How safe are environmental chemicals

We are directly exposed to a variety of diverse synthetic chemicals on a daily basis, for example when using cleaning products, cosmetics, drugs, plastics, and food additives. Many of these chemicals, e.g. environmental phenols, phthalates, and herbicides, can be detected in human blood or urine samples. Accordingly, due to the constant exposure to chemicals, it is essential to evaluate potential hazards and health risks. Within the EUs REACH program and the US National Toxicity Program, chemicals are studied for their potential endocrine disrupting effects. At the same time, alternatives to in vivo testing in the form of in silico / in vitro testing are evaluated. In silico predictions are highly useful to prioritize chemicals for in vitro / in vivo testing. Pharmacophore models are excellent in silico screening tools to select potentially active compounds from large chemical databases. However, so far they have hardly been used to suggest chemicals for toxicity evaluations. In the proposed project, a pharmacophore-based in silico screening platform will be developed to prioritize chemicals for mechanism-based toxicity evaluations. This platform will focus on 14 steroid- synthesizing and -metabolizing enzymes, which have not been considered in systematic toxicity studies so far. For each target, models will be experimentally validated to optimize their predictive power. Environmental chemical databases will be screened for potentially active compounds. Among the virtual hits, chemicals with direct consumer exposure or high annual production volume will be acquired and tested in vitro. Identified active chemical classes will be further investigated by testing structurally related compounds in the in vitro assays. Based on all experimental results, the pharmacophore models will be optimized to correctly separate active from inactive chemicals on the respective targets. For the studied chemical classes, structure-activity-relationship models will be built to further optimize the predictions within the respective compound class. The developed model collection and exemplified case studies will lay ground for future, systematic safety evaluations of chemicals. In the future, such in silico platforms combined with in vitro testing are expected to form one basis for toxicity predictions.

Safety of environmental chemicals The project "safety of environmental chemicals" aimed to identify chemicals, which may interfere with hormone homeostasis in the human body. For this, we aimed to establish computational models as pre-filters to focus time- and cost-intensive wet lab work on the most suspicious chemicals. We focused our investigations on industrial chemicals with high production volume in the EU, food contact materials, food additives such as conserving agents, substances used in cosmetic products, drugs and natural compounds, which are also used as food supplements. It is well known that chemicals can act like hormones themselves. However, the impact of chemicals on the biosynthesis and degradation of hormones has not been investigated that well. Synthesis and degradation, together called metabolism, are mediated by specific enzymes, which regulate the balance between active and inactive hormones in cells. The focus of this project lied on the potential inhibition of these enzymes by environmental chemicals. We developed a multi-step protocol for the selection of chemicals to test. First, we developed computational models for enzyme inhibition for essential enzyme involved in sex hormone biosynthesis. These models were extensively theoretically validated by classification experiments of known active and inactive compounds. Only models that passed these tests were further used in the project. Second, we selected chemicals with unknown effects on the enzymes for biological testing and evaluated, if the models could correctly predict the actual activity in vitro. Successful models were then employed predict potentially active compounds from environmental chemical databases. However, the main aim of this project was the development of high quality computational models, not (yet) their broad application to environmental chemicals - this will be scope of future projects. In the course of our proof of principle experiments, we could already identify several enzyme inhibitors among widely used chemicals. For example, parabens were discovered as a class of compounds inhibiting estrogen degradation. High intracellular estrogen levels may lead to adverse effects especially during sensitive phases in life just like pregnancy and puberty. They may promote feminization. However, parabens are degraded rapidly in the human body and the relevance of our finding must be evaluated by further experiments. The same is true for another chemical inhibiting estrogen degradation, ethyl vanillate, which is a flavoring agent sometimes used in chewing gum. Further examples include itraconazole and posaconazole, which can interfere with glucocorticoid balance. Especially during pregnancy, an excess of glucocorticoids can lead to disturbed development of the fetus. Finally, we identified epoxiconazole, an antifungal chemical used in agriculture, as inhibitor of cholesterol and aldosterone synthesis. This inhibition could influence the immune system and blood pressure regulation and needs follow-up studies to evaluate effects in vivo.