Ceramides are key components of the skin's permeability barrier. In atopic dermatitis, pathological hydrolysis of ceramide precursors - glucosylceramides and sphingomyelin - into lysosphingolipids, specifically glucosylsphingosine (GS) and sphingosine-phosphorylcholine (SPC), and free fatty acids (FFAs) has been proposed to contribute to impaired skin barrier function. This study investigated whether replacing ceramides with lysosphingolipids and FFAs in skin lipid barrier models would exacerbate barrier dysfunction. When applied topically to human stratum corneum sheets, SPC and GS increased water loss, decreased electrical impedance, and slightly disordered lipid chains. In lipid models containing isolated human stratum corneum ceramides, reducing ceramides by ≥ 30% significantly increased permeability to four markers, likely due to loss of long-periodicity phase (LPP) lamellae and phase separation within the lipid matrix, as revealed by X-ray diffraction and infrared spectroscopy. However, when the missing ceramides were replaced by lysosphingolipids and FFAs, no further increase in permeability was observed. Conversely, these molecules partially mitigated the negative effects of ceramide deficiency, particularly with 5%-10% SPC, which reduced permeability even compared to control with "healthy" lipid composition. These findings suggest that while ceramide deficiency is a key factor in skin barrier dysfunction, the presence of lysosphingolipids and FFAs does not aggravate lipid structural or functional damage, but may provide partial compensation, raising further questions about the behavior of lyso(sphingo)lipids in rigid multilamellar lipid environments, such as the stratum corneum, that warrant further investigation.

• Keywords
• ceramide, fatty acid, glucosylsphingosine, lipid model, lysolipid, permeability, skin barrier, sphingosine-phosphorylcholine,
• MeSH
• Ceramides * metabolism   deficiency   MeSH
• Phosphorylcholine analogs & derivatives   MeSH
• Skin * metabolism   drug effects   MeSH
• Fatty Acids, Nonesterified metabolism   MeSH
• Humans MeSH
• Lysophospholipids * metabolism   MeSH
• Permeability MeSH
• Sphingolipids * metabolism   MeSH
• Sphingosine analogs & derivatives   metabolism   pharmacology   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Ceramides * MeSH
• Phosphorylcholine MeSH
• Fatty Acids, Nonesterified MeSH
• Lysophospholipids * MeSH
• Sphingolipids * MeSH
• Sphingosine MeSH
• sphingosine phosphorylcholine MeSH Browser

Ceramides belong to sphingolipids, an important group of cellular and extracellular lipids. Their physiological functions range from cell signaling to participation in the formation of barriers against water evaporation. In the skin, they are essential for the permeability barrier, together with free fatty acids and cholesterol. We examined the periodical structure and permeability of lipid films composed of ceramides (Cer; namely, N-lignoceroyl 6-hydroxysphingosine, CerNH24, and N-lignoceroyl sphingosine, CerNS24), lignoceric acid (LIG; 24:0), and cholesterol (Chol). X-ray diffraction experiments showed that the CerNH24-based samples form either a short lamellar phase (SLP, d ∼ 5.4 nm) or a medium lamellar phase (MLP, d = 10.63-10.78 nm) depending on the annealing conditions. The proposed molecular arrangement of the MLP based on extended Cer molecules also agreed with the relative neutron scattering length density profiles obtained from the neutron diffraction data. The presence of MLP increased the lipid film permeability to the lipophilic model permeant (indomethacin) relative to the CerNS24-based control samples and the samples that had the same lipid composition but formed an SLP. Thus, the arrangement of lipids in various nanostructures is responsive to external conditions during sample preparation. This polymorphic behavior directly affects the barrier properties, which could also be (patho)physiologically relevant.

• Publication type
• Journal Article MeSH

Epidermal omega-O-acylceramides (ω-O-acylCers) are essential components of a competent skin barrier. These unusual sphingolipids with ultralong N-acyl chains contain linoleic acid esterified to the terminal hydroxyl of the N-acyl, the formation of which requires the transacylase activity of patatin-like phospholipase domain containing 1 (PNPLA1). In ichthyosis with dysfunctional PNPLA1, ω-O-acylCer levels are significantly decreased, and ω-hydroxylated Cers (ω-OHCers) accumulate. Here, we explore the role of the linoleate moiety in ω-O-acylCers in the assembly of the skin lipid barrier. Ultrastructural studies of skin samples from neonatal Pnpla1+/+ and Pnpla1-/- mice showed that the linoleate moiety in ω-O-acylCers is essential for lamellar pairing in lamellar bodies, as well as for stratum corneum lipid assembly into the long periodicity lamellar phase. To further study the molecular details of ω-O-acylCer deficiency on skin barrier lipid assembly, we built in vitro lipid models composed of major stratum corneum lipid subclasses containing either ω-O-acylCer (healthy skin model), ω-OHCer (Pnpla1-/- model), or combination of the two. X-ray diffraction, infrared spectroscopy, and permeability studies indicated that ω-OHCers could not substitute for ω-O-acylCers, although in favorable conditions, they form a medium lamellar phase with a 10.8 nm-repeat distance and permeability barrier properties similar to long periodicity lamellar phase. In the absence of ω-O-acylCers, skin lipids were prone to separation into two phases with diminished barrier properties. The models combining ω-OHCers with ω-O-acylCers indicated that accumulation of ω-OHCers does not prevent ω-O-acylCer-driven lamellar stacking. These data suggest that ω-O-acylCer supplementation may be a viable therapeutic option in patients with PNPLA1 deficiency.

• Keywords
• PNPLA1 deficiency, Skin, acylceramides, barrier function, ceramides, linoleic acid, lipids, model membranes, sphingolipids, stratum corneum,
• MeSH
• Acyltransferases MeSH
• Ceramides * chemistry   MeSH
• Epidermis MeSH
• Ichthyosis MeSH
• Skin * MeSH
• Linoleic Acid MeSH
• Lipase MeSH
• Mice MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Acyltransferases MeSH
• Ceramides * MeSH
• Linoleic Acid MeSH
• Lipase MeSH
• PNPLA1 protein, mouse MeSH Browser

Desulfation of cholesterol sulfate (CholS) to cholesterol (Chol) is an important event in epidermal homeostasis and necessary for stratum corneum (SC) barrier function. The CholS/Chol ratio decreases during SC maturation but remains high in pathological conditions, such as X-linked ichthyosis, characterized by dry and scaly skin. The aim of this study was to characterize the influence of the CholS/Chol molar ratio on the structure, dynamics, and permeability of SC lipid model mixtures. We synthesized deuterated CholS and investigated lipid models with specifically deuterated components using 2H solid-state NMR spectroscopy at temperatures from 25°C to 80°C. Although the rigid acyl chains in ceramides and fatty acids remained essentially rigid upon variation of the CholS/Chol ratio, both sterols were increasingly fluidized in lipid models containing higher CholS concentrations. We also show the X-ray repeat distance of the lipid lamellar phase (105 Å) and the orthorhombic chain packing of the ceramide's acyl chains and long free fatty acids did not change upon the variation of the CholS content. However, the Chol phase separation visible in models with high Chol concentration disappeared at the 50:50 CholS/Chol ratio. This increased fluidity resulted in higher permeabilities to model markers of these SC models. These results reveal that a high CholS/Chol ratio fluidizes the sterol fraction and increases the permeability of the SC lipid phase while maintaining the lamellar lipid arrangement with an asymmetric sterol distribution.

• Keywords
• ceramides, cholesterol, lipid packing, lipids, nanostructure, order parameter, permeability, skin, sterols,
• MeSH
• Ceramides chemistry   MeSH
• Cholesterol chemistry   MeSH
• Epidermis chemistry   MeSH
• Cholesterol Esters * MeSH
• Skin chemistry   MeSH
• Permeability MeSH
• Sterols * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Ceramides MeSH
• Cholesterol MeSH
• cholesteryl sulfate MeSH Browser
• Cholesterol Esters * MeSH
• Sterols * 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

The lipid phase of the uppermost human skin layer is thought to comprise highly rigid lipids in an orthorhombic phase state to protect the body against the environment. By synthesizing sphingosine-d28 deuterated N-lignoceroyl-d-erythro-sphingosine (ceramide [NS]), we compare the structure and dynamics of both chains of that lipid in biologically relevant mixtures using X-ray diffraction, 2 H NMR analysis, and infrared spectroscopy. Our results reveal a substantial fraction of sphingosine chains in a fluid and dynamic phase state at physiological temperature. These findings prompt revision of our current understanding of the skin lipid barrier, where an extended ceramide [NS] conformation is preferred and a possible domain structure is proposed. Mobile lipid chains may be crucial for skin elasticity and the translocation of physiologically important molecules.

• Keywords
• NMR spectroscopy, chain conformation, lipids, membranes, nanostructure,
• MeSH
• Ceramides chemistry   MeSH
• Cholesterol chemistry   MeSH
• Deuterium chemistry   MeSH
• Skin chemistry   metabolism   MeSH
• Humans MeSH
• Magnetic Resonance Spectroscopy MeSH
• Nanostructures chemistry   MeSH
• Sphingosine chemistry   MeSH
• Spectrophotometry, Infrared MeSH
• Temperature MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Ceramides MeSH
• Cholesterol MeSH
• Deuterium MeSH
• 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

Membrane models of the stratum corneum (SC) lipid barrier, either healthy or affected by recessive X-linked ichthyosis, constructed from ceramide [Cer; nonhydroxyacyl sphingosine N-tetracosanoyl-d-erythro-sphingosine (CerNS24) alone or with omega-O-acylceramide N-(32-linoleyloxy)dotriacontanoyl-d-erythro-sphingosine (CerEOS)], FFAs(C16-24), cholesterol (Chol), and sodium cholesteryl sulfate (CholS) were investigated. X-ray diffraction (XRD) revealed a previously unreported polymorphism of the membranes. In the absence of CerEOS, the membranes formed a short lamellar phase (SLP; the repeat distance d = 5.3 nm), a medium lamellar phase (MLP; d = 10.6 nm), or very long lamellar phases (VLLP; d = 15.9 and 21.2 nm). An increased CholS-to-Chol ratio modulated the membrane polymorphism, although the CholS phase separated at ≥ 7 weight% (of total lipids). The presence of CerEOS led to the stable long lamellar phase (LLP) with d = 12.2 nm and prevented VLLP formation. Our XRD results agree well with recently published cryo-electron microscopy data for vitreous skin sections, while also revealing new structures. Thus, lamellar phases with long repeat distances (MLP and VLLP) may be formed in the absence of omega-O-acylceramide, whereas these ultralong Cer species likely stabilize the final SC lipid architecture of LLP by riveting the adjacent lipid layers.

• Keywords
• X-ray crystallography, ceramide, cholesterol, cholesteryl sulfate, extracellular matrix, membranes/model, skin, skin barrier,
• MeSH
• Models, Biological * MeSH
• Cryoelectron Microscopy MeSH
• Ichthyosis, X-Linked genetics   metabolism   pathology   MeSH
• Skin chemistry   metabolism   pathology   MeSH
• Humans MeSH
• Membrane Lipids chemistry   metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Membrane Lipids MeSH

UNLABELLED: Cystic fibrosis is the most common genetic disease, in which symptoms may be alleviated but not fully eliminated. Ceramides have long been implicated in the inflammatory etiology of cystic fibrosis, with contradicting reports with regards to their role. Recently, significant biological and biophysical differences have been observed between long- and very long-chain ceramides. This work reveals that long-chain ceramides are upregulated whereas very long-chain ceramides are downregulated in cell lines, mouse animal model, and patients with cystic fibrosis, compared with their controls. Treatment with fenretinide decreases the levels of long-chain ceramides and increases the levels of very long-chain ceramides. Our results show that restoration of cystic fibrosis conductance regulator (CFTR) expression is associated with normalization of aberrant levels of specific ceramides. This demonstrates for the first time a correlation between CFTR protein expression and regulation of specific ceramide levels. Furthermore, using cystic fibrosis lung epithelial cell lines, we demonstrate that this effect can be attributed to the transcriptional downregulation of ceramide synthase 5 (Cers5) enzyme. We also discovered a partial synergism between fenretinide and zinc (Zn2+), which deficiency has been reported in patients with cystic fibrosis. Overall, in addition to having direct translational application, we believe that our findings contribute to the understanding of ceramide metabolism in cystic fibrosis, as well as other inflammatory diseases where imbalances of ceramides have also been observed. KEY MESSAGES: Long- and very long-chain ceramides (LCCs and VLCCs) are biochemically distinct. LCCs are upregulated whereas VLCCs are downregulated in cystic fibrosis. Fenretinide downregulates the levels of LCCs and upregulates the levels of VLCCs. Fenretinide changes the balance of LCCs and VLCCs by downregulating Cers5 enzyme. Fenretinide and zinc ions cooperate in the modulation of ceramide levels.

• Keywords
• Ceramides, Cystic fibrosis, Fenretinide,
• MeSH
• Transcriptional Activation drug effects   MeSH
• Cell Line MeSH
• Ceramides analysis   blood   metabolism   MeSH
• Cystic Fibrosis blood   drug therapy   metabolism   MeSH
• Adult MeSH
• Down-Regulation drug effects   MeSH
• Fenretinide therapeutic use   MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Disease Models, Animal MeSH
• Mice, Inbred C57BL MeSH
• Mice, Knockout MeSH
• PPAR gamma agonists   MeSH
• Sphingosine N-Acyltransferase antagonists & inhibitors   genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Clinical Trial MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Ceramides MeSH
• CERS5 protein, human MeSH Browser
• Fenretinide MeSH
• PPAR gamma MeSH
• Sphingosine N-Acyltransferase MeSH