Snyderwine E G, Davis C D, Schut H A, Roberts-Thomson S J
Chemical Carcinogenesis Section, Laboratory of Experimental Carcinogenesis, Division of Basic Sciences, National Cancer Institute, NIH, Bethesda, MD 20892-4255, USA.
Carcinogenesis. 1998 Jul;19(7):1209-15. doi: 10.1093/carcin/19.7.1209.
2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a heterocyclic amine derived from cooked meat that is a mammary gland carcinogen in rats. A carcinogenic dose-regimen of PhIP (75 mg/kg, p.o., 10 doses, once per day) was administered to 43-day old female Sprague-Dawley rats, and the rats were then placed on a defined high fat (23.5% corn oil) or low fat (5% corn oil) diet for up to 6 weeks. At various times after carcinogen and diet, and prior to carcinogenesis, we examined the percentage of proliferating cells in terminal end bud (TEB) epithelial structures of the rat mammary gland by proliferating cell nuclear antigen staining, mammary gland architecture by whole mounting, and PhIP-DNA adduct levels in mammary epithelial cells by the 32P-post-labeling assay. Immediately after dosing, the percentage of proliferating epithelial cells in TEBs was significantly higher in PhIP-treated rats than in control rats receiving vehicle only [7.5 +/- 0.9% (n = 99) versus 4.2 +/- 0.6% (n = 127), respectively]. The mammary glands of PhIP-treated rats showed a significantly lower density of alveolar buds (ABs) and a higher density of TEBs than control rats, which suggests that PhIP exposure partially inhibited the normal glandular differentiation of TEBs to ABs. After 6 weeks on the diet, proliferation in TEBs was statistically higher in rats given PhIP plus a high fat diet than in rats given vehicle plus a low fat diet. The mammary glands from rats on a high fat diet also showed a statistically higher density of TEBs when compared with rats on a low fat diet [2.08 +/- 0.34% versus 1.04 +/- 0.20%, respectively (n = 6)]. PhIP-DNA adduct levels were relatively high in mammary epithelial cells of treated rats. At 3 h after the last dose of PhIP, DNA adduct levels [relative adduct labeling (RAL) x 10(7), mean +/- SE] were 10.5 +/- 1.7 (n = 8) and 0.9 +/- 0.2 (n = 7) in epithelial cells isolated from mammary gland and in the liver, respectively. DNA adduct removal rates from the mammary gland were not different between rats on the high fat and low fat diets. Adducts were still detected after 6 weeks on either diet. Thus, events that occurred prior to neoplasia in the mammary glands of PhIP-treated rats include formation of PhIP-DNA adducts at relatively high levels, and enhanced proliferation in TEBs (putative sites of origin of mammary gland carcinomas) and partial inhibition of TEB differentiation. The high fat diet, a promoter of PhIP-induced mammary gland carcinogenesis, appeared to sustain the proliferative effect of PhIP in mammary gland TEBs at a time when PhIP-DNA adducts are still detectable. These early events may contribute to the targeting and carcinogenicity of PhIP to the mammary gland of rats.
2-氨基-1-甲基-6-苯基咪唑并[4,5-b]吡啶（PhIP）是一种源自熟肉的杂环胺，它是大鼠乳腺致癌物。给43日龄的雌性斯普拉格-道利大鼠给予致癌剂量方案的PhIP（75毫克/千克，口服，10剂，每天一次），然后将大鼠置于规定的高脂肪（23.5%玉米油）或低脂肪（5%玉米油）饮食中长达6周。在给予致癌物和饮食后的不同时间以及致癌作用发生之前，我们通过增殖细胞核抗原染色检查大鼠乳腺终末芽（TEB）上皮结构中增殖细胞的百分比，通过整体装片检查乳腺结构，并通过32P后标记法检测乳腺上皮细胞中的PhIP-DNA加合物水平。给药后立即发现，接受PhIP处理的大鼠TEB中增殖上皮细胞的百分比显著高于仅接受赋形剂的对照大鼠[分别为7.5±0.9%（n = 99）和4.2±0.6%（n = 127）]。接受PhIP处理的大鼠的乳腺显示，与对照大鼠相比，肺泡芽（AB）的密度显著降低，TEB的密度更高，这表明接触PhIP部分抑制了TEB向AB的正常腺泡分化。饮食6周后，给予PhIP加高脂肪饮食的大鼠TEB中的增殖在统计学上高于给予赋形剂加低脂肪饮食的大鼠。与低脂肪饮食的大鼠相比，高脂肪饮食的大鼠的乳腺中TEB的密度在统计学上也更高[分别为2.08±0.34%和1.04±0.20%（n = 6）]。处理大鼠的乳腺上皮细胞中PhIP-DNA加合物水平相对较高。在最后一剂PhIP后3小时，从乳腺分离的上皮细胞和肝脏中的DNA加合物水平[相对加合物标记（RAL）×10(7)，平均值±标准误]分别为10.5±1.7（n = 8）和0.9±0.2（n = 7）。高脂肪和低脂肪饮食的大鼠乳腺中DNA加合物的清除率没有差异。两种饮食6周后仍能检测到加合物。因此，在接受PhIP处理的大鼠乳腺肿瘤形成之前发生的事件包括形成相对高水平的PhIP-DNA加合物，TEB（乳腺腺癌的假定起源部位）中增殖增强以及TEB分化部分受到抑制。高脂肪饮食是PhIP诱导的乳腺致癌作用的促进剂，在PhIP-DNA加合物仍可检测到的时候，它似乎维持了PhIP在乳腺TEB中的增殖作用。这些早期事件可能有助于PhIP对大鼠乳腺的靶向性和致癌性。
