The Fate of Perfluoro‐Tagged Metabolites of L‐DOPA in Mice Brains

Abstract

A novel compound for use in magnetic resonance (MR) imaging was created by covalently bonding multiple ¹⁹F atom tags to L‐DOPA. Tagging L‐DOPA permits bypassing the rate‐limiting factor in the biosynthesis of dopamine (DA), the conversion of tyrosine into L‐DOPA. The next step in the biosynthetic pathway, the removal of the carboxyl group on the molecule by the enzyme L‐aromatic acid decarboxylase (AADC), happens rapidly after L‐DOPA is taken up into neurons. In order to be useful as a tool in MR imaging, the novel compound and/or its perfluoro‐tagged metabolites must accumulate in vesicles in dopaminergic neurons. We administered L‐DOPA with a nine ¹⁹F atom tag ( 250 mg/kg) to mice pups, waited 1.5 or 3 hr, and used high pressure liquid chromatography (HPLC) to examine neural tissue samples for tagged L‐DOPA and tagged DA. The isomer of L‐DOPA with the tag bonded at the 5 position yielded the highest conversion to tagged DA at 1.5 hr after an i.p. injection. This study provides the first direct evidence that L‐DOPA, tagged with nine fluorine atoms, is taken up into mammalian brain dopaminergic neurons where it is converted to perfluro‐tagged DA. The use of these tagged compounds may make it feasible to investigate the uptake and conversion of important neurotransmitter in vivo with fluorine imaging.

Keywords:

• Dopamine
• DOPA
• HPLC
• Neurotransmitter
• Fluorine imaging
• Mice

Acknowledgments

Use and care of animals in this study was approved by the animal care committee at the Nathan S. Kline Institute. This project was supported by grant R21 DA15872‐01 from the National Institute on Drug Abuse.