Gestational mercury vapor exposure and diet contribute to mercury accumulation in neonatal rats

Could Vitamin C Protect Against Mercuric Chloride Induced Lung Toxicity In The Offspring Rat: A Histological And Immunohistochemical Study

Mercury (Hg) is one of the most toxic heavy metals and widely utilized in various industries. Hg exposure causes serious health impacts through unfavorable pathological and biochemical effects. We aimed to assess the effect of mercuric chloride (HgCl2) prenatal exposure on the lung development and probable prophylactic effect of vitamin C. The 30 pregnant rats were used in this work and divided randomly into 3 equal groups: Group Ӏ given distilled water, Group ӀӀ given HgCl2 at dose of 4 mg/ BW/day and Group ӀӀӀ given HgCl2 and Vitamin C at dose of 200 mg/kg BW/day. The pups of each group at birth were collected, counted and weighted then lung specimens were extracted, weighted, anaesthetized and processed for the light, electron microscopic and immunohistochemical studies. Also, morphometric studies were performed. We found that prenatal HgCl2 exposure caused collapse of alveoli, thick interalveolar septa, degenerated type Ӏ and type Ӏ pneumocytes, extensive extravasation of RBCs, extensive collagen fibers deposition, positive iNOS immunoreaction and significant decrease in the body and lung weights. Vitamin C concomitant administration partially reversed HgCl2 induced lung degeneration. We concluded that prenatal HgCl2 exposure caused lung damage and vitamin C had protective effects against HgCl2 indued pulmonary toxicity.

Regulatory effects of dihydrolipoic acid against inorganic mercury-mediated cytotoxicity and intrinsic apoptosis in PC12 cells

Mercury (Hg) is an extremely dangerous environmental contaminant, responsible for human diseases including neurological disorders. However, the mechanisms of inorganic Hg (iHg)-induced cell death and toxicity are little known. Dihydrolipoic acid (DHLA) is the reduced form of a naturally occurring compound lipoic acid, which act as a potent antioxidant through multiple mechanisms. So we hypothesized that DHLA has an inhibitory role on iHg-cytotoxicity. The purposes of this research were to investigate mechanism/s of cytotoxicity of iHg, as well as, the cyto-protection of DHLA against iHg induced toxicity using PC12 cells. Treatment of PC12 cells with HgCl₂ (Hg²⁺) (0-2.5 μM) for 48 h resulted in significant toxic effects, such as, cell viability loss, high level of lactate dehydrogenase (LDH) release, DNA damage, cellular glutathione (GSH) level decrease and increased Hg accumulation. In addition, protein level expressions of akt, p-akt, mTOR, GR, NFkB, ERK1, Nrf2 and HO-1 in cells were downregulated; and cleaved caspase 3 and cytochrome c release were upregulated after Hg²⁺ (2.5 μM) exposure and thus inducing apoptosis. Hg²⁺induced apoptosis was also confirmed by flow cytometry. However, pretreatment with DHLA (50 μM) for 3 h before Hg²⁺ (2.5 μM) exposure showed inhibition against iHg²⁺-induced cytotoxicity by reversing cell viability loss, LDH release, DNA damage, GSH decrease and inhibiting Hg accumulation. Moreover, DHLA pretreatment reversed the protein level expressions of akt, p-akt, mTOR, GR, NFkB, ERK1, Nrf2, HO-1, cleaved caspase 3 and cytochrome c. In conclusion, results showed that DHLA could attenuate Hg²⁺-induced cytotoxicity via limiting Hg accumulation, boosting up of antioxidant defense, and inhibition of apoptosis in cells.

Comparative study on toxicity of methylmercury chloride and methylmercury hydroxide to the human neuroblastoma cell line SH-SY5Y

Toxicities of methylmercury chloride (CH₃HgCl) and methylmercury hydroxide (CH₃HgOH) to cultured neuroblastoma cell line SH-SY5Y in vitro are evaluated. This is the comparative study between two methylmercury compounds to find out the extent of toxicity of these compounds are toxic to SH-SY5Y cell line. Both cytotoxicity and genotoxicity experiments were carried out to find out the more toxic compound. For cytotoxicity study, four staining assay methods independently with trypan blue (TB), acridine orange/ethidium bromide (AO/EB), 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyl tetrazolium bromide (MTT), and neutral red (NR) were used and the comet assay method was done for genotoxicity study. The obtained toxicity data were used for probit analysis. In cytotoxicity, CH₃HgCl had minimum inhibitory concentration (MIC) value in each assay method as 3 mg/L invariably; LC₂₅ values were in the range 7.41 to 10.23 mg/L, and LC₅₀ values were 14.79 to 15.48 mg/L; while LC₇₅ values were 20.89 to 26.91 mg/L. Moreover, LC₁₀₀ value was 30 mg/L, known from comet assay experiments for CH₃HgCl. Similarly for CH₃HgOH, the MIC value in each assay method was invariably 3 mg/L, the LC₂₅ values were in the range 12.58 to 16.59 mg/L, and LC₅₀ values were 19.49 to 23.44 mg/L; LC₇₅ values were 27.54 to 30.90 mg/L and LC₁₀₀ value was 42 mg/L in each assay done for cytotoxicity and genotoxicity studies. Computed DNA fragmentation indices in comet assays were 98.6 ± 0.57 30 mg/L with CH₃HgCl and 76 ± 5.29 30 mg/L with CH₃HgOH. This study clearly indicated that methylmercury chloride is more toxic than methylmercury hydroxide to SH-SY5Y cell line. Toxicity of Hg had been quantified with in vitro cultured human neuroblastoma cell line; since it has neurotoxic effects, its neural evaluation has implications in environmental health issues.

Delayed neurochemical effects of prenatal exposure to MeHg in the cerebellum of developing rats

Human fetuses and neonates are particularly vulnerable to methylmercury (MeHg)-induced brain damage and are sensitive even to low exposure levels. Previous work of our group evidence that prenatal exposure to MeHg causes cognitive and behavioral alterations and disrupt hippocampus signaling. The current study aimed to investigate the effect of gestational exposure of rats to MeHg at low doses (1 or 2 mg/kg) on parameters of redox imbalance and key signaling pathways in the cerebellum of their offspring. Pregnant females received MeHg (treated group) or 0.9% saline water (control group) by gavage in alternated days from gestational day 5 (GD5) until parturition and analyzes were proceed in the cerebellum of 30-day-old pups. We found increased lipid peroxidation and protein carbonylation levels as well as decreased SH content in pups prenatally exposed to 2 mg/kg MeHg. In addition, misregulated SOD/catalase activities supported imbalanced redox equilibrium. We found decreased GSK3β(Ser9) phosphorylation, suggesting activation of this enzyme and dephosphorylation/inhibition of ERK1/2 and JNK pathways. Increased PKAα catalytic subunit could be upstream of hyperphosphorylated c-Raf(Ser259) and downregulated MAPK pathway. In addition, we found raised levels of the Ca²⁺-dependent protein phosphatase 2 B (PP2B). We also found preserved immunohistochemical staining for both glial fibrillary acidic protein (GFAP) and NeuN in MeHg-exposed pups. Western blot analysis showed unaltered levels of BAX/BCL-XL, BAD/BCL-2 and active caspase 3. Together, these findings support absence of reactive astrocytes, neuronal damage and apoptotic cell death in the cerebellum of MeHg treated pups. The present study provides evidence that prenatal exposure to MeHg leads to later redox imbalance and disrupted signaling mechanisms in the cerebellum of 30-day-old pups potentially predisposing them to long-lasting neurological impairments in CNS.

Alpha-lipoic acid reduces methylmercury-induced neuronal injury in rat cerebral cortex via antioxidation pathways

Methylmercury (MeHg), an extremely dangerous environmental pollutant, accumulating preferentially in central nervous system, causes a series of cytotoxic effects. The present study explored the mechanisms which contribute to MeHg-induced neurotoxicity focusing on the oxidative stress in rat cerebral cortex. In addition, the protective effects of alpha-lipoic acid (LA), a potent antioxidant on MeHg-mediated neuronal injury, was also investigated in current study. A MeHg poisoning model was established as 64 rats randomly divided into 4 groups of which saline control group, MeHg-treated groups (4 and 12 μmol kg^-1 ), and LA pretreatment (35 μmol kg^-1 ) group, respectively. After administration of 12 μmol kg^-1 MeHg for 4 weeks, it was found that obvious pathological changes and apoptosis in neuronal cells. Meanwhile, total Hg levels elevated significantly, superoxide dismutase (SOD) and gluthathione peroxidase (GSH-Px) activities were inhibited, and ROS formation elevated, which might be critical to aggravate oxidative stress in cerebral cortex. In addition, NF-E2-related factor 2 (Nrf2) pathways were activated, as heme oxygenase-1 (HO-1) and γ-glutamylcysteine synthetase heavy subunit (γ-GCSh) expressions were up-regulated obviously by MeHg exposure. Moreover, activities of Na⁺ -K⁺ -ATPase and Ca²⁺ -ATPase were inhibited, leading to intracellular calcium (Ca²⁺ ) overload. LA pre-treatment partially reduced MeHg neurotoxic effects via anti-oxidation pathways. In conclusion, these findings clearly indicated that MeHg aggravated oxidative stress and Ca²⁺ overload in cerebral cortex. LA possesses the ability to prevent MeHg neurotoxicity through its anti-oxidative properties. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 931-943, 2017.

Human Umbilical Cord Blood-Derived Neural Stem Cell Line as a Screening Model for Toxicity

The aim was to investigate whether a human neural stem cell (NSC) line derived from human umbilical cord blood (hUCB) can be used for toxicity study. Toxicity of both neurotoxic environmental xenobiotics, methyl mercury chloride (CH₃HgCl), lead acetate (CH₃COOPb), and chlorpyrifos (CP), and non-neurotoxic insecticide, dichlorvos, as well as non-neurotoxic drugs, theophylline and acetaminophen were assessed. Additionally, differentiation of neuronal and glial cell lines derived from hUCB was elucidated. It was observed that CH₃HgCl was more toxic to human NSCs in comparison to CH₃COOPb and CP. The minimum inhibitory concentration (MIC) value against NSCs was 3, 10, and 300 mg/L, in each staining process, acridine orange/ethidium bromide (AO/EB) staining, 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) assay, and Hoechst staining, for CH₃HgCl, CP, and CH₃COOPb, respectively. CH₃HgCl had the LC₂₅ value as 10.0, 14.4, and 12.7 mg/L, by staining method mentioned in succession. CP had the LC₂₅ value as 21.9, 23.7, and 18.4 mg/L; similarly, CH₃COOPb had LC₂₅ values, successively as 616.9, 719.2, and 890.3 mg/L. LC₅₀ values ranged from 18.2 to 21.7 mg/L for CH₃HgCl, 56.4 to 60.2 mg/L for CP, and 1000 to 1460.1 for CH₃COOPb. Theophylline, acetaminophen, and dichlorvos had no impact on the viability of NSCs. This work justified that hUCB-NSC model can be used for toxicity study.

Effects of early-onset radiofrequency electromagnetic field exposure (GSM 900 MHz) on behavior and memory in rats

Female Wistar rats, from an age of 14 days to 19 months, were exposed in the head region for 2 h per day, 5 days per week, to a GSM-modulated 900 MHz radiofrequency electromagnetic field (RF-EMF). The average specific absorption rates (SAR) in the brain were 0 (sham), 0.7, 2.5 and 10 W/kg. To ensure a primary exposure of the head region, rats were fixed in restraining tubes of different sizes according to their increasing body weight. During the experiment, a set of 4 behavioral and learning tests (rotarod, Morris water maze, 8-arm radial maze, open field) were performed 3 times in juvenile, adult and presenile rats. In these tests, no profound differences could be identified between the groups. Only presenile rats of the cage control group showed a lower activity in two of these tests compared to the other groups presumably due to the lack of daily handling. The rotarod data revealed on some testing days significantly longer holding times for the sham-exposed rat vs. the exposed rat, but these findings were not consistent. During the first year, body weights of sham-exposed and exposed rats were not different from those of the cage controls, and thereafter only marginally lower, so that the effect of stress as confounder was probably negligible. The results of this study do not indicate harmful effects of long-term RF-EMF exposure even when begun at an early age on subsequent development, learning skills and behavior in rats, even at relatively high SAR values.

Organic and inorganic mercury in neonatal rat brain after prenatal exposure to methylmercury and mercury vapor

BACKGROUND

Many populations are exposed to multiple species of mercury (Hg), predominantly organic Hg as methylmercury (MeHg) from fish, and inorganic Hg as Hg vapor from dental amalgams. Most of our knowledge of the neurotoxicity of Hg is based on research devoted to studying only one form at a time, mostly MeHg.

OBJECTIVES

In this study we investigated the effects of prenatal exposure to MeHg and Hg vapor on Hg concentrations in the brain of neonatal rats.

METHODS

Female Long-Evans hooded rats were exposed to MeHg (0, 3, 6, or 9 ppm as drinking solution), Hg vapor (0, 300, or 1,000 microg/m3 for 2 hr/day), or the combination of both, from 30 days before breeding through gestational day 18. On postnatal day 4, whole brains were taken from one male and one female from each of four litters in each treatment group to assess organic and inorganic Hg in the brain by cold vapor atomic absorption spectrometry.

RESULTS

Statistical analysis using linear mixed effects models showed that MeHg dose was the primary determinant of both organic and inorganic brain Hg levels. For both outcomes, we also found significant interactions between MeHg and Hg vapor exposure. These interactions were driven by the fact that among animals not exposed to MeHg, animals exposed to Hg vapor had significantly greater organic and inorganic brain Hg levels than did unexposed animals.

CONCLUSION

This interaction, heretofore not reported, suggests that coexposure to MeHg and Hg vapor at levels relevant to human exposure might elevate neurotoxic risks.

Mercury distribution in neonatal rat brain after intrauterine methylmercury exposure

Methylmercuric chloride (MMC) was orally administered to pregnant Wistar rats from gestational day 6 (G6) for 5 consecutive days. After delivery, the neonatal rats were decapitated and the cerebrum, cerebellum and hippocampus were excised on postnatal day (PND) 1, 7, 14, 21, 30 to determine total Hg contents and concentrations (six per stage). Both total Hg contents and concentrations in all the three regions increased as exposure dose increased and declined as postnatal time prolonged. Interestingly, differences of total Hg content between cerebrum and hippocampus at each time-point were significant (P<0.05). In the meantime, considering the Hg concentration, while no differences were observed before PND14 (P<0.05) among the three regions, Hg concentration in hippocampus was significantly higher than in cerebrum after that time period (P<0.05). We demonstrated that MeHg could pass through the placental and blood-brain barriers in a dose-dependent manner. Moreover, we found mercury redistribution occurred in offspring brain following the prolongation of postnatal time. The hippocampus was the major target of MeHg accumulation.

Alterações auditivas em trabalhadores expostos a mercúrio

OBJETIVO: identificar possíveis alterações auditivas periféricas e centrais, em trabalhadores de uma indústria de reciclagem de lâmpadas fluorescentes, que tiveram exposição ao mercúrio metálico. MÉTODOS: foram realizados os testes de audiometria tonal (via aérea e via óssea), audiometria vocal e imitanciometria (timpanometria e pesquisa do reflexo estapediano) em 13 trabalhadores, todos do sexo masculino, com idade média de 38,5 anos e tempo médio de exposição de seis anos. Após foram realizados os teste de processamento auditivo (dicótico de dígitos e PPS) em nove trabalhadores. RESULTADOS: dos 13 sujeitos que realizaram a audiometria e a imitanciometria, seis (46%) apresentaram perda auditiva sensório-neural e sete (54%) apresentaram alteração no reflexo estapediano. Dos nove sujeitos que realizaram o teste de processamento auditivo, três (33,5%) apresentaram resultados alterados tanto no teste dicótico de dígitos, quanto no PPS. CONCLUSÕES: foram identificadas tanto alterações auditivas periféricas quanto centrais.