Fourier transform raman spectroscopy of interactions between the penetration enhancer dimethyl sulfoxide and human stratum corneum

Effects and Action Mode of Oleic Acid and Azone on Release and Penetration Process of Levothyroxine Sodium Patches

In recent years, there has been a significant increase in the prevalence of thyroid diseases, particularly hypothyroidism. In this study, we investigated the impact and mechanisms of Chemical permeation enhancement(CPE) on transdermal permeation of levothyroxine sodium (L-T4) patches.We found that the combination of oleic acid (OA) and Azone (NZ) yielded the best transdermal permeation effect for L-T4.Subsequently, we also investigated the relevant propermeability mechanism.The results demonstrate that the combined application of OA and NZ significantly enhances the transdermal permeation of L-T4 compared to individual applications,it is attributed to two mechanisms: firstly, OA improves drug release by increasing the flowability of the pressure-sensitive adhesive (PSA) matrix; secondly, both OA and NZ act on the stratum corneum, especially facilitating L-T4 permeation through the hair follicle pathway. No skin irritation or cytotoxicity is observed with these final patches, which exhibit a remarkable therapeutic effect on hypothyroidism. this study contributes to the development of transdermal formulations of L-T4.

Bisphenols as promoters of the dysregulation of cellular junction proteins of the blood-testis barrier in experimental animals: A systematic review of the literature

Daily, people are exposed to chemicals and environmental compounds such as bisphenols (BPs). These substances are present in more than 80% of human fluids. Human exposure to BPs is associated with male reproductive health disorders. Some of the main targets of BPs are intercellular junction proteins of the blood-testis barrier (BTB) in Sertoli cells because BPs alter the expression or induce aberrant localization of these proteins. In this systematic review, we explore the effects of BP exposure on the expression of BTB junction proteins and the characteristics of in vivo studies to identify potential gaps and priorities for future research. To this end, we conducted a systematic review of articles. Thirteen studies met our inclusion criteria. In most studies, animals treated with bisphenol-A (BPA) showed decreased occludin expression at all tested doses. However, bisphenol-AF treatment did not alter occludin expression. Cx43, ZO-1, β-catenin, nectin-3, cortactin, paladin, and claudin-11 expression also decreased in some tested doses of BP, while N-cadherin and FAK expression increased. BP treatment did not alter the expression of α and γ catenin, E-cadherin, JAM-A, and Arp 3. However, the expression of all these proteins was altered when BPA was administered to neonatal rodents in microgram doses. The results show significant heterogeneity between studies. Thus, it is necessary to perform more research to characterize the changes in BTB protein expression induced by BPs in animals to highlight future research directions that can inform the evaluation of risk of toxicity in humans.

4'-OH as the Action Site of Lipids and MRP1 for Enhanced Transdermal Delivery of Flavonoids

To date, the transdermal delivery study mainly focused on the drug delivery systems' design and efficacy evaluation. Few studies reported the structure-affinity relationship of the drug with the skin, further revealing the action sites of the drugs for enhanced permeation. Flavonoids attained a considerable interest in transdermal administration. The aim is to develop a systematic approach to evaluate the substructures that were favorable for flavonoid delivery into the skin and understand how these action sites interacted with lipids and bound to multidrug resistance protein 1 (MRP1) for enhanced transdermal delivery. First, we investigated the permeation properties of various flavonoids on the porcine skin or rat skin. We found that 4'-OH (hydroxyl group on the carbon 4' position) rather than 7-OH on the flavonoids was the key group for flavonoid permeation and retention, while 4'-OCH₃ and -CH₂═CH₂-CH-(CH₃)₂ were unfavorable for drug delivery. 4'-OH could decrease flavonoids' lipophilicity to an appropriate log P and polarizability for better transdermal drug delivery. In the stratum corneum, flavonoids used 4'-OH as a hand to specifically grab the C═O group of the ceramide NS (Cer), which increased the miscibility of flavonoids and Cer and then disturbed the lipid arrangement of Cer, thereby facilitating their penetration. Subsequently, we constructed overexpressed MRP1 HaCaT/MRP1 cells by permanent transfection of human MRP1 cDNA in wild HaCaT cells. In the dermis, we observed that 4'-OH, 7-OH, and 6-OCH₃ substructures were involved in H-bond formation within MRP1, which increased the flavonoid affinity with MRP1 and flavonoid efflux transport. Moreover, the expression of MRP1 was significantly enhanced after the treatment of flavonoids on the rat skin. Collectively, 4'-OH served as the action site for increased lipid disruption and enhanced affinity for MRP1, which facilitate the transdermal delivery of flavonoids, providing valuable guidelines for molecular modification and drug design of flavonoids.

Enhanced intradermal delivery of Dragon's blood in biocompatible nanosuspensions hydrogel patch for skin photoprotective effect

Dragon's Blood is a member of the Chinese medicinal herb, having anti-oxygen and anti-inflammatory activity for the photoprotective effect. However, the poor water solubility of raw Dragon's Blood powder has limited its intradermal delivery process. In this study, we evaluated nanosuspensions to enhance intradermal delivery of Dragon's Blood exerting a photoprotective effect. The prepared nanosuspension was added to a composite hydrogel patch matrix for better skin application. In the present research, we used biocompatible materials hyaluronic acid and amino acid surfactants as nanosuspension stabilizers and agar/gelatin/sodium polyacrylate as hydrogel patch matrix. The prepared Dragon's Blood nanosuspension had a particle size of 447.0 ± 48.6 nm. The micro-structures morphology and viscoelasticity characteristics by SEM and rheological testing confirmed a sufficient crosslinked hydrogel network. The skin retention amount of Dragon's Blood nanosuspension was 1.48 times of raw Dragon's Blood powder water suspension, and the skin penetration amount of Dragon's Blood nanosuspension was only about 1/3 of Dragon's Blood DMSO solution. In the UVB-irradiated HaCaT cell phototoxicity model, Dragon's Blood nanosuspension also significantly increased cell viability by about 1 time of the model group and decreased the production of reactive oxygen species about 1/2 times of model group. In vivo safety and efficiency evaluation experiment illustrated that DB-NS hydrogel patch processes have favorable safety and photoprotective effect with no skin irritancy and phototoxicity. Furthermore, DB-NS and DB-NS hydrogel patches could protect skin from UVA and UVB irritating skin reactions. Overall, our study of the combined use of biocompatible and biodegradable materials as excipients of nanosuspension and hydrogel patch could be used as an effective additive of Intradermal delivery and skin photoprotection.

A theoretical investigation on the synergetic effect of hydrogen-bonding interactions and thermodynamic property in the 1: 2 (azacyclopentane-2-one: N-methylolacetamide) ternary complex

CONTEXT

Using chemical penetration enhancers to improve the penetration effect is one kind of important strategies in transdermal drug delivery system. Azone is a widely used transdermal absorption enhancer for transdermal drug delivery. To shed light on the permeation-promoting mechanism of azone, we selected ternary systems formed by azacyclopentane-2-one and N-methylolacetamide (1: 2) and explored the synergetic effect of hydrogen-bonding interactions among them and their thermodynamic properties. The findings indicate that the synergetic effects can enhance the ability of azone to change the original conformation of ceramides and even break the original hydrogen bonds, which is more beneficial for azone to destroy the 3D network structure of ceramides. When azone interacts with ceramide, the order of action tends to interact with one molecule of ceramide first and then with another molecule of ceramide.

METHODS

The synergetic effects of hydrogen-bonding interactions in ternary systems were computed at the B3LYP/6-311 +  + G** and MP2(full)/6-311 +  + G** levels. Thermodynamic parameters for two ternary-complex routes were worked out at the B3LYP/aug-cc-pVDZ level. The shift of the electron density occurring simultaneously with trimer formation was analyzed at the MP2(full)/6-311 +  + G** level. The above calculations were carried out using the Gaussian 03 program packages. Atoms in molecules (AIM) method and the AIMPAC program showed the topological charge density at the MP2(full)/6-311 +  + G** level. The synergetic effects of hydrogen-bonding interactions and thermodynamic property in the 1: 2 (azacyclopentane-2-one: N-methylolacetamide) ternary systems were investigated using the B3LYP and MP2(full) methods.

A Mechanistic Study on the Fluidization and Enhancement Effects of Cineole Toward Stratum Corneum Intercellular Lamellar Lipids: A Liquid Crystalline Model Approach

Background

The stratum corneum (SC) serves as the primary barrier for permeation in human skin. Penetration enhancers, such as 1,8-cineole, are utilized to enhance the permeation of drugs. Cineole increases the permeation of chemicals through different mechanisms. However, its mechanism, particularly at high concentrations, has not been well-studied and is the subject of the present investigation.

Objectives

In continuation of our previous studies, the present investigation aims to elucidate the mechanism of action and concentration dependency of the effects of 1,8-cineole on the structure, diffusional properties, and partitioning behavior of the SC at high concentrations. This will be achieved through lamellar liquid crystalline models and ex-vivo skin studies.

Methods

A lamellar liquid crystalline lipid matrix model in the presence (25 - 90%, w/w) and absence of cineole was prepared from SC lipids and characterized by X-ray diffraction, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and polarized light microscopy (PLM) studies. Release of the model lipophilic drug (diazepam) from cineole and cineole-treated matrices and the permeation of the drug from cineole and cineole-containing matrices (as a vehicle similar to the stratum corneum lipids) through excised rat skin were studied. Drug assay was performed by HPLC.

Results

The PLM, DSC, and X-ray studies showed that the model matrix had a lamellar gel-liquid crystalline structure, and cineole fluidized the structure concentration-dependently and created other mesomorphic textures, such as myelinic figures. Release experiments showed that diffusion coefficients remained almost constant at high cineole concentrations of 40-90%, suggesting similar fluidization states. Skin permeation studies indicated that the diffusion coefficient (estimated from lag-time) increased concentration-dependently and played a role in permeability coefficient (Kp) increments alongside the increased partitioning of the model drug into the skin. Data suggest that high concentrations of cineole at the skin surface might not provide enough cineole in the skin for full fluidization, despite the similarity of the vehicle to SC lipids and even at high concentrations.

Conclusions

The enhancement effect of cineole is concentration-dependent and might reach maximum fluidization at certain concentrations, but this maximum might not be easily achievable when cineole is used in formulations as pure or in a vehicle.

Improved Topical Drug Delivery: Role of Permeation Enhancers and Advanced Approaches

The delivery of drugs via transdermal routes is an attractive approach due to ease of administration, bypassing of the first-pass metabolism, and the large skin surface area. However, a major drawback is an inability to surmount the skin's stratum corneum (SC) layer. Therefore, techniques reversibly modifying the stratum corneum have been a classical approach. Surmounting the significant barrier properties of the skin in a well-organised, momentary, and harmless approach is still challenging. Chemical permeation enhancers (CPEs) with higher activity are associated with certain side effects restricting their advancement in transdermal drug delivery. Furthermore, complexity in the interaction of CPEs with the skin has led to difficulty in elucidating the mechanism of action. Nevertheless, CPEs-aided transdermal drug delivery will accomplish its full potential due to advancements in analytical techniques, synthetic chemistry, and combinatorial studies. This review focused on techniques such as drug-vehicle interaction, vesicles and their analogues, and novel CPEs such as lipid synthesis inhibitors (LSIs), cell-penetrating peptides (CPPs), and ionic liquids (ILs). In addition, different types of microneedles, including 3D-printed microneedles, have been focused on in this review.

Impact of optical clearing on ex vivo human skin optical properties characterized by spatially resolved multimodal spectroscopy

A spatially resolved multimodal spectroscopic device was used on a two-layered "hybrid" model made of ex vivo skin and fluorescent gel to investigate the effect of skin optical clearing on the depth sensitivity of optical spectroscopy. Time kinetics of fluorescence and diffuse reflectance spectra were acquired in four experimental conditions: with optical clearing agent (OCA) 1 made of polyethylene glycol 400 (PEG-400), propylene glycol and sucrose; with OCA 2 made of PEG-400 and dimethyl sulfoxide (DMSO); with saline solution as control and a "dry" condition. An increase in the gel fluorescence back reflected intensity was measured after optical clearing. Effect of OCA 2 turned out to be stronger than that of OCA 1, possibly due to DMSO impact on the stratum corneum keratin conformation. Complementary experimental results showed increased light transmittance through the skin and confirmed that the improvement in the depth sensitivity of the multimodal spectroscopic approach is related not only to the dehydration and refractive indices matching due to optical clearing, but also to the mechanical compression of tissues caused by the application of the spectroscopic probe.

Self-Assembled Palmitoyl-Glycine-Histidine as a Permeation Enhancer for Transdermal Delivery

The stratum corneum (SC) covers the outer surface of the skin and prevents the permeation of unwanted materials; however, the SC barrier also inhibits the desired permeation of active pharmaceutical ingredients (APIs). Therefore, the development of a novel method to enhance the permeation of APIs through the skin has been the focus of significant attention. Palmitoyl-glycine-histidine (Pal-GH)-comprising palmitic acid, glycine, and histidine-can be co-assembled with various additives to form a thixotropic hydrogel. Self-assembled Pal-GH enhances the permeation of ivermectin through the skin; however, the permeation mechanism is unclear and has not yet been discussed in detail. In the present study, the self-assembled structure of Pal-GH was analyzed using X-rays and infrared, and its permeation enhancement effect was verified. There was a correlation between the amount of Pal-GH in the skin and permeation enhancement, suggesting the involvement of the Pal-GH molecule. The presence of Pal-GH in the skin was confirmed by liquid chromatography-mass spectrometry and fluorescence labeling (labeling with Thioflavin T, a fluorescent dye that responds to β-sheets). The self-assembled Pal-GH permeated the SC without disrupting its organization. However, the structure of the Pal-GH caused changes to the lipid organization of the SC. The findings indicated that self-assembled Pal-GH is an effective permeation enhancer for transdermal delivery and does not induce skin irritation.

Skin hydration as a tool to control the distribution and molecular effects of intermediate polarity compounds in intact stratum corneum

The barrier function of the skin is mainly assured by its outermost layer, stratum corneum (SC), which consists of dead keratin-filled cells embedded in a lipid matrix. The skin is daily exposed to an environment with changing conditions in terms of hydration and different chemicals. Here we investigate how a molecule that has reasonable solubility in both hydrophobic and hydrophilic environments can be directed to certain regions in SC by changing the skin hydration. We use 1,2,3-trimethoxy propane (TMP) as a model substance and solid-state NMR on natural abundance ¹³C to obtain atomically resolved information on the molecular dynamics of TMP as well as SC lipid and protein components at varying hydration conditions. Upon dehydration, TMP redistributes from the hydrophilic corneocytes to the hydrophobic SC lipid regions. In this way, TMP can act to prevent the fluid-solid lipid transition in drying conditions and be present in the corneocytes in more humid conditions. Hydration can thereby be used as a switch to control the location and action of TMP or similar compounds in complex materials like SC. The general principles described here can also have impact on other applications including lipid-based formulations in food, drug delivery and cosmetics.

Sulfoxide-functionalized nanogels inspired by the skin penetration properties of DMSO

Among polymeric nanocarriers, nanogels are especially promising non-irritating delivery vehicles to increase dermal bioavailability of therapeutics. However, accurately tailoring defined interactions with the amphiphilic skin barrier is still challenging. To address this limited specificity, we herein present a new strategy to combine biocompatible nanogels with the outstanding skin interaction properties of sulfoxide moieties. These chemical motifs are known from dimethyl sulfoxide (DMSO), a potent chemical penetration enhancer, which can often cause undesired skin damage upon long-term usage. By covalently functionalizing the nanogels' polymer network with such methyl sulfoxide side groups, tailor-made dermal delivery vehicles are developed to circumvent the skin disrupting properties of the small molecules. Key to an effective nanogel-skin interaction is assumed to be the specific nanogel amphiphilicity. This is examined by comparing the delivery efficiency of sulfoxide-based nanogels (NG-SOMe) with their corresponding thioether (NG-SMe) and sulfone-functionalized (NG-SO2Me) analogues. We demonstrate that the amphiphilic sulfoxide-based NG-SOMe nanogels are superior in their interaction with the likewise amphipathic stratum corneum (SC) showing an increased topical delivery efficacy of Nile red (NR) to the viable epidermis (VE) of excised human skin. In addition, toxicological studies on keratinocytes and fibroblasts show good biocompatibility while no perturbation of the complex protein and lipid distribution is observed via stimulated Raman microscopy. Thus, our NG-SOMe nanogels show high potential to effectively emulate the skin penetration enhancing properties of DMSO without its negative side effects.

Enhanced Skin Permeation of Estradiol by Dimethyl Sulfoxide Containing Transdermal Patches

Dimethyl sulfoxide is a well-known and widely used dermal penetration enhancer. Its incorporation in transdermal patches would be highly desirable; however, due to its volatility this is extremely challenging. Here, we report on the feasibility of a dimethyl sulfoxide (DMSO) containing transdermal system containing estradiol as a model compound. Transdermal patches were prepared from duro-tak® 387-2510 containing various DMSO concentrations at different drying temperatures. The resulting patches were analyzed for DMSO content, estradiol and DMSO release, estradiol and DMSO permeation through excised porcine skin, and recrystallization during stability testing. Drying conditions in the range of 35° to 40° allowed a complete polymer solvents removal while retaining significant amounts of DMSO (≤10 mg/patch). Estradiol skin permeation increased 4-fold (Jss = 4.12 µg/cm-2·h-1) compared to DMSO-negative control (Jss = 1.1 ± 0.2 µg/cm-2·h-1). As additional benefit, estradiol recrystallization was inhibited by DMSO at even lowest solvent concentrations. Storage stability was limited to 6 months at 25 °C with a surprising discrepancy between DMSO content (significantly lower) and flux (not significantly different). Although the technical feasibility range is relatively narrow, such DMSO-containing matrix-type patches are able to significantly enhance drug permeation through the skin while ameliorating the product stability against recrystallization.

Skin Penetration Enhancement Strategies Used in the Development of Melanoma Topical Treatments

Malignant melanoma is an aggressive form of skin cancer for which there is currently no reliable therapy and is considered one of the leading health issues in the USA. At present, surgery is the most effective and acceptable treatment; however, surgical excision can be impractical in certain circumstances. Topical skin delivery of drugs using topical formulations is a potential alternative approach which can have many advantages aside from being a non-invasive delivery route. Nevertheless, the presence of the stratum corneum (SC) limits the penetration of drugs through the skin, lowering their treatment efficacy and raising concerns among physicians and patients as to their effectiveness. Currently, research groups are trying to circumvent the SC barrier by using skin penetration enhancement (SPE) strategies. The SPE strategies investigated include chemical skin penetration enhancers (CPEs), physical skin penetration enhancers (PPEs), nanocarrier systems, and a combination of SPE strategies (cream). Of these, PPEs and cream are the most advanced approaches in terms of preclinical and clinical studies, respectively.

Permeation enhancers in transdermal drug delivery: benefits and limitations

Introduction: Transdermal drug delivery has several clinical benefits over conventional routes of drug administration. To open the transdermal route for a wider range of drugs, including macromolecules, numerous physical and chemical techniques to overcome the natural low skin permeability have been developed.Areas covered: This review focuses on permeation enhancers (penetration enhancers, percutaneous absorption promoters or accelerants), which are chemicals that increase drug flux through the skin barrier. First, skin components, drug permeation pathways, and drug properties are introduced. Next, we discuss properties of enhancers, their various classifications, structure-activity relationships, mechanisms of action, reversibility and toxicity, biodegradable enhancers, and synergistic enhancer combinations.Expert opinion: Overcoming the remarkable skin barrier properties in an efficient, temporary and safe manner remains a challenge. High permeation-enhancing potency has long been perceived to be associated with toxicity and irritation potential of such compounds, which has limited their further development. In addition, the complexity of enhancer interactions with skin, formulation and drug, along with their vast chemical diversity hampered understanding of their mechanisms of action. The recent development in the field revealed highly potent yet safe enhancers or enhancer combinations, which suggest that enhancer-aided transdermal drug delivery has yet to reach its full potential.

Transcutaneous Cancer Vaccine Using a Reverse Micellar Antigen Carrier

Skin dendritic cells (DCs) such as Langerhans cells and dermal dendritic cells have a pivotal role in inducing antigen-specific immunity; therefore, transcutaneous cancer vaccines are a promising strategy to prophylactically prevent the onset of a variety of diseases, including cancers. The largest obstacle to delivering antigen to these skin DC subsets is the barrier function of the stratum corneum. Although reverse micellar carriers are commonly used to enhance skin permeability to hydrophilic drugs, the transcutaneous delivery of antigen, proteins, or peptides has not been achieved to date because of the large molecular weight of drugs. To achieve effective antigen delivery to skin DCs, we developed a novel strategy using a surfactant as a skin permeation enhancer in a reverse micellar carrier. In this study, glyceryl monooleate (MO) was chosen as a skin permeation enhancer, and the MO-based reverse micellar carrier enabled the successful delivery of antigen to Langerhans cells and dermal dendritic cells. Moreover, transcutaneous vaccination with the MO-based reverse micellar carrier significantly inhibited tumor growth, indicating that it is a promising vaccine platform against tumors.

The effect of hydrophilic penetration/diffusion enhancer on stratum corneum lipid models: Part II*: DMSO

To optimize dermal and transdermal administration of drugs, the barrier function of the skin, particularly the stratum corneum (SC), needs to be reduced reversibly. For this purpose, penetration/diffusion enhancers such as DMSO can be applied. However, there is the question whether DMSO is an aggressive penetration/diffusion enhancer in pharmaceutical and cosmetical relevant concentrations? Until now, it is unclear if this penetration/diffusion enhancement is caused by an interaction with the SC lipid matrix or related to effects within the corneocytes. Therefore, the effects of the hydrophilic enhancer DMSO on SC models with different dimensionality ranging from bilayers (liposomes) via oligo-layers to multilayers have been investigated in this study. The effects of DMSO should be compared to that of other relevant hydrophilic enhancers such as urea and taurine. An innovative spectrum of methods was applied to ascertain the mode of action of DMSO in relevant concentrations on a molecular scale. The experiments reveal that there is no specific interaction of 10% and 30% DMSO solutions with the SC model systems. Hence, if DMSO is applied in pharmaceutically and cosmetically relevant concentrations, it has no influence on the SC model systems used. Neither an additional water uptake in the head group region nor a decrease of the lipid chain packing density have been observed. The leakage studies on liposomes show that 10% DMSO is causing just a very slight leakage of 8%, lower than the leakage of 19.4% caused by 10% urea (Müller et al., 2016). Consequently, the interactions of DMSO with the SC model lipids used are very low in concentrations of 10% and 30%, respectively. Since the lipid composition in native SC lipid matrix is far more complex than this model mixture, the results can not be directly transferred to the native SC lipid matrix. However, the outcome of this study, together with various findings in the literature give rise to the assumption that the enhancing effect of DMSO concerning the diffusion of relevant hydrophilic drugs and actives appears to be realized via the corneocytes.

A human skin high-throughput formulation screening method using a model hydrophilic drug

Franz cell (FC) experiments in topical and transdermal drug development represent the gold standard in vitro method but require a relatively high quantity of human skin, are low-throughput, and are time-consuming to perform. To address these issues, we studied a micro-well plate-based screening method for permeability and retention that could enable the direct screening of large numbers of formulations simultaneously across human skin. Using freshly excised dermatomed human skin modified to reflect poor barrier function and a model hydrophilic compound, Sulforhodamine B (SRB), FC permeation and retention quantification was compared to the 96-well high-throughput system (HTS). The skin was analyzed using 2-photon microscopy to determine the drug distribution within the skin. A screen of 15 different formulations in triplicate in a single piece of human skin, using full factorial design was then conducted. Permeability of SRB across the skin as well as the drug distribution profile of SRB retained in the skin were similar for the FC and HTS system. The influence of different excipients on drug retention was observed in the full factorial formulation screen. The HTS method is promising for the investigation of large numbers of formulations and the influence of formulations changes in skin retention of drug.

Review of Modern Techniques for the Assessment of Skin Hydration

Skin hydration is a complex process that influences the physical and mechanical properties of skin. Various technologies have emerged over the years to assess this parameter, with the current standard being electrical probe-based instruments. Nevertheless, their inability to provide detailed information has prompted the use of sophisticated spectroscopic and imaging methodologies, which are capable of in-depth skin analysis that includes structural and composition details. Modern imaging and spectroscopic techniques have transformed skin research in the dermatological and cosmetics disciplines, and are now commonly employed in conjunction with traditional methods for comprehensive assessment of both healthy and pathological skin. This article reviews current techniques employed in measuring skin hydration, and gives an account on their principle of operation and applications in skin-related research.

UV Raman chemical imaging using compressed sensing

Different chemical (hyperspectral) imaging techniques have proven to be powerful tools to provide and illustrate insightful data within a broad range of research areas. The present communication includes proof-of-principle results of UV Raman hyperspectral imaging, achieved via compressed sensing measurements using coded apertures (CA) and a reconstruction algorithm. The simple and cheap CA set up, obtained by a 50% overall transmissive random binary mask (chromium on fused silica with 100 μm × 100 μm pixel size) positioned at the entrance plane of an imaging spectrograph, resulted in an overall high throughput for the UV region of interest. The mask was mounted on a translation stage, allowing reproducible switching to different CA, thus making possible for multi frame CA imaging. Results from a scene containing liquid droplets are shown as examples and, as expected, qualitative improvements in resolution and contrast could be observed in both the spatial and spectral domain as the number of CA frames was increased.

Action of surfactants on the mammal epidermal skin barrier

BACKGROUND

Daily skin washing routines can promote undesirable effects on skin barrier function. The stratum corneum (SC) lipid matrix is crucial for skin barrier function. Skin cleansing products are mostly composed of surfactants: surface-active molecules that interact with skin lipids in several ways. The main aim of this work was to investigate the effect produced by surfactants on skin barrier permeability. Porcine skin is a well-accepted and readily available model of the human skin barrier. The effect of two cleansing formulations (based on different surfactant mixtures) on the barrier properties of mammalian skin were evaluated.

METHODS

Water sorption/desorption (DVS) experiments were used to measure skin permeability. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and confocal Raman were useful to study SC lipid organization.

RESULTS

The results showed that while anionic surfactants (SLS) had a negative impact on the skin barrier, with a clear increase of alkyl chain disorder; cosurfactants present in the shampoo formulation diminished the detrimental effect of their primary ionic surfactant, inducing less modification on lipid intramolecular chain disorder.

CONCLUSIONS

The obtained results confirmed that the mild cleansing formulations studied had gentle interaction with skin. The capacity to discriminate between detergent systems was clearly established with both DVS and spectroscopy techniques.

Confocal Raman microspectroscopy as an alternative method to investigate the extraction of lipids from stratum corneum by emulsifiers and formulations

The purpose of this study was to investigate the impact of emulsifiers and formulations on intercellular lipids of porcine stratum corneum (SC) and evaluate confocal Raman microscopy (CRM) as an alternative method in this research context. To this end, four different formulations were used: three conventional creams that contained ionic and/or non-ionic emulsifiers and one surfactants-free emulsion stabilized by a polymeric emulsifier. Additionally, all emulsifiers were tested in aqueous solution/dispersion in the respective concentrations as present in the formulations. CRM and HPTLC were used to analyse changes in SC lipid content after treatment. Furthermore, lipid extraction was visualized by fluorescence staining and SC thickness was measured by CRM and light microscopy. Various emulsifiers and emulsifier mixtures showed different impact on SC lipid content and SC thickness, while none of the tested formulations had any effect on SC lipids. Emulsifiers and their mixtures that reduced the lipids content also reduced SC thickness, indicating lipid extraction is the reason for SC thinning. Results from CRM and conventional methods showed a strong positive correlation for both lipid content and SC thickness measurements. With easy sample preparation and fast analytical readout, CRM has the potential to be a standardized analytical method for skin lipids investigation.

Using Raman Spectroscopy in Studying the Effect of Propylene Glycol, Oleic Acid, and Their Combination on the Rat Skin

The permeability enhancement effect of oleic acid (OA) and propylene glycol (PG) as well as their (1:1 v/v) combined mixture was studied using rat skin. The percutaneous drug administration is a challenge and an opportunity for drug delivery. To date, there is limited research that illustrates the mechanism of penetration enhancers and their combinations on the skin. This project aims to explore the skin diffusion and penetration enhancement of PG, OA, and a combination of PG-OA (1:1 v/v) on rat skin and to identify the potential synergistic effect of the two enhancers utilizing Raman spectroscopy. Dissected dorsal skin was treated with either PG or OA or their combination for predetermined time intervals after which the Raman spectra of the treated skin were collected with the enhancer. A spectrum of the wiped and the washed skin were also collected. The skin integrity was tested before and after exposure to PG. The skin histology proved that the skin integrity has been maintained during experiments and the results indicated that OA disrupted rat skin lipid as evident by changes in the lipid peak. The results also showed that PG and OA improved the diffusion of each other and created faster, yet reversible changes of the skin peaks. In conclusion, Raman spectroscopy is a potential tool for ex vivo skin diffusion studies. We also concluded that PG and OA have potential synergistic reversible effect on the skin.

Getting Drugs Across Biological Barriers

The delivery of drugs to a target site frequently involves crossing biological barriers. The degree and nature of the impediment to flux, as well as the potential approaches to overcoming it, depend on the tissue, the drug, and numerous other factors. Here an overview of approaches that have been taken to crossing biological barriers is presented, with special attention to transdermal drug delivery. Technology and knowledge pertaining to addressing these issues in a variety of organs could have a significant clinical impact.

Potential of Stratum Corneum Lipid Liposomes for Screening of Chemical Skin Penetration Enhancers

The evaluation of effective skin chemical penetration enhancers (CPEs) is a crucial process in the development of transdermal and dermal formulations with the capacity to overcome the stratum corneum barrier. In the present study, we aimed to investigate the potential of stratum corneum lipid liposomes (SCLLs) as an alternative tool for the screening of various types and concentrations of CPEs. SCLLs were prepared using a thin-film hydration technique, and two types of fluorescent probes (sodium fluorescein [FL] or 1,6-diphenyl-1,3,5-hexatriene [DPH] were entrapped separately into SCLLs (FL-SCLL and DPH-SCLL, respectively). FL leakage from SCLLs as well as the fluidity of DPH-SCLLs were determined after incubating with various types of CPEs as a function of their concentrations. The obtained results showed a concentration-dependent relationship for most CPEs both for FL leakage and the fluidity of SCLLs. When observing these data in detail, however, the concentration profiles could be classified into five main categories depending on the mode of action of the CPEs. These results strongly suggest the usefulness of SCLLs for high-throughput screening of effective CPEs as well as the understanding of their possible mode of action, especially in the early stage of skin formulation development.

Tracking solvents in the skin through atomically resolved measurements of molecular mobility in intact stratum corneum

Solvents are commonly used in pharmaceutical and cosmetic formulations and sanitary products and cleansers. The uptake of solvent into the skin may change the molecular organization of skin lipids and proteins, which may in turn alter the protective skin barrier function. We herein examine the molecular effects of 10 different solvents on the outermost layer of skin, the stratum corneum (SC), using polarization transfer solid-state NMR on natural abundance ¹³C in intact SC. With this approach it is possible to characterize the molecular dynamics of solvent molecules when present inside intact SC and to simultaneously monitor the effects caused by the added solvent on SC lipids and protein components. All solvents investigated cause an increased fluidity of SC lipids, with the most prominent effects shown for the apolar hydrocarbon solvents and 2-propanol. However, no solvent other than water shows the ability to fluidize amino acids in the keratin filaments. The solvent molecules themselves show reduced molecular mobility when incorporated in the SC matrix. Changes in the molecular properties of the SC, and in particular alternation in the balance between solid and fluid SC components, may have significant influences on the macroscopic SC barrier properties as well as mechanical properties of the skin. Deepened understanding of molecular effects of foreign compounds in SC fluidity can therefore have strong impact on the development of skin products in pharmaceutical, cosmetic, and sanitary applications.

Mechanisms of imiquimod skin penetration

Imiquimod (IMQ) ia an immunostimulating drug used for the treatment of neoplastic skin diseases, such as actinic keratosis (AK) and superficial basal cell carcinoma (sBCC), and as adjuvant for vaccination. Imiquimod formulation and skin delivery is highly challenging because of its very low solubility in most pharmaceutical excipients and poor penetration properties. Objectives of the work were: (1) to evaluate IMQ solubility in different solvents and pharmaceutical excipients; (2) to evaluate IMQ skin retention after the application of simple saturated solutions; (3) to evaluate the role of stratum corneum and solvent uptake on IMQ skin retention and (4) to formulate IMQ in microemulsions - prepared using previously investigated components - and compare them with the commercial formulation. The results show that IMQ solubility is not related to the solubility parameter of the solvents considered. The highest solubility was found with oleic acid (74mg/ml); in the case of PEGs, the solubility increased linearly with MW (PEG 200: 1.9mg/ml; PEG 400 7.3mg/ml, PEG 600 12.8mg/ml). Imiquimod skin retention from saturated solutions (Tween 80, oleic acid, propylene glycol, PEG 200, PEG 400, PEG 600, Transcutol, 2-pyrrolidone, DMSO) resulted relatively similar, being 1.6μg/cm(2) in case of oleic acid (solubility 74mg/ml) and 0.18μg/cm(2) in case of propylene glycol (solubility 0.60mg/ml). Permeation experiments on stripped skin (no stratum corneum) and isolated dermis as well as uptake experiments on isolated stratum corneum sheets demonstrated that IMQ accumulation is related to skin solvent uptake. Finally, microemulsions (MEs) prepared with the above-studied components demonstrated a very good performance. In particular, a ME composed of 10% oleic acid, 35% Transcutol, 35% Tween 80 and 20% water is able to accumulate the same amount of drug as the commercial formulation but with far more efficiency, since its concentration was 12 times lower.

Skin barrier modification with organic solvents

The primary barrier to body water loss and influx of exogenous substances resides in the stratum corneum (SC). The barrier function of the SC is provided by patterned lipid lamellae localized to the extracellular spaces between corneocytes. SC lipids are intimately involved in maintaining the barrier function. It is generally accepted that solvents induce cutaneous barrier disruption. The main aim of this work is the evaluation of the different capability of two solvent systems on inducing changes in the SC barrier function. SC lipid modifications will be evaluated by lipid analysis, water sorption/desorption experiments, confocal-Raman visualization and FSTEM images. The amount of SC lipids extracted by chloroform/methanol was significantly higher than those extracted by acetone. DSC results indicate that acetone extract has lower temperature phase transitions than chloroform/methanol extract. The evaluation of the kinetics of the moisture uptake and loss demonstrated that when SC is treated with chloroform/methanol the resultant sample reach equilibrium in shorter times indicating a deterioration of the SC tissue with higher permeability. Instead, acetone treatment led to a SC sample with a decreased permeability thus with an improved SC barrier function. Confocal-Raman and FSTEM images demonstrated the absence of the lipids on SC previously treated with chloroform/methanol. However, they were still present when the SC was treated with acetone. Results obtained with all the different techniques used were consistent. The results obtained increases the knowledge of the interaction lipid-solvent, being this useful for understanding the mechanism of reparation of damaged skin.

Cryopreservation of cells: FT-IR monitoring of lipid membrane at freeze-thaw cycles

In the present study, FTIR spectroscopy was used to monitor the freeze-thaw cycle of two cellular lines (HuDe and Jurkat) suspended in three different media: phosphate buffer solution (PBS); dimethylsulfoxide (DMSO)/PBS solution at 0.1 DMSO molar fraction; and CryoSure (0.1 DMSO molar fraction PBS solution+dextran 5% w/v) solution. The Trypan Blue test was also applied before freezing and after thawing each cell sample to estimate the recovery of membrane integrity after thermal treatment, and correlate this datum with spectroscopic results. By following the temperature evolution of two different spectral components (the libration and bending combination mode νc(H2O) at 2000-2500 cm(-1), and the methylene symmetric stretching vibration νsym(CH2) at about 2850 cm(-1)) in the -120÷28°C range, we evidenced the main transition of lipid membrane in connection with cell dehydration, as induced by ice formation in the extracellular medium. In particular, in DMSO/PBS and CryoSure samples we observed a transition to a more rigid state of the lipid membrane together with an increased amount of non-freezable water in the extracellular medium; these results are connected to the role of DMSO as a cryoprotective agent irrespective of the nature of cell type.

Applications of Raman spectroscopy in skin research--From skin physiology and diagnosis up to risk assessment and dermal drug delivery

In the field of skin research, confocal Raman microscopy is an upcoming analytical technique. Substantial technical progress in design and performance of the individual setup components like detectors and lasers as well as the combination with confocal microscopy enables chemically selective and non-destructive sample analysis with high spatial resolution in three dimensions. Due to these advantages, the technique bears tremendous potential for diverse skin applications ranging from the analysis of physiological component distribution in skin tissue and the diagnosis of pathological states up to biopharmaceutical investigations such as drug penetration kinetics within the different tissue layers. This review provides a comprehensive introduction about the basic principles of Raman microscopy highlighting the advantages and considering the limitations of the technique for skin applications. Subsequently, an overview about skin research studies applying Raman spectroscopy is given comprising various in vitro as well as in vivo implementations. Furthermore, the future perspective and potential of Raman microscopy in the field of skin research are discussed.

Transdermal deferoxamine prevents pressure-induced diabetic ulcers

There is a high mortality in patients with diabetes and severe pressure ulcers. For example, chronic pressure sores of the heels often lead to limb loss in diabetic patients. A major factor underlying this is reduced neovascularization caused by impaired activity of the transcription factor hypoxia inducible factor-1 alpha (HIF-1α). In diabetes, HIF-1α function is compromised by a high glucose-induced and reactive oxygen species-mediated modification of its coactivator p300, leading to impaired HIF-1α transactivation. We examined whether local enhancement of HIF-1α activity would improve diabetic wound healing and minimize the severity of diabetic ulcers. To improve HIF-1α activity we designed a transdermal drug delivery system (TDDS) containing the FDA-approved small molecule deferoxamine (DFO), an iron chelator that increases HIF-1α transactivation in diabetes by preventing iron-catalyzed reactive oxygen stress. Applying this TDDS to a pressure-induced ulcer model in diabetic mice, we found that transdermal delivery of DFO significantly improved wound healing. Unexpectedly, prophylactic application of this transdermal delivery system also prevented diabetic ulcer formation. DFO-treated wounds demonstrated increased collagen density, improved neovascularization, and reduction of free radical formation, leading to decreased cell death. These findings suggest that transdermal delivery of DFO provides a targeted means to both prevent ulcer formation and accelerate diabetic wound healing with the potential for rapid clinical translation.

Confocal Raman microscopic investigation of the effectiveness of penetration enhancers for procaine delivery to the skin

A methodology that employs confocal Raman microscopy (CRM) on ex vivo skin samples is proposed for the investigation of drug content and distribution in the skin. To this end, the influence of the penetration enhancers propylene glycol and polyoxyethylene-23-lauryl ether on the penetration and permeation of procaine as a model substance was investigated. The drug content of skin samples that had been incubated with semisolid formulations containing one of these enhancers was examined after skin segmentation. The experiments showed that propylene glycol did not affect the procaine content that was delivered to the skin, whereas polyoxyethylene-23-lauryl ether led to higher procaine contents and deeper penetration. Neither substance was found to influence the permeation rate of procaine. It is thereby shown that CRM can provide additional information on drug penetration and permeation. Furthermore, the method was found to enhance the depth from which Raman spectra can be collected and to improve the depth resolution compared to previously proposed methods.

In vivo evaluation of lateral lipid chain packing in human stratum corneum

BACKGROUND/AIMS

The matrix of intercellular lipids (ICL) of stratum corneum (SC) plays an important role in the barrier function of SC. It is important to understand the structure of the ICL matrix for dermatology and cosmetic science. Several methods exist for the analysis of the structure; however, it is difficult to conduct these analyses noninvasively.

METHODS

We have developed a method for the analysis of the lateral packing of ICL using Raman spectroscopy. As a proof-of-principle experiment, we prepared a human SC sheet sample and analyzed its structure by the proposed method and by a conventional method involving X-ray diffraction. We compared the results of both methods. In addition, we applied the proposed method to living human skin, and we analyzed the lateral packing of ICL of SC taken from three separate body sites.

RESULTS

The results of our method corresponded to those of the conventional method. We detected regional differences of ICL lateral packing using our method in vivo. The results indicated that the packing of ICL in SC taken from the forearm and upper arm are more ordered than that taken from the cheek.

CONCLUSION

The results verify that our developed method allows the evaluation of the lateral packing of ICL inside the SC layer of the skin in vivo. Using this method, we can detect regional differences of SC samples taken from various body sites.

A comparative study between human skin substitutes and normal human skin using Raman microspectroscopy

Research in the field of bioengineered skin substitutes is motivated by the need to find new dressings for people affected by skin injuries (burns, diabetic ulcers), and to develop adequate skin models to test new formulations developed in vitro. Thanks to advances in tissue engineering, it is now possible to produce human skin substitutes without any exogenous material, using the self-assembly method developed by the Laboratoire d'Organogénèse Expérimentale. These human skin substitutes consist of a dermis and a stratified epidermis (stratum corneum and living epidermis). Raman microspectroscopy has been used to characterize and compare the molecular organization of skin substitutes with normal human skin. Our results confirm that the stratum corneum is a layer rich in lipids which are well ordered (trans conformers) in both substitutes and normal human skin. The amount of lipids decreases and more gauche conformers appear in the living epidermis in both cases. However, the results also show that there are fewer lipids in the substitutes and that the lipids are more organized in the normal human skin. Concerning the secondary structure of proteins and protein content, the data show that they are similar in the substitutes and in the normal human skin. In fact, the epidermis is rich in α-keratin, whereas the dermis contains mainly type I collagen.

Visualizing dermal permeation of sodium channel modulators by mass spectrometric imaging

Determining permeability of a given compound through human skin is a principal challenge owing to the highly complex nature of dermal tissue. We describe the application of an ambient mass spectrometry imaging method for visualizing skin penetration of sodium channel modulators, including novel synthetic analogs of natural neurotoxic alkaloids, topically applied ex vivo to human skin. Our simple and label-free approach enables successful mapping of the transverse and lateral diffusion of small molecules having different physicochemical properties without the need for extensive sample preparation.