Razieh Eskandari

Modulation of Starch Digestion for Slow Glucose Release through “Toggling” of Activities of Mucosal α-Glucosidases

Background: Proper breakdown of starch by hydrolytic enzymes to yield glucose has profound implications for avoiding type 2 diabetes and obesity. Results: Starch digestion by the different human enzymes is controlled using a panel of compounds. Conclusion: Inhibitors can be used to switch off selectively the different enzyme activities. Significance: More refined control of starch hydrolysis with the aim of slow glucose delivery is possible. Starch digestion involves the breakdown by α-amylase to small linear and branched malto-oligosaccharides, which are in turn hydrolyzed to glucose by the mucosal α-glucosidases, maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI). MGAM and SI are anchored to the small intestinal brush-border epithelial cells, and each contains a catalytic N- and C-terminal subunit. All four subunits have α-1,4-exohydrolytic glucosidase activity, and the SI N-terminal subunit has an additional exo-debranching activity on the α-1,6-linkage. Inhibition of α-amylase and/or α-glucosidases is a strategy for treatment of type 2 diabetes. We illustrate here the concept of “toggling”: differential inhibition of subunits to examine more refined control of glucogenesis of the α-amylolyzed starch malto-oligosaccharides with the aim of slow glucose delivery. Recombinant MGAM and SI subunits were individually assayed with α-amylolyzed waxy corn starch, consisting mainly of maltose, maltotriose, and branched α-limit dextrins, as substrate in the presence of four different inhibitors: acarbose and three sulfonium ion compounds. The IC50 values show that the four α-glucosidase subunits could be differentially inhibited. The results support the prospect of controlling starch digestion rates to induce slow glucose release through the toggling of activities of the mucosal α-glucosidases by selective enzyme inhibition. This approach could also be used to probe associated metabolic diseases.

Antiviral activities of sulfonium-ion glucosidase inhibitors and 5-thiomannosylamine disaccharide derivatives against dengue virus

Enzymes involved in N-glycan processing are targets of interest in the inhibition of host processes for the blockade of dengue virus (DENV) morphogenesis. Of the ten proteins encoded by DENV, three have N-glycosylation sites, namely pre-membrane/membrane protein (prM/M), envelope protein (E) and non-structural protein-1 (NS1). It is known that aberrations in the oligosaccharide portions at these N-glycan sites affect proper folding of these proteins during the translation process that, in turn, affects the morphogenesis of the budding DENV. Here we report on the testing for antiviral activity of four known sulfonium-ion α-glucosidase inhibitors and two 5-thiomannosylamine disaccharide derivatives against DENV. Two of the sulfonium ions tested, namely, kotalanol and its de-O-sulfonated derivative, naturally occurring potent intestinal α-glucosidase inhibitors, had comparable inhibitory activity [50% inhibitory concentration (IC(50))=25.1±13.1 μM and 50.4±8.6 μM, respectively] with that of ribavirin (IC(50)=25.2±8.3 μM), a commercially available antiviral agent. The 5-thiomannosylamines did not show any activity at the concentrations tested.

Investigations of the structures and inhibitory properties of intestinal maltase glucoamylase and sucrase isomaltase.

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Research progress reported at the 50th Anniversary of the Discovery of Congenital Sucrase-Isomaltase Deficiency Workshop.

C ongenital sucrase-isomaltase deficiency (CSID) is a rare autosomal intestinal disease caused by mutations of the sucrase-isomaltase gene. Patients with CSID have different phenotypes and enzymatic activities associated with sucrase-isomaltase ranging from mild reduction of sucrase activity to complete absence. Low sucrase activity leads to maldigestion of sucrose, resulting in dyspepsia-like symptoms such as chronic diarrhea, abdominal pain, and bloating. The severity of the symptom is related to the amount of sucrase activity and quantity of sucrose ingested. Reduced maltase activity is expected to occur in patients with CSID because both subunits of the SI complex contribute to the total mucosal maltose activity. Indeed, low maltase activity can also lead to maldigestion of starches contributing to the symptoms of dyspepsia. When children are assessed for this gene mutation, duodenal mucosal histology is invariably normal. Because there are no noninvasive methods for specific confirmation of sucrase-isomaltase deficiency, a novel noninvasive C-sucrose labeled substrate has been developed and validated as a sucrase activity breath test for screening and confirmation of CSID. It has been shown that primary sucrase deficiency can be confirmed using this new C breath test, as well as the effectiveness of sucrase replacement therapy. On December 21 and 22, 2011, the 8th Workshop of the Starch Digestion Consortium (SDC) was held at the Children’s Nutrition Research Center at the Baylor College of Medicine and Texas Children’s Hospital. The theme of the workshop was ‘‘50 Years of Progress Since Congenital Sucrase-Isomaltase Deficiency (CSID) Recognition.’’ This was a multidisciplinary workshop that blended clinical medicine with nutritional and food science. The purpose of this workshop was to review progress toward clinical diagnosis and management of sucrase-isomaltase enzyme deficiency during the past 50 years. The nutritional and food technological objectives of the conference were 2-fold: first, to define the role of sucrase-isomaltase enzyme complex in human starch digestion to glucose (a-glucogenesis), and second, by studying sucrase-isomaltase–deficient patients with CSID, envision approaches to botanical and technological alterations in food that will benefit all populations. More than 50 authors and attendees participated in this workshop from 12 different countries. Eighteen original communications were presented. Special thanks go to QOL Medical, the supplier of Sucraid oral enzyme supplement, for sponsoring this event. This supplement to the Journal of Pediatric Gastroenterology and Nutrition reports the proceedings of this workshop. E. Roseland Klein served as the technical editor of the workshop publication. Beth Mays was responsible for all travel arrangements and the workshop organization. Adam Gillum was responsible for graphic and audio arrangements. The group of participants standing among the lobby statuary at the SDC/CSID workshop held at the Children’s Nutrition Research Center, December 21–22, 2011 is shown in Figure 1. Statues are identified by italics; Borden is by Joseph Paderewski (1914–2000) and the others are copies of the work of Elizabet Ney (1833–1907). Research Progress Reported at the 50th Anniversary of the Discovery of Congenital Sucrase-Isomaltase Deficiency Workshop