Endovascular irradiation with the liquid beta-emitter Rhenium-188 to reduce restenosis after experimental wall injury.

OBJECTIVE: Postinterventional irradiation is a new therapeutic concept in the prevention of restenosis. The liquid beta-emitter Rhenium-188 allows endovascular brachytherapy using a conventional balloon catheter without the problem of centering the radiation source. In an animal model of restenosis the feasibility and the dose dependent effect of intravascular brachytherapy with a Rhenium-188 filled balloon catheter was investigated. METHODS: In 68 male New Zealand White rabbits after endothelial denudation of the right common carotid artery with a Fogarty catheter, endovascular irradiation was performed with a Rhenium-188 filled 3.0-mm balloon catheter using different dosages (0, 7.5, 15, 30, 45 and 60 Gy at the surface of the vessel). Then 4 weeks after the intervention the vessels were excised and histologically analyzed. RESULTS: Whereas at 7.5 Gy the intimal area (median [first quartile; third quartile]) did not differ significantly from the control (0.46 mm(2) [0.33 mm(2), 0.75 mm(2)] vs. 0.49 mm(2) [0.34 mm(2), 0.66 mm(2)]), neointimal hyperplasia was decreased significantly at 15 Gy (0.15 mm(2) [0.04 mm(2), 0.17 mm(2)]) and 30 Gy (0.07 mm(2) [0.04 mm(2), 0. 10 mm(2)]), and completely inhibited at the highest dosages (45 Gy: 0 mm(2) [0 mm(2), 0.04 mm(2)]; 60 Gy: 0 mm(2) [0 mm(2), 0.01 mm(2)]). CONCLUSIONS: Catheter transmitted endovascular irradiation with the liquid beta-emitter Rhenium-188 after vascular injury is feasible and effectively reduced neointimal hyperplasia in hypercholesterolemic rabbits. A significant reduction of the neointimal formation could be found already at a radiation absorbed dose of 15 Gy at the vessel surface. Following a surface dosage of 45 Gy the proliferative response to the vessel injury is almost completely abolished.

[In vitro model to investigate the effect of estrogens on neointima development after endothelial injury in the rabbit aorta]. / In vitro Modell zur Untersuchung der Wirkung von östrogenen auf die Neointimabildung nach Endothelverletzung an der Kaninchenaorta.

Animal experiments are widely accepted in arterosclerosis research. Estrogens have lipid lowering properties and beneficial effects on the vasomotion. They act antiproliferative on those cells of the vascular wall which play a major role in lumen narrowing after vascular injury and in atherogenesis. The aim of the present study was to establish an organ culture model (rabbit aorta) to investigate post injury estrogen effects in the vessel wall. We chose the rabbit abdominal aorta which is the target organ in various animal experiments on this matter. The endothelial mono-layer was manipulated in a way that caused a measurable and reproducible post injury reaction (neointima formation). Then the effect of different estrogens (17beta-Estradiol, the phytoestrogens Genistein and Daidzein) on neointima development was investigated in male and female rabbit aortae. In equivalent dosages of 50 microg/ml all three estrogens inhibited the neointima formation significantly in male and female vessels. By the use of this organ culture model it was possible to show post injury effects of different estrogens in the vasculature while the consumption of animals was significantly reduced. Because 10 aortic segments could be taken from one aortic vessel, the number of animals that would have been necessary for an in vivo experiment could be reduced by the factor 10.

Intracoronary beta-irradiation with a liquid (188)re-filled balloon: six-month results from a clinical safety and feasibility study.

BACKGROUND: Coronary irradiation is a new concept to reduce restenosis. We evaluated the feasibility and safety of intracoronary irradiation with a balloon catheter filled with (188)Re, a liquid, high-energy beta-emitter. METHODS AND RESULTS: Irradiation with 15 Gy at 0.5-mm tissue depth was performed in 28 lesions after balloon dilation (n=9) or stenting (n=19). Lesions included 19 de novo stenoses, 4 occlusions, and 5 restenoses. Irradiation time was 515+/-199 seconds in 1 to 4 fractions. There were no procedural complications. One patient died of noncardiac causes at day 23. One asymptomatic patient refused 6-month angiography. Quantitative angiography after intervention showed a reference diameter of 2. 77+/-0.35 mm and a minimal lumen diameter of 2.36+/-0.43 mm. At 6-month follow-up, minimal lumen diameter was 1.45+/-0.88 mm (late loss index 0.57). Target lesion restenosis rate (>50% in diameter) was low (12%; 3 of 26). In addition, we observed 9 stenoses at the proximal or distal end of the irradiation zone, potentially caused by the short irradiation segment and the decreasing irradiation dose at its borders ("edge" stenoses). The total restenosis rate was 46% and was significantly lower (29% vs 70%, P=0.042) when the length of the irradiated segment was more than twice the lesion length. CONCLUSIONS: Coronary irradiation with a (188)Re-filled balloon is technically feasible and safe, requiring only standard percutaneous transluminal coronary angioplasty techniques. The target lesion restenosis rate was low. The observed edge stenoses appear to be avoidable by increasing the length of the irradiated segment.

Incidence of intimal proliferation and apoptosis following balloon angioplasty in an atherosclerotic rabbit model.

OBJECTIVE: The aim of this study was to determine the occurrence of apoptosis in relation to the proliferative response in the intimal layer after experimental balloon angioplasty of a pre-existing plaque. METHODS: After induction of an intimal plaque in the right carotid artery by electrical stimulation, 26 rabbits underwent balloon angioplasty. Twelve animals served as a control group without performance of angioplasty after plaque induction. To study the time course of intimal apoptosis and cell proliferation the vessels were excised on day 7, 14 and 28 after balloon angioplasty. For in situ detection of apoptosis, the TUNEL-technique (TdT-mediated d-UTP fluorescein nick end labeling) was used. In addition, bromodeoxyuridine labeling in all animals allowed the determination of the percentage of cells undergoing DNA synthesis in the neointimal area. Additionally, smooth muscle cells were detected by immunostaining of alpha-actin and macrophages by a specific antibody (RAM 11). RESULTS: Within 28 days of balloon angioplasty, the number of cells undergoing apoptosis remained at a very low level and was not significantly different to the control group without interventional treatment (controls: 0.1 +/- 0.15%; 7 days: 0.44 +/- 0.68%; 14 days: 0.13 +/- 0.11%; 28 days: 0.1 +/- 0.1%). In contrast, the number of cells undergoing DNA synthesis was significantly increased at day 7 after angioplasty (3.72 +/- 2.0% vs. 0.51 +/- 0.29% in controls), resulting in an increase of the total intimal area from 0.088 +/- 0.037 mm2 in the control animals up to 0.256 +/- 0.172 mm2 at day 28 following balloon dilatation. CONCLUSIONS: Our data showed that significant changes in the occurrence of apoptosis are not involved in the regulation of cellular turnover during the examined time period after vessel wall injury. The lacking up-regulation of apoptosis in comparison to the increased cell proliferation in order to maintain the tissue balance is perhaps an important regulatory mechanism leading to intimal hyperplasia after vascular injury in this animal model. Overall, we suggest that there may be a delicate balance between cell proliferation and apoptosis in smooth muscle cells of the vessel wall, and only small shifts in this balance could account for both cellular accumulation in restenotic lesions as well as cell death in mature atheroma.

The phytoestrogens Genistein and Daidzein, and 17 beta-estradiol inhibit development of neointima in aortas from male and female rabbits in vitro after injury.

BACKGROUND: 17 beta-Estradiol and phytoestrogens are known to have beneficial effects on the cardiovascular systems of women. The exact mechanisms for how estrogens and phytoestrogens influence the cardiovascular system are not yet understood in detail. OBJECTIVE: The objective of this study was to investigate whether 17 beta-estradiol and the phytoestrogens Genistein and Daidzein have an effect on post-injury processes in vessel walls. METHODS: In this in-vitro experiment, the sex-specific effects of 50 micrograms/ml 17 beta-estradiol (equivalent to 180 mumol/l), and of the isoflavones Genistein (5 and 50 micrograms/ml, equivalent to 18.5 and 185 mumol/l), and Daidzein (5 and 50 micrograms/ml, equivalent to 19.7 and 197 mumol/l) on endothelium-denuded aortas from female and male rabbits after vascular injury were studied. Morphometry and immunohistochemistry were performed for quantitative and qualitative analysis. RESULTS: Neointimal cells were in part positive for alpha-actin staining of smooth muscle cells. Staining with 5'-bromo-2'deoxyuridine plus 2'-deoxycytidine showed that proliferative activity in the neointima had significantly decreased after 28 days for groups that had been treated with 50 micrograms/ml Genistein. Immunofluorescence staining for the expression of nuclear estrogen receptor protein in the arterial wall for aortic rings from female and male rabbits was positive. 17 beta-Estradiol, Genistein, and its analog Daidzein (with no protein tyrosine kinase activity) inhibited formation of neointima sex-independently at equivalent concentrations of 50 micrograms/ml. However, a concentration of 5 micrograms/ml Genistein decreased formation of neointima significantly for aortic rings from male rabbits only, whereas 5 micrograms/ml Genistein increased formation of neointima in rings from female rabbits, which corresponded to the increase in proliferative activity detected after 28 days. CONCLUSION: Genistein and Daidzein both inhibited proliferation at certain concentrations, so this effect is supposed to be independent from Genistein's protein tyrosine kinase activity. The antiproliferative properties of all three estrogens were observed in the absence of endothelium and therefore are independent from endothelium-mediated effects.

Effect of the antioxidant Nicanartine on the proliferative and inflammatory response after experimental balloon angioplasty.

BACKGROUND: Antioxidant treatment seems to reduce the development of restenosis after percutaneous transluminal angioplasty. In this study, the effect of Nicanartine, a new antioxidant drug with both antiproliferative and lipid-lowering properties, on the proliferative and inflammatory response after balloon angioplasty was investigated in a rabbit model of restenosis. METHODS: To induce pre-interventional plaques in the common carotid artery of 48 New Zealand White rabbits, electrostimulation was carried out for 28 days. After a break of 7 days, balloon angioplasty was performed in 36 animals, of which 18 received Nicanartine at a dose of 120 mg/kg body weight; the other 18 served as a control group. The vessels were excised by day 7 and 28 after balloon angioplasty and examined for intimal plaque size, macrophage content and proliferative activity. Bromodeoxyuridine labeling was used to determine proliferating cells in the dilated segment; macrophages were detected using the RAM-11 antibody. RESULTS: In the Nicanartine-treated group, immunohistological quantification 7 days after intervention showed a statistically significant (P< 0.05) reduction of both cells undergoing DNA synthesis (1.6+/-1.4% versus 3.7+/-2.2%) and intimal macrophages (0.7+/-1.2% versus 1.3+/-0.6%). Twenty-eight days after balloon angioplasty, proliferative activity in both groups was decreased to a level comparable to the non-dilated control groups. A clear trend towards smaller plaques could be seen in the Nicanartine group (0.146+/-0.077 mm2 versus 0.255+/-0.174 mm2). Total cholesterol levels did not differ significantly between the groups. CONCLUSION: Under treatment with Nicanartine a clear reduction in the proliferative and inflammatory response after balloon angioplasty was observed. Antioxidant treatment, especially with compounds having antiproliferative and lipid-lowering properties, appears to be an effective secondary preventive strategy after interventional treatment in patients with coronary artery disease.