Proteomic analysis of the response of EpiDerm cultures to sodium lauryl sulphate.

The analysis of EpiDerm cultures treated with the known skin irritant sodium lauryl sulphate (SLS) was performed using 2D-gel electrophoresis in order to understand the mechanism of action and thereby identify novel markers of skin irritation. A range of both broad and narrow pH gradient first-dimension gels were run (pH 4-7, 6-11, 4-5, 5-6 and 6-9) consistently followed by 12% SDS-PAGE in the second-dimension. Following treatment of EpiDerm with SLS, 67 proteins of interest were identified, of which 8 were selected as interesting: calmodulin-like skin protein, involucrin, epithelial cell marker protein, HS1, peroxiredoxin 1, serine protease inhibitor, KIAA0117 and ribosomal protein L17. Involucrin was confirmed as being up-regulated by both ELISA and Western blotting. The use of proteomics has identified a number of proteins which could be used as general markers for skin irritation and which may in particular be of value for the development of in vitro predictive models.

Gene expression analysis of EpiDerm following exposure to SLS using cDNA microarrays.

There is a need to investigate the mechanistic basis of the human skin irritation response if relevant in vitro test systems for the predictive identification of skin irritation hazards are to be developed. Recent progress in genomics technologies mean that tools for the identification and investigation of important biochemical events in the processes of skin irritation are now available. The aim of this work was to identify genes (for further mechanistic investigation) which may be regulated in response to skin irritation, following exposure of the EpiDerm skin model to the known skin irritant sodium lauryl sulphate (SLS). EpiDerm cultures were treated in triplicate with a non-cytotoxic dose of SLS (0.1 mg/ml, as determined by the MTT assay and histological examination) for 15 min, 30 min, 1 h, 2 h, 3 h, 4 h and 24 h. Total RNA was extracted from the pooled EpiDerm cultures and used to probe Atlas human arrays (Clontech) covering approximately 3600 genes. Preliminary data indicated an up-regulation at early time points (15-30 min) of a number of genes involved in transportation (e.g. the sodium and chloride dependent taurine transporter) and receptors (e.g. ZAP70 and protocadherin 42 precursor). The gene encoding the UV excision repair protein and other DNA repair genes (e.g. DNA-directed RNA polymerase II) were up-regulated after 1-3 h, along with TGF beta 3 and other tumour suppressors, which play a role in cellular development and wound healing. At the later time points of 4-24 h, genes involved in protein translation (e.g. Cathepsin D receptor) and metabolism (e.g. CYP27A) were up-regulated. In addition, a number of genes were down-regulated in response to treatment with SLS, although these followed less of a time dependent pattern. These results indicate the differential regulation of a number of genes in response to treatment with SLS, some of which may provide additional clues to the molecular events underpinning the irritation response to this particular surfactant and possibly to other chemical irritants.

The use of genomics technology to investigate gene expression changes in cultured human liver cells.

The field of genomics has great potential in toxicology; however, the technology is still in its infancy and there are many questions that need to be addressed. In this study we focus on the use of toxicogenomics for the determination of gene expression changes associated with hepatotoxicity. The human hepatoma cell line HepG2 was used to assess the toxic effects of two well-studied hepatotoxins, carbon tetrachloride (CCl(4)) and ethanol (EtOH). Replicate dishes of HepG2 cells were exposed to two concentrations of CCl(4) and EtOH--doses which caused 20% and 50% cell death (as determined by the MTT assay) were chosen [0.18% and 0.4% (v/v) CCl(4); 2.5% and 5% (v/v) EtOH] and the cells exposed for periods of 2 and 24 h. mRNA was extracted and used to probe Atlas Human Toxicology II arrays (Clontech). Preliminary data revealed that following a 2-h exposure at the low doses of both compounds, few changes in gene expression were detected. However, after 24-h exposure of the cells to the same low concentration of both compounds, multiple changes in gene expression were observed, many of which were specific to the individual hepatotoxins, presumably reflecting their different mechanisms of action. CCl(4) treatment of HepG2 cells gave rise to treatment specific up-regulation of genes involved in extracellular transport and cell signalling, whereas EtOH treatment gave rise predominantly to down-regulation of genes involved in stress response and metabolism. In addition, changes in regulation of certain genes (involved in stress response and cell cycle) were common to both treatments. Exposure of HepG2 cells to higher doses of the hepatotoxins gave rise to more changes in gene expression at lower exposure times. These results strongly suggest that different mechanisms of hepatotoxicity may be associated with specific patterns of gene expression, while some genes associated with common cellular responses may be useful as early markers of toxicity.