The isolated perfused human skin flap model: A missing link in skin penetration studies?

Abstract

Development of effective (trans)dermal drug delivery systems requires reliable skin models to evaluate skin drug penetration. The isolated perfused human skin flap remains metabolically active tissue for up to 6 hours during in vitro perfusion. We introduce the isolated perfused human skin flap as a close-to-in vivo skin penetration model. To validate the model's ability to evaluate skin drug penetration the solutions of a hydrophilic (calcein) and a lipophilic (rhodamine) fluorescence marker were applied. The skin flaps were perfused with modified Krebs-Henseleit buffer (pH 7.4).Infrared technology was used to monitor perfusion and to select a well-perfused skin area for administration of the markers. Flap perfusion and physiological parameters were maintained constant during the 6 hours experiments and the amount of markers in the perfusate was determined. Calcein was detected in the perfusate, whereas rhodamine was not detectable. Confocal images of skin cross-sections shoved that calcein was uniformly distributed through the skin, whereas rhodamine accumulated in the stratum corneum. For comparison, the penetration of both markers was evaluated on ex vivo human skin, pig skin and cellophane membrane. The proposed perfused flap model enabled us to distinguish between the penetrations of the two markers and could be a promising close-to-in vivo tool in skin penetration studies and optimization of formulations destined for skin administration.

Skin penetration and tissue permeation after topical administration of diclofenac

“…The penetration of topical products through the skin is dependent on the active drug substance and the formulation, yet optimal skin penetration may not consistently result in the optimal downstream delivery to tissue. While skin penetration assays are well understood, broadly used and robust, our evaluation of the available evidenceand that of other authors 80,92,93 indicates that their results may not be suitable for anticipating tissue penetration. This is in contrast to establishing that in vitro methods can reflect systemic bioavailability 94 , as this is not consistently reflective of target tissue permeation.…”

“…Forecasting whether a formulation and its APIs led to those APIs achieving active concentrations in target tissue may not be consistently accurate, as demonstrated in our previous examples and in the seeming dislocation of rate of skin penetration and tissue penetration/API pharmacokinetics. There are limitations with in vitro data 80,92 , and in silico based physiologically based pharmacokinetic (PBPK) modeling is relatively recent and focuses on predicting rates of penetration and plasma exposure rather than target tissue exposure 58,102,103 . Alternatives include more labor intensive in vivo approaches that can measure at the site of action, including microdialysis and (specific to knee OA) joint sampling techniques like synovial biopsies and arthroplasties 80,104,105 .…”

Human Organotypic Models for Anti-infective Research

“…In brief, a human skin explant was linked to an automated perfusion system via one vessel, thereby inducing a controlled, continuous flow. An infrared (IR) camera was used to constantly monitor the skin surface temperature, and thus the degree of skin perfusion (Ternullo et al 2017). In conclusion, skin models provide a new platform to study the effectiveness of various novel anti-infective compounds, as summarized in Fig.…”

Going skin deep: A direct comparison of penetration potential of lipid-based nanovesicles on the isolated perfused human skin flap model

“…The skin penetration of calcein and rhodamine from CLs, DLs and SLNs was evaluated on the recently established IPHSF model [20] 32 ºC. The formulation (7 mL) was applied onto the selected perfused skin diffusion area using an adhesive patch as described by Ternullo and colleagues [20]. The experiments were carried out for 6 h and sampling was performed by collecting the perfusate every hour, assuring the sink conditions throughout the experiment.…”

“…For the first time, we directly compared the skin penetration enhancement of three different lipid-based nanocarriers on the isolated human skin flap (IPHSF) model, a recently developed human skin perfusion model [20]. To follow the drug penetration from different lipid-based nanocarriers, two fluorescent markers with different lipophilicities, calcein and rhodamine, were employed and their penetration from the CLs, DLs and SLNs followed.…”