In vivo monitoring of epidermal absorption of hazardous substances by confocal Raman micro-spectroscopy.

BACKGROUND: Presently, percutaneous absorption of potentially hazardous chemicals in humans can only be assessed in animal experiments, in vitro, or predicted mathematically. Our aim was to demonstrate the proof-of-principle of a novel quantitative in vivo assay for percutaneous absorption: confocal Raman micro-spectroscopy (CRS). The advantages and limitations of CRS for health risk assessments are discussed. PATIENTS AND METHODS: 2-butoxyethanol, toluene, and pyrene were applied in pure form, diluted in water, or in ethanol on the skin of three healthy volunteers. CRS measurements were done following application for 15 min and 3 hours. The concentrations of the three substances as a function of distance to the skin surface were calculated and further analyzed with regard to mass transport into the stratum corneum (µg/cm(2)) and the flux through the stratum corneum (µg/cm(2)h). The results were compared with the available data from literature. RESULTS: Considering the preliminary nature of these data, good accordance with data from the literature was observed. In addition, we observed that 2-butoxyethanol penetrates markedly faster when dissolved in water as compared to ethanol. This observation is also in agreement with previous results. CONCLUSIONS: CRS has the potential to provide fast, accurate and reliable results for advanced studies of in vivo percutaneous absorption kinetics of hazardous substances in human skin. This will require further research with other substances and under differing conditions.

Studying the effectiveness of penetration enhancers to deliver retinol through the stratum cornum by in vivo confocal Raman spectroscopy.

The purpose of this study is to monitor in vivo the effect of chemical penetration enhancers on the delivery of trans-retinol into human skin. Chemical penetration enhancers reversibly alter barrier properties of the SC by disruption of the membrane structures or maximising drug solubility with the skin. So far, most of permeation or penetration experiments are performed in vitro. Raman spectroscopy is uniquely placed to be able to measure biological processes in vivo and this paper shows for the first time that the effect of penetration enhancer on the delivery of trans-retinol can successfully be measured in vivo using this technique. Here, the volar forearm of volunteers was treated with four formulations. One formulation is a highly effective model delivery system identified from ex vivo experiments: trans-retinol in Propylene Glycol (PG)/ethanol, with PG being a well-known and efficient penetration enhancer. The other three formulations are based on 0.3% trans-retinol in Caprylic/Capric Acid Triglyceride (MYRITOL 318), an oil commonly used in skin creams but in two of them a specific penetration enhancer is added. One contains a lipid extractor, Triton X 100, whereas another formulation contains a lipid fluidiser, Oleic Acid. Solutions were applied once and measurements were performed up to 6 h after treatment. Remarkable differences in the delivery of trans-retinol between formulation with or without penetration enhancer can clearly be seen. Moreover, the type of penetration enhancer is also shown to influence the delivery. While using the Oleic Acid, which is a lipid fluidiser, a better delivery of trans-retinol in the skin can be detected. For the first time, the effect of penetration enhancer on the delivery of trans-retinol has been monitored, non invasively in vivo, with time.

Lipid uptake and skin occlusion following topical application of oils on adult and infant skin.

BACKGROUND: Topical application of oils and oil-based formulations is common practice in skin care for both adults and infants. Only limited knowledge however is available regarding skin penetration and occlusive potential of oils and common methods for measuring skin moisturization fall short when it comes to the moisturizing effect of oils. OBJECTIVE: In this study we used in vivo confocal Raman microspectroscopy to test the efficacy of paraffin oil (mineral oil) and two vegetable oils in terms of skin penetration and occlusion. Petrolatum was used as a positive control. METHODS: The products were applied topically on the forearms of nine volunteers and seven infants and Raman spectra were acquired before and at 30 and 90 min following application. Depth concentration profiles for lipid and water were calculated from the Raman spectra. Skin occlusion was assessed from the amount of stratum corneum (SC) swelling measured from the water concentration profiles. RESULTS: The paraffin oil and the vegetable oils penetrate the top layers of the SC with similar concentration profiles, a result that was confirmed both for adult and infant skin. The three oils tested demonstrated modest SC swelling (10-20%) compared to moderate swelling (40-60%) for petrolatum. CONCLUSION: These data indicate that there is no statistical difference between the paraffin oil and vegetable oils in terms of skin penetration and skin occlusion. The results for petrolatum show that in vivo confocal Raman microspectroscopy is sensitive and specific enough to measure both lipid uptake and skin occlusion events following topical application.

An in vivo confocal Raman study of the delivery of trans retinol to the skin.

The purpose of this study is to monitor in vivo the delivery of trans-retinol into human skin. Delivery to real systems, such as skin, can be extremely difficult to execute and is problematic to confirm and measure. So far, methods for studying the delivery of compounds through the skin are mostly ex vivo and so inherently influence the skin and may not translate directly to the in vivo situation. Raman spectroscopy is uniquely placed to be able to measure biological processes in vivo, and this paper shows that the trans-retinol penetration into the skin can successfully be measured in vivo using this technique. This study measured the volar forearm of volunteers treated with 0.3% trans-retinol in propylene glycol (PG)/ethanol and 0.3% trans-retinol in caprylic/capric acid triglyceride (MYRITOL318), an oil found in skin creams. Solutions were applied and then confocal Raman depth profiles were obtained of the stratum corneum (SC) and into the viable epidermis (VE) up to 10 hours after treatment. Remarkable differences between a penetrating and a nonpenetrating solution can clearly be observed. Treating with trans-retinol in PG/ethanol results in trans-retinol penetrating through the SC and into the VE. Its penetration was also observed to be highly correlated with the depth of penetration of the PG, which is well known as an efficient penetration enhancer. In contrast, while treating with trans-retinol in MYRITOL318, trans-retinol hardly penetrates at all. For the first time, the penetration of trans-retinol has been monitored directly after application of solutions, in vivo without skin excision. Here, the effect of two different solutions on the delivery of trans-retinol into the skin was measured very effectively in vivo by Raman spectroscopy.

Surface-sensitive molecular information on polymers from UV-resonance Raman spectroscopy.

Ultraviolet resonance Raman spectroscopy (UV-RRS) has been applied to a series of samples of poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) and poly(ethylene terephthalate) (PET) of varying thickness. The spectra demonstrate that under resonance conditions, when absorption is very strong, only a very thin top layer of the sample is probed (hundreds of nanometers range). This allows probing molecular vibrational spectra of the top layer of the sample, with a surface-resolution at least an order of magnitude better than in the case of normal non-resonance Raman spectroscopy and using a microscope.