Mechanisms of MDMA-induced hyperthermia

描述(由申请人提供)：本提案中的工作涉及题为“MDMA：需要更多重视的研究领域(R21)”的计划公告(PA-06-525)。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，源于在热保存(外周血管收缩)的环境下，“非颤抖”代谢产热的急剧增加。MDMA诱导的体温过高会导致一系列危及生命的医疗并发症，包括骨骼肌崩溃、心血管衰竭、多器官衰竭和弥漫性血管内凝血。在动物中，高温也会强烈增强长期的神经毒性。目前还没有治疗方法来逆转MDMA和相关化合物引起的体温升高，最可能的原因是人类对正常(寒冷、进食、感染)和病理(MDMA、内分泌疾病)产热刺激的直接中介尚未确定。解偶联蛋白(UCP)是高度保守的生热分子，调节植物、线虫、苍蝇和脊椎动物线粒体的产热。在哺乳动物中，棕色脂肪UCP1被认为是发热反应的主要媒介，如果不是唯一重要的媒介的话。强烈反对这一观点的是这样一个事实，即成年人表达的棕色脂肪和UCP1的数量可以忽略不计，但确实表现出显著的非颤抖生热反应(即MDMA发热、饮食诱导的生热、发热)。骨骼肌是人类最重要的生热器官，也是MDMA诱导病理的主要靶点；因此，我们推测最近发现的主要在骨骼肌中表达的解偶联蛋白3(UCP3)可能介导了MDMA的高热。我们在缺乏UCP3的小鼠身上进行了测试。UCP3基因敲除小鼠几乎完全丧失了MDMA诱导的产热作用(~80%)，并在一定的致死剂量范围内完全免受MDMA诱导的死亡。与UCP3在诱导生热中的一般体温调节相关性一致，我们还观察到UCP3基因敲除小鼠失去了对细菌热原脂多糖的反应而产生发热的能力。关于UCP3的激活机制，我们观察到，在MDMA诱导的高热之前，UCP3在体外发挥作用所需的配体--游离脂肪酸--在血流中升高。此外，我们发现，高脂肪喂养会增加血浆游离脂肪酸水平，并相应地加强MDMA高热。该提案的总体目标是确定MDMA诱导的UCP3依赖的产热过程中涉及的组织靶点(S)和机制。具体目标#1：确定UCP3依赖的生热作用的靶组织。具体目的#2：研究体内游离脂肪酸在MDMA激活UCP3中的作用。总之，这些研究将极大地促进我们对这一新的、依赖于UCP3的人类产热途径的机制理解，并可能揭示治疗从体温过高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，题为“MDMA：需要更多重视的研究领域”。MDMA是世界上滥用最广泛的药物之一，过量服用会导致致命的体温过高。目前还没有针对MDMA高热的治疗方法。这项建议的工作旨在确定在动物接受MDMA治疗后，人体内哪里会产生热量，以及参与产生热反应的分子。希望这项工作将为开发首个能够直接关闭产热的有效热疗药物提供合理的依据。

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.