Donald F. Collins

Age‐dependent response of energy metabolism of human skin to UVA exposure: an in vivo study by 31P nuclear magnetic resonance spectroscopy

Purpose The aim of our study was to evaluate the in vivo energy metabolism of human skin as a function of age, in conditions of rest and after a mild stress caused by a suberythemal UVA irradiation.

Use of Reconstructed Skin Specimens to Analyze Stratum corneum Remodeling and Epidermal Modifications

The epidermis is the epithelial tissue lining the dermis. It is constituted of differentiating keratinocytes distributed in successive layers according to their degree of differentiation. It contains cycling cells with neurological, immune and sensorial functions, such as Langerhans cells, melanocytes, Swan cells, Merkel cells. The upper layers of the epidermis are constituted by fully differentiated corneocytes which constitute the stratum corneum or horny layer. The stratum corneum constitutes the interface between the body and the outside world. It modulates the exchanges of oxygen and water vapor with the environment. It harbors enzymes which contribute to its healthy maintenance. Some enzymes help the steady state renewal of the surface by cutting the inter-corneocyte bonds and allowing outer-layer corneocytes to be shed. Others catalyze the synthesis of factors of moisturization, such as urea. Other enzymes such as RNase fight viral infections while the colonization of the skin by film forming microorganisms is averted by proteases like trypsin and chymotrypsin. Defensins, specific peptides in the stratum corneum originating from sebaceous gland, exert an efficient anti-bacterial action. The stratum corneum reflects and refracts visible light and is thus partially responsible for the image of the individual in the eyes of the observer. When the stratum corneum is not in its optimal state, it is felt as conferring dryness, roughness, lack of flexibility, or general discomfort to the skin. Learning about the structure of the stratum corneum, and about ways to modify it to achieve a smooth, supple, flexible, extensible, translucent, shiny surface is one of the objects of surface biochemistry and of cosmetically-oriented scientific research. Reconstructed skin specimens can be prepared by mixing fibroblasts in a collagen suspension, allowing it to gellify and seeding keratinocytes on the top of it. Air exposed keratinocytes do differentiate and the cells can be kept alive for several days by feeding growth medium underneath the specimen (Prunieras et al, 1983). It is possible to explore the structure of the stratum corneum of reconstructed skin and to investigate the chemical or physical-chemical parameters which contribute to its structure. The absence of sebaceous glands, sweat glands, blood vessels or nervous endings makes it