慢性低水平镉暴露对一般人群血管内皮功能损害及其内源性代谢物变化的研究

Low doses of cadmium (Cd) (well below toxic concentrations)， in vivo and vitro, were shown to decrease nitric oxide production in vascular endothelial cell (VEC), inhibit VEC proliferation, and impair endothelial wound healing. We found strongly suggestive evidence that cadmium, at substantially low levels of exposure, remains an important determinant of cardiovascular mortality and peripheral arterial disease in general population. Vascular endothelial dysfunction is one of the earliest onsets of cardiovascular diseases, however, in human body, the effect of low-level cadmium on vascular endothelial function is not clear yet. Therefore, we take the following measures to aim to: (1) evaluate the linear and non-linear dose-response relations between low-level urine Cd (<5 μg/g creatinine) and flow-mediated vasodilatation of the brachial arteries (FMD) in general population. (2) set up 4 random subgroups by the strata of urine Cd increasing with FMD decreasing, then isolate and count the rare circulating endothelial cells (CEC) from whole blood using flow cytometry, and observe the morphology of CEC using scanning electron microscopy in 4 random subgroups. (3) explore the endogenous metabolites changes in both serum and urine using GC-MS and LC-MS/MS in 4 random subgroups, further identify the metabolic pathway of significant metabolites. We finally generalize the above results to systematically conclude the effects of chronic exposure to low-level cadmium on vascular endothelial function and the underlying mechanisms in general population. The conclusions would increase our understanding of the wide-adverse effects of low-level Cd on cardiovascular system in a new light, also, provide a prospective strategy to prevent early lesion of cardiovascular diseases.

离体和在体实验研究表明低剂量镉（Cd）可降低血管内皮细胞（VEC）的一氧化氮生成、抑制VEC的增殖、削弱内皮损伤的再生修复。我们前期研究发现，慢性低水平Cd暴露增加一般人群心血管疾病死亡和外周动脉疾病发病的风险并呈明显剂量反应关系。血管内皮损伤是心血管疾病的早期始发因素，但人体中低水平Cd能否损害血管内皮功能尚不清楚。为此，本研究拟：⑴在一般人群中分析低水平尿Cd[<5μg/(g肌酐)]与肱动脉血流介导血管舒张功能（FMD）的线性及非线性剂量反应关系；⑵建立尿Cd升高伴随FMD下降的4组随机样本，流式细胞术分选计数其血中内皮细胞数量及用扫描电镜观察细胞表面结构；⑶联合GC-MS和LC-MS/MS分析4组随机样本血清和尿液的内源性代谢物变化，寻找其代谢途径。探讨慢性低水平Cd暴露损害人体血管内皮功能及其机制。研究可能对低水平Cd影响机体心血管系统有新的认识，并为防治心血管早期病变提供新策略。

基于既往流行病学与实验研究证据，我们假设慢性低水平镉（Cd）暴露（尿Cd浓度< 5 μg/g肌酐）可能会损害人体的血管内皮功能，并存在剂量反应关系。为此，我们在典型的污染区及周边选择一般人群作为研究对象，同时开展离体实验，分别从三个方面进行：（1）分析尿Cd与肱动脉血流介导血管舒张功能（FMD）的剂量反应关系；（2）分析尿Cd与血管内皮损伤血清标志物（ADMA、VCAM-1、ICAM-1）的剂量反应关系；（3）探讨不同尿Cd水平与FMD不同等级群体的血清代谢物轮廓，进一步分析在低剂量Cd培养下血管内皮细胞的内源性小分子代谢物轮廓变化。研究从血管内皮功能障碍及血管内皮损伤的角度均表明Cd，即使是安全标准范围内的慢性低水平暴露，也可增加机体血管内皮功能损害的风险，该种损害风险尤其在男性中表现明显。此外，离体实验表明低剂量Cd引起血管内皮细胞功能损害的异常表型主要为一氧化氮合成减少、促炎反应产生，而氧化应激并不显著。研究进一步提示这些功能异常表型的发生机制可能与细胞三羧酸循环紊乱、氨基己糖合成途径的蛋白糖基化异常有关。本研究对慢性低水平Cd影响机体心血管系统有了新的认识，并为后续如何改善受损的血管内皮功能，防治与慢性低水平Cd暴露有关的心血管早期病变提供新的策略。