A new study from the University of Cincinnati is challenging the widely accepted amyloid-beta theory of Alzheimer's disease, suggesting that the reduction of amyloid-beta (Aβ42) protein levels in the brain, rather than the accumulation of amyloid plaques, is a primary driver of cognitive decline. This research, published in the journal Brain, analyzed data from approximately 26,000 individuals involved in clinical trials for monoclonal antibody treatments targeting Alzheimer's. The findings could significantly shift the focus of future research and drug development efforts.
Challenging the Amyloid Hypothesis
The prevailing amyloid hypothesis posits that the buildup of amyloid plaques in the brain is the main cause of Alzheimer's disease. However, Alberto Espay, MD, professor of neurology at the University of Cincinnati, and his team found that many individuals with amyloid plaques do not develop Alzheimer's. "By the age of 85 years, only one fifth of those with amyloid plaques develop Alzheimer’s disease," Espay noted. The key difference, according to their research, lies in the ability to maintain sufficient levels of Aβ42, a protein crucial for brain health.
Aβ42 as a Neuroprotective Agent
The study suggests that Aβ42 acts as a protective agent in the brain, reacting to toxic and infectious exposures. In this process, Aβ42 can transform into amyloid plaques, which Espay describes as "tombstones" of Aβ42. The researchers observed that monoclonal antibody treatments, while designed to reduce amyloid plaques, unintentionally increased Aβ42 levels. Analyzing data from clinical trials, they discovered that higher levels of Aβ42 after treatment were independently associated with slower cognitive impairment and clinical decline.
Implications for Future Therapies
These findings suggest a paradigm shift in Alzheimer's research. "Alzheimer’s is a process of loss (of Aβ42) not of gain (of amyloid)," Espay stated. He advocates for future medications to focus on directly increasing Aβ42 levels, rather than solely targeting the reduction of amyloid plaques. His team is currently evaluating therapies with the potential to increase Aβ42 as a form of rescue therapy.
Expert Commentary
David Merrill, MD, PhD, a geriatric psychiatrist at Providence Saint John’s Health Center, commented that the increase in Aβ42 could explain the marginal benefits observed with new Alzheimer's drugs. He also emphasized the importance of looking beyond amyloid for the causes of Alzheimer's disease, highlighting that the processing of amyloid precursor protein depends on numerous modifiable health factors.
Karen D. Sullivan, PhD, ABPP, a neuropsychologist, noted that these findings represent a "sea-change" from the currently accepted theory. She added that the idea that increased amyloid-beta levels may contribute to the helpful mechanism of action of anti-monoclonal antibody drugs will be a shock to many in the neuroscience community.
Broader Perspective on Alzheimer's Risk
Merrill pointed to the Lancet Commission on Alzheimer’s disease, which identifies at least 14 modifiable factors contributing to approximately 45% of all Alzheimer's cases. These factors include exercise, treatment of hearing and vision loss, and management of diabetes and hypertension. Adopting healthful habits and addressing these modifiable risk factors may lower plaque loads while increasing soluble Aβ42 and improving cognitive function over time.
