Heparin infusion prior to stenting (HIPS) trial: final results of a prospective, randomized, controlled trial evaluating the effects of local vascular delivery on intimal hyperplasia

Inhibitory effect of CP-25 on intimal formation and vascular hyperplasia via suppression of GRK2/ERK1/2/EVI1 signaling

Excessive proliferation, migration and dedifferentiation of vascular smooth muscle cells (VSMCs) are the center of intimal formation during in-stent restenosis and vein graft disease. Paeoniflorin-6'-O-benzene sulfonate (CP-25) is known to suppress inflammation and atherogenesis. However, the potential effect of CP-25 on intimal formation remains elusive. In the present study, we found that CP-25 significantly attenuated wire injury-induced intimal formation in C57BL/6 mice (intimal area: 2.64 ± 0.25 × 10⁴ μm² vs. 1.53 ± 0.21 × 10⁴ μm², P < 0.05) and vascular hyperplasia indicated by PCNA staining. In vitro experiments showed that CP-25 significantly alleviated human aortic smooth muscle cell (HASMC) proliferation, migration and dedifferentiation induced by PDGF-BB. Mechanistically, CP-25 inhibited GRK2 phosphorylation through PDGF receptor in the presence of PDGF-BB. In accordance with these results, CP-25 disrupted the interaction of GRK2 with ERK1/2 and suppressed the activation of ERK1/2 signaling in HASMCs. EVI1, which is considered as a downstream of ERK1/2 signaling and a novel transcription factor for VSMC differentiation, was also downregulated by CP-25 treatment. Moreover, overexpression of EVI1 partly restored the decreased proliferation and dedifferentiation of HASMCs treated by CP-25. Collectively, these findings suggested that CP-25 could alleviate intimal formation in response to wire injury via suppression of the interaction of GRK2 and ERK1/2 and EVI1 activation, indicating CP-25 might serve as a potent pharmaceutical for intimal formation.

Adeno-associated viral vectors based on serotype 3b use components of the fibroblast growth factor receptor signaling complex for efficient transduction

Adeno-associated virus type 3b (AAV3b) has been largely ignored by gene therapists because of the inability of vectors based on this serotype to transduce target tissues efficiently. Here we describe a phenomenon unique to AAV3b in that vectors based on this serotype mediate enhanced transduction in the presence of heparin. Among the many biological functions attributed to heparin, its interaction with, and ability to regulate, several growth factors (GFs) and growth factor receptors (GFRs) has been well characterized. Using GFR-overexpressing cell lines, soluble GFs and heparins, as well as specific GFR inhibitors, we have demonstrated a requirement for fibroblast growth factor receptor-2 (FGFR2) and FGF1 in the heparin-mediated augmentation of AAV3b vector transduction. In contrast to AAV2, we establish that heparin can be used as an adjunct with AAV3b to further increase transduction in a variety of cells and target tissues, additionally suggesting that AAV3b may be an attractive viral vector for clinical use during procedures in which heparin is used. In summary, AAV3b exhibits FGFR2-dependent, markedly enhanced transduction efficiency in the presence of heparin and FGFs, which could make it a useful vector for gene therapy in a variety of human diseases.

Prevention of coronary in-stent restenosis and vein graft failure: does vascular gene therapy have a role?

Coronary artery bypass grafting (CABG) and percutaneous coronary intervention (PCI), including stent insertion, are established therapies in both acute coronary syndromes (ACS) and symptomatic chronic coronary artery disease refractory to pharmacological therapy. These continually advancing treatments remain limited by failure of conduit grafts in CABG and by restenosis or thrombosis of stented vessel segments in PCI caused by neointimal hyperplasia, impaired endothelialisation and accelerated atherosclerosis. While pharmacological and technological advancements have improved patient outcomes following both procedures, when grafts or stents fail these result in significant health burdens. In this review we discuss the pathophysiology of vein graft disease and in-stent restenosis, gene therapy vector development and design, and translation from pre-clinical animal models through human clinical trials. We identify the key issues that are currently preventing vascular gene therapy from interfacing with clinical use and introduce the areas of research attempting to overcome these.

Drug delivery via nano-, micro and macroporous coronary stent surfaces

Drug-eluting stents (DESs) have revolutionized the treatment of occlusive coronary artery disease via marked reduction of in-stent restenosis. One critical feature for successful DESs is the sustained release of drugs, which is achieved using a polymer coating in the present generation of DESs. However, recent studies have raised a concern that polymers may trigger allergic reactions and/or prolonged inflammation in some patients. These untoward reactions may eventually lead to undesirable clinical events, including stent thrombosis and sudden cardiac death. A new drug delivery technology, using a porous stent surface, may offer desirable drug elution properties without the use of polymers, and may translate into an improved safety profile for the next-generation DESs.

The drug-based pipeline against restenosis

More than 1 million percutaneous coronary interventions (PCIs) are performed yearly worldwide. Restenosis is the recurrent narrowing that can occur within 6 months following an initially successful PCI. Although drug-eluting stents have accomplished remarkable success, restenosis has not been eliminated and optimisation of both the polymers and drugs associated with them is desirable. This article reviews the presently available and potential preventive approaches against restenosis, including the sirolimus and paclitaxel drug-eluting stents.

Pharmacological treatment for prevention of restenosis

Coronary artery disease (CAD) is the leading cause of mortality and morbidity among adults in the Western world. Coronary artery bypass grafting and percutaneous coronary interventions (PCI) have gained widespread acceptance for the treatment of symptomatic CAD. There has been an explosive growth worldwide in the utilisation of PCI, such as balloon angioplasty and stenting, which now accounts for over 50% of coronary revascularisation. Despite the popularity of PCI, the problem of recurrent narrowing of the dilated artery (restenosis) continues to vex investigators. In recent years, significant advances have occurred in the understanding of restenosis. Two processes seem to contribute to restenosis: remodelling (vessel size changes) and intimal hyperplasia (vascular smooth muscle cell [VSMC] proliferation and extracellular matrix [ECM] deposition). Despite considerable efforts, pharmacological approaches to decrease restenosis have been largely unsuccessful and the only currently applied modality to reduce the restenosis rate is stenting. However, stenting only prevents remodelling and does not inhibit intimal hyperplasia. Several potential targets for inhibiting restenosis are currently under investigation including platelet activation, the coagulation cascade, VSMC proliferation and migration, and ECM synthesis. In addition, new approaches for local drug therapy, such as drug eluting stents, are currently being evaluated in preclinical and clinical studies. In this article, we critically review the current status of drugs that are being evaluated for restenosis at various stages of development (in vitro, preclinical animal models and human trials).

Inhibition of Intimal Hyperplasia by Direct Thrombin Inhibitors in an Animal Vein Bypass Model

Many functions of the coagulation system have nonthrombotic effects. The indirect thrombin inhibitor heparin has been previously shown to be effective in limiting intimal hyperplasia (IH). We sought to study the effect of thrombin on IH by using two direct thrombin inhibitors (DTIs), argatroban and lepirudin. Sprague-Dawley rats underwent interposition vein grafting to the carotid artery. Vein grafts were treated with either saline (n = 6) or one of the two DTIs (n = 6 for both). At 30 days, the rats were sacrificed and vessels were perfusion fixed. Sections of the proximal carotid artery, graft, and both anastomoses were stained with both hematoxlyin/eosin and von Gieson's elastin stain. Sections were examined and compared for luminal area and intima-to-media (IM) ratio. The vessels treated with DTIs had less (p < 0.05) IH (IM ratio for proximal anastomosis: control 1.036 +/- 0.857, lepirudin 0.373 +/- 0.21, argatroban 0.182 +/- 0.118) and better lumen preservation than the control vessels (lumen area of proximal anastomosis: control 1.69 +/- 0.9, lepirudin 2.45 +/- 0.74, argatroban 2.81 +/- 0.78). There were no thromboses in the DTI-treated vessels. Dilatation of the graft segment was noted in the argatroban group. Thus, DTIs are effective at reducing IH in a small-animal model, suggesting that inhibition of thrombin has a protective role in IH. In addition, a difference of action between DTIs is suggested by the dilatation seen only in the argatroban-treated graft sections.

Sirolimus-eluting stents versus standard stents in patients with stenosis in a native coronary artery

BACKGROUND

Preliminary reports of studies involving simple coronary lesions indicate that a sirolimus-eluting stent significantly reduces the risk of restenosis after percutaneous coronary revascularization.

METHODS

We conducted a randomized, double-blind trial comparing a sirolimus-eluting stent with a standard stent in 1058 patients at 53 centers in the United States who had a newly diagnosed lesion in a native coronary artery. The coronary disease in these patients was complex because of the frequent presence of diabetes (in 26 percent of patients), the high percentage of patients with longer lesions (mean, 14.4 mm), and small vessels (mean, 2.80 mm). The primary end point was failure of the target vessel (a composite of death from cardiac causes, myocardial infarction, and repeated percutaneous or surgical revascularization of the target vessel) within 270 days.

RESULTS

The rate of failure of the target vessel was reduced from 21.0 percent with a standard stent to 8.6 percent with a sirolimus-eluting stent (P<0.001)--a reduction that was driven largely by a decrease in the frequency of the need for revascularization of the target lesion (16.6 percent in the standard-stent group vs. 4.1 percent in the sirolimus-stent group, P<0.001). The frequency of neointimal hyperplasia within the stent was also decreased in the group that received sirolimus-eluting stents, as assessed by both angiography and intravascular ultrasonography. Subgroup analyses revealed a reduction in the rates of angiographic restenosis and target-lesion revascularization in all subgroups examined.

CONCLUSIONS

In this randomized clinical trial involving patients with complex coronary lesions, the use of a sirolimus-eluting stent had a consistent treatment effect, reducing the rates of restenosis and associated clinical events in all subgroups analyzed.

Evolving Strategies for the Prevention and Treatment of Coronary Restenosis

Percutaneous coronary intervention has become an increasingly attractive alternative to medical therapy and surgical revascularization for the treatment of coronary artery disease. Over 1.5 million interventional procedures are performed annually worldwide, with the rate of procedures performed continuing to rise dramatically. Restenosis following percutaneous coronary intervention occurs at rates of 20% to 40% and has remained the Achilles heel of the procedure. Numerous early attempts at the prevention of restenosis with oral pharmacologic agents, such as antithrombotic therapies, lipid lowering agents, vasodilators, and growth factor inhibitors, failed to show benefit in clinical trials. The introduction of intracoronary stents resulted in a 30% reduction in restenosis rates by abolishing the early vessel recoil following angioplasty. However, as more complex lesions underwent percutaneous coronary intervention with stenting, rates of “in-stent” restenosis remained high (20% to 30%). With technologic advances and greater understanding of vascular pathobiology, novel therapeutic strategies, such as local delivery of ionizing radiation, immunosuppressive agents, and gene therapy, have been deployed to prevent coronary restenosis. In addition, a number of mechanical and radiation-based strategies have been used to treat those patients who develop restenosis. This review considers these emerging strategies for the prevention and treatment of restenosis.

Effect of atorvastatin on postcardiac transplant increase in low-density lipoprotein cholesterol reduces development of intimal hyperplasia and progression of endothelial dysfunction

Following cardiac transplantation, accelerated coronary disease limits long-term survival. Because statins may reduce the progression of the disease in part by their anti-inflammatory effects, this study was designed to assess if atorvastatin prevented neointimal hyperplasia and endothelial dysfunction independently of baseline cholesterol levels. Patients were randomized to usual therapy (n = 13) or to 10 to 20 mg of atorvastatin (n = 12). Control subjects received niacin when their low-density lipoprotein (LDL) cholesterol levels were >130 mg/dl (n = 4). Neointimal hyperplasia by intracoronary ultrasonography, endothelial dependent vascular reactivity, and coronary flow reserve were measured at baseline and 1 year. Control group total cholesterol (203 +/- 11 to 200 +/- 13 mg/dl) and LDL (116 +/- 10 to 119 +/- 11 mg/dl) remained stable, whereas there was a nonsignificant reduction at 12 months in the atorvastatin group (total cholesterol 216 +/- 28 to 178 +/- 21 mg/dl; LDL 126 +/- 17 to 100 +/- 18 mg/dl). At 2 to 3 months there was a significant increase in total cholesterol and LDL cholesterol that was reduced with atorvastatin. At 1 year, patients taking atorvastatin showed a decrease in new or progressing lesions (2.5 +/- 1.7 vs 4.2 +/- 1.8 lesions/patient, p = 0.02), progression of maximal intimal thickness (0.12 +/- 0.07 vs 0.52 +/- 0.17 mm, p = 0.04), and percent area stenosis (5.9 +/- 2.2% vs 19.0 +/- 5.5%, p = 0.04). Atorvastatin ameliorated progressive endothelial dysfunction, whereas coronary flow reserve was unchanged in both groups. Atorvastatin administered to patients with normal or mild hypercholesterolemia in the initial year after transplant reduced the initial increase in LDL cholesterol, and, by doing so, prevented the development and progression of coronary artery lesions and endothelial dysfunction with only mild long-term decreases in cholesterol levels.

Separate and combined effects of local and continuous intravenous administration of beta-cyclodextrin tetradecasulfate on intimal hyperplasia after angioplasty in porcine coronary arteries

BACKGROUND

Beta-Cyclodextrin tetradecasulfate binds fibroblast growth factors and possesses anticoagulant properties. This study was designed to assess the separate and combined effects of local intramural delivery and intravenous administration of beta-cyclodextrin tetrade-casulfate on neointimal formation and arterial damage following angioplasty.

METHODS AND RESULTS

Fifty-two pigs randomized into four groups underwent coronary artery angioplasty: 1) control, 2) continuous intravenous infusion of 100 mg/kg/d of beta-cyclodextrin tetradecasulfate, 3) intramural delivery of 1250 mg beta-cyclodextrin tetradecasulfate, 4) intramural delivery of 1250 mg beta-cyclodextrin tetradecasulfate followed by continuous intravenous infusion of 100 mg/kg/d. Fourteen days after injury, morphometric analysis revealed that arteries randomized to the intravenous beta-cyclodextrin tetradecasulfate groups had a decreased normalized neointima area: control, 3.03 +/- 0.75 mm(2); intravenous, 1.67 +/- 0.73 mm(2) (40% decrease; P < 10(-7)); intravenous plus local, 1.95 +/- 0.76 mm(2) (30% decrease; P < 10(-5)). There was no difference in neointimal response following local beta-cyclodextrin tetradecasulfate delivery only (2.82 +/- 1.14 mm(2)). Coronary arterial damage, defined as aneurysm, dissection, adventitial rupture, and retromedial hematoma was similar in all groups (12% in control and local groups, 10% in the intravenous group, 14% in the intravenous plus local; NS). Bleeding complications were more frequent in the intravenous and intravenous plus local groups compared to the local and control groups (23%vs 7.6% and 0%, respectively; P < 0.05).

CONCLUSIONS

Continuous intravenous administration of beta-cyclodextrin tetradecasulfate substantially reduced intimal hyperplasia, while intramural delivery had no effect, indicating that a single bolus of beta-cyclodextrin tetradecasulfate did not reduce intimal hyperplasia. There was no additive effect of local intramural delivery of beta-cyclodextrin tetradecasulfate. However, local delivery of beta-cyclodextrin tetradecasulfate induced less bleeding complications and did not lead to additional arterial injury, indicating that local delivery of an anticoagulant does not cause additional arterial injury.

Local delivery of a hydrophobic heparin reduces neointimal hyperplasia after balloon injury in rat carotid but not pig coronary arteries

BACKGROUND

Intimal hyperplasia following percutaneous interventional vascular procedures is a major cause of restenosis. Although heparin inhibits intimal hyperplasia, it has not proven clinically useful in part due to an inadequate duration of intramural drug residence. This study was designed to evaluate the efficacy of local delivery of hydrophobic heparin (PTIR-RS-1), exhibiting increased intramural binding, on neointimal hyperplasia after angioplasty injury.

METHODS AND RESULTS

PTIR-RS-1 was delivered locally into rat carotid arteries at three doses: 0.1 mM (440 IU), 0.3 mM (1320 IU), or 1.0 mM (4400 IU). Animals were killed at 14 days. In the pig, the doses tested were the low dose in the rat and a high dose 1 log higher. Animals were killed 28 days later. Morphometric analysis was performed to evaluate the intima: media ratio in rats and the normalized neointimal area in pigs. In rats a significant reduction in neointimal to medial area ratio from 0.73 +/- 0.15 for control vs 0.80 +/- 0.27 for sodium heparin (P = NS) and 0.15 +/- 0.07 for the 0.1 mM PTIR-RS-1 dose (P < 0.008). In pigs, PTIR-RS-1 the high dose reduced the normalized neointimal area by 16%, a difference that was not statistically significant.

CONCLUSIONS

Increased hydrophobicity of heparin reduced neointimal area following balloon overstretch injury in the rat carotid but not the pig coronary artery model. This study attests to the importance of performing studies evaluating the pharmacologic effect of local delivery of a medication in at least two animal models of restenosis.

Mechanisms of angioplasty and stent restenosis: implications for design of rational therapy

Restenosis after angioplasty or stenting remains the major limitation of both procedures. A vast array of drug therapies has been used to prevent restenosis, but they have proven to be predominantly unsuccessful. Recent trends in drug therapy have attempted to refine the molecular and biological targets of therapy, based on the assumption that a single biological process or molecule is critical to restenosis. In contrast, both stenting and brachytherapy, which are highly nonspecific, can successfully reduce restenosis after angioplasty or stenting, respectively. This review examines the biology of both angioplasty and stent stenosis, focussing on human studies. We also review the landmark human trials that have definitively proven successful therapies, such as stenting and brachytherapy. We suggest that the successful trials of stenting and brachytherapy and the failure of other treatments have highlighted the shortcomings of conventional animal models of arterial intervention, and gaps in our knowledge of human disease. In contrast to arguments advocating gene therapy, these studies suggest that the most likely successful drug therapy will have a wide therapeutic range, targeting as many of the components or biological processes contributing to restenosis as possible.

Extent and distribution of in-stent intimal hyperplasia and edge effect in a non-radiation stent population

Intimal hyperplasia within the body of the stent is the primary mechanism for in-stent restenosis; however, stent edge restenosis has been described after brachytherapy. Our current understanding about the magnitude of in vivo intimal hyperplasia and edge restenosis is limited to data obtained primarily from select, symptomatic patients requiring repeat angiography. The purpose of this study was to determine the extent and distribution of intimal hyperplasia both within the stent and along the stent edge in relatively nonselect, asymptomatic patients scheduled for 6-month intravascular ultrasound (IVUS) as part of a multicenter trial: Heparin Infusion Prior to Stenting. Planar IVUS measurements 1 mm apart were obtained throughout the stent and over a length of 10 mm proximal and distal to the stent at index and follow-up. Of the 179 patients enrolled, 140 returned for repeat angiography and IVUS at 6.4 +/- 1.9 months and had IVUS images adequate for analysis. Patients had 1.2 +/- 0.6 Palmaz-Schatz stents per vessel. There was a wide individual variation of intimal hyperplasia distribution within the stent and no mean predilection for any location. At 6 months, intimal hyperplasia occupied 29.3 +/- 16.2% of the stent volume on average. Lumen loss within 2 mm of the stent edge was due primarily to intimal proliferation. Beyond 2 mm, negative remodeling contributed more to lumen loss. Gender, age, vessel location, index plaque burden, hypercholesterolemia, diabetes, and tobacco did not predict luminal narrowing at the stent edges, but diabetes, unstable angina at presentation, and lesion length were predictive of in-stent intimal hyperplasia. In a non-radiation stent population, 29% of the stent volume is filled with intimal hyperplasia at 6 months. Lumen loss at the stent edge is due primarily to intimal proliferation.

Current approaches to therapy for vascular injury

Vascular injury is a ubiquitous phenomenon which can be both occult (such as with hyperlipidemia) and overt (such as with angioplasty). While the exact pathophysiology differs between acute and chronic atherosclerosis, both lesions can be mechanistically explained by the vasculature's exaggerated response to injury. Pharmacological attempts to treat atherosclerotic cardiovascular disease can be categorised by their role in modifying this inflammatory response. This manuscript reviews current therapy for cardiovascular injury at two levels: the chronic smouldering atheromatous lesion and intimal hyperplasia associated with acute vascular intervention. In addition, future therapeutic strategies, based within this inflammatory paradigm, are discussed.

Restenosis and gene therapy

Atherosclerosis is one of the main causes of mortality and morbidity in westernised countries. Treatment of symptomatic atherosclerosis by angioplasty involves major vascular responses such as neointima formation and constrictive vascular remodelling leading to restenosis. Stent placement prevents vasoconstriction but is associated with in-stent neointima formation. Therefore, stent placement requires adjunctive therapy. In this review we discuss the potential of local gene therapy for restenosis. More particularly, we focus on strategies to inhibit smooth muscle cell (SMC) proliferation and migration, prevent thrombosis, decrease oxidative stress in the arterial wall and enhance re-endothelialisation associated with adaptive remodelling. The potential of different vector systems and devices for local gene transfer in the arterial wall is discussed.

Novel approaches for the prevention of restenosis

Restenosis, the re-narrowing of the lumen of the coronary artery, in the months following a successful percutaneous balloon angioplasty or stenting, remains the main limitation to percutaneous coronary revascularisation. Serial intravascular ultrasound studies have shown that restenosis after conventional balloon angioplasty represents a complex interplay between elastic recoil, smooth muscle proliferation and vascular remodelling, while restenosis after stent deployment is due almost entirely to smooth muscle hyperplasia and matrix proliferation. Despite intensive investigation in animal models and in clinical trials, most pharmacological agents have been found to be ineffective in preventing restenosis after percutaneous balloon angioplasty or stenting. Although studies frequently report success in the suppression of neointimal proliferation in animal models of balloon vascular injury, few of them have been successful in clinical trials. Lately, the advent of endovascular radiation, new antiproliferative agents, recombinant DNA, growth factor regulators and novel local drug delivery systems have shown promising results. In the past five years, intracoronary radiation with gamma- and beta-emitting sources has been evaluated intensively with very encouraging results. This is the first potent non-pharmacological approach that has been successful in a large number of patients in controlling excessive tissue proliferation. It is very likely that a combination of stents and pharmacological and/or non-pharmacological inhibition of neointimal hyperplasia will likely result in further reductions in the incidence if restenosis. The continued attractiveness of percutaneous coronary revascularisation, as an alternative to medical treatment or bypass surgery for patients with coronary artery disease, will depend upon our ability to control the restenotic process. Due to the vast literature on the subject, this review will focus mainly on clinical trials that show the most promise and will highlight those that warrant further investigation.