Selective Activation of hTRPV1 by N-Geranyl Cyclopropylcarboxamide, an Amiloride-Insensitive Salt Taste Enhancer

Abstract

TRPV1t, a variant of the transient receptor potential vanilloid-1 (TRPV1) has been proposed as a constitutively active, non-selective cation channel as a putative amiloride-insensitive salt taste receptor and shares many properties with TRPV1. Based on our previous chorda tympani taste nerve recordings in rodents and human sensory evaluations, we proposed that N-geranylcyclopropylcarboxamide (NGCC), a novel synthetic compound, acts as a salt taste enhancer by modulating the amiloride/benzamil-insensitive Na+ entry pathways. As an extension of this work, we investigated NGCC-induced human TRPV1 (hTRPV1) activation using a Ca2+-flux signaling assay in cultured cells. NGCC enhanced Ca2+ influx in hTRPV1-expressing cells in a dose-dependent manner (EC50 = 115 µM). NGCC-induced Ca2+ influx was significantly attenuated by ruthenium red (RR; 30 µM), a non-specific blocker of TRP channels and capsazepine (CZP; 5 µM), a specific antagonist of TRPV1, implying that NGCC directly activates hTRPV1. TRPA1 is often co-expressed with TRPV1 in sensory neurons. Therefore, we also investigated the effects of NGCC on hTRPA1-expressing cells. Similar to hTRPV1, NGCC enhanced Ca2+ influx in hTRPA1-expressing cells (EC50 = 83.65 µM). The NGCC-induced Ca2+ influx in hTRPA1-expressing cells was blocked by RR (30 µM) and HC-030031 (100 µM), a specific antagonist of TRPA1. These results suggested that NGCC selectively activates TRPV1 and TRPA1 in cultured cells. These data may provide additional support for our previous hypothesis that NGCC interacts with TRPV1 variant cation channel, a putative amiloride/benzamil-insensitive salt taste pathway in the anterior taste receptive field.

Modulation of Human Neutrophil Responses by the Essential Oils from Ferula akitschkensis and Their Constituents

“…The molecular conformations of (−)-carveol, 6- tert -butyl- m -cresol, carvacrol, and thymol were used for the model of TRPV3/TRPM8 agonists 23 , whereas conformations of capsaicin, N -geranyl cyclopropylcarboxamide (NGCC) 12 , and compound 2k 13 were used for the model of TRPV1 agonists.…”

“…Indeed, the shapes of their molecular fields are quite different from Templates A and B (e.g., see Figure 8D), confirming that geranylacetone and isobornyl acetate do not interact with the same molecular targets reflected by Templates A and B . On the other hand, the molecular structure of geranylacetone resembles such TRPV1 agonists as capsaicin and its analogs 12, 13 . Indeed, the pharmacophore model of TRPV1 agonists based on capsaicin, NGCC, and compound 2k 12, 13 ( Template C ) differs substantially from pharmacophore Templates A and B and contains two different hydrophobic regions.…”

“…On the other hand, the molecular structure of geranylacetone resembles such TRPV1 agonists as capsaicin and its analogs 12, 13 . Indeed, the pharmacophore model of TRPV1 agonists based on capsaicin, NGCC, and compound 2k 12, 13 ( Template C ) differs substantially from pharmacophore Templates A and B and contains two different hydrophobic regions. A large area of negative field (blue area in Figure 8E) surrounds the overlapping carbonyl groups and electron acceptor substituents in the aromatic rings.…”

“…It should be noted that capsazepine had the lowest inhibitory activity on [Ca 2+ ] i flux in human neutrophils activated by Ferula essential oil-derived agonists, with the exception of geranylacetone. Although geranylacetone does not possess a vanillyl group like capsaicin, its structure exhibits spatial similarity with capsaicin and other TRPV1 agonists, such as compound 2k and NGCC 12, 13 . Indeed, the proposed bioactive conformation of geranylacetone fits well with the TRPV1 pharmacophore template and has hydrophobic, negative, and positive molecular field distributions similar to those of the template (Figure 8F).…”

Chemical composition and phagocyte immunomodulatory activity of Ferula iliensis essential oils

“…We used a ligand-based approach for molecular modeling employing fieldpoint methodology [32]. The structures of capsaicin, N-geranyl cyclopropylcarboxamide, and (Z)-N-(2,7-dimethylocta-2,6-dienyl)-2-phenylacetamide (compound 2k) [33,34] were imported for constructing a TRPV1 channel ligand-binding-site template, as described elsewhere [6]. Using the built-in capabilities of FieldTemplater software (Cresset Biomolecular Discovery Ltd., Hertfordshire, UK), we generated representative sets of conformations for the compound corresponding to local energy minima calculated within the extended electron distribution force field [32].…”