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

Microbiome and Postbiotics in Skin Health

The skin microbiome, a diverse and dynamic ecosystem of microorganisms, plays a pivotal role in maintaining skin health by interacting with skin cells, immune components, and structural barriers. It is essential for skin homeostasis, immune defense, and protection against pathogenic colonization. Dysbiosis in the microbiome has been implicated in numerous dermatological conditions, including acne, eczema, psoriasis, and rosacea. Acne, the most prevalent skin condition, affects up to 85% of individuals at some point in their lives, while eczema and psoriasis impose significant public health and economic burdens. The composition of the skin microbiome varies across skin types and anatomical sites, with sebaceous, moist, and dry areas fostering distinct microbial communities. Emerging therapeutic strategies such as microbiome-targeted treatments offer novel avenues for addressing skin diseases. Among these approaches, postbiotics have gained significant attention for their safety and efficacy. Unlike probiotics, postbiotics are non-viable microbial cells or their metabolites, which reduce safety concerns while providing functional benefits such as UV protection and wound healing. This review consolidates current insights into the role of the skin microbiome in health and disease, emphasizing postbiotics as a promising therapeutic strategy by exploring the clinical and commercial potential of microbiome-based treatments, particularly postbiotics, and their ability to redefine dermatological care and improve patient outcomes.

Ceramide as a Promising Tool for Diagnosis and Treatment of Clinical Diseases: A Review of Recent Advances

Background/Objectives: Ceramide, a sphingolipid metabolite, has emerged as a key player in various physiological and pathological processes. Changes in ceramide levels are associated with the occurrence and development of various diseases, highlighting its potential as a biomarker of various clinical diseases. Methods: The biosynthesis and metabolism of ceramide are discussed, along with its functions in cell signaling, apoptosis, and inflammation. This study further examines the potential of ceramide as a biomarker for disease diagnosis and treatment. Results: This article highlights the involvement of ceramide in several diseases, including cardiovascular diseases, dermatosis, cancer, neurodegenerative disorders and metabolic syndromes. For each disease, the potential of ceramide as a biomarker for disease diagnosis and prognosis is explored, and the feasibility of therapeutic strategies targeting ceramide metabolism are reviewed. Additionally, the challenges and future directions in the field of ceramide research are addressed. Conclusions: This review article provides an overview of the recent advances in understanding the role of ceramide in clinical diseases and its potential as a diagnostic and therapeutic tool.

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.

The epidermal lipid-microbiome loop and immunity: Important players in atopic dermatitis

BACKGROUND

The promotion of epidermal barrier dysfunction is attributed to abnormalities in the lipid-microbiome positive feedback loop which significantly influences the imbalance of the epithelial immune microenvironment (EIME) in atopic dermatitis (AD). This imbalance encompasses impaired lamellar membrane integrity, heightened exposure to epidermal pathogens, and the regulation of innate and adaptive immunity. The lipid-microbiome loop is substantially influenced by intense adaptive immunity which is triggered by abnormal loop activity and affects the loop's integrity through the induction of atypical lipid composition and responses to dysregulated epidermal microbes. Immune responses participate in lipid abnormalities within the EIME by downregulating barrier gene expression and are further cascade-amplified by microbial dysregulation which is instigated by barrier impairment.

AIM OF REVIEW

This review examines the relationship between abnormal lipid composition, microbiome disturbances, and immune responses in AD while progressively substantiating the crosstalk mechanism among these factors. Based on this analysis, the "lipid-microbiome" positive feedback loop, regulated by immune responses, is proposed.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The review delves into the impact of adaptive immune responses that regulate the EIME, driving AD, and investigates potential mechanisms by which lipid supplementation and probiotics may alleviate AD through the up-regulation of the epidermal barrier and modulation of immune signaling. This exploration offers support for targeting the EIME to attenuate AD.

Ceramides and Skin Health: New Insights

Ceramide has transitioned from an incidental discovery to a vital element in skincare, becoming a thoroughly studied compound in the quest to treat skin conditions. Creating a moisture barrier, preserving hydration, regulating pH, controlling inflammation, and enhancing skin functions and appearance are among its established benefits. It is often used medically to repair skin barrier defects, as observed in inflammatory skin conditions like atopic dermatitis (AD) and dry skin types. Furthermore, ceramide and its metabolites are commonly used as predictors before disease manifestation and for prognostication processes, thus can be used as biomarker for clinical diagnosis as well. In the last couple of decades, momentum was also seen in the pre-clinical studies involving anti-cancer and nanotechnology field, whereby ceramide was also used as a drug, a carrier, or even adjunct formulation to increase efficacy of treatment such as chemotherapy. Approaches to increase ceramide levels include directly replenishing lost ceramides with natural extracts, synthetic pseudo-ceramides, or ceramide-like analogues, as well as using supplements that stimulate the body's natural ceramide production. Although ceramide is a well-known treatment in skincare and for common skin conditions like AD and psoriasis, its development and related pharmacology for severe skin conditions, such as skin cancer, remain in pre-clinical stages. Hence, the purpose of this research is to explore the role of ceramide in skin health and its application in common skin diseases.

Skin Microbiota: Mediator of Interactions Between Metabolic Disorders and Cutaneous Health and Disease

Metabolic disorders, including type 2 diabetes mellitus (T2DM), obesity, and metabolic syndrome, are systemic conditions that profoundly impact the skin microbiota, a dynamic community of bacteria, fungi, viruses, and mites essential for cutaneous health. Dysbiosis caused by metabolic dysfunction contributes to skin barrier disruption, immune dysregulation, and increased susceptibility to inflammatory skin diseases, including psoriasis, atopic dermatitis, and acne. For instance, hyperglycemia in T2DM leads to the formation of advanced glycation end products (AGEs), which bind to the receptor for AGEs (RAGE) on keratinocytes and immune cells, promoting oxidative stress and inflammation while facilitating Staphylococcus aureus colonization in atopic dermatitis. Similarly, obesity-induced dysregulation of sebaceous lipid composition increases saturated fatty acids, favoring pathogenic strains of Cutibacterium acnes, which produce inflammatory metabolites that exacerbate acne. Advances in metabolomics and microbiome sequencing have unveiled critical biomarkers, such as short-chain fatty acids and microbial signatures, predictive of therapeutic outcomes. For example, elevated butyrate levels in psoriasis have been associated with reduced Th17-mediated inflammation, while the presence of specific Lactobacillus strains has shown potential to modulate immune tolerance in atopic dermatitis. Furthermore, machine learning models are increasingly used to integrate multi-omics data, enabling personalized interventions. Emerging therapies, such as probiotics and postbiotics, aim to restore microbial diversity, while phage therapy selectively targets pathogenic bacteria like Staphylococcus aureus without disrupting beneficial flora. Clinical trials have demonstrated significant reductions in inflammatory lesions and improved quality-of-life metrics in patients receiving these microbiota-targeted treatments. This review synthesizes current evidence on the bidirectional interplay between metabolic disorders and skin microbiota, highlighting therapeutic implications and future directions. By addressing systemic metabolic dysfunction and microbiota-mediated pathways, precision strategies are paving the way for improved patient outcomes in dermatologic care.

Gut microbiota and plasma metabolites in pregnant mothers and infant atopic dermatitis: A multi-omics study

Background

Many studies reported the influence of infants' gut microbiota on atopic dermatitis (AD) postnatally, yet the role of maternal gut microbiota and plasma metabolites in infants' AD remains largely unexplored.

Methods

Sixty-three pregnant mother-infants were enrolled and followed after childbirth in Guangzhou, China. Demographic information, maternal stool and plasma samples, and records for infants' AD were collected. Maternal gut microbiota/metabolome and plasma metabolome were profiled using shotgun metagenomics and non-targeted metabolomics. Logistic regression and multi-omics analysis were used to explore characteristic maternal gut microbiota in the AD and health groups.

Results

The α-diversity of maternal gut microbiota in health group was significantly higher than AD group (Shannon diversity P = 0.02, Simpson diversity P = 0.04). Short-chain fatty acids (SCFAs) producing microorganisms, including Faecalibacterium, Roseburia, Butyricicoccus, and Ruminococcus, as well as the abundance of phenylalanine, tyrosine, and tryptophan biosynthesis pathway, were enriched in health group (LDA>2 and P < 0.05). Virulent factors (VFs) involved in immune modulation were enriched in the health group, while VFs involving in adhesin were enriched in the AD group (P < 0.05). Metabolomic analysis showed that a polyunsaturated fatty acid/linoleic acid, 13S-hydroxyoctadecadienoic, were negatively associated with AD in both the gut and plasma samples (FDR<0.05). Several other linoleic acids and flavonoids were negatively associated with AD (FDR<0.05). Neural network analysis revealed that microorganisms enriched in health group may produce these protective fatty acids.

Conclusions

Our findings show that maternal gut microorganisms/metabolites and plasma metabolites during pregnancy impact subsequent pathogenesis of infants AD. This illuminates new strategies against early AD in offspring.

Lesional Psoriasis is Associated With Alterations in the Stratum Corneum Ceramide Profile and Concomitant Decreases in Barrier Function

Psoriasis is an inflammatory skin disease associated with an impaired skin barrier. The skin barrier function is dependent on the extracellular lipid matrix which surrounds the corneocytes in the stratum corneum. Ceramides comprise essential components of this matrix. Alterations in the stratum corneum ceramide profile have been directly linked to barrier dysfunction and might be an underlying factor of the barrier impairment in psoriasis. In this study, we investigated the ceramide profile and barrier function in psoriasis. Lesional and non-lesional skin of 26 patients and 10 healthy controls were analysed using in-depth ceramide lipidomics by liquid chromatography-mass spectrometry. Barrier function was assessed by measuring transepidermal water loss. Lesional skin showed a significant decrease in the abundance of total ceramides with significant alterations in the ceramide subclass composition compared to control and non-lesional skin. Additionally, the percentage of monounsaturated ceramides was significantly increased, and the average ceramide chain length significantly decreased in lesional skin. Altogether, this resulted in a markedly different profile compared to controls for lesional skin, but not for non-lesional skin. Importantly, the reduced barrier function in lesional psoriasis correlated to alterations in the ceramide profile, highlighting their interdependence. By assessing the parameters 2 weeks apart, we are able to highlight the reproducibility of these findings, which further affirms this connection. To conclude, we show that changes in the ceramide profile and barrier impairment are observed in, and limited to, lesional psoriatic skin. Their direct correlation provides a further mechanistic basis for the concomitantly observed impairment of barrier dysfunction.

Elongation of Very Long-Chain Fatty Acids (ELOVL) in Atopic Dermatitis and the Cutaneous Adverse Effect AGEP of Drugs

Atopic dermatitis (AD) is a common inflammatory skin disease, in particular among infants, and is characterized, among other things, by a modification in fatty acid and ceramide composition of the skin's stratum corneum. Palmitic acid and stearic acid, along with C16-ceramide and 2-hydroxy C16-ceramide, occur strikingly in AD. They coincide with a simultaneous decrease in very long-chain ceramides and ultra-long-chain ceramides, which form the outermost lipid barrier. Ceramides originate from cellular sphingolipid/ceramide metabolism, comprising a well-orchestrated network of enzymes involving various ELOVLs and CerSs in the de novo ceramide synthesis and neutral and acid CERase in degradation. Contrasting changes in long-chain ceramides and very long-chain ceramides in AD can be more clearly explained by the compartmentalization of ceramide synthesis. According to our hypothesis, the origin of increased C16-ceramide and 2-hydroxy C16-ceramide is located in the lysosome. Conversely, the decreased ultra-long-chain and very long-chain ceramides are the result of impaired ELOVL fatty acid elongation. The suggested model's key elements include the lysosomal aCERase, which has pH-dependent long-chain C16-ceramide synthase activity (revaCERase); the NADPH-activated step-in enzyme ELOVL6 for fatty acid elongation; and the coincidence of impaired ELOVL fatty acid elongation and an elevated lysosomal pH, which is considered to be the trigger for the altered ceramide biosynthesis in the lysosome. To maintain the ELOVL6 fatty acid elongation and the supply of NADPH and ATP to the cell, the polyunsaturated PPARG activator linoleic acid is considered to be one of the most suitable compounds. In the event that the increase in lysosomal pH is triggered by lysosomotropic compounds, compounds that disrupt the transmembrane proton gradient or force the breakdown of lysosomal proton pumps, non-HLA-classified AGEP may result.

An Observational Study: Association Between Atopic Dermatitis and Bacterial Colony of the Skin Based on 16S rRNA Gene Sequencing

Aim

Atopic dermatitis (AD) often accompanies skin infections, and bacterial skin infections often cause persistent and worsening symptoms. In this study, we explored the key changes in the microbiota of AD patients, as well as the effects of different ages and the severity of rash on changes in the microbiota.

Patients and Methods

A total of 95 AD patients and 77 healthy volunteers were recruited. The AD patients were divided into three groups based age and three groups according to the EASI score. Microorganisms collected from the skin were analyzed through 16S rRNA gene sequencing, revealing species diversity via α and β diversity analyses. Species compositions were compared at the phylum and genus levels. The significance of skin microbiota at the genus level was assessed using the random forest algorithm. Finally, the impact of relationships between different microbial communities on the microbial community composition and the pathogenesis of AD was explored using Pearson correlation coefficients.

Results

The species diversity of the skin microbiota in the AD group significantly decreased. Compared with that in the healthy volunteers (HV) group, the bacterial diversity in the two groups of samples significantly differed. Staphylococcus dominated the bacterial communities, and as AD symptoms gradually worsened, the abundance of Staphylococcus gradually increased. Among all bacterial genera with a relative abundance greater than 1%, Staphylococcus showed a negative correlation with other genera, and showed significant consistency in specimens from different age groups.

Conclusion

Changes in the abundance of Staphylococcus in the skin bacterial colonies are the main cause of AD. Brevundimonas, Paracoccus, Corynebacterium, and Veillonella may serve as characteristic biomarkers for AD. These results indicate that altering the microbiota composition of the skin may aid in the treatment of AD.

Gut microbiota, skin microbiota, and alopecia areata: A Mendelian randomization study

BACKGROUND

Observational studies have shown an association between skin microbiota and alopecia areata (AA), but the causal connection remains ambiguous.

METHODS

We obtained data on skin microbiota and AA from summary statistics of Genome-Wide Association Studies and applied statistical methods from Mendelian randomization (MR) to assess causal relationships. Additionally, we investigated whether the skin microbiota acts as a mediator in the pathway from gut microbiota to AA.

RESULTS

In the MR analysis of KORA FF4 and AA, the inverse-variance weighting method indicated that Corynebacterium (odds ratio [OR] = 0.82, 95% confidence interval [CI]: 0.70-0.96, p = 0.02) and asv037 (OR = 0.87, 95% CI: 0.76-0.99, p = 0.05) exerted protective effects, while Betaproteobacteria (OR = 1.21, 95% CI: 1.01-1.44, p = 0.03), asv015 (OR = 1.27, 95% CI: 1.05-1.54, p = 0.02), and Burkholderiales (OR = 1.20, 95% CI: 1.04-1.38, p = 0.01) were identified as risk factors in AA. In the MR analysis of PopGen and AA, asv001 (OR = 1.12, 95% CI: 1.01-1.24, p = 0.04), asv054 (OR = 1.13, 95% CI: 1.01-1.25, p = 0.03), and asv059 (OR = 1.14, 95% CI: 1.02-1.27, p = 0.02) were found to potentially increase the risk in AA. Furthermore, in the influence of gut microbiota on AA, the skin microbiota did not act as a mediator.

CONCLUSION

Our analysis suggests potential causal relationships between certain skin microbiota and AA, revealing insights into its pathogenesis and potential intervention strategies.

Constant vigilance! Managing threats to the skin barrier

OBJECTIVE

Skin barrier defects are one of the primary causes of atopic dermatitis (AD). The basis of skin barrier defects in AD is due to a deficiency in various barrier proteins including filaggrin, involucrin, claudins, and lipids such as ceramide, fatty acids, and cholesterol. This review updates a more detailed lipid dysregulation in the skin barrier of AD based on recent lipidomic analysis. The clinical implications, treatments, prevention, and predictive capability of skin barrier defects are also reviewed.

DATA SOURCES

Published literature obtained through PubMed searches.

STUDY SELECTIONS

Studies relevant to the mechanisms, clinical implications, treatments, prevention, and predictors of AD development.

RESULTS

Skin barrier defects contribute to transepidermal water loss, infections, IgE sensitizations, and cutaneous inflammation in AD. Preventive treatments include daily hydration and application of moisturizers. Because skin barrier defects precede the development of AD, they provide an opportunity for prediction and intervention.

CONCLUSION

Skin barrier defects play an important role in the comorbidities of AD including infectious complications, disease flare, and allergic diathesis. Current research focuses on prevention and prediction of AD development.

Preclinical Atopic Dermatitis Skin in Infants: An Emerging Research Area

Whereas clinically apparent atopic dermatitis (AD) can be confirmed by validated diagnostic criteria, the preclinical phenotype of infants who eventually develop AD is less well-characterized. Analogous to unaffected or nonlesional skin in established AD, clinically normal-appearing skin in infants who will develop clinical AD has distinct changes. Prospective studies have revealed insights into this preclinical AD phenotype. In this study, we review the structural, immunologic, and microbiome nature of the preclinical AD phenotype. Determination of markers that predict the development of AD will facilitate targeting of interventions to prevent the development or reduce the severity of AD in infants.

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.

Advanced fructo-oligosaccharides improve itching and aberrant epidermal lipid composition in children with atopic dermatitis

Introduction

The effects of fructo-oligosaccharides (FOS) on atopic dermatitis (AD) have not been determined.

Methods

In a randomized, double-blind, placebo-controlled trial, children with AD aged 24 months to 17 years received either advanced FOS containing 4.25 g of 1-kestose or a placebo (maltose) for 12 weeks.

Results

The SCORAD and itching scores were reduced in patients treated with both FOS (all p < 0.01) and maltose (p < 0.05 and p < 0.01). Sleep disturbance was improved only in the FOS group (p < 0.01). The FOS group revealed a decreased proportion of linoleic acid (18:2) esterified omega-hydroxy-ceramides (EOS-CERs) with amide-linked shorter chain fatty acids (C28 and C30, all p < 0.05), along with an increased proportion of EOS-CERs with longer chain fatty acids (C32, p < 0.01).

Discussion

FOS may be beneficial in alleviating itching and sleep disturbance, as well as improving skin barrier function in children with AD.

Physical influences on the skin barrier and pathogenesis of allergy

PURPOSE OF REVIEW

As the incidence of allergic conditions has increased in recent decades, the effects of climate change have been implicated. There is also increased knowledge on the effects of other physical influences, such as scratching and Staphylococcus aureus . The skin barrier is the first line of defense to the external environment, so understanding the ways that these factors influence skin barrier dysfunction is important.

RECENT FINDINGS

Although the impact on environmental exposures has been well studied in asthma and other allergic disorders, there is now more literature on the effects of temperature, air pollution, and detergents on the skin barrier. Factors that cause skin barrier dysfunction include extreme temperatures, air pollution (including greenhouse gases and particulate matter), wildfire smoke, pollen, scratching, S. aureus, and detergents.

SUMMARY

Understanding the ways that external insults affect the skin barrier is important to further understand the mechanisms in order to inform the medical community on treatment and prevention measures for atopic conditions.

Epidermal biomarkers of the skin barrier in atopic and contact dermatitis

Dysfunction of the skin barrier plays a critical role in the initiation and progression of inflammatory skin diseases, such as atopic dermatitis and contact dermatitis. Epidermal biomarkers can aid in evaluating the functionality of the skin barrier and understanding the mechanisms that underlay its impairment. This narrative review provides an overview of recent studies on epidermal biomarkers associated with the function and integrity of the skin barrier, and their application in research on atopic dermatitis and contact dermatitis. The reviewed studies encompass a wide spectrum of molecular, morphological and biophysical biomarkers, mainly obtained from stratum corneum tape strips and biopsies. Lipids, natural moisturizing factors, and structural proteins are the most frequently reported molecular biomarkers. Additionally, corneocyte surface topography and elasticity show potential as biomarkers for assessing the physical barrier of the skin. In contact dermatitis studies, biomarkers are commonly employed to evaluate skin irritation and differentiate between irritant and allergic contact dermatitis. In atopic dermatitis, biomarkers are primarily utilized to identify differences between atopic and healthy skin, for predictive purposes, and monitoring response to therapies. While this overview identifies potential biomarkers for the skin barrier, their validation as epidermal biomarkers for atopic dermatitis and contact dermatitis has yet to be established.