Summary of heparin
Heparin is a natural anticoagulant found in all mammal species. It is called heparin because heparin was first isolated from liver tissue in 1916. It is synthesized in mast cells and basophils and stored in secretory granules of these cells. Because mast cells are present in many tissue types, heparin can be derived from a range of extrahepatic tissues. Currently, the most common source of commercial preparations is the capsular mucosa of pig (porcine) intestines.
The structure of heparin
Heparin belongs to a family of complex carbohydrates called glycosaminoglycans (or mucopolysaccharides). In essence, glycosaminoglycans are long straight chains of repeating disaccharide units, each containing n-acetyl hexamine and hexose or hexuronic acids. One of the differences between heparin and other glycosaminoglycans is that it contains an unusually high proportion of disaccharide sulfate units. Thirty percent of the heparin molecule has a special and unique pentose sequence with high sulfur acidification, demonstrating the anticoagulant effect of heparin.
Anticoagulant effect and therapeutic use
Heparin prevents blood clotting due to the unique pentaglycose sequence contained in its structure, which binds tightly to antithrombin iii. Antithrombin III is a plasma protein that inhibits blood clotting by binding to several activated clotting factors, including clotting factors XIa, Xa, IXa and IIa(thrombin), thereby inhibiting their enzymatic action.
As with other clotting cascade inhibitors, the physiological function of antithrombin III is to prevent blood clotting in the body and thus maintain blood flow throughout the blood vessels. The effect of heparin binding is to increase antithrombin activity by more than 1000 times.
Heparin - Standardization of heparin salts
Heparin activity (concentration) is measured in international units (IU) or United States pharmacopoeia units as defined by world Health Organization (WHO) international standards.
The USP unit is defined as heparin content with 1.0 mL citric acid to prevent coagulation of sheep plasma within 1 hour of adding 0.2 mL of 1% calcium chloride solution. That's about 0.005 milligrams of heparin.
And the differences between IU USP units and IU USP units are small (7-10%), and action is being taken to unify the two units. Heparin sodium is the natural salt of heparin, which is used in medicine and laboratories.