Title:
Measurement and Prevention of Occlusive Arterial Thrombosis
Measurement and Prevention of Occlusive Arterial Thrombosis
Author(s)
Bresette, Christopher
Advisor(s)
Ku, David N.
Ethier, C. Ross
Ethier, C. Ross
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Abstract
Arterial thrombosis is the process of forming a blood clot in an artery and is a leading cause of ischemic events such as heart attacks and strokes. These ischemic events account for 20% of all deaths in the United States. In order to reduce the mortality from ischemic events we need better methods of predicting when arterial thrombi will form, new drugs that can prevent arterial thrombosis without increasing the risk of bleeding, and basic research into how large occlusive clots are structured and formed.
There is a large need for a device that can quantify a patient’s risk of arterial thrombosis based on a blood samples. However, previously developed assays fail to include the critical variables required for arterial thrombosis and are unable to reliably aid clinicians in predicting future events or making patient-specific changes in treatment for secondary prevention. A point-of-care (POC) test, called Thrombocheck, that recreates arterial thrombosis was built by incorporating the 3 key features of arterial thrombosis: high shear, a thrombogenic surface, and platelets and vWF. In addition to incorporating the 3 key features of thrombosis, the Thrombocheck has the advantage that it does not require chemical agonists to induce clotting and forms large, stable thrombi. We show that the Thrombocheck is a functional test for high shear clot formation, is sensitive to anti-platelet use and provides a unique endpoint for arterial thrombosis.
Current anti-thrombotic medications used to treat patients at high risk of forming arterial thrombi reduce the likelihood of forming arterial thrombi but also cause an increase in bleeding-related mortality. While pharmaceutical therapies for arterial thrombosis have historically acted through preventing platelet activation, it has been hypothesized that targeting the shear-sensitive von Willebrand Factor (vWF) could allow for prevention of arterial thrombosis without adverse effects on coagulation and low-shear hemostasis. N-acetylcysteine (NAC) is an existing drug currently used for treating acetaminophen overdose and cystic fibrosis which also cleaves vWF. By breaking the disulfide bonds that form the backbone of vWF, long vWF multimers are chopped into smaller, less active multimers. It has been used to shorten vWF, reduce platelet binding in a population with abnormally long vWF and lyse platelet aggregates. We show that in a healthy population N-acetylcysteine (NAC) prevents arterial thrombosis in a dose dependent manner, increasing occlusion times at concentrations of 3–5 mM and completely preventing platelet aggregation at concentrations at or above 10 mM. An in vivo murine model shows that the effect of NAC on arterial thrombosis is lasting, cumulative and does not increase bleeding time. NAC can therefore be repurposed as an anti-thrombotic, preventing arterial thrombosis without affecting bleeding.
Additional research into the basic science of platelet aggregation directs future studies attempting to predict and prevent thrombosis. While many studies have focused on single platelet attachments or small microfluidic aggregates, it is critical to understand how the aggregation of billions of individual platelets leads to the creation of a large, occlusive clot. These clots have a unique structure compared to coagulation clots at both the small aggregate level (1-10 um) and at the whole clot level (100-1,000 um). At the aggregate level arterial thrombi are extremely porous, while at the whole clot level they have increased mechanical strength and have striations which indicate the presence of a large-scale architecture (~100 um). In this work, large-scale clot architecture was characterized in multiple experimental systems and shown to appear as periodic clot “fingers" that grow perpendicular to the direction of flow. At occlusion, these distinct structures merge to form a single clot. A parsimonious model comprised of 4 platelet behaviors was able to recreate this large-scale architecture and to predict how clot structure changes based on initial conditions. By defining large-scale clot architecture and modeling its formation, we have a better understanding of the processes leading to thrombosis formation.
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Date Issued
2023-05-19
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Resource Type
Text
Resource Subtype
Dissertation