In an article published on September 12, 2016 in the peer-reviewed journal Toxicology In Vitro, Coraline Simon and colleagues from the Department of Food Science of University of Liege, Belgium report on the endocrine activity screening performed for 65 compounds previously shown to migrate from polycarbonate-replacement baby bottles. Other recent studies have examined the genotoxicity (FPF reported) and other health risks (FPF reported) of select migrants from these BPA-free baby bottles.
Here, in vitro cell line-based reporter gene assays were used to test for agonistic (receptor activating) and antagonistic (receptor blocking) activity mediated by 7 nuclear receptors: Estrogen receptor (ER), androgen receptor (AR), progesterone receptor (PR), glucocorticoid receptor (GR), peroxisome proliferator-activated receptor γ (PPARγ), thyroid receptor β (TRβ) and aryl hydrocarbon receptor (AhR). The AhR-responsive cell line was of mouse origin, all other cell lines used were of human origin. Compounds were tested in four concentrations, 0.001 mM, 0.01 mM, 0.1 mM, and 1 mM, the latter concentration being the highest recommended by the Organization for Economic Cooperation and Development (OECD) for testing of endocrine activity in vitro. The activity at nuclear receptors was evaluated only when the tested concentration was not cytotoxic (i.e. seriously damaging or causing cells to die off).
Out of 65 substances tested, 12 showed no activity in either of the assays. These compounds were: 3,5-di-tert-butylbenzoquinone (CAS 719-22-2), 2-methylnaphtalene (CAS 91-57-6), naphthalene (CAS 91-20-3), 4-methylthiobenzaldehyde (CAS 3446-89-7), palmitic acid (CAS 57-10-3), ethyl stearate (CAS 111-61-5), 2-butoxyethyl acetate (CAS 112-07-2), 2-ethylhexyl acetate (CAS 103-09-3), eucalyptol (CAS 470-82-6), p-propenylanisole (CAS 4180-23-8), 2,4-di-tert-butylphenol (CAS 96-76-4), and butylated hydroxytoluene (BHT, CAS 128-37-0). The remaining 53 compounds showed agonistic and/or antagonistic activity on at least one of the receptors tested.
For AR, PR, and GR no agonistic activity was detected with any of the tested substances. 35 compounds showed agonistic activity on at least one of the other four receptors: ER (29 substances), PPARγ (10 substances), AhR (5 substances) and TRβ (4 substances). With regard to receptor activation, four chemical classes of particular interest were phthalates, benzophenones, aromatic hydrocarbons, and phenols. In addition, weak ER agonism was observed for several fatty acids and fatty acid esters.
Antagonistic activity was observed for all 7 receptors tested, with 35 compounds inhibiting at least one of the receptors: anti-PPARγ (20 substances), anti-TRβ (15 substances), anti-PR (14 substances), anti-ER (12 substances), anti-GR (11 substances), anti-AR (8 substances) and anti-AhR (3 substances). With regard to receptor inhibition, three chemical classes of particular interest were benzaldehydes, ketones, and fatty acid esters. Of 20 PPARγ antagonists, 11 substances also inhibited the TRβ; both of these receptors have been implicated in obesity, diabetes, and cancer.
The nuclear receptors included in the test panel are considered to “cover the most important endocrine endpoints as they are involved in numerous processes such as reproduction, cellular differentiation, regulation of glucose and lipid metabolism, inflammation, immunity, etc., which explains why a hormonal disturbance could lead to a multitude of biological effects.” Based on the presented results, 12 compounds that demonstrated no activity at the tested receptors are considered to be of “low concern”. For the 53 compounds showing endocrine activity in vitro, further investigation is required to better understand their activity in vivo, and assess the possible health risks associated with their migration from baby bottles.
Simon, C., et al. (2016). “Screening of endocrine activity of compounds migrating from plastic baby bottles using a multi-receptor panel of in vitro bioassays.” Toxicology In Vitro (published September 12, 2016).