Interaction study of monoisoamyl dimercaptosuccinic acid with bovine serum albumin using biophysical and molecular docking approaches

Monoisoamyl 2,3-dimercaptosuccinic acid (MiADMSA), a lipophilic chelator has been evaluated for its potential use as an antidote in arsenic poisoning. The pharmacokinetics and pharmacodynamics properties of a drug could be understood via study its mechanism of interaction with bovine serum albumin protein (BSA). Therefore, the interaction between MiADMSA with BSA was investigated using various spectroscopic techniques and computational methods. Linear quenching of BSA intrinsic fluorescence intensity with the increasing concentration of MiADMSA was observed in the fluorescence study. Furthermore, synchronous results revealed that MiADMSA slightly changed the conformation of BSA. The binding constant value of the BSA-MiADMSA complex was found 1.60 × 104 M-1 at 298 K. The value of thermodynamic parameters ΔG, ΔH, and ΔS described that the process is spontaneous, endothermic, and hydrophobic forces are involved in the interaction of MiADMSA with BSA. Competitive site marker experiments showed that MiADMSA binds to site-II of BSA. Conformational changes of BSA with the interaction of MiADMSA were apparent by CD, UV-Visible, FT-IR, and 3D fluorescence spectroscopy. To strengthen the experimental findings we have also performed a theoretical study on the BSA-MiADMSA complex. Two sites were identified with docking score of - 6.642 kcal/mol at site IIa and - 3.80 kcal/mol for site IIb via molecular docking study. Molecular dynamics simulation study inferred the stability of the BSA-MiADMSA complex which was analyzed in a long simulation run. The experimental and computational studies have shown the effective binding of MiADMSA with BSA which is essential for the transportation and elimination of a drug from the body.

Chemoprotective effect of monoisoamyl 2, 3-dimercaptosuccinate (MiADMS) on cytokines expression in cadmium chloride treated human lung cells

Cadmium is commercially profitable element, but it causes toxicity in humans and animals leading to diseases in various organs. The main route of cadmium exposure to humans is through inhalation. Lungs respond to insult through secretion of cytokines. In this study, the chemoprotective effect of monoisoamyl 2, 3-dimercaptosuccinate (MiADMS) was evaluated on viability and cytokines expression in CdCl2 treated human lung A549 cells by cytokine array. Cells were treated with 0, 50, 75, and 100 µM CdCl2 alone, 300 µM MiADMS alone, and co-treated with 300 µM MiADMS and 75 µM CdCl2 for 24 h. The viability was measured by crystal violet dye. The level of cytokines in the cells' lysate and cell culture medium was measured using Ray Biotech's Human Cytokine Array 6 in control cells, 75 µM CdCl2 alone and MiADMS co-treated cells. Array results were validated by ELISA kit. The CdCl2 caused a dose dependent decrease in cell viability, while MiADMS co-treatment resulted in a significant increase in viability of CdCl2 treated cells. Morphology of the cells treated with CdCl2 was destroyed, while MiADMS restored the lost shape in CdCl2 treated cells. In addition, the cells co-treated with MiADMS and CdCl2 showed modulation of cytokines expression in comparison to the CdCl2 alone treated cells. The ELISA results showed the similar pattern of cytokine expression as Human Cytokine Array and validated the array results. These results clearly show the chemoprotective effect of MiADMS and suggest that MiADMS can be used as antidote at moderate dose against CdCl2 toxicity.

Alterations in apoptotic caspases and antioxidant enzymes in arsenic exposed rat brain regions: reversal effect of essential metals and a chelating agent

Arsenic (As) widely studied for its effects as a neurotoxicant. The present study was designed to evaluate the protective effect of calcium, zinc or monoisoamyl dimercaptosuccinic acid (MiADMSA), either individually or in combination on As induced oxidative stress and apoptosis in brain regions (cerebral cortex, hippocampus and cerebellum) of postnatal day (PND) 21, 28 and 3 months old rats. Arsenic exposure significantly decreased the activities of superoxide dismutase (SOD) isoforms, catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GR) with increase in glutathione s transferase (GST) while lipid peroxidation (LPx), arsenic levels, mRNA expression of caspase 3 and 9 were significantly increased in different brain regions. Arsenic induced alterations in these parameters were greater in PND 28 and more pronounced in cerebral cortex. From the results it is evident that combined supplementation of calcium and zinc along with MiADMSA would be most effective compared to individual administration in reducing arsenic induced neurotoxicity.

Monoisoamyl 2,3-dimercaptosuccinic acid attenuates arsenic induced toxicity: behavioral and neurochemical approach

Chronic exposure to arsenic in drinking water is associated with skin lesions, neurological effects, hypertension and high risk of cancer. The treatment in use at present employs administration of thiol chelators, such as meso-2,3-dimercaptosuccinic acid (DMSA) which are compromised with number of limitations due to their lipophobic nature. To address this problem, therapeutic efficacy of monoisoamyl meso-2,3-dimercaptosuccinic acid (MiADMSA), an analog of DMSA having lipophilic character, was examined against chronic arsenic poisoning in rats. Adult male Wistar rats were orally exposed to arsenic (2mg sodium arsenite/kg body weight) for 10 weeks followed by treatment with MiADMSA (50mg/kg, orally, once daily for 5 consecutive days). As-exposed rats showed significant differences in behavioral functions (open field behavior, total locomotor activity, grip strength and exploratory behavior) and water maze learning. Further, the biochemical studies performed on three brain regions (cerebellum, cortex and hippocampus) also showed significant elevation in malondialdehyde (MDA) levels with a concomitant decrease in the oxidative stress marker enzymes Mn-superoxide dismutase (Mn-SOD), Cu/Zn-superoxide dismutase (Cu/Zn-SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione-S-transferase (GST). The alterations were more pronounced in cortex compared to cerebellum and hippocampus. The results showed that MiADMSA significantly reversed the As-induced alterations in behavior and biochemical variables suggestive of oxidative injury.

MiADMSA protects arsenic-induced oxidative stress in human keratinocyte 'HaCaT' cells

Arsenic toxicity may lead to skin manifestations and arsenic accumulation in keratinised tissue. Thus human keratinocytes has been extensively used to study dermal effects of arsenic exposure. The present study was aimed to investigate time and dose-dependent effects of arsenic using HaCaT cell line. Another major focus of the study was to evaluate if treatment with monoisoamyl dimercaptosuccinic acid (MiADMSA) offers protection against arsenic-induced oxidative stress and apoptotic cell death using HaCaT cells. HaCaT cell lines were incubated to three different concentrations of arsenic (10, 30 and 50 μM) for 24 h to identify the toxic dose by measuring oxidative stress variables. Later, MiADMSA pre-incubation for an hour preceded arsenic exposure (30 μM). We evaluated cell morphology, lactate dehydrogenase, glutathione linked enzyme and antioxidant enzyme activities to measure oxidative stress status, while MTT assay and caspase 9 and 3 levels were determined for cell viability and apoptotic status. The present study suggests arsenic-induced toxicity in a concentration-dependant manner. Arsenic also caused a significant increase in lactate dehydrogenase accompanied by an elevated antioxidant enzyme activities (superoxide dismutase, glutathione peroxidase and caspase activity). Interestingly, pre-treatment of cell with MiADMSA elicited significant protection against arsenic-induced oxidative stress and apoptotic cell death. The present findings are of clinical relevance and suggest MiADMSA to be a promising candidate in protecting skin against arsenic-induced toxic effects, which need further exploration using in vivo experimental models.

Mitigative action of monoisoamyl-2,3-dimercaptosuccinate (MiADMS) against cadmium-induced damage in cultured rat normal liver cells

Cadmium is non-essential, carcinogenic and multitarget pollutant in the environment. Monoisoamyl-2,3-dimercaptosuccinate (MiADMS) is an ester of dimercaptosuccinic acid that acts as an antioxidant and chelator. Therefore, the mitigative action of MiADMS on viability, morphology, antioxidative enzymes and cell cycle were studied on rat liver cells treated with cadmium chloride (CdCl2). The cells were treated with 150 μM CdCl2 alone or cotreated with 300 μM MiADMS (concurrently, 2 h or 4 h post-CdCl2 treatment) for 24 h. The viability of cells treated with CdCl2 alone was decreased in comparison to the control cells. Cotreatment with MiADMS resulted in an increase in cell viability in comparison to the CdCl2 alone treated cells. The CdCl2 treatment altered the morphological shape of the cells, while cotreatment with MiADMS restored the shape. Antioxidative enzymes activities were decreased in the cells treated with CdCl2 alone, while MiADMS cotreatment resulted in an increase in enzyme activities. The CdCl2 arrested the cells in S phase of the cell cycle. Cotreatment with MiADMS alleviated cell cycle arrest by shifting to G1 phase. These results clearly show the mitigative action of MiADMS on CdCl2 toxicity and may suggest that MiADMS can be used as an antidote against cadmium.

On the interaction of vanadium species with the monoisoamyl ester of meso-2,3-dimercaptosuccinic acid

The interaction of the VO2+ cation with the monoisoamyl ester of meso-2,3-dimercaptosuccinic acid (MiADMSA) was investigated by electron absorption spectroscopy in aqueous solutions at different pH values. The spectral behavior, complemented with a spectrophotometric titration, shows the generation of a [VO(MiADMSA)2](4-) complex in which the oxocation interacts with two pairs of deprotonated -SH groups of the ester. Besides, MiADMSA rapidly reduces VO3(-) to VO2+, which might be chelated by an excess of the ester, and also produces relatively rapid reduction of V2O5 suspensions at pH = 6.5. The results of this study suggest that MiADMSA might be a potentially useful detoxification agent for vanadium.

Combinational chelation therapy abrogates lead-induced neurodegeneration in rats

Lead, a ubiquitous and potent neurotoxicant causes oxidative stress which leads to numerous neurobehavioral and physiological alterations. The ability of lead to bind sulfhydryl groups or compete with calcium could be one of the reasons for its debilitating effects. In the present study, we addressed: i) if chelation therapy could circumvent the altered oxidative stress and prevent neuronal apoptosis in chronic lead-intoxicated rats, ii) whether chelation therapy could reverse biochemical and behavioral changes, and iii) if mono or combinational therapy with captopril (an antioxidant) and thiol chelating agents (DMSA/MiADMSA) is more effective than individual thiol chelator in lead-exposed rats. Results indicated that lead caused a significant increase in reactive oxygen species, nitric oxide, and intracellular free calcium levels along with altered behavioral abnormalities in locomotor activity, exploratory behavior, learning, and memory that were supported by changes in neurotransmitter levels. A fall in membrane potential, release of cytochrome c, and DNA damage indicated mitochondrial-dependent apoptosis. Most of these alterations showed significant recovery following combined therapy with captopril with MiADMSA and to a smaller extend with captopril+DMSA over monotherapy with these chelators. It could be concluded from our present results that co-administration of a potent antioxidant (like captopril) might be a better treatment protocol than monotherapy to counter lead-induced oxidative stress. The major highlight of the work is an interesting experimental evidence of the efficacy of combinational therapy using an antioxidant with a thiol chelator in reversing neurological dystrophy caused due to chronic lead exposure in rats.

Combined administration of taurine and monoisoamyl DMSA protects arsenic induced oxidative injury in rats

Arsenic is a naturally occurring element that is ubiquitously present in the environment. High concentration of naturally occurring arsenic in drinking water is a major health problem in different parts of the world. Despite arsenic being a health hazard and a well documented carcinogen, no safe, effective and specific preventive or therapeutic measures are available. Among various recent strategies adopted, administration of an antioxidant has been reported to be the most effective. The present study was designed to evaluate the therapeutic efficacy of monoisoamyl dimercaptosuccinic acid (MiADMSA), administered either individually or in combination with taurine post chronic arsenic exposure in rats. Arsenic exposed male rats (25 ppm, sodium arsenite in drinking water for 24 weeks) were treated with taurine (100 mg/kg, i.p., once daily), monoisoamyl dimercaptosuccinic acid (MiADMSA) (50 mg/kg, oral, once daily) either individually or in combination for 5 consecutive days. Biochemical variables indicative of oxidative stress along-with arsenic concentration in blood, liver and kidney were measured. Arsenic exposure significantly reduced blood delta-aminolevulinic acid dehydratase (ALAD) activity, a key enzyme involved in the heme biosynthesis and enhanced zinc protoporphyrin (ZPP) level. Clinical hematological variables like white blood cells (WBC), mean cell hemoglobin (MCH), and mean cell hemoglobin concentration (MCHC) showed significant decrease with a significant elevation in platelet (PLT) count. These changes were accompanied by significant decrease in superoxide dismutase (SOD) activity and increased catalase activity. Arsenic exposure caused a significant decrease in hepatic and renal glutathione (GSH) level and an increase in oxidized glutathione (GSSG). These biochemical changes were correlated with an increased uptake of arsenic in blood, liver and kidney. Administration of taurine significantly reduced hepatic oxidative stress however co-administration of a higher dose of taurine (100 mg/kg) and MiADMSA provided more pronounced effects in improving the antioxidant status of liver and kidney and reducing body arsenic burden compared to the individual treatment of MiADMSA or taurine. The results suggest that in order to achieve better effects of chelation therapy, co-administration of taurine with MiADMSA might be preferred.

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 delta-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.

Combined administration of iron and monoisoamyl-DMSA in the treatment of chronic arsenic intoxication in mice

Co-administration of iron in combination with monoisoamyl dimercaptosuccinic acid (MiADMSA) against chronic arsenic poisoning in mice was studied. Mice preexposed to arsenic (25 ppm in drinking water for 6 months) mice were treated with MiADMSA (50 mg/kg, intraperitoneally) either alone or in combination with iron (75 or 150 mg/kg, orally) once daily for 5 days. Arsenic exposure led to a significant depletion of blood delta-aminolevulinic acid dehydratase (ALAD) activity, hematocrit, and white blood cell (WBC) counts accompanied by small decline in blood hemoglobin level. Hepatic reduced glutathione (GSH) level, catalase and superoxide dismutase (SOD) activities showed a significant decrease while, oxidized glutathione (GSSG) and thiobarbituric acid-reactive substances (TBARS) levels increased on arsenic exposure, indicating arsenic-induced hepatic oxidative stress. Liver aspartate and alanine transaminases (AST and ALT) activities also decreased significantly on arsenic exposure. Kidney GSH, GSSG, catalase level and SOD activities remained unchanged, while, TBARS level increased significantly following arsenic exposure. Brain GSH, glutathione peroxidase (GPx), and SOD activities decreased, accompanied by a significant elevation of TBARS level after chronic arsenic exposure. Treatment with MiADMSA was marginally effective in reducing ALAD activity, while administration of iron was ineffective when given alone. Iron when co-administered with MiADMSA restored blood ALAD activity. Administration of iron alone had no beneficial effects on hepatic oxidative stress, while in combination with MiADMSA it produced significant decline in hepatic TBARS level compared to the individual effect of MiADMSA. Renal biochemical variables were insensitive to any of the treatments. Combined administration of iron with MiADMSA also had no additional beneficial effect over the individual protective effect of MiADMSA on brain oxidative stress. Interestingly, combined administration of iron with MiADMSA provided more pronounced depletion of blood arsenic, while no additional beneficial effects on tissue arsenic level over the individual effect of MiADMSA were noted. The results lead us to conclude that iron supplementation during chelation has some beneficial effects particularly on heme synthesis pathway and blood arsenic concentration.

Reversal of lead-induced neuronal apoptosis by chelation treatment in rats: role of reactive oxygen species and intracellular Ca(2+)

Lead, a ubiquitous and potent neurotoxicant causes several neurophysiological and behavioral alterations. Toxic properties of lead have been attributed to its capability to mimic calcium and alter calcium homeostasis. In this study, we have addressed the following issues: 1) whether chelation therapy could circumvent the altered Ca(2+) homeostasis and prevent neuronal death in chronic lead-intoxicated rats, 2) whether chelation therapy could revert altered biochemical and behavioral changes, 3) whether combinational therapy using two different chelating agents was more advantageous over monotherapy in lead-treated rats, and 4) what could be the mechanism of neuronal apoptosis. Results indicated that lead caused a significant increase in reactive oxygen species, neuronal nitric-oxide synthetase, and intracellular free calcium levels along with altered behavioral abnormalities in locomotor activity, exploratory behavior, learning, and memory that were supported by changes in neurotransmitter levels. A fall in membrane potential, release of cytochrome c, and altered bcl(2)/bax ratio indicated mitochondrial-dependent apoptosis. Most of these alterations reverted toward normal level following combination therapy over monotherapy with calcium disodium EDTA (CaNa(2)EDTA) or monoisoamyl meso-2,3-dimercaptosuccinic acid (MiADMSA). It could be concluded from our present results that combined therapy with CaNa(2)EDTA and MiADMSA might be a better treatment protocol than monotherapy with these chelators in lead-induced neurological disorders. We for the first time report the role of Ca(2+) in regulating neurological dystrophy caused by chronic lead exposure in rats and its recovery with a two-course treatment regime of mono or combination therapy.

Arsenic induced oxidative stress and the role of antioxidant supplementation during chelation: a review

Arsenic is a naturally occurring metalloid, ubiquitously present in the environment in both organic and inorganic forms. Arsenic contamination of groundwater in the West Bengal basin in India is unfolding as one of the worst natural geoenvironmental disaster to date. Chronic exposure of humans to high concentration of arsenic in drinking water is associated with skin lesions, peripheral vascular disease, hypertension, Blackfoot disease and high risk of cancer The underlying mechanism of toxicity includes the interaction with the sulphydryl groups and the generation of reactive oxygen species leading to oxidative stress. Chelation therapy with chelating agents like British Anti Lewisite (BAL), sodium 2,3-dimercaptopropane 1-sulfonate (DMPS), meso 2,3 dimercaptosuccinic acid (DMSA) etc., is considered to be the best known treatment against arsenic poisoning. The treatment with these chelating agents however is compromised with certain serious drawbacks/side effects. The studies show that supplementation of antioxidants along with a chelating agent prove to be a better treatment regimen. This review attempts to provide the readers with a comprehensive account of recent developments in the research on arsenic poisoning particularly the role of oxidative stress/free radicals in the toxic manifestation, an update about the recent strategies for the treatment with chelating agents and a possible beneficial role of antioxidants supplementation to achieve the optimum effects.

Essential metal status, prooxidant/antioxidant effects of MiADMSA in male rats: age-related effects

Thiols are known to act as protectants in the biological system for their involvement in a number of metabolic regulations. In this study, we investigated the effect of a new and potent thiol-chelating agent, monoisoamyl 2,3-dimercaptosuccinic acid (MiADMSA), an analog of meso 2,3-dimercaptosuccinic acid, to find out if it could act as a prooxidant (because of its lipophilic character) or antioxidant (because of thiol moiety) that could supplement its chelating properties in different age groups of male rats (young, adult, and old rats) and produce effective clinical recoveries in the treatment of metal intoxication. Animals were treated with 25, 50, and 100 mg/kg of MiADMSA, i.p, once daily for 1 week to assess the effect on the antioxidant system in major organs based on sensitive biochemical variables indicative of oxidative stress. Results suggested that MiADMSA administration increased the activity of d-aminolevulinic acid dehydratase in all the age groups and increased blood glutathione (GSH) levels in young rats. MiADMSA also potentiated the synthesis of metallothioneine in liver and kidneys and GSH levels in liver and brain. Apart from this it also significantly reduced the glutathione disulfide levels in tissues. However, administration of MiADMSA caused some concern over the copper loss. MiADMSA was found to be safe in rats of all ages.

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 delta-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.

Combined administration of N-acetylcysteine and monoisoamyl DMSA on tissue oxidative stress during arsenic chelation therapy

The present study deals with the therapeutic potential of combined administration of N-acetylcysteine (NAC) along with monoisoamyl DMSA (MiADMSA) against chronic arsenic poisoning in guinea pigs. Animal were exposed to 50 ppm arsenic in drinking water for 8 mo and subsequently treated for 5 consecutive days with 100 mg/kg NAC (orally) and MiADMSA (intraperitoneally), individually or in combination (50 mg/kg each). Arsenic exposure produced a significant depletion of blood delta- aminolevulinic acid dehydrate (ALAD) activity, increased the blood zinc protoporphyrin (ZPP) level, and reduced blood and liver glutathione (GSH) levels in guinea pigs. Hepatic oxidized glutathione (GSSG) and thiobarbituric acid reactive substance (TBARS) levels showed a marked increase, whereas hepatic alkaline phosphatase (ALP) activity decreased and acid phosphatase (ACP) activity increased on arsenic exposure. Significant depletion of liver transaminase activities on arsenic exposure suggests organ injury. Administration of MiADMSA, alone and in combination with NAC after arsenic exposure, was able to significantly enhance hepatic GSH and to reduce GSSG and TBARS levels compared to the arsenic control. Biochemical variables indicative of liver injury generally remained insensitive to any of these treatments. The recoveries in parameters indicative of oxidative stress were more marked in guinea pigs treated with combined administration of NAC and MiADMSA than monotherapy. Interestingly, there was a more pronounced depletion of arsenic from blood and tissues after combined treatment with NAC plus MiADMSA than MiADMSA. Blood and tissues copper, zinc, iron, and calcium concentrations showed a significant increase after arsenic exposure, which showed improvement, particularly after combined administration of MiADMSA and NAC. Based on these data, a proposal can be made that greater effectiveness in chelation treatment against chronic arsenic poisoning (i.e., turnover in the oxidative stress and removed of arsenic from the system) could be achieved by combined administration of an antioxidant (preferably having a thiol moiety) with MiADMSA.

Beneficial role of monoesters of meso-2,3-dimercaptosuccinic acid in the mobilization of lead and recovery of tissue oxidative injury in rats

We investigated the therapeutic efficacy of meso-2,3-dimercaptosuccinic acid (DMSA) and two of its analogues, monomethyl dimercaptosuccinic acid (MmDMSA) and mono-cyclohexyl dimercaptosuccinic acid (MchDMSA) in reducing lead concentration in blood and soft tissues, and in recovering lead induced oxidative stress in rats. Male wistar rats were exposed to lead acetate in drinking water for 20 weeks, followed by 5 days of oral treatment with DMSA (100mg/kg, oral, once daily), MmDMSA or MchDMSA (50 and 100mg/kg). Biochemical variables indicative of oxidative stress along with lead, zinc and copper concentration were evaluated in blood and other soft tissues. Exposure to lead caused a significant decrease in blood delta-aminolevulinic acid dehydratase (ALAD) activity and glutathione (GSH) level. These changes were accompanied by inhibition of kidney ALAD and an increase in delta-aminolevulinic acid synthatase (ALAS) activity in liver and kidneys. Also seen were a pronounced depletion of brain GSH, glutathione peroxidase (GPx), glutathione-S-transferase (GST) and decreased superoxide dismutase (SOD) activity and an increase in thiobarbituric acid reactive substances (TBARS) and reactive oxygen species (ROS) levels. These biochemical changes were correlated with an increased uptake of lead in blood and soft tissues. Blood and kidneys zinc concentration decreased significantly following lead exposure while, copper concentration remained unchanged. No effect of chelation on hepatic zinc concentration was noted, only liver copper concentration showed significant depletion on treatment with DMSA and MmDMSA (100mg/kg). Treatment with DMSA, MmDMSA and MchDMSA provided significant recovery in altered biochemical variables and brain DNA damage besides significant depletion of tissue lead burden. Among the chelating agents used, MchDMSA and MmDMSA provided better recovery in altered biochemical variables and depletion of lead concentration in tissues compared to DMSA. The above results suggest DMSA monoesters to be a better treatment option than DMSA in eliciting recovery to the altered biochemical variables and in the depletion of body lead burden.

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.

Monoisoamyl dimercaptosuccinic acid induced changes in pregnant female rats during late gestation and lactation

Monoisoamyl dimercaptosuccinic acid (MiADMSA), a vicinal thiol chelating agent and an analogue of a conventional metal chelating agent, meso-2,3-dimercaptosuccinic acid (DMSA) has recently been gaining recognition to be more effective chelating agent than DMSA in mobilizing lead, mercury and arsenic. However, very little information is available on the toxicological properties of this chelator. In the present study, MiADMSA was administered to pregnant female rats from day 14 of gestation to day 21 of lactation at different doses through oral (p.o.) and intraperitoneal (i.p.) routes to examine the toxicity in the pups and dams. Results suggested that MiADMSA had no effect on period of gestation, litter-size, sex ratio, and viability and lactation. No skeletal defects were observed following the administration of the chelator. However, MiADMSA administration produced few signs of oxidative stress in dams particularly at the higher doses (100 and 200mg/kg) as evident from increased thiobarbituric acid reactive substances (TBARS) in RBCs and decrease in the delta-aminolevulinic acid dehydratase (ALAD) activity. Administration of MiADMSA also caused some alterations in the essential metal concentration in the soft tissues especially tissue copper loss in lactating mothers and pups, which would be of some concern. Apart from copper, changes were also observed in the tissue zinc concentrations in mothers and pups following MiADMSA administration. The study thus suggests that the chelator is relatively safe during late gestation and it does not cause any major alteration in the mothers and the developing pups. However, detailed studies with MiADMSA, post-toxic metal exposure in pregnant animals may provide useful information.

Lead-induced oxidative stress and hematological alterations and their response to combined administration of calcium disodium EDTA with a thiol chelator in rats

The therapeutic efficacy of calcium disodium ethylenediaminetetracetic acid (CaNa(2)EDTA) and the two thiol chelators, 2,3-dimercaptopropane 1-sulfonate (DMPS) and monoisoamyl dimercaptosuccinic acid (MiADMSA) was studied, both individually and in combination, in reducing lead concentration in blood and soft tissues and in restoring lead induced altered biochemical variables in rats. Exposure to subacute dose of lead implicated a critical role of reactive oxygen species (ROS) and oxidative stress in altering the normal values of these variables. Exposure to lead caused a significant inhibition of blood delta-aminolevulinic acid dehydratase (ALAD), an important enzyme in the haem synthesis pathway and glutathione (GSH) level. These changes were also accompanied by inhibition of ALAD activity in kidney, delta-aminolevulinic acid synthase (ALAS) activities in liver and changes in platelet counts in whole blood suggesting disturbed haem synthesis pathway. Lead exposure also led to a pronounced depletion of brain GSH contents, superoxide dismutase (SOD) activity, an increase in thiobarbituric acid reactive substances (TBARS), and activity of glutathione S-transferase (GST). Specific activities of membrane-bound enzymes, acetylcholinesterase (AChE) and monoamine oxidase (MAO), were significantly inhibited on lead exposure. These biochemical changes were correlated with increased uptake of lead in blood and soft tissues. Post lead exposure treatment with MiADMSA in particular provided significant recovery in altered biochemical variables besides significant depletion of tissue lead burden. Treatment with CaNa(2)EDTA and DMPS individually had only moderate beneficial effects on tissue oxidative stress, although they were equally effective in the removal of tissue lead burden. Tissue zinc and copper levels did not depict any significant depletion, although changes like marked depletion of zinc following CaNa(2)EDTA and copper after MiADMSA administration were of some concern. Combined administration of CaNa(2)EDTA, particularly with MiADMSA, was the most effective treatment protocol compared to all other treatments. It can be concluded from our present results that combined therapy with CaNa(2)EDTA and MiADMSA proved significantly better in restoring biochemical and clinical variables over monotherapy with these chelating agents against subacute lead exposure in adult rats.

Involvement of lipid peroxidation and organic peroxides in UVA-induced matrix metalloproteinase-1 expression

Ultraviolet A (UVA) irradiation causes human skin aging and skin cancer at least partially through the activation of matrix metalloproteinases (MMPs). MMP-1, the interstitial collagenase, is responsible for the degradation of collagen and is involved in tumor progression in human skin. The present study uses human skin fibroblast cells (FEK4) to investigate the involvement of lipid peroxidation and the role of peroxides as possible mediators in MMP-1 activation by UVA. Preincubation with the antioxidants butylated hydroxytoluene and Trolox reduced UVA-dependent MMP-1 upregulation, suggesting that peroxidation of membrane lipids is involved. Blocking the iron-driven generation of lipid peroxides and hydroxyl radicals by different iron chelators led to a decrease in UVA-induced MMP-1 mRNA accumulation. Moreover, modulation of glutathione peroxidase activity by use of the specific inhibitor mercaptosuccinate (MS) or by the depletion of glutathione (using buthionine-S, R-sulfoximine, BSO), enhanced the UVA-dependent MMP-1 response. Finally, UVA irradiation generated a significant increase in intracellular peroxide levels which is augmented by pretreatment of the cells with BSO or MS. Our results demonstrate that lipid peroxidation and the production of peroxides are important events in the signalling pathway of MMP-1 activation by UVA.

Chronic arsenic poisoning in the rat: treatment with combined administration of succimers and an antioxidant

The influence of the coadministration of vitamin C or vitamin E on the efficacy of two thiol chelators, meso-2,3-dimercaptosuccinic acid (DMSA) or monoisoamyl DMSA, in counteracting chronic arsenic toxicity was investigated in rats. Vitamin C and vitamin E were only mildly effective when given alone or in combination with the above chelators in mobilizing arsenic from the target tissues. However, combined administration of vitamin C plus DMSA and vitamin E plus MiADMSA led to a more pronounced depletion of brain arsenic. The supplementation of vitamins was significantly effective in restoring inhibition of blood delta-aminolevulinic acid dehydratase (ALAD) oxidative stress in liver, kidneys, and brain as reflected by reduced levels of thiobarbituric acid reactive substance and oxidized and reduced glutathione levels. The results thus lead us to suggest that coadministration of vitamin E or vitamin C may be useful in the restoration of altered biochemical variables (particularly the effects on heme biosynthesis and oxidative injury) although it has only a limited role in depleting arsenic burden.

Therapeutic potential of monoisoamyl and monomethyl esters of meso 2,3-dimercaptosuccinic acid in gallium arsenide intoxicated rats

The dose dependent effects of monoisoamyl and monomethyl esters of meso 2,3-dimercaptosuccinic acid (DMSA) (0.1, 0.3 and 0.5 mmol kg(-1), intraperitoneally (i.p.) once daily for 5 days) to offset the characteristic biochemical, immunological, oxidative stress consequences and DNA damage (based on DNA fragmentation and comet assay) following sub-chronic administration of gallium arsenide and the mobilization of gallium and arsenic were examined. The effects of these chelators alone in normal animals too were examined on above-mentioned variables. Male Wistar rats were exposed to 10 mg kg(-1), GaAs, orally once daily for 12 weeks and were administered DMSA or two of its monoesters (monoisoamyl or monomethyl) for 5 consecutive days. DMSA was used as a positive control. DMSA and its derivatives, when given alone, generally have no adverse effects on various parameters. After 5 days of chelation therapy in GaAs pre-exposed rats, MiADMSA was most effective in the reduction of inhibited blood delta-aminolevulinic acid dehydratase (ALAD) activity and zinc protoporphyrin level while, all three chelators effectively reduced urinary ALA excretion, compared to GaAs alone exposed rats. MiADMSA was also effective, particularly at a dose of 0.3 mmol kg(-1), in enhancing the inhibited hepatic transaminase activities. Parameters indicative of oxidative stress responded less favorably to the chelation therapy, however, three chelators significantly restored the altered immunological variables. MiADMSA was relatively more effective than the other two chelators. GaAs produced significant DNA damage in the liver and kidneys and the chelation treatment had moderate but significant influence in reducing DNA damage. All three chelators significantly reduced arsenic concentration and, however, MiADMSA was more effective than the other two chelators in depleting arsenic concentration from blood and other soft tissues. A dose of 0.3 mmol kg(-1) was found to be relatively better than the other two doses examined. Gallium contents of blood and soft tissues remained uninfluenced by the chelation therapy. Significant loss of copper after MiADMSA administration, however, is of concern and requires further exploration. Additionally, further studies are required for the choice of appropriate dose, duration of treatment and possible toxic/side effects. Keeping in view the promising role of MiADMSA in the treatment of GaAs poisoning, these data will be needed for the registration of this chelating agent as licensed drug for the treatment of gallium arsenide intoxication.

Arsenic induced inhibition of delta-aminolevulinate dehydratase activity in rat blood and its response to meso 2,3-dimercaptosuccinic acid and monoisoamyl DMSA

OBJECTIVE

The objective of this study was to investigate arsenic induced changes in blood delta-aminolevulinic acid dehydratase (ALAD) after in vitro and in vivo exposure to this element and its response to co-administration of meso 2,3-dimercaptosuccinic acid (DMSA) and monoisoamyl DMSA (MiADMSA) either individually or in combination.

METHODS

Rat whole blood was exposed to varying concentrations (0.1, 0.2 and 0.5 mmol/L) of arsenic (III) or arsenic (V), to assess their effects on blood ALAD activity. Varying concentrations of MiADMSA and DMSA (0.1, 0.5 and 1.0 mmol/L) were also tried in combination to determine its ability to mask the effect of arsenic induced (0.5 mmol/L) inhibition of blood ALAD in vitro. In vitro and in vivo experiments were also conducted to determine the effects of DMSA and MiADMSA either individually or in combination with arsenic, on blood ALAD activity and blood arsenic concentration.

RESULTS

In vitro experiments showed significant inhibition of the enzyme activity when 0.1-0.5 mmol/L of arsenic (III and V) was used. Treatment with MiADMSA increased ALAD activity when blood was incubated at the concentration of 0.1 mmol/L arsenic (III) and 0.1 mmol/L MiADMSA. No effect of 0.1 mmol/L MiADMSA on ALAD activity was noticed when the arsenic concentration was increased to 0.2 and 0.5 mmol/L. Similarly, MiADMSA at a lower concentration (0.1 mmol/L) was partially effective in the turnover of ALAD activity against 0.5 mmol/L arsenic (III), but at two higher concentrations (0.5 and 1.0 mmol/L) a complete restoration of ALAD activity was observed. DMSA at all the three concentrations (0.1, 0.5 and 1.0 mmol/L) was effective in restoring ALAD activity to the normal value.

CONCLUSIONS

The results thus suggest that arsenic has a distinct effect on ALAD activity. Another important toxicological finding of the present study, based on in vivo experiments further suggests that combined administration of DMSA and MiADMSA could be more beneficial for reducing blood ALAD inhibition and blood arsenic concentration than the individual treatment.

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.

Beneficial effect of combined administration of some naturally occurring antioxidants (vitamins) and thiol chelators in the treatment of chronic lead intoxication

Ameliorative effects of few naturally occurring antioxidants like ascorbic acid (vitamin C), alpha-tocopherol (vitamin E) either alone or in combination with meso-2,3-dimercaptosuccinic acid (DMSA) or monoisoamyl DMSA (MiADMSA), on parameters indicative of oxidative stress in the liver, kidney, brain and blood of lead-exposed rats were studied. Male Wistar rats were exposed to 0.1% lead acetate in drinking water for 3 months and treated thereafter with DMSA or its analogue MiADMSA (50 mg/kg, intraperitoneally), either individually or in combination with vitamin E (5 mg/kg, intramuscularly) or vitamin C (25 mg/kg, orally) once daily for 5 days. The effects of these treatments in influencing the lead-induced alterations in haem synthesis pathway, hepatic, renal and brain oxidative stress and lead concentration from the soft tissues were investigated. Exposure to lead produced a significant inhibition of delta-aminolevulinic acid dehydratase (ALAD) activity from 8.44+/-0.26 in control animals to 1.76+/-0.32 in lead control, reduction in glutathione (GSH) from 3.56+/-0.14 to 2.57+/-0.25 and an increase in zinc protoporphyrin level from 62.0+/-3.9 to 170+/-10.7 in blood, suggesting altered haem synthesis pathway. Both the thiol chelators and the two vitamins were able to increase blood ALAD activity towards normal, however, GSH level responded favorably only to the two thiol chelators. The most prominent effect on blood ALAD activity was, however, observed when MiADMSA was co-administered with vitamin C (7.51+/-0.17). Lead exposure produced a significant depletion of hepatic GSH from 4.59+/-0.78 in control animals to 2.27+/-0.47 in lead controls and catalase activity from 100+/-3.4 to 22.1+/-0.25, while oxidized glutathione (GSSG; 0.34+/-0.05 to 2.05+/-0.25), thiobarbituric acid reactive substance (TBARS; 1.70+/-0.45 to 5.22+/-0.50) and glutathione peroxidase (GPx) levels (3.41+/-0.09 to 6.17+/-0.65) increased significantly, pointing to hepatic oxidative stress. Altered, reduced and oxidized GSH levels showed significant recovery after MiADMSA and DMSA administration while, vitamins E and C were effective in reducing GSSG and TBARS levels and increasing catalase activity. Administration of MiADMSA alone and the combined administration of vitamin C along with DMSA and MiADMSA were most effective in increasing hepatic GSH levels to 4.88+/-0.14, 4.09+/-0.12 and 4.30+/-0.06, respectively. Hepatic catalase also reached near normal level in animals co-administered vitamin C with DMSA or MiADMSA (82.5+/-4.5 and 84.2+/-3.5, respectively). Combined treatments with vitamins and the thiol chelators were also able to effectively reduce lead-induced decrease in renal catalase activity and increase in TBARS and GPx level. Combination therapy, however, was unable to provide an effective reversal in the altered parameters indicative of oxidative stress in different brain regions, except in catalase activity. The result also suggests a beneficial role of vitamin E when administered along with the thiol chelators (particularly with MiADMSA) in reducing body lead burden. Blood lead concentration was reduced from 13.3+/-0.11 in lead control to 0.3+/-0.01 in MiADMSA plus vitamin E-treated rats. Liver and kidney lead concentration also showed a most prominent decrease in MiADMSA plus vitamin E co-administered rats (5.29+/-0.16 to 0.63+/-0.02 and 14.1+/-0.21 to 1.51+/-0.13 in liver and kidney, respectively). These results thus suggest that vitamin C administration during chelation with DMSA/MiADMSA was significantly beneficial in reducing oxidative stress however, it had little or no additive effect on the depletion of lead compared with the effect of chelators alone. Thus, the co-administration of vitamin E during chelation treatment with DMSA or MiADMSA could be recommended for achieving optimum effects of chelation therapy.

Haematological, hepatic and renal alterations after repeated oral and intraperitoneal administration of monoisoamyl DMSA. II. Changes in female rats

We recently reported the effects of repeated administration of the monoisoamyl ester of dimercaptosuccinic acid (MiADMSA) on a few selected biochemical variables indicative of haematopoietic, liver, kidney and brain toxicity, oxidative stress and essential metal status in male rats. The present investigation studies similar changes in female rats to fi nd out if the changes are independent of gender. The results suggest significant and pronounced toxic effects of MiADMSA on haem biosynthesis, liver and kidneys in female rats exposed to higher doses of orally (p.o.) or intraperitoneally (i.p.) administered MiADMSA, compared with the effects in male rats. No effects on brain tissues were seen. A pronounced depletion of copper was noted in the blood and liver of MiADMSA administered rats, irrespective of route of exposure. It can be concluded that the administration of MiADMSA in female rats is confounded with side-effects and may require caution during its use and further exploration.

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.

Haematological, hepatic and renal alterations after repeated oral or intraperitoneal administration of monoisoamyl DMSA. I. Changes in male rats

Monoisoamyl 2,3-dimercaptosuccinic acid (MiADMSA), a vicinal thiol chelator, is gaining recognition recently as a better chelator than meso 2,3-dimercaptosuccinic acid (DMSA) in decreasing heavy metal burden in tissues because of its lipophilic character. There is, however, little information available on the toxicological properties of this chelator after repeated administration in animals. In the present study, we investigated the dose-dependent effect of MiADMSA on various biochemical parameters suggestive of alterations in haem biosynthesis and hepatic, renal and brain oxidative stress after 21 days of repeated intraperitoneal (i.p.) or oral (p.o.) administration to rats. The concentration of essential metals in blood and soft tissues was determined along with histopathological observations of hepatic and renal tissues. The results suggest that MiADMSA administration had no effect on blood delta-aminolevulinic acid dehydratase activity. However, an increase in zinc protoporphyrin and a decrease in haemoglobin levels were noted in animals given MiADMSA i.p. A moderate increase in serum alkaline phosphatase suggested mild hepatotoxicity at the highest dose (100 mg kg(-1), i.p.). This was confirmed by histopathological examinations, which identified basophilic stippling, granulation of the cytoplasm, haemorrhage and congestion. At the highest dose, levels of hepatic thiobarbituric acid reactive substance and oxidized glutathione were increased above those of control values. Levels of hepatic reduced glutathione were decreased. Taken together, these observations point to oxidative stress. In animals administered MiADMSA i.p. there was an increase in the brain malondialdehyde levels at the two higher doses (50 and 100 mg kg(-1)). Essential metal status revealed a significant effect of MiADMSA (p.o.) in increasing blood zinc while significantly decreasing the kidney zinc level. The most significant adverse effect of MiADMSA was on copper concentration, which showed significant depletion from almost all major organs. Magnesium levels in blood decreased but increased in liver of MiADMSA-administered rats. Histopathological observations of liver and kidneys suggest few moderate lesions. It can be concluded that repeated administration of MiADMSA is compromised with some mild toxic effect, particularly the loss of copper. The effects during oral administration are comparatively less pronounced than by the i.p. route.

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.

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.

Combined administration of oxalic acid, succimer and its analogue for the reversal of gallium arsenide-induced oxidative stress in rats

Gallium arsenide (GaAs), a group III-VA intermetallic semiconductor, possesses superior electronic and optical properties and has a wide application in the electronics industry. Exposure to GaAs in the semiconductor industry is a potential occupational hazard because cleaning and slicing GaAs ingots to yield the desired wafer could generate GaAs particles. The ability of GaAs to induce oxidative stress has not yet been reported. The present study reports the role of oxidative stress in GaAs-induced haematological and liver disorders and its possible reversal overturn by administration of meso-2,3-dimercaptosuccinic acid (DMSA) and one of its analogue, monoisoamyl DMSA (MiADMSA), either individually or in combination with oxalic acid. While DMSA and MiADMSA are potential arsenic chelators, oxalic acid is reported to be an effective gallium chelator. Male rats were exposed to 10 mg/kg GaAs orally, 5 days a week for 8 weeks. GaAs exposure was then stopped and rats were given a 0.5 mmol/kg dose of succimers (DMSA or MiADMSA), oxalic acid or a combination of the two, intraperitoneally once daily for 5 consecutive days. We found a significant fall in blood delta-aminolevulinic acid dehydratase (ALAD) activity and blood glutathione (GSH) level, and an increased urinary excretion of delta-aminolevulinic acid (ALA) and an increased malondialdehyde (MDA) level in erythrocytes of rats exposed to GaAs. Hepatic GSH levels decreased, whereas there was an increase in GSSG and MDA levels. The results suggest a role of oxidative stress in GaAs-induced haematological and hepatic damage. Administration of DMSA and MiADMSA produced effective recovery in most of the above variables. However, a greater effectiveness of the chelation treatment (i.e. removal of both gallium and arsenic from body organs) could be achieved by combined administration of succimer (DMSA) with oxalic acid since, after MiADMSA administration, a marked loss of essential metals (copper and zinc) is of concern.

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.

The effects of sulfur, thiol, and thiol inhibitor compounds on arsine-induced toxicity in the human erythrocyte membrane

The mechanism of arsine (AsH(3)) toxicity is not completely understood. The first cytotoxic effect of AsH(3) is disruption of ion homeostasis, with a subsequent hemolytic action. The only accepted treatment for AsH(3) toxicity is exchange transfusion of the blood. In this study the effect of sulfur, sulfur compounds, thiol-containing compounds, and thiol inhibitors on AsH(3)-induced disruption of membrane transport and hemolysis in human erythrocytes was investigated in vitro. Elemental sulfur, sodium thiosulfate, 5, 5'-dithio-bis(2-nitrobenzoic acid), and meso-2,3-dimercaptosuccinic acid were successful in delaying hemolysis, but the most successful agent was the sulfhydryl inhibitor, N-ethylmaleimide (NEM). This indicated that sulfhydryl groups, possibly membrane sulfhydryls, are major factors in the hemolytic mechanism of AsH(3). Measuring intracellular ion concentrations tested the effect of NEM on AsH(3)-induced disruption of membrane transport. AsH(3) alone caused all ions tested to flow with their concentration gradients: Intracellular K+ and Mg++ decreased, whereas Na+, Cl-, and Ca++ increased. NEM was unable to prevent ion loss except for Ca++, whose increase was prevented for 1 h after AsH(3) treatment. The influx of Ca++ in AsH(3)-treated erythrocytes is an irreversible event leading to hemolysis. Reduction of oxygenated hemoglobin to carboxyhemoglobin completely inhibited AsH(3)-induced hemolysis. In addition, AsH(3) and NEM had no direct chemical interactions. We concluded that membrane sulfhydryl groups are likely targets of AsH(3) toxicity, with NEM being able to prevent AsH(3)-induced hemolysis.

Polymorphonuclear elastase as a diagnostic marker of acute pyelonephritis in children

OBJECTIVE

Experimental evidence suggests that neutrophils and their metabolites play an important role in the pathogenesis of pyelonephritis. The aim of this study was to investigate the diagnostic value of polymorphonuclear elastase-a(1)-antitrypsin complex (E-a(1)-Pi) for the detection of acute pyelonephritis in children.

METHODS

Eighty-three patients, 29 boys and 54 girls, 25 days to 14 years of age, with first-time symptomatic urinary tract infection were prospectively studied. Fifty-seven healthy children served as controls. Dimercaptosuccinic acid (DMSA) scan and voiding cystourethrography were performed in all patients. Plasma and urinary E-a(1)-Pi, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), neutrophil count, urinary N-acetyl-beta-glucosaminidase (NAG), N-acetyl-beta-glucosaminidase b (NAG b), and creatinine levels were measured in all patients on admission and 3 days after the introduction of antibiotics. The same markers were also measured in the control subjects.

RESULTS

Planar DMSA scintigraphy demonstrated changes of acute pyelonephritis in 30 of 83 children (group A). It was normal in the remaining 53 children (group B). The sex and age distributions were not significantly different between the 2 groups, as well as between the patients and the control subjects (group C). Nineteen of the 53 children with a normal DMSA had body temperature >/=38 degrees C, whereas all but 4 children with abnormal DMSA had temperature >/=38 degrees C. Therefore, the temperature was significantly different between these 2 groups. The sensitivity and specificity of fever (>/=38 degrees C) as an indicator of renal involvement based on isotopic findings were 86% and 64%, respectively. Given the significant number of the febrile children with normal DMSA scintiscans, group B was subdivided into B(1) with 19 febrile children (14 boys and 5 girls) and B(2) with 34 children whose body temperature was below 38 degrees C (8 boys and 26 girls). The sex and age distribution was significantly different between groups B(1) and B(2). The mean age of group B(1) was.78 years (range: 28 days to 9 years; median:.25 years; standard deviation: 2.1). All but 1 child in this group were younger than 1 year of age. In contrast, in group B(2), there were only 4 infants, the remaining 30 children were older than 2.5 years (mean age: 6 years; median: 7 years; standard deviation: 3.5; range: 34 days to 12 years). The mean duration of fever before hospital admission was 2.8 days for group A and 1.8 days for group B(1). This difference was not statistically significant. Similarly, body temperature was not significantly different between these 2 groups. The distribution of plasma E-a(1)-Pi values was normal in the control subjects. The sensitivity and specificity of plasma E-a(1)-Pi, as an indicator of renal involvement, were 96% and 50%, respectively, taking the 95th percentile of the reference range as a cutoff value. However, considering as a cutoff value the level of 72 microg/dL (95th percentile of group B(2)), its sensitivity and specificity were 74% and 86%, respectively. Plasma E-a(1)-Pi levels were significantly elevated in group A compared with group B and in both groups, the plasma E-a(1)-Pi values were significantly higher than in the control subjects. A significant difference also was noticed between group A and each of the subgroups B(1) and B(2) and also between the subgroups themselves. Plasma E-a(1)-Pi concentrations correlated significantly with neutrophil count in groups A (r =.3), B (r =.4), and B(2) (r =.46), but the correlation was not significant in group B(1.) ESR levels showed, among the different groups, similar differences with those of E-a(1)-Pi values. Unlike E-a(1)-Pi, CRP levels were comparable between groups A and B(1), which both consisted of febrile children. Neutrophil count was not significantly different between subgroups B(1) and B(2). (ABSTRACT TRUNCATED)

Influence of combined therapeutic potential of meso 2,3-dimercaptosuccinic acid and calcium disodium edetate on lead-induced testicular alterations in rats

The therapeutic efficacy of a combination of meso 2,3-dimercaptosuccinic acid (DMSA) and calcium disodium EDTA in protecting testicular disorders in chronic lead intoxication was investigated. The results indicate that two five-days courses of the combined therapy produced a more effective recovery in the lead induced biochemical and histopathological disorders compared to conventional single 5 days therapy. No adverse effect of the chelators, when administered individually or in combination, was noticed in the testes of control (without lead exposure) animals.

Cadmium-induced apoptosis in the urogenital organs of the male rat and its suppression by chelation

Cadmium-induced apoptosis is shown to occur, in vivo, in several organs of the male Wistar rat urogenital system, 48 h after cadmium administration i.p. at a dose of 0.03 mmol/kg. Characteristic DNA fragmentation (as measured by an enzyme-linked immunosorbent-assay, ELISA) and histopathologically observed changes characteristic of apoptosis are found in the kidney, prostate, seminal vesicles, testes, and epididymis. TUNEL assay also demonstrates the apoptosis. Such changes are absent from bladder and vas deferens tissue. Timely administration of an appropriate chelating agent capable of reaching intracellular cadmium binding sites can suppress the processes leading to apoptosis. Administration of monoisomyl meso-2,3-dimercaptosuccinate (Mi-ADMS, 0.5 mmol/kg i.p.) to cadmium-treated rats is effective in greatly reducing typical histopathologic signs of apoptosis and the associated chromatin DNA fragmentation as revealed by ELISA when the antagonist is administered 1 h after cadmium. Administration of the chelating agent at law times results in greater degradation of DNA into oligonucleotides and more prominent histopathological evidence of apoptotic changes in the affected organs of the rat urogenital system. There is also a progressive increase in apoptotic changes indicated by TUNEL assay, as the antagonist is administered at progressively greater intervals after cadmium.

Meso-2,3-dimercaptosuccinic acid mono-N-alkylamides: syntheses and biological activity as novel in vivo cadmium mobilizing agents

Three meso-2,3-dimercaptosuccinic acid mono-N-alkylamides (meso-RNHCOCH(SH)CH(SH)-COOH, where R = CHMe2, Mi-PDMA; CH2CHMe2, Mi-BDMA; and CH2CH2CHMe2, Mi-ADMA), were prepared via a synthetic route using the sulfhydryl-protected anhydride. 2,2-Dimethyl-1,3-dithiolane-4,5-cis-dicarboxylic acid anhydride was opened up with 1 mol of corresponding amine to give the SH-protected monoamide. Subsequent deblocking of the vicinal dithiol functionality was accomplished by conversion of the dithiolane into the mercury complex followed by reaction with H2S to give the target molecule. The potential utility of these compounds in chronic cadmium intoxication was examined by evaluation of their cadmium mobilizing efficacy in vivo in cadmium-loaded female albino rats using sodium N-benzyl-D-glucamine-N-carbodithioate (BGDTC) as the standard drug. Compared to BGDTC, the new compounds were, except at the highest dosage studied, equally or more effective in decreasing retention of hepatic cadmium, while mostly less effective in decreasing renal cadmium. The greatest reductions were obtained with Mi-BDMS at 4 x 1.5 mmol/kg, where liver and kidney cadmium levels were reduced to 12% and 59% of control levels, while at the same dosage BGDTC induced a reduction to 50% and 13% of control levels. The order of the efficacy of the monoamides as hepatic cadmium mobilizing agents was found to be Mi-PDMA > Mi-BDMA > Mi-ADMA. However, the isopropyl analog, though very effective at reducing hepatic cadmium at a low dosage, was found to be more toxic than the isobutyl and isoamyl monoamides. While the new compounds were shown to be effective cadmium mobilizing agents, the specific compounds examined did not possess optimized structures in terms of the balance between effectiveness and toxicity.

Assessment of the role of the glutathione and pentose phosphate pathways in the protection of primary cerebrocortical cultures from oxidative stress

Reactive oxygen species have been implicated in neuronal injury associated with various neuropathological disorders. However, little is known regarding the relationship between antioxidant enzyme capacity and resultant toxicity. The antioxidant pathways of primary cerebrocortical cultures were directly examined using a novel technique that measures pentose phosphate pathway (PPP) activity, which is enzymatically coupled to glutathione peroxidase (GPx) detoxification of hydrogen peroxide (H2O2). PPP activity was quantified from data obtained by gas chromatography/mass spectrometry analysis of released labeled lactate following metabolic degradation of [1,6-(13)C2, 6,6-(2)H2] glucose by cerebrocortical cultures. The antioxidant capacity of these cultures was systematically evaluated using H2O2, and the resultant toxicity was quantified by lactate dehydrogenase release. Exposure of primary mixed and purified astrocytic cultures to H2O2 caused stimulation of PPP activity in a concentration-dependent fashion from 0.25 to 22.2% and from 6.9 to 66.7% of glucose metabolized to lactate through the PPP, respectively. In the mixed cultures, chelation of iron before H2O2 exposure was protective and resulted in a correlation between PPP saturation and toxicity. Conversely, addition of iron, inhibition of GPx, or depletion of glutathione decreased H2O2-induced PPP stimulation and increased toxicity. These results implicate the Fenton reaction, reflect the pivotal role of GPx in H2O2 detoxification, and contribute to our understanding of the etiological role of free radicals in neuropathological conditions.

Hydrogen peroxide in relation to proliferation and apoptosis in BHK-21 hamster fibroblasts

Addition of H2O2 at 100 microM, or 1 mM, to the culture medium of BHK-21 fibroblasts results in increased intracellular levels of H2O2. Whilst exposure of BHK-21 cells to lower levels of H2O2 (1 microM) actually stimulates proliferation, these higher oxidant concentrations not only depress proliferation rates but also lead to an increase in the appearance of apoptotic-like cells in the cultures. Other agents such as inhibitors of glutathione peroxidase and catalase, or mimics of superoxide dismutase, which also bring about elevated cellular levels of H2O2 in BHK-21 cells, similarly lead to decreased proliferation and an apparent increase in cells with apoptopic features. Thus intracellular conditions which are considered more prooxidant than normal, appear to favour apoptosis over proliferation in BHK-21 fibroblasts. Additionally these abnormal cellular conditions also appear to favour excessive DNA replication, in remaining non-apoptotic cells.

Assessment of the protective activity of monisoamyl meso-2,3-dimercaptosuccinate against methylmercury-induced maternal and embryo/fetal toxicity in mice

The protective activity of monoisoamyl meso-2,3-dimercaptosuccinate (Mi-ADMS), a new monoester of 2,3-dimercaptosuccinic acid (DMSA), on methylmercury-induced maternal and developmental toxicity was assessed in mice. A series of four Mi-ADMS injections was given s.c. at 0.25, 6, 24, and 48 h after oral administration of 25 mg/kg of methylmercury chloride (MMC) given on day 10 of gestation. Mi-ADMS effectiveness was tested at 0, 23.8, 47.6 and 95 mg/kg. Cesarean sections were performed on gestation day 18. All live fetuses were examined for external, internal, and skeletal abnormalities. Oral MMC administration resulted in an increase in the number of resorptions, and a decrease in fetal body weight, whereas the incidence of cleft palate, micrognathia, and skeletal variations was also increased in the fetuses of the MMC-treated groups. Although significant amelioration of MMC-induced embryolethality by Mi-ADMS was not noted at any dose, MMC-induced fetotoxicity was reduced by administration of this agent at 23.8, 47.6, and 95 mg/kg. However, the intrinsic toxicity of Mi-ADMS would be a restrictive factor for the possible therapeutic use of this chelator in pregnant women exposed to organic mercury.

Effects of monoisoamyl meso-2,3-dimercaptosuccinate on arsenite-induced maternal and developmental toxicity in mice

The therapeutic efficacy of monoisoamyl meso-2,3-dimercaptosuccinate (Mi-ADMS), on arsenite-induced maternal and developmental toxicity was evaluated in the pregnant mouse. Sodium arsenite (12 mg/kg) was intraperitoneally injected into Swiss mice on day 9 of gestation, whereas Mi-ADMS was given subcutaneously at 0.25, 5, 24, and 48 hr after arsenite exposure. Amelioration by Mi-ADMS of arsenite-induced maternal and embryofetal toxicity was assessed at 23.8, 47.5, and 95 mg/kg/day. Controls received 0.9% saline with or without arsenite. Cesarean sections were performed on gestation day 18. In the positive control group (treated with arsenite only), 20.8% of the pregnant animals died, whereas 37.5% of the dams were carrying completely resorbed litters. No arsenite-induced maternal lethality was seen following treatment with Mi-ADMS at 23.8, 47.5 and 95 mg/kg/day. Also, administration of the drug at these doses significantly reduced the embryolethality, as well as the incidence of some skeletal variations provoked by sodium arsenite. Although based on these findings, Mi-ADMS might be suggested as a potential antidote to prevent the arsenite-induced maternal and developmental toxicity, due to their reduced toxicity compared to Mi-ADMS, DMSA and DMPS would probably be more advisable for pregnant women exposed to arsenite.

Prolonged oral treatment with two monoesters of meso-2,3-dimercaptosuccinic acid for depleting inorganic mercury retention in suckling rats

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

Effect of monoisoamyl meso-2,3-dimercaptosuccinate on the pathology of acute cadmium intoxication

The ability of monoisoamyl meso-2,3-dimercaptosuccinate (Mi-ADMS) to offset the characteristic organ pathology of intraperitoneally administered cadmium chloride (CdCl2) and that of the cadmium-cysteine complex has been examined in male Wistar rats. The tissues examined for damage were the testes, kidney, liver, pancreas, and bone marrow. At a high dose of CdCl2 (0.03 mmol/kg, ip) testicular damage was completely prevented by Mi-ADMS (0.50 mmol/kg, ip) given immediately. A decrease in the protective ability of the antagonist was observed following delayed administration of Mi-ADMS given at 1, 2, 4, and 24 h post CdCl2. At a lower dose of CdCl2 (0.006 mmol/kg, ip), Mi-ADMS furnished essentially full protection from testicular damage when given (0.50 mmol/kg, sc) at 0 and 1 h after CdCl2. The administration of cadmium-cysteine complex (0.01 mmol/kg, ip) induced notable renal tubular damage, which was antagonized by the administration of Mi-ADMS (0.50 mmol/kg, ip) as late as 4 h after the complex. At a 24-h delay, extensive tubular necrosis was found on sacrifice after 4 d. The administration of cadmium-cysteine complex ip reduced, but did not eliminate, the characteristic damage of the seminiferous tubules found for cadmium alone. There is a progressive reduction of testicular weight as the interval between cadmium and antagonist administration increases. The average kidney weights of the animals given CdCl2-cysteine complex were increased in comparison to normal controls. The antagonistic effects of Mi-ADMS treatment on cadmium intoxication in the kidneys and the testes of rats is very similar to that found for effective dithiocarbamate antagonists. In order to obtain complete protection of the testes from the deteterious effects of cadmium, such antagonists must be administered no later than about 1 h after the cadmium.

Monoisoamyl and mono-n-hexyl meso-2,3-dimercaptosuccinate in mobilizing 203Hg retention in relation to age of rats and route of administration

Monoisoamyl (Mi-ADMS) and mono-n-hexyl (Mn-HDMS) monoesters of meso-2,3-dimercaptosuccinic acid (DMSA) were given orally or parenterally for the mobilization of inorganic mercury in suckling and older rats. Chelators were administered at a dose of 2 x 0.5 mmol kg-1 on two consecutive days 2 weeks after a single 203Hg injection. Six days later, whole-body, kidney, liver and brain radioactivities were determined in gamma scintillation counters. Both Mi-ADMS and Mn-HDMS were found to be superior to DMSA in mobilizing mercury from body and organs. The results were similar after oral or parenteral treatment. The efficiency of both monoesters was even higher in younger than in older rats. This is the first report on the mobilization of mercury from the body of sucklings under conditions of late oral treatment.

Effect of chelators, monoisoamyl meso-2,3-dimercaptosuccinate and N-(4-methylbenzyl)-4-O-(beta-D-galactopyranosyl)-D-glucamine-N-carbodit hioate, on cadmium and essential element levels in mice

In experiments performed on male mice (ICR) the mobilizing effect of monoisoamyl meso-2,3-dimercaptosuccinate (Mi-ADMS) and a dithiocarbamate analogue, N-(4-methylbenzyl)-4-O-(beta-D-galactopyranosyl)-D-glucamine-N-carbod ithioate (MeBLDTC) on the cadmium deposits was studied. The influence of these compounds on the changes in the level of essential elements caused by cadmium was explored. CdCl2.H2O was injected intravenously. The chelators were administered every 48 h over 12 d. Both compounds are effective in mobilizing cadmium from the body in animal experiments. On an equimolar basis MeBLDTC was superior to Mi-ADMS. Mi-ADMS can, however, be administered orally. Both compounds were able to correct, at least partly, the changes in the level of essential elements caused by cadmium.

Reduction of lead retention by mono-3-methylbutan-1-yl meso-2,3-dimercaptosuccinate in suckling rats

The mono-3-methylbutan-1-yl (monoisoamyl) ester of meso-2,3-dimercaptosuccinic acid (Mi-ADMS) was previously found to be superior to meso-2,3-dimercaptosuccinic acid (DMSA) in mobilizing cadmium and mercury deposits in young and adult mice and rats. It was also tested to mobilize lead in and adult mice. It was also tested to mobilized lead in adult mice. The purpose of this study was to evaluate the ability of Mi-ADMS to chelate lead at a very young age, in sucking rats. Lead was applied intraperitoneally at the dose of 5 mg kg-1 in the form of lead acetate to six-day-old rats. Treatment with DMSA and Mi-ADMS was administered orally at the dose of 0.25 mmol kg-1, either as early (0.5 and 24 h) or a delayed (4th and 5th day after lead application) therapy. At the end of the experiment (6th day) lead was determined by atomic absorption spectrometry in the skeleton, liver, kidney and brain of the animals. Results showed that Mi-ADMS was more efficient than DMSA after early application in reducing the skeletal, kidney and brain content of lead. After delayed application it was either (skeleton and kidneys) or better (brain) than DMSA. There was no statistically significant influence of either chelator on liver lead content. The major finding is that Mi-ADMS at low doses causes a much higher reduction in brain retention of lead in sucklings than DMSA. This is important because the brain is considered to be the target organ of lead toxicity in the youngest age group.

Monoisoamyl meso-2,3-dimercaptosuccinate as a delayed treatment for mercury removal in rats

Monoisoamyl meso-2,3-dimercaptosuccinate (Mi-ADMS) was found to be superior to meso-2,3-dimercaptosuccinic acid (DMSA) in decreasing the body burden of 203Hg in rats under conditions of early treatment. In this experiment Mi-ADMS was used as late treatment for mercury removal. Albino rats aged 6 weeks and 7-day-old sucklings received a single intraperitoneal injection of 203Hg (as nitrate). Two weeks later they were treated with DMSA or Mi-ADMS (0.25 mmole/kg bw) on two consecutive days. The radioactivity in the carcass (whole body after removal of the gastrointestinal tract), liver, kidneys and brain was determined by solid crystal gamma scintillation counting six days after chelation therapy administration (3 weeks after 203Hg application). Both chelators reduced the body burden of mercury compared to controls. The effect of Mi-ADMS was superior to DMSA treatment in older rats for decreasing carcass and kidney retention, and in suckling rats for decreasing carcass, liver, and kidney retention. They were equally effective in decreasing brain retention in older rats and had no effect on brain retention in sucklings. The efficiency of Mi-ADMS in reducing the body burden of mercury was generally higher than the efficiency of the DMSA treatment. Therefore, Mi-ADMS deserves further attention as a late treatment for mercury removal.

Developmental toxicity evaluation of monoisoamyl meso-2,3-dimercaptosuccinate in mice

Monoisoamyl meso-2,3-dimercaptosuccinate (Mi-ADMS), a new dimercaptosuccinic acid (DMSA) analog with enhanced lipophilic properties, was evaluated for potential developmental toxicity. Intraperitoneal injections of Mi-ADMS were given to female Swiss mice (0, 47.5, 95, and 190 mg/kg) on gestational d 6-15. The maternal clinical status was monitored daily during treatment. At termination (gestational d 18), dams were evaluated for clinical status and gestational outcome. Each live fetus was weighed and examined for external, visceral, and skeletal abnormalities. Although no maternal mortality was observed, treatment with 95 and 190 mg/kg resulted in maternal toxicity, manifested as reduced body weight gain during treatment and increased relative liver weight. Embryo/fetal toxicity, consisting of a significant increase in the number of late resorptions as well as in the percentage of postimplantation loss, reduced (nonsignificant) fetal body weight, and an increase in the incidence of skeletal defects, was also observed at 190 mg/kg/d. However, no treatment-related external or soft-tissue malformations or developmental variations were found in any group. The no-observed-adverse-effect level (NOAEL) for maternal toxicity was 47.5 mg/kg/d, whereas the NOAEL for developmental toxicity was 95 mg/kg/d. These results indicate that Mi-ADMS did not produce developmental toxicity in mice in the absence of maternal toxicity.