Sexually dimorphic impact of preconceptional and gestational exposure to a real-life environmental chemical mixture (biosolids) on offspring growth dynamics and puberty in sheep

IMPACT OF REAL-LIFE ENVIRONMENTAL EXPOSURES ON REPRODUCTION: Biosolids and male reproduction

Over the past 50 years, there has been a concerning decline in male reproductive health and an increase in male infertility which is now recognised as a major health concern globally. While male infertility can be linked to some genetic and lifestyle factors, these do not fully explain the rate of declining male reproductive health. Increasing evidence from human and animal studies suggests that exposure to chemicals found ubiquitously in the environment may in part play a role. Many studies on chemical exposure, however, have assessed the effects of exposure to individual environmental chemicals (ECs), usually at levels not relevant to everyday human exposure. There is a need for study models which reflect the 'real-life' nature of EC exposure. One such model is the biosolids-treated pasture (BTP) sheep model which utilises biosolids application to agricultural land to examine the effects of exposure to low-level mixtures of chemicals. Biosolids are the by-product of the treatment of wastewater from industrial and domestic sources and so their composition is reflective of the ECs to which humans are exposed. Over the last 20 years, the BTP sheep model has published multiple effects on offspring physiology including consistent effects on the male reproductive system in fetal, neonatal, juvenile, and adult offspring. This review focuses on the evidence from these studies which strongly suggests that low-level EC exposure during gestation can alter several components of the male reproductive system and highlights the BTP model as a more relevant model to study real-life EC exposure effects.

Preconceptional and in utero exposure of sheep to a real-life environmental chemical mixture disrupts key markers of energy metabolism in male offspring

Over recent decades, an extensive array of anthropogenic chemicals have entered the environment and have been implicated in the increased incidence of an array of diseases, including metabolic syndrome. The ubiquitous presence of these environmental chemicals (ECs) necessitates the use of real-life exposure models to the assess cumulative risk burden to metabolic health. Sheep that graze on biosolids-treated pastures are exposed to a real-life mixture of ECs such as phthalates, per- and polyfluoroalkyl substances, heavy metals, pharmaceuticals, pesticides, and metabolites thereof, and this EC exposure can result in metabolic disorders in their offspring. Using this model, we evaluated the effects of gestational exposure to a complex EC mixture on plasma triglyceride (TG) concentrations and metabolic and epigenetic regulatory genes in tissues key to energy regulation and storage, including the hypothalamus, liver, and adipose depots of 11-month-old male offspring. Our results demonstrated a binary effect of EC exposure on gene expression particularly in the hypothalamus. Principal component analysis revealed two subsets (B-S1 [n = 6] and B-S2 [n = 4]) within the biosolids group (B, n = 10), relative to the controls (C, n = 11). Changes in body weight, TG levels, and in gene expression in the hypothalamus, and visceral and subcutaneous fat were apparent between biosolid and control and the two subgroups of biosolids animals. These findings demonstrate that gestational exposure to an EC mixture results in differential regulation of metabolic processes in adult male offspring. Binary effects on hypothalamic gene expression and altered expression of lipid metabolism genes in visceral and subcutaneous fat, coupled with phenotypic outcomes, point to differences in individual susceptibility to EC exposure that could predispose vulnerable individuals to later metabolic dysfunction.