The effect of chelating agents on the excretion of endogenous metals

Zinc deficiency induced by the chelating agent DTPA and its regulatory interpretation for developmental toxicity classification

Aminocarboxylic acid (ethylenediamine-based) chelating agents such as DTPA are widely used in a variety of products and processes. Recently, DTPA was classified in the European Union as a developmental toxicant CLP Category 1B. However, according to the CLP regulation (CLP, 2008) classification as a developmental toxicant requires a chemical to possess an intrinsic, specific property to do so. This paper provides overwhelming evidence that shows the developmental toxicity only seen at a sustained high dose of 1000 mg DTPA/kg bw/day in rats during pregnancy is mediated by zinc depletion which leads to non-specific secondary effects associated with zinc deficiency. Therefore, based on the CLP regulation itself, viz. the lack of a specific, intrinsic property, supported by significant differences in zinc kinetics and physiology between pregnant rats and pregnant women, DTPA should not be classified as a developmental toxicant. Moreover, classification for developmental toxicity resulting from zinc deficiency, and only observed at high doses, would not increase protection of human health; instead, it will only lead to onerous and disproportionate restrictions being placed on the use of this substance.

Engineering a Biodegradable Nanocarrier for Enhancing the Response of T98G Cells to Temozolomide

Temozolomide (TMZ), the most common DNA alkylating agent, is predominantly mediated by O⁶-methylguanine DNA lesions for the treatment of glioblastoma (GBM). When O⁶-methylguanine-DNA methyltransferase (MGMT) is present, TMZ-induced O⁶-methylguanine lesions are repaired, resulting in the emergence of resistance to chemotherapy. Herein, we attempted to enhance the response of T98G cells to TMZ by gene silencing of MGMT. In this work, we developed transition metal manganese (Mn)-doped mesoporous silica nanoparticles (MSNs) as a carrier system for the co-delivery of TMZ and 10-23 DNAzyme, and realized gene silencing to enhance the TMZ sensitivity in T98G cells. The intelligent theranostic platform based on manganese-doped mesoporous silica nanoparticles (Mn-MSNs) can be decomposed and release chemotherapy drugs under acidic pH and reducing conditions. Meanwhile, the produced Mn²⁺ could act as a cofactor of 10-23 DNAzyme to effectively cleave MGMT mRNA, knock down MGMT protein, and sensitize T98G cells to TMZ-induced apoptosis. By co-delivering TMZ and 10-23 DNAzyme employing Mn-MSNs, the concentrations of TMZ that needed to inhibit cell growth by 50% (IC₅₀ values) decreased (by more than 3.8-fold) compared with free TMZ. This work shows that the designed platform holds great promise for advancing the treatment of drug-resistant cancer.

Periodic trends and complexation chemistry of tetravalent actinide ions with a potential actinide decorporation agent 5-LIO(Me-3,2-HOPO): A relativistic density functional theory exploration

A relativistic density functional theory (DFT) study is reported which aims to understand the complexation chemistry of An⁴⁺ ions (An = Th, U, Np, and Pu) with a potential decorporation agent, 5-LIO(Me-3,2-HOPO). The calculations show that the periodic change of the metal binding free energy has an excellent correlation with the ionic radii and such change of ionic radii also leads to the structural modulation of actinide-ligand complexes. The calculated structural and binding parameters agree well with the available experimental data. Atomic charges derived from quantum theory of atoms in molecules (QTAIM) and natural bond order (NBO) analysis shows the major role of ligand-to-metal charge transfer in the stability of the complexes. Energy decomposition analysis, QTAIM, and electron localization function (ELF) predict that the actinide-ligand bond is dominantly ionic, but the contribution of orbital interaction is considerable and increases from Th⁴⁺ to Pu⁴⁺ . A decomposition of orbital contributions applying the extended transition state-natural orbital chemical valence method points out the significant π-donation from the oxygen donor centers to the electron-poor actinide ion. Molecular orbital analysis suggests an increasing trend of orbital mixing in the context of 5f orbital participation across the tetravalent An series (Th-Pu). However, the corresponding overlap integral is found to be smaller than in the case of 6d orbital participation. An analysis of the results from the aforementioned electronic structure methods indicates that such orbital participation possibly arises due to the energy matching of ligand and metal orbitals and carries the signature of near-degeneracy driven covalency.

Effects of Zinc and N-Acetylcysteine in Damage Caused by Lead Exposure in Young Rats

This study investigated the toxicity of rats exposed to lead acetate (AcPb) during the second phase of brain development (8-12 days postnatal) in hematological and cerebral parameters. Moreover, the preventive effect of zinc chloride (ZnCl₂) and N-acetylcysteine (NAC) was investigated. Pups were injected subcutaneously with saline (0.9% NaCl solution), ZnCl₂ (27 mg/kg/day), NAC (5 mg/kg/day) or ZnCl₂ plus NAC for 5 days (3rd-7th postnatal days), and with saline (0.9% NaCl solution) or AcPb (7 mg/kg/day) in the five subsequent days (8th-12th postnatal days). Animals were sacrificed 21 days after the last AcPb exposure. Pups exposed to AcPb presented inhibition of blood porphobilinogen-synthase (PBG-synthase) activity without changes in hemoglobin content. ZnCl₂ pre-exposure partially prevented PBG-synthase inhibition. Regarding neurotoxicity biomarkers, animals exposed to AcPb presented a decrease in cerebrum acetylcholinesterase (AChE) activity and an increase in Pb accumulation in blood and cerebrum. These changes were prevented by pre-treatment with ZnCl₂, NAC, and ZnCl₂ plus NAC. AcPb exposure caused no alteration in behavioral tasks. In short, results show that AcPb inhibited the activity of two important enzymatic biomarkers up to 21 days after the end of the exposure. Moreover, ZnCl₂ and NAC prevented the alterations induced by AcPb.

The role of chelation in the treatment of other metal poisonings

These proceedings will review the role of chelation in five metals-aluminum, cadmium, chromium, cobalt, and uranium-in order to illustrate various chelation concepts. The process of "chelation" can often be oversimplified, leading to incorrect assumptions and risking patient harm. For chelation to be effective, two critical assumptions must be fulfilled: the presumed "metal toxicity" must correlate with a given body or a particular compartment burden, and reducing this compartmental or the body burden (through chelation) attenuates toxicity. Fulfilling these assumptions requires an established dose-response relationship, a validated, reproducible means of toxicity assessment (clinical, biochemical, or radiographical), and an appropriate assessment mechanisms of body or compartment burden. While a metal might "technically" be capable of chelation (and readily demonstrable in urine or feces), this is an insufficient endpoint. Clinical relevance must be affirmed. Deferoxamine is an accepted chelator for appropriately documented aluminum toxicity. There is a very minimal treatment window in order to address chelation in cadmium toxicity. In acute toxicity, while no definitive chelation benefit is described, succimer (DMSA), diethylenetriaminepentaacetate (DTPA), and potentially ethylenediaminetetraacetic acid (EDTA) have been considered. In chronic toxicity, chelation is unsupported. There is little evidence to suggest that currently available chromium chelators are efficacious. Similarly, scant human evidence exists with which to provide recommendation for cobalt chelation. DTPA has been recommended for cobalt radionuclide chelation, although DMSA, EDTA, and N-acetylcysteine have also been suggested. DTPA is unsupported for uranium chelation. Sodium bicarbonate is currently recommended, although animal evidence is conflicting.

In vivo schistosomicidal activity of three novels 8-hydroxyquinoline derivatives against adult and immature worms of Schistosoma mansoni

Schistosomiasis control is widely dependent on a single drug, praziquantel (PZQ). The potential for development of resistance to PZQ has justified the search for new alternative chemotherapies. In a previous study, we have been reported that three of 8-hydroxyquinoline derivatives namely: 3-((8-hydroxyquinolin-5-yl) sulfonyl) pentane-2,4-dione (HQSP), 5-((2,4-diphenyl-3H-benzo[b][1,4]diazepin-3-yl) sulfonyl) quinolin-8-ol (HQBD), and 5-((2,4-diphenyl-3H-pyrido[3,4-b][1,4] diazepin-3-yl) sulfonyl) quinolin-8-ol (HQPD) possess a potent anti-schistosomal activity in vitro. The aim of the present study was to evaluate the in vivo schistosomicidal effect of these three compounds on adult and immature worms of Schistosoma mansoni and their induced pathology. Treatment of S. mansoni-infected mice with 1000, 250, 150, and 200 mg/kg body weight of PZQ, HQSP, HQBD, and HQPD, respectively, reduced adult and immature worm burden by 94.63 and 31.32%, 73.63 and 5.45%, 76.5 and 28.11%, and 81.25 and 56.84%, respectively, compared to infected untreated mice. Moreover, numbers of egg per gram liver and intestine were decreased by 84 and 95.51%, 47.84 and 46.28 %, 53.18 and 59.37 %, and 54.22 and 67.26 as a result of PZQ, HQSP, HQBD, and HQPD treatment, respectively. Hepatic granuloma volume was also reduced by 40.10, 42.96, 35.72, and 72.09% due to PZQ, HQSP, HQBD, and HQPD treatment, respectively. In addition, hepatic histopathological alterations and collagen fiber deposition that accompanied with S. mansoni infection were largely retrieved with different treatments, especially HQPD treatment. Furthermore, humoral immune response, especially IgG response against S. mansoni antigens, was augmented with different treatments. This study concluded that among the three tested 8-hydroxyquinoline derivatives, HQPD is the most effective compound against adult and pre-mature worms of S. mansoni and can be used for the development of a new schistosomicidal drug.

In vitro and in vivo effects of hesperidin treatment on adult worms of Schistosoma mansoni

Hesperidin has been reported to exert a wide range of pharmacological effects, including antifungal, antiviral, antioxidant, anti-inflammatory and anticarcinogenic activities. Herein, the schistosomicidal activity of this compound was evaluated in vitro and in vivo. Using an in vitro assay, a concentration of 200 μg/ml of hesperidin resulted in the mortality of 100% adult worms of Schistosoma (S.) mansoni within 72 h and a partial tegumental alteration in 10% of worms. However, after 144 h incubation, 50 and 100 μg/ml concentrations showed 0% and 10% mortality in adult worms, respectively, without any changes to the tegument. Sublethal doses did not influence egg output nor the development of eggs deposited by pairs of adult worms. In an in vivo study, mice infected with S. mansoni and treated with 600 mg hesperidin/kg body weight showed a respective reduction of 50, 45.2, 50 and 47.5% of males, females, worm pairs and total worm burden. In addition, a respective reduction, based on the number of eggs/g tissue, of 41.5, 63.7 and 58.6% was observed in the liver, intestine and liver/intestinal tissue combined. Furthermore, S. mansoni-specific IgG level significantly increased with hesperidin treatment, whereas IgA and IgE levels were not significantly changed. IgM levels decreased in response to cercarial antigen preparation but were not altered in response to soluble worm or soluble egg antigen. As in hesperidin-treated mice, praziquantel-treated mice showed a similar pattern of specific antibody response to S. mansoni antigens. The present study represents the first report on the effects of the schistosomicidal activity of hesperidin.

Locomotor damage and brain oxidative stress induced by lead exposure are attenuated by gallic acid treatment

We investigated the antioxidant potential of gallic acid (GA), a natural compound found in vegetal sources, on the motor and oxidative damages induced by lead. Rats exposed to lead (50 mg/kg, i.p., once a day, 5 days) were treated with GA (13.5mg/kg, p.o.) or EDTA (110 mg/kg, i.p.) daily, for 3 days. Lead exposure decreased the locomotor and exploratory activities, reduced blood ALA-D activity, and increased brain catalase (CAT) activity without altering other antioxidant defenses. Brain oxidative stress (OS) estimated by lipid peroxidation (TBARS) and protein carbonyl were increased by lead. GA reversed the motor behavior parameters, the ALA-D activity, as well as the markers of OS changed by lead exposure. CAT activity remained high, possibly as a compensatory mechanism to eliminate hydroperoxides during lead poisoning. EDTA, a conventional chelating agent, was not beneficial on the lead-induced motor behavior and oxidative damages. Both GA (less) and EDTA (more) reduced the lead accumulation in brain tissue. Negative correlations were observed between the behavioral parameters and lipid peroxidation and the lead levels in brain tissue. In conclusion, GA may be an adjuvant in lead exposure, mainly by its antioxidant properties against the motor and oxidative damages resulting from such poisoning.

Changes in levels of essential elements in suckling rats exposed to zinc and mercury

The effect of mercury and its interaction with zinc on the content of essential metals in tissues from neonate rats was investigated. Three-day-old Wistar rats were treated with saline or 27 mg kg(-1)d(-1) ZnCl2 (s.c.) for five consecutive days. From the 8th to the 12th day of life, the rats received one daily dose of saline or 5.0 mg kg(-1) HgCl2 (s.c). Twenty-four hours after the last injection liver, kidneys and blood were collected for metal quantification. The HgCl(2) exposure induced alterations on metal levels, such as increase of Fe, Hg and Zn in liver, decrease of Fe and Mg and increase of Cu and Hg contents in kidneys. The Hg exposure also increased Hg levels in the blood. The treatment with ZnCl2, administered previously to HgCl2, partially prevented the increase of Fe in the liver, and not only prevented the decrease of renal Mg but also increased it to levels higher than those found in control group. The Zn-Hg rats also presented higher renal Cu levels, and showed partially lower blood and hepatic Hg levels and higher renal Hg levels. The pre-administration of Zn caused no severe alterations in levels of essential metals (Cu, Fe, Mg and Mn). In short, Zn appears to be an alternative treatment of Hg poisoning in young animals in comparison to chelating drugs since these have low metal selectivity.

N-acetylcysteine as a potential antidote and biomonitoring agent of methylmercury exposure

BACKGROUND

Many people, by means of consumption of seafood or other anthropogenic sources, are exposed to levels of methylmercury (MeHg) that are generally considered to be quite low, but that may nevertheless produce irreversible brain damage, particularly in unborn babies. The only way to prevent or ameliorate MeHg toxicity is to enhance its elimination from the body.

OBJECTIVES

Using N-acetylcysteine (NAC), we aimed to devise a monitoring protocol for early detection of acute exposure or relatively low MeHg levels in a rodent model, and to test whether NAC reduces MeHg levels in the developing embryo.

RESULTS

NAC produced a transient, dose-dependent acceleration of urinary MeHg excretion in rats of both sexes. Approximately 5% of various MeHg doses was excreted in urine 2 hr after injection of 1 mmol/kg NAC. In pregnant rats, NAC markedly reduced the body burden of MeHg, particularly in target tissues such as brain, placenta, and fetus. In contrast, NAC had no significant effect on urinary MeHg excretion in preweanling rats.

CONCLUSIONS

Because NAC causes a transient increase in urinary excretion of MeHg that is proportional to the body burden, it is promising as a biomonitoring agent for MeHg in adult animals. In view of this and because NAC is effective at enhancing MeHg excretion when given either orally or intravenously, can decrease brain and fetal levels of MeHg, has minimal side effects, and is widely available in clinical settings, NAC should be evaluated as a potential antidote and biomonitoring agent in humans.

2,3-Dimercaptopropanol, 2,3-dimercaptopropane-1-sulfonic acid and meso-2,3-dimercaptosuccinic acid increase lead-induced inhibition of δ-aminolevulinate dehydratase in vitro and ex vivo

We investigated the effects of dimercaprol (BAL), meso-2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercapto-1-propanesulphonic acid (DMPS) on human blood delta-aminolevulinate dehydratase (delta-ALA-D) activity, the most reliable indicator of lead intoxication in humans, in the presence of lead in vitro. Furthermore, we studied the effects of the chelating agents, administered subcutaneously, on delta-ALA-D activity in blood and tissues of mice submitted to sub-acute lead exposure (50 mg/kg for 15 consecutive days, subcutaneously). In vitro results demonstrated that human blood delta-ALA-D activity was significantly inhibited (62%) by lead acetate. Lead acetate (1-1000 microM) pre-incubated with human blood increased the inhibitory potency of this compound on delta-ALA-D when compared to the assay without pre-incubation (89%). Chelating agents caused a marked potentiation of delta-ALA-D inhibition induced by lead, in vitro. One of the most notable observations in the present study was the correspondence between in vitro and ex vivo effects. In fact, BAL and DMPS increase the inhibitory effect of lead on delta-ALA-D activity from mice blood. The complexes formed (lead and chelators) were more inhibitory than lead alone in kidney and liver enzyme activity, ex vivo.

Cadmium induced testicular damage and its response to administration of succimer and diphenyl diselenide in mice

Acute effects of cadmium in mice testes were evaluated. Animals received a single dose of CdCl2 (2.5 mg/kg or 5 mg/kg, intraperitoneally) and a number of toxicological parameters in mice testes were examined such as delta-aminolevulinic acid dehydratase (delta-ALA-D) activity, lipid peroxidation, hemoglobin content and components of the antioxidant defenses (superoxide dismutase (SOD) activity and ascorbic acid concentration). Furthermore, a possible protective effect of meso-2,3-dimercaptosuccinic acid (DMSA) and diphenyl diselenide (PhSe)2 are studied. The results demonstrated inhibition of delta-ALA-D and SOD activities, reduction in ascorbic acid, increase of lipid peroxidation induced by cadmium, indicating testes damage. DMSA (400 micromol/Kg) and (PhSe)2 (100 micromol/Kg) protected inhibitory effect of 2.5 mg/kg CdCl2 on delta-ALA-D and restored the increase of TBARS levels. Otherwise, (PhSe)2 treatment was effective in reducing the increase of TBARS levels induced by 5 mg/kg CdCl2, whereas DMSA and (PhSe)2, in combination, were ineffective in reducing TBARS level. However, these compounds alone or in combination, were unable to protect SOD activity and to improve ascorbic acid levels near to the normal value. The use of combined therapy (DMSA plus (PhSe)2) not proved be better than the monotherapy, in improving toxicological parameters evaluated in this model of testicular damage induced by cadmium.

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.

Possible role of metal redistribution, hepatotoxicity and oxidative stress in chelating agents induced hepatic and renal metallothionein in rats

A study was planned to investigate possible role of oxidative stress, hepato- and nephrotoxicity and essential metal redistribution following administration of amino and thiol chelating agents on hepatic and renal metallothionein (MT) and the levels of some metalloenzymes in male rats. Animals were administered 50 mg/kg, intraperitoneally, twice daily for 15 consecutive days; a dose of three amino and four thiol chelators and were sacrificed 24 h after the last dose. The results indicate no evidence of oxidative stress in hepatic and renal tissues of rats administered thiol and amino chelators, except for some marginal changes in the animals treated with calcium disodium ethylenediaminetetraacetic acid (EDTA) and D-penicillamine (DPA). Redistribution of essential metal (particularly zinc), hepato- and nephrotoxicity seems to play a significant role in influencing the MT induction by amino chelators. Redistribution of essential metals may also be playing a significant role in a number of metalloenzymes, especially by amino chelators compared to thiol chelators. It can thus be concluded that toxic effects of chelating agents, including metal redistribution and hepatotoxicity, might be playing a crucial role in the metallothionein induction.

Influence of zinc oxide and eugenol sealer on concentration of zinc, calcium and copper in rat tissues

A zinc oxide and eugenol root canal sealer (Roth 811) and sterile saline solution were injected into the dorsal thoracic midline of 70 male Wistar-Furth rats. Every day for the next 7 days, 10 animals were sacrificed by either inhalation. The liver, heart, kidneys and brain were removed from the animals and analysed for zinc, calcium and copper concentrations by flame atomic absorption spectrophotometry. The tissue around the injection site was also surgically removed and prepared for histological evaluation under a microscope. The injection of Roth 811 significantly affected the concentrations of zinc, calcium and copper in some of the examined organs, especially on the 4th and 5th day. The inflammatory reaction adjacent to the material was severe during the first 3 days while on the 7th day the presence of connective tissue with collagen formation was observed.

Efficacy of succimer chelation for reducing brain Pb levels in a rodent model

Increasing evidence indicates that early low-level lead (Pb) exposure produces enduring cognitive impairment in children, underscoring the need to develop improved therapeutic intervention. Although chelating agents have been shown to effectively reduce body Pb levels, it is not yet known whether this treatment ameliorates Pb-induced cognitive dysfunction. Clinical research in this area is hampered by the need to rely on reductions in blood Pb levels as the index of treatment efficacy, despite the fact that brain Pb level is the exposure parameter of greatest relevance to neurocognitive outcomes. The present studies were designed to provide information that will aid future research in this area in both human and animal models. The objectives of these studies were (1) to evaluate the efficacy of different doses and durations of succimer (meso-2,3-dimercaptosuccinic acid; DMSA) chelation for reducing brain and blood Pb levels and (2) to determine the extent to which blood Pb can serve as a surrogate of brain Pb following chelation. Long-Evans hooded rats were exposed to Pb from birth until day 31 (Study 1) or day 40 (Study 2) of life, followed by oral treatment with a vehicle or one of two succimer regimens for a duration of either 7 or 21 days. Results indicated that 7 days of succimer treatment produced a 1.5- to 2.5-fold greater reduction of Pb in blood than in brain, relative to time-matched vehicle groups. Prolonged treatment (21) days did not further reduce blood Pb levels (relative to 7-day succimer treatment), but did produce further reductions in brain Pb level compared to time-matched vehicle groups. Thus, chelation-mediated reductions in brain Pb did not parallel reductions in blood Pb over the course of treatment. While the relevance of these data to humans may be confounded by anatomical and physiological differences between rodents and primates, as well as differences in the metabolism of succimer (DMSA), they suggest that clinical studies should exercise caution when using blood Pb as an index of the efficacy of chelation treatment for reducing brain Pb levels.

N-acetylcysteine as an antidote in methylmercury poisoning

Methylmercury is a ubiquitous environmental pollutant and potent neurotoxin. Treatment of methylmercury poisoning relies almost exclusively on the use of chelating agents to accelerate excretion of the metal. The present study demonstrates that oral administration of N-acetylcysteine (NAC), a widely available and largely nontoxic amino acid derivative, produces a profound acceleration of urinary methylmercury excretion in mice. Mice that received NAC in the drinking water (10 mg/ml) starting at 48 hr after methylmercury administration excreted from 47 to 54% of the 203Hg in urine over the subsequent 48 hr, as compared to 4-10% excretion in control animals. When NAC-containing water was given from the time of methylmercury administration, it was even more effective at enhancing urinary methylmercury excretion and at lowering tissue mercury levels. In contrast, excretion of inorganic mercury was not affected by oral NAC administration. The ability of NAC to enhance methylmercury excretion when given orally, its relatively low toxicity, and is wide availability in the clinical setting indicate that it may be an ideal therapeutic agent for use in methylmercury poisoning.

Relative efficacy of chelating agents on excretion and tissue distribution of manganese in mice

The effect of repeated parenteral administration of a number of structurally diverse chelating agents on the excretion and tissue distribution of manganese was assessed in mice following 4 weeks of manganese exposure. Males Swiss mice received s.c. injections of manganese(II) chloride tetrahydrate (8.9 mg Mn kg-1 body wt.) for 4 weeks (5 days per week). After the end of this exposure period, cyclohexanediaminetetraacetic acid (CDTA), ethyleneglycol-bis-(beta-aminoethylether)-N,N-tetraacetic acid (EGTA), N-(2-hydroxyethyl)ethylenediamine triacetic acid (HEDTA), isonicotinyl hydrazine (INH), L-dopa, sodium 4.5-dihydroxy-1.3-benzenedisulphonate (Tiron), p-aminosalicylic acid (PAS) or 0.9% saline (control group) were given i.p. for five consecutive days. The doses of the chelators were approximately equal to one-eighth of their respective LD50 values. Urine and faeces were daily collected for 5 days. Twenty-four hours after the final chelator injection, mice were killed and manganese concentrations were determined in various tissues. Although CDTA, EGTA and HEDTA significantly enhanced the elimination of manganese into urine, none of the chelators increased faecal excretion. Tissue concentrations of manganese were significantly reduced only by CDTA. According to these results, among the compounds tested only CDTA would mobilize effectively manganese in manganese-loaded mice.

DMSA chelation during co-exposure to lead: increased locomotor activity in lead-exposed mice but not controls

We investigated the effect of chelating agent meso-2,3 dimercaptosuccinic acid (DMSA) on indices of "hyperactive" behavior in lead-exposed and control Binghamton Heterogeneous Stock (Het) mice. As expected, 6 weeks of ingestion of 0.5% lead acetate in drinking water reduced immobility in a forced water swim relative to controls. DMSA did not attenuate this behavioral change. In fact, DMSA interacted with lead exposure to increase locomotor activity in the forced water swim. DMSA also apparently excacerbated lead's tendency to reduce immobility. While any generalizations to human populations should be cautioned, these results and others suggest the need for further research.

Therapeutic efficacy of combined meso 2,3-dimercaptosuccinic acid and calcium disodium edetate treatment during acute lead intoxication in rats

1. The therapeutic ability of Ca disodium EDTA and meso 2,3-dimercaptosuccinic acid (DMSA) was studied, both individually and when given in combination, in reducing lead concentration in blood and other soft tissues, and in restoring lead induced altered biochemical variables in acute lead intoxicated rats. 2. Combined treatment with the above two chelating agents was more beneficial in reducing blood and hepatic lead compared to treatment with these drugs alone. Kidney lead concentration however, remained high following combined treatment, indicating the possibility of extra renal burden following treatment. 3. Lead sensitive biochemical variables also responded more favourably to combined treatment than treatment with these drugs alone. However, clinical biochemical indices indicate caution regarding the use of this new treatment regimen, and further investigation is required.

Experimental study of the biocompatibility of four root canal sealers and their influence on the zinc and calcium content of several tissues

Four root canal sealers (AH-26, Roth 811, CRCS, and Sealapex) were tested for tissue biocompatibility in rat connective tissue. Each sealer was placed in Teflon tubes and implanted subcutaneously in Wistar-Furth rats. The implants were removed after 7, 14, and 21 days, fixed, and histologically prepared for microscopical evaluation. Brain, liver, kidneys, and uterus were removed from the animals killed at the first experimental period (7 days) and analyzed for zinc and calcium concentration by flame atomic absorption spectrophotometry. In total, 100 specimens were examined. At the seventh day, the most irritant material was seen to be AH-26, but this inflammatory reaction decreased with time. Roth 811 and Sealapex caused moderate-to-severe inflammatory reaction, whereas CRCS caused mild to moderate. CRCS and Roth 811 induced redistribution of zinc, whereas AH-26 induced changes in calcium content in some organs.

In vivo inhibition of serum dopamine-beta-hydroxylase by CaNa2 EDTA injection

1. In humans CaNa2EDTA increases urinary excretion of lead as well as that of essential metals such as zinc, ferrum and manganese but not that of copper. 2. We studied the effect of CaNa2EDTA injection on serum dopamine-beta-hydroxylase, a copper-dependent enzyme, in three male lead welders hospitalized for suspected lead poisoning. 3. Injection of CaNa2EDTA (1000 mg i.v.) resulted in rapid reduction of serum dopamine-beta-hydroxylase activity which returned to normal level within 24 hours. 4. Copper sulphate (8 microns) but not ethylmaleimide (10 mM) restored in vitro serum dopamine-beta-hydroxylase activity to pre-dosing values which indicates that CaNa2EDTA inhibits dopamine-beta-hydroxylase by removing copper from the enzyme. 5. An inverse dose effect relationship between injected CaNa2EDTA and residual serum dopamine-beta-hydroxylase activity was observed. 6. In spite of the reported lack of changes in copper serum concentration, CaNa2EDTA significantly affects the activity of a copper-dependent enzyme in the serum. 7. As CaNa2EDTA is currently the drug of choice for the treatment of asymptomatic lead poisoning in children, the effect of CaNa2EDTA on copper-enzymes requires further investigation.

Influence of naproxen on the zinc, copper, magnesium and calcium content of guinea pig tissues

The effect of the administration of chronic doses of naproxen on the zinc, copper, magnesium and calcium concentrations in guinea pig tissues was studied. One hundred mg naproxen/kg body weight/week were administered intraperitoneally to adult female guinea pigs in two doses twice a week for eight weeks. A statistically significant decrease was found of the zinc content in the brain, lung, heart, liver, kidney, spleen and adrenals, of the copper content in the liver, kidney and adrenal and of the magnesium content in the spleen and heart. A significant increase was observed of the calcium content in the adrenals, heart, spleen and uterus of the treated animals, while no significant changes were observed in the thigh bone concentrations of the various ions tested.

Stable isotopic tracers of lead mobilized by DMSA chelation in low lead-exposed rats

The ability of DMSA to mobilize skeletal lead or effect a redistribution of endogenous lead to other target organs in low lead-exposed organisms is unclear. Discrepant results of past studies of DMSA and other lead chelators (e.g., CaNa2EDTA) may be due, in part, to experimental differences and difficulties in distinguishing mobilized skeletal lead from other endogenous or exogenous lead sources. Therefore, the influence of DMSA on the mobilization and redistribution of lead in skeletal and soft tissue compartments of low lead-exposed female Wistar (115-125 g) rats was investigated using ultraclean stable lead isotope tracer techniques. Rats that had been reared on a low lead-level diet (lead intake approximately 80 ng Pb/g body/day) were fed 206Pb-enriched drinking water (210 ng Pb/ml) for 1.5 days and then were chelated with a single ip injection of a 0.11 mmol/kg dose of DMSA. Blood, kidney, brain, tibia, urine and feces were collected 24 hr after chelation and analyzed for lead concentrations by graphite furnace atomic absorption spectrometry and for lead isotopic compositions by thermal ionization mass spectrometry. These analyses demonstrated that DMSA chelation significantly increased (15-fold) the diuresis of labile soft tissue lead, but not skeletal lead. DMSA also appeared to effect a redistribution and input of a comparable amount of lead to the skeleton and smaller relative amounts of lead to the soft tissues (blood, kidney) of the chelated animals. The clinical significance of these latter observations beyond the context of this preliminary study is not clear.

Depletion of essential elements by calcium disodium EDTA treatment in the dog

The effect(s) of calcium disodium ethylenediaminetetraacetate (CaNa2EDTA) on the metabolism of Zn, Cu and Mn was investigated in mongrel female dogs. Dogs received either CaNa2EDTA (0.75 mmol/kg subcutaneously) or 0.9% NaCl (controls). Urine was collected every 6 h. Tissue samples were obtained from liver, kidney, duodenum, muscle, hair, skin and bone post exsanguination. CaNa2EDTA treatment increased urinary excretion of Zn, Cu and Mn, significantly when compared to controls (P less than 0.05, n = 5). Furthermore, CaNa2EDTA either decreased Zn levels (hair, duodenum, skin) and Mn levels (hair) or increased Cu levels in kidneys (P less than 0.05). These data suggest that the sustained urinary loss of Zn, Cu and Mn was probably associated, in part, with mobilization and redistribution of these essential elements from storage tissues as well as soft tissues. It was concluded that the use of calcium disodium EDTA for the management of heavy metal poisoning in dogs could adversely affect the metabolism of essential elements, particularly Zn, Cu and Mn.

Meso-2,3-dimercaptosuccinic acid (DMSA) affects maternal and fetal copper metabolism in Swiss mice

Meso-2,3-dimercaptosuccinic acid (DMSA) is a chelating agent used to treat heavy metal intoxication. DMSA has been reported to be teratogenic in the mouse, and it has been suggested that this teratogenicity may be secondary to DMSA-induced alterations in Zn metabolism. In the present study, 0, 400 or 800 mg DMSA/kg body weight were administered on gestation days 6-15 to pregnant Swiss mice by gavage (PO) or subcutaneous injection (SC). Mice were fed a diet containing 14 micrograms Zn, 10 micrograms Cu, 120 micrograms Fe, 1175 micrograms Mg and 6.8 mg Ca/g diet. A sub-group of mice in the 800 mg DMSA/kg SC group was fed a diet containing 250 micrograms Zn/g. DMSA administration did not result in overt maternal toxicity. There was no effect of the drug on fetal or placental weight, or on crown-rump length. However, some fetuses from DMSA-treated dams were characterized by skeletal abnormalities including supernumerary ribs, unossified anterior phalanges and malformed sternebrae. Drug exposure was not associated with consistent changes in tissue Zn, Fe, Ca or Mg levels. Supplemental Zn had no marked effects on the fetus. Fetal liver Cu concentrations exhibited dose-dependent decreases with increasing DMSA dose. This finding suggests that the developmental toxicity of DMSA may be mediated through disturbed maternal/fetal copper metabolism.

Influence of simultaneous supplementation of zinc and copper during chelation of lead in rats

The influence of zinc and copper supplementation during chelation therapy to reduce zinc and copper imbalance and promote lead elimination from the body, was investigated in rats poisoned with lead. The simultaneous supplementation of zinc and copper increased urinary lead excretion by calcium disodium ethylenediamine tetraacetic acid (CaNa2EDTA) compared to treatment with CaNa2EDTA alone. Combination therapy was effective in potentiating the depletion of blood and renal lead by CaNa2EDTA and meso 2,3-dimercapto succinic acid (DMSA). Combination therapy was also more effective in reducing hepatic lead by CaNa2EDTA and blood lead by 2,3-dimercapto propane sulphonate (DMPS). Zinc and copper supplementation produced a more effective reversal of inhibited blood delta-aminolevulinic acid dehydratase (ALAD) activity, urinary delta-aminolevulinic acid excretion and depleted body zinc and copper status.

Effects of three chelating agents, EDTA, NTA, and TPP, on the concentration of elements in rat tissues

Ethylene diamine tetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and tripolyphosphate (TPP) sodium salts were given orally to rats at the dose of 1 mmol/kg/d for 35 d. The concentrations of Na, K, Ca, Mg, P, S, Fe, Sr, Cu, and Zn were determined in blood, plasma, brain, heart, muscle, liver, kidney, duodenum, and bone of control rats and of the rats receiving EDTA, NTA, and TPP. The main effect induced by EDTA, NTA, and TPP was a decrease of the concentrations of several elements Ca, Mg, Fe, P in the duodenum. Otherwise, EDTA induced an increase of Zn in the kidney (+ 20%), NTA, an increase of Fe in liver (+ 29%), and particularly an increase of Zn in bone (+ 44%). TPP induced a slight decrease of Zn and Cu in liver. In conclusion, EDTA, NTA, and TPP taken orally at the dose of 1 mmol/kg/d for 35 d induced moderate changes of the concentrations of some elements in rat tissues, but without signs of toxicity.

Inhibition of human hepatocellular carcinoma and hepatoblastoma cell lines by deferoxamine

Inhibition of human hepatocellular carcinoma (PLC/PRF/5 and Hep3B) or hepatoblastoma (Hep G2) cell lines by inclusion of deferoxamine mesylate (desferrioxamine) (DFX) in the culture medium was evaluated. When PLC/PRF/5 cells were maintained for 7 days in 30 or 60 microM DFX, the cell number was decreased by 30-60%, little or no alpha-fetoprotein (AFP) was produced, and supernatant endpoint dilution titers of hepatitis B surface antigen (HBsAg) were reduced 1-2 logs. PLC/PRF/5 cells maintained for 7 days without DFX (simultaneous controls) grew to confluence, produced AFP that reached 10-60 ng/ml in the supernate, and the HBsAg titer remained constant or increased 1 log. Similar effects were observed in Hep3B and Hep G2 cells maintained in DFX (except that Hep G2 cells do not produce HBsAg), compared to simultaneous control cells grown in the absence of DFX. The growth of a human embryonic lung fibroblast cell line (Wl 38) was not significantly inhibited by DFX, although it grew at a slower rate than simultaneous control cells grown without DFX. Subsequent growth in FeSO4 of PLC/PRF/5, Hep3B, and Hep G2 cells that previously had been maintained in DFX did not reverse the effects of DFX. PLC/PRF/5 cells were also inhibited when maintained in medium containing equimolar concentrations of DFX and FeCl3 and in medium containing equimolar concentrations of DFX and FeSO4. PLC/PRF/5 cells were not inhibited by maintenance in up to 60 microM of another chelating agent that has a similar affinity for iron, calcium disodium versenate (EDTA). These studies show that DFX inhibits the growth of human hepatocellular carcinoma and hepatoblastoma cell lines regardless of the presence (PLC/PRF/5, Hep3B) or absence (Hep G2) of integrated hepatitis B virus DNA. The findings also suggest that the inhibition may have been due to mechanisms other than iron chelation.

The effects of thiamin on lead metabolism: whole body retention of lead-203

The effects of thiamin on the whole body retention of led were evaluated in CD-1 mice treated intragastrically or intraperitoneally while exposed to a single dose of lead acetate (100 micrograms) containing 100 mu Ci lead-203. They were administered thiamin (25 or 50 mg/kg body wt.), calcium ethylenediamine tetraacetic acid (CaEDTA) (50 mg/kg body wt.) or their combination in pretreatment or posttreatment regimens for 13 days. Both pre- and posttreatment with thiamin reduced the lead retention compared to the untreated lead-exposed mice, although the different patterns of lead retention were observed. The combined pretreatment (thiamin 50 mg/kg and CaEDTA) and the CaEDTA treatment alone reduced the whole body retention of lead most effectively. Thiamin, CaEDTA and the combined treatments decreased the absorption of lead-203 and the biological half-life of retained lead-203 following oral or intraperitoneal lead exposure. The reduced absorption and enhanced excretion of lead associated with thiamin administration may have therapeutic application for the treatment of lead poisoning.

Antidotal effects of dimercaptosuccinic acid

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

Effect of some arsenic antagonists on the toxicity, distribution and excretion of arsenite and arsenate in rats

1. Arsenite and arsenate poisoned rats were treated with either BAL (2,3-dimercapto-1-propanol), penicillamine (PA) (beta-beta dimethyl cystein) or selenium (Se) (as sodium selenite). 2. The minimal dose of each antagonist that treated arsenic-induced lethality (causing 100% survival) was the same for both arsenite and arsenate. 3. Arsenic mobilization from the tissues (blood, kidney, liver, lungs, spleen, muscles, brain, heart) and its excretion in urine and feces were higher in arsenite-intoxicated animals than in arsenate-intoxicated ones. 4. The effect of each antagonist, when injected alone, on the urinary and fecal excretion of endogenous metals (Cu, Zn, Fe, Ca and Mg) was also examined. 5. The results indicated marked differences in the relative ability of BAL, PA and Se to increase the excretion of the metals.

Beneficial effects of zinc supplementation during chelation treatment of lead intoxication in rats

The ability of zinc to enhance the efficacy of commonly used chelating drugs in lead intoxication and to reduce the resulting zinc imbalance, was investigated in rats. The simultaneous zinc supplementation increased urinary lead elimination by calcium disodium ethylenediaminetetraacetate (Ca disodium EDTA) and 2,3 dimercaptosuccinic acid (DMSA). Combination therapy was also effective in potentiating the depletion of blood, hepatic and renal lead by calcium disodium EDTA and D-penicillamine (DPA), renal lead by DMSA and reversal of inhibited blood delta-aminolevulinic acid dehydratase (ALAD) activity by calcium disodium EDTA and DPA. The body zinc status was also maintained as reflected by urinary, blood and tissue levels of zinc.

The effects of thiamin on the tissue distribution of lead

The effects of thiamin on the tissue distribution of lead were evaluated in Sprague-Dawley rats exposed to 1000 ppm lead acetate in drinking water and treated daily with thiamin (25 or 50 mg kg-1 body weight, i.p.), calcium ethylenediamine tetraacetic acid (50 mg kg-1 body weight, i.p.) or their combination for 8 weeks. The subtoxic dose of lead did not alter weight gains, feed and water consumption during the treatment period. Thiamin decreased the blood (P less than 0.0001), liver (P less than 0.0001) and kidney (P less than 0.0001) concentrations of lead. Thiamin (50 mg kg-1 body weight) reduced the lead concentrations in tissues more effectively than thiamin (25 mg kg-1 body weight). The combined treatment was more effective than the respective individual treatments.

Mobilization of lead by esters of meso-2,3-dimercaptosuccinic acid

An examination was made of the relative efficacies of 2,3-dimercapto-1-propanol (BAL) and three diesters ( [CH(SH)COOR]2; DMDMS, R = CH3; DEDMS, R = C2H5; and Di-PDMS, R = CH(CH3)2] of meso-2,3-dimercaptosuccinic acid (DMSA) in mobilizing freshly injected lead from mice. These diesters, like BAL, reduced the lead levels resulting from freshly injected lead in both the soft tissues (liver, kidneys, spleen, and brain) and the bone (tibia). After treatment with the dimethyl (DMDMS), the diethyl (DEDMS), and the diisopropyl (Di-PDMS) esters the lead content of each of the organs was significantly less than that present in the untreated controls. Each of the diesters reduced lead levels in the kidneys, liver, and spleen significantly below those levels found after BAL treatment. The action of the diesters in reducing brain lead levels was comparable to that of BAL. Di-PDMS was the most effective of these compounds and was significantly superior to BAL. Each of the esters was also significantly more effective than BAL in reducing the whole body level of lead.

Influence of metal chelators on metalloenzymes

The influence of chelating agents (1 mmol/kg/day X 6,i.p.) on trace metal mobilization and activities of certain metalloenzymes was investigated in rats. Calcium disodium ethylenediamine tetraacetate (CaNa2EDTA) and calcium trisodium diethylenetriamine pentaacetate (CaNa3DTPA) enhanced urinary excretion of Zn, while sodium 2,3-dimercaptopropane-1-sulfonate (NaDMPS) and sodium diethyldithiocarbamate (NaDDC) increased that of Cu. The activity of Zn-metalloenzymes-blood delta-aminolevulinic acid dehydratase (delta-ALA-D), plasma alkaline phosphatase (ALP) and that of Cu-metalloenzyme-plasma amine oxidase was decreased as a consequence of chelation therapy. However, hepatic levels of delta-ALA-D, ALP and alcohol dehydrogenase remained unaffected by chelation. The activity of hepatic Fe-metalloenzyme-catalase was increased by polyaminocarboxylic acids and lowered by thiol chelators. The metal chelators decreased the hepatic glutathione levels.

Meso-2,3-dimercaptosuccinic acid in the diagnosis and treatment of lead poisoning

Lead poisoning remains one of the hazards of industrialized civilization. CaNa2 EDTA and dimercaprol, the usual therapeutic measures, have many side effects and can be given by parenteral route alone. The authors present a case of chronic lead poisoning caused by ingestion of contaminated flour ground in a primitive flour mill. The diagnosis was confirmed by the CaNa2 EDTA provocative test. Dimercaptosuccinic acid (DMSA) was given orally as a further provocation and resulted in an 11-fold increase in urinary lead excretion. A 5-day course of treatment with DMSA was instituted, during which symptoms abated, urinary lead excretion increased and the blood lead level decreased. No side effects were noticed. There has been no relapse over several months of follow-up. The authors conclude that the oral use of DMSA is effective, safe and convenient both as a provocative test in establishing the diagnosis of lead poisoning and as a therapeutic tool.

Preventive and therapeutic effects of thiamine, ascorbic acid and their combination in lead intoxication

Thiamine, ascorbic acid and their combination were investigated for their ability to prevent or treat the experimental lead intoxication in rats. The combination of the two vitamins was most effective in reducing the lead induced inhibition in the activity of blood delta-aminolevulinic acid dehydratase, elevation in the level of blood zinc protoporphyrin and the urinary excretion of delta-aminolevulinic acid and the uptake of lead in blood, liver and kidney. The combined treatment post lead exposure was also most effective in restoring the lead induced biochemical alterations and mobilizing lead from the tissues. The order of effectiveness was, thiamine + ascorbic acid less than ascorbic acid less than thiamine. The lead induced changes in brain biogenic amines and the brain concentration of lead remained unaffected by these vitamins.

Induction of hepatic metallothionein in mouse liver following administration of chelating agents

Chelating agents commonly used in therapy of heavy metal intoxication alter the levels of essential metals in liver, kidneys, and serum. Induction of metallothionein synthesis in liver occurs following exposure to a variety of chemical and environmental insults and, in some cases, has been attributed to enhanced hepatic uptake of zinc. Therefore, the effect of acute exposure to seven common metal chelators on the concentration of metallothionein in liver was investigated. Adult male Swiss Webster mice were injected intraperitoneally with the chelators and hepatic metallothionein was quantified by the cadmium radioassay. Ethylenediaminetetraacetic acid (EDTA) produced a 5- to 6-fold increase in hepatic metallothionein 24 hr after injection of 0.75 to 3.0 g/kg. No significant increase in hepatic MT was observed until 12 hr following injection of EDTA (1.5 g/kg, ip). Maximal levels were reached between 12 and 48 hr following EDTA injection. Cadmium, a known inducer of hepatic metallothionein, produced a 15-fold increase in the concentration of MT in liver 24 hr following injection. By comparison, 2,3-dimercaptopropanol and diethyldithiocarbamate produced a 9-fold and 13-fold increase in hepatic metallothionein levels, respectively, 24 hr following injection. A 4- to 6-fold increase in metallothionein was observed 24 hr following injection of 2,3-dimercaptosuccinic acid, D,L-penicillamine, diethylenetriaminepentaacetic acid, and EDTA, while nitrilotriacetic acid elevated hepatic metallothionein levels by 2-fold. Alterations in the concentration of hepatic metallothionein by chelators may have implications for their efficacy in the treatment of cadmium intoxication.

A review of the environmental and mammalian toxicology of nitrilotriacetic acid

This article provides a review of available information on the chemistry, environmental toxicology, and mammalian toxicology of nitrilotriacetic acid (NTA). The ability of NTA to chelate metal ions such as Mg++ and Ca++ into water soluble complexes makes NTA useful as an additive to boiler water, as a builder in laundry detergents, and as a stabilizer in textile, paper, and pulp processing. Environmental fate studies show NTA biodegrades in wastewater treatment plants, in natural waters, and in soils under a wide variety of conditions. Studies on the environmental effects of NTA indicate that no adverse effects occur in treatment plants or receiving waters at anticipated levels. Monitoring programs have established that only low steady-state concentrations of NTA occur in natural waters as a result of NTA usage. In mammalian systems, NTA is not metabolized and is excreted rapidly by filtration in the kidney. No reproductive, teratogenic, or adverse bone effects have been observed at highly exaggerated doses. In numerous genotoxicity assay systems, both in vivo and in vitro, NTA is nongenotoxic. Chronic oral exposure of rodents to high doses of NTA is associated with tumorigenicity in, and restricted to, the urinary tract. The urinary tract tumors are the consequence of chronic toxicity that is caused by changes in Zn and Ca distributions between the urinary tract tissues and urine at high doses of NTA. Thresholds for the effects of NTA on Zn and Ca distributions are 10(5) to 10(6) greater than the possible maximum human exposure resulting from the low levels of NTA that are known to occur in the environment.