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Comparison of Technetium-99m-LL-EC Isomers in Rats and Humans

Division of Nuclear Medicine, Department of Radiology, Emory University School of Medicine and Department of Chemistry, Emory University, Atlanta, Georgia

Correspondence: For correspondence or reprints contact: Andrew Taylor, Jr., MD, Division of Nuclear Medicine, Department of Radiology, Emory University School of Medicine, 1364 Clifton Rd., Atlanta, GA 30322.

ABSTRACT

Technetium-99m-L,L-ethylenedicysteine (^99mTc-L,L-EC)is a new renal imaging agent with pharmacokinetic properties reported to be slightly superior to those of ^99mTc-mercaptoacetyltriglycine (^99mTc MAG3); however, to better define the potential of the enantiomer ^99mTc-DD-EC and the diastereomer ^99mTc-DL-EC as renal imaging agents, we compared the three EC stereoisomers with ¹³¹I-orthoiodohippurate (OIH) in a series of rats and humans. Methods: Each ^99mTc-EC stereoisomer was coinjected with OIH in six Sprague-Dawley rats for measurements of clearance and extraction fraction. Each stereoisomer was also coinjected wfth OIH in three human volunteers followed by sequential imaging, plasma clearance measurements and timed urine collections. Results: Technetium-99m-DD-EC had the highest clearance and extraction efficiency in rats (p 0.02). In humans, image quality was good with all three agents. The clearance ratio (EC/OIH) was 82% ± 8% for ^99mTc-DD-EC compared to 70% ± 3% and 40% ± 5% for ^99mTc-L,L-EC and ^99mTc-DL-EC, respectivaly. Technetium-99m-DD and ^99mTc-L,L-EC were excreted more rapidly than ^99mTc-DL-EC. Conclusion: Technetium-99m-DD-EC has excellent imaging properties and the data suggest that its clearance may approach that of OIH more closely than any other ^99mTc renal agent. A potential limitationis the fact that both ^99mTc-DD and LL-EC exist in dianionic (80%) and monoanionic (20%) forms at physiological pH and it is unlikely that these two forms have the same clearance or protein binding affinity.

Key Words: technetium-99m-DD-EC • technetium-99m-L,L-EC • tectinetium-99m-DL-EC • renal scintigraphy

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