Shirley G. Jones

Mobilization of aged cadmium deposits by dithiocarbamates

Mice with chronic cadmium intoxication were given low levels (0.6 mm/kg) of several dithiocarbamates (parent compounds: dihydroxyethylamine, iminodiacetic acid, methylhydroxyethylamine and sarcosine) in an attempt to reduce the cadmium present in the liver and kidney. Comparing the results with those obtained with the less polar sodium diethyldithiocarbamate (NaDDTC), only ammonium di(hydroxyethyl)dithiocarbamate (NH4DHE-DTC) possessed a similar ability to reduce kidney cadmium levels. Under the experimental conditions employed, the reduction obtained with NH4DHE-DTC was less than that effected by a comparable dose of NaDDTC. A subsequent dose-dependence study showed, however, that sodium di(hydroxyethyl)dithiocarbamate (NaDHE-DTC) is quite effective at higher dosage levels (up to 5.5 mmoles/kg) where substantial reductions in both kidney (89% mobilization) and liver (38% mobilization) stores of cadmium were observed. High doses of the NaDHE-DTC are well tolerated as the LD50 of this compound in mice is greater than 19.8 mmoles/kg.

Structural effects in the dithiocarbamate-enhanced biliary excretion of cadmium

The dithiocarbamate enhancement of the biliary excretion of cadmium in rats loaded with cadmium (by either the oral or sc route) was found to be strongly dependent on the structure of the groups attached to the nitrogen atom of the dithiocarbamate moiety. Those dithiocarbamates containing hydroxyl-bearing attached groups were found to be capable of causing the greatest enhancement of the cadmium content of the bile. For the compounds of this type that were examined, this enhancement of biliary cadmium content varied from 30-fold to over 2000-fold. No enhancement of the biliary excretion of cadmium was found subsequent to the administration of sodium diethyldithiocarbamate, though this compound is known to cause a significant increase in the fecal excretion of cadmium.

Mobilization of aged in vivo cadmium deposits by diethyl dimercaptosuccinate

Diethyl dimercaptosuccinate (DEDMS) was prepared and found to be capable of mobilizing cadmium from mice one month after they had been given an injection (i.p.) of 0.03 mg CdCl2.2.5H2O containing 1.0 microCi of 109 CdCl2. When pure, DEDMS is a waxy solid with a melting point of 61-62 degrees C which is soluble in warm peanut oil. Its LD50 value (i.p.) in mice is approximately 2.6 mmol/kg, a value which allows it to be given at a higher dosage than other known lipid-soluble dithiols. This compound is especially effective in reducing hepatic and whole body levels of cadmium; it is not as effective as 2,3-dimercaptopropanol (BAL) in reducing renal cadmium levels.

Effect of chelating agent structure on the mobilization of cadmium from intracellular deposits

An examination of the efficacy of several structural types of chelating agents in the removal of cadmium from its intracellular deposits in mouse liver and kidneys reveals that of the structural types examined, only dithiocarbamates and a vicinal dithiol were able to mobilize cadmium from such intracellular sites. Esters of L-cysteine, a macrocyclic thioether, and a disulfide of a dithiocarbamate were unable to cause any appreciable decrease in either renal or hepatic cadmium levels. Charged groups such as carboxylic acid groups reduce the efficacy as well as the toxicity of the structural types that can otherwise mobilize such cadmium. It was also found that the administration of a cadmium-binding polymer ip leads to only a very slight net excretion of cadmium, while the po administration of this polymer leads to no net additional cadmium excretion. Of the compounds newly reported here, some are approximately equal in cadmium-mobilizing efficacy to the most effective of previously reported compounds.

Effects of the mobilization of aged tissue cadmium by chelating agents.

An examination of the kidney and liver subsequent to the mobilization of aged cadmium deposits from them by the use of both dithiocarbamates and 1,2-dimercapto-1-propranolol (BAL) was carried out. No striking permanent effects due to cadmium mobilization were noted in the kidneys or livers for most of the chelating agents used. After the mobilization of part of the cadmium burden, the remaining cadmium gives evidence of undergoing a redistribution, leading to a renewed increase in both the kidney and liver levels of this element.

Structureactivity relationship with therapeutic chelating agents

Abstract Although the vast majority of therapeutic chelating agents are water soluble rather than lipid soluble (e.g. EDTA, D-penicillamine, DTPA, desferrioxamine and unithiol, among others,) recent studies [1, 2] have shown that lipid soluble chelating agents and those that give soluble metal chelates, may be the only effective means of mobilizing intracellular deposits of certain metals. This has been shown most strikingly in the case of cadmium present in the kidney (as metallothionein). Such deposits can be mobilized by both BAL and sodium diethyldithiocarbamate. Because it is possible to synthesize derivatives of sodium diethyldithiocarbamate with varying lipophilicity, we have undertaken to prepare some of these compounds and examine their behavior as antidotes for acute cadmium intoxication. The animal experiments have been carried out using procedure of Gale et al . [2, 3], while syntheses have been done using published procedures [4]. The dithiocarbamates prepared and examined are shown in Table I, together with information on their efficacy as antidotes. The behavior of these compounds as antidotes can be correlated using the pi substituent constants of Hansch, as tabulated by Chu [5]. For each compound the relative hydrophobic nature can be estimated as the sum of the pi substituent constants of R 1 and R 2 . These sums are shon in the last column of Table I. Figure 1 below shows the survival ratio variation with Σπ. One of the adverse effects of such dithiocarbamates is their ability to transport cadmium to the brain, an effect which is also related to the lipophilicity of the chelating agent. If the Net Efficacy of the chelating agent is defined as t001 . Antidotal Behavior of Dithiocarbamates ( −S 2 CNR 1 R 2 ) Compd. R 1 R 2 Relative Survival Ratio a Relative Brain Cd b Σπ A C 2 H 5 C 2 H 5 1.00 1.00 2.04 B CH 3 CH 3 1.00 0.88 1.12 C C 2 H 4 OH C 2 H 4 OH 0.88 0.30 −1.54 D CH 3 CH 2 COO − 0.63 0.14 −4.16 E CH 3 C 2 H 4 OH 1.00 0.00 −0.21 F CH 2 COO − 0.38 0.02 −5.44 a Relative Survival Ratio = Survival Rate/Survival Rate for A. b Relative Brain Cd = Brain Cd/Brain Cd for A. then such a net efficacy (with n = 2), as plotted in Fig. 2, can be seen to reach a maximum in the region Σπ≈0. It is possible that such correlations will prove useful in the development of optimal chelating agents for the removal of intracellularly deposited metal ions.

A comparative study of the influence of vicinal dithiols and a dithiocarbamate on the biliary excretion of cadmium in rat

The effect of two vicinal dithiols, 2,3-dimercaptopropan-1-ol (BAL) and N-(2,3-dimercaptopropyl)phthalamidic acid (DMPA), and a dithiocarbamate, sodium N-(4-methoxybenzyl)-D-glucamine dithiocarbamate (MeOBGDTC), on the biliary excretion of cadmium was examined in rats. Tissue cadmium levels were also determined following the measurements of biliary excretion of cadmium. At 30 min after the injection of CdCl2.2.5H2O (1 mg/kg, iv) each rat was given 400 mumol/kg ip of one of the compounds, BAL, DMPA or MeOBGDTC. While all the compounds increased the biliary excretion of cadmium, the most effective was MeOBGDTC, whose administration resulted in a 580% increase in biliary cadmium content. The effectiveness of the MeOBGDTC may be due to the presence of both nonpolar and nonionizing polar groups attached to nitrogen. MeOBGDTC was able to mobilize cadmium to the bile even after the occurrence of the synthesis of metallothionein and the incorporation of the cadmium into it. An attempt was also made to determine the chemical nature of the Cd-MeOBGDTC complex present in the bile by comparing a newly synthesized authentic sample of Cd(MeOBGDTC)2 complex with the hot dioxane extract of the freeze-dried bile samples using thin-layer chromatography and proton NMR. The results suggested that cadmium excreted in the bile in part, is complexed to MeOBGDTC and glutathione.

Dependence on chelating agent properties of nephrotoxicity and testicular damage in male mice during cadmium decorporation

An examination of the histopathological appearance of the kidneys of mice treated with cadmium chloride (s.c.) and simultaneously given 1 of 3 chelating agents (i.p.) reveals that the extent of nephrotoxicity is greatest when L-cysteine is the chelating agent. When either of 2 dithiocarbamates capable of mobilizing cadmium from its intracellular deposits, i.e. sodium N-methyl-D-glucamine dithiocarbamate (NaG) or sodium N-benzyl-D-glucamine dithiocarbamate (NaB) is used as the chelating agent, no morphological renal damage was evident. Under these same conditions the testes of the mice were protected to the extent of 95% by both of the dithiocarbamates, whereas the protection afforded by the L-cysteine was only about 50%. One factor governing the extent of nephrotoxicity appears to be the stability of the cadmium complexes which are formed and the manner in which this affects their behavior in vivo. Complexes which are preferentially excreted in the bile, cause little or no renal damage.

Dithiocarbamate treatment of chronic cadmium intoxication in mice

The dithiocarbamate analogs, N-benzyl-N-dithiocarboxy-D-glucamine (BDCG) and N-cyclohexyl-N-(2-hydroxy-3-sulfonatopropyl)dithiocarbamate (CAPSO-DTC), were evaluated as cadmium (Cd) antagonists in mice which had received repetitive injections of Cd to effect accumulation of substantial levels of metallothionein-bound Cd in kidneys and livers. BDCG was highly effective in lowering whole body Cd stores and renal Cd concentrations. While the percent of renal Cd mobilized decreased with increasing Cd concentrations, the total amount of Cd mobilized increased. CAPSO-DTC was also effective in reducing whole body Cd levels, but appeared to have less affinity for renal Cd than did BDCG. Treatment of Cd-laden mice with BDCG provoked only a modest elevation of serum creatinine levels, suggesting that the complex of Cd with BDCG may be less nephrotoxic than the complex of Cd with EDTA or dimercaprol. The log of the percent reduction of renal Cd by BDCG was found to be a linear function of the pretreatment renal Cd concentration, and reductions of whole body Cd burdens correlated closely with reductions of liver and kidney Cd concentrations. It was suggested that a Cd complexing agent of the dithiocarbamate class may have ultimate application in a provocative methodology to estimate body or organ Cd stores based upon the amount of Cd excreted following a standard dose of the chelator.

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.