Turnover of Human Extrinsic (Tissue-Type) Plasminogen Activator in Rabbits

Summary

The turnover of highly purified human extrinsic plasminogen activator (EPA) (one- and two-chain form) was studied in rabbits. Following intravenous injection, EPA-activity declined rapidly. The disappearance rate of EPA from the plasma could adequately be described by a single exponential term with a t ½ of approximately 2 min for both the one-chain and two-chain forms of EPA.

The clearance and organ distribution of EPA was studied by using ¹²⁵I-labeled preparations. Following intravenous injection of ¹²⁵I-1abeled EPA the radioactivity disappeared rapidly from the plasma also with a t ½ of approximately 2 min down to a level of 15 to 20 percent, followed by a small rise of blood radioactivity. Gel filtration of serial samples revealed that the secondary increase of the radioactivity was due to the reappearance of radioactive breakdown products in the blood. Measurement of the organ distribution of ¹²⁵I at different time intervals revealed that EPA was rapidly accumulated in the liver, followed by a release of degradation products in the blood.

Experimental hepatectomy markedly prolonged the half-life of EPA in the blood. Blocking the active site histidine of EPA had no effect on the half-life of EPA in blood nor on the gel filtration patterns of ¹²⁵I in serial plasma samples.

It is concluded that human EPA is rapidly removed from the blood of rabbits by clearance and degradation in the liver. Recognition by the liver does not require a functional active site in the enzyme. Neutralization in plasma by protease inhibitors does not represent a significant pathway of EPA inactivation in vivo.

Keywords

Extrinsic (tissue-type) plasminogen activator - Turnover in rabbits - Clearance mechanism - Inactivation

• References

• 1 Astrup T. Tissue activators of plasminogen. Fed Proc 1966; 25: 42-51
• 2 Cash JD. Control mechanisms of activator release. In: “Progress in Chemical Fibrinolysis and Thrombolysis, Vol.3”. Davidson JF, Rowan RM, Samama MM, Desnoyers PC. eds Raven Press; New York: 1978. p 65-75
• 3 Pandolfi M, Isacson S, Nilsson IM. Low fibrinolytic activity in the walls of veins of patients with thrombosis. Acta Med Scand 1969; 186: 1-5
• 4 Binder B, Spragg J. Purification of a plasminogen activator from venous occlusion plasma. Thromb Haemostas 1979; 42: 362 (abstract)
• 5 Rijken DC, Wijngaards G, Zaal-de JongM, Welbergen J. Purification and partial characterization of plasminogen activator from human uterine tissue. Biochim Biophys Acta 1979; 580: 140-153
• 6 Cole ER, Bachmann FW. Purification and properties of a plasminogen activator from pig heart. J Biol Chem 1977; 252: 3729-3737
• 7 Kok P, Astrup T. Isolation and purification of a tissue plasminogen activator and its comparison with urokinase. Biochemistry 1969; 8: 79-86
• 8 Rijken DC, Collen D. Purification and characterization of the plasminogen activator secreted by human melanoma cells in culture. J Biol Chem 1981; 256: 7035-7041
• 9 Wallén P, Ranby M. Tissue plasminogen activator. Its properties and mechanism of action In: “Protides of the Biological Fluids”, 28th annual colloquium. Brussels, Belgium: 1980. (abstract)
• 10 Hoylaerts M, Rijken D, Lijnen H, Collen D. Kinetics of plasminogen activation by tissue plasminogen activator. Role of fibrin Thromb Haemostas 1981; 46: 162 (abstract)
• 11 Matsuo O, Rijken DC, Collen D. Comparison of the relative fibrinogenolytic, fibrinolytic and thrombolytic properties of tissue plasminogen activator in vitro. Thromb Haemostas 1981; 45: 225-229
• 12 Korninger C, Collen D. Inhibition of human tissue plasminogen activator by human plasma: No evidence for a specific antiactivator. Thromb Haemostas 1981; 46: 280 (abstract)
• 13 Matsuo O, Rijken DC, Collen D. Thrombolysis by human tissue plasminogen activator and urokinase in rabbits with experimental pulmonary embolus. Nature 1981; 291: 590-591
• 14 Korninger C, Matsuo O, Suy R, Stassen J, Collen D. Thrombolytic properties of purified human tissue plasminogen activator in a dog femoral vein thrombosis model. Thromb Haemostas 1981; 46: 209 (abstract)
• 15 McFarlane A. Efficient trace-labelling of proteins with iodine. Nature 1958; 182: 53
• 16 Kettner C, Shaw E. D-Phe-Pro-Arg-CH₂Cl, a selective affinity label for thrombin. Thromb Res 1979; 14: 969-972
• 17 Fletcher AP, Biederman O, Moore D, Alkjaersig N, Sherry S. Abnormal plasminogen-plasmin system activity (fibrinolysis) in patients with hepatic cirrhosis: its cause and consequences. J Clin Invest 1964; 43: 681-695
• 18 Tytgat G, Collen D, De VrekerR, Verstraete M. Investigations on the fibrinolytic system in liver cirrhosis. Acta haematol 1968; 40: 256-274
• 19 Smith RA G, Dupe RJ, English PD, Green J. Fibrinolysis with acyl-enzymes: a new approach to thrombolytic therapy. Nature 1981; 290: 505-508