Kuwata Kazunori, Inoue Kaoru, Ichimura Ryohei, Takahashi Miwa, Kodama Yukio, Shibutani Makoto, Yoshida Midori
*Division of Pathology, National Institute of Health Sciences, Kamiyoga 1-18-1, Setagaya-ku, Tokyo 158-8501, Japan Safety Research Laboratories, Sohyaku. Innovative Research Division, Mitsubishi Tanabe Pharma Corporation, 2-2-50, Kawagishi, Toda-shi, Saitama 335-8505, Japan Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.
*Division of Pathology, National Institute of Health Sciences, Kamiyoga 1-18-1, Setagaya-ku, Tokyo 158-8501, Japan Food Safety Commission, Cabinet Office, Akasaka Park Bld 22F, 5-2-20 Akasaka, Minato-ku, Tokyo 107-6122, Japan.
Toxicol Sci. 2016 Jun;151(2):271-85. doi: 10.1093/toxsci/kfw040. Epub 2016 Feb 28.
Acifluorfen (ACI), a protoporphyrinogen oxidase (PROTOX) inhibitor herbicide, promotes the accumulation of protoporphyrin IX (PPIX), and induces tumors in the rodent liver. Porphyria is a risk factor for liver tumors in humans; however, the specific mechanisms through which ACI induces hepatocarcinogenesis in rodents are unclear. Here, we investigated the mode of action of ACI-induced hepatocarcinogenesis, focusing on constitutive androstane receptor (CAR, NR1I3), which is essential for the development of rodent liver tumors in response to certain cytochrome P450 (CYP) 2B inducers. Dietary treatment with 2500 ppm ACI for up to 13 weeks increased Cyp2b10 expression in the livers of wild-type (WT) mice, but not in CAR-knockout (CARKO) mice. Microscopically, ACI treatment-induced cytotoxic changes, including hepatocellular necrosis and inflammation, and caused regenerative changes accompanied by prolonged increases in the numbers of proliferating cell nuclear antigen-positive hepatocytes in WT mice. In contrast, these cytotoxic and regenerative changes in hepatocytes were significantly attenuated, but still observed, in CARKO mice. ACI treatment also increased liver PPIX levels similarly in both genotypes; however, no morphological evidence of porphyrin deposition was found in hepatocytes from either genotype. Treatment with 2500 ppm ACI for 26 weeks after initiation with diethylnitrosamine increased the incidence and multiplicities of altered foci and adenomas in hepatocytes from WT mice; these effects were significantly reduced in CARKO mice. These results indicated that prolonged cytotoxicity in the liver was a key factor for ACI-induced hepatocarcinogenesis, and that CAR played an important role in ACI-induced liver injury and tumor development in mice.
三氟羧草醚（ACI）是一种原卟啉原氧化酶（PROTOX）抑制剂除草剂，可促进原卟啉IX（PPIX）的积累，并在啮齿动物肝脏中诱发肿瘤。卟啉症是人类肝脏肿瘤的一个危险因素；然而，ACI在啮齿动物中诱导肝癌发生的具体机制尚不清楚。在此，我们研究了ACI诱导肝癌发生的作用模式，重点关注组成型雄甾烷受体（CAR，NR1I3），它对于啮齿动物肝脏肿瘤在对某些细胞色素P450（CYP）2B诱导剂的反应中的发展至关重要。用2500 ppm ACI进行长达13周的饮食处理可增加野生型（WT）小鼠肝脏中Cyp2b10的表达，但在CAR基因敲除（CARKO）小鼠中则不会。在显微镜下，ACI处理诱导了细胞毒性变化，包括肝细胞坏死和炎症，并在WT小鼠中引起了再生变化，伴随着增殖细胞核抗原阳性肝细胞数量的长期增加。相比之下，CARKO小鼠肝细胞中的这些细胞毒性和再生变化明显减弱，但仍可观察到。ACI处理在两种基因型中同样增加了肝脏PPIX水平；然而，在两种基因型的肝细胞中均未发现卟啉沉积的形态学证据。在用二乙基亚硝胺启动后，用2500 ppm ACI处理26周增加了WT小鼠肝细胞中改变灶和腺瘤的发生率和数量；这些效应在CARKO小鼠中显著降低。这些结果表明，肝脏中的长期细胞毒性是ACI诱导肝癌发生的关键因素，并且CAR在ACI诱导的小鼠肝损伤和肿瘤发展中起重要作用。
