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Pathophysiology of Acquired Coagulopathy
Pathophysiology of Acquired Coagulopathy K Tefera and R Sacher, University of Cincinnati, Cincinnati, OH, USA ã 2014 Elsevier Inc. All rights reserved.
Abbreviations: APS B2GP CD55 DIC ECs ET GPI HIT MAC NO NOS
Antiphospholipid syndrome Beta-2 glycoprotein Decay-accelerating factor Disseminated intravascular coagulation Endothelial cells Essential thrombosis Glycosylphosphatidylinositol Heparin-induced thrombocytopenia CD59 membrane attack complex Nitric oxide Nitric oxide synthase
Introduction
NS PAI-1 PDI PMN PNH PV TF TFPI TLR4 TNF u-PA VTE
Nephrotic syndrome Plasminogen activator inhibitor 1 Protein disulfide isomerase Polymorphonuclear leukocytes Paroxysmal nocturnal hemoglobinuria Polycythemia vera Tissue factor Tissue factor pathway inhibitor Toll-like receptor 4 Tissue necrosis factor Urokinase plasminogen activator Venous thromboembolic event
APS is highly prothrombotic state characterized by presence of specific antibodies. It is associated with both arterial and venous thromboembolic event (VTE) and recurrent unexplained miscarriage. Antibodies that are essential for the diagnosis of the APS include Immunoglobulin (Ig) A and IgM for anticardiolipin and anti-beta 2 glycoprotein (anti-B2GP I) or an assay for lupus anticoagulant (Figure 1). For the diagnosis of APS, a presence of high titer or positive assay for the aforementioned studies should be positive for more than 12 weeks. Currently, there are multiple proposed mechanisms for the high rate of thrombus and hypercoagulable state in APS. One of the most important pathophysiological findings in a patient with APS is an increased marker for oxidative state. There is a significant decrease in paraoxonase, an enzyme that accounts
the antioxidant property of high-density lipoprotein. There is also an increase in 8-epi-prostaglandin, a biomarker for lipid oxidation. These and other oxidative agents have shown to have a direct effect on the structure of (B2GP). The increased oxidative stress exposes beta-2 globulin protein’s structure and exposing it to the immune system. In nonoxidative states, the B2GP exists in a free thiol form, which is characterized by broken disulfide done in domains I and V of the structure. In oxidative states, the immunogenic states of B2GP I dominate, which is characterized by a disulfide bond on domains I and V (Figure 2). In immunogenic beta-2 globulin protein, the anti-B2GP antibody binds, which is correlated with a high risk of thrombosis. In a patient with APS, vascular endothelial repair and response to injury are impaired. Recent British study showed that this pathological finding is secondary to an increased activity of oxidant and decreased activity of the body’s anti-inflammatory mechanism. The same study also showed a reduced activity of the antioxidant protein paraoxonase. Patients with ASP also have decreased number of nitrite, which is a by-product of nitric oxide (NO) synthesis, showing indirect evidence for decreased production of NO. NO is produced by nitric oxide synthase (NOS) from L-arginine. It plays an important role in normal vascular endothelial function and thus in the prevention of thrombotic events. In animal model, the anti-B2GP I decreases the production of NO by directly antagonizing the function of NO; in turn, it impairs the integrity of blood vessels. The combination of decreased NO, impaired endothelial activity, and oxidative states plays a role in prothrombotic states of APS. However, further clinical studies needed to evaluate the direct effect of anti-beta 2 glycoprotein antibody on the synthesis of NO in human. Antiphospholipid antibodies increase the production of proadhesive molecules, that is, tissue factor (TF) and tissue necrosis factor (TNF) alpha in endothelial cells (ECs), monocytes, mitochondrial monocyte, and neutrophil. Antiphospholipid antibody stimulates the production of procoagulant and proadhesive through different lipid raft. In ECs, annexin,
Pathobiology of Human Disease: A Dynamic Encyclopedia of Disease Mechanisms
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Thrombosis is a state where physiological prothrombotic mechanisms of the body override its antithrombotic gatekeeper mechanism. It is classically caused by a defect in Virchow’s triad: stasis, hypercoagulable states, and vascular endothelial injury. While stasis and vascular endothelial injury play significant roles in the formation of thrombotic event, this article focuses on acquired hypercoagulable states. Hypercoagulable states can be from congenital or acquired causes. Congenital thrombophilia includes factor V Leiden mutation, protein C and protein S mutation, and antithrombin deficiency (Table 1). Acquired coagulopathies include antiphospholipid syndrome (APS), nephrotic syndrome (NS), livers disease, use of contraceptive, and different hematologic disease (Table 2). Hematologic diseases that can cause thrombotic states include essential thrombosis (ET), polycythemia vera (PV), paroxysmal nocturnal hemoglobinuria (PNH), and hematologic malignancies.
Acquired Thrombophilia Antiphospholipid Syndrome
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Table 1
Non-Malignant Hematopathology | Pathophysiology of Acquired Coagulopathy
Congenital hypercoagulable states
Antithrombin III deficiency Protein C deficiency Protein S deficiency Tissue plasminogen activator release deficiency Factor V Leiden mutation Prothrombin mutation Dysfibrinogenemia Fibrinolytic abnormalities Increased levels of plasminogen activator inhibitor
Table 2
Acquired hypercoagulable states
Antiphospholipid syndrome Cancer Pregnancy Myeloproliferative disorders Paroxysmal nocturnal hemoglobinuria Heparin-induced thrombocytopenia Pregnancy Oral contraceptive Nephrotic syndrome Postoperative states Obesity
APLA
ACA
LA
annexin. There are also some data showing CD12 and Toll like receptor 2 (TLR2) being activated by antiphospholipid antibody leading to the production of procoagulant molecules. In mitochondrial monocyte and neutrophil, direct disruption and release of reactive oxygen species lead to the release of TFs. TF is a transmembrane protein and a member of the class II cytokine and hematopoietic growth factor receptor family. The extracellular domain of TF serves as a receptor for activated factor (VIIa). Under normal circumstances, circulating factor VII is not exposed to TF. Following endothelial damage, TF forms a complex with factor VIIa that leads to the activation of factors IX and X activating the thrombotic cascade, resulting to higher rate of thrombin formation. Poorly controlled factor XI synthesis is associated with APS. An increase in factor XI is associated with VTE. Activated factor XI leads for activation of factor IX that leads to cascade for thrombus formation. Factor XI can be a substrate of the oxido-reductases thioredoxin 1 and protein disulfide isomerase (PDI), which attack the disulfide done interchain of factor XI. These will increase in free thiol form of factor XI. Further studies are warranted in this area to understand the role of thiol form of factor XI in the pathophysiology of thrombus formation in a patient with APS. The successful use of eculizumab (monoclonal antibody to terminal complement-5) for the treatment of microangiopathic thrombosis in renal transplant patients, and antiphospholipid antibody associated thrombosis in animal models, showed that there might be an association between activation of the complement system and thrombus formation. One can argue that complement activation plays important role in the thrombus formation in APS. However, there should be further investigation on the role of complement system in the hypercoagulable state in humans with APS. Significant number of patient with known APS will have no thrombotic event until a triggering factor happens; proving the two hit hypothesis for thrombotic event. These events can be trauma, new medications that are associated with thrombus, pregnancy, or surgery. Once these events happen, multiple factors including impaired endothelial healing, increased production of adhesive proteins, and procoagulant factors play a role on the actual thrombus formation.
b2 GPI
Paroxysmal Nocturnal Hemoglobinuria
Figure 1 Antiphospholipid antibodies (APLAs) with their different subtypes. ACA, anticardiolipin antibody; b2GP1, beta 2 glycoprotein 1; LA, lupus anticoagulant. Reproduced from Moll, S., et al., 2010. ASH-SAP 2010, 179–215.
Toll-like receptor 4 (TLR4), P38 mitogen-activated protein kinase (MAPK), calreticulin, and nucleolin play some role in the synthesis of procoagulant. In monocytes, there are some data showing that antiphospholipid antibodies induce production of procoagulant molecules by activation of TLR4 and
PNH is a rare acquired clonal stem cell disorder where glycosylphosphatidylinositol (GPI) anchor protein synthesis is defective. This is due to an abnormality in the PIG-A gene. The defect in PIG-A gene leads to a partial or complete absence of certain GPI-linked proteins, that is, CD59 (membrane attack complex (MAC) inhibitory factors) and CD55 (decayaccelerating factor). The clinical manifestation of this disease relates to the underlying hematopoietic function. These include hemolytic anemia, hypoplastic bone marrow, hypercoagulable states, and progression to myelodysplastic syndrome and acute leukemia. Hypercoagulable states result in VTEs in intra-abdominal, hepatic, and peripheral veins. PNH is also associated with arterial thrombus formation, though this is a relatively rare event compared to VTE.
Non-Malignant Hematopathology | Pathophysiology of Acquired Coagulopathy
Oxidized form (immunogenic)
Free thiol form (nonimmunogenic) SH32 SH60
S32 S60 B-cell epitope R39, R43
B-cell epitope R39, R43
K19
K19
R39
DI
R39
DI
R43
DII
DIII DIV
S
S
Oxidoreductases
S
S
Oxidation
S S
S S
S
S
S306
S
DIII DIV
S
SH288
T-cell epitope 276–290 Major species in healthy persons
S
DII
S
S281
S
S
S
S
S S
S
S
S
S306 S326
S
S
S
DV
S
S281
SH326
S
S
DV
S
R43
S
S
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S288
T-cell epitope 276–290 Major species in patients with the antiphospholipid syndrome
Figure 2 Schematic representation of the crystal structure (fishhook configuration) of beta 2-glycoprotein I (B2GP I). The carboxy-terminal amino acid cysteine (Cys) 326 forms a disulfide (S–S) bridge with Cys288. D, domain; K, lysine; R, arginine; SH, free thiol. The numbers indicate the position of the amino acid starting from the amino-terminal end of the protein.
The pathophysiology of hemolysis is mediated by the activated complement system. The degree of the hemolysis depends on the percentage of the clones evolved, the degree of complement activation and proportion of the cells that are abnormal. While we have a good explanation for the pathophysiology of hemolysis in PNH, the pathophysiology for the hypercoagulable states is not currently well explained. The current theory for the cause of the hypercoagulable states in PNH includes membrane fragmented from the intravascular hemolysis of hemoglobin-activating platelets, enhanced expression of TFs from damaged ECs, impaired fibrinolysis, and depleted NO. Normal platelets isolate MAC and remove them with vesiculation. If the vesicle is not removed, they will bind to factor V and become the assembly site for prothrombinase activity. The MAC complex tends to form more in a patient with PNH. This is primarily due to lack or decreased number of CD59 to prevent activation of C9. In vitro studies have shown that platelets in PNH are exposed more to factor V, confirming
the prothrombotic state. The study has also showed increased thrombus generation compared to normal platelets. Increased prothrombinase activity leads to the formation of thrombin, which in turn activates platelet aggregation and eventual clot formation. In areas where the flow of blood is slow, MAC complex attacks the EC of the blood vessels lead to the activation of the platelets as described earlier. This finding is a likely reason behind the localization of blood clot in areas that are unusual places like intra-abdominal venous system. While the toxic effect of free red blood cells (RBCs) to EC is known, the complement system’s directly toxicity to the EC is not clear. Some studies support involvement of the complement system. There is also decreased activation of clotting system with anticomplement eculizumab (a monoclonal antibody against complement factor C9). On the other side, studies have showed normal level of EC activation markers. Currently, there is no good evidence for clonal abnormality in EC. Further study is needed to evaluate the role of complement system in endothelial damage, which is a catalyst for the
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Non-Malignant Hematopathology | Pathophysiology of Acquired Coagulopathy
formation of thrombosis and hypercoagulable states in PNH. In a patient with PNH, there is markedly increased TF level compared to standard, and there are some data showing that the TF produced by complement-injured monocytes and macrophages lack both CD55 and CD59. Tissue factor pathway inhibitor (TFPI) is produced mainly by the endothelium microvasculature. It plays a major role in the body’s antithrombotic mechanism. It forms a complex with TF and prevents the activation of VII and activated X. In a normal cell, it is expressed with and upregulated in monocytes. In PNH, the monocyte lacks TFPI receptor. In the absence of these inhibitors, monocytes upregulate the production of TF synthesis, thus resulting in a prothrombotic state. Proteinase 3 (PR3) is a protein that is expressed on neutrophils and plays major role in prevention of platelet aggregation. It reduces thrombin-induced platelet activation; it also modulates the cleavage of endothelial protein C receptor and degrades TFPI, upregulation of EC TF, and cleavage of von Willebrand factor (vWF). The PNH clone is known to be inversely associated with circulating PR3 level. Low level of PR3 in PNH increases platelet activation and upregulation of TF, contributing to the high rate of thrombosis in PNH patient. NO helps the smooth muscle cell in blood vessel to relax. This is very important for the inhibition of platelet activation. It also has anti-inflammation effects. Free hemoglobin released from hemolysis is directly toxic to NO. In chronic hemolysis like in a patient with PNH, the body’s ability to clear the circulating free hemoglobin will be overwhelmed. The free hemoglobin that is not cleared by the normal body’s clearing mechanism will bind to NO irreversibly and form nitrate and methemoglobin. It also releases arginase that shunts away arginine, an important substance needed for the synthesis of NO to ornithine. In a patient with PNH, fibrinolysis is also impaired. In normal fibrinolysis cascade, plasminogen is converted to plasmin by urokinase plasminogen activator (u-PA) (Figure 3). For the u-PA to be active, it has to bind to GPI anchored u-PA receptor (u-PAR). In a patient with PNH, the plasma u-PAR level is elevated; this most likely shows its inability to be
attached to the cell membrane due to a lack of GPI anchor proteins. The freely available u-PAR attaches to u-PA and decreases the local availability of u-PA. With low-level u-PA, the conversion of plasminogen to plasmin will be impaired. This will affect proper fibrinolysis, thus contributing to the prothrombotic states of PNH. The combinations of endothelial injury from chronic hemolysis, increased production of TF, decreased synthesis of NO, and impaired fibrinolysis make factor PNH highly thrombotic states resulting in high incidence of thrombosis.
Myeloproliferative Neoplasms These are rare diverse groups of diseases that are derived from clonal myeloid stem cell-derived diseases. The most recent world health organization classification of myeloproliferative neoplasm (MPN) includes chronic myelogenic leukemia, PV, ET, primary myelofibrosis, mastocytosis, and myeloid and lymphoid neoplasia associated with eosinophilia and abnormalities of PDGFRA, PDGFRB, or FGFR1 (Table 3). Table 3
Current classification of myeloproliferative neoplasm
Myeloproliferative neoplasms (MPNs) Chronic myelogenous leukemia, BCR–ABL1-positive Chronic neutrophilic leukemia Polycythemia vera Primary myelofibrosis Essential thrombocythemia Chronic eosinophilic leukemia, not otherwise specified Systemic mastocytosis MPN, unclassifiable Myeloid (and lymphoid) neoplasms associated with eosinophilia and abnormalities of PDGFRA, PDGFRB, or FGFR1 Myeloid and lymphoid neoplasms associated with PDGFRA rearrangement Myeloid neoplasms associated with PDGFRB rearrangement Myeloid and lymphoid neoplasms associated with FGFR1 abnormalities Source: Medeiros, B.C., et al., 2010. ASH-SAP 2010, 397–442. FGFR ¼ fibroblast growth factor receptor; PDGFR ¼ platelet-derived growth factor receptor.
Plasminogen
Urokinase Streptokinase
Plasminogen activator inhibitor-1 (PAI-1)
tPA
TAFI Plasmin Cross-linked fibrin polymer
Fibrin degradation products
Figure 3 Fibrinolysis. TAFI, thrombin-activated fibrinolysis inhibitor; tPA, tissue plasminogen activator. Reproduced from Moll, S., et al., 2010. ASHSAP 2010, 179–215.
Non-Malignant Hematopathology | Pathophysiology of Acquired Coagulopathy
These diseases have clonal stem cell abnormality. Despite this common finding, they have diverse clinical presentations. Of these abnormalities, ET and PV are known to have increased risk of thrombosis. Two-thirds of thrombus diagnoses in PV are arterial, while one-third have venous thrombus. ET is also associated with increased risk of thrombosis. The thrombosis in ET is also occurring in both arterial and venous sites; the arterial event is much more frequent. Overall thrombotic event in ET are less frequent compared to PV. The pathophysiology for increased risk of thrombosis in PV includes hyperviscosity due to uncontrolled erythrocytosis, qualitative platelet dysfunction, and polymorphonuclear leukocytes (PMN) or granulocyte activation. Compared to healthy individuals, patients with ET and PV have elevated platelet–granulocyte and platelet–monocyte complex. PMN activation markers including CD11D and alkaline phosphatase (ALP), antaginase expression, and cellular and plasma elastase are also significantly increased in both ET and PV. The same study has shown an elevation of hypercoagulable markers, that is, thrombin–antithrombin; d-dimer level is elevated with increased level of PMN activation. In a patient with either PV or ET, there are an elevated number of markers for endothelial injury including thrombomodulin and vWF. From these findings, the most likely mechanism of increased risk of thrombosis formation in PV and ET is the combination of endothelial injury and increased rate interaction of activated and reactive platelet by leukocytosis and activated PMN. TF production by both monocyte and neutrophil increased in a patient with ET and PV. In vivo studies have showed a downregulation of neutrophil TF expression and neutrophil–platelet complex with treatment with hydroxyurea. It is important to note that 95% of PV and 50% of ET cases are associated with JAK2 V617F mutation. Attempt to evaluate the relation between this mutation and thrombus has showed minimum to no relationship between the Janus kinase (JAK) mutation and hypercoagulable state in PV and ET. The current recommendation is to place patient with low risk of bleeding on daily baby aspirin for prevention of thrombotic event.
Malignancy Includes Migratory Superficial Thrombophlebitis (Trousseau’s Syndrome) Patients with malignancy are known to have a hypercoagulable state. Cancer-associated thrombosis is known as Trousseau’s syndrome in honor of the person who described this event first in the 1860s. The incidence of thrombotic event varies for different neoplastic state. Certain malignancy tends to have a higher event of thrombotic event. Pancreatic and other colorectal malignancies, ovarian cancer, and acute promyelocytic leukemia are well known to have higher rates of malignancies. Certain malignancies, for example, leukemia (with the exception of APL), are not known to have increased risk of thrombus. Multiple factors play a role in increased risk thrombotic event in a patient with malignancy. Decreased physical activity, drugs (chemotherapeutic agents), invasive procedures, and infection play a major role in the formation of thrombotic events.
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In addition to these factors, there is good evidence that malignancy by itself is a hypercoagulable state without the aforementioned events. Malignant cancer cells produce high procoagulant factors. This can be a TF or cancer procoagulant factor (calciumdependent cysteine protease) by the malignant cell. When tumor cells interact with monocyte and macrophages, it induces the monocyte/macrophage to produce TF. These interactions also induce the release of interleukin 6 (IL-6), IL-1, and TNF. The release of this inflammatory markers leads to EC damage. Once the vascular bed is injured, it is exposed for thrombogenic activity. Increased production of TF and cysteine protease leads to activation of factor VII directly and factor X by activated VII leading to the formation of thrombin. Cancer procoagulant proteins can act directly to factor X independent of TF/factor and activate it to form a complex with VIII. This is especially true for sialic acid moieties of mucin from adenocarcinoma (Figure 4). There are multiple attempts done to understand the pathophysiology of chemotherapeutic agents association with thrombosis in cancer patient. Currently, there is no consensus on the underlying pathophysiology. However, it is well known that certain drug causes damage to EC and vascular wall bed. Cancer patient also tend to have more invasive vascular procedures, which also increase the risk of endothelial damage and platelet activation. Immunosuppressed patient, that is, cancer patient in chemotherapy, is also at increased risk for infection. Infection with gram-negative bacteria will lead to releases of endotoxin and includes endothelial damage.
Nephrotic Syndrome NS is a renal disease where a significant amount of protein (3.5 g m2 day1) is excreted through the urinary system. There are different underlying renal pathologies leading to these clinical findings. These include minimal change disease, membranoproliferative glomerulonephritis, and membranous glomerulonephritis. NS is also known for its hypercoagulable state. Patients with NS have increased level of venous thromboembolic events. There are also some data stating increased risk of arterial risk of thrombus especially in pediatric population (31–32). Currently, there is no consensus on the underlying pathophysiology for the hypercoagulable. Current theory includes increased activation of platelet, loss or decreased amount of endogenous anticoagulant, activation of the coagulation system, and decreased activity of fibrinolysis. In a patient with NS, there are increased markers of vWF, decreased cell deformity, and thrombocytosis. These are signs of active platelet transportation to affected vessel. Increased marker for platelet activation including CD62P and P-selectin was noticed in NS patient. However, further study needs to be done to establish the correlation of this laboratory parameter to in vivo clinical findings. Loss of small-molecular-weight proteins is a classical finding in NS. These include IX, X, XII, and, antithrombin. To compensate for this loss, the body increases protein production. Since high-molecular-weight proteins are less likely to be excreted, the patient will have increased number of high-
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Non-Malignant Hematopathology | Pathophysiology of Acquired Coagulopathy
Chemotherapy Monocyte or macrophage
Interleukin-1 Interleukin-6 Tumor necrosis factor
Malignant cell
Mucin: sialic acid Procoagulant activity
Tissue factor
Factor XII
Endothelial disruption
Factor XIIa
Factor X
Factor VII
Factor Xa
Factor VIIa
Thrombin
Prothrombin
Fibrin clot Fibrinogen
Figure 4 Mechanisms of thrombosis in cancer. Picture from Bick, R.L., 2003. NEJM 349, 109–111.
molecular-weight proteins like factors V and VIII and fibrinogen. An increase in fibrinogen and factor VIII level is associated with their procoagulant state. Increased production of prothrombotic protein and loss of antithrombotic small protein contribute to the hypercoagulable state. Decreased level of plasminogen was noticed in a patient with NS. The rate of this decline is associated with the level of proteinuria. Plasminogen is needed for normal function of fibrinolysis (Figure 3). The enzyme that is important for the activation of plasminogen to plasma, that is, tissue plasminogen activator (tPA), is also elevated, confirming decline of plasminogen. The other current interest is the role of increased low density lipoprotein and other lipoproteins, in hypercoagulable states associated with NS. Dyslipidemia that is associated with NS is associated with change in glomerular hemostatic system resulting in renal thrombotic event. However, the detailed pathophysiology is not currently known. Further study is needed to understand the relationship between hyperlipidemia of NS and hypercoagulable states.
Medications Multiple chemotherapeutic agents are known to be associated with thrombotic states. These medications include cytotoxic agents like mitomycin and asparaginase and noncytotoxic agent like tamoxifen, thalidomide and lenalidomide. Nonchemotherapeutic agents like estrogen-based contraceptives and heparin-induced thrombocytopenia (HIT) are also associated with hypercoagulable states. The mechanism of thrombus formation in these medications with the exception of HIT is not well described. HIT is a clinical condition where a patient exposed to heparin forms antibody not only to heparin but also to the platelet–heparin complex. The antibody attacks the complex and expedites the destruction of the complex by the spleen, thus removing the platelet resulting in thrombocytopenia. This clinical condition is also associated with hypercoagulable states with high rate of thrombus formation. About 50% of untreated patients with HIT develop thrombus known as heparin-induced thrombocytopenia.
Fondaparinux Unfractionated heparin
Low-molecular-weight heparin
Fcg RIIa
Platelet activation
Released microparticles Fcg RIIa
Immune complexes
(a) Monocyte and platelet microparticles
Extrinsic pathway
Intrinsic pathway Factor IX
Tissue factor
Factor X
Factor IXa
Factor VIIa
Factor XI
Factor XIa
Factor VIIIa
Factor Xa
Danaparoid fondaparinux
Factor X
Factor Va
Thrombin
Prothrombin
Argatroban Hirudin Lepirudin Bivalirudin
Fibrin clotting
Platelet activation
(b)
Figure 5 (a) Platelet activation by antibodies against the platelet factor 4 (PF4)–heparin complex. Heparin-induced thrombocytopenia (HIT) is caused by IgG antibodies that bind to PF4 when it is bound to heparin (the PF4–heparin complex). The formation of multimolecular complexes of PF4 and heparin depends on the concentrations of PF4 and heparin, the length of the heparin chain, and the degree of sulfation. Unfractionated heparin (3000–30 000 Da) forms larger complexes with PF4 than low-molecular-weight heparin (2000–9000 Da). Fondaparinux (1728 Da) is unlikely to form complexes large enough to cause platelet activation. Once pathogenic HIT antibodies cross-link Fc-g receptor IIa (FcgRIIa) on the platelet surface, platelets become activated, microparticles are released, and the coagulation cascade is triggered. (b) The coagulation cascade. The IgG–PF4–heparin immune complexes that characterize HIT bind to the FcgRIIa on platelets, Fc-g receptor I (FcgRI) on monocytes, and potentially other cell surfaces. Tissue factor is expressed on the surface of the cell and on the released microparticles. This enhances the activation of factor VIIa, which in turn activates factor Xa and ultimately generates thrombin. The tissue factor–factor VIIa complex also activates factor IX, a component of the intrinsic pathway of coagulation. The hypercoagulable state caused by HIT can result in venous or arterial thrombosis, particularly at sites of vascular damage. The agents used in treating HIT inhibit clotting downstream of these sites of activation. Danaparoid and fondaparinux inhibit factor Xa, whereas argatroban and the hirudin-related agents inhibit thrombin.
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Non-Malignant Hematopathology | Pathophysiology of Acquired Coagulopathy
Heparin–PF4 antibody complex activates platelets to release procoagulants. The complex also causes injury to the endothelial lining of a vessel. Injury to the EC can result in a release of inflammatory marker IL-6, vWF, and other adhesion molecules. HIT is also associated with decreased production of protein C and increased production of TFs. The combination of increased production of procoagulants, adhesive molecule TFs, and endothelial damage results in highly prothrombotic states resulting in both arterial and venous thromboses. If this disease is not diagnosed on time, it has a devastating result to the patient (Figure 5).
Pregnancy Pregnancy and postpartum period are known to have increased risk of VTE. In the United States, 1 in 500 pregnancies will have complication of VTE. Postpartum period tends to have more VTE than antepartum. Pregnancy has all the three classic Virchow’s triad: stasis, hypercoagulable stasis, and endothelial injury. Endothelial injury happens during delivery where a significant uteroplacental changes. This probably explains the increased risk of VTE. As for the hypercoagulability, there is a significant
elevation of coagulation factors including factors I, II, VIII, IX, and X, while the body’s natural anticoagulant protein C production decreases during pregnancy. At the same time, there is a significant decrease on production of antifibrinolytic protein. The other most important anatomical and physiological change associated with pregnancy is the compression of the inferior vena cava by the gravid uterus. Almost 88% of lower extremity deep vein thrombosis is seen on the left extremity. Patients with congenital hypercoagulable state (Table 1) have even high risk of thrombosis compared to patients with no known congenital hypercoagulable state. This is also true with the other acquired hypercoagulable state described earlier. Due to high risk of thrombosis, a hematologist should be involved in the care of pregnant women with any of the congenital or acquired hypercoagulable states.
Disseminated Intravascular Coagulation Disseminated intravascular coagulation (DIC) is a widespread activation of coagulation associated with severe systemic disease. Thought as primarily associated with severe bacterial
Tissue factor + factor VIIa Cytokines Factor IXa (+ factor VIII)
Factor Xa (+ factor V)
Plasminogen Plasminogen activators
Factor IIa (thrombin) Fibrinogen
Fibrin
Low levels of antithrombin III Impaired function of protein-C system Insufficient TFPI Impairment of anticoagulation pathways
Generation of thrombin mediated by tissue factor
Formation of fibrin
PAI-1
Plasmin
Fibrin
FDPs
Suppression of fibrinolysis by PAI-1
Inadequate removal of fibrin
Thrombosis of small and midsize vessels Figure 6 Pathogenetic pathways involved in disseminated intravascular coagulation (DIC). In patients with DIC, fibrin is formed as a result of the generation of thrombin mediated by tissue factor. Tissue factor, expressed on the surface of activated mononuclear cells and endothelial cells, binds and activates factor VII. The complex of tissue factor and factor VIIa can activate factor X directly (black arrows) or indirectly (white arrows) by means of activated factor IX and factor VIII. Activated factor X, in combination with factor V, can convert prothrombin (factor II) to thrombin (factor IIa). Simultaneously, all three physiological means of anticoagulation – antithrombin III, protein C, and tissue factor pathway inhibitor (TFPI) – are impaired. The resulting intravascular formation of fibrin is not balanced by adequate removal of fibrin because endogenous fibrinolysis is suppressed by high plasma levels of plasminogen activator inhibitor type 1 (PAI-1). The high levels of PAI-1 inhibit plasminogen activator activity and consequently reduce the rate of formation of plasmin. The combination of increased formation of fibrin and inadequate removal of fibrin results in disseminated intravascular thrombosis. FDPs denote fibrin degradation products. Reproduced from Mercel Levi, M.D., Hugo ten Cate, M.D., 1999. NEJM 341, 586–592.
Non-Malignant Hematopathology | Pathophysiology of Acquired Coagulopathy
infection, it can happen with any infection. It can also be associated with trauma, malignancy, vascular and immunologic disorder, and obstetric complication. The pathogenesis of DIC is associated with increased inflammatory cytokines like IL-6 and TNF alpha. Activation of these cytokines can be associated with any of the clinical scenarios described above. The cytokines play roles in the activation of thrombus formation, impairing the body’s anticoagulation proteins, and fibrinolytic activity. TF expressed mononuclear cell in response to cytokines that are produced with systemic disease. Activated TF attaches to factor VII. The combination of TF and VII in turn activates factors IX and X. This leads to an activation of thrombin, thus forming fibrin and thrombus. Antithrombin III, protein C, and TFPI are the most important endogenous inhibitors of coagulation. All these proteins were affected in DIC. Antithrombin III is consumed by the elastase released from activated neutrophils resulting to a low level. While there is no evidence of a decreased level of TFPI in DIC, there is evidence that the regulation of TF inhibition is decreased significantly in DIC. The synthesis of Protein C is decreased due to impaired thrombomodulin. Cytokine-mediated inflammatory markers, which are associated with DIC mediate this process. The protein S level also decreases in DIC, which is important for the proper function of protein C. Plasminogen activator inhibitor 1 (PAI-1) is an important inhibitor of the fibrinolytic system. In animal model of DIC, the production of PAI-1 is increased especially at the peak of coagulation. Increased production of PAI-1 overwhelms the production of fibrinolytic activity that is induced due to the formation of fibrin resulting in the production of thrombus. The combination of decreased endogenous anticoagulant, impairment of fibrinolytic activity, and increased thrombin formation makes the DIC highly thrombogenic state (Figure 6).
Further Reading Agar, C., van Os, G.M., Morgelin, M., Sprenger, R.R., Marquart, J.A., Urbanus, R.T., et al., 2010. Beta2-glycoprotein I can exist in 2 conformations: implications for our understanding of the antiphospholipid syndrome. Blood 116, 1336–1343. Allen, K.L., Fonseca, F.V., Betapudi, V., Willard, B., Zhang, J., McCrae, K.R., 2012. A novel pathway for human endothelial cell activation by antiphospholipid/anti-beta2 glycoprotein I antibodies. Blood 119, 884–893. Alvarez-Larran, A., Garcia-Pagan, J.C., Abraldes, J.G., Arellano, E., Reverter, J.C., Bosch, J., et al., 2004. Increased CD11b neutrophil expression in Budd–Chiari syndrome or portal vein thrombosis secondary to polycythaemia vera. Br. J. Haematol. 124, 329–335. Ames, P.R., Batuca, J.R., Ciampa, A., Iannaccone, L., Delgado Alves, J., 2010. Clinical relevance of nitric oxide metabolites and nitrative stress in thrombotic primary antiphospholipid syndrome. J. Rheumatol. 37, 2523–2530. Ames, P.R., Nourooz-Zadeh, J., Tommasino, C., Alves, J., Brancaccio, V., Anggard, E.E., 1998. Oxidative stress in primary antiphospholipid syndrome. Thromb. Haemost. 79, 447–449. Arellano-Rodrigo, E., Alvarez-Larran, A., Reverter, J.C., Villamor, N., Colomer, D., Cervantes, F., 2006. Increased platelet and leukocyte activation as contributing mechanisms for thrombosis in essential thrombocythemia and correlation with the JAK2 mutational status. Haematologica 91, 169–175. ASH-SAP, 2013. From American Society of Hematology, fifth ed. American Society of Hematology, Washington.
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Basavaraj, M.G., Gruber, F.X., Sovershaev, M., Appelbom, H.I., Osterud, B., Petersen, L.C., et al., 2010. The role of TFPI in regulation of TF-induced thrombogenicity on the surface of human monocytes. Thromb. Res. 126, 418–425. Cameron, J.S., 1984. Coagulation and thromboembolic complications in the nephrotic syndrome. Adv. Nephrol. Necker Hosp. 13, 75–114. Cameron, J.S., 1987. The nephrotic syndrome and its complications. Am. J. Kidney Dis. 10, 157–171. Charakida, M., Besler, C., Batuca, J.R., Sangle, S., Marques, S., Sousa, M., et al., 2009. Vascular abnormalities, paraoxonase activity, and dysfunctional HDL in primary antiphospholipid syndrome. JAMA 302, 1210–1217. Conway, E.M., Rosenberg, R.D., 1988. Tumor necrosis factor suppresses transcription of the thrombomodulin gene in endothelial cells. Mol. Cell. Biol. 8, 5588–5592. Creasey, A.A., Chang, A.C., Feigen, L., Wun, T.C., Taylor Jr., F.B., Hinshaw, L.B., 1993. Tissue factor pathway inhibitor reduces mortality from Escherichia coli septic shock. J. Clin. Invest. 91, 2850–2860. Cristina, L., Benilde, C., Michela, C., Mirella, F., Giuliana, G., Gualtiero, P., 2004. High plasma levels of factor VIII and risk of recurrence of venous thromboembolism. Br. J. Haematol. 124, 504–510. de Laat, B., Wu, X.X., van Lummel, M., Derksen, R.H., de Groot, P.G., Rand, J.H., 2007. Correlation between antiphospholipid antibodies that recognize domain I of beta2glycoprotein I and a reduction in the anticoagulant activity of annexin A5. Blood 109, 1490–1494. Delgado Alves, J., Ames, P.R., Donohue, S., Stanyer, L., Nourooz-Zadeh, J., Ravirajan, C., et al., 2002. Antibodies to high-density lipoprotein and beta2-glycoprotein I are inversely correlated with paraoxonase activity in systemic lupus erythematosus and primary antiphospholipid syndrome. Arthritis Rheum. 46, 2686–2694. Falanga, A., Marchetti, M., Evangelista, V., Vignoli, A., Licini, M., Balicco, M., et al., 2000. Polymorphonuclear leukocyte activation and hemostasis in patients with essential thrombocythemia and polycythemia vera. Blood 96, 4261–4266. Falanga, A., Marchetti, M., Vignoli, A., Balducci, D., Barbui, T., 2005. Leukocyte–platelet interaction in patients with essential thrombocythemia and polycythemia vera. Exp. Hematol. 33, 523–530. Francis Jr., R.B., Sandler, R.M., Levitan, D., Feinstein, E.I., Massry, S.G., Feinstein, D.I., 1985. Reduced alpha-2-antiplasmin levels in the nephrotic syndrome. Nephron 39, 325–329. Giannakopoulos, B., Gao, L., Qi, M., Wong, J.W., Yu, D.M., Vlachoyiannopoulos, P.G., et al., 2012. Factor XI is a substrate for oxidoreductases: enhanced activation of reduced FXI and its role in antiphospholipid syndrome thrombosis. J. Autoimmun. 39, 121–129. Gralnick, H.R., Vail, M., McKeown, L.P., Merryman, P., Wilson, O., Chu, I., et al., 1995. Activated platelets in paroxysmal nocturnal haemoglobinuria. Br. J. Haematol. 91, 697–702. Grau, E., Oliver, A., Felez, J., Barcelo, P., Fernandez, C., Ballarin, J.A., et al., 1988. Plasma and urinary heparin cofactor II levels in patients with nephrotic syndrome. Thromb. Haemost. 60, 137–140. Grunewald, M., Siegemund, A., Grunewald, A., Schmid, A., Koksch, M., Schopflin, C., et al., 2003. Plasmatic coagulation and fibrinolytic system alterations in PNH: relation to clone size. Blood Coagul. Fibrinolysis 14, 685–695. Helley, D., de Latour, R.P., Porcher, R., Rodrigues, C.A., Galy-Fauroux, I., Matheron, J., et al., 2010. Evaluation of hemostasis and endothelial function in patients with paroxysmal nocturnal hemoglobinuria receiving eculizumab. Haematologica 95, 574–581. Hoffman, R., Benz Jr., E.J., Silberstein, L.E., Heslop, H., Jeffrey Weitz, J., Anastasi, J., 2013. Hematology: Basic Principles and Practice, sixth ed., Elsevier. Ioannou, Y., Zhang, J.Y., Qi, M., Gao, L., Qi, J.C., Yu, D.M., et al., 2011. Novel assays of thrombogenic pathogenicity in the antiphospholipid syndrome based on the detection of molecular oxidative modification of the major autoantigen beta2glycoprotein I. Arthritis Rheum. 63, 2774–2782. Jankowska, A.M., Szpurka, H., Calabro, M., Mohan, S., Schade, A.E., Clemente, M., et al., 2011. Loss of expression of neutrophil proteinase-3: a factor contributing to thrombotic risk in paroxysmal nocturnal hemoglobinuria. Haematologica 96, 954–962. Kanfer, A., 1990. Coagulation factors in nephrotic syndrome. Am. J. Nephrol. 10 (Suppl 1), 63–68. Kanfer, A., Kleinknecht, D., Broyer, M., Josso, F., 1970. Coagulation studies in 45 cases of nephrotic syndrome without uremia. Thromb. Diath. Haemorrh. 24, 562–571. Kendall, A.G., Lohmann, R.C., Dossetor, J.B., 1971. Nephrotic syndrome. A hypercoagulable state. Arch. Intern. Med. 127, 1021–1027. Kessler, C.M., Tang, Z., Jacobs, H.M., Szymanski, L.M., 1997. The suprapharmacologic dosing of antithrombin concentrate for Staphylococcus aureus-induced disseminated intravascular coagulation in guinea pigs: substantial reduction in mortality and morbidity. Blood 89, 4393–4401.
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Kitchens, C.S., Konkle, B.A., Kessler, C.M., 2013 Consultative Hemostasis and Thrombosis. third ed., Elsevier Saunders, Philadelphia. Kyrle, P.A., 2003. High factor VIII and the risk of venous thromboembolism. Hamostaseologie 23, 41–44. Kyrle, P.A., Minar, E., Hirschl, M., Bialonczyk, C., Stain, M., Schneider, B., et al., 2000. High plasma levels of factor VIII and the risk of recurrent venous thromboembolism. N. Engl. J. Med. 343, 457–462. Levi, M., ten Cate, H., Bauer, K.A., van der Poll, T., Edgington, T.S., Buller, H.R., et al., 1994. Inhibition of endotoxin-induced activation of coagulation and fibrinolysis by pentoxifylline or by a monoclonal anti-tissue factor antibody in chimpanzees. J. Clin. Invest. 93, 114–120. Liebman, H.A., Feinstein, D.I., 2003. Thrombosis in patients with paroxysmal noctural hemoglobinuria is associated with markedly elevated plasma levels of leukocytederived tissue factor. Thromb. Res. 111, 235–238. Lonze, B.E., Singer, A.L., Montgomery, R.A., 2010. Eculizumab and renal transplantation in a patient with CAPS. N. Engl. J. Med. 362, 1744–1745. Loscalzo, J., Schafer, A.I., 2003. Thrombosis and Hemorrhage, third ed. Lippincott Williams & Wilkins, Philadelphia. Ma, K., Simantov, R., Zhang, J.C., Silverstein, R., Hajjar, K.A., McCrae, K.R., 2000. High affinity binding of beta 2-glycoprotein I to human endothelial cells is mediated by annexin II. J. Biol. Chem. 275, 15541–15548. Maciejewski, J.P., Young, N.S., Yu, M., Anderson, S.M., Sloand, E.M., 1996. Analysis of the expression of glycosylphosphatidylinositol anchored proteins on platelets from patients with paroxysmal nocturnal hemoglobinuria. Thromb. Res. 83, 433–447. Marde, V.J., Aird, W.C., Bennett, J.S., Schulman, S., White, G.C., 2013. Hemostasis and Thrombosis: Basic Principles and Clinical Practice, sixth ed. Lippincott Williams & Wilkins. Maroney, S.A., Cunningham, A.C., Ferrel, J., Hu, R., Haberichter, S., Mansbach, C.M., et al., 2006. A GPI-anchored co-receptor for tissue factor pathway inhibitor controls its intracellular trafficking and cell surface expression. J. Thromb. Haemost. 4, 1114–1124. Maroney, S.A., Haberichter, S.L., Friese, P., Collins, M.L., Ferrel, J.P., Dale, G.L., et al., 2007. Active tissue factor pathway inhibitor is expressed on the surface of coated platelets. Blood 109, 1931–1937. Maugeri, N., Giordano, G., Petrilli, M.P., Fraticelli, V., de Gaetano, G., Cerletti, C., et al., 2006. Inhibition of tissue factor expression by hydroxyurea in polymorphonuclear leukocytes from patients with myeloproliferative disorders: a new effect for an old drug? J. Thromb. Haemost. 4, 2593–2598. Mehls, O., Andrassy, K., Koderisch, J., Herzog, U., Ritz, E., 1987. Hemostasis and thromboembolism in children with nephrotic syndrome: differences from adults. J. Pediatr. 110, 862–867. Meijers, J.C., Tekelenburg, W.L., Bouma, B.N., Bertina, R.M., Rosendaal, F.R., 2000. High levels of coagulation factor XI as a risk factor for venous thrombosis. N. Engl. J. Med. 342, 696–701. Mesters, R.M., Mannucci, P.M., Coppola, R., Keller, T., Ostermann, H., Kienast, J., 1996. Factor VIIa and antithrombin III activity during severe sepsis and septic shock in neutropenic patients. Blood 88, 881–886. Miyakis, S., Lockshin, M.D., Atsumi, T., Branch, D.W., Brey, R.L., Cervera, R., et al., 2006. International consensus statement on an update of the classification criteria for definite antiphospholipid syndrome (APS). J. Thromb. Haemost. 4, 295–306. Nachman, R.L., Silverstein, R., 1993. Hypercoagulable states. Ann. Intern. Med. 119, 819–827. Nemerson, Y., 1988. Tissue factor and hemostasis. Blood 71, 1–8. Ninomiya, H., Abe, T., Fujita, T., 1989. Prolongation of red-cell life-span by incorporation of decay-accelerating factor (DAF) into red cells of paroxysmal nocturnal haemoglobinuria (PNH). Br. J. Haematol. 73, 132–133. Ninomiya, H., Hasegawa, Y., Nagasawa, T., Abe, T., 1997. Excess soluble urokinase-type plasminogen activator receptor in the plasma of patients with paroxysmal nocturnal hemoglobinuria inhibits cell-associated fibrinolytic activity. Int. J. Hematol. 65, 285–291. Oger, E., Lacut, K., Van Dreden, P., Bressollette, L., Abgrall, J.F., Blouch, M.T., et al., 2003. High plasma concentration of factor VIII coagulant is also a risk factor for venous thromboembolism in the elderly. Haematologica 88, 465–469. Osterud, B., Flaegstad, T., 1983. Increased tissue thromboplastin activity in monocytes of patients with meningococcal infection: related to an unfavourable prognosis. Thromb. Haemost. 49, 5–7. Palmer, R.M., Ashton, D.S., Moncada, S., 1988. Vascular endothelial cells synthesize nitric oxide from L-arginine. Nature 333, 664–666.
Parker, C., Omine, M., Richards, S., Nishimura, J., Bessler, M., Ware, R., et al., 2005. Diagnosis and management of paroxysmal nocturnal hemoglobinuria. Blood 106, 3699–3709. Perez-Sanchez, C., Ruiz-Limon, P., Aguirre, M.A., Bertolaccini, M.L., Khamashta, M.A., Rodriguez-Ariza, A., et al., 2012. Mitochondrial dysfunction in antiphospholipid syndrome: implications in the pathogenesis of the disease and effects of coenzyme Q(10) treatment. Blood 119, 5859–5870. Pierangeli, S.S., Girardi, G., Vega-Ostertag, M., Liu, X., Espinola, R.G., Salmon, J., 2005. Requirement of activation of complement C3 and C5 for antiphospholipid antibody-mediated thrombophilia. Arthritis Rheum. 52, 2120–2124. Rabelink, T.J., Zwaginga, J.J., Koomans, H.A., Sixma, J.J., 1994. Thrombosis and hemostasis in renal disease. Kidney Int. 46, 287–296. Raife, T.J., Cao, W., Atkinson, B.S., Bedell, B., Montgomery, R.R., Lentz, S.R., et al., 2009. Leukocyte proteases cleave von Willebrand factor at or near the ADAMTS13 cleavage site. Blood 114, 1666–1674. Ramesh, S., Morrell, C.N., Tarango, C., Thomas, G.D., Yuhanna, I.S., Girardi, G., et al., 2011. Antiphospholipid antibodies promote leukocyte-endothelial cell adhesion and thrombosis in mice by antagonizing eNOS via beta2GPI and apoER2. J. Clin. Invest. 121, 120–131. Raschi, E., Testoni, C., Bosisio, D., Borghi, M.O., Koike, T., Mantovani, A., et al., 2003. Role of the MyD88 transduction signaling pathway in endothelial activation by antiphospholipid antibodies. Blood 101, 3495–3500. Renesto, P., Si-Tahar, M., Moniatte, M., Balloy, V., Van Dorsselaer, A., Pidard, D., et al., 1997. Specific inhibition of thrombin-induced cell activation by the neutrophil proteinases elastase, cathepsin G, and proteinase 3: evidence for distinct cleavage sites within the aminoterminal domain of the thrombin receptor. Blood 89, 1944–1953. Rosse, W.F., Gutterman, L.A., 1970. The effect of iron therapy in paroxysmal nocturnal hemoglobinuria. Blood 36, 559–565. Rother, R.P., Bell, L., Hillmen, P., Gladwin, M.T., 2005. The clinical sequelae of intravascular hemolysis and extracellular plasma hemoglobin: a novel mechanism of human disease. JAMA 293, 1653–1662. Satta, N., Kruithof, E.K., Fickentscher, C., Dunoyer-Geindre, S., Boehlen, F., Reber, G., et al., 2011. Toll-like receptor 2 mediates the activation of human monocytes and endothelial cells by antiphospholipid antibodies. Blood 117, 5523–5531. Sims, P.J., Wiedmer, T., 1991. The response of human platelets to activated components of the complement system. Immunol. Today 12, 338–342. Sorice, M., Longo, A., Capozzi, A., Garofalo, T., Misasi, R., Alessandri, C., et al., 2007. Anti-beta2-glycoprotein I antibodies induce monocyte release of tumor necrosis factor alpha and tissue factor by signal transduction pathways involving lipid rafts. Arthritis Rheum. 56, 2687–2697. Steppich, B.A., Seitz, I., Busch, G., Stein, A., Ott, I., 2008. Modulation of tissue factor and tissue factor pathway inhibitor-1 by neutrophil proteases. Thromb. Haemost. 100, 1068–1075. Suffredini, A.F., Harpel, P.C., Parrillo, J.E., 1989. Promotion and subsequent inhibition of plasminogen activation after administration of intravenous endotoxin to normal subjects. N. Engl. J. Med. 320, 1165–1172. Tarry, W.C., Moser, A.J., Makhoul, R.G., 1993. Peripheral arterial thrombosis in the nephrotic syndrome. Surgery 114, 618–623. Taylor, F., Chang, A., Ferrell, G., Mather, T., Catlett, R., Blick, K., et al., 1991. C4b-binding protein exacerbates the host response to Escherichia coli. Blood 78, 357–363. Tefferi, A., Elliott, M., 2007. Thrombosis in myeloproliferative disorders: prevalence, prognostic factors, and the role of leukocytes and JAK2V617F. Semin. Thromb. Hemost. 33, 313–320. Thomson, C., Forbes, C.D., Prentice, C.R., Kennedy, A.C., 1974. Changes in blood coagulation and fibrinolysis in the nephrotic syndrome. Q. J. Med. 43, 399–407. Tkaczyk, M., Baj, Z., 2002. Surface markers of platelet function in idiopathic nephrotic syndrome in children. Pediatr. Nephrol. 17, 673–677. Vaziri, N.D., Ngo, J.L., Ibsen, K.H., Mahalwas, K., Roy, S., Hung, E.K., 1982. Deficiency and urinary losses of factor XII in adult nephrotic syndrome. Nephron 32, 342–346. Vega-Ostertag, M., Casper, K., Swerlick, R., Ferrara, D., Harris, E.N., Pierangeli, S.S., 2005. Involvement of p38 MAPK in the up-regulation of tissue factor on endothelial cells by antiphospholipid antibodies. Arthritis Rheum. 52, 1545–1554. Vellenga, E., Mulder, N.H., Nieweg, H.O., de Vries-Hospers, H.G., 1982. Endotoxin in paroxysmal nocturnal haemoglobulinuria (PNH). Br. J. Haematol. 50, 174–175. Villegas-Mendez, A., Montes, R., Ambrose, L.R., Warrens, A.N., Laffan, M., Lane, D.A., 2007. Proteolysis of the endothelial cell protein C receptor by neutrophil proteinase 3. J. Thromb. Haemost. 5, 980–988.
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Abbreviations: APS B2GP CD55 DIC ECs ET GPI HIT MAC NO NOS
Antiphospholipid syndrome Beta-2 glycoprotein Decay-accelerating factor Disseminated intravascular coagulation Endothelial cells Essential thrombosis Glycosylphosphatidylinositol Heparin-induced thrombocytopenia CD59 membrane attack complex Nitric oxide Nitric oxide synthase
Introduction
NS PAI-1 PDI PMN PNH PV TF TFPI TLR4 TNF u-PA VTE
Nephrotic syndrome Plasminogen activator inhibitor 1 Protein disulfide isomerase Polymorphonuclear leukocytes Paroxysmal nocturnal hemoglobinuria Polycythemia vera Tissue factor Tissue factor pathway inhibitor Toll-like receptor 4 Tissue necrosis factor Urokinase plasminogen activator Venous thromboembolic event
APS is highly prothrombotic state characterized by presence of specific antibodies. It is associated with both arterial and venous thromboembolic event (VTE) and recurrent unexplained miscarriage. Antibodies that are essential for the diagnosis of the APS include Immunoglobulin (Ig) A and IgM for anticardiolipin and anti-beta 2 glycoprotein (anti-B2GP I) or an assay for lupus anticoagulant (Figure 1). For the diagnosis of APS, a presence of high titer or positive assay for the aforementioned studies should be positive for more than 12 weeks. Currently, there are multiple proposed mechanisms for the high rate of thrombus and hypercoagulable state in APS. One of the most important pathophysiological findings in a patient with APS is an increased marker for oxidative state. There is a significant decrease in paraoxonase, an enzyme that accounts
the antioxidant property of high-density lipoprotein. There is also an increase in 8-epi-prostaglandin, a biomarker for lipid oxidation. These and other oxidative agents have shown to have a direct effect on the structure of (B2GP). The increased oxidative stress exposes beta-2 globulin protein’s structure and exposing it to the immune system. In nonoxidative states, the B2GP exists in a free thiol form, which is characterized by broken disulfide done in domains I and V of the structure. In oxidative states, the immunogenic states of B2GP I dominate, which is characterized by a disulfide bond on domains I and V (Figure 2). In immunogenic beta-2 globulin protein, the anti-B2GP antibody binds, which is correlated with a high risk of thrombosis. In a patient with APS, vascular endothelial repair and response to injury are impaired. Recent British study showed that this pathological finding is secondary to an increased activity of oxidant and decreased activity of the body’s anti-inflammatory mechanism. The same study also showed a reduced activity of the antioxidant protein paraoxonase. Patients with ASP also have decreased number of nitrite, which is a by-product of nitric oxide (NO) synthesis, showing indirect evidence for decreased production of NO. NO is produced by nitric oxide synthase (NOS) from L-arginine. It plays an important role in normal vascular endothelial function and thus in the prevention of thrombotic events. In animal model, the anti-B2GP I decreases the production of NO by directly antagonizing the function of NO; in turn, it impairs the integrity of blood vessels. The combination of decreased NO, impaired endothelial activity, and oxidative states plays a role in prothrombotic states of APS. However, further clinical studies needed to evaluate the direct effect of anti-beta 2 glycoprotein antibody on the synthesis of NO in human. Antiphospholipid antibodies increase the production of proadhesive molecules, that is, tissue factor (TF) and tissue necrosis factor (TNF) alpha in endothelial cells (ECs), monocytes, mitochondrial monocyte, and neutrophil. Antiphospholipid antibody stimulates the production of procoagulant and proadhesive through different lipid raft. In ECs, annexin,
Pathobiology of Human Disease: A Dynamic Encyclopedia of Disease Mechanisms
http://dx.doi.org/10.1016/B978-0-12-386456-7.07911-9
Thrombosis is a state where physiological prothrombotic mechanisms of the body override its antithrombotic gatekeeper mechanism. It is classically caused by a defect in Virchow’s triad: stasis, hypercoagulable states, and vascular endothelial injury. While stasis and vascular endothelial injury play significant roles in the formation of thrombotic event, this article focuses on acquired hypercoagulable states. Hypercoagulable states can be from congenital or acquired causes. Congenital thrombophilia includes factor V Leiden mutation, protein C and protein S mutation, and antithrombin deficiency (Table 1). Acquired coagulopathies include antiphospholipid syndrome (APS), nephrotic syndrome (NS), livers disease, use of contraceptive, and different hematologic disease (Table 2). Hematologic diseases that can cause thrombotic states include essential thrombosis (ET), polycythemia vera (PV), paroxysmal nocturnal hemoglobinuria (PNH), and hematologic malignancies.
Acquired Thrombophilia Antiphospholipid Syndrome
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Table 1
Non-Malignant Hematopathology | Pathophysiology of Acquired Coagulopathy
Congenital hypercoagulable states
Antithrombin III deficiency Protein C deficiency Protein S deficiency Tissue plasminogen activator release deficiency Factor V Leiden mutation Prothrombin mutation Dysfibrinogenemia Fibrinolytic abnormalities Increased levels of plasminogen activator inhibitor
Table 2
Acquired hypercoagulable states
Antiphospholipid syndrome Cancer Pregnancy Myeloproliferative disorders Paroxysmal nocturnal hemoglobinuria Heparin-induced thrombocytopenia Pregnancy Oral contraceptive Nephrotic syndrome Postoperative states Obesity
APLA
ACA
LA
annexin. There are also some data showing CD12 and Toll like receptor 2 (TLR2) being activated by antiphospholipid antibody leading to the production of procoagulant molecules. In mitochondrial monocyte and neutrophil, direct disruption and release of reactive oxygen species lead to the release of TFs. TF is a transmembrane protein and a member of the class II cytokine and hematopoietic growth factor receptor family. The extracellular domain of TF serves as a receptor for activated factor (VIIa). Under normal circumstances, circulating factor VII is not exposed to TF. Following endothelial damage, TF forms a complex with factor VIIa that leads to the activation of factors IX and X activating the thrombotic cascade, resulting to higher rate of thrombin formation. Poorly controlled factor XI synthesis is associated with APS. An increase in factor XI is associated with VTE. Activated factor XI leads for activation of factor IX that leads to cascade for thrombus formation. Factor XI can be a substrate of the oxido-reductases thioredoxin 1 and protein disulfide isomerase (PDI), which attack the disulfide done interchain of factor XI. These will increase in free thiol form of factor XI. Further studies are warranted in this area to understand the role of thiol form of factor XI in the pathophysiology of thrombus formation in a patient with APS. The successful use of eculizumab (monoclonal antibody to terminal complement-5) for the treatment of microangiopathic thrombosis in renal transplant patients, and antiphospholipid antibody associated thrombosis in animal models, showed that there might be an association between activation of the complement system and thrombus formation. One can argue that complement activation plays important role in the thrombus formation in APS. However, there should be further investigation on the role of complement system in the hypercoagulable state in humans with APS. Significant number of patient with known APS will have no thrombotic event until a triggering factor happens; proving the two hit hypothesis for thrombotic event. These events can be trauma, new medications that are associated with thrombus, pregnancy, or surgery. Once these events happen, multiple factors including impaired endothelial healing, increased production of adhesive proteins, and procoagulant factors play a role on the actual thrombus formation.
b2 GPI
Paroxysmal Nocturnal Hemoglobinuria
Figure 1 Antiphospholipid antibodies (APLAs) with their different subtypes. ACA, anticardiolipin antibody; b2GP1, beta 2 glycoprotein 1; LA, lupus anticoagulant. Reproduced from Moll, S., et al., 2010. ASH-SAP 2010, 179–215.
Toll-like receptor 4 (TLR4), P38 mitogen-activated protein kinase (MAPK), calreticulin, and nucleolin play some role in the synthesis of procoagulant. In monocytes, there are some data showing that antiphospholipid antibodies induce production of procoagulant molecules by activation of TLR4 and
PNH is a rare acquired clonal stem cell disorder where glycosylphosphatidylinositol (GPI) anchor protein synthesis is defective. This is due to an abnormality in the PIG-A gene. The defect in PIG-A gene leads to a partial or complete absence of certain GPI-linked proteins, that is, CD59 (membrane attack complex (MAC) inhibitory factors) and CD55 (decayaccelerating factor). The clinical manifestation of this disease relates to the underlying hematopoietic function. These include hemolytic anemia, hypoplastic bone marrow, hypercoagulable states, and progression to myelodysplastic syndrome and acute leukemia. Hypercoagulable states result in VTEs in intra-abdominal, hepatic, and peripheral veins. PNH is also associated with arterial thrombus formation, though this is a relatively rare event compared to VTE.
Non-Malignant Hematopathology | Pathophysiology of Acquired Coagulopathy
Oxidized form (immunogenic)
Free thiol form (nonimmunogenic) SH32 SH60
S32 S60 B-cell epitope R39, R43
B-cell epitope R39, R43
K19
K19
R39
DI
R39
DI
R43
DII
DIII DIV
S
S
Oxidoreductases
S
S
Oxidation
S S
S S
S
S
S306
S
DIII DIV
S
SH288
T-cell epitope 276–290 Major species in healthy persons
S
DII
S
S281
S
S
S
S
S S
S
S
S
S306 S326
S
S
S
DV
S
S281
SH326
S
S
DV
S
R43
S
S
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S288
T-cell epitope 276–290 Major species in patients with the antiphospholipid syndrome
Figure 2 Schematic representation of the crystal structure (fishhook configuration) of beta 2-glycoprotein I (B2GP I). The carboxy-terminal amino acid cysteine (Cys) 326 forms a disulfide (S–S) bridge with Cys288. D, domain; K, lysine; R, arginine; SH, free thiol. The numbers indicate the position of the amino acid starting from the amino-terminal end of the protein.
The pathophysiology of hemolysis is mediated by the activated complement system. The degree of the hemolysis depends on the percentage of the clones evolved, the degree of complement activation and proportion of the cells that are abnormal. While we have a good explanation for the pathophysiology of hemolysis in PNH, the pathophysiology for the hypercoagulable states is not currently well explained. The current theory for the cause of the hypercoagulable states in PNH includes membrane fragmented from the intravascular hemolysis of hemoglobin-activating platelets, enhanced expression of TFs from damaged ECs, impaired fibrinolysis, and depleted NO. Normal platelets isolate MAC and remove them with vesiculation. If the vesicle is not removed, they will bind to factor V and become the assembly site for prothrombinase activity. The MAC complex tends to form more in a patient with PNH. This is primarily due to lack or decreased number of CD59 to prevent activation of C9. In vitro studies have shown that platelets in PNH are exposed more to factor V, confirming
the prothrombotic state. The study has also showed increased thrombus generation compared to normal platelets. Increased prothrombinase activity leads to the formation of thrombin, which in turn activates platelet aggregation and eventual clot formation. In areas where the flow of blood is slow, MAC complex attacks the EC of the blood vessels lead to the activation of the platelets as described earlier. This finding is a likely reason behind the localization of blood clot in areas that are unusual places like intra-abdominal venous system. While the toxic effect of free red blood cells (RBCs) to EC is known, the complement system’s directly toxicity to the EC is not clear. Some studies support involvement of the complement system. There is also decreased activation of clotting system with anticomplement eculizumab (a monoclonal antibody against complement factor C9). On the other side, studies have showed normal level of EC activation markers. Currently, there is no good evidence for clonal abnormality in EC. Further study is needed to evaluate the role of complement system in endothelial damage, which is a catalyst for the
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Non-Malignant Hematopathology | Pathophysiology of Acquired Coagulopathy
formation of thrombosis and hypercoagulable states in PNH. In a patient with PNH, there is markedly increased TF level compared to standard, and there are some data showing that the TF produced by complement-injured monocytes and macrophages lack both CD55 and CD59. Tissue factor pathway inhibitor (TFPI) is produced mainly by the endothelium microvasculature. It plays a major role in the body’s antithrombotic mechanism. It forms a complex with TF and prevents the activation of VII and activated X. In a normal cell, it is expressed with and upregulated in monocytes. In PNH, the monocyte lacks TFPI receptor. In the absence of these inhibitors, monocytes upregulate the production of TF synthesis, thus resulting in a prothrombotic state. Proteinase 3 (PR3) is a protein that is expressed on neutrophils and plays major role in prevention of platelet aggregation. It reduces thrombin-induced platelet activation; it also modulates the cleavage of endothelial protein C receptor and degrades TFPI, upregulation of EC TF, and cleavage of von Willebrand factor (vWF). The PNH clone is known to be inversely associated with circulating PR3 level. Low level of PR3 in PNH increases platelet activation and upregulation of TF, contributing to the high rate of thrombosis in PNH patient. NO helps the smooth muscle cell in blood vessel to relax. This is very important for the inhibition of platelet activation. It also has anti-inflammation effects. Free hemoglobin released from hemolysis is directly toxic to NO. In chronic hemolysis like in a patient with PNH, the body’s ability to clear the circulating free hemoglobin will be overwhelmed. The free hemoglobin that is not cleared by the normal body’s clearing mechanism will bind to NO irreversibly and form nitrate and methemoglobin. It also releases arginase that shunts away arginine, an important substance needed for the synthesis of NO to ornithine. In a patient with PNH, fibrinolysis is also impaired. In normal fibrinolysis cascade, plasminogen is converted to plasmin by urokinase plasminogen activator (u-PA) (Figure 3). For the u-PA to be active, it has to bind to GPI anchored u-PA receptor (u-PAR). In a patient with PNH, the plasma u-PAR level is elevated; this most likely shows its inability to be
attached to the cell membrane due to a lack of GPI anchor proteins. The freely available u-PAR attaches to u-PA and decreases the local availability of u-PA. With low-level u-PA, the conversion of plasminogen to plasmin will be impaired. This will affect proper fibrinolysis, thus contributing to the prothrombotic states of PNH. The combinations of endothelial injury from chronic hemolysis, increased production of TF, decreased synthesis of NO, and impaired fibrinolysis make factor PNH highly thrombotic states resulting in high incidence of thrombosis.
Myeloproliferative Neoplasms These are rare diverse groups of diseases that are derived from clonal myeloid stem cell-derived diseases. The most recent world health organization classification of myeloproliferative neoplasm (MPN) includes chronic myelogenic leukemia, PV, ET, primary myelofibrosis, mastocytosis, and myeloid and lymphoid neoplasia associated with eosinophilia and abnormalities of PDGFRA, PDGFRB, or FGFR1 (Table 3). Table 3
Current classification of myeloproliferative neoplasm
Myeloproliferative neoplasms (MPNs) Chronic myelogenous leukemia, BCR–ABL1-positive Chronic neutrophilic leukemia Polycythemia vera Primary myelofibrosis Essential thrombocythemia Chronic eosinophilic leukemia, not otherwise specified Systemic mastocytosis MPN, unclassifiable Myeloid (and lymphoid) neoplasms associated with eosinophilia and abnormalities of PDGFRA, PDGFRB, or FGFR1 Myeloid and lymphoid neoplasms associated with PDGFRA rearrangement Myeloid neoplasms associated with PDGFRB rearrangement Myeloid and lymphoid neoplasms associated with FGFR1 abnormalities Source: Medeiros, B.C., et al., 2010. ASH-SAP 2010, 397–442. FGFR ¼ fibroblast growth factor receptor; PDGFR ¼ platelet-derived growth factor receptor.
Plasminogen
Urokinase Streptokinase
Plasminogen activator inhibitor-1 (PAI-1)
tPA
TAFI Plasmin Cross-linked fibrin polymer
Fibrin degradation products
Figure 3 Fibrinolysis. TAFI, thrombin-activated fibrinolysis inhibitor; tPA, tissue plasminogen activator. Reproduced from Moll, S., et al., 2010. ASHSAP 2010, 179–215.
Non-Malignant Hematopathology | Pathophysiology of Acquired Coagulopathy
These diseases have clonal stem cell abnormality. Despite this common finding, they have diverse clinical presentations. Of these abnormalities, ET and PV are known to have increased risk of thrombosis. Two-thirds of thrombus diagnoses in PV are arterial, while one-third have venous thrombus. ET is also associated with increased risk of thrombosis. The thrombosis in ET is also occurring in both arterial and venous sites; the arterial event is much more frequent. Overall thrombotic event in ET are less frequent compared to PV. The pathophysiology for increased risk of thrombosis in PV includes hyperviscosity due to uncontrolled erythrocytosis, qualitative platelet dysfunction, and polymorphonuclear leukocytes (PMN) or granulocyte activation. Compared to healthy individuals, patients with ET and PV have elevated platelet–granulocyte and platelet–monocyte complex. PMN activation markers including CD11D and alkaline phosphatase (ALP), antaginase expression, and cellular and plasma elastase are also significantly increased in both ET and PV. The same study has shown an elevation of hypercoagulable markers, that is, thrombin–antithrombin; d-dimer level is elevated with increased level of PMN activation. In a patient with either PV or ET, there are an elevated number of markers for endothelial injury including thrombomodulin and vWF. From these findings, the most likely mechanism of increased risk of thrombosis formation in PV and ET is the combination of endothelial injury and increased rate interaction of activated and reactive platelet by leukocytosis and activated PMN. TF production by both monocyte and neutrophil increased in a patient with ET and PV. In vivo studies have showed a downregulation of neutrophil TF expression and neutrophil–platelet complex with treatment with hydroxyurea. It is important to note that 95% of PV and 50% of ET cases are associated with JAK2 V617F mutation. Attempt to evaluate the relation between this mutation and thrombus has showed minimum to no relationship between the Janus kinase (JAK) mutation and hypercoagulable state in PV and ET. The current recommendation is to place patient with low risk of bleeding on daily baby aspirin for prevention of thrombotic event.
Malignancy Includes Migratory Superficial Thrombophlebitis (Trousseau’s Syndrome) Patients with malignancy are known to have a hypercoagulable state. Cancer-associated thrombosis is known as Trousseau’s syndrome in honor of the person who described this event first in the 1860s. The incidence of thrombotic event varies for different neoplastic state. Certain malignancy tends to have a higher event of thrombotic event. Pancreatic and other colorectal malignancies, ovarian cancer, and acute promyelocytic leukemia are well known to have higher rates of malignancies. Certain malignancies, for example, leukemia (with the exception of APL), are not known to have increased risk of thrombus. Multiple factors play a role in increased risk thrombotic event in a patient with malignancy. Decreased physical activity, drugs (chemotherapeutic agents), invasive procedures, and infection play a major role in the formation of thrombotic events.
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In addition to these factors, there is good evidence that malignancy by itself is a hypercoagulable state without the aforementioned events. Malignant cancer cells produce high procoagulant factors. This can be a TF or cancer procoagulant factor (calciumdependent cysteine protease) by the malignant cell. When tumor cells interact with monocyte and macrophages, it induces the monocyte/macrophage to produce TF. These interactions also induce the release of interleukin 6 (IL-6), IL-1, and TNF. The release of this inflammatory markers leads to EC damage. Once the vascular bed is injured, it is exposed for thrombogenic activity. Increased production of TF and cysteine protease leads to activation of factor VII directly and factor X by activated VII leading to the formation of thrombin. Cancer procoagulant proteins can act directly to factor X independent of TF/factor and activate it to form a complex with VIII. This is especially true for sialic acid moieties of mucin from adenocarcinoma (Figure 4). There are multiple attempts done to understand the pathophysiology of chemotherapeutic agents association with thrombosis in cancer patient. Currently, there is no consensus on the underlying pathophysiology. However, it is well known that certain drug causes damage to EC and vascular wall bed. Cancer patient also tend to have more invasive vascular procedures, which also increase the risk of endothelial damage and platelet activation. Immunosuppressed patient, that is, cancer patient in chemotherapy, is also at increased risk for infection. Infection with gram-negative bacteria will lead to releases of endotoxin and includes endothelial damage.
Nephrotic Syndrome NS is a renal disease where a significant amount of protein (3.5 g m2 day1) is excreted through the urinary system. There are different underlying renal pathologies leading to these clinical findings. These include minimal change disease, membranoproliferative glomerulonephritis, and membranous glomerulonephritis. NS is also known for its hypercoagulable state. Patients with NS have increased level of venous thromboembolic events. There are also some data stating increased risk of arterial risk of thrombus especially in pediatric population (31–32). Currently, there is no consensus on the underlying pathophysiology for the hypercoagulable. Current theory includes increased activation of platelet, loss or decreased amount of endogenous anticoagulant, activation of the coagulation system, and decreased activity of fibrinolysis. In a patient with NS, there are increased markers of vWF, decreased cell deformity, and thrombocytosis. These are signs of active platelet transportation to affected vessel. Increased marker for platelet activation including CD62P and P-selectin was noticed in NS patient. However, further study needs to be done to establish the correlation of this laboratory parameter to in vivo clinical findings. Loss of small-molecular-weight proteins is a classical finding in NS. These include IX, X, XII, and, antithrombin. To compensate for this loss, the body increases protein production. Since high-molecular-weight proteins are less likely to be excreted, the patient will have increased number of high-
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Chemotherapy Monocyte or macrophage
Interleukin-1 Interleukin-6 Tumor necrosis factor
Malignant cell
Mucin: sialic acid Procoagulant activity
Tissue factor
Factor XII
Endothelial disruption
Factor XIIa
Factor X
Factor VII
Factor Xa
Factor VIIa
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Prothrombin
Fibrin clot Fibrinogen
Figure 4 Mechanisms of thrombosis in cancer. Picture from Bick, R.L., 2003. NEJM 349, 109–111.
molecular-weight proteins like factors V and VIII and fibrinogen. An increase in fibrinogen and factor VIII level is associated with their procoagulant state. Increased production of prothrombotic protein and loss of antithrombotic small protein contribute to the hypercoagulable state. Decreased level of plasminogen was noticed in a patient with NS. The rate of this decline is associated with the level of proteinuria. Plasminogen is needed for normal function of fibrinolysis (Figure 3). The enzyme that is important for the activation of plasminogen to plasma, that is, tissue plasminogen activator (tPA), is also elevated, confirming decline of plasminogen. The other current interest is the role of increased low density lipoprotein and other lipoproteins, in hypercoagulable states associated with NS. Dyslipidemia that is associated with NS is associated with change in glomerular hemostatic system resulting in renal thrombotic event. However, the detailed pathophysiology is not currently known. Further study is needed to understand the relationship between hyperlipidemia of NS and hypercoagulable states.
Medications Multiple chemotherapeutic agents are known to be associated with thrombotic states. These medications include cytotoxic agents like mitomycin and asparaginase and noncytotoxic agent like tamoxifen, thalidomide and lenalidomide. Nonchemotherapeutic agents like estrogen-based contraceptives and heparin-induced thrombocytopenia (HIT) are also associated with hypercoagulable states. The mechanism of thrombus formation in these medications with the exception of HIT is not well described. HIT is a clinical condition where a patient exposed to heparin forms antibody not only to heparin but also to the platelet–heparin complex. The antibody attacks the complex and expedites the destruction of the complex by the spleen, thus removing the platelet resulting in thrombocytopenia. This clinical condition is also associated with hypercoagulable states with high rate of thrombus formation. About 50% of untreated patients with HIT develop thrombus known as heparin-induced thrombocytopenia.
Fondaparinux Unfractionated heparin
Low-molecular-weight heparin
Fcg RIIa
Platelet activation
Released microparticles Fcg RIIa
Immune complexes
(a) Monocyte and platelet microparticles
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Intrinsic pathway Factor IX
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Factor IXa
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Danaparoid fondaparinux
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Prothrombin
Argatroban Hirudin Lepirudin Bivalirudin
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Platelet activation
(b)
Figure 5 (a) Platelet activation by antibodies against the platelet factor 4 (PF4)–heparin complex. Heparin-induced thrombocytopenia (HIT) is caused by IgG antibodies that bind to PF4 when it is bound to heparin (the PF4–heparin complex). The formation of multimolecular complexes of PF4 and heparin depends on the concentrations of PF4 and heparin, the length of the heparin chain, and the degree of sulfation. Unfractionated heparin (3000–30 000 Da) forms larger complexes with PF4 than low-molecular-weight heparin (2000–9000 Da). Fondaparinux (1728 Da) is unlikely to form complexes large enough to cause platelet activation. Once pathogenic HIT antibodies cross-link Fc-g receptor IIa (FcgRIIa) on the platelet surface, platelets become activated, microparticles are released, and the coagulation cascade is triggered. (b) The coagulation cascade. The IgG–PF4–heparin immune complexes that characterize HIT bind to the FcgRIIa on platelets, Fc-g receptor I (FcgRI) on monocytes, and potentially other cell surfaces. Tissue factor is expressed on the surface of the cell and on the released microparticles. This enhances the activation of factor VIIa, which in turn activates factor Xa and ultimately generates thrombin. The tissue factor–factor VIIa complex also activates factor IX, a component of the intrinsic pathway of coagulation. The hypercoagulable state caused by HIT can result in venous or arterial thrombosis, particularly at sites of vascular damage. The agents used in treating HIT inhibit clotting downstream of these sites of activation. Danaparoid and fondaparinux inhibit factor Xa, whereas argatroban and the hirudin-related agents inhibit thrombin.
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Heparin–PF4 antibody complex activates platelets to release procoagulants. The complex also causes injury to the endothelial lining of a vessel. Injury to the EC can result in a release of inflammatory marker IL-6, vWF, and other adhesion molecules. HIT is also associated with decreased production of protein C and increased production of TFs. The combination of increased production of procoagulants, adhesive molecule TFs, and endothelial damage results in highly prothrombotic states resulting in both arterial and venous thromboses. If this disease is not diagnosed on time, it has a devastating result to the patient (Figure 5).
Pregnancy Pregnancy and postpartum period are known to have increased risk of VTE. In the United States, 1 in 500 pregnancies will have complication of VTE. Postpartum period tends to have more VTE than antepartum. Pregnancy has all the three classic Virchow’s triad: stasis, hypercoagulable stasis, and endothelial injury. Endothelial injury happens during delivery where a significant uteroplacental changes. This probably explains the increased risk of VTE. As for the hypercoagulability, there is a significant
elevation of coagulation factors including factors I, II, VIII, IX, and X, while the body’s natural anticoagulant protein C production decreases during pregnancy. At the same time, there is a significant decrease on production of antifibrinolytic protein. The other most important anatomical and physiological change associated with pregnancy is the compression of the inferior vena cava by the gravid uterus. Almost 88% of lower extremity deep vein thrombosis is seen on the left extremity. Patients with congenital hypercoagulable state (Table 1) have even high risk of thrombosis compared to patients with no known congenital hypercoagulable state. This is also true with the other acquired hypercoagulable state described earlier. Due to high risk of thrombosis, a hematologist should be involved in the care of pregnant women with any of the congenital or acquired hypercoagulable states.
Disseminated Intravascular Coagulation Disseminated intravascular coagulation (DIC) is a widespread activation of coagulation associated with severe systemic disease. Thought as primarily associated with severe bacterial
Tissue factor + factor VIIa Cytokines Factor IXa (+ factor VIII)
Factor Xa (+ factor V)
Plasminogen Plasminogen activators
Factor IIa (thrombin) Fibrinogen
Fibrin
Low levels of antithrombin III Impaired function of protein-C system Insufficient TFPI Impairment of anticoagulation pathways
Generation of thrombin mediated by tissue factor
Formation of fibrin
PAI-1
Plasmin
Fibrin
FDPs
Suppression of fibrinolysis by PAI-1
Inadequate removal of fibrin
Thrombosis of small and midsize vessels Figure 6 Pathogenetic pathways involved in disseminated intravascular coagulation (DIC). In patients with DIC, fibrin is formed as a result of the generation of thrombin mediated by tissue factor. Tissue factor, expressed on the surface of activated mononuclear cells and endothelial cells, binds and activates factor VII. The complex of tissue factor and factor VIIa can activate factor X directly (black arrows) or indirectly (white arrows) by means of activated factor IX and factor VIII. Activated factor X, in combination with factor V, can convert prothrombin (factor II) to thrombin (factor IIa). Simultaneously, all three physiological means of anticoagulation – antithrombin III, protein C, and tissue factor pathway inhibitor (TFPI) – are impaired. The resulting intravascular formation of fibrin is not balanced by adequate removal of fibrin because endogenous fibrinolysis is suppressed by high plasma levels of plasminogen activator inhibitor type 1 (PAI-1). The high levels of PAI-1 inhibit plasminogen activator activity and consequently reduce the rate of formation of plasmin. The combination of increased formation of fibrin and inadequate removal of fibrin results in disseminated intravascular thrombosis. FDPs denote fibrin degradation products. Reproduced from Mercel Levi, M.D., Hugo ten Cate, M.D., 1999. NEJM 341, 586–592.
Non-Malignant Hematopathology | Pathophysiology of Acquired Coagulopathy
infection, it can happen with any infection. It can also be associated with trauma, malignancy, vascular and immunologic disorder, and obstetric complication. The pathogenesis of DIC is associated with increased inflammatory cytokines like IL-6 and TNF alpha. Activation of these cytokines can be associated with any of the clinical scenarios described above. The cytokines play roles in the activation of thrombus formation, impairing the body’s anticoagulation proteins, and fibrinolytic activity. TF expressed mononuclear cell in response to cytokines that are produced with systemic disease. Activated TF attaches to factor VII. The combination of TF and VII in turn activates factors IX and X. This leads to an activation of thrombin, thus forming fibrin and thrombus. Antithrombin III, protein C, and TFPI are the most important endogenous inhibitors of coagulation. All these proteins were affected in DIC. Antithrombin III is consumed by the elastase released from activated neutrophils resulting to a low level. While there is no evidence of a decreased level of TFPI in DIC, there is evidence that the regulation of TF inhibition is decreased significantly in DIC. The synthesis of Protein C is decreased due to impaired thrombomodulin. Cytokine-mediated inflammatory markers, which are associated with DIC mediate this process. The protein S level also decreases in DIC, which is important for the proper function of protein C. Plasminogen activator inhibitor 1 (PAI-1) is an important inhibitor of the fibrinolytic system. In animal model of DIC, the production of PAI-1 is increased especially at the peak of coagulation. Increased production of PAI-1 overwhelms the production of fibrinolytic activity that is induced due to the formation of fibrin resulting in the production of thrombus. The combination of decreased endogenous anticoagulant, impairment of fibrinolytic activity, and increased thrombin formation makes the DIC highly thrombogenic state (Figure 6).
Further Reading Agar, C., van Os, G.M., Morgelin, M., Sprenger, R.R., Marquart, J.A., Urbanus, R.T., et al., 2010. Beta2-glycoprotein I can exist in 2 conformations: implications for our understanding of the antiphospholipid syndrome. Blood 116, 1336–1343. Allen, K.L., Fonseca, F.V., Betapudi, V., Willard, B., Zhang, J., McCrae, K.R., 2012. A novel pathway for human endothelial cell activation by antiphospholipid/anti-beta2 glycoprotein I antibodies. Blood 119, 884–893. Alvarez-Larran, A., Garcia-Pagan, J.C., Abraldes, J.G., Arellano, E., Reverter, J.C., Bosch, J., et al., 2004. Increased CD11b neutrophil expression in Budd–Chiari syndrome or portal vein thrombosis secondary to polycythaemia vera. Br. J. Haematol. 124, 329–335. Ames, P.R., Batuca, J.R., Ciampa, A., Iannaccone, L., Delgado Alves, J., 2010. Clinical relevance of nitric oxide metabolites and nitrative stress in thrombotic primary antiphospholipid syndrome. J. Rheumatol. 37, 2523–2530. Ames, P.R., Nourooz-Zadeh, J., Tommasino, C., Alves, J., Brancaccio, V., Anggard, E.E., 1998. Oxidative stress in primary antiphospholipid syndrome. Thromb. Haemost. 79, 447–449. Arellano-Rodrigo, E., Alvarez-Larran, A., Reverter, J.C., Villamor, N., Colomer, D., Cervantes, F., 2006. Increased platelet and leukocyte activation as contributing mechanisms for thrombosis in essential thrombocythemia and correlation with the JAK2 mutational status. Haematologica 91, 169–175. ASH-SAP, 2013. From American Society of Hematology, fifth ed. American Society of Hematology, Washington.
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Basavaraj, M.G., Gruber, F.X., Sovershaev, M., Appelbom, H.I., Osterud, B., Petersen, L.C., et al., 2010. The role of TFPI in regulation of TF-induced thrombogenicity on the surface of human monocytes. Thromb. Res. 126, 418–425. Cameron, J.S., 1984. Coagulation and thromboembolic complications in the nephrotic syndrome. Adv. Nephrol. Necker Hosp. 13, 75–114. Cameron, J.S., 1987. The nephrotic syndrome and its complications. Am. J. Kidney Dis. 10, 157–171. Charakida, M., Besler, C., Batuca, J.R., Sangle, S., Marques, S., Sousa, M., et al., 2009. Vascular abnormalities, paraoxonase activity, and dysfunctional HDL in primary antiphospholipid syndrome. JAMA 302, 1210–1217. Conway, E.M., Rosenberg, R.D., 1988. Tumor necrosis factor suppresses transcription of the thrombomodulin gene in endothelial cells. Mol. Cell. Biol. 8, 5588–5592. Creasey, A.A., Chang, A.C., Feigen, L., Wun, T.C., Taylor Jr., F.B., Hinshaw, L.B., 1993. Tissue factor pathway inhibitor reduces mortality from Escherichia coli septic shock. J. Clin. Invest. 91, 2850–2860. Cristina, L., Benilde, C., Michela, C., Mirella, F., Giuliana, G., Gualtiero, P., 2004. High plasma levels of factor VIII and risk of recurrence of venous thromboembolism. Br. J. Haematol. 124, 504–510. de Laat, B., Wu, X.X., van Lummel, M., Derksen, R.H., de Groot, P.G., Rand, J.H., 2007. Correlation between antiphospholipid antibodies that recognize domain I of beta2glycoprotein I and a reduction in the anticoagulant activity of annexin A5. Blood 109, 1490–1494. Delgado Alves, J., Ames, P.R., Donohue, S., Stanyer, L., Nourooz-Zadeh, J., Ravirajan, C., et al., 2002. Antibodies to high-density lipoprotein and beta2-glycoprotein I are inversely correlated with paraoxonase activity in systemic lupus erythematosus and primary antiphospholipid syndrome. Arthritis Rheum. 46, 2686–2694. Falanga, A., Marchetti, M., Evangelista, V., Vignoli, A., Licini, M., Balicco, M., et al., 2000. Polymorphonuclear leukocyte activation and hemostasis in patients with essential thrombocythemia and polycythemia vera. Blood 96, 4261–4266. Falanga, A., Marchetti, M., Vignoli, A., Balducci, D., Barbui, T., 2005. Leukocyte–platelet interaction in patients with essential thrombocythemia and polycythemia vera. Exp. Hematol. 33, 523–530. Francis Jr., R.B., Sandler, R.M., Levitan, D., Feinstein, E.I., Massry, S.G., Feinstein, D.I., 1985. Reduced alpha-2-antiplasmin levels in the nephrotic syndrome. Nephron 39, 325–329. Giannakopoulos, B., Gao, L., Qi, M., Wong, J.W., Yu, D.M., Vlachoyiannopoulos, P.G., et al., 2012. Factor XI is a substrate for oxidoreductases: enhanced activation of reduced FXI and its role in antiphospholipid syndrome thrombosis. J. Autoimmun. 39, 121–129. Gralnick, H.R., Vail, M., McKeown, L.P., Merryman, P., Wilson, O., Chu, I., et al., 1995. Activated platelets in paroxysmal nocturnal haemoglobinuria. Br. J. Haematol. 91, 697–702. Grau, E., Oliver, A., Felez, J., Barcelo, P., Fernandez, C., Ballarin, J.A., et al., 1988. Plasma and urinary heparin cofactor II levels in patients with nephrotic syndrome. Thromb. Haemost. 60, 137–140. Grunewald, M., Siegemund, A., Grunewald, A., Schmid, A., Koksch, M., Schopflin, C., et al., 2003. Plasmatic coagulation and fibrinolytic system alterations in PNH: relation to clone size. Blood Coagul. Fibrinolysis 14, 685–695. Helley, D., de Latour, R.P., Porcher, R., Rodrigues, C.A., Galy-Fauroux, I., Matheron, J., et al., 2010. Evaluation of hemostasis and endothelial function in patients with paroxysmal nocturnal hemoglobinuria receiving eculizumab. Haematologica 95, 574–581. Hoffman, R., Benz Jr., E.J., Silberstein, L.E., Heslop, H., Jeffrey Weitz, J., Anastasi, J., 2013. Hematology: Basic Principles and Practice, sixth ed., Elsevier. Ioannou, Y., Zhang, J.Y., Qi, M., Gao, L., Qi, J.C., Yu, D.M., et al., 2011. Novel assays of thrombogenic pathogenicity in the antiphospholipid syndrome based on the detection of molecular oxidative modification of the major autoantigen beta2glycoprotein I. Arthritis Rheum. 63, 2774–2782. Jankowska, A.M., Szpurka, H., Calabro, M., Mohan, S., Schade, A.E., Clemente, M., et al., 2011. Loss of expression of neutrophil proteinase-3: a factor contributing to thrombotic risk in paroxysmal nocturnal hemoglobinuria. Haematologica 96, 954–962. Kanfer, A., 1990. Coagulation factors in nephrotic syndrome. Am. J. Nephrol. 10 (Suppl 1), 63–68. Kanfer, A., Kleinknecht, D., Broyer, M., Josso, F., 1970. Coagulation studies in 45 cases of nephrotic syndrome without uremia. Thromb. Diath. Haemorrh. 24, 562–571. Kendall, A.G., Lohmann, R.C., Dossetor, J.B., 1971. Nephrotic syndrome. A hypercoagulable state. Arch. Intern. Med. 127, 1021–1027. Kessler, C.M., Tang, Z., Jacobs, H.M., Szymanski, L.M., 1997. The suprapharmacologic dosing of antithrombin concentrate for Staphylococcus aureus-induced disseminated intravascular coagulation in guinea pigs: substantial reduction in mortality and morbidity. Blood 89, 4393–4401.
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