Direct and indirect endocrine disruption : aromatase and estrogen receptor-mediated processes in breast cancer development

Endocrine disrupting chemicals (EDCs) have been defined by the World Health Organization as: “exogenous substances or mixtures that alters function(s) of the endocrine system and causes adverse health effects in an intact organism, or its progeny, or (sub)populations”. Synthetic, as well as, naturally occurring chemicals can disrupt the endocrine system. EDCs can exert their effect through multiple mechanisms. For example, compounds can bind to a steroid hormone receptor and subsequently block or induce the response. Estrogenic effects of chemicals have been subject of extensive research during the past decades. Interactions with the estrogen receptor (ER) could possibly lead to adverse effects in the human body and therefore, in the US, companies are obliged to test their compounds for estrogenic effects before being allowed to bring the product onto the market. In Japan and Europe, legislation forcing companies to perform tests for estrogenicity is being introduced. However, recently studies on chemicals affecting estrogen biosynthesis have attracted increasing attention. By enhancing estrogen synthesis, chemicals exert an indirect estrogenic effect. Estrogens play an important role in breast cancer development. Malignant tumors of the mammary gland are the most common type of cancer in women. Approximately 60% of all breast tumors are estrogen-responsive and depend on estrogens for growth. Therefore, chemicals that show estrogenic properties might be able to interfere with breast tumor growth. Epithelial breast tumor cells express ERs on their cell membrane to which endogenous and/or exogenous estrogens can bind. Connective tissue surrounding the tumor cells are able to produce estrogens through the aromatase aromatase enzyme. Aromatase activity is in turn increased by factors that are secreted by the epithelial tumor cells. In this way, a positive feedback loop is established, resulting in rapid growth of the tumor. This thesis describes estrogenic effects of frequently used UV-filters. Our studies showed that daily exposure to UV-filters through sunscreen products could possibly lead to estrogenic effects in humans. Methyl sulfonyl PCB-metabolites inhibit aromatase activity in primary human mammary connective tissue. Furthermore, several pesticides either induce or inhibit aromatase activity in human or rat cell lines. The R2C rat Leydig cell carcinoma cell line is suitable for detection of aromatase inhibitors and the H295R human adrenocortical carcinoma cell line is suitable to test for the detection of both inducers and inhibitors of aromatase activity. Increased estrogenic effects after aromatase induction and increased aromatase gene transcription after exposure to estrogenic compounds, suggest the presence of paracrine interactions between two cell types in our co-culture of MCF-7 human malignant breast tumor cells and primary human mammary fibroblasts. Indirect estrogenic effects caused by induction of aromatase activity should be considered when testing for estrogenic effects of compounds

Direct and indirect endocrine disruption : aromatase and estrogen receptor-mediated processes in breast cancer development

Endocrine disrupting chemicals (EDCs) have been defined by the World Health Organization as: “exogenous substances or mixtures that alters function(s) of the endocrine system and causes adverse health effects in an intact organism, or its progeny, or (sub)populations”. Synthetic, as well as, naturally occurring chemicals can disrupt the endocrine system. EDCs can exert their effect through multiple mechanisms. For example, compounds can bind to a steroid hormone receptor and subsequently block or induce the response. Estrogenic effects of chemicals have been subject of extensive research during the past decades. Interactions with the estrogen receptor (ER) could possibly lead to adverse effects in the human body and therefore, in the US, companies are obliged to test their compounds for estrogenic effects before being allowed to bring the product onto the market. In Japan and Europe, legislation forcing companies to perform tests for estrogenicity is being introduced. However, recently studies on chemicals affecting estrogen biosynthesis have attracted increasing attention. By enhancing estrogen synthesis, chemicals exert an indirect estrogenic effect. Estrogens play an important role in breast cancer development. Malignant tumors of the mammary gland are the most common type of cancer in women. Approximately 60% of all breast tumors are estrogen-responsive and depend on estrogens for growth. Therefore, chemicals that show estrogenic properties might be able to interfere with breast tumor growth. Epithelial breast tumor cells express ERs on their cell membrane to which endogenous and/or exogenous estrogens can bind. Connective tissue surrounding the tumor cells are able to produce estrogens through the aromatase aromatase enzyme. Aromatase activity is in turn increased by factors that are secreted by the epithelial tumor cells. In this way, a positive feedback loop is established, resulting in rapid growth of the tumor. This thesis describes estrogenic effects of frequently used UV-filters. Our studies showed that daily exposure to UV-filters through sunscreen products could possibly lead to estrogenic effects in humans. Methyl sulfonyl PCB-metabolites inhibit aromatase activity in primary human mammary connective tissue. Furthermore, several pesticides either induce or inhibit aromatase activity in human or rat cell lines. The R2C rat Leydig cell carcinoma cell line is suitable for detection of aromatase inhibitors and the H295R human adrenocortical carcinoma cell line is suitable to test for the detection of both inducers and inhibitors of aromatase activity. Increased estrogenic effects after aromatase induction and increased aromatase gene transcription after exposure to estrogenic compounds, suggest the presence of paracrine interactions between two cell types in our co-culture of MCF-7 human malignant breast tumor cells and primary human mammary fibroblasts. Indirect estrogenic effects caused by induction of aromatase activity should be considered when testing for estrogenic effects of compounds

Toxicogenomics in vitro as an alternative tool for safety evaluation of petroleum substances and PAHs with regard to prenatal developmental toxicity

The REACH legislation requires chemicals - including petroleum substances - that are put on the EU market in quantities greater than 1000 tonnes/year, to be tested for prenatal developmental toxicity. This will require large numbers of animals since prenatal development toxicity testing is animal-intensive. The application of toxicogenomic technologies might reduce the number of animals to study prenatal developmental toxicity of petroleum substances by allowing their grouping into categories with the same toxicological properties. This substance categorization may be supported by similarities in molecular fingerprints.The developmental toxicity effects observed in some oil products are most likely related to polycyclic aromatic hydrocarbons (PAHs) with high-molecular weight. However, the current review indicates that even though the available studies provide clues regarding the HOX, FOX, SHH and PAX family genes, which regulate functions in skeleton development, single individual genes cannot be used as biomarkers of PAHs exposure and subsequent prenatal developmental toxicity. Furthermore, it should be considered that toxicogenomic technologies applied to specific tissues/organs testing might lead to unreliable results regarding developmental toxicity due to induction of tissue-specific pathways. Thus, an approach which applies a battery of in vitro tests including the zebrafish embryo test, embryonic stem cells, and the whole embryo culture is suggested as it would be more relevant for studying developmental effects in the terms of substances categorization

The Use of Biomarkers of Toxicity for Integrating In Vitro Hazard Estimates Into Risk Assessment for Humans

The role that in vitro systems can play in toxicological risk assessment is determined by the appropriateness of the chosen methods, with respect to the way in which in vitro data can be extrapolated to the in vivo situation. This report presents the results of a workshop aimed at better defining the use of in vitro-derived biomarkers of toxicity (BoT) and determining the place these data can have in human risk assessment. As a result, a conceptual framework is presented for the incorporation of in vitro-derived toxicity data into the risk assessment process. The selection of BoT takes into account that they need to distinguish adverse and adaptive changes in cells. The framework defines the place of in vitro systems in the context of data on exposure, structural and physico-chemical properties, and toxicodynamic and biokinetic modeling. It outlines the determination of a proper point-of-departure (PoD) for in vitro-in vivo extrapolation, allowing implementation in risk assessment procedures. A BoT will need to take into account both the dynamics and the kinetics of the compound in the in vitro systems. For the implementation of the proposed framework it will be necessary to collect and collate data from existing literature and new in vitro test systems, as well as to categorize biomarkers of toxicity and their relation to pathways-of-toxicity. Moreover, data selection and integration need to be driven by their usefulness in a quantitative in vitro-in vivo extrapolation (QIVIVE)