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.
Ascorbic acid (AA) plays a significant role in preventing photobiological damage in human skin which could lead to cutaneous disorders such as premature aging or skin cancer. The aim of this work was to assess AA concentrations in human dermis by a microdialysis technique associated with gas chromatography-mass spectrometry (GC-MS). Due to the non-volatility of AA, it was necessary to derivatize this acid. Three methods, one methylation and two silylations, were validated and compared to determine the most sensitive. To validate the methods, calibration curves were plotted from AA concentrations ranging from 34 to 500 nmol mL-1. The calibration curves were linear with a good correlation coefficient (r ≥ 0.99). Repeatability and reproducibility were significant with a coefficient of variation of less than 10%. The accuracy of the techniques was meaningful as the bias was low (ranging from-5.6 to 5.0%). According to our results, silylation was the most sensitive method to assess AA. Thus, this method was performed to determine AA concentrations in microdialysates. In order to study AA in human dermis, a microdialysis method was used to sample AA and the GC-MS technique used to assess this acid in the microdialysates. Microdialysis can only partially collect AA from human dermis. An ex vivo recovery of AA was 30 ± 2% (n = 7). The average concentration of AA in microdialysates was 250 ± 66 nmol mL-1 (Mean ± SD, n = 5). In view of the AA recovery, AA concentrations in human skin ranged from 759 to 891 nmol mL-1 .
Until recently, the determination of metallic elements concentrations in normal skin, in vivo, was rare due to the lack of non-invasive techniques. Microdialysis has the advantage of being slightly invasive when applied to the collection in vivo of endogenous or exogenous substances from the skin.Iron is an active element in different cutaneous disorders. The aim of this work was to assess iron by atomic absorption spectrometry (AAS) after the collection of samples by microdialysis from human dermis. A first essential step, before determining the in vivo iron concentration in human dermis, was to establish an experimental protocol applicable to ex vivo as well as in vivo conditions. For this reason, this work deals only with the assessment of iron in ex vivo human dermis.A skin microdialysis technique and a calibration method, the No Net Flux, were used to quantify basal iron concentrations in human dermis and the same method was also used to determine in vitro and ex vivo iron recoveries. No differences were detected between in vitro and ex vivo recoveries. Ex vivo basal iron dermis concentrations ranged from 3.6 to 7.7 m mg/l.This study shows that non-invasive microdialysis is an efficient method for sampling iron from human skin. A sensitive and accurate AAS technique was able to assess low iron concentrations in human dermis. The strategy adopted for this work was efficient and appropriate for the determination of iron in human skin and experiments will be carried out in vivo.Key words microdialysis; iron; human skin dermis; atomic absorption spectrometry
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