Biocompatibility of Intensified Decellularized Equine Carotid Arteries in a Rat Subcutaneous Implantation Model and in a Human <i>In Vitro</i> Model

Abstract

Limited biocompatibility of decellularized scaffolds is an ongoing challenge in tissue engineering. We recently demonstrated that intensified detergent-based decellularization of equine carotid artery (dEAC_intens) removed residual cellular molecules from the scaffold more efficiently than a conventional decellularization (dEAC_con), although this approach did not eliminate its immunogenicity entirely. CCN1 has been shown to improve biocompatibility of dEAC_con in a sheep model. In this study, we tested the biocompatibility of dEAC_intens and dEAC_con with or without CCN1 coating after subcutaneous implantation in rats for up to 12 weeks. Explants were assessed by conventional histopathology and immunostaining for infiltrating M2 macrophages. Moreover, human macrophages derived from monocytes (MDM) or THP-1 cells (THP-derived macrophages [TDM]) were seeded onto dEAC_con and dEAC_intens, and activation was assessed either by cytokine expression or matrix metalloprotease 2 and 7 staining. dEAC_intens showed a significantly reduced inflammatory infiltration (52%; p < 0.0001), as well as an earlier and denser neovascularization (1.4-fold, p < 0.0001) independent of CCN1 coating, which, however, reduced fibrosis exclusively with dEAC_intens (26-53%; p < 0.05). Human MDM seeded for 48 h onto dEAC_intens showed higher transcript levels for anti-inflammatory IL-10 (2.3-fold), proinflammatory TNFα (2.2-fold), and macrophage/monocyte recruiting MIP1α (3.5-fold; all p < 0.05) and MCP (2.7-fold; p < 0.01), whereas 1.92-fold more TDM on dEAC_intens showed staining for MMP2 (p > 0.001). Thus, although being advantageous in regard to fibrosis, CCN1 coating of dEAC_intens does not appear to be necessary for further improving dEAC_intens excellent biocompatibility in rats. In humans, the unspecific cellular immune response toward dEAC_intens seemed to be more complex, but generally comparable to the mild acute inflammatory tissue reaction with high remodeling activity as observed after rat subcutaneous implantation.