Intestinal Barrier Failure Research Articles

Pathophysiology of increased intestinal permeability in obstructive jaundice

Despite advances in preoperative evaluation and postoperative care, intervention, especially surgery, for relief of obstructive jaundice still carries high morbidity and mortality rates, mainly due to sepsis and renal dysfunction. The key event in the pathophysiology of obstructive jaundice-associated complications is endotoxemia of gut origin because of intestinal barrier failure. This breakage of the gut barrier in obstructive jaundice is multi-factorial, involving disruption of the immunologic, biological and mechanical barrier. Experimental and clinical studies have shown that obstructive jaundice results in increased intestinal permeability. The mechanisms implicated in this phenomenon remain unresolved, but growing research interest during the last decade has shed light in our knowledge in the field. This review summarizes the current concepts in the pathophysiology of obstructive jaundice-induced gut barrier dysfunction, analyzing pivotal factors, such as altered intestinal tight junctions expression, oxidative stress and imbalance of enterocyte proliferation and apoptosis. Clinicians handling patients with obstructive jaundice should not neglect protecting the intestinal barrier function before, during and after intervention for the relief of this condition, which may improve their patients' outcome.

Allopurinol, oxidative stress and intestinal permeability in patients with cirrhosis: an open‐label pilot study

Cirrhosis is associated with intestinal barrier failure, related in part to enterocytes oxidative damage via xanthine oxidase overactivity. Experimentally, allopurinol, a xanthine oxidase inhibitor, reduces enterocytes' damage and bacterial translocation. To assess the short-term effects of allopurinol on intestinal permeability, oxidative stress and endotoxin-dependent cytokines in patients with cirrhosis. Nineteen patients with cirrhosis, in a stable condition (age: 56 years; Child A/B/C: 6/7/6; ascites: 12; alcoholic cirrhosis: 16/19; abstinence >2 weeks), were included. At baseline and day 10 of allopurinol 400 mg/day, intestinal permeability [lactulose/mannitol (Lac/Man) ratio test], oxidative stress (serum malondialdehyde), as well as TNF-soluble receptor-1, IL-6 and lipopolysaccharide-binding protein (which reflects exposition to endotoxin) were measured. Malondialdehyde decreased significantly (-23%, P<0.05), whereas no effects were seen on intestinal permeability and the endotoxin-associated systemic inflammatory response. At baseline, portal pressure correlated to the Lac/Man ratio (r=0.55, P<0.02). At day 10, changes in malondialdehyde correlated to changes in the Lac/Man ratio (r=0.51, P<0.05). A 10-day course of allopurinol in patients with cirrhosis is associated with a significant reduction in oxidative stress but no effect on intestinal permeability and inflammatory markers. Whether intestinal damage in cirrhosis can be accessible to antioxidant therapy requires further study.

MULTISPECIES PROBIOTICS ABOLISH ACUTE PANCREATITIS-ASSOCIATED MUCOSAL BARRIER FAILURE IN MURINE ILEUM

Intestinal mucosal barrier failure during acute pancreatitis is associated with translocation of luminal bacteria to extra-intestinal sites. Resulting infectious complications are a major cause of morbidity and mortality. Aim of this study was to determine if multispecies probiotics can diminish mucosal barrier failure in the course of experimental acute pancreatitis (AP). Mice were treated daily with a mixture of six probiotic strains (Ecologic 641®, Winclove BioIndustries, Amsterdam, The Netherlands, 2.5×109 bacteria/oral gavage) or placebo, from 2 days prior to cerulein induced AP (hourly intraperitoneal injections, 50μg/kg, for 10 hours) until termination 72 hours after the first injection. Sham procedure consisted of 10 hourly sterile saline injections, without probiotic or placebo treatment. Mucosal barrier function of the distal ileum was assessed by measurement of mucosal integrity (electrical resistance, R: Ω.cm2) and permeability (steady state transepithelial flux of 0.01 gr/l Na-fluorescin, flux: ng/cm2/h) at 36°C, in Ussing chambers. AP reduced mucosal integrity and increased permeability (AP (n = 13) vs. sham (n = 15): R = 28.1 ± 1.4 Ω.cm2 (mean ± SEM) vs. 37,5 ± 1.7, P = 0.002; flux = 400 ± 48 ng/cm2/h vs. 189 ± 18, P = 0.001, ANOVA). Probiotic treatment completely abolished the AP-induced mucosal barrier failure (placebo vs. probiotics (n = 15): R = 26.4 ± 2.6 vs. 34.9 ± 1.8, P = 0.003; flux = 427 ± 62 vs. 246 ± 32, P = 0.014). Mucosal resistance and permeability of probiotic treated mice were not different from those of healthy controls or sham (P = 0.551 and P = 0.194, respectively). Conclusions: Experimental acute pancreatitis results in decreased integrity and increased permeability of ileal mucosa. This mucosal barrier failure can be abolished by the used regime of selected multispecies probiotics. Support of mucosal barrier function by multispecies probiotics may provide a novel strategy to reduce infectious complications during acute pancreatitis.

Barrera intestinal del paciente crítico: realidades y tendencias

The disturbances of gut barrier in critically ill patients may influence their outcome and prognosis. Experiments in animals show that fasting and stress collaborate to produce intestinal atrophy and translocation of microorganisms and toxins. This fact is one of the main arguments to promote the use of early enteral feeding in critically ill patients. However, the intestinal barrier behaves differently in humans than in animals. The human enteral cells have a good tolerance to fasting and stress, mucosal atrophy is mild and it is not always associated with changes in intestinal permeability. Moreover, the relationship between intestinal permeability with sepsis and bacterial translocation is controversial. This last phenomenon also happens in normal subjects and may be a mechanism to build immunological memory. One of the most important factors that influence bacterial translocation is the microorganism, that under stress conditions can adhere to the intestinal cell and penetrate the intestinal barrier. Splanchnic ischemia and reperfusion is one of the main pathogenic factors in the failure of intestinal barrier. Finally, the fact that the small bowel is an inflammatory target of extra intestinal injuries, explains several clinical situations. The pathophysiology of the intestinal barrier definitely requires more research.

Intestinal barrier failure during experimental necrotizing enterocolitis: protective effect of EGF treatment

Necrotizing enterocolitis (NEC) is the most common intestinal disease of premature infants. Although increased mucosal permeability and altered epithelial structure have been associated with many intestinal disorders, the role of intestinal barrier function in NEC pathogenesis is currently unknown. We investigated the structural and functional changes of the intestinal barrier in a rat model of NEC. In addition, the effect of EGF treatment on intestinal barrier function was evaluated. Premature rats were divided into three groups: dam fed (DF), formula fed (NEC), or fed with formula supplemented with 500 ng/ml EGF (NEC + EGF); all groups were exposed to asphyxia/cold stress to develop NEC. Intestinal permeability, goblet cell density, mucin production, and composition of tight junction (TJ) proteins were evaluated in the terminal ileum, the site of NEC injury, and compared with the proximal jejunum, which was unaffected by NEC. Animals with NEC had significantly increased intestinal paracellular permeability compared with DF pups. Ileal goblet cell morphology, mucin production, and TJ composition were altered in animals with NEC. EGF treatment significantly decreased intestinal paracellular permeability, increased goblet cell density and mucin production, and normalized expression of two major TJ proteins, occludin and claudin-3, in the ileum. In conclusion, experimental NEC is associated with disruption of the intestinal barrier. EGF treatment maintains intestinal integrity at the site of injury by accelerating goblet cell maturation and mucin production and normalizing expression of TJ proteins, leading to improved intestinal barrier function.

Evidence for intestinal oxidative stress in patients with obstructive jaundice

Obstructive jaundice results in failure of the intestinal barrier with consequent systemic endotoxemia associated with septic complications. We have recently shown that gut barrier failure in experimental obstructive jaundice is associated with high intestinal oxidative stress. This study was undertaken to investigate whether oxidative alterations occur in the intestinal mucosa of patients with obstructive jaundice. Fifteen patients with malignant biliary obstruction and no signs of cholangitis and 15 control patients were subjected to duodenal biopsy to assess intestinal oxidative stress, estimated by lipid peroxidation (malondialdehyde - MDA) and glutathione redox state [reduced glutathione (GSH), glutathione disulphide (GSSG) and GSH/GSSG ratio]. In addition, mucosal biopsies were examined histologically and intestinal mucosal protein content was determined biochemically as an index of intestinal trophic state. Patients with obstructive jaundice presented high levels of intestinal oxidative stress, with significantly increased lipid peroxidation (P < 0.001). Glutathione redox state was also suggestive of high intestinal oxidative stress in jaundiced patients, indicated by significantly decreased GSH (P = 0.001) and GSH/GSSG ratio (P = 0.006) and increased GSSG (P = 0.026). Histological examination showed a mild infiltration of the lamina propria by chronic inflammatory cells in obstructive jaundice, whereas duodenal architecture remained intact and epithelial continuity was retained. Duodenal mucosa was atrophic in jaundiced patients as indicated by a significant reduction of mucosal protein content compared with controls (P = 0.001). Among oxidative stress parameters, intestinal GSH exhibited a significant positive correlation with mucosal protein content (r = 0.588, P = 0.021). Obstructive jaundice in humans induces intestinal oxidative stress, which may be a key factor contributing to intestinal barrier failure and the development of septic complications in this patient population.

Experimental obstructive jaundice alters claudin-4 expression in intestinal mucosa: Effect of bombesin and neurotensin

To investigate the influence of experimental obstructive jaundice and exogenous bombesin (BBS) and neurotensin (NT) administration on the expression of the tight junction (TJ)-protein claudin-4 in intestinal epithelium of rats. Forty male Wistar rats were randomly divided into five groups: I = controls, II = sham operated, III = bile duct ligation (BDL), IV = BDL+BBS (30 microg/kg per d), V = BDL+NT (300 microg/kg per d). At the end of the experiment on d 10, endotoxin was measured in portal and aortic blood. Tissue sections of the terminal ileum were examined histologically and immunohistochemically for evaluation of claudin-4 expression in intestinal epithelium. Obstructive jaundice led to intestinal barrier failure demonstrated by significant portal and aortic endotoxemia. Claudin-4 expression was significantly increased in the upper third of the villi in jaundiced rats and an upregulation of its lateral distribution was noted. Administration of BBS or NT restored claudin-4 expression to the control state and significantly reduced portal and aortic endotoxemia. Experimental obstructive jaundice increases claudin-4 expression in intestinal epithelium, which may be a key factor contributing to the disruption of the mucosal barrier. Gut regulatory peptides BBS and NT can prevent this alteration and reduce portal and systemic endotoxemia.

Mechanisms of nitric oxide-mediated intestinal barrier failure in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the leading intestinal emergency in premature infants. The underlying etiology of NEC remains elusive, but hypoxic conditions and early enteral feeding are consistently implicated as the main risk factors in the pathogenesis of NEC. We postulate that nitric oxide (NO) plays a key role as a molecular signaling "hub" in the generation of gut barrier failure in NEC. Clinical studies suggest that inflammatory cytokines and excessive NO production may contribute to the pathogenesis of NEC. One of the major challenges in defining the critical signaling pathways that lead to the development of NEC is the lack of specific biochemical markers that consistently delineate the early stages of NEC. Intestinal pathology and molecular markers derived from late-stage NEC represent end-stage findings and thus provide little insight into the early events that led to intestinal inflammation. Such markers may not represent viable therapeutic targets for the treatment or prevention of NEC. Therefore, novel strategies are needed to identify the patients at risk for NEC and define the clinically relevant molecules that characterize the early stages of NEC. This review will examine the mechanisms of NO-mediated gut barrier failure and propose novel genetic-based approaches for elucidating the critical molecular pathways in NEC.

The Pivotal Role of Tumor Necrosis Factor-?? in Signaling Apoptosis in Intestinal Epithelial Cells under Shock Conditions

Apoptosis is essential for the regulation of cell number and function of intestinal epithelial cells but may contribute to intestinal barrier failure after shock and other low-flow conditions to the gut. Caco2 intestinal cell monolayers were challenged with recombinant tumor necrosis factor (TNF). In a second group of experiments, Caco2 cells were exposed to bacteria and/or hypoxia followed by reoxygenation. Apoptosis was detected using annexin-V propidium-iodide staining. Cell culture supernatants were also obtained in the second group of experiments and TNF levels quantitated. Monolayer integrity was assessed by measurement of paracellular permeability and transepithelial electrical resistance. Apical but not basal recombinant TNF increased Caco2 apoptosis. Exposure to either bacteria alone or hypoxia/reoxygenation alone did not increase apoptosis; however, the combined insults significantly increased apoptosis. The increased apoptosis occurred in a delayed fashion in both groups. TNF was released in a polar fashion, and the greatest levels were noted after exposure to both bacteria and hypoxia-reoxygenation. There was also an increase in paracellular permeability in this group; however, no change in transepithelial electrical resistance was noted. The effects on apoptosis and permeability were abrogated by anti-TNF antibodies. Intestinal epithelial cell apoptosis contributes to barrier failure after shock conditions and is related to augmented TNF release.

ABC Transporters and Sterol Absorption

Recent molecular studies, in particular investigations of subjects with monogenic disorders of lipoprotein metabolism and studies of induced-mutant mice, have increased the understanding of intestinal sterol absorption. Some of these genes encode adenosine triphosphate [ATP] binding cassette (ABC) transporters that transport dietary cholesterol from enterocytes back out to the intestinal lumen, thereby limiting the amount of cholesterol absorbed. ABC transporters also provide an effective barrier against the absorption of plant sterols, which are normally not absorbed in significant quantities by humans. This mechanism was clarified by the discovery that defects in two adjacent genes encoding ABC transporters are the molecular basis of sitosterolemia, a rare autosomal recessive disease in which plant sterols are absorbed due to failure of intestinal barrier to their absorption. Furthermore, recent experiments performed in induced-mutant mice have solidified the importance of these transporters in intestinal sterol absorption. Together with new developments in the biology of bile acids, sterol absorption is providing interesting directions for metabolism research. In addition to elucidating some of the molecular mechanisms of sterol absorption, these recent findings may lead to new therapeutic options to treat hypercholesterolemia and to help patients at risk of vascular disease reach ever-more stringent target levels.

The role of the glutathione antioxidant system in gut barrier failure in a rodent model of experimental necrotizing enterocolitis

BackgroundEvidence suggests that intestinal barrier failure in necrotizing enterocolitis results in part from overproduction of nitric oxide and other toxic oxidant species that result in enterocyte death and intestinal barrier failure. We hypothesize that the glutathione detoxifying system is important in maintaining intestinal barrier integrity by protecting against nitrosative stress. MethodsNewborn rats were subjected to hypoxia (5% O2, tid) and fed formula by gavage (NEC), or were breast-fed without hypoxia (BF). Rats were killed and the distal ilea were harvested for RNA, protein, and morphologic studies. RNA underwent cDNA microarray analysis. To assess glutathione in protecting against nitrosative stress, IEC-6 cells were exposed to SIN-1 and/or L-buthionine-(S,R)-sulfoximine (BSO), a glutathione inhibitor. Cells were analyzed for glutathione-S-transferase activity, apoptosis and mitochondrial function. ResultsBF controls developed normal intestinal architecture, whereas NEC animals sustained damage to the intestinal epithelium. Microarray analysis demonstrated that 93 genes were overexpressed in NEC compared with controls. In the array, glutathione-S-transferase pi and alpha 2, GSH-dependent detoxifying enzymes, RNA were upregulated compared with BF controls. IEC-6 cells exposed to SIN-1/BSO produced an increase in apoptosis. Poly ADP-ribosylpolymerase cleavage and apoptosis-inducing factor (AIF) nuclear localization, markers of apoptosis, were seen in IEC-6 cells exposed to SIN-1/BSO as opposed to media controls. ConclusionThese data support the hypothesis that GSH antioxidant system plays a crucial role in gut barrier protection by attenuating enterocyte death.

Inflammatory cytokines and NO upregulate P-glycoprotein via a PI3K-dependent pathway

Introduction: Sustained upregulation of nitric oxide (NO), as seen in endotoxemia and necrotizing enterocolitis, promotes intestinal barrier failure. P-glycoprotein (PGP) is a transmembrane pump that expels toxins from the intestinal epithelium and thus plays a major role in mucosal defenses. Signaling via the PI3K pathway has been shown to upregulate PGP expression. We examined the effect of inflammatory cytokines, NO and PI3K inhibitors on PGP expression and function in the rat intestinal epithelial cell line IEC-6. Methods: IEC-6 cells were treated with a NO donor (SNAP 500 uM) or cytomix (IFNγ 1000 U/ml, IL-1β 100 U/ml and TNFα 10 ng/ml) ± PI3K inhibitor LY 294002 (10 uM), or NO scavenger CPTIO (100 uM) or inducible NO synthase inhibitor L-NIL (50 uM) for 24 h. Super-natant (SN) nitrite levels were measured by the Griess reaction. PGP expression was measured by western blot, and function by rhodamine 123 transport. Data represent the mean ± SEM; one way ANOVA was used to compare significant differences (p < 0.05) between groups. Results: Cytomix upregulated NO production as seen by increased SN nitrite levels (Table). LY and L-NIL blocked cytomix-mediated NO production. Cytomix and SNAP upregulated PGP expression. LY, CPTIO and L-NIL inhibited cytomix-mediated PGP upregulation. LY inhibited SNAP-mediated PGP upregulation. Rhodamine transport was increased by cytomix and SNAP, but blocked by LY (prelim. data). Conclusion: PGP expression and function in enterocytes is upregulated by proinflammatory cytokines and NO in a PI3K dependent manner. This effect may be part of an adaptive mechanism to limit epithelial injury in response to inflammatory conditions. TABLE—ABSTRACT P112Cytomix−−++++−−SNAP−−−−−−++LY−+−+−−−+CPTIO−−−−+−−−LNIL−−−−−−−−Nitrite (uM)2.8 ± 1.12.4 ± 0.919.4 ± 0.6∗11.5 ± 1.5#NA5.1 ± 1.4#NANAPGP/B-actin0.6 ± 0.20.4 ± 0.12.7 ± 0.8∗0.4 ± 0.1#0.8 ± 0.2#1.1 ± 0.1#3.6 ± 1.3∗0.5 ± 0.3$Transport (%)19 ± 113.164 ± 14∗6.7——71 ± 13∗18.9n = 1.∗P < 0.05 vs. media alone.#P < 0.05 vs. cytomix alone.$vs. Snap alone, NA = not applic.

Ischémie–reperfusion mésentérique lors des états de choc : principaux aspects physiopathologiques

Splanchnic ischemia-reperfusion, secondary to an interruption of blood supply or hypoperfusion, induces lesions of the intestinal mucosa and endothelial dysfunction. The consequences are at first an intestinal barrier failure with a defect for the entry of nutriments into the body. In parallel, splanchnic ischemia-reperfusion induces systemic inflammatory response. Gut reperfusion produces numerous mediators such as reactive oxygen metabolites, pro-inflammatory cytokines, nitric monoxide and activates numerous enzymes. The interaction between polymorphonuclear neutrophils and endothelial cells appear to play a key role in inducing damage to distant organ, particularly to the lungs. Briefly, splanchnic ischemia-reperfusion may be implicated in intestinal permeability, bacterial translocation and injury to distant organs. These effects are well observed in experimental models. In humans, the role of the gut remains always a controversial hypothesis. Nevertheless, the role of gut as a “motor of multiple organ failure” may be a tenable hypothesis, which warrants clinical research in this area.

The synergistic effects of hypoxia/reoxygenation or tissue acidosis and bacteria on intestinal epithelial cell apoptosis.

Clinical data indicate that gut perfusion deficits must be rectified within 24 hours after traumatic injury to decrease organ failure and death. Ischemia/reperfusion injury to the gut causes enterocyte apoptosis (Apo), which may contribute to intestinal barrier failure. The temporal response of enterocyte Apo to acidosis and hypoxia/reoxygenation (H/R) in vitro is unknown. The purpose of this study was to examine the effect of various time points of acidosis or H/R on enterocyte apoptosis and monolayer integrity in an in vitro model. Caco-2 cell monolayers were made acidic (Dulbecco's modified Eagle's medium, pH 6.9) by hydrochloric acid or exposed to 95% nitrogen/5% carbon dioxide (hypoxia) and then 21% oxygen (reoxygenation). Escherichia coli C-25 were added to the apical media in subsets. Apo and necrosis were quantified by flow cytometry. Permeability was determined by fluorescein isothiocyanate-dextran. Transepithelial electrical resistance (TEER) indexed monolayer. Extracellular acidosis and C-25 significantly increased apoptosis of Caco-2 cells at 18 hours (extracellular acidosis [EC] + C-25, 14.5 +/- 3.0; control, 3.8 +/- 0.8; p < 0.001 by analysis of variance). Similarly, the H/R + C-25 group showed a significant increase in apoptosis at 12 hours (H/R + C-25 vs. control, 22.86 +/- 2.12 vs. 3.74 +/- 0.7; p < 0.001 by analysis of variance). The permeability difference was not significant for EC + C-25 versus control at 18 hours (0.68 +/- 0.25 vs. 0.43 +/- 0.0.0.36, respectively; p > 0.05). The H/R + C-25 group had a profound increase in permeability over control at 12 hours (10.8 +/- 0.5 vs. 2.1 +/- 0.3, respectively; p < 0.001). The TEER was significantly lowered for EC versus control at 18 hours (458 +/- 1.5 vs. 468 +/- 8.2) and at 0, 6, and 18 hours for EC + C-25 (409 +/- 28.1, 443 +/- 16.8, and 438 +/- 8.9 vs. 455 +/- 6.5, 467 +/- 6.5, and 469 +/- 8.2, respectively). There was no significant change in the H/R and H/R + C-25 groups. Synergism of H/R or tissue acidosis and bacteria caused increased Apo, TEER, and permeability in vitro.

Intestinal Hypoperfusion Contributes to Gut Barrier Failure in Severe Acute Pancreatitis

Intestinal barrier failure and subsequent bacterial translocation have been implicated in the development of organ dysfunction and septic complications associated with severe acute pancreatitis. Splanchnic hypoperfusion and ischemia/reperfusion injury have been postulated as a cause of increased intestinal permeability. The urinary concentration of intestinal fatty acid binding protein (IFABP) has been shown to be a sensitive marker of intestinal ischemia, with increased levels being associated with ischemia/reperfusion. The aim of the current study was to assess the relationship between excretion of IFABP in urine, gut mucosal barrier failure (intestinal hyperpermeability and systemic exposure to endotoxemia), and clinical severity. Patients with a clinical and biochemical diagnosis of acute pancreatitis were studied within 72 hours of onset of pain. Polyethylene glycol probes of 3350 kDa and 400 kDa were administered enterally, and the ratio of the percentage of retrieval of each probe after renal excretion was used as a measure of intestinal macromolecular permeability. Collected urine was also used to determine the IFABP concentration (IFABP-c) and total IFABP (IFABP-t) excreted over the 24-hour period, using an enzyme-linked immunosorbent assay technique. The systemic inflammatory response was estimated from peak 0 to 72-hour plasma C-reactive protein levels, and systemic exposure to endotoxins was measured using serum IgM endotoxin cytoplasmic antibody (EndoCAb) levels. The severity of the attack was assessed on the basis of the Atlanta criteria. Sixty-one patients with acute pancreatitis (severe in 19) and 12 healthy control subjects were studied. Compared to mild attacks, severe attacks were associated with significantly higher urinary IFABP-c (median 1092 pg/ml vs. 84 pg/ml; P < 0.001) and IFABP-t (median 1.14 μg vs. 0.21 μg; P = 0.003). Furthermore, the control group had significantly lower IFABP-c (median 37 pg/ml; P = 0.029) and IFABP-t (median 0.06 μg; P = 0.005) than patients with mild attacks. IFABP correlated positively with the polyethylene glycol 3350 percentage retrieval ( r = 0.50; P < 0.001), CRP ( r = 0.51; P < 0.001), and inversely with serum IgM EndoCAb levels ( r = −0.32; P = 0.02). The results of this study support the hypothesis that splanchnic hypoperfusion contributes to the loss of intestinal mucosal integrity associated with a severe attack of pancreatitis. ( J Gastrointest Surg 2003;7:26–36.)

Acidomucin goblet cell expansion induced by parenteral nutrition in the small intestine of piglets.

Total parenteral nutrition (TPN) impairs small intestine development and is associated with barrier failure, inflammation, and acidomucin goblet cell expansion in neonatal piglets. We examined the relationship between intestinal goblet cell expansion and molecular and cellular indices of inflammation in neonatal piglets receiving TPN, 80% parenteral + 20% enteral nutrition (PEN), or 100% enteral nutrition (control) for 3 or 7 days. Epithelial permeability, T cell numbers, TNF-alpha and IFN-gamma mRNA expression, and epithelial proliferation and apoptosis were compared with goblet cell numbers over time. Epithelial permeability was similar to control in the TPN and PEN jejunum at day 3 but increased in the TPN jejunum by day 7. By day 3, intestinal T cell numbers were increased in TPN but not in PEN piglets. However, goblet cell expansion was established by day 3 in both the TPN and PEN ileum. Neither TNF-alpha nor IFN-gamma mRNA expression in the TPN and PEN ileum correlated with goblet cell expansion. Thus goblet cell expansion occurred independently of overt inflammation but in association with parenteral feeding. These data support the hypothesis that goblet cell expansion represents an initial defense triggered by reduced epithelial renewal to prevent intestinal barrier failure.

Elemental and intravenous total parenteral nutrition diet-induced gut barrier failure is intestinal site specific and can be prevented by feeding nonfermentable fiber.

Parenteral nutrition and elemental diets both cause bacterial translocation, immune dysfunction, and increased infection in laboratory animals, whereas elemental diets, with or without fiber, ameliorate some, but not all gut barrier failure. The purpose of this study is to investigate, in an Ussing chamber system, whether elemental vs. parenteral diets induce gut barrier failure in specific anatomical sites in the intestine and whether fiber can ameliorate this phenomenon. Controlled study in laboratory animals. University laboratory. Male Sprague-Dawley rats. Nutritional support was provided to rats for 7 days by oral total parenteral nutrition (TPN; elemental diet) 307 kcal/kg/day, intravenous TPN (parenteral diet) 307 kcal/kg/day via jugular venous catheters, or rodent chow (controls). Permeability to bacteria in intestinal segments of ileum, jejunum, and colon was evaluated in an Ussing chamber. Results were correlated with bacterial translocation to the mesenteric lymph nodes. Intravenous TPN caused greater bacterial translocation in all small intestinal segments and the cecum when compared with chow (p <.05). Oral TPN caused gut barrier failure only in the ileal segment, but not in the remainder of the small intestine (p <.001). Addition of cellulose provided a greater protection of the ileum to permeability than did pectin (p <.01). TPN causes global intestinal barrier failure, but elemental diet prevents barrier failure in parts of the small intestine other than the ileum. The addition of cellulose fiber to elemental diet can ameliorate further barrier failure in the ileum.

A tungsten supplemented diet attenuates bacterial translocation in chronic portal hypertensive and cholestatic rats: role of xanthine dehydrogenase and xanthine oxidase

BACKGROUNDBacterial translocation (BT) plays a major role in the pathophysiological process of spontaneous infections in portal hypertension (PH) and cholestatic jaundice. The major mechanisms promoting BT in experimental animal models...

Peroxynitrite (PN) effects on small intestinal enterocytes (IEC-6)

Purpose: Our laboratory has shown that intestinal barrier failure following necrotizing enterocolitis or LPS peritonitis is associated with upregulation of inducible nitric oxide synthase, 3-nitrotyrosine residues (the PN footprints), and apoptosis in the ileum. The mechanism of PN-mediated gut barrier failure remains elusive. This study examines PN-mediated epithelial cell injury in vitro.Methods: We incubated IEC-6 cells with 12.5 μM PN or phosphate-buffered saline (PBS) or media for 60 minutes followed by a recovery period of 6, 12, 18, or 24 hours in culture media. Apoptosis was measured by fluorescent-activated cell sorting using the propidium iodide method and electron microscopy. We also tested the ability of pretreatment with 3-aminobenzamide (3AB) (1 mM), an inhibitor of poly-ADP ribose synthetase, to alter the response of IEC-6 cells to PN.Results: A 60-minute exposure to PN followed by an 18-hour recovery period resulted in significant apoptosis (24 ± 4%) in IEC-6 cells as compared with PBS (2.7 ± .5%); p < .015 (Fig. 1). Peroxynitrite induced apoptosis in IEC-6 cells in a time-dependent fashion. There was no significant difference between PN and PN + 3AB (24 ± 4 v 17 ± 4). Electron microscopy demonstrated marked injury.Conclusions: Peroxynitrite injures small intestinal epithelial cells. Thus, inhibition or scavengers of PN may prevent gut barrier failure after endotoxemia.

Nitric oxide and intestinal barrier failure.

The systemic inflammatory response syndrome (SIRS) is a leading cause of morbidity and mortality in adults and children. Various proinflammatory mediators have been implicated in the pathogenesis of SIRS; however, their mechanisms of action are poorly defined. Recent evidence suggests that nitric oxide (NO) plays a regulatory role in gut barrier function. Sustained upregulation of NO production in the intestine can lead to intestinal epithelial injury through the formation of peroxynitrite. Peroxynitrite can nitrate mitochondrial proteins and inhibit cellular respiration. The resultant changes in mitochondrial function lead to activation of the caspase cascade, subsequent DNA fragmentation, and enterocyte apoptosis. Enterocyte apoptosis results in a transient "bare area" in the intestinal epithelium where bacteria can attach and then penetrate the lamina propria. Bacteria that successfully escape the immune system may in turn incite a systemic inflammatory response.