Polymorphonuclear neutrophil contribution to induced tolerance to bacterial lipopolysaccharide

Suppression of plasminogen activator inhibitor-1 (PAI-1) activity by crocin ameliorates lipopolysaccharide-induced thrombosis in rats

The imbalance between clot formation and fibrinolysis is mainly attributed to increased levels of plasminogen activator inhibitor type 1 (PAI-1), an inhibitor of fibrinolysis closely involved in inflammatory responses such as septic shock. This increase is mediated by many factors, including reactive oxygen species (ROS). The present study was designed to evaluate the prophylactic effect of crocin, a potent natural antioxidant, on PAI-1 in the rat model of endotoxic shock. Lipopolysaccharide-infused rats (500 μg/kg) showed significant changes in thrombosis-related haematological parameters such as decrease of platelet blood counts and increase (7 fold) of PAI-1 concentration in blood plasma. No effect on t-PA activity was observed. Crocin administration in two different doses (10 mg/kg and 100 mg/kg) 30 min prior to the injection of LPS, inhibited the reduction of platelet counts and ameliorated the concentration of PAI-1 in the liver and the brain. Moreover, crocin inhibited the deposition of fibrin in the renal glomeruli. No significant changes were recorded in the healthy groups of crocin (10 mg/kg and 100 mg/kg) compared to the control group. These data demonstrate the potential of crocin to prevent LPS-induced organ injury and suggest it is worthwhile to investigate the use of antioxidants for the treatment of septicemia.

Dual blockade of endothelin action exacerbates up-regulated VEGF angiogenic signaling in the heart of lipopolysaccharide-induced endotoxemic rat model

AIMS

Sepsis is a cluster of heterogeneous syndromes associated with progressive endotoxemic developments, ultimately leading to damage of multiple organs, including the heart. However, the pathogenesis of sepsis-induced myocardial dysfunction is still not fully understood. The present study is the first to examine alterations in expression of key angiogenic signaling system mediated by vascular endothelial growth factor (VEGF) in septic heart and the effects of endothelin dual blocker (ETDB) on it.

MAIN METHODS

Normal Wistar rats were either administered with: a) vehicle only (control group), b) lipopolysaccharide only (LPS: 15 mg/kg) and then sacrificed at different time points (1 h, 3 h, 6 h and 10 h), and c) the last group was co-administered with LPS and ETDB (SB-209670, 1 mg/kg body weight) for 6 h and then sacrificed.

KEY FINDINGS

Administration of LPS resulted in increases in levels of: a) serum tumor necrosis factor (TNF)-α, b) serum VEGF and c) serum endothelin (ET)-1 levels accompanied by up-regulation of cardiac VEGF and its downstream angiogenic signaling molecules. While cardiac TNF-α level was unchanged among experimental groups, cardiac ET-1 level was significantly higher in LPS-administered group.

SIGNIFICANCE

We conclude that elevation in VEGF angiogenic signaling may be triggered by diminished oxygenation in the myocardium following LPS administration as a consequence of sepsis-induced microvascular dysfunction. Because of this cardiac dysfunction, oxygen supply may be inadequate at microregional level to support the normal heart metabolism and function. ETDB at 6 h further increased the elevated levels of VEGF angiogenic signaling in endotoxemic heart.

Glycogen synthase kinase 3 inhibitor attenuates endotoxin-induced liver injury

BACKGROUND/AIMS

Endotoxin (lipopolysaccharide, LPS)-induced acute liver injury was attenuated by endotoxin tolerance (ET), which is characterized by phosphatidylinositol 3-kinase pathway/Akt signaling. Glycogen synthase kinase 3 (GSK-3) acts downstream of phosphatidylinositol 3-kinase pathway/Akt and GSK-3 inhibitor protects against organic injury. This study evaluates the hypothesis that ET attenuated LPS-induced liver injury through inhibiting GSK-3 functional activity and downstream signaling.

METHODS

Sprague-Dawley rats with or without low-dose LPS pretreatment were challenged with or without large dose of LPS and subsequently received studies. Serum tumor necrosis factor-alpha, interleukin-10, alanine aminotransferase, lactate dehydrogenase, and total bilirubin levels were analyzed, morphology of liver tissue was performed, glycogen content, myeloperoxidase content, phagocytosis activity of Kupffer cells, and the expression and inhibitory phosphorylation as well as kinase activity of GSK-3 were examined. Survival after LPS administration was also determined.

RESULTS

LPS induced significant increases of serum TNF-α, alanine aminotransferase, lactate dehydrogenase, and total bilirubin (P < 0.05), which were companied by obvious alterations in liver: the injury of liver tissue, the decrease of glycogen, the infiltration of neutrophils, and the enhancement of phagocytosis of Kupffer cells (P < 0.05). LPS pretreatment significantly attenuated these alterations, promoted the inhibitory phosphorylation of GSK-3 and inhibited its kinase activity, and improved the survival rate (P < 0.05).

CONCLUSIONS

ET attenuated LPS-induced acute liver injury through inhibiting GSK-3 functional activity and its downstream signaling.

Myocardial hypoxia-inducible HIF-1alpha, VEGF, and GLUT1 gene expression is associated with microvascular and ICAM-1 heterogeneity during endotoxemia

The systemic inflammatory response to infection is the leading cause of mortality in North American intensive-care units. Although much is known about inflammatory mediators, the relationships between microregional inflammation, microvascular heterogeneity, hypoxia, hypoxia-inducible gene expression, and myocardial dysfunction are unknown. Male Sprague-Dawley rats were injected intraperitoneally with LPS to test the hypothesis that sepsis-induced local inflammation and increased microvascular heterogeneity are spatially and temporally associated with hypoxia, hypoxia-inducible gene expression, and decreased left-ventricular contractility. Using a combination of three-dimensional microvascular imaging, tissue Po(2), and pressure-volume conductance measurements, we found that 5 h after LPS, minimum oxygen-diffusion distances increased (P < 0.05), whereas tissue oxygenation and contractility both decreased (P < 0.05) in the left ventricle. Real-time RT-PCR analysis revealed that the hypoxia-inducible genes hypoxia-inducible factor (HIF)-1alpha, VEGF, and glucose transporter (GLUT) 1 were all upregulated (P < 0.05) in the left ventricle. Tissue regions expressing ICAM-1, obtained by using laser-capture microdissection, had increased HIF-1alpha and GLUT1 (P < 0.05) gene expression. VEGF gene expression was more diffuse. In LPS rats, GLUT1 gene expression correlated (P < 0.05) with left-ventricular contractility. In 5-h hypoxic cardiomyocytes, we found strong transient HIF-1alpha, weak VEGF, and greater prolonged GLUT1 gene expression. By comparison, the HIF-1alpha-GLUT1 gene-induction pattern was reversed in the left ventricle of LPS rats. Together, these results show that LPS induces hypoxia in the left ventricle associated with increased microvascular heterogeneity and decreased contractility. HIF-1alpha and GLUT1 gene induction are related to a heterogeneous ICAM-1 expression and may be cardioprotective during the onset of septic injury.

Effects of dopexamine on the intestinal microvascular blood flow and leukocyte activation in a sepsis model in rats

INTRODUCTION

The administration of dopexamine may constitute a therapeutical option to improve hepatosplanchnic perfusion in sepsis. In order to verify this hypothesis, we administered dopexamine in an experimental sepsis model in rats.

METHODS

This prospective, randomized, controlled laboratory study was conducted in 42 Wistar rats. The animals were divided into 3 groups. Group 1 (CON group) served as control group. The Animals of groups 2 (LPS Group) and 3 received an endotoxin infusion (20 mg/kgfor 15 min). In addition, in group 3 (DPX group) dopexamine was administered 0.5 microg/kg/minover 4 hours. One half of the animals of each group underwent studies of intestinal microvascular blood flow (IMBF) using laser Doppler fluxmetry. In the other half an intravital microscopic evaluation of the leukocyte endothelium cell interaction in the intestinal microcirculation was performed. Functional capillary denstity (FCD) in the intestinal mucosaand the circular as well as the longitudinal muscle layer was estimated.

RESULTS

One hour after endotoxin challenge IMBF decreased significantly in the untreated LPS group to 51% compared to baseline (p<0.05). In DPX treated endotoxin animals we found significantly higher values at the level of CON group. The after endotoxin challenge impaired FCD was improved by dopexamine in the longitudinal (DPX + 33% vs. LPS; p <0.05) and in the circular muscle layer (DPX + 48% vs. LPS; p < 0.05) as a result of dopexamine administration. The administration of dopexamine reduced the count of firmly adherent leukocytes when compared to the untreated LPS group (-31%, p<0.05). TNF-alpha plasma levels were reduced by dopexamine infusion (LPS group 3637 +/- 553 pg/mL; DPXgroup 1933 +/- 201 pg/mL) one hour after endotoxin challenge.

CONCLUSIONS

The administration of dopexamine improved IMBF and FCD as parameters of intestinal microcirculation and reduced leukocyte activation as a parameter of inflammation in experimental sepsis.

Analysis of inflammation

In the past, inflammation has been associated with infections and with the immune system. But more recent evidence suggests that a much broader range of diseases have telltale markers for inflammation. Inflammation is the basic mechanism available for repair of tissue after an injury and consists of a cascade of cellular and microvascular reactions that serve to remove damaged and generate new tissue. The cascade includes elevated permeability in microvessels, attachment of circulating cells to the vessels in the vicinity of the injury site, migration of several cell types, cell apoptosis, and growth of new tissue and blood vessels. This review provides a summary of the major microvascular, cellular, and molecular mechanisms that regulate elements of the inflammatory cascade. The analysis is largely focused on the identification of the major participants, notably signaling and adhesion molecules, and their mode of action in the inflammatory cascade. We present a new hypothesis for the generation of inflammatory mediators in plasma that are derived from the digestive pancreatic enzymes responsible for digestion. The inflammatory cascade offers a large number of opportunities for development of quantitative models that describe various aspects of human diseases.

Endotoxin increases ascorbate recycling and concentration in mouse liver

Sublethal exposure to Escherichia coli endotoxin [lipopolysaccharide (LPS)] attenuates the lethal effects of subsequent insults associated with oxidative stress, such as higher LPS dose, septic peritonitis, and ischemia. Because administration of the antioxidant ascorbate protects against these same insults and injection of dehydroascorbic acid (DHAA) protects against ischemia, the hypothesis that sublethal LPS increases endogenous ascorbate concentration and recycling (i.e., synthesis from DHAA) was tested. Injection of LPS [5 x 10(6) endotoxin units/kg body weight, i.p.] in mice caused a temporary inhibition of food intake, which was significant by 20 h and recovered within 3 d. LPS increased ascorbate concentration in adrenal gland, heart, kidney, and liver. LPS had similar effects in wild-type and Slc23a2+/- mice despite the latter's deficiency in the ascorbate transporter SVCT2. In liver, the ascorbate response to LPS was not accompanied by change in glutathione concentration. LPS decreased gulonolactone oxidase activity, which is rate-limiting for de novo synthesis of ascorbate from glucose, but increased the rate of DHAA reduction to ascorbate. In conclusion, sublethal endotoxin increases ascorbate recycling in liver and ascorbate concentration in liver, adrenal gland, heart, and kidney. The enhanced rate of ascorbate production from DHAA may protect these organs against the reactive oxygen species produced by subsequent, potentially lethal challenges.

A new hypothesis for microvascular inflammation in shock and multiorgan failure: self-digestion by pancreatic enzymes

Shock is accompanied by a severe inflammatory cascade in the microcirculation, the origin of which has been hypothesized in the past to be associated with specific mediators such as endotoxin, oxygen free radicals, nitric oxide, cytokines, and lipid products. But no intervention with clinical effectiveness has been derived from these ideas to date. The authors propose here a new hypothesis suggesting that degradative enzymes, synthesized in the pancreas as part of normal digestion, may play a central role in shock and multiorgan failure. These powerful enzymes have the ability to digest almost every biological material. Self-digestion (i.e. autodegradation) is prevented by compartmentalizing the fully activated degradative enzymes in the intestinal lumen by the mucosal barrier. In shock, maintenance of the mucosal barrier is impaired and it becomes permeable to pancreatic enzymes. Digestive enzymes thereby gain access to the wall of the intestine and initiate self-digestion of submucosal extracellular matrix proteins and interstitial cells. The process leads to generation and release of a host of strong inflammatory mediators. The authors hypothesize that inhibition of pancreatic enzymes in the lumen of tile intestine can serve to attenuate formation of these inflammatory mediators in ischemic tissues following hemorrhagic shock, and consequently prevent cell and tissue injury as well as multiorgan failure.

Three-dimensional capillary geometry in gut tissue

Accurate characterization of capillary geometry is of the utmost importance for physiological tissue studies such as oxygen transport. We show that 3D microscopy can be used to measure tissue capillary geometry both in normal and disease states. We imaged fluorescently labeled gut mucosa capillary beds of three control rats and three rats 4 hours after i.p. injection of 9 mg/kg endotoxin. We used serial optical sectioning microscopy coupled with deconvolution to reconstruct 3D capillary geometry. Theoretical point spread functions accounting for depth into the specimen resulted in better reconstructions than experimentally measured point spread functions. We next derived the distribution of the shortest distances to the nearest capillary from all extravascular tissue voxels. In normal rats the shortest-distance distributions were remarkably constant despite widely varying capillary geometry. Furthermore, the mean of the shortest-distance distributions increased significantly for endotoxemic rats (4.8+/-0.4 microm) compared to controls (4.3+/-0.3 microm, P<0.05). Hence, serial sectioning microscopy provides an accurate venue for measuring physiologically relevant 3D capillary structure.

Staphylococcal alpha-toxin provokes neutrophil-dependent cardiac dysfunction: role of ICAM-1 and cys-leukotrienes

The role of polymorphonuclear neutrophils (PMN) in septic myocardial dysfunction is presently unknown. Staphylococcus aureus infections are frequently associated with septic sequelae. Therefore, we perfused isolated rat hearts with low doses of alpha-toxin, the major staphylococcal exotoxin, followed by application of human PMN, N-formyl-methionyl-leucyl-phenylalanine, and arachidonic acid. In contrast to sham-perfused hearts (no alpha-toxin), a rise in coronary perfusion pressure (CPP) and a reduction of contractile function were noted, and cardiac expression of intercellular adhesion molecule (ICAM)-1 was detected by immunohistochemical methods and real-time PCR. Histological analysis and myeloperoxidase activity indicated cardiac PMN accumulation in alpha-toxin-challenged hearts. Major quantities of cysteinyl (cys)-leukotrienes (LT), LTB4, and 5-hydroxyeicosatetraenoic acid (5-HETE) were found in the perfusate of alpha-toxin-exposed hearts. With an anti-ICAM-1 antibody, neutrophil accumulation, leukotriene (LT) synthesis, coronary vasoconstriction, and the accompanying cardiodepression were suppressed. Similarly, the lipoxygenase inhibitor MK-886 blocked LT synthesis and maintained cardiac function. We conclude that low-dose alpha-toxin provokes coronary endothelial ICAM-1 expression and neutrophil accumulation, with subsequent synthesis of cys-LTs, LTB4, and 5-HETE under conditions of appropriate stimulation. This response is linked with coronary vasoconstriction and contractile dysfunction, with cys-LT synthesis and maldistribution of perfusion offered as likely underlying mechanisms.

Peritonitis induces rat cardiac myocytes to promote polymorphonuclear leukocyte emigration and activate endothelial cells: effect of lipopolysaccharide pretreatment

OBJECTIVE

Peritonitis induced by cecal ligation and perforation results in inflammation and dysfunction of the rat myocardium, an organ remote from the locus of infection. This peritonitis-induced pathology can be prevented by pretreating these animals with lipopolysaccharide before cecal ligation and perforation. In the present study, we assessed a) whether cardiomyocytes obtained from rats subjected to cecal ligation and perforation could induce polymorphonuclear leukocyte transendothelial migration, b) whether these cardiomyocytes could activate endothelial cells (increased proadhesive phenotype), and c) whether these responses could be attenuated by lipopolysaccharide pretreatment.

DESIGN

Prospective animal study.

SETTING

Experimental animal laboratory.

SUBJECTS

Male Sprague Dawley rats.

INTERVENTIONS

Lipopolysaccharide pretreated and nonpretreated rats were subjected to cecal ligation and perforation or to laparotomy. Myocytes were isolated 6 hrs after surgery and used for in vitro experiments.

MEASUREMENTS AND MAIN RESULTS

Myocytes isolated from cecal ligation and perforation rats promoted migration of polymorphonuclear leukocytes across a rat endothelial cell monolayer, an effect prevented by platelet activating factor receptor antagonists. Myocytes isolated from these animals also increased surface level expression of intercellular adhesion molecule-1 on rat endothelial cells, an effect also prevented by platelet activating factor receptor antagonists. Myocytes isolated from rats pretreated with lipopolysaccharide and then subjected to cecal ligation and perforation did not a) promote polymorphonuclear leukocyte transendothelial migration or b) increase intercellular adhesion molecule-1 surface expression on endothelial cells.

CONCLUSIONS

Our findings indicate that induction of peritonitis results in a systemic response that induces cardiac myocytes to become proinflammatory (i.e., these myocytes produce chemotactic factors and activate endothelial cells). This effect of cecal ligation and perforation is abrogated by pretreating animals with lipopolysaccharide before induction of peritonitis.

Effects of endotoxin on neutrophil-mediated ischemia/reperfusion injury in the rat heart in vivo

We have previously shown that a nonlethal dose of lipopolysaccharide (LPS) decreases L-selectin expression of neutrophils (PMNs), thereby preventing PMN-mediated reperfusion injury in the isolated heart. In the present study we determined whether or not that dose of LPS would protect hearts during in vivo ischemia and reperfusion by preventing PMN-induced reperfusion injury. Rats receiving saline vehicle showed marked myocardial injury (necrotic area/area at risk = 82%+/-2%) and significant depression in left ventricular function as assessed in the isolated isovolumic heart preparation at constant flow rates of 5, 10, 15, and 20 ml/min. The administration of LPS (100 microg/kg body wt) 7 hr prior to ischemia resulted in a reduction in myocardial damage (necrotic area/area at risk = 42%+/-3%) and preservation of function. Myocardial function was similar to that of sham ischemic saline- and LPS-treated rats. Moreover, PMN infiltration as determined by histology was quantitatively more severe in hearts of saline-treated rats than in hearts of LPS-treated rats. Isolated hearts from vehicle- and LPS-treated animals undergoing sham ischemia in vivo recovered to the same extent after in vitro ischemia/reperfusion, suggesting that LPS did not induce protection by altering intrinsic properties of the heart. Our results indicate that LPS-induced protection of the heart from in vivo PMN-mediated ischemia/reperfusion injury may be due to decreased L-selectin expression of PMNs in LPS-treated animals.

Effects of endotoxin on neutrophil-mediated I/R injury in isolated perfused rat hearts

With the use of a syngeneic model, we demonstrate that rat polymorphonuclear neutrophils (PMNs) exacerbate ischemia-reperfusion injury in the isolated rat heart. However, PMNs (19 x 10(6) cells) from lipopolysaccharide (LPS)-treated rats (LPS-PMNs; 100 mg/kg administered 7 h before exsanguination) induce less reperfusion injury in the isolated heart. Average recovery of left ventricular developed pressure after 20 min of ischemia and 60 min of reperfusion was 51 +/- 4% in hearts receiving PMNs from saline-treated control rats (saline-PMNs) versus 78 +/- 2% in hearts receiving LPS-PMNs. Ischemic hearts reperfused with LPS-PMNs recovered to the same extent as did hearts reperfused with Krebs buffer only. LPS-PMNs and saline-PMNs showed no difference in basal or phorbol ester-induced superoxide production. Whereas twice the number of LPS-PMNs was positive for nitroblue tetrazolium, the percent positive for L-selectin, a receptor integral in PMN-adhesion to endothelium, was 50% less in LPS-PMNs than in controls. After reperfusion, three-fourths of the saline-PMNs remained within the hearts, whereas only one-fourth of LPS-PMNs were trapped. These data suggest that PMNs from LPS-treated rats do not exacerbate ischemia-reperfusion injury as do control PMNs, possibly, due to impaired PMN adhesion to endothelium as a result of decreased L-selectin receptors.

LPS tolerance in human endothelial cells: reduced PMN adhesion, E-selectin expression, and NF-kappaB mobilization

Cytokine release from inflammatory (CD14(+)) cells is reduced after repeated stimulation with lipopolysaccharide (LPS; LPS tolerance). However, it is not known whether LPS tolerance can be induced in CD14(-) cells. The aim of the present study was to determine whether endothelial cells [human umbilical vein endothelial cells (HUVEC)] could be rendered tolerant to LPS with respect to LPS-induced polymorphonuclear neutrophil (PMN) adhesion. LPS stimulation (0.5 microg/ml; 4 h) of naive HUVEC increased PMN adhesion. Pretreatment of HUVEC with LPS (0.5 microg/ml) for 24 h resulted in a reduction in the proadhesive effects of a subsequent LPS challenge. The initial LPS stimulation increased 1) mobilization of the nuclear transcription factor NF-kappaB to the nucleus and 2) surface levels of the adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and E-selectin. In LPS-tolerant HUVEC, a second LPS challenge resulted in 1) less accumulation of NF-kappaB in the nucleus, 2) a reduction in E-selectin expression, and 3) unchanged ICAM-1 expression. LPS-tolerant cells were still capable of mobilizing NF-kappaB in response to stimulation with either interleukin-1beta or tumor necrosis factor-alpha, resulting in elevated E-selectin levels and increased PMN adhesion. These studies show for the first time that LPS tolerance can be induced in endothelial cells with respect to PMN adhesion. This tolerance is specific for LPS and is associated with an inability of LPS to mobilize NF-kappaB, resulting in less E-selectin expression.

LPS pretreatment ameliorates peritonitis-induced myocardial inflammation and dysfunction: role of myocytes

Peritonitis induced by cecal ligation and puncture (CLP) produces a systemic inflammatory response that can be largely mitigated by pretreatment of the animals with lipopolysaccharide (LPS tolerance). Although cells of myeloid origin and endothelial cells have been shown to contribute to the development of LPS tolerance, little is known regarding the potential role of parenchymal cells in this phenomenon. The major aim of the present study was to assess whether cardiac parenchymal cells (myocytes) contribute to the development of LPS tolerance. Six hours after induction of CLP rats were neutropenic and acidotic, the myocardium contained a leukocyte infiltrate [myeloperoxidase (MPO) activity was increased], and myocardial contractile function was impaired (left ventricular developed pressure was decreased). In animals that were pretreated with LPS these manifestations of sepsis were largely reversed. Further studies focused on the responses of cardiac myocytes to CLP and whether myocytes contributed to the development of LPS tolerance. Myocytes were isolated from rat hearts 6 h after induction of CLP. These myocytes 1) exhibited an impaired ability to shorten in response to pacing, 2) contained the nuclear transcription factor NF-kappaB in their nuclei, 3) increased their surface levels of intercellular adhesion molecule-1 (ICAM-1), and 4) were hyperadhesive for neutrophils. All of these events did not occur in myocytes obtained from animals that were pretreated with LPS before induction of CLP. These findings indicate that LPS tolerance can be induced in myocytes with respect to polymorphonuclear leukocyte adhesion, presumably by an inability of CLP to mobilize NF-kappaB to the myocyte nuclei and, thereby, preventing an increase in surface levels of ICAM-1.

Treatment of neoplastic meningeal xenografts by intraventricular administration of an antiganglioside monoclonal antibody, 3F8

Leptomeningeal (LM) neoplastic metastases are painful, debilitating and inevitably lethal. Intrathecal (IT) anti-tumor antibodies may have therapeutic potential. We evaluated 3F8, an anti-G(D2) murine IgG(3) monoclonal antibody (MAb) in the treatment of human melanoma (SKMEL-1) and neuroblastoma (NMB7) xenografts in athymic rats. Both tumors were lysed efficiently in vitro by 3F8 in the presence of rat neutrophils or rat complement. Antibody-dependent cellular cytotoxicity (ADCC) was not augmented by recombinant human GM-CSF (rhGM-CSF), rhG-CSF, recombinant rat MIP-2 (rrMIP-2) or lipopolysaccharide (LPS). In vivo, continuous intraventricular administration of 3F8 and LPS prevented tumor engraftment, retarded tumor growth and eradicated 3-day-old established xenografts whereas 3F8 alone, LPS alone or F(ab)'(2) plus LPS had no or only marginal effects. Tumor establishment in brain was completely prevented in 36% of animals implanted with SKMEL-1 and 65% of animals implanted with NMB7. Twenty percent of established xenografts around the brain were eradicated but all animals had persistent tumor in the lumbosacral meninges despite treatment. Continuous intraventricular infusion of LPS produced a variable polymorphonuclear (PMN) pleocytosis that was dose-dependent. Continuous intraventricular infusion of 3F8 produced immunohistochemically detectable attachment to 86% of persistent brain deposits of tumor but <1% of spinal lumbosacral deposits. We conclude that regional therapy with anti-G(D2) MAb could target neutrophils to inhibit LM tumor growth. However, optimal activation and mobilization of neutrophils into the cerebrospinal fluid (CSF) and improved penetration of MAb to tumor sites remain critical variables.

Microvascular perfusion deficits are not a prerequisite for mucosal injury in septic rats

Our major objective was to investigate whether injury to the mucosa of the small intestine occurred in a normotensive model of sepsis and whether such injury was associated with microvascular perfusion deficits. Using fluorescence intravital microscopy, we show direct evidence of cell injury within the mucosa (pneumonia 12.4 +/- 2.6 cells/field, sham 2.2 +/- 0.7 cells/field), whereas use of 51Cr-labeled EDTA showed evidence of increased mucosal permeability (pneumonia 1.90 +/- 0.67 ml. min-1. 100 g-1; sham 0.24 +/- 0.04 ml. min-1. 100 g-1), 48 h following induction of pneumonia. Despite such injury the capillary density in the ileal mucosa and submucosa of pneumonic rats (1,027 +/- 77 and 1,717 +/- 86 mm2) was not significantly different compared with sham (998 +/- 63 and 1,812 +/- 101 mm2). However, a modest albeit significant decrease in capillary perfusion was measured in the muscularis layer of pneumonia (11.0 +/- 1.3 mm) compared with sham (13.9 +/- 0.63 mm) and appeared to be associated with leukocyte entrapment. Pretreatment using low doses of endotoxin to induce endotoxin tolerance not only increased muscularis capillary density but reduced the number of leukocytes trapped within the microvasculature, decreased myeloperoxidase activity within the ileum in pneumonic rats, and prevented mucosal injury. In conclusion, we have shown that pneumonia results in remote injury to the mucosa of the ileum and that such injury was not associated with concurrent mucosal perfusion deficits.

Leukocyte activation does not mediate myocardial leukocyte retention during endotoxemia in rabbits

Our goal was to determine whether coronary leukocyte retention after endotoxin infusion was due primarily to leukocyte activation. Leukocytes were activated by infusion of endotoxin into 12 blood donor rabbits. Separately, 12 isolated rabbit hearts were perfused with blood from an endotoxemic support rabbit to expose coronary endothelium to an inflammatory stimulus. During an infusion of 20 ml of donor blood into the isolated heart, the coronary transit time of leukocytes was determined by deconvolution of multiple measurements of injectate and collected leukocyte concentrations. With no leukocyte activation or inflammatory stimulation of endothelium, leukocyte transit time was 9.2 +/- 3.5 s, and 11.6 +/- 4.1 x 10(6) leukocytes were retained in the coronary circulation. Leukocyte activation alone did not alter transit time (9.8 +/- 3.2 s) or retention (9.3 +/- 4.6 x 10(6) leukocytes). Inflammatory stimulation of endothelium with and without leukocyte activation increased transit time (18.0 +/- 3.6 and 18.9 +/- 3.8 s, respectively; P < 0. 05) and retention (24.8 +/- 8.4 and 25.3 +/- 6.8 x 10(6) leukocytes, respectively; P < 0.05) to the same extent. Differential counts showed that neutrophils (but not lymphocytes) were slowed and retained. Inflammatory stimulation of endothelium caused coronary capillary endothelial swelling and pseudopod formation. Thus increased coronary neutrophil transit time and retention are due to structural changes of coronary endothelial cells or other effects of the inflammatory response occurring within coronary capillaries, not only due to activation of leukocytes.

Effect of crystalloid administration on oxygen extraction in endotoxemic pigs

We asked whether crystalloid administration improves tissue oxygen extraction in endotoxicosis. Four groups of anesthetized pigs (n = 8/group) received either normal saline infusion or no saline and either endotoxin or no endotoxin. We measured whole body (WB) and gut oxygen delivery and consumption during hemorrhage to determine the critical oxygen extraction ratio (ERO2 crit). Just after onset of ischemia (critical oxygen delivery rate), gut was removed for determination of area fraction of interstitial edema and capillary hematocrit. Radiolabeled microspheres were used to determine erythrocyte transit time for the gut. Endotoxin decreased WB ERO2 crit (0.82 +/- 0.06 to 0.55 +/- 0.08, P < 0.05) and gut ERO2 crit (0.77 +/- 0.07 to 0.52 +/- 0.06, P < 0.05). Unexpectedly, saline administration also decreased WB ERO2 crit (0.82 +/- 0.06 to 0.62 +/- 0.08, P < 0.05) and gut ERO2 crit (0.77 +/- 0.07 to 0.67 +/- 0.06, P < 0.05) in nonendotoxin pigs. Saline administration increased the area fraction of interstitial space (P < 0.05) and resulted in arterial hemodilution (P < 0.05) but not capillary hemodilution (P > 0.05). Saline increased the relative dispersion of erythrocyte transit times from 0.33 +/- 0.08 to 0.72 +/- 0.53 (P < 0.05). Thus saline administration impairs tissue oxygen extraction possibly by increasing interstitial edema or increasing heterogeneity of microvascular erythrocyte transit times.

L-2-Oxothiazolidine-4-carboxylic acid prevents endotoxin-induced cardiac dysfunction

We tested the hypothesis that treatment with the glutathione repleting agent, L-2-oxothiazolidine-4-carboxylic acid (OTZ), could prevent endotoxin-induced ventricular dysfunction. Rabbits were treated with OTZ 2.4 g/kg (10% solution subcutaneously), or an equal volume and osmolality of saline, 24 h prior to, and again (intravenously) just prior to, infusion of 1 mg/kg E. coli endotoxin (or vehicle control). Ventricular contractility was measured in isolated hearts perfused by support rabbits. Contractility did not change in control groups (Saline/Control [n = 7] or OTZ/Control [n = 7]) over 6 h. However, Emax decreased in the Saline/Endotoxin group (-16.1 +/- 4.5% from baseline, n = 7, p < 0.05) and this was prevented by pretreatment with OTZ in the OTZ/ Endotoxin group (+6.3 +/- 4.1%, n = 7, p < 0.05 by analysis of variance). To better understand the mechanism of this effect we measured myocardial glutathione concentration and found it to be greater in OTZ/Endotoxin animals (104 +/- 4 ng/g) than in the Saline/Endotoxin animals (80 +/- 3 ng/g, p < 0.05). OTZ did not appreciably alter the endotoxin-induced increase in serum concentration of tumor necrosis factor (TNF) or the endotoxin-induced increase in myocardial leukocyte content. We conclude that oxygen radicals contribute to the early decrease in left ventricular contractility after endotoxin infusion and this decrease may be prevented by OTZ.

Microvascular perfusion is impaired in a rat model of normotensive sepsis

We hypothesized that normotensive sepsis affects the ability of the microcirculation to appropriately regulate microregional red blood cell (RBC) flux. An extensor digitorum longus muscle preparation for intravital study was used to compare the distribution of RBC flux and the functional hyperemic response in SHAM rats and rats made septic by cecal ligation and perforation (CLP). Using intravital microscopy, we found that sepsis was associated with a 36% reduction in perfused capillary density (from 35.3 +/- 1.5 to 22.5 +/- 1.0 capillaries/mm of test line) and a 265% increase in stopped-flow capillaries (from 0.9 +/- 0.2 to 3.3 +/- 0.4 capillaries/mm); the spatial distribution of perfused capillaries was also 72% more heterogeneous. Mean intercapillary distance (ICD) increased 30% (from 25.7 +/- 0.8 to 33.5 +/- 1.6 microns), and the proportion of capillary pairs with intercapillary distances > 33.8 microns (the 75th percentile of ICDSHAM) was greater with sepsis. Mean capillary RBC velocity increased 17% in CLP rats (391 vs 333 microns/s). Laser Doppler flowmetry was used to assess the functional hyperemic response of the extensor digitorum longus muscle before and after a period of maximal twitch contraction designed to increase oxygen demand. RBC flux was 36% lower in the CLP rats at rest. After contraction, RBC flux increased in both SHAM and CLP rats; however, the relative increase was less in the CLP group. We concluded that sepsis affects the ability of the skeletal muscle microcirculation to appropriately distribute RBC flux and to respond to increases in oxygen need.

The immunocytochemical localization of tumour necrosis factor and leukotriene in the rat heart and lung during endotoxin shock

After the intravenous administration of lipopolysaccharide at a dose of 3.0 mg/100 g to rats, immunoreactive sites for tumour necrosis factor (TNF) and peptide leukotrienes (LTs) were examined in the heart and lung. Immunoreaction for TNF is preferentially localized on the apical endothelial cell surface of the vessels and in lysosomes of inflammatory and interstitial cells. Lysosomes of cardiac muscle cells which undergo degeneration are also reactive. Peptide LTs in inflammatory cells give almost the same reactions as those for TNF. However, the production of peptide LTs occurs uniquely in cardiac muscle cells in the media of the pulmonary vein, although lysosomes of intracardiac muscle cells which undergo degeneration do not show immunoreactivity. These results suggest that the degeneration of cardiac muscle cells may be induced not only by endogenous TNF but also by peptide LTs which are produced in muscle cells of the venous media and are transported to the myocardium via the coronary circulation.

Attenuation of the induction of nitric oxide synthase by endogenous glucocorticoids accounts for endotoxin tolerance in vivo

An enhanced formation of nitric oxide (NO) due to induction of a calcium-independent (inducible) NO synthase (iNOS) contributes importantly to the cardiovascular failure caused by bacterial endotoxin. Repeated challenges with small doses of endotoxin result in tolerance to both peripheral vascular failure and death caused by subsequent injection of a higher dose of endotoxin. Here we investigate whether tolerance to endotoxin is associated with a lack of induction of iNOS in vivo and whether endogenous glucocorticoids play a role in the development of endotoxin tolerance. In anesthetized rats, i.v. administration of Escherichia coli endotoxin [lipopolysaccharide (LPS); 2 mg.kg-1] resulted in a prolonged decrease in mean arterial blood pressure (MAP) and hyporeactivity to the contractile responses elicited by norepinephrine (NE; 10 nM) in aortic rings ex vivo. Hyporeactivity to NE was partially reversed by NG-nitro-L-arginine methyl ester (0.3 mM) in vitro, suggesting that an enhanced formation of NO contributes to this hyporeactivity. There was a substantial increase in the activity of iNOS in the lung 3 h after i.v. injection of LPS (0.2 +/- 0.1 to 6.6 +/- 0.6 pmol.mg-1.min-1; n = 5; P < 0.01). Rats injected i.p. with LPS (0.5 mg.kg-1) for 4 consecutive days became tolerant to an i.v. injection of LPS (2 mg.kg-1) in that both hypotension and vascular hyporeactivity to NE were significantly attenuated. Moreover, in these endotoxin-tolerant rats, the induction of iNOS by LPS in the lung was attenuated by 63% +/- 6%. Injection of LPS caused a 9-fold increase in plasma corticosterone (CCS) levels within 2 h and CCS levels remained significantly elevated 6 and 24 h after LPS. Animals rendered tolerant to endotoxin by administration of a low dose of LPS (0.5 mg.kg-1, i.p.) for 4 days still had a 6-fold increase in plasma CCS levels 24 h after the last injection of LPS. When endotoxin-tolerant rats were treated with the glucocorticoid receptor antagonist RU 486 (50 mg.kg-1, p.o. 3 h prior to LPS), there was a restoration of the effects of LPS (2 mg.kg-1, i.v.) in causing hypotension, vascular hyporeactivity to NE, and iNOS induction in the lung. However, in control rats RU 486 enhanced neither the decrease in MAP nor the induction of iNOS in response to LPS (2 mg.kg-1, i.v.). Thus, cardiovascular tolerance to endotoxin is accompanied and explained by reduced induction of iNOS in vivo due to the elevation of endogenous glucocorticoid levels.

The damaging potential of leukocyte activation in the microcirculation

Traditionally leukocytes have been regarded as beneficial cells, owing to their immunologic and antimicrobial activity. Recent evidence suggests, however, an additional role of granulocytes and monocytes as mediators of cardiovascular complications, such as ischemia, reperfusion, diabetes, physiologic shock, venous ulceration, and other conditions. Granulocytes and monocytes have a large volume, and stiff cytoplasm; they have the ability to adhere to endothelium and to other substrates; and they exert several forms of cytotoxicity. Granulocytes and monocytes may be trapped in the microcirculation, may obstruct capillaries and thereby induce a no-reflow phenomenon, and may initiate organ dysfunction via oxygen free radical production and proteolytic cleavage. Few organs seem to be spared from the potential destructive actions of these cells, and novel approaches are required to interfere with leukocyte accumulation in local regions of the peripheral circulation.