Comparison of Membrane Depth Determination Techniques for Active Ingredient Skin Penetration Studies Using Microdialysis

<b><i>Introduction:</i></b> The skin is a major physical barrier to the environment, and thus, percutaneous delivery of active ingredients to the dermal target site faces a unique set of hurdles. The efficacy of these active ingredients is governed by their release into the underlying epidermal and dermal tissue, especially when administered topically. <b><i>Objective:</i></b> The aim of this study was to understand if different physicochemical properties influence the skin penetration of active ingredients and the depth to which they penetrate into the dermis. <b><i>Methods:</i></b> A microdialysis (MD) setup was used to compare the percutaneous penetration in superficial and deep implanted MD membranes in porcine skin. The precise MD membrane depth was determined using histological sectioning paired with microscopy, ultrasound, and a novel computed tomographic approach. <b><i>Results:</i></b> In study A, the measured depth of the superficial and deep implanted MD membranes was compared using histological sectioning, ultrasound, and computed tomography. Experimental determination of the depth up to which penetration occurs was found to be crucial to percutaneous penetration studies. In study B, the lipophilic differences of the active ingredients and its influences on the penetration was tested using hydrophilic caffeine and lipophilic LIP1 as model compounds, which have an identical molecular weight with different lipophilic characteristics. It is assumed that the lipophilic characteristics of active ingredients influence their penetration and thus governs the concentration of these molecules reaching their target site. <b><i>Conclusion:</i></b> The transdermal penetration of caffeine was found to exceed that of LIP1 through the hydrophilic environment of the dermis. Thus, the findings of this study show that the precise MD dermis localization and the physicochemical properties, such as lipophilicity, influence the penetration rate of active ingredients and lay the foundation for creating optimized transdermal delivery systems.

Energy-Dependent Endocytosis Is Responsible for Skin Penetration of Formulations Based on a Combination of Indomethacin Nanoparticles and l-Menthol in Rat and Göttingen Minipig

We previously designed a Carbopol gel formulation (N-IND/MEN) based on a combination of indomethacin solid nanoparticles (IND-NPs) and l-menthol, and we reported that the N-IND/MEN showed high transdermal penetration. However, the detailed mechanism for transdermal penetration of IND-NPs was not clearly defined. In this study, we investigated whether endocytosis in the skin tissue of rat and Göttingen minipig is related to the transdermal penetration of IND-NPs using pharmacological inhibitors of endocytosis. The pharmacological inhibitors used in this study are as follows: 54 µM nystatin, a caveolae-mediated endocytosis (CavME) inhibitor; 40 µM dynasore, a clathrin-mediated endocytosis (CME) inhibitor; and 2 µM rottlerin, a micropinocytosis (MP) inhibitor. The N-IND/MEN was prepared by a bead mill method, and the particle size of solid indomethacin was 79–216 nm. In both rat and Göttingen minipig skin, skin penetration of approximately 80% IND-NPs was limited by the stratum corneum (SC), although the penetration of SC was improved by the combination of l-menthol. On the other hand, the treatment of nystatin and dynasore decreased the transdermal penetration of indomethacin in rats and Göttingen minipigs treated with N-IND/MEN. Moreover, in addition to nystatin and dynasore, rottlerin attenuated the transdermal penetration of IND-NPs in the Göttingen minipigs’ skin. In conclusion, we found that l-menthol enhanced the SC penetration of IND-NPs. In addition, this study suggests that the SC-passed IND-NPs are absorbed into the skin tissue by energy-dependent endocytosis (CavME, CME, and/or MP pathways) on the epidermis under the SC, resulting in an enhancement in transdermal penetration of IND-NPs. These findings provide significant information for the design of nanomedicines in transdermal formulations.

The transdermal penetration of novel amphiphilic MTC-Y carrier

A transdermal drug delivery system capable of transporting the active substance through skin is alternative path for drug delivery for different purposes. In an attempt to demonstrate the permeability of the active substance through the skin layers of the rats, the amphiphilic MTC-Y carrier was combined with fluorochromes of different chemical properties. After extraction, the skin material was subjected histological examination under fluorescence microscope Nikon Eclipse 80i UV-2A filter (EX330-380, DM-400, BA-420). Moreover, histological slides routinely stained with haematoxylin were analysed. Results indicate that use of the MTC-Y carrier seems to be very promising compound for drug delivery both locally and systematically

Improved Dermal and Transdermal Delivery of Curcumin with SmartFilms and Nanocrystals

Poor aqueous solubility of active compounds is a major issue in today’s drug delivery. In this study the smartFilm-technology was exploited to improve the dermal penetration efficacy of a poorly soluble active compound (curcumin). Results were compared to the dermal penetration efficacy of curcumin from curcumin bulk suspensions and nanocrystals, respectively. The smartFilms enabled an effective dermal and transdermal penetration of curcumin, whereas curcumin bulk- and nanosuspensions were less efficient when the curcumin content was similar to the curcumin content in the smartFilms. Interestingly, it was found that increasing numbers of curcumin particles within the suspensions increased the passive dermal penetration of curcumin. The effect is caused by an aqueous meniscus that is created between particle and skin if the dispersion medium evaporates. The connecting liquid meniscus causes a local swelling of the stratum corneum and maintains a high local concentration gradient between drug particles and skin. Thus, leading to a high local passive dermal penetration of curcumin. The findings suggest a new dermal penetration mechanism for active compounds from nano-particulate drug delivery systems, which can be the base for the development of topical drug products with improved penetration efficacy in the future.

Curcumin Loaded Ethosomal Gel for Improved Topical Delivery: Formulation, Characterization and Ex-vivo Studies

Background: Curcumin is a curcuminoid which is an active constituent of turmeric and is obtained from the rhizomes of Curcuma longa, family Zingiberaceae. Curcumin modulates the activity of various transcription factors and regulates the expression of inflammatory enzymes, cell survival proteins, adhesion molecules and cytokines by binding to a variety of proteins and inhibiting the activity of various kinases. Curcumin falls in the BCS class IV drug, with poor solubility and poor permeability which makes it very challenging in utilizing the maximum therapeutic potential of this moiety. Objective: The major aim of the study was to enhance transdermal penetration of curcumin via ethosomal gel and to overcome the barriers of poor permeability of transdermal drug delivery. Methods: Curcumin loaded ethosomes were prepared with varying quantities of ethanol and soya lecithin by cold method and were optimised based on entrapment efficiency, vesicular size and Ex-vivo studies. Optimised ethosomal formulation was further incorporated into a gel and was evaluated. Ex-vivo studies were performed with the ethosomal gel of curcumin and was compared with simple drug solution. Result: Prepared ethosomal system showed a vesicle size ranging from 211 to 320 nm with spherical, smooth surface and entrapment efficiency of 87 to 91%. Optimised ethosomal system (ET3) was incorporated into gel and was further evaluated. Conclusion: The findings of the research work suggested that the ethosomal gel holds an excellent potential for transdermal delivery of curcumin.

Nanosuspensions and Microneedles Roller as a Combined Approach to Enhance Diclofenac Topical Bioavailability

Topical application of the anti-inflammatory drug diclofenac (DCF) reduces the severity of systemic unwanted effects compared to its oral administration. A number of transdermal formulations are available on the market and routinely used in clinical and home-care settings. However, the amount of DCF delivered across the skin remains limited and often insufficient, thus making the oral route still necessary for achieving sufficient drug concentration at the inflamed site. In attempting to improve the transdermal penetration, we explored the combined use of DCF nanosuspensions with a microneedle roller. Firstly, DCF nanosuspensions were prepared by a top-down media milling method and characterized by spectroscopic, thermal and electron microscopy analyses. Secondly, the pore-forming action of microneedle rollers on skin specimens (ex vivo) was described by imaging at different scales. Finally, DCF nanosuspensions were applied on newborn pig skin (in vitro) in combination with microneedles roller treatment, assessing the DCF penetration and distribution in the different skin layers. The relative contribution of microneedle length, nanosuspension stabilizer and application sequence could be identified by systemically varying these parameters.

Comparative Evaluation of the Transdermal Permeation Effectiveness of Fu’s cupping therapy on eight different types of model drugs

Background:: Overcoming the skin barrier to achieve the transdermal penetration of drugs across the stratum corneum (SC) remains a significant challenge. Our previous study showed that Fu’s cupping therapy (FCT) contributes to the transdermal enhancement and percutaneous absorption rate of representative drugs and improves their clinical effects. This work was to evaluate the transdermal enhancement effect of FCT on drugs with different molecular weights (MW). Methods:: we investigated the enhancements in the transdermal penetration of eight types of model drugs through the skin from BALB/c-nu mice and Sprague Dawley rats using Franz diffusion devices. In addition, 3% azone, 5% azone, 3% pep-permint oil, and 5% peppermint oil were used as penetration enhancers to study the transdermal behaviour of these drugs. Results:: Our results showed that the BALB/c-nu mouse skin was the best transdermal media, and the optimal time for FCT was 10 min. Compared with other penetration enhancers, FCT exerted a significantly improved effect on enhancing the per-cutaneous penetration of the selected log(P)-model drugs in addition to the two large MW drugs (ginsenoside Rg1 and noto-ginsenoside R1). A statistical analysis revealed that the relationship between the log(P) of various model drugs and the per-meability coefficient [log(Pcm)] of the FCT group was log(Pcm)=0.080(log(P))2-0.136(log(P))-0.282. Conclusion:: FCT may be used as a novel method for enhancing the physical penetration and thus effectively promoting the transdermal absorption of drugs and might lay a foundation for future research on drug transdermal technology.

Visualisation of H2O2 penetration through skin indicates importance to develop pathway-specific epidermal sensing

Elevated amounts of reactive oxygen species (ROS) including hydrogen peroxide (H2O2) are observed in the epidermis in different skin disorders. Thus, epidermal sensing of H2O2 should be useful to monitor the progression of skin pathologies. We have evaluated epidermal sensing of H2O2 in vitro, by visualising H2O2 permeation through the skin. Skin membranes were mounted in Franz cells, and a suspension of Prussian white microparticles was deposited on the stratum corneum face of the skin. Upon H2O2 permeation, Prussian white was oxidised to Prussian blue, resulting in a pattern of blue dots. Comparison of skin surface images with the dot patterns revealed that about 74% of the blue dots were associated with hair shafts. The degree of the Prussian white to Prussian blue conversion strongly correlated with the reciprocal resistance of the skin membranes. Together, the results demonstrate that hair follicles are the major pathways of H2O2 transdermal penetration. The study recommends that the development of H2O2 monitoring on skin should aim for pathway-specific epidermal sensing, allowing micrometre resolution to detect and quantify this ROS biomarker at hair follicles.Graphical abstract