Parallel procoagulant and anticoagulant pathways for high molecular weight kininogen coagulant function

Area of Science:

• Biochemistry
• Hematology
• Molecular Biology

Background:

• High molecular weight kininogen (HK) plays a role in both coagulation and inflammation.
• Antithrombin III (AT) is a primary inhibitor of coagulation proteases.
• Heparin enhances AT's inhibitory activity.

Purpose of the Study:

• To investigate the effect of HK on heparin-mediated inhibition of plasma kallikrein and factor XIa by AT.
• To elucidate the role of HK's light and heavy chains in this interaction.
• To understand the potential anticoagulant implications of HK.

Main Methods:

• In vitro assays measuring the inactivation rates of plasma kallikrein and factor XIa by AT in the presence of heparin and varying concentrations of HK.
• Experiments using purified HK light and heavy chains.
• Analysis of heparin chain-length and salt dependence.

Main Results:

• HK, specifically its light chain, significantly potentiated heparin's enhancement of AT inactivation of plasma kallikrein and factor XIa (10-50-fold to ~1000-fold).
• This potentiation led to AT becoming the dominant inhibitor of these factors in heparinized normal plasma, but not in HK-deficient plasma.
• The observed potentiation exhibited dependence on heparin chain-length and salt concentration.

Conclusions:

• The procoagulant light chain of HK contributes to an anticoagulant effect by enhancing AT's inhibition of plasma kallikrein and factor XIa in a heparin-dependent manner.
• HK's function in modulating protease inhibition by AT suggests a dual role in hemostasis.
• The findings indicate a potential therapeutic application of HK in anticoagulant strategies.