Joint Effects of Heterogeneous Estrogenic Chemicals in the E-Screen—Exploring the Applicability of Concentration Addition

Abstract

In the last few years, significant advances have been made toward understanding the joint action of endocrine disrupting chemicals (EDCs). A number of studies have demonstrated that the combined effects of different types of EDCs (e.g., estrogenic, antiandrogenic, or thyroid-disrupting agents) can be predicted by the model of concentration addition (CA). However, there is still limited information on the effects of mixtures of large numbers of chemicals with varied structural features, which are more representative of realistic human exposure scenarios. The work presented here aims at filling this gap. Using a breast cancer cell proliferation assay (E-Screen), we assessed the joint effects of five mixtures, containing between 3 and 16 estrogenic agents, including compounds as diverse as steroidal hormones (endogenous and synthetic), pesticides, cosmetic additives, and phytoestrogens. CA was employed to predict mixture effects, which were then compared with experimental outcomes. The effects of two of the mixtures tested were additive, being accurately predicted by CA. However, for the three other mixtures, CA slightly overestimated the experimental observations. In view of these results, we hypothesized that the deviations were due to increased metabolism of steroidal estrogens in the mixture setting. We investigated this by testing the impact of two such mixtures on the activation and expression of steroidal estrogen metabolizing enzymes, such as cytochrome P450 (CYP) 1A1, CYP 1B1, and CYP 3A4. Activation of CYP 1B1 and, consequently, a reduction in the levels of steroidal estrogens in the mixture could contribute to the shortfall from the additivity prediction that we observed.

Screening of hormone-like activities in bottled waters available in Southern Spain using receptor-specific bioassays

“…When compounds interact additively, one compound can be replaced with a fraction of an equally effective concentration of another compound without changing the overall combined effect. Second, some deviations from additivity may be expected (Charles et al, 2002;Kjaerstad et al, 2010), either in a negative direction due to an increased metabolism of natural steroidal estrogens in the mixture (Silva et al, 2011) or in a positive direction because of synergistic interactions related to additional interactions with the AR at receptor sites other than the ligand-binding domain (Orton et al, 2012). Consequently, it should be taken into account that the presence of each individual chemical residue at a "no-observed-adverse-effect level" does not necessarily imply a zero effect and does not rule out a potential impact of the mixture (Kortenkamp et al, 2007;Scholze et al, 2014).…”

The risky cocktail: what combination effects can we expect between ecstasy and other amphetamines?

“…This means that each individual component contributes to the global joint effect by acting in proportion to its concentration, even below concentrations producing no effect. This model has been used to assess combination effects of agents with a common site of action (Backhaus et al 2000b;Silva et al 2011a). Experimental evidence from some studies showed that combination effects of drugs with dissimilar mechanisms of action are better described using the alternative approach, that is, IA, which considers each agent interacting at differing sites of action (Backhaus et al 2000a).…”

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“…It is now accepted that a mixture of contaminants could induce more pronounced effects than the sum of its individual components. 3 However, very little is known about the effects of these mixtures of compounds in humans, as much of our knowledge is based on experimental studies of laboratory animals. For obvious reasons, it is not possible to expose humans to mixtures of compounds in a controlled fashion.…”