Evaluation of dermal extracellular matrix and epidermal–dermal junction modifications using matrix‐assisted laser desorption/ionization mass spectrometric imaging, in vivo reflectance confocal microscopy, echography, and histology: effect of age and peptide applications

Summary This study was conducted to establish a new methodology for evaluating elements of dermal extracellular matrix ( ECM ), of epidermal–dermal junction ( EDJ ), and effects of molecules which can modulate their synthesis. This methodology is based on matrix‐assisted laser desorption/ionization mass spectrometric imaging ( MALDI ‐ MSI ). In vivo reflectance confocal microscopy ( in vivo RCM ) and echography were also used. Using immunohistochemistry methods on explants, age‐related modification data were obtained for selected dermal ECM and EDJ proteins (collagen I, collagen IV , collagen VII , collagen XVII , nidogen I, decorin/decorunt) and used as reference for MALDI ‐ MSI studies. A methodology was developed with MALDI ‐ MSI to map epidermis and dermis proteins. Then MALDI ‐ MSI was used to study age modifications. In vivo RCM and high‐frequency ultrasounds were used to evaluate ECM and EDJ undulation modifications caused by aging. Anti‐aging molecule evaluations were performed with a blend of palmitoyl oligopeptide and palmitoyl tetrapeptide‐7. Immunohistochemistry studies demonstrated that the selected proteins were found to be less abundant in aged group explants vs . young group except for decorin. MALDI ‐ MSI studies correlated the results obtained for decorin. In vivo RCM measurements indicated a decrease of EDJ undulation depth with age and ECM modifications in the upper part of dermis. Echography demonstrated that the peptide blend reduced subepidermal low‐echogenic band thickness and improved its density. In vivo RCM studies indicated that the peptides improved the ECM structure vs . placebo. This preliminary MALDI ‐ MSI study raised some technical difficulties that were overcome. Further studies will be conducted to identify more proteins and to demonstrate the interest of this method for cosmetic evaluations.