Core-multishell nanocarriers enhance drug penetration and reach keratinocytes and antigen-presenting cells in intact human skin

In reconstructed skin and diffusion cell studies, core-multishell nanocarriers (CMS-NC) showed great potential for drug delivery across the skin barrier. Herein, we investigated penetration, release of dexamethasone (DXM), in excised full-thickness human skin with special focus on hair follicles (HF). Four hours and 16 h after topical application of clinically relevant dosages of 10 μg DXM/cm² skin encapsulated in CMS-NC (12 nm diameter, 5.8% loading), presence of DXM in the tissue as assessed by fluorescence microscopy of anti-DXM-stained tissue sections as well as ELISA and HPLC-MS/MS in tissue extracts was enhanced compared to standard LAW-creme but lower compared to DXM aqueous/alcoholic solution. Such enhanced penetration compared to conventional cremes offers high potential for topical therapies, as recurrent applications of corticosteroid solutions face limitations with regard to tolerability and fast drainage. The findings encourage more detailed investigations on where and how the nanocarrier and drug dissociate within the skin and what other factors, e.g. thermodynamic activity, influence the penetration of this formulations. Microscopic studies on the spatial distribution within the skin revealed accumulation in HF and furrows accompanied by limited cellular uptake assessed by flow cytometry (up to 9% of total epidermal cells). FLIM clearly visualized the presence of CMS-NC in the viable epidermis and dermis. When exposed in situ a fraction of up to 25% CD1a⁺ cells were found within the epidermal CMS-NC⁺ population compared to approximately 3% CD1a⁺/CMS-NC⁺ cells after in vitro exposure in short-term cultures of epidermal cell suspensions. The latter reflects the natural percentage of Langerhans cells (LC) in epidermis suspensions and indicated that CMS-NC were not preferentially internalized by one cell type. The increased CMS-NC⁺ LC proportion after exposure within the tissue is in accordance with the strategic suprabasal LC-localization. More specifically we postulate that the extensive dendrite meshwork, their position around HF orifices and their capacity to modulate tight junctions facilitated a preferential uptake of CMS-NC by LC within the skin. This newly identified aspect of CMS-NC penetration underlines the potential of CMS-NC for dermatotherapy and encourages further investigations of CMS-NC for the delivery of other molecule classes for which intracellular delivery is even more crucial.

Visualizing Oxidative Cellular Stress Induced by Nanoparticles in the Subcytotoxic Range Using Fluorescence Lifetime Imaging

Nanoparticles hold a great promise in biomedical science. However, due to their unique physical and chemical properties they can lead to overproduction of intracellular reactive oxygen species (ROS). As an important mechanism of nanotoxicity, there is a great need for sensitive and high-throughput adaptable single-cell ROS detection methods. Here, fluorescence lifetime imaging microscopy (FLIM) is employed for single-cell ROS detection (FLIM-ROX) providing increased sensitivity and enabling high-throughput analysis in fixed and live cells. FLIM-ROX owes its sensitivity to the discrimination of autofluorescence from the unique fluorescence lifetime of the ROS reporter dye. The effect of subcytotoxic amounts of cationic gold nanoparticles in J774A.1 cells and primary human macrophages on ROS generation is investigated. FLIM-ROX measures very low ROS levels upon gold nanoparticle exposure, which is undetectable by the conventional method. It is demonstrated that cellular morphology changes, elevated senescence, and DNA damage link the resulting low-level oxidative stress to cellular adverse effects and thus nanotoxicity. Multiphoton FLIM-ROX enables the quantification of spatial ROS distribution in vivo, which is shown for skin tissue as a target for nanoparticle exposure. Thus, this innovative method allows identifying of low-level ROS in vitro and in vivo and, subsequently, promotes understanding of ROS-associated nanotoxicity.

Identification of polystyrene nanoparticle penetration across intact skin barrier as rare event at sites of focal particle aggregations

The question whether nanoparticles can cross the skin barrier is highly debated. Even in intact skin rare events of deeper penetration have been reported, but technical limitations and possible artifacts require careful interpretation. In this study, horizontal scanning by 2-photon microscopy (2 PM) of full-thickness human skin samples placed in a lateral position yielded highly informative images for skin penetration studies of fluorescently tagged nanoparticles. Scanning of large fields of view allowed for detailed information on interfollicular and follicular penetration in tissue blocks without damaging the sample. Images in histomorphological correlation showed that 2P-excited fluorescence signals of fluorescently tagged 20 and 200 nm polystyrene nanoparticles preferentially accumulated in the stratum corneum (SC) and in the upper part of vellus hair follicles (HFs). Rare events of deeper penetration in the SC and in the infundibulum of vellus HFs were observed at sites of high focal particle aggregations. Wide-field 2 PM allows for imaging of nanoparticle penetration in large tissue blocks, whereas total internal reflection microscopy (TIRFM) enables selective detection of individual nanoparticles as well as clusters of nanoparticles in the SC and within the epidermal layer directly beneath the SC, thus confirming barrier crossing with high sensitivity.

Crosstalk between core-multishell nanocarriers for cutaneous drug delivery and antigen-presenting cells of the skin

Owing their unique chemical and physical properties core-multishell (CMS) nanocarriers are thought to underlie their exploitable biomedical use for a topical treatment of skin diseases. This highlights the need to consider not only the efficacy of CMS nanocarriers but also the potentially unpredictable and adverse consequences of their exposure thereto. As CMS nanocarriers are able to penetrate into viable layers of normal and stripped human skin ex vivo as well as in in vitro skin disease models the understanding of nanoparticle crosstalk with components of the immune system requires thorough investigation. Our studies highlight the biocompatible properties of CMS nanocarriers on Langerhans cells of the skin as they did neither induce cytotoxicity and genotoxicity nor cause reactive oxygen species (ROS) or an immunological response. Nevertheless, CMS nanocarriers were efficiently taken up by Langerhans cells via divergent endocytic pathways. Bioimaging of CMS nanocarriers by fluorescence lifetime imaging microscopy (FLIM) and flow cytometry indicated not only a localization within the lysosomes but also an energy-dependent exocytosis of unmodified CMS nanocarriers into the extracellular environment.

White-Light Supercontinuum Laser-Based Multiple Wavelength Excitation for TCSPC-FLIM of Cutaneous Nanocarrier Uptake

We report here on a custom-built time-correlated single photon-counting (TCSPC)-based fluorescence lifetime imaging microscopy (FLIM) setup with a continuously tunable white-light supercontinuum laser combined with acousto-optical tunable filters (AOTF) as an excitation source for simultaneous excitation of multiple spectrally separated fluorophores. We characterized the wavelength dependence of the white-light supercontinuum laser pulse properties and demonstrated the performance of the FLIM setup, aiming to show the experimental setup in depth together with a biomedical application. We herein summarize the physical-technical parameters as well as our approach to map the skin uptake of nanocarriers using FLIM with a resolution compared to spectroscopy. As an example, we focus on the penetration study of indocarbocyanine-labeled dendritic core-multishell nanocarriers (CMS-ICC) into reconstructed human epidermis. Unique fluorescence lifetime signatures of indocarbocyanine-labeled nanocarriers indicate nanocarrier-tissue interactions within reconstructed human epidermis, bringing FLIM close to spectroscopic analysis.

Dendritic Core-Multishell Nanocarriers in Murine Models of Healthy and Atopic Skin

Dendritic hPG-amid-C18-mPEG core-multishell nanocarriers (CMS) represent a novel class of unimolecular micelles that hold great potential as drug transporters, e.g., to facilitate topical therapy in skin diseases. Atopic dermatitis is among the most common inflammatory skin disorders with complex barrier alterations which may affect the efficacy of topical treatment.Here, we tested the penetration behavior and identified target structures of unloaded CMS after topical administration in healthy mice and in mice with oxazolone-induced atopic dermatitis. We further examined whole body distribution and possible systemic side effects after simulating high dosage dermal penetration by subcutaneous injection.Following topical administration, CMS accumulated in the stratum corneum without penetration into deeper viable epidermal layers. The same was observed in atopic dermatitis mice, indicating that barrier alterations in atopic dermatitis had no influence on the penetration of CMS. Following subcutaneous injection, CMS were deposited in the regional lymph nodes as well as in liver, spleen, lung, and kidney. However, in vitro toxicity tests, clinical data, and morphometry-assisted histopathological analyses yielded no evidence of any toxic or otherwise adverse local or systemic effects of CMS, nor did they affect the severity or course of atopic dermatitis.Taken together, CMS accumulate in the stratum corneum in both healthy and inflammatory skin and appear to be highly biocompatible in the mouse even under conditions of atopic dermatitis and thus could potentially serve to create a depot for anti-inflammatory drugs in the skin.

Increased permeability of reconstructed human epidermis from UVB-irradiated keratinocytes

Extrinsic (photo) aging accelerates chronologically aging in the skin due to cumulative UV irradiation. Despite recent insights into the molecular mechanisms of fibroblast aging, age-related changes of the skin barrier function have been understudied. In contrast, the constantly increasing subpopulation of aged patients causes a clinical need for effective and safe (dermatological) treatment. Herein, we reconstructed human epidermis from UVB-irradiated keratinocytes (UVB-RHE). UVB-irradiated keratinocytes show higher activity of senescence associated β-galactosidase, less cell proliferation, and reduced viability. Higher amounts of β-galactosidase are also detectable in UVB-RHE. Moreover, UVB-RHE release more interleukin-1α and -8 into the culture medium and present altered differentiation with a thinner stratum corneum compared to normal RHE. For the first time, the permeation of testosterone and caffeine through UVB-irradiated RHE indicate a clear influence of the UVB stress on the skin barrier function. Impaired barrier function was confirmed by the increased permeation of testosterone and caffeine as well as by the increased penetration of dendritic core-multishell nanocarriers into the constructs. Taken together, UVB-RHE emulate hallmarks of skin aging and might contribute to an improved non-clinical development of medicinal or cosmetic products.

Poly[acrylonitrile-co-(N-vinyl pyrrolidone)] nanoparticles - Composition-dependent skin penetration enhancement of a dye probe and biocompatibility

Nanoparticles can improve topical drug delivery: size, surface properties and flexibility of polymer nanoparticles are defining its interaction with the skin. Only few studies have explored skin penetration for one series of structurally related polymer particles with systematic alteration of material composition. Here, a series of rigid poly[acrylonitrile-co-(N-vinyl pyrrolidone)] model nanoparticles stably loaded with Nile Red or Rhodamin B, respectively, was comprehensively studied for biocompatibility and functionality. Surface properties were altered by varying the molar content of hydrophilic NVP from 0 to 24.1% and particle size ranged from 35 to 244nm. Whereas irritancy and genotoxicity were not revealed, lipophilic and hydrophilic nanoparticles taken up by keratinocytes affected cell viability. Skin absorption of the particles into viable skin ex vivo was studied using Nile Red as fluorescent probe. Whilst an intact stratum corneum efficiently prevented penetration, almost complete removal of the horny layer allowed nanoparticles of smaller size and hydrophilic particles to penetrate into viable epidermis and dermis. Hence, systematic variations of nanoparticle properties allows gaining insights into critical criteria for biocompatibility and functionality of novel nanocarriers for topical drug delivery and risks associated with environmental exposure.

Dual-fluorescence pH probe for bio-labelling

Although seminaphtorhodafluor (SNARF) dyes are already widely used to measure pH in cells and at biofilms, their synthesis has low yield and results in an unspecific position of a carboxy-group. The separation of 5'- and 6'-carboxy-SNARF reveals a pKa difference of 0.15, calling into question pH measurements with the (commercially available) mixture. Here we replace the bulky external dicarboxyphenyl ring with a propionate group and evaluate the spectral properties of the new derivative. Proceeding to the ethyl-iodoacetamide, covalent linkage to cysteine protein sites is achieved efficiently as shown with a cyanobacterial phytochrome, extending the scarce application of SNARF in bio-labelling in the current literature. Application in fluorescence lifetime imaging is demonstrated both with the lifetime-based and ratiometric-yield method.

Light and pH-induced Changes in Structure and Accessibility of Transmembrane Helix B and Its Immediate Environment in Channelrhodopsin-2

A variant of the cation channel channelrhodopsin-2 from Chlamydomonas reinhardtii (CrChR2) was selectively labeled at position Cys-79 at the end of the first cytoplasmic loop and the beginning of transmembrane helix B with the fluorescent dye fluorescein (acetamidofluorescein). We utilized (i) time-resolved fluorescence anisotropy experiments to monitor the structural dynamics at the cytoplasmic surface close to the inner gate in the dark and after illumination in the open channel state and (ii) time-resolved fluorescence quenching experiments to observe the solvent accessibility of helix B at pH 6.0 and 7.4. The light-induced increase in final anisotropy for acetamidofluorescein bound to the channel variant with a prolonged conducting state clearly shows that the formation of the open channel state is associated with a large conformational change at the cytoplasmic surface, consistent with an outward tilt of helix B. Furthermore, results from solute accessibility studies of the cytoplasmic end of helix B suggest a pH-dependent structural heterogeneity that appears below pH 7. At pH 7.4 conformational homogeneity was observed, whereas at pH 6.0 two protein fractions exist, including one in which residue 79 is buried. This inaccessible fraction amounts to 66% in nanodiscs and 82% in micelles. Knowledge about pH-dependent structural heterogeneity may be important for CrChR2 applications in optogenetics.

A simulation-guided fluorescence correlation spectroscopy tool to investigate the protonation dynamics of cytochrome c oxidase

Fluorescence correlation spectroscopy (FCS) is a single molecule based technique to temporally resolve rate-dependent processes by correlating the fluorescence fluctuations of individual molecules traversing through a confocal volume. In addition, chemical processes like protonation or intersystem crossing can be monitored in the sub-microsecond range. FCS thereby provides an excellent tool for investigations of protonation dynamics in proton pumps like cytochrome c oxidase (CcO). To achieve this, the pH-dependent fluorescent dye fluorescein was attached as a protonation probe to the CcO surface via site-specific labeling of single reactive cysteines that are located close to the entry point of a proton input channel (K-pathway). The analysis of protonation dynamics is complicated by overlapping triplet and protonation rates of the fluorophore. A Monte Carlo simulation based algorithm was developed to facilitate discrimination of these temporally overlapping processes thus allowing for improved protonation reaction rate determination. Using this simulation-guided approach we determined precise local proton association and dissociation rates and provide information about protein surface effects, such as proton collecting antennae, on the transport properties of proton transfer channels.

Chromosome abnormalities in meningeal neoplasms: do they correlate with histology?

Thirty-three meningeal neoplasms were karyotyped, and the results were compared with histologic features. Thirteen neoplasms had no discernible abnormality or sex chromosome loss only; nine had monosomy or structural abnormality involving only chromosome 22; and 11 had other chromosome abnormalities with or without chromosome 22 involvement. Histologic evidence of invasion was not associated with an abnormal karyotype in the three angioblastic tumors examined. All seven fibroblastic meningiomas had abnormal karyotypes, with monosomy 22 the most common change. Abnormal karyotypes were detected in 76% of syncytial and 55% of transitional meningiomas. When these results were combined with those from 259 meningeal tumors reported since 1987, abnormal karyotypes were detected in at least half of all histologic types. Chromosome changes secondary to those involving chromosome 22 may indicate additional areas of the genome that play a role in tumor progression. In the combined series, chromosome losses were most frequently observed in meningiomatous and transitional histologies; chromosomes 1, 6, 14, 18, and Y each were lost in 10 or more meningiomas, whereas only chromosome 20 was gained at the same frequency. Structural abnormalities most frequently involved chromosome 1. These changes are distinctly different from those observed in other common intracranial neoplasms, specifically astrocytic neoplasms.