Mechanisms of MDMA-induced hyperthermia

描述（由申请人提供）：本提案中的工作涉及项目公告（PA-06-525），标题为“MDMA：需要更多强调的研究领域（R21）”。急性MDMA中毒最危险的副作用是体温过高，这是一种高代谢状态，源于在热量守恒（外周血管收缩）的情况下“非颤抖性”代谢产热急剧增加。MDMA诱导的高热导致一连串危及生命的医学并发症，包括骨骼肌分解、心血管衰竭、多器官衰竭和弥散性血管内凝血。在动物中，高温也强烈增强长期神经毒性。目前尚无逆转MDMA和相关化合物诱导的体温过高的治疗方法，这很可能是因为尚未确定人体对正常（寒冷、进食、感染）和病理性（MDMA、内分泌病）产热刺激的直接产热介质。解偶联蛋白（UCPs）是一类高度保守的产热分子，在植物、线虫、蝇和脊椎动物中调节线粒体产热。在哺乳动物中，棕色脂肪UCP 1被认为是主要的，如果不是唯一的显着介质的产热反应。强烈反对这一点的是，成年人表达的棕色脂肪和UCP 1的量可以忽略不计，但确实显示出显着的非颤抖性产热反应（即MDMA高热，饮食诱导的产热，发热）。骨骼肌是人类最重要的产热器官，也是MDMA诱导的病理学的主要靶点;因此，我们推断最近发现的解偶联蛋白3（主要在骨骼肌中表达）（UCP 3）可能介导MDMA高热。我们在缺乏UCP 3的小鼠中进行了测试。UCP 3敲除小鼠几乎完全丧失（~80%）MDMA诱导的产热作用，并且在致死剂量范围内完全免受MDMA诱导的死亡。与UCP 3在可诱导产热中的一般体温调节相关性一致，我们还观察到UCP 3敲除小鼠失去响应细菌热原脂多糖而产生发热的能力。关于UCP 3激活的机制，我们观察到游离脂肪酸（体外UCP 3功能所需的配体）在MDMA诱导的高温峰值之前在血液中升高。此外，我们发现高脂肪喂养增加血浆游离脂肪酸水平，并相应地增强MDMA体温过高。该提案的总体目标是确定参与MDMA诱导的UCP 3依赖性产热的组织靶点和机制。具体目标#1：鉴定UCP 3依赖性产热的靶组织。具体目标#2：表征游离脂肪酸在体内MDMA激活UCP 3中的作用。总之，这些研究将显着推进我们对这种新型的UCP 3依赖性生热途径的机制理解，并可能揭示治疗从高热到肥胖和糖尿病等一系列体温调节疾病的新药物靶点。本提案中的工作涉及项目公告PA-06-525，标题为“MDMA：需要更加重视的研究领域”。MDMA是世界上最广泛滥用的药物之一，过量服用可导致致命的体温过高。没有治疗MDMA高热的方法。该提案中的工作旨在确定动物在MDMA治疗后体内何处产生热量，以及参与产生热反应的分子。预计这项工作将为开发第一种能够直接关闭产热的有效热疗药物提供合理的基础。

DESCRIPTION (provided by applicant): Work in this proposal addresses the Program Announcement (PA-06-525) entitled "MDMA: Research Areas Needing More Emphasis (R21)". The most dangerous side effect of acute MDMA intoxication is hyperthermia, a hyper-metabolic condition that stems from a dramatic increase in "non-shivering" metabolic thermogenesis in the setting of heat conservation (peripheral vasoconstriction). MDMA-induced hyperthermia leads to a cascade of life threatening medical complications including skeletal muscle breakdown, cardiovascular collapse, multi-organ failure, and disseminated intravascular coagulation. In animals, hyperthermia also strongly potentiates long term neurotoxicity. No treatment exists for the reversal of hyperthermia induced by MDMA and related compounds, most likely because the direct mediators of human thermogenesis in response to normal (cold, feeding, infection) and pathologic (MDMA, endocrinopathies) thermogenic stimuli have not been identified. Uncoupling proteins (UCPs) are highly conserved thermogenic molecules that regulate mitochondrial heat production in plants, nematodes, flies, and vertebrates. In mammals, brown fat UCP1 is thought to be the dominant, if not the only significant mediator of thermogenic responses. Arguing strongly against this is the fact that adult humans express negligible amounts of brown fat and UCP1, yet do show significant non-shivering thermogenic responses (i.e. MDMA hyperthermia, diet induced thermogenesis, fever). Skeletal muscle is the most important thermogenic organ in humans, and a major target of MDMA-induced pathology; thus, we reasoned that the recently identified uncoupling protein 3, expressed primarily in skeletal muscle (UCP3) may mediate MDMA hyperthermia. We tested this in mice lacking UCP3. UCP3 knockout mice have a near complete loss (~80%) of MDMA-induced thermogenesis and are completely protected from MDMA-induced death over a range of lethal doses. Consistent with the general thermoregulatory relevance of UCP3 in inducible thermogenesis, we also observed that UCP3 knockout mice lose the capacity to generate a fever in response to the bacterial pyrogen lipopolysaccharide. With regard to mechanisms of UCP3 activation, we observed that free fatty acids - required ligands for UCP3 function in vitro - are elevated in the bloodstream prior to peak MDMA-induced hyperthermia. Additionally, we found that high fat feeding increases levels of plasma free fatty acids and correspondingly potentiates MDMA hyperthermia. The overall goal of this proposal is to identify the tissue target(s) and mechanisms involved in MDMA-induced UCP3-dependent thermogenesis. Specific Aim #1: To identify the target tissue of UCP3-dependent thermogenesis. Specific Aim #2: To characterize the role of free fatty acids in UCP3 activation by MDMA in vivo. Together, these studies will significantly advance our mechanistic understanding of this novel, UCP3-dependent thermogenic pathway in humans and may reveal novel drug targets for the treatment of a range of thermoregulatory illnesses ranging from hyperthermia to obesity and diabetes. Work in this proposal addresses the program announcement PA-06-525, entitled "MDMA: Research Areas Needing More Emphasis". One of the most widely abused drugs in the world, MDMA overdose can give rise to fatal hyperthermia. No treatment exists for MDMA hyperthermia. Work in this proposal aims to determine where in the body heat generation occurs after MDMA treatment in animals, and the molecules that are involved in generating the heat response. It is expected that this work will provide a rational basis for the development of the first effective hyperthermia medicine able to directly turn off heat production.