COMPARATIVE STUDIES ON ANTITHROMBIN III AFFINITY OF LOW MOLECULAR WEIGHT HEPARIN AND UNFRACTIONATED HEPARIN
Purpose: Low molecular weight(LMW)heparin shows stronger antifactor Xa(F-Xa) and weaker anti-thrombin(TH) activities compared with unfractionated(UF) heparin, and shows less bleeding tendency in the cases of clinical use. These characteristics were surmised to be depend on antithrombin III(AT-III) affinity of the heparin. Materials and methods: LMW heparin(Kabi and Pharmuka), UF heparin (Novo) and heparin cofactor II(HC-II) purified by our method were used. AT-III affinity column chromatography with 0.1 M Tris-buffer (pH 7.4)-NaCl 0.02 to 2.5 M linear gradient was performed. From the point of AT-III affinity strength, non-affinity(Na), low affinity (La) and high affinity(Ha) were separated, and aPTT, anti-F-Xa and anti-TH activities were assayed on each fractions. HC-II was assayed by biological activity.Results: (1) Kabi-LMW heparin; Na 34.5%, La 39.3%, Ha 26.2%, Pharmuka-LMW heparin; Na 58.0%, La 24.1%, Ha 17.3%. Novo; Na 0%, La 50%, Ha 50%. (2) APTT; Na showed no effect, but Ha showed the strongest prolonging effects on aPTTs even having less amount of uronic acid, and more prominent effects were observed in UF(Novo)-heparin than LMW heparins. (3) La showed higher activity of anti-F-Xa and anti-TH activities than Ha. (4) Anti-TH activity of AT-III was observed in both fractions of La and Ha, but that of HC-II was observed in each fractions including Na.Conclusion: It was surmised that the differences of the characteristics between LMW heparin and UF heparin were depend on to the strength of AT-III. The different characteristics of HC-II from AT-III to anti-TH were observed and surmised to be depend on the binding ability to the fractions.