Assay of oxidized fibrinogen reactivity (OFR) as a biomarker of oxidative stress in human plasma: the role of lysine analogs.

Background: There is accumulating evidence that fibrinogen is also a biomarker of oxidative stress in human plasma. Results of in vitro studies demonstrated that fibrinogen can bind to apolipoprotein(a) [apo(a)] component of lipoprotein(a) [Lp(a)] through both lysine-sensitive and lysine-insensitive mechanisms. The goal of the present study was to investigate oxidized fibrinogen reactivity (OFR) as a biomarker of oxidative stress in human plasma in the presence and absence of lysine analogs. Methods: Citrate anticoagulated peripheral venous blood samples were collected from 65 (36 M/29 F) consecutive patients with various peripheral vascular diseases. After centrifugation, the plasma was used promptly. Plasma OFR was determined in duplicate using a recently described kinetic photometric assay (358 nm, 37 degrees C) in the presence and in the absence of lysine analogs. Results: The inclusion of tranexemic acid (TRA) or epsilon-aminocaproic acid in the incubation medium resulted in a rapid increase in OFR in a dose-dependent manner. The peak effect was observed at a final concentration of 200 mmol/L TRA. OFR was significantly higher in patient plasma assayed in the presence of TRA compared with no TRA (163.1 +/- 73.5 vs. 63.4 +/- 20.7 U/L; p<0.0001). Bound OFR was also significantly higher than free OFR (99.7 +/- 56.3 vs. 63.4 +/- 20.7; p<0.001). Conclusions: On the basis of the present results it appears that oxidized fibrinogen resides in plasma in two compartments: free and bound to apo(a) of Lp(a). The relatively simple and cost-effective kinetic approach applied in this study makes routine determination of OFR available as a biomarker of oxidative stress, separately in both compartments. Clin Chem Lab Med 2010;48:379-82.