Cobalt oxide nanoparticles (Co₃O₄NPs) are increasingly recognized for their utility in biological applications, magnetic resonance imaging, and drug delivery. However, little is known about the toxicity of Co₃O₄NPs in human cells.

We investigated the possible mechanisms of genotoxicity induced byCo₃O₄NPs in human hepatocarcinoma (HepG2) cells. Cell viability,reactive oxygen species (ROS), glutathione, thiobarbituric acid reactive substance,apoptosis, and DNA damage were assessed in HepG2 cells afterCo₃O₄NPs and Co²⁺ exposure.

Co₃O₄NPs elicited a significant (P < 0.01)reduction in glutathione with a concomitant increase in lipid hydroperoxide, ROSgeneration, superoxide dismutase, and catalase activity after 24- and 48-hour exposure.Co₃O₄NPs had a mild cytotoxic effect in HepG2 cells; however, itinduced ROS and oxidative stress, leading to DNA damage, a probable mechanism ofgenotoxicity. The comet assay showed a statistically significant (P< 0.01) dose- and time-related increase in DNA damage forCo₃O₄NPs, whereas Co²⁺ induced less change thanCo₃O₄NPs but significantly more than control.

Our results demonstrated that Co₃O₄NPs induced cytotoxicity and genotoxicity in HepG2 cells through ROS and oxidative stress.