GLUT2 accumulation in enterocyte apical and intracellular membranes: a study in morbidly obese human subjects and ob/ob and high fat-fed mice

Gut microbiota alterations induced by Roux-en-Y gastric bypass result in glucose-lowering by enhancing intestinal glucose excretion

Roux-en-Y gastric bypass (RYGB) results in glucose-lowering in patients with type 2 diabetes mellitus (T2DM) and may be associated with increased intestinal glucose excretion. However, the contribution of intestinal glucose excretion to glycemic control after RYGB and its underlying mechanisms are not fully elucidated. Here, we confirmed that intestinal glucose excretion significantly increased in obese rats after RYGB, which was negatively correlated with postoperative blood glucose levels. Moreover, we also found that the contribution of Biliopancreatic limb length, an important factor affecting glycemic control after RYGB, to the improvement of glucose metabolism after RYGB attributed to the enhancement of intestinal glucose excretion. Subsequently, we further determined through multiple animal models that intestinal glucose excretion is physiological rather than pathological and plays a crucial role in maintaining glucose homeostasis in the body. Finally, we employed germ-free mice colonized with fecal samples from patients and rats to demonstrate that enhanced intestinal glucose excretion after RYGB is directly modulated by the surgery-induced changes in the gut microbiota. These results indicated that the gut microbiota plays a direct causal role in the hypoglycemic effect of RYGB by promoting intestinal glucose excretion, which may provide new insights for developing gut microbiota-based therapies for T2DM.

Glucose absorption by isolated, vascularly perfused rat intestine: A significant paracellular contribution augmented by SGLT1 inhibition

AIM

Intestinal glucose transport involves SGLT1 in the apical membrane of enterocytes and GLUT2 in the basolateral membrane. In vivo studies have shown that absorption rates appear to exceed the theoretical capacity of these transporters, suggesting that glucose transport may occur via additional pathways, which could include passive mechanisms. The aim of the study was to investigate glucose absorption in an in vitro model, which has proven useful for endocrine studies.

METHODS

We studied both transcellular and paracellular glucose absorption in the isolated vascularly perfused rat small intestine. Glucose absorbed from the lumen was traced with 14C-d-glucose, allowing sensitive and accurate quantification. SGLT1 and GLUT2 activities were blocked with phlorizin and phloretin. 14C-d-mannitol was used as an indicator of paracellular absorption.

RESULTS

Our results indicate that glucose absorption in this model involves two transport mechanisms: transport mediated by SGLT1/GLUT2 and a paracellular transport mechanism. Glucose absorption was reduced by 60% when SGLT1 transport was blocked and by 80% when GLUT2 was blocked. After combined luminal SGLT1 and GLUT2 blockade, ~30% of glucose absorption remained. d-mannitol absorption was greater in the proximal small intestine compared to the distal small intestine. Unexpectedly, mannitol absorption increased markedly when SGLT1 transport was blocked.

CONCLUSION

In this model, glucose absorption occurs via both active transcellular and passive paracellular transport, particularly in the proximal intestine, which is important for the understanding of, for example, hormone secretion related to glucose absorption. Interference with SGLT1 activity may lead to enhanced paracellular transport, pointing to a role in the regulation of the latter.

Intestinal IL-25 prevents high-fat diet-induced obesity by modulating the cholesterol transporter NPC1L1 expression in the intestinal epithelial cells

The intestine is essential for digestion and nutrient absorption, and its altered function contributes to metabolic dysregulation and obesity-induced intestinal inflammation. Intestinal immune responses have been associated with the regulation of metabolic dysfunction during obesity. Given that the epithelial cell-derived cytokine IL-25 has been demonstrated to regulate metabolic disorders, we sought to examine the role of intestinal IL-25 in modulating a high-fat diet (HFD)-induced obesity. We found that mice on a high-fat diet exhibited decreased IL-25 expression in the small intestine. Intestinal IL-25 mRNA levels displayed an inverse association with plasma triglycerides, total cholesterol, glucose levels, and the expression of the cholesterol transporter Npc1l1 in the intestine. In HFD-induced obesity, transgenic mice overexpressing IL-25 in the intestinal epithelial cells demonstrated diminished mRNA expression of intestinal genes related to glucose, cholesterol, and fat absorption, along with chylomicron production, while also systemically decreasing plasma glucose, total cholesterol, and triglyceride levels, fat accumulation, and weight gain. In vitro, IL-25 treatment of human intestinal Caco-2 cells directly decreased cholesterol uptake and downregulated the expression of NPC1L1 and its transcriptional regulator, SREBP2. These findings highlight IL-25 as a potential modulator in the intestine that regulates intestinal cholesterol absorption and systemic metabolism in obesity.

Metformin-regulated glucose flux from the circulation to the intestinal lumen

BACKGROUND

Through a retrospective analysis of existing FDG PET-MRI images, we recently demonstrated that metformin increases the accumulation of FDG in the intestinal lumen, suggesting that metformin stimulates glucose excretion into the intestine. However, the details of this phenomenon remain unclear. We here investigate the detailed dynamics of intestinal glucose excretion, including the rate of excretion and the metabolism of excreted glucose, in both the presence and absence of metformin.

METHODS

We quantified intestinal glucose excretion using newly developed FDG PET-MRI-based bioimaging in individuals with type 2 diabetes, both treated and untreated with metformin. The metabolism of excreted glucose was analyzed through mass spectrometry of fecal samples from mice intravenously injected with 13C-labeled glucose.

RESULTS

Continuous FDG PET/MRI image taking reveals that FDG is initially observed in the jejunum, suggesting its involvement in FDG excretion. Metformin-treated individuals excrete a significant amount of glucose (~1.65 g h-1 per body) into the intestinal lumen. In individuals not receiving metformin, a certain amount of glucose (~0.41 g h-1per body) is also excreted into the intestinal lumen, indicating its physiological importance. Intravenous injection of 13C-labeled glucose in mice increases the content of 13C in short-chain fatty acids (SCFAs) extracted from feces, and metformin increased the incorporation of 13C into SCFAs.

CONCLUSIONS

A previously unrecognized, substantial flux of glucose from the circulation to the intestinal lumen exists, which likely contributes to the symbiosis between gut microbiota and the host. This flux represents a potential target of metformin's action in humans.

Studies in vitro of equine intestinal glucagon-like peptide-2 secretion

Equine insulin dysregulation (ID) is a significant metabolic problem because the hyperinsulinaemia that develops increases the animal's risk of developing laminitis, a debilitating foot condition. The role of gastrointestinal factors, such as incretin hormones, in the pathogenesis of ID and hyperinsulinaemia in horses is poorly understood, particularly in comparison to other species. Glucagon-like peptide-2 (GLP-2) is an intestinotrophic peptide released from L cells in the gastrointestinal tract and is implicated in metabolic dysfunction in other species. The aim of this study in vitro was to establish basic physiological understanding about intestinal secretion of GLP-2 in horses. Basal and glucose-stimulated GLP-2 secretion was measured in post-mortem tissue samples from the duodenum, jejunum, and ileum. We observed that GLP-2 secretion was minimal in samples from the duodenum compared to the jejunum and ileum (5-9-fold higher; P < 0.05). Furthermore, GLP-2 secretion was not responsive to glucose stimulation in the ileum or duodenum but was responsive to glucose in the jejunum. This effect in the jejunum was inhibited by 30 % (P = 0.02) using phlorizin, a selective sodium-glucose cotransporter-1 (SGLT-1) inhibitor, and by 38 % (P = 0.04) using phloretin, a non-selective SGLT-1/GLUT-2 inhibitor. The localisation of glucose-responsive GLP-2 secretion in the jejunum might be relevant to the development of post-prandial hyperinsulinaemia. This study has provided data on GLP-2 secretion from the equine small intestine that will enable more complex and dynamic studies on the pathogenesis of ID.

Unraveling the impaired incretin effect in obesity and type 2 diabetes: Key role of hyperglycemia-induced unscheduled glycolysis and glycolytic overload

Glucagon-like peptide-1 (GLP-1) agonists and GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) co-agonists are major treatment options for subjects with obesity and patients with type 2 diabetes mellitus (T2DM). They counter without addressing the mechanistic cause of the impaired incretin effect associated with obesity and T2DM. Incretin effect impairment is characterized by decreased secretion of incretins from enteroendocrine cells and incretin resistance of pancreatic β-cells. It is linked to hyperglycemia. We present evidence that subversion of the gating of glucose entry into glycolysis, mainly by glucokinase (hexokinase-4), during persistent hyperglycemia in enteroendocrine cells, pancreatic β- and α-cells and appetite-regulating neurons contributes to the biochemical mechanism of the impaired incretin effect. Unscheduled glycolysis and glycolytic overload thereby produced decreases cell signalling of incretin secretion to glucose and other secretion stimuli and incretin receptor responses. This mechanism provides a guide for development of alternative therapies targeting recovery of the impaired incretin effect.

Metformin: Diverse molecular mechanisms, gastrointestinal effects and overcoming intolerance in type 2 Diabetes Mellitus: A review

Metformin, the first line treatment for patients with type 2 diabetes mellitus, has alternative novel roles, including cancer and diabetes prevention. This narrative review aims to explore its diverse mechanisms, effects and intolerance, using sources obtained by searching Scopus, PubMed and Web of Science databases, and following Scale for the Assessment of Narrative Review Articles reporting guidelines. Metformin exerts it actions through duration influenced, and organ specific, diverse mechanisms. Its use is associated with inhibition of hepatic gluconeogenesis targeted by mitochondria and lysosomes, reduction of cholesterol levels involving brown adipose tissue, weight reduction influenced by growth differentiation factor 15 and novel commensal bacteria, in addition to counteraction of meta-inflammation alongside immuno-modulation. Interactions with the gastrointestinal tract include alteration of gut microbiota, enhancement of glucose uptake and glucagon like peptide 1 and reduction of bile acid absorption. Though beneficial, they may be linked to intolerance. Metformin related gastrointestinal adverse effects are associated with dose escalation, immediate release formulations, gut microbiota alteration, epigenetic predisposition, inhibition of organic cation transporters in addition to interactions with serotonin, histamine and the enterohepatic circulation. Potentially effective measures to overcome intolerance encompasses carefully objective targeted dose escalation, prescription of fixed dose combination, microbiome modulators and prebiotics, in addition to use of extended release formulations.

Regular Exercise Training Induces More Changes on Intestinal Glucose Uptake from Blood and Microbiota Composition in Leaner Compared to Heavier Individuals in Monozygotic Twins Discordant for BMI

BACKGROUND/OBJECTIVES

Obesity impairs intestinal glucose uptake (GU) (intestinal uptake of circulating glucose from blood) and alters gut microbiome. Exercise improves intestinal insulin-stimulated GU and alters microbiome. Genetics influence the risk of obesity and gut microbiome. However, the role of genetics on the effects of exercise on intestinal GU and microbiome is unclear.

METHODS

Twelve monozygotic twin pairs discordant for BMI (age 40.4 ± 4.5 years, BMI heavier 36.7 ± 6.0, leaner 29.1 ± 5.7, 8 female pairs) performed a six-month-long training intervention. Small intestine and colonic insulin-stimulated GU was studied using [18F]FDG-PET and microbiota from fecal samples with 16s rRNA.

RESULTS

Ten pairs completed the intervention. At baseline, heavier twins had lower small intestine and colonic GU (p < 0.05). Response to exercise differed between twins (p = 0.05), with leaner twins increasing colonic GU. Alpha and beta diversity did not differ at baseline. During the intervention, beta diversity changed significantly, most prominently at the mid-point (p < 0.01). Beta diversity changes were only significant in the leaner twins when the twin groups were analyzed separately. Exercise was associated with changes at the phylum level, mainly at the mid-point (pFDR < 0.05); at the genus level, several microbes increased, such as Lactobacillus and Sellimonas (pFDR < 0.05). In type 1 analyses, many genera changes were associated with exercise, and fewer, such as Lactobacillus, were also associated with dietary sugar consumption (p < 0.05).

CONCLUSIONS

Obesity impairs insulin-stimulated intestinal GU independent of genetics. Though both twin groups exhibited some microbiota changes, most changes in insulin-stimulated colon GU and microbiota were significant in the leaner twins.

Expression of the C-allele of intronic rs8192675 in SLC2A2 is associated with improved glucose response to metformin

Glucose is a critical nutrient for energy metabolism. The SLC2A2 gene is essential for glucose sensing and homeostasis, as it encodes the facilitated glucose transporter GLUT2. During diabetes treatment, the C-allele of rs8192675 in SLC2A2 has been found to regulate the action of metformin and reduce the absolute level of HbA1c more effectively than the T-allele. In this study, stable HEK293T cell lines carrying the CC, CT, and TT genotypes of rs8192675 in SLC2A2 were generated using CRISPR/Cas9-mediated genome editing. GLUT2 mRNA and protein levels were elevated in cell clones with the TC genotype compared to those with the CC genotype but were reduced relative to the TT genotype. Additionally, high concentrations of glucose or fructose induced more GLUT2 protein production in CT-genotype cells than that induced in CC-genotype cells, yet less than that induced in TT-genotype cells. Metformin induced a greater increase in GLUT2 expression and a smaller increase in activated AMPK protein expression in CC-genotype cells than those induced in TT-genotype cells, resulting in a remarkable reduction in activated mTOR and S6 levels. This study directly supports the biological mechanism linking the C-allele of rs8192675 with improved treatment outcomes in metformin therapy for diabetes.

Intestinal fructose transporters GLUT5 and GLUT2 in children and adolescents with obesity and metabolic disorders

PURPOSE

The excessive fructose intake including high-fructose corn syrup (HFCS) may be responsible for increase of obesity occurrence. This study was designed to find potential differences in duodenal fructose transporters on mRNA and protein levels between obese and normal weight children and adolescents.

MATERIALS/METHODS

We performed a cross-sectional study on a group of 106 hospitalized patients aged 12 to 18. Glucose transporter 2 (GLUT2) and glucose transporter 5 (GLUT5) mRNA as well as protein levels (ELISA and Western blot methods) were assessed in duodenal mucosa biopsies of the patients categorized as obese or normal weight. Additionally, the expression of the aforementioned transporters was analyzed in patients based on the presence of insulin resistance (IR) and metabolic syndrome (MS).

RESULTS

In children with obesity, increased duodenal protein levels of GLUT5 (Relative protein GLUT5 expression/ACTB) (0.027 ​± ​0.009 vs. 0.011 ​± ​0.006, p ​< ​0.05) but not GLUT2 as compared with the normal weight group, were revealed. No significant differences in duodenal relative GLUT2 and GLUT5 genes expression between the studied groups were found. There was no relationship between the presence of IR or MS and intestinal mRNA GLUT2 and GLUT5 as well as GLUT2 protein expression.

CONCLUSION

The upregulation of the duodenal GLUT5 may contribute to obesity occurrence in children and adolescents.

Sugar assimilation underlying dietary evolution of Neotropical bats

Dietary specializations in animals lead to adaptations in morphology, anatomy and physiology. Neotropical bats, with their high taxonomic and trophic diversity, offer a unique perspective on diet-driven evolutionary adaptations. Here we assess the metabolic response to different dietary sugars among wild-caught bats. We found that insectivorous bats had a pronounced metabolic response to trehalose, whereas bats with nectar and fruit-based diets showed significantly higher blood glucose levels in response to glucose and sucrose, reaching levels over 750 mg dl-1. The genomic analysis of 22 focal species and two outgroup species identified positive selection for the digestive enzyme trehalase in insect eaters, while sucrase-isomaltase showed selection in lineages with omnivorous and nectar diets. By examining anatomical and cellular features of the small intestine, we discovered that dietary sugar proportion strongly impacted numerous digestive traits, providing valuable insight into the physiological implications of molecular adaptations. Using hybridization chain reaction (HCR) RNA fluorescence in situ hybridization, we observed unusually high expression in the glucose transporter gene Slc2a2 in nectar bats, while fruit bats increased levels of Slc5a1 and Slc2a5. Overall, this study highlights the intricate interplay between molecular, morphological and physiological aspects of diet evolution, offering new insights into the mechanisms of dietary diversification and sugar assimilation in mammals.

Manipulation of Post-Prandial Hyperglycaemia in Type 2 Diabetes: An Update for Practitioners

This review paper explores post-prandial glycemia in type 2 diabetes. Post-prandial glycemia is defined as the period of blood glucose excursion from immediately after the ingestion of food or drink to 4 to 6 hours after the end of the meal. Post-prandial hyperglycemia is an independent risk factor for cardiovascular disease with glucose "excursions" being more strongly associated with markers of oxidative stress than the fasting or pre-prandial glucose level. High blood glucose is a major promoter of enhanced free radical production and is associated with the onset and progression of type 2 diabetes. Oxidative stress impairs insulin action creating a vicious cycle where repeated post-prandial glucose spikes are key drivers in the pathogenesis of the vascular complications of type 2 diabetes, both microvascular and macrovascular. Some authors suggest post-prandial hyperglycemia is the major cause of death in type 2 diabetes. Proper management of post-prandial hyperglycemia could yield up to a 35% cut in overall cardiovascular events, and a 64% cut in myocardial infarction. The benefits of managing post-prandial hyperglycemia are similar in magnitude to those seen in type 2 diabetes patients receiving secondary prevention with statins - prevention which today is regarded as fundamental by all practitioners. Given all the evidence surrounding the impact of post-prandial glycemia on overall outcome, it is imperative that any considered strategy for the management of type 2 diabetes should include optimum dietary, pharma, and lifestyle interventions that address glucose excursion. Achieving a low post-prandial glucose response is key to prevention and progression of type 2 diabetes and cardiometabolic diseases. Further, such therapeutic interventions should be sustainable and must benefit patients in the short and long term with the minimum of intrusion and side effects. This paper reviews the current literature around dietary manipulation of post-prandial hyperglycemia, including novel approaches. A great deal of further work is required to optimize and standardize the dietary management of post-prandial glycemia in type 2 diabetes, including consideration of novel approaches that show great promise.

Understanding the action mechanisms of metformin in the gastrointestinal tract

Metformin is the initial medication recommended for the treatment of type 2 diabetes mellitus (T2DM). In addition to diabetes treatment, the function of metformin also can be anti-aging, antiviral, and anti-inflammatory. Nevertheless, further exploration is required to fully understand its mode of operation. Historically, the liver has been acknowledged as the main location where metformin reduces glucose levels, however, there is increasing evidence suggesting that the gastrointestinal tract also plays a significant role in its action. In the gastrointestinal tract, metformin effects glucose uptake and absorption, increases glucagon-like peptide-1 (GLP-1) secretion, alters the composition and structure of the gut microbiota, and modulates the immune response. However, the side effects of it cannot be ignored such as gastrointestinal distress in patients. This review outlines the impact of metformin on the digestive system and explores potential explanations for variations in metformin effectiveness and adverse effects like gastrointestinal discomfort.

Intestinal glucose excretion: A potential mechanism for glycemic control

The gut has been increasingly recognized in recent years as a pivotal organ in the maintenance of glucose homeostasis. Specifically, the profound and enduring improvement in glucose metabolism achieved through metabolic surgery to modify the anatomy of the gut has prompted scholars to acknowledge that the most effective strategy for treating type 2 diabetes mellitus (T2DM) involves the gut. The mechanisms underlying the regulation of glucose metabolism by the gut encompass gut hormones, bile acids, intestinal gluconeogenesis, gut microbiota, and signaling interactions between the gut and other organs (liver, brain, adipose, etc.). Recent studies have also revealed a novel phenomenon of glucose lowering through the gut: metabolic surgery and metformin promote the excretion of glucose from the circulation into the intestinal lumen by enterocytes. However, there is still limited understanding regarding the underlying mechanisms of intestinal glucose excretion and its contribution to glycemic control. This article reviews current research on intestinal glucose excretion while focusing on its role in T2DM management as well as potential mechanisms.

Transcellular Barriers to Glucose Delivery in the Body

Glucose is the universal fuel of most mammalian cells, and it is largely replenished through dietary intake. Glucose availability to tissues is paramount for the maintenance of homeostatic energetics and, hence, supply should match demand by the consuming organs. In its journey through the body, glucose encounters cellular barriers for transit at the levels of the absorbing intestinal epithelial wall, the renal epithelium mediating glucose reabsorption, and the tight capillary endothelia (especially in the brain). Glucose transiting through these cellular barriers must escape degradation to ensure optimal glucose delivery to the bloodstream or tissues. The liver, which stores glycogen and generates glucose de novo, must similarly be able to release it intact to the circulation. We present the most up-to-date knowledge on glucose handling by the gut, liver, brain endothelium, and kidney, and discuss underlying molecular mechanisms and open questions. Diseases associated with defects in glucose delivery and homeostasis are also briefly addressed. We propose that the universal problem of sparing glucose from catabolism in favor of translocation across the barriers posed by epithelia and endothelia is resolved through common mechanisms involving glucose transfer to the endoplasmic reticulum, from where glucose exits the cells via unconventional cellular mechanisms.

Association between higher duodenal levels of the fructose carrier glucose transporter-5 and nonalcoholic fatty liver disease and liver fibrosis

BACKGROUND

An increased dietary fructose intake has been shown to exert several detrimental metabolic effects and contribute to the pathogenesis of nonalcoholic fatty liver disease (NAFLD). An augmented intestinal abundance of the fructose carriers glucose transporter-5 (GLUT-5) and glucose transporter-2 (GLUT-2) has been found in subjects with obesity and type 2 diabetes. Herein, we investigated whether elevated intestinal levels of GLUT-5 and GLUT-2, resulting in a higher dietary fructose uptake, are associated with NAFLD and its severity.

METHODS

GLUT-5 and GLUT-2 protein levels were assessed on duodenal mucosa biopsies of 31 subjects divided into 2 groups based on ultrasound-defined NAFLD presence who underwent an upper gastrointestinal endoscopy.

RESULTS

Individuals with NAFLD exhibited increased duodenal GLUT-5 protein levels in comparison to those without NAFLD, independently of demographic and anthropometric confounders. Conversely, no difference in duodenal GLUT-2 abundance was observed amongst the two groups. Univariate correlation analyses showed that GLUT-5 protein levels were positively related with body mass index, waist circumference, fasting and 2 h post-load insulin concentrations, and insulin resistance (IR) degree estimated by homeostatic model assessment of IR (r = 0.44; p = 0.02) and liver IR (r = 0.46; p = 0.03) indexes. Furthermore, a positive relationship was observed between duodenal GLUT-5 abundance and serum uric acid concentrations (r = 0.40; p = 0.05), a product of fructose metabolism implicated in NAFLD progression. Importantly, duodenal levels of GLUT-5 were positively associated with liver fibrosis risk estimated by NAFLD fibrosis score.

CONCLUSION

Increased duodenal GLUT-5 levels are associated with NAFLD and liver fibrosis. Inhibition of intestinal GLUT-5-mediated fructose uptake may represent a strategy for prevention and treatment of NAFLD.

Human intestinal organoids: Modeling gastrointestinal physiology and immunopathology - current applications and limitations

Human intestinal organoids are an ideal model system for studying gastrointestinal physiology and immunopathology. Altered physiology and mucosal immune response are hallmarks of numerous intestinal functional and inflammatory diseases, including inflammatory bowel disease (IBD), coeliac disease, irritable bowel syndrome (IBS), and obesity. These conditions impact the normal epithelial functions of the intestine, such as absorption, barrier function, secretion, and host-microbiome communication. They are accompanied by characteristic intestinal symptoms and have significant societal, economic, and healthcare burdens. To develop new treatment options, cutting-edge research is required to investigate their etiology and pathology. Human intestinal organoids derived from patient tissue recapitulate the key physiological and immunopathological aspects of these conditions, providing a promising platform for elucidating disease mechanisms. This review will summarize recent reports on patient-derived human small intestinal and colonic organoids and highlight how these models have been used to study intestinal epithelial functions in the context of inflammation, altered physiology, and immune response. Furthermore, it will elaborate on the various organoid systems in use and the techniques/assays currently available to study epithelial functions. Finally, it will conclude by discussing the limitations and future perspectives of organoid technology.

Antihyperglycemic effects of Lysiphyllum strychnifolium leaf extract in vitro and in vivo

CONTEXT

Lysiphyllum strychnifolium (Craib) A. Schmitz (LS) (Fabaceae) has traditionally been used to treat diabetes mellitus.

OBJECTIVE

This study demonstrates the antidiabetic and antioxidant effects of aqueous extract of LS leaves in vivo and in vitro.

MATERIALS AND METHODS

The effects of aqueous LS leaf extract on glucose uptake, sodium-dependent glucose cotransporter 1 (SGLT1) and glucose transporter 2 (GLUT2) mRNA expression in Caco-2 cells, α-glucosidase, and lipid peroxidation were evaluated in vitro. The antidiabetic effects were evaluated using an oral glucose tolerance test (OGTT) and a 28-day consecutive administration to streptozotocin (STZ)-nicotinamide (NA)-induced type 2 diabetic mice.

RESULTS

The extract significantly inhibited glucose uptake (IC₅₀: 236.2 ± 36.05 µg/mL) and downregulated SGLT1 and GLUT2 mRNA expression by approximately 90% in Caco-2 cells. Furthermore, it non-competitively inhibited α-glucosidase in a concentration-dependent manner with the IC₅₀ and K_i of 6.52 ± 0.42 and 1.32 µg/mL, respectively. The extract at 1000 mg/kg significantly reduced fasting blood glucose levels in both the OGTT and 28-day consecutive administration models as compared with untreated STZ-NA-induced diabetic mice (p < 0.05). Significant improvements of serum insulin, homeostasis model assessment of insulin resistance (HOMA-IR), and GLUT4 levels were observed. Furthermore, the extract markedly decreased oxidative stress markers by 37-53% reduction of superoxide dismutase 1 (SOD1) in muscle and malondialdehyde (MDA) in muscle and pancreas, which correlated with the reduction of MDA production in vitro (IC₅₀: 24.80 ± 7.24 µg/mL).

CONCLUSION

The LS extract has potent antihyperglycemic activity to be used as alternative medicine to treat diabetes mellitus.

Metformin: update on mechanisms of action and repurposing potential

Currently, metformin is the first-line medication to treat type 2 diabetes mellitus (T2DM) in most guidelines and is used daily by >200 million patients. Surprisingly, the mechanisms underlying its therapeutic action are complex and are still not fully understood. Early evidence highlighted the liver as the major organ involved in the effect of metformin on reducing blood levels of glucose. However, increasing evidence points towards other sites of action that might also have an important role, including the gastrointestinal tract, the gut microbial communities and the tissue-resident immune cells. At the molecular level, it seems that the mechanisms of action vary depending on the dose of metformin used and duration of treatment. Initial studies have shown that metformin targets hepatic mitochondria; however, the identification of a novel target at low concentrations of metformin at the lysosome surface might reveal a new mechanism of action. Based on the efficacy and safety records in T2DM, attention has been given to the repurposing of metformin as part of adjunct therapy for the treatment of cancer, age-related diseases, inflammatory diseases and COVID-19. In this Review, we highlight the latest advances in our understanding of the mechanisms of action of metformin and discuss potential emerging novel therapeutic uses.

Strain differences in the drug transport capacity of intestinal glucose transporters in Sprague-Dawley versus Wistar rats, C57BL/6J versus Kunming mice

Designing oral drug delivery systems using intestinal glucose transporters (IGTs) may be one of the strategies for improving oral bioavailability of drugs. However, little is known about the biological factors affecting the drug transport capacity of IGTs. Gastrodin is a sedative drug with a structure very similar to glucose. It is a highly water-soluble phenolic glucoside. It can hardly enter the intestine through simple diffusion but exhibits good oral bioavailability of over 80%. We confirmed that gastrodin is absorbed via the intestinal glucose transport pathway. It has the highest oral bioavailability among the reported glycosides' active ingredients through this pathway. Thus, gastrodin is the most selective drug substrate of IGTs and can be used to evaluate the drug transport capacity of IGTs. Obviously, strain is one of the main biological factors affecting drug absorption. This study firstly compared the drug transport capacity of IGTs between SD rats and Wistar rats and between C57 mice and KM mice by pharmacokinetic experiments and single-pass intestinal perfusion experiments of gastrodin. Then, the sodium-dependent glucose transporter type 1 (SGLT1) and sodium-independent glucose transporters type 2 (GLUT2) in the duodenum, jejunum, ileum and colon of these animals were quantified using RT-qPCR and Western blot. The results showed that the oral bioavailability of gastrodin in Wistar rats was significantly higher than in SD rats and significantly higher in KM mice than in C57 mice. Gastrodin absorption significantly differed among different intestinal segments in SD rats, C57 mice and KM mice, except Wistar rats. RT-qPCR and Western blot demonstrated that the intestinal expression distribution of SGLT1 and GLUT2 in SD rats and C57 mice was duodenum ≈ jejunum > ileum > colon. SGLT1 expression did not differ among different intestinal segments in KM mice, whereas the intestinal expression distribution of GLUT2 was duodenum ≈ jejunum ≈ ileum > colon. However, the expression of SGLT1 and GLUT2 did not differ among different intestinal segments in Wistar rats. It was reported that the intestinal expression distribution of SGLT1 and GLUT2 in humans is duodenum > jejunum > ileum > colon. Hence, the intestinal expression distribution of SGLT1 and GLUT2 of SD rats and C57 mice was more similar to that in humans. In conclusion, the drug transport capacity of IGTs differs in different strains of rats and mice. SD rats and C57 mice are more suitable for evaluating the pharmacokinetics of glycosides' active ingredients absorbed via the intestinal glucose transport pathway.

Active glucose transport varies by small intestinal region and oestrous cycle stage in mice

NEW FINDINGS

What is the central question of this study? Body mass and food intake change during the female ovarian cycle: does glucose transport by the small intestine also vary? What is the main finding and its importance? We have optimised Ussing chamber methodology to measure region-specific active glucose transport in the small intestine of adult C57BL/6 mice. Our study provides the first evidence that jejunal active glucose transport changes during the oestrous cycle in mice, and is higher at pro-oestrus than oestrus. These results demonstrate adaptation in active glucose uptake, concurrent with previously reported changes in food intake.

ABSTRACT

Food intake changes across the ovarian cycle in rodents and humans, with a nadir during the pre-ovulatory phase and a peak during the luteal phase. However, it is unknown whether the rate of intestinal glucose absorption also changes. We therefore mounted small intestinal sections from C57BL/6 female mice (8-9 weeks old) in Ussing chambers and measured active ex vivo glucose transport via the change in short-circuit current (∆Isc ) induced by glucose. Tissue viability was confirmed by a positive ∆Isc response to 100 µM carbachol following each experiment. Active glucose transport, assessed after addition of 5, 10, 25 or 45 mM d-glucose to the mucosal chamber, was highest at 45 mM glucose in the distal jejunum compared to duodenum and ileum (P < 0.01). Incubation with the sodium-glucose cotransporter 1 (SGLT1) inhibitor phlorizin reduced active glucose transport in a dose-dependent manner in all regions (P < 0.01). Active glucose uptake induced by addition of 45 mM glucose to the mucosal chamber in the absence or presence of phlorizin was assessed in jejunum at each oestrous cycle stage (n = 9-10 mice per stage). Overall, active glucose uptake was lower at oestrus compared to pro-oestrus (P = 0.025). This study establishes an ex vivo method to measure region-specific glucose transport in the mouse small intestine. Our results provide the first direct evidence that SGLT1-mediated glucose transport in the jejunum changes across the ovarian cycle. The mechanisms underlying these adaptations in nutrient absorption remain to be elucidated.

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

OBJECTIVE

Prior evidence indicates that individuals with obesity have an accelerated intestinal glucose absorption. This cross-sectional study evaluated whether those with overweight or obesity display higher duodenal protein levels of the glucose carriers sodium-glucose cotransporter 1 (SGLT-1), glucose transporter 2 (GLUT-2), and glucose transporter 5 (GLUT-5).

METHODS

SGLT-1, GLUT-2, and GLUT-5 protein levels were assessed on duodenal mucosa biopsies of 52 individuals without diabetes categorized on the basis of their BMI as lean, with overweight, or with obesity.

RESULTS

Individuals with overweight and obesity exhibited progressively increased duodenal protein levels of SGLT-1 and GLUT-5 as compared with the lean group. Conversely, no differences in duodenal GLUT-2 abundance were found among the three groups. Univariate analysis showed that SGLT-1 and GLUT-5 protein levels were positively correlated with BMI, waist circumference, 1-hour post-load glucose, fasting and post-load insulin, and insulin secretion and resistance levels. Furthermore, a positive relationship was detected between intestinal GLUT-5 levels and serum uric acid concentrations, a product of fructose metabolism known to be involved in the pathogenesis of obesity and its complications.

CONCLUSIONS

Individuals with overweight and obesity display enhanced duodenal SGLT-1 and GLUT-5 abundance, which correlates with increased postprandial glucose concentrations, insulin resistance, and hyperinsulinemia.

A blast from the past: To tame time with metformin

The strong evidence of metformin use in subjects affected by type 2 diabetes (T2DM) on health outcomes, together with data from pre-clinical studies, has led the gerontological research to study the therapeutic potential of such a drug as a slow-aging strategy. However, despite clinical use for over fifty years as an anti-diabetic drug, the mechanisms of action beyond glycemic control remain unclear. In this review, we have deeply examined the literature, doing a narrative review from the metformin story, through mechanisms of action to slow down aging potential, from lower organisms to humans. Based on the available evidence, we conclude that metformin, as shown in lower organisms and mice, may be effective in humans' longevity. A complete analysis and follow-up of ongoing clinical trials may provide more definitive answers as to whether metformin should be promoted beyond its use to treat T2DM as a drug that enhances both healthspan and lifespan.

Glucose Uptake and Oxidative Stress in Caco-2 Cells: Health Benefits from Posidonia oceanica (L.) Delile

Posidonia oceanica (L.) Delile is an endemic Mediterranean marine plant of extreme ecological importance. Previous in vitro and in vivo studies have demonstrated the potential antidiabetic properties of P. oceanica leaf extract. Intestinal glucose transporters play a key role in glucose homeostasis and represent novel targets for the management of diabetes. In this study, the ability of a hydroalcoholic P. oceanica leaf extract (POE) to modulate intestinal glucose transporters was investigated using Caco-2 cells as a model of an intestinal barrier. The incubation of cells with POE significantly decreased glucose uptake by decreasing the GLUT2 glucose transporter levels. Moreover, POE had a positive effect on the barrier integrity by increasing the Zonulin-1 levels. A protective effect exerted by POE against oxidative stress induced by chronic exposure to high glucose concentrations or tert-butyl hydroperoxide was also demonstrated. This study highlights for the first time the effect of POE on glucose transport, intestinal barrier integrity, and its protective antioxidant effect in Caco-2 cells. These findings suggest that the P. oceanica phytocomplex may have a positive impact by preventing the intestinal cell dysfunction involved in the development of inflammation-related disease associated with oxidative stress.

The effect of additional acarbose on metformin-associated artificially high 18F-Fluorodeoxyglucose uptake in positron emission tomography/computed tomography

AIM

Metformin causes diffuse and intense fluorodeoxyglucose (FDG) uptake more frequently in the colon and less frequently in the small intestine. In this study, we aimed to investigate the effect of simultaneous use of acarbose and metformin on FDG uptake in positron emission tomography/computed tomography (PET/CT), which has not been investigated previously.

METHODS

Totally 145 patients with a median age of 65 years (range: 18-80 years), who underwent FDG PET/CT in the Department of Nuclear Medicine of Erciyes University Medical School between 2018 and 2021, were involved in the study. The patients undergoing PET/CT were categorized as metformin plus acarbose users (group MA), metformin users (group M), and control subjects without diabetes (group C). The maximum and mean standard uptake values (SUVmax and SUVmean) of FDG uptake of the all intestine segments were measured separately.

RESULTS

The number of participants in each group was 35, 51 and 59 in group MA, group M and group C, respectively. The FDG uptake of all intestine was significantly higher in group MA and group M than in group C. The FDG uptake of ascending, transverse, descending, and sigmoid colon was significantly lower in group MA than in group M. The FDG uptake of the small intestine was not different between group MA and group M. The FDG uptake of the rectum was lower in group MA than group M and it was significant for SUVmean, but not significant for SUVmax.

CONCLUSION

The addition of acarbose to metformin therapy decreased SUV and artificially high FDG uptake in the colon and may be an alternative recommendation to discontinuing metformin in patients going to PET/CT imaging.

Glucose Stimulates Gut Motility in Fasted and Fed Conditions: Potential Involvement of a Nitric Oxide Pathway

(1) Background: Type 2 diabetes (T2D) is associated with a duodenal hypermotility in postprandial conditions that favors hyperglycemia and insulin resistance via the gut-brain axis. Enterosynes, molecules produced within the gut with effects on the enteric nervous system, have been recently discovered and pointed to as potential key modulators of the glycemia. Indeed, targeting the enteric nervous system that controls gut motility is now considered as an innovative therapeutic way in T2D to limit intestinal glucose absorption and restore the gut-brain axis to improve insulin sensitivity. So far, little is known about the role of glucose on duodenal contraction in fasted and fed states in normal and diabetic conditions. The aim of the present study was thus to investigate these effects in adult mice. (2) Methods: Gene-expression level of glucose transporters (SGLT-1 and GLUT2) were quantified in the duodenum and jejunum of normal and diabetic mice fed with an HFD. The effect of glucose at different concentrations on duodenal and jejunal motility was studied ex vivo using an isotonic sensor in fasted and fed conditions in both normal chow and HFD mice. (3) Results: Both SGLT1 and GLUT2 expressions were increased in the duodenum (47 and 300%, respectively) and jejunum (75% for GLUT2) of T2D mice. We observed that glucose stimulates intestinal motility in fasted (200%) and fed (400%) control mice via GLUT2 by decreasing enteric nitric oxide release (by 600%), a neurotransmitter that inhibits gut contractions. This effect was not observed in diabetic mice, suggesting that glucose sensing and mechanosensing are altered during T2D. (4) Conclusions: Glucose acts as an enterosyne to control intestinal motility and glucose absorption through the enteric nervous system. Our data demonstrate that GLUT2 and a reduction of NO production could both be involved in this stimulatory contracting effect.

Jianpi Qinghua Fomula alleviates insulin resistance via restraining of MAPK pathway to suppress inflammation of the small intestine in DIO mice

Background

Jianpi Qinghua Fomula (JPQHF), a clinically proven prescription,has been applied to cure insulin resistance(IR) and type 2 diabetes (T2DM) for more than 20 years. Here, we will unravel the underlying molecular mechanisms relevant to the therapeutic actions of JPQHF.

Methods

High-fat(HF)diet-induced obesity(DIO)mouse were established in our research, along with insulin resistance. After the administration of JPQHF 5 or 6 weeks, the parameters of the glucose and lipid metabolism were measured. Flow cytometry and Luminex were utilized to assess the inflammation in small intestine,whilst Western blot was used to determine the relative expression levels of the MAPK pathway-related proteins. The glucose and lipid transporter of small intestine was assessed by immunofluorescence and ELISA, and the expression of insulin signaling pathway was detected by Western blot.

Results

The metabolic phenotypes of DIO mouse were ameliorated after 6-week oral administration of JPQHF; Meanwhile,JPQHF downregulated levels of IL-1β,IL-6, TNF-α and IFN-γ but upregulated the ratio of M2/M1 macrophages in the small intestine. The elevated expressions of p-P38 MAPK/P38 MAPK、p-JNK/JNK and p-ERK1/2/ERK1/2 were reversed by JPQHF. Moreover, JPQHF enhanced expression of PI3K,p-AKT/AKT, p-IRS1/ IRS1, p-IRS2/ IRS2 and apoB48 in small intestine, and facilitated the translocation of GLUT2 to the basal side of small intestine epithelial cells.

Conclusion

JPQHF alleviates insulin resistance in DIO mice, and this effect may be associated with its restraining of inflammation of small intestine via attenuating MAPK pathway, and then diminishes small intestinal glucose and lipid absorption.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-022-03595-0.

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

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

Developmental alterations of intestinal SGLT1 and GLUT2 induced by early weaning coincides with persistent low-grade metabolic inflammation in female pigs

Early-life adversity (ELA) is linked with the increased risk for inflammatory and metabolic diseases in later life, but the mechanisms remain poorly understood. Intestinal epithelial glucose transporters sodium-glucose-linked transporter 1 (SGLT1) and glucose transporter 2 (GLUT2) are the major route for intestinal glucose uptake but have also received increased attention as modulators of inflammatory and metabolic diseases. Here, we tested the hypothesis that early weaning (EW) in pigs, an established model of ELA, alters the development of epithelial glucose transporters and coincides with elevated markers of metabolic inflammation. The jejunum and ileum of 90-day-old pigs previously exposed to EW (16 days wean age), exhibited reduced SGLT1 activity (by ∼ 30%, P < 0.05) than late weaned (LW, 28 days wean age) controls. In contrast, GLUT2-mediated glucose transport was increased (P = 0.003) in EW pigs than in LW pigs. Reciprocal changes in SGLT1- and GLUT2-mediated transport coincided with transporter protein expression in the intestinal brush-border membranes (BBMs) that were observed at 90 days and 150 days of age. Ileal SGLT1-mediated glucose transport and BBM expression were inhibited by the β-adrenergic receptor (βAR) blocker propranolol in EW and LW pigs. In contrast, propranolol enhanced ileal GLUT2-mediated glucose transport (P = 0.015) and brush-border membrane vesicle (BBMV) abundance (P = 0.035) in LW pigs, but not in EW pigs. Early-weaned pigs exhibited chronically elevated blood glucose and C-reactive protein (CRP) levels, and adipocyte hypertrophy and upregulated adipogenesis-related gene expression in visceral adipose tissue. Altered development of intestinal glucose transporters by EW could underlie the increased risk for later life inflammatory and metabolic diseases.NEW & NOTEWORTHY These studies reveal that early-life adversity in the form of early weaning in pigs causes a developmental shift in intestinal glucose transport from SGLT1 toward GLUT2-mediated transport. Early weaning also induced markers of metabolic inflammation including persistent elevations in blood glucose and the inflammatory marker CRP, along with increased visceral adiposity. Altered intestinal glucose transport might contribute to increased risk for inflammatory and metabolic diseases associated with early-life adversity.

Regulation of Glucose Insulinotropic Peptide and Intestinal Glucose Transporters in the Diet-Induced Obese Mouse

Our recent studies have shown that glucose-dependent insulinotropic polypeptide (GIP), but not glucagon-like peptide 1 (GLP-1), augments Na-glucose transporter 1- (SGLT1-) mediated glucose absorption in mouse jejunum. Na-dependent glucose absorption sharply rose and peaked in 3 months of high-fat (i.e., obese) compared to normal (i.e., normal weight) diet fed animals. Previous studies have shown that GIP-augmented SGLT1 and PEPT1 (peptide transporter 1) are regulated by protein kinase A (PKA) signaling in mouse jejunum. Additional studies have indicated that cAMP and PI3 kinase signaling augment PEPT1 through EPAC and AKT activation pathways, respectively, through increased apical PEPT1 trafficking in intestinal epithelial cells. However, little is known about how the signaling glucose transport paradigm is altered over a long period. Early on, increased glucose absorption occurs through SGLT1, but as the obesity and diabetes progress, there is a dramatic shift towards a Na-independent mechanism. Surprisingly, at the peak of glucose absorption during the fifth month of the progression of obesity, the SGLT1 activity was severely depressed, while a Na-independent glucose absorptive process begins to appear. Since glucose transporter 2 (GLUT2) is expressed on the apical membrane of the small intestine in obese patients and animal models of obesity, it was hypothesized to be the new more efficient route. Western blot analyses and biotinylation of the apical membrane revealed that the GIP expression increases in the obese animals and its trafficking to the apical membrane increases with the GIP treatment.

Pathogenic Mechanism of Autoimmune Diabetes Mellitus in Humans: Potential Role of Streptozotocin-Induced Selective Autoimmunity against Human Islet β-Cells

Human type 1 diabetes mellitus is a chronic autoimmune disease characterized by the selective loss of insulin-producing β-cells in pancreatic islets of genetically susceptible individuals. In this communication, a new hypothesis is postulated which is based on the observations that streptozotocin (STZ), a chemically reactive and cytotoxic compound produced by certain gram-positive bacteria, can be preferentially taken up into islet β-cells and induce cytotoxicity and autoimmunity. It is hypothesized that humans might be occasionally exposed to STZ through opportunistic infections with the STZ-producing bacteria and/or through ingestion of certain food products that contain STZ. In addition, the potential presence of the STZ-producing bacteria in the gut microbiota of some individuals might be another source of long-term STZ exposure. Because of the high chemical reactivity of STZ and its breakdown products, these chemicals can covalently modify certain cellular macromolecules (e.g., DNA and proteins), and the covalently modified cellular components would serve as new antigens, potentially capable of inducing both humoral and cellular autoimmune responses in the islets of certain individuals. In addition to STZ exposure, the eventual development of autoimmunity against STZ-exposed islet β-cells also depends critically on the genetic predisposition of the susceptible individuals plus the opportunistic presence of a conducive, strong environmental trigger, which often is presented as severe febrile viral infections subsequently inducing strong aberrant reactions of the body’s immune system. The proposed pathogenic hypothesis is supported by a considerable body of direct and indirect evidence from laboratory animal studies and clinical observations. Certainly, more experimental and clinical studies are needed to carefully further examine each of the key components of the proposed pathogenic hypothesis.

An Exploratory Study of the Role of Dietary Proteins in the Regulation of Intestinal Glucose Absorption

Several studies have demonstrated that high protein diets improve glucose homeostasis. Nevertheless, the mechanisms underlying this effect remain elusive. This exploratory study aims to screen and compare the acute effects of dietary proteins from different sources on intestinal glucose absorption. Six dietary proteins from various sources were thus selected and digested thanks to the INFOGEST static gastrointestinal digestion protocol. The digested proteins were able to decrease intestinal glucose absorption in vitro and ex vivo. Moreover, acute ingestion of casein and fish gelatin led to improved glucose tolerance in Wistar rats without significant effect on insulin secretion. In parallel, GLUT2 mRNA expression in enterocytes was decreased following short-term incubation with some of the digested proteins. These results strengthen the evidence that digested protein-derived peptides and amino acids are key regulators of glucose homeostasis and highlight their role in intestinal glucose absorption.

Effect of Type 2 Diabetes and Impaired Glucose Tolerance on Digestive Enzymes and Glucose Absorption in the Small Intestine of Young Rats

The reactions of intestinal functional parameters to type 2 diabetes at a young age remain unclear. The study aimed to assess changes in the activity of intestinal enzymes, glucose absorption, transporter content (SGLT1, GLUT2) and intestinal structure in young Wistar rats with type 2 diabetes (T2D) and impaired glucose tolerance (IGT). To induce these conditions in the T2D (n = 4) and IGT (n = 6) rats, we used a high-fat diet and a low dose of streptozotocin. Rats fed a high-fat diet (HFD) (n = 6) or a standard diet (SCD) (n = 6) were used as controls. The results showed that in T2D rats, the ability of the small intestine to absorb glucose was higher in comparison to HFD rats (p < 0.05). This was accompanied by a tendency towards an increase in the number of enterocytes on the villi of the small intestine in the absence of changes in the content of SGLT1 and GLUT2 in the brush border membrane of the enterocytes. T2D rats also showed lower maltase and alkaline phosphatase (AP) activity in the jejunal mucosa compared to the IGT rats (p < 0.05) and lower AP activity in the colon contents compared to the HFD (p < 0.05) and IGT (p < 0.05) rats. Thus, this study provides insights into the adaptation of the functional and structural parameters of the small intestine in the development of type 2 diabetes and impaired glucose tolerance in young representatives.

Non-Centrifugal Sugar (NCS) and Health: A Review on Functional Components and Health Benefits

Non-centrifugal sugar (NCS) is the scientific term the Food and Agriculture Organization (FAO) uses to define a solid product, produced by sugarcane juice evaporation, which is unrefined or minimally refined. NCS is referred to in various names globally, the most significant ones are whole cane sugar, panela (Latin America), jaggery (India) and kokuto (Japan). NCS contains minerals, bioactive compounds, flavonoids and phenolic acids, which have therapeutic potentials from time immemorial. Even though the bioactive property is dependent on the composition, which relies mainly on the agronomic conditions and production process, NCS possesses antioxidant and anti-inflammatory properties. Hence, substituting the consumption of refined sugar with NCS might be helpful in the control of chronic diseases generally connected to oxidative stress and inflammation. Experimental facts from in vitro and in vivo models have proven that NCS plays an essential role in weight management, maintaining insulin sensitivity and preventing neurodegenerative diseases. NCS has also shown hypoglycemic and hypolipidemic effects. This review aims to synopsize the recent literature pertaining to the benefits of NCS in human health. The NCS can be considered a nutraceutical and functional food. However, detailed and regulated studies are important to enhance the beneficial effects in human and animal interventions.

Berberine Decreases Intestinal GLUT2 Translocation and Reduces Intestinal Glucose Absorption in Mice

Postprandial hyperglycemia is an important causative factor of type 2 diabetes mellitus, and permanent localization of intestinal GLUT2 in the brush border membrane is an important reason of postprandial hyperglycemia. Berberine, a small molecule derived from Coptidis rhizome, has been found to be potent at lowering blood glucose, but how berberine lowers postprandial blood glucose is still elusive. Here, we investigated the effect of berberine on intestinal glucose transporter 2 (GLUT2) translocation and intestinal glucose absorption in type 2 diabetes mouse model. Type 2 diabetes was induced by feeding of a high-fat diet and injection of streptozotocin and diabetic mice were treated with berberine for 6 weeks. The effects of berberine on intestinal glucose transport and GLUT2 translocation were accessed in isolated intestines and intestinal epithelial cells (IEC-6), respectively. We found that berberine treatment improved glucose tolerance and systemic insulin sensitivity in diabetic mice. Furthermore, berberine decreased intestinal glucose transport and inhibited GLUT2 translocation from cytoplasm to brush border membrane in intestinal epithelial cells. Mechanistically, berberine inhibited intestinal insulin-like growth factor 1 (IGF-1R) phosphorylation and thus reduced localization of PLC-β2 in the membrane, leading to decreased GLUT2 translocation. These results suggest that berberine reduces intestinal glucose absorption through inhibiting IGF-1R-PLC-β2-GLUT2 signal pathway.

Effect of a Chronic Intake of the Natural Sweeteners Xylitol and Erythritol on Glucose Absorption in Humans with Obesity

In patients with obesity, accelerated nutrients absorption is observed. Xylitol and erythritol are of interest as alternative sweeteners, and it has been shown in rodent models that their acute ingestion reduces intestinal glucose absorption. This study aims to investigate whether a chronic intake of xylitol and erythritol impacts glucose absorption in humans with obesity. Forty-six participants were randomized to take either 8 g of xylitol or 12 g of erythritol three times a day for five to seven weeks, or to be part of the control group (no substance). Before and after the intervention, intestinal glucose absorption was assessed during an oral glucose tolerance test with 3-Ortho-methyl-glucose (3-OMG). The effect of xylitol or erythritol intake on the area under the curve for 3-OMG concentration was not significant. Neither the time (pre or post intervention), nor the group (control, xylitol, or erythritol), nor the time-by-group interaction effects were significant (p = 0.829, p = 0.821, and p = 0.572, respectively). Therefore, our results show that a chronic intake of the natural sweeteners xylitol and erythritol does not affect intestinal glucose absorption in humans with obesity.

One-hour post-load hyperglycemia combined with HbA1c identifies individuals with augmented duodenal levels of sodium/glucose co-transporter 1

AIMS

Individuals with HbA1c-defined prediabetes (HbA1c 5.7-6.4%) and 1-hour post-load plasma glucose (1hPG) ≥ 155 mg/dl have an increased risk to develop type 2 diabetes (T2DM). T2DM is associated with a higher intestinal expression of sodium/glucose co-transporter 1 (SGLT-1) and glucose transporter 2 (GLUT-2). It is currently unsettled whether HbA1c-defined dysglycemic conditions combined to 1hPG ≥ 155 mg/dl are associated with changes in SGLT-1 and GLUT-2 duodenal abundance.

METHODS

SGLT-1 and GLUT-2 protein levels were assessed by western blot on duodenal mucosa biopsies of 57 individuals underwent an upper gastrointestinal endoscopy.

RESULTS

Compared with the normal group (HbA1c < 5.7%), individuals with HbA1c-defined pre-diabetes and diabetes exhibit no significant change in duodenal SGLT-1 abundance. Conversely, duodenal GLUT-2 levels were progressively increased in subjects with prediabetes and diabetes. Stratifying participants according to HbA1c and 1hPG we found that amongst subjects with HbA1c-defined normal or prediabetes condition those having 1hPG ≥ 155 mg/dl displayed higher duodenal levels of SGLT-1 as compared to their counterparts with 1hPG < 155 mg/dl; in contrast to GLUT-2 levels, which were similar between normal and with prediabetes subjects, regardless of 1hPG value.

CONCLUSION

A value of 1hPG ≥ 155 mg/dl may identify a subset of individuals within HbA1c-defined glycemic categories having a higher duodenal abundance of SGLT-1.

A review on interplay between obesity, lipoprotein profile and nutrigenetics with selected candidate marker genes of type 2 diabetes mellitus

BACKGROUND

Type 2 diabetes mellitus, a rapidly growing epidemic, and its frequently related complications demand global attention. The two factors commonly attributed to the epidemic are genetic factors and environmental factors. Studies indicate that the genetic makeup at an individual level and the environmental aspects influence the occurrence of the disease. However, there is insufficiency in understanding the mechanisms through which the gene mutations and environmental components individually lead to T2DM. Also, discrepancies have often been noted in the association of gene variants and type 2 diabetes when the gene factor is examined as a sole attribute to the disease.

STUDY

In this review initially, we have focused on the proposed ways through which CAPN10, FABP2, GLUT2, TCF7L2, and ENPP1 variants lead to T2DM along with the inconsistencies observed in the gene-disease association. The article also emphasizes on obesity, lipoprotein profile, and nutrition as environmental factors and how they lead to T2DM. Finally, the main objective is explored, the environment-gene-disease association i.e. the influence of each environmental factor on the aforementioned specific gene-T2DM relationship to understand if the disease-causing capability of the gene variants is exacerbated by environmental influences.

CONCLUSION

We found that environmental factors may influence the gene-disease relationship. Reciprocally, the genetic factors may alter the environment-disease relationship. To precisely conclude that the two factors act synergistically to lead to T2DM, more attention has to be paid to the combined influence of the genetic variants and environmental factors on T2DM occurrence instead of studying the influence of the factors separately.

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.

Identification of new GLUT2-selective inhibitors through in silico ligand screening and validation in eukaryotic expression systems

Glucose is an essential energy source for cells. In humans, its passive diffusion through the cell membrane is facilitated by members of the glucose transporter family (GLUT, SLC2 gene family). GLUT2 transports both glucose and fructose with low affinity and plays a critical role in glucose sensing mechanisms. Alterations in the function or expression of GLUT2 are involved in the Fanconi-Bickel syndrome, diabetes, and cancer. Distinguishing GLUT2 transport in tissues where other GLUTs coexist is challenging due to the low affinity of GLUT2 for glucose and fructose and the scarcity of GLUT-specific modulators. By combining in silico ligand screening of an inward-facing conformation model of GLUT2 and glucose uptake assays in a hexose transporter-deficient yeast strain, in which the GLUT1-5 can be expressed individually, we identified eleven new GLUT2 inhibitors (IC₅₀ ranging from 0.61 to 19.3 µM). Among them, nine were GLUT2-selective, one inhibited GLUT1-4 (pan-Class I GLUT inhibitor), and another inhibited GLUT5 only. All these inhibitors dock to the substrate cavity periphery, close to the large cytosolic loop connecting the two transporter halves, outside the substrate-binding site. The GLUT2 inhibitors described here have various applications; GLUT2-specific inhibitors can serve as tools to examine the pathophysiological role of GLUT2 relative to other GLUTs, the pan-Class I GLUT inhibitor can block glucose entry in cancer cells, and the GLUT2/GLUT5 inhibitor can reduce the intestinal absorption of fructose to combat the harmful effects of a high-fructose diet.

Western diet induces Paneth cell defects through microbiome alterations and farnesoid X receptor and type I interferon activation

Intestinal Paneth cells modulate innate immunity and infection. In Crohn's disease, genetic mutations together with environmental triggers can disable Paneth cell function. Here, we find that a western diet (WD) similarly leads to Paneth cell dysfunction through mechanisms dependent on the microbiome and farnesoid X receptor (FXR) and type I interferon (IFN) signaling. Analysis of multiple human cohorts suggests that obesity is associated with Paneth cell dysfunction. In mouse models, consumption of a WD for as little as 4 weeks led to Paneth cell dysfunction. WD consumption in conjunction with Clostridium spp. increased the secondary bile acid deoxycholic acid levels in the ileum, which in turn inhibited Paneth cell function. The process required excess signaling of both FXR and IFN within intestinal epithelial cells. Our findings provide a mechanistic link between poor diet and inhibition of gut innate immunity and uncover an effect of FXR activation in gut inflammation.

Dose-dependent accumulation of glucose in the intestinal wall and lumen induced by metformin as revealed by 18 F-labelled fluorodeoxyglucose positron emission tomography-MRI

AIM

To investigate the relationships between various clinical variables and the metformin-induced accumulation of fluorodeoxyglucose (FDG) in the intestine, with distinction between the intestinal wall and lumen, in individuals with type 2 diabetes who were receiving metformin treatment and underwent ¹⁸ F-labelled FDG ([¹⁸ F]FDG) positron emission tomography (PET)-MRI.

MATERIALS AND METHODS

We evaluated intestinal accumulation of [¹⁸ F]FDG with both subjective (a five-point visual scale determined by two experienced radiologists) and objective analyses (measurement of the maximum standardized uptake value [SUV_max ]) in 26 individuals with type 2 diabetes who were receiving metformin and underwent [¹⁸ F]FDG PET-MRI. [¹⁸ F]FDG accumulation within the intestinal wall was discriminated from that in the lumen on the basis of SUV_max .

RESULTS

SUV_max for the large intestine was correlated with blood glucose level (BG) and metformin dose, but not with age, body mass index, HbA1c level or estimated glomerular filtration rate (eGFR). SUV_max for the small intestine was not correlated with any of these variables. Visual scale analysis yielded essentially similar results. Metformin dose and eGFR were correlated with SUV_max for the wall and lumen of the large intestine, whereas BG was correlated with that for the wall. Multivariable analysis identified metformin dose as an explanatory factor for SUV_max in the wall and lumen of the large intestine after adjustment for potential confounders including BG and eGFR.

CONCLUSIONS

Metformin dose is an independent determinant of [¹⁸ F]FDG accumulation in the wall and lumen of the large intestine in individuals treated with this drug.

A Journey in Diabetes: From Clinical Physiology to Novel Therapeutics: The 2020 Banting Medal for Scientific Achievement Lecture

Insulin resistance and β-cell dysfunction are the core pathophysiological mechanisms of all hyperglycemic syndromes. Advances in in vivo investigative techniques have made it possible to quantify insulin resistance in multiple sites (skeletal and myocardial muscle, subcutaneous and visceral fat depots, liver, kidney, vascular tissues, brain and intestine), to clarify its consequences for tissue substrate selection, and to establish its relation to tissue perfusion. Physiological modeling of β-cell function has provided a uniform tool to measure β-cell glucose sensitivity and potentiation in response to a variety of secretory stimuli, thereby allowing us to establish feedbacks with insulin resistance, to delineate the biphasic time course of conversion to diabetes, to gauge incretin effects, and to identify primary insulin hypersecretion. As insulin resistance also characterizes several of the comorbidities of diabetes (e.g., obesity, hypertension, dyslipidemia), with shared genetic and acquired influences, the concept is put forward that diabetes is a systemic disease from the outset, actually from the prediabetic stage. In fact, early multifactorial therapy, particularly with newer antihyperglycemic agents, has shown that the burden of micro- and macrovascular complications can be favorably modified despite the rising pressure imposed by protracted obesity.

Effect of Hydrolyzable Tannins on Glucose-Transporter Expression and Their Bioavailability in Pig Small-Intestinal 3D Cell Model

Intestinal transepithelial transport of glucose is mediated by glucose transporters, and affects postprandial blood-glucose levels. This study investigates the effect of wood extracts rich in hydrolyzable tannins (HTs) that originated from sweet chestnut (Castanea sativa Mill.) and oak (Quercus petraea) on the expression of glucose transporter genes and the uptake of glucose and HT constituents in a 3D porcine-small-intestine epithelial-cell model. The viability of epithelial cells CLAB and PSI exposed to different HTs was determined using alamarBlue^®. qPCR was used to analyze the gene expression of SGLT1, GLUT2, GLUT4, and POLR2A. Glucose uptake was confirmed by assay, and LC–MS/ MS was used for the analysis of HT bioavailability. HTs at 37 µg/mL were found to adversely affect cell viability and downregulate POLR2A expression. HT from wood extract Tanex at concentrations of 4 µg/mL upregulated the expression of GLUT2, as well as glucose uptake at 1 µg/mL. The time-dependent passage of gallic acid through enterocytes was influenced by all wood extracts compared to gallic acid itself as a control. These results suggest that HTs could modulate glucose uptake and gallic acid passage in the 3D cell model.

IL-25 Treatment Improves Metabolic Syndrome in High-Fat Diet and Genetic Models of Obesity

INTRODUCTION

Endemic obesity is considered the driving force for the dramatic increase in incidence of type 2 diabetes (T2D). There is mounting evidence that chronic, low-grade inflammation driven by Th1/Th17 cells and M1 macrophages, is a critical link between obesity and insulin resistance. IL-25 promotes development of a Th2 immune response and M2 macrophages that counteract the inflammation associated with obesity and T2D.

METHODS

Mice were fed a high-fat diet (HFD) for 16 weeks and then treated with IL-25 or BSA as a control for 21 days. Body weight, blood glucose levels, intraperitoneal glucose tolerance, and gene expression were evaluated in mice treated with BSA or IL-25. Ob/ob mice fed a normal control diet were also treated with BSA or IL-25 and body weight and blood glucose levels were measured. Transepithelial electrical resistance and sodium-linked glucose absorption were determined in muscle-free small intestinal tissue and glucose absorption assessed in vitro in intestinal epithelial and skeletal muscle cell lines.

RESULTS

Administration of IL-25 to HFD fed mice reversed glucose intolerance, an effect mediated in part by reduction in SGLT-1 activity and Glut2 expression. Importantly, the improved glucose tolerance in HFD mice treated with IL-25 was maintained for several weeks post-treatment indicating long-term changes in glucose metabolism in obese mice. Glucose intolerance was also reversed by IL-25 treatment in genetically obese ob/ob mice without inducing weight loss. In vitro studies demonstrated that glucose absorption was inhibited by IL-25 treatment in the epithelial IPEC-1 cells but increased glucose absorption in the L6 skeletal muscle cells. This supports a direct cell-specific effect of IL-25 on glucose metabolism.

CONCLUSION

These results suggest that the IL-25 pathway may be a useful target for the treatment of metabolic syndrome.