Chitooligosaccharides Attenuate Cu2+-Induced Cellular Oxidative Damage and Cell Apoptosis Involving Nrf2 Activation

Alzheimer's disease (AD) is one of the common neurodegenerative diseases. Increase of labile copper pool plays an important role in the pathogenesis of AD. Nrf2(NF-E2-related factor-2)-ARE (antioxidant response element) signaling is an important intracellular manner to defend against oxidative stress. In this study, we used SH-SY5Y cells as a model of neuron to test the effect of chitooligosaccharides (COSs) on Cu2+-induced oxidative damage. SH-SY5Y cells were treated with different concentrations of COSs (100-800 mg/L) before incubated with Cu2+. Cell viability and cell damage and apoptosis were assessed. Both extracellular H2O2 and intracellular ROS were measured and the relative levels of Nrf2, phosphorylated Nrf2, and HO-1 were analyzed by Western blotting, and further HO-1 mRNA was relatively quantified by real-time quantitative PCR. The results indicated that Cu2+-induced decrease of cell viability and increase of LDH release. In cell-free solution, COSs alone or with Cu2+ cannot scavenge O-2 (-); however, COSs downregulate the levels of cellular oxidative stress and activated Caspase-3 induced by Cu2+. Further, the levels of pSer40-Nrf2 protein and both the transcription and the translation of HO-1 gene are dramatically increased in COSs-protective group compared with Cu2+ damage group. Therefore, these results indicate that Nrf2 activation might be involved in the protection of COSs against Cu2+-induced cellular oxidative damage. COSs contribute to the attenuation of oxidative damage and could be used as a nutritional agent for AD treatment.