Effect of antibody-mediated neutropenia on the cardiopulmonary response to endotoxemia

Role of Antithrombin and Factor XIII In Leukocyte-Independent Plasma Extravasation During Endotoxemia: An Intravital-Microscopic Study in the Rat

BACKGROUND

Platelet-endothelial interactions have been shown to be main mediators of leukocyte-independent endothelial damage. Besides altering platelet-endothelial interactions, both antithrombin and factor XIII reduce microvascular permeability in leukocyte-dependent experimental models. Thus, it was our aim to investigate the effects of antithrombin and factor XIII on microvascular permeability during leukocyte-independent endotoxemia.

MATERIAL AND METHODS

In male Wistar rats, venular wall shear rate, macromolecular efflux, and leukocyte-endothelial interaction were determined in mesenteric postcapillary venules using intravital microscopy at baseline, 60, and 120 min after the start of the experiment. Fucoidin and a continuous infusion of lipopolysaccharides were used to generate leukocyte-independent endotoxemia. The experiment was divided into two parts 1) an antithrombin study and 2) a factor XIII study.

RESULTS

No differences between groups in leukocyte rolling and venular wall shear rate could be observed in both parts of the experiment. Pretreatment with antithrombin reduced microvascular permeability significantly compared with control subjects (120 min: Fuco [untreated]: 0.14 +/- 0.03; Fuco/ETX [control]: 0.37 +/- 0.06; Fuco + ATIII/ETX: 0.15 +/- 0.02; P < 0.05). Factor XIII reduced microvascular permeability significantly after 60 min (Fuco [untreated]: 0.10 +/- 0.03; Fuco/ETX [control]: 0.36 +/- 0.07; Fuco + FXIII/ETX: 0.13 +/- 0.04; P < 0.05). This effect diminished after 120 min (Fuco [untreated]: 0.12 +/- 0.03; Fuco/ETX [control]: 0.5 +/- 0.08; Fuco + FXIII/ETX: 0.29 +/- 0.05; P < 0.05).

CONCLUSIONS

Antithrombin and factor XIII reduce leukocyte-independent microvascular permeability. Yet, factor XIII also shows a nonprotective effect on a long-term basis. These data emphasize the central role of platelets in leukocyte-independent endotoxemia.

Role of platelet-activating factor in leukocyte-independent plasma extravasation and mast cell activation during endotoxemia

BACKGROUND

Independently from leukocyte adherence, endothelial factors and mast cell activation seems to promote microvascular permeability. Platelet-activating factor (PAF) has been shown to play a significant role in endotoxin-induced leukocyte adherence. The aim of our study was to investigate if there is also a role for PAF in mediating leukocyte-independent microvascular permeability changes and activation of mast cells during endotoxemia. Therefore, during endotoxemia microvascular permeability and mast cell activation were determined after inhibition of L-selectin-mediated leukocyte adherence by fucoidin and after inhibition of PAF effects by the PAF receptor antagonist BN52021.

MATERIALS AND METHODS

In male Wistar rats, red cell velocity (V(RBC)), venular wall shear rate, microvascular permeability, leukocyte adherence, and mast cell activation were determined in mesenteric postcapillary venules using intravital microscopy at baseline and 60 and 120 min after start of a continuous infusion of endotoxin (ETX; 2 mg/kg/h, Escherichia coli O26:B6) (ETX group). Animals in the FUCO/ETX group received fucoidin (25 mg/kg body wt) in addition to the procedure described above. Animals in the FUCO/ETX/PAF-ANT group received fucoidin and the PAF receptor antagonist BN52021 (5 mg/kg body wt) prior to the continuous endotoxin infusion. Control animals (control group) received only equivalent volumes of NaCl 0.9%.

RESULTS

There were no microhemodynamic and macrohemodynamic differences between groups. In all endotoxin-challenged groups macromolecular leakage and mast cell activity increased significantly, starting at 60 min. Both macromolecular leakage and mast cell activity were significantly higher in the FUCO/ETX group than in the FUCO/ETX/PAF-ANT group and control group. Differences in macromolecular leakage between groups were significant at 120 min. Differences in mast cell activity between groups were significant at 60 and 120 min.

CONCLUSIONS

The results of our study demonstrate a leukocyte-independent plasma extravasation that can be inhibited by the PAF receptor antagonist BN52021, indicating the involvement of PAF in the pathophysiology of leukocyte-independent microvascular damage during early endotoxemia. Mast cell activity seems to precede leukocyte-independent macromolecular leakage.

Leukocyte-independent plasma extravasation during endotoxemia

OBJECTIVES

To determine the meaning of leukocyte-endothelial interactions for the development of endotoxin-induced vascular leakage.

DESIGN

Randomized, blinded, controlled trial.

SETTING

Experimental laboratory.

SUBJECTS

Twenty-four male Wistar rats.

INTERVENTIONS

After application of fucoidin to prevent leukocyte rolling and adherence (25 mg/kg; n = 8; fucoidin/LPS group) or saline 0.9% (n = 8; LPS group), animals were given an intravenous infusion of endotoxin (Escherichia coli lipopolysaccharide 026:B6; 2 mg/kg/hr) over 120 mins. Animals in the control group (n = 8) received an equivalent volume of saline 0.9%.

MEASUREMENTS AND MAIN RESULTS

Leukocyte rolling and leukocyte adherence, red cell velocity, vessel diameters, venular wall shear rate, volumetric blood flow, and macromolecular leakage were determined in mesenteric postcapillary venules using in vivo videomicroscopy at baseline, 60 mins, and 120 mins after start of a continuous endotoxin infusion. Fucoidin prevented leukocyte rolling (baseline, 3+/-2 rollers; 120 mins, 3+/-1 rollers; not significant vs. baseline; p < .01 vs. LPS group) and reduced the adherence of leukocytes at baseline and during endotoxemia and showed only a slight increase in adherent leukocytes (baseline, 100+/-38 cells/mm2; 120 mins, 244+/-68 cells/mm2; p < .05 vs. baseline; p < .01 vs. LPS group). In the LPS group, endotoxin exposure induced a marked increase in adherent leukocytes (baseline, 248+/-24 cells/mm2; 120 mins, 560+/-57 cells/mm2; p < .01). Leukocyte adherence in control animals (control group) did not increase significantly. Macromolecular leakage, expressed as the ratio of perivenular to intravenular fluorescence intensity after injection of fluorescence-labeled albumin, increased from 0.16+/-0.03 to 0.49+/-0.04 (p < .01 vs. baseline; p < .05 vs. control) during the infusion of endotoxin in the LPS group. Fucoidin application did not diminish the extravasation of albumin (baseline, 0.09+/-0.03; 120 mins, 0.61+/-0.10; p < .01 vs. baseline; p < .01 vs. control).

CONCLUSIONS

These results demonstrate that despite a significant reduction of adherent leukocytes to the endothelium by fucoidin, there is no reduction in macromolecular leakage, indicating that leukocyte-endothelial interactions only play a minor role for the development of macromolecular leakage and microvascular damage in the early phase of endotoxemia.

Gabexate mesilate, a synthetic protease inhibitor, attenuates endotoxin-induced pulmonary vascular injury by inhibiting tumor necrosis factor production by monocytes

OBJECTIVE

In order to determine whether gabexate mesilate, a synthetic protease inhibitor with anticoagulant properties, is useful for the treatment of adult respiratory distress syndrome, we examined its effect on endotoxin-induced pulmonary vascular injury in rats.

DESIGN

Prospective, randomized, controlled study.

SETTING

Research laboratory at a university medical center.

SUBJECTS

Male Wistar rats (180 to 220 g.)

INTERVENTIONS

Animals received intravenous infusions of endotoxin (5 mg/kg iv) or saline (control). Pulmonary vascular injury was assessed 6 hrs after administration of endotoxin in terms of the increase in vascular permeability. Rats received gabexate mesilate (10 mg/kg ip), heparin, antithrombin III, an inactive derivative of activated factor X (a selective inhibitor of thrombin generation), or N-[2-[4-(2,2-dimethyl-propionyloxy) phenylsulfonylamino] benzoyl] aminoacetic acid (ONO-5046) (a potent granulocyte elastase inhibitor) 30 mins before endotoxin administration. Leukocytopenia was induced by administration of methotrexate. The effects of the gabexate mesilate on the function of activated neutrophils and the production of tumor necrosis factor -alpha (TNF-alpha) by endotoxin-stimulated monocytes were examined in vitro using neutrophils and monocytes prepared from healthy human volunteers.

MEASUREMENTS AND MAIN RESULTS

Pulmonary vascular permeability was determined by measuring the vascular leakage of intravenously administered 125I-labeled bovine serum albumin. Intravenous administration of endotoxin significantly increased pulmonary vascular permeability. Gabexate mesilate significantly inhibited pulmonary vascular injury observed 6 hrs after the administration of endotoxin. Pulmonary vascular injury was not attenuated by the administration of heparin, heparin plus antithrombin III, or the inactive derivative of activated factor X, but pulmonary vascular injury was significantly attenuated in animals with methotrexate-induced leukocytopenia and in those animals treated with N-[2-[4-(2,2-dimethyl-propionyloxy) phenylsulfonylamino] benzoyl] aminoacetic acid. Gabexate mesilate in concentrations of 10(-4) to 10(-3) M inhibited the release of granulocyte elastase and leukocyte aggregation stimulated by N-formyl-methionyl-leucyl-phenylalanine and the opsonized zymosan-activated production of superoxide radical by neutrophils in vitro. Gabexate mesilate significantly inhibited the endotoxin-induced increase in the serum concentration of TNF-alpha in vivo and, at a concentration of 10(-8) M, the production of TNF-alpha by endotoxin-stimulated monocytes in vitro.

CONCLUSION

Our findings suggest that gabexate mesilate attenuated endotoxin-induced pulmonary vascular injury mainly by inhibiting TNF-alpha production by monocytes, which may play a central role in sepsis-related lung injury.

Multiple Organ Failure Syndrome—Part I: Epidemiology, Prognosis, and Pathophysiology

The multiple organ failure syndrome (MOFS) is the leading cause of death in intensive care units. Although sepsis is an important cause of MOFS, it is clear that MOFS can occur in the absence of infection. The pathophysiology of MOFS is complex and multifactorial and includes derangements in oxygen delivery and consumption, the release of inflammatory and vasoactive mediators capable of inflicting tissue damage, and alterations in the barrier function of the intestinal mucosa. Although advances have been made in our understanding of MOFS, treatment remains nonspecific and largely supportive. Early and aggressive restoration of tissue perfusion, adequate treatment of infection, timely nutritional support, and support of individual failed organs remain the mainstay of therapy. Therapeutic agents directed against the various mediators associated with the pathophysiology of MOFS may prove useful in the future.