Endogenous sphingosine-1-phosphate as a radioprotector of intestinal tissues

描述（由申请人提供）：神经酰胺和鞘氨醇-1-磷酸（S1 P）是通过激活特定信号通路调节细胞存活的生物活性脂质。神经酰胺在细胞中积聚以响应辐射并激活凋亡途径。抑制神经酰胺合成可防止辐射损伤。相比之下，神经酰胺代谢物SlP响应于应激促进细胞存活，并且对于血管生成是必需的。S1 P拮抗包括由神经酰胺和辐射诱导的凋亡途径。重要的是，S1 P可防止小鼠辐射诱导的细胞凋亡和不育。因此，虽然神经酰胺有助于放射性肠炎，但其转化为S1 P提供了一个内部微调信号，限制了辐射反应的强度。我们的初步研究表明，S1 P是一种有效的肠道辐射防护剂，在致死剂量的辐射后促进细胞、组织和动物的存活。然而，S1 P很难实现。因此，我们设计了一种替代方法来提高细胞内S1 P水平并实现辐射防护。S1 P被酶S1 P裂解酶（SPL）分解代谢。SPL在肠绒毛和结肠隐窝中高度表达，在那里它维持低SlP水平，促进细胞更新。SPL的表达是由DNA损伤和辐射在体外和体内诱导的，SPL的表达促进辐射诱导的细胞凋亡，而SPL抑制减弱DNA损伤后的细胞凋亡。四羟基丁基咪唑（THI）是焦糖色素中的一种小分子成分，最近被发现是SPL抑制剂。我们表明，口服THI小鼠降低SPL活性，提高结肠和肠组织中的S1 P水平。基于这些发现和在小鼠中观察到的S1 P的辐射防护作用，我们假设THI通过快速抑制SPL活性和升高内源性辐射防护剂S1 P的细胞内和循环水平，提供了在肠道和其他组织中实现辐射防护的安全手段。为了解决这种可能性，我们提出了三个综合的具体目标：1）确定THI提高组织和循环S1 P水平所需的动力学和剂量要求; 2）评估THI作为辐射诱导的肠道病理学的保护剂的暴露前和暴露后的功效; 3）评估THI施用是否可以延长辐射暴露后的存活。THI是一种理想的候选辐射防护剂，因为它易于递送，最小的相关毒性，以及快速产品开发和多器官辐射防护的潜力。

DESCRIPTION (provided by applicant): Ceramide and sphingosine-1-phosphate (S1P) are bioactive lipids that regulate cell survival through activation of specific signaling pathways. Ceramide accumulates in cells in response to radiation and activates apoptosis pathways. Inhibiting ceramide synthesis protects against radiation injury. In contrast, the ceramide metabolite S1 P promotes cell survival in response to stress and is essential for angiogenesis. S1 P antagonizes apoptotic pathways including those induced by ceramide and radiation. Importantly, S1P prevents radiation-induced apoptosis and sterility in mice. Thus, while ceramide contributes to radiation enteritis, its conversion to S1P provides an internal fine-tuning signal that limits the intensity of radiation responses. Our preliminary studies indicate that S1P is a potent radioprotectant of the gut, promoting cell, tissue and animal survival after lethal doses of radiation. However, S1P is difficult to deliver. Thus, we have devised an alternative approach to raise intracellular levels of S1P and achieve radioprotection. S1P is catabolized by the enzyme S1 P lyase (SPL). SPL is highly expressed in intestinal villi and colonic crypts, where it maintains low S1 P levels, promoting cell turnover. SPL expression is induced by DNA damage and radiation in vitro and in vivo, and SPL expression promotes radiation-induced apoptosis, whereas SPL inhibition attenuates apoptosis after DNA damage. Tetrahydroxybutyl-imidazole (THI), a small molecule constituent of caramel food coloring, was recently found to be an SPL inhibitor. We show that oral administration of THI to mice reduces SPL activity and elevates S1P levels in colonic and intestinal tissues. Based on these findings and the observed radioprotective effect of S1 P in mice, we hypothesize that THI provides a safe means of achieving radioprotection in the gut and other tissues by rapidly inhibiting SPL activity and elevating intracellular and circulating levels of the endogenous radioprotectant, S1 P. To address this possibility, we have proposed three integrated specific aims: 1) To define the kinetics and dose requirements needed for THI to raise tissue and circulating S1 P levels; 2) To evaluate the pre- and post-expo-sure efficacy of THI as a protector of radiation-induced intestinal pathology; 3) To assess whether THI administration can prolong survival after radiation exposure. THI is an ideal candidate radioprotective agent due to its ease of delivery, minimal associated toxicity profile, and potential for rapid product development and multi-organ radioprotection.