Thrombin spatial distribution determines Protein C activation during hemostasis and thrombosis

Rebalancing of the hemostatic system by targeting endogenous anticoagulant pathways, like the Protein C system, is being tested as a means of improving hemostasis in patients with hemophilia. Recent intravital studies of hemostasis demonstrated that, in some vascular contexts, thrombin activity is sequestered to the extravascular compartment. These findings raise important questions about the context-dependent contribution of activated Protein C (aPC) to the hemostatic response since Protein C activation occurs on the surface of endothelial cells. Here, we used a combination of pharmacologic, genetic, imaging, and computational approaches to examine the relationships among thrombin spatial distribution, Protein C activation, and aPC anticoagulant function. We found that inhibition of aPC activity, either in mice harboring the Factor V-Leiden mutation or infused with an aPC blocking antibody, significantly enhanced fibrin formation and platelet activation in a microvascular injury model, consistent with aPC's role as an anticoagulant. In contrast, inhibition of aPC activity had no effect on hemostasis following penetrating injury of the mouse jugular vein. Computational studies showed that differences in blood velocity, injury size, and vessel geometry determine the localization of thrombin generation and, consequently, the extent of Protein C activation. Computational predictions were tested in vivo and showed that when thrombin generation occurred intravascularly, without penetration of the vessel wall, inhibition of aPC significantly increased fibrin formation in the jugular vein. Together, these studies show the importance of thrombin spatial distribution in determining Protein C activation during hemostasis and thrombosis.

Evidence-Based Minireview: Should warfarin or a direct oral anticoagulant be used in patients presenting with thrombosis in the splanchnic or cerebral veins?

Case 1: A 23-year-old female third-year medical student who has no medical history seeks treatment for abdominal distention. She takes an estrogen-containing birth control pill and does not smoke or consume alcohol. Family history is unremarkable. Physical examination is significant for abdominal distention, and an abdominal fluid wave is detected. Complete blood count is normal. Imaging confirms occlusive thrombosis of the main portal vein. On endoscopy, grade 1 to 2 esophageal varices are noted and banded. Unfractionated heparin is begun. Subsequent workup reveals a homozygous factor V Leiden mutation. Long-term anticoagulation is planned, and she asks if warfarin can be avoided given her hectic ward rotations, erratic diet, and need for monitoring. Case 2: A 35-year-old woman who has no medical history seeks treatment for progressively worsening posterior headaches for 1 week. Magnetic resonance imaging of the brain shows dural sinus thrombosis with associated small areas of petechial cerebral hemorrhage. She is started on a continuous unfractionated heparin infusion and admitted to the hospital for further observation. Her grandmother is on warfarin for atrial fibrillation, and the patient would prefer to avoid warfarin because she does not think she can comply with the frequent monitoring that will be required. She inquires about other oral anticoagulant options for her condition.

The Association Between Parameters of Erythrocytes Morphology and Thrombophilia-Related Mutations

Background: Alterations in erythrocyte morphology parameters have been identified and associated with hematological disorders and other chronic and cardiovascular diseases. Erythrocytes are abundant in thrombus content. Their hemoglobin density and differences in the ratio of macrocytic and microcytic cells may be associated with hypercoagulopathy in those with a history of thrombosis. Objective: This cross-sectional study aimed to investigate the relationship between hemogram parameters and thrombophilia genetic parameters. Method: A total of 55 patients whose thrombophilia panel was reviewed due to the diagnosis of thrombosis were included in the study. %MIC, %MAC, %HPO, %HPR and all hemogram parameters were measured using Abbott Alinity HQ. Prothrombin G20210A, MTHFR C677T, MTHFR A1298C, Factor V Leiden G169A and PAI-1 4G/5G mutations were studied using Real Time-PCR. Results: The MTHFR C677T mutation was detected in 58.2% of the patients. The Factor V Leiden mutation was detected in 5.5% of the patients. The MTHFR A1298C mutation was detected in 58.2%, The PAI mutation was detected in 74.5%, and the Factor 13 mutation was detected in 29% of the patients. Prothrombin G20210A mutation was not detected in any of the patients. Red blood cell (RBC) and Hct values were higher in Factor 13 mutant group; the Hgb and Htc values were higher in the MTHFR C677T mutant group. Conclusion: The MTHFR C677T and Factor 13 mutations may be associated with high Hct and RBC, Hgb, and Htc values, respectively and coagulation tendency in patients with a history of thrombosis.

Abstract 17233: Primary Intimal Sarcoma Of The Pulmonary Artery In A Patient With Laboratory Confirmed Heterozygous Factor V Leiden Mutation: A Case Report

Pulmonary artery intimal sarcoma (PAIS) is a rare tumor associated with progressively increasing dyspnea, atypical chest pain, and pulmonary hypertension. Owing to overlap in presentation, PAIS can be misdiagnosed as pulmonary thromboembolism (PTE). Here we present the case of a 59-year-old male with heterozygous Factor V Leiden mutation, history of deep vein thrombosis (DVT), and recent PTE presenting to urgent care with cough, mild orthopnea, and exertional dyspnea. Transthoracic echocardiogram (TTE) revealed severely dilated right ventricle with moderately decreased function and severe pulmonary hypertension with pulmonary arterial (PA) pressure of 93mmHg. Computed tomography angiography of the chest revealed massive central PTE. Given hemodynamic stability, saturating well on room air and simplified PESI score of 0, Pulmonology recommended discharge with anticoagulation. The patient returned a month later with three weeks of increased dyspnea on exertion, worsened right ventricular function as well as possible new mobile thrombus extending into the right ventricular outflow tract (RVOT). Due to presumed failure of medical therapy, Cardiology placed the patient on venoarterial extracorporeal membrane oxygenation (VA-ECMO) followed by attempted mechanical thrombectomy using both the Angiovac and Penumbra CAT12 systems. Both systems failed to remove substantial material from the PA. The next day, TTE revealed increased PA pressure of 132mmHg.The patient underwent emergent bilateral thromboendarterectomy with a mass discovered involving the pulmonary valve (PV), RVOT, both left and right PAs, along with invasion into the PA wall. The mass was resected, the PV valve replaced, the main PA and left PA reconstructed, and pericardial patch reconstruction of the RVOT was performed. The mass was determined to be a PAIS of French Federation of Comprehensive Cancer Centres (FNCLCC) Grade 3. Two months after uncomplicated recovery, chemotherapy was initiated. Securing the diagnosis of PAIS is challenging. However, collaboration between clinicians, radiologists, and pathologists increases the likelihood of recognizing subtle markers that can differentiate PAIS from illnesses with a similar presentation.

Inherited Thrombophilias Are Associated with an Increased Risk of COVID-19 Associated Venous Thromboembolism: A Prospective Population-Based Cohort Study

Background: COVID-19 is associated with high rates of venous thromboembolism (VTE). The impact of common inherited thrombophilias on the development of COVID-19-associated VTE (COVID-19 VTE) is not well understood. Objective: To determine if the presence of inherited thrombophilias modifies the risk of COVID-19 VTE or COVID-19 mortality. Methods: Prospective population-based cohort study evaluating adult participants of the UK Biobank diagnosed with COVID-19 between November 2019 and May 2021. Individuals were of European descent and aged between 45 and 69 at recruitment to UK Biobank. We evaluated six single nucleotide polymorphisms including rs6025 (Factor V Leiden mutation) and rs1799963 (Prothrombin mutation) in addition to two polygenic risk scores (PRS-VTE and PRS-ABO). A genome-wide association study was performed for associations with COVID-19 VTE. COVID-19 VTE was defined using International Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) codes for VTE following COVID-19 diagnosis. COVID-19 mortality was defined using ICD-10 codes for COVID-19 on the death certificate. Results: Demographic and clinical characteristics are shown in Table 1. Of the 13 712 COVID-19 positive individuals included in the analysis, the median age was 54 years and 52.5% were female. There were 197 (1.4%) cases of COVID-19 VTE and 890 (6.5%) died due to COVID-19. The rs6025 variant, synonymous with FVL, was associated with a 1.8-fold risk of COVID-19 VTE (95% CI 1.040-2.931) (Table 2). The risk of COVID-VTE was also increased with rs2066865 (OR 1.345; 95% CI 1.074-1.675) and the PRS-VTE (OR 1.262; 95% CI 1.081-1.468) (Table 2). COVID-19 VTE was associated with increased COVID-19 mortality (OR 2.731; 95% CI 1.885-3.901) but this study found no association between the studied inherited thrombophilias and COVID-19 mortality (Table 2). On genome-wide analysis, two novel SNPs, rs4975019 and rs2875853, located on chromosomes 4 and 16 respectively, were associated with an increased occurrence of COVID-19 VTE. Conclusions: These data demonstrate that several inherited thrombophilias increase the risk of COVID-19 VTE and suggest that two novel SNPs are associated with COVID-19 VTE. These results suggest that certain inherited thrombophilias may assist in characterising a subgroup of COVID-19 patients at higher risk of thrombotic events who require individualised antithrombotic therapy. Future prospective studies are required to evaluate inherited thrombophilias in this patient cohort. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Heritable Thrombophilia in Venous Thromboembolism in Northern Pakistan: A Cross-Sectional Study

Background. Venous thromboembolism (VTE) is referred to as formation of clots in a deep vein or lodging of thrombus towards the lungs which could be fatal yet preventable. The risk of developing VTE can be increased by various factors. Where there are innumerable acquired causes, the possibility of inherited thrombophilia cannot be ignored. In view of this, we have evaluated all patients with venous thromboembolism for inherited thrombophilia. Objective. To evaluate the frequencies of antithrombin (AT) deficiency, protein C and S deficiencies, Factor V Leiden, and prothrombin gene mutations in patients harboring venous thromboembolism. Materials and Methods. A study comprising of 880 patients who were presented with manifestations of venous thromboembolism was conducted from July 2016 to June 2017. A blood sample collected from patients was screened for thrombophilia defects encompassing AT, protein C and S deficiencies, Factor V Leiden, and prothrombin gene mutations. All acquired causes of thrombosis were excluded. Results. Of 880 patients who underwent screening for thrombophilia, 182 patients demonstrated VTE history. Their age ranged from 1 to 58 years. Males constituted a predominant group. About 45 (24.7%) patients had evidence of heritable thrombophilia. Of these, 20 (10.9%) had AT deficiency, 9 (4.9%) had Factor V Leiden mutation, 6 (3.2%) had protein C deficiency, whereas protein S deficiency and prothrombin gene mutation both were found in 5 (2.7%) patients. Conclusion. Our study illustrated the highest frequency of antithrombin deficiency among other investigated thrombophilia defects.

Factor V H1299r (Hr2) Heterozygosity: A Risk Factor For Recurrent Implantation Failure Particularly In Non-Carriers For Factor V Leiden Mutation-A Case-Control Study

Objective: The association between recurrent implantation failure and thrombophilia is still controversial depending on the published reports with conflicting results. In this study, we aimed to assess the clinical relevance of screening women with recurrent implantation failure for some thrombophilic variants including factor V H1299R (FV HR2) haplotype. Study Design: A total of 279 women were recruited in this case-control study. 229 women with a history of recurrent implantation failure and 50 fertile control with no history of pregnancy losses were screened for eight specific gene mutations, regarding factor V G1691A gene (FV Leiden), FV HR2, factor II prothrombin G20210A, factor XIII V34L, PAI-1 4G/5G, MTHFR C677T, MTHFR A1298C and A3 haplotype of the endothelial cell protein C receptor gene. Results: Recurrent implantation failure group displayed a significantly higher prevalence of FV HR2 heterozygosity than fertile controls while the frequency of FV Leiden mutation was comparable between groups (p=0.011; p=0.619). Additionally, the difference in the prevalence of other specific or total gene mutations among women with recurrent implantation failure was also insignificant. Discussion: The primer outcome of this study was the co-existence of the higher prevalence of FV HR2 haplotype and the insignificant percentage of FV Leiden mutation in women with recurrent implantation failure. Thus, we emphasize that the HR2 haplotype may be associated with recurrent implantation failure particularly in non-carriers for FV Leiden mutation. In the necessity of screening for thrombophilia in recurrent implantation failure, HR2 haplotype should be involved in the searched gene panel particularly in the absence of FV Leiden mutation. Further large-scale prospective studies are needed to investigate whether screening or treatment for HR2 haplotype has any detrimental impact on implantation success in cases of recurrent implantation failure.

Extensive Thromboembolism in a Young Male with Asymptomatic COVID-19 Infection and Heterozygous Factor V Leiden Mutation

In this case report we present a previously healthy 21-year-old male with extensive thromboembolism in the setting of asymptomatic COVID-19 infection and heterozygous factor V Leiden mutation with no additional thrombophilic risk factors.