Strain difference in sensitivity of mice to renal toxicity of inorganic mercury

Inorganic mercury has a high affinity for the kidneys and causes acute renal failure. The present investigation was designed to determine the cause of the strain difference in sensitivity of mice to the renal toxicity of inorganic mercury. Renal damage caused by HgCl2 was estimated by histopathological and biochemical assessment, such as increase in blood urea nitrogen and plasma creatinine levels, and was found to be more remarkable in C3H/He than in C57BL/6 mice. Increase in renal lipid peroxidation in C3H/He was greater than that in C57BL/6 mice. However, no strain difference was observed in renal activities of glutathione (GSH) peroxidase, superoxide dismutase and GSH S-transferase in HgCl2-untreated mice. The GSH content and activities of catalase and GSSG reductase in kidney of HgCl2-untreated mice were higher in C3H/He than in C57BL/6. Background level of renal metallothionein content and the extent of metallothionein induction by HgCl2 showed no strain difference. On the other hand, renal mercury accumulation was higher and urinary mercury excretion was lower in C3H/He than in C57BL/6. The activity of renal gamma-glutamyltranspeptidase (gamma-GTP), which plays a key role in renal mercury accumulation, was higher in C3H/He than in C57BL/6. Furthermore, the increase in blood urea nitrogen by HgCl2, renal mercury accumulation and renal gamma-GTP activity in B6C3F1 mice were intermediate between those of the parent strains. These results suggest that the strain difference in renal toxicity of inorganic mercury seems to be caused by the discrepancy in renal mercury accumulation, and therefore, renal gamma-GTP may be an important factor determining the susceptibility of mice to the toxic action of inorganic mercury.     

Lactational exposure and neonatal kinetics of methylmercury and inorganic mercury in mice

The concentration of mercury in milk and the distribution pattern in the sucking pup was followed over time after administration of a single iv injection of 0.5 mg/kg body wt of 203Hg-labeled methylmercuric chloride or mercuric chloride to lactating mice on Day 10 of lactation. Mercury concentrations in milk of the dams and in whole body, blood, plasma, GI-tract, liver, kidneys, and brain of the offspring were followed up to 11 days after dosing (until lactational Day 21). Following the inorganic mercury dose to the dams, most of the mercury in milk was delivered to the pups during the first 24 h, but the maximum mercury concentration in plasma and tissues of pups was not reached until 7 days after dosing, indicating a prolonged absorption of inorganic mercury in the sucking pup. Pups of dams given methylmercury were exposed to a much lower and constant mercury concentration in milk. The estimated accumulated mercury dose via milk per pup of dams given methylmercury was less than half of that estimated after the inorganic mercury dose. When the accumulated dose via milk from methylmercury-exposed dams was compared to the amount of mercury in pup's carcass (whole body minus GI-tract including content), it was revealed that almost all mercury delivered via milk was absorbed, and that the suckling pups had a very low elimination of mercury until lactational Day 17. Lactational exposure following a maternal methylmercury or inorganic mercury dose resulted in almost similar mercury concentrations in liver, kidneys, and plasma of the suckling, but higher concentrations in brain (as most 14 times) and also twice as high mercury body burden in the methylmercury group. Thus, differences in kinetics indicate that lactational exposure of methylmercury is a greater hazard for the breast-fed infant than inorganic mercury.     

Enhanced toxicity for mice of combinations of bacterial lipopolysaccharide and vincristine

Sublethal doses of vincristine (VNC) and bacterial lipopolysaccharide (LPS) administered simultaneously to adult male mice resulted in markedly enhanced mortality. All of 10 strains of Pseudomonas aeruginosa tested, 4 of 7 strains of Bacteroides, and 6 of 10 strains of Listeria monocytogenes were able to substitute for purified LPS in enhancing mortality in VNC-treated mice. Inoculation of mice with each of 10 strains of Pseudomonas, each of 7 strains of Bacteroides, and about half of the 10 strains of Listeria tested elicited increased resistance to the lethal action of purified LPS. The patterns of responses of mice receiving a lethal combination of 2 mg of LPS/kg and 1 mg of VNC/kg resembled those of mice receiving a lethal dose of 10 mg of VNC/kg alone or 15 mg of LPS/kg alone with respect to (i) serum glutamic pyruvate transaminase activity, (ii) hematocrit values, and (iii) thrombocytopenia. The patterns of responses of mice receiving a lethal combination of LPS and VNC resembled those of mice receiving a lethal dose of LPS alone with respect to (i) hypothermia, (ii) retention of sulfobromophthalein, (iii) fibrinogen level, (iv) prothrombin activity, (v) blood urea nitrogen levels, and (vi) time of death. These data are consistent with the proposition that the combination of VNC and LPS produces a fatal renal failure. Histological studies confirmed that there was extensive renal damage in mice treated with lethal doses of LPS alone or a lethal combination of LPS and VNC.     

Form of mercury in stream fish exposed to high concentrations of dissolved inorganic mercury

The form of mercury predominating in mercury-contaminated fish from both pristine and industrialized waters in North America and Europe has almost universally been methylmercury. Sunfish (Lepomis auritus) living in a stream contaminated with 0.5-1 micrograms/L dissolved inorganic mercury accumulated greater concentrations of total mercury at headwater sites, where the dissolved mercury concentrations were greatest, than they did at downstream sites. However, despite evidence from laboratory studies that dissolved inorganic mercury is rapidly accumulated by fish without transformation to methylmercury, methylmercury constituted 85% or more of the total mercury concentration in fish at all sites.     

Reductions in renal mass and the nephropathy induced by mercury

The severity of renal injury induced by several graded doses of mercuric chloride and the disposition of mercury were evaluated and compared in control, uninephrectomized (50% NPX), and 75% nephrectomized (75% NPX) rats in an attempt to determine the effect of increased reductions of renal mass on the nephropathy induced by inorganic mercury. Consistent with previously published findings, proximal tubular necrosis (as assessed histopathologically and by the urinary excretion of lactate dehydrogenase (LDH) and total protein) was significantly more severe in 50% NPX rats than in control rats 24 hr after the administration of any of three lowest (1.0, 1.5, or 1.75 micromol/kg) doses of mercuric chloride used in the study. Interestingly, the severity of proximal tubular necrosis in the 75% NPX rats was not greater than that in control rats at these same doses. The reason for this appeared to be due to decreased renal accumulation of mercury, particularly in the renal cortex and outer stripe of the outer medulla. At the highest (8.0 micromol/kg) dose of mercuric chloride used, renal tubular injury was very extensive in all three groups of rats, with the level of injury being greatest in the 50% NPX rats. The injury was so severe in all three groups that acute renal failure was induced within the first 24 hr after the injection of mercury. An important finding that was made at this dose was that the level of blood urea nitrogen (BUN) was significantly greater in the 75% NPX rats than in either the 50% NPX or control rats, which indicates that 75% NPX rats may have entered into acute renal failure sooner than the 50% NPX or control rats. Overall, the findings from the present study indicate that as renal mass is reduced to a level at which renal function is not significantly impaired (50% NPX), the severity of the nephropathy induced by mercury is increased. By contrast, when the reduction of renal mass progresses to a level at which renal function begins to become impaired, the level of proximal tubular injury is not greatly different from that of animals with two kidneys, especially at low nephrotoxic doses of inorganic mercury. In addition, low nephrotoxic doses of inorganic mercury do not appear to affect significantly the reduced glomerular filtration rate in 75% NPX rats. However, it does appear that 75% NPX rats may be at greater risk of entering into acute renal failure at higher toxic doses of inorganic mercury than 50% NPX or control rats.     

Reduction of acetaminophen toxicity by sodium sulfate in mice

Twenty-one strains of Venezuelan encephalitis (VE) virus isolated from three habitats in Trinidad, W.I. during 1960 to 1972, were subtype III (Mucambo) VE virus by plaque-reduction neutralization tests. Like prototype Mucambo virus, each strain killed 8- to 15-week-old mice inoculated intraperitoneally. If the subtype I strain of VE virus that caused a major outbreak in Trinidad during 1943 to 1944 persisted on the island into the 1960s and early 1970s, it did not become the dominant VE virus in these three enzootic foci.     

Evaluation of the critical body burden concept based on inorganic and organic mercury toxicity to rainbow trout (Oncorhynchus mykiss)

Subadult rainbow trout (Oncorhynchus mykiss) were exposed to four waterborne concentrations each of 64-426 microg/L mercuric chloride (HgCl2) and 4-34 microg/L methylmercury chloride (CH3HgCl) until death to evaluate the critical body burden concept. Mean days to death for fish exposed to the highest and lowest concentrations of HgCl2 were 1 and 58 d, and 2 and > 100 d for fish exposed to CH3HgCl. Time to death was an important factor that influenced Hg tissue concentration, and was most evident among fish that died within a few days of exposure. Critical body burdens for Hg could be difficult to establish at the tissue level because no threshold concentrations were clearly indicated among the liver, kidney, spleen, brain, muscle, and gill that were monitored in this study. A critical burden for Hg was derived on a whole body basis for Hg in its organic form. An evaluation of this and other studies suggests whole body concentrations of 10-20 mg/kg Hg could be lethal to fish. Extrapolation from other studies indicate whole body concentrations of 1-5 mg/kg Hg could have chronic effects on fish and possibly other aquatic organisms. This concept could be used to assess the toxicological significance of chemical concentrations that are monitored in feral aquatic organisms. The tissue-based approach appears to have some advantages over current assessment protocols that focus on waterborne concentrations.     

Participation of mercuric conjugates of cysteine, homocysteine, and N-acetylcysteine in mechanisms involved in the renal tubular uptake of inorganic mercury

Mechanisms involved in the renal uptake of inorganic mercury were studied in rats administered a nontoxic 0.5 mumol/kg intravenous dose of inorganic mercury with or without 2.0 mumol/kg cysteine, homocysteine, or N-acetylcysteine. The renal disposition of mercury was studied 1 h after treatment in normal rats and rats that had undergone bilateral ureteral ligation. In addition, the disposition of mercury (including the urinary and fecal excretion of mercury) was evaluated 24 h after treatment. In normal rats, coadministering inorganic mercury plus cysteine or homocysteine caused a significant increase in the renal uptake of mercury 1 h after treatment. The enhanced renal uptake of mercury was due to increased uptake of mercury in the renal outer stripe of the outer medulla and/or renal cortex. Ureteral ligation caused reductions in the renal uptake of mercury in all groups except for the one treated with inorganic mercury plus N-acetylcysteine. Thus, it appears that virtually all of the mercury taken up by the kidneys of the normal rats treated with inorganic mercury plus N-acetylcysteine occurred at the basolateral membrane. Urinary excretory data also support this notion, in that the rate of excretion of inorganic mercury was greatest in the rats treated with inorganic mercury plus N-acetylcysteine. Our data also indicate that uptake of inorganic mercury in the kidneys of rats treated with inorganic mercury plus cysteine occurred equally at both luminal and basolateral membranes. In addition, the renal uptake of mercury in rats treated with inorganic mercury plus homocysteine occurred predominantly at the basolateral membrane with some component of luminal uptake. The findings of the present study confirm that there are at least two distinct mechanisms involved in the renal uptake of inorganic mercury, with one mechanism located on the luminal membrane and the other located on the basolateral membrane. Our findings also show that cysteine and homologs of cysteine, when coadministered with inorganic mercury, greatly influence the magnitude and/or site of uptake of mercuric ions in the kidney.     

ADP-ribosylation of brain neuronal proteins is altered by in vitro and in vivo exposure to inorganic mercury

ADP-ribosylation is an essential process in the metabolism of brain neuronal proteins, including the regulation of assembly and disassembly of biological polymers. Here, we examine the effect of HgCl2 exposure on the ADP-ribosylation of tubulin and actin, both cytoskeletal proteins also found in neurons, and B-50/43-kDa growth-associated protein (B-50/GAP-43), a neuronal tissue-specific phosphoprotein. In rats we demonstrate, with both in vitro and in vivo experiments, that HgCl2 markedly inhibits the ADP-ribosylation of tubulin and actin. This is direct quantitative evidence that HgCl2, a toxic xenobiotic, alters specific neurochemical reactions involved in maintaining brain neuron structure.     

An assessment of the developmental toxicity of inorganic arsenic

A critical analysis of the literature base regarding the reproductive and developmental toxicity of arsenic compounds, with emphasis on inorganic arsenicals, was conducted. The analysis was stimulated by the great number of papers that have purported to have shown an association between exposure of pregnant laboratory animals to arsenic compounds and the occurrence of offspring with cranial neural tube defects, particularly exencephaly. For the most part, the literature reports of arsenic developmental toxicity in experimental animals are inadequate for human risk assessment purposes. Despite the shortcomings of the experimental database, several conclusions are readily apparent when the animal studies are viewed collectively. First, cranial neural tube defects are induced in rodents only when arsenic exposure has occurred early in gestation (on Days 7 [hamster, mouse], 8 [mouse], or 9 [rat]). Second, arsenic exposures that cause cranial neural tube defects are single doses that are so high as to be lethal (or nearly so) to the pregnant animal. Third, the effective routes of exposure are by injection directly into the venous system or the peritoneal cavity; even massive oral exposures do not cause increases in the incidence of total gross malformations. Fourth, repetition of similar study designs employing exaggerated parenteral doses is the source of the large number of papers reporting neural tube defects associated with prenatal arsenic exposure. Fifth, in five repeated dose studies carried out following EPA Guidelines for assessing developmental toxicity, arsenic was not teratogenic in rats (AsIII, 101 micromol/kg/d, oral gavage; 101 micromol/m3, inhalation), mice (AsV, 338 micromol/kg/d, oral gavage; est. 402 micromol/kg/d, diet), or rabbits (AsV, 21 micromol/kg/d, oral gavage). Data regarding arsenic exposure and adverse outcomes of pregnancy in humans are limited to several ecologic epidemiology studies of drinking water, airborne dusts, and smelter environs. These studies failed to (1) obtain accurate measurements of maternal exposure during the critical period of organogenesis and (2) control for recognized confounders. The lone study that examined maternal arsenic exposure during pregnancy and the presence of neural tube defects in progeny failed to confirm a relationship between the two. It is concluded that under environmentally relevant exposure scenarios (e.g., 100 ppm in soil), inorganic arsenic is unlikely to pose a risk to pregnant women and their offspring.     

Intestinal handling of mercury in the rat: implications of intestinal secretion of inorganic mercury following biliary ligation or cannulation

Three sets of experiments were carried out to determine if there is an intestinal secretory component in the fecal excretion of administered inorganic mercury. In the first set of experiments the disposition of a nontoxic 0.5-micromol/kg intravenous dose of inorganic mercury was evaluated in control rats and rats whose bile duct had been ligated. Data collected 24 h after the administration of mercuric chloride indicated that some inorganic mercury had moved from the blood across the epithelium into the lumen of the stomach, small intestine, and large intestine. This secretory movement of mercury was most prominent in the small intestine. Interestingly, the renal uptake and accumulation of mercury were diminished significantly in the rats whose bile duct had been ligated. A time-course experiment showed that the maximum amount of secretory movement of mercury into the lumen of the small intestine occurred during the initial 12 h after the injection of mercuric chloride. By the end of 24 h after the injection of mercuric chloride, much of the inorganic mercury secreted in the small intestine appeared to have moved down into the large intestine. In a third experiment, the disposition of mercury was evaluated in control rats and rats who had their bile duct cannulated. The rationale for this third experiment was to study the disposition of mercury under conditions where obstruction of biliary outflow from the liver would not be as much of an issue as with ligation of the bile duct. Evidence for movement of mercury into the lumen of the intestines was also obtained from the rats whose bile duct had been ligated. Eighteen hours after the injection of mercuric chloride the amount of mercury in the luminal compartment of the small intestine was not statistically different between the two groups of rats. Approximately 1.7-2.1% of the administered dose was present in the luminal contents of the small intestine. Decreased renal uptake of mercury was also detected in the rats whose bile duct had been cannulated. The findings from the present study show that when bile flow is obstructed or diverted, clear evidence for secretory movement of mercury into the lumen of the gastrointestinal (GI) tract can be demonstrated. These findings also indicate that the secretory movement of mercury into the lumen of the GI tract is a mechanism that contributes significantly to the pool of mercury that is excreted in the feces.     

Reduced mercury excretion with feces in germfree mice after oral administration of methyl mercury chloride

When methyl mercury chloride was administered orally the amount of mercury excretion with feces of germfree mice was noticeably lower than that of the control mice. Germfree mice excreted 24 percent of the administered mercury within 10 days of administration while the control mice excreted 46 percent. Mercury retention in the organs of germfree mice was slightly higher than in the control mice. These results suggest that the existence of microorganisms in animal intestines are concerned with mercury excretion in the animal body.     

Enhanced ultrasonography in the diagnosis of renal tumors

Possible impairment of the L-arginine-nitric oxide (NO) pathway in the rostral ventrolateral medulla of adult spontaneously hypertensive rats (SHR) was investigated by microinjecting N(G)-nitro-L-arginine methyl ester (L-NAME), NOC 18 (an NO donor), or L-arginine. Unilateral injection of L-NAME (10 nmol/50 nL) into the rostral ventrolateral medulla significantly increased mean arterial pressure (MAP) in both SHR and Wistar-Kyoto rats (WKY). The increases in MAP did not differ significantly between the two strains (15+/-3 versus 10+/-2 mm Hg, respectively; n=8). In contrast, microinjection of L-arginine elicited significant (P<.05) dose-dependent decreases in MAP in both strains, and these depressor responses were significantly greater in SHR than in WKY (in 10 nmol of L-arginine: -29+/-2 versus -15+/-2 mm Hg, respectively; n=8, P<.01). Similarly, microinjection of NOC 18 (10 nmol/50 nL) reduced MAP in both strains, and the depressor response was also significantly greater in SHR than in WKY (-38+/-7 versus -22+/-3 mm Hg, respectively; n=8, P<.05). These results suggest that the L-arginine-NO pathway in the rostral ventrolateral medulla is impaired in SHR and that this impairment may contribute to the increase in arterial pressure in this animal model of genetic hypertension.     

In vitro toxicity of methyl mercury to fathead minnow cells

We have reported previously that serotonin (5-HT) stimulates the mitogenesis of bovine pulmonary artery smooth muscle cells (SMCs) through active transport of 5-HT and cellular signaling that includes elevation of superoxide (O2.-) and enhancement of protein tyrosine phosphorylation. Ginkgo biloba extract 501 (EGb 501), which has been demonstrated to act as an antioxidant, was found to block both the elevated O2.- and the proliferative and hypertrophic influences of 5-HT on SMCs, but not to directly inhibit the associated activation of NAD(P)H oxidase or the stimulation of phosphorylation of GTPase-activating protein (GAP). A similar effect of Ginkgo biloba extract 501 occurred on Chinese hamster lung fibroblasts (CCL-39), where 5-HT receptor, as opposed to transporter, action has been associated with mitogenesis. We conclude from these studies that Ginkgo biloba extract 501 quenches O2.- formation by 5-HT, thereby blocking its mitogenic effect. Stimulation of protein tyrosine phosphorylation of GAP by 5-HT appears to precede the elevation of O2.-.     

Minimal immunological effects on workers with prolonged low exposure to inorganic mercury

The growth-promoting activities of interleukin 6 (IL-6) in combination with early-acting hematopoietic factors, i.e., stem cell factor (SCF) and interleukin-1 alpha (IL-1 alpha), on primitive hematopoietic and megakaryocyte progenitors (high proliferative potential colony-forming cells [HPP-CFC] and colony-forming units-megakaryocyte [CFU-Mk], respectively) from 5-fluorouracil (5-FU)-treated murine bone marrow cells (BMC) were evaluated in serum-free fibrin clot cultures. IL-6 in combination with SCF and IL-1 induced an irregular and abortive hematopoiesis characterized by a reduction in colony size of at least 50% over those stimulated by SCF + IL-1 + IL-3 and an inability to continue growth to day 12. Moreover, IL-6 in combination with the early-acting factors, SCF and IL-1, had no effect on the formation of HPP-CFC. IL-6 is synergistic with SCF + IL-1 on day 7 CFU-Mk but did not stimulate large day 12 CFU-Mk. Our results suggest that, in the absence of serum, IL-6 prevents the continued proliferation of early hematopoietic and megakaryocytic progenitors initiated by SCF + IL-1 + IL-3. Optimization of cytokine combinations for use in ex vivo expansion of marrow progenitors, either for stem cell transplants or gene therapy, must consider not only the number of colonies but their size, as well as the contributions of serum components.     

Enhanced virus clearance by early inducible lymphocytic choriomeningitis virus-neutralizing antibodies in immunoglobulin-transgenic mice

Following infection of mice with lymphocytic choriomeningitis virus (LCMV), virus-neutralizing antibodies appear late, after 30 to 60 days. Such neutralizing antibodies play an important role in protection against reinfection. To analyze whether a neutralizing antibody response which developed earlier could contribute to LCMV clearance during the acute phase of infection, we generated transgenic mice expressing LCMV-neutralizing antibodies. Transgenic mice expressing the immunoglobulin mu heavy chain of the LCMV-neutralizing monoclonal antibody KL25 (H25 transgenic mice) mounted LCMV-neutralizing immunoglobulin M (IgM) serum titers within 8 days after infection. This early inducible LCMV-neutralizing antibody response significantly improved the host's capacity to clear the infection and did not cause an enhancement of disease after intracerebral (i.c.) LCMV infection. In contrast, mice which had been passively administered LCMV-neutralizing antibodies and transgenic mice exhibiting spontaneous LCMV-neutralizing IgM serum titers (HL25 transgenic mice expressing the immunoglobulin mu heavy and the kappa light chain) showed an enhancement of disease after i.c. LCMV infection. Thus, early-inducible LCMV-neutralizing antibodies can contribute to viral clearance in the acute phase of the infection and do not cause antibody-dependent enhancement of disease.     

Reduction by coenzyme Q10 of the acute toxicity of adriamycin in mice

Pretreatment for four days with coenzyme Q10 (COQ10) reduced the acute toxicity in mice treated with adriamycin. In two sequential protocols, adriamycin allowed only 36 and 42% survival, respectively. Pretreatment with COQ10 allowed 80 and 86% survival, respectively. The differences are significant, p less than 0.05. The mechanism for this reduction in the acute toxicity may be based upon the prevention by the supplementary COQ10 of the inhibition caused by adriamycin to COQ10-dependent enzymes in cardiac and and other tissues. The prospect of diminishing the toxicity of adriamycin in cancer patients remains promising and important.