Cultured 3T3L1 adipocytes dispose of excess medium glucose as lactate under abundant oxygen availability

White adipose tissue (WAT) produces lactate in significant amount from circulating glucose, especially in obesity;Under normoxia, 3T3L1 cells secrete large quantities of lactate to the medium, again at the expense of glucose and proportionally to its levels. Most of the glucose was converted to lactate with only part of it being used to synthesize fat. Cultured adipocytes were largely anaerobic, but this was not a Warburg-like process. It is speculated that the massive production of lactate, is a process of defense of the adipocyte, used to dispose of excess glucose. This way, the adipocyte exports glucose carbon (and reduces the problem of excess substrate availability) to the liver, but the process may be also a mechanism of short-term control of hyperglycemia. The in vivo data obtained from adipose tissue of male rats agree with this interpretation.

Evidence of systematic and proportional error in a widely used glucose oxidase analyser: Impact for clinical research?

Real time glycemia is a cornerstone for metabolic research, particularly when performing oral glucose tolerance tests (OGTT) or glucose clamps. From 1965 to 2009, the gold standard device for real time plasma glucose assessment was the Beckman glucose analyzer 2 (Beckman Instruments, Fullerton, CA), which technology couples glucose oxidase enzymatic assay with oxygen sensors. Since its discontinuation in 2009, today's researchers are left with few choices that utilize glucose oxidase technology. The first one is the YSI 2300 (Yellow Springs Instruments Corp., Yellow Springs, OH), known to be as accurate as the Beckman(1). The YSI has been used extensively for clinical research studies and is used to validate other glucose monitoring devices(2). The major drawback of the YSI is that it is relatively slow and requires high maintenance. The Analox GM9 (Analox instruments, London), more recent and faster, is increasingly used in clinical research(3) as well as in basic sciences(4) (e.g. 23 papers in Diabetes or 21 in Diabetologia). This article is protected by copyright. All rights reserved.

Thermogenesis induced by five different intravenous glucose/insulin infusions in healthy young men.

The thermogenic response induced by glucose/insulin administered intravenously was examined in 22 healthy male volunteers using indirect calorimetry in combination with the euglycaemic insulin clamp technique. Five increasing steady state levels of insulinaemia (62 muU/ml to 1132 muU/ml) were achieved by means of continuous infusions of insulin at 5 rates ranging from 0.5 mU/kg.min to 10 mU/kg.min. Euglycaemia was maintained at each insulin level by infusing glucose at different rates ranging from steady state values of 0.41 g/min to 0.77 g/min. These glucose/insulin infusions resulted in a significant net rise in resting energy expenditure from 0.33 kJ/min to 0.94 kJ/min over preinfusion baseline values for the lowest and the highest doses respectively. There was a highly significant relationship (r = 0.93, p<0.001, n = 42) between the amount of glucose infused and the net increase in energy expenditure over preinfusion baseline values. Intravenous glucose induced thermogenesis (GIT(iv)) was calculated as incremental values of energy expenditure related to step changes in glucose infusion rates. GIT(iv) was found to be approximately 5.5% a physiological plasma insulin levels (i.e. below 200 muU/ml) whereas at supraphysiological levels (i.e.>400 muU/ml) GIT(iv) was increased up to 8%. It was concluded that: 1. the magnitude of the GIT(iv) at physiological insulinaemia was similar to that found by other investigators who have administered glucose per os; 2. the elevated thermogenesis observed at high doses of glucose/insulin infusion is consistent with recent clinical findings showing a markedly increased energy expenditure in patients supported by large quantities of intravenous glucose (TPN).

Glut2-dependent glucose-sensing controls thermoregulation by enhancing the leptin sensitivity of NPY and POMC neurons.

The physiological contribution of glucose in thermoregulation is not completely established nor whether this control may involve a regulation of the melanocortin pathway. Here, we assessed thermoregulation and leptin sensitivity of hypothalamic arcuate neurons in mice with inactivation of glucose transporter type 2 (Glut2)-dependent glucose sensing. Mice with inactivation of Glut2-dependent glucose sensors are cold intolerant and show increased susceptibility to food deprivation-induced torpor and abnormal hypothermic response to intracerebroventricular administration of 2-deoxy-d-glucose compared to control mice. This is associated with a defect in regulated expression of brown adipose tissue uncoupling protein I and iodothyronine deiodinase II and with a decreased leptin sensitivity of neuropeptide Y (NPY) and proopiomelanocortin (POMC) neurons, as observed during the unfed-to-refed transition or following i.p. leptin injection. Sites of central Glut-2 expression were identified by a genetic tagging approach and revealed that glucose-sensitive neurons were present in the lateral hypothalamus, the dorsal vagal complex, and the basal medulla but not in the arcuate nucleus. NPY and POMC neurons were, however, connected to nerve terminals from Glut2-expressing neurons. Thus, our data suggest that glucose controls thermoregulation and the leptin sensitivity of NPY and POMC neurons through activation of Glut2-dependent glucose-sensing neurons located outside of the arcuate nucleus.

Quette place pour l'automesure glycémique dans la prise en charge du diabète de type 2 [Which role for self-monitoring of blood glucose in type 2 diabetes?]

There is a sustained controversy in the literature about the role and utility of self-monitoring of blood glucose (SMBG) in type 2 diabetes. The study results in this field do not provide really useful clues for the integration of SMBG in the follow-up of the individual patient, because they are based on a misconception of SMBG. It is studied as if it was a medical treatment whose effect on glycemic control is to be isolated. However, SMBG has no such intrinsic effect. It gains its purpose only as an inseparable component of a comprehensive and structured educational strategy. To be appropriate this strategy cannot be based on the health care professionals' view on diabetes only. It rather has to be tailored to the individual patient's needs through an ongoing process of shared reflection with him.

Comparison of thermogenic effect of fructose and glucose in normal humans.

After nutrient ingestion there is an increase in energy expenditure that has been referred to as dietary-induced thermogenesis. In the present study we have employed indirect calorimetry to compare the increment in energy expenditure after the ingestion of 75 g of glucose or fructose in 17 healthy volunteers. During the 4 h after glucose ingestion the plasma insulin concentration increased by 33 +/- 4 microU/ml and this was associated with a significant increase in carbohydrate oxidation and decrement in lipid oxidation. Energy expenditure increased by 0.08 +/- 0.01 kcal/min. When fructose was ingested, the plasma insulin concentration increased by only 8 +/- 2 microU/ml vs. glucose. Nonetheless, the increments in carbohydrate oxidation and decrement in lipid oxidation were significantly greater than with glucose. The increment in energy expenditure was also greater with fructose. When the mean increment in plasma insulin concentration after fructose was reproduced using the insulin clamp technique, the increase in carbohydrate oxidation and decrement in lipid oxidation were markedly reduced compared with the fructose-ingestion study; energy expenditure failed to increase above basal levels. To examine the role of the adrenergic nervous system in fructose-induced thermogenesis, fructose ingestion was also performed during beta-adrenergic blockade with propranolol. The increase in energy expenditure during fructose plus propranolol was lower than with fructose ingestion alone. These results indicate that the stimulation of thermogenesis after carbohydrate ingestion is related to an augmentation of cellular metabolism and is not dependent on an increase in the plasma insulin concentration per se.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain glucose sensing and neural regulation of insulin and glucagon secretion.

Glucose homeostasis requires the tight regulation of glucose utilization by liver, muscle and white or brown fat, and glucose production and release in the blood by liver. The major goal of maintaining glycemia at ∼ 5 mM is to ensure a sufficient flux of glucose to the brain, which depends mostly on this nutrient as a source of metabolic energy. This homeostatic process is controlled by hormones, mainly glucagon and insulin, and by autonomic nervous activities that control the metabolic state of liver, muscle and fat tissue but also the secretory activity of the endocrine pancreas. Activation or inhibition of the sympathetic or parasympathetic branches of the autonomic nervous systems are controlled by glucose-excited or glucose-inhibited neurons located at different anatomical sites, mainly in the brainstem and the hypothalamus. Activation of these neurons by hyper- or hypoglycemia represents a critical aspect of the control of glucose homeostasis, and loss of glucose sensing by these cells as well as by pancreatic β-cells is a hallmark of type 2 diabetes. In this article, aspects of the brain-endocrine pancreas axis are reviewed, highlighting the importance of central glucose sensing in the control of counterregulation to hypoglycemia but also mentioning the role of the neural control in β-cell mass and function. Overall, the conclusions of these studies is that impaired glucose homeostasis, such as associated with type 2 diabetes, but also defective counterregulation to hypoglycemia, may be caused by initial defects in glucose sensing.

Glucagon-like peptide-1 increases beta-cell glucose competence and proliferation by translational induction of insulin-like growth factor-1 receptor expression.

Glucagon-like peptide-1 (GLP-1) protects beta-cells against apoptosis, increases their glucose competence, and induces their proliferation. We previously demonstrated that the anti-apoptotic effect was mediated by an increase in insulin-like growth factor-1 receptor (IGF-1R) expression and signaling, which was dependent on autocrine secretion of insulin-like growth factor 2 (IGF-2). Here, we further investigated how GLP-1 induces IGF-1R expression and whether the IGF-2/IGF-1R autocrine loop is also involved in mediating GLP-1-increase in glucose competence and proliferation. We show that GLP-1 up-regulated IGF-1R expression by a protein kinase A-dependent translational control mechanism, whereas isobutylmethylxanthine, which led to higher intracellular accumulation of cAMP than GLP-1, increased both IGF-1R transcription and translation. We then demonstrated, using MIN6 cells and primary islets, that the glucose competence of these cells was dependent on the level of IGF-1R expression and on IGF-2 secretion. We showed that GLP-1-induced primary beta-cell proliferation was suppressed by Igf-1r gene inactivation and by IGF-2 immunoneutralization or knockdown. Together our data show that regulation of beta-cell number and function by GLP-1 depends on the cAMP/protein kinase A mediated-induction of IGF-1R expression and the increased activity of an IGF-2/IGF-1R autocrine loop.

Metabolism of oral glucose in children born small for gestational age : evidence for an impaired whole body glucose oxidation

Résumé Les études épidémiologiques indiquent que la restriction intra-utérine confère un risque accru de développement de diabète de type 2 au cours de la vie. Certaines études ont documenté la présence d'une résistance à l'insuline chez les jeunes adultes ou les adolescents nés petits pour l'âge gestationnel. Comme la plupart des études ont impliqués des individus post-pubères et comme la puberté influence de manière marquée le métabolisme énergétique, nous avons évalué le devenir du glucose administré oralement dans un groupe incluant essentiellement des enfants pré-pubères ou en début de puberté avec restriction intra-utérine, et chez des enfants matchés pour l'âge et pour le poids. Tous les enfants ont eu une évaluation de leur composition corporelle par mesure des plis cutanés. Ils ont ensuite été étudiés dans des conditions standardisées et ont reçu 4 charges consécutives orales de glucose à raison de 180 mg/kg de poids corporel jusqu'à atteindre un état d'équilibre relatif. La dépense énergétique et l'oxydation des substrats ont été évaluées durant la quatrième heure par calorimétrie indirecte. Comparativement avec les enfants matchés pour l'âge et le poids, les enfants nés petits pour l'âge gestationnel avaient une plus petite stature. Leur dépense énergétique n'était pas significativement abaissée, mais leur oxydation du glucose était plus basse. Ces résultats indiquent que des altérations métaboliques sont présentes précocement chez les enfants nés petits pour l'âge gestationnel, et qu'elles sont possiblement reliées à des altérations de la composition corporelle. Abstract: Epidemiological studies indicate that intrauterine growth restriction confers an increased risk of developing type 2 diabetes mellitus in subsequent life. Several studies have further documented the presence of insulin resistance in young adults or adolescent children born small for gestational age. Since most studies addressed postpubertal individuals, and since puberty markedly affects energy metabolism, we evaluated the disposal of oral glucose in a group including mainly prepubertal and early pubertal children with intrauterine growth restriction and in healthy age- and weight-matched control children. All children had an evaluation of their body composition by skinfold thickness measurements. They were then studied in standardized conditions and received 4 consecutive hourly loads of 180 mg glucose/kg body weight to reach a near steady state. Energy expenditure and substrate oxidation were evaluated during the fourth hour by indirect calorimetry. Compared to both age- and weight-matched children, children born small for gestational age had lower stature. Their energy expenditure was not significantly decreased, but they had lower glucose oxidation rates. These results indicate that metabolic alterations are present early in children born small for gestational age, and are possibly related to alterations of body composition.

Determination of salivary glucose in healthy adults

Objectives: Our aim in this study was to determine the concentration of salivary glucose in healthy individuals and to compare it with the capillary glycemia. Study design: Samples of unstimulated whole saliva were collected from 63 non-diabetic patients. The concentration of salivary glucose and capillary blood was measured in all of the patients. The salivary glucose was determined by enzymatic method and spectrophotometry. The data was then analyzed using the Spearman correlation test, considering values of p<0.05 to be significant. Results: The whole sample consisted of 47.6% males and 52.4% women, with an average age of 37.5±15.7 years old. The average rates of unstimulated salivary flow were 0.41±0.21 ml/min among males and 0.31±0.15 ml/min among females. No significant difference was found based on these results (p=0.078). The average blood glucose among the males studied was 100.05±13.51 mg/dL, and among females, it was 99.5±13.9 mg/dL. The average salivary glucose for the whole sample was 5.97±1.87 mg/dL, with 5.91±2.19 mg/dL among males and 5.97±1.56 mg/dL among females, respectively, without presenting any significant differences (p=0.908). The concentration of salivary glucose did not present any statistically significant correlation with the capillary glycemia (p=0.732). Conclusions: The results suggest that the concentration of salivary glucose is not dependent on capillary glycemia and that the concentration of salivary glucose does not present significant differences between the measurements for males and females.

Glutamate reduces glucose utilization while concomitantly enhancing AQP9 and MCT2 expression in cultured rat hippocampal neurons.

The excitatory neurotransmitter glutamate has been reported to have a major impact on brain energy metabolism. Using primary cultures of rat hippocampal neurons, we observed that glutamate reduces glucose utilization in this cell type, suggesting alteration in mitochondrial oxidative metabolism. The aquaglyceroporin AQP9 and the monocarboxylate transporter MCT2, two transporters for oxidative energy substrates, appear to be present in mitochondria of these neurons. Moreover, they not only co-localize but they interact with each other as they were found to co-immunoprecipitate from hippocampal neuron homogenates. Exposure of cultured hippocampal neurons to glutamate 100 μM for 1 h led to enhanced expression of both AQP9 and MCT2 at the protein level without any significant change at the mRNA level. In parallel, a similar increase in the protein expression of LDHA was evidenced without an effect on the mRNA level. These data suggest that glutamate exerts an influence on neuronal energy metabolism likely through a regulation of the expression of some key mitochondrial proteins.

Thermogenesis in obese women: effect of fructose vs. glucose added to a meal.

To assess the effect of a fructose meal on resting energy expenditure (EE), indirect calorimetry was used in 23 women (10 lean and 13 obese) for 30 min before and 6 h after the ingestion of a mixed meal containing 20% protein, 33% fat, and either 75 g glucose or 75 g fructose as carbohydrate source (47%). Expressed as a percentage of the energy content of the meal, the thermogenic response to the fructose meal was significantly greater (10.2 +/- 0.5%) than that of the glucose meal (8.4 +/- 0.4%, P less than 0.01). This difference was still apparent when the lean and obese women were considered separately. The mean respiratory quotient during the 6-h postprandial period was significantly greater (P less than 0.01) for the fructose (0.85 +/- 0.01) than for the glucose meal (0.83 +/- 0.01) in the combined subjects. In addition, cumulative carbohydrate oxidation was significantly greater after the fructose than after the glucose meal (51.1 +/- 2.3 vs. 40.9 +/- 2.0 g/6 h, respectively, P less than 0.01). Only small changes were observed in postprandial plasma levels of glucose and insulin after the fructose meal, but the plasma levels of lactate increased more with fructose than with the glucose meal. These results suggest that there might be some advantages (higher thermogenesis and carbohydrate oxidations) in using fructose as part of the carbohydrate source in diet of people with obesity and/or insulin resistance.

Glucose metabolism, gray matter structure, and memory decline in subjective memory impairment.

OBJECTIVE: To identify biological evidence for Alzheimer disease (AD) in individuals with subjective memory impairment (SMI) and unimpaired cognitive performance and to investigate the longitudinal cognitive course in these subjects. METHOD: [¹⁸F]fluoro-2-deoxyglucose PET (FDG-PET) and structural MRI were acquired in 31 subjects with SMI and 56 controls. Cognitive follow-up testing was performed (average follow-up time: 35 months). Differences in baseline brain imaging data and in memory decline were assessed between both groups. Associations of memory decline with brain imaging data were tested. RESULTS: The SMI group showed hypometabolism in the right precuneus and hypermetabolism in the right medial temporal lobe. Gray matter volume was reduced in the right hippocampus in the SMI group. At follow-up, subjects with SMI showed a poorer performance than controls on measures of episodic memory. Longitudinal memory decline in the SMI group was associated with reduced glucose metabolism in the right precuneus at baseline. CONCLUSION: The cross-sectional difference in 2 independent neuroimaging modalities indicates early AD pathology in SMI. The poorer memory performance at follow-up and the association of reduced longitudinal memory performance with hypometabolism in the precuneus at baseline support the concept of SMI as the earliest manifestation of AD.

The Lin28/let-7 axis regulates glucose metabolism.

The let-7 tumor suppressor microRNAs are known for their regulation of oncogenes, while the RNA-binding proteins Lin28a/b promote malignancy by inhibiting let-7 biogenesis. We have uncovered unexpected roles for the Lin28/let-7 pathway in regulating metabolism. When overexpressed in mice, both Lin28a and LIN28B promote an insulin-sensitized state that resists high-fat-diet induced diabetes. Conversely, muscle-specific loss of Lin28a or overexpression of let-7 results in insulin resistance and impaired glucose tolerance. These phenomena occur, in part, through the let-7-mediated repression of multiple components of the insulin-PI3K-mTOR pathway, including IGF1R, INSR, and IRS2. In addition, the mTOR inhibitor, rapamycin, abrogates Lin28a-mediated insulin sensitivity and enhanced glucose uptake. Moreover, let-7 targets are enriched for genes containing SNPs associated with type 2 diabetes and control of fasting glucose in human genome-wide association studies. These data establish the Lin28/let-7 pathway as a central regulator of mammalian glucose metabolism.

Multi-analyte detection for biological fluids. Towards continous monitoring of glucose, ionized calcium and pH using a viscometric affinity biosensor.

We present a viscometric affinity biosensor that can potentially allow continuous multi-analyte monitoring in biological fluids like blood or plasma. The sensing principle is based on the detection of viscosity changes of a polymeric solution which has a selective affinity for the analyte of interest. The chemico-mechanical sensor incorporates an actuating piezoelectric diaphragm, a sensing piezoelectric diaphragm and a flow-resisting microchannel for viscosity detection. A free-standing Anodic Alumina Oxide (AAO) porous nano-membrane is used as selective interface. A glucose-sensitive sensor was fabricated and extensively assessed in buffer solution. The sensor reversibility, stability and sensitivity were excellent during at least 65 hours. Results showed also a good degree of stability for a long term measurement (25 days). The sensor behaviour was furthermore tested in fetal bovine serum (FBS). The obtained results for glucose sensing are very promising, indicating that the developed sensor is a candidate for continuous monitoring in biological fluids. Sensitive solutions for ionized calcium and pH are currently under development and should allow multi-analyte sensing in the near future.