Endothelial Cell Recoverage and Intimal Hyperplasia after Endothelium Removal with or without Smooth Muscle Cell Necrosis in the Rabbit Carotid Artery

Abstract

Interventional-injury-induced intimal hyperplasia involves smooth muscle cell proliferation that may be limited by endothelial cell coverage. We hypothesized that endothelial cell coverage modulates intimal hyperplasia. Therefore rabbit carotid arteries were injured with (2-french Fogarty balloon) and without media necrosis (Prolene loop). After termination at 3, 7, 21 or 42 days, endothelial cell coverage was assessed with an antibody to CD 31 and cross-sectional intimal hyperplasia area was measured morphometrically. At 21 and 42 days, maximal intimal hyperplasia thickness was measured at a site where endothelium was present and where endothelium was absent. Proliferating cells were identified with an antibody to the nuclear antigen Ki-67. From 3 to 42 days, endothelial cell coverage progressed from the caudal and cranial ends of the lesion towards the center and was slower in balloon- versus loop-injured arteries (p < 0.001, Anova). At 21 and 42 days, intimal hyperplasia area was larger after balloon than after loop injury (21 days: 0.20 ± 0.01 vs. 0.09 ± 0.04 mm², p < 0.05; 42 days: 0.26 ± 0.03 vs. 0.08 ± 0.02 mm², p < 0.01). At 21 days, the intimal hyperplasia was maximal at the center of the lesion and diminished towards the edges in both balloon- and loop-injured arteries. Surprisingly, at 21 and 42 days, maximal intimal hyperplasia thickness was larger in CD31-positive compared to CD31-negative regions (104 ± 8 vs. 72 ± 12 µm, p < 0.01, paired t test). At 3 and 7 days, more medial proliferation was found after balloon than after loop injury (3 days: 46.2 ± 8.8 vs. 0.2 ± 0.1%, p < 0.01; 7 days: 18.5 ± 6.4 vs. 1.0 ± 0.4%, p < 0.01). In the same period, abundant adventitial proliferation was found after balloon injury that was entirely absent after loop injury. We conclude, first, that endothelial cell recoverage proceeded at a lower rate over damaged than over normal media. This retarded endothelial cell recoverage may contribute to enhanced intimal hyperplasia. Second, at a late stage of vascular healing, when intimal hyperplasia had already been formed, reendothelialization seems to have been enhanced over areas with thick intimal hyperplasia. Third, dilation-induced medial damage was accompanied with massive adventitial cell proliferation.

Mouse Model of Femoral Artery Denudation Injury Associated With the Rapid Accumulation of Adhesion Molecules on the Luminal Surface and Recruitment of Neutrophils

“…20,21 The femoral approach offers the advantage of bilateral injury and carries less risk of morbidity and mortality compared with the carotid artery. The time course of intimal hyperplasia in the present study is similar to that found in rabbit, 29 pig, 30 and baboon 31 models. The I/M ratios obtained are comparable to those of other animal models.…”

Photochemically Induced Endothelial Injury in the Mouse as a Screening Model for Inhibitors of Vascular Intimal Thickening

“…Previous studies have demonstrated that SMCs cease proliferation and migration when endothelial regeneration is complete. 18,19 A similar finding was observed in our mouse model of vascular injury: the proliferation of SMCs and the increase in intimal area ceased within 21 days of injury, a time at which the luminal surface was fully covered with new ECs.…”

Apoptosis of Vascular Smooth Muscle Cells is Induced by Fas Ligand Derived From Endothelial Cells

“…18 Moreover, during endothelial recovery after denudation, areas that are covered by EC show less intimal hyperplasia compared with the uncovered areas. 18 Spontaneous death of SMC in close proximity to EC was reported more than 20 years ago, 19 so all the research to date indicates that the endotheliumsmooth muscle interaction induces SMC death. However, it is also known that endothelial cell -smooth muscle cell interactions are frequent, and that this process activates latent tissue growth factor , a potent modulator of both SMC and EC.…”