Penetration Depth of Propylene Glycol, Sodium Fluorescein and Nile Red into the Skin Using Non-Invasive Two-Photon Excited FLIM

• Main Authors: Mohammad Alhibah (Author), Marius Kröger (Author), Sabine Schanzer (Author), Loris Busch (Author), Jürgen Lademann (Author), Ingeborg Beckers (Author), Martina C. Meinke (Author), Maxim E. Darvin (Author)
• Format: Book
• Published: MDPI AG, 2022-08-01T00:00:00Z.
• Subjects: article
• Online Access: Connect to this object online.

Summary

The stratum corneum (<i>SC</i>) forms a strong barrier against topical drug delivery. Therefore, understanding the penetration depth and pathways into the <i>SC</i> is important for the efficiency of drug delivery and cosmetic safety. In this study, TPT-FLIM (two-photon tomography combined with fluorescence lifetime imaging) was applied as a non-invasive optical method for the visualization of skin structure and components to study penetration depths of exemplary substances, like hydrophilic propylene glycol (<i>PG</i>), sodium fluorescein (<i>NaFl</i>) and lipophilic Nile red (<i>NR</i>) into porcine ear skin ex vivo. Non-fluorescent <i>PG</i> was detected indirectly based on the pH-dependent increase in the fluorescence lifetime of <i>SC</i> components. The pH similarity between <i>PG</i> and viable epidermis limited the detection of <i>PG</i>. <i>NaFl</i> reached the viable epidermis, which was also proved by laser scanning microscopy. Tape stripping and confocal Raman micro-spectroscopy were performed additionally to study <i>NaFl</i>, which revealed penetration depths of ≈5 and ≈8 μm, respectively. Lastly, <i>NR</i> did not permeate the <i>SC</i>. We concluded that the amplitude-weighted mean fluorescence lifetime is the most appropriate FLIM parameter to build up penetration profiles. This work is anticipated to provide a non-invasive TPT-FLIM method for studying the penetration of topically applied drugs and cosmetics into the skin.

Item Description

10.3390/pharmaceutics14091790
1999-4923