Quantitative histochemistry for macrophage biodistribution on mice liver and spleen after the administration of a pharmacological-relevant dose of polyacrylic acid-coated iron oxide nanoparticles.

Understanding in vivo biodistribution of iron oxide nanoparticles (IONs), and the involvement of the phagocyte system in this process, is crucial for the assessment of their potential health risk. In the present study, the histochemical expression of iron in liver and spleen sections of CD-1 mice (aged 8 weeks) was quantified, 24 h after intravenous administration of polyacrylic acid-coated IONs (PAA-coated IONs) (8, 20, 50 mg/kg). Organ sections were stained with Perls' Prussian blue for iron detection, followed by the quantification of iron deposition with ImageJ software. Our study revealed the existence of a linear dose-dependent increase of iron deposition in macrophages of both organs. Exposed animals showed hepatic iron deposition in all zones, although most marked in periportal region. In the spleen, no iron was detected in the white splenic pulp of both control and treated animals. When compared with control mice, a positive correlation between histochemical detection of iron and PAA-coated ION doses was observed in splenic red pulp of animals. The results confirmed our assumption that liver and spleen are involved in the clearance pathways of PAA-coated IONs from the blood. Excess iron was cytotoxic at the highest dose of PAA-coated IONs tested, but no significant morphologic alterations were observed for the lower doses. Clusters of early necrotic hepatocytes were observed in the hepatic periportal region of mice injected with the higher dose (50 mg/kg) of PAA-coated IONs. Further studies are necessary to determine if liver and spleen macrophages will degrade these IONs, or eventually exocytose both the degraded and intact ones.