Effect of Pentosan Polysulphate Administration in Man on the Formation of Covalent Complexes Between Heparin Cofactor II and Thrombin Generated in Plasma by Contact Activation

Pharmacokinetics of heparin and related polysaccharides

The pharmacodynamic profile of standard heparin (SH), a low molecular weight derivative (CY 216) and of dermatan sulfate (DS), a new potential antithrombotic drug, was investigated in the rabbit over a large range of doses. After bolus i.v. injection of low doses, the biological activity of SH disappeared exponentially; however, its half-life was prolonged when the dose injected increased, and over 158 micrograms/kg (100 anti-factor Xa U/kg) the biological activity disappeared as a concave-convex curve. CY 216 disappeared more slowly than SH at low doses but faster than SH at higher doses. More than 90% of the DS biological activity present 1 minute after the i.v. injection disappeared exponentially without dose-dependent effects. Increasing doses of the three drugs were then delivered for 5 h under continuous infusions. Below 500 micrograms/kg/h the DS and CY 216 plateau concentrations were higher than that of SH while above this dose the SH concentration was higher than that of DS and CY 216. These observations may be explained by the results of pharmacokinetics experiments where 125I-labeled compounds were delivered by bolus i.v. injection in association with increasing doses of their unlabeled counterparts. For SH there was a 10-fold difference between the half-life of the lower dose (32 micrograms/kg or 5 anti-factor Xa U/kg) and that of the higher dose (3200 micrograms/kg); it was demonstrated that the half-life of SH continuously shortened as its plasma concentration decreased. In contrast the CY 216 and DS half-lives were very close, independent of the dose delivered, and therefore longer than that of SH at low doses and shorter than that of SH at higher doses. The renal contribution to the clearance of SH, CY 216, and DS was also investigated by injecting a low dose (150-200 micrograms/kg) and a 10 times higher dose to sham-operated or binephrectomized animals: renal function is critical for the elimination of the three compounds from the blood except for SH at low doses. These observations are promising for the development of DS and may have clinical implications.

Inactivation of heparin cofactor II by polymorphonuclear leukocytes

Inactivation of purified human heparin cofactor II by polymorphonuclear leukocytes was investigated. A proteolytic mechanism of inactivation was demonstrated by SDS-polyacrylamide gel electrophoresis. Inactivation and related proteolysis did not occur in the presence of unstimulated leukocytes and were prevented by various protease inhibitors. Heparin cofactor II was inactivated more rapidly than antithrombin III. However, heparin (1-10 ug/ml) strongly accelerated the rate of antithrombin III inactivation and slightly protected heparin cofactor II, thus reversing the order of inactivation. Dermatan sulfate had no effect on this process.