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Cationic Technetium-99m Complexes of N-Substituted Pyridoxal Derivatives as Renal Function Agents

Faculty of Pharmaceutical Sciences, Fukuoka University, Fukuoka, Japan

Correspondence: For correspondence or reprints contact: Yoshiharu Karube, PhD, Faculty of Pharmaceutical Sciences, Fukuoka University, Nanakuma 8-19-1, Johnan-ku, Fukuoka, 814-01, Japan.

ABSTRACT

New cationic technetium-chelating agents containing a pyridinium group have been synthesized and evaluated as potential renal radiopharmaceuticals. Methods: The pyridinium compounds used in the study are N-methyl pyridoxal chloride, N-ethyl pyridoxal chloride, N-propyl pyridoxal chloride, 1-methyl-3-hydroxy-4-formylpyridinium chloride, 1-methyl-2-formyl-3-hydroxypyridinium chloride and the Schiff's bases of N-methyl pyridoxal chloride with amino acid, amino acid ester and amino acid amide. Complexes of these chelating agents with ^99mTc were prepared using a Na₂S₂O₄ or a SnCl₂ solution as a reducing agent. The purity of the ^99mTc complexes was determined by paper electrophoresis in 0.1 Mtris buffer. Results: Electrophoresis indicates slightly positive-charged species. The log P values of these complexes showed a hydrophilic nature. Urinary excretion of the ^99mTc N-alkylated pyridoxal derivatives, ^99mTc diethylenetriaminepentaacetic acid, ^99mTc-mercaptoacetylglycylglycylglycine (MAG3) and ¹³¹I-o-iodohippurate were determined in mice and rats at different time intervals. In a rat model, the pyridoxal-derived ^99mTc complexes are rapidly excreted in urine and provide clear renal scintigrams. Hepatobiliary excretion was negligible, reducing scan interference from the intestines. Total clearances were lower than that of ¹³¹I-hippurate and ^99mTc MAG3. Conclusions: The rate of urinary clearance of the new tracers was not significantly faster than ^99mTc diethylenetriaminepentaacetic acid and the inhibitor N¹-methylnicotinamide had only a minimal effect on the renal behavior. Though the new tracers have cationic properties, the pyridinium group did not contribute largely to the excretion of active transport.

Key Words: technetium-99m • N-alkyl pyridoxal • renal agents • radiopharmaceutical