In vitro evaluation of potential bitterness-masking terpenoids from the Canada goldenrod (Solidago canadensis).

In a screening of extracts of selected plants native to Ohio against the human bitterness receptor hTAS2R31, a chloroform-soluble extract of the aerial parts of Solidago canadensis (Canada goldenrod) was determined to have hTAS2R31 antagonistic activity and, thus, was fractionated for isolation of potential bitterness-masking agents. One new labdane diterpenoid, solidagol (1), and six known terpenoids, including two labdane diterpenoids (2 and 3), three clerodane diterpenoids (6ß-angeloyloxykolavenic acid, 6ß-tigloyloxykolavenic acid, and crotonic acid), and a triterpenoid (longispinogenin), were isolated. Among these compounds, 3ß-acetoxycopalic acid (2) was found to be the first member of the labdane diterpene class shown to have inhibitory activity against hTAS2R31 activation (IC50 8 µM). A homology model of hTAS2R31 was constructed, and the molecular docking of 2 to this model indicated that this diterpenoid binds well to the active site of hTAS2R31, whereas this was not the case for the closely structurally related compound 3 (sempervirenic acid). The content of 2 in the chloroform-soluble portion of the methanolic extract of S. canadensis was up to 2.24 g/100 g dry weight, as determined by HPLC.

Novel menthol-derived cooling compounds activate primary and second-order trigeminal sensory neurons and modulate lingual thermosensitivity.

We presently investigated 2 novel menthol derivatives GIV1 and GIV2, which exhibit strong cooling effects. In previous human psychophysical studies, GIV1 delivered in a toothpaste medium elicited a cooling sensation that was longer lasting compared with GIV2 and menthol carboxamide (WS-3). In the current study, we investigated the molecular and cellular effects of these cooling agents. In calcium flux studies of TRPM8 expressed in HEK cells, both GIV1 and GIV2 were approximately 40- to 200-fold more potent than menthol and WS-3. GIV1 and GIV2 also activated TRPA1 but at levels that were 400 times greater than those required for TRPM8 activation. In calcium imaging studies, subpopulations of cultured rat trigeminal ganglion and dorsal root ganglion cells responded to GIV1 and/or GIV2; the majority of these were also activated by menthol and some were additionally activated by the TRPA1 agonist cinnamaldehyde and/or the TRPV1 agonist capsaicin. We also made in vivo single-unit recordings from cold-sensitive neurons in rat trigeminal subnucleus caudalis (Vc). GIV 1 and GIV2 directly excited some Vc neurons, GIV1 significantly enhanced their responses to cooling, and both GIV1 and GIV2 reduced responses to noxious heat. These novel cooling compounds provide additional molecular tools to investigate the neural processes of cold sensation.

In vitro evaluation of flavonoids from Eriodictyon californicum for antagonist activity against the bitterness receptor hTAS2R31.

The leaves of the native North American plant, Eriodictyon californicum, were once used to mask the bitter taste of pharmaceuticals, an application currently of importance. Ten flavonoids (1-10) were isolated from the leaves of E. californicum, of which the structure and absolute configuration of 6-methoxyhesperetin (8) were assigned for the first time. In addition, the absolute configurations at C-2 were established for 4'-isobutyrylhomoeriodictyol (3) and 6-methoxyhomoeriodictyol (7). Using a cell-based assay, it was determined that the 7-methoxylated flavanones, sakuranetin (2) and 6-methoxysakuranetin (9), and the flavone, jaceosidin (10), are antagonists of hTAS2R31.

Activation of lumbar spinal wide-dynamic range neurons by a sanshool derivative.

The enigmatic sensation of tingle involves the activation of primary sensory neurons by hydroxy-alpha-sanshool, a tingly agent in Szechuan peppers, by inhibiting two-pore potassium channels. Central mechanisms mediating tingle sensation are unknown. We investigated whether a stable derivative of sanshool-isobutylalkenyl amide (IBA)-excites wide-dynamic range (WDR) spinal neurons that participate in transmission of chemesthetic information from the skin. In anesthetized rats, the majority of WDR and low-threshold units responded to intradermal injection of IBA in a dose-related manner over a >5-min time course and exhibited tachyphylaxis at higher concentrations (1 and 10%). Almost all WDR and low-threshold units additionally responded to the pungent agents mustard oil (allyl isothiocyanate) and/or capsaicin, prompting reclassification of the low-threshold cells as WDR. The results are discussed in terms of the functional role of WDR neurons in mediating tingle sensation.