Masako Muguruma

Threshold dose of piperonyl butoxide that induces reactive oxygen species-mediated hepatocarcinogenesis in rats

To determine the threshold dose of piperonyl butoxide (PBO) that induces hepatocellular tumor-promoting effects, reactive oxygen species (ROS) generation, and drug-metabolizing enzymes that protect against ROS generation, partial hepatectomized rats were fed diets containing 0, 0.015, 0.03, 0.06, 0.125, 0.25, or 0.5% PBO after an i.p. injection of N-diethylnitrosamine (DEN) to initiate hepatocarcinogenesis. Histopathologically, Glutathione S-transferase placental form (GST-P)-positive foci were significantly increased in a dose-dependent manner in rats given 0.25% PBO or higher. The formation of microsomal ROS in the liver was significantly increased in 0.25 and 0.5% PBO. Real-time RT-PCR showed that the expression of the CYP1A1, UDPGTr-2, and Mrp3 genes was significantly upregulated in rats given 0.03% PBO or higher. These results suggest that 0.25% is the threshold dose of PBO that induces ROS-mediated hepatocarcinogenesis in rats, although the CYP1A1 gene that is related to ROS generation and the UDPGTr-2 and Mrp3 genes that are involved in protection against ROS were induced in the livers of rats even at a PBO dose of 0.03%.

Gene expression analysis on the dicyclanil-induced hepatocellular tumors in mice.

Our previous studies showed the possibility that oxidative stress, including oxidative DNA damage, is involved in the mechanism of dicyclanil (DC)-induced hepatocarcinogenesis at the preneoplastic stage in mice. In this study, the expression analyses of genes, including oxidative stress-related genes, were performed on the tissues of hepatocellular tumors in a two-stage liver carcinogenesis model in mice. After partial hepatectomy, male ICR mice were injected with N-diethylnitrosamine (DEN) and given a diet containing 0 or 1500 ppm of DC for 20 weeks. Histopathological examinations revealed that the incidence of hepatocellular tumors (adenomas and carcinomas) significantly increased in the DEN + DC group. Gene expression analysis on the microdissected liver tissues of the mice in the DEN + DC group showed the highest expression levels of oxidative stress-related genes, such as Cyp1a1 and Txnrd1, in the tumor areas. However, no remarkable up-regulation of Ogg1—an oxidative DNA damage repair gene—was observed in the tumor areas, but the expression of Trail—an apoptosis-signaling ligand gene—was significantly down-regulated in the tumor tissues. These results suggest the possibility that the inhibition of apoptosis and a failure in the ability to repair oxidative DNA damage occur in the hepatocellular DC-induced tumors in mice.

A 26-Week Carcinogenicity Study of 2-Amino-3-Methylimidazo(4,5-f)Quinoline in rasH2 Mice

To evaluate the carcinogenic susceptibility of rasH2 mice to 2-amino-3-methylimidazo[4,5- f ]quinoline (IQ), 7-week-old rasH2 mice and their wild-type littermates (non-Tg mice) of both the sexes were fed a diet containing 0 or 300 ppm IQ for 26 weeks. Microscopical examinations revealed that the proliferative lesions of the forestomach, including squamous cell hyperplasias, papillomas, and carcinomas, were frequently encountered in male and female rasH2 mice fed with IQ. In non-Tg mice, no significant differences in the incidence of forestomach lesions were observed between the 0 ppm and 300 ppm groups. Histopathological changes such as periportal hepatocellular hypertrophy and oval cell proliferation in the liver were more apparent in female rasH2 and non-Tg mice than in males, and the incidence of hepatocellular altered foci significantly increased in female rasH2 mice in the 300 ppm group as compared to that in the 0 ppm group. These results suggest that the carcinogenic potential of IQ can be detected in rasH2 mice by a 26-week, short-term carcinogenicity test.