右美托咪啶在热射病中的保护作用及基于NLRP3炎症小体的机制研究

Heat stroke (HS) is a severe disease caused by hyperthermia, with high mortality. One of the important mechisams is systemic inflammation response caused by heat exposure. The level of inflammation is closely associated with multi-organ dysfunction and damage in HS patiants. Therefore, anti-inflammation is the key point for HS therapy. Dexmedetomidine (DEX), a new alpha 2 adrenergic receptor agonist, was approved by FDA for sedative and analgesic in ICU in 1999. It shows a significant protective effect in many kinds of diseases via decreasing inflammation both in clinical and non-clinical studies. However, the protective effect of DEX on HS remains unknown. Our previous experiment found that DEX could significantly prolong the survival time in HS mice, but the mechanism is unclear. Some studies demonstrated that liver dysfunction and damage caused by HS is directly depends on inflammation activation, especially NLRP3 inflammasome. Interestingly, DEX can suppress the level of IL-1β, HMGB1 or IL-18, key moleculars of NLRP3 signal pathway, in many kinds of diseases. We also found that DEX could decrease the level of serum IL-1β in HS mice. But it is unclear whether the protective effect of DEX on HS is via NLRP3 inflammasome. Therefore, my research will focus on validating the protective effect of DEX on HS, and further exploring the detailed mechanisms underlying the anti-inflammation of DEX in liver mainly, therefore providing potential new therapeutic drug for HS.

热射病（Heat stroke, HS）是一种重症中暑，高热导致的全身性炎症反应是其发病机制之一。HS患者的炎症水平与机体损伤程度密切相关，因此抗炎是HS治疗的关键。右美托咪啶（dexmedetomidine, DEX）是一种新型高选择性α2肾上腺素受体激动剂，用于临床镇静、镇痛等。临床和动物研究均发现它可通过抑制炎症在多种疾病中发挥保护作用。但DEX在HS中的作用尚未知。我的预实验发现DEX可明显提高HS小鼠的生存率，但机制尚不清楚。据报道，NLRP3炎症小体在HS所致的肝损伤中发挥了重要作用，而DEX可以通过抑制NLRP3通路的关键蛋白IL-1β、HMGB1等在多种疾病中发挥抗炎和脏器保护作用。我们也发现DEX可以降低HS小鼠血清IL-1β水平。基于此，本课题将深入研究DEX在HS中的保护作用，并以肝脏为重点从NLRP3通路的角度探究DEX的作用机制，为DEX用于HS的治疗提供依据。

热射病（Heatstroke，HS）是一种由高体温诱导、由热细胞毒作用、弥漫性血管内凝血和系统性炎症反应共同导致的一种多器官功能障碍性疾病，发病急，累及器官多，临床上尚无特异性的防治药物。HS与脓毒症的病理机制相似，肠道屏障损伤可导致内毒素血症的发生，进一步介导系统性炎症反应，并加重多器官损伤；基于此，肠道被认为是含HS在内的多种危重症的“发动器官”。右美托咪啶（Dexmedetomidine, DEX）是一种高选择性的α2肾上腺素受体（α2-AR）激动剂，广泛应用于危重症或围手术期的镇静或麻醉。据报道，DEX在临床应用过程中表现出显著的抗炎和器官保护作用，对脓毒症有良好的治疗作用，因此我们推测DEX对HS可能也有治疗作用。.经研究发现，HS发生后，立即腹腔注射给予DEX，可剂量依赖地降低HS小鼠的血清TNF-α和IL-6、IL-1β水平，可显著缓解HS小鼠的肝脏、肾脏、肺脏、脾脏和肠道等病理改变，并可降低血浆内毒素水平。肠道屏障功能实验显示，DEX可明显降低血浆FD4和D-乳酸水平。Western blot和免疫组织化学实验显示，DEX可明显提高HS小鼠的肠道紧密连接蛋白occludin和ZO-1的表达水平。超微结构检查发现，HS可致小鼠肠道上皮细胞出现微绒毛变短、脱落或被破坏，细胞间的紧密连接变松散、空泡化或裂开，细胞线粒体内部出现的肿胀、空泡化等特征，线粒体嵴模糊不清或外膜膨胀等变化，DEX处理后仅呈现轻微的线粒体肿胀和空泡化。.作用机制研究发现，DEX可提高HS小鼠肠道的α2A-AR水平，下调TLR4水平，且DEX可明显降低TLR4下游的NF-κB和NLRP3炎症小体信号通路活化水平，并降低肠道炎症因子的表达水平。同时，经研究发现DEX可提高抗凋亡蛋白Bax的表达，下调促凋亡蛋白Bcl-2的表达，并降低HS小鼠肠道的TUNEL阳性细胞的比例。给予α2A-AR拮抗剂BRL-44408干预， 发现BRL-44408可部分逆转DEX对HS小鼠肠道α2A-AR和TLR4表达水平的影响，逆转DEX对系统性炎症和多器官损伤的保护作用，说明DEX对HS的防治作用与α2A肾上腺素受体有关。.综上认为右美托咪啶在热射病的临床防治方面具有较好的应用前景。