The effects of pure and micellar solutions of different bile salts on mucosal morphology in rat jejunum in vivo

Effect of bile pigments on the compromised gut barrier function in a rat model of bile duct ligation

Background

Studies have shown that the absence of bile in the gut lumen, either by bile duct ligation or bile diversion, induces mucosal injury. However, the mechanism remains elusive. In this study, the role of bile pigments in gut barrier function was investigated in a rat model of bile duct ligation.

Methods

Male Sprague Dawley (SD) rats were used in this study. After ligation of bile duct, the animals were administrated with free bilirubin, bilirubin ditaurate, or biliverdin by intragastric gavage. 1, 2, or 3 days later, the animals were sacrificed and the damage of mucosa was assessed by histological staining as well as biochemical parameters such as changes of diamine oxidase (DAO) and D-lactate (D-Lac) in the blood. Trypsin and chymotrypsin of the gut were also measured to determine how these digestive proteases may relate to the observed effects of bile pigments.

Results

Bile duct ligation (BDL) caused significant increases in gut trypsin and chymotrypsin along with damage of the mucosa as demonstrated by the histological findings under microscope, the reduced expression of tight junction molecules like occludin, and significant changes in DAO and D-lac in the blood. Free bilirubin but not bilirubin ditaurate or biliverdin showed significant inhibitions on trypsin and chymotrypsin as well as alleviated changes of histological and biochemical parameters related to gut barrier disruption.

Conclusion

Bile may protect the gut from damage through inhibiting digestive proteases like trypsin and chymotrypsin by free bilirubin.

The problem of bacterial diarrhoea

The reported incidence of "pathogenic" bacteria, as judged by serotype, in the stools of children with acute diarrhoea has varied from 4 to 33% over the last twenty years. Techniques such as tissue culture provide a means for detecting enterotoxin-producing strains of bacteria, strains which often do not possess "pathogenic" serotypes. "Pathogenicity" requires redefinition, and the aetiological importance of bacteria in diarrhoea is probably considerably greater than previous reports have indicated. Colonization of the bowel by a pathogen will result in structural and/or mucosal abnormalities, and will depend on a series of complex interactions between the external environment, the pathogen, and the host and its resident bacterial flora. Enteropathogenic bacteria may be broadly classified as (i) invasive (e.g. Shigella, Salmonella and some Escherichia coli) which predominantly affect the distal bowel, or (ii) non-invasive (e.g. Vibrio cholerae and E. coli) which affect the proximal bowel. V. cholerae and E. coli elaborate heat-labile enterotoxins which activate adenylate cyclase and induce small intestinal secretion; the secretory effects of heat-stable E. coli and heat-labile Shigella dysenteriae enterotoxins are not accompanied by cyclase activation. The two major complications of acute diarrhoea are (i) hypernatraemic dehydration with its attendant neurological, renal and vascular lesions, and (ii) protracted diarrhoea which may lead to severe malnutrition. Deconjugation of bile salts and colonization of the small bowel with toxigenic strains of E. coli may be important in the pathophysiology of the protracted diarrhoea syndrome. The control of bacterial diarrhoea requires a corrdinated political, educational, social, public health and scientific attack. Bacterial diarrhoea is a major health problem throughout the world, and carries an appreciable morbidity and mortality. This is particularly the case during infancy, and in those developing parts of the world where malnutrition is common. This paper is concerned mainly with acute bacterial diarrhoea, and reviews the problem as a whole.

Enzyme changes in remodelling epithelial cells: a histochemical study of the rat jejunum in vivo during and following exposure to deoxycholic acid

Loops of rat jejunum were exposed in vivo to different concentrations of deoxycholic acid (DOC; 0, 2.5, 5, 10 and 20 mM). Following a 30 min exposure period, DOC was washed out of the loops and the intestines were allowed to recover for 15 or 150 min. Frozen tissue for enzyme histochemistry was collected during exposure and following the recovery periods. As shown previously, exposure to DOC caused a dose-dependent loss of epithelial cells at the villous tips and denudation of the lamina propria. Flattened epithelial cells bordering the denuded areas were, however, responsible for a rapid restoration of epithelial continuity, which was completed within 15 min. In the present study, these flattened cells showed normal reactivity for non-specific esterase and succinate dehydrogenase. In contrast, following a prolonged recovery period (150 min), a subpopulation of enterocytes at the villous tips that otherwise appeared normal showed decreased reactivity for brush border enzymes and non-specific esterase, and a positive reaction for mucin. A shutdown in the synthesis of cytoplasmic enzymes and redistribution of cell surface enzymes could be responsible for these late occurring enzyme changes, that were consistently observed after 150 min of recovery from DOC at 20 mM. Alternatively, retention of goblet cells and/or a modification in enzyme synthesis may explain the presence of mucin that was demonstrated in the epithelial cells which had low enzyme reactivity.

The effects of permeation enhancers on the surface morphology of the rat nasal mucosa: a scanning electron microscopy study

A rat model has been developed to compare relative morphological changes in the nasal mucosa after exposure to potential membrane permeation enhancers. Scanning electron microscopy was used to characterize gross structural and specific cellular changes following exposure. Micrographs of the rat nasal mucosa were scored in four categories: (1) mucosal surface integrity, (2) ciliary morphology, (3) mucus/extracellular debris, and (4) presence of red blood cells. The order of increasing morphological damage resulting from a 5-min exposure to each surfactant was 0.5% Solulan C-24 congruent to 0.5% Solulan C-24/0.5% sodium tauro-24,25-dihydrofusidate (STDHF) less than 0.5% STDHF less than 1.0% STDHF much less than 1.0% Laureth-9 less than 1.0% sodium taurodeoxycholate congruent to 1.0% sodium deoxycholate. The changes observed in the mucosal morphology after exposure to the various surfactants are in general agreement with data in the literature. This model is able to compare rapidly the relative morphological effects on the mucosal membrane of different nasal formulations.

Effect of albumin on oleic acid lymphatic absorption in rats

1. The aim of this study was to investigate how fatty acid absorption was affected when exogenous fatty acids were complexed with albumin in absence of bile. Experiments were carried out in vivo, in order to study overall absorption processes. 2. An equimolar mixture of 14C oleic acid, palmitic acid and monopalmitin was infused intraduodenally in bile- and pancreatic juice-diverted rats. 3. Lipids were emulsified with either sodium taurocholate or fatty acids complexed with albumin. 4. Lymphatic lipid output was compared during the 6 hr following infusion of 90 mumol of the radioactive lipid mixture. 5. Lymphatic radioactive lipid recovery was significantly decreased by albumin. 6. Only 17% of the infused radioactivity was recovered in lymph when fatty acids were complexed with albumin against 37% when lipids were emulsified with sodium taurocholate. 7. Unrecovered lymph radioactivity was found at the distal part of intestine. Moreover, albumin significantly decreased lymph flow. 8. We conclude that undigested albumin acted at the luminal level of lipid absorption processes and specifically decreased fatty acid uptake.

Studies on hydragogue drugs: light and electron microscopic examination of the isolated rat colonic mucosa exposed to deoxycholic acid and synthetic surfactants

Sacs of the stripped and everted, isolated descending rat colon were incubated for 2 hours in presence of the following surfactants at the mucosal side: Dodecylsulphate (DDS), dioctylsulphosuccinate (DOSS), cetrimonium bromide (CTMAB), Triton X100 and deoxycholic acid (DOC). After tissue fixation, the sacs were processed for light microscopy (LM) and for scanning (SEM) and transmission (TEM) electron microscopy. All three methods revealed that DOSS (1.3 X 10(-4) and 2.6 X 10(-4) mol/l, CTMAB (5 X 10(-5) and 1 X 10(-4) ) and Triton (2 X 10(-5), 5 X 10(-5) and 1 X 10(-4) ) caused only minor or moderate changes compared to parallel controls, as did also DDS at 1 X 10(-5) and 2 X 10(-5) mol/l. DDS at 2 X 10(-4) and 4 X 10(-4) mol/l and DOC at 1.5 X 10(-4) and 3 X 10(-4) mol/l caused more prominent changes. LM showed swollen, vacuolated cells with pycnotic nuclei; many of these cells seemed to be extruded. According to SEM, cells thus affected were most abundantly localized to the normal extrusion zone at the borders of the crypt-surface epithelial cell units. DOC tended to cause a more generalized affection within the units than DDS. In spite of these deleterious effects, gaps corresponding to missing epithelial cells were not observed. TEM indicated the mechanism responsible for restoration of epithelial continuity in spite of extensive cell loss: The remaining epithelial cells seemed to flatten out and re-establish cell-to-cell contact by pseudopod formation along the basement lamina. This repair mechanism seemed to operate at a rapid rate; however, incomplete closure of cellular gaps i.e. small denuded parts of the basement lamina were occasionally observed. The results of this study are discussed in relation to a functional study under identical experimental conditions (Gastroenterol. Clin. Biol. 1981, 5, 124), in which these surfactants caused a significant alteration of normal colonic transport function.

Synthesis and release of lipids and lipoproteins by isolated rat jejunal enterocytes in the presence of sodium taurocholate

Isolated rat jejunal villus and crypt cells prepared by differential scraping and hyaluronidase dispersion were used in the presence of 8 mM sodium taurocholate to study the incorporation of sn-[3H]glycerol-2-monooleate, [1-14C]palmitate, [1-14C]acetate, L-[4,5(n)-3H]leucine and D-[1-14C]glucosamine into cellular and medium lipids and proteins, respectively. The villus cells were capable of an apparently normal biosynthesis of triacylglycerols and phospholipids, as well as of proteins and glycoproteins despite an altered dye permeability and increased release of cytosolic and membrane enzymes. About 20-30% of the newly formed triacylglycerols and about 35% of the newly formed phospholipids were secreted into the medium and were recovered as triacylglycerol-rich particles. Labelled proteins and glycoproteins were also recovered from this fraction. The crypt cells synthesized about one-half as much triacylglycerol and phospholipid as did the villus cells, but secreted little or no labelled lipid into the postincubation medium. The release into the medium of triacylglycerols synthesized by the villus cells was blocked by a pretreatment of the isolated cells with the microtubule disruptors, nocodazole, colchicine and colcemid; by the amino sugar, D-galactosamine; by the inhibitors of protein synthesis, puromycin and cycloheximide, and by the inhibitor of the biosynthesis of phosphatidylcholine, chlorocholine. These results indicate that the secretion of labelled lipids, proteins and glycoproteins by the upper villus enterocytes in the presence of sodium taurocholate is not entirely due to cell breakage and spillage of contents. It is concluded that incubations of isolated villus cells of rat jejunum with mixed micellar solutions containing 8 mM taurocholate are compatible with an apparently normal biosynthesis and secretion of triacylglycerol-rich particles.

Do low doses of deoxycholate modify the release of rat jejunal brush border hydrolases?

The in-vivo effects of sodium deoxycholate (DOC) at low concentrations on the release of protein and some brush border hydrolases, sucrase (SA), maltase (MA), leucine aminopeptidase (LA), alkaline phosphatase (AP), have been investigated in the rat by a jejunal perfusion technique. During perfusion with DOC (0.125 or 0.25 mmol/l), enzyme release was not enhanced. After removal of DOC from the perfusion solution with 0.125 mmol/l DOC, there was a steady release of SA, MA and AP although enzyme release was increased linearly in the control and the 0.25 mmol/l DOC groups. The results also confirm the deep localization of AP within the membrane.

In vivo reversibility of the jejunal glucose and cation transport alteration caused by intraluminal surfactants in the rat

Tied jejunal loops in anaesthetized rats were under standardized conditions pre-exposed for 30 min. with Tyrode solution containing surfactants. 5, 20 or 150 min. after wash out of bulk surfactant, the loops were re-instilled with Tyrode containing glucose at 5--15 mmol/l. Net glucose, sodium and potassium transport were studied for 15 min. by changes in intraluminal amounts, and compared with results obtained in control rats. The surfactants (mmol/l) tested were the anionics dioctylsulphosuccinate (5.6) and dodecylsulphate (8.5--17), the cationics cetrimonium bromide (2.1--4.1) and benzalkonium chloride (2.1), the nonionics Triton X100 (0.25%) and Lubrol WX (0.25--0.5%) plus cholic acid (4.9) and desoxycholic acid (1.3--2.5). In most cases, the glucose transport was normal or fairly normal after 150 min., most of the restoration taking place shortly after surfactant removal. However, Lubrol in particular caused more irreversible effects. Generally, the changes in net cation transport tended to be less easily reversible than the alteration in glucose transport. In so far as a normal or near to normal glucose transport is unlikely to occur unless both functional and structural integrity of the epithelium is preserved, the results indicate that in most cases there is but insignificant epithelial damage under the experimental conditions. Since, furthermore, these surfactants can interact with glucose transport in the same technique even at lower concentration and shorter incubation time than used here, it is concluded that the interaction of surfactants with intestinal transport is not neccessarily linked to gross histo-pathological changes.