| Summary: | 碩士 === 中山醫學院 === 營養科學研究所 === 89 === The main objective of this study was to investigate the combined modulatory effect of source and amount of dietary fat and garlic oil on rat hepatic antioxidant and biotransformation enzyme activities and expression. Sprague-Dawley rats were fed either a low corn oil diet (LCO, 5% corn oil), high corn oil diet (HCO, 23.5% corn oil), or high fish oil diet (HFO, 3.5% corn oil + 20% fish oil) and received 0, 30, 80, 200 mg/kg body weight of garlic oil (corn oil as a vehicle, 1ml/kg bw) three times per week for 6 weeks.
Results showed that eicosapentaenoic acid and docosahexaenoic acid levels in hepatic phospholipids were higher in the fish oil-fed group than in the corn-oil fed groups (P<0.05). In contrast, the corn oil-fed groups had greater hepatic phospholipid arachidonic acid levels (P<0.05). Rats fed the HCO or HFO diet had significantly greater relative liver weights than rats fed the LCO diet (P<0.05). The relative lung, heart and kidney weights were not changed by dietary lipid and garlic oil. But the spleen weight was significantly changed by garlic oil (P<0.05). In each dietary lipid group, garlic oil dose-dependently increased the relative spleen weights. HDL-C in rats fed the HCO diet was significantly higher than rats fed the LCO or HFO diet (P<0.05). LDL-C, triacylglycerol and total cholesterol in rats fed the LCO diet were significantly greater than rats fed the HCO diet, and rats fed the HCO diet had significantly greater than rats fed the HFO diet (P<0.05). Rats fed the HCO diet had significantly greater hepatic total lipids than rats fed the LCO or HFO diet (P<0.05).
Rats fed the LCO or HFO diet had significantly greater hepatic GSH and total GSH levels than rats fed the HCO diet. The endogenous TBARS level in the liver tissues, however, was significantly higher in the HFO-fed group than
the LCO- or HCO-fed group (P<0.05). There was also an interaction between dietary fat and garlic oil on the hepatic TBARS levels. In each dietary group, garlic oil dose-dependently decreased glutathione peroxidase (GPx) activity (P<0.05). Regardless of dietary lipid, garlic oil caused a dose-dependent increase of hepatic glutathione reductase (GRd), glutathione S-transferase (GST), placental form of glutathione S-transferase (PGST) and superoxide dismutase (SOD) activities. Moreover, the hepatic GRd, PGST and SOD activities were highest in rats fed the HFO diet (P<0.05). In contrast to the lack of interaction noted on hepatic glutathione-related enzyme activities, garlic oil interacted with dietary fat on the SOD activity. The lipid peroxidation was also studied in the presence of exogenous oxidants. Ferrous sulfate (50μM)-induced lipid peroxidation was significantly suppressed by garlic oil (P<0.05).
In the red blood cells, total GSH, GSH/GSSG ratio and GRd activity were increased dose-dependently by garlic oil (P<0.05). Rats fed the fish oil diet had significantly higher GSSG level than rats fed the corn oil diets (P<0.05). GSH-related enzyme activity assays revealed that, with the exception of HCO-fed group had significantly greater GPx activity than HFO- or LCO- fed group (P<0.05), GRd and GST activities were not affected by dietary lipids. Garlic oil caused a dose-dependent decrease of GRd activity (P<0.05). In contrast, garlic oil tended to dose-dependently increased GST activity.
Regarding to the biotransformation enzymes in liver tissues, rats fed the fish oil diet had greater pentoxyresorufin O-depentylase (PROD), ethroxy-
resorufin O-deethylase (EROD) activities than rats fed the corn oil diets (P<0.05), and rats fed the HFO diet had greater N-nitrosodimethylamine demethylase (NDMAD) activity than those fed the LCO diet (P<0.05). In all dietary fat groups, garlic oil tended to dose-dependently increase PROD and EROD activities in low corn oil group. However, NDMAD activity in all dietary lipid groups was dose-dependently decreased by garlic oil.
Immunoblot assay showed that rats fed the HFO diet had the highest CYP 2B1, 1A1, 2E1, 3A1 and PGST proteins levels among threr dietary lipids groups. Besides the CYP 3A1 protein level, the protein levels of CYP 1A1, 2B1 and 2E1 in the HCO-fed group was higher than the LCO-fed group. To GST isozyme expression, HCO increased GST Ya, Yb, Yc protein levels as compared wuth LCO or HFO. It was also noted that garlic oil caused a dose-dependent increase with GST Ya, Yb, Yc, PGST and CYP 1A1, 2B1, 3A1 protein levels. On the contrary, garlic oil caused a dose-dependent decrease of CYP 2E1 pretein level. The induction of the hepatic CYP mRNA expression were consistent with the peotein levles. The mRNA expression of PGST, CYP 2B1, 1A1 and 3A1 were dose-dependently increased in the presence of garlic oil. These mRNA expression were highest in rats fed the HFO diet. In addition to the effect of fish oil, the mRNA expression of CYP enzymes in rats fed the HCO diet was higher than rats fed the LCO diet.
In conclusion, results suggest that the source and amount of dietary lipids and garlic oil are potentiate in modulation of the biotransformation enzymes. Moreover, fish oil and garlic oil independently regulated the expression of PGST, CYP 2B1, 1A1 and 3A1 protein and mRNA. Garlic oil increased antioxidant capacity by modulating the hepatic antioxidant enzyme activities.
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