Relationship between plasma ACE activity and the proliferative healing process in coronary vessel injury after coronary stenting

Effects of ramiprilat-coated stents on neointimal hyperplasia, inflammation, and arterial healing in a porcine coronary restenosis model

Background and Objectives

The renin-angiotensin-aldosterone system has been implicated in the pathogenesis of neointimal hyperplasia, and a role for angiotensin II in the migration and proliferation of vascular smooth muscle cells in restenotic lesions has been proposed. The aim of this study was to determine the anti-proliferative and anti-inflammatory effects of ramiprilat-coated stents in a porcine coronary overstretch restenosis model.

Subjects and Methods

Pigs were randomized into two groups in which the coronary arteries {16 pigs (16 coronaries in each group)} had a 3.0×17 mm ramiprilat-coated MAC stent or a 3.0×17 mm control MAC stent (AMG, Munich, Germany) implanted with oversizing (stent-to-artery ratio, 1.3 : 1) in porcine coronary arteries, and histopathologic analysis was assessed 28 days after stenting.

Results

There were no significant differences in the injury and inflammation scores between the two groups (1.20±0.43 vs. 1.23±0.57, p=0.8; and 1.21±0.39 vs. 1.25±0.49, p=0.6, respectively). Within the neointima, most inflammatory cells were lymphohistiocytes. Significant positive correlations existed between inflammatory cell counts and the neointima areas (r=0.567, p<0.001), and between inflammatory cell counts and the percent area stenosis (r=0.478, p<0.001). There was no significant difference in the inflammatory cell counts normalized to the injury (110±89 vs. 123±83, p=0.4) and fibrin scores (0.15±0.06 vs. 0.17±0.07, p=0.8) between the 2 groups. There were trends toward a smaller neointima area (1.06±0.51 mm² vs. 1.28±0.35 mm², p=0.083) and a smaller percent area stenosis (18.9±8.7% vs. 21.8±7.2%, p=0.088) in the ramiprilat-coated stent group.

Conclusion

Although the ramiprilat-coated stent did not show significant inhibitory effects on neointimal hyperplasia, the ramiprilat-coated stent showed good effects on the inflammatory reaction and arterial healing similar to the control stent in a porcine coronary restenosis model.

Angiotensin Antagonism in Coronary Artery Disease

The renin-angiotensin system (RAS) is an ancient and complex cascade of homeostatic reactions aimed at regulating primordial functions that ensure organ perfusion through the control of blood pressure and the regulation of renal-cardiac activity. However, the over-expression or lack of compensatory mechanisms of any of its components may initiate detrimental effects that potentially lead to disease, a balance that makes the RAS a sequence with a labile physiological equilibrium and with a strong harm potential. These characteristics of the RAS in general, and of the angiotensin converting enzyme (ACE) in particular, make it not only an important complex for the regulation of blood pressure and neuropeptide metabolism, but also a fascinating subject of study from a biochemical, evolutionary and genetic point of view. Pharmacological interventions that influence the RAS by inhibiting the ACE or the angiotensin II type 1 receptor (AT1R) have demonstrated sustained efficacy in reducing the incidence of cardiovascular events and, consequently, vascular mortality in several clinical situations. ACE inhibitors and angiotensin II receptor antagonists (ARAs) reduce blood pressure and have cardio- and vasculoprotective effects. Anti-atherosclerotic effects have also been attributed to these drugs. For these reasons, it has been hypothesised that RAS inhibitors could also reduce the recurrence of ischaemic events after myocardial revascularisation procedures, namely coronary artery by-pass graft surgery (CABG) or percutaneous coronary interventions (PCI). Information available on the effect of ACE inhibitors and ARAs in patients with coronary artery disease (CAD) previously treated with revascularisation techniques indicates a substantial reduction of mortality and infarction in these patients. However, data regarding the progression of CAD, restenosis or reocclusion of vascular conduits of the coronary circulation after myocardial revascularisation are inconsistent. In most studies, the administration of ACE inhibitors neither improved the ischaemic threshold nor reduced the need for new revascularisation procedures. On the contrary, ACE inhibitors have been associated with higher restenosis rates after PCI in some retrospective series. Conversely, a single, exploratory randomised trial demonstrated that the selective AT1R antagonist valsartan significantly reduced stent restenosis after PCI. In patients undergoing CABG, ACE inhibitors did not reduce the risk of graft degeneration or occlusion. Studies that evaluated a possible anti-atherosclerotic effect of ACE inhibitors (including some large randomised trials) have generally been negative.

Intracoronary β-irradiation prevents excessive in-stent neointimal proliferation in de novo lesions of patients with high plasma ACE levels. The BetAce randomized trial

BACKGROUND

This study evaluated vascular brachytherapy (VBT) as a potent antiproliferative treatment to prevent in-stent restenosis (ISR) after coronary angioplasty of de novo lesions in patients carrying the D allele of the I/D polymorphism of the ACE gene and high ACE plasma levels (>34 U/l).

METHODS AND MATERIALS

A prospective randomized trial was designed to detect a 30% improvement in the minimal lumen diameter (MLD) of the stenotic artery, as measured by quantitative coronary analysis (QCA), 6 months following VBT at the time of stented angioplasty. All patients were carriers of the D allele of the ACE gene, with plasma ACE levels >34 U/l.

RESULTS

Thirty-one patients (33 stenoses) were allocated to stent implantation (control group) and 30 patients (31 stenoses) to VBT and stented angioplasty. After angioplasty, in-stent MLD was similar in the two groups. At 6 months in the control group, in-stent MLD had decreased to 1.74+/-0.8 versus 2.25+/-1.05 mm in the VBT group (P=.04). The mean in-stent diameter was 2.3+/-0.8 mm in the control group versus 2.9+/-1.05 mm after VBT (P=.02), and the restenosis rate was 37.5% versus 17.9%, respectively (P=.08). At 6 months, a higher need for target vessel revascularization (TVR) was observed in the control group: 35.5% versus 13.3% (P=.04).

CONCLUSIONS

This randomized study confirms that patients with high plasma ACE concentrations are exposed to an increased risk for ISR after coronary stenting. The preventive use of VBT in these patients reduced neointimal formation by 65% such that the MLD at follow-up was increased by 29% compared with the control group.

Angiographic and three-dimensional intravascular ultrasound analysis of combined intracoronary beta radiation and self-expanding stent implantation in human coronary arteries

This study tested the combination of vascular brachytherapy (VBT) and self-expanding Wallstent implantation in coronary lesions of patients at high risk for restenosis as assessed angiographically by quantitative coronary analysis and by 3-dimensional intravascular ultrasound analysis. Twenty-nine "de novo" lesions were managed with a self-expanding stent alone (n = 19) or with a self-expanding stent after beta-VBT (n = 10) in 27 patients who had been identified by high levels of plasma angiotensin-converting enzyme as being prone to myointimal growth after stent implantation. At 6 months, the increase in stent strut diameter was similar in the 2 groups by quantitative coronary analysis and 3-dimensional intravascular ultrasound (Delta mean stent strut diameter -0.33 +/- 0.3 vs -0.40 +/- 0.3 mm, p = 0.5; Delta stent area -11.8 +/- 6.1 vs -12.0 +/- 6.1 mm(2), p = 0.9; Delta stent volume -96.9 +/- 112 vs -83.5 +/- 73 mm(3), p = 0.7; for groups treated with VBT and self-expanding stents and only self-expanding stents, respectively). In-stent neointimal proliferation was decreased in the group treated with VBT and self-expanding stents (minimal luminal diameter 2.5 +/- 0.8 vs 1.88 +/- 0.8 mm, p = 0.04) by quantitative coronary analysis (minimal luminal area 6.7 +/- 2.5 vs 4.1 +/- 1.9 mm(2), p = 0.01), by intravascular ultrasound, and proliferation volume (84.6 +/- 66.4 vs 159.2 +/- 103.5 mm(3), p = 0.05) by 3-dimensional intravascular ultrasound. Positive vessel and luminal remodelings were observed in 50% of the group treated with VBT and self-expanding stents and in 11% of the group treated only with self-expanding stents (p = 0.02). The combined use of VBT and self-expanding stents is a novel approach that enlarges vascular lumen by preventing vessel constriction and neointimal proliferation. The feasibility and good results of this experimental approach suggest that the simultaneous use of these 2 technologies may be an interesting alternative for difficult vascular districts with high restenosis rates, such as peripheral circulation in the lower limbs.

Association study of the I/D polymorphism and plasma angiotensin-converting enzyme (ACE) as risk factors for stent restenosis

The ID (insertion/deletion) polymorphism of the ACE (angiotensin-converting enzyme) gene controls plasma ACE levels. Both have been correlated with ISR (in-stent restenosis) in preliminary analyses, but not confirmed in larger studies. In the present study, baseline and 6-month quantitative coronary analysis were performed in 897 patients who had stent implantation and the ID polymorphism genotyped. Plasma ACE levels were measured in 848 patients (95%). Restenosis rates among genotypes were 31.2% DD, 25.5% ID and 28.8% II (not significant). Plasma ACE levels were significantly higher in restenotic patients compared with patients without restenosis (30.7+/-18.6 units/l compared with 22.8+/-12.8 units/l; P=0.0001) and a strong independent predictor of ISR [OR (odds ratio)=3.70; 95% CI (confidence interval), 2.40-5.71; P<0.0001], except in diabetics. In the subgroup of diabetics and patients with AMI (acute myocardial infarction), the DD genotypes actually had a lower risk of ISR than the II genotypes (diabetics, OR=0.16; 95% CI, 0.04-0.69; P=0.014; and patients with AMI, OR=0.21; 95% CI, 0.061-0.749; P=0.016). After exclusion of diabetics and patients with AMI, ISR rates for genotypes in 632 patients were 31.7% DD, 24.3% ID and 17.6% II (P=0.02; DD compared with non-DD OR=1.57; 95% CI, 1.09-2.25). The association between the D allele and ISR observed in selected populations does not hold with a larger sample size. Other than sample size, clinical variables can modulate the association between ID polymorphism and ISR. Plasma ACE level is a risk factor for ISR, independently of the ID genotype.