Sodium-dependent Glucose Transporter Research Articles

Remogliflozin etabonate, a selective inhibitor of the sodium‐dependent transporter 2 reduces serum glucose in type 2 diabetes mellitus patients

Remogliflozin etabonate (RE) is the pro-drug of remogliflozin (R), a selective inhibitor of renal sodium-dependent glucose transporter 2 (SGLT2) that improves glucose control via enhanced urinary glucose excretion (UGE). This study evaluated the safety, tolerability, pharmacokinetics and pharmacodynamics of repeated doses of RE in subjects with type 2 diabetes mellitus (T2DM). In a double-blinded, randomized, placebo-controlled trial, subjects who were drug-naïve or had metformin discontinued received RE [100 mg BID (n = 9), 1000 mg QD (n = 9), 1000 mg BID (n = 9)], or placebo (n = 8) for 12 days. Safety parameters were assessed, including urine studies to evaluate renal function. Plasma concentrations of RE and metabolites were measured with the first dose and at steady state. RE effects on glucose levels were assessed with fasting glucose concentrations, frequently sampled 24-h glucose profiles and oral glucose tolerance tests. No significant laboratory abnormalities or safety events were reported; the most frequent adverse events were headache and flatulence. Plasma exposure to RE and R were proportional to administered dose with negligible accumulation. Mean 24-h UGE increased in RE treatment groups. Compared with the placebo group, 24-h mean (95% CI) changes in plasma glucose were -1.2 (-2.2 to -0.3) (100 mg BID), -0.8 (-1.7 to 0.2) (1000 mg QD) and -1.7 (-2.7 to -0.8) mmol/l (1000 mg BID). Administration of RE for 12 days is well-tolerated and results in clinically meaningful improvements in plasma glucose, accompanied by changes in body weight and blood pressure in subjects with T2DM.

Effect of dietary phytic acid on performance and nutrient uptake in the small intestine of piglets1

An experiment was conducted with piglets to determine the effect of dietary phytic acid supplementation on performance, electrophysiological properties of jejunum mounted in Ussing chambers, sodium-dependent glucose transporter 1 (SGLT1) protein expression in jejunum, and plasma glucose and Na concentrations. Sixteen piglets with an average initial BW of 7.40 ± 0.36 kg were randomly assigned to 2 experimental diets with 8 piglets per diet. The diets were casein-cornstarch-based and were either unsupplemented or supplemented with 2% phytic acid (as Na phytate). The basal diet was formulated to meet the recommendation of NRC (1998) for energy, AA, minerals, and vitamins for piglets. The experiment lasted for 21 d, and at the end, BW gain and feed consumption were determined, and blood samples were collected for determination of plasma glucose and Na concentrations. The piglets were then euthanized to determine jejunal electrophysiological properties (transmural potential difference and short-circuit current) and SGLT1 protein expression. Phytic acid supplementation reduced ADG (P = 0.002), ADFI (P = 0.017), and G:F (P = 0.001) from 316.1 to 198.2 g, 437.4 to 360.3 g, and 0.721 to 0.539 g/g, respectively. Phytic acid supplementation also tended to reduce (P = 0.088) potential difference (-3.80 vs. -2.23 mV) and reduced (P = 0.023) short-circuit current from 8.07 to 0.1 μA/cm(2). However, phytic acid supplementation did not affect SGLT1 protein, and blood plasma glucose and Na concentrations. In conclusion, dietary phytic acid reduced growth performance and transmural short-circuit current in the jejunum of piglets. The reduced transmural short-circuit current in the jejunum by phytic acid implies reduced active Na transport in the jejunum by the phytic acid. Therefore, it seems that dietary phytic acid reduces growth performance of pigs partly through reduced capacity of the small intestine to absorb Na.

Effects of Na-butyrate supplementation in milk formula on plasma concentrations of GH and insulin, and on rumen papilla development in calves

Although the growth-promoting action of sodium-butyrate (Na-butyrate) used as a feed additive has been observed in calves and pigs, the precise mechanisms involved remain to be clarified. In this study, pre-weaning calves were given milk formula (MF) supplemented with butyrate for 6 weeks to investigate its effects on postprandial changes in the plasma concentrations of metabolic hormones, and, simultaneously, on growth performance, the weight of the digestive organs and rumen papilla development. Ingestion of MF increased (P<0.05) the plasma concentrations of GH and insulin as well as the glucose level, but decreased the non-esterified fatty acid concentration. Na-butyrate supplementation in MF or in lactose solution (with the same quantity of lactose contained in the MF, 5%) suppressed the increase in plasma insulin and GH concentrations, and the plasma IGF1 level was not changed. The length of the rumen papilla and the weight of the perirenal fat tended to increase in the calves fed with Na-butyrate-supplemented MF, but the weight of the liver, spleen, and stomach were not changed. In addition, there was no difference in the expression of mRNA for sodium-dependent glucose transporter-1 in the small intestinal epithelial tissues. We conclude that the accelerated growth performance related to the intake of Na-butyrate used as a feed additive reported previously in several species is partly due to improved insulin sensitivity and a better digestive functional development. These data could be applicable to animal and human nutrition.

Effects at early stage of life of elevated milk replacer feeding on growth rate, plasma IGF‐I concentration and intestinal nutrient transporter expression in Holstein bull calves

In order to evaluate the effects of an elevated amount of modified milk replacer on body weight, daily gain, starter intake, plasma endocrine parameters and expression of nutrient transporters in small intestinal epithelia, Holstein bull calves (n=24) were fed for 60days either with the usual amount of 24% crude protein (CP) and 20% fat milk (CF) replacer (C group), or with a double amount of a modified milk replacer of 28% CP and 16% CF (E group). Body weight from D20 to D60 and daily gain before D40 was greater or tended to be greater for the E group than the C group. Plasma concentrations of insulin-like growth factor-1 (IGF-I) and insulin were greater for the E group than the C group on D28 but not on D56, without changing plasma growth hormone levels. Gene expression for sodium-dependent glucose transporter 1 and fatty acid translocase (CD36) was altered in day- and intestine-dependent manners. From these findings, we conclude that an elevated intake of milk replacer given up to 40days old is sufficient to enhance body weight, which may be associated with increased plasma IGF-I concentrations, in Holstein bulls.

Eemergence of Promising Therapies in Diabetes Mellitus

Diabetes mellitus (DM) results from defects in insulin secretion (type 1) or insulin resistance (type 2). Insulin is used to manage type 1 DM, and oral hypoglycemic agents are used to manage type 2 DM. These therapies are inconsistent in maintaining glycemic control and cause some severe adverse effects such as undue weight gain and hypoglycemia. New and appropriate therapies are needed to overcome these problems. Drugs that are in the pipeline include oral insulins for type 1 DM and incretin mimetics, incretin enhancers, gastric inhibitory peptides, amylin analogues, peroxisome proliferator-activated receptor-α/γ ligands, sodium-dependent glucose transporter inhibitors, and fructose 1,6-bisphosphatase inhibitors for type 2 DM. This article describes the mechanisms of action and relative advantages and disadvantages of the promising therapies.

GLUTs and Mammalian Sperm Metabolism

Mammalian cells use glucides as a substrate that can be catabolized through glycolitic pathways or oxidative phosphorylation, used as a source of reducing potential, or used for anabolic aims. An important role in supplying cells with energy is played by different membrane proteins that can actively (sodium-dependent glucose transporters) or passively (glucose transporters; GLUT) transport hexoses through the lipidic bilayer. In particular, GLUTs are a family of 13 proteins that facilitate the transport of sugars and have a peculiar distribution in different tissues as well as a particular affinity for substrates. These proteins are also present in mature sperm cells, which, in fact, need carriers for uptake energetic sources that are important for maintaining cell basic activity as well as specific functions, such as motility and fertilization ability. Likewise, several GLUTs have been studied in various mammalian species (man, bull, rat, mouse, boar, dog, stallion, and donkey) to point out both their actual presence or absence and their localization on plasma membrane. The aim of this work is to give an overall picture of the studies available on GLUTs in mammalian spermatozoa at this moment, pointing out the species peculiarity, the possible role of these proteins, and the potential future research on this item.

Luminal and endocrine factors for regulation of intestinal monosaccharide and Ca 2+ transport

Intestinal glucose and calcium (Ca 2+) absorption as well as their respective regulatory processes have been studied in detail in different species. Regulation is mediated from the luminal and the blood side of the barrier. For increasing glucose uptake, L-type Ca 2+ channels in connection with cytoskeletal rearrangement have been identified as relevant factors for the insertion of glucose transporter 2 (GLUT2) into the apical membrane. Apical located sweet taste receptors can be stimulated by high luminal glucose concentrations or artificial sweeteners which also results in stronger GLUT2 insertion. During long-term adaptation, sweet taste receptors mediate the upregulation of a sodium-dependent glucose transport system (SGLT1), which involves the activation of cAMP pathway. Therefore, it is assumed that sweet taste receptors are able to modulate short-term as well as long-term adaptation through the activation of different pathways. For endocrine regulation glucagon-like peptides, glucose-dependent insulinotropic polypeptide and leptin are under discussion. For Ca 2+ para- and transcellular pathways contribute to Ca 2+ absorption which includes transient receptor potential channels (TRP). Controversy still exists on the essential role of calbindin-D 9k for cellular transfer of Ca 2+. Calcitriol, Ca 2+ itself and other nutritional factors such as carbohydrates and short-chain fatty acids are involved in regulation of intestinal Ca 2+ absorption.

SGLT1, a novel cardiac glucose transporter, mediates increased glucose uptake in PRKAG2 cardiomyopathy

Human mutations in the gene PRKAG2 encoding the γ2 subunit of AMP-activated protein kinase (AMPK) cause a glycogen storage cardiomyopathy. Transgenic mice (TG T400N) with the human T400N mutation exhibit inappropriate activation of AMPK and consequent glycogen storage in the heart. Although increased glucose uptake and activation of glycogen synthesis have been documented in PRKAG2 cardiomyopathy, the mechanism of increased glucose uptake has been uncertain. Wildtype (WT), TG T400N, and TG α2DN (carrying a dominant negative, kinase dead α2 catalytic subunit of AMPK) mice were studied at ages 2–8 weeks. Cardiac mRNA expression of sodium-dependent glucose transporter 1 (SGLT1), but not facilitated-diffusion glucose transporter 1 (GLUT1) or GLUT4, was increased ∼ 5- to 7-fold in TG T400N mice relative to WT. SGLT1 protein was similarly increased at the cardiac myocyte sarcolemma in TG T400N mice. Phlorizin, a specific SGLT1 inhibitor, attenuated cardiac glucose uptake in TG T400N mice by ∼ 40%, but not in WT mice. Chronic phlorizin treatment reduced cardiac glycogen content by ∼ 25% in TG T400N mice. AICAR, an AMPK activator, increased cardiac SGLT1 mRNA expression ∼3-fold in WT mice. Relative to TG T400N mice, double transgenic (TG T400N/TG α2DN) mice had decreased (∼ 50%) cardiac glucose uptake and decreased (∼ 70%) cardiac SGLT1 expression. TG T400N hearts had increased binding activity of the transcription factors HNF-1 and Sp1 to the promoter of the gene encoding SGLT1. Our data suggest that upregulation of cardiac SGLT1 is responsible for increased cardiac glucose uptake in the TG T400N mouse. Increased AMPK activity leads to upregulation of SGLT1, which in turn mediates increased cardiac glucose uptake.

Calcitriol mediates the activity of SGLT1 through an extranuclear initiated mechanism that involves intracellular signaling pathways

The present study explored whether calcitriol plays a role in the regulation of sodium-dependent glucose transporter protein 1 (SGLT1) activity. For this purpose, alpha-methyl glucoside (AMG) uptake in stable transfected Chinese hamster ovary (CHO-G6D3) cells expressing rabbit SGLT1 (rbSGLT1) was used. The involvement of second messengers, intracellular signaling pathways, and pro-inflammatory cytokines were examined using specific inhibitors before incubation with calcitriol for 15 min. The present study demonstrated the involvement of second messengers produced by phospholipase A(2), phospholipase C, calmodulin, diacylglycerol kinase, and phosphoinositide 3 kinase on calcitriol-regulated AMG uptake. Pretreatment with inhibitors of the mitogen-activated protein kinase (MAPK) signaling pathway increased calcitriol-induced AMG uptake. In contrast, inhibition of the phosphoinositide 3-kinase PI3K/Akt/mTOR signaling pathway decreased the effect of calcitriol on AMG uptake. These findings suggest that calcitriol regulates rbSGLT1 activity through a rapid, extranuclear initiated mechanism of action stimulated by MAPK and inhibited by PI3K/Akt/mTOR. Another important finding was the effect of pro-inflammatory cytokines on calcitriol-induced AMG uptake. Interleukin-6 increased while tumor necrosis factor-alpha decreased calcitriol-induced AMG uptake. In conclusion, the present study demonstrates the involvement of calcitriol in the regulation of rbSGLT1 activity. This is due to the activation of intracellular signaling pathways triggered by second messenger molecules and cytokines after a short time (15 min) exposure to calcitriol.

Effect and mechanism of action of pine bark extract on glucose uptake by Caco‐2 cells

This work investigated the effect of pine bark extract (PBE) on glucose uptake by Caco‐2 cells. Cells were incubated in presence of PBE and [14C] 3‐O‐methyl‐D‐glucose and the change in radioactivity of the incubation medium was measured. PBE reduced significantly glucose uptake but did affect neither the activity nor the expression of the Na+/K+ ATPase suggesting that PBE affects the level of apical glucose transporters. To test this hypothesis, glucose uptake was measured in presence of inhibitors of Sodium‐dependent Glucose Transporter 1(SGLT1) and Facilitated‐Diffusion Glucose Transporter 2 (GLUT2), as well as different signaling mediators known to be involved in glucose transport. The results showed that PBE acts by activating p38 Mitogen‐activated protein (MAP) kinase which in turn activates SGLT1 transporters and two different pathways that target GLUT2: an inhibitory one involving Phosphatidylinositol‐3 kinase and a stimulatory one involving MAP/Extracellular signal‐regulated kinase. The effect of PBE was not attributed to the major ingredient, proanthocyanidins, since glucose uptake was increased in its presence. Supported by URB.

Comparison of the transcellular transport of FDG and D-glucose by the kidney epithelial cell line, LLC-PK1

Almost all D-glucose (GLU) filtered through the glomerulus is reabsorbed by the renal proximal tubules, whereas a high portion of 2-[18F]fluoro-2-deoxy-D-glucose [(18F)FDG] is excreted through the urine. However, [18F]FDG is not entirely excreted in the urine suggesting that it may be partially reabsorbed by the proximal tubules. The purpose of this study was to compare the time course of transcellular transport of administered [14C] labeled FDG ([14C]FDG) with that of [14C] labeled GLU ([14C]GLU) using the kidney epithelial cell line, LLC-PK1. Transcellular transport of [14C]FDG and [14C]GLU by LLC-PK1 cells was measured in Na+-containing or Na+-free Dulbecco's phosphate-buffered saline [PBS(+) and PBS(-), respectively] in the presence or absence of phlorizin, phloretin, probenecid, or tetraethylammonium bromide inhibitors that predominantly inhibit sodium-dependent glucose transporters (SGLTs), sodium-independent glucose transporters, organic anion transporters, and organic cation transporters, respectively. When assayed in PBS(+), less [14C]FDG than [14C]GLU was reabsorbed by the proximal tubular cells over the entire incubation time. Reabsorption of [14C]FDG was mediated mainly by SGLT at early time points in the incubation, whereas high reabsorption of [14C]GLU was mediated by both SGLT and glucose transporter over 90 min of incubation. Secretion of [14C]FDG also tended to be slightly higher than that of [14C]GLU over 90 min of incubation. Transcellular transport of [14C]FDG over time by LLC-PK1 cells was clarified. The polarized distribution of transcellular transporters of [14C]FDG and [14C]GLU in LLC-PK1 cells differs.

Sodium-dependent Glucose Transporter Was Involved in Salidroside Absorption in Intestine of Rats

Sodium-dependent Glucose Transporter Was Involved in Salidroside Absorption in Intestine of Rats

Sodium-dependent Glucose Transporter Was Involved in Salidroside Absorption in Intestine of Rats

Aim To report saturable absorption process of salidroside in rat intestine and investigate whether Na +-dependent glucose transporter (SGLT1) was involved in the absorption of salidroside. Method Rats orally received 12, 24 and 48 mg·kg − of salidroside, plasma concentrations were measured and corresponding pharmacokinetic parameters were estimated. Everted gut sleeves from the jejunum of rats were used for assaying the uptakes of salidroside in absences or presence of SGLT1 inhibitor phlorizin. Absorption of salidroside was investigated in diabetic rats induced by streptozotocin (STZ) and effective permeability coefficients in the jejunum of rats was carried out using in situ intestine perfusion. Results Plasma concentration-time profiles were completely overlapped, following oral dose 24 and 48 mg·kg −1 of salidroside, accompanied by similar pharmacokinetic parameters. Salidroside uptake by the rat everted gut sleeves was concentration-dependent and SGLTI inhibitor phlorizin might inhibit the uptake in a concentration-dependent manner. Salidroside was absorbed faster in gastro intestines of diabetic rats than it did in normal rats, accompanied by higher effective permeability coefficients. Conclusion Saturable absorption process of salidroside occurred in rat intestine and SGLT1 may be involved in the process of salidroside absorption.

Absorption of anthocyanins through intestinal epithelial cells – Putative involvement of GLUT2

Anthocyanins bioavailability is a major issue regarding their biological effects and remains unclear due to few data available on this matter. This work aimed to evaluate the absorption of anthocyanins at the intestine using Caco-2 cells. Anthocyanin extract, rich in malvidin-3-glucoside, was obtained from red grape skins and tested on Caco-2 cells. The absorption of anthocyanins, in absence or presence of 1% ethanol, was detected by HPLC/DAD/LC-MS. Our results showed that this transport was significantly increased in the presence of ethanol especially after 60 min of incubation. In addition, cells that were pretreated for 96 h with anthocyanins (200 microg/mL) showed an increase of their own transport (about 50% increase). Expression of glucose transporters sodium-dependent glucose transporter 1, facilitative glucose transporters 5, and facilitative glucose transporters 2 was assessed by RT-PCR. It was found that facilitative glucose transporters 2 expression was increased (60%) in Caco-2 cells pretreated with anthocyanins, by comparison with controls. When the effect of anthocyanin extract on (3)H-2-deoxy-D-glucose uptake was tested, an inhibitory effect was observed (about 60% decrease). However, the malvidin aglycone was tested and had no effect. In conclusion, anthocyanins could be absorbed through Caco-2 cells, and can interfere with their own transport and also with glucose intestinal uptake.

The small intestinal epithelia of beef steers differentially express sugar transporter messenger ribonucleic acid in response to abomasal versus ruminal infusion of starch hydrolysate1,2

In mammals, the absorption of monosaccharides from small intestinal lumen involves at least 3 sugar transporters (SugT): sodium-dependent glucose transporter 1 (SGLT1; gene SLC5A1) transports glucose and galactose, whereas glucose transporter (GLUT) 5 (GLUT5; gene SLC2A5) transports fructose, across the apical membrane of enterocytes. In contrast, GLUT2 (gene SLC2A2) transports all of these sugars across basolateral and apical membranes. To compare the distribution patterns and sensitivity with nutritional regulation of these 3 SugT mRNA in beef cattle small intestinal tissue, 18 ruminally and abomasally catheterized Angus steers (BW approximately 260 kg) were assigned to water (control), ruminal cornstarch (partially hydrolyzed by alpha-amylase; SH), or abomasal SH infusion treatments (n = 6) and fed an alfalfa-cube-based diet at 1.3 x NE(m) requirement. The SH infusions amounted to 20% of ME intake. After 14- or 16-d of infusion, steers were killed; duodenal, jejunal, and ileal epithelia harvested; and total RNA extracted. The relative amount of SugT mRNA in epithelia was determined using real-time reverse transcription-PCR quantification methods. Basal expression of GLUT2 and SGLT1 mRNA was greater (P < 0.09) by jejunal than by duodenal or ileal epithelia, whereas basal content of GLUT5 mRNA was greater (P < or = 0.02) by jejunal and duodenal than by ileal epithelia. The content of GLUT5 mRNA in small intestinal epithelia was not affected (P > or = 0.16) by either SH infusion treatment. In contrast, GLUT2 and SGLT1 mRNA content in the ileal epithelium was increased (P < or = 0.05) by 6.5- and 1.3-fold, respectively, after abomasal SH infusion. Duodenal SGLT1 mRNA content also was increased (P = 0.07) by 64% after ruminal SH infusion. These results demonstrate that the ileum of beef cattle small intestine adapts to an increased luminal supply of glucose by increasing SGLT1 and GLUT2 mRNA content, whereas increased ruminal SH supply results in duodenal upregulation of SGLT1 mRNA content. These adaptive responses of GLUT2 and SGLT1 mRNA to abomasal or ruminal SH infusion suggest that beef cattle can adapt to increase their carbohydrate assimilation through small intestinal epithelia, assuming that altered SugT mRNA contents reflect the altered transport functional capacities.

Intestinal Glucose Uptake Protects Liver from Lipopolysaccharide and d-Galactosamine, Acetaminophen, and Alpha-Amanitin in Mice

We have recently observed that oral administration of D-glucose saves animals from lipopolysaccharide (LPS)-induced death. This effect is the likely consequence of glucose-induced activation of the sodium-dependent glucose transporter-1. In this study, we investigated possible hepatoprotective effects of glucose-induced, sodium-dependent, glucose transporter-1 activation. We show that oral administration of D-glucose, but not of either D-fructose or sucrose, prevents LPS-induced liver injury, as well as liver injury and death induced by an overdose of acetaminophen. In both of these models, physiological liver morphology is maintained and organ protection is confirmed by unchanged levels of the circulating markers of hepatotoxicity, such as alanine transaminase or lactate dehydrogenase. In addition, D-glucose was found to protect the liver from alpha-amanitin-induced liver injury. In this case, in contrast to the previously described models, a second signal had to be present in addition to glucose to achieve protective efficacy. Toll-like receptor 4 stimulation that was induced by low doses of LPS was identified as such a second signal. Eventually, the protective effect of orally administered glucose on liver injury induced by LPS, overdose of acetaminophen, or alpha-amanitin was shown to be mediated by the anti-inflammatory cytokine interleukin-10. These findings, showing glucose-induced protective effects in several animal models of liver injury, might be relevant in view of possible therapeutic interventions against different forms of acute hepatic injury.

Glucose and Glucose Transporters in Pig Uteri and Conceptuses.

Glucose, the main energy source for mammalian embryos during the peri-implantation period, may promote growth and development of conceptuses via the FRAP1 nutrient sensing cell signaling pathway. Therefore, mechanisms for glucose transport into the uterine lumen and uptake by conceptuses are essential. We reported significant increases in glucose in the uterine lumen during early pregnancy in sheep associated with increases in expression of both facilitative and sodium-dependent glucose transporters in the uterine endometrium that were regulated by pregnancy, progesterone (P4) and interferon tau (IFNT). However, little information is available on glucose transporters in uteri and conceptuses in other domestic animals including pigs. Experiment 1 determined effects of day of the estrous cycle and pregnancy on total recoverable glucose in uterine flushings from gilts on Days 5, 9, 12 and 15 of the estrous cycle (Cy) and Days 9, 10, 12, 13, 14 and 15 of pregnancy (Px) (n=4). Total recoverable glucose increased (P<0.05) with day of the Cy and Px. Experiment 2 determined recoverable glucose in uterine flushings of gilts ovariectomized on Day 12 and treated daily with either corn oil (OVX-CO; n=4) or 200 mg progesterone (OVX-P4; n=5) to Day 39 and hysterectomized on Day 40. Recoverable glucose in uterine flushings (mean + SEM; nmol) was greater for OVX-P4 than OVX-CO gilts (4,955+2534 vs 726+133), but this difference was not significant due to variability and the small number of gilts. Experiment 3 determined amounts of glucose in uterine flushings of gilts on Day 90 of pseudopregnancy (PP) that was induced by treatment with 5 mg/day estradiol benzoate on Days 11 to 15 after onset of estrus. The flushings (109+24 ml) contained significant amounts (nmol) of glucose (14,007+3,946). Uterine and conceptus tissues collected from experiments 1-3 were examined by in situ hybridization for expression of Facilitated Glucose Transporters SLC2A1, SLC2A2, SLC2A3 and SLC2A4. Results indicated that: 1) SLC2A3 mRNA was not detectable or very weak in conceptuses and endometria, respectively; 2) SLC2A1 mRNA was expressed by all cell types in conceptuses and was abundant in uterine luminal epithelia (LE) of Cy, Px, PP and OVX-P4 gilts; 3) SLC2A4 mRNA was moderately abundant in LE of Px, but not Cy gilts, only between Days 13 and 25 of Px and LE and GE of OVX-P4 gilts, and not detected in LE or GE of PP gilts; 4) SLC2A2 mRNA was abundant in conceptuses from Days 12 to 40 of pregnancy, decreased to Day 50 and then increased and was maintained specifically in placental areolae and basal crypts of the chorioallantois to Day 80 of gestation. SL2CA2 was also expressed in uterine LE of Px and PP gilts and LE and GE of OVX-P4 gilts. Results of these studies indicate that: 1) the availability of glucose increased in the uterine lumen of Cy and Px gilts between Days 9 to 15; 2) glucose was abundant in uterine flushings from PP and OVX-P4 gilts; 3) temporal and cell specific changes in abundance of mRNAs for specific glucose transporters in uterine LE and GE, as well as chorioallantois likely affect abundance of glucose in the uterus and conceptus; and 4) SLC2A1 expression in uterine endometrium was stimulated by P4. Thus, facilitative glucose transporters responsible for transport of glucose into the uterine lumen of pigs occurs primarily when the uterus is under the influence of progesterone and are available for transport of glucose to the conceptus. (poster)

Diabetes mellitus and expression of the enterocyte renin-angiotensin system: implications for control of glucose transport across the brush border membrane

Streptozotocin-induced (Type 1) diabetes mellitus (T1DM) in rats promotes jejunal glucose transport, but the trigger for this response remains unclear. Our recent work using euglycemic rats has implicated the enterocyte renin-angiotensin system (RAS) in control of sodium-dependent glucose transporter (SGLT1)-mediated glucose uptake across the jejunal brush border membrane (BBM). The aim of the present study was to examine whether expression of enterocyte RAS components is influenced by T1DM. The effects of mucosal addition of angiotensin II (AII) on [(14)C]-D-glucose uptake by everted diabetic jejunum was also determined. Two-week diabetes caused a fivefold increase in blood glucose level and reduced mRNA and protein expression of AII type 1 (AT(1)) and AT(2) receptors and angiotensin-converting enzyme in isolated jejunal enterocytes. Angiotensinogen expression was, however, stimulated by diabetes while renin was not detected in either control or diabetic enterocytes. Diabetes stimulated glucose uptake into everted jejunum by 58% and increased the BBM expression of SGLT1 and facilitated glucose transporter 2 (GLUT2) proteins, determined by Western blotting by 25% and 135%, respectively. Immunohistochemistry confirmed an enhanced BBM expression of GLUT2 in diabetes and also showed that this was due to translocation of the transporter from the basolateral membrane to BBM. AII (5 microM) or L-162313 (1 microM), a nonpeptide AII analog, decreased glucose uptake by 18% and 24%, respectively, in diabetic jejunum. This inhibitory action was fully accountable by an action on SGLT1-mediated transport and was abolished by the AT(1) receptor antagonist losartan (1 microM). The decreased inhibitory action of AII on in vitro jejunal glucose uptake in diabetes compared with that noted previously in jejunum from normal animals is likely to be due to reduced RAS expression in diabetic enterocytes, together with a disproportionate increase in GLUT2, compared with SGLT1 expression at the BBM.

SGLT1 is a novel cardiac glucose transporter that is perturbed in disease states

Cardiac myocytes depend on a delicate balance of glucose and free fatty acids as energy sources, a balance that is disrupted in pathological states such as diabetic cardiomyopathy and myocardial ischaemia. There are two families of cellular glucose transporters: the facilitated-diffusion glucose transporters (GLUT); and the sodium-dependent glucose transporters (SGLT). It has long been thought that only the GLUT isoforms, GLUT1 and GLUT4, are responsible for cardiac myocyte glucose uptake. However, we discovered that one SGLT isoform, SGLT1, is also an important glucose transporter in heart. In this study, we aimed to determine the human and murine cardiac expression pattern of SGLT1 in health and disease and to determine its regulation. SGLT1 was largely localized to the cardiac myocyte sarcolemma. Changes in SGLT1 expression were observed in disease states in both humans and mouse models. SGLT1 expression was upregulated two- to three-fold in type 2 diabetes mellitus and myocardial ischaemia (P < 0.05). In humans with severe heart failure, functional improvement following implantation of left ventricular assist devices led to a two-fold increase in SGLT1 mRNA (P < 0.05). Acute administration of leptin to wildtype mice increased cardiac SGLT1 expression approximately seven-fold (P < 0.05). Insulin- and leptin-stimulated cardiac glucose uptake was significantly (P < 0.05) inhibited by phlorizin, a specific SGLT1 inhibitor. Our data suggest that cardiac SGLT1 expression and/or function are regulated by insulin and leptin, and are perturbed in disease. This is the first study to examine the regulation of cardiac SGLT1 expression by insulin and leptin and to determine changes in SGLT1 expression in cardiac disease.

Identification of a novel sodium-dependent fructose transport activity in the hepatopancreas of the Atlantic lobsterHomarus americanus

[(3)H]Fructose and [(3)H]glucose transport were determined in brush-border membrane vesicles (BBMV), basolateral membrane vesicles (BLMV) and isolated cells (E, R, F, B) of H. americanus (Atlantic lobster) hepatopancreas. Glucose transport in BBMV was equilibrative in the absence of sodium and concentrative in the presence of sodium. Sodium-dependent glucose transport by BBMV was not inhibited by a tenfold molar excess of fructose. Glucose transport by BLMV was equilibrative and sodium independent. Fructose uptake by BBMV and BLMV was equilibrative in the absence of sodium and concentrative in the presence of sodium. This enhancement was not affected by a tenfold molar excess of glucose in the presence of sodium. E-, F- and B-cells showed sodium-dependent uptake of fructose, while R-cells did not. Sodium-dependent fructose uptake by E-cells was not inhibited by a tenfold molar excess of glucose or mannose. Western blot analysis of BBMV, BLMV and E-, R-, F- and B-cells using rabbit polyclonal antibodies directed against epitopes of mammalian GLUT2, GLUT5, SGLT1 and SGLT4 indicated the presence of cross-reacting lobster proteins. Sequence alignment of the mammalian proteins with translated, lobster expressed sequence tags also indicated significant identity between species. Comparison of fructose and glucose uptake in the absence and presence of sodium by BBMV, BLMV and isolated cells indicated the presence of a distinct sodium-dependent transport activity for each sugar in the Atlantic lobster.