Mizagliflozin, a novel selective SGLT1 inhibitor, exhibits potential in the amelioration of chronic constipation

SGLT1 contributes to glucose-mediated exacerbation of ischemia-reperfusion injury in ex vivo rat heart

Hyperglycaemia is common during acute coronary syndromes (ACS) irrespective of diabetic status and portends excess infarct size and mortality, but the mechanisms underlying this effect are poorly understood. We hypothesized that sodium/glucose linked transporter-1 (SGLT1) might contribute to the effect of high-glucose during ACS and examined this using an ex-vivo rodent heart model of ischaemia-reperfusion injury. Langendorff-perfused rat hearts were subjected to 35 min ischemia and 2 h reperfusion, with variable glucose and reciprocal mannitol given during reperfusion in the presence of pharmacological inhibitors of SGLT1. Myocardial SGLT1 expression was determined in rat by rtPCR, RNAscope and immunohistochemistry, as well as in human by single-cell transcriptomic analysis. High glucose in non-diabetic rat heart exacerbated reperfusion injury, significantly increasing infarct size from 45 ± 3 to 65 ± 4% at 11-22 mmol/L glucose, respectively (p < 0.01), an association absent in diabetic heart (32 ± 1-37 ± 5%, p = NS). Rat heart expressed SGLT1 RNA and protein in vascular endothelium and cardiomyocytes, with similar expression found in human myocardium by single-nucleus RNA-sequencing. Rat SGLT1 expression was significantly reduced in diabetic versus non-diabetic heart (0.608 ± 0.08 compared with 1.116 ± 0.13 probe/nuclei, p < 0.01). Pharmacological inhibitors phlorizin, canagliflozin or mizagliflozoin in non-diabetic heart revealed that blockade of SGLT1 but not SGLT2, abrogated glucose-mediated excess reperfusion injury. Elevated glucose is injurious to the rat heart during reperfusion, exacerbating myocardial infarction in non-diabetic heart, whereas the diabetic heart is resistant to raised glucose, a finding which may be explained by lower myocardial SGLT1 expression. SGLT1 is expressed in vascular endothelium and cardiomyocytes and inhibiting SGLT1 abrogates excess glucose-mediated infarction. These data highlight SGLT1 as a potential clinical translational target to improve morbidity/mortality outcomes in hyperglycemic ACS patients.

Examining linaclotide for the treatment of chronic idiopathic constipation

INTRODUCTION

Chronic idiopathic constipation (CIC) is characterized by infrequent bowel movements and hard stools lasting for at least three months or longer. This disease affects 8-12% of the US population and 10-17% of the world population. Treatment and management involve identifying the primary cause, changing dietary habits, and adequate physical activity. Linaclotide is a guanylate cyclase-agonist acting locally in the luminal surface of the intestinal enterocyte leading to a signal transduction cascade, activation of the cystic fibrosis transmembrane conductance regulator (CFTR), thus increasing secretion of chloride and bicarbonate into the intestinal lumen with eventual increased intestinal fluid and faster transit time.

AREAS COVERED

We reviewed multiple studies and did a thorough literature review on CIC including its pathophysiology. Through this literature review, we were able to discuss and give the context and rationale for drug regimens indicated for CIC.

EXPERT OPINION

The era we live in right now is akin to nutrient-rich and fertilized soil as knowledge and resources are abundant. The opportunities and potential are endless. Constipation being more extensively studied, our understanding of medications and diseases broadens, leading to novel medications being discovered. Linaclotide is a pioneer in this aspect and can pave the way for future generations.

Tongbian decoction restores intestinal microbiota and activates 5-hydroxytryptamine signaling: implication in slow transit constipation

Introduction

Slow transit constipation (STC) is a type of functional constipation. The detailed mechanism of STC, for which there is currently no effective treatment, is unknown as of yet. Tongbian decoction (TBD), a traditional Chinese medicinal formula, is commonly used to treat STC in clinical settings. However, the potential impact of TBD on the management of STC via modulation of the gut microbiota remains unclear.

Methods

Pseudo-germ-free rats were constructed after 6 days of treatment with bacitracin, neomycin, and streptomycin (abbreviated as ABX forthwith). Based on the successful construction of pseudo-germ-free rats, the STC model (ABX + STC) was induced using loperamide hydrochloride. After successful modeling, based on the different sources of donor rat microbiota, the ABX + STC rats were randomly divided into three groups: Control → ABX + STC, STC → ABX + STC, and STC + TBD → ABX + STC for fecal microbiota transplant (FMT). Body weight, fecal water content, and charcoal power propelling rate of the rats were recorded. Intestinal microbiota was detected by 16S rRNA sequencing, and the 5-hydroxytryptamine (5-HT) signaling pathway was examined by western blots, immunofluorescence, and immunohistochemical analysis.

Results

After treatment with fecal bacterial solutions derived from rats treated with Tongbian decoction (TBD), there was an increase in body weight, fecal water content, and the rate of charcoal propulsion in the rats. Additionally, activation of the 5-hydroxytryptamine (5-HT) signaling pathway was observed. The 16S rRNA sequencing results showed that the fecal bacterial solution from TBD-treated rats affected the intestinal microbiota of STC rats by increasing the proliferation of beneficial bacteria and suppressing the expansion of harmful bacteria.

Conclusion

Our study showed that TBD alleviated constipation in STC rats by modulating the structure of the intestinal microbiota.

A randomized double-blind phase Ib clinical trial of SY-009 in patients with type 2 diabetes mellitus

INTRODUCTION

SY-009 produces a hypoglycemic effect via inhibiting sodium/glucose cotransporter 1 (SGLT1) in type 2 diabetes mellitus (T2DM) patients. This randomized, double-blind, placebo-controlled, and multiple-dose escalation clinical trial aimed to evaluate the pharmacokinetic and pharmacodynamical characteristics as well as the safety and tolerability of SY-009 in T2DM patients.

METHOD

Fifty T2DM patients were randomized into experimental and placebo groups, and hospitalized for 9 days managed with a unified diet and rest management. Subjects were given SY-009 or placebo from day 1 to day 7 at different frequencies and dosages. Single dose cohort was defined as the first dose on day 1 and multiple dose cohort included all the dose from day 1 to 7. Blood samples were collected for pharmacokinetic analysis. Mixed meal tolerance tests were performed. Blood samples were collected to determine glucose, C-peptide, insulin, glucagon-like peptide-1 (GLP-1), and gastric inhibitory polypeptide (GIP).

RESULTS

PK parameters were not obtained because blood SY-009 concentrations were below the limit of quantitation in all subjects. SY-009 decreased the postprandial glucose. Blood glucose was controlled within 4 hours after taking the drug. Short-term administration of SY-009 (7 days) had no significant effects on fasting glucose but reduced the secretion of C-peptide, insulin, and GIP and increased GLP-1 secretion. The most common adverse event was gastrointestinal disorder manifesting abdominal pain, diarrhea, and bloating.

CONCLUSION

Plasma exposure of SY-009 and its metabolites was fairly low in T2DM patients at doses of 1.0-4.0 mg. SY-009 reduced postprandial glucose, C-peptide, and insulin levels, showing relative safety and tolerability in the dose range of 1.0-4.0 mg.

TRIALS REGISTRATION

ClinicalTrials.gov Identifier: NCT04345107.

SGLT-2 Inhibitors: The Next-generation Treatment for Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) has become a worldwide concern in recent years, primarily in highly developed Western societies. T2DM causes systemic complications, such as atherosclerotic heart disease, ischemic stroke, peripheral artery disease, kidney failure, and diabetes-related maculopathy and retinopathy. The growing number of T2DM patients and the treatment of long-term T2DM-related complications pressurize and exhaust public healthcare systems. As a result, strategies for combating T2DM and developing novel drugs are critical global public health requirements. Aside from preventive measures, which are still the most effective way to prevent T2DM, novel and highly effective therapies are emerging. In the spotlight of next-generation T2DM treatment, sodium-glucose co-transporter 2 (SGLT-2) inhibitors are promoted as the most efficient perspective therapy. SGLT-2 inhibitors (SGLT2i) include phlorizin derivatives, such as canagliflozin, dapagliflozin, empagliflozin, and ertugliflozin. SGLT-2, along with SGLT-1, is a member of the SGLT family of proteins that play a role in glucose absorption via active transport mediated by Na+/K+ ATPase. SGLT-2 is only found in the kidney, specifically the proximal tubule, and is responsible for more than 90% glucose absorption. Inhibition of SGLT-2 reduces glucose absorption, and consequently increases urinary glucose excretion, decreasing blood glucose levels. Thus, the inhibition of SGLT-2 activity ultimately alleviates T2DM-related symptoms and prevents or delays systemic T2DM-associated chronic complications. This review aimed to provide a more detailed understanding of the effects of SGLT2i responsible for the acute improvement in blood glucose regulation, a prerequisite for T2DM-associated cardiovascular complications control.

Comparison of SGLT1, SGLT2, and Dual Inhibitor biological activity in treating Type 2 Diabetes Mellitus

Diabetes Mellitus Type 2 (T2D) is an emerging health burden in the USand worldwide, impacting approximately 15% of Americans. Current front-line therapeutics for T2D patients include sulfonylureas that act to reduce A1C and/or fasting blood glucose levels, or Metformin that antagonizes the action of glucagon to reduce hepatic glucose production. Next generation glucomodulatory therapeutics target members of the high-affinity glucose transporter Sodium-Glucose-Linked-Transporter (SGLT) family. SGLT1 is primarily expressed in intestinal epithelium, whose inhibition reduces dietary glucose uptake, whilst SGLT2 is highly expressed in kidney - regulating glucose reabsorption. A number of SGLT2 inhibitors are FDA approved whilst SGLT1 and dual SGLT1 & 2 inhibitor are currently in clinical trials. Here, we discuss and compare SGLT2, SGLT1, and dual inhibitors' biochemical mechanism and physiological effects.

SGLT1 as an adverse prognostic factor in invasive ductal carcinoma of the breast

PURPOSE

Sodium/glucose cotransporter (SGLT) 1 and 2 expression in carcinoma cells was recently examined, but their association with the clinicopathological factors of the patients and their biological effects on breast carcinoma cells have remained remain virtually unknown. Therefore, in this study, we explored the expression status of SGLT1 and SGLT2 in breast cancer patients and examined the effects of SGLT1 inhibitors on breast carcinoma cells in vitro.

METHODS

SGLT1 and SGLT2 were immunolocalized and we first correlated the findings with clinicopathological factors of the patients. We then administered mizagliflozin and KGA-2727, SGLT1 specific inhibitors to MCF-7 and MDA-MB-468 breast carcinoma cell lines, and their growth-inhibitory effects were examined. Protein arrays were then used to further explore their effects on the growth factors.

RESULTS

The SGLT1 high group had significantly worse clinical outcome including both overall survival and disease-free survival than low group. SGLT2 status was not significantly correlated with clinical outcome of the patients. Both mizagliflozin and KGA-2727 inhibited the growth of breast cancer cell lines. Of particular interest, mizagliflozin inhibited the proliferation of MCF-7 cells, even under very low glucose conditions. Mizagliflozin downregulated vascular endothelial growth factor receptor 2 phosphorylation.

CONCLUSION

High SGLT1 expression turned out as an adverse clinical prognostic factor in breast cancer patient. This is the first study demonstrating that SGLT1 inhibitors suppressed breast carcinoma cell proliferation. These results indicated that SGLT1 inhibitors could be used as therapeutic agents for breast cancer patients with aggressive biological behaviors.

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.

A novel purgative mechanism of multiflorin A involves changing intestinal glucose absorption and permeability

BACKGROUND

Multiflorin A (MA) is a potential active ingredient of traditional herbal laxative, Pruni semen, with unusual purgative activity and an unclear mechanism, and inhibiting intestinal glucose absorption is a promising mechanism of novel laxatives. However, this mechanism still lacks support and a description of basic research.

PURPOSE

This study aimed to determine the main contribution of MA to the purgative activity of Pruni semen and elucidate the effect intensity, characteristics, site, and mechanism of MA in mice, and determine the novel mechanism of traditional herbal laxatives from the perspective of intestinal glucose absorption.

METHODS

We induced diarrhoea in mice by administering Pruni semen and MA, and the defecation behaviour, glucose tolerance, and intestinal metabolism were analysed. The effects of MA and its metabolite on peristalsis of the intestinal smooth muscle were evaluated using an intestinal motility assay in vitro. Intestinal tight junction proteins, aquaporins, and glucose transporters expression were analysed using immunofluorescence; gut microbiota and faecal metabolites were analysed using 16S rRNA and liquid chromatography-mass spectrometry.

RESULTS

MA administration (20 mg/kg) induced watery diarrhoea in over half of the experimental mice. The activity of MA in lowering peak postprandial glucose levels was synchronous with purgative action, with the acetyl group being the active moiety. MA was metabolised primarily in the small intestine, where it decreased sodium-glucose cotransporter-1, occludin, and claudin1 expression, then inhibited glucose absorption, resulting in a hyperosmotic environment. MA also increased the aquaporin3 expression to promote water secretion. Unabsorbed glucose reshapes the gut microbiota and their metabolism in the large intestine and the increasing gas and organic acid promoted defecation. After recovery, the intestinal permeability and glucose absorption function returned, and the abundance of probiotics such as Bifidobacterium increased.

CONCLUSION

The purgative mechanism of MA involves inhibiting glucose absorption, altering permeability and water channels to promote water secretion in the small intestine, and regulating gut microbiota metabolism in the large intestine. This study is the first systematic experimental study on the purgative effect of MA. Our findings provide new insight into the study of novel purgative mechanisms.

Structures of human SGLT in the occluded state reveal conformational changes during sugar transport

Sodium-Glucose Cotransporters (SGLT) mediate the uphill uptake of extracellular sugars and play fundamental roles in sugar metabolism. Although their structures in inward-open and outward-open conformations are emerging from structural studies, the trajectory of how SGLTs transit from the outward-facing to the inward-facing conformation remains unknown. Here, we present the cryo-EM structures of human SGLT1 and SGLT2 in the substrate-bound state. Both structures show an occluded conformation, with not only the extracellular gate but also the intracellular gate tightly sealed. The sugar substrate are caged inside a cavity surrounded by TM1, TM2, TM3, TM6, TM7, and TM10. Further structural analysis reveals the conformational changes associated with the binding and release of substrates. These structures fill a gap in our understanding of the structural mechanisms of SGLT transporters.

Structural mechanism of SGLT1 inhibitors

Sodium glucose co-transporters (SGLT) harness the electrochemical gradient of sodium to drive the uphill transport of glucose across the plasma membrane. Human SGLT1 (hSGLT1) plays a key role in sugar uptake from food and its inhibitors show promise in the treatment of several diseases. However, the inhibition mechanism for hSGLT1 remains elusive. Here, we present the cryo-EM structure of the hSGLT1-MAP17 hetero-dimeric complex in the presence of the high-affinity inhibitor LX2761. LX2761 locks the transporter in an outward-open conformation by wedging inside the substrate-binding site and the extracellular vestibule of hSGLT1. LX2761 blocks the putative water permeation pathway of hSGLT1. The structure also uncovers the conformational changes of hSGLT1 during transitions from outward-open to inward-open states.

Effects of Maren Pills on the Intestinal Microflora and Short-Chain Fatty Acid Profile in Drug-Induced Slow Transit Constipation Model Rats

Background: Slow transit constipation (STC) is becoming a common and frequently occurring disease in today’s society, and it is necessary to explore the safe and effective treatment of STC.

Method: Our study aimed to investigate whether the laxative effect of Maren pills (MRW) is associated with the regulation of intestinal microflora and intestinal metabolism in the colon. Loperamide hydrochloride-induced STC rats received MRW intragastrically for two consecutive weeks to evaluate the laxative effect of MRW involving the regulation of intestinal microflora, intestinal metabolism, and 5-HT signaling pathway. Intestinal microflora was detected by 16s rDNA sequencing, intestinal metabolism of short-chain fatty acids (SCFAs) was detected by HPLC, and the 5-HT signaling pathway was detected by WB, ELISA, immunofluorescence, and immunohistochemical analysis.

Results: Our results revealed that the treatments with MRW increased not only the body weight, 24-h fecal number, 24-h wet fecal weight, 24-h dry fecal weight, fecal water content, and the intestinal propulsion rate but also the colonic goblet cell number, colonic Muc-2 protein expression, and colonic mucus layer thickness in the STC model rats. Moreover, MRW activated the 5-HT pathway by increasing the levels of 5-HT, 5-HIAA, 5-HT4R, CFTR, cAMP, and PKA in the colon tissue of STC rats. The 16S rDNA sequencing results showed that MRW improved the colonic microflora structure in colonic contents of STC rats, mainly by increasing Lactobacillus and decreasing Prevotella. Finally, we found that MRW regulated the SCFA metabolism in the colonic contents of the STC rats, mainly by increasing the contents of acetic acid, propionic acid, and butyric acid; the relative abundance of Lactobacillus was positively correlated with either contents of acetic acid, propionic acid, and butyric acid, and the relative abundance of Clostridium was negatively correlated.

Conclusion: Our study further showed that MRW could improve constipation in STC rats, and the mechanism may be by regulating the intestinal microflora structure and improving the metabolism of SCFAs.

Emerging therapies in the management of Irritable Bowel Syndrome (IBS)

INTRODUCTION

Irritable bowel syndrome (IBS) is a common, symptom-based disorder of chronic abdominal pain and altered bowel habits. The pathogenesis of IBS is multifactorial, leading to the potential for the development of multiple, diverse treatment strategies. This mechanistic heterogeneity also leads to the realization that available therapies are only effective in a subset of IBS suffers. Current US Food and Drug Administration (FDA) approved therapies for IBS with diarrhea (IBS-D) and IBS with constipation (IBS-C) are reviewed. Limited symptom responses and side effect experiences lead to considerable patient dissatisfaction with currently available IBS treatments. Only a small percentage of IBS patients are on prescription therapies underscoring the potential market and need for additional therapeutic options.

AREAS COVERED

: Expanding on currently available therapies, the serotonergic and endogenous opioid receptor systems continue to be a focus of future IBS treatment development. Additional novel emerging therapies include the endogenous cannabinoid system, bile acid secretion and sequestration, and exploit our enhanced understanding of visceral sensory signaling and intestinal secretomotor function.

EXPERT OPINION

While challenges remain for the future development of IBS therapies, the diverse etiologies underlying the disorder present an opportunity for novel therapies. Hence, great potential is anticipated for future IBS treatment options.

Small bowel water content assessed by MRI in health and disease: a collation of single-centre studies

BACKGROUND

New developments in MRI have allowed the non-invasive, accurate measurement of the small bowel water content (SBWC).

AIMS

To collate studies measuring SBWC following ingestion of a range of foods in both health and disease to provide data for adequately powering future studies in this area.

METHODS

This collation brings together 29 studies including 954 participants (530 healthy, 54 diverticulosis, 255 IBS, 53 functional constipation, 12 cystic fibrosis, 15 Crohn's disease, 20 coeliac disease, 15 scleroderma) which have been carried out in a single centre using comparable study designs.

RESULTS

Fasting SBWC (mean 82 [SD 65] mL) shows high variability with a small decline with advancing age (healthy volunteers only; individual patient data). Fasting values are increased in untreated coeliac disease (202 [290] mL, P = 0.004). Post-prandial SBWC shows less intra-individual variability than fasting values in healthy volunteers. SBWC is increased by eating, most markedly by high fat meals but also by fibre, both viscous and particulate. Indigestible residue accumulates in late post-prandial period but empties soon after ingestion of a high calorie meal which produces a significant drop (by 50 [52] mL) in healthy volunteers. The associated fall in SBWC is abnormal in people with cystic fibrosis (SBWC reduced by 10 [121] mL, P = 0.002) and in people with irritable bowel syndrome with diarrhoea (SBWC reduced by 17 [43] mL, P = 0.007).

CONCLUSIONS

SBWC as assessed by MRI is a valuable biomarker indicating the balance of secretion and absorption in health and disease and the impact of treatments.

Mizagliflozin, a selective SGLT1 inhibitor, improves vascular cognitive impairment in a mouse model of small vessel disease

Previously, we showed that sodium/glucose cotransporter 1 (SGLT1) participates in vascular cognitive impairment in small vessel disease. We hypothesized that SGLT1 inhibitors can improve the small vessel disease induced-vascular cognitive impairment. We examined the effects of mizagliflozin, a selective SGLT1 inhibitor, and phlorizin, a non-selective SGLT inhibitor, on vascular cognitive impairment in a mouse model of small vessel disease. Small vessel disease was created using a mouse model of asymmetric common carotid artery surgery (ACAS). Two and/or 4 weeks after ACAS, all experiments were performed. Cerebral blood flow (CBF) was decreased in ACAS compared with sham-operated mice. Phlorizin but not mizagliflozin reversed the decreased CBF of ACAS mice. Both mizagliflozin and phlorizin reversed the ACAS-induced decrease in the latency to fall in a wire hang test of ACAS mice. Moreover, they reversed the ACAS-induced longer escape latencies in the Morris water maze test of ACAS mice. ACAS increased SGLT1 and proinflammatory cytokine gene expressions in mouse brains and phlorizin but not mizagliflozin normalized all gene expressions in ACAS mice. Hematoxylin/eosin staining demonstrated that they inhibited pyknotic cell death in the ACAS mouse hippocampus. In PC12HS cells, IL-1β increased SGLT1 expression and decreased survival rates of cells. Both mizagliflozin and phlorizin increased the survival rates of IL-1β-treated PC12HS cells. These results suggest that mizagliflozin and phlorizin can improve vascular cognitive impairment through the inhibition of neural SGLT1 and phlorizin also does so through the improvement of CBF in a mouse model of small vessel disease.

Antidiabetic Effects of a Tripeptide That Decreases Abundance of Na+-d-glucose Cotransporter SGLT1 in the Brush-Border Membrane of the Small Intestine

In enterocytes, protein RS1 (RSC1A1) mediates an increase of glucose absorption after ingestion of glucose-rich food via upregulation of Na⁺-d-glucose cotransporter SGLT1 in the brush-border membrane (BBM). Whereas RS1 decelerates the exocytotic pathway of vesicles containing SGLT1 at low glucose levels between meals, RS1-mediated deceleration is relieved after ingestion of glucose-rich food. Regulation of SGLT1 is mediated by RS1 domain RS1-Reg, in which Gln-Ser-Pro (QSP) is effective. In contrast to QSP and RS1-Reg, Gln-Glu-Pro (QEP) and RS1-Reg with a serine to glutamate exchange in the QSP motif downregulate the abundance of SGLT1 in the BBM at high intracellular glucose concentrations by about 50%. We investigated whether oral application of QEP improves diabetes in db/db mice and affects the induction of diabetes in New Zealand obese (NZO) mice under glucolipotoxic conditions. After 6-day administration of drinking water containing 5 mM QEP to db/db mice, fasting glucose was decreased, increase of blood glucose in the oral glucose tolerance test was blunted, and insulin sensitivity was increased. When QEP was added for several days to a high fat/high carbohydrate diet that induced diabetes in NZO mice, the increase of random plasma glucose was prevented, accompanied by lower plasma insulin levels. QEP is considered a lead compound for development of new antidiabetic drugs with more rapid cellular uptake. In contrast to SGLT1 inhibitors, QEP-based drugs may be applied in combination with insulin for the treatment of type 1 and type 2 diabetes, decreasing the required insulin amount, and thereby may reduce the risk of hypoglycemia.

Glucose transporters in the small intestine in health and disease

Absorption of monosaccharides is mainly mediated by Na+-D-glucose cotransporter SGLT1 and the facititative transporters GLUT2 and GLUT5. SGLT1 and GLUT2 are relevant for absorption of D-glucose and D-galactose while GLUT5 is relevant for D-fructose absorption. SGLT1 and GLUT5 are constantly localized in the brush border membrane (BBM) of enterocytes, whereas GLUT2 is localized in the basolateral membrane (BLM) or the BBM plus BLM at low and high luminal D-glucose concentrations, respectively. At high luminal D-glucose, the abundance SGLT1 in the BBM is increased. Hence, D-glucose absorption at low luminal glucose is mediated via SGLT1 in the BBM and GLUT2 in the BLM whereas high-capacity D-glucose absorption at high luminal glucose is mediated by SGLT1 plus GLUT2 in the BBM and GLUT2 in the BLM. The review describes functions and regulations of SGLT1, GLUT2, and GLUT5 in the small intestine including diurnal variations and carbohydrate-dependent regulations. Also, the roles of SGLT1 and GLUT2 for secretion of enterohormones are discussed. Furthermore, diseases are described that are caused by malfunctions of small intestinal monosaccharide transporters, such as glucose-galactose malabsorption, Fanconi syndrome, and fructose intolerance. Moreover, it is reported how diabetes, small intestinal inflammation, parental nutrition, bariatric surgery, and metformin treatment affect expression of monosaccharide transporters in the small intestine. Finally, food components that decrease D-glucose absorption and drugs in development that inhibit or downregulate SGLT1 in the small intestine are compiled. Models for regulations and combined functions of glucose transporters, and for interplay between D-fructose transport and metabolism, are discussed.

Sodium-glucose co-transporter (SGLT) inhibitor restores lost axonal varicosities of the myenteric plexus in a mouse model of high-fat diet-induced obesity

Diabetes impairs enteric nervous system functions; however, ultrastructural changes underlying the pathophysiology of the myenteric plexus and the effects of sodium-glucose co-transporter (SGLT) inhibitors are poorly understood. This study aimed to investigate three-dimensional ultrastructural changes in axonal varicosities in the myenteric plexus and the effect thereon of the SGLT inhibitor phlorizin in mice fed a high-fat diet (HFD). Three-dimensional ultrastructural analysis using serial block-face imaging revealed that non-treated HFD-fed mice had fewer axonal varicosities and synaptic vesicles in the myenteric plexus than did normal diet-fed control mice. Furthermore, mitochondrial volume was increased and lysosome number decreased in the axons of non-treated HFD-fed mice when compared to those of control mice. Phlorizin treatment restored the axonal varicosities and organelles in HFD-fed mice. Although HFD did not affect the immunolocalisation of PGP9.5, it reduced synaptophysin immunostaining in the myenteric plexus, which was restored by phlorizin treatment. These results suggest that impairment of the axonal varicosities and their synaptic vesicles underlies the damage to the enteric neurons caused by HFD feeding. SGLT inhibitor treatment could restore axonal varicosities and organelles, which may lead to improved gastrointestinal functions in HFD-induced obesity as well as diabetes.

Efficacy and safety of ipragliflozin as add-on to metformin for type 2 diabetes: a meta-analysis of double-blind randomized controlled trials

Objectives: To evaluate the efficacy and safety of ipragliflozin as add-on therapy to metformin in patients with type 2 diabetes mellitus.Methods: Systematic literature searches were performed in several databases across PubMed, the Cochrane Central Register of Controlled Trials, Embase, Medline, ClinicalTrials.gov, PsycINFO, and Web of Science from inception to 12 March 2019. After the extraction of data from eligible studies, randomized controlled trials (RCTs) were assessed for quality and analyzed statistically. Standardized mean difference (SMD) and risk ratio (RR) with 95% CIs were used to evaluate efficacy and safety end-points. Sensitivity analyses and subgroup analyses based on intervention times were also performed.Results: Five RCTs with 847 patients were included. Compared to metformin alone, ipragliflozin as an adjuvant to metformin reduced glycated hemoglobin (HbA1c) in 12 weeks and 24 weeks, respectively [12 w: SMD -0.30, 95% CI -0.51 to -0.10%, p = 0.004; 24 w: SMD -0.88, 95% CI -1.04 to -0.72%, p < 0.00001; Total: SMD -0.66, 95% CI -0.79 to -0.53%, p < 0.00001]. In addition, ipragliflozin as adjuvant therapy to metformin body weight (Total: SMD -1.47, 95% CI [-1.80,-1.14], p < 0.00001), waist circumference (Total: SMD -1.09, 95% CI [-1.62,-0.56], p < 0.00001), and blood pressure (SBP Total: SMD -3.36, 95% CI [-5.11.-1.61], p = 0.0002; DBP Total: SMD -2.18, 95% CI [-3.63,-0.74], p = 0.003). Compared to metformin alone, ipragliflozin as an adjuvant to metformin showed significant risks in the skin and subcutaneous tissue disorders and constipation.Conclusion: Compared to metformin alone, ipragliflozin plus metformin significantly improved glycemic control, reduced body weight, and lowered blood pressure; however, further high-quality trials are required to determine their long-term efficacy and safety.

Arbutus unedo L., (Ericaceae) inhibits intestinal glucose absorption and improves glucose tolerance in rodents

ETHNOPHARMACOLOGICAL RELEVANCE

Arbutus unedo L., (Ericaceae) is one of the most traditional plants commonly used to treat diabetes in people living in Eastern Morocco region particularly in Taza and Beni Mellal.

AIM OF THE STUDY

The aim of the study was to find if there is a scientific support to the ethnopharmacological relevance use of Arbutus unedo L., roots bark (AU) to treat diabetes.

MATERIALS AND METHODS

We studied the effects of crude aqueous extract of AU on intestinal glucose absorption using short-circuit current technique in vitro and oral glucose tolerance test in vivo.

RESULTS

The aqueous extract of AU (10 µg/mL to 1 mg/mL) induced concentration-dependent inhibition of sodium-dependent glucose transport across isolated mouse jejunum. The maximal inhibition was obtained with 1 mg/mL, which exhibited more than 80% of the Phloridzin inhibition with an IC₅₀ close to 216 µg/mL. A 6-week AU ingestion (2 g/(kg day)), improved oral glucose tolerance as efficiently as metformin (300 mg/(kg day)). Arbutus unedo L. and metformin also reduced body weight.

CONCLUSIONS

Arbutus unedo L. roots bark aqueous extract directly inhibited the electrogenic intestinal absorption of glucose in vitro. In addition it improved oral glucose tolerance and lowered body weight in rats after chronic oral administration in vivo. These results add a scientific support to the ethnopharmacological relevance use of Arbutus unedo L. roots bark to treat diabetes.

What does sodium-glucose co-transporter 1 inhibition add: Prospects for dual inhibition

Epithelial glucose transport is accomplished by Na+ -glucose co-transporters, SGLT1 and SGLT2. In the intestine, uptake of dietary glucose is for its majority mediated by SGLT1, and humans with mutations in the SGLT1 gene show glucose/galactose malabsorption. In the kidney, both transporters, SGLT1 and SGLT2, are expressed and recent studies identified that SGLT2 mediates up to 97% of glucose reabsorption. Humans with mutations in the SGLT2 gene show familial renal glucosuria. In the last three decades, significant progress was made in understanding the physiology of these transporters and their potential as therapeutic targets. Based on the structure of phlorizin, a natural compound acting as a SGLT1/2 inhibitor, initially several SGLT2, and later SGLT1 and dual SGLT1/2 inhibitors have been developed. Interestingly, SGLT2 knockout or treatment with SGLT2 selective inhibitors only causes a fractional glucose excretion in the magnitude of ∼60%, an effect mediated by up-regulation of renal SGLT1. Based on these findings the hypothesis was brought forward that dual SGLT1/2 inhibition might further improve glycaemic control via targeting two distinct organs that express SGLT1: the intestine and the kidney. Of note, SGLT1/2 double knockout mice completely lack renal glucose reabsorption. This review will address the rationale for the development of SGLT1 and dual SGLT1/2 inhibitors and potential benefits compared to sole SGLT2 inhibition.

Development of SGLT1 and SGLT2 inhibitors

Sodium-glucose cotransporters SGLT1 (encoded by SGLT1, also known as SLC5A1) and SGLT2 (encoded by SGLT2, also known as SLC5A2) are important mediators of epithelial glucose transport. While SGLT1 accounts for most of the dietary glucose uptake in the intestine, SGLT2 is responsible for the majority of glucose reuptake in the tubular system of the kidney, with SGLT1 reabsorbing the remainder of the filtered glucose. As a consequence, mutations in the SLC5A1 gene cause glucose/galactose malabsorption, whereas mutations in SLC5A2 are associated with glucosuria. Since the cloning of SGLT1 more than 30 years ago, big strides have been made in our understanding of these transporters and their suitability as drug targets. Phlorizin, a naturally occurring competitive inhibitor of SGLT1 and SGLT2, provided the first insights into potential efficacy, but its use was hampered by intestinal side effects and a short half-life. Nevertheless, it was a starting point for the development of specific inhibitors of SGLT1 and SGLT2, as well as dual SGLT1/2 inhibitors. Since the approval of the first SGLT2 inhibitor in 2013 by the US Food and Drug Administration, SGLT2 inhibitors have become a new mainstay in the treatment of type 2 diabetes mellitus. They also have beneficial effects on the cardiovascular system (including heart failure) and the kidney. This review focuses on the rationale for the development of individual SGLT2 and SGLT1 inhibitors, as well as dual SGLT1/2 inhibition, including, but not limited to, aspects of genetics, genetically modified mouse models, mathematical modelling and general considerations of drug discovery in the field of metabolism.

Potent Sodium/Glucose Cotransporter SGLT1/2 Dual Inhibition Improves Glycemic Control Without Marked Gastrointestinal Adaptation or Colonic Microbiota Changes in Rodents

The sodium/glucose cotransporters (SGLT1 and SGLT2) transport glucose across the intestinal brush border and kidney tubule. Dual SGLT1/2 inhibition could reduce hyperglycemia more than SGLT2-selective inhibition in patients with type 2 diabetes. However, questions remain about altered gastrointestinal (GI) luminal glucose and tolerability, and this was evaluated in slc5a1^-/- mice or with a potent dual inhibitor (compound 8; SGLT1 K_i = 1.5 ± 0.5 nM 100-fold greater potency than phlorizin; SGLT2 K_i = 0.4 ± 0.2 nM). ¹³C₆-glucose uptake was quantified in slc5a1^-/- mice and in isolated rat jejunum. Urinary glucose excretion (UGE), blood glucose (Sprague-Dawley rats), glucagon-like peptide 1 (GLP-1), and hemoglobin A1c (HbA1c) levels (Zucker diabetic fatty rats) were measured. Intestinal adaptation and rRNA gene sequencing was analyzed in C57Bl/6 mice. The blood ¹³C₆-glucose area under the curve (AUC) was reduced in the absence of SGLT1 by 75% (245 ± 6 vs. 64 ± 6 mg/dl⋅h in wild-type vs. slc5a1^-/- mice) and compound 8 inhibited its transport up to 50% in isolated rat jejunum. Compound 8 reduced glucose excursion more than SGLT2-selective inhibition (e.g., AUC = 129 ± 3 vs. 249 ± 5 mg/dl⋅h for 1 mg/kg compound 8 vs. dapagliflozin) with similar UGE but a lower renal glucose excretion threshold. In Zucker diabetic fatty rats, compound 8 decreased HbA1c and increased total GLP-1 without changes in jejunum SGLT1 expression, mucosal weight, or villus length. Overall, compound 8 (1 mg/kg for 6 days) did not increase cecal glucose concentrations or bacterial diversity in C57BL/6 mice. In conclusion, potent dual SGLT1/2 inhibition lowers blood glucose by reducing intestinal glucose absorption and the renal glucose threshold but minimally impacts the intestinal mucosa or luminal microbiota in chow-fed rodents.

Absorption, disposition, metabolism and excretion of [14C]mizagliflozin, a novel selective SGLT1 inhibitor, in rats

The pharmacokinetic and metabolite profiles of mizagliflozin, a novel selective sodium glucose co-transporter 1 inhibitor designed to act only in the intestine, were investigated in rats. Mizagliflozin administrated intravenously (0.3 mg/kg) and orally (3 mg/kg) declined with a short half-life (0.23 and 1.14 h, respectively). The absolute bioavailability was only 0.02%. Following intravenous administration of [¹⁴C]mizagliflozin (0.3 mg/kg), radioactivity in plasma was also rapidly declined. Up to 24 h after oral administration of [¹⁴C]mizagliflozin (1 mg/kg), radioactivity was recovered in the faeces (98.4%) and in the urine (0.8%). No remarkable accumulation of radioactivity in tissues was observed using tissue dissection technique and whole body autoradiography. Orally dosed [¹⁴C]mizagliflozin was mostly metabolised to its aglycone, KP232, in the intestine. In the plasma, KP232 and its glucuronide were predominant. KP232 glucuronide was also prominent in the bile and was recovered as KP232 in the faeces possibly because of the deconjugation by gut microflora. Mizagliflozin was observed neither in the urine nor the faeces. These findings suggest that orally administered mizagliflozin is poorly absorbed, contributing to low systemic exposure; if absorbed, mizagliflozin is rapidly cleared from circulation.