1 Department of Internal Medicine, Yale University School of Medicine , New Haven, Connecticut.
2 Center for Regenerative Medicine, The Research Institute at Nationwide Children's Hospital , Columbus, Ohio.
Tissue Eng Part C Methods. 2018 Aug;24(8):465-473. doi: 10.1089/ten.TEC.2018.0144. Epub 2018 Jul 31.
Tissue-engineered vascular grafts (TEVGs) have demonstrated potential for treating congenital heart disease (CHD); however, quantitative imaging for tracking functional and structural remodeling of TEVGs has not been applied. Therefore, we evaluated the potential of magnetic resonance (MR) imaging for assessing TEVG wall shear stress (WSS) and wall thickness in a large animal model.
Cell-seeded (n = 3) or unseeded (n = 3) TEVGs were implanted as inferior vena cava interposition grafts in juvenile lambs. Six months following implantation, two-dimensional phase-contrast MR imaging was performed at 3 slice locations (proximal, middle, and distal) to assess normalized WSS (i.e., WSS-to-cross sectional area). T2-weighted MR imaging was performed to assess TEVG wall thickness. Histology was qualitatively assessed, whereas immunohistochemistry was semiquantitatively assessed for smooth muscle cells (αSMA), macrophage lineage cells (CD11b), and matrix metalloproteinase activity (MMP-2 and MMP-9). Picrosirius Red staining was performed to quantify collagen content.
TEVG wall thickness was significantly higher for proximal, middle, and distal slices in unseeded versus cell-seeded grafts. Significantly higher WSS values existed for proximal versus distal slice locations for cell-seeded TEVGs, whereas no differences in WSS existed between slices for unseeded TEVGs. Additionally, no differences in WSS existed between cell-seeded and unseeded groups. Both groups demonstrated elastin formation, without vascular calcification. Unseeded TEVGs possessed greater content of smooth muscle cells when compared with cell-seeded TEVGs. No differences in macrophage, MMP activity, or collagen content existed between groups.
MR imaging allows for in vivo assessment of functional and anatomical characteristics of TEVGs and may provide a nonionizing approach that is clinically translatable to children undergoing treatment for CHD.
组织工程血管移植物（TEVG）已被证明具有治疗先天性心脏病（CHD）的潜力；然而，尚未应用定量成像技术来跟踪 TEVG 的功能和结构重塑。因此，我们评估了磁共振（MR）成像在大型动物模型中评估 TEVG 壁切应力（WSS）和壁厚的潜力。
将细胞接种（n=3）或未接种（n=3）的 TEVG 作为下腔静脉间置移植物植入幼年羊体内。植入后 6 个月，在 3 个切片位置（近端、中部和远端）进行二维相位对比 MR 成像，以评估归一化壁切应力（即 WSS 与横截面积的比值）。进行 T2 加权 MR 成像以评估 TEVG 壁厚。对组织学进行定性评估，对平滑肌细胞（αSMA）、巨噬细胞谱系细胞（CD11b）和基质金属蛋白酶活性（MMP-2 和 MMP-9）进行半定量免疫组织化学评估。进行苦味酸天狼星红染色以定量评估胶原含量。
未接种细胞的 TEVG 近端、中部和远端切片的壁厚度明显高于接种细胞的 TEVG。与远端切片相比，接种细胞的 TEVG 近端切片的 WSS 值明显更高，而未接种细胞的 TEVG 各切片之间的 WSS 无差异。此外，接种细胞和未接种细胞的 TEVG 之间的 WSS 无差异。两组均形成了弹性蛋白，没有血管钙化。与接种细胞的 TEVG 相比，未接种细胞的 TEVG 平滑肌细胞含量更高。各组之间的巨噬细胞、MMP 活性或胶原含量无差异。
MR 成像允许对 TEVG 的功能和解剖特征进行体内评估，并且可能提供一种非电离方法，可在临床上转化为接受 CHD 治疗的儿童。
