Effectiveness of N-acetylcysteine in protecting against mercuric chloride-induced nephrotoxicity

N-Acetylcysteine Displaces Glutathionyl-Moieties from Hg2+ and MeHg+ to Form More Hydrophobic Complexes at Near-Physiological Conditions

The anthropogenic release of Hg is associated with an increased human exposure risk. Since Hg2+ and MeHg+ have a high affinity for thiols, their interaction with L-glutathione (GSH) within mammalian cells is fundamentally involved in their toxicological chemistry and excretion. To gain insight into the interaction of these mercurials with multiple small molecular weight thiols, we have investigated their competitive interactions with GSH and N-acetylcysteine (NAC) at near-physiological conditions, using a liquid chromatographic approach. This approach involved the injection of each mercurial onto a reversed-phase (RP)-HPLC column (37 °C) using a PBS buffer mobile phase containing 5.0 mM GSH to simulate cytosolic conditions with Hg being detected in the column effluent by an inductively coupled plasma atomic emission spectrometer (ICP-AES). When the 5.0 mM GSH mobile phase was amended with up to 10 mM NAC, gradually increasing retention times of both mercurials were observed. To explain this behavior, the experiment with 5.0 mM NAC and 5.0 mM GSH was replicated using 50 mM Tris buffer (pH 7.4), and the Hg-containing fractions were analyzed by electrospray ionization mass spectrometry. The results revealed the presence of Hg(GS)(NAC) and Hg(NAC)2 for Hg2+ and MeHg(GS) and MeHg(NAC) for MeHg+, which suggests that the coordination/displacement of GS-moieties from each mercurial by the more hydrophobic NAC can explain their retention behavior. Since the biotransformations of both mercurials were observed at near-physiological conditions, they are of toxicological relevance as they provide a biomolecular explanation for some results that were obtained when animals were administered with each mercurial and NAC.

A review: Systematic research approach on toxicity model of liver and kidney in laboratory animals

Therapeutic experiments are commonly performed on laboratory animals to investigate the possible mechanism(s) of action of toxic agents as well as drugs or substances under consideration. The use of toxins in laboratory animal models, including rats, is intended to cause toxicity. This study aimed to investigate different models of hepatotoxicity and nephrotoxicity in laboratory animals to help researchers advance their research goals. The current narrative review used databases such as Medline, Web of Science, Scopus, and Embase and appropriate keywords until June 2021. Nephrotoxicity and hepatotoxicity models derived from some toxic agents such as cisplatin, acetaminophen, doxorubicin, some anticancer drugs, and other materials through various signaling pathways are investigated. To understand the models of renal or hepatotoxicity in laboratory animals, we have provided a list of toxic agents and their toxicity procedures in this review.

Mercury toxicity in pregnant and lactating rats: zinc and N-acetylcysteine as alternative of prevention

This study evaluated the toxic effects of inorganic mercury (Hg) in pregnant and lactating rats, as well as the possible protective effect of zinc (Zn) and N-acetylcysteine (NAC). Pregnant and lactating rats were pre-treated with ZnCl₂ (27 mg/kg) and/or NAC (5 mg/kg) and after 24 h, they were exposed to HgCl₂ (10 mg/kg). Animals were sacrificed 24 h after Hg exposure, and biochemical tests and metal determination were performed. Regarding pregnant rats, Hg exposure caused kidney, blood, and placenta δ-aminolevulinic acid dehydratase (δ-ALA-D) activity inhibition, and the pre-treatments showed a tendency of protection. Moreover, all the animals exposed to Hg presented high Hg levels in the kidney, liver, and placenta when compared with control group. Pregnant rats pre-exposed to Zn (Zn-Hg and Zn/NAC-Hg groups) presented an increase in hepatic metallothionein levels. Therefore, lactating rats exposed to Hg presented renal and blood δ-ALA-D inhibition; the pre-treatments showed a tendency to prevent the renal δ-ALA-D inhibition and prevented the blood δ-ALA-D inhibition caused by Hg. Lactating rats exposed to Hg presented high Hg levels in the kidney and liver. These results showed that 10 mg/kg of HgCl₂ causes biochemistry alterations in pregnant and lactating rats, and Zn and NAC present promising results against these damages.

Effect of mercury vapour exposure on urinary excretion of calcium, zinc and copper: relationship to alterations in functional and structural integrity of the kidney

Background: The kidney has a remarkable capacity to concentrate mercury (Hg) and as such is a primary target organ when exposure to Hg occurs, and it is also an organ for Hg excretion. Objective: The present work aims to investigate the effect of occupational Hg vapour exposure on the urinary excretion of calcium (Ca), zinc (Zn) and copper (Cu), and the possible association of this excretion to work duration as well as renal alterations. Methods: 83 non-smoker participants (36 referents, age: 35.69/9.5 years; 27 Hg vapour-exposed workers with 5/10 years work duration, age: 33.09/5.1 years; and 20 Hg vapour-exposed workers with]/11 years work duration, age: 39.509/8.50 years) were included in the present study. Urinary levels of microalbumin (U-Malb) and retinol-binding protein (U-RBP) as well as cytosolic glutathione S-transferase activity (U-GST) were measured to assess the glomerular and proximal tubular reabsorption functions as well as structural integrity of proximal tubules; respectively. In addition, blood Hg (B-Hg), serum levels of Hg (S-Hg) and Ca (S-Ca), and urinary levels of Hg (U-Hg), Ca (U-Ca), Zn (U-Zn), Cu (U-Cu) and creatinine (U-cr) were estimated. Results: In comparison to referents, all investigated parameters showed significant increase (except S-Ca and U-Zn/U-Cu ratio that significantly decreased among the workers as one group, S-Ca and U-Zn/U-Cu ratio that significantly and nonsignificantly decreased; respectively among workers with 5/10 years work duration, S-Ca and U-Zn/U-Cu ratio that significantly decreased among workers with]/11 years work duration). In addition, B-Hg was nonsignificantly increased and S-Ca was significantly decreased; also, both U-Hg and U-Zn/U-Cu were nonsignificantly decreased among workers with]/11 years work duration in comparison to those with 5/10 years work duration. Also, each of U-Hg, U-Ca, U-Zn and U-Cu was related to one another, while each of U-Ca, U-Zn and U-Cu was related to each of U-Malb, U-RBP and U-GST (except U-Zn was not related to U-GST). Conclusion: Hg vapour exposure leads to renal alterations which may parallel the change in proteinuria and enzymuria as well as the increased loss in urine of each of Ca, Zn and Cu. The urinary assessment of these metals may be used as a good indicator for renal dysfunction.

Zinc and N-acetylcysteine modify mercury distribution and promote increase in hepatic metallothionein levels

This study investigated the ability of zinc (Zn) and N-acetylcysteine (NAC) in preventing the biochemical alterations caused by mercury (Hg) and the retention of this metal in different organs. Adult female rats received ZnCl2 (27mg/kg) and/or NAC (5mg/kg) or saline (0.9%) subcutaneously and after 24h they received HgCl2 (5mg/kg) or saline (0.9%). Twenty-four hours after, they were sacrificed and analyses were performed. Hg inhibited hepatic, renal, and blood δ-aminolevulinic acid dehydratase (δ-ALA-D) activity, decreased renal total thiol levels, as well as increased serum creatinine and urea levels and aspartate aminotransferase activity. HgCl2-exposed groups presented an important retention of Hg in all the tissues analyzed. All pre-treatments demonstrated tendency in preventing hepatic δ-ALA-D inhibition, whereas only ZnCl2 showed this effect on blood enzyme. Moreover, the combination of these compounds completely prevented liver and blood Hg retention. The exposure to Zn and Hg increased hepatic metallothionein levels. These results show that Zn and NAC presented promising effects against the toxicity caused by HgCl2.

Metal Species in Biology: Bottom-Up and Top-Down LC Approaches in Applied Toxicological Research

Since the inception of liquid chromatography (LC) more than 100 years ago this separation technique has been developed into a powerful analytical tool that is frequently applied in life science research. To this end, unique insights into the interaction of metal species (throughout this manuscript “metal species” refers to “toxic metals, metalloid compounds, and metal-based drugs” and “toxic metals” to “toxic metals and metalloid compounds”) with endogenous ligands can be obtained by using LC approaches that involve their hyphenation with inductively coupled plasma-based element specific detectors. This review aims to provide a synopsis of the different LC approaches which may be employed to advance our understanding of these interactions either in a “bottom-up” or a “top-down” manner. In the “bottom-up” LC-configuration, endogenous ligands are introduced into a physiologically relevant mobile phase buffer, and the metal species of interest is injected. Subsequent “interrogation” of the on-column formed complex(es) by employing a suitable separation mechanism (e.g., size exclusion chromatography or reversed-phase LC) while changing the ligand concentration(s), the column temperature or the pH can provide valuable insight into the formation of complexes under near physiological conditions. This approach allows to establish the relative stability and hydrophobicity of metal-ligand complexes as well as the dynamic coordination of a metal species (injected) to two ligands (dissolved in the mobile phase). Conversely, the “top-down” analysis of a biological fluid (e.g., blood plasma) by LC (e.g., using size exclusion chromatography) can be used to determine the size distribution of endogenous metalloproteins which are collectively referred to as the “metalloproteome”. This approach can provide unique insight into the metabolism and the plasma protein binding of metal species, and can simultaneously visualize the dose-dependent perturbation of the metalloproteome by a particular metal species. The concerted application of these LC approaches is destined to provide new insight into biochemical processes which represent an important starting point to advance human health in the 21st century.

Protective effect of N-acetylcysteine on kidney as a remote organ after skeletal muscle ischemia-reperfusion

PURPOSE: To investigate whether N-acetylcysteine has a protective effect against renal injury as a remote organ after skeletal muscle ischemia-reperfusion in rats. METHODS: Twenty Wistar male rats were divided randomly into two experimental groups: group ischemia-reperfusion (group I) and group ischemia-reperfusion + N-acetylcysteine (group II). After ketamine and xylazine anesthesia, femoral artery was exposed. All animals were undergone 2h of ischemia by occlusion femoral artery and 24h of reperfusion. Rats that were treated with N-acetylcysteine given IV at a dose of 150 mg/kg-¹, immediately before reperfusion. After 24h of reperfusion, the blood samples were collected and submitted for evaluation of plasmatic urea, creatinine values and then rats were euthanized and left kidney harvested for histopathological analysis under light microscopy. RESULTS: The urea (35±7.84 mg.dL-1), creatinine (1.46±0.47 mg.dL-1) values were significantly lower in group II (P=0.000). Renal histopathologic study in group I showed extensive distal and proximal tubular cells necrosis and sloughing of epithelial cells into the tubular lumen, cast formation in tubule and glomerul, glomerul fibrosis and hemorrhage. Histopathologically, there was a significant difference (p=0.037) between two groups. CONCLUSION: The N-acetylcysteine was able to decrease renal injury induced by skeletal muscle ischemia reperfusion in rats.

Inhibition of hepatic δ-aminolevulinate dehydratase activity induced by mercuric chloride is potentiated by N-acetylcysteine in vitro

Mercuric chloride (HgCl)(2) is a toxic metal that causes oxidative damage in several tissues. N-acetylcysteine (NAC) is a sulfhydryl compound with antioxidant activity. In the present study, we investigated the in vitro effects of the association between HgCl(2) and NAC in tissues of mice. For this purpose, we evaluated the in vitro effect of HgCl(2)+NAC association on δ-aminolevulinate dehydratase (δ-ALA-D) activity and on thiobarbituric acid reactive substances (TBARS) levels in liver and kidney of mice. The results demonstrate that HgCl(2) inhibited δ-ALA-D activity in both tissues. Hepatic δ-ALA-D activity inhibited by HgCl(2) was potentiated by the highest concentration of NAC. The inhibition of hepatic δ-ALA-D activity seems to be related to sulfhydryl groups oxidation of the enzyme. We observed also that HgCl(2) increased TBARS levels in kidney and liver. Hepatic TBARS levels were reduced by NAC, at higher concentration. In contrast, NAC, at higher concentration, increased renal TBARS levels. In conclusion, the inhibition of hepatic δ-aminolevulinate dehydratase activity induced by HgCl(2) is potentiated by NAC in vitro, and this effect is not related to hepatic lipid peroxidation.

Low molecular weight thiols reduce thimerosal neurotoxicity in vitro: modulation by proteins

Thimerosal (TH), an ethylmercury complex of thiosalicylic acid has been used as preservative in vaccines. In vitro neurotoxicity of TH at high nM concentrations has been reported. Although a number of toxicological experiments demonstrated high affinity of mercury to thiol groups of the extracellular amino acids and proteins that may decrease concentration of free TH in the organism, less is known about the role of interactions between proteins and amino acids in protection against TH neurotoxicity. In the present study we examined whether the presence of serum proteins and of l-cysteine (Cys), d,l-homocysteine (Hcy), N-acetyl cysteine (NAC), l-methionine (Met) and glutathione (GSH) in the incubation medium affects the TH-induced changes in the viability, the intracellular levels of calcium and zinc and mitochondrial membrane potential in primary cultures of rat cerebellar granule cells. The cells were exposed to 500 nM TH for 48 h or to 15-25 μM TH for 10 min. Our results demonstrated a decrease in the cells viability evoked by TH, which could be prevented partially by serum proteins, albumin or in a dose-dependent manner by 60, 120 or 600 μM Cys, Hcy, NAC and GSH, but not by Met. This neuroprotection was less pronounced in the presence of proteins. Incubation of neurons with TH also induced the rise in the intracellular calcium and zinc concentration and decrease in mitochondrial membrane potential, and these effects were abolished by all the sulfur containing compounds studied and administered at 600 μM concentration, except Met. The loss of the ethylmercury moiety from TH as a result of interaction with thiols studied was monitored by (1)H NMR spectroscopy. This extracellular process may be responsible for the neuroprotection seen in the cerebellar cell cultures, but also provides a molecular pathway for redistribution of TH-derived toxic ethylmercury in the organism. In conclusion, these results confirmed that proteins and sulfur-containing amino acids applied separately reduce TH neurotoxicity, while their combination modulates in more complex way neuronal survival in the presence of TH.

Increased urinary excretion of carnitine and acylcarnitine by mercuric chloride is reversed by 2,3-dimercapto-1-propanesulfonic acid in rats

This investigation was aimed to study the effect of 2,3-dimercapto-1-propanesulfonic acid (DMPS) on mercuric chloride (HgCl(2))-induced alterations in urinary excretion of various carnitine fractions including free carnitine (FC), acylcarnitine (AC), and total carnitine (TC). Different groups of Wistar male rats were treated with HgCl(2) at the doses of 0.1, 0.5, 1.0, 2.0, and 3.0 mg/kg body weight, and the animals were sacrificed at 24 hours following HgCl(2) injection. A separate batch of animals received HgCl(2) (2 mg/kg) with or without DMPS (100 mg/kg) and sacrificed at 24 or 48 hours after dosing. Administration of HgCl(2) resulted in statistically significant and dose-dependent increase in the urinary excretion of FC, AC, and TC in rats. However, the ratio of urinary AC:FC was significantly decreased by HgCl(2). Pretreatment with DMPS offered statistically significant protection against HgCl(2)-induced alterations in various urinary carnitine fractions in rats.

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

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

Renal Toxicity of Mercuric Chloride at Different Time Intervals in Rats

This study was undertaken to study the renal toxicity of mercuric chloride in rats at different periods of time. The following groups of rats were studied: i) control, ii) placebo, iii) rats injected with a single ip dose of 100 mg/kg body weight of 2, 3 dimercapto-1-propanesulfonic acid, iv) rats injected with a single ip dose of 100 mg/kg body weight of 2, 3 dimercapto-1-propanesulfonic acid (DMPS) followed by a single dose ip of 2.0 mg HgCl2/kg body weight one hour after DMPS injection v) rats injected with a single ip dose of 2.0 mg HgCl2/kg body weight. Results indicate that mercuric chloride was more toxic after 48 hours of its administration when compared to 24 hours. Mercuric chloride administration caused an impairment of renal function which was evident from a significant decrease in urine volume, urinary excretion of urea, creatinine and glomerular filteration rate (P < 0.001) when compared to other treated groups. There was an increased excretion of protein, albumin and γ–-glutamyltransferase in the urine of mercuric chloride treated rats. Administration of 2, 3 dimercapto-1-propanesulfonic acid before mercuric chloride treatment caused the altered indices to return to near normal levels.

Mercury induces the externalization of phosphatidyl-serine in human renal proximal tubule (HK-2) cells

The underlying mechanism for the biological activity of inorganic mercury is believed to be the high affinity binding of divalent mercuric cations to thiols of sulfhydryl groups of proteins. A comprehensive analysis of published data indicates that inorganic mercury is one of the most environmentally abundant toxic metals, is a potent and selective nephrotoxicant that preferentially accumulates in the kidneys, and is known to produce cellular injury in the kidneys. Binding sites are present in the proximal tubules, and it is in the epithelial cells of these tubules that toxicants such as inorganic mercury are reabsorbed. This can affect the enzymatic activity and the structure of various proteins. Mercury may alter protein and membrane structure and function in the epithelial cells and this alteration may result in long term residual effects. This research was therefore designed to evaluate the dose-response relationship in human renal proximal tubule (HK-2) cells following exposure to inorganic mercury. Cytotoxicity was evaluated using the MTT assay for cell viability. The Annexin-V assay was performed by flow cytometry to determine the extent of phosphatidylserine externalization. Cells were exposed to mercury for 24 hours at doses of 0, 1, 2, 3, 4, 5, and 6 microg/mL. Cytotoxicity experiments yielded a LD50 value of 4.65 +/- 0.6 microg/mL indicating that mercury is highly toxic. The percentages of cells undergoing early apoptosis were 0.70 +/- 0.03%, 10.0 +/- 0.02%, 11.70 +/- 0.03%, 15.20 +/- 0.02%, 16.70 +/- 0.03%, 24.20 +/-0.02%, and 25.60 +/- 0.04% at treatments of 0, 1, 2, 3, 4, 5, and 6 microg/mL of mercury respectively. This indicates a dose-response relationship with regard to mercury-induced cytotoxicity and the externalization of phosphatidylserine in HK-2 cells.

Effectiveness of ZnCl2 in protecting against nephrotoxicity induced by HgCl2 in newborn rats

This work investigated the preventive effects of ZnCl(2) on renal and hepatic alterations induced by HgCl(2) in young rats. Wistar rats of 3 days old were treated (s.c.) on consecutive days with saline or ZnCl(2) 27 mg/kg/day from the 3rd to the 7th and with saline or HgCl(2) 5.0mg/kg/day from the 8th to the 12th day of life. Pups were sacrificed 24h after the last dose and samples were collected. The creatinine and urea dosages, used as renal parameters, presented increases of 35% and 500%, respectively. The alanine aminotransferase and lactic dehydrogenase activities, used as hepatic parameters, presented a decrease (40%) and no alteration, respectively, by mercury exposure. The glycemia was diminished and the hepatic glycogen was not modified by mercury. All the mercury effects were prevented by zinc. These results suggest that mercury intoxication of young rats alters the renal function but does not modify the hepatic parameters, and previous exposure to zinc is able to avoid the renal damage.

Tubular stress proteins and nitric oxide synthase expression in rat kidney exposed to mercuric chloride and melatonin

Stress proteins such as HSP70 members (HSP72 and GRP75) and metallothionein (MT) protect the kidney against oxidative damage and harmful metals, whereas inducible nitric oxide synthase (iNOS) regulates tubular functions. A single dose of mercuric chloride (HgCl(2)) can cause acute renal failure in rats, its main target being the proximal tubule. Oxidative damage has been proposed as one of its pathogenic mechanisms. In this study we tested whether melatonin (MEL), a powerful antioxidant compound, is effective against HgCl(2) nephrotoxicity. Rats were treated with saline, HgCl(2) (3.5 mg/kg), MEL (5 mg/kg), and MEL + HgCl(2) and examined after 24 hr for HSP72, GRP75, MT, and iNOS by immunohistochemistry and immunoblotting. Tubular effects of the treatment were then characterized by ultrastructure. In the HgCl(2) group, all markers were overexpressed in convoluted proximal tubules and sometimes in distal tubules. In the MEL + HgCl(2) group, GRP75 and iNOS decreased in convoluted and straight proximal tubules, whereas HSP72 and MT persisted more than the saline and MEL-only groups. Tubular damage and mitochondrial morphometry were improved by MEL pretreatment. In conclusion, the beneficial effect of MEL against HgCl(2) nephrotoxicity was outlined morphologically and by the reduction of the tubular expression of stress proteins and iNOS. These markers could represent sensitive recovery index against mercury damage.

N-acetylcysteine ameliorates amphotericin-induced nephropathy in rats

BACKGROUND

Amphotericin B may cause acute reduction in renal function. N-acetylcysteine (NAC) has a renoprotective activity in several nephrotoxic renal insults, but its effect on amphotericin-induced renal failure has not been investigated yet.

METHODS

Acute renal failure was induced in 30 Sprague-Dawley rats by a single intraperitoneal injection of amphotericin B (50 mg/kg). NAC (10 mg/kg) in isotonic saline or isotonic saline alone were administered daily for 4 days, starting 1 day before the amphotericin B injection. Glomerular filtration rate (GFR) was assessed using 99m-technetium diethylene triaminepentaacetic acid. Before and following amphotericin B administration, a 24-hour urine collection was performed for sodium, potassium and magnesium determination. The kidneys were preserved for pathologic examination.

RESULTS

Amphotericin B induced a significant decrease of GFR in both groups. Four days after amphotericin injection the GFR in the NAC-treated group was significantly higher than in the control group (0.62 +/- 0.20 vs. 0.46 +/- 0.14 ml/min, p = 0.042). Histologic signs of acute tubular necrosis were attenuated in the NAC-treated group. There were no significant differences between the groups in sodium, potassium and magnesium urine excretion after amphotericin injection.

CONCLUSIONS

NAC treatment exerted a renoprotective effect on deterioration of GFR in a rat model of amphotericin-induced renal failure. No functional protection on tubular function, as obviated by similar polyuria and urine losses of potassium and magnesium in both groups, was observed.

Modulation of cadmium chloride toxicity by sulphur amino acids in hepatoma cells

Cadmium is a toxic metal and no effective antidote exists at present. The aim of this study was to examine whether sulphur amino acids, involved in glutathione synthesis, can modulate cadmium toxicity in vitro. Two hepatoma cell lines (HepG2 and HTC cells) were exposed to cadmium chloride (0-100 microM) for 8h in control media or in media containing 1mM of homocysteine, cysteine or cystathionine. Cell viability was then assessed with the neutral red assay. In order to assess the mechanism by which homocysteine and cysteine modulate cadmium toxicity their ability to scavenge reactive oxygen species was determined as well as the potential to increase intracellular glutathione levels. The ability of the sulphur amino acids to prevent cadmium uptake by HTC and HepG2 cells was also assessed. The results indicate that homocysteine and cysteine protect efficiently both cell lines from cadmium chloride toxicity whereas cystathionine protects efficiently HTC cells but not HepG2 cells. This effect was shown to be dependent on the dose of each amino acid and increased protection from cadmium was observed with increasing concentrations of homocysteine and cysteine. Both amino acids prevented the formation of reactive oxygen species only when they were administered together with cadmium chloride. In addition homocysteine and cysteine did not increase intracellular glutathione levels. The results indicate that the mechanism by which sulphur amino acids protect from cadmium toxicity in vitro is due to the reduced uptake of the metal by the cells possibly by direct binding to the -SH group of the amino acids.

Effect of mercuric chloride on various hydroxyproline fractions in rat serum

Mercuric chloride (HgCl2) disturbs the collagen metabolism in the body which is reflected by altered hydroxyproline fractions in the serum. The aim of the present investigation was to study the effect of HgCl2 treatment on various hydroxyproline (Hyp) fractions in rat serum and the effect of 2,3-dimercapto-1-propane sulfonic acid (DMPS) treatment on serum Hyp fractions in HgCl2 treated rats. Other parameters studied included body weight, food intake, water intake and kidney weight. Doses of HgCl2 used were 0.1, 0.5, 1.0, 2.0, 3.0 mg/kg body weight and that of DMPS was 100 mg DMPS/kg body weight. All the doses of HgCl2 used caused significant (p < 0.01) alterations in free, peptide-bound and protein-bound Hyp in the serum when compared with control rats but a dose of 2 mg/kg body weight caused significant (p < 0.001) alteration even in the total serum Hyp when compared to control rats. Administration of DMPS prior HgCl2 treatment of rats sacrificed 24 h after the treatment caused a significant decrease of 52% (p < 0.01) in free Hyp when compared to similar HgCl2 treated rats. DMPS treatment with HgCl2 also caused an increase of 61% (p < 0.001) and 114% (p < 0.001) in peptide- and protein-bound Hyp respectively, when compared to HgCl2 treated rats sacrificed 24 h after mercuric chloride and DMPS treatment. Administration of DMPS followed by HgCl2 to rats which were sacrificed 48 h later caused no significant change in the total and free Hyp when compared to HgCl2 treated rats which were sacrificed 48 h after the treatment. But there was a significant decrease of 40% (p < 0.001) in peptide-bound Hyp and an increase in of 77% (p < 0.001) in protein-bound Hyp when compared to HgCl2 treated rats sacrificed 48 h after the treatment. The present study shows that HgCl2 treatment caused significant alterations in serum Hyp fractions reflecting disturbed composition of connective tissues which were not reversed by DMPS treatment.

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.

N-acetylcysteine ameliorates renal microcirculation: studies in rats

BACKGROUND

N-acetylcysteine (NAC) administration has been shown to ameliorate experimental acute renal failure induced by ischemia-reflow, and was found to prevent radiocontrast nephropathy in high-risk patients. While the protective effect of NAC has been primarily attributed to scavenging oxygen free radicals, improving renal microcirculation also may play a role in the prevention of acute renal failure.

METHODS

This study was designed to explore the effect of NAC on renal microcirculation. Blood pressure, total renal blood flow and selective regional cortical and outer medullary blood flow were continuously monitored in anesthetized Sprague Dawley rats with ultrasonic and laser-Doppler probes during the infusion of NAC (60 mg/kg).

RESULTS

In control intact rats blood pressure and renal microcirculation were unaffected by NAC. By contrast, following renal vasoconstriction induced by the radiocontrast agent iothalamate meglumine, NAC decreased total, cortical and medullary vascular resistance by 7 to 10% (P < 0.05). NAC also reduced renal vascular resistance by 16% when given during angiotensin II infusion (P < 0.05). Altered renal microcirculation, induced by the cyclooxygenase inhibitor indomethacin, by the nitric oxide synthase-inhibitor, Nomeganitro-l-arginine (L-NAME), or with their combination was partially restored by NAC. Nevertheless, NAC administration failed to attenuate renal function and morphology in a rat model of acute renal failure with selective outer medullary hypoxic injury, induced by indomethacin, L-NAME and iothalamate.

CONCLUSIONS

NAC ameliorates renal vasoconstriction, an effect that seems to be mediated by mechanisms other than prostaglandins and nitric oxide. The potential renoprotective outcome of NAC and the role of its vasodilating effect on the pre-constricted renal vasculature should be evaluated further.

alpha-Melanocyte-simulating hormone and interleukin-10 do not protect the kidney against mercuric chloride-induced injury

The anti-inflammatory cytokines alpha-melanocyte-stimulating hormone (MSH) and interleukin (IL)-10 inhibit acute renal failure (ARF) after ischemia or cisplatin administration; however, these agents have not been tested in a pure nephrotoxic model of ARF. Therefore, we examined the effects of alpha-MSH and IL-10 in HgCl(2)-induced ARF. Mice were injected subcutaneously with HgCl(2) and then given vehicle, alpha-MSH, or IL-10 by intravenous injection. Animals were killed to study serum creatinine, histology, and myeloperoxidase activity. Treatment with either alpha-MSH or IL-10 did not alter the increase in serum creatinine, tubular damage, or leukocyte accumulation at 48 h after HgCl(2) injection. Because alpha-MSH and IL-10 are active in other injury models that involve leukocytes, we studied the time course of tubular damage and leukocyte accumulation to investigate whether leukocytes caused the tubular damage or accumulated in response to the tubular damage. Tubular damage was present in the outer stripe 12 h after HgCl(2) injection. In contrast, the number of leukocytes and renal myleoperoxidase activity were normal at 12 h but were significantly increased at 24 and 48 h after injection. We conclude that neither alpha-MSH nor IL-10 altered the course of HgCl(2)-induced renal injury. Because the tubular damage preceded leukocyte infiltration, the delayed leukocyte accumulation may play a role in the removal of necrotic tissue and/or tissue repair in HgCl(2)-induced ARF.

Potential mechanism of fibronectin deposits in acute renal failure induced by mercuric chloride

Many glomerular diseases are associated with changes in the expression and distribution in the components of extracellular matrix. A remarkable feature in acute renal failure induced by mercuric chloride in rats was large fibronectin (Fn) deposits in kidneys 1 h post-HgCl2 injection (5 mg/kg body wt., s.c.). Our study examined some mechanisms as potential explanation of the early Fn deposits in mercuric chloride induced acute renal failure. Total tissue mRNA of livers and kidneys of control and treated rats were used in Northern blot to determine whether accumulation of Fn in kidney is associated with increases in the expression of this protein in the kidney and/or in the liver. Analysis of Fn levels by Western blot were also performed. Northern blot did not show significant difference between control and treated rats, while the abundance of polymerized-Fn in kidney tissue was increased 1 h and 5 h post HgCl2 injection. HgCl2 influence on Fn folding was studied in vitro to detect possible conformational changes that could altered its normal pattern of matrix assembly and/or binding to different ligands. In this context HgCl2 binding to Fn was measured following native tryptophan fluorescence of Fn in the presence of HgCl2 (0.5-250 mM). Binding parameters for the HgCl2-Fn complex formation were Kd = (1.6 +/- 0.2) 10(-4) M; n = 1 +/- 0.3, indicating a low apparent affinity and one type binding site. Thermal denaturation of Fn showed, between 30-60 degrees C, a soft reversible conformational change, while between 75-80 degrees C a highly and irreversible transition is produced suggesting a modification of the tertiary structure. HgCl2 abolished this transition. The kinetic of thermal unfolding of Fn was also measured and the effects observed due to HgCl2 presence reinforced the previous data. Finally, the effect of HgCl2 on Fn binding to denatured collagen (gelatin) was also measured as an index of the effect of this cation on biological properties of Fn. Fn binds gelatin strongest in the presence of HgCl2. Our results suggest that higher Fn deposits in kidney-treated rats seems not to be associated to augmented mRNA-Fn neither in kidney nor in liver. On the other hand, increased levels of polymerized Fn abundance was observed in kidney tissue from mercury-treated rats. We also describe that HgCl2 promotes, in vitro, conformational changes on Fn structure, inducing its denaturation and increasing its binding to gelatin, all events that could be related to the Fn deposits in renal tissues of HgCl2 treated rats, and could be expected in other situations that promoted interstitial fibrosis, not associated to overexpression of matrix-proteins.

Inhibition of nuclear factor-kappaB activation reduces cortical tubulointerstitial injury in proteinuric rats

BACKGROUND

Protein-induced chemokine expression in proximal tubular cells is mediated by the transcription factor nuclear factor-kappa B (NF-kappaB). We hypothesized that in vivo inhibition of renal NF-kappaB activation would reduce interstitial monocyte infiltration in a rat model of nonimmune proteinuric tubulointerstitial inflammation.

METHODS

Male Wistar rats received a single intravenous injection of doxorubicin hydrochloride [adriamycin (ADR), 7.5 mg/kg] and were studied 7, 14, 21, and 28 days later. In a second study, inhibitors of NF-kappaB [N-acetylcysteine (NAC; 150 mg/kg, b.i.d., i.p.), pyrrolidine dithiocarbamate (PDTC, 50 mg/kg, b. i.d., i.p.)] or vehicle were commenced on day 14 after the onset of proteinuria and were continued until day 30.

RESULTS

Rats injected with ADR had increased proteinuria (UpV, day 28, 474 +/- 57; control, 18 +/- 2 mg/day; P < 0.01) and cortical tubulointerstitial injury [tubule cell atrophy, interstitial volume, and monocyte/macrophage (ED-1) infiltration]. Electrophoretic mobility shift assay of nuclear extracts from whole cortex of ADR rats demonstrated that NF-kappaB activation (p50/65, p50/c-Rel) increased from day 7 (4.7 +/- 0.2 fold-increase above control; P < 0.01) was maximal at day 28 (6.2 +/- 0.7; P < 0.01) and correlated with UpV (r = 0.63; P < 0.05) and interstitial ED-1 infiltration (r = 0.67; P < 0.01). Chronic treatment of ADR rats with PDTC suppressed NF-kappaB activation (by 73%; P < 0.05) without any effect on UpV. NF-kappaB inhibition with PDTC was accompanied by a reduction in tubule cell atrophy (59%; P < 0.01), interstitial volume (49%; P < 0.05) and ED-1 infiltration (48%; P < 0.01), and cortical lipid peroxidation (41%; P < 0.05) compared with vehicle-treated ADR rats. In contrast NAC had no effect on NF-kappaB activation, tubulointerstitial injury, or UpV in ADR rats.

CONCLUSION

The activation of NF-kappaB may have an important role in mediating cortical interstitial monocyte infiltration and tubular injury in nonimmune proteinuric tubulointerstitial inflammation.

Verapamil protection against mercuric chloride-induced renal glomerular injury in rats

We have examined the effects of the calcium channel blocker verapamil on the renal glomerular structural damage produced by mercuric chloride in rats. Verapamil (75 micrograms/kg body wt iv) was administered 30 min prior to mercuric chloride injection (HgCl2, 5 mg/kg body wt sc). Verapamil prevented the glomerular proteinuria observed in HgCl2-treated rats. Isolated glomeruli from mercury-treated rats 1 h after injection presented a diminished cross-sectional area as compared with control glomeruli (control [micron2], 26,310 +/- 2545; HgCl2 [micron2], 18,474 +/- 1828) and increased glomerular calcium content (control, 23 +/- 6 nmol/mg protein; HgCl2, 43 +/- 7 nmol/mg protein). Verapamil pretreatment prevented glomerular cross-sectional area (GCSA) diminution and glomerular calcium content rise (GCSA [micron2] Vp + Hg, 28,281 +/- 4654, Ca2+ [nmol/mg protein] Vp + Hg, 18 +/- 5). Renal sections prepared for immunohistochemical detection and histochemical analysis showed increased deposits of fibronectin and lipids and enhanced cellularity in glomerular structures from HgCl2-treated rats. Renal sections from animals pretreated with verapamil showed fibronectin and lipid contents not different from control sections and their histological studies did not show any changes when compared with control. Verapamil pretreatment also protected glomeruli from enhanced leukocyte content (myeloperoxidase activity/mg protein): control, 59 +/- 7; HgCl2, 134 +/- 10; Vp + Hg, 79 +/- 11). HgCl2 also contracts GCSA in vitro; Vp prevented this GCSA diminution. The results described in this study indicate that mercuric chloride nephrotoxicity may be associated not only with changes in renal glomerular haemodynamics, but also with a direct effect on glomerular cells.

N-acetylcysteine as an antidote in methylmercury poisoning

Methylmercury is a ubiquitous environmental pollutant and potent neurotoxin. Treatment of methylmercury poisoning relies almost exclusively on the use of chelating agents to accelerate excretion of the metal. The present study demonstrates that oral administration of N-acetylcysteine (NAC), a widely available and largely nontoxic amino acid derivative, produces a profound acceleration of urinary methylmercury excretion in mice. Mice that received NAC in the drinking water (10 mg/ml) starting at 48 hr after methylmercury administration excreted from 47 to 54% of the 203Hg in urine over the subsequent 48 hr, as compared to 4-10% excretion in control animals. When NAC-containing water was given from the time of methylmercury administration, it was even more effective at enhancing urinary methylmercury excretion and at lowering tissue mercury levels. In contrast, excretion of inorganic mercury was not affected by oral NAC administration. The ability of NAC to enhance methylmercury excretion when given orally, its relatively low toxicity, and is wide availability in the clinical setting indicate that it may be an ideal therapeutic agent for use in methylmercury poisoning.

Understanding renal toxicity of heavy metals

The mechanisms by which metals induce renal injury are, in general, poorly understood. Characteristic features of metal nephrotoxicity are lesions that tend to predominate in specific regions of the nephron within specific cell types. This suggests that certain regions of the nephron are selectively sensitive to specific metals. Regional variability in sensitivity could result from the localization of molecular targets in certain cell populations and/or the localization of transport and binding ligands that deliver metals to targets within the nephron. Significant progress has been made in identifying various extracellular, membrane, and intracellular ligands that are important in the expression of the nephrotoxicity of metals. As an example, mercuric chloride induces a nephropathy that, at the lowest effective doses, is restricted primarily to the S3 segment of the proximal tubule, with involvement of the S2 and S1 segments at higher doses. This specificity appears to be derived, at least in part, from the distribution of enzymes and transport proteins important for the uptake of mercury into proximal tubule cells: apical gamma-glutamyltranspeptidase and the basolateral organic anion transport system. Regional distributions of transport mechanisms for binding proteins appear to be important in the expression of nephrotoxicity of metals. These and other new research developments are reviewed.

Comparative effects of the chelators sodium 4,5-dihydroxybenzene-1,3-disulfonate (Tiron) and diethylenetriaminepentaacetic acid (DTPA) on acute uranium nephrotoxicity in rats

Sodium 4,5-dihydroxybenzene-1,3-disulfonate (Tiron) and diethylenetriaminepentaacetic acid (DTPA) are two chelating agents that have been demonstrated to be effective in the treatment of experimental poisoning by a number of heavy metals. In this study, the effects of Tiron and DTPA on uranium-induced nephrotoxicity were evaluated in a rat model. A series of four Tiron or DTPA injections was administered intraperitoneally to adult male Sprague-Dawley rats immediately after a single subcutaneous injection of uranyl acetate dihydrate (5 mg/kg) and at 24, 48 and 72 h thereafter. Positive and negative control groups received 0.9% saline with or without uranyl acetate, respectively. Tiron effectiveness was assessed at 400, 800 and 1600 mg/kg, whereas DTPA was administered at 250, 500 and 1000 mg/kg. Although the urinary excretion of uranium was significantly enhanced by Tiron administration, significant amounts of uranium still remained in the kidney at the end of the treatment. However, the partial reduction of the renal uranium concentrations was in accordance with the amelioration noted in some urinary and serum indicators of uranium nephrotoxicity. Moreover, Tiron administration also reduced the severity of the uranium-induced histological alterations in the kidney. According to these results, Tiron offers only a modest encouragement with regard to its possible therapeutic potential to treat acute uranium-induced nephrotoxic effects. In turn, DTPA was less effective than Tiron in protecting against the nephrotoxicity of uranium in rats.

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.

Activation of functionally protective K(+) channels by methylmercury in rat alveolar macrophages

Methylmercury (MeHg) is generally known as a neurotoxic heavy metal while its effect on alveolar macrophages is still rarely studied. In this paper, we attempted to use whole cell and cell-attached patch-clamp recording technique and fura-2 fluorescence measurement to elucidate the effects of MeHg on rat alveolar macrophages. The results showed that extracellular application of MeHg induced a transient outward current I(O)(MeHg), 10-20 s in duration, 100-1000 pA in amplitude at -40 mV associated with a marked increase in conductance. The reversal potential depended distinctly on the external K(+) concentration. Removal of external Ca(2+) as well as bath applied verapamil caused a depression of I(O)(MeHg), and intracellular dialysis with 5 mM EGTA completely abolished I(O)(MeHg). Heparin (5 mg/ml) applied by intracellular dialysis greatly accelerated a run-down of I(O)(MeHg) induced by pressure ejection of MeHg. K(+) channel blockers such as quinine, and 4-aminopyridine especially low concentrations of dequalinium and apamin, but not tetraethylammonium inhibited I(O)(MeHg). Cell-attached single-channel recordings with the pipette solution containing 145 mM KCl revealed that the activation of single-channel currents with a conductance of 12 pS could be induced by application of MeHg outside the patch. Since MeHg increased [Ca(2+)](i), in a concentration-dependent manner which was partially blocked by either verapamil or Ca(2+)-free medium containing 1 mM EGTA, it is concluded that MeHg activates a Ca(2+)-dependent K(+) conductance by an increase of [Ca(2+)](i) through an influx from outside the cells as well as mobilization from intracellular store. A possibility that this membrane hyperpolarizing K(+) current may exhibit a functioning modulator in response to the harmful cytotoxic increase in [Ca(2+)](i) caused by MeHg was tested. Accordingly, this working hypothesis is verified by an increase of MeHg-induced cytotoxicity of cultured rat alveolar macrophages through a blockade of this Ca(2+)-activated K(+) channel by dequalinium.

Evidence for renal ischaemia as a cause of mercuric chloride nephrotoxicity

The present study was undertaken to investigate if the source of oxidative stress and the renal injury produced by mercuric chloride could be renal ischaemia. Verapamil Vp was used because it was described that calcium channel blockers protect cells from nephrotoxicants and from ischaemia. Vp (75 micrograms/kg, i.v.; 30 min before HgCl2 injection) prevented mercuric chloride renal injury observed 1 h post-HgCl2 injection as measured by clearance techniques. Vp also prevented the diminution of non-protein-sulfhydryls (NPSH) and the increased lipid peroxidation (LPO) induced by HgCl2 in renal tissue. Hg2+ toxicokinetic alterations were not observed in Vp plus HgCl2 treated rats, nor was Vp ability found as a free radical scavenger in renal tissue homogenates. The results described in this study give some evidence for the role of renal ischaemia in the production of oxidative stress, generating LPO and functional and morphological renal injury described in mercuric chloride treated rats.

Mercuric chloride effects on rat renal redox enzymes activities: SOD protection

This study was done to determine the effect of mercuric chloride treatment on the redox cycle enzymes in rat kidney ex-vivo. Glutathione peroxidase (GSH-Px) and catalase (Cat) activities were measured in kidney homogenates from rats with different nonprotein sulfhydrils levels and different mercury content. The results indicated that GSH-Px activity was enhanced in mercury-treated rats in direct relationship with kidney mercury content, whereas Cat activity was increased in the presence of the highest mercury kidney content obtained. Superoxide dismutase (SOD) was administered to rats prior to mercury chloride injection and renal function, development of lipid peroxidation and renal glutathione level were measured 1 h later. Renal function, renal glutathione, and renal lipid peroxidation production were maintained similar to control values. Moreover, SOD pretreatment also protected kidney from mercuric chloride histological alterations observed 24 h post mercury treatment. Thus, an inhibition of renal redox cycle enzymes "in vivo," did not appear to be an important determinant of the increased lipid peroxidation observed during mercuric chloride nephrotoxicity.

Potent and reversible interaction of silver with pure Na,K-ATPase and Na,K-ATPase-liposomes

The Na,K-ATPase (EC 3.6.1.37) is the receptor for cardioactive steroids, the only specific inhibitors known at the present time for this unique membrane bound transport system. We report here that silver is the most rapid and potent inhibitor of isolated Na,K-ATPase ever described. Inhibition of Na,K-ATPase activity by silver is immediate and strikingly distinct from other inhibitors: addition of 1 mM of cysteine or DMPS reactivates the silver blocked-enzyme immediately. The results reveal that silver interacts with Na,K-ATPase and inhibits differently by an on-off mechanism involving most likely a few critical sulfhydryl groups. Inhibition of Na-K transport by silver has been demonstrated also in an artificial membrane, e.g., in liposomes reconstituted with pure Na,K-ATPase performing active transport. Silver inhibits the active 86Rb transport mediated by the pure Na,K-ATPase molecule. The Na,K-ATPase contained in the liposomes was labeled specifically with 110mAg and appeared to bind two silver ions. Taken together, the results show that the mechanism of silver interaction with Na,K-ATPase might be different from other metals, for instance, mercury. The unique action mechanism of silver suggests a fundamental role of a few critical sulfhydryl groups for Na,K-transport.

Effect of different renal glutathione levels on renal mercury disposition and excretion in the rat

Mercury renal disposition has been studied following HgCl2 injection (5.0 mg/kg body wt., s.c.) in controls, diethylmaleate and N-acetylcysteine-treated rats. The different treatments were used to generate statistically different degrees of non-protein sulfhydryls concentration in kidneys. Diethylmaleate (4 mmol/kg body wt., i.p.) diminished kidney glutathione levels to 25% and N-acetylcysteine (2 mmol/kg body wt., i.p.) increased kidney non-protein sulfhydryls levels up to 75% compared with new controls. The amount of mercury in the kidneys, the mercury excretion rate in urine and the mercury plasma disappearance curves were calculated during 3 h post HgCl2 injection. BUN was measured in plasma at the same time period to determine the onset of kidney damage. The results indicate a higher HgCl2 renal clearance in N-acetylcysteine-treated rats compared to controls and less renal mercury accumulation. The data agree with diminished renal toxicity. On the other hand, renal mercury accumulation was higher and mercury renal clearance lower in diethylmaleate-treated animals, associated with higher renal toxicity. The results suggest that non-protein sulfhydryl levels (principally glutathione) might determine renal accumulation of mercury as well as its elimination rate and hence might enhance or mitigate the nephrotoxicity induced by the metal.

Mercuric chloride down-regulates T cell interferon-gamma production in brown Norway but not in Lewis rats; role of glutathione

Injection of a low dose of mercuric chloride into Brown Norway (BN) rats caused a marked decrease in the concanavalin A (ConA)-induced generation of interferon-gamma-producing cells (IFN-gamma pc) in spleen cell cultures prepared 1 h after mercury administration. A second injection 48 h later caused a further diminution of IFN-gamma pc down to 30% of the number generated in splenocyte cultures of phosphate-buffered saline (PBS)-injected controls. Injection of Lewis rats with either one or two doses of HgCl2 revealed no inhibitory effect on splenic IFN-gamma production. The presence of the reduced form of glutathione (GSH) in the culture medium was found to be essential in these experiments. In the absence of GSH there was an overall 20-fold reduction of the number of IFN-gamma pc in splenocyte cultures of normal or PBS-injected rats, which was further reduced to a 60- to 70-fold-lower level in cultures of rats exposed to HgCl2. This mercury-mediated extra reduction could be fully reversed with an excess (2 mM) of GSH in Lewis but not in BN splenocyte cultures. Since the bivalent Hg2+ ion is known to bind to and inactivate sulfhydryl groups of proteins and low molecular weight thiols, most notably GSH, we investigated a possible role for thiols in IFN-gamma production. It was found that the generation of IFN-gamma pc in normal BN and Lewis splenocyte cultures was strongly dependent on GSH or its precursor cysteine in the culture medium. Other thiol compounds were also effective but disulfides were completely inactive. Depletion of intracellular GSH in ConA-stimulated splenocytes by buthionine sulfoximide (BSO), an inhibitor of de novo GSH biosynthesis, strongly inhibited the generation of IFN-gamma pc. The inhibitory effect of BSO was not abolished by the addition of interleukin-2 (IL-2), but was mimicked with antibodies directed to the IL-2 receptor. The data stress the importance of GSH in the enhancement of IL-2-mediated IFN-gamma production and are most consistent with a model in which mercury interferes with T cell IFN-gamma production by affecting the intracellular availability of GSH. The strain-specific susceptibility to mercury-mediated inhibition of IFN-gamma production is discussed.