Vibrational microspectroscopy and imaging of molecular composition and structure during human corneocyte maturation

The outermost region of the epidermis, the stratum corneum (SC), provides an essential barrier to water loss and protects against exogenous substances. The functional integrity of the SC depends on a complex maturation and exfoliation process, which is often perturbed in skin diseases. The maturation of corneocytes isolated from different depths in healthy human SC was investigated using infrared (IR) spectroscopic imaging and Raman microscopy. Both IR and Raman spectral quality of individual corneocytes was high and revealed depth-dependent variations in molecular composition. Spectral changes were identified as arising from alterations in the concentration of the major constituents of natural moisturizing factor (NMF), important in maintaining SC hydration. A significant decrease in the concentration of NMF was observed for corneocytes isolated from superficial compared to deeper SC layers (layer 3 vs. layer 11, respectively). An IR parameter that measures the relative NMF concentration in corneocytes is introduced. The potential role of vibrational imaging to evaluate corneocyte composition and molecular structure in the treatment of NMF-related diseases is discussed.