Abstract
Introduction
Von Willebrand factor (vWF) changes conformation from globular to fibrillar in the range of shear rates above 5000 s-1. High shear rates, observed in severe aortic stenosis, create conditions for activation of vWF, which opens up access for platelets and coagulation factors to the previously hidden domains of the molecule. At the same time, vWF undergoes increased degradation by metalloproteinase ADAMTS13. Proteolytic cleavage of vWF leads to deficiency of hemostatically active high molecular weight multimers (HMWM) of vWF, while its mass concentration remains unaltered. This results in the development of acquired von Willebrand disease type 2A (vWD) and concomitant gastrointestinal bleeding. The combination of acquired vWD 2A and gastrointestinal bleeding, developed due to severe aortic stenosis, is called Heyde's syndrome. The correlation of shear stress activation of vWF and gastrointestinal bleeding in patients with Heyde's syndrome remains poorly studied.
The aim of the study was to measure vWF-mediated platelet adhesion to fibrinogen-coated surfaces under shear rates higher than 5000 s-1 in whole blood samples of healthy volunteers and patients with Heyde's syndrome.
Methods
A microfluidic system simulating blood flow in vessels was used to assess platelet adhesion. Platelet adhesion was measured by an increase in the intensity of laser radiation scattered from a fibrinogen-coated surface during a 15 minutes circulation of whole blood samples through a flow chamber under shear rates higher than 5000 s-1. Platelets in whole blood samples were activated with 5 μM ADP prior to measurement. The study included 5 patients with Heyde's syndrome 55–80 years old. The control group included 6 healthy volunteers 25–55 years old. vWF-mediated platelet adhesion was detected by blocking platelet-vWF binding with anti-GPIb monoclonal antibody (mAb). Fibrinogen-mediated platelet adhesion was detected by blocking platelet GPIIb/IIIa receptors with mAb.
Result
The inhibition of GPIb vWF-receptor reduced platelet adhesion by 7.6±3.5% (p<0.05) in patients with Heyde's syndrome, and by 16.5±3.3% (p<0.05) in healthy volunteers. The inhibition of GPIIb/IIIa fibrinogen receptor reduced platelet adhesion by 96±7% (p<0.05) in patients with Heyde's syndrome, and by 80.2±6.6% (p<0.05) in healthy volunteers.
Conclusion
Significantly reduced contribution of vWF to platelet adhesion under shear rates higher than 5000 s-1 may indicate a decrease in hemostatically active HMWM of vWF. Shear stress activation of vWF in the range of high shear rates and its subsequent inactivation by ADAMTS13 may lead to functional vWF deficiency and the development of gastrointestinal bleeding in Heyde's syndrome.
Funding Acknowledgement
Type of funding source: Foundation. Main funding source(s): The Russian Science Foundation
Shear stress induced activation of von Willebrand factor may predispose to gastrointestinal bleeding in syndrome of Heyde
