AOP key event relationship report: Linking decreased androgen receptor activation with decreased granulosa cell proliferation of gonadotropin-independent follicles

Epidemiologically relevant phthalates affect human endometrial cells in vitro through cell specific gene expression changes related to the cytoskeleton and mitochondria

Phthalates are endocrine disrupting chemicals (EDCs) found in common consumer products such as soft plastics and cosmetics. Although the knowledge regarding the adverse effects of phthalates on female fertility are accumulating, information on the hormone sensitive endometrium is still scarce. Here, we studied the effects of phthalates on endometrial cell proliferation and gene expression. Human endometrial primary epithelial and stromal cells were isolated from healthy fertile-aged women (n=3), and were compared to endometrial cell lines T-HESC and Ishikawa. Three different epidemiologically relevant phthalate mixtures were used, defined by urine samples in the Midlife Women Health Study (MWHS) cohort. Mono (2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) was used as a single phthalate control. Cells were harvested for proliferation testing and transcriptomic analyses after 24 h exposure. Even though all cell models responded differently to the phthalate exposures, many overlapping differentially expressed genes (DEGs, FDR<0.1), related to cell adhesion, cytoskeleton and mitochondria were found in all cell types. The qPCR analysis confirmed that MEHHP significantly affected cell adhesion gene vinculin (VCL) and NADH:ubiquinone oxidoreductase subunit B7 (NDUFB7), important for oxidative phosphorylation. Benchmark dose modelling showed that MEHHP had significant concentration-dependent effects on cytoskeleton gene actin-beta (ACTB). In conclusion, short 24 h phthalate exposures significantly altered gene expression cell-specifically in human endometrial cells, with six shared DEGs. The mixture effects were similar to those of MEHHP, suggesting MEHHP could be the main driver in the mixture. Impact of phthalate exposures on endometrial functions including receptivity should be addressed.

Methodology for developing data-rich Key Event Relationships for Adverse Outcome Pathways exemplified by linking decreased androgen receptor activity with decreased anogenital distance

The Adverse Outcome Pathway (AOP) framework has gained widespread acceptance in toxicological disciplines as a tool for aiding chemical hazard assessment. Despite increased activity in AOP development, progress towards a high volume of fully endorsed AOPs has been slow, partly due to the challenging task of constructing complete AOPs according to the AOP Developer's Handbook. To facilitate greater uptake of new knowledge units onto the open-source AOP-wiki platform, a pragmatic approach was recently proposed. This approach involves considering Key Event Relationships (KERs) for individual development through systematic approaches, as they represent essential units of knowledge from which causality can be inferred; from low complexity test data to adverse outcomes in intact organisms. However, more broadly adopted harmonized methodologies for KER development would be desirable. Using the AOP Developer's Handbook as a guide, a KER linking 'decreased androgen receptor (AR) activity' with 'reduced anogenital distance (AGD)' was developed to demonstrate a methodology applicable for future developments of KERs requiring systematic literature retrieval approaches.

Exposure to the phthalate metabolite MEHP impacts survival and growth of human ovarian follicles in vitro

Phthalates are found in everyday items like plastics and personal care products. There is an increasing concern that continuous exposure can adversely affect female fertility. However, experimental data are lacking to establish causal links between exposure and disease in humans. To address this gap, we tested the effects of a common phthalate metabolite, mono-(2-ethylhexyl) phthalate (MEHP), on adult human ovaries in vitro using an epidemiologically determined human-relevant concentration range (2.05 nM - 20.51 mM). Histomorphological assessments, steroid and cytokine measurements were performed on human ovarian tissue exposed to MEHP for 7 days in vitro. Cell viability and gene expression profile were investigated following 7 days of MEHP exposure using the human granulosa cancer cell lines KGN, and COV434, the germline tumor cell line PA-1, and human ovarian primary cells. Selected differentially expressed genes (DEGs) were validated by RT-qPCR and immunofluorescence in human ovarian tissue. MEHP exposure reduced follicular growth (20.51 nM) and increased follicular degeneration (20.51 mM) in ovarian tissue, while not affecting steroid and cytokine production. Out of the 691 unique DEGs identified across all the cell types and concentrations, CSRP2 involved in cytoskeleton organization and YWHAE as well as CTNNB1 involved in the Hippo pathway, were chosen for further validation. CSRP2 was upregulated and CTNNB1 downregulated in both ovarian tissue and cells, whereas YWHAE was downregulated in cells only. In summary, one-week MEHP exposure of human ovarian tissue can perturb the development and survival of human follicles through mechanisms likely involving dysregulation of cytoskeleton organization and Hippo pathway.

Exposure to the pesticides linuron, dimethomorph and imazalil alters steroid hormone profiles and gene expression in developing rat ovaries

Inhibition of androgen signaling during critical stages of ovary development can disrupt folliculogenesis with potential consequences for reproductive function later in life. Many environmental chemicals can inhibit the androgen signaling pathway, which raises the question if developmental exposure to anti-androgenic chemicals can negatively impact female fertility. Here, we report on altered reproductive hormone profiles in prepubertal female rats following developmental exposure to three pesticides with anti-androgenic potential: linuron (25 and 50 mg/kg bw/d), dimethomorph (60 and 180 mg/kg bw/d) and imazalil (8 and 24 mg/kg bw/d). Dams were orally exposed from gestational day 7 (dimethomorph and imazalil) or 13 (linuron) until birth, then until end of dosing at early postnatal life. Linuron and dimethomorph induced dose-related reductions to plasma corticosterone levels, whereas imazalil mainly suppressed gonadotropin levels. In the ovaries, expression levels of target genes were affected by linuron and dimethomorph, suggesting impaired follicle growth. Based on our results, we propose that anti-androgenic chemicals can negatively impact female reproductive development. This highlights a need to integrate data from all levels of the hypothalamic-pituitary-gonadal axis, as well as the hypothalamic-pituitary-adrenal axis, when investigating the potential impact of endocrine disruptors on female reproductive development and function.

AOP key event relationship report: Linking androgen receptor antagonism with nipple retention

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A full AOP KER description linking AR antagonism with nipple retention in rodents.

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Described KER 2133 is a non-adjacent KER of an intended AOP delineating anti-androgenicity as a mode for nipple retention.

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A case study for developing and publishing independent units of information under the AOP framework.

In rat developmental and reproductive toxicity studies, nipple/areola retention (NR) in male offspring is a biomarker for reduced androgen signaling during development. This is because nipples normally regress in male rats in response to androgen signaling during critical stages of development. NR is thus included as a mandatory endpoint in several OECD test guidelines for assessment of chemicals, particularly as a readout for anti-androgenic effects relevant for reproductive toxicity. With the growing interest in developing Adverse Outcome Pathways (AOPs) to aid in chemical risk assessment, a more pragmatic approach has been proposed, whereby essential units of knowledge could be developed independently of complete AOPs, not least emergent key event relationships (KERs). Herein, we have developed a KER linking “androgen receptor antagonism” and “increased areola/nipple retention”. The KER is based on a literature review conducted in a transparent semi-systematic manner in peer-reviewed databases with pre-defined inclusion criteria. Twenty-seven papers were included for development of the KER. The results support a qualitative relationship between the two key events (KEs) with a high weight of evidence; i.e., a causal relationship between androgen receptor (AR) antagonism and nipple retention in male rats exists.