Impaired basal glucose effectiveness but unaltered fasting glucose release and gluconeogenesis during short-term hypercortisolemia in healthy subjects

Excess cortisol has been demonstrated to impair hepatic and extrahepatic insulin action. To determine whether glucose effectiveness and, in terms of endogenous glucose release (EGR), gluconeogenesis, also are altered by hypercortisolemia, eight healthy subjects were studied after overnight infusion with hydrocortisone or saline. Glucose effectiveness was assessed by a combined somatostatin and insulin infusion protocol to maintain insulin concentration at basal level in the presence of prandial glucose infusions. Despite elevated insulin concentrations (P < 0.05), hypercortisolemia resulted in higher glucose (P < 0.05) and free fatty acid concentrations (P < 0.05). Furthermore, basal insulin concentrations were higher during hydrocortisone than during saline infusion (P < 0.01), indicating the presence of steroid-induced insulin resistance. Postabsorptive glucose production (P = 0.64) and the fractional contribution of gluconeogenesis to EGR (P = 0.33) did not differ on the two study days. During the prandial glucose infusion, the integrated glycemic response above baseline was higher in the presence of hydrocortisone than during saline infusion (P < 0.05), implying a decrease in net glucose effectiveness (4.42 +/- 0.52 vs. 6.65 +/- 0.83 ml.kg-1.min-1; P < 0.05). To determine whether this defect is attributable to an impaired ability of glucose to suppress glucose production, to stimulate its own uptake, or both, glucose turnover and "hot" (labeled) indexes of glucose effectiveness (GE) were calculated. Hepatic GE was lower during cortisol than during saline infusion (2.39 +/- 0.24 vs. 3.82 +/- 0.51 ml.kg-1.min-1; P < 0.05), indicating a defect in the ability of glucose to restrain its own production. In addition, in the presence of excess cortisol, glucose disappearance was inappropriate for the prevailing glucose concentration, implying a decrease in glucose clearance (P < 0.05). The decrease in glucose clearance was confirmed by the higher increment in [3-3H]glucose during hydrocortisone than during saline infusion (P < 0.05), despite the administration of identical tracer infusion rates. In conclusion, short-term hypercortisolemia in healthy individuals with normal beta-cell function decreases insulin action but does not alter rates of EGR and gluconeogenesis. In addition, cortisol impairs the ability of glucose to suppress its own production, which due to accumulation of glucose in the glucose space results in impaired peripheral glucose clearance. These results suggest that cortisol excess impairs glucose tolerance by decreasing both insulin action and glucose effectiveness.     

Affinity of glucose transport in Saccharomyces cerevisiae is modulated during growth on glucose.

By using a modified technique to measure glucose uptake in Saccharomyces cerevisiae, potential uncertainties have been identified in previous determinations. These previous determinations had led to the proposal that S. cerevisiae contained a constitutive low-affinity glucose transporter and a glucose-repressible high-affinity transporter. We show that, upon transition from glucose-repressed to -derepressed conditions, the maximum rate of glucose transport is constant and only the affinity for glucose changes. We conclude that the transporter or group of transporters is constitutive and that regulation of glucose transport occurs via a factor that modifies the affinity of the transporters and not via the synthesis of different kinetically independent transporters. Such a mechanism could, for instance, be accommodated by the binding of kinases causing a change in affinity for glucose.     

Control of L-phenylalanine production by dual feeding of glucose and L-tyrosine

Control of L-phenylalanine production by a recombinant of Escherichia coli AT2471 by means of the dual feeding of glucose and L-tyrosine was investigated. A novel method was developed for on-line monitoring of the maximum glucose uptake rate (MGUR), in which the length of time required for the consumption of added glucose was measured. Accumulation of acetic acid was successfully prevented throughout the whole period of the culture when the glucose concentration was kept below 0.1 g/L by controlling the glucose feeding on the basis of on-line monitoring of the MGUR and the cell concentration with a laser sensor.In a batch culture with glucose feeding, after L-tyrosine was depleted cell growth and the L-phenylalanine production rate decreased along with decreases in the specific enzyme activities of chorismate mutase-p-prephenate dehydratase (CMP) and 3-deoxy-D-arabinoheputulosonate 7-phosphate synthase (DAHP), which are the key enzymes in the L-phenylalanine synthesis pathway. Increasing the L-tyrosine feed rate by an appropriate amount, but not so far as to cause L-tyrosine accumulation in the culture, increased the activities of the enzymes and the specific rates of growth and production while the product yield based on glucose consumption decreased.The average specific rates of growth, production, and MGUR could be expressed as functions of the specific L-tyrosine consumption rate during both the earlier and later periods of L-tyrosine feeding. Estimations of the amount of L-phenylalanine produced, the product yield, and the cost factor by using these functions with several different combinations of two specific L-tyrosine consumption rates for two 10-h periods resulted in a suggested optimum L-tyrosine feeding strategy giving a lower specific L-tyrosine consumption rate in the later period, to suppress cell growth, in comparison to that in the earlier period. During L-tyrosine feeding, the three specific rates (growth, production, and MGUR) could be successfully controlled by adjusting the specific L-tyrosine consumption rate to the predicted value. The cost factor was lowest in this controlled culture, demonstrating experimentally the effectiveness of the strategy. (c) 1996 John Wiley & Sons, Inc.     

The activation of glucose dehydrogenase by p-chloromercuribenzoate

Summary P-Chloromercuribenzoate alters various reactions of rat liver glucose (hexose phosphate) dehydrogenase differently. The reagent has little effect on the glucose: NAD or the glucose: NADP oxidoreductases, doubles the rates of oxidations of galactose-6-phosphate and glucose-6-phosphate by NADP and greatly stimulates the oxidations of glucose-6-phosphate and galactose-6-phosphate by NAD. The reagent appears to react with a sulfhydryl group of the enzyme since activation is reversed and prevented by mercaptoethanol. The direct reaction of the reagent with the enzyme is indicated by its lower thermal stability in the presence of the p-chloromercuribenzoate. The size of the enzyme appears to be the same when determined by sucrose gradient centrifugation in the presence or absence of p-chloromercuribenzoate. In microsomes, the oxidation of NADH or NADPH hampers measurements of glucose dehydrogenase. Since p-chloromercuribenzoate inhibits microsomal oxidation of reduced nicontinamide nucleotides, it is possible to assay for glucose dehydrogenase accurately in the presence of the mercurial in microsomes and microsomal extracts and thus measure the effectiveness of a detergent in extracting the enzyme from microsomes.Abbreviation pcMB p-chloromercuribenzoic acid     

The role of glucose limitation in the regulation of the transport of glucose, gluconate and 2-oxogluconate, and of glucose metabolism in Pseudomonas aeruginosa.

The pathway of glucose metabolism in Pseudomonas aeruginosa was regulated by the availability of glucose and related compounds. On changing from an ammonium limitation to a glucose limitation, the organism responded by adjusting its metabolism substantially from the extracellular direct oxidative pathway to the intracellular phosphorylative route. This change was achieved by repression of the transport systems for gluconate and 2-oxogluconate and of the associated enzymes for 2-oxogluconate metabolism and gluconate kinase, while increasing the levels of glucose transport, hexokinase and glucose 6-phosphate dehydrogenase. The role of gluconate, produced by the action of glucose dehydrogenase, as a major inhibitory factor for glucose transport, and the possible significance of these regulatory mechanisms to the organism in its natural environment, are discussed.     

Bacterial bioassay of microgram to subnanogram quantities of glucose

A simple and highly sensitive bioassay for the measurement of glucose is described. The method is based on the fact that the yields of cultured bacteria depend on the amount of glucose input, which is a limiting factor in Davis minimal medium. The number of cells cultured under fixed conditions was shown to be dependent on the amount of glucose in the culture medium. Therefore, the concentration of glucose can be measured by counting the cell number after culturing the bacteria. With Davis medium depleted of sodium citrate, we used this method to detect a subnanogram level of glucose, although with the accuracy of order of magnitude estimation. In the microgram per milliliter range of glucose, the cell number can be measured optically, with proliferation being proportional to the input glucose. The high selectivity for glucose of this method is based on the preferential usage of glucose as a carbon and energy source by the bacteria adopted. The feasibility of applying this method to other substances is discussed.     

Macrokinetics and operational stability of immobilized glucose oxidase and catalase

Glucose oxidation by immobilized glucose oxidase (GlO) and catalase (Cat) has been investigated in batch and continuous reactions for operational studies. The macrokinetics of the process depend on coupled reaction steps and diffusion rates. The problem may be approximated by a simple pseudohomogeneous model taking into account both substrates of glucose oxidase and the intermediate reaction product H₂O₂. The effectiveness of both enzymes is enhanced in the coupled reaction path, the overall effectiveness nevertheless is very low. H₂O₂ causes the inactivation of both GlO and Cat. The rates of deactivation depend on the oxidation rates of glucose that give different quasistationary levels of H₂O₂ concentration. As a first approximation, the deactivation rates may be described by first-order reactions with respect to H₂O₂.     

Bifurcate effects of glucose on caspase-independent cell death during hypoxia

We investigated the effect of glucose on hypoxic death of rat cardiomyocyte-derived H9c2 cells and found that there is an optimal glucose concentration for protection against hypoxic cell death. Hypoxic cell death in the absence of glucose is accompanied by rapid ATP depletion, release of apoptosis-inducing factor from mitochondria, and nuclear chromatin condensation, all of which are inhibited by glucose in a dose-dependent manner. In contrast, excessive glucose also induces hypoxic cell death that is not accompanied by these events, suggesting a change in the mode of cell death between hypoxic cells with and without glucose supplementation.     

First phase release coefficient of insulin in subjects with normal glucose tolerance on glucose infusion analyzed by computer simulation

We report here a mathematical model using computer simulation to solve the phase fractionation coefficient (f) of instantaneous insulin release on glucose infusion. By extensive model testing with the cited parameters obtained from the literature, the values of the factor f were shown to lie in range of 0.93+/-0.02 (mean+/-2S.D., n=15), indicating that the high pulsatile bolus of glucose by i.v. infusion may trigger acute insulin release (AIR) corresponding to a fraction of more than 90% of the stored insulin release in the first phase from the secretory granules of pancreatic beta cells. In addition, the value of the factor f was shown to be independent of both the glucose infusion method and the non-insulin-dependent uptake of glucose.     

Transforming growth factor-beta 1 stimulates glucose uptake and the expression of glucose transporter mRNA in quiescent Swiss mouse 3T3 cells

Transforming growth factor-beta 1 (TGF-beta 1) is a multifunctional polypeptide that regulates the proliferation and differentiation of various types of animal cells. TGF-beta 1 stimulated glucose uptake and the expression of a brain-type glucose transporter (GLUT1) mRNA in quiescent mouse 3T3 cells. TGF-beta 1 also synergistically stimulated these activities when given together with calf serum, phorbol ester, fibroblast growth factor, or epidermal growth factor. The increases in glucose uptake and the GLUT1 mRNA level were induced by picomolar concentrations of TGF-beta 1 within 3 h of stimulation, reached a peak between 6 and 9 h, and then decreased gradually to basal levels before an increase in DNA synthesis. The stimulation of GLUT1 mRNA expression was completely abolished by actinomycin D, but was not affected by cycloheximide, suggesting that new protein synthesis was not required for the expression of GLUT1 mRNA. TGF-beta 1 had little mitogenic activity and did not affect serum-induced DNA synthesis in quiescent 3T3 cells. However, it stimulated DNA synthesis synergistically when given with fibroblast growth factor, epidermal growth factor, phorbol ester, or insulin. These results suggest that TGF-beta 1 mediates the stimulation of glucose uptake, GLUT1 mRNA expression, and DNA synthesis via a pathway(s) and cellular components distinct from those for other growth factors. The possible role of the TGF-beta 1-induced stimulation of glucose transport activity in the control of mouse fibroblast proliferation is also discussed.     

Clenbuterol prevents epinephrine from antagonizing insulin-stimulated muscle glucose uptake.

In the present study, we investigated the effects of chronic clenbuterol treatment on insulin-stimulated glucose uptake in the presence of epinephrine in isolated rat skeletal muscle. Insulin (50 microU/ml) increased glucose uptake in both fast-twitch (epitrochlearis) and slow-twitch (soleus) muscles. In the presence of 24 nM epinephrine, insulin-stimulated glucose uptake was completely suppressed. This suppression of glucose uptake by epinephrine was accompanied by an increase in the intracellular concentration of glucose 6-phosphate and a decrease in insulin-receptor substrate-1-associated phosphatidylinositol 3-kinase (IRS-1/PI3-kinase) activity. Clenbuterol treatment had no direct effect on insulin-stimulated glucose uptake. However, after clenbuterol treatment, epinephrine was ineffective in attenuating insulin-stimulated muscle glucose uptake. This ineffectiveness of epinephrine to suppress insulin-stimulated glucose uptake occurred in conjunction with its inability to increase the intracellular concentration of glucose 6-phosphate and attenuate IRS-1/PI3-kinase activity. Results of this study indicate that the effectiveness of epinephrine to inhibit insulin-stimulated glucose uptake is severely diminished in muscle from rats pretreated with clenbuterol.     

Effect of high levels of insulin on glucose utilization and glucose production in pregnant and nonpregnant sheep

The present study was conducted to test the hypothesis that pregnancy in sheep alters the effects of insulin on glucose utilization and glucose production. Euglycemic, hyperinsulinemic glucose clamp experiments were performed in chronically catheterized, unstressed, fed or 24-hr fasted, nonpregnant sheep and fed, pregnant sheep. Endogenous glucose production rate for the whole sheep and glucose utilization rate of the uterine and nonuterine maternal tissues were measured in control and high-insulin periods by tracer technique using [6-3H]glucose. Control glucose utilization rate in the fed, nonpregnant sheep was significantly (P less than 0.05) greater than that in the fasted, nonpregnant sheep, 2.29 +/- 0.17 and 1.86 +/- 0.11 mg/min/kg, respectively, and also in the nonuterine maternal tissues of the pregnant sheep (1.71 +/- 0.18 mg/min/kg). Insulin stimulated glucose utilization 116.4 +/- 14.8% in the fed, nonpregnant sheep but only 82.8 +/- 11.0% in the fasted, nonpregnant sheep and 94.2 +/- 14.3% in the nonuterine tissues of the fed, pregnant sheep. Also, insulin suppressed endogenous glucose production to 53.2 +/- 5.6% in the fed, nonpregnant sheep, to 3.9 +/- 3.1% in the fasted, nonpregnant sheep, and to 9.0 +/- 3.7% in the fed, pregnant sheep. In the pregnant animals, uterine glucose uptake and uterine glucose utilization were not different and were not altered by changes in maternal insulin concentration. The results indicate that during late pregnancy glucose utilization is reduced and resistance to the effect of insulin to enhance glucose utilization is present in the nonuterine maternal tissues compared with nonpregnant, fed sheep. In contrast, the effectiveness of insulin to suppress glucose production in the pregnant sheep is greater than that in nonpregnant, fed sheep. These results also demonstrate that differential changes in the effect of insulin can exist simultaneously between peripheral (glucose consuming) and central (glucose producing) tissues. The changes in glucose utilization and in insulin effect in the pregnant sheep are both qualitatively and quantitatively similar to those of the nonpregnant sheep when fasted, suggesting that similar substrate and/or hormonal factors may be involved.     

葡萄糖转运子4 转位信号转导通路的研究进展

葡萄糖是大部分细胞主要能量来源,它进入细胞的过程在生命的维持中无疑成为一个重要的步骤。而葡萄糖进入细胞是依赖于这些细胞上的葡萄糖转运子和相应的对其进行调节的因子。葡萄糖转运子4（GLUT4）在糖进入细胞维持血糖平衡中起了重要的作用。近年有关GLUT4的研究文献很多,但却总给人不系统的感觉。本文对GLUT4转位的胰岛素依赖和非胰岛素依赖的信号途径以及其远端过程及机制作一综述,同时分析了GLUT4转位的信号途径的研究中存在的问题和将来研究的方向。     

Intestinal transit of a glucose bolus and incretin kinetics: a mathematical model with application to the oral glucose tolerance test

The rate of appearance (R(a)) of exogenous glucose in plasma after glucose ingestion is presently measured by tracer techniques that cannot be used in standard clinical testing such as the oral glucose tolerance test (OGTT). We propose a mathematical model that represents in a simple way the gastric emptying, the transport of glucose along the intestinal tract, and its absorption from gut lumen into portal blood. The model gives the R(a) time course in terms of parameters with a physiological counterpart and provides an expression for the release of incretin hormones as related to glucose transit into gut lumen. Glucose absorption was represented by assuming two components related to a proximal and a distal transporter. Model performance was evaluated by numerical simulations. The model was then validated by fitting OGTT glucose and GLP-1 data in healthy controls and type 2 diabetic patients, and useful information was obtained for the rate of gastric emptying, the rate of glucose absorption, the R(a) profile, the insulin sensitivity, and the glucose effectiveness. Model-derived estimates of insulin sensitivity were well correlated (r = 0.929 in controls and 0.886 in diabetic patients) to data obtained from the euglycemic hyperinsulinemic clamp. Although the proposed OGTT analysis requires the measurement of an additional hormone concentration (GLP-1), it appears to be a reasonable choice since it avoids complex and expensive techniques, such as isotopes for glucose R(a) measurement and direct assessment of gastric emptying and intestinal transit, and gives additional correlated information, thus largely compensating for the extra expense.     

Upregulation of glucose metabolism by granulocyte-monocyte colony-stimulating factor

Alterations of glucose metabolism were investigated for 6 hours following an intraarterial injection of murine recombinant granulocyte-monocyte colony-stimulating factor (GM-CSF) (30 micrograms/kg body weight). GM-CSF resulted in a transient elevation of plasma glucose. The rate of whole body glucose appearance, as measured by infusion of [6-3H] glucose, was increased by about 10% between 0.5 and 3 hours following GM-CSF injection. In vivo glucose utilization of individual tissues was investigated by the tracer 2-deoxyglucose technique. At 30 min, GM-CSF increased glucose utilization by 80-90% in liver and lung, and 50-60% in skin and spleen. At 3 and 6 hours, glucose utilization by these tissues returned toward control levels except for lung. There was a 40-50% increase in glucose utilization by skeletal muscle 30 min after GM-CSF which was sustained for 6 hours. Glucose utilization of testis, ileum and kidney did not change significantly. Plasma concentrations of insulin, glucagon and tumor necrosis factor were not altered in response to GM-CSF. These findings indicate that some of the acute metabolic effects of a short-term administration of GM-CSF are observed in macrophage-rich tissues, and suggest that GM-CSF may be involved in the metabolic upregulation of immunologically active tissues.     

Factors responsible for glucose intolerance in Japanese subjects with impaired fasting glucose.

Impaired fasting glucose (IFG) represents risk of development of diabetes (DM) and its complications. We investigated insulin secretion and insulin sensitivity in 403 IFG subjects divided into three levels of 2-hour postchallenge glucose (2-h PG) to clarify the factors responsible in the development of glucose intolerance in Japanese IFG. Nearly 60% of the subjects at annual medical check-up with FPG of 6.1-7.0 mmol/l at the first screening were diagnosed by 75 g oral glucose tolerance test (OGTT) to have impaired glucose tolerance (IGT; FPG <7.0 mmol/l and 7.8 mmol/l <2-h PG <11.1 mmol/l) or DM (isolated postchallenge hyperglycemia (IPH); FPG <7.0 mmol/l and 11.1 mmol/l <2-h PG level). The primary factor in the decreased glucose tolerance was a decrease in early-phase insulin, with some contribution of increasing insulin resistance. In addition, IFG/IGT and IFG/IPH subjects showed a compensatory increase in basal insulin secretion sufficient to keep FPG levels within the non-diabetic range. IFG is composed of three different categories in basal, early-phase insulin secretion, and insulin sensitivity.     

Neuregulins mediate calcium-induced glucose transport during muscle contraction

Neuregulin, a growth factor involved in myogenesis, has rapid effects on muscle metabolism. In a manner analogous to insulin and exercise, neuregulins stimulate glucose transport through recruitment of glucose transporters to surface membranes in skeletal muscle. Like muscle contraction, neuregulins have additive effects with insulin on glucose uptake. Therefore, we examined whether neuregulins are involved in the mechanism by which muscle contraction regulates glucose transport. We show that caffeine-induced increases in cytosolic Ca2+ mediate a metalloproteinase-dependent release of neuregulins, which stimulates tyrosine phosphorylation of ErbB4 receptors. Activation of ErbB4 is necessary for Ca2+-derived effects on glucose transport. Furthermore, blockage of ErbB4 abruptly impairs contraction-induced glucose uptake in slow twitch muscle fibers, and to a lesser extent, in fast twitch muscle fibers. In conclusion, we provide evidence that contraction-induced activation of neuregulin receptors is necessary for the stimulation of glucose transport and a key element of energetic metabolism during muscle contraction.     

Molecular and cellular regulation of glucose transporter (GLUT) proteins in cancer

Malignant cells are known to have accelerated metabolism, high glucose requirements, and increased glucose uptake. Transport of glucose across the plasma membrane of mammalian cells is the first rate-limiting step for glucose metabolism and is mediated by facilitative glucose transporter (GLUT) proteins. Increased glucose transport in malignant cells has been associated with increased and deregulated expression of glucose transporter proteins, with overexpression of GLUT1 and/or GLUT3 a characteristic feature. Oncogenic transformation of cultured mammalian cells causes a rapid increase of glucose transport and GLUT1 expression via interaction with GLUT1 promoter enhancer elements. In human studies, high levels of GLUT1 expression in tumors have been associated with poor survival. Studies indicate that glucose transport in breast cancer is not fully explained by GLUT1 or GLUT3 expression, suggesting involvement of another glucose transporter. Recently, a novel glucose transporter protein, GLUT12, has been found in breast and prostate cancers. In human breast and prostate tumors and cultured cells, GLUT12 is located intracellularly and at the cell surface. Trafficking of GLUT12 to the plasma membrane could therefore contribute to glucose uptake. Several factors have been implicated in the regulation of glucose transporter expression in breast cancer. Hypoxia can increase GLUT1 levels and glucose uptake. Estradiol and epidermal growth factor, both of which can play a role in breast cancer cell growth, increase glucose consumption. Estradiol and epidermal growth factor also increase GLUT12 protein levels in cultured breast cancer cells. Targeting GLUT12 could provide novel methods for detection and treatment of breast and prostate cancer.