Immunotherapy in Alzheimer's disease: do we have all the pieces of the puzzle?

The path to next-generation disease-modifying immunomodulatory combination therapies in Alzheimer's disease

The cautious optimism following recent anti-amyloid therapeutic trials for Alzheimer's disease (AD) provides a glimmer of hope after years of disappointment. Although these encouraging results represent discernible progress, they also highlight the need to enhance further the still modest clinical efficacy of current disease-modifying immunotherapies. Here, we highlight crucial milestones essential for advancing precision medicine in AD. These include reevaluating the choice of therapeutic targets by considering the key role of both central neuroinflammation and peripheral immunity in disease pathogenesis, refining patient stratification by further defining the inflammatory component within the forthcoming ATN(I) (amyloid, tau and neurodegeneration (and inflammation)) classification of AD biomarkers and defining more accurate clinical outcomes and prognostic biomarkers that better reflect disease heterogeneity. Next-generation immunotherapies will need to go beyond the current antibody-only approach by simultaneously targeting pathological proteins together with innate neuroinflammation and/or peripheral-central immune crosstalk. Such innovative immunomodulatory combination therapy approaches should be evaluated in appropriately redesigned clinical therapeutic trials, which must carefully integrate the neuroimmune component.

Proteomics revealed an association between ribosome-associated proteins and amyloid beta deposition in Alzheimer's disease

Most scholars believe that amyloid-beta (Aβ) has the potential to induce apoptosis, stimulate an inflammatory cascade, promote oxidative stress and exacerbate the pathological progression of Alzheimer's disease (AD). Therefore, it is crucial to investigate the deposition of Aβ in AD. At approximately 6 months of age, APP/PS1 double transgenic mice gradually exhibit the development of plaques, as well as spatial and learning impairment. Notably, the hippocampus is specifically affected in the course of AD. Herein, 6-month-old APP/PS1 double transgenic mice were utilized, and the differentially expressed (DE) proteins in the hippocampus were identified and analyzed using 4D label-free quantitative proteomics technology and parallel reaction monitoring (PRM). Compared to wild-type mice, 29 proteins were upregulated and 25 proteins were downregulated in the AD group. Gene Ontology (GO) enrichment analysis of biological processes (BP) indicated that the DE proteins were mainly involved in 'ribosomal large subunit biogenesis'. Molecular function (MF) analysis results were primarily associated with '5.8S rRNA binding' and 'structural constituent of ribosome'. In terms of cellular components (CC), the DE proteins were mainly found in 'polysomal ribosome', 'cytosolic large ribosomal subunit', 'cytosolic ribosome', and 'large ribosomal subunit', among others. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis demonstrated that the results were mainly enriched in the 'Ribosome signaling pathway'. The key target proteins identified were ribosomal protein (Rp)l18, Rpl17, Rpl19, Rpl24, Rpl35, and Rpl6. The PRM verification results were consistent with the findings of the 4D label-free quantitative proteomics analysis. Overall, these findings suggest that Rpl18, Rpl17, Rpl19, Rpl24, Rpl35, and Rpl6 may have potential therapeutic value for the treatment of AD by targeting Aβ.

Estimating presymptomatic episodic memory impairment using simple hand movement tests: A cross-sectional study of a large sample of older adults

INTRODUCTION

Finding low-cost methods to detect early-stage Alzheimer's disease (AD) is a research priority for neuroprotective drug development. Presymptomatic Alzheimer's is associated with gait impairment but hand motor tests, which are more accessible, have hardly been investigated. This study evaluated how home-based Tasmanian (TAS) Test keyboard tapping tests predict episodic memory performance.

METHODS

1169 community participants (65.8 ± 7.4 years old; 73% female) without cognitive symptoms completed online single-key and alternate-key tapping tests and episodic memory, working memory, and executive function cognitive tests.

RESULTS

All single-key (R2 adj  = 8.8%, ΔAIC = 5.2) and alternate-key (R2 adj  = 9.1%, ΔAIC = 8.8) motor features predicted episodic memory performance relative to demographic and mood confounders only (R2 adj  = 8.1%). No tapping features improved estimation of working memory.

DISCUSSION

Brief self-administered online hand movement tests predict asymptomatic episodic memory impairment. This provides a potential low-cost home-based method for stratification of enriched cohorts.

HIGHLIGHTS

We devised two brief online keyboard tapping tests to assess hand motor function. 1169 cognitively asymptomatic adults completed motor- and cognitive tests online. Impaired hand motor function predicted reduced episodic memory performance. This brief self-administered test may aid stratification of community cohorts.

Ferroptosis, Pyroptosis, and Cuproptosis in Alzheimer's Disease

Alzheimer's disease (AD), the most common type of dementia, is a neurodegenerative disorder characterized by progressive cognitive dysfunction. Epidemiological investigation has demonstrated that, after cardiovascular and cerebrovascular diseases, tumors, and other causes, AD has become a major health issue affecting elderly individuals, with its mortality rate acutely increasing each year. Regulatory cell death is the active and orderly death of genetically determined cells, which is ubiquitous in the development of living organisms and is crucial to the regulation of life homeostasis. With extensive research on regulatory cell death in AD, increasing evidence has revealed that ferroptosis, pyroptosis, and cuproptosis are closely related to the occurrence, development, and prognosis of AD. This paper will review the molecular mechanisms of ferroptosis, pyroptosis, and cuproptosis and their regulatory roles in AD to explore potential therapeutic targets for the treatment of AD.

Oxidative stress induces tau hyperphosphorylation via MARK activation in neuroblastoma N1E-115 cells

Reactive oxygen species are considered a cause of neuronal cell death in Alzheimer's disease (AD). Abnormal tau phosphorylation is a proven pathological hallmark of AD. Microtubule affinity-regulating kinases (MARKs) regulate tau-microtubule binding and play a crucial role in neuronal survival. In this study, we hypothesized that oxidative stress increases the phosphorylation of Ser262 of tau protein through activation of MARKs, which is the main reason for the development of AD. We investigated the relationship between tau hyperphosphorylation on Ser262 and MARKs in N1E-115 cells subjected to oxidative stress by exposure to a low concentration of hydrogen peroxide. This work builds on the observation that hyperphosphorylation of tau is significantly increased by oxidative stress. MARKs activation correlated with tau hyperphosphorylation at Ser262, a site that is essential to maintain microtubule stability and is the initial phosphorylation site in AD. These results indicated that MARKs inhibitors might serve a role as therapeutic tools for the treatment of AD.

Immunotherapy for Alzheimer's disease: targeting β-amyloid and beyond

Alzheimer's disease (AD) is the most common neurodegenerative disease in the elderly worldwide. However, the complexity of AD pathogenesis leads to discrepancies in the understanding of this disease, and may be the main reason for the failure of AD drug development. Fortunately, many ongoing preclinical and clinical studies will continually open up avenues to unravel disease mechanisms and guide strategies for AD diagnosis and drug development. For example, immunotherapeutic strategies targeting amyloid-β (Aβ) and tau proteins were once deemed almost certainly effective in clinical treatment due to the excellent preclinical results. However, the repeated failures of clinical trials on vaccines and humanized anti-Aβ and anti-tau monoclonal antibodies have resulted in doubts on this strategy. Recently, a new anti-Aβ monoclonal antibody (Aducanumab) has been approved by the US Food and Drug Administration, which brings us back to the realization that immunotherapy strategies targeting Aβ may be still promising. Meanwhile, immunotherapies based on other targets such as tau, microglia and gut-brain axis are also under development. Further research is still needed to clarify the forms and epitopes of targeted proteins to improve the accuracy and effectiveness of immunotherapeutic drugs. In this review, we focus on the immunotherapies based on Aβ, tau and microglia and their mechanisms of action in AD. In addition, we present up-to-date advances and future perspectives on immunotherapeutic strategies for AD.

Aducanumab and Its Effects on Tau Pathology: Is This the Turning Point of Amyloid Hypothesis?

Alzheimer's disease (AD) is a neurodegenerative disorder affecting millions of people around the world. The two main pathological mechanisms underlying the disease are beta-amyloid (Aβ) plaques and intracellular neurofibrillary tangles (NFTs) of Tau proteins in the brain. Their reduction has been associated with slowing of cognitive decline and disease progression. Several antibodies aimed to target Aβ or Tau in order to represent hope for millions of patients, but only a small number managed to be selected to participate in clinical trials. Aducanumab is a monoclonal antibody recently approved by the Food and Drug Administration (FDA), which, targeting (Aβ) oligomers and fibrils, was able to reduce Aβ accumulation and slow the progression of cognitive impairment. It was also claimed to have an effect on the second hallmark of AD, decreasing the level of phospho-Tau evaluated in cerebrospinal fluid (CSF) and by positron emission tomography (PET). This evidence may represent a turning point in the development of AD-efficient drugs.

Immunization with Aβ3-10-KLH vaccine improves cognitive function and ameliorates mitochondrial dysfunction and reduces Alzheimer's disease-like pathology in Tg-APPswe/PSEN1dE9 mice

Alzheimer's disease is a common cause of dementia, for which no disease-modifying therapy is yet available. Aβ3-10-KLH, a vaccine for active immunization, has been shown to prevent pathological changes in young transgenic models of AD, but the effects of treatment with it and its effects on mitochondrial dysfunction remain unclear. We immunized 6-month-old Tg-APPswe/PSEN1dE9 mice with Aβ3-10-KLH to analyze whether it is capable of eliminating amyloid-β after its appearance. The vaccine effectively decreased amyloid-β deposits, improved cognitive function and ameliorated mitochondrial dysfunction. These results indicate the potential of Aβ3-10-KLH as a vaccine to treat AD.

Profiles of Cognitive Change in Preclinical and Prodromal Alzheimer's Disease Using Change-Point Analysis

BACKGROUND

Alzheimer's disease (AD) is now understood to have a long preclinical phase in which pathology starts to accumulate in the absence of clinical symptoms. Identifying the temporal stages of accelerated cognitive decline in this phase may help in developing more sensitive neuropsychological tools for early screening of preclinical cognitive decline. Change-point analyses are increasingly used to characterize the temporal stages of accelerated cognitive decline in the preclinical stages of AD. However, statistical comparisons of change-points between specific cognitive measures have not been reported.

OBJECTIVE

To characterize and compare the temporal stages of accelerated decline in performance on multiple cognitive tests in a sample of participants from the Baltimore Longitudinal Study on Aging (BLSA) who later developed AD.

METHODS

165 older adults (baseline age range: 61.1-91.2) from the BLSA developed AD during follow-up. Linear and non-linear mixed models were fit for 11 cognitive measures to determine change-points in rates of decline before AD diagnosis. Bootstrapping was used to compare the timing of change-points across cognitive measures.

RESULTS

Change-points followed by accelerated decline ranged from 15.5 years (Standard Error (S.E.) = 1.72) for Card Rotations to 1.9 years (S.E. = 0.68) for the Trail-Making Test Part A before AD diagnosis. Accelerated decline in Card Rotations occurred significantly earlier than all other measures, including learning and memory measures.

CONCLUSION

Results suggest that visuospatial ability, as assessed by Card Rotations, may have the greatest utility as an early predictive tool in identifying preclinical AD.

Early diagnosis and treatment of Alzheimer's disease: new definitions and challenges

The prevalence of Alzheimer's disease (AD), a progressive neurodegenerative disorder, is expected to more than double by 2050. Studies on the pathophysiology of AD have been changing our understanding of this disorder and setting a new scenario for drug development and other therapies. Concepts like the "amyloid cascade" and the "continuum of AD," discussed in this article, are now well established. From updated classifications and recommendations to advances in biomarkers of AD, we aim to critically assess the literature on AD, addressing new definitions and challenges that emerged from recent studies on the subject. Updates on the status of major clinical trials are also given, and future perspectives are discussed.

Current and emerging avenues for Alzheimer's disease drug targets

Alzheimer's disease (AD), the most frequent cause of dementia, is escalating as a global epidemic, and so far, there is neither cure nor treatment to alter its progression. The most important feature of the disease is neuronal death and loss of cognitive functions, caused probably from several pathological processes in the brain. The main neuropathological features of AD are widely described as amyloid beta (Aβ) plaques and neurofibrillary tangles of the aggregated protein tau, which contribute to the disease. Nevertheless, AD brains suffer from a variety of alterations in function, such as energy metabolism, inflammation and synaptic activity. The latest decades have seen an explosion of genes and molecules that can be employed as targets aiming to improve brain physiology, which can result in preventive strategies for AD. Moreover, therapeutics using these targets can help AD brains to sustain function during the development of AD pathology. Here, we review broadly recent information for potential targets that can modify AD through diverse pharmacological and nonpharmacological approaches including gene therapy. We propose that AD could be tackled not only using combination therapies including Aβ and tau, but also considering insulin and cholesterol metabolism, vascular function, synaptic plasticity, epigenetics, neurovascular junction and blood-brain barrier targets that have been studied recently. We also make a case for the role of gut microbiota in AD. Our hope is to promote the continuing research of diverse targets affecting AD and promote diverse targeting as a near-future strategy.

Vascular Dysfunction in Alzheimer's Disease: A Prelude to the Pathological Process or a Consequence of It?

Alzheimer's disease (AD) is the most prevalent form of dementia. Despite decades of research following several theoretical and clinical lines, all existing treatments for the disorder are purely symptomatic. AD research has traditionally been focused on neuronal and glial dysfunction. Although there is a wealth of evidence pointing to a significant vascular component in the disease, this angle has been relatively poorly explored. In this review, we consider the various aspects of vascular dysfunction in AD, which has a significant impact on brain metabolism and homeostasis and the clearance of β-amyloid and other toxic metabolites. This may potentially precede the onset of the hallmark pathophysiological and cognitive symptoms of the disease. Pathological changes in vessel haemodynamics, angiogenesis, vascular cell function, vascular coverage, blood-brain barrier permeability and immune cell migration may be related to amyloid toxicity, oxidative stress and apolipoprotein E (APOE) genotype. These vascular deficits may in turn contribute to parenchymal amyloid deposition, neurotoxicity, glial activation and metabolic dysfunction in multiple cell types. A vicious feedback cycle ensues, with progressively worsening neuronal and vascular pathology through the course of the disease. Thus, a better appreciation for the importance of vascular dysfunction in AD may open new avenues for research and therapy.

Early Aβ-HBc virus-like particles immunization had better effects on preventing the deficit of learning and memory abilities and reducing cerebral Aβ load in PDAPP mice

For nearly two decades, immunization against the β-amyloid peptide (Aβ) has been investigated as a potential treatment for Alzheimer's disease (AD). Despite some disappointing results in clinic trials, greater significance has been attached by some researchers to exploring the immune effects on pathological and cognitive changes in AD or producing new vaccines of AD. In the previous study, we have made a virus-like particles (Aβ-HBc VLPs) as Aβ vaccine candidate. Aβ-HBc VLPs could ameliorate the learning and memory abilities and reduce cerebral Aβ deposit in the old PDAPP mice. In the present study, to observe the preventive effect and the proper time of immunization, 3, 6 and 9-month old PDAPP mice were immunized with Aβ-HBc VLPs for 3 months. All mice generated high titer of anti-Aβ antibody after Aβ-HBc VLPs immunizations. When the mice were 15-month old, Morris Water Maze was used to test their learning and memory abilities. The escape latencies of Aβ-HBc VLPs immunized mice were shorter than that of control mice. These immunized mice entered platform region frequently and spent more time on the platform region and quadrant. 3 m and 6 m Aβ-HBc VLPs immunized groups performed better than the 9 m group. In immunohistochemistry tests, all the Aβ-HBc VLPs immunized mice had less amyloid deposit in cortex and hippocampus. ELISA results showed that soluble Aβ was reduced in the brain homogenates of the Aβ-HBc VLPs immunized mice, and 3- and 6-month groups had less soluble Aβ than the 9-month group. In conclusion, our study showed that Aβ-HBc VLPs immunization could elicit a strong immune response in adult APP mice, and early immunization had better effects on preventing learning and memory deficits, lowering Aβ burden in PDAPP mice.

Anti-Amyloid-β Monoclonal Antibodies for Alzheimer's Disease: Pitfalls and Promise

The majority of putative disease-modifying treatments in development for Alzheimer's disease are directed against the amyloid-β (Aβ) peptide. Among the anti-Aβ therapeutic approaches, the most extensively developed is immunotherapy-specifically, passive immunization through administration of exogenous monoclonal antibodies (mAbs). Although testing of mAbs has been fraught with failure and confusing results, the experience gained from these trials has provided important clues for better treatments. This review summarizes the experience to date with anti-Aβ mAbs to enter clinical trials for Alzheimer's disease and examines the evidence for clinical efficacy and the major problems with safety-i.e., amyloid-related imaging abnormalities. As mAbs differ considerably with regard to their epitopes and the conformations of Aβ that they recognize (monomers, oligomers, protofibrils, fibrils), the consequences of targeting different species are also considered. An often-cited explanation for the failure of anti-Aβ mAb trials is that they are set too late in the disease process. New trials are indeed evaluating treatments at prodromal and preclinical stages. We should expect to see additional studies of presymptomatic Alzheimer's disease to join the ongoing prevention trials, for which mAbs continue to serve as the mainstay.

A comparative evaluation of treatments with 17β-estradiol and its brain-selective prodrug in a double-transgenic mouse model of Alzheimer's disease

Estrogens are neuroprotective and, thus, potentially useful for the therapy of Alzheimer's disease; however, clinical use of hormone therapy remains controversial due to adverse peripheral effects. The goal of this study was to investigate the benefits of treatment with 10β,17β-dihydroxyestra-1,4-dien-3-one (DHED), a brain-selective prodrug of 17β-estradiol, in comparison with the parent hormone using APPswe/PS1dE9 double transgenic mice to model the pathology of the disease. Ovariectomized and intact females were continuously treated with vehicle, 17β-estradiol, or DHED via subcutaneous osmotic pumps from 6 to 8months of age. We confirmed that this prolonged treatment with DHED did not stimulate uterine tissue, whereas 17β-estradiol treatment increased uterine weight. Amyloid precursor protein decreased in both treatment groups of intact, but not in ovariectomized double transgenic females in which ovariectomy already decreased the expression of this protein significantly. However, reduced brain amyloid-β peptide levels could be observed for both treatments. Consequently, double-transgenic ovariectomized and intact mice had higher cognitive performance compared to untreated control animals in response to both estradiol and DHED administrations. Overall, the tested brain-selective 17β-estradiol prodrug proved to be an effective early-stage intervention in an Alzheimer's disease-relevant mouse model without showing systemic impact and, thus, warrants further evaluation as a potential therapeutic candidate.

Aβ-Immunotherapeutic strategies: a wide range of approaches for Alzheimer's disease treatment

Current therapies to treat Alzheimer's disease (AD) are focused on ameliorating symptoms instead of treating the underlying causes of AD. The accumulation of amyloid β (Aβ) oligomers, whether by an increase in production or by a decrease in clearance, has been described as the seed that initiates the pathological cascade in AD. Developing therapies to target these species is a vital step in improving AD treatment. Aβ-immunotherapy, especially passive immunotherapy, is a promising approach to reduce the Aβ burden. Up to now, several monoclonal antibodies (mAbs) have been tested in clinical trials on humans, but none of them have passed Phase III. In all likelihood, these trials failed mainly because patients with mild-to-moderate AD were recruited, and thus treatment may have been too late to be effective. Therefore, many ongoing clinical trials are being conducted in patients at the prodromal stage. New structures based on antibody fragments have been engineered intending to improve efficacy and safety. This review presents the properties of this variety of developing treatments and provides a perspective on state-of-the-art of passive Aβ-immunotherapy in AD.

The Peptide Vaccine Combined with Prior Immunization of a Conventional Diphtheria-Tetanus Toxoid Vaccine Induced Amyloid β Binding Antibodies on Cynomolgus Monkeys and Guinea Pigs

The reduction of brain amyloid beta (Aβ) peptides by anti-Aβ antibodies is one of the possible therapies for Alzheimer's disease. We previously reported that the Aβ peptide vaccine including the T-cell epitope of diphtheria-tetanus combined toxoid (DT) induced anti-Aβ antibodies, and the prior immunization with conventional DT vaccine enhanced the immunogenicity of the peptide. Cynomolgus monkeys were given the peptide vaccine subcutaneously in combination with the prior DT vaccination. Vaccination with a similar regimen was also performed on guinea pigs. The peptide vaccine induced anti-Aβ antibodies in cynomolgus monkeys and guinea pigs without chemical adjuvants, and excessive immune responses were not observed. Those antibodies could preferentially recognize Aβ₄₀, and Aβ₄₂ compared to Aβ fibrils. The levels of serum anti-Aβ antibodies and plasma Aβ peptides increased in both animals and decreased the brain Aβ₄₀ level of guinea pigs. The peptide vaccine could induce a similar binding profile of anti-Aβ antibodies in cynomolgus monkeys and guinea pigs. The peptide vaccination could be expected to reduce the brain Aβ peptides and their toxic effects via clearance of Aβ peptides by generated antibodies.

Advances in the therapy of Alzheimer's disease: targeting amyloid beta and tau and perspectives for the future

Worldwide multidisciplinary translational research has led to a growing knowledge of the genetics and molecular pathogenesis of Alzheimer's disease (AD) indicating that pathophysiological brain alterations occur decades before clinical signs and symptoms of cognitive decline can be diagnosed. Consequently, therapeutic concepts and targets have been increasingly focused on early-stage illness before the onset of dementia; and distinct classes of compounds are now being tested in clinical trials. At present, there is a growing consensus that therapeutic progress in AD delaying disease progression would significantly decrease the expanding global burden. The evolving hypothesis- and evidence-based generation of new diagnostic research criteria for early-stage AD has positively impacted the development of clinical trial designs and the characterization of earlier and more specific target populations for trials in prodromal as well as in pre- and asymptomatic at-risk stages of AD.

Biological markers of Alzheimer?s disease

The challenges for establishing an early diagnosis of Alzheimer’s disease (AD) have created a need for biomarkers that reflect the core pathology of the disease. The cerebrospinal fluid (CSF) levels of total Tau (T-tau), phosphorylated Tau (P-Tau) and beta-amyloid peptide (Aβ42) reflect, respectively, neurofibrillary tangle and amyloid pathologies and are considered as surrogate markers of AD pathophysiology. The combination of low Aβ42 and high levels of T-tau and P-Tau can accurately identify patients with AD at early stages, even before the development of dementia. The combined analysis of the CSF biomarkers is also helpful for the differential diagnosis between AD and other degenerative dementias. The development of these CSF biomarkers has evolved to a novel diagnostic definition of the disease. The identification of a specific clinical phenotype combined with the in vivo evidence of pathophysiological markers offers the possibility to make a diagnosis of AD before the dementia stage with high specificity.