ω-3多不饱和脂肪酸抗肿瘤新途径——抑制具核梭杆菌黏附宿主细胞

New anti-tumor mechanism of ω-3 polyunsaturated fatty acids ― inhibiting Fusobacterium nucleatum adherence to host cells

摘要:

【背景】大量文献报道ω-3多不饱和脂肪酸尤其是二十二碳六烯酸(Docosahexaenoic Acid，DHA)与二十碳五烯酸(Eicosapentaenoic Acid，EPA)具有抗肿瘤作用，但是其抗肿瘤机制还不够完善。【目的】探究ω-3多不饱和脂肪酸、具核梭杆菌以及结直肠癌三者之间的关联。【方法】在检测二十二碳六烯酸、二十碳五烯酸、α-亚麻酸(α-Linolenic Acid，ALA)等ω-3多不饱和脂肪酸对人结直肠腺癌细胞Caco-2、正常结肠上皮细胞NCM460生长影响的基础上，检测DHA等3种多不饱和脂肪酸对具核梭杆菌黏附人体细胞以及Fap2、FadA、RadD等具核梭杆菌毒力关键基因表达的影响。【结果】 30 μg/mL的DHA、EPA、ALA对Caco-2生长抑制分别为9.09%、4.95%、7.52%，而对NCM460生长抑制达31.15%、25.48%、29.11%，而且相关抑制作用仅具有浓度依赖性而无时间依赖性。经30 μg/mL的DHA、EPA、ALA预处理的具核梭杆菌黏附Caco-2细胞的能力分别下降81.04% (P=0)、93.63% (P=0)和68.63% (P=0)；而共培养时加入DHA、EPA、ALA对具核梭杆菌黏附Caco-2细胞的能力没有显著影响。同时，30 μg/mL DHA处理导致F. nucleatum的Fap2基因显著下降10.22% (P=0.027)；30 μg/mL EPA处理导致FadA、Fap2基因分别显著下降23.49% (P=0)、15.09% (P=0.003)；30 μg/mL ALA处理导致FadA基因显著下降26.75% (P=0.012)。【结论】综合上述实验结果以及DHA、EPA、ALA仅能短时间抑制具核梭杆菌生长等文献报道，我们认为，DHA、EPA等ω-3多不饱和脂肪酸并非简单地直接杀伤或抑制肿瘤细胞和F. nucleatum；抑制FadA、Fap2等黏附相关基因表达，降低F. nucleatum黏附宿主细胞能力是其抗肿瘤作用的关键组成部分。ω-3多不饱和脂肪酸等活性物质对F. nucleatum等在结直肠肿瘤发生、发展中发挥重要作用的肠道细菌的影响与机制应深入开展研究。

Abstract:

[Background] The antitumor mechanism of ω-3 polyunsaturated fatty acids represented by DHA and EPA has not been fully investigated. [Objective] To explore the relationship among ω-3 polyunsaturated fatty acids, Fusobacterium nucleatum and colorectal cancer. [Methods] After the suppressive effect of ω-3 polyunsaturated fatty acids (DHA, EPA, ALA) on human colon cancer cell line, Caco-2, and normal colon epithelium cell line, NCM460, was assayed, we investigated the impact of these ω-3 polyunsaturated fatty acids on F. nucleatum, including growth, adhesive ability to Caco-2 cells, and the expression of virulence genes such as Fap2, FadA and RadD. [Results] After treated with 30 μg/ml DHA, EPA or ALA respectively, the growth of Caco-2 cells were suppressed 9.09%, 4.95% and 7.52% correspondingly, meanwhile the growth of NCM460 cells were suppressed 31.15%, 25.48%, 29.11%, and only dose-dependent effect was identified. After treated with 30 μg/ml DHA, EPA and ALA for 12 hours, the adhesive ability of F. nucleatum to Caco-2 cells was inhibited by 81.04% (P=0), 93.63% (P=0) and 68.63% (P=0) respectively, which was consistent with the transcriptive level assay results of FadA, Fap2 in F. nucleatum. The expression of Fap2 was considerably suppressed by 10.22% (P=0.027) after 30 μg/mL DHA treatment; FadA, Fap2 were markedly suppressed by 23.49% (P=0) and 15.09% (P=0.003) by 30 μg/mL EPA; and for 30 μg/mL ALA treatment, FadA was significantly suppressed by 26.75% (P=0.012). [Conclusion] Based on our above results and previous reports that DHA, EPA and ALA only inhibited the growth of F. nucleatum temporally, we proposed that ω-3 polyunsaturated fatty acids i-e EPA and DHA significantly attenuated the adhesive ability of F. nucleatum to host cells via suppressing the expression of adhesion-related genes such as FadA, Fap2, which made major contribution to their antitumor activity, rather than inhibiting the growth of tumor cells and F. nucleatum directly. The effects and mechanisms of ω-3 polyunsaturated fatty acids i-e DHA and EPA on gut bacterium i-e F. nucleatum that play important roles in the initiation and progression of colorectal tumors deserve further research.