Effects of Tris(1,3-dichloro-2-propyl) phosphate and Tris(1-chloropropyl) phosphate on Cytotoxicity and mRNA Expression in Primary Cultures of Avian Hepatocytes and Neuronal Cells

Abstract

Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) and tris(1-chloropropyl) phosphate (TCPP) belong to a group of chemicals collectively known as triester organophosphate flame retardants (OPFRs). OPFRs are used in a wide range of consumer products and have been detected in biota, including free-living avian species; however, data on toxicological and molecular effects of exposure are limited. An in vitro screening approach was used to compare concentration-dependent effects of TDCPP and TCPP on cytotoxicity and messenger RNA (mRNA) expression in cultured hepatocytes and neuronal cells derived from embryonic chickens. TDCPP was toxic to hepatocytes (LC₅₀ = 60.3 ± 45.8μM) and neuronal cells (LC₅₀ = 28.7 ± 19.1μM), whereas TCPP did not affect viability in either cell type up to the highest concentration administered, 300μM. Real-time reverse transcription-PCR revealed alterations in mRNA abundance of genes associated with phase I and II metabolism, the thyroid hormone (TH) pathway, lipid regulation, and growth in hepatocytes. None of the transcripts measured in neuronal cells (D2, D3, RC3, and Oct-1) varied in response to TDCPP or TCPP exposure. Exposure to ≥ 10μM TDCPP and TCPP resulted in significant upregulation of CYP2H1 (4- to 8-fold), CYP3A37 (13- to 127-fold), and UGT1A9 (3.5- to 7-fold) mRNA levels. Transthyretin was significantly downregulated more than twofold by TCPP at 100μM; however, TDCPP did not alter its expression. Liver fatty acid-binding protein, TH-responsive spot 14-α, and insulin-like growth factor-1 were all downregulated (up to 10-fold) in hepatocytes exposed to ≥ 0.01μM TDCPP and TCPP. Taken together, our results indicate that genes associated with xenobiotic metabolism, the TH pathway, lipid regulation, and growth are vulnerable to TDCPP and TCPP administration in cultured avian hepatocytes. The mRNA expression data were similar to those from a previous study with hexabromocyclododecane.

In vitro assessment of thyroid hormone receptor activity of four organophosphate esters

“…Liu et al (2013a) evaluated the effects of TDCPP and TPP on six receptor-associated expression of mRNA in zebrafish embryos/ larvae, and the results showed that TH receptor-centered gene networks were altered by OPEs. Using real-time reverse transcription-PCR, it has been demonstrated that exposure to TDCPP and TCPP altered the mRNA abundance of genes associated with the TR pathway in cultured hepatocytes and neuronal cells derived from embryonic chickens (Crump et al, 2012;Farhat et al, 2013). According to the results of previous studies, TR pathway appears to be interfered by OPEs.…”

Review of OPFRs in animals and humans: Absorption, bioaccumulation, metabolism, and internal exposure research

“…However, because of the large time span and the limited magnitude of the reviewed studies, we cannot determine clear differences of OPFRs metabolites rates among individuals, sexes and species. Crump et al (2012) have mentioned that some metabolites of OPFRs are comparatively more stable than their parent compounds in the body; hence, some of the adverse effects of OPFRs may, in fact, be the result of their metabolites. Meeker et al (2013a) reported a significant or suggestive relationship between two urinary OPFR metabolites (BDCIPP and DPHP) and serum hormone levels in men.…”

Exposure of zebrafish embryos/larvae to TDCPP alters concentrations of thyroid hormones and transcriptions of genes involved in the hypothalamic–pituitary–thyroid axis

“…Liu et al (2012) demonstrated that treatment with TDCPP upregulated mRNA expression associated with steroidogenesis, downregulated mRNA expression of two sulfotransferase genes, and increased testosterone (T) and 17␤-estradiol (E2) productions in H295R cells and in zebrafish. Furthermore, results of epidemiological and controlled laboratory studies suggested that TDCPP affects the thyroid endocrine system and alters development-related mRNA expression (Crump et al, 2012;Liu et al, submitted for publication;Meeker and Stapleton, 2010). For example, Meeker and Stapleton (2010) reported that increased concentrations of TDCPP in house dust were associated with decreased concentrations of free thyroxin (T4) in the serum of adult men.…”