A Proposal to Make Biomedical Research into Alzheimer’s Disease More Democratic Following an International Survey with Researchers

Background: Therapeutic research into Alzheimer’s disease (AD) has been dominated by the amyloid cascade hypothesis (ACH) since the 1990s. However, targeting amyloid in AD patients has not yet resulted in highly significant disease-modifying effects. Furthermore, other promising theories of AD etiology exist. Objective: We sought to directly investigate whether the ACH still dominates the opinions of researchers working on AD and explore the implications of this question for future directions of research. Methods: During 2019, we undertook an international survey promoted with the help of the Alzheimer’s Association with questions on theories and treatments of AD. Further efforts to promote a similar study in 2021 did not recruit a significant number of participants. Results: 173 researchers took part in the 2019 survey, 22% of which held “pro-ACH” opinions, tended to have more publications, were more likely to be male, and over 60. Thus, pro-ACH may now be a minority opinion in the field but is nevertheless the hypothesis on which the most clinical trials are based, suggestive of a representation bias. Popular vote of all 173 participants suggested that lifestyle treatments and anti-tau drugs were a source of more therapeutic optimism than anti-amyloid treatments. Conclusion: We propose a more democratic research structure which increases the likelihood that promising theories are published and funded fairly, promotes a broader scientific view of AD, and reduces the larger community’s dependence on a fragile economic model.

Insulin Resistance as a Common Link Between Current Alzheimer’s Disease Hypotheses

Almost 115 years ago, Alois Alzheimer described Alzheimer’s disease (AD) for the first time. Since then, many hypotheses have been proposed. However, AD remains a severe health public problem. The current medical approaches for AD are limited to symptomatic interventions and the complexity of this disease has led to a failure rate of approximately 99.6%in AD clinical trials. In fact, no new drug has been approved for AD treatment since 2003. These failures indicate that we are failing in mimicking this disease in experimental models. Although most studies have focused on the amyloid cascade hypothesis of AD, the literature has made clear that AD is rather a multifactorial disorder. Therefore, the persistence in a single theory has resulted in lost opportunities. In this review, we aim to present the striking points of the long scientific path followed since the description of the first AD case and the main AD hypotheses discussed over the last decades. We also propose insulin resistance as a common link between many other hypotheses.

Alzheimer's disease research: past approaches and future directions

Background: Three decades after the amyloid cascade hypothesis was first proposed, research into discovery of effective treatments for Alzheimer's disease has not yet produced any disease-modifying treatments. Aims: This review outlines the progress made by dementia research thus far, and provides a brief overview of the therapeutic approaches resulting from the amyloid cascade hypothesis. It then describes the shift in research focus to the early stages of the condition, the challenges it presents and potential consequences for care. Methods: A literature overview was undertaken by reviewing research papers, published protocols and policy guidelines. Findings: Past research has failed to produce effective treatments for dementia, yet the causes of this failure remain debated. Discovery of affordable, early biomarkers has emerged as a key target of investigation as the focus has shifted from treatment to prevention of the condition. Conclusions: Failures in identifying effective treatments for dementia have highlighted the importance of earlyidentification and intervention in patients as a way to prevent neurodegeneration and progression to dementia. Discovery of biomarkers is a key focus of current research. In the future, regular screening for dementia may be recommended for all older people in an effort to assess individual risk. Care may reflect a combination of early pharmacological interventions and lifestyle modification programmesbased on risk.

The amyloid cascade hypothesis and Alzheimer’s disease: A mathematical model

The paper presents a conceptual mathematical model for Alzheimer’s disease (AD). According to the so-called amyloid cascade hypothesis, we assume that the progression of AD is associated with the presence of soluble toxic oligomers of beta-amyloid. Monomers of this protein are produced normally throughout life, but a change in the metabolism may increase their total production and, through aggregation, ultimately results in a large quantity of highly toxic polymers. The evolution from monomeric amyloid produced by the neurons to senile plaques (long and insoluble polymeric amyloid chains) is modelled by a system of ordinary differential equations (ODEs), in the spirit of the Smoluchowski equation. The basic assumptions of the model are that, at the scale of suitably small representative elementary volumes (REVs) of the brain, the production of monomers depends on the average degradation of the neurons and in turn, at a much slower timescale, the degradation is caused by the number of toxic oligomers. To mimic prion-like diffusion of the disease in the brain, we introduce an interaction among adjacent REVs that can be assumed to be isotropic or to follow given preferential patterns. We display the results of numerical simulations which are obtained under some simplifying assumptions. For instance, the amyloid cascade is modelled by just three ordinary differential equations (ODEs), and the simulations refer to abstract 2D domains, simplifications which can be easily avoided at the price of some additional computational costs. Since the model is suitably flexible to incorporate other mechanisms and geometries, we believe that it can be generalised to describe more realistic situations.

Computational Modeling of Catecholamines Dysfunction in Alzheimer’s Disease at Pre-Plaque Stage

Background: Alzheimer’s disease (AD) etiopathogenesis remains partially unexplained. The main conceptual framework used to study AD is the Amyloid Cascade Hypothesis, although the failure of recent clinical experimentation seems to reduce its potential in AD research. Objective: A possible explanation for the failure of clinical trials is that they are set too late in AD progression. Recent studies suggest that the ventral tegmental area (VTA) degeneration could be one of the first events occurring in AD progression (pre-plaque stage). Methods: Here we investigate this hypothesis through a computational model and computer simulations validated with behavioral and neural data from patients. Results: We show that VTA degeneration might lead to system-level adjustments of catecholamine release, triggering a sequence of events leading to relevant clinical and pathological signs of AD. These changes consist first in a midfrontal-driven compensatory hyperactivation of both VTA and locus coeruleus (norepinephrine) followed, with the progression of the VTA impairment, by a downregulation of catecholamine release. These processes could then trigger the neural degeneration at the cortical and hippocampal levels, due to the chronic loss of the neuroprotective role of norepinephrine. Conclusion: Our novel hypothesis might contribute to the formulation of a wider system-level view of AD which might help to devise early diagnostic and therapeutic interventions.

3. Beyond amyloid

‘Beyond amyloid’ outlines recent challenges to the amyloid cascade hypothesis of Alzheimer’s disease. This theory’s enduring popularity has not been matched by success in the clinic. Some people without dementia appear to have high amyloid levels and some brain-injured patients with more amyloid have better outcomes than those with less. One possible explanation is that neurodegeneration begins long before symptoms appear. Other theories include amyloid as the defence rather than cause, and the idea of an immune response to infection causing inflammation in the brain. All this points towards the importance of method and the acknowledgement of the roles played by other parts of the body and lifestyle factors.