In vitro and in vivo confocal Raman study of human skin hydration: Assessment of a new moisturizing agent,pMPC
ABSTRACT 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.
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ABSTRACT: This paper reviews some current methods for the in vivo assessment of local cutaneous bioavailability in humans after topical drug application. After an introduction discussing the importance of local drug bioavailability assessment and the limitations of model-based predictions, the focus turns to the relevance of experimental studies. The available techniques are then reviewed in detail, with particular emphasis on the tape stripping and microdialysis methodologies. Other less developed techniques, including the skin biopsy, suction blister, follicle removal and confocal Raman spectroscopy techniques are also described.Pharmaceutical Research 02/2008; 25(1):87-103. DOI:10.1007/s11095-007-9429-7 · 3.42 Impact Factor
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ABSTRACT: Dermatologists and cosmetic scientists are becoming increasingly interested in stratum corneum (SC) hydration because the SC plays an important role in keeping the skin surface soft and smooth. However, conventional in vivo noninvasive methods do not provide direct information about the depth profiles of water content or SC components that hold water. To study the depth profiles of water and SC components in vivo by Raman spectroscopy, and to analyse the changes due to age, anatomical location, season and water application. In vivo Raman spectra of the skin of the cheek and the volar forearm were obtained from 50 healthy Japanese volunteers of different ages (age range 22-76 years) with a confocal Raman spectrometer. The depth-dependent profiles of water and of SC water-binding components were calculated from the respective Raman spectra. The depth profile of the SC water content was observed in a pattern ranging from around 30% (water/wet tissue) at the outermost layer of the SC to about 70% at the deeper living layer. Although the water content at a depth of 10-30 microm in the forearm skin tended to be lower in older subjects than in younger subjects, no such difference was found in the much thinner SC of the cheek. Moreover, there was no seasonal difference in depth profile of water content from the mid part of the SC to an 80-microm depth from the skin surface both in the cheek and in the forearm. The water content of all the evaluated SC components showed a gradual decrease from the surface to deeper portions. The mean amounts of lactate in the forearm skin and cholesterol in the cheek skin were significantly higher in younger subjects than in older subjects. In contrast, the levels of free amino acids and trans-urocanic acid were higher in the forearm skin of older subjects than in younger subjects. The relative amounts of urea and lactate were the highest in summer, when that of trans-urocanic acid was the lowest. Prolonged water application on the forearm skin even for 90 min resulted in a remarkable increase in water content throughout the SC, even reaching the granular layer, which was only gradually released from the upper part of the SC after discontinuation of the hydration procedure. Our present findings suggest that changes in the concentration depth profiles of water, free amino acids and lipids in the skin depend on age, anatomical site and season. These findings indicate the important roles played by various water-holding substances in the SC in the regulation of SC water content.British Journal of Dermatology 03/2008; 158(2):251-60. DOI:10.1111/j.1365-2133.2007.08311.x · 4.28 Impact Factor
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ABSTRACT: 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. To validate the use of confocal Raman spectroscopy (CRS) to measure SC thickness and then use it to investigate the short- and long-term effects of moisturizers (one of which is known to improve SC barrier function) on SC thickness, water gradients and hydration. Two studies were conducted: (i) to validate the use of CRS for measuring SC thickness through comparison with optical coherence tomography (OCT); and (ii) once validated to use CRS to measure the long-term effects of three commercially available moisturizers (A, B, C) on SC thickness and water gradients, together with total hydration, over a 3-week period (2 weeks of treatment and 1 week regression) and compare the spectroscopy-derived hydration value with instrumentally derived capacitance hydration values. (i) A strong, positive correlation in SC thickness was obtained between CRS and OCT (OCT-derived thickness = 0.96 x CRS-derived thickness, r(2) = 0.93; P <0.0001). OCT was shown, however, to have a lower resolution than CRS in distinguishing SC thickness on thinner nonpalmoplantar body sites. Using the CRS method, differences in SC thickness were readily apparent on different body sites (cheek 12.8 +/- 0.9 microm, volar forearm 18.0 +/- 3.9 microm, leg 22.0 +/- 6.9 microm). (ii) Examining the effects of moisturizers in a blinded, randomized 3-week study in human volunteers (n = 14) demonstrated that only one commercially available formulation (A) changed SC water gradients, thickness and hydration as measured by CRS. These hydration data did not directly correlate with capacitance hydration values. (i) In vivo CRS was validated as a technique to measure SC thickness on both palmoplantar and, particularly, on nonpalmoplantar skin sites. (ii) Moisturizers improve skin moisturization but in this study only formulation A improved SC thickness, water gradients and hydration as measured by CRS. We hypothesize that this was due to compositional differences between the products. We believe that niacinamide (nicotinamide, vitamin B(3)) is probably contributing significantly to this effect, as it has been proven to increase epidermal lipogenesis and SC barrier function in other studies. These results show that by using CRS, we were able for the first time to determine the effect of moisturizer on multiple SC barrier endpoints including SC thickness, and water content as a function of depth and total SC water content.British Journal of Dermatology 06/2008; 159(3):567-77. DOI:10.1111/j.1365-2133.2008.08703.x · 4.28 Impact Factor