Parallel in vivo and in vitro transcriptomics analysis reveals calcium and zinc signalling in the brain as sensitive targets of HBCD neurotoxicity

Integrated risk assessment of dietary exposure and body burden of three brominated flame retardants in childbearing-aged Chinese women and breastfeeding infants

Based on the third Chinese National Human Milk Survey (NHMS) conducted in 2016-2019, three typical legacy brominated flame retardants (BFRs), namely decabromodiphenyl ether (BDE-209), tetrabromobisphenol A (TBBPA), and hexabromocyclododecanes (HBCDDs, sum of three isomers), were measured in 100 pooled human milk samples collected from 24 provinces across China. The median concentrations of BDE-209, TBBPA and HBCDDs were 0.27, 0.0468 and 5.01 ng/g lipid, respectively. BDE-209 and HBCDDs were detected in all samples, while TBBPA was detected in 97% of the samples, suggesting their widespread presence in the Chinese population. When compared to the two previous NHMSs conducted in 2007 and 2011-2013, respectively, the levels of BDE-209 and TBBPA showed in sharp decline in the most recent surveys. By contrast, HBCDD levels initially increased substantially but have since plateaued in the last two surveys. A comparison with data from the Chinese total diet study conducted in the same area and period reveal notable positive correlations between dietary intake of TBBPA and HBCDDs for childbearing-aged women (18-35 years old) through certain animal-derived foods and the corresponding BFR levels in human milk. For nursing infants, the average daily intake of TBBPA and BDE-209 is unlikely to pose considerable health risks. However, the 95th percentile (P95) and maximum margin of exposure (MOE) for HBCDDs were below the established MOE threshold, indicating that daily intake of HBCDDs could psoe health risks to infants in high-exposed areas, such as Northern China.

A physiologically based pharmacokinetic (PBPK) model describing the kinetics of a commercial mixture α-, β-, and γ-hexabromocyclododecane exposure in mice

Hexabromocyclododecane (HBCD) is a brominated flame retardant, that is added, but not chemically bonded, to consumer products. HBCD is sold as a commercial-grade HBCD mixture containing three major stereoisomers: alpha (α), beta (β), and gamma (γ), with relative amounts of 12% for α-HBCD, 6% for β-HBCD, and 82% for γ-HBCD. HBCDs are widely measured in the environment and in biological matrices. The toxicological effects of its exposure in humans are not clearly understood. A recent reassessment pointed out potential thyroid disruption as a primary effect. This current work aims to update a physiologically based pharmacokinetic (PBPK) model for γ-HBCD in C57BL/6 mice and incorporate equations and codes for α-HBCD and β-HBCD isomers and simulate them as a mixture. Physiological parameters were taken from the literature, calculated based on the log Kow or optimized with the dataset. The elimination of HBCDs in urine and feces was optimized to reflect the percent dose excreted, as published in the literature. Compared with data from the literature for α-HBCD, β-HBCD, and γ-HBCD in multiple tissues, the model simulations accurately described the pharmacokinetics of HBCDs in the mouse. The utility of the model was demonstrated by predicting blood concentrations from three studies in adult mice evaluating dopaminergic changes in the brain. Although this PBPK model for the mixture explicitly describes α-HBCD, β-HBCD, and γ-HBCD as individual exposures, but also as a mixture, more experimental data with commercial HBCD mixtures is still needed to improve the model.

Insights into brominated flame retardant neurotoxicity: mechanisms of hippocampal neural cell death and brain region-specific transcriptomic shifts in mice

Brominated flame retardants (BFRs) reduce flammability in a wide range of products including electronics, carpets, and paint, but leach into the environment to result in continuous, population-level exposure. Epidemiology studies have correlated BFR exposure with neurological problems, including alterations in learning and memory. This study investigated the molecular mechanisms mediating BFR-induced cell death in hippocampal cells and clarified the impact of hexabromocyclododecane (HBCD) exposure on gene transcription in the hippocampus, dorsal striatum, and frontal cortex of male mice. Exposure of hippocampus-derived HT-22 cells to various flame retardants, including tetrabromobisphenol-A (current use), HBCD (phasing out), or 2,2',4,4'-tetrabromodiphenyl ether (BDE-47, phased out) resulted in time, concentration, and chemical-dependent cellular and nuclear morphology alterations, alterations in cell cycle and increases in annexin V staining. All 3 BFRs increased p53 and p21 expression; however, inhibition of p53 nuclear translocation using pifthrin-α did not decrease cell death. Transcriptomic analysis upon low (10 nM) and cytotoxic (10 μM) BFR exposure indicated that HBCD and BDE-47 altered genes mediating autophagy-related pathways. Further evaluation showed that BFR exposure increased LC3-II conversion and autophagosome/autolysosome formation, and co-exposure with the autophagy inhibitor 3-methyladenine (3-MA) attenuated cytotoxicity. Transcriptomic assessment of select brain regions from subchronically HBCD-exposed male mice demonstrated alteration of genes mediating vesicular transport, with greater impact on the frontal cortex and dorsal striatum compared with the dorsal and ventral hippocampus. Immunoblot analysis demonstrated no increases in cell death or autophagy markers, but did demonstrate increases in the SNARE binding complex protein SNAP29, specifically in the dorsal hippocampus. These data demonstrate that BFRs can induce chemical-dependent autophagy in neural cells in vitro and provide evidence that BFRs induce region-specific transcriptomic and protein expression in the brain suggestive of changes in vesicular trafficking.

Association between dietary exposure to chemical contaminants and risk of dementia in older persons

BACKGROUND

Diet is a major route of exposure to potentially neurotoxic chemicals, yet the epidemiological association of diet contaminants with dementia is unknown. We studied the link between dietary exposure to multiple chemicals and dementia risk in older persons, considering interaction with dietary fat content, which may modify the bioavailability and toxicity of (lipophilic) chemicals.

METHODS

We included 1,288 non-demented participants from the French Three-City cohort who answered a food frequency questionnaire and 24-hour recall at baseline and were followed for incident dementia. Dietary exposure to 167 contaminants was assessed by combining food intakes with food chemical content from the French second Total Diet Study. We assessed the relation of each individual contaminant with dementia risk using multivariable-adjusted Cox models, exploring effect modification by high-fat diet (>35 % energy from fat). Among high-fat diet consumers, we looked for a signature of contaminants associated with dementia using elastic-net penalization and assess their joint effect.

RESULTS

Participants were 76 years-old on average at baseline and 62 % were women. In total, 314 individuals developed dementia over a median 10 years. No contaminant was associated with dementia in the whole population. However, having a high-fat diet was a strong effect modifier for 85 contaminants (FDR-corrected p < 0.05 for interactions) in single-chemical analyses, so that higher intakes were significantly associated with higher dementia risk among high-fat consumers only (n = 386). Among them, a multi-chemical approach revealed a signature of 9 contaminants related to dementia, including 4 perfluoroalkyl substances, 2 flame retardants hexabromocyclododecane (HBCDD) congeners, 2 mycotoxins, and nitrites. This selection included two top hits from the single-chemical analyses (α-HBCDD and perfluorooctanesulfonic acid [PFOS]), and was mainly provided by delicatessen meat, seafood and bread/crispbread.

CONCLUSION

In this large population-based study, dietary exposure to several chemicals was associated with higher dementia risk among older persons consuming > 35 % energy from fat in diet.

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) induced PANoptosis of chondrocytes via activation of the NLRP3 inflammasome and decreased the exercise ability of mice in vivo

Hexabromocyclododecane (HBCD) is a persistent organic pollutant (POP). HBCD is found in the blood and tissues of most populations and causes a range of toxicological damage to tissues and cells. However, the toxicological effects of HBCD on chondrocytes are not fully understood. Here, we evaluated the toxicological effects of HBCD on chondrocytes and cartilaginous tissue. For this, a model of primary cartilage cells was established. Chondrocytes were exposed to different concentrations of HBCD. Western blot, indirect immunofluorescence, ELISA and other biochemical experiments were performed to analyze the toxicological effects of HBCD on chondrocytes/articular cartilage tissue. Cell proliferation assays showed that HBCD caused a reduction in the proliferative capacity of chondrocytes, and further work indicated that HBCD induces chondrocyte death. Further experiments demonstrated that HBCD caused an inflammatory response in chondrocytes by evaluating the levels of inflammatory factors. We found that HBCD led to PANoptosis in chondrocytes by detecting panapoptosis-related marker molecules, and experimental data indicated that apoptosis markers (cleaved caspase-3/7), pyroptosis markers (caspase-1/GSDMD-N) and necroptosis markers (pMLKL/RIPK3) were upregulated after HBCD treatment. Subsequent experiments illustrated that HBCD activated the DAMP sensor NLRP3, which then mediated ZBP1-induced PANoptosis. In the in vivo model, the experimental animals were administered HBCD at 25, 50 and 100 µg/kg/week for 15 weeks. We found that HBCD led to an inflammatory response in articular cartilage tissue. The safranin O-fast green assay showed a certain degree of damage to cartilage tissue under HBCD treatment. Furthermore, HBCD resulted in an increase in MMP13 expression and a downregulation of COL2 expression in chondrocytes/cartilaginous tissues. HBCD decreased the exercise ability of mice in vivo. These data indicate that HBCD leads to chondrocyte damage. In summary, this study lays the foundation for further exploration of the toxicological effects of HBCD on bone and joints.

Unveiling the potential of proteomics in addressing food and feed safety challenges

The food and feed sector in Europe is rapidly evolving to address contemporary challenges, striving for fairer, safer, greener and more sustainable food systems. This includes the exploration of new protein sources for human consumption and animal feed such as protein derived from insects, algae or novel plant-derived proteins, and the re-evaluation of existing sources like processed animal protein (PAP). To generate reliable data on the diverse array of emerging protein sources for future food and feed safety assessments, a growing demand for the development and implementation of advanced analytical techniques exists. New approach methodologies (NAMs) including, mass spectrometry (MS)-based proteomics methods have been emerging as valuable techniques which potentially can be implemented in regulatory laboratory settings to complement conventional approaches in this realm. These MS-driven strategies have already proven their utility in diverse applications, including the detection of prohibited substances in feed, identification of allergens, differentiation of fish species in complex mixtures for fraud detection and the verification of novel foods and alternative protein sources. This EU-FORA programme was focused on three core objectives namely: (i) the training of the fellow in utilising MS-based proteomics for food and feed safety analyses, (ii) the involvement of the fellow in the development of standardised operating procedures (SOP) for targeted and non-targeted proteomic MS-based workflows for species and tissues specific PAP identification in a national reference laboratory (NRL) and (iii) the transfer and implementation of MS-based approaches and standardised protocols for PAP analysis at the fellow's home institution. Altogether, this programme facilitates the broadening and diversification of use of MS-based proteomic methodologies for reinforcing their significance within the domains of food and feed safety research and regulatory science applications.

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.

Tetrabromobisphenol A and hexabromocyclododecane, brominated flame retardants, trigger endoplasmic reticulum stress and activate necroptosis signaling in PC12 cells

Tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD) are brominated flame retardants commonly used in a variety of industrial and consumer products. In this study, we performed RNA sequencing analysis of PC12 cells to clarify the mechanisms by which TBBPA and HBCD induce neurotoxicity. Differential expression analysis demonstrated that 636 and 271 genes were differentially expressed after TBBPA and HBCD treatment, respectively. Gene Ontology (GO) enrichment analysis revealed that genes annotated with the GO term "endoplasmic reticulum unfolded protein response" were upregulated in both TBBPA- and HBCD-treated groups. Furthermore, protein expression of endoplasmic reticulum stress markers, such as HSPA5 and DDIT3, as well as cleaved caspase-3, an apoptosis marker, were induced by TBBPA and HBCD. We also found that the cytotoxicity induced by TBBPA and HBCD was blocked by necrostatin-1, a necroptosis inhibitor, indicating the contribution of necroptosis. Our findings provide new insight into the mechanisms of toxicity induced by these chemicals.

A PBPK model describing the pharmacokinetics of γ-HBCD exposure in mice

The brominated flame retardant, hexabromocyclododecane (HBCD), is added-but not bound-to consumer products and is eventually found in the environment and human tissues. Commercial-grade HBCD mixtures contain three major stereoisomers, alpha (α), beta (β), and gamma (γ), that are typically at a ratio of 12%:6%:82%, respectively. Although HBCD is widely used, the toxicological effects from its exposure in humans are not clearly understood. Using a physiologically based pharmacokinetic (PBPK) model could help improve our understanding of the toxicity of HBCD. The aim of this work was to develop a PBPK model, consisting of five permeability limited compartments (i.e., brain, liver, adipose tissue, blood, and rest of the body), to evaluate the pharmacokinetics of γ-HBCD in C57BL/6 mice. Physiological parameters related to body size, organ weights, and blood flow were taken from the literature. All partition coefficients were calculated based on the log Kow. The elimination in urine and feces was optimized to reflect the percent dose eliminated, as published in the literature. Compared with data from the literature for brain, liver, blood, and adipose tissue, the model simulations accurately described the mouse data set within 1.5-fold of the data points. Also, two examples showing the utility of the PBPK model supplement the information regarding the internal dose that caused the health effects observed during these studies. Although this version of the PBPK model expressly describes γ-HBCD, more efforts are needed to clarify and improve the model to discriminate between the α, β, and γ stereoisomers.

Transcriptomic Analysis of the Differential Nephrotoxicity of Diverse Brominated Flame Retardants in Rat and Human Renal Cells

Brominated flame retardants (BFRs) are environmentally persistent, are detected in humans, and some have been banned due to their potential toxicity. BFRs are developmental neurotoxicants and endocrine disruptors; however, few studies have explored their potential nephrotoxicity. We addressed this gap in the literature by determining the toxicity of three different BFRs (tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD), and tetrabromodiphenyl ether (BDE-47)) in rat (NRK 52E) and human (HK-2 and RPTEC) tubular epithelial cells. All compounds induced time- and concentration-dependent toxicity based on decreases in MTT staining and changes in cell and nuclear morphology. The toxicity of BFRs was chemical- and cell-dependent, and human cells were more susceptible to all three BFRs based on IC₅₀s after 48 h exposure. BFRs also had chemical- and cell-dependent effects on apoptosis as measured by increases in annexin V and PI staining. The molecular mechanisms mediating this toxicity were investigated using RNA sequencing. Principal components analysis supported the hypothesis that BFRs induce different transcriptional changes in rat and human cells. Furthermore, BFRs only shared nine differentially expressed genes in rat cells and five in human cells. Gene set enrichment analysis demonstrated chemical- and cell-dependent effects; however, some commonalities were also observed. Namely, gene sets associated with extracellular matrix turnover, the coagulation cascade, and the SNS-related adrenal cortex response were enriched across all cell lines and BFR treatments. Taken together, these data support the hypothesis that BFRs induce differential toxicity in rat and human renal cell lines that is mediated by differential changes in gene expression.

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.

Probing the Mechanism of Hepatotoxicity of Hexabromocyclododecanes through Toxicological Network Analysis

The prediction and mechanism analysis of hepatotoxicity of contaminants, because of their various phenotypes and complex mechanisms, is still a key problem in environmental research. We applied a toxicological network analysis method to predict the hepatotoxicity of three hexabromocyclododecane (HBCD) diastereoisomers (α-HBCD, β-HBCD, and γ-HBCD) and explore their potential mechanisms. First, we collected the hepatotoxicity related genes and found that those genes were significantly localized in the human interactome. Therefore, these genes form a disease module of hepatotoxicity. We also collected targets of α-, β-, and γ-HBCD and found that their targets overlap with the hepatotoxicity disease module. Then, we trained a model to predict hepatotoxicity of three HBCD diastereoisomers based on the relationship between the hepatotoxicity disease module and targets of compounds. We found that 593 genes were significantly located in the hepatotoxicity disease module (Z = 11.9, p < 0.001) involved in oxidative stress, cellular immunity, and proliferation, and the accuracy of hepatotoxicity prediction of HBCD was 0.7095 ± 0.0193 and the recall score was 0.8355 ± 0.0352. HBCD mainly affects the core disease module genes to mediate the adenosine monophosphate-activated kinase, p38MAPK, PI3K/Akt, and TNFα pathways to regulate the immune reaction and inflammation. HBCD also induces the secretion of IL6 and STAT3 to lead hepatotoxicity by regulating NR3C1. This approach is transferable to other toxicity research studies of environmental pollutants.

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.

Organic extract of indoor dust induces estrogen-like effects in human breast cancer cells

Indoor dust often contains organic contaminants, which adversely impacts human health. In this study, the organic contaminants in the indoor dust from commercial offices and residential houses in Nanjing, China were extracted and their effects on human breast cancer cells (MCF-7) were investigated. Both dust extracts promoted proliferation of MCF-7 cells at ≤24 μg/100 μL, with cell viability being decreased with increasing dust concentrations. Based on LC₅₀, house dust was less toxic than office dust. At 8 μg/100 μL, both extracts caused more MCF-7 cells into active cycling (G2/M + S) and increased intracellular Ca²⁺ influx, with house dust inducing stronger effects than office dust. Further, the expression of estrogen-responsive genes for TFF1 and EGR3 was enhanced by 3-9 and 4-9 folds, while the expression of cell cycle regulatory genes for cyclin D was enhanced by 2-5 folds. The results suggested that organic dust extract influenced cell viability, altered cell cycle, increased intracellular Ca²⁺ levels, and activated cell cycle regulatory and estrogen-responsive gene expressions, with house dust showing lower cytotoxicity but higher estrogenic potential on MCF-7 cells. The results indicate the importance of reducing organic contaminants in indoor dust to mitigate their adverse impacts on human health.

Polymer microchamber arrays for geometry-controlled drug release: a functional study in human cells of neuronal phenotype

Polyelectrolyte multilayer (PEM) microchambers can provide a versatile cargo delivery system enabling rapid, site-specific drug release on demand.

Polyelectrolyte multilayer (PEM) microchambers can provide a versatile cargo delivery system enabling rapid, site-specific drug release on demand. However, experimental evidence for their potential benefits in live human cells is scarce. Equally, practical applications often require substance delivery that is geometrically constrained and highly localized. Here, we establish human-cell biocompatibility and on-demand cargo release properties of the PEM or polylactic acid (PLA)-based microchamber arrays fabricated on a patterned film base. We grow human N2A cells (a neuroblastoma cell line widely used for studies of neurotoxicity) on the surface of the patterned microchamber arrays loaded with either a fluorescent indicator or the ubiquitous excitatory neurotransmitter glutamate. The differentiating human N2A cells show no detrimental effects on viability when growing on either PEM@PLA or PLA-based arrays for up to ten days in vitro. Firstly, we use two-photon (2P) excitation with femtosecond laser pulses to open individual microchambers in a controlled way while monitoring release and diffusion of the fluorescent cargo (rhodamine or FITC fluorescent dye). Secondly, we document the increases in intracellular Ca²⁺ in local N2A cells in response to the laser-triggered glutamate release from individual microchambers. The functional cell response is site-specific and reproducible on demand and could be replicated by applying glutamate to the cells using a pressurised micropipette. Time-resolved fluorescence imaging confirms the physiological range of the glutamate-evoked intracellular Ca²⁺ dynamics in the differentiating N2A cells. Our data indicate that the nano-engineering design of the fabricated PEM or PLA-based patterned microchamber arrays could provide a biologically safe and efficient tool for targeted, geometrically constrained drug delivery.

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

Hexabromocyclododecane (HBCD) is a widely applied brominated flame retardant (BFR) and is regarded as a persistent organic pollutant. It has been found in human tissues and has the potential to cause neurological disorders. However, our understanding of HBCD neurotoxicity at the diastereoisomer level remains lacking. Here, we investigated the neurotoxicity of three HBCD diastereoisomers, i.e., α-, β-, and γ-HBCD, in SH-SY5Y human neuroblastoma cells. Results showed that the HBCD diastereoisomers decreased cell viability, increased lactate dehydrogenase (LDH) release, and impaired cytoskeleton development. Typical morphological features and apoptosis rates showed that the HBCD diastereoisomers induced SH-SY5Y cell apoptosis. The expression levels of several cell apoptosis-related genes and proteins, including Bax, caspase-3, caspase-9, cytochrome c, Bcl-2, and X-linked inhibitor of apoptosis (XIAP), as well as the cell cycle arrest, DNA damage, adenosine triphosphate (ATP) consumption, reactive oxygen species (ROS) levels, and intracellular calcium ion (Ca²⁺) levels, were examined. Results showed that the HBCD diastereoisomer neurotoxicity was ranked β-HBCD > γ-HBCD > α-HBCD. The cell apoptosis and caspase expression levels of the three HBCD diastereoisomers followed the same order, suggesting that caspase-dependent apoptosis may be one mechanism responsible for the structure-selective HBCD diastereoisomer neurotoxicity. The levels of intracellular Ca²⁺ and ROS increased significantly. The ROS levels were ordered β-HBCD > γ-HBCD > α-HBCD, whereas those of intracellular Ca²⁺ were γ-HBCD > β-HBCD > α-HBCD. Thus, ROS may be a key factor regulating the neurotoxicity of HBCD diastereoisomers. To the best of our knowledge, this is the first study to report on the diastereoisomer-specific toxicity of HBCD in human neural cells and on the possible mechanisms responsible for the selective neurotoxicity of HBCD diastereoisomers.

Identification and evaluation of potentially mutagenic and carcinogenic food contaminants

Heat processing of food gives rise to a plethora of chemical compounds whose toxicological effects are largely unknown. Due to a general lack of experimental toxicological data, assessing the risks associated with the consumption of these substances remains a challenge. Computer models that allow for an in silico prediction of physicochemical and toxicological characteristics, may be able to fill current data gaps and facilitate the risk assessment of toxicologically uncharacterised chemicals, their transformation products and their biological metabolites. The overall aims of the present project were for the fellow: (i) to get acquainted with the application of computational toxicological analyses tools in risk assessment based on results and experiences from previous research performed at the German Federal Institute for Risk Assessment (BfR); and (ii) to apply the newly gained skills on historic and novel data using updated and additional in silico tools. The project contributed to the continuous further education of the fellow in the use of computational toxicology tools, corroborated findings related to the safety of heat‐induced contaminants and laid the foundations for future collaborations between the fellow's home institution, the Institute of Marine Research (IMR) in Norway, and the BfR in Germany.