Human stratum corneum lipids: characterization and regional variations.

Area of Science:

• Biochemistry
• Dermatology
• Skin Physiology

Background:

• The stratum corneum lipids are critical for regulating skin barrier function and permeability.
• Human skin exhibits significant regional variations in permeability across different body sites.
• Understanding these lipid variations is key to explaining differences in skin barrier properties.

Purpose of the Study:

• To quantitatively analyze the total lipid concentration, major lipid species distribution, and fatty acid composition of human stratum corneum.
• To investigate the lipid variations across four distinct skin sites (abdomen, leg, face, sole) with known differences in permeability.
• To determine the relationship between stratum corneum lipid composition and regional skin permeability.

Main Methods:

• Stratum corneum lipids were extracted using the Bligh-Dyer method from four human skin sites.
• Lipid extracts were analyzed for total lipid concentration, distribution of lipid species (polar and neutral), and fatty acid profiles.
• Quantitative analysis was performed to compare lipid composition across the different skin sites.

Main Results:

• Statistically significant differences in total lipid weight were observed across the four skin sites, inversely proportional to their permeability.
• Cholesterol sulfate was found in higher concentrations (1-7%) than previously reported.
• Neutral lipids (60-80%), including free sterols and n-alkanes, predominated over sphingolipids (15-35%).
• The neutral lipid to sphingolipid ratio generally correlated with skin permeability, with higher neutral lipids associated with better barrier function.
• Variations in neutral lipid content, rather than sphingolipids, appear to underlie regional differences in skin permeability.

Conclusions:

• This study provides the first detailed, quantitative analysis of human stratum corneum lipids across different body sites.
• Regional variations in human skin permeability are associated with distinct differences in stratum corneum lipid composition.
• Neutral lipids, particularly free sterols and n-alkanes, play a significant role in determining the barrier properties of the human skin.