Anke Sieg

Measuring the effects of topical moisturizers on changes in stratum corneum thickness, water gradients and hydration in vivo

Background  Moisturizers are the most commonly used topically applied product for the treatment of dry skin conditions. They affect many properties and functions of the stratum corneum but some moisturizers have been reported to be detrimental to barrier function. Stratum corneum barrier function is a composite of its total structure and thickness but few studies have taken this into account. As a biosensor, the stratum corneum (SC) will change its structure in response to treatment and a swelling effect has been clearly demonstrated by skin hydration. Recently several moisturizing agents have been shown to have an effect on SC swelling behaviour with conflicting results. However, there is a paucity of data reported for measuring the effects of long‐term usage of moisturizers on SC thickness in vivo as, until recently, traditional techniques did not have the resolution to measure the effects of moisturizers on nonpalmoplantar body sites. The development of confocal Raman spectroscopy for use in human subjects provides noninvasive, real‐time, in vivo measurement of SC water concentration profiles and we have also used this state of the art equipment to measure the effect of the long‐term use of moisturizers on SC thickness for the first time.

Diagnostic and therapeutic applications of iontophoresis

Owing to the excellent barrier properties of the stratum corneum, transdermal delivery remains a challenge for a high number of molecules. Iontophoresis is a noninvasive technique which uses a low current to administer polar and charged species through the skin, thereby enlarging the range of drug candidates for transdermal administration. Unlike other techniques of transdermal delivery enhancement, iontophoresis acts on the molecule itself allowing a better control of the dose applied. The symmetry of the technique can be employed for controlled extraction, allowing a relation to be established between extracted flux and subdermal concentration. This opened the way for innovative applications, notably in the field of noninvasive monitoring of glucose and xenobiotics. Rather than being an extensive review of the literature, this article summarizes the basic rules governing iontophoretic transport, discusses advantages and limitations of the technique, and provides an overview of promising therapeutic applications.

Simultaneous extraction of urea and glucose by reverse iontophoresis in vivo

AbstractPurpose. Reverse iontophoresis extracts glucose across the skin in the GlucoWatch Biographer, a device to monitor glycemia in diabetes. However, the device must first be calibrated with an invasive “finger-stick” and this has been perceived as a disadvantage. Here, urea, a neutral “internal standard” is extracted simultaneously in an attempt to render the technique completely non-invasive. Methods. In a 5-h experiment in human volunteers, reverse iontophoretic fluxes of glucose and urea (Jglu and Jurea, respectively) were measured periodically and correlated with the corresponding blood levels. In the case of glucose, a finger-tip blood sample was taken at the beginning of each collection interval; for urea, three blood samples were assayed: one before, one during, and one at the end of iontophoresis. Results. The ratio Jglu/Jurea divided by the ratio of the systemic concentrations (Cglu/Curea) yielded an extraction coefficient (K) that could be compared between subjects. Though Jglucose tracked Cglu faithfully when the volunteers were challenged with an oral glucose load, Jurea remained quite stable reflecting the fact that Curea did not change appreciably during the experiment. However, whereas the variability (expressed as the coefficient of variation) in the normalized extraction flux of urea (Jurea/Curea) was on the order of 25%, that for glucose was greater (>45%), with the result that the values of K (0.45 ± 0.25) were less constant than anticipated. Conclusions. Although urea performed quite reasonably as an internal standard, in that its extraction flux and systemic concentration both remained quite constant, the normalized, transdermal, iontophoretic flux of glucose showed interindividual variability due to mechanisms that were not entirely governed by electrotransport. That is, despite good qualitative tracking to blood levels, there appear to be other (biochemical, metabolic, contamination?) factors that impact upon the quantitative results obtained.

Extraction of amino acids by reverse iontophoresis: simulation of therapeutic monitoring in vitro.

Reverse iontophoresis across the skin has been investigated as alternative, non-invasive method for clinical and therapeutic drug monitoring. This research investigated the reverse iontophoretic extraction of 19 amino acids present at clinically relevant levels in the subdermal compartment of an in vitro diffusion cell. Over a simulated, systemic concentration range of 0-500 microM, the extraction of amino acids was linear. Charged amino acids were extracted towards the electrode of opposite polarity, while zwitterionic species were extracted to both anode and cathode with the latter predominating. The reverse iontophoretic extraction flux was a linear function of amino acid isoelectric point, reflecting the different contributions of electromigration and electroosmosis to electrotransport. Overall, the results confirm the feasibility of monitoring amino acids at clinically relevant levels and provide an incentive for in vivo research to further explore the clinical potential of reverse iontophoresis for the non-invasive monitoring of amino acids.

Confocal Raman microspectroscopy: measuring the effects of topical moisturizers on stratum corneum water gradient in vivo

The stratum corneum (SC) water concentration gradient is fundamental to skins role as a barrier, regulating its physical and biochemical properties. Standard instruments utilizing changes in SC electrical properties to estimate SC water concentration provide simple, rapid measurements but cannot provide true interval data as a function of depth. Confocal Raman spectroscopy (CRS) of human subjects provides non-invasive, real-time, in vivo measures of molecular concentration profiles. A state-of-the-art confocal Raman microspectrometer equipped with a fiber-coupled laser source operating at a wavelength of 671 nm was used to obtain measurements in the high wavenumber region (~2400-4000 cm-1). An aircooled, high-sensitivity back-illuminated, deep-depletion CCD camera captured radiation scattered inelastically from focal planes within the skin in vivo (a high-precision, computer-controlled piezo-electric stage and objective allowing depth resolutions of <5 μm, with over-sampling). High-wavenumber data were analyzed to provide semi-quantitative measures of water concentration ([water] / [protein + water]) across the SC. This new technique was used to study changes in SC water concentration gradients in human skin in vivo, in response to treatment with topical moisturizing products. The results of a blinded, randomized 3-week study in human volunteers will be presented, in particular, the significant, unique effects of a topical moisturizer containing niacinamide on SC water concentration gradient, as measured by CRS, in vivo. The approach to compare SC water gradient effects will be discussed and the utility of this exciting new method will be compared and contrasted to existing methodology.