Nrf2/ARE通路：唐古特大黄多糖预防辐射肠损伤的可能靶点

Radiation enteritis has been one of the most formidable complications in radiotherapy, especially in abdominopelvic cavity radiation treatment，and prevention is better than cure. Up to now, there still lack of effective prevention drugs against RE. Reactive oxygen species (ROS) - induced oxidative stress play a pivatol role in RE. As the most important endogenous defence against oxidative stress, Nrf2/ARE signal pathway has demonstrated critical role in prevention and treatment oxidative stress induced diseases.Drugs targeted on Nrf2 has entered into clinical trial phase. In the previous study,we found that RTP1 not only can protect intestinal mucosal from intestinal radiation injury and attenuate oxidative stress, but also an inducer of Nrf2 and leading to Nrf2 nuclear localization. According to the importmant role of ROS in RE and significant effect of Nrf2/ARE pathway, Nrf2/ARE pathway may be a new target for the prevention of RE. Based on this, Nrf2 knock out mice is intended to used to indentify that Nrf2/ARE pathway play an important role on RE and the pretection effect of RTP1 is mediatied by activating the Nrf2 pathway. In vitro experiment will be introduced to explore the possible pathway that induce Nrf2 nuclear localization. We hope to provide evidence for identifying effective and useful substances for prevention or rescue of GI injury from radiation exposure. Thus, this study will has certain clinical significance and potential value of application.

放射性肠炎(RE)是腹盆腔及腹膜后肿瘤放疗后最常见和棘手的并发症之一，且预防重于治疗，但目前缺乏有效的预防药物。氧自由基是RE发生最重要的因素，Nrf2/ARE通路是目前发现的最为重要的内源性抗氧化应激通路，调控该通路是预防和治疗氧化应激所致疾病的重要手段，基于该通路开发的数种药物已进入临床研究。我们发现，唐古特大黄多糖组分1(RTP1)能够减轻辐射所致肠黏膜损伤和氧化应激，且是Nrf2激活剂，能够诱发Nrf2活化转位入核，针对氧自由基在RE发病机制中扮演的重要角色及Nrf2/ARE通路的重要作用，推测Nrf2/ARE通路可能是RE预防的新靶点。基于此，本研究拟采用Nrf2基因敲除小鼠，明确Nrf2/ARE通路在RE中的保护作用及RTP1通过该通路发挥作用；采用离体细胞模型，探讨RTP1诱导Nrf2核转位可能的信号通路，为寻找有效的RE预防药物提供依据，具有重要的临床意义和潜在的应用价值。

放射性肠炎是由于盆腔、腹腔、腹膜后恶性肿瘤经放射性治疗后而引起的肠道损害。Nrf2/ARE信号通路是迄今为止发现的最为重要和关键的内源性抗氧化应激通路，该通路与多种疾病的发生发展密切相关。而对于放射性肠损伤发生后，Nrf2/ARE通路是否在其中起到保护作用以及其激活通路尚未阐明，同时前期研究发现唐古特大黄多糖具有显著肠损伤保护作用，但机制有待阐明。本课题首先通过采用不同剂量X射线，考察不同照射剂量对大鼠各项生理指标和大鼠肠组织病变的影响，以及肠上皮细胞生存情况建立辐射性肠损伤动物及细胞模型，继而通过免疫组化，蛋白印迹等技术考察不同时间点Nrf2/OH-1通路在辐射性肠损伤模型中的变化，并通过全转录分析明确该位点相关通路的改变情况，最终采用不同抑制剂考察Nrf2/OH-1通路在放射性肠损伤中的激活机制及保护作用并初步阐明唐古特大黄多糖改善辐射性肠损伤的机制。结果表明，10Gy照射剂量能够复制出适合的放射性肠损伤模型，大鼠肠道病变与该疾病的临床表现一致；Nrf2/ARE及其下游位点HO-1的mRNA和蛋白水平在放射性肠损伤中显著增高；全转录分析结果显示Nrf2上游位点PI3K/AKT通路显著改变； 且通过抑制该通路，阐明了PI3K/AKT通路是Nrf2/HO-1发挥放射性肠损伤保护作用的主要上游位点；而唐古特大黄多糖可通过调控PI3K/Nrf2/HO-1通路发挥放射性肠损伤保护作用。此外，研究中我们还发现辐射可使肠系膜血管出现明显缺血现象，肠系膜血管BH4/eNOS/NO通路发现显著改变，从而使得血管功能异常，肠系膜血管缺血与肠炎的发生密切相关，因此肠系膜缺血可能是导致放射性肠炎的又一诱因，但其作用机制及是否可通过改善肠系膜缺血改善辐射导致的肠损伤发生有待进一步研究，后续我们也将以此为研究方向深入探讨其作用机制，为辐射性肠损伤的防治提供新的解决方案。