Chelation of cadmium

Effects of chelating agents on the cadmium burden of cells in culture

The effects of some new chelating agents on the cadmium burden of CHO cells in culture were investigated. The chelators were sodium-N-(4-methoxybenzyl)-D-glucamine-dithiocarbamate (MeOBG-DTC), sodium-N-benzyl-D-glucaminedithiocarbamate (BG-DTC) and diisopropylmeso-2,3-dimercapto succinate (DiP-DMSA). The results were compared with the effect of the well known dimercaptopropanol (BAL). The derivates of dithiocarbamate are much less toxic than DiP-DMSA and BAL. All chelators effectively prevent Cd uptake into the cells. Mobilization of intracellular Cd, however, is more effective by the DTC-derivatives than by DiP-DMSA or BAL. Within the cell the major fraction of Cd after 48 hours incubation is found in the nuclei and cytosol and very little in the peroxisomes. The chelating agents remove the metal mostly from nuclei and cytosol. Incubation of the cells with cadmium leads to the induction of a Cd binding protein of an apparent molecular weight of 12500 Da, presumably metallothionein. MeOBG-DTC is more effective in removing the metal from this protein than BG-DTC.

Effects of macromolecular chelators on intestinal cadmium absorption in mice

Suppression of absorption by macromolecular chelators have been successful with several metals. In this paper a series of immobilized chelators ranging from DTPA to S-containing soft bases have been synthetized and investigated for ability to suppress intestinal uptake of 109Cd2+ in mice. Dextran-0-ethyl-mercaptan, xanthates derived from polysaccharides and polyvinyl alcohol, dithiocarbamates of polyethylene imine and aminoethyl cellulose, and DTPA immobilized on aminopropyl silica were all ineffective. DTPA immobilized on aminoethyl cellulose even enhanced the intestinal uptake. The macromolecular chelators were without extensive effect on organ distribution of absorbed cadmium, except for dithiocarbamate immobilized on polyethylene imine, which enhanced the deposition of cadmium in several organs including the brain. Although the results are discouraging, they indicate that design and synthesis of immobilized vicinal dithio compounds may represent an avenue for development of non-absorbable chelators with high affinity for cadmium.

Toxicity and carcinogenicity of nickel compounds

The toxicity and carcinogenicity of nickel compounds are considered in three broad categories: (1) systemic toxicology, (2) molecular toxicology, and (3) carcinogenicity. The systemic toxicity of nickel compounds is examined based upon human and animal studies. The major organs affected are discussed in three categories: (1) kidney, (2) immune system, and (3) other organs. The second area of concentration is molecular toxicology, which will include a discussion of the chemistry of nickel, its binding to small and large molecular weight ligands, and, finally, its cellular effects. The third major area involves a discussion of the carcinogenicity and genotoxicity of nickel compounds. This section focuses on mechanisms, using studies conducted in vivo and in vitro. It also includes a discussion of the assessment of the carcinogenicity of nickel compounds.

Oral cadmium chloride intoxication in mice: diethyldithiocarbamate enhances rather than alleviates acute toxicity

Diethyldithiocarbamate (DDC) is known to alleviate acute toxicity due to injection of cadmium salts. However, when cadmium chloride was administered by the oral route, DDC enhanced rather than alleviated the acute toxicity; both oral and intraperitoneal (i.p.) administration of DDC had this effect. Thus, orally administered DDC enhanced cadmium-induced duodenal and ileal tissue damage and inhibition of peristalsis, as indicated by an increased intestinal transit time. At low cadmium doses, the whole-body retention of cadmium was increased by oral DDC administration. Intraperitoneally administered DDC increased cadmium-induced acute mortality and testicular necrosis, and it enhanced cadmium-induced reduction of intestinal motility and increased the whole-body retention of cadmium, indicating increased intestinal cadmium absorption. Also, DDC changed the organ distribution of absorbed cadmium: after i.p. administration of DDC, the relative hepatic deposition was reduced, whereas the relative deposition in other organs, in particular the brain, was increased. This study indicates that medical use of DDC should be avoided in individuals with current exposure to cadmium.

Oral cadmium chloride intoxication in mice: effects of chelation

In acute oral cadmium intoxication, the immediate target organ is the gastrointestinal tract. In this study, toxic effects following oral administration of CdCl2 to mice by stomach tube included intestinal paralysis, constipation and necrosis of the gastrointestinal epithelia. Tissue damage in liver, kidneys and testes developed in survivors due to the systemic toxicity of absorbed cadmium. Chelation of the Cd2+ ion by STPP, EDTA or DTPA prior to oral administration reduced mortality, tissue damage and whole body retention of cadmium. Other chelators (cysteine, NTA, DDC) only marginally affected the whole-body retention. DDC even enhanced the inhibition of intestinal motility caused by cadmium. DTPA and DDC decreased the relative deposition in the liver and increased the relative renal deposition. DDC also increased the relative cadmium deposition in brain, lung, spleen and testes. Among the chelators tested, DTPA was most efficient in preventing toxic effects of oral cadmium.

Oral cadmium chloride intoxication in mice: effects of penicillamine, dimercaptosuccinic acid and related compounds

The antidotal efficacies of chelators during acute cadmium intoxication has previously been examined in experiments where both a soluble cadmium salt and the chelator were administered parenterally. In the present study, PA, DMSA and related compounds were studied as oral antidotes during oral CdCl2 intoxication. According to the antagonistic effects noted on mortality, peristaltic toxicity and intestinal cadmium uptake, the relative efficacies of the compounds tested were: DMSA greater than PAD greater than DMPS greater than MSA greater than PA greater than NAPA. None of the chelators induced major changes in the organ distribution of absorbed cadmium, in particular no increased cerebral deposition of cadmium. This study indicates that, in oral cadmium intoxication in humans, orally administered DMSA would be likely to offer protection against the local toxicity of cadmium in the gastrointestinal tract as well as to reduce the risk of systemic toxicity of absorbed cadmium.

Meso-2,3-dimercaptosuccinic acid and sodium N-benzyl-N-dithiocarboxy-D-glucamine as antagonists for cadmium intoxication

Orally administered meso-2,3-dimercaptosuccinic acid (DMSA) is an effective antagonist for acute oral cadmium chloride (1 mmol/kg) intoxication in mice when administered up to 8 h after cadmium ingestion. Administration of sodium N-benzyl-N-dithiocarboxy-D-glucamine (NaB) i.p. along with DMSA p.o. resulted in kidney and liver cadmium levels only marginally smaller than those obtained with DMSA alone. Both chelation treatment regimens permitted survival of 80% or more of the animals, in comparison to a survival rate of 40-50% in untreated animals. Intraperitoneally administered NaB by itself is a very effective antagonist for cadmium chloride administered intraperitoneally in either acute or chronic cadmium intoxication. A dose-response study was made of the mobilization of cadmium from the liver and kidney of cadmium-loaded mice by NaB; this showed that NaB is one of the most effective cadmium mobilizing agents developed to date. We have also confirmed the earlier report of Kojima and his co-workers of the ability of NaB to remove cadmium from animals which have been treated with cadmium over an extended period of time. NaB causes a very large increase in the biliary excretion of cadmium. Nuclear magnetic resonance (NMR) spectra of 113Cd in bile from treated animals and model solutions indicates that such cadmium is undergoing rapid ligand exchange.

Oral cadmium chloride intoxication in mice: effects of dose on tissue damage, intestinal absorption and relative organ distribution

The acute toxicity of soluble cadmium salts has almost exclusively been studied experimentally after parenteral exposures, where acute mortality is caused by hepatic necrosis. This report describes an alternative experimental model using oral exposure. A single oral toxic dose of CdCl2 to mice induced toxic gastroenteritis; subsequent hepatic and renal lesions were also observed. Whole-body gamma-counting after a single oral toxic 109CdCl2 dose to mice showed a dose-dependent delay of the fecal excretion of non-absorbed cadmium. This delay was absent when a low, non-toxic dose was administered. This effect is most likely due to decreased peristalsis and, at higher doses, intestinal atony due to oral cadmium toxicity. After fecal elimination of non-absorbed cadmium, the residual body burden of cadmium expressed as percent of initial dose reflects the fractional intestinal cadmium absorption due to slow reexcretion of absorbed cadmium. The fractional absorption increased with increasing doses of cadmium. The relative cadmium deposition in brain, testes and intestines decreased with increasing dose, whereas the relative liver deposition increased with dose. The delayed fecal elimination and increased fractional absorption of cadmium may significantly contribute to the development of both local and systemic toxicity in oral cadmium intoxication.

Effects of acetaminophen on cadmium metabolism in mice

Acetaminophen (ACM) administration to mice of the (C57BL/6 X DBA/2)F1 strain produced a typical hepatic centrilobular necrosis similar to that observed in rodents and humans. To determine the effects of this drug-induced necrosis on cadmium (Cd) metabolism, mice were given a sublethal dose of CdCl2 . 2.5 H2O containing 109CdCl2 and maintained for a period of time sufficient for Cd-metallothionein (Cd-MT) to be synthesized and distributed. Subsequent administration of ACM ip or po evoked a marked redistribution of Cd from livers to kidneys of mice, and increased the amount of Cd excreted in urine and feces. There were only minimal or no effects on Cd concentrations in other organs assessed. The effect of ACM on Cd redistribution was antagonized by administration of cysteine, a glutathione precursor, and was enhanced by pretreatment with phenobarbital, a potent inducer of the cytochrome P-450 mixed-function oxidase system. Pretreatment of mice with ACM 6 or 24 hr prior to Cd administration caused aberrations of the normal Cd distribution pattern, but no effect was noted when Cd administration was delayed for 48 hr after ACM injection, indicating recovery of the mechanisms of Cd-MT synthesis and sequestration. Sephadex G-75 gel filtration chromatography of serum from ACM-treated mice showed that most of the Cd was associated with high-molecular-weight proteins, and only a minor portion was present as Cd-MT. Cd excreted in urine was predominantly in a low-molecular-weight form, but there was evidence of two minor components of higher molecular weight, neither of which eluted as Cd-MT. Cd excreted in feces was insoluble following homogenization in 0.25 M sucrose solution. Cd in livers and kidneys of ACM-treated mice eluted as Cd-MT. It was concluded that persons who have a moderately high Cd burden may be at risk of Cd nephrotoxicity if they incur hepatic necrosis subsequent to ACM abuse.

Chelating agents and cadmium toxicity: problems and prospects

Symptoms and signs in humans after excessive exposure to cadmium usually involve the gastrointestinal tract after single oral intake, the lung after acute inhalation, and the kidney after long-term exposure. These organs are usually considered to be the "critical" organs, i.e., the organs most sensitive at a certain type of exposure. The type of Cd-related damage that is most common in humans is probably the renal toxicity after long-term exposure. Most animal experiments, including the most recently published ones, have involved study of gross toxicity and tissue distribution after injection of cadmium in acute experiments. The observations in the older literature that the influence of chelating agents on Cd distribution and excretion is confined to the early period after acute Cd exposure has been confirmed and extended, and the relationship to the time course of metallothionein synthesis has been demonstrated. Although the injection experiments concerning cadmium distribution, particularly those employing repeated exposure, may furnish information that can form a basis for speculation about long-term toxicity to the kidney, there is a lack of direct studies in animals of possible beneficial effects of chelating agents on renal toxicity of cadmium after prolonged exposure. Among the few studies reported, either an increased renal toxicity or a lack of influence on renal toxicity has been observed. The problems in finding a treatment scheme that can be beneficial for the renal toxicity resulting from long-term cadmium exposure thus remain; however, the prospects of finding such schemes in the future seem favorable in view of some of the recent observations.