Effects of different ischemic preconditioning strategies on physiological and cellular mechanisms of intestinal ischemia/reperfusion injury: Implication from an isolated perfused rat small intestine model.

BACKGROUND: Intestinal ischemia/reperfusion (I/R)-injury often results in sepsis and organ failure and is of major importance in the clinic. A potential strategy to reduce I/R-injury is the application of ischemic preconditioning (IPC) during which repeated, brief episodes of I/R are applied. The aim of this study was to evaluate physiological and cellular effects of intestinal I/R-injury and to compare the influence of in-vivo IPC (iIPC) with ex-vivo IPC (eIPC), in which blood derived factors and nerval regulations are excluded. METHODS: Using an established perfused rat intestine model, effects of iIPC and eIPC on physiological as well as cellular mechanisms of I/R-injury (60 min hypoxia, 30 min reperfusion) were investigated. iIPC was applied by three reversible occlusions of the mesenteric artery in-vivo for 5 min followed by 5 min of reperfusion before isolating the small intestine, eIPC was induced by stopping the vascular perfusion ex-vivo 3 times for 5 min followed by 5 min of reperfusion after isolation of the intestine. Study groups (each N = 8-9 animals) were: iIPC, eIPC, I/R (iIPC group), I/R (eIPC group), iIPC+I/R, eIPC+I/R, no intervention/control (iIPC group), no intervention/control (eIPC group). Tissue morphology/damage, metabolic functions, fluid shifts and barrier permeability were evaluated. Cellular mechanisms were investigated using signaling arrays. RESULTS: I/R-injury decreased intestinal galactose uptake (iIPC group: p<0.001), increased vascular perfusion pressure (iIPC group: p<0.001; eIPC group: p<0.01) and attenuated venous flow (iIPC group: p<0.05) while lactate-to-pyruvate ratio (iIPC group, eIPC group: p<0.001), luminal flow (iIPC group: p<0.001; eIPC group: p<0.05), goblet cell ratio (iIPC group, eIPC group: p<0.001) and apoptosis (iIPC group, eIPC group: p<0.05) were all increased. Application of iIPC prior to I/R increased vascular galactose uptake (P<0.05) while eIPC had no significant impact on parameters of I/R-injury. On cellular level, I/R-injury resulted in a reduction of the phosphorylation of several MAPK signaling molecules. Application of iIPC prior to I/R increased phosphorylation of JNK2 and p38δ while eIPC enhanced CREB and GSK-3α/ß phosphorylation. CONCLUSION: Intestinal I/R-injury is associated with major physiological and cellular changes. However, the overall influence of the two different IPC strategies on the acute phase of intestinal I/R-injury is rather limited.

Remote ischemic preconditioning attenuates intestinal mucosal damage: insight from a rat model of ischemia-reperfusion injury.

BACKGROUND: Remote ischemic preconditioning (RIPC) is a phenomenon, whereby repeated, non-lethal episodes of ischemia to an organ or limb exert protection against ischemia-reperfusion (I/R) injury in distant organs. Despite intensive research, there is still an apparent lack of knowledge concerning the RIPC-mediated mechanisms, especially in the intestine. Aim of this study was to evaluate possible protective effects RIPC on intestinal I/R injury. METHODS: Thirty rats were randomly assigned to four groups: I/R; I/R + RIPC; Sham; Sham + RIPC. Animals were anesthetized and the superior mesenteric artery was clamped for 30 min, followed by 60 min of reperfusion. RIPC-treated rats received 3 × 5 min of bilateral hindlimb I/R prior to surgery, sham groups obtained laparotomy without clamping. After I/R injury serum/tissue was analyzed for: Mucosal damage, Caspase-3/7 activity, expression of cell stress proteins, hydrogen peroxide (H2O2) and malondialdehyde (MDA) production, Hypoxia-inducible factor-1α (HIF-1α) protein expression and matrix metalloproteinase (MMP) activity. RESULTS: Intestinal I/R resulted in increased mucosal injury (P < 0.001) and elevated Caspase-3/7 activity (P < 0.001). RIPC significantly reduced the histological signs of intestinal I/R injury (P < 0.01), but did not affect Caspase-3/7 activity. Proteome profiling suggested a RIPC-mediated regulation of several cell stress proteins after I/R injury: Cytochrome C (+ 157%); Cited-2 (- 39%), ADAMTS1 (+ 74%). Serum concentrations of H2O2 and MDA remained unchanged after RIPC, while the reduced intestinal injury was associated with increased HIF-1α levels. Measurements of MMP activities in serum and intestinal tissue revealed an attenuated gelatinase activity at 130 kDa within the serum samples (P < 0.001) after RIPC, while the activity of MMPs within the intestinal tissue was not affected by I/R injury or RIPC. CONCLUSIONS: RIPC ameliorates intestinal I/R injury in rats. The underlying mechanisms may involve HIF-1α protein expression and a decreased serum activity of a 130 kDa factor with gelatinase activity.

Effects of hydroxyethyl starch (HES 130/0.42) on endothelial and epithelial permeability in vitro.

Hydroxyethyl starch (HES) is employed to sustain normovolemia in patients. Using a perfused organ model, we recently showed that HES impairs the intestinal barrier which is constituted of endothelial and epithelial cell layers. However, the target cells and molecular actions of HES in the intestine are mainly unknown. Employing a model of human endothelial (HUVEC) and intestinal epithelial cells (Caco-2), we investigated the impact of HES, albumin and HES/albumin on cellular integrity/permeability and evaluated underlying molecular mechanisms. Monolayers of HUVEC and Caco-2 were cultured with HES (3%), albumin (3%) or HES/albumin (1.5%/1.5%). Integrity and permeability of the cell layers were evaluated by FITC-dextran transfer, measurements of cell detachment, vitality, cell volume, LDH release and caspase-3/7 activity. Cellular mechanisms were analyzed by Westernblotting for P-akt, P-erk, claudin-3 and I-FABP. HES application resulted in higher numbers of non-adherent/floating HUVEC cells (P<0.05) but did not change vitality or cell volume. Both, HES and HES/albumin increased the permeability of HUVEC monolayers (P<0.001), while LDH release, caspase-3/7 activity, akt/erk phosphorylation and claudin-3 expression were not affected. HES and HES/albumin did not change any of the parameters in cultures of Caco-2 cells. HES is able to disturb the integrity of the endothelial but not the epithelial barrier in vitro. HES effects are unrelated to cell damage and apoptosis but may involve reduced cell-cell or cell-matrix adhesion.

Signalling mechanisms in PAF-induced intestinal failure.

Capillary leakage syndrome, vasomotor disturbances and gut atony are common clinical problems in intensive care medicine. Various inflammatory mediators and signalling pathways are involved in these pathophysiological alterations among them platelet-activating factor (PAF). The related signalling mechanisms of the PAF-induced dysfunctions are only poorly understood. Here we used the model of the isolated perfused rat small intestine to analyse the role of calcium (using calcium deprivation, IP-receptor blockade (2-APB)), cAMP (PDE-inhibition plus AC activator), myosin light chain kinase (inhibitor ML-7) and Rho-kinase (inhibitor Y27632) in the following PAF-induced malfunctions: vasoconstriction, capillary and mucosal leakage, oedema formation, malabsorption and atony. Among these, the PAF-induced vasoconstriction and hyperpermeability appear to be governed by similar mechanisms that involve IP3 receptors, extracellular calcium and the Rho-kinase. Our findings further suggest that cAMP-elevating treatments - while effective against hypertension and oedema - bear the risk of dysmotility and reduced nutrient uptake. Agents such as 2-APB or Y27632, on the other hand, showed no negative side effects and improved most of the PAF-induced malfunctions suggesting that their therapeutic usefulness should be explored.

Adverse effects of hydroxyethyl starch (HES 130/0.4) on intestinal barrier integrity and metabolic function are abrogated by supplementation with Albumin.

BACKGROUND: Volume resuscitation with hydroxyethyl starch (HES) is controversially discussed and we recently showed that HES perfusion impairs endothelial and epithelial intestinal barrier integrity. Here we investigated whether Albumin containing HES solutions are superior to HES alone in maintaining intestinal barrier function. METHODS: An isolated perfused model of the mouse small intestine was used to investigate the effects of: (i) 3 % Albumin (Alb), (ii) 3 % HES or (iii) 1.5 % HES/1.5 % Albumin (HES/Alb). Intestinal morphology, cell damage, metabolic functions, fluid shifts and endothelial/epithelial barrier permeability were evaluated. Potentially involved signaling mechanisms (Erk1/2, Akt and Stat5 phosphorylation) were screened. RESULTS: HES induced histomorphological damage (p < 0.01 vs. Alb), by trend elevated the amount of luminal intestinal fatty acid binding protein and reduced galactose uptake (p < 0.001 vs. Alb). Luminal and lymphatic flow rates were increased (p < 0.001 vs. Alb), while vascular flow was decreased (p < 0.001 vs. Alb) during HES perfusion. HES also increased the vascular to luminal FITC-dextran transfer (p < 0.001 vs. Alb), pointing towards a fluid shift from the vascular to the luminal and lymphatic compartments during HES perfusion. Addition of Alb (HES/Alb) reversed all adverse effects of HES (p < 0.05 vs. HES), restored barrier integrity (p < 0.05 vs. HES) and improved metabolic function of the intestine (p < 0.001 vs. HES; p < 0.05 vs. Alb). Mechanistically, HES/Alb perfusion resulted in an increased phosphorylation of Erk1/2 and Akt kinases (p < 0.001 vs. HES), while Stat5 remained unchanged. CONCLUSIONS: Albumin supplementation abrogates the adverse effects of HES in the intestine and underlying mechanism may function via phosphorylation of Erk1/2 and Akt. Albumin containing HES solutions are superior to HES alone and may improve the suitability of HES in the clinic.

Correction: Hydroxyethyl Starch (HES 130/0.4) Impairs Intestinal Barrier Integrity and Metabolic Function: Findings from a Mouse Model of the Isolated Perfused Small Intestine.

BACKGROUND: The application of hydroxyethyl starch (HES) for volume resuscitation is controversially discussed and clinical studies have suggested adverse effects of HES substitution, leading to increased patient mortality. Although, the intestine is of high clinical relevance and plays a crucial role in sepsis and inflammation, information about the effects of HES on intestinal function and barrier integrity is very scarce. We therefore evaluated the effects of clinically relevant concentrations of HES on intestinal function and barrier integrity employing an isolated perfused model of the mouse small intestine. METHODS: An isolated perfused model of the mouse small intestine was established and intestines were vascularly perfused with a modified Krebs-Henseleit buffer containing 3% Albumin (N=7) or 3% HES (130/0.4; N=7). Intestinal metabolic function (galactose uptake, lactate-topyruvate ratio), edema formation (wet-to-dry weight ratio), morphology (histological and electron microscopical analysis), fluid shifts within the vascular, lymphatic and luminal compartments, as well as endothelial and epithelial barrier permeability (FITC-dextran translocation) were evaluated in both groups. RESULTS: Compared to the Albumin group, HES perfusion did not significantly change the wet-to-dry weight ratio and lactate-to-pyruvate ratio. However, perfusing the small intestine with 3% HES resulted in a significant loss of vascular fluid (p<0.01), an increased fluid accumulation in the intestinal lumen (p<0.001), an enhanced translocation of FITC-dextran from the vascular to the luminal compartment (p<0.001) and a significantly impaired intestinal galactose uptake (p<0.001). Morphologically, these findings were associated with an aggregation of intracellular vacuoles within the intestinal epithelial cells and enlarged intercellular spaces. CONCLUSION: A vascular perfusion with 3% HES impairs the endothelial and epithelial barrier integrity as well as metabolic function of the small intestine.

Hydroxyethyl starch (HES 130/0.4) impairs intestinal barrier integrity and metabolic function: findings from a mouse model of the isolated perfused small intestine.

BACKGROUND: The application of hydroxyethyl starch (HES) for volume resuscitation is controversially discussed and clinical studies have suggested adverse effects of HES substitution, leading to increased patient mortality. Although, the intestine is of high clinical relevance and plays a crucial role in sepsis and inflammation, information about the effects of HES on intestinal function and barrier integrity is very scarce. We therefore evaluated the effects of clinically relevant concentrations of HES on intestinal function and barrier integrity employing an isolated perfused model of the mouse small intestine. METHODS: An isolated perfused model of the mouse small intestine was established and intestines were vascularly perfused with a modified Krebs-Henseleit buffer containing 3% Albumin (N=7) or 3% HES (130/0.4; N=7). Intestinal metabolic function (galactose uptake, lactate-to-pyruvate ratio), edema formation (wet-to-dry weight ratio), morphology (histological and electron microscopical analysis), fluid shifts within the vascular, lymphatic and luminal compartments, as well as endothelial and epithelial barrier permeability (FITC-dextran translocation) were evaluated in both groups. RESULTS: Compared to the Albumin group, HES perfusion did not significantly change the wet-to-dry weight ratio and lactate-to-pyruvate ratio. However, perfusing the small intestine with 3% HES resulted in a significant loss of vascular fluid (p<0.01), an increased fluid accumulation in the intestinal lumen (p<0.001), an enhanced translocation of FITC-dextran from the vascular to the luminal compartment (p<0.001) and a significantly impaired intestinal galactose uptake (p<0.001). Morphologically, these findings were associated with an aggregation of intracellular vacuoles within the intestinal epithelial cells and enlarged intercellular spaces. CONCLUSION: A vascular perfusion with 3% HES impairs the endothelial and epithelial barrier integrity as well as metabolic function of the small intestine.