Gene Induction Studies and Toxicity of Chemical Mixtures

• Published in: Environmental health perspectives 2002-12, Vol.110 (Suppl 6), p.947-956
• Main Authors: Mumtaz, M. M., Tully, D. B., El-Masri, H. A., De Rosa, C. T.
• Format: Article
• Language: English
• Subjects: Application of Cell and Molecular Technology to Chemical Mixtures; Biomarkers; Carcinoma, Hepatocellular - pathology; Cell lines; Chemical hazards; Chemical mixtures; Chloramphenicol O-Acetyltransferase - biosynthesis; Chloramphenicol O-Acetyltransferase - pharmacology; DNA damage; Dosage; Drug Interactions; Environmental health; Gene expression; Gene Expression Profiling; Gene Expression Regulation - drug effects; HeLa Cells; Hep G2 cells; Humans; Hydrocarbons, Chlorinated; Insecticides - adverse effects; Liver Neoplasms - pathology; Metals, Heavy - adverse effects; Oxidative stress; Pesticides; Receptors, Estrogen - drug effects; Receptors, Estrogen - physiology; Signal Transduction; Toxicity Tests - methods; Transcriptional Activation; Tumor Cells, Cultured
• ISSN: 0091-6765; 1552-9924
• DOI: 10.1289/ehp.02110s6947

As part of its mixtures program, the Agency for Toxic Substances and Disease Registry (ATSDR) supports in vitro and limited in vivo toxicity testing to further our understanding of the toxicity and health effects of chemical mixtures. There are increasing concerns that environmental chemicals adversely affect the health of humans and wildlife. These concerns have been augmented by the realization that exposure to chemicals often occurs to mixtures of these chemicals that may exhibit complex synergistic or antagonistic interactions. To address such concerns, we have conducted two studies with techniques that are being used increasingly in experimental toxicology. In the first study, six organochlorine pesticides (4,4′-DDT, 4,4′-DDD, 4,4′-DDE, aldrin, dieldrin, or endrin) were selected from the ATSDR Comprehensive Environmental Response, Compensation and Liability Act of 1980 (or Superfund) priority list and tested for their ability to modulate transcriptional activation of an estrogen-responsive reporter gene in transfected HeLa cells. In these assays, HeLa cells cotransfected with an expression vector encoding estrogen receptor and an estrogen-responsive chloramphenicol acetyltransferase (CAT) reporter plasmid were dosed with and without selected environmental chemicals either individually or in defined combinations. Estradiol consistently elicited 10- to 23-fold dose-dependent inductions in this assay. By contrast, all six of the organochlorine pesticides showed no detectable dose-related response when tested either individually or in binary combinations. Thus, these chemicals as binary mixtures do not exhibit any additional estrogenicity at the levels tested in these assays. In the second study, arsenic [As(V)], cadmium [Cd(II)], chromium [Cr(III, VI)], and lead [Pb(II)] were tested in a commercially developed assay system, CAT-Tox (L), to identify metal-responsive promoters and to determine whether the pattern of gene expression changed with a mixture of these metals. This assay employs a battery of recombinant HepG2 cell lines to test the transcriptional activation capacity of xenobiotics in any of 13 different signal-transduction pathways. Singly, As(V), Cd(II), Cr(III, VI), and Pb(II) produced complex induction profiles in these assays. However, no evidence of synergistic activity was detected with a mixture of Cd(II), Cr(III), and Pb(II). These results have shown metal activation of gene expression through several previously unreported signal-transd