Thyroid hormone action on glucose and energy metabolism in vivo studies

摘要：甲状腺激素在几乎所有器官的发育和功能中发挥着重要的调节作用，其稳态由高度调节的多步骤冗余系统维持。甲状腺激素的外周代谢通过调节活性激素 T3 的循环和细胞内水平，代表了激素作用的重要组织特异性前受体调节剂。脱碘酶是将激素原 T4 转化为其活性激素 T3 或代谢失活的 rT3 的硒酶。我们之前发现，2 型脱碘酶基因 (Thr92Ala) 的常见多态性与葡萄糖处理减少相关，并且在存在先前描述的失活 β-3 肾上腺素受体多态性的情况下，与体重指数小幅但显着的增加有关。有趣的是，这种多态性并不影响身体活跃的创始人群体（旧秩序阿米什人）的胰岛素抵抗指数，这表明基因与环境之间存在相互作用。我们推测 Thr92Ala 多态性产生了一种有缺陷的酶，从而导致 T4 到 T3 的细胞内转化减少，最终导致能量消耗减少和胰岛素依赖性葡萄糖转运蛋白 4（其基因受甲状腺激素调节）的转录受损。 今年，我们集中精力开发和实施一系列临床方案，旨在表征体内甲状腺激素外周代谢的作用及其在调节能量和葡萄糖代谢中的作用。 具体而言，已实施以下协议： 05-DK-0119 外周甲状腺激素转化以及葡萄糖和能量代谢。该临床方案旨在表征体内甲状腺激素外周代谢相对于葡萄糖和能量代谢的作用，被设计为双盲交叉研究，其中甲状腺功能减退患者接受 T4 或 T3 治疗，并在达到稳定的替代剂量后，进入临床中心的代谢科，对能量和葡萄糖稳态进行详细评估。目前，12 名患者已完成两个阶段的研究。从该方案获得的数据使我们能够表征左旋甲状腺素和碘塞罗宁的药物等效性。该信息具有临床相关性，因为治疗分化型甲状腺癌的制剂是基于碘塞罗宁替代左旋甲状腺素。从该方案获得的数据可以准确替代甲状腺激素替代品，从而最大限度地减少与过度或替代不足相关的不适和潜在风险。这些数据已发表在题为“左旋甲状腺素和碘塞罗宁的药效等效性。甲状腺切除患者的随机、双盲、交叉研究”的手稿中，该手稿最近接受在《临床内分泌学》上发表。我们目前正在分析两种甲状腺激素制剂在靶器官水平上的差异。 06-DK-0133 甲状腺激素诱导的脂肪分解：体内微透析研究。该临床方案旨在通过利用微透析技术研究甲状腺激素对脂肪组织的药理作用，并研究脱碘酶的体内作用。该研究分为四个阶段。目前正在招募健康志愿者，预计数据收集将于 10 财年完成。 07-DK-0202 人体暴露于低温时，甲状腺激素稳态和能量代谢发生变化。该临床方案旨在利用临床中心代谢单元新开放的呼吸室，在体内研究暴露于环境温度轻微变化期间循环甲状腺激素的变化。第一阶段研究已经完成，25名志愿者已成功完成研究。目前正在完成一份描述能量消耗、底物利用和激素变化变化的手稿。迄今为止获得的结果促使我们要求对方案进行修订，以便将招募范围扩大到肥胖和老年人，并进行 PET 研究，以分析棕色脂肪组织在冷诱导产热中的生理作用。 07-DK-0219 用于研究膳食谷甾醇对脂质、葡萄糖和能量代谢作用的营养基因组学干预。这是对 ABCG8 突变携带者和性别匹配的未受影响兄弟姐妹的营养基因组学干预，旨在研究 ABCG8 基因突变修饰与植物甾醇膳食含量之间相互作用的影响。我们假设ABCG8基因突变的携带者在接受高谷甾醇饮食的挑战时将进一步改善代谢综合征指数，并且在接受低谷甾醇饮食的治疗时将回归到非携带者对照。这项研究是在宾夕法尼亚州兰开斯特郡的旧秩序阿米什人群体中进行的，该群体是 ABCG8 突变发生率很高的创始群体。目前，三对同胞已经完成了第一阶段的研究。 NIDDK-NIAMS IRB 和马里兰大学 IRB 最近批准了一项要求将招募范围扩大到无兄弟姐妹的修正案。我们相信，对方案的这一改变将提高研究对象的应计率，从而完成研究。 08-DK-0165 在内源性分泌胆汁酸 (BA) 刺激过程中，甲状腺激素稳态和能量代谢发生变化。体外和动物数据表明，胆汁酸以内分泌方式激活 T4 向 T3 的转化，最终导致能量消耗增加。该转化方案旨在研究健康志愿者中宏量营养素和胆汁酸在食物热效应中的作用。该方案已获得 NIDDK/NIAMS IRB 批准，目前 16 名健康志愿者已成功完成该研究。 08-DK-0058 健康志愿者对促甲状腺素释放激素刺激的药物基因组学反应：常见 2 型脱碘酶遗传多态性对血清 T3 的影响。我们从 McCune-Albright 综合征患者获得的数据清楚地表明，甲状腺内 T4 转化为 T3 是在 cAMP 通路激活时发生的。因此，我们利用药物基因组学研究设计利用这一途径，通过分析三种基因型（Thr/Thr、Thr/Ala 和 Ala/Ala）携带者个体中 TRH 刺激 TSH 升高后 T3 水平的差异，评估 D2 (Thr92Ala) 常见多态性的体内影响。目前，预计 45 名研究志愿者中有 39 名已成功完成该研究。我们有信心这项研究将在 2010 财年年底前完成。

Summary: Thyroid hormone plays an important regulatory role in the development and function of virtually all organs and its homeostasis is maintained by a highly regulated, multi-step redundant system. The peripheral metabolism of thyroid hormone, by regulating the circulating and intracellular levels of the active hormone T3, represents an important tissue-specific pre-receptor modulator of the hormonal action. The deiodinases are selenoenzymes which convert the pro-hormone T4 into its active hormone T3 or into the metabolically inactive rT3. We previously discovered that a common polymorphism of the type 2 deiodianse gene (Thr92Ala) associates with decreased glucose disposal and, in the presence of a previously described inactivating beta-3 adrenergic receptor polymorphism, with a small but significant increase in body mass index. Interestingly, this polymorphism does not affect indices of insulin resistance in a physically active founder population, the Old Order Amish, suggesting a gene-environment interaction. We speculated that the Thr92Ala polymorphism generates a defective enzyme thus leading to a decrease intracellular conversion of T4 to T3, ultimately leading to reduced energy expenditure and impaired transcription of the insulin-dependent glucose transporter-4, whose gene is thyroid hormone-regulated. During this year we have focused our efforts in developing and implementing a portfolio of clinical protocols aimed to characterize in vivo the role of the peripheral metabolism of thyroid hormone and its role in modulating the energy and glucose metabolism. Specifically, the following protocols have been implemented: 05-DK-0119 Peripheral Thyroid Hormone Conversion and Glucose and Energy Metabolism. This clinical protocol aimed to characterize in vivo the role of the peripheral metabolism of thyroid hormone with respect to glucose and energy metabolism is designed as a double blind, cross over study in which hypothyroid patients are treated either with T4 or T3 and after reaching a stable replacement dose, are admitted to the Metabolic Unit of the Clinical Center for a detailed evaluation of the energy and glucose homeostasis. Presently twelve patients have completed both phases of the study. The data obtained from this protocol have allowed us to characterize the pharmaco-equivalency of levothyroxine and liothyronine. This information is of clinical relevance since the preparation for the treatment of differentiated thyroid cancer is based on the substitution of liothyronine for levothyroxine. The data obtained form this protocol allow an accurate substitution of the thyroid hormone replacement, thus minimizing the discomfort and the potential risks associated with over- or under-replacement. The data have been presented in a manuscript entitled: "The pharmacodynamic equivalence of levothyroxine and liothyronine. A randomized, double blind, cross-over study in thyroidectomized patients" recently accepted for publication in Clinical Endocrinology. We are currently analyzing the differences between the two thyroid hormone formulations at the target-organ level. 06-DK-0133 Thyroid hormone-induced lipolysis: an in vivo microdialysis study. This clinical protocol is aimed to study, by exploiting the microdialysis technique, the pharmacological action of thyroid hormone on the adipose tissue and to study in vivo the action of the deiodinases. The study is subdivided in four phases. Healthy volunteers are currently recruited and it is expected that the collection of the data will be completed by FY 10. 07-DK-0202 Thyroid hormones homeostasis and energy metabolism changes during exposure to cold temperature in humans. This clinical protocol is aimed to study in vivo, by taking advantage of the newly opened respiratory chamber in the Metabolic Unit of the Clinical Center, the changes of circulating thyroid hormones during exposure to mild changes in environmental temperature. The first phase of the study has been completed and 25 volunteers have successfully completed the study. A manuscript describing the changes in energy expenditure, substrate utilization and hormonal changes is currently being completed. The results obtained thus far have prompted us to request an amendment to the protocol in order to extend the recruitment to obese and elderly individuals, and to perform PET studies in order to analyze the physiological role of brown adipose tissue in the cold-induced thermogenesis. 07-DK-0219 A Nutrigenomics Intervention for the Study of the Role of Dietary Sitosterol on Lipid, Glucose and Energy Metabolism. This is a nutrigenomics intervention on ABCG8 mutation carriers and sex-matched unaffected siblings aimed to study the effects of the interaction between modifications of ABCG8 gene mutations and plant sterol dietary content. We hypothesize that carriers of the ABCG8 gene mutation will further improve metabolic syndrome indices when challenged with a high-sitosterol diet, and will regress toward the non-carrier controls when treated with a low-sitosterol diet. This study is conducted in the Old Order Amish population of Lancaster Co. PA, a founder population with a high prevalence of ABCG8 mutations. Currently three sib-pairs have completed the first phase of the study. An amendment requesting the extension of the recruitment to no-sibling has been recently approved by both NIDDK-NIAMS IRB and University of Maryland IRB. We are confident that this change to the protocol will allow an increase in the accrual rate of study subjects, allowing the completion of the study. 08-DK-0165 Thyroid hormones homeostasis and energy metabolism changes during stimulation of endogenously secreted bile acids (BAs). In vitro and animal data indicate that the bile acids activate in a endocrine fashion the conversion of T4 to T3 ultimately leading to an increase in energy expenditure. This translational protocol is aimed to study in healthy volunteers the role of macronutrients and bile acids in the thermic effects of food. The protocol has being approved by the NIDDK/NIAMS IRB and currently 16 healthy volunteers have successfully completed the study. 08-DK-0058 Pharmacogenomic Response to Thyrotropin-Releasing Hormone Stimulation in Healthy Volunteers: The Influence of a Common Type 2 Deiodinase Genetic Polymorphism on Serum T3. Our data obtained form McCune-Albright Syndrome patients clearly indicate that intra-thyroidal conversion of T4 in T3 occurs upon activation of the cAMP pathway. We are thus exploiting this pathway using a pharmacogenomic study design to assess in vivo the effects of a common polymorphism of the D2 (Thr92Ala) by analyzing the differences in T3 levels upon TRH-stimulated raise in TSH in individuals carriers of the three genotypes (Thr/Thr, Thr/Ala, and Ala/Ala). Currently 39 out of the projected 45 study volunteers have successfully completed the study. We are confident that this study will be completed by the end of FY10.