Expression of mRNA for glucose transport proteins in jejunum, liver, kidney and skeletal muscle of pigs

Immunometabolism of Liver Xenotransplantation and Prospective Solutions

End-stage liver diseases, such as hepatocellular carcinoma or acute liver failure, critically necessitate liver transplantation. However, the shortage of available organ donors fails to meet the rapidly growing transplantation demand. Due to the high similarity of liver tissue structure and metabolism between miniature pigs and humans, xenotransplantation of pig livers is considered as a potentially viable solution to organ scarcity. In the 2024, teams from China first time have successfully transplanted a genetically modified Bama miniature pig liver into a clinically brain-dead man lasting for 10 days. This milestone in human xenotransplantation research not only confirms the feasibility of clinical application of xenotransplantation, but also underscores the daunting and protracted nature of this pathway. Despite advanced gene-editing technologies theoretically circumventing the occurrence of most transplant rejection reactions, patients still face challenges such as chronic immune rejection, coagulation disorders, and thrombotic microangiopathy after receiving xenografts. Moreover, prolonged use of immunosuppressive drugs may induce irreversible immune dysfunction, leading to opportunistic infections and metabolic disorders. This article compares the similarities and differences in livers between humans and pigs, summarizes the immunometabolism of xenotransplantation based on current findings, and provides research perspectives on pre-transplantation and post-transplantation strategies for prolonging the survival time of xenografts.

Avenanthramides Ameliorate Insulin Resistance by Modulating Gluconeogenesis and Glycogen Synthesis in HepG2 Cells

Diabetes mellitus (DM) is a multifaceted metabolic condition, mainly defined by elevated blood glucose levels. A feature of type 2 DM includes insulin resistance (IR), which involves impairments within the insulin signaling pathways. Avenanthramides (AVNs) are phenolic alkaloids found in Avena sativa L. The major AVNs are AVN A, AVN B, and AVN C. They have been reported to offer benefits in preventing inflammation, cancer, and cardiovascular diseases. However, the effects of AVNs on the liver glucose metabolism pathways remain unknown. This study examined the effects and underlying mechanisms through which AVNs alleviate IR induced by free fatty acid (FFA) in HepG2 cells. The results indicated that FFA treatment significantly decreased glucose consumption by 34.54% compared to the control. However, treatments with AVN A, B, and C at 100 μM increased glucose uptake by 57.93%, 58.28%, and 53.10%, respectively, compared to FFA treatment alone. This effect occurs through the increased expression of glucose transporter 4. Furthermore, AVNs significantly enhanced the glycogen content. AVNs induced increased phosphorylation of insulin receptor substrate-1 (IRS-1), phosphatidylinositol-3-kinase (PI3K), and protein kinase B (Akt). AVNs treatment decreased the levels of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase in HepG2 cells. This effect was attributed to AMP-activated protein kinase activation and inhibition of forkhead box protein O1. Collectively, these results suggest that AVNs regulate glucose metabolism by activating the IRS-1/PI3K/Akt pathway, which is related to glycogen synthesis, and by inhibiting key molecules that promote gluconeogenesis.

Embryonic thermal challenge is associated with increased stressor resiliency later in life: Molecular and morphological mechanisms in the small intestine

Developing chick embryos that are subjected to increased incubation temperature are more stressor-resilient later in life, but the underlying process is poorly understood. The potential mechanism may involve changes in small intestine function. In this study, we determined behavioral, morphological, and molecular effects of increased embryonic incubation temperatures and post-hatch heat challenge in order to understand how embryonic heat conditioning (EHC) affects gut function. At 4 days post-hatch, duodenum, jejunum, and ileum samples were collected at 0, 2, and 12 h relative to the start of heat challenge. In EHC chicks, we found that markers of heat and oxidative stress were generally lower while those of nutrient transport and antioxidants were higher. Temporally, gene expression changes in response to the heat challenge were similar in control and EHC chicks for markers of heat and oxidative stress. Crypt depth was greater in control than EHC chicks at 2 h post-challenge, and the villus height to crypt depth ratio increased from 2 to 12 h in both control and EHC chicks. Collectively, these results suggest that EHC chicks might be more energetically efficient at coping with thermal challenge, preferentially allocating nutrients to other tissues while protecting the mucosal layer from oxidative damage. These results provide targets for future studies aimed at understanding the molecular mechanisms underlying effects of embryonic heat exposure on intestinal function and stressor resiliency later in life.

The relationship between SGLT2 and systemic blood pressure regulation

The sodium-glucose cotransporter 2 (SGLT2) is a glucose transporter that is located within the proximal tubule of the kidney's nephrons. While it is typically associated with the kidney, it was later identified in various areas of the central nervous system, including areas modulating cardiorespiratory regulation like blood pressure. In the kidney, SGLT2 functions by reabsorbing glucose from the nephron's tubule into the bloodstream. SGLT2 inhibitors are medications that hinder the function of SGLT2, thus preventing the absorption of glucose and allowing for its excretion through the urine. While SGLT2 inhibitors are not the first-line choice, they are given in conjunction with other pharmaceutical interventions to manage hyperglycemia in individuals with diabetes mellitus. SGLT2 inhibitors also have a surprising secondary effect of decreasing blood pressure independent of blood glucose levels. The implication of SGLT2 inhibitors in lowering blood pressure and its presence in the central nervous system brings to question the role of SGLT2 in the brain. Here, we evaluate and review the function of SGLT2, SGLT2 inhibitors, their role in blood pressure control, the future of SGLT2 inhibitors as antihypertensive agents, and the possible mechanisms of SGLT2 blood pressure control in the central nervous system.

Exercise-related alterations in MCT1 and GLUT4 expressions in the liver and pancreas of rats with STZ-induced diabetes

Background

The liver and pancreas tissues play a central role in controlling glucose homeostasis. In patients with type I diabetes mellitus (T1DM), the function of these tissues is impaired. The positive effects of exercise have been shown in diabetic patients. To demonstrate the positive effects of exercise in T1DM, we examined the effects of moderate-intensity endurance training (MIET) on the liver enzymes and expression of MCT1 and GLUT4 genes.

Methods

Male Wistar rats were allocated into 4 groups of control (C), training (T), diabetic control (DC), and diabetes + training (DT). The serum levels of liver enzymes such as alanine aminotransferase (ALT), aspartate transaminase (AST), and alkaline phosphatase (ALP) were determined by ELIZA. MCT1 and GLUT4 mRNA expressions in the liver and pancreas tissues were evaluated through real-time qPCR after 10 weeks of training.

Results

The mRNA levels of MCT1 and GLUT4 decreased in DC group and increased in DT group. T1DM led to weight loss, but the weight loss was less in the DT group. T1DM caused an increase in liver enzymes such as ALT, AST and ALP, whereas endurance training preserved enzymatic levels.

Conclusion

These results suggested that MIET increases levels of MCT1 and GLUT4 liver and pancreas in the diabetic rats and improves liver function tests. Upregulation of MCT1 and GLUT4 can probably improve the function of liver and pancreas tissues and promote glucose homeostasis in T1DM.

Review: A species comparison of the kinetic homogeneous and heterogeneous organization of sodium-dependent glucose transport systems along the intestine

The targeted use of carbohydrates by feed and food industries to create balanced and cost-effective diets has generated a tremendous amount of research in carbohydrate digestion and absorption in different species. Specifically, this research has led us to a larger observation that identified different organizations of intestinal sodium-dependent glucose absorption across species, which has not been previously collated and reviewed. Thus, this review will compare the kinetic segregation of sodium-dependent glucose transport across the intestine of different species, which we have termed either homogeneous or heterogeneous systems. For instance, the pig follows a heterogeneous system of sodium-dependent glucose transport with a high-affinity, super-low-capacity (Ha/sLc) in the jejunum, and a high-affinity, super-high-capacity (Ha/sHc) in the ileum. This is achieved by multiple sodium-dependent glucose transporters contributing to each segment. In contrast, tilapia have a homogenous system characterized by high-affinity, high-capacity (Ha/Hc) throughout the intestine. Additionally, we are the first to report glucose transporter patterns across species presented from vertebrates to invertebrates. Finally, other kinetic transport systems are briefly covered to illustrate possible contributions/modulations to sodium-dependent glucose transporter organization. Overall, we present a new perspective on the organization of glucose absorption along the intestinal tract.

Increased expression of sodium-glucose cotransporter 2 and O-GlcNAcylation in hepatocytes drives non-alcoholic steatohepatitis

AIMS

Steatosis reducing effects of sodium-glucose cotransporter 2 (SGLT2) inhibitors in non-alcoholic steatohepatitis (NASH) has been consistently reported in humans, but their mechanism remains uncertain. In this study, we examined the expression of SGLT2 in human livers and investigated the crosstalk between SGLT2 inhibition and hepatic glucose uptake, intracellular O-GlcNAcylation, and autophagic regulation in NASH.

MATERIALS AND METHODS

Human liver samples obtained from subjects with/without NASH were analyzed. For in vitro studies, human normal hepatocytes and hepatoma cells were treated with SGLT2 inhibitor under high-glucose and high-lipid conditions. NASH in vivo was induced by a high-fat, -fructose, and -cholesterol Amylin liver NASH (AMLN) diet for 10 weeks followed by an additional 10 weeks with/without SGLT2 inhibitor (empagliflozin 10 mg/kg/day).

RESULTS

Liver samples from subjects with NASH were associated with increased SGLT2 and O-GlcNAcylation expression compared with controls. Under NASH condition (in vitro condition with high glucose and lipid), intracellular O-GlcNAcylation and inflammatory markers were increased in hepatocytes and SGLT2 expression was upregulated; SGLT2 inhibitor treatment blocked these changes by directly reducing hepatocellular glucose uptake. In addition, decreased intracellular O-GlcNAcylation by SGLT2 inhibitor promoted autophagic flux through AMPK-TFEB activation. In the AMLN diet-induced NASH mice model, SGLT2 inhibitor alleviated lipid accumulation, inflammation, and fibrosis through autophagy activation related to decreased SGLT2 expression and O-GlcNAcylation in the liver.

CONCLUSIONS

This study firstly demonstrates increased SGLT2 expression in NASH and secondly reveals the novel effect of SGLT2 inhibition on NASH by activating autophagy mediated by inhibition of hepatocellular glucose uptake and consequently decreasing intracellular O-GlcNAcylation.

Interaction of dietary carbohydrate and fat on glucose metabolism in growing pigs

Increased consumption of fructose has been suggested to be a contributing cause of the increased rates of obesity in humans. Rodent studies have shown an increase in de novo lipogenesis and decreased insulin sensitivity in response to feeding high levels of fructose, but it is unclear if these effects occur in the same progression in humans. We aimed to develop a swine model for studying changes in glucose metabolism and insulin resistance resulting from dietary carbohydrate alone or in combination with high dietary fat. Two experiments were conducted to determine if the source of dietary carbohydrate, with or without added fat, had an effect on body weight gain, glucose metabolism, or insulin response in growing pigs. In the first experiment, pigs (24 barrows, initial body weight 28 kg) were fed one of 4 diets in which the source of carbohydrate was varied: 1) 20% starch; 2) 10% glucose + 10% starch; 3) 10% fructose + 10% starch; and 4) 20% fructose for 9 weeks. There were no differences in growth rate or glucose clearance observed. Experiment 2 was conducted as a 3 × 2 factorial with the main effects of carbohydrate source (20% starch, glucose, or fructose) and added fat level (0 vs 10%). Pigs (24 barrows, initial body weight 71 kg) were fed one of 6 experimental diets for 9 weeks. Compared to the other dietary treatments, pigs fed fructose with high fat had an elevated glucose area under the curve during the GTT (Carbohydrate x Fat interaction, P < 0.01). This same group had a lower insulin response (Carbohydrate x Fat, P < 0.05). This work demonstrates that pigs can be a viable model to assess the long-term effects of dietary carbohydrates on metabolism and body composition. Studies of longer duration are needed to determine if these changes are indicative of insulin resistance.

AMPK/PGC-1α/GLUT4-Mediated Effect of Icariin on Hyperlipidemia-Induced Non-Alcoholic Fatty Liver Disease and Lipid Metabolism Disorder in Mice

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease in the world. Therapeutic activity of icariin, a major bioactive component of Epimedii Herba, in NAFLD is still unknown. Herein, the C57BL/6J mice were fed with a high-fat diet for 16 weeks to establish a NAFLD model. Mice were assigned to five groups: control group, NAFLD group, and icariin treatment groups. Effects of icariin on blood indices, glucose tolerance, insulin sensitivity, histopathological morphology, cell apoptosis, lipid accumulation, and AMPK signaling were analyzed. In addition, another cohort of mice were assigned to five groups: control group, NAFLD group, dorsomorphin treatment group, icariin treatment group, and dorsomorphin + icariin treatment group. Expression of proteins in liver tissues associated with AMPK signaling, and levels of ALT and AST were evaluated. Icariin attenuated the NAFLD-induced increase of the TG, TC, LDL-C, ALT, AST levels. HDL-C levels were affected neither by NAFLD nor by icariin. Furthermore, icariin treatment (100-200 mg/kg) counteracted the NAFLD-reduced glucose tolerance and insulin sensitivity and modulated histopathological changes, cell apoptosis, and lipid accumulation in liver tissues. Additionally, icariin mitigated the NAFLD-induced up-regulation of the cleaved caspase 3/9, SREBP-1c, and DGAT-2 levels, and enhanced the expression level of CPT-1, p-ACC/ACC, AMPKα1, PGC-1α, and GLUT4. Effects of icariin on the AMPK signaling and levels of AST and ALT could be reversed by AMPK inhibitor, dorsomorphin. This paper investigates the glucose-reducing and lipid-lowering effects of icariin in NAFLD. Moreover, icariin might function through activating the AMPKα1/PGC-1α/GLTU4 pathway.

FDG-PET/CT: novel method for viability assessment of livers perfused ex vivo

PURPOSE

Ex vivo liver machine perfusion is a promising option to rescue marginal liver grafts mitigating the donated organ shortage. Recently, a novel liver perfusion machine that can keep injured liver grafts alive for 1 week ex vivo was developed and reported in Nature Biotechnology. However, liver viability assessment ex vivo is an unsolved issue and the value of 18F-fluorodeoxyglucose (FDG)-PET/CT for such purpose was explored.

MATERIALS AND METHODS

Discarded two human and six porcine liver grafts underwent FDG-PET/CT for viability assessment after 1 week of ex vivo perfusion. PET parameters [standardized uptake value (SUV)max, SUVmean, SUVpeak and total lesion glycolysis] were compared between hepatic lobes and between porcine and human livers. The prevalence of FDG-negative organ parts was recorded. The estimated effective radiation dose for PET/CT was calculated.

RESULTS

All organs were viable with essentially homogeneous FDG uptake. Of note, viability was preserved in contact areas disclosing the absence of pressure necrosis. Four porcine and two human organs had small superficial FDG-negative areas confirmed as biopsy sites. Total lesion glycolysis was significantly higher in the right hepatic lobe (P = 0.012), while there was no significant difference of SUVmax, SUVmean and SUVpeak between hepatic lobes. There was no significant difference in FDG uptake parameters between porcine and human organs. The estimated effective radiation dose was 1.99 ± 1.67 mSv per organ.

CONCLUSION

This study demonstrates the feasibility of FDG-PET/CT for viability assessment of ex vivo perfused liver grafts after 1 week.

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

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

Effect of Hydrolyzable Tannins on Glucose-Transporter Expression and Their Bioavailability in Pig Small-Intestinal 3D Cell Model

Intestinal transepithelial transport of glucose is mediated by glucose transporters, and affects postprandial blood-glucose levels. This study investigates the effect of wood extracts rich in hydrolyzable tannins (HTs) that originated from sweet chestnut (Castanea sativa Mill.) and oak (Quercus petraea) on the expression of glucose transporter genes and the uptake of glucose and HT constituents in a 3D porcine-small-intestine epithelial-cell model. The viability of epithelial cells CLAB and PSI exposed to different HTs was determined using alamarBlue^®. qPCR was used to analyze the gene expression of SGLT1, GLUT2, GLUT4, and POLR2A. Glucose uptake was confirmed by assay, and LC–MS/ MS was used for the analysis of HT bioavailability. HTs at 37 µg/mL were found to adversely affect cell viability and downregulate POLR2A expression. HT from wood extract Tanex at concentrations of 4 µg/mL upregulated the expression of GLUT2, as well as glucose uptake at 1 µg/mL. The time-dependent passage of gallic acid through enterocytes was influenced by all wood extracts compared to gallic acid itself as a control. These results suggest that HTs could modulate glucose uptake and gallic acid passage in the 3D cell model.

Comparison of intestinal glucose flux and electrogenic current demonstrates two absorptive pathways in pig and one in Nile tilapia and rainbow trout

The mucosal-to-serosal flux of ¹⁴C 3-O-methyl-d-glucose was compared against the electrogenic transport of d-glucose across ex vivo intestinal segments of Nile tilapia, rainbow trout, and pig in Ussing chambers. The difference in affinities (K_m "fingerprints") between pig flux and electrogenic transport of glucose, and the absence of this difference in tilapia and trout, suggest two absorptive pathways in the pig and one in the fish species examined. More specifically, the total mucosal-to-serosal flux revealed a super high-affinity, high-capacity (sHa/Hc) total glucose transport system in tilapia; a super high-affinity, low-capacity (sHa/Lc) total glucose transport system in trout and a low-affinity, low-capacity (La/Lc) total glucose transport system in pig. Comparatively, electrogenic glucose absorption revealed similar K_m in both fish species, with a super high-affinity, high capacity (sHa/Hc) system in tilapia; a super high-affinity/super low-capacity (sHa/sLc) system in trout; but a different K_m fingerprint in the pig, with a high-affinity, low-capacity (Ha/Lc) system. This was supported by different responses to inhibitors of sodium-dependent glucose transporters (SGLTs) and glucose transporter type 2 (GLUT2) administered on the apical side between species. More specifically, tilapia flux was inhibited by SGLT inhibitors, but not the GLUT2 inhibitor, whereas trout lacked response to inhibitors. In contrast, the pig responded to inhibition by both SGLT and GLUT2 inhibitors with a higher expression of GLUT2. Altogether, it would appear that two pathways are working together in the pig, allowing it to have continued absorption at high glucose concentrations, whereas this is not present in both tilapia and trout.

Sigmoidal kinetics define porcine intestinal segregation of electrogenic monosaccharide transport systems as having multiple transporter population involvement

Kinetic characterization of electrogenic sodium-dependent transport in Ussing chambers of d-glucose and d-galactose demonstrated sigmoidal/Hill kinetics in the porcine jejunum and ileum, with the absence of transport in the distal colon. In the jejunum, a high-affinity, super-low-capacity (Ha/sLc) kinetic system accounted for glucose transport, and a low-affinity, low-capacity (La/Lc) kinetic system accounted for galactose transport. In contrast, the ileum demonstrated a high-affinity, super-high-capacity (Ha/sHc) glucose transport and a low-affinity, high-capacity (La/Hc) galactose transport systems. Jejunal glucose transport was not inhibited by dapagliflozin, but galactose transport was inhibited. Comparatively, ileal glucose and galactose transport were both sensitive to dapagliflozin. Genomic and gene expression analyses identified 10 of the 12 known SLC5A family members in the porcine jejunum, ileum, and distal colon. Dominant SGLT1 (SLC5A1) and SGLT3 (SLC5A4) expression was associated with the sigmoidal Ha/sLc glucose and La/Lc galactose transport systems in the jejunum. Comparatively, the dominant expression of SGLT1 (SLC5A1) in the ileum was only associated with Ha glucose and La galactose kinetic systems. However, the sigmoidal kinetics and overall high capacity (Hc) of transport is unlikely accounted for by SGLT1 (SLC5A1) alone. Finally, the absence of transport and lack of pharmacological inhibition in the colon was associated with the poor expression of SLC5A genes. Altogether, the results demonstrated intestinal segregation of monosaccharide transport fit different sigmoidal kinetic systems. This reveals multiple transporter populations in each system, supported by gene expression profiles and pharmacological inhibition. Overall, this work demonstrates a complexity to transporter involvement in intestinal electrogenic monosaccharide absorption systems not previously defined.

Intestinal electrogenic sodium-dependent glucose absorption in tilapia and trout reveal species differences in SLC5A-associated kinetic segmental segregation

Electrogenic sodium-dependent glucose transport along the length of the intestine was compared between the omnivorous Nile tilapia ( Oreochromis niloticus) and the carnivorous rainbow trout ( Oncorhynchus mykiss) in Ussing chambers. In tilapia, a high-affinity, high-capacity kinetic system accounted for the transport throughout the proximal intestine, midintestine, and hindgut segments. Similar dapagliflozin and phloridzin dihydrate inhibition across all segments support this homogenous high-affinity, high-capacity system throughout the tilapia intestine. Genomic and gene expression analysis supported findings by identifying 10 of the known 12 SLC5A family members, with homogeneous expression throughout the segments with dominant expression of sodium-glucose cotransporter 1 (SGLT1; SLC5A1) and sodium-myoinositol cotransporter 2 (SMIT2; SLC5A11). In contrast, trout's electrogenic sodium-dependent glucose absorption was 20-35 times lower and segregated into three significantly different kinetic systems found in different anatomical segments: a high-affinity, low-capacity system in the pyloric ceca; a super-high-affinity, low-capacity system in the midgut; and a low-affinity, low-capacity system in the hindgut. Genomic and gene expression analysis found 5 of the known 12 SLC5A family members with dominant expression of SGLT1 ( SLC5A1), sodium-glucose cotransporter 2 (SGLT2; SLC5A2), and SMIT2 ( SLC5A11) in the pyloric ceca, and only SGLT1 ( SLC5A1) in the midgut, accounting for differences in kinetics between the two. The hindgut presented a low-affinity, low-capacity system partially attributed to a decrease in SGLT1 ( SLC5A1). Overall, the omnivorous tilapia had a higher electrogenic glucose absorption than the carnivorous trout, represented with different kinetic systems and a greater expression and number of SLC5A orthologs. Fish differ from mammals, having hindgut electrogenic glucose absorption and segment specific transport kinetics.

Degree of SGLT1 phosphorylation is associated with but does not determine segment-specific glucose transport features in the porcine small intestines

Glucose‐induced electrogenic ion transport is higher in the porcine ileum compared with the jejunum despite equal apical abundance of SGLT1. The objective of this study was a detailed determination of SGLT1 and GLUT2 expressions at mRNA and protein levels along the porcine small intestinal axis. Phosphorylation of SGLT1 at serine 418 was assessed as a potential modulator of activity. Porcine intestinal tissues taken along the intestinal axis 1 h or 3 h after feeding were analyzed for relative mRNA (RT‐PCR) and protein levels (immunoblot) of SGLT1, pSGLT1, GLUT2, (p)AMPK, β₂‐receptor, and PKA substrates. Functional studies on electrogenic glucose transport were done (Ussing chambers: short circuit currents (I_sc)). Additionally, effects of epinephrine (Epi) administration on segment‐specific glucose transport and pSGLT1 content were examined. SGLT1 and GLUT2 expression was similar throughout the small intestines but lower in the duodenum and distal ileum. pSGLT1 abundance was significantly lower in the ileum compared with the jejunum associated with significantly higher glucose‐induced I_sc. SGLT1 phosphorylation was not inducible by Epi. Epi treatment decreased glucose‐induced I_sc and glucose flux rates in the jejunum but increased basal I_sc in the ileum. Epi‐induced PKA activation was detectable in jejunal tissue. These results may indicate that SGLT1 phosphorylation at Ser418 represents a structural change to compensate for certain conditions that may decrease glucose transport (unfavorable driving forces/changed apical membrane potential) rather than being the cause for the overall differences in glucose transport characteristics between the jejunum and ileum.

Oyster mushroom functions as an anti-hyperglycaemic through phosphorylation of AMPK and increased expression of GLUT4 in type 2 diabetic model rats

OBJECTIVES

Traditionally, mushrooms have been used to reduce hyperglycaemia. However, the mechanism underlying this effect has not yet been explored. AMP-activated protein kinase (AMPK) is known to reduce hyperglycaemia through an insulin-independent pathway. This study aimed to observe the effect of oyster mushroom powder (OMP) on phosphorylation of AMPK (p-AMPK) and expression of GLUT4 mRNA in diabetic model rats.

METHODS

Long-Evans rats were used to develop type 2 diabetic model rats through intraperitoneal induction of streptozotocin (STZ). OMP was supplemented at 5% with the usual feed of rats for 8 consecutive weeks. Then, the rats were sacrificed. RNA was extracted by the TRIzol reagent, and proteins were extracted from different tissues with RIPA lysis buffer. Expression of GLUT4 mRNA was measured through cDNA-PCR techniques, and p-AMPK was detected using western blotting. The band intensities of the PCR products and proteins were measured using Image J software.

RESULTS

Supplementation of OMP for 8 weeks resulted in a reduction of the serum glucose level in STZ-induced, type 2 diabetic model rats. The levels of p-AMPK, as a ratio relative to β-actin, increased in the muscle and adipose tissues of mushroom-treated type 2 diabetic model rats, compared to those in control diabetic model rats. Expression of GLUT4, as a ratio relative to GAPDH, increased significantly in both the muscle and adipose tissues of mushroom-treated diabetic rats.

CONCLUSION

Oyster mushroom may decrease hyperglycaemia through increased p-AMPK and also expression of GLUT4 in the muscle and adipose tissues.

The Metabolic Flexibility of Hovering Vertebrate Nectarivores

Foraging hummingbirds and nectar bats oxidize both glucose and fructose from nectar at exceptionally high rates. Rapid sugar flux is made possible by adaptations to digestive, cardiovascular, and metabolic physiology affecting shared and distinct pathways for the processing of each sugar. Still, how these animals partition and regulate the metabolism of each sugar and whether this occurs differently between hummingbirds and bats remain unclear.

The effect of insulin on plasma glucose concentrations, expression of hepatic glucose transporters and key gluconeogenic enzymes during the perinatal period in broiler chickens

Chickens have blood glucose concentrations that are twofold higher than those observed in mammals. Moreover, the insulin sensitivity seems to decrease with postnatal age in both broiler and layer chickens. However, little is known about the response of insulin on plasma glucose concentrations and mRNA abundance of hepatic glucose transporters 1, 2, 3, 8, 9 and 12 (GLUT1, 2, 3, 8, 9 and 12) and three regulatory enzymes of the gluconeogenesis, phosphoenolpyruvate carboxykinase 1 and 2 (PCK1 and 2) or fructose-1,6-biphosphatase 1 (FBP1) in chicks during the perinatal period. In the present study, broiler embryos on embryonic day (ED)16, ED18 or newly-hatched broiler chicks were injected intravenously with bovine insulin (1μg/g body weight (BW)) to examine plasma glucose response and changes in hepatic mRNA abundance of the GLUTs, PCK1 and 2 and FBP1. Results were compared with a non-treated control group and a saline-injected sham group. Plasma glucose levels of insulin-treated ED18 embryos recovered faster from their minimum level than those of insulin-treated ED16 embryos or newly-hatched chicks. In addition, at the minimum plasma glucose level seven hours post-injection (PI), hepatic GLUT2, FBP1 and PCK2 mRNA abundance was decreased in insulin-injected embryos, compared to sham and control groups, being most pronounced when insulin injection occurred on ED16.

Calycosin Rebalances Advanced Glycation End Products-Induced Glucose Uptake Dysfunction of Hepatocyte In Vitro

Diabetes mellitus (DM) often accompanies liver dysfunction. Astragali Radix is a traditional Chinese herbal medicine that is widely administrated to ameliorate the symptoms of diabetes as well as liver dysfunction, but its acting mechanism is still not yet fully recognized. Advanced glycation end products (AGEs) play a key role in promoting diabetic organ dysfunction. Both hyperglycemia and AGEs can induce insulin resistance, hepatocyte damage and liver dysfunction. We designed this study to explore the effects of the phytoestrogen Calycosin, a major active component of Astragali Radix, on AGEs-induced glucose uptake dysfunction in the hepatocyte cell line and relevant mechanisms. MTT and BrdU methods were applied to evaluate cell viability. 2-NBDG was used to observe glucose uptake by a live cell imaging system. Immunofluorescence method was carried out to investigate GLUT1, GLUT4, and RAGE protein expressions on cell membrane. cAMP content was determined by an EIA method. We found Calycosin concentration-dependently ameliorated AGEs-induced hepatocyte viability damage. AGEs dramatically reduced basal glucose uptake in hepatocytes, and this reduction could be reversed by Calycosin administration. By immunofluorescence detection, we observed that Calycosin could inhibit AGEs-induced GLUT1 expression down-regulation via estrogen receptor (ER). Furthermore, Calycosin decreased AGEs-promoted RAGE and cAMP elevation in hepatocytes. These findings strongly suggest that Calycosin can ameliorate AGEs-promoted glucose uptake dysfunction in hepatocytes; the protection of cell viability and ER-RAGE and GLUT1 pathways play a significant role in this modulation.

Dynamic changes in genes related to glucose uptake and utilization during pig skeletal and cardiac muscle development

Skeletal and cardiac muscle have important roles in glucose uptake and utilization. However, changes in expression of protein coding genes and miRNAs that participate in glucose metabolism during development are not fully understood. In this study, we investigated the expression of genes related to glucose metabolism during muscle development. We found an age-dependent increase in gene expression in cardiac muscle, with enrichment in heart development- and energy-related metabolic processes. A subset of genes that were up-regulated until 30 or 180 days postnatally, and then down-regulated in psoas major muscle was significantly enriched in mitochondrial oxidative-related processes, while genes that up-regulated in longissimus doris muscle was significantly enriched in glycolysis-related processes. Meanwhile, expression of energy-related microRNAs decreased with increasing age. In addition, we investigated the correlation between microRNAs and mRNAs in three muscle types across different stages of development and found many potential microRNA-mRNA pairs involved in regulating glucose metabolism.

The glucose transporter 1 -GLUT1- from the white shrimp Litopenaeus vannamei is up-regulated during hypoxia

During hypoxia the shrimp Litopenaeus vannamei accelerates anaerobic glycolysis to obtain energy; therefore, a correct supply of glucose to the cells is needed. Facilitated glucose transport across the cells is mediated by a group of membrane embedded integral proteins called GLUT; being GLUT1 the most ubiquitous form. In this work, we report the first cDNA nucleotide and deduced amino acid sequences of a glucose transporter 1 from L. vannamei. A 1619 bp sequence was obtained by RT-PCR and RACE approaches. The 5´ UTR is 161 bp and the poly A tail is exactly after the stop codon in the mRNA. The ORF is 1485 bp and codes for 485 amino acids. The deduced protein sequence has high identity to GLUT1 proteins from several species and contains all the main features of glucose transporter proteins, including twelve transmembrane domains, the conserved motives and amino acids involved in transport activity, ligands binding and membrane anchor. Therefore, we decided to name this sequence, glucose transporter 1 of L. vannamei (LvGLUT1). A partial gene sequence of 8.87 Kbp was also obtained; it contains the complete coding sequence divided in 10 exons. LvGlut1 expression was detected in hemocytes, hepatopancreas, intestine gills, muscle and pleopods. The higher relative expression was found in gills and the lower in hemocytes. This indicates that LvGlut1 is ubiquitously expressed but its levels are tissue-specific and upon short-term hypoxia, the GLUT1 transcripts increase 3.7-fold in hepatopancreas and gills. To our knowledge, this is the first evidence of expression of GLUT1 in crustaceans.

Hepatic glucose sensing and integrative pathways in the liver

The hepatic glucose-sensing system is a functional network of enzymes and transcription factors that is critical for the maintenance of energy homeostasis and systemic glycemia. Here we review the recent literature on its components and metabolic actions. Glucokinase (GCK) is generally considered as the initial postprandial glucose-sensing component, which acts as the gatekeeper for hepatic glucose metabolism and provides metabolites that activate the transcription factor carbohydrate response element binding protein (ChREBP). Recently, liver receptor homolog 1 (LRH-1) has emerged as an upstream regulator of the central GCK-ChREBP axis, with a critical role in the integration of hepatic intermediary metabolism in response to glucose. Evidence is also accumulating that O-linked β-N-acetylglucosaminylation (O-GlcNAcylation) and acetylation can act as glucose-sensitive modifications that may contribute to hepatic glucose sensing by targeting regulatory proteins and the epigenome. Further elucidation of the components and functional roles of the hepatic glucose-sensing system may contribute to the future treatment of liver diseases associated with deregulated glucose sensors.

Hepatic expression and cellular distribution of the glucose transporter family

Glucose and other carbohydrates are transported into cells using members of a family of integral membrane glucose transporter (GLUT) molecules. To date 14 members of this family, also called the solute carrier 2A proteins have been identified which are divided on the basis of transport characteristics and sequence similarities into several families (Classes 1 to 3). The expression of these different receptor subtypes varies between different species, tissues and cellular subtypes and each has differential sensitivities to stimuli such as insulin. The liver is a contributor to metabolic carbohydrate homeostasis and is a major site for synthesis, storage and redistribution of carbohydrates. Situations in which the balance of glucose homeostasis is upset such as diabetes or the metabolic syndrome can lead metabolic disturbances that drive chronic organ damage and failure, confirming the importance of understanding the molecular regulation of hepatic glucose homeostasis. There is a considerable literature describing the expression and function of receptors that regulate glucose uptake and release by hepatocytes, the most import cells in glucose regulation and glycogen storage. However there is less appreciation of the roles of GLUTs expressed by non parenchymal cell types within the liver, all of which require carbohydrate to function. A better understanding of the detailed cellular distribution of GLUTs in human liver tissue may shed light on mechanisms underlying disease pathogenesis. This review summarises the available literature on hepatocellular expression of GLUTs in health and disease and highlights areas where further investigation is required.

Expression of Na+-D-glucose cotransporter SGLT2 in rodents is kidney-specific and exhibits sex and species differences

With a novel antibody against the rat Na(+)-D-glucose cotransporter SGLT2 (rSGLT2-Ab), which does not cross-react with rSGLT1 or rSGLT3, the ∼75-kDa rSGLT2 protein was localized to the brush-border membrane (BBM) of the renal proximal tubule S1 and S2 segments (S1 > S2) with female-dominant expression in adult rats, whereas rSglt2 mRNA expression was similar in both sexes. Castration of adult males increased the abundance of rSGLT2 protein; this increase was further enhanced by estradiol and prevented by testosterone treatment. In the renal BBM vesicles, the rSGLT1-independent uptake of [(14)C]-α-methyl-D-glucopyranoside was similar in females and males, suggesting functional contribution of another Na(+)-D-glucose cotransporter to glucose reabsorption. Since immunoreactivity of rSGLT2-Ab could not be detected with certainty in rat extrarenal organs, the SGLT2 protein was immunocharacterized with the same antibody in wild-type (WT) mice, with SGLT2-deficient (Sglt2 knockout) mice as negative control. In WT mice, renal localization of mSGLT2 protein was similar to that in rats, whereas in extrarenal organs neither mSGLT2 protein nor mSglt2 mRNA expression was detected. At variance to the findings in rats, the abundance of mSGLT2 protein in the mouse kidneys was male dominant, whereas the expression of mSglt2 mRNA was female dominant. Our results indicate that in rodents the expression of SGLT2 is kidney-specific and point to distinct sex and species differences in SGLT2 protein expression that cannot be explained by differences in mRNA.

The effect of dehydroepiandrosterone (DHEA) on renal function and metabolism in diabetic rats

Dehydroepiandrosterone (DHEA) is an endogenous steroid hormone involved in a number of biological actions in humans and rodents, but its effects on renal tissue have not yet been fully understood. The aim of this study is to assess the effect of DHEA treatment on diabetic rats, mainly in relation to renal function and metabolism. Diabetic rats were treated with subcutaneous injections of a 10mg/kg dose of DHEA diluted in oil. Plasma glucose and creatinine, in addition to urine creatinine, were quantified espectophotometrically. Glucose uptake and oxidation were quantified using radioactive glucose, the urinary Transforming Growth Factor β(1) (TGF-β(1)) was assessed by enzyme immunoassay, and the total glutathione in the renal tissue was also measured. The diabetic rats displayed higher levels of glycemia, and DHEA treatment reduced hyperglycemia. Plasmatic creatinine levels were higher in the diabetic rats treated with DHEA, while creatinine clearance was lower. Glucose uptake and oxidation were lower in the renal medulla of the diabetic rats treated with DHEA, and urinary TGF-β(1), as well as total gluthatione levels, were higher in the diabetic rats treated with DHEA. DHEA treatment was not beneficial to renal tissue, since it reduced the glomerular filtration rate and renal medulla metabolism, while increasing the urinary excretion of TGF-β(1) and the compensatory response by the glutathione system, probably due to a mechanism involving a pro-oxidant action or a pro-fibrotic effect of this androgen or its derivatives. In conclusion, this study reports that DHEA treatment may be harmful to renal tissue, but the mechanisms of this action have not yet been fully understood.

Developmental programming: differential effects of prenatal testosterone excess on insulin target tissues

Polycystic ovarian syndrome (PCOS) is the leading cause of infertility in reproductive-aged women with the majority manifesting insulin resistance. To delineate the causes of insulin resistance in women with PCOS, we determined changes in the mRNA expression of insulin receptor (IR) isoforms and members of its signaling pathway in tissues of adult control (n = 7) and prenatal testosterone (T)-treated (n = 6) sheep (100 mg/kg twice a week from d 30-90 of gestation), the reproductive/metabolic characteristics of which are similar to women with PCOS. Findings revealed that prenatal T excess reduced (P < 0.05) expression of IR-B isoform (only isoform detected), insulin receptor substrate-2 (IRS-2), protein kinase B (AKt), peroxisome proliferator-activated receptor-γ (PPARγ), hormone-sensitive lipase (HSL), and mammalian target of rapamycin (mTOR) but increased expression of rapamycin-insensitive companion of mTOR (rictor), and eukaryotic initiation factor 4E (eIF4E) in the liver. Prenatal T excess increased (P < 0.05) the IR-A to IR-B isoform ratio and expression of IRS-1, glycogen synthase kinase-3α and -β (GSK-3α and -β), and rictor while reducing ERK1 in muscle. In the adipose tissue, prenatal T excess increased the expression of IRS-2, phosphatidylinositol 3-kinase (PI3K), PPARγ, and mTOR mRNAs. These findings provide evidence that prenatal T excess modulates in a tissue-specific manner the expression levels of several genes involved in mediating insulin action. These changes are consistent with the hypothesis that prenatal T excess disrupts the insulin sensitivity of peripheral tissues, with liver and muscle being insulin resistant and adipose tissue insulin sensitive.

Functional characterization of mouse sodium/glucose transporter type 3b

Despite belonging to a family of sugar cotransporters, human sodium/glucose transporter type 3 (hSGLT3) does not transport sugar, but it depolarizes the cell in the presence of extracellular sugar, and thus it has been suggested to work as a sugar sensor. In the human genome there is one SGLT3 gene, yet in mouse there are two. In this study we cloned one of them, mouse SGLT3b (mSGLT3b) and characterized the protein. We found that mSGLT3b has low affinity for sugars, as does hSGLT3, but surprisingly, mSGLT3b transports sugar, although the sugar transport is not as tightly coupled to cations as in SGLT1. Moreover, the sugar specificity of mSGLT3b has characteristics reminiscent of both SGLT1 and hSGLT3: mSGLT3b does not respond to galactose, similar to hSGLT3, but neither does it respond to 1-deoxynojirimycin, unlike hSGLT3 but similar to SGLT1. mSGLT3b has low apparent affinities for sugar and Na(+) and, furthermore, displays pre-steady-state currents, which in SGLT1 report on conformational changes in the protein. Finally, phlorizin, the typical inhibitor of SGLT proteins, also inhibits mSGLT3b. In summary, although mSGLT3b has some characteristics that resemble SGLT1 and others that are similar to hSGLT3, its low sugar affinity and uncoupled sugar transport lead us to conclude that mSGLT3b likely functions as a physiological glucose sensor similar to hSGLT3.