Promoted Glucose Consumption Research Articles

Ginsenoside Rb1 upregulates expressions of GLUTs to promote glucose consumption in adiopcytes

Previous studies have shown that ginsenoside Rb1 (Rb1), one of active components in ginseng, can activate insulin signaling pathway and promote translocation of glucose transporters (GLUTs) to increase glucose uptake in adipocytes. However, the effect of Rb1 on the expressions of GLUTs remains unknown. In this study, the effects of Rb1 on GLUT1 and GLUT4 were observed in 3T3-L1 adipocytes and epididymal adipose tissue of db/db obese diabetic mice. Male db/db mice were treated with Rb1 by intraperitoneal injection at the dosage of 20 mg x kg(-1) for 14 d. Rb1 reduced HOMA-IR significantly (P < 0.05, n = 5), and FBG and FINS sowed declining trend after treatment with Rb1. Rb1 recovered the expressions of GLUT1 and GLUT4 and phosphorylation of AKT in adipose tissue of db/db mice. In vitro, glucose consumption in 3T3-L1 adipocytes treated with 10 micromol x L(-1) Rb1 for 24 h was elevated (P < 0.05, n=3), and mRNA of GLUT1 and GLUT4 were up-regulated (P < 0.05, n=3) and proteins of GLUT1 and GLUT4 were also increased. AKT was activated in adipocytes treated with Rb1 for 3 h. It can be concluded that ginsenoside Rb1 can up-regulate the expression of GLUTs in adipose tissue, in addition to activate insulin signalling pathway, which may partially account for its insulin sensitizing activity and regulating effect of glucose metabolism.

Effects of rutaecarpine on inflammatory cytokines in insulin resistant primary skeletal muscle cells

It is now well established that inflammation plays an important role in the development of numerous chronic metabolic diseases including insulin resistance (IR) and type 2 diabetes (T2DM). Skeletal muscle is responsible for 75% of total insulin-dependent glucose uptake; consequently, skeletal muscle IR is considered to be the primary defect of systemic IR development. Our pre- vious study has shown that rutaecarpine (Rut) can benefit blood lipid profile, mitigate inflammation, and improve kidney, liver, pan- creas pathology status of T2DM rats. However, the effects of Rut on inflammatory cytokines in the development of IR-skeletal muscle cells have not been studied. Thus, our objective was to investigate effects of Rut on inflammatory cytokines interleukiri (IL)-1, IL-6 and tumor necrosis factor (TNF)-α in insulin resistant primary skeletal muscle cells (IR-PSMC). Primary cultures of skeletal muscle cells were prepared from 5 neonate SD rats, and the primary rat skeletal muscle cells were identified by cell morphology, effect of ru- taecarpine on cell proliferation by MTT assay. IR-PSMC cells were induced by palmitic acid (PA), the glucose concentration was measured by glucose oxidase and peroxidase (GOD-POD) method. The effects of Rut on inflammatory cytokines IL-1, IL-6 and TNF-α in IR-PSMC cells were tested by enzyme-linked immunosorbent assay (ELISA) kit. The results show that the primary skeletal muscle cells from neonatal rat cultured for 2-4 days, parallel alignment regularly, and cultured for 7 days, cells fused and myotube formed. It was shown that Rut in concentration 0-180. 0 μmol x L(-1) possessed no cytotoxic effect towards cultured primary skeletal muscle cells. However, after 24 h exposure to 0.6 mmol x L(-1) PA, primary skeletal muscle cells were able to induce a state of insulin resistance. The results obtained indicated significant decrease (P < 0.05 to P < 0.001) IL-1, IL-6 and TNF-α production by cultured IR-PSMC cells when incubating 24 hours with Rut, beginning from 20 to 180.0 μmol x L(-1). IL-1, IL-6 and TNF-α in the Rut treated groups were dose-dependently decreased compared with that in the IR-PSMC control group. Our results demonstrated that the Rut promoted glucose consumption and improved insulin resistance possibly through suppression of inflammatory cytokines in the IR-PSMC cells.

Berberine promotes glucose consumption independently of AMP-activated protein kinase activation.

Berberine is a plant alkaloid with anti-diabetic action. Activation of AMP-activated protein kinase (AMPK) pathway has been proposed as mechanism for berberine’s action. This study aimed to examine whether AMPK activation was necessary for berberine’s glucose-lowering effect. We found that in HepG2 hepatocytes and C2C12 myotubes, berberine significantly increased glucose consumption and lactate release in a dose-dependent manner. AMPK and acetyl coenzyme A synthetase (ACC) phosphorylation were stimulated by 20 µmol/L berberine. Nevertheless, berberine was still effective on stimulating glucose utilization and lactate production, when the AMPK activation was blocked by (1) inhibition of AMPK activity by Compound C, (2) suppression of AMPKα expression by siRNA, and (3) blockade of AMPK pathway by adenoviruses containing dominant-negative forms of AMPKα1/α2. To test the effect of berberine on oxygen consumption, extracellular flux analysis was performed in Seahorse XF24 analyzer. The activity of respiratory chain complex I was almost fully blocked in C2C12 myotubes by berberine. Metformin, as a positive control, showed similar effects as berberine. These results suggest that berberine and metformin promote glucose metabolism by stimulating glycolysis, which probably results from inhibition of mitochondrial respiratory chain complex I, independent of AMPK activation.

Cyclocarya paliurus extract modulates adipokine expression and improves insulin sensitivity by inhibition of inflammation in mice

Ethnopharmacological relevanceCyclocarya paliurus Batal., a Chinese native plant, is the sole species in its genus and its leaves have been widely used as a remedy for diabetes in traditional folk medicine. The study was undertaken to evaluate the effects of Cyclocarya paliurus leaves extracts (CPE) on adipokine expression and insulin sensitivity in mice. Materials and methodsMice were stimulated with conditioned medium (prepared from activated macrophages, Mac-CM) to induce adipose dysfunction and insulin resistance. Then mice were treated with CPE (100, 200 and 500mg/kg, ig.) or metformin (200mg/kg, ig.), followed by glucose and insulin intolerance, adipokine expression, phosphorylation of insulin receptor substrate (IRS-1) and glucose consumption measurement. ResultsCPE, as well as metformin effectively promoted glucose disposal in oral glucose tolerance test in normal mice. Mac-CM challenge induced glucose and insulin intolerance, but CPE reversed these alternations with increased glycogen content in muscle and liver, well demonstrating its beneficial effects on glucose homeostasis. RT-qPCR analysis showed that CPE inhibited TNF-a, IL-6, MCP-1 and resistin overexpression and effectively enhanced adiponectin expression in adipose tissue when mice were exposed to Mac-CM stimulation. Inflammation impaired insulin signaling in muscle, whereas CPE inhibited inflammation-induced serine phosphorylation of IRS-1 and effectively restored the phosphorylation of both IRS-1 at tyrosine residues and downstream Akt phosphorylation in response to insulin. Moreover, independently of insulin, CPE promoted glucose consumption in adipocytes under normal and inflammatory conditions. ConclusionAbove-mentioned results demonstrated that CPE beneficially regulated adipokines expression and ameliorated insulin resistance through inhibition of inflammation in mice.

Insulin Promotes Glucose Consumption via Regulation of miR-99a/mTOR/PKM2 Pathway

Insulin is known to regulate multiple cellular functions and is used for the treatment of diabetes. MicroRNAs have been demonstrated to be involved in many human diseases, including Type 2 diabetes. In this study, we showed that insulin decreased miR-99a expression levels, but induced glucose consumption and lactate production, and increased the expression of mTOR, HIF-1α and PKM2 in HepG2 and HL7702 cells. Forced expression of miR-99a or rapamycin treatment blocked insulin-induced PKM2 and HIF-1α expression, and glucose consumption and lactate production. Meanwhile, knockdown of HIF-1α inhibited PKM2 expression and insulin-induced glucose consumption. Taken together, these findings will reveal the role and mechanism ofinsulin in regulating glycolytic activities via miR-99a/mTOR.

Palmatine a Novel Anti‐adipogenic and Anti‐diabetic Alkaloid from an Indian Medicinal Plant Tinospora cordifolia

Palmatine a naturally existing alkaloid isolated from a medicinal plant Tinospora cordifolia commonly used in Indian System of Medicine for various ailments has been tested for its biological activities. Palmatine in 3T3‐L1 (murine pre‐adipocytes) cells effectively inhibited adipocyte differentiation and promoted glucose consumption. Quantification of genes (Glut‐4, PPARα, PPARγ, LPL, FAS and Adiponectin) involved in diabetes and obesity using Real Time PCR and comparing the activity of Palmatine with specific inhibitors of insulin pathway (IRTK, PI3K, Glut 4) reveals that Palmatine is a novel anti‐adipogenic and anti‐diabetic molecule. It is also evidenced by the up regulation of Glut‐4 and PPARα; and down regulation of PPARγ, LPL and FAS. Oxidative stress is the common pathway linking and intensifying in all metabolic disorders. However, the anti‐oxidant property of Palmatine studied by hydrogen peroxide induced cytotoxicity study in 3T3 L1 cells was found to be mild as compared to the proven antioxidant flavonoid Quercitin. In conclusion, the results strongly support the anti‐diabetic, anti‐adipogenic and mild antioxidant activity of the naturally occurring Palmatine in Tinospora cordifolia an antidiabetic‐medicinal plant used in India which could serve as a lead pharmaceutical agent to benefit the growing diabetic/obese population. The work was sponsored by the Department of Science &amp; Technology, Govt. of India

A novel agonist of PPAR-γ based on barbituric acid alleviates the development of non-alcoholic fatty liver disease by regulating adipocytokine expression and preventing insulin resistance

Non-alcoholic fatty liver disease (NAFLD) is a frequent kind of metabolic syndrome, which included a wide spectrum of liver damage and closely associated with insulin resistance and other metabolic syndromes such as obesity, type II diabetes, hyperglycemia, etc. Recently, a new series of PPARγ ligands based on barbituric acid has been designed, in which 5-(4-(benzyloxy)benzylidene)pyrimidine-2,4,6(1H,3H,5H)-trione (SKLB102) showed a high affinity with PPARγ. The current study aimed to evaluate the protective effect of SKLB102 on NAFLD and investigate the underlying mechanisms. In vivo, oral administration of SKLB102 prevented the pathological development, as demonstrated by reducing liver weight and visceral fat effectively, decreasing the serum levels of alanine transaminase, TNF-α and glucose, diminishing the hepatic triglyceride and malondialdehyde content and recovering the abnormal down-regulation of LDL. Histological examination of liver sections by Oil Red O and H&E staining confirmed the protective effect of SKLB102 on NAFLD. Furthermore, SKLB102 elevated the serum level of adiponectin, reduced the serum level of leptin and prevented insulin resistance. Western blots indicated that SKLB102 increased the hepatic AMPK activities and CPT-1 expression. In vitro, SKLB102 showed the ability of significantly enhancing adiponectin expression and inhibiting leptin expression in 3T3-L1 adipocytes. Furthermore, SKLB102 could promote glucose consumption in HepG2 cells in the presence of 0.1 μM insulin. In conclusion, our current study provided strong evidence that SKLB102 had potent ability to reduce fat deposition and protect liver against NAFLD through regulating adipocytokine expression and preventing insulin resistance, which might be of protective value for the prevention of NAFLD.

Derivatives of Dictyostelium differentiation-inducing factors promote mitogen-activated IL-2 production via AP-1 in Jurkat cells

Aims Differentiation-inducing factors (DIFs) are chlorinated alkylphenones found in the cellular slime mold Dictyostelium discoideum. DIF derivatives exhibit antiproliferative activities and promote glucose consumption in mammalian cells in vitro. Here, we assessed the ability of DIFs to regulate the immune system in a mammalian cell-line and investigated their mechanisms of action. Main methods We examined the effects of 30 DIF derivatives on concanavalin A-induced interleukin-2 (IL-2) production (CIIP) in Jurkat T-cells. We also examined the effects of these DIF derivatives on the activity of three transcription factors required for CIIP: namely, activator protein-1 (AP-1), nuclear factor of activated T-cells (NFAT), and nuclear factor kappa B (NFκB). Key findings A reporter gene assay suggested that 2 DIF derivatives, termed DIF-1(+ 1) and DIF-3(3 M), significantly promoted CIIP in Jurkat cells, at least in part, by enhancing the activity of AP-1. These 2 DIF derivatives had no significant effect on concanavalin A-induced interferon-γ production. Significance The results suggest that DIF derivatives could be developed as novel drugs for the activation of IL-2 production and resultant stimulation of the immune system.

Regulation of IL-2 production in Jurkat cells by Dictyostelium-derived factors

Aims Differentiation-inducing factors (DIFs) are chlorinated alkylphenones found in the cellular slime mold Dictyostelium discoideum. DIF derivatives exhibit antiproliferative activities and promote glucose consumption in mammalian cells in vitro. In this study, we assessed the ability of DIFs to regulate the immune system and investigated their mechanisms of action. Main methods We examined the effects of 30 DIF derivatives on concanavalin A-induced IL-2 production (CIIP) in Jurkat T-cells. We also examined the effects of some DIF derivatives on the activity of AP-1 (activator protein-1), NFAT (nuclear factor of activated T-cells), and NFκB (nuclear factor kappa B), which are transcription factors required for CIIP. Key findings Of the derivatives tested, some compounds suppressed CIIP as well as the known immunosuppressants cyclosporine A and FK506. A reporter gene assay revealed that 4 DIF derivatives tested suppressed CIIP, at least in part, by inhibiting the activity of AP-1, NFAT, and/or NFκB. Unlike cyclosporine A and FK506, the DIF derivatives had little effect on concanavalin A-induced interferon-γ production in Jurkat cells. Significance The present results suggest that DIF derivatives could be developed as novel immunosuppressive drugs.

Biological activities of novel derivatives of DIF-1 isolated from Dictyostelium

The differentiation-inducing factor-1 (DIF-1) is a lipophilic signal molecule (chlorinated alkylphenone) that induces stalk cell differentiation in the cellular slime mold Dictyostelium discoideum. In addition, DIF-1 and its derivatives have been shown to possess anti-leukemic activity and glucose consumption-promoting activity in vitro in mammalian cells. In this study, to assess the chemical structure–effect relationship of DIF-1, we synthesized eight derivatives of DIF-1 and investigated their stalk cell-inducing activity in Dictyostelium cells and pharmacological activities in mammalian cells. Of the derivatives, two amide derivatives of DIF-1, whose hydrophobic indexes are close to that of DIF-1, induced stalk cell differentiation as strongly as DIF-1 in Dictyostelium cells. It was also found that some derivatives suppressed cell growth in human K562 leukemia cells and promoted glucose consumption in mouse 3T3-L1 cells. These results give us valuable information as to the chemical structure–effect relationship of DIF-1.

Exploitation of the derivatives of Dictyostelium differentiation-inducing factor-1, which promote glucose consumption in mammalian cells

Aims The differentiation-inducing factor-1 (DIF-1) is a signal molecule that induces stalk cell formation in the cellular slime mold Dictyostelium discoideum. DIF-1 has also been shown to possess pharmacological activities, such as the suppression of tumor cell growth and the promotion of glucose uptake in non-transformed mammalian cells. In this study, we tried to develop compounds that possess weaker anti-tumor activity and stronger glucose uptake-promoting activity than DIF-1. Main methods We investigated the in vitro effects of 12 derivatives of DIF-1 on glucose consumption in mouse 3T3-L1 cells and on cell growth in K562 human leukemia cells. We also examined the effect of a good compound on the blood glucose concentration in KK-Ay diabetic mice. Key findings We found that some derivatives at 20 μM promoted glucose consumption more than twice as fast as the control. Of the derivatives, a compound named DIF-1(3M), which has a weaker anti-leukemic effect than DIF-1, promoted glucose consumption as strongly as DIF-1 in confluent 3T3-L1 cells. While DIF-1 at 20 μM was inhibitory to the cell growth of 3T3-L1, DIF-1(3M) at 20 μM exhibited no inhibitory effect on the growing cells. We also found that DIF-1(3M) injected (10–12.5 mg/kg body weight) intraperitoneally in mice tended to lower the blood glucose concentration. Significance The present results open the possibility for the development of new agents that possess strong glucose-uptake-promoting activity but little anti-tumor activity and may have therapeutic potential for the treatment of diabetes and/or obesity.

Establishment of New Highly Insulin-Sensitive Cell Lines and Screening of Compounds to Facilitate Glucose Consumption

To obtain compounds that promote glucose uptake in muscle cells, the novel cell lines A31-IS derived from Balb/c 3T3 A31 and C2C12-IS from mouse myoblast C2C12 were established. In both cell lines, glucose consumption was induced by insulin and suppressed by the addition of Akt-activating kinase inhibitor. The A31-IS cells highly express the insulin receptor β chains, Glut4, and uncoupling protein-3, as compared to the parent Balb /c 3T3 A31 cells, and C2C12-IS cells highly express the insulin receptor β chain as compared to its parent cell line. Using A31-IS cells, we screened our library compounds and obtained three compounds, DF-4394, DF-4451, and DG-5451. These compounds dose-dependently promoted glucose consumption in A31-IS cells and facilitated [3H]-2-deoxyglucose uptake in differentiated C2C12-IS cells. The compounds that we obtained from the library screening will be good candidates for improving insulin resistance in muscle cells.

Acute effect of antidiabetic 1,4‐dihydropyridine compound cerebrocrast on cardiac function and glucose metabolism in the isolated, perfused normal rat heart

Diabetes mellitus (DM) is an important cardiovascular risk factor and is associated with abnormalities in endothelial and vascular smooth muscle cell function, evoked by chronic hyperglycemia and hyperlipidemia. Chronic insulin deficiency or resistance is marked by decreases in the intensity of glucose transport, glucose phosphorylation, and glucose oxidation, plus decreases in ATP levels in cardiac myocytes. It is important to search for new agents that promote glucose consumption in the heart and partially inhibit extensive fatty acid beta-oxidation observed in diabetic, ischemia. When the oxygen supply for myocardium is decreased, the heart accumulates potentially toxic intermediates of fatty acid beta-oxidation, that is, long-chain acylcarnitine and long-chain acyl-CoA metabolites. Exogenous glucose and heart glycogen become an important compensatory source of energy. Therefore we studied the effect of the antidiabetic 1,4-dihydropyridine compound cerebrocrast at concentrations from 10(-10) M to 10(-7) M on isolated rat hearts using the method of Langendorff, on physiological parameters and energy metabolism. Cerebrocrast at concentrations from 10(-10) M to 10(-7) M has a negative inotropic effect on the rat heart. It inhibits L-type Ca(2+)channels thereby diminishing the cellular Ca(2+) supply, reducing contractile activity, and oxygen consumption, that normally favors enhanced glucose uptake, metabolism, and production of high-energy phosphates (ATP content) in myocardium. Cerebrocrast decreases heart rate and left ventricular (LV) systolic pressure; at concentrations of 10(-10) M and 10(-9) M it evokes short-term vasodilatation of coronary arteries. Increase of ATP content in the myocytes induced by cerebrocrast has a ubiquitous role. It can preserve the integrity of the cell plasma membranes, maintain normal cellular function, and inhibit release of lactate dehydrogenase (LDH) from cells that is associated with diabetes and heart ischemia. Administration of cerebrocrast together with insulin shows that both compounds only slightly enhance glucose uptake in myocardium, but significantly normalize the rate of contraction and relaxation ( +/- dp/dt). The effect of insulin on coronary flow is more pronounced by administration of insulin together with cerebrocrast at a concentration of 10(-7) M. Cerebrocrast may promote a shift of glucose consumption from aerobic to anerobic conditions (through the negative inotropic properties), and may be very significant in prevention of cardiac ischemic episodes.