Chemical regulation of steroidogenic capacity in the male rat gonad

Abstract

The hypothalamic-pituitary-gonadal (HPG) axis is critical in the maturation and maintenance of reproductive organs, particularly the initiation of Sertoli and Leydig cell differentiation in males. Due to the presence of estrogen receptors (ER) throughout the HPG-axis, it is susceptible to disruption by a wide variety of endocrine disrupting chemicals (EDC), particularly those classified as estrogen mimicking compounds (EMC). This poses a great concern in male reproductive health. This dissertation describes the adverse effects of developmental exposure on testicular function in the rat model to environmental EDCs, such as the EMCs known commonly as forever chemicals, or per- and polyfluoroalkyl substances (PFAS), plasticizers Bisphenol A (BPA) and Bisphenol S (BPS), and the synthetic form of estrogen, 17α-ethynylestradiol (EE2), used in the manufacture of female oral contraceptives. Specifically, the second chapter of this dissertation compares the effects of legacy PFAS, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), to their emerging PFAS counterparts, perfluorobutanoic acid (PFBA) and perfluorobutanesulfonic acid (PFBS), while the third compares three common estrogen mimicking compounds, BPA, BPS, and EE2, all of which are of high prevalence in the environment. Leydig cells are the primary producers of the male sex steroid testosterone. Disruption of this process is shown to alter sexual differentiation and development of secondary sexual characteristics, as well as delaying puberty, or impacting male fertility. Sertoli cells act to support spermatogenesis by facilitating the interactions between germ cells and their regulatory hormones. The overall aim of this dissertation is to analyze the effect of EDCs in the rat testis. This aim is achieved using the following specific objectives: 1. Investigate comparative effects of prepubertal and pubertal legacy and emerging PFAS exposures on gonadal steroid hormone secretion 2. Investigate the effect of plasticizers BPA and BPA, and the synthetic estrogen, EE2, on steroid hormone secretion in the prepubertal male rat gonad To achieve the first objective, 21 day-old male rats were provided drinking water containing 0, 1, 10, 100 and 1000 ng/L PFOA and PFBA for 14 days to investigate prepubertal effects. We repeated the experiment using the same exposure paradigm to assess effects due to a sulfonic acid-containing legacy and emerging PFAS (PFOS, PFBS). Then, 21 day-old male rats were provided drinking water containing 0, 10, and 100 ng/L of a carboxylic acid-containing legacy and emerging PFAS, i.e., PFOA and PFBA and a sulfonic acid-containing legacy and emerging PFAS, i.e., PFOS and PFBS for 28 days to determine pubertal effects. Additionally, two separate experiments were conducted in which prepubertal male rats at 21 days of age were provided drinking water containing 10 ng/L of each test chemical and their combination at 5 ng/L of individual chemicals: control, PFOA, PFOS, PFOA+PFOS in the first experiment and control, PFBA, PFBS, PFBA+PFBS in the second. To achieve the second objective, three separate experiments were performed in which 21 day old prepubertal male rats were maintained on deionized water with graded doses, 0, 1, 5, 10, 15, or 20 µg/L, of BPA, BPS, or EE2 for 56 days. The findings from these objectives on the effects of PFAS and the estrogen mimicking compounds (BPA, BPS, and EE2) on testicular cells support the view that exposure of the population to environmental EDCs have the potential to impair reproductive health. Additional studies are warranted to elucidate the mechanisms by which these compounds, both individually and in mixtures, impact testicular cells and overall HPG-axis function and regulation.