Winner of SFT’s Award
for Best Thesis in Toxicology 2024:
Radwa Almamoun
Radwa Almamoun
Stockholms Universitet, Stockholm
Titel:
Toxicological studies of di-n-butyl phthalate (DBP):
Impact on the reproductive system and gut microbiota
SFT's motivation
Radwa Almamoun is awarded the prize for a thesis that combines experimental toxicology with innovative testing methodology and cutting-edge microbiome research. By investigating the effects of the widely used plasticizer di-n-butyl phthalate (DBP) in adult models, her work demonstrates long-lasting reproductive toxicity, an area previously studied mainly in developmental contexts.
The thesis stands out in terms of applicability, especially through the development of a novel 3D in vitro co-culture model of testicular cells. This model enables high-throughput screening of reprotoxic effects and holds great potential for future use in toxicological testing and regulatory frameworks.
Furthermore, Almamoun presents the first comprehensive compositional and functional profiling of the gut microbiota following DBP exposure and links these changes to immune and testicular toxicity. Her work highlights the growing importance of microbiota–chemical interactions in toxicology.
In a highly competitive evaluation, the decisive factor was the thesis’ broad scientific relevance, methodological innovation, and potential long-term impact, making Radwa Almamoun a worthy recipient of the 2024 award.
Abstract
The potential health impact of exposure to anthropogenic chemicals has raised major concerns worldwide. Phthalates are mainly used in the plastic industry and have been associated with adverse effects in humans. Di-n-butyl phthalate (DBP) is one of the dominant phthalates with a ubiquitous presence in the environment. While many studies have examined the endocrine disrupting properties of DBP, with a focus on developmental and reproductive dysfunctions, studies of its effects on the adult reproductive system and gut microbiota are limited. This thesis aimed to determine persistent effects of DBP on the adult male reproductive system, provide a high-throughput screening tool for identifying reproductive toxicants, and characterize the effects of DBP on the gut microbiota.
Paper I investigated if adult DBP exposure can induce persistent effects on the mature reproductive system. Adult male mice were orally exposed to 10 or 100 mg/kg/day for five weeks and testes were collected one week after the last dose. The results demonstrated a significant decrease in testosterone levels in the DBP-exposed groups. Mechanistically, the levels of steroidogenic enzymes, cell-specific markers and oxidative stress were increased. In paper II, elements of the in vivo testicular microenvironment, including functional testosterone production, were modeled using a three-dimensional (3D) heterogenous testicular cell co-culture derived from neonatal mice. Automated high-content imaging of cell-specific markers confirmed the presence of germ cells (DAZL+), Leydig cells (CYP11A1+), and Sertoli cells (SOX9+). DBP exposure decreased testosterone production, as well as levels of the steroidogenic enzyme CYP11A1, and the steroidogenic regulator StAR. Overall, this in vitro3D model recapitulates the testicular pathways involved in DBP toxicity, making it a relevant tool for assessing reprotoxic effects of chemicals.
Paper III investigated the impact of oral DBP exposure on the gut microbiota and the potential interplay with immune and testicular toxicity using 16S rRNA sequencing. DBP-treated mice showed a distinct microbial composition and numerous differentially abundant amplicon sequence variants. Interestingly, the microbial alterations correlated with an increase in non-classical monocytes observed in DBP-exposed mice. In paper IV, a shotgun metagenomic analysis was conducted to achieve a more comprehensive characterization of the DBP-induced effects on gut microbiota composition and function. The DBP-exposed mice had a higher abundance of Adlercreutzia mucosicola, a bacterium linked with intestinal inflammation. In contrast, the beneficial Akkermansia muciniphila was less abundant in DBP-exposed mice. Functional analysis demonstrated that DBP exposure increased the abundance of genes involved in environmental sensing and antimicrobial resistance.
In conclusion, this doctoral thesis demonstrates the antiandrogenic effects of DBP as well as potential underlying mechanisms of testicular dysfunction in adult mice. In addition, we established a powerful in vitro tool for screening reprotoxic effects. The gut microbiota was also impaired by DBP exposure, which may play a potential role in initiating or exacerbating the DBP-induced toxicity. Overall, this work highlights the potential health impact of the interplay between the two exposome components, chemical exposure and gut microbiota.
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