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

Deglycosylated anti-amyloid-beta antibodies eliminate cognitive deficits and reduce parenchymal amyloid with minimal vascular consequences in aged amyloid precursor protein transgenic mice

Systemic administration of anti-amyloid-beta (Abeta) antibodies results in reduced parenchymal amyloid but increased vascular amyloid and microhemorrhage in amyloid precursor protein (APP) transgenic mice. Here, we evaluate the effects of reducing effector interactions of the antibody via deglycosylation. Mice aged 20 months were treated weekly for 4 months and tested behaviorally before they were killed. APP transgenic mice receiving either anti-Abeta (2H6) or deglycosylated anti-Abeta (de-2H6) showed significant improvement in radial arm water maze performance compared with mice receiving a control antibody. Both groups receiving anti-Abeta antibodies showed significant reductions in total Abeta immunochemistry and Congo red. Significantly fewer vascular amyloid deposits and microhemorrhages were observed in mice administered the de-2H6 antibody compared with those receiving unmodified 2H6 antibody. Deglycosylated anti-Abeta antibodies may be preferable to unmodified IgG because they retain the cognition-enhancing and amyloid-reducing properties of anti-Abeta immunotherapy, while greatly attenuating the increased vascular amyloid deposition and microhemorrhage observed with unmodified IgG.

Immunology and immunotherapy of Alzheimer's disease

Although Alzheimer's disease is considered to be a degenerative brain disease, it is clear that the immune system has an important role in the disease process. As discussed in this Review, immune-based therapies that are designed to remove amyloid-beta peptide from the brain have produced positive results in animal models of the disease and are being tested in humans with Alzheimer's disease. Although immunotherapy holds great promise for the treatment of Alzheimer's disease, clinical trials of active amyloid-beta vaccination of patients with Alzheimer's disease were discontinued after some patients developed meningoencephalitis. New immunotherapies using humoral and cell-based approaches are currently being investigated for the treatment and prevention of Alzheimer's disease.

Virus and virus-like particle-based immunogens for Alzheimer's disease induce antibody responses against amyloid-beta without concomitant T cell responses

A vaccine targeting the amyloid-beta (Abeta) peptide is a promising potential immunotherapy for Alzheimer's disease patients. However, experience from a recent clinical trial of a candidate Abeta vaccine has suggested that it is important to develop techniques to induce high titer antibodies against Abeta associated with vaccine efficacy while reducing the T cell responses against Abeta that were potentially responsible for serious side effects. We have previously demonstrated that immunization with self- and foreign antigens arrayed in a repetitive fashion on the surface of virus-like particles (VLPs) induces high titer antibody responses at low doses and in the absence of potentially inflammatory adjuvants. In this study, we examined the antibody and T cell responses upon immunization with human papillomavirus VLP- and Qbeta bacteriophage-based Abeta vaccines. Immunization with Abeta conjugated to VLPs or Qbeta elicited anti-Abeta antibody responses at low doses and without the use of adjuvants. The flexibility of these virus-based display systems allowed us to link and induce antibodies against short Abeta-derived peptides from the amino- and carboxyl-termini of the peptide. Immunization of mice with Abeta peptide in combination with Freund's adjuvant elicited predominantly IgG2c antibodies and strong T cell proliferative responses against Abeta. In contrast, VLP-conjugated Abeta peptides elicited more balanced isotype responses, dominated by IgG1. Both VLP and Qbeta-based Abeta vaccines induced weak or negligible T cell responses against Abeta. T cell responses were largely directed against linked viral epitopes. Taken together, virus-based vaccines that allow the presentation of Abeta in a repetitive dense array are new and potentially more effective vaccine candidates for Alzheimer's disease.

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

Background

Immunotherapy for Alzheimer's disease (AD) is emerging as a potential treatment. However, a clinical trial (AN1792) was halted after adverse effects occurred in a small subset of subjects, which may have been caused by a T cell-mediated immunological response. In general, aging limits the humoral immune response, therefore, immunogens and vaccination regimes are required that induce a strong antibody response with less potential for an adverse immune response.

Method

In the current study, we immunized both wildtype and J20 APP-tg mice with a priming injection of Aβ1–40/42, followed by multiple intranasal boosts with the novel immunogen dAβ1–15 (16 copies of Aβ1–15 on a lysine tree), Aβ1–15 peptide or Aβ1–40/42 full length peptide.

Results

J20 APP-tg mice primed with Aβ1–40/42 subcutaneously and subsequently boosted intranasally with Aβ1–15 peptide did not generate a cellular or humoral immune response. In contrast, J20 APP-tg mice boosted intranasally with dAβ1–15 or full length Aβ1–40/42 produced high levels of anti-Aβ antibodies. Splenocyte proliferation was minimal in mice immunized with dAβ1–15. Wildtype littermates of the J20 APP-tg mice produced higher amounts of anti-Aβ antibodies compared to APP-tg mice but also had low T cell proliferation. The anti-Aβ antibodies were mainly composed of IgG2b and directed to an epitope within the Aβ1–7 region, regardless of the immunogen. Examination of the brain showed a significant reduction in Aβ plaque burden in the J20 APP-tg mice producing antibodies compared to controls. Biochemically, Aβ40 or Aβ42 were also reduced in brain homogenates and elevated in plasma but the changes did not reach significance.

Conclusion

Our results demonstrate that priming with full length Aβ40/42 followed by boosting with dAβ1–15 but not Aβ1–15 peptide led to a robust humoral immune response with a minimal T cell response in J20 APP-tg mice. In addition, Aβ plaque burden was reduced in mice producing anti-Aβ antibodies. Interestingly, wildtype mice produced higher levels of anti-Aβ antibodies, indicating that immune tolerance may be present in J20 APP-tg mice. Together, these data suggest that dAβ1–15 but not Aβ1–15 peptide may be useful as a boosting immunogen in an AD vaccination regime.

Amyloid-beta immunotherapy for the prevention and treatment of Alzheimer disease: lessons from mice, monkeys, and humans

Alzheimer disease (AD), the most common form of dementia, is without an effective cure or preventive treatment. Recently, amyloid-beta protein (Abeta) has become a major therapeutic target. Many efforts are underway to either reduce the production of Abeta or enhance its clearance. In 1999, Schenk and colleagues first showed that active immunization with full-length Abeta lowered cerebral Abeta levels in transgenic mice. These findings have been confirmed and extended in various transgenic mouse models of AD using both active and passive Abeta immunization. Cognitive improvement also has been reported in association with active and passive Abeta vaccination in AD-like mouse models, even in the absence of significant reductions in cerebral Abeta loads. In 2004, the authors reported that active immunization with full-length Abeta in aged nonhuman primates, Caribbean vervets, reduced cerebral Abeta levels and gliosis. Proposed mechanisms of Abeta clearance by immunotherapy include disruption of Abeta aggregates, Abeta phagocytosis by microglia, neutralization of Abeta oligomers at the synapse, and increased efflux of Abeta from brain to blood. A phase IIa clinical trial was halted in 2002 because of the appearance of meningoencephalitis in approximately 6% of the AD patients. Although the exact cause of these adverse events is unknown, the immunogen, full-length Abeta1-42, may have been recognized as a self-antigen leading to an autoimmune response in some patients. Limited cognitive stabilization and apparent plaque clearance have been reported in subsets of patients who generated antibody titers. Currently, a passive immunization trial with a recombinant humanized monoclonal Abeta antibody is underway in humans. In the meantime, the authors are developing novel Abeta peptide immunogens for active immunization to target Abeta B cell epitope(s) and avoid Abeta-specific T-cell reactions in order to generate a safe and effective AD vaccine. The authors remain optimistic about the potential of such a vaccine for the prevention and treatment of AD.

Short amyloid-beta (Abeta) immunogens reduce cerebral Abeta load and learning deficits in an Alzheimer's disease mouse model in the absence of an Abeta-specific cellular immune response

Amyloid-beta (Abeta) immunotherapy lowers cerebral Abeta and improves cognition in mouse models of Alzheimer's disease (AD). A clinical trial using active immunization with Abeta1-42 was suspended after approximately 6% of patients developed meningoencephalitis, possibly because of a T-cell reaction against Abeta. Nevertheless, beneficial effects were reported in antibody responders. Consequently, alternatives are required for a safer vaccine. The Abeta1-15 sequence contains the antibody epitope(s) but lacks the T-cell reactive sites of full-length Abeta1-42. Therefore, we tested four alternative peptide immunogens encompassing either a tandem repeat of two lysine-linked Abeta1-15 sequences (2xAbeta1-15) or the Abeta1-15 sequence synthesized to a cross-species active T1 T-helper-cell epitope (T1-Abeta1-15) and each with the addition of a three-amino-acid RGD (Arg-Gly-Asp) motif (R-2xAbeta1-15; T1-R-Abeta1-15). High anti-Abeta antibody titers were observed in wild-type mice after intranasal immunization with R-2xAbeta1-15 or 2xAbeta1-15 plus mutant Escherichia coli heat-labile enterotoxin LT(R192G) adjuvant. Moderate antibody levels were induced after immunization with T1-R-Abeta1-15 or T1-Abeta1-15 plus LT(R192G). Restimulation of splenocytes with the corresponding immunogens resulted in moderate proliferative responses, whereas proliferation was absent after restimulation with full-length Abeta or Abeta1-15. Immunization of human amyloid precursor protein, familial AD (hAPP(FAD)) mice with R-2xAbeta1-15 or 2xAbeta1-15 resulted in high anti-Abeta titers of noninflammatory T-helper 2 isotypes (IgG1 and IgG2b), a lack of splenocyte proliferation against full-length Abeta, significantly reduced Abeta plaque load, and lower cerebral Abeta levels. In addition, 2xAbeta1-15-immunized hAPP(FAD) animals showed improved acquisition of memory compared with vehicle controls in a reference-memory Morris water-maze behavior test that approximately correlated with anti-Abeta titers. Thus, our novel immunogens show promise for future AD vaccines.

The cerebral beta-amyloid angiopathies: hereditary and sporadic

We review the clinical, radiologic, and neuropathologic features of the hereditary and sporadic forms of cerebral amyloid angiopathy (CAA) associated with vascular deposition of the beta-amyloid peptide. Amino acid substitutions at 4 sites in the beta-amyloid precursor protein, all situated within the beta-amyloid peptide sequence itself, have been shown to cause heritable forms of CAA. The vascular diseases caused by these mutations are associated primarily with cerebral hemorrhages, white matter lesions, and cognitive impairment, and only variable extents of the plaque and neurofibrillary pathologies characteristic of Alzheimer disease. Sporadic CAA typically presents 20 or more years later than hereditary CAA, but is otherwise characterized by a comparable constellation of recurrent cerebral hemorrhages, white matter lesions, and cognitive impairment. The clinical, radiologic and pathologic similarities between hereditary and sporadic CAA suggest that important lessons for this common age-related process can be learned from the mechanisms by which mutation makes beta-amyloid tropic or toxic to vessels.

Mechanism of cerebral beta-amyloid angiopathy: murine and cellular models

Cerebral amyloid angiopathy of the beta-amyloid type (Abeta-CAA) is a risk factor for hemorrhagic stroke and independently is believed to contribute to dementia. Naturally occurring animal models of Abeta-CAA are scarce and not well suited for the laboratory. To this end, a variety of transgenic mouse models have been developed that, similar to cerebral Abeta-amyloidosis in humans, develop either Abeta-CAA only or both Abeta-CAA and parenchymal amyloid, or primarily parenchymal amyloid with only scarce Abeta-CAA. The lessons learned from these mouse models are: i) Abeta-CAA alone is sufficient to induce cerebral hemorrhage and associate pathologies including neuroinflammation, ii) the origin of vascular amyloid is mainly neuronal, iii) Abeta-CAA results largely from impaired Abeta clearance, iv) a high ratio Abeta40:42 favors vascular over parenchymal amyloidosis, and v) genetic risk factors such as ApoE modulate Abeta-CAA and CAA-induced hemorrhages. Therapeutic strategies to inhibit Abeta-CAA are poor at the present time. Once Abeta-CAA is present current Abeta immunotherapy strategies have failed to clear vascular amyloid and even run the risk of serious side effects. Despite this progress in deciphering the pathomechanism of Abeta-CAA, with these first generation mouse models of Abeta-CAA, refining these models is needed and will help to understand the emerging importance of Abeta-CAA for dementia and to develop biomarkers and therapeutic strategies.

Imaging and in vivo quantitation of beta-amyloid: an exemplary biomarker for Alzheimer's disease?

Alzheimer's disease (AD) is characterized pathologically by the presence of beta-amyloid plaques in the brain. A substantial body of research indicates that the presence of increased beta-amyloid peptide (Abeta) is neurotoxic and may initiate the further pathology observed in AD, including neurofibrillary tangles, synaptic loss and dysfunction, and neurodegeneration. The use of brain imaging in patients with or at risk for AD has increased our understanding of the pathophysiology of the disease and may potentially aid in diagnosis. The development of new therapeutics that reduce Abeta in the brain has also indicated a potential use for amyloid imaging in monitoring response to treatment. This review explores the utility of amyloid as a biomarker and the use of positron emission tomography and magnetic resonance imaging in the diagnosis and treatment of AD.

IgG-assisted age-dependent clearance of Alzheimer's amyloid beta peptide by the blood-brain barrier neonatal Fc receptor

The role of blood-brain barrier (BBB) transport in clearance of amyloid beta-peptide (Abeta) by Abeta immunotherapy is not fully understood. To address this issue, we studied the effects of peripherally and centrally administered Abeta-specific IgG on BBB influx of circulating Abeta and efflux of brain-derived Abeta in APPsw(+/-) mice, a model that develops Alzheimer's disease-like amyloid pathology, and wild-type mice. Our data show that anti-Abeta IgG blocks the BBB influx of circulating Abeta in APPsw(+/-) mice and penetrates into the brain to sequester brain Abeta. In young mice, Abeta-anti-Abeta complexes were cleared from brain to blood by transcytosis across the BBB via the neonatal Fc receptor (FcRn) and the low-density lipoprotein receptor-related protein (LRP), whereas in older mice, there was an age-dependent increase in FcRn-mediated IgG-assisted Abeta BBB efflux and a decrease in LRP-mediated clearance of Abeta-anti-Abeta complexes. Inhibition of the FcRn pathway in older APPsw(+/-) mice blocked clearance of endogenous Abeta40/42 by centrally administered Abeta immunotherapy. Moreover, deletion of the FcRn gene in wild-type mice inhibited clearance of endogenous mouse Abeta40/42 by systemically administered anti-Abeta. Our data suggest that the FcRn pathway at the BBB plays a crucial role in IgG-assisted Abeta removal from the aging brain.

Intracranial administration of deglycosylated C-terminal-specific anti-Abeta antibody efficiently clears amyloid plaques without activating microglia in amyloid-depositing transgenic mice

BACKGROUND

Antibodies against the Ass peptide clear Ass deposits when injected intracranially. Deglycosylated antibodies have reduced effector functions compared to their intact counterparts, potentially avoiding immune activation.

METHODS

Deglycosylated or intact C-terminal specific high affinity anti-Abeta antibody (2H6) were intracranially injected into the right frontal cortex and hippocampus of amyloid precursor protein (APP) transgenic mice. The untreated left hemisphere was used to normalize for the extent of amyloid deposition present in each mouse. Control transgenic mice were injected with an antibody against a drosophila-specific protein (amnesiac). Tissues were examined for brain amyloid deposition and microglial responses 3 days after the injection.

RESULTS

The deglycosylated 2H6 antibody had lower affinity for several murine Fcgamma receptors and human complement than intact 2H6 without a change in affinity for Ass. Immunohistochemistry for Abeta and thioflavine-S staining revealed that both diffuse and compact deposits were reduced by both antibodies. In animals treated with the intact 2H6 antibody, a significant increase in Fcgamma-receptor II/III immunostaining was observed compared to animals treated with the control IgG antibody. No increase in Fcgamma-receptor II/III was found with the deglycosylated 2H6 antibody. Immunostaining for the microglial activation marker CD45 demonstrated a similar trend.

CONCLUSION

These findings suggest that the deglycosylated 2H6 is capable of removing both compact and diffuse plaques without activating microglia. Thus, antibodies with reduced effector functions may clear amyloid without concomitant immune activation when tested as immunotherapy for Alzheimer's disease.

Clinical diagnosis and management of Alzheimer's disease

The diagnosis of dementia of the Alzheimer's type is defined by criteria from the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition and the National Institute of Neurologic, Communicative Disorders and Stroke-AD and Related Disorders Association. The latter divides diagnosis into definite, probable, and possible Alzheimer's disease (AD), with definitive diagnosis requiring pathologic confirmation. Both criteria require that other causes of dementia are excluded. A diagnosis of AD can be made with reasonably high accuracy using a combination of clinical criteria, neuropsychologic testing, and conventional CT and MR imaging. There is increasing emphasis on early recognition. Although current therapies produce a mild improvement in symptoms, there are several disease-modifying therapies on the horizon. This article reviews current standards in clinical diagnosis and management.

Clearance and prevention of prion infection in cell culture by anti-PrP antibodies

Prion diseases are transmissible and invariably fatal neurodegenerative disorders associated with a conformational transformation of the cellular prion protein (PrP(C)) into a self-replicating and proteinase K (PK)-resistant conformer, scrapie PrP (PrP(Sc)). Humoral immunity may significantly prolong the incubation period and even prevent disease in murine models of prionoses. However, the mechanism(s) of action of anti-PrP monoclonal antibodies (Mabs) remain(s) obscure. The murine neuroblastoma N2a cell line, infected with the 22L mouse-adapted scrapie strain, was used to screen a large library of Mabs with similar binding affinities to PrP, to identify those antibodies which could clear established infection and/or prevent infection de novo. Three Mabs were found capable of complete and persistent clearing of already-infected N2a cells of PrP(Sc). These antibodies were 6D11 (generated to PK-resistant PrP(Sc) and detecting PrP residues 93-109), and 7H6 and 7A12, which were raised against recombinant PrP and react with neighbouring epitopes of PrP residues 130-140 and 143-155, respectively. Mabs were found to interact with PrP(Sc) formation both on the cell surface and after internalization in the cytosol. Treatment with Mabs was not associated with toxicity nor did it result in decreased expression of PrP(C). Both preincubation of N2a cells with Mabs prior to exposure to 22L inoculum and preincubation of the inoculum with Mabs prior to infecting N2a cells resulted in a significant reduction in PrP(Sc) levels. Information provided in these studies is important for the rational design of humoral immune therapy for prion infection in animals and eventually in humans.

Abeta peptide immunization restores blood-brain barrier integrity in Alzheimer disease

Immunization with amyloid beta (Abeta) peptides or passive immunization with antibodies against Abeta has been reported to reduce plaque burden, neuritic dystrophy, early Tau pathology, microgliosis as well as reversing learning and memory deficits. This has created a central paradox: how does vaccination in peripheral tissues reduce plaque burden in the brain? No single explanation for these phenomena has yet been presented. To reconcile these observations, we demonstrate that the integrity of the blood-brain barrier (BBB), a structural barrier between the brain and the blood, is compromised in Tg2576 Alzheimer disease (AD) model mice. We immunized Tg2576 mice with Abeta before and after the onset of AD-type neuropathology and observed that BBB permeability, amyloid burden, and microgliosis are decreased in immunized mice. It is concluded that the integrity of the BBB is disrupted in AD mice, and after Abeta immunization the immune system clears Abeta from sources in the brain as it would in peripheral organs lacking barriers. Once Abeta is removed, the integrity of the BBB is restored. The data therefore provide an intellectual framework for understanding how the immune system can clear amyloid deposits from AD brains and suggest new strategies for limiting disease progression in amyloidopathies.

Association between CSF biomarkers and incipient Alzheimer's disease in patients with mild cognitive impairment: a follow-up study

BACKGROUND

Disease-modifying treatment strategies for Alzheimer's disease have led to an urgent need for biomarkers to identify the disease at a very early stage. Here, we assess the association between CSF biomarkers and incipient Alzheimer's in patients with mild cognitive impairment (MCI).

METHODS

From a series of 180 consecutive patients with MCI, we assessed 137 who underwent successful lumbar puncture at baseline. Patients at risk of developing dementia were followed clinically for 4-6 years. Additionally, 39 healthy individuals, cognitively stable over 3 years, served as controls. We analysed CSF concentrations of beta amyloid(1-42) (Abeta42), total tau (T-tau), and phosphorylated tau (P-tau181) using Luminex xMAP technology.

FINDINGS

During follow-up, 57 (42%) patients with MCI developed Alzheimer's disease, 21 (15%) developed other forms of dementia, and 56 (41%) remained cognitively stable for 5.2 years (range 4.0-6.8). A combination of CSF T-tau and Abeta42 at baseline yielded a sensitivity of 95% and a specificity of 83% for detection of incipient AD in patients with MCI. The relative risk of progression to Alzheimer's disease was substantially increased in patients with MCI who had pathological concentrations of T-tau and Abeta42 at baseline (hazard ratio 17.7, p<0.0001). The association between pathological CSF and progression to Alzheimer's disease was much stronger than, and independent of, established risk factors including age, sex, education, APOE genotype, and plasma homocysteine. The combination of T-tau and Abeta42/P-tau181 ratio yielded closely similar results (sensitivity 95%, specificity 87%, hazard ratio 19.8).

INTERPRETATION

Concentrations of T-tau, P-tau181, and Abeta42 in CSF are strongly associated with future development of Alzheimer's disease in patients with MCI.

Amyloid-β Immunotherapies in Mice and Men

Given the compelling genetic and biochemical evidence that has implicated amyloid-beta (Abeta) in the pathogenesis of Alzheimer's disease, many studies have focused on ways to inhibit Abeta production, to reverse or impede the formation of toxic forms of Abeta, or to facilitate the clearance of Abeta from the brain, in the hope of developing viable treatments for the disease. Using transgenic mouse models of Alzheimer's disease, many advances have been made in methodologies using different immunization techniques designed to clear soluble and aggregated forms of Abeta from the brain. We have highlighted how data derived from studies using transgenic mouse models have shaped our understanding of immunization-dependent Abeta clearance mechanisms and how these studies have influenced the development of anti-Abeta immunotherapies in humans.

BACE-1 inhibitory activities of new substituted phenyl-piperazine coupled to various heterocycles: Chromene, coumarin and quinoline

The protease beta-secretase plays a central role in the synthesis of pathogenic amyloid-beta in Alzheimer's disease. Here, we report a new series of analogues based on the phenyl-piperazine scaffold coupled to various heterocyclic moieties, which demonstrate improved inhibitory activities on BACE-1 (FRET assay) compared to already known naphthyl counterparts. The obtained results suggest further structural modifications to access to more potent BACE-1 inhibitors.

Abeta-induced meningoencephalitis is IFN-gamma-dependent and is associated with T cell-dependent clearance of Abeta in a mouse model of Alzheimer's disease

Vaccination against amyloid beta-peptide (Abeta) has been shown to be successful in reducing Abeta burden and neurotoxicity in mouse models of Alzheimer's disease (AD). However, although Abeta immunization did not show T cell infiltrates in the brain of these mice, an Abeta vaccination trial resulted in meningoencephalitis in 6% of patients with AD. Here, we explore the characteristics and specificity of Abeta-induced, T cell-mediated encephalitis in a mouse model of the disease. We demonstrate that a strong Abeta-specific T cell response is critically dependent on the immunizing T cell epitope and that epitopes differ depending on MHC genetic background. Moreover, we show that a single immunization with the dominant T cell epitope Abeta10-24 induced transient meningoencephalitis only in amyloid precursor protein (APP)-transgenic (Tg) mice expressing limited amounts of IFN-gamma under an myelin basic protein (MBP) promoter. Furthermore, immune infiltrates were targeted primarily to sites of Abeta plaques in the brain and were associated with clearance of Abeta. Immune infiltrates were not targeted to the spinal cord, consistent with what was observed in AD patients vaccinated with Abeta. Using primary cultures of microglia, we show that IFN-gamma enhanced clearance of Abeta, microglia, and T cell motility, and microglia-T cell immunological synapse formation. Our study demonstrates that limited expression of IFN-gamma in the brain, as observed during normal brain aging, is essential to promote T cell-mediated immune infiltrates after Abeta immunization and provides a model to investigate both the beneficial and detrimental effects of Abeta-specific T cells.

Current concepts in therapeutic strategies targeting cognitive decline and disease modification in Alzheimer's disease

Alzheimer's disease is a progressive neurodegenerative disorder and the leading cause of dementia in the Western world. Postmortem, it is characterized neuropathologically by the presence of amyloid plaques, neurofibrillary tangles, and a profound gray matter loss. Neurofibrillary tangles are composed of an abnormally hyperphosphorylated intracellular protein called tau, tightly wound into paired helical filaments and thought to impact microtubule assembly and protein trafficking, resulting in the eventual demise of neuronal viability. The extracellular amyloid plaque deposits are composed of a proteinacious core of insoluble aggregated amyloid-beta (Abeta) peptide and have led to the foundation of the amyloid hypothesis. This hypothesis postulates that Abeta is one of the principal causative factors of neuronal death in the brains of Alzheimer's patients. With multiple drugs now moving through clinical development for the treatment of Alzheimer's disease, we will review current and future treatment strategies aimed at improving both the cognitive deficits associated with the disease, as well as more novel approaches that may potentially slow or halt the deadly neurodegenerative progression of the disease.

Central nervous system drug development: an integrative biomarker approach toward individualized medicine

Drug development for CNS disorders faces the same formidable hurdles as other therapeutic areas: escalating development costs; novel drug targets with unproven therapeutic potential; and health care systems and regulatory agencies demanding more compelling demonstrations of the value of new drug products. Extensive clinical testing remains the core of registration of new compounds; however, traditional clinical trial methods are falling short in overcoming these development hurdles. The most common CNS disorders targeted for drug treatment are chronic, slowly vitiating processes manifested by highly subjective and context dependent signs and symptoms. With the exception of a few rare familial degenerative disorders, they have ill-defined or undefined pathophysiology. Samples selected for treatment trials using clinical criteria are inevitably heterogeneous, and dependence on traditional endpoints results in early proof-of-concept trials being long and large, with very poor signal to noise. It is no wonder that pharmaceutical and biotechnology companies are looking to biomarkers as an integral part of decision-making process supported by new technologies such as genetics, genomics, proteomics, and imaging as a mean of rationalizing CNS drug development. The present review represent an effort to illustrate the integration of such technologies in drug development supporting the path of individualized medicine.

Neuroprotection and neurodegenerative diseases: from biology to clinical practice

Neurodegenerative diseases and, in particular, Alzheimer disease, are characterized by progressive neuronal loss correlated in time with the symptoms of the disease considered. Whereas the symptoms of those incapacitating diseases are beginning to be managed with a relative efficacy, the ultimate objective of therapy nonetheless remains preventing cell (neuronal and/or astrocytic) death in a neurocytoprotective approach. In biologic terms, in the light of progress at basic research level, three strategies may be envisaged: (1) antagonizing the cytotoxic causal events (excess intracellular calcium, accumulation of abnormal proteins, excitotoxic effects of amino acids, oxidative stress, processes related to inflammation, etc.); (2) stimulating the endogenous protective processes (anti-free radical or DNA repair systems, production of neurotrophic factors, potential cytoprotective action of steroids, etc.); (3) promoting damaged structure repair strategies (grafts) or deep brain or cortical neurostimulation with a view to triggering (beyond the symptomatic actions) potential 'protective' cell mechanisms. The clinical transition of the various strategies whose efficacy is being tested in animal and/or cell models, experimental analogs of the diseases, and thus the objective demonstration in humans of pharmacological and/or surgical neurocytoprotection, is currently the subject of considerable methodological debate (What are the right psychometric assessment criteria? What are the most pertinent laboratory or neuroradiological markers, etc.?). A number of clinical trials have been completed or are ongoing with drugs that are reputed to be neuroprotective. Thus, elements of the response are beginning to be generated with a view to determining whether it will soon be possible to effectively slow or even stop the neurodegenerative process whose etiology, in most cases, remains obscure.

Immunotherapeutic relief from persistent infections and amyloid disorders

Persistent infections and amyloid disorders afflict a significant number of people worldwide. It would appear at first glance that the treatment of these afflictions should be entirely unrelated; however, in both cases components of the adaptive immune system have been harnessed in an attempt to provide some therapeutic relief. Given that the ability of a pathogen to establish persistence often depends in part on a shortcoming of the adaptive immune response, it seems logical to devise immunotherapies with the intention of supplementing (or replacing) the insufficient immunologic element. A case in point is an intervention referred as immunocytotherapy, which relies upon the adoptive transfer of pathogen-specific T lymphocytes into a persistently infected host. Remarkably, the adoptively transferred T lymphocytes not only have the capacity to clear the persistent infection, but can also provide the recipient with protection against subsequent rechallenge (i.e., immunologic memory). Treatment of amyloid disorders (e.g., Alzheimer disease, sporadic inclusion-body myositis) with a similar therapeutic approach is complicated by the fact that the aberrant protein accumulations are self-derived. Focusing the adaptive response on these aberrant self-proteins has the potential to result in autoimmune pathology. This review critically evaluates the importance of immunotherapeutic approaches for the treatment of persistent infections and amyloid disorders, and attempts to delineate the interventions that are most likely to succeed in an exceedingly complex disorder such as sporadic inclusion-body myositis.

Microglial phagocytosis induced by fibrillar beta-amyloid and IgGs are differentially regulated by proinflammatory cytokines

Microglia undergo a phenotypic activation in response to fibrillar beta-amyloid (fAbeta) deposition in the brains of Alzheimer's disease (AD) patients, resulting in their elaboration of inflammatory molecules. Despite the presence of abundant plaque-associated microglia in the brains of AD patients and in animal models of the disease, microglia fail to efficiently clear fAbeta deposits. However, they can be induced to do so during Abeta vaccination therapy attributable to anti-Abeta antibody stimulation of IgG receptor (FcR)-mediated phagocytic clearance of Abeta plaques. We report that proinflammatory cytokines attenuate microglial phagocytosis stimulated by fAbeta or complement receptor 3 and argue that this may, in part, underlie the accumulation of fAbeta-containing plaques within the AD brain. The proinflammatory suppression of fAbeta-elicited phagocytosis is dependent on nuclear factor kappaB activation. Significantly, the proinflammatory cytokines do not inhibit phagocytosis elicited by antibody-mediated activation of FcR, which may contribute to the efficiency of Abeta vaccination-based therapy. Importantly, the proinflammatory suppression of fAbeta phagocytosis can be relieved by the coincubation with anti-inflammatory cytokines, cyclooxygenase inhibitors, ibuprofen, or an E prostanoid receptor antagonist, suggesting that proinflammatory cytokines induce the production of prostaglandins, leading to an E prostanoid receptor-dependent inhibition of phagocytosis. These findings support anti-inflammatory therapies for the treatment of AD.

Invasion of hematopoietic cells into the brain of amyloid precursor protein transgenic mice

The significance of the peripheral immune system in Alzheimer's disease pathogenesis remains controversial. To study the CNS invasion of hematopoietic cells in the course of cerebral amyloidosis, we used a green fluorescence protein (GFP)-bone marrow chimeric amyloid precursor protein transgenic mouse model (APP23 mice). No difference in the number of GFP-positive invading cells was observed between young APP23 mice and nontransgenic control mice. In contrast, in aged, amyloid-depositing APP23 mice, a significant increase in the number of invading ameboid-like GFP-positive cells was found compared with age-matched nontransgenic control mice. Interestingly, independent of the time after transplantation, only a subpopulation of amyloid deposits was surrounded by invading cells. This suggests that not all amyloid plaques are a target for invading cells or, alternatively, all amyloid plaques attract invading cells but only for a limited time, possibly at an early stage of plaque evolution. Immunological and ultrastructural phenotyping revealed that macrophages and T-cells accounted for a significant portion of these ameboid-like invading cells. Macrophages did not show evidence of amyloid phagocytosis at the electron microscopic level, and no obvious signs for T-cell-mediated inflammation or neurodegeneration were observed. The observation that hematopoietic cells invade the brain in response to cerebral amyloidosis may hold an unrecognized therapeutic potential.

Developing Novel Immunogens for an Effective, Safe Alzheimer’s Disease Vaccine

Active amyloid beta (A beta) vaccination has been shown to be effective in clearing cerebral A beta and improving cognitive function in mouse models of Alzheimer's disease. However, an A beta vaccine clinical trial was suspended after meningoencephalitis was detected in a subset of subjects. Passive immunization has been suggested to be a safer alternative to active A beta immunization but there are reports of increased risk of microhemorrhages associated with its administration in aged beta-amyloid precursor protein transgenic mice bearing abundant vascular amyloid deposition. In addition, the cost may be prohibitive for large-scale clinical use. Therefore, we are designing novel A beta immunogens that encompass the B cell epitope of A beta but lack the T cell-reactive sites. These immunogens induced the production of A beta-specific antibodies in the absence of an A beta-specific cellular immune response in wild-type mice and are being tested in beta-amyloid precursor protein transgenic mice. These data together with published reports from several other groups suggest that a safe, active A beta vaccine is a tenable goal.

Circulating biomarkers of cognitive decline and dementia

Plasma and serum biochemical markers proposed for cognitive decline of degenerative (Alzheimer's disease, AD) or vascular origin and predementia syndromes (mild cognitive impairment and other related entities) are based on pathophysiologic processes such as lipoprotein metabolism (total cholesterol, apolipoprotein E, 24S-hydroxy-cholesterol), and vascular disease (homocysteine, lipoprotein(a)); SP formation (amyloid beta(Abeta)-protein, Abeta autoantibodies, platelet APP isoforms), oxidative stress (isoprostanes, vitamin E), and inflammation (cytokines). This review will focus on the current knowledge on circulating serum and plasma biomarkers of cognitive decline and dementia that are linked to cholesterol homeostasis and lipoprotein abnormalities, senile plaque formation and amyloid precursor protein (APP) metabolism, oxidative stress, and inflammatory reactions. Special emphasis will, however, be placed on biomarkers related to lipoprotein metabolism and vascular disease. Analytically, most plasma and serum proteins or metabolites lack reproducibility, sensitivity, or specificity for the diagnosis, risk and progression assessment, or therapeutic monitoring of AD and other dementing disorders. Measures linked to lipoprotein metabolism and vascular disease, APP metabolism, oxidative stress, or inflammation appear altered in AD relative to controls, but lack sufficient discriminatory power. Measures combining several biomarkers or incorporating a range of proteins in plasma and small molecule metabolites are promising approaches for the development of plasma or serum-based diagnostic tests for AD and other dementing disorders, as well as for predementia syndromes.

Current Pharmacotherapy for Alzheimer's Disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease that affects approximately 4.5 million people in the United States. The mainstays of current pharmacotherapy for AD are compounds aimed at increasing the levels of acetylcholine in the brain, thereby facilitating cholinergic neurotransmission through inhibition of the cholinesterases. These drugs, known as acetylcholinesterase inhibitors (AChEIs), were first approved by the U.S. Food and Drug Administration (FDA) in 1995 based on clinical trials showing modest symptomatic benefit on cognitive, behavioral, and global measures. In 2004 the FDA approved memantine, an NMDA antagonist, for treating dementia symptoms in moderate to severe AD cases. In clinical practice, memantine may be co-administered with an AChEI, although neither drug individually or in combination affects the underlying pathophysiology of dementia. Dementia in AD results from progressive synaptic loss and neuronal death. As knowledge of the mechanisms responsible for neurodegeneration in AD increases, it is anticipated that neuroprotective drugs to slow or prevent neuronal dysfunction and death will be developed to complement current symptomatic treatments.

The development of anti-amyloid therapy for Alzheimer's disease : from secretase modulators to polymerisation inhibitors

The leading hypothesis of the pathophysiology of Alzheimer's disease holds that the pivotal event is cleavage of the amyloid precursor protein to release intact the 42-amino-acid amyloid-beta peptide (Abeta); this hypothesis best explains the known genetic causes of Alzheimer's disease. If this theory is correct, optimal strategies for altering the disease process should be directed toward modifying the generation, clearance and/or toxicity of Abeta. Abeta is highly aggregable, spontaneously assuming a beta-sheet conformation and polymerising into oligomers, protofibrils, fibrils and plaques. The relative contribution of the various forms of Abeta to neuronal dysfunction in Alzheimer's disease remains uncertain; however, recent evidence implicates diffusible oligomeric species. This article reviews the range of strategies that have been investigated to target Abeta to slow the progression of Alzheimer's disease, from secretase modulators to anti-polymerisation agents. One amyloid-binding drug, tramiprosate (3-amino-1-propanesulfonic acid; Alzhemed), which is effective in reducing polymerisation in vitro and plaque deposition in animals, has now reached phase III clinical trials. Thus, it is plausible that an effective anti-amyloid strategy will become available for the treatment of Alzheimer's disease within the next few years.

Transgenic models of Alzheimer's disease: learning from animals

As the scope of the problem of Alzheimer's disease (AD) grows due to an aging population, research into the devastating condition has taken on added urgency. Rare inherited forms of AD provide insight into the molecular pathways leading to degeneration and have made possible the development of transgenic animal models. Several of these models are based on the overexpression of amyloid precursor protein (APP), presenilins, or tau to cause production and accumulation of amyloid-beta into plaques or hyperphosphorylated tau into neurofibrillary tangles. Producing these characteristic neuropathological lesions in animals causes progressive neurodegeneration and in some cases similar behavioral disruptions to those seen in AD patients. Knockout models of proteins involved in AD have also been generated to explore the native functions of these genes and examine whether pathogenesis is due to loss of function or toxic gain of function in these systems. Although none of the transgenic lines models the human condition exactly, the ability to study similar pathological processes in living animals have provided numerous insights into disease mechanisms and opportunities to test therapeutic agents. This chapter reviews animal models of AD and their contributions to developing therapeutic approaches for AD.

Modulation of the humoral and cellular immune response in Abeta immunotherapy by the adjuvants monophosphoryl lipid A (MPL), cholera toxin B subunit (CTB) and E. coli enterotoxin LT(R192G)

Abeta vaccination or passive transfer of human-specific anti-Abeta antibodies are approaches under investigation to prevent and/or treat Alzheimer's disease (AD). Successful active Abeta vaccination requires a strong and safe adjuvant to induce anti-Abeta antibody formation. We compared the adjuvants monophosphoryl lipid A (MPL)/trehalose dicorynomycolate (TDM), cholera toxin B subunit (CTB) and Escherichia coli heat-labile enterotoxin LT(R192G) for their ability to induce a humoral and cellular immune reaction, using fibrillar Abeta1-40/42 as a common immunogen in wildtype B6D2F1 mice. Subcutaneous (s.c.) administration with MPL/TDM resulted in anti-Abeta antibodies levels up to four times higher compared to s.c. LT(R192G). Using MPL/TDM, the anti-Abeta antibodies induced were mainly IgG2b, IgG1 and lower levels of IgG2a and IgM, with a moderate splenocyte proliferation and IFN-gamma production in vitro upon stimulation with Abeta1-40/42. LT(R192G), previously shown by us to induce robust titers of anti-Abeta antibodies, generated predominantly IgG2b and IgG1 anti-Abeta antibodies with very low splenocyte proliferation and IFN-gamma production. Weekly intranasal (i.n.) administration over 11 weeks of Abeta40/42 with CTB induced only moderate levels of antibodies. All immunogens generated antibodies that recognized mainly the Abeta1-7 epitope and specifically detected amyloid plaques on AD brain sections. In conclusion, MPL/TDM, in addition to LT(R192G), is an effective adjuvant when combined with Abeta40/42 and may aid in the design of Abeta immunotherapy.

The capacity to appoint a proxy and the possibility of concurrent proxy directives

With the projected increase in the number of persons with dementia (who eventually lose their capacity to give informed consent to treatment and research), third-party decision-making will become even more common than it is today. We argue that, because there are situations in which an appointed proxy is preferred over a de facto surrogate, it is ethically important to understand the capacity of persons with dementia to delegate their decision-making authority regarding treatment and research decisions. In this paper, focusing mainly on the research consent context, we examine the idea that persons suffering from neurodegenerative disorders may retain significant abilities-including sufficient capacity for delegating one's authority for giving consent to research-even if they are not capable of giving independent consent themselves. We first propose a rationale for assessing the capacity to appoint a proxy and then describe a novel interview instrument for assessing the capacity to appoint a proxy for research consent.

Immunotherapy of Alzheimer's disease (AD): From murine models to anti-amyloid beta (Aβ) human monoclonal antibodies

The deposition of amyloid beta (Abeta) protein is a key pathological feature in Alzheimer's disease (AD). In murine models of AD, both active and passive immunization against Abeta induce a marked reduction in amyloid brain burden and an improvement in cognitive functions. Preliminary results of a prematurely terminated clinical trial where AD patients were actively vaccinated with aggregated Abeta bear resemblance to those documented in murine models. Passive immunization of AD patients with anti-Abeta antibodies, in particular human antibodies, is a strategy that provides a more cautious management and control of any undesired side effects. Sera of all healthy adults contain anti-Abeta IgG autoimmune antibodies. Hence antigen-committed human B-cells are easily immortalized by Epstein-Barr virus (EBV) into anti-Abeta secreting cell lines. Two anti-Abeta human monoclonal antibodies which we recently prepared bind to the N-terminus of Abeta peptide and were shown to stain amyloid plaques in non-fixed brain sections from an AD patient. It is anticipated that specifically selected anti-Abeta human monoclonal antibodies could reduce and inhibit deposits of amyloid in brain while avoiding the cognitive decline that characterizes AD. In the future, this type of antibody may prove to be a promising immune therapy for the disease.

New pathways in drug discovery for alzheimer’s disease

Specific treatments for Alzheimer's disease (AD) were first introduced in the 1990s using the acetyl-cholinesterase inhibitors. More recently, the N-methyl-D-aspartate (NMDA) antagonist memantine has become available. Although these treatments do provide a modest improvement in the cognitive abnormalities present in AD, their pharmacology is based on manipulation of neurotransmitter systems, and there is no compelling evidence that they interfere with the underlying pathogenic process. Pathologic and genetic data have led to the hypothesis that a peptide called amyloid ss(Abeta) plays a primary role in the pathophysiology of AD. Several investigational therapies targeting Abeta are now undergoing clinical trials. This paper reviews the available data regarding Abeta-directed therapies that are in the clinic and summarizes the approach to biomarkers and clinical trial designs that can provide evidence of modification of the underlying disease process.

Current treatment of mild cognitive impairment and alzheimer’s disease

Current therapy for Alzheimer's disease (AD) consists of two classes of drugs: the cholinesterase inhibitors, of which there are three currently available medications; and the glutamate modulators, of which there is one. There has been no new information regarding efficacy of the cholinesterase inhibitors or memantine in AD over the past year, but a large, randomized trial concerning mild cognitive impairment was reported. Donepezil delayed conversion to dementia for 12 months but not longer in that trial, whereas vitamin E had no impact on outcomes. The results of the first immunization therapy for AD were released in 2005. Adverse events forced the premature discontinuation of the trial, but there were some grounds for optimism about the basic approach. Several new agents targeted directly at amyloid beta peptide production are currently in clinical trials, but no large studies have been reported over the past year.

Targeting amyloid-beta peptide (Abeta) oligomers by passive immunization with a conformation-selective monoclonal antibody improves learning and memory in Abeta precursor protein (APP) transgenic mice

Passive immunization of murine models of Alzheimer disease amyloidosis reduces amyloid-beta peptide (Abeta) levels and improves cognitive function. To specifically address the role of Abeta oligomers in learning and memory, we generated a novel monoclonal antibody, NAB61, that preferentially recognizes a conformational epitope present in dimeric, small oligomeric, and higher order Abeta structures but not full-length amyloid-beta precursor protein or C-terminal amyloid-beta precursor protein fragments. NAB61 also recognized a subset of brain Abeta deposits, preferentially mature senile plaques, and amyloid angiopathy. Using NAB61 as immunotherapy, we showed that aged Tg2576 transgenic mice treated with NAB61 displayed significant improvements in spatial learning and memory relative to control mice. These data implicated Abeta oligomers as a pathologic substrate for cognitive decline in Alzheimer disease.

Synaptic plasticity disruption by amyloid beta protein: modulation by potential Alzheimer's disease modifying therapies

AD (Alzheimer's disease) is characterized by a progressive and devastating mental decline that is usually presaged by impairment of a form of memory dependent on medial temporal lobe structures, including the hippocampus. The severity of clinical dementia correlates positively with the cerebral load of the AD-related protein Abeta (amyloid beta), particularly in its soluble form rather than the insoluble fibrillar Abeta found in amyloid plaques. Recent research in animal models of AD has pointed to a potentially important role for rapid disruptive effects of soluble species of Abeta on neural function in causing a relatively selective impairment of memory early in the disease. Our experiments assessing the mechanisms of Abeta inhibition of LTP (long-term potentiation), a correlate of memory-related synaptic plasticity, in the rodent hippocampus showed that low-n oligomers were the soluble Abeta species primarily responsible for the disruption of synaptic plasticity in vivo. Exogenously applied and endogenously generated anti-Abeta antibodies rapidly neutralized and prevented the synaptic plasticity disrupting effects of these very potent Abeta oligomers. This suggests that active or passive immunotherapeutic strategies for early AD should target Abeta oligomers in the brain. The ability of agents that reduce nitrosative/oxidative stress or antagonize stress-activated kinases to prevent Abeta inhibition of LTP in vitro points to a key role of these cellular mechanisms at very early stages in Abeta-induced neuronal dysfunction. A combination of antibody-mediated inactivation of Abeta oligomers and pharmacological prevention of cellular stress mechanisms underlying their synaptic plasticity disrupting effects provides an attractive strategy in the prevention of early AD.

Anti-Abeta42- and anti-Abeta40-specific mAbs attenuate amyloid deposition in an Alzheimer disease mouse model

Accumulation and aggregation of amyloid beta peptide 1-42 (Abeta42) in the brain has been hypothesized as triggering a pathological cascade that causes Alzheimer disease (AD). To determine whether selective targeting of Abeta42 versus Abeta40 or total Abeta is an effective way to prevent or treat AD, we compared the effects of passive immunization with an anti-Abeta42 mAb, an anti-Abeta40 mAb, and multiple Abeta(1-16) mAbs. We established in vivo binding selectivity of the anti-Abeta42 and anti-Abeta40 mAbs using novel TgBRI-Abeta mice. We then conducted a prevention study in which the anti-Abeta mAbs were administered to young Tg2576 mice, which have no significant Abeta deposition, and therapeutic studies in which mAbs were administered to Tg2576 or CRND8 mice with modest levels of preexisting Abeta deposits. Anti-Abeta42, anti-Abeta40, and anti-Abeta(1-16) mAbs attenuated plaque deposition in the prevention study. In contrast, anti-Abeta42 and anti-Abeta40 mAbs were less effective in attenuating Abeta deposition in the therapeutic studies and were not effective in clearing diffuse plaques following direct injection into the cortex. These data suggest that selective targeting of Abeta42 or Abeta40 may be an effective strategy to prevent amyloid deposition, but may have limited benefit in a therapeutic setting.

Novel Abeta peptide immunogens modulate plaque pathology and inflammation in a murine model of Alzheimer's disease

BACKGROUND

Alzheimer's disease, a common dementia of the elder, is characterized by accumulation of protein amyloid deposits in the brain. Immunization to prevent this accumulation has been proposed as a therapeutic possibility, although adverse inflammatory reactions in human trials indicate the need for novel vaccination strategies.

METHOD

Here vaccination with novel amyloid peptide immunogens was assessed in a transgenic mouse model displaying age-related accumulation of fibrillar plaques.

RESULTS

Immunization with any conformation of the amyloid peptide initiated at 12 months of age (at which time fibrillar amyloid has just begun to accumulate) showed significant decrease in total and fibrillar amyloid deposits and in glial reactivity relative to control transgenic animals. In contrast, there was no significant decrease in amyloid deposition or glial activation in mice in which vaccination was initiated at 16 months of age, despite the presence of similar levels anti-Abeta antibodies in young and old animals vaccinated with a given immunogen. Interestingly, immunization with an oligomeric conformation of Abeta was equally as effective as other amyloid peptides at reducing plaque accumulation. However, the antibodies generated by immunization with the oligomeric conformation of Abeta have more limited epitope reactivity than those generated by fAbeta, and the microglial response was significantly less robust.

CONCLUSION

These results suggest that a more specific immunogen such as oligomeric Abeta can be designed that achieves the goal of depleting amyloid while reducing potential detrimental inflammatory reactions. In addition, the data show that active immunization of older Tg2576 mice with any amyloid conformation is not as efficient at reducing amyloid accumulation and related pathology as immunization of younger mice, and that serum anti-amyloid antibody levels are not quantitatively related to reduced amyloid-associated pathology.

Prototype Alzheimer's disease epitope vaccine induced strong Th2-type anti-Abeta antibody response with Alum to Quil A adjuvant switch

Beta-amyloid (Abeta) peptide has been proposed to be a causal factor in Alzheimer's disease (AD). Currently being investigated, active and passive Abeta-immunotherapy significantly reduce Abeta plaque deposition, neuritic dystrophy, and astrogliosis in the brains of APP transgenic (APP/Tg) mice. Immunization with Abeta42 formulated in the Th1-type adjuvant QS21 was beneficial for AD patients with significant titers of anti-Abeta antibodies, however, 6% of participants developed meningoencephalitis, likely due to anti-Abeta-specific autoimmune Th1 cells. Thus, successful Abeta vaccination requires the development of strong antibody responses without Th1-type cellular immunity. In this study, we compared the induction of humoral immune responses with Th1-type (Quil A) and Th2-type (Alum) adjuvants singly and in combination, using our novel epitope vaccine composed of self B cell epitope Abeta(1-15) and foreign T cell epitope PADRE (PADRE-Abeta(1-15)-MAP). Formulated in Quil A, this vaccine resulted in significantly higher anti-Abeta antibody responses in both BALB/c (H-2d) and C57BL/6 (H-2b) mice, compared with Alum. Anti-Abeta antibodies induced by Alum were predominantly IgG1 type accompanied by lower levels of IgG2a and IgG2b. Quil A induced robust and almost equal titers of anti-Abeta antibodies of IgG1 and IgG2a isotypes and slightly lower levels of IgG2b. Switching adjuvants from Alum to Quil A induced higher concentrations of antibodies than injections with Alum only, however slightly lower than Quil A only. Switching both adjuvants did not change the profile of antibody responses generated by the initial adjuvant injected. These results suggest that switching from Alum to Quil A would be beneficial for AD patients because anti-Abeta antibody production was enhanced without changing the initially generated and likely beneficial Th2-type humoral response.

Persistent amyloidosis following suppression of Abeta production in a transgenic model of Alzheimer disease

BACKGROUND

The proteases (secretases) that cleave amyloid-beta (Abeta) peptide from the amyloid precursor protein (APP) have been the focus of considerable investigation in the development of treatments for Alzheimer disease. The prediction has been that reducing Abeta production in the brain, even after the onset of clinical symptoms and the development of associated pathology, will facilitate the repair of damaged tissue and removal of amyloid lesions. However, no long-term studies using animal models of amyloid pathology have yet been performed to test this hypothesis.

METHODS AND FINDINGS

We have generated a transgenic mouse model that genetically mimics the arrest of Abeta production expected from treatment with secretase inhibitors. These mice overexpress mutant APP from a vector that can be regulated by doxycycline. Under normal conditions, high-level expression of APP quickly induces fulminant amyloid pathology. We show that doxycycline administration inhibits transgenic APP expression by greater than 95% and reduces Abeta production to levels found in nontransgenic mice. Suppression of transgenic Abeta synthesis in this model abruptly halts the progression of amyloid pathology. However, formation and disaggregation of amyloid deposits appear to be in disequilibrium as the plaques require far longer to disperse than to assemble. Mice in which APP synthesis was suppressed for as long as 6 mo after the formation of Abeta deposits retain a considerable amyloid load, with little sign of active clearance.

CONCLUSION

This study demonstrates that amyloid lesions in transgenic mice are highly stable structures in vivo that are slow to disaggregate. Our findings suggest that arresting Abeta production in patients with Alzheimer disease should halt the progression of pathology, but that early treatment may be imperative, as it appears that amyloid deposits, once formed, will require additional intervention to clear.

Immunotherapy for Alzheimer's disease and other dementias

PURPOSE OF REVIEW

The aim of this article is to review the role of immunotherapy in the removal of proteins which accumulate abnormally in neurodegenerative disorders associated with dementia, in particular amyloid-beta accumulation in Alzheimer's disease.

RECENT FINDINGS

In both transgenic mouse models and in two trials of amyloid-beta immunotherapy for human Alzheimer's disease, active immunization with amyloid-beta 1-42 results in the removal of amyloid-beta plaques from the cerebral cortex associated with, in the mouse models, improvement in cognitive function. Cerebral amyloid angiopathy and neurofibrillary tangles persist, however, and there is also concern about T lymphocyte immune reactions in the meninges in the human cases. Active immunization schedules are being developed to minimize T lymphocyte reactions and to maximize antibody production and passive immunization protocols are being devised. Immunotherapy for removal of the proteins which accumulate in other neurodegenerative disorders associated with dementia such as prion proteins and alpha-synuclein are in the early stages of development.

SUMMARY

Dementias in the elderly are an increasing medical, social and economic problem and current treatments are only effective. In the majority of dementias, proteins accumulate within cells and in the extracellular compartments of the brain. In the most common dementia, Alzheimer's disease, amyloid-beta accumulates as plaques in the extracellular space of the grey matter and in artery walls as cerebral amyloid angiopathy and tau protein accumulates as neurofibrillary tangles within neurons.

Refining an Alzheimer’s vaccine to avoid an inflammatory response

The utility of vaccine strategies to treat neurodegenerative diseases such as Alzheimer's disease may still hold promise. Phase IIa clinical trials were halted due to a small but significant occurrence of meningoencephalitis. Knowledge gained from studies on amyloid-beta peptide (Abeta) immunotherapy will allow optimisation 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 Abeta, one that might have attenuated immune responses with robust disease-altering activity.

Transgenic potato expressing Aβ reduce Aβ burden in Alzheimer's disease mouse model

Beta amyloid (Abeta) is believed one of the major pathogens of Alzheimer's disease (AD), and the reduction of Abeta is considered a primary therapeutic target. Immunization with Abeta can reduce Abeta burden and pathological features in transgenic AD model mice. Transgenic potato plants were made using genes encoding 5 tandem repeats of Abeta1-42 peptides with an ER retention signal. Amyloid precursor protein transgenic mice (Tg2576) fed with transgenic potato tubers with adjuvant showed a primary immune response and a partial reduction of Abeta burden in the brain. Thus, Abeta tandem repeats can be expressed in transgenic potato plants to form immunologically functional Abeta, and these potatoes has a potential to be used for the prevention and treatment of AD.

Immune shaping and the development of Alzheimer's disease vaccines

Given the emotional, social, and financial devastation wrought by Alzheimer's disease (AD), it is imperative that effective therapeutics be devised to ameliorate this presently incurable disorder. Vaccine-based approaches have been developed to target and eliminate amyloid beta (Abeta), a key peptide implicated in AD pathogenesis. Preclinical successes in AD mouse models created excitement and impetus for the clinical application of an Abeta-based vaccine. Eliciting immune responses against a self-peptide (that is, a peptide produced by the organism itself), such as Abeta, carries with it the potential to induce autoimmune and inflammatory conditions in the vaccinated individual, a caveat borne out in multiple patients enrolled as part of a recent clinical trial. These clinical adverse events seemingly overshadowed interesting behavioral stabilization and alterations of Abeta burden in these and other vaccinated patients, thus speaking to the potential of immunotherapy for AD. Understanding the mechanisms by which vaccines reduce Abeta burden in AD brain and the types of immune responses raised, as well as developing new modalities of vaccine delivery that facilitate the modulation of elicited immune responses, will undoubtedly lead to a new generation of efficacious Abeta immunotherapeutics with improved safety profiles.

Induction of anti-inflammatory immune response by an adenovirus vector encoding 11 tandem repeats of Abeta1-6: toward safer and effective vaccines against Alzheimer's disease

Induction of an immune response to amyloid beta-protein (Abeta) is effective in treating animal models of Alzheimer's disease. Human clinical trials of vaccination with synthetic Abeta (AN1792), however, were halted due to brain inflammation, presumably induced by T cell-mediated immune responses. We have developed an adenovirus vector as a "possibly safer" vaccine. Here, we show that an adenovirus vector encoding 11 tandem repeats of Abeta1-6 can induce an immune response against amyloid beta-protein. Much higher titers against amyloid beta-protein were observed when an adenovirus vector encoding GM-CSF was co-administered. Immunoglobulin isotyping revealed a predominant IgG1 response, indicating anti-inflammatory Th2 type. Immunohistochemical analysis revealed no inflammation-related pathology in the brain of mice immunized with the adenovirus vector. Induced antibodies strongly reacted with amyloid plaques in the brain, demonstrating functional activity of the antibodies. Thus, the adenovirus vector encoding 11 tandem repeats of Abeta1-6 may be a safer alterative to peptide-based vaccines.

Alzheimer's disease-like neuropathology of gene-targeted APP-SLxPS1mut mice expressing the amyloid precursor protein at endogenous levels

Most transgenic mice used for preclinical evaluation of potential disease-modifying treatments of Alzheimer's disease develop major histopathological features of this disease by several-fold overexpression of the human amyloid precursor protein. We studied the phenotype of three different strains of gene-targeted mice which express the amyloid precursor protein at endogenous levels. Only further crossing with transgenic mice overexpressing mutant human presenilin1 led to the deposition of extracellular amyloid, accompanied by the deposition of apolipoprotein E, an astrocyte and microglia reaction, and the occurrence of dilated cholinergic terminals in the cortex. Features of neurodegeneration, however, were absent. The pattern of plaque development and deposition in these mice was similar to that of amyloid precursor protein overproducing strains if crossed to presenilin1-transgenics. However, plaque development started much later and developed slowly until the age of 18 months but then increased more rapidly.

Translational research on the way to effective therapy for Alzheimer disease

CONTEXT

Alzheimer disease (AD) is a major public health issue with a prediction of 12 million Americans being affected by 2025 from the present 4 million. Molecular and genetic findings have provided significant insights into the roles that amyloid, tau, and apolipoprotein E isoforms have in the causation of AD. A central issue in AD pathogenesis is the amyloid cascade hypothesis. It states that abnormal amyloid processing and accumulation is the primary causative factor of AD and other associated neuropathologic abnormalities are of secondary consequence. It is presented to provide the rationale for novel drug and vaccination therapeutic strategies. Future research directed at prediction and prevention of AD through a genomic and proteomic analysis with identification of multiple polymorphic genes that interact, resulting in increased risk for late-onset AD, are the realistic and ultimate goals. A new approach for drug development is required, one that will emphasize a genomic and proteomic analysis to identify at-risk gene sets whose genetic expression is sufficient to cause late onset, sporadic AD. Prediction and prevention of disease prior to clinical signs and symptoms are the goals.

OBJECTIVE

A review and analysis from electronic literature databases and subsequent reference searches of the molecular genetic data. including pertinent genetic mutations and abnormal biochemical findings causal of AD, are cited. The amyloid cascade hypothesis, the contributions of apolipoprotein E, and hyperphosphorylated tau are discussed as to their roles in pathogenesis. Molecular targets for potential drug and vaccination therapies are cited from a critical assessment of the molecular and biomedical data. These data form the basis for rational, target-specific drug and vaccination therapies currently employed and planned for the near future. Phase 2 and 3 clinical trial results of drug and vaccination therapies are cited.

CONCLUSIONS

A new approach is needed as current pharmacologic therapy directed at symptomatic relief has proved to be marginally effective. The genomic and proteomic basis of AD will be defined in the near future, and corresponding molecular therapeutic targets will be identified. Genomic neurology has arrived and its application to resolving AD is our best hope.

Early changes in Aβ levels in the brain of APPswe transgenic mice—Implication on synaptic density, α7 neuronal nicotinic acetylcholine- and N-methyl-d-aspartate receptor levels

Tg 2576 (APPswe) mice develop age-related amyloid deposition as well as behavioural- and electrophysiological changes in the brain. In this study, APPswe mice were investigated from 7 to 90 days of age. We observed high Abeta levels in the cortex of APPswe mice at 7 days of age, suggesting that these mice produce Abeta from birth. A positive correlation between Abeta and synaptophysin levels, followed by changes in ERK MAPK activity, indicated that Abeta causes altered synaptic function and an increase in the number of synaptic terminals. In addition, alterations in [(125)I]alphabungarotoxin- and [(3)H]MK-801 binding sites were also observed in APPswe mice compared to controls. In conclusion, over-expression of Abeta early in life causes changes in synaptophysin levels and number of [(125)I]alphabungarotoxin- and [(3)H]MK-801 binding sites. The results may provide important information about the onset and consequences of Abeta pathology in this transgenic mouse model.

Aberrant accentuation of neurofibrillary degeneration in the hippocampus of Alzheimer's disease with amyloid precursor protein 717 and presenilin-1 gene mutations

This study reports correlation of the hippocampal neurofibrillary tangles (NFT) density with beta-amyloid (Abeta) precursor protein (APP) 717 mutation, presenilin (PS)-1 mutation and apolipoprotein E (Apo-E) e4 alleles (E4), being graded as 3 forms (no-E4, one-E4 and two-E4) in autopsied brains from patients with familial and non-familial Alzheimer's disease (AD). We studied the density of NFT-free neurons, intracellular NFT (I-NFT), extracellular NFT (E-NFT) and total NFT (I-NFT plus E-NFT) in the six hippocampal subdivisions: cornu ammonis (CA) 1-CA4, subiculum and entorhinal cortex. The APP mutation cases showed significantly higher total NFT density in the CA1-CA2 region, and the PS-1 mutation cases also showed higher density of total NFT in the CA1-CA3 than non-familial cases. Moreover, high densities of the E-NFT contributed to these high total NFT densities. Non-familial AD cases showed a stereotypical NFT distribution with entorhinal accentuation in the hippocampus irrespective of E4 frequency. Thus, APP and PS-1 mutations predominantly affect the CA regions with profound neurodegeneration, which contributes early and severe clinical features of familial AD.