Gut-lymph hypothesis of systemic inflammatory response syndrome/multiple-organ dysfunction syndrome: validating studies in a porcine model

The role of gut barrier dysfunction in postoperative complications in liver transplantation: pathophysiological and therapeutic considerations

PURPOSE

Gut barrier dysfunction is a pivotal pathophysiological alteration in cirrhosis and end-stage liver disease, which is further aggravated during and after the operational procedures for liver transplantation (LT). In this review, we analyze the multifactorial disruption of all major levels of defense of the gut barrier (biological, mechanical, and immunological) and correlate with clinical implications.

METHODS

A narrative review of the literature was performed using PubMed, PubMed Central and Google from inception until November 29th, 2023.

RESULTS

Systemic translocation of indigenous bacteria through this dysfunctional barrier contributes to the early post-LT infectious complications, while endotoxin translocation, through activation of the systemic inflammatory response, is implicated in non-infectious complications including renal dysfunction and graft rejection. Bacterial infections are the main cause of early in-hospital mortality of LT patients and unraveling the pathophysiology of gut barrier failure is of outmost importance.

CONCLUSION

A pathophysiology-based approach to prophylactic or therapeutic interventions may lead to enhancement of gut barrier function eliminating its detrimental consequences and leading to better outcomes for LT patients.

Comparison of gastric reactance with commonly used perfusion markers in a swine hypovolemic shock model

Background

The gut has been hypothesized to be a protagonist tissue in multiple organ dysfunction syndrome (MODS) for the past three decades. Gastric reactance (XL) is a potential perfusion marker derived from gastric impedance spectroscopy (GIS), which is an emerging tool through which living tissue can be continuously measured to determine its pathophysiological evolution. This study aimed to compare the performance of XL [positive predictive values (PPV), negative predictive values (NPV), and area under the curve (AUC)] against commonly used perfusion markers before and during hypovolemic shock in swine subjects.

Methods

Prospective, controlled animal trial with two groups, control group (CG) N = 5 and shock (MAP ≤ 48 mmHg) group (SG) N = 16. Comparison time points were defined as T-2 (2 h before shock), T-1 (1 h before shock), T0 (shock), T1 (1 h after shock), and T2 (2 h after shock). Shock severity was assessed through blood gases, systemic and hemodynamic variables, and via histological examination for assessing inflammation-edema and detachment in the gastric mucosa. Macroscopic assessment of the gastric mucosa was defined in five levels (0—normal mucosa, 1—stippling or epithelial hemorrhage, 2—pale mucosa, 3—violet mucosa, and 4—marmoreal mucosa). Receiver Operating Characteristic (ROC) curves of perfusion markers and XL were calculated to identify optimal cutoff values and their individual ability to predict hypovolemic shock.

Results

Comparison among the CG and the SG showed statistically significant differences in XL measurements at T-1, T0, T1, and T2, while lactate showed statistically significant differences until T1 and T2. Statistically significant differences were detected in mucosa class (p < 0.001) and in inflammation-edema in the gastric body and the fundus (p = 0.021 and p = 0.043). The performance of the minimum XL value per subject  per event (XL_Min) was better (0.81 ≤ AUC ≤ 0.96, 0.93 ≤ PPV ≤ 1.00, 0.45 ≤ NPV ≤ 0.83) than maximum lactate value (Lac_Max) per subject per event (0.29 ≤ AUC ≤ 0.82, 0.82 ≤ PPV ≤ 0.91, 0.24 ≤ NPV ≤ 0.82). Cutoff values for XL_Min show progressive increases at each time point, while cutoff values for Lac_Max increase only at T2.

Conclusions

XL proved to be an indirect and consistent marker of inadequate gastric mucosal perfusion, which shows significant and detectable changes before commonly used markers of global perfusion under the hypovolemic shock conditions outlined in this work.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40635-022-00476-1.

Enteral feeding and the microbiome in critically ill children: a narrative review

OBJECTIVE

This narrative review summarizes our current knowledge on the interplay between enteral nutrition (EN) and gut microbiota in critically ill children, using examples from two commonly encountered diagnoses in the pediatric intensive care unit (PICU): severe sepsis and acute respiratory distress syndrome (ARDS). This review will also highlight potential areas of therapeutic interventions that should be explored in future studies.

BACKGROUND

Critically ill children display extreme dysbiosis in their gut microbiome. Factors within the PICU that are often associated with dysbiosis include the use of broad-spectrum antibiotics, proton-pump inhibitors (PPIs), intravenous morphine, and fasting. Dysbiosis can potentially lead to adverse clinical outcomes (e.g., nosocomial infection, and prolonged hospitalization). EN may modulate dysbiosis. The gut microbiota is involved in the breaking down of macronutrients, mainly carbohydrates and proteins. Fermentation of undigestible carbohydrate (e.g., inulin and oligosaccharides), and amino acids by large intestine microbiota produces short chain fatty acids (SCFAs). SCFAs serve as the main fuel source for enterocytes and help to maintain healthy gut lining. Changes to selected components of macronutrients can result in alterations in gut microbiome and have potentially beneficial effects in patients in the PICU.

METHODS

A comprehensive search of the MEDLINE, Cochrane Library and Google Scholar databases was conducted using appropriate MESH terms and keywords. In this narrative review, we provide a summary of current knowledge on effect of EN on gut microbiota in pediatric studies, but also describes animal- and lab-based, as well as adult studies where relevant.

CONCLUSIONS

The gut microbiome can be altered by dietary modifications and common PICU practices and treatment. Although there are strong associations in restoring eubiosis and improvement in clinical outcomes, proving causality remains challenging. Further microbiome research is needed to provide mechanistic insights into the impact of the ever changing gut microbiome. In the future, new microbiota targeted therapies could potentially be the treatment of challenging PICU conditions and restore homeostasis in these children.

Necrotizing enterocolitis and the gut-lung axis

The recently recognized connection between the gut microbiota and pulmonary disease has been termed the gut-lung axis. However, broader connections link the gut and the lungs and these organ systems are tightly interrelated in both homeostasis and disease. This concept is often ignored in the compartmentalized treatment of pulmonary or gastrointestinal disease. In newborns, the most severe gastrointestinal complication of prematurity, necrotizing enterocolitis, and the most severe pulmonary complication, bronchopulmonary dysplasia, both produce significant systemic morbidity. In this review, we highlight the often neglected pathophysiology of the gut-lung axis contributes to increased risk of bronchopulmonary dysplasia in premature infants with necrotizing enterocolitis.

Coronavirus disease-19 and the gut-lung axis

Gastrointestinal and respiratory tract diseases often occur together. There are many overlapping pathologies, leading to the concept of the ‘gut–lung axis’ in which stimulation on one side triggers a response on the other side. This axis appears to be implicated in infections involving severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), which has triggered the global coronavirus disease 2019 (COVID-19) pandemic, in which respiratory symptoms of fever, cough and dyspnoea often occur together with gastrointestinal symptoms such as nausea, vomiting, abdominal pain and diarrhoea. Besides the gut–lung axis, it should be noted that the gut participates in numerous axes which may affect lung function, and consequently the severity of COVID-19, through several pathways. This article focuses on the latest evidence and the mechanisms that drive the operation of the gut–lung axis, and discusses the interaction between the gut–lung axis and its possible involvement in COVID-19 from the perspective of microbiota, microbiota metabolites, microbial dysbiosis, common mucosal immunity and angiotensin-converting enzyme II, raising hypotheses and providing methods to guide future research on this new disease and its treatments.

Protective effect of Shenfu on gut epithelium in a porcine model of hemorrhagic shock

This study aimed to explore the protective effect of Shenfu on the hemodynamics and gut integrity in a porcine model of hemorrhagic shock. Hemorrhagic shock was induced in 32 domestic pigs with a rapid bleeding via the arterial sheath to a mean arterial pressure of 40 mm Hg within 10 min. Animals with hemorrhagic shock were then randomly assigned into the negative control group (n=8), receiving neither blood transfusion nor drug treatment; the blood transfusion group, in which animals were given blood transfusion alone; the saline group, in which animals were blood transfused and resuscitated with saline (3 mL/kg); and the Shenfu group, in which animals received blood transfusion and resuscitation with Shenfu (3 mL/kg). Blood tumor necrosis factor-alpha (TNF-ɑ) and interleukin-6 were measured using ELISAs. Tissue levels of superoxide dismutase (SOD), malondialdehyde (MDA), Na⁺/K⁺-ATPase, Ca++ATPase, myeloperoxidase (MPO), and fatty acid binding protein 2 (FABP2) were determined using respective quantitation kits. Fluid resuscitation with Shenfu significantly improved HR, CI, and MAP of pig with hemorrhagic shock, which was accompanied with mitigation of tissue damages in intestinal epithelium. Blood TNF-ɑ was reduced in the Shenfu group. Bcl-2 and cleaved caspase-3 expression in intestinal tissues were elevated and decreased, respectively, in pigs treated with Shenfu. Notably, treatment with Shenfu suppressed oxidative stress markers MDA, MPO, and FABP2 in the intestine. Oppositely, SOD, Na⁺/K⁺-ATPase and Ca++ATPase levels in intestinal tissues were promoted by Shenfu treatment. Shenfu demonstrates significant protective effect on the hemodynamics and gut epithelium of pigs with hemorrhagic shock.

Preclinical models for studying immune responses to traumatic injury

Traumatic injury initiates a large and complex immune response in the minutes after the initial insult, comprising of simultaneous pro- and anti-inflammatory responses. In patients that survive the initial injury, these immune responses are believed to contribute towards complications such as the development of sepsis and multiple organ dysfunction syndrome. These post-traumatic complications affect a significant proportion of patients and are a major contributing factor for poor outcomes and an increased burden on healthcare systems. Therefore, understanding the immune responses to trauma is crucial for improving patient outcomes through the development of novel therapeutics and refining resuscitation strategies. In order to do this, preclinical animal models must mimic human immune responses as much as possible, and as such, we need to understand the constraints of each species in the context of trauma. A number of species have been used in this field; however, these models are limited by their genetic background and their capacity for recapitulating human immune function. This review provides a brief overview of the immune response in critically injured human patients and discusses the most commonly used species for modelling trauma, focusing on how their immune response to serious injury and haemorrhage compares to that of humans.

Upregulation of proBDNF in the Mesenteric Lymph Nodes in Septic Mice

The immune status in the lymphatic system, especially mesenteric lymph nodes (MLNs), is critical to regulate the septic shock. Brain-derived neurotrophic factor (BDNF) in the enteric system has been reported to regulate enteric immunity. However, the role of its precursor, proBDNF, in the immune status of MLNs under sepsis condition is still unclear. This study aimed to characterize the expression pattern of proBDNF in MLNs after lipopolysaccharide (LPS) stimulation, and to investigate the association of pathogenesis of sepsis. LPS (20 mg/kg) was intraperitoneally injected to induce sepsis in mice. Survival curve analysis, routine blood tests, and liver and kidney function tests were performed to evaluate the severity of sepsis. QPCR and histological staining were performed to assess the mRNA levels of proinflammatory cytokines and degree of immune-inflammatory response in the MLNs. Furthermore, Western blotting, flow cytometry, and immunofluorescence were performed to examine the key molecules expression of proBDNF signaling. Intraperitoneal LPS injection significantly decreased the number of lymphocytes in blood but increased the number of T lymphocytes in MLNs. Serum alanine transaminase, aspartate transaminase, and blood urea nitrogen levels were increased in LPS-challenged mice compared to control mice. LPS administration upregulated proinflammatory cytokine gene expression and induced histological changes in the MLNs. LPS injection increased BDNF, proBDNF, and its receptor pan neutrophin receptor 75 (p75^NTR) expression in MLNs. The increased proBDNF was mainly localized on CD3⁺ and CD4⁺ T cells in the medulla of MLNs. LPS-induced sepsis upregulated proBDNF expression in medulla T cells of MLNs. ProBDNF upregulation may be involved in the pathogenesis of septic shock.

Blockade of Stellate Ganglion Remediates Hemorrhagic Shock-Induced Intestinal Barrier Dysfunction

BACKGROUND

Acute hemorrhage-induced excessive excitation of sympathetic-adrenal-medullary system (SAS) leads to gut hypoperfusion and barrier dysfunction, which is a critical event during hemorrhagic shock-induced multiple organ injury. Stellate ganglion blockade (SGB) has been widely used for suppression of sympathetic-adrenal-medullary system in the clinical practice. However, whether SGB improves intestinal barrier function after hemorrhagic shock remains unclear. Here, we hypothesized that the implementation of SGB restores intestinal barrier function and reduces gut injury.

MATERIALS AND METHODS

Male rats received the SGB pretreatment and underwent hemorrhagic shock followed by resuscitation. The 96-h survival rate, intestinal permeability and morphology, D-lactic acid concentration and diamine oxidase activity in plasma, and expressions of F-actin, Claudin-1, and E-cadherin in intestinal tissues were observed.

RESULTS

Pretreatment with SGB significantly enhances the 96-h survival rate in rats subjected to hemorrhagic shock (from 8.3% to 66.7%). Hemorrhagic shock reduced the coverage scale of intestinal mucus and intestinal villus width and height, enhanced the intestinal permeability to fluorescein isothiocyanate-dextran 4 and D-lactic acid concentration in plasma, and decreased the expressions of F-actin, Claudin-1, and E-Cadherin in intestinal tissue. These hemorrhagic shock-induced adverse effects were abolished by SGB treatment.

CONCLUSIONS

SGB treatment has a beneficial effect during hemorrhagic shock, which is associated with the improvement of intestine barrier function. SGB may be considered as a new therapeutic strategy for treatment of hemorrhagic shock.

Preconditioning but not postconditioning treatment with resveratrol substantially ameliorates post‑resuscitation myocardial dysfunction through the PI3K/Akt signaling pathway

Post-resuscitation myocardial dysfunction (PRMD) is a severe complication that arises in patients after cardiac arrest (CA). However, there are no safe or effective treatment strategies that are currently available to treat these patients. In the present study, it was investigated whether resveratrol administration could inhibit myocardial nitrative stress to alleviate PRMD. CA was induced in Sprague-Dawley rats by trans-oesophageal alternating electrical stimulation, followed by cardiopulmonary resuscitation. Rats were then randomly divided into a preconditioning or a postconditioning group. Left ventricular function (+dP/dt_max and -dP/dt_min) was recorded for 4 h after the return of spontaneous circulation (ROSC), after which the animals were euthanized. Myocardial nitrative stress was analysed using enzyme-linked immunosorbent assay, western blotting and immunohistochemistry. Wortmannin (a PI3K inhibitor) was used to investigate the involvement of the PI3k/Akt signalling pathway in the cardio-protective activity of resveratrol. After ROSC, resveratrol improved PRMD compared to the vehicle control; however, resveratrol administration significantly improved PRMD in the preconditioning group compared to the postconditioning group. Likewise, resveratrol preconditioning significantly decreased the expression of iNOS and nitrotyrosine in rat hearts but did not significantly ameliorate myocardial nitrative stress. Wortmannin partially inhibited the protective effect of resveratrol preconditioning and resulted in the deterioration of cardiac function and increase in iNOS and nitrotyrosine levels. Resveratrol preconditioning could alleviate PRMD by inhibiting myocardial nitrative stress. The PI3K/Akt signalling pathway may be partially involved in the process.

Gut-origin sepsis in the critically ill patient: pathophysiology and treatment

INTRODUCTION

Gut permeability is increased in critically ill patients, and associated with the development of the systemic inflammatory response syndrome and multiple organ dysfunction syndrome (MODS). The pathogenetic link(s) and potential therapies are an area of intense research over the last decades.

METHODS

We thoroughly reviewed the literature on gut-origin sepsis and MODS in critically ill patients, with emphasis on the implicated pathophysiological mechanisms and therapeutic interventions.

FINDINGS

Intestinal barrier failure leading to systemic bacterial translocation associated with MODS was the predominant pathophysiological theory for several years. However, clinical studies with critically ill patients failed to provide the evidence of systemic spread of gut-derived bacteria and/or their products as a cause of MODS. Newer experimental data highlight the role of the mesenteric lymph as a carrier of gut-derived danger-associated molecular patterns (DAMPs) to the lung and the systemic circulation. These substances are recognized by pattern recognition receptor-bearing cells in diverse tissues and promote proinflammatory pathways and the development MODS. Therefore, the gut becomes a pivotal proinflammatory organ, driving the systemic inflammatory response through DAMPs release in mesenteric lymph, without the need for systemic bacterial translocation.

CONCLUSIONS

There is an emerging need for application of sensitive non-invasive and easily measured biomarkers of early intestinal injury (e.g., citrulline, intestinal fatty acid protein, and zonulin) in our everyday clinical practice, guiding the early pharmacological intervention in critically ill patients to restore or prevent intestinal injury and improve their outcomes.

Induction of gut proteasome activity in hemorrhagic shock and its recovery by treatment with diphenyldihaloketones CLEFMA and EF24

Multiorgan failure in hemorrhagic shock is triggered by gut barrier dysfunction and consequent systemic infiltration of proinflammatory factors. Our previous study has shown that diphenyldihaloketone drugs 4-[3,5-bis[(2-chlorophenyl)methylene]-4-oxo-1-piperidinyl]-4-oxo-2-butenoic acid (CLEFMA) and 3,5-bis[(2-fluorophenyl)methylene]-4-piperidinone (EF24) restore gut barrier dysfunction and reduce systemic inflammatory response in hemorrhagic shock. We investigated the effect of hemorrhagic shock on proteasome activity of intestinal epithelium and how CLEFMA and EF24 treatments modulate proteasome function in hemorrhagic shock. CLEFMA or EF24 (0.4 mg/kg) were given 1 h after withdrawing 50% of blood from Sprague-Dawley rats; no other resuscitation was provided. After another 5 h of compensation, small gut was collected to process tissue for proteasome activity, immunoblotting, and mRNA levels of genes responsible for unfolded-protein response (XBP1, ATF4, glucose-regulated protein of 78/95 kDa, and growth arrest and DNA damage inducible genes 153/34), polyubiquitin B and C, and immunoproteasome subunits β type-8 and -10 and proteasome activator subunit 1. We found that hemorrhagic shock induced proteasome activity in gut tissue and reduced the amounts of ubiquitinated proteins displayed on antiubiquitin immunoblots. However, simultaneous induction of unfolded-protein response or immunoproteasome genes was not observed. CLEFMA and EF24 treatments abolished the hemorrhagic shock-induced increase in proteasome activity. Further investigations revealed that the induction of proteasome in hemorrhagic shock is associated with disassembly of 26S proteasome; CLEFMA and EF24 prevented this disassembly. Consistent with these data, CLEFMA and EF24 reduced hemorrhagic shock-induced degradation of 20S substrate ornithine decarboxylase in gut tissue. These results suggest that activated proteasome plays an important role in ischemic gut pathophysiology, and it can be a druggable target in shock-induced gut dysfunction. NEW & NOTEWORTHY Ischemic injury to the gut is a trigger for the systemic inflammatory response and multiple organ failure in trauma and hemorrhagic shock. We show for the first time that hemorrhagic shock induces the gut proteasome activity by engendering 26S proteasome disassembly. Diphenyldihaloketones 4-[3,5-bis[(2-chlorophenyl)methylene]-4-oxo-1-piperidinyl]-4-oxo-2-butenoic acid and 3,5-bis[(2-fluorophenyl)methylene]-4-piperidinone treatment prevented the 26S disassembly. Understanding the role of proteasome in shock-associated gut injury will assist in the development of therapeutic means to address it.

C1 Inhibitor Limits Organ Injury and Prolongs Survival in Swine Subjected to Battlefield Simulated Injury

Complement system activation is recognized as a deleterious component of the mammalian physiological response to traumatic injury with severe hemorrhage (TH). Female Yorkshire swine were subjected to a simulated austere prehospital battlefield scenario. Each animal underwent controlled hemorrhage of 22 mL/kg at 100 mL/min rate for approximately 10 min followed by soft tissue injury, femur fracture, and spleen injury. Subsequent blood loss was uncontrolled. Twenty-eight minutes postinjury the animals were randomized into treatment or no treatment with recombinant human C1 esterase inhibitor (C1INH) (500 IU/kg, n = 11) and into receiving or not permissive hypotensive resuscitation (n = 14) with infusion of 45 mL/kg lactated Ringer's solution (2× blood lost). Observation and animal maintenance continued for 6 h at which time the animals had either expired or were euthanized. Heart, lung, and small intestine tissue samples were collected. Pharmacokinetic, hemodynamic, and metabolic parameters as well as survival time, plasma complement activity and tissue deposition, cytokine levels, and tissue injury were determined. We found that administration of C1INH protected tissues from damage, reduced the levels of inflammatory cytokines, and improved blood chemistry. Immunohistochemical analyses revealed that C1INH administration following TH markedly reduced complement activation and deposition in tissues. Importantly, C1INH administration prolonged survival of animals particularly in those which received resuscitation fluid infusion. Our data urge early administration of C1INH to limit organ damage and prolong survival of those injured in the battlefield.

The role of NIGMS P50 sponsored team science in our understanding of multiple organ failure

The history of the National Institute of General Medical Sciences (NIGMS) Research Centers in Peri-operative Sciences (RCIPS) is the history of clinical, translational, and basic science research into the etiology and treatment of posttraumatic multiple organ failure (MOF). Born out of the activism of trauma and burn surgeons after the Viet Nam War, the P50 trauma research centers have been a nidus of research advances in the field and the training of future academic physician-scientists in the fields of trauma, burns, sepsis, and critical illness. For over 40 years, research conducted under the aegis of this funding program has led to numerous contributions at both the bedside and at the bench. In fact, it has been this requirement for team science with a clinician-scientist working closely with basic scientists from multiple disciplines that has led the RCIPS to its unrivaled success in the field. This review will briefly highlight some of the major accomplishments of the RCIPS program since its inception, how they have both led and evolved as the field moved steadily forward, and how they are responsible for much of our current understanding of the etiology and pathology of MOF. This review is not intended to be all encompassing nor a historical reference. Rather, it serves as recognition to the foresight and support of many past and present individuals at the NIGMS and at academic institutions who have understood the cost of critical illness and MOF to the individual and to society.

Diagnosis biomarkers in acute intestinal ischemic injury: so close, yet so far

Acute intestinal ischemic injury (i3) is a life-threatening condition with disastrous prognosis, which is currently difficult to diagnose at the early stages of the disease; a rapid diagnosis is mandatory to avoid irreversible ischemia, extensive bowel resection, sepsis and death. The overlapping protein expression of liver and gut related to the complex physiopathology of the disease, the heterogeneity of the disease and its relative rarity could explain the lack of a useful early biochemical marker of i3. Apart from non-specific biological markers of thrombosis, hypoxia inflammation, and infection, several more specific biomarkers in relation with the gut barrier dysfunction, the villi injury and the enterocyte mass have been used in the diagnosis of acute i3. It includes particularly D-lactate, intestinal fatty acid-binding protein (FABP) and citrulline. Herein, we will discuss leading publications concerning these historical markers that point out the main limitations reagrding their use in routine clinical practice. We will also introduce the first and limited results arising from omic studies, underlying the remaining effort that needs to be done in the field of acute i3 biological diagnosis, which remains a challenge.

Enteric glia cells are critical to limiting the intestinal inflammatory response after injury

Vagal nerve stimulation (VNS) has been shown to limit intestinal inflammation following injury; however, a direct connection between vagal terminals and resident intestinal immune cells has yet to be identified. We have previously shown that enteric glia cell (EGC) expression is increased after injury through a vagal-mediated pathway to help restore gut barrier function. We hypothesize that EGCs modulate immune cell recruitment following injury and relay vagal anti-inflammatory signals to resident immune cells in the gut. EGCs were selectively ablated from an isolated segment of distal bowel with topical application of benzalkonium chloride (BAC) in male mice. Three days following BAC application, mice were subjected to an ischemia-reperfusion injury (I/R) by superior mesenteric artery occlusion for 30 min. VNS was performed in a separate cohort of animals. EGC⁺ and EGC^- segments were compared utilizing histology, flow cytometry, immunohistochemistry, and intestinal permeability. VNS significantly reduced immune cell recruitment after I/R injury in EGC⁺ segments with cell percentages similar to sham. VNS failed to limit immune cell recruitment in EGC^- segments. Histologic evidence of gut injury was diminished with VNS application in EGC⁺ segments, whereas EGC^- segments showed features of more severe injury. Intestinal permeability increased following I/R injury in both EGC⁺ and EGC^- segments. Permeability was significantly lower after VNS application compared with injury alone in EGC⁺ segments only (95.1 ± 30.0 vs. 217.6 ± 21.7 μg/ml, P < 0.05). Therefore, EGC ablation uncouples the protective effects of VNS, suggesting that vagal-mediated signals are translated to effector cells through EGCs.NEW & NOTEWORTHY Intestinal inflammation is initiated by local immune cell activation and epithelial barrier breakdown, resulting in the production of proinflammatory mediators with subsequent leukocyte recruitment. Vagal nerve stimulation (VNS) has been shown to limit intestinal inflammation following injury; however, direct connection between vagal terminals and resident intestinal immune cells has yet to be identified. Here, we demonstrate that intact enteric glia cells are required to transmit the gut anti-inflammatory effects of VNS.

Pathophysiology of the Gut and the Microbiome in the Host Response

OBJECTIVE

To describe and summarize the data supporting the gut as the motor driving critical illness and multiple organ dysfunction syndrome presented at the National Institute of Child Health and Human Development MODS Workshop (March 26-27, 2015).

DATA SOURCES

Summary of workshop keynote presentation.

STUDY SELECTION

Not applicable.

DATA EXTRACTION

Presented by an expert in the field, the data assessing the role of gastrointestinal dysfunction driving critical illness were described with a focus on identifying knowledge gaps and research priorities.

DATA SYNTHESIS

Summary of presentation and discussion supported and supplemented by relevant literature.

CONCLUSIONS

The understanding of gut dysfunction in critical illness has evolved greatly over time, and the gut is now often considered as the "motor" of critical illness. The association of the gut with critical illness is supported by both animal models and clinical studies. Initially, the association between gut dysfunction and critical illness focused primarily on bacterial translocation into the bloodstream. However, that work has evolved to include other gut-derived products causing distant injury via other routes (e.g., lymphatics). Additionally, alterations in the gut epithelium may be associated with critical illness and influence outcomes. Gut epithelial apoptosis, intestinal hyperpermeability, and perturbations in the intestinal mucus layer have all been associated with critical illness. Finally, there is growing evidence that the intestinal microbiome plays a crucial role in mediating pathology in critical illness. Further research is needed to better understand the role of each of these mechanisms and their contribution to multiple organ dysfunction syndrome in children.

Modulating the Biologic Activity of Mesenteric Lymph after Traumatic Shock Decreases Systemic Inflammation and End Organ Injury

Introduction

Trauma/hemorrhagic shock (T/HS) causes the release of pro-inflammatory mediators into the mesenteric lymph (ML), triggering a systemic inflammatory response and acute lung injury (ALI). Direct and pharmacologic vagal nerve stimulation prevents gut barrier failure and alters the biologic activity of ML after injury. We hypothesize that treatment with a pharmacologic vagal agonist after T/HS would attenuate the biologic activity of ML and prevent ALI.

Methods

ML was collected from male Sprague-Dawley rats after T/HS, trauma-sham shock (T/SS) or T/HS with administration of the pharmacologic vagal agonist CPSI-121. ML samples from each experimental group were injected into naïve mice to assess biologic activity. Blood samples were analyzed for changes in STAT3 phosphorylation (pSTAT3). Lung injury was characterized by histology, permeability and immune cell recruitment.

Results

T/HS lymph injected in naïve mice caused a systemic inflammatory response characterized by hypotension and increased circulating monocyte pSTAT3 activity. Injection of T/HS lymph also resulted in ALI, confirmed by histology, lung permeability and increased recruitment of pulmonary macrophages and neutrophils to lung parenchyma. CPSI-121 attenuated T/HS lymph-induced systemic inflammatory response and ALI with stable hemodynamics and similar monocyte pSTAT3 levels, lung histology, lung permeability and lung immune cell recruitment compared to animals injected with lymph from T/SS.

Conclusion

Treatment with CPSI-121 after T/HS attenuated the biologic activity of the ML and decreased ALI. Given the superior clinical feasibility of utilizing a pharmacologic approach to vagal nerve stimulation, CPSI-121 is a potential treatment strategy to limit end organ dysfunction after injury.

Effect of liposome-encapsulated hemoglobin resuscitation on proteostasis in small intestinal epithelium after hemorrhagic shock

Gut barrier dysfunction is the major trigger for multiorgan failure associated with hemorrhagic shock (HS). Although the molecular mediators responsible for this dysfunction are unclear, oxidative stress-induced disruption of proteostasis contributes to the gut pathology in HS. The objective of this study was to investigate whether resuscitation with nanoparticulate liposome-encapsulated hemoglobin (LEH) is able to restore the gut proteostatic mechanisms. Sprague-Dawley rats were recruited in four groups: control, HS, HS+LEH, and HS+saline. HS was induced by withdrawing 45% blood, and isovolemic LEH or saline was administered after 15 min of shock. The rats were euthanized at 6 h to collect plasma and ileum for measurement of the markers of oxidative stress, unfolded protein response (UPR), proteasome function, and autophagy. HS significantly increased the protein and lipid oxidation, trypsin-like proteasome activity, and plasma levels of IFNγ. These effects were prevented by LEH resuscitation. However, saline was not able to reduce protein oxidation and plasma IFNγ in hemorrhaged rats. Saline resuscitation also suppressed the markers of UPR and autophagy below the basal levels; the HS or LEH groups showed no effect on the UPR and autophagy. Histological analysis showed that LEH resuscitation significantly increased the villus height and thickness of the submucosal and muscularis layers compared with the HS and saline groups. Overall, the results showed that LEH resuscitation was effective in normalizing the indicators of proteostasis stress in ileal tissue. On the other hand, saline-resuscitated animals showed a decoupling of oxidative stress and cellular protective mechanisms.

The antioxidant effects of pomegranate extract on local and remote organs in a mesenteric ischemia and reperfusion model

OBJECTIVES

We investigated whether pomegranate extract plays a protective antioxidant role against mesenteric ischemia-reperfusion injury (IR), which can lead to a systemic response and damage distant organs, such as the lung, liver, and kidney.

METHODS

Forty female Wistar-Albino rats were separated into four groups: laparotomy, laparotomy + PG, mesenteric IR, and mesenteric IR and pomegranate (IR + PG). In the laparotomy + PG and IR + PG groups, pomegranate (225 mg/kg) was given by oral gavage at the beginning of the study. Ischemia was induced for 30 minutes, and reperfusion was subsequently allowed for 60 minutes in the IR and IR + PG groups. The malondialdehyde (MDA) and total antioxidant activity (AOA) levels were evaluated in blood samples. Additionally, all tissues were removed for the measurement of AOA and total oxidant status as well as for subsequent histopathological evaluation. The oxidative stress index was calculated.

RESULTS

Histopathological changes in all organs were significantly higher in the IR group and significantly lower in the IR + PG group vs. the other groups. Serum MDA levels were significantly lower in the IR + PG group than in the IR group. No significant difference was found in AOA levels of the groups.

DISCUSSION

These data may explain the positive protective effects of pomegranate based on the histopathologic findings in ischemic conditions in an intestinal IR injury model.

Regulation of lung immunity and host defense by the intestinal microbiota

Every year in the United States approximately 200,000 people die from pulmonary infections, such as influenza and pneumonia, or from lung disease that is exacerbated by pulmonary infection. In addition, respiratory diseases such as, asthma, affect 300 million people worldwide. Therefore, understanding the mechanistic basis for host defense against infection and regulation of immune processes involved in asthma are crucial for the development of novel therapeutic strategies. The identification, characterization, and manipulation of immune regulatory networks in the lung represents one of the biggest challenges in treatment of lung associated disease. Recent evidence suggests that the gastrointestinal (GI) microbiota plays a key role in immune adaptation and initiation in the GI tract as well as at other distal mucosal sites, such as the lung. This review explores the current research describing the role of the GI microbiota in the regulation of pulmonary immune responses. Specific focus is given to understanding how intestinal “dysbiosis” affects lung health.

Mechanisms of Acute Alcohol Intoxication-Induced Modulation of Cyclic Mobilization of [Ca²⁺] in Rat Mesenteric Lymphatic Vessels

BACKGROUND

We have demonstrated that acute alcohol intoxication (AAI) increases the magnitude of Ca(2+) transients in pumping lymphatic vessels. We tested the contribution of extracellular Ca(2+) via L-type Ca(2+) channels and intracellular Ca(2+) release from the sarcoplasmic reticulum (SR) to the AAI-induced increase in Ca(2+) transients.

METHODS AND RESULTS

AAI was produced by intragastric administration of 30% alcohol to conscious, unrestrained rats; isovolumic administration of water served as the control. Mesenteric lymphatic vessels were isolated, cannulated, and loaded with Fura-2 AM to measure changes in intracellular Ca(2+). Measurements were made at intraluminal pressures of 2, 6, and 10 cm H2O. L-type Ca(2+) channels were blocked with nifedipine; IP-3 receptors were inhibited with xestospongin C; and SR Ca(2+) release and Ca(2+) pool (Ca(2+) free APSS) were achieved using caffeine. Nifedipine reduced lymphatic Ca(2+) transient magnitude in both AAI and control groups at all pressures tested, but reduced lymphatic contraction frequency only in the control group. Xestospongin C did not significantly change any of the Ca(2+) parameters in either group; however, fractional shortening increased in the controls at low transmural pressure. RyR (ryanodine receptor) activation with caffeine resulted in a single contraction with a greater Ca(2+) transient in lymphatics from AAI than those from controls. SR Ca(2+) pool was also greater in lymphatics isolated from AAI- than from control animals.

CONCLUSIONS

These data suggest that 1) L-type Ca(2+) channels contribute to the AAI-induced increase in lymphatic Ca(2+) transient, 2) blockage of IP-3 receptors could increase calcium sensitivity, and 3) AAI increases Ca(2+) storage in the SR in lymphatic vessels.

Remediation of hemorrhagic shock-induced intestinal barrier dysfunction by treatment with diphenyldihaloketones EF24 and CLEFMA

Gut is very sensitive to hypoperfusion and hypoxia, and deranged gastrointestinal barrier is implicated in systemic failure of various organs. We recently demonstrated that diphenyldihaloketone EF24 [3,5-bis(2-fluorobenzylidene)piperidin-4-one] improves survival in a rat model of hemorrhagic shock. In this study, we tested EF24 and its other analog CLEFMA (4-[3,5-bis(2-chlorobenzylidene)-4-oxo-piperidine-1-yl]-4-oxo-2-butenoic acid) for their effect on intestinal barrier dysfunction in hypovolemic shock. Hypovolemia was induced in rats by withdrawing 50% of blood. EF24 or CLEFMA (0.4 mg/kg i.p.) treatment was provided, without volume resuscitation, after 1 hour of hemorrhage. Ileum was collected 5 hours after the treatment to investigate the expression of tight junction proteins (zonula occludens, claudin, and occludin) and epithelial injury markers [myeloperoxidase, ileal lipid-binding protein (ILBP), CD163, and plasma citrulline]. The ileal permeability for dextran-fluoroisothiocyanate and Evan's blue dye was determined. EF24 and CLEFMA reduced the hypovolemia-induced plasma citrulline levels and the ileal expression of myeloperoxidase, ILBP, and CD163. The drugs also restored the basal expression levels of zonula occludens, claudin, and occludin, which were substantially deranged by hypovolemia. In ischemic ileum, the expression of phospho(tyrosine)-zonula occludens-1 was reduced, which was reinstated by EF24 and CLEFMA. In contrast, the drug treatments maintained the hypovolemia-induced expression of phospho(threonine)-occludin, but reduced that of phospho(tyrosine)-occludin. Both EF24 and CLEFMA treatments reduced the intestinal permeability enhanced by hypovolemia. EF24 and CLEFMA attenuate hypovolemic gut pathology and protect barrier function by restoring the status of tight junction proteins. These effects were observed in unresuscitated shock, implying the benefit of EF24 and CLEFMA in prehospital care of shock.

Intestinal barrier dysfunction in HIV infection: pathophysiology, clinical implications and potential therapies

INTRODUCTION

Current pathogenetic aspects on HIV infection highlight the importance of a chronic immune activation ultimately leading to T lymphocyte homeostasis disruption and immune deregulation associated with disease manifestations and progression. It is widely accepted that this continuous immune activation in HIV infection is principally driven by the phenomenon of pathological microbial translocation (MT).

METHODS

Review of the literature on the role of intestinal barrier dysfunction in HIV infection, with emphasis on the implicated pathophysiological mechanisms, clinical implications and potentially effective therapeutic interventions.

FINDINGS

MT in HIV infection is promoted by a multifactorial disruption of all major levels comprising the intestinal barrier defense. Specifically, HIV infection disrupts the integrity of the intestinal biological (quantitative and qualitative alterations of gut microecology, overgrowth of pathogenic bacteria), immune (depletion of CD4(+) T cells, especially Th17 cells, increased CD4+ FoxP3+ Tregs, decreased mucosal macrophages phagocytic capacity, development of intestinal proinflammatory milieu) and mechanical barrier (enterocytes' apoptosis, disruption of tight junctions). Intestinal barrier dysfunction allows the passage of microbes and immunostimulatory bioproducts from the gut lumen first in the lamina propria and thereafter in the systemic circulation, thus continuously promoting a local and systemic inflammatory response. This chronic immune activation is associated with HIV disease progression, suboptimal response to HAART and development of non-AIDS comorbidities.

CONCLUSIONS

We have reached a point where the effective control of HIV viremia by HAART should be combined with emerging pharmacological approaches aiming at the restoration of the intestinal barrier, targeting its diverse levels of structure and function. Elimination of the MT phenomenon would mitigate its effect on immune homeostasis, which might improve the prognosis of the HIV-infected patient in terms of morbidity and mortality.

Reduced RhoA activity mediates acute alcohol intoxication-induced inhibition of lymphatic myogenic constriction despite increased cytosolic [Ca(2+) ]

OBJECTIVES

We previously showed that AAI reduces lymphatic myogenic constriction in response to step increases in luminal pressure. Because of the known role of Ca(2+) in smooth muscle contractile responses, we investigated how alcohol impacts cyclic Ca(2+) and whether changes in RhoA/ROCK-mediated Ca(2+) sensitivity underlie the alcohol-induced reduction of myogenic responsiveness.

METHODS

AAI was produced by intragastric administration of 30% alcohol in rats. Mesenteric lymphatics were cannulated and loaded with Fura-2 AM to [Ca(2+) ]i for 30 minutes after AAI. Active GTP-bound RhoA levels were determined by ELISA. To determine ROCK's ability to restore myogenic responsiveness following AAI, isolated lymphatics were transfected with constitutively active ca-ROCK protein.

RESULTS

Lymphatics from alcohol-treated rats displayed significantly larger Ca(2+) transients. Also, step increases in luminal pressure caused a gradual rise in the basal [Ca(2+) ]i between transients that was greater in lymphatics submitted to AAI, compared to vehicle control. RhoA-GTP was significantly reduced in lymphatics from the AAI group, compared to vehicle control. Transfection with ca-ROCK protein restored the myogenic response of lymphatic vessels isolated from AAI animals.

CONCLUSIONS

The data strongly suggest that the alcohol-induced inhibition of mesenteric lymphatic myogenic constriction is mediated by reduced RhoA/ROCK-mediated Ca(2+) sensitivity.

Gastro-intestinal vascular emergencies

Gastro-Intestinal Vascular Emergencies include all digestive ischaemic injuries related to acute or chronic vascular and/or haemodynamic diseases. Gastro-intestinal ischaemic injuries can be occlusive or non-occlusive, arterial or venous, localized or generalized, superficial or transmural and share the risks of infarction, organ failure and death. The diagnosis must be suspected, at the initial presentation of any sudden, continuous and unusual abdominal pain, contrasting with normal physical examination. Risk factors are often unknown at presentation and no biomarker is currently available. The diagnosis is confirmed by abdominal computed tomography angiography identifying intestinal ischaemic injury, either with vascular occlusion or in a context of low flow. Recent knowledge in the pathophysiology of acute mesenteric ischaemia, clinical experience and existing recommendations have generated a multimodal and multidisciplinary management strategy. Based on the gastro-intestinal viability around a simple algorithm, and coordinated by gastroenterologists, the dual aim is to avoid large intestinal resections and death.

Role of mesenteric lymph pathway in the effects of exogenous somatostatin against early intestinal injury after ischemia-reperfusion in rats

Intestinal ischemia-reperfusion (I/R)-induced gut injury remains a challenge for critically ill patients. This study aims to test whether mesenteric lymph pathway is involved in intestinal I/R injury and whether somatostatin (SST) affects mesenteric lymph pathway after mesenteric reperfusion. Intestinal I/R rats were treated with SST-14 by intravenous injection combined with intraperitoneal injection before occlusion of the SMA until the end of the experiment. When intestinal I/R injury treated with SST, the volumes of mesenteric lymph flow at the 6th h after reperfusion following intestinal ischemia were increased ([0.55±0.24] ml/h vs [0.25±0.09] ml/h, p<0.05) and the number of intestinal lymphocytes per milliliter ([2.30±0.72]×10⁷/ml vs [1.16±0.63]×10⁷/ml, p<0.05) was also increased, which caused the number of intestinal lymphocytes output at the same period of time was significantly increased compared with intestinal I/R group ([1.33±0.88]×10⁷/h vs [0.28±0.15]×10⁷/h, p<0.05). Meanwhile, the number of ⁵¹Cr-lymphocytes migration from systemic circulation to the effector sites in GALT was significantly increased ([1.93±0.23]×10⁵/h vs [0.90±0.25]×10⁵/h, p<0.05), although the percentage of ⁵¹Cr-lymphocytes in the effector sites ([1.45±0.26]% vs [3.23±1.69]%, p<0.05) was sharply decreased compared with intestinal I/R group. The accompanying decreases of the endotoxin concentration ([0.038±0.017] EU/mL vs [0.110±0.028] EU/mL, compared with intestinal I/R group p<0.05) and the TNF-α levels ([37.50±10.45] ρg/ml) vs ([74.93±14.77] ρg/ml), compared with intestinal I/R group p<0.05) in mesenteric lymph and the improvement of vital organ dysfunction happened during the early intestinal I/R injury. Suppression of gut-derived toxic mediators reaching systemic circulation and increases of the number of lymphocytes homing to the effector sites in GALT to strengthen the effective immune responses in intestinal mucosa account for the protective effects of exogenous SST against early intestinal I/R injury.

Effects of synthetic colloids on oxidative stress and inflammatory response in hemorrhagic shock: comparison of hydroxyethyl starch 130/0.4, hydroxyethyl starch 200/0.5, and succinylated gelatin

INTRODUCTION

This study compared the effects of hydroxyethyl starch 130/0.4, hydroxyethyl starch 200/0.5, and succinylated gelatin on oxidative stress and the inflammatory response in a rodent hemorrhagic shock model.

METHODS

Sodium pentobarbital-anesthetized adult male Wistar rats (200 g to 220 g) were subjected to a severe volume-controlled hemorrhage using arterial blood withdrawal (30 mL/kg to 33 mL/kg) and resuscitated with a colloid solution at the same volume as blood withdrawal (hydroxyethyl starch 130/0.4, hydroxyethyl starch 200/0.5, or succinylated gelatin). Arterial blood gas parameters were monitored. Malondialdehyde (MDA) content and myeloperoxidase (MPO) activity in the liver, lungs, intestine, and brain were measured two hours after resuscitation. The levels of tumor necrosis factor-alpha (TNF-α) and interleukin-6 in the intestine were also measured.

RESULTS

Infusions of hydroxyethyl starch 130/0.4, but not hydroxyethyl starch 200/0.5 or succinylated gelatin, significantly reduced MDA levels and MPO activity in the liver, intestine, lungs and brain, and it also inhibited the production of TNF-α in the intestine two hours after resuscitation. However, no significant difference between hydroxyethyl starch 200/0.5 and succinylated gelatin was observed.

CONCLUSIONS

Hydroxyethyl starch 130/0.4, but not hydroxyethyl starch 200/0.5 or succinylated gelatin, treatment after hemorrhagic shock ameliorated oxidative stress and the inflammatory response in this rat model. No significant differences were observed after hydroxyethyl starch 200/0.5 or succinylated gelatin administration at doses of approximately 33 mL/kg.

Intestine-Specific Mttp Deletion Increases the Severity of Experimental Colitis and Leads to Greater Tumor Burden in a Model of Colitis Associated Cancer

Background

Gut derived lipid factors have been implicated in systemic injury and inflammation but the precise pathways involved are unknown. In addition, dietary fat intake and obesity are independent risk factors for the development of colorectal cancer. Here we studied the severity of experimental colitis and the development of colitis associated cancer (CAC) in mice with an inducible block in chylomicron secretion and fat malabsorption, following intestine-specific deletion of microsomal triglyceride transfer protein (Mttp-IKO).

Methodology/Principal Findings

Mttp-IKO mice exhibited more severe injury with ∼90% mortality following dextran sodium sulfate (DSS) induced colitis, compared to <20% in controls. Intestinal permeability was increased in Mttp-IKO mice compared to controls, both at baseline and after DSS administration, in association with increased circulating levels of TNFα. DSS treatment increased colonic mRNA expression of IL-1β and IL-17A as well as inflammasome expression in both genotypes, but the abundance of TNFα was selectively increased in DSS treated Mttp-IKO mice. There was a 2-fold increase in colonic tumor burden in Mttp-IKO mice following azoxymethane/DSS treatment, which was associated with increased colonic inflammation as well as alterations in cytokine expression. To examine the pathways by which alterations in fatty acid abundance might interact with cytokine signaling to regulate colonic epithelial growth, we used primary murine myofibroblasts to demonstrate that palmitate induced expression of amphiregulin and epiregulin and augmented the increase in both of these growth mediators when added to IL-1βor to TNFα.

Conclusions

These studies demonstrate that Mttp-IKO mice, despite absorbing virtually no dietary fat, exhibit augmented fatty acid dependent signaling that in turn exacerbates colonic injury and increases tumor formation.

Impact of intestinal ischemia/reperfusion and lymph drainage on distant organs in rats

AIM: To investigate the impact of intestinal ischemia/reperfusion (I/R) injury and lymph drainage on distant organs in rats.

METHODS: Thirty-two Sprague-Dawley male rats, weighing 280-320 g, were randomly divided into blank, sham, I/R, and ischemia/reperfusion and drainage (I/R + D) groups (n = 8). All rats were subjected to 60 min ischemia by clamping the superior mesenteric artery, followed by 120 min reperfusion. The rats in the I/R + D group received intestinal lymph drainage for 180 min. In the sham group, the abdominal cavity was opened for 180 min, but the rats received no treatment. The blank group served as a normal and untreated control. A chromogenic limulus assay kit was used for quantitative detection of serum endotoxin. The serum concentrations of tumor necrosis factor-α (TNF-α), interleukin (IL)-6, IL-1β, soluble cell adhesion molecules (sICAM-1), and high mobility group protein box 1 (HMGB1) were determined with an enzyme-linked immunosorbent assay kit. Histological evaluations of the intestine, liver, kidney, and lung were performed by hematoxylin and eosin staining and immunohistochemistry. HMGB1 protein expression was assayed by western blot analysis.

RESULTS: The serum levels of endotoxin and HMGB1 in the I/R and I/R + D groups were significantly higher than those in the sham group (endotoxin, I/R and I/R + D vs sham: 0.033 ± 0.004 EU/mL, 0.024 ± 0.003 EU/mL vs 0.017 ± 0.009 EU/mL, respectively, P < 0.05; HMGB1, I/R and I/R + D vs sham: 5.473 ± 0.963 EU/mL, 4.906 ± 0.552 EU/mL vs 0.476 ± 0.406 EU/mL, respectively, P < 0.05). In addition, endotoxin and HMGB1 were significantly lower in the I/R + D group compared to the I/R group (P < 0.05). The serum inflammatory factors IL-6, IL-1β, and sICAM-1 in the I/R and I/R + D groups were significantly higher than those in the sham group (IL-6, I/R and I/R + D vs sham: 41.773 ± 9.753 pg/mL, 19.204 ± 4.136 pg/mL vs 11.566 ± 2.973 pg/mL, respectively, P < 0.05; IL-1β, I/R and I/R + D vs sham: 144.646 ± 29.378 pg/mL, 65.829 ± 10.888 pg/mL vs 38.178 ± 7.157 pg/mL, respectively, P < 0.05; sICAM-1, I/R and I/R + D vs sham: 97.360 ± 12.714 ng/mL, 48.401 ± 6.547 ng/mL vs 33.073 ± 5.957 ng/mL, respectively; P < 0.05). The serum TNF-α in the I/R group were significantly higher than in the sham group (45.863 ± 11.553 pg/mL vs 18.863 ± 6.679 pg/mL, respectively, P < 0.05). These factors were significantly lower in the I/R + D group compared to the I/R group (P < 0.05). The HMGB1 immunohistochemical staining results showed no staining or apparent injury in the blank group, and slight staining at the top of the microvillus was detected in the sham group. In the I/R group, both the top of villi and the basement membrane were stained for HMGB1 in most areas, and injury in the I/R + D group was less than that in the I/R group. HMGB1 expression in the liver, kidney, and lung of rats in the I/R + D group was significantly lower than the rats in the I/R group (P < 0.05).

CONCLUSION: Lymph drainage could block the “gut-lymph” pathway, improve intestinal barrier function, and attenuate distant organ injury incurred by intestinal I/R.

Intestine-specific Mttp deletion decreases mortality and prevents sepsis-induced intestinal injury in a murine model of Pseudomonas aeruginosa pneumonia

BACKGROUND

The small intestine plays a crucial role in the pathophysiology of sepsis and has been referred to as the "motor" of the systemic inflammatory response. One proposed mechanism is that toxic gut-derived lipid factors, transported in mesenteric lymph, induce systemic injury and distant organ failure. However, the pathways involved are yet to be defined and the role of intestinal chylomicron assembly and secretion in transporting these lipid factors is unknown. Here we studied the outcome of sepsis in mice with conditional, intestine-specific deletion of microsomal triglyceride transfer protein (Mttp-IKO), which exhibit a block in chylomicron assembly together with lipid malabsorption.

METHODOLOGY/PRINCIPAL FINDINGS

Mttp-IKO mice and controls underwent intratracheal injection with either Pseudomonas aeruginosa or sterile saline. Mttp-IKO mice exhibited decreased seven-day mortality, with 0/20 (0%) dying compared to 5/17 (29%) control mice (p<0.05). This survival advantage in Mttp-IKO mice, however, was not associated with improvements in pulmonary bacterial clearance or neutrophil infiltration. Rather, Mttp-IKO mice exhibited protection against sepsis-associated decreases in villus length and intestinal proliferation and were also protected against increased intestinal apoptosis, both central features in control septic mice. Serum IL-6 levels, a major predictor of mortality in human and mouse models of sepsis, were elevated 8-fold in septic control mice but remained unaltered in septic Mttp-IKO mice. Serum high density lipoprotein (HDL) levels were reduced in septic control mice but were increased in septic Mttp-IKO mice. The decreased levels of HDL were associated with decreased hepatic expression of apolipoprotein A1 in septic control mice.

CONCLUSIONS/SIGNIFICANCE

These studies suggest that strategies directed at blocking intestinal chylomicron secretion may attenuate the progression and improve the outcome of sepsis through effects mediated by metabolic and physiological adaptations in both intestinal and hepatic lipid flux.

Activation of toll-like receptor 4 is necessary for trauma hemorrhagic shock-induced gut injury and polymorphonuclear neutrophil priming

Interactions of toll-like receptors (TLRs) with nonmicrobial factors play a major role in the pathogenesis of early trauma-hemorrhagic shock (T/HS)-induced organ injury and inflammation. Thus, we tested the hypothesis that TLR4 mutant (TLR4 mut) mice would be more resistant to T/HS-induced gut injury and polymorphonuclear neutrophil (PMN) priming than their wild-type littermates and found that both were significantly reduced in the TLR4 mut mice. In addition, the in vivo and ex vivo PMN priming effect of T/HS intestinal lymph observed in the wild-type mice was abrogated in TLR4 mut mice as well the TRIF mut-deficient mice and partially attenuated in Myd88 mice, suggesting that TRIF activation played a more predominant role than MyD88 in T/HS lymph-induced PMN priming. Polymorphonuclear neutrophil depletion studies showed that T/HS lymph-induced acute lung injury was PMN dependent, because lung injury was totally abrogated in PMN-depleted animals. Because the lymph samples were sterile and devoid of endotoxin or bacterial DNA, we investigated whether the effects of T/HS lymph was related to endogenous nonmicrobial TLR4 ligands. High-mobility group box 1 protein 1, heat shock protein 70, heat shock protein 27, and hyaluronic acid all have been implicated in ischemia-reperfusion-induced tissue injury. None of these "danger" proteins appeared to be involved, because their levels were similar between the sham and shock lymph samples. In conclusion, TLR4 activation is important in T/HS-induced gut injury and in T/HS lymph-induced PMN priming and lung injury. However, the T/HS-associated effects of TLR4 on gut barrier dysfunction can be uncoupled from the T/HS lymph-associated effects of TLR4 on PMN priming.

Minocycline ameliorates lung and liver dysfunction in a rodent model of hemorrhagic shock/resuscitation plus abdominal compartment syndrome

BACKGROUND

We sought to elucidate whether minocycline, a broad-spectrum tetracycline antibiotic with potent anti-inflammation capacity, could mitigate inflammatory response and organ dysfunction in the lungs and liver induced by hemorrhagic shock/resuscitation (HS) plus abdominal compartment syndrome (ACS).

MATERIALS AND METHODS

Adult male rats were randomized to receive HS plus ACS or HS plus ACS plus minocycline (denoted as the HS/A and HS/A-M group, respectively; n = 12). Sham-instrumentation groups were employed to serve as the controls. Hemorrhagic shock/resuscitation was induced by blood drawing (mean arterial pressure: 40-45 mm Hg for 60 min) followed by shed blood/saline mixture reinfusion. Subsequently, intra-abdominal pressure (IAP) was increased to 25 mm Hg by injecting air into the preplaced intraperitoneal latex balloon to induce ACS. Minocycline (20 mg/kg) was intravenously administered immediately after resuscitation. IAP was maintained at 25 mm Hg for 6 h. Then, all rats were euthanized.

RESULTS

The levels of polymorphonuclear leukocyte infiltration, the wet/dry weight ratio, and the concentrations of inflammatory molecules (e.g., chemokine, cytokine, and prostaglandin E2) in lung and liver tissues of the HS/A group were significantly higher than those of the HS/A-M groups (all P < 0.05). Moreover, the levels of lung dysfunction (assayed by arterial blood gas) and liver dysfunction (assayed by plasma concentrations of bilirubin, aspartate aminotransferase, and alaninine aminotransferase) of the HS/A group were significantly higher than those of the HS/A-M group (all P < 0.05).

CONCLUSIONS

Minocycline ameliorates inflammatory response and organ dysfunction in the lungs and liver induced by hemorrhagic shock/resuscitation plus abdominal compartment syndrome.

Toward computational identification of multiscale "tipping points" in acute inflammation and multiple organ failure

Sepsis accounts annually for nearly 10% of total U.S. deaths, costing nearly $17 billion/year. Sepsis is a manifestation of disordered systemic inflammation. Properly regulated inflammation allows for timely recognition and effective reaction to injury or infection, but inadequate or overly robust inflammation can lead to Multiple Organ Dysfunction Syndrome (MODS). There is an incongruity between the systemic nature of disordered inflammation (as the target of inflammation-modulating therapies), and the regional manifestation of organ-specific failure (as the subject of organ support), that presents a therapeutic dilemma: systemic interventions can interfere with an individual organ system's appropriate response, yet organ-specific interventions may not help the overall system reorient itself. Based on a decade of systems and computational approaches to deciphering acute inflammation, along with translationally-motivated experimental studies in both small and large animals, we propose that MODS evolves due to the feed-forward cycle of inflammation → damage → inflammation. We hypothesize that inflammation proceeds at a given, "nested" level or scale until positive feedback exceeds a "tipping point." Below this tipping point, inflammation is contained and manageable; when this threshold is crossed, inflammation becomes disordered, and dysfunction propagates to a higher biological scale (e.g., progressing from cellular, to tissue/organ, to multiple organs, to the organism). Finally, we suggest that a combination of computational biology approaches involving data-driven and mechanistic mathematical modeling, in close association with studies in clinically relevant paradigms of sepsis/MODS, are necessary in order to define scale-specific "tipping points" and to suggest novel therapies for sepsis.

The effects of n-3 PUFA and intestinal lymph drainage on high-mobility group box 1 and Toll-like receptor 4 mRNA in rats with intestinal ischaemia-reperfusion injury

The aim of the present study was to investigate the impacts of n-3 PUFA and lymph drainage (D) on intestinal ischaemia-reperfusion (I/R) injury in rats. A total of forty-eight Sprague-Dawley male rats were randomly divided into three groups (n 16): normal diet (N), enteral nutrition (EN) and EN plus n-3 PUFA. Each group was further divided into lymph drainage (I/R+D) and non-drainage (I/R) sub-groups (n 8). After 5 d with different nutrition regimens, the rats were subjected to 60 min ischaemia by clamping the superior mesenteric artery, followed by 120 min reperfusion. At the same time, the rats in the I/R+D sub-groups were treated with intestinal lymph drainage for 180 min. Organs were harvested and we detected the cytokine, endotoxin, and expression of Toll-like receptor (TLR) 4 mRNA and its endogenous ligand high-mobility group box 1 (HMGB1). We found that the serum levels of HMGB1, inflammatory cytokine and endotoxin in the three I/R+D sub-groups were significantly lower than those in the N (I/R) and EN (I/R) sub-groups (P < 0·05). The activation of NF-κB and the expression of HMGB1 and TLR4 mRNA significantly increased in the jejunum, ileum, liver and lung after intestinal I/R injury, but notably lower in the I/R+D groups than those in I/R (P < 0·05). The injury degree and HMGB1 expression were decreased in the n-3 PUFA group than in the N and EN groups. We preliminarily concluded that nutrition with n-3 PUFA and/or intestinal lymph drainage may reduce HMGB1 and inflammatory cytokine in serum and lymph and inhibit the expression and signal transmission of TLR4 mRNA, thereby alleviating intestinal I/R injury in rats.

Enterocytes’ tight junctions: From molecules to diseases

Tight junctions (TJs) are structures between cells where cells appear in the closest possible contact. They are responsible for sealing compartments when epithelial sheets are generated. They regulate the permeability of ions, (macro) molecules and cells via the paracellular pathway. Their structure at the electron microscopic level has been well known since the 1970s; however, only recently has their macromolecular composition been revealed. This review first examines the major macromolecular components of the TJs (occludin, claudins, junctional adhesion molecule and tricellulin) and then the associated macromolecules at the intracellular plaque [zonula occludens (ZO)-1, ZO-2, ZO-3, AF-6, cingulin, 7H6]. Emphasis is given to their interactions in order to begin to understand the mode of assembly of TJs. The functional significance of TJs is detailed and several mechanisms and factors involved are discussed briefly. Emphasis is given to the role of intestinal TJs and the alterations observed or speculated in diverse disease states. Specifically, intestinal TJs may exert a pathogenetic role in intestinal (inflammatory bowel disease, celiac disease) and extraintestinal diseases (diabetes type 1, food allergies, autoimmune diseases). Additionally, intestinal TJs may be secondarily disrupted during the course of diverse diseases, subsequently allowing the bacterial translocation phenomenon and promoting the systemic inflammatory response, which is often associated with clinical deterioration. The major questions in the field are highlighted.

Testosterone depletion or blockade in male rats protects against trauma hemorrhagic shock-induced distant organ injury by limiting gut injury and subsequent production of biologically active mesenteric lymph

BACKGROUND

We tested the hypothesis that testosterone depletion or blockade in male rats protects against trauma hemorrhagic shock-induced distant organ injury by limiting gut injury and subsequent production of biologically active mesenteric lymph.

METHODS

Male, castrated male, or flutamide-treated rats (25 mg/kg subcutaneously after resuscitation) were subjected to a laparotomy (trauma), mesenteric lymph duct cannulation, and 90 minutes of shock (35 mm Hg) or trauma sham-shock. Mesenteric lymph was collected preshock, during shock, and postshock. Gut injury was determined at 6 hours postshock using ex vivo ileal permeability with fluorescein dextran. Postshock mesenteric lymph was assayed for biological activity in vivo by injection into mice and measuring lung permeability, neutrophil activation, and red blood cell deformability. In vitro neutrophil priming capacity of the lymph was also tested.

RESULTS

Castrated and flutamide-treated male rats were significantly protected against trauma hemorrhagic shock (T/HS)-induced gut injury when compared with hormonally intact males. Postshock mesenteric lymph from male rats had a higher capacity to induce lung injury, Neutrophil (PMN) activation, and loss of red blood cell deformability when injected into naïve mice when compared with castrated and flutamide-treated males. The increase in gut injury after T/HS in males directly correlated with the in vitro biological activity of mesenteric lymph to prime neutrophils for an increased respiratory burst.

CONCLUSIONS

After T/HS, gut protective effects can be observed in males after testosterone blockade or depletion. This reduced gut injury contributes to decreased biological activity of mesenteric lymph leading to attenuated systemic inflammation and distant organ injury.

Impact of molecular mimicry on the clinical course and outcome of sepsis syndrome

We investigated the impact of molecular mimicry between pathogenic microbes and their antigenic surrounding on the clinical course and outcome of pneumonia induced sepsis. Using mathematical prediction, we estimated the mimicry tendency of the identified pathogenic flora of patients with the human proteome as well as intestinal microbes. Since gut bacteria become invasive and hostile in critical illness, mimicry between these organisms and the infectious flora is expected to be rather hyperinflammatory type, in contrast to the expectedly tolerogenic self versus pathogen cross-reactions. Differential effects of these two kinds of cross-reactions were studied. The predicted similarity of the identified pathogenic flora and intestinal microbes was higher in non-survivor patients compared to survivors (P=0.019). Higher values of "pathogen versus intestinal flora/pathogen versus human proteome" mimicry ratios (inflammatory quotients) were associated with mortality at a higher extent of significance (P<0.01), and correlated with admission APACHE II disease severity scores (R=0.311; P=0.017). We also found a correlation between the previously reported sepsis mortality rates by causative agent and the corresponding inflammatory quotients of these pathogens (R=0.738; P<0.05). Gram negative species showed higher similarity to intestinal bacteria and reached higher inflammatory quotients compared to Gram positives (P=0.01 and P<0.01, respectively). The disadvantageous effect of "pathogen versus intestinal flora" mimicry - presumably due to the extension of inflammation from the infectious focus to the already injured gut - is in accordance with the gut-lymph hypothesis, assessing that the destruction of the intestinal symbiosis culminates in the formation of damageous gut origin lymph. Our results raise the idea that molecular mimicry between pathogenic microbes and their antigenic surrounding might be a contributing factor behind the clinically and experimentally observed differences in microbiologically distinct forms of sepsis syndrome.

Trauma hemorrhagic shock-induced lung injury involves a gut-lymph-induced TLR4 pathway in mice

Background

Injurious non-microbial factors released from the stressed gut during shocked states contribute to the development of acute lung injury (ALI) and multiple organ dysfunction syndrome (MODS). Since Toll-like receptors (TLR) act as sensors of tissue injury as well as microbial invasion and TLR4 signaling occurs in both sepsis and noninfectious models of ischemia/reperfusion (I/R) injury, we hypothesized that factors in the intestinal mesenteric lymph after trauma hemorrhagic shock (T/HS) mediate gut-induced lung injury via TLR4 activation.

Methods/Principal Findings

The concept that factors in T/HS lymph exiting the gut recreates ALI is evidenced by our findings that the infusion of porcine lymph, collected from animals subjected to global T/HS injury, into naïve wildtype (WT) mice induced lung injury. Using C3H/HeJ mice that harbor a TLR4 mutation, we found that TLR4 activation was necessary for the development of T/HS porcine lymph-induced lung injury as determined by Evan's blue dye (EBD) lung permeability and myeloperoxidase (MPO) levels as well as the induction of the injurious pulmonary iNOS response. TRIF and Myd88 deficiency fully and partially attenuated T/HS lymph-induced increases in lung permeability respectively. Additional studies in TLR2 deficient mice showed that TLR2 activation was not involved in the pathology of T/HS lymph-induced lung injury. Lastly, the lymph samples were devoid of bacteria, endotoxin and bacterial DNA and passage of lymph through an endotoxin removal column did not abrogate the ability of T/HS lymph to cause lung injury in naïve mice.

Conclusions/Significance

Our findings suggest that non-microbial factors in the intestinal mesenteric lymph after T/HS are capable of recreating T/HS-induced lung injury via TLR4 activation.

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

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

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

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

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

Intravenous injection of mesenteric lymph produced during hemorrhagic shock decreases RBC deformability in the rat

OBJECTIVE

To test the hypothesis that gut-derived factors carried in trauma-hemorrhagic shock (T/HS) lymph are sufficient to induce red blood cells (RBC) injury, to investigate their potential mechanisms of action, and to define the time post-T/HS that these factors appear in the lymph.

METHODS

Mesenteric lymph collected from T/HS or trauma-sham shock (T/SS) rats over different time periods was injected intravenously into male rats at a rate of 1 mL/h for 3 hours. RBC deformability was measured using laser-assisted ektacytometer to calculate the elongation index. From the shear-stress elongation curve, the stress required for the erythrocytes to reach 50% of their maximal elongation was also determined. RBC deformability was measured before lymph infusion and at 1 hour and 3 hours after the initiation of lymph infusion. The effect of the lymph samples (5% v/v) was also determined in vitro by incubating naïve whole blood with the lymph samples. The potential role of T/HS lymph-induced RBC oxidant injury mediated by inducible nitric oxide synthase (iNOS)-generated oxidants and/or white blood cells (WBC) was investigated using iNOS inhibitors and WBC depletion, respectively. In all the in vivo studies, five to seven rats were studied per group.

RESULTS

The intravenous injection of T/HS lymph but not T/SS lymph caused in vivo RBC injury. The biological activity of T/HS lymph varied over time with the RBC-injurious factors being produced only during the first 3 hours postshock. The in vivo inhibition of iNOS did not prevent lymph-induced RBC injury. T/HS lymph incubated in vitro with naïve whole blood resulted in RBC injury, but this injury was not observed in blood depleted of WBC.

CONCLUSIONS

These results indicate that T/HS lymph produced during the initial 3-hour postshock period is sufficient to induce RBC injury in otherwise normal rats and that the lymph-induced RBC injury is not dependent on activation of the iNOS pathway but seems to require WBC.

Claude H. Organ, Jr. memorial lecture: splanchnic hypoperfusion provokes acute lung injury via a 5-lipoxygenase-dependent mechanism

Postinjury multiple organ failure (MOF) is the net result of a dysfunctional immune response to injury characterized by a hyperactive innate system and a suppressed adaptive system. Acute lung injury (ALI) is the first clinical manifestation of organ failure, followed by renal and hepatic dysfunction. Circulatory shock is integral in the early pathogenesis of MOF, and the gut has been invoked as the motor of MOF. Mesenteric lymph is recognized as the mechanistic link between splanchnic ischemia/reperfusion and distant organ dysfunction, but the specific mediators remain to be defined. Current evidence suggests the lipid fraction of postshock mesenteric lymph is central in the etiology of ALI. Specifically, our recent work suggests that intestinal phospholipase A2 generated arachidonic acid and its subsequent 5-lipoxygenase products are essential in the pathogenesis of ALI. Proteins conveyed via postshock mesenteric lymph also may have an important role. Elucidating these mediators and the timing of their participation in pulmonary inflammation is critical in translating our current knowledge to new therapeutic strategies at the bedside.

Surgical sepsis and organ crosstalk: the role of the kidney

Acute kidney injury (AKI) is a common complication of hospitalized patients, and clinical outcomes remain poor despite advances in renal replacement therapy. The accepted pathophysiology of AKI in the setting of sepsis has evolved from one of simple decreased renal blood flow to one that involves a more complex interaction of intra-glomerular microcirculatory vasodilation combined with the local release of inflammatory mediators and apoptosis. Evidence from preclinical AKI models suggests that crosstalk occurs between kidneys and other organ systems via soluble and cellular inflammatory mediators and that this involves both the innate and adaptive immune systems. These interactions are reflected by genomic changes and abnormal rates of cellular apoptosis in distant organs including the lungs, heart, gut, liver, and central nervous system. The purpose of this article is to review the influence of AKI, particularly sepsis-associated AKI, on inter-organ crosstalk in the context of systemic inflammation and multiple organ failure (MOF).

Protective effects of green tea on intestinal ischemia-reperfusion injury

OBJECTIVE

The intestinal mucosa is known to be adversely affected by ischemia-reperfusion (I/R). Previously we showed that green tea protects the intestinal mucosa from fasting-induced damage. The aim of this study is to determine whether green tea has any protective role in I/R of the intestine.

METHODS

Three groups of male rats were used in this study. Group I (I/R) underwent I/R of the intestine (30 min of ischemia followed by 1 h of reperfusion). Group II (green tea + I/R) was given green tea for 2 wk before inducing I/R. Group III (control) had sham I/R. After the experiments, the jejunum was removed and the tissues were processed for histopathologic examination and immunohistochemical analysis for cell proliferation markers and antioxidant enzymes.

RESULTS

The intestinal mucosa in group II was preserved compared with that in group I. The expressions of cellular proliferation markers (proliferating cell nuclear antigen and Ki-67) and cellular antioxidants (superoxide dismutase and catalase) in group II were similar to those in group III and much less than in group I, reflecting the protective effects of green tea in group II animals.

CONCLUSION

In this animal model, administration of green tea before inducing I/R protects the intestinal mucosa from injury.

Ethyl pyruvate prevents inflammatory responses and organ damage during resuscitation in porcine hemorrhage

Hemorrhage remains a common cause of death despite the recent advances in critical care, in part because conventional resuscitation fluids fail to prevent lethal inflammatory responses. Here, we analyzed whether ethyl pyruvate can provide a therapeutic anti-inflammatory potential to resuscitation fluids and prevent organ damage in porcine hemorrhage. Adult male Yorkshire swine underwent lethal hemorrhage with trauma and received no resuscitation treatment or resuscitation with Hextend alone, or supplemented with ethyl pyruvate. Resuscitation with ethyl pyruvate did not improve early hemodynamics but prevented hyperglycemia, the intrinsic coagulation pathway, serum aspartate aminotransferase, and myeloperoxidase in the major organs. Resuscitation with ethyl pyruvate provided an anti-inflammatory potential to restrain serum TNF and high-mobility group B protein 1 levels. Ethyl pyruvate inhibited nuclear factor [kappa]B in the spleen but not in the other major organs. In contrast, ethyl pyruvate inhibited NO in all the major organs, and it also inhibited TNF production in the major organs but in the lung and heart. The most significant effects were found in the terminal ileum where ethyl pyruvate inhibited cytokine production, restrained myeloperoxidase activity, preserved the intestinal epithelium, and prevented the systemic distribution of bacterial endotoxin. Ethyl pyruvate can provide therapeutic anti-inflammatory benefits to modulate splenic nuclear factor [kappa]B, restrain inflammatory responses, and prevent hyperglycemia, the intrinsic coagulation pathway, and organ injury in porcine hemorrhage without trauma.