. This review focuses on a novel therapeutic strategy to inhibit the de novo formation of protein aggregates. Inspired by strategies used in Nature and optimized over millions of years of evolution, we have created a bifunctional molecule [SLF (synthetic ligand for FK506-binding protein)–CR (Congo Red)] that is able to block Aβ (amyloid β) aggregation by borrowing the surface and steric bulk of a cellular chaperone.

Disease modifying strategies for the treatment of Alzheimer's disease targeted at modulating levels of the β-amyloid peptide

AD (Alzheimer's disease) is characterized neuropathologically by the presence of amyloid plaques, neurofibrillary tangles and profound grey matter loss. The ‘amyloid’ hypothesis postulates that the toxic Aβ (amyloid β) peptide, enzymatically derived from the proteolytic processing of a larger protein called APP (amyloid precursor protein), is one of the principal causative factors of neuronal cell death in the brains of AD patients. As such, methods for lowering Aβ levels in the brain are of significant interest with regard to identifying novel disease modifying therapies for the treatment of AD. In this review, we will review a variety of approaches and mechanisms capable of modulating levels of Aβ.

The immune system, amyloid-beta peptide, and Alzheimer's disease

In this review, the case is made that amyloid-beta peptide in the brain of patients with Alzheimer's disease is a primary cause of the disease and that immunotherapy directed against this peptide has the potential to halt and/or reverse disease progression. This supposition is supported by the capacity of anti-beta-amyloid peptide antibodies to prevent or reverse the disease in mouse models of Alzheimer's disease. Furthermore, preliminary results obtained in a small number of patients with Alzheimer's disease are consistent with the observations made in the mouse model of this disease. We review the relationship between the immune system, amyloid-beta peptide, and Alzheimer's disease and the progress made in applying immunotherapy to patients with Alzheimer's disease.

Interleukin 1 receptor antagonist knockout mice show enhanced microglial activation and neuronal damage induced by intracerebroventricular infusion of human beta-amyloid

Background

Interleukin 1 (IL-1) is a key mediator of immune responses in health and disease. Although classically the function of IL-1 has been studied in the systemic immune system, research in the past decade has revealed analogous roles in the CNS where the cytokine can contribute to the neuroinflammation and neuropathology seen in a number of neurodegenerative diseases. In Alzheimer's disease (AD), for example, pre-clinical and clinical studies have implicated IL-1 in the progression of a pathologic, glia-mediated pro-inflammatory state in the CNS. The glia-driven neuroinflammation can lead to neuronal damage, which, in turn, stimulates further glia activation, potentially propagating a detrimental cycle that contributes to progression of pathology. A prediction of this neuroinflammation hypothesis is that increased IL-1 signaling in vivo would correlate with increased severity of AD-relevant neuroinflammation and neuronal damage.

Methods

To test the hypothesis that increased IL-1 signaling predisposes animals to beta-amyloid (Aβ)-induced damage, we used IL-1 receptor antagonist Knock-Out (IL1raKO) and wild-type (WT) littermate mice in a model that involves intracerebroventricular infusion of human oligomeric Aβ1–42. This model mimics many features of AD, including robust neuroinflammation, Aβ plaques, synaptic damage and neuronal loss in the hippocampus. IL1raKO and WT mice were infused with Aβ for 28 days, sacrificed at 42 days, and hippocampal endpoints analyzed.

Results

IL1raKO mice showed increased vulnerability to Aβ-induced neuropathology relative to their WT counterparts. Specifically, IL1raKO mice exhibited increased mortality, enhanced microglial activation and neuroinflammation, and more pronounced loss of synaptic markers. Interestingly, Aβ-induced astrocyte responses were not significantly different between WT and IL1raKO mice, suggesting that enhanced IL-1 signaling predominately affects microglia.

Conclusion

Our data are consistent with the neuroinflammation hypothesis whereby increased IL-1 signaling in AD enhances glia activation and leads to an augmented neuroinflammatory process that increases the severity of neuropathologic sequelae.

Emerging prospects for the disease-modifying treatment of Alzheimer's disease

The currently approved therapies for Alzheimer's disease (AD) in the US are designed to modify the function of specific neurotransmitter systems in the brain. While these palliative treatments can benefit some patients for a period of time, they do not halt the relentless cognitive and behavioral deterioration that characterize this neurodegenerative disorder. Consequently, much current research on AD is directed toward illuminating the disease process itself, particularly the abnormal accumulation of certain proteins in brain: the amyloid-beta protein (Abeta) in senile plaques and cerebral blood vessels, and the tau protein in neurofibrillary tangles. Genetic, biochemical and pathologic evidence now favors a primary role of Abeta aggregation in the Alzheimer proteopathic cascade, and studies in mice indicate that lowering the amount of this protein in brain can be beneficial. Recently, Abeta-immunization therapy has emerged as a particularly promising therapeutic option for treating Alzheimer's disease, but unexpected treatment-related side-effects are an overriding issue. These adverse events were not anticipated from preclinical studies with rodents; hence, more biologically relevant models, such as nonhuman primates, are needed to test the safety and efficacy of novel therapies for Alzheimer's disease.

Amyloid beta protein immunotherapy neutralizes Abeta oligomers that disrupt synaptic plasticity in vivo

One of the most clinically advanced forms of experimental disease-modifying treatment for Alzheimer disease is immunization against the amyloid beta protein (Abeta), but how this may prevent cognitive impairment is unclear. We hypothesized that antibodies to Abeta could exert a beneficial action by directly neutralizing potentially synaptotoxic soluble Abeta species in the brain. Intracerebroventricular injection of naturally secreted human Abeta inhibited long-term potentiation (LTP), a correlate of learning and memory, in rat hippocampus in vivo but a monoclonal antibody to Abeta completely prevented the inhibition of LTP when injected after Abeta. Size fractionation showed that Abeta oligomers, not monomers or fibrils, were responsible for inhibiting LTP, and an Abeta antibody again prevented such inhibition. Active immunization against Abeta was partially effective, and the effects correlated positively with levels of antibodies to Abeta oligomers. The ability of exogenous and endogenous antibodies to rapidly neutralize soluble Abeta oligomers that disrupt synaptic plasticity in vivo suggests that treatment with such antibodies might show reversible cognitive deficits in early Alzheimer disease.

Meningoencephalitis associated with passive immunization of a transgenic murine model of Alzheimer's amyloidosis

Immunization against the Abeta peptide reverses the pathologic and behavioral manifestations of Alzheimer's disease in murine models. Since active immunization is associated with an autoimmune meningoencephalitis in a subset of humans, passive transfer of anti-Abeta immunoglobulin is being pursued as a potentially safer alternative. We have identified cases of meningoencephalitis subsequent to peripheral and intracerebral passive immunization of Tg2576 mice. The vasocentric mononuclear infiltrate localized only to brain regions affected by Abeta amyloid deposits suggesting that the inflammatory reaction was Abeta specific. This report indicates that current passive immunization in humans should proceed with careful regard for autoimmune complications.

Induction of a Th2 immune response by co-administration of recombinant adenovirus vectors encoding amyloid β-protein and GM-CSF

Lines of experimental evidence indicate that induction of humoral immune responses in transgenic mouse models of Alzheimer disease (AD) by repeated injection of synthetic amyloid beta-protein (Abeta) is effective in prevention and clearance of deposits of Abeta aggregates in the brain of the mice. We have tested a non-injection modality whereby replication-defective adenovirus vectors encoding Abeta or the 99-amino acid carboxyl terminal fragment of Abeta precursor were intranasally administered to mice to elicit immune responses against Abeta. When mice were immunized only with the adenovirus vectors, immune responses against Abeta were negligible. By co-immunization with an adenovirus vector encoding granulocyte-macrophage colony stimulating factor (GM-CSF), the adenovirus vector encoding Abeta effectively elicited an immune response against Abeta. Immunoglobulin isotyping demonstrated a predominant IgG1 and IgG2b response, suggesting a Th2 anti-inflammatory type. Thus, adjuvantation is essential for induction of an immune response against Abeta by adenovirus-mediated nasal vaccination.

HSV amplicon-mediated Aβ vaccination in Tg2576 mice: differential antigen-specific immune responses

Given the participation of amyloid beta (Abeta) in Alzheimer's disease (AD) pathogenesis the derivation of experimental therapeutics to prevent Abeta fibrillogenesis and/or enhance removal of parenchymal amyloid deposits represent viable disease-modifying approaches. Active Abeta-based immunotherapies have shown promise in mouse AD models, but application in human trials was accompanied by moderate brain inflammation in a subset of patients. Immune-shaping vaccine platforms may mitigate adverse effects. Herein, we describe the use of herpes simplex virus (HSV)-derived amplicons to elicit distinctive immune responses against Abeta. Two vaccine vectors were constructed: one expressing Abeta1-42 alone (HSVAbeta), and a second expressing Abeta1-42 fused with the molecular adjuvant tetanus toxin Fragment C (HSVAbeta/TtxFC). Peripheral administration of these vaccines augmented humoral responses to Abeta and reduced CNS Abeta deposition in Tg2576 AD mice. Interestingly and unexpectedly, HSVAbeta vaccination was uniquely toxic and incited the expression of pro-inflammatory molecule transcripts within the hippocampi of Tg2576 mice, suggesting that this paradigm may serve as a relevant model to study Abeta vaccine-elicited CNS inflammatory syndromes.

Future directions in the treatment of Alzheimer’s disease

Alzheimer's disease (AD) remains the most common of the neurodegenerative disorders. In the elderly, it represents the most frequently occurring form of dementia, especially if considered alongside concomitant cerebrovascular disease. Current treatment involves the use of acetylcholinesterase inhibitors, which have shown symptomatic benefits in the recognised domains of cognition, function and behaviour. While they may have intrinsic disease-modifying activity, this is yet to be proven, and strategies to alter the fundamental neuropathological changes in AD continue to be sought. Much of the evidence suggests that the accumulation of amyloid-beta may play a pivotal role, therefore the bulk of current research is focused on possible intervention along the amyloid pathways. However, the abnormal phosphorylation of tau is also a reasonable target and as the molecular basis of AD is better delineated, more targeted treatment approaches are being proposed. This paper reports on the current data that is setting the future directions for research into AD.

Toward modeling hemorrhagic and encephalitic complications of Alzheimer amyloid-beta vaccination in nonhuman primates

The potential of amyloid-beta (Abeta) immunization as a disease-modifying therapy for Alzheimer's disease is limited by the occurrence of encephalitic side effects in a subset of treated patients. The encephalitis was not predicted from immunization studies in transgenic, Abeta-depositing mice. More recently, studies in these same mice indicate that passive immunization with certain anti-Abeta antibodies can induce microhemorrhage. Cerebral amyloid angiopathy (CAA) may play a key role in determining the risk for these complications. Because aged nonhuman primates (NHPs) have a more human-like immune system than rodents, and because NHPs naturally develop senile plaques and CAA with age, NHPs appear to be important, adjunctive models for assessing the efficacy and safety of immunotherapeutics for Alzheimer's disease. Conversely, the ability to model the complications of Abeta immunotherapy will be important for elucidating the bases of these complications, and for developing protocols that minimize or eliminate the risks of these serious adverse effects.

The Future of Aging Therapies

Advances in understanding aging processes and their consequences are leading to the development of therapies to slow or reverse adverse changes formerly considered to be "normal" aging and processes that underlie multiple age-related conditions. Estimating the effectiveness of candidate aging therapies, whose effects on human aging may require many years to determine, is a particular challenge. Strategies for identifying candidate interventions can be developed through multiple approaches, including the screening of molecular targets and pathways in vitro and in animal models, informed as well by evidence from human genetic and epidemiologic data. A number of recently established programs and networks can serve as resources for such research. For all these research approaches, from in vitro molecular studies to clinical trials, contributions of cell and molecular biology are crucial and offer the prospect of therapeutic advances that address fundamental biological processes as well as the clinically important challenges of aging.

Activity of flurbiprofen and chemically related anti-inflammatory drugs in models of Alzheimer's disease

Currently, there is an intense debate on the potential use of nonsteroidal anti-inflammatory drugs (NSAIDs) in Alzheimer's disease (AD). NSAIDs are among the most widely prescribed drugs for the treatment of pain, fever, and inflammation. Their effects are largely attributed to the inhibition of the enzymatic activity of cyclooxygenase (COX)-1 and -2. The apparent activity of this class of drugs stems from one critical pathological process underlying AD and other neurodegenerative disorders, i.e., the presence of chronic neuroinflammation. In fact, prolonged use of NSAIDs is associated with reduced risk of AD. Besides COX inhibition, additional mechanisms could contribute to the potential activity of NSAIDs in AD. For example, several studies show that only a few selected NSAIDs also affect beta-amyloid (Abeta) deposition and metabolism. Among the Abeta-effective NSAIDs, flurbiprofen raised particular interest because of its multiple actions on key AD hallmarks. Studies in cell lines and animal models have shown that flurbiprofen racemate, its R-enantiomer and its nitric oxide (NO)-releasing derivatives, HCT 1026 and NCX 2216, are effective on AD amyloid pathology. Moreover, HCT 1026 and NCX 2216 differentially influence the cellular component of neuroinflammation (i.e., microglia activation) in some experimental settings, i.e., HCT 1026 inhibits the activation of microglia, while NCX 2216 can either enhance or inhibit microglial activation, depending upon the experimental conditions. It is still unclear which effects on microglia will prove most beneficial. Ultimately, clinical studies in AD patients will provide the best information as to whether selected NSAIDs will improve this devastating disease.

Molecular Rationale for the Pharmacological Treatment of Alzheimer??s Disease

Cerebral deposition of amyloid plaques containing amyloid beta-peptide (Abeta) has traditionally been considered the central feature of Alzheimer's disease (AD). Abeta is derived from amyloid precursor protein (APP), which is cleaved by several different proteases: alpha-, beta- and gamma-secretase. In the past decade, however, the molecular pathogenesis of AD has been shown to involve alterations in several neurotransmitter, inflammatory, oxidative, and hormonal pathways that represent potential targets for AD prevention and treatment. Much research has shown a direct link between cholinergic impairment and altered APP processing as a major pathogenetic event in AD. Three highly probable mechanisms of APP regulation through inhibition of acetylcholinesterase are thus current topics of investigation. Indeed, acetylcholinesterase inhibitors appear to cause selective muscarinic activation of alpha-secretase and to induce the translation of APP mRNA; they may also restrict amyloid fibre assembly. Activation of N-methyl-D-aspartate receptors is considered a probable cause of chronic neurodegeneration in AD, and memantine has been widely used in some countries in AD patients to block cerebral N-methyl-D-aspartate receptors that normally respond to glutamate. Further studies are needed to determine whether antioxidants such as vitamins C and E are effective, through various mechanisms, in patients with mild-to-moderate AD. Additional data are also required for non-steroidal anti-inflammatory drugs, some of which appear to possess experimental effects that may ultimately prove favourable in AD patients. Statins also warrant further investigation, since they have activated alpha-secretase and they reduced Abeta generation and amyloid accumulation in a transgenic mouse model. beta-Secretase would seem to be an ideal target for anti-amyloid therapy in AD, but potential clinical and pharmacological issues, such as ensuring selectivity of inhibition, stability, and ease of blood-brain barrier penetration and cellular uptake, remain to be addressed for beta-secretase inhibitors. gamma-Secretase is not an easy candidate for pharmacological manipulation. Immunotherapeutic strategies have targeted Abeta directly; however, intensive investigation of indirect approaches to the management of AD with immunotherapy is now underway.

Immunological and anti-chaperone therapeutic approaches for Alzheimer disease

Alzheimer disease (AD) is the most common cause of dementia. Currently available therapies only provide symptomatic relief. A number of therapeutic approaches are under development that aim to increase the clearance of brain Abeta peptides. These include immune mediated clearance of Abeta and the inhibition of the interaction between Abeta and its pathological chaperones. Both active and passive immunization has been shown to have robust effects in transgenic mouse models of AD on amyloid reduction and behavioral improvements. However, a human trial of active immunization has been associated with significant toxicity in a minority of patients. New generation vaccines are being developed which likely will reduce the potential for cell-mediated toxicity. In addition, the recent development of anti-chaperone therapy opens a new therapeutic avenue which is unlikely to be associated with toxicity.

Aβ42 immunization in Alzheimer's disease generates Aβ N-terminal antibodies

Serum samples from Alzheimer's disease (AD) patients immunized with Abeta42 (AN1792) were analyzed to determine the induced antibody properties including precise amyloid-beta peptide (Abeta) epitopes and amyloid plaque-binding characteristics. The predominant response in these patients is independent of whether or not meningoencephalitis developed and is against the free amino terminus of Abeta. The immunostaining of amyloid plaques in brain tissue by patient sera is adsorbable by a linear Abeta1-8 peptide, demonstrating that the antibodies are directed predominantly to this epitope and not dependent on Abeta conformations or aggregates specific to plaques. Furthermore, the antibodies are not capable of binding amyloid precursor protein and would be predicted to be competent in facilitating clearance of amyloid plaques in AD brains.

High mobility group box protein-1 inhibits microglial A? clearance and enhances A? neurotoxicity

One pathogenic characteristic of Alzheimer's disease (AD) is the formation of extracellular senile plaques with accumulated microglia. According to the amyloid hypothesis, the increase or accumulation of amyloid-beta (Abeta) peptides in the brain parenchyma is the primary event that influences AD pathology. Although the role of microglia in AD pathology has not been clarified, their involvement in Abeta clearance has been noted. High mobility group box protein-1 (HMGB1) is an abundant nonhistone chromosomal protein. We reported recently that HMGB1 was associated with senile plaques and the total protein level significantly increased in AD brain. In this study, diffuse HMGB1 immunoreactivity was observed around dying neurons in the kainic acid- and Abeta1-42 (Abeta42)-injected rat hippocampi. HMGB1 also colocalized with Abeta in the Abeta42-injected rats but not in transgenic mice, which show massive Abeta production without neuronal loss in their brains. Furthermore, coinjection of HMGB1 delayed the clearance of Abeta42 and accelerated neurodegeneration in Abeta42-injected rats. These results suggest that HMGB1 released from dying neurons may inhibit microglial Abeta42 clearance and enhance the neurotoxicity of Abeta42. HMGB1 may thus be another target in the investigation of a therapeutic strategy for AD.

Passive immunotherapy against Abeta in aged APP-transgenic mice reverses cognitive deficits and depletes parenchymal amyloid deposits in spite of increased vascular amyloid and microhemorrhage

Background

Anti-Aβ immunotherapy in transgenic mice reduces both diffuse and compact amyloid deposits, improves memory function and clears early-stage phospho-tau aggregates. As most Alzheimer disease cases occur well past midlife, the current study examined adoptive transfer of anti-Aβ antibodies to 19- and 23-month old APP-transgenic mice.

Methods

We investigated the effects of weekly anti-Aβ antibody treatment on radial-arm water-maze performance, parenchymal and vascular amyloid loads, and the presence of microhemorrhage in the brain. 19-month-old mice were treated for 1, 2 or 3 months while 23-month-old mice were treated for 5 months. Only the 23-month-old mice were subject to radial-arm water-maze testing.

Results

After 3 months of weekly injections, this passive immunization protocol completely reversed learning and memory deficits in these mice, a benefit that was undiminished after 5 months of treatment. Dramatic reductions of diffuse Aβ immunostaining and parenchymal Congophilic amyloid deposits were observed after five months, indicating that even well-established amyloid deposits are susceptible to immunotherapy. However, cerebral amyloid angiopathy increased substantially with immunotherapy, and some deposits were associated with microhemorrhage. Reanalysis of results collected from an earlier time-course study demonstrated that these increases in vascular deposits were dependent on the duration of immunotherapy.

Conclusions

The cognitive benefits of passive immunotherapy persist in spite of the presence of vascular amyloid and small hemorrhages. These data suggest that clinical trials evaluating such treatments will require precautions to minimize potential adverse events associated with microhemorrhage.

The immunotherapy of Alzheimer's disease

Only a small percentage of patients with Alzheimer's disease benefit from current drug therapy and for only a relatively short time. This is not surprising as the goal of these drugs is to enhance existing cerebral function in Alzheimer patients and not to block the progression of cognitive decline. In contrast, immunotherapy is directed at clearing the neurotoxic amyloid beta peptide from the brain that directly or indirectly leads to cognitive decline in patients with Alzheimer's disease. The single trial of active immunization with the amyloid beta peptide provided suggestive evidence of a reduction in cerebral amyloid plaques and of stabilization in cognitive function of half the patients who developed good antibody responses to the amyloid beta peptide. However, 6% of actively immunized Alzheimer patients developed sterile meningoencephalitis that forced the cessation of the clinical trial. Passive immunotherapy in animal models of Alzheimer's disease has provided similar benefits comparable to those seen with active immunotherapy and has the potential of being effective in the half of Alzheimer's disease patients who do not make a significant anti-amyloid beta peptide antibody response and without inducing T-cell-mediated encephalitis. Published studies of 5 patients with sporadic Alzheimer disease treated with intravenous immunoglobulin containing anti-amyloid beta peptide antibodies showed that amyloid beta peptide was mobilized from the brain and cognitive decline was interrupted. Further studies of passive immunotherapy are urgently required to confirm these observations.

Mechanisms of the inhibitory effects of amyloid β-protein on synaptic plasticity

Alzheimer's disease can be considered a protein misfolding disease. In particular, inappropriate processing of a proteolytic fragment of amyloid precursor protein, amyloid beta-protein (Abeta), in early stages of Alzheimer's disease may lead to stabilization of small oligomers that are highly mobile and have a potential to be extremely toxic assemblies. Recently, the importance of such soluble species of Abeta in triggering synaptic dysfunction, long before neuronal loss occurs, has become apparent. Animal models have revealed that plasticity of hippocampal excitatory synaptic transmission is relatively selectively vulnerable to Abeta both in vitro and in vivo. This review focuses on the mechanisms of Abeta inhibition of long-term potentiation at synapses in the rodent hippocampus from two complimentary perspectives. Firstly, we examine evidence that the synaptic activity of this peptide resides primarily in oligomeric rather than monomeric or fibrillar Abeta species. Secondly, the importance of different oxidative/nitrosative stress-linked cascades including JNK, p38 MAPK and NADPH oxidase/iNOS-generated reactive oxygen/nitrogen free radicals in mediating the inhibition of LTP by Abeta is emphasised. These mechanistic studies provide a plausible explanation for the sensitivity of hippocampus-dependent memory to impairment in the early preclinical stages of Alzheimer's disease.

Immunization of Alzheimer model mice with adenovirus vectors encoding amyloid β-protein and GM-CSF reduces amyloid load in the brain

Induction of anti-amyloid beta-protein (Abeta) antibodies in transgenic mouse models of Alzheimer disease (AD) by repeated injection of synthetic Abeta was shown to be effective in preventing and removing deposition of Abeta aggregates in the brain. Here, we have tested a non-invasive modality whereby a replication-defective adenovirus vector encoding Abeta was intranasally administered to mice to elicit immune responses against Abeta. Intranasal immunization only with the adenovirus vector failed to induce significant immune responses. When an adenovirus vector encoding granulocyte/macrophage-colony stimulating factor (GM-CSF) was used as an adjuvant in conjunction with the adenovirus encoding Abeta, a marked immune response was elicited against Abeta. Immunoglobulin isotyping revealed that the induced anti-Abeta antibodies are predominantly of the IgG2b and IgG1 isotypes, suggesting a Th-2 anti-inflammatory type. Furthermore, amyloid load in the brain of AD model mice (Tg2576) vaccinated with adenovirus vectors encoding Abeta and GM-CSF was much smaller than that in control Tg2576 mice. Thus, intranasal administration of adenovirus vectors encoding Abeta and GM-CSF may be effective in prevention and treatment of AD.

Immunotherapy for Alzheimer's disease

The utility of vaccine strategies to treat neurodegenerative diseases such as Alzheimer's disease (AD) may still hold promise. Both active and passive immunization strategies reduced AD-like pathology and restored cognitive deficits in transgenic mice. These results were initially met with considerable optimism; however, phase IIa clinical trials were halted because of a small but significant occurrence of meningoencephalitis. Knowledge gained from studies on amyloid-beta peptide (A beta) immunotherapy will allow optimization of new-generation vaccines, targeting highly specific epitopes while reducing undesired side effects. In harnessing and steering the immune system, an effective response can be generated against A beta. If this proves successful, A beta vaccination could provide the first definitive treatment for AD.

Prion diseases — close to effective therapy?

The transmissible spongiform encephalopathies could represent a new mode of transmission for infectious diseases--a process more akin to crystallization than to microbial replication. The prion hypothesis proposes that the normal isoform of the prion protein is converted to a disease-specific species by template-directed misfolding. Therapeutic and prophylactic strategies to combat these diseases have emerged from immunological and chemotherapeutic approaches. The lessons learned in treating prion disease will almost certainly have an impact on other diseases that are characterized by the pathological accumulation of misfolded proteins.

Current progress in beta-amyloid immunotherapy

As neuroscientists, we are taught that the brain is immune privileged and thus unlikely to be affected by the peripheral immune system. Accordingly, initial results demonstrating the effectiveness of beta-amyloid (Abeta) immunotherapy in mouse models of Alzheimer's disease (AD) were viewed with considerable surprise and some skepticism. Many groups have since demonstrated efficacy with Abeta immunotherapy in models of AD, using Abeta-based immunogens and anti-Abeta antibodies. Clinical trials involving Abeta immunotherapy for AD are in progress and are providing a wealth of information around the amyloid hypothesis of AD. Abeta immunotherapy is also raising new opportunities and questions about the general role of the immune system in neurodegenerative diseases.

Apolipoprotein Abeta: black sheep in a good family

Amyloid-beta (Abeta) has for a long time been thought to play a central role in the pathogenesis of Alzheimer disease (AD). Analysis of available data indicates that Abeta possesses properties of a metal-binding apolipoprotein influencing lipid transport and metabolism. Protection of lipoproteins from oxidation by transition metals, synaptic activity and role in the acute phase response represent plausible physiological functions of Abeta. However, these important biochemical qualities which may critically influence the development of AD, have been largely ignored by mainstream AD researchers, making Abeta appear to be a "black sheep" in a "good apolipoprotein" family. New studies are needed to shed further light on the physiological role of Abeta in lipid metabolism in the brain.

Strategies for disease modification in Alzheimer's disease

Treating Alzheimer's disease (AD) is the biggest unmet medical need in neurology. Current drugs improve symptoms, but do not have profound disease-modifying effects. Three main classes of disease-modification approaches can be defined: one that is broadly neurotrophic or neuroprotective, one that targets specific aspects of AD pathology, and one that is based on epidemiological observation. This review discusses all three approaches, with particular emphasis on anti-amyloid strategies - currently the most active area of investigation. The approaches that are reviewed include secretase inhibition, amyloid-beta aggregation inhibition, immunotherapy and strategies that might indirectly affect the amyloid pathway.

Alzheimer's disease abeta vaccine reduces central nervous system abeta levels in a non-human primate, the Caribbean vervet

Amyloid beta (Abeta) protein immunotherapy lowers cerebral Abeta and improves cognition in mouse models of Alzheimer's disease (AD). Here we show that Caribbean vervet monkeys (Chlorocebus aethiops, SK) develop cerebral Abeta plaques with aging and that these deposits are associated with gliosis and neuritic dystrophy. Five aged vervets were immunized with Abeta peptide over 10 months. Plasma and cerebral spinal fluid (CSF) samples were collected periodically from the immunized vervets and five aged controls; one monkey per group expired during the study. By Day 42, immunized animals generated plasma Abeta antibodies that labeled Abeta plaques in human, AD transgenic mouse and vervet brains; bound Abeta1-7; and recognized monomeric and oligomeric Abeta but not full-length amyloid precursor protein nor its C-terminal fragments. Low anti-Abeta titers were detected in CSF. Abetax-40 levels were elevated approximately 2- to 5-fold in plasma and decreased up to 64% in CSF in immunized vervets. Insoluble Abetax-42 was decreased by 66% in brain homogenates of the four immunized animals compared to archival tissues from 13 age-matched control vervets. Abeta42-immunoreactive plaques were detected in frontal cortex in 11 of the 13 control animals, but not in six brain regions examined in each of the four immunized vervets. No T cell response or inflammation was observed. Our study is the first to demonstrate age-related Abeta deposition in the vervet monkey as well as the lowering of cerebral Abeta by Abeta vaccination in a non-human primate. The findings further support Abeta immunotherapy as a potential prevention and treatment of AD.

[Pre-clinical evaluation of effects of acetylcholinesterase inhibition on the cerebral cholinergic neuronal system and cognitive function: PET study in conscious monkeys]

The present review described the effects of acetylcholinesterase (AChE) inhibition on the cerebral cholinergic neuronal system in the conscious monkey brains with PET. Somatosensory stimulation induced a regional cerebral blood flow (rCBF) response, revealed with [(15)O]H(2)O, in the contralateral somatosensory cortex. Scopolamine resulted in an abolished rCBF response to stimulation, and this abolished rCBF response was recovered by physostigmine, donepezil, and tacrine. Donepezil suppressed AChE activity, analyzed by [(11)C]MP4A, in all cortical regions in a dose-dependent manner. AChE inhibition by donepezil resulted in a dose-dependent increase in acetylcholine levels in the prefrontal cortex as measured by microdialysis. Binding of [(11)C](+)3-PPB to cortical muscarinic receptors was reduced by donepezil, probably in a competitive inhibition manner. Aged monkeys showed less reduction of [(11)C](+)3-PPB binding than young animals. As evaluated by an oculomotor delayed response task, aged monkeys showed impaired working memory performance compared to young monkeys, and the impaired performance was partly improved by the administration of donepezil, due to the facilitation of the cholinergic neuronal system by AChE inhibition by donepezil. These results demonstrated that PET imaging with specifically labeled compounds in combination with microdialysis and a behavioral cognition task could be a useful tool for pre-clinical evaluation of novel drugs.

Lessons from the AN 1792 Alzheimer vaccine: lest we forget

Recent clinical and neuropathological data show that the AN 1792 vaccine enhanced the production of Abeta antibodies in the sera of Alzheimer's disease (AD) patients, but it appears to have been ineffective at stimulating the removal of Abeta deposits from the brain or at slowing the rate of cognitive decline. The 19 cases of meningoencephalitis were not linked in an obvious way to serum antibody titre, but they may have been linked to infiltration of the brain by antibodies and/or T-cells. Brain imaging indicated that oedema associated with the neuroinflammation did not reflect the typical distribution of neuritic plaques in AD. These outcomes were not anticipated by experiments on transgenic mice because compared to humans, these mice have less genetic variability, and their plaques have a different chemical composition, making them far more soluble and easier to remove. Furthermore, the consequences of vaccination are different. Vaccination of transgenic mice removes superfluous human Abeta while leaving endogenous mouse Abeta intact, whereas in humans the immune response is directed against an endogenous target that occurs naturally and is present in healthy brain tissue. The most important lesson to be learned from the AN 1792 trials is that new strategies for treating AD should not be tested on humans until they have been extensively tested on non-murine species.

Evidence supporting a role for anti-Abeta antibodies in the treatment of Alzheimer's disease

Antibodies against Abeta have been suggested as potential therapeutic strategies for the treatment of Alzheimer disease (AD) for nearly 8 years. Animal studies have been very encouraging in that both active and passive immunization of transgenic mice can reduce amyloid load and reverse memory deficits found in these mice. Three mechanisms have been proposed to explain these results: (a). catalytic conversion of fibrillar Abeta to less toxic forms, (b). opsonization of Abeta deposits leading to microglial phagocytosis, or (c). promote the efflux of Abeta from the brain to the circulation. Evidence exists supporting all three mechanisms, which, it should be noted, are not mutually exclusive. Phase 2 clinical trials of active immunization with vaccines against human Abeta1-42 were halted due to an unacceptable incidence of meningoencephalitic reactions (6% of patients treated). However, a recent report from a fraction of the patients in this trial found that those patients developing antibodies which reacted with brain amyloid deposits had a significantly slower progression of cognitive loss over a period of 12 months. This supports the continued cautious testing of passive immunization and, possibly even active immunization against the Abeta peptide using preparations less likely to cause autoimmune reactions in the central nervous system.

Immunotherapy for Alzheimer's disease

Strong evidence exists indicating that chronic neuroinflammation contributes to the progression of Alzheimer's disease (AD). A major focus of AD-associated research has been amyloid-beta (Abeta) protein deposits. Vaccination with Abeta stimulates phagocytosis of Abeta in transgenic mouse models of AD, leading to clearance of the deposits. Similar vaccination in humans with AD has, however, led to meningoencephalitis in some cases. The difference probably depends on the initial level of brain inflammation, which is much higher in bona fide AD in humans than in the transgenic mice. Because both pro- and anti-inflammatory activation of immune cells are possible, stimulating the phagocytic action of microglia while simultaneously stimulating anti-inflammatory activity might be beneficial in AD.

Evidence-based ethics for neurology and psychiatry research

American bioethics, historically arising out of theology and philosophy, has been dominated by the method of normative analysis. Ethics as policy, however, requires in addition a solid evidence base. This paper discusses the background conditions that make neurotherapeutics research particularly challenging. Three key ethical issues are discussed within an evidence-based ethics framework: the ethical challenges arising from changes in the financial incentive structures for academic researchers and their institutions, the challenges of risk-benefit analysis for neurotherapeutics protocols testing innovative interventions, and the evolving issues surrounding impaired decision-making capacity and surrogate consent for research. For each of these issues, selected empirical data are reviewed, areas for further inquiry are noted, and the need for development of novel methods for bioethics policy research is discussed.

Transgenic animal models of Alzheimer's disease and related disorders: histopathology, behavior and therapy

Alzheimer's disease (AD) is a devastating neurodegenerative disease that affects more than 15 million people worldwide. Within the next generation, these numbers will more than double. To assist in the elucidation of pathogenic mechanisms of AD and related disorders, such as frontotemporal dementia (FTDP-17), genetically modified mice, flies, fish and worms were developed, which reproduce aspects of the human histopathology, such as beta-amyloid-containing plaques and tau-containing neurofibrillary tangles (NFT). In mice, the tau pathology caused selective behavioral impairment, depending on the distribution of the tau aggregates in the brain. Beta-amyloid induced an increase in the numbers of NFT, whereas the opposite was not observed in mice. In beta-amyloid-producing transgenic mice, memory impairment was associated with increased levels of beta-amyloid. Active and passive beta-amyloid-directed immunization caused the removal of beta-amyloid plaques and restored memory functions. These findings have since been translated to human therapy. This review aims to discuss the suitability and limitations of the various animal models and their contribution to an understanding of the pathophysiology of AD and related disorders.

Overcoming antigen masking of anti-amyloidbeta antibodies reveals breaking of B cell tolerance by virus-like particles in amyloidbeta immunized amyloid precursor protein transgenic mice

BACKGROUND

In prior work we detected reduced anti-Abeta antibody titers in Abeta-vaccinated transgenic mice expressing the human amyloid precursor protein (APP) compared to nontransgenic littermates. We investigated this observation further by vaccinating APP and nontransgenic mice with either the wild-type human Abeta peptide, an Abeta peptide containing the "Dutch Mutation", E22Q, or a wild-type Abeta peptide conjugated to papillomavirus virus-like particles (VLPs).

RESULTS

Anti-Abeta antibody titers were lower in vaccinated APP than nontransgenic mice even when vaccinated with the highly immunogenic Abeta E22Q. One concern was that human Abeta derived from the APP transgene might mask anti-Abeta antibodies in APP mice. To test this possibility, we dissociated antigen-antibody complexes by incubation at low pH. The low pH incubation increased the anti-Abeta antibody titers 20-40 fold in APP mice but had no effect in sera from nontransgenic mice. However, even after dissociation, the anti-Abeta titers were still lower in transgenic mice vaccinated with wild-type Abeta or E22Q Abeta relative to non-transgenic mice. Importantly, the dissociated anti-Abeta titers were equivalent in nontransgenic and APP mice after VLP-based vaccination. Control experiments demonstrated that after acid-dissociation, the increased antibody titer did not cross react with bovine serum albumin nor alpha-synuclein, and addition of Abeta back to the dissociated serum blocked the increase in antibody titers.

CONCLUSIONS

Circulating human Abeta can interfere with ELISA assay measurements of anti-Abeta titers. The E22Q Abeta peptide vaccine is more immunogenic than the wild-type peptide. Unlike peptide vaccines, VLP-based vaccines against Abeta abrogate the effects of Abeta self-tolerance.

Microglial activation facilitates Abeta plaque removal following intracranial anti-Abeta antibody administration

The mechanisms by which anti-Abeta antibodies clear amyloid plaques in Abeta depositing transgenic mice are unclear. In the current study, we demonstrate that inhibition of anti-Abeta antibody-induced microglial activation with anti-inflammatory drugs, such as dexamethasone, inhibits removal of fibrillar amyloid deposits. We also show that anti-Abeta F(ab')(2) fragments fail to activate microglia and are less efficient in removing fibrillar amyloid than the corresponding complete IgG. Diffuse Abeta deposits are cleared by antibodies under all circumstances. These data suggest that microglial activation is necessary for efficient removal of compact amyloid deposits with immunotherapy. Inhibition of this activation may result in an impaired clinical response to vaccination against Abeta.

Biomarkers of Alzheimer disease in plasma

Plasma and serum biochemical markers proposed for Alzheimer disease (AD) are based on pathophysiologic processes such as amyloid plaque formation [amyloid beta-protein (A beta), A beta autoantibodies, platelet amyloid precursor protein (APP) isoforms], inflammation (cytokines), oxidative stress (vitamin E, isoprostanes), lipid metabolism (apolipoprotein E, 24S-hydroxycholesterol), and vascular disease [homocysteine, lipoprotein (a)]. Most proteins or metabolites evaluated in plasma or serum thus far are, at best, biological correlates of AD: levels are statistically different in AD versus controls in some cohorts, but they lack sensitivity or specificity for diagnosis or for tracking response to therapy. Approaches combining panels of existing biomarkers or surveying the range of proteins in plasma (proteomics) show promise for discovering biomarker profiles that are characteristic of AD, yet distinct from nondemented patients or patients with other forms of dementia.

Clinical manifestations of cerebral amyloid angiopathy-related inflammation

To explore the clinical effects of inflammation associated with vascular deposits of the amyloid beta peptide (A beta), we analyzed 42 consecutive patients with pathologically diagnosed cerebral amyloid angiopathy (CAA) for evidence of an inflammatory response. Inflammation with giant-cell reaction surrounding amyloid-laden vessels was identified in 7 of the 42 cases. The clinical symptoms in each of the seven were subacute cognitive decline or seizure rather than hemorrhagic stroke, the primary clinical presentation in 33 of 35 patients with noninflammatory CAA (p < 0.001). Inflammatory CAA also was associated with radiographic white matter abnormalities, significantly younger age at presentation, and a marked overrepresentation of the apolipoprotein E epsilon 4/epsilon 4 genotype (71% vs 4%, p < 0.001). Of the six inflammatory CAA patients with available follow-up information, five demonstrated clinical and radiographic improvement after immunosuppressive treatment. The syndrome of CAA-related perivascular inflammation appears to represent a subset of CAA with clinically distinct symptoms that may respond to immunosuppressive treatment. These data add to evidence that inflammation against A beta can cause vascular dysfunction, a potential mechanism for the toxic response recently observed in clinical trials of A beta immunization.