dicyclanil and Carcinoma--Hepatocellular

To determine the threshold dose of dicyclanil (DC) that induces hepatocellular tumor-promoting effects associated with reactive oxygen species (ROS) generation via their metabolic pathways, partial hepatectomized ICR male mice were fed diets containing 0, 187.5, 375 or 750 ppm DC after an intraperitoneal injection of N-diethylnitrosamine (DEN) to initiate hepatocarcinogenesis. Immunohistochemically, the proliferating cell nuclear antigen (PCNA)-positive cell ratio was significantly increased in the DEN + 750 ppm DC group compared with the DEN alone group. However, significant increases in the number of gamma-glutamyltranspeptidase (GGT)-positive cells and formation of microsomal ROS were not observed in the DEN + DC groups compared with the DEN alone group. Real-time polymerase chain reaction (RT-PCR) showed that the expression of Cyp1a1, Cyp1a2, and OGG1genes was significantly up-regulated in mice given diets containing 375 ppm DC or more, 187.5 ppm DC or more, and 750 ppm DC, respectively. These results suggest that the threshold dose of DC that induces ROS-mediated liver tumor promotion in mice is more than 750 ppm, although expression of the Cyp1a2 gene, which is related to ROS generation, was up-regulated in the liver of mice, even at a DC dose of 187.5 ppm.

Topics: Animals; Carcinogens; Carcinoma, Hepatocellular; Cytochrome P-450 CYP1A1; Cytochrome P-450 CYP1A2; Diethylnitrosamine; DNA Glycosylases; Dose-Response Relationship, Drug; Drug Therapy, Combination; gamma-Glutamyltransferase; Gene Expression Regulation, Neoplastic; Hepatectomy; Juvenile Hormones; Liver Neoplasms; Male; Mice; Mice, Inbred ICR; Microsomes, Liver; Reactive Oxygen Species; Up-Regulation

Dicyclanil (DC) generates reactive oxygen species (ROS) due to Cyp1a1 induction, and DNA damage caused by oxidative stress is probably involved in hepatocarcinogenesis in mice. To clarify the modifying effect of the Siraitia grosvenorii extract (SGE), which has antioxidative properties, we employed a 2-stage liver carcinogenesis model in partially hepatectomized male ICR mice. Mice maintained on diet containing DC at a concentration of 1,500 ppm for 9 weeks after a single intraperitoneal injection of diethylnitrosamine (DEN) at a dose of 30 mg/kg and they were given water containing 2,500 ppm of SGE for 11 weeks including 2 weeks as pre-administration on DC. SGE inhibited the induction of gamma-glutamyltranspeptidase-positive hepatocytes, lipid peroxidation, and gene expression of Cyp1a1, all of which were caused by DC. To examine whether SGE indirectly inhibits Cyp1a1 expression induced by inhibition of aryl hydrocarbon receptor (Ahr)-mediated signal transduction caused by DC, mice with high (C57BL/6J mice) and low affinities (DBA/2J mice) to Ahr were given DC-containing diet and/or SGE-containing tap water for 2 weeks. Cyp1a1 gene expression was significantly lower in C57BL/6J mice administered DC + SGE than in C57BL/6J mice administered DC alone; there was no difference in the Cyp1a1 expression between DBA/2J mice administered DC + SGE and DC alone. These results suggest that SGE suppresses the induction of Cyp1a1, leading to inhibition of ROS generation and consequently inhibited hepatocarcinogenesis, probably due to suppression of Ahr activity.

Topics: Alkylating Agents; Animals; Antioxidants; Body Weight; Carcinogens; Carcinoma, Hepatocellular; Cell Proliferation; Cucurbitaceae; Cytochrome P-450 CYP1A1; Diethylnitrosamine; Dose-Response Relationship, Drug; gamma-Glutamyltransferase; Gene Expression; Hepatocytes; Juvenile Hormones; Liver Neoplasms, Experimental; Male; Mice; Mice, Inbred C57BL; Mice, Inbred ICR; Organ Size; Plant Extracts; Reactive Oxygen Species; Receptors, Aryl Hydrocarbon; RNA, Messenger; Signal Transduction; Thiobarbituric Acid Reactive Substances

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.

Topics: Animals; Apoptosis; Body Weight; Carcinoma, Hepatocellular; Cocarcinogenesis; Diethylnitrosamine; DNA Repair Enzymes; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Hepatectomy; Juvenile Hormones; Lasers; Liver; Liver Neoplasms, Experimental; Male; Metabolic Networks and Pathways; Mice; Mice, Inbred ICR; Microdissection; Oligonucleotide Array Sequence Analysis; Oxidative Stress; Precancerous Conditions; Reproducibility of Results; Reverse Transcriptase Polymerase Chain Reaction