Generation and degradation of fibrinopeptide A in stored platelet concentrate

The levels of fibrinopeptide A (FPA) were measured in samples from stored platelet concentrates (PC) by radioimmunoassay. In 27 standard, citrated PC, the mean FPA was 13.6 ng/ml, which is elevated 5-6X over background levels. This value did not change significantly over a 7-day storage period. Addition of PGE-1 and theophylline resulted in higher initial levels of FPA (18.0 ng/ml) and a pronounced rise during the storage period (to 43.4 ng/ml by day 10). In contrast, addition of a thrombin inhibitor, D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone-2 HCl (PPACK) or hirudin, resulted in lower initial levels of FPA relative to standard, citrated PC and a slow increase over time. Introduction of exogenous FPA into citrated PC resulted in a predicted elevation of FPA levels followed by a rapid loss of immunoreactivity (t1/2 = 18 h). Addition of PPACK did not affect this fall-off. However, PC prepared and stored in the presence of PGE-1 and theophylline showed a much slower fall-off of exogenous FPA (t1/2 = 38 h). These data indicate that FPA levels in samples from citrated PC represent a dynamic balance between generation and degradation processes and, thus, the data above underestimate the amount of thrombin activity present in stored, citrated PC.