• Skin barrier function is partly regulated by skin lipids
• Skin lipidomics can elucidate the relationships between skin lipidome and skin function
• Lipid profiles vary with depth, within and between humans
The most abundant lipids in the skin lipidome are ceramides, cholesterol, and free fatty acids. Triglycerides, diglycerides, and cholesteryl esters (another type of cholesterol lipids) are also commonly found in the skin. The skin’s lipid profile helps establish its barrier function; in particular, the lipidome regulates permeability to water and electrolytes. The lipidome also contributes to selection and promotion of a favorable skin microbiome.
Ceramide lipids, composed of a sphingoid base attached to a fatty acid, are critical to maintaining hydration in the skin. Changes in the relative abundance of the 12 ceramide subclasses in the skin have been linked to excessively oily or dry skin conditions. Accordingly, ceramides are of particular interest to researchers working in skin moisturizer research and development. The specialized roles of other lipid classes in skin barrier function remain under investigation.
The skin lipid profile is known to vary with factors like skin pigmentation, age, sex, season of the year, and certain skin conditions. These relationships have not been comprehensively characterized, but may affect skin barrier function.
Tape stripping for skin sampling: A skin sampling tape disc is placed on the respective body part and peeled off after a few seconds of pressure. Skin sticks to the tape, and its sebum lipids and stratum corneum lipids can be extracted for lipidomics analysis. Placing multiple tapes on the same spot at once can be used for quick triplicate sampling, and sequential tape stripping allows for skin depth analysis.
To address this gap, a collaborative study from researchers of Lipotype and University of Medicine, Wrocław characterized the lipid profile in skin samples from 104 individuals using mass spectrometry-based lipidomics. The results reveal how the skin lipidome varies with skin depth, within individuals, and between individuals.
Skin samples were collected from healthy volunteers using tape stripping. In brief, this method involved a 15 second application of a special tape to the site of interest followed by removal of the tape. The skin sample was then recovered from the tape and analyzed using a high-throughput shotgun mass spectrometry platform. This process was repeated: up to 20 times at the same site to assess the role of skin depth on the lipid profile; at multiple locations on the same individual to examine intra-individual variability; and from multiple individuals to evaluate inter-individual variability.
Impact of sampling depth on skin lipid composition: Lipidomics analysis of stratum corneum tape strips from female and male subjects. Drawn-through lines represent female skin lipid profiles, dashed lines represent male skin lipid profiles. A Means of total amounts of lipids measured in different layers. B Lipid profiles of lipid classes measured in different layers. Sadowski et al., Sci Rep (2017), doi: 10.1038/srep43761
The study revealed that both lipid composition and abundance depend on skin depth. Specifically, the lipid abundance decreases with increasing skin depth. The lipid composition also changes: the relative abundance of the glycerolipid classes triglycerides and diglycerides decreases, and that of cholesterol and ceramides increases, with increasing skin depth.
Impact of sampling site on skin lipid composition: Lipidomics analysis of stratum corneum tape strips from female and male subjects as means of total amounts of lipids measured in different sampling sites. Drawn-through lines represent female skin lipid profiles, dashed lines represent male skin lipid profiles. Sadowski et al., Sci Rep (2017), doi: 10.1038/srep43761
For a given person, the skin lipid profile is also highly dependent on location. Of the 14 skin sites sampled in this study, the lipid abundance was highest in skin on the face and lowest in skin on the heel. Further, skin on the face is enriched with triglycerides; a similar lipid composition is observed in samples from the neck and shoulder blades.
Impact of age on skin lipid composition: Lipidomics analysis of stratum corneum tape strips from female and male subjects. Lines represent 0-order polynomial smoothing function with 8 neighbors averaged. Drawn-through lines represent female skin lipid profiles, dashed lines represent male skin lipid profiles. A Means of total amounts of lipids measured in females and males at different age. B Lipid profiles of lipid classes of females and males of different age. Sadowski et al., Sci Rep (2017), doi: 10.1038/srep43761
The skin lipid profile is also influenced by both sex and age. In females, the total lipid content decreases with age. Simultaneously, the relative abundance of triglycerides and diglycerides decreases and that of cholesterol increases. Males exhibited a distinctive skin lipid profile with less pronounced changes in lipid composition with age. Interestingly enough, aging affects lipidomes of many organs, for example gut.
Overall, this study establishes the importance of skin depth and location, age, and sex on the skin lipid profile, a dynamic property that can regulate the organ’s function. However, how this inter- and intra-individual variability influences skin barrier function has yet to be fully elucidated. Future lipidomics-based studies may help reveal these connections; the subsequent results may serve as biomarkers of health and disease and inform skin product research and development.
Lipotype Skin Lipidomics technology can characterize the skin lipidome in small samples collected using non-invasive methods. These data describing lipid abundance and composition may be useful to researchers studying how drugs, environmental factors, the microbiome, cosmetics, and other factors affect keratinocytes and modulate skin function.
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The Wroclaw Medical University is one of the most renowned public medical schools in Poland and focuses on research in the fields of medicine, dentistry, pharmacy, and public health.
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