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Measurement of factor IX activity in plasma‐derived and recombinant concentrates: insights from thrombin generation and activation‐based assays
Author(s) -
Yu Y.,
Millar C. M.
Publication year - 2014
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/jth.12452
Subject(s) - thrombin generation , chemistry , factor ix , thrombogenicity , tissue factor , thrombin , coagulation , recombinant dna , partial thromboplastin time , thromboplastin , platelet activation , biochemistry , platelet , immunology , medicine , biology , gene
Summary Background Hemophilia B, resulting from a deficiency of coagulation factor IX , is treated effectively with either recombinant FIX (r‐ FIX ) or plasma‐derived FIX (pd‐ FIX ) concentrates, although differences in pharmacokinetics are observed. FIX is activated in vivo by both activated FXI ( FXI a) and tissue factor ( TF )–activated FVII ( FVII a); however, conventional activated partial thromboplastin time ( APTT )‐based assays assess only activation by FXI a. Objectives To examine the differences between pd‐ FIX and r‐ FIX concentrates with respect to their thrombogenicity and activation. Methods and results FIX ELISA was used to quantify antigenic FIX . Calibrated automated thrombography was performed to evaluate the effect of FIX on thrombin generation. FIX a was quantified by the cleavage of FIX a‐specific chromogenic substrate. FIX activation was studied in a purified system. Results We found that r‐ FIX had ~ 1.6‐fold greater specific activity than pd‐ FIX . r‐ FIX generated a markedly higher thrombin peak than pd‐ FIX at an equivalent antigen level when coagulation was initiated by TF , but this was not seen in contact activation‐triggered thrombin generation ( TG ). Interestingly, the amount of FIX a in r‐ FIX concentrate was 10 times higher than that in pd‐ FIX concentrate. In a purified system, the amount of r‐ FIX a generated by FXI a in the first 10 min of activation was 1.37‐fold that of pd‐ FIX a, whereas no difference between the concentrates was observed when triggered by TF – FVII a. Conclusions Clear differences were observed between pd‐ FIX and r‐ FIX concentrates, including the proportion of FIX a and the activation by FXI a. These may explain some of the discrepancies observed clinically, and suggest that the APTT may not reflect their resultant in vivo properties.