Xanthoceraside Of β-amyloid-induced Dementia Mice Learning And Memory Disorder Improving Action Research And Mitochondria-related Mechanisms

Aim: Xanthoceraside is a monomer extracted from the shell of the fruit of Xanthoceras sorbifolia Bunge. Our previous study showed that xanthoceraside could significantly improve learning and memory impairment in several AD animal models. In this study, we further investigated the effects of xanthoceraside on learning and memory impairment and the possible mechanism associated with the protection of mitochondria in Alzheimer’s disease (AD) model mice induced by Aβ1-42, which aims to explore the anti-AD effects and possible related mechanisms of xanthoceraside. Methods:We acquired learning and memory impairment mice model by intracerebroventricular (i.c.v.) injection of the aggregated Aβ1-42. Learning and memory ability was examined using Morris water-maze test, Y-maze test, novel object recognition test and step-through test in mice. Transmission electron microscope was used to observe the ultra-structure of mitochondria of neurons in cerebral cortex and hippocampus. The level of ATP in cerebral cortex and hippocampus was detected by bioluminescence assay. Percoll density gradient centrifugation method was applied to isolate free mitochondria from mice cerebral cortex. Transmission electron microscope observation, lactate dehydrogenase(LDH) level and cytochrome c oxidase (COX) activity assay were applied to confirm whether the mitochondria are intact and pure with good metabolic activity. The activities of COX, pyruvate dehydrogenase complex (PDHC) and a-ketoglutarate dehydrogenase complex (KGDHC) were detected using assay kits respectively with isolated free mitochondria. The ROS level in cerebral cortex and hippocampus was detected using fluorescence spectrophotometry. Immunohistochemistry was used to investigate the expression of8-OH-dG, the biomarker of DNA oxidative damage, and the release of cytochrome c from mitochondria. Results:Xanthoceraside significantly improved learning and memory impairment in mice induced by i.c.v. injection of Aβ1-42. Compared with model group, xanthoceraside (0.16～0.32mg/kg) significantly decreased the escape latency and swimming distance, increased the swimming time and percentage of the swimming distance in the fourth quadrant where the platform had been located in Morris-water maze test; increased the percentage of alternation behaviors in Y-maze test; increased the preferential index and discrimination index for the novel object in novel objective recognition test; and decreased the step-through latency in step-through test. Xanthoceraside improved the ultra-structure of mitochondria and increased the ATP level in cerebra cortex and hippocampus of model mice. Xanthoceraside significantly reversed the decrease of the activity of COX, PDHC and KGDHC and inhibited the abnormal increase of ROS induced by Aβ. Moreover, the results of immunohistochemistry showed that xanthoceraside significantly decreased the expression of8-OH-dG and reduced the release of cytochrome c from mitochondria in model mice. Conclusion:Xanthoceraside could improve learning and memory impairment, promote the function of mitochondria, decrease the production of ROS and inhibit oxidative stress. The improvement effects to mitochondria may be through withstanding the damage of Aβ to mitochondrial respiratory chain and the key enzymes in Kreb’s circle, decreasing the release of cytochrome c, and finally reducing the death of neurons. Therefore, the results from present study and previous study indicate that xanthoceraside could be a competitive candidate for the treatment of AD.