Molecular pathological analysis on the mechanism of liver carcinogenesis in dicyclanil-treated mice

To investigate the mechanism of hepatocarcinogenesis due to dicyclanil (DC), an insect growth regulator for sheep, histopathological and molecular biological analyses were performed in the liver of male ICR mice fed on a diet containing 1500 ppm of DC for 2 weeks (Experiment I; Exp. I). In gene expression analyses using a large-scale cDNA microarray and RT-PCR, fluctuations of expressions of metabolism-/oxidation-/reduction-related genes, such as CYP1A, aldehyde dehydrogenase family 1 subfamily A1 (Aldh1a1), and thioredoxin reductase 1 (Txnrd1), were predominantly observed in the liver of the DC-treated group. In Experiment II (Exp. II), small-scale and metabolism/oxidative stress-specific cDNA microarray, real-time RT-PCR, and measurement of NF-kappaB protein were performed in the mice liver using a two-stage hepatocarcinogenesis model, in which the male ICR mice were fed on a diet containing 1500 ppm of DC for 7 weeks after a single injection of dimethylnitrosamine (DMN). These mice were subjected to two-thirds partial hepatectomy (PH) at week 3. During histopathological examinations, a remarkable increase in gamma-glutamyltransferase-positive cells was observed in the DMN+DC+PH group. During the microarray and PCR analyses, the metabolism and oxidative stress-related genes, such as Cyp1a, P450 oxidoreductase (Por), and thioredoxin reductase 1 (Txnrd1); a few DNA damage/repair genes, such as 8-oxoguanine DNA-glycosylase 1 (Ogg1); and growth arrest and DNA-damage-inducible 45 alpha (Gadd45a), were fluctuated in this group, together with a slight increase in the concentration of activated NF-kappaB. These results suggest that DNA damages due to oxidative stress may be involved in the mechanism of DC-induced hepatocarcinogenesis in mice.