Aryl Phosphate Esters Within a Major PentaBDE Replacement Product Induce Cardiotoxicity in Developing Zebrafish Embryos: Potential Role of the Aryl Hydrocarbon Receptor

Abstract

Firemaster 550 (FM550) is an additive flame retardant formulation of brominated and aryl phosphate ester (APE) components introduced as a major replacement product for the commercial polybrominated diphenyl ether mixture (known as PentaBDE) used primarily in polyurethane foam. However, little is known about the potential effects of FM550-based ingredients during early vertebrate development. Therefore, we first screened the developmental toxicity of each FM550 component using zebrafish as an animal model. Based on these initial screening assays, we found that exposure to the brominated components as high as 10µM resulted in no significant effects on embryonic survival or development, whereas exposure to triphenyl phosphate (TPP) or mono-substituted isopropylated triaryl phosphate (mono-ITP)-two APEs comprising almost 50% of FM550-resulted in targeted effects on cardiac looping and function during embryogenesis. As these cardiac abnormalities resembled aryl hydrocarbon receptor (AHR) agonist-induced phenotypes, we then exposed developing embryos to TPP or mono-ITP in the presence or absence of an AHR antagonist (CH223191) or AHR2-specific morpholino. Based on these studies, we found that CH223191 blocked heart malformations following exposure to mono-ITP but not TPP, whereas AHR2 knockdown failed to block the cardiotoxic effects of both components. Finally, using a cell-based human AHR reporter assay, we found that mono-ITP (but not TPP) exposure resulted in a significant increase in human AHR-driven luciferase activity at similar nominal concentrations as a potent reference AHR agonist (β-naphthoflavone). Overall, our findings suggest that two major APE components of FM550 induce severe cardiac abnormalities during early vertebrate development.

Aryl organophosphate flame retardants induced cardiotoxicity during zebrafish embryogenesis: By disturbing expression of the transcriptional regulators

“…Considering both results of heart rate and SV-BA distance, 0-48 hpf is the most vulnerable developmental window in which cardiomyogenesis and cardiac function can be affected by TPhP and CDP, which is similar to the results found in TDCPP and ITP studies (McGee et al, 2012(McGee et al, , 2013.…”

“…McGee et al (2013) suggested that the similar cardiotoxicity phenotype induced by TPhP and ITP in zebrafish embryos were respectively through AHR independent and AHR1-dependent pathways. In order to understand the internal reason for TPhP and CDP induced cardiotoxicity, we further explored the changes in expressions of key transcriptional regulators in cardiac development.…”

“…As shown in Table 2, 96 h-EC50 of pericardium edema were lower than half of the 96 h-LC50 in both TPhP and CDP groups while were near or even higher than the 96 h-LC50 in other OPFRs groups. Combined with the discovery of McGee et al (2013), this phenomenon indicated that aryl-OPFRs have greater heart developmental toxicity than alkyl-OPFRs.…”

“…A recent study by McGee et al (2013) reported an alarming result that aryl-OPFRs TPhP and isopropylated triaryl phosphate (ITP) resulted in targeted effects on cardiac looping and function during zebrafish embryogenesis. Despite their similar molecular structures, TPhP and ITP induced cardiotoxicity in zebrafish embryos with different mechanisms: the ITP-induced cardiotoxicity was mediated through an AHR-dependent pathway, while the TPhP-induced cardiotoxicity was AHR-independent.…”

Multiple bio-analytical methods to reveal possible molecular mechanisms of developmental toxicity in zebrafish embryos/larvae exposed to tris(2-butoxyethyl) phosphate

“…Previous studies have demonstrated that several OP esters cause developmental toxicity and endocrine disruption in vivo and in vitro (Crump et al, 2012;Dishaw et al, 2012;Farhat et al, 2013;Fu et al, 2013;Liu et al, 2012bLiu et al, , 2013McGee et al, 2012McGee et al, , 2013Wang et al, 2013). For example, exposure of zebrafish embryos to tris(1,3-dichloro-2-propyl) phosphate (TDCPP) disrupted embryogenesis and caused larval malformation, with median lethal concentrations (LC 50 ) ranging from 3.7 to 7.0 mg/L (Fu et al, 2013;Liu et al, 2013;McGee et al, 2012;Wang et al, 2013).…”