Storage Conditions of Skin Affect Tissue Structure and Subsequent in vitro Percutaneous Penetration

Abstract

Storage of skin at low temperatures may affect its structure. There is no report in the literature on the correlation between spatially resolved skin structure and percutaneous penetration after different storage conditions. The present study applies imaging techniques (multiphoton excitation fluorescence microscopy) and in vitro percutaneous penetration of caffeine under four different storage conditions using skin samples from the same donors: fresh skin, skin kept at –20°C for 3 weeks (with or without the use of polyethylene glycol) and at –80°C. Our results show a correlation between increasing permeation of caffeine and tissue structural damage caused by the storage conditions, most so after skin storage at –80°C. The presented approach, which combines imaging techniques with studies on percutaneous penetration, enables the link between tissue damage at selected depths and penetration into the upper layers of the epidermis to be investigated.

Effect of Frozen Human Epidermis Storage Duration and Cryoprotectant on Barrier Function Using Two Model Compounds

“…Limited skin availability permitted the study only up to 12 months storage. The overall average permeability of caffeine through human skin fresh and stored up to 12 months with and without glycerol was (1.5 ± 0.79) × 10 −4 cm/h, the steady state flux 2.95 ± 1.5 μg/(cm 2 h) and the lag time 2.3 ± 1.5 h—results comparable to other studies [2, 34, 39], although one study reports a permeability ten times higher [17]. The coefficient of variance for steady state flux was 44.5% for the samples with glycerol and 51% for the ones without glycerol and 49.8% overall.…”

“…However, multiple comparisons versus the control of fresh skin by the Holm-Sidak method showed no significant differences. The regression indicated a slight increase of lag time with storage time, although others reported a decrease in lag time [17, 29]. …”

“…It is interesting to note several of those studies with human skin [17, 19] only observed storage time up to 6 weeks. Neilsen et al [17] concluded that tissue structural damage due to storage correlated to increasing permeation of caffeine, with effects most pronounced with storage at −80 °C for 3 weeks, based on very few samples: only two donors with a total of 3 samples (one diffusion cell for donor #1 and two diffusion cells for donor #2), resulting in a 4-fold increase in permeability for donor #1 and 1.7-fold increase for donor #2. Donor #1 is disproportionately responsible for the overall results, and the low sample number renders their conclusion statistically uncertain.…”

“…Multiphoton excitation fluorescence microscopy found tissue structural damage due to frozen storage correlated to increasing permeation of caffeine, with damage most pronounced in skin stored at −80°C [17]. Regardless of any effects on barrier function, heat separation and skin freezing ought not to be used in permeation studies requiring skin viability and metabolism [32].…”

Chronological Age Affects the Permeation of Fentanyl through Human Skin in vitro

“…The skin was frozen immediately following surgery and kept at -20°C for periods not exceeding 12 months. This has proven to maintain the barrier properties with no significant change in water permeability [21], whereas lower temperatures have been shown to have a damaging effect [22]. Skin samples were allowed to thaw for 1 h at room temperature before it were gently cleaned with tap water and paper tissue, cut into suitable pieces and mounted in Franz diffusion cells.…”