Cellular toxicity and lipid peroxidation in response to mercury

Oxidative stress in Arthrospira platensis by two organophosphate pesticides

Although it is known that organophosphate insecticides are harmfull to aquatic ecosystems, oxidative damages caused by Dimethoate and Chlorpyrifos are not studied on Arthrospira platensis Gomont. In this study, various Chlorpyrifos (0-150 µg mL-1) and Dimethoate (0-250 µg mL-1) concentrations were added to the culture medium in laboratory to evaulate growth rate, chlorophyll-a content and antioxidant parameters of A. platensis. Optical Density (OD560) and chlorophyll-a decreased compared to the control for seven days in both pesticide applications. Superoxide dismutase (SOD) activity increased at 50 µg mL-1 Chlorpyrifos concentration but it decreased at all concentrations. Although Ascorbate peroxidase (APX) and glutathione reductase (GR) activities increased with Chlorpyrifos application, they did not change with Dimethoate application. Malondialdehyde (MDA) amount decreased at 150 µg mL-1 Chlorpyrifos concentration but it increased in Dimethoate application. The H2O2 content were increased in both applications. Proline decreased in 50 and 75 µg mL-1 Chlorpyrifos concentrations and increased at 150 µg mL-1 concentration, while it increased at 25 µg mL-1 Dimethoate concentration. The results were tested at 0.05 significance level. These pesticides inhibit A. platensis growth and chlorophyll-a production and cause oxidative stress. The excessive use may affect the phytoplankton and have negative consequences in the aquatic ecosystem.

Pharmacological and ameliorative effects of Withania somnifera against cadmium chloride-induced oxidative stress and immune suppression in Nile tilapia, Oreochromis niloticus

This study was carried out to evaluate the effects of dietary supplementation of aqueous extract of Withania somnifera (W. somnifera) against cadmium chloride-induced toxicity in the Nile tilapia, Oreochromis niloticus. Five experimental groups were designed: group (I) was free from cadmium chloride and W. somnifera and served as a control, group (II) was exposed to 1.775 mg L^-1 of cadmium chloride only (which is equivalent to 1/4 96-h LC50), while groups (III), (IV), and (V) were exposed to 1.775 mg cadmium chloride L^-1 with co-supplementation of dietary W. somnifera in doses of 1.0, 2.0, and 3.0 mL kg^-1 body weight (bwt), respectively. The experiment lasted for 4 weeks. In the second and fourth weeks of the experiment, the following indicators were evaluated: hematological (hemogram and blood protein profile), biochemical (activities of serum liver enzymes, namely alanine transaminase (ALT) and aspartate transaminase (AST)), immunological (immunoglobulin M (IgM), serum lysozyme), and tissue antioxidant changes (malondialdehyde (MDA) levels and activities of catalase (CAT) and superoxide dismutase (SOD)). Additionally, gene expressions of glutathione-S-transferase (GST) in the liver were assessed. At the end of the experiment, all fish in all groups were experimentally challenged with Aeromonas hydrophila and the relative protection survival (RPS) was demonstrated. The results revealed that groups exposed to cadmium chloride toxicity and co-supplemented with dietary aqueous extract of W. somnifera at high doses showed significant ameliorative effects in hemogram parameters, total protein, globulin, IgM, and lysozyme against cadmium chloride-induced toxicity compared to the control group and the group exposed to a sublethal dose of cadmium chloride without co-suplemntation of W. somnifera. The results showed also that groups supplemented orally with W. somnifera at high doses have higher antioxidant activities of CAT and SOD and reduction of MDA formation. Levels of gene expressions of GST in the liver were higher in W. somnifera extract-supplemented groups more than those in the group exposed to cadmium chloride-induced toxicity without W. somnifera supplementation. In addition, the results revealed improved RPS with the dietary supply of W. somnifera extract in high doses. In conclusion, this study showed that the dietary supplementation of W. somnifera extract to diets of O. niloticus could be suggested as an effective way to overcome cadmium chloride-induced toxicity because it improves blood parameters and antioxidants, and it can be used as an immunostimulant against the invading bacterial pathogens.

Examining the link between dose-dependent dietary iron intake and Alzheimer's disease through oxidative stress in the rat cortex

BACKGROUND

Neurodegenerative diseases such as Alzheimer's and Parkinson's disease are characterized by the progressive deterioration of the structure and function of the nervous system. A number of environmental risk factors including potentially toxic elements such as iron, lead to negative effects on many metabolic reactions as well as neuroprotection. The aim of this study is to reveal whether long-term iron overload is one of the underlying factors in the pathogenesis of Alzheimer's disease (AD).

METHODS

15 young-adult male rats were randomly divided into 5 groups treated with iron through drinking water for 4 months. Following feeding, the iron content, reduced glutathione (GSH), and hydrogen peroxide (H₂O₂) levels of cortex tissues were measured. Specific enzyme activities were determined spectrophotometrically. mRNA expression profiles were measured using real-time PCR (qPCR).

RESULTS

Iron levels were elevated in case of non-toxic (0.87 and 3 μg/mL) iron administration. However, no changes were observed in toxic (30 and 300 μg/mL) iron administration. GSH and H₂O₂ levels altered with long-term iron overload. Glutathione peroxidase (GPx) enzyme activities significantly increased in all groups, while glutathione S-transferase (GST) activity increased only in case of 0.87 and 30 μg/mL iron administration. Expression levels of neuroprotective and AD-related genes were altered by 3 μg/mL iron overload in a dose-dependent manner. The expression and activity of acetylcholinesterase (AChE) were elevated at 3 μg/mL iron concentration.

CONCLUSION

The findings of the present study allow us to conclude that long-term dietary iron intake, especially at a dose of 3 μg/mL demonstrates negative effects on the rat cortex by provoking antioxidant metabolism and AD pathology in a dose-dependently.

Cytoprotective effects of imidazole-based [S1] and [S2]-donor ligands against mercury toxicity: a bioinorganic approach

Here we report the coordination behaviour of an imidazole-based [S1]-donor ligand, 1,3-dimethyl-imidazole-2(3H)-thione (L1), and [S2]-donor ligand, 3,3'-methylenebis(1-methyl-imidazole-2(3H)-thione) (L2) or 4,4'-(3,3'-methylenebis-(2-thioxo-2,3-dihydro-imidazole-3,1-diyl))dibutanoic acid (L3), with HgX2 (X = Cl, Br or I) in solution and the solid state. NMR, UV-Vis spectroscopic, and single crystal X-ray studies demonstrated that L1 or L2 coordinated rapidly and reversibly to the mercury center of HgX2 through the thione moiety. Treatment of L2 with HgCl2 or HgBr2 afforded 16-membered metallacycle k1-(L2)2Hg2Cl4 or k1-(L2)2Hg2Br4 where two Cl or Br atoms are located inside the ring. In contrast, treatment of L2 with HgI2 afforded a chain-like structure of k1-[L2Hgl2]n, possibly due to the large size of the iodine atom. Interestingly, [S1] and [S2]-donor ligands (L1, L2, and L3) showed an excellent efficacy to protect liver cells against HgCl2 induced toxicity and the strength of their efficacy is in the order of L3 > L2 > L1. 30% decrease of ROS production was observed when liver cells were co-treated with HgCl2 and L1 in comparison to those cells treated with HgCl2 only. In contrast, 45% and 60% decrease of ROS production was observed in the case of cells co-treated with HgCl2 and thiones L2 and L3, respectively, indicating that [S2]-donor ligands L2 and L3 have better cytoprotective effects against oxidative stress induced by HgCl2 than [S1]-donor ligand L1. Water-soluble ligand L3 with N-(CH2)3CO2H substituents showed a better cytoprotective effect against HgCl2 toxicity than L2 in liver cells.

Niacin prevents mitochondrial oxidative stress caused by sub-chronic exposure to methylmercury

Humans and animals can be exposed to different chemical forms of mercury (Hg) in the environment. For example, methylmercury (MeHg)-contaminated fish is part of the basic diet of the riparian population in the Brazilian Amazon Basin, which leads to high total blood and plasma Hg levels in people living therein. Hg induces toxic effects mainly through oxidative stress. Different compounds have been used to prevent the damage caused by MeHg-induced reactive oxygen species (ROS). This study aims to investigate the in vivo effects of sub-chronic exposure to low MeHg levels on the mitochondrial oxidative status and to evaluate the niacin protective effect against MeHg-induced oxidative stress. For this purpose, Male Wistar rats were divided into four groups: control group, treated with drinking water on a daily basis; group exposed to MeHg at a dose of 100 µg/kg/day; group that received niacin at a dose of 50 mg/kg/day in drinking water, with drinking water being administered by gavage; group that received niacin at a dose of 50 mg/kg/day in drinking water as well as MeHg at a dose of 100 µg/kg/day. After 12 weeks, the rats, which weighed 500-550 g, were sacrificed, and their liver mitochondria were isolated by standard differential centrifugation. Sub-chronic exposure to MeHg (100 µg/kg/day for 12 weeks) led to mitochondrial swelling (p < 0.05) and induced ROS overproduction as determined by increased DFCH oxidation (p < 0.05), increased gluthatione oxidation (p < 0.05), and reduced protein thiol content (p < 0.05). In contrast, niacin supplementation inhibited oxidative stress, which counteracted and minimized the toxic MeHg effects on mitochondria.

Evaluation of the toxic potential of calcium carbide in the third instar larvae of transgenic Drosophila melanogaster (hsp70-lacZ)Bg(9)

In the present study the toxic potential of calcium carbide (CaC2) was studied on the third instar larvae of transgenic Drosophila melanogaster (hsp70-lacZ)Bg(9). The third instar larvae were exposed to 2, 4, 8, 16 and 32×10(-3)g/ml of CaC2 in diet for 24h. The results reveal that the dose 2×10(-3)g/ml was not toxic but the remaining doses showed a dose dependent significant increase in the hsp70 expression, β-galactosidase activity, tissue damage, oxidative stress markers (lipid peroxidation and protein carbonyl content), glutathione-S-transferase activity, expression of Caspase 3 and 9, apoptotic index and DNA damage (midgut cells). A significant reduction as compared to control group in total protein, glutathione content and acetylcholinesterase activity was also observed. The Inductively Coupled Plasma Atomic Emission Spectroscopy analysis (ICPAES) reveals the presence of copper, iron, sodium, aluminium, manganese, calcium, nickel and mercury. The toxic effects of CaC2 in the present study may be attributed to the impurities present in it.

A review of metal-catalyzed molecular damage: protection by melatonin

Metal exposure is associated with several toxic effects; herein, we review the toxicity mechanisms of cadmium, mercury, arsenic, lead, aluminum, chromium, iron, copper, nickel, cobalt, vanadium, and molybdenum as these processes relate to free radical generation. Free radicals can be generated in cells due to a wide variety of exogenous and endogenous processes, causing modifications in DNA bases, enhancing lipid peroxidation, and altering calcium and sulfhydryl homeostasis. Melatonin, an ubiquitous and pleiotropic molecule, exerts efficient protection against oxidative stress and ameliorates oxidative/nitrosative damage by a variety of mechanisms. Also, melatonin has a chelating property which may contribute in reducing metal-induced toxicity as we postulate here. The aim of this review was to highlight the protective role of melatonin in counteracting metal-induced free radical generation. Understanding the physicochemical insights of melatonin related to the free radical scavenging activity and the stimulation of antioxidative enzymes is of critical importance for the development of novel therapeutic strategies against the toxic action of these metals.

Protective effect of curcumin against heavy metals-induced liver damage

Occupational or environmental exposures to heavy metals produce several adverse health effects. The common mechanism determining their toxicity and carcinogenicity is the generation of oxidative stress that leads to hepatic damage. In addition, oxidative stress induced by metal exposure leads to the activation of the nuclear factor (erythroid-derived 2)-like 2/Kelch-like ECH-associated protein 1/antioxidant response elements (Nrf2/Keap1/ARE) pathway. Since antioxidant and chelating agents are generally used for the treatment of heavy metals poisoning, this review is focused on the protective role of curcumin against liver injury induced by heavy metals. Curcumin has shown, in clinical and preclinical studies, numerous biological activities including therapeutic efficacy against various human diseases and anti-hepatotoxic effects against environmental or occupational toxins. Curcumin reduces the hepatotoxicity induced by arsenic, cadmium, chromium, copper, lead and mercury, prevents histological injury, lipid peroxidation and glutathione (GSH) depletion, maintains the liver antioxidant enzyme status and protects against mitochondrial dysfunction. The preventive effect of curcumin on the noxious effects induced by heavy metals has been attributed to its scavenging and chelating properties, and/or to the ability to induce the Nrf2/Keap1/ARE pathway. However, additional research is needed in order to propose curcumin as a potential protective agent against liver damage induced by heavy metals.

Comparative study on the inhibitory effect of caffeic and chlorogenic acids on key enzymes linked to Alzheimer's disease and some pro-oxidant induced oxidative stress in rats' brain-in vitro

This study sought to investigate and compare the interaction of caffeic acid and chlorogenic acid on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), and some pro-oxidants (FeSO(4), sodium nitroprusside and quinolinic acid) induced oxidative stress in rat brain in vitro. The result revealed that caffeic acid and chlorogenic acid inhibited AChE and BChE activities in dose-dependent manner; however, caffeic acid had a higher inhibitory effect on AChE and BChE activities than chlorogenic acid. Combination of the phenolic acids inhibited AChE and BChE activities antagonistically. Furthermore, pro-oxidants such as, FeSO(4), sodium nitroprusside and quinolinic acid caused increase in the malondialdehyde (MDA) contents of the brain which was significantly decreased dose-dependently by the phenolic acids. Inhibition of AChE and BChE activities slows down acetylcholine and butyrylcholine breakdown in the brain. Therefore, one possible mechanism through which the phenolic acids exert their neuroprotective properties is by inhibiting AChE and BChE activities as well as preventing oxidative stress-induced neurodegeneration. However, esterification of caffeic acid with quinic acid producing chlorogenic acid affects these neuroprotective properties.

Inhibitory effect of some tropical green leafy vegetables on key enzymes linked to Alzheimer's disease and some pro-oxidant induced lipid peroxidation in rats' brain

This study sought to investigate the inhibitory effect of some commonly consumed Nigerian green leafy vegetables (raw and blanched) on acetylcholinesterase and butyrylcholinesterase (key enzyme linked to Alzheimer's disease) activities and some pro-oxidants (FeSO4, Sodium nitroprusside and Quinolinic acid) induced lipid peroxidation in rat brain in vitro. Three commonly consumed green leafy vegetables in Nigeria [Amarantus cruentus (Arowojeja), Struchium sparganophora (Ewuro-odo) and Telfairia occidentalis (Ugwu] were blanched in hot water for 10 min, and the extracts of the raw and blanched vegetables were prepared and used for subsequent analysis. The result revealed that all the vegetables inhibited acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activity as well as the pro-oxidants induced lipid peroxidation in rat brain in a dose dependent manner; however, Amarantus cruentus extract (EC50 = 97.9 μg/ml) had the highest inhibitory effect on acetylcholinesterase activity while Telfairia occidentalis extract (EC50 = 52.7 μg/ml) had the highest inhibitory effect on butyrylcholinesterase activity. However, blanching of the vegetables caused a significant (P < 0.05) decrease in the inhibitory effect of the vegetables on AChE activities while it enhanced the inhibition of the pro-oxidants induced lipid peroxidation in rat brain in vitro. Therefore, some of the possible mechanism by which green leafy vegetables exert their neuroprotective activities could be through the inhibition of acetylcholinesterase and butyrylcholinesterase activities and prevention of lipid peroxidation in the brain. However, blanching of the vegetables could reduce their ability to inhibit acetylcholinesterase and butyrylcholinesterase activity.

Chronic HgCl2 treatment increases vasoconstriction induced by electrical field stimulation: role of adrenergic and nitrergic innervation

In the present study, we have investigated the possible changes in rat mesenteric artery vascular innervation function caused by chronic exposure to low doses of HgCl2 (mercuric chloride), as well as the mechanisms involved. Rats were divided into two groups: (i) control, and (ii) HgCl2-treated rats (30 days; first dose, 4.6 μg/kg of body weight; subsequent dose, 0.07 μg·kg−1 of body weight·day−1, intramuscularly). Vasomotor response to EFS (electrical field stimulation), NA (noradrenaline) and the NO donor DEA-NO (diethylamine NONOate) were studied, nNOS (neuronal NO synthase) and phospho-nNOS protein expression were analysed, and NO, O2− (superoxide anion) and NA release were also determined. EFS-induced contraction was higher in the HgCl2-treated group. Phentolamine (1 μmol/l) decreased the response to EFS to a greater extent in HgCl2-treated rats. HgCl2 treatment increased vasoconstrictor response to exogenous NA and NA release. L-NAME (NG-nitro-L-arginine methyl ester; 0.1 mmol/l) increased the response to EFS in both experimental groups, but the increase was greater in segments from control animals. HgCl2 treatment decreased NO release and increased O2− production. Vasodilator response to DEA-NO was lower in HgCl2-treated animals. Tempol increased DEA-NO-induced relaxation to a greater extent in HgCl2-treated animals. nNOS expression was similar in arteries from both experimental groups, whereas phospho-nNOS was decreased in segments from HgCl2-treated animals. HgCl2 treatment increased vasoconstrictor response to EFS as a result of, in part, reduced NO bioavailability and increased adrenergic function. These findings offer further evidence that mercury, even at low concentrations, is an environmental risk factor for cardiovascular disease.

Effects of mercury on Dictyostelium discoideum: proteomics reveals the molecular mechanisms of physiological adaptation and toxicity

Dictyostelium discoideum amoebae were exposed to Hg 2 microM corresponding to a sublethal concentration and Hg 10 microM with the first effects on mortality and replication rate. A total of 900 spots were visualized by 2-DE electrophoresis. Two-hundred fifty single proteins were identified by mass spectrometry. Low Hg concentration (2 microM) treatment induced up-regulation of 13 spots, mainly involved in oxidative stress response/detoxification, oxidoreductase activity, and metabolic processes. High Hg concentration (10 microM) treatment showed a different PES with 12 proteins downregulated and only two up-regulated, mainly involved in cellular metabolic processes, metal ion binding, and transferase activity. The analyses for the carbonylation show no changes after 2 microM Hg(2+) treatment and 13 differentially carbonylated proteins after 10 microM Hg(2+) involved in a broad range of cellular processes. Our findings provide insight into the mechanisms of physiological adaptation and toxicity to a low and an high mercury concentration, respectively, of Dictyostelium amoebae.

Mercury and Selenium - A Review on Aspects Related to the Health of Human Populations in the Amazon

Mercury (Hg) toxicity is governed by cellular thiol compounds and its capacity to generate reactive oxygen radicals and oxidative stress. Selenium (Se) plays a key role in the prevention of the toxic effects of Hg by modulating the activity of several Se-dependent enzymes, including glutathione peroxidase (GSH-Px). In addition, dietary Se can reduce Hg toxicity by directly interacting with either Hg(II) or methylmercury (MeHg) to form inert products, such as HgSe complexes.. Although experimental and environmental data have indicated a protective role for selenium against Hg toxicity, human data are more limited and somewhat conroversial In the Amazon Region of Brazil, Hg pollution is rampant as a result of gold (Au) mining and other anthropogenic factors, leading to pervasive release of large quantities of metallic Hg⁰ into the environment. Exposure to Hg in this region is associated with direct occupational exposure in the gold mining industry, as well as consumption by in inhabitants of riverside communities of a diet rich in MeHg-contaminated fish. Human exposure to MeHg in the Amazon through the diet has been monitored by measuring Hg and MeHg in hair samples. In this paper, we review the environmental contamination of Hg in the Amazon and detail human exposures in populations of this region. We conclude with a brief synopsis on Se levels in the Amazon population and provide a brief review of data available on the interaction between Hg and Se in this region. Overall, the literature supports the notion that low environmental Se is linked to susceptibility to Hg toxicity and that Se levels could be used as a bioindicator to monitor the health of Hg exposed subjects. However, in light of the limited human data on this subject, further epidemiological studies are needed to clarify how changes in Se levels modify the toxicity of environmental Hg.

A protein from Cajanus indicus Spreng protects liver and kidney against mercuric chloride-induced oxidative stress

Mercuric chloride (HgCl(2)) is a widespread environmental toxin that affects mainly liver and kidney. The present study has been carried out to investigate the protective action of a protein (the CI protein) isolated from the herb, Cajanus indicus Spreng against HgCl(2) induced renal and hepatic toxicities in mice. Intraperitoneal administration of HgCl(2) at a dose of 5 mg/kg body weight for 1 d significantly reduced the activities of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx). Moreover, it also depleted the glutathione to oxidized glutathione (GSH/GSSG) ratio. In addition, HgCl(2) increased the activities of serum marker enzymes (namely, glutamate pyruvate transaminase, GPT and alkaline phosphatase, ALP), creatinine, blood urea nitrogen and serum tumor necrosis factor alpha (TNF-alpha) level along with hepatic and renal lipid peroxidation. Besides, application of HgCl(2) to hepatocytes increased reactive oxygen species production and reduced the total antioxidant activity of the treated hepatocytes. Treatment with the CI protein intraperitoneally at a dose of 2 mg/kg body weight before or after HgCl(2) administration showed that it could scavenge free radicals in vitro and protect the alterations of the antioxidant molecules and the other parameters used in this particular study. Histological studies also revealed a milder lesion in kidney and liver samples of the CI protein treated mice compared to mice treated with HgCl(2) alone. Effects of a known antioxidant N-acetylcysteine have been used to compare its action to that of the CI protein.

Mercury concentrations in salmonids from western U.S. National Parks and relationships with age and macrophage aggregates

Mercury accumulation in aquatic foodwebs and its effects on aquatic biota are of growing concern both for the health of the fish and the piscivores that prey upon them. This is of particular concern for western U.S. National Parks because it is known that mountainous and Arctic areas are sinks for some contaminants. The Western Airborne Contaminants Assessment Project seeks, in part, to ascertain mercury concentrations and evaluate effects of contaminants on biota in 14 lakes from 8 National Parks or Preserves. In this paper we report that mercury has accumulated to concentrations in troutthat may negatively impact some piscivorous wildlife, indicating potential terrestrial ecosystem effects. Additionally, we show that mercury concentrations increase with age in 4 species of trout, providing evidence of bioaccumulation. Finally, we demonstrate that mercury is associated with tissue damage in the kidney and spleen, as indicated by increases in macrophage aggregates. This finding suggests that mercury, and possibly other contaminants, are Macrophage aggregates suggests that mercury, a negatively affecting the trout that inhabit these remote and protected ecosystems. Our results indicate that mercury is indeed a concern for the U.S. National Parks, from an organismic and potentially an ecosystem perspective.

Spirulina fusiformis provides protection against mercuric chloride induced oxidative stress in Swiss albino mice

Oxidative stress induced by mercuric chloride (5 mg/kg body weight i.p.) in mice substantially increases the lipid peroxidation level along with corresponding decrease in the reduced glutathione and various antioxidant enzymes in liver and increase in serum transaminases activity. Supplementation of Spirulina (800 mg/kg body weight orally, in olive oil, along with mercuric chloride) for 40 days resulted in decreased LPO level, serum glutamate oxaloacetate and serum glutamate pyruvate transaminase activity along with increase in liver GSH level. The activities of antioxidants enzymes superoxide dismutase, catalase and glutathione-S-transferase were also concomitantly restored to near normal level by Spirulina supplementation to mercuric chloride intoxicated mice. The results clearly demonstrate that Spirulina treatment augments the antioxidants defense mechanism in mercuric chloride induced toxicity and provides evidence that it may have a therapeutic role in free radical mediated diseases.

Eruca sativa seeds possess antioxidant activity and exert a protective effect on mercuric chloride induced renal toxicity

Mercuric chloride (HgCl(2)) is a well-known nephrotoxic agent. Increasing number of evidences suggest the role of oxidative stress in HgCl(2) induced nephrotoxicity. Eruca sativa is widely used in folklore medicines and has a good reputation as a remedy of renal ailments. In the present study, the antioxidant potential of ethanolic extract of E. sativa seeds was determined and its protective effect on HgCl(2) induced renal toxicity was investigated. The extract was found to possess a potent antioxidant effect, with a large amount of polyphenols and a high reducing ability. HPLC analysis of the extract revealed glucoerucin and flavonoids to be the major antioxidants present in it. E. sativa extract significantly scavenged several reactive oxygen species (ROS) and reactive nitrogen species (RNS). Feeding of the extract to rats afforded a significant protection against HgCl(2) induced renal toxicity. Subcutaneous administration of 4 mg/kg body weight HgCl(2) induced renal injury evident as a marked elevation in serum creatinine and blood urea nitrogen levels, and histopathological changes such as necrosis, oedema and congestion of stroma and glomeruli. Oxidative modulation of renal tissues following HgCl(2) exposure was evident from a significant elevation in lipid peroxidation and attenuation in glutathione (GSH) contents and activities of antioxidant enzymes viz., catalase (CAT), glutathione peroxidase (GPX), superoxide dismutase (SOD) and glutathione reductase (GR). Oral administration of E. sativa extract to rats at a dose regimen: 50-200 mg/kg body weight for 7 days prior to HgCl(2) treatment significantly and dose dependently protected against alterations in all these diagnostic parameters. The data obtained in the present study suggests E. sativa seeds to possess a potent antioxidant and renal protective activity and preclude oxidative damage inflicted to the kidney.

Ginkgo biloba extract protects against mercury(II)-induced oxidative tissue damage in rats

Mercury(II) is a highly toxic metal which induces oxidative stress in the body. In this study we aimed to investigate the possible protective effect of Ginkgo biloba (EGb), an antioxidant agent, against experimental mercury toxicity in rat model. Following a single dose of 5mg/kg mercuric chloride (HgCl(2); Hg group) either saline or EGb (150mg/kg) was administered for 5days. After decapitation of the rats trunk blood was obtained and the tissue samples from the brain, lung, liver, and kidney were taken for the determination of malondialdehyde (MDA) and glutathione (GSH) levels, myeloperoxidase (MPO) activity and collagen contents. Formation of reactive oxygen species in the tissue samples was monitored by chemiluminescence (CL) technique. BUN, creatinin, ALT, and AST levels and tumor necrosis factor-alpha (TNF-alpha) and lactate dehydrogenase (LDH) activity were assayed in serum samples. The results revealed that HgCl(2) induced oxidative damage caused significant decrease in GSH level, significant increase in MDA level, MPO activity and collagen content of the tissues. Treatment of rats with EGb significantly increased the GSH level and decreased the MDA level, MPO activity, and collagen contents. Similarly, serum ALT, AST and BUN levels, as well as LDH and TNF-alpha, were elevated in the Hg group as compared to control group. On the other hand, EGb treatment reversed all these biochemical indices. Our results implicate that mercury-induced oxidative damage in brain, lung, liver, and kidney tissues protected by G. biloba extract, with its antioxidant effects.

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.

Melatonin Protects Against Mercury(II)-Induced Oxidative Tissue Damage in Rats

Mercury exerts a variety of toxic effects in the body. Lipid peroxidation, DNA damage and depletion of reduced glutathione by Hg(II) suggest an oxidative stress-like mechanism for Hg(II) toxicity. Melatonin, the main secretory product of the pineal gland, was recently found to be a potent free radical scavenger and antioxidant. N-Acetylcysteine, a precursor of reduced glutathione and an antioxidant, is used in the therapy of acute heavy metal poisoning. In this study the protective effects of melatonin in comparison to that of N-acetylcysteine against Hg-induced oxidative damage in the kidney, liver, lung and brain tissues were investigated. Wistar albino rats of either sex (200-250 g) were divided into six groups, each consisting of 8 animals. Rats were intraperitoneally injected with 1) 0.9% NaCl, control (C) group; 2) a single dose of 5 mg/kg mercuric chloride (HgCl2), Hg group; 3) melatonin in a dose of 10 mg/kg, 1 hr after HgCl2 injection, Hg-melatonin group; 4) melatonin in a dose of 10 mg/kg one day before and 1 hr after HgCl2 injection, melatonin-Hg-melatonin group; 5) N-acetylcysteine in a dose of 150 mg/kg, 1 hr after HgCl2 injection, Hg-N-acetylcysteine group, and 6) N-acetylcysteine in a dose of 150 mg/kg one day before and 1 hr after HgCl2 injection, N-acetylcysteine-Hg-N-acetylcysteine group. Animals were killed by decapitation 24 hr after the injection of HgCl2. Tissue samples were taken for determination of malondialdehyde, an end-product of lipid peroxidation; glutathione (GSH), a key antioxidant, and myeloperoxidase activity, an index of neutrophil infiltration. The results revealed that HgCl2 induced oxidative tissue damage, as evidenced by increases in malondialdehyde levels. Myeloperoxidase activity was also increased, and GSH levels were decreased in the liver, kidney and the lungs. All of these effects were reversed by melatonin or N-acetylcysteine treatment. Since melatonin or N-acetylcysteine administration reversed these responses, it seems likely that melatonin or N-acetylcysteine can protect all these tissues against HgCl2-induced oxidative 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.

Contaminant exposure and effects in Baltic ringed and grey seals as assessed by biomarkers

The Baltic Sea ecosystem has suffered from a heavy pollutant load for more than three decades. Persistent organic pollutants (POPs) and heavy metals have been of most concern due to their persistence and toxic properties. Ringed seals (Phoca hispida baltica) and grey seals (Halichoerus grypus) living in the Baltic Sea have been suffering from pathological impairments, including reproductive disturbances, which have resulted in a depressed reproductive capacity. We investigated several biochemical parameters as potential biomarkers for exposure to and effects of the contaminant load in the Baltic seals. Seals from less polluted areas were used as reference material in terms of the pollution load. In both Baltic seal populations, the levels of some biochemical parameters diverged from those in the reference seals, and some of these showed a clear correlation with the individual contaminant load. Of the potential bioindicators, we propose cytochrome P4501A activity and vitamin E levels, in blubber or plasma, as exposure biomarkers for polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) in both species. The arylhydrocarbon receptor-mediated chemical-activated luciferase gene expression (CALUX) response reflects the whole PCB and DDT burden in ringed seals. Retinyl palmitate (vitamin A) levels showed a negative correlation with the individual POP load, and is proposed as potential effect biomarkers for the depletion of the vitamin A stores. As the nutritional levels of both vitamin A and E have an impact on the vitamin levels in the seals, more information on the dietary vitamin levels is needed before any conclusions can be drawn. As the relationship between biochemical parameters and contaminants varied between the two species, species-specific characteristics has to be considered when monitoring the health status and possible toxic effects of the contaminant load in ringed and grey seals.

Effects of Juglans sinensis Dode extract and antioxidant on mercury chloride-induced acute renal failure in rabbits

This study was undertaken to determine if Juglans sinensis Dode, an oriental medicinal herb, extract (JSE) and antioxidant exert beneficial effect against mercury-induced acute renal failure in rabbits. Acute renal failure was induced by subcutaneous injection of mercury chloride (10 mg/kg), and animals were pretreated with JSE (0.1 g/kg, orally) for 7 days or N,N'-diphenyl-p-phenylenediamine (0.5 g/kg, i.p.) 24 h prior to the injection of mercury chloride. Urine and blood samples were collected for 24 h before (the basal period) and after the administration of mercury chloride. Urine volume and GFR in mercury chloride-injected animals were decreased as compared with the basal values, which were accompanied by the increase in serum creatinine levels and fractional excretion of Na(+), indicating that the administration of mercury chloride produces acute renal failure. p-Aminohippurate uptake by renal cortical slices was inhibited by mercury chloride injection. Mercury chloride treatment in vivo increased lipid peroxidation in renal cortical tissues. Such changes were significantly prevented by JSE pretreatment. Mercury chloride-induced acute renal failure was also prevented by an antioxidant N,N'-diphenyl-p-phenylenediamine. Mercury chloride treatment in vitro increased lactate dehydrogenase release and lipid peroxidation in renal cortical slices, which were prevented by JSE. These results indicate that JSE exerts the beneficial effect against mercury chloride-induced acute renal failure and its effect may be due to antioxidant action. In addition, these results suggest that lipid peroxidation is responsible for the cell injury induced by mercury chloride in vivo and in vitro.

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

The present study was undertaken to examine the role of reactive oxygen species (ROS) and glutathione (GSH) in glia cells using human glioma cell line A172 cells. HgCl2 caused the loss of cell viability in a dose-dependent manner. HgCl2-induced loss of cell viability was not affected by H2O2 scavengers catalase and pyruvate, a superoxide scavenger superoxide dismutase, a peroxynitrite scavenger uric acid, and an inhibitor of nitric oxide N(G)-nitro-arginine Methyl ester. HgCl2 did not cause changes in DCF fluorescence, an H2O2-sensitive fluorescent dye. The loss of cell viability was significantly prevented by the hydroxyl radical scavengers dimethylthiourea and thiourea, but it was not affected by antioxidants DPPD and Trlox. HgCl2-induced loss of cell viability was accompanied by a significant reduction in GSH content. The GSH depletion was almost completely prevented by thiols dithiothreitol and GSH, whereas the loss of viability was partially prevented by these agents. Incubation of cells with 0.2 mM buthionine sulfoximine for 24 hr, a selective inhibitor of gamma-glutamylcysteine synthetase, resulted in 56% reduction in GSH content without any change in cell viability. HgCl2 resulted in 34% reduction in GSH content, which was accompanied by 59% loss of cell viability. These results suggest that HgCl2-induced cell death is not associated with generation of H2O2 and ROS-induced lipid peroxidation. In addition, these data suggest that the depletion of endogenous GSH itself may not play a critical role in the HgCl2-induced cytotoxicity in human glioma cells.

Lipid peroxidation and antioxidant enzyme activity in different organs of mice exposed to low level of mercury

The effects of mercuric chloride (Hg) on lipid peroxidation (LPO), glutathione reductase (GR), glutathione peroxidase (GPx), superoxide dismutase (SOD) and glutathione (GSH) levels in different organs of mice (CD-1) were evaluated. Mice were exposed (2 days/week) to 0.0 (control), 0.8 (low) and 8.0 (mid) and 80.0 (high) gHg/kg/day for 2 weeks. The high dose group was excluded from the study due to high mortality. LPO levels in kidney, testis and epididymus at low and mid doses; GR and GPx levels in testis at mid dose; SOD levels in brain and testis at both doses, liver and epididymus at mid dose; GSH levels in testis at both doses were significantly increased compared to their controls. However, the GR levels in kidney at both doses and in epididymus at mid dose; GPx levels in kidney and epididymus and SOD levels in kidney at both the doses; GSH levels in epididymus at mid dose were significantly decreased compared to their control. Body weight gain and food efficiency were significantly reduced (p<0.05) in mid dose. These results indicated that Hg treatment enhanced LPO in all tissues, but showed significant enhancement only in kidney, testis and epididymus suggesting that these organs were more susceptible to Hg toxicity. The increase in antioxidant enzyme levels in testis could be a mechanism protecting the cells against reactive oxygen species.

Cadmium induces apoptosis and genotoxicity in rainbow trout hepatocytes through generation of reactive oxygene species

Cadmium poses a serious environmental threat in aquatic ecosystems but the mechanisms of its toxicity remain unclear. The purpose of this work was first to determine whether cadmium induced apoptosis in trout hepatocytes, second to determine whether or not reactive oxygen species (ROS) were involved in cadmium-induced apoptosis and genotoxicity. Hepatocytes exposed to increasing cadmium concentrations (in the range of 1-10 microM) showed a molecular hallmark of apoptosis which is the fragmentation of the nuclear DNA into oligonucleosomal-length fragments, resulting from an activation of endogenous endonucleases and recognized as a 'DNA ladder' on conventional agarose gel electrophoresis. Exposure of hepatocytes to cadmium led clearly to the DEVD-dependent protease activation, acting upstream from the endonucleases and considered as central mediators of apoptosis. DNA strand breaks in cadmium-treated trout hepatocytes was assessed using the comet assay, a rapid and sensitive single-cell gel electrophoresis technique used to detect DNA primary damage in individual cells. Simultaneous treatment of trout hepatocytes with cadmium and the nitroxide radical TEMPO used as a ROS scavenger, reduced significantly DNA fragmentation, DEVD-related protease activity and DNA strand breaks formation. These results lead to a working hypothesis that cadmium-induced apoptosis and DNA strand breaks in trout hepatocytes are partially triggered by the generation of ROS. Additional studies are required for proposing a mechanistic model of cadmium-induced apoptosis and genotoxicity in trout liver cells, in underlying the balance between DNA damage and cellular defence systems in fish.

The nitroxide stable radical tempo prevents metal-induced inhibition of CYP1A1 expression and induction

Heavy metals are known to provoke oxidative stress in fish liver cells. Because H2O2, OH*- and intracellular superoxide are involved in this oxidation, we investigated the effect of nitroxide radical, 2,2,6,6-tetramethylpiperidinyl-N-oxyl (abbreviated as TEMPO), a cell-permeable agent possessing antioxidant properties, on CYP1A expression in trout (Oncorhynchus mykiss) hepatocytes. 3-methylcholanthrene (3-MC) induced the CYP1A-related EROD activity. This induction was inhibited by concomitant exposure to Cd (II), Cu (II), Pb (II) or Zn (II). CYP1A mRNA levels were also reduced. Simultaneous treatment with 3-MC, a heavy metal and TEMPO suppressed both the inhibition of EROD activity and the decrease of CYP1A mRNA expression. These results suggest a working hypothesis that heavy metals produce multiple oxidative effects, including generation of hydroxyl radicals, which could down-regulate CYP1A1 expression. This metal-induced inhibition was prevented by TEMPO, which might protect trout hepatocytes by scavenging free radicals and thus preventing their inhibitory effects on CYP1A induction and expression.

Presence of micronuclei in lymphocytes of mercury exposed workers

We have investigated the presence of micronuclei in mercury exposed workers. The study group consisted of 15 workers from a mercury-producing plant, mean age 39.5 years and a mean exposed period of 12 years. At the time of testing and for the six previous months, the exposed population had urinary mercury levels below the currently accepted limit of 50 ug/g creatinine. A significant increase in the percentage of micronuclei was observed in the mercury exposed individuals when compared to the non exposed group. We have not found any correlation between the percentage of micronuclei and age, length of exposure or urinary mercury concentrations. Our results suggest a genotoxic effect of mercury, which is observed in workers exposed chronically to levels considered biologically safe for the exposed population.

Current status of antioxidant therapy for Alzheimer's Disease

Accumulating evidence from preclinical and clinical studies supports the hypothesis that oxidative stress may be associated with the onset and progression of Alzheimer's Disease (AD). Antioxidant therapies are being promoted in the lay press to enhance mental functions and delay cognitive losses with aging. An increasing number of physicians are also recommending antioxidant therapies, such as high dose vitamin E, for subjects with AD and other neurodegenerative disorders. High dose vitamin E, ginkgo biloba, and selegiline are three putative antioxidants that have been tested in randomized multicenter trial conditions in the US. This paper summarizes the oxidative stress hypothesis of AD and reviews the strengths and limitations of published antioxidant studies in AD in relation to the role of such therapies in practice.

Mercuric ion inhibits the activity and fidelity of the human cell DNA synthesome

Mercuric ion is cytotoxic and mutagenic to cells; however, the mechanisms of mercuric ion-induced cytotoxicity are not well understood. Numerous studies have suggested that these effects may be due in part to the alteration and inhibition of a variety of cellular processes including DNA replication, DNA repair, RNA transcription, and protein synthesis. Studies utilizing whole cells to examine these activities are not able to specifically identify the precise mechanism or site of the effect. Other studies carried out using whole cell extracts and variously purified DNA polymerases are not able to adequately represent the highly ordered environment in which DNA replication occurs in the intact cell. We report here, for the first time, the use of an intact human cell multiprotein complex (which we have termed the DNA synthesome) to carry out full-length DNA replication and DNA synthesis in the presence of Hg2+ ion in vitro. In this study we report that DNA replication and DNA polymerase activity, as well as DNA replication fidelity of the human cell DNA synthesome, are specifically inhibited by physiologically attainable concentrations of mercuric ion.

Oxidative stress hypothesis in Alzheimer's disease

The major hurdle in understanding Alzheimer's disease (AD) is a lack of knowledge about the etiology and pathogenesis of selective neuron death. In recent years, considerable data have accrued indicating that the brain in AD is under increased oxidative stress and this may have a role in the pathogenesis of neuron degeneration and death in this disorder. The direct evidence supporting increased oxidative stress in AD is: (1) increased brain Fe, Al, and Hg in AD, capable of stimulating free radical generation; (2) increased lipid peroxidation and decreased polyunsaturated fatty acids in the AD brain, and increased 4-hydroxynonenal, an aldehyde product of lipid peroxidation in AD ventricular fluid; (3) increased protein and DNA oxidation in the AD brain; (4) diminished energy metabolism and decreased cytochrome c oxidase in the brain in AD; (5) advanced glycation end products (AGE), malondialdehyde, carbonyls, peroxynitrite, heme oxygenase-1 and SOD-1 in neurofibrillary tangles and AGE, heme oxygenase-1, SOD-1 in senile plaques; and (6) studies showing that amyloid beta peptide is capable of generating free radicals. Supporting indirect evidence comes from a variety of in vitro studies showing that free radicals are capable of mediating neuron degeneration and death. Overall, these studies indicate that free radicals are possibly involved in the pathogenesis of neuron death in AD. Because tissue injury itself can induce reactive oxygen species (ROS) generation, it is not known whether this is a primary or secondary event. Even if free radical generation is secondary to other initiating causes, they are deleterious and part of a cascade of events that can lead to neuron death, suggesting that therapeutic efforts aimed at removal of ROS or prevention of their formation may be beneficial in AD.

Renal oxidant injury and oxidant response induced by mercury

The role of oxidative stress in mercuric chloride (HgCl2)-induced nephrotoxicity is uncertain and controversial. We demonstrate that I.L.C-PK1 cells, exposed to HgCl2, generate massive amounts of hydrogen peroxide, the latter completely quenched by the hydrogen peroxide scavenger, pyruvate. HgCl2 exerts a dose-dependent cytotoxicity which is attenuated by pyruvate and catalase. Cellular generation of hydrogen peroxide arises, at least in part, from mitochondria since mitochondrial rates of generation of hydrogen peroxide increase in response to HgCl2; HgCl2 also provokes a shift in absorbance spectra in rhodamine 123 loaded-mitochondria and stimulates mitochondrial state 4 respiration. HgCl2, applied for one hour, impairs cellular vitality as demonstrated by the MTT assay, an assay dependent in part on mitochondrial function. HgCl2 impairs function in other organelles such as lysosomes that maintain a transmembrane proton gradient; these latter effects are partially attenuated by pyruvate. We complement these in vitro findings with in vivo evidence demonstrating that HgCl2 stimulates renal generation of hydrogen peroxide. The functional significance of such generation of hydrogen peroxide was evaluated in rats deficient in selenium and vitamin E, a nutrient deficiency that impairs the scavenging of hydrogen peroxide and promotes the toxicity of this oxidant. In these rats serum creatinine values were significantly higher on sequential days following the administration of HgCl2. To probe the renal response to oxidative stress induced by HgCl2, we examined hydrogen peroxide-scavenging enzymes and redox-sensitive genes. Catalase activity was unaltered whereas glutathione peroxidase activity was decreased, effects that may contribute to the net renal generation of hydrogen peroxide. The redox sensitive enzyme, heme oxygenase, was markedly up-regulated in the kidney in response to HgCl2. HgCl2 also induced members of the bcl family, bcl2 and bclx, genes that protect against apoptosis and oxidant injury. In another model of oxidant-induced renal injury, the glycerol model, bcl2 mRNA was not induced at 6 and 24 hours after the administration of glycerol. In summary, we demonstrate that HgCl2 potently stimulates renal generation of hydrogen peroxide in vitro and in vivo and such generation of peroxide contributes to renal dysfunction in vitro and in vivo. We also demonstrate that in response to HgCl2, redox sensitive genes are expressed including heme oxygenase and members of the bcl family.

A comparison of the 8-hydroxydeoxyguanosine, chromosome aberrations and micronucleus techniques for the assessment of the genotoxicity of mercury compounds in human blood lymphocytes

We compared the mechanism of action of micronuclei (MN), unstable chromosome aberrations, and 8-hydroxydeoxyguanosine (8-OHdG) levels to evaluate the genotoxicity of methyl mercuric chloride (CH3HgCl) and mercuric chloride (HgCl2) in human peripheral lymphocytes. The chromosome aberrations in human peripheral lymphocytes exposed to various concentrations of CH3HgCl or HgCl2 increased in a concentration-dependent manner and were significantly higher than the control when the cells were incubated with 1 x 10(-5) M (HgCl2) or 2 x 10(-6) M (CH3HgCl). The increase in the incidence of micronucleated lymphocytes was significant among the exposed groups, being 2 x 10(-5) M (HgCl2) and 5 x 10(-6) M (CH3HgCl) compared with the control. CH3HgCl was about 4-fold more potent than HgCl2. We determined the 8-OHdG levels in human peripheral blood mononuclear cells(PBMC) and found that they were significantly higher in the exposed groups at 1 x 10(-5) M (HgCl2) and 5 x 10(-6) M (CH3HgCl) compared with the control. A detectable (p < 0.05) increase in the level of 8-OHdG was induced by CH3HgCl at a concentration that was about 50% of the amount of HgCl2 required to produce a similar response. The data confirmed the value of the MN and/or chromosome aberration assays for assessing of HgCl2- and/or CH3HgCl-induced genotoxicity, and indicated that they are about the same concentration as the 8-OHdG assay. The presence of genotoxic effects in peripheral blood lymphocytes exposed to the mercuric compounds indicated by the chromosome aberrations and the MN assays could be partly due either to the disturbance of the spindle mechanism, or to the elevated level of 8-OHdG brought by the generation of reactive oxygen species.

Lipid peroxidation in rats administrated with mercuric chloride

Parenteral administration of mercuric chloride (HgCl2) to rats enhanced lipid peroxidation in liver, kidney, lung, testis, and serum (but not in heart, spleen, or muscle), as measured by the thiobarbituric acid reaction for malondialdehyde (MDA) in fresh tissue homogenates and body fluids. After sc injection of HgCl2 (5 mg/kg body wt), MDA concentrations in liver and kidney became significantly increased by 9 h and reached peak values at 24 h. Dose-response studies were carried out with male albino rats of the Fisher-344 strain (body wt 170-280 g) injected with 1, 3, 5 mg Hg/kg as HgCl2 and sacrificed after 24 h. In time-response studies, animals were administered 5 mg Hg/kg as HgCl2 and sacrificed after 3, 9, 18, 24, and 48 h. Studies in the authors' laboratory have shown that (1) concentrations of MDA are increased in targets (liver, kidney, lung, and testis) of HgCl2-treated rats; (2) severity of hepatotoxicity and nephrotoxicity is generally consistent with the elevation of Hg and MDA concentrations, based upon the time-course and dose-effect relationships observed after administration of HgCl2 to rats; and (3) concentrations of MDA are reduced in target tissues after pre-treatment with antioxidants and chelators to HgCl2-treated rats. The results of this study implicate that the lipid peroxidation is one of the molecular mechanisms for cell injury in acute HgCl2 poisoning.

Up-regulation of glutathione synthesis in rat kidney by methyl mercury. Relationship to mercury-induced oxidative stress

Prolonged exposure of rats to methyl mercury hydroxide (MMH) results, during the initial phase of exposure, in the rapid accumulation of mercury as Hg2+ by kidney cortex and in a significant increase in oxidative stress, as characterized by the rate of formation of thiobarbituric acid reactive substances (TBARS) by renal mitochondria. These events are accompanied by a progressive increase in steady-state levels of the mRNA encoding gamma-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in glutathione (GSH) synthesis and a 2- to 3-fold elevation in renal cortical GSH levels. The present study showed that the increase in GSH content was accompanied by a concomitant decrease in the rate of TBARS formation. Subsequent to these initial phase events, continued MMH exposure was characterized by equilibration in the rate of renal Hg2+ accumulation, a sharp decrease in both the TBARS formation rate and GCS mRNA level, but sustained elevation of renal cortical GSH content. Depletion of GSH with buthionine sulfoximine subsequent to the decline in the rate of TBARS formation did not result in a rebound of the TBARS formation rate. These findings suggest that oxidative stress during the initial phase of MMH exposure is derived from the transformation of CH3Hg+ to Hg2+, which, in turn, induces the synthesis of Hg(2+)- and/or oxidant-scavenging GSH molecules via the up-regulation of renal GCS mRNA. The findings also suggest that resistance to Hg(2+)-mediated oxidative stress may be more closely associated with the capacity for up-regulation of GSH synthesis than with elevated GSH levels per se.

Nephrotoxicity of xenobiotics

Nephrotoxicity can be grouped by the xenobiotics place of action, by the clinical presentation or by the generic toxic effect. The latter can be dose related, indirect, idiosyncratic or allergic. Nephrotoxicity of lithium, demeclocycline, aminoglycosides, cyclosporine, mercuric ion, nonsteroidal anti-inflammatory drugs, methoxyflurane, ethylene glycol, D-penicillamine and methicillin is reviewed in light of all these three viewpoints, but emphasis is on toxic mechanisms.

An insect model for assessing mercury toxicity: effect of mercury on antioxidant enzyme activities of the housefly (Musca domestica) and the cabbage looper moth (Trichoplusia ni)

The effect of mercury as Hg2Cl2 and HgCl2 on the antioxidant enzyme levels and its toxicity was investigated in an insect model comprised of adult females of the common housefly, Musca domestica, and fourth-instar larvae of the cabbage looper moth, Trichoplusia ni. HgCl2 was found to be more toxic than Hg2Cl2 to both M. domestica and T. ni. The LC50s for M. domestica were 1.17% and 0.38% w/v concentration for Hg2Cl2 and HgCl2, respectively. For the more tolerant T. ni, the LC50S were 5.15% for Hg2Cl2 and 0.96% w/w concentration for HgCl2. The minimally acute LC5 dose of both oxidation states of Hg was approximately 0.005% for both insects (w/v for M. domestica and w/w for T. ni). At the LC5, both forms of Hg significantly induced the activity of superoxide dismutase in both insect species. Catalase was induced by both Hg2Cl2 and HgCl2 in M. domestica but was only induced by HgCl2 in T. ni. Glutathione-S-transferase, its peroxidase activity, and glutathione reductase activities were also significantly altered in most cases by Hg in both insects although the pattern of alternation was different between the two insects. It is evident that mercury induces oxidative stress in insects as it does in vertebrates. Our findings suggest that insects may serve as a valuable, non-mammalian model species to assess Hg-induced oxidative stress as a component of environmental toxicity.

Effects of dietary alpha-tocopherol and beta-carotene on lipid peroxidation induced by methyl mercuric chloride in mice

Exposure of male CBA mice to methyl mercuric chloride, CH3HgCl, (10-40 mg/l in drinking water) for 2 weeks resulted in dose-related Hg deposition and enhanced lipid peroxidation in liver, kidney and brain. Mice were fed well-defined semisynthetic diets containing different levels of alpha-tocopherol (10, 100 or 1000 mg/kg) or beta-carotene (1000, 10,000 or 100,000 IU/kg) for four weeks, two groups on each diet. The concentrations of alpha-tocopherol and beta-carotene used corresponded to deficient, normal and high levels. During the last two weeks, one group on each diet was given 40 mg CH3HgCl/l of drinking water. High dietary alpha-tocopherol protected against CH3HgCl induced hepatic lipid peroxidation, whereas the alpha-tocopherol deficient diet further enhanced CH3HgCl induced hepatic lipid peroxidation. Similar, though statistically non-significant effects occurred in the kidneys, alpha-Tocopherol did not protect against CH3HgCl induced lipid peroxidation in the brain. Excess dietary beta-carotene further enhanced CH3HgCl induced lipid peroxidation in liver, kidney and brain. CH3HgCl significantly decreased the activity of total glutathione peroxidase (T-GSH-Px) and Se-dependent glutathione peroxidase (Se-GSH-Px) in the kidneys in all dietary groups. High dietary alpha-tocopherol enhanced the activity of Se-GSH-Px in liver and kidney compared to the activity in mice fed the normal level of alpha-tocopherol. This occurred in mice exposed to CH3-HgCl as well as in unexposed mice, and the difference between CH3HgCl exposed and unexposed mice was not diminished. High dietary alpha-tocopherol increased the activity of both Se-GSH-Px and T-GSH-Px in the brain of CH3HgCl-exposed mice. The dietary level of beta-carotene did not affect the activity of the two enzymes in the organs investigated.

Mercuric chloride affects protein secretion in rat primary hepatocyte cultures: a biochemical ultrastructural, and gold immunocytochemical study

The toxicity of mercury on hepatocytes was studied at the ultrastructural, biochemical, and immunocytochemical levels. Albumin metabolism was examined because it is a representative liver-specific function. A novel cytochemical method using the protein A-gold technique for the in situ localization of albumin in hepatocyte cultures was applied. Primary rat hepatocyte cultures were exposed to increasing HgCl2 concentrations. Cytotoxicity was assessed by measuring the release of lactic dehydrogenase from the cells. At the highest exposure concentration tested (50 microM), Hg was found to be significantly cytotoxic in contrast to what occurred at 5.0 and 0.5 microM. The level of albumin secreted, as measured by ELISA, was decreased by approximately 38% at 5.0 microM HgCl2 and was found not to be different from that of controls at lower concentrations. The ultrastructural analysis showed that hepatocytes treated with 5.0 microM HgCl2 undergo drastic morphological changes such as a decreased number of ribosomes associated with the rough endoplasmic reticulum, and the disappearance of the latter organelle, proliferation of the smooth endoplasmic reticulum, and dilatation of both the Golgi apparatus and the biliary canaliculus-like structures. Immunocytochemical detection of albumin-immunoreactive sites using protein A-gold labeling further revealed that these were less abundant in hepatocytes treated with 5.0 microM HgCl2 (-64%) as compared to control preparations. These results suggest that one of the effects of mercury on hepatocytes is to affect liver-specific functions such as albumin production, possibly through interference with ribosomal function. This study also demonstrates for the first time the applicability of the high-resolution protein A-gold technique for toxicological investigations on hepatocytes in vitro.

Distribution kinetics of inorganic mercury in the subcellular fractions of fish liver

The present study tries to find out the kinetics of distribution of mercury in the different subcellular fractions of the liver in a freshwater perch Anabas testudineus over a period of 48 h after a single i.m. injection of [203Hg]mercuric nitrate at a dose of 4 mg/kg body weight. The fish were killed at 15 min, 2 h, 6 h and 48 h post injection. In addition the interaction of this metal with different biomolecules, viz., protein, DNA and RNA, was also investigated. Cytosol was found to be the major site of mercury accumulation. Moderate amounts of accumulation occurred in the nuclear, mitochondrial and microsomal fractions, although varying with time, while the lysosomal fraction did not reveal any spectacular retention of mercury. A significant increase in the protein content of nuclear, mitochondrial, lysosomal and cytosolic fractions was also noticed at different time periods of mercury injection. In the nuclear, microsomal and cytosolic proteins, mercury binding increased more significantly over time than the mitochondrial and lysosomal proteins. A biphasic binding pattern of mercury was seen in nuclear and mitochondrial DNA and mitochondrial and cytosolic RNA.

The comparison of the effects of heavy metal ions on the antioxidant enzyme activities in human and fish Dicentrarchus labrax erythrocytes

1. The effect of the increasing concentrations of CuSO4 and HgCl2 (0.01-0.3 mmol/l) on erythrocyte haemolysis and the activities of peroxide metabolism enzymes: superoxide dismutase, catalase, peroxidase and glutathione peroxidase was investigated in human erythrocytes and the nucleated red blood cells of marine fish (Dicentrarchus labrax). 2. The results show that both heavy metal ions had only little effect on haemolysis and antioxidant enzyme activities in human erythrocytes; in contrast the effect of heavy metals on fish erythrocytes was statistically significant when compared to control values. 3. Copper was found to have more pronounced effect than mercury on the erythrocytes of Dicentrarchus labrax; otherwise there were no significant differences between the toxic effects of both ions on human erythrocytes. 4. We suggest that the mechanism of copper-induced haemolysis may be different from that of mercuric ion in the erythrocytes of Dicentrarchus labrax.

Experimentally induced lipid peroxidation after exposure to chromium, mercury or silver: interactions with carbon tetrachloride

Chromium, along with other heavy metals, induces an increased production of malondialdehyde (MDA), an indicator of lipid peroxidation, in liver and kidney tissue of NMRI male mice. After acute intoxications MDA levels remain high for 60 min. and thereafter return to normal in the kidney whereas MDA levels in liver are still increased 48 hr after exposure. Exposure of mice to chromium, mercury, or silver and another stimulator of lipid peroxidation, carbon tetrachloride, showed synergism between inorganic mercury and CCl4. Pre-exposure to chromium, organic mercury, or silver at selected doses did not enhance CCl4-toxicity as measured by organ content of MDA.

The closed chamber technique--uptake, endogenous production, excretion, steady-state kinetics and rates of metabolism of gases and vapors

The "closed chamber technique" (CCT) is presented. It allows investigation of pharmacokinetics of volatile substances in vivo in animals and in man and in vitro using tissue fractions. During the exposure period only the atmospheric concentrations of the substance are measured. The concentration-time data obtained are pharmacokinetically analyzed by a two compartment model describing uptake, endogenous production and excretion of the unchanged substance and its metabolic elimination. Using this model, pharmacokinetics of ethylene have been determined in rats and man. For both species, the results compared well with an estimation based on an allometric species scaling. Furthermore, the applicability of CCT is demonstrated in vivo on several other gases and vapors of solvents, e.g. trichloroethylene and 1,1,1-trichloroethane, and in vitro on 1,2-epoxybutene-3.

Mercuric chloride-induced kidney damage in mice: time course and effect of dose

The rate of elimination of mercury after a single oral or intraperitoneal administration of HgCl2 to male or female mice has recently been demonstrated to be inversely related to the dose size (Nielsen and Andersen, 1989, 1990). The present study demonstrates dose-related induction of renal tubular damage, followed by regeneration, after oral administration of HgCl2 to female mice. Dose-related increased fractional urinary mercury excretion (expressed as percent of dose) was also demonstrated. At increasing dose of HgCl2, the renal activity of selenium-dependent glutathione peroxidase decreased, and was only 50% of the activity in untreated controls after administration of 200 mumol HgCl2/kg. At higher doses, the renal concentration of glutathione was significantly reduced as well. The degree of tissue damage was inversely related to the fractional deposition of mercury in the kidneys. This study indicates that the reduction in fractional whole-body retention of mercury with increasing dose size previously demonstrated is due to increased urinary mercury excretion during transient renal damage followed by regeneration, as extensive leakage took place before extensive regeneration was noted.

Combined effects of methylmercury and ethanol on renal metallothionein and mercury residues in rats fed restricted amounts of a liquid diet

Simultaneous treatment of rats with ethanol (EtOH) and methylmercury (MeHg) increases the frequency of lesions in the rat kidney. Therefore, it was of interest to us to study the effects of simultaneous treatment of rats with MeHg and EtOH on kidney metallothionein (MT) and mercury residues levels in kidneys of rats maintained on 70% of ad libitum diet. Treatment with MeHg alone induced kidney MT the most (twice) compared to its pair-fed control. Simultaneous treatment with MeHg and EtOH also induced kidney MT but to a lesser degree than treatment with MeHg alone (by about 30%). Ethanol by itself caused a slight increase in kidney MT although starvation resulting from pair-feeding with mercury-treated animals may have contributed to this observation. Simultaneous treatment with MeHg and 2 g/kg EtOH caused a significant reduction in inorganic mercury levels in the kidney (P less than 0.05) compared to treatment with MeHg alone or in combination with 1 g/kg EtOH. Corresponding with the decrease in kidney inorganic mercury levels was a significant increase in urine inorganic mercury levels in this group compared to treatment with 1 g/kg ethanol + MeHg.

Oxidative mechanisms underlying methyl mercury neurotoxicity

Cerebellar granule cells from 5-12-day-old rats can be incubated in suspension at 37 degrees C for up to 3 hr with minimal decline in viability. Methyl mercury was found to produce time- and concentration-dependent cell killing with greater than 85% cell death after 3 hr exposure to a concentration of 20 microM. Previously characterized inhibition of protein and RNA synthesis as well as known methyl mercury-induced defects in cellular ATP production have been shown to be incapable of causing this degree of cell death. Here we report that methyl mercury induced a concentration-dependent increase in membrane lipoperoxidation and a rapid decline in reduced glutathione in this cerebellar neuronal preparation. Hydrogen peroxide at 5 mM was found to closely reproduce each of the cytotoxic effects manifested by methyl mercury suggesting that oxidizing conditions produced by methyl mercury may account for the observed cell death. Methyl mercury-induced lipoperoxidation was not the cause of cell death since malonaldehyde production could be blocked by alpha-tocopherol or EDTA without appreciable protecting against cell death. Significant protection from methyl mercury-induced cell death was observed, with EGTA, deferoxamine and KCN. We propose that oxidative events contribute to the toxic mechanism of action of methyl mercury in isolated cerebellar granule neurons.

Thiol antidotes effect on lipid peroxidation in mercury-poisoned rats

The effect of thiol antidotes 2,3-dimercapto-1-propanesulfonic acid (DMPS) and D-penicillamine (PA) on lipid peroxidation and on activities of some protecting enzymes in blood, liver and kidneys of mercury-poisoned rats has been studied. It has been found that Hg-poisoning is associated with increased lipid peroxidation in the liver and in the kidneys and with inactivation of superoxide dismutase (SOD) and catalase. Inhibition of SOD is caused by thiols treatment too, but in this case acceleration of lipid peroxidation has not been observed. Evidence is presented that in the liver, protection against mercury-induced lipid peroxidation is afforded by both thiols, while in the kidneys only PA has protective effect. In in vitro experiments it has been demonstrated that both antidotes can act as O2- scavengers and lipid peroxidation inhibitors, but PA is significantly more effective. On the basis of the obtained results a conclusion is drawn that in addition to the metal-removing ability, the antioxidant properties of the chelating agents may play an important role in manifestation of their beneficial effect in metal intoxications.