Fibrinolytic PLGA nanoparticles for slow clot lysis within abdominal aortic aneurysms attenuate proteolytic loss of vascular elastic matrix

Abstract

Abdominal aortic aneurysms (AAAs) involve chronic overexpression of proteases in the aortic wall that result in disruption of elastic fibers and consequent loss of vessel elasticity. Nearly 75% of AAAs contain flow-obstructing, fibrin-rich intraluminal thrombi (ILT), which act as a) a bioinert shield, protecting the underlying AAA wall from high hemodynamic stresses, and b) a reservoir of inflammatory cells and proteases that cause matrix breakdown. For these reasons, restoring flow through the aorta lumen and facilitating transmural diffusion of therapeutics from circulation to the AAA wall must be achieved by slow thrombolysis of the ILT to render it porous without rapid breakdown. Intravenously dosed tissue plasminogen activator (tPA) has been shown to rapidly lyse ILTs in acute stroke and myocardial infarctions. For future use in opening up AAA segments, in this study, we investigated the ability of tPA released from poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) to slowly lyse fibrin clots without inducing proteolytic injury and matrix synthesis-inhibitory effects on cultured rat aneurysmal smooth muscle cells (EaRASMCs). Fibrin clot lysis time was greatly extended over that in presence of exogenous tPA. Surface functionalization of NPs with a cationic amphiphile allowed them to bind to anionic fibrin clot, release tPA at a slower rate and to lyse the clot as a front proceeding outwards in unlike the more rapid and homogenous lysis that occurred due to anionic PLGA NPs. Elastic matrix content was decreased in EaRASMC cultures exposed to byproducts of clot lysis with exogenous tPA, but not tPA-NPs, and was likely due to increased proteolytic activity (MMPs, plasmin) in EaRASMC cultures exposed to exogenous tPA-lysed clots. Our results suggest that gradual ILT lysis via slow release of tPA from NPs will be likely beneficial over exogenous tPA delivery in preserving elastic matrix content and attenuating matrilysis in the adjoining AAA wall, in vivo, while rendering the ILT porous to facilitate transmural delivery of endoluminally delivered AAA therapeutics.

Targeted Delivery of Bioactive Molecules for Vascular Intervention and Tissue Engineering

“…Combining these approaches with other molecules such as tissue plasminogen activator, which allows for controlled fibrinolysis of clots, may enhance their effectiveness. Nanoparticle-mediated tissue plasminogen activator delivery has shown promise in vitro for this purpose ( Sivaraman et al, 2016 ). Ultimately, a more comprehensive approach where nanoparticles can first carefully dissolve clots in the aneurysm, and then deliver MMP inhibitors to stabilize the aneurysm, may be necessary.…”

Applications of Extracellular Vesicles in Abdominal Aortic Aneurysm

“…Based on these factors, it's important to steadily dissolve ILT to reduce its proteolytic effect while stabilizing its mechanical shielding structure to protect AAA wall. Sivaraman et al ( 105 ) encapsulated tissue plasminogen activator inside PLGA-nanoparticles and found the slow release of tissue plasminogen activator can gradually lyse ILT without damaging its general structure. Also, the porous structure of ILT facilitates the penetration of therapeutic drugs from circulation toward AAA wall.…”

Nanoparticles as Carriers in Medical Applications: A Review Focusing on the Preparation and Use of Nanoparticles in Tissue Regeneration

“…Stabilizer: Compound that interacts with the growing NPs to determine its size, usually limiting it. Stabilizers can help by forming dendritic or micellar arrangements [75][76][77].…”

“…Apart from the aqueous medium, polymers can be suspended in alcohols or apolar solvents such as chloroform, benzene, etc. [75,78].…”