Anti-lewisite activity and stability of meso-dimercaptosuccinic acid and 2,3-dimercapto-1-propanesulfonic acid

Meso-dimercaptosuccinic acid (DMSA) and the sodium salt of 2,3-dimercapto-1-propanesulfonic acid (DMPS) are analogous in chemical structure to dimercaprol (BAL, British Anti-Lewisite). Dimercaprol was among the first therapeutically useful metal chelating agents and was developed originally as an anti-lewisite agent. Either DMSA or DMPS protects rabbits from the lethal systemic action of dichloro(2-chlorovinyl)arsine (29.7 mumols/kg, also known as lewisite. The analogs are active in this respect when given either sc or po. The stability of each of the three dimercapto compounds in distilled H2O, pH 7.0 at 24 degrees, has been examined for seven days. DMSA retained 82% of its mercapto groups, but no titratable mercapto groups remained in the DMPS or BAL solutions. At pH 5.0, however, there was no striking difference in the stability of the three dimercapto compounds (78-87%) over a seven day period. DMSA and DMPS warrant further investigation as water soluble metal binding agents in both in vivo and in vitro experiments.     

Chelation therapy in intoxications with mercury,lead and copper

In the present review we provide an update of the appropriate use of chelating agents in the treatment of intoxications with compounds of mercury, lead and copper. The relatively new chelators meso-2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercapto-propanesulphonate (DMPS) can effectively mobilize deposits of mercury as well as of lead into the urine. These drugs can be administered orally and have relatively low toxicity compared to the classical antidote dimercaptopropanol (BAL). d-Penicillamine has been widely used in copper overload, although 2,3-dimercaptosuccinic acid or tetrathiomolybdate may be more suitable alternatives today. In copper-toxicity, a free radical scavenger might be recommended as adjuvant to the chelator therapy.     

Cadmium inhibits delta-aminolevulinate dehydratase from rat lung in vitro: interaction with chelating and antioxidant agents

The effect of cadmium (Cd(2+)) on delta-aminolevulinate dehydratase (delta-ALA-D) activity from rat lung in vitro was investigated. delta-ALA-D activity, a parameter for metal intoxication, has been reported as a target of Cd(2+) in different tissues. The protective effect of monotherapies with dithiol chelating (meso-2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercaptopropane-1-sulfonic acid (DMPS)) or antioxidant agents (ascorbic acid, diphenyl diselenide (PhSe)(2), and N-acetylcysteine (NAC)) was evaluated. The effect of a combined therapy (dithiol chelatingxantioxidant agent) was also studied. Zinc chloride (ZnCl(2)) and dithiothreitol (DTT) were used to investigate the mechanisms involved in cadmium, chelating and antioxidant effects on delta-ALA-D activity. Cadmium inhibited rat lung delta-ALA-D activity at low concentrations. DTT (3mM), but not ZnCl(2) (100microM), protected the inhibition of enzyme activity caused by Cd(2+). Chelating agents were not effective in restoring the enzyme activity. DMPS and DMSA presented inhibitory effect on enzyme activity. DTT restored the inhibition caused by both chelating agents, but ZnCl(2) restored only the inhibitory effect induced by DMSA. These compounds caused a marked potentiation of delta-ALA-D inhibition induced by Cd(2+). ZnCl(2) did not restore inhibition of enzyme activity caused by Cd(2+) plus chelating agents. Conversely, DTT restored the inhibition induced by Cd(2+)/DMSA, but not by Cd(2+)/DMPS. Antioxidants were not effective in ameliorating delta-ALA-D inhibition induced by Cd(2+), whereas ascorbic acid potentiated the enzyme inhibition induced by this metal. A combined effect of Cd(2+)xDMPSx(PhSe)(2) and Cd(2+)xDMPSxNAC was observed. There was no combined effect of Cd(2+)xchelatorxantioxidants when DMSA was used. This study demonstrated that Cd(2+)inhibited delta-ALA-D activity and chelating and antioxidant agents, alone or combined, did not restore the enzyme activity. In contrast, these compounds potentiated the inhibition induced by Cd(2+) in rat lung.     

Therapeutic potential of meso 2,3-dimercaptosuccinic acid or 2,3-dimercaptopropane 1-sulfonate in chronic arsenic intoxication in rats

The therapeutic efficacy of two thiol chelators, meso 2,3-dimercaptosuccinic acid (DMSA) or 2,3-dimercaptopropane sulfonate (DMPS) in treating chronic arsenic intoxication was investigated in male rats. Both the chelators were effective in promoting urinary arsenic excretion and restoring arsenic induced inhibition of blood -aminolevulinic acid dehydratase activity and hepatic glutathione level. Elevation of urinary -aminolevulinic acid excretion and arsenic concentration in blood, liver and kidneys were reduced significantly by both the chelators. Histopathological lesions induced by arsenic were also effectively reduced by the above chelators. DMSA being more effective than DMPS. The results suggest DMSA and DMPS to be effective antidotes for treating chronic arsenic toxicity in experimental animals.     

Effect of dithiol chelating agents on [3H]MK-801 and [3H]glutamate binding to synaptic plasma membranes

2,3-Dimercaptopropanol (BAL- British Anti-Lewesite) is a dithiol chelating agent used for the treatment of heavy metal poisoning, however, BAL can produce neurotoxic effects in a variety of situations. Based on the low therapeutic efficiency of BAL other dithiols were developed and DMSA (meso-2,3-dimercaptosuccinic acid) and DMPS (2,3-dimercaptopropane-1-sulfonic acid) are becoming used for treatments of humans exposed to heavy metals. In the present investigation the effect of dithiols in the glutamatergic system was examined. The results showed that BAL inhibited [³H]MK-801 and [³H]glutamate binding in a concentration-dependent manner. At 100 M BAL and DMSA caused a significantly inhibition of [³H]MK-801 binding to brain membranes (p < 0.05 by Duncan's multiple range test). BAL at 100 M caused an inhibition of 40% on [³H]glutamate binding. DMPS and DMSA had no significant effect on [³H]glutamate binding. Dithiotreitol (DTT), abolished the inhibitory effect of BAL on [³H]MK-801 binding. The protection exerted by DTT suggests that BAL inhibit [³H]MK-801 binding by interacting with cysteinyl residues that are important for redox modulation of receptor responses. ZnCl₂ inhibited [³H]glutamate and [³H]MK-801 binding to brain synaptic membrane; nevertheless, the inhibitory effect was slight more accentuated for [³H]MK-801 than [³H]glutamate binding (p < 0.05). The inhibition caused by 10 M ZnCl₂ on [³H]MK-801 binding was attenuated by BAL. The findings present in this study may provide the evidence that BAL affect the glutamatergic system and these effects can contributed to explain, at least in part, why BAL, in contrast to DMPS and DMSA is neurotoxic.     

In vitro assessment of chelating agents with regard to their abstraction efficiency of Cd(2+) bound to plasma proteins

The exposure of various human populations to Cd(2+) is of increasing health concern. After its gastrointestinal absorption into the bloodstream, Cd(2+) binds to α(2)-macroglobulin and serum albumin. Although animal studies have demonstrated that meso-2,3-dimercaptosuccinic acid (DMSA) and diethylenetriamine pentaacetic acid (DTPA) can effectively mobilize Cd(2+) to urine and decrease the Cd concentrations of the kidneys, the liver and the brain, not much is known about the abstraction of Cd(2+) from blood plasma proteins. We prepared a stock of Cd(2+) spiked rabbit plasma (2.0 μg of Cd(2+)/mL) and analyzed aliquots by size exclusion chromatography coupled on-line to an inductively coupled plasma atomic emission spectrometer (SEC-ICP-AES) while simultaneously monitoring the emission lines of Ca, Cd, Cu, Fe, and Zn. After the addition of 0.33 mM, 0.66 mM or 0.99 mM of DMSA, DTPA, 2,3-dimercapto-1-propanesulfonic acid (DMPS) or N-acetyl-l-cysteine (NAC) to plasma aliquots, the obtained mixtures were analyzed by SEC-ICP-AES after 5 min and 30 min. None of the investigated compounds adversely affected the plasma distribution of Fe at all investigated doses. At 0.33 mM, DTPA was most effective at mobilizing plasma protein bound Cd(2+) to a ～5 kDa Cd-species (100% removal), followed by DMPS (94%), DMSA (83%) and NAC (3%). All investigated compounds also mobilized Zn(2+) from plasma proteins to ～5 kDa Zn-species (DTPA: 80% removal; DMPS: 63%; DMSA: 29% and NAC: 3%). The addition of DTPA resulted in the dose-dependent elution of a [Ca-DTPA](3-) complex. Based on these results, 0.33 mM DMSA represents the best compromise that can be achieved between maximizing the abstraction of Cd(2+) from plasma proteins (83%), while minimizing the mobilization of Zn(2+) from plasma proteins (29%), and avoiding the complexation of Ca(2+).     

Arsenic induced blood and brain oxidative stress and its response to some thiol chelators in rats

Chronic arsenic toxicity is a widespread problem, not only in India and Bangladesh but also in various other regions of the world. Exposure to arsenic may occur from natural or industrial sources. The treatment that is in use at present employs administration of thiol chelators, such as meso 2,3-dimercaptosuccinic acid (DMSA) and sodium 2,3-dimercaptopropane 1-sulfonate (DMPS), which facilitate its excretion from the body. However, these chelating agents are compromised with number of limitations due to their lipophobic nature, particularly for their use in cases of chronic poisoning. During chronic exposure, arsenic gains access into the cell and it becomes mandatory for a drug to cross cell membrane to chelate intracellular arsenic. To address this problem, analogs of DMSA having lipophilic character, were examined against chronic arsenic poisoning in experimental animals. In the present study, therapeutic efficacy of meso 2,3-dimercaptosuccinic acid (DMSA), sodium 2,3-dimercaptopropane 1-sulfonate (DMPS), monoisoamyl DMSA (MiADMSA) were compared in terms of reducing arsenic burden, as well as recovery in the altered biochemical variables particularly suggestive of oxidative stress. Adult male Wistar rats were given 100-ppm arsenic for 10 weeks followed by chelation therapy with the above chelating agents at a dose of 50 mg/Kg (orally) once daily for 5 consecutive days. Arsenic exposure resulted in marked elevation in reactive oxygen species (ROS) in blood, inhibition of ALAD activity and depletion of GSH. These changes were accompanied by significant decline in blood hemoglobin level. MiADMSA was the most effective chelator in reducing ROS in red blood cells, and in restoring blood ALAD compared to two other chelators. Brain superoxide dismutase (SOD) and glutathione peroxidase (GPx) decreased, while ROS and TBARS increased significantly following arsenic exposure. There was a significant increase in the activity of glutathione-S-transferase (GST) with a corresponding decline in its substrate i.e. glutathione. Among all the three chelators, MiADMSA showed maximum reduction in the level of ROS in brain. Additionally, administration of MiADMSA was most effective in counteracting arsenic induced inhibition in brain ALAD, SOD and GPx activity. Based on these results and in particular higher metal decorporation from blood and brain, we suggest MiADMSA to be a potential drug of choice for the treatment of chronic arsenic poisoning. However, further studies are required for the choice of appropriate dose, duration of treatment and possible effects on other major organs.     

Factors influencing the efficiency of chelation therapy.

The purpose of the present study was to obtain new data on the effect of age, route, dose and time of metal and chelating agent administration on the efficiency of chelation therapy. The experiments were performed on 1-2 and 6-week-old rats which received radioisotopes of metals--203Pb, 115 mCd, 203Hg and 141Ce intraperitoneally or orally. Chelating agents calcium ethylenediaminetetraacetate (CaEDTA), calcium and zinc diethylenetriaminepentaacetate (CaDTPA, ZnDTPA), 2,3-dimercapto-propane-sulfonate-1 (DMPS), dimercaptosuccinic acid (DMSA) and sodium N-(4-methoxybenzyl)-D-glucamine dithiocarbamate monohydrate (MeOBDCG) were administered twice by intraperitoneal or oral administration as early (immediately and 24 hr after metals) or delayed treatment (24 and 48 or 48 and 72 hr after metals). The animals were killed six days after metal administration and the retention was determined in the whole body, carcass and gut. After intraperitoneal administration of metals and chelating agents chelation therapy had much lower efficacy in younger than older animals. After ingestion of metals oral chelation therapy was more effective in younger than older animals. In suckling rats the treatment effectively reduced metal retention and this was mostly due to decrease in gut retention. This treatment in sucklings was also very effective in condition of late administration. In older rats early oral DMPS treatment after 203Hg ingestion is contraindicated since it increases significantly mercury retention while DMSA and ZnDTPA treatments reduced mercury retention. Delayed oral treatment with ZnDTPA and DMSA caused increased cadmium retention in older rats and decreased retention in sucklings. Opposite to results with CaDTPA, MeOBDCG was effective in reducing cadmium retention also when given as delayed treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chelation in metal intoxication—Principles and paradigms

The present review provides an update of the general principles for the investigation and use of chelating agents in the treatment of intoxications by metals. The clinical use of the old chelators EDTA (ethylenediamine tetraacetate) and BAL (2,3-dimercaptopropanol) is now limited due to the inconvenience of parenteral administration, their own toxicity and tendency to increase the neurotoxicity of several metals. The hydrophilic dithiol chelators DMSA (meso-2,3-dimercaptosuccinic acid) and DMPS (2,3-dimercapto-propanesulphonate) are less toxic and more efficient than BAL in the clinical treatment of heavy metal poisoning, and available as capsules for oral use. In copper overload, DMSA appears to be a potent antidote, although d-penicillamine is still widely used. In the chelation of iron, the thiols are inefficient, since iron has higher affinity for ligands with nitrogen and oxygen, but the new oral iron antidotes deferiprone and desferasirox have entered into the clinical arena. Comparisons of these agents and deferoxamine infusions are in progress. General principles for research and development of new chelators are briefly outlined in this review.     

Determination of 2,3-dimercaptosuccinic acid in mice blood and tissues by HPLC with fluorescence detection

2,3-Dimercaptosuccinic acid (DMSA) is an orally effective chelating agent for the treatment of heavy metal poisoning. The increasing therapeutic use of DMSA has stimulated the need for sensitive and selective methods for its determination in biological samples, as well as study on pharmacokinetics and tissue distribution. According to the previously reported method, an improved method was established for the determination of DMSA in mice blood and tissues, in which oxidized DMSA was reduced by the disulfide-reducing agent, dithiothreitol (DTT), and DMSA was converted to a highly fluorescent and stable derivative by reaction with monobromobimane (mBBr) in alkaline solution. Acetonitrile was used for deproteinization and dichloromethane was used for condensation and purification, which significantly shortened the amount of time used to process the sample. Meanwhile isocratical elution was performed and excellent separation of the DMSA derivative was obtained, this enabled a run finish within 20 min. The limits of quantitation were 0.025 μg/ml in brain and 0.1 μg/ml in blood, lung, heart, intestine, liver, spleen and kidney, respectively. The calibration curves were linear in all samples (r² > 0.992) with a range of 0.025–1.6 μg/ml for brain homogenate and 0.1–6.4 μg/ml for blood and homogenates of lung, heart, intestine, liver, spleen and kidney, respectively. Therefore, the method is simple, rapid and sensitive, and it could be applicable to the studies in an animal model to evaluate the distribution of DMSA in blood and tissues.     

20 S proteasome from Saccharomyces cerevisiae is responsive to redox modifications and is S-glutathionylated

The 20 S proteasome core purified from Saccharomyces cerevisiae is inhibited by reduced glutathione (GSH), cysteine (Cys), or the GSH precursor gamma-glutamylcysteine. Chymotrypsin-like activity was more affected by GSH than trypsin-like activity, whereas the peptidylglutamyl-hydrolyzing activity (caspase-like) was not inhibited by GSH. Cys-sulfenic acid formation in the 20 S core was demonstrated by spectral characterization of the Cys-S(O)-4-nitrobenzo-2-oxa-1,3-diazole adduct, indicating that 20 S proteasome Cys residues might react with reduced sulfhydryls (GSH, Cys, and gamma-glutamylcysteine) through the oxidized Cys-sulfenic acid form. S-Glutahionylation of the 20 S core was demonstrated in vitro by GSH-biotin incorporation and by decreased alkylation with monobromobimane. Compounds such as N-ethylmaleimide (-S-sulfhydril H alkylating), dimedone (-SO sulfenic acid H reactant), or 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (either -SH or -SOH reactant) highly inhibited proteasomal chymotrypsin-like activity. In vivo experiments revealed that 20 S proteasome extracted from H(2)O(2)-treated cells showed decreased chymotrypsin-like activity accompanied by S-glutathionylation as demonstrated by GSH release from the 20 S core after reduction with NaBH(4). Moreover, cells pretreated with H(2)O(2) showed decreased reductive capacity assessed by determination of the GSH/oxidized glutathione ratio and increased protein carbonyl levels. The present results indicate that at the physiological level the yeast 20 S proteasome is regulated by its sulfhydryl content, thereby coupling intracellular redox signaling to proteasome-mediated proteolysis.     

Determination of reduced, oxidized, and protein-bound glutathione in human plasma with precolumn derivatization with monobromobimane and liquid chromatography

This assay measures reduced (GSH), oxidized (GSSG, GSSR), and protein-bound (glutathione-protein mixed disulfides, ProSSG) glutathione in human plasma. Oxidized glutathione and ProSSG are converted to GSH in the presence of NaBH4, and, after precolumn derivatization with monobromobimane, GSH is quantitated by reversed-phase liquid chromatography and fluorescence detection. The NaBH4 concentration is optimized so that total recovery of oxidized glutathione is obtained and no interference with the formation/stability of the GSH-bimane adduct occurs. The presence of 50 microM dithioerythritol prevents reduced recovery at low concentrations of GSH, and the standard curve for GSH is linear over a wide concentration range and is super-imposed upon that obtained with GSSG. Selective determination of oxidized glutathione exploits the fact that N-ethylmaleimide (NEM) blocks free sulfhydryl groups and excess NEM is inactivated by the subsequent addition of NaBH4. To measure total glutathione including the protein-bound forms, the protein is solubilized with dimethyl sulfoxide, which is compatible with the other reagents and slightly increases the yield of the fluorescent GSH derivative. The assay is characterized by a sensitivity (less than 2 pmol) sufficiently high to detect the various forms of glutathione in plasma, by an analytical recovery of GSH and GSSG close to 100%, and by a within-day precision corresponding to a coefficient of variation of 7%. The assay was used to determine the dynamic relationships among various glutathione species in human plasma.     

Quantification and identification of mitochondrial proteins containing vicinal dithiols

Vicinal dithiols may play a role in mitochondrial antioxidant defences and in redox signalling. We quantified protein vicinal dithiols within mammalian mitochondria using the vicinal dithiol-specific reagent phenylarsine oxide (PAO). We found 5-15% of thiols exposed on mitochondrial proteins were vicinal dithiols and that these thiols were particularly sensitive to oxidation by hydrogen peroxide. To visualise these proteins we used PAO to block vicinal dithiols, followed by alkylation of other thiols with N-ethylmaleimide (NEM). The PAO was then removed with 2,3-dimercapto-1-propanesulfonic acid (DMPS) and the exposed vicinal dithiols were labelled with iodoacetamide-biotin. To identify these proteins, we developed a selective proteomic methodology, based on Redox difference in gel electrophoresis (Redox-DIGE). Vicinal dithiol proteins were selectively labelled with a red fluorescent thiol-reactive Cy5 maleimide and mixed with Cy3 maleimide labelled protein in which vicinal dithiols remained untagged. Individual proteins were resolved by 2D gel electrophoresis and fluorescent scanning revealed vicinal dithiol proteins by the increase in Cy5 red fluorescence. These proteins were identified by peptide mass fingerprinting and mass spectrometry. These findings are consistent with roles for mitochondrial vicinal dithiol proteins in antioxidant defence and redox signalling and these methodologies will enable these roles to be explored.     

Response of lead-induced oxidative stress and alterations in biogenic amines in different rat brain regions to combined administration of DMSA and MiADMSA

The present study was planned to investigate if combined administration of meso-2,3-dimercaptosuccinic acid (DMSA) and monoisoamyl DMSA (MiADMSA) could achieve better recovery in the altered biochemical parameters suggestive of brain oxidative stress and depletion of lead from blood and brain following acute lead exposure. Male Wistar rats were exposed to lead nitrate (50 mg/kg, i.p., once daily for 5 days) followed by treatment with the above chelating agents using two different doses of 25 or 50 mg/kg (orally) either alone and in combination once daily for five consecutive days. Lead exposure resulted in the significant inhibition of δ-aminolevulinic acid dehydratase activity and depletion of glutathione (GSH) in blood. These changes were accompanied by significant reduction in blood hemoglobin, RBC levels and superoxide dismutase and catalase activities. Significant increase in blood reactive oxygen species (ROS) and thiobarbituric acid reactive substances (TBARS) levels were noted. We observed marked increase in brain ROS level while GSH/oxidized glutathione ratio showed significant decrease accompanied by a significant increase in blood and brain lead concentration. The levels of norepinephrine, dopamine and serotonin in different brain regions were also altered on lead exposure. Co-administration of DMSA and MiADMSA particularly at the lower dose was most effective in the recovery of lead-induced changes in the hematological variables and oxidative stress and resulted in more pronounced depletion of lead from blood and brain compared to monotherapy with these chelators. On the other hand, combined administration of MiADMSA (50 mg/kg) in combination with DMSA (25 mg/kg each) had additional beneficial effect over the individual effect of chelating agent in the recovery of altered levels of brain biogenic amines. The study suggests that administration of MiADMSA is generally a better lead chelator than DMSA while combined administration of DMSA and MiADMSA might be a better treatment option compared to monotherapy at least in the removal of lead from the target tissues.     

Determination of the in vivo redox status of cysteine, cysteinylglycine, homocysteine, and glutathione in human plasma.

An assay that measures the reduced, oxidized, and protein-bound forms of cysteine, cysteinylglycine, homocysteine, and glutathione in human plasma is described. Oxidized and protein-bound thiols are converted to their reduced counterparts by the use of NaBH4, and, following derivatization with monobromobimane (mBrB), the thiol-bimane adducts are quantified by reversed-phase ion-pair liquid chromatography and fluorescence detection. The presence of 50 microM dithioerythritol provides linearity of the standard curves at very low thiol concentrations. Selective determination of the oxidized forms was accomplished by blocking free sulfhydryl groups with N-ethylmaleimide (NEM) and excess NEM is inactivated by the subsequent addition of NaBH4. The reduced forms of the thiols in plasma were trapped with minimal oxidation by derivatizing blood samples at the time of collection. This was attained by drawing blood directly into tubes containing isotonic solutions of mBrB or NEM. The assay is sufficiently sensitive (less than 2 pmol) to detect the various forms of the four thiol compounds in human plasma. The analytical recovery of cysteine, cysteinylglycine, homocysteine, and glutathione was close to 100%, and the within-day precision corresponded to a coefficient of variation of 7, 8, 6, and 7%, respectively. The assay has been used to determine the various forms of the four thiol compounds in human plasma.     

Vanadium detoxification: on the interaction of oxovanadium(IV) and other vanadium species with 2,3-dimercapto-1-propanesulfonate

The interaction of the VO²⁺ cation with the sodium salt of 2,3-dimercapto-1-propanesulfonic acid (DMPS) was investigated by electron absorption spectroscopy in aqueous solution, in the pH range between 4 and 12. The spectral behavior points to the generation of a [VO(DMPS)₂]⁴⁻ complex in which the oxocation interacts with two pairs of deprotonated –SH groups of the ligand. By spectrophotometric monitoring it was found that DMPS rapidly reduces vanadates(V) to VO²⁺ which may be chelated by an excess of the acid. DMPS produces also the slow reduction of a V₂O₅ suspension at pH 7.1. The results of this study suggest that DMPS may be a potentially useful detoxification agent for vanadium.     

Gas chromatographic analysis of urinary dimercaptosuccinic acid

The therapeutic use of disulfhydryl compounds such as 2,3-dimercaptosuccinic acid (DMSA) for the treatment of heavy metal poisoning has generated a requirement for specific and sensitive methods to determine those compounds in biological media. We have developed a gas chromatographic assay for DMSA in urine. The use of capillary column technology eliminates the requirement for a preliminary clean-up step. Samples are first reduced electrochemically to liberate DMSA present as disulfides. The reduced product is then extracted into ethyl acetate and the organic phase removed by evaporation. The residue is derivatized with N,O-bis(trimethylsilyl)acetamide for gas chromatography. The silylated DMSA derivative is then detected with a flame ionization detector. The detection limit for DMSA is 1.9 nmol per 1-μl aliquot of derivatized extract injected on column (detector sensitivity at 1·10⁻¹¹ A/mV). The utility of the method was demonstrated by analyzing the urine of rats orally dosed with DMSA.     

Evaluation of the developmental effects on mice after prenatal, or pre- and postnatal exposure to 2,3-dimercaptopropane-1-sulfonic acid (DMPS)

The sodium salt of 2,3-dimercaptopropane-1-sulfonic acid (DMPS), a water soluble metal complexing agent, was administered to four groups of pregnant Swiss mice at 0, 70, 210, and 630 mg/kg/day by two dosing schedules: gestation day 14 until birth (prenatal exposure), and gestation day 14 until postnatal day 21 (pre- and postnatal section). Dams were allowed to deliver and the number of live and dead pups recorded. Each pup was sexed and weighed on days 0, 4, 14, and 21. Also, pinna detachment, incisor eruption and eye opening were monitored. No adverse effects on offspring survival or development were evident in either exposures at doses employed in this study. The "no observable effect level" (NOEL) for health hazard to the developing fetus or pup was 630 mg DMPS/kg/day. This dose is much higher than the amounts of DMPS usually administered in human heavy metal poisoning.     

Response of arsenic-induced oxidative stress,DNA damage,and metal imbalance to combined administration of DMSA and monoisoamyl-DMSA during chronic arsenic poisoning in rats

Arsenic and its compounds cause adverse health effects in humans. Current treatment employs administration of thiol chelators, such as meso-2,3-dimercaptosuccinic acid (DMSA) and sodium 2,3-dimercaptopropane 1-sulfonate (DMPS), which facilitate its excretion from the body. However, these chelating agents are compromised by number of limitations due to their lipophobic nature, particularly in case of chronic poisoning. Combination therapy is a new approach to ensure enhanced removal of metal from the body, reduced doses of potentially toxic chelators, and no redistribution of metal from one organ to another, following chronic metal exposure. The present study attempts to investigate dose-related effects of two thiol chelators, DMSA and one of its new analogues, monoisoamyl dimercaptosuccinic acid (MiADMSA), when administered in combination with the aim of achieving normalization of altered biochemical parameters suggestive of oxidative stress and depletion of inorganic arsenic following chronic arsenic exposure. Twenty-five adult male Wistar rats were given 25 ppm arsenic for 10 weeks followed by chelation therapy with the above chelating agents at a dose of 0.3 mmol/kg (orally) when administered individually or 0.15 mmol/kg and 0.3 mmol/kg (once daily for 5 consecutive days), respectively, when administered in combination. Arsenic exposure led to the inhibition of blood δ-aminolevulinic acid dehydratase (ALAD) activity and depletion of glutathione (GSH) level. These changes were accompanied by significant depletion of hemoglobin, RBC and Hct as well as blood superoxide dismutase (SOD) acitivity. There was an increase in hepatic and renal levels of thiobarbituric acid-reactive substances, while GSH:GSSG ratio decreased significantly, accompanied by a significant increase in metallothionein (MT) in hepatocytes. DNA damage based on denaturing polyacrylamide gel electrophoresis revealed significant loss in the integrity of DNA extracted from the liver of arsenic-exposed rats compared to that of normal animals. These changes were accompanied by a significant elevation in blood and soft-tissue arsenic concentration. Co-administration of DMSA and MiADMSA at lower dose (0.15 mmol/kg) was most effective not only in reducing arsenic-induced oxidative stress but also in depleting arsenic from blood and soft tissues compared to other treatments. This combination was also able to repair DNA damage caused following arsenic exposure. We thus recommend combined administration of DMSA and MiADMSA for achieving optimum effects of chelation therapy.     

Copper,zinc, and selenium in human blood and urine after injection of sodium 2,3-dimercaptopropane-1-sulfonate: a study on subjects with dental amalgam

This study investigated the effects of a single dose of intravenously administered sodium 2,3-dimercaptopropane-1-sulfonate (DMPS) on the essential elements copper, zinc, and selenium in human blood and urine. The possible role of dental amalgam was also addressed. Eighty individuals, divided in four groups according to the presence or absence of dental amalgam fillings and symptoms self-related to such fillings, were given DMPS (2 mg/kg body wt) and 500 mL Ringer’s acetate intravenously. Urine and blood were collected prior to the injection, and thereafter at intervals over a 24-h period. Cu, Zn, and Se concentrations were determined by atomic absorption spectrometry methods. A statistically significant increase in the concentrations of Cu and Zn in urine was observed 30 and 120 min after the DMPS injection compared to the preinjection concentrations. The concentrations of Se were not affected. The cumulated excretion over 24 h after DMPS injection constitutes only from 0.1% to 0.7% of the body content of these elements. There was no effect of different amalgam statuses on Cu and Zn excretion. We found a temporary decrease (4–7%) in the concentrations of Cu, Zn, and Se in blood 15 and 30 min after DMPS, but this seems to be the result of dilution factors. Administration of a single dose of DMPS does not affect the body stores of the essential elements Cu, Zn, and Se.