[Confusion and abdominal pain after COVID-19 vaccination]. / Verwardheid en buikpijn na covid-19-vaccinatie.

BACKGROUND: Vaccine-induced immune thrombotic trombocytopenia (VITT) is a rare phenomenon, that may present with diffuse and atypical symptoms. CASE DESCRIPTION: We present a case of 63 years old female patient with abdominal pain, confusion and tromboctytopenia. CT scan shows sinustrombosis and trombosis of the vena renalis. The diagnosis VITT was confirmed by a positive HIT test. After initiating treatment with immunoglobulines and a non-heparinoid anticoagulans, symptoms improved and platelet count increased. CONCLUSION: This case illustrates that awareness in case of atypical symptoms and a history of vaccination is important to recognize this phenomenon.

The half-life of infused factor VIII is shorter in hemophiliac patients with blood group O than in those with blood group A.

A considerable inter-individual variation in half-life of infused factor VIII is observed among patients with hemophilia A. The factors contributing to this wide range in factor VIII half-life are not known in detail. We analysed the pharmacokinetics of infused factor VIII in 32 patients with hemophilia A, comprising 20 brothers from 10 families, 3 and 4 brothers from 2 families, and 5 patients from 5 single families, respectively. Multiple linear regression analysis was used to assess the effect of several variables on factor VIII half-life. We found that the pre-infusion von Willebrand factor antigen levels (vWF:Ag) were positively correlated with factor VIII half-life (r = 0.52, p = 0.002), i.e., each variable was associated with about 27% of the variance of the other. In fraternal pairs, familial clustering was significant for ABO blood group (p < 0.001), but could not be detected for factor VIII half-lives or pre-infusion vWF:Ag levels. vWF:Ag level (p = 0.001) and ABO blood group (p = 0.003) significantly determined factor VIII half-life, whereas age, length, bodyweight, the presence or absence of a factor VIII gene inversion, and Rhesus phenotype did not. Patients with blood group O exhibited a statistically significant shorter factor VIII half-life than patients with blood group A (15.3 versus 19.7 h, respectively) (p = 0.003). Patients with blood group A and O differ in respect to the presence of anti-A antibodies in the latter. It is possible that these anti-A antibodies interact with endogenous vWF, thus affecting the half-life time of the factor VIII/vWF complex.

Kinetics of factor VIII-von Willebrand factor association.

The binding of factor VIII to von Willebrand factor (vWF) is essential for the protection of factor VIII against proteolytic degradation in plasma. We have characterized the binding kinetics of human factor VIII with vWF using a centrifugation binding assay. Purified or plasma vWF was immobilized with a monoclonal antibody (MoAb RU1) covalently linked to Sepharose (Pharmacia LKB Biotechnology, Uppsala, Sweden). Factor VIII was incubated with vWF-RU1-Sepharose and unbound factor VIII was separated from bound factor VIII by centrifugation. The amount of bound factor VIII was determined from the decrease of factor VIII activity in the supernatant. Factor VIII binding to vWF-RU1-Sepharose conformed to the Langmuir model for independent binding sites with a Kd of 0.46 +/- 0.12 nmol/L, and a stoichiometry of 1.3 factor VIII molecules per vWF monomer at saturation, suggesting that each vWF subunit contains a binding site for factor VIII. Competition experiments were performed with a recombinant vWF (deltaA2-rvWF), lacking residues 730 to 910 which contain the epitope for MoAB RU1. DeltaA2-rvWF effectively displaced previously bound factor VIII, confirming that factor VIII binding to vWF-RU1-Sepharose was reversible. To determine the association rate constant (k(on)) and the dissociation rate constant (k(off)), factor VIII was incubated with vWF-RU1-Sepharose for various time intervals. The observed association kinetics conformed to a simple bimolecular association reaction with k(on) = 5.9 +/- 1.9 x 10(6) M(-1) s(-1) and k(off) = 1.6 +/- 1.2 x 10(-3) s(-1) (mean +/- SD). Similar values were obtained from the dissociation kinetics measured after dilution of preformed factor VIII-vWF-RU1-Sepharose complexes. Identical rate constants were obtained for factor VIII binding to vWF from normal pooled plasma and to vWF from plasma of patients with hemophilia A. The kinetic parameters in this report allow estimation of the time needed for complex formation in vivo in healthy individuals and in patients with hemophilia A, in which monoclonally purified or recombinant factor VIII associates with endogenous vWF. Using the plasma concentration of vWF (50 nmol/L in monomers) and the obtained values for K(on) and K(off), the time needed to bind 50% of factor VIII is approximately 2 seconds.

Requirements of von Willebrand factor to protect factor VIII from inactivation by activated protein C.

The interaction of factor VIII with von Willebrand factor (vWF) was investigated on a quantitative and qualitative level. Binding characteristics were determined using a solid phase binding assay and protection of factor VIII by vWF from inactivation by activated protein C (aPC) was studied using three different assays. Deletion mutants of vWF, a 31-kD N-terminal monomeric tryptic fragment of vWF that contained the factor VIII binding site (T31) and multimers of vWF of different size were compared with vWF purified from plasma. We found that deletion of the A1, A2, or A3 domain of vWF had neither an effect on the binding characteristics nor on the protective effect of vWF on factor VIII. Furthermore, no differences in binding of factor VIII were found between multimers of vWF with different size. Also, the protective effect on factor VIII of vWF was not related to the size of the multimers of vWF. A 20-fold lower binding affinity was observed for the interaction of T31 with factor VIII, and T31 did not protect factor VIII from inactivation by aPC in a fluid-phase assay. Comparable results were found for a mutant of vWF that is monomeric at the N-terminus (vWF-dPRO). The lack of multimerization at the N-terminus may explain the decreased affinity of T31 and vWF-dPRO for factor VIII. Because of this decreased affinity, only a small fraction of factor VIII was bound to T31 and to vWF-dPRO. We hypothesized that this fraction was protected from inactivation by aPC but that this protection was not observed due to the presence of an excess of unbound factor VIII in the fluid phase. Therefore, vWF, T31, and vWF-dPRO were immobilized to separate bound factor VIII from unbound factor VIII in the fluid phase. Subsequently, the protective effect of these forms of vWF on bound factor VIII was studied. In this approach, all forms of vWF were able to protect factor VIII against inactivation by aPC completely. We conclude, in contrast with earlier work, that there is no discrepancy between binding of factor VIII to vWF and protection of factor VIII by vWF from inactivation by aPC. The protective effect of T31 was not recognized in previous studies due to its low affinity for factor VIII. The absence of multimerization observed for T31 and vWF-dPRO may explain the low affinity for factor VIII. No other domains than the binding site located at the D' domain were found to be involved in the protection of factor VIII from inactivation by aPC.

The affinity and stoichiometry of binding of human factor VIII to von Willebrand factor.

To study the interaction between factor VIII and von Willebrand factor (vWF), binding experiments were performed using immobilized plasma vWF. Plasma was obtained from healthy donors and from patients with severe hemophilia A. For normal and hemophilic vWF, the dissociation constants (kd) for binding of factor VIII to vWF were 0.21 +/- 0.04 and 0.22 +/- 0.05 nmol/L, respectively. At saturation, the stoichiometry was one factor VIII molecule per 50 vWF monomers. In gel-filtration experiments, vWF was saturated by 23 times more factor VIII. However, when this FVIII-vWF complex was immobilized on microtiter plates, the ratio of factor VIII/vWF decreased to the same ratio as in the solid-phase binding assay. To exclude any effect of antibody binding, colloidal gold particles with a diameter of 15 nm were coupled to purified vWF. This vWF-gold complex remained immunoreactive toward polyclonal and monoclonal antibodies, and was able to bind factor VIII, specifically, saturably, and reversibly. After incubation of vWF-gold with factor VIII, unbound and bound factor VIII were separated by centrifugation. Binding isotherms of these fluid-phase binding experiments indicated a kd of 0.32 +/- 0.09 nmol/L and a stoichiometry of approximately 0.5 factor VIII molecule per vWF monomer. We conclude that vWF-binding to a surface, with or without an antibody, may induce a conformational change causing a dissociation of bound factor VIII from vWF.

Thrombotic thrombocytopenic purpura. Clinical course and response to therapy in seven patients.

The clinical characteristics, treatment and outcome are reported in 7 patients with 8 episodes of thrombotic thrombocytopenic purpura (TTP). In all episodes a complete remission was reached. Plasma exchange therapy was successful as single treatment in two episodes. Combination with other treatment modalities, however, was necessary in six episodes, in which a complete hematologic and clinical remission was obtained with antiplatelet therapy (4 X), and with antiplatelet therapy and corticosteroids (2 X).