Recent US and EU legislation and high drug development failure rates have prompted the need to develop reliable human in vitro models for toxicity testing to replace, reduce and refine animal testing. This also stems from the response discrepancy among species and the need for novel approaches for mechanism-based high-throughput screening. In vitro models have been widely used, but the abnormality of continuous cell lines and restricted acquisition, source inconsistency and instability of primary cells limit their use. Adult stem cells derived from intact human tissue provides an innovative alternative that may more accurately predict in vivo toxicity.The objective of this research was to evaluate HL1-1 human hepatic stem cell line as a viable model for receptor-mediated toxicogenomic studies using the aryl hydrocarbon receptor (AhR) and peroxisome proliferator-activated receptor á (PPARá) as prototypical ligand activated transcription factors for comparative toxicogenomic investigation. AhR and PPARá are targets for environmental contaminants and pharmaceutical reagents and complementary species-specific hepatic responses are currently being studied.Comprehensive time course and dose-response gene expression studies were conducted in HL1-1 cells to assess the differential gene expression elicited by AhR and PPARá ligands incomparison to other in vitro and in vivo models. Some conserved responses with overlapping biological functions were identified. Although subsets of conserved differentially expressed genes are consistent with the known in vivo responses, the results suggest that species- and model-specific gene expression profiles are linked to species-specific physiology.HL1-1 cell were also immortalized by hTERT stable transfection (HLhT1) to overcome cell senescence and life span limitations. Immortalized HLhT1 cells maintain pluripotency characteristics as defined by stem cell and oval cell marker protein expression. The expression of functional AhR and PPARá and their ligand responsiveness is also comparable to the parental cell line. Collectively, human liver stem cells are viable models and warrant further development for mechanistic investigation of receptor-mediated hepatic toxicity and high throughput screening.
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