Biodistribution study and identification of inflammation sites using 99mTc-labelled stealth pH-sensitive liposomes

PURPOSETo investigate the biodistribution and the ability of stealth pH-sensitive liposomes radiolabelled with Tc to identify inflammatory regions in a rat focal inflammation model. METHODSPreformed glutathione-containing stealth pH-sensitive liposomes were labelled with Tc-hexamethylpropylene amine oxime (Tc-HMPAO). The Tc-HMPAO radiolabelled stealth pH-sensitive liposomes (Tc-SpHL) were administered intravenously in Wistar male rats with inflammation induced by injection subplantar of carrageenan in the right foot. At pre-established time intervals the animals were anaesthetized and tissues were removed and analysed for Tc content using an automatic scintillation apparatus. Scintigraphic imaging was also performed after 2, 4 and 8 h of intravenous injection of Tc-SpHL. RESULTSThe Tc-SpHL was significantly taken up by the spleen (19.21±2.98%ID/g at 30 min post-injection). Low radioactivity levels were found in the liver, lungs, and kidney. Moreover, the Tc-SpHL uptake was significantly higher in the inflamed foot when compared to the respective control (0.386±0.059 and 0.215±0.018%ID/g at 2 h post-injection, respectively). As early as 30 min after administration of Tc-SpHL, the focus of inflammation could be visualized scintigraphically. The value of the inflammatory and non-inflammatory site radioactivity counting ratio was greater than 5. CONCLUSIONThis result indicates that the Tc-SpHL presents a high tropism for inflammatory regions and may be useful as a radiopharmaceutical to identify these foci.