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

Beyond Heat Stress: Intestinal Integrity Disruption and Mechanism-Based Intervention Strategies

The current climate changes have increased the prevalence and intensity of heat stress (HS) conditions. One of the initial consequences of HS is the impairment of the intestinal epithelial barrier integrity due to hyperthermia and hypoxia following blood repartition, which often results in a leaky gut followed by penetration and transfer of luminal antigens, endotoxins, and pathogenic bacteria. Under extreme conditions, HS may culminate in the onset of “heat stroke”, a potential lethal condition if remaining untreated. HS-induced alterations of the gastrointestinal epithelium, which is associated with a leaky gut, are due to cellular oxidative stress, disruption of intestinal integrity, and increased production of pro-inflammatory cytokines. This review summarizes the possible resilience mechanisms based on in vitro and in vivo data and the potential interventions with a group of nutritional supplements, which may increase the resilience to HS-induced intestinal integrity disruption and maintain intestinal homeostasis.

Combined Effectiveness of Honey and Immunonutrition on Bacterial Translocation Secondary to Obstructive Jaundice in Rats: Experimental Study

BACKGROUND Obstructive jaundice is a serious, life-threatening condition that can lead to death as a result of sepsis and multiorgan failure due to bacterial translocation. Treatment should be started as soon as possible after diagnosis. MATERIAL AND METHODS Forty 24-week-old male Sprague Dawley rats, with an average weight of 250 g to 300 g, were included in this study. The rats were randomly placed into five groups, each group consisted of eight rats. The sham group underwent only common bile duct (CBD) dissection and no ligation was performed. CBD ligation was applied to the other groups. After the operation, one CBD group was fed with rat chow only, the others were fed with rat chow supplemented with honey, or immunonutrients, or honey plus immunonutrients. After 10 to 12 days, all rats were sacrificed; blood and tissue samples were collected for biochemical, microbiological, and histopathological evaluation. RESULTS In the groups that were fed with honey and immunonutrients, alanine aminotransferase (ALT) levels were decreased significantly compared to the other groups. Statistically significant differences were detected in terms of bacterial translocation (BT) rates among liver and spleen samples, and laboratory values of serum, except for MLNs of the BDL+HI group, when compared to other groups. We found mean mucosal thickness of ileum samples have been improved notably in the BDL+HI group compared to the other groups, especially compared to the C/BDL group. CONCLUSIONS Immunonutrition applied with honey had immunostimulant effects, decreased BT due to an additive effect, and had positive effects on intestinal mucosa.

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.

Oral Citrulline Mitigates Inflammation and Jejunal Damage via the Inactivation of Neuronal Nitric Oxide Synthase and Nuclear Factor-κB in Intestinal Ischemia and Reperfusion

BACKGROUND

Intestinal ischemia and reperfusion (I/R) is a life-threatening emergency accompanied by inflammation and organ damage. We compared the mechanisms and the effects of arginine, citrulline, and glutamine on inflammation and intestinal damage.

MATERIALS AND METHODS

Male Wistar rats underwent 60 minutes of superior mesenteric artery occlusion and either 3 (I/R3) or 24 (I/R24) hours of reperfusion and were orally administered vehicle, arginine, citrulline, or glutamine 15 minutes before reperfusion and at 3, 9, and 21 hours of reperfusion.

RESULTS

I/R3 rats experienced jejunal damage and apoptosis, and I/R24 rats had liver dysfunction compared with normal rats (one-way ANOVA, P < .05). Arginine and citrulline administrations improved jejunal morphology, and citrulline and glutamine administrations alleviated the loss of jejunal mass in I/R3 rats. I/R3-increased circulating nitrate/nitrite (NOx), tumor necrosis factor-α, and interleukin-6 were significantly decreased by citrulline, glutamine and citrulline, and arginine, glutamine, and citrulline, respectively. These amino acids decreased plasma NOx and interferon-γ in I/R24, decreased jejunal neuronal nitric oxide synthase (NOS) protein in I/R3 rats, and alleviated jejunal apoptosis in I/R3 and I/R24 rats. In addition, the jejunal phosphorylated to total nuclear factor-κB (NF-κB) ratio was decreased by arginine and citrulline in I/R24 rats.

CONCLUSION

Oral administration of arginine, citrulline, and glutamine may alleviate systemic inflammation, jejunal apoptosis, and neuronal NOS in intestinal I/R. Citrulline may further attenuate jejunal damage by preserving jejunal mass, partially via the inactivation of NOS and the NF-κB pathway. In conclusion, oral citrulline may have more benefits than arginine and glutamine in mitigating intestinal ischemia and reperfusion-induced adverse effects.

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.

Feeding the Postoperative Patient on Vasopressor Support: Feeding and Pressor Support

Initiating enteral nutrition in the postoperative patient can be challenging. Postoperative ileus and bowel edema, bowel anastomosis, and intra-abdominal pathology contribute to the reluctance and inability to achieve adequate nutrition in this patient population. The addition of vasopressors confounds the difficulties. Clinical data are sparse but suggest that most postoperative patients requiring vasopressor therapy can be safely initiated and advanced on enteral nutrition. Consideration of the vasopressor agent being utilized and its dose is imperative, as are individual patient characteristics. Temporal changes in the dosage should be closely monitored, as increasing doses may reflect worsening clinical status that can be due to intestinal ischemia. Well-designed prospective trials are clearly necessary to address this controversial topic.

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.

Organ-specific solutions and strategies for the intestinal preservation

Among the intraabdominal organs, the intestine is the most susceptible to storage injury and as a consequence its safe cold ischemic time in the clinic is restricted to below 10 hours. The current practice for the intestinal preservation (IP) consists of an in-situ vascular flush with iced University of Wisconsin or Histidine-Tryptophan-Ketoglutarate solution followed by cold storage at 4°C. Mucosal injury is initiated within 1 hour and rapidly progresses to mucosal breakdown; tissue injury worsens upon reperfusion and further impairs the mucosal barrier, favoring bacterial translocation and sepsis. In addition of releasing danger signals, an advanced ischemia-reperfusion injury (IRI) may increase graft immunogenicity and promote rejection. Several alternative approaches have been tested as alternatives to the static storage. The aim of this review is to summarize and discuss the various intraluminal interventions as additional strategies aiming to reduce the IP/reperfusion injury and highlight the underlying pathophysiological mechanisms.

Arginyl-glutamine dipeptide or docosahexaenoic acid attenuates hyperoxia-induced small intestinal injury in neonatal mice

BACKGROUND AND OBJECTIVE

Supplementation studies of glutamine, arginine, and docosahexaenoic acid (DHA) have established the safety of each of these nutrients in neonates; however, the potential for a more stable and soluble dipeptide, arginyl-glutamine (Arg-Gln) or DHA with anti-inflammatory properties, to exert benefits on hyperoxia-induced intestinal injury has not been investigated. Arg-Gln dipeptide has been shown to prevent retinal damage in a rodent model of oxygen-induced injury. The objective of the present study was to investigate whether Arg-Gln dipeptide or DHA could also attenuate markers of injury and inflammation to the small intestine in this same model.

METHODS

Seven-day-old mouse pups were placed with their dams in 75% oxygen for 5 days. After 5 days of hyperoxic exposure (P7-P12), pups were removed from hyperoxia and allowed to recover in atmospheric conditions for 5 days (P12-P17). Mouse pups received Arg-Gln (5g·kg·day) or DHA (5g·kg·day) or vehicle orally started on P12 through P17. Distal small intestine (DSI) histologic changes, myeloperoxidase (MPO), lactate dehydrogenase (LDH), inflammatory cytokines, and tissue apoptosis were evaluated.

RESULTS

Hyperoxic mice showed a greater distortion of overall villus structure and with higher injury score (P<0.05). Arg-Gln dipeptide and DHA supplementation groups were more similar to the room air control group. Supplementation of Arg-Gln or DHA reduced hyperoxia-induced MPO activity (P<0.05). Supplementation of Arg-Gln or DHA returned LDH activity to the levels of control. Hyperoxia induced apoptotic cell death in DSIs, and both Arg-Gln and DHA reversed this effect (P<0.05).

CONCLUSIONS

Supplementation with either Arg-Gln or DHA may limit some inflammatory and apoptotic processes involved in hyperoxic-induced intestinal injury in neonatal mice.

Treatment with ITF attenuates PAF-induced disruption of the F-actin cytoskeleton in an in vitro model of intestinal epithelium

AIM: To explore whether treatment with platelet-activating factor (PAF) disrupts the intestinal epithelial barrier by altering the F-actin cytoskeleton and, if so, whether treatment with intestinal trefoil factor (ITF) exerts a protective effect against PAF-induced disruption of the F-actin cytoskeleton.

METHODS: An in vitro model of intestinal epithelium was established with Caco-2 cells. PAF at different concentrations (0, 50, 100, 200 nmol/L) was incubated with postconfluent monolayers of Caco-2 cells for 24 h. Moreover, 100 nmol/L PAF was administered for different periods (0, 2, 4, 8, 12, 24, 48 h). ITF (0.3 mol/L) was administered 30 min before or after PAF treatment (100 nmol/L). Transendothelial electrical resistance (TEER) was measured to evaluate the permeability of intestinal epithelial cell monolayers. Immunofluorescent staining and flow cytometry were used to observe the morphological alterations and conduct protein quantitation of the F-actin cytoskeleton.

RESULTS: Compared with the control group, TEER decreased in cells treated with PAF (100 nmol/L) for 24 h (232.75 Ω/cm² ± 15.74 Ω/cm²vs 346.75 Ω/cm² ± 26.69 Ω/cm², P < 0.01). While compared with the model group, TEER had little enhancement in cells treated with ITF (313.75 Ω/cm² ± 18.28 Ω/cm², 299 Ω/cm² ± 13.16 Ω/cm²vs 232.75 Ω/cm² ± 15.74 Ω/cm², both P < 0.01). Treatment with PAF induced a significant decline in paracellular permeability. After treatment with PAF (100 nmol/L) for 24 h, extensive disorganization, kinking, condensation, and beading of the F-actin ring could be seen and the mean fluorescent intensity of F-actin had a significant decline (218.56 ± 23.18 vs 425.35 ± 40.31, P < 0.01). Treatment with ITF could reverse the high permeability of intestinal epithelial cell monolayers partly by recovering the normal structure of F-actin and increasing the content of F-actin (391.76 ± 58.57, 360.86 ± 8.68 vs 218.56 ± 23.18, both P < 0.01).

CONCLUSION: PAF plays an important role in the regulation of intestinal mucosal permeability and induces the structural alterations of the F-actin cytoskeleton. Treatment with ITF can protect intestinal epithelium by restricting the rearrangement of the F-actin cytoskeleton.

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.

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.

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.

Barrier effects of nutritional factors

High dietary intake of fruits and vegetables is associated with a reduced disease risk. Therefore, clinical interest is growing in therapies based on dietary supplements and effects of food components. Immune-modulatory and barrier-protective effects have been described for the amino acid glutamine and the trace element zinc. In Caco-2-cells, zinc is necessary to maintain the expression of proteins like ZO-1 and occludin, and experimental evidence exists that glutamine has enterocyte-protective effects and modulates intestinal barrier function in stressed animals and humans. Polyunsaturated fatty acids (PUFA) improve paracellular permeability after IL-4 incubation. Enhancement of barrier properties by long-chain PUFA is discussed controversially, but a beneficial role preventing the redistribution of occludin and ZO-1 and reduction of epithelial resistance by IFN-gamma and TNF-alpha exists. In addition, a group of secondary plant compounds, the polyphenols, are supposed to be important in this respect. The flavonoid quercetin and its metabolite DHBA increased epithelial resistance of Caco-2-cells to 157 +/- 4% of control values, and DHBA up to 119 +/- 4% of control values, respectively. This is due to a 2.3 +/- 0.1-fold expression rate of the tight junction protein claudin-4.

Glutamine, arginine, and leucine signaling in the intestine

Glutamine and leucine are abundant constituents of plant and animal proteins, whereas the content of arginine in foods and physiological fluids varies greatly. Besides their role in protein synthesis, these three amino acids individually activate signaling pathway to promote protein synthesis and possibly inhibit autophagy-mediated protein degradation in intestinal epithelial cells. In addition, glutamine and arginine stimulate the mitogen-activated protein kinase and mammalian target of rapamycin (mTOR)/p70 (s6) kinase pathways, respectively, to enhance mucosal cell migration and restitution. Moreover, through the nitric oxide-dependent cGMP signaling cascade, arginine regulates multiple physiological events in the intestine that are beneficial for cell homeostasis and survival. Available evidence from both in vitro and in vivo animal studies shows that glutamine and arginine promote cell proliferation and exert differential cytoprotective effects in response to nutrient deprivation, oxidative injury, stress, and immunological challenge. Additionally, when nitric oxide is available, leucine increases the migration of intestinal cells. Therefore, through cellular signaling mechanisms, arginine, glutamine, and leucine play crucial roles in intestinal growth, integrity, and function.

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.

Early enteral supplementation with key pharmaconutrients improves Sequential Organ Failure Assessment score in critically ill patients with sepsis: outcome of a randomized, controlled, double-blind trial

OBJECTIVE

To assess the safety and efficacy of an early enteral pharmaconutrition supplement containing glutamine dipeptides, antioxidative vitamins and trace elements, and butyrate in critically ill, septic patients.

DESIGN

A prospective, randomized, controlled, double-blind clinical trial.

SETTING

Adult intensive care unit in a university hospital.

PATIENTS

Fifty-five critically ill, septic patients requiring enteral feeding.

INTERVENTIONS

Patients received either an enteral supplement (500 mL of Intestamin, Fresenius Kabi) containing conditionally essential nutrients or a control solution via the nasogastric route for up to 10 days. Inclusion occurred within 24 hrs of intensive care unit admission. Additionally, patients received enteral feeding with an immunonutrition formula (experimental group) or standard formula (control group) initiated within 48 hrs after enrollment.

MEASUREMENTS AND MAIN RESULTS

Organ dysfunction was assessed by daily total Sequential Organ Failure Assessment (SOFA) score over the 10-day study period in both patient groups. Patients receiving the experimental supplement showed a significantly faster decline in the regression slopes of delta daily total SOFA score over time compared with control. The difference between the regression coefficients of the two slopes was significant irrespective of the level of analysis: intent to treat -0.32 vs. -0.14, p < .0001; per protocol -0.34 vs. -0.14, p < .0001; and completers (patients receiving > or = 80% of the calculated caloric target over a period of 6 days), -0.26 vs. -0.16, p = .0005. Vitamin C, as a marker of supplement absorption, increased from 10.6 (1.9-159.4) micromol/L (normal range 20-50 micromol/L) on day 1 to 58.7 (5.4-189.9) micromol/L by day 3 (p = .002) in the intervention group but remained below the normal range in the control group 17.0 (2.8-78.5) on day 1 and 14.3 (2.4-179.6) on day 3. Serum levels of glycine, serine, arginine, ornithine, vitamin E, and beta-carotene all increased significantly with treatment in the supplementation group.

CONCLUSIONS

In medical patients with sepsis, early enteral pharmaconutrition with glutamine dipeptides, vitamin C and E, beta-carotene, selenium, zinc, and butyrate in combination with an immunonutrition formula results in significantly faster recovery of organ function compared with control.

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.

Hypertonic saline resuscitation after mesenteric ischemia/reperfusion induces ileal apoptosis

BACKGROUND

We have previously demonstrated that hypertonic saline (HS) resuscitation decreased inflammation and mucosal injury after mesenteric ischemia/reperfusion (I/R). In contrast to I/R cell necrosis, apoptosis provides controlled cell death that minimizes inflammation. We therefore hypothesized that HS resuscitation after mesenteric I/R would induce apoptosis and decrease mucosal injury.

METHODS

Rats underwent 60 minutes of superior mesenteric artery occlusion (SMAO) and then received no resuscitation or resuscitation with 4 mL/kg of HS, 4 mL/kg of lactated Ringer's (LR) solution (equal volume), or 32 mL/kg of LR solution (equal salt load). Rats were killed at 6 hours of reperfusion, and ileum was harvested for analysis. DNA fragmentation (apoptosis) was assessed by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) and mucosal injury by histology (Chiu score 0-5). Caspase-3 (proapoptotic mediator) and Bcl-xL (antiapoptotic mediator) protein expression were analyzed by Western immunoblot.

RESULTS

SMAO with no resuscitation, SMAO with 4 mL/kg of LR, and SMAO with 32 mL/kg of LR increased apoptosis (quantitated by TUNEL) and I/R-induced mucosal injury (quantitated by Chiu score). This was associated with an increase to similar levels in both proapoptotic caspase-3 and antiapoptotic Bcl-xL protein expression. Moreover, SMAO with 4 mL/kg of HS further increased apoptosis but decreased mucosal injury. This was associated with a differential expression of proapoptotic caspase-3 over antiapoptotic Bcl-xL.

CONCLUSION

HS resuscitation after mesenteric I/R significantly increased ileal mucosal apoptosis while decreasing mucosal injury and may represent a novel mechanism by which HS resuscitation after mesenteric I/R reduces inflammation and imparts protection to the gut.

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.