Recombinant Kunitz protease inhibitory domain of the amyloid beta-protein precursor as an anticoagulant in venovenous extracorporeal circulation in rabbits

Investigations were performed to characterize a recombinant Kunitz protease inhibitory domain of the amyloid beta-protein precursor (rKPI) as anticoag ulants. After a single intravenous infusion of wild type rKPI into dogs, it s elimination fit a two compartment model with a t(1/2)alpha and t(1/2)beta of 5 and 77 min, respectively. Further investigations determined if a vari ant Corm of rKPI with 178-fold more potent anti-factor Xa activity (rKPI-DD 135, k(i) = 0.9 nM) could serve as an anticoagulant in a rabbit model of ex tracorporeal circulation using a venovenous shunt. A prospective investigat ion was initiated to compare standard heparin (n = 8) at 400 U/kg with diff erent infusion concentrations of rKPI-DD135. After a single intravenous inf usion of 1.89 mg/kg of rKPI-DD135 followed by a constant infusion at 0.003 (n = 3), 0.03 (n = 7), or 0.3 (n = 5) mg/kg/min, the anti-factor Xa activit y of the animals' plasma rapidly reaches a steady state for the two lower i nfusion concentrations of the agent. All infusions of rKPI-DD135 prolong th e activated clotting time with less variation than that seen with heparin a dministration. rKPI-DD135 anticoagulation does not prevent a drop in the pl atelet counts. Fibrinogen levels decrease only slightly when the circuit is anticoagulated with rKPI-DD135. rKPI-DD135 markedly prolongs the APTT, has little effect on the PT, and reduces plasma prekallikrein and plasminogen activation. The 0.3 mg/kg/min infusion concentration of rKPI-DD135 results in reduced deposition of (111)Indium-labeled platelets on the circuit when compared to heparin. Last, after a steady state level is achieved, 60% of t he plasma anti-factor Xa activity of rKPI-DD135 is eliminated within 60 min after stopping the infusion. These data show the rKPI-DD135 can provide si ngle agent anticoagulation in a rabbit extracorporeal circuit. Development of short acting factor Xa inhibitors may be useful anticoagulants for cardi opulmonary bypass.