The inflammatory response to endotoxin

In Vivo Effects of Neostigmine and Physostigmine on Neutrophil Functions and Evaluation of Acetylcholinesterase and Butyrylcholinesterase as Inflammatory Markers during Experimental Sepsis in Rats

Introduction

Recent studies have shown that acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) may serve as important diagnostic and therapeutic targets in sepsis. Since polymorphonuclear neutrophils (PMNs) play a pivotal role in the early phase of sepsis, we evaluated the potential therapeutic effects of cholinesterase inhibitors on PMN functions during cecal ligation and puncture- (CLP-) induced sepsis and investigated the roles of AChE and BChE as inflammatory markers under standardized experimental conditions.

Methods

Sham surgery or CLP was performed in male Wistar rats (n = 60). Animals were randomized into four groups: physostigmine, 100 μg/kg; neostigmine, 75 μg/kg; 0.9% saline (control group); and sham group, each applied four times over 24 h. The levels of reactive oxygen species (ROS) production and CD11b/CD62l expression were quantified by flow cytometry at t = 0, 6, 15, 20, and 24 h. Blood gas analysis as well as AChE and BChE activity levels was measured by validated point-of-care measurements. Clinical scores and survival times were determined.

Results

CLP induced a significant increase in ROS production and CD11b upregulation by rat PMNs. Treatment with physostigmine or neostigmine significantly reduced ROS production and CD11b upregulation by PMNs 20 h after CLP induction. In physostigmine-treated animals, survival times were significantly improved compared to the control animals, but not in neostigmine-treated animals. While AChE activity significantly decreased in the control animals at t > 6 h, AChE activity did not change in the sham group. BChE activity decreased at t > 20 h in the control animals.

Conclusion

While AChE activity may serve as an acute inflammatory marker, BChE activity shows a delayed decrease. Administration of centrally acting physostigmine in CLP-induced sepsis in rats has protective effects on PMN functions and improves survival times, which may be of interest in clinical practice.

Polymicrobial sepsis and endotoxemia promote microvascular thrombosis via distinct mechanisms

BACKGROUND

We reported recently that endotoxemia promotes microvascular thrombosis in cremaster venules of wild-type mice, but not in mice deficient in toll-like receptor 4 (TLR4) or von Willebrand factor (VWF).

OBJECTIVE

To determine whether the clinically relevant model of polymicrobial sepsis induced by cecal ligation/perforation (CLP) induces similar responses via the same mechanisms as endotoxemia.

METHODS

We used a light/dye-injury model of thrombosis in the cremaster microcirculation of wild-type mice and mice deficient in toll-like receptor-4 (C57BL/10ScNJ), toll-like receptor 2 (TLR2), or VWF. Mice underwent CLP or sham surgery, or an intraperitoneal injection of endotoxin (LPS) or saline. In the CLP model, we assessed the influence of fluid replacement on thrombotic responses.

RESULTS

Both CLP and LPS enhanced thrombotic occlusion in wild-type mice. In contrast to LPS, CLP enhanced thrombosis in TLR4- and VWF-deficient strains. While TLR2-deficient mice did not demonstrate enhanced thrombosis following CLP, LPS enhanced thrombosis in these mice. LPS, but not CLP, increased plasma VWF antigen relative to controls. Septic mice, particularly those undergoing CLP, developed significant hemoconcentration. Intravenous fluid replacement with isotonic saline prevented the hemoconcentration and prothrombotic responses to CLP, though fluids did not prevent the prothrombotic response to LPS.

CONCLUSIONS

Polymicrobial sepsis induced by CLP and endotoxemia promote microvascular thrombosis via distinct mechanisms; enhanced thrombosis induced by CLP requires TLR2 but not TLR4 or VWF. The salutary effects of intravenous fluid replacement on microvascular thrombosis in polymicrobial sepsis remain to be characterized.

Functional and phenotypic changes in polymorphonuclear neutrophils induced by catecholamines

PURPOSE

To elucidate differential functional and phenotypic changes in response to relevant catecholamines, the generation of oxidative free radicals by PMN, and changes in the expression of L-selectin and Mac-1 on the surface of PMN were examined in the presence of epinephrine, norepinephrine and dopamine in physiological and pharmacological concentrations.

MATERIALS AND METHODS

Human polymorphonuclear neutrophils were obtained from healthy donors and pretreated with 0.5 nM or 500 nM epinephrine; 1.18 nM or 1 180 nM norepinephrine; or 0.26 nM or 261 nM dopamine, followed by stimulation with FMLP. Stimulated neutrophils were incubated with antibodies against CD 11 b or CD 62 l and assessed by flow cytometry. Additional probes were assessed by flow cytometry for the generation of oxidative free radicals.

RESULTS

All catecholamines in high concentration inhibited the suppression of CD 62 l expression and CD 11 b upregulation following stimulation with FMLP. A high concentration of epinephrine suppresses generation of oxidative free radicals.

CONCLUSIONS

The effect of catecholamines on the expression of CD 62 l explains the increased expression of L-selection on PMN observed after trauma. The suppression of CD 11 b reduces leukocyte adherence and consecutive abnormalities in microvascular flow. Epinephrine inhibits the generation of oxidative free radicals by PMN with potentially detrimental effects with respect to bacterial clearance.

Differential role of von Willebrand factor and P-selectin on microvascular thrombosis in endotoxemia

OBJECTIVE

Endotoxin (lipopolysaccharide [LPS]) enhances microvascular thrombosis in mouse cremaster venules. Because von Willebrand factor (vWF) and P-selectin are suggested to mediate LPS-induced platelet-microvessel interactions, we determined whether vWF and P-selectin contribute to microvascular thrombosis in endotoxemia.

METHODS AND RESULTS

A light/dye-induced thrombosis model was used in cremaster microvessels of saline or LPS-injected mice (wild-type, P-selectin-deficient, vWF-deficient, or littermate controls). In each strain except vWF-deficient mice, LPS enhanced thrombosis in venules, resulting in approximately 30% to 55% reduction in times to thrombotic occlusion. LPS had no effect on thrombosis in vWF-deficient mice, although these mice had similar systemic responses to LPS (tachycardia, thrombocytopenia, and plasma coagulation markers). vWF-deficient mice demonstrated prolonged times to thrombotic occlusion relative to littermates. LPS increased plasma vWF in each strain studied. While immunofluorescence in wild-type mice failed to detect LPS-induced differences in microvascular vWF expression, it revealed markedly higher vWF expression in venules relative to arterioles.

CONCLUSIONS

vWF mediates light/dye-induced microvascular thrombosis and endotoxin-induced enhancement of thrombosis in mouse cremaster venules; P-selectin is not required for enhanced thrombosis in response to endotoxin. Enhanced vWF expression in venules relative to arterioles has potential implications for the differences in thrombotic responses among these microvessels.

Synthetic inotropes inhibit the expression of adhesion molecules and augment the expression of L-selectin in polymorphonuclear neutrophils

OBJECTIVES

To elucidate differential functional and phenotypic changes in response to clinically relevant synthetic inotropes plus the generation of oxidative free radicals by polymorphonuclear neutrophils (PMN), and changes in the expression of L-selectin and Mac-1 on the surface of PMN were examined in the presence of dobutamine and dopexamine in pharmacological concentrations.

DESIGN

Prospective, in vitro study.

SETTING

Research laboratory.

SUBJECTS

Human PMN obtained from healthy donors.

INTERVENTIONS

PMN were pretreated with dobutamine 147.99 nM or 147,990 nM, or dopexamine 100 nM or 100,000 nM, followed by stimulation with FMLP. Stimulated neutrophils were incubated with antibiodies against CD11b or CD62l and assessed by flow cytometry. Additional probes were assessed by flow cytometry for the generation of oxidative free radicals.

MEASUREMENTS AND MAIN RESULTS

Low concentrations of both synthetic inotropes significantly inhibit the suppression of CD62l expression following stimulation with N-formyl-l-methionyl-l-leucyl-l-phenylalanine; high concentrations antagonize this effect. High concentrations of both synthetic inotropes suppresses the expression of CD11b. Neither dobutamine nor dopexamine modified the generation of oxidative free radicals.

CONCLUSIONS

While the upregulation of Mac-1 expression is inhibited in a dose-dependent manner, the expression of L-selectin is enhanced at low concentrations of dobutamine and dopexamine and partly counter-regulated at high concentrations. It seems that synthetic inotropes can modulate the immunomodulatory ability by inhibition of PMN rolling and modification of PMN adherence and diapedese.

Microvascular function and rheologic changes in hyperdynamic sepsis

OBJECTIVE

To investigate the rheologic changes and circulatory abnormalities at the microvascular level during severe sepsis.

DESIGN

Prospective, controlled trial.

SETTING

Medical and surgical intensive care units of a university-affiliated hospital.

PATIENTS

Nine normal controls and eight adult patients with severe sepsis who met the study entrance criteria.

INTERVENTIONS

Forearm blood flow was measured at rest and during reactive hyperemia by air plethysmography. Simultaneous hemodynamic measurements and blood samples for rheologic measurements were taken.

MEASUREMENTS AND MAIN RESULTS

Red blood cell deformability index was determined using a simple filtration procedure. Leukocyte aggregation in whole human blood was detected by using a leukergy test. Expression of the neutrophil adhesion molecule CD11b/CD18 was measured using a monoclonal antibody and flow cytometry. All data were taken within 24 hrs of the patient meeting criteria for entrance into the study. Cardiac output, oxygen delivery, and oxygen consumption measurements were consistent with the hyperdynamic phase of severe sepsis. Forearm blood flow was significantly (p < .05) greater in septic patients (21 +/- 3 mL/min) than in controls (12 +/- 2 to 36 +/- 5 mL/min (p < .05), while in the septic patients, forearm blood flow during reactive hyperemia increased from 21 +/- 3 to 32 +/- 4 mL/min. The ratio of forearm blood flow during reactive hyperemia to forearm blood flow at rest was 3.2 +/- 0.1 in the controls and 1.6 +/- 0.1 in the septic patients (p < .01). The red blood cell deformability index in whole blood was significantly (p < .01) decreased in the septic patients compared with the control subjects (0.41 +/- 0.07 vs. 0.98 +/- 0.08 mL/min). This difference remained true when the hematocrit was adjusted to 45% (0.82 +/- 0.06 vs. 1.04 +/- 0.06 mL/min; p < .05). Increased expression of the neutrophil adhesion molecule CD11b/CD18 was observed in septic patients (349 +/- 46 logarithmic fluorescence units) as compared with control subjects (233 +/- 26 logarithmic fluorescence units; p < .05). Leukergy was also significantly (p < .05) increased in septic patients (17.7 +/- 3.8%) as compared with control subjects (8.9 +/- 1.6%). A significant correlation was observed between leukergy and the expression of the neutrophil adhesion molecule CD11b/CD18 in controls and septic patients (r2 = .62; p < .01). Leukergy was also inversely correlated with whole blood red blood cell deformability index (r2 = .28; p < .05).

CONCLUSIONS

Reactive hyperemia in the forearm is significantly diminished in patients with sepsis, suggesting impaired microvascular blood flow. Rheologic changes, including impaired red blood cell deformability, increased leukocyte aggregation, and endothelial adherence, may contribute to this abnormality by compromising effective capillary cross-sectional area.

Reduced response to intravenous endotoxin injections following repeated oral administration of endotoxin in the pig

Three prepubertal gilts were each given 100 mg of endotoxin (ET) in their ordinary feed rations, twice daily for 6 days; 3 other gilts received standard feed. Following ET feeding, all animals were injected intravenously (i.v.) with ET (1.0 microgram/kg b.w.) once daily for 5 days. Blood samples were collected and analysed for hematology and total serum bile acids (S-BA), glutamate dehydrogenase (S-GLDH), calcium (S-Ca), iron (S-Fe), zinc (S-Zn) and a blood plasma metabolite (15-ketodihydro-PGF2a; P-PG) of prostaglandin F2a. The animals showed no apparent clinical symptoms following ET-feeding, neither did the blood analyses reveal effects of oral ET. However, when iv ET injections were given, the ET-fed animals showed fewer clinical signs of endotoxemia following the 2nd to 5th injection. S-BA and S-GLDH increased markedly in the standard-fed group following the first injection, while the ET-fed animals showed a much smaller increase in S-BA and no change in S-GLDH on that day. The difference in response may be explained by a direct uptake of ET from the gastrointestinal tract in the ET-fed pigs, making them less sensitive to the injected ET.

A glycolipid precursor of bacterial lipopolysaccharide (lipid X) lacks activity against endothelial cells in vitro and is not toxic in vivo

Lipid X (2,3-diacylglucosamine-1-phosphate) accumulates in mutants of Escherichia coli incapable of assembling the disaccharide backbone of lipid A, the principle endotoxic moiety of bacterial lipopolysaccharide (LPS). We compared the effects of lipid X on cultured bovine aortic endothelial cell (BEC) viability and prostacyclin (PGI2) release with those of lipid A and LPS. At 10(-5) M, both LPS and lipid A produced significant BEC cytotoxicity (percentage cytotoxicity 69 +/- 4 for LPS and 51 +/- 11 for lipid A) and induced a variable but consistent increase in the release of PGI2 (11- to 73-fold increase for LPS and 4- to 6-fold increase for lipid A). Lipid X, in contrast, was not toxic and did not induce PGI2 release at 10(-4) M. Pretreatment and coincubation of BEC with lipid X, at a concentration 100 times greater than LPS, failed to prevent LPS-mediated cytotoxicity. Intravenous infusion of lipid X in goats had no effect except for a modest elevation in the pulmonary artery pressure during the period of infusion. Moreover, pretreatment of goats with lipid X (70 micrograms/kg) did not block the effects of a subsequent infusion of LPS (5 micrograms/kg). These data suggest that a fatty acid-substituted disaccharide is the minimal molecular requirement for the numerous effects in vivo and activity in vitro induced by LPS. Furthermore, these effects are not prevented by pretreatment with a monosaccharide precursor of lipopolysaccharide, lipid X, at a dose 10- to 100-fold greater than that of LPS.

Enhanced survival to endotoxin in guinea pigs fed IV fish oil emulsion

Improved survival to endotoxin has been demonstrated in rats pretreated with cyclooxygenase inhibitors or made essential fatty acid deficient, implying that excessive omega 6 fatty acids, possibly through their eicosanoid products, contribute to mortality. Following endotoxin administration, we also have shown improvement in survival with oral diets supplemented with fish oil. This study sought to explore whether parenteral fish oil ameliorates the adverse impact of endotoxin. Male Hartley-strain guinea pigs were obtained at a body weight of 500 g and fed a normal laboratory diet. Central venous lines through which the animals received either a 10% safflower oil emulsion (n = 11) or a 10% fish oil emulsion (n = 11) during two, 24-hr periods separated by two days were inserted. Two days after the second infusion, endotoxin (0.35 mg/100 g b.w.), was given intraperitoneally, and survival was noted. The animals received a total of 25.4 g of IV fat per kg b.w., including 5.3 g of eicosapentaenoic acid per kg b.w., for the fish oil group. From six hr after endotoxin through four days, there was better survival in the fish oil group (p less than .006). Final mortality showed 7/11 fish-fed vs 2/11 safflower-fed animals surviving. We conclude that the administration of parenteral fish oil, even for a brief time, can have a profound effect on subsequent survival to endotoxin.

Structural changes produced in Kupffer cells in the rat liver by injection of lipopolysaccharide

The fine structure of Kupffer cells has been studied at various times after an intravenous injection of lipopolysaccharide of Salmonella abortus equii. The most prominent effects were: an increase in the number and dimensions of phagocytic vacuoles (often containing ingested LPS and neutrophilic granulocytes); mitochondrial damage, including disintegration of the matrix and cristae; an increase in the amount of dilated, lucent rough endoplasmic reticulum; presence of fat droplets in the cytoplasm. Five days after injection of lipopolysaccharide, the Kupffer cells had resumed their normal ultrastructure. Several minutes after injection of lipopolysaccharide, platelets adhered to the Kupffer and endothelial cells. Between one and six hours, neutrophilic granulocytes accumulated in the liver sinusoids. The resulting obstruction of the hepatic microcirculation most probably affected cellular ultrastructure by ischaemia. At three days, the number of Kupffer cells was doubled, and increased further at later time intervals.

Hepatic damage in neonatal rat due to E. coli endotoxin

Liver from neonatal rats injected with LD50 E. coli endotoxin was studied by light and electron microscopy. By 2 hr, there was margination and migration of polymorphonuclear leukocytes. Single cell necrosis was seen after 8 hr. At 16 hr, there were numerous necrotic foci in the mid-zonal region of hepatic lobules, as well as accumulation of microvesicular fat. Necrosis and fatty change of hepatocytes were more extensive at 24 hr. Microvesicular fat accumulation may be related to alterations in fatty acid or oxidative metabolism. However, the pattern of mid-zonal damage in these animals is not typical of failure of oxidative metabolism and suggests that other mechanisms are involved.

Acute and chronic changes in the microcirculation of the liver in inbred strains of mice following infection with mouse hepatitis virus type 3

The acute and chronic effects of mouse hepatitis virus type 3 on the microcirculation of the liver in both semisusceptible C3HeB/FeJ and fully resistant A/J mice were studied. In the C3HeB/FeJ mice, abnormalities of microcirculatory flow were noted as early as 12 hr after infection and by 24 hr, localized avascular foci appeared. Disturbances were characterized by granular blood flow, sinusoidal microthrombi, distortion of sinusoids by edematous hepatocytes and necrotic lesions. Following the acute infection, Day 10, two patterns of chronic disease were observed. Eighty percent of the mice developed chronic granulomatous hepatitis whereas in the remaining 20% a more severe chronic aggressive hepatitis was observed which was characterized by ongoing hepatocellular necrosis and a marked mononuclear cell infiltrate. In both cases, in vivo microcirculatory abnormalities were found predominantly around visible lesions. Onset of the microcirculatory abnormalities was found to be concomitant with a rise in monocyte related procoagulant activity. Procoagulant activity rose acutely and remained elevated throughout the chronic phase but was higher in animals with severe disease. In contrast to the above, normal blood flow and histology were seen in the resistant A/J mice at all times following infection, and procoagulant activity remained at basal levels despite active viral replication as demonstrated by immunofluorescence studies and recovery of infectious virus. These observations suggest a role for monocyte procoagulant activity in the development of microcirculatory abnormalities following mouse hepatitis virus type 3 infection which may be important in the pathogenesis of the disease.

[Effect of phorbolmyristate acetate and bacterial lipopolysaccharides on the luminal chemiluminescence of neutrophil granulocytes]

Measurement of emitted photons by means of luminol dependent chemiluminescence enables to evaluate the oxidative metabolism of polymorphonuclear leukocytes (PMN). The effect of phorbol myristate acetate (PMA) and bacterial lipopolysaccharides (LPS) on the luminol dependent chemiluminescence of resting and phagocytosing PMN has been investigated. Both substances stimulate the emission of photones in resting PMN. In contrary an inhibitory effect on the emission of photones is found in dependence on the concentration and duration of influence on phagocytosing PMN. This phenomenon of inhibition is caused by an accelerated and shortly lasting reaction if PMA is added and by a delayed but prolonged reaction if LPS is added. The shape of emission curve of phagocytosing PMN from healthy adults influenced by LPS correspond closely to that of premature and mature newborns suffering from severe bacterial infections.