Paul S. Seifert

Coronary bare metal stent implantation in homozygous LDL receptor deficient swine induces a neointimal formation pattern similar to humans.

INTRODUCTION To date, most of all new developments in stent technologies are tested in normal animals. Although invaluable in the evaluation of device safety, the juvenile domestic swine (DS) do not follow the biological healing response occurring in humans following coronary stent implantation. By using a novel swine breed afflicted with familial hypercholesterolemia (FHS), we aimed to analyse the vascular response occurring following bare metal stent (BMS) implantation by comparing in vivo endovascular imaging and histological data. METHODS A total of 26 swine were included in this study (12 FHS and 14 DS). Sixty eight BMS (FHS=28 versus DS=40) were implanted using a 10% overstretch ratio. Imaging evaluation (IVUS and OCT) was conducted in all animals at 30 (n=14) or 90 (n=12) days following stent implantation. After imaging, the stented coronary segments were harvested for histological evaluation. RESULTS At 30 days, the degree of neointimal formation analysed by OCT (%AS=DS 21.9 ± 10% versus FHS 25.4 ± 12%; p=0.18) and histology (DS 24.6 ± 10% versus FHS 23.58 ± 10%; p=0.8) was similar between both animal groups. At 90 days, the degree of neointimal formation in the DS group decreased in all analysed variables (-40% in IVUS neointimal volume, -57% in OCT %AS, and -30% in %AS by histology) compared to the progression of neointimal formation observed in the FHS group (+29% in IVUS neointimal volume, +27% in OCT %AS and +43% in %AS by histology). CONCLUSION The pattern of neointimal formation following BMS implantation in the FHS follows a progressive course that does not occur in the DS. Therefore, by providing a progressive neointimal biological response to BMS implantation, the FHS could serve as an ideal efficacy model for the validation of drug eluting stent technologies.

Analysis of complement C3 activation products in human atherosclerotic lesions

Cleavage of the complement C3 protein is essential for complement activation. Saline extracts of human atherosclerotic lesions were examined by various techniques for the presence of C3 cleavage fragments. Crossed intermediate gel immunoelectrophoresis revealed that native C3 was the predominate C3 protein in extracts and that the C3dg fragment was also detected. SDS-PAGE/Western blot analyses of lesion extracts employing monoclonal antibodies directed at C3c and C3dg fragment determinants demonstrated molecular weight bands corresponding to the known molecular weights of all the physiologic C3 cleavage fragments, except C3b which is known to have a short half-life. After C3, the two most common fragments observed were C3c and C3dg. No bands other than those corresponding to known C3 cleavage fragments were observed and control antibody stains were always negative. In some blots bands with a greater molecular mass than C3 were evident, indicating that some of the C3 in lesions may be covalently bound to an activator. We have previously identified a large (100-500 nm) nonapoprotein containing lipid particle (LCA) as a major complement activating structure in human atherosclerotic lesions. Fractionation of lesion extracts by molecular sieve chromatography and sucrose density gradient centrifugation failed to reveal a concordance between LCA and C3 antigens. The results indicate that complement activation, i.e. C3 convertase formation, takes place in human atherosclerotic lesions and that activated C3 is degraded according to normal complement regulatory mechanisms.

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.

Peri-strut low-intensity areas in optical coherence tomography correlate with peri-strut inflammation and neointimal proliferation: an in-vivo correlation study in the familial hypercholesterolemic coronary swine model of in-stent restenosis.

BackgroundPeri-strut low-intensity area (PLI) is a common imaging finding during the evaluation of in-stent neointima using optical coherence tomography (OCT). We aimed to determine the biological significance of PLI by comparing in-vivo OCT images with the corresponding histological sections obtained from the familial hypercholesterolemic swine model of coronary stenosis. MethodsA total of 26 coronary vessels of nine familial hypercholesterolemic swine were injured with 30% balloon overstretch and then immediately followed by everolimus eluting or bare metal stent placement at 20% overstretch. At 30 days, all stented vessels were subjected to in-vivo OCT analysis and were harvested for histological evaluation. For OCT analysis, stent cross-sections (three per stent) were categorized into presence (PLI+) or absence (PLI−) of PLI. In histology, inflammation and fibrin deposition were scored semiquantitatively from 0 (none) to 3 (severe). ResultsPLI was found in 64.9% of stent sections. Peri-strut inflammation was more frequently observed in OCT sections PLI (+) compared with PLI (−) (56.0 vs. 7.4%, P=0.01). In contrast, peri-strut fibrin deposits was similar in both groups (PLI+=58.0% vs. PLI−=59.3%, P=0.94). Histological neointimal thickness was significantly higher in PLI (+) sections (mean±SE: 0.68±0.06 vs. 0.34±0.02 mm; P<0.01), yielding a higher percent area stenosis compared with PLI (–) (mean±SE: 59.0±4.4 vs. 34.1±2.2%, P<0.01). The PLI diagnostic sensitivity and specificity for inflammation were 80 and 76.1%, respectively (>56% PLI, area under the curve=0.86, P<0.01), whereas for fibrin deposition, the sensitivity and specificity were 42.2 and 76.1%, respectively (area under the curve=0.56, P=NS). Area under the receiver operating characteristic curve was significantly higher for identifying inflammation than fibrin (0.86 vs. 0.56, P<0.01). The severity of PLI correlated with the neointimal thickness when assessed by OCT (R=0.79, P<0.001). ConclusionThe presence of PLI in OCT correlates with neointimal thickness and appears to have a diagnostic value in the recognition of peri-strut inflammation, therefore possibly serving as a surrogate for in-vivo assessment of stent efficacy.

The apolipoprotein(a) moiety of lipoprotein(a) interacts with the complement activation fragment iC3b but does not functionally affect C3 activation or degradation

A previous study has shown that complement component C3 binds to recombinant apolipoprotein(a) (r-apo(a)). In the present report we have investigated the interactions between lipoprotein(a) (Lp(a)), r-apo(a) and C3 in relation to complement activation and degradation. Neither Lp(a) nor r-apo(a) affected complement activation as indicated by sheep and rabbit red blood cell hemolytic assays, and by assessment of the amount of C3a generated in zymosan-activated human serum in the presence or absence of Lp(a). Crossed immunoelectrophoretic analyses indicated that Lp(a) retarded the migration of iC3b in complement-activated serum but had no effects on C3, C3b, C3c or C3dg. Recombinant apo(a) exhibited the same properties as intact Lp(a) indicating that it is the apo(a) portion of Lp(a) that mediates this effect and not the lipid moiety. Low density lipoprotein had no effect on the migration of C3 cleavage fragments. Treatment of Lp(a) or apo(a) with neuraminidase abolished their capacity to alter iC3b migration. SDS-PAGE immunoblotting analysis of C3 activation fragments generated in the presence of Lp(a) demonstrated the usual physiologic C3 cleavage fragments. Rocket intermediate gel immunoelectrophoresis of complement-activated serum demonstrated that Lp(a) did not hinder or accelerate the generation of C3c and C3dg breakdown fragments of iC3b. The results indicate that the apo(a) moiety of Lp(a) alters the migration of iC3b in an electric field but does not affect complement activation or degradation of activated C3. The sialic acid residues on apo(a) are necessary for the apo(a)-iC3b interaction.

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.

BackgroundThe 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. MethodsA 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. ResultsAt 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. ConclusionThe 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.

TCT-643 Abluminal- Only Coating Everolimus Eluting Coronary Stent Provides an Anti-inflammatory Vascular Effect Compared to Bare Metal Stents in the Familial Hypercholesterolemic Swin

Background: The performance of zotarolimus-eluting stents (Medtronic Inc., Santa Clara, CA, USA) versus other limus-eluting stents (LES) and the possible improvements of Resolute zotarolimus-eluting stents (R-ZES) versus Endeavor zotarolimus-eluting stents (E-ZES) still remain to be defined. We sought to evaluate efficacy and safety of two zotarolimus-eluting stent generations versus other LES and to compare R-ZES versus E-ZES. Methods: We undertook a meta-analysis of trials in which patients were randomly assigned to percutaneous coronary interventions (PCI) with R-ZES versus LES or with E-ZES versus LES as well as an indirect comparison of R-ZES versus E-ZES, with LES as common comparator. The primary efficacy endpoint was ischemia-driven target vessel revascularization (ID-TVR); the primary safety endpoints were cardiac death and cumulative definite/probable stent thrombosis (ST). Results: Overall, 13,709 patients were assigned to PCI with R-ZES versus LES (n 7,185) or with E-ZES versus LES (n 6,524). The risk of ID-TVR (odds ratio [95% confidence interval] 1.06 [0.90-1.25], p 0.47), cardiac death (0.99 [0.69-1.42], p 0.96) and ST (1.18 [0.68-2.03], p 0.56) did not differ between R-ZES and LES. Patients receiving E-ZES were more likely to undergo ID-TVR as compared to those receiving LES (1.95 [1.40-2.73], p 0.0001). Cardiac death (1.02 [0.54-1.91], p 0.96) and ST (1.10 [0.50-2.44], p 0.81) were similar between E-ZES and LES. At indirect comparison, PCI with R-ZES versus E-ZES reduced the risk of ID-TVR (0.54 [0.37-0.78], p 0.001), without increasing cardiac death (0.97 [0.46-2.00], p 0.93) and ST (1.07 [0.40-2.80], p 0.88). Conclusions: The antirestenotic efficacy of Resolute zotarolimus-eluting stents is superior to Endeavor zotarolimus-eluting stents and similar to other limus-eluting stents. Endeavor zotarolimus-eluting stents increase the risk of reinterventions as compared to other limus-eluting stents. First and second zotarolimus-eluting stent generations have similar thrombogenicity compared to other limus-eluting stents.