ag-490 and Insulin-Resistance

Insulin resistance (IR) is considered as a major factor initiating type 2 diabetes mellitus and can lead to a reduction in glucose uptake that mainly occurs in the liver. Astragalus polysaccharide (APC), extracted from the traditional Chinese medicine, has been recorded to suppress IR. However, the underlying mechanism remains inadequately explored.. IR was induced in HepG2 cells which further underwent APC treatment. Cell viability was determined by cell counting kit-8 assay. Pretreatment with AG490, an inhibitor of signal transducer and activator of transcription 5 (STAT5) signaling, was performed for investigating the influence of STAT5 on APC. Glucose uptake level was reflected by 2-deoxyglucose-6-phosphate content determined through colorimetric assay. Expression levels of insulin-like growth factor 1 (IGF-1), IGF-1 receptor (IGF-1R), phosphorylated-STAT5/STAT5, and p-protein kinase B (AKT)/AKT in the cells were assessed by Western blot. Radioimmunoassay (RIA) was used to detect IGF-1 secretion in the cells.. APC at doses of 10 and 20 mg increased the viability of HepG2 cells with/without IR induction, and abrogated IR-induced inhibition of glucose intake. Meanwhile, APC (10 mg) offset IR-induced inhibition on the expressions of IGF-1R and IGF-1, the activation of AKT and STAT5, and the secretion of IGF-1 in HepG2 cells. More importantly, the reversal effect of APC on IR-induced alterations in HepG2 cells was counteracted by AG490.. APC ameliorates IR in HepG2 cells through activating the STAT5/IGF-1 pathway.

Topics: Diabetes Mellitus, Type 2; Glucose; Hep G2 Cells; Humans; Insulin Resistance; Insulin-Like Growth Factor I; Polysaccharides; Proto-Oncogene Proteins c-akt; STAT5 Transcription Factor

Children born small for gestational age (SGA) are at increased risk for short stature and type 2 diabetes mellitus as a result of growth hormone (GH) resistance and insulin resistance. The mechanisms of multiple hormone resistance remain unclear. This study was designed to investigate the relationship between GH resistance and insulin resistance in non-catch-up growth (NCU-SGA) rats, and how their signaling pathways are related based on their crosstalk on the insulin receptor substrate-1 phosphatidylinositol 3'-kinase (IRS-1-PI3K) pathway.. NCU-SGA rat model was developed by restricting prenatal food intake in pregnant dams. Activated levels of IRS-1 and Akt in liver protein extracts were compared between NCU-SGA and age- and sex-matched controls born appropriate for gestational age rats at baseline, after insulin stimulation, and after pretreatment with AG490 (GH-JAK2 pathway inhibitor) followed by insulin stimulation.. GH secretion was positively related to markedly increased insulin levels in NCU-SGA rats. There was no difference of IRS-1 phosphorylation in response to insulin between two groups, however, insulin-stimulated Akt phosphorylation was attenuated in NCU-SGA rats compared to appropriate for gestational age rats. Pretreatment with AG490 restored the Akt response to insulin demonstrated by significantly increased Akt phosphorylation.. GH plays a role in inducing insulin resistance via signaling crosstalk with insulin at the level of PI3K/Akt in NCU-SGA rats.

Topics: Adaptor Proteins, Signal Transducing; Animals; Animals, Newborn; Birth Weight; Diabetes Mellitus, Type 2; Disease Models, Animal; Enzyme Inhibitors; Female; Gestational Age; Growth Disorders; Growth Hormone; Humans; Infant, Newborn; Infant, Small for Gestational Age; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Male; Phosphatidylinositol 3-Kinases; Phosphorylation; Pregnancy; Proto-Oncogene Proteins c-akt; Signal Transduction; Tyrphostins

Insulin resistance is a metabolic syndrome commonly seen in obesity. Leptin, the obese gene product, plays a role in the regulation of cardiac function. Elevated leptin levels have been demonstrated under insulin-resistant states such as obesity and hypertension, although their role in cardiac dysfunction is unknown. This study was designed to determine the impact of prediabetic insulin resistance on leptin levels and leptin-induced cardiac contractile response. Whole-body insulin resistance was generated with a 10-week dietary sucrose feeding. Contractile and intracellular Ca(2+) properties were evaluated in ventricular myocytes using an IonOptix system. The contractile indices analyzed included peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR(90)), maximal velocity of shortening/relengthening (+/-dL/dt), fura-fluorescence intensity change (deltaFFI) and decay rate (tau). Sucrose-fed rats displayed significantly elevated body weight and plasma leptin levels, depressed PS, +/-dL/dt, shortened TPS, prolonged TR(90) and tau, as well as reduced deltaFFI compared to the starch-fed control group. Leptin (1-1000 nM) elicited a concentration-dependent depression of PS and deltaFFI in myocytes from both starch and sucrose groups. Leptin-induced contractile depression was abolished by the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyle ester, elevation of the extracellular Ca(2+) concentration, the Janus activated kinase 2 inhibitor AG-490 or the mitogen activated protein kinase inhibitor SB203580 in myocytes from both sucrose and starch groups. Moreover, AG-490 and SB203580 unmasked a positive response of PS in myocytes from both groups. These data indicate that insulin resistance directly induces hyperleptinemia and cardiac contractile dysfunction, without affecting leptin-mediated cardiac contractile function at the myocyte level.

Topics: Animals; Blood Glucose; Calcium; Enzyme Inhibitors; Glucose Tolerance Test; Imidazoles; Insulin Resistance; Leptin; Male; Myocardial Contraction; Myocytes, Cardiac; NG-Nitroarginine Methyl Ester; Pyridines; Radioimmunoassay; Rats; Rats, Sprague-Dawley; Tyrphostins; Ventricular Function