Sodium-dependent Glucose Cotransporter 1 Research Articles

Hypoxia and Giardia duodenalis: The Role of Hypoxia-Inducible Factor in Altered Epithelial Glucose Metabolism

The gastrointestinal system experiences frequent oxygenic fluctuations and must be able to maintain barrier integrity during periods of suboptimal oxygen concentration, or hypoxia. Epithelial cells rely on the Hypoxia-Inducible Factor (HIF) complex to activate genes that combat cellular stress and adapt cellular metabolism during hypoxia. Importantly, protozoan parasites can modulate host tissue oxygen tension and HIF activation, yet little is known regarding the relationship between enteric protozoa and hypoxia. This research aims to uncover the role of HIF upon Giardia duodenalis infection, a top cause of global diarrheal disease and an excellent infection model for the study of GI physiology. We hypothesize that HIF-target genes are activated upon Giardia infection, promoting alternative cellular glucose metabolism to sustain bioenergetic homeostasis. Caco-2 colonic epithelial cells were infected with Giardia isolate GS/M (MOI 10) for 1.5 or 4.5 hours under normoxic (21% O2) or hypoxic (~1%O2, STEMCELL hypoxia incubator) conditions to capture the early or peak activation of the oxygen-dependent HIF subunit (HIF-1α). RNA was extracted for assessment of transcriptional alterations of HIF-target genes via reverse transcriptase quantitative polymerase chain reaction. Investigation of HIF-mediated intracellular metabolic changes was carried out via liquid-chromatography mass-spectrometry analysis (hydrophilic-interaction chromatography method) on cocultures supplemented with a hypoxia mimetic (DMOG) or a HIF inhibitor (PX-478). Metabolomics experiments were repeated using Caco-2 cells transfected with sodium-dependent glucose cotransporter 1 (SGLT1), a key glucose transporter in the small intestine where Giardia localizes which is not reliably expressed in Caco-2 cells. Under normoxic conditions, genes that aid in cell stress responses ( VEGFA, ANKRD37, GADD45A) and glycolysis ( HK2, LDHA) are upregulated in Giardia-infected cells in a time-dependent manner (p<0.05). Fewer HIF-target genes are upregulated under hypoxic conditions (e.g., VEGFA, GADD45A, PGK1; p<0.05), indicating Giardia-infected cells exhibit a transcriptional profile similar to hypoxic uninfected cells. Interestingly, HIF1α was upregulated in Giardia-infected cells under hypoxic conditions at 1.5 hours (p<0.05). Analysis of the Caco-2 intracellular metabolome indicated HIF-dependent changes to nucleic acid (e.g., guanosine, inosine, uracil) and amino acid (e.g., glycine, threonine) metabolism. DMOG treatment increased the abundance of glycolytic intermediates (e.g., PEP, DHAP) in both cell lines and inhibited the depletion of the Kreb’s Cycle intermediate aconitate in the Caco-2-SGLT1 transfected cells, confirming the promotion of glycolytic flux by HIF. Taken together, our findings indicate Giardia-infected cells illustrate a hypoxic signature, a novel metabolic cell rescue mechanism in response to enteropathogens. Elucidating the role of HIF during enteric parasitic infections will aid in our understanding of the cellular adaptations underpinning GI pathophysiology, while also shedding light on the potential of HIF as a therapeutic target. Natural Science and Engineering Research Council of Canada. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Hatchery and Dietary Application of Synbiotics in Broilers: Performance and mRNA Abundance of Ileum Tight Junction Proteins, Nutrient Transporters, and Immune Response Markers.

This study investigated the effects of a synbiotic consisting of inulin, Enterococcus faecium, Pediococcus acidilactici, Bifidobacterium animalis, and Lactobacillus reuteri given orally to day (d)-of-hatch (DOH) broiler chicks at the hatchery and in the feed for a 21 d period. A total of 480 Cobb male broilers were randomly divided into one of four treatments using a 2 × 2 factorial design as follows: (1) control (CTRL) group receiving a gel-only oral application on DOH at the hatchery prior to transport and a non-medicated basal corn/soybean meal starter diet; (2) hatchery synbiotic (HS) receiving an oral gel containing the synbiotic (0.5 mL/bird) at the hatchery and the basal diet; (3) CTRL + dietary synbiotic at 0.5 kg/MT (DS); and (4) HS + dietary synbiotic at 0.5 kg/MT (HSDS). On d 7 and d 21, one bird per pen (eight replicate pens/group) was euthanized, and the ileum was immediately removed for qPCR analysis. Data were subjected to a 2-way ANOVA using GLM procedure (JMP Pro17). A significant diet × hatchery interaction was observed in feed conversion ratio (FCR) from d 14 to d 21 (p = 0.013) where the HS, DS, and HSDS treatments had a significantly lower FCR compared to the CTRL. However, no significant interaction effect was observed for body weight gain (BWG) or FCR during the overall experimental period. No significant interaction was observed in mRNA abundance of the evaluated genes in the ileum on d 7 and d 21. Gel application with the synbiotic significantly reduced sodium-dependent glucose cotransporter 1 (SGLT1) mRNA abundance on d 7 (p = 0.035) in comparison to birds receiving gel alone. Regardless of hatchery application, dietary synbiotic supplementation significantly reduced Toll-like receptor (TLR)2, TLR4, and interleukin (IL)-10 mRNA abundance on d 7 (p = 0.013). In conclusion, these findings showed that hatchery and dietary synbiotic application could have a potential beneficial impact on broiler intestinal immunity by regulating the TLR response, a key element of innate immunity. FCR was improved from d 14 to d 21 after synbiotic application. Future research involving extended grow-out studies with a disease challenge would expand on the implications of an early application of synbiotics.

Chinese bayberry (Myrica rubra Sieb. et Zucc.) leaves proanthocyanidins inhibit intestinal glucose transport in human Caco-2 cells.

Background: The hypoglycemic effects of Chinese bayberry leaves proanthocyanidins (BLPs) have been demonstrated. It is unclear, nevertheless, whether BLPs reduced postprandial blood glucose levels by regulating glucose uptake and glucose transport. Method: This study investigated the effect of BLPs (25, 50, and 100μg/mL) on glucose uptake and glucose transport in human intestinal epithelial cells (Caco-2 cells). The uptake of 2-Deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl) amino]-D-glucose (2-NBDG) and disaccharidases activity in Caco-2 cells were measured. The glucose transport ability across the cell membrane was determined using the established Caco-2 monolayer model. The transcript and protein levels of key glucose transporters were analyzed using real-time quantitative polymerase chain reaction (RT-qPCR) and western blotting, respectively. Results: The results showed that BLPs significantly decreased glucose uptake and disaccharidases activity (p < 0.05). Otherwise, BLPs treatment obviously inhibited glucose transport across the Caco-2 monolayer in both simulated-fast (5mM glucose) and simulated-fed (25mM glucose) conditions. It was attributed to the suppression of glucose transporter2 (GLUT2) and sodium-dependent glucose cotransporter 1 (SGLT1) by BLPs. BLPs were found to significantly downregulated the transcript level and protein expression of glucose transporters (p < 0.05). Meanwhile, the mRNA expression of phospholipase C (PLC) and protein kinase C (PKC) involved in the signaling pathway associated with glucose transport were decreased by BLPs. Conclusion: These results suggested that BLPs inhibited intestinal glucose transport via inhibiting the expression of glucose transporters. It indicated that BLPs could be potentially used as a functional food in the diet to modulate postprandial hyperglycemia.

Intestinal absorption of D-fructose isomers, D-allulose, D-sorbose and D-tagatose, via glucose transporter type 5 (GLUT5) but not sodium-dependent glucose cotransporter 1 (SGLT1) in rats.

D-allulose, D-sorbose and D-tagatose are D-fructose isomers that are called rare sugars. These rare sugars have been studied intensively in terms of biological production and food application as well as physiological effects. There are limited papers with regard to the transporters mediating the intestinal absorption of these rare sugars. We examined whether these rare sugars are absorbed via sodium-dependent glucose cotransporter 1 (SGLT1) as well as via GLUT type 5 (GLUT5) using rats. High-fructose diet fed rats, which express more intestinal GLUT5, exhibited significantly higher peripheral concentrations, Cmax and AUC0–180 min when D-allulose, D-sorbose and D-tagatose were orally administrated. KGA-2727, a selective SGLT1 inhibitor, did not affect the peripheral and portal vein concentrations and pharmacokinetic parameters of these rare sugars. The results suggest that D-allulose, D-sorbose and D-tagatose are likely transported via GLUT5 but not SGLT1 in rat small intestine.

Antihyperglycemic effects of Lysiphyllum strychnifolium leaf extract in vitro and in vivo

Context Lysiphyllum strychnifolium (Craib) A. Schmitz (LS) (Fabaceae) has traditionally been used to treat diabetes mellitus. Objective This study demonstrates the antidiabetic and antioxidant effects of aqueous extract of LS leaves in vivo and in vitro. Materials and methods The effects of aqueous LS leaf extract on glucose uptake, sodium-dependent glucose cotransporter 1 (SGLT1) and glucose transporter 2 (GLUT2) mRNA expression in Caco-2 cells, α-glucosidase, and lipid peroxidation were evaluated in vitro. The antidiabetic effects were evaluated using an oral glucose tolerance test (OGTT) and a 28-day consecutive administration to streptozotocin (STZ)-nicotinamide (NA)-induced type 2 diabetic mice. Results The extract significantly inhibited glucose uptake (IC50: 236.2 ± 36.05 µg/mL) and downregulated SGLT1 and GLUT2 mRNA expression by approximately 90% in Caco-2 cells. Furthermore, it non-competitively inhibited α-glucosidase in a concentration-dependent manner with the IC50 and Ki of 6.52 ± 0.42 and 1.32 µg/mL, respectively. The extract at 1000 mg/kg significantly reduced fasting blood glucose levels in both the OGTT and 28-day consecutive administration models as compared with untreated STZ-NA-induced diabetic mice (p < 0.05). Significant improvements of serum insulin, homeostasis model assessment of insulin resistance (HOMA-IR), and GLUT4 levels were observed. Furthermore, the extract markedly decreased oxidative stress markers by 37–53% reduction of superoxide dismutase 1 (SOD1) in muscle and malondialdehyde (MDA) in muscle and pancreas, which correlated with the reduction of MDA production in vitro (IC50: 24.80 ± 7.24 µg/mL). Conclusion The LS extract has potent antihyperglycemic activity to be used as alternative medicine to treat diabetes mellitus.

D-Allose is absorbed via sodium-dependent glucose cotransporter 1 (SGLT1) in the rat small intestine

d-Allose is the C3 epimer of d-glucose and has been reported to have beneficial health effects. The transporter mediating intestinal transport of d-allose is unknown. We examined whether d-allose is absorbed via sodium-dependent glucose cotransporter 1 (SGLT1) as well as via glucose transporter type 5 (GLUT5) using rats. For examination of absorption via SGLT1, KGA-2727, an SGLT1-specific inhibitor, and d-allose were orally administered. KGA-2727 blocked the increase of plasma d-allose levels and suppressed them throughout the experiment (0–180 min), whereas without KGA-2727, the plasma d-allose levels peaked at around 60–90 min. For examination of absorption via GLUT5, rats were fed a high-fructose diet for 3weeks to increase the abundance and activity of GLUT5 in the small intestine. High-fructose diet-fed rats did not exhibit significant changes in the plasma d-allose levels compared to control rats fed a high-glucose diet. These results indicate that SGLT1 but not GLUT5 mediates the intestinal absorption of d-allose.

Comparative studies on the physicochemical profile and potential hypoglycemic activity of different tea extracts: Effect on sucrase-isomaltase activity and glucose transport in Caco-2 cells

Tea is one of the most popular beverages in the world and is believed to be beneficial for health. The main components in tea change greatly depending on different processes, and thus, the effects of different teas on human health may differ. In this study, we compared the effect of green, oolong, black, and dark tea extracts on sucrase-isomaltase (SI) activity and glucose transport, which are two intervention options for postprandial blood glucose control, using Caco-2 cells as a model. Theaflavin-rich black tea extracts showed the highest inhibition of SI activity and retardation of the hydrolysis of sucrose, maltose, and isomaltose, with IC50 values of 8.34 μg/mL, 16.10 μg/mL, and 21.63 μg/mL, respectively. All four kinds of tea extracts caused a dose-dependent inhibition of glucose transport, which were closely related to the catechin content. Green tea extracts showed the highest inhibition of glucose transport and was more effective against sodium-dependent glucose cotransporter 1 (SGLT1) than glucose transporter 2 (GLUT2) in the management of glucose transport. Black tea extracts also inhibited glucose transport despite low level of catechins. The reason could partly lie in the suppression of Na+/K+-ATPase, which reduced the energy needed for SGLT1 to actively transport glucose. Furthermore, the mRNA level of SI, SGLT1, GLUT2, and Na+/K+-ATPase in Caco-2 cells were significantly reduced after treatment with tea extracts for 2 h. These in vitro studies suggested that tea could be used as a functional food in the diet to modulate postprandial hyperglycaemia for diabetic patients.

Glucose fluctuation accelerates cardiac injury of diabetic mice via sodium-dependent glucose cotransporter 1 (SGLT1)

Recent studies have shown that blood glucose fluctuation is associated with complications of diabetes mellitus (DM). SGLT1 (sodium-dependent glucose cotransporter 1), is highly expressed in pathological conditions of heart, and is expressed in cardiomyocytes induced by high glucose. Herein, we constructed a diabetic mouse model with glucose fluctuation to investigate whether SGLT1 is involved in glucose fluctuation-induced cardiac injury. Echocardiography, histology examination, and TUNEL staining were performed to evaluate cardiac dysfunction and damage. To assess glucose fluctuation-induced oxidative stress, reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) levels were measured. To assess mitochondrial dysfunction, mitochondrial membrane potential (MMP), ATP content, mitochondrial respiratory chain complex activity, and expression of mitochondrial fusion and fission proteins were determined. The results indicated that diabetic mice with glucose fluctuation showed elevation of cardiac SGLT1 expression, left ventricular dysfunction, oxidative stress and mitochondrial dysfunction. Knockdown of SGLT1 could abrogate the effects of glucose fluctuation on cardiac injury. Thus, our study highlighted that SGLT1 plays an important role in glucose fluctuation induced cardiac injury through oxidative stress and mitochondrial dysfunction.

Specific Lactobacillus probiotic strains decrease transepithelial glucose transport through GLUT2 downregulation in intestinal epithelial cell models

Although human clinical studies have suggested probiotic effects on blood glucose levels, knowledge about molecular mechanisms is still scarce. To test the hypothesis that selected Lactobacillus probiotic bacteria could regulate the activity of enterocyte glucose transporters, we aimed to measure in vitro effects of selected Lactobacillus probiotic bacteria on transcription and translation of intestinal glucose transporters sodium-dependent glucose cotransporter 1 (SGLT1) and glucose transporter 2 (GLUT2) as well as transepithelial glucose transport. Lactobacillus plantarum strains (PCS20 and PCS26), Lactobacillus rhamnosus GG (LGG) (ATCC 53103) and Lactobacillus acidophilus (L acidophilus) (ATCC 4356) were co-cultivated with noncarcinogenic porcine enterocytes (CLAB) and human epithelial colorectal adenocarcinoma cells (Caco-2) (ATCC HTB-37). Changes in transcription and expression of SGLT1 and GLUT2 were strain and cell line-specific. In CLAB, LGG was the most potent SGLT1 up-regulator, and PCS26 the most potent down-regulator of GLUT2 transcription, which was also reflected on the protein level. In Caco-2, all tested strains tended to downregulate GLUT2 gene expression, while L acidophilus most effectively reduced GLUT2 protein levels. Statistically significant effect of PCS26 and L acidophilus on GLUT2 molecular and protein levels in CLAB and Caco-2 cell lines, respectively, was also followed by a decreased rate of transepithelial glucose transport. Careful selection of specific Lactobacillus probiotic strains could be used to downregulate glucose absorption in intestinal epithelial cells and thereby could be beneficial as a support treatment of pathologies related to glucose homeostasis.

Guava (Psidium guajava) Fruit Extract Prepared by Supercritical CO2 Extraction Inhibits Intestinal Glucose Resorption in a Double-Blind, Randomized Clinical Study

Inhibition of intestinal glucose resorption can serve as an effective strategy for the prevention of an increase in blood glucose levels. We have recently shown that various extracts prepared from guava (Psidium guajava) inhibit sodium-dependent glucose cotransporter 1 (SGLT1)- and glucose transporter 2 (GLUT2)-mediated glucose transport in vitro (Caco-2 cells) and in vivo (C57BL/6N mice). However, the efficacy in humans remains to be confirmed. For this purpose, we conducted a parallelized, randomized clinical study with young healthy adults. Thirty-one volunteers performed an oral glucose tolerance test (OGTT) in which the control group received a glucose solution and the intervention group received a glucose solution containing a guava fruit extract prepared by supercritical CO2 extraction. The exact same extract was used for our previous in vitro and in vivo experiments. Blood samples were collected prior to and up to two hours after glucose consumption to quantitate blood glucose and insulin levels. Our results show that, in comparison to the control group, consumption of guava fruit extract resulted in a significantly reduced increase in postprandial glucose response over the basal fasting plasma glucose levels after 30 min (Δ control 2.60 ± 1.09 mmol/L versus Δ intervention 1.96 ± 0.96 mmol/L; p = 0.039) and 90 min (Δ control 0.44 ± 0.74 mmol/L versus Δ intervention −0.18 ± 0.88 mmol/L; p = 0.023). In addition, we observed a slightly reduced, but non-significant insulin secretion (Δ control 353.82 ± 183.31 pmol/L versus Δ intervention 288.43 ± 126.19 pmol/L, p = 0.302). Interestingly, storage time and repeated freeze-thawing operations appeared to negatively influence the efficacy of the applied extract. Several analytical methods (HPLC-MS, GC-MS, and NMR) were applied to identify putative bioactive compounds in the CO2 extract used. We could assign several substances at relevant concentrations including kojic acid (0.33 mg/mL) and 5-hydroxymethylfurfural (2.76 mg/mL). Taken together, this clinical trial and previous in vitro and in vivo experiments confirm the efficacy of our guava fruit extract in inhibiting intestinal glucose resorption, possibly in combination with reduced insulin secretion. Based on these findings, the development of food supplements or functional foods containing this extract appears promising for patients with diabetes and for the prevention of insulin resistance. Trial registration: 415-E/2319/15-2018 (Ethics Commissions of Salzburg).

Daily expression of sodium-dependent glucose cotransporter-1 protein in jejunum during rat ontogeny.

It is widely known that intestinal capacities such as the enzymatic hydrolysis of carbohydrates, lipids and proteins, and the subsequent absorption of the hydrolyzed products, are evolutionary matched to dietary loads and feeding behaviors. In this study, we demonstrate that the protein expression of apically located sodium-dependent glucose cotransporter-1 (SGLT-1) throughout rat ontogeny is daily adjusted to afford glucose uptake when the load of this metabolically essential monosaccharide in the intestinal lumen is maximum. The jejunal expression of SGLT-1 protein in 14 one-day-old suckling pups was found to increase at dark and early light phase (P < 0.05), when they have a better access to mother milk. In weaning 21-d-old and juvenile 28-d-old rats, the cotransporter expression was high throughout the entire day (P < 0.05). Finally, adult 90-d-old rats showed a well-developed circadian rhythm for SGLT-1 protein (P < 0.05), whose expression increased at late light and dark phase when the highest intestinal glucose load was achieved. To our knowledge, these results are the first reporting the daily profile of SGLT-1 expression during rat early developmental stage and may contribute to understand the biological significance of a well-established molecular capacity to deal with the crucial increase of glucose load in the diet during the weaning process.

Identification of novel small molecule inhibitors for solute carrier SGLT1 using proteochemometric modeling

Sodium-dependent glucose co-transporter 1 (SGLT1) is a solute carrier responsible for active glucose absorption. SGLT1 is present in both the renal tubules and small intestine. In contrast, the closely related sodium-dependent glucose co-transporter 2 (SGLT2), a protein that is targeted in the treatment of diabetes type II, is only expressed in the renal tubules. Although dual inhibitors for both SGLT1 and SGLT2 have been developed, no drugs on the market are targeted at decreasing dietary glucose uptake by SGLT1 in the gastrointestinal tract. Here we aim at identifying SGLT1 inhibitors in silico by applying a machine learning approach that does not require structural information, which is absent for SGLT1. We applied proteochemometrics by implementation of compound- and protein-based information into random forest models. We obtained a predictive model with a sensitivity of 0.64 ± 0.06, specificity of 0.93 ± 0.01, positive predictive value of 0.47 ± 0.07, negative predictive value of 0.96 ± 0.01, and Matthews correlation coefficient of 0.49 ± 0.05. Subsequent to model training, we applied our model in virtual screening to identify novel SGLT1 inhibitors. Of the 77 tested compounds, 30 were experimentally confirmed for SGLT1-inhibiting activity in vitro, leading to a hit rate of 39% with activities in the low micromolar range. Moreover, the hit compounds included novel molecules, which is reflected by the low similarity of these compounds with the training set (< 0.3). Conclusively, proteochemometric modeling of SGLT1 is a viable strategy for identifying active small molecules. Therefore, this method may also be applied in detection of novel small molecules for other transporter proteins.

Cardiac sodium-dependent glucose cotransporter 1 is a novel mediator of ischaemia/reperfusion injury

We previously reported that sodium-dependent glucose cotransporter 1 (SGLT1) is highly expressed in cardiomyocytes and is further up-regulated in ischaemia. This study aimed to determine the mechanisms by which SGLT1 contributes to ischaemia/reperfusion (I/R) injury. Mice with cardiomyocyte-specific knockdown of SGLT1 (TGSGLT1-DOWN) and wild-type controls were studied. In vivo, the left anterior descending coronary artery was ligated for 30 min and reperfused for 48 h. Ex vivo, isolated perfused hearts were exposed to 20 min no-flow and up to 2 h reperfusion. In vitro, HL-1 cells and isolated adult murine ventricular cardiomyocytes were exposed to 1 h hypoxia and 24 h reoxygenation (H/R). We found that TGSGLT1-DOWN hearts were protected from I/R injury in vivo and ex vivo, with decreased infarct size, necrosis, dysfunction, and oxidative stress. 5'-AMP-activated protein kinase (AMPK) activation increased SGLT1 expression, which was abolished by extracellular signal-related kinase (ERK) inhibition. Co-immunoprecipitation studies showed that ERK, but not AMPK, interacts directly with SGLT1. AMPK activation increased binding of the hepatocyte nuclear factor 1 and specificity protein 1 transcription factors to the SGLT1 gene, and HuR to SGLT1 mRNA. In cells, up-regulation of SGLT1 during H/R was abrogated by AMPK inhibition. Co-immunoprecipitation studies showed that SGLT1 interacts with epidermal growth factor receptor (EGFR), and EGFR interacts with protein kinase C (PKC). SGLT1 overexpression activated PKC and NADPH oxidase 2 (Nox2), which was attenuated by PKC inhibition, EGFR inhibition, and/or disruption of the interaction between EGFR and SGLT1. During ischaemia, AMPK up-regulates SGLT1 through ERK, and SGLT1 interacts with EGFR, which in turn increases PKC and Nox2 activity and oxidative stress. SGLT1 may represent a novel therapeutic target for mitigating I/R injury.

Process Development for a Locally Acting SGLT1 Inhibitor, LX2761, Utilizing sp3–sp2 Suzuki Coupling of a Benzyl Carbonate

Process development for the synthesis of a locally acting sodium-dependent glucose cotransporter 1 (SGLT1) inhibitor, LX2761, a drug candidate for the treatment of diabetes mellitus, is described. ...

Glucose uptake in the intestine of the common carp Cyprinus carpio: Indications for the involvement of the sodium-dependent glucose cotransporter 1 and its modulation under pathogen infection

Exploring the mechanism of glucose uptake in the fish intestine is a part of studies aiming to explain the possible usage of carbohydrate, which could reduce the dietary protein level in fish diet. This serves as an effort to make aquaculture more economically and environmentally sustainable. In mammals and few fish species, the sodium-dependent glucose cotransporter 1 (SGLT-1) is supposed to be involved in luminal glucose absorption. In the present study, the gene encoding SGLT-1 was partially identified in common carp (Cyprinus carpio) and the tissue distribution of gene transcripts was analysed semi-quantitatively. The activity of the co-transporter was observed in isolated intestinal samples by assessing the effects of adding phlorizin on short-circuit current. Finally, intestinal expression of mRNA encoding this gene was determined under infection of carp with Cyprinid herpesvirus 3 (CyHV-3) and Aeromonas hydrophila intubation. A cDNA sequence of 1396 bp was obtained, in silico translated into 465 aa, and confirmed as partial sequence of the gene encoding SGLT-1 in carp. The expression level of mRNA of this gene was higher in the upper part of the carp's mid gut than in the lower part. Besides the intestine, the SGLT-1 encoding gene was also highly expressed in the kidney and at a lower level in the liver, brain, gill, spleen and head kidney. This might indicate a diverse role of the co-transporter in glucose metabolism in common carp. In contrast to the expression level of the gene, samples from the lower mid gut of carp showed a higher level of short-circuit current reduction in comparison to samples from the upper mid gut after adding phlorizin. The transcriptional level of the SGLT-1 encoding gene was downregulated in the carp intestine during CyHV 3 infection but not during Aeromonas hydrophila infection. This downregulation of SGLT1 was found to correspond with a previously reported simultaneous increase in pro-inflammatory responses of the intestine, indicating that intestinal glucose uptake of carps is apparently impaired during infection processes.

Fibroblast growth factor 21 improves glucose homeostasis partially via down-regulation of Na+-d-glucose cotransporter SGLT1 in the small intestine

Fibroblast growth factor-21 (FGF-21), an endocrine hormone, is regarded as a therapeutic target for diabetes base on its potent effects on improving hyperglycemia. Sodium-dependent glucose cotransporter 1 (SGLT1) is mainly expressed in the small intestine (SI) for intestinal glucose absorption. It has been demonstrated that SGLT1 expression is increased in diabetes, which is thought to contribute to the rapidly rising postprandial blood glucose levels. Thus, we aim to examine whether FGF-21 regulates expression of intestinal SGLT1 in diabetes. The db/db mice were treated with insulin, low and high dose of FGF-21 for 5 weeks and then measured changes in glucose metabolism, intestinal glucose absorption and SGLT1 expression. The results showed that FGF-21 improved glucose homeostasis, inhibited intestinal glucose uptake and reduced intestinal SGLT1 expression compared with insulin in db/db mice. To further explore the mechanism of effects of FGF-21 on SGLT1 expression. The murine intestinal epithelial MODE-K cells were treated with FGF-21 for 3 h, 6 h, 12 h and 24 h and then measured glucose uptake, SGLT1 expression, another glucose transporter GLUT2 expression and associated mechanism. Our results showed that FGF-21 inhibited glucose uptake and reduced SGLT1 expression in MODE-K cells, which were due to inactivating SGK-1 pathway. Moreover, above effects of FGF-21 on MODE-K cells were abolished by PD173074, a FGFR1 inhibitor. In conclusion, FGF-21 regulates glucose level in diabetes partially due to inhibiting glucose absorption in the SI via inactivating SGK-1 pathway. These results expand our knowledge about how FGF-21 regulates glucose metabolism.

Effect of feeding soybean meal and differently processed peas on intestinal morphology and functional glucose transport in the small intestine of broilers

Peas are locally grown legumes being rich in protein and starch. However, the broad usage of peas as a feed component in poultry nutrition is limited to anti-nutritional factors, which might impair gut morphology and function. This study investigated the effect of feeding raw or differently processed peas compared with feeding a soybean meal-based control diet (C) on intestinal morphology and nutrient transport in broilers. A total of 360 day-old broiler chicks were fed with one of the following diets: The C diet, and 3 diets containing raw peas (RP), fermented peas (FP) and enzymatically pre-digested peas (EP), each supplying 30% of dietary crude protein. After 35 d, jejunal samples of broilers were taken for analyzing histomorphological parameters, active glucose transport in Ussing chambers and the expression of genes related to glucose absorption, intestinal permeability and cell maturation. Villus length (P = 0.017) and crypt depth (P = 0.009) of EP-fed broilers were shorter compared to birds received C. The villus surface area was larger in broilers fed C compared to those fed with the pea-containing feed (P = 0.005). Glucose transport was higher for broilers fed C in comparison to birds fed with the EP diet (P = 0.044). The sodium-dependent glucose co-transporter 1 (SGLT-1) expression was down-regulated in RP (P = 0.028) and FP (P = 0.015) fed broilers. Correlation analyses show that jejunal villus length negatively correlates with the previously published number of jejunal intraepithelial T cells (P = 0.014) and that jejunal glucose transport was negatively correlated with the occurrence of jejunal intraepithelial leukocytes (P = 0.041). To conclude, the feeding of raw and processed pea containing diets compared to a soybean based diet reduced the jejunal mucosal surface area of broilers, which on average was accompanied by lower glucose transport capacities. These morphological and functional alterations were associated with observed mucosal immune reactions. Further studies are required elucidating the specific components in peas provoking such effects and whether these effects have a beneficial or detrimental impact on gut function and animal health.

Resveratrol supplementation improves lipid and glucose metabolism in high-fat diet-fed blunt snout bream.

Here, we aimed to investigate whether resveratrol (RSV) can ameliorate high-fat diet (HFD)-induced metabolic disorder in fish. Blunt snout bream (Megalobrama amblycephala) with average weight 27.99±0.56g were fed a normal fat diet (NFD, 5% fat, w/w), a HFD (11% fat), or a HFD supplemented with 0.04, 0.36, or 1.08% RSV for 10weeks. As expected, fish fed a HFD developed hepatic steatosis, as shown by elevated hepatic and plasma triglycerides, raised whole body fat, intraperitoneal fat ratio and hepatosomatic index, and increased plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST). RSV supplementation lessened increases in body mass, whole body fat, and intraperitoneal fat, and alleviated development of hepatic steatosis, elevations of plasma triglyceride and glucose, and abnormalities of ALT and AST in HFD-fed fish. RSV supplementation increased SIRT1 messenger RNA (mRNA) expression and consequently hepatic mRNA expression of adipose triglyceride lipase (ATGL), carnitine palmitoyltransferase (CPT1a), and microsomal triglyceride transfer protein (MTTP), implying upregulation of lipolysis, β-oxidation, and lipid transport, respectively, in the liver. Conversely, hepatic lipoprotein lipase (LPL), sterol regulatory element-binding protein 1 (SREBP-1c), peroxisome proliferator-activated receptor γ (PPARγ), and ATP citrate lyase (ACLY) mRNA expression were decreased, implying suppression of fatty acid uptake, lipogenesis, and fatty acid synthesis. Additionally, RSV downregulated glucokinase (GCK) and sodium-dependent glucose cotransporter 1 (SGLT1) and upregulated glucose transporter 2 (GLUT2) mRNA expression, thus restoring normal glucose fluxes. Thus, RSV improves lipid and glucose metabolisms in blunt snout bream, which are potentially mediated by activation of SIRT1.

Ontogenic Changes of Villus Growth, Lactase Activity, and Intestinal Glucose Transporters in Preterm and Term Born Calves with or without Prolonged Colostrum Feeding.

Oral glucose supply is important for neonatal calves to stabilize postnatal plasma glucose concentration. The objective of this study was to investigate ontogenic development of small intestinal growth, lactase activity, and glucose transporter in calves (n = 7 per group) that were born either preterm (PT; delivered by section 9 d before term) or at term (T; spontaneous vaginal delivery) or spontaneously born and fed colostrum for 4 days (TC). Tissue samples from duodenum and proximal, mid, and distal jejunum were taken to measure villus size and crypt depth, protein concentration of mucosa and brush border membrane vesicles (BBMV), total DNA and RNA concentration of mucosa, mRNA expression and activity of lactase, and mRNA expression of sodium-dependent glucose co-transporter-1 (SGLT1) and facilitative glucose transporter 2 (GLUT2) in mucosal tissue. Additionally, protein expression of SGLT1 in BBMV and GLUT2 in crude mucosal membranes and immunochemical localization of GLUT2 in the enterocytes were determined. Villus height in distal jejunum was lower in TC than in T. Crypt depth in all segments was largest and the villus height/crypt depth ratio in jejunum was smallest in TC calves. Concentration of RNA was highest in duodenal mucosa of TC calves, but neither lactase mRNA and activity nor SGLT1 and GLUT2 mRNA and protein expression differed among groups. Localization of GLUT2 in the apical membrane was greater, whereas in the basolateral membrane was lower in TC than in T and PT calves. Our study indicates maturation processes after birth for mucosal growth and trafficking of GLUT2 from the basolateral to the apical membrane. Minor differences of mucosal growth, lactase activity, and intestinal glucose transporters were seen between PT and T calves, pointing at the importance of postnatal maturation and feeding for mucosal growth and GLUT2 trafficking.

Diet effects on glucose absorption in the small intestine of neonatal calves: Importance of intestinal mucosal growth, lactase activity, and glucose transporters

Colostrum (C) feeding in neonatal calves improves glucose status and stimulates intestinal absorptive capacity, leading to greater glucose absorption when compared with milk-based formula feeding. In this study, diet effects on gut growth, lactase activity, and glucose transporters were investigated in several gut segments of the small intestine. Fourteen male German Holstein calves received either C of milkings 1, 3, and 5 (d 1, 2, and 3 in milk) or respective formulas (F) twice daily from d 1 to d 3 after birth. Nutrient content, and especially lactose content, of C and respective F were the same. On d 4, calves were fed C of milking 5 or respective F and calves were slaughtered 2h after feeding. Tissue samples from duodenum and proximal, mid-, and distal jejunum were taken to measure villus size and crypt depth, mucosa and brush border membrane vesicles (BBMV) were taken to determine protein content, and mRNA expression and activity of lactase and mRNA expression of sodium-dependent glucose co-transporter-1 (SGLT1) and facilitative glucose transporter (GLUT2) were determined from mucosal tissue. Additionally, protein expression of SGLT1 in BBMV and GLUT2 in crude mucosal membranes and BBMV were determined, as well as immunochemically localized GLUT2 in the intestinal mucosa. Villus circumference, area, and height were greater, whereas crypt depth was smaller in C than in F. Lactase activity tended to be greater in C than in F. Protein expression of SGLT1 was greater in F than in C. Parameters of villus size, lactase activity, SGLT1 protein expression, as well as apical and basolateral GLUT2 localization in the enterocytes differed among gut segments. In conclusion, C feeding, when compared with F feeding, enhances glucose absorption in neonatal calves primarily by stimulating mucosal growth and increasing absorptive capacity in the small intestine, but not by stimulating abundance of intestinal glucose transporters.