Fiber length and shape-dependent differences in hepatic nanomaterial localization in mice following pulmonary exposure.

BACKGROUND: Inhaled nanomaterials can translocate from the lungs into systemic circulation and reach the liver, which is the main secondary organ for nanomaterial uptake, potentially causing adverse effects. Understanding how inhaled nanomaterials localize within liver tissue is important for understanding their clearance mechanisms and potential toxicity. Previous in vivo studies have primarily focused on spherical particles, highlighting the need for studies on fiber-shaped nanomaterials. METHODS: This study examines the hepatic distribution of five fiber-shaped nanomaterials (three multiwalled carbon nanotubes, gallium phosphide nanowires, and short TiO₂ nanotubes) compared to spherical TiO₂ nanoparticles. Liver samples were collected at 1, 3, 6, and 12 months after pulmonary exposure using a single intratracheal (IT) instillation in mice. Paraffin-embedded liver sections were stained with Hematoxylin and Eosin (H&E), and analyzed using enhanced darkfield microscopy. The localization of the nanomaterials within sections was categorized into four categories: hepatocyte, non-parenchymal cell, sinusoid/vessel, and another placement. Localization was further validated using cell-specific immunohistochemical staining. Furthermore, morphological changes were assessed in liver sections and 1 year post-exposure from mice following pulmonary exposure to eleven different MWCNTs. RESULTS: The hepatic localization of six different nanomaterials were assessed, with more than 10,000 fibers or particles manually counted across all samples. There were significant differences in the localization of long and thick fibers as compared to spherical nanoparticles and short and thin fibers, at all assessed post-exposure time points. Long and thick fiber-shaped nanomaterials were more frequently localized within the liver parenchyma compared to spherical particles and the short TiO2 tubes, which were more frequently found in non-parenchymal cells. Histological analysis revealed that short, thin, and entangled MWCNTs caused minor tissue alterations, including inflammatory cell infiltration and mild connective tissue hyperplasia in portal zones, whereas long and thick MWCNTs did not induce morphological changes. CONCLUSION: These findings demonstrate that the intrahepatic localization of nanomaterials is strongly influenced by fiber shape and dimensions.