Hepatic processing of mercuric ions facilitates delivery to renal proximal tubules.

Mercury (Hg) is a toxic heavy metal to which humans are exposed on a regular basis. Hg has a high affinity for thiol-containing biomolecules with the majority of Hg in blood being bound to albumin. The current study tested the hypothesis that circulating Hg-albumin complexes are taken up into hepatocytes and processed to form Hg-glutathione (GSH) conjugates (GSH-Hg-GSH). Subsequently, GSH-Hg-GSH conjugates are exported from hepatocytes into blood via multidrug resistance transporters (MRP) 3 and 5. To test this hypothesis, the portal vein and hepatic artery in Wistar rats were ligated to prevent delivery of Hg to the liver. Ligated and control rats were injected with HgCl2 or GSH-Hg-GSH (containing radioactive Hg) and the disposition of Hg was assessed in various organs. Renal accumulation of Hg was reduced significantly in ligated rats exposed to HgCl2. In contrast, when rats were exposed to GSH-Hg-GSH, the renal accumulation of Hg was similar in control and ligated rats. Experiments using HepG2 cells indicate that Hg-albumin conjugates are taken up by hepatocytes and additional experiments using inside-out membrane vesicles showed that MRP3 and MRP5 mediate the export of GSH-Hg-GSH from hepatocytes. These data are the first to show that Hg-albumin complexes are processed within hepatocytes to form GSH-Hg-GSH, which is, in part, exported back into blood via MRP3 and MRP5 for eventual excretion in urine.

Co-administration of Selenium with Inorganic Mercury Alters the Disposition of Mercuric Ions in Rats.

Mercury (Hg) is a common environmental toxicant to which humans are exposed regularly through occupational and dietary means. Although selenium supplementation has been reported to prevent the toxic effects of Hg in animals, the mechanisms for this prevention are not well understood. The purpose of the current study was to determine the effects of selenium on the disposition and toxicity of Hg. Wistar rats were injected intravenously with a non-nephrotoxic dose (0.5 µmol kg-1) or a nephrotoxic dose (2.5 µmol kg-1) of HgCl2 (containing radioactive Hg) with or without co-administration of sodium selenite (Na2SeO3). Twenty-four hours after exposure, rats were euthanized, and organs were harvested. Co-administration of SeO32- with HgCl2 reduced the renal burden of Hg and the urinary excretion of Hg while increasing the amount of Hg in blood and spleen. We propose that Hg reacts with reduced selenite in the blood to form large Hg-Se complexes that are unable to be filtered at the glomerulus. Consequently, these complexes remain in the blood and are able to accumulate in blood-rich organs. These complexes, which may have fewer toxic effects than other species of Hg, may be eliminated slowly over the course of weeks to months.

Protective Effect of Leaf Ethanolic Extract Etlingera hemisphaerica Blume Against Mercuric Chloride Toxicity in Blood of Mice.

This research was intended to investigate the protective effect of leaf ethanolic extract Etlingera hemisphaerica Blume (LE3H) against mercuric chloride (HgCl2) toxicity in blood of mice (Mus musculus). The experimental animals, 95 male M. musculus, received drink and food ad libitum. Three materials were tested: LE3H (0.13, 0.26, 0.39 mg/g body weight [bw]) was administered by gavage; HgCl2 (5 mg/kg bw) was administrated by gavage or intraperitoneal injection; and Imunos (the nutritional supplement to stimulate the immune system; 0.2 mg/g bw), as a positive control for LE3H treatment, was given by gavage. Blood samples were taken from the tails for determining number of blood cells. The animals were killed by cervical dislocation (CD), and then blood samples were collected from the hearts for protein electrophoresis. Results revealed the same number of leukocytes with LE3H (0.39 mg/g bw) treatment as with the Imunos treatment. HgCl2 administration increased leukocytes and decreased erythrocytes; HgCl2 administration followed by LE3H (0.39 mg/g bw) treatment protected the amount of blood cells as well as the control. HgCl2 administration showed a new 125 kDa protein and caused overexpression of 48 kDa protein; this protein profile could be protected by LE3H (0.39 mg/g bw) treatment as in the control condition. We conclude that LE3H provides a protective effect against HgCl2 toxicity in blood of M. musculus.

A polysaccharide-peptide with mercury clearance activity from dried fruiting bodies of maitake mushroom Grifola frondosa.

Mercury is considered to be "a global pollutant" and raises concern worldwide. Once mercury enters the body, it will be distributed all over the body but will accumulate in the brain, kidney and liver. To date, no substance originating from edible fungi capable of adsorbing mercury has been reported. We found that the mushroom Grifola frondosa exhibited mercury adsorption capacity. A polysaccharide-peptide (GFPP), displaying the unique N-terminal amino acid sequence of APPGMHQKQQ and 7 partial sequences with high reliability obtained by LC-MS/MS, was isolated by hot-water extraction of its fruiting bodies followed by ion exchange chromatography and gel filtration chromatography. Two rat models were employed to determine the dose and the duration of HgCl2 treatment (given by acute administration or continuous treatment) to test if G. frondosa could promote mercury elimination. For rats subjected to acute treatment with HgCl2, both GFPP and G. frondosa fruiting bodies (GFFF) could accelerate the decline of blood mercury level, which fell precipitously by 50% on the second day. GFPP and GFFF also promoted elimination of the burden of mercury in the liver and kidneys. For rats receiving continuous HgCl2 treatment, G. frondosa prevented the progressive increase of blood mercury level, and kept the blood mercury level within a relatively stable range.

Toxicological Effects of Mercury Chloride on Laying Performance, Egg Quality, Serum Biochemistry, and Histopathology of Liver and Kidney in Laying Hens.

The objective of this study was to determine the effects of mercury chloride (HgCl2) on laying performance, egg quality, hepatic and renal histopathology, and serum biochemical profiles in laying hens. A total of 768 Hy-line brown laying hens aged 40 weeks were randomly allocated to four groups (8 pens per group and 24 hens per pen). The concentrations of mercury (Hg) in four groups were 0.280, 3.325, 9.415, and 27.240 mg/kg. Results revealed that dietary Hg could significantly reduce laying performance (P < 0.05) and egg quality (P < 0.05) and was dose-dependently deposited in albumen, yolk, eggshell, and whole egg. Meanwhile, the thicknesses of palisade layer, mammillary layer, and total layer, and the percent of palisade layer were significantly decreased (P < 0.05), while the percent of mammillary layer was sharply increased (P < 0.05) in eggshell. In addition, with increasing dietary dosage of Hg, accumulation of Hg in viscera was significantly increased (P < 0.05), and histopathological damages in liver and kidney were more and more severe. Serum alanine aminotransferase, aspartate aminotransferase, and globulin were significantly increased (P < 0.05), while serum albumin and albumin to globulin ratio were significantly decreased (P < 0.05) in 27.240 mg/kg Hg group. Blood urea nitrogen, uric acid, and creatinine were significantly increased (P < 0.05) in 3.325, 9.415, and 27.240 mg/kg Hg groups. These results suggested that dietary HgCl2 could reduce laying performance and egg quality with hepatic and renal function disorders in laying hens.

Disposition of inorganic mercury in pregnant rats and their offspring.

Environmental toxicants such as methylmercury have been shown to negatively impact fetal health. Despite the prevalence of inorganic mercury (Hg(2+)) in the environment and the ability of methylmercury to biotransform into Hg(2+), little is known about the ability of Hg(2+) to cross the placenta into fetal tissues. Therefore, it is important to understand the handing and disposition of Hg(2+) in the reproductive system. The purpose of the current study was to assess the disposition and transport of Hg(2+) in placental and fetal tissues, and to test the hypothesis that acute renal injury in dams can alter the accumulation of Hg(2+) in fetal tissues. Pregnant Wistar rats were injected intravenously with 0.5 or 2.5 µmol kg(-1) HgCl2 for 6 or 48 h and the disposition of Hg(2+) was measured. Accumulation of Hg(2+) in the placenta was rapid and dose-dependent. Very little Hg(2+) was eliminated during the initial 48 h after exposure. When dams were exposed to the low dose of HgCl2, fetal accumulation of Hg(2+) increased between 6h and 48 h, while at the higher dose, accumulation was similar at each time point. Within fetal organs, the greatest concentration of Hg(2+) (nmol/g) was localized in the kidneys, followed by the liver and brain. A dose-dependent increase in the accumulation of Hg(2+) in fetal organs was observed, suggesting that continued maternal exposure may lead to increased fetal exposure. Taken together, these data indicate that Hg(2+) is capable of crossing the placenta and gaining access to fetal organs in a dose-dependent manner.

Cardiovascular responses to lead are biphasic, while methylmercury, but not inorganic mercury, monotonically increases blood pressure in rats.

Cardiovascular diseases, such as heart attack and stroke, are the major cause of death worldwide. It is well known that a high number of environmental and physiological risk factors contribute to the development of cardiovascular diseases. Although risk factors are additive, increased blood pressure (hypertension) is the greatest risk factor. Over the last two decades, a growing number of epidemiological studies associate environmental exposure to lead or mercury species with hypertension. However, cardiovascular effects beyond blood pressure are rarely studied and thresholds for effect are not yet clear. To explore effects of lead or mercury species on the cardiovascular system, normal male Wistar rats were exposed to a range of doses of lead, inorganic mercury or methylmercury through the drinking water for four weeks. High-resolution ultrasound was used to measure heart and vascular function (carotid artery blood flow) at baseline and at the end of the exposure, while blood pressure was measured directly in the femoral artery at the end of the 4-week exposure. After 4 weeks, blood pressure responses to lead were biphasic. Low lead levels decreased blood pressure, dilated the carotid artery and increased cardiac output. At higher lead doses, rats had increased blood pressure. In contrast, methylmercury-exposed rats had increased blood pressure at all doses despite dilated carotid arteries. Inorganic mercury did not show any significant cardiovascular effects. Based on the current study, the benchmark dose level 10% (BMDL10s) for systolic blood pressure for lead, inorganic mercury and methylmercury are 1.1, 1.3 and 1.0 µg/kg-bw/d, respectively. However, similar total mercury blood levels attributed to inorganic mercury or methylmercury produced strikingly different results with inorganic mercury having no observable effect on the cardiovascular system but methylmercury increasing systolic and pulse pressures. Therefore, adverse cardiovascular effects cannot be predicted by total blood mercury level alone and the mercury species of exposure must be taken into account.

Cinnabar is different from mercuric chloride in mercury absorption and influence on the brain serotonin level.

The toxicity of cinnabar, a naturally occurring mercury sulphide (HgS), has long been referred to soluble mercury chloride (HgCl2 ). To investigate whether the speciation of mercury plays a role in its disposition and toxicity, we hereby investigated and compared cinnabar with soluble HgCl2 and pure insoluble HgS in mice on mercury absorption, tissue distribution and in relation to the biological effects. The male C57BL/6J mice were treated by oral administration of various doses of cinnabar, with 0.01 g/kg of HgCl2 for comparison, or the same dose of cinnabar or pure HgS (0.1 g/kg), once a day for 10 consecutive days. The total mercury contents in serum and tissue (brain, kidney, liver) were measured by atomic fluorescence spectrometer (AFS). The biological effects investigated involved monoamine neurotransmitters (serotonin, 5-HT) in brain as an indicator of therapeutic function, and serum alanine transaminase (ALT) as a marker of hepatic damage, blood urea nitrogen (BUN) and serum creatinine as markers for renal function. The mercury absorption of cinnabar or HgS was much less than that of HgCl2 . The mercury levels in brains of the cinnabar group were only slightly changed and kept in a steady-state with the dose elevated. Cinnabar or HgS suppressed brain 5-HT levels. HgCl2 could not cause any changes in brain 5-HT although the mercury level increased considerably. The results revealed that cinnabar or HgS is markedly different from HgCl2 in mercury absorption, tissue distribution and influence on brain 5-HT levels, which suggests that the pharmacological and/or toxicological effects of cinnabar undertake other pathways from mercuric ions.

Protective role of melatonin in myocardial oxidative damage induced by mercury in murine model.

This study was designed to investigate the electrophysiological, hemodynamic and biochemical parameters of mercuric chloride and methylmercury exposure on cardiovascular functions and its modulation by melatonin in vivo. Wistar albino rats were divided into six group containing 10 animals each. Mercuric chloride (3.75 µM/L) in drinking water and methylmercury (0.5 mg/kg/day) through gavage, given for 1 month, induced a statistically significant increase (p < 0.001) in left ventricular end diastolic pressure, blood and cardiac tissue mercury content and myocardial lipid peroxides compared to control. Significant attenuation (p < 0.05) of baroreflex sensitivity and depletion of myocardial endogenous antioxidants (p < 0.001) viz. Reduced glutathione (GSH) and superoxide dismutase (SOD) were also found in the mercury-exposed groups as compared to control group. Mercury exposure followed by subacute treatment with melatonin (4 µg/mL/day) in drinking water for 1 month significantly lowered (p < 0.01) left ventricular end diastolic pressure and lipid peroxide levels and increased baroreceptor sensitivity (p < 0.001) and also levels of GSH and SOD (p < 0.001) as compared to mercury-exposed rats. The results of our study provide clear evidence that elevated oxidative stress and altered baroreflex mechanisms caused by mercury intoxication may be the contributing factors responsible for impairment of cardiovascular functions and melatonin may exhibit cardioprotective property against subacute heavy metal intoxication and enhance the antioxidant defense against mercury-induced oxidative myocardial injury in rats.

MRP2 and the handling of mercuric ions in rats exposed acutely to inorganic and organic species of mercury.

Mercuric ions accumulate preferentially in renal tubular epithelial cells and bond with intracellular thiols. Certain metal-complexing agents have been shown to promote extraction of mercuric ions via the multidrug resistance-associated protein 2 (MRP2). Following exposure to a non-toxic dose of inorganic mercury (Hg²+), in the absence of complexing agents, tubular cells are capable of exporting a small fraction of intracellular Hg²+ through one or more undetermined mechanisms. We hypothesize that MRP2 plays a role in this export. To test this hypothesis, Wistar (control) and TR(-) rats were injected intravenously with a non-nephrotoxic dose of HgCl2 (0.5 µmol/kg) or CH3HgCl (5 mg/kg), containing [²°³Hg], in the presence or absence of cysteine (Cys; 1.25 µmol/kg or 12.5mg/kg, respectively). Animals were sacrificed 24 h after exposure to mercury and the content of [²°³Hg] in blood, kidneys, liver, urine and feces was determined. In addition, uptake of Cys-S-conjugates of Hg²+ and methylmercury (CH3Hg+) was measured in inside-out membrane vesicles prepared from either control Sf9 cells or Sf9 cells transfected with human MRP2. The amount of mercury in the total renal mass and liver was significantly greater in TR⁻ rats than in controls. In contrast, the amount of mercury in urine and feces was significantly lower in TR⁻ rats than in controls. Data from membrane vesicles indicate that Cys-S-conjugates of Hg²+ and CH3Hg+ are transportable substrates of MRP2. Collectively, these data indicate that MRP2 plays a role in the physiological handling and elimination of mercuric ions from the kidney.

Toxicometabolomics approach to urinary biomarkers for mercuric chloride (HgCl2)-induced nephrotoxicity using proton nuclear magnetic resonance (¹H NMR) in rats.

The primary objective of this study was to determine and characterize surrogate biomarkers that can predict nephrotoxicity induced by mercuric chloride (HgCl2) using urinary proton nuclear magnetic resonance (¹H NMR) spectral data. A procedure for (1)H NMR urinalysis using pattern recognition was proposed to evaluate nephrotoxicity induced by HgCl2 in Sprague-Dawley rats. HgCl2 at 0.1 or 0.75 mg/kg was administered intraperitoneally (i.p.), and urine was collected every 24 h for 6 days. Animals (n=6 per group) were sacrificed 3 or 6 days post-dosing in order to perform clinical blood chemistry tests and histopathologic examinations. Urinary ¹H NMR spectroscopy revealed apparent differential clustering between the control and HgCl2 treatment groups as evidenced by principal component analysis (PCA) and partial least square (PLS)-discriminant analysis (DA). Time- and dose-dependent separation of HgCl2-treated animals from controls was observed by PCA of ¹H NMR spectral data. In HgCl2-treated rats, the concentrations of endogenous urinary metabolites of glucose, acetate, alanine, lactate, succinate, and ethanol were significantly increased, whereas the concentrations of 2-oxoglutarate, allantoin, citrate, formate, taurine, and hippurate were significantly decreased. These endogenous metabolites were selected as putative biomarkers for HgCl2-induced nephrotoxicity. A dose response was observed in concentrations of lactate, acetate, succinate, and ethanol, where severe disruption of the concentrations of 2-oxoglutarate, citrate, formate, glucose, and taurine was observed at the higher dose (0.75 mg/kg) of HgCl2. Correlation of urinary (1)H NMR PLS-DA data with renal histopathologic changes suggests that ¹H NMR urinalysis can be used to predict or screen for HgCl2-induced nephrotoxicity.

Seventy-five percent nephrectomy and the disposition of inorganic mercury in 2,3-dimercaptopropanesulfonic acid-treated rats lacking functional multidrug-resistance protein 2.

In the present study, we evaluated the disposition of inorganic mercury (Hg(2+)) in sham-operated and 75% nephrectomized (NPX) Wistar and transport-deficient (TR(-)) rats treated with saline or the chelating agent meso-2,3-dimercaptosuccinic acid (DMSA). Based on previous studies, DMSA and TR(-) rats were used as tools to examine the potential role of multidrug-resistance protein 2 (MRP2) in the disposition of Hg(2+) during renal insufficiency. All animals were treated with a low dose (0.5 mumol/kg i.v.) of mercuric chloride (HgCl(2)). At 24 and 28 h after exposure to HgCl(2), matched groups of Wistar and TR(-) rats received normal saline or DMSA (intraperitoneally). Forty-eight hours after exposure to HgCl(2), the disposition of Hg(2+) was examined. A particularly notable effect of 75% nephrectomy in both strains of rats was enhanced renal accumulation of Hg(2+), specifically in the outer stripe of the outer medulla. In addition, hepatic accumulation, fecal excretion, and blood levels of Hg(2+) were enhanced in rats after 75% nephrectomy, especially in the TR(-) rats. Treatment with DMSA increased both the renal tubular elimination and urinary excretion of Hg(2+) in all rats. DMSA did not, however, affect hepatic content of Hg(2+), even in the 75% NPX TR(-) rats. We also show with real-time polymerase chain reaction that after 75% nephrectomy and compensatory renal growth, expression of MRP2 (only in Wistar rats) and organic anion transporter 1 is enhanced in the remaining functional proximal tubules. We conclude that MRP2 plays a significant role in the renal and corporal disposition of Hg(2+) after a 75% reduction of renal mass.

Testicular toxicity in mercuric chloride treated rats: association with oxidative stress.

Mercury has been recognized as an industrial hazard that adversely affects male reproductive systems of humans and animals. However, less information is available concerning the underlying mechanism in the pathogenesis of male reproductive dysfunction. The present study investigated the possible involvement of oxidative stress to induce oxidative deterioration of testicular functions in adult rats. Wistar male rats (n=132) were continuously exposed to HgCl(2) at 0, 50 and 100 ppm during 90 days through oral administration in the drinking water. Mercury exposure for 90 days resulted in an increase in the absolute and relative wet weight of the testis and a decrease in the absolute and relative wet weight of the accessory sex glands, with respect to the matched control. Marked perturbation in testosterone serum level was also detected during the treatment for the treated groups. Cauda epididymal sperm count/motility decreased significantly in the mercury-treated group and qualitative examination of testicular sections revealed a fewer mature luminal spermatozoa in comparison to the control. When the mercury-treated males were mated with normal cyclic females, mercury exposure resulted in a decline of the reproductive performance of male rats. These effects were associated with a significant increase in mercury content of testes and blood in time-dependent and dose-dependent fashion, respectively. The HgCl(2) treatment was associated with oxidative stress. Evidence of induction of oxidative stress was obtained in terms of perturbations in antioxidant defense and a significant dose-dependent increase in the testicular lipid peroxidation as a consequence of pro-oxidant exposure. Taken together, the results suggest that an increase in free radical formation relative to loss of antioxidant defense system after mercury exposure may render testis more susceptible to oxidative damage leading to their functional inactivation.

Metallothionein, zinc, and mercury levels in tissues of young rats exposed to zinc and subsequently to mercury.

Several studies have described mercury toxicity and the role of metallothioneins (MT) in the detoxification and regulation of metal homeostasis. However, little data exist on this topic during the specific post-natal developmental phase in young mammals. This developmental phase is particularly important since young animals are more sensitive to toxicants than adults. The objective of this work was to investigate whether MT participates in the mechanism of protection conferred by zinc pre-treatment on the toxic effects induced by mercury in neonate rats. Pups were exposed to ZnCl(2) (5 doses of 27 mg/kg/day, s.c.) and subsequently to HgCl(2) (5 doses of 5 mg/kg/day, s.c.); metal (Zn and Hg) and MT contents were analyzed in the liver, kidney, and blood. MT was induced in the liver and kidney of pups of both Zn-sal and Zn-Hg groups, although the greatest increase was in neonates exposed to Zn only. A direct relationship exists between MT and metals for both hepatic and renal tissues, which indicates that the increase in metal levels occurs in parallel to the increase in MT content. Although the heat-treated cytosolic fraction is rich in MT and metals, higher Zn and Hg contents were detected in the insoluble fraction of all tissues. These results suggest that MT is, at least in part, responsible for preventing Hg accumulation in the liver and blood and decreasing renal toxicity.

Cystine alters the renal and hepatic disposition of inorganic mercury and plasma thiol status.

In the present study, we determined whether cystine can inhibit, under certain conditions, the renal tubular uptake of inorganic mercury in vivo. We co-injected (i.v.) cystine with a non-toxic dose of mercuric chloride to rats and then studied the disposition of inorganic mercury during the next 24 h. We also determined if pretreatment with cystine influences the disposition of administered inorganic mercury. Moreover, plasma thiol status was examined after the intravenous administration of cystine with or without mercuric chloride. During the initial hour after co-injection, the renal tubular uptake of mercuric ions was diminished significantly relative to that in control rats. The inhibitory effects of cystine were evident in both the renal cortex and outer stripe of the outer medulla. In contrast, the renal accumulation of mercury increased significantly between the 1st and 12th hour after co-treatment. Urinary excretion and fecal excretion of mercury were greatly elevated in the rats co-treated with cystine and mercuric chloride. Thus, when cystine and mercury are administered simultaneously, cystine can serve as an inhibitor of the renal tubular uptake of mercury during the initial hour after co-treatment. In rats pretreated with cystine, the renal uptake of inorganic mercury was enhanced significantly relative to that in rats not pretreated with cystine. This enhanced accumulation of inorganic mercury correlated with the increased circulating concentrations of the reduced cysteine and glutathione. Additionally, the present findings indicate that thiol status is an important determinant of renal and hepatic disposition, and urinary and fecal excretion, of inorganic mercury.

Hemolytic effects of sodium selenite and mercuric chloride in human blood.

Many works have reported the interaction between selenium and mercury in the mammalian body and that chalcogen seems to have a protective effect against mercury toxicity. The aim of this study was to investigate the hemolytic effects of sodium selenite and/or mercuric chloride in human blood under in vitro conditions. For this, total venous blood from healthy subjects (males and females) was heparinized and incubated at 37 degrees C for 90 min with different concentrations of sodium selenite and/or mercuric chloride. The hemolytic effects of compounds were evaluated by measuring plasma hemoglobin concentration after centrifugation. In addition, 2-thiobarbituric acid reactive substances (TBARS) from plasma and erythrocytes, as well as erythrocyte nonprotein thiols (NPSH), were also evaluated in order to investigate molecular mechanisms related to selenite- or mercury-induced hemolysis. Mercuric chloride and sodium selenite, alone (400 microM), promoted a small in vitro hemolytic effect in human erythrocytes. However, when blood was exposed to both compounds (200 microM of each), there was an extremely high synergistic hemolytic effect. The exposure of blood to sodium selenite (400 microM), mercuric chloride (400 microM), and both compounds (200 microM each) did not alter erythrocyte TBARS levels. Sodium selenite presented a high oxidant effect toward erythrocyte NPSH; however, this effect was inhibited by mercuric chloride. The current results point to a synergistic hemolytic effect of sodium selenite and mercuric chloride in human blood, suggesting new understanding on the selenium-mercury antagonism. Moreover, this observed hemolysis seems to be not related to lipoperoxidation or thiol depletion.

Induction of anti-metallothionein antibody and mercury treatment decreases bone mineral density in mice.

Mercuric chloride (HgCl2) is an industrial agent with toxic effects on the immune system, kidney, lung, and nervous tissue, but little is known about its effect on bone. Metallothionein (MT) is a cysteine-rich metal-binding protein that exerts cytoprotective effects against heavy metal toxins. It has been reported that the susceptibility of renal and pulmonary toxicity of mercury was markedly enhanced in MT-null mice compared to control mice. However, there is no report about the effects of anti-metallothionein (anti-MT) Ab induction on mercury toxicity. We investigated the effect of anti-MT Ab induction on mercury-induced bone injury. BALB/c mice were injected with MT (10 microg/mouse ic) five times to induce anti-MT Ab and then treated with HgCl2 (1 mg/kg sc) three times per week for 3 weeks. MT immunization plus HgCl2 treatment dramatically decreased bone mineral density (BMD), and the humoral bone formation indices, alkaline phosphatase (ALP) activity and osteocalcin. MT immunization or HgCl2 treatment alone did not affect either BMD or serum ALP activity and osteocalcin levels. MT immunization impeded HgCl2-induced increase of MT expression in the liver and led to an increase of mercury in serum and the liver but a decrease in the kidney. Furthermore, serum titers of IgE and IgG1 were significantly elevated in the MT-immunized plus HgCl2 treatment group compared with those in the HgCl2 treatment group. Similar results were also observed in splenic secretions of IL-4 and IL-10 based on anti-CD3 Ab stimulation. Taken together, our results indicate that anti-MT Ab induction causes mercury-induced bone injury in BALB/c mice and also enhances mercury-related immune disorders.

Regulation of heme oxygenase activity in rat liver during oxidative stress induced by cobalt chloride and mercury chloride.

Activities of heme oxygenase and tryptophan-2,3-dioxygenase and cytochrome P450 content in liver as well as absorption of the Soret band and optical density at 280 nm in serum were determined 2 and 24 h after administration of HgCl(2) and CoCl(2) and after co-administration of the metal salts with alpha-tocopherol. Administration of HgCl(2) and CoCl(2) increased the contents of hemolysis products in the serum, induced heme oxygenase, and decreased cytochrome P450 content in the liver. Injection of HgCl(2) increased the activity of tryptophan-2,3-dioxygenase holoenzyme and enzyme saturation with the heme, but administration of CoCl(2) decreased these parameters. Pretreatment with alpha-tocopherol completely blocked the changes induced by HgCl(2) after 24 h. Induction of heme oxygenase induced by CoCl(2) was not blocked by alpha-tocopherol, but this antioxidant normalized the increase in the level of hemolysis products in the serum and decrease in tryptophan-2,3-dioxygenase holoenzyme activity and cytochrome P450 content. Mechanisms of regulation of heme oxygenase by mercury and cobalt ions are discussed.

Structural basis of the antagonism between inorganic mercury and selenium in mammals.

Mercuric chloride toxicity in mammals can be overcome by co-administration of sodium selenite. We report a study of the mutual detoxification product in rabbit plasma, and of a Hg-Se-S-containing species synthesized by addition of equimolar mercuric chloride and sodium selenite to aqueous, buffered glutathione. Chromatographic purification of this Hg-Se-S species and subsequent structural analysis by Se and Hg extended X-ray absorption fine structure (EXAFS) spectroscopy revealed the presence of four-coordinate Se and Hg entities separated by 2.61 A. Hg and Se near-edge X-ray absorption spectroscopy of erythrocytes, plasma, and bile of rabbits that had been injected with solutions of sodium selenite and mercuric chloride showed that Hg and Se in plasma samples exhibited X-ray absorption spectra that were essentially identical to those of the synthetic Hg-Se-S species. Thus, the molecular detoxification product of sodium selenite and mercuric chloride in rabbits exhibits similarities to the synthetic Hg-Se-S species. The underlying molecular mechanism for the formation of the Hg-Se-S species is discussed.