Effects Of Calorie Restriction On Insulin Resistance And Expression Of Sirt1 And Sirt4 In Rats

Objective: In order to make a further insight into the regulation of energy metabolism of caloric restriction (CR), insulin resistance rats model was set up by high-caloric diets, compared with the CR rats. This study was aimed to explore the expression of SIRT1 and SIRT4 in response to different dietary regimens in rat model. The association of the SIRTs with insulin resistance (IR) was also investigated.Methods: Forty eight male Sprague-Dawley rats, eight-weeks old, with an average body weight of 200±20g, were randomly divided into four diet treatment groups: normal control (NC) group fed with standard rodent chow; calorie restriction (CR) group fed with 60% of the food intake from the NC group, high-fat (HFa) group fed with a high-fat diet containing 10% lard, 3% yolk, 1% cholesterol, 0.5% sodium cholate and 85.5% standard rodent chow; and the high-fructose group (HFr) fed with a diet containing fructose 66 %. These four groups were maintained separately for 12 weeks. Food intake and body weight of rats were recorded everyday, and the food supply of the CR group was adjusted accordingly. Blood samples were collected from tail veins every two weeks after fasting for 16h. Sera were immediately isolated from blood samples by centrifugation and then stored at -20°C until analyzed for fasting blood sugar, insulin, cholesterol and triglycerides. At the end of study, blood sugar was tested by the tail veins blood at 0, 30, 60 and 120 min after an intragastric administration of lg/kg body weight of glucose in sterile water. The next day, blood was collected by heart puncture after anesthetization and the animal was sacrificed by decapitation. Visceral fat, consisting of epididymis and perirenal fat, was isolated and weighed. The pancreas from each animal was immediately also removed. Immunohistochemical staining was performed to detect the locations of SIRT1 and SIRT4 proteins in the p-cell of rat pancreas. Expression of SIRT1 and SIRT4 proteins in pancreas was analyzed by Western blotting.Results: hyperglycemia, hyperinsulinemia, hyperlipidemia, and visceral obesity, were successfully induced in rats fed with the HFa or HFr diet. In contrast, rats treated with the CR diet had the lowest values for BW, FINS, Cho, TGs, VF and AUC. SIRT1 was presented in the nucleus and cytoplasm of the pancreatic p-cells, while SIRT4 was located in the cytoplasm. Treatment with the CR diet increased the expression of SIRT1 in both the pancreas (P<0.01), while treatment with the HFa and HFr diets caused a decrease. SIRT4 did not change with the CR diet treatment, but declined in HFa and HFr groups (P<0.01).Conclusion: In summary, the results of blood biochemical analysis and AUC indicated that HFa and HFr groups were insulin resistant, and CR rats were more healthier. SIRT1 and SIRT4 were both involved in the development of insulin resistance.