Function and structure of pressurized and perfused porcine carotid arteries: effects of in vitro balloon angioplasty

Elucidating the role of graft compliance mismatch on intimal hyperplasia using an ex vivo organ culture model

There is a growing clinical need to address high failure rates of small diameter (<6 mm) synthetic vascular grafts. Although there is a strong empirical correlation between low patency rates and low compliance of synthetic grafts, the mechanism by which compliance mismatch leads to intimal hyperplasia is poorly understood. To elucidate this relationship, synthetic vascular grafts were fabricated that varied compliance independent of other graft variables. A computational model was then used to estimate changes in fluid flow and wall shear stress as a function of graft compliance. The effect of compliance on arterial remodeling in an ex vivo organ culture model was then examined to identify early markers of intimal hyperplasia. The computational model prediction of low wall shear stress of low compliance grafts and clinical control correlated well with alterations in arterial smooth muscle cell marker, extracellular matrix, and inflammatory marker staining patterns at the distal anastomoses. Conversely, high compliance grafts displayed minimal changes in fluid flow and arterial remodeling, similar to the sham control. Overall, this work supports the intrinsic link between compliance mismatch and intimal hyperplasia and highlights the utility of this ex vivo organ culture model for rapid screening of small diameter vascular grafts. STATEMENT OF SIGNIFICANCE: We present an ex vivo organ culture model as a means to screen vascular grafts for early markers of intimal hyperplasia, a leading cause of small diameter vascular graft failure. Furthermore, a computational model was used to predict the effect of graft compliance on wall shear stress and then correlate these values to changes in arterial remodeling in the organ culture model. Combined, the ex vivo bioreactor system and computational model provide insight into the mechanistic relationship between graft-arterial compliance mismatch and the onset of intimal hyperplasia.

Pathological Safety Assessment in Preclinical Neurothrombectomy Studies

The design, production, and preclinical testing of neurothrombectomy devices is in a burgeoning phase as the demand escalates for safe and reliable treatment options following neurovascular stroke. Currently, there is a paucity of published data describing the development of iatrogenic vascular lesions occurring secondary to neurothrombectomy procedures. In an effort to test new devices, demonstrate device safety, satisfy regulatory requirements, and develop an understanding of the potential for associated vascular pathology, investigators are establishing appropriate methodology in suitable animal models. Significant challenges exist in identifying a single animal species that can be consistently utilized in all phases of device development. These aforementioned challenges are underscored by the intricacies of neurovascular pathology, thrombovascular interactions, and vascular responses to injury.

Transgene delivery to endothelial cultures derived from porcine carotid artery ex vivo

Carotid artery disease is a widespread cause of morbidity and mortality. Porcine models of vascular disease are well established in vivo, but existing endothelial systems in vitro (e.g. human umbilical vein endothelial cells, rat aortic endothelial cultures) poorly reflect carotid endothelium. A reliable in vitro assay would improve design of in vivo experiments and allow reduction and refinement of animal use. This study aimed (1) to develop ex vivo endothelial cultures from porcine carotid and (2) to test whether these were suitable for lentivector-mediated transgene delivery. Surplus carotid arteries were harvested from young adult female Large White pigs within 10 min post-mortem. Small sectors of carotid artery wall (approximately 4 mm×4 mm squares) were immobilised in a stable gel matrix. Cultures were exposed to HIV-derived lentivector (LV) encoding a reporter transgene or the equivalent integration-deficient vector (IDLV). After 7-14 days in vitro, cultures were fixed and labelled histochemically. Thread-like multicellular outgrowths were observed that were positive for endothelial cell markers (CD31, VEGFR2, von Willebrand factor). A minority of cells co-labelled for smooth muscle markers. Sensitivity to cytotoxic agents (paclitaxel, cycloheximide, staurosporine) was comparable to that in cell cultures, indicating that the gel matrix permits diffusive access of small pharmacological molecules. Transgene-expressing cells were more abundant following exposure to LV than IDLV (4.7, 0.1% of cells, respectively). In conclusion, ex vivo adult porcine carotid artery produced endothelial cell outgrowths that were effectively transduced by LV. This system will facilitate translation of novel therapies to clinical trials, with reduction and refinement of in vivo experiments.

Quantitative optical coherence tomography of arterial wall components

Optical coherence tomography (OCT) can be used to visualize the arterial wall and atherosclerotic plaques with high resolution. In this study, we verified the application of OCT to the quantitative analysis of plaque structural dimensions and optical attenuation coefficients of the components. We assessed the effect of balloon dilation on the OCT signal from the medial layer of porcine carotid artery ex vivo. Imaging of human autopsy samples was performed from the luminal side with a high (3.5 microm axial and 7 microm lateral) resolution OCT system (approximately 800 nm) or a regular (15-20 microm axial and 20 microm lateral resolution) OCT system (approximately 1,300 nm). For each sample, dimensions were measured by histomorphometry and OCT, and the optical attenuation was measured. In a tissue culture set-up, porcine carotid arteries were dilated and the attenuation coefficients of the dilated segments were compared to a control segment for 4 h. Quantitative analysis showed a strong and significant correlation between OCT and histology cap thickness measurements for both OCT systems. For both systems, the measured attenuation coefficients for diffuse intimal thickening and lipid-rich regions differed significantly from that of calcified tissue. Balloon dilation induced a time-dependent increase in the attenuation coefficient, which may be attributed to the induction of apoptosis. In conclusion both the high and regular resolution OCT systems can image the atherosclerotic plaques precisely. Quantitative analysis of the OCT signals allowed in situ determination of the intrinsic optical attenuation coefficient for atherosclerotic tissue components within regions of interest, which can help to discriminate between plaque and arterial wall components.