Anti-amyloid beta to tau - based immunization: Developments in immunotherapy for Alzheimer disease

DNA Aβ42 immunization via needle-less Jet injection in mice and rabbits as potential immunotherapy for Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia found in the elderly and disease progression is associated with accumulation of Amyloid beta 1-42 (Aβ42) in brain. An immune-mediated approach as a preventive intervention to reduce amyloid plaques without causing brain inflammation is highly desirable for future clinical use. Genetic immunization, in which the immunizing agent is DNA encoding Aβ42, has great potential because the immune response to DNA delivered into the skin is generally non-inflammatory, and thus differs quantitatively and qualitatively from immune responses elicited by peptides, which are inflammatory with production of IFNγ and IL-17 cytokines by activated T cells. DNA immunization has historically been proven difficult to apply to larger mammals. A potential barrier to use DNA immunization in large mammals is the method for delivery of the DNA antigen. We tested jet injection in mice and rabbits and found good antibody production and safe immune responses (no inflammatory cytokines). We found significant reduction of amyloid plaques and Aβ peptides in brains of the DNA Aβ42 immunized 3xTg-AD mouse model. This study was designed to optimize DNA delivery for possible testing of the DNA Aβ42 vaccine for AD prevention in a clinical trial.

The Protective A673T Mutation of Amyloid Precursor Protein (APP) in Alzheimer's Disease

Alzheimer's disease is a progressive neurodegenerative disorder characterized by extracellular amyloid beta peptides and neurofibrillary tangles consisted of intracellular hyperphosphorylated Tau in the hippocampus and cerebral cortex. Most of the mutations in key genes that code for amyloid precursor protein can lead to significant accumulation of these peptides in the brain and cause Alzheimer's disease. Moreover, some point mutations in amyloid precursor protein can cause familial Alzheimer's disease, such as Swedish mutation (KM670/671NL) and A673V mutation. However, recent studies have found that the A673T mutation in amyloid precursor protein gene can protect against Alzheimer's disease, even if it is located next to the Swedish mutation (KM670/671NL) and at the same site as A673V mutation, which are pathogenic. It makes us curious about the protective A673T mutation. Here, we summarize the most recent insights of A673T mutation, focus on their roles in protective mechanisms against Alzheimer's disease, and discuss their involvement in future treatment.

Exploring new avenues for modifying course of progression of Alzheimer's disease: The rise of natural medicine

With a constantly growing elderly population worldwide, a focus on developing efficient prevention and therapy for Alzheimer's disease (AD) seems timely and topical. Emphasis on natural medicine is increasingly popular in the search for drug candidates that are capable of preventing and treating AD related pathology, particularly where suppression of amyloid accumulation, neurofibrillary tangle formation, neuroinflammation and oxidative stress are equally significant. A number of phytochemical compounds have been shown to collectively reduce these AD hallmarks with the progression of natural drug candidates into human clinical trials. This review focuses on current research surrounding the therapies emerging within natural medicines and their related therapeutic potential for AD treatment.

Passive immunotherapy for N-truncated tau ameliorates the cognitive deficits in two mouse Alzheimer's disease models

Clinical and neuropathological studies have shown that tau pathology better correlates with the severity of dementia than amyloid plaque burden, making tau an attractive target for the cure of Alzheimer's disease. We have explored whether passive immunization with the 12A12 monoclonal antibody (26-36aa of tau protein) could improve the Alzheimer's disease phenotype of two well-established mouse models, Tg2576 and 3xTg mice. 12A12 is a cleavage-specific monoclonal antibody which selectively binds the pathologically relevant neurotoxic NH226-230 fragment (i.e. NH2htau) of tau protein without cross-reacting with its full-length physiological form(s). We found out that intravenous administration of 12A12 monoclonal antibody into symptomatic (6 months old) animals: (i) reaches the hippocampus in its biologically active (antigen-binding competent) form and successfully neutralizes its target; (ii) reduces both pathological tau and amyloid precursor protein/amyloidβ metabolisms involved in early disease-associated synaptic deterioration; (iii) improves episodic-like type of learning/memory skills in hippocampal-based novel object recognition and object place recognition behavioural tasks; (iv) restores the specific up-regulation of the activity-regulated cytoskeleton-associated protein involved in consolidation of experience-dependent synaptic plasticity; (v) relieves the loss of dendritic spine connectivity in pyramidal hippocampal CA1 neurons; (vi) rescues the Alzheimer's disease-related electrophysiological deficits in hippocampal long-term potentiation at the CA3-CA1 synapses; and (vii) mitigates the neuroinflammatory response (reactive gliosis). These findings indicate that the 20-22 kDa NH2-terminal tau fragment is crucial target for Alzheimer's disease therapy and prospect immunotherapy with 12A12 monoclonal antibody as safe (normal tau-preserving), beneficial approach in contrasting the early Amyloidβ-dependent and independent neuropathological and cognitive alterations in affected subjects.

Have there been improvements in Alzheimer's disease drug discovery over the past 5 years?

INTRODUCTION

Alzheimer's disease (AD) is the most important neurodegenerative disorder with a global cost worldwide of over $700 billion. Pharmacological treatment accounts for 10-20% of direct costs; no new drugs have been approved during the past 15 years; and the available medications are not cost-effective. Areas covered: A massive scrutiny of AD-related PubMed publications (ps)(2013-2017) identified 42,053ps of which 8,380 (19.60%) were associated with AD treatments. The most prevalent pharmacological categories included neurotransmitter enhancers (11.38%), multi-target drugs (2.45%), anti-Amyloid agents (13.30%), anti-Tau agents (2.03%), natural products and derivatives (25.58%), novel drugs (8.13%), novel targets (5.66%), other (old) drugs (11.77%), anti-inflammatory drugs (1.20%), neuroprotective peptides (1.25%), stem cell therapy (1.85%), nanocarriers/nanotherapeutics (1.52%), and others (<1% each). Expert opinion: Unsuccessful outcomes in AD therapeutics are attributed to pathogenic misconceptions, erratic procedures in drug development and inappropriate regulations. Recommendations for the future are as follows: (i) the reconsideration of dominant pathogenic theories, (ii) the identification of reliable biomarkers, (iii) the redefinition of diagnostic criteria, (iv) new guidelines for disease management, (v) the reorientation of drug discovery programs, (vi) the updating of regulatory requirements, (vii) the introduction of pharmacogenomics in drug development and personalized treatments, and (viii) the implementation of preventive programs.

Prospects for strain-specific immunotherapy in Alzheimer's disease and tauopathies

With increasing age, as the incidence of Alzheimer's disease is increasing, finding a therapeutic intervention is becoming critically important to either prevent or slow down the progression of the disease. Passive immunotherapy has been demonstrated as a successful way of reducing large aggregates and improving cognition in animal models of both tauopathies and Alzheimer's disease. However, with all the continuous attempts and significant success of immunotherapy in preclinical studies, finding a successful clinical therapy has been a great challenge, possibly indicating a lack of accuracy in targeting the toxic species. Both active and passive immunotherapy approaches in transgenic animals have been demonstrated to have pros and cons. Passive immunotherapy has been favored and many mechanisms have been shown to clear toxic amyloid and tau aggregates and improve memory. These mechanisms may differ depending on the antibodie's' target and administration route. In this regard, deciding on affinity vs. specificity of the antibodies plays a significant role in terms of avoiding the clearance of the physiological forms of the targeted proteins and reducing adverse side effects. In addition, knowing that a single protein can exist in different conformational states, termed as strains, with varying degrees of neurotoxicity and seeding properties, presents an additional level of complexity. Therefore, immunotherapy targeting specifically the toxic strains will aid in developing potential strategies for intervention. Moreover, an approach of combinatorial immunotherapies against different amyloidogenic proteins, at distinct levels of the disease progression, might offer an effective therapy in many neurodegenerative diseases.

Friend or foe: the dichotomous impact of T cells on neuro-de/re-generation during aging

The interaction between T cells and the central nervous system (CNS) in homeostasis and injury has been recognized being both pathogenic (CD4⁺ T-helper 1 - Th1, Th17 and γδT) and ameliorative (Th2 and regulatory T cells - Tregs). However, in-depth studies aimed to elucidate the precise in the aged microenvironment and the dichotomous role of Tregs have just begun and many aspects remain unclear. This is due, not only to a mutual dependency and reciprocal causation of alterations and diseases between the nervous and T cell immune systems, but also to an inconsistent aging of the two systems, which dynamically changes with CNS injury/recovery and/or aging process. Cellular immune system aging, particularly immunosenescence and T cell aging initiated by thymic involution - sources of chronic inflammation in the elderly (termed inflammaging), potentially induces an acceleration of brain aging and memory loss. In turn, aging of the brain via neuro-endocrine-immune network drives total body systemic aging, including that of the immune system. Therefore, immunotherapeutics including vaccination and “protective autoimmunity” provide promising means to rejuvenate neuro-inflammatory disorders and repair CNS acute injury and chronic neuro-degeneration. We review the current understanding and recent discoveries linking the aging immune system with CNS injury and neuro-degeneration. Additionally, we discuss potential recovery and rejuvenation strategies, focusing on targeting the aging T cell immune system in an effort to alleviate acute brain injury and chronic neuro-degeneration during aging, via the “thymus-inflammaging-neurodegeneration axis”.

Alzheimer's Disease: Characterization of the Brain Sites of the Initial Tau Cytoskeletal Pathology Will Improve the Success of Novel Immunological Anti-Tau Treatment Approaches

Alzheimer's disease (AD) represents the most frequent neurodegenerative disease of the human brain worldwide. Currently practiced treatment strategies for AD only include some less effective symptomatic therapeutic interventions, which unable to counteract the disease course of AD. New therapeutic attempts aimed to prevent, reduce, or remove the extracellular depositions of the amyloid-β protein did not elicit beneficial effects on cognitive deficits or functional decline of AD. In view of the failure of these amyloid-β-based therapeutic trials and the close correlation between the brain pathology of the cytoskeletal tau protein and clinical AD symptoms, therapeutic attention has since shifted to the tau cytoskeletal protein as a novel drug target. The abnormal hyperphosphorylation and intraneuronal aggregation of this protein are early events in the evolution of the AD-related neurofibrillary pathology, and the brain spread of the AD-related tau aggregation pathology may possibly follow a corruptive protein templating and seeding-like mechanism according to the prion hypothesis. Accordingly, immunotherapeutic targeting of the tau aggregation pathology during the very early pre-tangle phase is currently considered to represent an effective and promising therapeutic approach for AD. Recent studies have shown that the initial immunoreactive tau aggregation pathology already prevails in several subcortical regions in the absence of any cytoskeletal changes in the cerebral cortex. Thus, it may be hypothesized that the subcortical brain regions represent the "port of entry" for the pathogenetic agent from which the disease ascends anterogradely as an "interconnectivity pathology".

Genomics of Alzheimer Disease: A Review

IMPORTANCE

To provide a comprehensive review of knowledge of the genomics of Alzheimer disease (AD) and DNA amyloid β 42 (Aβ42) vaccination as a potential therapy.

OBSERVATIONS

Genotype-phenotype correlations of AD are presented to provide a comprehensive appreciation of the spectrum of disease causation. Alzheimer disease is caused in part by the overproduction and lack of clearance of Aβ protein. Oligomer Aβ, the most toxic species of Aβ, causes direct injury to neurons, accompanied by enhanced neuroinflammation, astrocytosis and gliosis, and eventually neuronal loss. The strongest genetic evidence supporting this hypothesis derives from mutations in the amyloid precursor protein (APP) gene. A detrimental APP mutation at the β-secretase cleavage site linked to early-onset AD found in a Swedish pedigree enhances Aβ production, in contrast to a beneficial mutation 2 residues away in APP that reduces Aβ production and protects against the onset of sporadic AD. A number of common variants associated with late-onset AD have been identified including apolipoprotein E, BIN1, ABC7, PICALM, MS4A4E/MS4A6A, CD2Ap, CD33, EPHA1, CLU, CR1, and SORL1. One or 2 copies of the apolipoprotein E ε4 allele are a major risk factor for late-onset AD. With DNA Aβ42 vaccination, a Th2-type noninflammatory immune response was achieved with a downregulation of Aβ42-specific effector (Th1, Th17, and Th2) cell responses at later immunization times. DNA Aβ42 vaccination upregulated T regulator cells (CD4+, CD25+, and FoxP3+) and its cytokine interleukin 10, resulting in downregulation of T effectors.

CONCLUSIONS AND RELEVANCE

Mutations in APP and PS-1 and PS-2 genes that are associated with early-onset, autosomal, dominantly inherited AD, in addition to the at-risk gene polymorphisms responsible for late-onset AD, all indicate a direct and early role of Aβ in the pathogenesis of AD. A translational result of genomic research has been Aβ-reducing therapies including DNA Aβ42 vaccination as a promising approach to delay or prevent this disease.

ACAID as a potential therapeutic approach to modulate inflammation in neurodegenerative diseases

The progressive loss of neurons and inflammation characterizes neurodegenerative diseases. Although the etiology, progression and outcome of different neurodegenerative diseases are varied, they share chronic inflammation maintained largely by central nervous system (CNS)-derived antigens recognized by T cells. Inflammation can be beneficial by recruiting immune cells to kill pathogens or to clear cell debris resulting from the primary insult. However, chronic inflammation exacerbates and perpetuates tissue damage. An increasing number of therapies that attempt to modulate neuroinflammation have been developed. However, so far none has succeeded in decreasing the secondary damage associated with chronic inflammation. A potential strategy to modulate the immune system is related to the induction of tolerance to CNS antigens. In this line, it is our hypothesis that this could be accomplished by using anterior chamber associated immune deviation (ACAID) as a strategy. Thus, we review current knowledge regarding some neurodegenerative diseases and the associated immune response that causes inflammation. In addition, we discuss further our hypothesis of the possible usefulness of ACAID as a therapeutic strategy to ameliorate damage to the CNS.

Dementias

This chapter will focus on the descriptive, analytic, and intervention-oriented epidemiology of dementia and its most frequent etiologic type due to Alzheimer's disease. The chapter opens with a brief presentation of the concept of dementia, followed by the presentation of dementia of the Alzheimer type (DAT), including natural history, clinical manifestation, neuropathology, medical prognosis, and management. Further, the chapter presents the prevalence and incidence of dementia, with special consideration of secular trends in prevalence and incidence of DAT, and prognosis of the socioeconomic impact of dementia. Thereafter the main risk factors for DAT are covered. The chapter also addresses the results of ongoing therapeutic and preventive intervention trials for DAT. Finally, the future challenges of the epidemiology of dementia with a focus on the impact of the new diagnostic criteria for neurocognitive disorders, as well as the development of biomarkers for DAT and other types of dementia, will be briefly discussed.

Anti-dementia medications: current prescriptions in clinical practice and new agents in progress

Almost three decades after the publication of the first clinical studies with tacrine, the pharmacological treatment of Alzheimer's disease (AD) remains a challenge. Randomized clinical trials have yielded evidence of significant - although modest and transient - benefit from cholinergic replacement therapy for people diagnosed with AD, and disease modification with antidementia compounds is still an urgent, unmet need. The natural history of AD is very long, and its pharmacological treatment must acknowledge different needs according to the stage of the disease process. Cognitive and functional deterioration evolves gradually since the onset of clinical symptoms, which may be preceded by several years or perhaps decades of silent, presymptomatic neurodegeneration. Therefore, the pharmacological treatment of AD must ideally comprise both a symptomatic effect to preserve or improve cognition and a disease-modifying effect to tackle the progression of the pathological process. Primary prevention is the ultimate goal, should these strategies be delivered to patients with preclinical AD. In this article, we briefly address the pharmaceutical compounds that are currently used for the symptomatic treatment of AD and discuss the ongoing strategies designed to modify its natural course.

Alzheimer's disease vaccine development: A new strategy focusing on immune modulation

Despite significant advances in the development of Alzheimer's disease (AD) vaccines effective in animal models, these prototypes have been clinically unsuccessful; apparently the result of using immunogens modified to prevent inflammation. Hence, a new paradigm is needed that uses entire AD-associated immunogens, a notion supported by recent successful passive immunotherapy results, with adjuvants that induce Th2-only while inhibiting without abrogating Th1 immunity. Here, we discuss the obstacles to AD vaccine development and Th2-adjuvants that by acting on dendritic and T cells, would elicit regardless of the antigen a safe and effective antibody response, while preventing damaging neuroinflammation and ameliorating immunosenescence.

T Cells-Protective or Pathogenic in Alzheimer's Disease?

Alzheimer's disease (AD) is the most common cause of dementia, and is characterised by deposits of amyloid β (Aβ), neurofibrillary tangles and neuronal loss. Neuroinflammatory changes have been identified as a feature of the disease, and recent studies have suggested a potential role for the peripheral immune system in driving these changes and, ultimately, the associated neuronal degeneration. A number of reports have detailed changes in the activation state and subtype of T cells in the circulation and CSF of AD patients and there is evidence of T cell infiltration into the brain. In this review, we examine the possible impact of T cell infiltration in the progression of pathology in AD and consider the data obtained from animal models of the disease. We consider how these cells infiltrate the brain, particularly in AD, and discuss whether the presence of T cells in the AD brain is protective or pathogenic. Finally we evaluate the current therapies, particularly those that involve immunization.

APOE-modulated Aβ-induced neuroinflammation in Alzheimer's disease: current landscape, novel data, and future perspective

Chronic glial activation and neuroinflammation induced by the amyloid-β peptide (Aβ) contribute to Alzheimer's disease (AD) pathology. APOE4 is the greatest AD-genetic risk factor; increasing risk up to 12-fold compared to APOE3, with APOE4-specific neuroinflammation an important component of this risk. This editorial review discusses the role of APOE in inflammation and AD, via a literature review, presentation of novel data on Aβ-induced neuroinflammation, and discussion of future research directions. The complexity of chronic neuroinflammation, including multiple detrimental and beneficial effects occurring in a temporal and cell-specific manner, has resulted in conflicting functional data for virtually every inflammatory mediator. Defining a neuroinflammatory phenotype (NIP) is one way to address this issue, focusing on profiling the changes in inflammatory mediator expression during disease progression. Although many studies have shown that APOE4 induces a detrimental NIP in peripheral inflammation and Aβ-independent neuroinflammation, data for APOE-modulated Aβ-induced neuroinflammation are surprisingly limited. We present data supporting the hypothesis that impaired apoE4 function modulates Aβ-induced effects on inflammatory receptor signaling, including amplification of detrimental (toll-like receptor 4-p38α) and suppression of beneficial (IL-4R-nuclear receptor) pathways. To ultimately develop APOE genotype-specific therapeutics, it is critical that future studies define the dynamic NIP profile and pathways that underlie APOE-modulated chronic neuroinflammation. In this editorial review, we present data supporting the hypothesis that impaired apoE4 function modulates Aβ-induced effects on inflammatory receptor signaling, including amplification of detrimental (TLR4-p38α) and suppression of beneficial (IL-4R-nuclear receptor) pathways, resulting in an adverse NIP that causes neuronal dysfunction. NIP, Neuroinflammatory phenotype; P.I., pro-inflammatory; A.I., anti-inflammatory.

A noninflammatory immune response in aged DNA Aβ42-immunized mice supports its safety for possible use as immunotherapy in AD patients

Aging in the immune system results in tendency to proinflammatory responses. Intradermal DNA immunization showed Th2 polarized noninflammatory immune responses. We tested here 18-month-old mice which were immunized with Aβ42 peptide, DNA Aβ42 trimer, or 2 different prime boost protocols identical to previous experiments. High Aβ42 antibody levels were found in aged mice which had received peptide immunizations (900 μg/mL plasma), and in mice which had received peptide prime and DNA boost immunizations (500 μg/mL), compared with antibodies in DNA Aβ42 immunized mice with 50 μg/mL. Although we found T-cell proliferation and inflammatory cytokines in mice which had received peptide or prime boost immunization, these were not found in DNA-immunized mice. The results are concordant with proinflammatory responses because of immunosenescence and contraindicate the use of Aβ42 peptide immunizations or prime boost immunization protocols for the use in elderly Alzheimer's disease patients. DNA Aβ42 immunization only on the other hand does lead to effective levels of antibodies without inflammatory cytokine or T-cell responses in the aged animal model tested.

Passive immunization targeting the N-terminal projection domain of tau decreases tau pathology and improves cognition in a transgenic mouse model of Alzheimer disease and tauopathies

Intraneuronal accumulation of abnormally hyperphosphorylated tau in the brain is a histopathological hallmark of Alzheimer's disease and a family of related neurodegenerative disorders collectively called tauopathies. At present there is no effective treatment available for these progressive neurodegenerative diseases which are clinically characterized by dementia in mid to old-age. Here we report the treatment of 14-17-months-old 3xTg-AD mice with tau antibodies 43D (tau 6-18) and 77E9 (tau 184-195) to the N-terminal projection domain of tau or mouse IgG as a control by intraperitoneal injection once a week for 4 weeks, and the effects of the passive immunization on reduction of hyperphosphorylated tau, Aβ accumulation and cognitive performance in these animals. We found that treatment with tau antibodies 43D and 77E9 reduced total tau level, decreased tau hyperphosphorylated at Ser199, Ser202/Thr205 (AT8), Thr205, Ser262/356 (12E8), and Ser396/404 (PHF-1) sites, and a trend to reduce Aβ pathology. Most importantly, targeting N-terminal tau especially by 43D (tau 6-18) improved reference memory in the Morris water maze task in 3xTg-AD mice. We did not observe any abnormality in general physical characteristics of the treated animals with either of the two antibodies during the course of this study. Taken together, our studies demonstrate for the first time (1) that passive immunization targeting normal tau can effectively clear the hyperphosphorylated protein and possibly reduce Aβ pathology from the brain and (2) that targeting N-terminal projection domain of tau containing amino acid 6-18 is especially beneficial. Thus, targeting selective epitopes of N-terminal domain of tau may present a novel effective therapeutic opportunity for Alzheimer disease and other tauopathies.

Sporadic inclusion-body myositis: A degenerative muscle disease associated with aging, impaired muscle protein homeostasis and abnormal mitophagy

Sporadic inclusion-body myositis (s-IBM) is the most common degenerative muscle disease in which aging appears to be a key risk factor. In this review we focus on several cellular molecular mechanisms responsible for multiprotein aggregation and accumulations within s-IBM muscle fibers, and their possible consequences. Those include mechanisms leading to: a) accumulation in the form of aggregates within the muscle fibers, of several proteins, including amyloid-β42 and its oligomers, and phosphorylated tau in the form of paired helical filaments, and we consider their putative detrimental influence; and b) protein misfolding and aggregation, including evidence of abnormal myoproteostasis, such as increased protein transcription, inadequate protein disposal, and abnormal posttranslational modifications of proteins. Pathogenic importance of our recently demonstrated abnormal mitophagy is also discussed. The intriguing phenotypic similarities between s-IBM muscle fibers and the brains of Alzheimer and Parkinson's disease patients, the two most common neurodegenerative diseases associated with aging, are also discussed. This article is part of a Special Issue entitled: Neuromuscular Diseases: Pathology and Molecular Pathogenesis.