Hudson E A, Dinh P A, Kokubun T, Simmonds M S, Gescher A
Medical Research Council Toxicology Unit, University of Leicester, United Kingdom.
Cancer Epidemiol Biomarkers Prev. 2000 Nov;9(11):1163-70.
Rice is a staple diet in Asia, where the incidence of breast and colon cancer is markedly below that in the Western world. We investigated potential colon and breast tumor-suppressive properties of rice, testing the hypothesis that rice contains phenols that interfere with the proliferation or colony-forming ability of breast or colon cells. Brown rice, its white milled counterpart, and bran from brown rice were boiled and extracted with ethyl acetate. The extracts were analyzed by high pressure liquid chromatography-mass spectrometry. Eight phenols, protocatechuic acid, p-coumaric acid, caffeic acid, ferulic acid, sinapic acid, vanillic acid, methoxycinnamic acid, and tricin, were identified in the extracts of bran and intact brown rice. These extracts were separated into nine fractions by column chromatography. The effect of bran extract and its fractions at 100 microg/ml on cell viability and colony-forming ability of human-derived breast and colon cell lines was assessed. Bran extract decreased numbers of viable MDA MB 468 and HBL 100 breast cells and colon-derived SW 480 and human colonic epithelial cells as judged by the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4 -sulfophenyl)-2H-tetrazolium assay. It also reduced colony formation of SW 480 colon and MDA MB 468 breast cells. Of the eight phenols identified in the brown rice bran, when applied at 50 microM, caffeic acid decreased numbers of all cell types except HBL 100. Tricin, ferulic acid, and methoxycinnamic acid interfered with cell viability in one or more cell lines. Tricin (50 microM) and the other phenols (200 microM) inhibited colony formation of SW 480 cells. Clonogenicity of MDA MB 468 cells was inhibited by caffeic acid, ferulic acid, and tricin (50 microM). Tricin was the most potent anticlonogenic of the compounds with IC50s of 16 microM in the SW 480 colon cells and 0.6 microM in the MDA MB 468 breast cells. The results suggest that: (a) brown rice and bran contain compounds with putative cancer chemopreventive properties; (b) certain phenols contained in brown rice bran, e.g., tricin, may be associated with this activity; and (c) these phenols are present at much lower levels in white than in brown rice. Thus, the consumption of rice bran or brown rice instead of milled white rice may be advantageous with respect to cancer prevention.
大米是亚洲的主食，在亚洲，乳腺癌和结肠癌的发病率明显低于西方世界。我们研究了大米潜在的抑制结肠癌和乳腺癌的特性，检验大米中含有的酚类物质会干扰乳腺或结肠细胞增殖或集落形成能力的假说。将糙米、其精白米及米糠进行煮沸，并用乙酸乙酯萃取。萃取物通过高压液相色谱 - 质谱联用仪进行分析。在米糠和完整糙米的萃取物中鉴定出8种酚类物质，即原儿茶酸、对香豆酸、咖啡酸、阿魏酸、芥子酸、香草酸、甲氧基肉桂酸和小麦黄素。这些萃取物通过柱色谱法分离成9个组分。评估了米糠萃取物及其组分在100微克/毫升浓度下对人源乳腺和结肠细胞系的细胞活力和集落形成能力的影响。通过3 -（4,5 - 二甲基噻唑 - 2 - 基）-5 -（3 - 羧基甲氧基苯基）-2 -（4 - 磺基苯基）-2H - 四氮唑检测法判断，米糠萃取物可减少存活的MDA MB 468和HBL 100乳腺细胞以及结肠来源的SW 480和人结肠上皮细胞的数量。它还减少了SW 480结肠细胞和MDA MB 468乳腺细胞的集落形成。在糙米糠中鉴定出的8种酚类物质中，当以50微摩尔的浓度应用时, 咖啡酸可减少除HBL 100外所有细胞类型细胞的数量。小麦黄素、阿魏酸和甲氧基肉桂酸在一种或多种细胞系中干扰细胞活力。小麦黄素（50微摩尔）和其他酚类物质（200微摩尔）抑制SW 480细胞的集落形成。咖啡酸、阿魏酸和小麦黄素（50微摩尔）抑制MDA MB 468细胞的克隆形成能力。小麦黄素是这些化合物中最有效的抗克隆形成剂，在SW 480结肠细胞中的IC50为16微摩尔，在MDA MB 468乳腺细胞中的IC50为0.6微摩尔。结果表明：（a）糙米和米糠含有具有潜在癌症化学预防特性的化合物；（b）糙米糠中含有的某些酚类物质，如小麦黄素，可能与这种活性有关；（c）这些酚类物质在精白米中的含量远低于糙米。因此，食用米糠或糙米而非精白米可能对癌症预防有益。
