猪肉中Neu5Gc消化吸收的机制及加工对其消化吸收和生物危害的影响

A large number of epidemiological studies show that long-term consumption of red meat and processed meat products is associated with the significant increase in cases of cancer, type 2 diabetes mellitus and cardia vascular diseases. Recently, it’s reported that N-glycolylneuraminic acid (Neu5c), a red eat rich variant of sialic acid, is incorporated into human cells and targeted by the circulating anti-Neu5Gc “xeno-antoantibodies”, leading to inflammatory process termed “xenosialitis”, which potentially promotes the initiation and aggravation of cancer and many other diseases. However, dietary survey on Neu5Gc in food is limited, the different forms of Neu5Gc in food have not been determined, little is known about it digestion and absorption, and the effects of food processing have never been considered. To solve all these issues, in the present proposal, with the employment of Caco-2 cells, Cmah-/- mice, glycomic tools and many other molecular techniques, the concentrations and forms of Neu5Gc in processed pork products in China will be surveyed, its changes in concentrations, forms and molecular structure in pork during processing will be studied, its digestion in the digestive tract, transport mechanisms across epithelial cell monolayers and metabolic kinetics in blood and urine will be defined, and the effects of food processing, especially maillard reaction, on its digestion, absorption and incorporation will be determined. Our study will provide new insight into the chemistry of Neu5Gc in food, which will be helpful for hazard control of Neu5Gc in processed meat products.

新近的研究证实，红肉中的N-羟乙酰神经氨酸（Neu5Gc）摄入人体后可整合到细胞表明，引起抗体抗原反应和慢性炎症，可能是与红肉相关的多种疾病的共同发病机理。但我国肉制品中Neu5Gc的含量和危害如何？肉制品中的Neu5Gc是如何被消化吸收进入人体的？食品加工对其危害有什么影响？本项目以猪肉为原料，利用Caco-2单层细胞和Cmah-/-小鼠模型，通过糖组学分析、体外消化吸收和体内代谢动力学研究，并利用HPLC、激光共聚焦显微术、免疫细胞/组织化学法等研究技术，调查分析我国主要猪肉制品中Neu5Gc的含量和存在形式；研究猪肉中Neu5Gc在加工和胃肠道消化过程中的变化和迁移规律；揭示Neu5Gc在小肠吸收、转运的分子机制和体内代谢动力学过程；明确加工，特别是美拉德反应对猪肉中Neu5Gc消化吸收和生物危害的影响；丰富和发展食品营养与安全控制理论，为肉品安全加工和Neu5Gc危害控制提供新思路。

红肉中的N-羟乙酰神经氨酸（Neu5Gc）摄入人体后可整合到细胞表面，引起抗体抗原反应和慢性炎症，可能是与红肉相关的多种疾病的共同发病机理。本项目利用动态体外消化系统、Caco-2细胞单层和Cmah-/-小鼠模型，利用DMB-HPLC、蛋白质印迹等模型和技术，分析了我国主要传统肉制品中Neu5Gc的含量和存在形式；研究了腌制、蒸煮、油炸和高压脉冲电场（PEF）处理等不同加工方式对猪肉中Neu5Gc影响，以及猪肉中Neu5Gc在胃肠道消化过程中的变化和迁移规律；揭示了小肠上皮细胞 Caco-2细胞摄取Neu5Gc及Neu5Gc转运出胞的机制；确证了Neu5Gc的细胞毒性并揭示了其诱导诱导细胞炎症、损伤肠道屏障功能的信号通路。研究结果表明，红肉中均含有Neu5Gc，其含量牛肉>羊肉>猪肉，牛肉中Neu5Gc含量最高，达12.19±0.54 ug/g，加工肉制品中Neu5Gc的含量普遍高于鲜肉，其中火腿中最高，达18.09±3.06 ug/g。禽肉、水产品和谷物、果蔬等植物源食品中未检出Neu5Gc。油炸可提高红肉中Neu5Gc的生物危害性，PEF处理可降低肉中Neu5Gc的含量，显示PEF可用于肉制品加工以降低Neu5Gc的危害性。胃消化能将结合态的Neu6Gc部分转化为游离态，并引起Neu5Gc向Neu5Ac转化。肠道消化对食物中Neu5Gc和Neu5Ac两种唾液酸的总量和存在形式都没有显著影响影响。小肠上皮细胞摄取Neu5Gc为主动转运过程，巨胞饮、网格蛋白和依赖的内吞均是Caco-2细胞摄取Neu5Gc的重要途径，且网格蛋白依赖的内吞途径和陷窝蛋白依赖的内吞途径之间存在代偿关系。在胞内转运（外排）方面，囊泡、内质网、高尔基体、溶酶体均参与了Neu5Gc的跨膜运输，同时可能存在独立于高尔基体之外的外排途径。一定浓度的Neu5Gc可降低Caco-2细胞活力，激活胞内NF-κB通路，对Caco-2细胞单层紧密连接造成破坏，进而破坏Caco-2细胞肠道屏障功能，可能是Neu5Gc导致慢性炎症进而引发结直肠癌的一种机制。本项目研究结果丰富和发展了食品营养与安全控制理论，为肉类的健康加工和科学消费提供了新的思考。