Brominated and organophosphate flame retardants target different neurodevelopmental stages, characterized with embryonic neural stem cells and neuronotypic PC12 cells

Abstract

In addition to their activity as endocrine disruptors, brominated and organophosphate flame retardants are suspected to be developmental neurotoxicants, although identifying their specific mechanisms for that activity has been elusive. In the current study, we evaluated the effects of several flame retardants on neurodifferentiation using two in vitro models that assess distinct “decision nodes” in neural cell development: embryonic rat neural stem cells (NSCs), which evaluate the origination of neurons and glia from precursors, and rat neuronotypic PC12 cells, which characterize a later stage where cells committed to a neuronal phenotype undergo neurite outgrowth and neurotransmitter specification. In NSCs, both brominated and organophosphate flame retardants diverted the phenotype in favor of glia and away from formation of neurons, leading to an increased glia/neuron ratio, a common hallmark of the in vivo effects of neurotoxicants. For this early decision node, the brominated flame retardants were far more potent than the organophosphates. In PC12 cells, the brominated flame retardants were far less effective, whereas tris (1,3-dichloro-2-propyl) phosphate, an organophosphate, was more effective. Thus, the two classes of flame retardants differentially impact the two distinct vulnerable periods of neurodifferentiation. Furthermore, the effects on neurodifferentiation were separable from outright cytotoxicity, an important requirement in establishing a specific effect of these agents on neural cell development. These results reinforce the likelihood that flame retardants act as developmental neurotoxicants via direct effects on neural cell differentiation, over and above other activities that can impact nervous system development, such as endocrine disruption.

Cytotoxic effects of parathion, paraoxon, and their methylated derivatives on a mouse neuroblastoma cell line NB41A3

“…Considering that organophosphate compounds generally inhibit the AChE enzyme that breaks down the neurotransmitter acetylcholine (De Jong and Benschop, 1988;Taylor, 2001), it is not surprising to find neurogenesis related genes in a responsive group. It has been reported that the development of neurons was the targeted biological process in developing zebrafish embryo and rat PC12 cells when exposed to chlorpyrifos-oxon (Jacobson et al, 2010) and to tris (1,3-dichloro-2-propyl) phosphate (Slotkin et al, 2017).…”

Tris (1,3-dichloro-2-propyl) phosphate treatment induces DNA damage, cell cycle arrest and apoptosis in murine RAW264.7 macrophages

“…Results of previous studies have indicated that TDCPP can cause neurotoxicity, developmental toxicity, endocrine disruption and hepatotoxicity (Li et al, 2015;Slotkin et al, 2017). Also, TDCPP exposure caused different toxicity in zebrafish, including cell cycle arrest, DNA damage and apoptosis (Chen et al, 2018).…”

Screening for neurotoxic potential of 15 flame retardants using freshwater planarians

“…While several of the 15 FRs that we screened have been previously studied in other systems, including rodents (Cope et al, 2015; EFSA, 2011; Moser et al, 2015; Nakajima et al, 2009; National Toxicology Program, 1991; Viberg and Eriksson, 2011) and other alternative models (Alzualde et al, 2018; Bailey and Levin, 2015; Cano-Sancho et al, 2017; Glazer et al, 2018; Oliveri et al, 2015; Slotkin et al, 2017; Usenko et al, 2016), only a handful of studies have performed direct multi-FR comparisons as provided here. Fourteen of the 15 unique FRs tested in this screen have been previously studied in developing zebrafish, nematodes, and in vitro cell-based (mouse embryonic stem cell, human neural stem cell, and rat neuron) systems with some FRs showing developmental toxicity or DNT.…”