叶酸、半胱氨酸代谢通路中重要极性小分子血清学水平与食管癌发病风险的队列研究

Esophageal cancer is closely associated with nutrition, and chemoprevention by appropriate nutrient is thought to be an efficient way for the prevention and control of esophageal cancer. Low intake of folate and one-carbon metabolism related B vitamins was found in patients with malignant tumors recently, and cysteine was thought to be a protective factor for gastrointestinal cancers by some scholars. However, metabolism of nutrients was closely interactive. For example, folate and one-carbon metabolism related B vitamins play important roles in the metabolism of cysteine, and cysteine and several amino acids can be transformed mutually. Most current studies regarding folic, cysteine and esophageal cancer were case-control studies focusing on single nutrient or based on the nutritional questionnaire, which were hard to investigate the long-term risk of esophageal cancer for the absorbed nutrients. Therefore, we plan to conduct a stratified case-cohort study among the 30,000 follow-up subjects of “Linxian Nutrition Intervention Trial”, which was established in 1985. Certain amount of cases and controls will be randomly stratified selected and tested for the serum samples collected in 1985 and 2000 in different nutritional status. Folate and one-carbon metabolism related B vitamins, and important amino acids related to the metabolism of cysteine will be tested by High Performance Liquid Chromatography and Triple Quadrupole Mass Spectrometer. The effect on the esophageal cancer and interactive mechanism of these important polar metabolites will be investigated, and the value of joint examination on the long-term risk of esophageal cancer will be evaluated. Protective and risk nutritional factors will be identified in this study as well, and finally provide scientific data for future studies regarding the chemoprevention and carcinogenesis of esophageal cancer.

营养与食管癌密切相关，寻找适宜营养素开展化学预防是食管癌防控的有效途径。研究提示，肿瘤病人叶酸及一碳代谢相关B族维生素摄入量较低，而半胱氨酸对食管癌可能有保护作用，但尚无定论。营养物质代谢密切相关，叶酸及一碳代谢相关B族维生素在半胱氨酸代谢中起重要作用，半胱氨酸与多种氨基酸存在转化关系。但现有研究多为基于营养问卷的病例对照研究或针对单一营养素，难以评估吸收态的多种营养素对食管癌发病的长期影响。本研究拟在1985年建立的林县营养干预试验队列中开展病例队列研究。选取部分病例和对照，使用高效液相色谱—三重四极杆质谱联用检测其1985年和2000年不同营养状况下留存血清中的叶酸及一碳代谢相关B族维生素和半胱氨酸代谢相关氨基酸，探讨上述重要极性小分子对食管癌发病的影响和交互作用，研究营养素联合检测对食管癌发病风险评估的作用，寻找营养学危险因素和保护因素，为食管癌的化学预防和致癌机理研究提供科学数据。

目前国际上罕见在长期随访队列中探讨危险因素和多种代谢物/谱与食管癌发病风险的病因学研究，现有研究多为横断面研究。因食管癌患病后，可显著影响机体营养物质的代谢吸收，基于横断面病例对照研究设计获得的食管癌血清代谢标志物，可作为潜在的诊断及治疗标志物，难以用于发病风险预测。本课题组1985年在河南林县建立了约3万人的人群营养干预队列，有详细的危险因素调查资料，在1985年和2000年采集了血清标本并长期随访追踪队列食管癌的发病和死亡情况。本项目是在该队列中开展的一项病例队列研究，选取2000年后发病的食管癌病例428名，按性别和年龄匹配482例对照，检测其食管癌发病前于2000年采集的血清标本中叶酸、半胱氨酸、同型半胱氨酸、维生素B12、维生素B6、甲硫氨酸和丝氨酸的含量。使用高效液相色谱—三重四极杆质谱联用方法，仅需0.1ml血清标本检测上述指标，但未能稳定测到叶酸，可能与叶酸在人体内血清含量低且存在易氧化基因有关。此外，维生素B6在使用肝素抗凝的血清中的检测率显著高于使用EDTA抗凝的血清。研究结果显示：血清维生素B12水平较高的人群食管癌的发病风险较高（OR=1.39, 95%CI=1.07-1.86，P=0.02）。选取使用肝素抗凝并测得6种代谢物的350例标本进行亚组分析，发现血清维生素B12水平较高者食管癌发病风险较高（OR=1.17, 95%CI=0.89-1.57，P=0.26），蛋氨酸（OR=0.56, 95%CI=0.39-0.77，P=0.0006）和丝氨酸（OR=0.65, 95%CI=0.46-0.91，P=0.013）水平较高者食管癌的发病风险较低。若经进一步研究验证，血清低水平甲硫氨酸和丝氨酸有望作为食管癌发病风险增高的预警指标，可鉴别高危人群，为食管癌的精准防治提供重要资料。此外，本项目发现各代谢产物间有较强的相关性，仅检测几种代谢物，难以确定食管癌发病的独立性预测指标。故扩展研究计划，选取210例研究对象，通过代谢组学方法对其1985年采集的血清中74种极性小分子进行联合检测，初步发现三种潜在的生物标志物。本研究也证实储存多年并保存良好的血清标本可用于代谢组学检测，为基于代谢组学的食管癌病因学研究提供了参考数据。