Meso-2,3-dimercaptosuccinic acid in the diagnosis and treatment of lead poisoning

24-Hour Provoked Urine Excretion Test for Heavy Metals in Children with Autism and Typically Developing Controls, a Pilot Study

INTRODUCTION

The complementary and alternative medicine practice of prescribing chelators to children with autism is based on the premise that the chronic symptoms of autism can be ameliorated by reducing heavy metal body burden. However, there has not been definitive evidence, published to date, to support the assertion that children with autism are at increased risk of an excess chelatable body burden of heavy metals. The oral chelator meso-2,3-dimercaptosuccinic acid (DMSA) can be used diagnostically to mobilize heavy metals from extravascular pools, enhancing the identification of individuals who have a chelatable body burden.

METHODS

Seventeen children with autism and five typically developing children were enrolled in a pilot study to test for chelatable body burden of Arsenic (As), Cadmium (Cd), Lead (Pb), and Mercury (Hg). Evaluation included a questionnaire regarding potential exposure to heavy metals, diet restrictions, a baseline 24-hour urine collection, and a DMSA-provoked urine collection. Urine collections were sent for As, Cd, Pb, and Hg quantification by Inductively Coupled Plasma-Mass Spectrometry. Unprovoked reference ranges were used in the interpretation of all collections.

RESULTS

Fifteen autistic children and four typically developing children completed the study. Three autistic subjects excreted one metal in greater quantity during the provoked excretion than baseline. Two of these were very close to the limit of detection. In the third case, the provoked excretion of mercury was between the upper limit of normal and lower limit of the potentially toxic reference range. Fish was removed from this child's diet for greater than one month, and the provoked excretion test repeated. The repeat excretion of mercury was within the normal range.

CONCLUSION

In the absence a proven novel mode of heavy metal toxicity, the proportion of autistic participants in this study whose DMSA provoked excretion results demonstrate an excess chelatable body burden of As, Cd, Pb, or Hg is zero. The confidence interval for this proportion is 0-22%.

Clinical evaluation of a lead mobilization test using the chelating agent dimercaptosuccinic acid

BACKGROUND

The lead mobilization test reflects the mobilizable and likely toxicologically active fraction of the lead body burden. We propose a safe and convenient protocol for this test, to assess concomitant copper and zinc excretion and to determine the size of the chelatable lead pool in nonoccupationally exposed adults.

METHODS

The study population included 80 white adults: 40 controls [median blood lead concentration (PbB), 25 microg/L] and 40 lead-exposed individuals (315 microg/L). After collection of 4- and 24-h baseline urine specimens and a blood sample, dimercaptosuccinic acid (DMSA) was administered orally (1 g), and additional 4- and 24-h urine specimens were obtained. Determinants of the chelatable urinary lead (DMSA-PbU) were traced by linear regression analysis.

RESULTS

Urinary DMSA and lead excretion peaked within 2-3 h after DMSA administration. The amounts of DMSA, lead, copper, and zinc recovered in the 4-h urinary collections were highly correlated with those in 24-h collections (r = 0.857, 0.859, 0.958, and 0.757, respectively). At PbB concentrations >300 microg/L, the relationship between DMSA-PbU and PbB showed a steep increase and a widespread dispersion of DMSA-PbU around the regression line. After DMSA, copper and zinc excretion rates were increased up to 91- and 33-fold, respectively. No side effects were reported after DMSA.

CONCLUSIONS

Determination of DMSA-PbU in a 4-h collection after DMSA is convenient, apparently safe, and inexpensive. An upper reference limit value of 22 microg/4 h is proposed for Belgian reference individuals. The diagnostic value of DMSA-PbU is likely to be contributive for PbB >300 microg/L.

Flour contamination as a source of lead intoxication

CASE REPORT

A 43-year-old man was hospitalized because of severe anemia and recurrent bouts of abdominal pain over 20 days. There was no known occupational exposure to toxins. Concomitantly, the patient's father complained of having the same symptoms. Familial lead poisoning was diagnosed when all 6 family members tested had high blood leads (31-64 micrograms/dL).

RESULTS

Following detailed examination of the potential sources common to all members of the household, the cause of poisoning was determined to be corn flour containing 38.7 mg/g lead. Physicians are reminded to consider lead poisoning in the differential diagnosis of individuals with unexplained symptoms, particularly those of abdominal discomfort and anemia.

The effect of 2,3 dimercaptosuccinic acid in the treatment of lead poisoning in adults

Four patients, aged 22-60, belonging to a single family that had been exposed to lead-contaminated food for an unknown period, and nine workers, aged 20-65, who had been exposed to air-borne lead for 6-8 years, were evaluated for lead poisoning in our centres. Blood lead levels were 3.57 +/- 0.39 micromol/L (mean +/- SD) in the family members and 3.46 +/- 0.43 micromol/L (mean +/- SD) in the group of workers. 2,3 dimercaptosuccinic acid (DMSA) therapy was instituted in the four family members while the nine workers were closely monitored after being removed from the contaminated environment without receiving any chelation therapy. DMSA therapy given for the duration of 19 days reduced the blood lead levels to 0.63 +/- 0.44 micromol/L (mean +/- SD), P<0.01, in the four family members. No significant change was observed in the untreated group. The exposure time in the untreated group was probably longer than that in the treated group. Following long-term exposure most of the lead in the body is found in the bones and therefore not easily removed by chelation therapy. No side-effects were reported in the treated group and no rebound elevation of blood lead levels was observed during the therapy period or during the 12-week follow-up period following cessation of therapy. We conclude that 19 days of chelation therapy with DMSA in adults with moderate to severe lead poisoning is effective and safe.

Provocative chelation with DMSA and EDTA: evidence for differential access to lead storage sites

OBJECTIVES--To validate a provocative chelation test with 2,3-dimercaptosuccinic acid (DMSA) by direct comparison with the standard ethylene diamine tetraacetic acid (EDTA) test in the same subjects; and to compare and contrast the predictors of lead excretion after DMSA with those after EDTA. A metal chelating agent given orally, DMSA may mobilise and enhance the excretion of lead from the storage sites in the body that are most directly relevant to the health effects of lead. A provocative chelation test with DMSA could thus have wide potential application in clinical care and epidemiological studies. METHODS--34 male lead workers in the Republic of Korea were given a single oral dose of 10 mg/kg DMSA, urine was collected over the next eight to 24 hours, and urine volume and urinary lead concentration determined at 0, 2, 4, 6, 8, and 24 hours. Either two weeks before or two weeks after the dose of DMSA 17 of these workers also received 1 g intravenous EDTA followed by an eight hour urine collection with fractionation at 0, 2, 4, 6, and 8 hours. RESULTS--Urinary lead concentration peaked at two hours after DMSA and four hours after EDTA. Lead excretion after DMSA was less than after EDTA, and cumulative excretion after DMSA plateaued at six to eight hours. The two hour and four hour cumulative lead excretions after DMSA were highly correlated with the eight hour total (r = 0.76 and 0.95). In multiple linear regression analyses, blood lead was found to be an important predictor of EDTA-chelatable lead, whereas urinary aminolevulinic acid (ALAU) was associated with DMSA-chelatable lead. Notably, lead excretion after DMSA was greatly increased if EDTA was given first. An earlier dose of EDTA also modified the relation between ALAU and DMSA-chelatable lead in that workers who received EDTA before DMSA showed a much steeper dose-response relation between these two measures. CONCLUSIONS--The predictors of lead excretion after DMSA and EDTA are different and an earlier dose of EDTA may increase lead excretion after a subsequent dose of DMSA. The results suggest that two hour or four hour cumulative lead excretion after DMSA may provide an estimate of lead in storage sites that are most directly relevant to the health effects of lead.

Antidotal effects of dimercaptosuccinic acid

Dimercaptosuccinic acid (DMS), HOOC-CH(SH)-CH(SH)-COOH, was first developed in China as an effective antidote for poisoning from many heavy metals, such as Pb, Hg, As, Cd, Sb, Tl, Au, Zn, Ni, Pt, Ag, Co and Sn. DMS increases the excretion of Ce, Pm, Sr and Po from the body. Hundreds of patients suffering from hepatolenticular degeneration (Wilson's disease) have been treated successfully with DMS. Recently, DMS was found to be effective also in treating certain non-metallic intoxications, like some of the new non-phosphate pesticides and mushroom poisonings.

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.

Lead encephalopathy from an imported Toby mug

Encephalopathy is an unusual manifestation of lead poisoning in an adult, the more common presentation being abdominal colic, anaemia and limb palsy. We report a case of adult lead encephalopathy and describe the use of a simple screening test for lead poisoning together with the increasing number of cases associated with imported ceramics.

Dithiocarbamate treatment of chronic cadmium intoxication in mice

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