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Biomedical subjects

P E Dekkers

Publications and source records attributed to P E Dekkers.

18 recordsLinked to original sources
PubMed2001

Tissue factor pathway inhibitor does not influence inflammatory pathways during human endotoxemia.

Activation of coagulation induces a proinflammatory response in in vitro and animal experiments. Inhibition of the tissue factor-dependent pathway of coagulation inhibits cytokine release and prevents death in gram-negative sepsis models in primates. This study investigated the influence of blocking the coagulation system by tissue factor pathway inhibitor (TFPI) on endotoxin-induced inflammatory responses in healthy humans. Eight men were studied in a double-blind, randomized, placebo-controlled cross-over study. They received a bolus intravenous injection of 4 ng/kg of endotoxin, followed by a 6-h continuous infusion of either TFPI (0.2 mg/kg/h after a bolus of 0.05 mg/kg) or placebo. Endotoxin induced-activation of coagulation was prevented completely by TFPI. In contrast, TFPI did not influence leukocyte activation, chemokine release, endothelial cell activation, or the acute phase response. Thus, complete prevention of coagulation activation by TFPI does not influence activation of inflammatory pathways during human endotoxemia.

Acute-Phase Reaction↗
PubMed2001

IC14, an anti-CD14 antibody, inhibits endotoxin-mediated symptoms and inflammatory responses in humans.

CD14 is a receptor for cell wall components of Gram-negative and Gram-positive bacteria that has been implicated in the initiation of the inflammatory response to sepsis. To determine the role of CD14 in LPS-induced effects in humans, 16 healthy subjects received an i.v. injection of LPS (4 ng/kg) preceded (-2 h) by i.v. IC14, a recombinant chimeric mAb against human CD14, at a dose of 1 mg/kg over 1 h, or placebo. In subjects receiving IC14, saturation of CD14 on circulating monocytes and granulocytes was >90% at the time of LPS injection. IC14 attenuated LPS-induced clinical symptoms and strongly inhibited LPS-induced proinflammatory cytokine release, while only delaying the release of the anti-inflammatory cytokines soluble TNF receptor type I and IL-1 receptor antagonist. IC14 also inhibited leukocyte activation, but more modestly reduced endothelial cell activation and the acute phase protein response. The capacity of circulating monocytes and granulocytes to phagocytose Escherichia coli was only marginally reduced after infusion of IC14. These data provide the first proof of principle that blockade of CD14 is associated with reduced LPS responsiveness in humans in vivo.

Acute-Phase Proteins↗
PubMed2001

Induction of cell-associated chemokines after endotoxin administration to healthy humans.

Erythrocytes express the Duffy antigen receptor for chemokines. Endotoxin injection into humans induced high levels of interleukin-8 (IL-8), growth-related oncogene alpha, and monocyte chemoattractant protein 1 in circulating erythrocytes. IL-8 was also recovered from mononuclear and polymorphonuclear cells. Cell-associated chemokines may more accurately reflect their production than plasma concentrations.

Adult↗
PubMed2001

Concurrent upregulation of urokinase plasminogen activator receptor and CD11b during tuberculosis and experimental endotoxemia.

Patients with tuberculosis had higher expression of monocyte urokinase receptor (uPAR) and CD11b than controls. In vitro, lipoarabinomannan and lipopolysaccharide (LPS) from Escherichia coli shared the ability to enhance uPAR and CD11b expression on monocytes and granulocytes. In healthy volunteers, LPS induced increases in monocyte and granulocyte uPAR and CD11b.

Adult↗
PubMed2000

Up-regulation of HIV coreceptors CXCR4 and CCR5 on CD4(+) T cells during human endotoxemia and after stimulation with (myco)bacterial antigens: the role of cytokines.

Concurrent infections in patients with human immunodeficiency virus (HIV) infection stimulate HIV replication. Chemokine receptors CXCR4 and CCR5 can act as HIV coreceptors. The authors hypothesized that concurrent infection increases the HIV load through up-regulation of CXCR4 and CCR5. Using experimental endotoxemia as a model of infection, changes in HIV coreceptor expression were assessed in 8 subjects injected with lipopolysaccharide (LPS, 4 ng/kg). The expression of CXCR4 and CCR5 on CD4(+) T cells was increased 2- to 4-fold, 4 to 6 hours after LPS injection. In whole blood in vitro, LPS induced a time- and dose-dependent increase in the expression of CXCR4 and CCR5 on CD4(+) T cells. Similar changes were observed after stimulation with cell wall components of Mycobacterium tuberculosis (lipoarabinnomannan) or Staphylococcus aureus (lipoteichoic acid), or with staphylococcal enterotoxin B. LPS increased viral infectivity of CD4-enriched peripheral blood mononuclear cells (PBMCs) with a T-tropic HIV strain. In contrast, M-tropic virus infectivity was reduced, possibly because of elevated levels of the CCR5 ligand cytokines RANTES and MIP-1beta. LPS-stimulated up-regulation of CXCR4 and CCR5 in vitro was inhibited by anti-TNF and anti-IFN gamma. Incubation with recombinant TNF or IFN gamma mimicked the LPS effect. Anti-interleukin 10 (anti-IL-10) reduced CCR5 expression, without influencing CXCR4. In accordance, rIL-10 induced up-regulation of CCR5, but not of CXCR4. Intercurrent infections during HIV infection may up-regulate CXCR4 and CCR5 on CD4(+) T cells, at least in part via the action of cytokines. Such infections may favor selectivity of HIV for CD4(+) T cells expressing CXCR4. (Blood. 2000;96:2649-2654)

Adult↗
PubMed2000

Expression of the chemokine receptors CXCR1 and CXCR2 on granulocytes in human endotoxemia and tuberculosis: involvement of the p38 mitogen-activated protein kinase pathway.

The chemokine receptors CXCR1 and CXCR2 critically determine the functional properties of granulocytes. To obtain insight in the regulation of these receptors during infection, CXCR expression was determined on blood granulocytes by fluorescence-activated cell sorter analysis in healthy subjects intravenously injected with lipopolysaccharide (LPS) and in patients with active tuberculosis. In healthy subjects, LPS induced a transient decrease in granulocyte CXCR1 and CXCR2 expression, whereas in tuberculosis patients, only CXCR2 showed reduced levels. In whole blood in vitro, LPS, lipoarabinomannan from Mycobacterium tuberculosis, and lipoteichoic acid from Staphylococcus aureus reduced expression of CXCR2 but not of CXCR1. CXCR2 down-regulation induced by LPS or tumor necrosis factor-alpha in vitro was abrogated by a p38 mitogen-activated protein kinase (MAPK) inhibitor. Granulocytes may down-regulate CXCR2 and, to a lesser extent, CXCR1 at their surface upon their first interaction with mycobacterial or bacterial pathogens by a mechanism that involves activation of p38 MAPK.

Adult↗
PubMed2000

The in vivo kinetics of tissue factor messenger RNA expression during human endotoxemia: relationship with activation of coagulation.

Triggering of the tissue factor (TF)-dependent coagulation pathway is considered to underlie the generation of a procoagulant state during endotoxemia. To determine the in vivo pattern of monocytic TF messenger RNA (mRNA) expression during endotoxemia, 10 healthy volunteers were injected with lipopolysaccharide (LPS, 4 ng/kg) and blood was collected before and 0.5, 1, 2, 3, 4, 6, 8, and 24 hours after LPS administration. Total blood RNA was isolated and amplified by NASBA (nucleic acid sequence-based amplification), followed by quantitation of TF mRNA by an electrochemiluminescence (ECL) assay. To compare the pattern of coagulation activation with the kinetics of monocytic TF mRNA expression, we measured plasma levels of markers of thrombin generation, thrombin-antithrombin (TAT) complexes, and prothrombin fragment 1 + 2 (F1 + 2). Baseline value (mean +/- SEM) of the number of TF mRNA molecules per monocytic cell was 0.08 +/- 0.02. A progressive and significant (P <.0001) increase in TF expression was observed after LPS injection (+0.5 hour: 0.3 +/- 0.1, +1 hour: 1.3 +/- 0.9, +2 hours: 4.1 +/- 0.9), peaking at +3 hours (10 +/- 1.9 TF mRNA molecules per monocyte). As TF mRNA levels increased, thrombin generation was augmented. Peak levels of TAT and F1 + 2 were reached later (at t +4 hours) than those of TF mRNA. TF mRNA, TAT, and F1 + 2 levels returned to baseline after 24 hours. In conclusion, we used a NASBA/ECL-based technique to quantify TF mRNA in whole blood during human endotoxemia and observed a 125-fold increase in TF mRNA levels. Our data demonstrate a pivotal role for enhanced TF gene activity in the activation of coagulation after LPS challenge. (Blood. 2000;96:554-559)

Adult↗
PubMed2000

Granulocyte colony-stimulating factor receptors on granulocytes are down-regulated after endotoxin administration to healthy humans.

Granulocyte colony-stimulating factor (G-CSF) is considered an important mediator of host defense against infection, and recombinant G-CSF is administered to patients with various infections. G-CSF binds to a specific receptor that is expressed on granulocytes and monocytes. To obtain insight about the regulation of the G-CSF receptor after an acute infectious challenge, 8 healthy subjects received an intravenous injection of lipopolysaccharide (LPS; 4 ng/kg), and receptor expression was determined on blood leukocytes by fluorescence-activated cell sorter analysis, both by measurement of saturation binding of recombinant G-CSF and by use of an anti-G-CSF-receptor antibody. LPS induced a transient decrease in granulocyte, but not monocyte, G-CSF-receptor expression. In whole blood in vitro, not only LPS but also gram-positive stimuli and proinflammatory cytokines were capable of down-modulating the G-CSF receptor on granulocytes. Bacterial antigens down-regulate the G-CSF receptor at the surface of granulocytes, which may impair neutrophil functions important for antibacterial host defense.

Adult↗
PubMed2000

Tissue factor pathway inhibitor dose-dependently inhibits coagulation activation without influencing the fibrinolytic and cytokine response during human endotoxemia.

Inhibition of the tissue factor pathway has been shown to attenuate the activation of coagulation and to prevent death in a gram-negative bacteremia primate model of sepsis. It has been suggested that tissue factor influences inflammatory cascades other than the coagulation system. The authors sought to determine the effects of 2 different doses of recombinant tissue factor pathway inhibitor (TFPI) on endotoxin-induced coagulant, fibrinolytic, and cytokine responses in healthy humans. Two groups, each consisting of 8 healthy men, were studied in a double-blind, randomized, placebo-controlled crossover study. Subjects were studied on 2 different occasions. They received a bolus intravenous injection of 4 ng/kg endotoxin, which was followed by a 6-hour continuous infusion of TFPI or placebo. Eight subjects received 0.05 mg/kg per hour TFPI after a bolus of 0.0125 mg/kg (low-dose group), and 8 subjects received 0.2 mg/kg per hour after a bolus of 0.05 mg/kg (high-dose group). Endotoxin injection induced the activation of coagulation, the activation and subsequent inhibition of fibrinolysis, and the release of proinflammatory and antiinflammatory cytokines. TFPI infusion induced a dose-dependent attenuation of thrombin generation, as measured by plasma F1 + 2 and thrombin-antithrombin complexes, with a complete blockade of coagulation activation after high-dose TFPI. Endotoxin-induced changes in the fibrinolytic system and cytokine levels were not altered by either low-dose or high-dose TFPI. The authors concluded that TFPI effectively and dose-dependently attenuates the endotoxin-induced coagulation activation in humans without influencing the fibrinolytic and cytokine response. (Blood. 2000;95:1124-1129)

Adult↗
PubMed2000

Endotoxin down-regulates monocyte and granulocyte interleukin-6 receptors without influencing gp130 expression in humans.

Interleukin (IL)-6 is important for host defense against various pathogens. The IL-6 receptor (IL-6R) complex consists of a ligand-binding component (IL-6R) and a signal-transducing component (gp130). In a study designed to obtain insight into the regulation of this receptor complex during inflammation, 8 healthy subjects received an intravenous injection of lipopolysaccharide (LPS; 4 ng/kg), and receptor expression was determined on blood leukocytes by use of fluorescence-activated cell cytometry. LPS induced a transient decrease in monocyte and granulocyte IL-6R expression but did not influence gp130. The plasma concentrations of soluble IL-6R and soluble gp130 did not change after LPS administration. Expression of the receptor for leukemia inhibitory factor, a member of the IL-6R family, remained unaltered after LPS injection. In whole blood in vitro, LPS and gram-positive stimuli and proinflammatory cytokines were capable of down-modulating the IL-6R. Monocytes and granulocytes may down-regulate IL-6R at their surface upon their first interaction with bacterial antigens.

Adult↗
PubMed2000

Reduced Th1, but not Th2, cytokine production by lymphocytes after in vivo exposure of healthy subjects to endotoxin.

Endotoxin (lipopolysaccharide [LPS]) tolerance is characterized by a reduced capacity of monocytes to produce proinflammatory cytokines upon restimulation in vitro. To determine whether LPS exposure induces a change in lymphocyte cytokine production and whether this results in a shift in the T-helper 1 (Th1)/Th2 balance, whole blood obtained from seven healthy subjects before and after an intravenous injection of LPS (4 ng/kg) was stimulated in vitro with the T-cell stimulus anti-CD3/CD28 or staphylococcal enterotoxin B. Whole-blood production of the Th1 cytokines gamma interferon (IFN-gamma) and interleukin-2 (IL-2) was markedly reduced at 3 and 6 h, while the production of the Th2 cytokines IL-4 and IL-5 was not influenced or was slightly increased. The IFN-gamma/IL-4 ratio was strongly decreased at 6 h. Serum obtained after LPS exposure could slightly inhibit the release of IFN-gamma but increased IL-4 production during stimulation of blood drawn from subjects not previously exposed to LPS. Normal serum also inhibited IFN-gamma production, albeit to a lesser extent. LPS exposure influences lymphocyte cytokine production, resulting in a shift toward a Th2 cytokine response, an effect that may be mediated in part by soluble factors present in serum after LPS administration in vivo.

Adult↗
PubMed2000

Upregulation of monocyte urokinase plasminogen activator receptor during human endotoxemia.

The receptor for urokinase-type plasminogen activator (uPAR) (CD87) plays an important role in leukocyte adhesion and migration. To assess the effect of endotoxin on cellular uPAR, uPAR expression was determined on leukocytes by fluorescence-activated cell sorter analysis in seven healthy subjects following intravenous injection of endotoxin (lot G; 4 ng/kg). Endotoxin induced a transient increase in uPAR expression on monocytes, reaching a 92% +/- 46% increase over baseline expression after 6 h (P < 0.05). Endotoxin did not influence uPAR expression on granulocytes, while uPAR remained undetectable on lymphocytes. Endotoxin also increased soluble uPAR levels in plasma (P < 0.05). Stimulation of human whole blood with endotoxin or gram-positive stimuli in vitro also resulted in an upregulation of monocyte uPAR expression. Although tumor necrosis factor alpha (TNF) upregulated monocyte uPAR expression, anti-TNF did not influence the endotoxin-induced increase in monocyte uPAR expression. These data suggest that infectious stimuli may influence monocyte function in vivo by enhancing the expression of uPAR.

Adult↗
PubMed1999

The effect of a metalloproteinase inhibitor (GI5402) on tumor necrosis factor-alpha (TNF-alpha) and TNF-alpha receptors during human endotoxemia.

Tumor necrosis factor-alpha (TNF-alpha) is released from the cell surface by cleavage of pro-TNF-alpha by metalloproteinases (MPs). In cell cultures, inhibition of MPs has been found not only to reduce the release of TNF-alpha, but also to enhance the surface expression of TNF-alpha and TNF-alpha receptors, which might lead to a proinflammatory effect. To determine the effect of MP inhibition during inflammation in humans, 7 healthy subjects were studied after intravenous injection of lipopolysaccharide (LPS; 4 ng/kg) preceded (-20 minutes) by an oral dose of the MP inhibitor GI5402 (100 mg) or matching placebo. GI5402 strongly reduced LPS-induced TNF-alpha release (P <.001), but did not influence the increase in monocyte-bound TNF-alpha. In addition, GI5402 attenuated the rise in plasma-soluble TNF-alpha receptors types I and II after LPS injection (both P <.001), but did not change the LPS-induced decreases in granulocyte and monocyte TNF-alpha receptor expression. These data suggest that MP inhibitors may be useful as a treatment modality in diseases in which excessive production of TNF-alpha is considered to play an important role. Furthermore, unlike in vitro, no evidence has been found in vivo with MP inhibition for a potential proinflammatory effect due to increases in membrane-bound TNF-alpha and TNF-alpha receptor number.

Adult↗
PubMed1999

Activation of mononuclear cells by interleukin-12: an in vivo study in chimpanzees.

Interleukin (IL)-12 is considered a central regulator of host resistance against a variety of pathogens. Therefore, IL-12 has been advocated as a potential therapeutic agent in infections. To determine the in vivo effects of IL-12 on mononuclear cells involved in the host immune response, four chimpanzees received an intravenous injection of recombinant IL-12 (1 microgram/kg). IL-12 induced a sustained decrease in lymphocyte counts, with decreases in CD3+/CD4+ and CD3+/CD8+ cells, while monocyte counts showed a transient increase. IL-12 injection resulted in a shift toward a Th1-mediated immune response as indicated by increased interferon-gamma production during whole-blood stimulation, while not influencing IL-4 production. IL-12-induced activation of NK cells and phagocytes, as indicated by increased NK cell cytotoxicity and increased plasma levels of granzymes A and B and of chitotriosidase activity. These data support the hypothesis that IL-12 may serve as a useful therapeutic agent in infections where a cell-mediated response is protective.

Animals↗
PubMed1999

Sequential measurements of chemokines in urosepsis and experimental endotoxemia.

Chemokines are a superfamily of small chemotactic proteins. While increased levels of interleukin-8 have been measured in serum and urine during urinary tract infection, little is known about other chemokines in this condition. Monocyte chemoattractant protein (MCP)-1, macrophage inflammatory protein (MIP)-1alpha, MIP-1beta and interferon-gamma inducible protein (IP)-10 were measured in 30 patients with culture-proven urosepsis during a 3-day follow-up and in 11 healthy humans after intravenous injection of endotoxin (4 ng/kg). Urine and serum levels of MCP-1, MIP-1beta, and IP-10, but not of MIP-1alpha were elevated in patients on admission, and decreased after initiation of antibiotic treatment. Endotoxin administration to healthy subjects induced increases in plasma and urine concentrations of all four chemokines. These data indicate that clinical and experimental gram-negative infection in humans is associated with enhanced production of chemokines that act mainly on mononuclear cells and that these chemokines are at least in part locally produced.

Adult↗
PubMed1999

Interleukin-12 induces sustained activation of multiple host inflammatory mediator systems in chimpanzees.

To determine in vivo effects of interleukin (IL)-12 on host inflammatory mediator systems, 4 healthy chimpanzees received recombinant human IL-12 (1 microg/kg) by intravenous injection. IL-12 induced increases in plasma concentrations of IL-15, IL-18, and interferon-gamma (IFN-gamma), plus a marked antiinflammatory cytokine response (IL-10, soluble tumor necrosis factor [TNF] receptors, IL-1 receptor antagonist) and secretion of alpha-chemokines (IL-8, IFN-gamma-inducible protein 10) and beta-chemokines (monocyte chemoattractant protein-1, macrophage inflammatory protein-1beta). In addition, IL-12 elicited neutrophilic leukocytosis, neutrophil degranulation (elastase-alpha1-antitrypsin complexes), coagulation activation (F1 + 2 prothrombin fragment, thrombin-antithrombin III complexes), and fibrinolytic activation (tissue-type plasminogen activator, plasmin-alpha2-antiplasmin complexes). IL-12-induced activation of multiple host mediator systems was found only after 8-24 h, remained detectable until the end of the 48-h observation period, and occurred in the absence of detectable TNF and IL-1beta. These data may contribute to understanding the role of IL-12 in the pathogenesis of sepsis syndrome and the toxicity found after repeated injections of IL-12.

Animals↗
PubMed1999

Divergent roles of tumor necrosis factor and platelet-activating factor in endotoxin-induced release of monocyte chemoattractant protein 1 and macrophage inflammatory protein 1beta in chimpanzees.

A platelet-activating factor receptor antagonist reduced the release of macrophage inflammatory protein 1beta (MIP-1beta) during endotoxemia in chimpanzees but did not influence the secretion of monocyte chemoattractant protein 1 (MCP-1). Anti-tumor necrosis factor alpha monoclonal antibody completely prevented MCP-1 release and simultaneously enhanced the secretion of MIP-1beta. Levels of MIP-1beta and MCP-1 release were differentially regulated during endotoxemia.

Animals↗