Characteristics of the intestinal epithelial barrier during dietary manipulation and glucocorticoid stress.

OBJECTIVES: a) To determine the significance of stress-induced alterations in intestinal permeability by measuring the transmucosal flux of formyl-methionyl-leucyl-phenylalanine (f-MLP), a ubiquitous neutrophilic chemoattractant present in the human and rodent colon; and b) to determine whether stress and/or diet influence(s) bacterial adherence-induced changes in epithelial permeability by affecting the production of secretory immunoglobulin A (IgA), the main immune mechanism preventing bacterial adherence. DESIGN: Prospective, randomized, controlled study. SETTING: University animal research laboratory. SUBJECTS: Female Fischer rats. INTERVENTIONS: Rats were randomly assigned to four groups of seven animals each. Groups of animals were assigned to receive saline or dexamethasone (0.8 mg/kg ip) and were either starved (5% dextrose in water ad libitum) or fed (water and rat chow) for 48 hrs. MEASUREMENTS AND MAIN RESULTS: Mucosal barrier function was evaluated by measuring secretory IgA, bacterial adherence to the intestinal mucosa, and transepithelial electrical resistance, a measure of tight junction permeability. The f-MLP permeation across the mucosa was also determined in segments with significant permeability changes. Results indicate that starvation in dexamethasone-treated rats significantly impairs secretory IgA, promotes bacterial adherence to the mucosa, and results in increased intestinal permeability to f-MLP. These effects are significantly attenuated by the feeding of rat chow. CONCLUSIONS: Alterations in intestinal barrier function are characterized by depressed IgA, bacterial adherence to the intestinal mucosa, and permeation of clinically relevant proinflammatory luminal macromolecules (f-MLP). Enteral stimulation with foodstuffs is a necessary protective measure to prevent altered epithelial barrier function during glucocorticoid stress.

The effect of dexamethasone administration on rat intestinal permeability: the role of bacterial adherence.

BACKGROUND/AIMS: Previous studies have shown that dexamethasone administration to rats results in diminution of biliary secretory immunoglobulin A concentration and alters intestinal barrier function to bacteria. The aims of this study were to examine and characterize the effect of dexamethasone on intestinal permeability and to determine the possible influence of bacterial adherence to the mucosa in this process. METHODS: Groups of adult Fisher rats were studied, and the effects of dexamethasone administration and bowel decontamination on bacterial adherence and intestinal permeability were determined in various bowel segments. RESULTS: Dexamethasone administration was associated with a significant increase in bacterial adherence to the mucosa, which was most pronounced in the cecum (4.33 +/- 0.2 colony forming units (cfu) (log10) per gram of mucosa for control vs. 6.23 +/- 0.2 for dexamethasone). This was accompanied by significant alterations in intestinal permeability as measured by a decrease in transepithelial electrical resistance (49.5 +/- 4.1 omega.cm2 for control vs. 25.4 +/- 2.5 omega.cm2 for dexamethasone). Dual sodium-mannitol flux analysis showed this defect to be predominantly paracellular. Antibiotic decontamination of the intestine completely abrogated the intestinal permeability defect observed in this model. CONCLUSIONS: Bacterial-mucosal cell interactions may be responsible for alterations in intestinal permeability after dexamethasone administration.

The effect of dexamethasone and endotoxin administration on biliary IgA and bacterial adherence.

Adherence of bacteria to the intestinal epithelial cell may be the crucial initiating event for invasion and translocation and is normally prevented by both immune (IgA) and nonimmune (mucus, peristalsis, desquamation) mucosal defense mechanisms. The purpose of the present study was to examine the effect of endotoxin administration on mucosal immunity and to define the role of glucocorticoids, commonly released during endotoxicosis, in this process. Thirty female Fisher rats were randomly assigned to three groups of 10 animals each. Group I (CONT), was fed rat chow and H2O ad lib., Group II (DEX) was administered 0.8 mg/kg subcutaneously of dexamethasone, and Group III (ETX) was given 1 mg/kg of endotoxin. Twenty-four hours later animals were sacrificed and mesenteric lymph nodes and vigorously washed stool-free ceca were collected and cultured. Bile was collected and assayed for IgA from 5 animals in each group. A significant decrease (P < 0.05) in secretory IgA was noted in animals treated with either dexamethasone or endotoxin (CONT = 332 +/- 42, DEX = 78 +/- 24, ETX = 68 +/- 16 micrograms/mg protein +/- SEM). No difference in S-IgA between animals in the dexamethasone-treated group and the endotoxin-treated group was noted (P = NS). A statistically significant increase (P < 0.001) in bacteria adherent to the cecal wall in both the dexamethasone-treated rats and the endotoxin-treated rats over that in = 7.5 +/- 0.8, CONT = 6.4 +/- 0.6 cfu/g(log10) +/- SD). Our results suggest that endotoxin or glucocorticoid administration results in significant bacterial adherence to the cecal mucosa and a decrease in IgA.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of glutamine-enriched TPN on gut immune cellularity.

Prolonged parenteral feeding with standard nutrient solutions results in significant alteration in the structural, hormonal, and immunological composition of the intestinal tract. The purpose of the following study was to evaluate the effect of glutamine-supplemented parenteral nutrition on the immune cellularity of the gut. Twenty-one Fischer rats were randomized to three groups of seven animals each. Group I was fed rat chow and water ad lib, Group II was fed a standard solution of total parenteral nutrition (TPN) (D25/4.25% amino acids) via a central venous catheter, and Group III was fed the standard solution of TPN with 2% glutamine which was isonitrogenous and isocaloric to Group II. Animals were fed their respective diets for 1 week and bile was collected and assayed for secretory IgA (s-IgA) and IgM. The terminal ileum was stained and assayed for IgA+, IgM+, IgG+, CD4+, and CD8+ plasma cells and lymphocytes. Results indicate that the feeding of a standard parenteral diet results in a significant decrease in biliary s-IgA and IgA+ plasma cells in the gut lamina propria compared to chow-fed animals (S-IgA: chow, 858 +/- 23 micrograms/ml; TPN, 494 +/- 41 micrograms/ml; IgA cells: chow, 35.7 +/- 1.8; TPN, 8.6 +/- 0.9 cells/hpf). In addition a marked depletion of CD4+ and CD8+ lymphocytes was observed with standard solutions of parenteral nutrition compared to chow (CD4+: chow, 36.8 +/- 6.6; TPN, 14.9 +/- 6.0; CD8+: chow, 18.8 +/- 5.6; TPN, 5.7 +/- 2.7 cells/hpf). The addition of glutamine to the standard TPN solution maintained both B and T cell populations at levels similar to chow-fed animals.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of glucocorticoid administration on bacterial translocation. Evidence for an acquired mucosal immunodeficient state.

Adherence of bacteria to intestinal epithelial cells may be the crucial initiating event for translocation and is normally prevented by both specific (secretory IgA) and nonspecific (mucus, bacterial antagonism, desquamation) mucosal defense mechanisms. The purpose of this study was to examine the effect of dexamethasone administration on mucosal immunity; specifically bacterial adherence and IgA. Twenty Fischer rats were randomly assigned to two groups of 10 animals each. Group I received 0.5 mL saline injection intraperitoneally (IP); and group II, 0.8 mg/150 g body weight dexamethasone IP per day for 2 consecutive days. The cecum mesenteric lymph nodes, and bile were aseptically collected, and bacterial adherence, bacterial translocation, and IgA concentration were determined. Results indicate that, compared with saline-treated animals, dexamethasone-treated animals had a fall in IgA (54 +/- 24 versus 232 +/- 41 micrograms/mg protein), an increase in bacterial adherence (8.2 +/- 0.5 versus 3.4 +/- 0.6 cfu (log10)/g cecum), and an increased incidence of bacterial translocation to the mesenteric lymph nodes (60% versus 0%). These data suggest that glucocorticoids may promote bacterial translocation by impairment of mucosal IgA synthesis.

Effect of commercially available chemically defined liquid diets on the intestinal microflora and bacterial translocation from the gut.

The effect of chemically defined liquid diets on the intestinal microflora and bacterial translocation from the gut was studied in the rat. Seventy-five female Fischer rats were randomized to five groups of 15 animals each. Group I was fed rat chow and water, group II was fed Vivonex TEN, group III was fed Ensure, group IV was fed Enrich, and group V was fed Ensure plus ground corn cobs, a crude fiber source. Animals were fed their respective diets ad libitum for 1 week and then killed. Quantitative culture of the mesenteric lymph nodes (MLN) and cecum was performed to determine bacterial translocation from the gut. A 66% translocation rate (10/15) of bacteria to MLN was observed in the animals fed Ensure and Enrich compared to 21% in the Vivonex TEN group (3/14) and 20% in the animals fed Ensure plus ground corn cobs (3/15). None of the animals in the control group eating their normal diets of rat chow and water developed positive MLN. Statistical significance (p less than 0.001) was achieved between the Ensure and Enrich groups when compared to controls but not between the Vivonex TEN and Ensure plus corn cobs. Cecal culture revealed a statistically significant rise in cecal bacteria in all groups when compared to the control group (group I). These results indicate that chemically defined liquid diets result in altered intestinal microflora and bacterial translocation from the gut.

Glutamine-supplemented total parenteral nutrition improves gut immune function.

Glutamine has been demonstrated to be an important source of fuel for the gut. The purpose of this study was to evaluate the effect of glutamine-supplemented hyperalimentation on gut immune function. Thirty-six female Fischer rats were randomized into three groups: group 1 (chow) was fed rat chow and water ad libitum, group 2 (total parenteral nutrition) received a standard hyperalimentation formula, and group 3 (total parenteral nutrition-glutamine) received a hyperalimentation solution that contained 2% glutamine. Animals were maintained on their respective diets for 2 weeks and then killed. Mesenteric lymph nodes were harvested for culture, bile was assayed for secretory IgA, and bowel was excised to assay bacterial adherence. Results indicated that glutamine-supplemented total parenteral nutrition protects against bacterial translocation from the gut seen with standard formulas. This effect may be mediated by the secretory IgA immune system.

Total parenteral nutrition promotes bacterial translocation from the gut.

Bacterial translocation from the gut may be the primary event in many disease processes. The purpose of this study was to examine the route of nutrient administration on bacterial translocation from the gut. Each of 90 female Fischer rats underwent placement of a central venous catheter and was randomized to one of three groups. Group I (control) received food and water ad libitum. Group II received standard TPN solution orally from a bottle sipper and drank the solution ad libitum. Group III underwent TPN via the central catheter by pair feeding of the animals with group II. Animals were fed for 2 weeks, and liver, spleen, mesenteric lymph nodes, blood, and cecum were aseptically obtained for culture. A statistically significant difference (p less than 0.014) was found between translocation rates of parenterally fed animals compared with enterally fed animals. Two thirds of the animals (18/27) fed parenterally had culture-positive mesenteric lymph nodes compared with one third (9/27) of the enterally fed group and none (0/30) of the control group. A statistically significant increase in the cecal bacterial count was demonstrated in the animals fed the TPN solution, independent of route. Parenteral nutrition promotes bacterial translocation from the gut by increasing the cecal bacterial count and impairing intestinal defense.