Studies On The Mechanisms Of Neuroprotective Effect Of Silibinin On Animal Models Of Alzheimer's Disease

Objectives:Alzheimer's disease(AD)is the most common type of dementia as a neurodegenerative disorder characterized by progressive cognitive dysfunction and memory impairment.Silibinin,a flavonoid derived from the herb milk thistle,has been mainly used as a hepato-protectant in the clinical treatment of liver disease.Extensive studies have shown that silibinin is effective for neuroprotection although the mechanisms are not fully elucidated.Thus,we used AD models induced respectively with LPS,?-amyloid 25-35(A?25-35)and A?1-42,to test the effects of silibinin and to explore the possible related mechanisms.This research will provide theoretical basis for the study of pharmacological mechanism of silibinin in organs such as skin,liver and pancreas.Methods:AD models used in this research induced by the intracerebroventricular(ICV)injection of LPS,hippocampally injection of A?25-35 and A?1-42,respectively.The rats were administered with silibinin(25,50 and 100 mg/kg),resveratrol(30 mg/kg),donepezil(1 mg/kg)or solution.The Y-maze,Morris water maze,novel object-recognition and elevated plus maze tests were performed,respectively,in the behavioral examinations.Morphological changes of neurons in hippocampus were examined by Nissl staining and Fluoro-Jade(FJB)staining.The levels of pro-inflammatory cytokines IL-1?,TNF? and anti-inflammatory cytokine IL-4 were measured by ELISA.Inflammatory,autophagic,estrogen receptors(ERs)and ERs-related protein expressions were assessed using western blot analysis.Results:In this study,LPS was used as a tool drug to establish a neuro-inflammatory model to study the neuroprotective effect of silibinin.Our results demonstrated that silibinin showed a significant protective effect against cognitive dysfunction of the rats induced with LPS.Compared with LPS-injected rats,silibinin significantly decreased the escape latency in Morris water maze test and increased percentage of alternation in Y-maze test.Silibinin ameliorated the inflammatory response by inhibiting the expression of pro-inflammatory cytokine IL-1? and increasing the expression of anti-inflammatory cytokine IL-4.Silibinin also activated the(reactive oxygen species)ROS-(brain-derived neurotrophic factor)BDNF-(tyrosine receptor kinase B)TrkB pathway in the hippocampus.On the basis of LPS model research,we established AD model with A?25-35.Silibinin treatment increased levels of GSH and decreased levels of MDA;inhibited expressions of NF-KB,COX-2 and iNOS;up-regulated autophagy level and BDNF-TrkB pathway in the hippocampus of A?25-35-injected rats.A?1-42 peptides can form prions that induce A? amyloid plaque pathology,compared to AP25-35,and plays a stronger toxic effect examined by the Morris water maze,Y maze and the elevated plus maze tests.Silibinin exerted neuroprotective effects in A?1-42-injected rats by down-regulating autophagy level,inhibiting inflammatory response and up-regulating BDNF-TrkB pathway.Since silibinin has estrogen-like effect and estrogen receptors(ERs)are highly expressed in neuronal cells,we speculate that the regulation of ERs involved in the neuroprotective effect of silibinin.We found that silibinin down-regulated the expressions of ERs as well as ERs-mediated PI3K-Akt and MAPKs pathways in A?1-42-injected ratsConclusions:Silibinin treatment reversed the learning and memory impairment induced with LPS,A?25-35 and A?1-42.The neuroprotective effect was mediated through inhibition of inflammatory response and oxidative stress,as well as the mediating of autophagy level and ERs-related signaling pathways in the hippocampus.This research provided us fundamental bases for developing silibinin as a neuroprotective drug and uncovered potential therapeutic targets for the development of anti-AD drugs targeting ERs-oxidative stress-autophagy-inflammation.