| Objectives:Alzheimer's disease (AD) is the most common cause of dementia in the elderly population. With the increasing of the population aging and incidence of AD, heavy burden was brought to society and family due to poor life quality in AD patients. The clinical manifestations of AD is a smart diminish and AD is characterized by the presence of two histo- pathological hallmark brain lesions, extracellular deposits ofβ-amyloid in neuritic plaques and intracellular neurofibrillary tangles (NFTs). The latter is composed of bundles of paired helical filaments (PHF), the major protein subunit of which is the microtubule-associated protein Tau. Tau in PHF is different from that in normal neurons. It is abnormally hyperphosphorylated, aggregated into filaments, and does not bind to microtubules or stimulate microtubule assembly. Evidence from several studies has indicated that the hyperphosphorylation of Tau is responsible for its loss of biological activity and its resistance to proteolytic degradation, and probably plays a key role in neurofibrillary degeneration in AD. Many studies have suggested that the number of NFTs is correlated with the degree of dementia in AD.Green tea is a drink made from the steamed and dried leaves of the Camellia sinesis plant, a natural oxidation inhibitor, a shrub native to Asia. It is a beverage that is widely consumed in China, Japan, and other Asian nations and that is becoming more popular in Western countries. Recently, green tea has attracted attention for its healthy benefits, particularly with respect to its potential for preventing and treating cancer, cardiovascular diseases, inflammatory diseases, and neurodegenerative diseases in humans. Some references suggest that TP can inhibition of amyloid fibril formation in vitro and protect neurons againstβ-amyloid-induced toxicity in vitro. However, it is still unclear whether the TP has a protective effect in the hyperphosphorylation of Tau protein of AD. The aim of this study is to explore the function of tea polyphenols (TP) on the Tau protein hyperphosphorylation in hippocampal neurons in rats, which is induced by okadaic acid (OA).Methods: We chose OA as the inducer of Tau protein hyper- phosphorylation. Healthy male SD rats were divided randomly into six groups (n=10): normal group, vehicle-control group, model group treated with OA, and three TP groups, pretreated with TP in 100 mg/kg,250 mg/kg and 625mg/kg. At the 21st day of the rats of TP-pretreated groups intragastric administration, we operated ethology (water maze) test. At the 27th day, the rats were anesthetized with 2% of sodium pentobarbital (40 mg / kg, ip), according to rat brain stereotactic map, restrained in a stereotaxis apparatus and microinjected OA (soluble in 10% DMSO) 1.5μL (0.473μg) into the right dorsal hippocampus (A: -3.8 mm, L: 2.5 mm from bregma, and V: 3mm) within 10min, staying for 5min. The vehicle-control group was microinjected 10%DMSO 1.5μL in the same position. At the 28th day, we made the exzamination of water maze, then sacrificed the rats and collected the samples. Paraffin slides were used for immunohistochemistry analysis of hyperphosphorylation of Tau protein. Hippocamp were prepared for western blot analysis of hyperphosphorylation of Tau protein. Quantified analysis of Western blot was performed later.Result:1. TP attenuates the expression of hyperphosphorylation of Tau induced by OA.Immunohistochemistry staining indicated that there is strong positive hyperphosphorylation of Tau granules in the OA group and abundant brown positive hyperphosphorylation of Tau granules were detected in the hipocamp of TP pretreated-groups, but weaker than OA group, especially in 250 and 625mg/kg TP groups.Furthermore, Western blot analysis showed that the average relative photodensity was obviously increased in the OA group compared with the normal group. With TP pretreated, hyperphosphorylation of Tau expression was decreased, and a significant difference between TP and OA group still could be seen (P < 0.01). 2. TP improves OA-induced spatial memory impairment in ratsWith the increasing of training number of time, the escape latency of each group shortened gradually. And there was a significant difference between the TP pre-treared groups and OA model group before the microinjection (P<0.01). There was a significant difference on the number of crossing platform among each group before and after OA microinjection. The total time was the same and there was a significant difference about the time that the rats stayed in the target quadrant of OA model group between before and after OA microinjection (P<0.01). After OA microinjection, there was a significant difference between the TP pre-treared groups and OA model group about the time that the rats stayed in the target quadrant (P<0.01). After OA microinjection, the percentage of swimming distance in target quadrant in total time of each group was smaller than that before OA microinjection, and there was a significant decreasingof OA model group (P<0.01). After OA microinjection, there was a significant difference between the TP pre-treared groups and OA model group about the percentage of swimming distance in target quadrant (P<0.01). These results suggested that OA can make rats space and memory impairment, in the manifestation of the reduction in the number of cross platform, shorten the time and swimming distance of staying in the target quadrant. But pretreated with TP can improve this impairment, showing that shortening the escape latency, increasing the number of rats across the platform and the time staying in the target quadrant and the swimming distance. The rats reasched the plat, according to some strategy.Conclusions: Our data suggested that OA can make Tau hyperphosphorylation and memory impairment, and TP can decrease the hyperphosphorylation and improve the impairment. |
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