Excised animal and human skins are frequently used in permeability testing in pharmaceutical
research. Several factors exist that may have influence on the results. In the current
study some of the skin parameters that may affect drug permeability were analysed
for human, mouse, rat and pig skin.Materials
and methodsClassic biophysical skin parameters were measured
(e.g. pH, hydration, permittivity, transepidermal water loss). Physiological characteristics
of the skins were also analysed by confocal Raman spectroscopy, scanning electron
microscopy and two‐photon microscopy.ResultsBased
on biophysical testing, skin barrier function was damaged in psoriatic mouse skin
and in marketed pig skin. Hydration and pH values were similar among the species,
but freezing and thawing reduced the water content of the skins and shifted the surface
pH to acidic. Aging reduced hydration and permittivity, resulting in impaired barrier
function. Mechanical sensitization used in permeability studies resulted in proportional
thinning of dead epidermis.DiscussionResults
indicate that depending on the scientific question it should be considered whether
fresh or frozen tissue is used, and for certain purposes rodent skins are well usable.
The structure of the skin tissue (ceramide, cholesterol, keratin, natural moisturizing
factor or urea) is similar in rats and mice, but due to the higher skin thickness
the lipid distribution is different in porcine skin. Psoriasis led to irregular chemical
composition of the skin.ConclusionA
comprehensive evaluation of skin samples of four species was performed. The biophysical
and microscopic observations should be considered when selecting drug penetration
models and experimental conditions.
