Diastereoisomer-specific neurotoxicity of hexabromocyclododecane in human SH-SY5Y neuroblastoma cells

Brominated Flame Retardant HBCD and Artificial Light at Night Synergically Caused Visual Disorder and Sleep Difficulty in Zebrafish Larvae

Sleep difficulty is a widespread health concern exacerbated by factors such as light and chemical pollution. Artificial light at night (ALAN) can disrupt natural sleep-wake cycles, whereas chemical pollutants can impair sleep-related processes. The prevalence of ALAN increases the health risk of coexposure, yet it has not gained sufficient attention. Meanwhile, visual inputs are important for sleep regulation, especially the non-image-forming circadian visual system centered around melanopsin. This study evaluated the light perception ability and sleep performance of zebrafish larvae exposed to flame retardant hexabromocyclododecanes (HBCDs) at environmentally relevant concentrations (2.5 and 25 μg/L) and to cotreatment of HBCD and ALAN. HBCD induced a longer sleep latency of 34.59 min under 25 μg/L (p < 0.01) versus control (26.04 min). The situation was intensified by coexposure with low-level ALAN (10 lx) to 48.04 min. Similar synergic effects were observed for upregulations of Xenopus-related melanopsin genes and downregulations of the melatonin synthesis gene aanat2, suggesting a melanopsin-aanat2-sleep retina-brain pathway. Image-forming opsins (opn1sw1 and opn1sw2) were also activated by HBCD to 1.29-1.53-fold (p < 0.05), together with elevated retina glutamate, but without synergic effects. Collectively, we found that HBCD and ALAN coexposure caused synergic effects on the non-image-forming visual system and caused sleep difficulty in zebrafish larvae.

Different Cytotoxicity Induced by Hexabromocyclododecanes on Mouse Neuroblastoma N2a Cells via Oxidative Stress and Mitochondrial Apoptotic Pathway

Hexabromocyclododecane (HBCD) is widely used in polystyrene foams, building materials, and electrical equipment as a brominated flame retardant (BFR) and persists in the environment and human body matrix. It has attracted increased attention since its neuroendocrine disorder effects have been observed in humans and animals. However, studies evaluating the neurotoxicity of HBCD diastereoisomers and the potential mechanisms involved are still limited. In this study, we compared the cytotoxicity induced by the three HBCD diastereoisomers (i.e., α-, β-, and γ-HBCD) in N2a cells and further investigated the underlying molecular mechanism. Our results showed that HBCD diastereoisomers decreased cell viability in the order of β-HBCD > α-HBCD > γ-HBCD. Moreover, α-HBCD and β-HBCD exposure led to different degrees of cell cycle disruption and oxidative stress of N2a cells, implying that oxidative stress-mediated differential cytotoxicity of HBCD diastereoisomers. The expressions of caspases and Bcl-2 were differentially regulated by α-HBCD and β-HBCD, suggesting that the mitochondrial apoptosis pathway may be critical in HBCDs-mediated N2a cell toxicity. Therefore, our studies provided novel evidence for the underlying mechanisms of the distinct cytotoxicity of HBCD diastereoisomers.

Inconsistent Transcriptomic Responses to Hexabromocyclododecane in Japanese Quail: A Comparative Analysis of Results From Four Different Study Designs

Efforts to use transcriptomics for toxicity testing have classically relied on the assumption that chemicals consistently produce characteristic transcriptomic signatures that are reflective of their mechanism of action. However, the degree to which transcriptomic responses are conserved across different test methodologies has seldom been explored. With increasing regulatory demand for New Approach Methods (NAMs) that use alternatives to animal models and high-content approaches such as transcriptomics, this type of comparative analysis is needed. We examined whether common genes are dysregulated in Japanese quail (Coturnix japonica) liver following sublethal exposure to the flame retardant hexabromocyclododecane (HBCD), when life stage and test methodologies differ. The four exposure scenarios included one NAM: Study 1-early-life stage (ELS) exposure via a single egg injection, and three more traditional approaches; Study 2-adult exposure using a single oral gavage; Study 3-ELS exposure via maternal deposition after adults were exposed through their diet for 7 weeks; and Study 4-ELS exposure via maternal deposition and re-exposure of nestlings through their diet for 17 weeks. The total number of differentially expressed genes (DEGs) detected in each study was variable (Study 1, 550; Study 2, 192; Study 3, 1; Study 4, 3) with only 19 DEGs shared between Studies 1 and 2. Factors contributing to this lack of concordance are discussed and include differences in dose, but also quail strain, exposure route, sampling time, and HBCD stereoisomer composition. The results provide a detailed overview of the transcriptomic responses to HBCD at different life stages and routes of exposure in a model avian species and highlight certain challenges and limits of comparing transcriptomics across different test methodologies. Environ Toxicol Chem 2024;00:1-11. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Modulating responses of indicator genes in cellular homeostasis, immune defense and apoptotic process in the Macrophthalmus japonicus exposed to di(2-ethylhexyl) phthalate as a plastic additive

Di(2-ethylhexyl) phthalate (DEHP), have been increasingly used as plasticizers to manufacture soft and flexible materials and ubiquitously found in water and sediments in the aquatic ecosystem. The aim of the present study was to evaluate the effect of DEHP exposure on cellular homeostasis (HSF1 and seven HSPs), immune responses (ILF), and apoptotic responses (p53, BAX, Bcl-2). DEHP exposure upregulated the expression of HSF1 and ILF. Moreover, it altered the expression levels of HSPs (upregulation of HSP70, HSP90, HSP40, HSP83, and HSP67B2 and downregulation of HSP60 and HSP21) in conjunction with HSF1 and ILF in the gills and hepatopancreas of M. japonicus exposed to DEHP. At the protein level, DEHP exposure changed apoptotic signals in both tissues of M. japonicus. These findings indicate that chronic exposures to several DEHP concentrations could disturb cellular balance, damage the inflammatory and immune systems, and induce apoptotic cell death, thereby affecting the survival of M. japonicus.

Distribution characteristics and migration trends of hexabromocyclododecanes between seawater-sediment system in different seasons of fishing grounds along the Yellow sea and East China sea coasts

Pollutants in the ecological environment of fishery seawater are harmful to the survival and reproduction of aquatic organisms. Hexabromocyclododecanes (HBCDs) were 42.9% detected within ND-48.89 ng/L in 177 seawater samples and 30.7% within ND-1.07 ng/g dw in 88 sediment samples of the fisheries in the Yellow Sea and East China Sea, respectively. γ-HBCD accounted for 65% of seawater and 89% of sediment samples. HBCDs in seawater in winter (ND-48.89 ng/L) were significantly higher than in summer (ND-4.99 ng/L), possibly because the re-suspension caused by winds and waves could re-migrate HBCDs from the sediment to the seawater in winter. However, seasonal differences of HBCDs in sediment were not significant. The fugacities indicated HBCDs' migrating trend from seawater to sediment due to their hydrophobic nature. There is almost no terrestrial input of HBCDs from the Yangtze and Yellow Rivers, and currently used fishery materials in marine may compose long-lasting sources of HBCDs.

Responses of multifunctional immune complement component 1q (C1q) and apoptosis-related genes in Macrophthalmus japonicus tissues and human cells following exposure to environmental pollutants

Apoptosis is a key defense process for multiple immune system functions, playing a central role in maintaining homeostasis and cell development. The purpose of this study was to evaluate the effects of environmental pollutant exposure on immune-related apoptotic pathways in crab tissues and human cells. To do this, we characterized the multifunctional immune complement component 1q (C1q) gene and analyzed C1q expression in Macrophthalmus japonicus crabs after exposure to di(2-ethylhexyl) phthalate (DEHP) or hexabromocyclododecanes (HBCDs). Moreover, the responses of apoptotic signal-related genes were observed in M. japonicus tissues and human cell lines (HEK293T and HCT116). C1q gene expression was downregulated in the gills and hepatopancreas of M. japonicus after exposure to DEHP or HBCD. Pollutant exposure also increased antioxidant enzyme activities and altered transcription of 15 apoptotic signaling genes in M. japonicus. However, patterns in apoptotic signaling in response to these pollutants differed in human cells. HBCD exposure generated an apoptotic signal (cleaved caspase-3) and inhibited cell growth in both cell lines, whereas DEHP exposure did not produce such a response. These results suggest that exposure to environmental pollutants induced different levels of immune-related apoptosis depending on the cell or tissue type and that this induction of apoptotic signaling may trigger an initiation of carcinogenesis in M. japonicus and in humans as consumers.

Occurrence and Health Effects of Hexabromocyclododecane: An Updated Review

Hexabromocyclododecane (HBCD) is a non-aromatic compound belonging to the bromine flame retardant family and is a known persistent organic pollutant (POP). This compound accumulates easily in the environment and has a high half-life in water. With a variety of uses, the HBCD is found in house dust, electronics, insulation, and construction. There are several isomers and the most studied are α-, β-, and γ-HBCD. Initially used as a substitute for other flame retardants, the polybrominated diphenyl ethers (PBDEs), the discovery of its role as a POP made HBCD use and manufacturing restricted in Europe and other countries. The adverse effects on the environment and human health have been piling, either as a result from its accumulation or considering its power as an endocrine disruptor (ED). Furthermore, it has also been proven that it has detrimental effects on the neuronal system, endocrine system, cardiovascular system, liver, and the reproductive system. HBCD has also been linked to cytokine production, DNA damage, increased cell apoptosis, increased oxidative stress, and reactive oxygen species (ROS) production. Therefore, this review aims to compile the most recent studies regarding the negative effects of this compound on the environment and human health, describing the possible mechanisms by which this compound acts and its possible toxic effects.

Lipoxin A4 methyl ester attenuated ketamine-induced neurotoxicity in SH-SY5Y cells via regulating leptin pathway

Ketamine, the widely used intravenous anesthetic, has been reported to cause neurotoxicity and disturbs normal neurogenesis. However, the efficacy of current treatment strategies targeting ketamine's neurotoxicity remains limited. Lipoxin A4 methyl ester (LXA4 ME) is relatively stable lipoxin analog, which serves an important role in protecting against early brain injury. The purpose of this study was to investigate the protective effect of LXA4 ME on ketamine-caused cytotoxicity in SH-SY5Y cells, as well as the underlying mechanisms. Cell viability, apoptosis and endoplasmic reticulum stress (ER stress) were detected by adopting experimental techniques including CCK-8 assay, flow cytometry, western blotting and transmission electron microscope. Furthermore, examining the expression of leptin and its receptor (LepRb), we also measured the levels of activation of the leptin signaling pathway. Our results showed that LXA4 ME intervention promoted the cell viability, inhibited cell apoptosis, and reduced the expression of ER stress related protein and morphological changes induced by ketamine. In addition, inhibition of leptin signaling pathway caused by ketamine could be reversed by LXA4 ME. However, as the specific inhibitor of leptin pathway, leptin antagonist triple mutant human recombinant (leptin tA) attenuated the cytoprotective effect of LXA4 ME against ketamine-induced neurotoxicity. In conclusion, our findings demonstrated LXA4 ME could exert a neuroprotective effect on ketamine-induced neuronal injury via activation of the leptin signaling pathway.

Heterocyclic aromatic amines induce Neuro-2a cells cytotoxicity through oxidative stress-mediated mitochondria-dependent apoptotic signals

Heterocyclic aromatic amines (HAAs) are a class of hazardous compounds produced in food thermal processing. These compounds raise concerns because they have mutagenic and carcinogenic properties. However, the neurotoxicity of these compounds has received limited attention. Here, the toxic effects of three HAAs, i.e. 9H-pyrido[3,4-b]indole (Norharman), 1-methyl-9H-pyrido[3,4-b]indole (Harman), and 2-amino-3-methylimidazole[4,5-f]quinoline (IQ) were investigated in Neuro-2a cells model. The results showed that the survival rate of cells decreased in a dose-dependent manner and apoptosis occurred after exposure to the three HAAs for 24 h and 48 h. Their neurotoxicity was ranked as Harman > Norharman > IQ. Further, treatment of Harman, Norharman, or IQ at 50 and 100 μM for 48 h led to intracellular REDOX imbalance, which was manifested as increased ROS and malondialdehyde (MDA) levels, decreased GSH/GSSG ratio, and reduced SOD and CAT activities. Moreover, Norharman and Harman up-regulated the expression level of nuclear factor erythroid 2-related factor 2 (Nrf2), as well as the mRNA levels of Heme oxygenase-1 (HO-1) and NAD(P)H quinone oxidoredutase1 (NQO1), while IQ had no significant effect on the levels of Nrf2, HO-1, and NQO1. Additionally, Harman, Norharman, or IQ exposure significantly reduced mitochondrial membrane potential and intracellular ATP levels and up-regulated the levels of apoptosis-related genes and proteins. Collectively, our finding suggested that HAAs were neurotoxic, with mechanisms related to induction of oxidative stress and mitochondrial dysfunction.

Multi-matrix distribution and contamination profiles of HBCDD isomers in a man-made saltwater lake near industrial complexes with high flame retardant consumption in Korea

South Korea is one of the largest consumers of flame-retardants worldwide. In this study, water, sediment, and biota samples were collected from a highly industrialized lake to investigate contamination, isomeric profiles, source, and the bioaccumulation potential of hexabromocyclododecanes (HBCDDs). Almost all of the sediments were severely contaminated by HBCDDs, which were some of the highest global levels compared to those found in previous studies. The highest concentrations and similar profiles to those of technical mixtures of HBCDDs were observed in creeks passing through industrial complexes, indicating on-going contamination by high consumption of HBCDDs from industrial activities. γ-HBCDD was dominant in water and sediment, whereas α-HBCDD was dominant in fish and shellfish. The diastereoisomeric profiles of HBCDDs in multiple matrices were influenced by proximity to industry and chemical properties. In-situ biota-sediment accumulation factors of α-HBCDDs were > 1 in benthic species, implying that HBCDDs are of great concern in sedimentary environments.

Update of the risk assessment of hexabromocyclododecanes (HBCDDs) in food

The European Commission asked EFSA to update its 2011 risk assessment on hexabromocyclododecanes (HBCDDs) in food. HBCDDs, predominantly mixtures of the stereoisomers α-, β- and γ-HBCDD, were widely used additive flame retardants. Concern has been raised because of the occurrence of HBCDDs in the environment, food and in humans. Main targets for toxicity are neurodevelopment, the liver, thyroid hormone homeostasis and the reproductive and immune systems. The CONTAM Panel concluded that the neurodevelopmental effects on behaviour in mice can be considered the critical effects. Based on effects on spontaneous behaviour in mice, the Panel identified a lowest observed adverse effect level (LOAEL) of 0.9 mg/kg body weight (bw) as the Reference Point, corresponding to a body burden of 0.75 mg/kg bw. The chronic intake that would lead to the same body burden in humans was calculated to be 2.35 μg/kg bw per day. The derivation of a health-based guidance value (HBGV) was not considered appropriate. Instead, the margin of exposure (MOE) approach was applied to assess possible health concerns. Over 6,000 analytical results for HBCDDs in food were used to estimate the exposure across dietary surveys and age groups of the European population. The most important contributors to the chronic dietary LB exposure to HBCDDs were fish meat, eggs, livestock meat and poultry. The CONTAM Panel concluded that the resulting MOE values support the conclusion that current dietary exposure to HBCDDs across European countries does not raise a health concern. An exception is breastfed infants with high milk consumption, for which the lowest MOE values may raise a health concern.

Flame retardants and neurodevelopment: An updated review of epidemiological literature

Purpose of Review

Flame retardant (FR) compounds can adversely impact neurodevelopment. This updated literature review summarizes epidemiological studies of FRs and neurotoxicity published since 2015, covering historical (polybrominated biphenyls [PBBs], polychlorinated biphenyls [PCBs]), contemporary (polybrominated diphenyl ethers [PBDEs], hexabromocyclododecane [HBCD], and tetrabromobisphenol A [TBBPA]), and current-use organophosphate FRs (OPFRs) and brominated FRs (2-ethylhexyl 2,3,4,5-tetrabromobezoate [EH-TBB] TBB), bis(2-ethylhexyl) tetrabromophthalate [BEH-TEBP]), focusing on prenatal and postnatal periods of exposure.

Recent Findings

Continuing studies on PCBs still reveal adverse associations on child cognition and behavior. Recent studies indicate PBDEs are neurotoxic, particularly for gestational exposures with decreased cognition and increased externalizing behaviors. Findings were suggestive for PBDEs and other behavioral domains and neuroimaging. OPFR studies provide suggestive evidence of reduced cognition and more behavioral problems.

Summary

Despite a lack of studies of PBBs, TBBPA, EH-TBB, and BEH-TEBP, and only two studies of HBCD, recent literature of PCBs, PBDEs, and OPFRs are suggestive of developmental neurotoxicity, calling for more studies of OPFRs.

Pesticide treatment reduces hydrophobic pollutant contamination in Cucurbita pepo through competitive binding to major latex-like proteins

Hydrophobic pollutants are still present in agricultural soil. The Cucurbitaceae family accumulates hydrophobic pollutants through roots, resulting in the contamination of aerial parts. Major latex-like proteins (MLPs), found in the Cucurbitaceae family, play an important role in the contamination by binding to these hydrophobic pollutants. Thus far, efficient cultivation methods for the production of safe crops with lower concentrations of hydrophobic pollutants have not been developed. Herein, we competitively inhibited the binding of MLPs to hydrophobic pollutants, pyrene and dieldrin, in roots by using MLP binding pesticides. By conducting a chemical array screening, we found that MLPs bound compounds with indole- and quinazoline-like structures. Commercially available pesticides amisulbrom and pyrifluquinazon, which possess such structures, successfully inhibited the binding of MLPs to pyrene and dieldrin in vitro. When zucchini plants were cultivated in the contaminated soil with 1.25 mmol/kg pyrene and 12.5 μmol/kg dieldrin, the concentration of pyrene and dieldrin in xylem sap was significantly decreased by 30% and 15%, respectively. Our results demonstrate that the pesticides binding to MLPs competitively inhibited the binding of MLPs to pyrene and dieldrin in roots, resulting in the reduction of overall contamination. This study proposes a novel approach to cultivate safer crops and advances the utilization of unknown functions of pesticides.

Cytotoxicity of hexabromocyclododecane, 1,2-dibromo-4-(1,2-dibromoethyl) cyclohexane and 1,2,5,6-tetrabromocyclooctane in human SH-SY5Y neuroblastoma cells

With the listing of the of cycloaliphatic brominated flame retardants (CBFR) hexabromocyclododecane (HBCD) as a persistent organic pollutant (POP) by the Stockholm Convention, much attention has been paid to the environmental behaviors and biological effects of HBCD, as well as its potential alternatives, such as 1,2-dibromo-4-(1,2-dibromoethyl) cyclohexane (TBECH) and 1,2,5,6-tetrabromocyclooctane (TBCO). In this study, the neurotoxicity of HBCD, TBECH, and TBCO in human SH-SY5Y cells were compared. The results showed that HBCD, TBECH, and TBCO induced cytotoxicity, including dose-dependent cell viability decreases, cell membrane permeability increases, cytoskeleton development damage, and apoptosis induction, with the cytotoxicity in the order of HBCD > TBCO > TBECH. The expression levels of apoptotic proteins (caspase-3, Bax, caspase-9, Bcl-2, and cytochrome c (Cyt c)) followed the same order, which indicated that mitochondrial apoptotic pathway may be one of the mechanisms responsible for their neurotoxicity. In order to study the mechanisms of cytotoxicity, CBFRs-induced reactive oxygen species (ROS) and the intracellular calcium levels were determined. The ROS levels were significantly elevated for three CBFRs treatment, suggesting that oxidative stress contributes to their cytotoxicity. The intracellular calcium concentrations were significantly enhanced for HBCD and TBCO treatment, but not for TBECH, indicating that in addition to ROS, cytotoxicity of HBCD and TBCO may follow Ca²⁺-mediated apoptotic pathway. This study first compared the neurotoxicity of different CBFRs, providing valuable information for their risk assessment.

Tetrabromoethylcyclohexane (TBECH) exhibits immunotoxicity in murine macrophages

Tetrabromoethylcyclohexane (TBECH) has been linked to endocrine disruption, hepatotoxicity, and reproductive toxicity. However, its immunotoxicity remains largely unknown. In the present study, RAW 264.7 cells, mouse macrophage cell line, were exposed to TBECH. MTT assays showed that TBECH significantly enhanced lactate dehydrogenase (LDH) release in RAW 264.7 cells. The mRNA expression of some proapoptotic genes was upregulated by TBECH. Accordingly, TBECH elevated caspase-3 activity. In addition, TBECH upregualted the mRNA levels of some pro-inflammatory cytokines, whereas it downregulated LPS-stimulated mRNA expression of these cytokines. Moreover, TBECH downregulated the mRNA expression of selected antigen presenting-related genes. Furthermore, TBECH increased reactive oxygen species level, reduced glutathione content and the activities of superoxide dismutase and catalase, and upregulated the mRNA expression of selected oxidative stress-related genes. The obtained data demonstrated that TBECH exhibits immunotoxicity in macrophages, and will help to evaluate its health risks.