Clifford Tasman-Jones

Comparative effects of three resistant starch preparations on transit time and short-chain fatty acid production in rats.

Abstract: A high-fiber diet may protect against colon cancer because of the butyrate generated in the colon by bacterial fermentation of nonstarch polysaccharides. Butryrate can reverse neoplastic changes, at least in vitro, and resistant starch (RS) represents a source of butyrate in vivo. We examined the effects of replacing normal maize starch in the diet of rats with three preparations of RS on the amounts of starch, butyrate, and other short-chain fatty acids in the cecum. We examined the effects on fecal bulking and transit time, which have been suggested to protect against colon cancer. The RS preparations that we tested were potato starch, high-amylose maize starch, and an a-amylase- treated high-amylose maize starch. All had major effects on fecal weight and on the weight of the cecum but only slightly shortened transit times. All increased the amount of starch reaching the cecum and increased short-chain fatty acid production in the cecum; potato starch had the greatest effect and high-amylose maize starch the least. Potato starch, unlike high-amylose maize starch, enhanced the proportion of butyrate. Thus there were marked differences among sources of RS, even though these were all classified as RS2. The significance for colon cancer is discussed.

Ammonia produced by Campylobacter pylori neutralizes H+ moving through gastric mucus.

We aimed to show that Campylobacter pylori infection increases the concentration of ammonia in the gastric mucus and alters the movement of H+ through the mucus. Mucus from uninfected and C. pylori-infected stomachs was collected at postmortem. Ammonia was measured enzymatically. The ammonia concentration in C. pylori-infected mucus was fourfold greater than in uninfected mucus. H+ movement experiments were carried out using an in vitro chamber, in which a layer of mucus separated a 0.1 M HCl solution from distilled H2O. The change in pH of the distilled H2O was measured over 30 min. A drop in pH was measured for uninfected mucus. A slight rise in pH was measured for C. pylori-infected mucus. We conclude that C. pylori infection is associated with reduced H+ movement through mucus and that this may be due to increased ammonia concentration within mucus.

Preservation of mucusIn situ in rat colon

Mucus, a hydrated complex consisting mainly of glycoproteins, forms a layer over the epithelial surface of the gastrointestinal tract. The usual preparative procedures for histological and scanning electron microscopic examination of the gut result in the loss or distortion of this mucus layer. Careful evaluation of two new methods reported to stabilize the mucus layer showed that acrolein vapor did not provide adequate fixation, but application of heat-inactivated antiserum raised in rabbits against rat colon mucus reliably preserved a continuous layer closely adherent to the epithelium. This stabilized layer is continuous with the mucus in the colonic crypts.Mucus, a hydrated complex consisting mainly of glycoproteins, forms a layer over the epithelial surface of the gastrointestinal tract. The usual preparative procedures for histological and scanning electron microscopic examination of the gut result in the loss or distortion of this mucus layer. Careful evaluation of two new methods reported to stabilize the mucus layer showed that acrolein vapor did not provide adequate fixation, but application of heat-inactivated antiserum raised in rabbits against rat colon mucus reliably preserved a continuous layer closely adherent to the epithelium. This stabilized layer is continuous with the mucus in the colonic crypts.

Disacchandase Levels of the Rat Jejunum Are Altered by Dietary Fibre

Rat jejunal disaccharidases were measured after feeding high fat fibre-free, high fat pectin, high fat cellulose, high fat galactomannan and high fat tannin diets for 27 weeks. Compared with the high fat fibre-free diet, pectin lowered both lactase and sucrase levels (p less than 0.025). Galactomannan and tannin lowered only the lactase level (p less than 0.05), while cellulose had no significant effect on disaccharidase levels. These data suggest that dietary fibre components have individual and specific effects on jejunal disaccharidase levels, in the presence of a high fat diet.

Distribution of Campylobacter pylori in the Human Stomach Obtained at Postmortem

The distribution of Campylobacter pylori, its prevalence, and its relationship to gastritis and urease activity have been studied in 54 postmortem stomachs. Infection was confirmed by finding C. pylori in a Gram-stained smear of gastric mucus harvested from the entire stomach. Eight tissue specimens were obtained from predetermined sites from each stomach and examined for histologic gastritis and urease activity. Thirty-seven per cent of stomachs were infected, and of these 80% had widespread histologic gastritis. The detection of urease activity provided information on the distribution of the organism and had a high correlation with histologic gastritis. The organism is capable of infecting any area of the stomach. Infection is common and is more prevalent in Polynesian subjects (60%) than in Caucasians (19%).

Intra-Caecal Short Chain Fatty Acids Are Altered by Dietary Pectin in the Rat

When Dark Agouti rats were changed from a conventional pellet diet containing 3.3% crude fibre and 4% fat to the experimental diet containing 5% pectin and 17% fat, the levels of n-butyrate in the caecum rapidly decreased more than fivefold. Such a change could be important as n-butyrate is known to be a major energy source for colonocytes, and to affect colon tumour cell development in vitro. Striking decreases in the caecal concentrations of the short chain fatty acids isobutyrate, n-valerate and isovalerate occurred when Wistar rats were fed an experimental diet containing 5% pectin as the only dietary fibre, compared to rats fed the experimental diet containing no dietary fibre. These large changes in the short chain fatty acid profile, caused by pectin supplementation, have important implications for the metabolism and health of the colon.

Effects of two contrasting dietary fibres on starch digestion, short-chain fatty acid production and transit time in rats.

Dietary fibres may cause dietary starch to escape digestion in the small intestine and enter the large intestine. If this results from the dietary fibres reducing the gastrointestinal transit time, those dietary fibres that reduce this the most would be expected to cause the most starch to escape digestion. We tested in rats the relative abilities of two contrasting dietary fibres, apple pectin (a soluble dietary fibre) and wheat straw (an insoluble, lignified dietary fibre), to reduce the whole gut transit time and to cause dietary starch to escape digestion. We provided male Wistar rats with a control, modified AIN-76™ diet containing 20% fat but no dietary fibre, and with this diet containing 10% dietary fibre; the dietary fibre replaced the equivalent weight of starch in the control diet. Both dietary fibres, but particularly wheat straw, reduced the transit time compared with the fibre-free control diet. Pectin, but not wheat straw, resulted in substantial amounts of starch in the caecal contents. This effect may result from the pectin increasing the viscosity of the digesta or causing it to gel. Large amounts of short-chain fatty acids were found only in the caeca of rats provided with pectin. © 2000 Society of Chemical Industry

Sucralfate interactions with gastric mucus

Sucralfate protects the stomach against a number of experimental damaging agents and is efficacious in the treatment of peptic ulcer disease. It binds with acidity to the base of an ulcer to form a protective barrier. Sucralfate also enhances prostaglandin synthesis and release in the mucosa. In this study, the rat stomach was examined to determine sucralfates interaction with gastric mucus. Mucus in the rat stomach forms a distinct and continuous blanket. In snap-frozen samples, pretreatment with phosphate-buffered saline as a control shows a layer of mucus of homogeneous structure thinner than the homogeneous layer after pretreatment with antibodies developed against rat gastric mucus. Pretreatment with the surface protective agent sucralfate shows some increase in the thickness of mucus with a thin dense sublayer adjacent to the epithelium and a less dense-appearing outer zone of variable thickness. Analysis of x-rays generated by the electron beam on windows of mucus and epithelium showed the expected gradients of sodium, potassium, chloride, and sulfur. The percentage of aluminum and sulfur in the mucus was higher in sucralfate-treated samples than in controls. Interaction between sucralfate and gastric mucus needs further investigation.

Pig gastric mucus: A one-way barrier for H+

Gastric mucus is thought to protect the underlying mucosal cells from mechanical hazards and back-diffusion of luminal H+. In health, a pH gradient exists across the mucus layer from the variable low pH of the lumen to a pH approaching neutrality at the epithelial cell surface. By current hypotheses this gradient is maintained by the combined effects of an unstirred layer, restricted or slowed diffusion of H+ in the mucus, and the epithelial cell secretion of bicarbonate, which is confined to the cell surface by the mucus layer. These mechanisms do not explain how H+ is secreted through mucus in the first place. Using a modified diffusion chamber we have shown that pig gastric mucus facilitates a low-efficiency Na+/H+ exchange--a property that helps to clarify some previously unexplained components of H+ secretion. When a solution containing Na+ was separated by a layer of fresh pig gastric mucus from a solution of similar pH containing a much lower concentration of sodium, the sodium-rich solution was electrically negative relative to the sodium-poor solution and its pH decreased significantly with time. A similar pH gradient developed when the barrier was a synthetic cation-exchange membrane, and one of opposite sign when it was an anion exchanger; no pH gradient developed across neutral barriers. It is suggested that similar electrical coupling of H+ diffusion to active Na+ transport might in vivo ensure that secreted H+ moves into the gastric lumen.

Aspirin changes the secretion rate and amino acid composition of human small intestinal mucin in subjects with ileal conduits.

The effect of aspirin on the rate of secretion and amino acid composition of human ileal mucin was studied, using subjects with ileal conduits as a model system in which mucin secreted from the ileal conduit tissue is flushed out in the urine and can be measured and analysed. Aspirin (600 mg per day, administered orally) increased the daily mucin output by 37–104% in subjects by days 3 or 4, but thereafter the mucin output declined to below the baseline level by day 10. Mucin samples, purified from the ileal conduit urine during the control period and during aspirin administration, were compared. There were no discernible changes in the degree of polymerisation or the density, but during aspirin administration the amino acid composition was significantly changed, and in particular threonine and proline were enriched. One possible explanation, consistent with the compositional analyses, is that the N- and C-terminal regions of the mucin subunits have been cleaved off and lost during aspirin administration. The observed changes in mucin secretion may have implications for the mechanism of the toxic effects of aspirin on the small intestine by altering the barrier properties of the mucus layer.