DHA、EPA抑制炎症、拮抗肥胖相关性肠癌作用的比较研究

Colorectal cancer, a common malignant tumor in digestive tract, has high morbidity and mortality. There is a lot of evidence that obesity is an independent risk factor for colorectal cancer, while inflammation is reported to be the bridge between obesity and colorectal cancer. Our previous study demonstrated that the development of obesity-related colon cancer was inhibited in fat-1 transgenic mice with the capacity of endogenously synthesis of n-3 polyunsaturated fatty acids. We proposed the hypothesis that n-3 polyunsaturated fatty acids may function to block the occurance of obesity-related colorectal cancer through inhibiting inflammation and promoting resolution. However, it is unclear which is more potent between DHA and EPA in anti-inflammation,and more suitable for anti-colorectal cancer related to obesity. Inflammation in adipose tissue was recently reported to be associated with the inadequancy in DHA rather than EPA. More importantly, washout of DHA from human body was found to be markedly slower than EPA. We proposed that DHA intervention will be more available for control of obesity-related colon cancer than EPA . The project is aimed to compare the efficiency of DHA and EPA in inhibition of inflammation in colon and reduction of colon cancer to explore the effective measures to control obesity-related colorectal cancer.

结直肠癌是常见的消化道恶性肿瘤，具有发病率高、死亡率高的特点。许多研究显示肥胖是结直肠癌的独立危险因子，而炎症可能是介导肥胖与癌症发生的重要因素。近年来n-3不饱和脂肪酸及其衍生的脂质介质的抗炎、促消退作用受到广泛关注。本课题组前期研究发现可内源性合成n-3不饱和脂肪酸的fat-1转基因小鼠、肥胖相关性肠癌受到明显抑制，为此我们提出“n-3不饱和脂肪酸可能通过抗炎、促消退抑制肥胖相关肠癌”的假说。目前为止，尚不清楚DHA与EPA何者抗炎作用强，更适于防治肥胖相关性肠癌。鉴于新近研究报道肥胖动物的脂肪组织炎症与DHA而非EPA不足有关，而DHA从人体内清除的速率曾被发现明显慢于EPA，我们认为在肥胖相关肠癌防治中DHA比EPA更具应用价值。为验证这些设想，本项目将通过细胞实验、动物实验以及人体试验，对比分析DHA、EPA的抑癌作用，为探索肥胖相关性肠癌的有效预防措施提供科学依据。

本研究着重探讨了 n-3PUFAs对肥胖相关性肠肿瘤的抑制作用及机制。首先以C57BL/6J雄性小鼠为对象，通过喂饲高脂肪饮食构建肥胖模型小鼠，然后以肥胖小鼠为对象，应用AOM/DSS联用的方式诱导结肠肿瘤，比较分析 n-3 PUFAs（DHA和EPA分别干预）对肥胖小鼠结肠肿瘤形成的影响及机制。结果发现DHA、EPA干预明显抑制肥胖小鼠结肠肿瘤的形成，其中EPA的作用更明显。进一步的机制研究显示，抑制炎症信号通路是n-3 PUFAs 抑制肥胖小鼠结肠肿瘤发生的重要机制，如下调结肠组织TNF-α/NF-κB、IL-6/Stat3、NLRP3/IL-1β、Wnt/β-catenin/c-myc通路，降低增殖相关的通路PI3K/Akt、MAPK/Erk的活化和增殖相关蛋白如PCNA、cyclin D1的表达，上调p53抑癌基因表达。n-3 PUFAs抑制肠肿瘤发生作用还与维持肠组织屏障相关蛋白Claudin-1、Occludin、TFF3表达有关。细胞实验结果也发现，n-3PUFAs降低巨噬细胞炎症因子TNF-α、IL-1β、IL-6表达，抑制M1型巨噬细胞标记物TNF-α、IL-1β、IL-6、CCR7 mRNA表达，增强M2型标记物CCL4 mRNA表达，诱导巨噬细胞表型转变；抑制TNF-α处理的结肠HT-29细胞炎症因子 IL-1β、IL-8表达、NF-κB的活化及ERK1/2、p-ERK1/2、JNK、p-JNK、Akt、p-Akt表达，抑制癌细胞增殖；进一步支持n-3 PUFAs抑制肠肿瘤发生作用与抑制炎症有关。短期的人群干预显示n-3 PUFAs（鱼油）干预虽未不影响肠道菌群的alpha多样性和beta多样性，但是明显改变菌群的构成和代谢通路。动物实验也提示，n-3 PUFAs (DHA和EPA)抑制肥胖小鼠肠肿瘤发生作用与调节肠道菌群，如短链脂肪酸生成菌丰度升高有关。值得一提的是，EPA在抑制炎症通路、降低细胞增殖相关通路以及诱导短链脂肪酸生成菌的丰度升高等方面均优于DHA。本研究还发现，DHA和EPA干预明显升高了肥胖动物过氧化物酶体增殖激活受体γ的表达，而后者是肠上皮代谢的关键调控子、n-3 PUFAs又是其配体，为此，有必要从过氧化物酶体增值激活受体γ的角度进一步深入解析 n-3PUFAs抑制肠道炎症以及肠肿瘤形成的作用机制。