CARCINOGENIC AND TOXICOLOGIC EFFECTS OF PHIP ON THE RODENT MAMMARY GLAND

2-氨基-1-甲基-6-苯基咪唑[4,5-b]吡啶（PhIP）是一种芳胺类物质，在熟肉中发现，是雌性大鼠的乳腺致癌物。在本项目中，我们采用大鼠模型来研究PhIP靶向乳腺的致癌机制和因素。在最近的一项研究中，将四剂量的PhIP （150 mg/kg, p.o，每天一次）给予哺乳期的Sprague-Dawley大鼠，使其与10天大的幼鼠分离，以启动腺体复旧。末次给药24 h后，TUNEL法测定对照组大鼠乳腺细胞凋亡指数显著高于phip组（4.757 %  1.066 vs 1.905 %  0.248, p<0.05）。与对照组相比，phip处理的大鼠乳腺的肺泡也明显变大，含有更多的分泌性上皮细胞。Western blotting检测细胞凋亡刺激因子Bax和细胞凋亡抑制因子Bcl-2的表达。因此，对照组大鼠Bax表达量高2.7倍，而phip处理大鼠Bcl-2表达量高3.1倍，两者变化具有统计学差异（学生t检验，p<0.05）。免疫组化进一步证实，phip处理的乳腺分泌性肺泡上皮细胞中Bax的表达较低，Bcl-2的表达较高。这些发现与暴露于PhIP通过部分抑制程序性细胞死亡来延缓衰老的观点是一致的。为了探讨PhIP对乳腺退化抑制作用的可能机制，我们在发情的早晨给药PhIP (150 mg/kg, p.o)，测量了具有规律发情周期的未交配大鼠的血清泌乳素水平。一个发情周期后，在发情的早晨，PhIP后血清催乳素水平比对照组高1.3倍（单因素方差分析，Fisher LSD多重比较检验，p<0.05）。在复发期间暴露于PhIP与乳腺良性肿瘤的诱导有关。12只大鼠中有7只发生了纤维腺瘤，1只在复发期间给予PhIP （150 mg/kg，每天一次，连续5天）和高脂肪饮食（23.5%玉米油）后一年内发生了管状乳头状癌。血清催乳素水平的升高和PhIP对乳腺细胞凋亡的影响可能与该化合物的乳腺癌变机制有关。-乳腺，乳腺癌，饮食，细胞凋亡，杂环胺，大鼠，退化，

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is an arylamine found cooked meat which is an established mammary gland carcinogen in female rats. In this project, we use the rat model to investigate the mechanisms and factors involved in the carcinogenic targeting of PhIP to the mammary gland. In a recent study, four doses of PhIP (150 mg/kg, p.o., once per day) were given to lactating Sprague-Dawley rats separated from their 10-day old pups to initiate involution of the gland. Twenty-four hours after the last dose, apoptotic index in the mammary gland, as measured by the TUNEL assay, was significantly higher in the gland from control rats than in the PhIP-treated rats (4.757 %  1.066 vs 1.905 %  0.248, p<0.05). In comparison to controls, alveoli in the mammary gland of PhIP-treated rats were also visibly larger and contained more secretory epithelial cells. The expression of Bax, a stimulator of apoptosis, and Bcl-2, an inhibitor of apoptosis, were quantitated by Western blotting. Accordingly, Bax expression was 2.7 - fold higher in control rats while Bcl-2 expression was 3.1-fold higher in PhIP-treated rats, both changes being statistically different (Students t-test, p<0.05). Immunohistochemistry further confirmed a lower expression of Bax and higher expression of Bcl-2 in secretory alveolar epithelial cells of the PhIP-treated mammary gland. The findings are consistent with the notion that exposure to PhIP retarded involution via partial inhibition of programmed cell death. To investigate possible mechanisms for the inhibitory effects of PhIP on mammary gland involution, serum levels of prolactin were measured in virgin rats with regular estrous cycles given PhIP (150 mg/kg, p.o.) on the morning of diestrous. After one estrous cycle, on the morning of proestrous, serum prolactin levels were 1.3-fold higher after PhIP than after control vehicle (one way ANOVA, Fisher LSD multiple comparison test, p<0.05). PhIP exposure during involution was associated with the induction of benign mammary tumors. Seven out of 12 rats developed fibroadenomas, and one developed a tubulopapillary carcinoma within one year after receiving PhIP administration during involution (150 mg/kg, p.o.once per day for five days) and a high fat diet (23.5% corn oil). An increase in serum prolactin level and the effects on mammary gland apoptosis seen with PhIP may have implications for the mechanisms of mammary gland carcinogenesis of this compound. - Mammary gland, Breast cancer, Diet, Apoptosis, Heterocyclic amines, Rat, Involution,