Sucrase-isomaltase Research Articles

Feeding Medium-Chain Triglycerides to Rats Decreases Degradation of Sucrase-Isomaltase Complex in the Jejunum

We demonstrated previously that feeding a diet containing medium-chain triglycerides (MCT) to rats causes an increase in the sucrase activity in jejunum relative to diets containing long-chain triglycerides (LCT). To explore the mechanism whereby MCT affect jejunal sucrase activity, 7-wk-old rats were fed a high LCT diet for 7 d, and then they were force-fed either the high LCT diet, a high MCT diet or a high carbohydrate (alpha-methylglucoside) diet for the subsequent 12 h. Feeding the high carbohydrate diet produced significantly greater sucrase and isomaltase activities in both upper and lower jejunum than feeding the LCT diet. Feeding the high MCT diet led to significantly greater sucrase activity in the lower jejunum, but isomaltase activity was not elevated. Rocket immunoelectrophoresis revealed that in the lower jejunum of the rats fed the high MCT diet the proportion of sucrase-isomaltase complex to its degradation product (i.e., isomaltase monomer) was elevated, suggesting that dietary MCT affects sucrase activity by retardation of degradation of sucrase-isomaltase. Because the amounts of total bile acids in the upper jejunum were 50% lower in rats fed the high MCT diet relative to animals fed the high LCT diet, it is likely that MCT feeding decreases secretion of bile into the lumen, which in turn decreases degradation of the sucrase subunit of the sucrase-isomaltase complex.

Severe pathogenic variants of intestinal sucrase-isomaltase interact avidly with the wild type enzyme and negatively impact its function and trafficking

Sucrase-isomaltase (SI) is the major disaccharidase of the small intestine, exhibiting a broad α-glucosidase activity profile. The importance of SI in gut health is typified by the development of sucrose and starch maldigestion in individuals carrying mutations in the SI gene, like in congenital sucrase-isomaltase deficiency (CSID). Common and rare defective SI gene variants (SIGVs) have also been shown to increase the risk of irritable bowel syndrome (IBS) with symptoms and clinical features similar to CSID and also in symptomatic heterozygote carriers. Here, we investigate the impact of the most abundant and highly pathogenic SIGVs that occur in heterozygotes on wild type SI (SIWT) by adapting an in vitro system that recapitulates SI gene heterozygosity. Our results demonstrate that pathogenic SI mutants interact avidly with SIWT, negatively impact its enzymatic function, alter the biosynthetic pattern and impair the trafficking behavior of the heterodimer. The in vitro recapitulation of a heterozygous state demonstrates potential for SIGVs to act in a semi-dominant fashion, by further reducing disaccharidase activity via sequestration of the SIWT copy into an inactive form of the enzymatic heterodimer. This study provides novel insights into the potential role of heterozygosity in the pathophysiology of CSID and IBS.

A Truncated Mutant – The Most Common Sucrase‐Isomaltase Deficiency in the Inuit Population: Cellular and Biochemical Characterization

Sucrase isomaltase (SI) is the most prominent disaccharidase in the small intestine responsible for the final steps of carbohydrate digestion. Mutations in the SI gene can lead to a drastic reduction or loss of the catalytic activity required for digestion of disaccharides, and thus can be associated with maldigestion and malabsorption of carbohydrates. Carbohydrate malabsorption is one of the most common gastrointestinal problems, where 70% of the population are affected. Congenital sucrase‐isomaltase deficiency (CSID) is an autosomal recessive disorder caused by defective SI activity; and it is clinically characterized by abdominal pain, flatulence, bloating, and diarrhea. Recently, a homozygous frameshift mutation, c.273_274delAG (p.Gly92Leufs*8), was identified in the Inuit population with an observed allele frequency of 17.2%. In this study, Cos‐1 cells were transiently transfected with cDNA encoding the Gly92Leufs*8 mutation or SI wild‐type (SI‐WT) as a control. The assessment of this new variant phenotype was investigated through enzymatic activity measurements, cellular localization and trafficking behavior. The truncation is associated with the elimination of all N‐glycosylation sites, whereas the Ser/Thr‐rich stalk region is retained pointing to a potential O‐glycosylation. In fact, treatment with benzyl 2‐acetamido‐2‐deoxy‐α‐D‐galactopyranoside, an inhibitor of O‐glycosylation in the Golgi, resulted in a substantial shift in the size of the mutant concomitant with transport competence of the mutant to O‐glycosylation in the Golgi Apparatus. The mutant is further trafficked to the cell surface as assessed by the detection of biotinylated forms of the mutant at the cell surface. This result was also corroborated by immunofluorescence images, which revealed the mutant at the cell surface. However, this mutant does not exhibit SI activity due to the absence of the sucrase and isomaltase domains. While our data unraveled the molecular basis for the onset of the clinical symptoms in patients homozygous to this mutation, further work is needed to determine whether heterozygotes with this mutation are also affected and to which extent.

Distal Small Bowel Resection Yields Enhanced Intestinal and Colonic Adaptation.

Murine ileocecal resection (ICR) has been used to investigate intestinal adaptation. The established model often includes the sacrifice of significant length of the proximal colon. Here, we optimized a highly selective vascular approach to the ICR, with primary jejunal-colic anastomosis yielding maximal colonic preservation. Forty C57BL/6 mice underwent a highly vascularly selective ICR. The terminal branches of the ileocecal artery are isolated apart from the mesenteric branches supplying the small bowel to be resected. The distal 50% of small bowel and cecum are resected; a primary jejuno-colonic anastomosis is performed. Animals were sacrificed at postoperative weeks 2 (n=10) and 10 (n=29). Proximal 50% small bowel resection (SBR) with jejuno-ileal anastomosis was also performed for comparison. The entire colon (with exception of the cecum) was preserved in 100% of animals. Ninety-seven percent of animals survived to postoperative week 10, and all exhibited structural adaptation in the remnant small intestine epithelium. Crypts deepened by 175%, and villi lengthened by 106%, versus 39% and 29% in the proximal SBR cohort, respectively. Colonic proliferation, structural adaptation, and functional adaptation (measured by p-histone 3, luminal-facing apical crypt border size, and sucrase isomaltase, respectively) were increased in ICR compared with proximal SBR. Highly selective isolation of the cecal vasculature allows for greater colon preservation and yields enhanced remnant intestine epithelial adaptation. ICR is also associated with greater colonic adaptation and unique plasticity toward an intestinal phenotype. These findings underscore major differences between resection sites and offer insights into the critical adaptive mechanisms in response to massive intestinal loss.

Abnormal transporter and tight junction protein expression in environmental enteric dysfunction

Environmental enteric dysfunction (EED), which is pervasive in severely underresourced regions with poor sanitation, is characterized by malabsorption and stunted growth and leads to irreversible deficits in physical and intellectual development. Previous studies have associated increased intestinal permeability with EED, but the molecular changes responsible for barrier loss and malabsorption have not been characterized. We sought to define expression of absorptive transport and tight junction proteins using quantitative morphometry of EED patient duodenal biopsies. Biopsies from Pakistani children with confirmed EED diagnoses were compared to those from age‐and sex‐matched North American healthy controls, celiac disease patients, and non‐celiac patients with villous atrophy or intraepithelial lymphocytosis. Claudin‐4 expression was increased in EED biopsies relative to all North American subject groups. Claudin‐4 expression was most increased within upper villous enterocytes, where it stained lateral membranes and, in EED, accumulated intracellularly. EED biopsies also demonstrated markedly increased occludin expression at tight junctions, lateral membranes, and within vesicular compartments. In contrast, expression of claudin‐2, claudin‐15, ZO‐1, JAM‐A, and E‐cadherin were similar in EED patients and controls. Villous expression of SGLT1, NHE3, and NaK‐ATPase, which drive absorption of glucose, Na+, and water, were all increased in EED. In contrast, PEPT1 expression was reduced in EED; expression of CFTR and sucrase isomaltase was unchanged. Increased expression of occludin and claudin‐4 were unexpected, as each of these increases tight junction barrier function in vitro. Further, the malabsorption that characterizes EED is at variance with increased SGLT1, NHE3, and NaK‐ATPase expression. Although further study is needed, it is possible that these changes represent unsuccessful adaptive responses intended to counteract barrier dysfunction and malabsorption. These data are paradoxical in that they demonstrate that, despite being characterized by malabsorption and barrier dysfunction, EED is associated with increased, rather than reduced, expression of barrier‐enhancing tight junction proteins or absorptive proteins. Further study is needed to fully understand the contributions of these alterations to the pathobiology of EED.

Calcium-sensing receptor is not expressed in the absorptive enterocytes of weaned piglets.

The calcium-sensing receptor (CaSR) is a kokumi receptor that plays an essential role in nutrient sensing and animal physiology, growth, and development. Pig CaSR (pCaSR) was identified and characterized in the intestine. However, further research is still needed to confirm the expression of CaSR in the epithelial cells isolated from weaned piglets. In this study, primary enterocytes were isolated and characterized from the ileum of weaned piglets by the Weiser distended intestinal sac technique and fluorescence-activated cell sorting (FACS) based on sucrase-isomaltase (SI) as an enterocyte-specific marker. The expression of CaSR was investigated in both primary enterocytes and the intestinal porcine enterocyte cell line-j2 (IPEC-J2) by droplet digital polymerase chain reaction (ddPCR), immunofluorescence staining, and Western blotting. Results demonstrated that porcine enterocytes could be obtained using FACS with the SI as the enterocyte-specific marker and that pCaSR is not expressed in both porcine ileal enterocytes and IPEC-J2 cells, which specifically identified the expression of pCaSR in ileal enterocytes with sensitive and specific approaches.

Inhibition of α-amylase and α-glucosidase by Morus australis fruit extract and its components iminosugar, anthocyanin, and glucose.

The inhibition of α-amylase and α-glucosidase are important for the maintenance of blood glucose level. Mammalian α-glucosidase includes maltase-glucoamylase and sucrase-isomaltase complexes. In this study, we examined the inhibitory effects of Morus australis fruit extract and its components, that is, three iminosugars (1-deoxynojirimycin [1-DNJ], fagomine, and 2-O-α-D-galactopyranosyl deoxynojirimycin), two anthocyanins (cyanidin-3-glucoside and cyanidin-3-rutinoside), and glucose, against α-amylase and α-glucosidase. We also quantified the concentration of each component in M. australis fruit extract. The IC50 values of the fruit extracts of four M. australis subspecies were >10 mg/ml for α-amylase, 1.1-1.7 mg/ml for maltase, 6.9-8.6 mg/ml for glucoamylase, 0.13-1.0 mg/ml for sucrase, and 0.46-1.4 mg/ml for isomaltase. When the IC50 value of each component and the concentration of each component in the fruit extract were taken into consideration, our results indicated that glucose are involved in the inhibition of α-amylase, and 1-DNJ and glucose are involved in the inhibition of α-glucosidase. This is in contrast to that in M. australis leaf, neither anthocyanin nor glucose are contained, and 1-DNJ is a main inhibitor. PRACTICAL APPLICATION: It is widely accepted that inhibition of α-amylase and α-glucosidase is one of the strategies to treat type-2 diabetes. Today, acarbose, miglitol, and voglibose are clinically used for this purpose. Our results that 1-DNJ and anthocyanin are present in Morus australis fruit and are involved in the inhibition of α-amylase and α-glucosidase suggest that M. australis fruit is a healthy sweetener.

New insights suggest isomaltooligosaccharides are slowly digestible carbohydrates, rather than dietary fibers, at constitutive mammalian α-glucosidase levels

Isomaltooligosaccharides (IMOs) have been characterized as dietary fibers that resist digestion in the small intestine; however, previous studies suggested that various α-glycosidic linkages in IMOs were hydrolyzed by mammalian α-glucosidases. This study investigated the hydrolysis of IMOs by small intestinal α-glucosidases from rat and human recombinant sucrase–isomaltase complex compared to commonly used fungal amyloglucosidase (AMG) in vitro. Interestingly, mammalian α-glucosidases fully hydrolyzed various IMOs to glucose at a slow rate compared with linear maltooligosaccharides, whereas AMG could not fully hydrolyze IMOs because of its very low hydrolytic activity on α-1,6 linkages. This suggests that IMOs have been misjudged as prebiotic ingredients that bypass the small intestine due to the nature of the assay used. Instead, IMOs can be applied in the food industry as slowly digestible materials to regulate the glycemic response and energy delivery in the mammalian digestive system, rather than as dietary fibers.

Nutritional and Physiological Constraints Contributing to Limitations in Small Intestinal Starch Digestion and Glucose Absorption in Ruminants

Increased efficiency of nutrient utilization can potentially be gained with increased starch digestion in the small intestine in ruminants. However, ruminants have quantitative limits in the extent of starch disappearance in the small intestine. The objective is to explore the nutritional and physiological constraints that contribute to limitations of carbohydrate assimilation in the ruminant small intestine. Altered digesta composition and passage rate in the small intestine, insufficient pancreatic α-amylase and/or small intestinal carbohydrase activity, and reduced glucose absorption could all be potentially limiting factors of intestinal starch assimilation. The absence of intestinal sucrase activity in ruminants may be related to quantitative limits in small intestinal starch hydrolysis. Multiple sequence alignment of the sucrase-isomaltase complex gives insight into potential molecular mechanisms that may be associated with the absence of intestinal sucrase activity, reduced capacity for intestinal starch digestion, and limitations in the efficiency of feed utilization in cattle and sheep. Future research efforts in these areas will aid in our understanding of small intestinal starch digestion and glucose absorption to optimize feeding strategies for increased meat and milk production efficiency.

Loss of Sucrase-Isomaltase Function Increases Acetate Levels and Improves Metabolic Health in Greenlandic Cohorts

The sucrase-isomaltase (SI) c.273_274delAG loss-of-function variant is common in Arctic populations and causes congenital sucrase-isomaltase deficiency, which is an inability to break down and absorb sucrose and isomaltose. Children with this condition experience gastrointestinal symptoms when dietary sucrose is introduced. We aimed to describe the health of adults with sucrase-isomaltase deficiency. The association between c.273_274delAG and phenotypes related to metabolic health was assessed in 2 cohorts of Greenlandic adults (n= 4922 and n= 1629). A sucrase-isomaltase knockout (Sis-KO) mouse model was used to further elucidate the findings. Homozygous carriers of the variant had a markedly healthier metabolic profile than the remaining population, including lower body mass index (β [standard error], -2.0 [0.5] kg/m2; P= 3.1× 10-5), body weight (-4.8 [1.4] kg; P= 5.1× 10-4), fat percentage (-3.3% [1.0%]; P= 3.7× 10-4), fasting triglyceride (-0.27 [0.07] mmol/L; P= 2.3× 10-6), and remnant cholesterol (-0.11 [0.03] mmol/L; P= 4.2× 10-5). Further analyses suggested that this was likely mediated partly by higher circulating levels of acetate observed in homozygous carriers (β [standard error], 0.056 [0.002] mmol/L; P= 2.1× 10-26), and partly by reduced sucrose uptake, but not lower caloric intake. These findings were verified in Sis-KO mice, which, compared with wild-type mice, were leaner on a sucrose-containing diet, despite similar caloric intake, had significantly higher plasma acetate levels in response to a sucrose gavage, and had lower plasma glucose level in response to a sucrose-tolerance test. These results suggest that sucrase-isomaltase constitutes a promising drug target for improvement of metabolic health, and that the health benefits are mediated by reduced dietary sucrose uptake and possibly also by higher levels of circulating acetate.

Neither low salivary amylase activity, cooling cooked white rice, nor single nucleotide polymorphisms in starch-digesting enzymes reduce glycemic index or starch digestibility: a randomized, crossover trial in healthy adults

It was suggested that low salivary-amylase activity (SAA) and cooling or stir-frying cooked starch decreases its digestibility and glycemic index. We determined the effects of SAA, cooling, and single-nucleotide polymorphisms (SNPs) in the salivary amylase (AMY1), pancreatic amylase (AMY2A, AMY2B), maltase-glucoamylase (MGAM), and sucrase-isomaltase (SI) genes on starch digestibility and glycemic index of cooked polished rice. Healthy subjects [pilot, n=12; main, n=20 with low-SAA (<50 U/mL), and n=20 with high-SAA (>105 U/mL)] consumed test meals containing 25g (pilot) or 50g (main) available carbohydrate at a contract research organization using open-label (pilot) or assessor-blinded (main), randomized, crossover, Latin-square designs (trial registration: NCT03667963). Pilot-trial test meals were dextrose, freshly cooked polished rice, cooked rice cooled overnight, stir-fried hot rice, or stir-fried cold rice. Main-trial test meals were dextrose, dextrose plus 10g lactulose, plain hot rice, or plain cold rice. In both trials, blood glucose was measured fasting and at intervals over 2h. In the main trial, breath hydrogen was measured fasting and hourly for 6h to estimate in vivo starch digestibility. Data were analyzed by repeated-measures ANOVA for the main effects of temperature and stir-frying (pilot trial) or the main effects of SAA and temperature (main trial) and their interactions. Effects of 24 single nucleotide polymorphisms (SNPs) were assessed separately. Means were considered to be equivalent if the 95% CI of the differences were within ±20% of the comparator mean for glucose response/glycemic index or ±7% for digestibility. Pilot: neither temperature nor stir-frying significantly affected glucose incremental AUC (primary endpoint, n=12). Main: mean±SEM glycemic index (primary endpoint, n=40) was equivalent for low-SAA compared with high-SAA (73±3 vs. 75±4) and cold rice compared with hot rice (75±3 vs. 70±3). Estimated starch digestibility (n=39) was equivalent for low-SAA compared with high-SAA (95%±1% vs. 92%±1%) and hot rice compared with cold rice (94%±1% vs. 93%±1%). No meaningful associations were observed between genotypes and starch digestibility or glycemic index for any of the SNPs. The results do not support the hypotheses that low-SAA, cooling, and common genetic variations in starch-digesting enzymes affect the glycemic index or in vivo carbohydrate digestibility of cooked polished rice. This trial was registered at clinicaltrials.gov as NCT03667963.

Vil-Cre specific Schlafen 3 knockout mice exhibit sex-specific differences in intestinal differentiation markers and Schlafen family members expression levels.

The intestinal epithelium requires self-renewal and differentiation in order to function and adapt to pathological diseases such as inflammatory bowel disease, short gut syndrome, and ulcers. The rodent Slfn3 protein and the human Slfn12 analog are known to regulate intestinal epithelial differentiation. Previous work utilizing a pan-Slfn3 knockout (KO) mouse model revealed sex-dependent gene expression disturbances in intestinal differentiation markers, metabolic pathways, Slfn family member mRNA expression, adaptive immune cell proliferation/functioning genes, and phenotypically less weight gain and sex-dependent changes in villus length and crypt depth. We have now created a Vil-Cre specific Slfn3KO (VC-Slfn3KO) mouse to further evaluate its role in intestinal differentiation. There were increases in Slfn1, Slfn2, Slfn4, and Slfn8 and decreases in Slfn5 and Slfn9 mRNA expression that were intestinal region and sex-specific. Differentiation markers, sucrase isomaltase (SI), villin 1, and dipeptidyl peptidase 4 and glucose transporters, glucose transporter 1 (Glut1), Glut2, and sodium glucose transporter 1 (SGLT1), were increased in expression in VC-Slfn3KO mice based on intestinal region and were also highly female sex-biased, except for SI in the ileum was also increased for male VC-Slfn3KO mice and SGLT1 was decreased for both sexes. Overall, the variations that we observed in these VC-Slfn3KO mice indicate a complex regulation of intestinal gene expression that is sex-dependent.

Effects of tea polyphenols on the growth performance, carbohydrate metabolism of grass carp ( Ctenopharyngodon idellus )

To investigate the effects of tea polyphenols (TPs) on the growth and carbohydrate metabolism of grass carp (Ctenopharyngodon idella), 0 (control group), 250, 500, 1000, 2000, and 4000 mg kg−1 TPs were added to the basal diet and fed to grass carps for 8 weeks. The results show that 500 mg kg−1 group exhibited the significantly highest feed conversion efficiency (FCE) and specific growth rate (SGR) (p < .05) and significantly higher activities of pyruvate kinase (PK), lactate dehydrogenase (LDH), malate dehydrogenase (MDH) and succinate dehydrogenase (SDH) (p < .05). The livers of the control group and 500 mg kg−1 group were subjected to RNA-Seq, and the expressions of glycogen phosphorylase (PYG) and sucrase-isomaltase (SI) genes were upregulated, while that of glucose-6-phosphatase (G6PC) was downregulated, and these promoted glycogen catabolism. The expressions of glucokinase (GK), PK, 6-phosphofructokinase (PFK), glucose-6-phosphate 1-dehydrogenase (G6PD) and fructose-bisphosphate aldolase A (ALDOA) genes were upregulated to promote glucose catabolism. The results indicate that 500 mg kg−1 TPs could upregulate the expressions of some genes that promote carbohydrate decomposition, increase the activities of carbohydrate decomposition enzymes and enhance the utilization of carbohydrates, thereby improving the FCE and SGR.

Theories behind the effect of starch‑ and sucrose‑reduced diets on gastrointestinal symptoms in irritable bowel syndrome (Review).

Increased amounts of starch and sugar have been added to the diet in the Western world during the last decades. Undigested carbohydrates lead to bacterial fermentation and gas production with diffusion of water, causing abdominal bloating, pain and diarrhea. Therefore, dietary advice is the first line of treatment of irritable bowel syndrome (IBS), a disease characterized by abdominal pain and altered bowel habits without any organic findings. Recently, a diet with a reduction of starch and sucrose led to a marked effect on gastrointestinal (GI) symptoms. The mechanism is unknown, but three possible mechanisms are presented in the present review. First, functional variants of the enzyme sucrase-isomaltase (SI) have been described in IBS. A subgroup of patients with IBS may thus suffer from partial SI deficiency with reduced digestion of starch and sucrose. Second, fructose absorption is less efficient than glucose absorption, which may lead to a physiological fructose malabsorption when ingesting high amounts of sucrose. A third mechanism is that high-sugar diets causing hyperglycemia, hyperinsulinemia and weight gain have led to painful neuropathy in animal models; whereas, improved metabolic control in humans has led to improvement of neuropathy. Starch- and sucrose-reduced diets lead to decreased levels of C-peptide, insulin, gastric inhibitory peptide, leptin and weight reduction. These metabolic changes may reduce the excitability of the hypersensitive nervous system often found in IBS and, thereby, lead to the reduced symptoms found after the diet. In conclusion, further studies are needed to investigate the pathophysiology behind development of symptoms after starch and sucrose intake, and the mechanisms behind symptom relief after reduced intake.

Staphylococcus aureus Infection Influences the Function of Intestinal Cells by Altering the Lipid Raft-Dependent Sorting of Sucrase-Isomaltase.

Staphylococcus aureus is an important nosocomial and community-acquired facultative intracellular pathogen. Many studies have reported that S. aureus infections are associated with intestinal symptoms, but little is known about the molecular mechanisms implicated in S. aureus-induced alterations of intestinal functions. In this study, we investigated the implication of lipid rafts in the interaction of S. aureus with Caco-2 cells. To assess potential alterations in the lipid raft structure and effects on the hydrolytic function, we utilized sucrase–isomaltase (SI) as the major intestinal α-glucosidase that is associated with and sorted to the apical membrane via lipid rafts. Seven days post-confluent, Caco-2 cells were infected with S. aureus Newman and further incubated for an additional 2 days. After 48 h, the levels of SI expression as well as the enzymatic function of this protein were assessed in the infected versus non-infected cells. Analysis of the sorting behavior of SI to the apical membrane constituted another crucial aspect in studying the effects of S. aureus on Caco-2 cells. For this purpose, the apical membranes or brush border membranes (BBMs; referred to as P2 fraction) were separated in both infected and non-infected cells from the basolateral and intracellular membranes (referred to as P1 fraction) by employing a cationic-based procedure using CaCl2. The data show that there is no significant change in the overall expression levels of SI in the infected versus non-infected cells as assessed by Western blotting analysis using monoclonal anti-SI antibodies. By contrast, a significant decrease in the localization as well as the specific hydrolytic activities of SI toward sucrose and isomaltose (Palatinose) was observed in the BBM (P2 fraction) in Caco-2 cells 48 h post-infection. Concomitantly, the specific SI activities increased in the basolateral membrane/intracellular fraction (P1). Noteworthy, the specific activity of SI in the BBM of infected cells was markedly reduced as compared with that of the non-infected counterparts. The data accumulated from this study strongly suggest that infections with S. aureus influence the final step in the lipid raft-associated trafficking of human SI and thereby may trigger secondary functional gastrointestinal disorders.

Prediction of hyaluronic acid target on sucrase-isomaltase (SI) with reverse docking and molecular dynamics simulations for inhibitors binding to SI.

Auricularia cornea (E.) polysaccharide is an important component of A. cornea Ehrenb, a white mutant strain of Auricularia with biological activities, such as enhancement of human immune function and cancer prevention. The hyaluronic acids (HAs) are important components of the A. cornea polysaccharide and have extremely high medicinal value. In this study, we used HA to search the target protein sucrase-isomaltase (SI). In addition, we also performed molecular dynamics (MD) simulations to explore the binding of three inhibitors (HA, acarbose and kotalanol) to SI. The MD simulations indicated that the binding of the three inhibitors may induce the partial disappearance of α helix in residues 530–580. Hence, the hydrogen bond for Gly570-Asn572, which was near the catalytic base Asp471 in SI, was broken during the binding of the three inhibitors. We reveal a new inhibitor for SI and provide reasonable theoretical clues for inhibitor binding to SI.

Comparative studies on the physicochemical profile and potential hypoglycemic activity of different tea extracts: Effect on sucrase-isomaltase activity and glucose transport in Caco-2 cells

Tea is one of the most popular beverages in the world and is believed to be beneficial for health. The main components in tea change greatly depending on different processes, and thus, the effects of different teas on human health may differ. In this study, we compared the effect of green, oolong, black, and dark tea extracts on sucrase-isomaltase (SI) activity and glucose transport, which are two intervention options for postprandial blood glucose control, using Caco-2 cells as a model. Theaflavin-rich black tea extracts showed the highest inhibition of SI activity and retardation of the hydrolysis of sucrose, maltose, and isomaltose, with IC50 values of 8.34 μg/mL, 16.10 μg/mL, and 21.63 μg/mL, respectively. All four kinds of tea extracts caused a dose-dependent inhibition of glucose transport, which were closely related to the catechin content. Green tea extracts showed the highest inhibition of glucose transport and was more effective against sodium-dependent glucose cotransporter 1 (SGLT1) than glucose transporter 2 (GLUT2) in the management of glucose transport. Black tea extracts also inhibited glucose transport despite low level of catechins. The reason could partly lie in the suppression of Na+/K+-ATPase, which reduced the energy needed for SGLT1 to actively transport glucose. Furthermore, the mRNA level of SI, SGLT1, GLUT2, and Na+/K+-ATPase in Caco-2 cells were significantly reduced after treatment with tea extracts for 2 h. These in vitro studies suggested that tea could be used as a functional food in the diet to modulate postprandial hyperglycaemia for diabetic patients.

The glucose-regulated protein GRP94 interacts avidly in the endoplasmic reticulum with sucrase-isomaltase isoforms that are associated with congenital sucrase-isomaltase deficiency

The glucose-regulated protein GRP94 is a molecular chaperone that is located in the endoplasmic reticulum (ER). Here, we demonstrate in pull down experiments an interaction between GRP94 and sucrase-isomaltase (SI), the most prominent disaccharidase of the small intestine. GRP94 binds to SI exclusively via its mannose-rich form compatible with an interaction occurring in the ER. We have also examined the interaction GRP94 to a panel of SI mutants that are associated with congenital sucrase-isomaltase deficiency (CSID). These mutants exhibited more efficient binding to GRP94 than wild type SI underlining a specific role of this chaperone in the quality control in the ER. In view of the hypoxic milieu of the intestine, we probed the interaction of GRP94 to SI and its mutants in cell culture under hypoxic conditions and observed a substantial increase in the binding of GRP94 to the SI mutants. The interaction of GRP94 to the major carbohydrate digesting enzyme and regulating its folding as well as retaining SI mutants in the ER points to a potential role of GRP94 in maintenance of intestinal homeostasis by chaperoning and stabilizing SI.

Acute Low-Intensity Treadmill Running Upregulates the Expression of Intestinal Glucose Transporters via GLP-2 in Mice.

The effects of exercise on nutrient digestion and absorption in the intestinal tract are not well understood. A few studies have reported that exercise training increases the expression of molecules involved in carbohydrate digestion and absorption. Exercise was also shown to increase the blood concentration of glucagon-like peptide-2 (GLP-2), which regulates carbohydrate digestion and absorption in the small intestine. Therefore, we investigated the effects of exercise on the expression of molecules involved in intestinal digestion and absorption, including GLP-2. Six-week-old male mice were divided into a sedentary (SED) and low-intensity exercise (LEx) group. LEx mice were required to run on a treadmill (12.5 m/min, 1 h), whereas SED mice rested. All mice were euthanized 1 h after exercise or rest, and plasma, jejunum, ileum, and colon samples were collected, followed by analysis via IHC, EIA, and immunoblotting. The levels of plasma GLP-2 and the jejunum expression of the GLP-2 receptor, sucrase-isomaltase (SI), and glucose transporter 2 (GLUT2) were higher in LEx mice. Thus, we showed that acute low-intensity exercise affects the expression of molecules involved in intestinal carbohydrate digestion and absorption via GLP-2. Our results suggest that exercise might be beneficial for small intestine function in individuals with intestinal frailty.

Molecular basis of heterozygosity in congenital sucrase‐isomaltase deficiency and functional gastrointestinal disorders

Congenital sucrase-isomaltase deficiency (CSID) is a genetically-determined gastrointestinal disorder caused mainly by homozygous or compound heterozygous hypomorphic variants in the sucrase isomaltase (SI) gene. Patients suffering from CSID present with abdominal pain, diarrhea, bloating and alterations in bowel pattern. Similar symptoms have been also observed in patients, who express low activities of sucrase in functional gastrointestinal disorders (FGIDs) as well in CSID heterozygotes. In this study, we assessed the effects of SI mutants that occur in heterozygotes on the trafficking and function of wild type SI (SI-WT). HA-tagged SI gene variants were co-expressed in COS-1 cells with FLAG-tagged SI-WT. The intracellular localization of individually or co-expressed SI isoforms was assessed by immunofluorescence and biochemically by endoglycosidase H treatment which primarily cleaves ER-located N-linked mannose-rich isoforms of glycoproteins and provides thus information on their trafficking pattern. Both approaches revealed a pronounced mutation-relevant diversity in the trafficking pattern of the SI mutants and a hierarchical pattern in their interaction with wild type SI. Highly pathogenic SI mutants, such as SI carrying the E801X mutation, override the transport competence of SI-WT and elicit its retention in the ER. Other mutants behave in a variable manner depending on their pathogenicity levels. Finally, the digestive capacities of SI-WT towards sucrose and palatinose were substantially reduced when co-expressed with SI mutants and correlated directly with the pathogenicity of the SI mutation. Our study demonstrates unequivocally that SI mutants interact intracellularly with SI-WT, negatively impact the biosynthetic, trafficking and functional properties of the resultant SI protein and provides a novel insight into the role of heterozygosity in the aetiology of CSID and FGID.