Late neointimal tissue growth behind the stent after intravascular γ-radiation

Combining sirolimus-eluting stents and external irradiation in cholesterol-fed rabbits increased incomplete stent apposition and decreased re-endothelialization

Restenosis after the implantation of a drug-eluting stent or after vascular irradiation therapy shares similar physiopathological mechanisms. No experimental data are currently available on vascular wall behavior after external irradiation on arteries stented with sirolimus-eluting stents (SES). Ten New Zealand white rabbits received a 0.5% cholesterol-enriched chow for 1 month. Bilateral iliac artery stent implantation was then performed with an SES (Cypher; Cordis Corp). The animals were randomized into either an irradiated group (I, 2 Gy external x-ray irradiation, n = 5) or a control group (C, n = 5). The cholesterol-enriched chow was continued for 1 additional month after stent implantation. The stented arteries were harvested for histological analyses. The number and the percentage of incompletely apposed stents struts (IASS) were significantly higher in irradiated versus control group (3.05 +/- 0.46 vs. 1.57 +/- 0.27 IASS, P < 0.01, and 28.44% +/- 3.97% vs. 15.2% +/- 2.46% of IASS, P < 0.01, respectively). The mean neointimal thickness behind the IASS was also higher in the irradiated group (I: 28.3 +/- 2.5 microm vs. C: 18.2 +/- 2.3 microm, P < 0.01). Re-endothelialization was lower in irradiated group (I: 44.6% +/- 17.5% vs. C: 75.2% +/- 5.7%, P < 0.01). The present study revealed that low-dose external irradiation increased incomplete stent apposition and reduced re-endothelialization of SES. These results underscore the potential deleterious cumulative side effects of these 2 procedures to prevent restenosis.

Regression of aortic valve stenosis by ApoA-I mimetic peptide infusions in rabbits

BACKGROUND AND PURPOSE

Aortic valve stenosis (AVS) is the most common valvular heart disease, and standard curative therapy remains open heart surgical valve replacement. The aim of our experimental study was to determine if apolipoprotein A-I (ApoA-I) mimetic peptide infusions could induce regression of AVS.

EXPERIMENTAL APPROACH

Fifteen New Zealand White male rabbits received a cholesterol-enriched diet and vitamin D(2) until significant AVS was detected by echocardiography. The enriched diet was then stopped to mimic cholesterol-lowering therapy and animals were allocated randomly to receive saline (control group, n=8) or an ApoA-I mimetic peptide (treated group, n=7), three times per week for 2 weeks. Serial echocardiograms and post mortem valve histology were performed.

KEY RESULTS

Aortic valve area increased significantly by 25% in the treated group after 14 days of treatment (P=0.012). Likewise, aortic valve thickness decreased by 21% in the treated group, whereas it was unchanged in controls (P=0.0006). Histological analysis revealed that the extent of lesions at the base of valve leaflets and sinuses of Valsalva was smaller in the treated group compared with controls (P=0.032). The treatment also reduced calcification, as revealed by the loss of the positive relationship observed in the control group (r=0.87, P=0.004) between calcification area and aortic valve thickness.

CONCLUSIONS AND IMPLICATIONS

Infusions of ApoA-I mimetic peptide lead to regression of experimental AVS. These positive results justify the further testing of high-density lipoprotein (HDL)-based therapies in patients with valvular aortic stenosis. Regression of aortic stenosis, if achieved safely, could transform the clinical treatment of this disease.

Optimization of dose prescription protocol and its impact on delivered dose and vascular response after beta-radiation for in-stent restenosis. A randomized trial with serial volumetric intravascular ultrasound and dose volume histograms

AIM

The incidence of restenosis within stented segment after intravascular brachytherapy with recommended dose prescription protocols is up to 25%. Therefore, we designed a randomized trial comparing recommended dose prescription protocol with dosing adjusted for the source-to-target distance.

METHODS

Fifty-one in-stent restenosis (ISR) lesions in 48 patients underwent centered source beta-irradiation with serial intravascular ultrasound. Patients randomly received 20 Gy at 1 mm either beyond lumen surface [n=25, standard group (S)] or external elastic membrane [n=26, dosing-adjusted (DA) group]. Minimum dose absorbed by 90% of adventitia (DV(90%Adv)) was calculated.

RESULTS

DV(90%Adv) was higher for the DA group than for the S group (21.63+/-5.67 vs. 12.05+/-4.88 Gy, P<.001). After 8.9+/-4.5 months there was complete lumen preservation in DA vs. lumen decrease subsequent to neointimal hyperplasia (NIH) in S group (0.10+/-1.20 vs. -0.61+/-1.29 mm3/mm, P<.05). Vessel volume increased significantly in the DA group and was unchanged in S group (+1.73, P=.002 vs. 0.14 mm3/mm, P=NS). DV(90%Adv) correlated inversely with NIH volume and positively with vessel volume change (r=-.405, P=.007 and r=.363, P=.017, respectively).

CONCLUSION

For beta-irradiation of ISR, dosing adjusted for the source-to-target distance leads to significant increase in target delivered doses, which is associated with complete NIH inhibition and induction of positive vessel remodeling.

Dissociation between vascular oxidative stress and cardiovascular function in Wistar Kyoto and spontaneously hypertensive rats

It has not been completely demonstrated if hypertension may, in part, develop as a result of increased oxidative stress (OS), inflammation and little is known about the short-term effects of antioxidant therapy. This study was designed to appreciate the effect of 7 days vitamin C-enriched diet (5 g/kg/day) on hemodynamic function and vascular OS in normotensive Wistar Kyoto rats and hypertensive rats (SHR). Aorta NAD(P)H oxidase activity was determinate and free radicals evaluated by electron spin resonance with a spin probe CP-H. Matrix metalloproteinase-1 (MMP-1) and monocyte chemoattractant protein-1 (MCP-1) expression were measured. The treatment with vitamin C did not change arterial pressure in SHR but prevented the increase in OS levels in SHR aortas. MMP-1 and MCP-1 expressions were more intense in the media of SHR aortas than in those of WKY rats but these expressions were not modified by vitamin C-pretreatment. Vitamin C-pretreatment was not able to protect heart against in vitro ischemia-reperfusion dysfunctions. These data may suggest that treatment with high doses of vitamin C in SHR can limit over-production of reactive oxygen species; however this effect was not accompanied with changes in arterial pressure and protection against I-R dysfunctions. Dissociation between vascular oxidative stress and cardiovascular function may be evoked.

NADPH oxidases are in part responsible for increased cardiovascular superoxide production during aging

The aim of our study was to examine in rats, age-related differences in myocardial ischemic recovery and to determine the possible relationship with modification of cardiac and vascular oxidative stress. Isolated perfused hearts from young (2 months), adult (6 months), and old (21 months) Wistar rats were subjected to a ischemia-reperfusion sequence. Vascular histomorphological analyses were performed and NADPH oxidase was studied. The expression of angiotensin AT(1) receptors was evaluated using immunostaining. During the preischemic period, but also after ischemia, an aged-related decrease in myocardial functional parameters was observed, and was associated with an increased release of reactive oxygen species. In aortas, the activity and expression of NADPH oxidase increased with age according to the ESR, fluorescence microscopy, and immunohistochemistry; the NADPH oxidase involved was localized in endothelial cells. We found an age-related increase in the expression of endothelial angiotensin AT(1). Our study suggests that myocardial function and adaptation to ischemia-reperfusion declined during aging and are related to a higher level of oxidative stress. Endothelial NADPH oxidase is a major contributor to age-related cardiovascular deterioration. One of the regulators of vascular NADPH oxidase activity, the renin-angiotensin system, may be involved in the modulation of vascular superoxide production during the aging process.

Short-term atorvastatin treatment does not modify neointimal morphology but reduces MMP-2 expression in normocholesterolemic rabbit stented arteries

The aim of our study was to explore some potential pleïotropic effects of atorvastatin, after stenting in the iliac arteries of normocholesterolemic rabbits. On day 0, 27 rabbits underwent stent implantation and were randomized into either the control group (standard chow, CTRL, n = 15) or the atorvastatin group (10 mg/kg/d per os, Ator, n = 12). On day 30, the stented arteries were harvested for histomorphometry and neointimal analysis [macrophages, matrix metalloproteinases (MMP-2), tissue inhibitor of metalloproteinase-2, vascular smooth muscle cells, and collagen]. Atorvastatin did not induce significant histomorphometric and inflammatory modifications but reduced neointimal expression of MMP-2 with no modification of tissue inhibitor of metalloproteinase-2, and also induced higher neointimal collagen content (Ator vs. CTRL: MMP-2: 0.05 +/- 0.03 vs. 0.70 +/- 0.20, P < 0.01; collagen: 17.0+/-0.7%/mm vs. 12.0 +/- 1.2%/mm(2) P < 0.01). Atorvastatin treatment also induced a significant decrease in neointimal vascular smooth muscle cells and cellular density (respectively: 2.0 +/- 0.2 vs. 1.4 +/- 0.2, P < 0.05; 5406 +/- 241 nuclei/mm(2) vs. 4402 +/- 163 nuclei/mm(2), P < 0.001). Our study provides new insights into the field of MMP response to stenting and the effects of statin therapy, which could have important implications in the field of in-stent restenosis.