Biophysical targeting of high-risk cerebral aneurysms

Abstract

Localized delivery of diagnostic/therapeutic agents to cerebral aneurysms, lesions in brain arteries, may offer a new treatment paradigm. Since aneurysm rupture leading to subarachnoid hemorrhage is a devastating medical emergency with high mortality, the ability to noninvasively diagnose high-risk aneurysms is of paramount importance. Moreover, treatment of unruptured aneurysms with invasive surgery or minimally invasive neurointerventional surgery poses relatively high risk and there is presently no medical treatment of aneurysms. Here, leveraging the endogenous biophysical properties of brain aneurysms, we develop particulate carriers designed to localize in aneurysm low-shear flows as well as to adhere to a diseased vessel wall, a known characteristic of high-risk aneurysms. We first show, in an in vitro model, flow guided targeting to aneurysms using micron-sized (2 μm) particles, that exhibited enhanced targeting (>7 folds) to the aneurysm cavity while smaller nanoparticles (200 nm) showed no preferable accumulation. We then functionalize the microparticles with glycoprotein VI (GPVI), the main platelet receptor for collagen under low-medium shear, and study their targeting in an in vitro reconstructed patient-specific aneurysm that contained a disrupted endothelium at the cavity. Results in this model showed that GPVI microparticles localize at the injured aneurysm an order of magnitude (>9 folds) more than control particles. Finally, effective targeting to aneurysm sites was also demonstrated in an in vivo rabbit aneurysm model with a disrupted endothelium. Altogether, the presented biophysical strategy for targeted delivery may offer new treatment opportunities for cerebral aneurysms.

Keywords: aneurysm targeting; cerebral aneurysm; glycoprotein VI (GPVI) coating; particle carriers; vascular models.

FIGURE 1

High‐risk cerebral aneurysms are associated with abnormal hemodynamics facilitating pathological biological processes. (a) Illustration of a saccular cerebral side aneurysm. (b) Illustration of disrupted endothelium with collagen fibers protruding through the gaps between the endothelial cells. (c) Computational fluid dynamic (CFD) simulation results showing ultra‐low wall shear stress (<1 dyne/cm²) on the surface of the cavity wall. (d) Illustration of healthy endothelium featuring an endothelial cell layer smooth muscle cells and extracellular matrix with collagen fibers. (e) Streamlines inside an aneurysm cavity showing circulatory flow. (f) Light sheet visualization of fluorescent particles circulation inside and aneurysm model

FIGURE 2

Localization of particles in aneurysm cavities. (a.1) Green fluorescent image of 2 μm carboxylated polystyrene particles in an aneurysm model showing enhanced deposition in cavity associated with low wall shear stress (WSS). (a.2) Green fluorescent image of the 200 nm particles in an aneurysm model showing enhanced deposition in parent artery and the impingement zone associated with high WSS. (a.3) WSS map on the aneurysm geometry showing high shear at the parent artery and low in the aneurysm. The impingement zone is marked by an arrow. (b) Bar graph of the LI for the 2 μm and the 200 nm particles showing that 2 μm had an LI of 0.86 ± 0.05 while 200 nm particles had an LI of 0.44 ± 0.06 (n = 3, p = 0.004). (a) Side view of the aneurysm cavity showing particles deposition. (a.1) 2 μm PLGA particle have localized predominantly at the bottom side of the cavity according to the direction of gravity. (c.2) 2 μm polystyrene particles coated the entire cavity with no evident bias due to gravity. (d) Deposition intensity (DI) distribution along the x axis showing that the PLGA 2‐μm particles have localized at the bottom of the cavity while the polystyrene particles distributed more evenly

FIGURE 3

Targeting an endothelium disturbed/injured patient‐specific aneurysm. (a) Illustration of GPVI functionalized particles adhering to exposed collagen. (b) Reconstruction of the CT scan of the internal carotid aneurysm obtained from AneuriskWeb repository (scan C0074). (c) Computational fluid dynamic (CFD) results on the patient‐specific geometry showing a low wall shear stress (WSS) recirculating flows within the aneurysm cavity. (d) Illustration of the injury model with endothelialized parent artery and exposed collagen in the cavity. (d.2) Fluorescent microscopy image of green stained ECs forming a disrupted endothelium. (d.3) Fluorescent microscopy image of green stained ECs forming a confluent layer. (e) Fluorescent microscopy image of the aneurysm model where the parent artery is covered with ECs (green) and GPVI‐coated 2‐μm polystyrene particles (red) localizing within the aneurysm cavity. (f) Fluorescent microscopy image of the aneurysm model where the parent artery is covered with ECs (green) and 2 μm polystyrene bovine serum albumin (BSA) particles (red) showing no preference to the cavity. (g) Bar graph of the ratio of particle concentrations between the aneurysm cavity and the parent artery. For GPVI‐coated particles, the ratio between the concentration within the aneurysm to the parent artery is 9.1 ± 2.2 while for the BSA‐coated particles the ratio is 1.2 ± 0.4 (n = 3, p = 0.017)

FIGURE 4

In vivo targeting of injured aneurysms. (a.1) 45‐μm thick DAPI (4′,6‐diamidino‐2‐phenylindole) stained slice taken from a rabbit aneurysm, 18 red fluorescent particles adhered to the inner surface of the aneurysm and marked by white arrows. (a.2) Movats' pentachromic staining of the adjacent slice showing that the aneurysm wall is almost devoid of endothelial cells with exposed collagen and fibrin to which the particle. (b.1) 45‐μm thick DAPI stained slice taken from a control vessel showing no adhered particles on the vessel wall. (b.2) Movats' pentachromic staining of the adjacent slice showing a healthy endothelial layer. (c) CT angiography image of an elastase induced aneurysm in rabbit. (d) LI distribution between the aneurysm and the control vessel (CV) showing a 4.9 ± 0.6 fold higher accumulation within the cavity (n = 3, p < 0.0008)