Advancing the 3Rs in Thrombosis Research: Blood-Vessel-on-a-Chip
By Kirk A. Taylor, Ph.D., and Alice Y. Pollitt, Ph.D.
Forty percent of cardiovascular-related deaths are attributed to inappropriate platelet activation and thrombotic complications. Platelets are therefore widely studied to understand their roles in disease and how they may be targeted to develop novel therapeutics. To this end, researchers routinely use in vivo studies to investigate platelets from animal models as a way to recapitulate in vitro findings and explore the impact of targeted gene deletions/mutations. However, these approaches have limitations, and advancement of organ-on-a-chip technology has potential to usher in personalized medicine approaches, while replacing, reducing, and refining animal models in thrombosis research.
Given their importance in human disease, researchers often study platelets and their vessel wall interactions in order to develop new approaches to improve patient care. However, as platelets lack a cell nucleus, standard molecular biology methods, such as gene silencing, cannot be applied to in vitro investigations. This limitation has resulted in the reliance of genetically modified animal models, particularly mice, in platelet research. Unfortunately, findings generated using mouse platelets do not always translate well to human platelets, partly due to differences in physiology and gene expression. This can lead to frustration as promising drug targets identified in mice often fail in human clinical trials due to these differences.
Advances in technology, which can model human tissue, could overcome these limitations in platelet studies and the current challenges in thrombosis and hemostasis research by providing alternatives to animal models. Using the principles of the 3Rs – Replacement, Reduction and Refinement –researchers are developing exciting new approaches to model disease and facilitate drug development without the need for animals, thus improving animal welfare. One of these novel methodologies is the organ-on-a-chip.
The organ-on-a-chip is an exciting new tool for human biology research modelling both healthy and diseased scenarios and everything from beating hearts to filtering kidneys. Thrombosis and hemostasis researchers have taken the organ-on-a-chip concept and created models of disease such as pulmonary hypertension and arterial thrombosis. This is how the blood-vessel-on-a-chip was born.
Blood-vessels-on-a-chip not only open the possibility to study platelet-vessel wall interactions in real time, but they also present opportunities to study different vessel architectures. Traditional laminar flow assays are great at modelling specific shear rates, but this oversimplifies the conditions under which thrombi form.
Therefore, one application of blood-vessels-on-a-chip is to answer how platelets respond to shear rates experienced at the aortic arch compared to the microvasculature. Advances in 3D printing and cell culture techniques now enable researchers to generate bespoke vessel geometries, bringing us closer to modelling stenosed and bifurcated vessels. Artificial blood vessels can also be generated using primary endothelial cells that are either commercially available or derived from patient blood samples (endothelial colony-forming cells). Utilizing patient cells in this manner could bring us a step closer to personalized medicine allowing us to better understand which therapies work for those with aspirin/clopidogrel resistance or platelet-related disorders.
Vessel-on-a-chip devices may pave a way to modelling a patient’s response to therapy. In addition, this technology can be combined with in vitro generated platelets, which can be genetically manipulated at the level of the platelet precursor, or with platelets directly modified from volunteers using new developments in platelet manipulation. Importantly, it will ensure that discoveries are applicable and translatable to humans.
Alice Pollitt holds funding from the NC3Rs (Grant number NC/S001441/1)