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Clot Formation, Fibrinolysis Assays May Help Show Important Differences Between Hemophilia A Treatments

Leveraging in vitro clot formulation and fibrinolysis assays may help guide personalized treatment for patients with hemophilia A, suggest findings from a new study.

Detailing their findings in Research & Practice in Thrombosis & Haemostasis, the researchers of the study found that in vitro clot formulation and fibrinolysis assays were able to determine the hemostatic effects of different replacement agents, as well as identify distinct pharmacodynamic responses across the different mechanisms of action.

"The variable performance of hemostatic drugs with differing mechanisms of action in clinical hemostasis assays complicates efforts to compare agents in preclinical settings, monitor postinfusion pharmacologic responses, and optimize dosing for efficacy and safety," explained the researchers. "Compared to normal plasma, hemophilia plasma delays clot formation and reduces stability in tissue factor-triggered assays, and products that enhance hemostasis improve these characteristics."

All tested replacement agents corrected reduced clot formation and increased fibrinolysis observed among hemophilia-pooled plasma samples. Notably, concentration relationships and effects varied by drug, suggesting that the assays were sensitive to the different mechanisms of action.

The researchers tested replacement products, including recombinant factor VIII (rfVIII) and PEGylated rFVIII, and bypassing products, including emicizumab and activated prothrombin complex concentrate, in pooled and individual platelet-poor plasma samples. The researchers observed clot formulation and stability improvements with bypassing agents and varying trends with replacement agents.

These findings were observed among a relatively small sample of plasmas, which included plasmas from 6 males with hemophilia for the plasma pool, plasmas from 11 males for individual samples, and plasmas from 8 healthy donors.

Across the plasma pool, interassay variability was under 15% across clot formulation parameters. Similar concentrations of rFVIII and PEGylated rFVIII yielded similar effects on the plasma samples and both significantly surpassed the normal range for rate at 1 IU/mL. Meanwhile, the same concentrations of polysialylated rFVIII had a more pronounced effect and the same concentrations of porcine rFVIII had a less pronounced effect.

Notably, interassay variability was higher for fibrinolysis. Across fibrinolysis assays, rFVIII and PEGylated rFVIII showed similar effects and polysialylated rFVIII showed more pronounced activity, significantly surpassing the normal range for rate at concentrations of 0.25 IU/mL or greater.

"Conventional endpoint assays (eg, activated partial thromboplastin time) provide information on the initial events leading to early thrombin generation and fibrin fiber formation. However, additional thrombin generation and fibrin formation, maturation of the fibrin network, and generation of antifibrinolytic mechanisms that protect the clot from premature degradation occur after the clotting time," wrote the researchers. "A strength of the in vitro clot formation and fibrinolysis assays tested here is that they can detect both the clotting onset as well as additional parameters that can differentiate normal and hemophilic clots. Consequently, these assays enabled us to study products with conventional effects on clotting, as well as nontraditional agents that do not alter onset time-based assays but enhance subsequent coagulation events that promote hemostasis."

Among individual samples used for clot formulation and fibrinolysis assays, baseline clotting varied significantly, which the researchers expected. While all replacement products resulted in procoagulant effects, the group observed notable differences in responses to different treatments across the plasmas.

Reference

Holle L, Pantazis J, Turecek P, Wolberg A. Clot formation and fibrinolysis assays reveal functional differences among hemostatic agents in hemophilia A plasma. Res Pract Thromb Haemost. 2024;8(1):102337.

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New Advances Offer Hope For Hemophilia Patients

(KYMA, CBS) - Hemophilia is a rare inherited bleeding disorder in which the blood doesn't clot properly, leading to excessive bruising, internal bleeding, and in severe cases, life-threatening complications.

There are two main types: Hemophilia A and the less common Hemophilia B, which affects about one in 20,000 births.

Traditionally, patients required frequent infusions of clotting factor proteins to prevent bleeds. But a newly FDA-approved gene therapy is changing treatment.

By delivering the missing gene directly to the liver, the body can begin producing clotting factor on its own, potentially offering long-term freedom from regular infusions.

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Patterns Of Bleeding Events In Women And Girls With Hemophilia

Researchers recently characterized several patterns and outcomes related to bleeding in women and girls with hemophilia in a report published in the journal Haemophilia.

"[Women and girls with hemophilia] present with symptoms related to reproductive health, as well as with bleeding events typically observed in [men] with [hemophilia]," the study investigators stated in their report.

The study was a retrospective, noninterventional review of records regarding women and girls with hemophilia from 3 hemophilia treatment centers in the United States, with data obtained from April 2012 through mid-November 2018. Outcomes were evaluated for patients who had 2 or more hemophilia treatment center visits for management of hemostasis, and who required medical or surgical treatment related to hemostasis.

A total of 47 women and girls with hemophilia were evaluated. Of these patients, 37 had factor VIII deficiency, and 10 had factor IX deficiency. The median age at diagnosis was 22.6 years, and most patients (79%) had a diagnosis of mild hemophilia. Diagnoses were typically confirmed by family history and/or laboratory evidence.

Patients' first-time visits to the hemophilia treatment centers were most commonly related to family history/genetic counseling. The second most common reason for initial hemophilia treatment center visits was to address spontaneous or traumatic bleeds. Of patients with these types of bleeds, easy bruising occurred in 59% of patients, epistaxis in 35% of patients, joint bleeds in 29% of patients, excessive dental bleeding in 24% of patients, and other bleeds in 24% of patients.

Nearly half (49%) of women and girls with hemophilia in this study experienced spontaneous, traumatic, or joint bleeds over the course of the study. These bleeding events were managed using factor concentrates, desmopressin, an antifibrinolytic, or other treatment. Initial treatment typically was successful, with bleeding stopped in 52.2% of cases or reduced in 39.1%.

Heavy menstrual bleeding, however, was not sufficiently controlled in the majority (57.1%) of the 14 patients who reported this complication. Additionally, of 25 patients who experienced pregnancies, excessive bleeding was reported in 44.0% during delivery or postpartum with at least 1 pregnancy.

The study investigators that indicated a lack of specific guidelines in treating women and girls with hemophilia has led to varied approaches to management for this patient population. "Furthering clinical care for [women and girls with hemophilia] is needed to reduce the psychosocial, emotional, and economic impacts of a bleeding disorder diagnosis," the researchers concluded in their report.

Disclosure: Some authors have declared affiliations with or received grant support from the pharmaceutical industry. Please refer to the original study for a full list of disclosures.

Reference

Chaudhury A, Sidonio Jr R, Jain N, et al. Women and girls with haemophilia and bleeding tendencies: outcomes related to menstruation, pregnancy, surgery and other bleeding episodes from a retrospective chart review. Haemophilia. Published online December 24, 2020. Doi:10.1111/hae.14232

This article originally appeared on Hematology Advisor

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