Novel radiochemical and biological characterization of 99mTc-histamine as a model for brain imaging

Histamine was successfully labeled with technetium-99 m ( 99m Tc). The studied reaction parameters included substrate concentration, reducing agent concentration, pH of the reaction mixture, reaction time, in vitro stability of the 99m Tc-histamine, and biodistribution in experimental animals. Accurately weighed 3 mg histamine was dissolved and transferred to an evacuated penicillin vial. Exactly 50 μg SnCl 2 dihydrate was added and the pH of the mixture was adjusted to 4 using 0.1N HCl, then the volume of the mixture was adjusted to one ml by N 2 -purged distilled water. One ml of freshly eluted 99m TcO4- (~ 400MBq) was added to the above mixture. The reaction mixture was vigorously shaken and allowed to react at room temperature for sufficient time to complete the reaction The complex gives a maximum labeling yield of 98.0% ± 0.34%, and maintained stability throughout the working period (6 h). Biodistribution investigation showed that the maximum uptake of the 99m Tc-histamine in the brain was 7.1% ± 0.12% of the injected activity/g tissue organ, at 5 min post-injection. The clearance from the mice appeared to proceed via the circulation mainly through the kidneys and urine (approximately 37.8% of the injected dose at 2 h after injection of the tracer). Brain uptake of 99m Tc-histamine is higher than that of ( 99m Tc-ECD and 99m Tc-HMPAO) therefore 99m Tc-histamine could be used for brain single-photon emission computed tomography (SPECT). Furthermore, 99m Tc-histamine could be considered as a novel radiopharmaceutical for brain imaging.