Buchmann A, Stinchcombe S, Körner W, Hagenmaier H, Bock K W
Institute of Toxicology, University of Tübingen, Germany.
Carcinogenesis. 1994 Jun;15(6):1143-50. doi: 10.1093/carcin/15.6.1143.
Using an initiation-promotion system, enzyme-altered putative preneoplastic liver foci were induced in female Wistar rats by application of diethylnitrosamine (10 mg/kg/day) for 5 days, followed by bi-weekly treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; corresponding to 100 ng/kg/day) or 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin (HCDD; corresponding to 5 micrograms/kg/day) for up to 17 weeks. Groups of animals were killed at various time intervals after start of promoter treatment. For evaluation of DNA synthesis, 5-bromo-2'-deoxyuridine was administered 24 h prior to killing the animals. Quantitative analysis of the number and volume fraction of adenosine-triphosphatase-deficient liver foci revealed that the promoting activity of both dioxins was roughly comparable under the experimental conditions employed. Nuclear labelling indices (LIs) of normal hepatocytes were not altered by TCDD or HCDD treatment, while a slight increase in LIs of non-parenchymal liver cells was observed. Using an immunohistochemical double-staining technique, hepatocytes within glutathione-transferase P-positive liver foci were found to show an approximately 5-to 10-fold higher LI than normal hepatocytes throughout all periods of investigation. During the time course of the experiment, LIs of foci from all treatment groups decreased with time. However, in TCDD-treated rats, and less pronounced in HCDD-treated rats, the initially high rate of proliferation persisted for a greater length of time than in non-dioxin-treated control animals. Assignment of liver foci into four transection size classes revealed that LIs in larger size classes varied considerably, indicating heterogeneity in the growth behaviour of individual liver lesions. Overall, both dioxins had no effects on the proliferation of normal hepatocytes, while LIs of enzyme-altered liver lesions were slightly enhanced by treatment with TCDD or HCDD. Whether the selective, albeit moderate increase in the proliferation of enzyme-altered liver cells is sufficient to explain the promoting activity of dioxins, or if additional factors (e.g. decrease in death rates of foci cells) are equally important, remains to be determined in further experiments.
采用启动-促癌系统，通过给雌性Wistar大鼠连续5天腹腔注射二乙基亚硝胺（10 mg/kg/天）诱导酶改变的假定癌前肝病灶，随后每两周用2,3,7,8-四氯二苯并-对-二噁英（TCDD；相当于100 ng/kg/天）或1,2,3,4,6,7,8-七氯二苯并-对-二噁英（HCDD；相当于5 μg/kg/天）处理长达17周。在启动子处理开始后的不同时间间隔处死动物组。为评估DNA合成，在处死动物前24小时给予5-溴-2'-脱氧尿苷。对三磷酸腺苷酶缺陷型肝病灶数量和体积分数的定量分析表明，在所采用的实验条件下，两种二噁英的促癌活性大致相当。TCDD或HCDD处理未改变正常肝细胞的核标记指数（LIs），而观察到非实质肝细胞的LIs略有增加。使用免疫组织化学双重染色技术，发现在整个研究期间，谷胱甘肽转移酶P阳性肝病灶内的肝细胞显示出比正常肝细胞高约5至10倍的LI。在实验过程中，所有处理组病灶的LIs均随时间下降。然而，在TCDD处理的大鼠中，以及在HCDD处理的大鼠中不太明显，最初较高的增殖率比未用二噁英处理的对照动物持续更长时间。将肝病灶分为四个横切尺寸类别显示，较大尺寸类别的LIs差异很大，表明单个肝损伤的生长行为存在异质性。总体而言，两种二噁英对正常肝细胞的增殖均无影响，而用TCDD或HCDD处理可使酶改变的肝损伤的LIs略有增强。酶改变的肝细胞增殖的选择性（尽管适度）增加是否足以解释二噁英的促癌活性，或者是否有其他因素（如病灶细胞死亡率降低）同样重要，仍有待进一步实验确定。
