Characterization of human cutaneous tissue autofluorescence: implications in topical drug delivery studies with fluorescence microscopy

Abstract

In pharmacokinetic studies of topical drugs, fluorescence microscopy methods can enable the direct visualization and quantification of fluorescent drugs within the skin. One potential limitation of this approach, however, is the strong endogenous fluorescence of skin tissues that makes straightforward identification of specific drug molecules challenging. To study this effect and quantify endogenous skin fluorescence in the context of topical pharmacokinetics, an integrating sphere-based screening tool was designed to collect fluorescence yield data from human skin specimens. Such information could be utilized to select specific donors in the investigation of drug uptake and distribution. Results indicated human facial skin specimens from a group of more than 35 individuals exhibited an at least 6fold difference in endogenous fluorescence. In visualizing drug distributions, the negative impact of autofluorescence could be exacerbated in cases where there are overlapping spatial distributions or spectral emission profiles between endogenous fluorophores and the exogenous fluorophore of interest. We demonstrated the feasibility of this approach in measuring the range of tissue endogenous fluorescence and selecting specimens for the study of drug pharmacokinetics with fluorescence microscopy.

Mangiferin and Hesperidin Transdermal Distribution and Permeability through the Skin from Solutions and Honeybush Extracts (Cyclopia sp.)—A Comparison Ex Vivo Study

“…It should be emphasised that fluorescence techniques are used to determine transdermal drug uptake, though they could be utilised only in the case of molecules with fluorescence properties that have different wavelengths than skin macromolecules [40,67,78,79]. As it was indicated in our research, hesperidin with its fluorescence properties can be successfully analysed with these techniques [66].…”

The Delivery of α1-Antitrypsin Therapy Through Transepidermal Route: Worthwhile to Explore

“…Similar experiments performed using a topical application of 0.2 mg AAT showed very strong fluorescence staining on the outermost layer of the epidermis and only a slight staining within keratinocyte cytosol ( Supplementary Figure 3B ). One potential limitation of this approach, however, is the strong endogenous fluorescence of skin models ( Hermsmeier et al., 2018 ).…”

Time-resolved fluorescence microscopy with phasor analysis for visualizing multicomponent topical drug distribution within human skin

“…When topical drugs have fluorescence properties, FLIM can be a powerful tool for extracting PK profiles within the skin by directly visualizing the local distribution of topical drug uptake. The key challenge in this method is that skin has a highly heterogeneous composition, including multiple endogenous fluorophores 26 . Moreover, the range of microenvironment in skin tissue can alter the fluorescence lifetimes of APIs taking up into the skin.…”