Studies for improved understanding of lipid distributions in human skin by combining stimulated and spontaneous Raman microscopy

Label-free mapping of cetuximab in multi-layered tumor oral mucosa models by atomic force-microscopy-based infrared spectroscopy

Sensitive mapping of drugs and drug delivery systems is pivotal for the understanding and improvement of treatment options. Since labeling alters the physicochemical and potentially the pharmacological properties of the molecule of interest, its label-free detection by photothermal expansion is investigated. We report on a proof-of-concept study to map the cetuximab distribution by atomic-force microscopy-based infrared spectroscopy (AFM-IR). The monoclonal antibody cetuximab was applied to a human tumor oral mucosa model, consisting of a tumor epithelium on a lamina propria equivalent. Hyperspectral imaging in the wavenumber regime between 903 cm-1 and 1312 cm-1 and a probing distance between the data points down to 10 × 10 nm are used for determining the local drug distribution. The local distinction of cetuximab from the tissue background is gained by linear combination modeling making use of reference spectra of the drug and untreated models. The results from this approach are compared to principal component analyses, yielding comparable results. Even single molecule detection appears feasible. The results indicate that cetuximab penetrates the cytosol of tumor cells but does not bind to structures in the cell membrane. In conclusion, AFM-IR mapping of cetuximab proved to sensitively determine drug concentrations at an unprecedented spatial resolution without the need for drug labeling.

Visualization of Nanocarriers and Drugs in Cells and Tissue

In this chapter, the visualization of nanocarriers and drugs in cells and tissue is reviewed. This topic is tightly connected to modern drug delivery, which relies on nanoscopic drug formulation approaches and the ability to probe nanoparticulate systems selectively in cells and tissue using advanced spectroscopic and microscopic techniques. We first give an overview of the breadth of this research field. Then, we mainly focus on topical drug delivery to the skin and discuss selected visualization techniques from spectromicroscopy, such as scanning transmission X-ray microscopy and fluorescence lifetime imaging. These techniques rely on the sensitive and quantitative detection of the topically applied drug delivery systems and active substances, either by exploiting their molecular properties or by introducing environmentally sensitive probes that facilitate their detection.

Topical delivery of gambogic acid assisted by the combination of low-frequency ultrasound and chemical enhancers for chemotherapy of cutaneous melanoma

Anti-cutaneous melanoma activity of the skin-delivered gambogic acid (GA) has been reported in our previous study. However, it is difficult for GA to diffuse passively through intact skin without any enhancement means. In this study, a combination of chemical enhancers (EN: azone and propylene glycol) and physical ultrasound (US) was used to improve the percutaneous permeation of GA and enhance the anti-melanoma activity. The enhancement effect of the combination of EN and US (EN-US) on GA in vitro and in vivo was studied, and the enhancement mechanism and skin irritation were also evaluated. We showed that the parameters of US application at a constant frequency (30 kHz) with a duty cycle of 100% and intensity of 1.75 W/cm² for 20 min were optimal. In vitro, EN-US showed a considerable enhancement of the permeation of GA, and the enhancement effect was stronger than that with the use of EN or US alone. In vivo antitumor study showed that the tumor growth was significantly inhibited after percutaneous administration of GA by EN-US, more than in the intravenous injection group. The penetration enhancement mechanism revealed that EN-US not only altered the structure of lipid bilayers and keratins to reduce the barrier effect of the stratum corneum but also produced diffusion channels in the skin under the cavitation effect of US, thereby promoting the skin penetration of GA. In addition, there was no observable skin irritation in mice after treatment with EN-US. Our study demonstrated that the combination of EN and US improved the skin permeation and retention of GA to enhance the anti-melanoma activity. This method also provides technical guidance for the future development of topical and transdermal therapeutic system of GA.

Looking for a perfect match: multimodal combinations of Raman spectroscopy for biomedical applications

Raman spectroscopy has shown very promising results in medical diagnostics by providing label-free and highly specific molecular information of pathological tissue ex vivo and in vivo. Nevertheless, the high specificity of Raman spectroscopy comes at a price, i.e., low acquisition rate, no direct access to depth information, and limited sampling areas. However, a similar case regarding advantages and disadvantages can also be made for other highly regarded optical modalities, such as optical coherence tomography, autofluorescence imaging and fluorescence spectroscopy, fluorescence lifetime microscopy, second-harmonic generation, and others. While in these modalities the acquisition speed is significantly higher, they have no or only limited molecular specificity and are only sensitive to a small group of molecules. It can be safely stated that a single modality provides only a limited view on a specific aspect of a biological specimen and cannot assess the entire complexity of a sample. To solve this issue, multimodal optical systems, which combine different optical modalities tailored to a particular need, become more and more common in translational research and will be indispensable diagnostic tools in clinical pathology in the near future. These systems can assess different and partially complementary aspects of a sample and provide a distinct set of independent biomarkers. Here, we want to give an overview on the development of multimodal systems that use RS in combination with other optical modalities to improve the diagnostic performance.

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.

Improved Skin Permeability after Topical Treatment with Serine Protease: Probing the Penetration of Rapamycin by Scanning Transmission X-ray Microscopy

Drug penetration in human skin ex vivo following a modification of skin barrier permeability is systematically investigated by scanning transmission X-ray microscopy. Element-selective excitation is used in the O 1s regime for probing quantitatively the penetration of topically applied rapamycin in different formulations with a spatial resolution reaching <75 nm. The data were analyzed by a comparison of two methods: (i) two-photon energies employing the Beer-Lambert law and (ii) a singular value decomposition approach making use of the full spectral information in each pixel of the X-ray micrographs. The latter approach yields local drug concentrations more reliably and sensitively probed than the former. The present results from both approaches indicate that rapamycin is not observed within the stratum corneum of nontreated skin ex vivo, providing evidence for the observation that this high-molecular-weight drug inefficiently penetrates intact skin. However, rapamycin is observed to penetrate more efficiently the stratum corneum when modifications of the skin barrier are induced by the topical pretreatment with the serine protease trypsin for variable time periods ranging from 2 to 16 h. After the longest exposure time to serine protease, the drug is even found in the viable epidermis. High-resolution micrographs indicate that the lipophilic drug preferably associates with corneocytes, while signals found in the intercellular lipid compartment were less pronounced. This result is discussed in comparison to previous work obtained from low-molecular-weight lipophilic drugs as well as polymer nanocarriers, which were found to penetrate the intact stratum corneum exclusively via the lipid layers between the corneocytes. Also, the role of the tight junction barrier in the stratum granulosum is briefly discussed with respect to modifications of the skin barrier induced by enhanced serine protease activity, a phenomenon of clinical relevance in a range of inflammatory skin disorders.

Polyglycerol-Based Thermoresponsive Nanocapsules Induce Skin Hydration and Serve as a Skin Penetration Enhancer

The use of penetration enhancers (chemical or physical) has been proven to dramatically improve the penetration of therapeutics. Nevertheless, their use poses great risks, as they can lead to permanent damage of the skin, reduce its barrier efficiency, and result in the intrusion of harmful substances. Among the most used skin penetration enhancers, water is greatly accepted because skin quickly recovers from its exposure. Nanocapsules (NCs) represent a promising combination of the carrier system and penetration enhancer because their water-containing void combined with their polymer-based shell can be used to induce high local skin hydration, while simultaneously aiding the transport of drugs across the skin barrier. In this study, NCs were synthesized with a void core of 100 nm in diameter, a thermoresponsive shell based on different ratios of poly(N-isopropylacrylamide) and poly(N-isopropylmethacrylamide) as thermoresponsive polymers, and dendritic polyglycerol as a macromolecular cross-linker. These NCs can shrink or swell upon a thermal trigger, which was used to induce the release of the entrapped water in a controlled fashion. The interactions and effects of thermoresponsive NCs on the stratum corneum of excised human skin were investigated using fluorescence microscopy, high-resolution optical microscopy, and stimulated Raman spectromicroscopy. It could be observed that the thermoresponsive NCs increase the amount of deuterated water that penetrated into the viable epidermis. Moreover, NCs increased the skin penetration of a high-molecular weight dye (Atto Oxa12 NHS ester, MW = 835 g/mol) with respect to formulations in water or 30% DMSO, emphasizing the features of the NCs as a skin penetration enhancer.

Label-free stimulated Raman scattering microscopy visualizes changes in intracellular morphology during human epidermal keratinocyte differentiation

Epidermal keratinocyte (KC) differentiation, which involves the process from proliferation to cell death for shedding the outermost layer of skin, is crucial for the barrier function of skin. Therefore, in dermatology, it is important to elucidate the epidermal KC differentiation process to evaluate the symptom level of diseases and skin conditions. Previous dermatological studies used staining or labelling techniques for this purpose, but they have technological limitations for revealing the entire process of epidermal KC differentiation, especially when applied to humans. Here, we demonstrate label-free visualization of three-dimensional (3D) intracellular morphological changes of ex vivo human epidermis during epidermal KC differentiation using stimulated Raman scattering (SRS) microscopy. Specifically, we observed changes in nuclei during the initial enucleation process in which the nucleus is digested prior to flattening. Furthermore, we found holes left behind by improperly digested nuclei in the stratum corneum, suggesting abnormal differentiation. Our findings indicate the great potential of SRS microscopy for discrimination of the degree of epidermal KC differentiation.

Mechanism investigation of ethosomes transdermal permeation

Ethosomes are widely used to promote transdermal permeation of both lipophilic and hydrophilic drugs, but the mechanism of interaction between the ethosomes and the skin remains unclear. In this work, it was exploded with several technologies and facilities. Firstly, physical techniques such as attenuated total reflectance fourier-transform infrared and laser confocal Raman were used and the results indicated that the phospholipids configuration of stratum corneum changes from steady state to unstable state with the treatment of ethosomes. Differential scanning calorimetry reflected the thermodynamics change in stratum corneum after treatment with ethosomes. The results revealed that the skin of Bama mini-pigs, which is similar to human skin, treated by ethosomes had a relatively low T_m and enthalpy. Scanning electron microscopy and transmission electron microscopy showed that the microstructure and ultrastructure of stratum corneum was not damaged by ethosomes treatment. Furthermore, confocal laser scanning microscopy revealed that lipid labeled ethosomes could penetrate the skin via stratum corneum mainly through intercellular route, while during the process of penetration, phospholipids were retained in the upper epidermis. Cell experiments confirmed that ethosomes were distributed mainly on the cell membrane. Further study showed that only the drug-loaded ethosomes increased the amount of permeated drug. The current study, for the first time, elucidated the mechanistic behavior of ethosomes in transdermal application from molecular configuration, thermodynamic properties, ultrastructure, fluorescent labeling and cellular study. It is anticipated that the approaches and results described in the present study will benefit for better design of drug-loaded ethosomes.

Qualifying X-ray and Stimulated Raman Spectromicroscopy for Mapping Cutaneous Drug Penetration

Research on topical drug delivery relies on reconstructed human skin (RHS) in addition to ex vivo human and animal skin, each with specific physiological features. Here, we compared the penetration of dexamethasone from an ethanolic hydroxyethyl cellulose gel into ex vivo human skin, murine skin, and RHS. For comprehensive insights into skin morphology and penetration enhancing mechanisms, scanning transmission X-ray microscopy (STXM), liquid chromatography tandem-mass spectrometry (LC-MS/MS), and stimulated Raman spectromicroscopy (SRS) were combined. STXM offers high spatial resolution with label-free drug detection and is therefore sensitive to tissue damage. Despite differences in sample preparation and data analysis, the amounts of dexamethasone in RHS, detected and quantified by STXM and LC-MS/MS, were very similar and increased during the first 100 min of exposure. SRS revealed interactions between the gel and the stratum corneum or, more specifically, its protein and lipid structures. Similar to both types of ex vivo skin, higher protein-to-lipid ratios within the stratum corneum of RHS indicated reduced lipid amounts after 30 min of ethanol exposure. Extended ethanol exposure led to a continued reduction of lipids in the ex vivo matrixes, while protein integrity appeared to be compromised in RHS, which led to declining protein signals. In conclusion, LC-MS/MS proved the predictive capability of STXM for label-free drug detection. Combining STXM with SRS precisely dissected the penetration enhancing effects of ethanol. Further studies on topical drug delivery should consider the potential of these complementary techniques.