Mobilization of aged in vivo cadmium deposits by diethyl dimercaptosuccinate

Metal-Induced Pulmonary Fibrosis

PURPOSE OF REVIEW

The incidence of pulmonary fibrosis is increasing worldwide and may, in part, be due to occupational and environmental exposures. Secondary fibrotic interstitial lung diseases may be mistaken for idiopathic pulmonary fibrosis with important implications for both disease management and prognosis. The purposes of this review are to shed light on possible underlying causes of interstitial pulmonary fibrosis and to encourage dialogue on the importance of acquiring a thorough patient history of occupational and environmental exposures.

RECENT FINDINGS

A recent appreciation for various occupational and environmental metals inducing both antigen-specific immune reactions in the lung and nonspecific "innate" immune system responses has emerged and with it a growing awareness of the potential hazards to the lung caused by low-level metal exposures. Advancements in the contrast and quality of high-resolution CT scans and identification of histopathological patterns of interstitial pulmonary fibrosis have improved clinical diagnostics. Moreover, recent findings indicate specific hotspots of pulmonary fibrosis within the USA. Increased prevalence of lung disease in these areas appears to be linked to occupational/environmental metal exposure and ethnic susceptibility/vulnerability. A systematic overview of possible occupational and environmental metals causing interstitial pulmonary fibrosis and a detailed evaluation of vulnerable/susceptible populations may facilitate a broader understanding of potential underlying causes and highlight risks of disease predisposition.

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.

Arsenic-induced changes in certain neurotransmitter levels and their recoveries following chelation in rat whole brain

Arsenic as sodium arsenite (100 ppm in drinking water) was administered to male rats for 16 weeks. Animals were then treated either with meso-2,3-dimercaptosuccinic acid (DMSA), sodium 2,3-dimercaptopropane 1-sulfonate (DMPS), dimethyl DMSA (DmDMSA), or diisopropyl DMSA (DiPDMSA) twice daily (50 mg/kg) intraperitoneally for 5 days. After 5 days of rest period, the animals were again given a second course of chelation therapy. The animals were sacrificed subsequently for the determination of whole brain biogenic amines levels, acetylcholinesterase (AChE), monoamine oxidase (MAO) and delta-aminolevulinic acid dehydratase (ALAD) activities. A number of biochemical parameters and arsenic concentrations in some tissues were also determined. The results suggest a significant increase in brain arsenic concentration accompanied by alterations in neurotransmitters levels following As(III) exposure. Although chelation treatment was effective in reducing As burden, the altered biochemical variables responded less favorably to chelation therapy. The DMSA-diesters, particularly DiPDMSA, produced a more pronounced increase in brain arsenic burden, as well as alterations in a few neurotransmitters. It can be concluded that the lipophilic character of As antidotes may lead to unfavorable results following intraperitoneal administration.

Therapeutic efficacy of new dimercaptosuccinic acid (DMSA) analogues in acute arsenic trioxide poisoning in mice

The therapeutic efficacy of six newly synthesized analogues of dimercaptosuccinic acid (DMSA) was investigated in acute arsenic trioxide poisoning in mice. Meso-2,3-di(acetylthio)succinic acid (DATSA) and meso-2,3- di(benzoylthio)succinic acid (DBTSA) are analogues of DMSA with protected thiol groups ("prodrugs"), and DMDMS, DEDMS, DnPDMS, and DiPDMS are various di-esters of DMSA with methyl, ethyl, n-propyl, and isopropyl alcohols, respectively. Thirty minutes after s.c. injection of an LD80 of arsenic trioxide (65 mumol/kg) male NMRI mice were treated with a single equimolar dose (0.7 mmol/kg) of DMSA i.p. or one of the analogues i.p. or via gastric tube (i.g.). Control animals received arsenic trioxide and saline 30 min later. The survival rate was recorded for 30 days. All of the animals treated with DMSA i.p. survived and all controls died within 2 days. Administered i.g., DATSA and DBTSA increased the survival rate to 29% and 43%, and injected i.p. to 86%. Treatment with DMDMS i.p. and i.g., and with DEDMS, DnPDMS, and DiPDMS i.g. did not reduce lethality. Given i.p., DnPDMS increased the survival rate to 72%, and DEDMS and DiPDMS to 86%, respectively. To investigate the efficacy of the DMSA analogues in reducing the tissue content of arsenic, male NMRI mice received an s.c. injection of an LD5 of arsenic trioxide containing a tracer dose of 73-As(III) (42.5 mumol/kg body wt). Thirty minutes later, saline (controls) or a single equimolar dose (0.7 mmol/kg) of DMSA i.p., or one of the analogues i.p. or i.g. was administered. The arsenic content of various organs (blood, liver, kidneys, heart, lungs, spleen, small intestine, large intestine, brain, testes, skeletal muscle, and skin) at 30 min, 2 h, 4 h, 6 h, and 8 h after the arsenic injection was measured using a gamma counter.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Human studies with the chelating agents, DMPS and DMSA

Meso-2,3-dimercaptosuccinic acid (DMSA) is bound to plasma albumin in humans and appears to be excreted in the urine as the DMSA-cysteine mixed disulfide. The pharmacokinetics of DMSA have been determined after its administration to humans po. For the blood, the tmax and t1/2 were 3.0 h + 0.45 SE and 3.2 h + 0.56 SE, respectively. The Cmax was 26.2 microM + 4.7 SE. To determine whether dental amalgams influence the human body burden of mercury, we gave volunteers the sodium salt of 2,3-dimercaptopropane-1-sulfonic acid (DMPS). The diameters of dental amalgams of the subjects were determined to obtain the amalgam score. Administration of 300 mg DMPS by mouth increased the mean urinary mercury excretion of subjects over a 9 h period. There was a positive correlation between the amount of mercury excreted and the amalgam score. DMPS might be useful for increasing the urinary excretion of mercury and thus increasing the significance and reliability of this measure of mercury exposure. DMSA analogs have been designed and synthesized in attempts to increase the uptake by cell membranes of the DMSA prototype chelating agents. The i.v. administration of the monomethyl ester of DMSA, the dimethyl ester of DMSA or the zinc chelate of dimethyl DMSA increases the biliary excretion of platinum and cadmium in rats.

Antidotal effects of dimercaptosuccinic acid

Dimercaptosuccinic acid (DMS), HOOC-CH(SH)-CH(SH)-COOH, was first developed in China as an effective antidote for poisoning from many heavy metals, such as Pb, Hg, As, Cd, Sb, Tl, Au, Zn, Ni, Pt, Ag, Co and Sn. DMS increases the excretion of Ce, Pm, Sr and Po from the body. Hundreds of patients suffering from hepatolenticular degeneration (Wilson's disease) have been treated successfully with DMS. Recently, DMS was found to be effective also in treating certain non-metallic intoxications, like some of the new non-phosphate pesticides and mushroom poisonings.

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.

Effect of chelating agent structure on the mobilization of cadmium from intracellular deposits

An examination of the efficacy of several structural types of chelating agents in the removal of cadmium from its intracellular deposits in mouse liver and kidneys reveals that of the structural types examined, only dithiocarbamates and a vicinal dithiol were able to mobilize cadmium from such intracellular sites. Esters of L-cysteine, a macrocyclic thioether, and a disulfide of a dithiocarbamate were unable to cause any appreciable decrease in either renal or hepatic cadmium levels. Charged groups such as carboxylic acid groups reduce the efficacy as well as the toxicity of the structural types that can otherwise mobilize such cadmium. It was also found that the administration of a cadmium-binding polymer ip leads to only a very slight net excretion of cadmium, while the po administration of this polymer leads to no net additional cadmium excretion. Of the compounds newly reported here, some are approximately equal in cadmium-mobilizing efficacy to the most effective of previously reported compounds.

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.

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

The esters of the general structure, [CH(SH)COOR]2, i.e., Di-BDMS, R = CH2CH(CH3)2; Ds-BDMS, R = CH(CH3)CH2CH3; Di-ADMS, R = CH2CH2CH(CH3)2; and D3-ADMS, R = CH(CH2CH3)2 from the reaction of meso-2,3-dimercaptosuccinic acid with isobutyl, sec-butyl, isoamyl, and 3-amyl alcohols, respectively, have been prepared, characterized, and examined as chelating agents for the removal of cadmium from its aged intracellular deposits. All of these compounds depleted cadmium from such deposits and significantly reduced the whole body levels of cadmium. In the case of three (Ds-BDMS, Di-BDMS, and Di-ADMS) of these compounds, the reductions achieved are equal to or greater than that produced by 2,3-dimercapto-1-propanol (BAL) under similar circumstances. None of these compounds caused any redistribution of cadmium to the brain, and two of them (Di-BDMS and Di-ADMS) caused a very much larger reduction in the liver levels of cadmium than BAL. None was as effective as BAL in reducing kidney levels of cadmium. These compounds are not soluble in water and are administered as solutions in peanut oil. A comparison of the behavior of these compounds with others which have been reported to be effective in reducing body burdens of cadmium in chronic cadmium intoxication reveals that they are among the most effective. An analysis of the manner in which mobilizing efficacy changes with structure indicates that higher, purely alkyl analogs are not expected to be superior to these compounds, though other structural variations may be.

Comparative mobilization of lead by chelating agents

The relative abilities of approximately 20 chelating agents to act as antagonists for acute and chronic lead poisoning have been examined in the mouse. The acute LD50 for lead acetate trihydrate was determined and found to be 135.3 mg Pb/kg for i.p. injection with a 95% confidence interval of 87.1-210.3 mg Pb/kg. The relative efficacy of chelating agents to reduce liver, kidney, spleen, bone and brain levels of lead was determined. The movement of lead from the liver to the bone was followed during the first 7 days post injection and was found to result in appreciable changes in the lead levels of these organs from day to day during this entire period. Of the compounds examined, the ones which were most effective in mobilizing lead under various conditions included meso-2,3-dimercaptosuccinic acid (DMSA), sodium 2,3-dimercaptopropane-1-sulfonate (DPMS), disodium calcium ethylene-diaminetetraacetate (Na2CaEDTA), trisodium zinc triethylenetetraminehexa-acetate, dicalcium ethylenediaminetetra(methylenephosphonate) (Ca2EDTPO) and diethyl dimercaptosuccinate (DEMSA) and 2,3-dimercapto-1-propanol (BAL).

Esters of meso-dimercaptosuccinic acid as cadmium-mobilizing agents

The dimethyl, diethyl, di-n-propyl, diisopropyl (Di-PDMS), and di-n-butyl esters of meso-2,3-dimercaptosuccinic acid were prepared by esterification of the parent acid and were subsequently purified and characterized. Their relative ability to mobilize cadmium from its aged (greater than 30 days) deposits was evaluated in mice in comparison with 2,3-dimercapto-1-propanol (BAL). All but the dimethyl ester were superior to BAL in reducing the hepatic cadmium levels, though none was superior in reducing renal cadmium levels. Their efficacy in reducing hepatic cadmium levels had the result that all except the dimethyl ester were significantly more effective than BAL in reducing total cadmium body burdens in mice. The most effective of these compounds, Di-PDMS, caused a reduction of whole body cadmium of 59% (i.e., to 41% of control values) under conditions where the corresponding reduction found for BAL was only 18% (i.e., to 82% of control value). The predominant route of excretion of cadmium subsequent to administration of these compounds is via the fecal route (greater than 99%). A synergistic effect was found in the reduction of whole body and kidney cadmium burdens when Di-PDMS was used in combination with trisodium calcium diethylenethriaminepentaacetate.