Comparative effects of TiO₂ and ZnO nanoparticles on growth and ultrastructure of ovarian antral follicles

Titanium dioxide (TiO₂) and zinc oxide (ZnO) nanoparticles (NP) have been demonstrated to reach the ovary. However, the potential detrimental effects of these metal-based NP on ovarian antral follicles and whether they can be directly taken up by follicular cells are unknown. The aim of this study was to evaluate whether TiO₂ and ZnO NP internalize into the antral follicle, and further compared any potential detrimental effects of either NP on growth, ultrastructure and viability of antral follicles. It has been described that TiO₂ and ZnO NP induce oxidative stress, thus this study indirectly assessed whether oxidative stress was involved. Antral follicles were cultured with TiO₂ (5, 25 and 50 μg/mL) or ZnO (5, 15 and 25 μg/mL) NP for 96 h. TiO₂ NP were internalized and agglomerated into cells, increased follicle diameter and disrupted the cytoskeleton arrangement, effects that were partially prevented by a co-exposure with trolox. Moreover, ZnO NP partially dissolved into culture media, decreased follicle diameter, and disrupted cytoskeletal arrangement, and these effects were not prevented by trolox. Ultrastructural alterations induced by exposure to both NP were evidenced by impaired transzonal projections and swelling mitochondria. Oxidative stress mediates TiO₂ NP-induced effects but not those from ZnO NP in antral follicle development. Our results suggest that both NP induced ovarian follicle toxicity through different toxic mechanisms, possibly due to a stimulation of ZnO NP solubility and agglomeration of TiO₂ NP into the follicular cells.