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

Purpose To investigate the biodistribution and the ability of stealth pH-sensitive liposomes radiolabelled with Tc-99m to identify inflammatory regions in a rat focal inflammation model. Methods Preformed glutathione-containing stealth pH-sensitive liposomes were labelled with Tc-99m-hexamethylpropylene amine oxime (Tc-99m-HMPAO). The Tc-99m-HMPAO radiolabelled stealth pH-sensitive liposomes (Tc-99m-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-99m content using an automatic scintillation apparatus. Scintigraphic imaging was also performed after 2,4 and 8 h of intravenous injection of Tc-99m-SpHL. Results The Tc-99m-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-99m-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-99m-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. Conclusion This result indicates that the Tc-99m-SpHL presents a high tropism for inflammatory regions and may be useful as a radiopharmaceutical to identify these foci.