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Validated prediction concepts for the effects of multiple mixtures of estrogenic agents

The predictability of mixture effects of multi-component mixtures of estrogenic chemicals was assessed for a number of in vitro assays measuring estrogenicity. The assays included an estrogen receptor binding assay (HRS), the yeast estrogen screen (YES), the E-Screen and the ER-CALUX assay. Five chemicals, i.e. ethynylestradiol, estradiol, bisphenol A, nonylphenol and octylphenol were tested in all assays. Concentration-response relationships were recorded, and this information was used to predict quantitatively the effects of combinations of all five agents. The mixture effect predictions were calculated using the concept of concentration addition. In all assays, there was good agreement between prediction and observation, although slight deviations from expectation were noted in the E-Screen. These results show that the joint effect of all chemicals is (concentration) additive in most cases. These studies were extended by examining mixtures composed of up to 19 components in the four in vitro assays. In most cases it was possible to predict with accuracy the resulting joint effects, by using the concentration addition concept.

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THE SCHOOL OF PHARMACY, UNIVERSITY OF LONDON
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