Effect of thermal injury in the rat on transfer of IgA protein into bile

Decreased IgA+ plasma cells and IgA expression in acute liver necrosis mice

AIM: To investigate the number of intestinal immunoglobulin A (IgA+) plasma cells and expression of intestinal IgA in mice with acute liver necrosis.

METHODS: A model of acute liver necrosis was established by intraperitoneal injection of galactosamine (GalN) and lipopolysaccharide (LPS). Sixty mice were randomly divided into one of 4 equal groups: normal control, acute liver necrosis, LPS, or GalN. Hematoxylin and eosin staining, immunohistochemistry, and an enzyme-linked immunosorbent assay were employed to assess liver and intestinal injury, count intestinal IgA+ plasma cells, and measure the expression level of IgA and interferon γ (IFN-γ) in the small intestinal mucosa of mice.

RESULTS: Injured intestinal mucosa was observed in the acute liver necrosis group but not in the normal, LPS or GalN groups. Compared with the normal group, intestinal IgA+ plasma cells were slightly decreased in the LPS and GalN groups [429 ± 20 per high power field (HPF), 406 ± 18/HPF, respectively], whereas they were markedly decreased in the acute liver necrosis group (282 ± 17/HPF vs 495 ± 26/HPF in normal group, P < 0.05). The expression of intestinal IgA was also slightly decreased in LPS and GalN groups, but was markedly reduced in the acute liver necrosis group as determined by enzyme-linked immunosorbent assay (P < 0.05). In contrast, the level of IFN-γ was slightly increased in LPS, GalN and acute liver necrosis groups, but with no statistical significance (P > 0.05).

CONCLUSION: Intestinal IgA+ plasma cells and IgA expression levels indicating that mucosal immune barrier dysfunction, does exist in acute liver necrosis.

Preventive effect of glutamine on intestinal barrier dysfunction induced by severe trauma

AIM: To investigate the mechanism underlying intestinal barrier function damage after severe trauma and the therapeutic effect of glutamine.

METHODS: Burned patients, and animal models of severe trauma replicated by hemorrhagic shock combined with endotoxin infusion and burn injury, were included in a serial experiment. Effects of oral glutamine on intestinal barrier function were observed in scalded rats. Parameters measured in these experiments were as follows: plasma levels of diamine oxidase (DAO), tumor necrosis factor (TNFα ), endotoxin (LPS), and lactate as well as D-lactate by biochemical methods, lactose/mannitol (L/M) ratio in urine by SP-3400, and pathological examination of intestinal mucosa under light microscopy.

RESULTS: Plasma DAO activity was significantly increased after injury. There was a negative correlation between plasma DAO and intestinal mucosal DAO or pHi (r = -0.93, plasma 0.80 ± 0.93, 2.83 ± 1.71, 1.14 ± 0.64, 2.36 ± 2.06 and 2.49 ± 1.67 vs intestinal 0.52 ± 0.12, 0.34 ± 0.03, 0.45 ± 0.18, 0.37 ± 0.26 and 0.41 ± 0.07; r = -0.533, plasma 0.87 ± 0.75, 1.89 ± 1.13, 1.21 ± 0.23, 3.03 ± 2.61 and 4.70 ± 1.22 vs pHi 7.03 ± 0.05, 7.05 ± 0.06, 7.14 ± 0.096, 7.20 ± 0.08 and 7.05 ± 0.07; P < 0.01-0.05). Positive correlations were found between DAO activity and plasma TNFα , LPS, lactate, L/M and D-lactate (r = 0.817, 0.842, 0.872, and 0.951; plasma DAO 0.87 ± 0.75, 1.89 ± 1.13, 1.21 ± 0.23, 3.03 ± 2.61 and 4.70 ± 1.22 vs TNFα 0.08 ± 0.02, 0.03 ± 0.25, 0.17 ± 0.09, 0.34 ± 0.15 and 0.33 ± 0.18; vs LPS 0.14 ± 0.03, 0.16 ± 0.04, 0.21 ± 0.02, 0.18 ± 0.16 and 0.37 ± 0.10; vs lactate 9.03 ± 2.19, 18.30 ± 2.56, 9.81 ± 2.83, 12.01 ± 6.83, 12.01 ± 6.84 and 43.61 ± 11.27; vs L/M 0.03 ± 0.01, 0.41 ± 0.27, 0.62 ± 0.20, 1.70 ± 0.60; r = 0.774, plasma DAO 1.25 ± 0.41, 2.17 ± 0.71, 2.29 ± 0.87, 1.23 ± 0.55 and 1.11 ± 0.47 vs D-lactate 8.37 ± 2.48, 18.25 ± 6.18, 13.96 ± 4.94, 8.93 ± 3.00 and 12.39 ± 4.94; all P < 0.01), repestively. Damage of intestinal mucosa was found by pathological examination. Intestinal barrier function was improved to a certain extent by oral glutamine in scalded rats.

CONCLUSION: Intestinal barrier function was damaged in the early stage after trauma. Plasma DAO activity, D-lactate content, intestinal pHi and urine L/M may be sensitive markers of intestinal mechanical injury, and glutamine may protect against intestinal barrier dysfunction after severe trauma.

Inhibition of bacterial translocation from the gastrointestinal tract of mice by oral administration of a culture condensate of Bifidobacterium longum

Bacterial translocation occurs when viable bacteria pass through the mucosa of the gastrointestinal tract to the mesenteric lymph nodes (MLN) and other organs. The ability of a diet containing 1% culture condensate of Bifidobacterium longum (MB) to inhibit bacterial translocation from the gastrointestinal tract was tested using antibiotic-decontaminated specific-pathogen-free (SPF) mice and germ-free mice, both of which were monoassociated with Escherichia coli C25. Feeding of MB diet decreased the number of E.coli C25 translocating to MLN to about half the number of the control diet group, but did not reduce the incidence of translocation to MLN. MB diet ingestion also decreased the number of E.coli C25 translocating to MLN in the SPF mice injected with zymosan, but it could not prevent bacteria translocation in mice receiving a 30% thermal injury.

Alterations in intestinal function in acute pancreatitis in an experimental model

Gastrointestinal tract failure may be involved in the development of systemic septic complications in acute pancreatitis. Systemic and intestinal circulation, intestinal permeability and absorptive function were evaluated in the early course of acute pancreatitis induced in rats by retrograde intraductal injection of 0.2 ml of 5 per cent sodium taurodeoxycholate and 0.4 nmol trypsin. A decrease in systemic arterial pressure and intestinal blood flow and an increase in intestinal permeability as measured by the leakage of 125I-labelled human serum albumin from blood to lumen were noted in the distal ileum and colon, reaching statistically significant differences 6 h after induction of pancreatitis. The transport of small molecular markers (sodium fluorescein and 51Cr-labelled ethylenediamine tetra-acetic acid) through the distal ileum and colon in vitro from the mucosal to the serosal site in Ussing chambers significantly increased in the early periodic (20-60 min) of incubation, while the passage of a macromolecular marker (ovalbumin) demonstrated a definite increase at 60-120 min of incubation. D-Xylose absorption from the gut lumen to the portal vein was significantly less in acute pancreatitis than after sham operation. Intravenous administration of the hydroxyl radical scavenger dimethylsulphoxide prevented the compromised intestinal permeability and gut absorptive capacity induced by acute pancreatitis, but did not affect the reduced arterial pressure and intestinal microcirculation. Cytotoxic oxygen-derived free radicals may contribute to the development of alterations in intestinal permeability and absorptive function found in the early stage of acute pancreatitis in the rat.

Regulation of protein secretion into bile: studies in mice with a disrupted mdr2 p-glycoprotein gene

BACKGROUND & AIMS

Protein is secreted into bile via several independent pathways. The aim of this study was to investigate whether these pathways are influenced by secretion of biliary lipid.

METHODS

Protein secretion and biliary lipid output were studied in wild-type mice (+/+), heterozygotes (+/-), and homozygotes (-/-) for mdr2 gene disruption. Biliary lipid and protein output were varied by infusion with taurocholate (TC) and tauroursodeoxycholate (TUDC).

RESULTS

Exocytosis and transcytosis were unaltered in (-/-) mice. Infusion with TC strongly induced secretion of alkaline phosphatase in (-/-) mice but had little effect in (+/-) and (+/+) mice. Infusion with TUDC had little effect on alkaline phosphatase output. In contrast, both TUDC and TC strongly stimulated secretion of aminopeptidase N and lysosomal enzymes in (+/+) mice but had no effect in (-/-) animals. Aminopeptidase N secretion correlated with phospholipid output, but only at high flux. At low flux, aminopeptidase N was secreted independently from both phospholipid and bile salts.

CONCLUSIONS

The canalicular membrane enzymes alkaline phosphatase and aminopeptidase N are secreted via separate pathways. Part of alkaline phosphatase output is controlled by bile salt hydrophobicity, whereas at high lipid flux, aminopeptidase N secretion seems to be coupled to phospholipid output. Lysosomal enzymes follow the latter pathway.

Chronic ethanol intake and burn injury: evidence for synergistic alteration in gut and immune integrity

OBJECTIVE

Chronic ethanol (EtOH) intake and injury are both associated with increased susceptibility to infection in the host. This study examined the immune and gastrointestinal alterations induced by chronic EtOH intake and injury, and compared the effects of enteral and intravenous administration of EtOH.

DESIGN

Rats received 20% EtOH daily for 14 days by gavage [oral (PO)] or superior vena cava [intravenous (i.v.)] infusion. Mean blood EtOH concentrations at 90 minutes after administration were 95.3 mg/dL (PO) and 94.4 mg/dL (i.v.). An additional group of animals underwent a 30% total body surface area full-thickness burn injury 4 hours after the final dose of EtOH or normal saline on experimental day 14. All animals were killed 4 days after burn injury.

MATERIALS AND METHODS

Nonadherent splenic lymphocytes were tested for mitogenic responses to the T-cell mitogens concanavalin A (ConA) and phytohemagglutinin (PHA), and the B-cell mitogens lipopolysaccharide (LPS) and pokeweed. Quantitative bacterial cultures of mesenteric lymph nodes and liver were also performed. Alterations of intestinal mucosa were determined by measurement of ileal mucosal weight, DNA, protein, and diamine oxidase content. Circulating plasma endotoxin concentrations were also measured.

MEASUREMENTS AND MAIN RESULTS

Chronic PO-EtOH intake induced a significant impairment in mitogenic response to T-cell mitogens, with a fourfold reduction in ConA and a twofold reduction in PHA response (p < 0.05 by analysis of variance) and increased bacterial translocation (70% vs. 10%). Chronic EtOH administered by the i.v. route did not reduce mitogenic response to any of the mitogens studied. Histologic examination of ileal segments demonstrated that chronic PO-EtOH administration was associated with significant mucosal disruption and exfoliation. Chronic administration of PO-EtOH prior to burn injury induced a significant impairment in spleen mitogenic response to ConA, PHA, and LPS when compared with all other burn injury groups. Chronic administration of EtOH by the i.v. route prior to burn injury did not alter splenic mitogenesis. In addition, chronic PO-EtOH prior to burn injury increased bacterial translocation rates (80% vs. 33%) and prevented the normal intestinal reparative response to burn injury (demonstrated by a significant reduction in ileal mucosal weight, DNA, and diamine oxidase content).

CONCLUSIONS

Enteral but not i.v. administration of EtOH induced significant immunologic dysfunction (demonstrated by altered spleen mitogenic response) and gastrointestinal dysfunction (demonstrated by depressed ileal mucosal weight, DNA, and diamine oxidase content, and increased bacterial translocation rates). In addition, the administration of chronic enteral EtOH prior to injury resulted in significant immune suppression and impaired the host's ability for normal intestinal repair. These results suggest that this EtOH-induced reduction in immunocompetence may be gut-mediated and that the administration of alcohol prior to injury may result in a synergistic alteration of gut and immune integrity.

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)

Effect of thermal injury on transfer of IR22 IgA myeloma protein into bile in the rat

We previously observed a 75-90% decrease in concentration of biliary IgA after thermal injury to rat skin. Decrease in biliary IgA might result from an alteration in supply of polymeric IgA delivered to the hepatocyte or from an alteration in hepatocyte transfer of polymeric IgA into bile. In the present study, we examined the transfer of intravenously administered 125I-IgA into bile. Purified IR22 rat IgA myeloma protein consisting of both monomeric and polymeric IgA was labelled with 125I. Sprague-Dawley rats (140-180 g) received a 20-30% body surface area scald-burn or sham treatment. The bile duct was cannulated 18-24 h later and 125I-IgA preparations were injected into the tail vein. Bile was collected under light ether anesthesia for 3 h. In rats injected with 125I-IR22 IgA myeloma protein there were no significant differences in total, TCA-precipitable, or immunoprecipitable radioactivity in bile from burn-injured or sham-treated animals. On Bio-Gel A-1.5 m gel permeation, the radioactivity in bile from sham-treated animals eluted in the region of polymeric IgA as expected; the radioactivity in the bile from burn-injured animals eluted equally in the same regions as polymeric IgA and monomeric IgA. In sham-treated rats injected with isolated polymeric IgA only, bile contained primarily polymeric IgA. In burn-injured rats injected with polymeric IgA only, bile contained a mixture of polymeric IgA and monomeric IgA. These findings suggest that hepatocyte processing of polymeric IgA is altered after thermal injury, resulting in the transformation of some polymeric IgA into its monomeric form.

Reduction in biliary IgA after burn injury. Role of diminished delivery via the thoracic duct and of enhanced loss from the systemic circulation

The concentration of biliary IgA is greatly reduced after scald burn injury in the rat, thereby contributing to a deficiency in upper intestinal immune defense. This reduction in biliary IgA might have several explanations, including failure of the transhepatic transport of polymeric IgA (pIgA) from the circulation, decreased delivery of pIgA to the hepatocyte, or decreased local synthesis of IgA in the liver. The authors examined whether burn injury reduces circulating pIgA available for delivery to the hepatocyte. In initial studies, they demonstrated that burn injury induces a decrease in circulating pIgA in bile-duct-ligated rats. They then sought to determine whether this decrease in pIgA was due to increased loss from the circulation or to a decreased supply of pIgA to the circulation through the thoracic duct. After injection of purified 125I-pIgA into bile duct-ligated rats, radioactivity was removed more rapidly from the circulation of burn-injured compared with control rats. The radioactivity localized in the skin and muscle at the site of burn injury. In another group of rats with patent bile ducts, the thoracic duct was cannulated and lymph collected for 12 hours. The total amount of IgA protein in lymph was found to be reduced in burn-injured compared with control animals. Thus, burn injury is accompanied by reduced circulating pIgA, which may be attributed to its enhanced loss from the circulation and to decreased delivery of pIgA from the intestinal mucosa to the systemic circulation via the thoracic duct.

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.

Effects of glutamine-supplemented diets on immunology of the gut

Recent research developments have identified the gastrointestinal tract as the most metabolically active organ after surgical stress. In addition to fulfilling its role as an organ of digestion and absorption, the gut must maintain immunologic function in order to protect the host from invading pathogens. Central to the function of the intestinal immune system is the expression of secretory IgA, the most abundant immunoglobulin in external secretions. The synthesis and expression of IgA in secretions appear to be sensitive to dietary alteration and may be impaired after surgical stress. Data are presented suggesting that maintenance of gut mass and barrier function to bacteria via dietary manipulation may be essential to ensure host survival during critical illness.