Trichloroethylene health risk assessment: a new and improved process

Expression profile of liver genes in response to hepatotoxicants identified using a SAGE-based customized DNA microarray system

Gene expression analysis using customized or focused DNA microarrays is favorable because of a reduction in the cost and time needed for the analysis. To examine the effect of chemicals on the liver, we developed an in-house cDNA microarray system, mouse Liver Stress Array ver. 1.0, containing 355 unique genes involved in drug metabolism, inflammation and liver-related proteins. These genes were selected for sensing the homeostasis of the liver and based on the information of liver transcriptome revealed by serial analysis of gene expression. By using this customized microarray, we analyzed gene expression changes in the mouse liver treated by 11 known hepatotoxicants. Gene expression measurements corresponding to the in vivo response to known hepatotoxicants revealed that profiles of chemicals with similar mechanisms clustered together. For each of the chemicals tested, several genes that were induced or repressed were common in each chemical exposure, whereas other genes were unique for the specific class compound. Ingenuity pathways analysis revealed that significant alterations in gene expression occurred in a number of biological networks by these treatments. Although the genes spotted on our array was limited to a highly focused set for toxicity classification, this work provides proof of concept that patterns of gene regulation assessed by a focused array system are useful to classify unknown chemicals.

A proposed methodology for selecting a trichloroethylene inhalation unit risk value for use in risk assessment

U.S. EPA's 2001 draft assessment of trichloroethylene (TCE) toxicity reviews the existing human and animal data on TCE carcinogenicity and proposes a 20-fold range of cancer potency values for use in risk assessment. Each value in the range is derived from a different source of data, either animal bioassays or epidemiology studies, and thus the range does not represent a distribution which can be characterized by statistical parameters such as a mean or 95% confidence interval. The U.S. EPA suggests users choose a single slope factor from among those it describes as appropriate for the population of interest and mode of exposure, but little guidance is given for making this choice. We propose an approach for determining the most scientifically defensible carcinogenic inhalation unit risk estimate from the range of slope factors developed by U.S. EPA, one that relies on accepted principles for evaluating scientific studies. Based on these considerations, we identify the most appropriate interim unit risk for low-level inhalation exposure as 9 x 10(-7) per microg/m(3). This approach may have fairly broad utility if U.S. EPA elects to use a similar approach in future assessments of other chemicals.

Characterization of P2X3, P2Y1 and P2Y4 receptors in cultured HEK293-hP2X3 cells and their inhibition by ethanol and trichloroethanol

Membrane currents and changes in the intracellular Ca2+ concentration ([Ca2+]i) were measured in HEK293 cells transfected with the human P2X3 receptor (HEK293-hP2X3). RT-PCR and immunocytochemistry indicated the additional presence of endogenous P2Y1 and to some extent P2Y4 receptors. P2 receptor agonists induced inward currents in HEK293-hP2X3 cells with the rank order of potency alpha,beta-meATP approximately ATP > ADP-beta-S > UTP. A comparable rise in [Ca2+]i was observed after the slow superfusion of ATP, ADP-beta-S and UTP; alpha,beta-meATP was ineffective. These data, in conjunction with results obtained by using the P2 receptor antagonists TNP-ATP, PPADS and MRS2179 indicate that the current response to alpha,beta-meATP is due to P2X3 receptor activation, while the ATP-induced rise in [Ca2+]i is evoked by P2Y1 and P2Y4 receptor activation. TCE depressed the alpha,beta-meATP current in a manner compatible with a non-competitive antagonism. The ATP-induced increase of [Ca2+]i was much less sensitive to the inhibitory effect of TCE than the current response to alpha,beta-meATP. The present study indicates that in HEK293-hP2X3 cells, TCE, but not ethanol, potently inhibits ligand-gated P2X3 receptors and, in addition, moderately interferes with G protein-coupled P2Y1 and P2Y4 receptors. Such an effect may be relevant for the interruption of pain transmission in dorsal root ganglion neurons following ingestion of chloral hydrate or trichloroethylene.