Neuroprotective Effect of Natural Alkaloid Fangchinoline Against Oxidative Glutamate Toxicity: Involvement of Keap1-Nrf2 Axis Regulation.

Oxidative glutamate toxicity plays a vital role in the neurodegeneration diseases, including Alzheimer's diseases (AD). This study set out with the aim to investigate the beneficial effects of fangchinoline (FAN), a natural alkaloid, against glutamate-induced oxidative damage, and to clarify the underlying cellular and biochemical mechanisms. FAN prevented HT22 cells death from oxidative glutamate cytotoxicity in a dose-dependent manner, and significantly attenuated the overproduction of intracellular reactive oxygen species (ROS) and reversed the reduction of superoxide dismutase (SOD) activity induced by glutamate. Further investigations on the underlying mechanisms demonstrated that FAN potently up-regulated the protein level of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase (HO-1), in glutamate-exposed HT22 cells. The protective effects of FAN were almost completely antagonized by inhibitor of Nrf2. Subsequent studies revealed that FAN could down-regulate Kelch-like ECH-associated protein 1 (Keap1) in both mRNA level and protein level. To sum up, our result demonstrated the protective effects of FAN against glutamate-induced oxidative neuronal damage, and for the first time clarified the anti-oxidative mechanisms of FAN involve activating endogenous antioxidant defense system including enhancing SOD activity and regulating Keap1/Nrf-2 antioxidation signaling through modulation of Keap1 expression. Above results shed more light on the molecular mechanisms of FAN's neuroprotective effects, and may provide important clues for the drug development in preventing oxidative stress-associated neurodegenerative diseases.