Stratum corneum lipidomics analysis reveals altered ceramide profile in atopic dermatitis patients across body sites with correlated changes in skin microbiome

Effect of Staphylococcus aureus colonization and immune defects on the pathogenesis of atopic dermatitis

Atopic dermatitis (AD) is a common and recurrent skin disease characterized by skin barrier dysfunction, inflammation and chronic pruritus, with wide heterogeneity in terms of age of onset, clinical course and persistence over the lifespan. Although the pathogenesis of the disease are unclear, epidermal barrier dysfunction, immune and microbial dysregulation, and environmental factors are known to be critical etiologies in AD pathology. The skin microbiota represents an ecosystem consisting of numerous microbial species that interact with each other as well as host epithelial cells and immune cells. Although the skin microbiota benefits the host by supporting the basic functions of the skin and preventing the colonization of pathogens, disruption of the microbial balance (dysbiosis) can cause skin diseases such as AD. Although AD is a dermatological disease, recent evidence has shown that changes in microbiota composition in the skin and intestine contribute to the pathogenesis of AD. Environmental factors that contribute to skin barrier dysfunction and microbial dysbiosis in AD include allergens, diet, irritants, air pollution, epigenetics and microbial exposure. Knowing the microbial combination of intestin, as well as the genetic and epigenetic determinants associated with the development of autoantibodies, may help elucidate the pathophysiology of the disease. The skin of patients with AD is characterized by microbial dysbiosis as a result of reduced microbial diversity and overgrowth of the pathogens such as Staphylococcus aureus. Recent studies have revealed the importance of building a strong immune response against microorganisms during childhood and new mechanisms of microbial community dynamics in modulating the skin microbiome. Numerous microorganisms are reported to modulate host response through communication with keratinocytes, specific immune cells and adipocytes to improve skin health and barrier function. This growing insight into bioactive substances in the skin microbiota has led to novel biotherapeutic approaches targeting the skin surface for the treatment of AD. This review will provide an updated overview of the skin microbiota in AD and its complex interaction with immune response mechanisms, as well as explore possible underlying mechanisms in the pathogenesis of AD and provide insights into new therapeutic developments for the treatment of AD. It also focuses on restoring skin microbial homeostasis, aiming to reduce inflammation by repairing the skin barrier.

Current Insights on Lipidomics in Dermatology: A Systematic Review

Inflammatory dermatoses and lipid disturbances are interrelated, especially due to chronic inflammatory conditions. The study aimed to investigate recent findings about lipidomic and dermatologic diseases, as well as on the sampling techniques developed to study lipidomics in vivo and analytical and statistical approaches employed. A systematic review was designed using the search algorithm "(lipidomics) AND (skin OR dermatology OR stratum corneum OR sebum OR epidermis) following PRISMA guidelines. The literature search identified 1013 references and, finally, only 48 were selected, including a total of 2651 participants with a mean age of 34.13±16.28. The dermatological diseases evaluated were atopic dermatitis (AD), acne, psoriasis, hidradenitis suppurativa (HS) and other skin diseases. Sebutape® was the primary sampling technique for lipidomics research. Most of the studies performed untargeted profiling through liquid chromatography with tandem mass spectrometry (LC-MS/MS) statistically analyzed with Principal Component Analysis (PCA), Orthogonal Partial Least-Squares Discriminate Analysis (OPLS-DA), heatmap and volcano plot models. The most consulted databases were LIPIDMAPS® Structure Database (LMSD), MetaboAnalyst and Human Metabolome Database (HMDB). A large heterogeneity of lipidomic and lipid metabolism profiles was observed in patients with skin diseases. Skin lipidomic analysis is valuable in exploring skin disease and has ample translational potential.

Ceramide 3 Effect on the Physical Properties of Ambora Extract and Chromabright-Loaded Transethosomes

Spontaneous self-assembly of phospholipids into lipid vesicles in aqueous media is called liposomes, and these structures are widely used as nanocarriers in the cosmeceutical industry. Transethosomes are ethanol and edge activator-containing liposomes that are proven to be very effective in topical applications for penetrating the skin barrier. Many cosmeceutical products contain formulations with ceramides to restore the skin barrier and treat eczema. However, due to the low solubility and penetration ability of the ceramides, the effectiveness of these products is limited. In this study, a transethosome formulation containing ceramide 3 (Cer 3) was achieved by introducing varying concentrations of cholesterol and an edge activator (Tween 80) to improve the effect of the skin products used to treat eczema. The obtained transethosomes were examined in terms of size, homogeneity, zeta potential, morphology, and one-month stability. Loading capability experiments were carried out with lipophilic Chromabright and hydrophilic Ambora extract. The effect of Cer 3 on the loading of the selected payloads was evaluated. Data were analyzed statistically with linear regression analysis and two-way analysis of variance. The results showed that the inclusion of Cer 3 had almost no effect on the physical properties of the loaded or empty transethosomes. Independently of the presence of Cer 3, loading of the lipophilic compound was more efficient than that of the hydrophilic one.

The impact of lipidome on five inflammatory skin diseases: a Mendelian randomization study

OBJECTIVE

Two-sample Mendelian randomization (TSMR) was employed to examine the association between lipidome and five inflammatory skin diseases.

METHOD

To evaluate the association between various molecular subtypes of lipidome and the risk of five inflammatory skin diseases, we analyzed a comprehensive GWAS dataset comprising 179 lipidome. The Two-Sample Mendelian Randomization (TSMR) method was employed to investigate causal relationships. Heterogeneity and pleiotropy were assessed using Cochran's Q test, MR-Egger intercept test, and MR-PRESSO global test. Additionally, a sensitivity analysis was conducted to evaluate the influence of individual single nucleotide polymorphisms on Mendelian Randomization study.

RESULTS

Using 179 serum lipidome as exposures and five common inflammatory skin diseases as outcomes, we investigated their associations in this large-scale study. Our findings reveal significant impacts of glycerophospholipids, glycerolipids, and sphingomyelins on inflammatory skin diseases. Glycerophospholipids were protective against pemphigus but predominantly posed risks for other inflammatory skin diseases. Specifically, phosphatidylcholine (16:0_0:0) exhibited the most significant risk association with lichen planus (OR = 1.25, 95% CI 1.11-1.40, P < 0.001). Conversely, glycerolipids showed no effect on lichen planus but were protective against pemphigus while potentially posing risks for other conditions. Triacylglycerol (46:2) showed the most substantial risk association with vitiligo (OR = 1.99, 95% CI 1.35-2.93, P < 0.001). Furthermore, sphingomyelins had no effect on atopic dermatitis but posed potential risks for other inflammatory skin diseases. Sphingomyelin (d40:1) notably emerged as a significant risk factor for pemphigus (OR = 1.91, 95% CI 1.37-2.66, P < 0.001).

CONCLUSIONS

This study has elucidated the potential harmful effects of glycerophospholipids, glycerolipids, and sphingomyelins on inflammatory skin diseases, while also providing valuable insights for future research into the pathophysiology, prevention and treatment of these conditions.

Changes in oral, skin, and gut microbiota in children with atopic dermatitis: a case-control study

Introduction

Atopic dermatitis (AD) is a common clinical recurrent atopic disease in dermatology, most seen in children and adolescents. In recent years, AD has been found to be closely associated with microbial communities.

Methods

To explore the synergistic effects between colonizing bacteria from different sites and AD, we comparatively analyzed the skin, oral, and gut microbiota of children with AD (50 individuals) and healthy children (50 individuals) by 16S rRNA gene sequencing. Twenty samples were also randomly selected from both groups for metabolic and macrogenomic sequencing.

Results

The results of our sequencing study showed reduced microbiota diversity in the oral, skin, and gut of children with AD (P < 0.05). Metabolomics analysis showed that serotonergic synapse, arachidonic acid metabolism, and steroid biosynthesis were downregulated at all three loci in the oral, skin, and gut of children with AD (P < 0.05). Macrogenomic sequencing analysis showed that KEGG functional pathways of the three site flora were involved in oxidative phosphorylation, ubiquitin-mediated proteolysis, mRNA surveillance pathway, ribosome biogenesis in eukaryotes, proteasome, basal transcription factors, peroxisome, MAPK signaling pathway, mitophagy, fatty acid elongation, and so on (P < 0.05).

Discussion

The combined microbial, metabolic, and macrogenetic analyses identified key bacteria, metabolites, and pathogenic pathways that may be associated with AD development. We provides a more comprehensive and in-depth understanding of the role of the microbiota at different sites in AD patients, pointing to new directions for future diagnosis, treatment and prognosis.

Blockade of interleukin-13 signalling improves skin barrier function and biology in patients with moderate-to-severe atopic dermatitis

BACKGROUND

Interleukin (IL)-13 is a key driver of inflammation and barrier dysfunction in atopic dermatitis (AD). While there is robust evidence that tralokinumab - a monoclonal antibody that neutralizes IL-13 - reduces inflammation and clinical disease activity, less is known about its effects on barrier function.

OBJECTIVES

To characterize the effects of tralokinumab treatment on skin barrier function.

METHODS

Transepidermal water loss (TEWL), stratum corneum hydration (SCH), natural moisturizing factor content, histopathological characteristics, biomarker expression and microbiome composition were evaluated in lesional, nonlesional and sodium lauryl sulfate-irritated skin of 16 patients with AD over the course of 16 weeks of tralokinumab treatment.

RESULTS

All clinical severity scores decreased significantly over time. At week 16, mean TEWL in target lesions decreased by 33% (P = 0.01) and SCH increased by 58% (P = 0.004), along with a histological reduction in spongiosis (P = 0.003), keratin 16 expression and epidermal thickness (P = 0.001). In parallel, there was a significant decrease in several barrier dysfunction-associated and proinflammatory proteins such as fibronectin (P = 0.006), CCL17/TARC (P = 0.03) and IL-8 (P = 0.01), with significant changes seen as early as week 8. Total bacterial load and Staphylococcus aureus abundance were significantly reduced from week 2.

CONCLUSIONS

Tralokinumab treatment improved skin physiology, epidermal pathology and dysbiosis, further highlighting the pleiotropic role of IL-13 in AD pathogenesis.

Bioactive lipids in the skin barrier mediate its functionality in health and disease

Our skin protects us from external threats including ultraviolet radiation, pathogens and chemicals, and prevents excessive trans-epidermal water loss. These varied activities are reliant on a vast array of lipids, many of which are unique to skin, and that support physical, microbiological and immunological barriers. The cutaneous physical barrier is dependent on a specific lipid matrix that surrounds terminally-differentiated keratinocytes in the stratum corneum. Sebum- and keratinocyte-derived lipids cover the skin's surface and support and regulate the skin microbiota. Meanwhile, lipids signal between resident and infiltrating cutaneous immune cells, driving inflammation and its resolution in response to pathogens and other threats. Lipids of particular importance include ceramides, which are crucial for stratum corneum lipid matrix formation and therefore physical barrier functionality, fatty acids, which contribute to the acidic pH of the skin surface and regulate the microbiota, as well as the stratum corneum lipid matrix, and bioactive metabolites of these fatty acids, involved in cell signalling, inflammation, and numerous other cutaneous processes. These diverse and complex lipids maintain homeostasis in healthy skin, and are implicated in many cutaneous diseases, as well as unrelated systemic conditions with skin manifestations, and processes such as ageing. Lipids also contribute to the gut-skin axis, signalling between the two barrier sites. Therefore, skin lipids provide a valuable resource for exploration of healthy cutaneous processes, local and systemic disease development and progression, and accessible biomarker discovery for systemic disease, as well as an opportunity to fully understand the relationship between the host and the skin microbiota. Investigation of skin lipids could provide diagnostic and prognostic biomarkers, and help identify new targets for interventions. Development and improvement of existing in vitro and in silico approaches to explore the cutaneous lipidome, as well as advances in skin lipidomics technologies, will facilitate ongoing progress in skin lipid research.

Multi-omics analysis to evaluate the effects of solar exposure and a broad-spectrum SPF50+ sunscreen on markers of skin barrier function in a skin ecosystem model

Sun exposure induces major skin alterations, but its effects on skin metabolites and lipids remain largely unknown. Using an original reconstructed human epidermis (RHE) model colonized with human microbiota and supplemented with human sebum, we previously showed that a single dose of simulated solar radiation (SSR) significantly impacted the skin metabolome and microbiota. In this article, we further analyzed SSR-induced changes on skin metabolites and lipids in the same RHE model. Among the significantly altered metabolites (log2-fold changes with p ≤ 0.05), we found several natural moisturizing factors (NMFs): amino acids, lactate, glycerol, urocanic acid, pyrrolidone carboxylic acid and derivatives. Analyses of the stratum corneum lipids also showed that SSR induced lower levels of free fatty acids and higher levels of ceramides, cholesterols and its derivatives. An imbalance in NMFs and ceramides combined to an increase of proinflammatory lipids may participate in skin permeability barrier impairment, dehydration and inflammatory reaction to the sun. Our skin model also allowed the evaluation of an innovative ultraviolet/blue light (UV/BL) broad-spectrum sunscreen with a high sun protection factor (SPF50+). We found that using this sunscreen prior to SSR exposure could in part prevent SSR-induced alterations in NMFs and lipids in the skin ecosystem RHE model.

Investigating Distinct Skin Microbial Communities and Skin Metabolome Profiles in Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disorder influenced by genetic predisposition, environmental factors, immune dysregulation, and skin barrier dysfunction. The skin microbiome and metabolome play crucial roles in modulating the skin's immune environment and integrity. However, their specific contributions to AD remain unclear. We aimed to investigate the distinct skin microbial communities and skin metabolic compounds in AD patients compared to healthy controls (HCs). Seven patients with AD patients and seven HCs were enrolled, from whom skin samples were obtained for examination. The study involved 16S rRNA metagenomic sequencing and bioinformatics analysis as well as the use of gas chromatography time-of-flight mass spectrometry (GC-TOF-MS) to detect metabolites associated with AD in the skin. We observed significant differences in microbial diversity between lesional and non-lesional skin of AD patients and HCs. Staphylococcus overgrowth was prominent in AD lesions, while Cutibacterium levels were decreased. Metabolomic analysis revealed elevated levels of several metabolites, including hypoxanthine and glycerol-3-phosphate in AD lesions, indicating perturbations in purine metabolism and energy production pathways. Moreover, we found a positive correlation between hypoxanthine and glycerol-3-phosphate and clinical severity of AD and Staphylococcus overgrowth. These findings suggest potential biomarkers for monitoring AD severity. Further research is needed to elucidate the causal relationships between microbial dysbiosis, metabolic alterations, and AD progression, paving the way for targeted therapeutic interventions.

Adding Fuel to the Fire? The Skin Microbiome in Atopic Dermatitis

Atopic dermatitis (AD) is a multifactorial, heterogeneous disease characterized by epidermal barrier dysfunction, immune system dysregulation, and skin microbiome alterations. Skin microbiome studies in AD have demonstrated that disease flares are associated with microbial shifts, particularly Staphylococcus aureus predominance. AD-associated S. aureus strains differ from those in healthy individuals across various genomic loci, including virulence factors, adhesion proteins, and proinflammatory molecules-which may contribute to complex microbiome barrier-immune system interactions in AD. Different microbially based treatments for AD have been explored, and their future therapeutic successes will depend on a deeper understanding of the potential microbial contributions to the disease.

Microbiome and lipidomic analysis reveal the interplay between skin bacteria and lipids in a cohort study

Human skin acts as a protective barrier between the body and the external environment. Skin microbiome and intercellular lipids in the stratum corneum (SC) are essential for maintaining skin barrier function. However, the interplay between skin bacteria and the lipids is not fully understood. In this study, we characterized the skin microbiome and SC lipid profiles from the forearm and face in a cohort of 57 healthy participants. 16S rRNA gene sequencing showed the skin microbial composition is significantly different between body locations and genders. Female forearm samples have the highest microbial diversity. The relative abundance of Staphylococcus hominis, Micrococcus luteus, Corynebacterium tuberculostearicum, Finegoldia magna, and Moraxellaceae sp. are significantly higher in the forearm than the face. The predictive functional analysis of 16S rRNA gene sequencing by Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt2) and ANCOM-BC showed different bacterial metabolic pathway profiles between body locations or genders, and identified 271 differential pathways, including arginine and polyamine biosynthesis, chorismate biosynthesis pathways, which are more abundant in the female forearm, and sulfur oxidation pathway, which is more abundant in the male face. The SC lipid profiles differ between the body locations as well. Total free fatty acids (FFA), cholesterol sulfate and sphingosine are more abundant in the face. Dihydro-/6-hydroxy/phyto-ceramides are more abundant in the forearm. The correlation analysis of 16S rRNA gene sequencing and lipids revealed novel interplay between the bacteria and skin lipids. Shannon entropy and S. hominis negatively correlated with FFA, cholesterol sulfate and sphingosine; while positively correlated with dihydro-/6-hydroxy/phyto-ceramides. The correlation of predictive pathway profiles and lipids identified pathways involved in amino acids metabolism, carbohydrates degradation, aromatic compounds metabolism and fatty acid degradation metabolism are positively correlated with dihydro-/6-hydroxy/phyto-ceramides and negatively correlated with FFA, cholesterol sulfate and sphingosine. This study provides insights on the potential correlation between skin microbiome and lipids.

Dupilumab-associated head and neck dermatitis shows a pronounced type 22 immune signature mediated by oligoclonally expanded T cells

Dupilumab, an IL4R-blocking antibody, has shown clinical efficacy for atopic dermatitis (AD) treatment. In addition to conjunctivitis/blepharitis, the de novo appearance of head/neck dermatitis is now recognized as a distinct side effect, occurring in up to 10% of patients. Histopathological features distinct from AD suggest a drug effect, but exact underlying mechanisms remain unknown. We profiled punch biopsies from dupilumab-associated head and neck dermatitis (DAHND) by using single-cell RNA sequencing and compared data with untreated AD and healthy control skin. We show that dupilumab treatment was accompanied by normalization of IL-4/IL-13 downstream activity markers such as CCL13, CCL17, CCL18 and CCL26. By contrast, we found strong increases in type 22-associated markers (IL22, AHR) especially in oligoclonally expanded T cells, accompanied by enhanced keratinocyte activation and IL-22 receptor upregulation. Taken together, we demonstrate that dupilumab effectively dampens conventional type 2 inflammation in DAHND lesions, with concomitant hyperactivation of IL22-associated responses.

Multi-omics analyses reveal interactions between the skin microbiota and skin metabolites in atopic dermatitis

Introduction

Atopic dermatitis (AD) is one of the most common inflammatory skin diseases. Skin microecological imbalance is an important factor in the pathogenesis of AD, but the underlying mechanism of its interaction with humans remains unclear.

Methods

16S rRNA gene sequencing was conducted to reveal the skin microbiota dynamics. Changes in skin metabolites were tracked by LC-MS metabolomics. We then explored the potential mechanism of interaction by analyzing the correlation between skin bacterial communities and metabolites in corresponding skin-associated samples.

Results

Samples from 18 AD patients and 18 healthy volunteers (HVs) were subjected to 16S rRNA gene sequencing and LC-MS metabolomics. AD patients had dysbiosis of the skin bacterial community with decreased species richness and evenness. The relative abundance of the genus Staphylococcus increased significantly in AD, while the abundances of the genera Propionibacterium and Brevundimonas decreased significantly. The relative abundance of the genera Staphylococcus in healthy females was significantly higher than those in healthy males, while it showed no difference in AD patients with or without lesions. The effects of AD status, sex and the presence or absence of rashes on the number of differentially abundant metabolites per capita were successively reduced. Multiple metabolites involved in purine metabolism and phenylalanine metabolism pathways (such as xanthosine/xanthine and L-phenylalanine/trans-cinnamate) were increased in AD patients. These trends were much more obvious between female AD patients and female HVs. Spearman correlation analysis revealed that the genus Staphylococcus was positively correlated with various compounds involved in phenylalanine metabolism and purine metabolic pathways. The genera Brevundimonas and Lactobacillus were negatively correlated with various compounds involved in purine metabolism, phenylalanine metabolism and sphingolipid signaling pathways.

Discussion

We suggest that purine metabolism and phenylalanine metabolism pathway disorders may play a certain role in the pathogenic mechanism of Staphylococcus aureus in AD. We also found that females are more likely to be colonized by the genus Staphylococcus than males. Differentially abundant metabolites involved in purine metabolism and phenylalanine metabolism pathways were more obvious in female. However, we should notice that the metabolites we detected do not necessarily derived from microbes, they may also origin from the host.

Umbilical therapy for promoting transdermal delivery of topical formulations: Enhanced effect and underlying mechanism

Umbilical paste therapy is a promising method to promote transdermal drug delivery of topical formulations. This work investigated the effect and mechanism of transdermal drug delivery through the umbilical skin. The transdermal permeation studies showed the phenomenon of higher cumulative penetration and faster penetration rates for drug through the umbilical skin compared with non-umbilical skin, namely umbilical pro-permeability. This special transdermal permeability of drugs is influenced by their molecular weight, logP value, ability to form hydrogen bonds, and molecular volume. The underlying mechanism of umbilical pro-permeability was elucidated from unique structure and regulation the effect of drugs on microcirculation in the umbilical skin. Mechanistic studies revealed that this phenomenon was not only associated with the structural and physiological properties of the skin but also to the interactions between drugs and different skin layers. The umbilical pro-permeation is attributed to the thinner stratum corneum layer, differences in stratum corneum lipid composition and keratin structure, and lower levels of intercellular tight junction proteins in the viable epidermis and dermis layer of the skin. Our research indicated that umbilical paste therapy enhanced the transdermal delivery and absorption of drugs by stimulating local blood flow through mast cell activation. Surprisingly, skin temperature modulation and calcitonin gene-related peptide and substance P levels did not appear to significantly affect this process. In conclusion, umbilical drug administration, as a straightforward and non-invasive approach to enhance transdermal drug delivery, presents novel concepts for continued investigation and practical implementation of transdermal drug delivery systems.

Biosignatures of defective sebaceous gland activity in sebum-rich and sebum-poor skin areas in adult atopic dermatitis

Atopic dermatitis (AD) is a composite disease presenting disruption of the skin permeability barrier (SPB) in the stratum corneum (SC). Recent evidence supports derangement of the sebaceous gland (SG) activity in the AD pathomechanisms. The objective of this study was to delineate profiles of both sebaceous and epidermal lipids and of aminoacids from SG-rich (SGR) and SG-poor (SGP) areas in AD. Both sebum and SC were sampled from SGR areas, while SC was sampled also from SGP areas in 54 adult patients with AD, consisting of 34 and 20 subjects, respectively with and without clinical involvement of face, and in 44 age and sex-matched controls. Skin biophysics were assessed in all sampling sites. Disruption of the SBP was found to be associated with dysregulated lipidome. Abundance of sapienate and lignocerate, representing, respectively, sebum and the SC type lipids, were decreased in sebum and SC from both SGR and SGP areas. Analogously, squalene was significantly diminished in AD, regardless the site. Extent of lipid derangement in SGR areas was correlated with the AD severity. The abundance of aminoacids in the SC from SGR areas was altered more than that determined in SGP areas. Several gender-related differences were found in both controls and AD subgroups. In conclusion, the SG activity was differently compromised in adult females and males with AD, in both SGR and SGP areas. In AD, alterations in the aminoacidome profiles were apparent in the SGR areas. Lipid signatures in association with aminoacidome and skin physical properties may serve the definition of phenotype clusters that associate with AD severity and gender.

The heterogeneity and complexity of skin surface lipids in human skin health and disease

The outermost epidermal layer of the skin, the stratum corneum, is not simply a barrier that safeguards skin integrity from external insults and invaders, it is also a delicately integrated interface composed of firm, essentially dead corneocytes and a distinctive lipid matrix. Together, the stratum corneum lipid matrix and sebum lipids derived from sebaceous glands give rise to a remarkably complex but quite unique blend of skin surface lipids that demonstrates tremendous heterogeneity and provides the skin with its indispensable protective coating. The stratum corneum lipid matrix is composed primarily of three major lipid classes: ceramides, non-esterified fatty acids and cholesterol, whereas sebum is a waxy mixture predominantly composed of acylglycerols, wax esters, non-esterified fatty acids, squalene, cholesterol and cholesterol esters. The balance of these skin surface lipids in terms of their relative abundance, composition, molecular organisation and dynamics, and their intricate interactions play a crucial role in the maintenance of healthy skin. For that reason, even minuscule alterations in skin surface lipid properties or overall lipid profile have been implicated in the aetiology of many common skin diseases including atopic dermatitis, psoriasis, xerosis, ichthyosis and acne. Novel lipid-based interventions aimed at correcting the skin surface lipid abnormalities have the potential to repair skin barrier integrity and the symptoms associated with such skin diseases, even though the exact mechanisms of lipid restoration remain elusive.

The Design and Optimization of Ceramide NP-Loaded Liposomes to Restore the Skin Barrier

The impairment of skin integrity derived from derangement of the orthorhombic lateral organization is mainly caused by dysregulation of ceramide amounts in the skin barrier. Ceramides, fatty acids, and cholesterol-containing nano-based formulations have been used to impair the skin barrier. However, there is still a challenge to formulate novel formulations consisting of ceramides due to their chemical structure, poor aqueous solubility, and high molecular weight. In this study, the design and optimization of Ceramide 3 (CER-NP)-loaded liposomes are implemented based on response surface methodology (RSM). The optimum CER-NP-loaded liposome was selected based on its particle size (PS) and polydispersity index (PDI). The optimum CER-NP-loaded liposome was imagined by observing the encapsulation by using a confocal laser scanning microscope (CLSM) within fluorescently labeled CER-NP. The characteristic liquid crystalline phase and lipid chain conformation of CER-NP-loaded liposomes were determined using attenuated total reflectance infrared spectroscopy (ATR-IR). The CER-NP-loaded liposomes were imagined using a field emission scanning electron microscope (FE-SEM). Finally, the in vitro release of CER-NP from liposomes was examined using modified Franz Cells. The experimental and predicted results were well correlated. The CLSM images of optimized liposomes were conformable with the other studies, and the encapsulation efficiency of CER-NP was 93.84 ± 0.87%. ATR-IR analysis supported the characteristics of the CER-NP-loaded liposome. In addition, the lipid chain conformation shows similarity with skin barrier lipid organization. The release pattern of CER-NP liposomes was fitted with the Korsmeyer-Peppas model. The cytotoxicity studies carried out on HaCaT keratinocytes supported the idea that the liposomes for topical administration of CER-NP could be considered relatively safe. In conclusion, the optimized CER-NP-loaded liposomes could have the potential to restore the skin barrier function.

Are the Cutaneous Microbiota a Guardian of the Skin's Physical Barrier? The Intricate Relationship between Skin Microbes and Barrier Integrity

The skin is a tightly regulated, balanced interface that maintains our integrity through a complex barrier comprising physical or mechanical, chemical, microbiological, and immunological components. The skin's microbiota affect various properties, one of which is the establishment and maintenance of the physical barrier. This is achieved by influencing multiple processes, including keratinocyte differentiation, stratum corneum formation, and regulation of intercellular contacts. In this review, we summarize the potential contribution of Cutibacterium acnes to these events and outline the contribution of bacterially induced barrier defects to the pathogenesis of acne vulgaris. With the combined effects of a Westernized lifestyle, microbial dysbiosis, epithelial barrier defects, and inflammation, the development of acne is very similar to that of several other multifactorial diseases of barrier organs (e.g., inflammatory bowel disease, celiac disease, asthma, atopic dermatitis, and chronic rhinosinusitis). Therefore, the management of acne requires a complex approach, which should be taken into account when designing novel treatments that address not only the inflammatory and microbial components but also the maintenance and strengthening of the cutaneous physical barrier.

The skin barrier: An extraordinary interface with an exceptional lipid organization

The barrier function of the skin is primarily located in the stratum corneum (SC), the outermost layer of the skin. The SC is composed of dead cells with highly organized lipid lamellae in the intercellular space. As the lipid matrix forms the only continuous pathway, the lipids play an important role in the permeation of compounds through the SC. The main lipid classes are ceramides (CERs), cholesterol (CHOL) and free fatty acids (FFAs). Analysis of the SC lipid matrix is of crucial importance in understanding the skin barrier function, not only in healthy skin, but also in inflammatory skin diseases with an impaired skin barrier. In this review we provide i) a historical overview of the steps undertaken to obtain information on the lipid composition and organization in SC of healthy skin and inflammatory skin diseases, ii) information on the role CERs, CHOL and FFAs play in the lipid phase behavior of very complex lipid model systems and how this knowledge can be used to understand the deviation in lipid phase behavior in inflammatory skin diseases, iii) knowledge on the role of both, CER subclasses and chain length distribution, on lipid organization and lipid membrane permeability in complex and simple model systems with synthetic CERs, CHOL and FFAs, iv) similarity in lipid phase behavior in SC of different species and complex model systems, and vi) future directions in modulating lipid composition that is expected to improve the skin barrier in inflammatory skin diseases.

Trajectory of stratum corneum lipid subclasses in the first year of life and associations with atopic dermatitis: A prospective cohort study

BACKGROUND

Trajectories of stratum corneum (SC) lipid subclasses and their associations with infant atopic dermatitis (AD) are unclear. This study aimed to quantify the trajectories of 15 SC subclasses and carbon chain lengths and their associations with AD within 12 months.

METHODS

In total, 213 newborns were enrolled at birth with nonlesional skin samples collected from the inner forearm at birth, 42 days, 3, 6, and 12 months, respectively. Lesional skin samples were collected from 120 AD patients at clinic with the disease onset within the first year of life. Mass spectrometry was applied to assess relative contents of 12 ceramide (CER), three free fatty acid (FFA) subclasses, and average carbon chain length (CCL). AD incident within 1 year old was diagnosed by dermatologists according to UK criteria.

RESULTS

Sixty-four (30.0%) cases of ADs occurred in the cohort. All SC lipid subclasses and CCLs, but EOP varied significantly during the first year. AD infants showed lower NP but higher NS, NH, AP, hydroxy FFA, and CCL of FFAs compared with nonaffected infants. After normalization by age, the differences remained and were more pronounced in lesional skin of clinical AD infants compared with non-ADs. NS, NH, and CCL of FFAs in lesional skin of AD infants showed positive and significant correlations with the levels of transepidermal water loss at 3 month; some evidence supports a negative correlation for NP.

CONCLUSIONS

We provide an overview of developmental trajectories of 15 CER and FFA subclasses across the first year of healthy infants and a link between the imbalance of some subclasses with the development of AD.

Novel methodologies for host-microbe interactions and microbiome-targeted therapeutics in 3D organotypic skin models

BACKGROUND

Following descriptive studies on skin microbiota in health and disease, mechanistic studies on the interplay between skin and microbes are on the rise, for which experimental models are in great demand. Here, we present a novel methodology for microbial colonization of organotypic skin and analysis thereof.

RESULTS

An inoculation device ensured a standardized application area on the stratum corneum and a homogenous distribution of bacteria, while preventing infection of the basolateral culture medium even during prolonged culture periods for up to 2 weeks at a specific culture temperature and humidity. Hereby, host-microbe interactions and antibiotic interventions could be studied, revealing diverse host responses to various skin-related bacteria and pathogens.

CONCLUSIONS

Our methodology is easily transferable to a wide variety of organotypic skin or mucosal models and different microbes at every cell culture facility at low costs. We envision that this study will kick-start skin microbiome studies using human organotypic skin cultures, providing a powerful alternative to experimental animal models in pre-clinical research. Video Abstract.

Looking into the Skin in Health and Disease: From Microscopy Imaging Techniques to Molecular Analysis

The skin is a complex organ that includes a wide variety of tissue types with different embryological origins [...].

Targeting Skin Barrier Function in Atopic Dermatitis

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease in the general population. Skin barrier dysfunction is the central abnormality leading to AD. The cause of skin barrier dysfunction is complex and rooted in genetic mutations, interactions between the immune pathway activation and epithelial cells, altered host defense mechanisms, as well as environmental influences that cause epithelial cell activation and release of alarmins (such as thymic stromal lymphopoietin) that can activate the type 2 immune pathway, including generation of interleukins 4 and 13, which induces defects in the skin barrier and increased allergic inflammation. These inflammatory pathways are further influenced by environmental factors including the microbiome (especially Staphylococcus aureus), air pollution, stress, and other factors. As such, AD is a syndrome involving multiple phenotypes, all of which have in common skin barrier dysfunction as a key contributing factor. Understanding mechanisms leading to skin barrier dysfunction in AD is pointing to the development of new topical and systemic treatments in AD that helps keep skin borders secure and effectively treat the disease.

Lipid Alterations and Metabolism Disturbances in Selected Inflammatory Skin Diseases

Lipidomics is a term used to define the field that analyzes the structure, functions, and interactions of lipids. Inflammatory dermatoses and lipid disturbances are interrelated, especially due to chronic inflammatory conditions. This review discusses lipidomics in selected inflammatory skin diseases: psoriasis, lichen planus, and atopic dermatitis, as well as the less commonly mentioned hidradenitis suppurativa, rosacea, and acne vulgaris. Lipid homeostasis disorders are common; they are especially well-documented in psoriasis, lichen planus, and atopic dermatitis. Future studies are required for better insight into this issue, particularly on the skin lipidome. Understanding lipidomics, in particular skin diseases, increases our knowledge about their pathogenesis, and may become useful in adjusting tailored management for each patient as well establishing prognosis. Noteworthily, it seems advisable to alert doctors to the need to analyze lipid parameters and the complications of abnormal lipid metabolism in dermatological patients, which could decrease their comorbidities and improve the life quality and health condition of dermatological patients.

Integrated transcriptomic and metabolomic analyses of DNCB-induced atopic dermatitis in mice

AIMS

Atopic dermatitis (AD) is a common chronic inflammatory skin disorder that affects up to 20 % of children and 10 % of adults worldwide; however, the exact molecular mechanisms remain largely unknown.

MATERIALS AND METHODS

In this study, we used integrated transcriptomic and metabolomic analyses to study the potential mechanisms of 1-chloro-2,4-dinitrobenzene (DNCB)-induced AD-like skin lesions.

KEY FINDINGS

We found that DNCB induced AD-like skin lesions, including phenotypical and histomorphological alterations and transcriptional and metabolic alterations in mice. A total of 3413 differentially expressed metabolites were detected between DNCB-induced AD-like mice and healthy controls, which includes metabolites in taurine and hypotaurine metabolism, phenylalanine metabolism, biosynthesis of unsaturated fatty acids, tryptophan metabolism, arachidonic acid metabolism, pantothenate and CoA biosynthesis, pyrimidine metabolism, and glycerophospholipid metabolism pathways. Furthermore, the differentially expressed genes associated (DEGs) with these metabolic pathways were analyzed using RNA sequencing (RNA-seq), and we found that the expression of pyrimidine metabolism-associated genes was significantly increased. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the glycolysis/gluconeogenesis, glucagon signaling pathway and pentose phosphate pathway-associated metabolic genes were dramatically altered.

SIGNIFICANCE

Our results explain the possible mechanism of AD at the gene and metabolite levels and provide potential targets for the development of clinical drugs for AD.

Alterations of Epidermal Lipid Profiles and Skin Microbiome in Children With Atopic Dermatitis

PURPOSE

We aimed to investigate epidermal lipid profiles and their association with skin microbiome compositions in children with atopic dermatitis (AD).

METHODS

Specimens were obtained by skin tape stripping from 27 children with AD and 18 healthy subjects matched for age and sex. Proteins and lipids of stratum corneum samples from nonlesional and lesional skin of AD patients and normal subjects were quantified by liquid chromatography tandem mass spectrometry. Skin microbiome profiles were analyzed using bacterial 16S rRNA sequencing.

RESULTS

Ceramides with nonhydroxy fatty acids (FAs) and C18 sphingosine as their sphingoid base (C18-NS-CERs) N-acylated with C16, C18 and C22 FAs, sphingomyelin (SM) N-acylated with C18 FAs, and lysophosphatidylcholine (LPC) with C16 FAs were increased in AD lesional skin compared to those in AD nonlesional skin and that of control subjects (all P < 0.01). SMs N-acylated with C16 FAs were increased in AD lesional skin compared to control subjects (P < 0.05). The ratio of NS-CERs with long-chain fatty acids (LCFAs) to short-chain fatty acids (SCFAs) (C24-32:C14-22), the ratio of LPC with LCFAs to SCFAs (C24-30:C16-22) as well as the ratio of total esterified omega-hydroxy ceramides to total NS-CERs were negatively correlated with transepidermal water loss (rho coefficients = -0.738, -0.528, and -0.489, respectively; all P < 0.001). The proportions of Firmicutes and Staphylococcus were positively correlated to SCFAs including NS ceramides (C14-22), SMs (C17-18), and LPCs (C16), while the proportions of Actinobacteria, Proteobacteria, Bacteroidetes, Corynebacterium, Enhydrobacteria, and Micrococcus were negatively correlated to these SCFAs.

CONCLUSIONS

Our results suggest that pediatric AD skin shows aberrant lipid profiles, and these alterations are associated with skin microbial dysbiosis and cutaneous barrier dysfunction.

Current insights into skin lipids and their roles in cutaneous health and disease

PURPOSE OF REVIEW

The unique and complex array of cutaneous lipids include essential components of the skin structure and signalling molecules mediating homeostasis and inflammation. Understanding skin lipid biology and metabolism can support our comprehension of health and disease, including systemic conditions with cutaneous involvement.

RECENT FINDINGS

Lipids found on the skin surface, produced by both the host and resident microbes, maintain and regulate the skin microbiome and the epidermal barrier, whilst altered contributions from either source can be detrimental to skin health. The unique lipid composition of the epidermal barrier is essential for its function, and recent studies have expanded our understanding of epidermal ceramide production. This has been supported by improved models available for skin research, including organotypic skin models enabling in-vitro production of complex acylceramides for the first time, and model systems facilitating in-silico exploration of the lipid profile changes observed in clinical samples. Studies have revealed further involvement of lipid mediators such as eicosanoids in cutaneous inflammation, as well as immune regulation in both healthy and diseased skin.

SUMMARY

Skin lipids offer exciting opportunities as therapeutic targets for many conditions, whether through topical interventions or nutritional supplementation.

Progress of metabolomics in atopic dermatitis: a systematic review

Atopic dermatitis (AD), a chronic inflammatory skin disorder characterized by recurrent eczema and intense pruritus, is a major skin-related burden worldwide. The diagnosis and treatment of AD is often challenging due to the high heterogeneity of AD, and its exact etiology is unknown. Metabolomics offers the opportunity to follow continuous physiological and pathological changes in individuals, which allows accurate diagnosis and management as well as providing deep insights into the etiopathogenesis of AD. Several metabolomic studies of AD have been published over the past few years. The aim of this review is to summarize these findings and help researchers to understand the rapid development of metabolomics for AD. A comprehensive and systematic search was performed using the PubMed, Embase, Cochrane Library and Web of Science databases. Twenty-six papers were finally included in the review after quality assessment. Significant differences in metabolite profiles were found between patients with AD and healthy individuals. This study provides a comprehensive overview of metabolomic research in AD. A better understanding of the metabolomics of AD may offer novel diagnostic, prognostic, and therapeutic approaches.

Desaturation of sebaceous-type saturated fatty acids through the SCD1 and the FADS2 pathways impacts lipid neosynthesis and inflammatory response in sebocytes in culture

Sebum is a lipid-rich mixture secreted by the sebaceous gland (SG) onto the skin surface. By penetrating through the epidermis, sebum may be involved in the regulation of epidermal and dermal cells in both healthy and diseased skin conditions. Saturated and monounsaturated fatty acids (FAs), found as free FAs (FFAs) and in bound form in neutral lipids, are essential constituents of sebum and key players of the inflammatory processes occurring in the pilosebaceous unit in acne-prone skin. Little is known on the interplay among uptake of saturated FFAs, their biotransformation, and induction of proinflammatory cytokines in sebocytes. In the human SG, palmitate (C16:0) is the precursor of sapienate (C16:1n-10) formed by insertion of a double bond (DB) at the Δ6 position catalysed by the fatty acid desaturase 2 (FADS2) enzyme. Conversely, palmitoleate (C16:1n-7) is formed by insertion of a DB at the Δ9 position catalysed by the stearoyl coenzyme A desaturase 1 (SCD1) enzyme. Other FFAs processed in the SG, also undergo these main desaturation pathways. We investigated lipogenesis and release of IL-6 and IL-8 pro-inflammatory cytokines in SZ95 sebocytes in vitro after treatment with saturated FFAs, that is, C16:0, margarate (C17:0), and stearate (C18:0) with or without specific inhibitors of SCD1 and FADS2 desaturase enzymes, and a drug with mixed inhibitory effects on FADS1 and FADS2 activities. C16:0 underwent extended desaturation through both SCD1 and FADS2 catalysed pathways and displayed the strongest lipoinflammatory effects. Inhibition of desaturation pathways proved to enhance lipoinflammation induced by SFAs in SZ95 sebocytes. Palmitate (C16:0), margarate (C17:0), and stearate (C18:0) are saturated fatty acids that induce different arrays of neutral lipids (triglycerides) and dissimilar grades of inflammation in sebocytes.

Lycopene, but not zeaxanthin, serves as a skeleton for the formation of an orthorhombic organization of intercellular lipids within the lamellae in the stratum corneum: Molecular dynamics simulations of the hydrated ceramide NS bilayer model

Carotenoids play an important role in the protection of biomembranes against oxidative damage. Their function depends on the surroundings and the organization of the lipid membrane they are embedded in. Carotenoids are located parallel or perpendicular to the surface of the lipid bilayer. The influence of carotenoids on the organization of the lipid bilayer in the stratum corneum has not been thoroughly considered. Here, the orientation of the exemplary cutaneous carotenoids lycopene and zeaxanthin in a hydrated ceramide NS24 bilayer model and the influence of carotenoids on the lateral organization of the lipid bilayer model were studied by means of molecular dynamics simulations for 32 °C and 37 °C. The results confirm that lycopene is located parallel and zeaxanthin perpendicular to the surface of the lipid bilayer. The lycopene-loaded lipid bilayer appeared to have a strong orthorhombic organization, while zeaxanthin-loaded and pure lipid bilayers were organized in a disordered hexagonal-like and liquid-like state, respectively. The effect is stronger at 32 °C compared to 37 °C based on p-values. Therefore, it was assumed that carotenoids without hydroxyl polar groups in their structure facilitate the formation of the orthorhombic organization of lipids, which provides the skin barrier function. It was shown that the distance between carotenoid atoms matched the distance between atoms in the lipids, indicating that parallel located carotenoids without hydroxyl groups serve as a skeleton for lipid membranes inside the lamellae. The obtained results provide reasonable prediction of the overall qualitative properties of lipid model systems and show the importance of parallel-oriented carotenoids in the development and maintenance of the skin barrier function.

Menopause induces changes to the stratum corneum ceramide profile, which are prevented by hormone replacement therapy

The menopause can lead to epidermal changes that are alleviated by hormone replacement therapy (HRT). We hypothesise that these changes could relate to altered ceramide production, and that oestrogen may have a role in keratinocyte ceramide metabolism. White Caucasian women were recruited into three groups: pre-menopausal (n = 7), post-menopausal (n = 11) and post-menopausal taking HRT (n = 10). Blood samples were assessed for hormone levels, transepidermal water loss was measured to assess skin barrier function, and stratum corneum lipids were sampled from photoprotected buttock skin. Ceramides and sphingomyelins were analysed by ultraperformance liquid chromatography with electrospray ionisation and tandem mass spectrometry. Post-menopausal stratum corneum contained lower levels of ceramides, with shorter average length; changes that were not evident in the HRT group. Serum oestradiol correlated with ceramide abundance and length. Ceramides had shorter sphingoid bases, indicating altered de novo ceramide biosynthesis. Additionally, post-menopausal women had higher sphingomyelin levels, suggesting a possible effect on the hydrolysis pathway. Treatment of primary human keratinocytes with oestradiol (10 nM) increased production of CER[NS] and CER[NDS] ceramides, confirming an effect of oestrogen on cutaneous ceramide metabolism. Taken together, these data show perturbed stratum corneum lipids post-menopause, and a role for oestrogen in ceramide production.

Congenital Ichthyosis: Clinical and Genetic Characteristics of the Disease

Congenital ichthyosis is a group (almost 100 clinical variants) of rare genetic skin diseases caused by pathogenic changes in more than 50 genes. Clinical features of ichthyosis, regardless of its genotype, are dry skin, peeling, hyperkeratosis frequently accompanied with erythroderma. These patients have extremely low quality of life due to changes in appearance, discomfort due to itching and functional limitations (pain during walking, impaired hands motor skills and functions due to hyperkeratosis foci in functionally relevant areas), as well as impaired functions of various organs and systems in syndromic forms of disease. Patients need daily skin care and systemic medications. By now, there is no definitive treatment for ichthyosis. Diagnostic difficulties in determining the clinical forms of congenital ichthyosis are associated with their clinical heterogeneity and with similarity in external manifestations. Difficulties in differential diagnosis with other dermatoses are particularly crucial in case of syndromic forms of disease. This review presents the modern classification of ichthyoses, provides data on disease clinical and genetic variants, diagnostic algorithms, treatment methods for patients with this severe disease.

Omics technologies in allergy and asthma research: An EAACI position paper

Allergic diseases and asthma are heterogenous chronic inflammatory conditions with several distinct complex endotypes. Both environmental and genetic factors can influence the development and progression of allergy. Complex pathogenetic pathways observed in allergic disorders present a challenge in patient management and successful targeted treatment strategies. The increasing availability of high-throughput omics technologies, such as genomics, epigenomics, transcriptomics, proteomics, and metabolomics allows studying biochemical systems and pathophysiological processes underlying allergic responses. Additionally, omics techniques present clinical applicability by functional identification and validation of biomarkers. Therefore, finding molecules or patterns characteristic for distinct immune-inflammatory endotypes, can subsequently influence its development, progression, and treatment. There is a great potential to further increase the effectiveness of single omics approaches by integrating them with other omics, and nonomics data. Systems biology aims to simultaneously and longitudinally understand multiple layers of a complex and multifactorial disease, such as allergy, or asthma by integrating several, separated data sets and generating a complete molecular profile of the condition. With the use of sophisticated biostatistics and machine learning techniques, these approaches provide in-depth insight into individual biological systems and will allow efficient and customized healthcare approaches, called precision medicine. In this EAACI Position Paper, the Task Force "Omics technologies in allergic research" broadly reviewed current advances and applicability of omics techniques in allergic diseases and asthma research, with a focus on methodology and data analysis, aiming to provide researchers (basic and clinical) with a desk reference in the field. The potential of omics strategies in understanding disease pathophysiology and key tools to reach unmet needs in allergy precision medicine, such as successful patients' stratification, accurate disease prognosis, and prediction of treatment efficacy and successful prevention measures are highlighted.

An Overview of the Latest Metabolomics Studies on Atopic Eczema with New Directions for Study

Atopic eczema (AE) is an inflammatory skin disorder affecting approximately 20% of children worldwide and early onset can lead to asthma and allergies. Currently, the mechanisms of the disease are not fully understood. Metabolomics, the analysis of small molecules in the skin produced by the host and microbes, opens a window to observe the mechanisms of the disease which then may lead to new drug targets for AE treatment. Here, we review the latest advances in AE metabolomics, highlighting both the lipid and non-lipid molecules, along with reviewing the metabolites currently known to reside in the skin.

Current Knowledge in Skin Metabolomics: Updates from Literature Review

Metabolomic profiling is an emerging field consisting of the measurement of metabolites in a biological system. Since metabolites can vary in relation to different stimuli, specific metabolic patterns can be closely related to a pathological process. In the dermatological setting, skin metabolomics can provide useful biomarkers for the diagnosis, prognosis, and therapy of cutaneous disorders. The main goal of the present review is to present a comprehensive overview of the published studies in skin metabolomics. A search for journal articles focused on skin metabolomics was conducted on the MEDLINE, EMBASE, Cochrane, and Scopus electronic databases. Only research articles with electronically available English full text were taken into consideration. Studies specifically focused on cutaneous microbiomes were also excluded from the present search. A total of 97 papers matched all the research criteria and were therefore considered for the present work. Most of the publications were focused on inflammatory dermatoses and immune-mediated cutaneous disorders. Skin oncology also turned out to be a relevant field in metabolomic research. Only a few papers were focused on infectious diseases and rarer genetic disorders. All the major metabolomic alterations published so far in the dermatological setting are described extensively in this review.

Biogeographic and disease-specific alterations in epidermal lipid composition and single cell analysis of acral keratinocytes

The epidermis is the outermost layer of skin. Here, we used targeted lipid profiling to characterize the biogeographic alterations of human epidermal lipids across 12 anatomically distinct body sites, and we used single-cell RNA-Seq to compare keratinocyte gene expression at acral and nonacral sites. We demonstrate that acral skin has low expression of EOS acyl-ceramides and the genes involved in their synthesis, as well as low expression of genes involved in filaggrin and keratin citrullination (PADI1 and PADI3) and corneodesmosome degradation, changes that are consistent with increased corneocyte retention. Several overarching principles governing epidermal lipid expression were also noted. For example, there was a strong negative correlation between the expression of 18-carbon and 22-carbon sphingoid base ceramides. Disease-specific alterations in epidermal lipid gene expression and their corresponding alterations to the epidermal lipidome were characterized. Lipid biomarkers with diagnostic utility for inflammatory and precancerous conditions were identified, and a 2-analyte diagnostic model of psoriasis was constructed using a step-forward algorithm. Finally, gene coexpression analysis revealed a strong connection between lipid and immune gene expression. This work highlights (a) mechanisms by which the epidermis is uniquely adapted for the specific environmental insults encountered at different body surfaces and (b) how inflammation-associated alterations in gene expression affect the epidermal lipidome.

Children with atopic dermatitis show increased activity of β- glucocerebrosidase and stratum corneum levels of glucosylcholesterol that are strongly related to local cytokine milieu

Background

Atopic dermatitis (AD) is characterized by immune dysregulations and an impaired skin barrier, including abnormalities in lipid organization. In the stratum corneum (SC), β‐glucocerebrosidase (GBA) mediates transformation of glucosylceramide (GlcCER) into ceramide (CER) and cholesterol into glucosylcholesterol (GlcChol). Alteration in GBA activity might contribute to skin barrier defects in AD.

Objectives

To investigate GBA activity in the SC of children with AD before and after topical corticosteroid therapy and to compare it with healthy controls; to determine SC levels of GlcCER‐ and CER‐containing hydroxysphingosine base (GlcCER[H] and CER[H], respectively) and GlcChol; and to relate them to disease severity, skin barrier function and the local cytokine milieu.

Methods

Lipid markers and cytokines of innate, T helper 1 and T helper 2 immunity were determined in SC collected from healthy children and from clinically unaffected skin of children with AD, before and after 6 weeks of therapy with topical corticosteroids. AD severity was assessed by Scoring Atopic Dermatitis and skin barrier function by transepidermal water loss (TEWL).

Results

Baseline GBA activity and GlcChol levels were increased in children with AD but declined after therapy. CER[H] levels and the CER[H] to GlcCER[H] ratio were increased in AD. GBA activity and GlcChol correlated with TEWL and levels of multiple cytokines, especially interleukin‐1α and interleukin‐18. GlcChol was strongly associated with disease severity.

Conclusions

We show increased GBA activity and levels of GlcChol in AD. Our data suggest an important role of inflammation in disturbed lipid processing. GBA activity or GlcChol might be useful biomarkers in the monitoring of therapeutic responses in AD.

What is already known about this topic?

Patients with atopic dermatitis (AD) have a reduced skin barrier, mainly caused by altered lipid organization.

The mechanisms underlying these lipid anomalies are not fully understood but likely reflect both genetic abnormalities in AD skin and the local cutaneous inflammatory environment.

What does this study add?

We show increased activity of the ceramide‐generating enzyme β‐glucocerebrosidase in AD. Activity of this enzyme was correlated with the local cytokine milieu and declined after local corticosteroid therapy.

We show that glucosylcholesterol levels in the stratum corneum are increased in AD.

The function of glucosylcholesterol and the physiological consequences of increased levels are not clear yet; however, its levels were strongly correlated with skin barrier function: high transepidermal water loss strongly correlated with high levels of glucosylcholesterol.

What is the translational message?

Correction of cutaneous inflammation largely restores alterations in lipid metabolism in the stratum corneum of infants with AD.

Association between barrier impairment and skin microbiota in atopic dermatitis from a global perspective: Unmet needs and open questions

Atopic diathesis encompassing atopic dermatitis (AD), allergic rhinoconjunctivitis, food allergy, eosinophilic esophagitis, and asthma is a widely prevalent condition with a broad heterogeneity in clinical course, age of onset, and lifespan persistence. A primary event in AD is the commonly inherited epidermal barrier dysfunction. Together with the host-microbiome interactions, barrier defect and allergen exposure modulate both innate and adaptive immunity, thus triggering and maintaining the inflammatory response. Microbiome diversity, together with the host's contact with nonpathogenic microbes in childhood, is a prerequisite for functional maturation of the immune system, which is in part mediated by microbiome-induced epigenetic changes. Yet, whether microbiome alterations are the result or the reason for barrier impairment and inflammatory response of the host is unclear. Exposure to locally prevalent microbial species could contribute to further modification of the disease course. The objective of this review is to reveal the link between changes in the skin microbiota, barrier dysfunction, and inflammation in AD. Addressing unmet needs includes determining the genetic background of AD susceptibility; the epigenetic modifications induced by the microbiota and other environmental factors; the role of globally diverse provoking factors; and the implementation of personalized, phenotype-specific therapies such as a epidermal barrier restoration in infancy and microbiota modulation via systemic or topical interventions, all of which open gaps for future research.

Revealing the Correlation between Altered Skin Lipids Composition and Skin Disorders

Human skin layers serve as a barrier between the body and the environment, by preventing water loss and blocking the entry of chemicals, allergens, and microbes. Recent data showed that skin lipids are vital ‘key players’ of several functions and mechanisms performing in the skin, such as, barrier function and microbiome composition. Abnormalities in lipid composition have been observed in inflammatory cutaneous diseases with a disrupted skin barrier. This review aims to demonstrate the fundamental role of keratinocytes, sebocytes, and microbiome-derived lipids in the maintenance of the skin barrier. Furthermore, it would reveal the correlation between altered skin lipids’ composition, microbiome, and the occurrence of certain dermatological disorders such as acne vulgaris, atopic dermatitis, psoriasis, and rosacea.

Antimicrobial peptides and proteins: Interaction with the skin microbiota

The cutaneous microbiota comprises all living skin microorganisms. There is increasing evidence that the microbiota plays a crucial role in skin homeostasis. Accordingly, a dysbiosis of the microbiota may trigger cutaneous inflammation. The need for a balanced microbiota requires specific regulatory mechanisms that control and shape the microbiota. In this review, we highlight the present knowledge suggesting that antimicrobial peptides (AMPs) may exert a substantial influence on the microbiota by controlling their growth. This is supported by own data showing the differential influence of principal skin-derived AMPs on commensal staphylococci. Vice versa, we also illuminate how the cutaneous microbiota interacts with skin-derived AMPs by modulating AMP expression and how microbiota members protect themselves from the antimicrobial activity of AMPs. Taken together, the current picture suggests that a fine-tuned and well-balanced AMP-microbiota interplay on the skin surface may be crucial for skin health.

Research Techniques Made Simple: Stratum Corneum Tape Stripping

Stratum corneum (SC)-derived biomarkers can provide relevant information on the skin's antimicrobial, physical, and immunological barriers. The SC is easily accessible, and collection by adhesive tapes (tape stripping [TS]) is robust and minimally invasive. Given its minimal invasiveness and simplicity, TS is particularly useful for studies in the pediatric population and when repetitive sampling over time is desirable, for example, in clinical trials. The palette of SC biomarkers is expanding in a wide variety of research areas, benefiting from advances in multiplex immunoassays and omics approaches, including proteomics, lipidomics, and transcriptomics. Although there is increasing interest in collecting SC samples, the lack of TS standardization hampers its broader implementation in research and clinical practice. In this article, we address the TS procedure as well as methodological challenges that should be considered in the development of an optimal sampling strategy.

Skin barrier dysfunction and filaggrin

Skin barrier dysfunction caused by endogenous or exogenous factors can lead to various disorders such as xerosis cutis, ichthyoses, and atopic dermatitis. Filaggrin is a pivotal structural protein of the stratum corneum (SC) and provides natural moisturizing factors that play a role in skin barrier functions. Filaggrin aggregates keratin filaments, resulting in the formation of a keratin network, which binds cornified envelopes and collapse keratinocytes to flattened corneocytes. This complex network contributes to the physical strength of the skin. Filaggrin is degraded by caspase-14, calpain 1, and bleomycin hydrolases into amino acids and amino acid metabolites such as trans-urocanic acid and pyrrolidone carboxylic acid, which are pivotal natural moisturizing factors in the SC. Accordingly, filaggrin is important for the pathophysiology of skin barrier disorders, and its deficiency or dysfunction leads to a variety of skin disorders. Here, the roles and biology of filaggrin, related skin diseases, and a therapeutic strategy targeting filaggrin are reviewed. In addition, several drug candidates of different mode of actions targeting filaggrin, along with their clinical efficacy, are discussed.