Short-term administration of dimercaptopropanol (BAL) and calcium disodium edetate (EDTA) for diagnostic and therapeutic lead mobilization

Heavy metal chelation in neurotoxic exposures

Metals such as iron and copper are critical to living organisms, whereas other metals such as lead and arsenic have no known biologic role. Any metals in large amounts may cause toxicity. Many metals cause pervasive systemic effects involving the nervous system, which can be subtle in some cases. Although challenging, the diagnosis and treatment of metal poisoning can be made based on history, physical examination, and the proper use of metal testing. This article focuses on the use, and misuse, of chelation in the diagnosis and management of metal intoxication.

Lead poisoning in an electrician: a bad substitute for a bad habit

An electrician presented with a four-month history of unexplained abdominal pain and constipation, which had prompted four hospital admissions and numerous investigations. Blood-film results suggested lead poisoning, and an occupational history revealed that he had chewed about a metre of electrical cable (which contains lead) daily for 10 years as a substitute for smoking.

Perspectives on lead toxicity

Lead toxicity causes hematological, gastrointestinal, and neurological dysfunction in adults and children. Symptoms are usually noted with blood lead greater than 1.93 mumol/L. Severe or prolonged exposure may also cause chronic nephropathy, hypertension, and reproductive impairment. Lead inhibits enzymes; alters cellular calcium metabolism; stimulates synthesis of binding proteins in kidney, brain, and bone; and slows nerve conduction. Less severe exposure to lead, designated by blood lead levels of 0.48-0.96 mumol/L, has been implicated in poor pregnancy outcome, impaired neurobehavioral development, reduced stature in young children, and higher blood pressure in adults. Biochemical and systemic effects of high and low level lead toxicity are described. Dust, water, and paint chips are still major sources of lead but lead from folk remedies, cosmetics, food supplements, food preparation utensils, and improperly prepared infant formula has caused epidemic and sporadic severe lead toxicity. Screening for pediatric low level lead exposure requires measurement of blood lead.

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.

The lead program at CPRI

A lead (Pb) screening program in operation at CPRI in London, Ontario, since 1977 involves simultaneous measurement of blood Pb and erythrocyte protoporphyrin (EP) in a randomized population of physically and/or mentally handicapped children and adolescents on admission, discharge and during outpatient visits. This 11-year study has yielded a large database for computerized evaluation. Based upon log normal transformation of data obtained from the admission and outpatient groups, the normal curve yielded a mean and standard deviation (SD) for blood Pb of 0.36 +/- 0.27 mumol/L (n = 4188). This fosters a downward revision of the upper reference limit to 0.89 mumol/L (95% confidence level). The overall mean for EP was 0.35 +/- 0.37 mumol/L and suggests an upper reference limit of 1.09 mumol/L. The direct correlation between annual means of blood Pb and EP retained its significance (r = 0.80; P less than 0.004). For both blood Pb and EP, there was no significant difference in values between admissions (n = 1455), discharges (n = 1310) and outpatient visits (n = 2963). Only in the case of blood Pb was the overall mean value of males (n = 3822) higher (0.46 +/- 0.34 mumol/L) than that of females (0.39 +/- 0.25 mumol/L; n = 1906), but by t-test the difference was not significant. Although annual means of both blood Pb and EP were highest in 1978 and 79 and lowest in 1987, there was no significant difference between any two years.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the mobilization of aged tissue cadmium by chelating agents

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

Occupational lead exposure: studies in two brothers showing differential susceptibility to lead

Unexpected differences in clinical and biochemical findings in two brothers occupationally exposed to the same source of lead for dissimilar lengths of time are presented. Only the brother with the shorter period of lead exposure was anemic and afflicted by nausea, vomiting, abdominal colic and arthralgia. His urinary PBG output yielded the high orders of magnitude found in acute intermittent porphyria in relapse. Prior to administration of a single dose of EDTA (1 g of the calcium disodium salt given intravenously in 325 mL 0.15 mol/L NaCl), his blood lead levels averaged 3.6 mumol/L. The amount of chelatable lead retrieved from his urine, 31 mumol/day, was more than twice that found in his asymptomatic counterpart who was exposed to lead for 13 months and whose pre-EDTA blood lead levels averaged 4.0 mumol/L. Not only the activity of delta-aminolaevulinic acid dehydratase, but also that of uroporphyrinogen I synthetase, was markedly inhibited by lead in red cells of both brothers. These activities were restored to normal levels in vitro by addition to the assay system of zinc and dithiothreitol. This ruled out a coexisting genetic deficiency of either enzyme. The anemia of the symptomatic brother with the shorter period of lead exposure was alleviated by folic acid, 15 mg/day. The differences in findings between the two brothers point to differential susceptibility to lead and illustrate the extent to which symptomatic lead poisoning may mimic biochemical and clinical features of the acute porphyrias.