Metabolism of no-carrier-added 2-[18F]fluoro-L-tyrosine in rats

No-carrier-added 2-[18F]Tyr was administered to awake rats equipped with chronic arterial and venous catheters. The time course of the plasma activity was studied by arterial blood sampling. The biodistribution of the activity in the main organs was studied at the end of the experiment. The distribution of radioactive species in plasma and brain regions was studied by acidic precipitation of the proteins and HPLC analysis of the supernatant.The absolute uptake of radioactivity in brain regions was homogenous. In awake rats, no-carrier-added 2-[18F]Tyr exhibits a fast and almost quantitative incorporation into the proteins fractions of cerebellum and cortex. In striatum, this incorporation into proteins and the unchanged fraction of the tracer detected by HPLC could be lower than in other brain regions.This study confirms the potential of 2-[18F]fluoro-L-tyrosine as a tracer for the assessment of the rate of protein synthesis by positron emission tomography. The observed metabolism suggests a need for a correction for the appearance of metabolites, at least in plasma.For years, amino acids, the basic units of proteins, have been identified as a potential tool for the study of the in vivo cellular kinetics of protein synthesis [1]. In order to achieve this in humans, implementing nuclear medicine applications, researchers must make use of either radioactive forms of natural amino acids or radioactive analogues which can be incorporated into proteins.Although radioactive iodinated derivatives have been studied for single photon emission computed tomography (SPECT) and are still of particular interest today [2], compounds labelled with positron emitters, suitable for the positron emission tomography (PET), were the main subjects of study in human functional imaging for the last twenty years. This relies on the high sensitivity and the quantitative capability of PET [3] and on the characteristics of carbon-11, an isotope of a naturally existing element in biological mole