Individual variation of human plantar stratum corneum lipids, determined by automated multiple development of high-performance thin-layer chromatography plates

Role of the liver X receptors in skin physiology: Putative pharmacological targets in human diseases

Liver X receptors (LXRs) are members of the nuclear receptor superfamily that have been shown to regulate various physiological functions such as lipid metabolism and cholesterol homeostasis. Concordant reports have elicited the possibility to target them to cure many human diseases including arteriosclerosis, cancer, arthritis, and diabetes. The high relevance of modulating LXR activities to treat numerous skin diseases, mainly those with exacerbated inflammation processes, contrasts with the lack of approved therapeutic use. This review makes an assessment to sum up the findings regarding the physiological roles of LXRs in skin and help progress towards the therapeutic and safe management of their activities. It focuses on the possible pharmacological targeting of LXRs to cure or prevent selected skin diseases.

Preparation and Characterization of Stealth Archaeosomes Based on a Synthetic PEGylated Archaeal Tetraether Lipid

The present studies were focused on the formation and characterization of sterically stabilized archaeosomes made from a synthetic PEGylated archaeal lipid. In a first step, a synthetic archaeal tetraether bipolar lipid was functionalized with a poly(ethylene glycol), PEG, and (PEG(45)-Tetraether) with the aim of coating the archaeosome surface with a sterically stabilizing hydrophilic polymer. In a second step, Egg-PC/PEG(45)-Tetraether (90/10 wt%) archaeosomes were prepared, and their physicochemical characteristics were determined by dynamic light scattering (size, polydispersity), cryo-TEM (morphology), and by high-performance thin layer chromatography (lipid composition), in comparison with standard Egg-PC/PEG(45)-DSPE formulations. Further, a fluorescent dye, the carboxyfluorescein, was encapsulated into the prepared archaeosomes in order to evaluate the potential of such nanostructures as drug carriers. Release studies have shown that the stability of Egg-PC/PEG(45)-Tetraether-based archaeosomes is significantly higher at 37°C than the one of Egg-PC/PEG(45)-DSPE-based liposomes, as evidenced by the slower release of the dye encapsulated into PEGylated archaeosomes. This enhanced stability could be related to the membrane spanning properties of the archaeal bipolar lipid as already described with natural or synthetic tetraether lipids.

Lipid analysis by thin-layer chromatography--a review of the current state

High-performance thin-layer chromatography (HPTLC) is a widely used, fast and relatively inexpensive method of separating complex mixtures. It is particularly useful for smaller, apolar compounds and offers some advantages over HPLC. This review gives an overview about the special features as well as the problems that have to be considered upon the HPTLC analysis of lipids. The term "lipids" is used here in a broad sense and comprises fatty acids and their derivatives as well as substances related biosynthetically or functionally to these compounds. After a short introduction regarding the stationary phases and the methods how lipids can be visualized on an HPTLC plate, the individual lipid classes will be discussed and the most suitable solvent systems for their separation indicated. The focus will be on lipids that are most abundant in biological systems, i.e. cholesterol and its derivates, glycerides, sphingo- and glycolipids as well as phospholipids. Finally, a nowadays very important topic, the combination between HPTLC and mass spectrometric (MS) detection methods will be discussed. It will be shown that this is a very powerful method to investigate the identities of the HPTLC spots in more detail than by the use of common staining methods. Future aspects of HPTLC in the lipid field will be also discussed.

Separation and mass spectrometric characterization of covalently bound skin ceramides using LC/APCI-MS and Nano-ESI-MS/MS

Ceramides covalently bound to keratinocytes are essential for the barrier function of the skin, which can be disturbed in diseases, such as psoriasis and atopic dermatitis. These ceramides of the classes omega-hydroxyacyl-sphingosine and omega-hydroxyacyl-6-hydroxysphingosine contain an omega-hydroxy fatty acid. For their separation and identification, a new analytical approach based on normal phase liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry and tandem nano-electrospray mass spectrometry, respectively, is presented here. Tandem mass spectrometry provided structural information about the sphingoid base as well as the fatty acid moieties. The chain lengths of the bases ranged from C12 to C22, the chain lengths of the fatty acids varied between C28 and C36. In total, 67 ceramide species have been identified in human skin. The analytical methods presented in this work can be helpful for investigating alterations in the ceramide composition of the skin as seen in psoriasis, atopic dermatitis, and diseases with impaired epidermal barrier function.

Microanalytical systems for separations of stratum corneum ceramides

The small amount of lipids from human skin obtained with noninvasive sampling method led us to investigate microanalytical separation techniques. The lipid class analysis was performed with a micro polyvinyl alcohol-silica (PVA-Sil) column. The gradient elution was from heptane to acetone/butanol 90:10 v/v in 4%/min at 78 microL/min. In addition an evaporative light scattering detector (ELSD) was modified for micro-LC. All solvents contained 0.1% of triethylamine and formic acid in stoichiometric amount, which increased the ELSD response. In these conditions, the cholesterol eluted before free fatty acid, and squalene and triglycerides close to the dead volume. The various ceramide classes eluted following the order of the increased number of hydroxyl groups. The LOD for ceramides was 2.2 ng. The advantages of this method are the use of a normal stationary phase more reliable due to its chemical stability, its surface homogeneity and its development in microchromatography without chlorinated solvents which offers small LOD and the whole profile of lipids present in stratum corneum (SC). A method using a narrow-bore PVA-Sil column was used to collect ceramide fraction. Then the molecular species were analysed with a porous graphitic carbon column in capillary LC using a gradient from CH3OH/CHCl3 70:30 v/v to CHCl3 at 2%/min with a flow rate at 5 microL/min. The LOD obtained for ceramide was 1 ng. Both methods were assessed with SC samples obtained by rinsing a 5.7 cm2 area of the forearm with 25 mL of ethanol.

Profiling of human stratum corneum ceramides by means of normal phase LC/APCI–MS

The ceramides of the stratum corneum are critical to maintaining the epidermal barrier function of the skin. A number of skin diseases and disorders are known to be related to impairments of the ceramide pattern. Therefore, obtaining mass spectrometric profiles of the nine ceramide classes known to exist aids our understanding of the underlying molecular mechanisms, which should eventually lead to new diagnostic opportunities: for example, the mass spectrometric profiles of patients suffering from serious skin diseases such as atopic dermatitis and psoriasis can be compared to those of healthy controls. Previous work on mass spectrometric analysis of ceramides relied mostly on GC/MS after hydrolysis and derivatization. The introduction of ESI-MS and LC/ESI-MS has provided new options for directly analyzing intact ceramides. However, some of the ceramide classes are not accessible to ESI-MS. However, as shown in this work, these limitations of GC/MS and ESI-MS can be overcome using a new approach based on normal phase LC interfaced with APCI-MS. Separation and online detection of the stratum corneum ceramide classes became possible in one run. Ceramide species with C26 and/or C28 fatty acid chains were the most abundant ones in Cer [NP], Cer [NH], Cer [AP], and Cer [AH]. The main component of Cer [AS] was C16. The omega-esterified ceramide classes Cer [EOS], Cer [EOP] and Cer [EOH] contained mostly species with fatty acids >C30. This was also the case for Cer [NS], suggesting an analogy to the omega-esterified ceramides. In addition, evidence for a new ceramide class Cer [NdS] was found.

Ceramide profiles of the uninvolved skin in atopic dermatitis and psoriasis are comparable to those of healthy skin

Ceramides are sphingolipids consisting of sphingoidbases, which are amide-linked to fatty acids. In the stratum corneum, they represent the major constituent of the free extractable intercellular lipids and play a significant role in maintaining and structuring the water permeability barrier of the skin. Using thin layer chromatography, which represents the method of the first choice in analyzing the stratum corneum ceramides, at least seven classes can be distinguished. Each ceramide class contains various species, which have the same head group and different chain lengths. As in many other skin disorders, atopic dermatitis and psoriasis show derangements in content and profile of the ceramides. Such derangements were reported for both the lesional involved as well as for the normal-appearing uninvolved skin. In this study, we focused on investigating the stratum corneum ceramides of the uninvolved skin in atopic dermatitis and psoriasis patients compared to healthy skin. The aim of the investigations was to explore possible significant and specific differences which can be accomplished for purposes of early diagnostics. The skin lipids were collected by means of an in vivo topical extraction procedure using an extraction mixture consisting of n-hexane and ethanol, (2:1). An automated multiple development-high performance thin layer chromatography (AMD-HPTLC) method with photodensitometric detection were applied to separate the ceramides and to estimate their contents. For studying their molecular profile within each ceramide class, a new method of normal phase HPLC with atmospheric pressure chemical ionization mass spectrometry were used. The results obtained by AMD-HPTLC exposed no significant alterations regarding the relative composition of the major stratum corneum lipids and primarily the ceramides. In addition, the mass spectrometric profiles within each ceramide class were similar in the patients and the healthy control subjects. In conclusion, this study revealed that the normal-appearing uninvolved skin of atopic dermatitis and psoriasis patients does not prove significant or specific deficiencies with respect to the free extractable major stratum corneum lipids and mainly the ceramides, when compared to healthy skin. Thus, they cannot be used for diagnostic purposes. Furthermore, our data are not consistent with the concept that impairments in the ceramide composition represent an obligate etiologic factor for both diseases.

Analysis of epidermal lipids of the healthy human skin: factors affecting the design of a control population

The intervariability of studies on the lipids of human epidermis and stratum corneum is high because of the different origin of the skin samples and the variety of extraction methods used. In the present work, a high-performance thin-layer chromatographic technique has been used to study the parameters age, sex, and anatomical site for their effects on the lipid profiles recovered from healthy epidermal skin biopsy specimens. It was found that sex-related differences were seen at the level of the total ceramide concentration. Observed decreases in lipid concentration, due to ageing, depended on the anatomical site. Therefore, these variables should be controlled in a reproducible and standardized way in order to be able to study the direct relationship between skin condition and barrier lipid composition. Only when this relation is established, results of topical treatment can be scientifically evaluated.

Thin-layer chromatography: challenges and opportunities

The purpose of this article is to identify core technologies with the potential to influence the development of thin-layer chromatography over the next decade or so. Core technologies are identified as: (i) methods to provide a constant and optimum mobile phase velocity (forced flow and electroosmotically-driven flow), (ii) video densitometry for recording multidimensional chromatograms, (iii) in situ scanning mass spectrometry, and (iv) bioactivity monitoring for selective detection. In combination with two-dimensional, multiple development and coupled column-layer separation techniques these core technologies could dramatically increase the use of thin-layer chromatography for the characterization of complex mixtures. It is also demonstrated that thin-layer chromatography has strong potential as a surrogate chromatographic model for estimating biopartitioning properties. To convert these opportunities into practice the current state-of-the-art of the core technologies is described and the principle obstacles to progress identified.

On-line solid-phase extraction of ceramides from yeast with ceramide III imprinted monolith

A molecularly imprinted polymeric monolith (MIPM) was prepared by in situ polymerization using styrene, glycidyl methacrylate and methacrylic acid as monomers, divinylbenzene and triallyl isocyanurate as cross-linking agents, and ceramide III as print molecule. The texture, pore size distribution, mobile phase flow characteristic, and chromatographic performance of the MIPM and a control monolith synthesized without the print molecule were examined, respectively. The results showed that using ceramide III as print molecule significantly affected the pore structure and pore distribution of the monolith, and greatly improved the retention of ceramide III and its analogues used in cosmetics as well. The retention of ceramide III on the MIPM could be reduced by increasing the ratio of chloroform to hexane in eluting buffer. The workability of the MIPM was firstly demonstrated through the separation of a model lipid mixture containing ceramide III and ergosterol, the main sterol impurity in yeast lipid extracts. The application of the ceramide III imprinted monolith to the isolation of ceramides from yeast lipid extracts was attempted and resulted in a considerable enrichment of ceramides, as shown by FIIR analysis. This indicates the potential of ceramide III imprinted monolith synthesized in the present study in the on-line solid-phase extraction of ceramides from yeast.

Improved procedure for the separation of major stratum corneum lipids by means of automated multiple development thin-layer chromatography

The separation of the major stratum corneum lipids, i.e., ceramides, fatty acids, cholesterol and its esters by means of high-performance thin-layer chromatography is hereby presented. The used automated multiple development technique allows the reproducible development of a 17-step solvent gradient also capable of separating seven ceramide classes in the same run. Reliable quantification has been performed after visualisation and densitometric scanning. The present approach is less time and solvent-consuming than previously described procedures. The application to samples obtained by in vivo skin surface extraction with hexane-ethanol (2:1) demonstrates that the method can be routinely used for diagnostic purposes.

Chromatographic analysis of plant sterols in foods and vegetable oils

This paper reviews recently published chromatographic methods for the analysis of plant sterols in various sample matrices with emphasis on vegetable oils. An overview of structural complexities and biological/nutritional aspects including hypocholesterolemic activities of phytosterols is provided in the Section 1. The principal themes of the review highlight the development and application of chromatographic techniques for the isolation, purification, separation and detection of the title compounds. Pertinent gas chromatographic and high-performance liquid chromatographic methods from the literature are tabulated to illustrate common trends and methodological variability. The review also covers specific analyses of natural/synthetic standard mixtures to shed light on potential applicability in plant sample assays. Examples of combined chromatographic techniques linked in tandem for the analysis of complex samples are included. Elution characteristics of sterol components are discussed in the context of analyte substituent effects, structural factors and stationary/mobile phase considerations.

Planar chromatography at the turn of the century

An overview of the state-of-the-art of modern thin-layer chromatography (planar chromatography) is presented with emphasis on the complementary features of thin-layer and column liquid chromatographic separations. The reasons for selecting thin-layer chromatography for a particular analysis are identified by its attributes: a disposable stationary phase; simultaneous parallel separations; static detection free of time constraints; storage device for chromatographic information; all sample components are observed in the chromatogram. Future prospects for improved separation performance in TLC using zone refocusing, forced flow and electroosmotic flow methods are discussed as well as increasing zone capacity by using two-dimensional development and coupling to column chromatographic methods. Advances in coupling thin-layer chromatography with spectroscopic methods for structural elucidation are also considered. Finally, some predictions are made for how thin-layer chromatography will be practiced in the future.

Quantification of lipids, liposomes, amino acids, and proteins by thermal ultramicrodigestion and an ultramicrocoulometric assay, based on the reaction of hypobromite with ammonia

The quantification of nitrogen in organic material is described. It is based on a novel thermal ultramicrodigestion in combination with an ultramicrocoulometric quantification. The lower detection limit of the coulometric measurement is 0.5 microg nitrogen, which corresponds to 20 microg lipid, 3 microg glycine, or 4 microg protein. Therefore it is as sensitive as the frequently used Lowry method. In contrast to the Lowry protein determination it is not disturbed by detergents and most other interfering substances.

Reconstructed human skin as model for liposome-skin interaction

Reconstructed human skin was prepared from human keratinoblasts. After 1 week of cultivation at the air-liquid interface a stratified layer developed, similar to native human epidermis. Liposomes with an average diameter of 50 nm, made of phosphatidylcholine (PC), phosphatidylserine (PS) and human stratum corneum lipids (hSCL) were applied on top of this culture system. The rate of penetration through the reconstructed human epidermis was 1.38, 0.55 and 0.013 ng lipidh-1cm-2 for PC, hSCL and PS liposomes, respectively. Electron microscopy and confocal laser scanning microscopy showed that PS and hSCL liposomes aggregated at the skin surface, while PC liposomes remained homogeneously dispersed. Fluorescence measurements demonstrated that vesicles, made of native human stratum corneum lipids rapidly mixed with PS liposomes, weakly with hSCL liposomes and did not mix with PC liposomes.

Physicochemical characterisation of human stratum corneum lipid liposomes

Liposomes were prepared from an extract of all human stratum corneum lipids (hSCL) and characterised in terms of temperature and the presence of Ca2+ by different physicochemical methods. Vesicle aggregation and lateral phase separation were induced by divalent cations with Ca2+ being more efficient than Mg2+. At 24.1 degrees C, i.e. well below physiological temperatures the suspensions consisted of a lamellar phase and crystalline cholesterol. At and above 37 degrees C, this cholesterol surplus was dissolved in the hSCL membranes. However, melting of the hSCL was not completed up to 60 degrees C. The presence of Ca2+ (> or = 9 mM) induced lateral phase separation and fusion of vesicles into extended multilamellar lipid sheets (MLLS) at and above 32.5 degrees C. Upon a subsequent cooling cycle recrystallisation of cholesterol occurred within the MLLS. Finally, membrane mixing of hSCL liposomes with vesicles made of synthetic lipids was investigated. No mixing was observed between either of DPPE/oleic acid, DPPC/DPPE, DPPC/lyso-PC and hSCL liposomes. Mixtures of DPPC/cholesterol hemisuccinate showed a temperature-dependent membrane mixing behaviour, whilst hSCL liposomes and phosphatidylserine liposomes fused temperature-independently with hSCL liposomes.

Oxidative damage of human skin lipids. Dependence of lipid peroxidation on sterol concentration

Photoprotection against sunburn and associated irradiation-induced damages of the human skin is mainly attributed to the darkening of the biochrome melanin by its oxidation. Human skin lipids were examined for an additional protection by sterols. Lipid vesicles prepared from extracted human skin lipids as well as from mixtures of typical lipids of the stratum corneum were irradiated by UV light in the presence and absence of oxygen. The oxidative degradation of various lipids was measured by quantitative HPTLC, by the dichlorofluorescein fluorescent assay, by the thiobarbituric acid assay and a novel luminol-based chemiluminescence technique. Electron spin resonance was used to look for certain radical intermediates. The results indicate, that sterols, mainly free cholesterol, with their high concentration in the lipid barrier of the stratum corneum (up to 50 mol%) effectively compete with the peroxidation of other human skin lipids (ceramides and free fatty acids).