Blood metabolism of [methyl- 11C]choline; implications for in vivo imaging with positron emission tomography

: Roivainen A, Forsback S, Gronroos T, Lehikoinen P, Kahkonen M, Sutinen E, Minn H

Publisher: SPRINGER VERLAG

: 2000

: European Journal of Nuclear Medicine

: EUROPEAN JOURNAL OF NUCLEAR MEDICINE

: EUR J NUCL MED

: 27

: 1

: 25

: 32

: 8

: 0340-6997

DOI: https://doi.org/10.1007/PL00006658

[methyl-C-11] Choline (C-11-choline) is a radioligand potentially useful for oncological positron emission tomography (PET). As a first step towards the development of a kinetic model for quantification of C-11-choline uptake, blood metabolism of C-11-choline during PET imaging was studied in humans. High-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC) were used for the analysis of C-11-choline and its radioactive metabolites. Prior to human PET imaging we studied ex vivo the biodistribution and metabolism of intravenously administered C-11-choline in rats. Our results revealed that the radioactivity accumulated particularly in kidney. lung, adrenal gland and liver. Chromatographic analysis showed that the level of unmetabolized C-11-choline in rat plasma decreased from 42%+/-20% (mean+/-SD) at 5 min to 21%+/-10% at 15 min after injection. In accordance with these findings, in humans the unmetabolized C-11-choline represents 62%+/-19% of the total radioactivity in arterial plasma at 5 min after injection and 27%+/-12% at 15 min. In human venous plasma the corresponding values were 85%+/-12% and 48%+/-12% at 5 and 10 min, respectively. The major metabolite observed in both human and rat plasma was identified as C-11-betaine, In human arterial plasma this maximally represented 82%+/-9% of the total radioactivity at 25 min after radiotracer injection. By 20 min after injection, the C-11-choline and C-11-betaine in human arterial plasma reached a plateau, and their fractional activities remained nearly constant thereafter. Although most of the circulating C-11-choline in blood is transported to tissues, it does not disappear totally from blood within the first 40 min after tracer injection.