Screening Of Chinese Herbal Medicine And Its Related Mechanisms With Inhibition Of Alzheimer 's Disease

Alzheimer’s disease is (AD) is a chronic neurodegenerative disorder which occurs in senile and presenile and characterized by progressive cognitive dysfunction and irreversible behavioral impairment. Cerebral formation and deposition of amyloid beta peptide (Aβ) have been shown to play a primary and key role in the pathogenesis of Alzheimer’s disease (AD). Aβ is derived from the amyloid precursor protein (APP) which is cleaved by β and y-secretases in the amyloidogenic pathway. Ample evidence exists to prove that Aβ fibrils are noxious to neurons. So it could be effective therapy of AD by inhibiting the activities of of β-secretase or (and) y-secretase.Firstly, we studied and screened the Chinese herbal compounds which could inhibit the production of Aβ and investigate the underlying mechanism. Ten kinds of compounds which have potential value in the treatment of AD were selected as initial screening trial. They are astragalosides (AST), gastrodin (GAS), panax notoginseng saponins (PNS), tetramethylpyrazine hydrochloride (TMP HC1), puerarin (PUE), osthole (OST), icariin (ICA), ginsenoside (Rbl), cryptonshinone (CTS), paeoniflorin (PNF). We studied effects of the ten kinds of compounds in293and CHO transgenic cell models.293transgenic cell models (117cells) over express Aβ and β-secretase, while CHO transgenic cell models (146cells) over express Aβ and γ-secretase. Extracellular Aβ was determined by ELISA after the cell models treated with different concentrations of compounds (0.5-100umol·L-1) respectively. Then the compounds were selected which could inhibit extracellular Aβ and their best concentration ranges were decided, too. Furthermore, the cell viability and apoptosis rate, the level of intracellular Aβ, β and y-secretases were determined after the cell models treated with different concentrations of selected compounds. The results showed that4of the10compounds could reduce the level of extracellular Aβ; they were cryptotanshinone, astragalosides, gastrodin and paeoniflorin, and their best concentration ranges were0.5-5.0,0.5-5.0,5.0-50,1.0-25μmol·L-1, respectively. Further study indicated that the4selected compounds were nontoxic to the cellular models and lowering intracellular Aβ were more effective compared with extracellular, what’s more, on117cells, the intracellular max inhibit rate of AP were82.0%,75.9%,75.2%and73.8%, the extracellular max inhibit rate of Aβ were76.5%,73.6%,72.6%and68.9%, respectively; on146cells, the intracellular max inhibit rate of Aβ were88.1%,70.3%,74.4%,82.0%, the extracellular max inhibit rate of Aβ were84.2%,67.1%,72.4%and75.4%, respectively. Astragalosides and gastrodin showed dose-dependent inhibition to the activities of β and γ-secretases, with the maximum inhibiting rates of78.2%and80.3%, respectively.In conclusion, cryptotanshinone, astragalosides, gastrodin and paeoniflorin could inhibit the expression and secretion of Aβ, and the underlying inhibiting mechanism of astragalosides and gastrodin were related with the reduction of the β and y-secretase activities, respectively.Secondly, in order to study the pharmacodynamics of AST and GAS, we researched the cognition and memory improvement and eradication of Aβ after AST and GAS treated the AD transgenic models. Our previous research found that AST and GAS which are bioactive substances derived from traditional Chinese medicinal herb radix astragali and gastrodia elata, respectively, have been evidenced to could inhibit the production of Aβ by lowing the activity of β and y-secretase activities, respectively. However, whether they could improve cognition and memory and eradicate Aβ of AD transgenic models should be fully understood. In this research, we used two AD transgenic models which are APP transgenic mice (J20mice) and APP/PS1transgenic mice (5XFAD mice). J20mice express a mutant form of the human APP bearing both the Swedish (K670N/M671L) and Indiana (V717F) mutations (APP Swlnd) while5XFAD mice over express both mutant human APP (695) with the Swedish (K670N, M671L), Florida (1716V), and London (V717I) mutations and human PS1harboring two FAD mutations, M146L and L286V.2-month-old5XFAD mice and3-month-old J20mice were divided randomly into7groups, respectively. And negative control mice were severed as control group. AST Groups were given the different levels of AST solution and GAS Groups were given the different levels of GAS solution while Tg and control groups were given the normal saline. All groups were intragastricly administered for3months. Then the spatial learning and memory ability were detected by Morris water maze test. At last, the mice were sacrificed, their brain tissue were harvested. The left brain tissue was made into cerebral homogenate and left brain tissue was used to immunohistochemistry. The result reported that both AST and GAS significantly attenuated amyloid plaque deposition in the brain of5XFAD and J20mice. In addition, they strongly improved spatial learning and memory in5XFAD and J20mice assessed by the Morris water maze testing.Taken together, our results indicated that AST and GAS had strong capacity of scavenging amyloid plaque and improved the cognitive ability of AD transgenic mice. Furthermore, their underlying mechanism of action related with the reduce of β-secretase activity and y-secretase activity, respectively. AST and GAS raised a promising novel way for the therapy of AD.