Comparative mobilization of lead by chelating agents

212Pb: Production Approaches and Targeted Therapy Applications

Over the last decade, targeted alpha therapy has demonstrated its high effectiveness in treating various oncological diseases. Lead-212, with a convenient half-life of 10.64 h, and daughter alpha-emitter short-lived ²¹²Bi (T_1/2 = 1 h), provides the possibility for the synthesis and purification of complex radiopharmaceuticals with minimum loss of radioactivity during preparation. As a benefit for clinical implementation, it can be milked from a radionuclide generator in different ways. The main approaches applied for these purposes are considered and described in this review, including chromatographic, solution, and other techniques to isolate ²¹²Pb from its parent radionuclide. Furthermore, molecules used for lead’s binding and radiochemical features of preparation and stability of compounds labeled with ²¹²Pb are discussed. The results of preclinical studies with an estimation of therapeutic and tolerant doses as well as recently initiated clinical trials of targeted radiopharmaceuticals are presented.

Synthesis and characterization of new 1-hydroxy-2-pyridinethione derivatives: Their lead complexes and efficacy in the treatment of acute lead poisoning in rats

A number of new mono- and dihydroxypyridinethione ligands have been synthesized via reaction of dimethylamine and amino acid esters with the active amide obtained from the reaction of 1-hydroxy-2-pyridinethione-4-carboxylic acid (1) and 1,1'-carbonyldiimidazole in DMF. Moreover, the lead complexes of these new ligands were also prepared. Structures of the newly synthesized compounds have been confirmed by different spectroscopic methods such as IR, ¹H NMR, and ¹³C NMR, and by elemental analysis. The effect of these synthesized ligands on the excretion of lead, iron, and zinc, and their distribution in kidneys, liver, and bones in acutely intoxicated rats was investigated and results, for lead, were compared with those of the known drug meso-2,3-dimercaptosuccinic acid (DMSA). Results obtained revealed that compound 5 exhibits remarkable ability in total fecal and urinary excretion of lead and was superior to DMSA. In addition, results show that the concentration of lead in soft tissues and bones was lower in rats treated with HTPL than those treated with DMSA. Furthermore, the concentration of lead in liver tissues obtained from sub-chronic lead-intoxicated rats treated with HTPL was lower than those treated with DMSA and calcium disodium ethylenediaminetetraacetic acid (CaNa₂EDTA).

Tungsten targets the tumor microenvironment to enhance breast cancer metastasis

The number of individuals exposed to high levels of tungsten is increasing, yet there is limited knowledge of the potential human health risks. Recently, a cohort of breast cancer patients was left with tungsten in their breasts following testing of a tungsten-based shield during intraoperative radiotherapy. While monitoring tungsten levels in the blood and urine of these patients, we utilized the 66Cl4 cell model, in vitro and in mice to study the effects of tungsten exposure on mammary tumor growth and metastasis. We still detect tungsten in the urine of patients' years after surgery (mean urinary tungsten concentration at least 20 months post-surgery = 1.76 ng/ml), even in those who have opted for mastectomy, indicating that tungsten does not remain in the breast. In addition, standard chelation therapy was ineffective at mobilizing tungsten. In the mouse model, tungsten slightly delayed primary tumor growth, but significantly enhanced lung metastasis. In vitro, tungsten did not enhance 66Cl4 proliferation or invasion, suggesting that tungsten was not directly acting on 66Cl4 primary tumor cells to enhance invasion. In contrast, tungsten changed the tumor microenvironment, enhancing parameters known to be important for cell invasion and metastasis including activated fibroblasts, matrix metalloproteinases, and myeloid-derived suppressor cells. We show, for the first time, that tungsten enhances metastasis in an animal model of breast cancer by targeting the microenvironment. Importantly, all these tumor microenvironmental changes are associated with a poor prognosis in humans.

Chelation for heavy metals (arsenic, lead, and mercury): protective or perilous?

Despite clinical experience that spans more than half a century, chelation for toxic heavy metals represents one of the most controversial and misapplied interventions in clinical toxicology. The prompt use of chelating agents to treat acute, life-threatening intoxication is an indication that is largely supported by experimental animal data and limited clinical research. Although chelating agents administered for chronic intoxication may accelerate the excretion of heavy metals, their therapeutic efficacy in terms of decreased morbidity and mortality is largely unestablished. Recent investigations suggest that their use in such settings might be associated with deleterious effects. Careful attention to risk-benefit issues is warranted, particularly in clinical situations in which the etiological role of heavy metals in the patient's illness is in question.

Succimer chelation normalizes reactivity to reward omission and errors in lead-exposed rats

This study evaluated the efficacy of a 3-week course of succimer treatment to alleviate behavioral deficits in rats exposed to lead (Pb) for the first 4 weeks of life. A 3 x 2 factorial design was used: three levels of lead exposure (No Pb, Moderate, and High Pb) and two levels of chelation (succimer or vehicle). Behavioral testing was conducted following chelation therapy, from 2 to 9 months of age; this report presents the results of two of the administered tasks: (1) a conditional olfactory discrimination task (baseline task), and (2) a conditional olfactory discrimination task with periodic reward omission on some correct trials (RO task). In the RO task, the performance disruption produced by committing an error on the previous trial was significantly greater for both unchelated lead-exposed groups than for controls. The High Pb rats were also more sensitive to reward omission than controls, providing converging evidence for impaired regulation of arousal or emotion. Importantly, succimer treatment was effective in normalizing the heightened reactivity of the lead-exposed animals to both errors and reward omission. In addition, non-lead-exposed rats that were treated with succimer tended to be more affected by a prior error than controls in their latency to respond on post-error trials. In sum, these findings provide new evidence that succimer chelation can significantly lessen the lasting neurobehavioral dysfunction produced by early lead exposure, but also suggest that there may be risks of administering the drug to individuals without elevated blood lead levels.

Lead mobilization during calcium disodium ethylenediaminetetraacetate chelation therapy in treatment of chronic lead poisoning

It has long been established that chronic lead (Pb) poisoning is a cause of renal insufficiency. However, although easily diagnosed, there is still no treatment available that will revert this type of poisoning. We report a study performed on 56 male Wistar rats administered Pb in drinking water (500 ppm Pb acetate) over a 90-day period. Twenty-one non-Pb-exposed animals served as the control group. Seven animals from each group were killed days 60 and 90. At the end of the 90-day period, 21 of the Pb-exposed animals were treated with disodium monocalcium EDTA (50 mg/kg/d for 5 days) intraperitoneally and 21 animals were administered serum saline by the same route. Three treatment courses were administered, separated by 9 days free of treatment. Seven animals from each subgroup were killed at the end of each treatment course. Pb levels were determined in blood, urine, liver, brain, kidney, and bone. Treatment with EDTA led to a greater and more rapid reduction in Pb contents in the brain and kidney. The decrease in hepatic Pb levels in the treated group of animals was similar to that in the group administered placebo. Bone Pb levels also failed to show a response to the chelating agent. Use of EDTA appears to result in a reduction in Pb deposits in such critical organs as the kidney and brain. However, the chelating agent does not seem to have access to bone Pb deposits, such that the skeleton becomes a permanent source of poisoning for other tissues.

The effects of succimer chelation therapy on auditory function in rhesus monkeys

Sixty-six female rhesus monkeys were randomly assigned to three lead exposure conditions (none, from birth to 1 year, and from birth to 2 years) by two chelation treatment (succimer and no succimer) conditions. Blood lead levels were maintained at 35-40 microg/dl beginning shortly after birth and continuing for 1 or 2 years postnatally. There were two separate chelation regimes: 53 and 65 weeks of age. Lead and lead-vehicle dosing were discontinued while succimer was administered. Succimer (or placebo) was administered orally at a dose of 30 mg/kg/day (divided into three doses per day) for 5 days and for 14 additional days at 20 mg/kg/day (divided into two doses per day) for a total 19-day treatment regimen. Auditory function was assessed in these monkeys at least 1 year after lead intake had been discontinued. The outcome measures included tympanometry to assess middle ear function, OAEs to assess cochlear function, and ABRs to assess the auditory nerve and brainstem pathways. There were no significant differences as a function of succimer treatment for any of the tympanometric variables measured. Suprathreshold and threshold distortion product otoacoustic emissions were comparable among the succimer and vehicle groups. However, there was a nonsignificant trend to smaller amplitude distortion products at the highest frequencies assessed (6.4-10.0 kHz). Finally, the auditory evoked response at levels from the auditory nerve to the cerebral cortex did not significantly differ as a function of succimer treatment.

The effects of elevated blood lead levels and succimer chelation therapy on physical growth in developing rhesus monkeys

Seventy-two female rhesus monkeys were randomly assigned to three lead exposure conditions (none, birth to 1 year, birth to 2 years). In a completely crossed design, the lead-exposed and control monkeys were randomized to placebo or chelation therapy which began at 1 year of age. Dosing was conducted daily beginning on day 8 postpartum. The lead dose levels were adjusted biweekly to gradually elevate the blood lead level of each monkey to a target of 1.69-1.93 micromol/L (35-40 microg/dL). Succimer (or placebo) was administered orally (30 mg/kg/day for 5 days and 20 mg/kg/day for 14 additional days) for a total 19-day treatment regimen. There were two separate chelation regimes at 53 and 65 weeks of age. Succimer therapy in combination with lead abatement reduced blood lead levels significantly faster than lead abatement alone; however, that advantage disappeared once succimer therapy was discontinued. Weight, crown-rump length, and head circumference were measured regularly. Growth in weight, length, and head circumference did not vary significantly as a function of blood lead levels. Succimer chelation therapy did not significantly affect weight, length, or head circumference through 2 years of age.

Efficacy of succimer chelation for reducing brain lead in a primate model of human lead exposure

The extent to which succimer (meso-2,3-dimercaptosuccinic acid [DMSA], Chemet) reduces brain lead (Pb) levels may be a primary consideration in evaluating its efficacy for reducing neurotoxicity. Clinical research in this area has been hampered by the need to use blood Pb levels as the index of treatment efficacy, despite the fact that brain Pb level is the exposure parameter of greater relevance to cognitive outcomes. Here, a nonhuman primate model of human Pb exposure was used to determine: (1) The efficacy of oral succimer for reducing brain Pb derived from chronic or recent exposures, and (2) The extent to which blood Pb levels reflect brain Pb prior to and following chelation. Adult rhesus monkeys were chronically exposed to Pb orally for 5 weeks to reach and maintain a target blood Pb level of 35-40 microg/dL. Chelation of Pb from recent exposures was assessed using a stable (204)Pb isotope tracer administered over 4 days prior to treatment. Immediately prior to chelation, a prefrontal cortex (PFC) biopsy was collected to determine pretreatment brain Pb levels. Subsequently, monkeys were assigned to vehicle (n = 5) or succimer (n = 6, 30 mg/kg/day x 5 days followed by 20 mg/kg/day x 14 days) groups. Blood and brain PFC, frontal lobe (FL), hippocampus (H), and striatum (S) were analyzed for total Pb and (204)Pb tracer concentrations by magnetic sector inductively coupled plasma-mass spectrometry. There were no measurable differences in brain Pb concentrations between the succimer and vehicle groups, indicating that succimer treatment was not efficacious in reducing brain Pb levels. In contrast, the cessation of Pb exposure significantly reduced brain (PFC) Pb ( approximately 34%) when compared to pretreatment levels (succimer and vehicle groups). Pb concentrations also varied among brain regions (PFC > FL approximately H > S). Finally, pretreatment PFC Pb concentrations were significantly correlated with the integrated blood Pb level (AUC) over the Pb exposure period, but not with the single pretreatment blood Pb collected concurrently with the PFC biopsy. Following treatment, blood Pb levels correlated only with Pb in the PFC, and not the other brain regions measured (FL, H, S). These data indicate that, under the conditions of this study, succimer treatment did not reduce brain Pb levels beyond the cessation of Pb exposure alone. Moreover, a single blood Pb measurement may be a poor predictor of brain Pb levels, reflecting limitations in the use of blood Pb level as an indicator of treatment efficacy.

The effects of CaNa(2)EDTA on brain lead mobilization in rodents determined using a stable lead isotope tracer

Studies have demonstrated the efficacy of CaNa(2)EDTA for reducing lead (Pb) levels in blood and soft tissues, including brain. However, a concern remains that a single dose of CaNa(2)EDTA may cause a significant increase in brain Pb levels due to a redistribution of endogenous Pb. Here we utilized a rodent model of Pb exposure in combination with a sensitive stable Pb isotope tracer methodology to assess the effects of CaNa(2)EDTA chelation treatment on the redistribution of Pb in brain, blood, kidney, and bone tissues. Thirty-two adult female albino rats (n = 6-7 animals/group) were exposed to 100 microg Pb/mL in drinking water for 4 weeks. Stable (204)Pb tracer was administered via i.p. injection over 2 days prior to chelation. CaNa(2)EDTA was administered i.p. at a dose of 150 mg/kg/day for 1 to 5 days. Statistical differences were evaluated with univariate ANOVA. Under the Pb exposure and chelation treatment regimens utilized here, there was no evidence of a measurable redistribution of endogenous Pb (as total Pb or labile (204)Pb tracer) into the brain after a single CaNa(2)EDTA dose. Further, CaNa(2)EDTA was not efficacious in measurably reducing brain or bone Pb levels, although brain levels of labile (204)Pb tracer were significantly reduced after 5 days of chelation. CaNa(2)EDTA treatment was effective in significantly reducing both blood and kidney Pb levels. Overall, these data substantiate the efficacy of CaNa(2)EDTA for reducing soft tissue Pb levels, but not total brain Pb, and they do not support concern for a transient increase in brain Pb levels with treatment.

Exposure of Rana ridibunda to lead I. Study of lead accumulation in various tissues and hepatic delta-aminolevulinic acid dehydratase activity

There are few data at present on the impact of lead (Pb) on amphibians, although declines in amphibian populations due to man-made changes in the environment have been recorded in recent years. The impact of Pb in adult frogs, Rana ridibunda, was therefore examined. Animals were exposed to 14 mg l(-1) (ppm) aqueous Pb [as Pb(NO3)2] for 4, 10 and 30 days. The chosen Pb concentration corresponded to one-tenth of the 96-h LC50 value for Pb (138.18 ppm). We measured the Pb content of the liver, kidneys, ventral skin and gastrointestinal (GI) tract, and the activity of hepatic delta-aminolevulinic acid dehydratase (delta-ALA-D). Gross morphological characteristics of the frogs were not affected by Pb accumulation in their tissues. At the end of the 30 days of exposure all tissues accumulated Pb. The accumulation of Pb in the liver, kidneys and ventral skin was correlated positively with the time of exposure. The Pb concentration in the GI tract reached a plateau at day 10 and there was no significant increase of Pb in the liver after day 10, suggesting excretion of Pb. The activity of hepatic delta-ALA-D decreased by 90% on day 30 compared to control values. The decrease of hepatic delta-ALA-D activity was correlated negatively with the concentration of Pb in liver and the time of exposure. This study suggests that the hepatic delta-ALA-D activity can be used as a biomarker of Pb intoxication for this species.

Efficacy of succimer chelation for reducing brain Pb levels in a rodent model

Increasing evidence indicates that early low-level lead (Pb) exposure produces enduring cognitive impairment in children, underscoring the need to develop improved therapeutic intervention. Although chelating agents have been shown to effectively reduce body Pb levels, it is not yet known whether this treatment ameliorates Pb-induced cognitive dysfunction. Clinical research in this area is hampered by the need to rely on reductions in blood Pb levels as the index of treatment efficacy, despite the fact that brain Pb level is the exposure parameter of greatest relevance to neurocognitive outcomes. The present studies were designed to provide information that will aid future research in this area in both human and animal models. The objectives of these studies were (1) to evaluate the efficacy of different doses and durations of succimer (meso-2,3-dimercaptosuccinic acid; DMSA) chelation for reducing brain and blood Pb levels and (2) to determine the extent to which blood Pb can serve as a surrogate of brain Pb following chelation. Long-Evans hooded rats were exposed to Pb from birth until day 31 (Study 1) or day 40 (Study 2) of life, followed by oral treatment with a vehicle or one of two succimer regimens for a duration of either 7 or 21 days. Results indicated that 7 days of succimer treatment produced a 1.5- to 2.5-fold greater reduction of Pb in blood than in brain, relative to time-matched vehicle groups. Prolonged treatment (21) days did not further reduce blood Pb levels (relative to 7-day succimer treatment), but did produce further reductions in brain Pb level compared to time-matched vehicle groups. Thus, chelation-mediated reductions in brain Pb did not parallel reductions in blood Pb over the course of treatment. While the relevance of these data to humans may be confounded by anatomical and physiological differences between rodents and primates, as well as differences in the metabolism of succimer (DMSA), they suggest that clinical studies should exercise caution when using blood Pb as an index of the efficacy of chelation treatment for reducing brain Pb levels.

Heavy metal toxicity, part II: lead and metal fume fever

This review is the second of a two-part review of heavy metal toxicity. This part will identify the salient features of the toxicopathophysiology, clinical presentation, and emergency department management of lead toxicity and metal fume fever.

Comparative in vivo lead mobilization of meso- and rac-2,3-dimercaptosuccinic acids in albino Wistar rats

Comparison of the racemic and meso forms of 2,3-dimercaptosuccinic acid (DMSA) in lead mobilization from lead-loaded albino Wistar rats demonstrates that the racemic form is significantly more effective in reducing femur lead levels. After four oral doses at 0.5 mmol/kg, femur lead levels were reduced to 87% of control values by meso-DMSA and to 50% of control levels by rac-DMSA. Similarly, when the dose was increased to 1.0 mmol/kg, femur lead levels were reduced to 69% of control levels by meso-DMSA and to 45% of control levels by rac-DMSA. A similar pattern was found for renal lead levels. Brain lead concentrations were significantly lower in treated groups than in control groups, but no differences were found between rac- and meso-DMSA. Rac-DMSA is more soluble than meso-DMSA in acetonitrile, ethyl acetate, and ethyl ether. The partition coefficient of rac-DMSA in the n-octanol/water system was found to be about 2.8. These results indicate that rac-DMSA deserves further attention as a possible substitute for meso-DMSA.

The relative efficacy of antidotes: the IPCS evaluation series. International Programme on Chemical Safety

Antidotes may play an important role in the treatment of poisoning. For many physicians and toxicologists an antidote is an antidote. According to the IPCS definition, an antidote is a therapeutic substance used to counteract the toxic action(s) of a specified xenobiotic. Given this wide definition, the efficacy of an antidote may vary considerably depending on which toxic action(s) is/are being counteracted and on the level of counteracting power: An almost 100% efficacy is seen using specific antagonists, such as naloxone in opiate poisoning or flumazenil in benzodiazepine poisoning, e.g. resulting in complete reversal of opiate toxicity unless complications, such as anoxic brain damage, have developed. At the other end of the efficacy scale, we may place chelating agents for heavy metal poisoning and diazepam for organophosphorus insecticide poisoning. Therefore, in the IPCS/EC evaluation series of antidotes, some chelating agents are considered only to be an adjunct to supportive care which is the cornerstone of treatment. When teaching clinical toxicology or recommending the use of antidotes in poisoned patients, the expected efficacy level of the antidote in question should be stressed. This may be particularly important in severe poisonings when the antidote may only be considered as an adjunct to supportive care, e.g. deferoxamine in acute iron poisoning. Unless this is stressed, the unexperienced physician may rely too much on the antidote and may not pay sufficient attention to the supportive care. In this presentation, the varying efficacy levels of antidotes are discussed as based on the presently ongoing IPCS/EC evaluation programme on antidotes.

Ultrastructural investigation of lead-induced intranuclear inclusion bodies in mice

By means of optical and electron microscopy and by atomic absorption spectrophotometry in a graphite chamber, this study evaluated the effect of temperature (22-35 degrees C) on lesions in the kidney, liver, and brain, and on concentrations of lead caused by the administration of 2 and 5 mg/kg/IP of lead acetate to Swiss mice. The most pronounced effects were observed in the kidney and in groups of animals receiving the highest doses (5 mg/kg at 22 and 35 degrees C). These effects consisted of significantly higher (p < .05) lead concentrations in the tissues, a significant decrease (p < .05) in kidney weights, and progressive kidney atrophy and fibrosis with, at the ultrastructural level, constant intranuclear inclusions, which were also observed in the cytoplasm of renal and endothelial cells.

Effect of environmental temperature on tissue lead accumulation in mice repeatedly treated with lead acetate

The effect of environmental temperature on lead accumulation in tissues of mice repeatedly treated with lead acetate (2 mg/kg per day and 5 mg/kg per day) for 3 or 6 weeks was studied. In blood, kidney and liver, the amount of lead accumulated after 3 weeks of treatment was markedly higher in animals exposed to 22 degrees C than those maintained at 35 degrees C. Conversely, when the treatment was extended to 6 weeks, lead concentrations in the liver and kidney were equal or higher respectively, in the mice exposed to 35 degrees C. In the brain, lead concentration was lower than that found in kidney and liver and it was independent of dose and ambient temperature of lead being higher at 35 degrees C than at 22 degrees C. These results demonstrate that environmental temperature influences the amount of lead accumulated in some rodent tissues, and that the duration of the treatment modifies the effect produced by temperature, suggesting that the changes elicited during the period of acclimation to the hot environment could be responsible for these findings.

The relative efficacy of antidotes

For many physicians an antidote is an antidote. According to the International Programme on Chemical Safety definition, an antidote is a therapeutic substance used to counteract the toxic action(s) of a specified xenobiotic. Given this wide definition, the efficacy of an antidote may vary considerably depending on which toxic action(s) being counteracted and the level of counteracting power. An almost 100% efficacy is seen using specific antagonists, such as naloxone in opiate poisoning or flumazenil in benzodiazepine poisoning, e.g. resulting in complete reversal of opiate toxicity unless complications, such as anoxic brain damage, have developed. At the other end of the efficacy scale, we may place chelating agents for heavy metal poisoning and diazepam for organophosphorus insecticide poisoning which are considered only to be an adjuncts to supportive care. When teaching clinical toxicology or recommending the use of antidotes in poisoned patients, the expected efficacy level of the antidote in question should be stressed. This may be particularly important in severe poisoning when the antidote may only be considered as an important adjunct to supportive care, e.g. deferoxamine in acute iron poisoning. Unless this is stressed, the unexperienced physician may rely too much on the antidote and pay insufficient attention to the supportive care. The varying efficacy levels will be discussed based on the presently ongoing International Programme on Chemical Safety/Commission of the European Communities evaluation program on antidotes.

Effect of chelate treatments on kidney, bone and brain lead levels of lead-intoxicated mice

The effects of chelating agent treatment with meso-2,3-dimercaptosuccinic acid (DMSA), Na2CaEDTA, Na2ZnEDTA, and Na3ZnDTPA on the organ lead levels of lead-loaded mice have been determined. At 1 mmol/kg/day i.p., all caused reductions in the lead levels of the kidney after four injections, but only Na2CaEDTA produced a significant reduction in brain lead. All chelating agents caused significant reductions in kidney and brain lead levels when administered at a daily dose of 1 mmol/kg/day for eight days, but only DMSA reduced the bone lead level. In animals given 50 mg Pb/kg or 100 mg Pb/kg, the administration of Na2CaEDTA or DMSA at 1 mmol/kg/day x 8 produced significant reductions in kidney, bone and brain lead levels, but DMSA produced greater reductions of bone lead in both groups and of kidney lead in the group given 100 mg Pb/kg. An examination of published data describing the effect of chelating agent treatment on brain lead levels indicates that DMSA produces a reduction in brain lead levels under all conditions examined to date.

Effects of different factors in lead- and cadmium-induced hypothermia in mice

The aim of this study was to investigate the relationship between the hypothermic effect induced by lead or cadmium chloride treatments and the cerebral metal levels attained. Mice were injected intraperitoneally with different doses of lead acetate or cadmium chloride at ambient temperatures of 22 degrees C and 35 degrees C, and rectal temperatures and brain metal levels were determined. At 22 degrees C, doses of lead acetate exceeding 25 mg/kg caused significant hypothermia and a rise of lead levels in the brain; this hypothermic effect was significantly inhibited at 35 degrees C. In mice repeatedly treated with 2 or 5 mg/kg lead acetate and exposed to 22 degrees C or 35 degrees C, no significant changes were observed in body temperature after the repeated exposure, although brain lead levels increased significantly. Cadmium chloride at 22 degrees C produced a significant fall in body temperature, and a rise in brain cadmium levels at doses of 2-4 mg/kg; the decrease in body temperature was partially inhibited at 35 degrees C. The results of the present study suggest that the hypothermic effect elicited by these heavy metals is related to both the level of metal absorbed by the brain and its rate of uptake.

Stable isotopic tracers of lead mobilized by DMSA chelation in low lead-exposed rats

The ability of DMSA to mobilize skeletal lead or effect a redistribution of endogenous lead to other target organs in low lead-exposed organisms is unclear. Discrepant results of past studies of DMSA and other lead chelators (e.g., CaNa2EDTA) may be due, in part, to experimental differences and difficulties in distinguishing mobilized skeletal lead from other endogenous or exogenous lead sources. Therefore, the influence of DMSA on the mobilization and redistribution of lead in skeletal and soft tissue compartments of low lead-exposed female Wistar (115-125 g) rats was investigated using ultraclean stable lead isotope tracer techniques. Rats that had been reared on a low lead-level diet (lead intake approximately 80 ng Pb/g body/day) were fed 206Pb-enriched drinking water (210 ng Pb/ml) for 1.5 days and then were chelated with a single ip injection of a 0.11 mmol/kg dose of DMSA. Blood, kidney, brain, tibia, urine and feces were collected 24 hr after chelation and analyzed for lead concentrations by graphite furnace atomic absorption spectrometry and for lead isotopic compositions by thermal ionization mass spectrometry. These analyses demonstrated that DMSA chelation significantly increased (15-fold) the diuresis of labile soft tissue lead, but not skeletal lead. DMSA also appeared to effect a redistribution and input of a comparable amount of lead to the skeleton and smaller relative amounts of lead to the soft tissues (blood, kidney) of the chelated animals. The clinical significance of these latter observations beyond the context of this preliminary study is not clear.

Lead poisoning--a family study

OBJECTIVE

A family study is used to highlight the varied manifestations of lead poisoning and difficulties in diagnosis and treatment.

CLINICAL FEATURES

A 42-year-old Italian woman with a known beta-thalassaemia trait presented with a two-year history of disabling pains and symptomatic anaemia, which were found to be caused by lead poisoning.

INTERVENTION AND OUTCOME

Screening for lead poisoning among her immediate family members identified two others with different manifestations of plumbism. All three needed active chelating, which resulted in resolution of their symptoms.

CONCLUSIONS

The similar haematological findings of beta-thalassaemia and lead poisoning may lead to a delay in diagnosis and treatment of lead poisoning when these two conditions coexist.

An oral treatment for lead toxicity

Chronic lead poisoning has traditionally been treated by parenteral agents. We present a case where a comparison of ethylene diaminetetra-acetic acid was made with 2,3-dimethyl succinic acid (DMSA) which has the advantage of oral administration associated with little toxicity and appeared to be at least as efficacious.

New developments in therapeutic chelating agents as antidotes for metal poisoning

An examination of the studies on therapeutic chelating agents that have been carried out during the last decade reveals that extensive efforts have been made to develop compounds superior to those previously available for the treatment of acute and chronic intoxication by many metals. These metals include primarily iron, plutonium, cadmium, lead, and arsenic, but also many other elements for which acute and chronic intoxication is less common. These studies have revealed the importance of several additional factors of importance in the design of such compounds and have led to many new compounds of considerable clinical promise. An additional development has been the introduction of previously developed chelating agents for use with certain metals on a broader scale.

Evaluation of the developmental toxicity of 2,3-dimercapto-1-propanesulfonate (DMPS) in mice. Effect on mineral metabolism

The sodium salt of 2,3-dimercapto-1-propanesulfonic acid (DMPS), a potent chelating agent used in the treatment of inorganic and organic heavy metal intoxications was evaluated for developmental toxicity in pregnant Swiss mice. DMPS was administered by gavage at doses of 0, 75, 150 and 300 mg/kg per day on gestational days 6-15. Females were evaluated for body weight gain, food consumption, appearance and behavior, survival rates and reproduction data. Cesarean sections were performed on gestation day 18. There were no maternal toxic effects, and no treatment-related changes were recorded in the number of total implants, resorption, the number of live and dead fetuses, fetal body weight or fetal sex distribution data. Gross external, soft tissue and skeletal examination of the DMPS-treated fetuses did not show significant differences at any dose in comparison with the controls. Mineral analysis of maternal and fetal tissues revealed slight effects of DMPS on metabolism of calcium, magnesium, zinc, copper and iron. The results of this study in mice indicate that DMPS is not a developmental toxicant at levels up to 300 mg/kg per day.

Chelating agents in the treatment of acute vanadyl sulphate intoxication in mice

Eighteen chelating or reducing agents were tested to determine their relative efficacy as antagonists in acute intramuscular vanadyl sulphate intoxication in mice. The chelating or reducing agents were administered intraperitoneally to male Swiss mice at doses equal to one-fourth of their respective LD50. Therapeutic effectiveness (TEF) was calculated. In a subsequent experiment, the effect of EDTA, glutathione, DFOA, ascorbic acid, succinic acid, monosodium phosphate, Tiron, DTPA, and 2-mercaptosuccinic acid on the excretion, and distribution of vanadium was determined. Of the compounds examined, Tiron followed by ascorbic acid, and 2-mercaptosuccinic acid were effective in increasing the urinary excretion of vanadium. Tiron, and 2-mercaptosuccinic acid were also effective in reducing the concentration of vanadium found in kidney, the main target organ of vanadium accumulation. Tiron appears to be the most effective agent of those tested in the prevention of acute vanadium (IV) intoxication in mice.

Evaluation of the developmental effects on mice after prenatal, or pre- and postnatal exposure to 2,3-dimercaptopropane-1-sulfonic acid (DMPS)

The sodium salt of 2,3-dimercaptopropane-1-sulfonic acid (DMPS), a water soluble metal complexing agent, was administered to four groups of pregnant Swiss mice at 0, 70, 210, and 630 mg/kg/day by two dosing schedules: gestation day 14 until birth (prenatal exposure), and gestation day 14 until postnatal day 21 (pre- and postnatal section). Dams were allowed to deliver and the number of live and dead pups recorded. Each pup was sexed and weighed on days 0, 4, 14, and 21. Also, pinna detachment, incisor eruption and eye opening were monitored. No adverse effects on offspring survival or development were evident in either exposures at doses employed in this study. The "no observable effect level" (NOEL) for health hazard to the developing fetus or pup was 630 mg DMPS/kg/day. This dose is much higher than the amounts of DMPS usually administered in human heavy metal poisoning.

Mobilization of lead by esters of meso-2,3-dimercaptosuccinic acid

An examination was made of the relative efficacies of 2,3-dimercapto-1-propanol (BAL) and three diesters ( [CH(SH)COOR]2; DMDMS, R = CH3; DEDMS, R = C2H5; and Di-PDMS, R = CH(CH3)2] of meso-2,3-dimercaptosuccinic acid (DMSA) in mobilizing freshly injected lead from mice. These diesters, like BAL, reduced the lead levels resulting from freshly injected lead in both the soft tissues (liver, kidneys, spleen, and brain) and the bone (tibia). After treatment with the dimethyl (DMDMS), the diethyl (DEDMS), and the diisopropyl (Di-PDMS) esters the lead content of each of the organs was significantly less than that present in the untreated controls. Each of the diesters reduced lead levels in the kidneys, liver, and spleen significantly below those levels found after BAL treatment. The action of the diesters in reducing brain lead levels was comparable to that of BAL. Di-PDMS was the most effective of these compounds and was significantly superior to BAL. Each of the esters was also significantly more effective than BAL in reducing the whole body level of lead.