PLASMIN

Originator

Actase,Ortho,US,1959

Uses

Plasmin is present in blood to prevent unwanted clotting by catalysing the breakdown of the fibrin polymer that provides the framework of a blood clot. Plasmin is formed from plasminogen, a process that occurs after plasminogen has been activated by forming a complex with fibrin. After certain tissue fragments had been shown to possess plasminogenactivating ability, a soluble fraction possessing this activity was extracted and purified. Cloning and expression of complementary DNA (cDNA) for human tissue-type plasminogen activator permitted commercial production of alteplase.
Alteplase was shown to be a potent thrombolytic agent by virtue of its ability to activate plasminogen, thus breaking down fibrin in the thrombus. An early clinical study in patients with coronary occlusion following myocardial infarction showed that it was an effective drug for dissolving clots in coronary arteries. It was marketed for this purpose in 1988.

Uses

Human plasmin has been used as an oligopeptide substrate in peptidase inhibition assays.

Uses

A complex between plasmin and an inhibitor has been isolated in a study via affinity chromatography from urokinase-activated human plasma. It has also been used in a study to investigate activation of human epithelial sodium channel (ENaC) by plasmin and chymotrypsin.

Definition

A proteolytic enzyme that dissolves fibrin and hastens the solution of clots that may form in the bloodstream. It is prepared by activating a fraction of normal human plasma with highly purified streptokinase.

Manufacturing Process

A 5 gallon drum of frozen plasma oxalated with a known anticoagulant quantity and proportion of oxalic acid and sodium oxalate as described in US Patent 2,394,566 is permitted to stand at room temperature (24° to 26°C) for 24 hours after which the remaining unmelted portion is broken up with an ice pick and a stainless steel warming coil containing running warm water at about 40°C is inserted into the mixture and the mixture stirred. The remaining frozen material is rapidly melted. The warming is then continued with vigorous agitation.
When the temperature of the plasma reaches about 5° to 8°C, the calculated quantity of calcium chloride solution is added in amount which is from 0.2 to 0.3% in excess of that needed to react with and precipitate the anticoagulant. The temperature of the plasma is allowed to rise to about 24°C. At 18° to 24°C strands of fibrin begin to appear and the vigor of stirring is increased to prevent a gel of fibrin from forming. Stirring is continued or 30 minutes after the fibrin is whipped out to allow for complete conversion of all prothrombin to thrombin and for the antithrombin to completely destroy all thrombin. At the end of this time the stirring is stopped, the fibrin allowed to rise to the surface and the clear serum siphoned off.
If, through failure to stir with enough vigor, a gel forms instead of strands of fibrin, when the temperature reaches about 18°C, the serum can also be obtained from the fibrin by working and kneading the gel in a cheesecloth bag while draining off the clear serum. However, this method is time-consuming and it is preferred to prevent gel formation by very vigorous stirring of the mixture.
The clear serum of this example is an amber liquid free from prothrombin, thrombin, fibrinogen and fibrin. It contains profibrinolysin and is excellently suited to further purification by salt precipitation fractionation, as given below.
The special serum is brought to a temperature of about 4° to 6°C (preferably 5°C) and saturated ammonium sulfate solution added drop by drop with constant stirring to about 24 to 26% of saturation (preferably 25%). The precipitated protein impurities are then centrifuged off and the supernatant brought to about -1° to +1°C (preferably 0°C). The degree of its saturation is then brought to about 28 to 31% of saturation (preferably 29%) by further addition of ammonium sulfate solution with stirring. This further degree of saturation precipitates the profibrinolysin which is collected by centrifugation and separated from soluble impurities. By washing the profibrinolysin several times with ammonium sulfate solution of a strength which is 29% of saturation a practically white solid is obtained which can be freeze-dried (frozen and dried under reduced pressure) to give a dry, white, product containing purified profibrinolysin free from thromboplastin, prothrombin, thrombin, fibrinogen and fibrin, (from US Patent 2,624,691), which is then activated to fibrinolysin.

Therapeutic Function

Thrombolytic

General Description

Fibrinolysin

Biochem/physiol Actions

Plasmin is a direct acting fibrinolytic enzyme present in blood. Its activity is independent of plasminogen presence during fibrinolysis. Plasmin is rapidly and irreversibly inhibited by α-2 antiplasmin.