No abstract

The structural similarity of eugenol with capsaicin suggests that these two agents may share molecular mechanisms to produce their effects. We investigated the effects of eugenol in comparison with those of capsaicin using whole-cell patch clamp and Fura-2-based calcium-imaging techniques in a heterologous expression system and with sensory neurons. In vanilloid receptor 1 (VR1)-expressing human embryonic kidney (HEK) 293 cells and trigeminal ganglion (TG) neurons, eugenol activated inward currents, whereas capsazepine, a competitive VR antagonist, and ruthenium red (RR), a functional VR antagonist, completely blocked eugenol-induced inward currents. Moreover, eugenol caused elevation of [Ca(2+)](i), and this was completely abolished by both capsazepine and ruthenium red in VR1-expressing HEK 293 cells and TG neurons. Our results provide strong evidence that eugenol produces its effects, at least in part, via VR1 expressed by the sensory nerve endings in the teeth.

No abstract

Curcumin has diverse therapeutic effects, such as anti-inflammatory, anti-oxidant, anti-cancer, and antimicrobial activities. The vanilloid moiety of curcumin is considered important for activation of the transient receptor potential vanilloid 1 (TRPV1), which plays an important role in nociception. However, very little is known about the effects of curcumin on nociception. In the present study, we investigated whether the anti-nociceptive effects of curcumin are mediated via TRPV1 by using nociceptive behavioral studies and in vitro whole-cell patch-clamp recordings in the trigeminal system. Subcutaneous injection of capsaicin in the vibrissa pad area of rats induced thermal hyperalgesia. Intraperitoneally administered curcumin blocked capsaicin-induced thermal hyperalgesia in a dose-dependent manner. Whereas curcumin reduced capsaicin-induced currents in a dose-dependent manner in both trigeminal ganglion neurons and TRPV1-expressing HEK 293 cells, curcumin did not affect heat-induced TRPV1 currents. Taken together, our results indicate that curcumin blocks capsaicin-induced TRPV1 activation and thereby inhibits TRPV1-mediated pain hypersensitivity.