Plasminogen is an inactive precursor of plasma fibrinolytic enzymes. Tissue activator t-PA, urokinase, or multiple enzymes in the coagulation contact stage are activated, and exogenous activators such as streptokinase can also activate. Plasmin degrades fibrin and fibrinogen and keeps blood vessels and glands unobstructed. Further studies have found that the function of plasmin also includes promoting collagenase activity and assisting in nutrition and cell movement.
Introductions
Plasminogen is the inactive precursor of plasmin and belongs to serine proteases. Plasmin can dissolve fibrin clots. Both inherited and acquired plasminogen deficiency can occur (more acquired). After plasmin is produced, its main target is fibrin. But it can also degrade several components of the extracellular matrix and convert some prohormones and cytokine precursors into their active forms. Plasminase may also be involved in the spread and metastasis of cancer (the main role of tPA activation is fibrinolysis. The main effect of uPA activation is non-fibrinolysis). The conversion of plasminogen to plasmin mainly occurs on the surface of fibrin, and the surface of fibrin will gather with plasminogen and its activator t-PA. Its inhibitor is mainly PAl-1 (plasminogen activator inhibitor-1).
Source
Plasminogen is synthesized in the liver and the concentration in plasma is about 200 mg/L. The reference interval for plasminogen activity is 75% to 135%. In full-term newborns, the plasminogen concentration is about half that of adults, and the level gradually rises to normal after 6 months. Plasminogen levels are related to age, sex and smoking habits in adult life. There is no day and night changes, and the level is not affected by exercise.
Clinical significance
Because the concentration of plasminogen fluctuates more easily, for patients with hyperfibrinolysis, the plasminogen assay is less sensitive than its inhibitor α2-antiplasmin assay. These two parameters are both expendable indicators and can only indirectly reflect the actual fibrinolytic activity. Determination of plasmin-α2-antiplasmin complex (PAP) is more suitable. The chromogenic substrate method is simpler and faster, and is more suitable than immunochemical methods. Except for a small number of type II defects, the correlation between activity and antigen detection is very good. Plasminogen deficiency will impair the body's ability to respond to hypercoagulability, such as extensive clinical thrombosis. In this case, the risk of embolization after surgery or thrombolytic therapy will increase. In other words, an increase in the concentration of plasminogen, once activated, can cause an increased risk of bleeding. The causes of plasminogen deficiency include: genetic defects, decreased liver synthesis, increased consumption (such as DIC, sepsis or thrombolytic therapy), and increased plasminogen concentrations in tumors and diabetic patients.
Plasminogen deficiency
As the core of the fibrinolytic system, plasminogen is of great significance for the evaluation of many diseases. Under normal circumstances, the reduction of plasminogen level will affect the body's ability to degrade fibrin and cause thrombus easily. There are many reports of hereditary plasminogen deficiency. However, it has also been reported that since plasminogen is the precursor of plasmin, most of the acquired deficiency is found to increase its fibrinolytic activity. The general acquired deficiency is mainly due to liver disease, DIC or treatment with plasminogen activator.
