MP2 Toxicity of Mixtures
255 Portland Ballroom
1:20 PM - 4:40 PM, Monday
() Dose-response curve analysis in chemical mixture toxicity: Evaluation of slope and EC50 in FETAX and MICROTOX®.
Dawson, D.1, Pöch, G.2, Schultz, T.3, 1 Ashland University, Ashland, OH, USA2 University of Graz, Graz, Austria3 The University of Tennessee, Knoxville, TN, USA
ABSTRACT- Mechanistic evaluation of combined effects of toxicants using dose-response curve (DRC) analysis has shown potential to improve understanding of the relationship between combined effects of toxicants and mechanism(s) of toxic action. A recent DRC analysis study of combined effects of osteolathyrogens, using a modified FETAX assay, indicated a strong relationship between primary molecular site of toxic action and the type of combined toxicity (e.g., dose-addition) obtained (Dawson et al., ETAP 16:13-23, 2004). This work demonstrated that binary and ternary mixtures of osteolathyrogens working at the same molecular site of action showed a dose-additive combined effect (chi-square goodness-of-fit-test), with slope and EC50 additivity quotients (AQ = actual mixture slope or EC50 / expected dose-addition slope or EC50) near 1.0. Non-dose-additive mixtures, in which the agents worked at different molecular sites, had AQs for slope and EC50 that were significantly below 1.0. To assess the value of this DRC analysis approach for other chemicals in another assay, agents from two groups of soft electrophiles (external vinyl Michael acceptors, alpha-haloactivation) and a group of carbonyl reactive agents were evaluated in binary mixtures using Microtox®. Ten intra-group combinations (i.e., common mechanism) and twelve inter-group combinations (i.e., different mechanisms) were tested. This selection of chemicals provided a rigorous test of the DRC analysis approach due to the similarity in DRC slopes of the agents examined. For each combination, each chemical was tested alone (six concentrations, in duplicate) and three replicates of their 1:1 mixture were tested (six concentrations, in duplicate / replicate). For the intra-group combinations 8 of 10 mean EC50 AQ and 7 of 10 mean slope AQ values were consistent with dose-addition. For the inter-group combinations, 7 of 12 mean EC50 AQ and 5 of 12 mean slope AQ values were consistent with dose-addition. Microtox®-derived mixture toxicity results showed lower mechanistic consistency, as compared with FETAX-derived results, in DRC analysis of chemical mixture toxicity. There are several potential explanations for this result, including alterations in potency on bacteria due to differing reaction rates and that the likely molecular site of action for both groups of soft electrophiles is glutathione.
Key words: chemical mixture toxicity, dose-response curve analysis, FETAX, MICROTOX