Potential Therapeutic Applications of Ecto-Nucleotidases in Lithium-induced NDI

描述(由申请人提供)：锂(Li)是一种公认的治疗双相情感障碍的药物，正在成为急性和慢性神经退行性疾病的潜在神经保护疗法。然而，LI治疗的一个显著副作用是肾源性尿崩症(NDI)。Li诱导的NDI被归因于髓质集合管(MCD)产生前列腺素E2(PGE2)的增加。目前，在锂诱导的NDI中，旨在直接抑制PGE2合成的治疗方法遇到了严重的副作用，包括锂中毒。基于对LI诱导的NDI分子病理生理学的更深入的了解，用新的药物取代现有的易产生副作用的药物将在临床上导致疗效的提高和副作用的减少。在此背景下，我们发现在LI诱导的NDI中，肾脏PGE2的产生增加可能与延髓集合管(MCD)中的细胞外核苷酸(ATP/UTP)受体P2Y2受体的超敏有关。在大鼠模型上进行的初步研究表明，给予apyrase(可溶性胞外核苷酸酶)可显著减少Li诱导的多尿，这与MCD增加P2Y2受体激动剂刺激的PGE2释放的正常化有关。我们还发现，P2Y2受体的基因缺失导致了对锂诱导的多尿的显著抵抗。基于这些发现，这一建议的中心假设是，超敏反应和通过P2Y2受体增强的信号在体内通过显著增加MCD产生PGE2而在LI诱导的NDI的发生中发挥重要作用。我们进一步认为，天然和工程的胞外核苷酸酶对胞外核苷酸的清除将为Li诱导的NDI的治疗提供一种有效和安全的方法。其具体目的是：(I)确定细胞外核苷酸的结构性清除是否能钝化Li诱导的NDI的发展。为了实现这一目标，我们将使用CD39(NTPDase1，一种外核苷酸酶)过表达转基因小鼠模型；以及(Ii)确定通过给予天然或工程可溶性NTPDase来清除细胞外核苷酸是否会改善Li诱导的大鼠多尿。这项建议的长期目标是通过清除细胞外核苷酸，基于特异性阻断P2Y2受体活性的方法，开发针对LI诱导的NDI的创新疗法。 公共卫生相关性：锂是一种治疗双相情感障碍的有效药物，约有2-3%的普通人群和4-6%的退伍军人受到影响。除了长期用于治疗双相情感障碍外，近年来锂还被确定为治疗急性和慢性神经退行性疾病的强效药物，如中风或阿尔茨海默氏症。然而，锂的使用与肾脏的不良副作用有关--诱发尿崩症或水型糖尿病。目前治疗尿崩症的方法都有严重的副作用，包括锂中毒。该项目确定了可能导致水和盐过度流失的新的分子途径，建议进一步研究这些途径，并有可能开发用于临床的创新疗法。

DESCRIPTION (provided by applicant): Lithium (Li), an established treatment for bipolar disorders, is emerging as a potential neuroprotective therapy for acute and chronic neurodegenerative diseases. However, a significant side effect of Li therapy is nephrogenic diabetes insipidus (NDI). Li-induced NDI has been attributed to increased production of prostaglandin E2 (PGE2) by the medullary collecting duct (mCD). Current therapies aimed at direct inhibition of PGE2 synthesis in Li-induced NDI are encountered with serious side effects, including Li intoxication. Replacement of the current side effect-prone drugs with new ones based on improved understanding of molecular pathophysiology of Li-induced NDI should result in improved efficacy and fewer side effects in the clinic. In this context, we discovered that increased production of renal PGE2 in Li-induced NDI may be related to the hypersensitivity of P2Y2 receptor, an extracellular nucleotide (ATP/UTP) receptor, in the medullary collecting duct (mCD). Preliminary studies conducted in rat model showed that administration of apyrase (soluble ecto-nucleotidase) causes significant reduction in Li-induced polyuria, associated with normalization of the augmented release of P2Y2 receptor agonist-stimulated PGE2 release by the mCD. We also found that genetic deletion of P2Y2 receptor results in marked resistance to the development of Li-induced polyuria. Based on these findings, the central hypothesis of this proposal is that hypersensitivity and enhanced signaling through P2Y2 receptor plays a significant role in vivo in the development of Li-induced NDI by markedly increasing the production of PGE2 by the mCD. We further propose that therapeutic scavenging of the extracellular nucleotides by native and engineered ecto-nucleotidases should offer an efficacious and safer approach for the treatment of Li-induced NDI. The specific aims are: (i) to determine whether constitutive scavenging of extracellular nucleotides blunts the development of Li-induced NDI. To achieve this goal, we will use CD39 (NTPDase1, an ecto-nucleotidase) over expressing transgenic mouse model; and (ii) to determine whether pharmacological scavenging of extracellular nucleotides by the administration of native or engineered soluble NTPDases will ameliorate the Li-induced polyuria in rats. The long-term objective of this proposal is to develop innovative therapies for Li-induced NDI based on the approach of specific blockade of the activity of P2Y2 receptor by scavenging the extracellular nucleotides. PUBLIC HEALTH RELEVANCE: Lithium is an effective drug for the treatment of bipolar disorders, which affect about 2-3% of general population and 4-6% of Veterans. In addition to its long-standing use for the treatment of bipolar disorders, in recent years lithium has been identified as a potent drug for the treatment of acute and chronic neurodegenerative disorders, such as stroke or Alzheimer's, respectively. However, the use of lithium is associated with adverse side effect on the kidney - induction of diabetes insipidus or water diabetes. Current therapies for the treatment of diabetes insipidus are encountered with serious side effects, including lithium intoxication. This project, which identifies novel molecular pathways that may be responsible for the excessive loss of water and salt, proposes to further investigate these pathways with a possibility to develop innovative therapies for use in the clinic.