Fragrance material review on laevo-carveol

Effects of camphor and related compounds on slowly adapting mechanoreceptors in the rat sinus hair follicle

Introduction

Camphor is a popular compound for therapeutic and cosmetic use with a distinctive odour, and somatosensory warming and cooling properties. The mechanisms for its action remain unclear.

Objective

The current study examined the effects of two enantiomers of camphor and related monoterpenoid compounds on mechanoreceptors.

Methods

Extracellular recordings were made in an in vitro bath preparation. Camphor, borneol, eugenol, carveol, and thymol were tested on the neural activity of St I and St II slowly adapting mechanoreceptors in the rat vibrissal hair follicle preparation.

Results

All compounds tested (0.5 – 2 mM bath concentrations) resulted in dose-dependent depression of spontaneous and mechanically evoked firing (dynamic and static phases). The mean latency of responses also increased. Both St I and St II were similarly affected, although (-)-camphor had a greater depressant effect on St II than on St I units. Differences were found across the different compounds for their effect on the dynamic and static phases. Thymol was found to have the greatest depressant effect on these phases. The broad spectrum TRP blocker ruthenium red did not reverse the depressant effects of camphor. The depressant effects of the compounds appeared similar to those obtained using the local anaesthetic lignocaine. The depressant effects of camphor and of lignocaine were partially reversed by the K⁺ channel blocker tetraethylammonium.

Conclusions

The results question whether the depressant effects of camphor and related compounds act through TRP channels. Perhaps the use of more selective blockers may reveal the molecular mechanisms through which these compounds act.

l-Carvyl esters as penetration enhancers for the transdermal delivery of 5-fluorouracil

To develop effective and safe penetration enhancers, a series of l-carvyl esters, namely, 5-isopropenyl-2-methylcyclohex-2-en-1-yl heptanoate (C-HEP), 5-isopropenyl-2- methylcyclohex-2-en-1-yl octanoate (C-OCT), 5-isopropenyl-2-methylcyclohex-2-en-1-yl decanoate (C-DEC), 5-isopropenyl-2-methylcyclohex-2-en-1-yl dodecanoate (C-DOD), 5-isopropenyl-2-methylcyclohex-2-en-1-yl tetradecanoate (C-TET), and 5-isopropenyl-2-methylcyclohex-2-en-1-yl palmitate (C-PAL), was synthesized from l-carveol and saturated fatty acids (C7-C16). The volatility of l-carveol and l-carvyl esters was evaluated by a live weight loss experiment. The enhancing effects of l-carvyl esters on 5-fluorouracil (FU) were investigated in the in vitro permeation experiment on rat skin. The stratum corneum (SC) uptakes of the enhancers were tested in vitro by gas chromatography. Only the l-carvyl esters with a moderate SC uptake, namely, C-OCT (C8), C-DEC (C10), and C-DOD (C12), showed a potential to enhance FU skin permeation. An evident parabolic relationship was found between the permeation enhancement of FU and the SC uptake of the l-carvyl esters. The l-carvyl esters with a chain length of C8-C12 seemed to be favorable for FU.