Establishment of an in vitro model using immortal cell lines derived from trout (Oncorhynchus mykiss) to assess the epigenetic toxicity of the flame retardant triphenyl phosphate

Abstract

Since the banning of polybrominated diphenyl ethers (PBDEs), the use of alternative flame retardants such as triphenyl phosphate (TPP) has greatly increased. TPP is an organophosphate flame retardant that is added to a wide variety of consumer and industrial products. TPP has been found present across all environmental compartments, yet there remains limited knowledge on the toxicological profile and the environmental implications of its widespread use. Some studies suggest that TPP may operate as an endocrine and metabolic disruptor as well as causing possible developmental toxicity, which indicates the possibility for toxicity to occur in future generations via epigenetic modifications. This study aimed to establish a model to evaluate epigenetic toxicity following TPP exposure in aquatic ecosystems, using the immortal trout (Oncorhynchus mykiss) cell lines STE-137 (derived from steelhead trout embryonic tissue) and RTG-W1 (derived rainbow trout gill epithelial tissue). Specifically, this study was designed to investigate the occurrence of histone H3 acetylation, an epigenetic modification. Due to difficulties in the growth and maintenance of STE-137 and RTG-W1, a portion of this study uses CD57BL/6 fetal mouse tissue to establish protocols that can be applied in future studies to investigate changes to histone H3 acetylation in STE-137 and RTG-W1 cell lines following exposure to TPP. Preliminary histone analysis results using liver tissue from CD57BL/6 fetal mice exposed to either 0, 5, 25, or 50 mg/kg of TPP in utero indicated that there was no significant difference in H3 acetylation at any treatment group dose compared to control, but a non-significant trend of increased acetylation with increased dose was observed. The results from the future application of this model may be important in order to guide policy decisions on the use of TPP, seeing as TPP is not currently monitored on any federally regulated substances list in Canada.