Kallikrein directly interacts with and activates Factor IX, resulting in thrombin generation and fibrin formation independent of Factor XI

Abstract

Kallikrein (PKa), generated by activation of its precursor prekallikrein (PK), plays a role in the contact activation phase of coagulation and functions in the kallikrein-kinin system to generate bradykinin. The general dogma has been that the contribution of PKa to the coagulation cascade is dependent on its action on FXII. Recently this dogma has been challenged by studies in human plasma showing thrombin generation due to PKa activity on FIX and also by murine studies showing formation of FIXa-antithrombin complexes in FXI deficient mice. In this study, we demonstrate high-affinity binding interactions between PK(a) and FIX(a) using surface plasmon resonance and show that these interactions are likely to occur under physiological conditions. Furthermore, we directly demonstrate dose- and time-dependent cleavage of FIX by PKa in a purified system by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and chromogenic assays. By using normal pooled plasma and a range of coagulation factor-deficient plasmas, we show that this action of PKa on FIX not only results in thrombin generation, but also promotes fibrin formation in the absence of FXII or FXI. Comparison of the kinetics of either FXIa- or PKa-induced activation of FIX suggest that PKa could be a significant physiological activator of FIX. Our data indicate that the coagulation cascade needs to be redefined to indicate that PKa can directly activate FIX. The circumstances that drive PKa substrate specificity remain to be determined.

Added Value of Blood Cells in Thrombin Generation Testing

“…117 The activation of the contact pathway induces FXI activation; it was also shown that FXIIa and kallikrein can both directly activate FIX. [117][118][119] Influence of Erythrocyte-Platelet Interaction on WB-TG Platelets and erythrocytes are the most abundant cells in circulating blood and their interactions may be an underestimated player in coagulation. Erythrocytes can directly activate platelets through the release of adenosine triphosphate (ATP) and adenosine diphosphate (ADP).…”

Mechanism, Functions, and Diagnostic Relevance of FXII Activation by Foreign Surfaces

“…75 Recently, and in line with the previous study, PKa-mediated FIX activation was confirmed in plasma ex vivo. 76 The clinical consequence of red blood cell-triggered coagulation may explain the procoagulant state in patients after blood transfusions.…”

Drugs in phase I and II clinical development for the prevention of stroke in patients with atrial fibrillation

“…It is possible that reduced conversion of prekallikrein to kallikrein by FXIIa may occur with FXIIa inhibitors, thereby modulating inflammation by inhibiting bradykinin generation which may lead to further beneficial clinical effects. Kallkrein has recently been shown to directly activate FIX [85][86][87][88]. This second mechanism implies that a further reduction of thrombin generation via direct kallikrein activation of FIX, independent of FXI, may be possible with FXIIa inhibitors.…”