Mechanism of Deca-BDE-induced apoptosis in Neuro-2a cells: Role of death-receptor pathway and reactive oxygen species-mediated mitochondrial pathway

Molecular insight into the binding properties of marine algogenic dissolved organic matter for polybrominated diphenyl ethers and their combined effect on marine zooplankton

Polybrominated diphenyl ethers (PBDEs) are widespread in marine ecosystems, despite the limits placed on several congeners, and pose a threat to marine organisms. Many coexisting factors, especially dissolved organic matter (DOM), affect the environmental behavior and ecological risk of PBDEs. Since blooms frequently occur in coastal waters, we used algogenic DOM (A-DOM) from the diatom Skeletonem costatum and examined the interaction of A-DOM with 2,2',4,4'-tetrabromodiphenyl ether (BDE-47). Moreover, their combined effect on the rotifer Brachionus plicatilis was analyzed. During the stationary period, A-DOM had more proteins than polysaccharides, and 7 extracellular proteins were identified. A-DOM fluorescence was statically quenched by BDE-47, and amide, carbonyl, and hydroxyl groups in A-DOM were involved. Molecular docking analysis showed that all 5 selected proteins of A-DOM could spontaneously bind with BDE-47 and that hydrophobic interactions, van der Waals forces and pi-bond interactions existed. The reproductive damage, oxidative stress and inhibition of mitochondrial activity induced by BDE-47 in rotifers were relieved by A-DOM addition. Transcriptomic analysis further showed that A-DOM could activate energy metabolic pathways in rotifers and upregulate genes encoding metabolic detoxification proteins and DNA repair. Moreover, A-DOM alleviated the interference effect of BDE-47 on lysosomes, the extracellular matrix pathway and the calcium signaling system. Alcian blue staining and scanning electron microscopy showed that A-DOM aggregates were mainly stuck to the corona and cuticular surface of the rotifers; this mechanism, rather than a real increase in uptake, was the reason for enhanced bioconcentration. This study reveals the complex role of marine A-DOM in PBDEs bioavailability and enhances the knowledge related to risk assessments of PBDE-like contaminants in marine environments.

Toxic effects of combined exposure to homoyessotoxin and nitrite on the survival, antioxidative responses, and apoptosis of the abalone Haliotis discus hannai

Homoyessotoxin (homo-YTX) and nitrite (NO2-N), released during harmful dinoflagellate cell lysis adversely affect abalones. However, their toxicity mechanisms in shellfish remain unclear. This study investigated the economic abalone species Haliotis discus hannai exposed to varying concentrations of homo-YTX (0, 2, 5, and 10 µg L-1) and NO2-N (0, 3, and 6 mg L-1) on the basis of their 12 h LC50 values (5.05 µg L-1 and 4.25 mg L-1, respectively) and the environmentally relevant dissolved concentrations during severe dinoflagellate blooms, including mixtures. The test abalones were exposed to homo-YTX and NO2-N for 12 h. The mortality rate (D), reactive oxygen species (ROS) levels, antioxidant defense capabilities, and expression levels of antioxidant-related, Hsp-related, and apoptosis-related genes in abalone gills were assessed. Results showed that the combined exposure to homo-YTX and NO2-N increased the D and ROS levels and upregulated B-cell lymphoma-2 (BCL2)-associated X (BAX) and caspase3 (CASP3) expression levels while reducing glutathione peroxidase (GPx) activity and GPx, CuZnSOD, and BCL2 expression levels. High concentrations of homo-YTX (10 µg L-1) and NO2-N (6 mg L-1) solutions and the combinations of these toxicants inhibited the activities of superoxide dismutase (SOD) and catalase (CAT) and downregulated the expression levels of MnSOD, CAT, Hsp70, and Hsp90. The ROS levels were negatively correlated with the activities of SOD, CAT, and GPx and the expression levels of MnSOD, CuZnSOD, CAT, GPx, Hsp70, Hsp90, and BCL2. These results suggest that homo-YTX, in conjunction with NO2-N, induces oxidative stress, disrupts antioxidant defense systems, and triggers caspase-dependent apoptosis in the gills of abalone. ROS-mediated antioxidative and heat-shock responses and apoptosis emerge as potential toxicity mechanisms affecting the survival of H. discus hannai due to homo-YTX and NO2-N exposure.

A critical review on BDE-209: Source, distribution, influencing factors, toxicity, and degradation

As the most widely used polybrominated diphenyl ether, BDE-209 is commonly used in polymer-based commercial and household products. Due to its unique physicochemical properties, BDE-209 is ubiquitous in a variety of environmental compartments and can be exposed to organisms in various ways and cause toxic effects. The present review outlines the current state of knowledge on the occurrence of BDE-209 in the environment, influencing factors, toxicity, and degradation. BDE-209 has been detected in various environmental matrices including air, soil, water, and sediment. Additionally, environmental factors such as organic matter, total suspended particulate, hydrodynamic, wind, and temperature affecting BDE-209 are specifically discussed. Toxicity studies suggest BDE-209 may cause systemic toxic effects on living organisms, reproductive toxicity, embryo-fetal toxicity, genetic toxicity, endocrine toxicity, neurotoxicity, immunotoxicity, and developmental toxicity, or even be carcinogenic. BDE-209 has toxic effects on organisms mainly through epigenetic regulation and induction of oxidative stress. Evidence regarding the degradation of BDE-209, including biodegradation, photodegradation, Fenton degradation, zero-valent iron degradation, chemical oxidative degradation, and microwave radiation degradation is summarized. This review may contribute to assessing the environmental risks of BDE-209 to help develop rational management plans.

Update of the risk assessment of polybrominated diphenyl ethers (PBDEs) in food

The European Commission asked EFSA to update its 2011 risk assessment on polybrominated diphenyl ethers (PBDEs) in food, focusing on 10 congeners: BDE-28, -47, -49, -99, -100, -138, -153, -154, -183 and ‑209. The CONTAM Panel concluded that the neurodevelopmental effects on behaviour and reproductive/developmental effects are the critical effects in rodent studies. For four congeners (BDE-47, -99, -153, -209) the Panel derived Reference Points, i.e. benchmark doses and corresponding lower 95% confidence limits (BMDLs), for endpoint-specific benchmark responses. Since repeated exposure to PBDEs results in accumulation of these chemicals in the body, the Panel estimated the body burden at the BMDL in rodents, and the chronic intake that would lead to the same body burden in humans. For the remaining six congeners no studies were available to identify Reference Points. The Panel concluded that there is scientific basis for inclusion of all 10 congeners in a common assessment group and performed a combined risk assessment. The Panel concluded that the combined margin of exposure (MOET) approach was the most appropriate risk metric and applied a tiered approach to the risk characterisation. Over 84,000 analytical results for the 10 congeners 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 Lower Bound exposure to PBDEs were meat and meat products and fish and seafood. Taking into account the uncertainties affecting the assessment, the Panel concluded that it is likely that current dietary exposure to PBDEs in the European population raises a health concern.

Toxic Effects and Mechanisms of Polybrominated Diphenyl Ethers

Polybrominated diphenyl ethers (PBDEs) are a group of flame retardants used in plastics, textiles, polyurethane foam, and other materials. They contain two halogenated aromatic rings bonded by an ester bond and are classified according to the number and position of bromine atoms. Due to their widespread use, PBDEs have been detected in soil, air, water, dust, and animal tissues. Besides, PBDEs have been found in various tissues, including liver, kidney, adipose, brain, breast milk and plasma. The continued accumulation of PBDEs has raised concerns about their potential toxicity, including hepatotoxicity, kidney toxicity, gut toxicity, thyroid toxicity, embryotoxicity, reproductive toxicity, neurotoxicity, and immunotoxicity. Previous studies have suggested that there may be various mechanisms contributing to PBDEs toxicity. The present study aimed to outline PBDEs' toxic effects and mechanisms on different organ systems. Given PBDEs' bioaccumulation and adverse impacts on human health and other living organisms, we summarize PBDEs' effects and potential toxicity mechanisms and tend to broaden the horizons to facilitate the design of new prevention strategies for PBDEs-induced toxicity.

Dinoflagellate Karenia mikimotoi on the growth performance, antioxidative responses, and physiological activities of the rotifer Brachionus plicatilis

The harmful dinoflagellate Karenia mikimotoi is responsible for the mortality of aquatic animals. However, the mechanism behind these toxic effects has not been fully determined. Herein, the toxic effects of K. mikimotoi on the growth performance, antioxidative responses, physiological activities, and energetic substance contents of rotifer Brachionus plicatilis were assessed. Rotifers were exposed to Nannochloropsis salina (Eustigmatophyceae), K. mikimotoi, and a mixture of N. salina and K. mikimotoi with biomass ratio proportions of 3:1, 1:1, and 1:3, respectively. Results indicated that K. mikimotoi negatively affected the population growth, survival, and specific growth rates of rotifers within 24 h. The level of reactive oxygen species (ROS), the content of malondialdehyde, and the activity of amylase increased. However, the total antioxidant capacity level, pepsase, cellulase, alkaline phosphatase, xanthine oxidase, and lactate dehydrogenase activities, and glycogen and protein contents decreased with increasing proportions of K. mikimotoi. The mixture of 50% N. salina and 50% K. mikimotoi promoted the increase in glutamic-pyruvic transaminase activity and triglyceride content. These findings underscore ROS-mediated antioxidative responses, physiological responses, and energetic substance content changes in B. plicatilis work together to affect population dynamics inhibition of rotifers by K. mikimotoi.

Mitochondrial Dysfunction Was Involved in Decabromodiphenyl Ethane-Induced Glucolipid Metabolism Disorders and Neurotoxicity in Zebrafish Larvae

Decabromodiphenyl ethane (DBDPE), a novel brominated flame retardant, is becoming increasingly prevalent in environmental and biota samples. While DBDPE has been shown to cause various biological adverse effects, the molecular mechanism behind these effects is still unclear. In this research, zebrafish embryos were exposed to DBDPE (50-400 μg/L) until 120 h post fertilization (hpf). The results confirmed the neurotoxicity by increased average swimming speed, interfered neurotransmitter contents, and transcription of neurodevelopment-related genes in zebrafish larvae. Metabolomics analysis revealed changes of metabolites primarily involved in glycolipid metabolism, oxidative phosphorylation, and oxidative stress, which were validated through the alterations of multiple biomarkers at various levels. We further evaluated the mitochondrial performance upon DBDPE exposure and found inhibited mitochondrial oxidative respiration accompanied by decreased mitochondrial respiratory chain complex activities, mitochondrial membrane potential, and ATP contents. However, addition of nicotinamide riboside could effectively restore DBDPE-induced mitochondrial impairments and resultant neurotoxicity, oxidative stress as well as glycolipid metabolism in zebrafish larvae. Taken together, our data suggest that mitochondrial dysfunction was involved in DBDPE-induced toxicity, providing novel insight into the toxic mechanisms of DBDPE as well as other emerging pollutants.

BDE-47 Induces Immunotoxicity in RAW264.7 Macrophages through the Reactive Oxygen Species-Mediated Mitochondrial Apoptotic Pathway

Polybrominated diphenyl ethers (PBDEs) are classic and emerging pollutants that are potentially harmful to the human immune system. Research on their immunotoxicity and mechanisms suggests that they play an important role in the resulting pernicious effects of PBDEs. 2,2',4,4'-Tetrabrominated biphenyl ether (BDE-47) is the most biotoxic PBDE congener, and, in this study, we evaluated its toxicity toward RAW264.7 cells of mouse macrophages. The results show that exposure to BDE-47 led to a significant decrease in cell viability and a prominent increase in apoptosis. A decrease in mitochondrial membrane potential (MMP) and an increase in cytochrome C release and caspase cascade activation thus demonstrate that cell apoptosis induced by BDE-47 occurs via the mitochondrial pathway. In addition, BDE-47 inhibits phagocytosis in RAW264.7 cells, changes the related immune factor index, and causes immune function damage. Furthermore, we discovered a significant increase in the level of cellular reactive oxygen species (ROS), and the regulation of genes linked to oxidative stress was also demonstrated using transcriptome sequencing. The degree of apoptosis and immune function impairment caused by BDE-47 could be reversed after treatment with the antioxidant NAC and, conversely, exacerbated by treatment with the ROS-inducer BSO. These findings indicate that oxidative damage caused by BDE-47 is a critical event that leads to mitochondrial apoptosis in RAW264.7 macrophages, ultimately resulting in the suppression of immune function.

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

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

Transcriptome and biochemical analyses of rainbow trout (Oncorhynchus mykiss) RTG-2 gonadal cells in response to BDE-47 stress indicates effects on cell proliferation

2,2',4,4'-Tetrabromodiphenyl ether (BDE-47) is a biotoxin of polybrominated diphenyl ether (PBDEs) frequently detected in the environment. Apoptosis and cell cycle arrest are important toxic phenomena of xenobiotics that inhibit cell proliferation. In this study, we investigated the effects of BDE-47 (5 μM, 10 μM, 20 μM, 40 μM) on cell viability, morphology, cell cycle and apoptosis. BDE-47 significantly decreased cell viability, and morphological alterations were observed. The significant increase in cells at G1 phase indicated the occurrence of G1 phase cell cycle arrest in RTG-2 cells. An acridine orange and ethidium bromide (AO/EB) staining assay was employed and revealed the induction of apoptosis in RTG-2 cells. The results indicated that BDE-47 exposure inhibits cell proliferation. Transcriptome analysis was applied for further evidence. A total of 1300 differentially expressed genes (DEGs) were identified in RTG-2 cells, among which 26 DEGs were associated with the cell cycle and apoptosis. Western blotting and qPCR analyses also showed the expression of cell cycle- and apoptosis-related proteins and genes. Mapping the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, p53, Tumor necrosis factor (TNF), Mitogen-activated protein kinase (MAPK), phosphatidylinositide 3-kinase-AKT (PI3K-AKT), and reaction oxygen species (ROS)-mediated signaling pathways were determined to be the major pathways involved in modulating the cell cycle and apoptosis. Since we demonstrated simultaneous ROS overproduction during BDE-47 exposure in a previous study, we speculated a possible explanation for the observation: BDE-47-induced ROS overproduction was the initiating signal, which activated cell cycle arrest and apoptosis and finally inhibited cell proliferation.

Reduced mitochondrial DNA copy number in occupational workers from brominated flame retardants manufacturing plants

Decabrominated diphenyl ether (BDE-209) and its substitute decabromodiphenyl ethane (DBDPE) are two flame retardants that have similar structure and are widely used in various industrial products. The accumulation and potential toxicity of them to human health have already aroused attention, and some research showed that they may affect mitochondrial function. Therefore, this study focused on the population with high exposure to brominated flame retardants (BFRs) and the related changes in mtDNA copy number (mtDNAcn) in whole blood. 334 blood samples were collected from three groups of people in Shandong Province, including 42 BDE-209 occupational exposure workers from the BDE-209 manufacturing plant, 131 DBDPE occupational exposure workers from the DBDPE manufacturing plant, and 161 non-BFRs occupational exposure residents from the BFRs contaminated area. We measured the levels of BDE-209, DBDPE in serum sample, and the mtDNAcn in whole blood sample and analyzed these data by multiple linear regression. The average concentrations of BDE-209, DBDPE and ∑(BDE-209 + DBDPE) in BDE-209 occupational workers were 3510, 639 and 4600 ng/g lw, respectively; the average concentrations of BDE-209, DBDPE and ∑(BDE-209 + DBDPE) in DBDPE occupational workers were 229, 4040 and 4470 ng/g lw, respectively; the average concentrations of BDE-209, DBDPE and ∑(BDE-209 + DBDPE) in non-BFRs occupational exposure residents were 66.3, 45.7 and 137 ng/g lw, respectively. The relative mtDNAcn was 0.823 in BDE-209 occupational workers, 0.845 in DBDPE occupational workers and 0.989 in non-BFRs occupational exposure residents. A 10-fold increase in BDE-209, DBDPE concentrations was separately associated with a 0.068 and 0.063 decrease in mtDNAcn. Therefore, our study implied that BFRs may affect mitochondrial function. As increasing BFRs exposure has emerged in recent years, the relationship between BFRs exposure and mitochondrial function needs further study.

The Bloom-Forming Dinoflagellate Karenia mikimotoi Adopts Different Growth Modes When Exposed to Short or Long Period of Seawater Acidification

Impacts of ocean acidification (OA) on noncalcifying organisms and the possibly responsible mechanism have aroused great research interests with the intensification of global warming. The present study focused on a noxious, noncalcifying, bloom-forming dinoflagellate, Karenia mikimotoi (K. mikimotoi), and its variation of growth patterns exposed to different periods of seawater acidification with stressing gradients was discussed. The dinoflagellates under short-time acidifying stress (2d) with different levels of CO₂ presented significant growth inhibition (p < 0.05). The cell cycle was obviously inhibited at S phase, and the photosynthetic carbon fixation was also greatly suppressed (p < 0.05). Apoptosis was observed and the apoptotic rate increased with the increment of pCO₂. Similar tendencies were observed in the key components of mitochondrial apoptotic pathway (the mitochondrial membrane potential (MMP), Caspase-3 and -9, and Bax/Bcl-2 ratio). However, under prolonged stressing time (8 d and 15 d), the growth of dinoflagellates was recovered or even stimulated, the photosynthetic carbon fixation was significantly increased (p < 0.05), the cell cycle of division presented little difference with those in the control, and no apoptosis was observed (p > 0.05). Besides, acidification adjusted by HCl addition and CO₂ enrichment resulted in different growth performances, while the latter had a more negative impact. The results of present study indicated that (1) the short-time exposure to acidified seawater led to reduced growth performance via inducing apoptosis, blocking of cell cycle, and the alteration in photosynthetic carbon fixation. (2) K. mikimotoi had undergone adaptive changes under long-term exposure to CO₂ induced seawater acidification. This further demonstrated that K. mikimotoi has strong adaptability in the face of seawater acidification, and this may be one of the reasons for the frequent outbreak of red tide. (3) Ions that dissociated by the dissolved CO₂, instead of H⁺ itself, were more important for the impacts induced by the acidification. This work thus provides a new perspective and a possible explanation for the dominance of K. mikimotoi during the occurrence of HABs.

Nephrotoxicity and possible mechanisms of decabrominated diphenyl ethers (BDE-209) exposure to kidney in broilers

The flame retardant decabrominated diphenyl ether (BDE-209) is a widely used chemical in a variety of products and exists extensively in the environment. BDE-209 has been reported to induce kidney injury and dysfunction. However, the causes and mechanisms of its nephrotoxicity are still under investigation. In this study, 150 male broilers were exposed to BDE-209 concentrations of 0, 0.004, 0.04, 0.4, 4.0 g/kg for 42 days. The relative kidney weight, histopathology, markers of renal injury, oxidative stress, inflammation, apoptosis and the expression of MAPK signaling pathways-related proteins were assessed. The results showed that the concentrations of blood urea nitrogen (BUN), creatinine (CRE) and the neutrophil gelatinase-associated lipocalin (NGAL), significantly increased after exposure to BDE-209 with the doses more than 0.04 g/kg. Similarly, severe damage of renal morphology was observed, including atrophy and necrosis of glomeruli, and swelling and granular degeneration of the renal tubular epithelium. In the renal homogenates, the oxidative stress was evidenced by the elevated concentrations of MDA and NO, and decreased levels of GSH-Px, GSH and SOD. Due to the inflammatory response, the level of NF-κB and the pro-inflammatory cytokines TNF-α, IL-1β, IL-18 were remarkably upregulated, while the content of the anti-inflammatory cytokine IL-10 decreased. Additionally, the apoptotic analysis showed notable upregulations of Bax/Bcl-2 ratio, the relative expression of p-ERK1/2 and p-JNK1/2, and the expression of Bax, cytochrome c and caspase 3. The present study indicates that BDE-209 exposure can cause nephrotoxicity in broilers through oxidative stress and inflammation, which activate the phosphorylation of key proteins of the MAPK signaling pathways, and subsequently induce mitochondria-mediated kidney apoptosis.

Cellular changes of microbial consortium GY1 during decabromodiphenyl ether (BDE-209) biodegradation and identification of strains responsible for BDE-209 degradation in GY1

Microbial consortium remediation has been considered to be a promising technique for BDE-209 elimination in water, soil and sediment. Herein, we studied malondialdehyde (MDA), membrane potential (MP), and reactive active species (ROS) of a microbial consortium GY1 exposed to BDE-209. The results indicated that the microbial antioxidant defense system was vulnerable by BDE-209. Both early and late apoptosis of microbial consortium induced by BDE-209 were observed. The sequencing results revealed that Stenotrophomonas, Microbacterium and Sphingobacterium in GY1 played major roles in BDE-209 degradation. Moreover, a novel facultative anaerobic BDE-209 degrading strain named Microbacterium Y2 was identified from GY1, by which approximately 56.1% of 1 mg/L BDE-209 was degraded within 7 days, and intracellular enzymes of which contributed great to the result. Overall, the current study provided new insights to deeply understand the mechanisms of BDE-209 degradation by microbial consortium.

Regulation of TBBPA-induced oxidative stress on mitochondrial apoptosis in L02 cells through the Nrf2 signaling pathway

Tetrabromobisphenol A (TBBPA) is a commonly used brominated flame retardant, which has a wide range of toxic effects on organisms. This study investigated the cytotoxic effects on human hepatocytes (L02 cells) after treated with 0, 5, 10, 20, and 40 μM of TBBPA. Results showed that TBBPA significantly increased intracellular reactive oxygen species (ROS), malondialdehyde (MDA) and the ratio of oxidized/reduced glutathione (GSSG/GSH) dose-dependently. TBBPA also decreased the cell mitochondrial membrane potential (MMP), caused the release of cytochrome C (Cyt C) to cytoplasm and promoted the expression of caspase-9 and caspase-3, and finally increased the level of apoptosis. The ROS inhibitor N-acetyl-L-cysteine (NAC) relieved the oxidative stress responses, and prevented the decrease of MMP and increase of apoptosis. In addition, TBBPA promoted the expression of antioxidant genes related to Nrf2, such as quinone oxidoreductase 1 (NQO1), catalase (CAT), and heme oxygenase 1 (HO-1). Oxidative stress initiated by TBBPA, activated mitochondrial apoptosis and Nrf2 pathway, and increased the degree of apoptosis in L02 cells.

Reactive oxygen species (ROS) and the calcium-(Ca2+) mediated extrinsic and intrinsic pathways underlying BDE-47-induced apoptosis in rainbow trout (Oncorhynchus mykiss) gonadal cells

The brominated flame retardant, 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), is well documented to exert potential negative impacts on different marine biota. However, the responsible mechanism remains unknown. The rainbow trout gonadal cell line RTG-2 was used as a model, and the mechanism and pathway underlying BDE-47 (6, 12.5 and 25 μM)-induced apoptosis and toxicity were examined in vitro. Apoptosis occurred in the RTG-2 cells exposed to BDE-47 in a clear concentration-dependent manner. The morphology of the mitochondrial alterations was observed using transmission electron microscopy. BDE-47 exposure decreased the cellular mitochondrial membrane potential, increased the cytochrome c released into the cytoplasm and elevated Fas protein expression. The mRNA expressions of Fas-associated death domain-containing protein (FADD), CHOP and GRP78 were also elevated, and similar increases were found in the activities of intracellular caspase-8, caspase-12, caspase-9 and caspase-3. These results indicated that the mitochondrial, endoplasmic reticulum and death-receptor pathways were involved in apoptosis in RTG-2 cells following BDE-47 exposure. ROS and Ca²⁺ were responsible for these changes because their overproduction was detected prior to apoptosis. However, the addition of the ROS scavenger N-acetyl-l-cysteine (NAC) and the intracellular calcium chelator (acetoxymethyl)-1,2-bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM) did not significantly alleviate the apoptosis rate. The results of the present study show that BDE-47 exposure induced apoptosis in RTG-2 cells via ROS- and Ca²-mediated mitochondrial, endoplasmic reticulum and death-receptor apoptotic pathways.

Delineation of 3D dose-time-toxicity in human pulmonary epithelial Beas-2B cells induced by decabromodiphenyl ether (BDE209)

Due to frequent detection in environment as well as in the human body, the adverse effects of decabromodiphenyl ether (BDE209) have been extensively studied in the past few years. However, information regarding the inhalation toxicity of BDE209 to humans is currently limited. In this study, the cytotoxicity, cell damage, and inflammation markers including IL-6, IL-8, and TNF-α in the Beas-2B cell line induced by BDE209 were measured using a central composite design. Results showed that as BDE209 concentrations (5-65 μg mL^-1) and exposure time (6-30 h) were increased, cell viability sharply decreased from 99.7% to 29.7% and LDH activity increased from 0.1% to 13.1%. Furthermore, expression of IL-6, IL-8 and TNF-α transcripts were enhanced from 4.7 to 29.1 fold, 3.4-68.9 fold, and 2.8-47.0 fold, respectively, and the concentration of IL-6 and IL-8 proteins increased from 5.4 to 16.7 pg mL^-1 and 71.0-550.0 pg mL^-1, respectively. Results indicate that BDE209 exposure can inhibit cell viability, increase LDH leakage, and upregulate the transcript (mRNA) and protein levels of inflammatory markers of IL-6 and IL-8 in Beas-2B cells. Moreover, these effects were both dose- and time-dependent, and dose and time had a synergistic effect - enhancing toxicity when in combination. Cell density affected both LDH activity and IL-8 release but had little effect on cell activity and IL-6 release in the Beas-2B cells. In contrast, TNF-α protein was not detected but its mRNA expression level was upregulated. This study will provide a reference for human health risk assessment, especially for the toxic damage that BDE209 exposure can elicit in the respiratory tract.

Role of Taurine in BDE 209-Induced Oxidative Stress in PC12 Cells

Polybrominated diphenyl ethers (PBDEs) are globally dispersed throughout the environment, and the levels of some PBDEs in the environment may still be increasing. Previous studies showed that BDE 209 exerted neurodevelopmental and neurobehavioral effects in humans and animals. Oxidative stress is a common mechanism reported in PBDEs-induced neurotoxicity. Taurine, as an antioxidant, whether it is effective in alleviating BDE 209-induced neurotoxicity is still unknown. PC12 cells were exposed to various concentrations of BDE 209 (6.25, 12.5, 25, 50, and 100 μM). 3-(4,5-Dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay was used to assess the cell viability. 2',7'-Dichlorofluorescin diacetate (DCFH-DA) detector was used to explore the production of ROS. Acridine orange was used to reflect the permeation of lysosomal membrane. Rhodamine 123 was used to reflect the permeation of mitochondrial membrane. Lactate dehydrogenase and catalase in PC12 cells exposed to BDE 209 were examined by kits. The results showed that taurine could significantly reverse the decreased viability, the serious oxidative stress and abnormal autophagy in PC12 cells exposed to BDE 209. Collectively, our results indicated that taurine could protect PC12 cells from BDE 209-induced neurotoxicity by alleviating oxidative stress.

Effect of 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47) and its metabolites on cell viability, oxidative stress, and apoptosis of HepG2

2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47), an extensively used brominated flame retardant (BFR), is frequently detected in biotic environments. To date, studies have reported that BDE-47 induces hepatotoxicity, reproductive toxicity, and neurotoxicity in vitro. However, little is known regarding BDE-47 metabolites-mediated cell toxicity in relevant human cell models. The cytotoxic effects of BDE-47 and its eight metabolites on hepatoblastoma cell line-HepG2 cells were investigated in this study. We found that BDE-47 and all its metabolites inhibited cell viability in both a dose- and time-dependent manner. For BDE-47 and its debromination products (BDE-28 and BDE-7), they had less severe effects on cell viability when the cells were pretreated with lower dose of the same compound, however, no significant difference was observed in control, suggesting that low concentrations have an adaptation effect on HepG2 cells. BDE-47 and its metabolites also induce changes in ROS generation, SOD and GSH activity, cell cycle regulation, DNA damage and cell apoptosis, indicating that the toxicity mechanisms of BDE-47 and its degradation products are mediated by oxidative stress, DNA damage and cell cycle dysregulation. Moreover, brominated phenol products (2,4-DBP and 4-BP) posed the highest toxic effects on HepG2, followed by hydroxylated products (6-OH-BDE-47, 5-OH-BDE-47, 2-OH-BDE-28, and 4-OH-BDE-17), and BDE-47 and its debromination products were comparatively less toxic to HepG2 cells. Taken together, these results demonstrate the hepatotoxic potential of BDE-47 and its metabolites.

A ROS-mediated mitochondrial pathway and Nrf2 pathway activation are involved in BDE-47 induced apoptosis in Neuro-2a cells

Our previous study showed that 2,2'-,4,4'-tetrabromodiphenyl ether (BDE-47) is cytotoxic and induces apoptosis in Neuro-2a cells. In the present study, we aimed to investigate whether nuclear factor (erythroid-derived 2)-like 2 (Nrf2), an antioxidant transcriptional regulator of oxidative stress and apoptosis, is involved in this process. The results of toxicological experiments showed that BDE-47 decreased the cellular mitochondrial membrane potential (MMP) and increased cytochrome c release to the cytoplasm, followed by an increase in intracellular caspase-9 and caspase-3 activity, suggesting that a mitochondrial pathway was involved in the apoptotic process. Intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) contents as well as the oxidized/reduced glutathione (GSSG/GSH) ratio were elevated simultaneously in a concentration-dependent manner, indicating that BDE-47 induced oxidative stress. The ROS scavenger N-acetyl-l-cysteine (NAC) not only alleviated the oxidative stress but also blocked apoptosis and the decrease in MMP induced by BDE-47, indicating that the overproduction of ROS participates in a mitochondria-mediated apoptotic pathway. Moreover, BDE-47 stimulated the transcriptional induction of the Nrf-2 gene and induced mRNA expression of the main antioxidant response genes in the Nrf-2 pathway, including heme oxygenase 1 (HO-1), NAD(P)H/quinone oxidoreductase-1 (NQO1), glutamate-cysteine ligase modifier (GCLM) and glutathione peroxidase (GPX). Additionally, NAC and the p38 mitogen activated protein kinase (MAPK) signaling pathway inhibitor SB 203580 greatly reduced Nrf2 and HO-1 induction. We hypothesized that the ROS mediated mitochondrial pathway is involved in the BDE-47-induced apoptosis in Neuro-2a cells and that the Nrf2 pathway helps protect Neuro-2a cells from BDE-47-induced apoptosis.

BDE-47 and BDE-209 inhibit proliferation of Neuro-2a cells via inducing G1-phase arrest

Cell proliferation is closely related to cell cycle which is strictly regulated by genes and regulatory proteins. In the present study, we comparatively analyzed the toxic effects of BDE-47 and BDE-209 on cell proliferation of Neuro-2a cells, and the possible mechanism was discussed. The results indicated that BDE-47 significantly inhibited the cell proliferation and the cell cycle were arrest at G1 phase, while BDE-209 had little effects on either cell proliferation or cell cycle. qRT-PCR and Western blot assay presented that BDE-47 up-regulated the gene expressions of p53 and p21, which down-regulated the expresseion of cyclinD1 and CDK2, and inhibited retinoblastoma protein (pRb) phosphorylation. This process could effectively arrest the cell cycle at G1 phase, which finally caused the inhibition on Neuro-2a cell proliferation. However, BDE-209 was only up-regulated the gene expressions of p53, also suggested to be involved in the inhibition on Neuro-2a cell proliferation.