Effects of plasma kallikrein deficiency on haemostasis and thrombosis in mice: Murine Ortholog of the Fletcher Trait

Abstract

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.

Factor XII full and partial null in rat confers robust antithrombotic efficacy with no bleeding

“…This contrast between outcomes with knockdown of the two targets supports the notion that FXII is the initiator of the intrinsic cascade, and plasma kallikrein is an amplifier [3]. This is also consistent with abundant data showing profound thrombo-protection in FXII knockout mice, whereas plasma kallikrein knockout mice exhibited only modest thrombo-protection [30].…”

Plasma Kallikrein Inhibitors in Cardiovascular Disease

“…On the other hand, plasma kallikrein also has antithrombotic and profibrinolytic actions via its pleiotropic effects on platelet aggregation and the fibrinolytic system. 22,23 Plasma kallikrein itself has no effect on platelet aggregation. At low concentrations (~10 nM), kallikrein promotes platelet aggregation induced by adenosine diphosphatase, collagen and adrenaline, and inhibits that induced by thrombin, arachidonic acid, and thrombofax (compound that stimulates the synthesis of thromboxane A2).…”

“…[32][33][34] Consistent with observations in humans, experimental evidence suggests that murine genetic depletion of FXII (FXII -/-), HK (Kgn1 -/-), or plasma kallikrein (Klkb1 -/-) yields animals with prolonged aPTT and no evidence of clinical bleeding, thus supporting the notion that unlike the extrinsic pathway of coagulation, the intrinsic pathway is dispensable for hemostasis. 22,35,36 However, studies have consistently demonstrated that FXII -/-, Kgn1 -/-, and Klkb1 -/-mice are protected from thrombosis. Using 3 different in vivo models to study platelet recruitment and thrombus formation at sites of arterial injury, it was demonstrated that FXII -/-mice are protected against arterial and venous thrombosis.…”

Future Therapy for Pediatric Hereditary Angioedema

“…26 They display prolonged activated partial thromboplastin time (aPTT), a marker of blood coagulation, but are not at increased risk of bleeding. In fact, they seem to be protected from both arterial and venous thrombosis, and plasma kallikrein inhibition has been considered as a possible preventive therapy for thrombotic disorders such as myocardial infarction and thrombotic stroke.…”

“…In fact, they seem to be protected from both arterial and venous thrombosis, and plasma kallikrein inhibition has been considered as a possible preventive therapy for thrombotic disorders such as myocardial infarction and thrombotic stroke. 26 Congenital plasma kallikrein inhibition has been identified in humans, where prekallikrein was historically referred to as ''Fletcher factor'' based on the name of the first identified family with the deficiency. 27 The index case was identified due to a prolonged aPTT on routine presurgical screening and, analogous to the mouse, no increased history of bleeding.…”