title: The biochemical and biophysical factors causing von Willebrand factor degradation during mechanical circulatory support
Creators: name: Smith, Amanda G
Publisher: name: Griffith University
Year: 2024
Subjects: subject: von Willebrand factor (VWF) degradation
subject: mechanical circulatory support
subject: calcium

description: Mechanical circulatory support (MCS) devices are crucial in managing heart and blood vessel disorders, which are the leading cause of death globally. MCS has become an integral component in acute and chronic care, despite their association with blood trauma and peri-operative bleeding. Given these devices are integrated into human vasculature, the efficacy of mechanical circulation depends on biological compatibility and minimising blood damage. And although many advancements have been made, the use of MCS continues to cause secondary bleeding complications such as acquired von Willebrand syndrome (AVWS), a serious bleeding disorder caused by degradation of von Willebrand factor (VWF). VWF is a large multimeric protein that exists as 500-20000 kDa in circulation, with the high molecular weight (HMW) form being most functional. When degraded into smaller multimers, VWF cannot facilitate platelet adhesion to collagen at vascular injury sites, leading to increased bleeding. Despite the strong correlation between AVWS, MCS, and bleeding complications, there are gaps in the literature regarding the biochemical mechanisms of VWF degradation; specifically, the role of calcium in maintaining its structural integrity during MCS. Addressing these gaps is essential for developing strategies to mitigate bleeding risk. The current gaps in knowledge may be attributed to the many challenges in quantifying VWF degradation. Due to the large size and complexity of the protein, traditional methods for protein quantification via Western blotting cannot be used. Modified Western blotting methods do exist; however, these methods are complex and often not reproducible. Additionally, the method lacks standardisation, and thus is often not comparable between labs. Therefore, the primary objectives of the present dissertation were two-fold: First, to develop an enhanced Western blot technique for VWF multimer analysis to overcome the limitations of time-intensiveness and inconsistent quantitative outcomes; and to advance the understanding of biochemically-dependent VWF multimer degradation during MCS. Specifically, to quantify the effect of calcium on VWF structure and function under mechanical stress, with an aim to develop effective strategies to mitigate bleeding complications associated with MCS. The present dissertation serves to enhance the current understanding of AVWS caused by MCS and will allow future research to have an improved approach to quantifying VWF degradation. The present thesis created a more time efficient and robust method for quantifying VWF using common lab materials, facilitating international and inter-laboratory comparisons. The present thesis also demonstrated that plasma calcium concentration significantly preserves HMW VWF from degradation independent of ADAMTS13 activity. Additionally, calcium may facilitate more complex VWF-self association to collagen and clot formation at vascular injury sites, thus opening new research questions around treatment of MCS patients. The findings from the collective studies of this thesis provide new insights into the biochemical mechanisms underlying VWF degradation in MCS patients and support the hypothesis that monitoring and possibly adjusting plasma calcium levels could mitigate bleeding risks associated with MCS use. These findings regarding calcium also have implications for the design and testing of MCS devices, especially when considering anticoagulant choice and the role of calcium in VWF function. And more importantly, improving knowledge on AVWS to reduce bleeding complications caused by MCS.