Heparin-based anticoagulants

Assay of the PABA standard individually in the presence of each plasma sample is necessary (Table 3.7.1 tubes 7 and 8) since some heparin-based anticoagulating agents sometimes used to prepare plasma may diminish the colour development, thus reducing the intensity of the colour. Falsely low activities would be measured in such a sample if the standard factor required to convert the absorbance units to nanomoles (see Calculation below), is determined in the absence of the plasma. 

Based on four randomized, double-blind trials aspirin is clearly effective in unstable angina (45-48). It reduces the risk of MI and cardiac death by 50 to 70% either alone or in concert with the anticoagulant heparin. Aspirin also has a role in reducing the incidence of early closure of saphenous vein bypass grafts of the coronary arteries and following coronary artery angioplasty (49-58). 

F4. Freeman, L., Engelberg, H., and Dudley, A., Plasma heparin levels I. A method for determination of plasma heparin based on anticoagulant activity. Am.. Clin. Pathol. 24, 599-606 (1954). 

Dettke M, Buchta C, Wiesinger H, Maas JH, Strate A, Chen Y. Anticoagulation in large-volume leukapheresis comparison between citrate-versus heparin-based anticoagulation on safety and CD34+ cell collection efficiency Coyote 2012 14(3) 350-8. 

Heparin is a carbohydrate-based (glycosaminoglycan) anticoagulant associated with many tissues, but mainly found stored intracellularly as granules in mast cells that line the endothelium of blood vessels. Upon release into the bloodstream, heparin binds to and thereby activates an additional plasma protein, namely antithrombin. The heparin-antithrombin complex then binds a number of activated clotting factors (including Ha, IXa, Xa, XIa and Xlla), thereby inactivating them. The heparin now disassociates from the complex and combines with another antithrombin molecule, thereby initiating another turn of this inhibitory cycle. 

Whole blood is blood that has been aseptically withdrawn from humans. A suitable anticoagulant is added (often heparin or a citrate-dextrose-based substance), although no preservative is present. The blood is usually stored at temperatures ranging from 1-8 °C, and has a short shelf life (48 h after collection if heparin is used as the anticoagulant, or up to 35 days if citrate-phosphate-dextrose with adenine is employed). 

The oleosin fusion procedure was used for the purification of the commercially valuable plant-based blood anticoagulant hirudin in transgenic Brassica carinata and Brassica napus. Hirudin, a natural protein from the medicinal leech Hirudo medicinalis, is superior to other anticoagulants such as heparin. Recombinant hirudin was cleaved from oil-bodies using endoproteinase Factor Xa. Released hirudin was biologically active, as determined by a colorimetric thrombin inhibition assay. 

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