Plasma crosslinked fibrin polymers: quantitation based on tissue plasminogen activator conversion to D-dimer and measurement in normal and patients with acute thrombotic disorders

Plasma crosslinked fibrin polymers (XLFP) are formed as a result of in vivo hemostatic activation and are elevated in thrombotic disease. We have investigated the plasmic degradation of plasma XLFP in vitro to provide information regarding the pattern of crosslinking and the composition of degradation products. Plasma XLFP were identified by sodium dodecyl sulfate (SDS)-agarose electrophoresis and Western blotting and quantitated by gel scanning. D-dimer was measured by enzyme-linked immunosorbent assay and the results were verified by SDS- polyacrylamide gel electrophoresis and Western blotting of the digests. Complete degradation of XLFP occurred only after supplementation of plasma with plasminogen (5 U/mL) and incubation with recombinant tissue plasminogen activator (rt-PA), indicating that the normal plasma plasminogen concentration limits plasmic degradation in vitro. Gel electrophoresis showed that the principal terminal degradation products of XLDP were fragments D, DD, and E, indicating that crosslinking occurred primarily through gamma chain dimers. After adding a low concentration of thrombin to plasma in vitro, XLFP increased progressively before clotting, and the concentration correlated with the increase in the D-dimer concentration after degradation (r = .98). Plasma XLFP and D-dimer concentrations in plasmic digests were significantly elevated in patients with stroke (150 +/- 83 micrograms/mL and 88 +/- 32 micrograms/mL), myocardial infarction (217 +/- 110 micrograms/mL and 84 +/- 30 micrograms/mL), and venous thrombosis (187 +/- 80 micrograms/mL and 86 +/- 19 micrograms/mL) compared with normals (28 +/- 12 micrograms/mL and 25 +/- 7 micrograms/mL). There was a strong correlation between the plasma concentration of XLFP and the D-dimer immunoreactivity of plasma after plasmic degradation (r = .87). The results indicate that XLFP in plasma are crosslinked primarily through gamma chains and degrade to fragment DD with plasminogen activation. Also, the immunoreactivity of in vitro plasmic digests of plasma reflects the concentration of XLFP and may provide a useful indirect measure of in vivo hemostatic activation in patients with thrombotic disease.