Exposure of adult zebrafish (Danio rerio) to Tetrabromobisphenol A causes neurotoxicity in larval offspring, an adverse transgenerational effect

Highlights

• Exposure of adult zebrafish to TBBPA results in neurotoxicity of larval offspring.

• TBBPA can accumulate in the ovary and testis and be transferred to offspring embryos.

• A reduction in T3 levels was observed in larvae and embryos originating from exposure of adult zebrafish to TBBPA.

• The disruption of dopamine production and mRNA expression of dopamine receptors were observed in larvae.

Abstract

Tetrabromobisphenol A (TBBPA) is one of the most extensively used brominated flame retardants and is universally detected in the environment. However, information related to its transgenerational toxicity is sparse. Using zebrafish as a study model, adult fish were exposed to TBBPA at different concentrations (0, 3, 30, or 300 μg/L) for 42 d and then, the exposed adults were spawned in TBBPA-free water. The neurobehavior of adults and larval offspring was evaluated, and the levels of thyroxine (T4), triiodothyronine (T3) and neurotransmitters (acetylcholine, dopamine and gamma-aminobutyric acid) were quantified in larvae and embryos. Our results showed that TBBPA was detected in embryo and the locomotor activity of larval offspring was significantly reduced, suggesting that TBBPA can transfer to offspring and result in neurotoxicity in larval offspring. Furthermore, a reduction in T3 levels was observed in both the larvae and embryos. We also found a significantly decreased content of dopamine in larval offspring, accompanied by downregulated mRNA expression of rdr2b and drd3. Our results demonstrated that TBBPA can be transferred to offspring embryos, and subsequently induce neurotoxicity in larval offspring by affecting the amount of T3 transferred from the parents to embryos and the production of dopamine in larvae.

Introduction

Tetrabromobisphenol A (TBBPA) is one of the most extensively used brominated flame retardant (BFR) in several commercial products (e.g., printed circuit boards and electronics components) as a reactive or additive flame retardant and accounts for over 50% of the total BFR market (Birnbaum and Staskal, 2004, Covaci et al., 2009, Law et al., 2006). In addition, TBBPA is inevitably released into the water environment during the manufacture, usage and disposal of related products. (Covaci et al., 2009, Liu et al., 2016, Malkoske et al., 2016, Yu et al., 2019). For example, on the sites close to the manufacture of TBBPA-containing product, the concentrations of TBBPA were 1.11–2.83 ng/L in water from Dongjiang catchment in Guangdong, China (He et al., 2013) while the concentrations of TBBPA were 28.3–174 ng/L in wastewater from a printed circuit board manufacturing facility in Shanghai, China (Zhou et al., 2014). TBBPA levels ranged from ND to 920 ng/L in water from an unnamed river surrounded by typical e-waste recycling and disposal sites in Southern China (Xiong et al., 2015) whereas high concentrations of TBBPA were found in the Detroit River (600–1840 ng/L) near industrialized cities (Quade et al., 2003). The highest concentrations of TBBPA were reported in water from the Lake Chaohu (850–4870 ng/L), China's fifth largest freshwater lake (Yang et al., 2012). Furthermore, TBBPA can be continually detected in biotic samples, such as human breast milk and maternal/cord blood samples (Fujii et al., 2014, Kim and Oh, 2014), raising public concern regarding its potential health risks to offspring.

Tremendous amounts of environmental pollution have been reported to transfer from parent to offspring and subsequently affecting progeny development. Therefore, in the past decades, attention has focused on the transgenerational effects of these pollutants, which aggravate environmental health risks to humans and wildlife (Ostrach et al., 2008). Although TBBPA might be a relatively safe compound in BFRs, a recent review emphasized the adverse effects of TBBPA on early developmental stages (Zhou et al., 2020) because immature tissues, organs and detoxification systems in the early developmental stages of organisms are known to be the most sensitive to environmental pollutants (Daston et al., 2004). A previous study showed that TBBPA in female parent zebrafish efficiently transferred to their embryos after a 42-day dietary exposure, and the bioaccumulation level of TBBPA in eggs (0.43 nmol/g lipid weight) was higher than that in the exposed female parent (0.06 nmol/g lipid weight) (Nyholm et al., 2008). However, considering the actual exposure scenario in the aquatic environment, the adverse effects of TBBPA on offspring development and the underlying mechanisms of its transgenerational effects have not been further evaluated following waterborne exposure of the parents.

Thyroid hormones (THs) are pivotal in the regulation of embryonic development and organ differentiation during early life stages (Oppenheimer et al., 1995). TBBPA structurally resembles thyronine (T4) or triiodothyronine (T3), and could thus disrupt the homeostasis of the thyroid endocrine system in vertebrates. TBBPA exposure could potentially cause an imbalance in the level of THs and affect mRNA expression of genes associated with the hypothalamic–pituitary–thyroid axis in fishes (Kuiper et al., 2007a, Zhu et al., 2018), amphibians (Kitamura et al., 2005, Zhang et al., 2014) and mammals (Kitamura et al., 2005). Furthermore, it is generally recognized that disruption of THs can affect neurodevelopmental outcomes, thereby causing adverse effects on locomotor behavior (Birnbaum and Staskal, 2004, Gilbert et al., 2012). For instance, zebrafish exposed to TBBPA delays motor neuron development during a developmental window, leading to a decrease in the locomotor activity of larvae (Chen et al., 2016b). Compared to TBBPA exposure alone, TBBPA exposure in the presence of T3 can eliminate TBBPA-induced neurobehavioral changes, suggesting that TBBPA-induced neurotoxicity in zebrafish larvae could be attributed to the disruption of T3 (Zhu et al., 2018). However, whether exposure of adults to TBBPA could cause a disruption of the thyroid endocrine system and further induce neurotoxicity in progeny remains unclear.

Collectively, we hypothesized that exposure of adult zebrafish to TBBPA would transfer this chemical to offspring and subsequently cause dysfunction of the thyroid endocrine system and neurotoxicity. The neurodevelopmental systems of zebrafish and mammals have similar genetic characteristics, and show homology in the basic processes of human neurodevelopment (Canestro et al., 2007). To test this hypothesis, zebrafish were selected as a model to investigate whether exposure of adults to TBBPA could disrupt the level of THs and affect the neurobehavioral performance of F1 generation larvae. Therefore, the objectives of this study were (1) to measure TBBPA concentrations in embryos originating from adults exposed to TBBPA to assess the transfer of TBBPA, (2) to measure the developmental endpoints and locomotor behavior in larval offspring originating from parent zebrafish exposed to TBBPA to explore the transgenerational effects of TBBPA, and (3) to measure the level of THs (T3 and T4) and neurotransmitters (acetylcholine (AChE), dopamine (DA) and gamma-aminobutyric acid (GABA)) in embryos and larvae to elucidate the possible mechanisms of transgenerational effects of TBBPA.