Comparative Effects of Di-(2-ethylhexyl)phthalate and Di-(2-ethylhexyl)terephthalate Metabolites on Thyroid Receptors: In Vitro and In Silico Studies

Abstract

Plasticizers added to polyvinylchloride (PVC) used in medical devices can be released into patients’ biological fluids. Di-(2-ethylhexyl)phthalate (DEHP), a well-known reprotoxic and endocrine disruptor, must be replaced by alternative compounds. Di-(2-ethylhexyl) terephthalate (DEHT) is an interesting candidate due to its lower migration from PVC and its lack of reprotoxicity. However, there is still a lack of data to support the safety of its human metabolites with regard to their hormonal properties in the thyroid system. The effects of DEHT metabolites on thyroid/hormone receptors (TRs) were compared in vitro and in silico to those of DEHP. The oxidized metabolites of DEHT had no effect on T3 receptors whereas 5-hydroxy-mono-(ethylhexyl)phthalate (5-OH-MEHP) appeared to be primarily an agonist for TRs above 0.2 µg/mL with a synergistic effect on T3. Monoesters (MEHP and mono-(2-ethylhexyl)terephthalate, MEHT) were also active on T3 receptors. In vitro, MEHP was a partial agonist between 10 and 20 µg/mL. MEHT was an antagonist at non-cytotoxic concentrations (2–5 µg/mL) in a concentration-dependent manner. The results obtained with docking were consistent with those of the T-screen and provide additional information on the preferential affinity of monoesters and 5-OH-MEHP for TRs. This study highlights a lack of interactions between oxidized metabolites and TRs, confirming the interest of DEHT.

Insights into the Endocrine Disrupting Activity of Emerging Non-Phthalate Alternate Plasticizers against Thyroid Hormone Receptor: A Structural Perspective

“…The differences in the two studies may be due to the two different molecular docking platforms used. However, our results on molecular docking of DEHP are supported by the results from this former study for DEHP metabolites [ 46 ]. Further, using a T-screen assay—a thyroid hormone-dependent rat pituitary tumor cell growth assay—Kambia et al reported that MEHP and 5-OH-MEHP induced concentration dependent agonist activity in the cells stimulating cell growth, which was synergically enhanced by the addition of T3 [ 46 ]; however, 5-oxo-MEHP showed antagonistic and cytotoxic activity.…”

“…Phthalate plasticizers, especially DEHP, have been shown to affect the hypothalamic-pituitary-thyroid axis and perturb the thyroid hormone homeostasis in epidemiological studies in humans [ 42 , 45 ] and in experimental laboratory animal and in vitro studies [ 40 , 46 , 47 ]. Alternative plasticizers are increasingly replacing phthalates in commercial and household products, such as food packaging, medical devices, cosmetic products, sealants, carpet, plastic tubing, fabrics, children’s toys, vinyl flooring, and several other applications [ 19 ].…”

“…Very limited studies are available on the structural binding aspects of the phthalate plasticizer, DEHP, against the TRα ligand-binding pocket. A recent study [ 46 ] reported in silico characterization of DEHP and its metabolites with TRα and DEHP was found to not bind to TRα but to its monoester, MEHP, and hydroxylated and oxidative metabolites, 5-OH-MEHP and 5-oxo-MEHP, closely imitated the binding mode in the TRα binding pocket. In the present study, we found that DEHP binds TRα with binding energy that was similar to that of native ligand, T3.…”

Comment on Bernard et al. Association between Urinary Metabolites and the Exposure of Intensive Care Newborns to Plasticizers of Medical Devices Used for Their Care Management. Metabolites 2021, 11, 252

“…Indeed, there were some questions raised relating to variations and reduced fetal weights secondary to decreased maternal food consumption; however, such effects need to be evaluated according to the respective OECD evaluation guidelines [ 24 ]. Interestingly, while this publication was submitted to the journal on 22 March 2021, several co-authors of L. Bernard recognized already on 29 November 2020, when submitting the publication by Kambia et al, 2021 [ 25 ], the lack of reproductive toxicity of DEHT, stating: “Di-(2-ethylhexyl) terephthalate (DEHT) is an interesting candidate due to its lower migration from PVC and its lack of reprotoxicity”.…”

Urinary Phthalate Metabolites in Pregnant Women: Occurrences, Predictors, and Association with Maternal Hormones

“…This is similar to a study in Australian(Bai et al, 2015), slightly higher total phthalate metabolite concentration were associated with insu cient activity.Normal thyroid function is important in maintain normal reproduction, and could be impacted by the endocrine disrupting effects of PAEs(Krassas et al, 2010). Recent studies in animals(Dong et al, 2019) and in vitro(Kambia et al, 2021) screening assays provide evidence that phthalate exposure might affect fetal neurodevelopment through thyroid signaling mechanisms. Our results showed that MEP and MBzP were negatively associated with FT4 and FT3.…”