Biodistribution study and identification of inflammatory sites using nanocapsules labeled with (99m)Tc-HMPAO

To evaluate the ability of polymeric nanocapsules (NCs) radiolabeled with technetium-99m D,L-hexamethylpropyleneamine oxime (Tc-HMPAO) to identify inflammatory process in an experimental model.

NCs were prepared by interfacial deposition of preformed biodegradable polymer [poly (D,L-lactic acid) (PLA) and PLA-PEG (polyethyleneglycol)] followed by a solvent displacement. The size and homogeneity, and zeta potential of the NC preparations were determined in a Zetasizer by photon correlation spectroscopy and laser Doppler anemometry, respectively. The NCs radiolabeled with Tc-HMPAO were administered intravenously to Wistar male rats bearing a focal inflammation induced by subplantar injection of carrageenan in the right foot. At preestablished time intervals, the animals were anesthetized, tissues were removed and radioactivity was determined using an automatic scintillation apparatus.

The average diameter calculated by photon correlation spectroscopy varied from 216 to 323 nm. The biodistribution studies showed a greater uptake of the PEG surface-modified Tc-HMPAO-NC by the inflamed paws when compared with the respective controls. There was no significant difference in the uptake of conventional Tc-HMPAO-NC and of free Tc-HMPAO by inflamed and control paws. These results indicate that the PLA-PEG Tc-NC showed a higher uptake in inflammation compared with free complex and may be useful as a radiotracer to identify these foci.