Influence of skin furrows on tape stripping in characterizing the depth of skin penetration

Innovative insight into the mechanism of enantioselective skin permeation for chiral drugs

OBJECTIVES

A profound comprehension of the molecular mechanisms underpinning the enantioselective transdermal permeation of chiral drugs is critical in the design and assessment of transdermal preparations. The primary objective of this study is to investigate the distinct skin permeation behaviors exhibited by enantiomers of non-steroidal anti-inflammatory drugs (NSAIDs) and elucidate the intricate molecular mechanism at play.

METHODS

In vitro and in vivo transdermal permeation studies of chiral NSAIDs were performed using transdermal patch and solution system. Chiral interaction between NSAIDs enantiomers and synthesized chiral ceramide present in the skin was characterized to clarify the different transdermal behaviors.

RESULTS

The S-enantiomers of NSAIDs exhibited higher permeability through the skin than R-enantiomer in vitro (1.5-fold) and in vivo (2.0-fold), which was attributed to a stronger interaction between S-enantiomer and ceramide caused by more favorable spatial conformations. S-enantiomer required lower activation energy (24.4 kJ/mol) and Gibbs energy (43.3 kJ/mol), which was favorable in forming the H-bond with ceramide in the skin, resulting in more permeation.

CONCLUSION

This research furnished an innovative comprehension of the molecular underpinnings governing the enantioselective permeation of drug enantiomers through the skin, fostering the minimization of undesired enantiomer ingestion (distomers) and amplifying therapeutic efficiency.

Revisiting techniques to evaluate drug permeation through skin

INTRODUCTION

Investigating the transportation of a drug molecule through various layers of skin and determining the amount of drug retention in skin layers is of prime importance in transdermal and topical drug delivery. The information regarding drug permeation and retention in skin layers aids in optimizing a formulation and provides insight into the therapeutic efficacy of a formulation.

AREAS COVERED

This perspective covers various methods that have been explored to estimate drug/therapeutics in skin layers using in vitro, ex vivo, and in vivo conditions. In vitro methods such as diffusion techniques, ex vivo methods such as isolated perfused skin models and in vivo techniques including dermato-pharmacokinetics employing tape stripping, and microdialysis are discussed. Application of all techniques at various stages of formulation development where various local and systemic effects need to be considered.

EXPERT OPINION

The void in the existing methodologies necessitates improvement in the field of dermatologic research. Standardization of protocols, experimental setups, regulatory guidelines, and further research provides information to select an alternative for human skin to perform skin permeation experiments to increase the reliability of data generated through the available techniques. There is a need to utilize multiple techniques for appropriate dermato-pharmacokinetics evaluation and formulation's efficacy.

Critical parameters for accurate monitoring of caffeine penetration in porcine skin using confocal Raman spectroscopy

In this research, we addressed a challenge while measuring the penetration performance of caffeine (CAF) using confocal Raman spectroscopy (CRS). Normally in the process of CRS analysis, skin sample was moved from an incubation setup to a specified CRS-measuring sample holder. Accurate data collection may be questioned due to the variation of the environment the skin placed in. Therefore, two critical parameters including the CRS measuring temperature and proper skin hydration were focused; accordingly, four different conditions were designed. First, the skin was incubated in a real-time device with the skin placing onto PBS-filled chamber where the temperature was adjusted to 32℃. This device can be fixed under the CRS microscope, enabling simultaneous skin incubation and dynamic CRS measurements (condition i, reference). The other conditions referred to skins incubated in Franz diffusion cells for simulating the common experimental procedures. In order to control variables of CRS measuring condition, skins were transferred from cells to real-time device and open device. In real-time device, proper skin hydration was maintained and the skin temperature was adjusted to 32℃ (condition ii) and room temperature (condition iii). In open device, the skin was in a less hydrated state by moving onto a PBS-soaked filter paper and wrapped with aluminum foil at room temperature (condition iv). The skin penetration performances measured in these conditions were compared with reference. Caffeine solution and gel formulation were separately applied to the skin. The results showed in both cases that the decrease of skin temperature and hydration in condition iii and iv would apparently induce the decrease of detected caffeine signal, resulting in the inaccurate data collection. To this point, it indicates the reduction of solubilized caffeine in skin layer. We suggest the forming of caffeine crystallization at varied skin conditions to be the factor. Achieved video image, CRS spectrum collection and surface scan demonstrated the caffeine crystallization process on superficial skin layer. Polarized microscopic images exemplified the crystalline drug on tape stripped skin layers. It can be a potential support of caffeine crystallization inside skin. In short, we suggest the consideration of these parameters during CRS measurements for accurate monitoring of topical drug delivery. Meanwhile, the use of real-time device for dynamic skin incubation and data collection provides advantages in saving time and efforts in this study.

Profiling skin penetration using PEGylated emulsifiers as penetration enhancers via confocal Raman spectroscopy and fluorescence spectroscopy

Non-ionic emulsifiers have been continuous research focus in skin analysis. With the aim of finding their role as penetration enhancers in dermal drug delivery systems, PEGylated emulsifiers of polyethylene glycol (PEG) ethers were targeted to be investigated ex-vivo. The effectiveness of them in the enhancement of skin penetration was examined by conventional tape stripping method and confocal Raman spectroscopy (CRS). Fluorescein sodium salt (Fluo-Na) and procaine HCl were respectively used as model drugs. The drug delivery performances were compared in the aspects of penetration amount and depth. Based on the results from both analyses, all investigated emulsifiers have the ability to enhance the amount of drug penetration. PEG-20 ethers showed higher ability than PEG-2 oleyl ether (O2) in promoting drug distribution by depth, especially PEG-20 cetyl ether (C20) showed a distinct effect. According to this study, their penetration enhancing performances seem to be linked to their interruption of intercellular lipids, which can be considered as the underlying mechanism for governing the ability of PEGylated emulsifiers as penetration enhancers. Further instrumental comparison highlighted the benefits of using CRS as an alternative in skin penetration analysis.