Duthie S J, Narayanan S, Brand G M, Grant G
Rowett Research Institute, Aberdeen, UK.
Eur J Nutr. 2000 Jun;39(3):106-11. doi: 10.1007/s003940070026.
Epidemiological studies report an inverse relationship between intake of the B vitamin folic acid and colon cancer. Folate is important for DNA synthesis and repair. Moreover, the production of S-adenosylmethionine (SAM), essential for normal DNA methylation and gene expression, is dependent on folic acid. Folate deficiency may increase the risk of malignant transformation by perturbing these pathways.
The principal aim of this study was to determine the effects of folate deficiency on DNA stability and DNA methylation in rat colonocytes in vivo. As the metabolic pathways of folate and other dietary methyl donors are closely linked, the effects of methionine and choline deficiency were also evaluated.
Male Hooded-Lister rats were fed a diet deficient in folic acid, or in methionine and choline, or in folate, methionine and choline for 10 weeks. DNA strand breakage and misincorporated uracil were determined in isolated colonocytes using alkaline single cell gel electrophoresis. Global DNA methylation was measured in colonic scrapings. Folate was measured in plasma, erythrocyte and liver samples.
Methyl donor deficiency induced DNA strand breakage in colonocytes isolated from all experimental groups. Uracil levels in colonocyte DNA remained unchanged compared with controls. DNA methylation was unaffected either by folate and/or methionine and choline depletion. Rats fed a folate-deficient diet had less folate in plasma, red blood cells and liver than controls.
Folate and methyl deficiency in vivo primarily affects DNA stability in isolated colonocytes of rats, without affecting overall DNA methylation.
流行病学研究报告称，B族维生素叶酸的摄入量与结肠癌之间存在负相关关系。叶酸对DNA的合成和修复至关重要。此外，正常DNA甲基化和基因表达所必需的S-腺苷甲硫氨酸（SAM）的产生依赖于叶酸。叶酸缺乏可能通过干扰这些途径增加恶性转化的风险。
本研究的主要目的是确定叶酸缺乏对大鼠体内结肠细胞DNA稳定性和DNA甲基化的影响。由于叶酸和其他膳食甲基供体的代谢途径密切相关，因此也评估了蛋氨酸和胆碱缺乏的影响。
将雄性Hooded-Lister大鼠喂食缺乏叶酸、或蛋氨酸和胆碱、或叶酸、蛋氨酸和胆碱的饮食10周。使用碱性单细胞凝胶电泳测定分离的结肠细胞中的DNA链断裂和错误掺入的尿嘧啶。测量结肠刮片中的整体DNA甲基化。测量血浆、红细胞和肝脏样本中的叶酸。
甲基供体缺乏在所有实验组分离的结肠细胞中诱导DNA链断裂。与对照组相比，结肠细胞DNA中的尿嘧啶水平保持不变。叶酸和/或蛋氨酸及胆碱缺乏对DNA甲基化没有影响。喂食叶酸缺乏饮食的大鼠血浆、红细胞和肝脏中的叶酸含量低于对照组。
体内叶酸和甲基缺乏主要影响大鼠分离结肠细胞中的DNA稳定性，而不影响整体DNA甲基化。
