Enteral glutamine but not alanine maintains small bowel barrier function after ischemia/reperfusion injury in rats

Nutrition in the critically ill surgical patient

PURPOSE OF REVIEW

The aim of this study was to discuss recent findings related to providing adequate and well tolerated nutrition to the critically ill surgical patient.

RECENT FINDINGS

The majority of nutritional studies in the critically ill have been performed on well nourished patients, but validated scoring systems can now identify high nutrition risk patients. Although it remains well accepted that early enteral nutrition with protein supplementation is key, mechanistic data suggest that hypocaloric feeding in septic patients may be beneficial. For critically ill patients unable to tolerate enteral nutrition, randomized pilot data demonstrate improved functional outcomes with early supplemental parenteral nutrition. Current guidelines also recommend early total parenteral nutrition in high nutrition risk patients with contraindications to enteral nutrition. When critically ill patients require low or moderate-dose vasopressors, enteral feeding appears well tolerated based on a large database study, while randomized prospective data showed worse outcomes in patients receiving high-dose vasopressors.

SUMMARY

Current evidence suggests early enteral nutrition with protein supplementation in critically ill surgical patients with consideration of early parenteral nutrition in high nutrition risk patients unable to achieve nutrition goals enterally. Despite established guidelines for nutritional therapy, the paucity of data to support these recommendations illustrates the critical need for additional studies.

Distinct cytoprotective roles of pyruvate and ATP by glucose metabolism on epithelial necroptosis and crypt proliferation in ischaemic gut

KEY POINTS

Intestinal ischaemia causes epithelial death and crypt dysfunction, leading to barrier defects and gut bacteria-derived septic complications. Enteral glucose protects against ischaemic injury; however, the roles played by glucose metabolites such as pyruvate and ATP on epithelial death and crypt dysfunction remain elusive. A novel form of necrotic death that involves the assembly and phosphorylation of receptor interacting protein kinase 1/3 complex was found in ischaemic enterocytes. Pyruvate suppressed epithelial cell death in an ATP-independent manner and failed to maintain crypt function. Conversely, replenishment of ATP partly restored crypt proliferation but had no effect on epithelial necroptosis in ischaemic gut. Our data argue against the traditional view of ATP as the main cytoprotective factor by glucose metabolism, and indicate a novel anti-necroptotic role of glycolytic pyruvate under ischaemic stress.

ABSTRACT

Mesenteric ischaemia/reperfusion induces epithelial death in both forms of apoptosis and necrosis, leading to villus denudation and gut barrier damage. It remains unclear whether programmed cell necrosis [i.e. receptor-interacting protein kinase (RIP)-dependent necroptosis] is involved in ischaemic injury. Previous studies have demonstrated that enteral glucose uptake by sodium-glucose transporter 1 ameliorated ischaemia/reperfusion-induced epithelial injury, partly via anti-apoptotic signalling and maintenance of crypt proliferation. Glucose metabolism is generally assumed to be cytoprotective; however, the roles played by glucose metabolites (e.g. pyruvate and ATP) on epithelial cell death and crypt dysfunction remain elusive. The present study aimed to investigate the cytoprotective effects exerted by distinct glycolytic metabolites in ischaemic gut. Wistar rats subjected to mesenteric ischaemia were enterally instilled glucose, pyruvate or liposomal ATP. The results showed that intestinal ischaemia caused RIP1-dependent epithelial necroptosis and villus destruction accompanied by a reduction in crypt proliferation. Enteral glucose uptake decreased epithelial cell death and increased crypt proliferation, and ameliorated mucosal histological damage. Instillation of cell-permeable pyruvate suppressed epithelial cell death in an ATP-independent manner and improved the villus morphology but failed to maintain crypt function. Conversely, the administration of liposomal ATP partly restored crypt proliferation but did not reduce epithelial necroptosis and histopathological injury. Lastly, glucose and pyruvate attenuated mucosal-to-serosal macromolecular flux and prevented enteric bacterial translocation upon blood reperfusion. In conclusion, glucose metabolites protect against ischaemic injury through distinct modes and sites, including inhibition of epithelial necroptosis by pyruvate and the promotion of crypt proliferation by ATP.

1H NMR studies on serum metabonomic changes over time in a kidney-Yang deficiency syndrome model

The central aim of this study was to investigate metabolite changes in metabolic pathwaysviametabonomic approaches in rats suffering from Kidney-Yang Deficiency Syndrome (KYDS) induced by hydrocortisone.

Protection by enteral glutamine is mediated by intestinal epithelial cell peroxisome proliferator-activated receptor-γ during intestinal ischemia/reperfusion

We have demonstrated that enteral glutamine provides protection to the postischemic gut, and that peroxisome proliferator-activated receptor-γ (PPARγ) plays a role in this protection. Using Cre/lox technology to generate an intestinal epithelial cell (IEC)-specific PPARγ null mouse model, we now investigated the contribution of IEC PPARγ to glutamine's local and distant organ-protective effects. These mice exhibited absence of expression of PPARγ in the intestine but normal PPARγ expression in other tissues. After 1 h of intestinal ischemia under isoflurane anesthesia, wild-type and null mice received enteral glutamine (60 mM) or vehicle followed by 6 h of reperfusion or 7 days in survival experiments and compared with shams. Small intestine, liver, and lungs were analyzed for injury and inflammatory parameters. Glutamine provided significant protection against gut injury and inflammation, with similar protection in the lung and liver. Changes in systemic tumor necrosis factor-α reflected those seen in the injured organs. Importantly, mice lacking IEC PPARγ had worsened injury and inflammation, and glutamine lost its protective effects in the gut and lung. The survival benefit found in glutamine-treated wild-type mice was not observed in null mice. Using an IEC-targeted loss-of-function approach, these studies provide the first in vivo confirmation in native small intestine and lung that PPARγ is responsible for the protective effects of enteral glutamine in reducing intestinal and lung injury and inflammation and improving survival. These data suggest that early enteral glutamine may be a potential therapeutic modality to reduce shock-induced gut dysfunction and subsequent distant organ injury.

Enteral glutamine differentially regulates Nrf 2 along the villus-crypt axis of the intestine to enhance glutathione levels

BACKGROUND AND AIM

Glutamine is an important energy source for the intestinal epithelium, and its supplementation protects intestinal epithelial cells by induction of glutathione. However, mechanisms of glutathione induction in cells at various stages of differentiation along the crypt to villus axis are not well understood. This study examined induction of glutathione in response to glutamine along the intestinal villus-crypt axis and evaluated regulatory mediators involved in the process.

METHODS

Animals were administered 4% glutamine in feed for 7 days, following which enterocytes at various stages of differentiation were isolated and glutathione levels and signaling mediators involved in its regulation were studied.

RESULTS

In control animals, glutathione levels were higher in the intestinal crypt than in the villus or middle region. This was accompanied by elevated expression of the modifier subunit of glutathione synthetase (GCLM) and the transcription factor Nrf2 when compared with cells from the villus and middle regions. These levels were further enhanced by glutamine throughout the intestine, although the effects were more dramatic in the crypt. In parallel to glutathione induction, glutamine supplementation also altered actin dynamics and proliferation in cells of the crypt.

CONCLUSIONS

These results suggest that the variation of glutathione levels along the villus-crypt axis in the intestine is due to gradients in expression of mediators such as glutamate cysteine ligase modifier subunit and Nrf2. The protective effects of glutamine supplementation seem to be most pronounced in the crypt, where it upregulates proliferation, glutathione levels and alters actin dynamics.

Enteral delivery of proteins enhances the expression of proteins involved in the cytoskeleton and protein biosynthesis in human duodenal mucosa

BACKGROUND

Amino acids are well known to be key effectors of gut protein turnover. We recently reported that enteral delivery of proteins markedly stimulated global duodenal protein synthesis in carbohydrate-fed healthy humans, but specifically affected proteins remain unknown.

OBJECTIVE

We aimed to assess the influence of an enteral protein supply on the duodenal mucosal proteome in carbohydrate-fed humans.

DESIGN

Six healthy volunteers received for 5 h, on 2 occasions and in random order, either an enteral infusion of maltodextrins alone (0.25 g · kg⁻¹ · h⁻¹) mimicking the fed state or maltodextrins with a protein powder (0.14 g proteins · kg⁻¹ · h⁻¹). Endoscopic duodenal biopsy specimens were then collected and frozen until analysis. A 2-dimensional polyacrylamide gel electrophoresis-based comparative proteomics analysis was then performed, and differentially expressed proteins (at least ±1.5-fold change; Student's t test, P < 0.05) were identified by mass spectrometry. Protein expression changes were confirmed by Western blot analysis.

RESULTS

Thirty-two protein spots were differentially expressed after protein delivery compared with maltodextrins alone: 28 and 4 spots were up- or downregulated, respectively. Among the 22 identified proteins, 11 upregulated proteins were involved either in the cytoskeleton (ezrin, moesin, plastin 1, lamin B1, vimentin, and β-actin) or in protein biosynthesis (glutamyl-prolyl-transfer RNA synthetase, glutaminyl-transfer RNA synthetase, elongation factor 2, elongation factor 1δ, and eukaryotic translation and initiation factor 3 subunit f).

CONCLUSIONS

Enteral delivery of proteins altered the duodenal mucosal proteome and mainly stimulated the expression of proteins involved in cytoskeleton and protein biosynthesis. These results suggest that protein supply may affect intestinal morphology by stimulating actin cytoskeleton remodeling.

Oxygen in the regulation of intestinal epithelial transport

The transport of fluid, nutrients and electrolytes to and from the intestinal lumen is a primary function of epithelial cells. Normally, the intestine absorbs approximately 9 l of fluid and 1 kg of nutrients daily, driven by epithelial transport processes that consume large amounts of cellular energy and O2. The epithelium exists at the interface of the richly vascularised mucosa, and the anoxic luminal environment and this steep O2 gradient play a key role in determining the expression pattern of proteins involved in fluid, nutrient and electrolyte transport. However, the dynamic nature of the splanchnic circulation necessitates that the epithelium can evoke co-ordinated responses to fluctuations in O2 availability, which occur either as a part of the normal digestive process or as a consequence of several pathophysiological conditions. While it is known that hypoxia-responsive signals, such as reactive oxygen species, AMP-activated kinase, hypoxia-inducible factors, and prolyl hydroxylases are all important in regulating epithelial responses to altered O2 supply, our understanding of the molecular mechanisms involved is still limited. Here, we aim to review the current literature regarding the role that O2 plays in regulating intestinal transport processes and to highlight areas of research that still need to be addressed.

Regional susceptibility to stress-induced intestinal injury in the mouse

Injury to the intestinal mucosa is a life-threatening problem in a variety of clinical disorders, including hemorrhagic shock, trauma, burn, pancreatitis, and heat stroke. The susceptibility to injury of different regions of intestine in these disorders is not well understood. We compared histological injury across the small intestine in two in vivo mouse models of injury, hemorrhagic shock (30% loss of blood volume) and heat stroke (peak core temperature 42.4°C). In both injury models, areas near the duodenum showed significantly greater mucosal injury and reductions in villus height. To determine if these effects were dependent on circulating factors, experiments were performed on isolated intestinal segments to test for permeability to 4-kDa FITC-dextran. The segments were exposed to hyperthermia (42°C for 90 min), moderate simulated ischemia (Po2 ∼30 Torr, Pco2 ∼60 Torr, pH 7.1), severe ischemia (Po2 ∼20 Torr, Pco2 ∼80 Torr, pH 6.9), or severe hypoxia (Po2 ∼0 Torr, Pco2 ∼35 Torr) for 90 min, and each group was compared with sham controls. All treatments resulted in marked elevations in permeability within segments near the duodenum. In severe hypoxia or hyperthermia, permeability was also moderately elevated in the jejunum and ileum; in moderate or severe ischemia, permeability was unaffected in these regions. The results demonstrate increased susceptibility of proximal regions of the small intestine to acute stress-induced damage, irrespective of circulating factors. The predominant injury in the duodenum may impact the pattern of acute inflammatory responses arising from breach of the intestinal barrier, and such knowledge may be useful for designing therapeutic strategies.

Use of immune micro-ecological nutrition as an alternative to traditional bowel preparation in minimally invasive treatment of colorectal cancer

AIM: To observe the effect of immune micro-ecological nutrition as a bowel preparation method on postoperative inflammatory reaction and immune condition in patients with colorectal cancer after laparoscopic radical resection.

METHODS: Sixty patients with colorectal cancer were randomly divided into either a trial group or a control group. Three-day conventional bowel preparation was administered in the control group, while immune micro-ecological nutrition was administered in the trial group. Quality of the preparation was estimated during operation. Intestinal flora in the stool, lymphocyte count, immune globulins, and serum C-reactive protein were measured before and 5 d after the operation. Meanwhile, the time required for intestinal function recovery and incidence of postoperative complications were recorded.

RESULTS: Good and excellent bowel preparation was achieved in 90% of patients in the trial group and in 93% of patients in the control group. There was no significant difference between the trial and control groups in the bowel clear effect. Preoperative intestinal flora, lymphocyte count, serum immunoglobulin and complement in blood showed no significant differences between the two groups. Postoperative lymphocyte count (1.40 ± 0.44 vs 1.15 ± 0.40, P < 0.05), immune globulins IgG (9.32 ± 2.11 vs 8.10 ± 2.34, P < 0.05), IgA (1.95 ± 0.31 vs 1.78 ± 0.27, P < 0.05), IgM (1.45 ± 0.45 vs 1.22 ± 0.51, P < 0.05), serum C3 (1.62 ± 0.27 vs 1.45 ± 0.24, P < 0.05) and C4 (0.87 ± 0.11 vs 0.71 ± 0.12, P < 0.05) were significantly higher in the trial group than in the control group, while postoperative serum C-reactive protein was significantly lower in the trail group than in the control group (16.0 ± 2.3 vs 18.2 ± 2.9, P < 0.05). The time required for intestinal function recovery was significantly shorter in the trial group than in the control group. The incidence of anastomotic fistula showed no statistical difference between the two groups.

CONCLUSION: Immune micro-ecological nutrition as a bowel preparation method is effective and feasible in reconstructing postoperative intestinal flora, recovering postoperative intestinal function, diminishing early postoperative inflammatory reaction and building up patients' immune function.

Syndecan 1 plays a novel role in enteral glutamine's gut-protective effects of the postischemic gut

Syndecan 1 is the predominant heparan sulfate proteoglycan found on the surface of epithelial cells and, like glutamine, is essential in maintaining the intestinal epithelial barrier. We therefore hypothesized that loss of epithelial syndecan 1 would abrogate the gut-protective effects of enteral glutamine. Both an in vitro and in vivo model of gut ischemia-reperfusion (IR) was utilized. In vitro, intestinal epithelial cells underwent hypoxia-reoxygenation to mimic gut IR with 2 mM (physiologic) or 10 mM glutamine supplementation. Permeability, caspase activity, cell growth, and cell surface and shed syndecan 1 were assessed. In vivo, wild-type and syndecan 1 knockout (KO) mice received ± enteral glutamine followed by gut IR. Intestinal injury was assessed by fluorescent dye clearance and histopathology, permeability as mucosal-to-serosal clearance ex vivo in everted sacs, and inflammation by myeloperoxidase (MPO) activity. In an in vitro model of gut IR, glutamine supplementation reduced epithelial cell permeability and apoptosis and enhanced cell growth. Shed syndecan 1 was reduced by glutamine without an increase in syndecan 1 mRNA. In vivo, intestinal permeability, inflammation, and injury were increased after gut IR in wild-type mice and further increased in syndecan 1 KO mice. Glutamine's attenuation of IR-induced intestinal hyperpermeability, inflammation, and injury was abolished in syndecan 1 KO mice. These results suggest that syndecan 1 plays a novel role in the protective effects of enteral glutamine in the postischemic gut.

Glutamine activates peroxisome proliferator-activated receptor-γ in intestinal epithelial cells via 15-S-HETE and 13-OXO-ODE: a novel mechanism

Glutamine possesses gut-protective effects both clinically and in the laboratory. We have shown in a rodent model of mesenteric ischemia-reperfusion that enteral glutamine increased peroxisome proliferator-activated receptor-γ (PPAR-γ) and was associated with a reduction in mucosal injury and inflammation. The mechanism by which glutamine activates PPAR-γ is unknown, and we hypothesized that it was via a ligand-dependent mechanism. Intestinal epithelial cells, IEC-6, were co-transfected with PPAR-γ response element-luciferase promoter/reporter construct. Cells were pretreated with increasing concentrations of glutamine ± GW9662 (a specific antagonist of PPAR-γ) and analyzed for PPAR-γ response element luciferase activity as an indicator of PPAR-γ activation. PPAR-γ nuclear activity was assessed by electrophoretic mobility shift assay. Cell lysates were subjected to tandem mass spectroscopy for measurement of prostaglandin and lipoxygenase metabolites. A time- and concentration-dependent increase in PPAR-γ transcriptional activity, but not mRNA or protein, was demonstrated. Activity was abrogated by the PPAR-γ inhibitor, GW9662, and changes in activity correlated with PPAR-γ nuclear binding. Glutamine, via degradation to glutamate, activated the metabolic by-products of the lipoxygenase and linoleic acid pathways, 15-S-hydroxyeicosatetraenoic acid and dehydrogenated 13-hydroxyoctaolecadienoic acid, known endogenous PPAR-γ ligands in the small bowel. This novel mechanism may explain the gut-protective effects of enteral glutamine.

Glutamine supplementation decreases intestinal permeability and preserves gut mucosa integrity in an experimental mouse model

BACKGROUND

Glutamine (GLN) is the preferred fuel for enterocytes, and GLN supplementation is critical during stressful conditions. The aim of this study was to evaluate the effect of GLN on intestinal barrier permeability and bacterial translocation in a murine experimental model.

METHODS

Swiss male mice (25-30 g) were randomized into 3 groups: (1) sham group; (2) intestinal obstruction (IO) group; (3) IO and GLN (500 mg/kg/d) group. Two different experiments were carried out to assess intestinal permeability and bacterial translocation. In the first experiment, the animals were divided into the 3 groups described above and received diethylenetriamine pentaacetate radiolabeled with technetium ((99m)Tc) on the eighth day. At different time points after intestinal obstruction, blood was collected to determine radioactivity. The animals were killed, and the small intestine was removed for histological analyses. In the bacterial translocation study, on the eighth day all groups received Escherichia coli labeled with (99m)Tc. After 90 minutes, the animals underwent intestinal obstruction and were killed 18 hours later. Blood, mesenteric lymph nodes, liver, spleen, and lungs were removed to determine radioactivity. Statistical significance was considered when P < or = .05.

RESULTS

The levels of intestinal permeability and bacterial translocation were higher in the IO group than in the sham and GLN groups (P < .05). GLN decreased intestinal permeability and bacterial translocation to physiologic levels in the treated animals and preserved intestinal barrier integrity.

CONCLUSIONS

GLN had a positive impact on the intestinal barrier by reducing permeability and bacterial translocation to physiologic levels and preserving mucosal integrity.

Glutamine protects against apoptosis via downregulation of Sp3 in intestinal epithelial cells

Glutamine plays a key role in intestinal growth and maintenance of gut function, and as we have shown protects the postischemic gut (Kozar RA, Scultz SG, Bick RJ, Poindexter BJ, Desoigne R, Weisbrodt NW, Haber MM, Moore FA. Shock 21: 433-437, 2004). However, the precise mechanisms of the gut protective effects of glutamine have not been well elucidated. In the present study, RNA microarray was performed to obtain differentially expressed genes in intestinal epithelial IEC-6 cells following either 2 mM or 10 mM glutamine. The result demonstrated that specificity protein 3 (Sp3) mRNA expression was downregulated 3.1-fold. PCR and Western blot confirmed that Sp3 expression was decreased by glutamine in a time- and dose-dependent fashion. To investigate the role of Sp3, Sp3 gene siRNA silencing was performed and apoptosis was assessed. Silencing of Sp3 demonstrated a significant increase in Bcl-2 and decrease in Bax protein expression, as well as a decrease in caspase-3, -8, and -9 protein expression and activity. The protein expression of apoptosis-related proteins after hypoxia/reoxygenation was similar to that of normoxia and correlated with a decrease in DNA fragmentation. Importantly, the addition of glutamine to Sp3-silenced cells did not further lessen apoptosis, suggesting that Sp3 plays a major role in the inhibitory effect of glutamine on apoptosis. This novel finding may explain in part the gut-protective effects of glutamine.

Intestinal ischemia/reperfusion: microcirculatory pathology and functional consequences

BACKGROUND

Intestinal ischemia and reperfusion (I/R) is a challenging and life-threatening clinical problem with diverse causes. The delay in diagnosis and treatment contributes to the continued high in-hospital mortality rate.

RESULTS

Experimental research during the last decades could demonstrate that microcirculatory dysfunctions are determinants for the manifestation and propagation of intestinal I/R injury. Key features are nutritive perfusion failure, inflammatory cell response, mediator surge and breakdown of the epithelial barrier function with bacterial translocation, and development of a systemic inflammatory response. This review provides novel insight into the basic mechanisms of damaged intestinal microcirculation and covers therapeutic targets to attenuate intestinal I/R injury.

CONCLUSION

The opportunity now exists to apply this insight into the translation of experimental data to clinical trial-based research. Understanding the basic events triggered by intestinal I/R may offer new diagnostic and therapeutic options in order to achieve improved outcome of patients with intestinal I/R injury.

Enteral arginine modulates inhibition of AP-1/c-Jun by SP600125 in the postischemic gut

We previously demonstrated that enteral arginine increased c-Jun/activator protein-1 (AP-1) DNA-binding activity and iNOS expression in a rodent model of mesenteric ischemia/reperfusion (I/R). The objective of this study was to specifically investigate the role of AP-1 in arginine's deleterious effect on the postischemic gut. We hypothesized that AP-1 inhibition would mitigate the effects of arginine. Using a rodent model of mesenteric I/R we demonstrated that gut neutrophil infiltration, activity of c-Jun/AP-1, as well as iNOS expression were increased by I/R and further increased by arginine while lessened by inhibition of c-Jun using the pharmacologic c-Jun N-terminal kinase inhibitor, SP600125. Similar results were demonstrated using a cell culture model of oxidant stress in IEC-6 cells. Importantly, effects of SP600125 were comparable to those of c-Jun silencing. Lastly, the specific iNOS inhibitor, 1400W, had no effect on either AP-1 or c-Jun. In conclusion, SP600125 attenuated the activity of c-Jun/AP-1, iNOS expression, and neutrophil infiltration induced by arginine following mesenteric I/R. Our data suggest that AP-1 inhibition mitigates the injurious inflammatory effects of arginine in the postischemic gut. Further investigation into the pathologic role of enteral arginine in the postischemic gut is warranted.

Glutamine treatment attenuates the development of ischaemia/reperfusion injury of the gut

Intestinal ischemia/reperfusion causes tissue hypoxia and damage, leading to the pathophysiology of inflammation. The aim of this study was to investigate the effects of glutamine on the tissue injury caused by ischemia/reperfusion of the gut. Ischemia/reperfusion injury of the intestine was caused by clamping both the superior mesenteric artery and the celiac trunk for 30 min followed by the release of the clamp allowing reperfusion for 1h. This procedure results in splanchnic artery occlusion-injury. Based on our findings we propose that the amino acid glutamine, administered 15 min before reperfusion at the dose of 1.5mg/kg, i.v. may be useful in the treatment of various ischemia and reperfusion diseases. The present study was performed in order to determine the pharmacological effects of glutamine ischemia/reperfusion-induced intestinal injury in rats. In particular, to gain a better insight into the mechanism(s) of action of glutamine, we evaluated the following endpoints of the inflammatory response: (1) histological damage; (2) neutrophil infiltration of the reperfused intestine (MPO activity); (3) NF-kappaB activation and cytokines production; (4) expression of ICAM-1 and P-selectin during reperfusion; (5) nitrotyrosine and poly-ADP-ribose formation; (6) pro-inflammatory cytokine production; (7) inducible nitric oxide synthase expression; (8) apoptosis as shown by TUNEL staining and (9) Bax/Bcl-2 expression.

Possible links between intestinal permeability and food processing: A potential therapeutic niche for glutamine

Increased intestinal permeability is a likely cause of various pathologies, such as allergies and metabolic or even cardiovascular disturbances. Intestinal permeability is found in many severe clinical situations and in common disorders such as irritable bowel syndrome. In these conditions, substances that are normally unable to cross the epithelial barrier gain access to the systemic circulation. To illustrate the potential harmfulness of leaky gut, we present an argument based on examples linked to protein or lipid glycation induced by modern food processing. Increased intestinal permeability should be largely improved by dietary addition of compounds, such as glutamine or curcumin, which both have the mechanistic potential to inhibit the inflammation and oxidative stress linked to tight junction opening. This brief review aims to increase physician awareness of this common, albeit largely unrecognized, pathology, which may be easily prevented or improved by means of simple nutritional changes.

HB-EGF protects the lungs after intestinal ischemia/reperfusion injury

BACKGROUND

Acute respiratory distress syndrome continues to be a major source of morbidity and mortality in critically-ill patients. Heparin binding EGF-like growth factor (HB-EGF) is a biologically active protein that acts as an intestinal cytoprotective agent. We have previously demonstrated that HB-EGF protects the intestines from injury in several different animal models of intestinal injury. In the current study, we investigated the ability of HB-EGF to protect the lungs from remote organ injury after intestinal ischemia/reperfusion (I/R).

METHODS

Mice were randomly assigned to one of the following groups: (1) sham-operated; (2) sham+HB-EGF (1200 microg/kg in 0.6 mL administered by intra-luminal injection at the jejuno-ileal junction immediately after identification of the superior mesenteric artery); (3) superior mesenteric artery occlusion for 45 min followed by reperfusion for 6 h (I/R); or (4) I/R+HB-EGF (1200 microg/kg in 0.6 mL) administered 15 min after vascular occlusion. The severity of acute lung injury was determined by histology, morphometric analysis and invasive pulmonary function testing. Animal survival was evaluated using Kaplan-Meier analysis.

RESULTS

Mice subjected to intestinal I/R injury showed histologic and functional evidence of acute lung injury and decreased survival compared with sham-operated animals. Compared with mice treated with HB-EGF (I/R+HB-EGF), the I/R group had more severe acute lung injury, and decreased survival.

CONCLUSION

Our results demonstrate that HB-EGF reduces the severity of acute lung injury after intestinal I/R in mice. These data demonstrate that HB-EGF may be a potential novel systemic anti-inflammatory agent for the prevention of the systemic inflammatory response syndrome (SIRS) after intestinal injury.

Recombinant factor XIII diminishes multiple organ dysfunction in rats caused by gut ischemia-reperfusion injury

Plasma factor XIII (FXIII) is responsible for stabilization of fibrin clot at the final stage of blood coagulation. Because FXIII has also been shown to modulate inflammation and endothelial permeability, we hypothesized that FXIII diminishes multiple organ dysfunction caused by gut I/R injury. A model of superior mesenteric artery occlusion (SMAO) was used to induce gut I/R injury. Rats were subjected to 45-min SMAO or sham SMAO and treated with recombinant human FXIII A2 subunit (rFXIII) or placebo at the beginning of the reperfusion period. Lung permeability, lung and gut myeloperoxidase activity, gut histology, neutrophil respiratory burst, and microvascular blood flow in the liver and muscles were measured after a 3-h reperfusion period. The effect of activated rFXIII on transendothelial resistance of human umbilical vein endothelial cells was tested in vitro. Superior mesenteric artery occlusion-induced lung permeability as well as lung and gut myeloperoxidase activity was significantly lower in rFXIII-treated versus untreated animals. Similarly, rFXIII-treated rats had lower neutrophil respiratory burst activity and ileal mucosal injury. Rats treated with rFXIII also had higher liver microvascular blood flow compared with the placebo group. Superior mesenteric artery occlusion did not cause FXIII consumption during the study period. In vitro, activated rFXIII caused a dose-dependent increase in human umbilical vein endothelial cell monolayer resistance to thrombin-induced injury. Thus, administration of rFXIII diminishes SMAO-induced multiple organ dysfunction in rats, presumably by preservation of endothelial barrier function and the limitation of polymorphonuclear leukocyte activation.

Magnetic resonance imaging detects intestinal barrier dysfunction in a rat model of acute mesenteric ischemia/reperfusion injury

OBJECTIVES

To develop an in vivo intestinal permeability assay applying magnetic resonance imaging (MRI) to monitor real-time gut barrier defects in animal models of acute mesenteric ischemia/reperfusion (I/R) insult.

MATERIALS AND METHODS

Twenty Wistar rats were divided to 2 groups for I/R challenge or sham controls. I/R rats received occlusion of superior mesenteric artery for 20 minutes and reperfusion for 1 hour. Sham-operation controls received laparotomy without manipulation of artery. To assess gut permeability, a 10-cm jejunal sac was created distal to the ligament of Treitz in both groups of rats after laparotomy, and a contrast agent (gadodiamide) was injected into the lumen of the ligated intestinal sac. The signals produced by gadodamide in the liver, kidney, and plasma before and after the start of reperfusion were examined by 1.5 Tesla MRI (GE Signa Excite), and the increment of signal-to-noise ratio (SNR) in these organs that parallels the luminal-to-serosal flux rate of the probe was used as an indicator of gut permeability. At the end of procedures, jejunal tissues and mucosal scrapings were collected for histologic examination and Western blotting for epithelial tight junctional proteins. Moreover, liver and spleen homogenates were cultured on fresh blood agar plates to measure the bacterial colony-forming units per gram of tissue.

RESULTS

In I/R rats, disrupted villous structure and decreased epithelial tight junctional expression were seen in the jejunum associated with massive enteric bacterial translocation to the liver and spleen. The SNR in the liver of I/R rats was higher than sham controls (2.65 +/- 0.56 vs. 0.65 +/- 0.26, P < 0.01) at 15 minutes postreperfusion. Elevation of SNR in the kidney was also found in I/R rats compared with sham controls (11.61 +/- 2.07 vs. 3.06 +/- 1.15, P < 0.05). The plasma gadodiamide concentration in I/R rats was significantly increased compared with sham controls (0.220 +/- 0.044 vs. 0.006 +/- 0.004 mM, P < 0.01) at 15 minutes postreperfusion.

CONCLUSIONS

This novel MRI-based intestinal permeability assay has shown a significant increase in the signal intensity in liver, kidney, and plasma samples that correlated with mucosal barrier defects in experimental models of acute mesenteric I/R.

The patient with circulatory shock: to feed or not to feed?

Controversy continues to surround the appropriate form and timing of nutrition support for the patient with circulatory shock. Clinical studies have demonstrated improvements in outcome with the administration of enteral nutrition to critically ill patients; however, the provision of enteral nutrition to critically ill patients with ongoing shock remains controversial. This article reviews gut perfusion during normal states and during circulatory shock as well as alterations in perfusion when enteral feeding is provided. Pharmaconutrients studied during ischemia and reperfusion are discussed.

Gene expression profile of duodenal epithelial cells in response to chronic metabolic acidosis

Chronic metabolic acidosis (CMA) affects ion transport, permeability, and metabolism of the intestinal absorptive cells. Most effects of CMA on the intestine are long-term adaptations at genomic level. To identify the CMA-regulated genes, the Illumina's microarray featuring high-performance BeadArray technology was performed on RNA samples from the rat duodenal epithelial cells exposed to long-standing acidemia. After 21 days of CMA, we found 423 transcripts upregulated and 261 transcripts downregulated. Gene ontology analysis suggested effects of CMA on cellular processes, such as cell adhesion, proliferation, fuel metabolism, and biotransformation. Interestingly, 27 upregulated transcripts (e.g., Aqp1, Cacnb1, Atp1a2, Kcnab2, and Slc2a1) and 13 downregulated transcripts (e.g., Slc17a7, Slc9a4, and Slc30a3) are involved in the absorption of water, ions, and nutrients. Some upregulated genes, such as Slc38a5 and Slc1a7 encoding glutamine transporters, may be parts of the total body adaptation to alleviate negative nitrogen balance. Therefore, the present results provided a novel genome-wide information for further investigations of the mechanism of CMA effect on the intestine.

Differential effects of luminal arginine and glutamine on metalloproteinase production in the postischemic gut

BACKGROUND

Matrix metalloproteinases (MMPs) are a group of endopeptidases induced under inflammatory conditions in the intestine which possess the capacity to degrade components of the extracellular matrix. We have previously demonstrated that MMP-2 expression correlates with increased inducible nitric oxide synthase (iNOS) production in the stomach and that iNOS is upregulated in the postischemic gut by the luminal nutrient arginine and repressed by luminal glutamine. We therefore hypothesized that arginine would enhance expression of MMP-2 in the postischemic gut.

METHODS

Jejunal sacs were created in rats at laparotomy and filled with either 60 mM glutamine, arginine, or magnesium sulfate (osmotic control) followed by 60 minutes of superior mesenteric artery occlusion (SMAO) and 6 hours of reperfusion and compared with shams. Jejunum was harvested, and membrane type-1 matrix metalloproteinase (MT1-MMP), MMP-2, and iNOS protein expression was determined by Western analysis and MMP-9 production by gelatin zymography.

RESULTS

MMP-2, MT1-MMP, MMP-9, and iNOS were all increased after SMAO compared with shams. Arginine maintained while glutamine inhibited the increase in iNOS, MT1-MMP, and MMP-2 expression in the postischemic gut. Pretreatment of the arginine group with a selective iNOS inhibitor blunted the induction of MMP-2 in the postischemic gut. There was no differential modulation of MMP-9 by the luminal nutrients.

CONCLUSIONS

The arginine-induced upregulation of iNOS may contribute to increased activity of MT1-MMP and MMP-2. The mechanism for this differential regulation by arginine warrants further investigation.

Enteral glutamine: a novel mediator of PPARgamma in the postischemic gut

Early enteral nutrition supplemented with glutamine, arginine, omega-3 fatty acids, and nucleotides has been shown to decrease infection complications in critically injured patients. Concern has been raised, however, that under conditions of hyperinflammation, these diets may be injurious through the induction of inducible NO synthase by enteral arginine. In a rodent model of gut ischemia/reperfusion, inflammation and injury are intensified by enteral arginine and abrogated by glutamine. These findings correlate with the degree of metabolic stress imposed upon the gut by hypoperfusion. Glutamine is metabolized by the gut and therefore, can contribute back energy in the form of ATP, whereas arginine is a nonmetabolizable nutrient, using but not contributing energy. Recent data suggest that one of the molecular mechanisms responsible for the gut-protective effects of enteral glutamine is the activation of peroxisome proliferator-activated receptor gamma. This anti-inflammatory transcription factor belongs to the family of nuclear receptors, plays a key role in adipocyte development and glucose homeostasis, and has been recognized as an endogenous regulator of intestinal inflammation. Preliminary clinical studies support the use of enteral glutamine in patients with gut hypoperfusion.

Enteral glutamine during active shock resuscitation is safe and enhances tolerance of enteral feeding

BACKGROUND

Feeding the hemodynamically unstable patient is increasingly practiced, yet few data exist on its safety. Because enteral glutamine is protective to the gut in experimental models of shock and improves clinical outcomes, it may benefit trauma patients undergoing shock resuscitation and improve tolerance if administered early. This pilot study aimed to evaluate gastrointestinal tolerance and safety of enteral feeding with glutamine, beginning during shock resuscitation in severely injured patients.

METHODS

In a prospective randomized trial, 20 patients were randomly assigned to either an enteral glutamine group (n = 10) or a control group (n = 10). Patients with severe trauma meeting standardized shock resuscitation criteria received enteral glutamine 0.5 g/kg/d during the first 24 hours of resuscitation and 10 days thereafter. Immune-enhancing diet began on postinjury day 1, with a target of 25 kcal/kg/d. Control patients received isonitrogenous whey powder plus immune-enhancing diet. Tolerance (vomiting, nasogastric output, diarrhea, and distention) was assessed throughout the study.

RESULTS

Glutamine was well tolerated and no adverse events occurred. Treated patients had significantly fewer instances of high nasogastric output (5 vs 23; p = .010), abdominal distention (3 vs 12; p = .021), and total instances of intolerance (8 vs 42; p = .011). Intensive care unit (ICU) and hospital length of stay were comparable. Control patients required supplemental parenteral nutrition (PN) to meet goals at day 7.

CONCLUSIONS

Enteral glutamine administered during active shock resuscitation and through the early postinjury period is safe and enhances gastrointestinal tolerance. A large clinical trial is warranted to determine if enteral glutamine administered to the hemodynamically unstable patient can reduce infectious morbidity and mortality.

Intraluminal Glutamine Administration During Ischemia Worsens Survival After Gut Ischemia-Reperfusion

BACKGROUND

Glutamine (GLN) treatment prior to gut ischemia-reperfusion (I/R) reportedly preserves gut glutathione levels and gut barrier function. We hypothesized that intraluminal GLN during ischemia would also protect against gut I/R.

MATERIAL AND METHODS

After randomization to control and GLN groups, mice were exposed to 75 min (Exp 1) or 50 min (Exp 2 and 3) gut I/R. One mL of 2% GLN solution was injected into the duodenal lumen at the onset of ischemia in the GLN group, whereas controls were given normal saline. In experiment 1, survival was monitored for 120 h (n = 38). In experiment 2, blood, small intestine, and liver samples were collected at 4 h after reperfusion (n = 13). Expressions of CD11a and CD11b on myeloid cells were measured. Reactive oxygen intermediate production by myeloid cells was determined with or without phorbol myristate acetate stimulation. Glutathione levels in the small intestine and liver were also evaluated. In experiment 3, hemodynamic parameters were measured before and after I/R (n = 6).

RESULTS

In experiment 1, survival time in the GLN group was reduced compared with the control group. In experiment 2, GLN increased expression of CD11b and reactive oxygen intermediate with phorbol myristate acetate, compared with controls. There were no significant differences in gut or liver glutathione levels between the two groups. In experiment 3, the GLN group showed a transient but significant reduction in systolic blood pressure after reperfusion compared with the control group.

CONCLUSION

Intraluminal GLN during severe gut ischemia worsens outcomes, possibly by enhancing circulating myeloid cell priming and activation, and by disturbing hemodynamics, without increasing organ glutathione levels.

Glutamine: mode of action in critical illness

A recent editorial in Critical Care Medicine was titled "Glutamine, a life-saving nutrient, but why?" (2003; 31:2555-2556). This review will attempt to utilize new understanding of gene-nutrient interactions and molecular medicine to address potential mechanisms by which glutamine may be lifesaving after critical illness and injury. Recent meta-analysis data reveal that glutamine seems to exert a beneficial effect on mortality in critically ill patients. However, this effect seems to be dose and route dependent. The questions that remain to be answered are in what settings and via what method of administration does this phamaconutrient show optimal benefit? It is likely that examination of the molecular mechanisms by which glutamine exerts its effects will lead to an understanding of how best to utilize glutamine as both a pharmacologic and a nutritional agent. Clearly, clinical critical illness leads to a marked deficiency in glutamine that is correlated with mortality in the intensive care unit setting. It makes obvious sense that the deficiency of this vital stress nutrient should be replaced. In addition, recent laboratory data reveal glutamine may act via mechanisms independent of its role as a metabolic fuel. These include enhanced stress protein response, attenuation of the inflammatory response, improved tissue metabolic function, and attenuation of oxidant stress. Present data indicate that glutamine functions as a metabolic fuel and "stress-signaling molecule" after illness and injury. Thus, deficiencies observed in critical illness demand replacement for both pharmacologic and metabolic optimization. Presently, randomized, multicenter, clinical trials utilizing glutamine as a pharmacologic and a nutritional agent are ongoing.

EFFECTS OF CHRONIC ETHANOL INGESTION ON TIGHT JUNCTION PROTEINS AND BARRIER FUNCTION OF ALVEOLAR EPITHELIUM IN THE RAT

Previous studies show that chronic alcohol abuse is an independent risk factor for acute lung injury (ALI) and impairs alveolar epithelial barrier function through glutathione depletion. However, the precise molecular structures that are damaged by chronic ethanol ingestion have not been identified. To test whether chronic ethanol ingestion impairs the alveolar epithelium barrier by tight junction protein deterioration and predisposes to ALI, this study determined the alterations in tight junction proteins occludin, zonula occludens (ZO)-1, and adherens junction protein E-cadherin in alveolar epithelium and observed the protective effect of glutamine (Gln) supplementation. Sixty Sprague-Dawley rats were assigned to control, ethanol (6 weeks' ethanol feeding), lipopolysaccharide ([LPS] 2 mg/kg, i.v.), ethanol plus LPS, ethanol plus Gln (0.3 g/kg, gavage daily), and ethanol plus Gln plus LPS groups. Treatment with both ethanol and LPS significantly increased bronchoalveolar epithelial permeability, and treatment with ethanol plus LPS further increased the permeability. Using immunofluorescence, immunoblotting, and reverse transcriptase-polymerase chain reaction, this study shows that treatment with both ethanol and LPS induced partial breakdown of membrane staining and decreased cytoplasm staining in alveolar epithelium and decreased the messenger RNA and protein expression of those molecules in alveolar epithelial cells. Treatment with ethanol plus LPS caused further deterioration. Moreover, Gln supplementation markedly attenuated the enhanced bronchoalveolar epithelial permeability and decreased messenger RNA and protein expression of those molecules induced by ethanol and ethanol plus LPS. These data suggest that chronic ethanol ingestion impairs the alveolar epithelial barrier function via occludin, ZO-1, and E-cadherin deterioration, and predisposes to ALI. Glutamine supplementation has protective effect.

Synbiotics, prebiotics, glutamine, or peptide in early enteral nutrition: a randomized study in trauma patients

BACKGROUND

Since the hepatosplanchnic region plays a central role in development of multiple-organ failure and infections in critically ill trauma patients, this study focuses on the influence of glutamine, peptide, and synbiotics on intestinal permeability and clinical outcome.

METHODS

One hundred thirteen multiple injured patients were prospectively randomized into 4 groups: group A, glutamine; B, fermentable fiber; C, peptide diet; and D, standard enteral formula with fibers combined with Synbiotic 2000 (Synbiotic 2000 Forte; Medifarm, Sweden), a formula containing live lactobacilli and specific bioactive fibers. Intestinal permeability was evaluated by measuring lactulose-mannitol excretion ratio on days 2, 4, and 7.

RESULTS

No differences in days of mechanical ventilation, intensive care unit stay, or multiple-organ failure scores were found between the patient groups. A total of 51 infections, including 38 pneumonia, were observed, with only 5 infections and 4 pneumonias in group D, which was significantly less than combined infections (p = .003) and pneumonias (p = .03) in groups A, B, and C. Intestinal permeability decreased only in group D, from 0.148 (0.056-0.240) on day 4 to 0.061 (0.040-0.099) on day 7; (p < .05). In group A, the lactulose-mannitol excretion ratio increased significantly (p < .02) from 0.050 (0.013-0.116) on day 2 to 0.159 (0.088-0.311) on day 7. The total gastric retention volume in 7 days was 1150 (785-2395) mL in group D, which was significantly more than the 410 (382-1062) mL in group A (p < .02), and 620 (337-1190) mL in group C (p < .03).

CONCLUSIONS

Patients supplemented with synbiotics did better than the others, with lower intestinal permeability and fewer infections.

Glutamine's protection against sepsis and lung injury is dependent on heat shock protein 70 expression

Glutamine (GLN) has been shown to protect against inflammatory injury and illness in experimental and clinical settings. The mechanism of this protection is unknown; however, laboratory and clinical trial data have indicated a relationship between GLN-mediated protection and enhanced heat shock protein 70 (HSP70) expression. The aim of this study was to examine the hypothesis that GLN's beneficial effect on survival, tissue injury, and inflammatory response after inflammatory injury is dependent on HSP70 expression. Mice with a specific deletion of the HSP70 gene underwent cecal ligation and puncture (CLP)-induced sepsis and were treated with GLN (0.75 g/kg) or a saline placebo 1 h post-CLP. Lung tissue NF-κB activation, inflammatory cytokine response, and lung injury were assessed post-CLP. Survival was assessed for 5 days post-CLP. Our results indicate that GLN administration improved survival in Hsp70+/+mice vs. Hsp70+/+mice not receiving GLN; however, GLN exerted no survival benefit in Hsp70−/−mice. This was accompanied by a significant decrease in lung injury, attenuation of NF-κB activation, and proinflammatory cytokine expression in GLN-treated Hsp70+/+mice vs. Hsp70+/+mice not receiving GLN. In the Hsp70−/−mice, GLN's attenuation of lung injury, NF-κB activation, and proinflammatory cytokine expression was lost. These results confirm our hypothesis that HSP70 expression is required for GLN's effects on survival, tissue injury, and the inflammatory response after global inflammatory injury.

The effect of glutamine-enriched enteral nutrition on intestinal permeability in very-low-birth-weight infants: a randomized controlled trial

BACKGROUND

Very-low-birth-weight (VLBW) infants are susceptible to glutamine depletion. Glutamine depletion has negative effects on intestinal integrity. The lower infection rate in VLBW infants receiving glutamine-enriched enteral nutrition may originate from improved intestinal integrity, as reflected by decreased intestinal permeability. The aim of our study was to investigate whether glutamine-enriched enteral nutrition in VLBW infants enhances the normal decrease in intestinal permeability, as measured by the sugar absorption test (SAT).

METHODS

In a double-blind, randomized, placebo-controlled trial, VLBW infants (gestational age <32 weeks or birth weight <1,500 g) received enteral glutamine supplementation (0.3 g/kg/d) or an isonitrogenous placebo supplementation (alanine) between days 3 and 30 of life. Intestinal permeability, determined from the urinary lactulose/mannitol (L/M) ratio after an oral dose of lactulose and mannitol, was assessed at 4 time points: before the start of the study, and at days 7, 14, and 30 of life.

RESULTS

At least 2 SATs were performed in 45/52 (86%) and 45/50 (90%) infants in the glutamine-supplemented and control groups, respectively. Baseline patient and nutrition characteristics were not different between the groups. There was no effect of glutamine-enriched enteral nutrition on the decrease of the L/M ratio between the start and end of the study (p = .78). In both treatment groups, median urinary lactulose concentrations decreased (p < .001), whereas median urinary mannitol concentrations increased (p = .003).

CONCLUSIONS

Glutamine-enriched enteral nutrition does not enhance the postnatal decrease in intestinal permeability in VLBW infants. Any beneficial effect of glutamine may involve other aspects of intestinal integrity; for example, modulation of the intestinal inflammatory response.

Effects of ischemia-reperfusion on the absorption and esterase metabolism of diltiazem in rat intestine

Intestinal ischemia-reperfusion (I/R) is a serious clinical condition that triggers a complex inflammatory response. Inflammatory processes affect some enzymatic systems related to intestinal drug metabolism and bioavailability. Diltiazem (DTZ) is a calcium channel blocker, which is extensively metabolised in the intestine by esterases and different CYP450 isoforms. The main biotransformation pathway of DTZ in rats is desacetylation by esterases. This study analysed the effect of I/R on intestinal absorption and metabolism of DTZ, focusing on esterase activity, through different methodologies, after 60 min of superior mesenteric artery occlusion and 30 min of reperfusion or sham surgical procedures. The rate of DTZ appearance in blood during in situ studies increased significantly in the I/R group (0.094+/-0.014 10(-5) cm/s vs 0.271+/-0.110 10(-5) cm/s) and the calculated metabolised fraction of DTZ decreased significantly, showing an important reduction in the desacetylase activity in the I/R group. These results were supported by microsomal incubations, where desacetylase activity was related to esterases by specific inhibition, using paraoxon and bis-nitrophenylphosphate, and also by studies in everted rings. DTZ metabolism was higher in the jejunum than in the ileum, the esterase activity being affected by I/R in both regions. The present findings suggest that I/R injury clearly affects the esterases' activity and modifies the amount of DTZ and its metabolites in blood during in situ perfusion. This modification of intestinal esterase activity could be important for the pharmacokinetic behaviour of other drugs and prodrugs after intestinal pathologies involving inflammation and oxidative stress.

Glutamine: role in gut protection in critical illness

PURPOSE OF REVIEW

Recent literature has focused on the role of the gut and increased gut permeability as a driver of systemic inflammation in critical illness. Thus, the therapeutic potential for an agent to prevent gut barrier compromise and attenuate gut-derived inflammatory response is significant.

RECENT FINDINGS

In laboratory and clinical settings, glutamine can attenuate gut permeability following critical illness and injury. Further, recent literature has revealed other mechanisms by which glutamine may attenuate the systemic inflammatory response driven by the gut. These findings reveal that glutamine may act at multiple levels to attenuate gut injury and potential subsequent gut-derived systemic inflammatory response. These mechanisms focus around glutamine's ability to induce the cellular protective stress response in the gut. This leads to enhanced protection of the gut epithelial barrier and attenuation of generation of inflammatory mediators.

SUMMARY

These mechanistic findings, combined with a limited amount of clinical data showing benefit on gut permeability in illness and injury, indicate more formal studies need to be carried out looking the role of glutamine in gut protection and as an antiinflammatory in critical illness.

Conventional dose hypertonic saline provides optimal gut protection and limits remote organ injury after gut ischemia reperfusion

BACKGROUND

Hypertonic saline (HS) resuscitation prevents neutrophil mediated injury after shock. The optimal dose is not known, but appears as a result of osmotic stress. We hypothesized that a dose dependent effect exists related to increasing tonicity and that the optimal gut protective dose would provide better protection against remote organ injury than large volume isotonic crystalloids.

METHODS

In experiment 1, rats were assigned to controls (sham/no resuscitation, sham/4 mL/kg 7.5% HS, superior mesenteric artery occlusion [SMAO]/no resuscitation), SMAO/equal volume (4 mL/kg 0.9% NS, 4 mL/kg 2.5% HS, 4 mL/kg 5% HS, 4 mL/kg 7.5% HS and 4 mL/kg 10% HS) or SMAO/equal sodium (33 mL/kg 0.9% NS, 12 mL/kg 2.5% HS, 6 mL/kg 5% HS, 4 mL/kg 7.5% HS, and 3 mL/kg 10% HS). In experiment 2, rats were assigned to the same control groups, and to either SMAO/NS (33 mL/kg 0.9% NS, equal salt load) or SMAO/HS (4 mL/kg 7.5% HS). The SMAO was clamped for 60 minutes and boluses given 5 minutes before clamp removal. After 6 hours of reperfusion, ileum and lungs were harvested for analysis of histologic injury, myeloperoxidase (MPO) as an index of neutrophil mediated injury, and serum ALT and AST drawn as markers of liver injury.

RESULTS

In experiment 1, equal volume and equal sodium decreased injury and inflammation with increasing tonicity in a dose dependent fashion, with the optimal effect seen at 7.5%. In experiment 2, NS resuscitation resulted in minimal improvement of SMAO-induced lung injury and inflammation or increases in serum ALT and AST whereas HS resuscitation significantly decreased these parameters.

CONCLUSION

The protective effect of HS is related to increased tonicity. While NS had little effect on SMAO-induced remote organ injury, optimal dose HS resuscitation was quite protective. This supports the growing evidence that HS protection may be because of its gut protective effects.

The immune-enhancing enteral agents arginine and glutamine differentially modulate gut barrier function following mesenteric ischemia/reperfusion

BACKGROUND

Immune-enhancing enteral diets have been shown to improve patient outcome. One contributing mechanism may be via maintenance of gut barrier function. While recent data has shown that glutamine is beneficial, arginine may be harmful. We therefore hypothesized that the immune-enhancing agents, glutamine and arginine, differentially modulate gut barrier function.

METHODS

At laparotomy, rats had jejunal sacs filled with 10 mmol/L glutamine, arginine, fructose, or magnesium sulfate (osmotic control) followed by 60 minutes of superior mesenteric artery occlusion and 2 hours of reperfusion. Jejunum was harvested for histology, deconvolution microscopy, F:G actin, ATP, and permeability measurements.

RESULTS

Glutamine and fructose minimized mucosal injury compared with controls and arginine. Deconvolution microscopy confirmed that glutamine and fructose preserved the actin cytoskeleton but there was disruption by arginine which correlated with F:G actin ratios and tissue ATP levels. Permeability was enhanced by arginine compared with the other groups.

CONCLUSION

Arginine resulted in worsened mucosal injury, disruption of the actin cytoskeleton, decreased tissue ATP and enhanced permeability compared with glutamine which appeared protective. The immune-enhancing agent arginine results in breakdown of gut barrier function which may have important implications for critically injured patients.

Oral glutamine enhances heat shock protein expression and improves survival following hyperthermia

No pharmacologic agent has shown benefit in treating heatstroke. Previous data indicate that enhanced heat shock protein 70 (HSP-70) expression can improve survival postexperimental heatstroke. Glutamine (GLN) can enhance HSP-70 expression in other injury models. This study assessed if orally administered GLN could enhance tissue HSP expression and could improve survival following whole body hyperthermia. Intestinal permeability and plasma endotoxin were assayed to determine if enhanced HSP expression correlated with improved organ function. GLN (0.65 g/kg) or an iso-nitrogenous control (Travasol; T) was given to rats via gavage twice daily for 5 days pre-heatstroke. Hyperthermia was performed in anesthetized rats by heating animals to 42 degrees C (rectal temperature) for 30 min. HSP-70 analyzed via Western blot. Gut permeability was measured 6 and 24 h post-hyperthermia. Plasma endotoxin was measured 24 h post-hyperthermia. Survival was analyzed for 5 days post-hyperthermia. GLN administration enhanced gut and lung HSP-70 post-hyperthermia. GLN administration led to significantly enhanced gut heat shock factor 1 (HSF-1) activation before heatstroke and at 1 h postheat stress. GLN decreased gut permeability at 6 and 24 h post-hyperthermia versus T. Plasma endotoxin also decreased in GLN-treated rats 24 h post-hyperthermia. Oral GLN therapy significantly improved survival (P < 0.05). Our results indicate that oral GLN can enhance tissue HSP-70 and HSF-1 activation post-hyperthermia. These results also indicate that enhanced HSP-70 may have functional significance as GLN-treated animals had decreased gut permeability, plasma endotoxin, and improve survival following lethal hyperthermia. Enhanced expression of HSP-70 may be an important mechanism leading to enhanced survival via GLN. These data indicate that oral GLN may useful in prevention of mortality from heatstroke in at risk populations.

Differential induction of PPAR-gamma by luminal glutamine and iNOS by luminal arginine in the rodent postischemic small bowel

Using a rodent model of gut ischemia-reperfusion (I/R), we have previously shown that the induction of inducible nitric oxide synthase (iNOS) is harmful, whereas the induction of heme oxygenase 1 (HO-1) and peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is protective. In the present study, we hypothesized that the luminal nutrients arginine and glutamine differentially modulate these molecular events in the postischemic gut. Jejunal sacs were created in rats at laparotomy, filled with either 60 mM glutamine, arginine, or magnesium sulfate (osmotic control) followed by 60 min of superior mesenteric artery occlusion and 6 h of reperfusion, and compared with shams. The jejunum was harvested for histology or myeloperoxidase (MPO) activity (inflammation). Heat shock proteins and iNOS were quantitated by Western blot analysis and PPAR-gamma by DNA binding activity. In some experiments, rats were pretreated with the PPAR-gamma inhibitor G9662 or with the iNOS inhibitor N-[3(aminomethyl)benzyl]acetamidine (1400W). iNOS was significantly increased by arginine but not by glutamine following gut I/R and was associated with increased MPO activity and mucosal injury. On the other hand, PPAR-gamma was significantly increased by glutamine but decreased by arginine, whereas heat shock proteins were similarly increased in all experimental groups. The PPAR-gamma inhibitor G9662 abrogated the protective effects of glutamine, whereas the iNOS inhibitor 1400W attenuated the injurious effects of arginine. We concluded that luminal arginine and glutamine differentially modulate the molecular events that regulate injurious I/R-mediated gut inflammation and injury. The induction of PPAR-gamma by luminal glutamine is a novel protective mechanism, whereas luminal arginine appears harmful to the postischemic gut due to enhanced expression of iNOS.

Glutamine improves intestinal barrier function in experimental biliary obstruction

OBJECTIVE

To determine the effects of enteral administration of glutamine on intestinal barrier function in experimental biliary obstruction.

BACKGROUND

Extrahepatic biliary obstruction is associated with the failure of intestinal barrier function, allowing bacteria and other substances from the intestine to enter the circulation and initiate a systemic inflammatory response, causing impairment of multiple organs. The amino acid glutamine has been shown to improve intestinal barrier function in other conditions, but its effects in biliary obstruction have not been fully examined.

METHODS

This study examined the effects of enteral administration of glutamine on intestinal permeability and on bacterial translocation from the intestine in a rodent model of biliary obstruction.

RESULTS

Glutamine was shown to reduce intestinal permeability measured as percentage excretion of 14C 7 days after biliary obstruction (0.35+/-0.03 vs. 0.56+/-0.085% in controls, p=0.028), and glutamine administration was also associated with a decreased incidence of bacterial translocation to extra-intestinal sites (p=0.03). Radiolabelled bacterial studies also demonstrated reduced translocation of bacterial fragments to extra-intestinal sites in glutamine-treated animals (p=0.01). There was also some evidence of decreased exposure to endotoxin, reduced systemic inflammation and increased bacterial killing by the immune system in glutamine-treated animals.

CONCLUSIONS

Glutamine modulates intestinal permeability and reduces bacterial translocation in an animal model of experimental biliary obstruction and may increase bacterial killing by the immune system.

Escherichia coli modulates extraintestinal spread of Staphylococcus aureus

Staphylococcus aureus remains one of the most frequent causes of life-threatening systemic infection in surgical and trauma patients. It is understood that S. aureus colonization predisposes to complicating infection, but extraintestinal dissemination of S. aureus from the intestinal lumen to the draining mesenteric lymph nodes has not been systematically studied. After oral inoculation with high numbers of S. aureus, otherwise normal mice had low levels of cecal S. aureus (6.7 log10/g) and the incidence of extraintestinal dissemination was 30%. As expected, parenteral Escherichia coli lipopolysaccharide (LPS) was associated with increased numbers of cecal S. aureus, but the incidence of translocation remained unchanged. Purified LPS had no effect on S. aureus internalization by cultured HT-29 enterocytes and no effect on S. aureus transmigration through confluent enterocytes. To begin to clarify the effect of alterations in cecal bacteria on S. aureus translocation, mice were orally inoculated with E. coli and S. aureus. Compared with mice inoculated with S. aureus alone, these mice had increased numbers of cecal E. coli and S. aureus, and the incidence of S. aureus translocation nearly doubled from 46% to 88%. Experiments with HT-29 enterocytes indicated that viable E. coli had no effect on S. aureus internalization, but viable E. coli was at least 40 times more potent in inducing S. aureus transmigration across confluent enterocytes compared with a corresponding amount of purified LPS. Thus, S. aureus disseminated from the intestinal tract of normal mice by a mechanism that could involve paracellular migration across the intestinal epithelial barrier.

Intraluminal injection of short chain fatty acids diminishes intestinal mucosa injury in experimental ischemia-reperfusion

PURPOSE: Investigated the effect of intraluminal short-chain fatty acids (SCFA) on the intestinal mucosa in the presence of ischemia-reperfusion injury (IRI). METHODS: Six blind sacs of the small bowel (3at the jejunum and 3 at the ileum) were created in ten Wistar rats. The lateral sacs of both bowel regions were subjected to IRI (15/15 minutes) while the medial sacs were let free to receive blood supply. In the lateral sacs, it was injected either a solution containing SCFA (butyrate, propionate and acetate) or pure saline at the bowel lumen. No fluid was injected in the medial sacs. RESULTS: Both at the jejunum and at the ileum the score of the mucosal injury was higher in saline than in control sacs. SCFA treated sacs showed lesser score at the ileum (p=0.03) but were not significantly different at the jejunum (p=0.83) when compared with saline sacs. It was found a significant greater number of neutrophils (p < 0.01) in the sacs treated with saline than in the other two sacs in both regions. CONCLUSION: SCFA protect the distal small bowel mucosa and diminishes infiltration of neutrophils to the gut lamina propria in IRI.

Influence of intestinal barrier function on pigment gallstone formation in guinea pig model

AIM: To investigate the possible action and mechanism of the intestinal barrier function in the pathogenesis of pigment gallstone.

METHODS: Eighty guinea pigs were randomly divided into three groups: normal group (CON), pigment gallstone group (PS) and intestinal mucosa protection group (GLN). Normal forage, pigment gallstone-forming forage and pigment gallstone-forming forage with supplemental intestinal mucosa protector (glutamine) were given to the animals of corresponding groups, respectively. The gallstone-forming rate, morphological changes of intestinal mucosa, intestinal permeability, serum endotoxin and biliary β-glucuronidase were detected after 8 wk.

RESULTS: The gallstone-forming rate was 73.9% in PS. In comparison with those in CON, the intestinal mucosa damage, serum endotoxin level [(1367±525)×10^-6 EU/L vs (77±43) ×10^-6 EU/L, P < 0.01] and activity of biliary β-glucuronidase (endogenous: from 209.8±47.5 vs 122.1±39.5 Fishman Unit, P < 0.01; exogenous: from 2206.6±983.9 vs 573.5±476.9 Fishman Unit, P < 0.01) were significantly increased in PS. In GLN, the gallstone-forming rate was decreased to 44.4%, which was markedly higher than that in PS (P < 0.05). The morphological changes of intestinal mucosa, intestinal permeability and serum endotoxin [(156±97)×10^-6 EU/L vs (1367±525)×10^-6 EU/L, P < 0.05] were notably decreased in GLN as compared with those in PS, and there was no significant difference in β-glucuronidase activity.

CONCLUSION: Intestinal barrier function is correlated with pigment gallstone formation. Intestinal barrier function disorder may promote pigment gallstone formation through bacteria translocation, endotoxemia and change of biliary β-glucuronidase activity.

The role of macronutrients in gastrointestinal blood flow

PURPOSE OF REVIEW

The presence of luminal nutrients after a meal increases gastrointestinal blood flow in a phenomenon called postprandial hyperemia. In many conditions related to splanchnic hypoperfusion, enteral nutrition may play a role in counterbalancing the installed splanchnic low-flow state by producing intestinal hyperemia. However, when the gut is hypoperfused there is a chance of enteral nutrition producing a mismatch of the oxygen demand: supply ratio with subsequence gut ischemia. This article aims to review the effects of macronutrients on gastrointestinal blood flow in both health and critical conditions, especially those related to hepatosplanchnic hypoperfusion.

RECENT FINDINGS

Splanchnic blood flow is related not only to the route (intravenous or enteral) and timing of nutritional support (during the course of the insult) but also to the composition of the formula. Critically ill patients with gut hypoperfusion may tolerate enteral nutrition, but this effect may be restricted to the early post-injury phase. During ischaemia reperfusion injury, immune nutrients may promote different outcomes: glutamine may protect whereas arginine may deteriorate the mucosal barrier and enhance permeability.

SUMMARY

Understanding the relationship between macronutrients and gastrointestinal blood flow is a major challenge. Ongoing research in nutritional support in hypoperfused, catecholamine-dependent patients will open the door to optimize the recovery of patients in critical care.

Immune-enhancing enteral nutrients differentially modulate the early proinflammatory transcription factors mediating gut ischemia/reperfusion

BACKGROUND

Recent reports suggest that enteral diets enriched with arginine may be harmful by enhancing inflammation. This is consistent with our gut ischemia/reperfusion (I/R) model in which arginine induced the proinflammatory mediator inducible nitric oxide synthase and resulted in injury and inflammation whereas glutamine was protective. We now hypothesize that arginine and glutamine differentially modulate the early proinflammatory transcription factors activated by gut I/R.

METHODS

At laparotomy, jejunal sacs were filled with either 60 mmol/L glutamine, arginine, or an iso-osmotic control followed by 60 minutes of superior mesenteric artery occlusion and 6 hours of reperfusion and compared with shams. Jejunum was harvested for nuclear factor (NF)-kappaB and activator protein-1 (AP-1) measured by electrophoretic mobility shift assay and c-jun and c-fos (AP-1 family) by supershift.

RESULTS

Both NF-kappaB and AP-1 were activated by gut I/R. Arginine and glutamine had no differential effect on NF-kappaB, whereas AP-1 expression (c-jun but not c-fos) was markedly enhanced by arginine and significantly lessened by glutamine.

CONCLUSION

Arginine enhanced expression of the early proinflammatory transcription factor AP-1 but not NF-kappaB. This represents a novel mechanism by which arginine may be harmful when administered to critically ill patients.