The effects of heparinase 1 and protamine on platelet reactivity.

Background: Protamine is currently the most widely used drug for the reversal of heparin anticoagulation. Heparinase 1 (heparinase) is being evaluated as a possible alternative to protamine for the reversal of heparin anticoagulation. The authors evaluated the effects of equivalent doses of heparinase and protamine on platelet reactivity by measuring agonist-induced P-selectin expression.
Methods: After Institutional Review Board (IRB) approval, informed consent was obtained from 12 healthy volunteers and 8 patients undergoing surgery requiring cardiopulmonary bypass (CPB). Twenty-four ml of blood was obtained from each volunteer; 10 ml of blood was obtained from each patient before the CPB, and another 10 ml was obtained after CPB. Heparin was neutralized using heparinase or protamine. Platelet reactivity was assessed by measuring the expression of P-selectin after stimulation of platelets with increasing concentrations of a thrombin receptor agonist peptide (TRAP). Data were analyzed using analysis of variance. P < 0.05 was considered significant.
Results: For the healthy volunteers, the activated coagulation times (ACTs) of the heparinized samples returned to baseline values with heparinase (12.5 U/ml) or protamine (32.5 microg/ml). For the 8 patients, the ACTs returned to baseline with heparinase (20 U/ml) or protamine (50 microg/ml). The authors found no difference in the expression of P-selectin in samples neutralized with heparinase, but samples neutralized with protamine showed a significant decrease in the expression of P-selectin when compared with heparinized samples.
Conclusions: At dosages that reverse the anticoagulant effects of heparin, heparinase has minimal effects on platelets, whereas platelet reactivity was markedly inhibited by protamine.