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Chronic exposure to sunlight may induce skin damage such as photoaging and photocarcinogenesis. These harmful effects are mostly caused by ultraviolet-B (UVB) rays. Yet, less is known about the contribution of low UVB doses to skin damage. The aim of this study was to determine the tissue changes induced by repeated exposure to a suberythemal dose of UVB radiation. Human keratinocytes in monolayer cultures and in skin equivalent were irradiated daily with 8 mJ/cm2 of UVB. Then structural, ultrastructural, and biochemical alterations were evaluated. The results show that exposure to UVB led to a generalized destabilization of the epidermis structure. In irradiated skin equivalents, keratinocytes displayed differentiated morphology and a reduced capacity to proliferate. Ultrastructural analysis revealed, not only unusual aggregation of intermediate filaments, but also disorganized desmosomes and larger mitochondria in basal cells. UVB irradiation also induced the secretion of metalloproteinase-9, which may be responsible for degradation of type IV collagen at the basement membrane. DNA damage analysis showed that both single and repeated exposure to UVB led to formation of (6-4) photoproducts and cyclobutane pyrimidine dimers. Although the (6-4) photoproducts were repaired within 24 h after irradiation, cyclobutane pyrimidine dimers accumulated over the course of the experiment. These studies demonstrate that, even at a suberythemal dose, repeated exposure to UVB causes significant functional and molecular damage to keratinocytes, which might eventually predispose to skin cancer.

To evaluate the epidermal barrier function of in vitro reconstructed epidermis, we measured the penetration of estradiol and water across human keratinocytes cultured in defined medium (DM), in the presence of proliferative fibroblasts (pF) or conditioned medium derived from pF, at the air-liquid interface on synthetic porous membrane, noncoated or coated with laminin, fibronectin, type I collagen or type IV collagen. Ultrastructural analysis showed a well-developed stratum corneum whatever the culture conditions. The permeability of reconstructed epidermis in DM on a noncoated porous membrane was 5- to 10-fold higher than human native epidermis, with both tracers. No significant change in barrier function was observed whatever the culture conditions.

A series of the solid emulsion gels with the oil volume fraction in the range of 0-50% were synthesized through a polycondensation reaction between activated p-nitrophenyl carbonate poly(ethylene glycol) and protein-stabilized oil-in-water emulsions. The resultant structures were investigated in terms of swelling behavior, composition, morphology, mechanical and skin hydration properties. Solid emulsions gels share the properties of both hydrogel and emulsion. Similar to the classical hydrogel, the SEG swells in water up to equilibrium swelling degree, which decreases as the oil volume fraction increases, and comprises immobilized drops of protein-stabilized oil. The impregnation of the oil phase is found to reduce tensile stiffness of the material, but improves material's extensibility. The mechanical properties of the constructs (Young moduli in the range of 9-15 kPa and the elongation at break of 120-220%) are interpreted according to the "rule of elasticity mixture" that considers the elasticity of the composite material to be a sum of the contributions from individual components, i.e. hydrogel and dispersed oil drops. An idealized model that takes into account the history of the material preparation has been proposed to explain the improved extensibility of the constructs. The results of the mechanical tests, equilibrium swelling, and the skin hydration effect of the solid emulsion gels in vivo are discussed from the perspective of the biomedical applications of the solid emulsion gels, in particular, for the transdermal delivery of hydrophilic and lipophilic drugs.

Culture of keratinocytes on a noncoated porous synthetic membrane maintained at the air-liquid interface allows the establishment of a fibroblast/keratinocyte co-culture, without direct cell-cell contact between the two cellular layers. The influence of fibroblasts (proliferating, confluent or blocked by mitomycin C) on epidermization (i.e., expression of integrins and markers of epidermal differentiation) was studied by immunohistochemistry in two culture media. In the medium supplemented with FCS or Ultroser G and in the absence of fibroblasts, alpha 2, alpha 3, alpha 5 and alpha 6 subunits of integrins are expressed by the basal keratinocytes, except alpha 5 which does not appear with the medium supplemented with Ultroser G. During stratification, the alpha 3 subunit is the only one to persist on suprabasal cells and all the markers of epidermal differentiation studied (filaggrin, involucrin, transglutaminase, keratins K1/K10) are expressed at the 14th day of emerged culture. The presence of fibroblasts modifies the expression profile of integrins: when they are proliferative, the expression of alpha 2 and alpha 6 chains is delayed in the medium supplemented with FCS, and the alpha 6 chain is absent in the medium supplemented with Ultroser G; when they are confluent or blocked by mitomycin C, greater changes are observed only in the medium supplemented with Ultroser G and lead to inhibition or delay of the expression of alpha 2 and alpha 6.(ABSTRACT TRUNCATED AT 250 WORDS)