Visualization of skin penetration using confocal laser scanning microscopy

Stratified quantitative analysis of the penetration of active ingredients in the skin by infrared spectroscopic imaging

A stratified quantitative analysis method for active ingredients in the skin was developed by integrating microscopic infrared spectroscopy, chemometrics, and machine learning. Hierarchical clustering of the stratum corneum, active epidermis, and dermis of control skin slice was performed by spectral clustering algorithm, followed by classification of the skin with active ingredients by linear discriminant analysis. The classification results matched well with the bright-field images obtained from the microscope. Based on the corresponding division of the hierarchical structure of the skin, the relative permeation concentrations of the active ingredients in each layer of the skin were calculated using non-negative least squares. Then, a correction factor was introduced by applying the same calculation process to formulations with known concentrations of active ingredients, converting the relative concentrations to the actual concentrations of the active ingredients in each layer of the skin. To demonstrate the effectiveness of this analytical method, hydroxypropyl tetrahydropyrantriol and a polypeptide were selected as active ingredients, and their penetration profiles in the skin were analyzed and visualized.

MEMS-Based Portable Reflection Confocal Microscope for In Vivo Skin Imaging

This study aims to develop a portable reflective confocal microscope (PCRM) based on MEMS micro-mirrors for in vivo skin imaging. The design of PCRM is intended to overcome the limitations of traditional invasive biopsies and bulky desktop microscopes, enabling handheld operation and access to hard-to-reach skin areas. This research innovatively integrates MEMS technology into the PCM through precise mechanical design, using an 830 nm laser and a commercial Olympus objective lens, achieving a lateral resolution of 1.24 μm and an axial resolution of 5.3 μm, with imaging at a speed of 11 f/s over a field of view of 530 × 500 μm. PCRM successfully imaged various skin layers, including capillary blood flow, demonstrating diagnostic potential for skin lesions and providing a compact, high-performance solution for non-invasive skin imaging suitable for clinical applications.

Quantitative Analysis of Salmon Calcitonin Hydroxyapatite Nanoparticle Permeation to substantiate Non-Invasive Bone Targeting via Sublingual Delivery

We earlier reported comparable efficacy in bone parameters of sublingually administered salmon calcitonin hydroxyapatite nanoparticles (SCT-HAP-NPs) compared to the subcutaneous injection, in the ovariectomy rat model, despite a bioavailability of barely ~ 15%. We ascribed this intriguing finding to targeted bone delivery, facilitated by translocation of significant quantity of intact NP into systemic circulation. In the present study we track the translocation of FITC-SCT-HAP-NPs (~ 100 nm) across porcine sublingual mucosa using the Franz diffusion cell to validate our hypothesis. Confocal Laser Scanning microscopy (CLSM) established that SCT-HAP-NPs permeated into the deeper layers of sublingual porcine mucosal tissue. We confirmed the nanoparticles were present in the receptor medium of the Franz diffusion cell by DLS and TEM. We also demonstrate for the first time quantification of the NPs (%) translocated across the porcine mucosa, using the Amnis Image StreamX Mk II imaging flow cytometer. Computation revealed transport of ~ 60% of the FITC-SCT-HAP-NPs across mucosa in 2 h, substantiated that high NP concentrations could reach systemic circulation. Such high NP concentration in systemic circulation coupled with the small size (~ 100 nm) and the high bone affinity of HAP, validate our hypothesis of targeted bone delivery following sublingual administration. Furthermore, quantification of translocated NPs, which we demonstrate for the first time, would permit rational development of optimal targeted nanoparticulate carriers for delivery by noninvasive routes.

Analysis of Drug Molecules in Living Cells

Cells are the fundamental units of life, comprising a highly concentrated and complex assembly of biomolecules that interact dynamic ally across spatial and temporal scales. Living cells are constantly undergoing dynamic processes, therefore, to understand the interactions between drug molecules and living cells is of paramount importance in the biomedical sciences and pharmaceutical development. Compared with traditional end-point assays and fixed cell analysis, analysis of drug molecules in living cells can provide more insight into the effects of drugs on cells in real-time and allowing for a better understanding of drug mechanisms and effects, which will contribute to the development of drug developing and testing and personalize medicine. However, the high demands of living cell analysis, including high costs, technical complexity, and throughput limitations, hinder the widespread application of this technology. In recent years, the rapid development of analytical methods such as Raman spectroscopy and fluorescence has made the in situ and real-time detection possible, allowing the analysis of single cell or cell populations at various conditions. In this review, we summarize the advanced analytical methods and technologies from last few years for drug detection in living cells.

The elastic system: A review of elastin-related techniques and hematoxylin-eosin/phloxine applicability for normal and pathological tissue description

The elastic system is one of the most developed interstitial elements in connective tissue. With diverse functions, pre-elastic and elastic fibers contribute to the distensibility and malleability of several organs. Also, microanalyses of the elastic system were obtained by different histological techniques that were employed over years to describe normal and pathological conditions. Compared to conventional stains, hematoxylin-eosin/phloxine (HE/P) under fluorescence and confocal microscopy presented a highly detailed observation of the elastic system in different organs and scenarios. This technique provides a better demarcation of the elastic fibers, favoring their description in relation to their deposition and aggregation in different organs. Also, fibrils with low aggregation or loss of this characteristic are observed in an optimal view in the skin, heart valves, and large-caliber blood vessels. Degradation, fragmentation, and rupture were also well described by the HE/P technique. Several organs, such as the mammary gland, prostate, skin, aorta, and lung, could be described with precision under this technique. In association with non-linear microscopy, the results of the research presented in this paper improved and detailed characteristics of precise pathogenesis. Thus, the HE/P technique presented an interesting efficiency to demonstrate alterations and structures in which the elastic system showed a relevant role, and when compared to other techniques it demonstrated a similar or better result. In addition, it is expected that future studies can reveal more information about the elastin and interactions with specific dyes, thus allowing a greater understanding of the great efficiency of this technique.

PAMAM dendrimers as mediators of dermal and transdermal drug delivery: a review

OBJECTIVES

Poly(amidoamine) dendrimers have been widely investigated as potential nanomaterials that can enhance the skin permeation of topically applied drugs. This article reviews the studies that have used dendrimers as penetration enhancers and examines the mechanisms by which enhancement is claimed.

KEY FINDINGS

A wide range of studies have demonstrated that, in certain circumstances and for certain drugs, the incorporation of dendrimers into a topically applied formulation can significantly increase the amount of drug passing into and through the skin. In some cases, dendrimers offered little or no enhancement of skin permeation, suggesting that the drug-dendrimer interaction and the selection of a specific dendrimer were central to ensuring optimal enhancement of skin permeation. Significant interactions between dendrimers and other formulation components were also reported in some cases.

SUMMARY

Dendrimers offer substantial potential for enhancing drug delivery into and across the skin, putatively by mechanisms that include occlusion and changes to surface tension. However, most of these studies are conducted in vitro and limited progress has been made beyond such laboratory studies, some of which are conducted using membranes of limited relevance to humans, such as rodent skin. Thus, the outcomes and claims of such studies should be treated with caution.

Photographic scale for the characterization of actinic keratosis through reflectance confocal microscopy: a quantitative approach to cellular transformation

Background

Actinic keratosis (AK) is a highly prevalent pre-cancerous skin lesion that often leads to cutaneous squamous cell carcinoma. There are different stages of evolution of the disease and several features that characterize keratosis. This study aimed to develop a qualitative and quantitative visual diagnostic tool to facilitate the identification of the characteristics and severity of the main cellular attributes of AK and to show its applicability in evaluating the evolution or treatment through image analysis.

Methods

Literature research on the main scientific databases and in the institute's database was carried out to gather all the different levels of cellular transformation. To validate the scale, a preliminary characterization study was carried out with 21 subjects who had clinically diagnosed AK lesions to classify the attributes in each skin layer and test the accuracy of the diagnosis of the scale. Afterward, and to show the possibility of a follow-up with a topical treatment, the subjects were divided into two treatment groups, receiving either a cream formulation containing retinoic acid, or a placebo formula. The evaluation was carried out through confocal reflectance microscopy and a digital camera with dermoscopic quality before and after 90 days of treatment.

Results

A table detailing the 18 attributes of AK, and a photographic scale containing RCM images graded by scores established for each characteristic and the frequency of spreading were developed. The results of the validation presented good repeatability, correlation with clinical evaluation, and capacity for differentiating treatments demonstrated by the significant improvement after topical treatment by the reduction of the score for 10 out of the 18 attributes. The preliminary study, evaluated by the detailed transformation scale highlights important differences in the subclinical approach that allows a deeper evaluation of the aspects of the lesion's re-incidence even after fully treated skin sites.

Conclusion

This study brings an innovative method based on RCM, to assist in the quantification of cell transformation level, provide early diagnosis, and deliver a powerful treatment evaluation tool to provide smoother treatment, as well as prevent re-incidence in the cases.

Fabrication of Hybrid Coated Microneedles with Donepezil Utilizing Digital Light Processing and Semisolid Extrusion Printing for the Management of Alzheimer's Disease

Microneedle (MN) patches are gaining increasing attention as a cost-effective technology for delivering drugs directly into the skin. In the present study, two different 3D printing processes were utilized to produce coated MNs, namely, digital light processing (DLP) and semisolid extrusion (SSE). Donepezil (DN), a cholinesterase inhibitor administered for the treatment of Alzheimer's disease, was incorporated into the coating material. Physiochemical characterization of the coated MNs confirmed the successful incorporation of donepezil as well as the stability and suitability of the materials for transdermal delivery. Optical microscopy and SEM studies validated the uniform weight distribution and precise dimensions of the MN arrays, while mechanical testing ensured the MNs' robustness, ensuring efficient skin penetration. In vitro studies were conducted to evaluate the produced transdermal patches, indicating their potential use in clinical treatment. Permeation studies revealed a significant increase in DN permeation compared to plain coating material, affirming the effectiveness of the MNs in enhancing transdermal drug delivery. Confocal laser scanning microscopy (CLSM) elucidated the distribution of the API, within skin layers, demonstrating sustained drug release and transcellular transport pathways. Finally, cell studies were also conducted on NIH3T3 fibroblasts to evaluate the biocompatibility and safety of the printed objects for transdermal applications.

Multi-vesicular Liposome and its Applications: A Novel Chemically Modified Approach for Drug Delivery Application

BACKGROUND

This study aimed to elaborate on all the aspects of multivesicular liposomes, including structure, function, topology, etc. Liposomes are a unique drug delivery system, in which both hydrophilic and hydrophobic drug molecules can be incorporated. Particularly, multivesicular liposomes have more advantages than other liposomes because of their unique structure. This study provides an overview of several works already performed by various researchers in this field. Numerous studies have reported on preparing and evaluating multivesicular liposomes for drug delivery applications. This study summarizes the process of formulating multivesicular liposomes and their application in drug delivery systems and provides details about how to resolve the problem of limited solubility and stability of biomolecules, along with controlled drug release kinetics, with the possibility of loading various drugs. There is no doubt that multivesicular liposome opens new avenues to develop novel drug delivery system for achieving the desired functional performances and expanding the applications in the drug delivery area.

Advances in laser speckle imaging: From qualitative to quantitative hemodynamic assessment

Laser speckle imaging (LSI) techniques have emerged as a promising method for visualizing functional blood vessels and tissue perfusion by analyzing the speckle patterns generated by coherent light interacting with living biological tissue. These patterns carry important biophysical tissue information including blood flow dynamics. The noninvasive, label-free, and wide-field attributes along with relatively simple instrumental schematics make it an appealing imaging modality in preclinical and clinical applications. The review outlines the fundamentals of speckle physics and the three categories of LSI techniques based on their degree of quantification: qualitative, semi-quantitative and quantitative. Qualitative LSI produces microvascular maps by capturing speckle contrast variations between blood vessels containing moving red blood cells and the surrounding static tissue. Semi-quantitative techniques provide a more accurate analysis of blood flow dynamics by accounting for the effect of static scattering on spatiotemporal parameters. Quantitative LSI such as optical speckle image velocimetry provides quantitative flow velocity measurements, which is inspired by the particle image velocimetry in fluid mechanics. Additionally, discussions regarding the prospects of future innovations in LSI techniques for optimizing the vascular flow quantification with associated clinical outlook are presented.

Review of optical methods for noninvasive imaging of skin fibroblasts-From in vitro to ex vivo and in vivo visualization

Fibroblasts are among the most common cell types in the stroma responsible for creating and maintaining the structural organization of the extracellular matrix in the dermis, skin regeneration, and a range of immune responses. Until now, the processes of fibroblast adaptation and functioning in a varying environment have not been fully understood. Modern laser microscopes are capable of studying fibroblasts in vitro and ex vivo. One-photon- and two-photon-excited fluorescence microscopy, Raman spectroscopy/microspectroscopy are well-suited noninvasive optical methods for fibroblast imaging in vitro and ex vivo. In vivo staining-free fibroblast imaging is not still implemented. The exception is fibroblast imaging in tattooed skin. Although in vivo noninvasive staining-free imaging of fibroblasts in the skin has not yet been implemented, it is expected in the future. This review summarizes the state-of-the-art in fibroblast visualization using optical methods and discusses the advantages, limitations, and prospects for future noninvasive imaging.

Lipid Nanocapsule: A Novel Approach to Drug Delivery System Formulation Development

Nanocapsules are polymeric nanoparticles encased in a polymeric coating composed of a predominantly non-ionic surfactant, macromolecules, phospholipids, and an oil core. Lipophilic drugs have been entrapped using various nanocarriers, including lipid cores, likely lipid nanocapsules, solid lipid nanoparticles, and others. A phase inversion temperature approach is used to create lipid nanocapsules. The PEG (polyethyleneglycol) is primarily utilised to produce nanocapsules and is a critical parameter influencing capsule residence time. With their broad drug-loading features, lipid nanocapsules have a distinct advantage in drug delivery systems, such as the capacity to encapsulate hydrophilic or lipophilic pharmaceuticals. Lipid nanocapsules, as detailed in this review, are surface modified, contain target-specific patterns, and have stable physical and chemical properties. Furthermore, lipid nanocapsules have target-specific delivery and are commonly employed as a marker in the diagnosis of numerous illnesses. This review focuses on nanocapsule synthesis, characterisation, and application, which will help understand the unique features of nanocapsules and their application in drug delivery systems.

Optical Methods for Non-Invasive Determination of Skin Penetration: Current Trends, Advances, Possibilities, Prospects, and Translation into In Vivo Human Studies

Information on the penetration depth, pathways, metabolization, storage of vehicles, active pharmaceutical ingredients (APIs), and functional cosmetic ingredients (FCIs) of topically applied formulations or contaminants (substances) in skin is of great importance for understanding their interaction with skin targets, treatment efficacy, and risk assessment-a challenging task in dermatology, cosmetology, and pharmacy. Non-invasive methods for the qualitative and quantitative visualization of substances in skin in vivo are favored and limited to optical imaging and spectroscopic methods such as fluorescence/reflectance confocal laser scanning microscopy (CLSM); two-photon tomography (2PT) combined with autofluorescence (2PT-AF), fluorescence lifetime imaging (2PT-FLIM), second-harmonic generation (SHG), coherent anti-Stokes Raman scattering (CARS), and reflectance confocal microscopy (2PT-RCM); three-photon tomography (3PT); confocal Raman micro-spectroscopy (CRM); surface-enhanced Raman scattering (SERS) micro-spectroscopy; stimulated Raman scattering (SRS) microscopy; and optical coherence tomography (OCT). This review summarizes the state of the art in the use of the CLSM, 2PT, 3PT, CRM, SERS, SRS, and OCT optical methods to study skin penetration in vivo non-invasively (302 references). The advantages, limitations, possibilities, and prospects of the reviewed optical methods are comprehensively discussed. The ex vivo studies discussed are potentially translatable into in vivo measurements. The requirements for the optical properties of substances to determine their penetration into skin by certain methods are highlighted.

Methodologies to Evaluate the Hair Follicle-Targeted Drug Delivery Provided by Nanoparticles

Nanotechnology has been investigated for treatments of hair follicle disorders mainly because of the natural accumulation of solid nanoparticles in the follicular openings following a topical application, which provides a drug "targeting effect". Despite the promising results regarding the therapeutic efficacy of topically applied nanoparticles, the literature has often presented controversial results regarding the targeting of hair follicle potential of nanoformulations. A closer look at the published works shows that study parameters such as the type of skin model, skin sections analyzed, employed controls, or even the extraction methodologies differ to a great extent among the studies, producing either unreliable results or precluding comparisons altogether. Hence, the present study proposes to review different skin models and methods for quantitative and qualitative analysis of follicular penetration of nano-entrapped drugs and their influence on the obtained results, as a way of providing more coherent study protocols for the intended application.

Confocal Laser Scanning Microscope Imaging of Custom-Made Multi-Cylinder Phantoms: Theory and Experiment

In this work, the image formation in a confocal laser scanning microscope (CLSM) is investigated for custom-made multi-cylinder phantoms. The cylinder structures were fabricated using 3D direct laser writing and consist of parallel cylinders with radii of 5 and 10 μm for the respective multi-cylinder phantom, with overall dimensions of about 200×200×200 μm3. Measurements were performed for different refractive index differences and by varying other parameters of the measurement system, such as pinhole size or numerical aperture (NA). For theoretical comparison, the confocal setup was implemented in an in-house developed tetrahedron-based and GPU-accelerated Monte Carlo (MC) software. The simulation results for a cylindrical single scatterer were first compared with the analytical solution of Maxwell's equations in two dimensions for prior validation. Subsequently, the more complex multi-cylinder structures were simulated using the MC software and compared with the experimental results. For the largest refractive index difference, i.e., air as the surrounding medium, the simulated and measured data show a high degree of agreement, with all the key features of the CLSM image being reproduced by the simulation. Even with a significant reduction in the refractive index difference by the use of immersion oil to values as low as 0.005, a good agreement between simulation and measurement was observed, particularly with respect to the increase in penetration depth.

Modified solid in oil nanodispersion containing vemurafenib-lipid complex- in vitro/ in vivo study

Background: Vemurafenib (VEM) was a licensed drug for the treatment of skin melanoma and is available only in the market as oral tablets prescribed in huge doses (1920 mg/day). One reason for the high dose is vemurafenib's low oral bioavailability. Methods: VEM-lipid complex (DLC) was predicted based on Conquest and Mercury programs and prepared using the solvent evaporation method using the lipid (phosphatidylethanolamine). DLC was subjected to characterization (FT-IR, Raman spectroscopy, DSC, TGA, P-XRD, and FESEM) to confirm complexation.  DLC was used to prepare solid in oil nanodispersion (DLC-SON) and subjected to in vitro, ex vivo, and in vivo evaluation in comparison to our recently prepared conventional SON (VEM-SON) and DLC-control. Results: Conquest and Mercury predict the availability of intermolecular hydrogen bonding between VEM and phosphatidylethanolamine (PE). All characterization tests of DLC ensure the complexation of the drug with PE. Ex vivo studies showed that the drug in DLC-SON has significantly (P<0.05) higher skin permeation than DLC-control but lower drug permeation than conventional SON but it has a higher % skin deposition (P<0.05) than others. The half-maximal inhibitory concentration (IC50) of the prepared DLC-SON is significantly high (P<0.05) in comparison to the conventional SON and pure VEM. In vivo permeation using confocal laser scanning microscopy (on the rat) results indicated that both conventional SON and DLC-SON can cross the SC and infiltrate the dermis and epidermis but DLC-SON has a higher luminance/gray value after 24 h in the dermis in comparison to the conventional SON. Conclusion: The novel lipid complex for VEM prepared using PE as a lipid and enclosed in SON showed higher anticancer activity and topical permeation as well as sustained delivery and good retention time in the dermis that localize the drug in a sufficient concentration to eliminate early diagnosed skin melanoma.

Modified solid in oil nanodispersion containing vemurafenib-lipid complex- in vitro/ in vivo study

Background: Vemurafenib (VEM) was a licensed drug for the treatment of skin melanoma and is available only in the market as oral tablets prescribed in huge doses (1920 mg/day). One reason for the high dose is vemurafenib's low oral bioavailability. Methods: VEM-lipid complex (DLC) was predicted based on Conquest and Mercury programs and prepared using the solvent evaporation method using the lipid (phosphatidylethanolamine). DLC was subjected to characterization (FT-IR, Raman spectroscopy, DSC, TGA, P-XRD, and FESEM) to confirm complexation.  DLC was used to prepare solid in oil nanodispersion (DLC-SON) and subjected to in vitro, ex vivo, and in vivo evaluation in comparison to our recently prepared conventional SON (VEM-SON) and DLC-control. Results: Conquest and Mercury predict the availability of intermolecular hydrogen bonding between VEM and phosphatidylethanolamine (PE). All characterization tests of DLC ensure the complexation of the drug with PE. Ex vivo studies showed that the drug in DLC-SON has significantly (P<0.05) higher skin permeation than DLC-control but lower drug permeation than conventional SON but it has a higher % skin deposition (P<0.05) than others. The half-maximal inhibitory concentration (IC50) of the prepared DLC-SON is significantly high (P<0.05) in comparison to the conventional SON and pure VEM. In vivo permeation using confocal laser scanning microscopy (on the rat) results indicated that both conventional SON and DLC-SON can cross the SC and infiltrate the dermis and epidermis but DLC-SON has a higher luminance/gray value after 24 h in the dermis in comparison to the conventional SON. Conclusion: The novel lipid complex for VEM prepared using PE as a lipid and enclosed in SON showed higher anticancer activity and topical permeation as well as sustained delivery and good retention time in the dermis that localize the drug in a sufficient concentration to eliminate early diagnosed skin melanoma.

Enhancement of the Transdermal Delivery of Nonsteroidal Anti-inflammatory Drugs Using Liposomes Containing Cationic Surfactants

New hybrid liposomes based on cationic amphiphiles with different structures of the head group (cetyltrimethylammonium bromide (CTAB), 3-hexadecyl-1-hydroxyethylimidazolium bromide (IA-16(OH)), 1-(butylcarbamoyl)oxyethyl-3-hexadecylimidazolium bromide (IAC 16(Bu)), and hexadecylmethylpyrrolidinium bromide (PR-16)) were developed for transdermal administration of nonsteroidal anti-inflammatory drugs. The different surfactant/lipid compositions were studied to obtain stable liposomes with high functionality. The hydrodynamic diameter of cationic liposomes was ∼110 nm. An admixture of cationic surfactants and PC liposomes improves the physicochemical properties of vesicles and transdermal diffusion rate and prolongs the release of drugs. Liposomal diclofenac sodium (DS) and ketoprofen (KP) were tested (using Franz cells) for transdermal penetration. Drug diffusion monitoring for 48 h demonstrated that the maximum DS and KP penetration through the synthetic membranes (Strat-M) is characterized by values of 255 ± 2 and 186 ± 3 μg/cm², respectively. The influence of the surfactant head group on the properties (stability, release profile, permeability) of cationic liposomes was shown for the first time. While the drug specificity is evident for the rate of release, the permeability increases as follows: conventional liposomes < CTAB/PC < PR-16/PC < IAC-16(Bu)/PC < IA-16(OH)/PC for both medicines. The rat paw edema model was used to assess the anti-inflammatory effect of the IA-16(OH)/PC leader formulation in vivo. It was found that liposomal DS and KP are effective for relieving rat paw edema. It should be noted that DS-loaded hybrid liposomes demonstrated the highest therapeutic efficacy compared to conventional vesicles.

Deep learning in food science: An insight in evaluating Pickering emulsion properties by droplets classification and quantification via object detection algorithm

Understanding the complicated emulsion microstructures by microscopic images will help to further elaborate their mechanisms and relevance. The formidable goal of the classification and quantification of emulsion microstructure appears difficult to achieve. However, object detection algorithm in deep learning makes it feasible. This paper reports a new technique for evaluating Pickering emulsion properties through classification and quantification of the emulsion microstructure by object detection algorithm. The trained neural network models characterize the emulsion droplets by distinguishing between different individual emulsion droplets and morphological mechanisms from numerous microscopic images. The quantified results of the emulsion droplets presented in this study, provide details of statistical changes at different concentrations of the Pickering interface and storage temperatures enabling elucidation of the mechanisms involved. This methodology provides a new quantitative and statistical analysis of emulsion microstructure and properties.

Application of Confocal Raman Microscopy for the Characterization of Topical Semisolid Formulations and their Penetration into Human Skin Ex Vivo

PURPOSE

The quality testing and approval procedure for most pharmaceutical products is a streamlined process with standardized procedures for the determination of critical quality attributes. However, the evaluation of semisolid dosage forms for topical drug delivery remains a challenging task. The work presented here highlights confocal Raman microscopy (CRM) as a valuable tool for the characterization of such products.

METHODS

CRM, a laser-based method, combining chemically-selective analysis and high resolution imaging, is used for the evaluation of different commercially available topical acyclovir creams.

RESULTS

We show that CRM enables the spatially resolved analysis of microstructural features of semisolid products and provides insights into drug distribution and polymorphic state as well as the composition and arrangement of excipients. Further, we explore how CRM can be used to monitor phase separation and to study skin penetration and the interaction with fresh and cryopreserved excised human skin tissue.

CONCLUSION

This study presents a comprehensive overview and illustration of how CRM can facilitate several types of key analyses of semisolid topical formulations and of their interaction with their biological target site, illustrating that CRM is a useful tool for research, development as well as for quality testing in the pharmaceutical industry.

Percutaneous egression: What do we know?

BACKGROUND

The process by which drugs leave the bloodstream to enter the skin compartments is important in determining appropriate routes of delivery and developing more efficacious medications. We conducted a general literature review on percutaneous egression mechanisms.

SUMMARY

Studies demonstrate that the stratum corneum (SC) is a compartment for systemically delivered drugs. Upon reviewing the available literature, it became apparent that there may be multiple mechanisms of percutaneous egression dependent upon drug physiochemical properties. These mechanisms include, but are not limited to, desquamation, sebum secretion, sweat transport and passive diffusion. While drugs often utilize one major pathway, it is possible that all mechanisms may play a role to varying extents.

KEY MESSAGES

Available literature suggests that hydrophilic substances tended to travel from blood to the upper layers of the skin via sweat, whereas lipophilic substances utilized sebum secretion to reach the SC. Upon reaching the skin surface, the drugs spread laterally before penetrating back into the skin as if they were topically administered. More data are warranted to identify additional percutaneous egression mechanisms, precise drug action sites and accelerate drug development.

Microneedle-mediated transdermal nanodelivery systems: a review

The greatest limitation in the development of transdermal drug delivery systems is that only a few drugs can permeate the skin due to the barrier function of the stratum corneum. Active and passive methods are generally available for improving the ability of drug transdermal delivery. However, nanoparticles, as a passive approach, exhibit capacity-constrained permeation enhancement. Thus, microneedle-mediated nanoparticles possess enormous potential and broad prospects. Microneedles promote the penetration of macromolecules by creating microchannels on the skin surface. In this review, the prevailing subknowledge on microneedles (mechanism, classification, and applications of microneedles combined with nanoparticles) is discussed to provide a guideline for readers and a basic reference for further in-depth studies of this novel drug delivery system.

Yeast cell microcarriers for delivery of a model bioactive compound in skin

This study aimed at developing a cell-based encapsulation carrier for topical delivery of bioactives to the skin. The overall objectives were to evaluate affinity of the yeast-cell based carrier to bind to the skin surface following topical application and to quantify controlled release of curcumin as a model bioactive in ex-vivo skin models using a combination of imaging, modeling and analytical measurements. Both porcine skin tissue and clinically obtained human skin biopsies were studied. The results demonstrated that upon incubation with the ex-vivo skin tissues, the cell carriers rapidly bound to the skin surface following topical delivery and provided sustained release of encapsulated curcumin. The microcarrier binding and penetration of curcumin in the dermal compartment also showed to increase with incubation time. The average flux of curcumin in human skin biopsies J_p was 0.89 ± 0.02 μg/cm²/h. These results illustrated the potential of a novel cell-based carrier for high affinity binding to skin surface, efficient encapsulation of a model bioactive and controlled release from the cell carrier to the skin with enhanced permeation to the dermis section. Overall, this study demonstrated a new class of cost-effective carriers for improving delivery of bioactives to the skin and potentially other epithelial tissues.

Formulation development and in vitro-in vivo assessment of protransfersomal gel of anti-resorptive drug in osteoporosis treatment

Osteoporosis is a major cause of morbidity, mortality, and economic burden worldwide. Despite being an effective in combating the bone-deteriorating disorders, bisphosphonates have several shortcomings including poor and variable bioavailability, low permeability, high toxicity, etc. In this study, we developed and optimized protransfersome formulation for the drug risedronate sodium (RIS-Na) with the goal of enhancing its bioavailability and hence patient compliance. Phase separation coacervation technique was utilized for development of optimized formulation. Optimization was achieved by using three-factor, three-level Box-Behnken design combined with Response Surface Methodology (RSM). This enabled us to decipher the effect of 3 independent variables (Phospholipid, Tween-80 and Sodium Deoxycholate) on three dependent parameters (entrapment efficiency, vesicle size and transdermal flux). Optimized formulation was further evaluated for pharmacokinetic and pharmacodynamic parameters. Smooth, spherical protransfersomes with a size of 260 ± 18 nm, having entrapment efficiency and flux of 80.4 ± 4.90% and 8.41 ± 0.148 μg/cm²/h, respectively were prepared. Ex vivo studies revealed a shorter lag time of 1.21 ± 0.18 h and higher flux associated with transdermal formulation. CLSM analysis further revealed better drug penetration (220 μm) through the skin in case of protransfersomes as compared to drug solution (72 μm). Additionally, biomechanical, biochemical, and histo-pathological studies further validated the results. Thus, it was concluded that protransfersome formulation has a great potential in providing better therapeutic efficacy of risedronate than its conventional counterpart.

Topical Delivery of Geranium/Calendula Essential Oil-Entrapped Ethanolic Lipid Vesicular Cream to Combat Skin Aging

The present study deals with the evaluation of the age-defying potential of topical cream formulations bearing Geranium essential oil/Calendula essential oil-entrapped ethanolic lipid vesicles (ELVs). Two types of cream formulations were prepared, viz., conventional and ELVs spiked o/w creams. Essential oil- (EO-) loaded ELVs were characterized by vesicle size, polydispersity index, encapsulation efficiency, and scanning electron microscopy. The cream formulations were evaluated for homogeneity, spreadability, viscosity, pH, in vitro antioxidant capacity, sun protection factor, and in vitro collagenase and elastase inhibition capacity. Confocal laser scanning microscopy (CLSM) was performed to ascertain skin permeation of conventional and vesicular cream. The results of in vitro antioxidant studies showed that GEO-/CEO-loaded vesicular creams have notable antioxidant capacity when compared to nonvesicular creams. GEO- or CEO-loaded vesicular creams exhibited the highest SPF value 10.26 and 18.54, respectively. Both the EO-based vesicular creams showed in vitro collagenase and elastase enzyme inhibition capacity. CLSM images clearly depicted that vesicular cream deep into the skin layers. From the research findings, the age-defying potential and photoprotective effects of GEO and CEO were confirmed. It can be concluded that ELVs are able to preserve the efficiency of EOs and have the potential to combat skin aging.

Evaluation of in vivo reflectance confocal microscopy in the diagnosis of extramammary Paget's disease

Extramammary Paget's disease (EMPD) is a rare cutaneous malignancy that most commonly affects the apocrine glands of older men and women. Because it is associated with other cancers, early diagnosis and evaluation are needed. This study is to evaluate the value of reflectance confocal microscopy (RCM) in diagnosing EMPD. A total of 73 patients with clinically suspicious diagnosis of EMPD were enrolled in this study, and the RCM device imaged their lesions. Moreover, 67 patients underwent skin biopsies to confirm the diagnosis. We retrospectively analyzed the results of RCM and histological diagnosis and then evaluated the RCM value of biopsy-confirmed lesions. Based on the RCM image analysis, 54 of 73 (74.0%) patients were diagnosed with EMPD. Of all 67 biopsied lesions, 52 (77.6%) were EMPD. Then, we analyzed the RCM characteristics of 52 cases of biopsy-confirmed EMPD, compared their RCM image characteristics of three different lesions of EMPD, and further concluded the key points of EMPD under RCM microscopy based on the 52 EMPD cases. Finally, we focused on the differential diagnosis of EMPD from other skin diseases. RCM showed great diagnostic value in diagnosing EMPD.

DESI-MS imaging to visualize spatial distribution of xenobiotics and endogenous lipids in the skin

The cutaneous biodistribution method (CBM) yields a high-resolution quantitative profile of drug deposition as a function of skin depth. However, it provides limited details about drug spatial distribution or penetration pathways. Mass spectrometry imaging (MSI) can complement the detailed quantitative data generated by CBM studies. The objectives of this work were to use desorption electrospray ionization (DESI)-MSI to (i) investigate the spatial cutaneous distributions of a topically applied drug and excipient and relate them to skin structures and (ii) image endogenous skin components and combine these results to gain insight into drug penetration routes. Porcine skin was used to compare two bioequivalent creams of econazole nitrate (ECZ) and a micelle formulation based on D-α-tocopheryl succinate polyethylene glycol 1000 (TPGS). DESI-MSI successfully imaged the cutaneous spatial distribution of ECZ and TPGS in 40 µm-thick horizontal sections and vertical cross-sections of the skin. Interestingly, clinically bioequivalent formulations did not appear to exhibit the same molecular distribution of ECZ in XY-horizontal sections. DESI-MSI also enabled visualization of TPGS (m/z 772.4706), mainly in the upper epidermis (≤80 µm). In conclusion, through co-localization of drugs and excipients with endogenous elements of the skin, DESI-MSI could further our understanding of the cutaneous penetration pathways of xenobiotics.

Hair growth promoting effect of bioactive extract from deer antler velvet-loaded niosomes and microspicules serum

Deer antler velvet (DAV) extract is important in stimulating the growth of skin and hair cells. The aim of this study was to develop DAV extract-loaded niosomes (NIs) and microspicules (MS) serum for effective hair growth. Bioactivities of DAV extract on human dermal papilla cells were studied. To develop protein delivery, NIs were prepared to entrap DAV extract and then loaded into MS serum (NI serum MS). Physicochemical properties and in vitro skin permeations were evaluated. The formulations were applied on human scalp and relative efficacies were evaluated. DAV extract at 2,000 µg/ml significantly enhanced cell proliferation and aggregation. DAV extract-loaded NI exhibited nanovesicle, narrow size distribution and negative surface charge. The vesicles were able to load into MS serum and showed significantly highest macromolecular protein permeation through the skin, with deposition into the deepest skin layer compared with other formulations. Applying the serum on human scalp for 14 and 30 days significantly enhanced hair elongation and melanin content, with increased skin hydration and decreased the erythema index, thereby promoting hair growth without skin irritation. NI serum MS containing DAV extract played an important role to deliver biomacromolecular protein through the skin and hair follicles, leading to effective hair growth.

High-Sensitivity Permeation Analysis of Ultrasmall Nanoparticles Across the Skin by Positron Emission Tomography

Ultrasmall nanoparticles (US-NPs; <20 nm in hydrodynamic size) are now included in a variety of pharmacological and cosmetic products, and new technologies are needed to detect at high sensitivity the passage of small doses of these products across biological barriers such as the skin. In this work, a diffusion cell adapted to positron emission tomography (PET), a highly sensitive imaging technology, was developed to measure the passage of gold NPs (AuNPs) in skin samples in continuous mode. US-AuNPs (3.2 nm diam.; TEM) were functionalized with deferoxamine (DFO) and radiolabeled with ⁸⁹Zr_(IV) (half-life: 3.3 days, matching the timeline of diffusion tests). The physicochemical properties of the functionalized US-AuNPs (US-AuNPs-PEG-DFO) were characterized by FTIR (DFO grafting; hydroxamate peaks: 1629.0 cm^-1, 1569.0 cm^-1), XPS (presence of the O═C-N C 1s peak of DFO at 287.49 eV), and TGA (organic mass fraction). The passage of US-AuNPs-PEG-DFO-⁸⁹Zr_(IV) in skin samples was measured by PET, and the diffusion parameters were extracted thereby. The signals of radioactive US-AuNPs-PEG-DFO-⁸⁹Zr_(IV) leaving the donor compartment, passing through the skin, and entering the acceptor compartment were detected in continuous at concentrations as low as 2.2 nM of Au. The high-sensitivity acquisitions performed in continuous allowed for the first time to extract the lag time to the start of permeation, the lag time to start of the steady state, the diffusion coefficients, and the influx data for AuNPs permeating into the skin. PET could represent a highly valuable tool for the development of nanoparticle-containing topical formulations of drugs and cosmetics.

Design and characterization of Nanostructured lipid carriers (NLC) and Nanostructured lipid carrier-based hydrogels containing Passiflora edulis seeds oil

This study aims to design and characterize Nanostructured lipid carriers (NLC) and Nanostructured lipid carrier-based hydrogels with Passiflora edulis seeds oil, a by-product from Madeira Island food industry. NLC were prepared by the ultrasonication technique, using passion fruit seeds oil as a liquid lipid and glyceryl distearate as a solid lipid. These NLC were then gelled with Poly (acrylic acid). Long-term stability studies were conducted with NLC and NLC-based hydrogels stored for 12 months. The following tests were performed: morphology, encapsulation efficiency, particle size analysis, polydispersity index analysis, zeta potential, pH measurement, color analysis, viscosity studies, texture analysis, in vitro occlusion test, ex vivo skin penetration study, tyrosinase inhibition activity, in vitro skin permeation experiments and in vitro cytotoxicity studies. The developed NLC had spherical shape and narrow particle sizes distribution with mean sizes in the range of 150 nm and PDI below 0.3, Zeta potential values around -30 mV and high Encapsulation efficiency. The tyrosinase inhibitory activity and skin retention of the nanoparticles was superior to that of the non-encapsulated oil. The developed formulations did not show cytotoxicity towards HaCat cells and presented suitable viscosity and texture properties for skin application, proving to be good candidates as depigmenting agent.

Analytical tools and evaluation strategies for nanostructured lipid carrier-based topical delivery systems

INTRODUCTION

The inception of nanostructured lipid carriers (NLCs) proved to be a revolutionary step toward the treatment of dermatological disorders. To uncover its true potential, it is imperative that the system be characterized and evaluated comprehensively.

AREAS COVERED

The present review has been written to furnish an in-depth account of analytical tools and evaluation procedures under one roof. Besides discussing the challenges of topical delivery and benefits of NLCs, the paper elaborates on their physicochemical characterization. Further, in vitro evaluation of NLCs for dermatological benefits, followed by their evaluation in a hydrogel/cream base is covered. Lastly, disease-specific evaluation of NLC-based formulations is presented.

EXPERT OPINION

The research endeavors for NLCs have largely focused on the fabrication of NLCs for different bioactives. However, scientific efforts should be aimed toward the lesser explored realm of NLCs, i.e. exploitation of analytical techniques, such as Parelectric spectroscopy, Electron Spin Resonance, and Nuclear Magnetic Resonance spectroscopy. NLCs have been proven for their potential to foster the therapeutic modalities applicable to cutaneous disorders. More attention needs to be devoted to their evaluation for disease-specific parameters. The futuristic steps must involve clinical studies, to lay the path for their commercialization.

Iontosomes: Electroresponsive Liposomes for Topical Iontophoretic Delivery of Chemotherapeutics to the Buccal Mucosa

The targeted local delivery of anticancer therapeutics offers an alternative to systemic chemotherapy for oral cancers not amenable to surgical excision. However, epithelial barrier function can pose a challenge to their passive topical delivery. The charged, deformable liposomes—“iontosomes”—described here are able to overcome the buccal mucosal barrier via a combination of the electrical potential gradient imposed by iontophoresis and their shape-deforming characteristics. Two chemotherapeutic agents with very different physicochemical properties, cisplatin (CDDP) and docetaxel (DTX), were co-encapsulated in cationic iontosomes comprising 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and Lipoid-S75. The entrapment of CDDP was improved by formulating it in anionic reverse micelles of dipalmitoyl-sn-glycero-3-phospho-rac-glycerol sodium (DPPG) prior to loading in the iontosomes. Cryo-TEM imaging clearly demonstrated the iontosomes’ electroresponsive shape-deformable properties. The in vitro transport study using porcine mucosa indicated that iontosomes did not enter the mucosa without an external driving force. However, anodal iontophoresis resulted in significant amounts of co-encapsulated CDDP and DTX being deposited in the buccal mucosa; e.g., after current application for 10 min, the deposition of CDDP and DTX was 13.54 ± 1.78 and 10.75 ± 1.75 μg/cm² cf. 0.20 ± 0.07 and 0.19 ± 0.09 μg/cm² for the passive controls—i.e., 67.7- and 56.6-fold increases—without any noticeable increase in their transmucosal permeation. Confocal microscopy confirmed that the iontosomes penetrated the mucosa through the intercellular spaces and that the penetration depth could be controlled by varying the duration of current application. Overall, the results suggest that the combination of topical iontophoresis with a suitable nanocarrier system can be used to deliver multiple “physicochemically incompatible” chemotherapeutics selectively to oral cancers while decreasing the extent of systemic absorption and the associated risk of side effects.

Characterization of microneedles and microchannels for enhanced transdermal drug delivery

Microneedle (MN)-based technologies are currently one of the most innovative approaches that are being extensively investigated for transdermal delivery of low molecular weight drugs, biotherapeutic agents and vaccines. Extensive research reports, describing the fabrication and applications of different types of MNs, can be readily found in the literature. Effective characterization tools to evaluate the quality and performance of the MNs as well as for determination of the dimensional and kinetic properties of the microchannels created in the skin, are an essential and critical part of MN-based research. This review paper provides a comprehensive account of all such tools and techniques.

Challenges and opportunities for small volumes delivery into the skin

Each individual's skin has its own features, such as strength, elasticity, or permeability to drugs, which limits the effectiveness of one-size-fits-all approaches typically found in medical treatments. Therefore, understanding the transport mechanisms of substances across the skin is instrumental for the development of novel minimal invasive transdermal therapies. However, the large difference between transport timescales and length scales of disparate molecules needed for medical therapies makes it difficult to address fundamental questions. Thus, this lack of fundamental knowledge has limited the efficacy of bioengineering equipment and medical treatments. In this article, we provide an overview of the most important microfluidics-related transport phenomena through the skin and versatile tools to study them. Moreover, we provide a summary of challenges and opportunities faced by advanced transdermal delivery methods, such as needle-free jet injectors, microneedles, and tattooing, which could pave the way to the implementation of better therapies and new methods.

Skin Barriers in Dermal Drug Delivery: Which Barriers Have to Be Overcome and How Can We Measure Them?

Although, drugs are required in the various skin compartments such as viable epidermis, dermis, or hair follicles, to efficiently treat skin diseases, drug delivery into and across the skin is still challenging. An improved understanding of skin barrier physiology is mandatory to optimize drug penetration and permeation. The various barriers of the skin have to be known in detail, which means methods are needed to measure their functionality and outside-in or inside-out passage of molecules through the various barriers. In this review, we summarize our current knowledge about mechanical barriers, i.e., stratum corneum and tight junctions, in interfollicular epidermis, hair follicles and glands. Furthermore, we discuss the barrier properties of the basement membrane and dermal blood vessels. Barrier alterations found in skin of patients with atopic dermatitis are described. Finally, we critically compare the up-to-date applicability of several physical, biochemical and microscopic methods such as transepidermal water loss, impedance spectroscopy, Raman spectroscopy, immunohistochemical stainings, optical coherence microscopy and multiphoton microscopy to distinctly address the different barriers and to measure permeation through these barriers in vitro and in vivo.

Emerging Optical Techniques for the Diagnosis of Onychomycosis

Onychomycosis is the most prevalent nail infection. Although it is not a life-threatening condition, it impacts the quality of life for many patients and often imposes a challenging diagnostic problem. The causative agents are dermatophytes, yeasts and non-dermatophytic moulds. Accurate and early diagnosis, including the identification of the causative species, is the key factor for rational therapy. Still, early diagnosis is not optimal as the current gold standard for the differentiation of the infectious agents is culture-based approaches. On the other hand, noninvasive optical technologies may enable differential diagnosis of nail pathologies including onychomycosis. When light penetrates and propagates along the nail tissue, it interacts in different ways with the components of either infected or healthy nail segments, providing a wealth of diagnostic information upon escaping the tissue. This review aims to assess alternative optical techniques for the rapid diagnosis of onychomycosis with a potential to monitor therapeutic response or even identify the fungal agent non-invasively and in real time in a clinical setting.

Nanogels for Skin Cancer Therapy via Transdermal Delivery: Current Designs

BACKGROUND

Recently, several strategies have been proposed for skin cancer therapy by transdermal delivery, and particularly the use of nanotechnology.

METHODS

This process disrupts the stratum corneum to deliver a drug through the skin, allowing it to accumulate at the tumor site.

RESULTS

Nanogels are drug delivery systems that can be applied to many diseases. Nanogel engineering has been widely studied for use in drug delivery, particularly in cancer theranostics. This review summarizes specific strategies for using nanogels to treat skin cancer, a topic that is limited in recent literature.

CONCLUSION

Advanced techniques for effective skin cancer therapy based on the nanogel's penetration and cellular uptake abilities will be discussed. Moreover, techniques for penetrating the skin, as well as drug release, permeation studies, and microscopic observations, will also be discussed.

Imaging and quantifying drug delivery in skin - Part 2: Fluorescence andvibrational spectroscopic imaging methods

Understanding the delivery and diffusion of topically-applied drugs on human skin is of paramount importance in both pharmaceutical and cosmetics research. This information is critical in early stages of drug development and allows the identification of the most promising ingredients delivered at optimal concentrations to their target skin compartments. Different skin imaging methods, invasive and non-invasive, are available to characterize and quantify the spatiotemporal distribution of a drug within ex vivo and in vivo human skin. The first part of this review detailed invasive imaging methods (autoradiography, MALDI and SIMS). This second part reviews non-invasive imaging methods that can be applied in vivo: i) fluorescence (conventional, confocal, and multiphoton) and second harmonic generation microscopies and ii) vibrational spectroscopic imaging methods (infrared, confocal Raman, and coherent Raman scattering microscopies). Finally, a flow chart for the selection of imaging methods is presented to guide human skin ex vivo and in vivo drug delivery studies.

Formulation and Characterization of Nanosized Ethosomal Formulations of Antigout Model Drug (Febuxostat) Prepared by Cold Method: In Vitro/Ex Vivo and In Vivo Assessment

Febuxostat (FXT) is a xanthine oxidase (XO) drug which indicated for the treatment of gout. FXT loaded nanosized ethosomes were prepared using cold method with varied concentrations of ethyl alcohol and soya lecithin (SL). The prepared ethosomes were characterized by size, entrapment efficiency (DEE), FT-IR, in vitro release, kinetic studies of in vitro release profile, in vitro skin permeation and deposition, and stability study. The selected ethosomal formulation was incorporated in HPMC gel and characterized for drug content, ex vivo diffusion study through rat skin, and in vivo study and determination of pharmacokinetic parameters using HPLC technique. The results of size analysis showed that minimum size was 124.2 ± 16.77 nm with PDI values between 0.2 and 0.6. The zeta potential was from - 43.5 ± 3.0 to - 20.6 ± 1.42 mV. DEE ranged from 48 to 86%. The results of in vitro skin permeation showed that the amount FXT permeated ranged from 43.33 ± 5.3 to 82.14 ± 5.8%, flux ranged from 14.85 to 28.02. The results of ex vivo study showed that the amount of FXT permeated from unprocessed FXT gel was 49.42 ± 3.29% which was lesser than from FXT ethosomal gel. The results of in vivo study showed that C_max and t_max were significantly different and higher for transdermal administration of FXT than oral administration. The developed FXT nanosized selected ethosome-based transdermal drug delivery gel system would provide a promising method for better management of gout.

Precise measurement of intradermal fluid delivery using a low activity technetium-99m pertechnetate tracer

A method was developed and validated to determine the intradermal (ID) fluid delivery potential of several ID devices, including hollow microneedles. The novel method used water soluble technetium-99 m pertechnetate (^99mTcO₄^-) diluted in normal saline to measure the volume of fluid delivered to and remaining in the skin. The fluid that back-flowed to the skin surface and the fluid left on the device surface were also quantified, thus capturing all fluid volumes deposited during intradermal injections. The technique described in this manuscript was used to assess the injection performance of conventional hypodermic needles and hollow microneedles ex vivo using porcine skin and in vivo with a rat model. Since only a small fraction, 1.1%, of the water-soluble tracer remained bound to the skin when applied topically, the technique can be used to differentiate between injected fluid and backflow. Counting of gamma radiation from ^99mTcO₄^- provided sub-nanoliter resolution for volume measurements, making the proposed method powerful, sensitive, and suitable for the assessments of ID injection devices, particularly for vaccine delivery.

A comparative study: the prospective influence of nanovectors in leveraging the chemopreventive potential of COX-2 inhibitors against skin cancer

Introduction

This study was conducted to elucidate the chemopreventive potential, cytotoxic, and suppression of cellular metastatic activity of etodolac (ETD)-loaded nanocarriers.

Methods

To esteem the effect of charge and composition of the nanovectors on their performance, four types of vectors namely, negative lipid nanovesicles; phosalosomes (N-Phsoms), positive phosalosomes (P-Phsoms), nanostructured lipid carriers (NLCs) and polymeric alginate polymer (AlgNPs) were prepared and compared. ETD was used as a model cyclo-oxygenase-2 (COX-2) inhibitor to evaluate the potency of these nanovectors to increase ETD permeation and retention through human skin and cytotoxicity against squamous cell carcinoma cell line (SCC). Moreover, the chemopreventive activity of ETD nanovector on mice skin cancer model was evaluated.

Results

Among the utilized nanovectors, ETD-loaded N-Phsoms depicted spherical vesicles with the smallest particle size (202.96±2.37 nm) and a high zeta potential of −24.8±4.16 mV. N-Phsoms exhibited 1.5, and 3.6 folds increase in the ETD amount deposited in stratum corneum, epidermis and dermis. Moreover, cytotoxicity studies revealed a significant cytotoxic potential of such nanovector with IC₅₀=181.76 compared to free ETD (IC₅₀=982.75), correlated to enhanced cellular internalization. Its efficacy extended to a reduction in the relative tumor weight with 1.70 and 1.51-fold compared to positive control and free ETD, that manifested by a 1.72-fold reduction in both COX-2 and proliferating cell nuclear antigen mRNA (PCNA-mRNA) levels and 2.63-fold elevation in caspase-3 level in skin tumors relative to the positive control group with no hepato-and nephrotoxicity.

Conclusion

Encapsulation of ETD in nanovector enhances its in-vitro and in-vivo anti-tumor activity and opens the door for encapsulation of more relevant drugs.

Methods to Evaluate Skin Penetration In Vitro

Dermal and transdermal drug therapy is increasing in importance nowadays in drug development. To completely utilize the potential of this administration route, it is necessary to optimize the drug release and skin penetration measurements. This review covers the most well-known and up-to-date methods for evaluating the cutaneous penetration of drugs in vitro as a supporting tool for pharmaceutical research scientists in the early stage of drug development. The aim of this article is to present various experimental models used in dermal/transdermal research and summarize the novel knowledge about the main in vitro methods available to study skin penetration. These techniques are: Diffusion cell, skin-PAMPA, tape stripping, two-photon microscopy, confocal laser scanning microscopy, and confocal Raman microscopic method.