Integral lipids of hair and stratum corneum

Antimicrobial Activity of Host-Derived Lipids

Host-derived lipids are increasingly recognized as antimicrobial molecules that function in innate immune activities along with antimicrobial peptides. Sphingoid bases and fatty acids found on the skin, in saliva and other body fluids, and on all mucosal surfaces, including oral mucosa, exhibit antimicrobial activity against a variety of Gram positive and Gram negative bacteria, viruses, and fungi, and reduce inflammation in animal models. Multiple studies demonstrate that the antimicrobial activity of lipids is both specific and selective. There are indications that the site of action of antimicrobial fatty acids is the bacterial membrane, while the long-chain bases may inhibit cell wall synthesis as well as interacting with bacterial membranes. Research in this area, although still sporadic, has slowly increased in the last few decades; however, we still have much to learn about antimicrobial lipid mechanisms of activity and their potential use in novel drugs or topical treatments. One important potential benefit for the use of innate antimicrobial lipids (AMLs) as antimicrobial agents is the decreased likelihood side effects with treatment. Multiple studies report that endogenous AML treatments do not induce damage to cells or tissues, often decrease inflammation, and are active against biofilms. The present review summarizes the history of antimicrobial lipids from the skin surface, including both fatty acids and sphingoid bases, in multiple human body systems and summarizes their relative activity against various microorganisms. The range of antibacterial activities of lipids present at the skin surface and in saliva is presented. Some observations relevant to mechanisms of actions are discussed, but are largely still unknown. Multiple recent studies examine the therapeutic and prophylactic uses of AMLs. Although these lipids have been repeatedly demonstrated to act as innate effector molecules, they are not yet widely accepted as such. These compiled data further support fatty acid and sphingoid base inclusion as innate effector molecules.

Effect of the multifunctional cosmetic ingredient sphinganine on hair loss in males and females with diffuse hair reduction

Sphingolipids are well known to promote keratinocyte differentiation and to induce ceramide production. In addition, they show anti-inflammatory and antimicrobial activities. Thus, the aim of this study is to investigate the potential effect of sphinganine on prolonging the hair anagen rate and improving the overall hair quality and scalp health. The inhibitory potential of sphinganine toward 5-α-reductase was studied using an in vitro assay. The stimulation of the antimicrobial peptide HBD2 by sphinganine was measured by real-time polymerase chain reaction and immunostaining. Sphinganine bioavailability was studied ex vivo using a pig skin model. A placebo-controlled, double-blind study was designed to evaluate the efficacy of sphinganine on hair loss and hair/scalp quality in vivo. In vitro results showed that sphinganine is a potent inhibitor of 5-α-reductase type I that prevents the conversion of testosterone to dihydrotestosterone, a key factor of androgenetic male baldness. In vivo results demonstrated efficacy in reducing non-illness-related hair loss among males. In terms of expert rating, all hair quality and scalp parameters improved after application of sphinganine. Improved scalp health might be linked to the observed increase of the antimicrobial peptide HBD2. Thus, sphinganine is well suited as a topical alternative for the improvement of scalp health and hair quality and anti-hair loss application.

Internal lipids of felted, yellowed and pathologically thin wool

The keratin fibers contain small amount of the internal lipids which are in free state or bound with fiber proteins via tioester of 18-methyleicosanoic acid. Today the origin of these lipids, their composition and functional properties are still not found. Therefore, our objective was to examine the content and composition of internal lipids in sheep's wool with different defects. We observed that regardless of the type of fibers defect there are significant changes especially in the quality composition of the internal lipids, although the total content of free and covalently bound lipids in all cases is practically identical. Notably, both free and covalently bound lipids composition of felted and simultaneously felted and yellowed wool is characterized by changes in contents mainly of free fatty acids and ceramides whereas abnormal thinning of fibers is accompanied only by a decrease of sulfolipids.

Properties of ceramides and their impact on the stratum corneum structure. Part 2: stratum corneum lipid model systems

The stratum corneum (SC) represents the outermost layer of the mammalian skin, exhibits the main skin barrier and plays an important role in the water penetration pathway through the SC. Knowing the structure and properties of the SC at the molecular level is essential for studying drug penetration through the SC and for the development of new dermal drug delivery systems. Therefore, research interest is focused on the SC lipid matrix and on water diffusion through it. Thus, the ultimate aim is to design a lipid mixture that mimics the barrier properties of the human SC to a high extent and that can substitute the SC in drug delivery systems. This review summarizes various studies performed on either isolated animal or human ceramide based SC model systems, coming to the result that using synthetic lipids with a well-defined architecture allows good extrapolation to the in vivo situation. This review is the continuation of part 1 that is focused on a detailed description of the thermotropic and/or lyotropic phase behaviour of single ceramide types obtained by various experimental techniques. The objective of part 2 is to reflect the numerous studies on SC lipid model systems, namely binary, ternary and multicomponent systems, during the last decade. In this context, neutron diffraction as a prospective tool for analyzing the internal membrane structure is addressed in particular. Based on these new insights, current SC models are presented, whose validations are still under discussion. A profound knowledge about SC lipid organization at the molecular level is still missing.

Investigation of human hair cuticle structure by microdiffraction: direct observation of cell membrane complex swelling

The cuticle of mammalian hair fibres protects the core of the fibre against physical and chemical stress. The structure and some of the properties of the cuticle have been extensively studied by electron microscopy. However, there is still a need for a less invasive structural probe. For this purpose, microdiffraction experiments have been carried out on human hair samples showing a characteristic small-angle X-ray scattering pattern for the cuticle. This pattern has been assigned to the cell membrane complex (CMC) between each cuticle scale. Using a simple model of the electron density within the CMC, values have been derived for the average thickness of the beta- and delta-layers which are close to those obtained by electron microscopy. In order to illustrate the potentialities of microdiffraction in studying the properties of the cuticle, the effect of water sorption has been monitored. Using the intensity modelling described above, a 10% swelling of the delta-layer's thickness has been observed. This study shows that structural modifications of the CMC by physical or chemical stress can be followed directly on the cuticle of human hair fibres by microdiffraction analysis.

A novel function for transglutaminase 1: attachment of long-chain omega-hydroxyceramides to involucrin by ester bond formation

Transglutaminases (TGases) are defined as enzymes capable of forming isopeptide bonds by transfer of an amine onto glutaminyl residues of a protein. Here we show that the membrane-bound form of the TGase 1 enzyme can also form ester bonds between specific glutaminyl residues of human involucrin and a synthetic analog of epidermal specific omega-hydroxyceramides. The formation of a approximately 5-nm-thick lipid envelope on the surface of epidermal keratinocytes is an important component of normal barrier function. The lipid envelope consists of omega-hydroxyceramides covalently linked by ester bonds to cornified envelope proteins, most abundantly to involucrin. We synthesized an analog of natural omega-hydroxyceramides N-[16-(16-hydroxyhexadecyl)oxypalmitoyl]sphingosine (lipid Z). When recombinant human TGase 1 and involucrin were reacted on the surface of synthetic lipid vesicles containing lipid Z, lipid Z was attached to involucrin and formed saponifiable protein-lipid adducts. By mass spectroscopy and sequencing of tryptic lipopeptides, the ester linkage formation used involucrin glutamine residues 107, 118, 122, 133, and 496 by converting the gamma-carboxamido groups to lipid esters. Several of these residues have been found previously to be attached to ceramides in vivo. Mass spectrometric analysis after acetonide derivatization also revealed that ester formation involved primarily the omega-hydroxyl group of lipid Z. Our data reveal a dual role for TGase 1 in epidermal barrier formation and provide insights into the pathophysiology of lamellar ichthyosis resulting from defects of TGase 1 enzyme.

In vitro reconstitution of stratum corneum lipid lamellae

In the final stages of differentiation in the epidermis of terrestrial mammals, lipids are extruded into the intercellular spaces. The initially extruded lipid becomes transformed into broad, multilamellar sheets that are found in the intercellular spaces throughout the stratum corneum. These lamellae display an unusual alternating broad-narrow-broad pattern of lucent bands as revealed by transmission electron microscopy (TEM). This arrangement results in two periodicities that can be measured from electron micrographs and are also evident in X-ray diffraction-5 nm (broad) and 13 nm (broad-narrow-broad). The goal of the present study was to reconstitute these lamellae in vitro. Porcine stratum corneum lipids were applied to Millipore filters. The disks were placed in water and heated to 80 degrees C for 1 h. After cooling, the disks were stored over desiccant. At each stage, the disks were prepared for TEM. TEM revealed that the application of the lipid solutions onto the disks resulted to deposition of mostly amorphous material. Heating in water resulted in the formation of many lamellae. The width of the lamellae was uniform and in the range of 5 to 6 nm with no broad-narrow-broad pattern; however, after storage under desiccating conditions, the broad-narrow-broad pattern was reproduced.