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COMPARISON OF MEDIUM CONCENTRATION VS. ACTUAL TISSUE DOSE IN IN VITRO NEUROTOXICANT MODELS.
Citation:
MEACHAM, C. A., K. M. CROFTON, T. M. FREUDENRICH, J. HARRILL, W. R. MUNDY, AND T. J. SHAFER. COMPARISON OF MEDIUM CONCENTRATION VS. ACTUAL TISSUE DOSE IN IN VITRO NEUROTOXICANT MODELS. Presented at DNT-TestSmart , Reston, VA, March 13 - 15, 2006.
Description:
In vitro methods have long been used to model the effects of toxicants on the nervous system. Generally, it is assumed that concentrations of toxicant present in the medium surrounding cells in in vitro models are an adequate biomarker of cell or tissue levels. However, this assumption has not been rigorously tested for many in vitro models. The present studies examined the relationship between medium concentration and tissue concentration (or dosage) in three common in vitro systems using neurotoxicants from several different chemical classes. The following in vitro cell models were examined; a cell line of nerve growth factor differentiated pheochromocytoma (PC12) cells, a primary culture of rat neocortical cells, and Xenopus laevis oocytes. Toxicants used included methylmercury, Aroclor 1254 (PCBs), 2,2',4,4'-tetrabromo[14C]diphenyl ether (PBDE-47), and 14C-deltamethrin (a pyrethroid pesticide). The hypothesis that concentration of toxicant in the medium was an accurate surrogate for tissue concentration was tested. In one hour, mercury accumulated in PC12 cells up to 17.7 ppm from a 0.33 ppm methylmercury serum-free medium concentration (53-fold increase). PC12 cells accumulated 66.7 ppm PCB (103-fold) after one hour from 0.65 ppm Aroclor 1254 serum-free medium. Neocortical cells accumulated 20.6 ppm PCB (32-fold) after one hour in the same medium (0.65 ppm Aroclor 1254). Neocortical cells accumulated PBDE-47 by 100 fold after one hour exposure; adding serum to the medium reduced accumulation into the cells, and doubling the volume of the medium increased accumulation. Deltamethrin medium concentration was a more accurate predictor for tissue dosage; deltamethrin accumulated in Xenopus oocytes up to 2-fold medium concentration after three hours. These data demonstrate that medium concentration is not always equivalent to the actual tissue dosage. Thus, caution is warranted when extrapolating results from in vitro models to in vivo exposures. (This is an abstract of a proposed presentation and does not necessarily reflect EPA policy).