scholarly journals Heparin-induced thrombocytopenia: in vitro studies on the interaction of dabigatran, rivaroxaban, and low-sulfated heparin, with platelet factor 4 and anti-PF4/heparin antibodies

Blood ◽  
2012 ◽  
Vol 119 (5) ◽  
pp. 1248-1255 ◽  
Author(s):  
Krystin Krauel ◽  
Christine Hackbarth ◽  
Birgitt Fürll ◽  
Andreas Greinacher
Keyword(s):  
Factor Xa ◽  
Platelet Factor 4 ◽  
Thrombin Inhibitors ◽  
Direct Thrombin Inhibitors ◽  
Platelet Factor ◽  
Heparin Induced Thrombocytopenia ◽  
Alternative Anticoagulation ◽  
Heparin Complexes ◽  
History Of

Abstract Heparin is a widely used anticoagulant. Because of its negative charge, it forms complexes with positively charged platelet factor 4 (PF4). This can induce anti-PF4/heparin IgG Abs. Resulting immune complexes activate platelets, leading to the prothrombotic adverse drug reaction heparin-induced thrombocytopenia (HIT). HIT requires treatment with alternative anticoagulants. Approved for HIT are 2 direct thrombin inhibitors (DTI; lepirudin, argatroban) and danaparoid. They are niche products with limitations. We assessed the effects of the DTI dabigatran, the direct factor Xa-inhibitor rivaroxaban, and of 2-O, 3-O desulfated heparin (ODSH; a partially desulfated heparin with minimal anticoagulant effects) on PF4/heparin complexes and the interaction of anti-PF4/heparin Abs with platelets. Neither dabigatran nor rivaroxaban had any effect on the interaction of PF4 or anti-PF4/heparin Abs with platelets. In contrast, ODSH inhibited PF4 binding to gel-filtered platelets, displaced PF4 from a PF4-transfected cell line, displaced PF4/heparin complexes from platelet surfaces, and inhibited anti-PF4/heparin Ab binding to PF4/heparin complexes and subsequent platelet activation. Dabigatran and rivaroxaban seem to be options for alternative anticoagulation in patients with a history of HIT. ODSH prevents formation of immunogenic PF4/heparin complexes, and, when given together with heparin, may have the potential to reduce the risk for HIT during treatment with heparin.

Platelet factor 4 binds to bacteria, inducing antibodies cross-reacting with the major antigen in heparin-induced thrombocytopenia

Blood ◽  
2011 ◽  
Vol 117 (4) ◽  
pp. 1370-1378 ◽  
Author(s):  
Krystin Krauel ◽  
Christian Pötschke ◽  
Claudia Weber ◽  
Wolfram Kessler ◽  
Birgitt Fürll ◽  
...  
Keyword(s):  
Bacterial Infections ◽  
Defense Mechanism ◽  
Platelet Factor 4 ◽  
Cross Sectional ◽  
Platelet Factor ◽  
Heparin Induced Thrombocytopenia ◽  
Host Defense Mechanism ◽  
Heparin Complexes ◽  
Major Antigen

AbstractA clinically important adverse drug reaction, heparin-induced thrombocytopenia (HIT), is induced by antibodies specific for complexes of the chemokine platelet factor 4 (PF4) and the polyanion heparin. Even heparin-naive patients can generate anti-PF4/heparin IgG as early as day 4 of heparin treatment, suggesting preimmunization by antigens mimicking PF4/heparin complexes. These antibodies probably result from bacterial infections, as (1) PF4 bound charge-dependently to various bacteria, (2) human heparin-induced anti-PF4/heparin antibodies cross-reacted with PF4-coated Staphylococcus aureus and Escherichia coli, and (3) mice developed anti-PF4/heparin antibodies during polymicrobial sepsis without heparin application. Thus, after binding to bacteria, the endogenous protein PF4 induces antibodies with specificity for PF4/polyanion complexes. These can target a large variety of PF4-coated bacteria and enhance bacterial phagocytosis in vitro. The same antigenic epitopes are expressed when pharmacologic heparin binds to platelets augmenting formation of PF4 complexes. Boosting of preformed B cells by PF4/heparin complexes could explain the early occurrence of IgG antibodies in HIT. We also found a continuous, rather than dichotomous, distribution of anti-PF4/heparin IgM and IgG serum concentrations in a cross-sectional population study (n = 4029), indicating frequent preimmunization to modified PF4. PF4 may have a role in bacterial defense, and HIT is probably a misdirected antibacterial host defense mechanism.

Pathogenic Role of Surface Platelet Factor 4 Complexes in Heparin-Induced Thrombocytopenia: Diagnostic and Therapeutic Implications.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 55-55 ◽  
Author(s):  
Lubica Rauova ◽  
Li Zhai ◽  
M. Anna Kowalska ◽  
Gowthami M. Arepally ◽  
Douglas B. Cines ◽  
...  
Keyword(s):  
Platelet Factor 4 ◽  
Thrombin Inhibitors ◽  
Current Therapy ◽  
Severe Thrombocytopenia ◽  
Pathogenic Role ◽  
Platelet Factor ◽  
Platelet Surface ◽  
Heparin Induced Thrombocytopenia

Abstract Heparin-induced thrombocytopenia (HIT) is caused by antibodies that recognize complexes between high molecular weight heparin and Platelet Factor 4 (PF4). Current therapy with direct thrombin inhibitors is not effective in all cases, likely because it acts downstream of antibody-induced platelet activation. More directed therapies to the underlying pathology in HIT may be more effective. Heparin and PF4 only bind HIT antibodies over a narrow molar ratio of reactants at which ultralarge soluble complexes are formed. We asked whether similar complexes form between PF4 and endogenous platelet glycosaminoglycans (GAG) and their pathogenic role in experimental HIT. Platelet surface GAG:PF4 complexes are indeed antigenic over a narrow molar range of reactants. Heparin is not required for either HIT-IgG or a HIT-like monoclonal antibody KKO to bind to PF4 on human or mouse platelet surfaces in vitro, but enhances antigenicity when very high levels of surface PF4 are present. Antigenicity is maximal at a PF4 concentration of 50 μg/mL (well within the range that can be achieved within a thrombus) and ~25 μg/mL heparin (~0.5 U/mL, which is within the therapeutic range) optimally enhances antigenicity when surface PF4 levels were increased 4-fold. Using transgenic mice lines each with platelets expressing a different level of hPF4, ranging from 0.5 – 6 X’s human platelet levels and all expressing FcRγIIA, were given KKO. The different lines developed thrombocytopenia proportional in severity and duration to hPF4 expression. A standard subcutaneous (sq) heparininzing dose (20 U/kg, sq daily) prolonged the duration of severe thrombocytopenia in high hPF4 expressing mice. We reasoned that altering the ratio of PF4 to GAG in either direction would alter antigenicity and could block the development of thrombocytopenia. In accordance with this concept, both high concentrations of anionic heparin (100 U/kg, sq daily) and cationic protamine sulfate (2 mg/kg, sq daily) decreased KKO binding in vitro and prevented KKO-induced thrombocytopenia in vivo as a demonstration of successful therapeutic intervention. These studies affirm a central role of surface GAG:PF4 complexes in the development of HIT, suggest ways to identify patients at high risk to develop HIT even prior to heparin exposure, and offers a new and rationale therapeutic paradigm based on disrupting surface antigen formation.

Pathophysiology of Heparin-Induced Thrombocytopenia

2000 ◽  
Vol 124 (11) ◽  
pp. 1657-1666 ◽  
Author(s):  
Fabrizio Fabris ◽  
Sarfraz Ahmad ◽  
Giuseppe Cella ◽  
Walter P. Jeske ◽  
Jeanine M. Walenga ◽  
...  
Keyword(s):  
Platelet Activation ◽  
Serotonin Release ◽  
Platelet Factor 4 ◽  
Thrombin Inhibitors ◽  
Platelet Factor ◽  
Cellular Activation ◽  
Heparin Induced Thrombocytopenia ◽  
New Information ◽  
Study Selection ◽  
Release Assay

Abstract Objective.—This review of heparin-induced thrombocytopenia (HIT), the most frequent and dangerous side effect of heparin exposure, covers the epidemiology, pathophysiology, clinical presentation, diagnosis, and treatment of this disease syndrome. Data Sources and Study Selection.—Current consensus of opinion is given based on literature reports, as well as new information where available. A comprehensive analysis of the reasons for discrepancies in incidence numbers is given. The currently known mechanism is that HIT is mediated by an antibody to the complex of heparin–platelet factor 4, which binds to the Fc receptor on platelets. New evidence suggests a functional heterogeneity in the anti-heparin-platelet factor 4 antibodies generated to heparin, and a “superactive” heparin-platelet factor 4 antibody that does not require the presence of heparin to promote platelet activation or aggregation has been identified. Up-regulation of cell adhesion molecules and inflammatory markers, as well as preactivation of platelets/endothelial cells/leukocytes, are also considered to be related to the pathophysiology of HIT. Issues related to the specificity of currently available and new laboratory assays that support a clinical diagnosis are addressed in relation to the serotonin-release assay. Past experience with various anticoagulant treatments is reviewed with a focus on the recent successes of thrombin inhibitors and platelet GPIIb/IIIa inhibitors to combat the platelet activation and severe thrombotic episodes associated with HIT. Conclusions.—The pathophysiology of HIT is multifactorial. However, the primary factor in the mediation of the cellular activation is due to the generation of an antibody to the heparin-platelet factor 4 complex. This review is written as a reference for HIT research.

scholarly journals Platelet Factor 4 (PF4) and Protamine Neutralisation of Heparin in Plasma

1977 ◽  
Author(s):  
R. Michalski ◽  
D.A. Lane ◽  
D. Pepper ◽  
V.V. Kakkar
Keyword(s):  
Intravenous Injection ◽  
Factor Xa ◽  
Weight Basis ◽  
Platelet Factor 4 ◽  
Assay System ◽  
Platelet Factor ◽  
Protamine Sulphate ◽  
Heparin Activity ◽  
Plasma Heparin

The ability of PF4 and protamine sulphate to neutralise heparin in plasma has been studied using a specific anti-Factor Xa assay and a KCCT assay to measure residual heparin. When heparin is added to plasma in vitro PF4 and protamine neutralise almost equivalent amounts of heparin on a weight basis, 1.0 unit of heparin being neutralised by approximately 20 μg of PF4 and 15 μg of protamine. Similar results are obtained using either of the heparin assays. However, following intravenous injection of heparin only about one half of the circulating heparin could be neutralised in vitro by PF4 or protamine when it was measured by anti-Factor Xa assay. Total neutralisation was obtained with both neutralising agents in the KCCT assay system. These results demonstrate that the choice of assay is important when a protamine titration is used to measure plasma heparin levels, and that PF4 and protamine are unable to totally neutralise circulating antithrombotic heparin activity.

Comparison of Clinical Outcomes in Patients with Heparin-Induced Thrombocytopenia Treated with Direct Thrombin Inhibitors.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3942-3942 ◽  
Author(s):  
John L. Francis ◽  
Ranjeev Sandhu ◽  
Alane Drexler ◽  
John Dougherty
Keyword(s):  
Length Of Stay ◽  
Clinical Outcomes ◽  
Clinical Syndrome ◽  
Thrombin Inhibitors ◽  
Direct Thrombin Inhibitors ◽  
Efficacy And Safety ◽  
Platelet Factor ◽  
Platelet Recovery ◽  
Heparin Induced Thrombocytopenia ◽  
All Cause Mortality

Abstract Heparin-induced thrombocytopenia (HIT) is a clinical syndrome that has been reported to occur in 3–5% of patients treated with unfractionated heparin. If untreated, 36–50% of patients diagnosed with HIT develop life or limb-threatening thromboses. The occurrence of thrombosis, the most common serious complication of HIT, results in rates of amputation and death of 10–20% and 20–30% respectively. Thus, the desired clinical outcomes in patients with HIT are the prevention of thromboembolic complications, limb amputation, and death. The three direct thrombin inhibitors available in the U.S. are lepirudin, argatroban and bivalirudin. Lepirudin and argatroban have both been shown in clinical trials to significantly decrease the incidence of these complications in patients with HIT. Our institution also has experience with bivalirudin as treatment for HIT. We therefore sought to confirm whether all-cause mortality, length of stay, bleeding rate, time to platelet recovery, absolute change in platelet count following therapy, and percentage of therapeutic APTTs differed among patients treated with these agents at our institution. Data were collected by retrospective chart reviews, and from the Florida Hospital pharmacy computer system. Length of stay was calculated as the time to hospital discharge following the finding of a positive heparin-platelet factor 4 antibody test. For the purposes of comparison, the therapeutic range for APTT was taken as 50–90 seconds. As shown in the table, there were no statistically significant differences in any of the endpoints, when the efficacy and safety of the three direct thrombin inhibitors were compared. It therefore appears that within our institution, each of the direct thrombin inhibitors are equally efficacious and safe in treating the clinical syndrome of HIT, with similar outcomes with respect to length of stay, recovery of platelet counts, incidence of bleeding, and overall mortality. We conclude that selection of a direct thrombin inhibitor can be guided by the patient’s clinical status and organ function instead of efficacy and safety considerations. Drug n All-cause mortality (%) Length of stay (days) Bleeding (%) Time to platelet recovery (days) Therapeutic APTT (%) Lepirudin 7 28.5 11.0 28.5 5.3 70 Argatroban 20 30.0 15.1 20.0 5.2 65 Bivalirudin 24 25.0 18.7 25.0 5.4 74 P-value NS NS NS NS NS

scholarly journals Anti–platelet factor 4/heparin antibodies in orthopedic surgery patients receiving antithrombotic prophylaxis with fondaparinux or enoxaparin

Blood ◽  
2005 ◽  
Vol 106 (12) ◽  
pp. 3791-3796 ◽  
Author(s):  
Theodore E. Warkentin ◽  
Richard J. Cook ◽  
Victor J. Marder ◽  
Jo-Ann I. Sheppard ◽  
Jane C. Moore ◽  
...  
Keyword(s):  
Cross Reactivity ◽  
Platelet Factor 4 ◽  
Low Molecular Weight ◽  
Igg Antibodies ◽  
Platelet Factor ◽  
Heparin Induced Thrombocytopenia ◽  
Antithrombotic Prophylaxis ◽  
High Concentrations ◽  
To Receive

Heparin-induced thrombocytopenia (HIT) is caused by platelet-activating IgG antibodies that recognize platelet factor 4 (PF4) bound to heparin. Immunogenicity of heparins differs in that unfractionated heparin (UFH) induces more anti–PF4/heparin antibodies than low-molecular-weight heparin (LMWH) and UFH also causes more HIT. Fondaparinux, a synthetic anticoagulant modeled after the antithrombin-binding pentasaccharide, is believed to be nonimmunogenic. We tested 2726 patients for anti–PF4/heparin antibodies after they were randomized to receive antithrombotic prophylaxis with fondaparinux or LMWH (enoxaparin) following hip or knee surgery. We also evaluated in vitro cross-reactivity of the IgG antibodies generated against PF4 in the presence of UFH, LMWH, danaparoid, or fondaparinux. We found that anti–PF4/heparin antibodies were generated at similar frequencies in patients treated with fondaparinux or enoxaparin. Although antibodies reacted equally well in vitro against PF4/UFH and PF4/LMWH, and sometimes weakly against PF4/danaparoid, none reacted against PF4/fondaparinux, including even those sera obtained from patients who formed antibodies during fondaparinux treatment. At high concentrations, however, fondaparinux inhibited binding of HIT antibodies to PF4/polysaccharide, indicating that PF4/fondaparinux interactions occur. No patient developed HIT. We conclude that despite similar immunogenicity of fondaparinux and LMWH, PF4/fondaparinux, but not PF4/LMWH, is recognized poorly by the antibodies generated, suggesting that the risk of HIT with fondaparinux likely is very low.

scholarly journals Heparin-induced thrombocytopenia and cardiovascular surgery

Hematology ◽  
2021 ◽  
Vol 2021 (1) ◽  
pp. 536-544
Author(s):  
Allyson M. Pishko ◽  
Adam Cuker
Keyword(s):  
Cardiac Surgery ◽  
Antiplatelet Agent ◽  
Serotonin Release ◽  
Functional Assay ◽  
Platelet Factor ◽  
Heparin Induced Thrombocytopenia ◽  
Heparin Complexes ◽  
Institutional Experience ◽  
History Of ◽  
Postoperative Setting

Abstract Clinicians generally counsel patients with a history of heparin-induced thrombocytopenia (HIT) to avoid heparin products lifelong. Although there are now many alternative (nonheparin) anticoagulants available, heparin avoidance remains challenging for cardiac surgery. Heparin is often preferred in the cardiac surgery setting based on the vast experience with the agent, ease of monitoring, and reversibility. To “clear” a patient with a history of HIT for cardiac surgery, hematologists must first confirm the diagnosis of HIT, which can be challenging due to the ubiquity of heparin exposure and frequency of thrombocytopenia in patients in the cardiac intensive care unit. Next, the “phase of HIT” (acute HIT, subacute HIT A/B, or remote HIT) should be established based on platelet count, immunoassay for antibodies to platelet factor 4/heparin complexes, and a functional assay (eg, serotonin release assay). As long as the HIT functional assay remains positive (acute HIT or subacute HIT A), cardiac surgery should be delayed if possible. If surgery cannot be delayed, an alternative anticoagulant (preferably bivalirudin) may be used. Alternatively, heparin may be used with either preoperative/intraoperative plasma exchange or together with a potent antiplatelet agent. The optimal strategy among these options is not known, and the choice depends on institutional experience and availability of alternative anticoagulants. In the later phases of HIT (subacute HIT B or remote HIT), brief intraoperative exposure to heparin followed by an alternative anticoagulant as needed in the postoperative setting is recommended.

Antibodies to Macromolecular Platelet Factor 4-Heparin Complexes in Heparin-induced Thrombocytopenia: a Study of 44 Cases

1995 ◽  
Vol 73 (01) ◽  
pp. 021-028 ◽  
Author(s):  
J Amiral ◽  
F Bridey ◽  
M Wolf ◽  
C Boyer-Neumann ◽  
E Fressinaud ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Platelet Aggregation ◽  
Early Diagnosis ◽  
Healthy Subjects ◽  
Platelet Factor 4 ◽  
Platelet Factor ◽  
Heparin Induced Thrombocytopenia ◽  
Sulphated Polysaccharides ◽  
Major Interest ◽  
Heparin Complexes

SummaryAs heparin-PF4 (H-PF4) complexes are the target for antibodies associated to heparin-induced thrombocytopenia (HIT), an ELISA has been developed and optimised for testing antibodies binding to H-PF4. This test was consistently negative in 50 healthy subjects (A492 <0.3) and 35 patients with other causes of thrombocytopenia (A492 <0.5). In contrast, 43 out of 44 HIT patients showed antibodies to H-PF4 (A492 = 1.70 ± 0.81) including 5 patients with a negative platelet aggregation test. In one patient with HIT, antibodies to H-PF4 were already present at day 7, whereas platelet counts dropped ≤ 100 × 109/l only at days 11–12. Surprisingly, among 41 patients under heparin for >7 days, 5 showed antibodies to H-PF4, without HIT. These findings underline the major interest of this ELISA for the early diagnosis of HIT. We also showed that LMWH as well as other sulphated polysaccharides can bind to HIT antibodies in the presence of PF4 and that their reactivity is dependent on the molecular weight and the sulphation grade. The mechanism for HIT involves platelet PF4 receptors which bind the macromolecular H-PF4 complexes formed in the presence of a well defined heparin/PF4 ratio.

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