Anti-amyloid trials raise scientific and ethical questions

An Ethical Argument for Ending Human Trials of Amyloid-Lowering Therapies in Alzheimer's Disease

Given the past two decades of over 40 failed trials of amyloid-lowering therapies in Alzheimer's Disease (AD), many of which succeeded in lowering amyloid as designed, we present an ethical argument for emptying the drug pipeline of tests of amyloid-lowering agents so as to end the historical dominance of the amyloid-reducing therapeutic approach in AD.

Controversial Past, Splendid Present, Unpredictable Future: A Brief Review of Alzheimer Disease History

Background: The concept of Alzheimer disease (AD)-since its histological discovery by Alzheimer to the present day-has undergone substantial modifications. Methods: We conducted a classical narrative review of this field with a bibliography selection (giving preference to Medline best match). Results: The following subjects are reviewed and discussed: Alzheimer's discovery, Kraepelin's creation of a new disease that was a rare condition until the 1970's, the growing interest and investment in AD as a major killer in a society with a large elderly population in the second half of the 20th century, the consolidation of the AD clinicopathological model, and the modern AD nosology based on the dominant amyloid hypothesis among many others. In the 21st century, the development of AD biomarkers has supported a novel biological definition of AD, although the proposed therapies have failed to cure this disease. The incidence of dementia/AD has shown a decrease in affluent countries (possibly due to control of risk factors), and mixed dementia has been established as the most frequent etiology in the oldest old. Conclusions: The current concept of AD lacks unanimity. Many hypotheses attempt to explain its complex physiopathology entwined with aging, and the dominant amyloid cascade has yielded poor therapeutic results. The reduction in the incidence of dementia/AD appears promising but it should be confirmed in the future. A reevaluation of the AD concept is also necessary.

Finding the falsification threshold of the toxic proteinopathy hypothesis in neurodegeneration

A biomedical hypothesis is a theoretical assumption amenable to being tested in a randomized clinical trial. The main hypotheses in neurodegenerative disorders are based on the concept that proteins accumulate in an aggregated fashion and trigger toxicity. The toxic proteinopathy hypothesis posits that neurodegeneration is caused by toxicity of aggregated amyloid in Alzheimer's disease (toxic amyloid hypothesis), aggregated α-synuclein in Parkinson's disease (toxic synuclein hypothesis), and aggregated tau in progressive supranuclear palsy (toxic tau hypothesis). To date, we have accumulated 40 negative anti-amyloid randomized clinical, 2 anti-synuclein trials, and 4 anti-tau trials. These results have not prompted a major reconsideration of the toxic proteinopathy hypothesis of causality. Imperfections in trial design and execution (incorrect dosage, insensitive endpoints, too-advanced population) but not in the underlying hypotheses have prevailed as explaining the failures. We review here the evidence suggesting that the threshold of hypothesis falsifiability may be too high and advocate in favor of a minimal set of rules that facilitate the interpretation of negative clinical trials as falsifying the driving hypotheses, in particular if the desirable change in surrogate endpoints has been achieved. We propose four steps to refute a hypothesis in future-negative surrogate-backed trials and argue that for the actual rejection to take place, refutation must be accompanied by the proposal of an alternative hypothesis. The absence of alternative hypotheses may be the single greatest reason why there remains hesitancy in rejecting the toxic proteinopathy hypothesis: in the absence of alternatives, we have no clear guidance as to where to redirect or focus.

Advances in Recapitulating Alzheimer's Disease Phenotypes Using Human Induced Pluripotent Stem Cell-Based In Vitro Models

Alzheimer's disease (AD) is an incurable neurodegenerative disorder and the leading cause of death among older individuals. Available treatment strategies only temporarily mitigate symptoms without modifying disease progression. Recent studies revealed the multifaceted neurobiology of AD and shifted the target of drug development. Established animal models of AD are mostly tailored to yield a subset of disease phenotypes, which do not recapitulate the complexity of sporadic late-onset AD, the most common form of the disease. The use of human induced pluripotent stem cells (HiPSCs) offers unique opportunities to fill these gaps. Emerging technology allows the development of disease models that recapitulate a brain-like microenvironment using patient-derived cells. These models retain the individual's unraveled genetic background, yielding clinically relevant disease phenotypes and enabling cost-effective, high-throughput studies for drug discovery. Here, we review the development of various HiPSC-based models to study AD mechanisms and their application in drug discovery.