Influence of surfactant mixtures on intercellular lipid fluidity and skin barrier function

Abstract

Background/aims: Surfactant mixtures are used in cosmetic and pharmaceutical formulas in order to establish product efficacy while maintaining mildness and skin lipids. The electron paramagnetic resonance (EPR) technique of the spin labeling method with a nitroxide spin probe is a valuable method in the study of biological membranes. The objective of this study was to define the influence of surfactant mixtures on intercellular lipid fluidity and correlate EPR spectral data with in vivo safety data. Methods: EPR experiment: EPR spectra of 5‐doxyl stearic acid (5‐DSA) labeled stratum corneum treated with sodium lauryl sulfate (SLS), sodium lauroyl glutamate (SLG) and their mixtures were measured and order parameters were calculated. Clinical testing: Fifteen healthy volunteers free of skin disease and with no history of atopic dermatitis were treated with SLS solutions (0.25%, 0.50%, 0.75%, 1.00%), 1.00% SLG solution and 1.00% surfactant mixture solutions: 0.75% SLS+0.25% SLG, 0.50% SLS+0.50% SLG, 0.25% SLS+0.75% SLG. One hundred μl of solution was applied using a polypropylene chamber for 24 h. Transepidermal water loss (TEWL) was measured with an evaporimeter before and after the application of surfactant solutions and each site was also visually graded according to Lee (1). Results: The order parameter (S) calculated from 1.00 %wt SLS treated stratum corneum was 0.56 ± 0.03, indicating disordering of lipid structure. On the contrary, the high S value (0.82 ± 0.02) for 1.00 %wt SLG suggests a reduced effect on the structured lipid, almost equaling the value of water. Treatment with 0.25 %wt, 0.50 %wt and 0.75 %wt SLS solutions revealed intermediate levels between 1.00 %wt SLG and SLS. The order parameters at each SLS concentration (0.25, 0.50, 0.75 and 1.00 %wt SLS) with 1.00 %wt SLG showed higher values than those of SLS only solutions. There were statistically significant differences between with and without 1.00 %wt SLG (P < 0.05). These results suggest that the addition of 1.00 %wt SLG inhibits the fluidization of intercellular lipid induced by SLS. The visual scores and TEWL values of 1.00% SLG solution were lower than those of the other test solutions (except for the vehicle control: deionized water). The 1.00% surfactant mixture solutions showed lower visual scores and TEWL values of the 1.00% SLS solution. An increase of SLG concentration decreased the visual scores and TEWL values. Order parameter S obtained from EPR spectra correlated with the clinical study. The correlation coefficient (r2) of visual score and TEWL values was 0.73 and 0.83, respectively. Conclusion: SLS disorder (fluidity) intercellular lipids at low concentrations, such as 0.25 %wt, presumably due to the SLS molecules being intercalated into the intercellular lipids. However, EPR spectral data suggest that the addition of 1.00 %wt SLG to an SLS solution (<1.00 %wt) inhibits the fluidization of intercellular lipid induced by SLS. A reasonable correlation between order parameters and human clinical data (visual scores and TEWL valu...

Stratum Corneum Lipid Structure Investigated by EPR Spin‐Probe Method: Application of Terpenes

“…On the other hand, EPR is a sensitive and nondestructive technique to measure the probe moieties in the lipid bilayers at ambient temperature [1][2][3][4][5][6]. The EPR probe method can provide an insight into the SC lipid organization as well as its dynamics.…”

“…The effect of chemical enhancers on SC lipids can be found by the analyses of aliphatic spin probes incorporated into intercellular lamella lipids using electron paramagnetic resonance (EPR). EPR in conjunction with a spin probe method non-destructively measures the ordering of the lipid bilayer of SC [1][2][3][4][5][6]. Moreover, limited investigations have focused on the mechanisms of the permeation of chemicals.…”

Kinetic Measurements Using EPR Imaging with a Modulated Field Gradient

“…The diffusion of substances into the skin is restricted by the horny layer of the skin (stratum corneum) consisting in a lipid rich layer from keratinocytes separated by intracellular lipids which are structured into multilamellar bilayers (26,27). The physical and chemical properties of these lipids are thought to be of major importance in maintaining the barrier function of the skin.…”

In Vitro Cytotoxicity and Phototoxicity Assessment of Acylglutamate Surfactants Using a Human Keratinocyte Cell Line

“…The HaCaT cell line was exposed to100 μL of different concentrations of acylglutamate surfactants and CPZ solutions (1,5,10,20,40, 80, 160 and 320 μg/mL, pH 7.2), followed by incubation for 24 h and cell viability was assessed by MTS assay.…”

“…Acylglutamate surfactants are remarkably superior to conventional surfactants in characteristic features. They have an excellent skin moisturization effect without a taut feeling, ability to improve conventional surfactant mildness, and usable even by patients suffering from skin disease [9][10][11][12].…”