Caffeine delivery in porcine skin: a confocal Raman study
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Confocal Raman microscopy is a novel optical method for studies of pro-drug and drug delivery. This method is a promising technique that enables non-destructive measurement of the permeation profile through skin layers. Peaks of compounds are usually normalised to skin peaks (amino-acid and amide I) for semi-quantitative evaluation. The present study seeks to optimise a methodology for complete quantitative measurement of the amount of an active compound at different depths. Caffeine was used as a tracer to evaluate compound’s skin penetration using confocal Raman microscopy. A semi-quantitative depth profile of caffeine was obtained with normalisation of the Raman intensities. These ratios of Raman intensities were correlated with the caffeine concentration using an external calibration curve. The calibration curve was carried out with porcine skin incubated in different concentrations of caffeine; afterwards, each skin sample was analysed by confocal Raman microscopy and HPLC to determine the relation between the Raman signal intensity and the caffeine concentration per skin mass and to create a depth profile. These correlation curves allow the full quantification of the caffeine in skin from Raman intensity ratios at different depths.
KeywordsCaffeine Percutaneous penetration Confocal Raman microscopy Quantitative evaluation
The authors are grateful to Montserrat Rigol Muxart and Núria Solanes Batlló of the Department of Cardiology (Institut d’Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS) Hospital Clínic, Universitat de Barcelona, Spain) for supplying the porcine skin biopsies. We thank Anna Quintana of Almirall for her collaboration and contribution in this project.
This work was partially funded by the Spanish Ministry of Economy and Competitiveness, project code RTC-2014-1901-1.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. Animal handling was approved by the Institutional Review Board and Ethics Committee of Institut d’Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS) Hospital Clínic, Universitat de Barcelona, Barcelona, Spain. The management of the Landrace Large White pigs used in this study conforms to the Guide for the Care and Use of Laboratory Animals published by the United States National Institutes of Health (Eighth Edition. Washington, DC: The National Academies Press, 2011).
This study did not require formal informed consent.
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