Effects of Oritavancin on Coagulation Tests in the Clinical Laboratory.

Previous studies have shown that some lipoglycopeptide and lipopeptide antimicrobial agents may cause falsely elevated values for some phospholipid-dependent coagulation tests. The effect of oritavancin, a lipoglycopeptide antibiotic, on coagulation test results was explored using pooled human plasma samples spiked with drug and in a clinical study after an infusion of a single 1,200-mg intravenous dose of oritavancin in normal healthy volunteers. Pooled plasma with oritavancin added ex vivo showed concentration-dependent prolongation of prothrombin time/international normalized ratio (PT/INR), activated partial thromboplastin time (aPTT), and dilute Russell viper venom time (DRVVT) test results. In contrast, oritavancin had no effect on the activated protein C resistance assay, chromogenic anti-factor Xa assay (anti-FXa), thrombin time, and an immunoassay for the laboratory diagnosis of heparin-induced thrombocytopenia. In participants that received a single dose of oritavancin, elevations in PT/INR result, aPTT, DRVVT, activated clotting time, and silica clotting time occurred, with the maximum times to resolution of test interference determined to be 12, 120, 72, 24, and 18 h, respectively. The anti-FXa assay was unaffected, whereas transient elevations in D dimer levels were observed in 30% of participants, with a maximum time to resolution of 72 h. Although oritavancin has no impact on the coagulation system in vivo, a single dose of oritavancin can produce falsely elevated values of some coagulation tests used to monitor hemostasis. The interference of oritavancin on affected tests is transient, and the test results revert to normal ranges within specified times after dosing.

CD32a antibodies induce thrombocytopenia and type II hypersensitivity reactions in FCGR2A mice.

The CD32a immunoglobulin G (IgG) receptor (Fcγ receptor IIa) is a potential therapeutic target for diseases in which IgG immune complexes (ICs) mediate inflammation, such as heparin-induced thrombocytopenia, rheumatoid arthritis, and systemic lupus erythematosus. Monoclonal antibodies (mAbs) are a promising strategy for treating such diseases. However, IV.3, perhaps the best characterized CD32a-blocking mAb, was recently shown to induce anaphylaxis in immunocompromised "3KO" mice. This anaphylactic reaction required a human CD32a transgene because mice lack an equivalent of this gene. The finding that IV.3 induces anaphylaxis in CD32a-transgenic mice was surprising because IV.3 had long been thought to lack the intrinsic capacity to trigger cellular activation via CD32a. Such an anaphylactic reaction would also limit potential therapeutic applications of IV.3. In the present study, we examine the molecular mechanisms by which IV.3 induces anaphylaxis. We now report that IV.3 induces anaphylaxis in immunocompetent CD32a-transgenic "FCGR2A" mice, along with the novel finding that IV.3 and 2 other well-characterized CD32a-blocking mAbs, AT-10 and MDE-8, also induce severe thrombocytopenia in FCGR2A mice. Using recombinant variants of these same mAbs, we show that IgG "Fc" effector function is necessary for the induction of anaphylaxis and thrombocytopenia in FCGR2A mice. Variants of these mAbs lacking the capacity to activate mouse IgG receptors not only failed to induce anaphylaxis or thrombocytopenia, but also very potently protected FCGR2A mice from near lethal doses of IgG ICs. Our findings show that effector-deficient IV.3, AT-10, and MDE-8 are promising candidates for developing therapeutic mAbs to treat CD32a-mediated diseases.

Recruitment of monocytes/macrophages by tissue factor-mediated coagulation is essential for metastatic cell survival and premetastatic niche establishment in mice.

Tissue factor (TF) expression by tumor cells correlates with metastasis clinically and supports metastasis in experimental settings. However, the precise pathways coupling TF to malignancy remain incompletely defined. Here, we show that clot formation by TF indirectly enhances tumor cell survival after arrest in the lung, during experimental lung metastasis, by recruiting macrophages characterized by CD11b, CD68, F4/80, and CX(3)CR1 (but not CD11c) expression. Genetic or pharmacologic inhibition of coagulation, by either induction of TF pathway inhibitor ex-pression or by treatment with hirudin, respectively, abrogated macrophage recruitment and tumor cell survival. Furthermore, impairment of macrophage function, in either Mac1-deficient mice or in CD11b-diphtheria toxin receptor mice in which CD11b-positive cells were ablated, decreased tumor cell survival without altering clot formation, demonstrating that the recruitment of functional macrophages was essential for tumor cell survival. This effect was independent of NK cells. Moreover, a similar population of macrophages was also recruited to the lung during the formation of a premetastatic niche. Anticoagulation inhibited their accumulation and prevented the enhanced metastasis associated with the formation of the niche. Our study, for the first time, links TF induced coagulation to macrophage recruitment in the metastatic process.

Evaluation of Latex Immunoturbidimetric Assay Thresholds and HIT in Cardiothoracic Surgery.

BACKGROUND: Heparin-induced thrombocytopenia (HIT) is a common differential diagnosis in cardiothoracic surgery. The latex immunoturbidimetric assay (LIA) is an enhanced immunoassay that has recently been introduced for the detection of total HIT immunoglobulin and retains a higher specificity of 95% compared to the enzyme-linked immunosorbent assay. OBJECTIVES: To investigate if a semiquantitative relationship exists between increasing LIA levels beyond the current positivity threshold and its correlation to positive serotonin release assay results in cardiothoracic surgery. METHODS: This was a multicenter, observational cohort of cardiothoracic surgery patients initiated on anticoagulation with heparin-based products. To conduct sensitivity and specificity analysis of LIA values, HIT positive was defined as a LIA value ≥1 unit/mL and HIT negative was defined as a LIA level <1 unit/mL. A receiver operating characteristic (ROC) analysis was utilized to evaluate the predictive performance of the LIA. RESULTS: At manufactures' cutoffs of ≥1.0 unit/mL, LIA sensitivity and specificity was 93.8% and 22%, respectively, yielding a false positive rate of 78%. At a higher cutoff of 4.5 units/mL, LIA sensitivity and specificity was 75% and 71%, respectively, yielding a false positive rate of 29% and an area under the ROC curve of 0.75 (P = .01; 95% confidence interval: 0.621-0.889). Bivalirudin was initiated in 84.6% of false positive LIA results. CONCLUSION: This study suggests that the diagnostic accuracy of the LIA can be optimized by increasing the LIA positivity threshold. Proposing a higher LIA cutoff, may mitigate unwarranted anticoagulation and bleeding outcomes.

Anti-CD40L immune complexes potently activate platelets in vitro and cause thrombosis in FCGR2A transgenic mice.

Anti-CD40L immunotherapy in systemic lupus erythematosus patients was associated with thromboembolism of unknown cause. We previously showed that monoclonal anti-CD40L immune complexes (ICs) activated platelets in vitro via the IgG receptor (FcgammaRIIa). In this study, we examined the prothrombotic effects of anti-CD40L ICs in vivo. Because mouse platelets lack FcgammaRIIa, we used FCGR2A transgenic mice. FCGR2A mice were injected i.v. with preformed ICs consisting of either anti-human CD40L mAb (M90) plus human CD40L, or a chimerized anti-mouse CD40L mAb (hMR1) plus mouse CD40L. ICs containing an aglycosylated form of hMR1, which does not bind FcgammaRIIa, were also injected. M90 IC caused shock and thrombocytopenia in FCGR2A but not in wild-type mice. Animals injected with hMR1 IC also experienced these effects, whereas those injected with aglycosylated-hMR1 IC did not, demonstrating that anti-CD40L IC-induced platelet activation in vivo is FcgammaRIIa-dependent. Sequential injections of individual IC components caused similar effects, suggesting that ICs were able to assemble in circulation. Analysis of IC-injected mice revealed pulmonary thrombi consisting of platelet aggregates and fibrin. Mice pretreated with a thrombin inhibitor became moderately thrombocytopenic in response to anti-CD40L ICs and had pulmonary platelet-thrombi devoid of fibrin. In conclusion, we have shown for the first time that anti-CD40L IC-induced thrombosis can be replicated in mice transgenic for FcgammaRIIa. This molecular mechanism may be important for understanding thrombosis associated with CD40L immunotherapy. The FCGR2A mouse model may also be useful for assessing the hemostatic safety of other therapeutic Abs.

Heparin-platelet factor 4 antibodies in intensive care patients: an observational seroprevalence study.

Heparin-platelet factor 4 (PF4) antibodies mediate heparin-induced thrombocytopenia (HIT) and, irrespective of thrombocytopenia, are associated with poorer outcomes in some patients. The prevalence of heparin-PF4 antibodies, including platelet-activating ones, in patients in the medical, neurotrauma, or shock-trauma intensive care unit (ICU) remains unclear. In this single-center, observational study, heparin-PF4 antibodies (IgG/A/M) were measured by ELISA in 185 adults (median APACHE II score, 16) admitted to the medical (n = 27), neurotrauma (n = 96), or shock-trauma (n = 62) ICU and after 7 +/- 2 days. Seropositive patients and heparin-treated patients with unexplained, new-onset thrombocytopenia were also tested for platelet-activating antibodies using a serotonin release assay (SRA). Of 185 patients, seropositivity occurred in 20 patients (10.8%; 95% CI 6.7-16.2%) at admission and 54 (29.2%, 95% CI 22.8-36.3%) after 7 days (P < 0.001). Platelet-activating antibodies occurred in 4 seropositive patients at admission and 9 seropositive patients after 7 days (including in 1 patient at each assessment), each without thrombocytopenia or new thrombosis. Of 12 seropositive patients with platelet-activating antibodies, 6 had an ELISA optical density (OD) >1.0. ELISA-positive, SRA-negative, suspected HIT occurred in 1 patient. Heparin-PF4 antibodies are present in 10.8% of medical, neurotrauma, or shock-trauma ICU patients at admission and increase significantly to 29.2% within 7 days. Approximately 17-20% of seropositive ICU patients, often those with an ELISA OD >1.0, have platelet-activating heparin-PF4 antibodies.

Human platelets contain and release TWEAK.

The multifunctional cytokine, TWEAK (TNF-like weak inducer of apoptosis), is a member of the TNFα superfamily. TWEAK is found in a broad range of cell types and has been linked to cell growth and survival, angiogenesis and other inflammatory processes. These functions and their importance in inflammatory diseases have made TWEAK an attractive pharmaceutical target, particularly for immunotherapy with monoclonal antibodies (mAbs). Immunotherapy targeting another TNFα family member, CD154, was associated with thrombosis in clinical trials. Subsequent studies identified platelets, which contain CD154, as a possible contributing factor to thrombosis in these trials. Since clinical trials with anti-TWEAK mAbs have already begun, we considered it important to determine whether platelets contain TWEAK. Using a variety of immunologic methods we found that, upon activation, human platelets expose TWEAK antigen and release it in soluble form (sTWEAK). By flow cytometry we determined that human platelets activated by TRAP (Thrombin Receptor Agonist Peptide) and other agonists expose TWEAK antigen (22% median positivity) and release TWEAK positive microparticles. The presence of TWEAK on platelets was confirmed by confocal microscopy. By ELISA, we found that sTWEAK is released by activated platelets. Finally, western blot analysis revealed TWEAK protein (34 kDa) in washed platelet lysates. The finding that human platelets contain TWEAK raises important questions about its possible functions in normal physiology, as well as in inflammatory diseases and their treatment.

Tissue factor procoagulant activity of plasma microparticles is increased in patients with early-stage prostate cancer.

Tissue factor (TF) plays a critical role in tumour growth and metastasis, and its enhanced release into plasma in association with cellular microparticles (MPs) has recently been associated with pathological cancer progression. We have previously demonstrated significantly elevated levels of plasma TF antigen as well as systemic coagulation and platelet activation in patients with localised prostate cancer. In this prospective study, we used a highly sensitive one-stage clotting assay to measure preoperative TF-specific procoagulant activity (PCA) of plasma MPs in 68 consecutive patients with early-stage prostate cancer to further explore the relevance of circulating TF in this tumour entity. Automated calibrated thrombography was used to monitor thrombin generation in cell-free plasma samples in the absence of exogenous TF or phospholipids. Compared to healthy male controls (n=20), patients had significantly increased levels of both D-dimer and TF-specific PCA of plasma MPs (p<0.001). Furthermore, MP-associated TF PCA was higher in patients with (n=29) than in those without (n=39) laboratory evidence of an acute-phase reaction (p=0.004) and decreased to normal levels within one week after radical prostatectomy. Overall, we found a significant correlation between TF-specific PCA of plasma MPs and plasma D-dimer (p=0.002), suggesting that plasma MPs contributed to in-vivo coagulation activation in a TF-dependent manner. Thrombin generation in plasma was also significantly increased in patients compared to controls (p<0.01). Collectively, our findings suggest that TF-specific PCA of plasma MPs contributes to intravascular coagulation activation in patients with early-stage prostate cancer and may represent a potential link between hypercoagulability, inflammation, and disease progression.

Evaluation of a rapid and automated heparin-induced thrombocytopenia immunoassay.

INTRODUCTION: Heparin-induced thrombocytopenia (HIT) is a potentially life-threatening adverse reaction of heparin. Laboratory evaluation of HIT is often not available within a reasonable time. We evaluated the HemosIL® HIT-Ab(PF4-H) (Instrumentation Laboratory), a rapid, on-demand, fully automated, latex immunoturbidimetric assay (LIA). MATERIALS AND METHODS: Following determination of the LIA's reference interval and cutoff values, a multicenter study was conducted between March 2013 and June 2015. Plasma samples of HIT-suspected patients (n = 632) were collected and evaluated by LIA on the ACL TOP® Family systems (Instrumentation Laboratory), enzyme-linked immunosorbent assays (EIA), and serotonin release assay (SRA). Patient characteristics, medical conditions, comorbidities, laboratory results, and medications were collected via medical chart review. The pretest clinical probability of HIT was also calculated for each patient. RESULTS: Based on the 95% reference interval for healthy donors and HIT-negative patients, a LIA value ≥1.0 U/mL was interpreted positive. The overall agreement of LIA versus EIA and SRA results were 90% (95% CI 88%-92%) and 79% (95% CI 75%-82%), respectively. The negative predictive value for LIA and EIA was comparable (87%) with SRA. The positive and negative percent agreements with the clinical probability were 89% (95% CI 69%-97%) and 86% (95% CI 83%-89%), respectively, with a negative predictive value of 99.6% (95% CI 98%-100%). DISCUSSION: Overall, the LIA results were comparable to those of EIA and SRA. This fully automated assay with a remarkable short analytical turnaround time of <20 minutes can be performed on-demand, which would greatly facilitate more prompt management of HIT.

Plasma tissue factor antigen in localized prostate cancer: distribution, clinical significance and correlation with haemostatic activation markers.

Tissue factor (TF) is involved in cancer growth and metastasis, and haemostatic abnormalities are found in most patients with advanced malignancies, including prostate cancer (PC). Because anti-haemostatic agents are increasingly screened for their potential to prolong survival in tumor patients, a detailed characterization of haemostatic markers in selected cancer subtypes and clinical stages is warranted. In this study, we measured preoperative plasma TF antigen in a large cohort of patients with localized PC and correlated its levels with markers of coagulation and platelet activation, prostate-specific antigen (PSA), and histopathological findings to explore its potential as a prognostic marker in this tumor entity. Out of 140 patients, 19% and 23% had plasma TF antigen levels of <40 pg/ml (low-TF) and >200 pg/ml (high-TF), respectively, which was substantially higher than in 42 healthy male controls. Patients also had low-grade systemic coagulation activation as evidenced by elevated D-dimer, F1 + 2, and PAP plasma levels. Furthermore, similar to sP-selectin and sCD40L antigen, flow cytometric analysis of platelet-derived microparticles in plasma revealed significantly increased numbers in high-TF as compared to low-TF patients and controls. Whereas elevated D-dimer was associated with larger and less differentiated tumors, preoperative plasma TF antigen levels (median [IQR]) were higher in patients with (161 pg/ml [100-236]) than in those without recurrent PC (105 pg/ml [52-182]), as indicated by a serum PSA of >0.1 ng/ml during ambulatory follow-up. In patients with localized PC, preoperative plasma TF antigen levels correlate with platelet activation in vivo and may indicate an increased risk for recurrent disease.

Anti-metastatic effect of a non-anticoagulant low-molecular-weight heparin versus the standard low-molecular-weight heparin, enoxaparin.

Low-molecular-weight heparins (LMWH) exhibit potent anticoagulant efficacy via their plasmatic effects on thrombin and factor Xa. These agents are also effective in releasing endothelial tissue factor pathway inhibitor (TFPI), the natural inhibitor of tissue factor, and exhibit significant anti-metastatic effects in experimental animal models. However, the potential for bleeding complications has slowed down the more widespread adoption of LMWH therapy in cancer patients. In this study, the effect of a non-anticoagulant form of LMWH (NA-LMWH) on experimental lung metastasis and tumor cell-induced platelet aggregation in vivo was compared to the LMWH enoxaparin. Using the B16 melanoma mouse model of metastasis, subcutaneous (s.c.) injection of NA-LMWH or enoxaparin (10 mg/kg), three hours before intravenous (i.v.) injection of metastatic melanoma cells, followed by daily doses for 14 days, reduced lung tumor formation by 70% (P < 0.001). I.v. injection of tumor cells resulted in a significant (50-62%, P < 0.01) fall in platelet counts. Pre-injection (i.v.) of enoxaparin completely abolished the tumor cell-induced thrombocytopenia, whereas NA-LMWH had no effect. Four hours after a single s.c. dose, enoxaparin but not NA-LMWH prolonged the clotting time three-fold and delayed the time to clot initiation more than 10-fold as measured by a Sonoclot analyzer and by thromboelastography, respectively. Enoxaparin but not NA-LMWH demonstrated a significant anticoagulant effect in mice. Both NA-LMWH and enoxaparin caused similar TFPI release from endothelial cells in vitro. These data provide evidence to support the potential of NA-LMWH as an anti-metastatic agent without any significant impact on coagulation.

Striking back at heparin-induced thrombocytopenia.

This immune reaction to a common anticoagulant can have devastating consequences. Learn how to recognize who's at risk and how to intervene if trouble hits.

Microvesicle-associated tissue factor procoagulant activity for the preoperative diagnosis of ovarian cancer.

BACKGROUND: Tissue factor (TF) is involved in tumor growth and metastasis and contributes to venous thromboembolism (VTE) in cancer, including gynecological malignancies. The diagnostic value of microvesicle-associated TF procoagulant activity (MV TF PCA) in women with suspected ovarian cancer, however, has not been studied. OBJECTIVE: To evaluate MV TF PCA as a diagnostic tool in women with an ovarian mass of unknown etiology and as a predictive biomarker for perioperative VTE. METHODS: Plasma MVs were isolated by high-speed centrifugation and analyzed for TF-specific PCA by single-stage clotting assay. In addition, plasma TF antigen and soluble P-selectin (sCD62P) were measured by ELISA. RESULTS: D-Dimer, MV TF PCA, and sCD62P, but not the tumor marker, CA-125, significantly differentiated patients with malignant (n=40) from those with benign tumors (n=15) and healthy controls (n=34). In cancer patients, only D-Dimer and CA-125 correlated with the FIGO stage. An abnormal D-dimer had the highest sensitivity for the diagnosis of cancer, while MV TF PCA above the ROC curve-derived cut-off value of 182U/mL had the highest specificity. By multivariate logistic regression analysis, addition of MV TF PCA conferred diagnostic benefit to the single variables, CA-125 (p=0.052) and D-dimer (p=0.019). Perioperative VTE occurred in 16% of cancer patients and was associated with an advanced FIGO stage, but not MV TF PCA. There was no difference in plasma TF antigen levels between study groups. CONCLUSIONS: MV TF PCA, but not plasma TF antigen, may provide valuable additional information for the diagnostic work-up of women with suspected ovarian cancer.

Detection and significance of heparin-platelet factor 4 antibodies.

Heparin-induced thrombocytopenia (HIT) represents an immune reaction to heparin, which if unrecognized and untreated, has the potential for catastrophic thrombotic events. The demonstration of antibodies directed against the heparin-platelet factor 4 (H-PF4) complex is an important component of the diagnosis of HIT. Typically, test results are not rapidly available, and the diagnosis therefore rests principally on clinical grounds. Nevertheless, the presence of H-PF4 antibodies provides important confirmation of the diagnosis, and may predict for adverse cardiac events even in the absence of HIT. Although more research is certainly required, the use of alternative (non-heparin) anticoagulants for cardiac surgery and other cardiovascular procedures would substantially reduce the incidence of HIT and could possibly improve patient outcomes.

The role of CD40 in CD40L- and antibody-mediated platelet activation.

Our initial finding that CD40- and CD40 ligand (CD40L)-deficient mice displayed prolonged tail bleeding and platelet function analyzer (PFA-100) closure times prompted us to further investigate the role of the CD40-CD40L dyad in primary hemostasis and platelet function. Recombinant human soluble CD40L (rhsCD40L), chemical cross-linking of which suggested a trimeric structure of the protein in solution, activated platelets in a CD40-dependent manner as evidenced by increased CD62P expression. CD40 monoclonal antibody (mAb) M3, which completely blocked rhsCD40L-induced platelet activation, also prolonged PFA-100 closure times of normal human blood. In contrast, CD40 mAb G28-5 showed less potential in blocking rhsCD40L-induced CD62P expression and did not affect PFA-100 closure times. However, when added to the platelets after rhsCD40L, G28-5 significantly enhanced the platelet response by causing clustering of, and signaling through, FcgammaRII. Similarly, higher order multimeric immune complexes formed at a 1/3 molar ratio of M90, a CD40L mAb, to rhsCD40L induced strong Fcgamma RII-mediated platelet activation when translocated to the platelet surface in a CD40-dependent manner, including the induction of morphological shape changes, fibrinogen binding, platelet aggregation, dense granule release, microparticle generation and monocyte-platelet-conjugate formation. The results suggest that CD40 may play a role in primary hemostasis and platelet biology by two independent mechanisms: First, by functioning as a primary signaling receptor for CD40L and, second, by serving as a docking molecule for CD40L immune complexes. The latter would also provide a potential mechanistic explanation for the unexpected high incidence of CD40L mAb-associated thrombotic events in recent human and animal studies.

Effect of argatroban on the activated partial thromboplastin time: a comparison of 21 commercial reagents.

Argatroban is a direct thrombin inhibitor used for the treatment of heparin-induced thrombocytopenia. The drug is administered by continuous infusion, at a recommended initial dose of 2 microg/kg per min, to achieve activated partial thromboplastin times (aPTTs) 1.5-3.0 times baseline. We evaluated the effect of argatroban, at clinically relevant concentrations, on aPTTs using 21 commercially available reagents. The aPTTs of plasma containing argatroban at 0.125-8.0 microg/ml (final concentration) were assessed using each reagent and an ACL 3000+ coagulation analyzer. Argatroban increased aPTTs (and aPTT ratios relative to control) in a broadly comparable fashion among reagents. Concentration-aPTT ratio profiles linearized well using logarithmic-logarithmic transformation (r > 0.98), with the regression slope taken as the reagent's sensitivity to argatroban. Sensitivity ranged from 0.304 +/- 0.006 to 0.364 +/- 0.007. Only the least and two most sensitive reagents (all now unavailable in the United States) differed significantly in sensitivity from the other reagents (P < 0.05). aPTT ratios of 2.25 occurred for all reagents at 0.41-0.92 mug/ml argatroban, and for 14 (67%) reagents at 0.53-0.67 microg/ml. This corresponds to a approximately 0.5 microg/kg per min dose difference in healthy subjects. We conclude that most aPTT reagents are similarly sensitive to argatroban, and reagent choice is unlikely to significantly affect argatroban monitoring in patients with heparin-induced thrombocytopenia.

Delayed-onset heparin-induced thrombocytopenia.

BACKGROUND: Heparin-induced thrombocytopenia presents 5 to 12 days after heparin exposure, with or without arterial or venous thromboemboli. Delayed recognition and treatment of heparin-induced thrombocytopenia contribute to poor patient outcomes. OBJECTIVE: To describe and increase awareness of a clinical scenario in which the onset or manifestations of heparin-induced thrombocytopenia are delayed. DESIGN: Retrospective case series. SETTING: Three large urban hospitals (with active cardiovascular surgery programs). PATIENTS: 14 patients seen over a 3-year period in whom heparin-induced thrombocytopenia became apparent on delayed presentation with thromboembolic complications. MEASUREMENTS: Platelet counts, onset of objectively determined thromboembolism, results of heparin-induced platelet factor 4 antibody tests, and outcomes. RESULTS: Patients went home after hospitalizations that had included heparin exposure--in most cases, with no thrombocytopenia recognized--only to return to the hospital (median, day 14) with thromboembolic complications. Thromboemboli were venous (12 patients, 7 with pulmonary emboli) or arterial (4 patients) or both. Platelet counts were mildly decreased in all but 2 patients on second presentation. On readmission, 11 patients received therapeutic heparin, which worsened the patients' clinical condition and, in all 11 cases, decreased the platelet count (mean at readmission, 143 x 10(9) cells/L; mean nadir after heparin re-exposure, 39 x 10(9) cells/L). Results of serologic tests for heparin-induced antibodies were positive in all patients. Subsequent treatments included alternative anticoagulants (11 patients), thrombolytic drugs (3 patients), inferior vena cava filters (3 patients) and, eventually, warfarin (11 patients). Three patients died. CONCLUSIONS: Delayed-onset heparin-induced thrombocytopenia is increasingly being recognized. To avoid disastrous outcomes, physicians must consider heparin-induced thrombocytopenia whenever a recently hospitalized patient returns with thromboembolism; therapy with alternative anticoagulants, not heparin, should be initiated.

Tissue factor-dependent and -independent pathways of systemic coagulation activation in acute myeloid leukemia: a single-center cohort study.

BACKGROUND: In acute myeloid leukemia (AML), disseminated intravascular coagulation (DIC) contributes to morbidity and mortality, but the underlying pathomechanisms remain incompletely understood. METHODS: We conducted a prospective study on 69 patients with newly diagnosed AML to further define the correlates of systemic coagulation activation in this hematological malignancy. Tissue factor procoagulant activity (TF PCA) of isolated peripheral blood mononuclear cells (PBMCs) and TF expression by circulating microparticles (MPs) were assessed by single-stage clotting and thrombin generation assay, respectively. Soluble plasma TF antigen and secretion of vascular endothelial growth factor (VEGF) by cultured PBMCs were measured by ELISA. Cell-free plasma DNA was quantified by staining with a fluorescent dye. RESULT: TF PCA of PBMCs was significantly increased in AML patients as compared to healthy controls. Furthermore, TF PCA was significantly associated with decompensated DIC at presentation, as defined by a plasma fibrinogen level of ≤1 g/L (n = 11). In addition to TF PCA and circulating blasts, serum lactate dehydrogenase, a surrogate marker for leukemic cell turnover, correlated with plasma D-Dimer in the total patient cohort and was significantly increased in DIC patients, suggesting a role for myeloblast apoptosis/necrosis in activation of the TF-dependent coagulation pathway. Consistently, TF-bearing plasma MPs were more frequently detected and levels of soluble TF antigen were significantly higher in DIC vs. non-DIC patients. No association was found between TF PCA expression and VEGF secretion by isolated PBMCs, but significantly increased levels of cell-free plasma DNA pointed to a contribution of the intrinsic contact pathway to systemic coagulation activation in the total patient cohort and in patients with lower TF PCA expression. While PBMC-associated TF PCA had no effect on long-term survival, DIC occurrence at presentation increased the risk of early mortality. CONCLUSION: In newly diagnosed AML, TF expression by PBMCs and shedding of TF-bearing plasma MPs are central to the pathogenesis of DIC, but additional pathways, such as DNA liberation, may contribute to systemic coagulation activation.

Inhibition of tumor cell-induced platelet aggregation and lung metastasis by the oral GpIIb/IIIa antagonist XV454.

Platelets are known to play a role in blood borne metastasis. Previous experimental studies have suggested that platelet GpIIb/IIIa may be a therapeutic target. However, the need for intravenous administration limits the potential application of current GpIIb/IIIa inhibitors to cancer therapy. The aim of the present study was to assess the efficacy of a novel, non-peptide oral GpIIb/IIIa antagonist (XV454) on tumor cell-induced platelet aggregation in vivo and on experimental metastasis. A Lewis lung carcinoma (LL2) mouse model of experimental metastasis was used in this study. XV454 (100 micro g) was administered intravenously (via tail vein) or orally (gavages) to 20 g mice. To determine the effect of XV454 on platelet aggregation, blood samples were collected by cardiac puncture 10 minutes after intravenous and 1-24 hrs after oral XV454, and platelet function was assessed by aggregometry, thrombelastography and the Platelet Function Analyzer (PFA100). The effect of XV454 on tumor cell-induced thrombocytopenia was determined 10 minutes after intravenous and 3 hrs after oral XV454 administration. Tumor cells (2 x 10(6)) were injected intravenously and 15 minutes after cell injection, platelet count was measured and compared to baseline (pre-injection) counts. To assess the effect on metastasis, XV454 was administered intravenous or orally 10 minutes and 3 hrs before tumor cell injection, respectively. Eighteen days later, surface lung tumor nodules were counted and the total lung tumor burden assessed. In a fourth group, in addition to the initial oral dose (before tumor cell injection), oral XV454 was given daily for the first week and three times in the second week. Administration of XV454 (5 mg/kg) completely inhibited platelet aggregation and this effect persisted for at least 24 hrs after oral delivery. Both intravenous and oral XV454 significantly inhibited tumor cell-induced thrombocytopenia (P < 0.01), the number of surface lung tumor nodules (80-85%; P < 0.001) and total tumor burden (83% for intravenous group; 50% oral [single treatment] group; 91% oral [multiple treatment] group, P < 0.001). Overall, these data provide further evidence for the effect of oral and intravenous GpIIb/IIIa antagonism on tumor cell-platelet interaction and metastasis.

Tissue factor pathway inhibitor reduces experimental lung metastasis of B16 melanoma.

The importance of tissue factor (TF) in tumor biology has been highlighted by studies suggesting its involvement in cell signaling, metastasis and angiogenesis. Since many animal studies have shown that anticoagulant therapy can reduce experimental metastasis, we studied whether the natural inhibitor of TF-mediated blood coagulation, Tissue Factor Pathway Inhibitor (TFPI), might be similarly effective. Using a murine experimental model, we found that intravenous injection of recombinant murine TFPI immediately before introduction of tumor cells reduced metastasis by 83% (P < 0.001). B16 murine melanoma cells stably transfected with a TFPI expression vector exhibited reduced lung seeding following intravenous injection by 81% (P < 0.001) compared with controls. No difference in primary tumor growth was observed between TFPI+ and control cells. Mice receiving intravenous somatic gene transfer of sense TFPI expression vector developed 78% fewer lung nodules than controls (P < 0.05). We conclude that TFPI has significant anti-metastatic activity in this experimental model.