Parent artery-initiated and stent-mediated neointima formation in a rat saccular side wall model

Abstract

Background: Unlike clipping that forms an immediate barrier of blood flow into intracranial aneurysms, endovascular treatments rely on thrombus organization and neointima formation. Therefore, a continuous endothelial cell layer is crucial to prevent blood flow in the former aneurysm. This study investigates the origin of endothelial cells in the neointima of endovascular treated aneurysms, specifically whether cells from the parent artery play a role in neointima formation.

Methods: In male rats, decellularized and vital side wall aneurysms were treated by coil (n=16) or stent embolization (n=15). The cell tracer CM-Dil dye was injected into the clamped aorta before aneurysm suture to mark initial endothelial cells in the parent artery and enable tracking of their proliferation during follow-up. Aneurysms were analyzed for growth, thrombus formation, and recurrence. Histological evaluation followed with cell counts for specific regions-of-interest.

Results: During follow-up, none of the 31 aneurysms ruptured. Macroscopic residual perfusion was observed in 12/16 rats after coiling and in 1/15 after stenting. Amounts of CM-Dil +cells in coiled versus stented decellularized aneurysms significantly decreased in the thrombus on day 7 (p=0.01) and neointima on day 21 (p=0.04). For vital aneurysms, the number of CM-Dil +cells in the neointima on day 21 showed no significant difference.

Conclusions: Healing patterns were worse in coil-treated than stent-treated aneurysms. Cell migration forming a neointima seemed mainly dependent on the adjacent vessel in decellularized aneurysms, but appeared buoyed by recruitment from aneurysm wall cells in vital aneurysms. Therefore, a cell-rich parent artery might be crucial.

Keywords: aneurysm; coil; intervention; stent; vessel wall.

Figure 1

Flowchart of the study design. Of a total of 38 rats, 31 were included for final analysis and seven were excluded (three in the pilot study and four early dropouts).

Figure 2

Left panel shows cell count comparison between different regions of interest (ROI) in coil- and stent-treated decellularized aneurysms. Graph depicts the cumulative relative cell counts for CM-Dil +cells in decellularized aneurysms sutured on the abdominal part of the aorta, either coil- or stent-treated. Treatments were compared for coiled and stented groups in decellularized aneurysms on days 7 and 21. Significant differences in the proportion of CM-Dil +cells in the neointima for day 21 and thrombus for day 7 (p<0.05) were observed. Right panel shows cell count comparison between different ROIs in coil- and stent-treated vital aneurysms. Graph depicts the cumulative relative cell counts for CM-Dil +cells in vital aneurysms sutured on the abdominal part of the aorta, either coil- or stent-treated. Treatments were compared for coiled and stented groups in vital aneurysms on days 7 and 21. Significant differences in the proportion of CM-Dil +cells in the parent artery for day 7 (p<0.05) were observed.

Figure 3

Illustrative panel of CM-Dil +cell distribution in a decellularized aneurysm with coil- and stent-treatment postoperatively. Panel A, coil day 7/stent day 7. Left-side depicts a coil-treated aneurysm, immunostaining for neointima (A) and parent artery (B) performed. Right side shows same setting performed for stenting 7 days postoperatively. CM-Dil +cells are found in the neointima more pronounced for stent-treatment (scale bar 100 μm left, 200 μm right). Middle, image overview of monoclonal anti-α muscle actin (a-SMA) positive cells (twofold magnification) with stent-treatment 7 days postoperatively; $ shows fixation artifact. In panel B (coil day 21/stent day 21), immunostaining for neointima (A) and parent artery (B) demonstrates decreased CM-Dil +cells in coil-treated compared with stent-treated aneurysms (p<0.05). (A) Magnified area of the neointima. CM-Dil +cells are found in the neointima (scale bar 100 μm left, 100 μm right). (B) As well, CM-Dil uptake is registrated in the parent artery. Middle, image overview of monoclonal anti-α muscle actin (a-SMA) positive cells in an aneurysm with a twofold magnification after coil treatment 21 days postoperatively is shown. *Lumen of the parent artery; ^#coil artifact.