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The development of sulfur compounds for use in heavy-metal detoxification has resulted in the preparation and use of compounds which are highly effective for this purpose because of the great stability of many types of metal-sulfur linkages. The ability of many of these compounds to penetrate cellular membranes has made them useful in situations in which the more readily ionized oxygen based chelating agents are quite ineffective. This review describes the use of mono-, di-, and polythiols, cysteine derivatives, and dithiocarbamates for the detoxification of arsenic, mercury, lead, cadmium, and copper, with some attention to other types of sulfur compounds and other toxic metals.

Formation constants for the Hg2+ complexes of 5 potentially octadentate chelating agents have been determined utilizing a mercury electrode. The ligands, which were reported in an earlier paper, are [(H2NC2H4S)2CH]2, (H2NC2H4S)2CHCH2CH(SC2H4NH2)2, [(H2NC2H4S)2CHCH2]2, (H2NC2H4S)2CH(CH2)3−CH(SC2H4NH2)2 and C6H4[CH(SC2H4NH2)2]2. They each have been observed to form complexes with mercuric ion in the diprotonated form, (LH22+). In addition, from pH titrations, the order of decreasing stability for complexes of these ligands with various divalent metal ions was observed to be Hg2+ > Cu2+ > Ni2+ > Zn2+ > Cd2+ > Co2+ > Mg2+ > Ca2+. Numerous problems were encountered when measurement of the formation constants with these other metal ions was attempted and only estimates of the stability constants are presented here.

Four new chelating agents containing vicinal thioether groups have been prepared by the addition of the appropriate thiols to acetylenedicarboxylic acid. These new compounds are 4,5-Dicarboxy-3,6-dithiaoctanedioic acid, 2,9-Diamino-5,6-dicarboxy-4,7-dithiadecanedioic acid, 3,6-Dithiaoctanediamine-4,5-dicarboxylic acid dihydrochloride, and Disodium-3,6-dithia-1,8-octanediol-4,5-dicarboxylate. Reasonably stable complexes are formed with several divalent metal ions, through precipitation interfered with the complete characterization of the mercury(II) complexes in some cases. For all of these, the stability constants of the mercury(II) complexes were appreciably lower than the stability constants of structurally similar complexes containing vicinal mercaptal groups and the degree of selectivity for mercury(II) was also less. These chelating agents exhibit a very minimal tendency to bind calcium ions.

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.

The administration of sodium N-methyl-N-dithiocarboxy-D-glucamine (NaG) at 500 mg/kg, i.p., or sodium calcium diethylenetriaminepentaacetic acid (DTPA) at 632.5 mg/kg, i.p., reduces the serum enzyme levels characteristic of hepatic damage following the intravenous administration of cadmium chloride (3.5 mg CdCl/sub 2/ x 2.5H/sub 2/O/kg). Some effect on serum enzyme levels was found even when the interval between administration of cadmium chloride and that of the antagonist was as great as 4 h. The enzymes examined included aspartate aminotransferase (AST), ..gamma..-glutamyl transpeptidase (GGT), alanine aminotransferase (SGPT), and alkaline phosphatase (AP). A histopathological examination of the livers of such animals also reveals the presence of a significant protective action.

Between 1913 and 1985, 323 cases of infantile subglottic hemangiomas have been reported in the English language literature. The purpose of this study is to review these cases, to report The Johns Hopkins Hospital experience with ten additional cases, and to compare the various methods of treatment in an attempt to identify the regimens associated with the best outcome. The majority of the patients presented before the age of 6 months with respiratory distress, most commonly inspiratory stridor. There was a 2:1 female to male preponderance. The diagnosis was established by endoscopy in the majority and confirmed by biopsy in one third, without serious bleeding complications. A plethora of treatment methods have been described, including the following: corticosteroids, tracheotomy, radiation therapy, radioactive implant therapy, surgical excision, cryotherapy, and carbon dioxide laser. These methods were reviewed and their results compared to our own. We conclude that several methods are effective, each having its advantages and disadvantages. We believe that immediate tracheotomy should be performed in cases with severe airway obstruction. Smaller lesions may be vaporized with the carbon dioxide laser without tracheotomy if postoperative care is provided in a pediatric intensive care unit. Corticosteroids may be used alone or in combination with other modalities. External radiation therapy and injection of sclerosing agents are not advised.

N-(n-Propyl)-, N-(n-butyl)-, and N-(n-amyl)-N-dithiocarboxy-D-glucamine were newly synthesized by (a) addition of each n-alkylamine to glucose, (b) high-pressure catalytic reduction of each glucosamine thus formed to the corresponding glucamine, and (c) reaction of the resultant secondary amines with CS2 to form the dithiocarboxy derivatives. Each compound was evaluated as an antagonist of acute cadmium (Cd) toxicity and as a complexing agent for intracellular metallothionein-bound Cd (Cd-MT) in mice. N-Benzyl-N-dithiocarboxy-D-glucamine (BDCG) was used as a positive control compound. Each congener afforded partial or complete protection against the lethal effects of 10.0 mg/kg CdCl2.2.5 H2O, and retarded accumulation of Cd in livers and kidneys when given 2 h after the acutely toxic dose of Cd. Each derivative was also effective in mobilizing Cd from MT-bound sites in livers and kidneys of mice which had received a sub-lethal dose of CdCl2 along with 109CdCl2 2 weeks earlier. Excretion of mobilized Cd was almost exclusively by the fecal route. Potency of the analogs, as well as the octanol/aqueous partition coefficients, increased with the overall length of the N-(n-alkyl) carbon chain. Each compound readily complexed Cd from partially purified Cd-MT in vitro. Serum Cd from mice treated with BDCG was associated principally with proteins of high molecular weight.

The esters of the general structure, [CH(SH)COOR] 2 , i.e., D i -BDMS, RCH 2 CH(CH 3 ) 2 ; D s -BDMS, RCH(CH 3 )CH 2 CH 3 ; D i -ADMS, RCH 2 CH 2 CH(CH 3 ) 2 ; and D3-ADMS, RCH(CH 2 CH 3 ) 2 from the reaction of meso -2,3-dimercaptosuccinic acid with isobutyl, sec -butyl, isoamyl, and 3-amyl alcohols, respectively, have been prepared, characterized, and examined as chelating agents for the removal of cadmium from its aged intracellular deposits. All of these compounds depleted cadmium from such deposits and significantly reduced the whole body levels of cadmium. In the case of three (D s -BDMS, D i -BDMS, and D i -ADMS) of these compounds, the reductions achieved are equal to or greater than that produced by 2,3-dimercapto-1-propanol (BAL) under similar circumstances. None of these compounds caused any redistribution of cadmium to the brain, and two of them (D i -BDMS and D i -ADMS) caused a very much larger reduction in the liver levels of cadmium than BAL. None was as effective as BAL in reducing kidney levels of cadmium. These compounds are not soluble in water and are administered as solutions in peanut oil. A comparison of the behavior of these compounds with others which have been reported to be effective in reducing body burdens of cadmium in chronic cadmium intoxication reveals that they are among the most effective. An analysis of the manner in which mobilizing efficacy changes with structure indicates that higher, purely alkyl analogs are not expected to be superior to these compounds, though other structural variations may be.

The newly synthesized dithiocarbamate analog, N-(4-methoxybenzyl)-N-dithiocarboxy-D-glucamine (MeOBDCG) reduced whole-body cadmium levels 66% in cadmium-laden mice when given as 3 injections at 1.0 mmol/kg. Renal and hepatic Cd concentrations were reduced 78 and 85%, respectively. After 6 injections, the whole-body cadmium burden was reduced 71%, while renal and hepatic levels were lowered 84% and 91%, respectively. Mobilized cadmium was excreted almost exclusively by the fecal route. There was no evident toxicity consequent to treatment as judged by mouse body weights and by gross appearance of organs upon dissection. On a molar dose basis, MeOBDCG was more effective than N-benzyl-N-dithiocarboxy-D-glucamine (BDCG) in removing cadmium from both renal and hepatic deposits. An in-vitro assessment of the interaction of MeOBDCG, BDCG and N-methyl-N-dithiocarboxy-D-glucamine with murine cadmium-metallothionein (Cd-MT) revealed a direct relationship between the extent of cadmium depletion from Cd-MT and the relative in-vivo efficacies of the 3 analogs.

Various aspects of the coordination chemistry of cadmium in its dithiocarbamate complexes, which are known to affect the in vivo distribution of this toxic metal ion have been examined. Under appropriate conditions, solid complexes of the composition Cd(DTC)2 have been obtained as reaction products with seven dithiocarbamates. The general properties, octanol/water partition coefficients, mass spectra, 1H, 13C and 113Cd NMR spectra and infrared spectra have been obtained. The molecular structure of the Cd{S2CN(n-C4H9)2}2 complex has been determined. This compound forms monoclinic crystals C2/c a= 23.577(7), b=16.877(8), c=16.209(9) A, β= 126.93(3)o, V=5156(8) A3, Z=8, density=1.343 g cm−3. For the structure determination: λ(Mo Kα)= 0.71073 A, μ=1.076 mm−1, F(000)=2160, T= 296 K and R=0.064 for 1330 observed reflections. The Cd ion is coordinated to four S atoms at distances ranging from 2.513(5) to 2.601(7) A and to a fifth one at the much longer distance of 2.888(5) A. Two of the short metal-sulphur distances are realized by the S atoms of one of the chelate moieties whilst the S atoms of the other moiety realize one short and the longest [2.888(5) A] metal sulphur distance. The other short bond is subtended to a sulphur atom of an asymmetry-related ligand. The coordination polyhedron can be described as either a very distorted tetragonal pyramid or a very distorted trigonal bi-pyramid. The shortest CdCd distance is 3.772(6) A.

Stability constants have been determined for several metal ions and chelating agents prepared by the condensation of dialdehydes and β-mercaptopropionic acid. For each of the four chelating agents examined, a pronounced selectivity for Hg(II) was observed. This is apparently due to the fact that Hg(II) is one of the relatively few coordination centers that forms stable bonds with thioethers in an aqueous environment. A number of solid complexes formulated as M2Y · xH2O are also reported.

Nine new sulfur containing chelating agents have been prepared by the reaction of aldehydes with appropriate compounds containing sulfhydryl groups. These compounds all contain thioether donor groups and several contain carboxylate groups as well. Three of the compounds which are tetracarboxylic acids have carboxyl groups whose ionization is practically independent and give titration curves with but a single inflection point. A method is presented for obtaining all four dissociation constants in such cases.

Eight new polymeric chelating materials based on phenolic, polythioester and polyurethane groups containing oxygen sulfur and nitrogen donor groupings bind mercury(II) preferentially to other ions. The polythiolesters which contain sulfur atoms in potential chelate configurations are somewhat selective towards mercury; those with other donor groups are less selective for mercury, but each polymer shows a fairly characteristic pattern of coordination preferences. The functional groups which are present and the nature of the polymerization linkages appear to be less important in determining the hydrophobic/hydrophilic character of the polymers than the extent of potential cross-linkage and the presence of extensive non-polar segments. These polymers are capable of taking up substantial amounts of mercury(II) from a 1 M solution of mercuric perchlorate (up to 45%) and some of them retain more than half of such mercury after washing with a 1 M solution of potassium cyanide.

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.

An examination of a variety of experimental data shows that several types of rate determining steps can drastically limit the ability of a chelating agent to react with a toxic metal ion in vivo . Such limitations are important for many metal–chelate formation reactions with very favorable overall thermodynamic changes. Two of the most important of these are the slow ligand exchange reactions and slow rates of movement of ionic chelating agents across cellular membranes to achieve contact with intracellular deposits of toxic metal ions. They have drastic effects on the overall stoichiometry of the decorporation process. A simple model is developed which allow rates of mobilization to be estimated. This model is also applied to the problem of overly rapid metal mobilization which frequently leads to adverse effects. The nature of synergistic effects in chelate therapy is also examined and it is seen that many of these can be explained on the basis of the catalysis of ligand exchange processes or on the basis of the different in vivo distribution of lipophilic and hydrophilic chelating agents.

Nine phenolic chelating agents were examined as antidotes for acute uranyl acetate intoxication. The ability of these compounds to promote survival was determined and the ability of two of them to remove uranium from the liver and kidney was compared with that of Na3 CaDTPA. The most effective compounds of this type in promoting survival were found to be Tiron and p‐aminosalicylic acid, but Tiron was much more effective in decreasing the uranium burden of the liver and kidneys. These compounds exhibit an antidotal action at higher uranium levels than the compounds reported in earlier studies. The compounds all seem to possess a very modest toxicity when administered ip.

The theory of hard and soft acids and bases (HSAB theory) can be used to correlate information on metal ion toxicity and the relative effectiveness of therapeutic chelating agents with parameters used to characterize “hardness” and “softness”. HSAB considerations appear to govern at least some of the non-specific aspects of metal ion toxicity. They are also useful in explaining some of the known patterns of metal ion detoxification and how situations arise where the rate behavior, rather than equilibrium factors, may be of importance in determining the success of a given chelating agent in enhancing the excretion of a given toxic metal. In many instances an effective evaluation of the applicability of HSAB theory to such systems is prevented by the limited availability of the necessary biological data. The correlations found can be used to estimate the toxicity of chemical species for which HSAB parameters but not toxicity data are available, as well as to preselect the most promising chelating agents for therapeutic testing.

Several equilibrium models are presented for the calculation of the lethality curves due to toxic metal ions. In the first, a generalized Langmuir model is used to examine the occupancy of linear arrays of 1, 2, ..., 6 interacting adsorption sites on a macromolecular species. This model permits one to take into account cooperative or anticooperative interaction of occupied adjacent sites. In the second model, a variety of nonlinear distributions of interacting sites (in triangular, square, tetrahedral, and octahedral array) are analyzed, and the corresponding adsorption isotherms are calculated. The third model treated, the Ising model, represents a linear infinite array of sites with nearest-neighbor interactions. The fourth and fifth models examined are the Bragg-Williams model and the quasi-chemical model, both of which permit approximate treatment of infinite arrays of adsorption sites having arbitrary numbers of interacting nearest neighbors. These models are then combined with the assumption that the differential distribution of mortality is a known function of the fraction of sites occupied by the toxic metal ion to generate lethality curves. Results are computed for the special case in which the differential mortality distribution is Gaussian, and it is shown that all of the models are capable of generating lethality curves of the sort found experimentally when plots are made of percentage lethality versus log dosage. The models can also be used for situations in which toxic effects other than lethality arise from the interaction of a toxic molecule or ion with more than one site on a linear macromolecule or for reactions involving certain other arrays of specified configuration.

Twenty-seven chelating agents have been screened for efficacy as antidotes for acute Ni(II) acetate intoxication. Of these, thirteen have been found to be good to excellent antidotes when administered intraperitoneally at a level of chelate to Ni(II) of 10:1. An examination of the log of the ratio ( K NiX / K CaX ) for those compounds which are effective as antidotes showed values ranging from 3 up to 10. From the results obtained it would appear that there should be a very large number of chelating agents which should be capable of acting as antidotes in acute Ni(II) intoxication or in other circumstances where it was desired to enhance the urinary excretion of Ni(II). Sodium diethyldithiocarbamate, the antidote of choice for nickel carbonyl intoxication is not effective as an antidote in Ni(II) intoxication. The fact that N-Acetyl- d , l -penicillamine has none of the antidotal activity of d -penicillamine shows the essential role of nitrogen donor atom in this compound. Chelate molecules containing S, N, or O donors may be effective and no single type of donor atom can be described as essential to the functioning of these antidotes, though N and O seem somewhat better than S. Zinc diethylenetriaminepentaacetate is not an antidote, even though the stability constants favor its transformation into the nickel complex. In this case the slow rate of the transformation may be responsible for the absence of antidotal activity.

An alternative model is presented for the selection of therapeutic chelating agents to enhance the mobilization and excretion of a toxic metal. The model is based on the in vivo patterns of absorption, distribution, reaction and excretion of the chelating agent, a typical toxic metal ion and complexes of the two. The model emphasizes the kinetic aspects of the processes involved and indicates how other processes may be incorporated such as redox reactions involving the chelating agent or metal. The identification of rate determining steps and methods for their manipulation are assumed to be of importance. The application of this model to specific metals is outlined.

Multiple primary (MP) malignancies were found in 9.7% of 1961 patients with primary head and neck cancer diagnosed at The Johns Hopkins Hospital, Baltimore, during the years 1975 to 1985. The index tumors were divided into six main groups. Out of the 190 MP malignancies, 46.9% were synchronous and 53.1% were metachronous. Seventy-four percent of MP lesions were noted during the first year after diagnosis of the index primary tumor. Patients with an index tumor in the upper aerodigestive tract had a significantly increased risk of developing a second cancer in the head and neck area. This risk was 5.94 for the oral cavity, 6.98 for the pharynx, 3.57 for the larynx, and 7.02 for the esophagus. Patients with an index tumor in the salivary gland or the thyroid gland had, respectively, a 3.59 and a 7.38 higher risk than the general population of developing a second tumor. Efforts aimed at improving the survival of patients with head and neck cancer must incorporate strategies for the prevention, early detection, and treatment of MP neoplasms.

The nephrotoxicity of cis-platinum (CDDP) in the rat can be controlled throughout a series of weekly administrations of CDDP (each of 5 mg kg−1, i.v.) for at least three weeks by a combination of protective measures involving pretreatment with dithiocarbamates and diuretics and the administration of appropriate dithiocarbamates given 1h after the CDDP. The use of dithiocarbamates with polar substitutents is effective in removing both renal and hepatic deposits of platinum from rats subsequent to its administration and in this respect these compounds are significantly superior to meso-2,3-dimercaptosuccinic acid (DMSA) in the rate at which platinum is removed and in the amounts removed. The most effective of the dithiocarbamates remove ca. 70% of the platinum from the kidneys and the liver; the least effective remove ca. 50% of the platinum from these organs when given at a level of 1.57 mmol kg−1 i.p. for 6 days subsequent to the administration of CDDP. Acetazolamide was shown to be much less effective in preventing renal damage than the dithiocarbamates and was not effective in reducing renal or hepatic levels of platinum. Pretreatment with sodium diethyldithiocarbamate 12h prior to the administration of the CDDP was more effective in preventing renal damage than the administration of this compound 30 min before the cis-platinum. Several dithiocarbamates are found to be superior to sodium diethyldithiocarbamate in reducing renal platinum burdens of rats given CDDP at the level of 6 mg kg−1, and dose—response curves for the removal of renal and hepatic platinum were determined for sodium N-methyl-D-glucamine dithiocarbamate (NaG). The use of dithiocarbamates, other than sodium diethyldithiocarbamate, to control the nephrotoxicity of CDDP may possess some advantages in the clinic.

A study involving (a) the structural chemistry of Hg(II) complexes with thiol containing ligands, (b) the stability constants for such systems and (c) the relative efficacy of 29 compounds as antidotes for mercury poisoning has been carried out to determine the structural requirements for Hg(II) antidotes. This leads to the suggestion that instances in which two thiol groups on the same chelate molecule are simultaneously bonded to the same Hg(II) species in a complex, water soluble or otherwise, are not found and Hg(II) species bearing two sulfur donors generally have a bond angle of 180° or so between these two bonds. It was hypothesized, from this, that chelating agents bearing a single sulfhydryl group might be almost as effective as mercury antidotes as those bearing two groups. Data on the stability constants and antidotal effectiveness are presented for such structures, but in general molecules which do not have the potential ability to chelate are also inferior as antidotes. From the data assembled it would appear that the presence of a second donor group is required. Because of the lability of the mercury-thiol bond, this second site seems necessary to provide the required kinetic stability for the complex. In the case of dithiols, the mercury may move back and forth from one sulfur donor site to another but may not (and possibily cannot) bind firmly and simultaneously to both donor sites.

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.

The principles involved in the design of enterohepatic chelating agents , which facilitate the biliary rather than the renal excretion of toxic metal ions are outlined. The syntheses of some novel chelating agents designed to exhibit such behavior are presented. The basic features exploited in the design of such enterohepatic chelating agents are those which (1) make the chelating agent large enough and sufficiently non-polar to prevent renal filtration, and/or (2) provide it with a structure which allows it to participate in the enterohepatic circulation of the bile acids and their derivatives. The altered electric charge subsequent to metal ion chelation is the major factor acting to prevent the continuing enterohepatic recycling of the metal chelate complex. These agents promote the fecal rather than the urinary excretion of the toxic metals and hence should ameliorate the nephrotoxicity which is a not unusual accompaniment of those chelating agents which facilitate the renal excretion of toxic metals.

Twenty-one chelating agents have been examined to determine their relative efficacy as antidotes for acute cadmium chloride intoxication when administered 20 min after the injection of cadmium chloride. In agreement with earlier studies in which cadmium salt and antidote were administered simultaneously, the most effective antidotes were the polyamino-polycarboxylates, such as DTPA, EDTA and EGTA, administered as their calcium or zinc complexes. In the case of DTPA, the administration of the compound as its zinc chelate provided no improvement in the survival rate over the calcium chelate. ZnDTPA and CaDTPA are, by a significant margin, the most effective antidotes. The efficacy of these compounds as antidotes is dependent both on the stability constants of the cadmium complexes and the toxicity of the cadmium complexes which are formed. For chelating agents of the EDTA type a very close correlation was observed between the log stability constant value of the cadmium complex and the survival ratio obtained. The correlation does not appear to extend to other structural types of antidotes under the conditions used by us. The conditions used in these studies were sufficiently severe to show that chelating agents may be effective antidotes for low level acute cadmium intoxication and yet not show any antidote activity in the procedure given here because of the inherent toxicity of the cadmium chelates themselves.

The simultaneous i.p. administration of the two chelating agents bis(2-hydroxyethyl)dithiocarbamate (DEDTC) and 4-carboxamidopiperidinedithiocarbamate (INADTC) to rats given cadmium in their drinking water at a level of 50 mg cadmium/liter for 39 days led to a large synergistic effect on the biliary excretion of cadmium. A much smaller synergistic effect on the urinary excretion of cadmium was also noted. When treated with a similar mixture of chelating agents after a similar cadmium-drinking water exposure of 180 days, rats showed significant decreases in both renal and brain cadmium levels.

The Topliss scheme, which designates a special series of substituents for use in sequence in the search for suitably substituted aromatic compounds with biological properties superior to the parent unsubstituted aromatic compound, has been applied to the design of new chelating agents for the decorporation of cadmium from its deposits in vivo. Substituted benzylamines have been used in the syntheses of the corresponding substituted sodium N-benzyl-D-glucamine-N-carbodithioates, i.e., RC6H4CH2N(CS2Na)CH2(CHOH)4CH2OH (or RBGDTC): CF3BGDTC, R = 3-CF3; MeBGDTC, R = 4-CH3; MeOBGDTC, R = 4-OCH3; ClBGDTC, R = 4-Cl. Examination of the behavior of these compounds as agents for the mobilization of cadmium from its deposits in vivo shows that such substitution can have an appreciable effect on the organ selectivity for cadmium removal, as well as the efficacy. Of the four compounds suggested by the Topliss scheme for pilot studies, two were much more effective than the parent compound (BGDTC), and of these the best one, sodium N-(4-methoxybenzyl)-D-glucamine-N-carbodithioate (MeOBGDTC) reduced kidney cadmium levels to 30% and liver cadmium levels to 50% of those obtained with the parent compound. Sodium N-[3-(trifluoromethyl)benzyl]-D-glucamine-N-carbodithioate (CF3BGDTC) was also found to be superior to the parent compound in reducing the liver cadmium levels, though it was equivalent in reducing renal cadmium levels.

The effect of certain kinetic factors on thermodynamic evaluations of several therapeutic chelating agents is examined. This allows the in vivo behavior of these drugs to be understood in more detail. The main kinetic factors examined are: (a) the pharmacokinetics of the chelating agents in vivo; (b) the kinetics by which the toxic metal ions are distributed between the serum and other organs; and (c) the rates of the reactions between the therapeutic chelating agent and the complexes formed by the toxic metal ion with serum constituents. A new parameter is proposed for predicting the efficacy of metal binding in plasma. This takes into account changes in the chelating agent concentration with time. Predictions of the relative efficacy of the therapeutic agents based solely on thermodynamic calculations are shown to provide a useful differential indicator for spontaneous detoxification processes, whereas kinetic factors become more important in delayed treatments or when the chelating agents exhibit similar thermodynamic behavior.

The examination of some of the species involved in the in vivo processes in which dithiocarbamates mobilize cadmium from its intracellular deposits indicates that several competing reactions occur. Rates of hydrolytic decomposition of a series of dithiocarbamates capable of mobilizing cadmium in vivo have been determined, and the solubility behavior and nuclear magnetic resonance (NMR) spectra of their cadmium complexes have been examined. Some of the dithiocarbamates most effective in this mobilization process are shown to undergo slow conversion to oxazolidine-2-thiones in the presence of cadmium. All of the cadmium complexes involved in the mobilization process are shown to undergo rapid ligand exchange. While dissociative mechanisms based on the turnover of metallothionein are inconsistent with the experimental data, at least two associative mechanisms are possible. These involve attack on the metallothionein by the dithiocarbamate itself or by a compound derived from it by known metabolic processes.

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.

One month after termination of a 3-mo exposure of rats to cadmium (Cd in drinking water at a concentration of 50 mg/l), the effects of dithiocarbamate analogs on the excretion and distribution of the cadmium were determined. Sodium salts of three dithiocarbamates [sodium bis(hydroxyethyl) dithiocarbamate, DEDTC; sodium N-methyl-D-glucamine dithiocarbamate, MGDTC; and sodium 4-carboxamidopiperidine dithiocarbamate, INADTC] were given to rats ip 2 times at 2.46 mmol/kg. In the following administration of the first injection of DEDTC, cadmium excretion via the urine amounted to 15.8 micrograms and via bile amounted to 124.4 micrograms Cd. Following administration of MGDTC, the urinary and biliary excretions of cadmium were 14.5 and 47 micrograms, respectively, while in the case of INADTC the corresponding values were 23.6 and 7.9 micrograms cadmium. In control animals the urinary and biliary excretion per 12 h reached 0.09 and 0.12 micrograms Cd. Gel permeation chromatography (GPC) analysis of bile revealed differences in the distribution of Cd in the elution fractions after the first injections of the individual dithiocarbamates. For all three dithiocarbamates, significant decreases of the concentrations of cadmium in the liver and kidney were found. DEDTC (but neither of the other compounds) increased the concentration of cadmium in the brain from control levels of 49 +/- 5 ppb to 105 +/- 16 ppb.

Nine chelating agents were tested as antidotes for acute bismuth intoxication in mice. Of these, those with sulfhydryl groups, adjacent aromatic hydroxy groups or appropriately positioned phosphonate groups proved themselves to be effective antidotes. Of the compounds currently approved for therapeutic use, D-penicillamine was the most effective.

An examination of metallothionein induction by toxic metal ions reveals that induction is especially prominent by ions with the electronic configurations (n − 1)d8, (n − 1)d9, (n − 1)d10, and ns2(n − 1)d10. These electronic configurations are also those of both the ‘softest’ and many of the most toxic of the metal ions. The induction process for this protein appears to be one capable of sensing the electronic configurations of these species through the formation of a trans acting induction complex. The relative ability of toxic heavy metals to induce metallothionein is found to be correlated inversely with their softness parameters, σp. Examination of the acceptor properties of these inducing ions suggests that an SH or SeH group (soft base) is the critical reactant site for these ions, as these two species form stable bonds with ions that have such electronic configurations. The involvement of SH or SeH in the initial step of the induction process, i.e. as a component of the trans acting element, in a reaction with ions of such electronic configurations would provide the cell with an appropriate response to the presence of species capable of depleting its supply of glutathione, cysteine t-RNA, selenocysteine t-RNA and similar essential species containing SH or SeH. The enchancement of metal ion toxicity in states of selenium deficiency suggests that an SeH containing molecule participates in this step. Two general mechanisms, based on the reaction of inducing metals with selenocysteine t-RNA, are suggested for the initial step in the induction process. The problem of species which are expected on the basis of their electronic configurations to induced MT, but which have not yet been shown to do so is apparently connected with the attempt to use non-labile complexes or extensively hydrolyzed or insoluble compounds as the inducing species.

Treatment with any one of six different dithiocarbamates subsequent to the administration of cis -platinum (CDDP) is snown to promote the biliary excretion of platinum. The administration of the most effective of these compounds, sodium diethyldithiocarbamate (DDTC) at 1.57 mmol/kg, led to a 30-fold increase in the biliary excretion of platinum. For the other dithiocarbamates investigated, a similar dosage led to increases ranging from approximately 5-fold for sodium iminodiacetic acid dithiocarbamate, to 26-fold for sodium sarcosine dithiocarbamate. The presence of alkyl groups on the nitrogen of the dithiocarbamate increased the effectiveness of the compounds. There is no increase in the platinum levels of the brain when DDTC is used in this manner. A histopathological evaluation of the kidneys of rats given 15 mg CDDP/kg in 6.3% saline with and without the use of dithiocarbamates for renal protection shows significant additional protection due to the use of the dithiocarbamates. Dithiocarbamates given at an appropriate dosing schedule can lead to a significant reduction in the renal damage which is revealed by microphotographs. It is suggested that part of the renal protection obtained by the use of dithiocarbamates may be due to this shift of platinum excretion to the bile which obviates additional renal exposure to platinum. It was also found that the simultaneous injection of a dithiocarbamate with the cis -platinum has no obvious effect on the anti-cancer action of cis -platinum against the Walker 256 carcinosarcoma in rats.

Five new potentially octadentate chelating agents have been prepared by the reaction of mercaptoethylamine with bis-aldehydes. Each of the resulting compounds contains four amine nitrogen donor atoms and four thioether sulfur donor atoms. The compounds prepared are [(H2NC2H4S)2CH]2 (H2NC2H4S)2CHCH2CH(SC2H4NH2)2, [(H2NC2G4S)2CHCH2]2 (H2NC2H4S2CH(CH2)3CH(SC2H4NH2)2, and C6H4[CH(SC2H4NH2)2]2. These compounds have been characterized via elemental analysis, infrared absorption, and proton NMR spectra of their tetrahydrochlorides. The analyses and spectra show clearly that the final products of the syntheses do not contain any Schiff base compounds or thiazolidine ring structures, each of which might have been a possible major reaction product under different reaction conditions.

Simple methods for the preparation of water soluble dithiocarbamates, several of which are newly synthesized, are presented along with some of their physical properties and a preliminary examination of their acute toxicity and their ability to offset acute mercuric chloride poisoning. Such compounds, although they do not possess great thermal stability, recommend themselves for wider application because of their ease of preparation and general effectiveness in binding those metal ions which form insoluble sulfides. Those compounds which possess an appreciable water solubility because of polar groups possess a rather slight degree of toxicity when administered intraperitoneally to mice. Some of these compounds are clearly effective as antidotes for acute mercury poisoning.

A venous clot model in rats was used to compare the ability of locally infused thrombolytic agents to lyse clots. Urokinase and a combination of streptokinase and human plasminogen (Thrombolysin) proved to be equally effective in lysing clots. In comparison, streptokinase alone was not as effective a thrombolytic agent in this model.

The ionization constants of four recently prepared thioethercarboxylic acid chelating agents have been determined along with the stability constants of the complexes of these chelating agents with Hg2+, Zn2+, Ca2+, Ni2+, Mg2+, Cd2+, and Cu2+. The marked selectivity of these chelating agents for Hg2+ is quite striking. For ions with which a bond to a thioether sulfur is not strong, the stability constants are fairly low. A combination of pH measurements and pM measurements were used to determine the stability constants of the species MY and MHY. Because of the geometry of these chelating agents the proton in MHY is far removed from the metal bonding site and a consequence of this is the fact that the stability constants for MY and MHY may be quite close in some cases.

A new chelating agent, phthalytetrathioacetic acid, (PTTA), has been characterized and found to be highly selective for Hg 2+ . All four of its ionization constants have been determined and the stability constants of its complexes with Hg 2+ , Ca 2+ , Zn 2+ , Co 2+ , Pb 2+ , Ni 2+ , and Cd 2+ estimated. The mercury complex has a stability constant greater than those of the other complexes by a factor of at least 10 10 . The high selectivity for the Hg 2+ ion is due to a closely spaced group of thioether sulfurs and a rather wide separation of the carboxylic acid groups which are potential members of chelate rings. The mercury complexes present in aqueous solution are Hg(PTTA)H 2 , log K = 18·8 at low pH and Hg(PTTA) (OH) 2 , log K = 45 at high pH. The presence of thioether, rather than thiol sulfur atoms has the result that the chelate with Pb 2+ is of low stability.

Sodium N-methyl-N-dithiocarboxyglucamine (MDCG) was evaluated for its efficacy in mobilizing and promoting excretion of metallothionein-bound 109 Cd using mice which had received 0.03 mg of CdCl 2 ·2.5H 2 O along with 1.0 >Ci of 109 CdCl 2 three weeks earlier. The MDCG-induced change in the fecal excretion of Cd ranged from a 15-fold increase over the control rate at the lowest dose level used (2.2 mmol/kg; 684 mg/kg) up to a 72-fold increase at the highest dose (8.8 mmol/kg; 2736 mg/kg) following three daily injections. The latter treatment regimen resulted in a fecal excretion of almost 30% of the administered Cd over a 3-day period of observation. Urinary Cd excretion was insignificant in both the control and treated groups. The whole body burden of Cd was reduced by over 50% following seven thrice-weekly i.p. injections of MDCG at 8.8 mmol/kg. There was a 60–65% reduction in both the liver and kidney Cd levels following the same treatment regimen. Radioassay of ten other organs and tissues revealed only modest changes. Testicular Cd was decreased slightly at the highest dose level, and heart tissue from each treated group contained slightly more Cd than controls. Results indicated a rather marked specificity of MDCG in lowering the Cd content of two organs most susceptible to Cd-induced toxicity.

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.

Eighteen different chelating agents, including all of those previously shown to have a protective action in vanadium intoxication, have been compared as antidotes for acute vanadium intoxication using mice. Of these compounds, those found to be effective antidotes for both vanadate (VO3(-3)) and vanadyl (VO2+) include ascorbic acid, deferoxamine, D-penicillamine, sodium calcium diethylenetriaminepentaacetic acid (Na3CaDTPA), Na2CaEDTA, glutathione, Tiron, and ethylenediaminetetra(methylene phosphonate). Of the compounds examined, ascorbic acid appeared to be the most promising for human use. When administered at the levels used in this study, it is an effective antidote for intoxication due to either the vanadate or the vanadyl ion. Certain compounds are able to act as antidotes for vanadate solely by virtue of their action as a reducing agent; when these compounds are unable to form complexes with the reduction product (vanadyl ion), they are effective antidotes for the higher oxidation state only when the concentration of vanadyl produced is less than the level that results in toxic effects.

Equations are developed which describe the method of continuous variations for the case of a single complex with an arbitrarily large number of types of ligands. The restrictions which apply to the use of the absorption of light in the study of such a case are also developed. When any other complex is present, the maximum concentration of the principal complex will be found in a solution which contains the reactants in a mole ratio other than that in which they enter the complex. Such displacements have been found in a large number of systems reported in the literature and may be expected to be an inevitable, but not necessarily obvious, feature of such studies. The wide use of the method of continuous variations has resulted in its application to a large number of systems for which there is no corresponding complete theoretical treatment. The purpose of this paper is to present a general continuous variations solution for the case of a single complex containing an arbitrarily large number of ligands. The results of the examination of this general case can then be applied to the examination of some typical cases from the literature.

The kinetics of the oxidation of glycol-telluric acid esters by periodate has been investigated and found to obey a rate law which is first order in ester. The esterification causes a marked decrease in the rate at which a glycol is oxidized by periodate. The postulated mechanism involves a slow hydrolysis of one of the ester linkages between glycol and tellurate, followed by the rapid transfer of the glycol to periodate with the formation of a cyclic species and the subsequent rapid breakdown of this periodate complex to give products.

A method is presented which can be used to determine the stability constants of moderately stable enzyme-metal complexes. The data required are those giving the relationship between metal ion concentration and enzyme activity over a range of metal ion concentrations but at constant concentration of substrate. Where the metal is complexed to independent groups, the equilibrium constant is obtained by determing the active enzyme: inactive enzyme ratio and estimating the free metal ion concentration. This method may be used even with very impure enzyme preparations if the ratio active enzyme: inactive enzyme changes slowly enough with changes in the metal ion concentration. The application of this method to the L -leucine amino-exopeptidase-manganous ion complex gives a value of log 10 of the stability constant of 4.65 at 40° and an ionic strength of 0.1 and a pH = 8.

Competitive bromination of mixtures of 8-hydroxyquinoline and its chelates with iron (III), chromium (III) and cobalt (III) results in preponderant bromination of the metal chelates when insufficient bromine is used. From infra-red analysis of the products it can be estimated that the metal chelates brominate approximately thirty-five times faster than the free ligand. The heats of the bromination reactions in chloroform are very similar for the free ligand and the chromium (III) and cobalt (III) complexes, but that of the free ligand is apparently slightly greater. The reconciliation of diverse reports on the reactions of coordinated aromatic ligands is possible if the literal electron pair donor picture of the coordinate bond is recognized as inadequate for the description of the charge distribution in such bonds in metal complexes.