限食对高脂喂养大鼠肝脏内质网应激的影响

目的：观察限食对高脂喂养大鼠肝脏内质网应激标志伴侣蛋白78 kD糖调节蛋白（GRP78）mRNA表达的影响，以进一步了解饮食控制对肥胖及胰岛素抵抗影响的机制。方法：雄性Wistar大鼠24只，随机分为正常对照组（NC）、高脂饮食组（HF）、热卡限制组（CR），每组8只。NC组和HF组分别给予普通饲料（脂肪热卡比18.94%）和高脂饲料（脂肪热卡比50.55%）喂养12周，自由进食。CR组给予自由高脂饲料8周后，改为半量正常饲料（半量为同龄对照组自由进食量的一半）继续喂养4周。造模结束后检测动物胰岛素抵抗指数（HOMAIR）、内脏脂肪重量/体重比值和血清生化指标变化，光镜和电镜下观察大鼠肝脏组织学改变，RT-PCR半定量检测大鼠肝脏GRP78 mRNA的表达。结果：（1）HF组空腹血胰岛素(FIns) (27.51±3.51) mU/L vs (15.46±2.25) mU/L、甘油三酯（TG）(1.35±0.25) mmol/L vs (0.67±0.10) mmol/L、胆固醇（TC）(2.59±0.34) mmol/L vs (1.41±0.28) mmol/L及胰岛素抵抗指数HOMAIR(5.85±0.23) vs (2.85±0.60)较NC组明显升高(P＜0.01)，且肝脏中脂质沉积明显。（2）限食4周后，CR组的Fins(11.25±2.42) mU/L vs (27.51±3.51) mU/L、TG(0.45±0.06) mmol/L vs (1.35±0.25) mmol/L、TC(1.06±0.15) mmol/L vs (2.59±0.34) mmol/L和HOMAIR(1.91±0.38) vs (5.85±0.23)明显低于HF组(P＜0.01)，同时肝脏中脂质沉积也减轻。（3）电镜下，HF组内质网肿胀断裂，核糖体脱落，糖原溶解，CR组则基本恢复正常。（4）HF组大鼠肝脏中GRP78 mRNA表达明显高于NC组（29.36±3.54 vs 16.51±1.73），而CR组则明显低于HF组（13.70±2.35 vs 29.36±3.54）。结论：合理限制饮食能有效减轻高脂喂养所致的脂质代谢紊乱和胰岛素抵抗，其作用机制至少与肝脏组织中的内质网应激相关蛋白GRP78的mRNA表达受抑有关。

Effect of calories restriction on ER stress in the liver of high fat diet rats

AIM: To study the effect of calories restriction on endoplasmic reticulum(ER) chaperone protein 78-kD glucose regulated protein (GRP78) mRNA expression in the liver of high fat diet rats, in order to explore the mechanism of how calories restriction improves insulin resistance. METHODS: Wistar rats (n=24) were randomly divided into 3 groups: normal chow (NC) group, was fed free normal chow (18.94% of calories as fat) for 12 weeks; high fat group (HF) was fed high fat diet (50.55% of calories as fat) for 12 weeks; calories restriction group (CR) was fed high fat diet for 8 weeks at first, then given 50% of diet consumed by the same age NC group. Changes of body weight, height, and food intake were recorded. At the end of experiment, HOMAIR, the rate of visceral fat (including perirenal fat and epididymal fat) vs weight, plasma protein, blood lipid (including total cholesterol and triglyceride), hepatic GRP78 mRNA and hepatic histological changes (including light microscopic studies and electron microscopic studies) were detected. RESULTS: (1) Animals in HF group had an obviously elevation of fasting insulin (27.51±3.51) mU/L vs (15.46±2.25) mU/L, triglyceride (1.35±0.25) mmol/L vs (0.67±0.10) mmol/L, total cholesterol (2.59±0.34) mmol/L vs (1.41±0.28) mmol/L and insulin resistance index HOMAIR (5.85±0.23 vs 2.85±0.60) compared with NC group, and also had obviously lipid accumulations in the liver. (2) After calories restriction, all the abnormal elevated biochemical indicators were decreased to normal levels, the hepatic lipid accumulations were also improved. (3) The changes of liver ultrastructure in HF group showed rough endoplasmic reticulum enlargement, fragmentation, taking off grain, and with glycogen solution. The changes in CR group were nearly the same as those in NC group. (4) High fat diet induced the expression of GRP78 mRNA, calories restriction might reverse it. CONCLUSION: Reasonable food calories restriction is a good method to improve insulin resistance, partly due to improvement of endoplasmic reticulum stress in liver.