Lysosphingolipids in ceramide-deficient skin lipid models.

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.

Lipid Monolayer on Cell Surface Protein Templates Functional Extracellular Lipid Assembly.

When the ancestors of men moved from aquatic habitats to the drylands, their evolutionary strategy to restrict water loss is to seal the skin surface with lipids. It is unknown how these rigid ceramide-dominated lipids with densely packed chains squeeze through narrow extracellular spaces and how they assemble into their complex multilamellar architecture. Here it is shown that the human corneocyte lipid envelope, a monolayer of ultralong covalently bound lipids on the cell surface protein, templates the functional barrier assembly by partly fluidizing and rearranging the free extracellular lipids in its vicinity during the sculpting of a functional skin lipid barrier.

The intriguing molecular dynamics of Cer[EOS] in rigid skin barrier lipid layers requires improvement of the model.

Omega-O-acyl ceramides such as 32-linoleoyloxydotriacontanoyl sphingosine (Cer[EOS]) are essential components of the lipid skin barrier, which protects our body from excessive water loss and the penetration of unwanted substances. These ceramides drive the lipid assembly to epidermal-specific long periodicity phase (LPP), structurally much different than conventional lipid bilayers. Here, we synthesized Cer[EOS] with selectively deuterated segments of the ultralong N-acyl chain or deuterated or C-labeled linoleic acid and studied their molecular behavior in a skin lipid model.

Polymorphism, Nanostructures, and Barrier Properties of Ceramide-Based Lipid Films.

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.

Cholesterol sulfate fluidizes the sterol fraction of the stratum corneum lipid phase and increases its permeability.

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.

Effects of ()- and ()-α-Hydroxylation of Acyl Chains in Sphingosine, Dihydrosphingosine, and Phytosphingosine Ceramides on Phase Behavior and Permeability of Skin Lipid Models.

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 -C )/cholesterol, and a minor component, cholesteryl sulfate. Namely, Cers with ()-α-hydroxy lignoceroyl chains attached to sphingosine (Cer AS), dihydrosphingosine (Cer AdS), and phytosphingosine (Cer AP) were compared to their unnatural ()-diastereomers and to Cers with non-hydroxylated lignoceroyl chains attached to sphingosine (Cer NS), dihydrosphingosine (Cer NdS), and phytosphingosine (Cer NP).

Acidic pH Is Required for the Multilamellar Assembly of Skin Barrier Lipids In Vitro.

Lipid membrane remodeling belongs to the most fundamental processes in the body. The skin barrier lipids, which are ceramide dominant and highly rigid, must attain an unusual multilamellar nanostructure with long periodicity to restrict water loss and prevent the entry of potentially harmful environmental factors. Our data suggest that the skin acid mantle, apart from regulating enzyme activities and keeping away pathogens, may also be a prerequisite for the multilamellar assembly of the skin barrier lipids.

The Sphingosine and Acyl Chains of Ceramide [NS] Show Very Different Structure and Dynamics That Challenge Our Understanding of the Skin Barrier.

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-d 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, 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.

Behavior of 1-Deoxy-, 3-Deoxy- and N-Methyl-Ceramides in Skin Barrier Lipid Models.

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.

Effects of omega--acylceramide structures and concentrations in healthy and diseased skin barrier lipid membrane models.

Ceramides (Cers) with ultralong (∼32-carbon) chains and ω-esterified linoleic acid, composing a subclass called omega--acylceramides (acylCers), are indispensable components of the skin barrier. Normal barriers typically contain acylCer concentrations of ∼10 mol%; diminished concentrations, along with altered or missing long periodicity lamellar phase (LPP), and increased permeability accompany an array of skin disorders, including atopic dermatitis, psoriasis, and ichthyoses. We developed model membranes to investigate the effects of the acylCer structure and concentration on skin lipid organization and permeability.

Long and very long lamellar phases in model stratum corneum lipid membranes.

Membrane models of the stratum corneum (SC) lipid barrier, either healthy or affected by recessive X-linked ichthyosis, constructed from ceramide [Cer; nonhydroxyacyl sphingosine -tetracosanoyl-d--sphingosine (CerNS24) alone or with omega-acylceramide -(32-linoleyloxy)dotriacontanoyl-d--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 = 5.

Permeability and microstructure of cholesterol-depleted skin lipid membranes and human stratum corneum.

Cholesterol (Chol) is one of the major skin barrier lipids. The physiological level of Chol in the stratum corneum (SC) appears to exceed its miscibility with other barrier lipids, as some Chol is phase separated. Chol synthesis is essential for epidermal homeostasis, yet the role of these Chol domains in SC permeability is unknown.

DNA-DOPE-gemini surfactants complexes at low surface charge density: from structure to transfection efficiency.

DNA condensation, structure and transfection efficiency of complexes formed by gemini surfactants alkane-α,ω-diyl-bis(dodecyldimethylammonium bromide)s (CnGS12, n = 3, 6 and 12 is the number of alkane spacer carbons), dioleoylphosphatidylethanolamine (CnGS12/DOPE = 0.3 mol/mol) and DNA at low surface charge density were investigated through different techniques. Small angle X-ray diffraction showed a condensed lamellar phase with marked dependence of DNA-DNA distance on (+/-) charge ratio.

Probing the role of ceramide hydroxylation in skin barrier lipid models by H solid-state NMR spectroscopy and X-ray powder diffraction.

In this work, we studied model stratum corneum lipid mixtures composed of the hydroxylated skin ceramides N-lignoceroyl 6-hydroxysphingosine (Cer[NH]) and α-hydroxylignoceroyl phytosphingosine (Cer[AP]). Two model skin lipid mixtures of the composition Cer[NH] or Cer[AP], N-lignoceroyl sphingosine (Cer[NS]), lignoceric acid (C24:0) and cholesterol in a 0.5:0.

Effects of Ceramide and Dihydroceramide Stereochemistry at C-3 on the Phase Behavior and Permeability of Skin Lipid Membranes.

Ceramides (Cer) are key components of the skin permeability barrier. Sphingosine-based CerNS and dihydrosphingosine-based CerNdS (dihydroCer) have two chiral centers; however, the importance of the correct stereochemistry in the skin barrier Cer is unknown. We investigated the role of the configuration at C-3 of CerNS and CerNdS in the organization and permeability of model skin lipid membranes.

Permeability Barrier and Microstructure of Skin Lipid Membrane Models of Impaired Glucosylceramide Processing.

Ceramide (Cer) release from glucosylceramides (GlcCer) is critical for the formation of the skin permeability barrier. Changes in β-glucocerebrosidase (GlcCer'ase) activity lead to diminished Cer, GlcCer accumulation and structural defects in SC lipid lamellae; however, the molecular basis for this impairment is not clear. We investigated impaired GlcCer-to-Cer processing in human Cer membranes to determine the physicochemical properties responsible for the barrier defects.

Permeability and microstructure of model stratum corneum lipid membranes containing ceramides with long (C16) and very long (C24) acyl chains.

The Stratum corneum (SC) prevents water loss from the body and absorption of chemicals. SC intercellular spaces contain ceramides (Cer), free fatty acids (FFA), cholesterol (Chol) and cholesteryl sulfate (CholS). Cer with "very long" acyl chains (for example, N-lignoceroyl-sphingosine, CerNS24) are important for skin barrier function, whereas increased levels of "long" acyl Cer (for example, N-palmitoyl-sphingosine, CerNS16) occur in patients suffering from atopic eczema or psoriasis.

Effects of 6-Hydroxyceramides on the Thermotropic Phase Behavior and Permeability of Model Skin Lipid Membranes.

Ceramides (Cer) based on 6-hydroxysphingosine are important components of the human skin barrier, the stratum corneum. Although diminished concentrations of 6-hydroxyCer have been detected in skin diseases such as atopic dermatitis, our knowledge on these unusual sphingolipids, which have only been found in the skin, is limited. In this work, we investigate the biophysical behavior of N-lignoceroyl-6-hydroxysphingosine (Cer NH) in multilamellar lipid membranes composed of Cer/free fatty acids (FFAs) (C16-C24)/cholesterol/cholesteryl sulfate.

Stimuli responsive polymorphism of C12NO/DOPE/DNA complexes: Effect of pH, temperature and composition.

N,N-dimethyldodecylamine-N-oxide (C12NO) is a surfactant that may exist either in a neutral or cationic protonated form depending on the pH of aqueous solutions. Using small angle X-ray diffraction (SAXD) we observe the rich structural polymorphism of pH responsive complexes prepared due to DNA interaction with C12NO/dioleoylphosphatidylethanolamine (DOPE) vesicles and discuss it in view of utilizing the surfactant for the gene delivery vector of a pH sensitive system. In neutral solutions, the DNA uptake is low, and a lamellar Lα phase formed by C12NO/DOPE is prevailing in the complexes at 0.

Different phase behavior and packing of ceramides with long (C16) and very long (C24) acyls in model membranes: infrared spectroscopy using deuterated lipids.

Ceramides (Cer) are the central molecules in sphingolipid metabolism that participate in cellular signaling and also prevent excessive water loss by the skin. Previous studies showed that sphingosine-based Cer with a long 16C chain (CerNS16) and very long 24C-chain ceramides (CerNS24) differ in their biological actions. Increased levels of long CerNS16 at the expense of the very long CerNS24 have been found in atopic dermatitis patients, and this change correlated with the skin barrier properties.

Effects of sphingomyelin/ceramide ratio on the permeability and microstructure of model stratum corneum lipid membranes.

The conversion of sphingomyelin (SM) to a ceramide (Cer) by acid sphingomyelinase (aSMase) is an important event in skin barrier development. A deficiency in aSMase in diseases such as Niemann-Pick disease and atopic dermatitis coincides with impaired skin barrier recovery after disruption. We studied how an increased SM/Cer ratio influences the barrier function and microstructure of model stratum corneum (SC) lipid membranes.

The role of the trans double bond in skin barrier sphingolipids: permeability and infrared spectroscopic study of model ceramide and dihydroceramide membranes.

Dihydroceramides (dCer) are members of the sphingolipid family that lack the C4 trans double bond in their sphingoid backbone. In addition to being precursors of ceramides (Cer) and phytoceramides, dCer have also been found in the extracellular lipid membranes of the epidermal barrier, the stratum corneum. However, their role in barrier homeostasis is not known.

Study of interaction of long-chain n-alcohols with fluid DOPC bilayers by a lateral pressure sensitive fluorescence probe.

The excimer 1,2-dipyrenedecanoyl-sn-glycero-3-phosphatidylcholine (dipy10PC) fluorescence probe was used to determine effects of aliphatic alcohols (CnH2n+1OH, n = 12-18 is the even number of carbons in alkyl chain) on fluid dioleoylphosphatidylcholine (DOPC) +dioleoylphosphatidylserine (DOPS) bilayers in multilamellar vesicles at molar ratio DOPC/DOPS = 24.7. The excimer to monomer fluorescence intensity ratio increases with the increase of CnH2n+1OH/DOPC molar ratio and decreases with the CnH2n+1OH alkyl chain length n at a constant CnH2n+1OH/DOPC = 0.

The microstructure of DNA-egg yolk phosphatidylcholine-gemini surfactants complexes: effect of the spacer length.

Background: The length of spacer of gemini surfactants affects the DNA packing in DNA-neutral phospholipid-gemini surfactant complexes.

Methods: The microstructure of complexes DNA-egg yolk phosphatidylcholine (EYPC)-alkane-α,ω-diyl-bis(dodecyl\xaddimethylammonium bromides) (CnGS, spacer n=2-12, n is even) was studied using small angle X-ray diffraction.

Results: At EYPC:CnGS=1:1 mol/mol, the condensed lamellar phase was identified in complexes with CnGS, n=2-4, whereas longer spacer (n≥6) induced a hexagonal phase.