Measurement of carboxypeptidase U (active thrombin-activatable fibrinolysis inhibitor) in plasma: Challenges overcome by a novel selective assay.

This article introduces a novel assay for the measurement of carboxypeptidase U (CPU) in plasma using the selective CPU substrate Bz-o-cyano-Phe-Arg (N-benzoyl-ortho-cyano-phenylalanyl-arginine), thereby limiting the interference of plasma carboxypeptidase N (CPN) as well as the intrinsic activity of procarboxypeptidase U (proCPU). A limit of detection of 0.05U/L (10pM) was reached. In addition, the current assay has the advantage of being easy to perform and shows excellent linearity and variability, rendering it a useful tool in the screening of samples for the presence of CPU in several patient populations and encouraging in-depth exploration of the pathophysiological role of the proCPU/CPU system.