Background: Serum homocysteine (Hcy) level is considered to be an important biomarker for Alzheimer’s disease (AD); however, the status of Hcy in brain tissue, and the association between brain and serum levels of Hcy in AD patients remain unclear. Objective: We aimed to examine whether the changes of three thiols are consistent in serum of AD patients and the brain of APP/PS1 mice, and to verify the effectiveness of Hcy as a biomarker for early AD detection. Methods: The levels of Hcy, cysteine (Cys), and glutathione (GSH) in Aβ 1–42-treated PC12 cells, the brain and hippocampus of APP/PS1 mouse, and the serum of AD patients were evaluated using 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) and ELISA assay or LC-MS. Results: Measurement by Probe 1 revealed a significant increase in Hcy level, and a decrease in Cys and GSH levels in Aβ1–42-treated PC12 cells and the serum of AD patients. 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. 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. Conclusion: Changes in Hcy, Cys, and GSH levels in the brain of APP/PS1 mice and Aβ 1–42-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 increases in Hcy levels.

Floridoside is a low-molecular-weight organic compound, which can be accumulated by red algae under stressful conditions to protect cells via its excellent antioxidant properties. In the present study, we investigated the antioxidant mechanism of floridoside toward human hepatocyte L-02 cells. We found that floridoside had no toxicity to L-02 cells, and no reactive oxidative species were induced by it either. However, the expression of hemoxygenase-1 (HO-1) protein was up-regulated upon exposure to floridoside, and two antioxidant enzymes, superoxide dismutase (SOD) and GSH-Px, were activated by floridoside. Moreover, we investigated the pathway involved in the production of these antioxidants, p38/extracellular signal-regulated kinase (ERK) MAPK-nuclear factor-erythroid-2-related factor 2 (Nrf2) pathway. ERK1/2 and p38 phosphorylation, nuclear translocation of Nrf2, and activation of ARE luciferase activity were observed upon exposure to floridoside. siRNA interference and inhibitor treatment suppressed the HO-1 expression and the phosphorylation of ERK1/2 and p38, respectively. These results indicated that floridoside exerted its antioxidant activity by activating HO-1 expression via p38/ERK MAPK-Nrf2 pathway in human hepatocyte L-02 cells.

A sensitive fluorescent probe (E)-4-(3-(benzo[d]thiazol-2-yl)-4-hydroxy-5-methylstyryl)-1-methylpyridin-1-ium iodide (HBTMP) for the monitoring of pH in mitochondria was rationally exploited.

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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.