Citrulline adjunctive therapy for cerebral malaria

描述（由申请人提供）：我们最近在《自然医学》上发表了低一氧化氮（NO）生物利用度导致脑型疟疾（CM），这是一种每年导致200多万人死亡的神经系统疾病；因此，提高一氧化氮的生物利用度代表了这种致命疾病的潜在辅助治疗。辅助治疗是很重要的，因为尽管有适当的抗寄生虫化疗，大约30%的CM患者还是会死亡。实验性脑疟疾（ECM）中NO生物利用度低导致炎症和血管泄漏。在其他疾病中，低NO生物利用度有助于血小板激活和聚集、内皮功能障碍、血管泄漏和免疫激活和调节；这些事件也导致了复杂的疟疾综合征。因此，一氧化氮治疗可能对这种复杂的疾病有效，因为它对上述过程具有多效抑制作用。事实上，吸入NO和静脉注射NO供者显著（P<0.05）保护了ECM死亡率，为CM的潜在辅助治疗提供了理论依据。不幸的是，上述两种NO疗法都不适合在疟疾流行地区资源贫乏的诊所实施。然而，在这些诊所中，有其他方法可以在ECM期间恢复NO的生物利用度。由于CM期间一氧化氮的低生物利用度部分是由严重的低精氨酸血症引起的，这导致内皮一氧化氮合酶衍生的一氧化氮生成减少，一种方法是通过静脉注射氨基酸来恢复精氨酸水平。这是Anstey及其同事正在进行的试验的基础，这些试验表明，在人类恶性疟疾期间，no依赖性内皮细胞功能显著恢复。我们假设瓜氨酸将是一种更有效的方法来恢复精氨酸水平，从而提高一氧化氮的生物利用度，因为(i)瓜氨酸抑制疟疾期间红细胞释放的精氨酸酶，（ii）瓜氨酸不被肝脏代谢，（iii）瓜氨酸比精氨酸毒性更小，（iv）瓜氨酸比精氨酸本身更好地改善低精氨酸血症。瓜氨酸通过肾脏转化为精氨酸。事实上，我们的初步研究表明，瓜氨酸完全保护所有接受者免受ECM死亡，而相同剂量的精氨酸则导致毒性和早期死亡。为了提供向IND迈进所需的概念的初步证明，我们在目标1中提议测量精氨酸和瓜氨酸治疗的药代动力学。在目标2中，我们比较了等摩尔精氨酸和瓜氨酸在ECM期间预防死亡率的功效。由于瓜氨酸和精氨酸治疗的死亡率只能通过降低ECM发病机制和恢复NO的产生来改善，因此我们将通过发病机制和NO生物利用度研究来证实死亡率的差异。目的3确定辅助治疗是否影响抗寄生虫化疗。根据瓜氨酸对ECM的完全保护作用，以及在心血管和镰状细胞病领域的研究，我们预计瓜氨酸是一种新的IND，用于治疗脑疟疾这一威胁生命的神经系统疾病。因此，拟议的疗法符合R21翻译研究探索性/发展性项目的指导方针，该项目旨在测试尚未得到大量数据和先例支持的机制的新疗法。

DESCRIPTION (provided by applicant): We recently published in Nature Medicine that low nitric oxide (NO) bioavailability contributes to cerebral malaria (CM), the neurological disorder that kills over 2 million people annually; thus, improving NO bioavailability represents a potential adjunctive therapy for this deadly disease. Adjunctive therapy is important because about 30% of CM patients succumb despite appropriate anti-parasite chemotherapy. Low NO bioavailability in experimental cerebral malaria contributes to inflammation and vascular leak during experimental cerebral malaria (ECM). In other diseases, low NO bioavailability contributes to platelet activation and aggregation, endothelial dysfunction, vascular leak, and immune activation and regulation; these events also contribute to the complex malaria syndrome. NO therapy may therefore be effective against this complex disease because of its pleiotropic inhibitory effects of the above processes. Indeed, inhaled NO and i.v. injection of a NO donor significantly (P<0.05) protected against ECM mortality, providing the rationale for being a potential adjunctive therapy for CM. Unfortunately, neither of the above NO therapies are suitable for implementation in resource poor clinics in malaria endemic areas. There are, however, alternate approaches to restore NO bioavailability during ECM that will work in these clinics. Because the low NO bioavailability during CM is caused in part by severe hypoargininemia, which leads to decreased endothelial nitric oxide synthase-derived NO production, one approach is to restore arginine levels by parenteral administration of the amino acid. This is the basis for Anstey and colleagues ongoing trials that have shown marked restoration of NO-dependent endothelial cell function during human falciparum malaria. We posit that citrulline will be a more effective approach to restore arginine levels and hence NO bioavailability because (i) citrulline inhibits arginases released from RBCs during malaria, (ii) citrulline is not metabolized by the liver, (iii) citrulline is less toxic than arginine, and (iv) citrulline ameliorates hypoargininemia better than arginine itself. Citrulline is converted by the kidneys into arginine. Indeed, our preliminary indicate that citrulline completely protects all recipients against ECM mortality whereas the same dose of arginine caused toxicity and early death. To provide the initial proof of concept required to move toward an IND, we propose in aim 1 to measure the pharmacokinetics of arginine and citrulline therapy. In aim 2, we compare the efficacy of equimolar arginine and citrulline in protecting against mortality during ECM. Because mortality by citrulline and arginine therapy can only be improved by decreasing ECM pathogenesis and restoring NO production, we will confirm the differences in mortality with pathogenesis and NO bioavailability studies. Aim 3 determines whether the adjunctive therapy affects anti-parasite chemotherapy. Based on the complete protection against ECM by citrulline and the studies in the cardiovascular and sickle cell disease fields, we anticipate that citrulline represents a novel IND for cerebral malaria, a life threatening neurological disorder. As such, the proposed therapy meets the guidelines for the R21 Exploratory/developmental Projects in Translation Research, which is designed to test new therapeutics with mechanisms not as yet supported by substantial data and precedent. Public Health Relevance: We have reported the low nitric oxide bioavailability contributes to the pathogenesis of experimental cerebral malaria. This research finding is translated into a potential adjunctive therapy for cerebral malaria that rescues patients from their neurological disease. The proposed research generates proof-of-principle data needed to move the proposed adjunctive therapy toward an Investigational New Drug application. Disclaimer: Please note that the following critiques were prepared by the reviewers prior to the Study Section meeting and are provided in an essentially unedited form. While there is opportunity for the reviewers to update or revise their written evaluation, based upon the group's discussion, there is no guarantee that individual critiques have been updated subsequent to the discussion at the meeting. Therefore, the critiques may not fully reflect the final opinions of the individual reviewers at the close of group discussion or the final majority opinion of the group. Thus the Resume and Summary of Discussion is the final word on what the reviewers actually considered critical at the meeting.