Dependent Glucose Co-transporter Research Articles

THE USE OF SODIUM-DEPENDENT GLUCOSE CO-TRANSPORTER-2 INHIBITORS IN PATIENTS IN THE ACUTE PHASE OF MYOCARDIAL INFARCTION

The purpose of the work– to analyze the data of modern literature concerning expediencyof using sodium- dependent glucose cotransporter type 2 inhibitors in the early stages ofacute myocardial infarction to improve the prognosis and reduce mortality.Conclusions. The analysis of literature data shows the growing evidence of iNZKTG2effectiveness as the newest generation of cardiorenal protectors. The potential effects ofiNZCTH2 may be particularly beneficial for patients with acute myocardial infarction.Proving the effectiveness of iNZCTH2 in acute myocardial infarction may become thebasis for revising the standards of treatment of this common acute cardiovascular disease,which leads to significant complications and mortality.

Abstract 1843: Dianhydrogalactitol (VAL-083) for the treatment of glioblastoma multiforme (GBM): Impact of glucose transporters for crossing the blood brain barrier (BBB)

Abstract Glucose transporters at the blood brain barrier (BBB) maintain the continuous high glucose and energy demands of the brain. These transporters have been targets for the creation of therapeutic molecules as a means to cross the BBB. The BBB has been a major limitation for the successful development of treatments for brain tumors. To date, only a limited number of lipophilic small chemical entities, which can cross the BBB, have been approved for the treatment of GBM. These include the nitrosoureas such as carmustine (BCNU) and lomustine (CCNU) and temozolomide (TMZ). VAL-083 is a di-epoxide substituted hexitol sugar (galactitol). It has a molecular weight of 146 and is highly water soluble. VAL-083 is active against several GBM cell lines and animal models and acts as a DNA targeting agent rapidly forming cross-links at the N7 position of guanine, resulting in lethal DNA double strand breaks and cancer cell death. Its is active in GBM patients, both newly diagnosed and recurrent. Furthermore, its activity is independent of the DNA repair enzyme MGMT which limits the effectiveness of O6 guanine alkylating agents such as the nitrosoureas and TMZ.In clinical pharmacology studies, VAL-083 rapidly accumulates in the cerebrospinal fluid (CSF) and brain tumor tissue. Studies with radiolabeled VAL-083 have shown a half-life of ~ 20 h in CSF vs 2h for plasma post-IV infusion. Recent clinical studies in newly diagnosed GBM patients demonstrated levels of VAL-083 in CSF at least as high as in plasma two hours post infusion (ratio 1.24 ± 0.35). In comparison, peak TMZ concentrations in the CSF are ~30% of that of the plasma.Due to its structural similarity with glucose, we have initiated in vitro glucose transporter studies to identify if SGLTs (sodium dependent glucose cotransporters) or GLUTs (glucose transporters) are contributing to brain penetration. Our initial studies evaluated VAL-083 as a substrate of the human SGLT1 and SGLT2 SLC (solute carrier) transporters. HEK293 cells expressing either the SGLT1 or SGLT2 transporter were exposed to VAL-083 at 3 and 15 µM for 2 and 20 min. The probe substrate methyl-α-D- glucopyranoside (AMG) was used as a positive control, as well as comparison against the reference inhibitors phloridzin dihydrate (100 µM, 20 min) for SGLT1 and dapagliflozin (0.3 µM, 10 min) for SGLT2. Surprisingly, no transporter-specific accumulation of VAL-083 by SGLT1 or SGLT2 was observed. Ongoing studies in CaCo-2 cells are investigating whether VAL-083 is transported via other glucose transporters including GLUT1. GLUT1 is expressed on erythrocytes and the endothelial cells of the BBB and may be highly relevant to the uptake of VAL-083 into brain tissue. The results of these studies will be reported at the meeting. Citation Format: John M. Langlands, Sarath Kanekal, Anne Steino, Armando Mendez, Zoltan Karman, Beata Martonne Toth, Krisztina Heredi-Szabo, Dennis Brown. Dianhydrogalactitol (VAL-083) for the treatment of glioblastoma multiforme (GBM): Impact of glucose transporters for crossing the blood brain barrier (BBB) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1843.

The sodium-glucose cotransporter isoform 1 (SGLT-1) is important for sperm energetics, motility, and fertility†.

Glucose is a key substrate for supporting sperm energy production and function. Previous studies have demonstrated that sperm glucose uptake is facilitated by several isoforms of the glucose transporters (GLUT). Here, we report that sperm also expresses the Na+-dependent sodium glucose cotransporter (SGLT). This was first suggested by our observation that genetic deletion of the testis-specific Na,K-ATPase α4, which impairs the sperm plasma membrane Na+ gradient, reduces glucose uptake and ATP production. Immunoblot analysis revealed the presence of an SGLT in sperm, with specific expression of isoform 1 (SGLT-1), but not of isoform 2 (SGLT-2). Immunocytochemistry identified SGLT-1 in the mid- and principal piece of the sperm flagellum. Inhibition of SGLT-1 with the isotype-selective inhibitor phlorizin significantly reduced glucose uptake, glycolytic activity, and ATP production in noncapacitated and capacitated sperm from wild-type mice. Phlorizin also decreased total sperm motility, as well as other parameters of sperm movement. In contrast, inhibition of SGLT-1 had no significant effect on sperm hyperactivation, protein tyrosine phosphorylation, or acrosomal reaction. Importantly, phlorizin treatment impaired the fertilizing capacity of sperm. Altogether, these results demonstrate that mouse sperm express a functional SGLT transport system that is important for supporting sperm energy production, motility, and fertility.

Dual-Target Compounds against Type 2 Diabetes Mellitus: Proof of Concept for Sodium Dependent Glucose Transporter (SGLT) and Glycogen Phosphorylase (GP) Inhibitors.

A current trend in the quest for new therapies for complex, multifactorial diseases, such as diabetes mellitus (DM), is to find dual or even multi-target inhibitors. In DM, the sodium dependent glucose cotransporter 2 (SGLT2) in the kidneys and the glycogen phosphorylase (GP) in the liver are validated targets. Several (β-D-glucopyranosylaryl)methyl (het)arene type compounds, called gliflozins, are marketed drugs that target SGLT2. For GP, low nanomolar glucose analogue inhibitors exist. The purpose of this study was to identify dual acting compounds which inhibit both SGLTs and GP. To this end, we have extended the structure-activity relationships of SGLT2 and GP inhibitors to scarcely known (C-β-D-glucopyranosylhetaryl)methyl arene type compounds and studied several (C-β-D-glucopyranosylhetaryl)arene type GP inhibitors against SGLT. New compounds, such as 5-arylmethyl-3-(β-D-glucopyranosyl)-1,2,4-oxadiazoles, 5-arylmethyl-2-(β-D-glucopyranosyl)-1,3,4-oxadiazoles, 4-arylmethyl-2-(β-D-glucopyranosyl)pyrimidines and 4(5)-benzyl-2-(β-D-glucopyranosyl)imidazole were prepared by adapting our previous synthetic methods. None of the studied compounds exhibited cytotoxicity and all of them were assayed for their SGLT1 and 2 inhibitory potentials in a SGLT-overexpressing TSA201 cell system. GP inhibition was also determined by known methods. Several newly synthesized (C-β-D-glucopyranosylhetaryl)methyl arene derivatives had low micromolar SGLT2 inhibitory activity; however, none of these compounds inhibited GP. On the other hand, several (C-β-D-glucopyranosylhetaryl)arene type GP inhibitor compounds with low micromolar efficacy against SGLT2 were identified. The best dual inhibitor, 2-(β-D-glucopyranosyl)-4(5)-(2-naphthyl)-imidazole, had a Ki of 31 nM for GP and IC50 of 3.5 μM for SGLT2. This first example of an SGLT-GP dual inhibitor can prospectively be developed into even more efficient dual-target compounds with potential applications in future antidiabetic therapy.

Restoration of the Attenuated Neuroprotective Effect of Ischemic Postconditioning in Diabetic Mice by SGLT Inhibitor Phlorizin.

The study has been commenced to discover the potential of sodium dependent glucose co-transporters (SGLT) in neuroprotective mechanism of ischemic postconditioning (iPoCo) in diabetic and non-diabetic mice. Cerebral ischemic injury in mice was induced by bilateral carotid artery occlusion (BCAO) for 12 min followed by reperfusion for 24 hr. For iPoCo, three episodes of carotid artery reperfusion and occlusion of 10 sec each were instituted immediately after BCAO, followed by 24 hr reperfusion. Learning and memory were evaluated using the Morris water maze test. Motor coordination was assessed using rotarod test, inclined beam walking test, neurological severity score (NSS), and lateral push response. Glutathione and Thiobarbituric acid reactive species level was quantified to evaluate the oxidative stress; the cholinergic activity of the brain was estimated in terms of acetylcholinestrase activity, and the levels of myeloperoxidase were measured as inflammation marker. Cerebral infarct size was evaluated using triphenyltetrazolium chloride staining. Fasting blood glucose levels of animals were taken before and 6 hr after the surgical procedure. BCAO resulted in impairment of memory and motor coordination and biochemical alterations along with a marked rise in cerebral infarct size and NSS. iPoCo diminished the deadly effect of BCAO in non-diabetic mice; however, it failed to abolish the deleterious effects of ischemia- reperfusion injury in diabetic mice. Pretreatment of Phlorizin (SGLT-inhibitor) potentiated the neuroprotective effects of iPoCo in non-diabetics and restored the protective effect of iPoCo in diabetic mice. It may be concluded that the neuroprotective effect of iPoCo is abolished in diabetic mice, and SGLT plays an important role in neuroprotection.

Integrated computational approach on sodium-glucose co-transporter 2 (SGLT2) Inhibitors for the development of novel antidiabetic agents

Nowadays, diabetes mellitus has become a global health concern. Various marketed drugs are available to treat diabetes but many of them produced undesirable side effects. From past few decades, sodium dependent glucose co-transporter 2 (SGLT2) is regarded as a hot target for type 2 diabetes mellitus due to its novel mechanism of action with less side effects. A majority of computational studies have been performed by many researchers to find out novel inhibitors to the target SGLT2. In the present study, we performed computational analysis using different drug designing tools to ascertain the best possible molecules from a dataset of 90 C-aryl glucoside analogues obtained from literature. The pharmacophore mapping study was performed to determine the key functional features responsible for the activity. The 3D-QSAR (CoMFA, CoMSIA and atom based QSAR) analysis was carried out by using 63 molecules as a training set & rest of the 27 as test sets to know the contribution of different fields & atoms for model development. The MFA with PLS method was used to generate a statistically significant model (q2 = 0.7387, r2 = 0.8670). The QSAR model was validated using LOO cross-validation (r2CV = 0.5305) & external validation (r2pred = 0.985). The homology model of SGLT2 was constructed using co-crystallized structure (PDB: 2XQ2_A) as templates & validated by Ramachandran plot. The docking study of potent C-aryl glucoside analogues (22, 23 and 26) showed highest SP docking scores (-7.22, -7.012 & -6.867) with the involvement of critical interactions with amino acid residues Asn75, His80, Glu99, Ser287, Tyr290 & Trp291. ADME analysis provides valuable information about drugability of newly designed compounds. Correlating the docking results with the 3D-QSAR and binding free energy calculations by MMGBSA analysis can suggest the active conformation of SGLT2 inhibitors and the nature of interactive fields important for binding and activity.

Effectiveness in the inhibition of dapagliflozin and canagliflozin on M-type K+ current and α-methylglucoside-induced current in pituitary tumor (GH3) and pheochromocytoma PC12 cells

Dapagliflozin (DAPA) or canagliflozin (CANA), Na+-dependent glucose co-transporter type 2 (SGLT2) inhibitors, were used for treatment of type II diabetes mellitus. Addition of DAPA or CANA suppressed M-type K+ current (IK(M)) in pituitary tumor (GH3) and pheochromocytoma PC12 cells. The IC50 value for DAPA- or CANA-mediated inhibition of IK(M) in GH3 cells was 0.11 or 0.42 μM, respectively. The presence of DAPA (0.1 μM) shifted the steady-state activation of IK(M) to less depolarized potential without changing the gating charge of the current. During high-frequency depolarizing pulses, IK(M) magnitude was reduced by DAPA; however, DAPA-induced block of IK(M) remained effective. The amplitude of neither erg-mediated K+ current nor hyperpolarization-activated cation current in GH3 cells was modified in the presence of 1 μM DAPA. Alternatively, addition of DAPA, CANA, phlorizin or chlorotoxin effectively suppressed α-methylglucoside-(αMG-) induced current (IαMG) in GH3 cells, albeit inability of tefluthrin (activator of INa) to suppress this current. DAPA shifted the charge-voltage relation of presteady-state IαMG in a rightward and downward direction with no change in the gating charge of the IαMG. Under current-clamp recordings, subsequent additions of DAPA, but still in the continued presence of αMG, increased the firing rate of spontaneous action potentials stimulated by αMG. Our results suggested that activity of SGLT was expressed functionally in GH3 and PC12 cells. Therefore, inhibitory actions of DAPA or CANA on the amplitude and gating of IK(M) might provide a yet unidentified mechanism through which the SGLT1 or SGLT2 activity were attenuated in unclamped cells occurring in vivo.

Moderate Alcohol Consumption Uniquely Regulates Sodium-Dependent Glucose Co-Transport in Rat Intestinal Epithelial Cells In Vitro and In Vivo

Chronic alcohol use often leads to malnutrition. However, how the intestinal absorption of nutrients such as glucose may be affected during moderate ethanol use has not been investigated. Glucose is absorbed via sodium (Na)-dependent glucose co-transport (SGLT1; SLC5A1) along the brush border membrane (BBM) of intestinal absorptive villus cells. The aim of this study was to investigate how moderate alcohol consumption affects the absorption of glucose via SGLT1. Intestinal epithelial cells (IEC-18; rat) were exposed to 8.64mM ethanol over 1, 3, 6, and 12 h. Rats (16-wk-old, male, Sprague-Dawley) were administered 2g/kg ethanol over 1, 3, and 6 h. Na-dependent 3H-O-methyl-d-glucose uptake was measured to assess SGLT1 activity. Na-K-ATPase activity was measured as a function of inorganic phosphate release. Protein expression was analyzed by Western blot analysis and immunohistochemical staining. Ethanol significantly decreased Na-dependent glucose absorption in enterocytes in vitro (ethanol treatment: 48.4% of controls at 1 h; P<0.01) and in vivo (ethanol treatment: 60.0% of controls at 1 h; P<0.01). Na-K-ATPase activity was significantly inhibited in vitro (ethanol treatment: 36.9% of controls at 1 h; P<0.01) and in vivo (ethanol treatment: 42.1% of controls at 1 h; P<0.01). Kinetic studies showed that the mechanism of inhibition of Na-glucose co-transport was secondary to a decrease in the affinity (1/Km) of the co-transporter for glucose both in vitro and in vivo. Western blots and immunohistochemistry further demonstrated unaltered amounts of SGLT1 after ethanol treatment. Moderate ethanol significantly decreases glucose absorption in IEC-18 cells and in villus cells of Sprague-Dawley rats. The inhibition of SGLT1 is secondary to an altered Na gradient at the cellular level and secondary to diminished affinity of the co-transporter for glucose at the protein level in the BBM. These observations may, at least in part, explain 1 possible mechanism of the onset of malnutrition associated with alcohol consumption.

Na+-Coupled Nutrient Cotransport Induced Luminal Negative Potential and Claudin-15 Play an Important Role in Paracellular Na+ Recycling in Mouse Small Intestine

Many nutrients are absorbed via Na+ cotransport systems, and therefore it is predicted that nutrient absorption mechanisms require a large amount of luminal Na+. It is thought that Na+ diffuses back into the lumen via paracellular pathways to support Na+ cotransport absorption. However, direct experimental evidence in support of this mechanism has not been shown. To elucidate this, we took advantage of claudin-15 deficient (cldn15−/−) mice, which have been shown to have decreased paracellular Na+ permeability. We measured glucose-induced currents (ΔIsc) under open- and short-circuit conditions and simultaneously measured changes in unidirectional 22Na+ fluxes (ΔJNa) in Ussing chambers. Under short-circuit conditions, application of glucose resulted in an increase in ΔIsc and unidirectional mucosal to serosal 22Na+ (∆JNaMS) flux in both wild-type and cldn15−/− mice. However, under open-circuit conditions, ΔIsc was observed but ∆JNaMS was strongly inhibited in wild-type but not in cldn15−/− mice. In addition, in the duodenum of mice treated with cholera toxin, paracellular Na+ conductance was decreased and glucose-induced ∆JNaMS increment was observed under open-circuit conditions. We concluded that the Na+ which is absorbed by Na+-dependent glucose cotransport is recycled back into the lumen via paracellular Na+ conductance through claudin-15, which is driven by Na+ cotransport induced luminal negativity.

In silico modeling and in vitro activity of vitexin and isovitexin against SGLT2

The homology model of hSGLT2 (human sodium dependent glucose co-transporter 2) was used as a target for diabetes mellitus. Molecular docking and dynamics simulations were carried out on vitexin- and isovitexin-SGLT2 complexes with dapagliflozin as positive control. The results show that both vitexin and isovitexin have weaker binding energies compared to dapagliflozin, indicating that both ligands may exhibit weak anti-diabetic effects through inhibiting SGLT2. The poor binding mode of vitexin and isovitexin may be responsible for their weak anti-diabetic effect. These results are in accordance with the inhibitory activity against hSGLT2 in vitro test with the inhibitory rate 26.3% of vitexin and 11.2% of isovitexin at the dose of 10[Formula: see text][Formula: see text]mol[Formula: see text][Formula: see text][Formula: see text]L[Formula: see text]. The results of calculation and in vitro test may explain the possible inhibiting mechanism of vitexin and isovitexin against SGLT2, and therefore enhance our understanding of the structure-activity relationships of SGLT2 inhibitors.

In silico modeling of aspalathin and nothofagin against SGLT2

Aspalathin and nothofagin are the major dihydrochalcones found in rooibos (Aspalathus linearis), which display anti-diabetic activities, but the mechanism is still unclear. In this paper, hSGLT2 (human sodium dependent glucose co-transporter 2), a target for diabetes mellitus, was built using homology modeling method. Molecular docking and dynamics simulations were carried out on aspalathin, nothofagin and SGLT2 complexes with dapagliflozin as positive control. The results show that both the binding energies and binding modes of aspalathin and nothofagin are similar to dapagliflozin, indicating that either component of rooibos may exhibit anti-diabetic effects through inhibiting SGLT2 receptor. However, the predicted permeability value of aspalathin and nothofagin is low, which may cause poor absorption, resulting in weak SGLT2 inhibition. Calculation results elucidate the possible inhibiting mechanism of aspalathin and nothofagin against SGLT2, and therefore enhance our understanding of anti-diabetic activities of rooibos.

Corrigendum: Lactoferrin ameliorates prostaglandin E2-mediated inhibition of Na+-glucose cotransport in enterocytes

J.R. Talukder, A. Griffin, A. Jaima, B. Boyd, and J. Wright. Department of Biology, LeMoyne-Owen College, 807Walker Avenue, Memphis, TN 38126, USA. Corresponding author: Jamilur R. Talukder (e-mail: Jamil_Talukder@loc.edu). Fig. 8. Kinetics of Na+-dependent glucose cotransport (SGLT1) in rat intestinal epithelial (IEC-6) cells. Data are representative of 3 such experiments. IEC-6 cells were grown in complete Dulbecco’s modified Eagle media on 6-well transwell plates. IEC-6 cells were treated with 50 nmol/L of PGE2 (filled circles), the control group received same volume of vehicle (open circles) at 9 days postconfluence for 24 h. Glucose uptake experiments were performed in the presence or absence of Na+ at 10 days postconfluence. 3-O-methyl-D-[1-3H]glucose ([3H]-OMG) uptake values obtained with extracellular Na+-free buffer were subtracted from the total uptake obtained in the presence of Na+ to calculate Na+dependent glucose uptake. The data were analyzed with a GraphPad Prism 5 software and derived from the Michaelis–Menten equation and are presented in Table 1. Fig. 12. Effect of lactoferrin (Lf) on the kinetics of PGE2-induced inhibition of Na+-dependent glucose uptake in rat intestinal epithelial (IEC-6) cells. The data are representative of 3 such experiments. IEC-6 cells were grown in Dulbecco’s modified Eagle media on transwell plates. The treated (Lf+PGE2) group received Lf (150 nmol/L) at 1 h before PGE2 (50 nmol/L) treatment (filled circle), the control group received the same volume of vehicle (open circle) in 9 days postconfluent for 24 h. Uptake experiments were performed in the presence or absence of Na+ in 10 days postconfluent. The data were analyzed with GraphPad Prism 5 software and derived from the Michaelis–Menten equation and are presented in Table 1. 519

Tu2012 Impact of a 2-Week Very Low Calorie Diet (VLCD) on Glucose Sensing, Absorption, Transporters, Incretin Hormones and Glycemia in Morbidly Obese Humans

We showed that glucose absorption is accelerated in the proximal intestine of morbidly obese humans, associated with increased expression of sodium dependent glucose co-transporter 1 (SGLT1), an altered incretin profile, hyperinsulinemia and hyperglycemia. This study aimed to examine the effects of energy restriction on glucose absorption, expression of intestinal glucose transporters and sweet taste receptors (STR), incretin hormone responses and glycemia in the morbidly obese. Methods: 10 non-diabetic, morbidly obese subjects (2M:8F; 45±3yrs, BMI: 46±3kg/m2) were studied before and after a 2-week VLCD (750kcal/day). On each occasion, endoscopic duodenal biopsies were collected before and after intraduodenal glucose infusion (30g glucose over 30 min, with 3g 3-O-methylglucose (3-OMG) to estimate glucose absorption). Blood glucose and plasma concentrations of 3-OMG, glucosedependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and insulin were measured over 240 min. Absolute expression of SGLT-1, GLUT2 and STR (T1R2) transcripts was quantified by PCR. Results After 2 weeks of VLCD, body weight (-5.6±0.5kg, P<0.001), HbA1c (-0.32±0.08%, P=0.001), fasting blood glucose (-0.5±0.1mmol/L, P=0.02) and fasting expression of T1R2 (-54±22%, P=0.03), SGLT1 (-30±7%, P=0.004) and GLUT2 (-50±15%, P=0.008) were lower than at baseline. Prior to VLCD, intra-duodenal glucose had no impact onT1R2, SGLT-1 and GLUT2 expression, but after VLCD, intra-duodenal glucose stimulated increased expression of T1R2 (45±30%, P=0.03) and GLUT2 (57±14%, P=0.003). The blood glucose (P=0.002), plasma GIP (P=0.03) and plasma insulin (P=0.002) responses to intra-duodenal glucose were all reduced after VLCD, while plasma 3-OMG and GLP-1 concentrations were unchanged. CONCLUSIONS: The improvement in glycemic control after short-term VLCD in morbid obesity is most likely mediated by reduced insulin resistance from weight loss, but not via a reduction in intestinal glucose absorption or an increased incretin response. Although VCLD reduces the fasting expression of both STR and glucose transporters, these increase rapidly on exposure to glucose. Further studies with inhibitors of STR and/or glucose transporters are warranted to determine whether the changes in receptor expressional dynamics are responsible for the observed incretin responses.

579 Accelerated Glucose Absorption in Proximal Intestine and Its Relationship to Glucose Transporters, Incretin Hormones and Glycaemia in Morbidly Obese Humans: the “X-Factor” of the Foregut Theory?

Glucose absorption in the small intestine is mediated by sodium dependent glucose cotransporter 1 (SGLT-1) and glucose transporter-2 (GLUT2), and is potentially linked to sweet taste receptor (STR) signaling and incretin hormone secretion. Both glucose absorption and expression of SGLT-1 are increased in obese rats, but human data is lacking. This study aimed to examine intestinal glucose absorption inmorbidly obese humans, and its relationship to glycemia, incretin responses, SGLT-1, GLUT2, and STR expression. Methods: 17 nondiabetic, morbidly obese subjects (5M:12F; 45 ± 3yrs, BMI: 48 ± 4kg/m2) and 11 lean controls (10M:1F; 44 ± 6yrs, BMI: 25 ± 1kg/m2) underwent endoscopic duodenal biopsies prior to intraduodenal glucose infusion (30g glucose over 30 min, with 3g 3-O-methylglucose (3-OMG) to estimate glucose absorption). Blood glucose and plasma concentrations of 3OMG, glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP1), insulin, and glucagon were measured over 240 min. Absolute expression of SGLT-1, GLUT2 and STR (T1R2) transcripts was quantified by PCR. Results: Both the rate of glucose absorption, as assessed by the rise in plasma 3-OMG concentrations (P<0.001) and blood glucose concentrations (P<0.0001) were substantially greater in obese than lean subjects (Fig AB Fig C), but not GLUT2 or T1R2, was higher in the obese than lean subjects, and was related to peaked plasma 3OMG (r=0.61, P=0.01). CONCLUSIONS: Glucose absorption in the proximal intestine is (i) accelerated in morbid obesity, (ii) associated with an incretin profile that potentially promotes both hyperinsulinemia and hyperglycemia, and (iii) associated with increased expression of SGLT-1. These novel findings suggest that accelerated glucose absorption in the proximal gutmay be the X-factor accounting for the foregut theory of obesity and diabetes.

580 Ezetimibe Modulates Endogenous LXR Ligands to Regulate Intestinal LDLR Receptors via IDOL

Glucose absorption in the small intestine is mediated by sodium dependent glucose cotransporter 1 (SGLT-1) and glucose transporter-2 (GLUT2), and is potentially linked to sweet taste receptor (STR) signaling and incretin hormone secretion. Both glucose absorption and expression of SGLT-1 are increased in obese rats, but human data is lacking. This study aimed to examine intestinal glucose absorption inmorbidly obese humans, and its relationship to glycemia, incretin responses, SGLT-1, GLUT2, and STR expression. Methods: 17 nondiabetic, morbidly obese subjects (5M:12F; 45 ± 3yrs, BMI: 48 ± 4kg/m2) and 11 lean controls (10M:1F; 44 ± 6yrs, BMI: 25 ± 1kg/m2) underwent endoscopic duodenal biopsies prior to intraduodenal glucose infusion (30g glucose over 30 min, with 3g 3-O-methylglucose (3-OMG) to estimate glucose absorption). Blood glucose and plasma concentrations of 3OMG, glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP1), insulin, and glucagon were measured over 240 min. Absolute expression of SGLT-1, GLUT2 and STR (T1R2) transcripts was quantified by PCR. Results: Both the rate of glucose absorption, as assessed by the rise in plasma 3-OMG concentrations (P<0.001) and blood glucose concentrations (P<0.0001) were substantially greater in obese than lean subjects (Fig AB Fig C), but not GLUT2 or T1R2, was higher in the obese than lean subjects, and was related to peaked plasma 3OMG (r=0.61, P=0.01). CONCLUSIONS: Glucose absorption in the proximal intestine is (i) accelerated in morbid obesity, (ii) associated with an incretin profile that potentially promotes both hyperinsulinemia and hyperglycemia, and (iii) associated with increased expression of SGLT-1. These novel findings suggest that accelerated glucose absorption in the proximal gutmay be the X-factor accounting for the foregut theory of obesity and diabetes.

Tu2013 A Short Bowel Syndrome Rodent Model Mimicking the Human Pathology Results in Increased AgRP/NPY and Decreased POMC/TRH Expression in the Hypothalamus

We showed that glucose absorption is accelerated in the proximal intestine of morbidly obese humans, associated with increased expression of sodium dependent glucose co-transporter 1 (SGLT1), an altered incretin profile, hyperinsulinemia and hyperglycemia. This study aimed to examine the effects of energy restriction on glucose absorption, expression of intestinal glucose transporters and sweet taste receptors (STR), incretin hormone responses and glycemia in the morbidly obese. Methods: 10 non-diabetic, morbidly obese subjects (2M:8F; 45±3yrs, BMI: 46±3kg/m2) were studied before and after a 2-week VLCD (750kcal/day). On each occasion, endoscopic duodenal biopsies were collected before and after intraduodenal glucose infusion (30g glucose over 30 min, with 3g 3-O-methylglucose (3-OMG) to estimate glucose absorption). Blood glucose and plasma concentrations of 3-OMG, glucosedependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and insulin were measured over 240 min. Absolute expression of SGLT-1, GLUT2 and STR (T1R2) transcripts was quantified by PCR. Results After 2 weeks of VLCD, body weight (-5.6±0.5kg, P<0.001), HbA1c (-0.32±0.08%, P=0.001), fasting blood glucose (-0.5±0.1mmol/L, P=0.02) and fasting expression of T1R2 (-54±22%, P=0.03), SGLT1 (-30±7%, P=0.004) and GLUT2 (-50±15%, P=0.008) were lower than at baseline. Prior to VLCD, intra-duodenal glucose had no impact onT1R2, SGLT-1 and GLUT2 expression, but after VLCD, intra-duodenal glucose stimulated increased expression of T1R2 (45±30%, P=0.03) and GLUT2 (57±14%, P=0.003). The blood glucose (P=0.002), plasma GIP (P=0.03) and plasma insulin (P=0.002) responses to intra-duodenal glucose were all reduced after VLCD, while plasma 3-OMG and GLP-1 concentrations were unchanged. CONCLUSIONS: The improvement in glycemic control after short-term VLCD in morbid obesity is most likely mediated by reduced insulin resistance from weight loss, but not via a reduction in intestinal glucose absorption or an increased incretin response. Although VCLD reduces the fasting expression of both STR and glucose transporters, these increase rapidly on exposure to glucose. Further studies with inhibitors of STR and/or glucose transporters are warranted to determine whether the changes in receptor expressional dynamics are responsible for the observed incretin responses.

Segmental diversity of electrogenic glucose transport characteristics in the small intestines of weaned pigs

It has been shown in several species that the intestinal Na+-dependent glucose co-transporter 1 (SGLT1) is more abundant in the jejunum than in ileum. In contrast, the efficiency of intestinal glucose uptake rates in suckling piglets or weaned pigs is not clearly fitting with this segmental distribution. The aim of this study was to evaluate SGLT1 mediated glucose absorption in the jejunum and ileum of growing pigs (Sus scrofa) in more detail. In Ussing chambers, basal short-circuit currents were significantly more positive in the jejunum. It could be demonstrated that the electrogenic ileal glucose transport was significantly more pronounced in different breeds and occurred at 5mmol∙L−1 glucose 7 times faster in the ileum, although slightly higher jejunal expression of glycosylated SGLT1 was detected by Western blotting. This expression pattern was connected to significantly lower phlorizin sensitivity in the jejunum. As the more efficient ileal glucose absorption was also observable with glucose uptake studies into isolated brush-border membrane vesicles without differences in abundance and activity of the Na+/K+-ATPase in both segments, we conclude that the segmental differences in porcine glucose transport characteristics may be based on direct or indirect modulations of SGLT1 activity.

Structural Insights into the Active Site of Human Sodium Dependent Glucose Co-Transporter 2: Homology Modelling, Molecular Docking, and 3D - QSAR Studies

Human sodium dependent glucose co-transporter 2 (hSGLT2) is a target for diabetes mellitus type 2 (T2DM). The 3D (three dimensional) homology model of hSGLT2 comprising 14 transmembrane helical domains was constructed and molecular docking of the inhibitors, C-aryl glucoside analogues, into the active site was studied. The 3D-QSAR (quantitative structure activity relationship) analysis was carried out on 43 C-aryl glucoside analogues as a training set. The molecular field analysis (MFA) with G/PLS (genetic partial least-squares) method was used to generate statistically significant 3D-QSAR (r2 = 0.857) based on a molecular field generated using electrostatic and steric probes. The QSAR model was validated using leave-one-out cross-validation, bootstrapping, and randomisation methods, and finally with an external test set comprising 10 inhibitors. The molecular docking studies provide structural insights into the active site and key interactions involved in the binding of inhibitors to hSGLT2 and these results corroborate with the 3D-QSAR analysis that provide the active conformation of inhibitors and the nature of interactive fields important for activity.

Overexpression of SGLT1 and EGFR in colorectal cancer showing a correlation with the prognosis

Na+-dependent glucose cotransporter (SGLT1), reported overexpression in tumor tissues while its clinical significance was not established, and epidermal growth factor receptor (EGFR) with potential relation to SGLT1 were studied in order to investigate their clinical significance in colorectal cancer (CRC). Eighty-five patients of CRC who received chemotherapy in Sun Yat-sen Cancer Center from March 1st 2005 to December 31st 2008 were enrolled. SGLT1 and EGFR expression in these cancer tissues and 28 normal tissues were tested by immunohistochemistry. (1) Expression of SGLT1 (P = 0.00) and EGFR (P = 0.01) in cancer tissues was higher than that in normal tissues. (2) Their expression related with clinical stage (P = 0.03 and P = 0.02), but not with other clinical characteristics. (3) For first-line chemotherapy, expression of SGLT1 (P = 0.06 and P = 0.21) and EGFR (P = 0.37 and P = 0.31) had no influence on objective response rate (ORR) and disease control rate (DCR). EGFR overexpression was associated with lower disease-free survival (P = 0.00) and overall survival (P = 0.01), while SGLT1 did not (P = 0.79 and P = 0.34). Conclusions Both SGLT1 and EGFR overexpression in CRC was related to higher clinical stages. SGLT1 had a potential impact on the ORR of first-line chemotherapy in CRC. EGFR was associated with prognosis, while SGLT1 did not.

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.