In vitro intestinal toxicity of copper oxide nanoparticles in rat and human cell models

Abstract

Human oral exposure to copper oxide nanoparticles (NPs) may occur following ingestion, hand-to-mouth activity, or mucociliary transport following inhalation. This study assessed the cytotoxicity of Cupric (II) oxide (CuO) and Cu₂O-polyvinylpyrrolidone (PVP) coated NPs and copper ions in rat (intestine epithelial cells; IEC-6) and human intestinal cells, two- and three-dimensional models, respectively. The effect of pretreatment of CuO NPs with simulated gastrointestinal (GI) fluids on IEC-6 cell cytotoxicity was also investigated. Both dose- and time-dependent decreases in viability of rat and human cells with CuO and Cu₂O-PVP NPs and Cu²⁺ ions was observed. In the rat cells, CuO NPs had greater cytotoxicity. The rat cells were also more sensitive to CuO NPs than the human cells. Concentrations of H₂O₂ and glutathione increased and decreased, respectively, in IEC-6 cells after a 4-h exposure to CuO NPs, suggesting the formation of reactive oxygen species (ROS). These ROS may have damaged the mitochondrial membrane of the IEC-6 cells causing a depolarization, as a dose-related loss of a fluorescent mitochondrial marker was observed following a 4-h exposure to CuO NPs. Dissolution studies showed that Cu₂O-PVP NPs formed soluble Cu whereas CuO NPs essentially remained intact. For GI fluid-treated CuO NPs, there was a slight increase in cytotoxicity at low doses relative to non-treated NPs. In summary, copper oxide NPs were cytotoxic to rat and human intestinal cells in a dose- and time-dependent manner. The data suggests Cu₂O-PVP NPs are toxic due to their dissolution to Cu ions, whereas CuO NPs have inherent cytotoxicity, without dissolving to form Cu ions.

Keywords:

• Intestine
• nanoparticles
• copper oxide
• in vitro
• toxicity
• reactive oxygen species

Acknowledgements

The authors thank Drs. David Thomas and William Boyes for their review of an earlier version of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by internal funds from the Office of Research and Development, U.S. Environmental Protection Agency.