The main lipid compounds of the outermost layer of human skin are ceramides (CERs), free fatty acids, and cholesterol. Although numerous studies performed in the past could demonstrate the importance of these lipids for an intact skin barrier function, knowledge about the impact of each single component on the lamellar lipid films is still lacking. Especially, the CERs are a very heterogeneous group with high relevance for a proper barrier. It was found that the reason for the high stability of the lamellae is related to the lipid structure and function, with the type and extent of interactions between the head groups of the individual CER subspecies being particularly important. Elucidating these at the molecular level could help us to understand CER phase behavior in general. Using grazing incidence X-ray diffraction and measurements of Langmuir isotherms, the current work investigated the lateral packing of the monolayers of different subclasses of C18:0 CERs at air-water interfaces, including phytosphingosine, sphingosine, and dihydrosphingosine CERs, all with either α-hydroxy and nonhydroxy N-acylated fatty acyl. We were able to observe clear effects of the minimal differences in the polar headgroup structures of the sphingoid bases, with respect to the number and position of hydroxyl groups and double bonds, on the CER arrangement regarding the compressibility and structure of the films they formed, revealing that the hydroxyl group at the C4 of the phytosphingosine CERs leads not only to the formation of a hydrogen bond network but also to a stable suprastructure, which might be of high benefit for the barrier properties of intact skin.

• MeSH
• Ceramides * chemistry   MeSH
• X-Ray Diffraction MeSH
• Humans MeSH
• Structure-Activity Relationship MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Ceramides * MeSH

Ceramides (Cers) with α-hydroxylated acyl chains comprise about a third of all extractable skin Cers and are required for permeability barrier homeostasis. We have probed here the effects of Cer hydroxylation on their behavior in lipid models comprising the major SC lipids, Cer/free fatty acids (C 16-C 24)/cholesterol, and a minor component, cholesteryl sulfate. Namely, Cers with (R)-α-hydroxy lignoceroyl chains attached to sphingosine (Cer AS), dihydrosphingosine (Cer AdS), and phytosphingosine (Cer AP) were compared to their unnatural (S)-diastereomers and to Cers with non-hydroxylated lignoceroyl chains attached to sphingosine (Cer NS), dihydrosphingosine (Cer NdS), and phytosphingosine (Cer NP). By comparing several biophysical parameters (lamellar organization by X-ray diffraction, chain order, lateral packing, phase transitions, and lipid mixing by infrared spectroscopy using deuterated lipids) and the permeabilities of these models (water loss and two permeability markers), we conclude that there is no general or common consequence of Cer α-hydroxylation. Instead, we found a rich mix of effects, highly dependent on the sphingoid base chain, configuration at the α-carbon, and permeability marker used. We found that the model membranes with unnatural Cer (S)-AS have fewer orthorhombically packed lipid chains than those based on the (R)-diastereomer. In addition, physiological (R)-configuration decreases the permeability of membranes, with Cer (R)-AdS to theophylline, and increases the lipid chain order in model systems with natural Cer (R)-AP. Thus, each Cer subclass makes a distinct contribution to the structural organization and function of the skin lipid barrier.

• Keywords
• biophysics, ceramides, hydroxylation, lipids, permeability, skin barrier, stratum corneum,
• MeSH
• Acylation MeSH
• Ceramides chemistry   MeSH
• Hydroxylation MeSH
• Skin chemistry   metabolism   MeSH
• Humans MeSH
• Permeability MeSH
• Sphingosine analogs & derivatives   chemistry   MeSH
• Phase Transition * MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Ceramides MeSH
• phytosphingosine MeSH Browser
• safingol MeSH Browser
• Sphingosine MeSH

Ceramides (Cer) are essential components of the skin permeability barrier. To probe the role of Cer polar head groups involved in the interfacial hydrogen bonding, the N-lignoceroyl sphingosine polar head was modified by removing the hydroxyls in C-1 (1-deoxy-Cer) or C-3 positions (3-deoxy-Cer) and by N-methylation of amide group (N-Me-Cer). Multilamellar skin lipid models were prepared as equimolar mixtures of Cer, lignoceric acid and cholesterol, with 5 wt% cholesteryl sulfate. In the 1-deoxy-Cer-based models, the lipid species were separated into highly ordered domains (as found by X-ray diffraction and infrared spectroscopy) resulting in similar water loss but 4-5-fold higher permeability to model substances compared to control with natural Cer. In contrast, 3-deoxy-Cer did not change lipid chain order but promoted the formation of a well-organized structure with a 10.8 nm repeat period. Yet both lipid models comprising deoxy-Cer had similar permeabilities to all markers. N-Methylation of Cer decreased lipid chain order, led to phase separation, and improved cholesterol miscibility in the lipid membranes, resulting in 3-fold increased water loss and 10-fold increased permeability to model compounds compared to control. Thus, the C-1 and C-3 hydroxyls and amide group, which are common to all Cer subclasses, considerably affect lipid miscibility and chain order, formation of periodical nanostructures, and permeability of the skin barrier lipid models.

• MeSH
• Cell Membrane metabolism   MeSH
• Ceramides chemistry   metabolism   MeSH
• Skin metabolism   MeSH
• Membranes, Artificial * MeSH
• Permeability MeSH
• Water metabolism   MeSH
• Phase Transition MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Ceramides MeSH
• Membranes, Artificial * MeSH
• Water MeSH