Endocrine effects of hexabromocyclododecane (HBCD) in a one-generation reproduction study in Wistar rats

Co-metabolic degradation and metabolite detection of hexabromocyclododecane by Shewanella oneidensis MR-1

Hexabromocyclododecane (HBCD) is a widely used brominated flame retardant; however, it is a persistent organic pollutant as well as affects the human thyroid hormones and causes cancer. However, the degradation of HBCD has received little attention from researchers. Due to its bioaccumulative and hazardous properties, an appropriate strategy for its remediation is required. In this study, we investigated the biodegradation of HBCD using Shewanella oneidensis MR-1 under optimized conditions. The Box-Behnken design (BBD) was implemented for the optimization of the physical degradation parameters of HBCD. S. oneidensis MR-1 showed the best degradation performance at a temperature of 30 °C, pH 7, and agitation speed of 115 rpm, with an HBCD concentration of 1125 μg/L in mineral salt medium (MSM). The strain tolerated up to 2000 μg/L HBCD. Gas chromatography-mass spectrometry analysis identified three intermediates, including 2-bromo dodecane, 2,7,10-trimethyldodecane, and 4-methyl-1-decene. The results provide an insightful understanding of the biodegradation of HBCD by S. oneidensis MR-1 under optimized conditions and could pave the way for further eco-friendly applications. KEY POINTS: • HBCD biodegradation by Shewanella oneidensis • Optimization of HBCD biodegradation by the Box-Behnken analysis • Identification of useful metabolites from HBCD degradation.

Low-dose polystyrene microplastics exposure impairs fertility in male mice with high-fat diet-induced obesity by affecting prostate function

The harmful effects of microplastics (MPs) on male fertility are receiving more and more attention. However, the impact of low-dose MPs exposure on the reproductive function of male mice is still unclear. In this study, we exposed male mice to low-dose MPs (25-30 μg/kg body weight/day) or low-dose MPs combined with high-fat diet (HFD) feeding. Our results showed that low-dose MPs exposure or HFD feeding significantly reduced sperm quality and the number of offspring born, while low-dose MPs exposure combined with HFD feeding further enhanced the above effects. The combination of low-dose MPs exposure and HFD feeding resulted in a notable elevation of inflammatory level within the prostate of mice and induced apoptosis of prostate epithelium and a decrease in nutrients (zinc, citrate) in seminal plasma fluid. Our findings in this study could provide valuable clues for better understanding the influence of low-dose MPs exposure on the reproductive system under metabolic disorders and facilitate the development of the prevention of reproductive toxicity caused by MPs exposure.

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.

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.

Cellular and physiological mechanisms of halogenated and organophosphorus flame retardant toxicity

Flame retardants (FRs) are chemical substances used to inhibit the spread of fire in numerous industrial applications, and their abundance in modern manufactured products in the indoor and outdoor environment leads to extensive direct and food chain exposure of humans. Although once considered relatively non-toxic, FRs are demonstrated by recent literature to have disruptive effects on many biological processes, including signaling pathways, genome stability, reproduction, and immune system function. This review provides a summary of research investigating the impact of major groups of FRs, including halogenated and organophosphorus FRs, on animals and humans in vitro and/or in vivo. We put in focus those studies that explained or referenced the modes of FR action at the level of cells, tissues and organs. Since FRs are highly hydrophobic chemicals, their biophysical and biochemical modes of action usually involve lipophilic interactions, e.g. with biological membranes or elements of signaling pathways. We present selected toxicological information about these molecular actions to show how they can lead to damaging membrane integrity, damaging DNA and compromising its repair, changing gene expression, and cell cycle as well as accelerating cell death. Moreover, we indicate how this translates to deleterious bioactivity of FRs at the physiological level, with disruption of hormonal action, dysregulation of metabolism, adverse effects on male and female reproduction as well as alteration of normal pattern of immunity. Concentrating on these subjects, we make clear both the advances in knowledge in recent years and the remaining gaps in our understanding, especially at the mechanistic level.

Dietary phytoestrogen diosgenin interrupts metabolism, physiology, and reproduction of Swiss albino mice: Possible mode of action as an emerging environmental contaminant, endocrine disruptor and reproductive toxicant

Dietary phytoestrogens are the main source of environmental contamination due to their estrogen-mimicking and endocrine-disrupting effects, posing a threat to microbial, soil, plant, and animal health. Diosgenin, a phytosteroid saponin, is used in many traditional medicines, nutraceuticals, dietary supplements, contraceptives, and hormone replacement therapies against numerous diseases and disorders. It is important to be aware of the potential risks associated with diosgenin, as well as its potential to cause reproductive and endocrine toxicity. Due to the lack of research on the safety and probable adverse side effects of diosgenin, this work evaluated the endocrine-disrupting and reproductive toxicity of diosgenin in albino mice by following acute toxicity (OECD-423), repeated dose 90-day oral toxicity (OECD-468), and F₁ extended one-generation reproductive toxicity (OECD-443) studies. Diosgenin was found to be slightly toxic, with LD₅₀ for male and female mice being 546.26 and 538.72 mg/kg, respectively. Chronic exposure of diosgenin (10, 50, 100, and 200 mg/kg) generated oxidative stress, depleted antioxidant enzymes, disturbed homeostasis of the reproductive hormones, and interrupted steroidogenesis, germ cell apoptosis, gametogenesis, sperm quality, estrous cycle, and reproductive performance in the F₀ and F₁ offspring. Long-term oral exposure of diosgenin to the mice disturbed the endocrine and reproductive functions and generated transgenerational reproductive toxic effects in F₀ and F₁ offspring. These results suggest that diosgenin should be used carefully in food products and medical applications due to its potential endocrine-disrupting and reproductive toxic effects. The findings of this study provide a better understanding of the potential adverse effects of diosgenin and the need for appropriate risk assessment and management of its use.

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.

Occurrence and tissue-specific partitioning of alternative brominated flame retardants in northwest Atlantic harbor seal pups (Phoca vitulina vitulina)

Brominated flame retardants such as polybrominated diphenyl ethers (PBDEs) have been used for decades until evidence of negative health effects led to bans in many countries. PBDEs have since been replaced by alternative legacy compounds or newly developed chemicals. In this study, eight alternative brominated flame retardants were analyzed in blubber and liver of harbor seal pups (≤6 months) from the Northwest Atlantic collected during 2001-2010 to elucidate concentrations, patterns, contamination trends, potential maternal transfer, and tissue partitioning. All compounds were detected in liver and blubber tissues with hexabromocyclododecane (HBCD) isomers and 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB) predominating. Overall, α-HBCD was the dominant HBCD isomer in both tissues although the concentrations of γ-HBCD exceeded those of α-HBCD in seven pups, indicating their mothers may have had alternative dietary patterns or recent exposure to the commercial mixture. Although it was detected in less than half of the samples, to our knowledge, this is the first study to report tetrabromobisphenol A (TBBPA) concentrations in multiple tissues of a top marine predator. For the brominated components of Firemaster® flame retardants, TBB concentrations exceeded bis-(2-ethylhexyl)-tetrabromophthalate (TBPH). This pattern may result from recent exposure to commercial mixtures in which TBB exceeds TBPH 4:1 or from differences in perinatal or lactational transfer efficiency of the two compounds. Between the two tissues, lipid-normalized β-HBCD, γ-HBCD, TBB and decabromodiphenyl ethane (DBDPE) concentrations were significantly higher in liver than blubber. This indicates that the bioaccumulation of these chemicals is not simply related to lipid dynamics but may be linked to blood proteins. This study demonstrates that harbor seal pups from this region are contaminated with alternative flame retardants passed to them via placental or lactational transfer. Given the evidence for negative health effects of these chemicals, this contamination adds additional pressure on the first year survival of these young, developing animals.

The last 50 years of organic contamination of a highly anthropized tributary of the Po River (Italy)

We examined the temporal profiles of many organic micropollutants analysed in a sediment core sampled from a highly anthropized tributary of the Po River, the Lambro River. Analysed for extractable organic halogens (EOX), total petroleum hydrocarbons (C₁₀-C₄₀TPH), polycyclic aromatic hydrocarbons (PAHs), common legacy pollutants (DDTs, PCBs), halogenated flame retardants (PBDEs, DBDPE, TBBPA-bis, TCBPA, TBBPA, HBCDs), organotins (TBT, TPhT), antimicrobials (TCS, TCC), fragrances (AHTN, HHCB) and phthalates (DMP, DEP, DnBP, BBP, DEHP, DnOP), the dated sediment core revealed the historical record of 50 years of chemical contamination discharged into the Lambro and thereby the Po River. In this regard, the peak levels of PCBs and DDTs found in Lambro sediments were also identified in other sediment cores collected from the Po River prodelta in the Adriatic Sea, thus hundreds of kilometres downstream (Combi et al., 2020). The highest risk to aquatic organisms was associated with decades of high levels of C₁₀-C₄₀ TPH, PBDEs, PCBs, PAHs, DDTs, EOX, TCC, AHTN and DEHP, which in different periods of the contamination history, showed exceedances of guideline/threshold values. C₁₀-C₄₀ TPH and TCC, for example, were very high in the 1960s, whereas PCBs, DDTs, and PBDEs, peaked from the 1980s onward. The corresponding sums of PEC quotients ranged between 0.48 and 28.63, with a mean value (±SD) for the entire recording period of 10.62 ± 9.83. Environmental legislations and improved wastewater treatments were the main drivers of the recent downward trends observed for most of the chemicals investigated. Floods in turn resulted in macroscopic yet temporary improvements in the chemical quality of the tributary, conveying contaminated sediments into the Po River.

Concentrations and isomer profiles of hexabromocyclododecanes (HBCDDs) in floor, elevated surface, and outdoor dust samples from Basrah, Iraq

Concentrations of the α, β, and γ- diastereomers of hexabromocyclododecane (α-, β-, and γ-HBCDD) were measured in 60 dust samples from 20 homes across Basrah, Iraq. From each home, two indoor dust (ID) samples (specifically one collected from elevated surfaces (ESD) and one from the floor (FD)) were collected from the living room, with one outdoor dust (OD) sample collected from the front yard of the house. Concentrations of HBCDDs decreased in the following sequence ESD > FD > OD. For ID, ΣHBCDD concentrations varied from 5.3 ng g^-1 in FD to 150 ng g^-1 in ESD, with median levels of 60 and 40 ng g^-1 in ESD and FD respectively. Concentrations of γ-HBCDD, and consequently of ΣHBCDDs in ESD, significantly (p < 0.05) exceeded those in FD. For adults, this implies that exposure assessments based on FD only may underestimate exposure, as adults are more likely to ingest ESD. Concentrations of ΣHBCDDs in OD ranged between 7.4 and 120 ng g^-1 with a median of 35 ng g^-1 and were significantly exceeded (p < 0.05) by those in ID samples. Concentrations of ΣHBCDDs in OD from houses with car parking areas exceeded (p < 0.05) those in OD from other homes, implying vehicles as potential emission sources of HBCDDs. Simultaneously, there was moderate correlation (R = 0.510-0.609, p < 0.05) between concentrations in ID and OD, implying that the indoor environment is an important source of OD contamination. The isomer pattern of HBCDDs in dust samples displayed a predominance of α-HBCDD, which represented 56%, 52% and 59% ΣHBCDD in ESD, FD and OD samples respectively. Derived from the concentrations reported in this study, the median and 95^th percentile estimated daily intakes (EDI) for Iraqi adults and toddlers through house dust ingestion did not exceed the reference dose (RfD) value for HBCDD.

Analysis of brominated flame retardants in the aquatic environment: a review

The most common and consequently analysed brominated flame retardants (BFRs) are polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), tetrabromobisphenol A (TBBPA), tetrabromobisphenol S (TBBPS), and hexabromocyclododecane (HBCD). As these persistent organic pollutants are widespread in the environment and have a number of harmful effects on human health, the production and use of most has been banned for several years. The aquatic environment is polluted by these compounds through their deposition from the atmosphere, sewage sludge, wastewater treatment plants, and landfills, and higher levels are found in areas with developed industry and agriculture and near landfills. Each compound also seems to show preference for specific compartments of the aquatic environment, i.e. water, sediment, or aquatic organisms, according to their physicochemical properties. The aim of this review was to take a closer look at the analysis of BFRs, as without reliable analysis we would not be able to determine their levels and distribution across the aquatic compartments and assess human exposure and health risks. Particularly worrying are the health risks associated with PBDEs in fish, whose levels generally exceed the permitted values.

Bone toxicity induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the retinoid system: A causality analysis anchored in osteoblast gene expression and mouse data

Dioxin exposures impact on bone quality and osteoblast differentiation, as well as retinoic acid metabolism and signaling. In this study we analyzed associations between increased circulating retinol concentrations and altered bone mineral density in a mouse model following oral exposure to 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD). Additionally, effects of TCDD on differentiation marker genes and genes involved with retinoic acid metabolism were analysed in an osteoblast cell model followed by benchmark dose-response analyses of the gene expression data. Study results show that the increased trabecular and decreased cortical bone mineral density in the mouse model following TCDD exposure are associated with increased circulating retinol concentrations. Also, TCDD disrupted the expression of genes involved in osteoblast differentiation and retinoic acid synthesis, degradation, and nuclear translocation in directions compatible with increasing cellular retinoic acid levels. Further evaluation of the obtained results in relation to previously published data by the use of mode-of-action and weight-of-evidence inspired analytical approaches strengthened the evidence that TCDD-induced bone and retinoid system changes are causally related and compatible with an endocrine disruption mode of action.

Health toxicity effects of brominated flame retardants: From environmental to human exposure

Hexabromocyclododecane (HBCD) and Tetrabromobisphenol A (TBBP-A) are brominated flame retardants widely used in variety of industrial and consumer products (e.g., automobiles, electronics, furniture, textiles and plastics) to reduce flammability. HBCD and TBBPA can also contaminate the environment, mainly water, dust, air and soil, from which human exposure occurs. This constant exposure has raised some concerns against human health. These compounds can act as endocrine disruptors, a property that gives them the ability to interfere with hormonal function and quantity, when HBCD and TBBPA bind target tissues in the body. Studies in human and animals suggest a correlation between HBCD and TBBPA exposure and adverse health outcomes, namely thyroid disorders, neurobehavior and development disorders, reproductive health, immunological, oncological and cardiovascular diseases. However, in humans these effects are still poorly understood, once only a few data evaluated the human health effects. Thus, the purpose of this review is to present the toxicity effects of HBCD and TBBPA and how these compounds affect the environment and health, resorting to data and knowledge of 255 published papers from 1979 to 2020.

A meta-analysis of factors influencing concentrations of brominated flame retardants and organophosphate esters in indoor dust

Current assessments of human exposure to flame retardants (FRs) via dust ingestion rely on measurements of FR concentrations in dust samples collected at specific points in time and space. Such exposure assessments are rendered further uncertain by the possibility of within-room and within-building spatial and temporal variability, differences in dust particle size fraction analysed, as well as differences in dust sampling approach. A meta-analysis of peer-reviewed data was undertaken to evaluate the impact of these factors on reported concentrations of brominated flame retardants (BFRs) and organophosphate esters (OPEs) in dust and subsequent human exposure estimates. Except for a few cases, concentrations of FRs in elevated surface dust (ESD) exceeded significantly those in floor dust (FD). The implications of this for exposure assessment are not entirely clear. However, they imply that analysing FD only will underestimate exposure for adults who likely rarely ingest floor dust, while analysing ESD only would overestimate exposure for toddlers who likely rarely ingest elevated surface dust. Considerable within-building spatial variability was observed with no specific trend between concentrations of either BFRs or OPEs in living rooms and bedrooms in the same homes, implying that exposure assessments based solely on sampling one room are uncertain. Substantial differences in FR concentrations were observed in different particle size fractions of dust. This is likely partly attributable to the presence of abraded polymer particles/fibres with high FR concentrations in larger particle size fractions. This has implications for exposure assessment as adherence to skin and subsequent FR uptake via ingestion and dermal sorption varies with particle size. Analysing dust samples obtained from a householder vacuum cleaner (HHVC) compared with researcher collected dust (RCD) will underestimate human exposure to the most of studied contaminants. This is likely due to the losses of volatile FRs from HHVC dust over the extended period such dust spends in the dust bag. Temporal variability in FR concentrations is apparent during month-to-month or seasonal monitoring, with such variability likely due more to changes in room contents rather than seasonal temperature variation.

Effects of a high-fat diet and global aryl hydrocarbon receptor deficiency on energy balance and liver retinoid status in male Sprague-Dawley rats

The physiological functions of the aryl hydrocarbon receptor (AHR) are only beginning to unfold. Studies in wildtype and AHR knockout (AHRKO) mice have recently disclosed that AHR activity is required for obesity and steatohepatitis to develop when mice are fed with a high-fat diet (HFD). In addition, a line of AHRKO mouse has been reported to accumulate retinoids in the liver. Whether these are universal manifestations across species related to AHR activity level is not known yet. Therefore, we here subjected wildtype and AHRKO male rats (on Sprague-Dawley background) to HFD feeding coupled with free access to 10% sucrose solution and water; controls received a standard diet and water. Although the HFD-fed rats consumed more energy throughout the 24-week feeding regimen, they did not get overweight. However, relative weights of the brown and epididymal adipose tissues were elevated in HFD-fed rats, while that of the liver was lower in AHRKO than wildtype rats. Moreover, the four groups exhibited diet- or genotype-dependent differences in biochemical variables, some of which suggested marked dissimilarities from AHRKO mice. Expression of pro- and anti-inflammatory genes was induced in livers of HFD-fed AHRKO rats, but histologically they did not differ from others. HFD reduced the hepatic concentrations of retinyl palmitate, 9-cis-4-oxo-13,14-dihydroretinoic acid and (suggestively) retinol, whereas AHR status had no effect. Hence, the background strain/line of AHRKO rat is resistant to diet-induced obesity, and AHR does not modulate this or liver retinoid concentrations. Yet, subtle AHR-dependent differences in energy balance-related factors exist despite similar weight development.

Effects of flame retardants on ovarian function

Flame retardants have been added to a variety of consumer products and are now found ubiquitously throughout the environment. Epidemiological, in vivo, and in vitro studies have shown that polybrominated diphenyl ether (PBDE) flame retardants may have a negative impact on human health; this has resulted in their phase-out and replacement by alternative flame retardants, such as hexabromocyclododecane (HBCDD), tetrabromobisphenol A (TBBPA), and organophosphate esters (OPEs). Evidence suggests that some of these chemicals induce ovarian dysfunction and thus may be detrimental to female fertility; however, the effects of many of these flame retardants on the ovary remain unclear. In this review, we present an overview of the effects of brominated and organophosphate ester flame retardants on ovarian function and discuss the possible mechanisms which may mediate these effects.

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.

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.

Assessing the cytotoxic effect of hexabromocyclododecane (HBCD) on liver tissue cultures from fathead minnow (Pimephales promelas)

Hexabromocyclododecane (HBCD) is a ubiquitous environmental contaminant of current concern despite its global ban in 2013 due to its characteristics as a persistent organic pollutant. While the toxicity of HBDC in vertebrates has been extensively studied, the specific molecular mechanisms underlying its toxicity in fish are not fully understood to date. Therefore, the aim of this work was to determine the in vitro cytotoxicity of HBCD in the fathead minnow (Pimephales promelas) using liver explants, and to investigate the molecular mechanisms underlying these effects. Explants were incubated with nine different concentrations of HBCD (0.00032, 0.0016, 0.008, 0.04, 0.2, 1, 5, 25 and 125 mg HBCD/L) for 6 and 24 h, and cytotoxicity was tested by using the Lactate Dehydrogenase (LDH) assay. The expression of genes with a key role in the regulation of apoptosis, oxidative stress, cryoprotective responses to reactive oxygen species (ROS), and xenobiotic metabolism was also measured in liver explants after exposure to 0.00032, 0.0016, 0.008, 0.2, and 25 mg HBCD/L. After 6 h, a concentration-dependent significant increase in cytotoxicity was found between 0.008 and 1 mg/L HBCD, followed by a decrease between 1 and 25 mg/L. Cytotoxicity reached 100 % at a concentration of 125 mg/L HBCD. After 24 h, HBCD showed a biphasic response with a concentration-dependent decrease in cytotoxicity between 0.0016 and 1 mg/L that returned to baseline levels at 5 mg/L. Then, cytotoxicity increased at concentrations greater than 5 mg/L to reach a maximum value at 125 mg/L. Changes in the expression of genes related to apoptosis (apoEn, apoIn, caspase2, caspase9 and bax) were also time- and concentration-dependent. Genes related to antioxidant responses such as gst and catalase were generally decreased after 6 h of incubation and increased after 24 h. The same pattern was observed for cyp1a and cyp3a, both related to xenobiotic metabolism. The expression of genes related to cryoprotective responses anti ROS (akt and pi3k) decreased at almost all HBCD concentrations tested after 6 h but remained unaltered after 24 h. Overall, we demonstrated that the cytotoxic effect of HBCD in fathead minnow liver explant was not proportional to its concentration in the culture media. Cytotoxicity was highly dynamic and did not follow a typical concentration-response pattern, complicating its toxicological characterization.

Thymoquinone protection against 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin induced nephrotoxicity in rats

We investigated the effects of thymoquinone (TQ) on kidney tissues of Wistar rats with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced nephrotoxicity. We used 50 rats divided into five groups; control, corn oil, TCDD, TQ, TCDD + TQ. We found that malondialdehyde (MDA), total oxidant status (TOS), blood urea nitrogen (BUN), creatinine, interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α) levels in the TCDD treated group increased significantly compared to the other groups, while reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT) and total antioxidant status (TAS) levels decreased in the TCDD group. In the TQ treated group, we found that GSH, SOD, CAT, TAS levels increased and MDA, TOS, IL-6 and TNF-α levels decreased compared to the other groups. The effects of TCDD on oxidative stress parameters, inflammatory markers and histological changes were ameliorated by TQ treatment.

Effects of endocrine disruptor furan on reproductive physiology of Sprague Dawley rats: An F1 Extended One-Generation Reproductive Toxicity Study (EOGRTS)

The present study investigated the reproductive toxicity of furan in an Extended One-Generation Reproductive Toxicity Study in rats. Sprague Dawley F0 weaning rats (30 per sex per group) were exposed to furan orally at 0, 1, 2.5, 5, and 10 mg kg^-1 for 10 weeks (males) and 2 weeks (females) and then mated. Results of F0 indicated that in the furan-treated groups (5 mg kg^-1 and 10 mg kg^-1), body weight (bw) gain decreased during prebreed and gestational period while increased during lactation periods. F0 animals prebreeding exposure resulted in head tilt and foot splay at 10 mg kg^-1. Number of live pups at birth were decreased (p < 0.001) at 10 mg kg^-1. At postnatal day (PND) 70, a significant (p = 0.03) decrease in testosterone levels of male rats and estrogen levels of female rats (p = 0.05) was observed in 10 mg kg^-1 furan-treated group in F1 generation. Luteinizing hormone, follicle-stimulating hormone, and progesterone levels were also reduced, but their reduction was not statistically significant in all groups. In higher dose furan group (10 mg kg^-1), testicular and ovarian weights were reduced in F1 generation at PND 70, with decreased daily sperm production (p = 0.01) and disturbed estrous cyclicity (p < 0.01). Some histopathological changes were also observed in testis and ovaries in groups whose parents were previously exposed to 10 mg kg^-1 bw of furan group. Based on the above results, it is suggested that exposure to food-based contaminant furan induced remarkable changes in the F0 (parental stage) and F1 (offspring, pubertal, and adult stage) generations of Sprague Dawley rats.

Sarcopenia negatively affects hip structure analysis variables in a group of Lebanese postmenopausal women

BACKGROUND

The current study's purpose is to compare hip structural analysis variables in a group of postmenopausal women with sarcopenia and another group of postmenopausal women with normal skeletal muscle mass index. To do so, the current study included 8 postmenopausal women (whose ages ranged between 65 and 84 years) with sarcopenia and 60 age-matched controls (with normal skeletal muscle mass index (SMI)). Body composition and bone parameters were evaluated by dual-energy X-ray absorptiometry (DXA).

RESULTS

Weight, lean mass, body mass index, femoral neck cross-sectional area (FN CSA), FN section modulus (Z), FN cross sectional moment of inertia (CSMI), intertrochanteric (IT) CSA, IT Z, IT CSMI, IT cortical thickness (CT), femoral shaft (FS) CSA, FS Z and FS CSMI were significantly greater (p < 0.05) in women with normal SMI compared to women with sarcopenia. In the whole population, SMI was positively associated with IT CSA, IT Z, IT CSMI, IT CT, FS CSA, FS Z, FS CSMI, FS CT but negatively correlated to IT buckling ratio (BR) and FS BR.

CONCLUSION

The current study suggests that sarcopenia has a negative effect on hip bone strength indices in postmenopausal women.

Exposure to HBCD promotes adipogenesis both in vitro and in vivo by interfering with Wnt6 expression

Hexabromocyclododecane (HBCD) is a widely used brominated flame retardant, and a ubiquitous environmental contaminant. However, effects and mechanisms underlying HBCD and the development of obesity remain largely unknown. Here, we investigated the effects and underlying mechanisms of HBCD on adipogenesis. Our results firstly disclosed that both murine 3T3-L1 and human HPA-V preadipocyte exposed to HBCD displayed markedly enhanced adipogenesis, manifesting with increase of triglyceride accumulation and expression of adipogenic marker genes. HBCD was further identified to play roles mainly during early-stage adipogenesis and increased expression of Pparγ, a key adipogenic regulator. Interestingly, HBCD didn't affect early key event mitotic clonal expansion (MCE), expression and activation of early pivotal factor C/EBPβ. In virtue of RNA sequencing, HBCD was further demonstrated to specially block Wnt6 gene expression and inhibited the Wnt/β-catenin pathway at an early stage of adipogenesis. Consistent with cellular finding, C57BL/6 male mice chronically exposed to HBCD exhibited specially increased epididymal white adipose tissue (eWAT) weight gain, elevated expression of master adipogenic genes and down-regulated expression of Wnt6 in eWAT. Taking together, our findings firstly revealed that HBCD promotes adipogenesis in vitro and in vivo by specifically inhibiting Wnt6 expression, presumably connecting exposure of HBCD to the development of obesity.

Mass balance study of brominated flame retardants in female captive peregrine falcons

Little is known about brominated flame retardant (BFR) dynamics in birds, especially large molecules such as decabromodiphenyl ether (BDE-209). In particular, bioaccumulation from food and transfer dynamics to eggs are poorly understood. Therefore, an input-output mass balance study of tri-decaBDEs, DBDPE and HBCDD was performed in three female peregrine falcons from a captive breeding program by analyzing their naturally contaminated food (quail, chicken (cockerels)), plasma, feces and eggs. Predominant BFRs in cockerels and quail were BDE-209 and DBDPE, as well as HBCDD in quail. The predominant BFRs found in falcon plasma were BDE-209, -153 and -183, in eggs, HBCDD, BDE-209 and -153 and in feces, BDE-209. Mean absorption efficiencies (AE) for the tetra-octabrominated BDEs ranged from 84-100% and 70% for HBCDD. The AEs for BDE-206, -207, -208 and -209 varied due to the large variability seen for feces fluxes. All egg/plasma ratios for BDEs were similar and greater than one (range 1.1-2.7), including for BDE-209, indicating efficient transfer from females to the eggs. Excretion via egg-laying was approximately 6.0-29% of the initial, pre-breeding body burden of individual penta-decaBDE congeners, (15-45% for BDE-206). HBCDD was not detected in plasma but was found in eggs, also indicating efficient transfer and excretion via eggs. Input fluxes from food exceeded the output fluxes (feces, eggs) indicating considerable metabolism for tetra-octaBDEs, possibly also for the nona-decaBDEs and HBCDD. Bioaccumulation factors calculated from lipid weight concentrations in plasma and food (BAFp) were highest for BDE-208 (31), -153 (23), -209 (19) and -207 (16) and from eggs and food (BAFe), were highest for HBCDD (140), BDE-153 (41), -208 (42), BDE-207 (24) and BDE-209 (21). BAFe and BAFp values were below 10 for BDE-47, -99 and -100. For one falcon, egg results were available from three different years and estimated half-lives were 65 d (BDE-99), 624 d (BDE-153), 31 d (BDE-154), 349 d (BDE-183), 77 d (BDE-196) and 89 d (BDE-197).

Stereoisomer specific reaction of hexabromocyclododecane with reduced sulfur species in aqueous solutions

The individual degradation rates of the three dominant stereoisomers (α, β, γ) of hexabromocyclododecane (HBCDD) with bisulfide and polysulfides were investigated at pH 9 in methanol/water solutions at two different temperatures (25 °C and 40 °C). Under all conditions investigated, α-HBCDD reacts 10 to 20 times slower with bisulfide than β-HBCDD and γ-HBCDD. The difference in reactivity of HBCDD isomers can be explained by the different populations of stable conformers with large dihedral angle between the vicinal bromine atoms. It was also observed that the reaction of HBCDD with polysulfides is about six times faster than with bisulfide. The experiments performed in solvent mixtures with increased water content at 40 °C indicated that the reaction of HBCDD with bisulfide is faster with higher percentage of water. The much slower abiotic reaction of α-HBCDD compared to β-HBCDD and γ-HBCDD could potentially contribute to the fact that α-HBCDD is more persistent in the environment than γ-HBCDD. Only one isomer of tetrabromocyclododecene (TBCDe-5) was identified as a degradation product of the reaction of HBCDD with reduced sulfur species. TBCDe-5 itself reacts about ten times slower with bisulfide and twenty times slower with polysulfide than HBCDD. The study demonstrates that polysulfides and bisulfides can reduce HBCDD sufficiently in natural anoxic environments and the dominant pathway for the degradation of HBCDD by reduced sulfur species is very likely to be the reductive debromination of vicinal dibromides via concerted anti-elimination.

Concentrations of brominated and phosphorous flame retardants in Finnish house dust and insights into children's exposure

Brominated and phosphorous flame retardants (BFRs, PFRs) are added to household and consumer products to reduce their flammability. Some FRs are persistent in the environment and may have adverse health effects. As exposure indoors contributes significantly to total exposure, we wanted to estimate the exposure of children (3 years of age) through dust ingestion, inhalation, and dermal absorption. We measured 17 BFRs and 10 PFRs in indoor dust, predicted their respective concentrations in the indoor air and assessed children's exposure. Among the BFRs, decabromodiphenyl ether (BDE-209) had highest median level in the dust (411 ng/g) followed by decabromodiphenyl ethane (DBDPE, 119 ng/g) and bis-ethylhexyl tetrabromophthalate (BEH-TEBP, 106 ng/g). Among the PFRs, trisbutoxyethyl phosphate (TBOEP) had the highest concentration (11100 ng/g) followed by tris(2-chloroisopropyl) phosphate (TCIPP, 1870 ng/g) and triphenyl phosphate (TPHP, 773 ng/g). FR concentration in air predicted from dust concentrations were within the interquartile range of experimental data for 10/13 of BFRs and 4/8 of PFRs compared. Dust ingestion was the major route of exposure (75-99%) for higher molecular weight BFRs, TBOEP and phenyl based PFRs (73-77%). Inhalation was important for volatile BFRs like pentabromobenzene (PBB 71%) and pentabromotoluene (PBT 52%) and dermal exposure for volatile chlorinated PFRs (TCEP 84%, TCIPP 77%). Margins of Exposure (MoE) were calculated as the ratio of total exposure to oral Reference Dose (RfD). MoEs were lowest for TCEP (220), TBOEP (240) and TCIPP (830), and > 1000 for all other FRs. These MoEs imply no risk for Finnish children by the studied FRs.

Hepatic transcriptional dose-response analysis of male and female Fischer rats exposed to hexabromocyclododecane

Hexabromocyclododecane (HBCD) is a brominated flame retardant found in the environment and human tissues. The toxicological effects of HBCD exposure are not clearly understood. We employed whole-genome RNA-sequencing on liver samples from male and female Fischer rats exposed to 0, 250, 1250, and 5000 mg technical mixture of HBCD/kg diet for 28 days to gain further insight into HBCD toxicity. HBCD altered 428 and 250 gene transcripts in males and females, respectively, which were involved in metabolism of xenobiotics, oxidative stress, immune response, metabolism of glucose and lipids, circadian regulation, cell cycle, fibrotic activity, and hormonal balance. Signature analysis supported that HBCD operates through the constitutive androstane and pregnane X receptors. The median transcriptomic benchmark dose (BMD) for the lowest statistically significant pathway was within 1.5-fold of the BMD for increased liver weight, while the BMD for the lowest pathway with at least three modeled genes (minimum 5% of pathway) was similar to the lowest apical endpoint BMD. The results show how transcriptional analyses can inform mechanisms underlying chemical toxicity and the doses at which potentially adverse effects occur. This experiment is part of a larger study exploring the use of toxicogenomics and high-throughput screening for human health risk assessment.

Effects of low-levels of three hexabromocyclododecane diastereomers on the metabolic profiles of pak choi leaves using high-throughput untargeted metabolomics approach

The ecological toxicity of hexabromocyclododecane (HBCD) on animals, including fish and mice, has been reported, but its effects in plants, particularly its toxic mechanism, have rarely been investigated. An untargeted metabolomics approach for comprehensive assessment was selected to study the alterations in the metabolic profiles in pak choi leaves induced by exposure to trace-level amounts of HBCD diastereomers over 30 days. A supervised orthogonal partial least-squares-discriminant analysis (OPLS-DA) was performed to investigate differences between the HBCD and control groups. The discriminating metabolites were identified using public databases. The results indicated that the toxicity of the HBCD diastereomers was ordered as γ-HBCD > α-HBCD > β-HBCD. 13 metabolites were identified as potential biomarkers to discriminate the presence of HBCD toxicity. The lipid, carbohydrate, nucleotide and amino acid metabolic pathways affected were found in accordance with animals and humans, and also HBCD could induce the interference of the secondary metabolite pathways. The system of the stress defences was activated, including signalling pathway, antioxidant defence system, shikimate and phenylpropanoid metabolism. The carbohydrate and amino acid metabolism were disturbed by HBCD intervention, and the lipid, amino acid and secondary metabolite metabolism were regulated for HBCD stress prevention. These results provide insights into the mechanism and degree of HBCD phytotoxicity.

Biomagnification of Hexabromocyclododecane (HBCD) in a coastal ecosystem near a large producer in China: Human exposure implication through food web transfer

Hexabromocyclododecane (HBCD) is a widely used brominated flame retardant which is mainly produced in China. Many HBCD facilities are located at the coast and the released HBCD may enter into the coastal ecosystem. There is a risk that HBCD can transfer through the food web to the diet of local population. Therefore, the coastal organisms near one of the biggest HBCD facilities in China were investigated. Variation was observed for the bioaccumulation of HBCD between the detrital food chain and the grazing food chain. In the studied species, the mullet was most contaminated which may be caused by its feeding on detritus. At the same time, the transfer of HBCD along the food web was investigated, and HBCD was biomagnified from the prey to the predator in the grazing food chains. Among the three diastereoisomers, α-HBCD was biomagnified with increasing trophic levels in the food web while β- and γ-HBCD were not. To assess the human dietary exposure, the dietary intake of HBCD from seafood was estimated, and the estimated daily intake (EDI) was 5.22ng/kg/day for adults, and 16.39ng/kg/day for children. The EDI for local residents were tens of times higher than that for general population in China, but the risk through dietary intake was very low in terms of existing reference dose.

Liver volatolomics to reveal poultry exposure to γ-hexabromocyclododecane (HBCD)

Hexabromocyclododecane (HBCD) is a critical emerging brominated flame retardant to which consumers can be exposed at high doses through a single food intake. Based on an animal experiment involving 3 groups of laying hens fed during 70 days with a control diet or γ-HBCD-contaminated diets at 0.1 or 10 μg γ-HBCD g^-1 feed, this study aims to use the volatolome of biological samples for revealing markers of livestock exposure to HBCD. Liquid chromatography-tandem mass spectrometry was used to monitor the time-course of HBCD levels in bodily samples. Each liver was analyzed by solid-phase microextraction-gas chromatography-mass spectrometry for volatolome profiling. After 70 days, γ-HBCD concentrations in egg yolk, fat, liver and serum reached 54 ± 4, 85 ± 6, 31 ± 6, and 32 ± 4 ng g^-1 lw, respectively, for the low exposure level and 4.6+/5.7, 7.8+/6.5, 3.9+/3.0 and 3.9+/6.1 μg g^-1 lw, respectively, for the high exposure level. Isomerization of γ-HBCD into α- and β-HBCD was observed in all tissues, at least for the high exposure level. Volatolome data allowed a significant discrimination between control and exposed animals whatever the feed contamination load, demonstrating a liver metabolic response to γ-HBCD exposure. The relevance of the twenty nine volatile exposure markers tentatively identified was discussed in light of literature data.

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

Hexabromocyclododecane (HBCD) is a brominated flame retardant (BFR) that accumulates in humans and affects the nervous system. To elucidate the mechanisms of HBCD neurotoxicity, we used transcriptomic profiling in brains of female mice exposed through their diet to HBCD (199 mg/kg body weight per day) for 28 days and compared with those of neuronal N2A and NSC-19 cell lines exposed to 1 or 2 µM HBCD. Similar pathways and functions were affected both in vivo and in vitro, including Ca²⁺ and Zn²⁺ signalling, glutamatergic neuron activity, apoptosis, and oxidative stress. Release of cytosolic free Zn²⁺ by HBCD was confirmed in N2A cells. This Zn²⁺ release was partially quenched by the antioxidant N-acetyl cysteine indicating that, in accordance with transcriptomic analysis, free radical formation is involved in HBCD toxicity. To investigate the effects of HBCD in excitable cells, we isolated mouse hippocampal neurons and monitored Ca²⁺ signalling triggered by extracellular glutamate or zinc, which are co-released pre-synaptically to trigger postsynaptic signalling. In control cells application of zinc or glutamate triggered a rapid rise of intracellular [Ca²⁺]. Treatment of the cultures with 1 µM of HBCD was sufficient to reduce the glutamate-dependent Ca²⁺ signal by 50%. The effect of HBCD on zinc-dependent Ca²⁺ signalling was even more pronounced, resulting in the reduction of the Ca²⁺ signal with 86% inhibition at 1 µM HBCD. Our results show that low concentrations of HBCD affect neural signalling in mouse brain acting through dysregulation of Ca²⁺ and Zn²⁺ homeostasis.

Changes in Flame Retardant and Legacy Contaminant Concentrations in Indoor Air during Building Construction, Furnishing, and Use

A newly constructed university building was selected for targeted assessment of changes in the levels of flame retardants and legacy contaminants during the installation of building equipment, furniture, electronics, and first year of building use. Indoor air samples were collected during several periods of intensive equipment installation to determine a relationship between newly introduced equipment and changes in the concentrations and profiles of contaminants in indoor air. Samples were analyzed for polybrominated diphenyl ethers (PBDEs), hexabromocyclododecanes (HBCDDs), and new types of flame retardants: brominated (BFRs) and organophosphate esters (OPEs). Additionally, typical outdoor contaminants such as polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were also analyzed for comparison. From the set of 90 compounds analyzed here, hexabromobenzene (HBB) and tris(2-chloroisopropyl)phosphate (TCIPP) showed a significant concentration increase in indoor air concentrations during computer installation and operation, suggesting emission by operating computers, while an order of magnitude concentration increase in tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) and tri-m-cresyl phosphate (TMTP) was observed after the furniture and carpet was introduced to the computer room, suggesting furniture or carpet as a source. However, the majority of compounds had no systematic change in concentrations during equipment installation, indicating that no sources of target compounds were introduced or, that source introduction was not reflected in indoor air concentrations. Generally, low levels of legacy flame retardants compared to their novel alternatives were observed.

Biological effects of new-generation dialkyl phosphinate flame retardants and their hydrolysates in BALB/C mice

Aluminum methylcyclohexylphosphinate (AMHP), calcium methylcyclohexylphosphinate (CMHP), aluminum diethylphosphinate (ADEP), and aluminum methylethylphosphinate (AMEP) are organic dialkyl phosphinates (DPs) and emerging phosphorus-based flame retardants. The broad-spectrum DPs flame retardants occupy high-end industrial markets, but their ecologic risk has been reported rarely. By exposing male BALB/c mice to DPs and dialkyl phosphinic acids, we studied the toxic effects of these chemicals, and measured AMHP and methylcyclohexylphosphinic acid (MHPA) in blood and feces. We found that DPs and their main hydrolysates had mild toxicity in BALB/c mice. Exposure to 10 and 50 mg/kg/d of AMEP and ADEP caused mild hepatotoxicity in mice. Toxicity of CMHP was in the liver and kidneys. Toxicity of AMHP and its hydrolysate MHPA was low and affected the liver. These data suggest that AMHP has lower toxicity than the other DPs that we tested. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1578-1586, 2017.

Toxicological characterisation of two novel selective aryl hydrocarbon receptor modulators in Sprague-Dawley rats

The aryl hydrocarbon receptor (AHR) mediates the toxicity of dioxins, but also plays important physiological roles. Selective AHR modulators, which elicit some effects imparted by this receptor without causing the marked toxicity of dioxins, are presently under intense scrutiny. Two novel such compounds are IMA-08401 (N-acetyl-N-phenyl-4-acetoxy-5-chloro-1,2-dihydro-1-methyl-2-oxo-quinoline-3-carboxamide) and IMA-07101 (N-acetyl-N-(4-trifluoromethylphenyl)-4-acetoxy-1,2-dihydro-5-methoxy-1-methyl-2-oxo-quinoline-3-carboxamide). They represent, as diacetyl prodrugs, AHR-active metabolites of the drug compounds laquinimod and tasquinimod, respectively, which are intended for the treatment of autoimmune diseases and cancer. Here, we toxicologically assessed the novel compounds in Sprague-Dawley rats, after a single dose (8.75-92.5mg/kg) and 5-day repeated dosing at the highest doses achievable (IMA-08401: 100mg/kg/day; and IMA-07101: 75mg/kg/day). There were no overt clinical signs of toxicity, but body weight gain was marginally retarded, and the treatments induced minimal hepatic extramedullary haematopoiesis. Further, both the absolute and relative weights of the thymus were significantly decreased. Cyp1a1 gene expression was substantially increased in all tissues examined. The hepatic induction profile of other AHR battery genes was distinct from that caused by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The only marked alterations in serum clinical chemistry variables were a reduction in triglycerides and an increase in 3-hydroxybutyrate. Liver and kidney retinol and retinyl palmitate concentrations were affected largely in the same manner as reported for TCDD. In vitro, the novel compounds activated CYP1A1 effectively in H4IIE cells. Altogether, these novel compounds appear to act as potent activators of the AHR, but lack some major characteristic toxicities of dioxins. They therefore represent promising new selective AHR modulators.

Screening for halogenated flame retardants in European consumer products, building materials and wastes

To fulfill national and international fire safety standards, flame retardants (FRs) are being added to a wide range of consumer products and building materials consisting of flammable materials like plastic, wood and textiles. While the FR composition of some products and materials has been identified in recent years, the limited global coverage of the data and the large diversity in consumer products necessitates more information for an overall picture of the FR composition in common products/materials. To address this issue, 137 individual samples of various consumer products, building materials and wastes were collected. To identify and characterize potential sources of FRs in indoor environment, all samples were analyzed for content of polybrominated diphenyl ethers (PBDEs), hexabromocyclododecanes (HBCDDs) and novel flame retardants (NFRs). The most frequently detected were HBCDDs (85%), with the highest median concentration of Σ₄HBCDDs of 300 mg kg^-1 in polystyrenes. The highest median concentration of Σ₁₀PBDEs was found in recycled plastic materials, reaching 4 mg kg^-1. The lowest concentrations were observed for NFRs, where the median of Σ₁₂NFRs reached 0.4 mg kg^-1 in the group of electrical & electronic equipment wastes. This suggests that for consumer products and building materials that are currently in-use, legacy compounds still contribute to the overall burden of FRs. Additionally, contrasting patterns of FR composition in recycled and virgin plastics, revealed using principle component analysis (PCA), suggest that legacy flame retardants are reentering the market through recycled products, perpetuating the potential for emissions to indoor environments and thus for human exposure.

Gender specific differences in the liver proteome of rats exposed to short term and low-concentration hexabromocyclododecane (HBCD)

The influence of short term (7-day) exposure of male rats to the brominated flame retardant hexabromocyclododecane (HBCD) was studied by investigation of the liver proteome, both in euthyroid and hypothyroid rats and by comparing results with general data on animal physiology and thyroid hormone, leptin, insulin and gonadotropin concentrations determined in parallel. Proteome analysis of liver tissue by two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) revealed that only small protein pattern changes were induced by exposure in males, on just a few proteins with different functions and not involved in pathways in common. This is in contrast to previous findings in similarly exposed eu- and hypothyroid female rats, where general metabolic pathways had been shown to be affected. The largest gender-dependent effects concerned basal concentrations of liver proteins already in control and hypothyroid animals, involving mainly the pathways which were also differently affected by HBCD exposure. Among them were differences in lipid metabolism, which - upon exposure to HBCD - may also be the reason for the considerably higher ratio of γ-HBCD accumulated in white adipose tissue of exposed female rats compared to males. The results further elucidate the already suggested different sensitivity of genders towards HBCD exposure on the protein level, and confirm the need for undertaking toxicological animal experiments in both genders.

Carcinogenetic mechanisms of endocrine disruptors in female cancers (Review)

Endocrine disruptors (EDs) are pollutants that alter the endocrine system and are involved in carcinogenesis. EDs have multiple and complex levels of action. They can affect the synthesis, release and transport of natural hormones. In target tissues, EDs can reduce or increase the effects of natural hormones on their receptors and change signaling cascades. When ED exposure happens at critical periods of life, from embryo to puberty, they can act at doses considered safe for an adult. Furthermore, their epigenetic effects can also influence the cancer risk of future generations. The cancer mechanisms of known EDs are hereby reviewed, There are thousands of newly introduced substances whose potential endocrine-disrupting and cancer effects are completely unknown. Although there are still gaps in our knowledge, these data support the urgent need for health and environmental policies aimed at protecting the public and in particular, the developing fetus and women of reproductive age.

Assessment of the occupational and environmental risks of hexabromocyclododecane (HBCD) in China

In 2013, hexabromocyclododecane (HBCD) was listed in the Stockholm Convention on Persistent Organic Pollutants obligated to be phased out worldwide. China is a major producer and user of HBCD. Based on Chinese HBCD production and processing conditions, we classified the existing 599 HBCD production and processing plants into six occupational exposure scenarios. We also used occupational environmental monitoring and occupational health risk assessment models to estimate exposure levels. Occupational internal exposure levels for HBCD in China were estimated to range from 0.61 to 840 μg kg(-1) d(-1), which suggests that approximately 453-840 workers, or 72% of all workers in this industry, may have occupational exposure risk. As such, the occupational risks of HBCD should not be ignored. In our study area, HPLC-MS/MS revealed HBCD concentrations ranging from 0.11 to 560 ng g dry weight (dw)(-1), 20.4-24.2 ng g dw(-1), and 166-1964 ng g lipid weight (lw)(-1) in soil, sediment, and biological samples, respectively, consistent with previous monitoring results. These data suggest potential risk to marine environments due to sustained and large-scale HBCD production and processing. Thus, timely measures to control HBCD-related risk are necessary and may bring significant occupational health and environmental benefits in areas where HBCD is prevalent.

NMR- and LC-MS/MS-based urine metabolomic investigation of the subacute effects of hexabromocyclododecane in mice

In the present study, both untargeted and targeted metabolomics approaches were used to evaluate the subacute effects of hexabromocyclododecane (HBCD) on mice urine metabolome. Untargeted metabolomics based on (1)H NMR showed that HBCD exposure disturbed mice metabolism in both dosed groups, especially in high dosed group. The low-dose HBCD led to a decrease in alanine, malonic acid, and trimethylamine (TMA). High-dose HBCD-treated mice developed high levels of citric acid and 2-ketoglutarate, together with decreased alanine, acetate, formate, TMA, 3-hydroxybutyrate, and malonic acid. Targeted metabolomics for metabolic profiling of 20 amino acids identified alanine, lysine, and phenylalanine as significantly disturbed metabolites. These results indicated that subchronic exposure to HBCD caused a disturbance of mice metabolism, especially in TCA cycle, lipid metabolism, gut microbial metabolism, and homeostasis of amino acids, and the application of untargeted and targeted metabolomics combined with conventional toxicology approaches to evaluate the subacute effects of pollutants will provide more comprehensive information and aid in predicting health risk of these pollutants.

New Insights into the Cytotoxic Mechanism of Hexabromocyclododecane from a Metabolomic Approach

The toxic effects of hexabromocyclododecane (HBCD) are complex, and the underlying toxicological mechanisms are still not completely understood. In this study, a pseudotargeted metabolomic approach based on the UHPLC/Q-Trap MS system was developed to assess the HBCD-intervention-related metabolic alteration in HepG2 cells. In addition, some physiologic indicators and relevant enzyme activities were measured. HBCD exposure obviously impaired metabolic homeostasis and induced oxidative stress, even at an environmentally relevant dose (0.05 mg/L). Metabolic profiling and multivariate analysis indicated that the main metabolic pathways perturbed by HBCD included amino acid metabolism, protein biosynthesis, fatty acid metabolism, and phospholipid metabolism. HBCD suppressed the cell uptake of amino acids, mainly through inhibition of the activity of membrane transport protein Na(+)/K(+)-ATPase. HBCD down-regulated glycolysis and β-oxidation of long-chain fatty acids, causing a large decrease of ATP production. As a result, the across-membrane transport of amino acids was further inhibited. Meanwhile, HBCD induced a significant increase of total phospholipids, mainly through the remodeling of phospholipids from the increased free fatty acids. The obtained metabolomic results also provided some new evidence and clues regarding the toxicological mechanisms of HBCD that contribute to obesity, diabetes, nervous system damage, and developmental disorders.

Leaching behaviour of hexabromocyclododecane from treated curtains

A series of laboratory experiments were conducted, whereby two HBCDD treated polyester curtain samples were contacted with deionised Milli-Q water as leaching fluid and HBCDD determined in the resulting leachate. As well as single batch (no replenishment of leaching fluid), serial batch (draining of leachate and replenishment with fresh leaching fluid at various time intervals) experiments were conducted. In single batch experiments at 20 °C, ΣHBCDD concentrations increased only slightly with increasing contact time (6 h, 24 h, and 48 h). This is supported by serial batch tests at 20 °C in which leaching fluid was replaced after 6 h, 24 h, 48 h, 72 h, 96 h, and 168 h. Data from these experiments show that while concentrations of HBCDD in leachate after 24 h cumulative contact time exceed those at 6 h; concentrations in samples collected at subsequent contact times remained steady at ∼50% of those in the 24 h sample. Consistent with this, leaching is shown to be second order, whereby a period of initially intense dissolution of more labile HBCDD is followed by a slower stage corresponding to external diffusion of the soluble residue within the textile. In experiments conducted at 20 °C, α-HBCDD is preferentially leached compared to β- and γ-HBCDD. However, at higher temperatures, the relatively more hydrophobic diastereomers are proportionally more readily leached, i.e. raising the temperature from 20 °C to 80 °C increased concentrations of γ-HBCDD in the leachate by a factor of 28-33 while corresponding α-HBCDD concentrations only increased by a factor of 4.3-4.8.

Hexabromocyclododecane (HBCD) induced changes in the liver proteome of eu- and hypothyroid female rats

Hexabromocyclododecane (HBCD) is a brominated flame retardant known for its low acute toxicity as observed in animal experiments. However, HBCD exposure can affect liver functioning and thyroid hormone (TH) status. As exact mechanisms are unknown and only limited toxicological data exists, a gel-based proteomic approach was undertaken. In a eu- and hypothyroid female rat model, rats were exposed to 3 and 30 mg/kg bw/day HBCD for 7 days via their diet, and exposure was related to a range of canonical endpoints (hormone status, body weight) available for these animals. Alterations in the liver proteome under HBCD exposure were determined in comparison with patterns of control animals, for both thyroid states. This revealed significantly changed abundance of proteins involved in metabolic processes (gluconeogenesis/glycolysis, amino acid metabolism, lipid metabolism), but also in oxidative stress responses, in both euthyroid and hypothyroid rats. The results provide a more detailed picture on the mechanisms involved in these alterations, e.g. at the protein level changes of the proposed influence of HBCD on the lipid metabolism. Present results show that proteomic approaches can provide further mechanistic insights in toxicological studies.

Indoor Pollutant Hexabromocyclododecane Has a Modest Immunomodulatory Effect on House Dust Mite Induced Allergic Asthma in Mice

Hexabromocyclododecane (HBCD) has been recognized as an indoor pollutant. HBCD is added as a flame retardant to many consumer products and leaches from the products into house dust. HBCD might be potentially hazardous to the airways because of inhalation of house dust. Sensitization to house dust mite (HDM) is a risk factor for the development of allergic asthma. In this study, we examined whether HBCD can affect the immune response to HDM allergens. Bone-marrow-derived dendritic cells (BMDCs) were exposed simultaneously to HBCD and HDM in vitro. HBCD enhanced oxidative stress in HDM-pulsed BMDCs, which was accompanied by a higher production of Interleukin (IL)-6 and -10. Adoptive transfer of HDM/HBCD-exposed BMDCs into naı̈ve mice resulted in enhanced levels of IL-17A after inhalational challenge with HDM. Direct mucosal exposure to HBCD during HDM inhalation enhanced IL-4 or IL-17A production, depending on the HDM extract used, but did not aggravate the eosinophilic airway inflammation or airway hyper-reactivity. Our results indicate that exposure to HBCD can have a mild immune-modulating effect by enhancing the inflammatory cytokine production in response to inhaled HDM in mice.

Exposure of Female Rats to an Environmentally Relevant Mixture of Brominated Flame Retardants Targets the Ovary, Affecting Folliculogenesis and Steroidogenesis

Brominated flame retardants (BFRs) are incorporated into various consumer products to prevent flame propagation. These compounds leach into the domestic environment, resulting in chronic exposure and contamination. Pregnancy failure is associated with high levels of BFRs in human follicular fluid, raising serious questions regarding their impact on female reproductive health. The goal of this study is to elucidate the effects of an environmentally relevant BFR mixture on female rat ovarian functions (i.e., folliculogenesis and steroidogenesis). A BFR dietary mixture formulated to mimic the relative BFR congener levels in North American house dust was administered to adult female Sprague-Dawley rats from 2 to 3 wk before mating until Gestational Day 20; these diets were designed to deliver nominal doses of 0, 0.06, 20, or 60 mg/kg/day of the BFR mixture. Exposure to BFRs triggered an approximately 50% increase in the numbers of preantral and antral follicles and an enlargement of the antral follicles in the ovaries of the dams. A significant reduction in the expression of catalase, an antioxidant enzyme, and downregulation of the expression of insulin-like factor 3 (Insl3) and 17alpha-hydroxylase (Cyp17a1) were observed in the ovary. In addition, BFR exposure affected steroidogenesis; we observed a significant decrease in circulating 17-hydroxypregnenolone and an increase in testosterone concentrations in BFR-exposed dams. Thus, BFRs target ovarian function in the rat, adversely affecting both folliculogenesis and steroidogenesis.