SciCombinator

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Concept: Glucose transporter

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In order to evaluate the relationship between the in vitro and in vivo potency of sodium-glucose cotransporter (SGLT) inhibitors, a pharmacokinetic and pharmacodynamic (PK-PD) study was performed using normal rats. A highly selective SGLT2 inhibitor, tofogliflozin, and four other inhibitors with different in vitro inhibition potency to SGLT2 and selectivity toward SGLT2 versus SGLT1 were used as test compounds, and the time courses for urinary glucose excretion (UGE) and the plasma glucose and compound concentrations were monitored after administration of the compounds. A PK-PD analysis of the UGE caused by SGLT inhibition was performed based on a nonlinear parallel tube model which took into consideration the consecutive reabsorption by different glucose transport properties of SGLT2 and SGLT1. The model adequately captured the time course of cumulative UGE caused by SGLT inhibition; then the in vivo inhibition constants (K(i)) of inhibitors for both SGLT1 and SGLT2 were estimated. The in vivo selectivity toward SGLT2 showed a good correlation with the in vitro data (r = 0.985, p < 0.05), with in vivo K(i) values for SGLT2 in the range of 0.3- to 3.4-fold the in vitro data. This suggests that in vitro inhibition potency to both SGLT2 and SGLT1 is reflected in vivo. Furthermore, the complementary role of SGLT1 to SGLT2 and how selectivity toward SGLT2 affects the inhibitory potency for renal glucose reabsorption were discussed using the PK-PD model.

Concepts: Inhibitor, Glucose transporter, Cotransporter, Co-transport, Robert K. Crane, Sodium-glucose transport proteins, SLC5A1, Symporter

28

Distinguishing malignant mesotheliomas from benign mesothelial proliferations on hematoxylin and eosin-stained sections can be extremely challenging. Various immunohistochemical stains have been suggested to help in making this distinction, but all are controversial. Recently, IMP3 (insulin-like growth factor II mRNA binding protein 3) and GLUT-1 (glucose transporter protein 1) have been proposed as immunohistochemical markers that are positive in mesotheliomas but not in benign proliferations. We evaluated the performance of these markers on a tissue microarray containing 30 malignant mesotheliomas and 48 benign thoracic or abdominal mesothelial proliferations. IMP3 was positive in 53% of malignant and 27% of benign cases (P=0.03), whereas GLUT-1 was positive in 60% of malignant and 13% of benign cases (P=0.0003). Forty-three percent of malignant cases, but only 4% of benign cases, were positive for both IMP3 and GLUT-1 (P=0.00003). We conclude that, statistically, both IMP3 and GLUT-1 are more frequently positive in malignant compared with benign mesothelial processes; however, the frequency of positive staining in benign cases is too high to allow their diagnostic use as single stains. The combination of both markers may be of greater diagnostic value, but this hypothesis should be confirmed in further studies.

Concepts: Antibody, Protein, Glucose, Histology, Immunohistochemistry, Glucose transporter, Staining, GLUT1

28

The aim of this study was to develop polyurethane (PU) based fibro-porous membranes and to investigate the size-effect of hierarchical porous structure on permeability and surface properties of the developed electrospun membranes. Non-woven Selectophore™ PU membranes having tailored fibre diameters, pore sizes, and thickness were spun using electrospinning, and their chemical, physical and glucose permeability properties were characterised. Solvents, solution concentration, applied voltage, flow rate and distance to collector, each were systematically investigated, and electrospinning conditions for tailoring fibre diameters were identified. Membranes having average fibre diameters - 347, 738 and 1102 nm were characterized, revealing average pore sizes of 800, 870 and 1060 nm and pore volumes of 44, 63 and 68% respectively. Hydrophobicity increased with increasing fibre diameter and porosity. Effective diffusion coefficients for glucose transport across the electrospun membranes varied as a function of thickness and porosity, indicating high flux rates for mass transport. Electrospun PU membranes having significantly high pore volumes, extensively interconnected porosity and tailorable properties compared to conventional solvent cast membranes can find applications as coatings for sensors requiring analyte exchange.

Concepts: Petroleum, Concentration, Solvent, Glucose transporter, Length, Diameter, Soil mechanics

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Sodium-glucose cotransporter 2 (SGLT2) is the major, and SGLT1 the minor, transporter responsible for renal glucose reabsorption. Increasing urinary glucose excretion (UGE) by selectively inhibiting SGLT2 improves glycemic control in diabetic patients. We generated Sglt1 and Sglt2 knockout (KO) mice, Sglt1/Sglt2 double KO (DKO) mice, and wildtype (WT) littermates to study their relative glycemic control and to determine contributions of SGLT1 and SGLT2 to UGE. Relative to WTs, Sglt2 KOs had improved oral glucose tolerance and were resistant to streptozotocin-induced diabetes. Sglt1 KOs fed glucose-free high fat diet (G-free HFD) had improved oral glucose tolerance accompanied by delayed intestinal glucose absorption and increased circulating glucagon-like peptide-1 (GLP-1), but had normal tolerance to intraperitoneal glucose. On G-free HFD, Sglt2 KOs had 30%, Sglt1 KOs 2% and WTs < 1% of the UGE of DKO mice. Consistent with their increased UGE, DKOs had lower fasting blood glucose, and improved tolerance to intraperitoneal glucose, compared to Sglt2 KO mice. In conclusion, 1) Sglt2 is the major renal glucose transporter, however Sglt1 reabsorbs 70% of filtered glucose if Sglt2 is absent; 2) mice lacking Sglt2 display improved glucose tolerance despite UGE that is at best 30% of maximum; 3) Sglt1 KO mice respond to oral glucose with increased circulating GLP-1; and 4) mice lacking Sglt1 and Sglt2 have improved glycemic control over mice lacking Sglt2 alone. These data suggest that dual SGLT1/SGLT2 inhibition is an approach that may further improve glycemic control over SGLT2 inhibition alone in patients with type 2 diabetes.

Concepts: Insulin, Diabetes mellitus, Glucose, Diabetes, Blood sugar, Glucose tolerance test, Glucose transporter, Cotransporter

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Vulvovaginitis, balanitis, and related genital infections are common in patients with type 2 diabetes. Glucosuria, which is an outcome of treatment with sodium glucose cotransporter 2 (SGLT2) inhibitors, is among the possible causes. Dapagliflozin, an SGLT2 inhibitor with demonstrated glycemic benefits in patients with diabetes, has been studied across a broad spectrum of patients. Analysis of multi-trial safety data may better define the relationship between glucosuria and genital infection.

Concepts: Diabetes mellitus, Glucose transporter, Cotransporter

26

The sodium glucose co-transporter 2 (SGLT2) has received considerable attention in recent years as a target for the treatment of type 2 diabetes mellitus. This report describes the design, synthesis and structure-activity relationship (SAR) of C-glycosides with benzyltriazolopyridinone and phenylhydantoin as the aglycone moieties as novel SGLT2 inhibitors. Compounds 5p and 33b demonstrated high potency in inhibiting SGLT2 and high selectivity against SGLT1. The in vitro ADMET properties of these compounds will also be discussed.

Concepts: Insulin, Diabetes mellitus type 2, Diabetes mellitus, Glucose, Obesity, Glucose transporter, Co-transport, Sodium-glucose transport proteins

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Fractionation techniques can facilitate the isolation of intracellular organelles containing insulin-sensitive glucose transporter isoform 4 (GLUT4), which is mobilized from GLUT4 storage vesicles in fat and muscle cells in response to insulin. This protocol for the full membrane fractionation of 3T3-L1 adipocytes results in five distinct fractions. A heavy membrane-containing pellet is produced and then further separated into the plasma membrane, mitochondrial and nuclear, and high-density membrane fractions. The initial supernatant is subjected to a series of centrifugation steps to isolate the low-density membrane fraction, which contains the majority of the insulin-sensitive pool of GLUT4; the supernatant produced in this step is the soluble fraction. The distribution of GLUT4 in fractions from insulin-stimulated versus untreated cells is assessed via immunoblotting.

Concepts: Cell, Glucose, Cytosol, Cell membrane, Organelle, Cytoplasm, Glycogen, Glucose transporter

23

The primary aim of the CANagliflozin cardioVascular Assessment Study-Renal (CANVAS-R) is to determine whether the favourable effects of inhibition of the sodium glucose co-transporter 2 (SGLT2) on blood glucose, blood pressure and body weight are accompanied by protection against adverse renal outcomes.

Concepts: Kidney, Blood, Glucose, Blood sugar, Aldosterone, Glucose transporter, Renin, Sodium-glucose transport proteins

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This study assessed the efficacy/safety of canagliflozin (CANA), a sodium glucose cotransporter 2 (SGLT2) inhibitor, plus metformin extended-release (MET) initial therapy in drug-naïve type 2 diabetes.

Concepts: Glucose transporter, Sodium-glucose transport proteins

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What is the central question of this study? Although SGLT2 inhibitors represent a promising treatment for patients suffering from diabetic nephropathy, the influence of metabolic disruption on the expression and function of glucose transporters is largely unknown. What is the main finding and its importance? In vivo models of metabolic disruption (Goto-Kakizaki type II diabetic rat and junk-food diet) demonstrate increased expression of SGLT1, SGLT2 and GLUT2 in the proximal tubule brush border. In the type II diabetic model, this is accompanied by increased SGLT- and GLUT-mediated glucose uptake. A fasted model of metabolic disruption (high-fat diet) demonstrated increased GLUT2 expression only. The differential alterations of glucose transporters in response to varying metabolic stress offer insight into the therapeutic value of inhibitors. SGLT2 inhibitors are now in clinical use to reduce hyperglycaemia in type II diabetes. However, renal glucose reabsorption across the brush border membrane (BBM) is not completely understood in diabetes. Increased consumption of a Western diet is strongly linked to type II diabetes. This study aimed to investigate the adaptations that occur in renal glucose transporters in response to experimental models of diet-induced insulin resistance. The study used Goto-Kakizaki type II diabetic rats and normal rats rendered insulin resistant using junk-food or high-fat diets. Levels of protein kinase C-βI (PKC-βI), GLUT2, SGLT1 and SGLT2 were determined by Western blotting of purified renal BBM. GLUT- and SGLT-mediated d-[(3) H]glucose uptake by BBM vesicles was measured in the presence and absence of the SGLT inhibitor phlorizin. GLUT- and SGLT-mediated glucose transport was elevated in type II diabetic rats, accompanied by increased expression of GLUT2, its upstream regulator PKC-βI and SGLT1 protein. Junk-food and high-fat diet feeding also caused higher membrane expression of GLUT2 and its upstream regulator PKC-βI. However, the junk-food diet also increased SGLT1 and SGLT2 levels at the proximal tubule BBM. Glucose reabsorption across the proximal tubule BBM, via GLUT2, SGLT1 and SGLT2, is not solely dependent on glycaemic status, but is also influenced by diet-induced changes in glucose metabolism. We conclude that different metabolic disturbances result in complex adaptations in renal glucose transporter protein levels and function.

Concepts: Nutrition, Insulin, Diabetes mellitus, Glucose, Obesity, Insulin resistance, Glucose transporter, Sodium-glucose transport proteins