Enhanced Skin Deposition of Betamethasone Dipropionate from a Novel Formulation and Drug Delivery Technology

INTRODUCTION

Effective topical drug delivery is the essence of dermatologic treatment. The drug must be applied to the skin surface, be released from the vehicle, enter the stratum corneum, traverse the epidermis, and enter the dermis pharmacologically intact. New advances have improved emulsion-type formulation and drug delivery technology by encapsulating dispersed oil droplets in a robust multimolecular aqueous film of surfactants, oil, and water, enabling a multifold decrease in surfactant concentration compared to conventional creams. In the research reported here, we studied this new concept, termed polyaphron dispersion (PAD) technology, by comparing skin delivery of betamethasone dipropionate from a novel oil-in-water emulsion system of calcipotriene and betamethasone dipropionate (CAL/BDP) cream to that from a traditional topical suspension (CAL/BDP TS) utilizing in vitro and in vivo detection methods.

METHODS

The amount of BDP released from the CAL/BDP cream and CAL/BDP TS was evaluated using both in vitro Franz cell analysis and in vivo human tape stripping from ten female human volunteers after a single application of CAL/BDP cream or CAL/BDP TS. For the tape stripping analysis, 20 circular tape strips were taken from forearm application sites at 1, 2, 4, and 8 h after application and analyzed for the amount of BDP in the tape strip using liquid chromatography-mass spectrometry (LC-MS).

RESULTS

The in vitro Franz cell analysis demonstrated that the cumulative amount of BDP that diffused through the epidermis was statistically significantly greater for the CAL/BDP cream compared to the CAL/BDP TS at all time points. In addition, consistently higher amounts of BDP were recovered following CAL/BDP cream application than following CAL/BDP TS application at 1, 2, 4, and 8 h following application utilizing the in vivo tape stripping technique.

CONCLUSION

The novel PAD technology-based cream formulation delivered more BDP into the upper stratum corneum and lower epidermis than a traditional topical suspension.

Combinatory effects of Dipterocarpus alatus twig emulgel: Wound-restoring, antibacterial, and anti-inflammatory activities against methicillin-resistant Staphylococcus aureus-infected mouse superficial wounds

Dipterocarpus alatus has been used for the treatment of infectious skin diseases and ulcerative wounds in Thai traditional medicine. A major pathogen in human superficial skin infections is methicillin-resistant Staphylococcus aureus (MRSA). This study determined the wound healing, antibacterial, and anti-inflammatory activities of D. alatus twig emulgel against MRSA-infected mouse superficial skin wounds. Ethyl acetate-methanol crude extract of D. alatus twig was incorporated into emulgel at concentrations of 20 and 40 mg/g (D20 and D40) and its activity was compared to tetracycline emulgel (160 μg/g, Tetra). MRSA-infected superficial wounds demonstrated decreased skin barrier strength, increased transepidermal water loss (TEWL), and mast cell accumulation. Expression of toll-like receptor 2 (TLR-2), NF-κβ, TNFα, IL-1β, IL-6 and IL-10 genes were induced after MRSA infection. Daily application of 100 μL of D20 or D40 for 9 days restored skin barrier strength and TEWL while reducing mast cell and MRSA numbers compared to the non-treated group (MRSA-NT). The wounds treated with D20 and D40 were entirely healed on day 9. Expression of TLR-2 and cytokine-related genes NF-κβ, TNFα, IL-1β, IL-6 and IL-10 were normalized by treatment with either D20 or D40. Therefore, emulgel containing 20 to 40 mg/g ethyl acetate-methanol crude D. alatus twig extract is a good candidate for development as a topical formulation for MRSA-infected ulcerated wounds.

Challenges in Noninvasive Skin Biomarker Measurements in Daily Practice: A Longitudinal Study on Skin Surface Protein Detection by the Transdermal Analysis Patch in Pediatric Psoriasis

INTRODUCTION

Skin surface proteins are potential biomarkers in psoriasis and can be measured noninvasively with the transdermal analysis patch (TAP). This study aimed to assess markers measured by TAP over time in daily clinical practice, explore their correlation with disease severity in pediatric psoriasis, and compare the TAP and tape stripping detection capability.

METHODS

In this prospective observational daily clinical practice study, pediatric psoriasis patients (aged >5 to <18 years) were followed during 1 year. At each visit, TAPs were applied to lesional (n = 2), peri-lesional (n = 2), and non-lesional (n = 1) sites. Post-lesional skin was sampled if all lesions on the arms, legs, or trunk cleared. Treatment and psoriasis severity data were collected. IL-1RA, hBD-2, IL-1α, IL-8, VEGF, CXCL-1/2, CCL-27, IL-23, hBD-1, IL-22, IL-17A, KLK-5, and IL-4 levels were quantified by spot-ELISA. For the statistical analysis, Wilcoxon signed rank tests, Mann-Whitney U tests, and Spearman correlations were used. Detection capability of the TAP was compared to tape stripping in a separate cohort of adult psoriasis patients.

RESULTS

32 patients (median age 15.0 years, median Psoriasis Area and Severity Index [PASI] 5.2) were followed for a mean of 11.3 (±3.4) months with a total of 104 visits. In lesional skin (n = 197), significantly higher IL-1RA, hBD-2, IL-8, VEGF, CXCL-1/2, IL-23, hBD-1, IL-22, CCL-27, and IL-17A levels were found compared to non-lesional skin (n = 104), while IL-1α was higher in non-lesional skin. Marker levels were highly variable over time and did not correlate with disease severity measured by PASI or SUM scores. Comparison of the TAP and tape strip detection capability in adult psoriasis patients (n = 10) showed that lesional hBD-2, IL1-α, IL-8, and VEGF and non-lesional IL-1RA, hBD-2, IL-8, and VEGF were more frequently detected in tape extracts than TAPs.

CONCLUSION

Due to the lack of correlation with clinical disease severity and the current detection capability of the markers measured by TAP in psoriasis, its use in regular practice is still a bridge too far.

Dimethoate absorption: A complementary in vitro and in vivo assessment

This work attempts to evaluate dermal exposure (DE) of farm workers to dimethoate after 4 h of routine application to a lemon plantation. Dimethoate was measured on the workers' clothes as well as in stratum corneum (SC) and in saliva. In vitro permeation tests (IVPT) were performed through rat, pig and human skin and pig buccal, esophageal and sublingual mucosas. The mean of dimethoate DE was 342.19 ± 487.14 mg/d, the percentage of toxic dose per hour was higher than the other pesticides, and the SC penetration factors ranged between 0.5 and 14.81 and 0.05-53.96 % for back of neck and arms respectively. In the supporting IVPT study, dimethoate absorption through human skin was 14.75 % and the default value in the absence of experimental data for this product is 70%. These results show that in family farming the deficiency of correct clothing during the application of pesticides leaves workers more vulnerable.

Investigator Impact on Reproducibility of Drug Bioavailability in Stratum Corneum Sampling by Tape Stripping

PURPOSE

Skin sampling by tape stripping measures the local bioavailability of topical drug products in the stratum corneum (SC). The goal of the current study was to evaluate the impact of different investigators in studies that utilize a tape stripping protocol designed to minimize investigator variability.

METHODS

Two open-label clinical studies compared two lidocaine patches and a diclofenac patch and solution in twelve healthy volunteers. The mass of drug was determined in SC samples collected on tape strips at three time points following product removal in duplicate by two investigators. Investigator results were compared with each other and with results for the diclofenac solution measured by another laboratory using a similar protocol.

RESULTS

For drug mass, the geometric mean ratio comparing two investigators is within the acceptable bioequivalence interval for most measurement times and drug products. Drug uptake into the SC from the diclofenac solution was not statistically different from that determined in another laboratory. The average flux from the SC over the clearance intervals for the four drug products correspond well with flux measurements from in vitro permeation tests.

CONCLUSIONS

Results from different investigators are reproducible within the limitations of measurement variability, which can be managed by increasing volunteer numbers.

Tape Stripping: Investigational, Diagnostic and Therapeutic Uses in Dermatology

Adhesive tape has been used in the scientific study of human skin for over 90 years. Using the tape stripping method in dermatology has aided in the research and diagnose of different skin diseases. Basic science, identification, and therapeutic interventions in skin diseases such as psoriasis, atopic dermatitis, non-melanoma skin cancer, and melanoma have been studied using this technique. Among many promising applications that will be discussed throughout this paper, the Pigmented Lesion Assay (PLA) will be discussed in depth in relation to melanoma. This product carries considerable and significant research towards early detection of melanoma. Tape stripping is unique and advantageous in its ability to provide a non-surgical approach to evaluating the human epidermis. The cellular and molecular components of the skin are used to diagnose different skin conditions without invasive skin biopsy.

Influence of mechanical skin treatment (massage, ultrasound, microdermabrasion, tape stripping and microneedling) on dermal penetration efficacy of chemical compounds

The influence of mechanical skin treatments (massage, ultrasound, microdermabrasion, tape stripping and microneedling) on the dermal penetration efficacy was investigated. Results show that microneedling was the most effective tool. It increased the penetration efficacy (amount of penetrated active and penetration depth) by a factor > 2. Microdermabrasion and tape stripping remove parts of the stratum corneum (SC). This reduces the barrier function and increases the penetration efficacy. Microdermabrasion removed about 23% of the SC. Tape stripping removed about 34% of the SC and thus resulted in a slightly more pronounced increase in the penetration efficacy (+31% after tape stripping and +18% after microdermabrasion). Massage and skin treatment with ultrasound decreased the penetration efficacy by about one third when compared to skin where the formulations were applied without any mechanical treatment. The penetration reducing effect is caused by mechanical stress (pressure), which reduces the thickness of the SC. The increased density of the SC is considered to decrease the intercellular space within the SC and with this the flux for chemical compounds. Therefore, massage and other mechanical treatments that increase the density of the SC should be avoided if efficient dermal penetration is required.

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.

The influence of skin barrier impairment on the iontophoretic transport of low and high molecular weight permeants

The effect of skin barrier impairment on the iontophoretic transport of low (acetaminophen (ACM), lidocaine (LD), ketorolac (KT)) and high molecular weight permeants, (cytochrome c (Cyt c) and ribonuclease T1 (RNase T1)), was evaluated using tape-stripping (TS) and fractional laser ablation for "large-scale" and "localized" barrier disruption. Interestingly, removal of the stratum corneum did not invariably lead to an increase in iontophoretic delivery of the permeants. Decrease of electroosmotic (EO) flow and facilitated transport of Cl^- ions in the cathode-to-anode direction, which reduced cation electromigration (EM), both impacted cation delivery by anodal iontophoresis but the effects were partly offset by enhanced passive diffusion. Decrease in EO increased cathodal iontophoresis of KT but not that of RNase T1. Permeability coefficients confirmed the superiority of EM over EO for small molecules, LD > KT > ACM. A combination of fractional laser ablation and iontophoresis was advantageous for both positively and negatively charged small molecules as passive penetration was significantly enhanced. In conclusion, results demonstrated that (i) skin ablation prior to anodal iontophoresis decreased EO and EM but could be advantageous for delivery if the ablative technique enhanced passive penetration thereby compensating reduction of electrotransport and (ii) reduced EO favored cathodal electrotransport.

Dendrimer-mediated permeation enhancement of chlorhexidine digluconate: Determination of in vitro skin permeability and visualisation of dermal distribution

Chlorhexidine digluconate (CHG) is a cationic bisbiguanide used in the UK as the first-line skin antiseptic prior to surgery in the UK due to its favourable efficacy and safety profile, high affinity for skin binding and minimal reports of resistance. Despite this, bacteria remain within deeper skin layers, furrows and appendages that are considered inaccessible to CHG, due to its poor dermal penetration. In this study a third generation, polyamidoamine dendrimer (G3 PAMAM-NH₂) was utilised to improve dermal penetration of CHG. A topical gel formulation was optimised to maximise CHG delivery (containing 0.5% gelling agent and 4% drug), followed by drug and dendrimer co-formulation into a commercially viable gel. The gel containing 4% CHG and 1 mM PAMAM dendrimer significantly increased the depth permeation of CHG compared to the commercial benchmark (Hibiscrub®, containing 4% w/v CHG) (p < 0.05). The optimised formulation was further characterised using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), which indicated that the depth of dermal penetration achieved was sufficient to reach the skin strata that typically harbours pathogenic bacteria, which is currently inaccessible by commercial CHG formulations. This study therefore indicates that a G3 PAMAM-NH₂ dendrimer gel may be viable as a permeation enhancer of CHG, for improved skin antisepsis in those at risk of a skin or soft tissue infection as a result of surgical intervention.

The stratum corneum transcriptome in atopic dermatitis can be assessed by tape stripping

BACKGROUND

Skin biopsies represent a gold standard in skin immunology and pathology but can cause pain and induce scarring. Non-invasive techniques will facilitate study recruitment of e.g. patients with paediatric atopic dermatitis (AD), hand eczema or facial dermatitis.

OBJECTIVE

By RNA sequencing, we examined whether the stratum corneum transcriptome in AD skin can be assessed by tape stripping, as compared to the epidermal transcriptome of AD in skin biopsies. To make the procedure clinically relevant tape strips were stored and shipped at room temperature for up to 3 days.

METHODS

Nine adult Caucasian AD patients and three healthy volunteers were included. Tape samples were collected from non-lesional and lesional skin. Biopsies were collected from lesional skin and were split into epidermis and dermis. Total RNA was extracted, and shotgun sequencing was performed.

RESULTS

Shotgun sequencing could be performed on skin cells obtained from two consecutive tape strips which had been stored and shipped at room temperature for up to three days. The most prominent differences between the tape strip and biopsy derived transcriptome were due to structural genes, while established molecular markers of AD, including CCL17, CCL22, IL17A and S100A7-S100A9, were also identified in tape strip samples. Furthermore, the tape strip derived transcriptome showed promise in also analysing the skin microbiome.

CONCLUSION

Our study shows that the stratum corneum (SC) transcriptome of AD can be assessed by tape stripping the skin, supporting that this method may be central in future skin biomarker research. NCBI GEO data accession: GSE160501.

Ex vivo penetration analysis and anti-inflammatory efficacy of the association of ferulic acid and UV filters

BACKGROUND

Unprotected chronic exposure to ultraviolet (UV) radiation generates many harmful effects to human skin and sunscreens are essential to health, however, traditional products do not provide enough protection against cutaneous oxidative stress, a process amplified by UV radiation. Therefore, the development of multifunctional photoprotective formulations seems to be a more efficacious approach, since these enable the absorption/reflection of UV radiation and maintain the cutaneous homeostasis.

OBJECTIVES

In the present study, ferulic acid (FA), a well-known antioxidant, has been combined with two UV filters, bemotrizinol and ethylhexyl triazone, and the safety and efficacy of this formulation has been assessed combining ex vivo and in vivo methods.

METHODS

Skin permeation assays were performed by applying the formulation in the volar forearm of participants, after which consecutive samples of the stratum corneum were collected by tape stripping, and the quantification of FA, bemotrizinol and ethylhexyl triazone was performed by high-performance liquid chromatography (HPLC). Also, the FA anti-inflammatory action in combination with the UV filters was probed through a method employing Laser Doppler flowmetry to measure the vasodilatory response to methyl nicotinate topical application.

RESULTS

Skin permeation assay was able to characterize the penetration depth of each substance. It should also be noted that a specific HPLC analytical method was developed in this study to enable the rapid simultaneous quantification of the three substances. Results from Laser Doppler flowmetry showed that the FA was able to mitigate the vasodilatory response.

CONCLUSIONS

FA proved to be a valuable resource in a multifunction sunscreen, not only providing an increase in the SPF of sunscreens, previously published, but also decreasing the extent of inflammation.

Topical buparvaquone nano-enabled hydrogels for cutaneous leishmaniasis

Leishmaniasis is a neglected disease presenting cutaneous, mucosal and visceral forms and affecting an estimated 12 million mostly low-income people. Treatment of cutaneous leishmaniasis (CL) is recommended to expedite healing, reduce risk of scarring, prevent parasite dissemination to other mucocutaneous (common with New World species) or visceral forms and reduce the chance of relapse, but remains an unmet need. Available treatments are painful, prolonged (>20 days) and require hospitalisation, which increases the cost of therapy. Here we present the development of optimised topical self-nanoemulsifying drug delivery systems (SNEDDS) loaded with buparvaquone (BPQ, a hydroxynapthoquinone from the open Malaria Box) for the treatment of CL from New World species. The administration of topical BPQ-SNEDDS gels for 7 days resulted in a reduction of parasite load of 99.989 ± 0.019% similar to the decrease achieved with intralesionally administered Glucantime® (99.873 ± 0.204%) in a L. amazonensis BALB/c model. In vivo efficacy was supported by ex vivo permeability and in vivo tape stripping studies. BPQ-SNEDDS and their hydrogels demonstrated linear flux across non-infected CD-1 mouse skin ex vivo of 182.4 ± 63.0 μg cm^-2 h^-1 and 57.6 ± 10.8 μg cm^-2 h^-1 respectively localising BPQ within the skin in clinically effective concentrations (227.0 ± 45.9 μg and 103.8 ± 33.8 μg) respectively. These levels are therapeutic as BPQ-SNEDDS and their gels showed nanomolar in vitro efficacy against L. amazonensis and L. braziliensis amastigotes with excellent selectivity index toward parasites versus murine macrophages. In vivo tape stripping experiments indicated localisation of BPQ within the stratum corneum and dermis. Histology studies confirmed the reduction of parasitism and indicated healing in animals treated with BPQ-SNEDDS hydrogels. These results highlight the potential clinical capability of nano-enabled BPQ hydrogels towards a non-invasive treatment for CL.

Pesticide dermal absorption: Case study x in vitro study

In order to evaluate dermal absorption during typical working conditions in family farming, the amount of dimethoate on clothing and in the stratum corneum (SC) was measured in three rural workers. This was achieved by using cotton patches on the worker's clothes and SC quantification by the tape stripping approach. To mimic the above study, an in vitro approach was performed using Franz cells by applying dimethoate (0.4 and 1.8 μg) direct to pig skin or, on a section of cotton before contact with pig skin. The in vivo case results demonstrated the high levels and variability of agrochemicals to which these farmers are subjected, with the total potential dermal absorption between 0.87-2.85 mg/person/h and the estimated SC penetration factor (PF) between 0-54.0 and 0-28.9 % for the back of the neck and the arms respectively. This probably demonstrates the impact of correct protective clothing. For the in vitro study, the amount of pesticide retained in the SC was 52.63 ± 10.73and 135.15 ± 31.8 ng/cm² after applying 0.4 and 1.8 μg of pesticide directly on SC, and demonstrated close agreement with the in vivo approach. Further studies performed with this and other pesticides with different characteristics will contribute to the understanding of their transport through the skin.

Effects of lecithin-based nanoemulsions on skin: Short-time cytotoxicity MTT and BrdU studies, skin penetration of surfactants and additives and the delivery of curcumin

Surfactants are important ingredients in pharmaceutical and cosmetic formulations, as in creams, shampoos or shower gels. As conventional emulsifiers such as sodium dodecyl sulfate (SDS) have fallen into disrepute due to their skin irritation potential, the naturally occurring lecithins are being investigated as a potential alternative. Thus, lecithin-based nanoemulsions with and without the drug curcumin, known for its wound healing properties, were produced and characterised in terms of their particle size, polydispersity index (PDI) and zeta potential and compared to SDS-based formulations. In vitro toxicity of the produced blank nanoemulsions was assessed with primary human keratinocytes and fibroblasts using two different cell viability assays (BrdU and EZ4U). Further, we investigated the penetration profiles of the deployed surfactants and oil components using combined ATR-FTIR/tape stripping experiments and confirmed the ability of the lecithin-based nanoemulsions to deliver curcumin into the stratum corneum in tape stripping-UV/Vis experiments. All manufactured nanoemulsions showed droplet sizes under 250 nm with satisfying PDI and zeta potential values. Viability assays with human skin cells clearly indicated that lecithin-based nanoemulsions were superior to SDS-based formulations. ATR-FTIR tests showed that lecithin and oil components remained in the superficial layers of the stratum corneum, suggesting a low risk for skin irritation. Ex vivo tape stripping experiments revealed that the kind of oil used in the nanoemulsion seemed to influence the depth of curcumin penetration into the stratum corneum.

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

The stratum corneum (SC), the outermost layer of the skin and its major barrier for penetration, contains furrows of different depths on its surface. The presence of these furrows might lead to erroneous interpretation of the results in skin permeation studies using tape stripping, in which the material trapped in the furrows removed by the tapes representing different layers of the SC might be interpreted as material penetrating within these layers. The present objective was to investigate the effect of skin furrows on tape stripping results. Non-penetrating fluorescent materials were topically applied to split-thickness human and full-thickness porcine skin samples. Tape stripping was applied, and the tapes were assessed by fluorescence microscopy and quantitative analyses. The microscopy images were assessed visually to determine the presence of the applied material in the furrows. The penetration depth of the material was examined and the fluorescence content and pattern in each tape were analyzed. The results suggested that skin furrows could be important in the first 10 tapes, affecting the quantification of materials in the SC, particularly in permeation studies of materials with low penetration into the SC. Depending on the properties of the materials, skin rinsing could reduce the impact of furrows.

Analysis of chlorhexidine gluconate in skin using tape stripping and ultrahigh-performance liquid chromatography-tandem mass spectrometry

BACKGROUND

Topical chlorhexidine gluconate (CHG) is used widely to reduce healthcare-associated infection. The optimal therapeutic dose for maximum efficacy and reduced toxicity is unclear, in part because of the lack of analytical methods to monitor CHG levels in skin. A novel method was developed to accurately measure CHG levels in skin after topical application with the goal of determining its pharmacokinetics in skin.

METHODS

Ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was used to develop a validated assay for measuring CHG levels in skin cells collected by a non-invasive adhesive tape-stripping method. CHG levels in the skin stratum corneum of healthy adult volunteers were measured at 0.5, 4, 8, and 24 h after its application.

RESULTS

Conditions for extraction of CHG were optimized and the assay was linear in the range 0.1-50 μg/mL (corresponding to 0.2-100 μg chlorhexidine/tape), with an intra-assay precision of 1.74-10.50 % and a relative error of ≤10 %. The inter-assay accuracy was in the range of 5.86-10.96 % with a relative error <9 %. CHG was stable on tapes stored at 4 °C and ambient temperature for 14 and 3 days, respectively. The recovery of CHG from the tape was quantitative and the matrix effect was determined as 2.1-14.8 %. CHG levels in healthy adult volunteer skin following topical application decreased rapidly over a 24 h period.

CONCLUSIONS

A rapid, accurate and specific UHPLC-MS/MS method was developed for the measurement of CHG in the skin obtained by tape stripping that was linear over a large dynamic range. This assay afforded a simple and convenient non-invasive approach to monitor CHG levels in skin after topical application that can be applied to enable the optimal dose to prevent infection and minimize toxicity.

Transcutaneous anaesthetic nano-enabled hydrogels for eyelid surgery

Local anaesthetics are administered as a diffuse superficial slow injection in blepharoplasty. Current transcutaneous local anaesthetic formulations are not licensed for use on the face due to safety concerns. Here we report for the first time the permeation of local anaesthetics (lidocaine, bupivacaine loaded SNEDDS and their hydrogels) across human eyelid and mouse skin as a novel and ocular safe formulation for eyelid surgery. SNEDDS were loaded with high levels of anaesthetics and incorporated within carbomer hydrogels to yield nano-enabled gels. Lidocaine hydrogels have a significantly reduced lag time compared to EMLA, while they enhance lidocaine flux across human eyelid skin by 5.2 fold. Ex vivo tape stripping experiments indicated localisation of anaesthetics within the stratum corneum and dermis. Initial histopathological studies have shown no apparent signs of skin irritation. These results highlight the potential clinical capability of nano-enabled anaesthetic hydrogels as a non-invasive anaesthetic procedure for eyelid surgery.

Topical application of highly concentrated water-in-oil emulsions: Physiological skin parameters and skin penetration in vivo - A pilot study

Important aspects in the development of new dermal drug delivery systems are the formulations' physicochemical properties and stability. Moreover, their influence on skin physiology and their penetration performance in vivo are of crucial interest. We have recently developed novel concentrated water-in-oil emulsions based on a non-ionic silicone surfactant; the present study deals with the effect of these formulations on physiological skin parameters of healthy volunteers after repeated application. Variations in skin condition and barrier integrity were investigated using classical biophysical and spectroscopic techniques. After four weeks of continuous treatment, no signs of skin irritation could be observed. Both tested emulsions had a positive effect on skin properties despite their relatively high water content and low lipid content. In vivo tape stripping studies revealed penetrated amounts of the incorporated model drug fluorescein sodium of almost 50% of the applied dose, with a superior performance of emulsions with isopropyl myristate when compared to liquid paraffin. In summary, our study confirmed the suitability of the developed W/O emulsions for pharmaceutic and cosmetic applications.

Multifunctional Cosmetic Containing Blueberry and Tinosorb M®-Loaded Microparticles Improves Sunscreen Performance

Purpose: We aimed to evaluate the effect of blueberry extract and microparticles (MP) on sunscreen performance of multifunctional cosmetics. Octocrylene (OCT), benzophenone-3 (BENZ-3) and Tinosorb® M (MBBT) were employed as UV filters.

Methods: An in-silico modeling was used to determine the UV filters concentrations to obtain high values of sunscreen protection factor (SPF) and UVA protection factor (UVA-PF). MBBT and blueberry-loaded microparticles (MP_MB+B) and MBBT-loaded microparticles (MP_MBBT) were prepared by spray-drying. OCT and BENZ-3 were added in the oil phase of cosmetics. Cosmetics A and B contained MP_MB+B and MP_MBBT, respectively, and cosmetic C was prepared without MP. Characterization, physicochemical stability and in vitro SPF was performed. UV filters distribution in human stratum corneum (SC) for each cosmetic was performed. Anti-oxidant activity of blueberry extract was evaluated.

Results: Sunscreen combination with the highest SPF was selected for formulations. Formulations A and B maintained their rheological behavior over time, unlike formulation C. In-vitro SPFs for formulations A, B and C were 51.0, 33.7 and 49.6, respectively. We also developed and validated a method for analysis of the UV filters by HPLC/ PDA suitable for the in-vivo assay. In Tape stripping test, MBBT showed SC distribution similar for all cosmetic formulations. OCT and BENZ-3 distribution to formulation A and C was also similar. Blueberry extract showed antioxidant capacity of 16.71 μg/mL equivalent to vitamin C.

Conclusion: Cosmetics containing MPs presented better physical stability. Blueberry increased the photoprotective capacity of the formulations and added extra benefits due to its anti-oxidant and anti-aging properties.

Production of LMWH-conjugated core/shell hydrogels encapsulating paclitaxel for transdermal delivery: In vitro and in vivo assessment

Topical applications that reduce systemic toxic effects while increasing therapeutic efficacy are a promising alternative strategy. The aim of this study was to provide an enhanced transdermal delivery of low molecular weight heparin (LMWH) through the stratum corneum by using cationic carrier as a novel permeation enhancer. Recent studies have shown that heparin-conjugated biomaterials can be effective in inhibiting tumor growth during cancer treatment due to their high ability to bind growth factors. Paclitaxel (PCL) was co-encapsulated into the same cationic carrier for the purpose of improving of therapeutic efficacy for a combined cancer treatment with LMWH. In vitro and in vivo studies showed that the LMWH and PCL release was significantly affected by polymer molecular weight and block composition. Skin penetration tests have indicated that larger amounts of LMWH were absorbed from LMWH-gel conjugate through SC, than aqueous formula. However, it was found that the plasma transition of LMWH released from gel conjugate was lower compared to the plasma concentration of LMWH released from aqueous solution. It is recommended that PCL-loaded LMWH-conjugated core/shell hydrogels can be used as promising drug release systems for transdermal applications that can improve therapeutic efficacy and reduce side effects in a combined cancer treatment.

Increasing the percutaneous absorption and follicular penetration of retinal by topical application of proretinal nanoparticles

Topical retinoids are frequently applied for therapeutic and cosmeceutical reasons although their bioavailability is low due to their chemical and photochemical instability. Moreover, skin irritation is a common side effect. Therefore, proretinal nanoparticles (PRN) as a novel formulation of topical retinoids, which are based on chitosan grafted with retinal through reversible linkage, were developed and their skin penetration behavior was studied. As nanoparticles preferably penetrate into the hair follicles, the follicular penetration depths of PRN at different time points were investigated. Moreover, the release capacity of the nanoparticulate system was studied using fluorescein as a model drug. Additionally, the concentration of retinal in the stratum corneum and in the hair follicles was quantified after application in particulate and non-particulate form. The results showed that the nanocarriers reached the infundibular area of the hair follicles, irrespective of the incubation time. The nanoparticles were able to release their model drug within the hair follicle. The retinal concentration delivered to the stratum corneum and the hair follicles was significantly higher when retinal was applied in the particulate form. In conclusion, the presented proretinal nanoparticle system may help to overcome the main problems of topical retinoid therapy, which are skin irritation, chemical and photochemical instability and low bioavailability, thus improving the topical retinoid therapy.

Development of a Novel Approach to Studying Corneodesmosomes and Stratum Corneum Adhesion: Extending Knowledge on the Pathophysiology of Sensitive Skin

BACKGROUND/AIMS

Aberrant skin barrier and intercorneocyte adhesion are potential contributors to the pathomechanism of sensitive skin (SS). Here we aimed to develop a novel and easy-to-apply method to analyze corneodesmosomes and to interrogate potential differences between corneocytes of subjects with SS and non-SS (NSS).

METHODS

Corneocytes of the volar forearm and upper outer quadrant of the left buttock of SS (n = 10) and NSS (n = 8) subjects were extracted as a function of depth using adhesive tape and stained with anti-desmoglein 1 (DSG1) antibody. The total area of corneocytes and the number and average size of cells per tape was estimated using image processing.

RESULTS

The total area of extracted corneocytes and the quantity of DSG1 decreased with depth. The level of decrease, total area of corneocytes, and average area of individual cells differed between anatomical locations. In SS, a larger total area of extracted corneocytes and a larger average cell size per tape was found at all inspected depths.

CONCLUSION

The developed novel and easy-to-apply approach allows investigation of corneodesmosome components. We confirm a role of altered corneocytes in the pathomechanism of SS. The disclosed protocol can further be optimized in studies of skin conditions with strongly affected corneodesmosomes.

Epicutaneous immunotherapy in rhino-conjunctivitis and food allergies: a review of the literature

Background

Epicutaneous immunotherapy (EPIT) is a new way of allergen administration that has a high rate of adherence and safety. The aim of this manuscript is to review clinical trials on EPIT for respiratory and food allergies published in the last 10 years, taking into account how different variables (i.e., dose, patch application duration, skin preparation, and efficacy and safety evaluation) have influenced study results.

Main body

From a review of the literature, we identified eight placebo-controlled, double-blind trials conducted on children and adults, including four studies on grass pollen rhino-conjunctivitis, one on cow’s milk allergy and three on peanut allergy. Different methods for skin pre-treatment, such as skin abrasion and tape stripping or stratum corneous hydration by an occlusive system, different endpoints and cumulative allergen doses, and different durations of patch application and tape stripping, were used in the rhino-conjunctivitis studies. A visual analogue system was used for the efficacy evaluation. Several local skin reactions (eczema) and some systemic adverse reactions were reported at higher rates in the active group compared to placebo in one study, but this was not shown by other authors. Local eczema reactions were correlated to the times for applying the tape stripping, while systemic side effects were correlated to the deepness of scraping. In the food allergy trials, differences in the food challenge thresholds, endpoints and allergen sites of the cutaneous patch application influenced the study results. A slight dose-dependent efficacy was found in the peanut allergy studies, which was confirmed by a more significant increase in the following progressive open study. Few adverse events and high adherence in all of the food allergen trials were reported.

Conclusions

Overall, the EPIT study results, even if they were affected by great heterogeneity among the methodologies applied, have shown not only the high safety and adherence with this kind of immunotherapy but also suggested the possibility for obtaining definitive evidence of the efficacy of EPIT, especially for food allergies.

Inter-laboratory study of the skin distribution of 4-n-butyl resorcinol in ex vivo pig and human skin

4-n-butyl resorcinol (4-nBR) is a highly effective tyrosinase inhibitor, and can be used in cosmetic product for depigmentation purpose. Its efficacy correlates with 4-nBR that absorbed by skin. In this study, skin distribution of 4-nBR within either human or pig skin ex vivo was studied and compared by three independent laboratories. Good agreement was observed in each compartment considering usual inter-lab variability. This study supports the use of pig skin as an alternative source of skin when the availability of human skin is a limiting factor.

Penetration monitoring of drugs and additives by ATR-FTIR spectroscopy/tape stripping and confocal Raman spectroscopy - A comparative study

Vibrational spectroscopy is a useful tool for analysis of skin properties and to confirm the penetration of drugs and other formulation compounds into the skin. In particular, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and confocal Raman spectroscopy (CRS) have been optimised for skin analysis. Despite an impressive amount of data on these techniques, a comparative methodological assessment for skin penetration monitoring of model substances is still amiss. Thus, in vitro skin penetration studies were conducted in parallel using the same porcine material and four model substances, namely sodium laureth sulfate (SLES), sodium dodecyl sulfate (SDS), sulfathiazole sodium (STZ) and dimethyl sulfoxide (DMSO). ATR-FTIR spectroscopy in combination with tape stripping and CRS were employed to evaluate the skin penetration of the applied substances. In addition, the skin hydration status or change in skin hydration after application was investigated. The results show that both methods provide valuable information on the skin penetration potential of applied substances. The penetration profiles determined by CRS or ATR-FTIR/tape stripping were comparable for all substances; a slow decrease in relative substance concentration was visible from the skin surface inwards within the stratum corneum (SC). In general, deeper penetration into the SC was observed with CRS, which may be related to the depth resolution of the employed device. However, when related to the respective total SC thickness of each experiment, the penetration depths determined by parallel CRS and ATR-FTIR analysis were in good agreement for all model substances. The observed order of the penetration depth was DMSO > SDS > SLES > STZ with both techniques. A decrease of the relative concentration to 10% of the maximum value was found approximately between 34 and 89% of total SC thickness. Summarising these findings, advantages and drawbacks of the two techniques for in vitro skin penetration studies are discussed.

The optimal age for epicutaneous sensitization following tape-stripping in BALB/c mice

BACKGROUND

Direct contact of food proteins with eczematous lesions is thought to be the main cause of epicutaneous sensitization. To further investigate the development and pathogenesis of food allergy in vivo, a good mouse model of epicutaneous sensitization is needed. However, a fundamental problem in that regard is that the optimal age for epicutaneous sensitization of mice is unknown. In this study, we attempted to elucidate that optimal age.

METHODS

Dorsal skin of wild-type BALB/c female mice (1, 3, 8 and 24 weeks old) was shaved, depilated and tape-stripped. A Finn chamber containing a 20-μl-aliquot of 20-mg/ml (OVA) was applied to the tape-stripped skin on 3 consecutive days/week, for 3 weeks. The body temperature was measured after intraperitoneal OVA challenge. Serum OVA-specific IgE titers and OVA-induced cytokine production by spleen cells were measured by ELISA. Dendritic cells (DCs) that migrated to the draining lymph nodes were quantified by FITC-labeled OVA and flow cytometry. The mRNA expression levels in the dorsal skin were measured by qPCR.

RESULTS

A significant age-dependent body temperature decline was observed after OVA challenge. The serum OVA-specific IgE titer, OVA-induced cytokine production (i.e., IL-4, IL-5 and IL-13) by spleen cells, and number of FITC-OVA-engulfing DCs increased with age. In addition, mRNA for IL-33, but not TSLP or IL-25, was significantly induced in the skin by tape-stripping and increased with age.

CONCLUSIONS

Twenty-four-week-old mice showed the greatest DC migration, Th2 polarization, IgE production and body temperature decline. Skin-derived IL-33 is likely to play key roles in those changes.

Safety and Antioxidant Efficacy Profiles of Rutin-Loaded Ethosomes for Topical Application

Topical application of dermocosmetics containing antioxidant and/or the intake of antioxidants through diet or supplementation are remarkable tools in an attempt to slow down some of the harmful effects of free radicals. Rutin is a strong antioxidant compound used in food and pharmaceutical industries. It was established that rutin presents a low skin permeation rate, a property that could be considered an inconvenience to the satisfactory action for a dermocosmetic formulation to perform its antioxidant activity onto the skin. Therefore, it is indispensable to improve its delivery, aiming at increasing its antioxidant capacity in deeper layers of the epidermis, being a possibility to associate the rutin to liposomal vesicles, such as ethosomes. Thus, in this work, the pre-clinical safety of rutin-loaded ethosomes was investigated employing an in vitro method, and the clinical safety and efficacy were also assessed. Rutin-loaded ethosomes were efficaciously obtained in a nanoscale dimension with a relevant bioactive compound loading (80.2%) and provided antioxidant in vitro activity in comparison with the blank sample. Pre-clinical and clinical safety assays assured the innocuous profile of the rutin-loaded ethosomes. The ethosomes containing the bioactive compound accomplished a more functional delivery system profile, since in the tape stripping assay, the deeper layers presented higher rutin amounts than the active delivered in its free state. However, the ex vivo antioxidant efficacy test detected no positive antioxidant activity from the rutin-loaded ethosomes, even though the in vitro assay demonstrated an affirmative antioxidant action.

Measurement of lidocaine and 2,6-dimethylaniline in minipig plasma, skin, and dermal tapes using UHPLC with electrospray MS/MS

Sensitive LC-MS/MS methods were developed to measure lidocaine and its metabolite 2,6-dimethylaniline (2,6-DMA) with application to transdermal studies. The methods for lidocaine in minipig plasma, tissue biopsies, and dermal tapes utilized mixed mode/SCX solid phase extraction, with lower quantitation limits of 25 pg/mL in plasma, 15 ng/g tissue, and 5 ng/tape. 2,6-DMA was measured in plasma and skin tissue homogenates by ultrafiltration and (for tissue) by further derivatization with 4-methoxybenzoyl chloride to form the corresponding benzamide derivative, which extended the lower limit of quantitation to 200 pg/mL. The methods allowed local measurement of lidocaine in stratum corneum, punch biopsies, and plasma and of 2,6-DMA in plasma and biopsies obtained from minipigs dosed with experimental transdermal formulations. Quantitation limits were approximately 7-fold lower than previously reported for lidocaine and 3-fold lower for 2,6-DMA.

Investigation of cis-trans isomer dependent dermatotoxicokinetics of UV filter ethylhexyl methoxycinnamate through stratum corneum in vivo

2-Ethylhexyl methoxycinnamate (EHMC) is one of the most used ultraviolet filters in personal care products. It undergoes cis/trans isomerization in sunlight, and there is limited toxicological understanding of the effects of the cis-isomer. It is known that two geometric isomers of one compound can have different physico-chemical properties and effects. However, there are no studies focusing on toxicokinetics of EHMC isomerization products to compare their potential difference in dermal exposure to cis-EHMC and trans-EHMC due to the difference in their dermatotoxicokinetics. In this study, dermal absorption of the parental trans-EHMC and its cis isomer was studied. A commercially available sunscreen lotion containing trans-EHMC and spiked with laboratory-prepared cis-EHMC was locally applied on the forearm skin of two volunteers. After 8 h of skin exposure, the stratum corneum (SC) layer was removed by tape stripping. The removed thickness of the SC was determined spectrophotometrically using a total protein assay. The concentration of both isomers in the removed SC was measured by HPLC-DAD. A new diffusion and permeability coefficient of both EHMC isomers in SC were determined by Fick's second law of diffusion in vivo. The difference in dermatotoxicokinetic parameters between the two isomers was not statistically significant. However, separate toxicological studies of isomeric forms and the determination of their dermatotoxicokinetic parameters are crucial for refinement of human risk assessment.

Evaluation of critical parameters for in vitro skin permeation and penetration studies using animal skin models

In vitro skin permeation/penetration studies may be affected by many sources of variation. Herein, we aimed to investigate the major critical procedures of in vitro skin delivery studies. These experiments were performed with model drugs according to official guidelines. The influence of skin source on penetration studies was studied as well as the use of a cryopreservation agent on skin freezing evaluated by transepidermal water loss, electrical resistance, permeation/penetration profiles and histological changes of the skin. The best condition for tape stripping procedure was validated through the evaluation of the distribution of corneocytes, mass of stratum corneum (SC) removed and amount of protein removed using finger pressure, a 2kg weight and a roller. The interchangeability of the tape stripping procedures followed by the epidermis and dermis homogenate and the micrometric horizontal cryostat skin sectioning methods were also investigated, besides the effect of different formulations. Noteworthy, different skin sources were able to ensure reliable interchangeability for in vitro permeation studies. Furthermore, an increased penetration was obtained for stored frozen skin compared to fresh skin, even with the addition of a cryoprotectant agent. The best method for tape stripping was the finger pressure followed by the addition of a propylene glycol solvent leading to better SC removal. Finally, no significant difference was found in skin penetration studies performed by different methods suggesting their possible interchangeability.

Comparison of the Effect of Skin Preparation Pads on Transepidermal Water Loss in Ex Vivo Human Skin

Introduction

Pre-treatment of the skin to remove scales and crusts prior to photodynamic therapy (PDT) is essential to enhance the uptake of topically applied methyl aminolevulinate (MAL) and to improve treatment efficacy. This study compared the effect of two different skin preparation pads on skin integrity in ex vivo human skin.

Methods

Ex vivo human skin samples from three donors were pre-treated in triplicates with PREPSTER™ (PR) skin preparation pad (6, 8, and 10 passages) or Ambu Unilect™ (A-UN) skin preparation pad (6, 8, and 10 passages). In addition, skin samples were pre-treated with tape strippings (10 adhesive tape strips) as a reference method for comparison. Transepidermal water loss (TEWL) was measured on intact skin and following skin barrier impairment using skin preparation pads and tape stripping. Histological analysis was performed to verify the impairment of the stratum corneum (SC) barrier function in samples from intact skin (control), 10 tape strippings (reference method), 10 passages of PR, and 10 passages of A-UN.

Results

TEWL increased with the increasing number of passages of skin preparation pads, with 2.4- and 3.3-fold increases following 10 passages of A-UN and PR, respectively, versus a 2.2-fold increase with 10 tape strippings (reference). Histological analysis showed only partial removal of the SC, with no damage observed on the epidermis, regardless of the procedure used.

Conclusion

Pre-treatment of skin using PR and A-UN skin preparation pads markedly increases TEWL, indicating slight impairment of the SC barrier function. Comparison of both skin preparation pads showed that PR pad consistently induced significantly higher TEWL than A-UN pad (p < 0.05), regardless of the number of passages. Both skin preparation pads are thought to increase the uptake of MAL and can therefore be used for the preparation of skin prior to PDT.

Funding

Nestlé Skin Health – Galderma R&D.

Dendrimer pre-treatment enhances the skin permeation of chlorhexidine digluconate: Characterisation by in vitro percutaneous absorption studies and Time-of-Flight Secondary Ion Mass Spectrometry

Skin penetration and localisation of chlorhexidine digluconate (CHG) within the skin have been investigated in order to better understand and optimise the delivery using a nano polymeric delivery system of this topically-applied antimicrobial drug. Franz-type diffusion cell studies using in vitro porcine skin and tape stripping procedures were coupled with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) to visualise the skin during various treatments with CHG and polyamidoamine dendrimers (PAMAM). Pre-treatment of the skin with PAMAM dendrimers significantly increased the amount and depth of permeation of CHG into the skin in vitro. The effect observed was not concentration dependant in the range 0.5-10mM PAMAM. This could be important in terms of the efficiency of treatment of bacterial infection in the skin. It appears that the mechanism of enhancement is due to the PAMAM dendrimer disrupting skin barrier lipid conformation or by occluding the skin surface. Franz-type diffusion cell experiments are complimented by the detailed visualisation offered by the semi-quantitative ToF-SIMS method which provides excellent benefits in terms of sensitivity and fragment ion specificity. This allows a more accurate depth profile of chlorhexidine permeation within the skin to be obtained and potentially affords the opportunity to map the co-localisation of permeants with skin structures, thus providing a greater ability to characterise skin absorption and to understand the mechanism of permeation, providing opportunities for new and more effective therapies.

Monitoring Skin Dendritic Cells in Steady State and Inflammation by Immunofluorescence Microscopy and Flow Cytometry

Skin dendritic cells (DC) are strategically positioned at the body's second largest epithelial border to the environment. Hence they are the first antigen presenting cells that encounter invading pathogens and environmental antigens, including contact sensitizers and carcinogens penetrating the skin. Moreover, DC have the unique ability to induce immunity or tolerance and thus take center stage in regulating innate and adaptive immune responses. Skin DC can be divided into several phenotypically and functionally distinct subtypes. The three main subsets are Langerin⁺ epidermal Langerhans cells (LC) and Langerin⁺ as well as Langerin^neg dermal DC. In the steady state skin DC form a dense network to survey the periphery for pathogens and harmful substances breaching the cutaneous barrier. During inflammation DC become rapidly activated and start their migration to skin-draining lymph nodes where they initiate antigen-specific T cell responses. The homeostasis and mobilization of DC in the skin can be visualized by immunofluorescent staining of epidermal and dermal sheet preparations or skin sections. Here, we describe in detail how inflammation can be induced in the skin with tape stripping or FITC painting and how the skin DC network can be monitored using immunofluorescence microscopy and flow cytometry.

Anti-inflammatory activity of Punica granatum L. (Pomegranate) rind extracts applied topically to ex vivo skin

Coadministered pomegranate rind extract (PRE) and zinc (II) produces a potent virucidal activity against Herpes simplex virus (HSV); however, HSV infections are also associated with localised inflammation and pain. Here, the objective was to determine the anti-inflammatory activity and relative depth penetration of PRE, total pomegranate tannins (TPT) and zinc (II) in skin, ex vivo. PRE, TPT and ZnSO₄ were dosed onto freshly excised ex vivo porcine skin mounted in Franz diffusion cells and analysed for COX-2, as a marker for modulation of the arachidonic acid inflammation pathway, by Western blotting and immunohistochemistry. Tape stripping was carried out to construct relative depth profiles. Topical application of PRE to ex vivo skin downregulated expression of COX-2, which was significant after just 6h, and maintained for up to 24h. This was achieved with intact stratum corneum, proving that punicalagin penetrated skin, further supported by the depth profiling data. When PRE and ZnSO₄ were applied together, statistically equal downregulation of COX-2 was observed when compared to the application of PRE alone; no effect followed the application of ZnSO₄ alone. TPT downregulated COX-2 less than PRE, indicating that tannins alone may not be entirely responsible for the anti-inflammatory activity of PRE. Punicalagin was found throughout the skin, in particular the lower regions, indicating appendageal delivery as a significant route to the viable epidermis. Topical application of TPT and PRE had significant anti-inflammatory effects in ex vivo skin, confirming that PRE penetrates the skin and modulates COX-2 regulation in the viable epidermis. Pomegranates have potential as a novel approach in ameliorating the inflammation and pain associated with a range of skin conditions, including cold sores and herpetic stromal keratitis.

Drug delivery across intact and disrupted skin barrier: Identification of cell populations interacting with penetrated thermoresponsive nanogels

Nanoscaled soft particles, such as nanogels, can be designed to incorporate different types of compounds and release them in a controlled and triggered manner. Thermoresponsive nanogels (tNG), releasing their cargo above a defined temperature, are promising carrier systems for inflammatory skin diseases, where the temperature of diseased skin differs from that of healthy skin areas. In this study a polyglycerol-based tNG with diameter of 156nm was investigated for penetration and release properties upon topical application on ex vivo human skin with intact or disrupted barrier. Furthermore, temperature-triggered effects and the internalization of tNG by skin cells upon translocation to the viable skin layers were analyzed. The investigated tNG were tagged with indodicarbocyanine and loaded with fluorescein, so that fluorescent microscopy and flow cytometry could be used to evaluate simultaneously particle penetration and release of the fluorochrome. Topically applied tNG penetrated into the SC of both intact and disrupted skin explants. Only in barrier-disrupted skin significant amounts of released fluorochrome and tNG penetrated in the epidermis and dermis 2h after topical application. When a thermal trigger was applied by infrared radiation (30s, 3.9mJ/cm²), a significantly higher penetration of tNG in the SC and release of the dye in the epidermis were detected with respect to non-triggered samples. Penetrated tNG particles were internalized by skin cells in both epidermis and dermis. Only few CD1a-positive Langerhans cells associated with tNG were found in the epidermis. However, in the dermis a significant percentage of cells associated with tNG were identified to be antigen presenting cells, i.e. HLA-DR+and CD206+cells. Thus, tNG represent promising carrier systems for the treatment of inflammatory skin diseases, not only because of their improved penetration and controlled release properties, but also because of their ability to effectively reach dermal dendritic cells in barrier-disrupted skin.

Topical application of superoxide dismutase mediated by HIV-TAT peptide attenuates UVB-induced damages in human skin

The purpose of this study was to evaluate whether topical application of superoxide dismutase with cell penetrating peptide (HIV-TAT) could protect against skin damage induced by UVB irradiation in humans. The permeability through stratum corneum of large proteins linked to TAT peptide was firstly confirmed by confocal microscopy and tape stripping. Ten healthy volunteers with either Fitzpatrick skin type II or III were recruited in this clinical study. TAT-SOD (300units/cm(2)) and vehicle cream were applied on two symmetric areas of both inner upper arms 1h prior to UVB irradiation. After one hour of pretreatment, subjects received 10 incremental doses of UVB on pretreated areas. 24h later, erythema, blood flow and apoptotic cells were measured. Pretreatment with TAT-SOD 1h prior to UVB radiation promoted a mean minimal erythema dose (MED) increase of 36.6±18.4% (p=0.013<0.05. n=10) compared to vehicle control. The median blood flow values of all subjects following 2 and 3-MED of UVB were 107.8±51.0units and 239.5±88.0units respectively, which account for 26% and 25% decrease with respect to vehicle groups. These data suggest that TAT-SOD significantly suppresses UVB induced erythema formation and blood flow rise. Furthermore, pretreatment with TAT-SOD 1h prior to 2-MED of UVB irradiation reduced the apoptotic sunburn cell formation by 47.6±8.6% (p<0.0001) in all subjects. Evaluating results generated from all measurements, we conclude that topical application of TAT-SOD significantly attenuates UVB-induced skin damage in man. These biological effects of TAT-SOD are probably mediated via its free radical scavenging properties, clearly differentiating it from other physical sunscreen agents.

Chemical ultraviolet absorbers topically applied in a skin barrier mimetic formulation remain in the outer stratum corneum of porcine skin

The objective of the present study was to evaluate the fate of three chemical sunscreens, isoamyl p-methoxycinnamate (IPMC), diethylamino hydroxybenzoyl hexyl benzoate (DHHB), and bis-ethylhexylphenol methoxyphenyl triazine (BEMT), topically applied to mammalian skin from a skin barrier mimetic oil-in-water formulation. High Performance Liquid Chromatography (HPLC) methods were developed for the analysis of each molecule and validated. Franz cell permeation studies were conducted following application of finite doses of the formulations to excised porcine skin. A vehicle formulation containing no sunscreens was evaluated as a control. Permeation studies were conducted for 12h after which full mass balance studies were carried out. Analysis of individual UV sunscreens was achieved with HPLC following application of the formulation to the skin with no interference from the vehicle components. No skin permeation of any of the chemical sunscreens was evident after 12h. While sunscreens were detected in up to 12 tape strips taken from the SC, 87% or more of the applied doses recovered in the first 5 tape strips. When corrected for the amount of protein removed per tape strip this corresponded to a penetration depth in porcine stratum corneum of ∼1.7μm. Mass balance studies indicated total recovery values were within accepted guidelines for cosmetic formulations. Overall, only superficial penetration into the SC was observed for each compound. These findings are consistent with the physicochemical properties of the selected UV absorbing molecules and their formulation into an ordered biomimetic barrier formulation thus support their intended use in topical consumer formulations designed to protect from UV exposure. To our knowledge this is the first report of depth profiling of chemical sunscreens in the SC that combines tape stripping and protein determination following in vitro Franz cell studies.

Lipid composition and molecular interactions change with depth in the avian stratum corneum to regulate cutaneous water loss

The outermost 10-20 µm of the epidermis, the stratum corneum (SC), consists of flat, dead cells embedded in a matrix of intercellular lipids. These lipids regulate cutaneous water loss (CWL), which accounts for over half of total water loss in birds. However, the mechanisms by which lipids are able to regulate CWL and how these mechanisms change with depth in the SC are poorly understood. We used attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) to measure lipid-lipid and lipid-water interactions as a function of depth in the SC of house sparrows (Passer domesticus Linnaeus) in the winter and summer. We then compared these molecular interactions at each depth with lipid composition at the same depth. We found that in both groups, water content increased with depth in the SC, and likely contributed to greater numbers of gauche defects in lipids in deeper levels of the SC. In winter-caught birds, which had lower rates of CWL than summer-caught birds, water exhibited stronger hydrogen bonding in deeper layers of the SC, and these strong hydrogen bonds were associated with greater amounts of polar lipids such as ceramides and cerebrosides. Based on these data, we propose a model by which polar lipids in deep levels of the SC form strong hydrogen bonds with water molecules to increase the viscosity of water and slow the permeation of water through the SC.

Enhancement of in vivo human skin penetration of resveratrol by chitosan-coated lipid microparticles

In this study, lipid microparticles (LMs) uncoated or coated with chitosan, and containing the antioxidant polyphenol, resveratrol were developed in order to enhance its in vivo skin permeation. The LMs loaded with resveratrol were prepared by melt emulsification and sonication, using tristearin as lipidic material and hydrogenated phosphatidylcholine as the surfactant. Two different methods were examined for the coating of the LMs: chitosan addition during LM preparation or treatment of already formed LMs with a chitosan solution. The latter method achieved a better modulation of the in vitro release of resveratrol and hence was used for subsequent studies. The resveratrol loading and mean diameter of the LMs were 4.1 ± 0.3% (w/w) and 5.7 μm and 3.8 ± 0.2 % (w/w) and 6.1 μm for the uncoated and the chitosan-coated LMs, respectively. Chitosan coating changed the LM surface charge, from a negative zeta potential value (-17.8 ± 4.8 mV) for the uncoated particles, to a higher positive values (+64.2 ± 4.4 mV) for the chitosan-coated ones. Creams containing resveratrol free, encapsulated in the uncoated or chitosan-coated LMs were applied to the forearm of human volunteers and the penetration of the polyphenol in the stratum corneum was investigated in vivo by the tape stripping technique. Uncoated LMs did not produce any significant increase in the fraction of the applied resveratrol dose diffused in the stratum corneum (32.8 ± 8.9 %) compared to the control cream containing the non-encapsulated polyphenol (26.2 ± 5.6 % of the applied dose). On the other hand, application of the cream containing the chitosan-coated LMs produced a significant enhancement in the in vivo permeation of resveratrol to 49.3 ± 5.9% of the applied dose, the effect being more marked in the upper region of the horny layer. The observed improvement in the human stratum corneum penetration of resveratrol achieved by the LMs coated with chitosan should favour the efficiency of its topical application.

Doxorubicin liposomes as an investigative model to study the skin permeation of nanocarriers

The objectives of this study were to develop an innovative investigative model using doxorubicin as a fluorophore to evaluate the skin permeation of nanocarriers and the impact of size and surface characteristics on their permeability. Different doxorubicin-loaded liposomes with mean particle size <130 nm and different surface chemistry were prepared by ammonium acetate gradient method using DPPC, DOPE, Cholesterol, DSPE-PEG 2000 and 1,1-Di-((Z)-octadec-9-en-1-yl) pyrrolidin-1-ium chloride (CY5)/DOTAP/1,2-dioleoyl-sn-glycero-3-phosphate (DOPA) as the charge modifier. There was minimal release of doxorubicin from the liposomes up to 8h; indicating that fluorescence observed within the skin layers was due to the intact liposomes. Liposomes with particle sizes >600 nm were restricted within the stratum corneum. DOTAP (p<0.01) and CY5 (p<0.05) liposomes demonstrated significant permeation into the skin than DOPA and PEG liposomes. Tape stripping significantly (p<0.01) enhanced the skin permeation of doxorubicin liposomes but TAT-decorated doxorubicin liposomes permeated better (p<0.005). Blockage of the hair follicles resulted in significant reduction in the extent and intensity of fluorescence observed within the skin layers. Overall, doxorubicin liposomes proved to be an ideal fluorophore-based model. The hair follicles were the major route utilized by the liposomes to permeate skin. Surface charge and particle size played vital roles in the extent of permeation.

Development and validation of an alternative disturbed skin model by mechanical abrasion to study drug penetration

Pharmaceuticals and cosmetics for dermal application are usually tested on healthy skin, although the primary permeation barrier, the stratum corneum, is often impaired by skin diseases or small skin lesions, especially on the hands. These skin conditions can considerably influence the permeation of chemicals and drugs. Furthermore, risk assessment for example of nanoparticles should be performed under various skin conditions to reflect the true circumstances. Therefore, an alternative and reproducible method for a high throughput of skin samples with impaired skin barrier was developed and verified by skin permeation studies (25 h) of caffeine, sorbic acid and testosterone compared to healthy (untreated) and tape-stripped skin. Skin barrier disruption was controlled by TEWL measurement.

Skin permeation of the three substances was increased in tape-stripped and abraded skin compared to untreated skin due to the reduced barrier integrity. Enhancement of drug uptake was highest for the most hydrophilic substance, caffeine, followed by sorbic acid and lipophilic testosterone. No significant difference in drug uptake studies was observed between the new abrasion method with an aluminum-coated sponge and the tape-stripping method. The obtained results demonstrate that this abrasion method is an alternative way to achieve a disturbed skin barrier for drug and chemical uptake studies.

Influence of the composition of monoacyl phosphatidylcholine based microemulsions on the dermal delivery of flufenamic acid

Although microemulsions are one of the most promising dermal carrier systems, their clinical use is limited due to their skin irritation potential. Therefore, microemulsions based on naturally derived monoacyl phosphatidylcholine (MAPL) were developed. The influence of the water, oil and surfactant content on dermal delivery of flufenamic acid was systematically investigated for the first time. A water-rich microemulsion led to significantly higher in vitro skin penetration of flufenamic acid compared to other microemulsions. The superiority of the water-rich microemulsion over a marketed flufenamic acid containing formulation was additionally confirmed. Differences in drug delivery could be explained by alterations of the microemulsions after application. Evaporation of isopropanol led to crystal-like structures of MAPL on the skin surface from the surfactant- or oleic acid-rich microemulsions. In contrast, the formation of this additional barrier was hindered in case of the water-rich microemulsion. The skin penetration of MAPL was additionally analyzed by combined ATR-FTIR and tape stripping experiments, where MAPL itself penetrated only into the initial layers of the stratum corneum, independent of the microemulsion composition. Since a surfactant must penetrate the skin to cause irritation, MAPL can be presumed as a skin-friendly emulsifier with the ability to stabilize pharmaceutically acceptable microemulsions.