The mobilization of intracellular cadmium by butyl and amyl esters of meso-2,3-dimercaptosuccinic acid

Strategies for Safe and Effective Therapeutic Measures for Chronic Arsenic and Lead Poisoning

Exposure to toxic metals remains a widespread occupational and environmental problem in world. There have been a number of reports in the recent past suggesting an incidence of childhood lead poisoning and chronic arsenic poisoning due to contaminated drinking water in many areas of West Bengal in India and Bangladesh has become a national calamity. Low level metal exposure in humans is caused by air, food and water intake. Lead and arsenic generally interferes with a number of body functions such as the central nervous system (CNS), the haematopoietic system, liver and kidneys. Over the past few decades there has been growing awareness and concern that the toxic biochemical and functional effects are occurring at a lower level of metal exposure than those that produce overt clinical and pathological signs and symptoms. Despite many years of research, we are still far from an effective treatment of chronic plumbism and arsenicosis. Medical treatment of acute and chronic lead and arsenic toxicity is furnished by chelating agents. Chelating agents are organic compounds capable of linking together metal ions to form complex ring-like structures called chelates. They have been used clinically as antidotes for acute and chronic poisoning. 2, 3-dimercaprol (BAL) has long been the mainstay of chelation therapy for lead or arsenic poisoning. Meso 2, 3, -dimercaptosuccinic acid (DMSA) has been tried successfully in animals as well as in a few cases of human lead and arsenic poisoning. DMSA could be a safe and effective method for treating lead or arsenic poisoning, but one of the major disadvantages of chelation with DMSA has been its inability to remove lead from the intracellular sites because of its lipophobic nature. Further, it does not provide protection in terms of clinical/ biochemical recovery. A new trend in chelation therapy is to use combined treatment. This includes the use of structurally different chelators or a combination of an adjuvant and a chelator to provide better clinical/biochemical recovery in addition to lead mobilization. The present review article attempts to provide update information about the current strategies being adopted for a safe, effective and specific treatment for two major toxic metals or metalloid.

Cadmium-mediated activation of the metal response element in human neuroblastoma cells lacking functional metal response element-binding transcription factor-1

Metal response element-binding transcription factor-1 (MTF-1) binds specifically to metal response elements (MREs) and transactivates metallothionein (MT) gene expression in response to zinc and cadmium. This investigation contrasts the mechanism of mouse MT gene (mMT-I) promoter activation by cadmium and zinc in IMR-32 human neuroblastoma cells to determine whether MTF-1 binding to the MRE is necessary for activation by these metals. Cadmium activated a mMT-1 promoter (-150 base pairs) luciferase reporter 20-25-fold through a MRE-dependent mechanism. In contrast, zinc had little effect on the mMT-1 luciferase reporter. IMR-32 cells lacked MRE binding activity, and treatment with zinc in vitro or in vivo did not generate a MTF-1. MRE complex, suggesting that IMR-32 cells lack functional MTF-1. Overexpression of mMTF-1 regenerated a zinc-mediated induction of the MRE without affecting cadmium activation. Because no other transition metals tested activated the MRE, this effect appeared to be cadmium-specific. These data demonstrate that in IMR-32 human neuroblastoma cells, zinc and cadmium can use independent mechanisms for activation of the mMT-I promoter and cadmium-mediated MRE activation is independent of MTF-1 and zinc.

Combined chelation treatment for polonium after simulated wound contamination in rat

Contaminated puncture wounds were simulated in rat by intramuscular injection of 210Po. The aim of the study was to determine the effectiveness of chelation treatment as a function of time, dosage, and route of chelate administration. Ten newly synthesized substances containing vicinal sulphydryl and carbodithioate groups were used and their effect was compared with that of chelators clinically applicable in man--BAL (2,3-dimercaptopropane-1-ol), DMPS (2,3-dimercaptopropane-1-sulphonate), DMSA (meso-2,3-dimercaptosuccinic acid), and DDTC (sodium diethylamine-N-carbodithioate). The results indicate first that complete removal of 210Po from the injection site is achieved by only two local injections of DMPS, beginning as late as 2 h after injection of 210Po. Second, many of the substances used merely induce translocation of 210Po from the injection site into other tissues. Third, a combined local treatment at the injection site with DMPS plus repeated systemic, subcutaneous, treatments with HOEtTTC (N,N'-di-(2-hydroxyethyl)ethylenediamine-N,N-biscarbodithioate), a derivative of DDTC, results after 2 weeks in a reduction of the estimated total body retention of 210Po to about one-third of that in untreated controls. In the latter case the cumulative excretion of 210Po increased from 8 to 54%, mainly via the faeces.

meso-2,3-dimercaptosuccinic acid monoalkyl esters: effects on mercury levels in mice

Seven monoesters of meso-2,3-dimercaptosuccinic acid (DMSA) were evaluated for relative activities in mobilizing and promoting excretion of mercury in mercury-laden mice. Compounds assessed were the ethyl (M-EDMS), n-propyl (Mn-PDMS), isopropyl (Mi-PDMS), n-butyl (Mn-BDMS), isobutyl (Mi-BDMS), n-amyl (Mn-ADMS), and isoamyl (Mi-ADMS) esters. 2,3-Dimercaptopropane-1-sulfonate (DMPS) and DMSA were used as positive controls. After the first oral dose of each compound at 0.5 mmol/kg, DMSA and DMPS reduced the corporal mercury burden 16% and 24%, respectively, compared to controls, while the monoesters effected reductions of 35% (M-EDMS) to 49% (Mi-ADMS). After the second treatment at the same dose, the respective reductions produced by DMSA and DMPS were 24% and 38%, and those conferred by the monoesters ranged from 52% (M-EDMS) to 61% (Mn-BDMS). Determination of the comparative dose-response relationships of DMSA and Mi-ADMS on corporal and renal mercury concentrations revealed the monoester to be more active than DMSA on both parameters at each dose used. The cumulative amount of mercury excreted in urine by control mice over a 3-day period was 7.08 micrograms; this was increased 22%, 85%, and 94% by daily i.p. injections of DMSA, DMPS, and Mi-ADMS, respectively, at a daily dose of 0.1 mmol/kg. The respective cumulative 3-day totals recovered in feces from control mice and from mice treated with DMSA, DMPS, and Mi-ADMS were 9.76, 8.21, 10.44, and 11.73 micrograms. Parallel daily measurements of retained whole body radioactivity from 203Hg in mice were in good agreement with the values calculated from the excretion data.

Cadmium mobilization in vivo by intraperitoneal or oral administration of monoalkyl esters of meso-2,3-dimercaptosuccinic acid in the mouse

The relative activities of a series of nine monoalkyl esters of meso-2,3-dimercaptosuccinic acid have been examined as agents for the mobilization of cadmium from mice one week after intraperitoneal administration of cadmium chloride. Eight of these are newly synthetized; all are of the type ROOCCH(SH)CH(SH)COOH, were R = Me, MMDMS; R = C2H5, MEDMS; R = (CH2)2CH3, Mn-PDMS; R = CHMe2, Mi-PDMS; R = (CH2)3CH3, Mn-BDMS; R = CH2CHMe2, Mi-BDMS; R = (CH2)4CH3, Mn-ADMS; R = (CH2)2CHMe2, Mi-ADMS; and R = (CH2)5CH3, Mn-HDMS. All are soluble in dilute sodium bicarbonate solutions and can be administered as aqueous solutions. Cadmium mobilization data were collected on each compound using mice previously loaded with cadmium; the monoesters were administered at a level of 0.40 mmol/kg intraperitoneally daily for five days. Data on whole body cadmium mobilization indicated that the monoester with the isoamyl group was the most effective under the conditions used. The relative whole body cadmium mobilization increased with the number of carbon atoms in the alkyl group of the monoester up to C5 and then decreased for the C6 compound. Cadmium removal from the kidneys and liver was also measured. It was found that the monoisoamyl ester was the most effective in removing cadmium from both the liver and the kidneys. The monoisoamyl ester also proved to be very effective in mobilizing cadmium from both the liver and the kidneys when given orally. This is the first compound which is reported capable of mobilizing cadmium in vivo from aged deposits after oral administration.

New developments in therapeutic chelating agents as antidotes for metal poisoning

An examination of the studies on therapeutic chelating agents that have been carried out during the last decade reveals that extensive efforts have been made to develop compounds superior to those previously available for the treatment of acute and chronic intoxication by many metals. These metals include primarily iron, plutonium, cadmium, lead, and arsenic, but also many other elements for which acute and chronic intoxication is less common. These studies have revealed the importance of several additional factors of importance in the design of such compounds and have led to many new compounds of considerable clinical promise. An additional development has been the introduction of previously developed chelating agents for use with certain metals on a broader scale.

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.

Structural influences on intracellular cadmium mobilization by dithiols

An examination of 5 dithiols, N-(2,3-dimercaptopropyl)phthalamidic acid (DMPA), benzene-1,2-dithiol (BDT), toluene-3,4-dithiol (TDT), alpha, alpha'-dimercapto-o-xylene (DOX), and 4,5-dimethyl-alpha,alpha'-dimercapto-o-xylene (DDOX), reveals that these compounds are all inferior to previously reported compounds as agents for the in vivo mobilization of cadmium from its intracellular sites, although all possess sulfhydryl groups capable of reacting with cadmium. The results demonstrate the considerable importance of those parts of the molecule which do not participate directly in the formation of chelate rings in the determination of the ultimate behavior of such compounds in vivo.