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

Chemistry, Pharmacology, and Toxicology of Monoisoamyl Dimercaptosuccinic Acid: A Chelating Agent for Chronic Metal Poisoning

Arsenic, a metalloid, is known to cause deleterious effects in various body organs, particularly the liver, urinary bladder, and brain, and these effects are primarily mediated through oxidative stress. Chelation therapy has been considered one of the promising medical treatments for arsenic poisoning. Meso 2,3- dimercaptosuccinic acid (DMSA) has been recognized as one of the most effective chelating drugs to treat arsenic poisoning. However, the drug is compromised with a number of shortcomings, including the inability to treat chronic arsenic poisoning due to its extracellular distribution. Monoisoamyl 2,3-dimercaptosuccinic acid, one of the analogues of meso 2,3-dimeraptosuccinic acid (DMSA), is a lipophilic chelator and has shown promise to be considered as a potential future chelating agent/antidote not only for arsenic but also for a few other heavy metals like lead, mercury, cadmium, and gallium arsenide. The results from numerous studies carried out in the recent past, mainly from our group, strongly support the clinical application of MiADMSA. This review paper summarizes most of the scientific details including the chemistry, pharmacology, and safety profile of MiADMSA. The efficacy of MiADMSA mainly against arsenic toxicity but also a few other heavy metals was also discussed. We also reviewed a few other strategies in order to achieve the optimum effects of MiADMSA, like combination therapy using two chelating agents or coadministration of a natural and synthetic antioxidant (including phytomedicine) along with MiADMSA for treatment of metal/metalloid poisoning. We also briefly discussed the use of nanotechnology (nano form of MiADMSA i.e. nano-MiADMSA) and compared it with bulk MiADMSA. All these strategies have been shown to be beneficial in getting more pronounced therapeutic efficacy of MiADMSA, as an adjuvant or as a complementary agent, by significantly increasing the chelating efficacy of MiADMSA.

Protective effect of Monoisoamyl-2, 3-Dimercaptosuccinic Acid against Manganese-induced Neurotoxicity in rats

BACKGROUND

Apart from being an essential heavy metal, manganese (Mn) serves as an important component of the antioxidant enzyme system in humans. Overexposure to manganese leads to the development of manganism, which is characterized by motor dysfunction along with neurodegeneration. The management of manganism often utilizes chelation therapy. In this regard, Monoisoamyl-2, 3-Dimercaptosuccinic Acid (MiADMSA) has been reported as a novel arsenic chelator, due to the presence of vicinal sulfhydril group. MiADMSA has been reported to reduce the level in divalent ions (like copper) therefore, it may be hypothesized that MiADMSA would be helpful in Mn-induced neurotoxicity.

OBJECTIVE

This study is envisaged to explore the protective effect of MiADMSA on Mn-induced neurotoxicity.

METHOD

Mn exposure was carried out by intraperitoneal administration of Mn (as manganese chloride, 10 mg/kg; i.p.). The animals were treated with MiADMSA (50 mg/kg; p.o.) either alone or in combination with Mn. The effect of different treatments on neurobehavioral functions was observed by assessing spontaneous locomotor activity, motor rotarod test, and depression-like behavior in the forced swim test. After behavioral evaluations, all the animals were sacrificed and the brain and liver were isolated for metal estimations.

RESULTS

Mn exposure leads to loss of motor coordination as observed in spontaneous locomotor activity and rotarod test. However, treatment with MiADMSA significantly improved motor impairments as compared to Mn exposed animals. Accumulation of Mn in the liver and brain has been recorded with Mn exposure; however, MiADMSA treatment significantly reduced the Mn content from the liver and brain.

CONCLUSION

The outcome of the study suggests that treatment with MiADMSA reversed Mn-induced neurotoxicity by reducing Mn load. Therefore, the use of MiADMSA may be suggested in manganese toxicity, after careful investigation.

Ameliorative Effect of Vernonia amygdalina Plant Extract on Heavy Metal-Induced Liver and Kidney Dysfunction in Rats

Heavy metal toxicity contributes to liver and kidney dysfunction and damage through oxidative stress mechanisms; however, from previous studies, extracts from the Vernonia amygdalina plant have shown to possess potent antioxidant properties. This study was aimed at uncovering the potential ameliorative effects of ethanolic extract from Vernonia amygdalina plant in heavy metal toxicity-induced liver and kidney dysfunction. For this study, 44 Sprague Dawley rats were divided into three groups. The control group received a basal diet and water only while the treatment groups received varied dosages of the heavy metals. The copper (Cu) and lead (Pb) groups had five subgroups. The Cu only and Cu recovery subgroups were administered with 16 mg/kg Cu intraperitoneally daily for 14 days, whereas the Pb only and Pb recovery subgroups were administered with 13 mg/kg Pb intraperitoneally daily for 14 days. Subsequently, the Pb only and Cu only subgroups were sacrificed. The three Pb and Cu treatment subgroups received oral graded doses (100 mg/kg, 200 mg/kg, and 300 mg/kg) of the extract for 21 days. The Cu recovery and Pb recovery subgroups were left to recover for 21 days. After histological examinations, the Pb and Cu pretreatment groups showed evidence of focal necrosis accompanied by inflammatory cell infiltrations. The serum levels of liver biomarkers AST, ALT, and GGT, as well as urea and creatinine, were significantly elevated (P=0.01) following copper and lead exposure. Upon posttreatment of the rats with the extract, the physiological levels of the biomarkers were restored and tissue architecture of the organs improved. Thus, the ethanolic extract of Vernonia amygdalina is capable of ameliorating the effects of heavy metal toxicity through potent antioxidative mechanisms.

Gallic acid and MiADMSA reversed arsenic induced oxidative/nitrosative damage in rat red blood cells

Arsenic (As) is naturally occurring toxic metalloid which is considered as a serious environmental and health concern. Red blood cells are the prime target for any toxicants as their population is higher in systemic circulation. High prevalence of anaemia too has been reported from arsenic contaminated area, suggesting possible linkage between arsenic and the damaging effects on RBCs. The exact mechanism for these effects is still not clear, however, oxidative/nitrosative stress might be one of the causative factors to play a key role. The present study was planned to evaluate the protective effects of a metal chelator, MiADMSA either alone or in combination with a natural antioxidant (gallic acid) for the reversal of arsenic induced oxidative damage in red blood cells. We collected rat RBCs and cultured them in appropriate medium. They were incubated with MiADMSA and gallic acid and then treated with sodium arsenite at 37 °C. Hemolysates were prepared and assayed for various biochemical parameters such as oxidative/nitrosative variables, osmotic fragility, acetylcholinesterase activity, and cellular metal accumulation. We found there was reversibility of oxidative/nitrosative stress variables, elevated cellular antioxidant power, and decreased osmotic fragility of red blood cells both in MiADMSA alone as well as in combination with gallic acid treated group compared with arsenic treated group. In conclusion, MiADMSA efficiently participated in the reversal of arsenic induced oxidative/nitrosative damage in red blood cells where as Gallic acid improved its reversal when given in combination with MiADMSA.

The effect of diosmin against lead exposure in rats‡

In this study, the effect of diosmin against the adverse effects of lead exposure in rats was investigated. Wistar Albino race 40 male rats weighing 150-200 g 2-3 months were used. A total of 4 groups were assigned, one of which was control and the other 3 were trial groups. The rats in the control group were treated with dimethyl sulfoxide, which was used only as a vehicle in diosmin administration. Groups 2, 3, and 4 from the experimental group were given diosmin at a dose of 50 mg/kg.bw, lead acetate at the dose of 1000 ppm, lead acetate at the dose of 1000 ppm, and diosmin at a dose of 50 mg/kg.bw for 6 weeks, respectively. Application of lead acetate with drinking water and also diosmin was performed by oral catheter. At the end of the experimental period, blood was taken to dry and with heparin by puncture to the heart under light ether anesthesia. Following the blood samples, some organs of the rats (the liver, kidney, brain, heart, and testis) were removed. Some biochemical parameters (glucose, triglyceride, cholesterol, BUN, creatinine, uric acid, LDH, AST, ALT, ALP, total protein, albumin) were measured in serum. Some oxidative stress parameters in tissue samples and blood (MDA, NO, SOD, CAT, GSH-Px, GSH) were evaluated. Body and organ (the liver, kidney, brain, heart, and testis) weights were also evaluated at the end of the study. No significant change was observed in the parameters examined in the diosmin alone-treated group by comparison to control group. On the other hand, significant changes were found in the values ​​of lead acetate-treated group comparing control group. It was observed that the values approached the values of the control group in the combination of lead and diosmin. Exposure to lead acetate at a dose of 1000 ppm for 6 weeks causes organ damage; however the diosmin application at a dose of 50 mg/kg.bw had a positive effect on the regression of tissue damage.

Oxidative stress and neurobehavioural changes in rats following copper exposure and their response to MiADMSA and d-penicillamine

An increase in copper concentration in body may lead to hepatolenticular degeneration which is considered as one clinical feature of Wilson’s disease. Chelation therapy using d-penicillamine is the preferred medical treatment for reducing the toxic effects of copper. However, a few shortcomings associated with d-penicillamine led us to search of an alternative antidote for copper toxicity. Monoisoamyl-2, 3-dimercaptosuccinic acid (MiADMSA), a potent arsenic chelator under clinical trial, has been reported to reduce system copper level. Thus, the present study was envisaged to explore the ameliorative effect of MiADMSA against copper toxicity. Copper pre-exposed animals (CuSO4.5H2O; 100 mg/kg; p.o., for 6 weeks) were segregated in different groups and were administered equimolar dose (0.3 mEq/kg/day; p.o.) of d-penicillamine and MiADMSA for 5 days. The effect of different treatments on spontaneous locomotor activity, muscle coordination, depression like behaviour and contextual fear memory was analysed using neurobehavioural battery test. Biochemical variables related to oxidative stress, zinc and copper concentration were determined in liver, kidney and brain. The results suggested that copper exposure led to oxidative stress in liver, kidney and blood, along with moderate effects in brain. Treatment with d-penicillamine and MiADMSA reduced liver copper load. MiADMSA produced more pronounced beneficial effect compared to d-penicillamine by increasing brain GPx activity. Our study suggests that MiADMSA might be equally effective as d-penicillamine in depleting body copper load. More detailed studies using different doses are required to suggest whether MiADMSA could be an alternative for d-penicillamine in reducing oxidative injury, neurobehavioural changes and depleting body copper burden.

Combinatorial drug delivery strategy employing nano-curcumin and nano-MiADMSA for the treatment of arsenic intoxication in mouse

Chelation therapy is the mainstream treatment for heavy metal poisoning. Apart from this, therapy using antioxidant/herbal extracts are the other strategies now commonly being tried for the treatment. We have previously reported individual beneficial efficacy of nanoparticle mediated administration of an antioxidant like 'curcumin' and an arsenic chelator 'monoisoamyl 2,3-dimercaptosuccinic acid (MiADMSA)' for the treatment of arsenic toxicity compared to bulk drugs. The present paper investigates our hypothesis that a combination drug delivery therapy employing two nanosystems, a chelator and a strong antioxidant, may produce more pronounced therapeutic effects compared to individual effects in the treatment of arsenic toxicity. An in-vivo study was conducted wherein arsenic as sodium arsenite (100 ppm) was administered in drinking water for 5 months to Swiss albino mice. This was followed by a treatment protocol comprising of curcumin encapsulated chitosan nanoparticles (nano-curcumin, 15 mg/kg, orally for 1 month) either alone or in combination with MiADMSA encapsulated polymeric nanoparticles (nano-MiADMSA, 50 mg/kg for last 5 days) to evaluate the therapeutic potential of the combination treatment. Our results demonstrated that co-treatment with nano-curcumin and nano-MiADMSA provided beneficial effects in a synergistic way on the adverse changes in oxidative stress parameters and metal status induced by arsenic.

Microenvironmental Scenario of the Bone Marrow of Inorganic Arsenic-Exposed Experimental Mice

Exposure to arsenic on a regular basis, mainly through drinking water, agricultural pesticide, and sometimes therapeutic dose, results in various diseases of different tissues including the bone marrow hematopoietic system. Hematopoiesis is a dynamic process by which bone marrow (BM) hematopoietic stem/progenitor cells (HSPCs) generate a relatively constant pool of functionally mature blood cells by the support of microenvironmental components. The present study has been aimed to understand stem cell microenvironmental status during arsenic toxicity and the consequent reflection of dysregulation involving the hematopoietic machinery in experimental mice. Swiss albino mice were experimentally exposed to 10 μg arsenic trioxide/g body weight through oral gavage and 5 μg arsenic trioxide/g body weight intraperitoneally for a period of 30 days. Altered hemogram values in peripheral blood reflected the impaired hematopoiesis which was further validated by the reduced BM cellularity along with the deviated BM cell morphology as observed by scanning electron microscopy post arsenic exposure. The stromal cells were unable to establish a healthy matrix and the sustainability of hematopoietic progenitors was drastically affected in arsenic-exposed mouse groups, as observed in in vitro explant culture. The inability of stromal cells to establish supportive matrix was also explained by the decreased adherent colony formation in treated animals. Furthermore, the flow cytometric characterization of CXCR4⁺ and Sca-1⁺ CD44⁺ receptor expressions confirmed the dysregulation in the hematopoietic microenvironment. Thus, considering the importance of microenvironment in the maintenance of HSPC, it can be concluded that arsenic toxicity causes microenvironmental damage, leading to niche derangement and impaired hematopoiesis.

Nanoencapsulation of DMSA monoester for better therapeutic efficacy of the chelating agent against arsenic toxicity

AIMS

Exposure to toxic metals remains a widespread occupational and environmental problem in world. Chelation therapy is a mainstream treatment used to treat heavy metal poisoning. This paper describes the synthesis, characterization and therapeutic evaluation of monoisoamyl 2,3-dimercaptosuccinic acid (MiADMSA)-encapsulated polymeric nanoparticles as a detoxifying agent for arsenic poisoning.

MATERIALS & METHODS

Polymeric nanoparticles entrapping the DMSA monoester, which can evade the reticulo-endothelial system and have a long circulation time in the blood, were prepared. Particle characterization was carried out by transmission electron microscopy and dynamic light scattering. An in vivo study was conducted to investigate the therapeutic efficacy of MiADMSA-encapsulated polymeric nanoparticles (nano- MiADMSA; 50 mg/kg orally for 5 days) and comparison drawn with bulk MiADMSA. Swiss albino mice exposed to sodium arsenite for 4 weeks were treated for 5 days to evaluate alterations in blood, brain, kidney and liver oxidative stress variables. The study also evaluated the histopathological changes in tissues and the chelating potential of the nanoformulation.

RESULTS

Our results show that nano-MiADMSA have a narrow size distribution in the 50-nm range. We observed an enhanced chelating potential of nano-MiADMSA compared with bulk MiADMSA as evident in the reversal of biochemical changes indicative of oxidative stress and efficient removal of arsenic from the blood and tissues. Histopathological changes and urinary 8-OHdG levels also prove better therapeutic efficacy of the novel formulation for arsenic toxicity.

CONCLUSION

The results from our study show better therapeutic efficacy of nano-MiADMSA in removing arsenic burden from the brain and liver.

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 (MiADMSA) demonstrates higher efficacy by oral route in reversing arsenic toxicity: a pharmacokinetic approach

Monoisoamyl DMSA (MiADMSA), a lipophilic chelating agent has emerged as a promising drug for the treatment of arsenic. The present study aimed at exploring the optimum dose and route of administration for achieving maximum arsenic elimination with minimal side effects. We also carried out a pharmacokinetic analysis of this drug to support arsenic chelation. Rats were exposed to arsenic (25 ppm) for 6 months and later received MiADMSA (50 or 100 mg/kg) orally and via i.p. route for 5 days. Oxidative stress parameters and arsenic levels in soft tissues, liver function test and histopathology of liver and kidney were performed. Plasma kinetic of MiADMSA (plasma-free drug and total drug) at 50 and 100 mg/kg p.o. was carried out. Arsenic exposure resulted in significant oxidative stress and hepatotoxicity. MiADMSA at 50 mg/kg dose administered orally provided about 45% and 75% protection against oxidative stress and in lowering body arsenic burden, respectively, against 25% and 40% via i.p. route. Pharmacokinetic analysis supported prolonged availability of the drug through oral administration. Collectively, these findings led us to conclude that oral administration of MiADMSA was more effective than intraperitoneal administration and that the minimum effective dose with least side effects was 50 mg/kg.

Arsenic-induced oxidative stress and its reversibility

This review summarizes the literature describing the molecular mechanisms of arsenic-induced oxidative stress, its relevant biomarkers, and its relation to various diseases, including preventive and therapeutic strategies. Arsenic alters multiple cellular pathways including expression of growth factors, suppression of cell cycle checkpoint proteins, promotion of and resistance to apoptosis, inhibition of DNA repair, alterations in DNA methylation, decreased immunosurveillance, and increased oxidative stress, by disturbing the pro/antioxidant balance. These alterations play prominent roles in disease manifestation, such as carcinogenicity, genotoxicity, diabetes, cardiovascular and nervous systems disorders. The exact molecular and cellular mechanisms involved in arsenic toxicity are rather unrevealed. Arsenic alters cellular glutathione levels either by utilizing this electron donor for the conversion of pentavalent to trivalent arsenicals or directly binding with it or by oxidizing glutathione via arsenic-induced free radical generation. Arsenic forms oxygen-based radicals (OH(•), O(2)(•-)) under physiological conditions by directly binding with critical thiols. As a carcinogen, it acts through epigenetic mechanisms rather than as a classical mutagen. The carcinogenic potential of arsenic may be attributed to activation of redox-sensitive transcription factors and other signaling pathways involving nuclear factor κB, activator protein-1, and p53. Modulation of cellular thiols for protection against reactive oxygen species has been used as a therapeutic strategy against arsenic. N-acetylcysteine, α-lipoic acid, vitamin E, quercetin, and a few herbal extracts show prophylactic activity against the majority of arsenic-mediated injuries in both in vitro and in vivo models. This review also updates the reader on recent advances in chelation therapy and newer therapeutic strategies suggested to treat arsenic-induced oxidative damage.

Chelation in metal intoxication

Chelation therapy is the preferred medical treatment for reducing the toxic effects of metals. Chelating agents are capable of binding to toxic metal ions to form complex structures which are easily excreted from the body removing them from intracellular or extracellular spaces. 2,3-Dimercaprol has long been the mainstay of chelation therapy for lead or arsenic poisoning, however its serious side effects have led researchers to develop less toxic analogues. Hydrophilic chelators like meso-2,3-dimercaptosuccinic acid effectively promote renal metal excretion, but their ability to access intracellular metals is weak. Newer strategies to address these drawbacks like combination therapy (use of structurally different chelating agents) or co-administration of antioxidants have been reported recently. In this review we provide an update of the existing chelating agents and the various strategies available for the treatment of heavy metals and metalloid intoxications.

Monoisoamyl dimercaptosuccinic acid abrogates arsenic-induced developmental toxicity in human embryonic stem cell-derived embryoid bodies: comparison with in vivo studies

The ability of human embryonic stem (ES) cells to differentiate into the three germ layers has proposed its application in studying human developmental toxicity in vitro. In the current study we investigated if the prompted application could be utilized to evaluate the efficacy of a newly developed arsenic antidote, monoisoamyl dimercaptosuccinic acid (MiADMSA) against arsenic (III) and if the results obtained in vitro were in concordance with the animal model for studying developmental toxicity. On the basis of real time PCR (qRT-PCR) and cytotoxicity analysis of human embryoid bodies (EBs), we observed that arsenic (III) caused a significant down regulation of gene expression in all the three germ layers, which could be correlated with high mortality, visceral and skeletal defects in pups. Reversal of arsenic-induced dysfunctioning could be observed with concomitant treatment of MiADMSA in vitro and in vivo, indicating ES-EB model could provide toxicity information similar to in vivo model. IR spectroscopy further suggested that MiADMSA bind to arsenic to form adduct, which prevents arsenic from exerting its toxic effect in both models. To our knowledge this study provides first experimental evidence suggesting human ES cells could be utilized in studying the efficacy of drugs in a comparable manner with animal models. We conclude that the ES-EB model seems to be an effective, faster, cost effective method for predicting efficacy of a drug.

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.

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.

Changes in brain biogenic amines and haem biosynthesis and their response to combined administration of succimers and Centella asiatica in lead poisoned rats

This study was designed to investigate the therapeutic potential of meso 2,3-dimercaptosuccinic acid (DMSA) and one of its monoesters, monoisoamyl DMSA (MiADMSA), individually or when administered in combination with an extract of Centella asiatica against experimental lead intoxication in rats. Biochemical variables indicative of alterations in the central nervous system and haem biosynthesis were investigated to determine the toxicity in male Wistar rats. Thirty five rats were exposed to 0.2% lead acetate for 10 weeks, followed by 10 days of treatment with DMSA and MiADMSA (50 mg kg(-1), i.p., once daily) alone and in combination with C. asiatica (200 mg kg(-1), p.o., once daily). Biochemical variables indicative of oxidative stress and brain biogenic amines, along with lead concentration in blood and brain, were measured. Lead exposure caused a significant depletion of blood and brain delta-aminolevulinic acid dehydratase (ALAD) activity, an important enzyme of the haem biosynthesis pathway, and glutathione (GSH) level. These changes were accompanied by a marked increase in reactive oxygen species (ROS) level, thiobarbituric acid reactive substances (TBARS), delta-aminolevulinic acid synthase (ALAS) and oxidized glutathione (GSSG) activity in blood and brain. Significant depletion of brain noradrenaline (norepinephrine, NE), 5-hydroxytryptamine (5-HT), dopamine (DA) and acetylcholinesterase (AChE) also were observed following lead exposure. Also seen was a significant depletion in brain glutathione peroxidase (GPx), glutathione S-transferase (GST) and monoamine oxidase activity, as well as blood and brain superoxide dismutase (SOD) activity. These biochemical changes were correlated with an increased uptake of lead in blood and brain. Combined administration of MiADMSA and C. asiatica was most effective in reducing these alterations, including biogenic amines, besides reducing body lead burden, compared with individual treatment with MiADMSA. Certain other biochemical variables responded favourably to combination therapy and monotherapy with MiADMSA. Thus, supplementation of C. asiatica during chelation could be recommended for achieving optimum effects of chelation therapy.

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.

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

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

Arsenic antagonism studies with monoisoamyl DMSA and zinc in male mice

Administration of zinc either alone or in combination with monoisoamyl dimercaptosuccinic acid (DMSA) during and post-arsenic exposure was investigated in male mice. The animals were administered 2mgkg(-1) arsenic as sodium arsenite, intraperitoneally, once daily for 5 days either alone or in combination with 10mgkg(-1), zinc (as zinc acetate, orally), 50mgkg(-1) monoisoamyl dimercaptosuccinic acid (MiADMSA) given orally (p.o.), 2h after arsenic administration. Another group of arsenic treated animals was given both zinc (10mgkg(-1)) and MiADMSA (50mgkg(-1), p.o.). Animals were sacrificed 24h after the last dose. In another set of experimentation, arsenic pre-exposed mice (2mgkg(-1), i.p. for 5 days) were treated with saline, zinc, MiADMSA or zinc plus MiADMSA for next 3 days and sacrificed thereafter. Exposure to arsenic led to a significant inhibition of blood δ-aminolevulinic acid dehydratase (ALAD), depletion of glutathione (GSH) level and marginal elevations of zinc protoporphyrin (ZPP). Arsenic exposure caused a significant decrease in hepatic and renal GSH level and an increase in liver oxidized glutathione (GSSG) and liver and kidney thiobarbituric acid reactive substance (TBARS) levels. Concomitant administration of zinc with arsenic provided significant protection to blood ALAD activity while, GSH and ZPP levels remained unaltered. Co-administration of MiADMSA with arsenic significantly prevented accumulation of arsenic in blood, liver and kidney while, zinc had no effect on tissue arsenic concentration. Combined administration of zinc and MiADMSA had no major additional beneficial effects over their individual effects. Interestingly, post-arsenic exposure treatment with MiADMSA provided significant recovery in blood ALAD activity while, zinc supplementation alone had no effect. The best results however, were obtained when MiADMSA was administered along-with zinc. Most of the biochemical variables indicative of hepatic oxidative stress responded favorably to MiADMSA treatment while, zinc administration had no effect. Administration of MiADMSA significantly depleted arsenic concentration from the soft tissues while, combined zinc and MiADMSA had no additional beneficial effect over the individual effect of MiADMSA. The results thus lead us to conclude that in order to achieve best effects of chelation therapy, co-administration of zinc with chelator might be preferred. However, detailed experimental studies with variable doses and after chronic arsenic exposure are required.

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.