Lumiflavin and Lumichrome Transport in the Central Nervous System

The transport of the lipid‐soluble sugarless flavins, [ 14 C]lumiflavin and [ 14 C]lumichrome, into and from the isolated choroid plexus and brain slices was studied in vitro. The isolated choroid plexus accumulated both [ 14 C] flavins by a saturable, energy‐requiring process that did not depend on binding or intracellular metabolism of the [ 14 C] flavins. Both sugar‐containing and sugarless flavins, as well as cyclic organic acids, significantly inhibited [ 14 C]lumiflavin and [ 14 C]Iumichrome uptake by the isolated choroid plexus. Within 2.5 min, 75% of the [ 14 C]lumiflavin accumulated by the isolated choroid plexus was released into the medium. Brain slices accumulated [ 14 C]lumiflavin by a saturable process that did not meet all the criteria for active transport. Ninety‐five percent of the [ 14 C]lumiflavin accumulated by brain slices was released into the medium within 7.5 min. In vivo , 2 h after the intraventricular injection of 6.5 nmol [ 14 C]lumiflavin, almost all of the [ 14 C]flavin was cleared from the CNS. Addition of 3.5 μmol FMN to the intraventricular injectate significantly decreased the clearance of [ 14 C]lumiflavin from the CNS. These studies document that the sugarless flavins are transported by the flavin transport systems in the CNS.