Alzheimer's Disease and Age-Related Changes in the Cu Isotopic Composition of Blood Plasma and Brain Tissues of the APP^NL-G-F Murine Model Revealed by Multi-Collector ICP-Mass Spectrometry

Simple Summary Alzheimer's disease is the most prevalent form of dementia and is associated with multiple alterations in biological processes. The most profound changes consist of the formation of two types of protein aggregations, called & beta;-amyloid plaques and neurofibrillary tangles of tau proteins. Different biologically relevant metals are believed to play a role during the development of Alzheimer's disease, including copper. In Alzheimer's disease, copper has been reported to interact with & beta;-amyloid plaques and neurofibrillary tangles, while in addition its homeostasis and metabolism are known to be affected. Therefore, Cu was investigated in a murine model mimicking Alzheimer's disease. These mice were genetically manipulated, resulting in the presence of typical Alzheimer's disease symptoms. By making use of two inductively coupled plasma-mass spectrometry (ICP-MS) based analysis techniques, the Cu concentration and the ratio between the natural Cu-65 and Cu-63 isotopes (Cu-65/Cu-63) were determined in blood plasma and four different brain regions-brain stem, cerebellum, cortex, and hippocampus-of young and aged Alzheimer's mice and age-matched healthy controls. The Cu concentration in blood plasma was significantly altered in response to both age- and Alzheimer's-related effects, whereas the blood plasma Cu isotope ratio was affected in the Alzheimer's-affected mice only. Both the brain stem and cerebellum showed changes in Cu concentration and Cu-65/Cu-63 isotope ratio as a result of ageing and the development of Alzheimer's disease. Finally, a correlation was observed between the Cu-65/Cu-63 isotope ratio in the cerebellum and blood plasma. Determination of Cu concentration and isotope ratio is therefore a relevant tool to unravel the role of Cu in ageing and Alzheimer's disease. Alzheimer's' disease (AD) is characterized by the formation of & beta;-amyloid (A & beta;) plaques and neurofibrillary tangles of tau protein in the brain. A & beta; plaques are formed by the cleavage of the & beta;-amyloid precursor protein (APP). In addition to protein aggregations, the metabolism of the essential mineral element Cu is also altered during the pathogenesis of AD. The concentration and the natural isotopic composition of Cu were investigated in blood plasma and multiple brain regions (brain stem, cerebellum, cortex, and hippocampus) of young (3-4 weeks) and aged (27-30 weeks) APP(NL-G-F) knock-in mice and wild-type controls to assess potential alterations associated with ageing and AD. Tandem inductively coupled plasma-mass spectrometry (ICP-MS/MS) was used for elemental analysis and multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) for high-precision isotopic analysis. The blood plasma Cu concentration was significantly altered in response to both age- and AD-related effects, whereas the blood plasma Cu isotope ratio was only affected by the development of AD. Changes in the Cu isotopic signature of the cerebellum were significantly correlated with the changes observed in blood plasma. The brain stem showed a significant increase in Cu concentration for both young and aged AD transgenic mice compared with healthy controls, whereas the Cu isotopic signature became lighter as a result of age-related changes. In this work, ICP-MS/MS and MC-ICP-MS provided relevant and complementary information on the potential role of Cu in ageing and AD.