SGLT1 and SGLT2 inhibition, circulating metabolites, and cerebral small vessel disease: a mediation Mendelian Randomization study.

BACKGROUND: Sodium-glucose cotransporter 2 (SGLT2) and SGLT1 inhibitors may have additional beneficial metabolic effects on circulating metabolites beyond glucose regulation, which could contribute to a reduction in the burden of cerebral small vessel disease (CSVD). Accordingly, we used Mendelian Randomization (MR) to examine the role of circulating metabolites in mediating SGLT2 and SGLT1 inhibition in CSVD. METHODS: Genetic instruments for SGLT1/2 inhibition were identified as genetic variants, which were both associated with the expression of encoding genes of SGLT1/2 inhibitors and glycated hemoglobin A1c (HbA1c) level. A two-sample two-step MR was used to determine the causal effects of SGLT1/2 inhibition on CSVD manifestations and the mediating effects of 1400 circulating metabolites linking SGLT1/2 inhibition with CSVD manifestations. RESULTS: A lower risk of deep cerebral microbleeds (CMBs) and small vessel stroke (SVS) was linked to genetically predicted SGLT2 inhibition. Better white matter structure integrity was also achieved, as evidenced by decreased mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD), as well as lower deep (DWMH) and periventrivular white matter hyperintensity (PWMH) volume. Inhibiting SGLT2 could also lessen the incidence of severe enlarged perivascular spaces (EPVS) located at white matter, basal ganglia (BG) and hippocampus (HIP). SGLT1 inhibition could preserve white matter integrity, shown as decreased MD of white matter and DWMH volume. The effect of SGLT2 inhibition on SVS and MD of white matter through the concentration of 4-acetamidobutanoate and the cholesterol to oleoyl-linoleoyl-glycerol (18:1 to 18:2) ratio, with a mediated proportion of 30.3% and 35.5% of the total effect, respectively. CONCLUSIONS: SGLT2 and SGLT1 inhibition play protective roles in CSVD development. The SGLT2 inhibition could lower the risk of SVS and improve the integrity of white matter microstructure via modulating the level of 4-acetamidobutanoate and cholesterol metabolism. Further mechanistic and clinical studies research are needed to validate our findings.

Canagliflozin inhibits PASMCs proliferation via regulating SGLT1/AMPK signaling and attenuates artery remodeling in MCT-induced pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) was a devastating disease characterized by artery remodeling, ultimately resulting in right heart failure. The aim of this study was to investigate the effects of canagliflozin (CANA), a sodium-glucose cotransporter 2 inhibitor (SGLT2i) with mild SGLT1 inhibitory effects, on rats with PAH, as well as its direct impact on pulmonary arterial smooth muscle cells (PASMCs). PAH rats were induced by injection of monocrotaline (MCT) (40 mg/kg), followed by four weeks of treatment with CANA (30 mg/kg/day) or saline alone. Pulmonary artery and right ventricular (RV) remodeling and dysfunction in PAH were alleviated with CANA, as assessed by echocardiography. Hemodynamic parameters and structural of pulmonary arteriole, including vascular wall thickness and wall area, were reduced by CANA. RV hypertrophy index, cardiomyocyte hypertrophy, and fibrosis were decreased with CANA treatment. PASMCs proliferation was inhibited by CANA under stimulation by platelet-derived growth factor (PDGF)-BB or hypoxia. Activation of AMP kinase (AMPK) was induced by CANA treatment in cultured PASMCs in a time- and concentration-dependent manner. These effects of CANA were attenuated when treatment with compound C, an AMPK inhibitor. Abundant expression of SGLT1 was observed in PASMCs and pulmonary arteries, while SGLT2 expression was undetectable. SGLT1 increased in response to PDGF-BB or hypoxia stimulation, while PASMCs proliferation was inhibited and beneficial effects of CANA were counteracted by knockdown of SGLT1. Our research demonstrated for the first time that CANA inhibited the proliferation of PASMCs by regulating SGLT1/AMPK signaling and thus exerted an anti-proliferative effect on MCT-induced PAH.

The inflammatory injury of porcine small intestinal epithelial cells induced by deoxynivalenol is related to the decrease in glucose transport.

The present study aimed to investigate the effects of deoxynivalenol (DON) stimulation on inflammatory injury and the expression of the glucose transporters sodium-dependent glucose transporter 1 (SGLT1) and glucose transporter protein 2 (GLU2) in porcine small intestinal epithelial cells (IPEC-J2). Additionally, the study aimed to provide initial insights into the connection between the expression of glucose transporters and the inflammatory injury of IPEC-J2 cells. DON concentration and DON treatment time were determined using the CCK­8 assay. Accordingly, 1.0 µg/mL DON and treatment for 24 h were chosen for subsequent experiments. Then IPEC-J2 cells were treated without DON (CON, N = 6) or with 1 µg/mL DON (DON, N = 6). Lactate dehydrogenase (LDH) content, apoptosis rate, and proinflammatory cytokines including interleukin (IL)-1ß, Il-6, and tumor necrosis factor α (TNF-α) were measured. Additionally, the expression of AMP-activated protein kinase α1 (AMPK-α1), the content of glucose, intestinal alkaline phosphatase (AKP), and sodium/potassium-transporting adenosine triphosphatase (Na+/K+-ATPase) activity, and the expression of SGLT1 and GLU2 of IPEC-J2 cells were also analyzed. The results showed that DON exposure significantly increased LDH release and apoptosis rate of IPEC-J2 cells. Stimulation with DON resulted in significant cellular inflammatory damage, as evidenced by a significant increase in proinflammatory cytokines (IL-1ß, IL-6, and TNF-α). Additionally, DON caused damage to the glucose absorption capacity of IPEC-J2 cells, indicated by decreased levels of glucose content, AKP activity, Na+/K+-ATPase activity, AMPK-α1 protein expression, and SGLT1 expression. Correlation analysis revealed that glucose absorption capacity was negatively correlated with cell inflammatory cytokines. Based on the findings of this study, it can be preliminarily concluded that the cell inflammatory damage caused by DON may be associated with decreased glucose absorption.

Glucose is one of the most basic nutrients necessary to sustain animal life and plays a crucial role in animal body composition and energy metabolism. Previous studies suggested a link between glucose absorption and inflammatory injury. In the present study, deoxynivalenol (DON) stimulation caused severe inflammatory injury and reduced the glucose absorption capacity of IPEC-J2 cells. Pearson's correlation analysis revealed a negative correlation between glucose absorption capacity and cell inflammatory cytokines. Ultimately, it can be speculated that the cellular inflammatory response triggered by DON may be related to the altered expression of glucose transporters.

Sodium-glucose cotransporter 1 promotes the biofunctions of perivascular preadipocytes mediated by Akt/mTOR/p70S6K signaling pathway.

The influence of SGLT-1 on perivascular preadipocytes (PVPACs) and vascular remodeling is not well understood. This study aimed to elucidate the role and mechanism of SGLT-1-mediated PVPACs bioactivity. PVPACs were cultured in vitro and applied ex vivo to the carotid arteries of mice using a lentivirus-based thermosensitive in situ gel (TISG). The groups were treated with Lv-SGLT1 (lentiviral vector, overexpression), Lv-siSGLT1 (RNA interference, knockdown), or specific signaling pathway inhibitors. Assays were conducted to assess changes in cell proliferation, apoptosis, glucose uptake, adipogenic differentiation, and vascular remodeling in the PVPACs. Protein expression was analyzed by Western blotting, immunocytochemistry, and/or immunohistochemistry. The methyl thiazolyl tetrazolium (MTT) assay and Hoechst 33342 staining indicated that SGLT-1 overexpression significantly promoted PVPACs proliferation and inhibited apoptosis in vitro. Conversely, SGLT-1 knockdown exerted the opposite effect. Oil Red O staining revealed that SGLT-1 overexpression facilitated adipogenic differentiation, while its inhibition mitigated these effects. 3H-labeled glucose uptake experiments demonstrated that SGLT-1 overexpression enhanced glucose uptake by PVPACs, whereas RNA interference-mediated SGLT-1 inhibition had no significant effect on glucose uptake. Moreover, RT-qPCR, Western blotting, and immunofluorescence analyses revealed that SGLT-1 overexpression upregulated FABP4 and VEGF-A levels and activated the Akt/mTOR/p70S6K signaling pathway, whereas SGLT-1 knockdown produced the opposite effects. In vivo studies corroborated these findings and indicated that SGLT-1 overexpression facilitated carotid artery remodeling. Our study demonstrates that SGLT-1 activation of the Akt/mTOR/p70S6K signaling pathway promotes PVPACs proliferation, adipogenesis, glucose uptake, glucolipid metabolism, and vascular remodeling.NEW & NOTEWORTHY SGLT-1 is expressed in PVPACs and can affect preadipocyte glucolipid metabolism and vascular remodeling. SGLT-1 promotes the biofunctions of PVPACs mediated by Akt/mTOR/p70S6K signaling pathway. Compared with caudal vein or intraperitoneal injection, the external application of lentivirus-based thermal gel around the carotid artery is an innovative attempt at vascular remodeling model, it may effectively avoid the transfection of lentiviral vector into the whole body of mice and the adverse effect on experimental results.

Genetic Evidence of Causal Relation Between Intestinal Glucose Absorption and Early Postprandial Glucose Response: A Mendelian Randomization Study.

The postprandial glucose response is an independent risk factor for type 2 diabetes. Observationally, early glucose response after an oral glucose challenge has been linked to intestinal glucose absorption, largely influenced by the expression of sodium-glucose cotransporter 1 (SGLT1). This study uses Mendelian randomization (MR) to estimate the causal effect of intestinal SGLT1 expression on early glucose response. Involving 1,547 subjects with class II/III obesity from the Atlas Biologique de l'Obésité Sévère cohort, the study uses SGLT1 genotyping, oral glucose tolerance tests, and jejunal biopsies to measure SGLT1 expression. A loss-of-function SGLT1 haplotype serves as the instrumental variable, with intestinal SGLT1 expression as the exposure and the change in 30-min postload glycemia from fasting glycemia (Δ30 glucose) as the outcome. Results show that 12.8% of the 1,342 genotyped patients carried the SGLT1 loss-of-function haplotype, associated with a mean Δ30 glucose reduction of -0.41 mmol/L and a significant decrease in intestinal SGLT1 expression. The observational study links a 1-SD decrease in SGLT1 expression to a Δ30 glucose reduction of -0.097 mmol/L. MR analysis parallels these findings, associating a statistically significant reduction in genetically instrumented intestinal SGLT1 expression with a Δ30 glucose decrease of -0.353. In conclusion, the MR analysis provides genetic evidence that reducing intestinal SGLT1 expression causally lowers early postload glucose response. This finding has a potential translational impact on managing early glucose response to prevent or treat type 2 diabetes.

Sugar binding of sodium-glucose cotransporters analyzed by voltage-clamp fluorometry.

Sugar absorption is crucial for life and relies on glucose transporters, including sodium-glucose cotransporters (SGLTs). Although the structure of SGLTs has been resolved, the substrate selectivity of SGLTs across diverse isoforms has not been determined owing to the complex substrate-recognition processes and limited analysis methods. Therefore, this study used voltage-clamp fluorometry (VCF) to explore the substrate-binding affinities of human SGLT1 in Xenopus oocytes. VCF analysis revealed high-affinity binding of D-glucose and D-galactose, which are known transported substrates. D-fructose, which is not a transported substrate, also bound to SGLT1, suggesting potential recognition despite the lack of transport activity. VCF analysis using the T287N mutant of the substrate-binding pocket, which has reduced D-glucose transport capacity, showed that its D-galactose-binding affinity exceeded its D-glucose-binding affinity. This suggests that the change in the VCF signal was due to substrate binding to the binding pocket. Both D-fructose and L-sorbose showed similar binding affinities, indicating that SGLT1 preferentially binds to pyranose-form sugars, including D-fructopyranose. Electrophysiological analysis confirmed that D-fructose binding did not affect the SGLT1 transport function. The significance of the VCF assay lies in its ability to measure sugar-protein interactions in living cells, thereby bridging the gap between structural analyses and functional characterizations of sugar transporters. Our findings also provide insights into SGLT substrate selectivity and the potential for developing medicines with reduced side effects by targeting non-glucose sugars with low bioreactivity.

Mechanistic Modeling of Empagliflozin: Predicting Pharmacokinetics, Urinary Glucose Excretion, and Investigating Compensatory Role of SGLT1 in Renal Glucose Reabsorption.

The aim of this study was to use a combination of physiologically based pharmacokinetic (PBPK) modeling and urinary glucose excretion (UGE) modeling to predict the time profiles of pharmacokinetics (PK) and UGE for the sodium-glucose cotransporter 2 (SGLT2) inhibitor empagliflozin (EMP). Additionally, the study aims to explore the compensatory effect of SGLT1 in renal glucose reabsorption (RGR) when SGLT2 is inhibited. The PBPK-UGE model was developed using physicochemical and biochemical properties, renal physiological parameters, binding kinetics, glucose, and Na+ reabsorption kinetics by SGLT1/2. For area under the plasma concentration-time curve, maximum plasma concentration, and cumulative EMP excretion in urine, the predicted values fell within a range of 0.5-2.0 when compared to observed data. Additionally, the simulated UGE data also matched well with the clinical data, further validating the accuracy of the model. According to the simulations, SGLT1 and SGLT2 contributed approximately 13% and 87%, respectively, to RGR in the absence of EMP. However, in the presence of EMP at doses of 2.5 and 10 mg, the contribution of SGLT1 to RGR significantly increased to approximately 76%-82% and 89%-93%, respectively, in patients with type 2 diabetes mellitus. Furthermore, the model supported the understanding that the compensatory effect of SGLT1 is the underlying mechanism behind the moderate inhibition observed in total RGR. The PBPK-UGE model has the capability to accurately predict the PK and UGE time profiles in humans. Furthermore, it provides a comprehensive analysis of the specific contributions of SGLT1 and SGLT2 to RGR in the presence or absence of EMP.

Deletion of the Sodium Glucose Cotransporter 1 (Sglt-1) impairs mouse sperm movement.

The Sodium Glucose Cotransporter Isoform 1 (Sglt-1) is a symporter that moves Na+ and glucose into the cell. While most studies have focused on the role of Sglt-1 in the small intestine and kidney, little is known about this transporter's expression and function in other tissues. We have previously shown that Sglt-1 is expressed in the mouse sperm flagellum and that its inhibition interferes with sperm metabolism and function. Here, we further investigated the importance of Sglt-1 in sperm, using a Sglt-1 knockout mouse (Sglt-1 KO). RNA, immunocytochemistry, and glucose uptake analysis confirmed the ablation of Sglt-1 in sperm. Sglt-1 KO male mice are fertile and exhibit normal sperm counts and morphology. However, Sglt-1 null sperm displayed a significant reduction in total, progressive and other parameters of sperm motility compared to wild type (WT) sperm. The reduction in motility was exacerbated when sperm were challenged to swim in media with higher viscosity. Parameters of capacitation, namely protein tyrosine phosphorylation and acrosomal reaction, were similar in Sglt-1 KO and WT sperm. However, Sglt-1 KO sperm displayed a significant decrease in hyperactivation. The impaired motility of Sglt-1 null sperm was observed in media containing glucose as the only energy substrate. Interestingly, the addition of pyruvate and lactate to the media partially recovered sperm motility of Sglt-1 KO sperm, both in the low and high viscosity media. Altogether, these results support an important role for Sglt-1 in sperm energetics and function, providing sperm with a higher capacity for glucose uptake.

Influence of SGLT1 Sugar Uptake Inhibitors on Water Transport.

Sodium glucose cotransporters (SGLTs) are cotransporters located in the cell membrane of various epithelia that uptake glucose or galactose and sodium into the cell. Its founding member, SGLT1, represents a major pharmaceutically relevant target protein for development of new antidiabetic drugs, in addition to being the target protein of the oral rehydration therapy. Previous studies focused primarily on the transport of substrates and ions, while our study focuses on the effect of water transport. SGLT1 is implicated in the absorption of water, yet the exact mechanism of how the water absorption occurs or how inhibitors of SGLT1, such as phlorizin, are able to inhibit it is still unclear. Here we present a comprehensive study based on molecular dynamics simulations with the aim of determining the influence of the energetic and dynamic properties of SGLT1, which are influenced by selected sugar uptake inhibitors on water permeation.

Collective Domain Motion Facilitates Water Transport in SGLT1.

The human sodium-glucose cotransporter protein (SGLT1) is an important representative of the sodium solute symporters belonging to the secondary active transporters that are critical to the homeostasis of sugar, sodium, and water in the cell. The underlying transport mechanism of SGLT1 is based on switching between inward- and outward-facing conformations, known as the alternating access model, which is crucial for substrate transport, and has also been postulated for water permeation. However, the nature of water transport remains unclear and is disputed along the passive and active transport, with the latter postulating the presence of the pumping effect. To better examine the water transport in SGLT1, we performed a series of equilibrium all-atom molecular dynamics simulations, totaling over 6 µs of sample representative conformational states of SGLT1 and its complexes, with the natural substrates, ions, and inhibitors. In addition to elucidating the basic physical factors influencing water permeation, such as channel openings and energetics, we focus on dynamic flexibility and its relationship with domain motion. Our results clearly demonstrate a dependence of instantaneous water flux on the channel opening and local water diffusion in the channel, strongly supporting the existence of a passive water transport in SGLT1. In addition, a strong correlation found between the local water diffusion and protein domain motion, resembling the "rocking-bundle" motion, reveals its facilitating role in the water transport.

The effect of gastric bypass surgery on cognitive function of Alzheimer's disease and the role of GLP1-SGLT1 pathway.

OBJECTIVE: Gastric bypass surgery has been shown to improve metabolic profiles via GLP1, which may also have cognitive benefits for Alzheimer's disease (AD) patients. However, the exact mechanism requires further investigation. METHODS: Roux-en-Y gastric bypass or sham surgery was performed on APP/PS1/Tau triple transgenic mice (an AD mice model) or wild type C57BL/6 mice. Morris Water Maze (MWM) test was used to evaluate the cognitive function of mice and animal tissue samples were obtained for measurements two months after the surgery. Additionally, STC-1 intestine cells were treated with siTAS1R2 and siSGLT1, and HT22 nerve cells were treated with Aß, siGLP1R, GLP1 and siSGLT1 in vitro to explore the role of GLP1-SGLT1 related signaling pathway in cognitive function. RESULTS: The MWM test showed that bypass surgery significantly improved cognitive function in AD mice as measured by navigation and spatial probe tests. Moreover, bypass surgery reversed neurodegeneration, down-regulated hyperphosphorylation of Tau protein and Aß deposition, improved glucose metabolism, and up-regulated the expression of GLP1, SGLT1, and TAS1R2/3 in the hippocampus. Furthermore, GLP1R silencing down-regulated SGLT1 expression, whereas SGLT1 silencing increased Tau protein deposition and exacerbated dysregulated of glucose metabolism in HT22 cells. However, RYGB did not alter the level of GLP1 secretion in the brainstem (where central GLP1 is mainly produced). Additionally, GLP1 expression was upregulated by RYGB via TAS1R2/3-SGLT1 activation sequentially in the small intestine. CONCLUSION: RYGB surgery could improve cognition function in AD mice through facilitating glucose metabolism and reducing Tau phosphorylation and Aß deposition in the hippocampus, mediated by peripheral serum GLP1 activation of SGLT1 in the brain. Furthermore, RYGB increased GLP1 expression through sequential activation of TAS1R2/TAS1R3 and SGLT1 in the small intestine.

Obesity and overweight are linked to increased sodium-glucose cotransporter 1 and glucose transporter 5 levels in duodenum.

OBJECTIVE: Prior evidence indicates that individuals with obesity have an accelerated intestinal glucose absorption. This cross-sectional study evaluated whether those with overweight or obesity display higher duodenal protein levels of the glucose carriers sodium-glucose cotransporter 1 (SGLT-1), glucose transporter 2 (GLUT-2), and glucose transporter 5 (GLUT-5). METHODS: SGLT-1, GLUT-2, and GLUT-5 protein levels were assessed on duodenal mucosa biopsies of 52 individuals without diabetes categorized on the basis of their BMI as lean, with overweight, or with obesity. RESULTS: Individuals with overweight and obesity exhibited progressively increased duodenal protein levels of SGLT-1 and GLUT-5 as compared with the lean group. Conversely, no differences in duodenal GLUT-2 abundance were found among the three groups. Univariate analysis showed that SGLT-1 and GLUT-5 protein levels were positively correlated with BMI, waist circumference, 1-hour post-load glucose, fasting and post-load insulin, and insulin secretion and resistance levels. Furthermore, a positive relationship was detected between intestinal GLUT-5 levels and serum uric acid concentrations, a product of fructose metabolism known to be involved in the pathogenesis of obesity and its complications. CONCLUSIONS: Individuals with overweight and obesity display enhanced duodenal SGLT-1 and GLUT-5 abundance, which correlates with increased postprandial glucose concentrations, insulin resistance, and hyperinsulinemia.

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 AUC0­180 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.

Phloretin Improves Ultrafiltration and Reduces Glucose Absorption during Peritoneal Dialysis in Rats.

BACKGROUND: Harmful glucose exposure and absorption remain major limitations of peritoneal dialysis (PD). We previously showed that inhibition of sodium glucose cotransporter 2 did not affect glucose transport during PD in rats. However, more recently, we found that phlorizin, a dual blocker of sodium glucose cotransporters 1 and 2, reduces glucose diffusion in PD. Therefore, either inhibiting sodium glucose cotransporter 1 or blocking facilitative glucose channels by phlorizin metabolite phloretin would reduce glucose transport in PD. METHODS: We tested a selective blocker of sodium glucose cotransporter 1, mizagliflozin, as well as phloretin, a nonselective blocker of facilitative glucose channels, in an anesthetized Sprague-Dawley rat model of PD. RESULTS: Intraperitoneal phloretin treatment reduced glucose absorption by >30% and resulted in a >50% higher ultrafiltration rate compared with control animals. Sodium removal and sodium clearances were similarly improved, whereas the amount of ultrafiltration per millimole of sodium removed did not differ. Mizagliflozin did not influence glucose transport or osmotic water transport. CONCLUSIONS: Taken together, our results and previous results indicate that blockers of facilitative glucose channels may be a promising target for reducing glucose absorption and improving ultrafiltration efficiency in PD.

A Fatty Diet Induces a Jejunal Ketogenesis Which Inhibits Local SGLT1-Based Glucose Transport via an Acetylation Mechanism-Results from a Randomized Cross-Over Study between Iso-Caloric High-Fat versus High-Carbohydrate Diets in Healthy Volunteers.

BACKGROUND AND AIMS: Insights into the nature of gut adaptation after different diets enhance the understanding of how food modifications can be used to treat type 2 diabetes and obesity. The aim was to understand how diets, enriched in fat or carbohydrates, affect glucose absorption in the human healthy jejunum, and what mechanisms are involved. METHODS: Fifteen healthy subjects received, in randomised order and a crossover study design, two weeks of iso-caloric high-fat diet (HFD) and high-carbohydrate diet (HCD). Following each dietary period, jejunal mucosa samples were retrieved and assessed for protein expression using immunofluorescence and western blotting. Functional characterisation of epithelial glucose transport was assessed ex vivo using Ussing chambers. Regulation of SGLT1 through histone acetylation was studied in vitro in Caco-2 and human jejunal enteroid monolayer cultures. RESULTS: HFD, compared to HCD, decreased jejunal Ussing chamber epithelial glucose transport and the expression of apical transporters for glucose (SGLT1) and fructose (GLUT5), while expression of the basolateral glucose transporter GLUT2 was increased. HFD also increased protein expression of the ketogenesis rate-limiting enzyme mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase (HMGCS2) and decreased the acetylation of histone 3 at lysine 9 (H3K9ac). Studies in Caco-2 and human jejunal enteroid monolayer cultures indicated a ketogenesis-induced activation of sirtuins, in turn decreasing SGLT1 expression. CONCLUSION: Jejunal glucose absorption is decreased by a fat-enriched diet, via a ketogenesis-induced alteration of histone acetylation responsible for the silencing of SGLT1 transcription. The work relates to a secondary outcome in ClinicalTrials.gov (NCT02088853).

Insight on Glucose and Fructose Absorption and Relevance in the Enterocyte Milieu.

Although epidemiological studies indicate a strong correlation between high sugar intake and metabolic diseases, the biological mechanisms underlying this link are still controversial. To further examine the modification and crosstalk occurring in enterocyte metabolism during sugar absorption, in this study we evaluate the diffusion and intestinal metabolism of glucose, fructose and sucrose, which were supplemented in equimolar concentration to Caco-2 cells grown on polyester membrane inserts. At different time points after supplementation, changes in metabolite concentration were evaluated in the apical and basolateral chambers by nuclear magnetic resonance (NMR) and gas-chromatography (GC). Sucrose was only minimally hydrolyzed by Caco-2 cells. Upon supplementation, we observed a faster uptake of fructose than glucose, the pentose sugar being also faster catabolized. Monosaccharide absorption was concomitant to the synthesis/transport of other metabolites, which occurred differently in glucose and fructose supplemented cells. Our results confirm the prominent role of intestinal cells in fructose metabolism and clearance after absorption, representing a further step forward in the understanding of the role of dietary sugars. Future research, including targeted analysis on specific transporters/enzymes and the use of labeled substrates, will be helpful to confirm the present results and their interpretation.

The expression and survival significance of sodium glucose transporters in pancreatic cancer.

BACKGROUND: Sodium glucose transporters (SGLTs) play vital roles in glucose uptake in many solid cancers, including pancreatic cancer (PC). However, their expression profile in pancreatic cancer and correlation with prognosis are not clear. Thus, we aimed to analyse the expression profile and prognostic significance of SGLT-1 and SGLT-2 in PC. METHODS: Eighty-eight patients with pancreatic ductal adenocarcinoma (PDAC) undergoing surgery in Huashan Hospital, Fudan University, from July 2017 to June 2020 were enrolled in the study. Specimens for immunohistochemistry were obtained through surgical resection. Bioinformatics analysis was performed based on the Gene Expression Omnibus (GEO), Oncomine and The Cancer Genome Atlas (TCGA) databases. The statistics were calculated using IBM SPSS Statistics, version 20 and R 4.1.1. P values lower than 0.05 were considered to indicate statistical significance. RESULTS: SGLT-1 but not SGLT-2 was significantly overexpressed in PDAC. Survival analysis showed that the median overall survival (OS) and progression-free survival (PFS) of patients with high SGLT-1 expression were significantly longer than that of patients with low SGLT-1 expression. Cox regression indicated that high SGLT-1 expression was an independent predictor for a better prognosis, while residual tumour status (R1 and R2) was an independent risk factor for a poor prognosis. Finally, PDZK1-interacting protein 1 (PDZK1IP1), a protein participating in the generation of reactive oxygen species, was overexpressed in PDAC and its expression was significantly correlated with SGLT-1. CONCLUSIONS: SGLT-1 but not SGLT-2 was overexpressed in PDAC, and the overexpression of SGLT-1 could be a predictor of a better prognosis. Residual tumour status (R1 and R2) was a risk factor for poor prognosis and disease progression.

Structural Basis of the Selective Sugar Transport in Sodium-Glucose Cotransporters.

Sodium-glucose cotransporters (SGLTs) are responsible for sugar absorption in small intestine and renal tubule epithelial cells. These proteins have attracted clinical attention as a cause of malabsorption and as a target for diabetes drugs. Each SGLT isoform has strict selectivity for its monosaccharide substrate. Few studies have attempted to elucidate the structural basis of sugar selectivity by allowing generating SGLT mutants that bind substrates not normally transported or by reproducing the substrate specificity of other isoforms. In this study, we built a structural homology model for the substrate binding states of human SGLT1 (hSGLT1), which primarily transports glucose and galactose. We also performed electrophysiological analysis of hSGLT1 using various natural sugars and mutants. By mutating the K321 residue, which forms hydrophilic interactions in the sugar binding pocket, we induced mannose and allose transport. We also changed the glucose/galactose transport ratio, which reproduces the substrate specificity of the prokaryotic galactose transporter. By adding mutations one-by-one to the residues in the binding pocket, we were able to reproduce the substrate specificity of SGLT4, which transports fructose. This suggests that fructose, which exhibits various structures in equilibrium, binds to SGLT in a pyranose conformation. These results reveal one state of the structural basis that determines selective transport by SGLT. These findings will be useful for predicting the substrates of other glucose transporters and to design effective inhibitors.

Role of the macula densa sodium glucose cotransporter type 1-neuronal nitric oxide synthase-tubuloglomerular feedback pathway in diabetic hyperfiltration.

An increase of glomerular filtration rate (GFR) is a common observation in early diabetes and is considered a key risk factor for subsequent kidney injury. However, the mechanisms underlying diabetic hyperfiltration have not been fully clarified. Here, we tested the hypothesis that macula densa neuronal nitric oxide synthase (NOS1) is upregulated via sodium glucose cotransporter type 1 (SGLT1) in diabetes, which then inhibits tubuloglomerular feedback (TGF) promoting glomerular hyperfiltration. Therefore, we examined changes in cortical NOS1 expression and phosphorylation, nitric oxide production in the macula densa, TGF response, and GFR during the early stage of insulin-deficient (Akita) diabetes in wild-type and macula densa-specific NOS1 knockout mice. A set of sophisticated techniques including microperfusion of juxtaglomerular apparatus in vitro, micropuncture of kidney tubules in vivo, and clearance kinetics of plasma fluorescent-sinistrin were employed. Complementary studies tested the role of SGLT1 in SGLT1 knockout mice and explored NOS1 expression and phosphorylation in kidney biopsies of cadaveric donors. Diabetic mice had upregulated macula densa NOS1, inhibited TGF and elevated GFR. Macula densa-selective NOS1 knockout attenuated the diabetes-induced TGF inhibition and GFR elevation. Additionally, deletion of SGLT1 prevented the upregulation of macula densa NOS1 and attenuated inhibition of TGF in diabetic mice. Furthermore, the expression and phosphorylation levels of NOS1 were increased in cadaveric kidneys of diabetics and positively correlated with blood glucose as well as estimated GFR in the donors. Thus, our findings demonstrate that the macula densa SGLT1-NOS1-TGF pathway plays a crucial role in the control of GFR in diabetes.

Structure and mechanism of the SGLT family of glucose transporters.

Glucose is a primary energy source in living cells. The discovery in 1960s that a sodium gradient powers the active uptake of glucose in the intestine1 heralded the concept of a secondary active transporter that can catalyse the movement of a substrate against an electrochemical gradient by harnessing energy from another coupled substrate. Subsequently, coupled Na+/glucose transport was found to be mediated by sodium-glucose cotransporters2,3 (SGLTs). SGLTs are responsible for active glucose and galactose absorption in the intestine and for glucose reabsorption in the kidney4, and are targeted by multiple drugs to treat diabetes5. Several members within the SGLT family transport key metabolites other than glucose2. Here we report cryo-electron microscopy structures of the prototypic human SGLT1 and a related monocarboxylate transporter SMCT1 from the same family. The structures, together with molecular dynamics simulations and functional studies, define the architecture of SGLTs, uncover the mechanism of substrate binding and selectivity, and shed light on water permeability of SGLT1. These results provide insights into the multifaceted functions of SGLTs.