Department of Nanoengineering, University of California, San Diego, 9500 Gilman Dr. #0448, La Jolla, CA 92093-0448, USA.
Biomaterials. 2013 Dec;34(37):9559-65. doi: 10.1016/j.biomaterials.2013.08.040. Epub 2013 Sep 10.
The use of microbubbles as ultrasound contrast agents is one of the primary methods to diagnose deep venous thrombosis. However, current microbubble imaging strategies require either a clot sufficiently large to produce a circulation filling defect or a clot with sufficient vascularization to allow for targeted accumulation of contrast agents. Previously, we reported the design of a microbubble formulation that modulated its ability to generate ultrasound contrast from interaction with thrombin through incorporation of aptamer-containing DNA crosslinks in the encapsulating shell, enabling the measurement of a local chemical environment by changes in acoustic activity. However, this contrast agent lacked sufficient stability and lifetime in blood to be used as a diagnostic tool. Here we describe a PEG-stabilized, thrombin-activated microbubble (PSTA-MB) with sufficient stability to be used in vivo in circulation with no change in biomarker sensitivity. In the presence of actively clotting blood, PSTA-MBs showed a 5-fold increase in acoustic activity. Specificity for the presence of thrombin and stability under constant shear flow were demonstrated in a home-built in vitro model. Finally, PSTA-MBs were able to detect the presence of an active clot within the vena cava of a rabbit sufficiently small as to not be visible by current non-specific contrast agents. By activating in non-occlusive environments, these contrast agents will be able to detect clots not diagnosable by current contrast agents.
微泡作为超声对比剂的应用是诊断深静脉血栓的主要方法之一。然而，目前的微泡成像策略需要血栓足够大以产生循环充盈缺损，或者需要血栓具有足够的血管化程度以允许对比剂的靶向积累。之前，我们报道了一种微泡制剂的设计，该制剂通过在包封壳中包含含有适配体的 DNA 交联来调节其与凝血酶相互作用产生超声对比的能力，从而能够通过声学活性的变化来测量局部化学环境。然而，这种对比剂在血液中的稳定性和半衰期不足以作为诊断工具。在这里，我们描述了一种具有足够稳定性的聚乙二醇稳定的、凝血酶激活的微泡（PSTA-MB），可以在体内循环中使用，而不会改变生物标志物的敏感性。在正在凝结的血液存在下，PSTA-MB 的声活性增加了 5 倍。在内部构建的体外模型中证明了对凝血酶存在的特异性和在恒定剪切流下的稳定性。最后，PSTA-MB 能够检测到兔腔静脉内存在一个足够小的活跃血栓，而目前的非特异性对比剂无法检测到。通过在非闭塞环境中激活，这些对比剂将能够检测到目前对比剂无法诊断的血栓。
