Background: Nanomaterials have gained increasing attention because of their novel properties, including a large specific surface area and high reaction activity. This study was designed to investigate the cytotoxic effects of CuO nanopaticles on brain, spleen, and embryo NMRI pregnant mice.

Materials and Methods: In this experimental study, forty two female NMRI mice of (weighting 30±3.0 g) were randomly divided into six groups (four experimental groups, one sham group and one control group).The experimental mice on days 3 and 12 of pregnancy received CuO nanoparticle with concentrations 50, 100, 150, 200 mg/kg intraperitoneal injection. On day 17 pregnancy, brain, spleen and fetus weights were measured.Tissues for histopathological evaluation were stained with hematoxylin and eosin.

Results: Based on the macroscopic observations of embryos weight with increasing concentration of nanoparticle compared to control reduces its toxicity increased (p&le0.05). Spleen only at concentration of 600 mg/kg showed significant changes compared to control (p&le0.05). Histopathologic examination on brain and spleen following IP administration of CuO nanoparticle showed signs of cytotoxicity (congestion, necrosis, inflammatory cell infiltration, vacuolar degeneration) and (congestion, necrosis, increased hemosiderin) compared to control group, respectively.

Conclusion: The present study clearly showed that CuO-NPs can produce the histopathological abnormalities on brain and spleen tissues of NMRI mice in a dose-dependent manner.