Molecular Dynamics and Partitioning of Di‐tert‐butyl Nitroxide in Stratum Corneum Membranes: Effect of Terpenes

Abstract

In this work, we have used electron paramagnetic resonance (EPR) spectroscopy of the small spin label di-tert-butyl nitroxide (DTBN), which partitions the aqueous and hydrocarbon phases, to study the interaction of the terpenes alpha-terpineol, 1,8-cineole, L(-)-carvone and (+)-limonene with the uppermost skin layer, the stratum corneum, and the membrane models of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). The EPR spectra indicated that the terpenes increase both the partition coefficient and the rotational correlation time of the spin labels in the stratum corneum membranes, whereas similar effects were observed in the DMPC and DPPC bilayers only at temperatures below the liquid-crystalline phase. The EPR parameter associated to probe polarity inside the membranes showed thermotropically induced changes, suggesting relocations of spin probe, which were dependent on the membrane phases. While the DMPC and DPPC bilayers showed abrupt changes in the partitioning and rotational correlation time parameters in the phase transitions, the SC membranes were characterized by slight changes in the total range of measured temperatures, presenting the greatest changes or membranes reorganizations in the temperature range of approximately 50 to approximately 74 degrees C. The results suggest that terpenes act as spacers, weakening the hydrogen-bonded network at the polar interface and thus fluidizing the stratum corneum lipids.

Vitex Agnus-Castus L. Essential Oil Increases Human Erythrocyte Membrane Fluidity

“…Anjos and co-workers (29) have shown, using EPR with 5-DS, that 1,8-cineole, a main constituent of Vac, modifies the properties of cell membranes by rupturing the hydrogen-bonded network at the membrane-water interface, but not by changing membrane fluidity near the surface. Similar results were obtained for limonene and other related compounds (30). The ability to increase the susceptibility of the membrane to the penetration of various compounds seems to be a general characteristic of cyclic terpens (31).…”

Effects of terpenes on fluidity and lipid extraction in phospholipid membranes

“…Terpenes in combination with ethanol also increased the permeability of luteinizing hormone releasing hormone through porcine skin by enhancing the extraction of stratum corneum lipids [28]. It has been shown that the membrane partition coefficients of the small watersoluble spin labels TEMPO and DTBN in the stratum corneum and in DPPC membranes increase with increasing temperature, with the greatest increases for temperatures above the phase transition of the membranes [14,15]. In this work, the EPR signal of 5-DMS in terpene micelles present in the system of DPPC vesicles:terpenes was generally observed for temperatures below 30°C, suggesting that with increasing temperature more terpenes penetrate in DPPC bilayers, forming a minor amount of micelles.…”

“…The electron paramagnetic resonance (EPR) spectroscopy of spin labels has been employed to investigate the mechanisms by which monoterpenes act as enhancers of skin permeation [12][13][14][15]. The intercellular lipid matrix of the outermost skin layer, the stratum corneum, which is the major permeability barrier of the skin, becomes more fluid in the presence of the monoterpenes L-menthol and 1,8-cineole [12,13], and several monoterpenes increase the membrane partition coefficients of the small water-soluble spin labels TEMPO and DTBN in stratum corneum membranes [14,15].…”

“…The intercellular lipid matrix of the outermost skin layer, the stratum corneum, which is the major permeability barrier of the skin, becomes more fluid in the presence of the monoterpenes L-menthol and 1,8-cineole [12,13], and several monoterpenes increase the membrane partition coefficients of the small water-soluble spin labels TEMPO and DTBN in stratum corneum membranes [14,15]. Recently, EPR spectroscopy has been used to show that terpenes can cause pronounced increases in the plasma membrane fluidity of Leishmania amazonensis promastigotes at terpene concentrations similar to those that inhibit the growth of the parasite [16].…”

Terpenes Increase the Lipid Dynamics in the Leishmania Plasma Membrane at Concentrations Similar to Their IC50 Values

“…Electron paramagnetic resonance (EPR) spectroscopy using spin labels has been employed to investigate the mechanisms underlying the acceleration of skin permeation by monoterpenes [20]–[23]. The intercellular lipid matrix of the stratum corneum, the outermost skin layer, which represents the major permeability barrier of the skin, becomes more fluid in the presence of the monoterpenes L-menthol and 1,8-cineole [20], [21].…”