| Objective: With the development of economics and the improvement of people's living standard, morbidity of non-alcoholic fatty liver diease (NAFLD) is escalating year after year. NAFLD,which is often associated with obese individuals and patients with hyperinsulinemia, dyslipidemia, hepertension or type 2 diabetes, is a clinicopathological syndrome. NAFLD divide into simple steatosis, steatophetatitis and hepatic cirrhosis in pathology. The exact pathogenesis of NAFLD has not been fully illustrated, in which insulin resistance (IR) and its relative disorder of metabolism play a very important role in the course of generation of NAFLD. Rosiglitazone belongs to thiazolidinediones (TZDs), a kind of novel oral insulin sensitizer, which plays important roles in reducing IR and reducing serum insulin level and hyperglycemia. In recent years, many researches have found Rosiglitazone also has the functions like improving the dyslipidemia, relieving the accumulation of liver fat, and the level of the inflammably change in pathological. Metformin not only can reduces hyperglycemia by increasing glucose intaking and inhibiting glyconeogenesis and glycogenolysis, but also plays significant part in improving the dyslipidemia. Therefore, The rats model of type 2 diabetic for studying was set up by feeding female SD rats with a high-sucrose-high-fat diet and by injecting streptozotin(STZ) to them intrapenitoneally. This model has such features as hyperglycemia , dyslipidemia, IR. Then we make an intervention in type 2 diabetic rats with Rosiglitazone and metformin after 8 weeks. On this condition, to observe the abnormal metabolism linked to insulin resistance and investigate the pathophysiological mechanism of NAFLD. And illustrating the functional mechanism of rosiglitazone and metformin in improving NAFLD. Methods: Female SD rats were randomly assigned into two groups: normal control group(NC) and diabetic group(DM). Normal control group rats were fed with the normal diet, while diabetic group were fed with the diet containing 10%sucrose, 15%lard, 2%cholesterol and 0.25%cholic acid to induce insulin resistance. Hyperglycemia was developed by intrapenitoneal injection STZ (30mg·kg-1) in diabetic group rats after 4 weeks on this diet . At 8 weeks diabetic rats were randomly devided into three subgroups: diabetic control group (DM-C) ,diabetic group treated with rosiglitazone (3mg·kg-1d-1) (DM-R) and diabetic group treated with metformin (625mg·kg-1d-1) (DM-M). Body weight, fasting blood glucose, fasting serum insulin, serum triglyceride and serum cholestrol were measured respectively after 4, 8 and 18weeks. Serum tumor necrosisfactor-alpha (TNF-α), serum leptin and ALT were respectively observed after 18 weeks. Liver specimen were prepared for H.E.-stained, Suda IV-stained and immunohischemistry. The protein expression of TNF-αwas examined by immunohischemistry. H.E.-stained sections were assessed blindly for the severity of steatosis and inflammatory cell infiltration according to criteria. Morever, the correlation between the factors linked to insulin resistance and insulin sensitivity index and the liver cells' severity of steatosis and inflammatory were respectively analyzed. Results 1. In diabetic group, fed with high-sucrose-high -fat diet for 4 weeks, body weight was markedly increased compared with normal control group (P<0.01); serum triglyceride, serum cholestrol and serum insulin level were markedly increased compared with normal control group (P<0.05, P<0.05, P<0.01); fasting blood glucose had no difference with normal control group (P>0.05); HOMA-IR was markedly increased compared with normal control group (P<0.01).So insulin resistance was induced in diabetic group . 2. After 8 weeks, injecting a low dose of STZ intrapenitoneally, rats body weight in diabetic group increased but had no change compared with normal control group (P>0.05); fasting blood glucose level, serum triglyceride, serum cholestrol were markedly increased compared with normal control group (P<0.01, P<0.01, P<0.01), and serum insulin levelwere decreased compared with 4 weeks before, but had no difference with normal control group (P>0.05); HOMA-IR was markedly increased compared with normal control group (P<0.01).This show that insulin resistance still existed in diabetic group . Now the rat model of type 2 diabetes mellitus with insulin resistance had been set up successfully. 3. Liver weight and liver weight/body weight had were markedly increased compared with NC in DM-C by the end of 18 weks(P<0.01,P<0.01). Compared with DM-C there were significant decrease in liver weight and liver weight/body weight in DM-R and DM-M (P<0.05,P<0.01; P<0.01, P<0.01). Compared with DM-C there were significant decrease in fasting blood glucose and serum insulin in DM-R and DM-M (P<0.05, P<0.01; P<0.01, P<0.05) ; compared with DM-C, HOMA-IR was markedly decrease in DM-R and DM-M (P<0.01,P<0.05). Compared with DM-C there was a significant decrease in serum triglyceride, serum ALT and liver triglyceride content in DM-R and DM-M (P<0.01,P<0.05; P<0.01,P<0.01; P<0.01,P<0.01). 4. compared with DM-C, the score of fatty liver and score of inflammation were markedly decrease in DM-R and DM-M (P<.01,P<0.05; p<0.01 p<0.05). There were significant decrease in serum TNF-αand leptin in DM-R (P<.01,P<0.05), but the serum Leptin was not markedly decreased in DM-M(P>0.05). 5. Light microscopy shows: Liver tissue panlobular microvesicular and macrovesicular steatosis and accasional fociof inflammation in DM-C. Liver tissue panlobular microvesicular and macrovesicular steatosis and accasional foci of inflammation were improved obviously by rosiglitazone in DM-R group. Electron microscope shows: Mitochondria were swelling, and mitochondrial crista were fusion and disappear in DM-C. The dimension of mitochondria was compressed in DM-R. 6. Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) was significantly positive correlation with serum TNF-α, serum leptin, serum TG and liver index in DM-C groups. Conclusions 1. Fed with high-sucrose-high -fat diet for 4 weeks, then rats were injected a low dose of STZ intrapenitoneally, by which the rat model of type 2 diabetes mellitus can be established. This rat model of type 2 diabetes mellitus with hyperglycemia, dyslipidemia and IR is similar to type 2 diabetes of human being. So this model may be used to study chronic complications of type 2 diabetes mellitus in human. 2.The metabolic abnormalities of type 2 diabetes mellitus are the risk factors of the developing of NAFLD. 3. HOMA-IR was significantly positive correlation with serum TNF-αlevel in diabetic rats. And the protein expression of TNF-αwas elevated markedly on liver tissue in diabetic rats, which shows TNF-αcan play important roles in developing NAFLD. |
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