The lipid fraction of post-hemorrhagic shock mesenteric lymph (PHSML) inhibits neutrophil apoptosis and enhances cytotoxic potential

Vagus nerve stimulation modulates arachidonic acid production in the mesenteric lymph following intestinal ischemia-reperfusion injury

BACKGROUND

Inflammatory lipid mediators in mesenteric lymph (ML), including arachidonic acid (AA), are considered to play an important role in the pathogenesis of multiple-organ dysfunction after hemorrhagic shock. A previous study suggested that vagus nerve stimulation (VNS) could relieve shock-induced gut injury and abrogate ML toxicity, resulting in the prevention of multiple-organ dysfunction. However, the detailed mechanism of VNS in lymph toxicity remains unclear. The study aimed to investigate the relationship between VNS and inflammatory lipid mediators in ML.

METHODS

Male Sprague-Dawley rats underwent laparotomy and superior mesenteric artery obstruction (SMAO) for 60 minutes to induce intestinal ischemia followed by reperfusion and observation. The ML duct was cannulated, and ML samples were obtained both before and after SMAO. The distal ileum was removed at the end of the observation period. In one group of animals, VNS was performed from 10 minutes before 10 minutes after SMAO (5 V, 0.5 Hz). Liquid chromatography-electrospray ionization-tandem mass spectrometry analysis of AA was performed for each ML sample. The biological activity of ML was examined using a monocyte nuclear factor κ-light-chain-enhancer of activated B cells activation assay. Western blotting of phospholipase A2 group IIA (PLA2-IIA) was also performed for ML and ileum samples.

RESULTS

Vagus nerve stimulation relieved the SMAO-induced histological gut injury. The concentration of AA and level of nuclear factor κ-light-chain-enhancer of activated B cells activation in ML increased significantly after SMAO, whereas VNS prevented these responses. Western blotting showed PLA2-IIA expression in the ML and ileum after SMAO; however, the appearance of PLA2-IIA band was remarkably decreased in the samples from VNS-treated animals.

CONCLUSION

The results suggested that VNS could relieve gut injury induced by SMAO and decrease the production of AA in ML by altering PLA2-IIA expression in the gut and ML.

The Gut-Lung Axis in Systemic Inflammation. Role of Mesenteric Lymph as a Conduit

Emerging evidence shows that after injury or infection, the mesenteric lymph acts as a conduit for gut-derived toxic factors to enter the blood circulation, causing systemic inflammation and acute lung injury. Neither the cellular and molecular identity of lymph factors nor their mechanisms of action have been well understood and thus have become a timely topic of investigation. This review will first provide a summary of background knowledge on gut barrier and mesenteric lymphatics, followed by a discussion focusing on the current understanding of potential injurious factors in the lymph and their mechanistic contributions to lung injury. We also examine lymph factors with antiinflammatory properties as well as the bidirectional nature of the gut-lung axis in inflammation.

Gut Ischemia Reperfusion Injury Induces Lung Inflammation via Mesenteric Lymph-Mediated Neutrophil Activation

Gut ischemia/reperfusion (I/R) injury is a common clinical problem associated with significant mortality and morbidities that result from systemic inflammation and remote organ dysfunction, typically acute lung injury. The mechanisms underlying the dissemination of gut-derived harmful mediators into the circulation are poorly understood. The objective of our study was to determine the role of mesenteric lymphatic circulation in the systemic and pulmonary inflammatory response to gut I/R. Using a murine intestinal I/R model, we evaluated whether and how blocking mesenteric lymph flow affects the inflammatory response in local tissues (gut) and remote organs (lungs). We further explored the mechanisms of post-I/R lymph-induced systemic inflammation by examining neutrophil activity and interaction with endothelial cells in vitro. Mice subjected to intestinal I/R displayed a significant inflammatory response in local tissues, evidenced by neutrophil infiltration into mucosal areas, as well as lung inflammation, evidenced by increased myeloperoxidase levels, neutrophil infiltration, and elevated microvascular permeability in the lungs. Mesenteric lymph duct ligation (MLDL) had no effect on gut injury per se, but effectively attenuated lung injury following gut I/R. Cell experiments showed that lymph fluid from post-I/R animals, but not pre-I/R, increased neutrophil surface CD11b expression and their ability to migrate across vascular endothelial monolayers. Moreover, post-I/R lymph upregulated neutrophil expression of pro-inflammatory cytokines and chemokines, which was mediated by a mechanism involving nuclear factor (NF)-κB signaling. Consistently, gut I/R activated NF-κB in lung neutrophils, which was alleviated by MLDL. In conclusion, all these data indicate that mesenteric lymph circulation contributes to neutrophil activation and lung inflammation following gut I/R injury partly through activating NF-κB.

Precious cargo: Modulation of the mesenteric lymph exosome payload after hemorrhagic shock

BACKGROUND

Trauma/hemorrhagic shock (T/HS) causes a release of proinflammatory mediators into the mesenteric lymph (ML) that may trigger a systemic inflammatory response and subsequent organ failure. Recently, we showed that exosomes in postshock ML are biologically active mediators of this inflammation. Because the specific inflammatory mediators in postshock ML exosomes have yet to be characterized, we hypothesized that T/HS would lead to a distinct ML proinflammatory exosome phenotype that could be identified by proteomic analysis. We further hypothesized that their regulation by the neuroenteric axis via the vagus nerve would modify this proinflammatory profile.

METHODS

Male rats underwent an established T/HS model including 60 minutes of HS followed by resuscitation. Mesenteric lymph was collected before HS (preshock) and after resuscitation (postshock). A subset of animals underwent cervical vagus nerve electrical stimulation (VNS) after the HS phase. Liquid chromatography with tandem mass spectroscopy (LC-MS/MS) followed by protein identification, label free quantification, and bioinformatic analysis was performed on exosomes from the pre-shock and post-shock phases in the T/HS and T/HS + vagus nerve electrical stimulation groups. Biological activity of exosomes was evaluated using a monocyte nuclear factor kappa B (NF-κB) activity assay.

RESULTS

ML exosomes express a distinct protein profile after T/HS with enrichment in pathways associated with cell signaling, cell death and survival, and the inflammatory response. Stimulation of the vagus nerve following injury attenuated the transition of ML exosomes to this T/HS-induced inflammatory phenotype with protein expression remaining similar to pre-shock. Monocyte NF-κB activity was increased after exposure to ML exosomes harvested after T/HS, while ML exosomes from preshock had no effect on monocyte NF-κB expression.

CONCLUSION

Postshock ML exosomes carry a distinct, proinflammatory protein cargo. Stimulating the vagus nerve prevents the T/HS-induced changes in ML exosome protein payload and suggests a novel mechanism by which the neuroenteric axis may limit the systemic inflammatory response after injury.

Lymphatic Pump Treatment Mobilizes Bioactive Lymph That Suppresses Macrophage Activity In Vitro

Context

By promoting the recirculation of tissue fluid, the lymphatic system preserves tissue health, aids in the absorption of gastrointestinal lipids, and supports immune surveillance. Failure of the lymphatic system has been implicated in the pathogenesis of several infectious and inflammatory diseases. Thus, interventions that enhance lymphatic circulation, such as osteopathic lymphatic pump treatment (LPT), should aid in the management of these diseases.

Objective

To determine whether thoracic duct lymph (TDL) mobilized during LPT would alter the function of macrophages in vitro.

Methods

The thoracic ducts of 6 mongrel dogs were cannulated, and TDL samples were collected before (baseline), during, and 10 minutes after LPT. Thoracic duct lymph flow was measured, and TDL samples were analyzed for protein concentration. To measure the effect of TDL on macrophage activity, RAW 264.7 macrophages were cultured for 1 hour to acclimate. After 1 hour, cell-free TDL collected at baseline, during LPT, and after TDL was added at 5% total volume per well and co-cultured with or without 500 ng per well of lipopolysaccharide (LPS) for 24 hours. As a control for the addition of 5% TDL, macrophages were cultured with phosphate-buffered saline (PBS) at 5% total volume per well and co-cultured with or without 500 ng per well of LPS for 24 hours. After culture, cell-free supernatants were assayed for nitrite (NO2-), tumor necrosis factor α (TNF-α) and interleukin 10 (IL-10). Macrophage viability was measured using flow cytometry.

Results

Lymphatic pump treatment significantly increased TDL flow and the flux of protein in TDL (P<.001). After culture, macrophage viability was approximately 90%. During activation with LPS, baseline TDL, TDL during LPT, and TDL after LPT significantly decreased the production of NO2-, TNF-α, and IL-10 by macrophages (P<.05). However, no significant differences were found in viability or the production of NO2-, TNF-α, or IL-10 between macrophages cultured with LPS plus TDL taken before, during, and after LPT (P>.05).

Conclusion

The redistribution of protective lymph during LPT may provide scientific rationale for the clinical use of LPT to reduce inflammation and manage edema.

Lymphatic Vessel Network Structure and Physiology

The lymphatic system is comprised of a network of vessels interrelated with lymphoid tissue, which has the holistic function to maintain the local physiologic environment for every cell in all tissues of the body. The lymphatic system maintains extracellular fluid homeostasis favorable for optimal tissue function, removing substances that arise due to metabolism or cell death, and optimizing immunity against bacteria, viruses, parasites, and other antigens. This article provides a comprehensive review of important findings over the past century along with recent advances in the understanding of the anatomy and physiology of lymphatic vessels, including tissue/organ specificity, development, mechanisms of lymph formation and transport, lymphangiogenesis, and the roles of lymphatics in disease. © 2019 American Physiological Society. Compr Physiol 9:207-299, 2019.

Expression profiles and circulation dynamics of rat mesenteric lymph microRNAs

Mesenteric lymph is vital for immune cell trafficking and intestinal fluid and chyle transport, which aid homeostatic maintenance. There have been few reports investigating the profiles and circulatory dynamics of mesenteric lymph microRNAs (miRNAs). The present study aimed to provide a comprehensive analysis of miRNAs in normal rodent mesenteric lymph. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR)-based array analysis was performed to examine the expression levels of 375 miRNAs in normal rat mesenteric lymph. Using differential centrifugation, the presence of miR-150, a representative lymph miRNA, in exosomes was assessed. Rat small intestine epithelial cell line IEC-6-derived exosomes were prepared from culture supernatants of cells transfected with cel-miR-238-3p, and were used to trace the administered exosomes in vivo and to investigate the in vivo delivery of lymph miRNAs via mesenteric lymphatics into the systemic circulation following injection of cel-miR-238-3p-exosomes. RT-qPCR-based array analysis detected 287 miRNAs in lymph, and 21 miRNAs that were significantly differentially expressed between lymph and plasma. Lymph fractionation analysis demonstrated that some cell-free lymph miR-150 was distributed in the exosome-containing microsomal fraction. Furthermore, in vivo analysis of lymph miRNA delivery revealed that exosomal cel-miR-238-3p was markedly distributed in the lung compared with in the liver, kidney and spleen, thus indicating that the lung is the major organ responsible for clearance of exosomal lymph miRNAs. These findings provide novel insights into the modulation of gene expression by mesenteric lymph miRNAs in the lung.

Trauma-hemorrhagic shock induces a CD36-dependent RBC endothelial-adhesive phenotype

OBJECTIVE

Microvascular dysfunction is a key element in the development of the multiple organ dysfunction syndrome. Although the mechanisms for this response are unclear, RBC adhesion to endothelium may initiate intravascular occlusion leading to ischemic tissue injury. Thus, we tested the hypothesis that trauma-hemorrhage induces RBC-endothelial cell adhesion.

DESIGN

Prospective in vivo and in vitro animal study and analysis of patient blood samples.

SETTING

University research laboratory and hospital emergency and trauma units.

INTERVENTION

We initially assayed RBC adhesion to endothelial cells in vitro using RBCs obtained from rats subjected to trauma-hemorrhagic shock or sham shock as well as from severely injured trauma patients. Subsequently, we measured the role of putative RBCs and endothelial cell receptors in the increased RBC-endothelial cell adhesive response.

MAIN RESULTS

In both rats and humans, trauma-hemorrhagic shock increased RBC adhesion to endothelium as well as increasing several putative RBC surface adhesion molecules including CD36. The critical factor leading to RBC-endothelial cell adhesion was increased surface RBC CD36 expression. Adhesion of trauma-hemorrhagic shock RBCs was mediated, at least in part, by the binding of RBC CD36 to its cognate endothelial receptors (αVβ3 and VCAM-1). Gut-derived factors carried in the intestinal lymphatics triggered these trauma-hemorrhagic shock-induced RBC changes because 1) preventing trauma-hemorrhagic shock intestinal lymph from reaching the systemic circulation abrogated the RBC effects, 2) in vitro incubation of naïve whole blood with trauma-hemorrhagic shock lymph replicated the in vivo trauma-hemorrhagic shock-induced RBC changes while 3) injection of trauma-hemorrhagic shock lymph into naïve animals recreated the RBC changes observed after actual trauma-hemorrhagic shock.

CONCLUSIONS

1) Trauma-hemorrhagic shock induces rapid RBC adhesion to endothelial cells in patients and animals. 2) Increased RBC CD36 expression characterizes the RBC-adhesive phenotype. 3) The RBC phenotypic and functional changes were induced by gut-derived humoral factors. These novel findings may explain the microvascular dysfunction occurring after trauma-hemorrhagic shock, sepsis, and other stress states.

Group VIB Ca(2+)-independent phospholipase A(2γ) is associated with acute lung injury following trauma and hemorrhagic shock

BACKGROUND

Gut-derived mediators are carried via mesenteric lymph duct into systemic circulation after trauma/hemorrhagic shock (T/HS), thus leading to acute lung injury (ALI)/multiple-organ dysfunction syndrome. Phospholipase A2 (PLA(2)) is a key enzyme for the production of lipid mediators in posthemorrhagic shock mesenteric lymph (PHSML). However, the precise functions of PLA(2) subtype, such as cytosolic PLA(2), secretory PLA(2), and Ca-independent PLA(2), in the acute phase of inflammation have remained unclear. Our previous study has suggested that the activation of Group VIB Ca-independent PLA(2γ) (PLA(2γ)) may be associated with increased lyso-phosphatidylcholines (LPCs) in the PHSML. Therefore, our purpose was to verify the role of iPLA(2γ) on the production of 2-polyunsaturated LPC species and the pathogenesis of T/HS-induced ALI using an iPLA(2γ)-specific inhibitor, R-(E)-6-(bromoethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one (R-BEL).

METHODS

Male Sprague-Dawley rats were anesthetized and cannulated in blood vessels and mesenteric lymph duct. Animals in the T/HS group underwent a midline laparotomy plus hemorrhagic shock (mean arterial pressure, 35 mm Hg, 30 minutes) and 2-hour resuscitation with shed blood and 2× normal saline. Trauma/sham shock rats were performed the identical procedure without hemorrhage. R-BEL or DMSO was administered 30 minutes before T/HS or trauma/sham shock. Polyunsaturated LPCs and arachidonic acid in the PHSML were analyzed with a liquid chromatography/electrospray ionization-mass spectrometry. Furthermore, ALI was assessed by lung vascular permeability, myeloperoxidase activity, and histology.

RESULTS

T/HS increased 2-polyunsaturated LPCs and arachidonic acid in the PHSML. The R-BEL pretreatment significantly decreased these lipids and also inhibited ALI.

CONCLUSION

The iPLA(2γ) enzyme is possibly involved in the pathogenesis of ALI following T/HS through the mesenteric lymph pathway.

Early trauma-hemorrhage-induced splenic and thymic apoptosis is gut-mediated and toll-like receptor 4-dependent

Immune depression after trauma-hemorrhage has been implicated as an important factor in the pathogenesis of sepsis and septic-organ failure. Although recent studies have implicated immune-cell apoptosis as an important factor in the evolution of this posttrauma immune-suppressed state, neither the initial triggers that induce this response nor the cellular pathways through which these triggering pathways act have been fully defined. Thus, the current study tests the hypothesis that acute splenic and thymic immune-cell apoptosis developing after trauma-hemorrhagic shock (T/HS) is due to gut-derived factors carried in intestinal lymph and that this T/HS lymph-induced immune depressed state is mediated through Toll-like receptor 4 (TLR4). The first set of experiments documented that T/HS caused both thymic and splenic immune-cell apoptosis as measured by TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) and caspase-3 immunohistochemistry and that this increase in apoptosis was totally abrogated by mesenteric lymph duct ligation. In subsequent experiments, mesenteric lymph collected from animals subjected to T/HS or trauma-sham shock were injected into TLR4-deficient (TLR4mut) mice or their wild-type (WT) littermates. Trauma-hemorrhagic shock, but not trauma-sham shock, lymph caused splenic apoptosis in the WT mice. However, the TLR4mut mice were resistant to T/HS lymph-induced splenic apoptosis. Furthermore, the WT, but not the TLR4mut mice developed splenic apoptosis after actual T/HS. In conclusion, gut-derived factors appear to initiate a sequence of events that leads to an acute increase in splenic and thymic immune-cell apoptosis, and this process is TLR4-dependent.

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.

Lipidomics analysis of mesenteric lymph after trauma and hemorrhagic shock

BACKGROUND

After trauma and hemorrhagic shock (T/HS), a variety of inflammatory mediators enter the systemic circulation through mesenteric lymph ducts, leading to acute lung injury and multiple-organ dysfunction syndrome. Recent studies have demonstrated that post-HS mesenteric lymph (PHSML) activates polymorphonuclear leukocytes (PMNs) and causes vascular endothelial cell and red blood cell dysfunction. Furthermore, PHSML contains proinflammatory mediators, such as biologically active lipids. The purpose of this study was to identify the lipid mediators in PHSML and plasma by liquid chromatography/electrospray ionization mass spectrometry and then estimate the biologic activities of the identified lipids on PMNs.

METHODS

PHSML was collected from male Sprague-Dawley rats undergoing trauma (laparotomy) plus HS (40 mm Hg, 30 minutes) or sham shock (SS). The lipids in PHSML and plasma were extracted using the methods of Bligh and Dyer, and liquid chromatography/electrospray ionization mass spectrometry was performed. The biologic activities (superoxide production and elastase release) of identified lipids on human PMNs were tested.

RESULTS

Phosphatidylcholine, lysophosphatidylcholine (LPC), phosphatidylethanolamine, lysophosphatidylethanolamine (LPE), and sphingomyelin were detected in the PHSML. Furthermore, linoleoyl, arachidonoyl, and docosahexaenoyl LPCs and LPEs significantly increased in the PHSML of the T/HS group as compared with those of the T/SS group. In the plasma, arachidonoyl and docosahexaenoyl LPCs of the T/HS group also significantly increased in comparison with that of the T/SS group. Linoleoyl and arachidonoyl LPCs and LPEs showed the priming activity on N-formyl-methionyl-leucyl-phenylalanine-activated PMNs. The elastase release was also induced by linoleoyl and arachidonoyl LPCs.

CONCLUSION

Mesenteric lymph after T/HS contains biologically active lipids, such as LPCs and LPEs with polyunsaturated fatty acids, which may be involved in the pathogenesis of acute lung injury/multiple-organ dysfunction 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.

Heparin use in a rat hemorrhagic shock model induces biologic activity in mesenteric lymph separate from shock

Experimental data have shown that mesenteric lymph from rats subjected to trauma-hemorrhagic shock (THS) but not trauma-sham shock induces neutrophil activation, cytotoxicity, decreased red blood cell (RBC) deformability, and bone marrow colony growth suppression. These data have led to the hypothesis that gut factors produced from THS enter the systemic circulation via the mesenteric lymphatics and contribute to the progression of multiple organ failure after THS. Ongoing studies designed to identify bioactive lymph agents implicated factors associated with the heparin use in the THS procedure. We investigated if heparin itself was responsible for reported toxicity to human umbilical vein endothelial cells (HUVECs). Human umbilical vein endothelial cell toxicity was not induced by lymph when alternate anticoagulants (citrate and EDTA) were used in THS. Human umbilical vein endothelial cell toxicity was induced by lymph after heparin but not saline or citrate injection into trauma-sham shock and naive animals and was dose dependent. Activities of both heparin-releasable lipases (lipoprotein and hepatic) were detected in the plasma and lymph from THS and naive animals receiving heparin but not citrate or saline. Lymph-induced HUVEC toxicity correlated with lymph lipase activities. Finally, incubation of HUVECs with purified lipoprotein lipase added to naive lymph-induced toxicity in vitro. These data show that heparin, not THS, is responsible for the reported lymph-mediated HUVEC toxicity through its release of lipases into the lymph. These findings can provide alternative explanations for several of the THS effects reported in the literature using heparin models, thus necessitating a review of previous work in this field.

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.

Gut lymph and lymphatics: a source of factors leading to organ injury and dysfunction

Major trauma, shock, sepsis, and other conditions can lead to the acute respiratory distress syndrome (ARDS), which may progress to the highly lethal multiple organ dysfunction syndrome (MODS). Although a number of therapeutic strategies have been initiated, their success has been limited largely due to an incomplete understanding of the biology of MODS. However, recent studies indicate that the intestinal lymphatics serve as the primary route for nonbacterial, tissue injurious gut-derived factors, which can induce acute ARDS and MODS. The gut lymph hypothesis of ARDS and MODS thus helps clarify several important issues. First, because the lung is the first organ exposed to mesenteric lymph and not the liver (i.e., mesenteric lymph enters the subclavian vein via the thoracic duct, which, in turn, empties directly into the heart and lungs), it would explain the clinical observation that the lung is generally the first organ to fail. Second, this hypothesis provides new pathophysiologic information, thereby providing a basis for novel therapies. Finally, by studying the composition of lymph, MODS-inducing factors can be isolated and identified.

Current theories on the pathophysiology of multiple organ failure after trauma

Despite the enormous efforts to elucidate the mechanisms of the development of multiple organ failure (MOF) following trauma, MOF following trauma is still a leading cause of late post-injury death and morbidity. Now, it has been proven that excessive systemic inflammation following trauma participates in the development of MOF. Fundamentally, the inflammatory response is a host-defence response; however, on occasion, this response turns around to cause deterioration to host depending on exo- and endogenic factors. Through this review we aim to describe the pathophysiological approach for MOF after trauma studied so far and also introduce the prospects of this issue for the future.

Mesenteric lymph duct ligation improves survival in a lethal shock model

The goal of this study was to test the hypothesis that factors released from the gut and carried in the mesenteric lymph contribute to mortality in a lethal gut I/R model. To test this hypothesis, a lethal splanchnic artery occlusion (SAO) shock model was used in male Sprague-Dawley rats. In the first set of experiments, ligation of the mesenteric lymph duct (LDL), which prevents gut-derived factors carried in the intestinal lymphatics from reaching the systemic circulation, significantly improved 24-h survival after a 20-min SAO insult (0% vs. 60% survival; P < 0.05). This increase in survival in the LDL-treated rats was associated with a blunted hypotensive response. Because increased iNOS-induced NO levels have been implicated in SAO-induced shock, we measured plasma nitrite/nitrate levels and liver iNOS protein levels in a second group of animals. Ligation of the mesenteric lymph duct significantly abrogated the SAO-induced increase in plasma nitrite/nitrate levels and the induction of hepatic iNOS (P < 0.05). In an additional series of studies, we documented that LDL increased not only 24-h but also long-term 7-day survival. During the course of these studies, we made the unexpected finding that Sprague-Dawley rats from different animal vendors had differential resistance to SAO, and that the time of the year that the experiments were carried out also influenced the results. Nonetheless, in conclusion, these studies support the hypothesis that factors carried in the mesenteric lymph significantly contribute to the development of irreversible shock after SAO.

Animal models for trauma research: what are the options?

Even if trauma patients initially avoid death after trauma (due to massive blood volume loss, primary severe brain injury), they are still at risk for multiple organ failure. Thus, it is crucial to elucidate the underlying pathophysiological mechanisms of trauma/hemorrhagic shock and the immune response involved. As of now, many hemorrhagic shock/trauma studies have used various types of animal models. Despite a large number of results from these efforts, some authors have argued that animal model results are difficult to translate directly into the clinical scenario. This review summarizes the advantages and the disadvantages of using animal models in trauma/hemorrhagic shock studies and discusses the relevance of various animal studies to the clinical scenario.

Mesenteric lymph duct ligation prevents trauma/hemorrhage shock-induced cardiac contractile dysfunction

Clinical and experimental studies have shown that trauma combined with hemorrhage shock (T/HS) is associated with myocardial contractile dysfunction. However, the initial events triggering the cardiac dysfunction are not fully elucidated. Thus we tested the hypothesis that factors carried in intestinal (mesenteric) lymph contribute to negative inotropic effects in rats subjected to a laparotomy (T) plus hemorrhagic shock (HS; mean arterial blood pressure of 30-40 Torr for 90 min) using a Langendorff isolated heart preparation. Left ventricular (LV) function was assessed 24 h after trauma plus sham shock (T/SS) or T/HS by recording the LV developed pressure (LVDP) and the maximal rate of LVDP rise and fall ( +/- dP/dt(max)) in five groups of rats: 1) naive noninstrumented rats, 2) rats subjected to T/SS, 3) rats subjected to T/HS, 4) rats subjected to T/SS with mesenteric lymph duct ligation (T/SS+LDL), or 5) rats subjected to T/HS+LDL. Cardiac function was comparable in hearts from naive, T/SS, and T/SS+LDL rats. Both LVDP and +/- dP/dt(max) were significantly depressed after T/HS. The T/HS hearts also manifested a blunted responsiveness to increases in coronary flow rates and Ca(2+), and this was prevented by LDL preceding T/HS. Although electrocardiograms were normal under physiological conditions, when the T/HS hearts were perfused with low Ca(2+) levels ( approximately 0.5 mM), prolonged P-R intervals and second-degree plus Wenckebach-type atrioventricular blocks were observed. No such changes occurred in the control or T/HS+LDL hearts. The effects of T/HS were similar to those of the Ca(2+) channel antagonist diltiazem, indicating that an impairment of cellular Ca(2+) handling contributes to T/HS-induced cardiac dysfunction. In conclusion, gut-derived factors carried in mesenteric lymph are responsible for acute T/HS-induced cardiac dysfunction.

Arachidonic acid in postshock mesenteric lymph induces pulmonary synthesis of leukotriene B4

Mesenteric lymph is the mechanistic link between splanchnic hypoperfusion and acute lung injury (ALI), but the culprit mediator(s) remains elusive. Previous work has shown that administration of a phospholipase A(2) (PLA(2)) inhibitor attenuated postshock ALI and also identified a non-ionic lipid within the postshock mesenteric lymph (PSML) responsible for polymorphonuclear neutrophil (PMN) priming. Consequently, we hypothesized that gut-derived leukotriene B(4) (LTB(4)) is a key mediator in the pathogenesis of ALI. Trauma/hemorrhagic shock (T/HS) was induced in male Sprague-Dawley rats and the mesenteric duct cannulated for lymph collection/diversion. PSML, arachidonic acid (AA), and a LTB(4) receptor antagonist were added to PMNs in vitro. LC/MS/MS was employed to identify bioactive lipids in PSML and the lungs. T/HS increased AA in PSML and increased LTB(4) and PMNs in the lung. Lymph diversion decreased lung LTB(4) by 75% and PMNs by 40%. PSML stimulated PMN priming (11.56 +/- 1.25 vs. 3.95 +/- 0.29 nmol O(2)(-)/min; 3.75 x 10(5) cells/ml; P < 0.01) that was attenuated by LTB(4) receptor blockade (2.64 +/- 0.58; P < 0.01). AA stimulated PMNs to produce LTB(4), and AA-induced PMN priming was attenuated by LTB(4) receptor antagonism. Collectively, these data indicate that splanchnic ischemia/reperfusion activates gut PLA(2)-mediated release of AA into the lymph where it is delivered to the lungs, provoking LTB(4) production and subsequent PMN-mediated lung injury.

Intestinal crosstalk: a new paradigm for understanding the gut as the "motor" of critical illness

For more than 20 years, the gut has been hypothesized to be the "motor" of multiple organ dysfunction syndrome. As critical care research has evolved, there have been multiple mechanisms by which the gastrointestinal tract has been proposed to drive systemic inflammation. Many of these disparate mechanisms have proved to be important in the origin and propagation of critical illness. However, this has led to an unusual situation where investigators describing the gut as a "motor" revving the systemic inflammatory response syndrome are frequently describing wholly different processes to support their claim (i.e., increased apoptosis, altered tight junctions, translocation, cytokine production, crosstalk with commensal bacteria, etc). The purpose of this review is to present a unifying theory as to how the gut drives critical illness. Although the gastrointestinal tract is frequently described simply as "the gut," it is actually made up of (1) an epithelium; (2) a diverse and robust immune arm, which contains most of the immune cells in the body; and (3) the commensal bacteria, which contain more cells than are present in the entire host organism. We propose that the intestinal epithelium, the intestinal immune system, and the intestine's endogenous bacteria all play vital roles driving multiple organ dysfunction syndrome, and the complex crosstalk between these three interrelated portions of the gastrointestinal tract is what cumulatively makes the gut a "motor" of critical illness.

Acute pancreatitis severity is exacerbated by intestinal ischemia-reperfusion conditioned mesenteric lymph

OBJECTIVE

To determine the effect of intestinal ischemia-reperfusion (IIR) on acute pancreatitis (AP) and the role of mesenteric lymph.

SUMMARY BACKGROUND DATA

Intestinal ischemia is an early feature of AP and is related to the severity of disease. It is not known whether this contributes to the severity of AP or is a consequence.

METHODS

Two experiments are reported here using intravital microscopy and a rodent model of mild acute pancreatitis (intraductal 2.5% sodium taurocholate). In the first, rats had an episode of IIR during AP that was produced by temporary occlusion of the superior mesenteric artery (30 min or 3 x 10 min) followed by 2h reperfusion. In a second study rats with AP had an intravenous infusion of mesenteric lymph collected from donor rats that had been subjected to IIR. In both experiments the pancreatic erythrocyte velocity (EV), functional capillary density (FCD), leukocyte adherence (LA), histology and edema index were measured.

RESULTS

The addition of IIR to AP caused a decline in the pancreatic microcirculation greater than that of AP alone (EV 42% of baseline vs. 73% of baseline AP alone, FCD 43% vs 72%, LA 7 fold increase vs 4 fold increase). This caused an increased severity of AP as evidenced by 1.4-1.8 fold increase of pancreatic edema index and histologic injury respectively. A very similar exacerbation of microvascular failure and increased pancreatitis severity was then demonstrated by the intravenous infusion of IIR conditioned mesenteric lymph from donor animals.

CONCLUSIONS

Unidentified factors released into the mesenteric lymph following IIR injury are capable of exacerbating AP. This highlights an important role for the intestine in the pathophysiology of AP pathogenesis and identifies mesenteric lymph as a potential therapeutic target.

Intravenous injection of trauma-hemorrhagic shock mesenteric lymph causes lung injury that is dependent upon activation of the inducible nitric oxide synthase pathway

OBJECTIVE

To test the hypothesis that gut-derived factors carried in trauma-hemorrhagic shock (T/HS) lymph is sufficient to induce lung injury. Additionally, because our previous studies showed that T/HS-induced nitric oxide production was associated with lung injury, we examined whether T/HS lymph-induced lung injury occurs via an inducible nitric oxide synthase (iNOS)-dependent pathway.

BACKGROUND

We have previously shown that T/HS-induced lung injury is mediated by gut-derived humoral factors carried in the mesenteric lymph. However, it remains unclear whether T/HS lymph itself is sufficient to induce lung injury, or requires the activation of other factors during the T/HS period to exert its effect.

METHODS

Mesenteric lymph collected from T/HS or trauma-sham shock (T/SS) animals was injected intravenously into male rats at a rate of 1 mL/h for 3 hours. At the end of infusion, lung injury was assessed by lung permeability and lung histology. The effect of iNOS inhibition on T/HS lymph-induced lung injury was studied and this was further confirmed in iNOS knockout mice. Finally, iNOS immunohistochemistry was performed to identify the cells of origin of iNOS.

RESULTS

The injection of T/HS lymph, but not sham shock lymph, caused lung injury. This was associated with increased plasma nitrite/nitrate levels as well as induction of iNOS protein in the lung, liver, and gut. Treatment with the selective iNOS inhibitor aminoguanidine prevented T/HS lymph-induced lung injury. iNOS knockout mice, but not their wild-type controls, were resistant to T/HS lymph-induced lung injury. By immunohistochemistry, neutrophils and macrophages, rather than parenchymal cells, were the source of T/HS lymph-induced lung iNOS.

CONCLUSIONS

These results indicate that T/HS lymph is sufficient to induce acute lung injury and that lymph-induced lung injury occurs via an iNOS-dependent pathway.

BIOACTIVITY OF POSTSHOCK MESENTERIC LYMPH DEPENDS ON THE DEPTH AND DURATION OF HEMORRHAGIC SHOCK

Mesenteric hypoperfusion due to circulatory shock is a key event in the pathogenesis of subsequent distant organ injury. Postshock mesenteric lymph (PSML) has been shown to contain proinflammatory mediators elaborated from the ischemic gut. We hypothesize that the relative bioactivity of PSML depends on the depth and duration of circulatory shock. To first determine the timing of PSML bioactivity, we subjected rats to hemorrhagic shock (30 mm Hg x 45 min) and then resuscitation with 50 vol% of shed blood and normal saline (4x shed blood) over 2 h. Mesenteric lymph was collected hourly up to 6 h after shock. Superoxide release was measured from human neutrophils (polymorphonuclear neutrophils [PMNs]) incubated with lymph fractions collected from each of the hourly time points. Rats were then subjected to four different shock variations: (1) 30 mm Hg x 45 min, (2) 30 mm Hg x 15 min, (3) 45 mm Hg x 45 min, and (4) 45 mm Hg x 15 min, and were resuscitated. PSML flow depends on depth of shock, but not duration of shock or resuscitation volume. Maximal PSML bioactivity, as measured by PMN priming for the respiratory burst, occurred during the third postshock hour, which correlated with peak lymph flow rate. PSML bioactivity was greatest with 30 mm Hg x 45 min, followed by 30 mm Hg x 15 min, 45 mm Hg x 45 min, and 45 mm Hg x 15 min. Hemorrhagic shock provokes the release of bioactive agents in PSML that is dependent on both depth and duration of shock.

LYMPH FROM A PRIMATE BABOON TRAUMA HEMORRHAGIC SHOCK MODEL ACTIVATES HUMAN NEUTROPHILS

We have reported that toxic factors in intestinal lymph are responsible for acute lung injury and bone marrow suppression and that they contribute to a systemic inflammatory state based on studies in rodent models of trauma-hemorrhagic shock. Rodent models may not completely reflect the responses of injured patients. Thus, it is important to confirm these findings in primates before applying them to injured human patients with trauma. Thus, we have recently established baboon trauma-hemorrhagic shock (T/HS) and trauma-sham shock (T/SS) models that showed that gut-derived factors carried in the lymph potentiates lung injury and causes human endothelial dysfunction and suppresses human bone marrow progenitor cell growth. Here, we further investigated the effects of these primate lymph samples on human neutrophils. We hypothesized that toxic factors in baboon lymph may prime and/or activate human polymorphonuclear leukocyte (PMN) leading to overproduction of superoxide, thereby contributing to the development of adult respiratory distress syndrome and multiple organ failure. To this effect, we have examined the priming effect of baboon T/HS and T/SS lymph on PMN respiratory burst and expression of adhesion molecule in human neutrophils. The results of these studies indicate that PMN treated with baboon T/HS lymph showed significantly induced respiratory burst responses compared with PMN treated with T/SS lymph or medium when phorbol myristate acetate PMA was applied after lymph pretreatment. Secondly, we found that the expression of CD11b adhesion molecule was increased by incubation with T/HS lymph. These results suggest that baboon lymph from T/HS models can increase respiratory burst and adhesion molecule expression in human PMN, thereby potentially contributing to PMN-mediated organ injury.

Trauma-hemorrhagic shock mesenteric lymph from rat contains a modified form of albumin that is implicated in endothelial cell toxicity

It has been proposed that factors originating from the gut after severe trauma/shock are introduced into the systemic circulation through the mesenteric lymphatics and are responsible for the cellular injury and inflammation that culminates in acute multiple organ dysfunction syndrome (MODS). Indeed, it has been shown that lymph collected from shocked but not sham-shocked animals causes endothelial cell death, neutrophil activation, and bone marrow (BM) colony growth suppression in vitro. In an attempt to isolate the factor(s) in lymph responsible for endothelial cell toxicity, lymph from shock and sham animals was fractionated by solid phase extraction (SPE) and ion exchange chromatography (IEX). The separation of shock lymph by both methodologies yielded two fractions having major detectable toxicity to endothelial cells, whereas no toxicity was detected from sham lymph separations by either method. Subsequent analysis of each SPE toxic fraction by gel electrophoresis and mass spectrometry suggests the toxicity is associated with a modified form of rat serum albumin (mod-RSA) and multiple lipid-based factors. Therefore, we have been able to demonstrate by two different separation techniques that shock lymph contains two or more factors that may account for the toxicity to endothelial cells. Further investigations are needed to determine the type of RSA modification and the identity of the lipid factors and their role in MODS.

Role of the gastrointestinal tract in burn sepsis

During the last 50 years, our understanding of the role of the gastrointestinal tract as a first-line defense against the development of postburn sepsis has increased dramatically. Starting with the concept of that gut-derived bacteria cause distant injury, investigators have delineated a complex series of physical changes in the barrier of the gastrointestinal tract. Along with an understanding of these physical changes has come an appreciation of the role of the immune system in modulating postburn organ failure. Importantly, recent investigations into the role of mesenteric lymph have fundamentally changed the paradigm of organ failure and have implicated the gut as a cytokine-secreting organ. This article traces the development of key concepts in the study of burn sepsis and their clinical implications.

Hemorrhagic shock induces endothelial cell apoptosis, which is mediated by factors contained in mesenteric lymph

OBJECTIVE

Trauma-hemorrhagic shock is one of the leading causes of acute respiratory distress syndrome. This syndrome is associated with disruption of the alveolar barrier consisting of both epithelial and endothelial cells, which leads to a major increase in epithelial and microvascular permeability in the lungs. Although alveolar epithelial cell apoptosis has been documented as a contributing factor to this increase in permeability, it is unclear whether endothelial cell apoptosis occurs following trauma-hemorrhagic shock and, if so, the source of factors leading to this process.

DESIGN

Prospective animal study with concurrent control.

SETTING

Small-animal laboratory.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTIONS

Trauma-hemorrhagic shock in rats was induced by laparotomy followed by blood withdrawal to achieve a mean arterial blood pressure of 30 mm Hg for 90 mins. At the end of the shock period, the rats were resuscitated, and 3 hrs later lungs were taken for histologic analysis. In other experiments, mesenteric lymph was collected from trauma-hemorrhagic shock and trauma-sham shock rats, and the biological activity of these lymph samples was tested for their ability to kill cultured endothelial cells or endothelial cells of isolated femoral veins.

MEASUREMENTS AND MAIN RESULTS

Trauma-hemorrhagic shock triggered endothelial cell apoptosis in the lung as assessed using the Tunnel assay as well as by light and electron microscopic analysis. Since our previous studies have documented that mesenteric lymph is a major contributor to lung injury following shock, we also tested the hypothesis that factors in the mesenteric lymph were responsible for the endothelial cell apoptosis-inducing effect of shock. Preventing the mesenteric lymph from reaching the lung by mesenteric lymph duct ligation decreased endothelial cell apoptosis. Mesenteric lymph obtained from rats subjected to trauma-hemorrhagic shock elicited apoptosis in cultured endothelial cells and when placed into isolated femoral vein as well as increased endothelial cell monolayer permeability.

CONCLUSIONS

Trauma-hemorrhagic shock induces endothelial as well as epithelial cell apoptosis in the lung via factors contained in the mesenteric lymph, thereby contributing to the pathophysiology of the acute respiratory distress syndrome.

Effects of intestinal lymph on expression of neutrophil adhesion factors and lung injury after trauma-induced shock

AIM: To study how intestinal lymph after trauma-induced shock (TIS) interferes with expression of neutrophil adhesion factors (CD11b and CD18) and causes lung injury.

METHODS: Thirty-two adult healthy Sprague-Dawley rats were randomly divided into four experimental groups. Groups 1 and 2 included rats with TIS caused by hitting the mid-upper part of both side femoral bones with a 2 500 kg raw-iron, and with or without ligation of mesenteric lymph duct. Groups 3 and 4 included rats with sham-TIS and with or without ligation of mesenteric lymph duct. Expression of neutrophil CD18 and CD11b in at 1 and 3 h after a 90-min TIS/sham-TIS was evaluated. These rats were killed at 3 h after TIS/sham-TIS, and lungs were taken immediately. The main lung injury indexes (the MPO activity and lung injury score) were measured.

RESULTS: The expressions of CD18 and CD11b at 1 and 3 h after a 90-min TIS and the main lung injury indexes were significantly increased compared with those in the sham-TIS groups (P < 0.05). Moreover, at 1 and 3 h after TIS, the expressions of CD18 (32.12 ± 1.25 and 33.46 ± 0.98) and CD11b (29.56 ± 1.35 and 30.56 ± 1.85) were significantly decreased in rats with ligation of mesenteric lymph duct, compared with those (52.3 ± 1.12 and 50.21 ± 1.25, and 42.24 ± 1.24 and 42.81 ± 1.12, respectively) in those without the ligation (all P < 0.05). The main lung injury indexes in rats with TIS with ligation of mesenteric lymph duct (0.96 ± 0.12 and 6.54 ± 0.35) were also significantly decreased, compared with those (1.56 ± 0.21 and 9.56 ± 0.23) in rats with TIS without the ligation (both P < 0.05). However, there was no significant difference in expressions of CD18 and CD11b and the main lung injury indexes between the two sham-TIS groups.

CONCLUSION: Previous ligation of mesenteric lymph ducts prevents or alleviates the up-regulated expression of PMN CD18 and CD11b and the lung injury induced by TIS. Our findings also indicate that neutrophil adhesion molecule activation and lung injury during TIS appear to be caused by some factors that are released or produced by post-ischemic intestine through the mesenteric lymph pathway.

Systemic Neutrophil Priming by Lipid Mediators in Post-Shock Mesenteric Lymph Exists Across Species

BACKGROUND

Post-hemorrhagic shock mesenteric lymph (PHSML) has been linked with neutrophil (PMN) priming, endothelial cell (EC) activation, and acute lung injury (ALI) in rodent models. We have previously identified the lipid fraction of PHSML as containing the causative agent(s). Due to the lesson learned from the rodent gut bacterial translocation experience, we sought to confirm this phenomenon using a large animal model; hypothesizing that lymph collected from the porcine gut following ischemia/reperfusion (I/R) would cause PMN priming.

METHODS

Mesenteric lymph was collected from adult pigs before, during, and for 2 hours after non-lethal hemorrhagic shock (mean arterial pressure = 30 mm Hg x 45 minutes). Whole lymph and the extracted lipid fractions of the lymph were then added to isolated human and porcine PMNs and superoxide production was measured by cytochrome C reduction.

RESULTS

Hemorrhagic shock profoundly affected mesenteric lymph flow from baseline (pre-shock) flow rates of 75.63 +/- 8.86 mL/hr to 49.38 +/- 5.76 mL/hr during shock and increasing to 253.38 +/- 27.62 mL/hr after 2 hours of resuscitation. Human PMNs exposed to both whole lymph (PHSML) and its extracted lipids (PHSML Lipid) collected 2 hours after shock exhibited more than a two-fold increase in superoxide release upon activation compared with pre-shock samples: PHSML- 6.27 +/- 0.83 versus 2.56 +/- 0.60 nmolO2(-)/ 3.75 cells/mL/min, respectively (p = 0.007), PHSML Lipid- 4.93 +/- 0.34 versus 2.49 +/- 0.11 nmolO2(-)/ 3.75 cells/mL/min (p < 0.001). Similarly, porcine PMNs exhibited close to a two-fold activation when exposed to the lymph and lipid fraction: PHSML- 4.51 +/- 0.42 versus 1.06 +/- 0.28 nmolO2(-)/ 3.75 cells/mL/min (p = 0.008), PHSML Lipid-4.80 +/- 0.81 versus 1.55 +/- 0.23 nmolO2(-)/ 3.75 cells/mL/min (p = 0.002).

CONCLUSION

Mesenteric lymphatics serve as the conduit for inflammatory mediators elaborated by the post-ischemic gut in both small and large animal models. Further, the causal agent(s) exist in the lipid fraction of the lymph and are active on both human and animal PMNs.

Albumin protects against gut-induced lung injury in vitro and in vivo

OBJECTIVE

Since albumin has the ability to detoxify, we assessed whether low-dose albumin could protect against trauma/hemorrhagic shock (T/HS)-induced endothelial cell, lung, gut, and red blood cell (RBC) injury in vivo and endothelial cell injury in vitro.

SUMMARY BACKGROUND DATA

T/HS cause ischemic insult to the gut, resulting in the release of biologically active factors into the mesenteric lymph, which then cause injury to multiple distant organs.

METHODS

In vitro experiments tested the ability of albumin to reduce the cytotoxicity of mesenteric lymph from male rats subjected to T/HS (laparotomy + MAP 30 mm Hg for 90 minutes) for human umbilical vein endothelial cell (HUVEC). In subsequent in vivo experiments, the ability of albumin given as part of the resuscitation regimen to protect against T/HS-induced injury was tested by comparing the magnitude of injury in T/HS rats receiving human albumin (shed blood + 0.12, 0.24, or 0.36 g/kg) or lactated Ringer's solution (shed blood + 2 x volume of shed blood as LR) with that observed in rats subjected to trauma/sham shock. Rats were killed after a 3-hour recovery period and had lung permeability evaluated by bronchoalveolar lavage and myeloperoxidase assays, intestinal microvillous injury by histology, and RBC deformability using ektacytometry.

RESULTS

Both bovine and human albumin prevented T/HS lymph-induced HUVEC cytotoxicity in vitro, even when added 30 minutes after the lymph (viability 15 +/- 4% to 88 +/- 3%, P < 0.01). In vivo RBC deformability was better preserved by blood plus albumin than blood plus lactated Ringer's solution (P < 0.01). Likewise, albumin administration reduced T/HS-induced lung permeability and neutrophil sequestration in a dose-dependent fashion, with 0.36 g/kg of albumin effecting total lung protection (P < 0.01). In contrast, albumin treatment did not prevent T/HS-induced gut injury.

CONCLUSIONS

Low-dose albumin protects against gut lymph-induced lung, HUVEC, and RBC injury by neutralizing T/HS lymph toxicity.

A study of the biologic activity of trauma-hemorrhagic shock mesenteric lymph over time and the relative role of cytokines

BACKGROUND

Gut-derived factors in intestinal lymph have been recently shown to cause lung injury, activate neutrophils, and injure endothelial cells in rats subjected to hemorrhagic shock (T/HS). However, the time course of the appearance and disappearance of these factors in intestinal lymph is unclear. Thus the goal of this study was to characterize the biologic activity of T/HS lymph collected at various times during and after shock.

METHODS

Male rats subjected to trauma (laparotomy) plus hemorrhagic shock (mean arterial pressure, 90 mm Hg x 90 min) (T/HS) or trauma plus sham shock (T/SS) had their mesenteric lymph duct catheterized. Mesenteric lymph collected before shock, during shock, and hourly for 6 hours after shock was assayed for cytokine levels (tumor necrosis factor, granulocyte-macrophage colony-stimulating factor, interleukin-1, and transforming growth factor-beta) as well as biologic activity on endothelial cells (cytotoxicity and permeability) and neutrophils (CD11b adhesion molecule expression and respiratory burst activity).

RESULTS

T/HS, but not T/SS, lymph injured endothelial cells and activated neutrophils, although the cytokine levels did not differ between the T/HS and T/SS lymph samples. The biologic activity of T/HS lymph appeared during the shock (gut ischemic) period. The temporal pattern of activity varied on the basis of the biologic activity being tested, with the neutrophil-activating properties of the T/HS lymph persisting longest.

CONCLUSIONS

These results suggest that gut ischemia itself is sufficient to induce the production of biologically active T/HS lymph and that the temporal pattern of biologic activity varies over time on the basis of the property being tested. Consequently, studies directed at identifying the active factors in T/HS lymph must take these temporal patterns of activity into account.

Factors in intestinal lymph after shock increase neutrophil adhesion molecule expression and pulmonary leukosequestration

BACKGROUND

Because the ischemic gut may produce factors that initiate systemic inflammation, we tested the hypothesis that factors released from the gut into the mesenteric lymphatics increase neutrophil (PMN) adhesion molecule expression after trauma and shock.

METHODS

At 1 and 4 hours after hemorrhagic shock (30 mm Hg x 90 minutes) plus trauma (laparotomy) (T/HS) or sham-shock (T/SS), with or without mesenteric lymph duct ligation, PMN CD11b and CD18 expression was assessed in male rats. In additional rats, mesenteric lymph samples were tested for their ability to increase PMN CD11b expression in vitro. Lastly, at 4 hours after T/SS or T/HS with or without lymph duct ligation, pulmonary PMN sequestration was measured.

RESULTS

Compared with T/SS rats, T/HS was associated with up-regulation of PMN CD11b and CD18 expression, which was largely prevented by ligation of the mesenteric lymph duct (p < 0.01). Lymph duct ligation also prevented T/HS-induced pulmonary leukocyte sequestration (p < 0.01). In addition, mesenteric lymph from rats subjected to T/HS but not T/SS increased CD11b expression (p < 0.01).

CONCLUSION

Factors produced or released by the postischemic intestine and carried in the mesenteric lymph appear responsible for PMN activation and pulmonary PMN sequestration after an episode of T/HS.

Clinically relevant hypertonicity prevents stored blood- and lipid-mediated delayed neutrophil apoptosis independent of p38 MAPK or caspase-3 activation

BACKGROUND

Delayed apoptosis of primed neutrophils (PMNs) may facilitate PMN-mediated tissue injury leading to postinjury multiple organ failure. Aged (42-day-old) stored red blood cells (RBC42) delay PMN apoptosis through proinflammatory phospholipids such as platelet-activating factor (PAF) and lyso-phosphatidylcholine (LPC). Hypertonic saline (HTS) attenuates PMN cytotoxic functions. We hypothesized that clinically relevant HTS would provoke PMN apoptosis, as well as prevent stored blood- and lipid-mediated delayed PMN apoptosis through activation of p38 mitogen-activated protein kinase (MAPK) and caspase-3.

METHODS

PMNs harvested from healthy volunteers were incubated (5% CO(2), 37 degrees C, 24 hr) with RBC42 plasma, PAF (20 microM), or LPC (4.5 microM), with or without the p38 MAPK inhibitor SB 203580, the caspase-3 inhibitor zDEVD-fmk (10 micromol/L) or the pan-caspase inhibitor zVAD-fmk (20 micromol/L). Duplicate samples were preincubated in HTS (Na [180 mM]). Apoptotic index (% PMNs undergoing apoptosis) was assessed morphologically. p38 MAPK activation was assessed by Western blotting. Caspase-3 activity was measured colorimetrically.

RESULTS

PAF, LPC, and RBC42 plasma delayed apoptosis; HTS increased apoptosis compared with controls. HTS prevented PAF, LPC, and RBC42-delayed apoptosis. p38 MAPK was not activated by HTS; its inhibition had no effect on the actions of HTS. Caspase inhibition attenuated the ability of HTS to increase apoptosis, but it did not affect the ability of HTS to restore healthy PMN apoptosis in the presence of RBC42.

CONCLUSION

HTS increases PMN apoptosis and prevents stored blood- and lipid-mediated delayed PMN apoptosis. HTS may activate caspase-3, but alternative signaling pathways appear to be involved in modulating the effects of lipids on PMN apoptosis.

Hypertonic saline resuscitation limits neutrophil activation after trauma-hemorrhagic shock

There is evidence suggesting that the ischemic gut is a major source of factors that lead to neutrophil activation, and that neutrophil activation can be reduced by hypertonic saline resuscitation. Thus, we tested whether trauma-hemorrhagic shock-induced neutrophil activation can be reduced by hypertonic saline resuscitation, as well as whether hypertonic saline reduces the ability of mesenteric lymph from shocked animals to activate neutrophils. Male Sprague-Dawley rats subjected to trauma (laparotomy), plus 90 min of shock [mean arterial pressure (MAP) MAP = 30 mmHg] or sham shock were resuscitated with Ringer's lactate or 7.5% hypertonic saline at an equivalent sodium load. Whole blood samples were collected before shock as well as at 1 and 2 h after the end of the shock period for neutrophil CD11b and CD18 expression measurements. In a second set of experiments, mesenteric lymph samples collected from rats subjected to trauma plus hemorrhagic shock (T/HS) or trauma plus sham-shock (T/SS) and resuscitated with Ringer's lactate or hypertonic saline were tested for their ability to modulate PMN CD11b, CD18, or L-selectin expression, as well as prime PMN for an augmented respiratory burst. To avoid confounding results due to interspecies differences, while at the same time looking at potential human responses, both naive rat and human PMN were tested. Both CD11b and CD18 expression were increased in PMN harvested from rats subjected to T/HS and resuscitated with Ringer's lactate solution, but not in T/HS rats resuscitated with hypertonic saline. These results indicate that PMN activation is increased to a greater extent in Ringer's lactate-resuscitated than hypertonic saline-resuscitated animals. Likewise, mesenteric lymph from the T/HS rats resuscitated with Ringer's lactate increased naive rat and human PMN CD11b and CD18 expression to a greater extent than did T/HS lymph from the hypertonic saline-treated rats. Additionally, T/HS lymph from the Ringer's lactate- but not the hypertonic saline-treated rats induced PMN L-selectin shedding. Lastly, T/HS lymph from the Ringer's lactate-treated rats induced the greatest PMN respiratory burst. These results indicate that resuscitation from T/HS with hypertonic saline is associated with less PMN activation than resuscitation with Ringer's lactate, and that factors produced or released by the postischemic intestine and carried in the mesenteric lymph contribute to neutrophil activation after an episode of T/HS.

Neutrophil apoptosis is delayed by trauma patients' plasma via a mechanism involving proinflammatory phospholipids and protein kinase C

BACKGROUND

Delayed apoptosis of primed neutrophils (PMNs) may facilitate PMN-mediated tissue injury leading to multiple organ failure (MOF). We previously reported delayed apoptosis and priming of PMNs in severely injured patients at risk for MOF. Our in vitro and in vivo data have implicated phospholipids in PMN cytotoxicity following trauma and shock. The phospholipid signaling pathway remains to be elucidated, but may involve protein kinase C (PKC). We hypothesized that circulating platelet-activating factor (PAF) and PAF-like proinflammatory phospholipids mediate delayed postinjury PMN apoptosis and that PKC is integral to the signaling pathway.

METHODS

Blood was drawn from severely injured patients (n = 6; mean injury severity score = 21 and transfusion = 10 units) at 6 h postinjury. The plasma fraction was isolated and incubated (5% CO(2), 37 degrees C, 24 h) with PMNs harvested from healthy volunteers. Some PMNs were preincubated with a PAF receptor antagonist (WEB 2170, 400 microM) or a PKC inhibitor (Bis I, 1 microM). Apoptotic index (% PMNs undergoing apoptosis) was assessed morphologically.

RESULTS

Trauma patients' plasma delayed PMN apoptosis compared with plasma from controls. The PMN apoptotic index was not altered by WEB 2170 or Bis I alone; however, WEB 2170 or Bis I pretreatment abrogated delayed PMN apoptosis in response to trauma patients' plasma.

CONCLUSION

Trauma patients' plasma delays apoptosis of PMNs. Our data implicate PAF-like phospholipids in this effect, and PKC appears to be integral in the signaling process. Further elucidation of specific lipids and signaling pathways may reveal clinically accessible therapeutic targets to prevent PMN-mediated hyperinflammation.

Trauma-hemorrhage-induced neutrophil priming is prevented by mesenteric lymph duct ligation

Our objective in this study was to test the hypothesis that priming of neutrophils (PMN) in vivo by trauma-hemorrhagic shock (T/HS) is mediated by factors carried in intestinal lymph that prime PMNs by enhancing their responses to inflammatory mediators. Previous studies have shown that T/HS-induced lung injury is mediated by factors contained in mesenteric lymph and that ligation of the main mesenteric lymph duct (LDL) can prevent T/HS-induced lung injury. Since T/HS-induced lung injury is associated with PMN infiltration, one mechanism underlying this protective effect may be the prevention of PMN priming and activation. Therefore, we assessed the ability of T/HS to prime PMN responses to inflammatory agonists, and the ability of mesenteric lymph duct division to protect against such T/HS-induced PMN priming in an all-rat system. PMN were collected from male rats 6 h after laparotomy (trauma) plus hemorrhagic shock (30 mmHg for 90 min; T/HS) or trauma plus sham shock (T/SS). Uninstrumented rats were used as controls (UC). In a second set of experiments, rats were subjected to T/HS with or without mesenteric lymph duct division. PMN were then stimulated with chemokine (GRO, MIP-2) and lipid (PAF) chemoattractants, and cell calcium flux was used to quantify responses to those agonists. T/SS primed PMN responses to GRO, MIP-2. and PAF in comparison to UC rats, but the addition of shock (T/HS) amplified PMN priming in a significant manner, especially in response to GRO. Mesenteric lymph duct division prior to T/HS diminished PMN priming to the levels seen in T/SS. This reversal of priming was significant for GRO and GRO/MIP-2 given sequentially, with the other agonist regimens showing similar trends. The results support the concept that trauma and hemorrhagic shock play important additive roles in inflammatory PMN priming. Entry of gut-derived inflammatory products into the circulation via mesenteric lymph seems to play a dominant role in mediating the conversion of physiologic shock insults into immunoinflammatory PMN priming. Shock-induced gut lymph priming enhances PMN responses to many important chemoattractants, most notably the chemokines, and mesenteric lymph duct division effectively reverses such priming to priming levels seen in trauma without shock.

Hyperosmolarity abrogates neutrophil cytotoxicity provoked by post-shock mesenteric lymph

Hypertonic saline (HTS) resuscitation inhibits acute lung injury in animal models of shock, but some argue this may simply represent more efficient fluid resuscitation. Inflammatory mediators within mesenteric lymph have been identified as a link between splanchnic hypoperfusion and acute respiratory distress syndrome (ARDS). We hypothesize that HTS resuscitation abrogates post-shock lymph-mediated neutrophil (PMN) priming and PMN-mediated human endothelial cell cytotoxicity. Mesenteric lymph was collected from rats (n = 5) before (control), during non-lethal hemorrhagic shock, defined as a mean arterial pressure (MAP) of 40 mmHg for 30 min, and after resuscitation (shed blood + 2 x lactated Ringers (LR) versus 7.5% NaCl, 4 cc/kg, over 5 min). Isolated human PMNs were primed with physiologic concentrations (5% v:v) of lymph either from animals resuscitated with LR or HTS and activated with either PMA or fMLP. In a separate set of experiments, human PMNs were primed with LR lymph after incubation with HTS (180 mM NaCl). The maximal rate of superoxide production was measured by reduction of cytochrome C. In addition, the effect of HTS pretreatment on PMN adherence to human pulmonary microvascular endothelial cells (HMVEC) and PMN-mediated cytotoxicity was determined after lymph-mediated PMN priming. PHSML primed isolated PMNs above buffer controls and pre-shock lymph in a normotonic environment; HTS resuscitation abrogated this effect. HTS preincubation of isolated PMNs inhibited PHSML-induced PMN priming, adherence to HMVECs, and PMN-mediated HMVEC cytotoxicity. Hypertonic resuscitation (HTS) abrogates PHSML pniming of the PMN and PMN-mediated HMVEC cytotoxicity. Furthermore, incubation of PMNs in clinically relevant HTS (180 mM NaCl) prevents PHSML PMN priming and PMN:HMVEC interactions. These studies suggest inhibition of PMN signal transduction is a mechanism whereby HTS resuscitation abrogates acute lung injury.

Pooled human albumin primes neutrophils

Human pooled albumin has traditionally been used both to pacify the artificial surfaces in a cardiopulmonary bypass circuit and also for volume repletion following surgery. In evaluating the routine use of albumin in multiple phases of cardiac surgery, conscientious surgical teams must assess both the physiological and financial price of albumin. Albumin indiscriminately binds many plasma proteins and lipids. In this series of experiments, we explored the influence of highly purified albumin devoid of bound lipids and globulins on both receptor-dependent (FMLP) and receptor-independent (PMA) priming/activation of human neutrophils. We believe that it is important to distinguish the direct influence of albumin from the albumin-bound proteins and lipids. We, therefore, also examined the effect of clinically accessible human pooled albumin on human neutrophils. We observed a dose-dependent priming/activation (elastase release) of human neutrophils by both pooled and purified albumin. We conclude that it is increasingly difficult to justify the routine use of albumin in cardiac surgical patients.

Mesenteric lymph is responsible for post-hemorrhagic shock systemic neutrophil priming

BACKGROUND

Hemorrhagic shock-induced splanchnic hypoperfusion has been implicated as a priming event in the two event model of multiple organ failure (MOF). We have previously shown that early postinjury neutrophil (PMN) priming identifies the injured patient at risk for MOF. Recent in vitro studies have demonstrated that postshock mesenteric lymph primes isolated human neutrophils. We hypothesize that lymphatic diversion before hemorrhagic shock abrogates systemic PMN priming and subsequent lung injury.

METHODS

Sprague-Dawley rats (n >or= 5 per group) underwent hemorrhagic shock (MAP 40 mm Hg x 30 min) and resuscitation (shed blood + 2x crystalloid) with and without mesenteric lymphatic duct diversion. Sham animals underwent anesthesia and laparotomy. Whole blood was taken 2 hours after resuscitation, heparinized, and incubated for 5 min at 37 degrees C. Surface expression of CD11b (a marker for PMN priming) was determined by flow-cytometry compared with isotype controls. In addition, lung myeloperoxidase (MPO) was measured for PMN sequestration, and Evans blue lung leak was assessed in the bronchoalveolar lavage fluid in sham, and shock +/- lymph diversion animals.

RESULTS

Hemorrhagic shock resulted in increased surface expression of PMN CD11b relative to sham (23.8 +/- 6.7 vs. 9.9 +/- 0.6). Mesenteric lymphatic diversion before hemorrhagic shock abrogated this effect (8.0 +/- 2.6). Lung PMN accumulation, as assessed by MPO, was greater in the lungs of nondiverted (113 +/- 14 MPO/mg lung) versus sham (55 +/- 4 MPO/mg lung, p < 0.05); lymph diversion reduced lung PMNs to control levels (71 +/- 6.5 MPO/mg lung, p < 0.05). Evans blue lung leak was 1.6 times sham in the hemorrhagic shock group; this was returned to sham levels after lymph diversion (p < 0.05).

CONCLUSION

Post-hemorrhagic shock mesenteric lymph primes circulating PMNs, promotes lung PMN accumulation, and provokes acute lung injury. Lymphatic diversion abrogates these pathologic events. These observations further implicate the central role of mesenteric lymph in hemorrhagic shock-induced lung injury. Characterizing the PMN priming agents could provide insight into the pathogenesis of postinjury MOF and ultimately new therapeutic strategies.

Secondary abdominal compartment syndrome is a highly lethal event

BACKGROUND

Recent reports have described resuscitation-induced, "secondary" abdominal compartment syndrome (ACS) in trauma patients without intra-abdominal injuries. We have diagnosed secondary ACS in a variety of nontrauma as well as trauma patients. The purpose of this review is to characterize patients who develop secondary ACS.

METHODS

Our prospective ACS database was reviewed for cases of secondary ACS. Physiologic parameters and outcomes were recorded. Data are expressed as mean +/- SEM.

RESULTS

Fourteen patients (13 male, aged 45 +/- 5 years) developed ACS 11.6 +/- 2.2 hours following resuscitation from shock. Eleven (79%) had required vasopressors; the worst base deficit was 14.1 +/- 1.9. Resuscitation included 16.7 +/- 3.0 L crystalloid and 13.3 +/- 2.9 red blood cell units. Decompressive laparotomy improved intra-abdominal, systolic, and peak airway pressures, as well as urine output; however, mortality was 38% among trauma and 100% among nontrauma patients.

CONCLUSIONS

Secondary ACS may be encountered by general surgeons in a variety of clinical scenarios; resuscitation from severe shock appears to be the critical factor. Early identification and abdominal decompression are essential. Unfortunately, in our experience, this is a highly lethal event.