Effects of the mobilization of aged tissue cadmium by chelating agents

N-benzyl-N-lactyl dithiocarbamate treatment of mice after chronic cadmium administration

Administration of N-benzyl-N-lactyl dithiocarbamate (BLDTC) to mice after chronic cadmium (Cd) administration evoked a prompt, dose-dependent reduction of the whole body burden; 75% of the retained Cd was mobilized and excreted after 20 i.p. injections of BLDTC at 1.0 mmol/kg/injection. This same dose regimen produced 71% and 98% reductions of the renal and hepatic Cd concentrations, respectively. There was no reduction by BLDTC of the endogenous level of any of seven other metals measured: iron, magnesium, selenium, copper, calcium, zinc, and manganese. Renal proximal tubular damage in mice which received Cd followed by BLDTC was much less than that observed in kidneys from mice which received Cd alone. Chronic Cd administration led to substantial epithelial vacuolar damage to renal distal tubules, and this process was not apparently reversed or antagonized by BLDTC treatment to the extent observed in proximal tubules.

Evidence of active transport of cadmium complexing dithiocarbamates into renal and hepatic cells in vivo

A study was made of the effects of certain inhibitors of transport systems on the actions of four cadmium (Cd) complexing N,N-disubstituted dithiocarbamates (DTCs) in mobilizing murine renal and hepatic Cd in vivo. Probenecid, the prototypical antagonist of organic anion transport in the kidney, when given 1 hr prior to each DTC, sharply suppressed the DTC-induced reduction of renal Cd but was virtually without effect on mobilization of Cd from liver. Sulfinpyrazone, which blocks tubular reabsorption of uric acid and also inhibits transport of a variety of organic acids, inhibited markedly the mobilization of both renal and hepatic Cd by DTCs. Phlorizin, an inhibitor of tubular sugar reabsorption, did not affect the Cd mobilizing actions of DTCs in any consistent fashion. We propose that the high degree of selectivity of DTCs in mobilizing renal and hepatic Cd is dependent, at least in part, upon active transport of DTCs into these tissues via the organic anion transport systems. This report presents the first evidence that compounds of the (R)2NCSS- class may gain access to intracellular space by an active, carrier-mediated process.

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.

Dithiocarbamates of improved efficacy for the mobilization of retained cadmium from renal and hepatic deposits

The preparation and properties of two novel cadmium-mobilizing dithiocarbamates namely, sodium N-(4-methylbenzyl)-and sodium N-(4-methoxybenzyl)-4-O-(beta-D-galactopyranosyl)-D-glucamine-N-carbo dithioates derived from alpha-lactose and substituted benzylamines are described. These compounds are more effective than previously prepared compounds of this type for the mobilization of cadmium from its aged deposits in both the liver and the kidneys. An examination of the structural features of the more effective compounds for the mobilization of cadmium from its aged deposits reveals that the combination of a high molecular weight with a suitable amphipathic structure in which the polar and non-polar groups are in an appropriate balance are key features. A histopathological evaluation of the animals from which cadmium is removed by these compounds indicates no variations from the normal for the kidney and no evidence of hepatic damage resulting from the removal of the cadmium. On the basis of the trends observed in cadmium mobilizing efficacy, there are grounds for suspecting that agents which are significantly more effective than any prepared so far, should also be accessible.

Intracellular cadmium mobilization sequelae

The consequences of the mobilization of aged intracellular cadmium from its in vivo deposits in mice by chelating agents were examined. The chelating agents used were BAL, sodium N-benzyl-D-glucamine dithiocarbamate (NaB), Diisopropyl meso-2,3-dimercaptosuccinate(Di-PDMS) and sodium N-(4-methoxybenzyl)-D-glucamine dithiocarbamate(4-Me0), all previously shown capable of causing statistically significant decreases in either renal or hepatic cadmium burdens in rodents. They were given at a level of 400 mumol/kg (i.p.) daily for 10 days to mice previously loaded with a total of 10 mg CdCl2.2.5 H2O/kg. Under these conditions a significant decrease in the renal cadmium level occurred following treatment with BAL, NaB, and 4-MeO; hepatic cadmium levels decreased significantly following treatment with NaB and 4-MeO. Pathological examination of the kidneys, liver, and testes in these animals showed that chelate mobilization of the cadmium produced no noticeable changes in the histopathology of these organs in comparison with that observed for the animals which had been given only cadmium and had undergone no chelate treatment. The results suggest that the mobilization of such aged cadmium from in vivo deposits need not result in any deleterious changes in the kidneys, liver or testes.

Selective removal of cadmium from aged hepatic and renal deposits: N-substituted talooctamine dithiocarbamates as cadmium mobilizing agents

The preparation and examination of three dithiocarbamates derived from N-substituted D-gluco-L-talooctamine reveals that the 4-methoxybenzyl derivative (MeOBGD) is superior to any previously prepared dithiocarbamates as an agent for the mobilization of aged intracellular hepatic cadmium deposits from mice. All of these compounds are also quite effective in reducing whole body burdens of cadmium. The use of these compounds does not result in any increase in the cadmium content of the brain. The selection of these chelating agents for synthesis was suggested by an analysis of the log dose-response curves for the mobilization of renal cadmium by previously studied dithiocarbamates. This revealed that the slope of the percentage renal cadmium mobilized vs the log dosage curve is determined to a considerable extent by the sum of the Hansch pi parameters for the substituents, while the intercept is largely determined by the molecular weight of the compound. The implication of such a correlation is that the ability of a chelating agent to remove cadmium from its aged deposits is determined to some extent by its molecular weight, provided the polarity of the overall molecule is appropriate.

Effects of diethyldithiocarbamate on the toxicokinetics of cadmium chloride in mice

Diethyldithiocarbamate (DDC) efficiently alleviates the acute toxicity of injected cadmium chloride, but enhances the acute toxicity of orally administered cadmium chloride. Further, DDC induces extensive changes in organ distribution of cadmium, and mobilizes aged cadmium depots. The present study investigates effects of DDC on the toxicokinetics of cadmium at lower doses of cadmium than those used in previous studies. During single exposure to subtoxic oral doses of cadmium chloride DDC enhanced intestinal cadmium absorption, both after intraperitoneal and oral administration of DDC. In such acute exposure experiments orally administered DDC only slightly changed the relative organ distribution of absorbed cadmium, while intraperitoneal administration of DDC induced extensive changes in organ preference of absorbed cadmium. The relative hepatic and testicular deposition was reduced, while the relative deposition in heart, spleen, lungs, brain and carcass was increased. Bi-weekly intraperitoneal injections of DDC enhanced the rate of elimination of aged cadmium depots and changed the organ distribution of retained cadmium, compared to the control group. Chronic exposure to DDC in the feed and cadmium chloride in the drinking water did however not result in increased whole-body retention, and the organ distribution in the DDC-exposed group was similar to that in the control group. This result could be due to both increased rate of absorption and increased published extensive changes in the toxicokinetics of cadmium induced by DDC are mainly due to the high cadmium doses employed and the intraperitoneal administration of DDC. At lower doses and more realistic administration routes for cadmium and DDC, the effect of DDC is less. However, still DDC does not seem to have any potential as an antidote for cadmium or for mobilization of cadmium depots in humans.

Effects of dithiocarbamates on intestinal absorption and organ distribution of cadmium chloride in mice

Earlier publications have demonstrated that diethyldithiocarbamate (DDC) antagonizes the acute toxicity of injected CdCl2 but enhances the acute toxicity of orally administered CdCl2, most likely due to the high lipophilicity of DDC and the complex formed with the Cd++ ion. This study demonstrates that the hydrophilic dithiocarbamates dihydroxyethyldithiocarbamate (DHE-DTC) and N-methyl-N-glucamyl dithiocarbamate (NMG-DTC) also enhance the intestinal absorption of orally administered CdCl2 in mice, although less efficiently than DDC. After oral as well as intraperitoneal administration 15 min. after a single oral dose of CdCl2 the dithiocarbamates tested enhanced the intestinal cadmium uptake with a relative efficiency, DDC greater than DHE-DTC greater than NMG-DTC, which correlated to the lipophilicity of both the dithiocarbamates and the complexes formed with the Cd++ ion. Intraperitoneal administration of DDC induced extensive changes in the relative organ distribution of absorbed cadmium, compared to the distribution of CdCl2 administered alone. However, the only noticeable effect of administration of DHE-DTC and NMG-DTC was decreased gastrointestinal deposition of cadmium, irrespective of the administration route of the dithiocarbamates. Earlier studies have demonstrated that DDC and various other dithiocarbamates are capable of mobilizing intracellular cadmium deposits, presumably due to some lipophilicity. This study demonstrates that these dithiocarbamates may also enhance the intestinal absorption of cadmium.

Effects of tetraethylthiuram disulfide on the toxicokinetics of cadmium in mice

This study examines the effects of tetraethylthiuram disulfide (TTD; disulfiram, Antabuse) on the toxicokinetics in mice of 109Cd-labelled cadmium chloride, as determined by whole-body and organ gamma-counting. At the highest single dose of orally administered CdCl2, i.e. 70 mumol/kg, orally administered TTD enhanced the inhibitory effect of CdCl2 on intestinal motility and increased the fractional whole-body retention of the dose of cadmium chloride, indicating enhanced intestinal cadmium absorption. Also, TTD induced extensive changes in organ distribution of absorbed cadmium; the relative hepatic and testicular deposition was reduced, while the relative deposition in heart, spleen, lungs, brain and carcass was increased. In a prolonged exposure experiment where CdCl2 was added to the drinking water and TTD to the feed, TTD increased the intestinal absorption of cadmium by more than four-fold as compared to the controls. Further, decreased deposition was seen in the carcass and increased deposition in intestines and liver. In a third experiment, oral doses of TTD given twice weekly had no influence on the rate of excretion of aged cadmium depots, and also the organ distribution was unchanged. Thus, the effect of TTD on cadmium metabolism seems to be exerted only during intestinal absorption and the distribution phase immediately thereafter.

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.

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.

Antagonists for acute oral cadmium chloride intoxication

An examination has been carried out on the relative efficacy of a number of chelating agents when acting as antagonists for oral cadmium chloride intoxication in mice. The compounds were administered orally after the oral administration of cadmium chloride at 1 mmol/kg. Of the compounds examined, several were useful in terms of enhancing survival, but by far the most effective in both enhancing survival and leaving minimal residual levels of cadmium in the liver and the kidney, was meso-2,3-dimercaptosuccinic acid (DMSA). Several polyaminocarboxylic acids also enhanced survival. The most effective of these in reducing liver and kidney levels of cadmium were diethylenetriaminepentaacetic acid (DTPA), trans-1,2-diaminocyclohexane-N,N,N'N'-tetraacetic acid (CDTA), and triethylenetetraminehexaacetic acid (TTHA). D-Penicillamine (DPA) was found to promote survival but also led to kidney cadmium levels higher than those found in the controls. Sodium 2,3-dimercaptopropane-1-sulfonate (DMPS) was as effective in promoting survival as DMSA but left levels of cadmium in the kidney and liver that were approximately four times greater than those found with DMSA.