Thrombin

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Thrombin is a white to off-white non-crystalline substance, generally a freeze-dried powder. Thrombin hemostatic agent, clinically mainly used to stop bleeding of small blood vessels, capillaries and solid organs that are difficult to stop bleeding; used for trauma, surgery, oral cavity, ear, nose, throat, urinary, burn, orthopedics, nerve Hemostasis of bleeding in surgery, ophthalmology, obstetrics and gynecology, and digestive tract. Thrombin acts directly on the last step of the blood coagulation process to promote the conversion of soluble fibrinogen in plasma into insoluble fibrin, so as to achieve the purpose of quick-acting hemostasis. It can also promote the mitosis of epithelial cells and accelerate wound healing. It is a fast-acting local hemostatic agent. Thrombin is suitable for bleeding of small blood vessels, capillaries, solid organs and other kinds of bleeding that are difficult to stop bleeding.

Figure 1. Structure of thrombin.

Mechanism of action

In the coagulation pathway, the role of thrombin is to convert factor XI into XIa, VIII into Villa, V into Va, fibrinogen into fibrin, and XIII into XIIIa. Factor XIIIa is a transglutaminase that catalyzes the formation of covalent bonds between lysine and glutamine residues in fibrin. The covalent bond increases the stability of the fibrin clot. Thrombin interacts with thrombomodulin. As part of the activity of the coagulation cascade, thrombin also promotes platelet activation and aggregation by activating protease-activated receptors on the platelet cell membrane.

Source

Thrombin is produced by the enzymatic hydrolysis of coagulation factor X (Xa) at two sites on prothrombin. By combining with the activated factor V (Va) called prothrombinase complex, the activity of factor Xa is greatly enhanced. Prothrombin is produced in the liver and is co-translationally modified in a vitamin K-dependent reaction that converts 10-12 glutamic acids at the N-terminus of the molecule into γ-carboxyglutamate (Gla). [11] In the presence of calcium, Gla residues promote the binding of prothrombin to the phospholipid bilayer. Vitamin K deficiency or taking the anticoagulant warfarin can inhibit the production of γ-carboxyglutamate residues, thereby delaying the activation of the coagulation cascade.

Clinical significances

The activation of prothrombin is essential in physiology and pathology of coagulation. Thrombin is an effective vasoconstrictor and mitogen, and is a major factor in vasospasm after subarachnoid hemorrhage. Blood from a ruptured cerebral aneurysm coagulates around the cerebral artery, releasing thrombin. This can cause acute and prolonged narrowing of blood vessels, which may lead to cerebral ischemia and infarction (stroke). In addition to playing a key role in the dynamic process of thrombosis, thrombin also has obvious pro-inflammatory properties, which may affect the onset and development of atherosclerosis. Thrombin is related to the physiology of blood clots. Its presence indicates the presence of a clot. In 2013, a system to detect the presence of thrombin in mice was developed. It incorporates a peptide-coated iron oxide attached to the "reporter chemical". When the peptide binds to the thrombin molecule, the report is released and appears in the urine, where it can be detected.

Application

• Research tool

Due to its high proteolytic specificity, thrombin is a valuable biochemical tool. After the fusion protein is purified, thrombin can be used to selectively cleave between the arginine and glycine residues at the cleavage site, thereby effectively removing the purification tag from the target protein with high specificity.

• Medicine

Prothrombin complex concentrate and fresh frozen plasma are coagulation factor preparations rich in prothrombin, which can be used to correct prothrombin defects (usually caused by drugs). Indications include refractory bleeding caused by warfarin. The manipulation of prothrombin is critical to the mode of action of most anticoagulants. Warfarin and related drugs inhibit the vitamin K-dependent carboxylation of various coagulation factors including prothrombin. Heparin can increase the affinity of antithrombin for thrombin (and factor Xa). Direct thrombin inhibitors are newer drugs that directly inhibit thrombin by binding to the active site of thrombin.