Mechanisms Of Action For Salidroside To Improve Insulin Resistance

Objective:Recent reports have suggested that Salidroside (SAL) could stimulate glucose uptake in skeletal muscle cells by activating AMP-activated protein kinase (AMPK). The aim of this study is to evaluate the therapeutic effects of SAL on type2diabetes (T2DM) and to explore the underlying mechanisms.Methods:The db/db mice were used as a rodent model for T2DM in vivo study. Increasing doses of SAL (25,50and100mg-kg-1d-1) were orally administrated to db/db mice for8weeks and the postprandial blood glucose and body weight of mice were monitored weekly. Biochemical analysis and histopathological examinations were conducted to evaluate the therapeutic effects of SAL after treatment. Primary cultured mouse hepatocytes were used to further explore the underlying mechanisms of SAL by combination of phosphorylation of AMPK detections and other biochemical analysis in vitro.Results:SAL dramatically reduced blood glucose and serum insulin levels and alleviated insulin resistance (IR). Biochemical analysis results were shown that the levels of serum total cholesterol (TC), triglycerides (TG), LDL-cholesterol (LDL-C) and Non-esterified fatty acids (NEFA) were decreased, and the levels of serum HDL-cholesterol (HDL-C) was increased after SAL treatment. Moreover, SAL treatment decreased the TG contents in liver and skeletal muscle tissues, and increased the glycogen level in liver tissue. Histopathological examinations revealed the increase in adipocyte and pancreatic islets size in db/db mice was blunted after SAL treatment, and SAL resulted in reduction in the number of macrophages in adipose tissues. SAL treatment increased the phosphorylations of AMPK and acetyl coenzyme A carboxylase (ACC) in liver and skeletal muscle tissues, as well as the phosphorylation of Akt in adipose tissues. In cultured primary mouse hepatocytes, SAL effectively triggered the phosphorylations of AMPK, ACC, Akt and glycogen synthase kinase3β (GSK3P). SAL-induced phosphorylations as noted above were inhibited by preincubation with AMPK inhibitor, Compound C. Moreover, SAL-induced Akt and GSK3β phosphorylations were inhibited by preincubation with phosphatidylinositol3-kinase (PI3K) inhibitor LY294002, but pretreatment with LY294002did not alter the phosphorylations of AMPK and ACC induced by SAL. In addition, SAL inhibited gluconeogenesis and lipid accumulation and improved the insulin sensitivity in hepatocytes. Moreover, SAL increased the AMP/ATP ratio and moderately depolarized mitochondrial membrane potential in hepatocytes. Furthermore, SAL inhibited mitochondrial respiratory chain at complex I in isolated mitochondria in oxygen consumption detection.Conculsions:SAL exerts antidiabetic effect by improving cellular metabolic flux through activating a mitochondria-related AMPK/P13K/Akt/GSK3p pathway. Objective:Salidroside (SAL) alleviates severity of Nonalcoholic fatty liver disease (NAFLD) in db/db mice were oberverd in our results of part I. The aim of this study is to evaluate the therapeutic effects of SAL on NAFLD and to explore the underlying mechanisms.Methods:The NAFLD model was induced in mice by fed a high-fat diet (HFD). SAL (100mg.kg-1d-1) was orally administrated to HFD mice for8weeks and the postprandial blood glucose and body weight of mice were monitored weekly. Biochemical analysis and histopathological examinations were conducted to evaluate the therapeutic effects of SAL after treatment. Primary cultured mouse hepatocytes were cultured in medium containing high glucose plus insulin to induce lipid deposition and insulin resistance (IR) in vitro. The hepatocytes were used to further explore the underlying mechanisms of SAL through analysis of AMP-activated protein kinase (AMPK) activity, insulin sensitivity and NLRP3inflammasome activation.Results:SAL dramatically reduced blood glucose and serum insulin levels and alleviated IR. Biochemical analysis results were shown that the levels of serum total cholesterol (TC), triglycerides (TG), LDL-cholesterol (LDL-C), Non-esterified fatty acids (NEFA), aspartate aminotransferase (AST), alanine aminotransferase (ALT), malondialdehyde (MDA) and interleukin-1β (IL-β) were decreased, and the levels of serum HDL-cholesterol (HDL-C) and superoxide dismutase (SOD) were increased after SAL treatment. Moreover, SAL treatment decreased the TC, TG and MDA contents, and increased the SOD content in liver tissue. Histopathological examinations revealed the SAL treatment decreased the scoring of Steatosis grade、 Ballooning、Inflammation and NAFLD Activity in liver tissues, and reduced the number of macrophages in adipose tissues. Moreover, the results of Realtime-PCR were shown that SAL suppressed gene expressions of FAS, TNF-α, Caspase-land IL-1β in liver tissue. And SAL treatment increased the phosphorylations of AMPK and acetyl coenzyme A carboxylase (ACC), as well as the phosphorylations of Akt and glycogen synthase kinase3β (GSK3β) in liver tissue of HFD mice after injected with insulin. Furthermore, SAL suppressed the activations of Caspase-1and IL-1β in liver tissue. SAL effectively inhibited lipid deposition, increased the phosphorylations of AMPK and ACC and enhanced the effects of insulin-stimulated phosphorylations of Akt and GSK3β in a dose-dependent manner in cultured primary mouse hepatocyte exposed to high glucose plus insulin. And the NLRP3inflammasome activation also inhibited after SAL incubation. In addition, SAL decreased the reactive oxygen species (ROS) level and thioredoxin-interacting protein (TXNIP) expression level in hepatocytes exposed to high glucose plus insulin as noted above.Conculsions:SAL exerts therapeutic effect on NAFLD by activating AMPK and alleviating lipid metabolism disorder, IR and inflammatory response.