Selective hair therapy: bringing science to the fiction

A niche in the spotlight: Could external factors critically disturb hair follicle homeostasis and contribute to inflammatory hair follicle diseases?

The anatomy of the hair follicle and the dynamics of its barrier provide a special space for interactions between macromolecules and the underlying tissue. Translocation across the hair follicle epithelium and immune recognition have been confirmed for proteins, nucleic acids, engineered particles, virus particles and others. Tissue responses can be modulated by pro-inflammatory stimuli as demonstrated in penetration and transcutaneous immunization studies. Even under physiological conditions, hair follicle openings are filled with exogenous material ranging from macromolecules, engineered particles to natural particles including diverse communities of microbes. The exposed position of the infundibulum suggests that local inflammatory insults could disturb the finely tuned balance and may trigger downstream responses that initiate or facilitate local outbreaks of inflammatory hair diseases typically occurring in close spatial association with the infundibulum as observed in cicatricial alopecia. The question as to how microbial colonization or deposition of contaminants on the surface of the hair follicle epithelium interact with the barrier status under the influence of individual predisposition, may help us understand local flare-ups of inflammatory hair diseases. Specifically, learning more about skin barrier alterations in the different types of inflammatory hair diseases and cross-talk with exogenous compounds could give new insights in this less explored aspect of hair follicle homeostasis. Such knowledge may not only be used to develop supportive measures to maintain a healthy scalp. It may have wider implications for our understanding on how external factors influence inflammation and immunological responses in the skin.

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.

Tight Junction barriers in human hair follicles - role of claudin-1

Barrier function of hair follicles (HFs) is of great interest because they might be an entry port for allergens/pathogens, but could on the other hand be used for drug delivery or vaccination. Therefore we investigated tight junction (TJ) barrier function in human HFs. We show that there is a TJ barrier in the outermost living layer bordering to the environment from the infundibulum to the lower central part and between Henle’s and Huxles layer of anagen HFs. In club hair typical for catagen and telogen HFs a TJ barrier is found surrounding the club. This demonstrates that there is a continuous TJ barrier along interfollicular epidermis and HFs in different phases of HF cycle. However, interestingly, in cell culture experiments we can show that barrier is less tight in HF keratinocytes compared to interfollicular keratinocytes. Knock-down of the TJ protein claudin-1, which we demonstrate here to be less expressed in HFs of lesional atopic dermatitis skin, results in impaired barrier function, decreased proliferation and increased apoptosis of hair keratinocytes. This is in line with a hair growth phenotype in claudin-1 deficient patients (NISCH syndrome) and corresponding knock-out mice and indicates an important role of claudin-1 in HF barrier function and growth.

Ethyl cellulose nanocarriers and nanocrystals differentially deliver dexamethasone into intact, tape-stripped or sodium lauryl sulfate-exposed ex vivo human skin - assessment by intradermal microdialysis and extraction from the different skin layers

Understanding penetration not only in intact, but also in lesional skin with impaired skin barrier function is important, in order to explore the surplus value of nanoparticle-based drug delivery for anti-inflammatory dermatotherapy. Herein, short-term ex vivo cultures of (i) intact human skin, (ii) skin pretreated with tape-strippings and (iii) skin pre-exposed to sodium lauryl sulfate (SLS) were used to assess the penetration of dexamethasone (Dex). Intradermal microdialysis was utilized for up to 24h after drug application as commercial cream, nanocrystals or ethyl cellulose nanocarriers applied at the therapeutic concentration of 0.05%, respectively. In addition, Dex was assessed in culture media and extracts from stratum corneum, epidermis and dermis after 24h, and the results were compared to those in heat-separated split skin from studies in Franz diffusion cells. Providing fast drug release, nanocrystals significantly accelerated the penetration of Dex. In contrast to the application of cream and ethyl cellulose nanocarriers, Dex was already detectable in eluates after 6h when applying nanocrystals on intact skin. Disruption of the skin barrier further accelerated and enhanced the penetration. Encapsulation in ethyl cellulose nanocarriers delayed Dex penetration. Interestingly, for all formulations highly increased concentrations in the dialysate were observed in tape-stripped skin, whereas the extent of enhancement was less in SLS-exposed skin. The results were confirmed in tissue extracts and were in line with the predictions made by in vitro release studies and ex vivo Franz diffusion cell experiments. The use of 45kDa probes further enabled the collection of inflammatory cytokines. However, the estimation of glucocorticoid efficacy by Interleukin (IL)-6 and IL-8 analysis was limited due to the trauma induced by the probe insertion. Ex vivo intradermal microdialysis combined with culture media analysis provides an effective, skin-sparing method for preclinical assessment of novel drug delivery systems at therapeutic doses in models of diseased skin.

Current application of phytocompound-based nanocosmeceuticals for beauty and skin therapy

Phytocompounds have been used in cosmeceuticals for decades and have shown potential for beauty applications, including sunscreen, moisturizing and antiaging, and skin-based therapy. The major concerns in the usage of phyto-based cosmeceuticals are lower penetration and high compound instability of various cosmetic products for sustained and enhanced compound delivery to the beauty-based skin therapy. To overcome these disadvantages, nanosized delivery technologies are currently in use for sustained and enhanced delivery of phyto-derived bioactive compounds in cosmeceutical sectors and products. Nanosizing of phytocompounds enhances the aseptic feel in various cosmeceutical products with sustained delivery and enhanced skin protecting activities. Solid lipid nanoparticles, transfersomes, ethosomes, nanostructured lipid carriers, fullerenes, and carbon nanotubes are some of the emerging nanotechnologies currently in use for their enhanced delivery of phytocompounds in skin care. Aloe vera, curcumin, resveratrol, quercetin, vitamins C and E, genistein, and green tea catechins were successfully nanosized using various delivery technologies and incorporated in various gels, lotions, and creams for skin, lip, and hair care for their sustained effects. However, certain delivery agents such as carbon nanotubes need to be studied for their roles in toxicity. This review broadly focuses on the usage of phytocompounds in various cosmeceutical products, nanodelivery technologies used in the delivery of phytocompounds to various cosmeceuticals, and various nanosized phytocompounds used in the development of novel nanocosmeceuticals to enhance skin-based therapy.

Selective co-deposition of anionic silica particles at hydrophobic surfaces from formulations of oppositely charged polymers and surfactants

The surface-selective surface deposition of anionic hydrophilic silica particles from aqueous polymer-surfactant formulations was investigated by in-situ null-ellipsometry. The formulations, with or without silica particles, contained anionic sodium dodecylsulfate (SDS) and a cationic polymer, cationic hydroxyethyl cellulose (cat-HEC) or a copolymer of acrylamide and methacrylamidopropyl trimethylammonium chloride (AAm/MAPTAC). Surface deposition from the formulations onto model surfaces of either anionic hydrophilic, or hydrophobized, silica was induced by controlled dilution of the formulations into the coacervation region, and was monitored with time by ellipsometry. The dilution simulated a rinsing process in a typical application. In all cases a steady-state surface layer remained after extensive dilution. An enhanced deposition from the silica-containing formulations was found on the hydrophobized silica surface, indicating a substantial co-deposition of silica particles. Much less co-deposition, or none at all, was found on hydrophilic silica. The opposite trend, enhanced co-deposition on hydrophilic silica, was previously found in similar experiments with hydrophobic silicone oil droplets as co-deposants (Clauzel et al., 2011). The amphiphilic cationic polymers evidently favor a "mismatched" co-deposition of anionic particles to hydrophobic surfaces, or vice versa. The findings suggest a strategy for surface-specific delivery of particles to surfaces.

Hair Coloration by Gene Regulation: Fact or Fiction?

The unravelling of hair pigmentation genetics and robust delivery systems to the hair follicle (HF) will allow the development of a new class of colouring products. The challenge will be changing hair colour from inside out by safely regulating the activity of target genes through the specific delivery of synthetic/natural compounds, proteins, genes, or small RNAs.

Novel nanosome delivery system combined with siRNA targeting the antimicrobial gene DFB4: a new approach for psoriasis management?

In a recently published issue of the journal, Bracke et al. demonstrate an impressive improvement in psoriasiform features in allogeneic human skin grafts transplanted onto immune-deficient mice. This improvement was achieved using a novel nanosome (SECosome) as a vehicle for delivering topically applied siRNA to human epidermis. Targeting the gene DFB4 with this delivery system, they prevented translation of the antimicrobial peptide, human β defensin-2(hBD2), thus normalizing the psoriasiform epidermal phenotype of siRNA/SECosome-treated human skin grafts. This study encourages the exploration of topical gene silencing strategies in dermatology and refocuses our attention on both, the role of hBD2 in psoriasis pathogenesis and the thorny question which animal model reflects human psoriasis most faithfully.

Interaction of dermatologically relevant nanoparticles with skin cells and skin

The investigation of nanoparticle interactions with tissues is complex. High levels of standardization, ideally testing of different material types in the same biological model, and combinations of sensitive imaging and detection methods are required. Here, we present our studies on nanoparticle interactions with skin, skin cells, and biological media. Silica, titanium dioxide and silver particles were chosen as representative examples for different types of skin exposure to nanomaterials, e.g., unintended environmental exposure (silica) versus intended exposure through application of sunscreen (titanium dioxide) or antiseptics (silver). Because each particle type exhibits specific physicochemical properties, we were able to apply different combinations of methods to examine skin penetration and cellular uptake, including optical microscopy, electron microscopy, X-ray microscopy on cells and tissue sections, flow cytometry of isolated skin cells as well as Raman microscopy on whole tissue blocks. In order to assess the biological relevance of such findings, cell viability and free radical production were monitored on cells and in whole tissue samples. The combination of technologies and the joint discussion of results enabled us to look at nanoparticle-skin interactions and the biological relevance of our findings from different angles.