Development of a mechanistically-based genetically engineered PC12 cell system to detect p53-mediated cytotoxicity

Identification of transcriptome signatures and biomarkers specific for potential developmental toxicants inhibiting human neural crest cell migration

The in vitro test battery of the European research consortium ESNATS (‘novel stem cell-based test systems’) has been used to screen for potential human developmental toxicants. As part of this effort, the migration of neural crest (MINC) assay has been used to evaluate chemical effects on neural crest function. It identified some drug-like compounds in addition to known environmental toxicants. The hits included the HSP90 inhibitor geldanamycin, the chemotherapeutic arsenic trioxide, the flame-retardant PBDE-99, the pesticide triadimefon and the histone deacetylase inhibitors valproic acid and trichostatin A. Transcriptome changes triggered by these substances in human neural crest cells were recorded and analysed here to answer three questions: (1) can toxicants be individually identified based on their transcript profile; (2) how can the toxicity pattern reflected by transcript changes be compacted/dimensionality-reduced for practical regulatory use; (3) how can a reduced set of biomarkers be selected for large-scale follow-up? Transcript profiling allowed clear separation of different toxicants and the identification of toxicant types in a blinded test study. We also developed a diagrammatic system to visualize and compare toxicity patterns of a group of chemicals by giving a quantitative overview of altered superordinate biological processes (e.g. activation of KEGG pathways or overrepresentation of gene ontology terms). The transcript data were mined for potential markers of toxicity, and 39 transcripts were selected to either indicate general developmental toxicity or distinguish compounds with different modes-of-action in read-across. In summary, we found inclusion of transcriptome data to largely increase the information from the MINC phenotypic test.

Toxicity of depleted uranium complexes is independent of p53 activity

The p53 tumor suppressor protein is one of the key checkpoints in cellular response to a variety of stress mechanisms, including exposure to various toxic metal complexes. Previous studies have demonstrated that arsenic and chromium complexes are able to activate p53, but there is a dearth of data investigating whether uranium complexes exhibit similar effects. The use of depleted uranium (DU) has increased in recent years, raising concern about DU's potential carcinogenic effects. Previous studies have shown that uranyl acetate and uranyl nitrate are capable of inducing DNA strand breaks and potentially of inducing oxidative stress through free radical generation, two potential mechanisms for activation of p53. Based on these studies, we hypothesized that either uranyl acetate or uranyl nitrate could act as an activator of p53. We tested this hypothesis using a combination of cytotoxicity assays, p53 activity assays, western blotting and flow cytometry. All of our results demonstrate that there is not a p53-mediated response to either uranyl acetate or uranyl nitrate, demonstrating that any cellular response to uranium exposure likely occurs in a p53-independent fashion under the conditions studied.

Methylmercury chloride induces alveolar type II epithelial cell damage through an oxidative stress-related mitochondrial cell death pathway

Mercury, one of the widespread pollutants in the world, induces oxidative stress and dysfunction in many cell types. Alveolar type II epithelial cells are known to be vulnerable to oxidative stress. Alveolar type II epithelial cells produce and secrete surfactants to maintain morphological organization, biophysical functions, biochemical composition, and immunity in lung tissues. However, the precise action and mechanism of mercury on alveolar type II epithelial cell damage remains unclear. In this study, we investigate the effect and possible mechanism of methylmercury chloride (MeHgCl) on the human lung invasive carcinoma cell line (Cl1-0) and mouse lung tissue. Cl1-0 cells were exposed to MeHgCl (2.5-10 microM) for 24-72 h. The results showed a decrease in cell viability and an increase in malondialdehyde (MDA) level and ROS production at 72 h after MeHgCl exposure in a dose-dependent manner. Caspase-3 activity, sub-G1 contents and annexin-V binding were dramatically enhanced in Cl1-0 cells treated with MeHgCl. MeHgCl could also activate Bax, release cytochrome c, and cleave poly(ADP-Ribose) polymerase (PARP), and decrease surfactant proteins mRNA levels. Moreover, in vivo study showed that mercury contents of blood and lung tissues were significantly increased after MeHgCl treatment in mice. The MDA levels in plasma and lung tissues were also dramatically raised after MeHgCl treatment. Lung tissue sections of MeHgCl-treated mice showed pathological fibrosis as compared with vehicle control. The mRNA levels of proteins in apoptotic signaling, including p53, mdm-2, Bax, Bad, and caspase-3 were increased in mice after exposure to MeHgCl. In addition, the mRNA levels of surfactant proteins (SPs), namely, SP-A, SP-B, SP-C, and SP-D (alveolar epithelial cell functional markers) were significantly decreased. These results suggest that MeHgCl activates an oxidative stress-induced mitochondrial cell death in alveolar epithelial cells.