Tanaka T, Kojima T, Suzui M, Mori H
First Department of Patology, Gifu University School of Medicine, Japan.
Cancer Res. 1993 Sep 1;53(17):3908-13.
Our previous study has shown that dietary administration of protocatechuic acid (PCA) acts as potential chemopreventive agent in inhibiting diethylnitrosamine-induced liver carcinogenesis in male F344 rats. The present study was designed to determine the modifying effect of PCA on azoxymethane (AOM)-induced colon carcinogenesis in male F344 rats and the effect on intermediate biomarkers, i.e., colonic mucosal ornithine decarboxylase activity and colonic epithelial proliferation, which can be used as effective predictors of colon cancer. Staring at 6 weeks of age, groups of animals were fed the basal diet and experimental diet containing PCA at dose levels of 250, 500, and 1000 ppm. At 7 weeks of age, all animals except the PCA alone group (1000 ppm) and untreated controls were given s.c. injections of AOM at a dose level of 15 mg/kg body weight/week for 3 weeks. PCA at 3 doses was fed during the initiation phase (before 1 week, during, and after 1 week of AOM exposure) or postinitiation phase (for 28 weeks starting 1 week after the last injection of AOM). All animals were then killed at 32 weeks after the start and colonic tumor incidence and multiplicity were determined. Animals intended for cell proliferation study were given injections of bromodeoxyuridine/5-fluoro-2'-deoxyuridine (1 ml/100 g body weight) 1 h prior to be killing. The rate of colonic cell proliferation in the distal portion was assessed by immunohistochemistry using antibromodeoxyuridine and by counting silver-stained nucleolar organizer regions protein. The colonic mucosal ornithine decarboxylase activity was also measured at the termination. The results indicate that dietary PCA administration at 500 and 1000 ppm during the initiation or postinitiation phase significantly inhibited intestinal carcinogenesis induced by AOM as revealed by the reduction of tumor incidence and multiplicity. The data also demonstrate that PCA at 500 ppm and 1000 ppm significantly inhibited bromodeoxyuridine labeling index and also silver-stained nucleolar organizer regions protein number at three doses when animals were fed PCA at the initiation or postinitiation stage. Also, feeding of PCA at 1000 ppm during the initiation and postinitiation phase exerted a pronounced inhibitory effect on the colonic ornithine decarboxylase levels. PCA feeding did not cause any toxicity. These results demonstrate that PCA is a possible new chemopreventive agent for colon carcinogenesis through the suppression of manifestation of intermediate biomarkers induced by AOM, although the precise mechanisms of PCA-induced inhibition during the initiation and postinitiation phases remain to be elucidated.
我们之前的研究表明，膳食给予原儿茶酸（PCA）可作为潜在的化学预防剂，抑制雄性F344大鼠中由二乙基亚硝胺诱导的肝癌发生。本研究旨在确定PCA对雄性F344大鼠中由偶氮甲烷（AOM）诱导的结肠癌发生的调节作用，以及对中间生物标志物的影响，即结肠黏膜鸟氨酸脱羧酶活性和结肠上皮细胞增殖，这些可作为结肠癌的有效预测指标。从6周龄开始，将动物分组，分别喂食基础饮食和含有剂量水平为250、500和1000 ppm PCA的实验饮食。在7周龄时，除单独给予PCA组（1000 ppm）和未处理的对照组外，所有动物均皮下注射AOM，剂量为15 mg/kg体重/周，共注射3周。在启动阶段（AOM暴露前1周、暴露期间和暴露后1周）或启动后阶段（在最后一次注射AOM后1周开始，持续28周）喂食3种剂量的PCA。然后在开始后的32周处死所有动物，测定结肠肿瘤发生率和多发性。用于细胞增殖研究的动物在处死前1小时注射溴脱氧尿苷/5-氟-2'-脱氧尿苷（1 ml/100 g体重）。通过使用抗溴脱氧尿苷的免疫组织化学方法并计数银染核仁组织区蛋白，评估远端结肠细胞增殖率。在实验结束时还测量了结肠黏膜鸟氨酸脱羧酶活性。结果表明，在启动阶段或启动后阶段给予500和1000 ppm的膳食PCA，可通过降低肿瘤发生率和多发性，显著抑制AOM诱导的肠道癌变。数据还表明，当动物在启动阶段或启动后阶段喂食PCA时，500 ppm和1000 ppm的PCA在3种剂量下均显著抑制溴脱氧尿苷标记指数以及银染核仁组织区蛋白数量。此外，在启动阶段和启动后阶段喂食1000 ppm的PCA对结肠鸟氨酸脱羧酶水平有明显的抑制作用。喂食PCA未引起任何毒性。这些结果表明，PCA可能是一种新的结肠癌化学预防剂，通过抑制AOM诱导的中间生物标志物的表现发挥作用，尽管PCA在启动阶段和启动后阶段诱导抑制的确切机制仍有待阐明。
