Butyrate Hastens Restoration of Barrier Function after Thermal and Detergent Injury to Rat Distal Colon in Vitro A. Venkatraman, B. S. Ramakrishna & A. B. Pulimood The Wellcome Trust Research Laboratory, Dept. of Gastrointestinal Sciences, Christian Medical College and Hospital, Vellore, India Venkatraman A, Ramakrishna BS, Pulimood AB. Butyrate hastens restoration of barrier function after thermal and detergent injury to rat distal colon in vitro. Scand J Gastroenterol 1999;34:1087–1092. Background: Epithelial migration restores barrier function after superﬁcial injury to any mucosa. The present study aimed to determine whether butyrate, important to colonic epithelial physiology in diverse ways, inﬂuences restoration of barrier function in the injured rat colon. Methods: Rat distal colon was transiently exposed in vitro to heat (55 °C for 10 sec) or to detergent (deoxycholic acid, 7.5 mM, for 15 min), and tissue damage was veriﬁed histologically. Epithelial barrier function was assessed, in colon tissue mounted in Ussing chambers, by measuring electric resistance and passive serosa-to-mucosa ﬂuxes of 22 Na and of 14 C PEG 4000 under voltage clamp conditions. Studies were done in the absence and presence of 25 mM butyrate in the bathing solutions. Results: Heat exposure induced superﬁcial epithelial damage, and the electric resistance decreased signiﬁcantly. This was accompanied by increase in ﬂux of 14 C PEG and increased passive ﬂux of 22 Na. Electric resistance was signiﬁcantly higher, and PEG ﬂux signiﬁcantly lower, in tissues bathed with butyrate. Exposure to deoxycholic acid also induced superﬁcial epithelial damage, reduced tissue electric resistance, and increased passive ﬂux of Na and PEG. Electric resistance was signiﬁcantly higher, and PEG ﬂux signiﬁcantly lower, in injured tissues bathed in butyrate, than in injured tissues bathed in butyrate-free solution. The effect of butyrate on restoration of electric resistance towards normal was seen in colon both from adult rats and from younger rats that were 2 or 6 weeks old. Conclusions: Butyrate enhanced restoration of mucosal barrier function in rat distal colon in response to heat and detergent injury. Key words: Butyrate; epithelial restitution; mucosal barrier; permeability Dr. B. S. Ramakrishna, Dept. of Gastrointestinal Sciences, Christian Medical College Hospital, Vellore 632004, India (fax: +91 416 232035) T he colonic mucosa is an important barrier separating potentially noxious elements in the bowel lumen from the internal milieu of the body. The barrier, which is a function of colonic epithelial cells and intervening tight junctions (1), prevents pro-inﬂammatory molecules in the bowel lumen from gaining access to the lamina propria. Any disturbance of barrier function, irrespective of the underlying cause, is followed by mucosal inﬂammation (2). In health, the paracellular pathway is the main pathway of passive absorp- tion across the mucosa. In disease, increased mucosal permeability correlates with the presence of intestinal mucosal inﬂammation. Mucosal permeability to ethylenedia- minetetraacetic acid and to polyethylene glycol 600 are increased in active ulcerative colitis (3, 4) and in Crohn disease patients and their relatives (5). Similarly, colitis in experimental animals is associated with an increased perme- ability to polyethylene glycol 4000 (6). Impaired mucosal barrier function is equally important in infectious diarrhoea, and the increased permeability may contribute to diarrhoea. Defects of barrier function in cultured intestinal epithelial cell monolayers have been shown to result from infection with bacteria and parasites and from exposure to bacterial toxins (7–9). Superﬁcial injury to the colonic mucosa has been used as a technique to study breakdown and repair of the epithelial barrier. As an immediate response to breakdown of the barrier, actin arcs and rings form in an effort to approximate the edges of the wounded area (10). Simultaneously, adjacent epithelial cells extend lamellipodia, leading to ﬂattening and migration of the crypt epithelium to cover gaps in the surface (11). This phenomenon, called epithelial restitution, occurs within a few hours and is followed hours later by increased epithelial cell proliferation and re-epithelialization (12). The alteration in barrier function can be assessed functionally by studying whole intestinal wall mounted in ﬂux chambers and measuring electric resistance in addition to passive transport of molecules of different sizes (13–15). Butyrate, a short-chain fatty acid produced in the colon by bacterial fermentation of unabsorbed carbohydrate, plays an important physiologic role in the maintenance of the health and integrity of the colonic epithelium (16). In cultured colonic cell lines not exposed to deleterious inﬂuences, ORIGINAL ARTICLE  Scandinavian University Press 1999 Scand J Gastroenterol Downloaded from informahealthcare.com by Tufts University on 08/26/13 For personal use only.