Small Intestinal Brush Border Research Articles

CGMP-dependent kinase 2, Na+/H+ exchanger NHE3, and PDZ-adaptor NHERF2 co-assemble in apical membrane microdomains.

Trafficking, membrane retention, and signal-specific regulation of the Na+/H+ exchanger 3 (NHE3) are modulated by the Na+/H+ Exchanger Regulatory Factor (NHERF) family of PDZ-adapter proteins. This study explored the assembly of NHE3 and NHERF2 with the cGMP-dependent kinase II (cGKII) within detergent-resistant membrane microdomains (DRMs, "lipid rafts") during in vivo guanylate cycle C receptor (Gucy2c) activation in murine small intestine. Small intestinal brush border membranes (siBBMs) were isolated from wild type, NHE3-deficient, cGMP-kinase II-deficient, and NHERF2-deficient mice, after oral application of the heat-stable Escherichia coli toxin (STa) analog linaclotide. Lipid raft and non-raft fractions were separated by Optiprep density gradient centrifugation of Triton X-solubilized siBBMs. Confocal microscopy was performed to study NHE3 redistribution after linaclotide application in vivo. In the WT siBBM, NHE3, NHERF2, and cGKII were strongly raft associated. The raft association of NHE3, but not of cGKII, was NHERF2 dependent. After linaclotide application to WT mice, lipid raft association of NHE3 decreased, that of cGKII increased, while that of NHERF2 did not change. NHE3 expression in the BBM shifted from a microvillar to a terminal web region. The linaclotide-induced decrease in NHE3 raft association and in microvillar abundance was abolished in cGKII-deficient mice, and strongly reduced in NHERF2-deficient mice. NHE3, cGKII, and NHERF2 form a lipid raft-associated signal complex in the siBBM, which mediates the inhibition of salt and water absorption by Gucy2c activation. NHERF2 enhances the raft association of NHE3, which is essential for its close interaction with the exclusively raft-associated activated cGKII.

Inhibition mechanism of oligopeptides from soft-shelled turtle egg against α-glucosidase and their gastrointestinal digestive properties.

Peptides derived from egg protein hydrolysate have potential hypoglycemic benefits by inhibiting α-glucosidase. Herein, fluorescence spectroscopy and molecular docking were performed to investigate the α-glucosidase inhibitory mechanism of the oligopeptides ARDASVLK and HNKPEVEVR from soft-shelled turtle eggs. Gastrointestinal digestion characteristics of the two oligopeptides were further determined by LC-QTOF-MS/MS. The static fluorescence quenching of α-glucosidase by ARDASVLK and HNKPEVEVR indicated the formation of a stable α-glucosidase-peptide complex, mainly driven by hydrogen bonds and hydrophobic interactions. ARDASVLK and HNKPEVEVR could easily insert into the active pocket of α-glucosidase (docking scores of -157.1 and -158.4, respectively), thereby inhibiting enzyme activity by preventing substrate binding and inducing enzymatic conformation change. After gastrointestinal digestion, 14.3% and 30.4% of ARDASVLK and HNKPEVEVR were maintained intact, respectively, and their digestive products (mainly DASVLK and HNKPEVEV) still showed high inhibitory effects on α-glucosidase (about 35% inhibition). This study sheds light on the mechanism of oligopeptides derived from soft-shelled turtle eggs as a novel α-glucosidase inhibitor for diabetes. PRACTICAL APPLICATIONS: Oligopeptides from egg protein hydrolysate have potential hypoglycemic properties by inhibiting α-glucosidase. This study has provided insights into the inhibitory mechanism of oligopeptides from soft-shelled turtle egg on α-glucosidase. Interestingly, despite the fact that the oligopeptides are largely degraded during gastrointestinal digestion, their digestive metabolites displayed strong α-glucosidase inhibitory activities. Because α-glucosidase is highly expressed in small intestine brush border, our findings support the possibility of these oligopeptides as an attractive health-benefit compound to control glucose without being absorbed by intestinal epithelial cells, unlike other enzyme inhibitors such as ACE inhibitors, which have poor oral bioavailability. This study may facilitate the applications of oligopeptides from soft-shelled turtle egg as α-glucosidase inhibitors and food functional ingredients for the therapy of diabetes.

Influence of Blastocystis hominis on the small intestine and lactase enzyme activity.

Blastocystis hominis is a cosmopolitan protozoan that has been associated with several gastrointestinal disturbances involving lactose intolerance. However, the underlying pathogenic factors remain indistinct. 20 Swiss albino mice were utilized and assembled into four groups, each of five mice: group-I: received neither infection nor lactose (healthy control), group-II: received a single dose of 10,000 cysts of Blastocystis and lactose diets in a dose of 12.5g/day/mouse for 7 consecutive days starting from day 14 p.i., group-III: non-infected mice with oral doses of lactose (12.5g/day/mouse) for 7 consecutive days (positive control), group-IV: infected mice on lactose free diet (negative control). We investigated the histopathological changes using H&E stain.s Also, lactase enzyme activity was measured using spectrophotometry and the production of TNF-α and apoptotic events were explored via immunohistochemistry and compared in the small intestine of all groups. The active inflammatory changes in the infected animals were moderate in the form of loss of villous architecture, increased ILC (P-value > 0.001) besides scattered forms of the parasite as compared to non-infected mice. There was a reduction in lactase enzyme activity p.i. The TNF-α levels were induced p.i. as compared to non-infected mice (P-value > 0.001). The expression of Bax protein was upgraded, while Bcl-2 expression decreased significantly with a reverse in Bax/Bcl2 ratio in infected animals. Blastocystis infection appears to humble lactase enzyme activity via the induction of apoptosis in the epithelial cells of the small intestinal brush border in a TNF-α associative pathway.

Intestinal brush border assembly during the peri-hatch period and its contribution to surface area expansion

Microvilli generate the small intestinal brush border, the main site of nutrient digestion and absorption. Mucosal structuring of the small intestine of chicken during the perihatch period has been widely researched, yet the developmental dynamics of microvilli during this period have not been fully characterized. In this study, we examined the structural and molecular characteristics of microvilli assembly and maturation during the perihatch period. Small intestines of broiler embryos and chicks were sampled at prehatch ages 17 E and 19 E, at day of hatch (DOH) and at 1, 3, 7, and 10 d posthatch. Morphological evaluations and measurements were conducted by scanning electron microscopy (SEM) and light microscopy (LM) (n = 3/timepoint), and expression of microvilli structural genes Plastin 1, Ezrin, and Myo1a was examined by Real-Time qPCR (n = 6/timepoint). Results revealed dissimilar patterns of microvilli and villi development during the perihatch period. From 19 E to 1 d, microvilli lengths increased 4.3-fold while villi lengths increased 2.8-fold (P < 0.0001). From 3 to 7 d, villi lengths increased by 20% (P < 0.005), while microvilli lengths decreased by 41% (P = 0.001). At 10 d, microvilli lengths stabilized, while villi continued to elongate by 26% (P < 0.0001). Estimations of the microvilli amplification factor (MAF) and total enterocyte surface area (TESA) revealed similar trends, with peak values of 78.53 and 1961.67 µm2, respectively, at 3 d. Microvilli structural gene expression portrayed diverse patterns. Expression of Plastin 1, which bundles and binds actin cores to the terminal web, increased 8.7-fold between 17 E and DOH (P = 0.005), and gradually increased up to 7 d (P = 0.045). Ezrin and Myo1a, both actin core-cell membrane cross-linkers, portrayed different expression patterns throughout the perihatch period, as Ezrin expression was relatively stable, while Myo1a expression increased 15.8-fold between 17 E and 10 d (P < 0.0001). We conclude that microvilli assembly during the perihatch period is a rapid, coordinated process, which dramatically expands the digestive and absorptive surface area of the small intestine before the completion of villi maturation.

Expression of the fructose transporter GLUT5 in patients withfructose malabsorption.

Patients with abdominal symptoms are frequently diagnosed with fructose malabsorption (FM). Fructose is absorbed by monosaccharide transporters located in the brush border of the human small intestine. The aim of this study was to investigate the histoanatomical distribution of the main fructose transporter GLUT5. We studied 223 patients diagnosed with FM by a hydrogen breath test and grouped according to their response to a fructose-free diet. The control group were 42 healthy individuals and 29 patients with celiac disease (CD). The fructose breath test was done with 50 g fructose. The expression of Glut5 in duodenal biopsy specimens was studied by immunohistochemistry. The Kruskal-Wallis-test and Mann-Whitney U-test were used to carry out the statistical analysis. The histoanatomical expression pattern of GLUT5 did not differ significantly between those patients with FM who responded completely to a fructose-free diet (n = 183) and healthy individuals (n = 42); nor did it correlate to H2 production measured in fructose breath testing. In patients with FM, the GLUT5 expression pattern did not differ between those individuals responding to a fructose-free diet and those who did not. However, GLUT5 expression pattern was significantly different in patients with CD (n = 29) compared to patients with FM and to healthy individuals (p = 0.009). GLUT5 expression patterns are not be related to adult patients with FM. However, in secondary malabsorption, a decreased GLUT5 expression was found. Further investigation is needed to understand the essential factors in FM and the influence on functional gastrointestinal disorders.

Plant origin prebiotics affect duodenal brush border membrane functionality and morphology, in vivo (Gallus Gallus).

The intra-amniotic administration approach has been used to evaluate the effects of plant origin prebiotics on intestinal health and on brush border membrane functionality and morphology. Prebiotics are fermentable dietary fibers, which can positively affect the host by selectively stimulating the growth and activity of colon bacteria, thus improving intestinal health. The consumption of prebiotics increases digestive tract motility, which leads to hyperplasia and/or hypertrophy of intestinal cells, increasing nutrient digestive and absorptive surface area. This review collates information about the effects and relationship between prebiotic consumption on small intestinal brush border membrane functionality and morphology by utilizing the intra-amniotic administration approach. To date, research has shown that the intra-amniotic administration of prebiotics affects the expression of key brush border membrane functional proteins, intestinal surface area (villi height/width), and goblet cell number/size. These effects may improve brush border membrane functionality and digestive/absorptive capabilities.

Probing sulfatide-tissue lectin recognition with functionalized glycodendrimersomes.

SummaryThe small 3-O-sulfated galactose head group of sulfatides, an abundant glycosphingolipid class, poses the (sphinx-like) riddle on involvement of glycan bridging by tissue lectins (sugar code). First, synthesis of head group derivatives for functionalization of amphiphilic dendrimers is performed. Aggregation of resulting (biomimetic) vesicles, alone or in combination with lactose, demonstrates bridging by a tissue lectin (galectin-4). Physiologically, this can stabilize glycolipid-rich microdomains (rafts) and associate sulfatide-rich regions with specific glycoproteins. Further testing documents importance of heterobivalency and linker length. Structurally, sulfatide recognition by galectin-8 is shown to involve sphingosine's OH group as substitute for the 3′-hydroxyl of glucose of lactose. These discoveries underscore functionality of this small determinant on biomembranes intracellularly and on the cell surface. Moreover, they provide a role model to examine counterreceptor capacity of more complex glycans of glycosphingolipids and to start their bottom-up glycotope surface programming.

Targeting the gut to prevent sepsis from a cutaneous burn.

Severe burn injury induces gut barrier dysfunction and subsequently a profound systemic inflammatory response. In the present study, we examined the role of the small intestinal brush border enzyme, intestinal alkaline phosphatase (IAP), in preserving gut barrier function and preventing systemic inflammation after burn wound infection in mice. Mice were subjected to a 30% total body surface area dorsal burn with or without intradermal injection of Pseudomonas aeruginosa. Mice were gavaged with 2000 units of IAP or vehicle at 3 and 12 hours after the insult. We found that both endogenously produced and exogenously supplemented IAP significantly reduced gut barrier damage, decreased bacterial translocation to the systemic organs, attenuated systemic inflammation, and improved survival in this burn wound infection model. IAP attenuated liver inflammation and reduced the proinflammatory characteristics of portal serum. Furthermore, we found that intestinal luminal contents of burn wound–infected mice negatively impacted the intestinal epithelial integrity compared with luminal contents of control mice and that IAP supplementation preserved monolayer integrity. These results indicate that oral IAP therapy may represent an approach to preserving gut barrier function, blocking proinflammatory triggers from entering the portal system, preventing gut-induced systemic inflammation, and improving survival after severe burn injuries.

A Rare Case of Ileitis and Colitis: when the Appearance is Deceiving

A 77-year-old male patient experienced a seven Kg weight loss and 4-5 bowel movements per day with the greasy and foul-smelling stools. He had arterial hypertension treated with olmesartan 20 mg per day for the previous five years. A colonoscopy was normal and histology showed a collagenous colitis. For the failure of budesonide treatment he was admitted to our Department. An upper gastrointestinal endoscopy showed the disappearance of duodenal villi and histology showed severe atrophy of the duodenal villi with lymphocytic infiltrate in the epithelium and lamina propria. A diagnosis of ileitis and collagenous colitis associated with malabsorption due to the olmesartan therapy was made. The long delay between the onset of Olmesartan therapy and the development of enteropathy suggests that the reaction is a localized, delayed hypersensitivity response which is cell-mediated and results in damage to the small intestinal brush border and collagenous colitis.

3D-QSAR Analysis and Molecular Docking Studies on 3-Arylcoumarin Derivatives as Potential α- Glucosidase Inhibitors

α-glucosidase inhibitors (AGI) are the structural moieties that are found to be of utmost importance in the fields of pharmacy and which involves delaying the absorption of carbohydrates by blocking of alpha-glucosidase enzyme in the brush border of small intestine and plays an important role in constituting a promising therapeutic class against diabetic disease (Type II). In this study, the three-dimensional quantitative structure-activity relationship (3D-QSAR) and docking models were developed using Fujito-Ban analysis in VALSTAT software and Molegro Virtual Docker 6.0. The theoretical models were generated from 29 3-arylcoumarin inhibitors of α-glucosidase. A robust QSAR model with good prediction in internal and external verification was constructed, where r2 and q2 were 0.821 and 0.646 respectively. The QSAR study suggested that substitution of group at R1 position on 3-arylcoumarin ring with electron withdrawing group favourable for the anti-diabetic activity. Molecular docking studies were performed with the coordinates of the α-glucosidase crystal structure (PDB ID: 3WY2), as the results we found that the ligands would form the hydrogen bond interactions with Asp 202, Arg 400 and Glu 271 of the protein receptor generally. For better α-glucosidase inhibitory activity, dipole seems to give good results. These results of the QSAR analysis and molecular docking provided some useful information for designing new and effective α-glucosidase inhibitors in significance of stability and the binding interaction between ligand the receptor site by considering the validation parameters.

EFFECT OF CINNAMON AND GINGER METHANOLIC EXTRACTS ON MURINE INTESTINAL CRYPTOSPORIDIOSIS.IN-VIVO EVALUATION

Cryptosporidium species the Apicomplexa protozoan parasites, causing diarrheal disease in man and animals, due to the lack of a licensed vaccine and resistance to the available effective therapy. This study explored the curative and the prophylactic effect of the cinnamon and ginger methanolic extracts separately and combined with nanazoxide on the experimentally infected mice with Cryptosporidium. Ninety Swiss albino mice, weight of 23-25gm, aged 7-8 weeks were divided into nine groups to assess the therapeutic and the prophylactic effect of cinnamon and ginger methanolic extracts separately then combined with nanazoxide. The result was assessed parasitologically, histopathlogically and by TEM. The best efficacy was three weeks post infection in all groups. Therapeutic effect of ginger was better than cinnamon extract, but combined ginger and nanazoxide gave the least oocyst shedding. The prophylactic dose of ginger and cinnamon methanolic extracts showed marked decrease in oocysts shedding and ginger was the best. Histopathological sections showed immune cells infiltration with a decrease in number of tissue parasite that was absent in the prophylactic groups given ginger extract. The results were confirmed by transmission electron microscopy explored a great improvementin the small intestinal brush border of the same groups.

Sucrase-Isomaltase Deficiency as a Potential Masquerader in Irritable Bowel Syndrome.

Patients with irritable bowel syndrome (IBS) frequently have meal-related symptoms and can recognize specific trigger foods. Lactose intolerance is a well-established carbohydrate malabsorption syndrome that causes symptoms similar to IBS such as bloating, abdominal pain, and diarrhea. However, the prevalence of sucrase-isomaltase deficiency (SID) in this population is poorly defined. SID is a condition in which sucrase-isomaltase, an enzyme produced by brush border of small intestine to metabolize sucrose, is deficient. Just like lactase deficiency, SID causes symptoms of maldigestion syndromes including abdominal pain, bloating, gas, and diarrhea. In this study, we aim to determine the prevalence of SID in patients with presumed IBS-D/M and characterize its clinical presentation. Patients with a presumed diagnosis of IBS-D/M based on symptoms of abdominal pain, diarrhea, and/or bloating who underwent esophagogastroduodenoscopy with duodenal biopsies and testing for disaccharidase deficiency were included. Patients with a history of inflammatory bowel disease, gastrointestinal malignancy, or celiac disease were excluded. Odds ratio was calculated for abdominal pain, diarrhea, and bloating in patients with versus without SID. A total of 31 patients with clinical suspicion for IBS-D/M were included with a median age of 46years (IQR 30.5-60) and with 61% females. SID was present in 35% of patients. Among patients with SID, 63.6% had diarrhea, 45.4% had abdominal pain, and 36.4% had bloating. Patients with SID were less likely than controls to have abdominal pain (OR 0.16, 95% CI 0.03-0.81, p = 0.04) although no difference in diarrhea or bloating was found. Only two patients with SID underwent sucrose breath testing of which only one had a positive result. However, this patient also had a positive glucose breath test and may have had small intestinal bacterial overgrowth as a confounder. SID was found in 35% of patients with presumed IBS-D/M and should be considered in the differential diagnosis of patients presenting with abdominal pain, diarrhea, or bloating. Further studies should better characterize the clinical features of SID and investigate the effects of dietary modification in this group of patients.

Phylogenetic analysis reveals key residues in substrate hydrolysis in the isomaltase domain of sucrase-isomaltase and its role in starch digestion

BackgroundStarch constitutes one of the main sources of nutrition in the human diet and is broken down through a number of stages of digestion. Small intestinal breakdown of starch-derived substrates occurs through the mechanisms of small intestinal brush border enzymes, maltase-glucoamylase and sucrase-isomaltase. These enzymes each contain two functional enzymatic domains, and though they share sequence and structural similarities due to their evolutionary conservation, they demonstrate distinct substrate preferences and catalytic efficiency. The N-terminal isomaltase domain of sucrase-isomaltase has a unique ability to actively hydrolyze isomaltose substrates in contrast to the sucrase, maltase and glucoamylase enzymes. MethodsThrough phylogenetic analysis, structural comparisons and mutagenesis, we were able to identify specific residues that play a role in the distinct substrate preference. Mutational analysis and comparison with wild-type activity provide evidence that this role is mediated in part by affecting interactions between the sucrase and isomaltase domains in the intact molecule. ResultsThe sequence analysis revealed three residues proposed to play key roles in isomaltase specificity. Mutational analysis provided evidence that these residues in isomaltase can also affect activity in the partner sucrase domain, suggesting a close interaction between the domains. Major conclusionsThe sucrase and isomaltase domains are closely interacting in the mature protein. The activity of each is affected by the presence of the other.General Significance: There has been little experimental evidence previously of the effects on activity of interactions between the sucrase-isomaltase enzyme domains. By extension, similar interactions might be expected in the other intestinal α-glucosidase, maltase-glucoamylase.

Bile Duct Obstruction Leads to Increased Intestinal Expression of Breast Cancer Resistance Protein With Reduced Gastrointestinal Absorption of Imatinib

Liver dysfunction reduces systemic clearance of drugs that are primarily eliminated by the liver. However, liver dysfunction can cause a reduction in the plasma concentration profiles of certain drugs, including several tyrosine kinase inhibitors, after oral administration. The aim of the present study was to clarify the reduction in oral absorption of a tyrosine kinase inhibitor, imatinib, and the mechanisms of action involved under conditions of hepatic dysfunction, focusing on intestinal transporters. The maximum plasma concentration of imatinib after oral administration in mice subjected to bile duct ligation (BDL) was lower than that in sham-operated mice, whereas the plasma concentration profile after intravenous administration was essentially unaffected by BDL. The change in maximum plasma concentration was compatible with a reduction in small intestinal permeability of imatinib observed in the in situ closed loop. Gene expression of abcg2 was increased in BDL mice compared with that in sham-operated mice. Expression of breast cancer resistance protein and P-glycoprotein in the small intestinal brush border membrane fraction from BDL mice was also increased compared with that in sham-operated mice. In summary, the intestinal absorption and permeability of imatinib was decreased in BDL mice, and this may be attributed to the up-regulation of the efflux transporter(s).

In Vitro Digestibility of Galactooligosaccharides: Effect of the Structural Features on Their Intestinal Degradation.

Small intestinal brush border membrane vesicles from pig were used to digest galactooligosaccharides from lactose (GOS) and from lactulose (OsLu). Dissimilar hydrolysis rates were detected after digestion. Predominant glycosidic linkages and monomeric composition affected the resistance to intestinal digestive enzymes. The β(1→3) GOS mixture was the most susceptible to hydrolysis (50.2%), followed by β(1→4) (34.9%), whereas β(1→6) linkages were highly resistant to digestion (27.1%). Monomeric composition provided a better resistance in β(1→6) OsLu (22.8%) compared to β(1→6) GOS (27.1%). This was also observed for β-galactosyl fructoses and β-galactosyl glucoses, where the presence of fructose provided higher resistance to digestion. Thus, the resistance to small intestinal digestive enzymes highly depends upon the structure and composition of prebiotics. Increasing knowledge in this regard could contribute to the future synthesis of new mixtures of carbohydrates, highly resistant to digestion and with potential to be tailored prebiotics with specific properties, targeting, for instance, specific probiotic species.

Trans-\u03b2-galactosidase activity of pig enzymes embedded in the small intestinal brush border membrane vesicles

This work highlights the utility of brush border membrane vesicles (BBMV) from the pig small intestine as a reliable model for gathering information about the reaction mechanisms involved in the human digestion of dietary carbohydrates. Concretely, the elucidation of the transgalactosylation mechanism of pig BBMV to synthesize prebiotic galacto-oligosaccharides (GOS) is provided, unravelling the catalytic activity of mammalian small intestinal β-galactosidase towards the hydrolysis of GOS. This study reveals that pig BBMV preferably synthesizes GOS linked by β-(1 → 3) bonds, since major tri- and disaccharide were produced by the transfer of a galactose unit to the C-3 of the non-reducing moiety of lactose and to the C-3 of glucose, respectively. Therefore, these results point out that dietary GOS having β-(1 → 3) as predominant glycosidic linkages could be more prone to hydrolysis by mammalian intestinal digestive enzymes as compared to those linked by β-(1 → 2), β-(1 → 4), β-(1 ↔ 1) or β-(1 → 6). Given that these data are the first evidence on the transglycosylation activity of mammalian small intestinal glycosidases, findings contained in this work could be crucial for future studies investigating the structure-small intestinal digestibility relationship of a great variety of available prebiotics, as well as for designing tailored fully non-digestible GOS.

Molecular mechanisms of long-chain fatty acids absorption

The article presents about the role of several lipid-binding proteins expressed by the small intestine brush border membrane in the main steps of intestinal absorption of long-chain fatty acids and about changes in lipid profile caused by failed absorbtion. The system literature search is performed on Scopus databases, Web of Science, MedLine.

Effect of Tea/Tea Extracts on α‐Glucan Hydrolysis by Enzymes In Vitro and In Vivo − With Parallel Impacts on Health

The digestion of starch and starch derivatives in humans is a multi‐enzyme process which generates glucose as the major dietary energy source. Digestible or amorphous starch may be depolymerised by digestive (pancreatic) α‐amylase to generate dextrins, maltooligosaccharides, and maltose. The small intestine brush border located maltase‐glucoamylase (MGAM) may then convert maltose and maltooligosaccharides with an α‐(1–4) bonding configuration to glucose. The similarly located sucrase‐isomaltase enzyme complex may also convert maltose to glucose and isomaltose or α‐(1–6) linked oligosaccharides to glucose too. Some components in the diet (for example tea) may interact with enzymes in the digestive system associated with α‐glucan digestion. Tea is consumed in different formats around the world and is considered to provide many health benefits. Most often tea is consumed without milk − which is popular in some countries − where the milk proteins bind to the bioactive components of the tea. Health related conditions may be linked to the control of energy generation via glucose in the gut − although tea and tea extracts are associated with broader health impacts.

Na+ /H+ exchanger 3 blockade ameliorates type 2 diabetes mellitus via inhibition of sodium-glucose co-transporter 1-mediated glucose absorption in the small intestine.

To elucidate the role of Na+ /H+ exchanger 3 (NHE3) in sodium-glucose co-transporter 1 (SGLT1)-mediated small intestinal brush border membrane (BBM) glucose absorption and its functional implications in type 2 diabetes mellitus (T2DM). Human jejunal samples were obtained from patients undergoing gastrectomy. 14 C-glucose absorption was measured by liquid scintillation counting. NHE3 expression was suppressed by siRNA-mediated knockdown or augmented in Caco2 cells. Glucose and insulin tolerance in db/db and m+/db mice was assessed with oral and intraperitoneal glucose tolerance tests, and an intraperitoneal insulin tolerance test. Insulin resistance and β-cell function were assessed using homeostatic model assessment of insulin resistance and β-cell function. NHE3 expression was upregulated in db/db mouse jejunal BBM and high-glucose-treated Caco2 cells. NHE3 blockade impaired SGLT1-mediated glucose absorption in human jejunum, m+/db and db/db mouse jejunums, and Caco2 cells, via serum/glucocorticoid-regulated kinase 1 (SGK1). NHE3 knockdown suppressed SGLT1-mediated glucose uptake and reduced mRNA and protein levels of SGK1 and SGLT1, which were conversely enhanced by NHE3 overexpression. Chronic S3226 treatment diminished postprandial glucose levels and ameliorated glucose intolerance in db/db mice. NHE3 is essential in the modulation of small intestinal BBM glucose absorption. Our findings provide a rationale for future possible clinical application of NHE3 for treatment of T2DM through reducing intestinal glucose uptake and counteracting postprandial hyperglycaemia.

Glycol chitosan: A stabilizer of lipid rafts in the intestinal brush border

Chitosan is a polycationic polysaccharide consisting of β-(1–4)-linked glucosamine units and due to its mucoadhesive properties, chemical derivatives of chitosan are potential candidates as enhancers for transmucosal drug delivery. Recently, glycol chitosan (GC), a soluble derivative of chitosan, was shown to bind specifically to lipid raft domains in model bilayers. The small intestinal brush border membrane has a unique lipid raft composition with high amounts of glycolipids cross-linked by lectins, and the aim of the present work therefore was to study the interaction of FITC-conjugated GC (FITC-GC) with the small intestinal epithelium. Using organ culture of pig jejunal mucosal explants as a model system, we observed widespread binding of luminal FITC-GC to the brush border. Only little uptake via constitutive endocytosis into apical early endosomes occurred, unless endocytosis was induced by the simultaneous presence of cholera toxin B subunit (CTB). Biochemically, GC bound to microvillus membrane vesicles and caused a change in the density profile of detergent resistant membranes (DRMs). Collectively, the results showed that FITC-GC binds passively to lipid raft domains in the brush border, i.e. without inducing endocytosis like CTB. Instead, and unlike CTB, FITC-GC seems to exert a stabilizing, detergent-protective effect on the lipid raft organization of the brush border.