Fibrin digestion by thrombin. Comparison with plasmin-digested fibrinogen.

Area of Science:

• Biochemistry
• Hematology
• Proteolysis

Background:

• Fibrinogen is the precursor to fibrin, the main structural component of blood clots.
• Factor XIII is a transglutaminase that crosslinks fibrin, stabilizing clots.
• Thrombin and plasmin are key proteases involved in hemostasis and fibrinolysis, respectively.

Purpose of the Study:

• To investigate the fibrinolytic activity of thrombin on human fibrin clots.
• To compare the degradation products and kinetics of thrombin-induced fibrinolysis with plasmin-induced fibrinolysis.
• To elucidate the role of Factor XIII in thrombin-mediated clot dissolution.

Main Methods:

• Preparation of plasminogen-free human fibrinogen solutions, with and without Factor XIII.
• Clotting with thrombin and incubation under sterile conditions.
• Analysis of clot dissolution rates, proteolytic degradation products via gel electrophoresis and immunoelectrophoresis, and inhibition studies.

Main Results:

• Thrombin-induced clot dissolution occurred over 2-15 days, depending on Factor XIII content.
• Proteolysis generated fragments similar to plasmin digests (X, Y, D, E), with D and E appearing later.
• Soybean trypsin inhibitor did not affect dissolution, while hirudin completely inhibited it.
• Thrombin hydrolysis released fewer bonds than plasmin when fibrinogen becomes unclottable.

Conclusions:

• Thrombin possesses intrinsic fibrinolytic activity, distinct from plasmin.
• Factor XIII influences the rate of thrombin-mediated fibrin clot dissolution.
• Thrombin proteolysis of fibrin yields characteristic degradation products, differing in kinetics from plasmin.