Ishikawa Shin-Ichi, Asano Takayuki, Takenoshita Shingo, Nozawa Yuuya, Arihara Keizo, Itoh Makoto
School of Veterinary Medicine, Kitasato University, Towada, Aomori 034-8628, Japan.
Nutr Res. 2009 Jan;29(1):64-9. doi: 10.1016/j.nutres.2008.12.003.
Dietary proteins can influence colonic carcinogenesis; some proteins have a promotional effect, whereas others exhibit a preventive effect. Dietary egg yolk proteins have been reported to suppress the expression of colon tumors in rats. In this study, we investigated the effect of consumption egg yolk proteins on cell proliferation in a rat model of azoxymethane (AOM)-induced colon cancer. We hypothesize, based on the literature of egg yolk protein actions, that they protect against colon tumor development. Therefore, male F344 rats were fed a purified AIN-93G diet containing either 20% casein (control) or 20% egg yolk proteins for 5 weeks. After 1 week on the experimental diet, the rats were administered weekly subcutaneous injections of saline or AOM for 2 weeks to induce aberrant crypt foci. Rats were administered an intraperitoneal injection of 5-bromo-2'-deoxyuridine 1 hour before being euthanized for examination of DNA synthesis in the colonic mucosa. The contents of the cecum were analyzed for the presence of short-chain fatty acids (SCFAs). In the AOM-injected rats, the yolk protein diet suppressed aberrant crypt foci formation and reduced the proliferative 5-bromo-2'-deoxyuridine-labeling index in the proximal colon when compared with the control diet. A significant increase in cecal SCFAs was observed in the rats that were fed egg yolk proteins. These results indicate that dietary egg yolk proteins have a preventive effect on AOM-induced large bowel carcinogenesis in rats; it exerts this effect by altering cell proliferation through SCFA production. This study suggests that the consumption of egg yolk proteins might be protective against colon carcinogenesis.
膳食蛋白质可影响结肠癌的发生；一些蛋白质具有促进作用，而另一些则表现出预防作用。据报道，膳食中的蛋黄蛋白可抑制大鼠结肠肿瘤的表达。在本研究中，我们调查了食用蛋黄蛋白对氧化偶氮甲烷（AOM）诱导的大鼠结肠癌模型中细胞增殖的影响。基于蛋黄蛋白作用的文献，我们假设它们可预防结肠肿瘤的发展。因此，给雄性F344大鼠喂食含有20%酪蛋白（对照）或20%蛋黄蛋白的纯化AIN-93G饮食，持续5周。在实验饮食1周后，每周给大鼠皮下注射生理盐水或AOM，持续2周，以诱导异常隐窝灶。在对大鼠实施安乐死以检查结肠黏膜中的DNA合成前1小时，给其腹腔注射5-溴-2'-脱氧尿苷。分析盲肠内容物中短链脂肪酸（SCFA）的存在情况。与对照饮食相比，在注射AOM的大鼠中，蛋黄蛋白饮食抑制了异常隐窝灶的形成，并降低了近端结肠中增殖性5-溴-2'-脱氧尿苷标记指数。在喂食蛋黄蛋白的大鼠中，观察到盲肠SCFA显著增加。这些结果表明，膳食中的蛋黄蛋白对AOM诱导的大鼠大肠癌变具有预防作用；它通过SCFA的产生改变细胞增殖来发挥这种作用。本研究表明，食用蛋黄蛋白可能对结肠癌具有保护作用。
