Koujiro Yoshida

Inhibitory effects of troglitazone, a peroxisome proliferator-activated receptor γ ligand, in rat tongue carcinogenesis initiated with 4-nitroquinoline 1-oxide

Ligands for peroxisome proliferator‐activated receptor (PPAR) γ have been implicated in growth inhibition and cell differentiation in certain malignancies. In this study, the effects of troglitazone, a PPARy ligand, given during the postinitiation phase of oral carcinogenesis initiated with 4‐nitroquinoline 1‐oxide (4‐NQO) were investigated in male F344 rats. Rats aged 6 weeks were given 4‐NQO at 20 ppm for 8 weeks to induce tongue neoplasms. Starting 1 week after the cessation of 4‐NQO exposure, animals were fed diets containing 0, 30 or 100 ppm troglitazone for 22 weeks. At the end of the study (week 32), the incidences of 4‐NQO‐induced tongue neoplasms and preneoplasms were determined histo‐pathologically and cell proliferation activity was estimated by counting bromodeoxyuridine (BrdU)‐labeling indices and cyclin D1‐positive cell ratios. In addition, immunohistochemical expression of cyclooxygenase (COX)‐2 and PPARγ was assessed in the tongue lesions. Feeding with 100 ppm troglitazone significantly decreased the incidence of squamous cell carcinoma when compared to the group without troglitazone treatment (5.0% vs. 45.8%, P<0.005). Interestingly, the BrdU‐labeling index and cyclin D1‐positive cell ratio assessed in the non‐lesional tongue squamous epithelium were reduced by dietary administration of troglitazone (P<0.0001–0.005). Additionally, the immunoreactivity of COX‐2 in the tongue lesions was also decreased by the treatment (P<0.01–0.05). These results clearly showed that dietary troglitazone inhibits 4‐NQO‐induced tongue carcinogenesis and such inhibition is related to suppression of increased cell proliferation and/or COX‐2 expression. This study warrants further investigation on the use of PPARy ligands as a novel preventive approach for oral malignancy. (Cancer Sci 2003; 94: 365–371)

Dietary supplementation of the citrus antioxidant auraptene inhibits N,N-diethylnitrosamine-induced rat hepatocarcinogenesis.

Objectives: We have previously reported that an antioxidant, auraptene (AUR), isolated from citrus fruit effectively inhibits chemically induced carcinogenesis in digestive tracts, such as the oral cavity, esophagus and large bowel. In this study, we investigated the modifying effects of dietary supplementation with AUR on N,N-diethylnitrosamine (DEN)-initiated hepatocarcinogenesis in male F344 rats in two different experiments to determine whether the compound exerts a cancer-chemopreventive action in other organs. Methods: In the first experiment, animals were fed diets containing AUR at dose levels of 100 and 500 ppm for 7 weeks 1 week before, during, and 1 week after the start of liver carcinogenesis induced by DEN (40 ppm in drinking water for 5 weeks) to predict the modulatory effect on hepatocarcinogenesis. After 7 weeks, the numbers of hepatocellular enzyme-altered foci (EAF; cm2) which stained positive for the placental form of glutathione S-transferase (GST-P) and transforming growth factor (TGF)-α were determined on immunohistochemically stained sections. In the second experiment conducted to confirm the findings, animals subjected to DEN treatment were fed AUR-containing diets (100 and 500 ppm) during either the initiation stage (‘initiation’ feeding for 7 weeks) or post-initiation phase (‘post-initiation’ feeding for 25 weeks) of DEN-induced hepatocarcinogenesis. Results: In the first experiment, feeding with AUR at both doses during DEN exposure decreased the mean numbers of GST-P-positive and TGF-α-positive EAF/cm2, and the reduction in the number of TGF-α-positive EAF by feeding 500 ppm AUR was statistically significant (p < 0.005). In the second experiment, the ‘initiation’ feeding with 500 ppm AUR significantly inhibited the incidence (33 vs. 83%, p = 0.000511) and multiplicity (0.67 ± 1.09 vs. 1.96 ± 1.85, p < 0.005) of liver cell carcinoma. Also, the ‘post-initiation’ feeding with AUR at both doses significantly reduced the development of hepatocellular carcinoma (100 ppm: incidence, 15%, p = 0.000006; multiplicity: 0.25 ± 0.64, p < 0.001; 500 ppm: incidence, 11%, p = 0.000002; multiplicity, 0.26 ± 0.81, p < 0.001). In addition, AUR feeding reduced cell proliferation and the apoptotic index in liver cell neoplasms. Conclusions: The results suggest that the citrus antioxidant AUR is a potential chemopreventive agent against DEN-induced hepatocarcinogenesis in rats.