Biology of human sodium glucose transporters

SGLT2 Inhibitors and the Clinical Implications of Associated Weight Loss in Type 2 Diabetes: A Narrative Review

INTRODUCTION

The obesity epidemic is closely linked to the rising prevalence of type 2 diabetes (T2D). Body weight reduction remains an important challenge in patients with T2D, as it requires changing their overall metabolic control. Of all glucose-lowering therapies, only sodium-glucose cotransporter 2 inhibitors (SGLT2is) and glucagon-like peptide 1 receptor agonists (GLP-1 RAs) consistently result in weight improvement. Moreover, the same two classes have important cardiovascular and renal benefits. We summarize the key available information related to the weight loss effect of SGLT2is in T2D, focusing on the unexploited potential of these drugs.

METHODS

Data on weight change with SGLT2is in patients with T2D were extracted from published cardiovascular outcomes trials (CVOTs). A discussion on patient perspectives about weight change is based on key preclinical and clinical trials, meta-analyses, and reviews and is supplemented by the authors' clinical judgment and research experience in the field.

RESULTS

SGLT2is have a unique mode of action resulting in caloric loss through glycosuria. The anticipated weight loss with SGLT2is is not reflected in clinical trial results. There is a discrepancy between the magnitude of improvement in glycemic control and the weight loss, cardiovascular, and renal benefits obtained in large clinical trials.

CONCLUSION

The relationships between the magnitude of weight loss, improvement in glycemic control, and cardiorenal benefits with SGLT2i are still unclear. Potential mechanisms other than simple glycemic efficacy should be revealed and explained. Better weight control may be achieved if adequately intensive lifestyle changes are implemented and monitored in the T2D population treated with SGLT2is.

3-Deoxyglucosone reduces glucagon-like peptide-1 secretion at low glucose levels through down-regulation of SGLT1 expression in STC-1 cells

CONTEXT

Sodium glucose co-transporter 1 (SGLT1) triggers low glucose-induced glucagon-like peptide-1 (GLP-1) secretion. We reported that a two-week administration of 3-deoxyglucosone (3DG), an independent factor associated with the development of pre-diabetes, reduces basal GLP-1 secretion in rats.

OBJECTIVE

This study investigated the effects of 3DG on GLP-1 secretion and SGLT1 pathway under low-glucose conditions in STC-1 cells.

METHODS

STC-1 cells were incubated with phloridzin or 3DG at 5.6 mM glucose. SGLT1 expression (by western blotting), GLP-1 and cyclic adenosine monophosphate (cAMP) levels (by ELISA), and intracellular Ca²⁺ concentration (by Fluo-3/AM) were measured.

RESULTS

Phloridzin inhibited GLP-1 secretion. SGLT1 protein expression in STC-1 cells cultured in 5.6 mM glucose is higher than that in 25 mM glucose. Exposure to 3DG for 6 h reduced GLP-1 secretion, SGLT1 protein expression, and intracellular concentrations of cAMP and Ca²⁺.

CONCLUSIONS

3DG reduces low glucose-induced GLP-1 secretion in part through reduction of SGLT1 expression.

SGLT2 Inhibitors as Calorie Restriction Mimetics: Insights on Longevity Pathways and Age-Related Diseases

Sodium-glucose cotransporter-2 (SGLT2) inhibitors induce glycosuria, reduce insulin levels, and promote fatty acid oxidation and ketogenesis. By promoting a nutrient deprivation state, SGLT2 inhibitors upregulate the energy deprivation sensors AMPK and SIRT1, inhibit the nutrient sensors mTOR and insulin/IGF1, and modulate the closely linked hypoxia-inducible factor (HIF)-2α/HIF-1α pathways. Phosphorylation of AMPK and upregulation of adiponectin and PPAR-α favor a reversal of the metabolic syndrome which have been linked to suppression of chronic inflammation. Downregulation of insulin/IGF1 pathways and mTOR signaling from a reduction in glucose and circulating amino acids promote cellular repair mechanisms, including autophagy and proteostasis which confer cellular stress resistance and attenuate cellular senescence. SIRT1, another energy sensor activated by NAD+ in nutrient-deficient states, is reciprocally activated by AMPK, and can deacetylate and activate transcription factors, such as PCG-1α, mitochondrial transcription factor A (TFAM), and nuclear factor E2-related factor (NRF)-2, that regulate mitochondrial biogenesis. FOXO3 transcription factor which target genes in stress resistance, is also activated by AMPK and SIRT1. Modulation of these pathways by SGLT2 inhibitors have been shown to alleviate metabolic diseases, attenuate vascular inflammation and arterial stiffness, improve mitochondrial function and reduce oxidative stress-induced tissue damage. Compared with other calorie restriction mimetics such as metformin, rapamycin, resveratrol, and NAD+ precursors, SGLT2 inhibitors appear to be the most promising in the treatment of aging-related diseases, due to their regulation of multiple longevity pathways that closely resembles that achieved by calorie restriction and their established efficacy in reducing cardiovascular events and all-cause mortality. Evidence is compelling for the role of SGLT2 inhibitors as a calorie restriction mimetic in anti-aging therapeutics.

Possible Preventative/Rehabilitative Role of Gliflozins in OSA and T2DM. A Systematic Literature Review-Based Hypothesis

Obstructive sleep apnoea (OSA) is characterized by frequent apnoea episodes during sleep due to upper airway obstruction. The present review summarizes current knowledge on inter-relationships between OSA and type 2 diabetes mellitus (T2DM) and suggests the former as a possible target for sodium-glucose co-transporter-2 inhibitors (SGLT-2i). Based on pathophysiological mechanisms underlying OSA onset and renal SGLT-2 effects, we suggest that SGLT-2i indications might expand beyond current ones, including glucose, lipids, uric acid, blood pressure, and body weight control as well as chronic heart failure and kidney disease prevention.

The Na/K-ATPase Signaling and SGLT2 Inhibitor-Mediated Cardiorenal Protection: A Crossed Road?

In different large-scale clinic outcome trials, sodium (Na⁺)/glucose co-transporter 2 (SGLT2) inhibitors showed profound cardiac- and renal-protective effects, making them revolutionary treatments for heart failure and kidney disease. Different theories are proposed according to the emerging protective effects other than the original purpose of glucose-lowering in diabetic patients. As the ATP-dependent primary ion transporter providing the Na⁺ gradient to drive other Na⁺-dependent transporters, the possible role of the sodium–potassium adenosine triphosphatase (Na/K-ATPase) as the primary ion transporter and its signaling function is not explored.

Mechanisms of Glucose Absorption in the Small Intestine in Health and Metabolic Diseases and Their Role in Appetite Regulation

The worldwide prevalence of metabolic diseases such as obesity, metabolic syndrome and type 2 diabetes shows an upward trend in recent decades. A characteristic feature of these diseases is hyperglycemia which can be associated with hyperphagia. Absorption of glucose in the small intestine physiologically contributes to the regulation of blood glucose levels, and hence, appears as a putative target for treatment of hyperglycemia. In fact, recent progress in understanding the molecular and cellular mechanisms of glucose absorption in the gut and its reabsorption in the kidney helped to develop a new strategy of diabetes treatment. Changes in blood glucose levels are also involved in regulation of appetite, suggesting that glucose absorption may be relevant to hyperphagia in metabolic diseases. In this review we discuss the mechanisms of glucose absorption in the small intestine in physiological conditions and their alterations in metabolic diseases as well as their relevance to the regulation of appetite. The key role of SGLT1 transporter in intestinal glucose absorption in both physiological conditions and in diabetes was clearly established. We conclude that although inhibition of small intestinal glucose absorption represents a valuable target for the treatment of hyperglycemia, it is not always suitable for the treatment of hyperphagia. In fact, independent regulation of glucose absorption and appetite requires a more complex approach for the treatment of metabolic diseases.

Electrophysiological characterization of a diverse group of sugar transporters from Trichoderma reesei

Trichoderma reesei is an ascomycete fungus known for its capability to secrete high amounts of extracellular cellulose- and hemicellulose-degrading enzymes. These enzymes are utilized in the production of second-generation biofuels and T. reesei is a well-established host for their production. Although this species has gained considerable interest in the scientific literature, the sugar transportome of T. reesei remains poorly characterized. Better understanding of the proteins involved in the transport of different sugars could be utilized for engineering better enzyme production strains. In this study we aimed to shed light on this matter by characterizing multiple T. reesei transporters capable of transporting various types of sugars. We used phylogenetics to select transporters for expression in Xenopus laevis oocytes to screen for transport activities. Of the 18 tested transporters, 8 were found to be functional in oocytes. 10 transporters in total were investigated in oocytes and in yeast, and for 3 of them no transport function had been described in literature. This comprehensive analysis provides a large body of new knowledge about T. reesei sugar transporters, and further establishes X. laevis oocytes as a valuable tool for studying fungal sugar transporters.

The Potential Roles of Osmotic and Nonosmotic Sodium Handling in Mediating the Effects of Sodium-Glucose Cotransporter 2 Inhibitors on Heart Failure

Concomitant type 2 diabetes and chronic kidney disease increases the risk of heart failure. Recent studies demonstrate beneficial effects of sodium-glucose cotransporter 2 (SGLT2) inhibitors on chronic kidney disease progression and heart failure hospitalization in patients with and without diabetes. In addition to inhibiting glucose reabsorption, SGLT2 inhibitors decrease proximal tubular sodium reabsorption, possibly leading to transient natriuresis. We review the hypothesis that SGLT2 inhibitor’s natriuretic and osmotic diuretic effects mediate their cardioprotective effects. The degree to which these benefits are related to changes in sodium, independent of the kidney, is currently unknown. Aside from effects on osmotically active sodium, we explore the intriguing possibility that SGLT2 inhibitors could also modulate nonosmotic sodium storage. This alternative hypothesis is based on emerging literature that challenges the traditional 2-compartment model of sodium balance to provide support for a 3-compartment model that includes the binding of sodium to glycosaminoglycans, such as those in muscles and skin. This recent research on nonosmotic sodium storage, as well as direct cardiac effects of SGLT2 inhibitors, provides possibilities for other ways in which SGLT2 inhibitors might mitigate heart failure risk. Overall, we review the effects of SGLT2 inhibitors on sodium balance and sensitivity, cardiac tissue, interstitial fluid and plasma volume, and nonosmotic sodium storage.

SGLT2 inhibitors have cardiovascular benefits that include HF outcomes in patients with and without diabetes. Because the underlying mechanisms are only partly explained by improvements in BP, body weight, or glucose control, other mechanisms have been proposed. We focus here on a central role for effects on sodium as underlying the positive benefits of SGLT2 inhibitors in HF. We explore the new (although still unconfirmed) idea that SGLT2 inhibitors exert some of their positive effects by affecting nonosmotic sodium (ie, sodium bound to muscles and skin and not dissolved in the blood).

SGLT2 inhibitors have emerged as a class of drugs, previously prescribed for patients with T2D, that have in more recent years been shown to have substantial heart and kidney clinical benefits in patients with and without T2D.

The degree to which these benefits are related to kidney-independent changes in sodium homeostasis is currently unknown.

A better understanding of the nonosmotic mechanisms underpinning the benefits of SGLT2 inhibition on HF (with reduced or preserved left ventricular ejection fraction) may allow researchers to assess the effects of SGLT2 inhibitors in combination with other treatments that affect sodium balance.

Swertisin, a novel SGLT2 inhibitor, with improved glucose homeostasis for effective diabetes therapy

Failing pancreas and subsequent loss of pancreatic β cells worsen diabetic conditions which are further alleviated by the mounting up of glucose levels. Inhibition of sodium glucose cotransporter 2 (SGLT2) in the kidney responsible for glucose reabsorption strikingly reduces blood glucose levels. Bioactive swertisin showed a promising glucose-lowering effect. Hence, we aimed to mechanistically dissect the glucose lowering property of swertisin. A systematic in silico, in vitro, and in vivo approach was directed for target analysis of swertisin. Molecular docking was performed with Swertisn-hSGLT2 complex. Glucose uptake assay and protein expression for SGLT2 and regulatory proteins were performed under swertisin effect. Various physiological and metabolic parameters were evaluated in STZ induced BALB/c mice using swertisin treatment. SGLT2 expression was evaluated in the kidney tissue of mice. Swertisn-hSGLT2 molecularly docked complex showed similar binding energy compared to the Canagliflozin-hSGLT2 complex. Swertisin inhibited glucose uptake and decreased expression of SGLT2 in HEK293 cells. Swertisin does not affect GLUT mediated glucose transport. Swertisin treated diabetic mice demonstrated remarkable improvement in overall glucose homeostasis. Reduced expression of SGLT2 was found in kidney tissue along with reduced PKC expression which is one of the key regulators of SGLT2. Our study explored SGLT2 as a selective target of swertisin for its swift glucose-lowering action which not only inhibits SGLT2 but also reduces its expression in diabetic condition. Thus, the potential property of swertisin as a glucose-lowering agent is remarkable which points towards the likelihood of a wider avenue of diabetes therapy.

Anti-diabetic drugs and NASH: from current options to promising perspectives

Introduction: Accumulating evidence supports a bidirectional association between nonalcoholic steatohepatitis (NASH) and type 2 diabetes (T2D). There is a clinical challenge to consider pharmaceutical strategies targeting the metabolic dysfunction common to NASH and T2D pathogenesis.Areas covered: By using PubMed, we performed a literature search to review the potential beneficial effect of anti-diabetic and metabolic investigational drugs on NASH.Expert opinion: Since insulin resistance is central in the pathophysiology of both T2D and NASH, there is an urgent need for new insulin sensitizers. Peroxisome proliferator-activated receptor (PPAR) agonists, especially PPARγ and pan-PPARs agonists, have shown some beneficial effects on both NASH and liver fibrosis, but their routine use should be limited by their safety profile. Incretin-based therapies, including glucagon-like peptide 1 receptor agonists (GLP-1 RAs) and the polyagonists (GLP-1, GIP, glucagon) under development are the most promising anti-diabetic drugs for NASH treatment, mainly due to their action on body weight loss. Preliminary, preclinical and early phase studies suggest that SGLT2 inhibitors and fibroblast growth factor (FGF)19 and FGF21-based therapies are promising targets for NASH and T2D treatment. The common weakness for all of these drugs is their limited effect on liver fibrosis, potentially due to short-term trial design.

Long-term (52-week) efficacy and safety of dapagliflozin as an adjunct to insulin therapy in Japanese patients with type 1 diabetes: Subgroup analysis of the DEPICT-2 study

AIM

To examine the long-term efficacy and safety of dapagliflozin, a sodium-glucose co-transporter-2 (SGLT2) inhibitor used to treat type 1 diabetes, in the Japanese subpopulation of the DEPICT-2 study.

MATERIALS AND METHODS

Patients with type 1 diabetes were randomized to dapagliflozin 5 mg (n = 55), dapagliflozin 10 mg (n = 41) or placebo (n = 58) plus insulin for a 24-week, double-blind period followed by a 28-week, single-blind extension phase.

RESULTS

From baseline to 24 weeks, dapagliflozin reduced HbA1c compared with placebo (mean change of -0.58% and -0.80% for 5 and 10 mg, respectively), and an HbA1c reduction was observed up to 52 weeks. Compared with placebo, dapagliflozin 5 and 10 mg increased the proportion of patients achieving HbA1c reductions of 0.5% or more without severe hypoglycaemia events and reduced glycaemic variability assessed via continuous glucose monitoring. Both dapagliflozin doses decreased body weight and total daily insulin dose at 24 weeks compared with placebo; these reductions were maintained up to 52 weeks. Diabetic ketoacidosis occurred in both dapagliflozin groups (one and two cases, respectively) but not with placebo.

CONCLUSIONS

Efficacy and safety results from the Japanese subpopulation of the DEPICT-2 study were generally consistent with those from the overall population, indicating that long-term dapagliflozin adjunct to insulin therapy improves glycaemic control without an increased risk of hypoglycaemia but with a risk of diabetic ketoacidosis in Japanese patients with type 1 diabetes.

Sodium-glucose cotransporter 2 inhibitors as an add-on therapy to insulin for type 1 diabetes mellitus: Meta-analysis of randomized controlled trials

AIMS

The aim was to systematically review the efficacy and safety of sodium-glucose cotransporter inhibitor (SGLT2i) as an adjunct to insulin at different follow-up durations in randomized, double-blind clinical trials in patients with type 1 diabetes.

METHODS

We conducted a search on Medline, Embase, and the Cochrane Library for relevant studies published before May 2020. According to the duration of follow-up, the subgroup analysis included four periods: 1-4, 12-18, 24-26, and 52 weeks. In the five trials included both 24-26 and 52 weeks of follow-up, we compared the efficacy by the placebo-subtracted difference and changes in SGLT2i groups.

RESULTS

Fifteen trials including 7109 participants were analyzed. The combination of SGLT2i and insulin improved hemoglobin A1c (HbA1c), fasting plasma glucose (FPG), daily insulin dose, body weight, and blood pressure, which varied greatly by different follow-ups. Compared with %HbA1c at 24-26 weeks, placebo-subtracted differences and changes in the SGLT2i groups slightly increased. SGLT2i plus insulin treatment showed no difference in the occurrence of urinary tract infections (UTIs), hypoglycemia, or severe hypoglycemia but increased the risk of genital tract infections (GTIs) in a duration-dependent manner. SGLT2i treatment was associated with a significantly higher rate of ketone-related SAEs and diabetic ketoacidosis (DKA) at 52 weeks.

CONCLUSION

SGLT2i as an add-on therapy to insulin improved glycemic control and body weight and decreased the required dose of insulin without increasing the risk of hypoglycemia. However, after 6 months the benefits of SGLT2is on glycemic control may weaken and the risks of GTIs and DKA increased.

From Pinocytosis to Methuosis-Fluid Consumption as a Risk Factor for Cell Death

The volumes of a cell [cell volume (CV)] and its organelles are adjusted by osmoregulatory processes. During pinocytosis, extracellular fluid volume equivalent to its CV is incorporated within an hour and membrane area equivalent to the cell's surface within 30 min. Since neither fluid uptake nor membrane consumption leads to swelling or shrinkage, cells must be equipped with potent volume regulatory mechanisms. Normally, cells respond to outwardly or inwardly directed osmotic gradients by a volume decrease and increase, respectively, i.e., they shrink or swell but then try to recover their CV. However, when a cell death (CD) pathway is triggered, CV persistently decreases in isotonic conditions in apoptosis and it increases in necrosis. One type of CD associated with cell swelling is due to a dysfunctional pinocytosis. Methuosis, a non-apoptotic CD phenotype, occurs when cells accumulate too much fluid by macropinocytosis. In contrast to functional pinocytosis, in methuosis, macropinosomes neither recycle nor fuse with lysosomes but with each other to form giant vacuoles, which finally cause rupture of the plasma membrane (PM). Understanding methuosis longs for the understanding of the ionic mechanisms of cell volume regulation (CVR) and vesicular volume regulation (VVR). In nascent macropinosomes, ion channels and transporters are derived from the PM. Along trafficking from the PM to the perinuclear area, the equipment of channels and transporters of the vesicle membrane changes by retrieval, addition, and recycling from and back to the PM, causing profound changes in vesicular ion concentrations, acidification, and-most importantly-shrinkage of the macropinosome, which is indispensable for its proper targeting and cargo processing. In this review, we discuss ion and water transport mechanisms with respect to CVR and VVR and with special emphasis on pinocytosis and methuosis. We describe various aspects of the complex mutual interplay between extracellular and intracellular ions and ion gradients, the PM and vesicular membrane, phosphoinositides, monomeric G proteins and their targets, as well as the submembranous cytoskeleton. Our aim is to highlight important cellular mechanisms, components, and processes that may lead to methuotic CD upon their derangement.

Sweet Taste Is Complex: Signaling Cascades and Circuits Involved in Sweet Sensation

Sweetness is the preferred taste of humans and many animals, likely because sugars are a primary source of energy. In many mammals, sweet compounds are sensed in the tongue by the gustatory organ, the taste buds. Here, a group of taste bud cells expresses a canonical sweet taste receptor, whose activation induces Ca²⁺ rise, cell depolarization and ATP release to communicate with afferent gustatory nerves. The discovery of the sweet taste receptor, 20 years ago, was a milestone in the understanding of sweet signal transduction and is described here from a historical perspective. Our review briefly summarizes the major findings of the canonical sweet taste pathway, and then focuses on molecular details, about the related downstream signaling, that are still elusive or have been neglected. In this context, we discuss evidence supporting the existence of an alternative pathway, independent of the sweet taste receptor, to sense sugars and its proposed role in glucose homeostasis. Further, given that sweet taste receptor expression has been reported in many other organs, the physiological role of these extraoral receptors is addressed. Finally, and along these lines, we expand on the multiple direct and indirect effects of sugars on the brain. In summary, the review tries to stimulate a comprehensive understanding of how sweet compounds signal to the brain upon taste bud cells activation, and how this gustatory process is integrated with gastro-intestinal sugar sensing to create a hedonic and metabolic representation of sugars, which finally drives our behavior. Understanding of this is indeed a crucial step in developing new strategies to prevent obesity and associated diseases.

High Carbohydrate Diet Increased Glucose Transporter Protein Levels in Jejunum but Did Not Lead to Enhanced Post-Exercise Skeletal Muscle Glycogen Recovery

We examined the effect of dietary carbohydrate intake on post-exercise glycogen recovery. Male Institute of Cancer Research (ICR) mice were fed moderate-carbohydrate chow (MCHO, 50%cal from carbohydrate) or high-carbohydrate chow (HCHO, 70%cal from carbohydrate) for 10 days. They then ran on a treadmill at 25 m/min for 60 min and administered an oral glucose solution (1.5 mg/g body weight). Compared to the MCHO group, the HCHO group showed significantly higher sodium-D-glucose co-transporter 1 protein levels in the brush border membrane fraction (p = 0.003) and the glucose transporter 2 level in the mucosa of jejunum (p = 0.004). At 30 min after the post-exercise glucose administration, the skeletal muscle and liver glycogen levels were not significantly different between the two diet groups. The blood glucose concentration from the portal vein (which is the entry site of nutrients from the gastrointestinal tract) was not significantly different between the groups at 15 min after the post-exercise glucose administration. There was no difference in the total or phosphorylated states of proteins related to glucose uptake and glycogen synthesis in skeletal muscle. Although the high-carbohydrate diet significantly increased glucose transporters in the jejunum, this adaptation stimulated neither glycogen recovery nor glucose absorption after the ingestion of post-exercise glucose.

Current Understanding of the Intestinal Absorption of Nucleobases and Analogs

It has long been suggested that a Na⁺-dependent carrier-mediated transport system is involved in the absorption of nucleobases and analogs, including some drugs currently in therapeutic use, for their uptake at the brush border membrane of epithelial cells in the small intestine, mainly based on studies in non-primate experimental animals. The presence of this transport system was indeed proved by the recent identification of sodium-dependent nucleobase transporter 1 (SNBT1/Slc23a4) as its molecular entity in rats. However, this transporter has been found to be genetically deficient in humans and higher primates. Aware of this deficiency, we need to revisit the issue of the absorption of these compounds in the human small intestine so that we can understand the mechanisms and gain information to assure the more rational use and development of drugs analogous to nucleobases. Here, we review the current understanding of the intestinal absorption of nucleobases and analogs. This includes recent knowledge about the efflux transport of those compounds across the basolateral membrane when exiting epithelial cells, following brush border uptake, in order to complete the overall absorption process; the facilitative transporters of equilibrative nucleoside transporter 1 (ENT1/SLC29A1) and equilibrative nucleobase transporter 1 (ENBT1/SLC43A3) may be involved in that in many animal species, including human and rat, without any major species differences.

Sodium-Glucose Co-transporter-2 Inhibitors and Nephroprotection in Diabetic Patients: More Than a Challenge

Diabetic nephropathy is the most common cause of end-stage renal disease worldwide. Control of blood glucose and blood pressure (BP) reduces the risk of developing this complication, but once diabetic nephropathy is established, it is then only possible to slow its progression. Sodium-glucose cotransporter-2 inhibitors (SGLT2is) are a novel class of oral hypoglycemic agents that increase urinary glucose excretion by suppressing glucose reabsorption at the renal proximal tubule. SGLT2is lower glycated hemoglobin (HbA1c) without increasing the risk of hypoglycemia, induce weight loss and improve various metabolic parameters including BP, lipid profile, albuminuria and uric acid. Several clinical trials have shown that SGLT2is (empagliflozin, dapagliflozin canagliflozin, and ertugliflozin) improve cardiovascular and renal outcomes and mortality in patients with type 2 diabetes. Effects of SGLT2is on the kidney can be explained by multiple pathways. SGLT2is may improve renal oxygenation and intra-renal inflammation thereby slowing the progression of kidney function decline. Additionally, SGLT2is are associated with a reduction in glomerular hyperfiltration, an effect which is mediated by the increase in natriuresis, the re-activation of tubule-glomerular feedback and independent of glycemic control. In this review, we will focus on renal results of major cardiovascular and renal outcome trials and we will describe direct and indirect mechanisms through which SGLT2is confer renal protection.

SGLT-2 inhibitors: A step forward in the treatment of heart failure with reduced ejection fraction

Heart failure (HF) is a major health problem with a significant impact on morbidity, mortality, quality of life and healthcare costs. Despite the positive impact of disease-modifying therapies developed over the last four decades, HF mortality and hospitalization remain high. We aim at reviewing the evidence supporting the use of sodium-glucose co-transporter-2 (SGLT-2) inhibitors, as a novel strategy for HF with reduced ejection fraction (HFrEF) treatment. The consistent observation of a reduction in HF hospitalizations in type-2 diabetes cardiovascular safety trials EMPA-REG OUTCOME, CANVAS, DECLARE-TIMI 58 and VERTIS raised the hypothesis that SGLT-2 inhibitors could have an impact in HF treatment. This hypothesis was first confirmed in 2019 with the DAPA-HF publication showing that dapagliflozin on top of optimized HFrEF therapy, reduced HF-hospitalizations and cardiovascular mortality. This was reinforced by the EMPEROR-Reduced publication in 2020 showing that empagliflozin on top of optimized HFrEF therapy, reduced HF-hospitalizations. Both studies established SGLT-2 inhibitors as a fourth pillar of HFrEF prognosis-modifying therapy, in addition to the gold standard triple neurohormonal modulation/blockade.

Changes in the transcriptional activity of the entero-insular axis genes in streptozotocin-induced diabetes and after the administration of TNF-α non-selective blockers

OBJECTIVE

The aim of the present study was to investigate the transcriptional activity of the GLP-1R, DPP-4, SGLT-1, INSR, and IGF-1R genes in GALT cells of rats with streptozotocin-induced diabetes in both untreated and treated with pentoxifylline, as a non-specific blocker of TNF-α.

METHODS

The expression of GLP-1R, DPP-4, SGLT-1, INSR, and IGF-1R genes in GALT cells of rats was studied by real time quantitative polymerase chain reaction.

RESULTS

It was shown that the development of diabetes was accompanied by the decrease of GLP-1R and an increase of DPP-4 genes expression in rat ileum. The administration of pentoxifyl-line to diabetic animals led to an increase in the transcriptional activity of GLP-1R on the 4th week and decrease in transcriptional activity of DPP-4 on the 2nd and 4th weeks of the experiment. An increase in the normalized expression of SGLT-1 on the 4th week of the experimental diabetes was also noted, while the administration of pentoxifylline to diabetic animals did not lead to significant changes in this index. The transcriptional activity of the INSR and IGF-1R genes was reduced in diabetic rats and the administration of the non-specific TNF-α blocker - pentoxifylline led to a significant increase only for INSR gene in animals on the 4th week of the experimental diabetes.

CONCLUSIONS

The expression of incretins, glucose transporters, and pro-inflammatory cytokines (e.g. TNF-α) in immune cells may be used as markers of several autoimmune pathologies progression such as type 1 diabetes due to their effect on the balance of pro- and anti-inflammatory factors.

Medical treatment of heart failure with reduced ejection fraction: the dawn of a new era of personalized treatment?

Recent trials have shown the efficacy of new drugs for the medical therapy of heart failure and reduced ejection fraction (HFrEF). Sodium-glucose cotransporter 2 inhibitors (SGLT2i) reduced hospitalizations for HF, HF events, and cardiovascular death in patients with HFrEF or hospitalized for HF. Iron repletion with ferric carboxymaltose (FCM) improved symptoms, functional capacity, and quality of life in chronic HFrEF patients, and decreased the risk of subsequent HF hospitalizations in subjects with acutely decompensated HF. New-generation potassium binders may allow initiation and up-titration of renin-angiotensin-aldosterone system inhibitors (RASi). Lastly, the guanylate cyclase stimulator vericiguat and the myosin activator omecamtiv mecarbil reduced the primary endpoint in two major controlled trials. These results open novel pathways for the treatment of HFrEF. This review discusses new opportunities of an individualized approach to HFrEF pharmacotherapy, where new compounds expand a spectrum of drugs that target primarily neuroendocrine activation. SGLT2i can be safely applied once daily at a fixed dose to the vast majority of patients with HFrEF, including those with moderate renal dysfunction and/or systolic blood pressure as low as 95-100 mmHg. Additional medications are suitable for more specific phenotypes, with ivabradine providing benefit in patients with sinus rhythm and heart rates ≥70 beats per minute, FCM in the presence of iron deficiency, and potassium-lowering agents to implement RASi when hyperkalaemia occurs. Vericiguat and omecamtiv mecarbil also have potential for tailored approaches towards the hemodynamic status. Thus, a new era is starting for a more personalized medical treatment of HFrEF.

Influence of Luseogliflozin on Vaginal Bacterial and Fungal Populations in Japanese Patients With Type 2 Diabetes

Background

Selective sodium-glucose cotransporter 2 inhibitors, known to lower the blood glucose levels by promoting the urinary glucose excretion, can predispose to genitourinary infections. This prospective study investigated the influence of selective sodium-glucose cotransporter 2 inhibitors luseogliflozin on the vaginal flora of the pre- and postmenopausal women with type 2 diabetes mellitus.

Methods

Twelve premenopausal and 24 postmenopausal female Japanese patients with type 2 diabetes mellitus took luseogliflozin 2.5 mg once daily for 6 months. The intravaginal fungal and bacterial populations, together with the body weight and serum parameters of diabetes mellitus and lipid metabolism were measured before and after the treatment.

Results

After luseogliflozin treatment, the body weight, body mass index and hemoglobin A1c decreased, and the serum levels of high-density lipoprotein cholesterol increased significantly. Luseogliflozin treatment revealed to increase vaginal colony concentrations of Enterococcus faecalis (P = 0.0077) and E. coli (P = 0.0201) in premenopausal patients, and Enterococcus faecalis (P = 0.0051) and Candida albicans (P = 0.0355) in postmenopausal patients. In both pre- and postmenopausal patients, colony concentrations of Staphylococcus spp. had decreased (P = 0.0261 and P = 0.0161).

Conclusions

Treatment with selective sodium-glucose cotransporter 2 inhibitors luseogliflozin was associated with changes of the vaginal flora. These findings provide basic data on the increased susceptibility to genital infections during luseogliflozin treatment.

Low-Dose Empagliflozin Improves Systolic Heart Function after Myocardial Infarction in Rats: Regulation of MMP9, NHE1, and SERCA2a

The effects of the selective sodium-glucose cotransporter 2 (SGLT2) inhibitor empagliflozin in low dose on cardiac function were investigated in normoglycemic rats. Cardiac parameters were measured by intracardiac catheterization 30 min after intravenous application of empagliflozin to healthy animals. Empagliflozin increased the ventricular systolic pressure, mean pressure, and the max dP/dt (p < 0.05). Similarly, treatment with empagliflozin (1 mg/kg, p.o.) for one week increased the cardiac output, stroke volume, and fractional shortening (p < 0.05). Myocardial infarction (MI) was induced by ligation of the left coronary artery. On day 7 post MI, empagliflozin (1 mg/kg, p.o.) improved the systolic heart function as shown by the global longitudinal strain (−21.0 ± 1.1% vs. −16.6 ± 0.7% in vehicle; p < 0.05). In peri-infarct tissues, empagliflozin decreased the protein expression of matrix metalloproteinase 9 (MMP9) and favorably regulated the cardiac transporters sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA2a) and sodium hydrogen exchanger 1 (NHE1). In H9c2 cardiac cells, empagliflozin decreased the MMP2,9 activity and prevented apoptosis. Empagliflozin did not alter the arterial stiffness, blood pressure, markers of fibrosis, and necroptosis. Altogether, short-term treatment with low-dose empagliflozin increased the cardiac contractility in normoglycemic rats and improved the systolic heart function in the early phase after MI. These effects are attributed to a down-regulation of MMP9 and NHE1, and an up-regulation of SERCA2a. This study is of clinical importance because it suggests that a low-dose treatment option with empagliflozin may improve cardiovascular outcomes post-MI. Down-regulation of MMPs could be relevant to many remodeling processes including cancer disease.

Sodium/glucose cotransporter 1-dependent metabolic alterations induce tamoxifen resistance in breast cancer by promoting macrophage M2 polarization

Endocrine therapy is the standard treatment for estrogen receptor (ER)-positive breast cancer, but tumors eventually develop resistance. However, endocrine therapy resistance mechanisms mediated through interactions between breast cancer cells and tumor-associated macrophages (TAMs) are still unclear. Here, we characterized sodium/glucose cotransporter 1 (SGLT1) overexpression drives the highly glycolytic phenotype of tamoxifen-resistant breast cancer cells where enhanced lactic acid secretion promotes M2-like TAM polarization via the hypoxia-inducible factor-1α/signal transducer and activator of transcription-3 pathway. In turn, M2-like TAMs activate breast cancer cells through EGFR/PI3K/Akt signaling, providing feedback to upregulate SGLT1 and promote tamoxifen resistance and accelerate tumor growth in vitro and in vivo. Higher expression of SGLT1 and CD163⁺ TAMs was associated with endocrine-resistant ER-positive breast cancers. Our study identifies a novel vicious cycle of metabolic reprogramming, M2-like TAM polarization, and endocrine therapy resistance, which involves SGLT1, proposing SGLT1 as a therapeutic target to overcome endocrine therapy resistance in breast cancer.

Dapagliflozin Alleviates Hepatic Steatosis by Restoring Autophagy via the AMPK-mTOR Pathway

As a newly approved oral hypoglycaemic agent, the sodium-glucose cotransporter 2 (SGLT2) inhibitor dapagliflozin, which is derived from the natural product phlorizin can effectively reduce blood glucose. Recent clinical studies have found that dapagliflozin alleviates non-alcoholic fatty liver disease (NAFLD), but the specific mechanism remains to be explored. This study aimed to investigate the underlying mechanism of dapagliflozin in alleviating hepatocyte steatosis in vitro and in vivo. We fed the spontaneous type 2 diabetes mellitus rats with high-fat diets and cultured human normal liver LO2 cells and human hepatocellular carcinoma HepG2 cells with palmitic acid (PA) to induce hepatocellular steatosis. Dapagliflozin attenuated hepatic lipid accumulation both in vitro and in vivo. In Zucker diabetic fatty (ZDF) rats, dapagliflozin reduced hepatic lipid accumulation via promoting phosphorylation of acetyl-CoA carboxylase 1 (ACC1), and upregulating lipid β-oxidation enzyme acyl-CoA oxidase 1 (ACOX1). Furthermore, dapagliflozin increased the expression of the autophagy-related markers LC3B and Beclin1, in parallel with a drop in p62 level. Similar effects were observed in PA-stimulated LO2 cells and HepG2 cells. Dapagliflozin treatment could also significantly activated AMPK and reduced the phosphorylation of mTOR in ZDF rats and PA-stimulated LO2 cells and HepG2 cells. We demonstrated that dapagliflozin ameliorates hepatic steatosis by decreasing lipogenic enzyme, while inducing fatty acid oxidation enzyme and autophagy, which could be associated with AMPK activation. Moreover, our results indicate that dapagliflozin induces autophagy via the AMPK-mTOR pathway. These findings reveal a novel clinical application and functional mechanism of dapagliflozin in the treatment of NAFLD.

"The pharmacological profile of SGLT2 inhibitors: Focus on mechanistic aspects and pharmacogenomics"

Diabetes, characterized by high glucose levels, has been listed to be one of the world's major causes of death. Around 1.6 million deaths are attributed to this disease each year. Persistent hyperglycemic conditions in diabetic patients affect various organs of the body leading to diabetic complications and worsen the disease condition. Current treatment strategies for diabetes include biguanides, sulfonylureas, alpha-glucosidase inhibitors, thiazolidinediones, insulin and its analogs, DPP-4(dipeptidyl peptidase-4) and GLP-1 (glucagon-like peptide) analogs. However, many side effects contributing to the devastation of the disease are associated with them. Sodium glucose co-transporter-2 (SGLT2) inhibition has been reported to be new insulin-independent approach to diabetes therapy. It blocks glucose uptake in the kidneys by inhibiting SGLT2 transporters, thereby promoting glycosuria. Dapagliflozin, empagliflozin and canagliflozin are the most widely used SGLT2 inhibitors. They are effective in controlling blood glucose and HbA1c levels with few side effects including hypoglycemia or weight gain which makes them preferable to other anti-diabetic drugs. However, treatment is found to be associated with inter-individual drug response to SGLT2 inhibitors and adverse drug reactions which are also affected by genetic variations. There have been very few pharmacogenetics trials of these drugs. This review discusses the various SGLT2 inhibitors, their pharmacokinetics, pharmacodynamics and genetic variation influencing the inter-individual drug response.

A guide to plasma membrane solute carrier proteins

This review aims to serve as an introduction to the solute carrier proteins (SLC) superfamily of transporter proteins and their roles in human cells. The SLC superfamily currently includes 458 transport proteins in 65 families that carry a wide variety of substances across cellular membranes. While members of this superfamily are found throughout cellular organelles, this review focuses on transporters expressed at the plasma membrane. At the cell surface, SLC proteins may be viewed as gatekeepers of the cellular milieu, dynamically responding to different metabolic states. With altered metabolism being one of the hallmarks of cancer, we also briefly review the roles that surface SLC proteins play in the development and progression of cancer through their influence on regulating metabolism and environmental conditions.

SGLT2-inhibitors; more than just glycosuria and diuresis

Heart failure (HF) continues to be a serious public health challenge despite significant advancements in therapeutics and is often complicated by multiple other comorbidities. Of particular concern is type 2 diabetes mellitus (T2DM) which not only amplifies the risk, but also limits the treatment options available to patients. The sodium-glucose linked cotransporter subtype 2 (SGLT2)-inhibitor class, which was initially developed as a treatment for T2DM, has shown great promise in reducing cardiovascular risk, particularly around HF outcomes - regardless of diabetes status.There are ongoing efforts to elucidate the true mechanism of action of this novel drug class. Its primary mechanism of inducing glycosuria and diuresis from receptor blockade in the renal nephron seems unlikely to be responsible for the rapid and striking benefits seen in clinical trials. Early mechanistic work around conventional therapeutic targets seem to be inconclusive. There are some emerging theories around its effect on myocardial energetics and calcium balance as well as on renal physiology. In this review, we discuss some of the cutting-edge hypotheses and concepts currently being explored around this drug class in an attempt better understand the molecular mechanics of this novel agent.

Implication of actin in the uptake of sucrose and valine in the tap root and leaf of sugar beet

Actin microfilaments (F-actin) are major components of the cytoskeleton essential for many cellular dynamic processes (vesicle trafficking, cytoplasmic streaming, organelle movements). The aim of this study was to examine whether cortical actin microfilaments might be implicated in the regulation of nutrient uptake in root and leaf cells of Beta vulgaris. Using antibodies raised against actin and the AtSUC1 sucrose transporter, immunochemical assays demonstrated that the expression of actin and a sucrose transporter showed different characteristics, when detected on plasma membrane vesicles (PMVs) purified from roots and from leaves. The in situ immunolabeling of actin and AtSUC1 sites in PMVs and tissues showed their close proximity to the plasma membrane. Using co-labeling in protoplasts, actin and sucrose transporters were localized along the internal border and in the outermost part of the plasma membrane, respectively. This respective membrane co-localization was confirmed on PMVs and in tissues using transmission electronic microscopy. The possible functional role of actin in sucrose uptake (and valine uptake, comparatively) by PMVs and tissues from roots and leaves was examined using the pharmacological inhibitors, cytochalasin B (CB), cytochalasin D (CD), and phalloidin (PH). CB and CD inhibited the sucrose and valine uptake by root tissues in a concentration-dependent manner above 1 μM, whereas PH had no such effect. Comparatively, the toxins inhibited the sucrose and valine uptake in leaf discs to a lesser extent. The inhibition was not due to a hindering of the proton pumping and H⁺ -ATPase catalytic activity determined in PMVs incubated in presence of these toxins.

Pleiotropic Effects of Sodium-Glucose Cotransporter-2 Inhibitors: Renoprotective Mechanisms beyond Glycemic Control

Diabetes mellitus is a major cause of chronic kidney disease and end-stage renal disease. However, the management of chronic kidney disease, particularly diabetes, requires vast improvements. Recently, sodium-glucose cotransporter-2 (SGLT2) inhibitors, originally developed for the treatment of diabetes, have been shown to protect against kidney injury via glycemic control, as well as various other mechanisms, including blood pressure and hemodynamic regulation, protection from lipotoxicity, and uric acid control. As such, regulation of these mechanisms is recommended as an effective multidisciplinary approach for the treatment of diabetic patients with kidney disease. Thus, SGLT2 inhibitors are expected to become key drugs for treating diabetic kidney disease. This review summarizes the recent clinical evidence pertaining to SGLT2 inhibitors as well as the mechanisms underlying their renoprotective effects. Hence, the information contained herein will advance the current understanding regarding the pleiotropic effects of SGLT2 inhibitors, while promoting future research in the field.

A novel mouse model of heatstroke accounting for ambient temperature and relative humidity

Background

Heatstroke is associated with exposure to high ambient temperature (AT) and relative humidity (RH), and an increased risk of organ damage or death. Previously proposed animal models of heatstroke disregard the impact of RH. Therefore, we aimed to establish and validate an animal model of heatstroke considering RH. To validate our model, we also examined the effect of hydration and investigated gene expression of cotransporter proteins in the intestinal membranes after heat exposure.

Methods

Mildly dehydrated adult male C57/BL6J mice were subjected to three AT conditions (37 °C, 41 °C, or 43 °C) at RH > 99% and monitored with WetBulb globe temperature (WBGT) for 1 h. The survival rate, body weight, core body temperature, blood parameters, and histologically confirmed tissue damage were evaluated to establish a mouse heatstroke model. Then, the mice received no treatment, water, or oral rehydration solution (ORS) before and after heat exposure; subsequent organ damage was compared using our model. Thereafter, we investigated cotransporter protein gene expressions in the intestinal membranes of mice that received no treatment, water, or ORS.

Results

The survival rates of mice exposed to ATs of 37 °C, 41 °C, and 43 °C were 100%, 83.3%, and 0%, respectively. From this result, we excluded AT43. Mice in the AT 41 °C group appeared to be more dehydrated than those in the AT 37 °C group. WBGT in the AT 41 °C group was > 44 °C; core body temperature in this group reached 41.3 ± 0.08 °C during heat exposure and decreased to 34.0 ± 0.18 °C, returning to baseline after 8 h which showed a biphasic thermal dysregulation response. The AT 41 °C group presented with greater hepatic, renal, and musculoskeletal damage than did the other groups. The impact of ORS on recovery was greater than that of water or no treatment. The administration of ORS with heat exposure increased cotransporter gene expression in the intestines and reduced heatstroke-related damage.

Conclusions

We developed a novel mouse heatstroke model that considered AT and RH. We found that ORS administration improved inadequate circulation and reduced tissue injury by increasing cotransporter gene expression in the intestines.

The dawn of the four-drug era? SGLT2 inhibition in heart failure with reduced ejection fraction

Sodium-glucose cotransporter type 2 (SGLT2) inhibitors are a relatively new class of antihyperglycemic drug with salutary effects on glucose control, body weight, and blood pressure. Emerging evidence now indicates that these drugs may have a beneficial effect on outcomes in heart failure with reduced ejection fraction (HFrEF). Post-approval cardiovascular outcomes data for three of these agents (canagliflozin, empagliflozin, and dapagliflozin) showed an unexpected improvement in cardiovascular endpoints, including heart failure hospitalization and mortality, among patients with type 2 diabetes mellitus (T2DM) and established cardiovascular disease or risk factors. These studies were followed by a placebo controlled trial of dapagliflozin in patients with HFrEF both with and without T2DM, showing a reduction in all-cause mortality comparable to current guideline-directed HFrEF medical therapies such as angiotensin-converting enzyme inhibitors and beta-blockers. In this review, we discuss the current landscape of evidence, safety and adverse effects, and proposed mechanisms of action for use of these agents for patients with HFrEF. The United States (US) and European guidelines are reviewed, as are the current US federally approved indications for each SGLT2 inhibitor. Use of these agents in clinical practice may be limited by an uncertain insurance environment, especially in patients without T2DM. Finally, we discuss practical considerations for the cardiovascular clinician, including within-class differences of the SGLT2 inhibitors currently available on the US market (217/300).

Cardiovascular benefits of sodium-glucose cotransporter 2 inhibitors in diabetic and nondiabetic patients

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) were developed as antidiabetic agents, but accumulating evidence has shown their beneficial effects on the cardiovascular system. Analyses of the EMPA-REG OUTCOME trial (Empagliflozin Cardiovascular Outcome Event Trial in Type 2 Diabetes Mellitus Patients) suggested that these benefits are independent of glycemic control. Several large-scale outcome trials of SGLT2i also showed cardiovascular benefits in nondiabetic patients, strengthening this perspective. Extensive animal and clinical studies have likewise shown that mechanisms other than the antihyperglycemic effect underlie the cardiovascular benefits. Recent clinical guidelines recommend the use of SGLT2i in patients with type 2 diabetes mellitus and cardiovascular diseases because of the proven cardiovascular protective effects. Since the cardiovascular benefits are independent of glycemic control, the therapeutic spectrum of SGLT2i will likely be extended to nondiabetic patients.

Targeting Colorectal Cancer with Conjugates of a Glucose Transporter Inhibitor and 5-Fluorouracil

Overexpression of glucose transporters (GLUTs) in colorectal cancer cells is associated with 5-fluorouracil (1, 5-FU) resistance and poor clinical outcomes. We designed and synthesized a novel GLUT-targeting drug conjugate, triggered by glutathione in the tumor microenvironment, that releases 5-FU and GLUTs inhibitor (phlorizin (2) and phloretin (3)). Using an orthotopic colorectal cancer mice model, we showed that the conjugate exhibited better antitumor efficacy than 5-FU, with much lower exposure of 5-FU during treatment and without significant side effects. Our study establishes a GLUT-targeting theranostic incorporating a disulfide linker between the targeting module and cytotoxic payload as a potential antitumor therapy.

Central administration of sodium-glucose cotransporter-2 inhibitors increases food intake involving adenosine monophosphate-activated protein kinase phosphorylation in the lateral hypothalamus in healthy rats

INTRODUCTION

Sodium glucose cotransporter-2 (SGLT2) inhibitors are widely used for diabetes treatment. Although SGLT2 inhibitors have been clinically observed to increase food intake, roles or even the presence of SGLT2 in the central nervous system (CNS) has not been established. We aimed to elucidate potential functions of SGLT2 in the CNS, and the effects of CNS-targeted SGLT2 inhibitors on food intake.

RESEARCH DESIGN AND METHODS

We administered three kinds of SGLT2 inhibitors, tofogliflozin, dapagliflozin, and empagliflozin, into the lateral ventricle (LV) in rats and evaluated their effects on food intake. We also evaluated the effects of tofogliflozin administration in the third (3V) and fourth ventricle (4V). Intraperitoneal administration of liraglutide, a glucagon-like peptide-1 (GLP-1) receptor agonist known to suppress food intake, was combined with central tofogliflozin to elucidate whether GLP-1 signaling antagonizes the effect of central SGLT2 inhibitors on food intake. To elucidate potential molecular mechanisms mediating changes in feeding, hypothalamic areas associated with food intake regulation were harvested and analyzed after intracerebroventricular administration (ICV) of tofogliflozin.

RESULTS

Bolus ICV injection of tofogliflozin induced a robust increase in food intake starting at 1.5 hours postinjection, and lasting for 5 days. No effect was observed when the same dose of tofogliflozin was administered intraperitoneally. ICV dapagliflozin and empagliflozin significantly enhanced food intake, although the strength of these effects varied among drugs. Food intake was most markedly enhanced when tofogliflozin was infused into the LV. Fewer or no effects were observed with infusion into the 3V or 4V, respectively. Systemic administration of liraglutide suppressed the effect of ICV tofogliflozin on food intake. ICV tofogliflozin increased phosphorylation of AMPK and c-fos expression in the lateral hypothalamus.

CONCLUSIONS

SGLT2 inhibitors in the CNS increase food intake. SGLT2 activity in the CNS may regulate food intake through AMPK phosphorylation in the lateral hypothalamic area.

Function Trumps Form in Two Sugar Symporters, LacY and vSGLT

Active transport of sugars into bacteria occurs through symporters driven by ion gradients. LacY is the most well-studied proton sugar symporter, whereas vSGLT is the most characterized sodium sugar symporter. These are members of the major facilitator (MFS) and the amino acid-Polyamine organocation (APS) transporter superfamilies. While there is no structural homology between these transporters, they operate by a similar mechanism. They are nano-machines driven by their respective ion electrochemical potential gradients across the membrane. LacY has 12 transmembrane helices (TMs) organized in two 6-TM bundles, each containing two 3-helix TM repeats. vSGLT has a core structure of 10 TM helices organized in two inverted repeats (TM 1–5 and TM 6–10). In each case, a single sugar is bound in a central cavity and sugar selectivity is determined by hydrogen- and hydrophobic- bonding with side chains in the binding site. In vSGLT, the sodium-binding site is formed through coordination with carbonyl- and hydroxyl-oxygens from neighboring side chains, whereas in LacY the proton (H₃O⁺) site is thought to be a single glutamate residue (Glu325). The remaining challenge for both transporters is to determine how ion electrochemical potential gradients drive uphill sugar transport.

Angiotensin II-induced upregulation of SGLT1 and 2 contributes to human microparticle-stimulated endothelial senescence and dysfunction: protective effect of gliflozins

BACKGROUND

Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduced cardiovascular risk in type 2 diabetes patients independently of glycemic control. Although angiotensin II (Ang II) and blood-derived microparticles are major mediators of cardiovascular disease, their impact on SGLT1 and 2 expression and function in endothelial cells (ECs) and isolated arteries remains unclear.

METHODS

ECs were isolated from porcine coronary arteries, and arterial segments from rats. The protein expression level was assessed by Western blot analysis and immunofluorescence staining, mRNA levels by RT-PCR, oxidative stress using dihydroethidium, nitric oxide using DAF-FM diacetate, senescence by senescence-associated beta-galactosidase activity, and platelet aggregation by aggregometer. Microparticles were collected from blood of patients with coronary artery disease (CAD-MPs).

RESULTS

Ang II up-regulated SGLT1 and 2 protein levels in ECs, and caused a sustained extracellular glucose- and Na+-dependent pro-oxidant response that was inhibited by the NADPH oxidase inhibitor VAS-2780, the AT1R antagonist losartan, sotagliflozin (Sota, SGLT1 and SGLT2 inhibitor), and empagliflozin (Empa, SGLT2 inhibitor). Ang II increased senescence-associated beta-galactosidase activity and markers, VCAM-1, MCP-1, tissue factor, ACE, and AT1R, and down-regulated eNOS and NO formation, which were inhibited by Sota and Empa. Increased SGLT1 and SGLT2 protein levels were observed in the rat aortic arch, and Ang II- and eNOS inhibitor-treated thoracic aorta segments, and were associated with enhanced levels of oxidative stress and prevented by VAS-2780, losartan, Sota and Empa. CAD-MPs promoted increased levels of SGLT1, SGLT2 and VCAM-1, and decreased eNOS and NO formation in ECs, which were inhibited by VAS-2780, losartan, Sota and Empa.

CONCLUSIONS

Ang II up-regulates SGLT1 and 2 protein expression in ECs and arterial segments to promote sustained oxidative stress, senescence and dysfunction. Such a sequence contributes to CAD-MPs-induced endothelial dysfunction. Since AT1R/NADPH oxidase/SGLT1 and 2 pathways promote endothelial dysfunction, inhibition of SGLT1 and/or 2 appears as an attractive strategy to enhance the protective endothelial function.

Discovery through Machine Learning and Preclinical Validation of Novel Anti-Diabetic Peptides

While there have been significant advances in drug discovery for diabetes mellitus over the past couple of decades, there is an opportunity and need for improved therapies. While type 2 diabetic patients better manage their illness, many of the therapeutics in this area are peptide hormones with lengthy sequences and a molecular structure that makes them challenging and expensive to produce. Using machine learning, we present novel anti-diabetic peptides which are less than 16 amino acids in length, distinct from human signalling peptides. We validate the capacity of these peptides to stimulate glucose uptake and Glucose transporter type 4 (GLUT4) translocation in vitro. In obese insulin-resistant mice, predicted peptides significantly lower plasma glucose, reduce glycated haemoglobin and even improve hepatic steatosis when compared to treatments currently in use in a clinical setting. These unoptimised, linear peptides represent promising candidates for blood glucose regulation which require further evaluation. Further, this indicates that perhaps we have overlooked the class of natural short linear peptides, which usually come with an excellent safety profile, as therapeutic modalities.

Personalized Profiling Reveals Donor- and Lactation-Specific Trends in the Human Milk Proteome and Peptidome

BACKGROUND

Human milk is the most genuine form of personalized nutrition, whereby its nutritional and bioactive constituents support the changing needs of the growing infant. Personalized proteome profiling strategies may provide insights into maternal-infant relationships. Proteins and endogenous peptides in human milk play an important role as nutrients for growth and have distinct functionality such as immune defense. Comprehensive monitoring of all of the human milk proteinaceous components, including endogenous peptides, is required to fully understand the changing role of the human milk proteome throughout lactation.

OBJECTIVE

We aimed to investigate the personalized nature of the human milk proteome and peptidome for individual mother-infant dyads.

METHODS

Two individual healthy milk donors, aged 29 and 32 y and both of a normal BMI, were longitudinally observed over weeks 1, 2, 3, 4, 6, 8, 10, 12, and 16 postpartum. Milk collection was standardized. Comprehensive variations in the human milk proteinaceous components were assessed using quantitative LC-MS/MS methods.

RESULTS

We longitudinally profiled the concentrations of >1300 milk proteins and 2000 endogenous milk peptides spanning 16 wk of lactation for 2 individual donors. We observed many gradual and alike changes in both donors related to temporal effects, for instance early lactation was marked by high concentrations of proteins and peptides involved in lactose synthesis and immune development. Uniquely, in 1 of the 2 donors, we observed a substantial anomaly in the milk composition, exclusively at week 6, likely indicating a response to inflammation and/or infection.

CONCLUSIONS

Here, we provide a resource for characterizing the lactational changes in the human milk proteome, encompassing thousands of proteins and endogenous peptides. Further, we demonstrate the feasibility and benefit of personalized profiling to monitor the influence of milk on the development of the newborn, as well as the health status of each individual mother-infant pair.

Endothelial function and dysfunction: Impact of sodium-glucose cotransporter 2 inhibitors

Diabetes mellitus is associated with endothelial dysfunction that leads to cardiovascular complications. Sodium-glucose cotransporter 2 (SGLT2) inhibitors demonstrated efficacy in glycemic control in type 2 diabetes patients with positive cardiovascular outcome. Recent research revealed a link between SGLT2 inhibition and improved macro- and microvascular endothelial functions. Mechanisms underlying this phenomenon could be due to the role of SLGT2 in the regulation of endothelial physiology. In this review, current knowledge and hypothesis on the link between SGLT2 and endothelial function were critically appraised and the impact of SGLT2 inhibitors on endothelial dysfunction in pre-clinical and clinical studies was discussed.

Role of Modulation of Hippocampal Glucose Following Pilocarpine-Induced Status Epilepticus

Status epilepticus (SE) is defined as continuous and self-sustaining seizures, which trigger hippocampal neurodegeneration, mitochondrial dysfunction, oxidative stress, and energy failure. During SE, the neurons become overexcited, increasing energy consumption. Glucose uptake is increased via the sodium glucose cotransporter 1 (SGLT1) in the hippocampus under epileptic conditions. In addition, modulation of glucose can prevent neuronal damage caused by SE. Here, we evaluated the effect of increased glucose availability in behavior of limbic seizures, memory dysfunction, neurodegeneration process, neuronal activity, and SGLT1 expression. Vehicle (VEH, saline 0.9%, 1 μL) or glucose (GLU; 1, 2 or 3 mM, 1 μL) were administered into hippocampus of male Wistar rats (Rattus norvegicus) before or after pilocarpine to induce SE. Behavioral analysis of seizures was performed for 90 min during SE. The memory and learning processes were analyzed by the inhibitory avoidance test. After 24 h of SE, neurodegeneration process, neuronal activity, and SGLT1 expression were evaluated in hippocampal and extrahippocampal regions. Modulation of hippocampal glucose did not protect memory dysfunction followed by SE. Our results showed that the administration of glucose after pilocarpine reduced the severity of seizures, as well as the number of limbic seizures. Similarly, glucose after SE reduced cell death and neuronal activity in hippocampus, subiculum, thalamus, amygdala, and cortical areas. Finally, glucose infusion elevated the SGLT1 expression in hippocampus. Taken together our data suggest that possibly the administration of intrahippocampal glucose protects brain in the earlier stage of epileptogenic processes via an important support of SGLT1.

Sodium Transporters in Human Health and Disease

Sodium (Na+) electrochemical gradients established by Na+/K+ ATPase activity drives the transport of ions, minerals, and sugars in both excitable and non-excitable cells. Na+-dependent transporters can move these solutes in the same direction (cotransport) or in opposite directions (exchanger) across both the apical and basolateral plasma membranes of polarized epithelia. In addition to maintaining physiological homeostasis of these solutes, increases and decreases in sodium may also initiate, directly or indirectly, signaling cascades that regulate a variety of intracellular post-translational events. In this review, we will describe how the Na+/K+ ATPase maintains a Na+ gradient utilized by multiple sodium-dependent transport mechanisms to regulate glucose uptake, excitatory neurotransmitters, calcium signaling, acid-base balance, salt-wasting disorders, fluid volume, and magnesium transport. We will discuss how several Na+-dependent cotransporters and Na+-dependent exchangers have significant roles in human health and disease. Finally, we will discuss how each of these Na+-dependent transport mechanisms have either been shown or have the potential to use Na+ in a secondary role as a signaling molecule.

Cellular Fucosylation Inhibitors Based on Fluorinated Fucose-1-phosphates*

Fucosylation of glycans impacts a myriad of physiological and pathological processes. Inhibition of fucose expression emerges as a potential therapeutic avenue for example in cancer, inflammation, and infection. In this study, we found that protected 2-fluorofucose 1-phosphate efficiently inhibits cellular fucosylation with a four to seven times higher potency than known inhibitor 2FF, independently of the anomeric stereochemistry. Nucleotide sugar analysis revealed that both the α- and β-GDP-2FF anomers are formed inside the cell. In conclusion, we developed A2FF1P and B2FF1P as potent new tools for studying the role of fucosylation in health and disease and they are potential therapeutic candidates.

Are oral rehydration solutions optimized for treating diarrhea?

BACKGROUND

A historical turning point occurred in the treatment of diarrhea when it was discovered that glucose could enhance intestinal sodium and water absorption. Adding glucose to salt water (oral rehydration solution, ORS) more efficiently replaced intestinal water and salt losses.

AIM

Provide a novel hypothesis to explain why mainstream use of ORS has been strongly recommended, but weakly adopted.

METHODS

Traditional (absorptive) and novel (secretory) physiological functions of glucose in an ORS were reviewed.

RESULTS

Small amounts of glucose can stimulate both intestinal absorption and secretion. Glucose can exacerbate a net secretory state and may aggravate pathogen-induced diarrhea, particularly for pathogens that affect glucose transport.

CONCLUSION

A hypothesis is made to explain why glucose-based ORS does not appreciably reduce diarrheal stool volume and why modern food science initiatives should focus on ORS formulations that replace water and electrolytes while also reducing stool volume and duration of diarrhea.

Prokaryotic Solute/Sodium Symporters: Versatile Functions and Mechanisms of a Transporter Family

The solute/sodium symporter family (SSS family; TC 2.A.21; SLC5) consists of integral membrane proteins that use an existing sodium gradient to drive the uphill transport of various solutes, such as sugars, amino acids, vitamins, or ions across the membrane. This large family has representatives in all three kingdoms of life. The human sodium/iodide symporter (NIS) and the sodium/glucose transporter (SGLT1) are involved in diseases such as iodide transport defect or glucose-galactose malabsorption. Moreover, the bacterial sodium/proline symporter PutP and the sodium/sialic acid symporter SiaT play important roles in bacteria–host interactions. This review focuses on the physiological significance and structural and functional features of prokaryotic members of the SSS family. Special emphasis will be given to the roles and properties of proteins containing an SSS family domain fused to domains typically found in bacterial sensor kinases.

Mechanisms and Perspectives of Sodium-Glucose Co-transporter 2 Inhibitors in Heart Failure

Heart failure (HF) is a common complication or late-stage manifestation of various heart diseases. Numerous risk factors and underlying causes may contribute to the occurrence and progression of HF. The pathophysiological mechanisms of HF are very complicated. Despite accumulating advances in treatment for HF during recent decades, it remains an intractable clinical syndrome with poor outcomes, significantly reducing the quality of life and expectancy of patients, and imposing a heavy economic burden on society and families. Although initially classified as antidiabetic agents, sodium-glucose co-transporter 2 (SGLT2) inhibitors have demonstrated reduced the prevalence of hospitalization for HF, cardiovascular death, and all-cause death in several large-scale randomized controlled clinical trials. These beneficial effects of SGLT-2 inhibitors can be attributed to multiple hemodynamic, inflammatory and metabolic mechanisms, not only reducing the serum glucose level. SGLT2 inhibitors have been used increasingly in treatment for patients with HF with reduced ejection fraction due to their surprising performance in improving the prognosis. In addition, their roles and mechanisms in patients with HF with preserved ejection fraction or acute HF have also attracted attention. In this review article, we discuss the possible mechanisms and applications of SGLT2 inhibitors in HF.

Effect of sodium-glucose cotransporter-2 inhibitors on renal handling of electrolytes

Sodium-glucose cotransporter-2 inhibitors (SGLT2i) are the latest introduction into the armamentarium of diabetes care in the present decade. By virtue of their beneficial effects, such as blood pressure-lowering, bodyweight reduction and significant renal and cardioprotective effects which extends beyond their glycaemic control effects, SGLT2i have become one of the most preferred oral antihyperglycaemic agents of recent times. However, they can influence tubular handling of electrolytes that can result in some electrolyte disturbances such as alteration in the serum levels of magnesium, potassium and phosphate levels. Some of these changes are mild or transient and may not have significant clinical implications. The underlying putative mechanism(s) responsible for disturbances of electrolytes are yet to be deciphered. In this review, we aim to describe electrolytes and acid-base abnormalities due to SGLT2i as well as to elucidate the underlying mechanism.

Renoprotective effects of sodium-glucose cotransporter-2 inhibitors and underlying mechanisms

PURPOSE OF REVIEW

Emerging data have demonstrated that sodium-glucose cotransporter-2 (SGLT2) inhibitors prevent cardiovascular events, especially heart failure-associated endpoints. Cardiovascular outcome trials have also suggested their renoprotective effects. One large clinical trial investigated renal primary endpoints and demonstrated that SGLT2 inhibitors slowed the progression of diabetic kidney disease (DKD). This review summarizes clinical trial data on renal outcomes and discusses potential underlying mechanisms.

RECENT FINDINGS

The EMPA-REG, CANVAS, and DECLARE-TIMI 58 studies revealed that SGLT2 inhibitors reduce the risk of cardiovascular events and concomitantly suggested that these drugs slow the progression of kidney disease in type 2 diabetes. The CREDENCE trial on patients with high-risk type 2 diabetes and chronic kidney disease demonstrated that canagliflozin treatment reduced the relative risk of a composite outcome, including end-stage kidney disease, serum creatinine doubling, and renal/cardiovascular death, by 30% in these patients. Animal experiments revealed that oxidative stress, inflammation, fibrosis, and tubuloglomerular feedback are underlying renoprotective mechanisms behind SGLT2 inhibitors.

SUMMARY

Recent clinical trials have established the renoprotective effects of SGLT2 inhibitors. Further investigations on mechanisms of these renoprotective effects will provide deeper insights and understanding of pathogenetic properties of DKD.