Summary
Plasma kallikrein is a multifunctional serine protease involved in contact activation
of coagulation. Deficiency in humans is characterised by prolonged activated partial
thromboplastin time (aPTT); however, the balance between thrombosis and haemostasis
is not fully understood. A study of plasma kallikrein-deficient mice revealed increased
aPTT, without prolonged bleeding time. Prekallikrein antisense oligonucleotide (ASO)
treatment in mice suggested potential for a positive therapeutic index. The current
goal was to further define the role of plasma kallikrein in coagulation. Blood pressure
and heart rate were normal in plasma kallikrein-deficient mice, and mice were completely
protected from occlusion (100 ± 1.3% control flow) in 3.5% FeCl3 -induced arterial thrombosis versus heterozygotes (20 ± 11.4%) and wild-type littermates
(8 ± 0%). Vessels occluded in 8/8 wild-type, 7/8 heterozygotes, and 0/8 knockouts.
Anti-thrombotic protection was less pronounced in 5% FeCl3-induced arterial injury. Integrated blood flow was 8 ± 0% control in wild-type and
heterozygotes, and significantly (p<0.01) improved to 43 ± 14.2% in knockouts. The
number of vessels occluded was similar in all genotypes. Thrombus weight was significantly
reduced in knockouts (−47%) and heterozygotes (−23%) versus wild-type in oxidative
venous thrombosis. Average tail bleeding time increased modestly in knockout mice
compared to wild-type. Average renal bleeding times were similar in all genotypes.
These studies confirm and extend studies with prekallikrein ASO, and demonstrate that
plasma kallikrein deletion prevents occlusive thrombus formation in mice with a minimal
role in provoked bleeding. Additional support for the significance of the intrinsic
pathway in the coagulation cascade is provided, as well as for a potential new anti-thrombotic
approach.
Keywords
Protease - animal model - gene knockout