Multicenter evaluation of light transmission platelet aggregation reagents: communication from the ISTH SSC Subcommittee on Platelet Physiology

BACKGROUND

Light transmission aggregation (LTA) is used widely by the clinical and research communities. Although it is a gold standard, there is a lack of interlaboratory harmonization.

OBJECTIVES

The primary objective was to assess whether sources of activators (mainly adenosine diphosphate [ADP], collagen, arachidonic acid, epinephrine, and thrombin receptor activating peptide6) and ristocetin contribute to poor LTA reproducibility. The secondary objective was to evaluate interindividual variability of results to appreciate the distribution of normal values and consequently better interpret pathologic results.

METHODS

An international multicenter study involving 28 laboratories in which we compared LTA results obtained with center-specific activators and a comparator that we supplied.

RESULTS

We report variability in the potency (P) of activators in comparison with the comparator. Thrombin receptor activating peptide 6 (P, 1.32-2.68), arachidonic acid (P, 0.87-1.43), and epinephrine (P, 0.97-1.34) showed the greatest variability. ADP (P, 1.04-1.20) and ristocetin (P, 0.98-1.07) were the most consistent. The data highlighted clear interindividual variability, notably for ADP and epinephrine. Four profiles of responses were observed with ADP from high-responders, intermediate-responders, and low-responders. A fifth profile corresponding to nonresponders (5% of the individuals) was observed with epinephrine.

CONCLUSION

Based on these data, the establishment and adoption of simple standardization principles should mitigate variability due to activator sources. The observation of huge interindividual variability for certain concentrations of activators should lead to a cautious interpretation before reporting a result as abnormal. Confidence can be taken from the fact that difference between sources is not exacerbated in patients treated with antiplatelet agents.

An international collaborative study to assign value for Total Factor XIII-B Subunit Antigen to the WHO 1st International Standard for Factor XIII Plasma, (02/206): Communication from the ISTH SSC Subcommittee on Factor XIII and Fibrinogen

BACKGROUND

Factor XIII (FXIII)-B subunit measurements are required for the diagnosis and characterization of the type of FXIII deficiency. Furthermore, therapy for FXIII-A deficiency with recombinant FXIII (rFXIII-A) relies on available FXIII-B.

OBJECTIVE

To carry out a collaborative study to calibrate and assign value to the current WHO 1st International Standard (IS) FXIII Plasma for Total FXIII-B subunit, relative to locally collected normal plasma pools.

METHODS

Laboratories were instructed to use a validated method (specific ELISA antibodies provided) for assessment of Total FXIII-B subunit antigen potency. All laboratories used this method with one laboratory using an additional in-house method. Nine data sets were received from seven laboratories (37 assays in total), which provided a total of 35 valid estimates for this new assignment. Total FXIII-B subunit estimates were calculated relative to locally collected normal plasma pools, using an arbitrary value of 1.00 unit of Total FXIII-B subunit per ml, for each pool.

RESULTS

Combination of results produced an overall mean of 0.98 units/mL with an inter-laboratory variability (geometric coefficients of variation - GCV%) of 18.3% [95% confidence interval: 0.86-1.11]. Real-time and bench stability studies indicated good stability and preservation of the FXIII-B subunit analyte in the WHO 1st IS FXIII Plasma (02/206).

CONCLUSION

Following agreement by study participants, ISTH/SSC Experts, WHO-ISTH Liaison Group and the SSC Board, the WHO/ECBS established the current WHO 1st IS Factor XIII plasma (NIBSC code 02/206) by additionally assigning it with a Total FXIII-B subunit antigen value of 0.98 IU/ampoule, in October 2019.

Plasma Peptidylarginine Deiminase IV Promotes VWF-Platelet String Formation and Accelerates Thrombosis After Vessel Injury

RATIONALE

PAD4 (peptidylarginine deiminase type IV), an enzyme essential for neutrophil extracellular trap formation (NETosis), is released together with neutrophil extracellular traps into the extracellular milieu. It citrullinates histones and holds the potential to citrullinate other protein targets. While NETosis is implicated in thrombosis, the impact of the released PAD4 is unknown.

OBJECTIVE

This study tests the hypothesis that extracellular PAD4, released during inflammatory responses, citrullinates plasma proteins, thus affecting thrombus formation.

METHODS AND RESULTS

Here, we show that injection of r-huPAD4 in vivo induces the formation of VWF (von Willebrand factor)-platelet strings in mesenteric venules and that this is dependent on PAD4 enzymatic activity. VWF-platelet strings are naturally cleaved by ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type-1 motif-13). We detected a reduction of endogenous ADAMTS13 activity in the plasma of wild-type mice injected with r-huPAD4. Using mass spectrometry and in vitro studies, we found that r-huPAD4 citrullinates ADAMTS13 on specific arginine residues and that this modification dramatically inhibits ADAMTS13 enzymatic activity. Elevated citrullination of ADAMTS13 was observed in plasma samples of patients with sepsis or noninfected patients who were elderly (eg, age >65 years) and had underlying comorbidities (eg, diabetes mellitus and hypertension) as compared with healthy donors. This shows that ADAMTS13 is citrullinated in vivo. VWF-platelet strings that form on venules of Adamts13^-/- mice were immediately cleared after injection of r-huADAMTS13, while they persisted in vessels of mice injected with citrullinated r-huADAMTS13. Next, we assessed the effect of extracellular PAD4 on platelet-plug formation after ferric chloride-induced injury of mesenteric venules. Administration of r-huPAD4 decreased time to vessel occlusion and significantly reduced thrombus embolization.

CONCLUSIONS

Our data indicate that PAD4 in circulation reduces VWF-platelet string clearance and accelerates the formation of a stable platelet plug after vessel injury. We propose that this effect is, at least in part, due to ADAMTS13 inhibition.

Discovery of a Selective Inhibitor for the YEATS Domains of ENL/AF9

Eleven-nineteen leukemia (ENL) contains an epigenetic reader domain (YEATS domain) that recognizes lysine acylation on histone 3 and facilitates transcription initiation and elongation through its interactions with the super elongation complex (SEC) and the histone methyl transferase DOT1L. Although it has been known for its role as a fusion protein in mixed lineage leukemia (MLL), overexpression of native ENL, and thus dysregulation of downstream genes in acute myeloid leukemia (AML), has recently been implicated as a driver of disease that is reliant on the epigenetic reader activity of the YEATS domain. We developed a peptide displacement assay (histone 3 tail with acylated lysine) and screened a small-molecule library totaling more than 24,000 compounds for their propensity to disrupt the YEATS domain-histone peptide binding. Among these, we identified a first-in-class dual inhibitor of ENL ( K_d = 745 ± 45 nM) and its paralog AF9 ( K_d = 523 ± 53 nM) and performed "SAR by catalog" with the aim of starting the development of a chemical probe for ENL.

Patients' preference for administration of endocrine treatments by injection or tablets: results from a study of women with breast cancer

BACKGROUND

Endocrine therapies for advanced breast cancer include tablets and intramuscular injections. When treatments have similar efficacy and tolerability profiles, addressing preferences about routes of administration is important.

PATIENTS AND METHODS

Two hundred and eight women>2 years post-breast cancer diagnosis were interviewed about their preferences for daily tablets or monthly intramuscular injections. Health-care professionals treating the women estimated patients' preferences.

RESULTS

Sixty-three per cent of patients preferred tablets, 24.5% preferred the injection and 12.5% had no preference. The most cited reasons for tablet preference were convenience and dislike of needles; for injection preference, adherence and convenience. Variables associated with preferences were body mass index, educational level, attitudes towards injections and efficacy perceptions. Estimates about patients' preferences by health-care professionals varied widely. When asked to imagine scenarios where injections produced fewer hot flushes, or where two injections monthly improved efficacy, injection preference increased to 60.6% and 74.5%, respectively. Disturbingly, approximately 50% of patients admitted they sometimes forgot or chose not to take their current oral medication.

CONCLUSIONS

The majority of breast cancer patients preferred hormone therapy via daily tablets rather than monthly injections. Information about side-effects or improved efficacy altered these preferences. Adherence to treatment cannot be assumed; patients' preferences about drug administration may influence this.