Influence of valsartan-eluting stent implantation into rabbit abdominal aorta on collagen deposition and AT2 receptor expression / 中国组织工程研究

ABSTRACT

BACKGROUND:Clinical trials have shown that oral administration of valsartan can decrease in-stent restenosis after stent implantation.But whether valsartan used locally also has the sanle effect and the possible mechanism should be validated.OBJECTIVE:To observe the effect of valsartan-eluting stents on collagen deposition in neointima and AT2 receptor expression after implanting valsartan-eluting stents into rabbit abdominal orta.DESIGN:Randomized and controlled animal experiment.SETTING:Beijing Friendship Hospital.MATERIALS:The experiment was performed at the Laboratory of Beijing Friendship Hospital between October 2004 and March 2006.Fifteen New Zealand white rabbits,irrespective of gender,weighing 2.75-3.25 kg were selected(Animal Laboratory of Beijing Friendship Hospital).The rabbits were adaptively fed for one week.All the operations of rabbits during the experiment were accorded with animal ethical standards.Valsartan powder was presented as a gift by Novartis.China;Reagent of MASSON was provided by Department of Pathology of Beijing Friendship Hospital;1%picrosirius solution was provided by the Department of Pathology of China-Japan Friendship Hospital:Mice-anti-rabbit monoclonal AT2 antibody was product of Santa Cruz Biotechnology (USA);Envision reagent was purphased from Dako;primers were synthesized by SBS Genetech(SBS).METHODS:①The animals were randomized into bare-metal stent group,carrier-eluting stent group and valsartan-eluting stent group with 5 animals in each group.All rabbits were implanted with corresponding types of above-mentioned stents into abdominal aortas down below renal artery.②Quantitative angiography before,immediately after and 3 months after stent implantation were performed to compare vascular diameters of the aortas.③Three months Iater,the rabbits were executed after anaesthesia.The vessels with stents were processed with HE staining.Indices of the vascular neointimal formation,I.e. iBrier and external elastic membrane luminal area,the maximal intimal thickness,neointimal area and stenosis area percent were measured.④The collagen deposition in neointima was observed through MASSON staining,and the type of collagen was identified through picrosirius stain.⑤The expressions of AT2R mRNA and proteins were also compared by RT-PCR and immunohistochemistry among three groups.MAIN OUTCOME MEASURES:①The diameters of aorta with stent at different time;②Inner and extemal elastic membrane luminal area,the maximal intimal thickness,neointimal area and stenosis area percent;③Collagen deposition and type of collagen of the aorta with stent;④AT2R mRNA and protein expressions.RESULTS:Of 15 rabbits selected in the experiment,1 rabbit of the bare-metal stent group died during stent implanting,and 1 of the carrier-eluting stent group died during breeding after stenting.Finally,13 rabbits were included in final analysis.①There were no significant differences in the mean aortic diameters between any two of the three groups before,immediately after and 3 months after stent implantation(P＞0.05).②A larger 1uminal area and a less neointimal hyperplasia in valsartan eluting-stents group were found compared with the other two groups(P＜0.01).③MASSON staining showed that collagen deposition was rich in neointima of bare-metal stent group and carrier-eluting stent group while rare in neointima of valsartan eluting stent group.Pierosirius staining suggested that the deposited collagen was type Ⅲ collagen predominantly accompanied by type Ⅰ collagen around stents struts;the type Ⅲcollagen deposition was obviously decreased in valsartan eluting stent group.④AT2R protein only expressed in adventitia of bare-metal stet group and arrier-eluting stent group while expressed in all layers of valsartan eluting-stents group.The AT2R mRNA/a-Actin mRNA of valsartan eluting stent group was significantly higher than that in the other two groups(P＜0.01).CONCLUSION:Valsartan eluting-stents inhibits neointimal hyperplasia after stenting by decreasing collagen deposition.especially collagen Ⅲ.The mechanism may be related with the upregulation of AT2R mRNA and protein expressions by valsartan-eluting stent.