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Alzheimer’s disease: cosmochemistry for the benefit of the brain

By applying tools developed for the study of planet formation to the brains of Alzheimer's patients, scientists at the Paris Institute of Earth Physics and the University of Paris Faculty of Health have revealed a particular balance in the chemical composition of metals contained in amyloid plaques and tau fibrils in the patients' brains.

Alzheimer’s disease: cosmochemistry for the benefit of the brain

Publication date: 14/10/2020

Press, Research

Related themes : Origins

One of the consequences of Alzheimer’s disease is the formation of metal-rich extracellular plaques in the brain: amyloid plaques and tau fibrils. The metals present in these extracellular plaques include copper and zinc. Concentrations of these metals in human tissue vary naturally over time, with diet for example. Measuring their concentrations alone is therefore not a very good indicator of the formation of amyloid plaques and tau fibrils.

MRI of the brain of an Alzheimer's patient.

The originality of this study lies in the fact that the researchers used techniques traditionally used in cosmochemistry, in order to characterise in greater detail the metals present in the extracellular plaques obtained from samples of the brains of Alzheimer’s patients.

For all chemical elements (copper, zinc, etc.), each atom exists naturally in several forms that are very close to each other: isotopes. The difference between two isotopes is the number of neutrons they contain. Two isotopes of copper, for example, do not have the same mass but have very similar chemical and physical properties. In nature, the different isotopes of the same element (copper or zinc, for example) do not exist in equal quantities, and the ratio between the quantities of each isotope of the same element in a given medium – the isotope ratio – is characteristic of the chemical processes from which that medium originates. For example, a chemical reaction will favour the presence of one isotope of an element over another in the reaction products, depending on their slight difference in mass. Calculations of isotope ratios are therefore widely used in geochemistry and cosmochemistry to trace the history of a sample. For example, it was measurements of variations in the isotopic abundances of copper and zinc that enabled IPGP researchers to understand the origin of the Moon!

In the study Copper and zinc isotopic excursions in the human brain affected by Alzheimer’s Disease, the researchers measured the isotopic ratios of copper and zinc in tissue samples from brains affected by Alzheimer’s Disease and tissue samples from healthy brains.

In the samples analysed, they found that the presence of amyloid plaques in the brain of a person with Alzheimer’s disease alters the isotopic ratio for copper. The brain of a patient is thus richer in light copper isotopes than a healthy brain. This is explained by a change in the oxidation state of copper during the formation of amyloid plaques and tau fibrils.

These results, published on 13 October 2020 in the journal Alzheimer & Dementia: Diagnosis, Assessment and Disease Monitoring, open up the prospect of being able to monitor the progression of Alzheimer’s disease by measuring the copper isotope ratio in patients’ brains. The teams involved will now continue their studies to determine whether similar changes could be detected in the blood or in the cerebrospinal fluid, which is easier to analyse than brain tissue.

Ref : Moynier F, Le Borgne M, Laoud E, Mahan B, Mouton-Ligier F, Hugon J, Paquet C. Copper and zinc isotopic excursions in the human brainaffected by Alzheimer’s Disease. Alzheimer’s Dement. 2020;12:e12112. https://doi.org/10.1002/dad2.12112

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