III. Instantaneous inhibition by compound 48/80 of tissue factor-initiated extrinsic coagulation is mediated by the downregulation of factor VII activation

Mast Cells Granular Contents Are Crucial for Deep Vein Thrombosis in Mice

RATIONALE

Deep vein thrombosis (DVT) and its complication pulmonary embolism have high morbidity reducing quality of life and leading to death. Cellular mechanisms of DVT initiation remain poorly understood.

OBJECTIVE

We sought to determine the role of mast cells (MCs) in DVT initiation and validate MCs as a potential target for DVT prevention.

METHODS AND RESULTS

In a mouse model, DVT was induced by partial ligation (stenosis) of the inferior vena cava. We demonstrated that 2 strains of mice deficient for MCs were completely protected from DVT. Adoptive transfer of in vitro differentiated MCs restored thrombosis. MCs were present in the venous wall, and the number of granule-containing MCs decreased with thrombosis. Pharmacological depletion of MCs granules or prevention of MC degranulation also reduced DVT. Basal plasma levels of von Willebrand factor and recruitment of platelets to the inferior vena cava wall after DVT induction were reduced in MC-deficient mice. Stenosis application increased plasma levels of soluble P-selectin in wild-type but not in MC-deficient mice. MC releasate elevated ICAM-1 (intercellular adhesion molecule-1) expression on HUVEC (human umbilical vein endothelial cells) in vitro. Topical application of compound 48/80, an MC secretagogue, or histamine, a Weibel-Palade body secretagogue from MCs, potentiated DVT in wild-type mice, and histamine restored thrombosis in MC-deficient animals.

CONCLUSIONS

MCs exacerbate DVT likely through endothelial activation and Weibel-Palade body release, which is, at least in part, mediated by histamine. Because MCs do not directly contribute to normal hemostasis, they can be considered potential targets for prevention of DVT in humans.

Tissue factor upregulation drives a thrombosis-inflammation circuit in relation to cardiovascular complications

The extrinsic coagulation is recognized as an 'inducible' signalling cascade resulting from tissue factor (TF) upregulation by exposure to clotting zymogen FVII upon inflammation or tissue injury. Following the substantial initiation, an array of proteolytic activation generates mediating signals (active serine proteases: FVIIa, FXa and FIIa) that lead to hypercoagulation with fibrin overproduction manifesting thrombosis. In addition, TF upregulation plays a central role in driving a thrombosis-inflammation circuit. Coagulant mediators (FVIIa, FXa and FIIa) and endproduct (fibrin) are proinflammatory, eliciting tissue necrosis factor, interleukins, adhesion molecules and many other intracellular signals in different cell types. Such resulting inflammation could ensure 'fibrin' thrombosis via feedback upregulation of TF. Alternatively, the resulting inflammation triggers platelet/leukocyte/polymononuclear cell activation thus contributing to 'cellular' thrombosis. TF is very vulnerable to upregulation resulting in hypercoagulability and subsequent thrombosis and inflammation, either of which presents cardiovascular risks. The prevention and intervention of TF hypercoagulability are of importance in cardioprotection. Blockade of inflammation reception and its intracellular signalling prevents TF expression from upregulation. Natural (activated protein C, tissue factor pathway inhibitor, or antithrombin III) or pharmacological anticoagulants readily offset the extrinsic hypercoagulation mainly through FVIIa, FXa or FIIa inhibition. Therefore, anticoagulants turn off the thrombosis-inflammation circuit, offering not only antithrombotic but anti-inflammatory significance in the prevention of cardiovascular complications.

Novel anticoagulant activity of polybrene: inhibition of monocytic tissue factor hypercoagulation following bacterial endotoxin induction

The enhanced extrinsic coagulation in response to inflammation could contribute to disseminated intravascular coagulation, often manifesting cardiovascular complications. The complex mechanism remains unclear. Nor is the effective anticoagulation well established. The search for arresting hypercoagulation is of antithrombotic relevance. The ability of polybrene (PB) to inhibit tissue factor (TF)-initiated extrinsic blood coagulation was demonstrated at the protein and cellular levels as well as in human plasma samples. In a single-stage clotting assay, PB dose-dependently offset bacterial endotoxin (lipopolysaccharide)-induced monocytic TF (mTF) hypercoagulation and inhibited rabbit brain thromboplastin (rbTF) procoagulation. Consistent with these findings, the significantly prolonged prothrombin time indicated the depressed extrinsic coagulation by PB. However, PB showed no effect on thrombin time. We dissected the extrinsic pathway to further determine the inhibitory site(s) of PB. A two-stage chromogenic assay monitoring S-2288 hydrolysis showed that PB readily blocked mTF-dependent or rbTF-dependent FVII activation, which was verified by the diminished activated factor VII (FVIIa) formation derived from the proteolytic cleavage of its zymogen factor VII on Western blotting analyses. PB had no effect on FVIIa and activated factor X amidolytic activity. Nor was the dissected TF/FVIIa-catalyzed factor X activation affected. In conclusion, the preferential downregulation of factor VII activation was responsible for the depressed extrinsic coagulation. PB could present a novel anticoagulant antagonizing the extrinsic hypercoagulation for the prevention of thrombotic complication following sepsis and inflammations.

Protamine inhibits tissue factor-initiated extrinsic coagulation

The enhanced extrinsic coagulation in response to inflammation could contribute to disseminated intravascular coagulation, often manifesting cardiovascular complications. The complex mechanism remains unclear and effective management is not well established. The ability of protamine to offset bacterial endotoxin (LPS)-induced tissue factor (TF)-initiated extrinsic coagulation was demonstrated in human peripheral blood monocytes and cultured human leukaemia THP-1 monocytes, which was consistent with the inhibition of rabbit brain thromboplastin (rbTF) procoagulant activity in a cell-free in vitro model. Protamine significantly prolonged prothrombin time, further confirming the downregulation of the extrinsic pathway. However, thrombin time remained unaltered. Chromogenic assays were performed to dissect the extrinsic pathway, identifying inhibitory site(s). Protamine significantly inhibited factor VII (FVII) activation but not the dissected FX activation. The amidolytic activities of FVIIa and FXa were unaffected. The inhibited FVII activation in the presence of protamine was confirmed by the diminished FVIIa formation on Western blot analyses. Protamine preferentially inhibited TF-catalysed FVII activation, downregulating the extrinsic cascade. Protamine could be of anticoagulant significance in the management of the extrinsic hypercoagulation.

Involvement of MAPK activation in bacterial endotoxin-inducible tissue factor upregulation in human monocytic THP-1 cells

BACKGROUND

Monocytic tissue factor (mTF) hypercoagulation leading to thrombotic complications is commonly observed following sepsis.

OBJECTIVE

We herein study the intracellular mechanism of mTF upregulation in human model monocytic THP-1 cells in response to bacterial endotoxin (lipopolysaccharide, LPS; Escherichia coli O111:B04), determining if mitogen-activated protein kinase (MAPK) activation is involved in the signaling.

METHODS

We assessed mTF upregulation by its cell surface expression, protein synthesis, and functional activity based on flow cytometry, Western blotting analysis, and a single-stage clotting assay, respectively.

RESULTS

A 3-h challenge with LPS (100 ng/ml) drastically induced mTF functional activity, accompanied by elevated surface mTF expression and synthesis. The suppression by genistein (G) of LPS-inducible mTF upregulation implied the involvement of protein tyrosine kinase activation in mTF upregulation. LPS activated MAPK, which was significantly depressed by G, SB 203580 (SB), and PD 98058 (PD). Interestingly, inclusion of SB and PD also markedly diminished LPS-inducible mTF upregulation. The parallelism between MAPK and mTF activities revealed the involvement of MAPK activation in such mTF upregulation. Based on the ability of SB and PD to respectively block LPS-inducible tyrosine phosphorylation of p38 MAPK and Erk1/2, it was evident that tyrosine phosphorylation of MAPKs is required for mediating LPS-inducible mTF synthesis and upregulation. Contrasting with the established prevention of mTF upregulation by these inhibitors, failure to offset the already LPS-induced mTF activity seemed to be consistent with the view that LPS readily activated MAPK responsible for mTF synthesis.

CONCLUSION

Our data suggest that the tyrosine phosphorylation of MAPKs (p38 and Erk1/2) leading to their activation could be a prerequisite for LPS induction of mTF synthesis contributing to the upregulation of mTF-initiated extrinsic coagulation.

Blockade by ruthenium red of tissue factor-initiated coagulation

The ability of ruthenium red (RuR) to inhibit tissue factor (TF)-initiated blood coagulation was demonstrated at the protein and cellular levels as well as in human plasma. In a single-stage clotting assay, RuR concentration-dependently inhibited rabbit brain thromboplastin (rbTF)-induced coagulation and offset bacterial endotoxin (LPS)-induced monocytic TF (mTF) hypercoagulation; the IC(50)s were estimated at 7.5 and 12.3 microM, respectively. A 15-min preincubation of RuR with rbTF or monocyte suspension resulted in the pronounced inhibition with a significantly lowered IC(50) at 1.8 or 7.7 microM for rbTF or mTF procoagulation, respectively. The differences in IC(50)s between rbTF and mTF without or with the preincubation indicated that TF was a primary target for RuR action. The effect of RuR on the physiological function of TF in FVII activation was demonstrated by the proteolytic cleavage of FVII zymogen to its active forms of serine protease on Western blotting analyses. RuR readily blocked TF-catalyzed FVII activation (diminished FVIIa formation), thus down regulating the initiation of blood coagulation. Inclusion of RuR into human plasma samples in vitro significantly prolonged prothrombin time, indicating the depressed coagulation. FVII activity was inhibited by 30 - 60% depending on the dose; as a result, FX activity also decreased. However, RuR showed no effect on thrombin time. Thus, RuR inhibited FVII activation to block the initiation of coagulation.

IV. Anticoagulant activity of compound 48/80: inhibition of factor VII activation in leukemia THP-1 monocytes

Our previous study described a novel biologic function of compound 48/80 (48/80) in the downregulation of monocytic tissue factor (TF)-initiated hypercoagulation in response to bacterial endotoxin (lipopolysaccharide; LPS). The inhibition was not due to the blockade of LPS cell signaling, as evidenced by the unaffected LPS-induced TF synthesis. We herein determined the mechanism by which 48/80 inhibits the extrinsic coagulation in agonist-challenged THP-1 monocytes. LPS as well as A23187 substantially induced TF activity. TF synthesis was enhanced by LPS but not by A23187. However, the elevated FVII binding to monocytes accompanying the upregulation of factor VII (FVII) activation was uniformly observed in both cases. A 5-min preincubation of the cells with a sheep anti-humanTF antibody (anti-hTF Ab) showed the downregulation of FVII activation, indicating a regulatory role of FVII binding in the modulation of the extrinsic coagulation. The 48/80 blocked FVII binding to monocytes, leading to the preferential inhibition of FVII activation. As the result of the diminished FVIIa formation, monocytic TF-initiated extrinsic coagulation was downregulated in agonist-challenged THP-1 monocytes.