Intestinal Epithelial Cells Modulate PMN Activation and Apoptosis Following Bacterial and Hypoxic Challenges

Hypoxia-induced intestinal barrier changes in balloon-assisted enteroscopy

KEY POINTS

Balloon-assisted enteroscopy (BAE) is an emerging standard procedure by utilizing distensible balloons to facilitate deep endoscopy in the small and large intestine. Sporadic cases of bacteraemia were found after BAE. Balloon distension by BAE caused gut tissue hypoxia. The impact of balloon distension-induced hypoxia on intestinal barriers remains unclear. Murine models of BAE by colonic balloon distension showed that short- and long-term hypoxia evoked opposite effects on epithelial tight junctions (TJs). Short-term hypoxia fortified TJ integrity, whereas long-term hypoxia caused damage to barrier function. Our data showed for the first time the molecular mechanisms and signalling pathways of epithelial barrier fortification and TJ reorganization by short-term hypoxia for the maintenance of gut homeostasis. The findings suggest avoiding prolonged balloon distension during BAE to reduce the risk of hypoxia-induced gut barrier dysfunction.

ABSTRACT

Balloon-assisted enteroscopy (BAE) is an emerging standard procedure that uses distensible balloons to facilitate deep endoscopy. Intestines are known to harbour an abundant microflora. Whether balloon distension causes perturbation of blood flow and gut barrier dysfunction, and elicits risk of bacterial translocation remains unknown. Our aims were to (1) conduct a prospective study to gather microbiological and molecular evidence of bacterial translocation by BAE in patients, (2) establish a murine model of colonic balloon distension to investigate tissue hypoxia and intestinal barrier, and (3) assess the effect of short- and long-term hypoxia on epithelial permeability using cell lines. Thirteen patients were enrolled for BAE procedures, and blood samples were obtained before and after BAE for paired comparison. Four of the 13 patients (30.8%) had positive bacterial DNA in blood after BAE. Post-BAE endotoxaemia was higher than the pre-BAE level. Nevertheless, no clinical symptom of sepsis or fever was reported. To mimic clinical BAE, mice were subjected to colonic balloon distension. Local tissue hypoxia was observed during balloon inflation, and reoxygenation after deflation. A trend of increased gut permeability was seen after long-term distension, whereas a significant reduction of permeability was observed by short-term distension in the proximal colon. Human colonic epithelial Caco-2 cells exposed to hypoxia for 5-20 min exhibited increased tight junctional assembly, while those exposed to longer hypoxia displayed barrier disruption. In conclusion, sporadic cases of bacteraemia were found after BAE, without septic symptoms. Short-term hypoxia by balloon distension yielded a protective effect whereas long-term hypoxia caused damage to the gut barrier.

Gut Microbial Influences on the Mammalian Intestinal Stem Cell Niche

The mammalian intestinal epithelial stem cell (IESC) niche is comprised of diverse epithelial, immune, and stromal cells, which together respond to environmental changes within the lumen and exert coordinated regulation of IESC behavior. There is growing appreciation for the role of the gut microbiota in modulating intestinal proliferation and differentiation, as well as other aspects of intestinal physiology. In this review, we evaluate the diverse roles of known niche cells in responding to gut microbiota and supporting IESCs. Furthermore, we discuss the potential mechanisms by which microbiota may exert their influence on niche cells and possibly on IESCs directly. Finally, we present an overview of the benefits and limitations of available tools to study niche-microbe interactions and provide our recommendations regarding their use and standardization. The study of host-microbe interactions in the gut is a rapidly growing field, and the IESC niche is at the forefront of host-microbe activity to control nutrient absorption, endocrine signaling, energy homeostasis, immune response, and systemic health.

Over-starvation aggravates intestinal injury and promotes bacterial and endotoxin translocation under high-altitude hypoxic environment

AIM: To study whether over-starvation aggravates intestinal mucosal injury and promotes bacterial and endotoxin translocation in a high-altitude hypoxic environment.

METHODS: Sprague-Dawley rats were exposed to hypobaric hypoxia at a simulated altitude of 7000 m for 72 h. Lanthanum nitrate was used as a tracer to detect intestinal injury. Epithelial apoptosis was observed with terminal deoxynucleotidyl transferase dUTP nick end labeling staining. Serum levels of diamino oxidase (DAO), malondialdehyde (MDA), glutamine (Gln), superoxide dismutase (SOD) and endotoxin were measured in intestinal mucosa. Bacterial translocation was detected in blood culture and intestinal homogenates. In addition, rats were given Gln intragastrically to observe its protective effect on intestinal injury.

RESULTS: Apoptotic epithelial cells, exfoliated villi and inflammatory cells in intestine were increased with edema in the lamina propria accompanying effusion of red blood cells. Lanthanum particles were found in the intercellular space and intracellular compartment. Bacterial translocation to mesenteric lymph nodes (MLN) and spleen was evident. The serum endotoxin, DAO and MDA levels were significantly higher while the serum SOD, DAO and Gln levels were lower in intestine (P < 0.05). The bacterial translocation number was lower in the high altitude hypoxic group than in the high altitude starvation group (0.47 ± 0.83 vs 2.38 ± 1.45, P < 0.05). The bacterial translocation was found in each organ, especially in MLN and spleen but not in peripheral blood. The bacterial and endotoxin translocations were both markedly improved in rats after treatment with Gln.

CONCLUSION: High-altitude hypoxia and starvation cause severe intestinal mucosal injury and increase bacterial and endotoxin translocation, which can be treated with Gln.

The protective effects of intravenous anesthetics and verapamil in gut ischemia/reperfusion-induced liver injury

BACKGROUND

We investigated the protective effects of IV anesthetics and verapamil in gut ischemia/reperfusion-induced liver injury.

METHODS

Forty male Wistar Albino rats were randomly assigned to four groups of 10 rats each. Anesthesia was induced and maintained with propofol in Groups 1 and 3 and with thiopental in Groups 2 and 4 during the experiment. All animals developed intestinal ischemia after occlusion of the superior mesenteric artery for 30 min. Reperfusion was induced by removal of the microvascular clamp and was allowed to continue for 120 min. The animals in Groups 3 and 4 were given verapamil 10 min before reperfusion. Liver and ileum samples were taken for measurement of malondialdehyde (MDA) and histopathologic examination before ischemia and 30 and 120 min after reperfusion. Blood samples were also obtained for measurement of plasma tumor necrosis factor-alpha and interleukin-6 levels.

RESULTS

Gut ischemia/reperfusion-induced significant increases in MDA contents of liver and gut and serum cytokines, consistent with histopathologic injury scores. Propofol effectively stabilized the MDA levels and decreased the tissue injury scores of the liver and gut. Tumor necrosis factor-alpha and interleukin-6 levels increased less in the propofol groups than in the thiopental groups. There was no additive preventive effect of verapamil on propofol. The addition of verapamil to thiopental was effective in decreasing the serum cytokines and liver MDA content.

CONCLUSION

Propofol may offer advantages by inhibiting lipid peroxidation and inflammatory cytokine production in an animal model of gut ischemia/reperfusion-induced liver injury.

Ethanol Effects Proinflammatory State of Neutrophils in Shock

INTRODUCTION

Ethanol (EtOH) intoxication plays an important role in the etiology of traumatic events and has often been described as having immunosuppressive effects. EtOH has been shown to affect intestinal barrier function in prior studies. The ability of gut derived factors on neutrophil function in this setting is unknown. This study looks at the role of ethanol in modulating proinflammatory states in the neutrophil in vitro.

METHODS

Confluent Caco2 monolayers were exposed to 0.1% EtOH and/or Escherichia coli C-25 (EC) under normoxia (21% O(2)) or hypoxia (5% O(2)) followed by normoxic conditions (H/R). Neutrophils were then incubated with the supernatants from the treated cells. Chemotaxis, elastase and superoxide anion release, and CD11b measurements were undertaken in these neutrophils and compared with controls.

RESULTS

In the presence of EtOH, Caco2 cells undergoing H/R and bacterial challenge demonstrated a proinflammatory effect on neutrophils. The production of both elastase and superoxide anion were significantly increased from controls. Additionally, the presence of EtOH in Caco2 cells undergoing H/R with/without EC showed a statistically significant increase in CD11b expression and chemotaxis, when compared with controls.

CONCLUSIONS

EtOH has a proinflammatory role in the activation of neutrophils at the intestinal epithelial cell barrier in shock states. EtOH may play an important role in worsening septic complication in severely traumatized patients via dysregulation of neutrophils.