Carbohydrate Metabolism minisymposium

Published: March 16, 2012

The Whistler Center will speak at the Carbohydrate Metabolism Minisymposium at Experimental Biology 2012 Annual Meeting at San Diego Convention Center Room 29D on April 23, 2012 from 3:00 p.m. to 5:00 p.m.

This is the third Carbohydrate Metabolism Minisymposium held at EB since 2010. It is organized by the collaborator, Dr. Buford Nichols at USDA Children's Nutrition Res Ctr at Baylor College of Medicine, and will be chaired by Dr. Bruce R. Hamaker and Dr. Buford L. Nicholas.


3:00 p.m.

Concept of slowly released dietary glucose: a focus on starch digestion at the mucosal alpha-glucosidase level. A.H-M. Lin, B.L. Nichols and B.R. Hamaker. Purdue Univ. and USDA and Baylor Col. of Med. (638.11)

3:15 p.m.

Modulation of starch digestion for slow glucose release through 'toggling' of mucosal alpha-glucosidases by acarbose. B-H. Lee, R. Eskandari, B.M. Pinto, B.L. Nichols and B.R. Hamaker. Purdue Univ., Simon Fraser Univ., Canada and Baylor Col. of Med. (638.7)

3:00 p.m.

Novel secreted maltase activity enables suckling mouse pup starch digestion. B.L. Nichols, M. Diaz-Sotomayor, S. Avery, S. Chacko, D. Hadsell, S. Baker, L. Yan, A. Lin, Z-H. Ao, R. Quezada-Calvillo and B. Hamaker. Baylor Col. of Med., Univ. at Buffalo, SUNY, Purdue Univ. and Autonomous Univ. of San Luis Potosi, Mexico. (638.2)

3:34 p.m.

Use of 13C-labelled carbohydrates to trace microbial metabolism in the colon: light in the tunnel! K. Venema, A.J.H. Maathuis, M.N. Steijart and A.A. de Graaf. TNO Hlth. Living, Zeist, Top Inst. Food and Nutr., Wageningen and Netherlands Consortium for Systs. Biol., Amsterdam. (638.1)

4:00 p.m.

How analysis of data from alpha-amylase catalysed starch digestibility performed in vitro contributes to an understanding of rates and extent of digestion starchy foods in vivo. P.J. Butterworth, F.J. Warren, C.H. Edwards, T. Grassby, H. Patel and P.R. Ellis. Sch. of Med., King's Col. London. (638.9)

4:15 p.m.

Influence of cultivar, processing, and food form on the glycemic index of barley. A. Aldughpassi, T.M.S. Wolever and E.M. Abdel-Aal. Univ. of Toronto and Agr. and Agri-Food Canada, Guelph. (638.16)

4:30 p.m.

Gut fermentation and health effects of Louisiana sweet potato varieties. K.L. McCutcheon, D.R. LaBonte, D.H. Picha, C.C. Williams, M.J. Keenan and R.J. Martin. LSU AgCtr. (638.18)


Concept of slowly released dietary glucose: a focus on starch digestion at the mucosal ?-glucosidase level

Amy Hui-Mei Lin, Buford L. Nichols, Bruce R. Hamaker

The aim of our research is to control dietary glucose delivery rate to the body for potential health benefit. There are six enzymes, two alpha-amylase and four small intestinal mucosal glucosidases, involved the digestion of starch. The convention view is that alpha-amylase is the key enzyme that determines digestion rate, and mucosal alpha-glucosidases have a more simple function of rapidly converting the small molecules generated from alpha-amylase digestion to glucose. We investigated the digestion patterns of four recombinant alpha-glucosidases on various starches in an in vitro system. The notable finding was that starches with different molecular structures have different digestibility by the mucosal alpha-glucosidases following through digestion by alpha-amylase, and that various starch molecules have different susceptibilities to the individual alpha-glucosidases. Furthermore, a small fraction of starch molecules was digested at a very low rate, indicating structures that are additionally difficult to digest at the brush border level. Our group has further showed that slowly released glucose causes reduced gastric emptying in a dose response manner. To take benefit of slowly released glucose, the mucosal alpha-glucosidases is a potential control point for controlling glucose delivery to the body. This work was supported by internal funding from the Whistler Center for Carbohydrate Research of Purdue Univ.

Modulation of starch digestion for slow glucose release through ?toggling? of mucosal ?-glucosidases by acarbose

Byung-Hoo Lee, Razieh Eskandari, B. Mario Pinto, Buford L. Nichols, Bruce R. Hamaker

For digestion of starch, alpha-amylase first hydrolyzes the starch structure to alpha-limit dextrins ( alpha-LDx's). Complete hydrolysis to glucose then takes place through the combined action of mucosal maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI), which have two subunits each (N- and C- terminal). In this study, we applied the concept of 'toggling' through differential inhibition of subunits to examine control of glucogenesis from alpha-LDx's with the aim of attaining slow glucose delivery to the body. Mammalian recombinant MGAM and SI subunits were individually reacted with alpha-LDx's with varying concentrations of acarbose, a well known alpha-glucosidase inhibitor. Released glucose amounts were analyzed for hydrolysis activity. Notably, results showed selective inhibitory effect on C-terminal subunits by acarbose for starch digestion. Furthermore, Ki values of C-terminal subunits were lower than human alpha-amylases which can be applied that certain amount of acarbose had inhibitory effect on the hydrolysis of alpha-LDx's by C-terminal subunits but not on alpha-amylase for moderating glucogenesis. This result supports the concept of controlling starch digestion rate for slow glucose release through the 'toggling' of activities of the mucosal alpha-glucosidases by selective enzyme inhibition. Conceivably this approach could be used to treat Type II diabetes by extending postprandial blood glucose delivery to the body, and may apply as well to other metabolic syndrome-associated diseases and condition. This research was supported from Whistler Center for Carbohydrate Research and USDA/AFRI.

Novel secreted maltase activity enables suckling mouse pup starch digestion

Buford Nichols, Maricela Diaz-Sotomayor, Stephen Avery, Shaji Chacko, Darrel Hadsell, Susan Baker, Like Yan, Amy Hui-Mei Lin, Zi-Hua Ao, Roberto Quezada-Calvillo, Bruce Hamaker

Starch requires 6 enzymes for digestion to free glucose: 2 alpha-amylases (salivary and pancreatic) and 4 mucosal maltase activities; Sucrase-isomaltase (Si) and Maltase-glucoamylase complexes (Mgam). All 6 activities are deficient in suckling rodents. Objective: Test 13C-starch digestion before weaning (at 21d) from mother's milk by measuring enrichment of blood 13C-glucose in Mgam Null and Wild Type mice. Methods: Mgam gene was ablated at the N-terminal expressing the membrane binding domain. Dams were fed low 13C-diet and litters kept on low 13C-diet. Pups were weaned at 21d. Digestion was tested at 13d and 25d by intragastric feeding of amylase predigested UL 13C-alpha-limit dextrins (LDx). Blood 13C-glucose enrichment was measured by GCRMS using pentaacetate derivatives. Results: 4 h after feeding, blood 13C-glucose MPE% was enriched by 26x103in null and 18x103foldat 13d and 0.3x103and 0.2x103 fold at 25d (vs. fasting p = 0.045 and p = 0.045). By jejunal enzyme assay, imunohistochemistry or Western blots there was no maltase activity or brush border staining with anti-Si or Mgam antibodies at 13d but these were fully developed in WT by 25d. In 13d null mice lumenal contents were stained by both specific antibodies. Conclusion: 1. 13C-LDx was rapidly digested to 13C-glucose in 13d mice independent of age, Mgam genotype or mucosal maltase activity. 2. This novel observation demonstrates that a maltase activity is secreted which enables suckling pup starch digestion well before brush border enzyme development. 3. The origin of this secreted starch digesting activity is presently uncertain.

Use of 13C-labelled carbohydrates to trace microbial metabolism in the colon; light in the tunnel!

Koen Venema, Annet J.H. Maathuis, Marvin N. Steijart, Albert A. de Graaf.

The aim of this research was to study the fermentative processes by the microbiota in the human colon using stable isotope (13C)-labeled carbohydrates. The technology was set up in TNO's validated, dynamic, computer-controlled in vitro model of the colon (nick-named TIM-2). Using Stable-Isotope Probing the 13C-incorporation in microbial biomass was determined. Using LC-MS and NMR, the production of 13C-labeled microbial metabolites were traced. Microbiotas originated from babies, adults or elderly, and a range of different 13C-substrates were used. Differences in production of the major microbial metabolites, the short-chain fatty acids, were observed. For instance, the baby microbiota did not produce propionate on fructo-oligosaccharides. Instead, lactate was the major metabolite produced by the baby microbiota. Appearance of label in minor metabolites such as glycerol, ethanol and several amino acids could be detected. In a pilot study, a nasal catheter was used to infuse 13C-labeled lactose in the colon of 4 human volunteers. Label could be traced into metabolites sampled from the lumen of the colon and plasma, as well as in exhaled CO2. The technology allows for detailed characterization of colonic fermentation, a process which is still considered to be a black box, and therefore provides light in the tunnel of the GI-tract. This research was supported by TNO, Top Institute Food & Nutrition, and Abbott Nutrition.

How analysis of data from alpha-amylase catalysed starch digestibility performed in vitro contributes to an understanding of rates and extent of digestion starchy foods in vivo

Peter J. Butterworth, Frederick J. Warren, Cathrina H. Edwards, Terri Grassby, Hamung Patel, Peter R. Ellis.

Ingestion of different foods containing identical amounts of starch can result in very different postprandial rises in blood glucose and insulin concentrations. Limitation of the early rises in blood glucose and insulin levels seems to be beneficial to human health in the long term. Many studies of starch digestion in vitro are made to understand the molecular basis for differences in digestion rates in vivo to enable prediction of likely rates of digestion of particular starchy foods. Michaelis-Menten kinetics of starch digestibility provides estimates of available (digestible) substrate as starch samples are hydrothermally treated. Combined with studies of starch structure using calorimetry and FTIR spectroscopy, key features influencing rates of amylolysis were identified. Measurement of product formation during prolonged incubations of starch with ?-amylase produces digestibility curves. Use of logarithm of slope (LOS) plots to analyse the curves by 1st order kinetics gave values for digestibility rate constants and the total digestible starch, C?. An important conclusion is that contrary to many reports in the literature, cooked starches do not contain distinct fractions of rapidly and slowly digested material. These kinetic approaches have also been used in studies of plant-encapsulated starch to understand how cell walls influence access of amylase to starch. This work was funded by the BBSRC, UK (DRINC BB/H004866/1).

Influence of Cultivar, Processing, and Food Form on the Glycemic Index of Barley

Ahmed Aldughpassi, Thomas MS Wolever, Elsayed M Abdel-Aal.

Replacement of refined high glycemic index (GI) carbohydrates by whole grain products such as barley may prevent the progression of cardio-metabolic disorders due to their favourable effects on glycemia. However, processing, cultivar variation, physiochemical properties and food form may alter their impact on glycemia. To examine these factors on the GI of barley, 3 experiments were performed in separate groups of 10 healthy subjects. GI was determined using standard methodology and in vitro starch digestibility was measured. Cultivars varied in starch and ?-glucan content. In Experiments 1 and 2 cultivars were processed into four fractions ranging from hull removal only to hull, bran, germ, and crease removal. Experiment 3, a wet pasta-like product was made from 100% barley flour with wet semolina pasta as a control. In experiments 1 and 2 the GI range was (22.8 - 40.9); processing increased the GI significantly (p>0.05). Cultivars differed in their nutrient composition (p = 0.024), but without significant interaction between pearling and cultivars (p>0.05). Regardless of the cultivar, the least processed kernels had significantly lower total starch and higher total low molecular sugars, insoluble and total fiber. Resistant starch (RS) was inversely correlated with the GI (r = -0.58; p< 0.05). The barley pasta had medium-high GI values similar to semolina pasta. Results suggest that processing affects the GI and the physiochemical properties. These results will improve knowledge in the development of low-GI functional foods and improve future consumer guidelines. Financial support from the Ontario Ministry of Agriculture.

Gut fermentation and health effects of Louisiana sweet potato varieties

Kathleen Lee McCutcheon, Don R LaBonte, David H Picha, Cathleen C Williams, Michael J Keenan, Roy J Martin.

Both are naturally low in calories and fat, high in vitamins, minerals and fiber with similar carbohydrate starch, sugar and fiber profiles, but preparation methods affect starch digestion in WP. Thus, 20% of carbohydrates in SP are resistant starches (RS) that slows digestion and the release of sugar. RS is fermented by microflora to produce short chain fatty acids (SCFA), affect peptide secretion, and improve absorption. New SP varieties developed for disease and pest resistance by the LSU AgCenter's Sweet Potato Research Station were tested in vivo to determine health benefits when included in a daily diet. For 12 weeks, rats were fed daily a purified diet with freshly baked potatoes as the carbohydrate source (2 orange flesh (O), 2 white flesh (W) SP varieties and a control WP). All SP groups had significantly less body fat with variety differences between WSP (lowest body fat) and OSP (lowest pH). Daily intake of SP can increase health benefits from gut fermentation as indicated by significantly lower cecal pH, larger cecum weights and greater production of total SCFA in all SP fed groups.