Acquired factor V inhibitor: a nation-wide study of 38 patients.

Acquired factor V inhibitor (AFVI) is an extremely rare disorder that may cause severe bleeding. To identify factors associated with bleeding risk in AFVI patients, a national, multicentre, retrospective study was made including all AFVI patients followed in 21 centres in France between 1988 and 2015. All patients had an isolated factor V (FV) deficiency <50% associated with inhibitor activity. Patients with constitutional FV deficiency and other causes of acquired coagulation FV deficiencies were excluded. The primary outcome was incident bleeding and factors associated with the primary outcome were identified. Thirty-eight (74 [36-100] years, 42·1% females) patients with AFVI were analysed. Bleeding was reported in 18 (47·4%) patients at diagnosis and in three (7·9%) during follow-up (7 [0·2-48.7] months). At diagnosis, FV was <10% in 31 (81·6%) patients. Bleeding at diagnosis was associated with a prolonged prothrombin time that strongly correlated with the AFVI level measured in plasma {r = 0·63, 95% confidence interval (CI) [0·36-0·80], P < 0·05}. Bleeding onset during follow-up was associated with a slow AFVI clearance (P < 0·001). The corresponding receiver operating characteristics curve showed that AFVI clearance was predictive of bleeding onset with an AFVI clearance of seven months with a sensitivity of 100% (95% CI: 29-100) and a specificity of 86% (95% CI: 57-98, P = 0·02). Kaplan-Meier analysis showed that AFVI clearance >7 months increased the risk of bleeding by 8 (95% CI: [0·67-97], P = 0·075). Prothrombin time at diagnosis and time for clearance of FV inhibitor during follow-up are both associated with bleeding in patients with AFVI.

Successful Management of Acquired Factor V Inhibitor by Monitoring Factor V Activity, Antigen, and Inhibitor Values during Immunosuppressive Therapy.

Acquired factor V inhibitor (AFVI) results from the formation of autoantibodies to coagulation factor V (FV), and the clinical phenotype can range from asymptomatic laboratory abnormalities to life-threatening bleeds. We describe a 74-year-old man who developed AFVI along with a massive subcutaneous hematoma. He was initially treated with prednisolone (PSL), but AFVI recurred when the dose was reduced after a short period. We subsequently increased the PSL dose and added cyclophosphamide (CY), which resulted in a complete response. We then gradually tapered PSL and stopped CY, and the patient has since remained free of recurrent AFVI symptoms. We monitored FV activity, antigen concentrations, and inhibitor titers of this patient throughout the clinical course. The ratio of FV activity to antigen concentration was low at diagnosis and gradually increased along with the patient's improvement. This ratio might be a useful parameter for evaluating the effects of immunosuppressive therapy in patients with AFVI.

Acquired Factor V Inhibitor with Hemorrhagic Symptoms after Prasugrel Hydrochloride Treatment.

Acquired factor V inhibitor (AFVI) is a rare coagulopathy. It may be triggered by specific antigens such as antibiotics. We herein report the first case of AFVI after treatment with prasugrel hydrochloride (prasugrel) in an 80-year-old male who underwent percutaneous coronary intervention because of angina pectoris 6 years ago and was initiated on aspirin and ticlopidine hydrochloride. He was switched from ticlopidine hydrochloride to prasugrel before undergoing percutaneous coronary intervention for myocardial infarction. Fifteen days later, he developed sudden nasal hemorrhage, hematuria, and systemic purpura. Coagulation tests revealed prolonged prothrombin time-international normalized ratio (11.35) and activated partial thromboplastin time (170 s). The coagulation factor profile revealed a decreased FV activity (1%). The Bethesda assay for FV inhibitor was positive. AFVI was diagnosed; prasugrel was immediately discontinued, and administration of recombinant activated factor VII and prednisolone were initiated. Hemorrhagic symptoms immediately disappeared; FV activity improved, and the FV inhibitor titer was normalized.

[Acquired factor V inhibitor].

Since acquired factor V inhibitor (FV-INH) has been first reported in Germany in 1955, about 200 cases have been recorded globally. The incidence of FV-INH is extremely low, with a rate of 0.023-0.09 per million persons per year. FV-INH formation is caused by infection, use of antibiotics and other drugs, surgery, and diseases, including malignancy and autoimmune disorder. Some patients with FV-INH present with abnormal clinical laboratory test results but have no hemorrhagic symptoms. Others experience life-threatening bleeding. Moreover, thrombosis can sometimes occur. The diagnosis is based on prolonged prothrombin time (PT) and activated partial thromboplastin time (APTT), an inhibitor pattern shown by a cross-mixing test of PT and APTT, decreased factor V activity, and detection of FV-INH. Treatment includes hemostatic and immunosuppressive therapy. However, in some cases, the monitoring of progression alone is appropriate. In terms of hemostatic therapies, infusion of platelet concentrates and administration of recombinant factor VIIa are highly useful. However, no definitive treatment strategy has been established. In about 50% of cases, FV-INH is eliminated spontaneously. Therefore, immunosuppressive therapy is recommended only for hemorrhagic patients or those at high risk of hemorrhage. Prednisolone is generally used for the management of immunosuppression. However, some reports have shown that the administration of rituximab, cyclophosphamide, and intravenous immunoglobulin and plasma-exchange can be utilized as treatments.

[Acquired factor V inhibitor associated with apixaban].

Acquired factor V inhibitor is an acquired coagulation disorder that is rare. We report the case of a patient who was treated with apixaban and developed acquired factor V inhibitor. The patient was a 76-year-old man who has been on long-term treatment with aspirin and clopidogrel after undergoing percutaneous coronary intervention (PCI) and carotid artery stenting. In June, he developed a cerebral infarction six days after the second PCI. Apixaban was added to his treatment regimen for cariogenic cerebral embolism. Three months later, intramuscular hemorrhage occurred in his left leg after a fall. However, the hemorrhage improved upon aspirin withdrawal. Unexpectedly, subcutaneous and intramuscular hemorrhage recurred three months after the patient commenced anticoagulation therapy. At this time, the APTT was 242.5 seconds and the PT was over the reference range. Although clopidogrel and apixaban were discontinued, these abnormalities did not improve. However, a cross-mixing test showed an inhibitor pattern, with factor V activity being less than 1% and its inhibitor level being 8.0 BU/ml. Based on these findings, the patient was finally diagnosed of acquired factor V inhibitor. One month after prednisolone administration at 20 mg/day, the PT and APTT were normalized, and prednisolone was tapered off. Although the use of dabigatran has been associated with iatrogenic acquired factor V inhibitor, we describe the first case of acquired factor V inhibitor associated with direct Xa inhibitor.

A very potent factor V inhibitor interferes with the levels of all coagulation factors and causes a fatal hemorrhagic syndrome.

We report a very high factor V inhibitor affecting the measurement of all coagulation factors besides fibrinogen, all these factors being dramatically decreased. This inhibitor could be linked to antibiotic use. The patient died of massive hemorrhage before a plasma exchange could be initiated.

Acquired Factor V Deficiency Associated with CFPM Administration.

BACKGROUND: Acquired factor V deficiency (AFVD) caused by Factor V (FV) inhibition is a rare event, characterized by prolonged prothrombin time and activated partial thromboplastin time. To date, various factors were reported as triggers for developing FV inhibitor. Clinical symptoms range from asymptomatic to life-threatening bleeding. Case Report and Conclusions: Here, we report an 84-year-old Japanese male on hemodialysis due to renal failure who developed subcutaneous hemorrhage after administration of cefepime (CFPM) to treat bacteremia. Deficient FV activity (< 1.0%) was identified and AFVD with FV inhibitor titer of 9 BU/mL was diagnosed. Although the patient had multiple risks for developing FV inhibitor, CFPM was thought to be the major culprit in this case. After the diagnosis, oral prednisolone (30 mg/day) was initiated, but the patient died of respiratory/cardiac failure, unrelated to AFVD.

Transfusion management of factor V deficiency: three case reports and review of the literature.

BACKGROUND: Factor V (FV) deficiency may be inherited as an autosomal recessive disease or acquired as a result of autoantibody formation, either spontaneously or secondary to exposure to bovine thrombin or medications. Congenital FV deficiency has traditionally been treated with plasma transfusions. However, recent evidence has suggested that platelet (PLT) transfusions may be a better alternative as FV stored within PLT alpha granules has greater procoagulant potential and is released locally at sites of vascular injury. We report three cases of FV deficiency, one congenital and two acquired, and emphasize the different management approaches. CASE REPORTS: Patient 1 was a 30-year-old man with congenital FV deficiency who presented with a trauma-induced hematoma of his lower extremity. He was treated with 5 PLT units over 48 hours. Patient 2 was a 64-year-old woman who presented with an upper-extremity thrombus and was discovered to have a FV inhibitor, likely secondary to antibiotics. Patient 3 was a 75-year-old woman with hepatitis C virus (HCV) who presented with minor ecchymosis and was found to have a FV inhibitor secondary to either HCV or antibiotic exposure. Corticosteroids alone were able to eradicate the inhibitors in both patients with acquired inhibitors. CONCLUSIONS: FV deficiency can present with a diverse range of symptoms. For bleeding patients, PLT transfusions should be the initial therapy. In patients with thrombosis, the risks and benefits of anticoagulation must be carefully assessed before treatment. For patients with minor bleeds, transfusions may be withheld, and elimination of the inhibitor should be the primary objective.

Factor Xa activation of factor V is of paramount importance in initiating the coagulation system: lessons from a tick salivary protein.

BACKGROUND: Generation of active procoagulant cofactor factor Va (FVa) and its subsequent association with the enzyme activated factor X (FXa) to form the prothrombinase complex is a pivotal initial event in blood coagulation and has been the subject of investigative effort, speculation, and controversy. The current paradigm assumes that FV activation is initiated by limited proteolysis by traces of (meizo) thrombin. METHODS AND RESULTS: Recombinant tick salivary protein TIX-5 was produced and anticoagulant properties were studied with the use of plasma, whole blood, and purified systems. Here, we report that TIX-5 specifically inhibits FXa-mediated FV activation involving the B domain of FV and show that FXa activation of FV is pivotal for plasma and blood clotting. Accordingly, tick feeding is impaired on TIX-5 immune rabbits, displaying the in vivo importance of TIX-5. CONCLUSIONS: Our data elucidate a unique molecular mechanism by which ticks inhibit the host's coagulation system. From our data, we propose a revised blood coagulation scheme in which direct FXa-mediated FV activation occurs in the initiation phase during which thrombin-mediated FV activation is restrained by fibrinogen and inhibitors.

Management of bleeding in severe factor V deficiency with a factor V inhibitor.

Factor V (FV) inhibitor arises rarely after using fresh frozen plasma (FFP) to treat inherited FV deficiency and is often a real therapeutic challenge. Here, we report a patient with a severe FV deficiency who developed such an inhibitor and was then treated with recombinant activated FVII (rFVIIa) and platelet concentrates (PC). Monitoring was assessed by thrombin generation assay (TGA). PC were more effective than rFVIIa in treating bleeding, but there was no correlation between the TGA results and clinical efficacy.

Successful management of a possible antibiotic-related acquired factor V inhibitor: a case report and review of the literature.

Acquired factor inhibitors are rare. We report a case of an elderly male who presented with a bleeding diathesis associated with an elevated prothrombin time and an activated partial thromboplastin time. Work-up revealed undetectable factor V activity and a factor V inhibitor level of >50 Bethesda units. The inhibitor may have been triggered by antibiotics. With a multimodality approach using steroids, platelet transfusions, intravenous immunoglobulin, factor VIII inhibitor bypass activity agent and cyclophosphamide, we successfully eliminated the inhibitor and controlled the bleeding.

Leishmania amazonensis exhibits phosphatidylserine-dependent procoagulant activity, a process that is counteracted by sandfly saliva.

Leishmania parasites expose phosphatidylserine (PS) on their surface, a process that has been associated with regulation of host's immune responses. In this study we demonstrate that PS exposure by metacyclic promastigotes of Leishmania amazonensis favours blood coagulation. L. amazonensis accelerates in vitro coagulation of human plasma. In addition, L. amazonensis supports the assembly of the prothrombinase complex, thus promoting thrombin formation. This process was reversed by annexin V which blocks PS binding sites. During blood meal, Lutzomyia longipalpis sandfly inject saliva in the bite site, which has a series of pharmacologically active compounds that inhibit blood coagulation. Since saliva and parasites are co-injected in the host during natural transmission, we evaluated the anticoagulant properties of sandfly saliva in counteracting the procoagulant activity of L. amazonensis . Lu. longipalpis saliva reverses plasma clotting promoted by promastigotes. It also inhibits thrombin formation by the prothrombinase complex assembled either in phosphatidylcholine (PC)/PS vesicles or in L. amazonensis . Sandfly saliva inhibits factor X activation by the intrinsic tenase complex assembled on PC/PS vesicles and blocks factor Xa catalytic activity. Altogether our results show that metacyclic promastigotes of L. amazonensis are procoagulant due to PS exposure. Notably, this effect is efficiently counteracted by sandfly saliva.

A case of factor V inhibitor with complete correction of the PT and aPTT upon mixing.

We read with interest Gartrell's recent report of a woman who developed a factor V inhibitor. Gartrell noted in his report that the inhibitor appeared to exhibit time dependence, as the mixing study showed slightly more prolongation of both the PT and the aPTT after 1 hr than immediately following mixing. We believe Gartrell's article may shed light on a recent intriguing case of a patient with factor V inhibitor at our institution.

Generation of an anticoagulant aptamer that targets factor V/Va and disrupts the FVa-membrane interaction in normal and COVID-19 patient samples.

Coagulation cofactors profoundly regulate hemostasis and are appealing targets for anticoagulants. However, targeting such proteins has been challenging because they lack an active site. To address this, we isolate an RNA aptamer termed T18.3 that binds to both factor V (FV) and FVa with nanomolar affinity and demonstrates clinically relevant anticoagulant activity in both plasma and whole blood. The aptamer also shows synergy with low molecular weight heparin and delivers potent anticoagulation in plasma collected from patients with coronavirus disease 2019 (COVID-19). Moreover, the aptamer's anticoagulant activity can be rapidly and efficiently reversed using protamine sulfate, which potentially allows fine-tuning of aptamer's activity post-administration. We further show that the aptamer achieves its anticoagulant activity by abrogating FV/FVa interactions with phospholipid membranes. Our success in generating an anticoagulant aptamer targeting FV/Va demonstrates the feasibility of using cofactor-binding aptamers as therapeutic protein inhibitors and reveals an unconventional working mechanism of an aptamer by interrupting protein-membrane interactions.

An anticoagulant RNA aptamer that inhibits proteinase-cofactor interactions within prothrombinase.

The interaction of factor Xa with factor Va on membranes to form prothrombinase profoundly increases the rate of the proteolytic conversion of prothrombin to thrombin. We present the characterization of an RNA aptamer (RNA(11F7t)) selected from a combinatorial library based on its ability to bind factor Xa. We show that RNA(11F7t) inhibits thrombin formation catalyzed by prothrombinase without obscuring the active site of Xa within the enzyme complex. Selective inhibition of protein substrate cleavage arises from the ability of the aptamer to bind to factor Xa and exclude interactions between the proteinase and cofactor within prothrombinase. Competition for enzyme complex assembly results from the binding of RNA(11F7t) to factor Xa with nanomolar affinity in a Ca(2+)-dependent interaction. RNA(11F7t) binds equivalently to the zymogen factor X as well as derivatives lacking gamma-carboxyglutamic acid residues. We suggest that the ability of RNA(11F7t) to compete for the Xa-Va interaction with surprisingly high affinity likely reflects a significant contribution from its ability to indirectly impact regions of Xa that participate in the proteinase-cofactor interaction. Thus, despite the complexity of the macromolecular interactions that underlie the assembly of prothrombinase, efficient inhibition of enzyme complex assembly and thrombin formation can be achieved by tight binding ligands that target factor Xa in a discrete manner.

Protamine sulfate down-regulates thrombin generation by inhibiting factor V activation.

Protamine sulfate is a positively charged polypeptide widely used to reverse heparin-induced anticoagulation. Paradoxically, prospective randomized trials have shown that protamine administration for heparin neutralization is associated with increased bleeding, particularly after cardiothoracic surgery with cardiopulmonary bypass. The molecular mechanism(s) through which protamine mediates this anticoagulant effect has not been defined. In vivo administration of pharmacologic doses of protamine to BALB/c mice significantly reduced plasma thrombin generation and prolonged tail-bleeding time (from 120 to 199 seconds). Similarly, in pooled normal human plasma, protamine caused significant dose-dependent prolongations of both prothrombin time and activated partial thromboplastin time. Protamine also markedly attenuated tissue factor-initiated thrombin generation in human plasma, causing a significant decrease in endogenous thrombin potential (41% +/- 7%). As expected, low-dose protamine effectively reversed the anticoagulant activity of unfractionated heparin in plasma. However, elevated protamine concentrations were associated with progressive dose-dependent reduction in thrombin generation. To assess the mechanism by which protamine mediates down-regulation of thrombin generation, the effect of protamine on factor V activation was assessed. Protamine was found to significantly reduce the rate of factor V activation by both thrombin and factor Xa. Protamine mediates its anticoagulant activity in plasma by down-regulation of thrombin generation via a novel mechanism, specifically inhibition of factor V activation.