Insulin Receptor Protein Kinase Research Articles

Avenanthramides Ameliorate Insulin Resistance by Modulating Gluconeogenesis and Glycogen Synthesis in HepG2 Cells.

Diabetes mellitus (DM) is a multifaceted metabolic condition, mainly defined by elevated blood glucose levels. A feature of type 2 DM includes insulin resistance (IR), which involves impairments within the insulin signaling pathways. Avenanthramides (AVNs) are phenolic alkaloids found in Avena sativa L. The major AVNs are AVN A, AVN B, and AVN C. They have been reported to offer benefits in preventing inflammation, cancer, and cardiovascular diseases. However, the effects of AVNs on the liver glucose metabolism pathways remain unknown. This study examined the effects and underlying mechanisms through which AVNs alleviate IR induced by free fatty acid (FFA) in HepG2 cells. The results indicated that FFA treatment significantly decreased glucose consumption by 34.54% compared to the control. However, treatments with AVN A, B, and C at 100 μM increased glucose uptake by 57.93%, 58.28%, and 53.10%, respectively, compared to FFA treatment alone. This effect occurs through the increased expression of glucose transporter 4. Furthermore, AVNs significantly enhanced the glycogen content. AVNs induced increased phosphorylation of insulin receptor substrate-1 (IRS-1), phosphatidylinositol-3-kinase (PI3K), and protein kinase B (Akt). AVNs treatment decreased the levels of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase in HepG2 cells. This effect was attributed to AMP-activated protein kinase activation and inhibition of forkhead box protein O1. Collectively, these results suggest that AVNs regulate glucose metabolism by activating the IRS-1/PI3K/Akt pathway, which is related to glycogen synthesis, and by inhibiting key molecules that promote gluconeogenesis.

Discovery and identification of natural alkaloids with potential to impact insulin resistance syndrome in Cyclocarya paliurus. (Batal) leaves by UPLC-QTOF-MS combined with HepG2 cells

Cyclocarya paliurus (Batal.) leaves, which contain a range of bioactive compounds, have been used as a traditional Chinese medicine homologous food since ancient times. However, there is a paucity of literature on comprehensive studies of alkaloids in the leaves of Cyclocarya paliurus (Batal.). For the first time, this study aimed to discover and identify alkaloids extracted from Cyclocarya paliurus (Batal.) leaves by ultra-high performance liquid chromatography-quadrupole-time-of-flight tandem mass spectrometry (UPLC-QTOF-MS). A total of ten alkaloids have been identified from Cyclocarya paliurus (Batal.) leaves based on accurate mass spectra (mass accuracy, isotopic spacing and distribution) and comparison to fragmentation spectra reported in the literature. In vitro, alkaloids alleviated insulin resistance by increasing glucose consumption and glycogen content in insulin resistance HepG2 cells. The RNA-seq and western blotting results showed that alkaloids could upregulate the expression of phosphatidylinositol 3-kinase (PI3K), and increase the phosphorylation of insulin receptor protein kinase B (AKT). This study not only clarified the chemical constituents and revealed that diverse alkaloids also presented from Cyclocarya paliurus (Batal.) leaves, also, it will provide chemical information on potential compounds for developing new drugs.

Identification of 1,3,4-Thiadiazolyl-Containing Thiazolidine-2,4-dione Derivatives as Novel PTP1B Inhibitors with Antidiabetic Activity.

Forty-one 1,3,4-thiadiazolyl-containing thiazolidine-2,4-dione derivatives (MY1-41) were designed and synthesized as protein tyrosine phosphatase 1B (PTP1B) inhibitors with activity against diabetes mellitus (DM). All synthesized compounds (MY1-41) presented potential PTP1B inhibitory activities, with half-maximal inhibitory concentration (IC50) values ranging from 0.41 ± 0.05 to 4.68 ± 0.61 μM, compared with that of the positive control lithocholic acid (IC50 = 9.62 ± 0.14 μM). The most potent compound, MY17 (IC50 = 0.41 ± 0.05 μM), was a reversible, noncompetitive inhibitor of PTP1B. Circular dichroism spectroscopy and molecular docking were employed to analyze the binding interaction between MY17 and PTP1B. In HepG2 cells, MY17 treatment could alleviate palmitic acid (PA)-induced insulin resistance by upregulating the expression of phosphorylated insulin receptor substrate and protein kinase B. In vivo, oral administration of MY17 could reduce the fasting blood glucose level and improve glucose tolerance and dyslipidemia in mice suffering from DM.

Regulated dynamic subcellular GLUT4 localization revealed by proximal proteome mapping in human muscle cells.

Regulation of glucose transport, which is central for control of whole-body metabolism, is determined by the amount of GLUT4 glucose transporter (also known as SLC2A4) in the plasma membrane (PM) of fat and muscle cells. Physiologic signals [such as activated insulin receptor or AMP-activated protein kinase (AMPK)] increase PM GLUT4. Here, we show that the distribution of GLUT4 between the PM and interior of human muscle cells is dynamically maintained, and that AMPK promotes PM redistribution of GLUT4 by regulating exocytosis and endocytosis. Stimulation of exocytosis by AMPK is mediated by Rab10 and the Rab GTPase-activating protein TBC1D4. APEX2 proximity mapping reveals that GLUT4 traverses both PM-proximal and PM-distal compartments in unstimulated muscle cells, further supporting retention of GLUT4 by a constitutive retrieval mechanism. AMPK-stimulated translocation involves GLUT4 redistribution among the same compartments traversed in unstimulated cells, with a significant recruitment of GLUT4 from the Golgi and trans-Golgi network compartments. Our comprehensive proximal protein mapping provides an integrated, high-density, whole-cell accounting of the localization of GLUT4 at a resolution of ∼20 nm that serves as a structural framework for understanding the molecular mechanisms regulating GLUT4 trafficking downstream of different signaling inputs in a physiologically relevant cell type.

Role of Oxidative Stress on Insulin Resistance in Diet-Induced Obesity Mice.

Insulin resistance is the link between obesity and type 2 diabetes mellitus. The molecular mechanism by which obese individuals develop insulin resistance has not yet been fully elucidated; however, inconclusive and contradictory studies have shown that oxidative stress may be involved in the process. Thus, this study aimed to evaluate the effect of reactive species on the mechanism of insulin resistance in diet-induced obese mice. Obese insulin-resistant mice were treated with N-acetylcysteine (NAC; 50 mg/kg per day, for 15 days) by means of oral gavage. Twenty-four hours after the last NAC administration, the animals were euthanized and their tissues were extracted for biochemical and molecular analyses. NAC supplementation induced improved insulin resistance and fasting glycemia, without modifications in food intake, body weight, and adiposity. Obese mice showed increased dichlorofluorescein (DCF) oxidation, reduced catalase (CAT) activity, and reduced glutathione levels (GSH). However, treatment with NAC increased GSH and CAT activity and reduced DCF oxidation. The gastrocnemius muscle of obese mice showed an increase in nuclear factor kappa B (NFκB) and protein tyrosine phosphatase (PTP1B) levels, as well as c-Jun N-terminal kinase (JNK) phosphorylation compared to the control group; however, NAC treatment reversed these changes. Considering the molecules involved in insulin signaling, there was a reduction in insulin receptor substrate (IRS) and protein kinase B (Akt) phosphorylation. However, NAC administration increased IRS and Akt phosphorylation and IRS/PI3k (phosphoinositide 3-kinase) association. The results demonstrated that oxidative stress-associated obesity could be a mechanism involved in insulin resistance, at least in this animal model.

Efficiency of Biobran/MGN-3, an Arabinoxylan Rice Bran, in Attenuating Diabetes-Induced Cognitive Impairment of the Hippocampus via Oxidative Stress and IR/Akt/NF-κB in Rats.

Type 2 diabetes mellitus (T2DM) is a common metabolic disease accompanied by cognitive impairment, hippocampal malfunctioning, and inflammation. Biobran/MGN-3, an arabinoxylan rice bran, has been shown to have an antidiabetic effect in streptozotocin-induced diabetic rats. The present study investigates Biobran's effect against diabetes-induced cognitive impairment and synaptotoxicity in the hippocampus via oxidative stress and the IR/A/NF-κB signaling pathway in rats. Diabetes was induced via i.p. injection of streptozotocin (STZ) (40 mg/kg BW); STZ-treated rats were then administered Biobran (100 mg/kg BW) for 4 wks. Biobran supplementation improved motor coordination and muscular strength, as assessed by Kondziella's inverted screen test. Biobran also improved concentration levels of glutathione (GSH), antioxidant enzymes, acetylcholine (ACh), dopamine, serotonin, insulin receptor (IR), and alpha serine-threonine protein kinase (Akt); it protected against elevated levels of glucose, total cholesterol, triglycerides, oxidative stress markers, TBARS, NO, AChE, and MAO; and it significantly decreased inflammatory cytokines levels of IL-1β, NF-κB, TNF-α, and amyloid β1-42. Moreover, Biobran ameliorated hippocampal histological alterations. Immunohistochemical observations showed that Biobran reduced overexpression of hippocampal synaptophysin and Ki67 relative to untreated diabetic rats. Biobran may ameliorate hippocampal alterations in diabetic rats via its antidiabetic, antiproliferative, anti-inflammatory, antiapoptotic, and antioxidant effects.

Assessment of Novel Oligopeptides from Rapeseed Napin (Brassica napus) in Protecting HepG2 Cells from Insulin Resistance and Oxidative Stress.

Oligopeptides (Thr-His-Leu-Pro-Lys (THLPK), His-Pro-Leu-Lys (HPLK), Leu-Pro-Lys (LPK), His-Leu-Lys (HLK), and Leu-His-Lys (LHK)) are newly identified from rapeseed napin (Brassica napus) protein-derived hydrolysates with the capability of upregulating glucose transporter-4 (GLUT4) expression and translocation. However, whether each of them enhances GLUT4 expression and translocation and their specific mechanisms remain unclear. Here, we assess the effects of the oligopeptides against insulin resistance (IR) and oxidative stress in hepatocytes and screen out the most antidiabetic one. Specifically, compared with other oligopeptides, LPK not only remarkably elevated glucose consumption to 8.45 mmol/L protein; superoxide dismutase (SOD) activity to 319 U/mg protein; GLUT4 expression and translocation; and phosphorylated level of insulin receptor substrate-1 (IRS-1), phosphatidylinositol 3-kinase (PI3K), and protein kinase B (Akt) (P < 0.05) but also remarkably attenuated the reactive oxygen species (ROS) level to 2255, lactate dehydrogenase (LDH) activity to 20.5 U/mg protein, malondialdehyde (MDA) content to 241 nmol/mg protein, and NO content to 1302 μmol/mL protein (P < 0.05). These findings demonstrated that antidiabetic oligopeptide LPK possessed the most potential to protect HepG2 cells from IR and oxidative stress via activating IRS-1/PI3K/Akt/GLUT4 and regulating common oxidative markers in vitro.

Genistein suppresses the inflammation and GSK-3 pathway in an animal model of spontaneous ovarian cancer

Background/aim Numerous studies show that cancer risk is reduced by consumption of soy-based foods containing genistein, but its effects on the glycogen synthase kinase-3 pathway (GSK-3) in ovarian cancer is unknown. Therefore, we tested the properties of genistein on inflammatory biomarkers and GSK-3 signaling pathways in the ovaries of old laying hens with ovarian cancer. Materials and methods A total of 300 laying hens were distributed into three groups as follows: group 1, animals fed a standard diet (comprising 22.39 mg of genistein/kg of diet); groups 2 and 3, animals fed a standard diet reconstituted with supplementation of 400 mg or 800 mg of genistein/kg of diet, respectively.Results Genistein modulated the inflammatory biomarkers by decreasing serum tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-8 (IL-8), and vascular endothelial growth factor (VEGF) compared with control (p < 0.001). Moreover, it upregulated insulin receptor substrate-1 (p-IRS-1) and protein kinase B (p-AKT), but downregulated GSK-3α and β after treatment. It acts in a dose-dependent manner. Conclusion Genistein exhibited an anticancer effect by reducing proinflammatory biomarkers levels and inhibiting GSK-3 expression in the ovaries of old laying hens. It is a potential candidate in the chemoprevention and/or treatment of ovarian cancer.

The insulin receptor family and protein kinase B (Akt) are activated in the heart by alkaline pH and α1-adrenergic receptors.

Insulin and insulin-like growth factor stimulate protein synthesis and cardioprotection in the heart, acting through their receptors (INSRs, IGF1Rs) and signalling via protein kinase B (PKB, also known as Akt). Protein synthesis is increased in hearts perfused at alkaline pHo to the same extent as with insulin. Moreover, α1-adrenergic receptor (α1-AR) agonists (e.g. phenylephrine) increase protein synthesis in cardiomyocytes, activating PKB/Akt. In both cases, the mechanisms are not understood. Our aim was to determine if insulin receptor-related receptors (INSRRs, activated in kidney by alkaline pH) may account for the effects of alkaline pHo on cardiac protein synthesis, and establish if α1-ARs signal through the insulin receptor family. Alkaline pHo activated PKB/Akt signalling to the same degree as insulin in perfused adult male rat hearts. INSRRs were expressed in rat hearts and, by immunoblotting for phosphorylation (activation) of INSRRs/INSRs/IGF1Rs, we established that INSRRs, together with INSRs/IGF1Rs, are activated by alkaline pHo. The INSRR/INSR/IGF1R kinase inhibitor, linsitinib, prevented PKB/Akt activation by alkaline pHo, indicating that INSRRs/INSRs/IGF1Rs are required. Activation of PKB/Akt in cardiomyocytes by α1-AR agonists was also inhibited by linsitinib. Furthermore, linsitinib inhibited cardiomyocyte hypertrophy induced by α1-ARs in cultured cells, reduced the initial cardiac adaptation (24 h) to phenylephrine in vivo (assessed by echocardiography) and increased cardiac fibrosis over 4 days. We conclude that INSRRs are expressed in the heart and, together with INSRs/IGF1Rs, the insulin receptor family provide a potent system for promoting protein synthesis and cardioprotection. Moreover, this system is required for adaptive hypertrophy induced by α1-ARs.

Activation of Hippocampal IR/IRS-1 Signaling Contributes to the Treatment with Zuogui Jiangtang Jieyu Decoction on the Diabetes-Related Depression.

Background Zuogui Jiangtang Jieyu decoction (ZJJ) is mainly used for the treatment of diabetes-related depression in current clinical applications and research. This study aims to investigate whether the brain IR/IRS-1 signaling pathway is involved in the therapeutic effect of ZJJ on depression-like behavior in diabetic rats. Methods Sprague–Dawley rats were fed with high-fat diet and subjected to streptozotocin injection to establish the diabetes animal model. After treatment with different doses of ZJJ (20.530 g/kg or 10.265 g/kg) for 4 weeks, the blood glucose level and peripheral insulin resistance were measured. The forced-swimming test (FST) and Morris water maze test (MWMT) were applied for the mood and cognitive function assessment. Then, the Western blot method was used to analyze the protein levels of insulin receptor (IR), insulin receptor substrate-1 (IRS-1), phosphatidylonositol-3-kinase (PI3K), and protein kinase B (PKB, also as known as AKT) in the hippocampus of diabetic rats. Meanwhile, the immunofluorescence method was performed to analyze the above proteins' expression in the neuron and astrocyte. At last, the levels of glycogen, lactate, and ATP were tested by the ELISA method. Additionally, the insulin-sensitive glucose transporter 4 (GLUT4) and the lactate transporter monocarboxylate transporter 4 (MCT4) were analyzed by the Western blot method. Results ZJJ administration significantly decreased the level of blood glucose and improved the peripheral insulin resistance in diabetic rats. Besides, ZJJ attenuated the depression-like behavior and the cognitive dysfunction in rats with diabetes. Furthermore, we found the upregulation of protein expression of phospho-IR, phospho-IRS-1, phospho-PI3K, and phospho-AKT in the hippocampus of diabetic rats after being treated with ZJJ. Moreover, the above proteins are increased not only in the neuron but also in the astrocyte after ZJJ administration. In addition, ZJJ increased the content of ATP, glycogen, and lactate, as well as the expression of GLUT4 and MCT4 in the hippocampus of diabetic rats. Conclusions These findings suggest that ZJJ improves the depression-like behavior of diabetic rats by activating the IR/IRS-1 signaling pathway in both hippocampal neuron and astrocyte. And the brain IR/IRS-1 signaling pathway plays an important role in astrocyte-neuron metabolic coupling, providing a potential mechanism by which the IR/IRS-1 signaling pathway may contribute to the treatment of ZJJ on diabetes-related depression.

Insulin-mediated glycemic responses and glucose homeostasis in black sea bream (Acanthopagrus schlegelii) fed different carbohydrate sources

The present study was conducted to investigate the effects of dietary carbohydrate sources on insulin mediated glycemic responses and glucose homeostasis in black seabream. Four isonitrogenous (48%) and isolipidic (12%) diets were formulated to contain 20% glucose (GLU), sucrose (SUC), dextrin (DEX) and wheat starch (WS), respectively. The black seabream was randomly distributed into 12 tanks (n = 3) at a stocking density of 12 fish per tank. After 2 weeks of feeding, fishes were starved for 48 h then re-fed and sampled at 0, 1, 3, 6, 12, and 24 h. The results showed that the concentration of serum glucose increased at 1 h, peaked at 3 h, decreased at 12 h, and returned to basal level at 24 h in all dietary groups (p < 0.05). In contrast, there were significant differences in postprandial insulin levels among all treatments, especially in the DEX group, which showed higher insulin level at 3 h after feeding (p < 0.05). Compared with 0 h, liver glycogen in the WS and DEX groups increase significantly at 6 h and was depleted at 24 h (p < 0.05). Hepatic enzyme activities such as glucokinase (GCK) and pyruvate kinase (PK) were influenced by sampling time and dietary carbohydrate sources (p < 0.05). Fish fed with the DEX diet showed the highest hepatic GCK and PK activities and the lowest phosphoenol pyruvate carboxykinase (PEPCK) activity at 3 h among all the treatments. Slightly but not significantly higher phosphofructo kinase (PFK) activity was observed in fish fed with the SUC diet than those fed with the GLU diet at 6 h post prandial (p > 0.05). The relative expression of insulin signaling pathways such as insulin receptor substrate1 (irs1) and protein kinase B (akt1) were significantly up-regulated at 3 h in the DEX group (p < 0.05). Meanwhile, the mRNA expression levels of glucokinase (gk) and pyruvate kinase (pk) were sensitive to hepatic glycolysis, and their expressions were up-regulated at 1, 3, 6 h, especially at 3 h in the DEX group. Genes such as glucose 6 phosphatase (g6pc) and phosphoenol pyruvate carboxykinase (pepck) played an important role in hepatic gluconeogenesis, and their expressions were inhibited at 1, 3 h. Overall, the results of present study indicated that dietary carbohydrate sources resulted in a hyperglycaemic situation 3 h after feeding, most likely as a response to glucose loading. Moreover, glucose metabolic responses were regulated by different carbohydrate sources at different time points, and plays a important role in clearing glucose through increased activity of insulin, glycolysis, and glycogenesis, along with gluconeogenesis suppression.

Structural characterization, hypoglycemic effects and antidiabetic mechanism of a novel polysaccharides from Polygonatum kingianum Coll. et Hemsl

The rhizome of Polygonatum kingianum has been used as a traditional medicine in China. In this study, a novel polysaccharides (PKPs-1) was isolated from P. kingianum and characterized by its molecular weight, primary structure. The hypoglycemic activity of PKPs-1was investigated by in vitro assay with the HepG2 cell line and in vivo test using STZ-induced diabetic mice. Results showed that the average molecular weight of PKPs-1 was 14.05 kDa and is composed mainly of glucose and mannose. Methylation analysis indicated that this polysaccharides fraction consisted mainly of β1,2-link glucose. Besides, PKPs-1 exhibited significant anti-hyperglycemic activity on STZ-induced mice, improved insulin tolerance, and affected the metabolism of serum lipids. Results of real-time quantitative PCR (RT-PCR) showed that PKPs-1 significantly increased the expression of insulin receptor substrate-1 (IRS-1), phosphoinositide 3-kinase (PI3K) and protein kinase B (AKT), indicating that PKPs-1 regulates glucose metabolism by activating the PI3K/AKT signaling pathway. This study provides new insights for investigating the hypoglycemic effects of PKPs-1 and suggests that PKPs-1 could be a promising functional food or medicine for treating T2DM.

Polyphenol-rich Trapa quadrispinosa pericarp extract ameliorates high-fat diet induced non-alcoholic fatty liver disease by regulating lipid metabolism and insulin resistance in mice.

In China, Trapa quadrispinosa (also called water caltrop) has long been used as a function food and folk medicine to treat diabetes mellitus for years. In the present study, the extract of T. quadrispinosa pericarp (TQPE) which mainly contains hydrolysable tannins was prepared to investigate the potential therapeutic action in non-alcoholic fatty liver disease (NAFLD) mice induced by high fat-diet (HFD). After the administration of TQPE (15, 30 mg/kg/day) for 8 weeks, the increased weight of body and liver were significantly suppressed. TQPE also ameliorated liver lipid deposition and reduced lipids parameters of blood in mice. Moreover, TQPE attenuated oxidative stress and showed a hepatoprotective effect in mice. TQPE was also found to decrease the value of homeostatic model assessment for insulin resistance. In addition, TQPE administration increased the phosphorylation of AMP-activated protein kinase (AMPK) and Acetyl-CoA carboxylase (ACC) and inhibited sterol regulatory element-binding protein (SREBP) in the liver tissue. Meanwhile, TQPE elevated insulin receptor substrate-1 (IRs-1) and protein kinase B (Akt) phosphorylation. These results reflected that, as a nature product, TQPE is a potential agent for suppressing the process of NAFLD via regulation of the AMPK/SREBP/ACC and IRs-1/Akt pathways.

Effects of Piceatannol and Resveratrol on Sirtuins and Hepatic Inflammation in High-Fat Diet-Fed Mice.

Piceatannol (PIC) is a natural hydroxylated analog of resveratrol (RSV) and considered as a potential metabolic regulator. The purpose of this study was to compare the effects of PIC and RSV on parameters affecting inflammation, oxidative stress, and sirtuins (Sirt). Male C57BL/6J mice, 20 weeks old, were assigned to the following groups; (1) lean control, (2) high-fat diet control (HF), (3) HF_PIC, and (4) HF_RSV. Oral administration of PIC and RSV (10 mg/kg/day) for 4 weeks improved glucose control as shown by decreasing levels of area under the curve (AUC) during the oral glucose tolerance test compared with HF group. PIC improved glycemic control by increasing hepatic levels of insulin receptor and AMP-activated protein kinase. PIC increased the levels of Sirt1, Sirt3, and Sirt6 and also increased two downstream targets of Sirt, peroxisome proliferator-activated receptor gamma coactivator 1-alpha and forkhead box O1, in the liver. The inflammatory markers, interleukin (IL)-1 and IL-6, in the liver were downregulated by RSV treatment. Exposure to PIC and RSV significantly lowered hepatic levels of tumor necrosis factor-alpha. However, PIC and RSV treatments showed minimal effects on hepatic markers of oxidative stress. The levels of antioxidant enzyme, NAD(P)H:quinone oxidoreductase 1 (NQO1), were only increased in livers of RSV-treated mice compared with HF control mice. In conclusion, PIC was superior to an equal concentration of RSV in the regulation of Sirt and its downstream targets as well as insulin signaling-related parameters, while RSV potentially suppressed levels of proinflammatory markers and increased NQO1 protein levels.

Insulin and Insulin Receptors in Adipose Tissue Development.

Insulin is a major endocrine hormone also involved in the regulation of energy and lipid metabolism via the activation of an intracellular signaling cascade involving the insulin receptor (INSR), insulin receptor substrate (IRS) proteins, phosphoinositol 3-kinase (PI3K) and protein kinase B (AKT). Specifically, insulin regulates several aspects of the development and function of adipose tissue and stimulates the differentiation program of adipose cells. Insulin can activate its responses in adipose tissue through two INSR splicing variants: INSR-A, which is predominantly expressed in mesenchymal and less-differentiated cells and mainly linked to cell proliferation, and INSR-B, which is more expressed in terminally differentiated cells and coupled to metabolic effects. Recent findings have revealed that different distributions of INSR and an altered INSR-A:INSR-B ratio may contribute to metabolic abnormalities during the onset of insulin resistance and the progression to type 2 diabetes. In this review, we discuss the role of insulin and the INSR in the development and endocrine activity of adipose tissue and the pharmacological implications for the management of obesity and type 2 diabetes.

Telmisartan increases hepatic glucose production via protein kinase C ζ-dependent insulin receptor substrate-1 phosphorylation in HepG2 cells and mouse liver.

BackgroundDysregulation of hepatic glucose production (HGP) contributes to the development of type 2 diabetes mellitus. Telmisartan, an angiotensin II type 1 receptor blocker (ARB), has various ancillary effects in addition to common blood pressure-lowering effects. The effects and mechanism of telmisartan on HGP have not been fully elucidated and, therefore, we investigated these phenomena in hyperglycemic HepG2 cells and high-fat diet (HFD)-fed mice.MethodsGlucose production and glucose uptake were measured in HepG2 cells. Expression levels of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase α (G6Pase-α), and phosphorylation levels of insulin receptor substrate-1 (IRS-1) and protein kinase C ζ (PKCζ) were assessed by western blot analysis. Animal studies were performed using HFD-fed mice.ResultsTelmisartan dose-dependently increased HGP, and PEPCK expression was minimally increased at a 40 μM concentration without a change in G6Pase-α expression. In contrast, telmisartan increased phosphorylation of IRS-1 at Ser302 (p-IRS-1-Ser302) and decreased p-IRS-1-Tyr632 dose-dependently. Telmisartan dose-dependently increased p-PKCζ-Thr410 which is known to reduce insulin action by inducing IRS-1 serine phosphorylation. Ectopic expression of dominant-negative PKCζ significantly attenuated telmisartan-induced HGP and p-IRS-1-Ser302 and -inhibited p-IRS-1-Tyr632. Among ARBs, including losartan and fimasartan, only telmisartan changed IRS-1 phosphorylation and pretreatment with GW9662, a specific and irreversible peroxisome proliferator-activated receptor γ (PPARγ) antagonist, did not alter this effect. Finally, in the livers from HFD-fed mice, telmisartan increased p-IRS-1-Ser302 and decreased p-IRS-1-Tyr632, which was accompanied by an increase in p-PKCζ-Thr410. ConclusionThese results suggest that telmisartan increases HGP by inducing p-PKCζ-Thr410 that increases p-IRS-1-Ser302 and decreases p-IRS-1-Tyr632 in a PPARγ-independent manner.

Hepatoprotective Effect of Loquat Leaf Flavonoids in PM2.5-Induced Non-Alcoholic Fatty Liver Disease via Regulation of IRs-1/Akt and CYP2E1/JNK Pathways.

Ambient air particulate matter (PM) represents a class of heterogeneous substances present in polluted air, which contains many harmful components. Exposure to ambient particulate matter in fine rages (PM2.5) is associated with non-alcoholic fatty liver disease (NAFLD). Loquat Leaf possesses pharmacological actions on NAFLD. As the main biological active ingredients, the potential therapeutic role of total flavonoids (TF) isolated from Loquat Leaf in PM2.5-induced NAFLD model remains unclear. The present study was designed to explore the hepatoprotective effect of TF in PM2.5-induced NAFLD mice with its related mechanisms of action. Mice were exposed to PM2.5 to induce NAFLD, and body weight, the ratio of liver to body weight, and blood lipids increased significantly compared with the control group. It was found that TF significantly reduced the above parameters in PM2.5-induced NAFLD mice. TF treatment alleviated oxidative stress by preventing the accumulation of oxidative product malondialdehyde (MDA) and by strengthening the anti-oxidative capacity of superoxide dismutase (SOD). TF was also found to reduce the alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity in the PM2.5 group. In addition, TF repaired the PM2.5-induced decline of insulin receptor substrate-1 (IRs-1) and protein kinase B (Akt) phosphorylation. Meanwhile, the data showed TF suppressed the expression of cytochrome P450 2E1(CYP2E1) and the phosphorylation of c-jun N-terminal kinase (JNK) in PM2.5-induced NAFLD. Taken together, these findings show that TF alleviate PM2.5-induced NAFLD via regulation of IRs-1/Akt and CYP2E1/JNK pathways, which may have potential for further development as novel therapeutic agents for NAFLD.

Obesity-induced insulin resistance and macrophage infiltration of the adipose tissue: A vicious cycle.

Obesity-induced insulin resistance and macrophage infiltration of the adipose tissue: A vicious cycle.

Neuritin promotes neurite and spine growth in rat cerebellar granule cells via L-type calcium channel-mediated calcium influx.

Neuritin is a neurotrophic factor that is activated by neural activity and neurotrophins. Its major function is to promote neurite growth and branching; however, the underlying mechanisms are not fully understood. To address this issue, this study investigated the effects of neuritin on neurite and spine growth and intracellular Ca2+ concentration in rat cerebellar granule neurons (CGNs). Incubation of CGNs for 24 h with neuritin increased neurite length and spine density; this effect was mimicked by insulin and abolished by inhibiting insulin receptor (IR) or mitogen‐activated protein kinase kinase/extracellular signal‐regulated kinase (ERK) activity. Calcium imaging and western blot analysis revealed that neuritin enhanced the increase in intracellular Ca2+ level induced by high K+, and stimulated the cell surface expression of CaV1.2 and CaV1.3 α subunits of the L‐type calcium channel, which was suppressed by inhibition of IR or mitogen‐activated protein kinase kinase/ERK. Treatment with inhibitors of L‐type calcium channels, calmodulin, and calcineurin (CaN) abrogated the effects of neuritin on neurite length and spine density. A similar result was obtained by silencing nuclear factor of activated T cells c4, which is known to be activated by neuritin in CGNs. These results indicate that IR and ERK signaling as well as the Ca2+/CaN/nuclear factor of activated T cells c4 axis mediate the effects of neuritin on neurite and spine growth in CGNs.Open Practices Open Science: This manuscript was awarded with the Open Materials Badge.For more information see: https://cos.io/our-services/open-science-badges/ Cover Image for this issue: doi: 10.1111/jnc.14195.

Egg white hydrolysate and peptide reverse insulin resistance associated with tumor necrosis factor-\u03b1 (TNF-\u03b1) stimulated mitogen-activated protein kinase (MAPK) pathway in skeletal muscle cells

PurposeExcessive formation of tumor necrosis factor-α (TNF-α), a pro-inflammatory cytokine, has been implicated in the development of insulin resistance in obesity and type-2 diabetes. In skeletal muscle, chronic exposure to TNF-α impairs insulin-stimulated glucose uptake and insulin signaling. The aim of this study is to investigate the effects of enzymatic egg white hydrolysate (EWH) and its responsible peptide, IRW, on TNF-α-induced insulin resistance and the underlying molecular mechanisms using rat skeletal muscle cells (L6 cells).MethodsInsulin resistance was induced by treating L6 cells with 5 ng/ml TNF-α for 24 h. Effects of EWH and IRW on glucose uptake were detected by glucose uptake assay, glucose transporter 4 (GLUT4) translocation by immunofluorescence, and western blot, while insulin-signaling pathway and mitogen-activated protein kinase (MAPK) pathway were investigated using western blot.ResultsAdding both EWH and IRW significantly improved glucose uptake in TNF-α-treated cells, increased activation of insulin receptor substrate (IRS-1) tyrosine residue and protein kinase B (Akt), whereas decreased activation of IRS-1 serine residue. In addition, TNF-α-induced activation of p38-mitogen-activated protein kinase (p38) and c-Jun N-terminal kinases (JNK) 1/2 were decreased by either EWH or IRW treatment.ConclusionEWH and IRW improve impaired insulin sensitivity by down-regulating the activation of p38 and JNK1/2 in TNF-α-treated skeletal muscle cells.