Lee G H, Ooasa T, Osanai M
Department of Pathology, Asahikawa Medical College, Nishikagura, Japan.
Cancer Res. 1998 Apr 15;58(8):1665-9.
Phenobarbital (PB), a classical rodent hepatopromoter, remarkably enhances hepatocarcinogenesis initiated by diethylnitrosamine (DEN) in adult B6C3F1 mice. However, it is also known to strongly inhibit liver tumor development in the B6C3F1 mice initiated with DEN in their infancy. The present study aimed to elucidate the unknown biological mechanisms for this paradoxical, inhibitory effect of PB on B6C3F1 mouse hepatocarcinogenesis. Male 12-day-old infant B6C3F1 mice were injected i.p. with DEN and, at 6 weeks of age, divided into PB-treated (PB+ group) and untreated (PB- group) animals. At 24 weeks, PB treatment was ceased for half of the PB+ animals (PB+/- group) and started for half of the PB- animals (PB-/+ group). Finally, all mice were sacrificed at 36 weeks and examined for the development of liver tumors. The mean multiplicity of gross tumors in the PB+ group was only one-fifteenth of that for the PB- group. PB-/+ animals developed fewer than half of the tumors found in PB- mice, indicating that the PB effect depends solely on the treatment duration, rather than the animal age. The effect was proven to be reversible, because the mean tumor multiplicity for the PB+/- group was seven times larger than that for the PB+ group. Stereological analysis revealed the mean volume of hepatocellular proliferative lesions in the PB- animals to be 7.7- and 4.1-fold the values for the PB+ and PB-/+ groups, respectively. The mean proliferating cell nuclear antigen-labeling indices for hepatocellular adenomas in PB+ and PB-/+ animals were also one-third of that for tumors in PB- animals, whereas no significant differences were observed with regard to the mean apoptotic index. In conclusion, the inhibitory effect of PB seemed to be primarily caused by the suppression of tumor cell proliferation. Irrespective of the group, most lesions observed were basophilic hepatocellular adenomas or foci, positive for Bcl-2 oncoprotein. They were thus distinct from the eosinophilic Bcl-2- lesions that predominate with PB promotion after the initiation of adult B6C3F1 mice. This age-dependent nature of initiation, together with the differential responses of Bcl-2+ and Bcl-2- lesions, may be responsible for the apparently contradictory outcomes of PB treatment in infant and adult B6C3F1 mice.
苯巴比妥（PB）是一种经典的啮齿动物肝脏促癌剂，能显著增强成年B6C3F1小鼠由二乙基亚硝胺（DEN）引发的肝癌发生。然而，已知它也能强烈抑制幼年时用DEN引发的B6C3F1小鼠的肝脏肿瘤发展。本研究旨在阐明PB对B6C3F1小鼠肝癌发生这种矛盾的抑制作用的未知生物学机制。12日龄的雄性幼年B6C3F1小鼠腹腔注射DEN，6周龄时分为PB处理组（PB +组）和未处理组（PB -组）。24周时，对一半的PB +动物停止PB处理（PB + / -组），对一半的PB -动物开始PB处理（PB - / +组）。最后，所有小鼠在36周时处死，检查肝脏肿瘤的发生情况。PB +组肉眼可见肿瘤的平均多发性仅为PB -组的十五分之一。PB - / +动物发生的肿瘤不到PB -小鼠的一半，这表明PB的作用仅取决于处理持续时间，而非动物年龄。这种作用被证明是可逆的，因为PB + / -组的平均肿瘤多发性比PB +组大7倍。体视学分析显示，PB -动物肝细胞增殖性病变的平均体积分别是PB +组和PB + / -组的7.7倍和4.1倍。PB +和PB + / -动物肝细胞腺瘤中增殖细胞核抗原标记指数的平均值也是PB -动物肿瘤的三分之一，而平均凋亡指数方面未观察到显著差异。总之，PB的抑制作用似乎主要是由肿瘤细胞增殖的抑制引起的。无论组别如何，观察到的大多数病变都是嗜碱性肝细胞腺瘤或灶，Bcl - 2癌蛋白呈阳性。因此，它们与成年B6C3F1小鼠启动后PB促进作用时占主导的嗜酸性Bcl - 2阴性病变不同。这种启动的年龄依赖性性质，以及Bcl - 2阳性和Bcl - 2阴性病变的不同反应，可能是幼年和成年B6C3F1小鼠PB处理结果明显矛盾的原因。
