Summary
The variant serpin α1-PI M358R inhibits thrombin and other proteases such as activated protein C (APC)
and factor XIa. We previously described recombinant proteins HAPI M358R (α1-PI M358R containing an N-terminal extension corresponding to residues 1–75 of heparin
cofactor II) and HAPI RCL5 (HAPI M358R with F352-I356 and I360 substituted for the
corresponding residues of antithrombin), with enhanced selectivity for thrombin over
APC inhibition. We tested the hypotheses that these recombinant proteins would limit
thrombosis in three mouse models, and that the HAPI chimeric proteins would be more
effective than α1-PI M358R. Recombinant serpins were purified from Escherichia coli by nickel chelate and ion exchange affinity chromatography, and administered to mice
intravenously. HAPI RCL5 reduced incorporation of radiolabelled fibrin(ogen) into
thrombi in the ferric chloride-injured vena cava in a dose-dependent manner; HAPI
M358R was less effective and α1-PI M358R was without effect. In a model of murine endotoxaemia, HAPI RCL5 was more
effective than α1-PI M358R in reducing radiolabelled fibrin(ogen) deposition in heart and kidneys;
immunohis-tochemistry of tissue sections showed lesser staining with anti-fibrin(ogen)
antibodies with both treatments. In the ferric chloride-injured murine carotid artery,
administration of both recombinant serpins was equally effective in lengthening the
vessel’s time to occlusion. Our results show that the antithrombotic efficacy of the
recombinant serpins correlates with their potency as thrombin inhibitors, since HAPI
RCL5 inhibits thrombin, but not factors Xa, XIa, XIIa, or neutrophil elastase, more
rapidly than α1-PI M358R.
Keywords
Serpins - coagulation - heparin cofactor II - α
1-proteinase inhibitor - thrombosis - protein engineering - molecular biology