TRPV1 antagonist activity of the extract and compounds from the fruits of Tetradium daniellii

Vanilloid receptor type 1 (TRPV1), which confers noxious heat and inflamatory pain signals in the peripheral nervous system, has recently been implicated as novel target in painkiller drug discovery [1]. Evodia species have been recognised as a source of TRPV1 ligands. Quinazolinocarboline alkaloids from E. rutaecarpa, evodiamine and rutaecarpine, are potent agonists of TRPV1 [2,3]. We noted that different extracts from Tetradium daniellii (Benn.) T.G.Hartley (syn. Evodia hupehensis Dode) affects Ca²⁺-uptake via TRPV1. The cyclohexane extract from fresh fruits of T. daniellii inhibited capsaicin-induced TRPV1 in NIH3T3 cells ectopically expressing the receptor. Dose-dependent inhibition of TRPV1 was determined in bioactivity-guided fractionation of the extracts.

The cyclohexane phase was consecutively subjected to 1) open column chromatography (OCC), 2) vacuum-liquid chromatography, 3) RP-OCC and 4) preparative TLC fractionation, which afforded two active constituents. The structures of the isolated compounds were determined by ¹H- and ¹³C-NMR experiments as cis-9,cis-12-linoleic acid and (2E,4E)-N-isobutyldeca-2,4-dienamide (=pellitorine). Both compounds inhibited the capsaicin-evoked Ca²⁺-uptake with an IC₅₀ of 80 and 200µg/ml, respectively. Our separation process allowed also identification of N-isobutyl-4,5-epoxy-2E-decadienamide and furocoumarins, which proved to be inactive. Our study provides additional evidence that polyunsaturated fatty acids and aliphatic alkylamides can inhibit channel opening of TRPV1.

References: [1] Olah Z. et al. (2001) J. Biol. Chem. 276: 11021–110301. [2] Calixto JB. et al. (2005) Pharmacol. Therapeut. 106: 179–208. [3] Pearce L V. et al. (2004) Org. Biomol. Chem. 2: 2281–2286.