Roberts R A, Soames A R, Gill J H, James N H, Wheeldon E B
Zeneca Central Toxicology Laboratory, Alderley Park, Macclesfield, UK.
Carcinogenesis. 1995 Aug;16(8):1693-8. doi: 10.1093/carcin/16.8.1693.
Non-genotoxic hepatocarcinogenesis may involve suppression of the hepatocyte apoptosis that would normally remove damaged or initiated cells. These protected hepatocytes could then remain as preferential targets for promotion by this class of compounds. Here we demonstrate clearly that the non-genotoxic liver carcinogens and hepatomitogens cyproterone acetate (CPA) and nafenopin, a peroxisome proliferator, both suppress the basal level of rat liver apoptosis in vivo. After 10 days of dosing with CPA (120 mg/kg/day) or nafenopin (25 mg/kg/day) there were 0.005 +/- 0.010 and 0.002 +/- 0.021 apoptotic bodies/100 hepatocytes respectively, compared with 0.031 +/- 0.008 per 100 in controls. Concomitant with this suppression of apoptosis, bromodeoxyuridine (BrdU) labelling indices and mitotic figures rose, confirming a perturbation of both sides of the growth equation between cell death and replication. Withdrawal of CPA or nafenopin resulted in a 100- to 200-fold elevation in apoptosis. This was inhibited by the re-administration of either compound. To investigate if cells protected from apoptosis by non-genotoxic carcinogens are targets for replication, we examined the replicative history of the apoptotic bodies generated upon withdrawal of CPA or nafenopin. Rats were administered BrdU during the hyperplastic phase of compound administration (0-10 days). Livers were examined 5 days after compound withdrawal. With both CPA and nafenopin, apoptotic bodies and S phase were predominantly in the periportal region. However, despite this zonal co-localization, very few (< 10%) of the apoptotic bodies were labelled with BrdU. Overall, our data provide in vivo evidence to support the hypothesis that non-genotoxic hepatocarcinogens such as CPA and the peroxisome proliferators suppress apoptosis. Surprisingly, the majority of the hepatocytes generated during compound-induced hyperplasia were protected from apoptosis during liver regression. These data contribute to our understanding of clonal selection and promotion during non-genotoxic hepatocarcinogenesis.
非遗传毒性肝癌发生可能涉及抑制肝细胞凋亡，而正常情况下肝细胞凋亡会清除受损或起始细胞。这些受到保护的肝细胞随后可能会成为这类化合物促癌作用的优先靶点。在此我们清楚地证明，非遗传毒性肝致癌物和肝有丝分裂原醋酸环丙孕酮（CPA）以及过氧化物酶体增殖剂萘酚平，在体内均能抑制大鼠肝脏的基础凋亡水平。用CPA（120毫克/千克/天）或萘酚平（25毫克/千克/天）给药10天后，每100个肝细胞中分别有0.005±0.010和0.002±0.021个凋亡小体，而对照组每100个肝细胞中有0.031±0.008个凋亡小体。与凋亡抑制相伴的是，溴脱氧尿苷（BrdU）标记指数和有丝分裂象增加，证实了细胞死亡与复制之间生长平衡的双方均受到了干扰。停用CPA或萘酚平会导致凋亡增加100至200倍。再次给予这两种化合物中的任何一种均可抑制这种增加。为了研究免受非遗传毒性致癌物诱导凋亡的细胞是否为复制靶点，我们检查了停用CPA或萘酚平后产生的凋亡小体的复制历史。在化合物给药的增生期（0至10天）给大鼠注射BrdU。在停用化合物5天后检查肝脏。对于CPA和萘酚平，凋亡小体和S期主要位于门静脉周围区域。然而，尽管存在这种区域共定位，但很少（<10%）的凋亡小体被BrdU标记。总体而言，我们的数据提供了体内证据支持如下假说：CPA和过氧化物酶体增殖剂等非遗传毒性肝致癌物会抑制凋亡。令人惊讶的是，在化合物诱导的增生过程中产生的大多数肝细胞在肝脏消退过程中免受凋亡。这些数据有助于我们理解非遗传毒性肝癌发生过程中的克隆选择和促癌作用。
