人参皂甙Re和Rg1抗细菌内毒素LPS的作用及其机理研究

It is a major mechanism for Gram negative bacterial infection that endotoxin (LPS) causes the production of large amount inflammatory mediators by activating TLR4 receptor, leading to general inflammatory reactions such as fever. There are no specific drugs for LPS-induced diseases. Our previous investigations have showed that ginsenosides Re and Rg1 can act on TLR4 to perform adjuvant activity, and suppress the fever induced by LPS. Based on these results, we hypothesize that ginsenosides Re and Rg1 have the pharmacological action against LPS by interfering the bonding of LPS to TLR4 receptor. Therefore, it is proposed to study the inhibitory effects of Re and Rg1 on the release of inflammatory mediators by macrophages as well as the therapeutic effects of Re and Rg1 on LPS-induced sepsis in animal model and mastitis caused by natural intramammary infection of E. coli in dairy cows so as to demonstrate the activities of Re and Rg1 against bacterial endotoxin. To investigate the mechanisms of anti-LPS properties of Re and Rg1, how to interfere Re and Rg1 to bond to TLR4 will be studied. The results obtained from proposed research would provid the basis for development of new drugs against bacterial endotoxin.

细菌内毒素（LPS）激活TLR4受体，使机体产生大量的炎症介质，导致动物发热等全身炎症反应，是革兰氏阴性菌感染的重要病理机制。目前临床上尚无针对LPS的特异性治疗药物。我们前期研究发现人参皂苷Re和Rg1可作用于TLR4发挥佐剂作用，并可抑制LPS诱导的体温升高作用。在此基础上，我们假设人参皂甙Re和Rg1可以通过干扰LPS和TLR4受体结合而发挥抗内毒素的药理作用。因此，本项目通过研究人参皂甙Re和Rg1对LPS诱导巨噬细胞释放炎症介质的抑制作用，对LPS毒血症动物模型的治疗作用以及对奶牛大肠杆菌性乳房炎的治疗作用，证明Re和Rg1具有抗细菌内毒素的功效；通过研究Re和Rg1对LPS结合到TLR4的干扰作用，探讨Re和Rg1的抗细菌内毒素的作用机理，为开发抗细菌内毒素新药奠定基础。

革兰氏阴性细菌感染是导致动物死亡的重要原因之一。细菌感染动物以后释放内毒素（LPS）作用于机体的TLR4受体，使动物机体产生大量的炎症介质，导致动物发生严重的全身性炎症反应，甚至死亡。目前临床上尚缺乏针对LPS的特异性治疗药物。我们前期研究发现人参皂甙Re和Rg1可通过TLR4信号通路发挥免疫调节作用。本研究的重要发现是Rg1和Re也可与细菌内毒素LPS发生竞争结合到TLR4受体，抑制炎症介质释放，缓解LPS引起过分强烈的炎症反应。Rg1可以通过细胞膜，分布在细胞内，而Re不能透过细胞膜，只分布在细胞外。因此，Rg1比Re具有更强的抗炎症作用。动物实验证明，Rg1和Re对LPS染毒的大鼠和小鼠具有保护作用；Rg1还可增强多粘菌素B（PMB）对大肠杆菌感染家兔的治疗效果；Rg1静脉注射对LPS诱导的奶山羊急性乳房炎具有治疗作用。因此，人参皂苷Rg1和Re对TLR4受体的作用具有两面性：一方面它们可适度激活TLR4信号通路，发挥免疫调节作用；另一方面Rg1和Re与LPS竞争，干扰LPS与TLR4受体的结合，抑制LPS诱导的过分强烈的炎症反应，进而产生抗LPS作用。在实践中我们既可以利用人参皂甙的免疫调节特性来增强机体的免疫力；又可以利用人参皂甙和LPS竞争性结合TLR4受体的特性抗LPS引起的炎症反应。通过本课题研究，发表SCI论文5篇，培养博士1名，硕士1名，注册新兽药证书1个，申报国家发明专利1个，若干名学生参加国内外学术会议。