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

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.

Hexabromocyclododecane (HBCD) exposure induced premature testicular aging via NCOA4/Fe2+/ROS mediation

Hexabromocyclododecane (HBCD) has been detected in animals and humans blood. As an environment contamination, HBCD damages tissues and organs in animals and humans and produces cytotoxicity. In current study, we explored the effect of HBCD on premature testicular aging in vivo and in vitro. In vivo, C57 mice (8-week-old) were used as model to estimate the effect of HBCD on premature testicular aging. The results showed that testes were premature aging through measuring several aging-related markers (such as p16INK4a, hereafter p16; p21CIP, hereafter p21) in response to HBCD exposure for 20 weeks. In addition, HBCD exposure can cause oxidative stress and inflammation. Further, mouse spermatogonial cells (GC-1spg cells) were premature senescence after HBCD exposure by the evaluation of cellular senescence marker molecules. Hence, GC-1spg cell line was applied for cell model to investigate the molecule mechanism by which HBCD cause premature testicular aging., Through eliminating Fe2+ in senescent GC-1spg cells, cellular senescence was greatly alleviated. Thus, Fe2+ was identified as the key driver molecule in HBCD-induced premature cellular senescence. Next, we found that elevated iron levels in HBCD-triggered senescent GC-1spg cells were due to Nuclear receptor coactivator 4 (NCOA4)-mediated ferritinophagy. Furthermore, our results revealed that HBCD-induced senescence was caused by Fe2+ mediated oxidative stress. In summary, HBCD-induced premature testicular aging is dependent on NCOA4/Fe2+/ROS signaling molecule. The current study lays the foundation for further exploration of the effects of HBCD on reproductive toxicology.

Hexabromocyclododecane in sediments from riverine, port, and coastal areas of Kaohsiung, Taiwan: levels, spatial distribution, and potential ecological risk

The widespread use of hexabromocyclododecane (HBCD), a brominated flame retardant, is a major public health concern because of the toxic, persistent, and bioaccumulative nature of HBCD. However, there is limited information available regarding the distribution and transportation of HBCD in sediments across various environmental settings, spanning from riverine to marine environments in the Kaohsiung area of Taiwan. In this study, we comprehensively investigated the level and distribution of and potential ecological risk posed by HBCD in surface sediments in the Kaohsiung area of Taiwan. In sediment samples from stations on the Love River and Kaohsiung Port area, the concentrations of HBCD ranged from 10.6 to 320.1 μg/kg dry weight (dw) and nondetectable (n.d.) to 58.4 μg/kg dw, respectively. The concentrations of HBCD in sediment collected from the M1, M2, and M3 sites, located in the Cijin coastal area, were 896.2 μg/kg dw, 3.2 μg/kg dw ( 1. The M1 site had the highest risk level (RQ = 5.27). These data suggest that domestic sewage and industrial wastewater discharge pose a potential risk to marine environments. Consequently, timely measures to control HBCD-related risks are required. Our study offers insight into the environmental effects of HBCD contamination of sediment and provides valuable information that can be used to guide environmental policy and safety measures.

Investigating the adverse outcome pathways (AOP) of neurotoxicity induced by DBDPE with a combination of in vitro and in silico approaches

Current studies have shown an association between DBDPE and neurotoxicity. In this study, the adverse outcome pathway (AOP) and mechanistic analysis of DBDPE-induced neurotoxicity were explored by a combination of in vitro and in silico approaches in SK-N-SH cells. DBDPE-induced oxidative stress caused DNA strand breaks, resulting in the activation of poly (ADP-ribose) (PAR) polymerase-1 (PARP-1). Activation of PARP1 could cause toxic damage in various organ systems, especially in the nervous system. DBDPE-induced apoptosis via the caspase-dependent intrinsic mitochondrial pathway and the PARP1-dependent pathway. Activation of PARP1 by DBDPE was deemed the initiating event, thereby affecting the key downstream biochemical events (e.g., ROS production, DNA damage, membrane potential changes, and ATP reduction), which induced apoptosis. Furthermore, excessive activation of PARP1 was accompanied by the translocation of the apoptosis-inducing factor (AIF), which was associated with PARP1-dependent cell death. The inhibition of PARP1 by PJ34 reduced DBDPE-induced apoptosis and maintained cellular ATP levels. PJ34 also prevented the translocation of AIF from the mitochondria to the nucleus. These findings improve the understanding of the mechanism of DBDPE-induced neurotoxic effects and provide a theoretical basis for the ecological risk of DBDPE.

In vitro neurotoxic potential of emerging flame retardants on neuroblastoma cells in an acute exposure scenario

Since 2004, some legacy flame retardants (FRs) were restricted or removed from the European markets due to their concern on human health. Both organophosphorus FRs (OPFRs) and novel brominated FRs (NBFRs) have replaced them because they are presumably safer and less persistent emerging FRs (EFRs) and their exposure is currently occurring in indoor environments at high levels. Little is known about the neurotoxic potential risk of these EFRs in humans. The present study was aimed at assessing the acute neurotoxicity potential of Tris(1, 3-dichloro-2-propyl)phosphate (TDCPP), triphenyl phosphate (TPhP), Bis(2-ethylhexyl)tetrabromophthalate (BEH-TEBP) and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB) on human neuroblastoma cells (SH-SY5Y). SH-SY5Y were exposed to these EFRs at low concentrations -ranging 2.5-20 μM. during 2-24 h. We investigated viability, mitochondrial function, oxidative stress, inflammatory response, as well as neural plasticity and development. The results have demonstrated that selected EFRs (TDCPP, TPhP, EH-TBB and BEH-TBP) did not impair neural function on SH-SY5Y as acute response. To the best of our knowledge, this has been the first study focused on evaluating the neural affection of TPhP on SH-SY5Y cells and of EH-TBB and BEH-TBP on neural cells. We also assessed for the first time almost all endpoints after FR exposure on neural cell lines.

Mechanochemical destruction and mineralization of solid-phase hexabromocyclododecane assisted by microscale zero-valent aluminum

Hexabromocyclododecane (HBCD) has been listed in Annex A of the Stockholm Convention as a persistent and bio-accumulative chemical. While HBCD is often present in the solid form for its low solubility, cost-effective technologies have been lacking for the degradation of solid-phase HBCD. In this work, mechanochemical (MC) destruction of high-energy ball milling was employed for direct destruction of solid-phase HBCD, where a strong reducer, microscale zero-valent aluminum (mZVAl), was used as the co-milling agent. The new mZVAl-assisted MC process achieved complete debromination and mineralization of HBCD within 3 h milling. The optimal operating parameters were determined, including the milling atmosphere, the milling speed, the mZVAl-to-HBCD molar ratio, and the ball-to-mZVAl mass ratio. Fourier transform infrared spectrometry and Raman analyses revealed that the organic structures of HBCD were destroyed and organic bromine was completely converted into inorganic bromide, accompanied by the generation of amorphous and graphite carbon. Analysis of the milled samples by GC-MS demonstrated the absence of obvious organic matter after MC treatment, also indicating the complete degradation and conversion of HBCD to inorganic compounds. Further X-ray photoelectron spectroscopic analysis indicates that the fresh surface of mZVAl was generated upon the MC treatment, and Al(0) served as a strong reducing agent (e-donor) for reductive debromination and destruction of the carbon skeleton. The mZVAl-assisted MC milling appears promising as a non-combustion approach for effective destruction and carbonization/mineralization of solid-phase HBCD or potentially other persistent organic pollutants.

Organophosphate flame retardants induce oxidative stress and Chop/Caspase 3-related apoptosis via Sod1/p53/Map3k6/Fkbp5 in NCI-1975 cells

Organophosphate flame retardants (OPFRs) have been ubiquitously detected in dust and air which could cause damage to human health through inhalation. Currently the understanding of their adverse effects and potential mechanisms on the lung are still limited. In this study, human non-small cell lung cancer cell line NCI-H1975 was used to investigate the cytotoxicity, oxidative stress, cellular apoptosis of 9 typical OPFRs with concentrations varied from 0 to 200 μM, and their toxic mechanism associated with molecular structure was compared. After 72 h, tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) displayed the highest cytotoxicity, followed by 2-ethylhexyl diphenyl phosphate (EHDPP), tris(2-butoxyethyl) phosphate (TBOEP) and tris(2-chloroisopropyl) phosphate (TCIPP), while tris(2-chloroethyl) phosphate (TCEP) and tris(2-ethylhexyl) phosphate (TEHP) exhibited the least suppression on cell viability. These results indicated that the variation of cytotoxicity on OPFRs could only be partially explained by their ester linkage. Moreover, the overexpression of intracellular reactive oxygen species (ROS), free Ca²⁺ and cellular apoptosis suggested that exposure to OPFRs can lead to apoptosis related to oxidative stress. Six genes associated with oxidative stress and apoptosis were upregulated dramatically compared with the control, demonstrating OPFRs induced Chop/Caspase 3-related apoptosis by activating Sod1/p53/Map3k6/Fkbp5 expression in NCI-H1975 cells. This is the first study to investigate cytotoxicity and related mechanism on commonly-used OPFRs in NCI-H1975 cells.

Dual-Targeting Antiproliferation Hybrids Derived from 1-Deoxynojirimycin and Kaempferol Induce MCF-7 Cell Apoptosis through the Mitochondria-Mediated Pathway

1-Deoxynojirimycin, an α-glucosidase inhibitor, possesses various biological activities such as antitumor, antidiabetic, and antiviral effects. However, the application of 1-deoxynojirimycin is restricted by its poor lipophilicity and low bioavailability. In this study, three 1-deoxynojirimycin derivatives (8-10) comprising 1-deoxynojirimycin and kaempferol were designed and synthesized to modify their pharmacokinetics and improve their antitumor efficacy. Among them, compound 10, a conjugate of 1-deoxynojirimycin and kaempferol linked through an undecane chain, exhibited excellent lipophilicity, antiproliferative effects, and α-glucosidase inhibitory activity. Compared with 1-deoxynojirimycin, kaempferol, and their combination, compound 10 downregulated cyclooxygenase-2 (COX-2) expression, arrested the cell cycle at the S phase, induced cellular apoptosis, and inhibited the migration of MCF-7 cells. Moreover, further investigation indicated that compound 10 induced MCF-7 cell apoptosis through a mitochondrial-mediated pathway via the loss of mitochondrial membrane potential. This led to increasing intracellular levels of reactive oxygen species (ROS) and Ca²⁺, the downregulation of Bcl-2 expression, and the upregulation of Bax levels.

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.