Assessment of the water content of the stratum corneum using a sorption-desorption test.

BACKGROUND/AIM: Various instruments based on electrical properties of the skin are currently used to assess the stratum corneum (SC) hydration state or water holding capacity. However, no direct relation with the quantity of water measured is provided. The objective of the present study was to calibrate the Corneometer, a device displaying electrical-capacitance-related values (which reflect the skin hydration state), and the amount and behaviour of the water taken up by the outer part of the SC during a sorption-desorption test. METHODS: The experiment was performed on the ventral forearms of 20 healthy volunteers after a rest in an environmentally controlled room. Corneometer and transepidermal water loss (TEWL) values were measured at intervals over the desorption process. The areas under the TEWL-versus-time curve provided the absolute amounts of residual sorbed water. RESULTS: The decrease kinetics of both signals after subtraction of prehydration values were very similar and bi-exponential, both showing a rapid, then a slower phase. The absolute amount of water taken up by the SC (hygroscopicity) and the two desorption rates were obtained. The Corneometer values were mono-exponentially related to the amount of water remaining within the SC. This allowed the in vivo calibration of the Corneometer in terms of absolute amount of water over the desorption range. CONCLUSION: The method may be used to calibrate in vivo other electrical devices aimed at assessing SC hydration during a sorption-desorption test. It may also provide new ways to measure SC water uptake and water holding capacity following application of products.

Simple equilibrium dialysis-high-performance liquid chromatographic method for the in vitro assessment of 5-methoxypsoralen bound to human albumin.

Increasingly used in therapeutics, 5-methoxypsoralen (5-MOP), a linear furocoumarin, associated with UVA irradiation (PUVA), is now an established treatment for skin diseases such as vitiligo, mycosis funcoides and particularly psoriasis. Successful PUVA therapy depends on a sufficiently high peak 5-MOP plasma concentration coinciding with the UVA irradiation. However, as with most drugs, only the free plasma fraction is able to enter the target cells and has a pharmacological effect. In this work, the binding of 5-MOP to human albumin was studied in vitro, using a dialysis chamber. Bound and free 5-MOP fractions were quantified by a modification of Stolk's high-performance liquid chromatographic method. Dialysis was performed at 37 degrees C and pH 7.4 for 2 h, against a 4% albumin solution in phosphate buffer. The 5-MOP concentrations used were from 5 x 10(-5) to 5 x 10(-2) g/l in 1 x 10(-1) g/l steps. The 5-MOP bound strongly to human albumin in an unsaturable way. The mean 5-MOP binding to albumin was 95.3%. These results are in accordance with those published by Artuc et al. and not with those of Veronese et al., who found a lower saturable fixation (91%). These two research groups used tritiated 5-MOP. The technique used in this work is simple and inexpensive. It can be employed easily in vivo, e.g., for the assessment of 5-MOP free fractions in different therapeutic conditions.

Assessment of aging of the human skin by in vivo ultrasonic imaging.

The ultrasonic imaging technique that we have developed provides cross-sectional images of human skin in vivo with a resolution of about 80 microns axially (i.e., deep into the skin) and 250 microns lateral (parallel to the surface). In order to study aging skin, we obtained ultrasonic images from the mid-forearm (volar and dorsal sides) of 142 women. Ultrasonically, on the images, the dermis appears composed of two bands: a dark superficial one where the ultrasonic waves are propagated in a relatively homogeneous or non-echogenic medium, and a deeper one, which is lighter in color, suggesting a heterogeneous medium. Our results show that skin is thicker on the dorsal than on the volar forearm. In contrast to previously published results, skin thickness remains constant until the seventh decade of life, diminishing thereafter. The relative thickness of the two bands show marked variations with age: a progressive thickening of the dark band, from zero in infants to approximately 75% of total skin thickness in aged subjects, while the light band shows the inverse trend. Comparing the amplitude of the bands on the volar and dorsal forearm, the relative thickness of the dark band is larger on the dorsal (exposed) side and increases with age. These findings and the analysis of variously stained biopsies taken in some of our patients lead us to assign this dark band to a zone in the upper dermis where the collagen network is delicate, dense, and well organized. This is supported by some data in the literature. The thickness of this subepidermal non-echo-genic band appears to be a far more sensitive marker of skin aging at the dermal level than is the measurement of skin thickness.

A quantitative method for the assessment of the microtopography of human skin.

The skin relief influences the exterior aspect of the skin which is very sensitive to aging. It could also be related to the mechanical properties and structure of both dermis and stratum corneum. Consequently, quantitative measurement of the skin surface roughness would seem most useful, as it would permit a quantification of skin aging, an in vivo analysis of mechanical forces acting on the skin structure, and the detection of abnormalities otherwise not visible. The method described comprises three steps: (1) making a silicone rubber negative replica, (2) making an Araldite positive cast, (3) roughness measurement of the cast with a device commonly used in engineering, which provides quantitative parameters: Ra, Rp, Rt, Rmax and others. The reliability of each of these steps was checked, and also the absolute need to locate precisely the site of sampling and to know the angle of the scanning direction with the main axis of the limb or the body. The method seems useful for studying aging, either normal or affected by UV rays and other physiopathological events influencing the skin surface.