In vitro and in vivo confocal Raman study of human skin hydration: assessment of a new moisturizing agent, pMPC.

The hydration capacities of a biomimetic polymer, 2-methacryloyloxethylphosphorylcholine polymer (pMPC), alone and microencapsulated, in association with another well known hydrating polymer, Hyaluronic acid, were investigated in vitro on skin models and in vivo on volunteers by using confocal Raman microspectroscopy. The hydration impact and the relative water content in the Stratum corneum were calculated from the Raman spectra using the OH (water)/CH3 (protein) ratio. Moreover, the follow-up of the presence of pMPC through the Stratum corneum was possible with confocal Raman microspectroscopy, using a characteristic vibration of pMPC, different from that of the encapsulating material. From our in vitro measurements, the improved hydration of the Stratum corneum was confirmed by the use of the encapsulated form of pMPC, which was higher when combined with Hyaluronic acid. On the basis of these in vitro findings, we validated this trend in in vivo measurements on 26 volunteers, and found a good correlation with the in vitro results. Mechanical and ultrastructural studies have been carried out to demonstrate the positive effects of the pMPC on the Stratum corneum function, namely the interaction with lamellar lipids and the plasticizing effects, which are both supposed to spell out the moisturizing effect. This study demonstrates the efficiency of a original hydrating agent, pMPC, entrapped with Hyaluronic acid in a new type of microcapsules by the use of a novel tool developed for both in vitro and in vivo approaches. This indicates a new step to evaluate and improve new moisturizers in response to the cosmetics or dermatologic demands.

Ultrastructure of the human stratum corneum.

The ultrastructural study of the intercellular spaces of the human stratum corneum was based on transmission electron microscopy of thin vertical sections and freeze-fracture replicas, field emission scanning electron microscopy and immunofluorescence confocal laser scanning microscopy. The maturation of the corneosomes and their enzymatic degradation could be depicted at strategic interfaces. These sharp and rapid metamorphoses are now relatively well understood from a morphological point of view. But morphology raises a lot of unsolved physiological problems.

Persistence of both peripheral and non-peripheral corneodesmosomes in the upper stratum corneum of winter xerosis skin versus only peripheral in normal skin.

To understand the biochemical abnormalities that underlie the reduced desquamation observed in dry skin, we analyzed corneodesmosome degradation in normal and winter xerosis skin. Western blotting of total proteins from corneocytes obtained by varnish-strippings from the legs of 56 volunteers with normal (26) or xerotic (30) skin was performed using antibodies specific for (corneo)desmosome proteins. In the whole population, the amounts of desmoglein 1 and plakoglobin were found to be correlated, but were not related to the amounts of corneodesmosin. This suggests simultaneous proteolysis for the former proteins differing from that of corneodesmosin. Neither entire desmoplakins nor any proteolysis-derived fragments were detected. The amounts of corneodesmosin, desmoglein 1, and plakoglobin detected were found to be significantly higher in xerotic compared with normal skin extracts. Conventional and freeze-fracture electron microscopy showed the absence of nonperipheral corneodesmosomes in the upper stratum corneum of normal skin but the presence of a significant number of these structures in the same layer of winter xerosis skin. These results provide a more precise description of the proteolysis of corneodesmosome components in the upper cornified layer of the epidermis. They support previous studies demonstrating the importance of corneodesmosome degradation in desquamation and reveal that the nonperipheral corneodesmosomes, which are totally degraded during maturation of the stratum corneum in normal skin, persist in winter xerosis, probably leading to abnormal desquamation.

Cryo-techniques applied to stratum corneum with description of a new sample holder for cryo-scanning electron microscopy of freeze-fractured samples.

Stratum corneum structure greatly differs from that of the living epidermis and specific sample cryo-preparation techniques have to be used. Practical aspects of these cryo-techniques applied to stratum corneum are discussed. Emphasis is placed on scanning electron microscopy of cryo-fixed samples. A new sample holder designed for cryo-scanning electron microscopy of freeze-fractured stratum corneum is described.