Effects of silica nanoparticles on isolated rat uterine smooth muscle

In spite of their widespread use, toxicity of silica nanoparticles (SiO₂ NPs) to mammalian has not been extensively investigated. In the present study, it is aimed to investigate the effects and the mechanism of action of 20 nm sized SiO₂ NPs on isolated uterine smooth muscle. A total number of 84 preparations of uterine strips were used in the experiments. Study was designed as four groups: group I (control), group II (0.2 mM SiO₂ NPs), group III (0.4 mM SiO₂ NPs) and group IV (0.8 mM SiO₂ NPs). Spontaneous contractions were recorded using mechanical activity recording system. Superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities and malondialdehyde (MDA) levels were measured using the spectrophotometric methods. Apoptosis of the cells was detected using immunofluorescence staining assay. SiO₂ NP distribution and ultrastructural changes were determined by transmission electron microscopy. In groups II-IV, the frequency of contraction was significantly lower than that of the group I, whereas the contraction energy significantly decreased only in group IV. SOD and GSH-Px activities were significantly lower in experimental groups compared to the control group. MDA level and apoptotic cells were significantly higher in all SiO₂ groups compared to the control group. Numerous SiO₂ NPs in cytoplasm and connective tissue were observed in all dose groups. These findings showed that 20 nm sized SiO₂ NPs enter the connective tissue and cytoplasm of uterine muscle cells and cause oxidative stress and apoptosis leading to impaired uterine contractile activity.