Current Status of Clinical Trials on Tau Immunotherapies

Time-Dependent Long-Term Effect of Memantine following Repetitive Mild Traumatic Brain Injury

Repetitive mild traumatic brain injury (rmTBI, e.g., sports concussions) may be associated with both acute and chronic symptoms and neurological changes. Despite the common occurrence of these injuries, therapeutic strategies are limited. One potentially promising approach is N-methyl-D-aspartate receptor (NMDAR) blockade to alleviate the effects of post-injury glutamatergic excitotoxicity. Initial pre-clinical work using the NMDAR antagonist, memantine, suggests that immediate treatment following rmTBI improves a variety of acute outcomes. It remains unclear (1) whether acute memantine treatment has long-term benefits and (2) whether delayed treatment following rmTBI is beneficial, which are both clinically relevant concerns. To test this, animals were subjected to rmTBI via a weight drop model with rotational acceleration (five hits in 5 days) and randomized to memantine treatment immediately, 3 months, or 6 months post-injury, with a treatment duration of one month. Behavioral outcomes were assessed at 1, 4, and 7 months post-injury. Neuropathological outcomes were characterized at 7 months post-injury. We observed chronic changes in behavior (anxiety-like behavior, motor coordination, spatial learning, and memory), as well as neuroinflammation (microglia, astrocytes) and tau phosphorylation (T231). Memantine treatment, either immediately or 6 months post-injury, appears to confer greater rescue of neuroinflammatory changes (microglia) than vehicle or treatment at the 3-month time point. Although memantine is already being prescribed chronically to address persistent symptoms associated with rmTBI, this study represents the first evidence of which we are aware to suggest a small but durable effect of memantine treatment in mild, concussive injuries. This effect suggests that memantine, although potentially beneficial, is insufficient to treat all aspects of rmTBI alone and should be combined with other therapeutic agents in a multi-therapy approach, with attention given to the timing of treatment.

The Enigma of Tau Protein Aggregation: Mechanistic Insights and Future Challenges

Tau protein misfolding and aggregation are pathological hallmarks of Alzheimer's disease and over twenty neurodegenerative disorders. However, the molecular mechanisms of tau aggregation in vivo remain incompletely understood. There are two types of tau aggregates in the brain: soluble aggregates (oligomers and protofibrils) and insoluble filaments (fibrils). Compared to filamentous aggregates, soluble aggregates are more toxic and exhibit prion-like transmission, providing seeds for templated misfolding. Curiously, in its native state, tau is a highly soluble, heat-stable protein that does not form fibrils by itself, not even when hyperphosphorylated. In vitro studies have found that negatively charged molecules such as heparin, RNA, or arachidonic acid are generally required to induce tau aggregation. Two recent breakthroughs have provided new insights into tau aggregation mechanisms. First, as an intrinsically disordered protein, tau is found to undergo liquid-liquid phase separation (LLPS) both in vitro and inside cells. Second, cryo-electron microscopy has revealed diverse fibrillar tau conformations associated with different neurodegenerative disorders. Nonetheless, only the fibrillar core is structurally resolved, and the remainder of the protein appears as a "fuzzy coat". From this review, it appears that further studies are required (1) to clarify the role of LLPS in tau aggregation; (2) to unveil the structural features of soluble tau aggregates; (3) to understand the involvement of fuzzy coat regions in oligomer and fibril formation.

New insights into the therapeutic approaches for the treatment of tauopathies

Tauopathies are a group of neurological disorders, including Alzheimer's disease and frontotemporal dementia, which involve progressive neurodegeneration, cognitive deficits, and aberrant tau protein accumulation. The development of tauopathies cannot currently be stopped or slowed down by treatment measures. Given the significant contribution of tau burden in primary tauopathies and the strong association between pathogenic tau accumulation and cognitive deficits, there has been a lot of interest in creating therapies that can alleviate tau pathology and render neuroprotective effects. Recently, small molecules, immunotherapies, and gene therapy have been used to reduce the pathological tau burden and prevent neurodegeneration in animal models of tauopathies. However, the major pitfall of the current therapeutic approach is the difficulty of drugs and gene-targeting modalities to cross the blood-brain barrier and their unintended side effects. In this review, the current therapeutic strategies used for tauopathies including the use of oligonucleotide-based gene therapy approaches that have shown a promising result for the treatment of tauopathies and Alzheimer's disease in preclinical animal models, have been discussed.

Clathrin mediated endocytosis in Alzheimer's disease: cell type specific involvement in amyloid beta pathology

This review provides a comprehensive examination of the role of clathrin-mediated endocytosis (CME) in Alzheimer's disease (AD) pathogenesis, emphasizing its impact across various cellular contexts beyond neuronal dysfunction. In neurons, dysregulated CME contributes to synaptic dysfunction, amyloid beta (Aβ) processing, and Tau pathology, highlighting its involvement in early AD pathogenesis. Furthermore, CME alterations extend to non-neuronal cell types, including astrocytes and microglia, which play crucial roles in Aβ clearance and neuroinflammation. Dysregulated CME in these cells underscores its broader implications in AD pathophysiology. Despite significant progress, further research is needed to elucidate the precise mechanisms underlying CME dysregulation in AD and its therapeutic implications. Overall, understanding the complex interplay between CME and AD across diverse cell types holds promise for identifying novel therapeutic targets and interventions.

Therapeutic approaches in proteinopathies

A family of maladies known as amyloid disorders, proteinopathy, or amyloidosis, are characterized by the accumulation of abnormal protein aggregates containing cross-β-sheet amyloid fibrils in many organs and tissues. Often, proteins that have been improperly formed or folded make up these fibrils. Nowadays, most treatments for amyloid illness focus on managing symptoms rather than curing or preventing the underlying disease process. However, recent advances in our understanding of the biology of amyloid diseases have led to the development of innovative therapies that target the emergence and accumulation of amyloid fibrils. Examples of these treatments include the use of small compounds, monoclonal antibodies, gene therapy, and others. In the end, even if the majority of therapies for amyloid diseases are symptomatic, greater research into the biology behind these disorders is identifying new targets for potential therapy and paving the way for the development of more effective treatments in the future.

Evolving therapeutic interventions for the management and treatment of Alzheimer's disease

Alzheimer's Disease (AD) patients experience diverse symptoms, including memory loss, cognitive impairment, behavioral abnormalities, mood changes, and mental issues. The fundamental objective of this review is to discuss novel therapeutic approaches, with special emphasis on recently approved marketed formulations for the treatment of AD, especially Aducanumab, the first FDA approved moiety that surpasses the blood-brain barrier (BBB) and reduces amyloid plaques in the brain, thereby reducing associated cognitive decline. However, it is still in the phase IV trial and is to be completed by 2030. Other drugs such as lecanemab are also under clinical trial and has recently been approved by the FDA and is also discussed here. In this review, we also focus on active and passive immunotherapy for AD as well as several vaccines, such as amyloid-beta epitope-based vaccines, amyloid-beta DNA vaccines, and stem cell therapy for AD, which are in clinical trials. Furthermore, ongoing pre-clinical trials associated with AD and other novel strategies such as curcumin-loaded nanoparticles, Crispr/ cas9, precision medicine, as well as some emerging therapies like anti-sense therapy are also highlighted. Additionally, we discuss some off-labeled drugs like non-steroidal anti-inflammatory drugs (NSAID), anti-diabetic drugs, and lithium, which can manage symptoms of AD and different non-pharmacological approaches are also covered which can help to manage AD. In summary, we have tried to cover all the therapeutic interventions which are available for the treatment and management of AD under sections approved, clinical phase, pre-clinical phase or futuristic interventions, off-labelled drugs, and non-pharmacological interventions for AD, offering positive findings and well as challenges that remain.

In vivo PET classification of tau pathologies in patients with frontotemporal dementia

Frontotemporal dementia refers to a group of neurodegenerative disorders with diverse clinical and neuropathological features. In vivo neuropathological assessments of frontotemporal dementia at an individual level have hitherto not been successful. In this study, we aim to classify patients with frontotemporal dementia based on topologies of tau protein aggregates captured by PET with 18F-florzolotau (aka 18F-APN-1607 and 18F-PM-PBB3), which allows high-contrast imaging of diverse tau fibrils in Alzheimer's disease as well as in non-Alzheimer's disease tauopathies. Twenty-six patients with frontotemporal dementia, 15 with behavioural variant frontotemporal dementia and 11 with other frontotemporal dementia phenotypes, and 20 age- and sex-matched healthy controls were included in this study. They underwent PET imaging of amyloid and tau depositions with 11C-PiB and 18F-florzolotau, respectively. By combining visual and quantitative analyses of PET images, the patients with behavioural variant frontotemporal dementia were classified into the following subgroups: (i) predominant tau accumulations in frontotemporal and frontolimbic cortices resembling three-repeat tauopathies (n = 3), (ii) predominant tau accumulations in posterior cortical and subcortical structures indicative of four-repeat tauopathies (n = 4); (iii) amyloid and tau accumulations consistent with Alzheimer's disease (n = 4); and (iv) no overt amyloid and tau pathologies (n = 4). Despite these distinctions, clinical symptoms and localizations of brain atrophy did not significantly differ among the identified behavioural variant frontotemporal dementia subgroups. The patients with other frontotemporal dementia phenotypes were also classified into similar subgroups. The results suggest that PET with 18F-florzolotau potentially allows the classification of each individual with frontotemporal dementia on a neuropathological basis, which might not be possible by symptomatic and volumetric assessments.

Tau Immunotherapies for Alzheimer's Disease and Related Tauopathies: Status of Trials and Insights from Preclinical Studies

 The tau protein undergoes pathological changes in Alzheimer's disease and other tauopathies that eventually lead to functional impairments. Over the years, several therapeutic approaches have been examined to slow or halt the progression of tau pathology but have yet to lead to an approved disease-modifying treatment. Of the drugs in clinical trials that directly target tau, immunotherapies are the largest category and mostly consist of antibodies in different stages of development. There is a reasonable optimism that at least some of these compounds will have a clinically meaningful efficacy. This view is based on the significant although modest efficacy of some antibodies targeting amyloid-β in Alzheimer's disease and the fact that tau pathology correlates much better with the degree of dementia than amyloid-β lesions. In Alzheimer's disease, clearing pathological tau may therefore improve function later in the disease process than when removing amyloid-β. This review provides a brief update on the active and passive clinical tau immunization trials with insight from preclinical studies. Various epitopes are being targeted and some of the antibodies are said to target extracellular tau but because almost all of pathological tau is found intracellularly, the most efficacious antibodies should be able to enter the cell.

Monoclonal antibodies for treating early Alzheimer disease-a commentary on recent 'positive' trials

Recent phase 3 randomised controlled trials of amyloid-targeting monoclonal antibodies in people with pre-clinical or early Alzheimer disease have reported positive results, raising hope of finally having disease-modifying drugs. Given their far-reaching implications for clinical practice, the methods and findings of these trials, and the disease causation theory underpinning the mechanism of drug action, need to be critically appraised. Key considerations are the representativeness of trial populations; balance of prognostic factors at baseline; psychometric properties and minimal clinically important differences of the primary efficacy outcome measures; level of study fidelity; consistency of subgroup analyses; replication of findings in similar trials; sponsor role and potential conflicts of interest; consistency of results with disease causation theory; cost and resource estimates; and alternative prevention and treatment strategies. In this commentary, we show shortcomings in each of these areas and conclude that monoclonal antibody treatment for early Alzheimer disease is lacking high-quality evidence of clinically meaningful impacts at an affordable cost.

Protein Misfolding in Pregnancy: Current Insights, Potential Mechanisms, and Implications for the Pathogenesis of Preeclampsia

Protein misfolding disorders are a group of diseases characterized by supra-physiologic accumulation and aggregation of pathogenic proteoforms resulting from improper protein folding and/or insufficiency in clearance mechanisms. Although these processes have been historically linked to neurodegenerative disorders, such as Alzheimer's disease, evidence linking protein misfolding to other pathologies continues to emerge. Indeed, the deposition of toxic protein aggregates in the form of oligomers or large amyloid fibrils has been linked to type 2 diabetes, various types of cancer, and, in more recent years, to preeclampsia, a life-threatening pregnancy-specific disorder. While extensive physiological mechanisms are in place to maintain proteostasis, processes, such as aging, genetic factors, or environmental stress in the form of hypoxia, nutrient deprivation or xenobiotic exposures can induce failure in these systems. As such, pregnancy, a natural physical state that already places the maternal body under significant physiological stress, creates an environment with a lower threshold for aberrant aggregation. In this review, we set out to discuss current evidence of protein misfolding in pregnancy and potential mechanisms supporting a key role for this process in preeclampsia pathogenesis. Improving our understanding of this emerging pathophysiological process in preeclampsia can lead to vital discoveries that can be harnessed to create better diagnoses and treatment modalities for the disorder.

Using NMR diffusion data to validate MD models of disordered proteins: Test case of N-terminal tail of histone H4

MD simulations can provide uniquely detailed models of intrinsically disordered proteins (IDPs). However, these models need careful experimental validation. The coefficient of translational diffusion Dtr, measurable by pulsed field gradient NMR, offers a potentially useful piece of experimental information related to the compactness of the IDP's conformational ensemble. Here, we investigate, both experimentally and via the MD modeling, the translational diffusion of a 25-residue N-terminal fragment from histone H4 (N-H4). We found that the predicted values of Dtr, as obtained from mean-square displacement of the peptide in the MD simulations, are largely determined by the viscosity of the MD water (which has been reinvestigated as a part of our study). Beyond that, our analysis of the diffusion data indicates that MD simulations of N-H4 in the TIP4P-Ew water give rise to an overly compact conformational ensemble for this peptide. In contrast, TIP4P-D and OPC simulations produce the ensembles that are consistent with the experimental Dtr result. These observations are supported by the analyses of the 15N spin relaxation rates. We also tested a number of empirical methods to predict Dtr based on IDP's coordinates extracted from the MD snapshots. In particular, we show that the popular approach involving the program HYDROPRO can produce misleading results. This happens because HYDROPRO is not intended to predict the diffusion properties of highly flexible biopolymers such as IDPs. Likewise, recent empirical schemes that exploit the relationship between the small-angle x-ray scattering-informed conformational ensembles of IDPs and the respective experimental Dtr values also prove to be problematic. In this sense, the first-principle calculations of Dtr from the MD simulations, such as demonstrated in this work, should provide a useful benchmark for future efforts in this area.

Strategies for translating proteomics discoveries into drug discovery for dementia

Tauopathies, diseases characterized by neuropathological aggregates of tau including Alzheimer's disease and subtypes of frontotemporal dementia, make up the vast majority of dementia cases. Although there have been recent developments in tauopathy biomarkers and disease-modifying treatments, ongoing progress is required to ensure these are effective, economical, and accessible for the globally ageing population. As such, continued identification of new potential drug targets and biomarkers is critical. "Big data" studies, such as proteomics, can generate information on thousands of possible new targets for dementia diagnostics and therapeutics, but currently remain underutilized due to the lack of a clear process by which targets are selected for future drug development. In this review, we discuss current tauopathy biomarkers and therapeutics, and highlight areas in need of improvement, particularly when addressing the needs of frail, comorbid and cognitively impaired populations. We highlight biomarkers which have been developed from proteomic data, and outline possible future directions in this field. We propose new criteria by which potential targets in proteomics studies can be objectively ranked as favorable for drug development, and demonstrate its application to our group's recent tau interactome dataset as an example.

Tau and Alzheimer's disease: Past, present and future

My journey with tau started when in 1974 for the first time I isolated neurofibrillary tangles of paired helical filaments (PHFs) from autopsied Alzheimer's disease (AD) brains and discovered that they were made up of a ~50-70 KDa protein on SDS-polyacrylamide gels. Subsequently my team discovered that this PHF protein and the microtubule-associated factor called tau were one and the same protein. However, we found that tau in neurofibrillary tangles/PHFs in AD brain was abnormally hyperphosphorylated, and unlike normal tau, which promoted the assembly of tubulin into microtubules, the AD-hyperphosphorylated tau inhibited microtubule assembly. These discoveries of tau pathology in AD opened a new and a major area of research on tau and on the molecular pathology of this major cause of dementia in middle- and old-age individuals. Tau pathology, which without fail is made up of the aggregated hyperphosphorylated state of the protein, is also the hallmark lesion of a family of around 20 related neurodegenerative diseases, called tauopathies. Currently, tau pathology is a major drug target for the treatment of AD and related tauopathies. Both active and passive tau immunization human clinical trials at various stages are underway. Initial results range from negative to partially promising. Future studies will reveal whether tau therapy alone or in combination with drugs targeting Aβ and/or neurodegeneration will be required to achieve the most effective treatment for AD and related disorders.

Measuring Antibody-Mediated Tau Fibril Uptake in Microglia by Flow Cytometry

Microglia are brain-resident phagocytic cells, considered to be the innate immune cells of the central nervous system. Microglia respond to both infectious pathogens in the brain and sterile cellular debris, including the proteinaceous aggregates that accumulate in the brains of patients with Alzheimer's disease (AD). Microtubule-associated protein Tau is an intracellular protein that self-aggregates into neurofibrillary tangles in Alzheimer's disease and many other neurodegenerative diseases. Ongoing clinical trials are testing whether therapeutic antibodies specific to Tau protein aggregates can reduce pathological protein deposition and improve the course of disease. Data suggest that Tau-specific antibodies act on extracellular Tau aggregates by promoting uptake into microglia cells and thus preventing its prion-like spread to unaffected neurons. Here we describe a protocol to test the effect of Tau-specific antibodies on Tau uptake into microglia by flow cytometry. Recombinant Tau protein is fibrillized in vitro and tagged with a fluorescent label. Then, fibrillized Tau is incubated with the antibody of interest and applied to microglial cells in culture. Uptake of Tau into microglia is then assessed by measuring fluorescence intensity by flow cytometry. With slight modifications, this assay can be used to test effects of many antibodies, various Tau protein compositions, and different microglial sources in a high-throughput format.

Alzheimer's Disease Immunotherapy: Current Strategies and Future Prospects

Alzheimer's disease (AD) is an extremely complex and heterogeneous pathology influenced by many factors contributing to its onset and progression, including aging, amyloid-beta (Aβ) plaques, tau fibril accumulation, inflammation, etc. Despite promising advances in drug development, there is no cure for AD. Although there have been substantial advancements in understanding the pathogenesis of AD, there have been over 200 unsuccessful clinical trials in the past decade. In recent years, immunotherapies have been at the forefront of these efforts. Immunotherapy alludes to the immunological field that strives to identify disease treatments via the enhancement, suppression, or induction of immune responses. Interestingly, immunotherapy in AD is a relatively new approach for non-infectious disease. At present, antibody therapy (passive immunotherapy) that targets anti-Aβ aimed to prevent the fibrillization of Aβ peptides and disrupt pre-existing fibrils is a predominant AD immunotherapy due to the continuous failure of active immunotherapy for AD. The most rational and safe strategies will be those targeting the toxic molecule without triggering an abnormal immune response, offering therapeutic advantages, thus making clinical trial design more efficient. This review offers a concise overview of immunotherapeutic strategies, including active and passive immunotherapy for AD. Our review encompasses approved methods and those presently under investigation in clinical trials, while elucidating the recent challenges, complications, successes, and potential treatments. Thus, immunotherapies targeting Aβ throughout the disease progression using a mutant oligomer-Aβ stimulated dendritic cell vaccine may offer a promising therapy in AD.

Senescence, brain inflammation, and oligomeric tau drive cognitive decline in Alzheimer's disease: Evidence from clinical and preclinical studies

Aging, tau pathology, and chronic inflammation in the brain play crucial roles in synaptic loss, neurodegeneration, and cognitive decline in tauopathies, including Alzheimer's disease. Senescent cells accumulate in the aging brain, accelerate the aging process, and promote tauopathy progression through their abnormal inflammatory secretome known as the senescence-associated secretory phenotype (SASP). Tau oligomers (TauO)-the most neurotoxic tau species-are known to induce senescence and the SASP, which subsequently promote neuropathology, inflammation, oxidative stress, synaptic dysfunction, neuronal death, and cognitive dysfunction. TauO, brain inflammation, and senescence are associated with heterogeneity in tauopathy progression and cognitive decline. However, the underlying mechanisms driving the disease heterogeneity remain largely unknown, impeding the development of therapies for tauopathies. Based on clinical and preclinical evidence, this review highlights the critical role of TauO and senescence in neurodegeneration. We discuss key knowledge gaps and potential strategies for targeting senescence and TauO to treat tauopathies. HIGHLIGHTS: Senescence, oligomeric Tau (TauO), and brain inflammation accelerate the aging process and promote the progression of tauopathies, including Alzheimer's disease. We discuss their role in contributing to heterogeneity in tauopathy and cognitive decline. We highlight strategies to target senescence and TauO to treat tauopathies while addressing key knowledge gaps.

Monoclonal Antibody Therapy in Alzheimer's Disease

Alzheimer's disease is a neurodegenerative condition marked by the progressive deterioration of cognitive abilities, memory impairment, and the accumulation of abnormal proteins, specifically beta-amyloid plaques and tau tangles, within the brain. Despite extensive research efforts, Alzheimer's disease remains without a cure, presenting a significant global healthcare challenge. Recently, there has been an increased focus on antibody-based treatments as a potentially effective method for dealing with Alzheimer's disease. This paper offers a comprehensive overview of the current status of research on antibody-based molecules as therapies for Alzheimer's disease. We will briefly mention their mechanisms of action, therapeutic efficacy, and safety profiles while addressing the challenges and limitations encountered during their development. We also highlight some crucial considerations in antibody-based treatment development, including patient selection criteria, dosing regimens, or safety concerns. In conclusion, antibody-based therapies present a hopeful outlook for addressing Alzheimer's disease. While challenges remain, the accumulating evidence suggests that these therapies may offer substantial promise in ameliorating or preventing the progression of this debilitating condition, thus potentially enhancing the quality of life for the millions of individuals and families affected by Alzheimer's disease worldwide.

Minding the Gap: Exploring Neuroinflammatory and Microglial Sex Differences in Alzheimer's Disease

Research into Alzheimer's Disease (AD) describes a link between AD and the resident immune cells of the brain, the microglia. Further, this suspected link is thought to have underlying sex effects, although the mechanisms of these effects are only just beginning to be understood. Many of these insights are the result of policies put in place by funding agencies such as the National Institutes of Health (NIH) to consider sex as a biological variable (SABV) and the move towards precision medicine due to continued lackluster therapeutic options. The purpose of this review is to provide an updated assessment of the current research that summarizes sex differences and the research pertaining to microglia and their varied responses in AD.

Tau-targeting therapies for Alzheimer disease: current status and future directions

Alzheimer disease (AD) is the most common cause of dementia in older individuals. AD is characterized pathologically by amyloid-β (Aβ) plaques and tau neurofibrillary tangles in the brain, with associated loss of synapses and neurons, which eventually results in dementia. Many of the early attempts to develop treatments for AD focused on Aβ, but a lack of efficacy of these treatments in terms of slowing disease progression led to a change of strategy towards targeting of tau pathology. Given that tau shows a stronger correlation with symptom severity than does Aβ, targeting of tau is more likely to be efficacious once cognitive decline begins. Anti-tau therapies initially focused on post-translational modifications, inhibition of tau aggregation and stabilization of microtubules. However, trials of many potential drugs were discontinued because of toxicity and/or lack of efficacy. Currently, the majority of tau-targeting agents in clinical trials are immunotherapies. In this Review, we provide an update on the results from the initial immunotherapy trials and an overview of new therapeutic candidates that are in clinical development, as well as considering future directions for tau-targeting therapies.

Neuronal Glycogen Breakdown Mitigates Tauopathy via Pentose Phosphate Pathway-Mediated Oxidative Stress Reduction

Tauopathies encompass a range of neurodegenerative disorders, such as Alzheimer's disease (AD) and frontotemporal dementia (FTD). Unfortunately, current treatment approaches for tauopathies have yielded limited success, underscoring the pressing need for novel therapeutic strategies. We observed distinct signatures of impaired glycogen metabolism in the Drosophila brain of the tauopathy model and the brain of AD patients, indicating a link between tauopathies and glycogen metabolism. We demonstrate that the breakdown of neuronal glycogen by activating glycogen phosphorylase (GlyP) ameliorates the tauopathy phenotypes in flies and induced pluripotent stem cell (iPSC) derived neurons from FTD patients. We observed that glycogen breakdown redirects the glucose flux to the pentose phosphate pathway to alleviate oxidative stress. Our findings uncover a critical role for increased GlyP activity in mediating the neuroprotection benefit of dietary restriction (DR) through the cAMP-mediated protein kinase A (PKA) activation. Our studies identify impaired glycogen metabolism as a key hallmark for tauopathies and offer a promising therapeutic target in tauopathy treatment.

Accelerating Alzheimer's therapeutic development: The past and future of clinical trials

Alzheimer's disease (AD) research has entered a new era with the recent positive phase 3 clinical trials of the anti-Aβ antibodies lecanemab and donanemab. Why did it take 30 years to achieve these successes? Developing potent therapies for reducing fibrillar amyloid was key, as was selection of patients at relatively early stages of disease. Biomarkers of the target pathologies, including amyloid and tau PET, and insights from past trials were also critical to the recent successes. Moving forward, the challenge will be to develop more efficacious therapies with greater efficiency. Novel trial designs, including combination therapies and umbrella and basket protocols, will accelerate clinical development. Better diversity and inclusivity of trial participants are needed, and blood-based biomarkers may help to improve access for medically underserved groups. Incentivizing innovation in both academia and industry through public-private partnerships, collaborative mechanisms, and the creation of new career paths will be critical to build momentum in these exciting times.

Alzheimer's disease: From immunotherapy to immunoprevention

Recent Aβ-immunotherapy trials have yielded the first clear evidence that removing aggregated Aβ from the brains of symptomatic patients can slow the progression of Alzheimer's disease. The clinical benefit achieved in these trials has been modest, however, highlighting the need for both a deeper understanding of disease mechanisms and the importance of intervening early in the pathogenic cascade. An immunoprevention strategy for Alzheimer's disease is required that will integrate the findings from clinical trials with mechanistic insights from preclinical disease models to select promising antibodies, optimize the timing of intervention, identify early biomarkers, and mitigate potential side effects.

Cis P-tau is a central circulating and placental etiologic driver and therapeutic target of preeclampsia

Preeclampsia (PE) is the leading cause of maternal and fetal mortality globally and may trigger dementia later in life in mothers and their offspring. However, the etiological drivers remain elusive. Cis P-tau is an early etiological driver and blood biomarker in pre-clinical Alzheimer's and after vascular or traumatic brain injury, which can be targeted by stereo-specific antibody, with clinical trials ongoing. Here we find significant cis P-tau in the placenta and serum of PE patients, and in primary human trophoblasts exposed to hypoxia or sera from PE patients due to Pin1 inactivation. Depletion of cis P-tau from PE patient sera by the antibody prevents their ability to disrupt trophoblast invasion and endovascular activity and to cause the PE-like pathological and clinical features in pregnant humanized tau mice. Our studies uncover that cis P-tau is a central circulating etiological driver and its stereo-specific antibody is valuable for early PE diagnosis and treatment.

Targeting epigenetics: A novel promise for Alzheimer's disease treatment

So far, the search for a cure for Alzheimer Disease (AD) has been unsuccessful. The only approved drugs attenuate some symptoms, but do not halt the progress of this disease, which affects 50 million people worldwide and will increase its incidence in the coming decades. Such scenario demands new therapeutic approaches to fight against this devastating dementia. In recent years, multi-omics research and the analysis of differential epigenetic marks in AD subjects have contributed to our understanding of AD; however, the impact of epigenetic research is yet to be seen. This review integrates the most recent data on pathological processes and epigenetic changes relevant for aging and AD, as well as current therapies targeting epigenetic machinery in clinical trials. Evidence shows that epigenetic modifications play a key role in gene expression, which could provide multi-target preventative and therapeutic approaches in AD. Both novel and repurposed drugs are employed in AD clinical trials due to their epigenetic effects, as well as increasing number of natural compounds. Given the reversible nature of epigenetic modifications and the complexity of gene-environment interactions, the combination of epigenetic-based therapies with environmental strategies and drugs with multiple targets might be needed to properly help AD patients.

De Novo Design of a β-Helix Tau Protein Scaffold: An Oligomer-Selective Vaccine Immunogen Candidate for Alzheimer's Disease

Tau pathology is associated with many neurodegenerative disorders, including Alzheimer's disease (AD), where the spatio-temporal pattern of tau neurofibrillary tangles strongly correlates with disease progression, which motivates therapeutics selective for misfolded tau. Here, we introduce a new avidity-enhanced, multi-epitope approach for protein-misfolding immunogen design, which is predicted to mimic the conformational state of an exposed epitope in toxic tau oligomers. A predicted oligomer-selective tau epitope 343KLDFK347 was scaffolded by designing a β-helix structure that incorporated multiple instances of the 16-residue tau fragment 339VKSEKLDFKDRVQSKI354. Large-scale conformational ensemble analyses involving Jensen-Shannon Divergence and the embedding depth D showed that the multi-epitope scaffolding approach, employed in designing the β-helix scaffold, was predicted to better discriminate toxic tau oligomers than other "monovalent" strategies utilizing a single instance of an epitope for vaccine immunogen design. Using Rosetta, 10,000 sequences were designed and screened for the linker portions of the β-helix scaffold, along with a C-terminal stabilizing α-helix that interacts with the linkers, to optimize the folded structure and stability of the scaffold. Structures were ranked by energy, and the lowest 1% (82 unique sequences) were verified using AlphaFold. Several selection criteria involving AlphaFold are implemented to obtain a lead-designed sequence. The structure was further predicted to have free energetic stability by using Hamiltonian replica exchange molecular dynamics (MD) simulations. The synthesized β-helix scaffold showed direct binding in surface plasmon resonance (SPR) experiments to several antibodies that were raised to the structured epitope using a designed cyclic peptide. Moreover, the strength of binding of these antibodies to in vitro tau oligomers correlated with the strength of binding to the β-helix construct, suggesting that the construct presents an oligomer-like conformation and may thus constitute an effective oligomer-selective immunogen.

Protein disulfide isomerases as CSF biomarkers for the neuronal response to tau pathology

INTRODUCTION

Cerebrospinal fluid (CSF) biomarkers for specific cellular disease processes are lacking for tauopathies. In this translational study we aimed to identify CSF biomarkers reflecting early tau pathology-associated unfolded protein response (UPR) activation.

METHODS

We employed mass spectrometry proteomics and targeted immunoanalysis in a combination of biomarker discovery in primary mouse neurons in vitro and validation in patient CSF from two independent large multicentre cohorts (EMIF-AD MBD, n = 310; PRIDE, n = 771).

RESULTS

First, we identify members of the protein disulfide isomerase (PDI) family in the neuronal UPR-activated secretome and validate secretion upon tau aggregation in vitro. Next, we demonstrate that PDIA1 and PDIA3 levels correlate with total- and phosphorylated-tau levels in CSF. PDIA1 levels are increased in CSF from AD patients compared to controls and patients with tau-unrelated frontotemporal and Lewy body dementia (LBD).

HIGHLIGHTS

Neuronal unfolded protein response (UPR) activation induces the secretion of protein disulfide isomerases (PDIs) in vitro. PDIA1 is secreted upon tau aggregation in neurons in vitro. PDIA1 and PDIA3 levels correlate with total and phosphorylated tau levels in CSF. PDIA1 levels are increased in CSF from Alzheimer's disease (AD) patients compared to controls. PDIA1 levels are not increased in CSF from tau-unrelated frontotemporal dementia (FTD) and Lewy body dementia (LBD) patients.

Tau and neuroinflammation in Alzheimer's disease: interplay mechanisms and clinical translation

Alzheimer's Disease (AD) contributes to most cases of dementia. Its prominent neuropathological features are the extracellular neuritic plaques and intercellular neurofibrillary tangles composed of aggregated β-amyloid (Aβ) and hyperphosphorylated tau protein, respectively. In the past few decades, disease-modifying therapy targeting Aβ has been the focus of AD drug development. Even though it is encouraging that two of these drugs have recently received accelerated US Food and Drug Administration approval for AD treatment, their efficacy or long-term safety is controversial. Tau has received increasing attention as a potential therapeutic target, since evidence indicates that tau pathology is more associated with cognitive dysfunction. Moreover, inflammation, especially neuroinflammation, accompanies AD pathological processes and is also linked to cognitive deficits. Accumulating evidence indicates that inflammation has a complex and tight interplay with tau pathology. Here, we review recent evidence on the interaction between tau pathology, focusing on tau post-translational modification and dissemination, and neuroinflammatory responses, including glial cell activation and inflammatory signaling pathways. Then, we summarize the latest clinical trials targeting tau and neuroinflammation. Sustained and increased inflammatory responses in glial cells and neurons are pivotal cellular drivers and regulators of the exacerbation of tau pathology, which further contributes to its worsening by aggravating inflammatory responses. Unraveling the precise mechanisms underlying the relationship between tau pathology and neuroinflammation will provide new insights into the discovery and clinical translation of therapeutic targets for AD and other tau-related diseases (tauopathies). Targeting multiple pathologies and precision therapy strategies will be the crucial direction for developing drugs for AD and other tauopathies.

Receptor-mediated drug delivery of bispecific therapeutic antibodies through the blood-brain barrier

Therapeutic antibody drug development is a rapidly growing sector of the pharmaceutical industry. However, antibody drug development for the brain is a technical challenge, and therapeutic antibodies for the central nervous system account for ~3% of all such agents. The principal obstacle to antibody drug development for brain or spinal cord is the lack of transport of large molecule biologics across the blood-brain barrier (BBB). Therapeutic antibodies can be made transportable through the blood-brain barrier by the re-engineering of the therapeutic antibody as a BBB-penetrating bispecific antibody (BSA). One arm of the BSA is the therapeutic antibody and the other arm of the BSA is a transporting antibody. The transporting antibody targets an exofacial epitope on a BBB receptor, and this enables receptor-mediated transcytosis (RMT) of the BSA across the BBB. Following BBB transport, the therapeutic antibody then engages the target receptor in brain. RMT systems at the BBB that are potential conduits to the brain include the insulin receptor (IR), the transferrin receptor (TfR), the insulin-like growth factor receptor (IGFR) and the leptin receptor. Therapeutic antibodies have been re-engineered as BSAs that target the insulin receptor, TfR, or IGFR RMT systems at the BBB for the treatment of Alzheimer's disease and Parkinson's disease.

Tau pathology in neurodegenerative disease: disease mechanisms and therapeutic avenues

Tauopathies are disorders associated with tau protein dysfunction and insoluble tau accumulation in the brain at autopsy. Multiple lines of evidence from human disease, as well as nonclinical translational models, suggest that tau has a central pathologic role in these disorders, historically thought to be primarily related to tau gain of toxic function. However, a number of tau-targeting therapies with various mechanisms of action have shown little promise in clinical trials in different tauopathies. We review what is known about tau biology, genetics, and therapeutic mechanisms that have been tested in clinical trials to date. We discuss possible reasons for failures of these therapies, such as use of imperfect nonclinical models that do not predict human effects for drug development; heterogeneity of human tau pathologies which may lead to variable responses to therapy; and ineffective therapeutic mechanisms, such as targeting of the wrong tau species or protein epitope. Innovative approaches to human clinical trials can help address some of the difficulties that have plagued our field's development of tau-targeting therapies thus far. Despite limited clinical success to date, as we continue to refine our understanding of tau's pathogenic mechanism(s) in different neurodegenerative diseases, we remain optimistic that tau-targeting therapies will eventually play a central role in the treatment of tauopathies.

Focusing on oligomeric tau as a therapeutic target in Alzheimer's disease and other tauopathies

INTRODUCTION

Tau has commanded much attention as a potential therapeutic target in neurodegenerative diseases. Tau pathology is a hallmark of primary tauopathies, such as progressive supranuclear palsy (PSP), corticobasal syndrome (CBS), and subtypes of frontotemporal dementia (FTD), as well as secondary tauopathies, such as Alzheimer's disease (AD). The development of tau therapeutics must reconcile with the structural complexity of the tau proteome, as well as an incomplete understanding of the role of tau in both physiology and disease.

AREAS COVERED

This review offers a current perspective on tau biology, discusses key barriers to the development of effective tau-based therapeutics, and promotes the idea that pathogenic (as opposed to merely pathological) tau should be at the center of drug development efforts.

EXPERT OPINION

An efficacious tau therapeutic will exhibit several primary features: 1) selectivity for pathogenic tau versus other tau species; 2) blood-brain barrier and cell membrane permeability, enabling access to intracellular tau in disease-relevant brain regions; and 3) minimal toxicity. Oligomeric tau is proposed as a major pathogenic form of tau and a compelling drug target in tauopathies.

Intrathecal Pseudodelivery of Drugs in the Therapy of Neurodegenerative Diseases: Rationale, Basis and Potential Applications

Intrathecal pseudodelivery of drugs is a novel route to administer medications to treat neurodegenerative diseases based on the CSF-sink therapeutic strategy by means of implantable devices. While the development of this therapy is still in the preclinical stage, it offers promising advantages over traditional routes of drug delivery. In this paper, we describe the rationale of this system and provide a technical report on the mechanism of action, that relies on the use of nanoporous membranes enabling selective molecular permeability. On one side, the membranes do not permit the crossing of certain drugs; whereas, on the other side, they permit the crossing of target molecules present in the CSF. Target molecules, by binding drugs inside the system, are retained or cleaved and subsequently eliminated from the central nervous system. Finally, we provide a list of potential indications, the respective molecular targets, and the proposed therapeutic agents.

Microglial autophagy in Alzheimer's disease and Parkinson's disease

Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common neurodegenerative diseases, characterized by gradual and selective loss of neurons in the central nervous system. They affect more than 50 million people worldwide, and their incidence increases with age. Although most cases of AD and PD are sporadic, some are caused by genetic mutations that are inherited. Both sporadic and familial cases display complex neuropathology and represent the most perplexing neurological disorders. Because of the undefined pathogenesis and complex clinical manifestations, there is still no effective treatment for both AD and PD. Understanding the pathogenesis of these important neurodegenerative diseases is important for developing successful therapies. Increasing evidence suggests that microglial autophagy is associated with the pathogenesis of AD and PD, and its dysfunction has been implicated in disease progression. In this review, we focus on the autophagy function in microglia and its dysfunction in AD and PD disease models in an attempt to help our understanding of the pathogenesis and identifying new therapeutic targets of AD and PD.

Alzheimer's and Parkinson's disease therapies in the clinic

Alzheimer's disease (AD) and Parkinson's disease (PD) are the most prevalent neurodegenerative diseases, affecting millions and costing billions each year in the United States alone. Despite tremendous progress in developing therapeutics that manage the symptoms of these two diseases, the scientific community has yet to develop a treatment that effectively slows down, inhibits, or cures neurodegeneration. To gain a better understanding of the current therapeutic frontier for the treatment of AD and PD, we provide a review on past and present therapeutic strategies for these two major neurodegenerative disorders in the clinical trial process. We briefly recap currently US Food and Drug Administration-approved therapies, and then explore trends in clinical trials across the variables of therapy mechanism of disease intervention, administration route, use of delivery vehicle, and outcome measures, across the clinical phases over time for "Drug" and "Biologic" therapeutics. We then present the success rate of past clinical trials and analyze the intersections in therapeutic approaches for AD and PD, revealing the shift in clinical trials away from therapies targeting neurotransmitter systems that provide symptomatic relief, and towards anti-aggregation, anti-inflammatory, anti-oxidant, and regeneration strategies that aim to inhibit the root causes of disease progression. We also highlight the evolving distribution of the types of "Biologic" therapies investigated, and the slowly increasing yet still severe under-utilization of delivery vehicles for AD and PD therapeutics. We then briefly discuss novel preclinical strategies for treating AD and PD. Overall, this review aims to provide a succinct overview of the clinical landscape of AD and PD therapies to better understand the field's therapeutic strategy in the past and the field's evolution in approach to the present, to better inform how to effectively treat AD and PD in the future.

Current Peptide Vaccine and Immunotherapy Approaches Against Alzheimer's Disease

Peptide vaccines and immunotherapies against aggregating proteins involved in the pathogenesis and progression of Alzheimer's disease (AD) - the β-amyloid peptide (Aβ) and tau - are promising therapeutic avenues against AD. Two decades of effort has led to the controversial FDA approval of the monoclonal antibody Aducanumab (Aduhelm), which has subsequentially sparked the revival and expedited review of promising monoclonal antibody immunotherapies that target Aβ. In this review, we explore the development of Aβ and tau peptide vaccines and immunotherapies with monoclonal antibodies in clinical trials against AD.

Tau Protein as Therapeutic Target for Cancer? Focus on Glioblastoma

Despite being extensively studied for several decades, the microtubule-associated protein Tau has not finished revealing its secrets. For long, Tau has been known for its ability to promote microtubule assembly. A less known feature of Tau is its capability to bind to cancer-related protein kinases, suggesting a possible role of Tau in modulating microtubule-independent cellular pathways that are associated with oncogenesis. With the intention of finding new therapeutic targets for cancer, it appears essential to examine the interaction of Tau with these kinases and their consequences. This review aims at collecting the literature data supporting the relationship between Tau and cancer with a particular focus on glioblastoma tumors in which the pathological significance of Tau remains largely unexplored. We will first treat this subject from a mechanistic point of view showing the pivotal role of Tau in oncogenic processes. Then, we will discuss the involvement of Tau in dysregulating critical pathways in glioblastoma. Finally, we will outline promising strategies to target Tau protein for the therapy of glioblastoma.

Opportunities and challenges in delivering biologics for Alzheimer's disease by low-intensity ultrasound

Low-intensity ultrasound combined with intravenously injected microbubbles (US^+MB) is a novel treatment modality for brain disorders, including Alzheimer's disease (AD), safely and transiently allowing therapeutic agents to overcome the blood-brain barrier (BBB) that constitutes a major barrier for therapeutic agents. Here, we first provide an update on immunotherapies in AD and how US^+MB has been applied to AD mouse models and in clinical trials, considering the ultrasound and microbubble parameter space. In the second half of the review, we compare different in vitro BBB models and discuss strategies for combining US^+MB with BBB modulators (targeting molecules such as claudin-5), and highlight the insight provided by super-resolution microscopy. Finally, we conclude with a short discussion on how in vitro findings can inform the design of animal studies, and how the insight gained may aid treatment optimization in the clinical ultrasound space.

Single domain antibodies targeting pathological tau protein: Influence of four IgG subclasses on efficacy and toxicity

BACKGROUND

Eleven tau immunoglobulin G (IgG) antibodies have entered clinical trials to treat tauopathies, including Alzheimer's disease, but it is unclear which IgG subclass/subtype has the ideal efficacy and safety profile. Only two subtypes, with or without effector function, have been examined in the clinic and not for the same tau antibody. The few preclinical studies on this topic have only compared two subtypes of one antibody each and have yielded conflicting results.

METHODS

We selected two single domain antibodies (sdAbs) derived from a llama immunized with tau proteins and utilized them to generate an array of Fc-(sdAb)2 subclasses containing identical tau binding domains but differing Fc region. Unmodified sdAbs and their IgG subclasses were tested for efficacy in primary cultures and in vivo microdialysis using JNPL3 tauopathy mice.

FINDINGS

Unmodified sdAbs were non-toxic, blocked tau toxicity and promoted tau clearance. However, the efficacy/safety profile of their Fc-(sdAb)2 subclasses varied greatly within and between sdAbs. For one of them, all its subtypes were non-toxic, only those with effector function cleared tau, and were more effective in vivo than unmodified sdAb. For the other sdAb, all its subtypes were toxic in tauopathy cultures but not in wild-type cells, suggesting that bivalent binding of its tau epitope stabilizes a toxic conformation of tau, with major implications for tau pathogenesis. Likewise, its subclasses were less effective than the unmodified sdAb in clearing tau in vivo.

INTERPRETATION

These findings indicate that tau antibodies with effector function are safe and better at clearing pathological tau than effectorless antibodies, Furthermore, tau antibodies can provide a valuable insight into tau pathogenesis, and some may aggravate it.

FUNDING

Funding for these studies was provided by the National Institute of Health (R01 AG032611, R01 NS077239, RF1 NS120488, R21 AG 069475, R21 AG 058282, T32AG052909), and the NYU Alzheimer's Disease Center Pilot Grant Program (via P30 AG008051).

Tau antibody 77G7 targeting microtubule binding domain suppresses proteopathic tau to seed tau aggregation

INTRODUCTION

Neurofibrillary tangle (NFT) of hyperphosphorylated tau is a hallmark of Alzheimer's disease (AD) and related tauopathies. Tau lesion starts in the trans-entorhinal cortex, from where it spreads to limbic regions, followed by neocortical areas. The regional distribution of NFTs associates with the progression of AD. Accumulating evidence suggests that proteopathic tau can seed tau aggregation in a prion-like fashion in vitro and in vivo. Inhibition of tau seeding activity could provide a potential therapeutic opportunity to block the propagation of tau pathology in AD and related tauopathies.

AIMS

In the present study, we investigated the role of 77G7, a monoclonal tau antibody to the microtubule-binding repeats, in repressing the seeding activity of proteopathic tau.

RESULTS

We found that 77G7 had a higher affinity toward aggregated pathological tau fractions than un-aggregated tau derived from AD brain. 77G7 inhibited the internalization of tau aggregates by cells, blocked AD O-tau to capture normal tau, and to seed tau aggregation in vitro and in cultured cells. Tau pathology induced by hippocampal injection of AD O-tau in 3xTg-AD mice was suppressed by mixing 77G7 with AD O-tau. Intravenous administration of 77G7 ameliorated site-specific hyperphosphorylation of tau induced by AD O-tau in the hippocampi of Tg/hTau mice.

CONCLUSION

These findings indicate that 77G7 can effectively suppress the seeding activity of AD O-tau and thus could be developed as a potential immunotherapeutic drug to inhibit the propagation of tau pathology in AD and related tauopathies.

Exploring the Formation of Polymers with Anti-Amyloid Properties within the 2′3′-Dihydroxyflavone Autoxidation Process

Amyloid-β and α-synuclein aggregation into amyloid fibrils is linked to the onset and progression of Alzheimer’s and Parkinson’s diseases. While there are only a few disease-modifying drugs, it is essential to search for new, more effective ways to encounter these neurodegenerative diseases. Multiple research articles have shown that the autoxidation of flavone is a critical factor for activating the inhibitory potential against the protein aggregation. Despite this, the structure of the newly-formed inhibitors is unknown. In this research, we examined the autoxidation products of 2′,3′-dihydroxyflavone that were previously shown to possess one of the most prominent inhibitory effects against amyloid-β aggregation. Their analysis using HPLC suggested the formation of polymeric molecules that were isolated using a 3 kDa cut-off. These polymeric structures were indicated as the most potent inhibitors based on protein aggregation kinetics and AFM studies. This revelation was confirmed using MALDI-TOF and NMR. We also show that active molecules have a tendency to reduce the Amyloid-β and α-synuclein aggregates toxicity to SH-SY5Y cells.

Therapeutic Effects of Hydrogen Gas Inhalation on Trimethyltin-Induced Neurotoxicity and Cognitive Impairment in the C57BL/6 Mice Model

Oxidative stress (OS) is one of the causative factors in the pathogenesis of various neurodegenerative diseases, including Alzheimer’s disease (AD) and cognitive dysfunction. In the present study, we investigated the effects of hydrogen (H₂) gas inhalation in trimethyltin (TMT)-induced neurotoxicity and cognitive dysfunction in the C57BL/6 mice. First, mice were divided into the following groups: mice without TMT injection (NC), TMT-only injection group (TMT only), TMT injection + lithium chloride-treated group as a positive control (PC), and TMT injection + 2% H₂ inhalation-treated group (H₂). The TMT injection groups were administered a single dosage of intraperitoneal TMT injection (2.6 mg/kg body weight) and the H₂ group was treated with 2% H₂ for 30 min once a day for four weeks. Additionally, a behavioral test was performed with Y-maze to test the cognitive abilities of the mice. Furthermore, multiple OS- and AD-related biomarkers such as reactive oxygen species (ROS), nitric oxide (NO), calcium (Ca²⁺), malondialdehyde (MDA), glutathione peroxidase (GPx), catalase, inflammatory cytokines, apolipoprotein E (Apo-E), amyloid β (Aβ)-40, phospho-tau (p-tau), Bcl-2, and Bcl-2- associated X (Bax) were investigated in the blood and brain. Our results demonstrated that TMT exposure alters seizure and spatial recognition memory. However, after H₂ treatment, memory deficits were ameliorated. H₂ treatment also decreased AD-related biomarkers, such as Apo-E, Aβ-40, p-tau, and Bax and OS markers such as ROS, NO, Ca²⁺, and MDA in both serum and brain. In contrast, catalase and GPx activities were significantly increased in the TMT-only group and decreased after H₂ gas treatment in serum and brain. In addition, inflammatory cytokines such as granulocyte colony-stimulating factors (G-CSF), interleukin (IL)-6, and tumor necrosis factor alpha (TNF-α) were found to be significantly decreased after H₂ treatment in both serum and brain lysates. In contrast, Bcl-2 and vascular endothelial growth factor (VEGF) expression levels were found to be enhanced after H₂ treatment. Taken together, our results demonstrated that 2% H₂ gas inhalation in TMT-treated mice exhibits memory enhancing activity and decreases the AD, OS, and inflammatory-related markers. Therefore, H₂ might be a candidate for repairing neurodegenerative diseases with cognitive dysfunction. However, further mechanistic studies are needed to fully clarify the effects of H₂ inhalation on TMT-induced neurotoxicity and cognitive dysfunction.

Targeting tau only extracellularly is likely to be less efficacious than targeting it both intra- and extracellularly

Aggregation of the tau protein is thought to be responsible for the neurodegeneration and subsequent functional impairments in diseases that are collectively named tauopathies. Alzheimer's disease is the most common tauopathy, but the group consists of over 20 different diseases, many of which have tau pathology as their primary feature. The development of tau therapies has mainly focused on preventing the formation of and/or clearing these aggregates. Of these, immunotherapies that aim to either elicit endogenous tau antibodies or deliver exogenous ones are the most common approach in clinical trials. While their mechanism of action can involve several pathways, both extra- and intracellular, pharmaceutical companies have primarily focused on antibody-mediated clearance of extracellular tau. As we have pointed out over the years, this is rather surprising because it is well known that most of pathological tau protein is found intracellularly. It has been repeatedly shown by several groups over the past decades that antibodies can enter neurons and that their cellular uptake can be enhanced by various means, particularly by altering their charge. Here, we will briefly describe the potential extra- and intracellular mechanisms involved in antibody-mediated clearance of tau pathology, discuss these in the context of recent failures of some of the tau antibody trials, and finally provide a brief overview of how the intracellular efficacy of tau antibodies can potentially be further improved by certain modifications that aim to enhance tau clearance via specific intracellular degradation pathways.

[Disease-modifying treatment approaches for Alzheimer's disease]

Die Alzheimer-Krankheit ist eine der großen Volkskrankheiten mit bisher allein symptomatischen Therapieoptionen. Neue Erkenntnisse zu einem Krankheitskontinuum mit einer sehr langen präklinischen und frühsymptomatischen Krankheitsphase sowie molekulare Therapiestrategien, die auf den Erkenntnissen zur molekularen Neurobiologie der Erkrankung fußen, eröffnen eine Vielzahl neuer therapeutischer Strategien. Im Jahr 2021 ist erstmals ein Antiamyloidantikörper in den USA als krankheitsmodifizierende Therapie bei Alzheimer-Krankheit zugelassen worden, was einen ersten, sehr kontrovers diskutierten Schritt hin zu einer molekularen, ursachenorientierten Therapie darstellt. Die Übersicht stellt die am weitesten entwickelten molekularen Therapiestrategien sowie die Auswirkungen der zugelassenen Antikörpertherapie für die Praxis vor. Die Besonderheiten einer Langzeittherapie mit i.v. Infusionen in einer besonders vulnerablen Patientenpopulation und einem speziellen Nebenwirkungsprofil wird für die Implementierung in die Praxis große Herausforderungen mit sich bringen und ein hohes Maß an Kooperation erfordern. Die Zukunft der Alzheimer-Therapie mit einem multimodalen Therapieansatz mit verschiedenen Substanzen wird diesen Trend wahrscheinlich noch verstärken.

Oxidative Stress and Beta Amyloid in Alzheimer's Disease. Which Comes First: The Chicken or the Egg?

The pathogenesis of Alzheimer's disease involves β amyloid (Aβ) accumulation known to induce synaptic dysfunction and neurodegeneration. The brain's vulnerability to oxidative stress (OS) is considered a crucial detrimental factor in Alzheimer's disease. OS and Aβ are linked to each other because Aβ induces OS, and OS increases the Aβ deposition. Thus, the answer to the question "which comes first: the chicken or the egg?" remains extremely difficult. In any case, the evidence for the primary occurrence of oxidative stress in AD is attractive. Thus, evidence indicates that a long period of gradual oxidative damage accumulation precedes and results in the appearance of clinical and pathological AD symptoms, including Aβ deposition, neurofibrillary tangle formation, metabolic dysfunction, and cognitive decline. Moreover, oxidative stress plays a crucial role in the pathogenesis of many risk factors for AD. Alzheimer's disease begins many years before its symptoms, and antioxidant treatment can be an important therapeutic target for attacking the disease.