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GENE INDUCTION STUDIES AND TOXICITY OF CHEMICAL MIXTURES
Citation:
Mumtaz, M. M., D B. Tully, H. E. Masri, AND C. T. DeRosa. GENE INDUCTION STUDIES AND TOXICITY OF CHEMICAL MIXTURES. Application of Technology to Chemical Mixture Research Conference, Fort Collins, CO, January 9-11, 2001.
Description:
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 increasingly used 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 CERCLA 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 acetyl transferase (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 and 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 transduction pathways and thus suggest new directions for future studies into their biochemical mechanisms of toxicity. In conclusion, the in vitro methods used in these studies provide insights into complex interactions that occur in cellular systems and could be used to identify biomarkers of exposure to other environmental chemical mixtures.