Glucose Entry Research Articles

Incretin Hormone Release Does Not Involve Hepatic Portal Vein Glucose Sensors

The incretin effect, which is defective in individuals with T2D, involves the secretion of GLP-1 and GIP when glucose is given orally, but not when it is infused via a peripheral vein. Glucose ingestion results in a hepatic portal vein/arterial glucose gradient. This activates portal vein glucose sensors which play an important role in the regulation of glucose metabolism during feeding. It is unknown whether these sensors contribute to GLP-1 or GIP secretion during glucose ingestion. To test the hypothesis that portal but not peripheral vein glucose infusion would stimulate incretin hormone secretion, intraportal (infusion) and femoral artery (sampling) catheters were placed in 6 dogs. Two weeks later the animals were administered an oral glucose tolerance test (OGTT; 0.9 g/kg) and one and two weeks after that the arterial plasma glucose profile which occurred during each OGTT was matched by infusing glucose either into the portal (Po) or a peripheral (Pe) vein. The AUCs for glucose (0-180 min; total) were nearly identical: 8251±325, 8219±334 and 8200±341 mg/dl (180 min) in the OGTT, Po and Pe treatments, respectively. The total glucose administered was reduced in the Pe (562±76 mg/kg) compared to the OGTT and Po treatments (900±0 and 856±92 mg/kg, respectively). During the 1st hour the arterial insulin and c-peptide responses were ∼25% greater in the OGTT compared to the other treatments, whereas there was <5% difference in their levels in Po vs. Pe. Arterial glucagon fell modestly in all treatments. Oral glucose administration increased arterial GLP-1 and GIP levels by >6-fold over basal, but their levels did not change in Po or Pe. The 0-180 min AUCs for GLP-1 were 669±218, 315±128 and 323±81 pg/ml, and for GIP were 14725±1506, 2556±529 and 2658±316 pg/ml in the OGTT, Po and Pe treatments, respectively. Thus, activation of portal vein glucose sensors did not stimulate the release of, or insulinotropic response to, incretin hormones in the overnight fasted dog, but portal vein glucose entry enhanced glucose clearance. Disclosure D.S. Edgerton: Speaker's Bureau; Self; Novo Nordisk A/S. G. Kraft: None. M.S. Smith: None. L. Moore: None. B. Farmer: None. H. Sara: None. M. Scott: None. M. Moore: None. M.A. Nauck: Advisory Panel; Self; AstraZeneca, Boehringer Ingelheim GmbH, Eli Lilly and Company, Fractyl Laboratories, Inc., GlaxoSmithKline plc., Berlin-Chemie AG, Merck Sharp & Dohme Corp., Novo Nordisk A/S. Speaker's Bureau; Self; AstraZeneca, Boehringer Ingelheim GmbH, Eli Lilly and Company, Berlin-Chemie AG, Merck Sharp & Dohme Corp., Medscape, Novo Nordisk A/S. Research Support; Self; AstraZeneca, Berlin-Chemie AG, Eli Lilly and Company, Merck Sharp & Dohme Corp., Novartis AG, GlaxoSmithKline plc., Novo Nordisk A/S. Consultant; Self; Nordic Bioscience, Empros. A.D. Cherrington: Advisory Panel; Self; Biocon. Consultant; Self; Boston Scientific Corporation. Research Support; Self; Boston Scientific Corporation. Consultant; Self; Eli Lilly and Company. Advisory Panel; Self; Fractyl Laboratories, Inc.. Stock/Shareholder; Self; Fractyl Laboratories, Inc.. Consultant; Self; Galvani Bioelectronics Limited. Research Support; Self; Galvani Bioelectronics Limited. Consultant; Self; MedImmune. Advisory Panel; Self; Metavention. Stock/Shareholder; Self; Metavention. Consultant; Self; Novo Nordisk Inc.. Research Support; Self; Novo Nordisk Inc.. Advisory Panel; Self; NuSirt Biopharma, Inc., Sensulin Labs, LLC.. Other Relationship; Self; Sensulin Labs, LLC.. Consultant; Self; Silver Lake. Research Support; Self; Silver Lake. Consultant; Self; Thermalin Diabetes, LLC., Thetis Pharmaceuticals LLC.. Stock/Shareholder; Self; Thetis Pharmaceuticals LLC.. Advisory Panel; Self; VTV Therapeutics. Consultant; Self; VTV Therapeutics. Advisory Panel; Self; Zafgen. Research Support; Self; Zafgen. Stock/Shareholder; Self; Zafgen. Consultant; Self; Abvance. Other Relationship; Self; Abvance. Consultant; Self; California Institute for Biomedical Research (Calibr). Advisory Panel; Self; These Three Medical, Inc (T3M).

Upregulation of Krebs cycle and anaerobic glycolysis activity early after onset of liver ischemia.

The liver is a highly vascularized organ receiving a dual input of oxygenated blood from the hepatic artery and portal vein. The impact of decreased blood flow on glucose metabolism and how hepatocytes could adapt to this restrictive environment are still unclear. Using the left portal vein ligation (LPVL) rat model, we found that cellular injury was delayed after the onset of liver ischemia. We hypothesized that a metabolic adaptation by hepatocytes to maintain energy homeostasis could account for this lag phase. Liver glucose metabolism was characterized by 13C- and 1H-NMR spectroscopy and analysis of high-energy metabolites. ALT levels and caspase 3 activity in LPVL animals remained normal during the first 12 h following surgery (P<0.05). Ischemia rapidly led to decreased intrahepatic tissue oxygen tension and blood flow (P<0.05) and increased expression of Hypoxia-inducible factor 1-alpha. Intrahepatic glucose uptake, ATP/ADP ratio and energy charge level remained stable for up to 12 h after ligation. Entry of glucose in the Krebs cycle was impaired with lowered incorporation of 13C from [U-13C]glucose into glutamate and succinate from 0.25 to 12 h after LPVL. However, total hepatic succinate and glutamate increased 6 and 12 h after ischemia (P<0.05). Glycolysis was initially reduced (P<0.05) but reached maximum 13C-lactate (P<0.001) and 13C-alanine (P<0.01) enrichments 12 h after LPVL. In conclusion, early liver homeostasis stems from an inherent ability of ischemic hepatocytes to metabolically adapt through increased Krebs cycle and glycolysis activity to preserve bioenergetics and cell viability. This metabolic plasticity of hepatocytes could be harnessed to develop novel metabolic strategies to prevent ischemic liver damage.

Loss of a Negative Regulator of mTORC1 Induces Aerobic Glycolysis and Altered Fiber Composition in Skeletal Muscle

SUMMARYThe conserved GATOR1 complex consisting of NPRL2-NPRL3-DEPDC5 inhibits mammalian target of rapamycin complex 1 (mTORC1) in response to amino acid insufficiency. Here, we show that loss of NPRL2 and GATOR1 function in skeletal muscle causes constitutive activation of mTORC1 signaling in the fed and fasted states. Muscle fibers of NPRL2 knockout animals are significantly larger and show altered fiber-type composition, with more fast-twitch glycolytic and fewer slow-twitch oxidative fibers. NPRL2 muscle knockout mice also have altered running behavior and enhanced glucose tolerance. Furthermore, loss of NPRL2 induces aerobic glycolysis and suppresses glucose entry into the TCA cycle. Such chronic activation of mTORC1 leads to compensatory increases in anaplerotic pathways to replenish TCA intermediates that are consumed for biosynthetic purposes. These phenotypes reveal a fundamental role for the GATOR1 complex in the homeostatic regulation of mitochondrial functions (biosynthesis versus ATP) to mediate carbohydrate utilization in muscle.

Dissociation of Hexokinase II Binding to VDAC Increases State 3 Respiration and Reduces Membrane Potential Repolarization Time in Mitochondria Isolated From Brain and Heart

Hexokinase II (HKII) plays a critical role in ATP production by catalyzing the initial step in glucose metabolism and maintaining the gradient for glucose entry into the cell. HKII also closely interacts with the mitochondrial outer membrane protein, voltage dependent anion channel (VDAC), to permit the channeling of mitochondrial generated ATP, its substrate, for use in cellular metabolism. It has been reported that adding protease to mitochondrial isolation buffer may improve mitochondrial respiration. However, proteases could potentially degrade the HKII‐VDAC protein interaction at the interphase between mitochondrial outer membrane and extra‐matrix space. We hypothesize that protease interferes with the association of HKII to VDAC and this alters mitochondrial bioenergetics. To test this, we isolated mitochondria from brain and heart of guinea pigs to determine the consequences of HKII binding and unbinding to VDAC on mitochondrial respiration and membrane potential (ΔΨm). Mitochondria were isolated by differential centrifugation using the same isolation buffers except one with and one without the presence of protease. We examined the HKII binding to mitochondria, specifically to VDAC, between the two mitochondrial groups using Western blot (WB) and immunoprecipitation (IP). We measured the rate of O2 consumption using mitochondrial substrates before and after adding ADP and evaluated changes in ΔΨm using TMRM fluorescent dye. WB showed, in both heart and brain mitochondria, binding of HKII to mitochondria in the absence of protease was evident, but this was not detected in mitochondria isolated in the presence of protease. Moreover, IP experiments with cross‐linking revealed HKII‐VDAC association in the protease‐free isolation buffer, but not in the buffer containing protease. Mitochondrial respiration as determined by states 3 (ADP respiration) and 4 (ADP depleted respiration) respiration was significantly slower when HKII was bound to VDAC compared to when it was not bound to VDAC. ΔΨm repolarization following ADP‐induced depolarization (state 3 respiration) was substantially delayed when mitochondria were isolated in the absence, in contrast to the presence, of protease. Our results indicate that HKII binding to isolated mitochondria directly modulates oxidative phosphorylation, possibly by regulating the transfer of substrates and metabolites, including ADP/ATP, via VDAC. Overexpression of HKII has been implicated in cytoprotection; however, the underlying mechanisms is not well understood. The implications of the increased association or dissociation of HKII‐VDAC in cell physiology (survival) and/or pathophysiology (cell death) will be further explored in intact cardiac and brain cells.Support or Funding InformationThis work was supported in part by the Veterans Administration (BX‐002539‐01) and the National Institutes of Health (R01 HL131673‐01A1 and P01‐GM066730).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Upregulation of sodium-glucose cotransporter 2 (SGLT2) expression in cultured senescent endothelial cells and in arterial sites at risk in vivo in rats

Endothelial senescence is thought to promote endothelial dysfunction and the subsequent development of cardiovascular diseases. The EMPA-REG trial has shown that sodium-glucose cotransporter 2 (SGLT2) inhibition is associated with a reduced risk of cardiovascular mortality in type 2 diabetic patients, but the protective mechanism remains unclear. SGLT2 mRNA has not been detected in control endothelial cells (ECs). This study examined the possibility that SGLT2 contributes to endothelial senescence and dysfunction and, if so, to characterize the underlying mechanism. Endothelial cells isolated from porcine coronary arteries were used at passage 1. Senescence was assessed using senescence-associated beta-galactosidase activity (SA-beta-gal activity), protein level by Western blot analysis, oxidative stress using dihydroethidium, and NO formation by electronic paramagnetic resonance. Exposure of ECs to HG (25 mM) for 96 h increased the level of SA-beta-gal activity and of senescence markers (p21 and p16) and oxidative stress, decreased eNOS expression and NO formation, and increased the expression of VCAM-1 and tissue factor (TF). Both HG and H 2 O 2 induced the appearance of SGLT2 mRNA, increased SGLT2 protein level and SGLT2-mediated glucose entry in ECs. An increased expression level of SGLT2 and VCAM-1, and a down-regulation of eNOS were observed at arterial sites at risk (aortic cross) compared with those at low risk (thoracic aorta) in young rats. These findings indicate that premature ECs ageing is characterized by the down-regulation of NO formation and the expression of pro-atherothrombotic factors, and is associated with the redox-sensitive upregulation of SGLT2 expression promoting excessive glucose entry. The fact that an increased SGLT2 expression level is observed in vivo at arterial sites at risk, suggests that inhibition of SGLT2 might be an attractive strategy to protect the cardiovascular system.

Galanin enhances systemic glucose metabolism through enteric Nitric Oxide Synthase-expressed neurons

ObjectiveDecreasing duodenal contraction is now considered as a major focus for the treatment of type 2 diabetes. Therefore, identifying bioactive molecules able to target the enteric nervous system, which controls the motility of intestinal smooth muscle cells, represents a new therapeutic avenue. For this reason, we chose to study the impact of oral galanin on this system in diabetic mice. MethodsEnteric neurotransmission, duodenal contraction, glucose absorption, modification of gut–brain axis, and glucose metabolism (glucose tolerance, insulinemia, glucose entry in tissue, hepatic glucose metabolism) were assessed. ResultsWe show that galanin, a neuropeptide expressed in the small intestine, decreases duodenal contraction by stimulating nitric oxide release from enteric neurons. This is associated with modification of hypothalamic nitric oxide release that favors glucose uptake in metabolic tissues such as skeletal muscle, liver, and adipose tissue. Oral chronic gavage with galanin in diabetic mice increases insulin sensitivity, which is associated with an improvement of several metabolic parameters such as glucose tolerance, fasting blood glucose, and insulin. ConclusionHere, we demonstrate that oral galanin administration improves glucose homeostasis via the enteric nervous system and could be considered a therapeutic potential for the treatment of T2D.

Molecular mechanism for ET-1-induced insulin resistance in skeletal muscle cells

Insulin resistance is a condition where the sensitivity to insulin of the tissues expressing insulin receptor (InsR) is decreased due to a functional disturbance of InsR-mediated intracellular signaling. Insulin promotes the entry of glucose into the tissues and skeletal muscle is the most important tissue responsible for the insulin's action of decreasing blood glucose levels. Endothelin-1 (ET-1), a potent vasoconstrictor and pro-inflammatory peptide, induces insulin resistance through a direct action on skeletal muscle. However, the signaling pathways of ET-1-induced insulin resistance in skeletal muscle remain unclear. Here we show molecular mechanism underlying the inhibitory effect of ET-1 on insulin-stimulated Akt phosphorylation and glucose uptake in myotubes of rat L6 skeletal muscle cell line. mRNA expression levels of differentiation marker genes, MyoD and myogenin, were increased during L6 myoblasts differentiation into myotubes. Some of myotubes possessed the ability to spontaneously contract. In myotubes, insulin promoted Akt phosphorylation at Thr308 and Ser473, and [3H]-labelled 2-deoxy-D-glucose ([3H]2-DG) uptake. The insulin-facilitated Akt phosphorylation and [3H]2-DG uptake were inhibited by ET-1. The inhibitory effect of ET-1 was counteracted by blockade of ET type A receptor (ETAR), inhibition of Gq/11 protein, and siRNA knockdown of G protein-coupled receptor kinase 2 (GRK2). The exogenously overexpressed GRK2 directly bound to endogenous Akt and their association was facilitated by ET-1. In summary, activation of ETAR with ET-1 inhibits insulin-induced Akt phosphorylation and [3H]2-DG uptake in a Gq/11 protein- and GRK2-dependent manner in skeletal muscle. These findings indicate that ETAR and GRK2 are potential targets for insulin resistance.

Sulforaphane Delays Fibroblast Senescence by Curbing Cellular Glucose Uptake, Increased Glycolysis, and Oxidative Damage

Increased cell senescence contributes to the pathogenesis of aging and aging-related disease. Senescence of human fibroblasts in vitro may be delayed by culture in low glucose concentration. There is also accumulating evidence of senescence delay by exposure to dietary bioactive compounds that activate transcription factor Nrf2. The mechanism of cell senescence delay and connection between these responses is unknown. We describe herein that the cruciferous vegetable-derived metabolite, sulforaphane (SFN), activates Nrf2 and delays senescence of human MRC-5 and BJ fibroblasts in vitro. Cell senescence is associated with a progressive and marked increased rate of glucose metabolism through glycolysis. This increases mitochondrial dysfunction and overwhelms defences against reactive metabolites, leading to increasing proteomic and genomic oxidative damage. Increased glucose entry into glycolysis in fibroblast senescence is mainly mediated by increased hexokinase-2. SFN delayed senescence by decreasing glucose metabolism on the approach to senescence, exhibiting a caloric restriction mimetic-like activity and thereby decreased oxidative damage to cell protein and DNA. This was associated with increased expression of thioredoxin-interacting protein, curbing entry of glucose into cells; decreased hexokinase-2, curbing entry of glucose into cellular metabolism; decreased 6-phosphofructo-2-kinase, downregulating formation of allosteric enhancer of glycolysis fructose-2,6-bisphosphate; and increased glucose-6-phosphate dehydrogenase, downregulating carbohydrate response element- (ChRE-) mediated transcriptional enhancement of glycolysis by Mondo/Mlx. SFN also enhanced clearance of proteins cross-linked by transglutaminase which otherwise increased in senescence. This suggests that screening of compounds to counter senescence-associated glycolytic overload may be an effective strategy to identify compounds with antisenescence activity and health beneficial effects of SFN in longevity may involve delay of senescence through glucose and glycolytic restriction response.

Inflow of oxygen and glucose in brain tissue induced by intravenous norepinephrine: relationships with central metabolic and peripheral vascular responses.

As an essential part of sympathetic activation that prepares the organism for "fight or flight," peripheral norepinephrine (NE) plays an important role in regulating cardiac activity and the tone of blood vessels, increasing blood flow to the heart and the brain and decreasing blood flow to the organs not as necessary for immediate survival. To assess whether this effect is applicable to the brain, we used high-speed amperometry to measure the changes in nucleus accumbens (NAc) levels of oxygen and glucose induced by intravenous injections of NE in awake freely moving rats. We found that NE at low doses (2-18 μg/kg) induces correlative increases in NAc oxygen and glucose, suggesting local vasodilation and enhanced entry of these substances in brain tissue from the arterial blood. By using temperature recordings from the NAc, temporal muscle, and skin, we show that this central effect is associated with strong skin vasoconstriction and phasic increases in intrabrain heat production, indicative of metabolic neural activation. A tight direct correlation between NE-induced changes in metabolic activity and NAc levels of oxygen and glucose levels suggests that local cerebral vasodilation is triggered via a neurovascular coupling mechanism. Our data suggest that NE, by changing vascular tone and cardiac activity, triggers a visceral sensory signal that rapidly reaches the central nervous system via sensory nerves and induces neural activation. This neural activation leads to a chain of neurovascular events that promote entry of oxygen and glucose in brain tissue, thus preventing any possible metabolic deficit during functional activation. NEW & NOTEWORTHY Using high-speed amperometry and thermorecording in freely moving rats, we demonstrate that intravenous norepinephrine at physiological doses induces rapid correlative increases in nucleus accumbens oxygen and glucose levels coupled with increased intrabrain heat production. Although norepinephrine cannot cross the blood-brain barrier, by changing cardiac activity and vascular tone, it creates a sensory signal that reaches the central nervous system via sensory nerves, induces neural activation, and triggers a chain of neurovascular events that promotes intrabrain entry of oxygen and glucose.

Insulin and Its Cardiovascular Effects: What Is the Current Evidence?

In this article, we examine the nature of the complex relationship between insulin and cardiovascular disease. With metabolic abnormalities comes increased risk for cardiovascular complications. We discuss the key factors implicated in development and progression of cardiovascular disease, its relationship to insulin therapy, and what can be learned from large, recent cardiovascular outcome studies. Preclinical studies suggest that insulin has positive effects of facilitating glucose entry into cells and maintaining euglycemia and negative effects of favoring obesity and atherogenesis under certain conditions. Confounding this relationship is that cardiovascular morbidity is linked closely to duration and control of diabetes, and insulin is often used in patients with diabetes of longer duration. However, more recent clinical studies examining the cardiovascular safety of insulin therapy have been reassuring. Diabetes and cardiovascular outcomes are closely linked. Many studies have implicated insulin resistance and hyperinsulinemia as a major factor for poor cardiovascular outcomes. Additional studies link the anabolic effects of therapeutic insulin to weight gain, along with hypoglycemia, which may further aggravate cardiovascular risk in this population. Though good glycemic control has been shown to improve microvascular risks in type 1 and type 2 diabetes, what are the known cardiovascular effects of insulin therapy? The ORIGIN trial suggests at least a neutral effect of the basal insulin glargine on cardiovascular outcomes. Recent studies have demonstrated that ultra-long-acting insulin analogs like insulin degludec are non-inferior to insulin glargine with regard to cardiovascular outcomes.

PTEN, Insulin Resistance and Cancer.

The tumor suppressor PTEN serves as a negative regulator of PI3K/PTEN/Akt signaling pathway that regulates cellular functions such as cell growth, differentiation, proliferation and migration. The PI3K/PTEN/Akt signaling cascades might also have effect on glucose uptake via translocation of GLUT-4. Insulin controls energy storage and the whole body glucose homeostasis. Its binding to insulin receptor on the surface of diverse cells allows glucose entry into cells, and activates a variety of cellular actions. Insulin resistance is a common metabolic feature and established risk factor of many diseases. Its fundamental principle is inability of insulin to exert its normal metabolic effects, and nutrient imbalance and abnormal lipid accumulation in skeletal muscle, liver and adipose tissues. We review the literature on the structure and function of PTEN and its involvement in insulin resistance and tumor regulation, and summarized the detailed scientific achievements on this topic. Suppressing PTEN expression plays a role in pro- or anti-inflammatory state during insulin resistance associated with obesity. Selective disruption of PTEN in pancreatic α-cells demonstrates that a lack of PTEN reduces circulating glucagon levels and protects against hyperglycemia and insulin resistance in high-fat diet-fed mice. Loss-of-function PTEN mutations in adipose tissue results in systemic glucose tolerance and insulin sensitivity improvement because of ascended recruitment of the GLUT-4 towards the membrane. Targeting tissuespecific PTEN deletion improves insulin sensitivity and protects from systemic insulin resistance. PTEN, as an important tumor suppressor gene, is frequently deleted or mutated in a variety of human tumors. Inactivation of PTEN by loss-of-function mutations leads to deregulated hyperproliferation of cells, leading to oncogenic transformation. Considering PTEN's important role in insulin resistance and tumor regulation, targeting the PTEN gene and/or protein will likely provide an efficient strategy for therapeutic intervention in cancer and metabolic diseases like type 2 diabetes mellitus, obesity, and cardiovascular dysfunction.

IL-7 Restores T Lymphocyte Immunometabolic Failure in Septic Shock Patients through mTOR Activation

T lymphocyte alterations are central to sepsis pathophysiology, whereas related mechanisms remain poorly understood. We hypothesized that metabolic alterations could play a role in sepsis-induced T lymphocyte dysfunction. Samples from septic shock patients were obtained at day 3 and compared with those from healthy donors. T cell metabolic status was evaluated in the basal condition and after T cell stimulation. We observed that basal metabolic content measured in lymphocytes by nuclear magnetic resonance spectroscopy was altered in septic patients. Basal ATP concentration, oxidative phosphorylation (OXPHOS), and glycolysis pathways in T cells were decreased as well. After stimulation, T lymphocytes from patients failed to induce glycolysis, OXPHOS, ATP production, GLUT1 expression, glucose entry, and proliferation to similar levels as controls. This was associated with significantly altered mTOR, but not Akt or HIF-1α, activation and only minor AMPKα phosphorylation dysfunction. IL-7 treatment improved mTOR activation, GLUT1 expression, and glucose entry in septic patients' T lymphocytes, leading to their enhanced proliferation. mTOR activation was central to this process, because rapamycin systematically inhibited the beneficial effect of recombinant human IL-7. We demonstrate the central role of immunometabolism and, in particular, mTOR alterations in the pathophysiology of sepsis-induced T cell alterations. Our results support the rationale for targeting metabolism in sepsis with recombinant human IL-7 as a treatment option.

Abstract P414: Blockade of Sodium Glucose Cotransporter 2 by Canagliflozin Suppresses High Glucose-induced Angiotensinogen Augmentation in Renal Proximal Tubular Cells

Intrarenal angiotensinogen (AGT) is mainly expressed in proximal tubular cells (PTC). AGT is increased by hyperglycemia (HG) in type 1 and 2 diabetes mellitus, which causes elevated intrarenal angiotensin formation contributing to the development of hypertension and kidney injury. Sodium glucose co-transporter 2 (SGLT2) is abundantly expressed in early PTC and may promote increased intrarenal AGT by increasing intracellular glucose levels. This study tested the effects of canagliflozin (CANA), an SGLT2 inhibitor, on HG-induced AGT elevation in cultured PTC. Mouse PTC were treated with 5, 10 or 25 mM glucose. 0-10 μM CANA was applied one hour before glucose treatment. AGT mRNA and protein levels were measured by digital PCR and western blot analysis. Levels of intracellular reactive oxygen species (ROS) were determined with H 2 DCF-DA. Tempol, an antioxidant, was used to test if elevated ROS is involved in HG-induced AGT upregulation. 10 mM glucose increased AGT protein levels at 12 hours (3.06±0.48-fold compared with 5 mM glucose) and treatment with 10 μM CANA attenuated the AGT augmentation (1.68±0.05-fold). AGT protein levels were also increased by 25 mM glucose; but CANA did not suppress the AGT levels caused by this glucose concentration. In PTC treated with 10 mM glucose for 12 hours, the suppressing effect on AGT upregulation was observed with 1 and 10 μM CANA. Lower concentrations of CANA (0.01 and 0.1 μM) did not lower AGT protein levels significantly. Elevated AGT mRNA expression by glucose was also attenuated by CANA. Treatment of PTC with 1 mM pyruvate also increased AGT expression levels, indicating that glycolysis is involved in HG-induced AGT upregulation. After incubation of PTC with 10 mM glucose for 12 hours, intracellular ROS levels were elevated compared to baseline (4.24±0.23-fold) and these were also inhibited by CANA (0.2±0.08-fold). Furthermore, tempol attenuated AGT upregulation in HG-treated PTC. These results indicate that enhanced glucose entry via SGLT2 into PTC elevates intracellular ROS generation by stimulation of glycolysis and consequent AGT augmentation. Thus, SGLT2 inhibition by CANA may limit HG-induced AGT stimulation which suppress intrarenal angiotensin formation and reduce kidney injury in diabetes mellitus.

Glucose Uptake Measurement and Response to Insulin Stimulation in In Vitro Cultured Human Primary Myotubes.

Skeletal muscle is the largest glucose deposit in mammals and largely contributes to glucose homeostasis. Assessment of insulin sensitivity of muscle cells is of major relevance for all studies dedicated to exploring muscle glucose metabolism and characterizing metabolic alterations. In muscle cells, glucose transporter type 4 (GLUT4) proteins translocate to the plasma membrane in response to insulin, thus allowing massive entry of glucose into the cell. The ability of muscle cells to respond to insulin by increasing the rate of glucose uptake is one of the standard readouts to quantify muscle cell sensitivity to insulin. Human primary myotubes are a suitable in vitro model, as the cells maintain many features of the donor phenotype, including insulin sensitivity. This in vitro model is also suitable for the test of any compounds that could impact insulin responsiveness. Measurements of the glucose uptake rate in differentiated myotubes reflect insulin sensitivity. In this method, human primary muscle cells are cultured in vitro to obtain differentiated myotubes, and glucose uptake rates with and without insulin stimulation are measured. We provide a detailed protocol to quantify passive and active glucose transport rates using radiolabeled [3H] 2-deoxy-D-Glucose ([3H]2dG). Calculation methods are provided to quantify active basal and insulin-stimulated rates, as well as stimulation fold.

A non-linear mixed-effects model to describe the effect of acarbose intake on postprandial glycaemia in a single rat

A non-linear mixed-effects model is proposed to assess the impact of acarbose over time on postprandial glycaemia in a single rat. The model is based on two compartments, one representing the entry of glucose in the blood and the other its exit. The rat was submitted to two treatments: ingestion of starch and ingestion of starch plus acarbose. The model showed great suitability, with inferences on the behavior of glucose levels in response to treatments and supplying a richer description than just the area under the curve. The marginal curves for the two treatments are similar during the first moments; however, after reaching the peak of glucose concentration, they progressively became separate due to acarbose treatment and reached the initial levels more quickly. The proposed model, albeit with a single sample unit, showed similar results to those with larger samples; in other words, acarbose significantly attenuates glycaemia after ingestion of starch.

The carboxy-terminal region of the TBC1D4 (AS160) RabGAP mediates protein homodimerization

TBC1D4 (also known as AS160) is a Rab·GTPase-activating protein (RabGAP) which functions in insulin signaling. TBC1D4 is critical for translocation of glucose transporter 4 (GLUT4), from an inactive, intracellular, vesicle-bound site to the plasma membrane, where it promotes glucose entry into cells. The TBC1D4 protein is structurally subdivided into two N-terminal phosphotyrosine-binding (PTB) domains, a C-terminal catalytic RabGAP domain, and a disordered segment in between containing potential Akt phosphorylation sites. Structural predictions further suggest that a region C-terminal to the RabGAP domain adopts a coiled-coil motif. We show that C-terminal region (CTR) region is largely α-helical and mediates TBC1D4 RabGAP dimerization. RabGAP catalytic activity and thermal stability appear to be independent of CTR-mediated dimerization.

Dissecting copper homeostasis in diabetes mellitus.

Diabetes Mellitus (DM) is characterized by elevated blood glucose levels (hyperglycemia). It can occur due to impaired secretion or action of the hormone insulin, which is produced by pancreatic beta-cells to promote the entry of glucose into the cells. It is known that hyperglycemia has an important role in the production of reactive oxygen species in all types of DM and that an imbalance of transition metal as Cu and Fe plays a pivotal role in stimulating the oxidative stress. Different levels of some transition metals, as Cu, Fe, Mn, and Zn has been reported comparing diabetic animal models with the control group. An increased Cu status is also described in diabetic patients. Homeostasis of Cu depends on distinct proteins, where Cu(I)-ATPases are important transmembrane proteins for acquisition, active transport, distribution and elimination of Cu ions. In this review we first provide an overview of the literature about the relationship between diabetes and copper, the modulation of Cu(I)-ATPases activity and protein expression in DM, to next discuss the alternative treatments for diabetes using Cu chelation. © 2016 IUBMB Life, 69(4):255-262, 2017.

Gluconeogenesis, non-essential amino acid synthesis and substrate partitioning in chicken embryos during later development

We aimed to quantify the rate of gluconeogenesis (GNG), non-essential amino-acid (NEAA) synthesis, and substrate partitioning to the Krebs cycle in embryonic (e) day e14 and e19 chicken embryos. An in ovo continuous tracer infusion approach was employed to test the hypotheses that GNG and NEAA synthesis in developing chicken embryo increases from e14 to e19. [13 C6]Glucose or [13 C3]glycerol was continuously infused (8 h) into the chorio-allantoic compartment of eggs on e14 and e19. Glucose entry rate, Cori cycling, and GNG were higher (P < 0.05) in e19 compared to e14 embryos, presumably to support higher glycogen deposition in liver and muscle. Whereas de novo synthesis of alanine, aspartate, and glutamate via glycolysis and the Krebs cycle was higher (P < 0.01) in e14 embryos, synthesis of these NEAA from glycerol was higher (P < 0.05) in e19 compared to e14 embryos. These patterns of glucose and glycerol utilization suggest a metabolic shift to conserve glucose for glycogen synthesis and an increased utilization of yolk glycerol (from triacylglyceride) after e14. Although the contribution of glycerol to GNG in e19 embryos was higher (P < 0.05) than that in e14 embryos, the contribution of glycerol to GNG (1.3 to 6.0%) was minor. Based on [13 C6]glucose tracer kinetics, the activities of both pyruvate carboxylase (PC) and pyruvate dehydrogenase (PDH) in the liver were higher (P < 0.05) in e19 embryos; whereas the higher (P < 0.01) relative activity of liver PC compared to PDH in e14 embryos suggests a greater anaplerotic flux into the Krebs cycle. In summary, the in ovo continuous tracer infusion approach allowed for a measurement of chicken embryo whole body and liver metabolism over a shorter window of development. This study provided quantitative estimates of the developmental shifts in substrate utilization, GNG, and NEAA synthesis by chicken embryos, as well as qualitative estimates of the activities of enzymes central to the Krebs cycle, glucose, and fatty acid metabolism.

Implicaciones hemodinámicas y renales de los inhibidores del cotransportador sodio-glucosa tipo 2 en el contexto de la diabetes mellitus tipo 2

In DM2, there is increased expression of the proximal glucose transporter SGLT2. The increased glucose reabsorption from the urine to the proximal tubule and subsequently to the bloodstream, has three direct effects on the prognosis of patients with DM2: a) it increases the daily glucose load by raising the renal threshold for glucose, thus augmenting requirements for oral antidiabetics and insulin. This progressive increase occurs throughout the course of the disease and in parallel with the increase in renal mass (renal hypertrophy); b) because of the greater glucose reabsorption, glycosuria is lower than the level corresponding to glycaemia, decreasing the stimulus on the tubuloglomerular feedback system of the distal nephron. As a result, the glomerular vasodilation caused by hyperglycaemia is not arrested, maintaining glomerular hyperfiltration, and c) the excess glucose transported to the proximal tubular cells modifies their redox status, increasing local production of glycosylating products and activating local production of proinflammatory and profibrotic proliferative mediators. These mediators are responsible for the direct free radical damage to proximal tubular cells, for increased SGLT2 expression, increased production of collagen IV and extracellular matrix, and activation of monocyte/macrophages able to cause endothelial injury. The use of SGLT2 inhibitors not only reduces the reabsorption of glucose from the glomerular filtrate back into the circulationthus improving metabolic control in diabetesbut also restores tubuloglomerular feedback by increasing glycosuria and distal urinary flow. However, the most notable effect is due to inhibition of glucose entry to the proximal tubular cells. Glycosuria is toxic to the kidney: it harms glucosetransporting cells, that is, the proximal cells, which contain SGLT2. In animal models, SGLT2 inhibition reduces local production of oxygen-free radicals, the formation of mesangial matrix and collagen IV, glomerular infiltration by inflammatory cells and monocyte/macrophage-dependent arteriosclerosis. In humans, SGLT2 have a demonstrated ability to reduce renal injury and cardiovascular risk in patients with type 2 diabetes mellitus.

Collagen Matrix Density Drives the Metabolic Shift in Breast Cancer Cells

Increased breast density attributed to collagen I deposition is associated with a 4–6 fold increased risk of developing breast cancer. Here, we assessed cellular metabolic reprogramming of mammary carcinoma cells in response to increased collagen matrix density using an in vitro 3D model. Our initial observations demonstrated changes in functional metabolism in both normal mammary epithelial cells and mammary carcinoma cells in response to changes in matrix density. Further, mammary carcinoma cells grown in high density collagen matrices displayed decreased oxygen consumption and glucose metabolism via the tricarboxylic acid (TCA) cycle compared to cells cultured in low density matrices. Despite decreased glucose entry into the TCA cycle, levels of glucose uptake, cell viability, and ROS were not different between high and low density matrices. Interestingly, under high density conditions the contribution of glutamine as a fuel source to drive the TCA cycle was significantly enhanced. These alterations in functional metabolism mirrored significant changes in the expression of metabolic genes involved in glycolysis, oxidative phosphorylation, and the serine synthesis pathway. This study highlights the broad importance of the collagen microenvironment to cellular expression profiles, and shows that changes in density of the collagen microenvironment can modulate metabolic shifts of cancer cells.