Coronary restenosis: a review of mechanisms and management

[Restenosis following endovascular interventions: clinical and experimental studies]

Restenosis following endovascular interventions is the main limitation of their long-term success. The incidence of restenosis varies according to the method (stenting, endarterectomy) and the treated vascular region, but the pathomechanism and risk factors are similar. The current article reviews of the author's previous studies in this field. In clinical studies, we compared the restenosis rate after carotid artery stenting and carotid endarterectomy. We also analyzed the complement activation profile after these interventions. In another study, we investigated the role of two polymorphisms of the estrogen receptor alpha in the occurrence of carotid restenosis after either carotid artery stenting or carotid endarterectomy. In an animal model of carotid endarterectomy, we studied the role of the nitrite-oxide-cyclic guanosine monophosphate signaling and the effect of the phosphodiesterase-5 inhibitor therapy in neointimal hyperplasia. Our results suggest that higher incidence of restenosis following carotid endarterectomy can be correlated with the more highly expressed complement activation after this type of carotid intervention. Polymorphisms in the estrogen receptor alpha gene could contribute to the restenosis formation, especially in women. Neointimal hyperplasia can be attenuated by increased cyclic guanosine monophosphate signaling.

The short-term effect on restenosis and thrombosis of a cobalt-chromium stent eluting two drugs in a porcine coronary artery model

The aim of this article was to study the effect of dual drug-eluting stent (DES) on both restenosis and thrombosis in a porcine coronary artery model. This study reports on the use of two drugs coated on the stent to simultaneously minimize both restenosis and thrombosis. The DES was prepared by spray coating a bare metal stent with a biodegradable polymer loaded with sirolimus and triflusal, to treat against restenosis and thrombosis, respectively. The two-layered dual drug-coated stent was characterized in vitro for surface properties before and after expansion, as well as for possible delamination by cross-sectioning the stent in vitro. In vivo animal studies (in a pig model) were then performed for acute thrombosis, inflammation, and restenosis. The results show a significant reduction in restenosis with a stent coated with both drugs compared with the controls (a bare metal stent, a sirolimus-coated, and a pure polymer-coated stent). The reduction in restenosis with a sirolimus/triflusal-eluting stent is associated with an inhibition of inflammation and thrombus formation, suggesting that such dual DES have a role to play for the treatment of coronary artery diseases.

Cost-effectiveness of the Taxus paclitaxel-eluting stent in the Swedish healthcare system

OBJECTIVE

To analyse the cost-effectiveness of Taxus compared to a bare-metal stent in patients with coronary artery disease in the Swedish healthcare setting.

DESIGN

A decision-analytic model combining clinical data on revascularization rates with Swedish unit costs for medical resources and utility data from the literature.

RESULTS

For patients of moderate risk, the average cost per patient at 12 months is 72,200 SEK for Taxus and 66,900 SEK for a bare-metal stent, while the average cost for high risk patients is nearly equivalent (73,000 vs. 71,700 SEK). The cost per revascularization avoided is generally favourable, while the incremental cost per QALY gained varies depending on the assumptions made; from 2,351,000 SEK for patients of moderate risk at 12-months to cost saving at 24 months for high risk patients. Budget impact scenarios at 12 months are cost-neutral.

CONCLUSION

The Taxus stent is cost-effective in high risk patients, particularly at 24 months. Although it may be less cost-effective for the general population, there is still a substantial offset of initial procedure costs through lower rate of repeat revascularizations.

Preparation and in vitro release profiles of drug-eluting controlled biodegradable polymer coating stents

In the present study, the different drug-eluting controlled biodegradable polymer coatings were fabricated on stainless steel stents. The coatings were not only uniform and smooth but also had excellent mechanical property. The drug release profiles of drug-eluting stents were studied in detail in this study. Depending on the drug type, different drug-eluting stents exhibited different drug release profile. There were two basic release profiles for different drug-eluting stents, i.e., two-phase release profile with burst release or linear release profile without burst release. Incorporating heparin in the rapamycin or curcumin eluting stents can improve the average drug release rate of both and the burst release of rapamycin. The average drug release rate increased with the increase of drug loading but was not proportional to increase of the ratio of drug/polymer. Fabricating the control release layer on rapamycin-eluting stent surface can prevent the burst release of rapamycin and prolong the release period of rapamycin. All results showed that the drug release profile of drug-eluting stents depends on many parameters including drug type, ratio of drug/polymer, and drug carrier properties.

Regulation of arterial remodeling and angiogenesis by urokinase-type plasminogen activatorThis article is one of a selection of papers from the NATO Advanced Research Workshop on Translational Knowledge for Heart Health (published in part 2 of a 2-part Special Issue)

A wide variety of disorders are associated with an imbalance in the plasminogen activator system, including inflammatory diseases, atherosclerosis, intimal hyperplasia, the response mechanism to vascular injury, and restenosis. Urokinase-type plasminogen activator (uPA) is a multifunctional protein that in addition to its fibrinolytic and matrix degradation capabilities also affects growth factor bioavailability, cytokine modulation, receptor shedding, cell migration and proliferation, phenotypic modulation, protein expression, and cascade activation of proteases, inhibitors, receptors, and modulators. uPA is the crucial protein for neointimal growth and vascular remodeling. Moreover, it was recently shown to be implicated in the stimulation of angiogenesis, which makes it a promising multipurpose therapeutic target. This review is focused on the mechanisms by which uPA can regulate arterial remodeling, angiogenesis, and cell migration and proliferation after arterial injury and the means by which it modulates gene expression in vascular cells. The role of domain specificity of urokinase in these processes is also discussed.

Coronary ischemia and percutaneous intervention

The interventional treatment of ischemia is a complex issue grounded on an understanding of basic pathophysiology, but translated and implemented in practice by extensive clinical trial data representing patients with a spectrum of ischemia-causing clinical syndromes and anatomical variations of coronary artery disease (CAD). Percutaneous coronary intervention (PCI) has evolved to treat ischemia within this matrix of clinical and anatomical subsets using a wide array of techniques. Initial techniques using balloon angioplasty were promising, but demonstrated significant rates of restenosis due to negative arterial remodeling. The advent of stent technology prevented arterial recoil and provided a viable treatment for flow-limiting coronary dissections, thereby facilitating improved long-term patency of coronary vessels without the need for repeat revascularization. In-stent restenosis has been successfully addressed with drug elution, but late stent thrombosis has emerged as a complex issue involving dual antiplatelet therapy, patient compliance, and reexamination of the delicate balance between reducing restenosis and promoting endothelial proliferation. Finally, complex coronary lesions associated with heavy calcification or extensive plaque/thrombus burden that introduce unique challenges in obtaining ideal angiographic results have led to the development of new debulking devices aimed at optimizing procedural outcomes. This review will describe a variety of percutaneous coronary interventional techniques and technologies that are employed in the invasive treatment of ischemia under the guidance of clinical guidelines and evidence-based medicine.

Computerized gradual balloon inflation: a novel strategy of coronary angioplasty superior to a standard manual approach

BACKGROUND

Mechanical trauma caused by PCI is a primary reason for restenosis and subsequent target lesion revascularization (TLR). To minimize this trauma, we developed a computerized angioplasty pressure sensor and inflator device (CAPSID) for gradual inflation. The objective of this prospective randomized study was to examine whether use of CAPSID reduces early and late cardiac events in patients undergoing PCI.

METHODS

Patients undergoing PCI were eligible and randomized to CAPSID or standard balloon inflation (plain old balloon angioplasty). In the CAPSID group, a slow, gradual balloon inflation was performed by a personal computer. Stenting was used in both groups only for suboptimal results. Patients with total occlusions and vein grafts were excluded. Clinical follow-up for major adverse cardiac events (MACE) was performed at 6 and 12 months, with repeat coronary angiography performed for clinical symptoms or positive stress testing.

RESULTS

A total of 234 patients completed the study. At 1-year follow-up, the CAPSID group had a significantly lower rate of MACE (21% vs. 37%, P<.005). In patients who underwent angiography, there was a significantly lower rate of restenosis in the CAPSID group (20.2% vs. 35.5%). The reduction in TLR was even more pronounced in the subgroup undergoing stenting (8% vs. 24%; P<.001).

CONCLUSIONS

We conclude that gradual computerized balloon inflation is more effective than standard manual balloon inflation in reducing adverse coronary events. The combination of CAPSID and subsequent stent deployment was especially effective in reducing TLR.

A new wave in treatment of vascular occlusive disease: biodegradable stents--clinical experience and scientific principles

Stent-based therapies in percutaneous vascular intervention are associated with significant long-term complications related to in-stent restenosis. A growing body of literature demonstrates the feasibility of biodegradable materials for endovascular stents, which may, in theory, circumvent many of the immunologic and inflammatory response issues seen with long-term metallic stent failure in coronary and peripheral applications. This review describes the history of endovascular stents and the challenges encountered with metallic, drug-eluting, and biodegradable stents. A review of the basic engineering principles of biodegradable stents is provided, along with a discussion of the cellular mechanisms of restenosis.

Avoiding restenosis: is there a role for glucocorticoids in the drug-eluting stent era?

Restenosis is an important limitation of percutaneous coronary interventions (PCI). In-stent restenosis is mainly due to neointimal hyperplasia, a proliferative process modulated by inflammatory mechanisms. Numerous technical and pharmacological means have been tested to reduce restenosis rates, with frequently disappointing clinical results. Drug-eluting stents (DES) have demonstrated a high efficacy in reducing restenosis, but there are some associated problems that limit its generalized utilization. Glucocorticoids (GC), as potent anti-inflammatory agents, may exert beneficial effects on neointimal proliferation. Clinical studies with oral and intracoronary GC therapy have demonstrated reduction in restenosis rates in selected patients. Although further investigations are warranted, GC might have a potential role for restenosis prevention in selected cases.

Interactions between stainless steel, shear stress, and monocytes

Angioplasty with stent placement is commonly used to treat coronary atherosclerosis. However, 20-40% of stainless steel stents restenose within 6 months via a prolonged inflammatory response mediated by monocytic infiltration and cytokine secretion. In the current study, we tested a hypothesis that blood flow and monocytes interact to alter stent corrosion. We assessed the effects of THP1 monocytes on the corrosion rate of 316L stainless steel (316LSS) under shear stress (0.5-50 dyn/cm(2)). In addition, THP1 cytokine secretion was determined using cytokine arrays and ELISA analyses. Data were compared using ANOVA and Tukey post hoc analysis (alpha = 0.05). Monocytes significantly lowered 316LSS corrosion rates without limiting current density. However, shear stress alone did not alter the corrosion rate of 316LSS. THP1 cells adhered to the 316LSS surface at all flow rates. Exposure to the 316LSS/corrosion test under high fluid flow rates increased (>twofold) the secretion of 7 of the 42 cytokines tested (angeogenin, GRO, I309, interleukin 8, interleukin 6, interleukin 1beta, and macrophage chemoattractant protein-1). Each of these cytokines play a role in wound healing, macrophage differentiation, and cell proliferation, all hallmarks of in-stent restenosis. Furthermore, only IL8 levels were significantly higher than any of the system controls during the 316LSS/corrosion test conditions. The IL8 levels from the 316LSS/corrosion tests were not significantly different from the +LPS control. Together, these data suggest that monocytic cells maybe activated by exposure to 316LSS stents and could contribute to in-stent restenosis and altered corrosion of the stent.

CCN1 knockdown suppresses neointimal hyperplasia in a rat artery balloon injury model

OBJECTIVE

CCN1 (Cyr61) is an extracellular matrix-associated protein involved in cell proliferation and survival. CCN1 is bound to vascular smooth muscle cells (VSMCs) via integrins and is expressed in VSMCs in atherosclerotic lesions, suggesting involvement in the regulation of vascular smooth muscle cell (VSMC) proliferation and atherosclerosis. We hypothesized that knockdown of CCN1 may inhibit VSMC proliferation and suppress neointimal hyperplasia.

METHODS AND RESULTS

We examined the effect of the knockdown of CCN1 using rat cultured VSMCs and a rat balloon injury model. CCN1 stimulated adhesion and migration of VSMCs in a dose-dependent manner, and this was blocked by an antibody for integrin alpha(6)beta(1). Moreover, knockdown of endogenous CCN1 by lentiviral delivery of siRNA significantly inhibited proliferation of VSMCs and the uptake of 5-bromo-2'-deoxyuridine (BrdU). Replenishment with recombinant CCN1 reversed the effect of siRNA knockdown. Interestingly, knockdown of CCN1 significantly suppressed neointimal hyperplasia in a rat carotid artery balloon injury model at days 14 and 28 after injury. Gene transfer of CCN1 to smooth muscle reversed the effect of CCN1 knockdown on neointimal formation. These results suggest that endogenous CCN1 regulates proliferation of VSMCs and neointimal hyperplasia.

CONCLUSIONS

Inhibition of CCN1 may provide a promising strategy for the prevention of restenosis after vascular interventions.

Immediate and long-term outcomes of drug-eluting stent implantation for unprotected left main coronary artery disease: comparison with bare-metal stent implantation

BACKGROUND

The efficacy and safety of drug-eluting stent (DES) implantation for unprotected left main coronary artery (LMCA) disease remain to be established in different clinical settings.

METHODS

Elective DES implantation for unprotected LMCA stenosis was performed in 220 patients at the Fu Wai Hospital, China, from April 2003 to February 2006. Data derived from the latter group were compared with those derived from 224 patients treated with bare-metal stents (BMSs) before March 2003 in a Chinese registry of unprotected LMCA stenting.

RESULTS

Compared with the historical BMS control group, the DES group had more multivessel disease and underwent more bifurcation stenting. The inhospital major adverse cardiac events were significantly higher in the DES than in the BMS recipients (4.1% vs 0.9%, P = .030) because of more complex lesions and procedures in the DES group. During the 15-month mean follow-up period, cumulative cardiac death (0.5% vs 4.9%, P = .004), target-vessel revascularization (5.9% vs 11.6%, P = .034), and major adverse cardiac event (9.5% vs 16.5%, P = .029) rates were significantly lower in the DES than in the BMS group. There was no significant difference in clinical efficacy between sirolimus- and paclitaxel-eluting stents. Angiographic follow-up was performed in 46.4% of DES and 45.7% of BMS recipients, respectively; and the binary restenosis rate was significantly lower in the DES versus the BMS control group (16.7% vs 31.4%, P = .014).

CONCLUSIONS

Based on this comparison with a historical control, DES implantation for unprotected LMCA appears safe in selected patients and might be more effective in preventing major adverse cardiac events compared with BMS implantation over a mean follow-up period of 15 months.

Echolucent carotid plaques predict in-stent restenosis after bare metal stenting in native coronary arteries

Echolucent carotid plaque is considered to predict coronary events. This study examined whether echolucent carotid plaque may predict in-stent restenosis (ISR) in coronary arteries. This study included 202 patients who had elective and successful percutaneous coronary intervention (PCI) with bare metal stents in de novo lesions of native coronary arteries for symptomatic coronary artery disease (CAD). Carotid plaque echolucency was assessed by ultrasound with integrated backscatter (IBS) analysis (intima-media IBS value minus adventitia IBS) 1 day before PCI. All patients underwent planned coronary angiography (CAG) at 6 months after PCI, or CAG before 6 months due to acute coronary syndromes. ISR (defined as >50% diameter stenosis) was found in 65 (32%) patients. The calibrated IBS values of carotid plaques were inversely correlated with late luminal loss of the stented lesions. Using multivariate logistic regression analysis, the presence of echolucent carotid plaques (<or=-13.7 dB, arbitrarily determined by an ROC curve) served as an independent predictor of ISR (odds ratio 3.8, 95% CI 1.9-7.3, p=0.01) and target lesion revascularization (n=48) (odds ratio 2.8, 95% CI 1.4-5.7, p=0.01). In conclusion, echolucent carotid plaques with low IBS values were independently and closely associated with ISR in native coronary arteries.

The future of drug-eluting stents

This review aims to provide a glimpse into the future of drug-eluting stents (DES). Since their arrival in 2002, DES have transformed the practice of interventional cardiology by drastically reducing restenosis and the need for repeat revascularization. However, data about the potentially fatal long-term risk of stent thrombosis have spurred on research and development to improve upon the first generation of devices. The initial commercially available DES used a stainless steel platform coated with a permanent polymer to provide controlled release of the anti-restenotic drug. The platform, polymer and drug are all targets for improvement. More advanced metallic and fully biodegradable stent platforms are currently under investigation. The permanent polymer coating, a likely contributor adverse events, is being superseded by biocompatible and bioabsorbable alternatives. New drugs and drug combinations are also a research goal, as interventional cardiologists and the industry strive towards safer anti-restenotic DES.

Serum C-reactive protein response to percutaneous coronary intervention in patients with unstable or stable angina pectoris is associated with the risk of clinical restenosis

BACKGROUND

Inflammation plays a pivotal role in the pathogenesis of atherosclerosis. Previous reports have used vaccination as a model to stimulate inflammation. The aim of the present study was to investigate the role of C-reactive protein response to PCI in the risk of clinical restenosis or new coronary stenosis, considering PCI as a model to stimulate inflammation.

MATERIAL AND METHODS

Eight hundred and ninety-one patients with stable or unstable angina pectoris and with normal serum troponin T<or=0.03 microg/L before PCI were investigated. The survivors after a follow-up period of 2.6 years (850 patients) were included. Serum CRP and troponin T concentration were measured before and the day after PCI. Restenosis and new coronary stenosis, detected by coronary angiography due to symptomatic coronary heart disease, were determined.

RESULTS

CRP response to PCI, unstable angina pectoris, the number of vessels dilated and lack of stent implantation were associated with restenosis or new coronary stenosis. In multivariate analysis, patients in the highest tertile of CRP, induced by PCI, had an increased risk (risk ratio 1.7 [95% CI 1.1-2.9]) for restenosis or new coronary stenosis. Furthermore, patients with restenosis had an increased CRP response to PCI compared with those with new coronary stenosis.

CONCLUSION

The CRP response to PCI, as a model to stimulate inflammation, is associated with an increased risk of clinical restenosis. The results emphasize the role of CRP in the pathogenesis of coronary artery disease progression and in particular restenosis.

The pathophysiology and burden of restenosis

The introduction of percutaneous transluminal coronary angioplasty (PTCA) revolutionized the surgical treatment of coronary artery disease. However, despite increased surgical experience and technical breakthroughs, restenosis occurs in 30%-50% of patients undergoing simple balloon angioplasty and in 10%-30% of patients who receive an intravascular stent. Animal and human data indicate that restenosis is a response to injury incurred during PTCA. The need for reintervention in a high percentage of patients due to restenosis remains an important limitation to the long-term success of PTCA. Stenting reduces initial elastic recoil and limits negative arterial remodeling; however, bare-metal stents may promote intimal hyperplasia by eliciting an immune and proliferative response. Consistent with these data, clinical studies suggest that drug-eluting stents, coated with anti-inflammatory or antiproliferative agents, reduce the risk for restenosis. Stenting represents a considerable cost burden. Treatment strategy should focus on selective use of expensive drug-eluting stents in populations where they have been found to be more clinically effective than bare-metal stents--patients who are at high risk for restenosis or who develop restenosis with bare-metal stents. Recent studies suggest that the pharmacologic management of restenosis is now feasible. Together, the judicious use of stents and oral pharmacotherapy promise to reduce the risk for restenosis, even among high-risk patients.

The impact of insulin resistance on endothelial function, progenitor cells and repair

The structural and functional integrity of the vascular endothelium plays a critical role in vascular homeostasis. Insulin resistance, an important risk factor for cardiovascular disease, is thought to promote atherosclerosis through a reciprocal relationship with endothelial dysfunction. In health, cumulative damage to endothelial cells incurred by exposure to risk factors is mitigated by endogenous reparative processes. Disruption of the balance between endothelial damage and repair may mediate atherosclerotic progression. Bone marrow-derived 'endothelial progenitor cells' (EPC) have been identified as significant contributors to endogenous vascular repair. Insulin resistance is associated with a spectrum of biochemical abnormalities which have the potential to reduce the availability of EPCs and diminish their capacity for vascular repair. Many lifestyle and pharmacological interventions which improve insulin resistance also increase the numbers and functionality of EPCs. Cell-based therapies may also hold promise for the prevention and treatment of cardiovascular disease.

Use of heparin-coated stents in neurovascular interventional procedures: preliminary experience with 10 patients

OBJECTIVE

Currently, there is minimal published data on the use of heparin-coated stents in the neurovasculature; however, these stents have a proven clinical record in the treatment of coronary disease. This article details our experience with the safety and technical aspects of stent deployment in the first 10 patients who had heparin-coated stents placed in the intracranial and cervical vasculature and the preliminary follow-up in most cases.

METHODS

We retrospectively reviewed the clinical history, intra- and periprocedural data, and imaging for the patients who received heparin-coated stents in the cervical and intracranial vasculature for cerebrovascular disease between October 2002 and October 2003.

RESULTS

Thirteen heparin-coated stents were placed in 10 patients. Seven out of the 10 patients had heparin-coated stents placed in the posterior circulation; the remaining three patients had stents placed in the anterior circulation. Four patients had stents placed intracranially. There was no acute or subacute in-stent thrombosis and no procedure-related complications. Follow-up was performed on most patients, with no clinical symptoms attributable to restenosis in any patient.

CONCLUSION

This small series suggests that heparin-coated stents are safe for use in the treatment of cervical and intracranial atherosclerotic disease. Longer-term follow-up is needed to study the heparin coating effect on in-stent restenosis rates and to assess the long-term durability and clinical efficacy of this stent. The use of drug-coated stents in the cerebrovascular circulation is an area that warrants further investigation.

Preparation, characterization and anticoagulation of curcumin-eluting controlled biodegradable coating stents

Curcumin is pharmaceutically active in many ways, having properties including anticoagulation, anti-proliferation, anti-inflammatory, and may be used to fabricate drug-eluting stents to treat in-stent restenosis after stent implantation. Here we describe our investigations of curcumin-eluting PLGA coatings formed using the biodegradable polymer PLGA (polylactic acid-co-glycolic acid) as drug carrier and uniformly fabricated on the surface of 316L stainless steel stents by an ultrasonic spray method. Three doses were explored--low dose ( approximately 140 microg per stent or 115 microg/cm(2)), moderate dose ( approximately 280 microg per stent or 230 microg/cm(2)), and high dose ( approximately 490 microg per stent or 408 microg/cm(2)). Pre- and post-expansion morphologies of the stent coating were examined by optical microscopy (OM) and scanning electron microscopy (SEM), indicating that the coating not only was very smooth and uniform but also had the ability to withstand the compressive and tensile strains imparted without cracking from the stent during the expansion process. Atomic force microscopy (AFM) images indicated the topography of the PLGA-only and moderate dose curcumin-eluting stent that showed an average roughness below 1 nm; no drug particles could be seen on the stent surface, indicating that curcumin can be mixed with PLGA at the molecular level using an ultrasonic atomization spray method. The structure of the coating films was characterized by Fourier Transform Infrared (FTIR) spectroscopy and X-ray electron spectroscopy (XPS), with results suggesting that there was no chemical reaction between curcumin and the drug. The results of in vitro measurements of drug release from curcumin-eluting stents showed that all the curcumin-eluting stents studied exhibited a nearly linear sustained-release profile with no significant burst releases within the measurement period. The in vitro anticoagulation behavior of curcumin-eluting stents was investigated by static platelet adhesion and APTT (activated partial thromboplastin time) tests, revealing that the anticoagulation properties of curcumin-eluting stents are superior to those for stainless steel stents and PLGA-only-coated stents. The anticoagulation behavior of curcumin stents improved significantly as the drug dose was increased.

Antiatherosclerotic and antithrombotic effects of omega-3 fatty acids

Omega-3 fatty acids from both marine and plant sources have been shown to reduce the risk of coronary artery disease death. Although their beneficial cardiovascular effects are thought to be due to their antiarrhythmic properties, omega-3 fatty acids also have been shown to have a wide range of antiatherosclerotic and antithrombotic effects in animal and human studies. Review of the findings of randomized, controlled trials published through August 2005 shows that omega-3 fatty acids of marine origin consistently lower elevated plasma triglyceride levels in a dose-dependent fashion, with greater efficacy at higher triglyceride levels. Smaller effects on lowering blood pressure, improving endothelial function, and increasing plasma levels of high-density lipoprotein cholesterol were also found. No consistent effects on other lipid, hemostatic, inflammatory, glucose tolerance, or plaque stabilization parameters were found. Epidemiologic studies show more consistent reductions in the incidence of nonfatal myocardial infarction and ischemic stroke than do the clinical trials of increased omega-3 fatty acid intake, which suggests important confounding factors in observational studies. Ongoing clinical trials may clarify the non-antiarrhythmic benefits of omega-3 fatty acid supplementation.

Drug-Eluting Stents and the Future of Coronary Artery Bypass Surgery: Facts and Fiction

The treatment of patients with coronary artery disease continues to evolve. Recent, exciting data on the use of drug-eluting stents in diseased coronary vessels has generated immense enthusiasm within the interventional community leading to claims that "drug-eluting stents will put bypass surgeons out of business." However, despite promising short-term and midterm outcomes of this revolutionary new technology, valid concerns regarding long-term safety and efficacy of drug-eluting stents persist. This review article evaluates current status of drug-eluting stents with special emphasis on real and potential drawbacks of this emerging percutaneous coronary interventional modality and its impact on the practice of coronary artery bypass surgery.

Corrosion rates of stainless steel under shear stress measured by a novel parallel-plate flow chamber

A unique parallel-plate flow chamber has been engineered to assess the corrosion properties of implant materials in biological environments under shear flow. This parallel-plate flow chamber provides a novel approach to investigate hypotheses regarding cellular-material-mechanical-force interactions that influence the success or failure of implant devices. The results of the current study demonstrated that physiological stresses (0.5-50 dynes/cm2) from laminar flow from cell culture media did not significantly alter corrosion rates of stainless steel, providing baseline information for an extensive study of the cellular-material-mechanical-force interactions. Furthermore, this study demonstrated that this device is electrochemically stable and provides reproducible results within test parameters. In addition, the results were not significantly different from corrosion tests on bulk samples. Therefore, this system will be useful for investigating cell-material interactions under shear stress for implant alloys or other opaque materials. This information is currently lacking. The results of the present study also support further development of this test system to assess cellular responses to these materials under shear stresses.

Ursolic acid inhibits neointima formation in the rat carotid artery injury model

Triterpenoids are natural compounds that are found in a large variety of plants and vegetarian foods, and are used for medicinal purposes in many Asian countries. Pentacyclic triterpenes, such as ursolic acid, have been reported to exhibit anticancer and anti-inflammatory properties. The present study was designed to assess the effects of ursolic acid in the migration and proliferation of vascular smooth muscle cells (VSMC), and in a vascular injury model. The exposure of VSMC to ursolic acid results in a chemotaxis inhibition, in a reduction of the expression of proliferating cell nuclear antigen (PCNA) and in a disorganization of beta-tubulin and vimentin cytoskeletal proteins. Administration of ursolic acid in the rat carotid balloon catheter injury model shows a significant inhibition of neointimal hyperplasia. Thus, we have demonstrated that daily doses of 6 mg/kg body weight for 10 days reduce both the ratio of intimal to medial areas and the degree of stenosis by 80%, and suppress the expression of PCNA in both neointima and media. These results suggest that pentacyclic triterpenes may be of potential therapeutic value in vascular injury, and a possible treatment strategy for the prevention of the progression of atherosclerosis and restenosis after angioplasty.

The Road to Bioabsorbable Stents: Reaching Clinical Reality?

This article provides an overview of the evolution of revascularization devices since Grüntzig's initial introduction of balloon angioplasty in 1977. In-stent restenosis (ISR) is the major shortcoming of conventional (permanent-implant) stent therapy; even with the innovation and promising benefits of drug-eluting stents, management of ISR is very difficult. ISR is mainly caused by the interaction between the blood and the stent surface and a permanent mechanical irritation of the vascular tissue. Thus stenting technology has moved toward the development of temporary implants composed of biocompatible materials which mechanically support the vessel during the period of high risk for recoil and then completely biodegrade in the long term. Preclinical and first clinical experiences with bioabsorbable magnesium stents are discussed.

Estrogen enhances vasoconstrictive remodeling after injury in male rabbits

The complete spectrum of estrogen vascular effects remains unclear. In particular, estrogen effects in the vascular response to profound injury in males have not been explored in detail. Therefore, we submitted 44 male New Zealand rabbits weighing 3.4 +/- 0.6 kg to overdistention balloon injury of the right iliac artery. Rabbits were given 17beta-estradiol (5.45 micromol/day, sc) or vehicle for 7 days before and 14 days after injury, when the arteries were examined by post-mortem histomorphometry. Arteriographic caliber was assessed in vivo at baseline and before sacrifice. On day 14 after injury, in vivo arteriographic caliber (baseline = 2.44 +/- 0.43 mm) was decreased by 23.1 +/- 0.1% in controls and by 44.5 +/- 0.1% in estrogen-treated rabbits (P < 0.001). Neither the neointimal area nor the neointima/media area ratio changed after estrogen treatment. Collagen fraction was increased in the media and neointima of estrogen-treated rabbits vs control (1.38 +/- 1.30 vs 0.35 +/- 0.67, respectively, P = 0.01). Taken together, these findings suggest that estrogen increased negative vascular remodeling. Transcription of endothelial and inducible nitric oxide synthases (eNOS and iNOS) was analyzed by RT-PCR. eNOS mRNA expression was marginally increased after estrogen (P = 0.07) and injury. iNOS mRNA was increased 2- to 3-fold on day 14 after injury. With estrogen treatment, iNOS mRNA increased in uninjured arteries and exhibited a further 5.5-fold increase after injury. We concluded that estrogen increased lumen loss after balloon injury in male rabbits, likely by increased negative remodeling, which may be related to increased iNOS transcriptional rates.

Early elevation of interleukin-1beta and interleukin-6 levels after bare or drug-eluting stent implantation in patients with stable angina

INTRODUCTION

Drug-eluting stent (DES) implantation represents an important innovation in the treatment of coronary artery disease. However, inflammatory-related complications, including subacute thrombosis and in-stent restenosis, are still important limitations to percutaneous coronary intervention (PCI). The aim of this study was to compare early local release of interleukin 1beta (IL-1beta) and IL-6 proinflammatory cytokines after elective placement of either bare metal stents or DES.

MATERIALS AND METHODS

IL-1beta and IL-6 levels were assayed in plasma obtained from the coronary sinus both before and 20 min after stent implantation in 59 patients with stable angina, who were randomly assigned to receive bare, paclitaxel-, or sirolimus-eluting stents during elective PCI.

RESULTS

We found that IL-1beta and IL-6 levels were significantly increased in the coronary sinus of patients receiving either bare, paclitaxel- or sirolimus-eluting stents 20 min after stent implantation as compared with basal concentrations. The variation in the level of both cytokines was comparable among the three study groups.

CONCLUSIONS

A local release of proinflammatory cytokines occurs shortly after coronary stent placement, including DES, which is possibly related to plaque rupture and/or endothelium traumatism following the stenting procedure. This suggests that precocious anti-inflammatory treatment could be of benefit to further improve the PCI clinical outcome.

Biocompatibility screening in cardiovascular implants

BACKGROUND

Interest in information on biocompatibility of implants is increasing. The purpose of this paper is to discuss methods and results of pathological biocompatibility screening of explanted cardiovascular implants.

METHODS

Use of standard histology after embedding in paraffin is limited since metallic implants have to be removed during workup with disruption of the specimen. Alternatively, tissue blocks containing an implant can be embedded in methylmethacrylate or hydroxyethylmethacrylate and processed by sectioning with a diamond cutter and grinding, thus leaving the implant in situ and saving the tissue/implant interface for detection of local inflammatory reactions. Another important aspect of evaluation is the progress of thrombus organisation after initial fibrin clotting on the metal surface or in the inner part of occlusion devices. New methacrylate resins and embedding techniques allow for specific immunohistochemical staining of the specimen thus enabling characterisation of tissues surrounding the implant. Information on endothelialisation of the vascular surface of the implant can be obtained by means of immunohistochemistry or by scanning electron microscopy.

RESULTS

Illustrating the use of these technologies, we demonstrate findings in tissue specimens from animal studies with different types of devices (i.e. stents, occlusion devices). We present corresponding findings in human specimens with implants that were removed during corrective surgery for congenital heart defects. Early endothelialisation of the vascular surface was seen after implantation in all types of devices. Cells within occlusion devices could be characterised histologically and immunohistochemically as fibromuscular cells as seen in intimal hyperplasia after stent implantation. Inflammatory implant-host reactions ranged from mild to moderate (medical grade stainless steel, nitinol) to severe (polytetrafluoroethylene [PTFE]).

CONCLUSIONS

With an optimal work-up of cardiovascular implants, ingrowth and endothelialisation as well as inflammatory reactions in the surrounding tissue can be assessed. This information allows evaluation of individual tissue reactions to the implant and may serve as valuable basis for optimisation of biocompatibility by implant modification.

A frequent toll-like receptor (TLR)-2 polymorphism is a risk factor for coronary restenosis

Restenosis is a major problem for patients undergoing percutaneous transluminal coronary angioplasty (PTCA). Inflammatory processes and genetic factors have been suggested to be involved in the pathogenesis of both atherosclerosis and restenosis. The recently discovered family of Toll-like receptors (TLRs) consists of molecules that initiate signaling after host-pathogen interactions. Recently it has been shown that the TLRs are involved in the development and progression of atherosclerosis by interfering with lipid metabolisms and by mediating inflammation. TLR-2 is a key innate immunity receptor for sensing both endogenous inflammatory mediators and ligands of several microbial pathogens postulated to be involved in atherosclerosis. A frequent single nucleotide polymorphism (SNP) for the TLR-2 gene, resulting in a non-functional receptor, has been described. By genotyping two independent groups of patients receiving PTCA, followed by stent implantation in one group, we found a significantly enhanced frequency of the TLR-2 Arg753Gln SNP in patients with restenosis as compared to those without restenosis (PTCA: 7.21 versus 2.45%, P = 0.014; PTCA/stent: 6.86 versus 1.53%, P = 0.013). In contrast, a common TLR-4 SNP was similarly distributed among the patient groups investigated. We furthermore compared the frequency of both SNPs in the patients with an age-matched group of individuals without atherosclerosis and found a trend towards a lower frequency of the TLR-4 SNP in the atherosclerotic group (PTCA: 5.58; PTCA/stent: 3.85 versus 7.14%). We conclude that in restenosis a functional TLR-2 is protective and potentially involved in a reaction pattern preventing restenosis. Screening for the TLR-2 Arg753Gln SNP may be of importance for stratifying a patient's risk and for preventive and therapeutic measures.

Signature patterns of gene expression in mouse atherosclerosis and their correlation to human coronary disease

The propensity for developing atherosclerosis is dependent on underlying genetic risk and varies as a function of age and exposure to environmental risk factors. Employing three mouse models with different disease susceptibility, two diets, and a longitudinal experimental design, it was possible to manipulate each of these factors to focus analysis on genes most likely to have a specific disease-related function. To identify differences in longitudinal gene expression patterns of atherosclerosis, we have developed and employed a statistical algorithm that relies on generalized regression and permutation analysis. Comprehensive annotation of the array with ontology and pathway terms has allowed rigorous identification of molecular and biological processes that underlie disease pathophysiology. The repertoire of atherosclerosis-related immunomodulatory genes has been extended, and additional fundamental pathways have been identified. This highly disease-specific group of mouse genes was combined with an extensive human coronary artery data set to identify a shared group of genes differentially regulated among atherosclerotic tissues from different species and different vascular beds. A small core subset of these differentially regulated genes was sufficient to accurately classify various stages of the disease in mouse. The same gene subset was also found to accurately classify human coronary lesion severity. In addition, this classifier gene set was able to distinguish with high accuracy atherectomy specimens from native coronary artery disease vs. those collected from in-stent restenosis lesions, thus identifying molecular differences between these two processes. These studies significantly focus efforts aimed at identifying central gene regulatory pathways that mediate atherosclerotic disease, and the identification of classification gene sets offers unique insights into potential diagnostic and therapeutic strategies in atherosclerotic disease.

Assessment of coronary artery stents using 16-slice MDCT angiography: evaluation of a dedicated reconstruction kernel and a noise reduction filter

To compare the effect of different reconstruction kernels and a noise-reducing postprocessing filter on the delineation of coronary artery stents in 16-slice CT-angiography. Ten patients with coronary stents (seven LAD, five RCX and three RCA) were examined with a 16-slice MDCT using standard acquisition parameters. Images were reconstructed using a medium soft (B30f) and a dedicated, edge-enhancing kernel (B46f). Additional postprocessing with an edge-preserving filter was performed on B46f images to reduce the image noise. In multiplanar reformations (MPRs) along and perpendicular to the stent axis, intraluminal attenuation values and the visible lumen diameter were measured. Image noise was measured in the subcutaneous fat using a region of interest (ROI) technique. Arterial enhancement in the aorta was 275.1 HU. Attenuation in the stent lumen was 390.4, 340.0 and 346.8 HU in MPRs derived from B30f, original B46 and postprocessed B46f images. The mean noise level was 20.4, 35.0 and 24.9 HU respectively. The visible lumen diameter was significantly greater in B46f and postprocessed B46f images (2.17 and 2.16 mm), compared to 1.93 mm in B30f images (p<0.01). Edge-enhancing reconstruction kernels increase the visible stent lumen, but also increase image noise. Dedicated postprocessing filters can reduce the introduced noise without a loss of spatial resolution.

Sirolimus-eluting stent implantation for unprotected left main coronary artery stenosis

OBJECTIVES

This study was designed to compare the clinical and angiographic outcomes of sirolimus-eluting stent (SES) and bare metal stent (BMS) implantation for unprotected left main coronary artery (LMCA) stenosis.

BACKGROUND

The safety and effectiveness of SES implantation for unprotected LMCA stenosis have not been ascertained.

METHODS

Elective SES implantation for de novo unprotected LMCA stenosis was performed in 102 consecutive patients with preserved left ventricular function from March 2003 to March 2004. Data from this group were compared to those from 121 patients treated with BMS during the preceding two years.

RESULTS

Compared to the BMS group, the SES group received more direct stenting, had fewer debulking atherectomies, had a greater number of stents, had more segments stented, and underwent more bifurcation stenting. The procedural success rate was 100% for both groups. There were no incidents of death, stent thrombosis, Q-wave myocardial infarction (MI), or emergent bypass surgery during hospitalization in either group. Despite less acute gain (2.06 +/- 0.56 mm vs. 2.73 +/- 0.73 mm, p < 0.001) in the SES group, SES patients showed a lower late lumen loss (0.05 +/- 0.57 mm vs. 1.27 +/- 0.90 mm, p < 0.001) and a lower six-month angiographic restenosis rate (7.0% vs. 30.3%, p < 0.001) versus the BMS group. At 12 months, the rate of freedom from death, MI, and target lesion revascularization was 98.0 +/- 1.4% in the SES group and 81.4 +/- 3.7% in the BMS group (p = 0.0003).

CONCLUSIONS

Sirolimus-eluting stent implantation for unprotected LMCA stenosis appears safe with regard to acute and midterm complications and is more effective in preventing restenosis compared to BMS implantation.

Alterations in wall shear stress predict sites of neointimal hyperplasia after stent implantation in rabbit iliac arteries

Restenosis resulting from neointimal hyperplasia (NH) limits the effectiveness of intravascular stents. Rates of restenosis vary with stent geometry, but whether stents affect spatial and temporal distributions of wall shear stress (WSS) in vivo is unknown. We tested the hypothesis that alterations in spatial WSS after stent implantation predict sites of NH in rabbit iliac arteries. Antegrade iliac artery stent implantation was performed under angiography, and blood flow was measured before casting 14 or 21 days after implantation. Iliac artery blood flow domains were obtained from three-dimensional microfocal X-ray computed tomography imaging and reconstruction of the arterial casts. Indexes of WSS were determined using three-dimensional computational fluid dynamics. Vascular histology was unchanged proximal and distal to the stent. Time-dependent NH was localized within the stented region and was greatest in regions exposed to low WSS and acute elevations in spatial WSS gradients. The lowest values of WSS spatially localized to the stented area of a theoretical artery progressively increased after 14 and 21 days as NH occurred within these regions. This NH abolished spatial disparity in distributions of WSS. The results suggest that stents may introduce spatial alterations in WSS that modulate NH in vivo.

Antisense oligodeoxyribonucleotide as to the growth factor midkine suppresses neointima formation induced by balloon injury

Restenosis is the major clinical problem of angioplasty. We have previously shown that neointima formation is strikingly suppressed in midkine (MK)-deficient mice. Neointima formation is restored if MK protein is administrated to the deficient mice. MK is a heparin-binding growth factor and implicated in the migration of inflammatory cells and vascular smooth muscle cells. Consistently, the suppression of neointima formation in the deficient mice is accompanied by suppression of recruitment of inflammatory cells into the vascular wall. Here, we evaluated the potential of MK antisense oligodeoxyribonucleotide (ODN) for the prevention of restenosis. We cloned the cDNA of rabbit MK, which showed a strongly conserved sequence in mammals. The balloon injury induced MK expression, with the maximum level occurring 7-14 days after angioplasty, in the rabbit carotid artery. Two antisense ODNs suppressed the production of MK in a rabbit kidney cell line, RK13 cells, one of which was then transfected into the arterial wall by means of lipofection immediately after balloon treatment. The antisense ODN suppressed MK induction in vivo and consequently suppressed neointima formation to 60% of the control level. These results suggest that MK is a candidate molecular target for the therapy for vascular restenosis.

Drug-eluting stents: a mechanical and pharmacologic approach to coronary artery disease

Coronary artery disease is the largest killer of men and women in the United States and costs the health care system billions of dollars annually. Several advances in both mechanical and pharmacologic treatment of coronary artery disease have occurred in recent decades. Mechanically, percutaneous coronary intervention is commonly used to treat coronary atherosclerosis. This approach has dramatically reduced both morbidity and mortality for patients with different levels of severity of coronary artery disease. However, percutaneous coronary intervention is limited by restenosis, which is an increase in growth of the intimal layer of the vessel wall. Despite the introduction of intracoronary stents and the addition of systemic pharmacotherapy, restenosis still affects a significant number of patients. The new technology of drug-eluting stents combines mechanical and pharmacologic approaches to prevent restenosis. Various types of these stents exist in different stages of development; several have been shown to prevent or reduce intimal growth after stent deployment. An understanding of how this combined mechanical and pharmacologic approach reduces restenosis requires consideration of complex issues in pathophysiology and pharmacology.

Drug-coated Stents

Since its introduction in 1977, the success of percutaneous interventional cardiology has been limited by the occurrence of restenosis. Drug-eluting stents, particularly sirolimus- and paclitaxel-coated stents, have been shown in randomized controlled trials to dramatically reduce restenosis in single, de novo, native coronary arteries. Over the last 2 years, investigators have reported that these stents can also reduce restenosis in more complex patient situations such as in diabetics, during acute coronary syndromes, in long atherosclerotic lesions and small arteries, and even after in-stent restenosis. These outcomes increase the clinical value of this technology to "real world" practice. This article reviews the current state of our knowledge regarding drug-eluting stents and identifies areas for further research.

Attenuation of neointima formation through the inhibition of DNA repair enzyme PARP-1 in balloon-injured rat carotid artery

Increased oxidative stress is a major characteristic of restenosis after angioplasty. The oxidative stress is mainly created by oxidants such as reactive oxygen species (ROS), which are assumed to play an important role in neointima formation after angioplasty. DNA is a sensitive target for oxidants; however, oxidative DNA damage remains a poorly examined field in the pathogenesis of restenosis. In the present study, we demonstrated that the expression of the oxidative DNA damage marker 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxo-dG) was quickly increased in rat carotid arteries after balloon injury. It reached its peak at 14 days after injury and still kept high expression at 28 days after injury. The immunostaining of 8-oxo-dG was present predominantly in the neointima. In response to oxidative DNA damage, the DNA repair enzyme poly(ADP-ribose) polymerase-1 (PARP-1) was significantly increased after balloon injury. The time course change and location of PARP-1 is similar to that of 8-oxo-dG. Daily injections of the PARP-1 inhibitor PJ34 (5 mg.kg(-1).day(-1) ip) attenuated neointima formation by approximately 40% at 7, 14, and 28 days after balloon injury. Treatment with PJ34 inhibited leukocyte infiltration and improved both anatomic (reendothelialization) and functional (endothelial function) recovery of endothelial cells after balloon injury. In conclusion, levels of oxidative DNA damage and the DNA repair enzyme PARP-1 are increased in vessels after balloon injury. Inhibition of PARP-1 attenuates neointima formation through inhibition of leukocyte infiltration and improvement of endothelial cell recovery after balloon injury. Targeting of the DNA repair enzyme might be a therapeutic strategy for restenosis.