HBCDD-induced sustained reduction in mitochondrial membrane potential, ATP and steroidogenesis in peripubertal rat Leydig cells

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.

Chlorinated organophosphorus flame retardants-induced mitochondrial abnormalities and the correlation with progesterone production in mLTC-1 cells

Environmental monitoring data have indicated that three chlorinated organophosphorus flame retardants (Cl-OPFRs), including tris(2-chloroethyl)-phosphate (TCEP), tris(2-chloropropyl)-phosphate (TCPP), and tris(1,3-dichloro-2-propyl)-phosphate (TDCPP) are the predominant chemicals in various environmental matrices and exhibit reproductive endocrine disrupting activities. Currently, mitochondrial abnormality is a new paradigm for evaluating chemical-mediated cell dysfunction. However, a comprehensive correlation between these two aspects of Cl-OPFRs remains unclear. In this research, the effects of TCEP, TCPP, and TDCPP on progesterone production and mitochondrial impairment were investigated by using mouse Leydig tumor cells (mLTC-1). The half maximal inhibitory concentration (IC₅₀) values at 48 h exposure indicated that the rank order of anti-androgenic activity was TDCPP > TCPP. Whereas, TCEP exhibited elevation of progesterone production. At concentrations close to IC₅₀ of progesterone production by TCPP and TDCPP, the elevation of intracellular reactive oxygen species (ROS), depletion of mitochondrial membrane potential (MMP), reduction of cellular adenosine triphosphate (ATP) content, and alteration of mitochondrial structures was observed. In addition, the expression of main genes related to progesterone synthesis was dramatically down-regulated by TCPP and TDCPP treatments. These results imply that the inhibition effect of TCPP and TDCPP on progesterone production might be related to mitochondrial damage and down-regulated steroidogenic genes.

Testosterone synthesis in testicular Leydig cells after long-term exposure to a static electric field (SEF)

China's clean energy and resources are mainly located in the west and north while electric load center is concentrated in the middle and east. Thus, these resources and energy need to be converted into electrical energy in situ and transported to electric load center through ultra-high voltage direct current (UHVDC) transmissions. China has built 25,000 km UHVDC transmission lines of 800 kV and 1100 kV, near which the impact of electric field on health has attracted public attention. Previous studies showed that time-varying electromagnetic field exposure could disturb testosterone secretion. To study the effect of non-time-varying electric field caused by direct current transmission lines on testosterone synthesis, male ICR mice were continually (24 h/d) exposed to static electric field of 56.3 ± 1.4 kV/m. Results showed that on the 3^rd day of exposure and on the 7^th day after ceasing the exposure of 28 d, serum testosterone level and testicular oxidative stress indicators didn't change significantly. On the 28^th day of exposure, serum testosterone levels, testicular glutathione peroxidase (GSH-Px) activity, the mRNA and protein levels of testicular StAR, PBR, CYP11A1 decreased significantly, and testicular malondialdehyde (MDA) content increased significantly. Meanwhile, electron-dense edges and vacuolation appeared in lipid droplets of Leydig cells. The gap between inner mitochondrial membrane (IMM) and outer mitochondrial membrane (OMM) enlarged, which would cause the swelling of mitochondria, the rupture and deficiency of mitochondrial membranes. Analysis showed that testicular oxidative stress could induce the damage of mitochondrial structure in Leydig cells, which would decrease the rate of cholesterol transport from cytoplasm to mitochondria. Since cholesterol is the necessary precursor of testosterone synthesis, testosterone synthesis was inhibited. The decrease of the mRNA and protein expression levels of StAR and PBR in testes could diminish the cholesterol transported from OMM to IMM. The decrease of the mRNA and protein expression levels of CYP11A1 could reduce the pregnenolone required in testosterone synthesis and inhibit testosterone synthesis consequently.

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.

BDE-47 Decreases Progesterone Levels in BeWo Cells by Interfering with Mitochondrial Functions and Genes Related to Cholesterol Transport

Polybrominated diphenyl ethers (PBDEs) have been reported to exert reproductive endocrine toxicity, but the mechanisms for this process remain unclear. Currently available studies have concentrated on the enzymatic reactions during steroidogenesis, but the results are not consistent. In this study, we explored the effects of 2,2',4,4'-tertrabromodiphenyl ether (BDE-47) on progesterone biosynthesis and the potential mechanisms in human placental choriocarcinoma cells. The results showed that BDE-47 decreased progesterone production in a dose-dependent manner but had no effect on key enzymes (Cyp11a1 and 3β-HSD). BDE-47 exposure depolarized the mitochondrial membrane potential and downregulated adenosine triphosphate levels. The gene expression levels of Mfn2, Tspo, Atad3, Vdac1, Fis1, and Drp1, which are involved in mitochondrial dynamics and cholesterol transport, were disturbed. The demethylation of some CpG loci of mitochondrial biomarkers (Drp1, Opa1, Vdac2, and Atad3) was induced in the 1 μM BDE-47 exposure group, but no methylation change was observed with 50 μM treatment. Our findings unveiled that the reduction of progesterone synthesis induced by BDE-47 might be associated with cholesterol transportation, mitochondrial dynamics, and mitochondrial functions. These findings provide substantial data on the reproductive endocrine toxicity of PBDEs.

Inhibition effects of perfluoroalkyl acids on progesterone production in mLTC-1

Perfluoroalkyl substances (PFASs) are a class of fluorine substituted carboxylic acid, sulfonic acid and alcohol, structurally similar to their corresponding parent compounds. Previous study demonstrated the potential endocrine disruption and reproductive toxicity of perfluorooctane sulfonic acid and perfluorooctanoic acid, two dominant PFASs in animals and humans. We explored the relationship between eleven perfluoroalkyl acids (PFAAs) with different carbon chain length and their ability to inhibit progesterone production in mouse Leydig tumor cells (mLTC-1). We found an obvious dose-response relationship between progesterone inhibition rate and PFAA exposure concentration in mLTC-1. The relative inhibition rate of progesterone by PFAAs was linearly related to the carbon chain length and molar refractivity of PFAAs. Mitochondrial membrane potential (MMP) decreased after PFAA exposure at the half-maximal inhibitory effect concentration (IC₅₀) of progesterone production in mLTC-1, while the reactive oxygen species (ROS) content increased significantly. These results imply that the inhibition effect of PFAAs on progesterone production might be due, in part, to ROS damage and the decrease in MMP in mLTC-1.