Pellitorine, an extract of Tetradium daniellii, is an antagonist of the ion channel TRPV1

Abstract

Background: Transient Receptor Potential Vanilloid 1 (TRPV1) confers noxious heat and inflammatory pain signals in the peripheral nervous system. Clinical trial of resiniferatoxin from Euphorbia species is successfully aimed at TRPV1 in cancer pain management and heading toward new selective painkiller status that further validates this target for drug discovery efforts. Evodia species, used in traditional medicine for hundreds of years, are a recognised source of different TRPV1 agonists, but no antagonist has yet been reported.

Hypothesis/purpose: In a search for painkiller leads, we noted for the first time a TRPV1 antagonist activity in the fresh fruits of Tetradium daniellii (Benn.) T.G. Hartley (syn. Evodia hupehensis Dode).

Methods: Through a combination of extraction and purification methods with functional TRPV1-specific Ca²⁺ uptake assays (bioactivity-guided fractionation/isolation/purification); we isolated a new painkiller candidate that is a distant structural homologue of capsiate exovanilloids and endovanilloids such as anandamide, but a putative competitive inhibitor of the TRPV1. Four additional inactive compounds (N-isobutyl-4,5-epoxy-2E-decadienamide, geranylpsoralen, 8-(7',8'-epoxygeranyloxy)psoralen, and xanthotoxol) were also co-purified with pellitorine. Their structures were established by extensive 1D- and 2D-NMR spectroscopic analysis.

Results: ¹H- and ¹³C NMR determination of the chemical structure revealed it to be pellitorine, (2E,4E)-N-(2-methylpropyl)deca-2,4-dienamide, which can compete structurally with algesics released in inflammation. In contrast to previous isolates from Evodia species, pellitorine blocked capsaicin-evoked Ca²⁺ uptake with an IC₅₀ of 154 µg/ml (0.69 mM/l). N-Isobutyl-4,5-epoxy-2E-decadienamide and geranylpsoralen, 8-(7',8'-epoxygeranyloxy)psoralen, and xanthotoxol did not affect the TRPV1.

Conclusion: This is the first evidence that pellitorine, an aliphatic alkylamide analogue of capsaicin, can serve as an antagonist of the TRPV1 and may inhibit exovanilloid-induced pain.

Keywords: Calcium transport; Pain; Pellitorine; TRP channels; Tetradium daniellii.