Confocal Raman microscopy and multivariate statistical analysis for determination of different penetration abilities of caffeine and propylene glycol applied simultaneously in a mixture on porcine skin ex vivo.
Propylene glycol is one of the known substances added in cosmetic formulations as a penetration enhancer. Recently, nanocrystals have been employed also to increase the skin penetration of active components. Caffeine is a component with many applications and its penetration into the epidermis is controversially discussed in the literature. In the present study, the penetration ability of two components - caffeine nanocrystals and propylene glycol, applied topically on porcine ear skin in the form of a gel, was investigated ex vivo using two confocal Raman microscopes operated at different excitation wavelengths (785nm and 633nm). Several depth profiles were acquired in the fingerprint region and different spectral ranges, i.e., 526-600cm(-1) and 810-880cm(-1) were chosen for independent analysis of caffeine and propylene glycol penetration into the skin, respectively. Multivariate statistical methods such as principal component analysis (PCA) and linear discriminant analysis (LDA) combined with Student's t-test were employed to calculate the maximum penetration depths of each substance (caffeine and propylene glycol). The results show that propylene glycol penetrates significantly deeper than caffeine (20.7-22.0μm versus 12.3-13.0μm) without any penetration enhancement effect on caffeine. The results confirm that different substances, even if applied onto the skin as a mixture, can penetrate differently. The penetration depths of caffeine and propylene glycol obtained using two different confocal Raman microscopes are comparable showing that both types of microscopes are well suited for such investigations and that multivariate statistical PCA-LDA methods combined with Student's t-test are very useful for analyzing the penetration of different substances into the skin.
Center of Experimental and Applied Cutaneous Physiology, Department of Dermatology, Venerology and Allergology, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany; Centro de Investigación e Innovación Tecnológica (CIITEC) del Instituto Politécnico Nacional (IPN), Cerrada de Cecati S/N, Col. Santa Catarina Azcapotzalco, México D.F. CP: 02250, Mexico.
Saul
S
Mujica Ascencio
Center of Experimental and Applied Cutaneous Physiology, Department of Dermatology, Venerology and Allergology, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany; Kim Il Sung University, Ryongnam-Dong, Taesong District, Pyongyang, Democratic People's Republic of Korea.
ChunSik
C
Choe
Center of Experimental and Applied Cutaneous Physiology, Department of Dermatology, Venerology and Allergology, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany.
Martina C
MC
Meinke
Institute of Pharmacy, Department of Pharmaceutics, Biopharmaceutics & NutriCosmetics, Freie Universität Berlin, Kelchstraße 31, 12169 Berlin, Germany.
Rainer H
RH
Müller
M.V. Lomonosov Moscow State University, Department of Biophysics, Faculty of Biology, Leninskie Gory, 1-12, 119991 Moscow, Russia.
George V
GV
Maksimov
Bioskin GmbH, Burchardstrasse 17, 20095 Hamburg, Germany.
Walter
W
Wigger-Alberti
Center of Experimental and Applied Cutaneous Physiology, Department of Dermatology, Venerology and Allergology, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany.
Juergen
J
Lademann
Center of Experimental and Applied Cutaneous Physiology, Department of Dermatology, Venerology and Allergology, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany. Electronic address: maxim.darvin@charite.de.
Maxim E
ME
Darvin
D000818:Animals; D002110:Caffeine / Q000008:administration & dosage*; D066298:In Vitro Techniques; D057230:Limit of Detection; D018613:Microscopy, Confocal / Q000379:methods*; D015999:Multivariate Analysis; D019946:Propylene Glycol / Q000008:administration & dosage*; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013552:Swine
D002110:Caffeine; D019946:Propylene Glycol
Epidermis; Multispeed penetration; Penetration enhancer; Propanediol; Stratum corneum; Stratum spinosum; Toxicity; Vibrational spectroscopy