Near‐infrared Fourier transform Raman spectroscopic analysis of proteins, water and lipids in intact normal stratum corneum and psoriasis scales

Abstract:  Previous biochemical studies demonstrated differences in the structure of lipids in normal skin and psoriatic lesions. Raman spectroscopy provides a unique possibility of studying the molecular structure of proteins, lipids and water in intact skin. Near‐infrared Fourier transform Raman spectroscopy was used to study changes in molecular structure and conformation of proteins and lipids of stratum corneum in healthy persons and patients with psoriasis. In vitro Raman spectra were obtained from intact psoriatic scales in 11 patients and from normal stratum corneum of forearm, elbow and heel in a group of age‐matched healthy persons. The spectra of stratum corneum differed between psoriasis and normal skin but not between investigated regions. No major changes of lipid band positions in Raman spectra were found, but the crystalline lipid structure was disrupted in psoriatic scales (assessed as the ratio of the symmetric methylene C–H stretching‐mode intensities, Slat). Major spectral differences were seen in the molecular structure of the proteins. In the spectra of psoriatic scales, the peak position of the amide I band, in comparison with the normal skin, was shifted to higher wavenumbers, suggesting unfolding of proteins. Moreover, alterations in the disulfide stretch bonds of proteins were found in psoriasis scales, resulting in a less energetically favourable gauche–gauche–trans conformation (band around 520 cm−1). Psoriatic scales and normal stratum corneum did not statistically differ in their water content. The findings further define the molecular abnormalities in the stratum corneum in psoriasis.