Studies of urinary cystine precipitation in vitro: ontogeny of cystine nephrolithiasis and identification of meso-2,3-dimercaptosuccinic acid as a potential therapy for cystinuria

Children with fully recessive (Type I/I) cystinuria have a high risk of stone formation in the first decade of life. To assess the tendency for cystine to precipitate in individual urine samples, we developed an in vitro assay in which radiolabelled cystine (4mM) was dissolved in urine at 37 degrees C after alkalization to pH 10. Samples were then brought to pH 5, cooled, and centrifuged. The % decrease in supernatant cpm was used as a measure of cystine precipitation (CP). CP varied widely among normal children (74%+/-34) whereas variability of repeated determinations on a single adult individual was modest (64%+/-3.3). The assay was used to compare various potential therapies for cystinuria. Precipitation of exogenous cystine from normal urine was strongly inhibited by addition of D-penicillamine (CP: 8%+/-3) or dimercaptosuccinic acid (DMSA) (CP: 5%+/-1), at urinary concentrations attained by standard oral doses of each drug. Mercaptopropionylglycine (MPG) was moderately effective (CP: 43%+/-9), whereas captopril was a weak inhibitor (CP: 63%+/-12). Precipitation of endogenous cystine (2191 micromol/L) from a cystinuric patient showed that DMSA and D-penicillamine were again highly effective compared to the other agents. In addition DMSA and penicillamine added to the same patient's urine reduced the free cystine by 50% (as measured by automated amino acid analyzer) whereas MPG and captopril had no effect. In conclusion, DMSA is comparable to D-penicillamine as an in vitro inhibitor.

Reversal of cadmium induced oxidative stress by chelating agent, antioxidant or their combination in rat

The influence of an antioxidant agent such as N-acetyl cysteine (NAC) or mannitol on the cadmium chelating ability of monoisoamyl 2,3-dimercaptosuccinate (MiADMS) was investigated in cadmium pre-exposed rats. This ester of 2,3-dimercaptosuccinic acid (DMSA), an accepted drug for lead poisoning, being lipophilic in nature was expected to be an efficient cadmium chelator. The treatment of cadmium intoxicated animals with MiADMS reversed cadmium induced increase in blood catalase, superoxide dismutase (SOD) and malondialdehyde (MDA), liver MDA and brain SOD and MDA levels but not the decrease in blood, liver brain reduced glutathione (GSH) and increase in oxidized glutathione (GSSG) levels, consistent with the lowering of tissue cadmium burden. The administration of NAC or mannitol reversed the cadmium induced alterations in blood and liver GSH, GSSG, blood catalase, SOD, MDA, liver SOD, MDA and brain MDA levels without lowering blood and tissue cadmium contents. However, treatments with the combination of MiADMS and NAC or MiADMS and mannitol reversed these alterations as well as reduced blood and tissue cadmium concentrations. The combined treatment with MiADMS and mannitol was better than that with MiADMS and NAC, and was significantly more effective in normalizing blood, liver GSH, GSSG, brain GSSG, and their GSH/GSSG ratios than that by either of them alone. The combined treatments also improved liver and brain endogenous zinc levels, which were decreased due to cadmium toxicity. The results suggest that the administration of an antioxidant during chelation of cadmium may provide beneficial effects by reducing oxidative stress without its cadmium removing ability.

Ascorbic Acid Supplementation Does Not Improve Efficacy of meso -Dimercaptosuccinic Acid Treatment in Lead-Exposed Suckling Rats

It was suggested that ascorbic acid as a natural chelating agent can influence lead toxicokinetics and improve chelating properties of dimercaptosuccinic acid (DMSA) in adult rats. In this paper potential benefits of ascorbic acid supplementation, alone or combined with DMSA, in decreasing lead retention in suckling rats were evaluated. Such data in young mammals are not available. L-Ascorbic acid (daily dose 650 mg/kg b.wt.) and/or DMSA (daily dose 91 mg/kg b.wt.) were administered orally to suckling Wistar rats either during ongoing 8-day oral lead exposure (as acetate; daily dose 2 mg lead/kg b.wt.) or after 3-day lead exposure (total dose 12 mg lead/kg b.wt.). Lead concentrations were analysed in the carcass (skeleton), liver, kidneys and brain by atomic absorption spectrometry. By ascorbic acid supplementation lead retention was not reduced under either lead exposure condition. Lead concentration was even increased in the carcass. Treatment with DMSA under both exposure conditions significantly reduced lead in all analysed tissues. Combined treatment with ascorbic acid and DMSA during ongoing lead exposure was substantially less effective than DMSA treatment alone, and did not affect DMSA efficacy when administered after lead exposure. It was concluded that ascorbic acid administered either during or after lead exposure in suckling rats has no beneficial effect on either lead retention or DMSA chelation effectiveness.

Metal chelators change the human sperm motility pattern

OBJECTIVE

To investigate the influence of zinc on the generation of motility.

DESIGN

Prospective study.

SETTINGS

Outpatient clinic of the Center of Dermatology and Andrology.

PATIENT(S)

Seventy-three patients and 10 sperm donors.

INTERVENTION(S)

Motile spermatozoa were isolated by swim-up and incubated for 1, 2, 4 or 6 hours with DL-penicillamine, 2,3-dimercaptopropan-1-sulfonate, and meso-2,3-dimercapto-succinimic acid at concentrations of 1, 10, and 100 micro mol/L.

MAIN OUTCOME MEASURE(S)

Motility was analyzed by means of computer-assisted semen analysis (CASA).

RESULT(S)

Significant dose-dependent changes in nonlinear motility, progressive motility, and velocity straight line (VSL) were observed. After only 1 hour of incubation, nonlinear motility decreased, and progressive motility and VSL increased. The percentage of immotile spermatozoa was not affected. Time-dependent changes in motility were observed on a significantly higher or lower level as compared to the control. Comparing the chelators after 2 hours revealed that DL-penicillamine showed the strongest effect on the sperm.

CONCLUSION(S)

The results imply that chelators can eliminate at least some part of the zinc from the flagellum. This zinc elimination appears to lead to comparable changes of the outer dense fibers as seen in vivo during epididymal maturation, finally resulting in improved motility.

Interaction of dimercaptosuccinic acid (DMSA) with angiotensin II on calcium mobilization in vascular smooth muscle cells

Dimercaptosuccinic acid (DMSA) was shown to lower blood pressure in rat models of arterial hypertension. Thus, there is evidence that-besides its chelating properties-DMSA has a direct vascular effect, e.g. through scavenging of reactive oxygen species (ROS). We speculated that, in addition, intracellular calcium mobilization may be involved in this action. Therefore, the present study examined the effects of DMSA on Ca(2+) mobilization in cultured vascular smooth muscle cells (VSMCs) from rat aorta. Intracellular free Ca(2+) concentration ([Ca(2+)](i)) was measured with fura-2 AM. In a first series of experiments DMSA, 10(-11) to 10(-6)M, induced an immediate dose-dependent up to 4-fold rise of [Ca(2+)](i) (P<0.001) which was almost completely blunted by the calcium channel blocker verapamil or the intracellular calcium release blocker TMB-8. In a second series of experiments, when VSMCs were exposed acutely to DMSA (10(-11) to 10(-6)M), the angiotensin (ANG) II (10(-8)M)-induced rise in [Ca(2+)](i) to 295+/-40nM was attenuated at the average by 49% independent of the dose of DMSA. Preincubation of VSMCs with DMSA (10(-6)M) for 60min reduced basal [Ca(2+)](i) by 77% (P<0.001) and dose-dependently attenuated the ANG II (10(-8)M)-induced rise in [Ca(2+)](i) between 28 and 69% at concentrations between 10(-9) and 10(-5)M DMSA, respectively (P<0.05 and <0.01). In the presence of TMB-8, which attenuated the ANG II (10(-8)M)-induced rise in [Ca(2+)](i) by 66%, DMSA (10(-6)M) had no additional suppressive effect on [Ca(2+)](i). The results suggest that DMSA acutely raises [Ca(2+)](i) by stimulating transmembrane calcium influx via L-type calcium channels and by calcium release from intracellular stores followed by a decrease in [Ca(2+)](i) probably due to cellular calcium depletion. Thus, in addition to its action as scavenger of ROS, which in part mediate the vasoconstrictor response, e.g. to ANG II, DMSA may exert its hypotensive effect through decreasing total cell calcium, thereby attenuating the vasoconstrictor-induced rise in [Ca(2+)](i) in VSMCs.

Combined efficacies of lipoic acid and meso-2,3-dimercaptosuccinic acid on lead-induced erythrocyte membrane lipid peroxidation and antioxidant status in rats

One of the most intriguing phenomenon observed during lead toxicity has been attributed to lead-induced oxidative stress. The combined effect of DL-alpha-lipoic acid (LA) and meso-2,3-dimercaptosuccinic acid (DMSA) on lead-induced alterations in selected parameters, which are indicators of oxidative stress in erythrocytes, have been studied. Lead acetate (Pb, 0.2%) was administered in drinking water for 5 weeks to induce toxicity. LA (25 mg/ kg body weight per day i.p.) and DMSA (20 mg/kg body weight per day i.p.) were administered individually and also in combination during week 6. Clinical evidence of toxic exposure was evident from the elevated blood lead levels (BPb) along with lowered levels of haemoglobin (Hb) and haematocrit (Ht). Lead-exposed animals showed enhanced membrane lipid peroxidation (LPO) in the erythrocytes. Damage to the erythrocyte membrane was evident from the decline in the activities of the transmembrane enzymes, viz., Na+, K(+)-ATPase, Ca(2+)-ATPase and Mg(2+)-ATPase. Lead-exposed rats also suffered an onslaught on the antioxidant defence system witnessed by lowered activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and reduced glutathione (GSH). Serum glutamic-oxoloacetic transaminase (SGOT) and serum glutamic-pyruvic transaminase (SGPT) were also elevated in lead-exposed rats. Treatment with either LA or DMSA reversed the lead-induced biochemical disturbances encountered by the erythrocytes, but combined treatment with LA and DMSA was very effective in mitigating all the parameters indicative of oxidative stress.

Effects of dietary lead and/or dimercaptosuccinic acid exposure on regional serotonin and serotonin metabolite content in rainbow trout (Oncorhynchus mykiss)

The lead (Pb) chelator, meso-2,3-dimercaptosuccinic acid (DMSA) may be effective in reversing some of the adverse effects of Pb exposure. Pb-induced behavioral deficits observed in fish are due to disruptions in the integrative functioning of the medulla, cerebellum, and optic tectum. Pb exposure increased serotonin (5-HT) content in all three brain regions without an effect on 5-hydroxy-3-indoleacetic acid (5-HIAA). Pb exposure followed by no Pb in the diet increased 5-HT and 5-HIAA content in all three brain regions. The replacement of dietary Pb with DMSA had no effect on 5-HT and increased 5-HIAA content. DMSA increased 5-HIAA content in all three brain regions and increased 5-HT content only the optic tectum. Treatment with DMSA may be more effective than removal of Pb from the diet in reversing Pb-induced alterations in 5-HT.

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 role of oxidative stress in the in vitro induction of micronuclei by pesticides in mouse lung fibroblasts

The involvement of the antioxidant enzymes catalase and glutathione peroxidase (both at 0.1 mg/ml) in defence against the genotoxicity of phosphamidon (80 microg/ml) and dieldrin (25 microM) was investigated in order to demonstrate that the two pesticides damage DNA through the generation of reactive oxygen species and therefore of oxidative stress. The pesticide genotoxicity was determined by the cytokinesis-block micronucleus test performed on primary mouse lung fibroblast cultures. Also, 3-aminotriazole (40 mM) and mercaptosuccinate (0.5 mM), inhibitors of catalase and glutathione peroxidase, respectively, were added to the cultures. Data indicate that catalase causes a decrease only in the damage induced by phosphamidon, while glutathione peroxidase protects against damage induced by both phosphamidon and dieldrin. Simultaneous treatment with antioxidant inhibitors and pesticides results in a decrease in micronucleus frequency and cell number, due to apoptotic death. Our results indicate that clastogenic DNA damage produced by the two pesticides is modulated by antioxidant enzymes and their inhibitors and thus could be due to oxidative stress induction.

The efficacy of monoisoamyl ester of dimercaptosuccinic acid in chronic experimental arsenic poisoning in mice

The therapeutic efficacy of monoisoamyl meso-2,3-dimercaptosuccinic acid (MiADMSA), a new monoester of 2,3-dimercaptosuccinic acid on arsenic induced oxidative stress in liver and kidneys, alterations in hematopoietic system and depletion of arsenic burden was assessed, in mice. Three different doses of MiADMSA (25, 50 or 100 mg/kg) for five consecutive days were administered in chronically arsenic exposed mice (10 ppm in drinking water for six months). Oral administration of MiADMSA particularly at a dose of 50 mg/kg, produced relatively more pronounced beneficial effects on the inhibited blood delta-aminolevulinic acid dehydratase (ALAD), biochemical variables indicative of hepatic and renal oxidative stress and depletion of arsenic concentration in blood, liver and kidneys, compared with intraperitoneal administration of the drug. The treatment with MiADMSA although, produced essential metals imbalance which could be a restrictive factor for the possible therapeutic use of this compound in chronic arsenic poisoning and thus require further exploration.

Arsenic uptake by native fern species in Thailand: effect of chelating agents on hyperaccumulation of arsenic by Pityrogramma calomelanos

Nineteen native fern species collected from an area in Thailand with high arsenic concentration in soil and in ground water as a result of tin mining was screened for elevated arsenic concentration in fronds. Two species of fern were found to contain elevated arsenic in their fronds in nature: Pityrogramma calomelanos (108-1156 microg g(-1) dried weight) and Pteris vittata (79 microg g(-1) dried weight). Under hydroponic culture Pityrogramma calomelanos (a silver back fern) accumulated arsenic in its shoot at rate of 4616 microg(-1) (dried weight). The accumulation of arsenic in Pityrogramma calomelanos shoot doubled with the addition of an EDTA (Ethelenediamine tetraacetic acid) chelating agent. The highest accumulation occurred 6 weeks after exposure to 10 mg L(-1) arsenic as disodium hydrogen arsenate. The addition of another chelating agent, DMS (Dimercaptosuccinic acid), resulted in a 5-fold decrease in arsenic concentration in the Pityrogramma calomelanos shoot compared to control after 6 weeks of exposure to arsenic. The contrasting effect of the EDTA and DMSA chelating agent was attributed to the strong binding of the thiol group to arsenic ion. This study indicated that Pityrogramma calomelanos uptake and translocate arsenic in the form of arsenate and arsenite rather than the As-DMSA complex. Using phytoextraction efficiency calculations, it was determined that Pityrogramma calomelanos gave the highest arsenic phytoextraction efficiency at 6 weeks after exposure to arsenic in the EDTA treatment, with an efficiency of 77.8 mg As based on whole plant biomass.

Reversal of lead-induced oxidative stress by chelating agent, antioxidant, or their combination in the rat

The influence of N-acetyl cysteine (NAC), an antioxidant, on the therapeutic efficacy of meso-2,3-dimercaptosuccinic acid (DMSA), a hydrophilic, and its ester, monoisoamyl 2,3-dimercaptosuccinate (MiADMS), a lipophilic, both soft tissue lead mobilizers, was investigated in lead-preexposed rats. The subsequent treatment of lead-exposed animals with DMSA, MiADMS, or NAC reversed the lead-induced alterations in blood delta-aminolevulinic acid dehydratase, catalase, malondialdehyde (MDA), reduced glutathione, oxidized glutathione, and brain MDA levels. The combined treatment with DMSA and NAC was more effective than that with MiADMS and NAC in enhancing the restoration of all these parameters indicative of lead-induced oxidative stress. These reversals were consistent with the lead-removing ability of DMSA and MiADMS but not that of NAC. As the reversal of these parameters by NAC was independent of its lead-mobilizing capability, this ought to be mainly due to its strong antioxidant property. The increase in blood and brain zinc levels upon lead exposure appears to be the result of the redistribution of endogenous zinc due to lead. Subsequent treatment with DMSA, MiADMS, NAC, or their combination decreased the brain zinc as its excretable complexes with a transient increase in blood zinc level. The ideal treatment of lead poisoning seems to be a combination of a lead chelator and an antioxidant.

Lipoic acid in combination with a chelator ameliorates lead-induced peroxidative damages in rat kidney

The deleterious effect of lead has been attributed to lead-induced oxidative stress with the consequence of lipid peroxidation. The present study was designed to investigate the combined effect of DL-alpha-lipoic acid (LA) and meso-2,3-dimercaptosuccinic acid (DMSA) on lead-induced peroxidative damages in rat kidney. The increase in peroxidated lipids in lead-poisoned rats was accompanied by alterations in antioxidant defence systems. Lead acetate (Pb, 0.2%) was administered in drinking water for 5 weeks to induce lead toxicity. LA (25 mg/kg body weight per day i.p.) and DMSA (20 mg/kg body weight per day i.p.) were administered individually and also in combination during the sixth week. Nephrotoxic damage was evident from decreases in the activities of gamma-glutamyl transferase and N-acetyl beta- D-glucosaminidase, which were reversed upon combined treatment with LA and DMSA. Rats subjected to lead intoxication showed a decline in the thiol capacity of the cell, accompanied by high malondialdehyde levels along with lowered activities of catalase, superoxide dismutase, glutathione peroxidase and glutathione metabolizing enzymes (glutathione reductase, glucose-6-phosphate dehydrogenase, glutathione- S-transferase). Supplementation with LA as a sole agent showed considerable changes over oxidative stress parameters. The study has highlighted the combined effect of both drugs as being more effective in reversing oxidative damage by bringing about an improvement in the reductive status of the cell.

Meso 2,3-dimercaptosuccinic acid (DMSA) and monoisoamyl DMSA effect on gallium arsenide induced pathological liver injury in rats

The effect of meso 2,3-dimercaptosuccinic acid (DMSA) and monoisoamyl DMSA (MiADMSA) on gallium arsenide (GaAs) induced liver damage was studied. The oral feeding rat model was used in this study. The animals were exposed to 10 mg/kg GaAs, orally, once daily, 5 days a week for 24 weeks and treated thereafter with single oral daily dose of either 0.3 mmol/kg DMSA or MiADMSA for two course of 5 days treatment. The animals were sacrificed thereafter. Lipid peroxidation was assessed by measuring liver thiobarbituric acid reactive substance (TBARS). Liver damage was assessed by number of biochemical variables and by light microscopy. The activity of superoxide dismutase (SOD) and delta-aminolevulinic acid dehydratase (ALAD) beside reduced glutathione (GSH) concentration was measured in blood. Exposure to GaAs produced a significant reduction in GSH while, increased the oxidized glutathione (GSSG) concentration. Hepatic glutathione peroxidase (GPx) and catalase activity increased significantly while level of serum transaminase increased moderately. Gallium arsenide exposure also produced marked hepatic histopathological lesions. Overall, treatment with MiADMSA proved to be better than DMSA in the mobilization of arsenic and in the turnover of some of the above mentioned GaAs sensitive biochemical alterations. Histopathological lesions also, responded more favorably to chelation treatment with MiADMSA than DMSA.

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 microM 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 microM 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 microM 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.

Anti microbial activity of dimercaptosuccinic acid (DMSA): a new chelating agent

Successful outcome of endodontic treatment depends on elimination of bacteria and their products present in the root canal. It has been reported that after careful chemicomechanical preparation, smear layer is formed on the walls of canal, which contains bacteria and their products. Chelating agents, when used during chemicomechanical preparation, remove the smear layer. DMSA--a new chelating agent, when used in root canals, removes the smear layer more than EDTA when used as irrigant in root canals. This study was conducted to determine whether DMSA has anti microbial activity and compare it with EDTA. The results show that EDTA (10% & 15%) had marked anti microbial activity, both on culture plates and in broth. DMSA (10% & 15%) did not show anti microbial activity on culture plates while in broth it had marked activity.

Effect of L-arginine, dimercaptosuccinic acid (DMSA) and the association of L-arginine and DMSA on tissue lead mobilization and blood pressure level in plumbism

Lead (Pb)-induced hypertension is characterized by an increase in reactive oxygen species (ROS) and a decrease in nitric oxide (NO). In the present study we evaluated the effect of L-arginine (NO precursor), dimercaptosuccinic acid (DMSA, a chelating agent and ROS scavenger), and the association of L-arginine/DMSA on tissue Pb mobilization and blood pressure levels in plumbism. Tissue Pb levels and blood pressure evolution were evaluated in rats exposed to: 1) Pb (750 ppm, in drinking water, for 70 days), 2) Pb plus water for 30 more days, 3) Pb plus DMSA (50 mg kg(-1) day(-1), p.o.), L-arginine (0.6%, in drinking water), and the combination of L-arginine/DMSA for 30 more days, and 4) their respective matching controls. Pb exposure increased Pb levels in the blood, liver, femur, kidney and aorta. Pb levels in tissues decreased after cessation of Pb administration, except in the aorta. These levels did not reach those observed in nonintoxicated rats. All treatments mobilized Pb from the kidney, femur and liver. Pb mobilization from the aorta was only effective with the L-arginine/DMSA treatment. Blood Pb concentrations in Pb-treated groups were not different from those of the Pb/water group. Pb increased blood pressure starting from the 5th week. L-arginine and DMSA treatments (4th week) and the combination of L-arginine/DMSA (3rd and 4th weeks) decreased blood pressure levels of intoxicated rats. These levels did not reach those of nonintoxicated rats. Treatment with L-arginine/DMSA was more effective than the isolated treatments in mobilizing Pb from tissues and in reducing the blood pressure of intoxicated rats.

The effects of elevated blood lead levels and succimer chelation therapy on physical growth in developing rhesus monkeys

Seventy-two female rhesus monkeys were randomly assigned to three lead exposure conditions (none, birth to 1 year, birth to 2 years). In a completely crossed design, the lead-exposed and control monkeys were randomized to placebo or chelation therapy which began at 1 year of age. Dosing was conducted daily beginning on day 8 postpartum. The lead dose levels were adjusted biweekly to gradually elevate the blood lead level of each monkey to a target of 1.69-1.93 micromol/L (35-40 microg/dL). Succimer (or placebo) was administered orally (30 mg/kg/day for 5 days and 20 mg/kg/day for 14 additional days) for a total 19-day treatment regimen. There were two separate chelation regimes at 53 and 65 weeks of age. Succimer therapy in combination with lead abatement reduced blood lead levels significantly faster than lead abatement alone; however, that advantage disappeared once succimer therapy was discontinued. Weight, crown-rump length, and head circumference were measured regularly. Growth in weight, length, and head circumference did not vary significantly as a function of blood lead levels. Succimer chelation therapy did not significantly affect weight, length, or head circumference through 2 years of age.

Effects of Lewisite on cell membrane integrity and energy metabolism in human keratinocytes and SCL II cells

Lewisite is a highly toxic arsenic compound which can cause skin damage. In the present study effects of Lewisite on cell membrane integrity and energy metabolism as well as antidotal effects of DL-2,3-dimercaptopropanesulfonate (DMPS), and meso-2,3-dimercaptosuccinic acid (m-DMSA) were investigated in a keratinocyte derived cell line (SCL II) and primary human keratinocytes (HK). Cells were incubated in Lewisite (60 microM) containing medium for 5 min. During the following 6 h lactate dehydrogenase (LDH) activity in the supernatant, intracellular ATP content, tetrazolium reduction, glucose consumption and lactate formation were measured. Glucose consumption and lactate production were decreased in both cell lines after Lewisite exposure. In SCL II cells an increase of LDH activity in the supernatant, a decrease of ATP content, and an impaired ability to reduce tetrazolium was found 3 h after Lewisite exposure. In HK cultures tetrazolium reduction was significantly decreased already after 2 h, whereas LDH increase in the supernatant and ATP content decrease occurred only at 6 h after Lewisite exposure. When DMPS or m-DMSA was added directly after Lewisite exposure to SCL II cells, glucose consumption and lactate formation were restored and LDH leakage was prevented. SCL II cells might be more prone to membrane damage whereas in keratinocytes mitochondrial impairment seems to be the predominant effect of Lewisite.

Oral succimer decreases the gastrointestinal absorption of lead in juvenile monkeys

Although succimer (Chemet, meso-2,3-dimercaptosuccinic acid, DMSA) is considered to be a safe and effective chelating agent for the treatment of lead poisoning in humans, there is concern that it may increase the gastrointestinal (GI) absorption and retention of Pb from exposures suffered concurrent with treatment. This concern is justified because the availability of Pb-safe housing during outpatient treatment with oral succimer is limited. We used a juvenile nonhuman primate model of moderate childhood Pb intoxication and a sensitive double stable Pb isotope tracer methodology to determine whether oral succimer chelation affects the GI absorption and whole-body retention of Pb. Infant rhesus monkeys (n = 17) were exposed to Pb daily for 1 year postpartum to reach and maintain a target blood lead (BPb) level of 35-40 microg/dL. Animals were administered succimer (n = 9) or vehicle (n = 8) over two successive 19 day succimer treatment regimens beginning at 53 and 65 weeks of age. The present study was conducted over the second chelation regimen only. Animals received a single intravenous (iv) dose of stable (204)Pb tracer (5 microg, 24.5 nmol) followed by a single oral dose of stable (206)Pb tracer (72.6 microg, 352 nmol) immediately before chelation, in order to specifically evaluate GI Pb absorption and whole-body Pb retention with treatment. We collected complete urine and fecal samples over the first 5 days and whole blood over the first 8 days of treatment for analyses of stable Pb isotopes using magnetic sector inductively-coupled plasma mass spectrometry. Results indicate that succimer significantly reduced the GI absorption of Pb (vehicle, 64.9% +/- 5.5; succimer, 37.0% +/- 5.8; mean +/- SEM). Succimer also significantly increased the urinary excretion of endogenous Pb by approximately 4-fold over the vehicle treatment, while endogenous fecal Pb excretion was decreased by approximately 33%. Finally, although succimer reduced the whole-body retention of endogenous Pb by approximately 10% compared to vehicle, the majority (77%) of the administered internal dose of Pb tracer was retained in the body when assessed after 5 days of treatment. These data do not support the concern that succimer treatment increases GI Pb absorption.

Mobilization and detoxification of polonium-210 in rats by 2,3-dimercaptosuccinic acid and its derivatives

PURPOSE

To reduce retention and toxicity of the alpha particle emitter polonium-210 in rats by newly developed chelating agents.

MATERIALS AND METHODS

Repeated subcutaneous chelation was conducted after intravenous injection of 210Po nitrate. For reduction of 210Po retention the treatment with vicinal dithiols meso-and rac-2,3-dimercaptosuccinic acid (DMSA), mono-i-amylmeso-2,3-dimercapto succinate (Mi-ADMS) and mono-N-(i-butyl)-meso-2,3-dimercapto succinamide (Mi-BDMA) were used. For the reduction of toxic effects of 210Po, treatment effectiveness of Mi-BDMA was compared with that of N,N'-di(2-hydroxyethyl)ethylenediamine-N,N'-biscarbodithioate (HOEtTTC, reference compound).

RESULTS

Treatment with meso-DMSA and rac-DMSA altered the main excretion route of 210Po, reduced its contents in the liver but increased its deposition in the kidneys. Treatment with Mi-ADMS or Mi-BDMA increased total excretion of 210Po, mainly via the faeces. Only Mi-BDMA decreased 210Po levels in the kidneys. The effectiveness of all chelators decreased with delay in the start of treatment. In a survival study, the lives of rats treated early with Mi-BDMA or delayed with HOEtTTC were prolonged three-fold when compared with rats receiving a lethal amount of 210Po only.

CONCLUSIONS

Of the vicinal dithiols examined, Mi-BDMA was the best mobilizing chelating agent for 210Po and it reduced 210Po toxicity when the treatment started immediately. However, the detoxification efficacy of the immediate treatment with HOEtTTC, observed in our previous study, was superior to that of the present result with Mi-BDMA.

Galactosylated liposomes as carriers for targeting meso-2,3-dimercaptosuccinic acid to cadmium storage sites in cadmium exposed mice

In this study an attempt has been made to examine the efficacy of meso-2,3-dimercaptosuccinic acid (DMSA) using galactosylated liposomes as carriers for mobilization of cadmium from the body of mice preexposed to cadmium chloride (0.005 mmoles/kg intraperitoneally daily for 4 days). Cadmium-exposed mice after a rest period of 8 weeks were administered DMSA intravenously, two injections 15 micromoles/kg with an interval of 48 h, as free form of DMSA, or DMSA encapsulated in liposomes composed of phosphatidyl choline, cholesterol and phosphatidyl ethanolamine (7:2:1; PC-lip-DMSA) or in liposomes to which p-aminophenyl galactoside had been anchored (Gal-lip-DMSA). Excretion of cadmium through urine and feces was monitored for 5 days. Thereafter animals were sacrificed, liver, kidneys, spleen and isolated hepatocytes were analysed for cadmium, copper and zinc concentration. Efficacy for cadmium mobilization from the body was found to be in the order Gal-lip-DMSA>PC-lip-DMSA>DMSA. These results show that liposomes can be used as targeted carrier system for chelating agents safely and efficiently as compared to administration of free chelating agent.

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.

Effect of thiamine on the cadmium-chelating capacity of thiol compounds

The influence of thiamine on the efficacy of meso-2,3-dimercaptosuccinic acid (DMSA), diethyldimercapto succinate (DEDMS), alpha mercapto-beta-(2-furyl) acrylic acid (MFA) and alpha-mercapto-beta-(2-thienyl) acrylic acid (MTA) to mobilize cadmium and reverse cadmium-induced biochemical alterations was investigated in cadmium-exposed rats. The thiamine coadministration enhanced the efficacy of MFA and MTA in reducing hepatic and renal burden of cadmium and that of DMSA and DEDMS in mobilizing hepatic cadmium. It also improved the efficacy of DMSA, DEDMS and MFA in reversing the cadmium-induced increase in urinary alkaline phosphatase and aspartate and alanine amino transaminases. The combined treatment with thiamine and DMSA or MFA restricted the urinary loss of zinc and that with thiamine and DEDMS reduced the loss of fecal copper, a general effect of chelation. In conclusion, the administration of thiamine during chelation therapy in cadmium poisoning may be beneficial and more effective than thiol chelating agents alone, which needs to be confirmed in humans.

Succimer and the reduction of tissue lead in juvenile monkeys

The extent to which succimer (2,3-dimercaptosuccinic acid, DMSA) chelation reduces target organ lead (Pb) levels, including the skeleton, relative to the cessation of Pb exposure is a primary consideration in evaluating its efficacy for reducing toxicity in children. Here, we utilized a rhesus monkey model of childhood Pb exposure and a sensitive stable (204)Pb isotope tracer methodology to determine the efficacy of succimer for reducing Pb in blood, liver, and skeletal tissues from chronic (>/=1 year) versus short-term (3-4 days) Pb exposures. Specific attention was paid to the efficacy of succimer treatment compared to the cessation of Pb exposure. Infant rhesus monkeys (n = 48) were exposed to Pb daily for 1 year or >1 year postpartum to reach and maintain a target blood Pb level of 35-40 microg/dL. Two successive 19-day succimer treatment regimens were administered at 53 and 65 weeks of age (30 mg/kg/day x 5 days followed by 20 mg/kg/day x 14 days). Blood was collected over the course of treatment, and liver and bone biopsy samples were collected on days 0, 5, and 20, relative to the start of treatment (day 0). Complete 24-h urine collections were conducted over the course of treatment. Results of the first chelation indicate that a single regimen of succimer treatment led to significant reductions in blood and liver Pb levels, relative to the placebo group. However, the cessation of Pb exposure alone (i.e., placebo) also led to significant reductions in blood and liver compared to pretreatment levels. Neither succimer nor the cessation of Pb exposure had a significant impact on bone lead levels. Blood Pb levels in the succimer-treated group rebounded within 5 days after treatment ended, becoming comparable with levels in the placebo group from that point on. Results from the second chelation indicate that succimer treatment is essentially equally efficacious in reducing blood Pb at moderate (20 microg/dL) levels where exposures ended >3 months previously and more elevated (40-50 microg/dL) levels where exposures ended just prior to treatment, relative to the placebo treatment. Finally, similar overall outcomes were observed for tissue Pb from recent exposures (i.e., (204)Pb tracer levels), indicating little or no apparent difference in the chelation of Pb from recent (3-4 days) versus long-term exposures. These data demonstrate that succimer does not reduce skeletal Pb levels, and they show that the efficacy of succimer for reducing blood Pb levels does not persist beyond the completion of treatment due to posttreatment rebounds in blood Pb from endogenous sources. They also demonstrate the relative benefit of eliminating Pb exposures, which serves to underscore the importance of primary prevention of Pb exposure. The extent to which these data reflect the efficacy of succimer for reducing neurocognitive impairment is not yet known, although those data are forthcoming.