Inhibitory effects of curcumin on H₂O₂-induced cell damage and APP expression and processing in SH-SY5Y cells...

Alzheimer's disease (AD) is a neurodegenerative disorder, and the pathological mechanism of the disease is still far to understand. According to the amyloid cascade hypothesis in AD, Amyloid-β (Aβ) is considered as a key substance that contributes AD development. Aβ is a β-cleaving product from Amyloid-β protein precursor (APP). Mutations of APP including APP_{KM670/671670NL} (Swedish mutation) result in Aβ overproduction and the development of early-onset familial AD. Increase of oxidative stress and damage also occurs in early stage of AD. In this study, we used a SH-SY5Y cell line that stably expresses APP gene with Swedish mutation (SH-SY5Y-APPswe), and the inhibitory effects of curcumin on H₂O₂-induced cell damage and APP processing were investigated. Cells were treated with curcumin (0 ~ 5 μM) for 4 h before hydrogen peroxide (H₂O₂). Cell growth was detected with CCK-8 assay, and cell damage was determined through the evaluation of release of lactate dehydrogenase (LDH) from the cytosol to the culture medium and the morphological change of nucleus. The ability of mitochondrial stress and the depolarization of mitochondrial membrane potential were assayed through the measuring the oxygen consumption rate (OCR) and the green/red fluorescence ratio of JC-1 dye respectively. The protein levels of APP, sAPPα, sAPPβ, and BACE1 were analyzed with Western blot assay. Aβ production was measured with enzyme-linked immunosorbent assay (ELISA). The results indicated that curcumin inhibits H₂O₂-induced decrease of cell growth and cell damage. Curcumin attenuates H₂O₂-induced damage on the ability to mitochondrial oxidative phosphorylation and membrane potential. Curcumin inhibits H₂O₂-induced increase of APP cleavage through β-cleavage pathway and of intracellular Aβ production. These results imply that curcumin can be used to treat AD through inhibiting oxidative damage-induced APP β-cleavage and intracellular Aβ generation.