Comparison of the effect of fish oil and corn oil on chemical-induced hepatic enzyme-altered foci in rats

The effects of fish oil and corn oil diets on diethylnitrosamine initiation /phenobarbital promotion of hepatic enzyme-altered foci in female Sprague-D awley rats were investigated. Groups of 12 rats were initiated with diethyl nitrosamine (15 mg/kg) at 24 h of age. After weaning, they received diets c ontaining either 13.5% fish oil plus 1.5% corn oil or 15% corn oil for 24 w eeks. Rats fed Fish oil had significantly greater liver weight, relative li ver weight, spleen weight, and relative spleen weight than rats fed corn oi l (p < 0.05). Hepatic phospholipid fatty-acid profile was significantly aff ected by the type of dietary lipid. The rats fed fish oil had significantly greater hepatic phospholipid 20:5 and 22:6 than rats fed corn oil; in cont rast, the rats fed corn oil had significantly greater hepatic phospholipid 18:2 and 20:4 than rats fed fish oil (p ( 0.05). Rats fed fish oil had sign ificantly lower hepatic vitamin E and PGE(2) content but significantly grea ter hepatic lipid peroxidation than rats fed corn oil (p < 0.05). The hepat ic levels of antioxidant enzymes (GSH reductase and GST) were significantly greater in rats fed fish oil than in rats fed corn oil (p < 0.05). Except for PGST-positive foci (foci area/tissue area), all the other foci paramete rs (GGT-positive foci area/tissue area, GGT-positive foci no./cm(2), GGT-po sitive foci no./cm(3), PGST-positive foci no./cm(2), and PGST-Dositive foci no./cm(3)) measured in the fish oil group were 10-30% of those in the corn oil group (p < 0.05). Analyses of Pearson correlation coefficient revealed a positive correlation between hepatic GGT- or PGST-positive foci number ( no./cm(2)) and PGE(2) content (r = 0.66, P = 0.01; r = 0.56, P = 0.02, resp ectively) but a negative correlation between GGT- and PGST-positive foci (n o./cm(2)) and lipid peroxidation (r = -0.8, P = 0.0006; r = -0.58, P = 0.01 , respectively), GSH/GSH + GSSG) ratio (r = -0.61, P = 0.05; r = -0.4, P = 0.14, respectively), GSH reductase (r = -0.75, P = 0.002; r = -0.53, P = 0. 02, respectively), and GST activities (r = -0.65, P = 0.01; -0.44, P = 0.07 , respectively). Similar correlation between foci number (no./cm(3)) and PG E(2), lipid peroxidation, GSH/ (GSH + GSSG) ratio, GSH reductase, and GST a ctivities were obtained. The results of this study show that dietary fish o il significantly inhibited hepatic enzyme-altered foci formation compared w ith corn oil in rats. These results suggest that the possible mechanisms in volved in this process are the stimulation of hepatic detoxification system , changes in membrane composition, inhibition of PGE(2) synthesis, the enha ncement of GSH-related antioxidant capacity, and the enhancement of lipid p eroxidation by fish oil.