Hazard assessment of engineered nanomaterials - impacts on hepatic and renal models
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This study was conducted as part of a large consortium (FP7 project – ENPRA) to investigate the potential hazard of a wide range of nanomaterials (one Ag, two ZnO, two MWCNTs and five TiO2) on the liver and the kidneys for the purpose of risk assessment. The in vitro C3A hepatocyte model demonstrated that Ag and ZnO NMs were consistently more potent with respect to cytotoxicity and cytokine production. In comparison the MWCNT and TiO2 nanomaterials investigated revealed relatively lower toxicity. The cytotoxicity of ZnO may be related to its solubility, but this is less likely for the Ag NMs. Urea and albumin production were measured as indicators of hepatic function. These markers were only altered by the coated and uncoated ZnO, which significantly decreased albumin production. The C3A model also showed that the NM which induced a low cytotoxicity (TiO2 and MWCNTs) generated intracellular ROS, induced oxidative stress (GSH depletion) and that an oxidative mechanism was involved in both the induction of IL8 protein production and genotoxicity. The C3A cells were demonstrated to be a very good model to investigate nanomaterial induced effects on hepatocytes when compared to primary human hepatocytes. The results also suggested that biotransformation enzymes in hepatocytes are not important in terms of determining nanotoxicology. In vivo mice models demonstrated that the instilled Ag, ZnO and positively charged TiO2 result in distal effects on the liver in the form of oxidative stress. While all NMs with the exception of the two MWCNTs instilled via the lungs caused changes in gene expression in the liver in varying degrees. The intravenous exposure of mice to the NMs resulted in a neutrophil influx into the liver. These leukocytes play an important in the initiation of the immune response to the NMs. However the NMs were not sufficient to cause any long term neutrophil mediated inflammation or damage to the liver tissue. Any changes that were observed after 24 hr post exposure in terms of leukocyte infiltration into the tissue, antioxidants status and changes in gene expression related to inflammation, oxidative stress and apoptosis had resolved 72 hr post exposure. Next, we show that Kupffer cells are very important in the liver immune response to the NMs with a significant change in the cytokine profile following the enrichment of the macrophage population. Finally, investigations using the HK-2 renal model demonstrated that ZnO and Ag NMs were consistently more potent with respect to cytotoxicity, cytokine production (IL6 and IL8) and intracellular reactive oxygen species production. These results were consistent with those observed in the hepatocyte models. We noted that short term sub-lethal exposure to the Ag and two of the TiO2 NMs (positively charged and the 94 nm TiO2) resulted in most evident DNA damage.