Towards Biomicrofluidic Models of Endothelial Dysfunction for Nanotherapy Screening

Atherosclerosis is an inflammation-based disorder of the arteries and one of the leading causes of mortality and morbidity worldwide. The initial hallmark of atherosclerosis is dysfunctional endothelium (Dys-En), which refers to maladaptive changes and abnormal functionalities of the vasculature endothelium.

Dysfunctional endothelium results in compromised integrity and loss of cell-cell junctions, thus enhancing the permeability across the endothelium. Furthermore, cellular adhesion molecules (e.g., VCAM-1) show overexpression on dysfunctional endothelium of atherosclerotic lesions. The enhanced permeability and the overexpression of VCAM-1 can be considered as promising strategies to target nanoparticles (NPs) to dysfunctional endothelium, and thus to atherosclerotic lesions.

The application of smart nanoparticles to target atherosclerosis is a relatively new area and is still in its infancy. In this study, we developed different biomimetic in vitro models of dysfunctional endothelium and then recruited them for nanoparticle screenings in order to understand any structure-activity-relationship behavior of nanoparticles and their potential to target dysfunctional endothelium, based on the enhanced permeability and VCAM-1 binding.

For this purpose, we first investigated the effect of a range of atherosclerotic-relevant inflammatory mediators (i.e., TNF-α, IL1-β, thrombin, histamine, oxLDL, IL-6, and c-reactive protein) on endothelial cells in order to develop the most optimal in vitro models of Dys-En. Based on these studies, TNFα, IL1-β, and thrombin were the most potent inducers of dysfunctional endothelium.

At the next step, we established a library of nanoparticles with different properties, conjugated with various VCAM-1 targeting peptides. Then, we studied the effect of NP properties on their permeability and binding across the developed models of dysfunctional endothelium. These investigations revealed that NP size is a more dominant driver of NP permeability and binding to dysfunctional endothelium, compared to other NP properties.

Furthermore, our finding suggested that smaller nanoparticles (in the range of 30-60 nm) are more optimal candidates for targeting dysfunctional endothelium. These results, which emphasizes the crucial role of NP size in targeting atherosclerotic lesions, can shed more light on the design of more effective nanoparticles for further in vivo and clinical studies.

These investigations were first carried out using static biomimetic models of Dys-En. Subsequently, a biomicrofluidic model of dysfunctional endothelium was developed on a microchip and utilized for the nanoparticle screenings. The developed biomicrofluidic Dys-En model (Dys-En-on-a-chip) not only could mimic the pathophysiological shear condition, but also showed loss of VE-cadherin at cellular borders, change of cytoskeleton organization to form actin stress fibers, and overexpression of VCAM-1, which are all indicators of a successful dysfunctional endothelium model.

The recruitment of Dys-En-on-a-chip for the screening of VCAM-1 targeted nanoparticles confirmed that NP size governs NP permeability and binding. Additionally, the developed Dys-En-on-a-chip was used to study the restorative effect of annexin A1, an anti-inflammatory mediator, on dysfunctional endothelium.

Our findings revealed that this inflammation resolving mediator could inhibit the loss of junctional proteins on Dys-En models; hence it can be used as a potent therapeutic agent for restoration and normalization of dysfunctional endothelium in atherosclerosis treatment.