A US study has found that African green monkeys showed no measurable memory decline despite persistent Alzheimer’s-related brain changes one year after exposure to synthetic amyloid-β (Aβ) clusters, opening new avenues for studying the early stages of Alzheimer’s disease. 

Alzheimer’s disease is the most common cause of dementia and biological changes associated with the disease, such as accumulation of Aβ plaques and neuronal death, can begin years before memory decline becomes apparent. African green monkeys naturally develop some Alzheimer’s-like brain changes as they age, including Aβ plaque accumulation, making them a useful model for studying aspects of the disease.  

Researchers from Yale University gave five female African green monkeys injections of synthetic Aβ oligomers – the building blocks of Aβ plaques – into the cerebrospinal fluid, which surrounds the brain and spinal cord, over four weeks. One year after exposure, the monkeys showed no decline in their ability to recognise a previously seen shape on a screen among other shapes, shortly after seeing it for the first time. Yet, their cerebrospinal fluid had persistent changes in proteins associated with immune responses, neuronal communication, blood vesselsand clotting. These changes were detectable using less than one millilitre of cerebrospinal fluid, demonstrating the potential of this approach for monitoring biological changes in living subjects over time using small samples. However, it is still necessary to compare the protein changes with those found in human samples to determine which markers could be relevant to human disease.  

“What would be premature is to assume that every molecular change we see in the monkeys represents early Alzheimer's disease in humans,” said Bianca Brown, researcher from Yale University and one of the lead authors of the study published in Communications Biology.