Genomic and Hormonal Biomarkers of Phthalate-Induced Male Rat Reproductive Developmental Toxicity Part II: A Targeted RT-qPCR Array Approach that Defines a Unique Adverse Outcome Pathway.

Previously, we demonstrated that exposure to some diortho-phthalate esters during sexual differentiation disrupts male reproductive development by reducing fetal rat testis testosterone production (T Prod) and gene expression in a dose-related manner. The objectives of the current project were to expand the number of test compounds that might reduce fetal T Prod, including phthalates, phthalate alternatives, pesticides, and drugs, and to compare reductions in T Prod with altered testis mRNA expression. We found that PEs that disrupt T Prod also reduced expression of a unique “cluster” of mRNAs for about 35 genes related to sterol transport, testosterone and insulin-like hormone 3 hormone syntheses, and lipoprotein signaling and cholesterol synthesis. However, phthalates had little or no effect on mRNA expression of genes in peroxisome proliferator-activated receptor (PPAR) pathways in the fetal liver, whereas the 3 PPAR agonists induced the expression of mRNA for multiple fetal liver PPAR pathway genes without reducing testis T Prod. In summary, phthalates that disrupt T Prod act via a novel adverse outcome pathway including down regulation of mRNA for genes involved in fetal endocrine function and cholesterol synthesis and metabolism. This profile was not displayed by PEs that did not reduce T Prod, PPAR agonists or the other chemicals. Reductions in fetal testis gene expression and T Prod in utero can be used to establish relative potency factors that can be used quantitatively to predict the doses of individual PEs and mixtures of phthalates that produce adverse reproductive tract effects in male offspring.

Impact/Purpose

We demonstrate that phthalates esters (PEs) that disrupt T Prod act via a novel AOP including down regulation of mRNA for genes involved in fetal endocrine function and cholesterol synthesis and metabolism resulting in a unique postnatal phenotype, identified as the Phthalate Syndrome. One of the most unique effects of these PEs in utero is the reduction in Insl3 which is causally related to agenesis and elongation of the gubernaculum in male offspring, which in turn can result in testis nondescent or abnormal descent of the testes. Lastly, the fact that PEs cause the Phthalate Syndrome via a common AOP provides biological plausibility for their inclusion in a common mechanism group for cumulative assessments. Furthermore, peer-reviewed publications over the last 15 years have repeatedly demonstrated that they effects of PEs mixtures can be accurately predicted using dose- but not response addition statistical models (Gray L. E. et al. 2001; Howdeshell et al. 2005; Gray LE et al. 2006; Howdeshell et al. 2008; Rider Cynthia V. et al. 2009; Rider C. V. et al. 2009; Howdeshell et al. 2015; Howdeshell et al. 2016; Conley et al. 2018). Additional research also shows that the reductions in fetal testis gene expression and T Prod in utero reported herein can be used to establish relative potency factors that can be used quantitatively to predict the doses of individual PEs and mixtures of PEs that produce adverse reproductive tract effects in male offspring (Gray LE, Jr. et al. 2016).

Citation

Gray, E., C. Lambright, J. Conley, N. Evans, J. Furr, B. Hannas, V. Wilson, H. Sampson, AND P. Foster. Genomic and Hormonal Biomarkers of Phthalate-Induced Male Rat Reproductive Developmental Toxicity Part II: A Targeted RT-qPCR Array Approach that Defines a Unique Adverse Outcome Pathway. Society of Toxicology, RESTON, VA, 182(2):195-214, (2021). [DOI: 10.1093/toxsci/kfab053]

DOI: Genomic and Hormonal Biomarkers of Phthalate-Induced Male Rat Reproductive Developmental Toxicity Part II: A Targeted RT-qPCR Array Approach that Defines a Unique Adverse Outcome Pathway.