Renal glutathione and mercury uptake by kidney

Seasonal and age-dependent differences in mercury concentrations in Apodemus sp. in the north-western region of Slovakia

Pollution of ecosystems by heavy metals such as mercury is currently a great concern. Mercury (Hg) can be released into the environment anthropogenically, but it is also naturally present in small quantities in all environmental compartments. Many different factors contribute to different rates of Hg deposition in animal bodies. The aim of this work is to describe how Hg concentrations in the bodies of small rodents change throughout the season at a site where massive anthropogenic pollution is not expected. Mice of the genus Apodemus were sampled during the whole year. Samples of blood, hair, liver, kidney, and brain were analyzed. Total Hg concentrations were measured by DMA-80. The mean Hg concentrations in examined organs were in the order hairs > kidney > liver > blood > brain, and their values decreased from 0.0500 to 0.0046 mg kg-1 dry weight. Males and females did not differ in contamination levels, but age-dependent differences in Hg concentrations were found. It was also identified how Hg concentrations in different organs correlate with each other. Different levels of seasonal variability were detected in Hg concentrations in blood, hair, and kidney.

Interaction of mercury species with proteins: towards possible mechanism of mercurial toxicology

The nature of the binding of mercurials (organic and inorganic) and their subsequent transformations in biological systems is a matter of great debate as several different hypotheses have been proposed and none of them has been conclusively proven to explain the characteristics of Hg binding with the proteins. Thus, the chemical nature of Hg-protein binding through the possible transportation mechanism in living tissues is critically reviewed herein. Emphasis is given to the process of transportation, and binding of Hg species with selenol-containing biomolecules that are appealing for toxicological studies as well as the advancement of environmental and biological research.

Breast milk contribution to tissue mercury levels in rat pups examined by cross-fostering at birth

The developing perinatal brain is vulnerable to methylmercury (MeHg) exposure. The contribution of breast milk to tissue MeHg levels in offspring is a significant public health concern because breast milk contains a certain amount of MeHg. Here, the contribution of MeHg transferred via breast milk to the Hg levels in the tissues of pups (Wistar rats) was investigated. Mated maternal rats were fed a MeHg (2 ppm)-supplemented or a control diet during pregnancy. Following parturition, male neonates from each group were cross-fostered between exposed or control dams, and they were further raised by dams fed a MeHg-supplemented diet or a control diet during lactation. Consequently, we evaluated three pup groups, which were raised by dams exposed to MeHg during pregnancy (P pups), lactation (L pups), or pregnancy and lactation (PL pups). Total mercury (THg) concentrations in the tissues of the offspring were measured at birth (postnatal day 0 [PD0]), during lactation (PD6, PD12, and PD19), and after weaning (PD29 and PD36). Blood and brain THg levels in the P and PL pups declined dramatically during lactation, however, there were no considerable differences between the two groups at PD6 and PD12. In contrast, blood and brain THg levels in the L pups increased slightly during lactation. The increase in the THg levels in the blood and brain of L pups at PD12 were approximately 3.3% and 1.5%, respectively, compared to the corresponding THg levels in the neonates in the P and PL groups. Our results suggest that if the MeHg exposure level during pregnancy is not high enough to cause neuronal development defects in the fetus, the exposure via breast milk is not a significant concern.

Brain methylmercury uptake in fetal, neonate, weanling, and adult rats

Fetuses and neonates are known to be highly susceptible to methylmercury (MeHg) toxicity, but little is known about the relative uptake of MeHg from blood to the developing brain. We measured time-course changes in mercury (Hg) concentrations in the brain of fetal, neonate, weanling, and adult rats after an injection of 0.08 μg (0.4 nmol) Hg/g MeHg. In the prenatal experiment, MeHg was subcutaneously injected to pregnant dams on embryonic days 17, 18, 18.5, 19, 19.5, or 20, and Hg concentrations in tissues were measured in both mothers and fetuses on embryonic day 21 (1 day before parturition). Brain Hg levels in fetuses peaked 2 days after injection and were approximately 1.5 times higher than in mothers. In the postnatal experiment, the same MeHg dose was injected subcutaneously to male rats on postnatal days 1 (neonates), 35 (weanlings), or 56 (adults). Mercury concentrations in tissues were measured 1, 2, 3, 4, 5, or 6 days after the injection. Brain Hg levels peaked most rapidly in neonates, and were approximately 1.5 times higher than levels in weanlings or adults. Throughout the examined period, peak Hg levels in the brain and the Hg brain/blood ratio 24 h after injection were highest in fetuses, followed by the levels in neonates, and decreased with life stage. These findings suggest that relatively higher brain MeHg uptake is an important factor in the vulnerability of fetuses and neonates to MeHg exposure.

Mechanisms involved in the transport of mercuric ions in target tissues

Mercury exists in the environment in various forms, all of which pose a risk to human health. Despite guidelines regulating the industrial release of mercury into the environment, humans continue to be exposed regularly to various forms of this metal via inhalation or ingestion. Following exposure, mercuric ions are taken up by and accumulate in numerous organs, including brain, intestine, kidney, liver, and placenta. In order to understand the toxicological effects of exposure to mercury, a thorough understanding of the mechanisms that facilitate entry of mercuric ions into target cells must first be obtained. A number of mechanisms for the transport of mercuric ions into target cells and organs have been proposed in recent years. However, the ability of these mechanisms to transport mercuric ions and the regulatory features of these carriers have not been characterized completely. The purpose of this review is to summarize the current findings related to the mechanisms that may be involved in the transport of inorganic and organic forms of mercury in target tissues and organs. This review will describe mechanisms known to be involved in the transport of mercury and will also propose additional mechanisms that may potentially be involved in the transport of mercuric ions into target cells.

Protective Effects of Quercetin Against HgCl₂-Induced Nephrotoxicity in Sprague-Dawley Rats

Mercury is a well-known environmental pollutant that can cause nephropathic diseases, including acute kidney injury (AKI). Although quercetin (QC), a natural flavonoid, has been reported to have medicinal properties, its potential protective effects against mercury-induced AKI have not been evaluated. In this study, the protective effect of QC against mercury-induced AKI was investigated using biochemical parameters, new protein-based urinary biomarkers, and a histopathological approach. A 250 mg/kg dose of QC was administered orally to Sprague-Dawley male rats for 3 days before administration of mercury chloride (HgCl2). All animals were sacrificed at 24 h after HgCl2 treatment, and biomarkers associated with nephrotoxicity were measured. Our data showed that QC absolutely prevented HgCl2-induced AKI, as indicated by biochemical parameters such as blood urea nitrogen (BUN) and serum creatinine (sCr). In particular, QC markedly decreased the accumulation of Hg in the kidney. Urinary excretion of protein-based biomarkers, including clusterin, kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), monocyte chemoattractant protein-1 (MCP-1), tissue inhibitor of metalloproteinases 1 (TIMP-1), and vascular endothelial growth factor (VEGF) in response to HgCl2 administration were significantly decreased by QC pretreatment relative to that in the HgCl2-treated group. Furthermore, urinary excretion of metallothionein and Hg were significantly elevated by QC pretreatment. Histopathological examination indicated that QC protected against HgCl2-induced proximal tubular damage in the kidney. A TUNEL assay indicated that QC pretreatment significantly reduced apoptotic cell death in the kidney. The administration of QC provided significant protective effects against mercury-induced AKI.

A systematic study of the disposition and metabolism of mercury species in mice after exposure to low levels of thimerosal (ethylmercury)

Thimerosal (TM) is an ethylmercury (etHg)-containing preservative used in some vaccines despite very limited knowledge on the kinetics and direct interaction/effects in mammals׳ tissues after exposure. Thus, this study aimed to evaluate the kinetics of Hg species in mice in a time course analysis after intramuscular injection of TM, by estimating Hg half-lives in blood and tissues. Mice were exposed to one single intramuscular dose of 20 µg of Hg as TM. Blood, brain, heart, kidney and liver were collected at 0.5 hour (h), 1 h, 8 h, 16 h, 144 h, 720 h and 1980 h after TM exposure (n=4). Hg species in animal tissues were identified and quantified by speciation analysis via liquid chromatography hyphenated with inductively coupled mass spectrometry (LC-ICP-MS). It was found that the transport of etHg from muscle to tissues and its conversion to inorganic Hg (inoHg) occur rapidly. Moreover, the conversion extent is modulated in part by the partitioning between EtHg in plasma and in whole blood, since etHg is rapidly converted in red cells but not in a plasma compartment. Furthermore, the dealkylation mechanism in red cells appears to be mediated by the Fenton reaction (hydroxyl radical formation). Interestingly, after 0.5 h of TM exposure, the highest levels of both etHg and inoHg were found in kidneys (accounting for more than 70% of the total Hg in the animal body), whereas the brain contributed least to the Hg body burden (accounts for <1.0% of total body Hg). Thirty days after TM exposure, most Hg had been excreted while the liver presented the majority of the remaining Hg. Estimated half-lives (in days) were 8.8 for blood, 10.7 for brain, 7.8 for heart, 7.7 for liver and 45.2 for kidney. Taken together, our findings demonstrated that TM (etHg) kinetics more closely approximates Hg(2+) than methylmercury (meHg) while the kidney must be considered a potential target for etHg toxicity.

Luminal transport of thiol S-conjugates of methylmercury in isolated perfused rabbit renal proximal tubules

Lumen-to-cell transport, cellular accumulation, and toxicity of L-cysteine (Cys), glutathione (GSH) and N-acetylcysteine (NAC) S-conjugates of methylmercury (CH(3)Hg(+)) were evaluated in isolated, perfused rabbit proximal tubular segments. When these conjugates were perfused individually through the lumen of S(2) segments of the proximal tubule it was found that Cys-S-CH(3)Hg and GSH-S-CH(3)Hg were transported avidly, while NAC-S-CH(3)Hg was transported minimally. In addition, 95% of the (203)Hg taken up by the tubular cells was associated with precipitable proteins of the tubule, while very little was found in the acid-soluble cytosol. No visual cellular pathological changes were observed during 30min of study. Luminal uptake of Cys-S-CH(3)Hg was temperature-dependent and inhibited significantly by the amino acids L-methionine and l-cystine. Rates of luminal uptake of GSH-S-CH(3)Hg were twice as great as that of Cys-S-CH(3)Hg and uptake was inhibited significantly (74%) by the presence of acivicin. When 2,3-bis(sulfanyl)propane-1-sulfonate (DMPS) was added to the bathing or luminal fluid, luminal uptake of Cys-S-CH(3)Hg was diminished significantly. Overall, our data indicate that Cys-S-CH(3)Hg is likely a transportable substrate of one or more amino acid transporters (such as system B(0,+) and system b(0,+)) involved in luminal absorption of L-methionine and L-cystine along the renal proximal tubule. In addition, GSH-S-CH(3)Hg appears to be degraded enzymatically to Cys-S-CH(3)Hg, which can then be taken up at the luminal membrane. By contrast NAC-S-CH(3)Hg and Cys-S-CH(3)Hg (in the presence of DMPS) are not taken up avidly at the luminal membrane of proximal tubular cells, thus promoting the excretion of CH(3)Hg(+) into the urine.

Relationships between the renal handling of DMPS and DMSA and the renal handling of mercury

Within the body of this review, we provide updates on the mechanisms involved in the renal handling mercury (Hg) and the vicinal dithiol complexing/chelating agents, 2,3-bis(sulfanyl)propane-1-sulfonate (known formerly as 2,3-dimercaptopropane-1-sulfonate, DMPS) and meso-2,3-bis(sulfanyl)succinate (known formerly as meso-2,3-dimercaptosuccinate, DMSA), with a focus on the therapeutic effects of these dithiols following exposure to different chemical forms of Hg. We begin by reviewing briefly some of the chemical properties of Hg, with an emphasis on the high bonding affinity between mercuric ions and reduced sulfur atoms, principally those contained in protein and nonprotein thiols. A discussion is provided on the current body of knowledge pertaining to the handling of various mercuric species within the kidneys, focusing on the primary cellular targets that take up and are affected adversely by these species of Hg, namely, proximal tubular epithelial cells. Subsequently, we provide a brief update on the current knowledge on the handling of DMPS and DMSA in the kidneys. In particular, parallels are drawn between the mechanisms participating in the uptake of various thiol S-conjugates of Hg in proximal tubular cells and mechanisms by which DMPS and DMSA gain entry into these target epithelial cells. Finally, we discuss factors that permit DMPS and DMSA to bind intracellular mercuric ions and mechanisms transporting DMPS and DMSA S-conjugates of Hg out of proximal tubular epithelial cells into the luminal compartment of the nephron, and promoting urinary excretion.

Effects of vitamin E on mercuric chloride-induced renal interstitial fibrosis in rats and the antioxidative mechanism

OBJECTIVE

To observe the effects of vitamin E (Vit E) on mercuric chloride (HgCl2)-induced renal interstitial fibrosis (RIF) in rats and discuss its antioxidative mechanism.

METHODS

A total of 32 Sprague-Dawley rats were randomly assigned to three groups: normal group, model group and Vit E group. RIF was induced by oral administration of HgCl(2) at a dose of 8 mg/kg body weight once a day for 9 weeks. Rats in Vit E group were administered with Vit E capsule at 100 mg/kg body weight, and rats in normal and model groups were treated with normal saline. At the end of the 9th week, rats were sacrificed and renal hydroxyproline (Hyp)'s trichrome and periodic acid-silver methenamine (PASM) staining. The activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and contents of glutathione (GSH) and malondialdehyde (MDA) in kidney tissue were tested with commercial kits. The expressions of nuclear factor-κB (NF-κB), inhibitor-κB (IκB), phospho-IκB (p-IκB) and tumor necrosis factor-α (TNF-α) were determined by Western blot. The expression of α-smooth muscle actin (α-SMA) was assayed by Western blot and immunofluorescent staining.

RESULTS

Renal Hyp content, HE, Masson's trichrome and PASM staining results and α-SMA expression confirmed development of HgCl2-induced RIF in rats. Oxidative stress markers GSH, GSH-Px and MDA confirmed oxidative stress in RIF rats. Compared with model rats, rats in Vit E group had lower kidney Hyp content (P<0.01). GSH and MDA contents decreased significantly in Vit E group compared with model group (P<0.01). The expressions of NF-κB and IκB had no significant difference among all groups (P>0.05). In Vit E group, the expressions of p-IκB and TNF-α decreased significantly compared with model group (P<0.01). The expression of α-SMA in Vit E group was also decreased significantly compared with model group (P<0.01).

CONCLUSION

Vit E has a protective effect on experimental RIF induced by HgCl(2) in rats and it is related to inhibition of lipid peroxidation, which involves blocking of NF-κB signaling pathway and the activation of cells producing extracellular matrix.

Transport of inorganic mercury and methylmercury in target tissues and organs

Owing to the prevalence of mercury in the environment, the risk of human exposure to this toxic metal continues to increase. Following exposure to mercury, this metal accumulates in numerous organs, including brain, intestine, kidneys, liver, and placenta. Although a number of mechanisms for the transport of mercuric ions into target organs were proposed in recent years, these mechanisms have not been characterized completely. This review summarizes the current literature related to the transport of inorganic and organic forms of mercury in various tissues and organs. This review identifies known mechanisms of mercury transport and provides information on additional mechanisms that may potentially play a role in the transport of mercuric ions into target cells.

Immunology of mercury

The heavy metal mercury is ubiquitously distributed in the environment resulting in permanent low-level exposure in human populations. Mercury can be encountered in three main chemical forms (elemental, inorganic, and organic) which can affect the immune system in different ways. In this review, we describe the effects of these various forms of mercury exposure on immune cells in humans and animals. In genetically susceptible mice or rats, subtoxic doses of mercury induce the production of highly specific autoantibodies as well as a generalized activation of the immune system. We review studies performed in this model and discuss their implications for the role of environmental chemicals in human autoimmunity.

Interactive toxicity of inorganic mercury and trichloroethylene in rat and human proximal tubules: effects on apoptosis, necrosis, and glutathione status

Simultaneous or prior exposure to one chemical may alter the concurrent or subsequent response to another chemical, often in unexpected ways. This is particularly true when the two chemicals share common mechanisms of action. The present study uses the paradigm of prior exposure to study the interactive toxicity between inorganic mercury (Hg(2+)) and trichloroethylene (TRI) or its metabolite S-(1,2-dichlorovinyl)-l-cysteine (DCVC) in rat and human proximal tubule. Pretreatment of rats with a subtoxic dose of Hg(2+) increased expression of glutathione S-transferase-alpha1 (GSTalpha1) but decreased expression of GSTalpha2, increased activities of several GSH-dependent enzymes, and increased GSH conjugation of TRI. Primary cultures of rat proximal tubular (rPT) cells exhibited both necrosis and apoptosis after incubation with Hg(2+). Pretreatment of human proximal tubular (hPT) cells with Hg(2+) caused little or no changes in GST expression or activities of GSH-dependent enzymes, decreased apoptosis induced by TRI or DCVC, but increased necrosis induced by DCVC. In contrast, pretreatment of hPT cells with TRI or DCVC protected from Hg(2+) by decreasing necrosis and increasing apoptosis. Thus, whereas pretreatment of hPT cells with Hg(2+) exacerbated cellular injury due to TRI or DCVC by shifting the response from apoptosis to necrosis, pretreatment of hPT cells with either TRI or DCVC protected from Hg(2+)-induced cytotoxicity by shifting the response from necrosis to apoptosis. These results demonstrate that by altering processes related to GSH status, susceptibilities of rPT and hPT cells to acute injury from Hg(2+), TRI, or DCVC are markedly altered by prior exposures.

Mercury exposure and public health

Mercury is a metal that is a liquid at room temperature. Mercury has a long and interesting history deriving from its use in medicine and industry, with the resultant toxicity produced. In high enough doses, all forms of mercury can produce toxicity. The most devastating tragedies related to mercury toxicity in recent history include Minamata Bay and Niagata, Japan in the 1950s, and Iraq in the 1970s. More recent mercury toxicity issues include the extreme toxicity of the dimethylmercury compound noted in 1998, the possible toxicity related to dental amalgams, and the disproved relationship between vaccines and autism related to the presence of the mercury-containing preservative, thimerosal.

Mercury and methylmercury accumulation and excretion in prairie voles (Microtus ochrogaster) receiving chronic doses of methylmercury

Methylmercury cation (MeHg) and divalent mercury (Hg++) accumulation in liver, kidney, and brain were quantified in prairie voles (Microtus ochrogaster) at 0, 3, 6, and 12 weeks during chronic exposure to aqueous MeHg. Dose groups received deionized water or aqueous solutions containing 9, 103, or 920 ng MeHg/ml. Our study presents temporal patterns of Hg++ and MeHg concentrations in organ tissues and makes inter-tissue comparisons at each time point to illustrate the accumulation and distribution of Hg species during the study. MeHg was accumulated in tissues for 3 weeks and then concentrations plateaued. Mercury accumulated in brain, liver, and kidney to average concentrations of 510 ng/g, 180 ng/g, and 3400 ng/g, respectively. MeHg and Hg++ concentrations were roughly equivalent in liver, kidney, and urine. MeHg concentrations in brain tissue were 2 to 20 times the concentrations of Hg++. Regression analysis was also used to demonstrate the utility of urinalysis as an indicator of Hg++ and MeHg concentrations in organ tissue (p < 0.001).

The toxicology of mercury and its chemical compounds

This review covers the toxicology of mercury and its compounds. Special attention is paid to those forms of mercury of current public health concern. Human exposure to the vapor of metallic mercury dates back to antiquity but continues today in occupational settings and from dental amalgam. Health risks from methylmercury in edible tissues of fish have been the subject of several large epidemiological investigations and continue to be the subject of intense debate. Ethylmercury in the form of a preservative, thimerosal, added to certain vaccines, is the most recent form of mercury that has become a public health concern. The review leads to general discussion of evolutionary aspects of mercury, protective and toxic mechanisms, and ends on a note that mercury is still an "element of mystery."

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.

Molecular and ionic mimicry and the transport of toxic metals

Despite many scientific advances, human exposure to, and intoxication by, toxic metal species continues to occur. Surprisingly, little is understood about the mechanisms by which certain metals and metal-containing species gain entry into target cells. Since there do not appear to be transporters designed specifically for the entry of most toxic metal species into mammalian cells, it has been postulated that some of these metals gain entry into target cells, through the mechanisms of ionic and/or molecular mimicry, at the site of transporters of essential elements and/or molecules. The primary purpose of this review is to discuss the transport of selective toxic metals in target organs and provide evidence supporting a role of ionic and/or molecular mimicry. In the context of this review, molecular mimicry refers to the ability of a metal ion to bond to an endogenous organic molecule to form an organic metal species that acts as a functional or structural mimic of essential molecules at the sites of transporters of those molecules. Ionic mimicry refers to the ability of a cationic form of a toxic metal to mimic an essential element or cationic species of an element at the site of a transporter of that element. Molecular and ionic mimics can also be sub-classified as structural or functional mimics. This review will present the established and putative roles of molecular and ionic mimicry in the transport of mercury, cadmium, lead, arsenic, selenium, and selected oxyanions in target organs and tissues.

Mercuric conjugates of cysteine are transported by the amino acid transporter system b(0,+): implications of molecular mimicry

Humans and other mammals continue to be exposed to various forms of mercury in the environment. The kidneys, specifically the epithelial cells lining the proximal tubules, are the primary targets where mercuric ions accumulate and exert their toxic effects. Although the actual mechanisms involved in the transport of mercuric ions along the proximal tubule have not been defined, current evidence implicates mercuric conjugates of cysteine, primarily 2-amino-3-(2-amino-2-carboxyethylsulfanylmercuricsulfanyl)propionic acid (Cys-S-Hg-S-Cys), as the most likely transportable species of inorganic mercury (Hg(2+)). Because Cys-S-Hg-S-Cys and the amino acid cystine (Cys-S-S-Cys) are structurally similar, it was hypothesized that Cys-S-Hg-S-Cys might act as a molecular mimic of cystine at one or more of the amino acid transporters involved in the luminal absorption of this amino acid. One such candidate is the Na(+)-independent heterodimeric transporter system b(0,+). Therefore, the transport of Cys-S-Hg-S-Cys and cystine was studied in MDCK II cells that were or were not stably transfected with b(0,+)AT-rBAT. Transport of Cys-S-Hg-S-Cys and cystine across the luminal plasma membrane was similar in the transfected cells, indicating that Cys-S-Hg-S-Cys can behave as a molecular mimic of cystine at the site of system b(0,+). Moreover, only the b(0,+)AT-rBAT transfectants became selectively intoxicated during exposure to Cys-S-Hg-S-Cys. These findings indicate that system b(0,+) likely contributes to the nephropathy induced by Hg(2+) in vivo. These data represent the first direct molecular evidence for the participation of a specific transporter in the luminal uptake of a large divalent metal cation in proximal tubular cells.

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.

Lead reduces the nephrotoxicity of mercuric chloride

The nephrotoxic effect of a single intraperitoneal dose of mercuric chloride (HgCl(2); 6 mg/kg) on adult CD-1 female mice was reduced at 24 and 48 h after injection, by a 48-h pretreatment nontoxic dose of lead acetate (Pb; 5 mg/kg) delivered by intravenous tail-vein injection (intravenous). While protection is temporally associated with lead-induced mitosis, occurring about 39 h after intracardiac lead injection (D. D Choie and G. W. Richter, 1974, Lab. Invest. 30, 447-451), the mechanism of the observed protection remains to be established.

Molecular homology and the luminal transport of Hg2+ in the renal proximal tubule

The aim of this study was to define mechanisms involved in the luminal uptake of inorganic mercury in the kidney using isolated perfused straight (S2) segments of the proximal tubule. When mercuric conjugates of glutathione (GSH), cysteinylglycine. or cysteine (containing 203Hg2+) were perfused through the lumen, the rates of luminal disappearance flux (JD) of inorganic mercury were approximately 39, 53, and 102 fmol/min per' min, respectively. Thus, the rates of luminal uptake of mercury are greater when the mercury is in the form of a mercuric conjugate of cysteine than in the form of a mercuric conjugate of cysteinylglycine or GSH. Addition of acivicin to the perfusate, to inhibit activity of the y-glutamyltransferase, caused significant reductions in the J,, for mercury in tubules perfused with mercuric conjugates of GSH. Addition of cilastatin, an inhibitor of dehydropeptidase- l (cysteinylglycinase) activity, caused significant reductions in the uptake of mercury in tubules perfused with mercuric conjugates of cysteinylglycine. These findings indicate that a significant amount of the luminal uptake of mercury, when mercuric conjugates of GSH are present in the lumen, is dependent on the activity of both y-glutamyltransferase and cysteinylglycinase. Finally, the JD for mercury in tubules perfused with mercuric conjugates of cysteine was reduced by approximately 50% when 3.0 mM L-lysine or 5.0 mM cycloleucine was added to the perfusate. It is concluded that these findings indicate that at least some of the luminal uptake of mercuric conjugates of cysteine occurs at the site of one or more amino acid transporters via a mechanism involving molecular homology.

Relationships between alterations in glutathione metabolism and the disposition of inorganic mercury in rats: effects of biliary ligation and chemically induced modulation of glutathione status

Influences of biliary ligation and systemic depletion of glutathione (GSH) or modulation of GSH status on the disposition of a low, non-nephrotoxic i.v. dose of inorganic mercury were evaluated in rats in the present study. Renal and hepatic disposition, and the urinary and fecal excretion, of inorganic mercury were assessed 24 h after the injection of a 0.5-micromol/kg dose of mercuric chloride in control rats and rats pretreated with acivicin (two 10-mg/kg i.p. doses in 2 ml/kg normal saline, 90 min apart, 60 min before mercuric chloride), buthionine sulfoximine (BSO; 2 mmol/kg i.v. in 4 ml/kg normal saline, 2 h before mercuric chloride) or diethylmaleate (DEM; 3.37 mmol/kg i.p. in 2 ml/kg corn oil, 2 h before mercuric chloride) that either underwent or did not undergo acute biliary ligation prior to the injection of mercury. Among the groups that did not undergo biliary ligation, the pretreatments used to alter GSH status systemically had varying effects on the disposition of inorganic mercury in the kidneys, liver, and blood. Biliary ligation caused the net renal accumulation of mercury to decrease under all pretreatment conditions. By contrast, biliary ligation caused significant increases in the hepatic burden of mercury in all pretreatment groups except in theacivicin-pretreated group. Blood levels of mercury also increased as a result of biliary ligation, regardless of the type of pretreatment used. The present findings indicate that biliary ligation combined with methods used to modulate GSH status systemically have additive effects with respect to causing reductions in the net renal accumulation of mercury. Additionally, the findings indicate that at least some fraction of the renal accumulation of inorganic mercury is linked mechanistically to the hepato-biliary system.

Disposition of inorganic mercury following biliary obstruction and chemically induced glutathione depletion: dispositional changes one hour after the intravenous administration of mercuric chloride

Influences of biliary obstruction and systemic depletion of glutathione (GSH) on the disposition of a low nontoxic iv dose of inorganic mercury were evaluated in rats in the present study. Specifically, the disposition of mercury in the kidneys, liver, small and large intestines, and blood was assessed 1 h after the injection of 0.5 micromol/kg mercuric chloride in control rats and rats pretreated with acivicin, buthionine sulfoximine (BSO), or diethylmaleate (DEM) that did or did not undergo acute biliary ligation prior to the injection of mercury. Among the groups that did not undergo biliary ligation, the pretreatments used to alter GSH status systemically had varying effects on the disposition of inorganic mercury in the kidneys, liver, intestines, and blood. Biliary ligation caused the net renal accumulation of mercury to decrease under all pretreatment conditions. By contrast, biliary ligation caused significant increases in the hepatic burden of mercury in all pretreatment groups except the acivicin-pretreated group. Blood levels of mercury also increased as a result of biliary ligation, regardless of the type of pretreatment used. Evidence for a secretory-like movement of mercury into the lumen of the intestines is also provided in the animals that underwent biliary ligation. The present findings indicate that biliary ligation combined with methods used to alter GSH status systemically have additive effects with respect to causing reductions in the net renal accumulation of mercury. In addition, the findings indicate that at least some fraction of the renal accumulation of inorganic mercury is linked mechanistically to the hepatobiliary system.

Basolateral uptake of inorganic mercury in the kidney

Renal disposition of administered inorganic mercury was studied in rats that had undergone an acute bilateral ureteral ligation shortly before being injected with a nontoxic 0.5-micromol/kg iv dose of inorganic mercury with or without 2.0 micromol/kg glutathione (GSH) or cysteine. Ureteral ligation and induction of "stop-flow" conditions were carried out to decrease glomerular filtration rate to negligible levels prior to the administration of inorganic mercury. The disposition of mercury was studied in the kidneys, liver, and blood 1 h after treatment. In rats given only mercuric chloride, the renal burden of mercury was approximately 20-25% of the administered dose of mercury, which is approximately 50% of the renal burden of mercury detected on average in normal rats. Coadministration of inorganic mercury with GSH or cysteine caused a significant increase in the renal uptake of mercury 1 h after treatment. The enhanced uptake of mercury in the kidneys was due to increased uptake of mercury in the renal cortex and outer stripe of the outer medulla. Pretreatment with para-aminohippuric acid caused significant reductions in the renal concentration and burden of inorganic mercury in all the rats administered inorganic mercury, regardless of whether the inorganic mercury was coadministered with GSH or cysteine. Overall, the findings from the present study provide additional evidence that there is basolateral uptake of inorganic mercury in the kidneys and that the primary mechanism involved in this basolateral uptake is dependent on the activity of the organic anion transporter. More importantly, the present findings also show that GSH and cysteine enhance the basolateral uptake of mercuric ions in the kidney when they are coadministered with inorganic mercury (presumably in the form of mercuric conjugates). On the basis of the present findings, one is led to believe that mercuric conjugates of GSH and cysteine are taken up at the basolateral membrane following exposure to inorganic forms of mercury.

Development of a model for classification of toxin-induced lesions using 1H NMR spectroscopy of urine combined with pattern recognition

Pattern recognition approaches were developed and applied to the classification of 600 MHz 1H NMR spectra of urine from rats dosed with compounds that induced organ-specific damage in either the liver or kidney. Male rats were separated into groups (n = 5) and each treated with one of the following compounds; adriamycin, allyl alcohol, 2-bromoethanamine hydrobromide, hexachlorobutadiene, hydrazine, lead acetate, mercury II chloride, puromycin aminonucleoside, sodium chromate, thioacetamide, 1,1,2-trichloro-3,3,3-trifluoro-1-propene or dose vehicle. Urine samples were collected over a 7 day time-course and analysed using 600 MHz 1H NMR spectroscopy. Each NMR spectrum was data-reduced to provide 256 intensity-related descriptors of the spectra. Data corresponding to the periods 8-24 h, 24-32 h and 32-56 h post-dose were first analysed using principal components analysis (PCA). In addition, samples obtained 120-144 h following the administration of adriamycin and puromycin were included in the analysis in order to compensate for the late onset of glomerular toxicity. Having established that toxin-related clustering behaviour could be detected in the first three principal components (PCs), three-quarters of the data were used to construct a soft independent modelling of class analogy (SIMCA) model. The remainder of the data were used as a test set of the model. Only three out of 61 samples in the test set were misclassified. Finally as a further test of the model, data from the 1H NMR spectra of urine from rats that had been treated with uranyl nitrate were used. Successful prediction of the toxicity type of the compound was achieved based on NMR urinalysis data confirming the robust nature of the derived model.

Small aliphatic dicarboxylic acids inhibit renal uptake of administered mercury

We evaluated the effects of pretreating rats intravenously with small aliphatic dicarboxylic acids on the renal disposition of injected inorganic mercury. Three different sets of experiments were carried out. When rats were pretreated with succinic acid, glutaric acid, or adipic acid 5 min prior to the injection of a 0.5-mumol/kg dose of mercuric chloride, there was a significant dose-dependent inhibitory effect on the renal disposition of mercury during the first hour after the administration of mercuric chloride. Both glutaric and adipic acid, at a dose of 1.0 mmol/kg, caused the greatest level of inhibition in the renal tubular uptake of inorganic mercury. By the end of the first hour after the injection of mercuric chloride, the renal burden of mercury in rats pretreated with either glutaric or adipic acid was 27-35% lower than in corresponding control rats. Malonic acid at a dose of 1.0 mmol/kg had no effect on the renal disposition of inorganic mercury. The inhibitory effect of succinic, glutaric, or adipic acid on the overall renal uptake of mercury was due to effects in both the cortex and outer stripe of the outer medulla. Findings from an experiment in which rats had their ureters ligated showed that the inhibitory effect of glutaric acid on the renal tubular uptake of mercury was due to inhibition of the uptake of mercury at the basolateral membrane. Our findings confirm that one of the mechanisms involved in the proximal tubular uptake of inorganic mercury is located on the basolateral membrane. According to findings from our previous studies, this mechanism appears to involve the activity of the organic anion transporter. The inhibitory effects of dicarboxylic acids on the renal tubular uptake of administered inorganic mercury, especially in rats whose ureters had been ligated, are consistent with the hypothesis that the organic anion transport system is involved in the basolateral uptake of inorganic mercury along the proximal tubule.

The role of transport in chemical nephrotoxicity

Various physiologic factors play a role in determining the extent of chemical-induced nephrotoxicity. One such factor relates to the transport systems that exist in the kidney. Several examples can be given of organic substances that are nephrotoxic only after being transported into renal tubular cells. Some of the cephalosporin antibiotics have been shown to produce proximal tubular necrosis after transport into those cells. Blockade of transport by competitors eliminates or reduces the nephrotoxic response. Citrinin, a secondary product of fungal metabolism, also produces proximal tubular necrosis, but only after transport into proximal tubular cells. Both the cephalosporins and citrinin utilize the organic anion transporter for entry into the cells, a transporter present in adult animals of all species and probably important physiologically for moving metabolic substrates into cells. Various glutathione conjugates (e.g., S-(1,2-dichlorovinyl) glutathione [DCVG]) also are transported into proximal tubular cells with a resulting nephrotoxicity. DCVG utilizes the sodium-dependent transport process that moves glutathione into proximal tubular cells, a process that is inhibited by probenecid. Finally, certain heavy metals also are transported into renal tubular cells. For example, mercuric ion enters proximal cells both from the luminal and peritubular sides and sulfhydryl compounds modify the transport. Movement of mercury from the peritubular side of the cell may be modified by certain organic anions. The characteristics of these mechanisms are less well understood than the mechanisms for the organic compounds.

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.

Binding of mercury in renal brush-border and basolateral membrane-vesicles

The influence of the thiols L-cysteine (CYS), glutathione (GSH), and 2,3-dimercapto-1-propanesulfonate (DMPS) on the binding and transport of inorganic mercury (Hg2+) in luminal (brush-border) and basolateral membrane-vesicles isolated from the kidneys of rats was studied using radiolabeled mercury (203HgCl2). Membrane-vesicles were exposed to 1, 10, or 100 microM Hg2+ in the presence or absence of a 3:1 or 10:1 mole-ratio of CYS, GSH, or DMPS relative to Hg2+. Equilibration of mercury with the membrane-vesicles occurred very rapidly, essentially being complete within 5 sec. By 60 sec, binding accounted for 87-97% of intravesicular Hg2+ in the absence of exogenous thiols. All three thiols significantly reduced the fraction of binding, with DMPS being the most effective agent. CYS enhanced the association of Hg2+ with luminal membrane-vesicles relative to that when Hg2+ was added alone, suggesting that conjugation of Hg2+ with CYS promotes the transport of low concentrations of Hg2+. In contrast, an excess of either GSH or DMPS relative to Hg2+ interfered significantly with both the binding and transport of Hg2+ into either luminal or basolateral membrane-vesicles. In summary, the present study is the first to describe the association of Hg2+ with renal luminal and basolateral membrane-vesicles. Evidence was obtained for the involvement of a Hg2+-CYS conjugate as a mechanism by which Hg2+ uptake and binding to luminal membranes occur and for an inhibitory effect of GSH and the chelator DMPS with regard to Hg2+ uptake and binding, demonstrating that extracellular thiols can modulate significantly the renal accumulation of Hg2+.

Comparative biochemical effects of low doses of mercury II chloride in the F344 rat and the multimammate mouse (Mastomys natalensis)

The biochemical effects and comparative nephroxicity of mercury II chloride (HgCl2) dosed at 0.75 mg/kg i.p. was investigated in the Fisher 344 rat (F344) and Mastomys natalensis using high resolution 1H nuclear magnetic resonance (NMR) spectroscopy of urine, histopathology and clinical chemical techniques. The effects of HgCl2 treatment were followed for up to 4 days post-dosing (p.d.). In F344 rats there was extensive proximal tubular damage and renal cortical necrosis together with elevated levels of urinary gamma-glutamyl transpeptidase (gamma GT), alkaline phosphatase (ALP) and lactate dehydrogenase (LDH). The 1H NMR spectra of urine obtained from Hg-treated F344 rats also showed increased levels of glucose, alanine, lactate, valine and hippurate (0-48h p.d.) with decreased levels of citrate, succinate and 2-oxoglutarate (24-48h p.d.). Mastomys were found to be highly resistant to HgCl2 toxicity at 0.75 mg/kg and the histological appearance of the renal cortex of treated animals was virtually identical to controls. There were no elevations in urinary ALP, gamma GT and LDH activities in HgCl2-treated Mastomys and there were no biochemical abnormalities in low MW components of Mastomys urine following HgCl2-treatment, as shown by 1H NMR spectroscopy. Urinary gamma GT activity was found to be much higher in F344 rats than Mastomys. Since gamma GT activity is involved in the tubular reabsorption of Hg2+, the lower levels of gamma GT in Mastomys might partially account for the lower toxicity of Hg2+ in this species.

Pretreatment with p-aminohippurate inhibits the renal uptake and accumulation of injected inorganic mercury in the rat

The effects of intravenous pretreatment with the organic anion p-aminohippurate (PAH) on the disposition of intravenously administered inorganic mercury in the kidneys, liver and blood were evaluated in rats. In dose-response experiments, the renal uptake (and/or accumulation) of mercury, 1 h after the injection of a nontoxic 0.5 mumol/kg dose of mercuric chloride (HgCl2), was significantly reduced in rats when a 1.0, 3.3 or 10 mmol/kg dose of PAH was administered 5 min prior to the injection of HgCl2. This reduction was due to reduced uptake of mercury in both the renal cortex and outer stripe of the outer medulla. Near maximal inhibition appeared to be achieved with the 10 mmol/kg dose of PAH. Inhibition of the uptake (an/or accumulation) of mercury in the renal cortex and outer stripe of the outer medulla, 1 h after the injection of the nontoxic dose of HgCl2, was also detected in experiments where HgCl2 was injected 5, 30, 60 or 180 min after pretreatment with a 10 mmol/kg dose of PAH. The renal uptake of mercury was inhibited significantly when the nontoxic dose of inorganic mercury was administered 5, 30, or 60, but not 180 min after pretreatment with the 10 mmol/kg dose of PAH. In another experiment, the renal burden of mercury was significantly reduced for 24 h when pretreatment with a 10 mmol/kg dose of PAH was administered 5 min prior to the injection of HgCl2. Pretreatment with PAH did not have an effect on the hepatic disposition of mercury, but it did cause a significant increase in the fraction of mercury present in the plasma of blood. In summary, the findings in the present study indicate that pretreatment with PAH inhibits the renal uptake of injected inorganic mercury in a dose-dependent and time-dependent manner. In addition, the findings tend to indicate that some fraction of the mercury that enters into renal tubular epithelial cells is by a mechanism involving the organic anion transport system.

Precision-cut tissue slices: applications in pharmacology and toxicology

Almost a decade has passed since the first paper describing the isolation and maintenance of precision-cut liver slices produced using a mechanical tissue slicer was published (1). Although tissue slices of various organs have been employed as an in vitro system for several decades, the lack of reproducibility within the slices and the relatively limited viability of the tissue preparations has prevented a widespread acceptance of the technique. The production of an automated slicer, capable of reproducibly producing relatively thin slices of tissue, as well as the development of a dynamic organ culture system, overcame several of these obstacles. Since that time, significant advances in the methods to produce and culture tissue slices have been made, as well as the application of the technique to several other organs, including kidney, lung and heart. This review will i) summarize the historical use of tissue slices prior to the development of the precision-cut tissue slice system; ii) briefly analyze current methods to produce precision-cut liver, kidney, lung and heart slices; and iii) discuss the applications of this powerful in vitro system to the disciplines of pharmacology and toxicology.

Luminal and basolateral mechanisms involved in the renal tubular uptake of inorganic mercury

The principle aim of the present study was to provide evidence for the existence of both a luminal and a basolateral mechanism involved in the renal tubular uptake of inorganic mercury. To accomplish this aim, we examined individually and collectively the effects of a "stop-flow" technique designed to reduce glomerular filtration to negligible levels and pretreatment with the organic anion p-aminohippurate (PAH) on the renal uptake and disposition of administered inorganic mercury. More specifically, we compared the disposition of inorganic mercury in groups of surgical control rats, rats that underwent a unilateral ureteral ligation, and rats that underwent a bilateral ureteral ligation that were pretreated with either normal saline or a 7.5 mmol/kg intravenous dose of PAH 5 min prior to receiving a nontoxic 0.5-mumol/kg intravenous dose of mercuric chloride. The disposition of mercury was evaluated at both 1 h and 24 h after the dose of inorganic mercury had been administered. In brief, the "stop-flow" conditions induced by either unilateral or bilateral ureteral ligation caused a significant reduction in the uptake and content of mercury in the kidneys (whose ureter was ligated) both at 1 h and 24 h after the intravenous injection of the nontoxic dose of mercuric chloride. This decreased renal uptake of mercury was due specifically to decreased uptake of mercury in the renal cortex and outer stripe of the outer medulla. Assuming that glomerular filtration was reduced to negligible levels, the amount of mercury not taken up during ureteral ligation represents the portion of mercury that is presumably taken up by a luminal mechanism. Pretreatment with PAH also caused a significant reduction in the renal uptake of mercury, specifically in the cortex and outer stripe of the outer medulla. The effects were most prominent 1 h after the injection of inorganic mercury. When either unilateral or bilateral ureteral ligation was combined with PAH pretreatment, an additive inhibitory effect occurred with respect to the renal uptake of mercury. In fact, the renal uptake of mercury was reduced by approximately 85% at 1 h after the injection of mercuric chloride. Since the luminal uptake of mercury was blocked by ureteral ligation, the effect of PAH on the renal uptake of mercury must have occurred at the basolateral membrane. Thus, the findings from the present study indicate that there are two distinct mechanisms involved in the uptake of mercury, with one mechanism located on the luminal membrane and another located on the basolateral membrane (presumably on proximal tubular epithelial cells).

Role of extracellular glutathione and gamma-glutamyltranspeptidase in the disposition and kidney toxicity of inorganic mercury in rats

The role of extracellular glutathione (GSH) and membrane-bound gamma-glutamyltranspeptidase (gamma-GT) as contributory factors in the disposition and toxicity of inorganic mercury (HgCl2, 1 mg kg-1, i.p.) was investigated in rats pretreated with acivicin (AT-125, 10 mg kg-1), a gamma-GT inhibitor. A high degree of gamma-GT inhibition (75%) and of protection (90%) against HgCl2-induced nephrotoxicity was obtained in gamma-GT-inhibited rats 24 h post-treatment. Pretreatment with acivicin affected the fractional distribution profile of 203 Hg, resulting in a twofold decrease in the renal incorporation of mercury 4 h post-treatment and a threefold increase in the 24-h urinary excretion of mercury. Plasma radioactivity remained constant over 24 h in rats dosed with 203Hg alone, whereas it decreased by 60% between 4 h and 24 h in gamma-GT-inhibited rats. In gamma-GT-inhibited rats treated with HgCl2 the renal and plasma reduced glutathione (GSH) content increased by 68% and 330% respectively, as compared to controls. The gamma-GT inhibition affected the distribution profile of mercury within urinary proteins, shifting the binding of mercury from the high-molecular-weight fraction (3% against 80%) to the low-molecular-weight fraction (72% against 10%). A significant but less impressive shift of mercury from the high- to the low-molecular-weight fraction also arose in the plasma. These results taken together support the pivotal role of extracellular GSH and membrane-bound gamma-GT in the renal incorporation, toxicity and excretion of inorganic mercury in rats.

Glutathione mercaptides as transport forms of metals

Among the many cellular functions of GSH, the roles of this tripeptide in metal transport, storage, and metabolism have recently received considerable attention. Although these roles had often been overlooked, they are critical for normal cellular metabolism and for protection from xenobiotics. Indeed, a number of the protective and regulatory functions of GSH are related to its ability to chelate reactive metals. GSH functions in the mobilization and delivery of metals between ligands, in the transport of metals across cell membranes, as a source of cysteine for metal binding, and as a reductant or cofactor in redox reactions involving metals. However, the interaction between GSH and metals can also produce or exacerbate cell injury. For example, GSH appears to be involved in the renal accumulation and toxicity of a number of metals, and in the carcinogenicity of chromium. Additional work is clearly needed to identify the mechanisms involved, and to better define the roles of GSH in metal homeostasis.

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.

Primary cultures of rabbit renal proximal tubule cells. III. Comparative cytotoxicity of inorganic and organic mercury

The present study further developed primary cultures of rabbit renal proximal tubule cells (RPTC) as an in vitro model to study chemical-induced toxicity by investigating the comparative cytotoxicity of mercuric chloride (HgCl2) and methyl mercury chloride (CH3HgCl) to RPTC. Confluent monolayer cultures of RPTC exposed to HgCl2 and CH3HgCl for 24 hr exhibited a concentration-dependent loss in cell viability at culture medium concentrations greater than 25 and 2.5 microM, respectively. Vital dye exclusion was a more sensitive indicator of cytotoxicity than the amount of lactate dehydrogenase activity, alkaline phosphatase activity, N-acetylglucosaminidase activity, and protein content remaining on the culture dish. On the basis of vital dye exclusion, HgCl2 was less toxic to proximal tubule cells in culture than CH3HgCl after 24 hr of exposure, whether cytotoxicity was based on LC50 values (34.2 microM HgCl2 vs 6.1 microM CH3HgCl) or total cellular mercury uptake (4.6 nmol Hg2+/10(5) cells vs 1.25 nmol CH3Hg+/10(5) cells). Differences in the extent and rate of metal uptake were also evident. Maximum cellular uptake of Hg2+ occurred within 6-24 hr after exposure and was not concentration-dependent, whereas maximum uptake of CH3Hg+ occurred within 3 hr of exposure and was concentration-dependent. The intracellular distribution of both mercurials between acid-soluble and acid-insoluble binding sites also differed. At noncytotoxic concentrations of HgCl2 (0.04-5 microM), intracellular Hg2+ bound increasingly to acid-soluble binding sites as a function of time, from 15-30% after 6 hr of exposure to 40-60% after 72 hr of exposure. However, at subcytotoxic (25 microM) and cytotoxic (34.2 microM) concentrations, Hg2+ binding to acid-soluble binding sites remained constant at approximately 30-40% for 6, 12, 24, and 72 hr after exposure. In contrast, only 20% of total cellular CH3Hg+ was bound to acid-soluble binding sites after exposure to 0.039 to 6.1 microM CH3HgCl for 6, 12, and 24 hr. Total cellular glutathione content was unaffected after exposure to 0.04-5 microM HgCl2 and 0.039-6.1 microM CH3HgCl, but was depleted 6 hr after exposure to 25 and 34.2 microM HgCl2. These results indicate that CH3HgCl was a more potent cytotoxicant to RPTC in primary culture than HgCl2. Furthermore, compared to Hg2+, the low binding of CH3Hg+ to acid-soluble binding sites and the absence of a redistribution of CH3Hg+ from acid-insoluble to acid-soluble binding sites appeared to contribute to its more potent toxicity to cultured cells.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Effects of mercuric chloride on renal plasma membrane function after depletion or elevation of renal glutathione

The role of renal nonprotein sulfhydryls (NPSH) in mercuric chloride-induced nephrotoxicity has been studied in various laboratories. Similarly, the importance of NPSH for mercuric ion accumulation by renal tissue also has been studied. In this study the potential role of NPSH was examined with respect to mercuric ion effects on membrane transport utilizing isolated membrane vesicles prepared from Sprague-Dawley rat kidneys. Sodium gradient-driven p-aminohippurate (PAH) transport in basolateral vesicles and glucose transport in brush border vesicles were studied. Depletion of NPSH, primarily glutathione (GSH), appeared to alter PAH but not glucose transport. HgCl2 (1 mg/kg) had no effect on either transport system in vesicles isolated from kidneys with normal GSH content, but it markedly disrupted both PAH and glucose transport in vesicles isolated from GSH-depleted rats. The most consistent effects were observed after GSH depletion with diethyl maleate plus buthionine sulfoximine. Elevation of renal GSH by administration of glutathione monoethyl ester blocked the effect of mercuric chloride (4 mg/kg) on glucose transport reported earlier. These data indicate that renal sulfhydryls not only modulate the effects of mercuric chloride, but they also may be important for normal physiological functioning of the PAH transport system.

The interactions of cis-diamminedichloroplatinum with metallothionein and glutathione in rat liver and kidney

The involvement of metallothionein (MT) in the nephrotoxicity of cis-diamminedichloroplatinum (c-DDP) was investigated in rats using enzyme excretion and histology as indicators of renal damage. In addition, the effects of renal glutathione (GSH) depletion on the nephrotoxicity of c-DDP was assessed by organic anion transport in renal cortical slices. A dose of 6.0 mg c-DDP/kg body wt, i.p. was administered to rats either as a single injection of 6.0 mg/kg or as six daily injections of 1.0 mg/kg. Concentrations of platinum (Pt) after c-DDP injection in both dosing regimens were approximately 12 micrograms/g in kidney and 2 micrograms/g in liver. However, there were no increases in either hepatic or renal concentrations of MT after both series of c-DDP injections. Fractionation of kidney cytosols from c-DDP injected rats on Sephadex G-75 columns revealed that 60-70% of cytosolic Pt was associated with proteins of high molecular weight and 15-20% of the Pt associated with the low molecular weight ligands. No discernable Pt peak was detected in the elution volume of MT. Pretreatment of rats with ZnSO4 increased both hepatic and renal concentrations of MT, but there was no Pt associated with the MT fraction after a subsequent injection of c-DDP. Small increases in the urinary excretion of the lysosomal enzyme, N-acetyl-beta-D-glucosaminidase and two brush border enzymes, alkaline phosphatase and gamma-glutamyltranspeptidase were observed 2 and 3 days after a single injection of c-DDP (6.0 mg/kg body wt, i.p.). Urinary creatinine excretion decreased by 50% 1 day after c-DDP injection and continued to decrease for the next 2 days. On the third day after c-DDP treatment, a small but significant decrease in body weight was also observed in the c-DDP injected animals. Pretreatment with Zn did not alter the c-DDP-induced enzymuria or renal tubular damage but slightly attenuated both the decrease in creatinine excretion and the loss in body weight. Uptake of the organic anion, p-aminohippuric acid (PAH) was reduced at 12 and 24 h after c-DDP injection. Reduction of tissue GSH concentrations by pretreatment with buthionine sulfoxime (BSO), resulted in only a slight increase in the c-DDP-induced inhibition of PAH uptake at 24 h after c-DDP injection. These results suggest that, in rats, neither MT nor GSH appear to play major roles in the binding or nephrotoxicity of c-DDP.

Cellular glutathione as a determinant of sensitivity to mercuric chloride toxicity. Prevention of toxicity by giving glutathione monoester

Depletion of glutathione (GSH) by treatment of mice with buthionine sulfoximine (BSO), an effective inhibitor of gamma-glutamylcysteine synthetase, markedly enhanced (about 10-fold) the lethal and renal toxicity of mercuric chloride. The lethal toxicity of HgCl2 was prevented by administration of GSH monoester; this was observed in mice pretreated with BSO and given a low dose of HgCl2, and also in untreated mice that were given a much higher dose of HgCl2. In contrast, administration of GSH did not protect. Since administered GSH is not transported effectively into cells, whereas GSH monoester is transported and split intracellularly to GSH, the findings indicate that protection against HgCl2 requires intracellular GSH. The experimental approaches used here suggest that cellular GSH is a major determinant of sensitivity to HgCl2 toxicity, and also that administration of GSH esters may be useful for prevention of HgCl2 toxicity.

Promotion of trans-platinum in vivo effects on renal heme and hemoprotein metabolism by D,L-buthionine-S,R-sulfoximine. Possible role of glutathione

We have examined the toxicity of trans-platinum (trans-diamminedichloroplatinum II) to heme and hemoprotein metabolism in the kidney of glutathione (GSH)-depleted rats and compared it with that produced by cis-platinum. Unlike cis-platinum treatment (7.0 mg/kg, i.v.) which caused after 7 days significant increases in cytochromes P450 and b5, and a marked decrease in porphyrin content of the kidney, trans-platinum alone (7 mg/kg, i.v.) did not elicit notable changes in these variables when measured 1 or 7 days after treatment. Also, cis-platinum treatment significantly altered the heme degradation pathway by increasing the activity of heme oxygenase and decreasing that of biliverdin reductase; trans-platinum treatment did not elicit a response in these activities. However, when rats were given the inhibitor of GSH synthesis, D,L-buthionine-S,R-sulfoximine (BSO), the subsequent administration (2 hr later) of trans-platinum produced, in 1 day, the spectrum of responses that were mediated by cis-platinum after 7 days. In the kidneys of rats treated with BSO plus trans-platinum the concentration of platinum measured only about 50% of that detected in the kidneys of rats treated with trans-platinum alone. In the liver, trans-platinum by itself or in combination with BSO was ineffective in altering the measured variables of heme metabolism. The possibility that similarity between cis-platinum and trans-platinum plus BSO may extend to systems other than heme metabolism, e.g. GSH synthesis and degradation, was examined. cis-Platinum caused significant inhibition of both renal gamma-glutamyl synthetase and gamma-glutamyl transpeptidase after 7 days, but not after 1 day. Twenty-four hours after treatment, BSO + trans-platinum caused inhibition of gamma-glutamylcysteine synthetase activity, whereas this activity in animals treated with BSO alone had returned to control values. At this time point, neither oxidized glutathione (GSSG)-reductase nor gamma-glutamyl transpeptidase activity was affected by trans-platinum + BSO treatment. The findings suggest that GSH constitutes an important defense mechanism against trans-platinum alteration of heme metabolism and may play a role in cellular accumulation of the drug in an inactive complex. It is proposed that BSO treatment, despite resulting in a diminished intracellular concentration of trans-platinum, allows reaction of the metal complex with target molecules by virtue of its ability to deplete GSH.

Role of gamma-glutamyltranspeptidase in renal uptake and toxicity of inorganic mercury in mice

The role of renal glutathione (GSH) metabolism as a mediating factor in the renal uptake and toxicity of inorganic mercury was investigated in mice by preadministering a gamma-glutamyltranspeptidase (GGT) inhibitor, acivicin. Pretreatment with acivicin (0.25, 1.0 or 2.5 mmol/kg, i.p.) led to a dose-dependent decrease in renal mercury content and increases in mercury and GSH contents in urine measured 2 h after HgCl2 injection (18 mumol/kg, i.v.). Acivicin pretreatment also ameliorated the renal and lethal toxicity caused by administration of inorganic mercury. Treatment of the mice with 1,2-dichloro-4-nitrobenzene (DCNB, 2.5 mmol/kg, i.p.), a specific depletor of hepatic GSH, prior to HgCl2 injection substantially reduced renal Hg content and consequently reduced the renal damage. In addition, coadministration of GSH (36 mumol/kg, i.v.) with HgCl2 increased the renal Hg content measured 5 min after HgCl2 injection to 2.6 fold higher than that of mice treated with HgCl2 alone. These results suggest that renal uptake of inorganic mercury, which is supposedly transported to the kidney as a mercury-GSH complex, is dependent on a reaction catalyzed by GGT on the outer surface of the renal brush border membrane in the same manner as the metabolism of GSH.

Renal glutathione depletion and nephrotoxicity of cadmium-metallothionein in rats

Renal glutathione (GSH) concentrations were reduced approximately 80% at 4 hr after a single injection of buthionine sulfoxime (BSO) (4 mmol/kg body wt) and remained reduced for at least 16 hr in male rats. Following BSO injection, rats were injected with a nephrotoxic dose of cadmium-metallothionein (Cd-MT) (0.3 mg Cd as Cd-MT/kg body wt) and killed 1, 4, or 12 hr later. Damage to the kidney was assessed histologically and by measurement of p-aminohippuric acid (PAH) uptake into renal cortical slices. Although the renal accumulation of Cd following Cd-MT injection was significantly lower in BSO-pretreated rats as compared to nonpretreated rats, the damage to kidney was more severe. At 4 and 12 hr, both Cd-MT-induced inhibition of PAH uptake and morphological damage were significantly increased in BSO-pretreated rats. In certain experiments, the induction of renal intracellular MT synthesis by zinc pretreatment slightly decreased the renal toxicity of Cd-MT in the BSO-treated rats. The results demonstrate that although GSH depletion decreases the renal accumulation of Cd in rats injected with Cd-MT, the nephrotoxicity of Cd-MT is increased. Preinduction of MT in the kidney can only partially overcome this increase in toxicity. Therefore both GSH and intracellular MT levels can influence the renal toxicity of injected Cd-MT.

Unilateral nephrectomy in the rat: effects on mercury handling and renal cortical subcellular distribution

As unilateral nephrectomy (UNX) is associated with enhanced mercuric chloride nephrotoxicity, studies were undertaken to characterize the effects of UNX on the tissue content, urinary excretion, and renal cortical subcellular distribution of mercury in the rat. Animals were studied immediately, 2 days or 14 days following UNX, during separate phases of compensatory renal hypertrophy. As compared to sham surgery controls, mercury content in renal cortex was higher in all UNX groups at 24 hr following injection and in the immediate and 2-day groups at 1 or 3 hr. However, UNX was not associated with any alteration in mercury content within outer or inner medulla, liver, plasma, or red blood cells. Subcellular distribution studies demonstrated that cytosolic mercury was uniformly elevated in all UNX groups at 1, 3, and 24 hr following injection while mercury bound to "metallothionein-like" proteins or free in the cytosol was increased only at 1 or 3 hr. Nuclear, mitochondrial, or microsomal mercury content was elevated in the animals studied immediately or 14 days after UNX at 3 or 24 hr following injection, while animals studied 2 days after UNX demonstrated a nearly uniform increase at 1, 3, and 24 hr. Single-kidney urinary mercury excretion was elevated in all UNX groups while excretion per gram kidney weight was increased only in the animals studied immediately or 2 days after surgery. These studies suggest that all phases of compensatory renal hypertrophy are associated with an enhanced content of mercury within the cell cytoplasm and in critical cellular organelles, which may explain the enhanced nephrotoxicity seen following UNX.