动脉粥样硬化斑块MRI和近红外分子影像的实验研究

Molecular imaging of atherosclerosis in mice with MRI and near-infrared fluorescence imaging t

目的探讨7．0TMRI和近红外荧光成像（NIRF）检测动脉粥样硬化（AS）斑块的可行性。方法对14周龄ApoE-／-小鼠按高脂饮食喂养20周，建立AS模型，以正常C57BL／6小鼠作为对照。Mill实验中，5只ApoE-/-小鼠及5只C57小鼠经尾静脉注入超微超顺磁性氧化铁颗粒（USPIO）前及36h后分别行7．0TMRI。NIRF实验中，10只ApoE-/-小鼠和4只C57小鼠经尾静脉注入抗氧化修饰的低密度脂蛋白（oxLDL）抗体-NIR797（抗-oxLDL-抗体-NIR797）近红外探针，4只ApoE-/-小鼠经尾静脉注入非特异性IgG-NIR797，另4只ApoE-／-小鼠注入PBS，24h后分别行NIRF。用SPSS17．0软件对计量数据行独立样本t检验和单因素方差分析。结果ApoE-／-小鼠注入USPIO36h后，在T2WI上腹主动脉斑块信号较注射前减低，相对信号强度分别为0．70±0．04和1．28±0．06，差异有统计学意义（t=3．376，P〈0．05），信号改变率达（-56．58±4．25）％；普鲁士蓝染色证实斑块内有铁沉积。注入抗-oxLDL-抗体-NIR79724h后，ApoE-／-小鼠主动脉离体NIRF示强荧光信号（SNR为42．51±5．24）聚集于主动脉根、主动脉弓及降主动脉起始段，而非特异性IgG-NIR797组（19．58-4-3．06）、PBS组（4．19±0．82）及对照C57小鼠（2．29±1．11）仅见较弱荧光信号，与靶向探针组比较差异有统计学意义（F=25．104，P〈0．05）。斑块油红0染色与NIRF阳性面积分别为（41．69±5．29）％和（39．45±5．35）％，两者呈线性相关（r=0．738，P〈0．05，n=8），免疫荧光证实斑块内oxLDL的表达与巨噬细胞共区域。结论应用新型分子影像探针在7．0TMRI和NIRF上可有效检测AS斑块，有助于鉴别高危斑块，可为AS多模式成像提供依据。

[ Abstract] Objective To explore the feasibility of detecting atherosclerotic plaques with 7.0 T MRI and near-infrared fluorescence imaging （NIRF） using molecular imaging probes. Methods Athero- sclerotic plaques were established in male atherosclerotic apolipoprotein E knockout （ApoE-/-） mice fed with high-cholesterol diet for 20 weeks. Wild-type C57BL/6 mice were used as negative controls. 7.0 T MRI was performed before and 36 h after intravenously administration of ultrasmall superparamagnetic parti-cal of iron oxide （USPIO）. NIR 797 was conjugated with anti-mouse-oxidized modified low density lipopro- tein （oxLDL） antibodies to construct an anti-oxLDL-Ab-NIR 797 probe while non-specific IgG-NIR 797 and PBS used as controls. NIRF was performed 24 h after tail vein injection of the probe. Independent sample t- test and one-way analysis of variance were used to analyze the data by SPSS 17.0. Results In ApoE-/- mice, in vivo 36 h post-USPIO T2WI images revealed strong focal signal loss in the abdominal aorta than that of pre-USPIO, with relative signal intensity 0.70± 0.04 and 1.28 ± 0. 06, respectively （ t = 3. 376, P 〈 0. 05）. The percent of signal reduced was （ - 56.58 ± 4.25） %, The Prussian blue staining confirmed thedepositions of iron particles m the plaque lesions, bignificant tluorochrome accumulation m atherosclerotlc plaques was demonstrated in aortic root, aortic arch and the starting of descending aorta 24 h after injection of the anti-oxLDL-Ab-NIR 797 probe. Minimal antibody uptake was observed in normal vessels from wild- type mice receiving the anti-oxLDL-Ab-NIR 797 （ SNR： 2.29± 1.11 ） and in atherosclerotic vessels from ApoE-/- mice receiving the non-specific IgG-NIR 797 （ 19.58 ±3.06） or PBS （4.19 ±0.82）, which was significantly different from the uptake of anti-oxLDL-Ab-NIR 797 group （42.51±5.24, F =25. 104, P 〈0.05 ）. Comparison between oil red O staining and NIRF 24 h after injection of NIR 797 labeled oxLDL-anti- body revealed a significant correlation （ r = 0. 738, P 〈 0. 05, n = 8 ）. The positive areas in imaging were （41.69 ± 5.29） % and （39.45 ± 5.35 ） %, respectively. Immunofluorescence staining demonstrated that the expression of oxLDL was closely associated to macrophage infiltrates. Conclusion This study demon- strates that atherosclerotic plaque MRI and NIRF imaging are feasible by using novel molecular imaging probes and may help to identify high-risk plaques , providing a foundation for multimodality imaging of ather- osclerosis.