Experiments with different antidotes in acute poisoning by different mercury compounds. Effects on survival and on distrinution and excretion of mercury

Effect of chlorophyllin on mercuric chloride-induced clastogenicity in mice

The effect of chlorophyllin (1.5 mg/kg body weight) on the clastogenicity of mercuric chloride (HgCl2) was studied in vivo in mouse bone marrow cells. HgCl2 (3.0, 6.0 and 12.0 mg/kg body weight) administered by gavage induced chromosomal aberrations at frequencies directly proportional to the dose. Chlorophyllin was not clastogenic, and significantly reduced the mitotic index when given alone. Chlorophyllin administered simultaneously with HgCl2 significantly reduced the frequencies of chromosomal aberrations in a dose-dependent manner. When given simultaneously with the lowest HgCl2 concentration tested (3.0 mg/kg body weight), chlorophyllin provided total protection. A lower degree of protection was given by chlorophyllin administered 2 hr before HgCl2. The data demonstrate the potential of green plant components to modify the genotoxic activity of HgCl2 when administered orally.

Octanol/water partition coefficients as a model system for assessing antidotes for methylmercury(II) poisoning, and for studying mercurials with medicinal applications

1-Octanol/water partition coefficients, [HgII]octanol/[HgII]water, provide a simple but limited model system for aspects of the biological behavior of methylmercury(II) and commonly used organomercury(II) medicinal compounds. In an octanol/water system some widely studied antidotes for mercury poisoning at least partly displace the biological thiols L-cysteine and glutathione from binding to MeHgII at pH 6.9. Addition of the antidote meso-dimercaptosuccinic acid to MeHgII in the presence of glutathione results in formation of metallic mercury. For RHgII derivatives of L-cysteine and glutathione, octanol/water partition coefficients follow the order Ph greater than Et greater than Me. An exceptionally high value for diphenylmercury, compared with PhHgII derivatives of L-cysteine and glutathione, is consistent with reported results of the distribution of mercury compounds in rats. Ethylmercury(II) is partly displaced from thimerosal by L-cysteine and glutathione in the octanol/water system, indicating that the active form of thimerosal in vivo may involve binding of EtHgII to biological ligands.

Chelation therapy for methylmercury(II) poisoning. Synthesis and determination of solubility properties of MeHg(II) complexes of thiol and dithiol antidotes

Methylmercury(II) complexes of the most widely studied antidotes for mercury poisoning have been prepared, and both the water solubility and 1-octanol/water partition coefficients determined for these complexes and the L-cysteine complex. New complexes of N-acetyl-D,L-penicillamine, 2-mercaptosuccinic acid, meso-dimercaptosuccinic acid, and Unithiol have been synthesized and characterized, and are found to have the formulations MeHgSCMe2CH(NHCOMe)CO2H, MeHgSCH(CO2H)CH2CO2H, MeHgSCH(CO2H)CH(CO2H)SHgMe, and Na[MeHgSCH2CH-(SHgMe)CH2SO3], respectively. Trends in octanol/water partition coefficients are consistent with reported studies of the effectiveness of antidotes for MeHg(II) poisoning and redistribution of MeHg(II) on administration of antidotes, particularly for British anti-Lewisite, Unithiol, and meso-dimercaptosuccinic acid.

Thiol antidote to inorganic mercury toxicity with an uncharacteristic mechanism

alpha-Mercapto-beta-(2-furyl)acrylic acid (MFA) significantly reduced the lethality of mercuric chloride to rats (2.2 mg Hg/kg, ip) when administered (25 mg/kg, po) at 1, 24, 48, and 72 hr. Daily administration of MFA (25 mg/kg, po) significantly reduced the lethality of daily injection of increasing amounts of mercuric chloride (1 mg Hg/kg X 7 days, 2 mg Hg/kg X 7 days, 4 mg Hg/kg X 14 days, ip). Mercury concentration in kidneys of MFA-treated rats was significantly higher than in vehicle-treated controls, whereas concentration in liver was (nonsignificantly) lower. Enhanced mercury deposition in kidney as a manifestation of antidotal effect is not characteristic of thiol chelators used in practice for mercury poisoning.

The protective effect of sulfur-containing steroids against nephrocalcinosis induced by mercuric chloride in rats

1. Experiments were conducted on rats and structure-activity correlations were performed using sulfur-containing steroids against nephrocalcinosis induced by mercuric chloride (HgCl2). 2. The protective effect of spironolactone has been described previously and we have now demonstrated the activity of 7-mercapto-17-hydroxy-3-oxo-4-androsten-17-propionic acid-lactone. 3. The activity of the sulfhydryl radical present in this molecule has been shown to be slightly lower than that of the thioacetyl radical present in spironolactone. 4. The importance of the steroid structure to which a specific radical is attached has become evident during these experiments with the inactivity of 7-mercapto-3,20-dioxo-4-pregnene-16-carbothiamineacetate which possesses a thioacetyl group in the same position as spironolactone (i.e. only the two lateral chains in position 16 and 17 are different between these two steroids). 5. Thus, both the composition of the sulfur-containing radical and the steroid moiety are important for protection against inorganic mercury poisoning.

The many faces of methylmercury poisoning

Methylmercury (MM) is a very potent neurotoxic agent. Its role in polluting the environment is well documented. A vast amount of study over the past several decades has finally provided insight into many aspects of its effect. Exposure to MM may be through ingestion of poisoned fish or inadvertent misuse of grain treated with the poison as a fungicide. Major epidemics have occurred in Japan (Fetal Minamata disease), Iraq, Pakistan, Guatemala, and Ghana. Sporadic incidences have occurred in the United States and Canada. There is no effective antidote to counteract the effect of MM on the central nervous system, although the information documented should provide hope for more effective therapy in acute cases.

Evaluation of methyl mercury chelating agents using red blood cells and isolated hepatocytes

The relative efficacy of thiol-containing mercurial scavengers was assayed by using cellular suspensions of erythrocytes or isolated hepatocytes. The blood cells incubated in a buffer (pH 7.4) containing 1 mM glucose (10% hematocrit) were exposed to 5 microM methyl mercuric chloride. In the absence of extracellular thiols the red blood cells took up more than 90% of methyl mercury from the surrounding medium during 5--10 min. This uptake was almost completely inhibited by dimercaptosuccinic acid (DMSA) (1 mM) and the same chelant could rapidly remove 80% of the mercury from 'pre-loaded' erythrocytes. Hepatocytes prepared according to the method of Seglen [11] in a suspension of 10(6) cells/ml in a buffer containing 5 mM glucose and 5 mg/ml of bovine serum albumin were also exposed to methyl mercuric chloride (4 microM). Almost 50% of the mercurial was taken up by the cells slowly during the incubation period of 240 min. DMSA (1 mM) almost completely blocked the methyl mercury binding by the hepatocytes. 2-Mercaptopropionylglycin (Thiola) or mercaptosuccinic acid (MSA) was almost as effective mercurial scavengers as DMSA in hepatocytes and in red blood cells. Diethyldithiocarbamate (DDC) and dimercaptopropanol (BAL) were considerably less effective than DMSA to inhibit the mercurial binding to hepatocytes. Experiments in vivo have shown that DMSA is a better mercurial chelator than Thiola or MSA, whereas DDC and BAL may both be considered to be inapplicable in methyl mercury poisonings. Our cellular assay provides preliminary information of the efficiency of chelating thiols and may serve as a useful first approximation when planning further experiments.

Influence of mercury of the anesthetic response to and distribution of thiopental in rats

Pretreatment with HgCl2 (2 mg/kg sc) 24 h before administration of thiopental (35 mg/kg ip) significantly potentiated the duration of thiopental sleeping time in adult male rats but did not influence the onset time for anesthesia. The plasma concentration of free thiopental was significantly higher in the Hg-treated animals 15 and 45 min after thiopental injection (i.e., during the period of thiopental anesthesia), with a concomitant increase of the free thiopental concentration in the brain at 15 min. However, total and free brain thiopental concentrations in Hg-treated rats at the time of awakening were not different from those in saline-treated animals. Urinary thiopental remained unchanged from 0 to 2 h, but was increased in the treated urine from 0 to 27 h. In vitro studies showed a strong inhibition of thiopental binding in 24-h Hg-treated plasma. The results suggest that the prolongation of thiopental anesthesia induced by Hg pretreatment is probably related to changes in the disposition of thiopental in the plasma and brain rather than to an alteration in the sensitivity of the central nervous system.

Treatment of methyl mercury poisoning in mice with 2,3-dimercaptosuccinic acid and other complexing thiols

Treatment with 2,3-dimercaptosuccinic acid was more effective than N-acetyl-DL-penicillamine and monomercaptosuccinic acid in mobilizing mercury from mice after the injection of methyl mercuric chloride. Dimercaptosuccinic acid treatment started 4 days after the mercury injection and given for 8 days at a dose of 1 mmol SH/kg per day removed more than 2/3 of the mercury in the brain, while acetylpenicillamine and mercaptosuccinate correspondingly removed less than 1/2 of the brain deposits. Neither treatment with 2,3-dimercaptorropano-1-sulphonate nor with a new thiolated resin, mercaptostarch, mobilized significant amounts of mercury from the brain. Since the toxicity of dimercaptosuccinate seems to be almost as low as that of D-penicillamine this dithiol may provide a potentially useful agent in clinical poisoning due to methyl mercury.

The effect of oral doses of a polythiol resin on the excretion of methylmercury in mice treated with cysteine, D-penicillamine or phenobarbitone

Mice dosed with methylmercury chloride (0.5 to 2.0 mg Hg/kg i.p.) labeled with the 203Hg isotope were given polythiol resin in their food (2% w/w). The effect of pretreatment with phenobarbitone, or co-administration of D-penicillamine or L-cysteine, was tested on the efficacy of the resin to accelerate the excretion of methylmercury. The effect of the polythiol resin in enhancing fecal excretion was dependent on the dose of methylmercury, it being significantly greater at doses of 1.0 and 2.0 than at 0.5 mg Hg/kg. In animals given the resin and phenobarbitone (0.1% w/w drinking water), fecal excretion was approx. 36% greater than in animals given resin alone. Penicillamine (2.5 mg/ml drinking water) actually retarted elimination of methylmercury in animals given the resin. Despite the enhanced efficacy of the resin plus phenobarbitone, the brain levels of methylmercury were not reduced beyond those seen in animals given resin alone. The mechanisms and implications of these effects are discussed.

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.

The excretion and distribution of inorganic mercury in the rat as influenced by several chelating agents

Among 15 chelating agents tested, sodium-2,3-dimercaptopropane 1 sulfonate (DMPS), 2,3-dimercaptopropanol (BAL), sodium-mercaptoethyliminodiacetate (MEIDA), and D-penicillamine (PA) exerted an influence on the excretion of Hg and its distribution in the organs. The excretion pattern however, is different for these compounds, and, from the practical point of view, a favourable effect is exhibited only by DMPS which enhances the urinary excretion rate and lowers the Hg-concentration in all organs.

Effect of 2,3-dimercaptopropanol (BAL) on urinary excretion and brain content of mercury

2,3-Dimercaptopropanol (BAL) given to rats in doses used for the treatment of acute mercury chloride poisoning in man increases the excretion of mercury. The mercury content of the brain was unaffected by 2,3-dimercaptopropanol unless it was given a short time after the mercuric chloride, when there was a 24% increase. The relevance of these findings to therapy with BAL is discussed.