Delta opioid receptor expression correlates to skin ageing and melanin expression in Asian women.

While the evidence for the implication of opioid receptors (OPr) in ageing is growing, there is, to our knowledge, no study focusing directly on changes in vivo cutaneous OPr expression with increasing age. We thus investigated OPr expression in 30 healthy female Asian volunteers in Southern China whose ages range from the early 20s to the early 60s. Excisional biopsies were taken from the sun-exposed extensor area of the lower arm and the photo-protected area of the upper inner arm. The thickness of the epidermal layers, melanin content, as well as expression of mu-opioid receptors (MOPr) and delta-opioid receptors (DOPr) were compared between different age ranges and photo-exposure status. Significant increased epidermal hypertrophy on the extensor surface was observed. There was significant reduction of DOPr in the epidermis with increasing age, independent of photo-ageing. The increase of melanin was significantly correlated with epidermal DOPr expression, not with MOPr expression. DOPr expression could thus serve as a marker for real biological ageing unaffected by chronic photo-exposure. Additionally, DOPr expression was inversely correlated with the deposition of melanin. Based on these results, we hypothesise that regulation of DOPr expression could be used to improve aged skin, including hyperpigmentation.

Demonstration of Convolutional Neural Networks to Determine Patch Test Reactivity.

Background: Convolutional neural networks (CNNs) have the potential to assist allergists and dermatologists in the analysis of patch tests. Such models can help reduce interprovider variability and improve consistency of patch test interpretations. Objective: Our aim is to evaluate the performance of a CNN model as a proof of concept in discriminating between patch tests with reactions and patch tests without reactions. Methods: We performed a retrospective analysis of patch test images from March 2020 to March 2021. The CNN model was trained as a binary classifier to discriminate between reaction and nonreaction patches. Performance of the model was determined using summary statistics and receiver operator characteristics (ROC) curves. Results: In total, 13,622 images from 125 patients were recorded for analysis. The majority of patients in the cohort were female (81.6%) with Fitzpatrick skin types I-II (88.0%). The area under curve was 0.940, indicating a high discriminative performance of the model for this data set. This resulted in a total accuracy of 90.1%, sensitivity of 86.0%, and specificity of 90.2%. Conclusions: CNNs have the capacity to determine the presence of delayed-type reactions in patch tests. Future prospective studies are required to assess the generalizability of such models.

The Diagnostic Value of Delayed-Type Reactions to Perennial Aeroallergens for Atopic Disease.

Background: Delayed-type reactions to aeroallergens have been observed, however, their clinical significance continues to be debated. Objective: We assessed the prevalence and significance of delayed-type reactions to aeroallergens in atopic patients. Methods: Retrospective study including 266 patients with history or evidence of atopic disease (atopic dermatitis [AD], allergic rhinitis, and/or allergic asthma) and tested via either the intradermal skin test (IDT) or atopy patch test for common aeroallergens, specifically house dust mites (Dermatophagoides farinae, Dermatophagoides pteronyssinus) and perennial molds (Aspergillus fumigatus, Penicillium notatum). All patients were tested via IDT with both immediate (15 minute) and delayed (2 and 4 days) readings. Delayed reading was considered positive if the IDT injection site demonstrated at least 5 mm induration 48 hours after inoculation. Results: In total, 195 (73.3%) patients demonstrated an immediate-type reaction, whereas 118 (44.4%) had a delayed-type reaction. In total, 75 (28.2%) patients experienced both immediate- and delayed-type reactions, 43 (16.2%) reacted delayed-type only, and 85.3% of delayed-type reactions to individual aeroallergens were associated with eczematous lesions predominantly in air-exposed areas. Conclusion: Delayed-type reactions to aeroallergens are prevalent and clinically significant as a component of extrinsic AD and atopic diseases. The data support delayed reading of the IDT to guide diagnosis and management in these patients.

Honey flower dermatitis: Contact allergy to ellagic acid in Melianthuscomosus.

A case study is reported whereby a patient with no prior allergies developed a strong and spreading delayed-type hypersensitivity reaction to Melianthus plants, nectar and synthetic pigment derived from it after frequent handling of these substances. The lesions improved after treatment with topical steroids and allergen avoidance within 1-2 weeks. Subsequent patch testing with the plants, nectar and synthetic ingredients identified ellagic acid (EA) as the sensitizing agent. This is the first proven case of allergic contact dermatitis to EA, a phenolic substance present in numerous plants, fruits, and nuts regularly consumed by humans. Melianthus use is growing worldwide as an ornamental plant. Moreover, it is used in traditional South African medicine for its anti-inflammatory effects. In recent years, these extracts and EA have been added to natural, plant-based topical formulations for the treatment of inflammatory skin disorders. Our observation that the EA found in Melianthus can induce severe contact allergy should caution for the possible dangers of specific allergic sensitizations to these increasingly used additives in natural medicines.

What You Need to Know About Hand Hygiene and Dermatitis During the Coronavirus Pandemic.

Increased attention towards infection control measures during the COVID-19 pandemic have brought to light the dermatological consequences of intensified hand hygiene measures. Healthcare workers are inherently at an increased risk of developing both allergic and irritant contact dermatitis. Individuals with a history of atopy are especially vulnerable given their impaired native skin barriers and increased sensitivities at baseline. Examination gloves not only induce contact allergies from manufacturing chemicals, but also serve as an occlusive catalyst for facilitating contact sensitization and irritant dermatitis. Similarly, handwashing practices with soap and alcohol-based hand rubs (ABHRs) undermine the natural skin barriers with increasing frequency of use. We highlight clinical pearls for the frontline healthcare worker experiencing COVID-19 surges and offer practical measures to minimize the development of hand-based dermatitis.

Atopic Patients Who Fulfilled Rome III Criteria for Irritable Bowel Syndrome Had Higher Animal Danders Sensitization.

BACKGROUND/AIMS: The relationship between animal exposure and irritable bowel syndrome (IBS) is debated. Epidemiological studies have shown that atopy is more prevalent in IBS patients and vice versa. We set out to examine the association between animal danders sensitization and IBS-like symptoms in atopic patients. METHODS: We recruited 69 consecutive atopic patients from the allergy clinic of a tertiary hospital. Subjects completed validated bowel questionnaires, underwent skin prick test, blood was collected for serum total immunoglobulin E, and ImmunoCAP immune solidphase allergen chip (ISAC) IgE multiplex assay. RESULTS: Twenty-eight (41.0%) atopic patients fulfilled the Rome III IBS criteria (atopy-IBS). There were no differences in gender, age, pet ownership, total serum IgE, or food allergen sensitization between atopy-IBS group and atopy-non-IBS group. We found that atopy- IBS group had significantly higher number of positive skin prick test for cat dander (64.3% vs 24.4%, P < 0.001), dog dander (64.3% vs 41.5%, P = 0.015) and weed pollens (32.1% vs 14.6%, P = 0.050) compared to atopy-non-IBS group. Out of 112 components from 51 allergen sources (both aeroallergen and food allergens), only Fel d1 (a major cat dander antigen) IgE is significantly higher in atopy-IBS group than atopy-non-IBS group (21.4% vs 2.4%, P = 0.029). Majority of atopy-IBS patients had mixed-type IBS. CONCLUSIONS: We demonstrated an association between animal danders sensitization, in particular cat dander sensitization, and IBS-like symptoms in atopic patients. Future studies are needed to explore the relationship between aeroallergen and functional gastrointestinal disorders. Sensitization may be related to the pathophysiology of IBS or it could be that we are missing aeroallergen-induced gut allergy.

Role of Skin pH in Psoriasis.

Not much is known about the role of skin pH in skin pathophysiology, in particular in psoriasis. However, there is compelling evidence that the epidermal pH can influence the skin homeostasis and affect the skin barrier by changing the activity of cutaneous enzymes and through the modulation of skin inflammation and microbial colonization. This includes the activation of secretory phospholipase A and interaction with the peroxisome proliferators-activated receptor and retinoid pathways. In addition, pH in skin affects the activity of aquaporins and this controls the hydration of the epidermis. Changes in skin homeostasis, differentiation, barrier defects, and inflammation play a crucial role in the pathogenesis of psoriasis. There is evidence that skin pH can affect all of these important factors. However, more studies are needed to examine objectively and precisely the pH in the various skin layers in psoriatic lesional and non-lesional skin and compare it to normal skin. This additional know-how is essential to understand the role of skin pH in psoriasis with ultimately great potential of manipulations of skin pH for topical approaches in the management of psoriasis.

Physiological Doses of Red Light Induce IL-4 Release in Cocultures between Human Keratinocytes and Immune Cells.

Phototherapy is routinely used for the treatment of various skin conditions and targeted therapy of superficial cancers. However, the molecular mechanisms behind their biological effects and the need for efficacy enhancing photosensitizers are not well addressed. Particularly, not much is known about the inherent effect of light from the visible spectrum on cytokine release and its downstream effects in keratinocytes and immune cells located in skin and therefore exposed to light. To address this, we delivered calibrated doses of well-defined light qualities (380 to 660 nm) to cocultures of human keratinocytes and macrophage/dendritic cells in the absence or presence of the commonly used photosensitizer 8-methoxypsoralen (8-MOP). The experiments identified IL-4 as a key effector cytokine released by this coculture model with need for 8-MOP in the UVA1 /blue (380 nm) and no requirement for photosensitizer in the red light spectrum (627 nm). 3D organotypic skin cultures treated with IL-4 showed thickening of the epidermal layer and delayed differentiation. However unlike IL-4 and UVA1 /blue light treatment, red light did not reduce the expression of keratinocyte differentiation markers or increase signs of photo-oxidative damage. This supports the application of isolated red light as a possible alternative for photo-immunotherapy without need for additional photosensitizers.

Investigating endogenous µ-opioid receptors in human keratinocytes as pharmacological targets using novel fluorescent ligand.

Opioids in skin function during stress response, regeneration, ageing and, particularly in regulating sensation. In chronic pruritus, topical treatment with Naltrexone changes µ-opioid receptor (µ-OR) localization to relieve itch. The molecular mechanisms behind the effects of Naltrexone on µ-OR function in reduction of itching behavior has not been studied. There is an immediate need to understand the endogenous complexity of µ-OR dynamics in normal and pathological skin conditions. Here we evaluate real-time behavior of µ-OR-Endomorphine complexes in the presence of agonist and antagonists. The µ-OR ligand Endomorphine-1 (EM) was conjugated to the fluorescent dye Tetramethylrhodamine (TAMRA) to investigate the effects of agonist and antagonists in N/TERT-1 keratinocytes. The cellular localization of the EM-TAMRA was followed through time resolved confocal microscopy and population analysis was performed by flow cytometry. The in vitro analyses demonstrate fast internalization and trafficking of the endogenous EM-TAMRA-µ-OR interactions in a qualitative manner. Competition with Endomorphine-1, Naltrexone and CTOP show both canonical and non-canonical effects in basal and differentiated keratinocytes. Acute and chronic treatment with Naltrexone and Endomorphine-1 increases EM-TAMRA binding to skin cells. Although Naltrexone is clinically effective in relieving itch, the mechanisms behind re-distribution of µ-ORs during clinical treatments are not known. Our study has given insight into cellular mechanisms of µ-OR ligand-receptor interactions after opioid agonist and antagonist treatments in vitro. These findings potentially offer opportunities in using novel treatment strategies for skin and peripheral sensory disorders.

Synthetic Peptide Drugs for Targeting Skin Cancer: Malignant Melanoma and Melanotic Lesions.

BACKGROUND: Peptides play decisive roles in the skin, ranging from host defense responses to various forms of neuroendocrine regulation of cell and organelle function. Synthetic peptides conjugated to radionuclides or photosensitizers may serve to identify and treat skin tumors and their metastatic forms in other organs of the body. In the introductory part of this review, the role and interplay of the different peptides in the skin are briefly summarized, including their potential application for the management of frequently occurring skin cancers. Special emphasis is given to different targeting options for the treatment of melanoma and melanotic lesions. Radionuclide Targeting: α-Melanocyte-stimulating hormone (α-MSH) is the most prominent peptide for targeting of melanoma tumors via the G protein-coupled melanocortin-1 receptor that is (over-)expressed by melanoma cells and melanocytes. More than 100 different linear and cyclic analogs of α-MSH containing chelators for 111In, 67/68Ga, 64Cu, 90Y, 212Pb, 99mTc, 188Re were synthesized and examined with experimental animals and in a few clinical studies. Linear Ac-Nle-Asp-His-D-Phe-Arg-Trp-Gly-Lys-NH2 (NAP-amide) and Re-cyclized Cys- Cys-Glu-His-D-Phe-Arg-Trp-Cys-Arg-Pro-Val-NH2 (Re[Arg11]CCMSH) containing different chelators at the N- or C-terminus served as lead compounds for peptide drugs with further optimized characteristics. Alternatively, melanoma may be targeted with radiopeptides that bind to melanin granules occurring extracellularly in these tumors. Photosensitizer targeting: A more recent approach is the application of photosensitizers attached to the MSH molecule for targeted photodynamic therapy using LED or coherent laser light that specifically activates the photosensitizer. Experimental studies have demonstrated the feasibility of this approach as a more gentle and convenient alternative compared to radionuclides.

Opioids and skin homeostasis, regeneration and ageing - What's the evidence?

What has the opioid receptor system, known for beneficial as well as disastrous effects in the central nervous system, to do with skin? The question is appropriate considering the fact that the nervous system and the skin both derive from the ectoderm. As part of the skin neuroendocrine system, the opioid receptor system exemplifies the closeness between the nervous system and the skin. Overexpression of the δ-opioid receptor in keratinocytes yields dysregulation of involucrin, loricrin, and filaggrin, proteins essential to the integrity of the skin barrier. The µ-opioid receptor ligand ß-endorphin, produced in the pituitary gland and a variety of skin cells, promotes wound healing via regulation of cytokeratin 16 and TGF-ß type II receptor expression in keratinocytes. These and other published results discussed in this viewpoint are evidence for the fundamental role of the skin opioid receptor system in skin homeostasis, regeneration and ageing. While considerable progress in understanding the opioid receptors' function on the cellular level has been made, there is a need to link these results to physiological observations for the development of local skin therapies.

Differential Expression between Human Dermal Papilla Cells from Balding and Non-Balding Scalps Reveals New Candidate Genes for Androgenetic Alopecia.

Androgenetic alopecia (AGA) is a common heritable and androgen-dependent hair loss condition in men. Twelve genetic risk loci are known to date, but it is unclear which genes at these loci are relevant for AGA. Dermal papilla cells (DPCs) located in the hair bulb are the main site of androgen activity in the hair follicle. Widely used monolayer-cultured primary DPCs in hair-related studies often lack dermal papilla characteristics. In contrast, immortalized DPCs have high resemblance to intact dermal papilla. We derived immortalized human DPC lines from balding (BAB) and non-balding (BAN) scalp. Both BAB and BAN retained high proportions of dermal papilla signature gene and versican protein expression. We performed expression analysis of BAB and BAN and annotated AGA risk loci with differentially expressed genes. We found evidence for AR but not EDA2R as the candidate gene at the AGA risk locus on chromosome X. Further, our data suggest TWIST1 (twist family basic helix-loop-helix transcription factor 1) and SSPN (sarcospan) to be the functionally relevant AGA genes at the 7p21.1 and 12p12.1 risk loci, respectively. Down-regulated genes in BAB compared to BAN were highly enriched for vasculature-related genes, suggesting that deficiency of DPC from balding scalps in fostering vascularization around the hair follicle may contribute to the development of AGA.

Structural and Functional Analysis of Intact Hair Follicles and Pilosebaceous Units by Volumetric Multispectral Optoacoustic Tomography.

Visualizing anatomical and functional features of hair follicle development in their unperturbed environment is key in understanding complex mechanisms of hair pathophysiology and in discovery of novel therapies. Of particular interest is in vivo visualization of the intact pilosebaceous unit, vascularization of the hair bulb, and evaluation of the hair cycle, particularly in humans. Furthermore, noninvasive visualization of the sebaceous glands could offer crucial insight into the pathophysiology of follicle-related diseases and dry or seborrheic skin, in particular by combining in vivo imaging with other phenotyping, genotyping, and microbial analyses. The available imaging techniques are limited in their ability for deep tissue in vivo imaging of hair follicles and lipid-rich sebaceous glands in their entirety without biopsy. We developed a noninvasive, painless, and risk-free volumetric multispectral optoacoustic tomography method for deep tissue three-dimensional visualization of whole hair follicles and surrounding structures with high spatial resolution below 80 µm. Herein we demonstrate on-the-fly assessment of key morphometric parameters of follicles and lipid content as well as functional oxygenation parameters of the associated capillary bed. The ease of handheld operation and versatility of the newly developed approach poise it as an indispensable tool for early diagnosis of disorders of the pilosebaceous unit and surrounding structures, and for monitoring the efficacy of cosmetic and therapeutic interventions.

What happens in the skin? Integrating skin permeation kinetics into studies of developmental and reproductive toxicity following topical exposure.

Animal-based developmental and reproductive toxicological studies involving skin exposure rarely incorporate information on skin permeation kinetics. For practical reasons, animal studies cannot investigate the many factors which can affect human skin permeation and systemic uptake kinetics in real-life scenarios. Traditional route-to-route extrapolation is based on the same types of experiments and requires assumptions regarding route similarity. Pharmacokinetic modeling based on skin physiology and structure is the most efficient way to incorporate the variety of intrinsic skin and exposure-dependent parameters occurring in clinical and occupational settings into one framework. Physiologically-based pharmacokinetic models enable the integration of available in vivo, in vitro and in silico data to quantitatively predict the kinetics of uptake at the site of interest, as needed for 21st century toxicology and risk assessment. As demonstrated herein, proper interpretation and integration of these data is a multidisciplinary endeavor requiring toxicological, risk assessment, mathematical, pharmaceutical, biological and dermatological expertise.

The role of opioid receptors in migration and wound recovery in vitro in cultured human keratinocytes and fibroblasts.

We have previously described significant changes in skin differentiation and the delay in wound healing from delta-opioid receptor knockout mice. In addition, we have shown that opioid receptor ligands and their receptor systems affect wound healing in vitro and the migration pattern of human skin cells, such as keratinocytes and fibroblasts (Bigliardi-Qi et al., Differentiation 74:174-185, 2006; Bigliardi et al., Exp Dermatol 18:424-430, 2009; Bigliardi et al., J Recept Signal Transduct Res 22:191-199, 2002). This observation is true for both primary keratinocytes and fibroblasts derived from foreskin or normal human skin as well as for immortalized cell lines such as HaCaT cells.

The δ-opioid receptor affects epidermal homeostasis via ERK-dependent inhibition of transcription factor POU2F3.

Neuropeptides and their receptors are present in human skin, and their importance for cutaneous homeostasis and during wound healing is increasingly appreciated. However, there is currently a lack of understanding of the molecular mechanisms by which their signaling modulates keratinocyte function. Here, we show that δ-opioid receptor (DOPr) activation inhibits proliferation of human keratinocytes, resulting in decreased epidermal thickness in an organotypic skin model. DOPr signaling markedly delayed induction of keratin intermediate filament (KRT10) during in vitro differentiation and abolished its induction in the organotypic skin model. This was accompanied by deregulation of involucrin (IVL), loricrin, and filaggrin. Analysis of the transcription factor POU2F3, which is involved in regulation of KRT10, IVL, and profilaggrin expression, revealed a DOPr-mediated extracellular signal-regulated kinase (ERK)-dependent downregulation of this factor. We propose that DOPr signaling specifically activates the ERK 1/2 mitogen-activated protein kinase pathway to regulate keratinocyte functions. Complementing our earlier studies in DOPr-deficient mice, these data suggest that DOPr activation in human keratinocytes profoundly influences epidermal morphogenesis and homeostasis.

Opioids and the skin--where do we stand?

The common ectodermal origin of the skin and nervous systems can be expected to predict likely interactions in the adult. Over the last couple of decades much progress has been made to elucidate the nature of these interactions, which provide multidirectional controls between the centrally located brain and the peripherally located skin and immune system. The opioid system is an excellent example of such an interaction and there is growing evidence that opioid receptors (OR) and their endogenous opioid agonists are functional in different skin structures, including peripheral nerve fibres, keratinocytes, melanocytes, hair follicles and immune cells. Greater knowledge of these skin-associated opioid interactions will be important for the treatment of chronic and acute pain and pruritus. Topical treatment of the skin with opioid ligands is particularly attractive as they are active with few side effects, especially if they cannot cross the blood-brain barrier. Moreover, cutaneous activation of the opioid system (e.g. by peripheral nerves, cutaneous and immune cells, especially in inflamed and damaged skin) can influence cell differentiation and apoptosis, and thus may be important for the repair of damaged skin. While many of the pieces of this intriguing puzzle remain to be found, we attempt in this review to weave a thread around available data to discuss how the peripheral opioid system may impact on different key players in skin physiology and pathology.

Treatment of pruritus with topically applied opiate receptor antagonist.

BACKGROUND: Pruritus is the most common and distressing skin symptom, and treatment of itch is a problem for thousands of people. The currently available therapies are not very effective. Therefore there is an urgent need to find new effective topical drugs against itching. OBJECTIVE: We conducted two separate studies to evaluate the efficacy of topically applied naltrexone, an opioid receptor antagonist, in the treatment of severe pruritus. The objective of the first open study was to correlate the clinical efficacy of topically applied naltrexone in different pruritic skin disorders to a change of epidermal mu-opiate receptor (MOR) expression. The second study was a double-blind, placebo-controlled, crossover study on pruritus in atopic dermatitis. METHODS: Initially we performed an open pilot study on 18 patients with different chronic pruritic disorders using a topical formulation of 1% naltrexone for 2 weeks. A punch biopsy was performed in 11 patients before and after the application of the naltrexone cream and the staining of epidermal MOR was measured. Subsequently, a randomized, placebo-controlled, crossover trial was performed with the same formulation. We included in this trial 40 patients with localized and generalized atopic dermatitis with severe pruritus. RESULTS: In the open study more than 70% of the patients using the 1% naltrexone cream experienced a significant reduction of pruritus. More interestingly, the topical treatment with naltrexone caused an increase of epidermal MOR staining. The regulation of the epidermal opioid receptor correlated with the clinical assessment. The placebo-controlled, crossover trial demonstrated clearly that the cream containing naltrexone had an overall 29.4% better effect compared with placebo. The formulation containing naltrexone required a median of 46 minutes to reduce the itch symptoms to 50%; the placebo, 74 minutes. LIMITATIONS: We could only take biopsy specimens in 11 patients, which means that a satisfactory statistical analysis of the changes of epidermal MOR staining was not possible. In addition, there was an insufficient number of patients with nephrogenic pruritus and pruritic psoriasis to draw definitive conclusions. CONCLUSIONS: The placebo-controlled study showed a significant advantage of topically applied naltrexone over the placebo formulation. This finding is supported by the biopsy results from the open studies, showing a regulation of MOR expression in epidermis after treatment with topical naltrexone, especially in atopic dermatitis. These results clearly show potential for topically applied opioid receptor antagonist in the treatment of pruritus. The placebo formulation also had some antipruritic effects. This underlines the importance of rehydration therapy for dry skin in the treatment of pruritus.