13C/15N-Enriched l -Dopa as a Triple-Resonance NMR Probe to Monitor Neurotransmitter Dopamine in the Brain and Liver Extracts of Mice

Abstract

In an attempt to monitor μm-level trace constituents, we applied here 1H-{13C-15N} triple-resonance nuclear magnetic resonance (NMR) to 13C/15N-enriched l-Dopa as the inevitable precursor of the neurotransmitter dopamine in the brain. The perfect selectivity (to render endogenous components silent) and μm-level sensitivity (700 MHz spectrometer equipped with a cryogenic probe) of triple-resonance allowed the unambiguous and quantitative metabolic and pharmacokinetic analyses of administered l-Dopa/dopamine in the brain and liver of mice. The level of dopamine generated in the brain (within the range 7-76 μm, which covers the typical stimulated level of -30 μm) could be clearly monitored ex vivo, but was slightly short of the detection limit of a 7 T MR machine for small animals. This work suggests that μm-level trace constituents are potential targets of ex vivo monitoring as long as they contain N atom(s) and their appropriate 13C/15N-enrichment is synthetically accessible. Traces via triple resonance! Tripleresonance high-resolution NMR with a cryogenic probe at 16.4 T is sensitive and selective enough to perform quantitative metabolic/pharmacokinetic analysis of l-Dopa/dopamine in brain and liver extracts from mice. This work suggests that μm-level trace constituents are potential targets of ex vivo monitoring as long as they contain N atoms and their appropriate 13C/15N-enrichment is synthetically accessible.