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

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.

Potential protective roles of curcumin against cadmium-induced toxicity and oxidative stress

Curcumin, used as a spice and traditional medicine in India, exerts beneficial effects against several diseases, owing to its antioxidant, analgesic, and anti-inflammatory properties. Evidence indicates that curcumin might protect against heavy metal-induced organ toxicity by targeting biological pathways involved in anti-oxidation, anti-inflammation, and anti-tumorigenesis. Curcumin has received considerable attention owing to its therapeutic properties, and the mechanisms underlying some of its actions have been recently investigated. Cadmium (Cd) is a heavy metal found in the environment and used extensively in industries. Chronic Cd exposure induces damage to bones, liver, kidneys, lungs, testes, and the immune and cardiovascular systems. Because of its long half-life, exposure to even low Cd levels might be harmful. Cd-induced toxicity involves the overproduction of reactive oxygen species (ROS), resulting in oxidative stress and damage to essential biomolecules. Dietary antioxidants, such as chelating agents, display the potential to reduce Cd accumulation and metal-induced toxicity. Curcumin scavenges ROS and inhibits oxidative damage, thus resulting in many therapeutic properties. This review aims to address the effectiveness of curcumin against Cd-induced organ toxicity and presents evidence supporting the use of curcumin as a protective antioxidant.

The Role of Mesenchymal Stem Cells with Ascorbic Acid and N-Acetylcysteine on TNF-α, IL 1β, and NF-κβ Expressions in Acute Pancreatitis in Albino Rats

Severe acute pancreatitis (SAP) is a necrotic pancreatic inflammation associated with high mortality rate (up to 70%). Bone marrow (BM) mesenchymal stem cells (MSCs) have been investigated in pancreatic cellular regeneration, but still their effects are controversial. Therefore, the present study is aimed at examining the enrichment of the stem cells with ascorbic acid (AA) and N-acetylcysteine (NAC) and explore their combined action on the expression of the inflammatory cytokines: interleukin 1β (IL 1β), tumor necrosis factor-α (TNF-α), and nuclear factor-κβ (NF-κβ). A total of twenty adult male Sprague-Dawley albino rats were divided into four groups: the control group, cerulein group (to induce acute pancreatitis), BM-MSCs group, and combined BM-MSCs with AA and NAC group. Homing and proliferation of stem cells were revealed by the appearance of PKH26-labelled BM-MSCs in the islets of Langerhans. AA and NAC combination with BM-MSCs (group IV) was demonstrated to affect the expression of the inflammatory cytokines: IL 1β, TNF-α, and NF-κβ. In addition, improvement of the biochemical and histological parameters is represented in increasing body weight, normal blood glucose, and insulin levels and regeneration of the islet cells. Immunohistochemical studies showed an increase in proliferating cell nuclear antigen (PCNA) and decrease in caspase-3 reactions, detected markedly in group IV, after the marked distortion of the classic pancreatic lobular architecture was induced by cerulein. It could be concluded that treatment with BM-MSCs combined with antioxidants could provide a promising therapy for acute pancreatitis and improve the degeneration, apoptosis, necrosis, and inflammatory processes of the islets of Langerhans. TNF-α, IL 1β, and NF-κβ are essential biomarkers for the evaluation of MSC regenerative effectiveness.

Arsenal of Phytochemicals to Combat Against Arsenic-Induced Mitochondrial Stress and Cancer

Significance: Phytochemicals are important dietary constituents with antioxidant properties. They affect various signaling pathways involved in the overall maintenance of interior milieu of the cell. Arsenic, an environmental toxicant, is well known for its deleterious consequences, such as various diseases, including cancers in humans. Mitochondria are the cell's powerhouse that fuel all metabolic energy requirements. Dysfunctional mitochondria due to stressors may lead to abnormal functioning of the organelle, hampering the crucial cellular cross talks and ultimately leading to cancer. Application of phytochemicals against arsenic-induced mitochondrial disorders may be a preventive measure to counteract the ruinous impacts of the metalloid. Recent Advances: In recent years, extensive research on the role of mitochondria in cancer gives a better understanding of the areas the organelle covers in maintaining a healthy cell or in inducing carcinogenicity. Detailed knowledge of the mitochondrial governances would enable researchers to administer numerous phytochemicals to ameliorate altered oxidative phosphorylation, mitochondrial membrane potential (MMP), mitochondrial oxidative stress, unfolded protein response, glycolysis, or even apoptosis. Critical Issues: In this review, we have addressed how various phytochemicals belonging to diverse classes combat against arsenic-induced mitochondrial oxidative stress, depletion of MMP, cell cycle abrogation, apoptosis, glycolytic damages, oncogenic regulations, chaperones, mitochondrial complexes, and mitochondrial membrane pore formation in both in vitro and in vivo models. Future Directions: Insightful application of mitoprotective phytochemicals against arsenic-induced mitochondrial oxidative stress and carcinogenesis may guide researchers to develop preclinical chemopreventive agents to fight arsenic toxicity in humans.

The Hormetic Effect of Arsenic Trioxide on Rat Pulpal Cells: An In Vitro Preliminary Study

Objectives  Despite the agreement that there is no longer any indication for arsenic use in modern endodontics, some concerns are surfacing about the minute amount of arsenic trioxide (As ₂ O ₃ ) released from Portland cement-based materials. The present study investigated the effect of different concentrations of As ₂ O ₃ on rat pulpal cells and the efficacy of N -acetylcysteine (NAC) in preventing As ₂ O ₃ -mediated toxicity.

Materials and Methods  Cytotoxicities of 50, 10, or 5 µm As ₂ O ₃ and the effect of cells co-treatment with 50 µm As ₂ O ₃ and 5,000 µm NAC or 500 µm NAC were tested at 24 hours or 3 days. Cell viability was assessed by means of MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and cellular morphological changes were observed under phase contrast microscope.

Statistical Analysis  Two-way analysis of variance with Tukey’s post-hoc test was used to evaluate differences between the groups (α = 0.05).

Results  At both exposure times, 50 µm As ₂ O ₃ resulted in lower optical density (OD) values when compared with 10 or 5 µm As ₂ O ₃ . At 24 hours, 10 µm As ₂ O ₃ resulted in a higher OD value compared with the control; however, at 3 days the difference was statistically insignificant. At each exposure time, the OD value of 5 µm As ₂ O ₃ group was comparable to the control and 10 µm As ₂ O ₃ group. There were no significant differences between 50 µm As ₂ O ₃ group and 500 μm NAC+50 μm As ₂ O ₃ group; however, these two groups had lower OD values when compared with 5,000 μm NAC+50 μm As ₂ O ₃ group at 24 hours and 3 days. The latter group showed significantly lower OD value in comparison with the control at 24 hours and 3 days. Control cells were polygonal-shaped while 50 µm As ₂ O ₃ -treated cells exhibited contracted and spherical morphology with increased intercellular spaces. At 24 hours, 10 μm and 5 µm As ₂ O ₃ -treated cells were slightly hypertrophic. Cells co-treated with NAC and As ₂ O ₃ showed increased intercellular spaces and lower cellular density compared with the control.

Conclusions  As ₂ O ₃ displayed a hormetic effect on pulpal cells; however, the proliferative effect induced by low As ₂ O ₃ concentrations should be interpreted with caution. NAC did not prevent As ₂ O ₃ -mediated toxicity; however, it demonstrated potential for ameliorating this toxicity.

Mitigation of arsenic driven utero-ovarian malfunction and changes of apoptotic gene expression by dietary NAC

An oral painless dietary therapy is also indispensable in the management of arsenic toxicity despite of its conventional painful therapeutic management. The present study focused on the management of arsenic mediated female reproductive dysfunctions by dietary therapy of N-acetyl cysteine (NAC). Here, sodium arsenite was given at the dose of 10 mg/kg body weight orally for the first 8 day. Day 9 onwards up to day 16 these arsenicated rats were provided with NAC (250 mg/kg body weight) enriched basal diet once daily. Arsenic intoxicated group exhibited a comparable inactivation of antioxidant enzymes superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) due to oxidative stress in reproductive organs along with a simultaneous elevation of lipid peroxidation state and decline in non-protein soluble thiols (NPSH) level in female reproductive organs. Arsenic intoxication also accomplished with the up-regulation of inflammatory markers tumour necrosis factor (TNF α) and nuclear factor κB (NF κB). Pro-apoptotic Bax gene and p53 gene expressions were also raised due to arsenic intoxication while anti-apoptotic Bcl-2 gene expression was suppressed. In fact, arsenication decreased the circulating level of vitamin B₁₂ and folic acid. Dietary NAC supplementation significantly reversed back the activity of antioxidant enzymes in arsenite fed rats towards normalcy and also sustained the normal reproductive cyclicity, utero-ovarian histo-morphology and estradiol receptor α (ER-α) expression in these reproductive organs. Dietary NAC exerted its positive action against arsenic intoxication by up-regulation of Bcl-2 gene expression along with the suppression of pro-apoptotic Bax gene and p53 gene. Thus, dietary NAC also plays anti-apoptotic, anti-inflammatory, and anti-oxidative role against arsenic toxicity. NAC also regulates the components (vitamin B₁₂ and folic acid) of S-adenosylmethionine pool in the way of probable removal of arsenic from the system.

Arsenic intoxication: general aspects and chelating agents

Arsenic (As) is widely used in the modern industry, especially in the production of pesticides, herbicides, wood preservatives, and semiconductors. The sources of As such as contaminated water, air, soil, but also food, can cause serious human diseases. The complex mechanism of As toxicity in the human body is associated with the generation of free radicals and the induction of oxidative damage in the cell. One effective strategy in reducing the toxic effects of As is the usage of chelating agents, which provide the formation of inert chelator–metal complexes with their further excretion from the body. This review discusses different aspects of the use of metal chelators, alone or in combination, in the treatment of As poisoning. Consideration is given to the therapeutic effect of thiol chelators such as meso-2,3-dimercaptosuccinic acid, sodium 2,3-dimercapto-1-propanesulfonate, 2,3-dimercaptopropanol, penicillamine, ethylenediaminetetraacetic acid, and other recent agents against As toxicity. The review also considers the possible role of flavonoids, trace elements, and herbal drugs as promising natural chelating and detoxifying agents.

A Review on Coordination Properties of Thiol-Containing Chelating Agents Towards Mercury, Cadmium, and Lead

The present article reviews the clinical use of thiol-based metal chelators in intoxications and overexposure with mercury (Hg), cadmium (Cd), and lead (Pb). Currently, very few commercially available pharmaceuticals can successfully reduce or prevent the toxicity of these metals. The metal chelator meso-2,3-dimercaptosuccinic acid (DMSA) is considerably less toxic than the classical agent British anti-Lewisite (BAL, 2,3-dimercaptopropanol) and is the recommended agent in poisonings with Pb and organic Hg. Its toxicity is also lower than that of DMPS (dimercaptopropane sulfonate), although DMPS is the recommended agent in acute poisonings with Hg salts. It is suggested that intracellular Cd deposits and cerebral deposits of inorganic Hg, to some extent, can be mobilized by a combination of antidotes, but clinical experience with such combinations are lacking. Alpha-lipoic acid (α-LA) has been suggested for toxic metal detoxification but is not considered a drug of choice in clinical practice. The molecular mechanisms and chemical equilibria of complex formation of the chelators with the metal ions Hg2+, Cd2+, and Pb2+ are reviewed since insight into these reactions can provide a basis for further development of therapeutics.

Heavy metal toxicity: An update of chelating therapeutic strategies

AIM

This review illustrates heavy metals toxicity, currently available therapies and the role and efficacy of chelation therapy for its management.

SUMMARY

Heavy metals are necessary for various biological processes, but they become harmful in excess. Specifically, they induce oxidative stress by generating free radicals and reducing antioxidant levels. Heavy metals also alter the confirmation of protein and DNA and inhibit their function. Chelation therapy is commonly used to treat metals toxicity. Chelation is a chemical process that occurs when interaction between a central metal atom/ion and ligand leads to formation of a complex ring-like structure. The ligand has a donor ion/molecule, which has a lone pair of electrons and may be monodentate to polydentate. Each metal has a different reactivity with a ligand, so a specific chelation agent is required for each metal. Combination therapy with a chelating agent and an antioxidant led to improved outcome.

CONCLUSION

Heavy metal poisoning is a common health problem because of mining, smelting, industrial, agricultural and sewage waste. Heavy metals can be efficiently excreted from the body following treatment with proper chelation agents.

Interventions to Address Environmental Metabolism-Disrupting Chemicals: Changing the Narrative to Empower Action to Restore Metabolic Health

Metabolic disease rates have increased dramatically over the last four decades. Classic understanding of metabolic physiology has attributed these global trends to decreased physical activity and caloric excess; however, these traditional risk factors insufficiently explain the magnitude and rapidity of metabolic health deterioration. Recently, the novel contribution of environmental metabolism-disrupting chemicals (MDCs) to various metabolic diseases (including obesity, diabetes, and non-alcoholic fatty liver disease) is becoming recognized. As this burgeoning body of evidence has matured, various organic and inorganic pollutants of human and natural origin have emerged as metabolic disease risk factors based on population-level and experimental data. Recognition of these heretofore underappreciated metabolic stressors now mandates that efforts to mitigate the devastating consequences of metabolic disease include dedicated efforts to address environmental drivers of disease risk; however, there have not been adequate recommendations to reduce exposures or to mitigate the effects of exposures on disease outcomes. To address this knowledge gap and advance the clinical translation of MDC science, herein discussed are behaviors that increase exposures to MDCs, interventional studies to reduce those exposures, and small-scale clinical trials to reduce the body burden of MDCs. Also, we discuss evidence from cell-based and animal studies that provide insights into MDC mechanisms of action, the influence of modifiable dietary factors on MDC toxicity, and factors that modulate MDC transplacental carriage as well as their impact on metabolic homeostasis. A particular emphasis of this discussion is on critical developmental windows during which short-term MDC exposure can elicit long-term disruptions in metabolic health with potential inter- and transgenerational effects. While data gaps remain and further studies are needed, the current state of evidence regarding interventions to address MDC exposures illuminates approaches to address environmental drivers of metabolic disease risk. It is now incumbent on clinicians and public health agencies to incorporate this knowledge into comprehensive strategies to address the metabolic disease pandemic.

An overview of plant-based interventions to ameliorate arsenic toxicity

The industrial and technological advancements in the world have also contributed to the rapid deterioration in the environment quality through introduction of obnoxious pollutants that threaten to destroy the subtle balance in the ecosystem. The environment contaminants cause severe adverse effects to humans, flora and fauna that are mostly irreversible. Chief among these toxicants is arsenic, a metalloid, which is considered among the most dangerous environmental toxins that leads to various diseases which affect the quality of life even when present in small quantities. Treatment of arsenic-mediated disorders still remains a challenge due to lack of effective options. Chelation therapy has been the most widely used method to detoxify arsenic. But this method is associated with deleterious effects leading various toxicities such as hepatotoxicity, neurotoxicity and other adverse effects. It has been discovered that indigenous drugs of plant origin display effective and progressive relief from arsenic-mediated toxicity without any side-effects. Further, these phytochemicals have also been found to aid the elimination of arsenic from the biological system and therefore can be more effective than conventional therapeutic agents in ameliorating arsenic-mediated toxicity. This review presents an overview of the toxic effects of arsenic and the therapeutic strategies that are available to mitigate the toxic effects with emphasis on chelation as well as protective and detoxifying activities of different phytochemicals and herbal drugs against arsenic. This information may serve as a primer in identifying novel prophylactic as well as therapeutic formulations against arsenic-induced toxicity.

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.

The consequence of NAC on sodium arsenite-induced uterine oxidative stress

Arsenic consumption through drinking water is a worldwide major health problem. Management of arsenic intoxication with invasive, painful therapy using metal chelators is usually used as a conventional treatment strategy in human. In this present study, we examined the efficacy of oral administration of N-acetyl l-cysteine (NAC) in limiting arsenic-mediated female reproductive disorders and oxidative stress in female Wistar rats. The treatment was continued for 8 days (2 estrus cycles) on rats with sodium arsenite (10 mg/Kg body weight) orally. We examined the electrozymographic imprint of three different enzymatic antioxidants in uterine tissue. Rats fed with sodium arsenite exhibited a significant lessening in the activities of superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx). Uterine DNA breakage, necrosis, ovarian and uterine tissue damage, disruption in steroidogenesis were also found in arsenic treated rats. Co-administration of NAC at different doses (50 mg/kg body weight, 100 mg/kg body weight, respectively) significantly reversed the action of uterine oxidative stress markers like malondialdehyde (MDA), conjugated dienes (CD) and non protein soluble thiol (NPSH); and noticeably improved antioxidant status of the arsenic fed rats. This ultimately resulted in the uterine tissue repairing followed by improvement of ovarian steroidogenesis. However, this effective function of NAC might be crucial for the restoration of arsenic-induced female reproductive organ damage in rats.

N-acetylcysteine and meso-2,3-dimercaptosuccinic acid alleviate oxidative stress and hepatic dysfunction induced by sodium arsenite in male rats

Environmental exposure to arsenic represents a serious challenge to humans and other animals. The aim of the present study was to test the protective effect of antioxidant N-acetylcysteine (NAC) either individually or in combination with a chelating agent, meso-2,3-dimercaptosuccinic acid (DMSA), against sodium arsenite oral toxicity in male rats. Five groups were used: control; arsenic group (orally administrated in a concentration of 2 mg/kg body weight [b.w.]); the other three groups were orally administrated sodium arsenite in a concentration of 2 mg/kg b.w. followed by either NAC (10 mg/kg b.w., intraperitoneally [i.p.]), DMSA (50 mg/kg b.w., i.p.) or NAC plus DMSA. Arsenic toxicity caused significant rise in serum aspartate aminotransferase, alanine aminotransferase and total bilirubin, and a significant decrease in total protein (TP) and albumin levels after 3 weeks of experimental period. In addition, arsenic-treated rats showed significantly higher arsenic content in liver and significant rise in hepatic malondialdehyde level. By contrast, sharp decreases in glutathione content and catalase and glutathione reductase activities were discernible. NAC and/or DMSA counteracted most of these physiologic and biochemical defects. NAC monotherapy was more effective than DMSA in increasing TP, while DMSA was more effective in decreasing alanine aminotransferase. The combined treatment was superior over monotherapies in recovery of TP and glutathione. Biochemical data were well supported by histopathological and ultrastructural findings. In conclusion, the combination therapy of NAC and DMSA may be an ideal choice against oxidative insult induced by arsenic poisoning.

Nano drug delivery systems: a new paradigm for treating metal toxicity

INTRODUCTION

The standard medical treatment for metal toxicity is chelation therapy. Chelating agents work by forming less toxic complexes with the toxic metal ions which are readily excreted from the body. These compounds, based on their hydrophilic/lipophilic property, can either remove toxic metal ions from extracellular sites or can penetrate the intracellular compartments to facilitate the removal of toxic metal ions. However, there are various disadvantages associated with this kind of therapy, notably, selectivity. Other problems and challenges are that the therapy regime is expensive, time consuming and has poor patient compliance. Two chelating agents, dimercaptosuccinic acid (DMSA) and dimercaptopropionicsulfonate (DMPS) have gained increased acceptance among clinicians, undoubtedly improving the management of metal intoxications.

AREAS COVERED

The present review provides an insight into the conventional chelating agents, new chelators under development, and the new opportunities presented by the use of nanotherapy for the treatment of metal poisoning cases.

EXPERT OPINION

Today's research should not only focus towards development of alternate chelators but also targeted therapy such as the nanotherapy.

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.

Chelation: harnessing and enhancing heavy metal detoxification--a review

Toxic metals such as arsenic, cadmium, lead, and mercury are ubiquitous, have no beneficial role in human homeostasis, and contribute to noncommunicable chronic diseases. While novel drug targets for chronic disease are eagerly sought, potentially helpful agents that aid in detoxification of toxic elements, chelators, have largely been restricted to overt acute poisoning. Chelation, that is multiple coordination bonds between organic molecules and metals, is very common in the body and at the heart of enzymes with a metal cofactor such as copper or zinc. Peptides glutathione and metallothionein chelate both essential and toxic elements as they are sequestered, transported, and excreted. Enhancing natural chelation detoxification pathways, as well as use of pharmaceutical chelators against heavy metals are reviewed. Historical adverse outcomes with chelators, lessons learned in the art of using them, and successes using chelation to ameliorate renal, cardiovascular, and neurological conditions highlight the need for renewed attention to simple, safe, inexpensive interventions that offer potential to stem the tide of debilitating, expensive chronic disease.

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.

Beneficial effects of Centella asiatica aqueous extract against arsenic-induced oxidative stress and essential metal status in rats

The efficacy of an aqueous extract of Centella asiatica (100, 200 and 500 mg/kg for 5 consecutive days) was studied in the depletion of arsenic and in the recovery of a few altered biochemical variables in arsenic pre-exposed rats (20 ppm in drinking water for 5 weeks). Exposure to arsenic significantly depleted delta-aminolevulinic acid dehydratase (ALAD) activity, reduced glutathione (GSH) level, superoxide dismutase (SOD) and increased thiobarbituric acid reactive substance (TBARS) activity in red blood cells. Significant depletion of ALAD activity, GSH level, glutathione peroxidase (GPx), SOD and catalase (CAT) activities and an increase in TBARS levels in liver tissues was also noted. There was a significant depletion of SOD, CAT and GPx activities in kidneys and an increased TBARS levels in kidney and brain accompanied by increased arsenic concentration in blood and soft tissues. Treatment with aqueous extract of Centella asiatica provided significant protection against ALAD, GSH and TBARS levels, particularly at doses of 200 and 500 mg. Centella asiatica also provided significant recovery in the inhibited liver ALAD and G6PD activities. Arsenic concentration in blood and soft tissues remained uninfluenced after Centella asiatica administration. The present study thus suggests a beneficial effect of Centella asiatica against arsenic-induced oxidative stress but possesses no chelating property.

Oxidative metabolism of lung macrophages exposed to sodium arsenite

Arsenic pollution has become increasingly severe. It occurs as the result of geological processes and different human activities. Arsenic toxicity at the respiratory level occurs mainly by inhalation of products of coal combustion. The aim of this study was to evaluate sodium arsenite (As(3+)) toxicity in murine alveolar macrophages (AMs) in vitro and its association with the alterations in cell metabolism. No changes in viability, apoptosis or cell area were detected in AMs treated with As(3+) concentrations up to 2 microM for 24-96 h. A marked decrease in these end-points was observed for As(3+) concentrations ranging from 2.5 microM to 10 microM. Regarding the dynamics of the endo-exocytic process triggered by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell incorporation, no variations were detected for As(3+) concentrations lower than 2 microM while higher concentrations markedly modified this response. MTT specific activity, as a measure of cell metabolic activity, was not modified irrespective of the As(3+) concentration assayed. However, nitroblue tetrazolium (NBT) specific activity, as a measure of superoxide anion generation, is responsive but only to low As(3+) doses. Although this study focuses on lung macrophages, the effects of As(3+) described herein may also apply to the response of macrophages residing in other organs. Arsenite modifies the metabolic and the oxidative status of AMs in vitro. When macrophages are in an As(3+) rich medium, they exhibit a reduction in respiratory burst levels and lose their intrinsic capacity to respond to toxicants.

Effects of combined administration of captopril and DMSA on arsenite induced oxidative stress and blood and tissue arsenic concentration in rats

We compared the therapeutic efficacy of captopril and a thiol chelating agent, meso 2,3-dimercaptosuccinic acid (DMSA) either individually or in combination against arsenite induced oxidative stress and mobilization of metal in rats. Animals were exposed to 100 ppm arsenite as sodium arsenite in drinking water for six weeks followed by treatment with DMSA (50 mg/kg, orally), captopril (50 mg/kg, intraperitoneally) either alone or in combination, once daily for 5 consecutive days. Arsenite exposure led to a significant depletion of blood delta-aminolevulinic acid dehydratase (ALAD) activity, glutathione and platelet levels while significantly increased the level of reactive oxygen species (in RBCs). Hepatic reduced glutathione (GSH) level showed a significant decrease while, thiobarbituric acid reactive substances (TBARS) levels increased on arsenite exposure indicating arsenite induced hepatic oxidative stress. Kidney GSH, GSSG, catalase and TBARS remained unchanged on arsenite exposure. Treatment with DMSA was effective in increasing ALAD activity while, captopril was ineffective when given alone. Captopril when co-administered with DMSA also provided no additional beneficial effect on blood ALAD activity but significant brought altered platelet counts back to the normal value. In contrast, administration of captopril alone provided significant beneficial effects on hepatic oxidative stress, and in combination with DMSA provided a more pronounced recovery in the TBARS level compared to the individual effect of DMSA and captopril. Renal biochemical variables remained insensitive to arsenite and any of the treatments. Interestingly, combined administration of captopril with DMSA had a remarkable effect in depleting total arsenic concentration from blood and soft tissues. These results lead us to conclude that captopril administration during chelation treatment had some beneficial effects particularly on the protection of inhibited blood ALAD activity, and depletion of arsenic level. The study supports our earlier conclusion that a co-administration of an antioxidant is more beneficial than monotherapy with the chelating agents, in order to achieve optimal effects of chelation in arsenite toxicity.