CHARACTERIZATION OF THE HUMAN HEPATOCELLULAR CARCINOMA (HEPG2) CELL LINE AS AN IN VITRO MODEL FOR CADMIUM TOXICITY STUDIES

Altered gene expression in human hepatoma HepG2 cells exposed to low-level 2,4-dichlorophenoxyacetic acid and potassium nitrate

2,4-dichlorophenoxyacetic acid (2,4-D) and nitrate are agricultural contaminants found in rural ground water. It is not known whether levels found in groundwater pose a human or environmental health risk, nor is the mechanism of toxicity at the molecular/cellular level understood. This study focused on determining whether 2,4-D or nitrate at environmentally realistic levels elicit gene expression changes in exposed cells. cDNA microarray technology was used to determine the impact of 2,4-D and nitrate in an in vitro model of exposure. Human hepatoma HepG2 cells were incubated with 2,4-D or nitrate alone for 24 h. Cell viability (neutral red assay) and proliferation (BrdU incorporation) were assessed following exposure. Total RNA from treated and control cells were isolated, reverse transcribed and reciprocal labelled with Cy3 or Cy5 dyes, and hybridized to a human cDNA microarray. The hybridized microarray chips were scanned, quantified and analyzed to identify genes affected by 2,4-D or nitrate exposure based on a two-fold increase or decrease in gene expression and reproducibility (affected in three or more treatments). Following filtering, normalization and hierarchical clustering initial data indicate that numerous genes were found to be commonly expressed in at least three or more treatments of 2,4-D or nitrate tested. The affected genes indicate that HepG2 cells respond to environmental, low-level exposure and produce a cellular response that is associated with alterations in the expression of many genes. The affected genes were characterized as stress response, cell cycle control, immunological and DNA repair genes. These findings serve to highlight new pathway(s) in which to further probe the effects of environmental levels of 2,4-D and nitrate.

Organochlorine insecticides: impacts on human HepG2 cytochrome P4501A, 2B activities and glutathione levels

This study examined the effects of the organochlorine (OC) insecticides chlordane, o,p'-DDT, dieldrin, endosulfan, kepone, methoxychlor, and toxaphene on human HepG2 cytochrome P450 (1A-EROD and 2B-PROD) activities and glutathione (GSH) levels. Cells were exposed for 24 h at high concentrations (1, 5 or 10 mM) and for 48 h at lower concentrations ranging from 0.01 to 1 mM to evaluate dose responses. Our results show that after 48 h all but dieldrin significantly induced both P4501A and 2B. P4502B responses were greater at all exposure concentrations and times. Mixed responses in GSH levels were observed. All OCs except dieldrin and MXC significantly depleted GSH after 24 h. At 48 h, chlordane, endosulfan and toxaphene significantly increased GSH at low levels and decreased GSH at high levels, while kepone and methoxychlor produced significant declines in GSH at all concentrations. These results support findings of OC insecticides inducing CYP1A, 2B in rats, with CYP2B responses more important. GSH levels declined when P4502B activity was significantly elevated and were significantly increased in the absence of significant P450 activity, suggesting that GSH levels influence the catalytic activity of the cytochrome P450s and the cytochrome P450s influence the cell's ability to regulate GSH.