Experimental evaluation of efficacy and healing response of everolimus-eluting stents in the familial hypercholesterolemic swine model: a comparative study of bioabsorbable versus durable polymer stent platforms.

BACKGROUND: The utility of animal models for the prediction of drug-eluting stent (DES) efficacy in human clinical trials is still unclear. The familial hypercholesterolemic swine (FHS) model has been shown to induce a human-like neointimal response to bare metal stent (BMS) implantation. However, its utility to discriminate efficacy signals following DES implantation is unknown. In this study, we aimed to test the efficacy and healing response of several everolimus-eluting stent (EES) platforms in the coronary territory of the FHS. METHODS: A total of 19 EES platforms (SYNERGY=6, SYNERGY½-dose=7, and PROMUS Element=6) and an identical BMS control (Element=6) were implanted into the coronary arteries of nine FHS. All implants were performed under intravascular ultrasound guidance using a 1.2 : 1 overstretch ratio. At 30 days, the vascular response to the implant was evaluated by quantitative coronary angiography, optical coherence tomography, and histology. RESULTS: At 28 days, all EES platforms showed a significant decrease in angiographic late lumen loss (between 27 and 37%) compared with the BMS control group. This finding was confirmed both by optical coherence tomography (mean neointimal thickness=28-42% reduction) and by histology (mean neointimal thickness=44-55% reduction). All EES platforms showed similar degrees of neointimal inhibition. The presence of moderate to severe para-strut inflammation was observed in 83% of the stent sections in the BMS group compared with 28.6% in the SYNERGY½-dose group and 0% in the SYNERGY and PROMUS groups (P=0.0002). There was a 68-95% reduction in MMP9 expression in the media in all EES platforms compared with the BMS controls. The presence of mild to moderate para-strut fibrin deposits ranged from 66.7 to 83.4% in all EES platforms compared with 16.7% in the EBMS group. CONCLUSION: The FHS coronary injury model showed the efficacy of several EES platforms compared with an identical BMS control. Everolimus eluted from different polymeric platforms showed lower levels of inflammation and slightly higher fibrin deposits compared with BMS controls.

Vascular responses to drug-eluting and bare metal stents in diabetic/hypercholesterolemic and nonatherosclerotic porcine coronary arteries.

BACKGROUND: Animal models used to gain insight into the vascular response to drug-eluting stents are generally juvenile and nonatherosclerotic, whereas stents are placed in patients with complex atherosclerosis and comorbidities. Hence, models reflecting these complexities are needed to help elucidate the vascular effects of drug-eluting stents. We compared the vascular responses with bare metal stent (BMS) and paclitaxel-eluting stent (PES) implantation in a diabetic/hypercholesterolemic (DM/HC) porcine model of advanced coronary atherosclerosis with the standard juvenile porcine model. METHODS AND RESULTS: Two studies using similar stent procedural protocols were performed in either DM/HC (n=20) or domestic swine (non-DM/HC, n=20). Animals pretreated with dual-antiplatelet therapy, underwent BMS or PES implantation (1/artery, 2 stents per animal) and were euthanized 30 or 90 days later. DM/HC resulted in a 24% increase in platelet aggregation (P=0.05 versus baseline), whereas dual-antiplatelet therapy reduced platelet aggregation in both groups (P<0.0001). DM/HC pigs developed substantially greater neointimal area versus non-DM/HC pigs, regardless of stent type, (P=0.004 for BMS at 30 days and P=0.002 at 90 days, P=0.005 for PES at 30 days, P=0.002 at 90 days). Compared with non-DM/HC pigs, reendothelialization was delayed in DM/HC pigs, more so after PES implantation. Increased para-strut leukocytes were observed for PES compared with BMS in the DM/HC pigs at both 30 days (P=0.023) and 90 days (P=0.04). As well, increased T-lymphocyte infiltration was seen in the DM/HC pigs. CONCLUSIONS: Stent implantation in a DM/HC swine model provides a metabolic environment closer to human disease, including hyperglycemia, hypercholesterolemia, and increased platelet aggregation. This model augmented differences in the vascular response between PES and BMS that are not as clearly evident in the non-DM/HC swine, including increased neointimal area, delayed reendothelialization, and greater, persistent vascular inflammation.

Early vascular response to overlapped paclitaxel-eluting stents in swine coronary arteries.

BACKGROUND: The early response to the TAXUS Express2 paclitaxel-eluting stent (PES) system was compared to the response to the Express2 bare metal stent (BMS) system in porcine arteries. METHODS: Swine coronary arteries were implanted with overlapping PES or BMS and examined at 1, 2, 4, 10, and 20 days postimplantation using scanning electron microscopy or light microscopy. RESULTS: Vascular healing in terms of strut coverage, reendothelialization, degree of inflammation, and absence of thrombus was equivalent in both groups from 1 to 20 days. Interstrut member spaces were unaffected by stent deployment and remained covered with endothelium from Day 1. In both groups at 2 days, small patches of endothelial cells covered approximately 5-10% of the stent surface. At 4 days, endothelial cell coverage progressed to nearly 50% in both groups. After 10 days, endothelial cell strut coverage was nearly complete (>90%), with regions of incomplete coverage located primarily in strut overlap regions in both groups. BMS exhibited a fibrocellular neointima and no parastrut fibrin, whereas PES exhibited a developing but immature fibrocellular neointima and prominent parastrut fibrin. By Day 20, an endothelialized neointima was present in both groups, with comparable coverage of proximal and distal stented regions. The neointima of PES was more fibrocellular and parastrut fibrin was still comparable to that at 10 days. CONCLUSION: Early vascular response was comparable for both PES and BMS, with similar rates of reendothelialization, limited inflammatory response, and absence of thrombus, but differed parastrut fibrin clearance and neointimal maturation rate.