Changes in Biothiol Levels are Closely Associated with Alzheimer's Disease

Abstract Background：Alzheimer’s disease (AD) is a progressive, neurodegenerative disease of the brain. Serum homocysteine (Hcy) level is considered to be an important biomarker for AD, however, the status of Hcy in brain tissue and neuronal cells, and the association between brain and serum levels of Hcy in clinical AD patients currently remain unclear. Methods: The levels of Hcy and other biothiols such as cysteine (Cys) and glutathione (GSH) in clinical blood samples were evaluated using a non-cytotoxic and stable multi-signal fluorescent probe, ethyl (E)-3-(9-chloro-11-oxo-2,3,6,7-tetrahydro-1H,5H,11H-pyrano[2,3-f] pyrido[3,2,1 -ij]quinolin-10-yl)-2-cyanoacrylate (Probe 1), which were verified by ELISA. Results: Measurement by Probe 1 revealed a significant increase in Hcy level, and a decrease in Cys and GSH levels in PC12 cells treated with in Aβ1-42. The hippocampus and whole brain of APP/PS1 mice also showed a significant increase in Hcy level alongside the accumulation of age-related AD symptoms, while levels of Cys and GSH decreased simultaneously. This change was also observed in serum samples acquired from patients with AD. The upregulation of Hcy and the downregulation of Cys and GSH were reversed in the Aβ1-42-treated PC12 cells and the brain of APP/PS1 mice when supplemented with VB6, an important coenzyme in Hcy metabolism. Conclusions: Changes in Hcy, Cys and GSH levels in the brain of APP/PS1 mice and Aβ1-42-treated PC12 cells were observed in situ with a new fluorescent probe, which were consistent with the abnormal changes in Hcy, Cys and GSH levels in the serum of AD patients. VB6 supplementation was successful in ameliorating abnormal upregulation of Hcy in the brain of APP/PS1 mice and in Aβ1-42-treated PC12 cells.