Intracoronary brachytherapy for the prevention of restenosis after percutaneous coronary revascularization

Long-term safety of drug-eluting stents

Stent implantation in coronary stenosis has revolutionized the treatment of coronary artery disease. The introduction of antirestenotic drug coatings further improved their efficacy in reducing target vessel revascularizations. With increasing use of drug-eluting stents (DES), stent thrombosis (ST) rose as potentially fatal major complication. Initially, the incidence of ST late after stent implantation seemed to be similar for DES and bare metal stents until several studies proved otherwise in first-generation DES. Since then, the design and components of DES have been changed and new polymers, drugs and different combinations of platelet inhibitors have been introduced to further improve the safety of DES. In this review, the authors focus on the relationship between DES, lesion anatomy, implantation technique and pharmacology to avoid the occurrence of ST. Furthermore, the relationship between dual antiplatelet therapy, bleeding rate and its significant impact on patient outcome is discussed. Finally, some promising future concepts are highlighted.

Catheter-Based Treatment of Coronary Artery Disease

September 2007 marked the 30-year anniversary of the first human percutaneous coronary intervention, an index event that changed the course of modern-day cardiovascular care. Before that first procedure, adult invasive cardiology focused on diagnostic angiography as well as hemodynamic assessment of structural heart disease. Since that initial procedure, percutaneous coronary intervention has become the most frequently performed coronary revascularization procedure worldwide. Several factors have been responsible for this dramatic paradigm shift, the most prominent being identification of opportunities for technical improvement and the application of innovation and investigation in concert with colleagues, professional societies, and industry. These approaches will continue to be of paramount importance as new technologies are brought to bear on an increasingly broader group of patients with cardiovascular disease.

Increased expression of nuclear NF-kappaB after coronary artery balloon injury can be inhibited by intracoronary beta-irradiation

PURPOSE

Molecular mechanisms by which balloon angioplasty injury-induced neointimal hyperplasia can be reduced by intravascular brachytherapy are unclear. We investigated the role of nuclear factor-kappaB (NF-kappaB) in neointimal hyperplasia following intracoronary irradiation.

MATERIALS AND METHODS

Fifty-four coronary arteries from 30 pigs were divided into 6 groups: sham control, balloon angioplasty injury alone, beta-irradiation at doses of 14 or 20 Gy, and 14 or 20 Gy beta-irradiation immediately followed by balloon injury. Coronary arteries were injured by overstretch balloon angioplasty and then the arteries were irradiated using a Rhenium-188 ((188)Re) beta-emitting solution-filled balloon. Pigs were scarified one day or one week after coronary interventions for molecular detection and six weeks after the procedures for histological examination.

RESULTS

Six weeks after coronary interventions, the histological results show that balloon angioplasty injury had induced intimal hyperplasia in coronary artery but the response was significantly reduced by 28% and 60% when the injury was immediately treated by 14 and 20 Gy (188)Re beta-irradiation, respectively. The expression of arterial NF-kappaB p65, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) were detected at one day and one week after the procedures. The treatment of balloon injury could significantly induce the NF-kappaB p65 expression in both gene and protein levels, and such induction could be significantly reduced by (188)Re beta-irradiation at dose of 20 Gy. However, the similar result on the regulation of gene expression affected by the beta-irradiation could not be observed in ICAM-1 and VCAM-1.

CONCLUSION

The inhibitory effect of intracoronary brachytherapy on neointimal formation following overstretch balloon angioplasty could involve inhibition of NF-kappaB p65.

Analysis of arterial intimal hyperplasia: review and hypothesis

BACKGROUND

Despite a prodigious investment of funds, we cannot treat or prevent arteriosclerosis and restenosis, particularly its major pathology, arterial intimal hyperplasia. A cornerstone question lies behind all approaches to the disease: what causes the pathology?

HYPOTHESIS

I argue that the question itself is misplaced because it implies that intimal hyperplasia is a novel pathological phenomenon caused by new mechanisms. A simple inquiry into arterial morphology shows the opposite is true. The normal multi-layer cellular organization of the tunica intima is identical to that of diseased hyperplasia; it is the standard arterial system design in all placentals at least as large as rabbits, including humans. Formed initially as one-layer endothelium lining, this phenotype can either be maintained or differentiate into a normal multi-layer cellular lining, so striking in its resemblance to diseased hyperplasia that we have to name it "benign intimal hyperplasia". However, normal or "benign" intimal hyperplasia, although microscopically identical to pathology, is a controllable phenotype that rarely compromises blood supply. It is remarkable that each human heart has coronary arteries in which a single-layer endothelium differentiates early in life to form a multi-layer intimal hyperplasia and then continues to self-renew in a controlled manner throughout life, relatively rarely compromising the blood supply to the heart, causing complications requiring intervention only in a small fraction of the population, while all humans are carriers of benign hyperplasia. Unfortunately, this fundamental fact has not been widely appreciated in arteriosclerosis research and medical education, which continue to operate on the assumption that the normal arterial intima is always an "ideal" single-layer endothelium. As a result, the disease is perceived and studied as a new pathological event caused by new mechanisms. The discovery that normal coronary arteries are morphologically indistinguishable from deadly coronary arteriosclerosis continues to elicit surprise.

CONCLUSION

Two questions should inform the priorities of our research: (1) what controls switch the single cell-layer intimal phenotype into normal hyperplasia? (2) how is normal (benign) hyperplasia maintained? We would be hard-pressed to gain practical insights without scrutinizing our premises.

Low-energy gamma-emitting stents inhibit intimal hyperplasia with minimal "edge effects" in a pig coronary artery model

PURPOSE

The objective of this study was to determine the effects of different doses of gamma-emitting radioactive stents on intimal hyperplasia in a porcine coronary stent model at 28 days.

METHODS

Sixty-four bare stents and those coated with palladium-103 [activities of 0 (control), 0.5, 1.0, 2.0, and 4.0 mCi] were implanted in the coronary arteries of 32 pigs. Stented segments were evaluated by histomorphometry at 28 days.

RESULTS

There was significantly more intima in the 0.5- and 1-mCi stents than in controls (4.27+/-0.52 and 4.71+/-1.13 vs. 1.71+/-0.61 mm(2); P<.0001). Neointimal formation in 2-mCi stents was similar to that in controls, while that in 4-mCi stents was reduced compared to that in controls (2.34+/-1.61 and 0.82+/-0.25 vs. 1.71+/-0.61 mm(2); P=NS and P<.05, respectively). Stent margin neointimal response was representative of that within the stent body, with nonsignficant modest increases in intimal area at adjacent nonstented segments in radioactive stent groups. There was a dose-dependent increase in inflammation scores. Radioactive stents had lower intimal smooth muscle and higher fibrin scores. There was an increase in adventitial fibrosis in 1- and 2-mCi stents versus controls (1.26+/-0.99, and 2.25+/-1.27 vs. 0.21+/-0.31; P<.001).

CONCLUSION

Dose-response inhibition of in-stent hyperplasia with minimal "edge effects" occurs with low-energy gamma-emitting stents. An increased inflammatory response at higher doses in palladium-103 stents indicates that later follow-up studies are necessary.

Predictors of recurrent in-stent restenosis after beta-radiation: An analysis from the START 40/20 trial

OBJECTIVE

The purpose of this study was to identify potential predictors, including clinical, procedural, angiographic, and intravascular ultrasound (IVUS) parameters, for recurrent in-stent restenosis (ISR) following beta-radiation 90Strontium/Yttrium (90Sr/Y) in a large multicenter trial.

BACKGROUND

Although adjunct brachytherapy reduces recurrent ISR after primary catheter-based intervention, recurrence of stenosis after brachytherapy still occurs.

METHODS

We analyzed 185 IVUS cohort patients in the STent And Restenosis Therapy (START) 40/20 trial where a 40-mm, 90Sr/Y, radioactive source train was exclusively used for treatment of ISR to be treatable with a 20-mm balloon.

RESULTS

Thirty-nine patients underwent target lesion revascularization. Preliminary univariate analysis showed that age, smoking, balloon/artery ratio, geographic miss, minimum lumen diameter, and diameter stenosis at baseline were associated with target lesion revascularization, while none of IVUS variables were (minimum lumen area, minimum stent area, or residual plaque burden). The multivariate logistic regression analysis showed that younger age, lower balloon/artery ratio, and presence of geographic miss were independent predictors of target lesion revascularization.

CONCLUSIONS

Even with adjunct beta-radiation therapy, initial mechanical optimization, such as appropriate balloon sizing and positioning, may be critical for the prevention of recurrent ISR.

Development of a polymeric matrix metalloproteinase inhibitor as a bioactive stent coating material for prevention of restenosis

Drug-eluting stents have been developed to prevent restenosis derived from excessive growth of smooth muscle cells (SMCs) after stenting. In almost every case, however, less- or non-biocompatible polymers were selected for the platform material for impregnating drugs on the stent strut. Consideration was given principally to the physical properties of the polymers, such as their adhesion to the strut and the drug dispersibility in the polymeric matrix. In this study, we designed a matrix metalloproteinase inhibitor (MMPI)-derivatized hydrophobic polymer (PMMPI) for use as a bioactive material for stent coating. This was a copolymer of n-butylmethacrylate and a vinyl monomer of synthetic MMPI (N-Hydroxy-5-carboxyethylcarbonyloxy-2(S)-methy-4(S)-(4-phenoxybenzoyl)amino-pentanamide: ONO-M11-335) with a molecular weight of about 32,000 and MMPI content of 45 per molecule. The precursor of the MMPI monomer produced significant activity in temporally inhibiting SMC proliferation without any cellular damage. After coating with the PMMPI, adhesion and proliferation of SMCs were manifestly prevented even when a small amount of MMPI was released from the polymer. The MMPI-immobilized surface may thus be effective for inhibiting both adhesion and proliferation of SMCs, which is the first step toward in vivo experimentation. It is very much expected that coating stent struts with PMMPI containing an appropriate combination of impregnated drugs will provide a powerful tool for prevention of restenosis with little cytotoxicity.

The effect of tyrphostin AG-556 on intimal thickening in a mouse model of arterial injury

BACKGROUND

Inflammation has been shown to play an important role in promoting the response to arterial injury and proinflammatory cytokines, such as tumor necrosis factor (TNF) alpha, are candidate mediators. AG-556 is a tyrosine kinase inhibitor proven to be effective in a model of multiple sclerosis-like syndrome in mice due to its immunomodulating effect. In the current study, we investigated the effect of the tyrphostin AG-556 on neointimal thickening and cytokine profile in a model of arterial injury in the mouse.

METHODS

Injury was induced by external cuff placement on the left femoral artery of wild-type C57BL/6 mice. AG-556 dissolved in DMSO was injected intraperitoneally daily to the injured mice in a dosage of 2 mg/mouse. Control mice received DMSO injections. Histological analysis was carried out to assess neointimal formation. Splenocytes were cultured in the absence and presence of a mitogen for evaluation of thymidine incorporation and cytokine production.

RESULTS

AG-556 treatment significantly attenuated intimal thickening (43,000+/-17,000 microm2; n=11) when compared to DMSO administration (286,000+/-127,000 microm2; n=10; P<0.05). Basal interferon-gamma production by splenocytes from AG-556-treated mice was increased by approximately 20-fold in comparison with levels in DMSO-treated animals, whereas Con-A induced secretion of the cytokine was similar between both groups. Levels of TNF-alpha, IL-4 and IL-10 in the culture supernatant from treated and non-treated animals did not differ significantly.

CONCLUSION

The tyrosine kinase inhibitor AG-556 may have a role in the reduction of intimal thickening. The effect could be mediated via an immune modulating effect involving a significant increase in the smooth muscle cell inhibitory cytokine IFN-gamma.