Modulate Glucose Uptake Research Articles

Quantification, Variability, and Reproducibility of Basal Skeletal Muscle Glucose Uptake in Healthy Humans Using 18F-FDG PET/CT.

The quantification and variability of skeletal muscle glucose utilization (SMGU) in healthy subjects under basal (low insulin) conditions are poorly known. This information is essential early in clinical drug development to effectively interrogate novel pharmacologic interventions that modulate glucose uptake. The aim of this study was to determine test-retest characteristics and variability of SMGU within and between healthy subjects under basal conditions. Furthermore, different kinetic modeling strategies were evaluated to find the best-fitting model to assess SMGU studied by 18F-FDG. Six healthy male volunteers underwent 2 dynamic 18F-FDG PET/CT scans with an interval of 24 h. Subjects were admitted to the clinical unit to minimize variability in daily activities and food intake and restrict physical activity. 18F-FDG PET/CT scans of gluteal and quadriceps muscle area were obtained with arterial input. Regions of interest were drawn over the muscle area to obtain time-activity curves and standardized uptake values (SUVs) between 60 and 90 min. Spectral analysis of the data and kinetic modeling was performed using 2-tissue-irreversible (2T3K), 2-tissue-reversible, and 3-tissue-sequential-irreversible (3T5KS) models. Reproducibility was assessed by intraclass correlation coefficients (ICCs) and within-subject coefficient of variation (WSCV). SUVs in gluteal and quadriceps areas were 0.56±0.09 and 0.64±0.07. ICCs (with 90% confidence intervals in parentheses) were 0.88 (0.64-0.96) and 0.96 (0.82-0.99), respectively, for gluteal and quadriceps muscles, and WSCV for gluteal and quadriceps muscles was 2.2% and 3.6%, respectively. The rate of glucose uptake into muscle was 0.0016±0.0004 mL/mL⋅min, with an ICC of 0.94 (0.93-0.95) and WSCV of 6.6% for the 3T5KS model, whereas an ICC of 0.98 (0.92-1.00) and WSCV of 2.8% was obtained for the 2T3K model. 3T5KS demonstrated the best fit to the measured experimental points. Minimal variability in skeletal muscle glucose uptake was observed under basal conditions in healthy subjects. SUV measurements and rate of glucose uptake values were reproducible, with an average WSCV of less than 5%. Compared with SUV, the 3-tissue model adds information about kinetics between blood, intra- and intercellular compartments, and phosphorylation that may highlight the exact mechanisms of metabolic changes after pharmacologic intervention.

Preconditioning L6 Muscle Cells with Naringin Ameliorates Oxidative Stress and Increases Glucose Uptake.

Enhanced oxidative stress contributes to pathological changes in diabetes and its complications. Thus, strategies to reduce oxidative stress may alleviate these pathogenic processes. Herein, we have investigated Naringin mediated regulation of glutathione (GSH) & intracellular free radical levels and modulation of glucose uptake under oxidative stress in L6 cell lines. The results from the study demonstrated a marked decrease in glutathione with a subsequent increase in free radical levels, which was reversed by the pretreatment of Naringin. We also observed that the increased malondialdehyde level, the marker of lipid peroxidation on induction of oxidative stress was retrieved on Naringin pretreatment. Addition of Naringin (100 μM) showed approximately 40% reduction in protein glycation in vitro. Furthermore, we observed a twofold increase in uptake of fluorescent labeled glucose namely 2-(N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)Amino)-2-Deoxyglucose (2 - NBDG) on Naringin treatment in differentiated L6 myoblast. The increased uptake of 2-NBDG by L6 myotubes may be attributed due to the enhanced translocation of GLUT4. Our results demonstrate that Naringin activate GSH synthesis through a novel antioxidant defense mechanism against excessive Reactive Oxygen Species (ROS) production, contributing to the prevention of oxidative damage in addition to its effect on glycemic control.

Insulin therapy in insulin resistance: Could it be part of a lethal pathway?

Insulin therapy in insulin resistance: Could it be part of a lethal pathway?

Identification of adenine modulating AMPK activation in NIH/3T3 cells by proteomic approach.

AMPK is a fuel sensing enzyme that responds to a central role of energy homeostasis and contributes to the acceleration of insulin signaling. Recently, we have shown that exogenous adenine exerted anti-inflammatory effects through activation of AMPK, suggesting the treatment is a potent therapeutic strategy against hyperglycemia. Adenine had similar effects with 5-amino-4-imidazole-carboxamide riboside (AICAR, an AMPK activator) in modulating glucose uptake via AMPK-mediated signaling. In this study, we performed a 2DE-DIGE/MS-based approach to investigate the mechanism of exogenous adenine in NIH/3T3 cells. Our results provide evidence of a novel role for adenine in AMPK-mediated signaling and glucose metabolism and suggest potential therapeutic perspectives in insulin resistance and metabolic dysfunctions.

Procyanidins and their healthy protective effects against type 2 diabetes.

This review focuses on the role of procyanidins, the main group of flavonoids, on type 2 diabetes mellitus (T2DM) and insulin resistance. We compile the role of procyanidins on several animal models, and we evaluate their effects on target tissues and analyze the mechanisms involved. Procyanidin treatments in fructose or high-fat induced insulin resistant models were found to improve the damage induced by the diet, thus improving glycemia and insulin sensitivity. The same positive effects were also reported in models of late stage T2DM, in which pancreatic β-cells can no longer counteract hyperglycemia. More controversial results were found in genetically obese or cafeteria diet-induced insulin resistant models. Human studies, although limited, further support the hypoglycemic effect of procyanidins. Regarding their mechanisms, procyanidins have been found to target several tissues involved in glucose homeostasis, which is also discussed in the present review. In insulin-sensitive tissues, procyanidins modulate glucose uptake and lipogenesis and improve their oxidative/inflammatory state, the disruption of which is important in T2DM development. In the insulin-producing tissue, the pancreas, procyanidins modulate insulin secretion and production and β-cell mass, although the available results are divergent. Finally, the gut is another potential target for procyanidins. The available data suggest that modulation of the active glucagon-like peptide-1 (GLP-1) levels could partially explain the reported antihyperglycemic effect of these natural compounds.

The effect of tunicamycin on the glucose uptake, growth, and cellular adhesion in the protozoan parasite Crithidia fasciculata.

Crithidia fasciculata represents a very interesting model organism to study biochemical, cellular, and genetic processes unique to members of the family of the Trypanosomatidae. Thus, C. fasciculata parasitizes several species of insects and has been widely used to test new therapeutic strategies against parasitic infections. By using tunicamycin, a potent inhibitor of glycosylation in asparaginyl residues of glycoproteins (N-glycosylation), we demonstrate that N-glycosylation in C. fasciculata cells is involved in modulating glucose uptake, dramatically impacting growth, and cell adhesion. C. fasciculata treated with tunicamycin was severely affected in their ability to replicate and to adhere to polystyrene substrates and losing their ability to aggregate into small and large groups. Moreover, under tunicamycin treatment, the parasites were considerably shorter and rounder and displayed alterations in cytoplasmic vesicles formation. Furthermore, glucose uptake was significantly impaired in a tunicamycin dose-dependent manner; however, no cytotoxic effect was observed. Interestingly, this effect was reversible. Thus, when tunicamycin was removed from the culture media, the parasites recovered its growth rate, cell adhesion properties, and glucose uptake. Collectively, these results suggest that changes in the tunicamycin-dependent glycosylation levels can influence glucose uptake, cell growth, and adhesion in the protozoan parasite C. fasciculata.

A novel role of exogenous carbon monoxide on protecting cardiac function and improving survival against sepsis via mitochondrial energetic metabolism pathway.

Septic cardiac dysfunction is the main cause of death in septic patients. Here we investigate whether exogenous carbon monoxide can protect cardiac function and improve survival against sepsis by interfering with mitochondrial energetic metabolism. Male C57BL/6 mice were subjected to cecal ligation and puncture to induce sepsis. Exogenous carbon monoxide delivered from Tricarbonyldichlororuthenium (II) dimer (carbon monoxide releasing molecule II, 8mg/kg) was used intravenously as intervention. We found that carbon monoxide significantly improved cardiac function (LVEF 80.26 ± 2.37% vs. 71.21 ± 1.37%, P < 0.001; LVFS 43.52 ± 1.92% vs. 34.93 ± 1.28%, P < 0.001) and increased survival rate of septic mice (63% vs. 25%, P < 0.01). This phenomenon might be owing to the beneficial effect of carbon monoxide on abolishing the elevation of cardiac enzyme activity, cytokines levels and apoptosis rate, then attenuating cardiac injury in septic mice. Meanwhile, carbon monoxide significantly reversed the loss of mitochondrial number, effectively inhibited cardiac mitochondrial damage in septic mice by modulating glucose uptake, adenosine triphosphate and lactate content. Furthermore upregulation of peroxisome proliferator-activated receptor-γ coactivator-1α, nuclear respiratory factor 1 and mitochondrial transcription factor A genes in cardiac tissue were revealed in septic mice treated with carbon monoxide. Taken together, the results indicate that exogenous carbon monoxide effectively modulated mitochondrial energetic metabolisms by interfering with expression of peroxisome proliferator-activated receptor-γ coactivator-1α, nuclear respiratory factor 1 and mitochondrial transcription factor A genes, consequently exerted an important improvement in sepsis-induced cardiac dysfunction.

Screening for bioactive metabolites in plant extracts modulating glucose uptake and fat accumulation.

Dichloromethane and methanol extracts of seven different food and medicinal plants were tested in a screening platform for identification of extracts with potential bioactivity related to insulin-dependent glucose uptake and fat accumulation. The screening platform included a series of in vitro bioassays, peroxisome proliferator-activated receptor (PPAR) γ-mediated transactivation, adipocyte differentiation of 3T3-L1 cell cultures, and glucose uptake in both 3T3-L1 adipocytes and primary porcine myotubes, as well as one in vivo bioassay, fat accumulation in the nematode Caenorhabditis elegans. We found that dichloromethane extracts of aerial parts of golden root (Rhodiola rosea) and common elder (Sambucus nigra) as well as the dichloromethane extracts of thyme (Thymus vulgaris) and carrot (Daucus carota) were able to stimulate insulin-dependent glucose uptake in both adipocytes and myotubes while weekly activating PPARγ without promoting adipocyte differentiation. In addition, these extracts were able to decrease fat accumulation in C. elegans. Methanol extracts of summer savory (Satureja hortensis), common elder, and broccoli (Brassica oleracea) enhanced glucose uptake in myotubes but were not able to activate PPARγ, indicating a PPARγ-independent effect on glucose uptake.

Cocoa flavonoids attenuate high glucose-induced insulin signalling blockade and modulate glucose uptake and production in human HepG2 cells

Insulin resistance is the primary characteristic of type 2 diabetes. Cocoa and its main flavanol, (−)-epicatechin (EC), display some antidiabetic effects, but the mechanisms for their preventive activities related to glucose metabolism and insulin signalling in the liver remain largely unknown. In the present work, the preventive effect of EC and a cocoa polyphenolic extract (CPE) on insulin signalling and on both glucose production and uptake are studied in insulin-responsive human HepG2 cells treated with high glucose. Pre-treatment of cells with EC or CPE reverted decreased tyrosine-phosphorylated and total levels of IR, IRS-1 and -2 triggered by high glucose. EC and CPE pre-treatment also prevented the inactivation of the PI3K/AKT pathway and AMPK, as well as the diminution of GLUT-2 levels induced by high glucose. Furthermore, pre-treatment of cells with EC and CPE avoided the increase in PEPCK levels and the diminished glucose uptake provoked by high glucose, returning enhanced levels of glucose production and decreased glycogen content to control values. These findings suggest that EC and CPE improved insulin sensitivity of HepG2 treated with high glucose, preventing or delaying a potential hepatic dysfunction through the attenuation of the insulin signalling blockade and the modulation of glucose uptake and production.

Characterization and Modulation of Glucose Uptake in a Human Blood–Brain Barrier Model

The blood-brain barrier (BBB) plays a key role in limiting and regulating glucose access to glial and neuronal cells. In this work glucose uptake on a human BBB cell model (the hCMEC/D3 cell line) was characterized. The influence of some hormones and diet components on glucose uptake was also studied. ³H-2-deoxy-D-glucose ([³H]-DG) uptake for hCMEC/D3 cells was evaluated in the presence or absence of tested compounds. [³H]-DG uptake was sodium- and energy-independent. [³H]-DG uptake was regulated by Ca²⁺ and calmodulin but not by MAPK kinase pathways. PKC, PKA and protein tyrosine kinase also seem to be involved in glucose uptake modulation. Progesterone and estrone were found to decrease ³H-DG uptake. Catechin and epicatechin did not have any effect, but their methylated metabolites increased [³H]-DG uptake. Quercetin and myricetin decreased [³H]-DG uptake, and glucuronic acid-conjugated quercetin did not have any effect. These cells expressed GLUT1, GLUT3 and SGLT1 mRNA.

Overexpression of Ecdysoneless in Pancreatic Cancer and Its Role in Oncogenesis by Regulating Glycolysis

To study the expression and function of a novel cell-cycle regulatory protein, human ecdysoneless (Ecd), during pancreatic cancer pathogenesis. Immunohistochemical expression profiling of Ecd was done in nonneoplastic normal pancreatic tissues and pancreatic ductal adenocarcinoma lesions (from tissue microarray and Rapid Autopsy program) as well as precancerous PanIN lesions and metastatic organs. To analyze the biological significance of Ecd in pancreatic cancer progression, Ecd was stably knocked down in pancreatic cancer cell line followed by in vitro and in vivo functional assays. Normal pancreatic ducts showed very weak to no Ecd expression compared to significant positive expression in pancreatic cancer tissues (mean ± SE composite score: 0.3 ± 0.2 and 3.8 ± 0.2 respectively, P < 0.0001) as well as in PanIN precursor lesions with a progressive increase in Ecd expression with increasing dysplasia (PanIN-1-PanIN-3). Analysis of matched primary tumors and metastases from patients with pancreatic cancer revealed that Ecd is highly expressed in both primary pancreatic tumor and in distant metastatic sites. Furthermore, knockdown of Ecd suppressed cell proliferation in vitro and tumorigenicity of pancreatic cancer cells in mice orthotopic tumors. Microarray study revealed that Ecd regulates expression of glucose transporter GLUT4 in pancreatic cancer cells and was subsequently shown to modulate glucose uptake, lactate production, and ATP generation by pancreatic cancer cells. Finally, knockdown of Ecd also reduced level of pAkt, key signaling molecule known to regulate aerobic glycolysis in cancer cells. Ecd is a novel tumor-promoting factor that is differentially expressed in pancreatic cancer and potentially regulates glucose metabolism within cancer cells.

AMP-Activated Protein Kinase Upregulates Glucose Uptake in Thyroid PCCL3 Cells Independent of Thyrotropin

Glucose is transported into cells by specific glucose transporter proteins (GLUTs) that are widely expressed in a tissue-specific manner. The mechanisms that regulate glucose uptake and metabolism in thyroid cells are poorly defined. Recently, our group showed that AMP-activated protein kinase (AMPK) plays a pivotal role in the rat thyroid gland, downregulating iodide uptake by thyroid cells even in the presence of its main stimulator thyrotropin (TSH). Since AMPK increases glucose uptake in different tissues, and taken into consideration that in pathophysiological conditions such as thyroid cancer a negative correlation between iodide and glucose uptake occurs, we hypothesized that AMPK might modulate glucose uptake in thyroid cells. Rat follicular thyroid PCCL3 cells cultivated in Ham's F-12 supplemented with 5% calf serum and hormones were exposed to the AMPK pharmacological activator 5-aminoimidazole-4 carboxamide ribonucleoside (AICAR) or AMPK antagonist compound C for 24 hours either in the presence or absence of TSH. Glucose uptake was assessed in vitro using 2-deoxy-D-[(3)H]glucose. AMPK activation by AICAR induced a significant increase in glucose uptake by PCCL3 cells, an effect that was completely reversed by the AMPK inhibitor compound C. Also, the AICAR mediated increase in glucose uptake was detected either in the presence or absence of TSH. The mechanism by which AICAR increases glucose uptake is related to higher levels of GLUT 1 protein content and hexokinase (HK) activity in thyroid cells. Our results show that AMPK activation significantly upregulates GLUT 1 content and glucose uptake, and it also stimulates hexokinase activity, the first step of glycolysis.

Zingiber officinale extract exhibits antidiabetic potential via modulating glucose uptake, protein glycation and inhibiting adipocyte differentiation: an in vitro study.

Ginger, the rhizome of Zingiber officinale Roscoe (Zingiberaceae), a perennial herbaceous plant is native to Southern Asia. Study was aimed to evaluate antioxidant and antidiabetic potential of ginger extract and its characterization. Possible mode of action to elicit antidiabetic activity was also evaluated. Ethyl acetate extract of ginger (EAG) was evaluated for its antioxidant activity in terms of DPPH radical scavenging potential with an IC₅₀ value of 4.59 µg/ml. Antidiabetic activity of EAG was evaluated by estimating antiglycation potential (IC₅₀ 290.84 µg/ml). HPLC profiling of EAG revealed the presence of phenolic components, gingerol and shoagol as major constituents. After determining sub-toxic concentration of EAG (50 µg/ml), efficacy of extract to enhance glucose uptake in cell lines were checked in L6 mouse myoblast and myotubes. EAG was effective at 5 µg/ml concentration in both cases. Antibody based studies in treated cells revealed the effect of EAG in expressing Glut 4 in cell surface membrane compared to control. The antidiabetic effect of ginger was experimentally proved in the study and has concluded that the activity is initiated by antioxidant, antiglycation and potential to express or transport Glut4 receptors from internal vesicles.

Modulation of adipogenesis and glucose uptake by Curcuma longa extract in 3T3L1 and L6 cell lines – An in vitro study

ObjectiveTo evaluate the effects of ethyl acetate extract of Curcuma longa against modulation of glucose uptake and adipogenesis in cell line models. MethodsWe used 3T3L1 and L6 cells to investigate cytotoxicity, glucose uptake with 2-NBDG as probe and adipogenesis. All the analysis was done with flowcytometry. ResultsThe results showed that the extract did not possess any significant glucose uptake activity but it exhibited significant adipocyte differentiation potential. ConclusionsEthyl acetate extract of Curcuma longa exhibits significant antiadipogenesis and can be used as an effective drug for the treatment of obesity and other associated complications.

Mouse Resistin Modulates Adipogenesis and Glucose Uptake in 3T3-L1 Preadipocytes Through the ROR1 Receptor

Mouse resistin, a cysteine-rich protein primarily secreted from mature adipocytes, is involved in insulin resistance and type 2 diabetes. Human resistin, however, is mainly secreted by immune mononuclear cells, and it competes with lipopolysaccharide for the binding to Toll-like receptor 4, which could mediate some of the well-known proinflammatory effects of resistin in humans. In addition, resistin has been involved in the regulation of many cell differentiation and proliferation processes, suggesting that different receptors could be involved in mediating its numerous effects. Thus, a recent work identifies an isoform of Decorin (Δ Decorin) as a functional resistin receptor in adipocyte progenitors that may regulate white adipose tissue expansion. Our work shows that the mouse receptor tyrosine kinase-like orphan receptor (ROR)1 could mediate some of the described functions of resistin in 3T3-L1 adipogenesis and glucose uptake. We have demonstrated an interaction of mouse resistin with specific domains of the extracellular region of the ROR1 receptor. This interaction results in the inhibition of ROR1 phosphorylation, modulates ERK1/2 phosphorylation, and regulates suppressor of cytokine signaling 3, glucose transporter 4, and glucose transporter 1 expression. Moreover, mouse resistin modulates glucose uptake and promotes adipogenesis of 3T3-L1 cells through ROR1. In summary, our results identify mouse resistin as a potential inhibitory ligand for the receptor ROR1 and demonstrate, for the first time, that ROR1 plays an important role in adipogenesis and glucose homeostasis in 3T3-L1 cells. These data open a new line of research that could explain important questions about the resistin mechanism of action in adipogenesis and in the development of insulin resistance.

VEGF-induced ROS generation from NAD(P)H oxidases protects human leukemic cells from apoptosis

Vascular endothelial growth factor (VEGF) and reactive oxygen species (ROS) play critical roles in vascular pathophysiology and in hematological malignancies. VEGF is supposed to utilize ROS as messenger intermediates downstream of the VEGF receptor-2. NAD(P)H oxidase (Nox) family is a major source of cellular ROS and is implicated in increased ROS production in tumor cells. We previously demonstrated that B1647 cells, a human leukemic cell line, express Nox2 and Nox4, both at mRNA and protein level. We suggest here that the VEGF-induced increase in ROS can be related to Nox2 and Nox4 activities. Nox-derived ROS are involved in early signaling events such as the autophosphorylation of VEGF receptor-2, and in the modulation of glucose uptake, a cellular activity strictly bound to VEGF-induced leukemic cell proliferation, as shown by experiments with antioxidants and Nox inhibitors and siRNA. Nox-generated ROS are required to sustain B1647 cell viability and proliferation; in fact, antioxidants such as EUK-134 or Nox inhibitors and siRNA direct cells to apoptotic cell death, suggesting that manipulation of cellular Nox2 and Nox4 could affect survival of leukemic cells.

Placental expression of myostatin and follistatin-like-3 protein in a model of developmental programming

Maternal undernutrition during gestation is known to be detrimental to fetal development, leading to a propensity for metabolic disorders later in the adult lives of the offspring. Identifying possible mediators and physiological processes involved in modulating nutrient transport within the placenta is essential to prevent and/or develop treatments for the effects of aberrant nutrition, nutrient transfer, and detrimental changes to fetal development. A potential role for myostatin as a mediator of nutrient uptake and transport from the mother to the fetus was shown through the recent finding that myostatin acts within the human placenta to modulate glucose uptake and therefore homeostasis. The mRNA and protein expression of myostatin and its inhibitor, follistatin-like-3 (FSTL3), was studied in the placenta and skeletal muscle of a transgenerational Wistar rat model of gestational maternal undernutrition in which the F2 offspring postweaning consumed a high-fat (HF) diet. Alterations in placental characteristics and offspring phenotype, specifically glucose homeostasis, were evident in the transgenerationally undernourished (UNAD) group. Myostatin and FSTL3 protein expression were also higher (P < 0.05) in the placentae of the UNAD compared with the control group. At maturity, UNAD HF-fed animals had higher (P < 0.05) skeletal muscle expression of FSTL3 than control animals. In summary, maternal undernutrition during gestation results in the aberrant regulation of myostatin and FSTL3 in the placenta and skeletal muscle of subsequent generations. Myostatin, through the disruption of maternal nutrient supply to the fetus, may thus be a potential mediator of offspring phenotype.

Resistin modulates glucose uptake and glucose transporter‐1 (GLUT‐1) expression in trophoblast cells

The adipocytokine resistin impairs glucose tolerance and insulin sensitivity. Here, we examine the effect of resistin on glucose uptake in human trophoblast cells and we demonstrate that transplacental glucose transport is mediated by glucose transporter (GLUT)-1. Furthermore, we evaluate the type of signal transduction induced by resistin in GLUT-1 regulation. BeWo choriocarcinoma cells and primary cytotrophoblast cells were cultured with increasing resistin concentrations for 24 hrs. The main outcome measures include glucose transport assay using [3H]-2-deoxy glucose, GLUT-1 protein expression by Western blot analysis and GLUT-1 mRNA detection by quantitative real-time RT-PCR. Quantitative determination of phospho(p)-ERK1/2 in cell lysates was performed by an Enzyme Immunometric Assay and Western blot analysis. Our data demonstrate a direct effect of resistin on normal cytotrophoblastic and on BeWo cells: resistin modulates glucose uptake, GLUT-1 messenger ribonucleic acid (mRNA) and protein expression in placental cells. We suggest that ERK1/2 phosphorylation is involved in the GLUT-1 regulation induced by resistin. In conclusion, resistin causes activation of both the ERK1 and 2 pathway in trophoblast cells. ERK1 and 2 activation stimulated GLUT-1 synthesis and resulted in increase of placental glucose uptake. High resistin levels (50–100 ng/ml) seem able to affect glucose-uptake, presumably by decreasing the cell surface glucose transporter.

Adiponectin Reduces Glucotoxicity-Induced Apoptosis of INS-1 Rat Insulin-Secreting Cells on a Microfluidic Chip

Diabetes mellitus is a metabolic disorder characterized by elevated blood sugar and progressive failure of insulin-producing beta-cells. Persistent hyperglycemia and blood sugar fluctuation are two general phenomena in diabetic patients, and both of them can result in an increased frequency of beta-cell apoptosis. Therefore, rescuing pancreatic beta-cells from glucotoxicity-induced beta-cell apoptosis is increasing viewed as a promising means for curing. The aim of this study was to investigate whether adiponectin, an important cytokine expressed in adipose tissue, has a potential for the application as the antiapoptotic strategy. INS-1 rat insulin-secreting cell line was used in this study as a model of pancreatic beta-cells, because INS-1 cells show the susceptibility to glucotoxicity, as seen in beta-cells. INS-1 cells were cultured on a novel microfluidic chip with persistent perfusion and subsequently exposed to sustained high glucose (SHG) (25 mmol/l) or intermittent high glucose (IHG) (11.1 and 25 mmol/l glucose alternating every 12 h) in the absence or presence of adiponectin for 72 h. Using this device, we showed that IHG induced more serious impairment in INS-1 cells than did SHG, and adiponectin partially rescued INS-1 cells from glucotoxicity-induced apoptosis, dysfunction and reduction of insulin gene expression. Simultaneously, the mRNA expression of AMP-activated protein kinase (AMPK), which is a signaling protein that acts to modulate glucose uptake in skeletal muscle, was restored in the presence of adiponectin. Based on the above evidence, we suggest that adiponectin could reduce glucotoxicity-induced apoptosis of beta-cells, at least in part, by transiently activating AMPK signaling pathway.

Mildronate decreases carnitine availability and up-regulates glucose uptake and related gene expression in the mouse heart

Aims l-carnitine has been shown to play a central role in both fat and carbohydrate metabolisms. This study investigated whether acute and long-term treatments with an l-carnitine biosynthesis inhibitor, mildronate (3-(2,2,2-trimethylhydrazinium) propionate), modulate glucose uptake. Main methods The effects of acute and long-term administration of mildronate at a dose of 200 mg/kg (i.p. daily for 20 days) were tested in mouse blood plasma and heart. Key findings Acute administration of mildronate in vivo, or in vitro administration with perfusion buffer in isolated heart experiments, did not induce any effects on glucose blood concentration and uptake in the heart. Mildronate long-term treatment significantly decreased carnitine concentration in plasma and heart tissues, as well as increased the rate of insulin-stimulated glucose uptake by 35% and the expression of glucose transporter 4, hexokinase II, and insulin receptor proteins in mouse hearts. In addition, expression of both carnitine palmitoyltransferases IA and IB were significantly increased. Mildronate long-term treatment statistically significantly decreased fed state blood glucose from 6 ± 0.2 to 5 ± 0.1 mM, but did not affect plasma insulin and C-peptide levels. Significance Our experiments demonstrate for the first time that long-term mildronate treatment decreases carnitine content in the mouse heart and leads to increased glucose uptake and glucose metabolism-related gene expression.