Role of reactive oxygen species and glutathione in inorganic mercury-induced injury in human glioma cells

Secondary exposure to heavy metal in genetically susceptible mice leads to acceleration of autoimmune response

Exposure to mercury (Hg) and silver (Ag) has been shown to induce autoimmune diseases in genetically susceptible rodents. Here, A.SW mice were initially exposed to HgCl2, AgNO3 or tap water (control) for 3 weeks. After 13 weeks of stoppage, all mice had secondary exposure to 203HgCl2. After secondary exposure, higher and earlier ANoA titers were observed in mice initially exposed to Hg or Ag compared to control. Further, mice initially exposed to Ag showed higher total IgG1 and IgG2a, Whole Body Retention and lymph nodes and spleen accumulation of Hg compared to mice initially exposed to Hg and controls. These findings showed an earlier and stronger immunological response in A.SW mice compared with control, following re-exposure to heavy metals indicating an immunological memory. Additionally, secondary exposure to a different heavy metal may aggravate the effects of exposure of at least one of the metals indicating cross-reactivity.

Experimental and computational investigation of heteroatom substitution in nucleolytic Cu(II) cyclen complexes for balancing stability and redox activity

Cu(II) complexes of cyclen-based ligands CuL¹-CuL⁶ were synthesized and characterized. The corresponding ligands L¹-L⁶ comprise different donor sets including S and O atoms. Whereas cyclen (L¹) is commercially available, L²-L⁶ were synthesized according to protocols available in the literature. Cleavage activity of the complexes towards plasmid DNA was tested in the presence and absence of ascorbate as a reducing agent (oxidative vs. hydrolytic cleavage). As previously shown, the substitution of N donor atoms with hard donor O atoms leads to efficient oxidative nucleases, but dissociation of the complex upon reduction. We thus opted for S substitution (soft donors) to stabilize the reduced Cu(I) species. Increasing the S content, however, leads to species that are difficult to reoxidize in order to ensure efficient oxidative DNA cleavage. We are showing by experimental (cyclic voltammetry) and computational means (DFT) that the rational combination of O and S atoms next to two nitrogen donors within the macrocycle (oxathiacyclen complex CuL⁶) leads to the stabilization of both redox states. The complex thus exhibits the highest oxidative DNA cleavage activity within this family of cyclen-based Cu(II) complexes - without leaching of the metal ion during reduction.

Effect of Solanum vegetables on memory index, redox status, and expressions of critical neural genes in Drosophila melanogaster model of memory impairment

African eggplant (Solanum macrocarpon L) (AE) and Black Nightshade (Solanum nigrum L) (BN) leaves are green leafy vegetables with nutritional and ethnobotanical values. We have previously characterized the vegetables via HPLC/LC-MS to reveal notable phenolic acids, flavonoids and alkaloids. In this present study, we addressed the efficacy of the two vegetables in mitigating mercuric chloride (HgCl₂)-induced neurotoxicity and memory impairment in Drosophila melanogaster. Flies were exposed to HgCl₂ (0.30 mg/g) alone or in combination with the vegetables (0.1 and 1.0%) of both samples in their diets for seven days. The results showed that HgCl₂ (Hg)-exposed flies had significantly reduced survival rate and memory index, which were ameliorated in the Hg-exposed flies fed AE or BN. This was accompanied by increased reactive oxygen species (ROS) levels, reduced total thiol, as well as catalase, glutathione transferase (GST) and acetylcholine esterase (AChE) activities in Hg-exposed fly heads, but ameliorated in Hg-exposed flies fed dietary inclusions of the vegetables. In addition, the Hg-induced alterations in SOD, NF-ҝB/Relish, Dronc and Reaper mRNA levels were statistically indistinguishable from controls in Hg-treated flies fed diets containing AE or BN. Normalization of cnc/Nrf2 and FOXO were observed only in Hg-treated flies fed BN. These findings suggest that dietary AE or BN leaves offer protection against Hg-induced memory impairment and neurotoxicity in D. melanogaster, and further justify them as functional foods with neuroprotective properties.

Molecular and functional characaterization of the novel odorant-binding protein gene AccOBP10 from Apis cerana cerana

Odorant-binding proteins (OBPs) play an important role in odour perception and transport in insects. However, little is known about whether OBPs perform other functions in insects, particularly in Apis cerana cerana. Within this study, an OBP gene (AccOBP10) was isolated and identified from A. c. cerana. Both homology and phylogenetic relationship analyses indicated that the amino acid sequence of AccOBP10 had a high degree of sequence identity with other members of the gene family. Analysis of quantitative real-time PCR (qRT-PCR) showed that AccOBP10 mRNA was expressed at higher levels in the venom gland than in other tissues. The mRNA transcript expression of AccOBP10 was upregulated by low temperature (4°C), hydrogen peroxide (H2O2), pyridaben, methomyl and imidacloprid but downregulated by heat (42°C), ultraviolet light, vitamin C, mercuric chloride, cadmium chloride, paraquat and phoxim. Expression of AccOBP10 under abiotic stress was analysed by western blotting, and the results were consistent with those of qRT-PCR. And as a further study of AccOBP10 function, we demonstrated that knockdown of AccOBP10 by RNA interference could slightly increase the expression levels of some stress-related genes. Collectively, these results suggest that AccOBP10 is mainly involved in the response to stress conditions.

Identification of a mitogen-activated protein kinase kinase (AccMKK4) from Apis cerana cerana and its involvement in various stress responses

The mitogen-activated protein kinase (MAPK) cascade pathway is a ubiquitous signal transduction pathway in eukaryotes that regulates a variety of immune responses. This study accomplished the first isolation of an AccMKK4 gene from Apis cerana cerana and explored its function. Yeast two-hybrid experiments proved that AccMKK4 can interact with Accp38b, and the silencing of AccMKK4 in honeybees downregulated the expression level of Accp38b, which suggests that AccMKK4 might participate in the oxidative stress response through the p38 MAPK pathway. Tissue-specific expression levels of AccMKK4 analysis showed that AccMKK4 in the thorax, particularly muscle tissue, was higher than that in other tissues. The qRT-PCR results from different conditions demonstrated that AccMKK4 responds to various environmental stresses. After AccMKK4 silencing, the transcription level of some antioxidant genes and the activity of antioxidant-related enzymes are reduced, which indicated that AccMKK4 plays an important role in resistance against oxidative stress caused by external stimuli. In summary, our findings indicate that AccMKK4 probably plays an indispensable role in the response of honeybees to environmental stress and might aid for further research on the role of the MAPK cascade pathway in the antioxidant defence mechanisms of insects.

Underlying mechanisms of cytotoxicity in HepG2 hepatocarcinoma cells exposed to arsenic, cadmium and mercury individually and in combination

BACKGROUND

Toxicity data regarding combinational exposure of humans to arsenic, cadmium and mercury is scarce. Although hepatotoxicity has been reported, limited information is available on their mechanistic underpinnings. The cytotoxic mechanisms of these metals were determined in HepG2 hepatocarcinoma cell lines after individual and combinational exposure.

METHODS

HepG2 cells were exposed to heavy metals (sodium arsenite, cadmium chloride, and mercury chloride) individually or in combination for 24 h, after which cell density, mitochondrial membrane potential (ΔΨm), reactive oxygen species (ROS), reduced glutathione (GSH), adenosine triphosphate (ATP) and caspase-3/7 activity was assessed.

RESULTS AND DISCUSSION

Cadmium (IC₅₀ = 0.43 mg/L) and the combination (0.45 mg/L, arsenic reference) were most cytotoxic, followed by arsenic (6.71 mg/L) and mercury (28.23 mg/L). Depolarisation of the ΔΨm and reductions in ROS, GSH and ATP levels occurred. Arsenic, cadmium and the combination increased caspase-3/7 activity, while mercury reduced it.

CONCLUSION

The combination produced a greater, albeit mechanistically similar, cytotoxicity compared to individual metals. Cytotoxicity was dependent on altered mitochondrial integrity, redox-status, and bioenergetics. Although the combination's cytotoxicity was associated with caspase-3/7 activity, this was not true for mercury. Heavy metal interactions should be assessed to elucidate molecular underpinnings of cytotoxicity.

Zinc-pretreatment triggers glutathione and Nrf2-mediated protection against inorganic mercury-induced cytotoxicity and intrinsic apoptosis in PC12 cells

Mercury (Hg) is a hazardous metal, poses environmental problems with severe human health effects; whereas zinc (Zn) is an essential micronutrient with antioxidant properties. The purpose of this research was to investigate the effect of Zn on inorganic Hg-induced cytotoxicity in the PC12 cells. The cells were treated with HgCl₂ (5 μM) for 48 h with/without 1 h prior ZnCl₂-treatment (100 μM) and deliberated for further analysis. After 48 h of incubation with only Hg²⁺, the cell showed reduced cell viability, compromised cell membrane, DNA degradation, depleted glutathione level, ROS generation and drastically increased apoptosis. Subsequently, Hg²⁺-treated cells demonstrated a significant downregulation of akt, mTOR, ERK1, Nrf2, HO1, Bcl-2, Bcl-xL, and upregulation of p53, Bax, cytochrome c and cleaved caspase 3, indicating intrinsic apoptosis induction. However, cells pretreated with Zn²⁺ before Hg²⁺-exposure showed a significant improvement in cell viability, cell membrane, DNA damage, glutathione level, ROS amount and apoptotic cells, with a significant upregulation in mTOR, akt, ERK1, Nrf2, HO1, Bcl-2 and Bcl-xL, and downregulation in p53, Bax, cytochrome c and cleaved caspase 3, indicating inhibition of apoptosis. The findings suggested that Zn²⁺-pretreatment not only improves glutathione content but also induces activation of Nrf2-HO1 pathway, which would tend to suppress Hg-cytotoxicity.

Selenium modulates inorganic mercury induced cytotoxicity and intrinsic apoptosis in PC12 cells

Mercury (Hg) in its all forms, including inorganic Hg (iHg) is an environmental contaminant due to toxicity and diseases in human. However, a little is known about the underlying mechanisms responsible for iHg toxicity. Selenium (Se) is an essential trace element, recognized as an antioxidant and protective agent against metal toxicities. The purpose of this research was to investigate ameliorations of Se counter to iHg-mediated toxicity in PC12 cells. Cytotoxic assays have been shown that iHg (5 μM) caused oxidative stress and intrinsic apoptosis via ROS generation, oxidizing glutathione, damaging DNA, degrading cell membrane integrity, down-regulating mTOR, p-mTOR, akt and ERK1, and up-regulating cleaved caspase 3 and cytochrome c release in PC12 cells 48 h after incubation. Co-treatment of Se (5 μM) inhibited intrinsic apoptosis and oxidative stress induced by iHg (5 μM) via inhibiting ROS formation, boosting GPx contents, increasing reduced glutathione, limiting DNA degradation, improving cell membrane integrity, up-regulating mTOR, p-mTOR, akt, ERK1 and caspase 3, and down-regulating cleaved caspase 3 and cytochrome c leakage in PC12 cells. In conclusion, these results recommended that excessive ROS generation acts a critical role in iHg-influenced oxidative stress and co-treatment of Se attenuates iHg-cytotoxicity through its antioxidant properties.

Amelioration of butylated hydroxytoluene against inorganic mercury induced cytotoxicity and mitochondrial apoptosis in PC12 cells via antioxidant effects

Mercury (Hg) is a toxic metal, well-known for its dangerous health effects on human. Butylated hydroxytoluene (BHT) is a phenolic component generally consumed as a food additive as an antioxidant. However, BHT induced antioxidant properties against heavy metals-influenced toxicity are little studied. We hypothesized that BHT has a regulatory effect on Hg-induced cytotoxicity. The objective of this research was to assess the protecting effects of BHT against inorganic Hg (iHg)-toxicity in PC12 cells, where cells were treated with/without HgCl₂ (Hg²⁺) (5 μM) and BHT (100 μM) for 48 h and analyzed further. Cells treated by Hg caused a significant cell viability reduction, membrane damage, glutathione reduction, DNA fragmentation, ROS generation, with suppressed expressions of akt, mTOR, ERK1, Nrf2 and HO1; and elevated apoptotic expressions of p53, Bax, cytochrome c and active caspase 3. However, BHT and Hg²⁺ co-exposure showed prevention against Hg²⁺-toxicity by improving GSH content and inhibiting ROS generation and oxidative stress mediated damages. Additionally, BHT co-treatment inverted the pro-apoptotic proteins by augmenting pro-survival regulatory proteins akt, mTOR, ERK1, Nrf2 and HO1. These findings proved that BHT inhibits Hg²⁺-toxicity, hindering ROS generation and intrinsic apoptosis, via enhancing glutathione and antioxidants; and suggested BHT implications as therapeutic.

Antioxidant and cytoprotective properties of loganic acid isolated from seeds of Strychnos potatorum L. against heavy metal induced toxicity in PBMC model

Present work carried out with the objectives to isolate active component of S. potatorum and also to evaluate its free radical scavenging activity and preventing capacity against heavy metal toxicity. Solvents of different polarity were used to prepare crude extracts of S. potatorum seeds and screened for antioxidant activity. Among the crude extracts, methanolic extract was found to exhibit higher antioxidant activity (81.22%) which was fractionated by liquid-liquid partitioning method. Among the different fractions (LF1-LF4), LF-2 showed higher antioxidant activity (98.24%) as compared to other three liquid fractions and hence LF-2 was further purified by column chromatography. Among nine column fractions (CF1-CF9), fraction CF-7 was found to have higher antioxidant activity (92.14%), which was further analyzed using LC-MS and NMR and identified as loganic acid. In vitro radical scavenging assays showed remarkable antioxidant activity of loganic acid in terms of DPPH scavenging (IC₅₀ 149 µg/ml), superoxide radical scavenging (IC₅₀ 632.43 µg/ml) and hydroxyl radical scavenging (IC₅₀ 29.78 µg/ml). Loganic acid exhibited 81% prevention of heavy metal toxicity through the mechanism of inhibiting ROS generation (2046 AU vs. 5264 AU in control) and lipid peroxidation (95.01%). Thus, the active compound (loganic acid) isolated from S. potatorum has strong free radical scavenging activity and remarkable cyto-protective effect against heavy metal mediated toxicity.

A fluorescence assay for the detection of hydrogen peroxide and hydroxyl radicals generated by metallonucleases

Metal complexes can initiate DNA cleavage by the formation of reactive oxygen species (ROS). A conventional assay to probe for ROS is to add quenchers in a gel electrophoresis experiment. As we show here, such an assay is neither selective nor reliable. Instead, we suggest the use of simple fluorogens, as tested here with several metallonucleases for the detection of H2O2 and HO˙.

Genome-Wide Association Study to Identify Genes Related to Renal Mercury Concentrations in Mice

BACKGROUND

Following human mercury (Hg) exposure, the metal accumulates in considerable concentrations in kidney, liver, and brain. Although the toxicokinetics of Hg have been studied extensively, factors responsible for interindividual variation in humans are largely unknown. Differences in accumulation of renal Hg between inbred mouse strains suggest a genetic interstrain variation regulating retention or/and excretion of Hg. A.SW, DBA/2 and BALB/C mouse strains accumulate higher amounts of Hg than B10.S.

OBJECTIVES

We aimed to find candidate genes associated with regulation of renal Hg concentrations.

METHODS

A.SW, B10.S and their F1 and F2 offspring were exposed for 6 weeks to 2.0 mg Hg/L drinking water. Genotyping with microsatellites was conducted on 84 F2 mice for genome-wide scanning with ion pair reverse-phase high-performance liquid chromatography (IP RP HPLC). Quantitative trait loci (QTL) were established. Denaturing HPLC was used to detect single nucleotide polymorphisms for haplotyping and fine mapping in 184 and 32 F2 mice, respectively. Candidate genes (Pprc1, Btrc and Nfkb2) verified by fine mapping and QTL were further investigated by real-time polymerase chain reaction. Genes enhanced by Pprc1 (Nrf1 and Nrf2) were included for gene expression analysis.

RESULTS

Renal Hg concentrations differed significantly between A.SW and B10.S mice and between males and females within each strain. QTL analysis showed a peak logarithm of odds ratio score 5.78 on chromosome 19 (p = 0.002). Haplotype and fine mapping associated the Hg accumulation with Pprc1, which encodes PGC-1-related coactivator (PRC), a coactivator for proteins involved in detoxification. Pprc1 and two genes coactivated by Pprc1 (Nrf1 and Nrf2) had significantly lower gene expression in the A.SW strain than in the B10.S strain.

CONCLUSIONS

This study supports Pprc1 as a key regulator for renal Hg excretion.

CITATION

Alkaissi H, Ekstrand J, Jawad A, Nielsen JB, Havarinasab S, Soderkvist P, Hultman P. 2016. Genome-wide association study to identify genes related to renal mercury concentrations in mice. Environ Health Perspect 124:920-926; http://dx.doi.org/10.1289/ehp.1409284.

Characterization of a Decapentapletic Gene (AccDpp) from Apis cerana cerana and Its Possible Involvement in Development and Response to Oxidative Stress

To tolerate many acute and chronic oxidative stress-producing agents that exist in the environment, organisms have evolved many classes of signal transduction pathways, including the transforming growth factor β (TGFβ) signal pathway. Decapentapletic gene (Dpp) belongs to the TGFβ superfamily, and studies on Dpp have mainly focused on its role in the regulation of development. No study has investigated the response of Dpp to oxidative pressure in any organism, including Apis cerana cerana (A. cerana cerana). In this study, we identified a Dpp gene from A. cerana cerana named AccDpp. The 5΄ flanking region of AccDpp had many transcription factor binding sites that relevant to development and stress response. AccDpp was expressed at all stages of A. cerana cerana, with its highest expression in 15-day worker bees. The mRNA level of AccDpp was higher in the poison gland and midgut than other tissues. Furthermore, the transcription of AccDpp could be repressed by 4°C and UV, but induced by other treatments, according to our qRT-PCR analysis. It is worth noting that the expression level of AccDpp protein was increased after a certain time when A. cerana cerana was subjected to all simulative oxidative stresses, a finding that was not completely consistent with the result from qRT-PCR. It is interesting that recombinant AccDpp restrained the growth of Escherichia coli, a function that might account for the role of the antimicrobial peptides of AccDpp. In conclusion, these results provide evidence that AccDpp might be implicated in the regulation of development and the response of oxidative pressure. The findings may lay a theoretical foundation for further genetic studies of Dpp.

Riluzole-triggered GSH synthesis via activation of glutamate transporters to antagonize methylmercury-induced oxidative stress in rat cerebral cortex

OBJECTIVE

This study was to evaluate the effect of riluzole on methylmercury- (MeHg-) induced oxidative stress, through promotion of glutathione (GSH) synthesis by activating of glutamate transporters (GluTs) in rat cerebral cortex.

METHODS

Eighty rats were randomly assigned to four groups, control group, riluzole alone group, MeHg alone group, and riluzole + MeHg group. The neurotoxicity of MeHg was observed by measuring mercury (Hg) absorption, pathological changes, and cell apoptosis of cortex. Oxidative stress was evaluated via determining reactive oxygen species (ROS), 8-hydroxy-2-deoxyguanosine (8-OHdG), malondialdehyde (MDAs), carbonyl, sulfydryl, and GSH in cortex. Glutamate (Glu) transport was studied by measuring Glu, glutamine (Gln), mRNA, and protein of glutamate/aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1).

RESULT

(1) MeHg induced Hg accumulation, pathological injury, and apoptosis of cortex; (2) MeHg increased ROS, 8-OHdG, MDA, and carbonyl, and inhibited sulfydryl and GSH; (3) MeHg elevated Glu, decreased Gln, and downregulated GLAST and GLT-1 mRNA expression and protein levels; (4) riluzole antagonized MeHg-induced downregulation of GLAST and GLT-1 function and expression, GSH depletion, oxidative stress, pathological injury, and apoptosis obviously.

CONCLUSION

Data indicate that MeHg administration induced oxidative stress in cortex and that riluzole could antagonize this situation through elevation of GSH synthesis by activating of GluTs.

Role of non-enzymatic antioxidants on the bivalves' adaptation to environmental mercury: Organ-specificities and age effect in Scrobicularia plana inhabiting a contaminated lagoon

This study aimed to investigate the role of non-enzymatic antioxidants on adaptive skills over time in the bivalve Scrobicularia plana environmentally exposed to mercury. Inter-age (2(+), 3(+), 4(+), 5(+) year old) and organ-specific (gills, digestive gland) approaches were applied in bivalves collected from moderately and highly contaminated sites at Ria de Aveiro (Portugal). S. plana's adaptive skills were dependent on the contamination extent; under moderate contamination scenario, the intervention of the different antioxidants took place harmoniously, evidencing an adjustment capacity increasing with the age. Under higher contamination degree, S. plana failed to cope with mercury threat, showing an age-dependent deterioration of the defense abilities. In organ-specific approach, the differences were particularly evident for thiol-compounds, since only gills displayed the potential to respond to moderate levels by increasing non-protein thiols and total glutathione. Under high contamination degree, both organs were unable to increase thiol-compounds, which were compensated by the ascorbic acid elevation.

Mangiferin, a dietary xanthone protects against mercury-induced toxicity in HepG2 cells

Mercury is one of the noxious heavy metal environmental toxicants and is a cause of concern for human exposure. Mangiferin (MGN), a glucosylxanthone found in Mangifera indica, reported to have a wide range of pharmacological properties. The objective of this study was to evaluate the cytoprotective potential of MGN, against mercury chloride (HgCl(2) ) induced toxicity in HepG2 cell line. The cytoprotective effect of MGN on HgCl(2) induced toxicity was assessed by colony formation assay, while antiapoptotic effect by fluorescence microscopy, flow cytometric DNA analysis, and DNA fragmentation pattern assays. Further, the cytoprotective effect of MGN against HgCl(2) toxicity was assessed by using biochemical parameters like reduced glutathione (GSH), glutathione-S-transferase (GST), superoxide dismutase (SOD), catalase (CAT) by spectrophotometrically, mitochondrial membrane potential by flowcytometry and the changes in reactive oxygen species levels by DCFH-DA spectrofluoremetric analysis. A significant increase in the surviving fraction was observed with 50 μM of MGN administered two hours prior to various concentrations of HgCl(2) . Further, pretreatment of MGN significantly decreased the percentage of HgCl(2) induced apoptotic cells. Similarly, the levels of ROS generated by the HgCl(2) treatment were inhibited significantly (P < 0.01) by MGN. MGN also significantly (P < 0.01) inhibited the HgCl(2) induced decrease in GSH, GST, SOD, and CAT levels at all the post incubation intervals. Our study demonstrated the cytoprotective potential of MGN, which may be attributed to quenching of the ROS generated in the cells due to oxidative stress induced by HgCl(2) , restoration of mitochondrial membrane potential and normalization of cellular antioxidant levels.

Quercetin accumulates in nuclear structures and triggers specific gene expression in epithelial cells

Quercetin is a flavonol modifying a number of cell processes in different cell lines. Here, we present evidence that nonconjugated quercetin enters cells possibly via organic anion transporter polypeptides and quickly accumulates in the nucleus where it concentrates at distinct foci. Furthermore, it induces major transcriptional events with a high number of transcripts being modified over time and about 2200 transcripts being continuously influenced by the agent. The latter transcripts are related to cell cycle and adhesion, xenobiotic metabolism, immune-related factors and transcription. In addition, quercetin up-regulates the expression of estrogen receptors α and β. The overall outcome on cell fate is reflected by an inhibition of cell proliferation, cell cycle arrest in the G1 phase and reduction of the cells' migratory potential due to actin cytoskeleton disorganization. Finally, we report that the flavonol modifies the transcription and/or activity of numerous transcription factors. In conclusion, our data support the idea that quercetin may actively accumulate in discrete cell structures and exert more than just antioxidant actions on epithelial cells by regulating mechanisms related to gene transcription.

Scopoli's work in the field of mercurialism in light of today's knowledge: past and present perspectives

The Idrija Mercury Mine (1490-1994) appointed its first physician, Joannes Antonius Scopoli, in 1754. Most of his descriptions of mercurialism are still relevant today. This study highlights Scopoli's observations on the interaction between elemental mercury (Hg degrees ) and alcohol, on the appearance of lung impairment, insomnia, and depressive mood in mercurialism. This presentation is based on Scopoli's experiences presented in his book, De Hydrargyro Idriensi Tentamina (1761), current knowledge, and our own experience acquired through health monitoring of occupational Hg degrees exposure. Some studies have confirmed Scopoli's observation that alcohol enhances mercurialism and his hypothesis that exposure to high Hg degrees concentrations causes serious lung impairment. Neurobiological studies have highlighted the influence of Hg degrees on sleep disorder and depressive mood observed by Scopoli. Although today's knowledge provides new perspectives of Scopoli's work on mercurialism, his work is still very important and can be considered a part of occupational medicine heritage.

Effect of uric acid on nephrotoxicity induced by mercuric chloride in rats

Oxidative stress is an important mechanism in mercury poisoning. We studied the effect of uric acid, a natural and potent reactive oxygen species and peroxynitrite scavenger, in HgCl( 2)-induced nephrotoxicity. Rats were injected with a unique dose of HgCl(2) (2.5 mg/kg body weight, subcutaneously) and then vehicle (for 3 days, twice daily) or HgCl(2) (unique dose) and intraperitoneal uric acid suspension (250 mg/kg body weight, twice daily, for 3 days), and then killed at 24, 48 and 72 hours after HgCl(2) administration (n = 5 for each group). At the end of the experimental study, kidneys and blood samples were taken. Tissues were prepared and examined under light microscopy. Uric acid significantly prevented the increase in plasma levels of creatinine and blood urea nitrogen (BUN); it helped maintain systemic nitrate/nitrite concentration and total antioxidant capacity. Uric acid attenuated the increase of renal lipid peroxidation and it markedly diminished nitrotyrosine signal and histopathological changes as early as 24 hours after HgCl(2) administration. Uric acid did not prevent a decrease in beta-actin signal caused by mercuric chloride, but it promoted a faster recovery when compared to the HgCl(2) alone group. Our results indicate that UA could play a beneficial role against HgCl(2) toxicity by preventing systemic and renal oxidative stress and tissue damage.

Structural, chemical and biological aspects of antioxidants for strategies against metal and metalloid exposure

Oxidative stress contributes to the pathophysiology of exposure to heavy metals/metalloid. Beneficial renal effects of some medications, such as chelation therapy depend at least partially on the ability to alleviate oxidative stress. The administration of various natural or synthetic antioxidants has been shown to be of benefit in the prevention and attenuation of metal induced biochemical alterations. These include vitamins, N-acetylcysteine, alpha-lipoic acid, melatonin, dietary flavonoids and many others. Human studies are limited in this regard. Under certain conditions, surprisingly, the antioxidant supplements may exhibit pro-oxidant properties and even worsen metal induced toxic damage. To date, the evidence is insufficient to recommend antioxidant supplements in subject with exposure to metals. Prospective, controlled clinical trials on safety and effectiveness of different therapeutic antioxidant strategies either individually or in combination with chelating agent are indispensable. The present review focuses on structural, chemical and biological aspects of antioxidants particularly related to their chelating properties.

Prevention of methylmercury-induced mitochondrial depolarization, glutathione depletion and cell death by 15-deoxy-delta-12,14-prostaglandin J(2)

Methylmercury (MeHg) is an environmental toxin that causes severe neurological complications in humans and experimental animals. In addition to neurons, glia in the central nervous system are very susceptible to MeHg toxicity. Pretreatment of glia with the prostaglandin derivative, 15-deoxy-delta-12,14-prostaglandin J(2) (15d-PGJ(2)), caused a significant protection against MeHg cytotoxicity. Results with the C6 glioma cells demonstrated that the protection was dependent on the duration of pretreatment, suggesting that time was required for the up-regulation of cellular defenses. Subsequent experiments indicated that 15d-PGJ(2) prevented MeHg induced mitochondrial depolarization. Similar protection against MeHg cytotoxicity was observed in primary cultures of mouse glia. Analysis of cellular glutathione (GSH) levels indicated that 15d-PGJ(2) caused an up-regulation of GSH and prevented MeHg-induced GSH depletion. Buthionine sulfoximine (BSO), a GSH synthesis inhibitor, completely inhibited the GSH induction by 15d-PGJ(2). However, BSO did not prevent the stabilization of mitochondrial potential and only partially prevented the protection caused by 15d-PGJ(2). While induction of heme oxygenase-1 was implicated in the cytoprotection by 15d-PGJ(2) under some experimental conditions, additional experiments indicated that this enzyme was not involved in the cytoprotection observed in this system. Together, these results suggested that while up-regulation of GSH by 15d-PGJ(2) might help cells to defend against MeHg toxicity, there may be other yet unidentified mechanism(s) initiated by 15d-PGJ(2) treatment that contributed to its protection against MeHg cytotoxicity.

Glutathione level after long-term occupational elemental mercury exposure

Many in vitro and in vivo studies have elucidated the interaction of inorganic mercury (Hg) and glutathione. However, human studies are limited. In this study, we investigated the potential effects of remote long-term intermittent occupational elemental Hg vapour (Hg degrees ) exposure on erythrocyte glutathione levels and some antioxidative enzyme activities in ex-mercury miners in the period after exposure. The study included 49 ex-mercury miners divided into subgroups of 28 still active, Hg degrees -not-exposed miners and 21 elderly retired miners, and 41 controls, age-matched to the miners subgroup. The control workers were taken from "mercury-free works". Reduced glutathione (GSH) and oxidized disulphide glutathione (GSSG) concentrations in haemolysed erythrocytes were determined by capillary electrophoresis, while total glutathione (total GSH) and the GSH/GSSG ratio were calculated from the determined values. Catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR) activities in erythrocytes were measured using commercially available reagent kits, while urine Hg (U-Hg) concentrations were determined by cold vapour atomic absorption (CVAAS). No correlation of present U-Hg levels, GSH, GSSG, and antioxidative enzymes with remote occupational biological exposure indices were found. The mean CAT activity in miners and retired miners was significantly higher (p<0.05) than in the controls. No differences in mean GPx activity among the three groups were found, whereas the mean GR activity was significantly higher (p<0.05) in miners than in retired miners. The mean concentrations of GSH (mmol/g Hb) in miners (13.03+/-3.71) were significantly higher (p<0.05) than in the control group (11.68+/-2.66). No differences in mean total GSH, GSSG levels, and GSH/GSSG ratio between miners and controls were found. A positive correlation between GSSG and present U-Hg excretion (r=0.41, p=0.001) in the whole group of ex-mercury miners was observed. The significantly lower GSH level (p<0.05) determined in the group of retired miners (9.64+/-1.45) seems to be age-related (r= -0.39, p=0.001). Thus, the moderate but significantly increased GSH level, GR and CAT activity in erythrocytes in the subgroup of miners observed in the period after exposure to Hg degrees could be an inductive and additive response to maintain the balance between GSH and antioxidative enzymes in interaction with the Hg body burden accumulated during remote occupational exposure, which does not represent a severely increased oxidative stress.

Protection against arsenic trioxide-induced autophagic cell death in U118 human glioma cells by use of lipoic acid

Arsenic is an environmental toxicant found naturally in ground water. Epidemiological studies have suggested a correlation between chronic arsenic exposure and potential brain tissue damage in clinical case and animal experiments. Lipoic acid (LA) is a thiol-compound naturally occurring in plants and animals, which is thought to be a strong antioxidant and possess neuroprotective effects. The objective of this study was to determine if the AS(2)O(3)-induced glial cell toxicity could be prevented by LA. The human malignant glioma cell (U118) was selected as a research model. By using acridine orange staining and flow cytometry analysis, we found that autophagic, but not apoptotic, cell death was significantly induced by AS(2)O(3) in U118 cells, and that AS(2)O(3)-mediated autophagic cell death was nearly completely attenuated by LA. Down-regulation of p53 and Bax proteins and the up-regulation of Bcl-2 and HSP-70 proteins were observed by western blot in AS(2)O(3)-mediated autophagic cell death. Our results implied that LA completely inhibited U118 cells autophagic cell death induced by AS(2)O(3). We suggested that LA may emerge as a useful protective agent against arsenic-induced glial cell toxicity and reversing arsenic-induced damage in human brain.

Novel selenoorganic compounds as modulators of oxidative stress in blood platelets

Many selenoorganic compounds play an important role in biochemical processes and act as antioxidants, enzyme inhibitors, or drugs. The effects of five new synthesized selenoorganic compounds (2-(5-chloro-2-pyridyl)-7-azabenzisoselenazol-3(2H)-one; 2-phenyl-7-azabenzisoselenazol-3(2H)-one; 2-(pyridyl)-7-azabenzisoselenazol-3(2H)-one; 7-azabenzisoselenazol-3(2H)-one; bis(2-aminophenyl) diselenide) on oxidative changes in human blood platelets and in plasma were studied in vitro and compared with those of ebselen, a well known antioxidant. Our studies demonstrated that bis(2-aminophenyl) diselenide has distinctly protective effects against oxidative stress in blood platelets and in plasma. It might have greater biological relevance and stronger pharmacological effects than ebselen.

Hg(II) exposure exacerbates UV-induced DNA damage in MRC5 fibroblasts: a comet assay study

When exposed to UVR, MRC5 fibroblasts incubated with mercuric chloride (0-15 microM) for 1 hour show increased DNA damage (as measured by the comet assay) compared to control cells (UVR irradiated but no mercuric chloride). This demonstrates that mercuric chloride and UVR in combination increase DNA damage in a synergistic manner. This may have implications to those exposed to mercury as it suggests that exposure to mercury in the environment may increase sensitivity to sunlight-induced carcinogenesis.

Bull Spermatozoa under Mercury Stress

Defective sperm function is the most prevalent cause of male infertility and is difficult to treat. This study was designed to evaluate the effect of mercuric chloride (HgCl2) at 50-300 micromol/l concentration range, in vitro, on the sperm membrane and DNA integrity, viability, reduced glutathione (GSH) content and acrosomal status of the bull spermatozoa. The samples were processed for sperm analyses using semen-diluting fluid [phosphate-buffered saline (PBS), pH 7.2]. I recorded a meaningful increase in the lipid peroxidation (LPO) rate and a drastic fall in the spermatocrit values under mercury additions, dominantly at 300 microM mercury concentration, indicating a deleterious effect of mercury on the sperm membrane intactness. There was also a strong negative correlation between LPO rate and percentage of viable spermatozoa (r = -0.9, p < 0.001). GSH content was significantly impaired. Data obtained from Comet assay [single-cell gel electrophoresis (SCGE)] technique revealed that mercury is capable of inducing DNA breaks in the sperm nuclei. Interestingly, 90% of DNA breaks were double-stranded. The correlation between LPO rate and percentage of DNA breaks was found to be 0.9 (p < 0.001). Results of the gelatin test indicate that mercury is capable of altering the integrity of acrosomal membranes, showing an abnormal acrosome reaction. In this regard, a strong correlation was found between LPO rate and percentage of halos (r = -0.9, p < 0.001). In conclusion, mercury proved to be a potential oxidant in the category of 'environmental factors' to bull spermatozoa. Hence, considering the widespread use of mercury and its compounds, these metals should be regarded with more concern.

Effects of lipopolysaccharides from gram-negative bacteria on the level of thiols in blood platelets

Lipopolysaccharide (endotoxin, LPS) activates blood platelets and stimulates generation of free radicals in these cells. The mechanism of platelet activation induced by LPS is not known. The aim of the present study was to examine how glutathione (GSH) and other thiol-containing compounds are involved in the oxidative stress in blood platelets caused by LPS. The HPLC technique has been used on the analysis of non-protein thiols from human blood platelets treated with lipopolysaccharides of different gram-negative bacteria (Proteus mirabilis, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa). Our results show that LPSs caused an increase (about 10%) of the level of reduced glutathione (GSH) and other nonprotein thiols such as cysteine (CSH) and cysteinylglycine (CGSH), whereas the total pool of these compounds was almost unchanged. LPS may react directly with thiols, since after incubation of LPSs with glutathione alone (in reduced form) we observed a distinct decrease of the level of platelet GSH.

Modulatory effect of glutathione status and antioxidants on methylmercury-induced free radical formation in primary cultures of cerebral astrocytes

Excessive free radical formation has been implicated as one of the causative factors in neurotoxic damage associated with variety of metals, including methylmercury (MeHg). Although the mechanism(s) associated with MeHg-dependent neurotoxicity remains far from clear, overwhelming data give credence to a mediatory role for astrocytes, a major cell type that preferentially accumulates MeHg. To extend our recent findings of MeHg-induced increase in ROS formation (G. Shanker, J.L. Aschner, T. Syversen et al., Free radical formation in cerebral cortical astrocytes in culture induced by methylmercury, Mol. Brain Res. 128 (2004) 48-57), the present studies were designed to assess the effect of modulating intracellular glutathione (GSH) content, on ROS generation, in the absence and presence of MeHg. Intracellular GSH was reduced by treatment with 100 microM buthionine-L-sulfoxane (BSO) for 24 h, and increased by treatment with 1 mM l-2-oxothiazolidine-4-carboxylic acid (OTC) for 24 h. Additionally, the effects of the selective antioxidants, catalase (1000 U/ml for 1 h), an H2O2 scavenger, and n-propyl gallate (100 microM for 1 h), a superoxide radical (*O2-) and possibly hydroxyl radical (*OH) scavenger on MeHg-induced ROS formation were examined. After these treatments, astrocytes were exposed to +/-10 microM MeHg for 30 min, following which the fluorescent probes, CM-H2DCFA and CM-H2XRos were added; 20 min later, laser scanning confocal microscopy (LSCM) images were obtained. Exposure of astrocytes for 24 h to 100 microM BSO, a GSH synthesis inhibitor, led to a significant increase in mitochondrial ROS (i.e., *O2-, *NO, and ONOO-) formation, as assessed with CM-H2XRos mitotracker red dye. Similarly, BSO increased ROS formation in various intracellular organelles, as assessed with CM-H2DCFDA. BSO in combination with MeHg increased fluorescence levels in astrocytes to levels above those noted with BSO or MeHg alone, but this effect was statistically indistinguishable from either of these groups (BSO or MeHg). Pretreatment of astrocytes for 24 h with 1 mM OTC abolished the MeHg-induced increase in ROS. Results similar to those obtained with OTC were observed with the free radical scavenger, n-propyl gallate (n-PG). The latter had no significant effects on astrocytic fluorescence when administered alone. This *O2- and possibly *OH radical scavenger significantly attenuated MeHg-induced ROS formation. Catalase, an H2O2 scavenger, was less effective in reducing MeHg-induced ROS formation. Taken together, these studies point to the important protective effect of adequate intracellular GSH content as well as antioxidants against MeHg-triggered oxidative stress in primary astrocyte cultures.

Free radical formation in cerebral cortical astrocytes in culture induced by methylmercury

Oxidative stress has been implicated in neurotoxic damage associated with various metals, including methylmercury (MeHg). Although the mechanism(s) of MeHg-induced neurotoxicity remains unclear, evidence supports a mediatory role for astrocytes, a cell type that preferentially accumulates MeHg. Using scanning confocal microscopy (LSCM), the present study was undertaken to examine the role of astrocytes as the site of reactive oxygen species (ROS). Three redox-sensitive fluorescent probes were used for ROS analysis, (a) CM-H2DCFDA (chloromethyl derivative of dichlorodihydrofluorescein diacetate), a probe for intracellular hydrogen peroxide (H2O2); (b) hydroethidine (HETH), a probe for superoxide anion (*O2-), and (c) CM-H2XRos (chloromethyl derivative of dihydro X-rosamine), and a probe that is selective for mitochondrial reactive oxygen intermediates. Astrocytes were treated with 10 microM MeHg for 30 min, following which the various fluorescent probes were added; 20 min later LSCM images were collected. Astrocytes loaded with CM-H2DCFDA and HE demonstrated a significant MeHg-induced increase in fluorescence intensity indicative of increased intracellular H2O2 and *O2-, respectively. Similar results were obtained with the mitotracker dye, CM-H2XRos. Additionally, exposure of astrocytes for 24 h to 100 microM buthionine-L-sulfoxane (BSO), a glutathione (GSH) synthesis inhibitor, caused a significant increase in ROS formation. Furthermore, BSO pretreatment significantly enhanced the MeHg-induced formation of *O2-, indicating an important role for GSH in the maintenance of optimal cellular redox status. Time-course experiments performed in the simultaneous presence of CM-H2XRos and CM-H2DCFDA demonstrated that the MeHg-induced CM-H2XRos fluorescence changes preceded those of CM-H2DCFDA, suggesting that the mitochondria represent an early primary site for ROS formation. Taken together, these studies illustrate that MeHg induces the generation of astrocyte-derived ROS and support a role for astrocytic ROS in MeHg-associated neurotoxic damage.

Cytotoxicity of inorganic mercury in murine T and B lymphoma cell lines: involvement of reactive oxygen species, Ca(2+) homeostasis, and cytokine gene expression

Mercury is a highly toxic heavy metal; exposure to mercury in humans and animals causes damage in several organs or systems including the immune system. To characterize the toxicity of mercury in the immune cells, the cytotoxic effects of inorganic mercury were studied in two distinct lymphoma lines, the murine T lymphoma (EL4) and B lymphoma (A20) cells. Mercury concentration-dependently decreased cell viability, membrane integrity, and proliferation in both EL4 and A20 cells. Mercury increased the reactive oxygen species (ROS) production in both EL4 and A20 cells, and pretreatment with antioxidants reversed mercury-induced ROS generation. Pretreatment of cells with antioxidants N-acetylcysteine (NAC) and silymarin decreased mercury-induced lactate dehydrogenase (LDH) release in both types of cells; however, Ca(2+) channel blocker lanthanum (La(2+)) decreased it only in A20 cells. The mode of cytotoxicity was a mixture of both apoptosis and necrosis. Mercury-induced apoptosis and necrosis in the two cell lines were indicated by staining with Hoechst 33258, propidium iodide, and co-staining with annexin V and propidium iodide. Both mercury-induced apoptosis and necrosis were attenuated by antioxidants. Mercury increased gene expression of IL-4 and TNFalpha in EL4 cells; these cytokines were not expressed in A20 cells. Data suggested different pathways of mercury-induced cytotoxicity in T and B lymphoma cells and involvement of ROS, Ca(2+) homeostasis, and inflammatory cytokine gene expression.