Reduction of the suppressive effects of gurmarin on sweet taste responses by addition of beta-cyclodextrin

Cyclodextrins (CDs) have the remarkable ability to form inclusion complexes with a wide variety of guest molecules. In the present study, possible influences of CDs on gurmarin inhibition of the chorda tympani responses to sucrose were examined in C57BL mice. Responses to sucrose were suppressed to approximately 50% of control by treatment of the tongue with 30 micrograms/ml (approximately 7.1 microM) gurmarin. Rinsing the tongue with 15 mM beta-CD after gurmarin gave rapid recovery of the suppressed sucrose responses to approximately 85% of control, whereas 15 mM alpha- or gamma-CD did not. When gurmarin was mixed with beta-CD, the suppressive effects of gurmarin on sucrose responses were largely reduced. No such reduction was observed for mixtures with alpha- and gamma-CD. Gurmarin includes tyrosine and tryptophan residues whose aromatic rings are directed outward and can probably form inclusion complexes with beta-CD. Therefore, the observed reduction of the effects of gurmarin may be due to steric hindrances in inclusion complexes of gurmarin with beta-CD that may interfere with gurmarin binding to sweet taste receptors.