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Upon chronological aging, human skin undergoes structural and molecular modifications, especially at the level of type I collagen. This macromolecule is one of the main dermal structural proteins and presents several age-related alterations. It exhibits a triple helical structure and assembles itself to form fibrils and fibers. In addition, water plays an important role in stabilizing the collagen triple helix by forming hydrogen-bonds between collagen residues. However, the influence of water on changes of dermal collagen fiber orientation with age has not been yet understood. Polarized-Fourier Transform Infrared (P-FTIR) imaging is an interesting biophotonic approach to determine in situ the orientation of type I collagen fibers, as we have recently shown by comparing skin samples of different ages. In this work, P-FTIR spectral imaging was performed on skin samples from two age groups (35- and 38-year-old on the one hand, 60- and 66-year-old on the other hand), and our analyses were focused on the effect of H2O/D2O substitution. Spectral data were processed with fuzzy C-means (FCM) clustering in order to distinguish different orientations of collagen fibers. We demonstrated that the orientation was altered with aging, and that D2O treatment, affecting primarily highly bound water molecules, is more marked for the youngest skin samples. Collagen-bound water-related spectral markers were also highlighted. Our results suggest a weakening of water/collagen interactions with age. This non-destructive and label-free methodology allows us to understand better the importance of bound water in collagen fiber orientation alterations occurring with skin aging. Obtaining such structural information could find benefits in dermatology as well as in cosmetics.

During chronological skin aging, alterations in dermal structural proteins cause morphological modifications. Modifications are probably due to collagen fiber (type I collagen) rearrangement and reorientation with aging that have not been researched until now. FTIR microspectroscopy appears as an interesting method to study protein structure under normal and pathological conditions. Associated with a polarizer, this vibrational technique permits us to probe collagen orientation within skin tissue sections, by computing the ratio of integrated intensities of amide I and amide II bands. In this study, we used the polarized-FTIR imaging to evaluate molecular modifications of dermal collagen during chronological aging. The data processing of polarized infrared data revealed that type I collagen fibers become parallel to the skin surface in aged skin dermis. Our approach could find innovative applications in dermatology as well as in cosmetics.

BACKGROUND: During pathological and/or physiological processes, such as tumoral progression or aging, human skin undergoes molecular and structural changes mainly due to alterations of dermal structural proteins such as type I collagen. These modifications in dermis are probably due to collagen fibers rearrangement and reorientation which have not been thoroughly studied up to now. FT-IR (Fourier transform infrared) microspectroscopy associated to polarization measurement appears as an interesting method to determine in situ the alignment of type I collagen fibers.OBJECTIVE: In this paper, two different clustering algorithms were applied to determine different layers in human skin. Besides, we used polarized FT-IR imaging to evaluate the molecular organization of dermal collagen.METHODS: To do this, a cryosection of skin from 48-year-old woman was analyzed. Acquired FT-IR images were firstly processed using K-means and fuzzy C-means (FCM). FCM was chosen on polarized FT-IR images in order to highlight the molecular orientation of dermal collagen fibrils. The ratio of Amide I/Amide II bands integrated intensities was computed in order to assess the orientation of collagen fibrils.RESULTS AND CONCLUSION: This methodology permitted to reveal the potential of polarized FT-IR microspectroscopy for the characterization of type I collagen network in human skin. Our approach could help to find innovative applications in dermatology as well as in cosmetics. [ABSTRACT FROM AUTHOR]