SGL5213, a novel and potent intestinal SGLT1 inhibitor, suppresses intestinal glucose absorption and enhances plasma GLP-1 and GLP-2 secretion in rats

A comprehensive in-vitro/in-vivo screening toolbox for the elucidation of glucose homeostasis modulating properties of plant extracts (from roots) and its bioactives

Plant extracts are increasingly recognized for their potential in modulating (postprandial) blood glucose levels. In this context, root extracts are of particular interest due to their high concentrations and often unique spectrum of plant bioactives. To identify new plant species with potential glucose-lowering activity, simple and robust methodologies are often required. For this narrative review, literature was sourced from scientific databases (primarily PubMed) in the period from June 2022 to January 2024. The regulatory targets of glucose homeostasis that could be modulated by bioactive plant compounds were used as search terms, either alone or in combination with the keyword "root extract". As a result, we present a comprehensive methodological toolbox for studying the glucose homeostasis modulating properties of plant extracts and its constituents. The described assays encompass in-vitro investigations involving enzyme inhibition (α-amylase, α-glucosidase, dipeptidyl peptidase 4), assessment of sodium-dependent glucose transporter 1 activity, and evaluation of glucose transporter 4 translocation. Furthermore, we describe a patch-clamp technique to assess the impact of extracts on KATP channels. While validating in-vitro findings in living organisms is imperative, we introduce two screenable in-vivo models (the hen's egg test and Drosophila melanogaster). Given that evaluation of the bioactivity of plant extracts in rodents and humans represents the current gold standard, we include approaches addressing this aspect. In summary, this review offers a systematic guide for screening plant extracts regarding their influence on key regulatory elements of glucose homeostasis, culminating in the assessment of their potential efficacy in-vivo. Moreover, application of the presented toolbox might contribute to further close the knowledge gap on the precise mechanisms of action of plant-derived compounds.

Mechanistic evaluation of the inhibitory effect of four SGLT-2 inhibitors on SGLT 1 and SGLT 2 using physiologically based pharmacokinetic (PBPK) modeling approaches

Sodium-glucose co-transporter type 2 (SGLT 2, gliflozins) inhibitors are potent orally active drugs approved for managing type 2 diabetes. SGLT 2 inhibitors exert a glucose-lowering effect by suppressing sodium-glucose co-transporters 1 and 2 in the intestinal and kidney proximal tubules. In this study, we developed a physiologically based pharmacokinetic (PBPK) model and simulated the concentrations of ertugliflozin, empagliflozin, henagliflozin, and sotagliflozin in target tissues. We used the perfusion-limited model to illustrate the disposition of SGLT 2 inhibitors in vivo. The modeling parameters were obtained from the references. Simulated steady-state plasma concentration-time curves of the ertugliflozin, empagliflozin, henagliflozin, and sotagliflozin are similar to the clinically observed curves. The 90% prediction interval of simulated excretion of drugs in urine captured the observed data well. Furthermore, all corresponding model-predicted pharmacokinetic parameters fell within a 2-fold prediction error. At the approved doses, we estimated the effective concentrations in intestinal and kidney proximal tubules and calculated the inhibition ratio of SGLT transporters to differentiate the relative inhibition capacities of SGLT1 and 2 in each gliflozin. According to simulation results, four SGLT 2 inhibitors can nearly completely inhibit SGLT 2 transporter at the approved dosages. Sotagliflozin exhibited the highest inhibition activity on SGLT1, followed by ertugliflozin, empagliflozin, and henagliflozin, which showed a lower SGLT 1 inhibitory effect. The PBPK model successfully simulates the specific target tissue concentration that cannot be measured directly and quantifies the relative contribution toward SGLT 1 and 2 for each gliflozin.

Effects of Polyphenols on Glucose-Induced Metabolic Changes in Healthy Human Subjects and on Glucose Transporters

Dietary polyphenols interact with glucose transporters in the small intestine and modulate glucose uptake after food or beverage consumption. This review assesses the transporter interaction in vitro and how this translates to an effect in healthy volunteers consuming glucose. As examples, the apple polyphenol phlorizin inhibits sodium-glucose linked transporter-1; in the intestinal lumen, it is converted to phloretin, a strong inhibitor of glucose transporter-2 (GLUT2), by the brush border digestive enzyme lactase. Consequently, an apple extract rich in phlorizin attenuates blood glucose and insulin in healthy volunteers after a glucose challenge. On the other hand, the olive phenolic, oleuropein, inhibits GLUT2, but the strength of the inhibition is not enough to modulate blood glucose after a glucose challenge in healthy volunteers. Multiple metabolic effects and oxidative stresses after glucose consumption include insulin, incretin hormones, fatty acids, amino acids, and protein markers. However, apart from acute postprandial effects on glucose, insulin, and some incretin hormones, very little is known about the acute effects of polyphenols on these glucose-induced secondary effects. In summary, attenuation of the effect of a glucose challenge in vivo is only observed when polyphenols are strong inhibitors of glucose transporters.

SGLT-1-specific inhibition ameliorates renal failure and alters the gut microbial community in mice with adenine-induced renal failure

Sodium-dependent glucose cotransporters (SGLTs) have attracted considerable attention as new targets for type 2 diabetes mellitus. In the kidney, SGLT2 is the major glucose uptake transporter in the proximal tubules, and inhibition of SGLT2 in the proximal tubules shows renoprotective effects. On the other hand, SGLT1 plays a role in glucose absorption from the gastrointestinal tract, and the relationship between SGLT1 inhibition in the gut and renal function remains unclear. Here, we examined the effect of SGL5213, a novel and potent intestinal SGLT1 inhibitor, in a renal failure (RF) model. SGL5213 improved renal function and reduced gut-derived uremic toxins (phenyl sulfate and trimethylamine-N-oxide) in an adenine-induced RF model. Histological analysis revealed that SGL5213 ameliorated renal fibrosis and inflammation. SGL5213 also reduced gut inflammation and fibrosis in the ileum, which is a primary target of SGL5213. Examination of the gut microbiota community revealed that the Firmicutes/Bacteroidetes ratio, which suggests gut dysbiosis, was increased in RF and SGL5213 rebalanced the ratio by increasing Bacteroidetes and reducing Firmicutes. At the genus level, Allobaculum (a major component of Erysipelotrichaceae) was significantly increased in the RF group, and this increase was canceled by SGL5213. We also measured the effect of SGL5213 on bacterial phenol-producing enzymes that catalyze tyrosine into phenol, following the reduction of phenyl sulfate, which is a novel marker and a therapeutic target for diabetic kidney disease DKD. We found that the enzyme inhibition was less potent, suggesting that the change in the microbial community and the reduction of uremic toxins may be related to the renoprotective effect of SGL5213. Because SGL5213 is a low-absorbable SGLT1 inhibitor, these data suggest that the gastrointestinal inhibition of SGLT1 is also a target for chronic kidney diseases.

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.

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.