The Neuroprotective Effects And The Involving Mechanisms Of Active Compounds From Yin-tonic Herbs On Neurodegenerative Diseases

Alzheimer’s disease(AD) and Parkinson’s disease(PD) are two most common age-related neurodegenerative diseases, characterized pathologically by cholinergic neurons and dopaminergic neurons progressive degeneration and lost respectively. Neurotrophic factors, especially brain derived neurotrophic factor(BDNF) and Glial cell line- derived neurotrophic factor(GDNF) play significant roles in neuronal survival, growth and development. Several lines of evidence support the involvement of BDNF and GDNF in mechanisms underlying neurodegenerative diseases. Thus, to develop natural products and small molecules that can induce endogenous BDNF/GDNF expressions is a novel and important strategy in neurodegenerative diseases drug development. In this paper, we investigate the effects of HAR and SMI on BDNF/GDNF expression, to further clarify their common mechanisms on neurodegenerative diseases.On one hand, we focus on the involving mechanisms of HAR on BDNF expression and MAPK/PI3 K pathways in vitro and in vivo models of Alzheimer’s disease. The purpose of the present study was to observe whether HAR has effect on AD models to further explain the mechanism of the Yin-tonic herbs on neurodegenerative diseases. In in vivo study we assessed the effects of HAR on learning and memory function of Aβ1-40 induced AD rats. Rats injected with Aβ1–40 displayed impaired spatial learning and memory in a Y-maze test and novel object recognition test. Motor function had no difference between each group in open field test. While after 60 days administration of HAR ameliorated Aβ1–40 induced behavioral deficits. Considering the effects of BDNF and its signaling pathways on learning and memory, we adopted enzyme-Linked Immuno Sorbent Assay(ELISA) to test BDNF content. Meanwhile western blot was used to detect cortical and hippocampal ERK, p-ERK, AKT and p-AKT as well as synaptic proteins. The results showed that HAR administration up-regulated the decreased BDNF levels both in entorhinal cortex and hippocampus, activated the extracellular-regulated protein kinase(ERK) and the phosphatidylinositol 3-kinase(PI3-kinase) pathways both in cerebral cortex and hippocampus of Aβ-lesioned rat model. The contents of synaptic proteins were no significant differences between each group.In in vitro study, primary cortical neurons were insulted by Aβ1–42 as AD cell models. MTT and immunocytochemical assay were used to detect the cell viability and choline acetyl transferase(ChAT) positive neuron number and its neurite outgrowth of the primary cortical neurons respectively. The results showed that HAR pretreatment dose-dependently attenuated the decrease of cell viability and increased ChAT positive neuron number and neurite outgrowth length in Aβ1–42-injured cortical neurons. In addition, HAR elevated the ratio of p-ERK and ERK, as well as the ratio of p-AKT and AKT in Aβ1–42 injured cortical neurons. Considering the effects of BDNF on neuronal viability, we employed tyrosine kinase inhibitor K252 a or anti-BDNF antibody to block BDNF effect. When BDNF action was blocked, the protective effect of HAR on Aβ1–42-induced neurodegeneration in cortical neuron was almost or partially inhibited.On the other hand, the other purpose of this paper is to study the effect of SMI on dopamine neurons and locomotor ability in aged rats. Experiments were also carried out on young and aged Sprague-Dawley rats, which were daily administration with either SMI(18mg/kg/day) or vehicle(0.5% CMCNa). The behavioral results revealed that motor performance was impaired in aged rats and was improved by oral administration of SMI(open field test and Rotarod tests). Likewise, SMI increased the TH-positive neuron numbers in the substantia nigra pars compacta(immunohistochemical assay and unbiased stereological counting), elevated the striatal DAT density(125I-FP-CIT autoradiography) and brain dopamin D1, D2 receptor density in aged rats. Meanwhile, SMI elevated the expression of GDNF protein in aged rats.Taken together, our results for the first time suggested that HAR treatment might up-regulate BDNF protein levels as well as accompanied with activating its downstream signaling pathways, e.g., MAPK/PI3 K pathways to protect cholinergic neurons against Aβ neurotoxicity, eventually ameliorated learning and memory deficits in Aβ-induced AD rat model. While, SMI may attenuate dopamine neuron degeneration and age-related motor decline through elevating GDNF protein levels in aged rats. It suggests that the two active compounds from Yin-tonic herbs may have similarly mechanisms on neurodegenerative diseases, both of which might induce several kinds of neurotrophic factors to protect cholinergic neurons and dopaminergic neurons against degeneration. It raises the possibility that HAR and SMI may become effective therapeutic strategies aiming at delaying the progressive process of neurodegenerative diseases. These results provide the theoretical basis for further developing new drugs for prevention and treatment of neurodegenerative diseases.