Oxidative stress and renal toxicity after subacute exposure to decabrominated diphenyl ether in Wistar rats

Selenomethionine alleviates decabromodiphenyl ether-induced oxidative stress and ferroptosis via the NRF2/GPX4 pathway in the chicken brain

Decabromodiphenyl ether (BDE209) is a toxic environmental pollutant that can cause neurotoxicity, behavioral abnormalities, and cognitive impairment in animals. However, the specific mechanisms of BDE209-induced neurological injury and effective preventative and therapeutic interventions are lacking. Even though selenomethionine (Se-Met) has a significant detoxification effect and protects the nervous system, it remains unclear whether Se-Met can counteract the toxic effects of BDE209. For the in vivo test, we randomly divided 60 1-week-old hy-line white variety chicks into the Con, BDE209, Se-Met, and BDE209 +Se-Met groups. In vitro experiments were performed, exposing chick embryo brain neurons to BDE209, Se-Met, N-Acetylcysteine (NAC, a ROS inhibitor), and RSL3 (a GPX4 inhibitor). We demonstrated that BDE209 induced oxidative stress and ferroptosis in the chicken brain, which mainly manifested as mitochondrial atrophy, cristae breakage, increased Fe2+ and MDA content, decreased antioxidant enzyme activity, and the inhibition of the NRF2/GPX4 signaling pathway in the brain neurons. However, Se-Met supplementation reversed these changes by activating the NRF2/GPX4 pathway, reducing mitochondrial damage, enhancing antioxidant enzyme activity, and alleviating ferroptosis. This study provides insight into the mechanism of BDE209-related neurotoxicity and suggests Se-Met as an effective preventative and control measure against BDE209 poisoning.

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.

Oxidative damage in the Vesper mouse (Calomys laucha) exposed to a simulated oil spill-a multi-organ study

Small wild mammals have been used to measure the damage caused by exposure to oil-contaminated soil, including deer mice. However, the study of toxic effects of crude oil using oxidative damage biomarkers in the wild rodent Calomys laucha (Vesper mouse) is absent. This investigation aimed to evaluate the effects of acute exposure to contaminated soil with different concentrations of crude oil (0, 1, 2, 4 and 8% w/w), simulating an accidental spill, using oxidative stress biomarkers in the liver, kidneys, lungs, testes, paw muscle, and lymphocytes of C. laucha. Animals exposed to the contaminated soil showed increases in lipid peroxidation and protein carbonylation at the highest exposure concentrations in most organ homogenates analyzed and also in blood cells, but responses to total antioxidant capacity were tissue-dependent. These results showed that acute exposure to oil-contaminated soil caused oxidative damage in C. laucha and indicate these small mammals may be susceptible to suffer the impacts of such contamination in its occurrence region, threatening the species' survival.

Time dependent cisplatin dosing differences on hypoalgesia focusing on oxidative stress

Although cisplatin is a key drug in cancer chemotherapy, it often causes sensory peripheral neuropathy, presenting as allodynia in the early stage and hypoalgesia in the serious stage. Chronotherapy has previously been shown to ameliorate cisplatin-induced peripheral neuropathy that was severe enough to cause hypoalgesia in rats. It also has adverse effects such as renal dysfunction and ototoxicity, which are induced by oxidative stress. Here, we show that oxidative stress causes severe cisplatin-induced peripheral neuropathy, and that differences in oxidative stress occur depending on the dosing time of cisplatin. Cisplatin was administered to rats at 5:00 or 17:00 every seven days for four weeks. The antioxidant agent, 1,3-Dimethylthiourea (DMTU), was administered before and after the administration of cisplatin. The hot plate test was used to assess hypoalgesia. Oxidative stress in the sciatic nerve was assessed from thiobarbituric acid reactive substances (TBARs) and superoxide dismutase (SOD) activity. Nerve apoptosis was analysed with qRT-PCR. We observed an increase in TBARs and a decrease in SOD activity with the development of cisplatin-induced hypoalgesia, which was ameliorated by DMTU treatment. Furthermore, differences in the dosing time of cisplatin caused differences in oxidative stress which were correlated with cisplatin-induced hypoalgesia. Severe oxidative stress caused cisplatin-induced hypoalgesia, and chronotherapy with cisplatin ameliorated hypoalgesia by reducing oxidative stress. In the future, chronotherapy with cisplatin may contribute to the treatment of cancer in humans.

New insight into the perplexing toxic features of PCBs: A study of nephrotoxicity in an animal model

The present study investigated the effects of PCBs on the rat kidneys with attention given to the determination critical effect dose (CED) using the Benchmark dose (BMD) approach. Male albino Wistar rats (7 animals per group) were given by oral gavage Aroclor 1254 dissolved in corn oil at doses of 0.0, 0.5, 1, 2, 4, 8, or 16 mg/kg b.w./day for 28 days. The PCB nephrotoxicity was manifested by a dose-dependent changes in serum urea levels. The study has also revealed PCB-induced oxidative stress induction in kidneys. The observed nephrotoxic effects can be partly explained by oxidative damage of lipids and proteins in the kidneys due to observed reduced CuZnSOD activity and disturbances in antioxidant protection. Аll the renal oxidative stress parameters showed dependence on PCB oral doses as well as internal, measure kidney PCB levels. Calculated BMDL values were lower than estimated no observed adverse effect levels (NOAEL) based on the study, suggesting the importance of BMD approach use in future risk assessment.

Use of enzymatic biomarkers of Labeo rohita to study the effect of polybrominated diphenyl ether (BDE- 209) via dietary exposure in laboratory conditions

Fishes have been widely used as a representative to estimate the health of an aquatic ecosystem. In the present study, Labeo rohita was selected for biomarker study against decabromodiphenyl ether (BDE-209), a persistent organic pollutant (POP), as it is a widely used Indian carp. The results suggested significant effects on the optimum metabolism of Labeo rohita. After 48 to 72 h of exposure, most of the biomarkers such as lactate dehydrogenase (LDH), creatine kinase (CK), serum glutamic pyruvic transaminase (SGPT), serum glutamic oxaloacetic transaminase (SGOT), and hepatosomatic index (HSI) increased drastically indicating the higher index of tissue and liver damage. On the contrary, succinic dehydrogenase (SDH), acetylcholinesterase (AChE), and alkaline phosphatase (ALP) showed a reverse trend suggesting the shifting of fish metabolism towards anaerobic respiration mode because of induced stress. Increased catalase (CAT) activity was also observed, which indicated increased abundance of reactive hydroxyl species and therefore a possible oxidative stress in fishes. It is further suggested to understand and examine the biotransformation characteristics and degradation pathways of polybrominated diphenyl ether (PBDE)s, which would be useful to comprehend their environmental fate.

Oxidative stress and endoplasmic reticulum stress contributed to hepatotoxicity of decabromodiphenyl ethane (DBDPE) in L-02 cells

Decabromodiphenyl ethane (DBDPE) is one of the most commonly used novel brominated flame retardants (NBFRs), and its mass production and widespread application have caused health threats to the human being. Existing studies have shown that DBDPE has hepatotoxicity. And we have found that DBDPE could change cytochrome P450 3A (CYP3A) expression levels in rat livers, whereas the mechanism is unclear. In this study, we exposed human normal hepatocyte (L-02) to DBDPE to further study the effect and mechanism of DBDPE on hepatocellular injury and liver metabolic enzyme CYP3A changes in vitro. The results showed that DBDPE caused L-02 cell viability decrease, lactate dehydrogenase (LDH) and transaminase release, ultrastructural damage, and apoptosis. Moreover, DBDPE exposure induced oxidative stress (i.e., increased ROS generation and MDA levels and decreased GSH content, SOD activity, and mitochondrial membrane potential) and endoplasmic reticulum (ER) stress in L-02 cells as evidenced by the elevated PERK and IRE-1α expression levels. These results confirmed that DBDPE is toxic to hepatocytes. Besides, the CYP3A expression level was decreased in DBDPE exposed L-02 cells. However, pretreatment of L-02 cells with antioxidant N-Acetyl-l-cysteine (NAC) and endoplasmic reticulum stress inhibitor 4-PBA inhibited DBDPE-induced oxidative stress, endoplasmic reticulum stress, CYP3A expression decrease, and apoptosis. Therefore, we demonstrated that DBDPE could exert toxic effects and decrease CYP3A expression on L-02 cells by inducing ER stress and oxidative stress.

Oxidative stress, metallomics and blood toxicity after subacute low-level lead exposure in Wistar rats: Benchmark dose analyses

Exposure to lead (Pb) is still rising concern worldwide, having in mind that even low-dose exposure can induce various harmful effects. Thus, in-depth knowledge of the targets of Pb toxicity and corresponding mechanisms is essential. In the presented study, the six groups (male Wistar rats, n = 6) received 0.1; 0.5; 1; 3; 7; 15 mg Pb/kg body weight/day for 28 days, each day by oral gavage, while the control group received distilled water only. All animals were sacrificed 24 h after the treatment, and blood was collected for the analysis of hematological, biochemical, oxidative status and essential elements levels. An external and internal dose-response relationship was performed using PROASTweb 70.1 software. The results showed that low doses of Pb affect hematological parameters and lipid profile after 28 days. The possible mechanisms at examined Pb dose levels were a decrease in SOD, O₂^•- and Cu and an increase in Zn levels. The dose-dependent nature of changes in cholesterol, HDL cholesterol, O₂^.-, SOD, AOPP in serum and hemoglobin, Fe, Zn, Cu in blood were obtained in this study. The most sensitive parameters that were alerted are Cu blood levels (BMDL₅: 1.4 ng/kg b.w./day) and SOD activity (BMDL₅: 0.5 μg/kg b.w./day). The presented results provide information that may be useful in further assessing the health risks of low-level Pb exposure.

BDE-47 induces nephrotoxicity through ROS-dependent pathways of mitochondrial dynamics in PK15 cells

2,2',4,4'-tetrabromodiphenyl ether (BDE-47)-induced nephrotoxicity is closely associated with oxidative stresses and mitochondrial abnormalities. Mitochondrial fusion and fission dynamics are crucial for maintaining mitochondrial and cellular physiological homeostasis. However, the detailed mechanisms through which BDE-47 disrupts this dynamic and contributes to renal injuries are still not fully understood. The porcine kidney-15 (PK15) cell line, a well-defined in vitro animal renal toxicological model, was exposed to BDE-47 with concentrations of 12.5, 25, 50, and 100 μM, respectively. Cell viability, the levels of reactive oxygen species (ROS) and adenosine triphosphate (ATP), the mitochondrial membrane potential (MMP), and the expression levels of key mitochondrial fusion and fission proteins were assessed. BDE-47 reduced cell viability and disrupted mitochondrial dynamics by inhibiting mitochondrial fusion and fission simultaneously, leading to MMP decreases, ROS overgeneration, ATP depletion, and cellular disintegration in a dose-dependent manner. Additionally, the mitochondrial division inhibitor (Mdivi-1) with the concentration of 20 μM observed to restore the downregulation of mitochondrial fusion and fission proteins, alleviate damages in mitochondrial morphology and functionality, correct ROS overproduction, and enable cell survival. The antioxidant N-acety-L-cysteine (NAC) with the concentration of 1 mM also simultaneously reversed the imbalance of mitochondrial dynamics, decreased ROS production, and restored mitochondrial morphology in PK15 cells exposed to BDE-47. Our data provide new insights indicating that BDE-47 disrupts mitochondrial fusion/fission dynamics to induce mitochondrial abnormalities, triggering oxidative stresses and thus contributing to PK15 cell dysfunction. ROS-dependent pathways in mitochondrial dynamics may provide a new avenue for developing effective strategies to protect cells against BDE-47-induced nephrotoxicity.

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

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

Effects of Decabrominated Diphenyl Ether Exposure on Growth, Meat Characteristics and Blood Profiles in Broilers

Decabrominated diphenyl ether (BDE-209) is widely used as a flame retardant and is detected at high levels in the environment. Its toxicities have been reported and have attracted attention. In the present study, broilers were used to determine the response in growth performance, carcass traits, meat quality, blood profiles and antioxidant system to BDE-209 exposure at doses of 0, 0.02, 0.4 and 4 mg/kg. The results showed that BDE-209 exposure at levels of 0.02 or 0.4 mg/kg increased feed intake and decreased feed efficiency. BDE-209 altered the blood profiles, such as reducing the numbers of white blood cells, lymphocytes and neutrophilic granulocytes. As compared with the control, BDE-209 exposure significantly increased abdominal fat percentages of broilers at 64.9-159.5% and adversely affected the selected biochemical indicators, including alkaline phosphatase (ALP), aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatine (CRE), which indicated its toxicity to liver and kidney functions. Moreover, BDE-209 exposure significantly increased plasma malondialdehyde (MDA) concentrations and decreased the activities of glutathione peroxidase (GSH-px) and superoxide dismutase (SOD), which implied aggravating oxidant stress and decline of antioxidant capacity in broilers. In conclusion, our data demonstrated that the environmental pollutant BDE-209 adversely influenced growth performance, increased the deposition of abdominal fat, impaired antioxidant capacity and the immune system and had potential toxicity to the liver and kidney of broilers.

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.

Oral exposure to BDE-209 modulates metastatic spread of melanoma in C57BL/6 mice inoculated with B16-F10 cells

Polybrominated diphenyl ethers (PBDEs) are brominated, persistent and bioaccumulative flame retardants widely used in the manufacture of plastic products. Decabromodiphenyl ether (BDE-209) is the most prevalent PBDE in the atmosphere and found in human blood, breast milk and umbilical cord. In vitro studies showed that BDE-209 interferes with murine melanoma cells (B16F10), modulating cell death rates, proliferation and migration, important events for cancer progression. In order to evaluate if BDE-209 modulates metastasis formation in murine models, C57BL/6 mice were exposed to BDE-209 (0.08, 0.8 and 8 μg⁄kg) via gavage (5-day intervals for 45 days) (9 doses in total). Then, mice were inoculated with melanoma cells (B16-F10) at caudal vein receiving 4 additional doses of BDE-209. At 20th day post-cell inoculation, blood, lung, liver, kidney and brain were sampled for hematological, biochemical and morphological analyses. The slightly higher levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in the blood and pro-oxidant state in the liver of BDE-exposed mice indicated liver damage. Although the in vivo approach is for metastasis formation in the lung, they were unexpectedly observed in non-target organs (liver, brain, kidney and gonads). The similarity test showed high proximity among individuals from the control and a dissimilarity index between the control and exposed groups. The present data corroborate the known hepatotoxicity of BDE-209 to mice (C57BL/6) and demonstrate for the first time the increase of metastatic dissemination of B16F10 cells in vivo due to previous and continuous BDE-209 exposure, revealing possible implications of this organic compound with melanoma malignancy related traits.

Perinatal exposure to octabromodiphenyl ether mixture, DE-79, alters the vasopressinergic system in adult rats

Polybrominated diphenyl ethers (PBDEs) are persistent environmental pollutants considered as neurotoxicants and endocrine disruptors with important biological effects ranging from alterations in growth, reproduction, and effects on the hypothalamus-pituitary-adrenal axis. The vasopressinergic (AVPergic) system is a known target for pentaBDEs mixture (DE-71) and the structurally similar chemicals, polychlorinated biphenyls. However, the potential adverse effects of mixtures containing octaBDE compounds, like DE-79, on the AVPergic system are still unknown. The present study aims to examine the effects of perinatal DE-79 exposure on the AVPergic system. Dams were dosed from gestational day 6 to postnatal day 21 at doses of 0 (control), 1.7 (low) or 10.2 (high) mg/kg/day, and male offspring from all doses at 3-months-old were subjected to normosmotic and hyperosmotic challenge. Male offspring where later assessed for alterations in osmoregulation (i.e. serum osmolality and systemic vasopressin release), and both vasopressin immunoreactivity (AVP-IR) and gene expression in the hypothalamic paraventricular and supraoptic nuclei. Additionally, to elucidate a possible mechanism for the effects of DE-79 on the AVPergic system, both neuronal nitric oxide synthase immunoreactivity (nNOS-IR) and mRNA expression were investigated in the same hypothalamic nuclei. The results showed that perinatal DE-79 exposure AVP-IR, mRNA expression and systemic release in adulthood under normosmotic conditions and more evidently under hyperosmotic stimulation. nNOS-IR and mRNA expression were also affected in the same nuclei. Since NO is an AVP regulator, we propose that disturbances in NO could be a mechanism underlying the AVPergic system disruption following perinatal DE-79 exposure leading to osmoregulation deficits.

Approaching reactive species in the frame of their clinical significance: A toxicological appraisal

Redox biology and toxicology are interrelated fields that have produced valuable evidence regarding the role and clinical significance of reactive species. These issues are analyzed herein by presenting 6 arguments, as follows: Argument 1: There is no direct connection of redox-related pathologies with specific reactive species; Argument 2: The measurement of reactive species concentration is a major challenge due to their very short half lives; Argument 3: There is an interplay between reactive species generation and fundamental biological processes, such as energy metabolism; Argument 4: Reactive species exert beneficial biological action; Argument 5: Reactive species follow the hormesis phenomenon; Argument 6: Oxidative modifications of redox-related molecules are not necessarily interpreted as oxidative damage. We conclude that reactive species do not seem to exert clinical significance, which means that they lack a measurable cause-effect relation with chronic diseases. Unpredictable results could, nevertheless, arise through novel experimental setups applied in the field of toxicology. These are related to the real-life exposure scenario via the regimen of long-term low-dose (far below NOAEL) exposure to mixtures of xenobiotics and can potentially offer perspectives in order to investigate in depth whether or not reactive species can be introduced as clinically significant redox biomarkers.

Bioaccumulation of decabromodiphenyl ether affects the antioxidant system in the clam Mactra veneriformis

Antioxidant enzymes play vital roles against oxidative stress induced by decabromodiphenyl ether (BDE-209), being widespread in marine environment. However, the effect of BDE-209 on antioxidant enzymes remains poorly understood in marine bivalves. In this study, the clams Mactra veneriformis were exposed to 0.1, 1, and 10 μg/L BDE-209 for 7 days and then maintained in clean seawater for 3 days as the depuration. The bioaccumulation of BDE-209 and the effects on superoxide dismutase, catalase, and glutathione peroxidase were investigated. BDE-209 accumulation was concentration-dependent and decreased by 36%-52% after recovery. Malondialdehyde contents increased in a time- and dose-dependent manner. mRNA expression and activity of antioxidant enzymes changed with different patterns and recovered after depuration. These results suggested that antioxidant systems were triggered to protect the clams from oxidative damage caused by BDE-209. Thus, this research is helpful in elucidating the effect of BDE-209 on antioxidant system in marine bivalves.

Overview of Cadmium Thyroid Disrupting Effects and Mechanisms

Humans are exposed to a significant number of chemicals that are suspected to produce disturbances in hormone homeostasis. Hence, in recent decades, there has been a growing interest in endocrine disruptive chemicals. One of the alleged thyroid disrupting substances is cadmium (Cd), a ubiquitous toxic metal shown to act as a thyroid disruptor and carcinogen in both animals and humans. Multiple PubMed searches with core keywords were performed to identify and evaluate appropriate studies which revealed literature suggesting evidence for the link between exposure to Cd and histological and metabolic changes in the thyroid gland. Furthermore, Cd influence on thyroid homeostasis at the peripheral level has also been hypothesized. Both in vivo and in vitro studies revealed that a Cd exposure at environmentally relevant concentrations results in biphasic Cd dose-thyroid response relationships. Development of thyroid tumors following exposure to Cd has been studied mainly using in vitro methodologies. In the thyroid, Cd has been shown to activate or stimulate the activity of various factors, leading to increased cell proliferation and a reduction in normal apoptotic activity. Evidence establishing the association between Cd and thyroid disruption remains ambiguous, with further studies needed to elucidate the issue and improve our understanding of Cd-mediated effects on the thyroid gland.

Transcriptome profiling of HepG2 cells exposed to the flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO)

The flame retardant, 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO), has been receiving great interest given its superior fire protection properties, and its predicted low level of persistence, bioaccumulation, and toxicity. However, empirical toxicological data that are essential for a complete hazard assessment are severely lacking. In this study, we attempted to identify the potential toxicological modes of action by transcriptome (RNA-seq) profiling of the human liver hepatocellular carcinoma cell line, HepG2. Such insight may help in identifying compounds of concern and potential toxicological phenotypes. DOPO was found to have little cytotoxic potential, with lower effective concentrations compared to other flame retardants studied in the same cell line. Differentially expressed genes revealed a wide range of molecular effects including changes in protein, energy, DNA, and lipid metabolism, along with changes in cellular stress response pathways. In response to 250 μM DOPO, the most perturbed biological processes were fatty acid metabolism, androgen metabolism, glucose transport, and renal function and development, which is in agreement with other studies that observed similar effects of other flame retardants in other species. However, treatment with 2.5 μM DOPO resulted in very few differentially expressed genes and failed to indicate any potential effects on biology, despite such concentrations likely being orders of magnitude greater than would be encountered in the environment. This, together with the low levels of cytotoxicity, supports the potential replacement of the current flame retardants by DOPO, although further studies are needed to establish the nephrotoxicity and endocrine disruption of DOPO.