4.7. In Vivo Biodistribution Studies

Studies were carried out in male Wistar rats (200–250 g) obtained from Harlan (Barcelona, Spain) and the protocols were approved by the Ethical Committee for Animal Experimentation of the University of Navarra (protocol numbers 117-12 [31 October 2012] and 059-13 [21 June 2013]). Prior to the experiments, animals were placed in metabolic cages and drink was provided ad libitum.

For radiolabeled nanoparticles, animals received a single dose of nanoparticles (10 mg gallium-67-citrate-NP). Animals were anesthetized with isofluorane and placed in prone position on the gamma camera. The SPECT-CT images were obtained 2 and 24 h after the administration of the radiolabeled nanoparticles in a Symbia^® gamma camera (Siemens Medical Systems, Malvern, PA, USA).

For fluorescently labelled nanoparticles, 30 mg nanoparticles in 1 mL water were administered to animals. Two hours later, the animals were sacrificed, and their gastrointestinal tract was removed. Jejunum portions of 1 cm were stored in the tissue proceeding medium OCT and frozen at −80 °C. Each portion was then cut into 5-µm sections on a cryostat and attached to glass slides. Finally, the samples were fixed with formaldehyde and incubated with DAPI for 15 min. The samples were examined in a fluorescence microscope (Axioimager M1, Zeiss, Oberkochem, Germany) with a coupled camera (Axiocam ICc3, Zeiss) and fluorescent source (HBO 100, Zeiss).