Evaluation of Endocrine Disrupting Effects of Nitrate after In Utero Exposure in Rats and of Nitrate and Nitrite in the H295R and T-Screen Assay

Abstract

Animal studies have shown that nitrate acts as an endocrine disrupter affecting the androgen production in adult males. This raises a concern for more severe endocrine disrupting effects after exposure during the sensitive period of prenatal male sexual development. As there are no existing studies of effects of nitrate on male sexual development, the aim of the study was to examine how in utero exposure to nitrate would affect male rat fetuses. Pregnant dams were dosed with nitrate in the drinking water from gestational day (GD) 7 to GD21 at the following dose levels 17.5, 50, 150, 450, and 900 mg/l. At GD21, fetuses were examined for anogenital distance, plasma thyroxine levels, testicular and plasma levels of testosterone and progesterone, and testicular testosterone production and histopathology. In addition, endocrine disrupting activity of nitrate and nitrite were studied in two in vitro assays, the H295R assay and T-screen. There were no consistent indications that nitrate induces anti-androgenic effects in male fetuses or that prenatal nitrate exposure affected the thyroid axis. However, a more comprehensive study with long-term exposure before and during pre- and postnatal development would be relevant to sufficiently address the concerns based on the indications for endocrine disrupting effects in adult animals.

Thyroid endocrine system disruption by pentachlorophenol: An in vitro and in vivo assay

“…Both deiodinases have an important role for maintaining local T3 levels in the brain and pituitary in vivo. The T-Screen assay successfully predicted the effects of certain thyroid hormone disrupting chemicals, such as plasticizers, alkylphenols, pesticides, polychlorinated biphenyls, brominated flame-retardants and personal care products (Ghisari and BonefeldJorgensen, 2005;Hamers et al, 2006;Schriks et al, 2006;Hansen et al, 2009;Taxvig et al, 2011;Hinther et al, 2011).…”

In vitro bioassays for the study of endocrine-disrupting food additives and contaminants

“…The A-screen is an androgen-responsive CPA based on the MCF-7 cell line transfected with the human-androgen receptor [62]. The T-screen is another CPA used to detect binding and activation of the thyroid receptor (TR), thereby determining the ability of a compound to be a thyroid hormone receptor agonist or antagonist [20,[63][64][65]. These assays are limited in that only effects related to binding can be detected but not effects linked to the disturbance of hormone-synthesis pathways or hormone transport.…”

“…A mixture of all tested phytoestrogens (PEs) increased 17b-E2 production and decreased testosterone production, indicating increased aromatase activity [25]. In addition, it has been used to study androgenic effects of a mixture of three azole fungicides [11], and endocrine-disrupting effects of nitrate and nitrite [20] and parabens [63].…”

“…Recent advances in cell biology and biotechnology have allowed development of a new generation of bioassays focused on hormonal nuclear receptor signaling [14][15][16][17][18] and steroidogenesis pathways [11,[19][20][21][22][23][24][25]. Some of these new bioassays are based on the ability to introduce specific properties and reporter genes into stable cellular systems.…”

“…Given the wide scope of potential working mechanisms and sites of action of EDCs, the review focuses on those bioassays measuring interference of EDCs with nuclear receptor signaling (see sub-section 2.1) or Has been applied to known food contaminants, either as single compound [20,23,24], or as mixtures [11,25] The hormone production (see sub-section 2.2), These mechanisms are very complementary and the bioassays and their use very well documented. We give attention to assays validated or being validated by control organizations.…”