Endotoxin-Induced Activation of the Coagulation Cascade in Humans

Abstract

Abstract-During Gram-negative septic shock, lipopolysaccharide (LPS, endotoxin) induces tissue factor (TF) expression.TF expression is mediated by nuclear factor B and amplified by activated platelets. TF forms a highly procoagulant complex with activated coagulation factor VII (FVIIa). Hence, we hypothesized that aspirin, which inhibits LPS-induced, nuclear factor B-dependent TF expression in vitro and platelet activation in vivo, may suppress LPS-induced coagulation in humans. Therefore, we studied the effects of aspirin on systemic coagulation activation in the established and controlled setting of the human LPS model. Thirty healthy volunteers were challenged with LPS (4 ng/kg IV) after intake of either placebo or aspirin (1000 mg). Acetaminophen (1000 mg) was given to a third group to control for potential effects of antipyresis. Neither aspirin nor acetaminophen inhibited LPS-induced coagulation. However, LPS increased the percentage of circulating TF ϩ monocytes by 2-fold. This increase was associated with a decrease in FVIIa levels, which reached a minimum of 50% 24 hours after LPS infusion. Furthermore, LPS-induced thrombin generation increased plasma levels of circulating polymerized, but not cross-linked, fibrin (ie, thrombus precursor protein), whereas levels of soluble fibrin were unaffected. In summary, a single 1000-mg dose of aspirin did not decrease LPS-induced coagulation. However, our study showed, for the first time, that LPS increases TF ϩ monocytes, substantially decreases FVIIa levels, and enhances plasma levels of thrombus precursor protein, which may be a useful marker of fibrin formation in humans. ). 1,2 DIC is defined by enhanced activity of coagulation factors, exhaustion of endogenous coagulation inhibitors, and activation and depletion of platelets by formation of thrombi in the vasculature. 3 Results of several studies suggest that initiation of coagulation in sepsis is driven primarily by the tissue factor (TF)-dependent pathway of coagulation. 4,5 Inhibition of the TF-dependent activation of coagulation using antibodies against TF or activated factor VII (FVIIa) completely prevents LPS-induced activation of coagulation in animals. 6 -8 Thus, inhibition of TF expression on monocytes during endotoxemia may present a promising therapeutic option for dampening the coagulation cascade. A recent in vitro study showed that acetylsalicylic acid (ASA) reduces LPS-induced TF expression on isolated monocytes. 9 Conversely, whole-blood experiments showed that ASA enhanced TF activity on monocytes. 10,11 Furthermore, TF expression on human monocytes is enhanced by the presence of granulocytes and activated platelets, suggesting an even more complex regulation of TF in vivo. [12][13][14][15][16] In addition, results of animal studies suggest that inhibition of thromboxane A 2 -mediated platelet activation may improve DIC induced by LPS. 3 Besides in vitro studies and experiments in animals, infusion of small doses of LPS into humans has emerged as a valuable tool to explore the pathogenesis ...

Heparin Blunts Endotoxin-Induced Coagulation Activation

“…In accordance with our own previous findings, 18 TFpositive monocytes doubled after LPS infusion in the placebo group. The clinical relevance of our finding is supported by a report that high tissue thromboplastin activity on monocytes predicted adverse outcome in patients with Neisseria meningitidis infection.…”

“…23 Thus, we confirm our previous finding that TpP levels increase during endotoxemia. 18 We also showed that UFH and LMWH equally blunted the TpP increase after LPS (Figure 2). In contrast, using a chromogenic assay based on fibrin-mediated conversion of plasminogen to plasmin, 22 we found no increase in any study subject.…”

“…17 Because all samples required immediate processing to avoid artificial activation of leukocytes, cells were stained before and 2, 6, and 24 hours after LPS infusion. The fluorescein-isothiocyanate-coupled anti-TF monoclonal antibody was purchased from American Diagnostics Inc. 18 …”

Tissue factor-expressing monocytes inhibit fibrinolysis through a TAFI-mediated mechanism, and make clots resistant to heparins

“…[15][16][17] In particular, an increase in TF-expressing circulating monocytes has been documented in various conditions, including human lowdose endotoxemia, venous thrombosis accompanying different diseases and disseminated intravascular coagulation (DIC), especially sepsis-associated DIC. [27][28][29][30] In these conditions, the number of blood TF-positive monocytes, as assessed by flow cytometry, was reported to range between 5-60%, the highest values being present in septic patients with DIC. Therefore, an important question to be addressed is whether fibrinolysis can be inhibited by a concentration of TF-expressing cells comparable to that attainable in vivo.…”

Deletion of the Braun Lipoprotein-Encoding Gene and Altering the Function of Lipopolysaccharide Attenuate the Plague Bacterium

“…Similarly, both Lpp and LPS activate the complement cascade, coagulation cascade, and other inflammatory mediators (24)(25)(26)(27). In addition, Lpp purified from Y. enterocolitica synergizes with its LPS to induce production of proinflammatory cytokines in vitro and in vivo, leading to septic shock (28).…”