Study On The Mechanisms Of Hepatic Lipid Deposition In High-fructose-fed Wistar Rats And The Effect Of Fenofibrate Intervention

Objective: To explore the mechanisms of hepatic lipid deposition induced by high-fructose diet and the effect of fenofibrate intervention by detecting the expression of diacylglycerol acyltransferase 2(DGAT2), microsomal triglygeride transfer protein (MTP) and forkhead transcription factor O1 (FoxO1) at mRNA and protein levels in liver.Methods: Seventy-two male Wistar rats were randomly divided into 3 groups: normal control group (NC group, n=24), high-fructose-fed group, (HF group, n=24) and high-fructose-fed group with fenofibrate intervention (HFF group, n=24). The rats in NC group were fed with a normal diet, containing 65.5% of carbohydrate, 24.2% of protein and 10.3% of fat as a percentage of total calories; while the rats in HF group and HFF group received a high-fructose diet, containing 77% of carbohydrate (34.5% of fructose), 16.3 % of protein and 6.7% of fat as a percentage of total calories. The rats in HFF group were given fenofibrate 30 mg·kg^-1·d^-1 through intragastric administration once a day; while the rats in the other two groups were given 2ml of saline once a day.At the end of the eighth and sixteenth week, the rats were killed after oral glucose tolerance test and hyperinsulinemic-euglycemic clamp test. After executing, serum fasting blood glucose(FBG), fasting serum insulin (FINS), triglyceride(TG), total cholesterol(TC), free fatty acids(FFAs), alanine aminotransferase(ALT) and aspartate aminotransferase(AST) were measured by drawing blood from carotid artery. Liver tissues were stained with HE staining and oil red O staining and were observed by light microscope. Ultrastructural changes of liver tissues were observed by electronic microscope. Liver tissues were isolated, cut into a number of portions, and stored at ?70°C refrigerator. Hepatic TG was extracted from total tissue homogenate and was detected by using reagent kits. Reverse transcription polymerase chain reaction (RT-PCR) was used to detect mRNA expression of DGAT2, MTP and FoxO1, while western blotting was used to detect protein expression of DGAT2, MTP and FoxO1.Results:1 At the end of the eighth and sixteenth week, the serum levels of TG, TC and FFAs in HF group were significantly higher than those in NC group (P<0.01); The serum levels of TG, TC and FFAs in HFF group were significantly lower than those in HF group (P<0.05) while still higher than those in NC group (P<0.05).2 At the end of the eighth and sixteenth week, compared with NC group, the levels of FBG, FINS and AUC_glu were significantly higher (P<0.01) and glucose infusion rate was significantly lower (P<0.01) in HF group; compared with HF group, the levels of FBG, FINS and AUC_glu were significantly lower (P<0.05) and glucose infusion rate was significantly higher (P<0.05) in HFF group; the levels of FBG, FINS and AUC_glu in HFF group were still higher than those in NC group (P<0.05), and glucose infusion rate was still lower than that in NC group (P<0.01).3 At the end of the eighth week, there were no differences in the serum levels of ALT and AST between NC group, HF group and HFF group (P>0.05). At the end of the sixteenth week, the serum levels of ALT and AST in HF group were significantly higher than those in NC group (P<0.01); The serum levels of ALT and AST in HFF group were significantly lower than those in HF group (P<0.01), and there were no differences between HFF group and NC group (P>0.05).4 At the end of the eighth and sixteenth week, the content of hepatic TG in HF group were significantly higher than that in NC group (P<0.01); the content of hepatic TG in HFF group were significantly lower than that in HF group (P<0.01) while still higher than that in NC group (P<0.01).5 The histology of liver with HE staining and oil red O staining under light microscope were observed the rats of NC group showed the normal histology of liver, there were obvious lipid deposition in liver tissues of HF group, and with a prolonged high fructose feeding, it became worse; hepatic lipid deposition were attenuated by fenofibrate intervention. Electronic microscope showed: cell nucleus and rough endoplasmic reticulum in liver cells of NC group were normal; in HF group, there were so many ellipse shape fat droplets in cytoplasm, fusion and degranulation of rough endoplasmic reticulum granules, part of the double-membrane fusion and disappearance of nucleus gap.6 At the end of the eighth week, there were no significant differences in DGAT2, MTP and FoxO1 expression at mRNA and protein levels between NC, HF and HFF group (P>0.05). At the end of the sixteenth week, both of the mRNA and protein expression of DGAT2, MTP and FoxO1 were significantly increased in HF group (P<0.01) than those in NC group; both of the mRNA and protein expression of DGAT2, MTP and FoxO1 in HFF group was reduced compared with those in HF group (P<0.01), while still higher than those in NC group (P<0.01).Conclusions:1 High-fructose diet can lead to insulin resistance, hyperlipidemia and hepatic lipid deposition in rats.2 Pathological changes of liver cells were observed by light microscope and electron microscope. The liver cells in rats fed on high-fructose diet showed a series of damage as follows: microvesicular and macrovesicular steatosis, fusion and degranulation of rough endoplasmic reticulum granules, part of the double-membrane fusion and disappearance of nucleus gap.3 DGAT2 expression at mRNA and protein levels were increased in liver tissues of high-fructose-fed rats. The synthesis of hepatic triglyceride were increased.4 MTP expression at mRNA and protein levels were increased in liver tissues of high-fructose-fed rats with a up-regulation in FoxO1 mRNA and protein expression. 5 Fenofibrate improved the insulin resistance, hyperlipidemia and hepatic lipid deposition in high-fructose-fed rats and altered the expression at mRNA and protein levels of DGAT2, MTP and FoxO1 in liver tissues.