LX2761, a Sodium/Glucose Cotransporter 1 Inhibitor Restricted to the Intestine, Improves Glycemic Control in Mice

Transport and inhibition mechanism of the human SGLT2-MAP17 glucose transporter

Sodium-glucose cotransporter 2 (SGLT2) is imporant in glucose reabsorption. SGLT2 inhibitors suppress renal glucose reabsorption, therefore reducing blood glucose levels in patients with type 2 diabetes. We and others have developed several SGLT2 inhibitors starting from phlorizin, a natural product. Using cryo-electron microscopy, we present the structures of human (h)SGLT2-MAP17 complexed with five natural or synthetic inhibitors. The four synthetic inhibitors (including canagliflozin) bind the transporter in the outward conformations, while phlorizin binds it in the inward conformation. The phlorizin-hSGLT2 interaction exhibits biphasic kinetics, suggesting that phlorizin alternately binds to the extracellular and intracellular sides. The Na+-bound outward-facing and unbound inward-open structures of hSGLT2-MAP17 suggest that the MAP17-associated bundle domain functions as a scaffold, with the hash domain rotating around the Na+-binding site. Thus, Na+ binding stabilizes the outward-facing conformation, and its release promotes state transition to inward-open conformation, exhibiting a role of Na+ in symport mechanism. These results provide structural evidence for the Na+-coupled alternating-access mechanism proposed for the transporter family.

Effect of Sotagliflozin on Early Mortality and Heart Failure-Related Events: A Post Hoc Analysis of SOLOIST-WHF

BACKGROUND

Approximately 25% of patients admitted to hospitals for worsening heart failure (WHF) are readmitted within 30 days.

OBJECTIVES

The authors conducted a post hoc analysis of the SOLOIST-WHF (Effect of Sotagliflozin on Cardiovascular Events in Patients With Type 2 Diabetes Post-WHF) trial to evaluate the efficacy of sotagliflozin versus placebo to decrease mortality and HF-related events among patients who began study treatment on or before discharge from their index hospitalization.

METHODS

The main endpoint of interest was cardiovascular death or HF-related event (HF hospitalization or urgent care visit) occurring within 90 and 30 days after discharge for the index WHF hospitalization. Treatment comparisons were by proportional hazards models, generating HRs, 95% CIs, and P values.

RESULTS

Of 1,222 randomized patients, 596 received study drug on or before their date of discharge. Sotagliflozin reduced the main endpoint at 90 days after discharge (HR: 0.54 [95% CI: 0.35-0.82]; P = 0.004) and at 30 days (HR: 0.49 [95% CI: 0.27-0.91]; P = 0.023) and all-cause mortality at 90 days (HR: 0.39 [95% CI: 0.17-0.88]; P = 0.024). In subgroup analyses, sotagliflozin reduced the 90-day main endpoint regardless of sex, age, estimated glomerular filtration rate, N-terminal pro-B-type natriuretic peptide, left ventricular ejection fraction, or mineralocorticoid receptor agonist use. Sotagliflozin was well-tolerated but with slightly higher rates of diarrhea and volume-related events than placebo.

CONCLUSIONS

Starting sotagliflozin before discharge in patients with type 2 diabetes hospitalized for WHF significantly decreased cardiovascular deaths and HF events through 30 and 90 days after discharge, emphasizing the importance of beginning sodium glucose cotransporter treatment before discharge.

Anti-Diabetic Therapy and Heart Failure: Recent Advances in Clinical Evidence and Molecular Mechanism

Diabetic patients have a two- to four-fold increase in the risk of heart failure (HF), and the co-existence of diabetes and HF is associated with poor prognosis. In randomized clinical trials (RCTs), compelling evidence has demonstrated the beneficial effects of sodium-glucose co-transporter-2 inhibitors on HF. The mechanism includes increased glucosuria, restored tubular glomerular feedback with attenuated renin-angiotensin II-aldosterone activation, improved energy utilization, decreased sympathetic tone, improved mitochondria calcium homeostasis, enhanced autophagy, and reduced cardiac inflammation, oxidative stress, and fibrosis. The RCTs demonstrated a neutral effect of the glucagon-like peptide receptor agonist on HF despite its weight-reducing effect, probably due to it possibly increasing the heart rate via increasing cyclic adenosine monophosphate (cAMP). Observational studies supported the markedly beneficial effects of bariatric and metabolic surgery on HF despite no current supporting evidence from RCTs. Bromocriptine can be used to treat peripartum cardiomyopathy by reducing the harmful cleaved prolactin fragments during late pregnancy. Preclinical studies suggest the possible beneficial effect of imeglimin on HF through improving mitochondrial function, but further clinical evidence is needed. Although abundant preclinical and observational studies support the beneficial effects of metformin on HF, there is limited evidence from RCTs. Thiazolidinediones increase the risk of hospitalized HF through increasing renal tubular sodium reabsorption mediated via both the genomic and non-genomic action of PPARγ. RCTs suggest that dipeptidyl peptidase-4 inhibitors, including saxagliptin and possibly alogliptin, may increase the risk of hospitalized HF, probably owing to increased circulating vasoactive peptides, which impair endothelial function, activate sympathetic tones, and cause cardiac remodeling. Observational studies and RCTs have demonstrated the neutral effects of insulin, sulfonylureas, an alpha-glucosidase inhibitor, and lifestyle interventions on HF in diabetic patients.

Sodium-Glucose Cotransporter Inhibitors as Antidiabetic Drugs: Current Development and Future Perspectives

Sodium-glucose cotransporter 2 (SGLT-2) inhibitors (gliflozins) represent the most recently approved class of oral antidiabetic drugs. SGLT-2 overexpression in diabetic patients contributes significantly to hyperglycemia and related complications. Therefore, SGLT-2 became a highly interesting therapeutic target, culminating in the approval for clinical use of dapagliflozin and analogues in the past decade. Gliflozins improve glycemic control through a novel insulin-independent mechanism of action and, moreover, exhibit significant cardiorenal protective effects in both diabetic and nondiabetic subjects. Therefore, gliflozins have received increasing attention, prompting extensive structure-activity relationship studies and optimization approaches. The discovery that intestinal SGLT-1 inhibition can provide a novel opportunity to control hyperglycemia, through a multifactorial mechanism, recently encouraged the design of low adsorbable inhibitors selectively directed to the intestinal SGLT-1 subtype as well as of dual SGLT-1/SGLT-2 inhibitors, representing a compelling strategy to identify new antidiabetic drug candidates.

Revisiting the concept of incretin and enteroendocrine L-cells as type 2 diabetes mellitus treatment

The significant growth in type 2 diabetes mellitus (T2DM) prevalence strikes a common threat to the healthcare and economic systems globally. Despite the availability of several anti-hyperglycaemic agents in the market, none can offer T2DM remission. These agents include the prominent incretin-based therapy such as glucagon-like peptide-1 receptor (GLP-1R) agonists and dipeptidyl peptidase-4 inhibitors that are designed primarily to promote GLP-1R activation. Recent interest in various therapeutically useful gastrointestinal hormones in T2DM and obesity has surged with the realisation that enteroendocrine L-cells modulate the different incretins secretion and glucose homeostasis, reflecting the original incretin definition. Targeting L-cells offers promising opportunities to mimic the benefits of bariatric surgery on glucose homeostasis, bodyweight management, and T2DM remission. Revising the fundamental incretin theory is an essential step for therapeutic development in this area. Therefore, the present review explores enteroendocrine L-cell hormone expression, the associated nutrient-sensing mechanisms, and other physiological characteristics. Subsequently, enteroendocrine L-cell line models and the latest L-cell targeted therapies are reviewed critically in this paper. Bariatric surgery, pharmacotherapy and new paradigm of L-cell targeted pharmaceutical formulation are discussed here, offering both clinician and scientist communities a new common interest to push the scientific boundary in T2DM therapy.

Glycaemia and body weight are regulated by sodium-glucose cotransporter 1 (SGLT1) expression via O-GlcNAcylation in the intestine

Objective

Methods

Results

Conclusion

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Intestine-specific OGT depletion results in weight loss and hypoglycaemia.

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It reduces SGLT1 expression, resulting in glucose absorption from the gut.

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OGT knockdown may contribute to diminish glucose-induced incretin secretion.

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OGT may regulate SGLT1 expression via the cAMP/CREB-dependent pathway.

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O-GlcNAcylation regulates SGLT1 expression in the intestine and the kidney.

Targeting the Enteroendocrine System for Treatment of Obesity

Mimetics of the anorexigenic gut hormone glucagon-like peptide 1 (GLP-1) were originally developed as insulinotropic anti-diabetic drugs but also evoke significant weight loss, leading to their recent approval as obesity therapeutics. Co-activation of receptors for GLP-1 and other gut hormones which reduce food intake - peptide YY (PYY_3-36), cholecystokinin (CCK) and glucose-dependent insulinotropic peptide (GIP) - is now being explored clinically to enhance efficacy. An alternative approach involves pharmacologically stimulating endogenous secretion of these hormones from enteroendocrine cells (EECs) to recapitulate the metabolic consequences of bariatric surgery, where highly elevated postprandial levels of GLP-1 and PYY_3-36 are thought to contribute to improved glycaemia and weight loss.

Protective effect of SGL5213, a potent intestinal sodium-glucose cotransporter 1 inhibitor, in nonalcoholic fatty liver disease in mice

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic disease. SGL5213, which is minimally absorbed and is restricted to the intestinal tract, is a potent intestinal sodium-glucose cotransporter 1 (SGLT1) inhibitor. In this study, we investigated the protective effect of SGL5213 in a rodent model of NAFLD.

METHODS

Using a rodent model of NAFLD, we compared SGL5213 efficacy with miglitol, which is an α-glucosidase inhibitor. We used a high-fat and high-sucrose diet-induced NAFLD model.

RESULTS

SGL5213 and miglitol improved obesity, liver dysfunction, insulin resistance, and the NAFLD severity. To further investigate the effects of SGL5213, we analyzed the mRNA expression of genes involved in lipid metabolism, inflammation, and liver fibrosis, and cecal pH levels. SGL5213 and miglitol treatment significantly decreased mRNA expression of factors involved in inflammation and liver fibrosis. SGL5213 treatment significantly decreased cecal pH levels, which did not occur with miglitol.

CONCLUSIONS

SGL5213 had a protective effect on the pathogenesis of NAFLD in a rodent model. We considered that inhibiting glucose absorption and increasing glucose content in the gastrointestinal tract with SGL5213 might have contributed to the protective effect in NAFLD. SGL5213 is a promising therapeutic agent for NAFLD with obesity and insulin resistance.

High-Throughput Screening of Mouse Gene Knockouts Identifies Established and Novel High Body Fat Phenotypes

PURPOSE

Obesity is a major public health problem. Understanding which genes contribute to obesity may better predict individual risk and allow development of new therapies. Because obesity of a mouse gene knockout (KO) line predicts an association of the orthologous human gene with obesity, we reviewed data from the Lexicon Genome5000TM high throughput phenotypic screen (HTS) of mouse gene KOs to identify KO lines with high body fat.

MATERIALS AND METHODS

KO lines were generated using homologous recombination or gene trapping technologies. HTS body composition analyses were performed on adult wild-type and homozygous KO littermate mice from 3758 druggable mouse genes having a human ortholog. Body composition was measured by either DXA or QMR on chow-fed cohorts from all 3758 KO lines and was measured by QMR on independent high fat diet-fed cohorts from 2488 of these KO lines. Where possible, comparisons were made to HTS data from the International Mouse Phenotyping Consortium (IMPC).

RESULTS

Body fat data are presented for 75 KO lines. Of 46 KO lines where independent external published and/or IMPC KO lines are reported as obese, 43 had increased body fat. For the remaining 29 novel high body fat KO lines, Ksr2 and G2e3 are supported by data from additional independent KO cohorts, 6 (Asnsd1, Srpk2, Dpp8, Cxxc4, Tenm3 and Kiss1) are supported by data from additional internal cohorts, and the remaining 21 including Tle4, Ak5, Ntm, Tusc3, Ankk1, Mfap3l, Prok2 and Prokr2 were studied with HTS cohorts only.

CONCLUSION

These data support the finding of high body fat in 43 independent external published and/or IMPC KO lines. A novel obese phenotype was identified in 29 additional KO lines, with 27 still lacking the external confirmation now provided for Ksr2 and G2e3 KO mice. Undoubtedly, many mammalian obesity genes remain to be identified and characterized.

Chemosensing in enteroendocrine cells: mechanisms and therapeutic opportunities

PURPOSE OF REVIEW

Enteroendocrine cells (EECs) are scattered chemosensory cells in the intestinal epithelium that release hormones with a wide range of actions on intestinal function, food intake and glucose homeostasis. The mechanisms by which gut hormones are secreted postprandially, or altered by antidiabetic agents and surgical interventions are of considerable interest for future therapeutic development.

RECENT FINDINGS

EECs are electrically excitable and express a repertoire of G-protein coupled receptors that sense nutrient and nonnutrient stimuli, coupled to intracellular Ca2+ and cyclic adenosine monophosphate. Our knowledge of EEC function, previously developed using mouse models, has recently been extended to human cells. Gut hormone release in humans is enhanced by bariatric surgery, as well as by some antidiabetic agents including sodium-coupled glucose transporter inhibitors and metformin.

SUMMARY

EECs are important potential therapeutic targets. A better understanding of their chemosensory mechanisms will enhance the development of new therapeutic strategies to treat metabolic and gastrointestinal diseases.

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.

Sotagliflozin Decreases Postprandial Glucose and Insulin Concentrations by Delaying Intestinal Glucose Absorption

CONTEXT

The effect of sotagliflozin (a dual sodium-glucose cotransporter [SGLT] 2 and SGLT1 inhibitor) on intestinal glucose absorption has not been investigated in humans.

OBJECTIVE

To measure rate of appearance of oral glucose (RaO) using a dual glucose tracer method following standardized mixed meals taken after single sotagliflozin or canagliflozin doses.

SETTING

Clinical research organization.

DESIGN AND PARTICIPANTS

In a double-blind, 3-period crossover study (NCT01916863), 24 healthy participants were randomized to 2 cohorts of 12 participants. Within each cohort, participants were randomly assigned single oral doses of either sotagliflozin 400 mg, canagliflozin 300 mg, or placebo on each of test days 1, 8, and 15. On test days, Cohort 1 had breakfast containing [6,6-2H2] glucose 0.25 hours postdose and lunch containing [1-2H1] glucose 5.25 hours postdose; Cohort 2 had breakfast containing no labeled glucose 0.25 hours postdose and lunch containing [6,6-2H2] glucose 4.25 hours postdose. All participants received a 10- to 15-hour continuous [U-13C6] glucose infusion starting 5 hours before their first [6,6-2H2] glucose-containing meal.

MAIN OUTCOME

RaO, postprandial glucose (PPG), and postprandial insulin.

RESULTS

Sotagliflozin and canagliflozin decreased area under the curve (AUC)0-1 hour and/or AUC0-2 hours for RaO, PPG, and insulin after breakfast and/or the 4.25-hour postdose lunch (P < .05 versus placebo). After the 5.25-hour postdose lunch, sotagliflozin lowered RaO AUC0-1 hour and PPG AUC0-5 hours versus both placebo and canagliflozin (P < .05).

CONCLUSIONS

Sotagliflozin delayed and blunted intestinal glucose absorption after meals, resulting in lower PPG and insulin levels, likely due to prolonged local inhibition of intestinal SGLT1 that persisted for ≥5 hours after dosing.

Novel natural and synthetic inhibitors of solute carriers SGLT1 and SGLT2

Selective analogs of the natural glycoside phloridzin are marketed drugs that reduce hyperglycemia in diabetes by inhibiting the active sodium glucose cotransporter SGLT2 in the kidneys. In addition, intestinal SGLT1 is now recognized as a target for glycemic control. To expand available type 2 diabetes remedies, we aimed to find novel SGLT1 inhibitors beyond the chemical space of glycosides. We screened a bioactive compound library for SGLT1 inhibitors and tested primary hits and additional structurally similar molecules on SGLT1 and SGLT2 (SGLT1/2). Novel SGLT1/2 inhibitors were discovered in separate chemical clusters of natural and synthetic compounds. These have IC50-values in the 10-100 μmol/L range. The most potent identified novel inhibitors from different chemical clusters are (SGLT1-IC50 Mean ± SD, SGLT2-IC50 Mean ± SD): (+)-pteryxin (12 ± 2 μmol/L, 9 ± 4 μmol/L), (+)-ε-viniferin (58 ± 18 μmol/L, 110 μmol/L), quinidine (62 μmol/L, 56 μmol/L), cloperastine (9 ± 3 μmol/L, 9 ± 7 μmol/L), bepridil (10 ± 5 μmol/L, 14 ± 12 μmol/L), trihexyphenidyl (12 ± 1 μmol/L, 20 ± 13 μmol/L) and bupivacaine (23 ± 14 μmol/L, 43 ± 29 μmol/L). The discovered natural inhibitors may be further investigated as new potential (prophylactic) agents for controlling dietary glucose uptake. The new diverse structure activity data can provide a starting point for the optimization of novel SGLT1/2 inhibitors and support the development of virtual SGLT1/2 inhibitor screening models.

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.

Sotagliflozin, the first dual SGLT inhibitor: current outlook and perspectives

Sotagliflozin is a dual sodium-glucose co-transporter-2 and 1 (SGLT2/1) inhibitor for the treatment of both type 1 (T1D) and type 2 diabetes (T2D). Sotagliflozin inhibits renal sodium-glucose co-transporter 2 (determining significant excretion of glucose in the urine, in the same way as other, already available SGLT-2 selective inhibitors) and intestinal SGLT-1, delaying glucose absorption and therefore reducing post prandial glucose. Well-designed clinical trials, have shown that sotagliflozin (as monotherapy or add-on therapy to other anti-hyperglycemic agents) improves glycated hemoglobin in adults with T2D, with beneficial effects on bodyweight and blood pressure. Similar results have been obtained in adults with T1D treated with either continuous subcutaneous insulin infusion or multiple daily insulin injections, even after insulin optimization. A still ongoing phase 3 study is currently evaluating the effect of sotagliflozin on cardiovascular outcomes (ClinicalTrials.gov NCT03315143). In this review we illustrate the advantages and disadvantages of dual SGLT 2/1 inhibition, in order to better characterize and investigate its mechanisms of action and potentialities.

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

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

Sotagliflozin: a dual sodium-glucose co-transporter-1 and -2 inhibitor for the management of Type 1 and Type 2 diabetes mellitus

AIMS

To evaluate the evidence for the novel dual sodium-glucose co-transporter-1 (SGLT1) and -2 (SGLT2) inhibitor, sotagliflozin, which may enhance the efficacy of SGLT2 inhibitors by additionally reducing intestinal glucose absorption.

METHODS

The search terms 'sotagliflozin', 'LX4211', 'SGLT' and 'diabetes' were entered into PubMed. Evidence for the pharmacokinetics, pharmacodynamics, safety and efficacy of sotagliflozin in Type 1 and 2 diabetes was extracted from the retrieved literature, critically evaluated, and contextualized in relation to data on existing SGLT2 inhibitors.

RESULTS

There is convincing evidence from a range of phase II and III clinical trials that sotagliflozin significantly improves glycaemic control in both Type 1 and Type 2 diabetes. Additional benefits, such as smaller postprandial plasma glucose excursions, lower insulin requirements, appetite suppression and weight loss have been documented. While this is encouraging, several safety concerns remain; a dose-dependent increase in the rate of diabetic ketoacidosis, diarrhoea and genital mycotic infection is apparent, although statistical exploration of the data regarding such events is currently lacking. Speculatively, use of a 200-mg rather than a 400-mg dose may help to limit unwanted effects.

CONCLUSIONS

The current evidence for sotagliflozin in diabetes appears promising. Further studies sufficiently powered to assess present and emerging safety concerns, as well as to identify individuals for whom sotagliflozin may be of particular benefit/harm would now be informative for regulatory decision-making. Direct comparisons with existing SGLT2 inhibitors are also needed to determine relative safety/efficacy profiles for the different indications.

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.

Novel and Unexpected Functions of SGLTs

It has been 30 years since the intestinal sodium glucose cotransporter SGLT1 was cloned, and, in the intervening years, there have been many advances that have influenced physiology and medicine. Among the first was that SGLT1 is the founding member of the human gene family SLC5, containing 11 diverse transporters and a glucose sensor. Equally surprising was that SGLTs are members of a structural family of cotransporters and exchangers in different gene families. This led to the conclusion that these proteins operate by a mechanism where transport involves the opening and closing of external and internal gates. The mechanism is shared by a wide variety of transporters in different structural families, e.g., the human facilitated glucose transporters (SLC2) in the huge major facilitator superfamily (MFS). Not surprising is the finding that mutations in Sglt genes cause the rare diseases glucose-galactose-malabsorption (GGM) and familial renal glucosuria (FRG). However, it was not envisaged that SGLT inhibitors would be used to treat diabetes mellitus, and these drugs may be able to treat cancer. Finally, in 2017, we have just learned that SGLT1 may be required to resist infection and to avoid recurrent pregnancy loss.