RESUMEN
This study is conducted to determine the effects of dietary levels of corn and tuna oils on the formation of preneoplastic lesions in die-thylnitrosamine (DEN) induced rat hepatocarcinogenesis. Weanling male Sprague-Dawley rats were fed 2.5, 5, 15, 25% (w/w) corn or tuna oils. Hepatocellular carcinogenesis was induced by DEN (200 mg/kg body weight) and two-thirds partial hepactectomy was carried out 3 weeks later and were sacrificed 8 weeks after DEN initiation. Tuna oil group showed smaller area of placental glutathione S-transferase (GST-P) positive foci than corn oil group. Corn oil group of 25% (w/w) showed the widest area of GST-P positive foci, and tuna oil group showed significantly smaller area of GST-P positive foci than corn oil in 25% (w/w) level but had no differences between oil levels. Thiobarbituric acid reactive substances (TBARS) content was the highest in 25% (w/w) level of tuna oil group fed long chain and highly polyunsaturated fatty acids. Also serum gamma-glutamyltranspeptidase (GGT) activities in 25% level of tuna oil group were significantly higher than by other levels. As oil contents increased, glucose 6-phosphatase (G6Pase) seems to decrease in corn oil groups but remained the same in tuna oil groups. Glutathione reductase (GR) activities were significantly higher in tuna oil group, and the higher the level of tuna oil, the higher GR activities. But Cu/Zn superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities didn't seem to be influenced by levels and kind of dietary fats. Therefore, as oil levels increased, corn oil rich in n-6 fatty acids promoted carcinogenesis but tuna oil rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) of n-3 fatty acids suppressed. Although lipid peroxidation products were elevated in 25% (w/w) tuna oil group, GST-P positive foci didn't increase. Therefore preneoplastic lesions might be reduced through mediation of a lipid peroxidation process in tuna oil. As fat contents of tuna oil increased, elevated GR activities may give a rise to produce more reduced glutathione in order to protect against free radical attack, and high G6Pase activities remained the same and they contributed to membrane stability. So tuna oil diet seems to protect hepatocarcinogenesis.