Characterization of Inflammatory and Fibrotic Aspects of Tissue Remodeling of Acellular Dermal Matrix in a Nonhuman Primate Model

Abstract

Human acellular dermal matrices (hADMs) are applied in various soft tissue reconstructive surgeries as scaffolds to support tissue remodeling and regeneration. To evaluate the clinical efficacy of hADM implants, it is integral that the hADM does not induce a host chronic inflammatory response leading to fibrotic encapsulation of the implant. In this study, we characterized the inflammatory and fibrosis-related tissue remodeling response of 2 commercial hADM products (SimpliDerm and AlloDerm RTU) in a nonhuman primate model using histology and gene expression profiling.

Methods: Eighteen African green monkeys with abdominal wall defects were applied to evaluate the performance of SimpliDerm and AlloDerm RTU implants (N = 3) at 2, 4, and 12-weeks post-implantation. Using histology and gene expression profiling, tissue responses such as implant integration, degradation, cell infiltration, immune response, neovascularization, and pro-fibrotic responses over time were evaluated.

Results: SimpliDerm showed a lower initial inflammatory response and slower implant degradation rate than AlloDerm RTU evidenced by histomorphological analysis. These factors led to a more anti-inflammatory and pro-remodeling microenvironment within SimpliDerm, demonstrated by lower TNFα levels and lower expression levels of pro-fibrotic markers, and promoted tissue repair and regeneration by 3-months post-implantation.

Conclusions: Overall, histology and gene expression profiling analyses shown in this study demonstrated an effective model for analyzing hADM performance in terms of host inflammatory and fibrotic response. Further studies are warranted to fully evaluate the utility of this novel hADM in the clinical setting and verify the prognosis of our pre-clinical analysis model.

Fig. 1.

Histomorphological evaluation of SimpliDerm and AlloDerm RTU implants at 4 and 12 weeks. Histology images of H&E, MT, and immunostaining against CD68 images of SimpliDerm (A–C, G, I) and AlloDerm RTU (D–F, H, J) implants harvested from the abdominal wall of NHP after 4 weeks and 12 weeks post-implantation. Darker contrast regions indicate hADM implants, whereas lighter regions represent host tissue. Arrows shown on CD68 images (C, F) indicate the presence of CD68-positive inflammatory cells. A 500 μm scale bar is shown.

Fig. 2.

Analysis of host inflammatory response in SimpliDerm and AlloDerm RTU implants. A, Histopathological evaluation score of general inflammation and inflammatory subtypes present in SimpliDerm and AlloDerm RTU implants at 4 weeks and 12 weeks. The score is based on the scoring matrix shown in Table 1. B, The amount of TNFα protein present in SimpliDerm and AlloDerm RTU implants for 2, 4, and 12-week time points as analyzed by ELISA. The error bar represents the calculated SD, with asterisk (*) representing P < 0.05 (actual P = 0.034).

Fig. 3.

Gene expression analysis related to collagen synthesis and vascularization. The relative gene expression levels (normalized to week 2 of each group) of key ECM components: Col3a1 (A) and Col1a1 (B), angiogenic factor VEGF (C), and blood vessel maturation marker Col4a1 (D) in SimpliDerm and AlloDerm RTU implants for 2, 4, and 12-week time points. Error bars represent the calculated SD, with single asterisk (*) representing P < 0.05 (actual P = 0.04) (B, C) and triple asterisks (***) representing P < 0.001 (A, D).

Fig. 4.

Gene expression analysis related to fibrosis and matrix remodeling. The relative expression levels (normalized to week 2 of each group) of fibrosis-associated genes, including (A) TGFβ1, (B) αSMA, (C) CTGF, and (D) LH2b in SimpliDerm and AlloDerm RTU implants for 2, 4, and 12-week time points. Error bars represent the calculated SD, with single asterisk (*) representing P < 0.05 and double asterisks (**) representing P < 0.01. Actual P are (A) 0.01, (B) 0.006, (C) 0.049, and (D) 0.027.