To study the potential relationship between melatonin and beta-amyloid (Abeta), we established a liquid chromatography–mass spectrometry (LC-MS) method to quantitatively analyze melatonin, deuterated isotopes (melatonin-D4), and internal standard 6-iodo-2-(4'-dimethylamino-) phenyl-imidazo(1,2) pyridine (IMPY) under positive (+) mode. The gradient elution was set to 6 min, and the corresponding peak time of melatonin and its isotope melatonin-D4 was 3.14 min, while the peak time for the internal standard IMPY was 3.24 min. Next, we established and optimized the molecule receptor saturation binding assay based on LC-MS to determine the melatonin affinity for beta-amyloid (Abeta). Melatonin showed a high and specific binding for Abeta. The corresponding equilibrium dissociation constant (Kd) of melatonin with Abeta 1-40 and Abeta 1-42 was 814.37 ± 36.62 and 628.33 ± 13.57 nmol·L⁻¹; besides, the Kd of melatonin with mixed plaques (1-40 and 1-42) was 461.13 ± 45.37 nmol·L⁻¹. The results may suggest the potential mechanism of action of MT on Abeta and provide a theoretical basis for the improvement of MT treatment of Alzheimer's disease.

中文翻译：

---

褪黑激素以高亲和力和特异性与 β-淀粉样蛋白结合：LC-MS 提供对阿尔茨海默病治疗的深入了解

为了研究褪黑激素和 β-淀粉样蛋白 (Abeta) 之间的潜在关系，我们建立了液相色谱-质谱 (LC-MS) 方法来定量分析褪黑激素、氘代同位素 (melatonin-D4) 和内标 6-iodo-2 -(4'-二甲氨基-) 苯基-咪唑(1,2) 吡啶 (IMPY) 在正 (+) 模式下。梯度洗脱设置为6 min，褪黑激素及其同位素melatonin-D4的相应峰时间为3.14 min，而内标IMPY的峰时间为3.24 min。接下来，我们建立并优化了基于 LC-MS 的分子受体饱和结合测定，以确定褪黑激素对β-淀粉样蛋白 (Abeta) 的亲和力。褪黑激素显示出对 Abeta 的高特异性结合。相应的平衡解离常数 ( Kd) Abeta 1-40 和 Abeta 1-42 的褪黑激素分别为 814.37 ± 36.62 和 628.33 ± 13.57 nmol·L ^-1；此外，具有混合斑块（1-40和1-42）的褪黑激素的K d 为461.13 ± 45.37 nmol·L ^-1。研究结果可能提示MT对Abeta的潜在作用机制，为改善阿尔茨海默病的MT治疗提供理论依据。