Arbab Ali S, Wilson Lindsey B, Ashari Parwana, Jordan Elaine K, Lewis Bobbi K, Frank Joseph A
Experimental Neuroimaging Section, Laboratory of Diagnostic Radiology Research, National Institutes of Health, Bethesda, Maryland, USA.
NMR Biomed. 2005 Oct;18(6):383-9. doi: 10.1002/nbm.970.
Ferumoxides, dextran-coated superparamagnetic iron oxide (SPIO) particles, form ferumoxide-transfection agent (FE-TA) complexes that are internalized into endosomes/lysosomes and have been used to label cells for in vivo MRI tracking and localization studies. A better understanding of the physical state of the FE-TA complexes during endocytosis could improve their use. The purpose of this study was to measure the rate of the degradation of iron particles under varying physiological conditions. FE-TA complexes were incubated in seven different buffers containing different chelates with different pH. Reducible iron concentrations, T2 relaxation rates and gradient echo (GRE) magnetic resonance images (MRI) were obtained from each condition immediately after incubation and at 6, 24, 48, 72 and 96 h and days 7, 14 and 21. The dynamics of FE-TA in the endosome/lysosomes within the cells were visualized with electron microscopy. Sodium citrate buffer at pH 4.5 rapidly dissolved FE-TA complexes. However, FE-TA complexes were less soluble in the same buffer at pH 5.5. Similarly, FE-TA complexes were not readily soluble in any of the other buffers with or without chelates, regardless of pH. Electron microscopic images showed degraded FE-TA in some intracellular endosome/lysosomes between days 3 and 5. In the cellular environment, some of the FE-TA-containing endosomes were found to fuse with lysosomes, causing rapid dissociation at low pH and exposing the iron core to chelates that resulted in soluble Fe(III) within the lysosomes. The studies presented represent a first step in identifying the important cellular environmental parameters affecting the integrity of FE-TA complexes.
超顺磁性氧化铁（SPIO）颗粒——铁氧化物，形成铁氧化物-转染剂（FE-TA）复合物，该复合物被内化到内体/溶酶体中，并已用于标记细胞以进行体内磁共振成像（MRI）追踪和定位研究。更好地了解内吞作用期间FE-TA复合物的物理状态可以改善其应用。本研究的目的是测量在不同生理条件下铁颗粒的降解速率。将FE-TA复合物在七种不同的含有不同螯合剂且pH不同的缓冲液中孵育。在孵育后立即以及在6、24、48、72和96小时以及第7、14和21天从每种条件下获得可还原铁浓度、T2弛豫率和梯度回波（GRE）磁共振图像（MRI）。用电子显微镜观察细胞内体/溶酶体内FE-TA的动态变化。pH 4.5的柠檬酸钠缓冲液能迅速溶解FE-TA复合物。然而，FE-TA复合物在pH 5.5的相同缓冲液中溶解度较低。同样，无论有无螯合剂，FE-TA复合物在任何其他缓冲液中都不易溶解，无论pH值如何。电子显微镜图像显示在第3天至第5天期间，一些细胞内的内体/溶酶体中有降解的FE-TA。在细胞环境中，发现一些含有FE-TA的内体与溶酶体融合，在低pH下导致快速解离，并使铁核暴露于螯合剂中，从而在溶酶体内产生可溶性Fe（III）。本研究是确定影响FE-TA复合物完整性的重要细胞环境参数的第一步。
