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In vitro intestinal toxicity of copper oxide nanoparticles in rat and human cell models
Citation:
Henson, T., J. Navratilova, A. Tennant, K. Bradham, K. Rogers, AND M. Hughes. In vitro intestinal toxicity of copper oxide nanoparticles in rat and human cell models. Nanotoxicology. Informa Healthcare, London, Uk, 13(6):795-811, (2019). https://doi.org/10.1080/17435390.2019.1578428
Impact/Purpose:
Ingestion of NPs may occur incidentally by hand-to-mouth activity, from the diet of contaminated food or water, or swallowing material inhaled and transported to the pharynx. Information on the effect of NPs on the gastrointestinal (GI) tract following ingestion is lacking. NPs may be absorbed systemically by this route, but the mechanism of absorption is not well defined. NPs may injure the epithelial lining of the GI tract, which may increase their systemic absorption. The stability and agglomeration of ingested NPs may also be affected by GI fluids. The objective of this study was to assess the cytotoxicity of two copper oxide NPs in a two- dimensional rat intestinal model and a three-dimensional human intestinal model. Three-dimensional cellular models of human tissue offer more similarity to human tissue in vivo than two-dimensional cellular models. The three-dimensional intestinal tissue used in this study has celluar polarity, villi and brush border membranes. The NPs tested varied in valence and surface modification. As a source of Cu2+ ions, CuSO4 was tested in both cellular models. In addition, CuO NPs treated with simulated GI fluids were tested for cytotoxicity. A potential mechanism of toxicity, generation of ROS, was also investigated. We observed that with cupric oxide (oxidation state 1), that the rat cells were more sensitive than the human model. For cuprous oxide nanoparticles (coated with polyvinyl pyrrolidone) (Cu2O-PVP) and Cu2+ ions, the cytotoxicity was similar. We also observed that the Cu2O-PVP NPs also dissolved more readily to copper ions than the CuO NPs. This suggested that the CuO NPs have inherent toxicological properties and the Cu2O-PVP NPs dissolute to copper ions in order to generate a toxic response. For pre-treating the CuO NPs with simulated gastrointestinal fluids, the data suggests agglomeration of the particles at low pH (2) when incubated with pepsin. Raising the pH decreased particle agglomeration. Agglomeration may impact cytotoxic potential of the particles. When the rat cells were exposed to the pre-treated NPs, there was a slight enhancement of cytotoxicity at the lower concentrations relative to pristine nanoparticles. Users of the data include risk assessors in OCSPP as copper oxide nanoparticles have several uses such as pesticide, catalyst and others. An impact of this study is that copper oxide nanoparticles are cytotoxic to intestinal cells, but one must take into consideration of the valence of the particle, surface modification, and type of cellular model used. Pre-treating CuO NPs with simulated gastrointestinal fluids increased their agglomeration at low pH, but raising the pH appeared to have lessened the agglomeration. A slight enhancement of cyotoxicity of pre-treated NPs relative to pristine NPs was observed in rat cells at low concentration of NP. In summary, 1) copper oxide nanoparticles are cytotoxic in rat and human intestinal cells, with rat cells being more sensitive to CuO NPs than human cells; 2) reactive oxygen species are formed by copper oxide nanoparticles which may impact the mitochondrial membrane, causing it to depolarize as a pathway of toxicity; 3) pre-treating copper oxide nanoparticles with simulated gastric intestinal fluids impact their physico-chemcial properties by causing the particles to agglomerate at low pH. The cytotoxicity of the copper oxide nanoparticles pre-treated with the fluids was slightly enhanced relative to pristine nanoparticles at low concentrations in rats intestinal cells.
Description:
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 CuO and Cu2O-polyvinylpyrrolidone (PVP) coated NPs and Cu2+ ions in rat (IEC-6) and human intestinal cells, two- and three-dimensional models, respectively. The effect of pre-treatment 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 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 CuO NPs have inherent cytotoxicity, without dissolving and forming toxic Cu2+ ions, whereas Cu2O-PVP NPs are toxic due to their dissolution to these ions.
URLs/Downloads:
DOI: In vitro intestinal toxicity of copper oxide nanoparticles in rat and human cell models
https://www.tandfonline.com/doi/pdf/10.1080/17435390.2019.1578428