Perigraft adventitia and intima remodeling after synthetic patch implantation in sheep carotid artery: Role of apoptosis and proliferation

Background: The mechanisms of neointima formation after synthetic vascular grafting are not clear. The aim of this study was to investigate the intima and perigraft adventitia remodeling process in terms of cell apoptosis versus proliferation after synthetic patch implantation. Methods: Female Merino sheep were randomized equally into two groups and underwent implantion with a patch of gelatin sealed Dacron graft into the left common carotid artery. At 1 and 6 months, grafted vessels were harvested, processed, and assessed. Intimal area and lumen sizes were measured with histologic assessment of eight segments from each animal assisted with image analysis. Immunohistochemical labeling of α-actin and D33 desmin was performed on tissue sections of perigraft adventitia, graft matrix, and intima. Cell proliferation and cell phenotype were determined with double immunohistochemical staining with anti-proliferating cell nuclear antigen and anti-α-actin or antimacrophage antibodies (HAM 56) in perigraft adventitia, graft matrix, and intima. Apoptosis was detected with in situ terminal deoxynucleiotidyl transferase-mediated 2′-deoxyuridine 5′-triphosphate-fluorescence nick end labeling (TUNEL) in perigraft adventitia, graft matrix, and intima. Results: The carotid artery lumen size at 6 months was significantly larger than at 1 month ( P ≤ .05). The intimal area was significantly reduced at 6 months compared with 1 month ( P < .05). At 1 month and 6 months, perigraft adventitia, graft matrix, and intima showed positive α-actin expression but negative desmin staining. In the anastomotic area, a small number of intimal cells suggested their muscle origin (expression α-actin and desmin). The number of proliferating cells in the intima was significantly greater at 1 month than at 6 months ( P = .01). TUNEL-positive cells were significantly greater in the intima at 1 month than at 6 months ( P < .05), whereas TUNEL-positive cells were significantly greater at 6 months in the perigraft adventitia ( P < .05). HAM 56-positive cells in the intima at 1 month were significantly greater compared with 6 months ( P < .05), whereas in graft and perigraft regions, no significant difference was seen between 1 month and 6 months. Conclusion: The cell proliferation and cell phenotype change in intima and perigraft adventitia are associated with thickening of perigraft adventitia and intima at 1 month. The balance between cell proliferation and apoptosis could account in part for the