Exploring the effects of Factor Xa inhibitors on thrombin generation in people with haemophilia

Optimal management of cardiovascular disease (CVD) in people with haemophilia (PWH) is a growing issue, given the continuing improvement in life expectancy among PWH. The evolving treatment paradigms targeting higher trough levels and the advent of non-factor replacement therapies (NFRT) means much of the 'protection' PWH were thought to have against CVD may be lost. There is a paucity of evidence regarding the safety of using anticoagulants in PWH. We designed a study assessing the thrombin generation (TG) of PWH of different severities and treatments, compared to non-haemophilia patients receiving a Factor Xa (FXa) inhibitor (apixaban or rivaroxaban), healthy controls, and assessing TG parameters of adding FXa inhibitor to the plasma of PWH receiving emicizumab prophylaxis. In total, 40 patients were included. TG was initiated with 5pM tissue factor (TF) using the calibrated automated thrombinoscope. Compared to those with mild haemophilia, patients receiving a FXa inhibitor had higher endogenous thrombin potential (ETP) (1278.42 vs 1831.36) and velocity index (40.71 vs 112.56), but both had a similar peak height (154.0 vs 262.63) and time to peak (both 5.83). People with severe haemophilia receiving emicizumab had significantly improved TG parameters compared to those not receiving emicizumab - ETP 1678.11 vs 809.96 and peak height 233.8 vs 92.05; however, when FXa inhibitor was added their TG parameters deteriorated to the severe haemophilia range (ETP 1179.60 and peak height 103.05). TG may provide additional useful information regarding the use of anticoagulants in PWH.

Venous Thromboembolism and Estrogen-Containing Gender-Affirming Hormone Therapy

Gender-affirming therapy involves the use of hormones to develop the physical characteristics of the identified gender and suppressing endogenous sex hormone production. Venous thromboembolism (VTE) is a known risk of exogenous estrogen therapy, and while evidence of VTE risk among transgender women using modern gender-affirming hormone therapy (GAHT) is still emerging, it is thought to affect up to 5% of transgender women. Historically, GAHT was associated with a high risk of VTE; however, modern preparations are less thrombogenic mainly due to significantly lower doses used as well as different preparations. This review presents the available literature regarding the following four topics: (1) risk of VTE among transgender women receiving estradiol GAHT, (2) how the route of administration of estradiol affects the VTE risk, (3) perioperative management of GAHT, (4) VTE risk among adolescents on GAHT. There is a need for large, longitudinal studies of transgender women using GAHT to further characterize VTE risk and how this is affected by factors such as patient age, duration of GAHT use, tobacco use, body mass index, and comorbidities. Future studies in these areas could inform the development of clinical guidelines to improve the care of transgender people.

Reducing the risk of atherosclerotic cardiovascular disease in people with hemophilia: the importance of primary prevention

Revolutionary advances in the treatment of hemophilia has led to a significant improvement in life expectancy. Associated with this has been an increase in age-related diseases especially atherosclerotic cardiovascular disease (CVD). While people with hemophilia (PWH) develop atherosclerosis at rates similar to those of the general population, rates of atherothrombosis and mortality related to CVD have been much lower, due to their hypocoagulable state. Changing treatment paradigms, aimed at reducing the risk of bleeding by improving hemostasis to levels approaching normality, has meant that the protection they are thought to have had may be lost. CVD risk factors are just as common in PWH as in the general population, but appear to be undertreated. In particular, primary prevention of CVD is vital in all individuals, but particularly in PWH as treatment of established CVD can be difficult. Active identification and management of CVD risk factors, such as obesity, physical inactivity, hypertension, and hypercholesterolemia, is required. In particular, statins have been shown to significantly reduce cardiovascular and all-cause mortality with few adverse events and no increased risk of bleeding in the general population, and their use needs urgent assessment in PWH. Further longitudinal research into preventing CVD in PWH, including accurate CVD risk assessment, is required to optimize prevention and management.

Thrombo-inflammatory response in hospitalised patients with COVID-19: a single institution experience

BACKGROUND

Severe COVID-19 causes acute inflammation, which is complicated by venous thromboembolism events (VTE). However, it is unclear if VTE risk has evolved over time since the COVID-19 outbreak.

AIMS

To determine markers of thrombo-inflammation and rates of symptomatic VTE in patients hospitalised for COVID-19 in a metropolitan hospital in Sydney, Australia.

METHODS

A retrospective, single-centre, cohort study was performed by reviewing electronic medical records of consecutive patients admitted to Royal Prince Alfred Hospital between March 2020 and September 2021. This period included three waves of COVID-19 outbreaks in Australia with the ancestral, alpha and delta variants. Standard coagulation assays and inflammatory markers were recorded over 4 weeks.

RESULTS

A total of 205 patients were consecutively admitted during the study period. Activated partial thromboplastin time, neutrophil count and C-reactive protein (CRP) were significantly increased in patients hospitalised in the intensive care unit (ICU) compared with non-ICU patients. The use of anti-inflammatory medication increased in 2021 compared with 2020. The mortality rate was 7.3% in our cohort. Ninety-four per cent of patients received anticoagulation with 6.3% of patients developing VTE.

CONCLUSION

We observed lower rates of VTE compared to the internationally reported rate for the same period. We conclude that in the setting of controlled hospital admission rate and standard anticoagulation guidelines, COVID-19 resulted in similar thrombo-inflammatory response and VTE rates over the first 1.5 years of the pandemic.

Adherence and persistence to direct factor Xa inhibitors in the community following newly diagnosed venous thromboembolism: a retrospective pharmacy-linkage study

OBJECTIVES

To assess adherence and persistence to the direct factor Xa inhibitor oral anticoagulants in the community following newly diagnosed venous thromboembolism (VTE).

METHODS

We retrospectively reviewed community pharmacy dispensing data on all patients with newly diagnosed VTE who were prescribed direct factor Xa inhibitors, apixaban or rivaroxaban, between January 2018 and December 2019 at our institution. Proportion of days covered (PDC) was used to assess adherence at 90 days, and 6- and 12 months. Persistence was measured by participants having both dispensed supply of a factor Xa inhibitor at the end of the treatment period and no significant gaps (maximum of 60 days) in supply.

KEY FINDINGS

There were 225 patients identified. Overall PDC at 90 days, 6- and 12 months were 84.6%, 86.2% and 86.1%, respectively. Apixaban had a higher mean overall PDC than rivaroxaban (86.2% and 80.6%, respectively). Females demonstrated higher PDC compared with males (87.3% versus 81.2%). Overall, 133 patients (64%) were persistent with therapy.

CONCLUSIONS

In patients with newly diagnosed VTE treated with a factor Xa inhibitor, adherence rates are high at >80%, with females and those prescribed apixaban exhibiting higher adherence. These findings may assist clinicians in identifying those patients with VTE at risk of poor adherence.

Venous anomalies and thromboembolism

Patients with venous anomalies are at increased risk of developing venous thromboembolism (VTE) and subsequent complications, but they are often under-recognised. While unprovoked VTE may trigger testing for inherited thrombophilias and malignancy screening, anatomic variants are considered less often. Venous anomalies increase the risk due to venous flow disturbance, resulting in hypertension, reduced flow velocity and turbulence. Recognition is important as endovascular or surgical intervention may be appropriate, these patients have a high rate of VTE recurrence if anticoagulation is ceased, and the anomalies can predispose to extensive VTE and severe post-thrombotic syndrome (PTS). In this case series, we present representative cases and radiological images of May-Thurner syndrome (MTS), inferior vena cava (IVC) variants and venous aneurysms, and review the available literature regarding optimal diagnosis and management in each condition.

Measuring Emicizumab Levels in the Hemostasis Laboratory

Emicizumab is a bi-specific antibody that in recent years has been introduced in many countries as a prophylactic agent for bleed prevention in cases of severe hemophilia A, and in some cases of moderate HA. It can be used in individuals with HA with and without FVIII inhibitors, because the drug is not a target for these inhibitors. Emicizumab was developed as a fixed weight-based dose and does not normally need laboratory monitoring, but in some circumstances such as a treated HA patient with unexpected bleeding episodes, a laboratory assay is justified. This chapter describes to performance of a one-stage clotting assay to measure emicizumab.

C-reactive protein, immunothrombosis and venous thromboembolism

C-reactive protein (CRP) is a member of the highly conserved pentraxin superfamily of proteins and is often used in clinical practice as a marker of infection and inflammation. There is now increasing evidence that CRP is not only a marker of inflammation, but also that destabilized isoforms of CRP possess pro-inflammatory and pro-thrombotic properties. CRP circulates as a functionally inert pentameric form (pCRP), which relaxes its conformation to pCRP* after binding to phosphocholine-enriched membranes and then dissociates to monomeric CRP (mCRP). with the latter two being destabilized isoforms possessing highly pro-inflammatory features. pCRP* and mCRP have significant biological effects in regulating many of the aspects central to pathogenesis of atherothrombosis and venous thromboembolism (VTE), by directly activating platelets and triggering the classical complement pathway. Importantly, it is now well appreciated that VTE is a consequence of thromboinflammation. Accordingly, acute VTE is known to be associated with classical inflammatory responses and elevations of CRP, and indeed VTE risk is elevated in conditions associated with inflammation, such as inflammatory bowel disease, COVID-19 and sepsis. Although the clinical data regarding the utility of CRP as a biomarker in predicting VTE remains modest, and in some cases conflicting, the clinical utility of CRP appears to be improved in subsets of the population such as in predicting VTE recurrence, in cancer-associated thrombosis and in those with COVID-19. Therefore, given the known biological function of CRP in amplifying inflammation and tissue damage, this raises the prospect that CRP may play a role in promoting VTE formation in the context of concurrent inflammation. However, further investigation is required to unravel whether CRP plays a direct role in the pathogenesis of VTE, the utility of which will be in developing novel prophylactic or therapeutic strategies to target thromboinflammation.

Understanding vaccine-induced thrombotic thrombocytopenia (VITT)

Vaccine‐induced thrombotic thrombocytopenia (VITT) is a rare, but serious, syndrome characterised by thrombocytopenia, thrombosis, a markedly raised D‐dimer and the presence of anti‐platelet factor‐4 (PF4) antibodies following COVID‐19 adenovirus vector vaccination. VITT occurs at a rate of approximately 2 per 100 000 first‐dose vaccinations and appears exceedingly rare following second doses. Our current understanding of VITT pathogenesis is based on the observations that patients with VITT have antibodies that bind to PF4 and have the ability to form immune complexes that induce potent platelet activation. However, the precise mechanisms that lead to pathogenic VITT antibody development remain a source of active investigation. Thrombosis in VITT can manifest in any vascular bed and affect multiple sites simultaneously. While there is a predilection for splanchnic and cerebral venous sinus thrombosis, VITT also commonly presents with deep vein thrombosis and pulmonary embolism. Pillars of management include anticoagulation with a non‐heparin anticoagulant, intravenous immunoglobulin and ‘rescue’ therapies, such as plasma exchange for severe cases. VITT can be associated with a high mortality rate and significant morbidity, but awareness and optimal therapy have significantly improved outcomes in Australia. A number of questions remain unanswered, including why VITT is so rare, reasons for the predilection for thrombosis in unusual sites, how long pathological antibodies persist, and the optimal duration of anticoagulation. This review will provide an overview of the presentation, diagnostic workup and management strategies for patients with VITT.

Measurable Residual Disease in Acute Myeloid Leukemia Using Flow Cytometry: A Review of Where We Are and Where We Are Going

The detection of measurable residual disease (MRD) has become a key investigation that plays a role in the prognostication and management of several hematologic malignancies. Acute myeloid leukemia (AML) is the most common acute leukemia in adults and the role of MRD in AML is still emerging. Prognostic markers are complex, largely based upon genetic and cytogenetic aberrations. MRD is now being incorporated into prognostic models and is a powerful predictor of relapse. While PCR-based MRD methods are sensitive and specific, many patients do not have an identifiable molecular marker. Immunophenotypic MRD methods using multiparametric flow cytometry (MFC) are widely applicable, and are based on the identification of surface marker combinations that are present on leukemic cells but not normal hematopoietic cells. Current techniques include a "different from normal" and/or a "leukemia-associated immunophenotype" approach. Limitations of MFC-based MRD analyses include the lack of standardization, the reliance on a high-quality marrow aspirate, and variable sensitivity. Emerging techniques that look to improve the detection of leukemic cells use dimensional reduction analysis, incorporating more leukemia specific markers and identifying leukemic stem cells. This review will discuss current methods together with new and emerging techniques to determine the role of MFC MRD analysis.

5,5-trans lactone-containing inhibitors of serine proteases: identification of a novel, acylating thrombin inhibitor

Synthesis of a variety of 5,5-trans fused lactones, related to compounds found in extracts of Lantana camara, has provided a series of novel acylating inhibitors of human thrombin, trypsin, chymotrypsin and human leucocyte elastase. The most effective thrombin inhibitor is 7 with an IC50 of 130 nM and a Kobs/[1] of 4,000 M-1 s-1.

Endocytosis of beta-adrenergic ligands by rat liver. Comparison of beta-adrenergic receptor and adenylate cyclase distribution in endosome and plasma-membrane fractions

The internalization of beta-adrenergic receptors was investigated in rat livers perfused with an agonist ([3H]isoprenaline) or an antagonist ([125I]iodocyanopindolol). Analytical centrifugation of liver homogenates indicated that the ligands were transferred rapidly to endosomal and lysosomal positions in sucrose gradients. Endosome fractions contained beta-adrenergic binding sites, but adenylate cyclase activity was low and poorly activated by isoprenaline. The results indicate that the receptor-regulatory-protein-adenylate cyclase complex was disassembled during uptake of beta-adrenergic ligands, with the adenylate cyclase being retained at the plasma membrane.