Zn-alloy provides a novel platform for mechanically stable bioresorbable vascular stents.

Metallic Zn alloys have recently gained interest as potential candidates for developing platforms of bioresorbable vascular stents (BVS). Previous studies revealed that Mg alloys used for BVS can degrade too early, whereas PLLA materials may fail to provide effective scaffolding properties. Here we report on results of a new bioresorbable, metallic stent made from a Zn-Ag alloy studied in a porcine animal model of thrombosis and restenosis. While the tensile strength (MPa) of Zn-3Ag was higher than that of PLLA and resembled Mg's (WE43), fracture elongation (%) of Zn-3Ag was much greater (18-fold) than the PLLA's or Mg alloy's (WE43). Zn-3Ag exposed to HAoSMC culture medium for 30 days revealed degradation elements consisting of Zn, O, N, C, P, and Na at a 6 nm surface depth. Platelet adhesion rates and blood biocompatibility did not differ between Zn-3Ag, PLLA, Mg (WE43), and non-resorbable Nitinol (NiTi) stent materials. Balloon-expandable Zn-3Ag alloy BVS implanted into iliofemoral arteries of 15 juvenile domestic pigs were easily visible fluoroscopically at implantation, and their bioresorption was readily detectable via X-ray over time. Histologically, arteries with Zn-3Ag BVS were completely endothelialized, covered with neointima, and were patent at 1, 3, and 6 months follow-up with no signs of stent thrombosis. Zn-3Ag alloy appears to be a promising material platform for the fabrication of a new generation of bioresorbable vascular stents.

Transient hyperoxic reoxygenation reduces cytochrome C oxidase activity by increasing superoxide dismutase and nitric oxide.

Oxygen therapies have been shown to be cytoprotective in a dose-dependent fashion. Previously, we have characterized the protective effects of moderate hyperoxia on cell viability of ischemic human cardiomyocytes and their mitochondrial membrane potential by transient addition of oxygenated perfluorocarbons to the cell medium. Now, we report that the activity and expression of cytochrome c oxidase (COX) after prolonged ischemia depend on the amount of oxygen delivered during reoxygenation. Transient hyperoxia during reoxygenation results in a decrease of COX activity by 62 +/- 15% and COX expression by 67 +/- 5%, when hyperoxic tensions of approximately = 300 mm Hg are reached in the cell medium. This decrease in COX expression is prevented by the inhibition of inducible nitric-oxide synthase (iNOS). Immunoblot analysis of ischemic human cardiomyocytes revealed that hyperoxic reoxygenation causes a 2-fold increase of iNOS, leading to a rise in nitric oxide production by 140 +/- 45%. Hyperoxic reoxygenation is further responsible for a 2-fold activation of hydrogen peroxide production and an increase in cytosolic superoxide dismutase expression by 35 +/- 10%. NADPH availability has no effect on the hyperoxia-induced decrease of superoxide. Overall, these results indicate that transient hyperoxic reoxygenation in optimal concentrations increases the level of nitric oxide by activation of iNOS and superoxide dismutase, thereby inducing respiration arrest in mitochondria of ischemic cardiomyocytes.

Differences of platelet adhesion and thrombus activation on amorphous silicon carbide, magnesium alloy, stainless steel, and cobalt chromium stent surfaces.

BACKGROUND: Coronary stenting is considered to be the gold standard of percutaneous coronary interventions, because stents are able to reduce early and late elastic recoil (negative remodeling) and restenosis in comparison with balloon angioplasty alone. OBJECTIVE: It is known that stent thrombogenicity and neointimal formation are determined by the surface characteristics of the stent platform, electrochemical features of the stent surface, and the degree of degradation after implantation. Metallic stents coated with amorphous silicon carbide and biodegradable stents made of magnesium alloy have been introduced clinically, but there are no data available comparing the biocompatibility of these novel stent materials with conventional stents. METHODS: We demonstrate simple and reproducible in vitro methods assessing the rate of platelet adhesion and thrombus activation for biocompatibility tests of different stent surfaces. RESULTS: We show that amorphous silicon carbide and magnesium alloy stent surfaces markedly lower the rate of platelet adhesion and platelet/fibrin activation when compared with uncoated stainless steel or cobalt chromium alloy surfaces. Semiconductor materials on the stent surface reduce platelet and fibrin activation by increasing the critical electron gap to greater than 0.9 eV resulting in a lower electron transfer out of the stent material. CONCLUSION: Passive stent coatings with specific semiconducting properties such as amorphous silicon carbide or magnesium alloy reduce thrombogenicity and may improve biocompatibility of a stent platform.

Oxygenated perfluorochemicals improve cell survival during reoxygenation by pacifying mitochondrial activity.

Perfluorochemicals (PFCs) are known to provide a unique tool for controlled uptake and delivery of oxygen. We have characterized the effects of incremental oxygen delivery on cell viability of human ischemic cardiomyocytes using chemically inert PFCs as oxygen carrier. We have found that cell viability after prolonged ischemia depends on the dose of oxygen supplementation by oxygenated (ox) PFCs during reoxygenation. Although reoxygenation with the transient addition of oxPFCs in high concentrations (2250 microMO2 in 0.4 muM PFCs) results in decreased cell viability compared with normoxic reoxygenation, cell survival increases by 30 +/- 4% after reoxygenation with moderate oxPFC concentrations (750 muM O2 in 0.1 microM PFCs). Immunoblot analysis revealed that oxPFC-supplemented reoxygenation causes marked (16-fold) deactivation of death-associated protein kinase (DAPK) signaling an increase in mitochondrial membrane potential and a decreased steady-state level of superoxide by 19 +/- 3%. Reoxygenation with oxPFCs is further responsible for a 2-fold activation of AMP-activated protein kinase (AMPK) signaling an inadequate ATP supply by oxidative phosphorylation during reoxygenation. Addition of oxPFCs stabilizes both hypoxia-inducible factor (HIF) 1-alpha and 2-alpha during reoxygenation. Overall, these results indicate that moderate doses of oxPFCs can improve cell survival during reoxygenation, causing deactivation of DAPK, up-regulation of AMPK, and HIF1-alpha and 2-alpha stabilization. These effects of oxPFCs are dose-dependent, and they lead to a stabilization of the mitochondrial membrane potential, decreased steady-state levels of superoxide, and pacification of mitochondrial activity.

Reoxygenation of human coronary smooth muscle cells suppresses HIF-1alpha gene expression and augments radiation-induced growth delay and apoptosis.

BACKGROUND AND PURPOSE: Catheter-based coronary brachytherapy with beta- and gamma-radiation is an evidence-based method to prevent restenosis after percutaneous transluminal coronary angioplasty (PTCA) and stent implantation, but the outcome may be subject to improvements. Physiological studies suggest that most of the target cells of brachytherapy in coronary arteries after PTCA are hypoxic. A lack of oxygen decreases the effect of low LET (linear energy transfer) irradiation. The authors assumed that reoxygenation of hypoxic human coronary smooth muscle cells (HCSMCs) improves the results of coronary brachytherapy. The expression of hypoxia-inducible factor 1alpha (HIF-1alpha) gene, and the rates of growth and apoptosis of hypoxic and reoxygenated HCSMCs after gamma-irradiation were therefore analyzed. MATERIAL AND METHODS: An in vitro model of megacolonies of HCSMCs was developed. After exposure to chronic hypoxia the HCSMCs were irradiated with graded doses of 2, 4, 8, and 16 Gy using a (60)Co source either under hypoxia (pO(2) < 3 mmHg) or after reoxygenation (pO(2) approximately 150 mmHg). RT-PCR (reverse transcription-polymerase chain reaction) analysis was used to quantify HIF-1alpha gene expression and the growth of HCSMC megacolonies was measured serially. The oxygen enhancement ratio (OER) was calculated from the specific growth delay. Apoptosis of HCSMCs was quantified by counting cells with specific DNA strand breaks using the TUNEL assay. RESULTS: HIF-1alpha gene expression was markedly suppressed in reoxygenated cells versus hypoxic cells 30 min after gamma-irradiation at all radiation doses (158 +/- 46% vs. 1,675 +/- 1,211%; p < 0.01). Apoptosis was markedly increased in reoxygenated HCSMCs. The OER was 1.8 (95% CI [confidence interval] 1.3-2.4). Therefore, reoxygenated HCSMCs require 44% less radiation dose to achieve the equivalent biological radiation effect compared to hypoxic HCSMCs. CONCLUSION: Reoxygenation of coronary smooth muscle cells should be considered an option to increase efficacy of coronary brachytherapy. This could be used to reduce radiation dose and associated late side effects.

Particle debris from a nanoporous stent coating obscures potential antiproliferative effects of tacrolimus-eluting stents in a porcine model of restenosis.

Polymer stent coatings may not be suitable for drug elution because of inherent proinflammatory effects. A previous study suggested a beneficial effect of a stent eluting tacrolimus from a nanoporous ceramic aluminum oxide coating in a rabbit restenosis model. We investigated whether this stent is effective in preventing in-stent restenosis in a porcine restenosis model. Thirty-four juvenile swine underwent balloon overstretch injury and were subjected to implantation of either stainless steel (bare) stents, bare stents coated with nanoporous aluminum oxide alone, and coated stents eluting 50 and 180 mug of tacrolimus (FK506). In-stent restenosis was quantified at 1 and 3 months after stent placement by histomorphometry. A significant increase of neointimal hyperplasia was noted with the stents coated with aluminum oxide alone compared with bare stents (2.92 +/- 1.02 and 1.38 +/- 0.51 mm(2), respectively; P < 0.02). In all arteries containing coated stents, particle debris was found in the media and neointima, resulting in augmented vascular inflammation. In the group of stents coated with aluminum oxide, FK506 elution at a dose 180 mug reduced neointimal hyperplasia vs. no drug elution (1.66 +/- 0.49 vs. 2.92 +/- 1.02 mm(2); 180 mug vs. ceramic alone; P < 0.03). At a dose of 50 mug stent-based delivery of FK506, no reduction of neointimal hyperplasia was found (2.88 +/- 1.31 and 2.92 +/- 1.02 mm(2), respectively; P = NS; FK506 vs. ceramic alone). In summary, particle debris shed from a drug-eluting aluminum oxide coating of a stainless steel stent counteracts potential antiproliferative effects of stent-based tacrolimus delivery in a porcine model of restenosis. We propose that stent coatings eluting drugs need to be routinely tested for being tightly anchored into the stent surface. Alternatively, omission of any coating used as a drug reservoir may eliminate inflammatory particle debris after placement of drug-eluting stents.

Reoxygenation of hypoxic coronary smooth muscle cells amplifies growth-retarding effects of ionizing irradiation.

BACKGROUND: Hypoxic human coronary smooth muscle cells (HCSMCs) are possible targets for brachytherapy to prevent restenosis after percutaneous transluminal coronary angiography. It is unclear whether growth kinetics and gene expression of these cells undergoing gamma-irradiation are changed by reoxygenation. METHODS AND RESULTS: Hypoxic (H) and hypoxia-reoxygenated (H-R) HCSMCs were irradiated with gamma-radiation at single doses of 4, 8, and 16 Gy using a 60Co-source. Vascular endothelial growth factor gene expression of HCSMCs was dramatically suppressed in H-R versus H cells independent of the radiation dose (15+/-7% versus 2183+/-2023%, P<0.01, H-R versus H cells). An oxygen enhancement ratio of 1.8 was calculated after irradiation from the retarded growth of H-R versus hypoxic HCSMCs. Production of reactive oxygen species by HCSMCs after irradiation increased by 15+/-2% in H-R cells versus 7+/-1% in H cells (P<0.05). CONCLUSIONS: Reoxygenation of hypoxic HCSMCs markedly amplifies growth-retarding effects of ionizing irradiation. On the basis of these findings, oxygenating radiosensitizers should be analyzed with regard to suitability for coronary brachytherapy to prevent restenosis.

Drug-eluting stent: the "magic bullet" for prevention of restenosis?

The need for repeat interventions after initially successful PTCA due to restenosis has been called the "Archilles heel" of a percutaneous revascularization procedure. The incidence of restenosis varies between 20-50 % depending on the stent material, the presence of risk factors, and the location of vascular disease. Some risk factors such as diabetes have been clearly identified, others are currently debated. After years of failures trying to reduces restenosis rates, locally administered antiproliferative means have been shown to successfully inhibit excessive cell growth in response to PTCA. Local radiotherapy of in-stent restenosis results in a reduction of recurrent stenosis versus a conventional PTCA procedure. However, long-term evaluation indicated that restenosis may only be delayed with radiation therapy. Moreover, the restenosis rates were reduced, but the restenotic process was not eliminated. Coronary stents eluting the anti-proliferative agent rapamycin have demonstrated for the first time, that restenosis rates of zero percent are achievable after percutaneous revascularization procedures. Thus, it is intriguing to believe that the elimination of restenosis may have become reality. The purpose of this review is to discuss, whether a stent eluting drugs should be considered as the "magic bullet" for prevention of restenosis after PTCA.

Role of the "dogbone" effect of balloon-expandable stents: quantitative coronary analysis of DUET and NIR stent implantation introducing a novel indexing system.

UNLABELLED: Stent design and deployment characteristics of balloon-expandable stents may play an important role in determining both early and late outcomes of stenting. The purpose of this study was to compare the percent residual stenosis (RS) of two new-generation stent delivery systems, DUET and NIR, in patients with CAD. From September 1998 1999, a total of 100 consecutive patients with CAD receiving either a DUET (18 or 23 mm length; n = 50) or NIR stent (16 or 25 mm length; n = 50) using a 3.0 or 3.5 mm stent delivery system were compared by quantitative coronary analysis. The ability of each balloon delivery system to fully expand the stent was assessed using a new scoring index entitled the stent delivery balloon expansion ratio (SDBR; %). A high SDBR correlates with the angiographic appearance of a "dogbone" that is sometimes seen during stent deployment. A stent "scalloping" score was developed to quantitatively assess the cobblestone appearance observed angiographically with plaque protrusion after stent implantation. Mean deployment pressures were 14 +/- 2 atm (DUET) and 13 +/- 2 atm (NIR) (p=NS). Extent of elastic recoil was similar (6 +/- 5% for DUET vs. 6 +/- 4% for NIR; (p=NS). "Scalloping" was more pronounced in the DUET stent (score, 0.66 +/- 0.6 for DUET vs. 0.24 +/- 0.4 for NIR; p < 0.001). SDBR and RS were higher with DUET than with NIR stent implantation (SDBR, 15 +/- 5% vs. 12 +/- 5%; RS, 14 +/- 5% vs. 11 +/- 6%; p < 0.01). Multivariate analysis showed that SDBR and stent recoil, but not "scalloping", were associated with increased RS after stent implantation (r = 0.45 and p < 0.001 for "dogbone" effect; r = 0.39 and p < 0.001 for stent recoil). CONCLUSION: The second-generation DUET and NIR stents and their respective delivery systems show angiographically different acute performance characteristics. Insufficient deployment of stents visualized by the "dogbone" effect plays a role in the extent of RS after stenting. The introduced angiographic indexes require further validation.