Chemicals with Endocrine-Disrupting Potential: A Threat to Human Health?

Alkylphenols disrupt estrogen homeostasis via diradical cross-coupling reactions: A novel pathway of endocrine disruption

Estrogen, being an essential class of sex hormone, is an important target of endocrine disruption chemicals. It is well known that environmental disruptors could activate or inhibit estrogen receptors, acting as agonists or antagonists, and thus affect the circulating estrogen concentrations. Here, we report enzyme-mediated diradical cross-coupling reactions between alkylphenols (e.g., 2,4-di-tert-butylphenol [DBP], 4-nonylphenol [4-NP], and 4-tert-octylphenol [4-t-OP]) and estrogens (e.g., estradiol [E2]) that generate coupling metabolites and disrupt estrogen homeostasis. Among the phenolic xenobiotics, the screening of metabolic products revealed that alkylphenols had the highest reaction activities and generated coupling metabolites with high abundances (DBP-O-E2, 4-t-OP-O-E2, and 4-NP-O-E2). The coupling reactions were catalyzed by cytochrome P450 3A4 (CYP3A4) and verified by the detection of the coupling products in general populations. In vitro and in vivo exposures together with CYP3A4 inhibition demonstrated that cross-coupling reactions of phenols and E2 significantly reduced the normal levels of E2. We further established a unique spin-trapping-based high-throughput screening method to show the existence of diradicals in the coupling reaction. Density functional theory calculations revealed that spin aromatic delocalization was the fundamental cause of the high rebound barrier and sufficient lifetime of phenoxy radicals that enabled phenolic cross-coupling triggered by cytochrome P450. The identified mechanistic details for diradical cross-coupling reactions provide a novel pathway for phenolic chemicals to disrupt estrogen homeostasis.

Visible light and iodate/iodide mediated degradation of bisphenol A by self-assembly 3D hierarchical BiOIO3/Bi5O7I Z-scheme heterojunction: Intermediates identification, radical mechanism and DFT calculation

Broadening the light absorption and inhibiting carrier's recombination are vital to the improvement of photocatalytic performance. Herein, self-assembly 3D hierarchical microsphere BiOIO₃/Bi₅O₇I Z-scheme heterojunction with carrier transfer channel was firstly fabricated by in-situ solvothermal method. The degradation efficiency for bisphenol A (BPA) reached 98.9 % within 60 min visible light irradiation. The enhanced photocatalytic activity was benefited from the Z-scheme system assisted by iodate/iodide (IO₃^-/I^-) as carrier transfer channel that not only accelerated the interfacial charge separation, but also provided massive reactive centers for obtaining high redox capacity. The vulnerable sites and the degradation pathways of BPA were identified by density functional theory calculations and liquid chromatography-mass spectrometry analyses. The toxicity of BPA and its intermediates were predicted by ECOlogical Structure Activity Relationship (ECOSAR) and the results demonstrated that BPA was eventually mineralized to harmless products. The Z-scheme charge transfer mechanism was deeply elucidated based on the role of active species (·O₂^-, ·OH and h⁺), band structure and carrier separation efficiency. This study provides a promising strategy for the photoactivity enhancement of bismuth based heterojunction in environment purification.

Imprinted Oxide and MIP/Oxide Hybrid Nanomaterials for Chemical Sensors †

The oxides of transition, post-transition and rare-earth metals have a long history of robust and fast responsive recognition elements for electronic, optical, and gravimetric devices. A wide range of applications successfully utilized pristine or doped metal oxides and polymer-oxide hybrids as nanostructured recognition elements for the detection of biologically relevant molecules, harmful organic substances, and drugs as well as for the investigative process control applications. An overview of the selected recognition applications of molecularly imprinted sol-gel phases, metal oxides and hybrid nanomaterials composed of molecularly imprinted polymers (MIP) and metal oxides is presented herein. The formation and fabrication processes for imprinted sol-gel layers, metal oxides, MIP-coated oxide nanoparticles and other MIP/oxide nanohybrids are discussed along with their applications in monitoring bioorganic analytes and processes. The sensor characteristics such as dynamic detection range and limit of detection are compared as the performance criterion and the miniaturization and commercialization possibilities are critically discussed.

Rational Selection of the 3D Structure of Biomacromolecules for Molecular Docking Studies on the Mechanism of Endocrine Disruptor Action

Molecular modeling has become an essential tool in predicting and simulating endocrine disrupting effects of chemicals. A key prerequisite for successful application of molecular modeling lies in the correctness of 3D structure for biomacromolecules to be simulated. To date, there are several databases that can provide the experimentally-determined 3D structures. However, commonly, there are many challenges or disadvantageous factors, e.g., (a) lots of 3D structures for a given biomacromolecular target in the protein database; (b) the quality variability for those structures; (c) belonging to different species; (d) mutant amino acid residue in key positions, and so on. Once an inappropriate 3D structure of a target biomacromolecule was selected in molecular modeling, the accuracy and scientific nature of the modeling results could be inevitably affected. In this article, based on literature survey and an analysis of the 3D structure characterization of biomacromolecular targets belonging to the endocrine system in protein databases, six principles were proposed to guide the selection of the appropriate 3D structure of biomacromolecules. The principles include considering the species diversity, the mechanism of action, whether there are mutant amino acid residues, whether the number of protein chains is correct, the degree of structural similarity between the ligand in 3D structure and the target compounds, and other factors, e.g., the experimental pH conditions of the structure determined process and resolution.

Principles of Pharmacology and Toxicology Also Govern Effects of Chemicals on the Endocrine System

The present debate on chemicals with Hormonal activity, often termed 'endocrine disruptors', is highly controversial and includes challenges of the present paradigms used in toxicology and in hazard identification and risk characterization. In our opinion, chemicals with hormonal activity can be subjected to the well-evaluated health risk characterization approach used for many years including adverse outcome pathways. Many of the points arguing for a specific approach for risk characterization of chemicals with hormonal activity are based on highly speculative conclusions. These conclusions are not well supported when evaluating the available information.

Endocrine disruption: fact or urban legend?

Endocrine disruptors (EDs) are substances that cause adverse health effects via endocrine-mediated mechanisms in an intact organism or its progeny or (sub) populations. Purported EDCs in personal care products include 4-MBC (UV filter) or parabens that showed oestrogenic activity in screening tests, although regulatory toxicity studies showed no adverse effects on reproductive endpoints. Hormonal potency is the key issue of the safety of EDCs. Oestrogen-based drugs, e.g. the contraceptive pill or the synthetic oestrogen DES, possess potencies up to 7 orders of magnitude higher than those of PCP ingredients; yet, in utero exposure to these drugs did not adversely affect fertility or sexual organ development of offspring unless exposed to extreme doses. Additive effects of EDs are unlikely due to the multitude of mechanisms how substances may produce a hormone-like activity; even after uptake of different substances with a similar mode of action, the possibility of additive effects is reduced by different absorption, metabolism and kinetics. This is supported by a number of studies on mixtures of chemical EDCs. Overall, despite of 20 years of research a human health risk from exposure to low concentrations of exogenous chemical substances with weak hormone-like activities remains an unproven and unlikely hypothesis.

Surface molecular imprinting onto fluorescein-coated magnetic nanoparticles via reversible addition fragmentation chain transfer polymerization: a facile three-in-one system for recognition and separation of endocrine disrupting chemicals

In this study, we present a general protocol for the making of surface-imprinted magnetic fluorescence beads via reversible addition-fragmentation chain transfer polymerization. The resulting composites were characterized by X-ray diffraction analysis, transmission electron microscopy, scanning electron microscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy, and energy dispersive spectroscopy. The as-synthesized beads exhibited homogeneous polymer films (thickness of about 5.7 nm), spherical shape, high fluorescence intensity and magnetic property (Magnetization (Ms)=3.67 emu g(-1)). The hybrids bind the original template 17β-estradiol with an appreciable selectivity over structurally related compounds. In addition, the resulting hybrids performed without obvious deterioration after five repeated cycles. This study therefore demonstrates the potential of molecularly imprinted polymers for the recognition and separation of endocrine disrupting chemicals.

Safety of botanical ingredients in personal care products/cosmetics

The key issue of the safety assessment of botanical ingredients in personal care products (PCP) is the phytochemical characterisation of the plant source, data on contamination, adulteration and hazardous residues. The comparative approach used in the safety assessment of GM-plants may be applied to novel botanical PCP ingredients. Comparator(s) are the parent plant or varieties of the same species. Chemical grouping includes definition of chemical groups suitable for a read-across approach; it allows the estimation of toxicological endpoints on the basis of data from related substances (congeneric groups) with physical/chemical properties producing similar toxicities. The Threshold of Toxicological Concern (TTC) and Dermal Sensitisation Threshold (DST) are tools for the assessment of trace substances or minor ingredients. The evaluation of skin penetration of substances present in human food is unnecessary, whereas mixtures may be assessed on the basis of physical/chemical properties of individual substances. Adverse dermal effects of botanicals include irritation, sensitisation, phototoxicity and immediate-type allergy. The experience from dietary supplements or herbal medicines showed that being natural is not equivalent to being safe. Pragmatic approaches for quality and safety standards of botanical ingredients are needed; consumer safety should be the first objective of conventional and botanical PCP ingredients.

Development and validation of a fluorescence HPLC-based screening assay for inhibition of human estrogen sulfotransferase

Human estrogen sulfotransferase (SULT1E1) is involved in the regulation of 17beta-estradiol responsiveness and is believed to protect peripheral tissues from excessive estrogenic effects. Several assays already have been developed to investigate the inhibitory effect of endocrine-disrupting compounds (EDCs) on SULT1E1. However, most of these assays make use of the radiolabeled cofactor [(35)S]3'-phosphoadenosine 5'-phosphosulfate (PAPS) or radiolabeled substrate [(3)H]estradiol. In this article, we describe the development and validation of an assay for the inhibition of human SULT1E1 that is rapid and simple and that uses the nonradioactive and noncarcinogenic 1-hydroxypyrene. A gradient HPLC separation of 15 min using a C18-RP column was developed to detect 1-hydroxypyrene and its metabolite pyrene 1-sulfate fluorescently. Time- and protein-dependent formation of pyrene 1-sulfate was investigated, and enzyme kinetics was determined (K(m)=6.4+/-0.8 nM and V(max)=158+/-19 pmol/min/microg SULT1E1). At higher 1-hydroxypyrene concentrations, the assay displayed non-Michaelis-Menten kinetics involving substrate inhibition. IC(50) values have been determined for eight known SULT1E1 inhibitors or competing substrates (17beta-estradiol, 17alpha-estradiol, genistein, 17alpha-ethynylestradiol, estrone, diethylstilbestrol, estriol, and hexestrol) and two previously unknown SULT1E1 inhibitors (zearalenone and dienestrol). The method was demonstrated to be easy, feasible, and highly reproducible for SULT1E1 screening assay inhibition studies.