A global comparative field study to evaluate the factor VIII activity of efanesoctocog alfa by one-stage clotting and chromogenic substrate assays at clinical haemostasis laboratories.

INTRODUCTION: Structural and chemical modifications of factor VIII (FVIII) products may influence their behaviour in FVIII activity assays. Hence, it is important to assess the performance of FVIII products in these assays. Efanesoctocog alfa is a new class of FVIII replacement therapy designed to provide both high sustained factor activity levels and prolonged plasma half-life. AIM: Evaluate the accuracy of measuring efanesoctocog alfa FVIII activity in one-stage clotting assays (OSAs) and chromogenic substrate assays (CSAs). METHODS: Human plasma with no detectable FVIII activity was spiked with efanesoctocog alfa or a full-length recombinant FVIII product comparator, octocog alfa, at nominal concentrations of 0.80 IU/mL, 0.20 IU/mL, or 0.05 IU/mL, based on labelled potency. Clinical haemostasis laboratories (N = 35) tested blinded samples using in-house assays. Data from 51 OSAs (14 activated partial thromboplastin time [aPTT] reagents) and 42 CSAs (eight kits) were analyzed. RESULTS: Efanesoctocog alfa activity was reliably (±25% of nominal activity) measured across all concentrations using OSAs with Actin FSL and multiple other aPTT reagents. Under- and overestimation of FVIII activity occurred with some reagents. No specific trend was observed for any class of aPTT activators. A two- to three-fold overestimation was consistently observed using CSAs and the OSA with Actin FS as the aPTT reagent across evaluated concentrations. CONCLUSION: Under- or overestimation occurred with some specific OSAs and most CSAs, which has been previously observed with other modified FVIII replacement products. Efanesoctocog alfa FVIII activity was measured with acceptable accuracy and reliability using several OSA methods and commercial plasma standards.

In vitro validation of chromogenic substrate assay for evaluation of surrogate FVIII-activity of emicizumab.

[Introduction] Emicizumab, a bispecific antibody mimicking activated factor VIII (FVIII), is increasingly used in prophylaxis against bleeding in hemophilia A. Human factor-based chromogenic substrate assay (hCSA) shows concentration-dependency between emicizumab and reported FVIII activity. However, the assay measurement settings have not been optimized for emicizumab, and the reported FVIII activity cannot be directly referred as surrogate FVIII activity. [Materials and Methods] For in vitro validation of hCSA-reported surrogate FVIII activity, we compared the equation curves for emicizumab concentration with surrogate FVIII activity using spiked plasma in the thrombin generation assay (TGA), hCSA, and clot waveform analysis (CWA). Then, we generated conversion equations for hCSA-reported surrogate FVIII value to that of TGA. We also assessed the additive effect of rFVIII onto 340 nM (i.e., 50 µg/mL) emicizumab using the same assays. [Results] With 1:20 diluted plasma, halving hCSA-reported surrogate FVIII activity can be approximated to that in TGA triggered by the extrinsic pathway reagent (27.3 IU/dL vs. 13.9 IU/dL) under therapeutic emicizumab concentration. Both in TGA and hCSA, the additive effect of added FVIII on therapeutic emicizumab concentration (340 nM) was maintained at low levels of FVIII but gradually decreased at higher levels. [Conclusions] Surrogate FVIII activity can be estimated simply by halving hCSA-reported FVIII value, and the additive effect of FVIII on emicizumab diminishes at high concentrations. Based on our in vitro study, a clinical study is currently being conducted to compare individual variation of surrogate FVIII activity in hCSA and TGA.

Activity measurements of dalcinonacog alfa.

INTRODUCTION: Many recombinant and modified FIX products have been, and continue to be, developed with the aim of improving treatment for patients with haemophilia B. One such new product is dalcinonacog alfa, a recombinant FIX with modifications to provide improved features such as subcutaneous administration. AIM: In view of previously observed assay discrepancies with modified FIX therapeutics, the aim of this study was to assess potential discrepancies in potency measurement of dalcinonacog alfa between and within different assay methods. METHODS: Potency of dalcinonacog alfa was measured against the 5th International Standard (IS) for FIX Concentrate and the 4th IS for FIX Plasma by One-Stage Clotting Assay, using 9 different APTT reagents and 2 commercially available FIX chromogenic kits. Plasma-derived concentrate and recombinant FIX samples were also included for comparison in every assay. RESULTS: Substantial discrepancies were observed when assaying dalcinonacog alfa using the one-stage clotting assay against both standards. No statistically valid results were obtained when testing dalcinonacog alfa using either chromogenic kit. Increasing the incubation time with the activation reagent in both chromogenic kits resulted in valid assays and increased the potency to become more in line with potencies by one-stage clotting assays. Increasing the incubation time in the chromogenic kits had no effect on the potencies of the plasma-derived or recombinant samples. However, incubation time influenced in the one-stage clotting assay using Dapttin. CONCLUSIONS: Within and between assay method discrepancy was found when assaying dalcinonacog alfa. Methods for potency labelling and clinical monitoring should be given careful consideration.

Chromogenic substrates as fundamental tool to design new thrombin inhibitors. Determination of inhibition equilibrium constants.

The structure-activity relationship of dipetalogastin II, the strongest thrombin inhibitor isolated and cloned from the bug Dipetalogaster maximus, was examined by introducing gradual changes into the molecule by means of molecular biological methods. The effect upon its inhibition equilibrium constant was determined after each change by a chromogenic assay. This structural information was fundamental to design new dipetalogastin II-derived inhibitors. Our results suggested that the acidic sequence DEHDHDFEDT corresponding to amino acid residues 49 to 58 of dipetalogastin II reacts with the anion binding exosite (ABE) 1 of thrombin. Based on this finding, we constructed a chimeric molecule consisting of the active site blocking segment of dipetalogastin II (amino acid residues 1 to 48) and the ABE 1 blocking segment of hirudin. This construct showed better thrombin inhibitory activity than both separated segments only after the introduction of a glycine linker between both blocking segments. We thus obtained a thrombin inhibitor called dipetarudin with an inhibition equilibrium constant comparable to that of dipetalogastin II and a molecular mass below that of dipetalogastin.

Candidiasis vaginal en primigestas / Vaginal candidiasis in primigravidas

Determinar evidencias de candidiasis vaginal en pacientes que acuden a la consulta prenatal de la Maternidad Castillo Plaza, utilizando como medio diagnóstico el test Intray Colotex Yeast. Se estudiaron embarazadas primigestas con sospecha clínica de candidiasis vaginal. Las muestras de secreción vaginal se inocularon en el medio Intray Colorex Yeast e incubaron a 37°C durante 48 a 72 horas. Maternidad Castillo Plaza de Maracaibo, Estado Zulia. Se demostró que un 38 por ciento (24 pacientes) presentaron candidiasis vaginal. Candida albicans fue la especie más frecuente (88 por ciento), seguida por glabrata (8 por ciento) y krusei (4 por ciento). El desarrollo de colonias verdes, rosado claro (albicans, glabrata y krusei respectivamente) sugiere la utilidad del medio Intray Colorex Yest para la identificación rápida de las principales especies productoras de candidiasis

[Chromogenic substrate as antidote against the thrombin inhibitor Melagatran?]. / Chromogenes Substrat als Antidot gegen den Thrombininhibitor Melagatran?

It could be shown in vitro that a chromogenic substrate (Chromozym TH, Roche Mannheim) acts at least partially as antidote against the new thrombin inhibitor Melagatran (AstraZeneca, Mölndal, Sweden). It is discussed that this antidote effect of a chromogenic substrate might be due to a substrate competition of fibrinogen, thrombin inhibitor, and chromogenic substrate for thrombin. Further animal experiments will clarify whether this in vitro observation is of practical relevance in vivo, too.

[Determination of clotting factor VIII activity in mammals using the one-stage clotting and the chromogenic methods]. / Bestimmung der Aktivität des Gerinnungsfaktors VIII beim Säugetier mit der koagulometrischen und der chromogenen Methode.

Two different laboratory assays exist for the determination of clotting factor VIII activities in human plasma. One method is based on the one-stage clotting principle, the other one on the chromogenic principle. To evaluate the suitability for veterinary medicine human plasma and plasma of ten mammalian species (pig, cattle, dog, cat, zebra, llama, snow leopard, greater kudu, horse-like antelope, mink) were examined with each method. Factor VIII activities in human plasma determined using both assays were in a good agreement. Results of factor VIII activities in plasma of mammals obtained with both methods were similar, if a species-specific reference plasma was used. The practicability of the chromogenic method was reduced. However, the factor VIII activities differed nonsystematically up to 500% between both methods, if a human plasma was used as a reference plasma. Determination of factor VIII activities in plasma of mammals using the chromogenic assay cannot be recommended.

Selective inhibition of the contractile apparatus. A new approach to modification of infarct size, infarct composition, and infarct geometry during coronary artery occlusion and reperfusion.

BACKGROUND: Myocardial reperfusion is associated with calcium overload and cell contracture, mechanisms that may precipitate cell death. In this study, we tested the hypothesis that in vivo inhibition of this contracture could lead to cell preservation in an open-chest large animal model. METHODS AND RESULTS: Regional myocardium function was measured during a selective intracoronary infusion of 2,3-butanedione monoxime (BDM), a specific inhibitor of actin-myosin coupling, in the control state (10 pigs) and in a protocol of a 51-minute coronary occlusion followed by reperfusion (40 pigs). The effects on coronary artery blood flow in the basal state were also studied (seven pigs). Intramyocardial distribution of the infusate during coronary occlusion, myocardial water content after 30 minutes of reperfusion and area at risk, infarct size, type of histological necrosis, and infarct geometry after 24 hours of reperfusion were assessed. Methods used included electromagnetic flowmeter, radiolabeled microspheres, subendocardial sonomicrometers, fluorescein, triphenyl tetrazolium chloride and Masson's trichrome staining, and computer quantification of infarct edges. In the absence of ischemia, BDM infusion inhibited regional shortening in a dose-dependent manner up to full systolic bulging while producing marked regional increase in coronary blood flow. During early reperfusion, BDM reduced end-diastolic length 76% more than the control infusion (p less than 0.05) and increased systolic bulging by 420% compared with no change in control animals. The ratio of infarct size/area at risk was reduced by 31% with BDM (p less than 0.05), with striking modifications of infarct histology and infarct geometry; specifically, the extent of contraction band necrosis was reduced by 63% from 105.5 +/- 18.2 to 39.2 +/- 13.6 mm2 (p less than 0.02), and more patches of necrosis (6.5 +/- 2.1 versus 1.6 +/- 0.4, p less than 0.05) and higher contour (7.7 +/- 1.2 versus 5.03 +/- 0.2, p less than 0.05) and fractal (12.1 +/- 1.3 versus 7.8 +/- 0.2, p less than 0.05) indexes were found. CONCLUSIONS: Selective intracoronary infusion of BDM at doses inhibiting regional wall motion decreased infarct size after reperfusion. The effects of BDM on regional function, the reduction in contraction band necrosis at histology, and the peculiar configuration of these infarcts all suggest that inhibition of contracture can interfere with cell-to-cell progression of myocardial necrosis, supporting a role for contracture in reperfusion-induced cell death.