Understanding the implications of dissolved organic carbon when assessing antagonism in vitro: An example with an estrogen receptor assay. (September 2015)

• Record Type: Journal Article
• Authors: Neale, Peta A.; Escher, Beate I.; Leusch, Frederic D.L.
• Is Part Of: Chemosphere. Volume 135(2015)
• Page Start: 341
• Page End: 346
• Publication Date: 2015-09
• Subjects: Antagonism -- Dissolved organic carbon -- Estrogen receptor -- In vitro; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2015.04.084
• Languages: English
• ISSNs: 0045-6535

Abstract

Graphical abstract: Highlights: Dissolved organic carbon stated to cause apparent antagonism in in vitro bioassays. DOC shifted 17β-estradiol (E2) concentration-effect curves to higher concentrations. Shift was not due to DOC being an antagonist or interfering with bioassay reading. Increase in EC50 was due to DOC reducing the bioavailable E2 concentration. DOC in water samples may cause E2 suppression and be reported as anti-estrogenic. Abstract: Both estrogenic and anti-estrogenic activity has been observed in water samples. Some studies have suggested that dissolved organic carbon (DOC), which can be co-extracted during sample enrichment, contributes to the apparent antagonistic effect. DOC has a high sorption capacity for the estrogen receptor (ER) agonist 17β-estradiol, which may reduce the available 17β-estradiol concentration in the antagonist testing mode and potentially lead to apparent antagonism. The aim of the study was to determine the influence of DOC when assessing antagonism in an ER reporter gene assay. The presence of DOC shifted the 17β-estradiol concentration-effect curve to higher concentrations, increasing the nominal EC50 value by up to 0.3 log units. However, this shift was within the usual variability associated with repeated measurements of concentration-effect curves. This shift was not due to DOC being an antagonist itself or interfering with fluorescence measurements, but was due to DOC reducing the bioavailability of 17β-estradiol. This was demonstrated by modelling the DOC sorption corrected 17β-estradiol concentration using experimental DOC-water partition coefficients ( K DOC ). While the shift in the 17β-estradiol concentration-effect curve was minor, sorption of 17β-estradiol to DOC can have an impact when assessing antagonism. At the EC50 agonist concentration, both modelled and experimental results showed that DOC at concentrations similar to that co-extracted in water samples caused suppression of the agonist at levels that would be classified as antagonism. The suppression was less pronounced at the EC80 agonist concentration, hence this is recommended when assessing antagonism of DOC rich samples, such as surface water and wastewater.