Vicki Escalante

Apixaban as an Alternate Oral Anticoagulant for the Management of Patients With Heparin-Induced Thrombocytopenia:

Due to the pronounced hypercoagulable state in heparin-induced thrombocytopenia (HIT), alternatives to heparin that do not interact with HIT antibodies are needed for anticoagulation management. This study was designed to determine whether the oral factor Xa inhibitor apixaban could be used. Functional platelet activation with apixaban in the presence of HIT antibodies was evaluated by the 14C-serotonin release assay (SRA; washed platelets) and the heparin-induced platelet aggregation assay (PA-HIT; platelet-rich plasma). A consistent absence of platelet activation by apixaban (0.05-50 μg/mL) was observed: SRA (n = 35) 11 ± 4% and PA-HIT (n = 37) 8 ± 3% (mean ± standard error of the mean; positive is >20%) versus heparin (0.1 U/mL) 82 ± 3% SRA and 78 ± 6% PA-HIT (P < 0.01) versus enoxaparin (10 μg/mL) 73 ± 5% SRA and 62 ± 7% PA-HIT. Apixaban may provide an option for oral anticoagulation in patients with HIT, particularly for extended management and prevention.

Murine Monoclonal Antibody to Platelet Factor 4/Heparin Complexes as a Potential Reference Standard for Platelet Activation Assays in Heparin-Induced Thrombocytopenia

Quality control of the platelet activation assays to diagnose heparin-induced thrombocytopenia (HIT), 14C-serotonin release assay (SRA) and platelet aggregation test (PAT) has yet to be established due to lack of reference standards and the difficulty of obtaining significant amounts of HIT antibodies from patients with HIT. We prepared a murine monoclonal antibody to human platelet factor 4 (hPF4)/heparin complexes (HIT-MoAb) and investigated the platelet activating action of HIT-MoAb by using SRA and PAT. The HIT-MoAb activated human platelets at low heparin concentration and the platelet activations were inhibited at high heparin concentration in both SRA and PAT. The HIT-MoAb produced a concentration-dependent effect. Moreover, the platelet activation at low heparin concentration was inhibited by anti-FcγRIIa antibody. These results indicated that HIT-MoAb has characteristics similar to human HIT antibodies regarding heparin-dependent platelet activation. Therefore, it is suggested that HIT-MoAb has the potential to be a positive control or reference standard in platelet activation assays.

Left ventricular assist device-induced coagulation and platelet activation and effect of the current anticoagulant therapy regimen.

Left ventricular assist devices (LVADs) are mechanical pumps that enhance cardiac function in patients with heart failure. In all, 7 patients with an LVADs (1.8 international normalized ratio warfarin, 81 mg aspirin) were evaluated monthly for 3 months for platelet and coagulation activation (controls: 5 healthy adults and 5 patients having warfarin). Platelet works revealed greater inhibition of collagen (31.8% vs 7.9%; P = .004), arachidonate- (30.9% vs 8.2%; P = .001), and adenosine diphosphate- (10.9% vs 6.1%; P = .004)-induced platelet aggregation for LVADs. Thrombelastography (recalcified whole blood) showed inhibition of clot initiation time (R; 8.81 vs 6.02 min; P = .001) and stronger clot formation (maximum amplitude; 69.1 vs 64.9 mm; P = .016). Platelet function determined by plateletMapping and flow cytometry was within the normal range. The LVADs had increased ratio of von Willebrand Factor (vWF) antigen and vWF propeptide, indicating increased degradation of vWF (2.04 vs 1.44; P = .144). Coagulation and platelet activation caused by LVAD is suppressed by pharmacotherapy, yielding a profile similar to that of patients on warfarin alone.

Comparative studies on branded enoxaparin and a US generic version of enoxaparin.

Enoxaparin, a complex, biologically derived low-molecular-weight heparin, is approved for a range of clinical indications. This study was carried out to compare the potency profile and pharmacodynamic responses of branded enoxaparin (Lovenox; Sanofi, US) with a generic enoxaparin (enoxaparin sodium injection, USP). Five batches of each product were tested. Although the average molecular weight, anti-factor Xa, and anti-factor IIa potencies were similar for the two products, differences were observed in the in vitro thrombin generation and kinetics of clot formation (P = .01) and in the ex vivo pharmacodynamics regarding thrombin generation inhibition (P = .029), tissue factor pathway inhibitor release (P = .006), and inhibition of the active form of thrombin-activated fibrinolysis inhibitor (P = .023). These findings suggest that simple analytical characterization can establish good quality control in manufacturing, but they may not assure similarity in biological performance between the branded and the generic enoxaparin.

A colorimetric, metabolic dye reduction assay detects highly activated platelets: application in the diagnosis of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is caused by antibodies, elicited in response to heparin anticoagulant therapy, which can cause extreme platelet activation and result in a highly procoagulant state. Most diagnostic tests for HIT antibodies measure in vitro platelet activation by detecting aggregation or granule release responses. This study demonstrates that the high level of activation by HIT antibodies leads to a rapid breakdown of platelet metabolic activity. Resting or mildly activated platelets metabolize tetrazolium-based indicator dye to a dark colored product, in proportion to cell concentration and dye incubation time. Highly activated, procoagulant platelets resulting from incubation with HIT antibodies fail to metabolize dye and remain light in color. The loss of ability to metabolically reduce indicator dye provides a colorimetric endpoint that can be used in an in vitro washed platelet activation assay to detect HIT antibodies. In a prospective evaluation, 145 diagnostic specimens were tested concurrently by both the colorimetric, dye reduction assay and the clinical laboratory standard, radiolabeled-serotonin release assay (14C-SRA). Results were in agreement for 96–100% of cases, depending on the chosen stringency of assay cut-off values. This study demonstrates that the metabolic dye reduction assay is comparable to the 14C-SRA for HIT diagnosis. In addition, this novel assay may have even wider applicability, facilitating studies on the physiologic and clinical relevance of highly activated platelet populations.

Identification of Novel Hemostatic Biomarkers of Adverse Clinical Events in Patients Implanted With a Continuous-Flow Left Ventricular Assist Device

Heart failure affects over 5 million people in the United States. Its rising prevalence and the limited supply of donor hearts is increasing the use of mechanical cardiac support with the implantation of continuous-flow ventricular assist devices (CF-VAD). Patients with CF-VAD implants are at risk of complications, specifically adverse hemostatic events such as nonsurgical bleeding and thrombosis. Development of a pump thrombus requires clinical intervention and/or surgical replacement significantly increasing the risk of patient morbidity and mortality. Identification of biomarkers for these events could improve current risk assessment models, subsequent treatment, and quality of life prognoses for VAD-implanted patients. The standard means for identifying thrombus in VAD patients is currently limited to monitoring levels of lactate dehydrogenase (>2× upper limit of normal), which is incapable of predicting a future event, but describes the risk of a present thrombus. Surface-enhanced laser desorption ionization time-of-flight mass spectrometry is a technique used to identify biomarkers. In this study, 3 groups of unique peaks were identified in plasma from patients with left ventricular assist devices: 8.1-kDa, 11.7-kDa, and a 15.2-/16.1-kDa pair. Unique correlations were found for each peak, respectively, with microparticles (MPs) and MP procoagulant activity, C-reactive protein, and MP-tissue factor. Furthermore, the use of 8.1-kDa peaks may be able to differentiate thrombotic events from other hemostatic events.