Capillary electrophoretic analysis of ethylene dicysteine, a precursor of the radiopharmaceutical 99mTc ethylene dicysteine.

L,L-Ethylene dicysteine (EC) is a ligand used in nuclear medicine for the preparation of 99mTc-L,L-EC, a tracer agent for renal function studies. A capillary zone electrophoretic method is described which allows us to monitor the purity of ethylene dicysteine, for which no other suitable method has been reported to date. A fused-silica capillary (L = 70 cm, l = 62 cm, 75 microns i.d.) was used with 10 mM sodium tetraborate, pH 10.0, as the background electrolyte. The voltage applied was 20 kV and the temperature was 25 degrees C. Benzyl alcohol served as the internal standard. The limit of detection was 0.07% and the limit of quantitation was 0.15%.

Technetium-99m L,L-ethylenedicysteine clearance and correlation with iodine-125 orthoiodohippurate for the determination of effective renal plasma flow.

Technetium-99m L,L-ethylenedicysteine (99mTc-L,L-EC) is a new renal tubular tracer that allows the determination of the effective renal plasma flow (ERPF). The aim of this study was to derive simplified methods for the estimation of 99mTc-L,L-EC clearance using one or two plasma samples after bolus injection. Fifty-nine multiple plasma dual-tracer samples (nine samples from 5 to 120 min after injection) were obtained after injection of kit-formulated 99mTc-L,L-EC and iodine-125 orthoiodohippurate (OIH). The studies were performed in 25 stable and 24 unstable transplant recipients, in five patients with renal insufficiency (four on chronic haemodialysis) and in five normal volunteers. This allowed a wide range of renal function values to be covered, with ERPF (estimated by OIH clearance) ranging from 25.4 to 604.0 ml/min. The reference 99mTc-L,L-EC clearance, as calculated from the multisample model, could be estimated from two samples at 15 and 90 min with an error of 11.3 ml/min and from one sample at 90 min with an error of 17.8 ml/min. Using appropriate linear regression analysis, ERPF could be estimated by the two- and one-sample 99mTc-L,L-EC clearance with an error of 24.2 and 22.8 ml/min, respectively. In conclusion, 99mTc-L,L-EC clearance can be accurately estimated by simplified one- or two-sample methods. Moreover, these methods can be used to estimate ERPF with an error that remains acceptable for clinical purposes.

Effect of an equal volume replacement with 500 mL 6% hydroxyethyl starch on the blood and plasma volume of healthy volunteers.

The effect of an equal volume replacement with 6% low molecular weight (200,000) hydroxyethyl starch (substitution ratio 0.60-0.66) (Elohaes) on the blood volume and plasma volume of eight healthy volunteers was investigated with special attention to volume overshooting. After replacement of 500 mL whole blood, blood volume was measured repeatedly for 8 1/2 h using chromium-51 labelled erythrocytes. Red cell volume and plasma volume were calculated from standard formulae. After replacement, blood and plasma volumes were unchanged from control (4754 +/- 630 mL and 2900 +/- 450 mL, respectively). The haematocrit decreased from 43.7 +/- 2.5% to 39.0 +/- 1.4% (1 h after starch infusion) and 41.1 +/- 1.9% (7.5 h after starch infusion). There were no significant changes in haemodynamic variables (systolic and diastolic blood pressure; heart rate), liver function (bilirubin; transaminases), renal function (serum creatinine; serum sodium) or coagulation (activated partial thromboplastin time). Alpha-amylase was significantly increased, which is a well known effect of starches. The replacement of 500 mL whole blood by hydroxyethyl starch maintains isovolaemia for at least 8 h in normal volunteers without any significant volume overshooting; this is not what was seen in earlier studies. This should increase safety in patients with cardiac disease.

Synthesis and biological evaluation of the four isomers of 99mTc-cysteinyltriglycine, an amino substituted derivative of 99mTc-MAG3.

Cysteinyltriglycine (CYSG3) is a derivative of MAG3 in which the mercaptoacetyl group is replaced by a cysteinyl moiety. This implies the presence of a primary amino group on the ligand, as in case of p-amino-hippuric acid, the compound with the highest renal tubular secretion known. The present study was undertaken to investigate the influence of this amino group on the biological behaviour of complexes of 99mTc with MAG3-like molecules. The L- and D-isomers of cysteinyltriglycine were synthesized as S-benzyl N1-CBO protected precursors. After removal of the protective groups with Na/NH3, the isomers were labelled with 99mTc. This resulted in the formation of two diastereomeric complexes (A and B in the order of HPLC-elution) for each of them. The biodistribution of the four HPLC-purified isomers was tested in mice. Isomers DA and LB showed slightly superior or similar renal excretion characteristics compared to 99mTc-MAG3, whereas the two other isomers were cleared at a lower rate by the kidneys and more through the liver and the intestines. The results indicate that substitution of 99mTc-MAG3 with an amino function may somewhat improve the rate of renal excretion, but the configuration of the 99mTc-labelled complexes appears to be more important to its biological behaviour.

Evaluation of technetium-99m-L,L-EC in renal transplant recipients: a comparative study with technetium-99m-MAG3 and iodine-125-OIH.

UNLABELLED: The clinical usefulness of kit-formulated 99mTc-L,L-EC, a new renal tubular tracer agent based on a diaminodithiol ligand was evaluated in a large population of renal transplant recipients. METHODS: Fifty patients with transplants were studied. Five patients with renal insufficiency and five normal volunteers were also included to extend the range of renal function values. The labeling efficiency of 99mTc-L,L-EC in routine conditions, i.e., without HPLC purification, and the safety of the tracer were evaluated. RESULTS: The mean radiochemical purity of 99mTc-L,L-EC determined by thin-layer chromatography was 97.4%. No side effects or significant biochemical changes were observed. The clearance of 99mTc-L,L-EC and 125I-OIH ranged from 10.7 to 417.5 and from 27.6 to 602.7 ml/min/1.73 m2, respectively. The clearance of 99mTc-L,L-EC and 99mTc-MAG3 averaged respectively 71% and 52% of that of 125I-OIH. CONCLUSION: The labeling procedure of kit-formulated 99mTc-L,L-EC is easy and efficient. This tracer is safe and suitable for both imaging and quantitative measurement of the renal tubular function. Technetium-99m-L,L-EC represents an excellent alternative to 99mTc-MAG3.

First experience in healthy volunteers with technetium-99m L,L-ethylenedicysteine, a new renal imaging agent.

Animal studies have indicated that technetium-99m L,L-ethylenedicysteine (99mTc-L,L-EC) may be a promising tracer agent for renal function studies. We have performed a paired study with 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) and 99mTc-L,L-EC in six male volunteers. In both cases, iodine-131-labelled o-iodohippurate was co-injected as an internal biological standard. The analog images between 0 and 30 min p.i. were of identical diagnostic value for both tracer agents. The two renograms were similar in all volunteers. The mean 1-h plasma clearance for 99mTc-MAG3 and 99mTc-L,L-EC was significantly different, respectively 382.9 +/- 17.1 ml/min per 1.73 m2 versus 460.2 +/- 47.7 ml/min per 1.73 m2 (P < 0.003). The urinary excretion after 30 min p.i. was 69.4% +/- 5.6% of the injected dose for 99mTc-MAG3 versus 66.5% +/- 2.5% for 99mTc-L,L-EC (P > 0.05) and after 60 min p.i. respectively 83.1% +/- 3.9% versus 79.8% +/- 4.3% (P > 0.05). 99mTc-L,L-EC has a very low plasma protein binding (31% +/- 6.8%) as compared to 99mTc-MAG3 (88% +/- 5.2%) and a larger volume of distribution. Although the exact mechanism responsible for the high plasma clearance of 99mTc-L,L-EC is not yet fully known, we conclude that this new agent merits further clinical evaluation in patients to establish its value as a renal radiopharmaceutical.

Technetium-99m-L,L-ethylenedicysteine: a renal imaging agent. I. Labeling and evaluation in animals.

L,L-ethylenedicysteine (L,L-EC) can be labeled efficiently with 99mTc at pH 12 to obtain a highly pure and very stable tracer agent (99mTc-L,L-EC). The biological behavior of 99mTc-L,L-EC was studied in mice and a baboon. In mice, 99mTc-L,L-EC demonstrated a more rapid urinary excretion and less retention in the kidneys, the liver, the intestines, and the blood than did 99mTc-MAG3 at 10 and 60 min p.i. Urinary excretion decreased in probenecid pretreated mice, which indicates active tubular transport. In the baboon, the renograms for 99mTc-MAG3 and 99mTc-L,L-EC were comparable. Plasma-protein binding of 99mTc-L,L-EC was lower than that of 99mTc-MAG3 while its distribution volume and 1-hr plasma clearance were clearly higher. The promising results of the animal experiments suggest that 99mTc-L,L-ethylenedicysteine may be a useful alternative to 99mTc-MAG3 for renal function studies in humans.