[Development of Body Phantom for Evaluation of Appropriate Administered Radioactivities and Image Quality on 99mTc-DMSA Scintigraphy in Pediatric Nuclear Medicine].

PURPOSE: We conducted a field survey about pediatric nuclear medicine. As a result, it was suggested that 99mTc-DMSA scintigraphy was performed at many institutions, whereas various examinations such as image acquisition and processing are not carried out using the renal phantom. Therefore, we developed the body phantom for the evaluation of appropriate administered radioactivities and image quality with renal scintigraphy in pediatric nuclear medicine. METHODS: We created three differently sized body phantoms (1-, 5-, and 20-year-old models). These pediatric body phantoms were filled with a 99mTc solution based on the consensus guideline of pediatric radiopharmaceutical administered radioactivity in Japan. The planar image was evaluated using acquisition count, uniformity and defect contrast. SPECT images were evaluated with a recovery coefficient (RC). RESULTS: The acquisition counts for pediatric body phantoms were relatively corresponded to the clinical study. The appropriate acquisition counts and the pixel size for the planar image were approximately 140 counts per pixel and 1.23-1.35 mm at 5 min acquisition times in 1- and 5-year-old pediatric body phantom studies, respectively. Although the uniformity and the cold contrast did not depend on pixel size and body size, the cold contrast was affected by body size. The RC for SPECT images depended on the performance of SPECT systems, the resolution recovery algorithm and body phantom size. CONCLUSION: The developed pediatric body phantom could allow us to establish optimal image acquisition and more evidence on renal scintigraphy in pediatric nuclear medicine.

Determination of 2,3-dimercaptosuccinic acid in mice blood and tissues by HPLC with fluorescence detection.

2,3-Dimercaptosuccinic acid (DMSA) is an orally effective chelating agent for the treatment of heavy metal poisoning. The increasing therapeutic use of DMSA has stimulated the need for sensitive and selective methods for its determination in biological samples, as well as study on pharmacokinetics and tissue distribution. According to the previously reported method, an improved method was established for the determination of DMSA in mice blood and tissues, in which oxidized DMSA was reduced by the disulfide-reducing agent, dithiothreitol (DTT), and DMSA was converted to a highly fluorescent and stable derivative by reaction with monobromobimane (mBBr) in alkaline solution. Acetonitrile was used for deproteinization and dichloromethane was used for condensation and purification, which significantly shortened the amount of time used to process the sample. Meanwhile isocratical elution was performed and excellent separation of the DMSA derivative was obtained, this enabled a run finish within 20 min. The limits of quantitation were 0.025 microg/ml in brain and 0.1 microg/ml in blood, lung, heart, intestine, liver, spleen and kidney, respectively. The calibration curves were linear in all samples (r(2)>0.992) with a range of 0.025-1.6 microg/ml for brain homogenate and 0.1-6.4 microg/ml for blood and homogenates of lung, heart, intestine, liver, spleen and kidney, respectively. Therefore, the method is simple, rapid and sensitive, and it could be applicable to the studies in an animal model to evaluate the distribution of DMSA in blood and tissues.

Analysis of meso-2,3-dimercaptosuccinic acid in human urine by capillary electrophoresis using direct injection.

meso-2,3-Dimercaptosuccinic acid ( meso-DMSA) is an effective chelating agent for the treatment of lead poisoning. We have developed a capillary electrophoresis (CE) method to monitor the urinary excretion of meso-DMSA in human beings. The urine sample was directly injected for analysis in CE without the requirement of solid-phase extraction (SPE). The meso-DMSA was detected in 20 mM borate buffer (pH 8.3) using a 60-cm length bare fused-silica capillary (75-microm ID, 52.5-cm effective length). The meso-DMSA can be extensively biotransformed during metabolism, and no meso-DMSA in urine samples was found in our studies. Any metabolized meso-DMSA can be successfully converted to free meso-DMSA by chemical reduction with dithiothreitol (DTT). In addition, samples were also treated with ethylenediaminetetraacetic acid (EDTA) to transchelate any meso-DMSA that is coordinated with metal ions present in the urine samples. The total amount of meso-DMSA present as these chemical forms was quantified after chemical reduction and addition of EDTA. The detection limit of meso-DMSA was about 50 microM, the RSD of peak area and migration time of meso-DMSA were 4-8% and less than 1%, respectively.

Predictors of DMSA chelatable lead, tibial lead, and blood lead in 802 Korean lead workers.

OBJECTIVES: To examine the interrelations among chelatable lead (by dimercaptosuccinic acid, DMSA), tibial lead, and blood lead concentrations in 802 Korean workers with occupational exposure to lead and 135 employed controls with only environmental exposure to lead. METHODS: This was a cross sectional study wherein tibial lead, DMSA chelatable lead, and blood lead were measured. Linear regression was used to identify predictors of the three lead biomarkers, evaluating the influence of age, job duration, sex, education level, alcohol and tobacco use, creatinine clearance rate, and body mass index. RESULTS: DMSA chelatable lead concentrations ranged from 4.8 to 2102.9 microg and were positively associated with age, current smoking, and creatinine clearance rate. On average, women had 64 microg less DMSA chelatable lead than men. When blood lead and its square were added to a model with age, sex, current smoking, body mass index, and creatinine clearance rate, blood lead accounted for the largest proportion of the variance and sex became of borderline significance. Tibial lead concentrations ranged from -7 to 338 microg/g bone mineral and were positively associated with age, job duration, and body mass index. Women had, on average, 9.7 microg/g less tibial lead than men. Blood lead concentrations ranged from 4.3 to 85.7 microg/dl and were positively associated with age and tibial lead, whereas current smokers had higher blood lead concentrations and women had lower blood lead concentrations. CONCLUSIONS: The data suggest that age and sex are both predictors of DMSA chelatable lead, blood lead, and tibial lead concentrations and that tibial lead stores in older subjects are less bioavailable and may contribute less to blood lead concentrations than tibial lead stores in younger subjects. Although blood lead concentrations accounted for a large proportion of the variance in DMSA chelatable lead concentrations, suggesting that measurement of both in epidemiological studies may not be necessary, the efficacy of each measure in predicting health outcomes in epidemiological studies awaits further investigation.

The presence of lead decreases the availability of meso-2, 3-dimercaptosuccinic acid for analysis in the monobromobimane assay.

meso-2,3-Dimercaptosuccinic acid is a suitable chelating agent for routine pharmacotherapy of lead poisoning in children. Administration of meso-2,3-dimercaptosuccinic acid presumably permits complexation of lead in vivo, allowing excretion through urine or feces. Quantification of the lead is achieved independently from the analysis of meso-2,3-dimercaptosuccinic acid and metabolites from the monobromobimane assay. To date, no direct chemical characterization of the Pb species excreted in urine has been successful. Pharmacokinetic correlation of lead excretion with excretion of meso-2,3-dimercaptosuccinic acid and metabolites has been utilized as an indirect method to draw conclusions regarding the identity of the active chelating agent. In this study, we hypothesized that the Pb-coordinated thiols are not reactive with respect to monobromobimane, and thus, the active chelator contained in the lead complex escapes detection. We performed variations of the assay and found that (1) the fluorescence detector response for the meso-2,3-dimercaptosuccinic acid-monobromobimane adduct was clearly attenuated as a function of added Pb, (2) when meso-2, 3-dimercaptosuccinic acid and monobromobimane were mixed prior to the addition of lead, the lead had no effect on detector response, (3) the addition of dithiothreitol does not affect the ability of Pb to react with meso-2,3-dimercaptosuccinic acid and verifies that oxidation of meso-DMSA had not occurred, and (4) the addition of ethylenediaminetetraacetic acid to the assay reverses the result found in point 1, presumably through trans chelation of the Pb-DMSA complex. Indirect quantification of the Pb-DMSA complexes found in urine might be accomplished through modification of the standard monobromobimane assay for analysis of meso-2,3-dimercaptosuccinic acid.

Pharmacokinetics of meso-2,3-dimercaptosuccinic acid in patients with lead poisoning and in healthy adults.

We compared the pharmacokinetics of meso-2,3-dimercaptosuccinic acid (DMSA) in three children with lead poisoning, three adults with lead poisoning, and five healthy adult volunteers. All subjects received DMSA orally. Maximum blood concentration and time to maximum blood concentration of total DMSA concentration were not statistically different among the groups. Unaltered DMSA was detected in the blood of all poisoned patients but in only one of five healthy volunteers. Elimination half-life of total DMSA (parent drug plus oxidized metabolites) was longer in children with lead poisoning (3.0 +/- 0.2 hours) than in adults with lead poisoning (1.9 +/- 0.4 hours) and healthy adults (2.0 +/- 0.2 hours). Renal clearance of total DMSA was greater in healthy adults (77.0 +/- 13.2 ml/min per square meter) than in either adults (24.7 +/- 3.3 ml/min per square meter) or children with lead poisoning (16.6 ml/min per square meter); renal clearance of the metabolites of DMSA was also greater in healthy adults (64.6 +/- 10.1 ml/min per square meter) than in either adults (35.4 +/- 8.4 ml/min per square meter) or children with lead poisoning (19.5 ml/min per square meter). The DMSA appeared to enter the erythrocytes of patients with lead poisoning to a greater extent than in healthy adults. We conclude that renal clearance of DMSA and its metabolites may be impaired and that the distribution of DMSA in children with lead poisoning may be different from that in adults.

A gamma-ray detector for capillary zone electrophoresis and its use in the analysis of some radiopharmaceuticals.

The construction and evaluation of a gamma-ray detector for capillary zone electrophoresis is described. The detector was shown to have a linear response from the limit of detection 10 to 500 Bqcm-3 corresponding to 5.1 x 10(-17) to 2.55 x 10(-15) gcm-3 43Tc99m. The application of the detector for the analysis of some radiopharmaceuticals is presented.

Determination and metabolism of dithiol chelating agents: X. In humans, meso-2,3-dimercaptosuccinic acid is bound to plasma proteins via mixed disulfide formation.

meso-2,3-Dimercaptosuccinic acid (DMSA) is orally effective for the treatment of chronic lead intoxication in humans. Earlier studies have shown that the majority of DMSA, given p.o. to normal humans, is excreted in the urine as mixed disulfides with L-cysteine. We have developed an assay for the determination of DMSA that has made possible the determination of the form of DMSA in blood and plasma. After p.o. administration of 10 mg DMSA/kg to four normal young men, no unaltered DMSA (unaltered DMSA is the unbound, parent compound; total DMSA consists of unaltered DMSA plus oxidized (disulfide) DMSA and is determined after reduction with dithiothreitol) was found in the blood over an 8-hr period. Only after treatment of blood or plasma with the disulfide-reducing agent, dithiothreitol, was DMSA detected. This indicates that DMSA is in disulfide linkage with plasma proteins and/or non-protein sulfhydryl compounds. Most of the DMSA in the plasma (92-95%) was found to be bound to plasma proteins, mainly albumin. The remaining DMSA may be bound to small molecular weight (less than 10,000 MW) nonprotein sulfhydryl compounds such as cysteine. Plasma protein appears to serve as a depot and reservoir of DMSA, which can exchange for cysteine. The urinary excretion of unaltered DMSA and DMSA mixed disulfides with L-cysteine suggests that this exchange takes place at the kidney.(ABSTRACT TRUNCATED AT 250 WORDS)

meso-2,3-Dimercaptosuccinic acid: chemical, pharmacological and toxicological properties of an orally effective metal chelating agent.

The primary purpose of this article is to summarize the recent investigations dealing with the pharmacology and toxicology of meso-2,3-dimercaptosuccinic acid, an orally effective chelating agent. The need for a better chelating agent for treating young children and pregnant women with lead intoxication has been apparent for some time. Preclinical and clinical evidence now indicate that meso-2,3-dimercaptosuccinic acid, an Orphan Drug, shows the most promise for being effective in this regard. It has an extracellular distribution that may be responsible for its low toxicity compared to other dithiols. No attempt has been made to compare it in a rigorous and thorough manner with other chelating agents. That has not been the purpose of this review. The advantages of meso-DMSA, however, compared to CaNa2EDTA for the treatment of lead intoxication, have been outlined. Significant advances have been made recently in elucidating the structures of the metal chelates of DMSA. There is a striking difference between the structures of the lead chelate of meso-DMSA and those of racemic-DMSA. The former chelates by coordination of one sulfur and one oxygen atom with Pb. The latter can form chelates via the two sulfur atoms or via one oxygen and one sulfur atom. Solubility of the lead chelates depends on the ionization of the noncoordinated thiol and carboxylic acid groups. Bimane derivatization, HPLC, and fluorescence, as well as gas chromatography can be used for analysis of DMSA in biological fluids. The acid dissociation constants for meso- and racemic-DMSA have been summarized from the literature as have the formation constants of some of the DMSA chelates. DMSA is biotransformed to a mixed disulfide in humans. By 14 hr after DMSA administration (10 mg/kg), only 2.5% of the administered DMSA is excreted in the urine as unaltered DMSA and 18.1% of the dose is found in the urine as altered forms of DMSA. Most altered DMSA in the urine is in the form of a mixed disulfide. It consists of DMSA in disulfide linkages with two molecules of L-cysteine. One molecule of cysteine is attached to each of the sulfur atoms of DMSA. The remaining 10% of the altered DMSA was in the form of cyclic disulfides of DMSA. So far, the mixed disulfide has been found in human but not in rabbit, mouse, or rat urine. Apparently there are species differences in how organisms metabolize meso-DMSA.(ABSTRACT TRUNCATED AT 400 WORDS)

Determination and metabolism of dithiol-chelating agents: electrolytic and chemical reduction of oxidized dithiols in urine.

The presence of oxidized species of the dithiol-chelating agents, meso-2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercaptopropane-1-sulfonic acid (DMPS), in human urine was determined by chemical and electrolytic reduction methods. Urine from a human given either DMSA or DMPS was treated with electrolysis, dithiothreitol, or sodium tetrahydridoborate (NaBH4). The SH groups were derivatized with monobromobimane for the determination of unaltered dithiols. Total dithiol (unaltered and oxidized) was determined by reduction followed by derivatization with monobromobimane. The bimane derivatives were identified and quantified by HPLC and fluorescence. Although all three reduction methods gave similar results, electrolytic reduction of oxidized DMSA and chemical reduction with NaBH4 of oxidized DMPS are recommended based upon both day to day reproducibility and recovery of standards. After reduction a 4-fold increase in DMSA and a 20-fold increase in DMPS were found in urine by 12 h after an oral dose of DMSA or DMPS. These new methods for the determination of dithiols and their oxidized forms should lead to a better understanding of the metabolic properties of these increasingly important orally effective chelating agents.

Formation of labelled colloid in 99Tcm-DMSA due to the presence of bactericidal fluid.

The possibility that traces of bactericidal fluid in 99Tcm-DMSA could lead to the formation of labelled colloid, was explored. In vitro investigations were undertaken using ultracentrifugation techniques and photon correlation spectroscopy. The latter showed that both contaminated and uncontaminated DMSA contained colloidal (or particulate) material. However the presence of 10 microliters bactericidal fluid as contaminant was shown by ultracentrifugation to result in labelling of this colloidal material when 99Tcm was added to DMSA. Studies in a normal volunteer confirmed the results of the in vitro studies, in that significant liver and spleen uptake was observed after the administration of contaminated 99Tcm-DMSA.

Comparative examinations of 99mTc-DMS preparations obtained by labelling dimercaptosuccinate kits with different formulations. II. Comparison of chemical and biological characteristics of TcP-5 and MPI kits.

The chemical and biological characteristics of two dimercaptosuccinate kits were examined and compared: TcP-5 (produced at the Boris Kidric Institute - Vinca) in the freeze-dried form and MPI - the aqueous solution of tin dimercaptosuccinate. The radiochemical composition of the injection solutions was examined by various methods and the method of ascending paper chromatography in 50% aqueous methanol was found as satisfactory. Both preparations has similar compositions. Both preparations showed maximum renal concentrations 3-4 hrs after injection. Liver uptake of MPI was higher than that of TcP-5. The bench-life of both preparations was compared by measuring organ distribution. TcP-5 had a bench-life at least six hrs with a kidney/liver uptake ratio from 5.60 to 8.52, whereas MPI had a satisfactory bench-life of less than half an hour after labelling; thereafter, hepatic concentration rose and the kidney/liver uptake ratio dropped to 1.64.

Differential pulse polarographic determination of 2,3-dimercaptosuccinic acid and tin (II) in radiopharmaceuticals.

A differential pulse polarographic procedure was developed for the assay of dimercaptosuccinic acid and tin(II), components of a commercially available pharmaceutical kit for kidney scintigraphy. The method is quantitative and qualitative for both the chelated and unchelated forms of dimercaptosuccinic acid and tin(II) in a mixture of the two.