Independent Glucose Transport Research Articles

Saturated fatty acids inhibit unsaturated fatty acid induced glucose uptake involving GLUT10 and aerobic glycolysis in bovine granulosa cells

Fatty acids have been shown to modulate glucose metabolism in vitro and in vivo. However, there is still a need for substantial evidence and mechanistic understanding in many cell types whether both saturated and unsaturated fatty acids (SFAs and UFAs) pose a similar effect and, if not, what determines the net effect of fatty acid mixes on glucose metabolism. In the present study, we asked these questions by treating granulosa cells (GCs) with the most abundant non-esterified fatty acid species in bovine follicular fluid. Results revealed that oleic and alpha-linolenic acids (UFAs) significantly increased glucose consumption compared to palmitic and stearic acids (SFAs). A significant increase in lactate production, extracellular acidification rate, and decreased mitochondrial activity indicate glucose channeling through aerobic glycolysis in UFA treated GCs. We show that insulin independent glucose transporter GLUT10 is essential for UFA driven glucose consumption, and the induction of AKT and ERK signaling pathways necessary for GLUT10 expression. To mimic the physiological conditions, we co-treated GCs with mixes of SFAs and UFAs. Interestingly, co-treatments abolished the UFA induced glucose uptake and metabolism by inhibiting AKT and ERK phosphorylation and GLUT10 expression. These data suggest that the net effect of fatty acid induced glucose uptake in GCs is determined by SFAs under physiological conditions.

A novel phenolic formulation for treating hepatic and peripheral insulin resistance by regulating GLUT4-mediated glucose uptake

Chronic insulin resistance suppresses muscle and liver response to insulin, which is partially due to impaired vesicle trafficking. We report here that a formula consisting of resveratrol, ferulic acid and epigallocatechin-3-O-gallate is more effective in ameliorating muscle and hepatic insulin resistance than the anti-diabetic drugs, metformin and AICAR. The formula enhanced glucose transporter-4 (GLUT4) translocation to the plasma membrane in the insulin-resistant muscle cells by regulating both insulin-independent (calcium and AMPK) and insulin-dependent (PI3K) signaling molecules. Particularly, it regulated the subcellular location of GLUT4 through endosomes to increase glucose uptake under insulin-resistant condition. Meanwhile, this phytochemicals combination increased glycogen synthesis and decreased glucose production in the insulin-resistant liver cells. On the other hand, this formula also showed anti-diabetic potential by the reduction of lipid content in the myotubes, hepatocytes, and adipocytes. This study demonstrated that the three phenolic compounds in the formula could work in distinct mechanisms and enhance both insulin-dependent and independent vesicles trafficking and glucose transport mechanisms to improve carbohydrate and lipid metabolism.

Glycemic, insulinemic and methylglyoxal postprandial responses to starches alone or in whole diets in dogs versus cats: Relating the concept of glycemic index to metabolic responses and gene expression

Species differences between domestic cats (Felis catus) and dogs (Canis familiaris) has led to differences in their ability to digest, absorb and metabolize carbohydrates through poorly characterized mechanisms. The current study aimed to first examine biopsied small intestine, pancreas, liver and skeletal muscle from laboratory beagles and domestic cats for mRNA expression of key enzymes involved in starch digestion (amylase), glucose transport (sodium-dependent SGLTs and –independent glucose transporters, GLUT) and glucose metabolism (hexokinase and glucokinase). Cats had lower mRNA expression of most genes examined in almost all tissues compared to dogs (p < 0.05). Next, postprandial glucose, insulin, methylglyoxal (a toxic glucose metabolite) and d-lactate (metabolite of methylglyoxal) after single feedings of different starch sources were tested in fasted dogs and cats. After feeding pure glucose, peak postprandial blood glucose and methylglyoxal were surprisingly similar between dogs and cats, except cats had a longer time to peak and a greater area under the curve consistent with lower glycolytic enzyme expression. After feeding starches or whole diets to dogs, postprandial glycemic response, glycemic index, insulin, methylglyoxal and d-lactate followed reported glycemic index trends in humans. In contrast, cats showed very low to negligible postprandial glycemic responses and low insulin after feeding different starch sources, but not whole diets, with no relationship to methylglyoxal or d-lactate. Thus, the concept of glycemic index appears valid in dogs, but not cats. Differences in amylase, glucose transporters, and glycolytic enzymes are consistent with species differences in starch and glucose handling between cats and dogs.

The "sugar dilemma".

Type 2 diabetes mellitus is characterized by insulin resistance and elevated blood glucose levels. Treatment protocols generally include dietary restriction of sugar, as well as drugs aiming at a reduction of blood glucose, mainly by activating the insulin system or supplementing insulin. This established approach does not take into account the outstanding physiological role of glucose as a key molecule in metabolism. Glucose is crucial to meet the high energy demand of the brain, which depends on it as an exclusive nutrient. Insulin independent glucose transporters GLUT1 import glucose into the brain. Reduction of blood glucose, as in current treatment concepts, may lead to energy deficiency in the brain and consecutively to worsening of - possibly already impaired - neurocognitive function. Reduced cell membrane fluidity of the vascular endothelium of the bloodbrain-barrier (BBB) - due to malnutrition and/or aging - is considered a major factor in pathogenesis of the cerebral metabolic syndrome, which is a key step in neurodegeneration. Under this aspect we suggest a novel approach to prophylaxis and treatment focusing on a sufficient supply of glucose to the brain.

DNA methylation status influences insulin-induced glucose transport in 3T3-L1 adipocytes by mediating p53 expression

Researchers frequently use 3T3-L1 adipocytes as a fat cell line, but the capacity of this line for insulin-mediated glucose transport is lower than that of primary isolated fat cells. In this study, we found that 5-azacytidine (5-aza-C), DNA methyltransferase 1 inhibitor, enhanced insulin-stimulated 2-deoxyglucose (2-DG) transport in 3T3-L1 cells after adipogenic differentiation. We next examined the expression of the genes related to glucose transport and insulin signal transduction. The insulin independent glucose transporter, glucose transporter 1 (GLUT1), showed lower expression in 5-aza-C pre-treated 3T3-L1 adipocytes, than in un-treated control adipocytes, while the expression of insulin dependent transporter GLUT4 remained unchanged. In addition, insulin receptor substrate-1 (IRS-1) was highly expressed in 5-aza-C pre-treated adipocytes. Based on DNA microarray and functional annotation analysis, we noticed that 5-aza-C pretreatment activated the tumor suppressor p53 pathway. We confirmed that in 5-aza-C adipocytes, p53 expression was markedly higher, and the methylation level of CpGs in its promoter region was lower than in un-treated control adipocytes. Moreover, pharmacological inhibition of p53 restored GLUT1 and IRS-1 expression to the same level as in un-treated 3T3-L1 adipocytes, and significantly decreased insulin-mediated 2-DG uptake. These results suggest that glucose transport capacity in adipocytes is influenced by DNA methylation status, and demethylation induced by 5-aza-C increased it possibly through the p53 signaling pathway.

Altered DNA methylation of glucose transporter 1 and glucose transporter 4 in patients with major depressive disorder

Alterations in brain glucose metabolism and in peripheral glucose metabolism have frequently been observed in major depressive disorder (MDD). The insulin independent glucose transporter 1 (GLUT1) plays a key role in brain metabolism while the insulin-dependent GLUT4 is the major glucose transporter for skeletal and cardiac muscle. We therefore examined methylation of GLUT1 and GLUT4 in fifty-two depressed inpatients and compared data to eighteen healthy comparison subjects. DNA methylation of the core promoter regions of GLUT1 and GLUT4 was assessed by bisulfite sequencing. Further factors determined were fasting glucose, cortisol, insulin, interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α). We found significantly increased methylation of the GLUT1 in depressed inpatients compared to healthy comparison subjects (CG). Further findings comprise increased concentrations of fasting cortisol, glucose, insulin, and increased IL-6 and TNF-α. After six weeks of inpatient treatment, significantly lower GLUT1 methylation was observed in remitted patients compared to non-remitters. GLUT4 methylation was not different between depressed patients and CG, and did not differ between remitted and non-remitted patients. Although preliminary we conclude from our results that the acute phase of major depressive disorder is associated with increased GLUT1 methylation and mild insulin resistance. The successful treatment of depression is associated with normalization of GLUT1 methylation in remitters, indicating that this condition may be reversible. Failure of normalization of GLUT1 methylation in non-remitters may point to a possible role of impeded brain glucose metabolism in the maintenance of MDD.

Inhibition of Intestinal α-Glucosidase and Glucose Absorption by Feruloylated Arabinoxylan Mono- and Oligosaccharides from Corn Bran and Wheat Aleurone.

The effect of feruloylated arabinoxylan mono- and oligosaccharides (FAXmo) on mammalian α-glucosidase and glucose transporters was investigated using human Caco-2 cells, rat intestinal acetone powder, and Xenopus laevis oocytes. The isolated FAXmo from wheat aleurone and corn bran were identified to have degree of polymerization (DP) of 4 and 1, respectively, by HPLC-MS. Both FAXmo extracts were effective inhibitors of sucrase and maltase functions of the α-glucosidase. The IC50 for FAXmo extracts on Caco-2 cells and rat intestinal α-glucosidase was 1.03–1.65 mg/mL and 2.6–6.5 mg/mL, respectively. Similarly, glucose uptake in Caco-2 cells was inhibited up to 40%. The inhibitory effect of FAXmo was dependent on their ferulic acid (FA) content (R = 0.95). Sodium independent glucose transporter 2 (GLUT2) activity was completely inhibited by FAXmo in oocytes injected to express GLUT2. Our results suggest that ferulic acid and feruloylated arabinoxylan mono-/oligosaccharides have potential for use in diabetes management.

Functional characterization of a putative disaccharide membrane transporter in crustacean intestine (908.7)

Mechanisms of transepithelial absorption of dietary sucrose in the American lobster, Homarus americanus, were investigated to determine if disaccharide sugars can be transported across an animal gut intact. Intestines were mounted in a perfusion chamber to measure mucosal to serosal (MS) 14C‐sucrose transport. MS sucrose transport was a hyperbolic function of luminal sugar concentration, suggesting the presence of carrier‐mediated transport. Sodium‐dependent glucose transport inhibitor, phloridzin, partially decreased MS 14C‐sucrose transport, suggesting hydrolysis of 14C‐sucrose to glucose during transport. Phloretin, an inhibitor of Na+‐independent basolateral glucose transport, partially decreased MS 14C‐sucrose transport, suggesting that some 14C‐sucrose radioactivity may be transported to the blood as 14C‐glucose. Decreased MS 14C‐sucrose transport also occurred in the presence of the disaccharide trehalose. Thin‐layer chromatography (TLC) was used to identify the chemical nature of radioactively‐labeled sugars in the bath following transport and revealed that 14C‐sucrose was transported across the intestine largely as an intact molecule. Results suggest that disaccharide sugars may be transported intact across crustacean intestine and provide support for the occurrence of a disaccharide membrane transporter that has not previously been functionally characterized.Grant Funding Source: This project was supported by Agriculture and Food Research Initiative Competitive Grant no. 2010‐65

Glucose transport in brain – effect of inflammation

Glucose is transported across the cell membrane by specific saturable transport system, which includes two types of glucose transporters: 1) sodium dependent glucose transporters (SGLTs) which transport glucose against its concentration gradient and 2) sodium independent glucose transporters (GLUTs), which transport glucose by facilitative diffusion in its concentration gradient. In the brain, both types of transporters are present with different function, affinity, capacity, and tissue distribution. GLUT1 occurs in brain in two isoforms. The more glycosylated GLUT1 is produced in brain microvasculature and ensures glucose transport across the blood brain barrier (BBB). The less glycosylated form is localized in astrocytic end-feet and cell bodies and is not present in axons, neuronal synapses or microglia. Glucose transported to astrocytes by GLUT1 is metabolized to lactate serving to neurons as energy source. Proinflammatory cytokine interleukin (IL)-1β upregulates GLUT1 in endothelial cells and astrocytes, whereas it induces neuronal death in neuronal cell culture. GLUT2 is present in hypothalamic neurons and serves as a glucose sensor in regulation of food intake. In neurons of the hippocampus, GLUT2 is supposed to regulate synaptic activity and neurotransmitter release. GLUT3 is the most abundant glucose transporter in the brain having five times higher transport capacity than GLUT1. It is present in neuropil, mostly in axons and dendrites. Its density and distribution correlate well with the local cerebral glucose demands. GLUT5 is predominantly fructose transporter. In brain, GLUT5 is the only hexose transporter in microglia, whose regulation is not yet clear. It is not present in neurons. GLUT4 and GLUT8 are insulin-regulated glucose transporters in neuronal cell bodies in the cortex and cerebellum, but mainly in the hippocampus and amygdala, where they maintain hippocampus-dependent cognitive functions. Insulin translocates GLUT4 from cytosol to plasma membrane to transport glucose into cells, and GLUT8 from cytosol to rough endoplasmic reticulum to recover redundant glucose to cytosol after protein glycosylation. In autoimmune diseases, the enhanced glucose uptake was found in inflamed peripheral tissue, mainly due to proliferating fibroblasts and activated macrophages. In our experimental model of rheumatoid arthritis (adjuvant arthritis), enhanced 2-deoxy-2[F-18]fluoro-D-glucose was found in the hippocampus and amygdala two days after the induction of the disease which, similarly as in the peripheral joints, can be ascribed to the activated macrophages. The knowledge on the glucose transport and the role of glucose transporters in the brain during systemic autoimmune inflammation is still incomplete and needs further investigations.

Kardiovaskuläre Effekte inkretinbasierter Therapien

Pharmacological modulation of the glucagon-like peptide-1 (GLP-1) system has emerged as a new therapeutic option for treatment of diabetes mellitus. In addition to the glucose lowering potential GLP-1 was found to have a variety of cardioprotective effects. GLP-1 reduced the size of myocardial infarction during acute ischemia by activation of prosurvival pathways including PI3-kinase, Akt und ERK1/2. In addition, GLP-1 prevented atherosclerotic lesion formation in experimental models and improved endothelial function while acting anti-inflammatory. Furthermore GLP-1 was found to improve chronic heart failure by increasing insulin independent cellular glucose transport. Consequently GLP-1 based therapies might reduce cardiovascular events in diabetic patients which is currently evaluated in clinical endpoint studies.

TH‐B‐224‐03: FDG for Dose Painting: A Rational Choice

A straightforward way to improve local tumour control is to increase the radiation dose further, which is hampered by normal tissue constraints. Therefore, the concept of “dose painting” has been introduced, i.e. delivering a higher dose towards the more resistant tumour areas and reducing the dose towards the more sensitive area. Using this individualized strategy, the burden to the normal tissues can be kept constant; Probably the most investigated methodology for visualizing intra tumour radio‐resistance are hypoxia tracers. However, these tracers can have limitations, e.g. slow clearance of the unbound tracer in non‐hypoxic areas, low test re‐test performance, and low tumour to reference activity ratios can be observ. Also, as hypoxia is only one of several causes for radio‐resistance, there is a lot of uncertainty about how specific these hypoxia tracers relate to radio‐resistance;Another important micro‐environmental factor is tumour glucose metabolism, commonly assessed by the glucose analogue 18F‐deoxyglucose (FDG) for PET imaging. FDG is the workhorse in the field of oncology for diagnostic and prognostic purposes that has led to improved clinical decision making in a large quantity of cancer patients. Many investigations have shown that high FDG uptake is prognostic for worse survival for patients both treated with radiotherapy and surgery. During the past decades FDG has become widely available and a lot of progress was made in standardisation and reproducibility of FDG‐PET imaging, further improving the usability in the clinic.The underlying biology for FDG uptake is complex as it measures the uptake of glucose in cells by ATP independent glucose transporters. This makes FDG uptake specific to the metabolic pathway although this pathway is known to influence numerous other processes to facilitate cancer. Consequently, in contrast to hypoxia tracers, FDG uptake in the tumour does not reflect a single biologic characteristic, but is correlated to, although certainly not specific for, radio‐resistance, proliferation, cell density, hypoxia, mitochondrial dysfunction, and lipogenesis. Furthermore, in a pre‐clinical investigation, it has been shown that an increase of radiation dose showed a higher local control for tumours with higher FDG uptake compared to tumours with lower FDG uptake, affirming the relation between FDG‐uptake and radio‐resistance. Another argument is that the locations of the patterns of relapse are associated with the pre‐treatment high FDG uptake areas. Last year, our group has shown that the residual metabolic active areas after treatment show a high overlap with the high FDG uptake areas before treatment. This was confirmed in a study by the group of Dresden. These studies show that the location within the tumour with a high chance of metabolic relapse, and probably more radio‐resistant, can be identified before treatment using a single FDG‐PET‐CT scan. Furthermore, it was shown that these high FDG uptake areas remain stable during a course of radiotherapy, making it possible to keep a similar dose painting plan during treatment.As FDG corresponds to several biologic characteristics important for radio‐ resistance, due to the confirmed relation with the locations of relapse, the wide availability, the standardized imaging protocols, and the stability of the uptake patterns during RT, FDG is an attractive tracer for dose painting. Due to these favourable characteristics and because of sufficient improvements in the accuracy of imaging and dose delivery techniques, we believe that the time is right to more towards carefully designed clinical trials, by redistributing the dose towards the high pre‐treatment FDG uptake areas. A randomized phase 2 trial in lung cancer started in 2010 in The Netherlands.

Expression of Na+/glucose co-transporter 1 (SGLT1) in the intestine of piglets weaned to different concentrations of dietary carbohydrate

Na+/glucose co-transporter 1 (SGLT1) transports dietary sugars from the lumen of the intestine into enterocytes. Regulation of this protein is essential for the provision of glucose to the body and, thus, is important for maintenance of glucose homeostasis. We have assessed expression of SGLT1 at mRNA, protein and functional levels in the intestinal tissue of 28 d old piglets weaned onto isoenergetic diets with differing concentrations of digestible carbohydrate (CHO). We show that expression of SGLT1 remains constant when piglets are fed up to 40 % CHO-containing diets. However, there is a significant increase in SGLT1 expression when the CHO content of the diet is>50 %. Morphometric analyses indicate that the increased expression is not due to a trophic effect. It has been proposed that in rat intestine, in response to a high-CHO diet, GLUT2 (the classical basolateral membrane monosaccharide transporter) is translocated to the luminal membrane of enterocytes to absorb excess dietary glucose. We show, using immunohistochemistry and Western blotting with antibodies raised to amino acids in different epitopes of GLUT2, that under all dietary conditions, low to high CHO, GLUT2 is expressed on the basolateral membrane of pig enterocytes. Furthermore, functional studies indicate that there is no uptake of 2-deoxy-D-glucopyranoside, a specific substrate of Na+-independent glucose transporters into brush-border membrane vesicles isolated from the intestines of piglets either maintained on low- or high-CHO diets. Thus, SGLT1 is the major route for absorption of dietary sugars across the luminal membrane of swine enterocytes.

Glucose transport in interlobular ducts isolated from rat pancreas

Pancreatic duct cells express Na(+)-dependent glucose transporter, SGLT1 and Na(+)-independent glucose transporters, GLUT1, GLUT2, and GLUT8. We examined transepithelial glucose transport by pancreatic duct. Interlobular ducts were isolated from rat pancreas. During overnight culture both ends of the duct segments sealed spontaneously. The lumen of the sealed duct was micropunctured and the luminal fluid was replaced by HEPES-buffered solution containing 10.0 mM or 44.4 mM glucose. The bath was perfused with HEPES-buffered solution at 37 degrees C containing 10.0 or 44.4 mM glucose. Transepithelial differences in osmolality were balanced with mannitol. Glucose transport across ductal epithelium was measured by monitoring changes in luminal volume. When the lumen was filled with 44.4 mM glucose, with either 10.0 or 44.4 mM glucose in the bath, the luminal volume decreased to 65 approximately 70% of the initial volume in 15 min. Luminally-injected phlorizin, an inhibitor of SGLT1, abolished the decrease in luminal volume. With 10.0 mM glucose in the lumen and 44.4 mM glucose in the bath, the luminal volume did not change significantly. Luminal application of phlorizin under identical condition led to an increase in luminal volume. The data suggest that both active and passive transport mechanisms of glucose are present in pancreatic ductal epithelium.

A Functional Role for Sodium-Dependent Glucose Transport across the Blood-Brain Barrier during Oxygen Glucose Deprivation

In the current study, we determined the functional significance of sodium-dependent/-independent glucose transporters at the neurovasculature during oxygen glucose deprivation (OGD). Confluent brain endothelial cells cocultured with astrocytes were exposed to varying degrees of in vitro stroke conditions. Glucose transporter (GLUT) 1 and sodium glucose cotransporter (SGLT) activity were investigated by luminal membrane uptake and transport studies using [(3)H]D-glucose and also by [(14)C]alpha-methyl D-glucopyranoside (AMG), a specific, nonmetabolized substrate of SGLT. In vivo middle cerebral artery occlusion experiments were tested to determine whether blood-brain barrier (BBB) SGLT activity was induced during ischemia. Increases in luminal D-glucose and AMG uptake and transport were observed with in vitro stroke conditions. Specific inhibitor experiments suggest a combined role for both SGLT and GLUT1 at the BBB during OGD. A time-dependent increase in the uptake of AMG was also seen in mice exposed to permanent focal ischemia, and this increase was sensitive to the SGLT inhibitor, phlorizin. Infarct and edema ratio during ischemia were significantly decreased by the inhibition of this transporter. These results show that both GLUT1 and SGLT play a role at the BBB in the blood-to-brain transport of glucose during ischemic conditions, and inhibition of SGLT during stroke has the potential to improve stroke outcome. Pharmacological modulation of this novel BBB transporter could prove to be a brain vascular target in stroke.

Intestinal Permeability to Glucose after Experimental Traumatic Brain Injury: Effect of Gadopentetate Dimeglumine Administration

Traumatic injuries are the leading cause of mortality in individuals aged 1-44 years, and brain injury significantly contributes to the outcome in nearly one half of all deaths from trauma. At the intestinal level, traumatic brain injury (TBI) induces profound effects, including gastrointestinal mucosa ischaemia and motility dysfunction. However, nothing is known concerning the effect of TBI on the intestinal absorption of glucose. Hence, the aim of this study was to investigate the effect of TBI on the intestinal absorption of glucose by investigating the effect of TBI on the jejunal mucosal-to-serosal apparent permeability (AP-to-BL P(app)) to two glucose model substrates, (3)H-2-deoxy-D-glucose ((3)H-DG) and (3)H-3-O-methyl-D-glucose ((3)H-OMG), and to (14)C-sorbitol. Additionally, we tested if gadopentetate dimeglumine administration could prevent any of the changes observed after TBI. Traumatic brain injury induced an increase in the AP-to-BL P(app) to (3)H-DG. After a 100-min. perfusion of the jejunum, the AP-to-BL P(app) to (3)H-DG in TBI rats was almost 70% higher than in the control rats. There was no change, however, in the AP-to-BL P(app) to neither (3)H-OMG nor (14)C-sorbitol. Interestingly enough, gadopentetate dimeglumine was able to prevent the increase in the AP-to-BL P(app) to (3)H-DG observed after TBI. Given the differences in transport characteristics between (3)H-DG and (3)H-OMG, our results point to the possibility of the Na(+)-independent glucose transporter 2 (GLUT2) being activated by TBI (as the P(app) to (3)H-DG, a GLUT2 substrate, was increased) and the Na(+)-dependent glucose co-transporter (SGLT1) being inhibited by TBI (as the P(app) to (3)H-OMG, a GLUT2 and SGLT1 substrate, remained unchanged). Moreover, gadopentetate dimeglumine prevented these changes associated with TBI.

Mechanisms by which lipoic acid prevents high fat diet‐induced insulin resistance in skeletal muscle.

High fat diet‐induced insulin resistance is associated with impaired insulin signal transduction and reduced glucose transport in skeletal muscle. The anti‐oxidant alpha‐lipoic acid (LA) has been shown to improve insulin action in high fat fed animal models, yet little is known about the underlying mechanism. We hypothesize that LA acts by directly inhibiting stress kinases, such as c‐Jun N‐terminal kinase (JNK), known to interfere with insulin signaling intermediates. Male Wistar rats were fed a high fat diet (HFD, 60% calories from fat) for six weeks, while controls received a low fat diet (20% calories from fat). Half of the rats in each group received daily LA injections (30 mg/kg body wt). LA increased whole body glucose disposal in both diet groups as measured by oral glucose tolerance tests. LA treatment effectively restored insulin responsiveness in soleus muscles from rats fed a HFD, as seen by insulin‐stimulated pAkt/Akt and 2‐deoxyglucose uptake. LA treatment reduced the elevation of JNK (pJNK/JNK) seen with the HFD and increased activation of p38 MAPK and AMPK (pAMPK/AMPK), a mediator of insulin independent glucose transport. In addition, LA increased expression of heat shock protein 70 (HSP70), a protein previously shown to directly inhibit JNK activation, in rats fed a HFD. In conclusion, LA reversed HFD induced insulin resistance by reducing JNK, and increasing p38 MAPK, AMPK and HSP70 activation.

Carbohydrate Transport in Human Macrophages.

The lipid sensor LXR, a nuclear receptor expressed in macrophages, is activated by oxysterols (bioactive derivatives of cholesterol), and also by glucose and could be the connection between atherosclerosis and diabetes. Our hypothesis is that LXR has an interplay role between lipid and glucose metabolism in human macrophages. Methods: THP1 cells were differentiated into macrophages with PMA (24h, 100nM).Then, macrophages were challenged with insulin concentration and time courses before glucose transport was measured using [3H]-2-deoxy glucose. In a second set of experiences, cells were treated with T0901317 (LXR agonist) during 48 hours in a concentration course (0,1-1μM) in presence of absence of insulin (100nM, 30 min) and glucose transport measured. Finally total RNA from macrophages treated with T0901317 or/and 9cis retinoic acid (1μM), 48 hours, was purified (Trizol) and retro-transcribed into cDNA. The genetic expressions levels of GLUT1, GLUT3, GLUT4 and GLUT5 were measured using quantitative PCR. Results: Insulin induces a maximal response at 100nm that was maintained at 150nm and 200nM. For the time course, the optimal time was 30 min since insulin-induced glucose transport was transitory and returned to basal level after 45 min. T0901317 alone triggers glucose transport, but its effect was invalidated in presence of insulin. T0901317 and the 9 cis retinoic acid induced an increase in the GLUT1, GLUT3 and GLUT5 expression but increasing doses repressed these inductions. GLUT4 was no detected Conclusions: THP1 exhibits a transitory insulin-dependent glucose transport (GLUT3). Activation of LXRs triggers an insulin-independent glucose transport (GLUT1) that is blunted in presence of insulin. The repression of the insulin independent glucose transport by insulin associated with the decreasing induction of GLUTs while increased activation of LXRs/RXR suggest that the LXRs-induced glucose transport may be sensible to intracellular glucose levels.

Topiramate stimulates glucose transport through AMP-activated protein kinase-mediated pathway in L6 skeletal muscle cells

The use of topiramate (TPM) in the treatment of binge-eating disorder, bulimia nervosa, and antipsychotic-induced weight gain has recently increased, however, the exact molecular basis for its effects on body weight reduction and improved glucose homeostasis, is yet to be elucidated. Here we investigated the effect and signaling pathway of TPM on glucose uptake in L6 rat skeletal muscle cells, which account for >70% of glucose disposal in the body. Intriguingly, we found that TPM (10 microM) stimulated the rate of glucose uptake up to twofold increase. And TPM-stimulated glucose transport was inhibited with the overexpression of dominant-negative form of AMP-activated protein kinase (AMPK), an important mediator in glucose transport, implicating that AMPK-mediated pathway is involved. The TPM-stimulated glucose transport was blocked by SB203580, a specific inhibitor of AMPK downstream mediator, p38 mitogen-activated protein kinase (MAPK) protein. LY294002, an inhibitor of phosphatidylinositol (PI) 3-kinase, which is another crucial mediator in independent glucose transport pathway, did not inhibit TPM-stimulated glucose transport. We also found that TPM increased the phosphorylation level of AMPK and p38 MAPK, whereas no effect on the activity of PI 3-kinase of TPM, when assessed by PI 3-kinase assay, was observed. These results together suggest that TPM stimulates glucose transport, not via PI 3-kinase mediated, but via AMPK-mediated pathway in skeletal muscle cells, thereby contributing to the body weight regulation and glucose homeostasis.

Dehydroascorbic acid uptake by coronary artery smooth muscle: effect of intracellular acidification

Dehydroascorbic acid (DHAA) enters cells via Na+-independent glucose transporters (GLUT) and is converted to ascorbate. However, we found that Na+ removal inhibited [14C]DHAA uptake by smooth-muscle cells cultured from pig coronary artery. The uptake was examined for 2–12min at 10–200μM DHAA in either the presence of 134mM Na+ or in its absence (N-methyl d-glucamine, choline or sucrose replaced Na+). This inhibition of DHAA uptake by Na+ removal was paradoxical because it was inhibited by 2-deoxyglucose and cytochalasin B, as expected of transport via the GLUT pathway. We tested the hypothesis that this paradox resulted from an inefficient intracellular reduction of [14C]DHAA into [14C]ascorbate upon intracellular acidosis caused by the Na+ removal. Consistent with this hypothesis: (i) the Na+/H+-exchange inhibitors ethylisopropyl amiloride and cariporide also decreased the uptake, (ii) Na+ removal and Na+/H+-exchange inhibitors lowered cytosolic pH, with the decrease being larger in 12min than in 2min, and (iii) less of the cellular 14C was present as ascorbate (determined by HPLC) in cells in Na+-free buffer than in those in Na+-containing buffer. This inability to obtain ascorbate from extracellular DHAA may be detrimental to the coronary artery under hypoxia-induced acidosis during ischaemia/reperfusion.

Dehydroascorbic acid uptake by coronary artery smooth muscle: effect of intracellular acidification.

Dehydroascorbic acid (DHAA) enters cells via Na(+)-independent glucose transporters (GLUT) and is converted to ascorbate. However, we found that Na(+) removal inhibited [(14)C]DHAA uptake by smooth-muscle cells cultured from pig coronary artery. The uptake was examined for 2-12 min at 10-200 microM DHAA in either the presence of 134 mM Na(+) or in its absence (N-methyl D-glucamine, choline or sucrose replaced Na(+)). This inhibition of DHAA uptake by Na(+) removal was paradoxical because it was inhibited by 2-deoxyglucose and cytochalasin B, as expected of transport via the GLUT pathway. We tested the hypothesis that this paradox resulted from an inefficient intracellular reduction of [(14)C]DHAA into [(14)C]ascorbate upon intracellular acidosis caused by the Na(+) removal. Consistent with this hypothesis: (i) the Na(+)/H(+)-exchange inhibitors ethylisopropyl amiloride and cariporide also decreased the uptake, (ii) Na(+) removal and Na(+)/H(+)-exchange inhibitors lowered cytosolic pH, with the decrease being larger in 12 min than in 2 min, and (iii) less of the cellular (14)C was present as ascorbate (determined by HPLC) in cells in Na(+)-free buffer than in those in Na(+)-containing buffer. This inability to obtain ascorbate from extracellular DHAA may be detrimental to the coronary artery under hypoxia-induced acidosis during ischaemia/reperfusion.