Prolonged Oral Treatment with Two Monoesters of meso-2,3-Dimercaptosuccinic Acid for Depleting Inorganic Mercury Retention in Suckling Rats

Abstract: Two monoesters of meso-2,3-dimercaptosuccinic acid (DMSA), monoisoamyl meso-2,3-dimercaptosuccinate (Mi-ADMS) and mono-n-hexyl meso-2,3-dimercaptosuccinate (Mn-HDMS) were compared to DMSA in their efficiency to mobilize ²⁰³Hg in mercury-laden suckling rats. Seven-day-old pups were given ²⁰³Hg (18.5 kBq) with a dose of 0.5 mg Hg/kg/day as HgCl₂ for five days. Seven days after the beginning of Hg loading a ten-day oral treatment with DMSA, Mi-ADMS, or Mn-HDMS was administered at a dose of 0.25 mmol/kg/day. At the end of experiment, radioactivity was measured in the whole body, liver, both kidneys, and brain. Monoesters of DMSA were superior to DMSA in decreasing body and organ Hg retention. The highest reduction in comparison to controls in groups treated with DMSA, Mi-ADMS, or Mn-HDMS occurred in the kidneys (48%, 97%, and 96%), followed by reduction in the liver (24%, 84%, and 83%), and in the brain (8%, 23%, and 23%, respectively). For both, Mi-ADMS and Mn-HDMS, the reductions in the whole body and organs were significantly greater than in controls or DMSA-treated rats. No difference between the efficiency of the two DMSA-monoesters was found.     

Comparative in vivo Lead Mobilization of meso- and rac-2,3-Dimercaptosuccinic Acids in Albino Wistar Rats

Abstract: Comparison of the racemic and meso forms of 2,3-dimercaptosuccinic acid (DMSA) in lead mobilization from lead-loaded albino Wistar rats demonstrates that the racemic form is significantly more effective in reducing femur lead levels. After four oral doses at 0.5 mmol/kg, femur lead levels were reduced to 87% of control values by meso-DMSA and to 50% of control levels by rac-DMSA. Similarly, when the dose was increased to 1.0 mmol/kg, femur lead levels were reduced to 69% of control levels by meso-DMSA and to 45% of control levels by rac-DMSA. A similar pattern was found for renal lead levels. Brain lead concentrations were significantly lower in treated groups than in control groups, but no differences were found between rac- and meso-DMSA. Rac-DMSA is more soluble than meso-DMSA in acetonitrile, ethyl acetate, and ethyl ether. The partition coefficient of rac-DMSA in the n-octanol/water system was found to be about 2.8. These results indicate that rac-DMSA deserves further attention as a possible substitute for meso-DMSA.     

Combined Oral Treatment with racemic and meso-2,3-Dimercaptosuccinic Acid for Removal of Mercury in Rats

Abstract: Racemic dimercaptosuccinic acid (DMSA) was found more efficient than the meso-isoform in enhancing the removal of mercury in rats. However. racemic-DMSA has recently been found more toxic. The efficiency of combined oral treatment with the two isoforms of DMSA for removal of mercury has now been evaluated. Female albino rats were treated orally for four days with meso- (M) and/or racemic- (R) DMSA (1 mmol/kg each), five days after a single intraperitoneal administration of ²⁰³Hg with 0.5 mg HgCl₂/kg. The animals were divided into six groups according to the number of treatments with each isomer: control (untreated), 4M, 1R + 3M, 2R + 2M, 3R+1M, and 4R. Whole body, kidney, liver and brain mercury contents were measured nine days after ²⁰³Hg administration. In all treated groups retention in the whole body and kidneys was greatly reduced. The groups treated with racemic-DMSA, regardless of the number of doses, showed a greater removal of mercury than the group treated with meso-DMSA alone (4M). All treatments were less efficient in reducing liver retention, and the brain retention was not affected. It was concluded that even a single application of the more toxic racemic-DMSA during a four-day oral treatment regimen is sufficient to improve the removal by meso-DMSA of mercury from rats.     

Die Verteilung von Hg203-Mersalyl und Hg203-Chlormerodrin in der Niere,untersucht mit Hilfe der Gefrierschnitt-Autoradiographie

Zusammenfassung 2 Std nach i.m. Injektion von markiertem Mersalyl wurden mittels Gefrierschnitt-Autoradiographie selektive Anreicherungen von Hg²⁰³ vor allem im distalen, nach Injektion von markiertem Chlormerodrin vor allem im mittleren Abschnitt der Hauptstücke beobachtet.Mit 3 TextabbildungenMit Unterstützung des Bundesministeriums für wissenschaftliche Forschung.     

二巯丁二酸对小鼠的急性毒性作用

目的探讨二巯丁二酸（DMSA）对小鼠的急性毒性作用。方法20只昆明小鼠，雌雄各半，体质量（21．2±2．3）g，适应性喂养3d，按体质量随机分为对照组和实验组，给药前禁食12h，实验组每只小鼠于24h内分4次经口给予DMSA160mg，对照组给予等体积的去离子水，观察1周，然后摘除眼球取血，置于肝素化试管，5000r／min，离心5min，取血浆；处死小鼠，取其脑、心脏、肝脏和肾脏，0．9％氯化钠溶液清洗。测定抗氧化酶系统、过氧化产物、血尿素氮、血肌酐及氨基转移酶水平。结果（1）试验观察期内小鼠出现消化道症状，进食减少，体质量降低，腹腔轻度积水，此外未见其他明显中毒症状；（2）脑组织、肝脏和肾脏超氧化物歧化酶（SOD）活性降低，但差异无统计学意义（P〉0．05），谷胱甘肽过氧化物酶（GSH—PX）活性明显降低（P〈0．01），肝脏丙二醛（MDA）显著性升高（P〈0．01）；（3）血尿素氮和肌酐水平显著性升高（P〈0．001）；血氨基转移酶升高（P〈0．001），而肝肾氨基转移酶无显著性变化。结论二巯丁二酸抑制机体抗氧化系统，对肝脏和肾脏具有毒性作用。     

Mobilization of lead by esters of meso-2,3-dimercaptosuccinic acid

An examination was made of the relative efficacies of 2,3-dimercapto-1-propanol (BAL) and three diesters ( [CH(SH)COOR]2; DMDMS, R = CH3; DEDMS, R = C2H5; and Di-PDMS, R = CH(CH3)2] of meso-2,3-dimercaptosuccinic acid (DMSA) in mobilizing freshly injected lead from mice. These diesters, like BAL, reduced the lead levels resulting from freshly injected lead in both the soft tissues (liver, kidneys, spleen, and brain) and the bone (tibia). After treatment with the dimethyl (DMDMS), the diethyl (DEDMS), and the diisopropyl (Di-PDMS) esters the lead content of each of the organs was significantly less than that present in the untreated controls. Each of the diesters reduced lead levels in the kidneys, liver, and spleen significantly below those levels found after BAL treatment. The action of the diesters in reducing brain lead levels was comparable to that of BAL. Di-PDMS was the most effective of these compounds and was significantly superior to BAL. Each of the esters was also significantly more effective than BAL in reducing the whole body level of lead.     

Determination and metabolism of dithiol chelating agents. IV. Urinary excretion of meso-2,3-dimercaptosuccinic acid and mercaptosuccinic acid in rabbits given meso-2,3-dimercaptosuccinic acid

The water-soluble dithiol chelating agents meso-2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercaptopropane-1-sulfonic acid (DMPS) are becoming of increasing importance for the treatment of lead, arsenic and mercury poisoning. There is, however, a paucity of data about their metabolic transformation. Male rabbits were given DMSA (0.20 mmol/kg) i.m., and urine was collected over a 6-hr period. Monobromobimane derivatization, HPLC separation, and fluorescence detection, along with [U-14C]DMSA data, demonstrated that the total 14C found in the urine was distributed as 73% unaltered DMSA, 7% mercaptosuccinic acid and 6 and 14% of two unknowns. Electrolytic reductive treatment of the urine did not increase the urinary content of DMSA, indicating that oxidative biotransformation is not a major pathway for DMSA in the rabbit. This latter result is strikingly different from that for DMPS in rabbit.     

Uptake of 203Hg2+ in the olfactory system in pike

Inorganic mercury ²⁰³Hg²⁺ was applied to the olfactory chambers or was given i.v. to pike (Esox lucius) and the uptake of the metal in the olfactory system and the brain was examined by autoradiography and gamma spectrometry. Application of ²⁰³Hg²⁺ in the olfactory chambers resulted in an accumulation of the metal in the olfactory nerves and the anterior parts of the olfactory bulbs of the brain. The levels of ²⁰³Hg²⁺ in other brain areas, such as the telencephalon, the optic tecti and the cerebellum, remained low. Application of ²⁰³Hg²⁺ in only one olfactory chamber resulted in an uptake of the metal only in the ipsilateral olfactory nerve and olfactory bulb. Intravenous injection of the ²⁰³Hg²⁺ resulted in a labelling of the olfactory system and the brain, which was much lower than of the blood. These results indicate that the ²⁰³Hg²⁺ is taken up in the olfactory neurones from the olfactory receptor cells in the olfactory rosettes and is transported to the terminal parts of the olfactory neurones in the olfactory bulbs. The uptake of mercury as well as some other metals in the olfactory system may result in noxious effects and this may be an important component in the toxicology of metals in fish.     

Effect of meso-2,3-dimercaptosuccinic acid on urinary lead excretion in exposed men

The efficacy of meso-2,3-dimercaptosuccinic acid (DMSA) was evaluated in workers occupationally exposed to lead (Pb; blood level >50 microg/dL). Ten men were given 600 mg of DMSA per orem daily, for five days. Pb concentrations of whole blood and urine were determined throughout therapy. Hematology analyses, blood chemistry, and urinalysis were obtained at the start of the study, at the end of the DMSA treatment, and at 72 hours after the administration of the final dose. DMSA therapy had no influence on hepatic, hematologic, or renal functions and was effective in decreasing the concentration of blood Pb in all the subjects without adverse drug reactions.     

Mobilization of cadmium by liposome-encapsulated meso-2,3-dimercaptosuccinic acid in pre-exposed mice.

meso-2,3-Dimercaptosuccinic acid (DMSA) treatment in free of liposome-encapsulated form was given to mice pre-exposed to cadmium as CdCl2 (2 intraperitoneal injections; 0.5 mg Cd/kg along with 5 microCi 109CdCl2 in 4 ml volume within 24 h). Both treatments removed cadmium from liver, spleen, testis and blood with liposomal DMSA exhibiting higher efficacy in mobilizing cadmium not only from whole organs but also from liver proteins. It also resulted in higher excretion of cadmium via urine as compared with free DMSA or saline treatment. Whereas this treatment eliminated significantly higher amounts of cadmium via the fecal route throughout the period examined, free DMSA responded only 48 h after treatment and was less effective. The results suggest mobilization of cadmium from intracellular sites of deposition. However, DMSA in the dose administered (24 mumol/kg i.v.) in either form was ineffective in decorporating cadmium from the kidney, the critical organ in cadmium intoxication.     

Combined Therapeutic Potential of meso-2,3-Dimercaptosuccinic Acid and Calcium Disodium Edetate on the Mobilization and Distribution of Lead in Experimental Lead Intoxication in Rats

Asymptomatic lead poisoning remains a serious public healthproblem in developed and developing countries. Chelation therapyparticularly with calcium disodium ethelenediamine tetra-aceticacid (CaNa₂EDTA) is often used therapeutically to reduce thebody burden of lead. This chelating drug has serious side effectsand drawbacks primarily related to redistribution of lead, nephrotoxicity,and essential metal depletion. The present study was plannedto determine the effectiveness of CaNa₂EDTA and meso-2,3-dimercaptosuccinicacid (DMSA) used in combination. Both drugs, when administeredindividually, resulted in significant urinary excretion of leadand lowered the tissue lead burden. Combined treatment withCaNa₂EDTA and DMSA elicits an additive response in promotingurinary lead elimination, depleting body lead burden, and restoringaltered lead-sensitive biochemical variables. Further, no redistributionof lead to brain or any other soft organ following combinedDMSA-CaNa₂EDTA treatment was observed indicating a definiteadvantage of combined therapy over the conventional treatmentwith CaNa₂EDTA or DMSA alone. However, an elevation of serumtransaminase activity, creatinine level, and depletion of bloodzinc level may limit the usefulness of this combined treatment.     

Enterohepatic circulation of 64Cu, 52Mn and 203Hg in rats

The intestinal absorption of ⁶⁴CuCl₂, ⁵²MnCl₂ and ²⁰³HgCl₂ was compared with those of biliary excreted radiometals in rats during 24 h after intraduodenal administration. Biliary excreted metals were obtained from rats (donors) given previously intravenously ⁶⁴CuCl₂, ⁵²MnCl₂ and ²⁰³HgCl₂. The metals in form of chloride salts as well as the metals excreted via bile were given to control or acceptor rats in the same dose intraduodenally. In manganese, given as ⁵²MnCl₂ 15.04±8.48%, whereas given biliary excreted ⁵²Mn 35.45±5.72% was absorbed. Biliary excreted manganese is probably in the bile in form suitable for intestinal absorption. In both other metals the intestinal absorption was higher when metal in form of chloride salt was administered (in ⁶⁴Cu 46.45±11.46% respectively 16.74±8.53%; in ²⁰³Hg 40.9±8.52% respectively 21.08±10.7%).A possibility of treatment of metal's intoxication by influencing of enterohepatic circulation of metals is shortly discusses.     

2,3-Dimercaptopropane-1-sulfonic acid and meso-2,3-dimercaptosuccinic acid increase mercury- and cadmium-induced inhibition of delta-aminolevulinate dehydratase

Compounds derived from Dimercaprol, such as meso-2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercaptopropane-1-sulfonic acid (DMPS), are becoming common agents for treating humans exposed to heavy metals. Heavy metals such as Pb(2+), Hg(2+) and Cd(2+) can inhibit delta-aminolevulinate dehydratase (delta-ALA-D) activity. Delta-ALA-D catalyzes the condensation of two delta-aminolevulinic acid (delta-ALA) molecules with the formation of porphobilinogen, a heme precursor. The effects of DMSA and DMPS alone or in combination with Cd(2+), Hg(2+), or Pb(2+) on hepatic delta-ALA-D were examined. DMPS and DMSA caused a dose-dependent inhibition of hepatic delta-ALA-D. In the presence of Hg(2+) or Cd(2+) the inhibitory potency of DMPS increased. Similarly, the inhibitory effects of Hg(2+) and Cd(2+) were markedly increased in the presence of DMSA. In contrast, the inhibitory effect of DMPS was not changed by inclusion of Pb(2+). As observed with DMSA, Zn(2+) did not modified the inhibitory effect of DMPS. Data of the present report support the idea that the complexes formed (metals-DMSA or DMPS) were more inhibitory than the metal (Hg(2+) and Cd(2+)) or the chelating agent alone to the hepatic delta-ALA-D activity, in vitro. The mechanism of hepatic delta-ALA-D inhibition by Hg(2+)-DMPS/DMSA and Cd(2+)-DMPS/DMSA complexes involve the essential thiol groups of the enzyme.     

The mobilization of intracellular cadmium by alkoxyethyl esters of meso-2,3-dimercaptosuccinic acid

The cadmium mobilizing properties of two newly synthesized esters of meso-2,3-dimercaptosuccinic acid in mice have been examined. They are: di(2'-methoxyethyl) meso-2,3-dimercaptosuccinate ([-CH(SH)COOCH2CH2OR]2, R = CH3; MEDMS), and di(2'-ethoxyethyl) meso-2,3-dimercaptosuccinate ([-CH(SH)COOCH2CH2OR]2, R = CH2CH3; EEDMS), conveniently prepared from dimercaptosuccinate acid with 2-methoxyethanol and 2-ethoxyethanol, respectively. Mobilization studies in mice of aged in vivo cadmium deposits using five ip injections of 0.40 mmol/kg of each chelator in peanut oil clearly indicate that both compounds, MEDMS and EEDMS, are significantly superior to 2,3-dimercaptopropan-1-ol (BAL) in depleting the whole body burden of cadmium. The reductions caused by MEDMS and EEDMS were approximately 20 and 26%, respectively, whereas under similar dosage regimens BAL effected about only a 12% reduction. The esters were neither equal nor superior to BAL for the reduction of renal cadmium levels, MEDMS being the least effective. For the mobilization of hepatic cadmium deposits, both were quite promising (MEDMS, 20%; EEDMS, 34% reduction) compared to BAL (only 2% reduction). There was no accumulation of cadmium with either MEDMS or EEDMS in any of the other organs examined--spleen, testes, pancreas, and particularly the brain. These compounds enhance the fecal excretion of cadmium by a factor of 25- to 40-fold but have very little effect on the urinary excretion of this element. The present study reveals that the order of overall efficacy is EEDMS greater than MEDMS greater than BAL, considering the liver and whole body burdens of cadmium, but BAL greater than EEDMS greater than MEDMS in terms of the efficacy in reducing cadmium levels in the kidneys.     

2,3-Dimercaptopropanol, 2,3-dimercaptopropane-1-sulfonic acid and meso-2,3-dimercaptosuccinic acid increase lead-induced inhibition of delta-aminolevulinate dehydratase in vitro and ex vivo.

We investigated the effects of dimercaprol (BAL), meso-2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercapto-1-propanesulphonic acid (DMPS) on human blood delta-aminolevulinate dehydratase (delta-ALA-D) activity, the most reliable indicator of lead intoxication in humans, in the presence of lead in vitro. Furthermore, we studied the effects of the chelating agents, administered subcutaneously, on delta-ALA-D activity in blood and tissues of mice submitted to sub-acute lead exposure (50 mg/kg for 15 consecutive days, subcutaneously). In vitro results demonstrated that human blood delta-ALA-D activity was significantly inhibited (62%) by lead acetate. Lead acetate (1-1000 microM) pre-incubated with human blood increased the inhibitory potency of this compound on delta-ALA-D when compared to the assay without pre-incubation (89%). Chelating agents caused a marked potentiation of delta-ALA-D inhibition induced by lead, in vitro. One of the most notable observations in the present study was the correspondence between in vitro and ex vivo effects. In fact, BAL and DMPS increase the inhibitory effect of lead on delta-ALA-D activity from mice blood. The complexes formed (lead and chelators) were more inhibitory than lead alone in kidney and liver enzyme activity, ex vivo.     

Mobilisation of cadmium by meso- and racemic-2,3-dimercaptosuccinic acid (DMSA) in rats

A higher efficiency of cadmium binding with racemic than with meso-2,3-dimercaptosuccinic acid (rac-DMSA; meso-DMSA) was found in an in vitro speciation model by Fang et al. (1996). This finding has not yet been tested in vivo. This paper presents results on mobilisation of cadmium by meso- and rac-DMSA in rats. Cadmium chloride was administered as the radioactive isotope 109Cd intraperitoneally to all animals. One group was an untreated control and two groups were treated with meso- and rac-DMSA, respectively. Treatment with chelators was applied twice, immediately after 109Cd and 24 hr afterwards intraperitoneally at the dose of 1 mmol/kg, each. Six days later radioactivity was measured in the liver and kidneys. Whole-body counting was carried out on days 1, 2, 3 and 6 of the experiment. At the end of the experiment, both treatments caused a decrease in 109Cd whole-body retention with rac-DMSA being more efficient (decrease from 83% in control to 74% and 64% in groups treated with meso- and rac-DMSA, respectively). The same reduction of 109Cd was obtained by both chelators in the liver (from 57% to about 47%). In the kidney only rac-DMSA produced significant reduction of 109Cd (from 5.3% to 3.5%). In conclusion, these results show modest reduction of cadmium in the body by two isoforms of DMSA with rac-DMSA being slightly more efficient than meso-DMSA.     

Reversal of cadmium-induced vascular dysfunction and oxidative stress by meso-2,3-dimercaptosuccinic acid in mice

Cadmium (Cd) is a heavy metal which causes concern as an environmental toxicant. Therapy with chelating agents is considered to be the rational treatment against metal poisoning. This study was designed to evaluate whether meso-2,3-dimercaptosuccinic acid (DMSA) could alleviate oxidative stress and vascular dysfunction in mice with subchronic exposure to Cd. Male ICR mice received CdCl₂ (100 mg/L) via drinking water for 8 weeks. After Cd exposure, DMSA at a dose of 25 mg/kg or 50 mg/kg was intragastrically administered once daily for 5 consecutive days at the end of Cd treatment. It was found that Cd-induced hypertension and markedly blunted vascular responses to vasoactive agents, including acetylcholine, phenylephrine and sodium nitroprusside. Treatment with DMSA significantly restored blood pressure and improved vascular responsiveness when compared with Cd-treated controls. Moreover, DMSA protected against Cd-induced severe oxidative stress by normalization of the redox ratios of glutathione to glutathione disulfide and suppression of plasma malondialdehyde, plasma protein carbonyl, urinary nitrate/nitrite, and superoxide production from thoracic aorta. DMSA partially reduced Cd contents in the blood, heart, liver and kidneys. In conclusion, our present study provides the first evidence of the therapeutic efficacy of DMSA against oxidative stress and vascular dysfunction in Cd-intoxicated mice.     

Mobilization of lead in mice by administration of monoalkyl esters of meso-2,3-dimercaptosuccinic acid.

The following six monoalkyl esters of meso-2,3-dimercaptosuccinic acid (DMSA) were synthesized and evaluated for relative activities in mobilizing lead from kidneys and brains of lead-bearing mice: n-propyl (Mn-PDMS), i-propyl (Mi-PDMS), n-butyl (Mn-BDMS), i-butyl (Mi-BDMS), n-amyl (Mn-ADMS) and i-amyl meso-2,3-dimercaptosuccinate (Mi-ADMS). DMSA was used as a positive control. When each was administered intraperitoneally (i.p.) as a single dose of 2.0 mmol/kg, DMSA lowered the kidney lead concentration 52%, while the monoesters effected reductions of 54-75%. Mn-ADMS was toxic at this dose. DMSA lowered the brain lead level 20% when given as a single dose, while the monoesters conferred reductions of 64-87%. When given as 5 daily i.p. injections at 0.5 mmol/kg, DMSA reduced the kidney lead concentration 45%, while the monoesters caused reductions of 56-73%. DMSA lowered the brain lead concentration 35% on the 5-day treatment regimen, while the monoesters evoked reductions of 59-75%. Mi-ADMS was equally effective when given orally or i.p. The i.p. LD50 value of this analog in mice is 3.0 mmol/kg, a value which lies between the reported LD50 doses of DMSA (16.0 mmol/kg) and dimercaprol (1.1 mmol/kg). It is suggested that the ability of these monoesters to cross cell membranes may account for their superiority to DMSA in mobilizing brain lead in this animal model.