Department of Radiology, Washington University School of Medicine, Saint Louis, MO, 63110, United States of America.
Departments of Medicine and Pathology and Immunology, Washington University School of Medicine, Saint Louis, MO, 63110, United States of America.
Nucl Med Biol. 2023 Jul-Aug;122-123:108370. doi: 10.1016/j.nucmedbio.2023.108370. Epub 2023 Jul 26.
Diabetes mellitus is a chronic progressive metabolic disorder that affects millions of people worldwide. Emerging evidence suggests the important roles of sphingolipid metabolism in diabetes. In particular, sphingosine-1-phosphate (S1P) and S1P receptor 2 (S1PR2) have important metabolic functions and are involved in several metabolic diseases. In diabetes, S1PR2 can effectively preserve β cells and improve glucose/insulin tolerance in high-fat diet induced and streptozotocin (STZ)-induced diabetic mouse models. We previously developed a group of potent and selective S1PR2 ligands and radioligands.
In this study, we continued our efforts and characterized our leading S1PR2 radioligand, [C]TZ34125, in a STZ-induced diabetic mouse model. [C]TZ34125 was radiosynthesized in an automated synthesis module and in vitro saturation binding assay was performed using recombinant human S1PR2 membrane. In vitro saturation autoradiography analysis was also performed to determine the binding affinity of [C]TZ34125 against mouse tissues. Type-1 diabetic mouse model was developed following a single high dose of STZ in C57BL/6 mice. Ex vivo biodistribution was performed to evaluate the distribution and amount of [C]TZ34125 in tissues. In vitro autoradiography analysis was performed to compare the uptake of [C]TZ34125 between diabetic and control animals in mouse spleen and pancreas.
Our in vitro saturation binding assay using [C]TZ34125 confirmed [C]TZ34125 is a potent radioligand to recombinant human S1PR2 membrane with a K value of 0.9 nM. Saturation autoradiographic analysis showed [C]TZ34125 has a K of 67.5, 45.9, and 25.0 nM to mouse kidney, spleen, and liver tissues respectively. Biodistribution study in STZ-induced diabetic mice showed the uptake of [C]TZ34125 was significantly elevated in the spleen (2 fold higher) and pancreas (1.4 fold higher) compared to normal controls. The increased uptake of [C]TZ34125 was further confirmed using autoradiographic analysis in the spleen and pancreases of STZ-induced diabetic mice, indicating S1PR2 can potentially act as a biomarker of diabetes in pancreases and inflammation in spleen. Future mechanistic analysis and in vivo quantitative assessment using non-invasive PET imaging in large animal model of diabetes is worthwhile.
Overall, our data showed an increased uptake of our lead S1PR2-specific radioligand, [C]TZ34125, in the spleen and pancreases of STZ-induced diabetic mice, and demonstrated [C]TZ34125 has a great potential for preclinical and clinical usage for assessment of S1PR2 in diabetes and inflammation.
糖尿病是一种影响全球数百万人的慢性进行性代谢紊乱。新出现的证据表明，神经酰胺代谢在糖尿病中具有重要作用。特别是，鞘氨醇-1-磷酸（S1P）和 S1P 受体 2（S1PR2）具有重要的代谢功能，并参与多种代谢疾病。在糖尿病中，S1PR2 可以有效地保护β细胞，并改善高脂肪饮食诱导和链脲佐菌素（STZ）诱导的糖尿病小鼠模型中的葡萄糖/胰岛素耐受性。我们之前开发了一组有效的、选择性的 S1PR2 配体和放射性配体。
在这项研究中，我们继续努力，使用 STZ 诱导的糖尿病小鼠模型对我们的 S1PR2 放射性配体 [C]TZ34125 进行了表征。[C]TZ34125 在自动化合成模块中进行放射性合成，并用重组人 S1PR2 膜进行体外饱和结合测定。还进行了体外饱和放射自显影分析，以确定 [C]TZ34125 对小鼠组织的结合亲和力。在 C57BL/6 小鼠中单次高剂量 STZ 诱导 1 型糖尿病模型。进行了离体生物分布实验，以评估 [C]TZ34125 在组织中的分布和数量。在体外放射自显影分析中，比较了糖尿病和对照动物在小鼠脾脏和胰腺中 [C]TZ34125 的摄取情况。
我们使用 [C]TZ34125 进行的体外饱和结合测定证实 [C]TZ34125 是一种对重组人 S1PR2 膜具有强大亲和力的放射性配体，K 值为 0.9 nM。饱和放射自显影分析显示 [C]TZ34125 对小鼠肾脏、脾脏和肝脏组织的 K 值分别为 67.5、45.9 和 25.0 nM。在 STZ 诱导的糖尿病小鼠中的生物分布研究表明，与正常对照相比，[C]TZ34125 在脾脏（约 2 倍）和胰腺（约 1.4 倍）中的摄取显著增加。在 STZ 诱导的糖尿病小鼠的脾脏和胰腺中使用放射自显影分析进一步证实了 [C]TZ34125 的摄取增加，表明 S1PR2 可能作为胰腺中糖尿病和脾脏中炎症的生物标志物。未来使用大动物糖尿病模型进行非侵入性正电子发射断层扫描成像的机制分析和体内定量评估是值得的。
总之，我们的数据表明，在 STZ 诱导的糖尿病小鼠的脾脏和胰腺中，我们的 S1PR2 特异性放射性配体 [C]TZ34125 的摄取增加，并证明 [C]TZ34125 在评估糖尿病和炎症中的 S1PR2 方面具有很大的临床前和临床应用潜力。
