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

Alkyl organophosphate flame retardants (OPFRs) induce lung inflammation and aggravate OVA-simulated asthmatic response via the NF-кB signaling pathway

Alkyl organophosphate flame retardants (OPFRs), tri-n-butyl phosphate (TnBP) and tris(2-butoxyethyl) phosphate (TBOEP), are ubiquitously detected in indoor and outdoor environments and their inhalation may result in lung damage. This study examined pulmonary toxicity after exposure to TnBP or TBOEP and investigated aggravation of inflammation and immunoreaction by TnBP in an ovalbumin (OVA)-induced mice model. Transcriptomics were used to further reveal the underlying mechanism. Exposure to TnBP or TBOEP resulted in pathological damage, including edema and thickened alveolar septum. In comparison with the control, enhanced levels of superoxide dismutase (SOD) (p < 0.01 in TnBP (High) group and p < 0.05 in TBOEP (High) group), glutathione peroxidase (GSH-px) (p < 0.05), malondialdehyde (MDA) (p < 0.01), and cytokines under a dose-dependent relationship were noted, and the expression of the Fkbp5/Nos3/MAPK/NF-кB signaling pathway (p < 0.01) was upregulated in the TnBP and TBOEP groups. Moreover, the combined exposure of TnBP and OVA exacerbated the allergic inflammatory response, including airway hyperresponsiveness, leukocytosis, cellular exudation and infiltration, secretion of inflammatory mediators, and higher expression of IgE (p < 0.01). Transcriptomics results demonstrated that the PI3K/Akt/NF-кB signal pathway was involved in TnBP-aggravated asthmatic mice. Exposure to TnBP or TBOEP resulted in oxidative damage and leukocyte-induced lung injury. TnBP can further facilitate OVA-induced asthma through an inflammatory response. This study is the first to reveal the pulmonary toxicity and potential mechanism induced by OPFRs through an in-vivo model.

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.

Chlorinated Flame-Retardant Dechlorane 602 Potentiates Type 2 Innate Lymphoid Cells and Exacerbates Airway Inflammation

Chlorinated flame-retardant dechloranes are emerging substitutes for restricted flame retardants. Recent studies have demonstrated that they are accumulated in wildlife and detectable in humans; however, their effects on human health are poorly understood. Here, for the first time, we revealed that widely used chlorinated flame-retardant dechlorane 602 (Dec 602) exacerbated airway inflammation in two mouse models induced by house dust mite (HDM) or IL-33, respectively. Deteriorated airway inflammation by Dec 602 was associated with a higher production of type 2 cytokines including IL-4, IL-5, and IL-13, and IgE, accompanied by enhanced mRNA expression of proinflammatory cytokines such as TNF-α and IL-6. Mechanistically, we found that Dec 602 directly potentiated mouse and human group 2 innate lymphoid cells and, as such, promoted airway inflammation even in the absence of conventional T cells in Rag ^-/- mice. These findings provide novel immunological insights necessary for further studies of the health impact of emerging flame-retardant dechloranes including Dec 602.

Tetrabromoethylcyclohexane (TBECH) exhibits immunotoxicity in murine macrophages

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

Isomer-Specific Hexabromocyclododecane (HBCDD) Levels in Top Predator Fish from Across Canada and 36-Year Temporal Trends in Lake Ontario

Hexabromocyclododecane (HBCDD) is a high concern environmental pollutant due to its persistent, bioaccumulative, and toxic properties. The spatial distribution of HBCDD was investigated in top predator fish (lake trout, walleye, or brook trout) collected in 2013 ( n = 165) from 19 sampling sites and in 2015 ( n = 145) from 20 sites across Canada. HBCDD was measurable in at least one sample at each sampling site regardless of sampling year with the exception of walleye from the south basin of Lake Winnipeg (2013). Sampling sites in or near the Laurentian Great Lakes had greater ΣHBCDD concentrations compared to locations to the west or east. The greatest mean ΣHBCDD concentration was 72.6 ng/g lw in fish from Lake Huron-Goderich (2015). Regardless of the sampling sites, α-HBCDD was the dominant congener followed by γ-HBCDD, whereas β-HBCDD was barely detectable. In fish from the same waterbody there were comparable α/γ isomer concentration ratios. The greatest ratio was 20.8 in fish from Lake Ontario, whereas the lowest ratio was 6.3 for fish from Lac Memphrémagog (Québec) likely related to more recent emissions of a technical HBCDD mixture. Temporal trends of HBCDD in lake trout from Lake Ontario showed a significant decreasing trend for γ-HBCDD with a half-life estimate of 10 years over a 36-year period (1979-2015), and for α-HBCDD with a half-life of 11 years over the years of 2008 to 2015. The proportion of α-HBCDD to ΣHBCDD increased significantly during 1979 to 2015. The present study provided novel information on the isomer-specific HBCDDs in Canada freshwater fish.

Immunotoxicity of organophosphate flame retardants TPHP and TDCIPP on murine dendritic cells in vitro

Organophosphate flame retardants (PFRs) are commonly used as alternatives for the banned polybrominated diphenyl ethers (PBDEs) and are ubiquitously detected in indoor dust. PFRs can be potentially hazardous to respiratory health via the inhalation of house dust. Dendritic cells (DCs) are crucial in the immunological defense against pathogens in the airways. In respiratory allergy however, an aberrant immune response is induced against innocuous proteins, like house dust mite allergens. In this study, we examined whether exposure to PFRs Triphenylphosphate (TPHP) and Tris(1,3-dichloroisopropyl) phosphate (TDCIPP) affected activation/maturation of DCs at steady state and during exposure to house dust mite allergens (HDM). Bone marrow-derived dendritic cells (BMDCs) were exposed to a concentration range of each PFR (0.1-100 μM) with or without HDM in vitro to analyze the effect on the expression of major histocompatibility complex class II (MHCII), co-stimulatory molecules and cytokine production. Concentrations of TPHP and TDCIPP of ≥50 μM were cytotoxic to BMDCs. At these cytotoxic concentrations, TPHP exposure induced an activated phenotype in steady state DCs, while HDM exposed DCs acquired a tolerogenic phenotype. In contrast, TDCIPP exposure had no effect at steady state DCs but suppressed the expression of MHCII, costimulatory molecules, and the IL-6 production in HDM exposed DCs. The cytotoxic concentrations induced the anti-oxidant enzyme hemeoxigenase-1, which is a marker for oxidative stress. These results demonstrate that PFRs can be immunotoxic for DCs and suggest the necessity to evaluate the effects on the immune system on a cellular level during the risk assessment of these alternative flame retardants.

Advance of antioxidants in asthma treatment

Asthma is an allergic disease, characterized as a recurrent airflow limitation, airway hyperreactivity, and chronic inflammation, involving a variety of cells and cytokines. Reactive oxygen species have been proven to play an important role in asthma. The pathogenesis of oxidative stress in asthma involves an imbalance between oxidant and antioxidant systems that is caused by environment pollutants or endogenous reactive oxygen species from inflammation cells. There is growing evidence that antioxidant treatments that include vitamins and food supplements have been shown to ameliorate this oxidative stress while improving the symptoms and decreasing the severity of asthma. In this review, we summarize recent studies that are related to the mechanisms and biomarkers of oxidative stress, antioxidant treatments in asthma.

The Role of Mitochondria and Oxidative/Antioxidative Imbalance in Pathobiology of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a common preventable and treatable disease, characterized by persistent airflow limitation that is usually progressive and associated with an enhanced chronic inflammatory response in the airways and the lung to noxious particles or gases. The major risk factor of COPD, which has been proven in many studies, is the exposure to cigarette smoke. However, it is 15-20% of all smokers who develop COPD. This is why we should recognize the pathobiology of COPD as involving a complex interaction between several factors, including genetic vulnerability. Oxidant-antioxidant imbalance is recognized as one of the significant factors in COPD pathogenesis. Numerous exogenous and endogenous sources of ROS are present in pathobiology of COPD. One of endogenous sources of ROS is mitochondria. Although leakage of electrons from electron transport chain and forming of ROS are the effect of physiological functioning of mitochondria, there are various intra- and extracellular factors which may increase this amount and significantly contribute to oxidative-antioxidative imbalance. With the coexistence with impaired antioxidant defence, all these issues lead to oxidative and carbonyl stress. Both of these states play a significant role in pathobiology of COPD and may account for development of major comorbidities of this disease.

Indoor pollutant hexabromocyclododecane enhances house dust mite-induced activation of human monocyte-derived dendritic cells

The indoor pollutant hexabromocyclododecane (HBCD) has been added as flame retardant to many consumer products but detaches and accumulates in house dust. Inhalation of house dust leads to exposure to house dust mite (HDM) allergens in the presence of HBCD. Activation of dendritic cells is crucial in the sensitization to HDM allergens. The current study examined whether exposure to HBCD affected activation/maturation of HDM-exposed human dendritic cells (DC). Human monocyte-derived DC (moDC) were exposed simultaneously to HDM and a concentration range of HBCD (0.1-20 μM) in vitro. HDM exposure of moDC induced expression of co-stimulatory molecule CD80 and production of pro-inflammatory cytokines interleukin (IL)-6, IL-8, and tumor necrosis factor (TNF)-α. However, simultaneous exposure of moDC to HBCD and HDM enhanced the expression of antigen presenting molecule HLA-DR, co-stimulatory molecule CD86 and pro-inflammatory cytokine IL-8 depending on the dose of HBCD. Our results indicate that simultaneous exposure of HDM and HBCD can enhance the antigen presentation and maturation/activation of DC.