Influence of metal chelators on metalloenzymes

Prevention of acute cadmium toxicity by Picroliv

The potential of Picroliv, a herbal extract against acute cadmium (Cd) intoxication, was evaluated in male rats. Biochemical and histopathological profile in rats pretreated with Picroliv (12 mg/kg, oral) followed by a single dose of Cd as cadmium chloride (CdCl2) (3 mg/kg, ip) revealed marked suppression of oxidative stress in liver and testes. The Cd-induced enhanced levels of lipid peroxidation, membrane fluidity and reduced levels of nonprotein sulphydryls and Na+K+ATPase were significantly restored to near normal by Picroliv pretreatment. In addition, the Cd-induced serum levels of glutamate oxaloacetate transaminase, glutamate pyruvate transaminase, gamma glutamyl transpeptidase and lactate dehydrogenase were restored to near basal levels. Hepatic and testicular histopathological damage was also minimized. The results strongly suggest definite hepatoand testicular protection by Picroliv. The antioxidant potential of the herbal extract in the major part, and not its chelating property, seems to be responsible for its ameliorative action.

Modulation of the chelatable Zn pool in the brain by diethyldithiocarbamate is associated with behavioral impairment in adult zebrafish

DEDTC leads to a buildup of DEDTC in the brain with consequent chelation of reactive Zn and behavioral impairment of zebrafish.

A differential behavior of α-amylase, in terms of catalytic activity and thermal stability, in response to higher concentration CaCl2

A differential relationship was observed between thermal stability and catalytic activity of α-amylase in the presence of different concentrations of CaCl(2). The enzyme displays optimum catalytic activity in the presence of 1.0-2.0 mM CaCl(2). Further addition of CaCl(2) leads to inhibition of the enzyme, however, at the same time the enzyme gains an additional resistance against thermal denaturation. It was evident that the enzyme is thermodynamically more stable (compared to the active enzyme) in the presence of inhibitory concentration of CaCl(2). For example, the thermal transition temperature (T(m)) of optimally active α-amylase was found to be 64±1°C, whereas, for the less active enzyme (in the presence 10 mM CaCl(2)) the value was determined to be 71±1°C. Similarly, the activation energy of thermal inactivation (Ea) was found to be 228±12 kJ/mol and 291±15 kJ/mol for the optimally active enzyme and the enzyme in the presence of 10 mM CaCl(2), respectively. Biophysical analysis of different states of the enzymes in response to variable calcium level indicates no significant change in the secondary structure in response to different concentration of CaCl(2), however the less active but thermodynamically stable enzyme (in the presence of higher concentration of CaCl(2)) was shown to have relatively more compact structure. The results suggest that the enzyme has separate catalytic and structure stabilizing domains and they significantly vary in their functional attributes in response to calcium level.

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

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

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.

2,3-Dimercaptopropanol, 2,3-dimercaptopropane-1-sulfonic acid, and meso-2,3-dimercaptosuccinic acid inhibit delta-aminolevulinate dehydratase from human erythrocytes in vitro

The effects of dithiol chelating agents meso-2,3-dimercaptosuccinic acid (DMSA), 2,3-dimercaptopropane-1-sulfonic acid (DMPS), and 2,3-dimercaptopropanol (BAL) on delta-aminolevulinate dehydratase (delta-ALA-D) from human erythrocytes were evaluated. Furthermore, possible protective effects of zinc chloride (ZnCl(2)), dithiothreitol (DTT), and cysteine were studied. delta-ALA-D activity from human erythrocytes was inhibited by dithiol chelating agents in a concentration-dependent manner. Cysteine, at all concentrations tested, did not protect the inhibitory effect of 1 and 4 mM DMPS and DMSA, but protected 1 mM BAL inhibition. Dithiotreitol was able to protect the inhibition caused by 1 mM BAL (28%), DMPS (56%), and DMSA (40%) in a concentration-dependent manner. Zinc chloride protected and restored 1 mM BAL inhibitory effect on delta-ALA-D. Zinc chloride at 500 microM and 1 mM, respectively, protected inhibitory effects of DMPS and DMSA (1 and 4 mM), but did not reverse its effects. The preincubation of dithiol chelating agents with enzyme demonstrated that DMSA was the most potent delta-ALA-D inhibitor of human erythrocytes. These data are in agreement with delta-ALA-D activity from purified enzyme. ZnCl(2) (1 microM) added, in the reaction mixture, increased enzyme activity and DTT (100 microM) totally restored the enzyme activity for all chelating agents tested.

Interaction between metals and chelating agents affects glutamate binding on brain synaptic membranes

The present study investigates the possible effects of Hg2+, Pb2+, and Cd2+ on [3H]-glutamate binding. To better understand the role of the thiol-disulfide status on the toxicity of such metals toward glutamatergic neurotransmission, we used three thiol chelating agents, 2,3-dimercaptopropanol (BAL), 2,3-dimercaptopropane 1-sulfonate (DMPS), and meso-2,3-dimercaptosuccinic acid (DMSA). Dithiotreitol (DTT) was tested for its ability to prevent metals-induced inhibition on [3H]-glutamate binding. Hg2+, Pb2+, and Cd2+ showed a concentration-dependent inhibition on [3H]-glutamate binding, and mercury was the most effective inhibitor. BAL did not prevent [3H]-glutamate binding inhibition by Hg2+, Cd2+, and Pb2+. However, DMPS and DMSA prevented the inhibition caused by Cd2+ and Pb2+, but not by Hg2+. DTT did not prevent the inhibition on [3H]-glutamate binding caused by 10 microM Hg2+. In contrast, it was able to partially prevent [3H]-glutamate binding inhibition caused by 40 microM Pb2+ and Cd2+. These results demonstrated that the heavy metals present an inhibitory effect on [3H]-glutamate binding. In addition, BAL was less effective to protect [3H]-glutamate binding inhibition caused by these metals than other chelating agents studied.

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.

Cisplatin-induced loss of kidney copper and nephrotoxicity is ameliorated by single dose diethyldithiocarbamate, but not mesna

Platinum, copper, and zinc concentrations in kidney and liver were monitored following administration of cis-diamminedichloroplatinum (Cisplatin, CDDP) alone or in combination with diethyldithiocarbamate (DDC) or mercaptoethanesulfonate (mesna). Compounds were administered in saline to F344 female rats as single bolus ip doses: 7.5 mg CDDP/kg body wt; 500 mg DDC/kg body wt 1 hr after CDDP; and 100 mg mesna/kg body wt 1 hr before CDDP, at the same time as CDDP, or 1 hr after CDDP. Tissues were collected at 4 hr, 1 day, 4 days, and 7 days post-CDDP dosing. CDDP alone produced significant increases in blood urea nitrogen (fourfold) and plasma creatinine (threefold) concentrations by Day 4. Concurrent with the toxicity, CDDP lowered kidney copper (-71%) by Day 4, but had little effect on liver copper except in copper-pretreated rats. Copper-pretreated rats initially had a twofold higher kidney copper concentration and a fourfold higher liver copper concentration, but by Day 4, CDDP lowered copper concentrations in both organs to near the noncopper-treated levels. Platinum in kidney and liver rose 72-100% of peak levels within 4 hr post-CDDP and was relatively stable throughout the 7-day test period. Kidney zinc rose significantly by day 4 only in CDDP-treated rats. DDC protected against the kidney toxicity of CDDP and markedly changed kidney copper loss. Within 4 hr, DDC reduced kidney copper 60% while increasing kidney platinum to the highest concentration of any of the treatments. By Day 4, DDC-treated rats had approximately 50% lower kidney platinum while copper returned toward control levels. A single dose of mesna did not significantly protect against CDDP nephrotoxicity and had little effect on kidney platinum, copper, or zinc. The patterns of copper loss and toxicity from CDDP alone or with DDC suggest that copper be further evaluated for its role in the mechanism of CDDP cytotoxicity.

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.