Williams G M, Gebhardt R, Sirma H, Stenbäck F
American Health Foundation, Valhalla, NY 10595.
Carcinogenesis. 1993 Oct;14(10):2149-56. doi: 10.1093/carcin/14.10.2149.
Neoplastic conversion induced in rat liver by diethylnitrosamine (DEN) was quantified by measuring preneoplastic and neoplastic lesions over a 34 week period in the beginning of which the carcinogen was given at three dose levels and two dose rates for the first 10 weeks, after which animals were maintained for 24 weeks with either no further exposure or were fed phenobarbital (PB) to promote neoplastic development of cells converted by DEN. DEN was injected s.c. in male F344 rats at weekly or biweekly intervals for total doses of 1, 2 or 4 mmol/kg body wt and then the rats were maintained on basal diet alone or diet containing 0.05% PB. At the end of exposure, DEN had produced a dose-related decrease in centrilobular glutamine synthetase-expressing (GS+) hepatocytes which is indicative of mild cytotoxicity. All doses induced foci that were gamma-glutamyltranspeptidase-positive and iron storage-deficient. The multiplicity of foci in the middle dose exceeded that in the low dose by about a factor of two and, in the high dose, was > 10-fold greater. A few GS+ foci were found in the high dose group only. At 34 weeks, neoplasms were present in the middle and high dose groups. Administration of PB after DEN increased the multiplicity of foci in all dose groups, most substantially in the low dose group. The effect of PB on liver neoplasm yield was marginal in the low non-carcinogenic dose, whereas it enhanced the multiplicity in the weakly carcinogenic middle dose by approximately 10-fold. Four principal findings were made: (i) even at the low doses used, a mild cytotoxic response not evidenced by morphological changes in conventional histopathology was manifested in the GS+ centrilobular subpopulation of hepatocytes; (ii) the dose response over a 4-fold dose range of DEN alone and when followed by PB was non-linear; (iii) the precursor role of foci in the evolution of liver neoplasms was evident and was most conspicuous in the case of GS+ foci; and (iv) a high level of foci induction was required for the evolution of neoplasms, even with PB promotion. The finding of non-linearity with increasing doses of DEN raises questions about the assumption that effects of carcinogens at high doses can be quantitatively extrapolated to low doses.
通过在34周内测量癌前和肿瘤病变，对二乙基亚硝胺（DEN）诱导的大鼠肝脏肿瘤转化进行了定量分析。在实验开始的前10周，以三种剂量水平和两种给药速率给予致癌物，之后，对动物进行24周的观察，期间要么不再接触致癌物，要么喂食苯巴比妥（PB）以促进由DEN转化的细胞的肿瘤发展。雄性F344大鼠每周或每两周皮下注射一次DEN，总剂量为1、2或4 mmol/kg体重，然后大鼠单独维持基础饮食或喂食含0.05% PB的饮食。在暴露结束时，DEN导致表达谷氨酰胺合成酶（GS+）的小叶中央肝细胞数量呈剂量相关减少，这表明存在轻度细胞毒性。所有剂量均诱导出γ-谷氨酰转肽酶阳性且铁储存缺乏的病灶。中剂量组病灶的数量比低剂量组大约多两倍，高剂量组则比低剂量组多>10倍。仅在高剂量组发现了一些GS+病灶。在34周时，中剂量组和高剂量组出现了肿瘤。DEN给药后给予PB增加了所有剂量组病灶的数量，在低剂量组增加最为显著。PB对低非致癌剂量肝脏肿瘤发生率的影响很小，而在弱致癌的中剂量组，它使病灶数量增加了约10倍。得出了四个主要发现：（i）即使使用低剂量，在常规组织病理学中未表现出形态学变化的情况下，GS+小叶中央肝细胞亚群中也出现了轻度细胞毒性反应；（ii）单独使用DEN以及随后使用PB时，在4倍剂量范围内的剂量反应是非线性的；（iii）病灶在肝脏肿瘤演变中的前体作用很明显，在GS+病灶的情况下最为显著；（iv）即使有PB促进作用，肿瘤的演变也需要高水平的病灶诱导。随着DEN剂量增加而出现非线性的发现，对高剂量致癌物的影响可定量外推至低剂量这一假设提出了质疑。
