Mutagenicity study on mice given mercuric chloride

The mutagenic activity of different concentrations of mercuric chloride (0, 2, 4 and 6 mg HgCl2 per kg body wt) has been analysed in Swiss Albino mice at several periods (12, 24, 36 and 48 h) after intraperitoneal injection. No increased frequency of chromosomal aberrations was observed in bone marrow cells or in spermatogonia.     

Toxicokinetics of mercuric chloride and methylmercuric chloride in mice.

Future human exposure to inorganic mercury will probably lead to a few individuals occupationally exposed to high levels and much larger populations exposed to low or very low levels from dental fillings or from food items containing inorganic mercury; human exposure to methylmercury will be relatively low and depending on intake of marine food. Ideally, risk assessment is based on detailed knowledge of relations between external and internal dose, organ levels, and their relation to toxic symptoms. However, human data on these toxicokinetic parameters originate mainly from individuals or smaller populations accidentally exposed for shorter periods to relatively high mercury levels, but with unknown total body burden. Thus, assessment of risk associated with exposure to low levels of mercury will largely depend on data from animal experiments. Previous investigations of the toxicokinetics of mercuric compounds almost exclusively employed parenteral administration of relatively high doses of soluble mercuric salts. However, human exposure is primarily pulmonary or oral and at low doses. The present study validates an experimental model for investigating the toxicokinetics of orally administered mercuric chloride and methylmercuric chloride in mice. Major findings using this model are discussed in relation to previous knowledge. The toxicokinetics of inorganic mercury in mice depend on dose size, administration route, and sex, whereas the mouse strain used is less important. The "true absorption" of a single oral dose of HgCl2 was calculated to be about 20% at two different dose levels. Earlier studies that did not take into account the possible excretion of absorbed mercury and intestinal reabsorption during the experimental period report 7-10% intestinal uptake. The higher excretion rates observed after oral than after intraperitoneal administration of HgCl2 are most likely due to differences in disposition of systemically delivered and retained mercury. After methylmercury administration, mercury excretion followed first-order kinetics for 2 wk, independently of administration route, strain, or sex. However, during longer experimental periods, the increasing relative carcass retention (slower rate of excretion) caused the elimination to deviate from first-order kinetics. Extensive differences in the toxicokinetics of methylmercury with respect to excretion rates, organ deposition, and blood levels were observed between males and females.(ABSTRACT TRUNCATED AT 400 WORDS)     

Immunological and biochemical responses in mice treated with mercuric chloride

Adult B6C3F1 male mice were given water containing 3, 15, and 75 ppm mercury (as mercuric chloride) for 7 weeks. There were dose-related increases in blood and kidney mercury levels but only the former showed a time-dependent change. Mercury was not detected in any of the lymphoid organs except for the spleen. There was no mortality and only minimal histological changes occurred in kidneys of dosed mice. Nonspecific toxicity occurred at the 75 ppm dose level, consisting of small differences in body and organ weights, hematological changes, and general enzyme inhibition in the bone marrow and spleen. However, there were specific immunotoxic and biochemical alterations in lymphoid organs of mice treated at the lower doses of mercury. The immunological defects were consistent with altered T-cell function as evidenced by decreases in both T-cell mitogen and mixed leukocyte responses. There was a particular association between the T-cell defects and inhibition of thymic pyruvate kinase, the rate-limiting enzyme for glycolysis. The differences in the pattern of enzyme responses among lymphoid organs implied that two mechanisms of mercury toxicity were operative--one at high concentrations that caused physicochemical enzyme inhibition and another at low concentrations that caused indirect enzyme inhibition.     

Oral mercuric chloride exposure in mice: effects of dose on intestinal absorption and relative organ distribution

Human intoxications with inorganic mercury occur via the oral or pulmonar routes. However, earlier experimental studies of the acute toxicity of inorganic mercury primarily used parenteral administration of soluble inorganic mercury salts. The present study evaluated the effect of dose size on intestinal absorption and relative organ distribution of orally administered mercuric chloride. Experiments were performed with male mice of 2 strains (inbred CBA/Bom and outbred Bom: NMRI). At the highest dose of HgCl2, a delay in fecal elimination of non-absorbed mercury was observed indicating a decreased peristaltic rate. The fractional whole-body retention of mercury at 14 days after dosage was inversely related to the dose size, conceivably due either to saturation of the uptake mechanism or to damage to the kidneys resulting in loss of mercury with the urine at the highest dose levels. The relative organ distribution of mercury after oral exposure was quantitatively different from that reported in the literature after parenteral administration of inorganic mercury. Thus, the relative hepatic deposition was larger than after injection of mercury, presumably due to the first pass effect. A dose dependency in the relative organ distribution of retained mercury was observed, characterized by increasing relative deposition in liver, stomach, intestines, testes, spleen and carcass but decreasing relative renal deposition with increasing dose. The toxicokinetics of inorganic mercury was similar in the 2 mice strains. The present study demonstrates that the toxicokinetics of orally administered inorganic mercury is different from that of parenterally administered inorganic mercury as earlier reported in the literature.     

Toxicities of combinations of pentachloronitrobenzene with mercuric chloride or cadmium chloride,and hexachlorobenzene with mercuric chloride administered to rats

1. Pentachloronitrobenzene (PCNB) and HgCl₂, PCNB and CdC1₂, and hexachlorobenzene (HCB) and HgCl₂ were investigated for their acute oral toxicity in rats, individually and as combinations in various ratios of the organochlorine pesticides to the heavy metal chlorides.

2. The toxicity of mixtures of low dosages of the pairs tested was higher than the sum of the toxicities produced by the individual doses.

3. At increased dosages of the components in the combinations PCNB-HgCl₂ and PCNB-CdCl₂, the combined lethality tended towards the sums of the effects of the individual doses.     

Diphenyl diselenide potentiates nephrotoxicity induced by mercuric chloride in mice

Following our long‐standing interest in the mechanisms involved in selenium toxicity, the aim of this work was to extend our previous studies to gain a better understanding of mercuric chloride (HgCl₂) + diphenyl diselenide (PhSe)₂ toxicity. Mice received one daily dose of HgCl₂ (4.6 mg kg^?1, subcutaneously) for three consecutive days. Thirty minutes after the last injection of HgCl₂, mice received a single dose of (PhSe)₂ (31.2 mg kg^?1, subcutaneously). Five hours after (PhSe)₂ administration, mice were euthanized and δ‐aminolevulinate dehydratase, catalase (CAT), glutathione S‐transferase (GST) and Na⁺, K⁺‐ATPase activities as well as thiobarbituric acid‐reactive substances (TBARS), ascorbic acid and mercury levels were determined in kidney and liver. Parameters in plasma (urea, creatinine, protein and erythropoietin), whole blood (hematocrit and hemoglobin) and urine (protein) were also investigated. HgCl₂ + (PhSe)₂ exposure caused a decrease in renal GST and Na⁺, K⁺‐ATPase activities and an increase in renal ascorbic acid and TBARS concentrations when compared with the HgCl₂ group. (PhSe)₂ potentiated the increase in plasma urea caused by HgCl₂. HgCl₂ + (PhSe)₂ exposure caused a reduction in plasma protein levels and an increase in hemoglobin and hematocrit contents when compared with the HgCl₂ group. There was a significant reduction in hepatic CAT activity and an increase in TBARS levels in mice exposed to HgCl₂ + (PhSe)₂ when compared with the HgCl₂ group. The results demonstrated that (PhSe)₂ did not modify mercury levels in mice. In conclusion, (PhSe)₂ potentiated damage caused by HgCl₂ affecting mainly the renal tissue. Copyright © 2011 John Wiley & Sons, Ltd.     

Methyl mercuric chloride toxicokinetics in mice. I: Effects of strain, sex, route of administration and dose

The toxicokinetics of methyl mercury is studied most intensively in the rat. However, the toxicokinetics of methyl mercury in man is closer to the toxicokinetics in the mouse. This study describes the effects of dose, route of administration, and strain and sex on the toxicokinetics of methyl mercuric chloride in mice. Half-time values, fractional whole-body retentions and relative organ distributions of mercury were compared after a single oral or intraperitoneal administration of methyl mercuric chloride. The intestinal absorption was almost complete in accordance with earlier published results. The route of methyl mercury administration did not affect the whole-body retention of mercury significantly, but male mice retained lower amounts of mercury than did female mice. The elimination of mercury was demonstrated to follow first order kinetics during the two week study period independently of administration route, strain or sex. An inverse relationship between administered dose and whole-body retention was observed and by indirect evidence demonstrated not to be caused by an effect on the intestinal uptake mechanism. Absorbed and retained mercury at day 14 was primarily deposited in the carcass, but major deposits were also found in liver, kidneys and intestinal tract. Dose and route of administration did not affect the relative organ distribution of mercury significantly. However, the relative kidney deposition in male mice was about twice that in females. A significant difference in whole-body retention of mercury was observed between different strains of inbred mice at day 14 after administration. The relative organ distribution of mercury also varied significantly between different strains of mice.     

Neurotoxicological effects of low-dose methylmercury and mercuric chloride in developing offspring mice

Mercury is a well-known toxic metal and potently induces severe neurotoxicological effects, especially in infants and children. The purpose of this study was to explore the underlying mechanisms of neurotoxic effects of mercurial compounds on the different stages of developing mice. Low-doses (the probability of human exposure in mercury-contaminated areas) of methylmercury (MeHg) (M, 0.02 mg/kg/day) and mercury chloride (HgCl₂) (H, 0.5 mg/kg/day) were administered to mice of the following groups: (1) treatment with distilled water for 7 consecutive weeks after weaning (control-vehicle (CV)); exposure to mercurial compounds at different stages; (2) for 7 consecutive weeks after weaning (control-MeHg (CM) and control-HgCl₂ (CH)); (3) only during perinatal and weaning stages (MeHg-vehicle (MV) and HgCl-vehicle (HV)); and (4) in all experimental stages (MeHg-MeHg (MM) and HgCl₂-HgCl₂ (HH)). Results revealed the neurobehavioral defects (increased locomotor activities, motor equilibrium impairment, and auditory dysfunction) that correlated with increasing Hg accumulation in CM and CH groups. However, it revealed a decrease and an increase in locomotor activities in MV and HV groups, respectively; these became more severe in MM and HH groups than in MV and HV groups. Motor equilibrium performance in MV and HV groups remained normal, while that in MM and HH groups was decreased. The most severe auditory defects (altered auditory brainstem response, ABR test) found in MM and HH groups than those in the respective CM and CH, MV and HV, including absolute wave III delays and interwave I-III latencies, which suggested that the irreversible auditory dysfunction caused by mercurial compounds. Furthermore, the alteration of lipid peroxidation (LPO), Na⁺/K⁺-ATPase activities, and nitric oxide (NO_x) in the brain tissues contributed to the observed neurobehavioral dysfunction and hearing impairment. These findings provide evidence that fetuses were much more susceptible to the effects of mercurial compounds with regard to inducing severely neurotoxicological injuries as that found in human beings. The signaling of ROS/Na⁺-K⁺-ATPase/NO_x plays a crucial role in the underlying mechanism for mercurial compound-induced toxic effects in offspring.     

Disposition and retention of mercuric chloride in mice after oral and parenteral administration

The present study compares effects of dose size on whole-body retention and relative organ distribution of 203HgCl2, after oral and intraperitoneal administration to female mice of two strains (inbred CBA/Bom and outbred Bom:NMRI). Using whole-body retention data of oral and intraperitoneal administration, an estimated "true absorption" of a single oral dose of inorganic mercury was calculated to be about 20% at two different dose levels. At the highest oral dose, a delay in fecal elimination of nonabsorbed mercury was observed, indicating a decreased peristaltic rate. The relative hepatic deposition was larger after oral than after intraperitoneal administration, presumably due to a first-pass effect, and a correspondingly lower relative renal deposition was seen. Increasing doses at both exposure routes resulted in increasing relative deposition in liver, stomach, intestines, and spleen but decreasing relative deposition in lungs and kidneys. Bom:NMRI mice deposited a larger fraction of the whole-body burden in the kidneys and a smaller fraction in the livers than did CBA/Bom mice. Comparison to a previous study with male mice (Nielsen and Andersen, 1989) demonstrates that male and female mice deposit similar fractions of their body burden in the liver, while male mice deposit significantly larger amounts of mercury in the kidneys and smaller amounts in the carcass than do female mice. Thus, the toxicokinetics of inorganic mercury in mice depend on dose size, administration route, and sex; the mouse strain is of less importance than the other factors investigated. The absorption of inorganic mercury was estimated to be about 20%, that is, twice as high as earlier estimates.     

Coagulation and fibrinolysis in rats poisoned with mercuric chloride

The effect of mercuric chloride on blood coagulation and fibrinolysis in rats was studied. The mercurial was administered to the animals intragastrically in a single dose of 17.9 mg Hg/kg and the effects were tested on the 1st, 3rd and 7th day. The symptoms of hypercoagulability accompanied by decreased fibrinolytic activity of the plasma were observed in the poisoned rats. The main reason of the lowered fibrinolytic activity seemed to be the inhibition of plasma plasminogen activator or the inhibition of plasminogen activation reaction catalyzed by this enzyme.     

Prevention of death in mice infected with coxsackievirus A16 using guanidine HCl mixed with substituted benzimidazoles

A significant reduction in the death rate of infant mice infected with ten 50% lethal doses (LD50) of coxsackievirus A16 was observed when they were treated 58 h after infection with two injections of guanidine at 145 mg/kg per injection. Tremors occurred at this level but disappeared after treatment was discontinued. Tremors were apparent, but less severe at 97 mg/kg per injection and did not occur at 48 mg/kg per injection. No antiviral effect could be detected at either of these levels of guanidine. When an inactive level of guanidine (97 mg/kg per injection) was combined with 1.7 mg/kg per injection of LY122771-72, LY127123, or 2-(alpha-hydroxybenzyl)benzimidazole (HBB) and 17 mg/kg per injection of 2-guanidino-benzimidazole (GB), significant activity resulted with 2-8 treatments begun 58 h after infection. The same treatment schedule using 136 mg/kg per injection of LY122771-72, 90 mg/kg per injection of LY127123, 136 mg/kg per injection of HBB and 68 mg/kg per injection of GB produced no effect. Guanidine-associated tremors were also enhanced by the addition of the substituted benzimidazoles. When guanidine was reduced to 48 mg/kg per injection, 34 mg/kg per injection of LY122771-72 was required to produce a significant reduction in the death rate and no tremors were observed.     

Protective effect of vitamin E against mercuric chloride reproductive toxicity in male mice

Mercury intoxication has been associated with male reproductive toxicity in experimental animals and mercury may have the potential to produce adverse effects on fertility in men. Vitamin E may protect against toxic effects of mercury in the liver and other tissues. To investigate the protective role of vitamin E against mercuric chloride toxicity for the testis, epididymis, and vas deferens of adult male mice, animals were treated with either mercuric chloride 1.25 mg/kg/day, vitamin E 2 mg/kg/kg, or a combination of the two treatments. Control animals were treated with water. Treatments were administered by daily gavage for 45 days. An additional group of animals treated with mercuric chloride were permitted to recover for 45 days after mercuric chloride treatments. Parameters studied included serum testosterone, epididymal sperm count, motility, and morphology, epididymal and vas deferens adenosine triphosphatase (ATPase), phosphorylase, sialic acid, glycogen and protein, testicular succinate dehydrogenase (SDH), phosphatases, cholesterol, ascorbic acid, and glutathione. Fertility was evaluated by sperm positive vaginal smears after overnight cohabitation with a female. Mercuric chloride produced a reduction in epididymal sperm count, sperm motility, and sperm viability, and there were no sperm-positive smears in this group. Biochemical tests from the male reproductive organs were also altered by mercuric chloride treatment. Coadministration of vitamin E with mercuric chloride prevented the changes in sperm and biochemical parameters and was associated with control rates of sperm positive smears after cohabitation. Animals given vitamin E with mercuric chloride also had lower concentrations of mercury in the testis, epididimyis, and vas deferens. Permitting animals to recover for 45 days after mercuric chloride treatment resulted in partial recovery of sperm and biochemical parameters. Vitamin E cotreatment has a protective role against mercury-induced male reproductive toxicity.     

Antagonism by naloxone of tolerance and dependence in mice given a single dose of morphine

The effect of naloxone given at various times after morphine administration on the development of tolerance to and dependence on a single dose of morphine was studied. Naloxone antagonized the analgesic effect of morphine and the development of tolerance to and dependence on morphine, dose dependently. The time course of the development of tolerance to a single dose of morphine almost paralleled that of dependence on morphine but the time course of the disappearance of tolerance did not coincide with that of dependence. When start of the duration of action of morphine was blocked by naloxone for various time intervals, the degree of tolerance to and dependence on morphine was antagonized, time dependently. When the end of the duration of action of morphine was antagonized by naloxone for various time intervals, tolerance and dependence which developed up to that time was completely antagonized by naloxone.     

Effect of various amounts of selenium on the metabolism of mercuric chloride in mice

Male ddY mice were given one injection of (1) mercury (mercuric chloride) simultaneously with various doses of selenium (sodium selenite), (2) mercury alone, or (3) various doses of selenium alone. The interaction between mercury and selenium in the liver and kidneys at 1, 5, 24, 120, and 240 hr after administration was investigated. The concentrations of mercury in the liver of mice receiving mercury and selenium simultaneously were higher than those after administration of mercury alone, while the concentrations of mercury in the kidney decreased markedly over a 1-120 hr period after administration, depending on the dose of selenium administered simultaneously with mercury. Clearly, selenium had a different effect on the accumulation of mercury in the liver and kidneys. Subcellular distribution studies revealed that mercury and selenium which were administered simultaneously were incorporated into the crude nuclear and mitochondrial fractions as stable complexes. The transport of these complexes to the kidneys seems to be limited. In addition, gel filtration of supernatant fractions of liver and kidney through a Sephadex G-75 column indicated that the proportion of mercury bound to metallothionein fraction decreased depending on the dose of selenium administered simultaneously with the mercury. This reduction was attributed to the decreased synthesis of mercury-thionein due to a reduction in the activity of Hg2+ which results from binding between mercury and selenium in the cells.     

The effects of dimercaptosuccinic acid on the excretion and distribution of mercury in rats and mice treated with mercuric chloride and methylmercury chloride.

1 All five rats in a group survived if dimercaptosuccinic acid (DMSA), a water soluble derivative of 2,3-dimercaptopropanol (BAL), was given in doses of 10-40 mg/kg intraperitoneally 30 min, 4 and 24 h after administration of 2.4 mg/kg Hg as HgCl2, whereas three out of a group of five died if DMSA was not given. DMSA 20 mg/kg increased urinary excretion and decreased the body burden significantly more than 10 mg/kg DMSA, but further doubling of the dose had only marginal effects. 2 DMSA was able to reduce body burden and increase urinary excretion of Hg when intraperitoneal treatment started eight days after the subcutaneous administration of HgCl2. 3 DMSA was effective in decreasing body burden and the brain concentration of Hg in rats dosed orally with methylmercury (MeHgCl) when intraperitoneal treatment started with 40 mg/kg DMSA 24 h after Hg. Increase in the urinary excretion of mercury was responsible for the decrease in body burden. 4 DMSA was effective when given in the drinking water of rats or mice both against inorganic Hg and MeHgCl. In mice treated intraperitoneally with MeHgCl, DMSA 19.5 mug/ml in the drinking water caused a significant decrease in the body burden and increase in the excretion of Hg. 5 DMSA was about four times more efficient than D-penicillamine in decreasing the body burden of Hg. As their toxicity is in the same range, the higher efficiency of DMSA offers a larger margin of safety for the mobilization of Hg.