Novel approaches for the prevention of restenosis

Variation in the human soluble epoxide hydrolase gene and risk of restenosis after percutaneous coronary intervention

Background

Restenosis represents the major limiting factor for the long-term efficacy of percutaneous coronary intervention (PCI). Several genetic factors involved in the regulation of the vascular system have been described to play a role in the pathogenesis of restenosis. We investigated whether the EPHX2 K55R polymorphism, previously linked to significantly higher risk for coronary heart disease (CHD), was associated with the occurrence of restenosis after PCI. The association with incident CHD should have been confirmed and a potential correlation of the EPHX2 K55R variant to an increased risk of hypertension was analysed.

Methods

An overall cohort of 706 patients was studied: This cohort comprised of 435 CHD patients who had undergone successful PCI. Follow-up coronary angiography in all patients was performed 6 months after intervention. Another 271 patients in whom CHD had been excluded by coronary angiography served as controls. From each patient EDTA-blood was drawn at the baseline ward round. Genomic DNA was extracted from these samples and genotyping was performed by real-time PCR and subsequent melting curve analysis.

Results

In CHD patients 6 month follow-up coronary angiography revealed a restenosis rate of 29.4%, classified as late lumen loss as well as lumen re-narrowing ≥ 50%.

Statistical analysis showed an equal genotype distribution in restenosis patients and non-restenosis patients (A/A 82.0% and A/G + G/G 18.0% versus A/A 82.1% and A/G + G/G 17.9%). Moreover, neither a significant difference in the genotype distribution of CHD patients and controls nor an association with increased risk of hypertension was found.

Conclusion

The results of the present study indicate that the EPHX2 K55R polymorphism is not associated with restenosis after PCI, with incidence of CHD, or with an increased risk of hypertension and therefore, can not serve as a predictor for risk of CHD or restenosis after PCI.

A Novel αvβ3 Integrin Antagonist Suppresses Neointima Formation for More Than 4 Weeks After Balloon Injury in Rats

OBJECTIVES

We performed a detailed kinetic analysis in a rat balloon injury model to clarify the essential roles of alphavbeta3 integrin and endothelial cell (EC) regeneration in neointima formation. Using this model, we evaluated the antistenotic effect of Dainippon compound BS-1417, a novel alphavbeta3 integrin antagonist.

METHODS AND RESULTS

Kinetic analysis using RT-PCR showed that alphavbeta3 integrin-related genes are upregulated before neointima formation. Morphological and functional analyses revealed that EC regeneration requires >4 weeks after injury, and that recovery of EC normal function coincides with the arrest of neointima formation. Subcutaneous infusion of BS-1417 for 2, 4, 7, or 12 weeks after injury potently inhibited neointima formation without affecting EC regeneration. Although withdrawal of treatment with BS-1417 after short-term administration after injury resulted in catch-up growth of neointima, a long-term study suggested that this catch-up growth can be prevented by continuous administration of BS-1417 until EC regeneration.

CONCLUSIONS

We clarified that alphavbeta3 integrin and EC regeneration play an essential role in neointima formation, and that continuous administration of BS-1417 potently and stably inhibits neointima formation without affecting EC regeneration. These findings suggest that BS-1417 might be useful as a novel systemic drug for the treatment of restenosis.

Polymers incorporating nitric oxide releasing/generating substances for improved biocompatibility of blood-contacting medical devices

The current state-of-the-art with respect to the preparation, characterization and biomedical applications of novel nitric oxide (NO) releasing or generating polymeric materials is reviewed. Such materials show exceptional promise as coatings to prepare a new generation of medical devices with superior biocompatiblity. Nitric oxide is a well-known inhibitor of platelet adhesion and activation, as well as a potent inhibitor of smooth muscle cell proliferation. Hence, polymers that release or generate NO locally at their surface exhibit greatly enhanced thromboresistivity and have the potential to reduce neointimal hyperplasia caused by device damage to blood vessel walls. In this review, the use of diazeniumdiolates and nitrosothiols as NO donors within a variety polymeric matrixes are summarized. Such species can either be doped as discrete NO donors within polymeric films, or covalently linked to polymer backbones and/or inorganic polymeric filler particles that are often employed to enhance the strength of biomedical polymers (e.g., fumed silica or titanium dioxide). In addition, very recent efforts to create catalytic polymers possessing immobilized Cu(II) sites capable of generating NO from endogenous oxidized forms of NO already present in blood and other physiological fluids (nitrite and nitrosothiols) are discussed. Preliminary literature data illustrating the efficacy of the various NO release/generating polymers as coatings for intravascular sensors, extracorporeal blood loop circuits, and arteriovenous grafts/shunts are reviewed.

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).

Discovery of a potent and selective αvβ3 integrin antagonist with strong inhibitory activity against neointima formation in rat balloon injury model

A new series of phenylpiperazine-based derivatives with strong antagonistic activity for alpha v beta 3 integrin were synthesized. Of these derivatives, the fluorine-substituted compound 8 showed strong inhibitory activity and high selectivity for alpha v beta 3 integrin receptor (IC(50) = 0.055 nM). In vivo evaluation of the antistenotic effects of 8 indicated that this compound significantly inhibits neointima formation in rat balloon injury model.

Bioresorbable polymeric stents: current status and future promise

Metal stents and, more recently, polymer-coated metal stents are used to stabilize dissections, eliminate vessel recoil, and guide remodeling after balloon angioplasty and other treatments for arterial disease. Bioresorbable polymeric stents are being developed to improve the biocompatibility and the drug reservoir capacity of metal stents, and to offer a transient alternative to the permanent metallic stent implant. Following a brief review of metal stent technology, the emerging class of expandable, bioresorbable polymeric stents is described, with emphasis on developments in the authors' laboratory.