Standard and Method Independent Units for Heparin Anticoagulant Activities

Summary

It is discussed why the current USP unit of heparin anticoagulant activity necessarily will render inaccurately the anticoagulant activities of low molecular weight heparins. It is shown that the outcome is bound to vary with the method used for comparison of the sample and the standard and with the nature of the standard used. As an alternative we define a unit of heparin in terms of anti-factor Xa- and antithrombin-activity that is independent of the heparin standard and of the assay method, but that is based upon a quantitative description of the catalytic effect of heparin on AT III mediated thrombin- and factor Xa breakdown. Expression of the results of existing anti-factor Xa- and antithrombin tests in terms of these units will allow to express heparin levels in plasma in terms of concentrations of active anticoagulant material. This approach makes it possible to separate heparin pharmacodynamics from heparin pharmacokinetics. Introduction of this unit does not require adaptation of current laboratory practice but changes the way in which the results obtained are expressed.

• References

• 1 Howell WH. The purification of heparin and its presence in blood. Am J Physiol 1925; 71: 553-562
• 2 Duclos JP. L’héparine, fabrication, structure, propriétés, analyse Masson, edts. Paris: 1984: 233-308
• 3 Van DedemG, Van HoudenhovenF, Hennink W. The USP heparin assay, fact and artifact. In: Chemistry and Biology of Heparin. Lundblad RJ. et al. (eds) New York, Amsterdam, Oxford: Elsevier/North Holland; 1981: 19-28
• 4 Barrowcliffe TW, Curtis AD, Johnson EA, Thomas DP. An international standard for low molecular weight heparin. Thromb Haemostas 1988; 60: 001-008
• 5 Coyne E, Outschoorn AS. Some thoughts on a new USP heparin assay – Aren’t we ready for an upgrade? Pharmacopeial Forum. 1991; 17: 1492-1494
• 6 Coyne E, Outschoorn AS. Stimuli to the revision process: A clarification of quality attribute tests for heparin and heparin products. Pharmacopeial Forum 1991; 17: 1495-1497
• 7 Abilgaard U. Highly purified antithrombin III with heparin cofactor activity prepared by disc electrophoresis. Scand J Clin Lab Invest 1968; 21: 89-91
• 8 Yin ET, Wessler S, Stoll PJ. Biological properties of the naturally occuring inhibitor to activated factor X. J Biol Chem 1971; 246: 3701-3711
• 9 Rosenberg RD, Damus PS. The purification and mechanism of action of human antithrombin-heparin cofactor. J Biol Chem 1973; 248: 6490-6505
• 10 Rosenberg RD. Actions and interactions of antithrombin and heparin. N Engl J Med 1975; 292: 146-151
• 11 Casu B. Structure and biological activity of heparin. Adv Carb Chem Biochem 1985; 43: 051-134
• 12 Barrowcliffe TW, Johnson EA, Thomas DP. Low molecular weight heparin. Chichester: John Wiley & Sons; 1992
• 13 Béguin S, Wielders S, Hemker HC. The mode of action of CY216 and CY222 in plasma. Thromb Haemostas 1992; 67: 33-41
• 14 Bendetowicz AV, Pacaud E, Béguin S, Uzan A, Hemker HC. On the relationship between molecular mass and anticoagulant activity in a low molecular weight heparin (enoxaparin). Thromb Haemostas 1992; 67: 556-562
• 15 Olson ST, Shore JD. Transient kinetics of heparin-catalysed protease inactivation by antithrombin III: The reaction step limiting heparin turnover in thrombin neutralization. J Biol Chem 1986; 261: 13151-13159
• 16 Hemker HC, Béguin S, Bendetowicz AV, Wielders S. The determination of the levels of unfractionated and low molecular weight heparins in plasma. Their effect on thrombin mediated feedback reactions in vivo. Preliminary results on samples after subcutaneous injection. Haemostasis 1991; 21: 258-272
• 17 Béguin S, Dol F, Hemker HC. The consumption of antithrombin III and heparin during coagulation, its consequences for the calculation of prothrombinase activity and the standardisation of heparin activity. Thromb Haemostas 1992; 68: 136-142
• 18 Béguin S, Lindhout T, Hemker HC. The mode of action of heparin in plasma. Thromb Haemostas 1988; 60: 457-462
• 19 Hemker HC, Béguin S. Letter to the editor. Thromb Haemostas 1993; 70: 717-718
• 20 Sandset PM, Abildgaard U. Extrinsic Pathway Inhibitor – The key to feedback control of blood coagulation initiated by tissue thromboplastin. Haemostasis 1991; 21: 219-231
• 21 Walenga J, Petitou M, Lormeau JC, Samama M, Fareed J, Choay J. Antithrombotic activity of a synthetic heparin pentasaccharide in a rabbit stasis thrombosis model using different thrombogenic challenges. Thromb Res 1987; 46: 187-198
• 22 Ofosu FA, Buchanan MR, Anvari N, Smith LM, Blajchman MA. Plasma anticoagulant mechanisms of heparin, heparan sulfate and dermatan sulfate. In: Heparin and Related Polysaccharides. Structures and Activities. Ann New York Acad Sci 1989; 556: 123-131
• 23 Van PuttenJJ, van deRuit M, Beunis M, Hemker HC. Interindividual variations in the relationship between plasma heparin concentrations and the results of five heparin assays. Clin Chim Acta 1982; 122: 260-271
• 24 Hemker HC, Wielders S, Kessels H, Béguin S. Continuous registration of thrombin generation in plasma, its use for the determination of the thrombin potential. Thromb Haemostas. 1993 in press