Tsimikas S, Palinski W, Halpern S E, Yeung D W, Curtiss L K, Witztum J L
Department of Medicine, University of California, San Diego, La Jolla 92093-0682, USA.
J Nucl Cardiol. 1999 Jan-Feb;6(1 Pt 1):41-53. doi: 10.1016/s1071-3581(99)90064-8.
Oxidatively modified low-density lipoprotein (LDL) is present in atherosclerotic but not normal arteries and plays a crucial role in the pathogenesis and adverse consequences of atherosclerotic lesions. We previously generated a series of monoclonal antibodies (MoAb) against oxidation-specific neo-epitopes formed during the oxidative modification of LDL. MDA2, a prototype MoAb, recognizes malondialdehyde-lysine epitopes (eg, in malondi-aldehyde-modified LDL) within atherosclerotic lesions. We describe the in vivo characteristics of MDA2 and initial noninvasive imaging studies of atherosclerosis in rabbits.
To assess the in vivo specificity of MDA2 for atherosclerotic lesions, iodine 125-MDA2 was intravenously injected into 7 LDL-receptor deficient Watanabe heritable hyperlipidemic (WHHL) and 2 normal New Zealand white (NZW) rabbits, and the aortic plaque uptake was evaluated 24 hours later. 125I-Halb, an isotype-matched irrelevant MoAb that binds to human albumin, was injected into 5 WHHL and 2 NZW rabbits as a control. Aortic autoradiography was performed, and the mean uptake of MoAbs was measured as the percent injected dose per gram aortic tissue. Gamma camera imaging was then carried out in 7 WHHL rabbits and 2 NZW rabbits with 99mTc-MDA2. Imaging was carried out at 10 minutes and at 12 or 24 hours. Malondialdehyde-LDL was then injected to clear the blood pool signal, and final images were obtained 2 hours later.
Mean uptake of 125I-MDA2 in the entire aorta was 17.4-fold higher in WHHL than in NZW aortas (P < .001), and 2.8-fold higher than 125I-Halb in WHHL aortas. 125I-MDA2 also had higher specificity for lesioned areas than 125I-Halb (plaque/normal ratio 6.3 vs 2.9, P < .001). Autoradiograph of aortas of 125I-MDA2-injected WHHL rabbits revealed uptake in lipid-stained lesions with absence of signal in adjacent normal arterial tissue. Immunostaining of WHHL lesions, which accumulated MDA2 as noted on autoradiography, revealed that uptake was highest in areas with abundant foam cells and in lipid-rich necrotic core areas. Autoradiograph of aortas from NZW rabbits injected with 125I-MDA2 did not yield any visible signal. Planar gamma camera in vivo scintigraphy revealed a visible signal in 4/7 WHHL rabbits, which was confirmed by aortic Sudan staining.
Radiolabeled MDA2 shows excellent in vivo uptake and specificity for atherosclerotic lesions containing abundant oxidation-specific epitopes. The in vivo imaging studies suggest that noninvasive imaging of oxidation-rich atherosclerotic lesions with radiolabeled MDA2 may be feasible in human beings with optimization of the imaging methods.
氧化修饰的低密度脂蛋白（LDL）存在于动脉粥样硬化病变的动脉中，而正常动脉中不存在，并且在动脉粥样硬化病变的发病机制和不良后果中起关键作用。我们之前制备了一系列针对LDL氧化修饰过程中形成的氧化特异性新表位的单克隆抗体（MoAb）。MDA2是一种原型MoAb，可识别动脉粥样硬化病变内的丙二醛-赖氨酸表位（如在丙二醛修饰的LDL中）。我们描述了MDA2的体内特性以及兔动脉粥样硬化的初步无创成像研究。
为了评估MDA2对动脉粥样硬化病变的体内特异性，将碘125-MDA2静脉注射到7只低密度脂蛋白受体缺陷的渡边遗传性高脂血症（WHHL）兔和2只正常新西兰白兔（NZW）中，并在24小时后评估主动脉斑块摄取情况。将125I-Halb（一种与人类白蛋白结合的同型匹配无关MoAb）注射到5只WHHL兔和2只NZW兔中作为对照。进行主动脉放射自显影，并将MoAb的平均摄取量测量为每克主动脉组织注射剂量的百分比。然后用99mTc-MDA2对7只WHHL兔和2只NZW兔进行γ相机成像。在10分钟以及12或24小时进行成像。然后注射丙二醛-LDL以清除血池信号，并在2小时后获得最终图像。
125I-MDA2在整个主动脉中的平均摄取量在WHHL兔中比在NZW兔中高17.4倍（P <.001），在WHHL兔主动脉中比125I-Halb高2.8倍。125I-MDA2对病变区域的特异性也高于125I-Halb（斑块/正常比值为6.3对2.9，P <.001）。注射125I-MDA2的WHHL兔主动脉的放射自显影显示脂质染色病变中有摄取，而相邻正常动脉组织中无信号。如放射自显影所示，积累MDA2的WHHL病变的免疫染色显示，在富含泡沫细胞的区域和富含脂质的坏死核心区域摄取最高。注射125I-MDA2的NZW兔主动脉的放射自显影未产生任何可见信号。平面γ相机体内闪烁显像显示7只WHHL兔中有4只出现可见信号，经主动脉苏丹染色证实。
放射性标记的MDA2对含有丰富氧化特异性表位的动脉粥样硬化病变显示出优异的体内摄取和特异性。体内成像研究表明，通过优化成像方法，用放射性标记的MDA2对富含氧化的动脉粥样硬化病变进行无创成像在人类中可能是可行的。
