尿石素A激活自噬改善糖尿病小鼠肝脏胰岛素抵抗研究

目的研究尿石素A(UA)对2型糖尿病模型小鼠肝脏胰岛素信号通路的影响及与自噬的关系。方法将C57BL/6小鼠按体质量随机分成4组,即对照组、模型组、尿石素A(50 mg/kg)组、尿石素A(50 mg/kg)联合氯喹(50 mg/kg)组,高脂饲料喂养6周后,ip链脲佐菌素(STZ)建立2型糖尿病模型。各组小鼠ig给药7周,检测小鼠体质量、饮水量、血脂、空腹血糖(FBG)、空腹胰岛素(FINS)水平;计算胰岛素抵抗指数(HOMA-IR)、胰岛素敏感指数(ISI);HE染色观察小鼠肝组织病理变化;蛋白免疫印迹法检测小鼠肝组织磷酸化蛋白激酶B(p-Akt)、葡萄糖转运蛋白2(Glut2)、磷酸化糖原合酶激酶-3β(p-GSK3β)及自噬相关蛋白微管相关蛋白质1轻链3Ⅱ/Ⅰ(LC3 Ⅱ/Ⅰ)、选择性自噬接头蛋白(p62)表达水平。结果与模型组比较,UA能够显著改善糖尿病模型小鼠肝组织脂肪变和水肿;显著降低血浆三酰甘油(TG)、游离脂肪酸(FFA)、低密度脂蛋白-胆固醇(LDL-C)、FBG、FINS水平,升高高密度脂蛋白-胆固醇(HDL-C)水平(P0.01);显著降低HOMA-IR,升高ISI(P0.01);上调肝组织p-Akt、Glut2、p-GSK3β、LC3Ⅱ/Ⅰ蛋白表达,抑制p62蛋白表达(P0.01)。联合氯喹后,小鼠FBG、FINS、HOMA-IR增加,ISI降低(P0.05);肝组织水肿和脂肪病变明显加重;肝组织p-Akt、Glut2、LC3Ⅱ/Ⅰ蛋白表达水平降低,p62蛋白表达水平升高(P0.05),显示自噬抑制剂氯喹明显削弱了UA的作用。结论 UA可能是通过激活肝脏自噬改善糖尿病小鼠肝脏胰岛素抵抗。     

Adiposity and estrogen receptor-positive,postmenopausal breast cancer risk: Quantification of the mediating effects of fasting insulin and free estradiol

Adiposity increases estrogen receptor (ER)-positive postmenopausal breast cancer risk. While mechanisms underlying this relationship are uncertain, dysregulated sex-steroid hormone production and insulin signaling are likely pathways. Our aim was to quantify mediating effects of fasting insulin and free estradiol in the adiposity and ER-positive postmenopausal breast cancer association. We used data from a case–cohort study of sex hormones and insulin signaling nested within the Melbourne Collaborative Cohort Study. Eligible women, at baseline, were not diagnosed with cancer, were postmenopausal, did not use hormone therapy and had no history of diabetes or diabetes medication use. Women with ER-negative disease or breast cancer diagnosis within the first follow-up year were excluded. We analyzed the study as a cumulative sampling case–control study with 149 cases and 1,029 controls. Missing values for insulin and free estradiol were multiply imputed with chained equations. Interventional direct (IDE) and indirect (IIE) effects were estimated using regression-based multiple-mediator approach. For women with body mass index (BMI) >30 kg/m² compared to women with BMI 18.5–25 kg/m², the risk ratio (RR) of breast cancer was 1.75 (95% confidence interval [CI] 1.05–2.91). The estimated IDE (RR) not through the mediators was 1.03 (95% CI 0.43–2.48). Percentage mediated effect through free estradiol was 72% (IIE-RR 1.56; 95% CI 1.11–2.19). There was no evidence for an indirect effect through insulin (IIE-RR 1.12; 95% CI 0.68–1.84; 28% mediated). Our results suggest that circulating free estradiol plays an important mediating role in the adiposity–breast cancer relationship but does not explain all of the association.     

Scutellarin,a modulator of mTOR,attenuates hepatic insulin resistance by regulating hepatocyte lipid metabolism via SREBP‐1c suppression

High levels of consumption of saturated lipids have been largely associated with the increasing prevalence of metabolic diseases. In particular, saturated fatty acids such as palmitic acid (PA) have been implicated in the development of insulin resistance (IR). Scutellarin (Scu) is one of the effective traditional Chinese medicines considered beneficial for liver diseases and diabetes. In this study, we investigated the effect of Scu on IR and lipid metabolism disorders in vitro and in high fat diet (HFD)‐fed mice. In vitro, we found that Scu decreased insulin‐dependent lipid accumulation and the mRNA expression of CD36, Fasn, and ACC in PA‐treated HepG2 cells. Additionally, Scu upregulated Akt phosphorylation and improved the insulin signalling pathway. Moreover, Scu downregulated mammalian target of rapamycin (mTOR) phosphorylation and the n‐SREBP‐1c protein level and also reduced lipid accumulation via the mTOR‐dependent pathway, as confirmed by the molecular docking of Scu to mTOR. In HFD‐fed C57BL/6 mice, Scu improved oral glucose tolerance, pyruvate tolerance and the IR index and also increased the Akt phosphorylation level. Moreover, Scu reduced hepatocyte steatosis, decreased lipid accumulation and triglyceride levels, inhibited mTOR phosphorylation, and decreased the SREBP‐1c level in the liver. Taken together, these findings suggest that Scu ameliorates hepatic IR by regulating hepatocyte lipid metabolism via the mTOR‐dependent pathway through SREBP‐1c suppression.