Xiaoming Deng

The influence of intestinal ischemia and reperfusion on bidirectional intestinal barrier permeability, cellular membrane integrity, proteinase inhibitors, and cell death in rats.

Intestinal ischemia and reperfusion injury (I/R) is probably involved in the pathogenesis of intestinal barrier dysfunction, associated with the concomitant translocation of enteric bacteria and toxins and the potential development of multiple organ failure. The intestinal endothelial and epithelial layers play a major role preventing the entry of toxic substances from the gut, but the influence of protease-antiprotease systemic balance on these barrier functions and the relationship between epithelial DNA synthesis, apoptosis, and endothelial and epithelial barrier macromolecule permeability are not fully investigated. Endothelial and epithelial barrier macromolecular permeability, epithelial DNA synthesis, the endothelial and epithelial plasma membrane system, apoptosis and oncosis, plasma levels of proteinase inhibitors, and proenzymes were measured in rats subjected to 20 and 40 min intestinal ischemia and 1, 3, 6, or 12 h reperfusion. Endothelial permeability increased after both 20 and 40 min intestinal ischemia. Epithelial permeability significantly increased during 1-6 h reperfusion after 20 min ischemia and during 1-12 h reperfusion after 40 min ischemia. Epithelial DNA synthesis increased in animals with 20 min ischemia followed by 12 h reperfusion. Plasma levels of prekallikrein, C1-esterase inhibitor, and alpha1-macroglobulin were significantly lower following both 20 and 40 min ischemia from 3 h reperfusion and on. Apoptotic epithelial cells significantly increased in animals subjected to 20 min ischemia followed by 12 h reperfusion. The severity of reperfusion injury in the intestinal endothelial and epithelial barrier seems to correlate with the period of ischemia and the pathway of cell damage and death, together with proteinase-antiproteinase imbalance.

The Influence of Apoptosis on Intestinal Barrier Integrity in Rats

BACKGROUND Apoptosis is a critical step responsible for maintaining the cellular balance between proliferation and death and for controlling tumorigenesis. Although an increase in intestinal apoptotic cells has been considered to be associated with the pathogenesis of gastrointestinal injury, little is understood concerning the role of apoptosis in the development of intestinal barrier dysfunction. METHODS Apoptosis induced by intraperitoneal injection of doxorubicin in rats was evaluated by transmission electron microscopy and the TUNEL histochemistry method. Treatment with deoxy-D-glucose (a glycolytic pathway inhibitor) or cycloheximide (a protein synthesis inhibitor) was performed after doxorubicin challenge. Passage of human serum albumin from blood to the intestinal interstitium and the intestinal lumen or from the intestine to the intestinal interstitium and blood was evaluated by means of albumin clearance. RESULTS A significant increase in gut water content, albumin flux, and bidirectional clearance of albumin accompanied by apoptotic epithelial cell increase was noted in doxorubicin-challenged rats treated with saline. The increase in endothelial and epithelial permeability and the increase of apoptosis could partly be prevented by treatment with deoxy-D-glucose or cycloheximide. CONCLUSION Doxorubicin-increased epithelial apoptosis within the intestine occurs simultaneously with increased bidirectional permeability of the intestinal barrier, probably associated with both glycolytic and protein synthesis pathways. Apoptosis may thus play a role in the pathogenesis of intestinal barrier dysfunction.

Antioxidant and Calcium Channel Blockers Counteract Endothelial Barrier Injury Induced by Acute Pancreatitis in Rats

BACKGROUND Multiple organ failure is the major mortality-related complication in severe acute pancreatitis. Endothelial barrier injury may be involved in its pathophysiology. METHODS The present study evaluated alterations in endothelial barrier integrity in different organs/tissues 12 h after induction of acute pancreatitis by intraductal infusions of bile. Potential effects of oxygen free radicals and calcium influx were evaluated by pretreatment with an antioxidant, N-acetyl-L-cysteine, and calcium channel antagonists, verapamil and diltiazem. RESULTS Tissue edema, reflected by an increase in tissue water content, was noted in the stomach, proximal small intestine, cecum, spleen, pancreas, kidneys, liver, lungs, heart, and brain in rats with pancreatitis. Also, an increased endothelial barrier permeability, as evidenced by the leakage of radiolabeled human serum albumin from blood to tissues, occurred in the stomach, proximal small intestine, colon, peritoneum, spleen, pancreas, kidneys, liver, lungs, and heart, accompanied by altered liver functions, increased levels of pancreatic enzymes, compromised renal function, and delayed intestinal motility. N-acetyl-L-cysteine prevented tissue edema and endothelial permeability changes in most organs/tissues, whereas the effects of verapamil and diltiazem were less marked. The preventive effects occurred in an organ-dependent manner. CONCLUSIONS Endothelial barrier injury is found in all investigated organs/tissues in acute experimental pancreatitis. Oxygen free radicals and calcium influx may play a role in the development of these changes.

Effect of a Platelet-Activating Factor Antagonist on Pancreatitis-Associated Gut Barrier Dysfunction in Rats

Platelet-activating factor (PAF) may play a critical and primary role in the pathogenesis of acute pancreatitis and pancreatitis-associated distant organ injury. The present study evaluated the effect of a PAF antagonist, lexipafant (an (S)-4-methyl-2 (methyl-imidazo {4,5-c} pyridin-l-ylmethyl)-benzenesulphonyl]-amino} pentanoic acid ethyl ester, BB-882; British Biotech Ltd.), on the potential prevention of gut barrier dysfunction, by measuring gut origin sepsis, bidirectional permeability of the intestinal barrier, and pancreatic capillary endothelial barrier integrity, in acute pancreatitis induced by intraductal infusion of 5% sodium taurodeoxycholate. Pancreatic endothelial permeability significantly increased in animals with acute pancreatitis, whereas pretreatment with lexipafant had a preventive effect (p <0.05 vs. pancreatitis with saline). Similarly, alterations noted in hematocrit and plasma levels of lipase and calcium were counteracted by the PAF antagonist. It also prevented the increase in albumin leakage from blood to the mucosal interstitium and from blood to the intestinal lumen in acute pancreatitis. Albumin passage from the gut lumen to blood in animals with pancreatitis pretreated with saline increased from 3 h and on, and lexipafant prevented alterations in mucosal epithelial permeability. Bacterial translocation was commonly seen in pancreatitis, whereas only a few positive cultures were observed in pancreatitis animals given lexipafant. Microthrombosis in intestinal villi seemed less frequent after lexipafant pretreatment. We conclude that (a) PAF may play a role in the pathogenesis of pancreatitis-associated intestional dysfunction, (b) PAF may be involved in the development of distant organ dysfunction by triggering endothelial barrier dysfunction, and (c) PAF antagonists may provide potential agents for preventing pancreatitis-associated gut barrier dysfunction.

Phagocytic and intestinal endothelial and epithelial barrier function during the early stage of small intestinal ischemia and reperfusion injury.

ABSTRACT The effects of intestinal ischemia and reperfusion (I/R) on small intestinal mucosal endothelial and epithelial barrier integrity and phagocytic function were assessed in rats subjected to 20‐ or 40‐min mesenteric ischemia and a 3‐h reperfusion. The results showed that human serum albumin (125I‐HSA) flux through the endothelial layer to the interstitial space increased as did 125I‐HSA clearance from blood to the gut lumen and 131I‐HSA flux from the gut lumen to the interstitial space in rats with I/R. E.coli adhering to microvilli, invading and passing into the microvessels, were noted on the small intestinal mucosa in animals subjected to 40‐min ischemia and a 3‐h reperfusion. Phagocytic function increased, especially in the small intestinal wall, lungs, liver, and spleen in the groups with I/R, correlating with the length of ischemia. The results imply that both endothelial and epithelial barrier integrity is impaired in the early phase after I/R and that the epithelial barrier more effectively restricts macromolecular leakage compared with the endothelial barrier. I/R impairs the intestinal barrier not only by causing tissue hypoxia but also by activating the phagocytic system and aggravating barrier damage, which finally may result in bacterial translocation and remote organ dysfunction.

Gut barrier permeability, reticuloendothelial system function and protease inhibitor levels following intestinal ischaemia and reperfusion--effects of pretreatment with N-acetyl-L-cysteine and indomethacin.

BACKGROUND Pathophysiological mechanisms and ways to intervene on intestinal barrier dysfunction following small intestinal ischaemia and prolonged reperfusion are still not fully clarified. AIMS To evaluate the effect of oxygen free radical and prostaglandin inhibition on intestinal barrier injury following intestinal ischaemia/reperfusion. METHODS Endothelial and epithelial barrier permeability was evaluated by clearance of radiolabelled albumin. Parameters included 125I-Escherichia coli uptake rate index, host reticuloendothelial system function and organ distribution, as well as protease inhibitor and proenzyme activities in rats subjected to small intestinal ischaemia for 40 minutes followed by 12 hours reperfusion (ischaemia/reperfusion), pretreated with N-acetyl-L-cysteine or indomethacin. RESULTS Following ischaemia/reperfusion, endothelial and epithelial permeability increased, reticuloendothelial system activation occurred and plasma protease inhibitors were consumed. N-acetyl-L-cysteine pretreatment resulted in improved endothelial and epithelial barrier integrity, a decrease in protease inhibitor consumption and less pronounced reticuloendothelial system activation. Pretreatment with indomethacin was not effective. CONCLUSION Oxygen free radicals seem to play an important role in the development of intestinal barrier impairment following ischaemia/reperfusion. N-acetyl-L-cystine may be a potential agent for preventing ischaemia/reperfusion damage.

Treatment with lexipafant ameliorates the severity of pancreatic microvascular endothelial barrier dysfunction in rats with acute hemorrhagic pancreatitis

SummaryConclusion: Treatment with lexipafant reduced the severity of pancreatitis-associated endothelial barrier compromise, also associated with a decrease in systemic concentrations of interleukin (IL) 1. Thus, the present findings imply that platelet-activating factor (PAF) may play an important role in the pathogenesis of pancreatic endothelial dysfunction by signaling and triggering the production and release of certain cytokines.Background: Pancreatic capillary endothelial barrier dysfunction is an initial and characteristic feature of acute pancreatic injury and pancreatitis. PAF, a proinflammatory mediator and an intercellular signaling substance, has been considered to be involved in the inflammatory reaction and the systemic endothelial dysfunction of acute pancreatitis.Methods: The development of pancreatic capillary endothelial barrier dysfunction was monitored by tissue edema and exudation of plasma albumin into the interstitium, 3 and 12 h after induction of acute pancreatitis by intraductal infusion of 5% sodium taurodeoxycholate in rats. Pancreatic leukocyte recruitment was reflected by measuring myeloperoxidase activity. Serum levels of IL-1β and IL-6 were determined by an enzyme-linked immunosorbent assay (ELISA).Results: Pretreatment with lexipafant, a potent PAF receptor antagonist, significantly reduced the pancreatitis-induced increase in pancreatic endothelial barrier dysfunction, pancreatic leukocyte recruitment, and serum levels of IL-1β, although a difference persisted between animals with sham operation and pancreatitis.

The Influence of Circulatory and Gut Luminal Challenges on Bidirectional Intestinal Barrier Permeability in Rats

BACKGROUND The endothelial and epithelial barriers are important for maintenance of intestinal barrier function. The present study evaluated the response of these barriers after various challenges. METHODS Mucosal endothelial and epithelial barrier integrity was evaluated by the leakage of human serum albumin, labeled with different isotopes, from the circulation to the interstitium and the intestinal lumen, or from the intestinal lumen to the interstitium and the circulation, in rats with endothelial or epithelial challenge. RESULTS Epithelial barrier dysfunction and alterations in epithelial microvillous ultrastructure showed a pattern dependent on the dose of the intraluminal detergents, whereas only higher doses induced an increase in endothelial barrier permeability. Intravenous challenge with CHAPS or Triton caused a dose-dependent increase in both endothelial and epithelial barrier permeability. The development of endothelial barrier dysfunction was related to a decrease in blood pH values. CONCLUSIONS The results indicate that capillary endothelial barrier integrity may play an important role in maintaining intestinal barrier function and that endothelial injury may initiate or at least be involved in the development of intestinal barrier failure.

Alterations In Endothelial Barrier Permeability In Multiple Organs During Overactivation Of Macrophages In Rats

ABSTRACT Macrophage hyperactivity has been suggested to play an important role in septic complications and the development of multiple organ failure. Intraperitoneal administration of macrophage stimulants, e.g., zymosan, induce a systemic inflammatory response, with concomitant gut origin sepsis, and organ dysfunction. However, little is known about alterations in endothelial permeability during macrophage hyperactivation. In the present study, the effect of macrophage hyperactivation on endothelial permeability, assessed by 125l-labeled HSA and 51Cr-labeled EDTA, and the difference between cytolytic and noncytolytic inflammatory macrophages induced by i.p. injection of .25 or .50 mg/g of zymosan, concanavalin A (Con A) or thioglycollate medium (TM) diluted in 4 mL of paraffin, as well as the potential relationship with the doses used, were evaluated in the rat. Overactivation of cytolytic inflammatory macrophages induced a pronounced alteration in endothelial barrier permeability, characterized by a decrease in whole body plasma volume and an increase in whole body interstitial fluid volume, while overactivation of noncytolytic inflammatory macrophages only induced leakage of proteins and plasma to several of the organs studied. Macrophage activators, like zymosan, Con A and TM, exhibited varying effects on endothelial permeability related to the dose used. The results in the present study imply that overactivation of cytolytic inflammatory macrophages may play an important role in endothelial barrier injury and that zymosan possesses a more potent effect as compared to Con A when administered at the same dose.

The involvement of multiple protease-antiprotease systems and gut origin sepsis in zymosan-associated endothelial barrier injury and multiple organ dysfunction in rats

Multiple organ dysfunction syndrome is a dominant cause of mortality in the intensive care unit. Experimentally, a condition similar to the multiple organ dysfunction syndrome can be induced by the intraperitoneal injection of sterile zymosan. In the present study we investigate potential alterations in multiple organ functions, endothelial permeability, and antiproteinases after intraperitoneal injection of zymosan at various doses. Zymosan-induced generalized inflammation lead to endothelial barrier injury in multiple organs/tissues, a decrease in systemic arterial pressure, impaired organ function and gut defence function, and consumption of protease inhibitors, particularly the consumption of alpha2 antiplasmin. Endothelial barrier injury appears to present a dose- and organ-dependent pattern in multiple organs/tissues, and the increase in endothelial barrier permeability occurred prior to organ dysfunction. Zymosan induced the development of multiple organ dysfunction syndrome, probably initiating multiple protease-antiprotease systems, particularly the fibrinolytic system, leading to endothelial barrier injury, tissue edema, parenchymal cell damage, and eventual organ dysfunction, potentially augmented by a secondary bacterial infection.