Effect Of High-fructose Diet On Oxidative Stress And PPARα Expression In Rat Liver And Fenofibrate INtervention Study

Objective: To observe the change in oxidative stress and expression of PPARαin liver in Wistar rat fed on high-fructose diet and the intervention effect by fenofibrate.Methods: 72 rats were randomly divided into 3 groups: normal control group (N, n=24), high-fructose diet group (F, n=24), and high-fructose diet group treated with fenofibrate (FF, n=24). Rats were treated with either fenofibrate or vehicle(saline) once daily by gavage for 16 weeks (30 mg/kg-1 . day-1). After 8-weeks-feeding, 12 rats were randomly selected from each group. Eight rats were randomly selected from the above 12 rats for oral glucose tolerance test (OGTT). After body weight weighed, the liver of each rat was excised and weighed under pentobarbital sodium anesthesia. Blood samples were simultaneously collected. Liver was stained by oil red O to observe lipid deposition in liver tissue under light microscopy. Serum total triglycerides, total cholesterol, blood glucose, ALT, AST and the content of the liver triglyceride were detected by biochemical methods. Liver malondialdehyde (MDA), glutathione peroxidase (GSH-PX), superoxide dismutase (SOD), catalase (CAT) were measured by chemical colorimetric method. The mRNA and protein expression of PPARαin liver were analyzed by RT-PCR and Western blotting. After 16 weeks of feeding, 8 rats of the remaining 12 rats were randomly selected to do OGTT. After body weight weighed, the liver of 12 rats was excised and weighed under pentobarbital sodium anesthesia and blood samples were simultaneously obtained. The same index was detected by the same methods as those in week 8.Results: (1) The change in body weight and liver weight: at the end of 8 weeks and 16 weeks, there was no significant difference in body weight in each group. At 8th week and 16th week, liver weight was significantly higher in FF group compared with other groups (P<0.01). The ratio of body weight to liver weight was significantly higher in F group compared with N group (P <0.05). (2) Liver staining with oil red O: at the 8th week and 16th week, there was significant lipid deposition in liver in F group. Reduced liver lipid deposition was observed in FF group. (3) Fasting blood glucose level: At the 8th and 16th week, blood glucose of F group was significantly higher than that in N group (P<0.01) . Blood glucose was significantly decreased in FF group compared with that F group (P<0.05). The blood glucose was significantly higher in F group than that in N group(P<0.05). (4) Glucose area under the curve(AUCglu) in OGTT: At the 8th week and 16th week, AUCglu were significantly higher in F group than in the others (P<0.01). Compared with F group, AUCglu was significantly decreased after fenofibrate intervention(P <0.01) while it's still significantly higher than in control group(P<0.01). (5)Serum biochemistry index:①After 8 weeks'feeding, there was no significant difference in serum ALT. After 16 weeks'feeding, serum ALT in F group was significantly higher than in the control group (P<0.01) and was significantly improved by fenofibrate treatment (P<0.01). At both the 8th week and 16th week, serum AST in F group was significantly higher than in the control group (P<0.01) and fenofibrate intervention significantly decreased serum AST (P<0.01);②At the end of the 8th week and 16th week, serum triglyceride levels were significantly higher in F group than in N group (P <0.01). In FF group, fenofibrate intervention significantly decreased serum triglyceride levels compared with F group (P<0.05);③At the end of the 8th week and 16th week, serum cholesterol levels were significantly higher in F group than in N group (P<0.01). In FF group, fenofibrate intervention significantly decreased serum cholesterol levels compared with F group (P<0.01); (6) Liver triglyceride level: After 8 weeks and 16 weeks of high fructose feeding,the level of liver triglyceride were significantly increased (P<0.01). Fenofibrate intervention significantly decreased liver triglyceride levels (P<0.01); (7) Oxidative stress:①After both 8 weeks and 16 weeks of feeding, the level of malondialdehyde (MDA) in F group (2.33±0.05 and 1.99±0.21nmol/mgprot) were significantly higher than N group (1.87±0.14 and 4.80±0.74nmol/mgprot) (P<0.01). After fenofibrate intervention, MDA were decreased significantly in FF group (1.89±0.20 and 2.80±0.29nmol/mgprot) compared with F group(P<0.01);②Eight weeks and 16 weeks after high fructose feeding, superoxide dismutase (SOD) activity in rat liver (381.23±33.58 and 347.44±5.41U/mgprot) in F group was significantly lower than in N group (280.40±25.24 and 277.34±21.90 U / mgprot) (P<0.01). SOD activity in FF group was significantly increased;③at 8th week and 16th week, liver glutathione peroxidase activity in F group(GSH-PX)(378.04±13.78 and 287.21±18.95 activity unit) was significantly lower than in N (418.91±16.53 and 411.14±19.14 activity unit) (P<0.01), the activity of GSH-PX (358.80±12.65 and 294.78±19.91)after fenofibrate treatment was not significantly increased;④at the end of 8 weeks and 16 weeks catalase (CAT) activity (56.92±4.64 and 53.45±5.97U/mgprot) was significantly higher in FF group than in F group (40.97±1.15 and 38.17±1.82U/mgprot) and N group (41.75±2.46 and 39.00±3.53U/mgprot) (P <0.01). There was no significant difference in CAT activity in F group and N group; (8) PPARαprotein and mRNA expression: after 8 weeks and 16 weeks, compared with N group, both mRNA and protein expression of PPARαin F group was decreased(P<0.01), while enofibrate intervention significantly increased the protein expression of PPARα(P <0.01).Conclusions:1 High fructose diet induces a significant increased fasting blood glucose and an impaired glucose tolerance in rats. Fenofibrate treament improves glucose tolerance induced by high fructose diet.2 High fructose diet leads to rat hypertriglyceridemia, liver lipid deposition, and hypercholesterolemia. Fenofibrate treatment improves lipid disorders and liver lipid deposition induced by high fructose diet.3 High fructose diet induces oxidative stress and decreased SOD and GSH activity in liver in rats. Fenofibrate relieves oxidative stress in the liver induced by high fructose diet, which might be attributed to significantly increased CAT and SOD activity in the liver after fenofibrate intervention.4 High fructose diet significantly inhibites the expression of liver PPARαwhile fenofibrate treatment significantly stimulates the expression of PPARα.