Structure-Pungency Relationships and TRP Channel Activation of Drimane Sesquiterpenes in Tasmanian Pepper (Tasmannia lanceolata).

Sensory-guided fractionation of extracts of Tasmanian pepper berries revealed 20 drimane sesquiterpens, among which polygodial, warburganal, and 1ß-acetoxy-9-deoxy-isomuzigadial exhibited the lowest pungency threshold concentrations on the tongue surface (0.6-2.8 nmol/cm2) and elicited a dose-dependent calcium influx into mTRPA1 expressing CHO cells with the lowest EC50 values (4.5 ± 1.0 to 16.7 ± 7.5 µmol/L) and a good correlation to oral pungency thresholds (R2 = 0.986, linear regression). Calcium imaging assays demonstrated these chemosensates to induce a calcium influx into cultured trigeminal neurons prepared from wildtype (TRPA1+/+) mice, whereas no calcium influx was observed in neurons from TRPA1 knockout mice (TRPA1-/-), thus confirming the α,ß-unsaturated 1,4-dialdehyde structure to be the required structural motif for a low oral puncency thresholds and activation of the Transient Receptor Potential Channel A1 (TRPA1). Time-resolved NMR experiments confirmed the pungency mediating mechanism for electrophilic drimane sesquiterpene dialdehydes to be different from that found for other electrophilic pungent agents like isothiocyanates, which have been shown to undergo a covalent binding with cysteine residues in TRPA1. Instead, the high-impact chemosensates polygodial, warburganal, and 1ß-acetoxy-9-deoxy-isomuzigadial showed immediate reactivity with the ε-amino group of lysine side chains to give pyrrole-type conjugates, thus showing evidence for TRPA1 activation by covalent lysine modification.