Open AccessUnderestimation of N‐glyco PEG ylated factor IX one‐stage clotting activity owing to contact activator‐impaired activation
Author(s) -
Persson Egon,
La Cour Christoffersen Carsten
Publication year - 2017
Publication title -
research and practice in thrombosis and haemostasis
Language(s) - English
Resource type - Journals
ISSN - 2475-0379
DOI - 10.1002/rth2.12046
Subject(s) - chemistry , reagent , activator (genetics) , clotting factor , partial thromboplastin time , factor ix , chromatography , coagulation , biochemistry , medicine , receptor , organic chemistry
Essentials Nonacog beta pegol (N9‐GP) activity can be underestimated in clot method using diverse reagents. Mimicking clotting phase with representative reagents reveals impaired FIX and N9‐GP activation. Polyethylene glycol conjugation amplifies contact activator‐induced decrease in FIX activation. The reagent is a pivotal factor for accurate measurement of N9‐GP activity in clinical samples.Background In clinical practice, factor IX ( FIX ) activity is routinely quantified by measurement of the activated partial thromboplastin time ( APTT ) in a one‐stage ( OS ) FIX clotting assay. APTT reagents provide a contact activator and phospholipid surfaces required for triggering and sustaining the plasma clotting process. The large diversity in reagent components is reflected in the variable recovery of nonacog beta pegol (N9‐ GP ; N‐glyco PEG ylated recombinant FIX ) activity when assayed against a FIX standard. This variation warrants mechanistic studies and is plausibly attributable to the nature and amount of contact activator. Objective To identify the cause of the N9‐ GP activity underestimation observed with a heterogeneous group of APTT reagents. Methods Experiments mimicking the clotting phase (omitting the contact activation phase) of the OS assay, complemented by measurements of activated factor XI ( FXI a) activity, were performed to characterize and explain the influence of APTT reagents/contact activators on the conversion of N9‐ GP and regular FIX (N9) to activated FIX ( FIX a). Results In the presence of an intact underestimating APTT reagent or the isolated contact activator, clotting phase activation of N9‐ GP proceeded at a reduced rate compared with that of N9. APTT reagent and contact activator negatively affected the activity of FXI a, conceivably as a consequence of FXI a adsorption. Thus, activation of FIX apparently poses a greater steric challenge after polyethylene glycol ( PEG ) conjugation. Conclusions Some OS clotting assay contact activators reduce FXI a‐mediated activation of N9‐ GP to a larger degree than that of N9, causing underestimation of N9‐ GP activity of potential clinical significance.