Inhibitory Effects Of Astaxanthin On Glutamate-induced Apoptosis And The Underliny Mechanisms

Glutamate is an excitatory neurotransmitter that is important for learning and memory. However, excessive glutamate in neuronal cells leads to excitotoxicity. In this study, human neuroblastoma SH-SY5 Y cell line is used as a model to study the protective effects of astaxanthin against glutamate-induced apoptosis and the underlying mechanisms.The results show that, AST significantly inhibits Glu induced reduction in cell viability and apoptosis of SH-SY5 Y. Treatment with Glu promotes the expression level of Bak, decreases that of Bcl-2, and increases activity of caspase3; however, pre-treatment with AST（50μg/L） reverses these apoptosis signals induced by Glu. Therefore, AST may inhibit Glu induced cytotoxicity by ameliorate Glu induced apoptosis signals. Besides, Glu triggers increase of the level of intracellular reactive oxygen species（ROS）, and loss of mitochondrial membrane potential（MMP）, leading to the mitochondrial dysfunction; however, pre-treatment with AST inhibitis increase of ROS and makes cell maintaining normal MMP. It is found in Western blot that, pre-treatment with AST attenuates Glu induced increase in the phosphorylation level of p38 mitogen-activated protein kinase（MAPK）, while there is no significant change happens in the activity level of extracellular signal regulated kinase（ERK）. In another aspect, Glu induces augment the level of intracellular Ca²⁺, the level of protein expression and activity of Ca²⁺-dependent calpain; pre-treatment with AST decreases the level of Ca²⁺ and calpain activity, and maintains the calcium homeostasis. The studies on the endoplasmic reticulum stress（ERS） signaling pathway related proteins find that, AST inhibits Glu-induced ERS related proteins, GRP78 and CHOP. In conclusion, AST may protect SH-SY5 Y against Glu-induced neurotoxicity and apoptosis by inhibiting Glu-induced oxidative stress, Ca²⁺ influx and ERS signaling pathway.