What does this research mean for the field?

Activated platelets enhance Factor VIII activity compared to phospholipid vesicles by stabilizing the A2 domain against dissociation and protecting the protein from degradation by activated protein C. Novelty: ClaimNovelty.NOVEL_FINDING. Consensus alignment: ConsensusAlignment.NEUTRAL.

What question did this study set out to answer?

To identify the mechanisms through which activated platelets support factor VIII (FVIII) activity at significantly lower concentrations than synthetic phospholipid vesicles.

August 22, 2026Blood AdvancesOpen Access

Activated Platelets Protect Factor VIIIa from Degradation by Activated Protein C and from Subunit Dissociation

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Authors

VNValerie A NovacovicVA Boston Healthcare System JSJialan ShiBrigham and Women's Hospital GGGary E. GilbertVA Boston Healthcare System

Discussion

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Implication

In vitro study demonstrates that activated platelets stabilize factor VIIIa against A2 subunit dissociation and protein C degradation, highlighting mechanisms supporting potent clotting.

Key Points

To identify the mechanisms through which activated platelets support factor VIII (FVIII) activity at significantly lower concentrations than synthetic phospholipid vesicles.
Compared the procoagulant activity of FVIIIa and emicizumab in the presence of activated platelets versus phospholipid vesicles (PLV).
Assessed steady-state Xase kinetics and clotting times using wild-type FVIII and engineered variants resistant to APC cleavage (FVIIIQQ), stabilized against A2 domain dissociation (FVIIIVV), or both (FVIIIQQVV).
Platelet-to-PLV procoagulant activity ratios for FVIII ranged from 2:1 to 40:1, with highest ratios at lower FVIII concentrations, whereas emicizumab activity did not differ between surfaces.
Engineered FVIIIVV and FVIIIQQVV showed equivalent clotting times on platelets and PLV, indicating that platelets inherently slow A2 subunit dissociation.
Activated platelets and platelet microparticles slowed APC-mediated inactivation of FVIII to an extent comparable to the degradation-resistant FVIIIQQ variant on PLV.

Cite This Study

Novacovic et al. (2026) studied this question.

synapsesocial.com/papers/6a895f41ca7ade938187db45 https://doi.org/10.1182/bloodadvances.2026020584

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Implication

In vitro study demonstrates that activated platelets stabilize factor VIIIa against A2 subunit dissociation and protein C degradation, highlighting mechanisms supporting potent clotting.

Activated Platelets Protect Factor VIIIa from Degradation by Activated Protein C and from Subunit Dissociation

Discussion

Member takes

Implication

Key Points

Cite This Study

Activated Platelets Protect Factor VIIIa from Degradation by Activated Protein C and from Subunit Dissociation

Discussion

Member takes

Implication

Key Points

Cite This Study

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