The present study was performed to confirm protective effects against oxidative stress and Alzheimer’s disease (AD) of the extract from Engelhardtia chrysolepis leaf. The protective activity from oxidative stress was evaluated under in vitro, cellular system and Aβ-injected AD in vivo model.
The extract from E. chrysolepis leaf showed strong radical scavenging effects against 2,2-diphenyl-1-picrylhadrazyl, hydroxyl radical and nitric oxide (NO) as a concentration-dependent manner. Particularly, strong scavenging activity against the ·OH and NO radical were observed with the IC50 value of 1.30 μg/mL and 12.61 μg/mL, respectively.
The study was investigated the protective role of E. chrysolepis extract against oxidative stress-induced neuronal cell damage using C6 glial cells. The treatment of amyloid beta (Aβ25-35) to C6 glial cells showed decrease of cell viability and elevation of reactive oxygen species (ROS) level. However, the treatment of E. chrysolepis extract increased cell viability and decreased the ROS level. In addition, the treatment of Aβ25-35 to C6 glial cells up-regulated the AD-related proteins expression, amyloid precursor protein (APP), β-secretase (β-site APP cleaving enzyme; BACE) and phospho-tau (p-Tau), while it down-regulated expression of brain derivated neurotrophic factor (BDNF). The E. chrysolpis extract treatment inhibited protein expressions of APP, C-terminal fragment-β (CTF-β), BACE and p-Tau proteins in C6 glial cells, whereas increased expression of BDNF at all concentration. This results indicated that the extract exerted the protective effect from neuronal oxidative stress through the regulation of AD-related proteins expressions.
Also, the effect of E. chrysolepis extract on cognitive impairment and protective abilities was investigated using Aβ25-35-injected AD mouse model. To develop an AD in vivo model, mice were injected Aβ25-35 intracerebroventricularly. The E. chrysolepis extract was administered at an oral dose of 100 or 200 mg/kg/day for 2 weeks. The protective effects of E. chrysolepis extract from AD was observed by the behavioral tests including T-maze, novel object recognition, and Morris water maze tests. The control group injected with Aβ25-35 revealed impairments of recognition and memory function. However, the administration of E. chrysolepis extract showed improvement of cognition and memory function. Furthermore, the administration of E. chrysolepis extract protected from Aβ25-35-induced lipid peroxidation and inhibited NO production in the brain, kidney and liver. In addition, the Aβ25-35-injected mice exhibited the up-regulation of inflammation-related protein expression such as nuclear factor kappa B (NF-κB), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) and interleukin 1 beta (IL-1β) levels in the brain of AD mouse model, however, E. chrysolepis extract treatment decreased the protein expression of pro-inflammatory mediators and cytokines. The treatment of E. chrysolepis extract also reduced protein expressions related to apoptosis such as cleaved caspase-3, cleaved caspase-9, cleaved PARP and Bax. Aβ25-35-injected mice increased AD-related protein expression such as APP, BACE and p-Tau, while E. chrysolepis extract treatment reduced these protein expression. Therefore, these results demonstrated that E. chrysolepis extract improved Aβ25-35-induced memory deficit and cognition impairment in mice and protected against oxidative stress by regulation of protein expressions related to inflammation, apoptosis and AD in Aβ25-35-injected brain.
In conclusion, the present study suggests that extract from E. chrysolepis leaf would have the protective effect from oxidative stress under Aβ25-35-induced C6 glial cells. In addition, the protective role of the E. chrysolepis extract against impairments of memory and cognitive ability in AD mouse model induced by Aβ25-35 was also confirmed and it was related to the regulation of inflammation- , apoptosis- and AD- related protein expressions.