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Ceramides from intercellular lipids of skin stratum corneum are known to play an essential role in maintaining and structuring the lipid barrier of the skin. Internal wool lipids (IWL), which are also rich in ceramides, have a composition similar to that of the stratum corneum lipids. IWL extracted with chloroform/methanol azeotrope at the laboratory scale have been shown to be capable of forming liposomes with a stable bilayer structure. Furthermore, topical application of these IWL liposomes on intact and compromised skin has been demonstrated to improve barrier skin properties.In this study we evaluated the effect on human skin repair of different IWL extract compositions obtained by two extraction methodologies. The formation and characteristics of the liposomes prepared were greatly influenced by the IWL composition, primarily the sterol sulfate content. The IWL liposomes improved skin barrier integrity and increased skin hydration when applied onto intact skin. These improvements were slightly enhanced in the case of IWL liposomes that were richer in polar lipids.

Internal wool lipids (IWLs) are rich in cholesterol, free fatty acids, cholesteryl sulfate, and, mainly, ceramides. The repairing effect of these lipids structured as liposomes was demonstrated by reinforcing the skin-barrier integrity and increasing the water-holding capacity when applied onto the skin. This work was focused on the formation of liposomes with IWLs rich in ceramides, obtained at pilot plant level with organic solvent extraction by using methanol and acetone. The lipid composition of the two extracts was quantitatively analyzed. IWL extracts containing different amounts of sterol sulfate were used to form liposomes at physiologic p(H). Vesicle size distribution, polydispersity index, and zeta potential of all liposomes were determined to characterize them and to study their stability. The results obtained showed that IWL extract composition, which was different depending on the extraction methodologies used, greatly influences the characteristics of the liposomes formed. Vesicular size and polydispersity index liposomes were smaller when the extract composition contained a higher proportion of either free fatty acids or sterol sulfate. Moreover, liposome stability was improved when some amount of sterol sulfate was added to the composition of methanol and acetone extracts. This natural mixture with keratinaceous origin could have a special interest for cosmetic or dermopharmaceutical companies.

The role played by the ceramides (Cer) in the interaction of Triton X-100 (T(X-100)) with liposomes modeling the stratum corneum (SC) lipid composition was studied. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (K) were determined at sublytic level by monitoring the changes in the fluorescence intensity of liposomes due to the 5(6)-carboxyfluorescein (CF) released from the interior of vesicles. Higher and lower Cer proportions than those existing in the SC (40%) led respectively to a fall and to a rise in the surfactant ability to alter these liposomes. However, the surfactant partitioning between bilayers and water (bilayer affinity with vesicles) exhibited a maximum for 40% Cer. Thus, at low Cer proportions the ability of T(X-100) molecules to alter these bilayers was maximum despite their reduced partitioning into bilayers, in line with the reported interaction of the anionic surfactant model sodium dodecyl sulfate with these vesicles. These findings underline the fragility of these bilayers as an effective barrier and could explain in part the reported dependencies of low level of Cer in skin lipids and function barrier abnormalities. The fact that the free surfactant concentration needed to achieve the two interaction levels investigated was lower than the surfactant CMC indicates that permeability alterations were mainly ruled by the action of surfactant monomers, regardless of Cer proportion in bilayers.

The solubilization of liposomes modeling the stratum corneum (SC) lipid composition and those obtained varying the proportion of ceramides by means of dodecyl betaine (C(12)-Bet)/sodium dodecyl sulfate (SDS) mixtures was studied. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (K) were determined by monitoring the changes in the static light scattering of the system during solubilization. The fact that the free surfactant concentration was always similar to its critical micelle concentration (CMC) indicates that the liposome solubilization was mainly ruled by the formation of mixed micelles. The mole fraction of the zwitterionic component (X(zwitter)) of 0.4 showed the lowest ability to saturate or solubilize liposomes, although exhibiting the highest degree of partitioning into liposomes. This X(zwitter) corresponded to the highest derivation of the CMCs of these mixtures (negative synergism) and to the highest reduction in the skin irritation with respect to the anionic component. Higher and lower proportion of ceramides in the mixture led to a fall and to a rise in both the activity and the partitioning of a specific surfactant mixture (X(zwitter)=0.4). This finding could be related to the recently reported dependences of the level of ceramides in skin and function barrier abnormalities. Comparison of the present Re and K values with those reported for phosphatidylcholine (PC) liposomes shows that, although SC liposomes were more resistant to the action of surfactant mixtures, the surfactant partitioning into SC bilayers was similar to that reported for PC ones in all cases.

The sublytic interactions of a mixture of N-dodecyl-N, N-dimethylbetaine dodecyl betaine (C12-Bet)/sodium dodecyl sulfate (SDS) (mole fraction of the zwitterionic surfactant=0.6) with stratum corneum (SC) lipid liposomes varying the proportion of ceramides type III (Cer) were investigated. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (K) were determined by monitoring the changes in the fluorescence intensity of liposomes due to the 5(6) carboxyfluorescein (CF) released from the interior of vesicles. The fact that the free surfactant mixture concentration was always lower than its critical micelle concentration indicates that permeability changes were ruled by the action of surfactant monomers in all cases. Higher and lower Cer proportions than that of the SC lipids led to a fall and to a rise in the activity of the surfactant mixture on these bilayer structures. However, the surfactant partitioning into liposomes (or affinity with these bilayer structures) increased as the proportion of Cer increased up to the highest value was achieved for a Cer proportion similar to that in the SC lipids (about 40-45%). Thus, at low Cer proportions the ability of the surfactant mixture to alter the permeability of these bilayer structures was higher than that for liposomes approximating the SC lipid composition despite their reduced partitioning into liposomes. These findings are in agreement with the recently reported dependencies of the level of ceramides in skin lipids and function barrier abnormalities and could explain in part these dependencies.

The role played by the ceramides in the sublytic interactions of sodium dodecyl sulfate (SDS) with liposomes modeling the stratum corneum (SC) lipid composition was studied. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (k) were determined by monitoring the changes in the fluorescence intensity of liposomes due to the 5(6) carboxyfluorescein (CF) released from the interior of vesicles. The presence in liposomes of higher and lower ceramide proportions than that existing in the SC lipids led to a fall and to a rise in the sublytic activity of SDS on these structures. However, the SDS partitioning into liposomes (or affinity with these bilayer structures) increased as the proportion of Cer increased up to achieve almost a constant value for a Cer proportion similar to that in the SC lipids (about 40%). Thus, at low Cer proportions the ability of SDS molecules to alter these bilayer structures was higher than that for liposomes approximating the SC lipid composition despite their reduced partitioning into liposomes. These findings are in agreement with the recently reported dependencies of the level of ceramides in skin lipids and function barrier abnormalities and could explain in part these dependencies. The fact that the free surfactant concentration needed to achieve the two interaction levels investigated was lower than the surfactant critical micellar concentration (CMC) indicates that permeability alterations were mainly ruled by the action of surfactant monomers, regardless of the liposome lipid composition.

Presents a letter to the editor about ceramides from lanolin or wool wax.