沒食子酸預防大鼠血管性失智之研究

Abstract

血管性失智症是老年失智症主要類別之一，盛行率僅次於阿滋海默症。各種天然酚酸廣泛存在於植物性食材之中，具備諸多生理活性。本研究主旨在於探討天然酚酸對於血管性失智症之預防，以缺氧缺葡萄糖造成已分化PC12細胞損傷之模式，進行咖啡酸(caffeic acid)、氯原酸(chlorogenic acid)、肉桂酸(cinnamic acid)、香豆酸(coumaric acid)、阿魏酸(ferulic acid)、沒食子酸(gallic acid)、原兒茶酸(proto-catechuic acid)與香草酸(vanillic acid) 這八種酚酸細胞保護功效之初步篩選，實驗中酚酸濃度為12.5~200μm。發現以gallic acid在100μm濃度下，對於PC12細胞的保護效果最大，細胞存活率為90.2 ± 4.1%，並可顯著抑制LDH酵素之釋放，且會經由鈣離子釋出之抑制而提升PC12細胞之自噬作用。以掃描式電子顯微鏡進行觀察進一步瞭解PC12細胞自噬作用與形態之關聯，證實此自噬作用的提升有助保持PC12神經細胞形態完整。以上細胞實驗結果顯示，酚酸在適當濃度下可能減輕腦缺血時神經細胞之損傷。接續以兩血管阻斷再灌流模式(two-vessel occlusion model of forebrain ischemia; 2-VO)促使餵食gallic acid與否之大鼠發生血管性失智症，然後進行動物行為實驗，複驗gallic acid預防大鼠血管性失智症之功效。大鼠犧牲後，分析血清生化分析結果顯示，餵食gallic acid大鼠與假手術組之間，血清電解質、總膽固醇、肝功能與腎功能等安全性指標皆無顯著性之差異。鼠腦切片染色，可以明顯觀察到大腦皮質部與海馬迴之梗塞現象；進行腦梗塞面積百分比之測定，發現gallic acid可以明顯的降低腦部阻塞。心臟、腎臟與肝臟切片發現gallic acid餵食劑量對動物無毒性。行為實驗分析證實gallic acid能夠保護大鼠之學習及記憶能力，且其功效隨樣品濃度(10、50至100mg/kg)之提升而提升。抗氧化酵素活性分析方面，發現餵食gallic acid可以提升大鼠腦皮質部與海馬迴組織中TAS、SOD、GSH濃度，同時降低iNOS活性與TBARS含量。腦組織免疫化學染色分析發現，餵食gallic acid組可以降低HIF-1α與增加Ki-67之表現，並增加了Nrf2與HO-1於腦部之表現量，對神經細胞具有保護作用。

Vascular dementia is a major type of senile dementia. Its prevalence is second to Alzeimer disease only. Phenolic acids occur widely in plant food materials with various functionalities. In this study, the object of is “Screening and confirmation of natural phenolic acids for their alleviative effect on vascular dementia in cell and animal models”. The screening was performed in an oxygen-glucose deprivation PC12 cell model, and followed with the confirmation in two-vessel occlusion forebrain ischemia model of rats. In the cell model, eight phenolic acids, including caffeic acid, chlorogenic acid, cinnamic acid, coumaric acid, ferulic acid, gallic acid, proto-catechuic acid and vanillic acid, in various concentrations between 12.5 and 200μm were used and the cytoprotective effects were evaluated. Gallic acid at 100μm was found to be the most cytoprotective, with a PC12 cell survival rate at 90.2 ± 4.1%, to inhibit the release of LDH enzyme, and to enhance cell autophagy via the release of calcium ions. Scanning electron microscopic observation confirmed that the enhancement in autophagy helps PC12 nerve cells to maintain its morphological integrity. A two-vessel occlusion model of rats was then used to further validate the alleviative effect of gallic acid on vascular dementia in vivo. Animal behavioral experiments, including passive avoidance performance and Morris water maze test, showed that gallic acid, at 10, 50, and 100mg/kg, is able to improve the memory and learning ability in rats with dose dependency. Immuohistochemical straining and the evaluation of biochemical parameters in serum and antioxidant enzymes activities in brain was performed to elucidate the safety of gallic acid intake and mechanism for gallic acid to improve vascular dementia. Based on the experiment data, we propose that gallic acid promotes TAS, SOD and GSH activities while decreases iNOS activity and TBARS levels in cortex and hippocampus. Immunohistochemical stain of brain tissue found that gallic acid downregulates HIF-1α expression while upreguilates Ki-67, Nrf2 and HO-1 expression, indicating that gallic acid may prevent vascular dementia via the promotion of nerve cell regeneration.