dicyclanil and Precancerous-Conditions

Our previous study suggested the possibilities that dicyclanil (DC), a nongenotoxic carcinogen, produces oxidative stress in the liver of the two-stage hepatocarcinogenesis model of mice and the stress induced probably causes secondary oxidative DNA damage. However, clear evidences demonstrating the relationship between DC-induced hepatocarcinogenesis, oxidative stress, and oxidative DNA damage have not been obtained. To clarify the relationship, further investigations were performed in the liver of the partially hepatectomized (PH) mice maintained on diet containing 1,500 ppm of DC for 13 and 26 weeks after intraperitoneal injection of dimethylnitrosamine (DMN). Significant increases in mRNA expressions of some metabolism- and oxidative stress-related genes with a formation of gamma-glutamyltranspeptidase (GGT) positive foci were observed in the DMN + DC + PH group by the treatment of DC for 13 and 26 weeks. The levels of 8-hydroxy-deoxyguanosine (8-OHdG) in the liver DNA also significantly increased in mice of the DMN + DC + PH group at weeks 13 and 26 and mice given DC alone for 26 weeks. The in vitro measurement of reactive oxygen species (ROS) generation from the mouse liver microsomes showed a significant increase of ROS production in the presence of DC. These results suggest that DC induces oxidative stress which is probably derived from its metabolic pathway, partly, and support our previous speculation that oxidative stress plays one of the important roles in the DC-induced hepatocarcinogenesis in mice.

Topics: 8-Hydroxy-2'-Deoxyguanosine; Animals; Carcinogens; Cell Transformation, Neoplastic; Cytochrome P-450 CYP1A1; Deoxyguanosine; DNA Damage; DNA Glycosylases; gamma-Glutamyltransferase; Juvenile Hormones; Liver; Liver Neoplasms, Experimental; Male; Mice; Mice, Inbred ICR; Oxidative Stress; Oxidoreductases; Precancerous Conditions; Reactive Oxygen Species; RNA, Messenger; Superoxide Dismutase; Superoxide Dismutase-1; Thioredoxin Reductase 1; Thioredoxin-Disulfide Reductase; Time Factors

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

In order to clarify the in vivo genotoxicity of dicyclanil with the potential of hepatocarcinogenicity, the stomach, colon, liver, kidney, urinary bladder, lung, brain and bone marrow of male ddY mice given a single oral administration of 100 and 200 mg/kg body weight of dicyclanil were evaluated in an alkaline single-cell gel electrophoresis (comet) assay. In addition, to investigate its possible initiation activity, partially hepatectomized male F344 rats given a single oral administration of 75 mg/kg body weight of dicyclanil were examined by a short-term liver initiation assay. Three and 24 hr after administration, cell migration, as a marker of DNA damage in comet assay, was not observed in any of the tissues of dicyclanil-treated mice. There were no significant differences in the number and area of glutathione S-transferase placental form (GST-P) positive foci, as a marker of hepatocellular preneoplastic lesions in rats, between treated and control groups. These results indicate that dicyclanil has neither in vivo genotoxicity nor initiation activity, and suggest that the hepatocarcinogenicity in mice induced by dicyclanil is attributable to a non-genotoxic mechanism.

Topics: Administration, Oral; Animals; Carbon Tetrachloride; Carcinogens; Comet Assay; Dose-Response Relationship, Drug; Glutathione Transferase; Hepatectomy; Image Processing, Computer-Assisted; Immunohistochemistry; Juvenile Hormones; Liver; Liver Neoplasms, Experimental; Male; Mice; Mice, Inbred Strains; Mutagens; Precancerous Conditions