Lipidomic analysis of epidermal lipids: a tool to predict progression of inflammatory skin disease in humans

Metabolomic and lipidomic fingerprints in inflammatory skin diseases - Systemic illumination of atopic dermatitis, hidradenitis suppurativa and plaque psoriasis

Auto-inflammatory skin diseases place considerable symptomatic and emotional burden on the affected and put pressure on healthcare expenditures. Although most apparent symptoms manifest on the skin, the systemic inflammation merits a deeper analysis beyond the surface. We set out to identify systemic commonalities, as well as differences in the metabolome and lipidome when comparing between diseases and healthy controls. Lipidomic and metabolomic LC-MS profiling was applied, using plasma samples collected from patients suffering from atopic dermatitis, plaque-type psoriasis or hidradenitis suppurativa or healthy controls. Plasma profiles revealed a notable shift in the non-enzymatic anti-oxidant defense in all three inflammatory disorders, placing cysteine metabolism at the center of potential dysregulation. Lipid network enrichment additionally indicated the disease-specific provision of lipid mediators associated with key roles in inflammation signaling. These findings will help to disentangle the systemic components of autoimmune dermatological diseases, paving the way to individualized therapy and improved prognosis.

Comparative study of melasma in patients before and after treatment based on lipomics

BACKGROUND

Skin barrier alterations play a crucial function in melasma development. Past researches have demonstrated variations in lipid content between the epidermis of melasma lesions and normal tissues, along with the varied expression of lipid-related genes in melasma. This study aimed to analyze the lipidome profiles of skin surface lipids (SSL) in patients with melasma before and after treatment to understand associated abnormalities.

METHODS

Melasma was treated with tranexamic acid orally and hydroquinone cream topically. Disease was assessed using the Melasma Area and Severity Index (MASI), and the impact to life was evaluated with Melasma Quality of Life (MELASQoL) score. Epidermal melanin particles were observed using reflection confocal microscopy (RCM), whereas epidermal pigment and blood vessel morphology were observed using dermoscopy, and SSL samples were collected. Specific information regarding alterations in lipid composition was obtained through multivariate analysis of the liquid chromatography-mass spectrometry data.

RESULTS

After treatment, patients with melasma exhibited decreased MASI and MELASQoL scores (P < 0.001); RCM revealed reduced melanin content in the lesions, and dermoscopy revealed fewer blood vessels. Fifteen lipid subclasses and 382 lipid molecules were identified using lipidomic assays. The expression levels of total lipids, phosphatidylcholine, and phosphatidylethanolamine in the melasma lesions decreased after treatment (P < 0.05).

CONCLUSION

This study revealed alterations in the SSL composition after effective melasma treatment, suggesting a compensatory role for lipids in melasma barrier function. The mechanism involving SSL and the lipid barrier, which influences melasma's occurrence, needs further elucidation.

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 immunological and structural epidermal barrier dysfunction and skin microbiome in atopic dermatitis-an update

Atopic dermatitis (AD) is a common, chronic and relapsing inflammatory skin disease with various clinical presentations and combinations of symptoms. The pathophysiology of AD is complex and multifactorial. There are several factors involved in the etiopathogenesis of AD including structural and immunological epidermal barrier defect, imbalance of the skin microbiome, genetic background and environmental factors. Alterations in structural proteins, lipids, proteases, and their inhibitors, lead to the impairment of the stratum corneum which is associated with the increased skin penetration and transepidermal water loss. The elevated serum immunoglobulin E levels and blood eosinophilia have been shown in the majority of AD patients. Type 2 T-helper cell immune pathway with increased expression of interleukin (IL)-4, IL-5, and IL-13, has an important role in the etiopathogenesis of AD. Both T cells and keratinocytes contribute to epidermal barrier impairment in AD via a dynamic interaction of cytokines and chemokines. The skin microbiome is another factor of relevance in the etiopathogenesis of AD. It has been shown that during AD flares, Staphylococcus aureus (S. aureus) colonization increased, while Staphylococcus epidermidis (S. epidermidis) decreased. On the contrary, S. epidermidis and species of Streptococcus, Corynebacterium and Propionibacterium increased during the remision phases. However, it is not clear whether skin dysbiosis is one of the symptoms or one of the causes of AD. There are several therapeutic options, targeting these pathways which play a critical role in the etiopathogenesis of AD. Although topical steroids are the mainstay of the treatment of AD, new biological therapies including IL-4, IL-13, and IL-31 inhibitors, as well as Janus kinase inhibitors (JAKi), increasingly gain more importance with new advances in the therapy of AD. In this review, we summarize the role of immunological and structural epidermal barrier dysfunction, immune abnormalities, impairment of lipids, filaggrin mutation and skin microbiome in the etiopathogenesis of AD, as well as the therapeutic options for AD and their effects on these abnormalities in AD skin.

Lipidome Investigation of Carnosine Effect on Nude Mice Skin to Prevent UV-A Damage

The lipid profile of skin is fundamental in the maintenance of the protective barrier against the external environment. Signaling and constitutive lipids of this large organ are involved in inflammation, metabolism, aging, and wound healing, such as phospholipids, triglycerides, FFA, and sphingomyelin. Skin exposure to ultraviolet (UV) radiation results in a photoaging process that is an accelerated form of aging. UV-A radiation deeply penetrates the dermis and promotes damage to DNA, lipids, and proteins by increasing the generation of reactive oxygen species (ROS). Carnosine, an endogenous β-alanyl-L-histidine dipeptide, demonstrated antioxidant properties that prevent photoaging and modification of skin protein profiling, making carnosine a compelling ingredient to consider for use in dermatology. The aim of this research was to investigate the modification of skin lipidome after UV-A treatment in presence or not of topic administration of carnosine. Quantitative analyses based on high-resolution mass spectrometry of nude mice skin-extracted lipids resulted in several modifications of barrier composition after UV-A radiation, with or without carnosine treatment. In total, 328 out of 683 molecules showed significant alteration-262 after UV-A radiation and 126 after UV-A and carnosine treatment versus controls. Importantly, the increased oxidized TGs after UV-A radiation, responsible of dermis photoaging, were completely reverted by carnosine application to prevent the UV-A damage. Network analyses also showed that the production of ROS and the calcium and TNF signaling were modulated by UV-A and carnosine. In conclusion, lipidome analyses attested the carnosine activity to prevent the UV-A damage, reducing the lipid oxidation, the inflammation, and the dysregulation of lipid skin barrier.

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.

Preclinical study models of psoriasis: State-of-the-art techniques for testing pharmaceutical products in animal and nonanimal models

Local and systemic treatments exist for psoriasis, but none can do more than control its symptoms because of its numerous unknown mechanisms. The lack of validated testing models or a defined psoriatic phenotypic profile hinders antipsoriatic drug development. Despite their intricacy, immune-mediated diseases have no improved and precise treatment. The treatment actions may now be predicted for psoriasis and other chronic hyperproliferative skin illnesses using animal models. Their findings confirmed that a psoriasis animal model could mimic a few disease conditions. However, their ethical approval concerns and inability to resemble human psoriasis rightly offer to look for more alternatives. Hence, in this article, we have reported various cutting-edge techniques for the preclinical testing of pharmaceutical products for the treatment of psoriasis.

Nanodelivery Strategies for Skin Diseases with Barrier Impairment: Focusing on Ceramides and Glucocorticoids

The human epidermis has a characteristic lipidic composition in the stratum corneum, where ceramides play a crucial role in the skin barrier homeostasis and in water-holding capacity. Several skin diseases, such as atopic dermatitis and psoriasis, exhibit a dysfunction in the lipid barrier with altered ceramide levels and increased loss of transepidermal water. Glucocorticoids are normally employed in the therapeutical management of these pathologies. However, they have shown a poor safety profile and reduced treatment efficiency. The main objective of this review is to, within the framework of the limitations of the currently available therapeutical approaches, establish the relevance of nanocarriers as a safe and efficient delivery strategy for glucocorticoids and ceramides in the topical treatment of skin disorders with barrier impairment.

CTIP2 and lipid metabolism: regulation in skin development and associated diseases

INTRODUCTION

COUP-TF INTERACTING PROTEIN 2 (CTIP2) is a crucial transcription factor exhibiting its control through coupled modulation of epigenetic modification and transcriptional regulation of key genes related to skin, immune, and nervous system development. Previous studies have validated the essential role of CTIP2 in skin development and maintenance, propagating its effects in epidermal permeability barrier (EPB) homeostasis, wound healing, inflammatory diseases, and epithelial cancers. Lipid metabolism dysregulation, on the other hand, has also established its independent emerging role over the years in normal skin development and various skin-associated ailments. This review focuses on the relatively unexplored connections between CTIP2-mediated control of lipid metabolism and alteration of EPB homeostasis, delayed wound healing, inflammatory diseases exacerbation, and cancer promotion and progression.

AREAS COVERED

Here we have discussed the intricate interplay of various endogenous lipids and lipoproteins accompanying skin development and associated disease processes and the possible link to CTIP2-mediated regulation of lipid metabolism.

EXPERT OPINION

Establishing the link between CTIP2 and lipid metabolism alterations in the context of skin morphogenesis and diverse types of skin diseases including cancer can help us identify novel targets for effective therapeutic intervention.

The skin redoxome

Redoxome is the network of redox reactions and redox active species (ReAS) that affect the homeostasis of cells and tissues. Due to the intense and constant interaction with external agents, the human skin has a robust redox signalling framework with specific pathways and magnitudes. The establishment of the skin redoxome concept is key to expanding knowledge of skin disorders and establishing better strategies for their prevention and treatment. This review starts with its definition and progress to propose how the master redox regulators are maintained and activated in the different conditions experienced by the skin and how the lack of redox regulation is involved in the accumulation of several oxidation end products that are correlated with various skin disorders.

Analytical approaches to assess metabolic changes in psoriasis

Psoriasis is one of the most common human skin diseases, although its development is not limited to one tissue, but is associated with autoimmune reactions throughout the body. Overproduction of pro-inflammatory cytokines and growth factors systemically stimulates the proliferation of skin cells, which manifests as excessive exfoliation of the epidermis, and/or arthritis, as well as other comorbidities such as insulin resistance, metabolic syndrome, hypertension, and depression. Thus, there is a great need for a thorough analysis of the pathophysiology of psoriatic patients, including classical methods, such as spectrophotometry, chromatography, or Western blot, and also novel omics approaches such as lipidomics and proteomics. Moreover, the extensive pathophysiology forces increased research examining biological changes in both skin cells, and systemically. A wide range of techniques involved in lipidomic research based on a combination of mass spectrometry and different types of chromatography (RP-LC-QTOF-MS/MS, HILIC-QTOF-MS/MS or RP-LC-QTRAP-MS/MS), have allowed comprehensive assessment of lipid modification in psoriatic skin and provided new insight into the role of lipids and their mechanism of action in psoriasis. Moreover, proteomic analysis using gel-nanoLC-OrbiTrap-MS/MS, as well as MALDI-TOF/TOF techniques facilitates the description of panels of enzymes involved in lipidome modifications, and the response of the endocannabinoid system to metabolic changes. Psoriasis is known to alter the expression of proteins that are involved in the inflammatory and antioxidant response, as well as protein biosynthesis, degradation, as well as cell proliferation and apoptosis. Knowledge of changes in the lipidomic and proteomic profile will not only allow the understanding of psoriasis pathophysiology, but also facilitate proper and early diagnosis and effective pharmacotherapy.

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.

Interactions between the Cell Membrane Repair Protein S100A10 and Phospholipid Monolayers and Bilayers

Protein S100A10 participates in different cellular mechanisms and has different functions, especially at the membrane. Among those, it forms a ternary complex with annexin A2 and the C-terminal of AHNAK and then joins the dysferlin membrane repair complex. Together, they act as a platform enabling membrane repair. Both AHNAK and annexin A2 have been shown to have membrane binding properties. However, the membrane binding abilities of S100A10 are not clear. In this paper, we aimed to study the membrane binding of S100A10 in order to better understand its role in the cell membrane repair process. S100A10 was overexpressed by E. coli and purified by affinity chromatography. Using a Langmuir monolayer as a model membrane, the binding parameters and ellipsometric angles of the purified S100A10 were measured using surface tensiometry and ellipsometry, respectively. Phosphorus-31 solid-state nuclear magnetic resonance spectroscopy was also used to study the interaction of S100A10 with lipid bilayers. In the presence of a lipid monolayer, S100A10 preferentially interacts with unsaturated phospholipids. In addition, its behavior in the presence of a bilayer model suggests that S100A10 interacts more with the negatively charged polar head groups than the zwitterionic ones. This work offers new insights on the binding of S100A10 to different phospholipids and advances our understanding of the parameters influencing its membrane behavior.

Skin lipids in health and disease: A review

Our skin is the interface between us and our environment - a flexible barrier that has evolved for protection, immunity, regulation and sensation. Once regarded as inert, we now know that it is a dynamic environment. Skin lipids are crucial to the structure and function of skin. From deep in the hypodermis, through the ceramide-rich epidermis, to the lipids of the skin surface, there are a vast array of different lipids with important roles to play. This review firstly discusses the lipid composition of human skin and secondly, changes that have been found in skin lipid composition in different skin diseases. Further research into skin lipids facilitated by ever-improving methodologies will no doubt generate new knowledge, paving the way for diagnosis, prevention and treatment of skin disorders and diseases.

Lipidomic analysis of facial skin surface lipid reveals the causes of pregnancy-related skin barrier weakness

Self-reported skin discomfort is a common problem during pregnancy, but it is not clear whether skin barrier function is altered in the process. Few studies have described the skin barrier function during pregnancy. In this work, we used highly sensitive and high-resolution ultra performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) to distinguish skin surface lipid (SSL) combined with multivariate analysis of lipids and metabolic changes to determine the relationship between SSL changes and skin physiology during pregnancy in order to better understand the skin condition of pregnant women. The results showed a significant reduction in the total lipid content in pregnant women. A total of 2270 lipids were detected, and the relative abundances of fatty acyls and glycerolipids were significantly reduced, while glycerophospholipids (GPs), sphingolipids, and saccharolipids was significantly increased in the pregnancy group. Multivariate data analysis indicated that 23 entities constituted the most important individual species responsible for the discrimination and phosphatidylcholine was the most abundant lipid in pregnancy group. In addition, compared to SSL profile of control group, it was observed that the average chain length of ceramides and fatty acids both decreased in SSL profile of pregnancy group. The main and most commonly affected pathway was that of GP pathways. These findings indicate that skin lipids are significantly altered in mid-pregnancy compared to the control group. Changes in ostrogen during pregnancy also make the skin more susceptible to inflammatory factors and lead to more fragile and susceptible skin, weakening the skin barrier along with the lipid alterations.

Lipidomics profiling of skin surface lipids in senile pruritus

Background

Senile pruritus is common, yet its etiology remains unknown. Aging-associated skin barrier defects and skin surface lipid (SSL) alterations have been postulated to play important roles in its occurrence. In the present study, the lipidomic profiles of SSLs in elderly patients were examined to better understand the potential causes of senile pruritus.

Methods

Transepidermal water loss (TEWL) was evaluated to assess the skin barrier function. The Ameliorated Kawashima Itch Scale score was used to measure the pruritus severity. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and multivariate data analysis were employed to investigate SSL alterations.

Results

The results showed that senile pruritus patients had higher TEWL values than control subjects (13.13 ± 4.28 versus 6.71 ± 2.45, p < 0.01). LC-MS/MS revealed significant differences in the lipidomic profiles and identified 81 species of SSLs that differed between the two groups. Compared with control subjects, senile pruritus patients had increased levels of ceramides (Cers), diacylglycerols, fatty acids, phosphatidylcholines, phosphatidylethanolamines, phytosphingosines, sphingosines, diacylceryl-3-O-carboxyhydroxymethylcholine, diacylglyceryl trimethylhomoserine, and unsaturated free fatty acids, but decreased levels of triacylglycerol. Cer-EOS, Cer-NDS, and Cer-NS were positively correlated with TEWL value (p < 0.05). Pruritus severity score was positively correlated with sphingomyelin, Cer-NP, Cer-AS, Cer-NDS, and Cer-NS, but negatively correlated with Cer-BS, Cer-EODS, Cer-EOS, and Cer-AP.

Conclusions

The present study indicated that patients with senile pruritus have impaired skin barrier function and altered SSL composition. Certain SSL species identified in this study may be potential targets for future studies on the pathogenesis of senile pruritus.

Trial registration

Peking University International Hospital (Number: YN2018QN04; date: January 2019).

AHNAK C-Terminal Peptide Membrane Binding-Interactions between the Residues 5654-5673 of AHNAK and Phospholipid Monolayers and Bilayers

The dysferlin membrane repair complex contains a small complex, S100A10-annexin A2, which initiates membrane repair by recruiting the protein AHNAK to the membrane, where it interacts via binding sites in the C-terminal region. However, no molecular data are available for the membrane binding of the various proteins involved in this complex. Therefore, the present study investigated the membrane binding of AHNAK to elucidate its role in the cell membrane repair process. A chemically synthesized peptide (pAHNAK), comprising the 20 amino acids in the C-terminal domain of AHNAK, was applied to Langmuir monolayer models, and the binding parameters and insertion angles were measured with surface tensiometry and ellipsometry. The interaction of pAHNAK with lipid bilayers was studied using ³¹P solid-state nuclear magnetic resonance. pAHNAK preferentially and strongly interacted with phospholipids that comprised negatively charged polar head groups with unsaturated lipids. This finding provides a better understanding of AHNAK membrane behavior and the parameters that influence its function in membrane repair.

The Skin Epilipidome in Stress, Aging, and Inflammation

Lipids are highly diverse biomolecules crucial for the formation and function of cellular membranes, for metabolism, and for cellular signaling. In the mammalian skin, lipids additionally serve for the formation of the epidermal barrier and as surface lipids, together regulating permeability, physical properties, acidification and the antimicrobial defense. Recent advances in accuracy and specificity of mass spectrometry have allowed studying enzymatic and non-enzymatic modifications of lipids-the epilipidome-multiplying the known diversity of molecules in this class. As the skin is an organ that is frequently exposed to oxidative-, chemical- and thermal stress, and to injury and inflammation, it is an ideal organ to study epilipidome dynamics, their causes, and their biological consequences. Recent studies uncover loss or gain in biological function resulting from either specific modifications or the sum of the modifications of lipids. These studies suggest an important role for the epilipidome in stress responses and immune regulation in the skin. In this minireview we provide a short survey of the recent developments on causes and consequences of epilipidomic changes in the skin or in cell types that reside in the skin.

The impact of recent advances in lipidomics and redox lipidomics on dermatological research

Dermatological research is a major beneficiary of the rapidly developing advances in lipid analytic technology and of bioinformatic tools which help to decipher and interpret the accumulating big lipid data. At its interface with the environment, the epidermis develops a blend of lipids that constitutes the epidermal lipid barrier, essential for the protection from water loss and entry of dangerous noxae. Apart from their structural role in the barrier, novel intra- and inter-cellular signaling functions of lipids and their oxidation products have been uncovered in most cutaneous cell types over the last decades, and the discovery rate has been boosted by the advent of high resolution and -throughput mass spectrometric techniques. Our understanding of epidermal development has benefited from studies on fetal surface lipids, which appear to signal for adaptation to desiccation post partum, and from studies on the dynamics of epidermal lipids during adjustment to the atmosphere in the first months of life. At birth, external insults begin to challenge the skin and its lipids, and recent years have yielded ample insights into the dynamics of lipid synthesis and -oxdiation after UV exposure, and upon contact with sensitizers and irritants. Psoriasis and atopic dermatitis are the most common chronic inflammatory skin diseases, affecting at least 3% and 7% of the global population, respectively. Consequently, novel (redox-) lipidomic techniques have been applied to study systemic and topical lipid abnormalities in patient cohorts. These studies have refined the knowledge on eicosanoid signaling in both diseases, and have identified novel biomarkers and potential disease mediators, such as lipid antigens recognized by psoriatic T cells, as well as ceramide species, which specifically correlate with atopic dermatitis severity. Both biomarkers have yielded novel mechanistic insights. Finally, the technological progress has enabled studies to be performed that have monitored the consequences of diet, lifestyle, therapy and cosmetic intervention on the skin lipidome, highlighting the translational potential of (redox-) lipidomics in dermatology.

Epidermal Lipids: Key Mediators of Atopic Dermatitis Pathogenesis

The skin barrier keeps the 'inside in' and the 'outside out', forming a protective blanket against external insults. Epidermal lipids, such as ceramides, fatty acids (FAs), triglycerides, and cholesterol, are integral components driving the formation and maintenance of the epidermal permeability barrier (EPB). A breach in this lipid barrier sets the platform for the subsequent onset and progression of atopic dermatitis (AD). Such lipids are also important in the normal functioning of organisms, both plants and animals, and in diseases, including cancer. Given the doubling of the number of cases of AD in recent years and the chronic nature of this disorder, here we shed light on the multifaceted role of diverse types of lipid in mediating AD pathogenesis.

Enrichment of Short-Chain Ceramides and Free Fatty Acids in the Skin Epidermis, Liver, and Kidneys of db/db Mice, a Type 2 Diabetes Mellitus Model

Patients with diabetes mellitus (DM) often suffer from diverse skin disorders, which might be attributable to skin barrier dysfunction. To explore the role of lipid alterations in the epidermis in DM skin disorders, we quantitated 49 lipids (34 ceramides, 14 free fatty acids (FFAs), and cholesterol) in the skin epidermis, liver, and kidneys of db/db mice, a Type 2 DM model, using UPLC-MS/MS. The expression of genes involved in lipid synthesis was also evaluated. With the full establishment of hyperglycemia at the age of 20 weeks, remarkable lipid enrichment was noted in the skin of the db/db mice, especially at the epidermis and subcutaneous fat bed. Prominent increases in the ceramides and FFAs (>3 fold) with short or medium chains (<C26) occurred in the skin epidermis (16NS, 18NS, 24NS, 16NDS, 18NDS, 20NDS, 22NDS, 24NDS, C16:1FA, C18:2FA, and C18:1FA) and the liver (16NS, 18NS, 20NS, 24:1NS, 18NDS, 20NDS, 22NDS, C16:1FA, C18:2FA, C18:1FA), whereas those with very long chains were not affected. In the kidney, only slight increases (<3 fold) were observed for 16NS, 18NS, 20NS, 26NDS, C26FA, and C22:1FA. Consistently, LXRα/β and PPARγ, nuclear receptors promoting lipid synthesis, lipid synthesis enzymes such as elongases 1, 4, and 6, and fatty acid synthase and stearoyl-CoA desaturase were highly expressed in the skin and livers of the db/db mice. Collectively, our study demonstrates an extensive alteration in the skin and systemic lipid profiles of db/db mice, which could contribute to the development of skin disorders in DM.

Ceramide and Regulation of Vascular Tone

In addition to playing a role as a structural component of cellular membranes, ceramide is now clearly recognized as a bioactive lipid implicated in a variety of physiological functions. This review aims to provide updated information on the role of ceramide in the regulation of vascular tone. Ceramide may induce vasodilator or vasoconstrictor effects by interacting with several signaling pathways in endothelial and smooth muscle cells. There is a clear, albeit complex, interaction between ceramide and redox signaling. In fact, reactive oxygen species (ROS) activate different ceramide generating pathways and, conversely, ceramide is known to increase ROS production. In recent years, ceramide has emerged as a novel key player in oxygen sensing in vascular cells and mediating vascular responses of crucial physiological relevance such as hypoxic pulmonary vasoconstriction (HPV) or normoxic ductus arteriosus constriction. Likewise, a growing body of evidence over the last years suggests that exaggerated production of vascular ceramide may have detrimental effects in a number of pathological processes including cardiovascular and lung diseases.

Leveraging Multilayered "Omics" Data for Atopic Dermatitis: A Road Map to Precision Medicine

Atopic dermatitis (AD) is a complex multifactorial inflammatory skin disease that affects ~280 million people worldwide. About 85% of AD cases begin in childhood, a significant portion of which can persist into adulthood. Moreover, a typical progression of children with AD to food allergy, asthma or allergic rhinitis has been reported (“allergic march” or “atopic march”). AD comprises highly heterogeneous sub-phenotypes/endotypes resulting from complex interplay between intrinsic and extrinsic factors, such as environmental stimuli, and genetic factors regulating cutaneous functions (impaired barrier function, epidermal lipid, and protease abnormalities), immune functions and the microbiome. Though the roles of high-throughput “omics” integrations in defining endotypes are recognized, current analyses are primarily based on individual omics data and using binary clinical outcomes. Although individual omics analysis, such as genome-wide association studies (GWAS), can effectively map variants correlated with AD, the majority of the heritability and the functional relevance of discovered variants are not explained or known by the identified variants. The limited success of singular approaches underscores the need for holistic and integrated approaches to investigate complex phenotypes using trans-omics data integration strategies. Integrating omics layers (e.g., genome, epigenome, transcriptome, proteome, metabolome, lipidome, exposome, microbiome), which often have complementary and synergistic effects, might provide the opportunity to capture the flow of information underlying AD disease manifestation. Overlapping genes/candidates derived from multiple omics types include FLG, SPINK5, S100A8, and SERPINB3 in AD pathogenesis. Overlapping pathways include macrophage, endothelial cell and fibroblast activation pathways, in addition to well-known Th1/Th2 and NFkB activation pathways. Interestingly, there was more multi-omics overlap at the pathway level than gene level. Further analysis of multi-omics overlap at the tissue level showed that among 30 tissue types from the GTEx database, skin and esophagus were significantly enriched, indicating the biological interconnection between AD and food allergy. The present work explores multi-omics integration and provides new biological insights to better define the biological basis of AD etiology and confirm previously reported AD genes/pathways. In this context, we also discuss opportunities and challenges introduced by “big omics data” and their integration.

Lipids and the Permeability and Antimicrobial Barriers of the Skin

The primary purpose of the epidermis of terrestrial vertebrates is to produce the stratum corneum, which serves as the interface between the organism and the environment. As such, the stratum corneum provides a permeability barrier which both limits water loss through the skin and provides a relatively tough permeability barrier. This provides for a degree of resistance to mechanical trauma and prevents or limits penetration of potentially harmful substances from the environment. The stratum corneum consists of an array of keratinized cells embedded in a lipid matrix. It is this intercellular lipid that determines the permeability of the stratum corneum. The main lipids here are ceramides, cholesterol, and fatty acids. In addition, the skin surface of mammals, including humans, is coated by a lipid film produced by sebaceous glands in the dermis and secreted through the follicles. Human sebum consists mainly of squalene, wax monoesters, and triglycerides with small proportions of cholesterol and cholesterol esters. As sebum passes through the follicles, some of the triglycerides are hydrolyzed by bacteria to liberate free fatty acids. Likewise, near the skin surface, where water becomes available, some of the ceramides are acted upon by an epithelial ceramidase to liberate sphingosine, dihydrosphingosine, and 6-hydroxysphingosine. Some of the free fatty acids, specifically lauric acid and sapienic acid, have been shown to have antibacterial, antifungal, and antiviral activity. Also, the long-chain bases have broad spectrum antibacterial activity.

Epithelial barrier dysfunctions in atopic dermatitis: a skin-gut-lung model linking microbiome alteration and immune dysregulation

BACKGROUND

Atopic dermatitis is a systemic disorder characterized by abnormal barrier function across multiple organ sites. Causes of epidermal barrier breakdown are complex and driven by a combination of structural, genetic, environmental and immunological factors. In addition, alteration in microflora diversity can influence disease severity, duration, and response to treatment. Clinically, atopic dermatitis can progress from skin disease to food allergy, allergic rhinitis, and later asthma, a phenomenon commonly known as the atopic march. The mechanism by which atopic dermatitis progresses towards gastrointestinal or airway disease remains to be elucidated.

OBJECTIVES

This review addresses how epithelial dysfunction linking microbiome alteration and immune dysregulation can predispose to the development of the atopic march.

METHODS

A literature search was conducted using the PubMed database for relevant articles with the keywords 'atopic dermatitis', 'epithelial barrier', 'skin', 'gut', 'lung', 'microbiome' and 'immune dysregulation'.

RESULTS

Initial disruption in the skin epidermal barrier permits allergen sensitization and colonization by pathogens. This induces a T helper 2 inflammatory response and a thymic stromal lymphopoietin-mediated pathway that further promotes barrier breakdown at distant sites, including the intestinal and respiratory tract.

CONCLUSIONS

As there are no immediate cures for food allergy or asthma, early intervention aimed at protecting the skin barrier and effective control of local and systemic inflammation may improve long-term outcomes and reduce allergen sensitization in the airway and gut.

Profiling of epidermal lipids in a mouse model of dermatitis: Identification of potential biomarkers

Lipids are important structural and functional components of the skin. Alterations in the lipid composition of the epidermis are associated with inflammation and can affect the barrier function of the skin. SHARPIN-deficient cpdm mice develop a chronic dermatitis with similarities to atopic dermatitis in humans. Here, we used a recently-developed approach named multiple reaction monitoring (MRM)-profiling and single ion monitoring to rapidly identify discriminative lipid ions. Shorter fatty acyl residues and increased relative amounts of sphingosine ceramides were observed in cpdm epidermis compared to wild type mice. These changes were accompanied by downregulation of the Fasn gene which encodes fatty acid synthase. A profile of diverse lipids was generated by fast screening of over 300 transitions (ion pairs). Tentative attribution of the most significant transitions was confirmed by product ion scan (MS/MS), and the MRM-profiling linear intensity response was validated with a C17-ceramide lipid standard. Relative quantification of sphingosine ceramides CerAS(d18:1/24:0)2OH, CerAS(d18:1/16:0)2OH and CerNS(d18:1/16:0) discriminated between the two groups with 100% accuracy, while the free fatty acids cerotic acid, 16-hydroxy palmitic acid, and docosahexaenoic acid (DHA) had 96.4% of accuracy. Validation by liquid chromatography tandem mass spectrometry (LC-MS/MS) of the above-mentioned ceramides was in agreement with MRM-profiling results. Identification and rapid monitoring of these lipids represent a tool to assess therapeutic outcomes in SHARPIN-deficient mice and other mouse models of dermatitis and may have diagnostic utility in atopic dermatitis.

Lipid abnormalities in atopic skin are driven by type 2 cytokines

Lipids in the stratum corneum of atopic dermatitis (AD) patients differ substantially in composition from healthy subjects. We hypothesized that hyperactivated type 2 immune response alters AD skin lipid metabolism. We have analyzed stratum corneum lipids from nonlesional and lesional skin of AD subjects and IL-13 skin-specific Tg mice. We also directly examined the effects of IL-4/IL-13 on human keratinocytes in vitro. Mass spectrometric analysis of lesional stratum corneum from AD subjects and IL-13 Tg mice revealed an increased proportion of short-chain (N-14:0 to N-24:0) NS ceramides, sphingomyelins, and 14:0-22:0 lysophosphatidylcholines (14:0-22:0 LPC) with a simultaneous decline in the proportion of corresponding long-chain species (N-26:0 to N-32:0 sphingolipids and 24:0-30:0 LPC) when compared with healthy controls. An increase in short-chain LPC species was also observed in nonlesional AD skin. Similar changes were observed in IL-4/IL-13-driven responses in Ca2+-differentiated human keratinocytes in vitro, all being blocked by STAT6 silencing with siRNA. RNA sequencing analysis performed on stratum corneum of AD as compared with healthy subjects identified decreased expression of fatty acid elongases ELOVL3 and ELOVL6 that contributed to observed changes in atopic skin lipids. IL-4/IL-13 also inhibited ELOVL3 and ELOVL6 expression in keratinocyte cultures in a STAT6-dependent manner. Downregulation of ELOVL3/ELOVL6 expression in keratinocytes by siRNA decreased the proportion of long-chain fatty acids globally and in sphingolipids. Thus, our data strongly support the pathogenic role of type 2 immune activation in AD skin lipid metabolism.

Bioactive Lipid Mediator Profiles in Human Psoriasis Skin and Blood

Psoriasis is a chronic immune-mediated disease that represents a unique model for investigating inflammation at local and systemic levels. Bioactive lipid mediators (LMs) are potent compounds reported to play a role in the development and resolution of inflammation. Currently, it is not known to what extent these LMs are involved in psoriasis pathophysiology and related metabolic dysfunction. Here, we use targeted and untargeted liquid chromatography-tandem mass spectrometry approaches to quantify LMs in skin and peripheral blood from psoriasis patients and compared them with those of healthy individuals. Lesional psoriasis skin was abundant in arachidonic acid metabolites, as 8-, 12- and 15-hydroxyeicosatetraenoic acid, compared with adjacent nonlesional and skin from healthy individuals. Additionally, a linoleic acid-derived LM, 13-hydroxyoctadecadienoic acid, was significantly increased compared with healthy skin (607.9 ng/g vs. 5.4 ng/g, P = 0.001). These psoriasis skin differences were accompanied by plasma decreases in antioxidant markers, including glutathione, and impaired lipolysis characterized by lower concentrations of primary and secondary bile acids. In conclusion, our study shows that psoriasis skin and blood have disease-specific phenotype profiles of bioactive LMs represented by omega-6 fatty acid-oxidized derivatives. These findings provide insights into psoriasis pathophysiology that could potentially contribute to new biomarkers and therapeutics.

Emerging Diagnostic and Therapeutic Potentials of Human Hair Proteomics

The use of noninvasive human substrates to interrogate pathophysiological conditions has become essential in the post- Human Genome Project era. Due to its high turnover rate, and its long term capability to incorporate exogenous and endogenous substances from the circulation, hair testing is emerging as a key player in monitoring long term drug compliance, chronic alcohol abuse, forensic toxicology, and biomarker discovery, among other things. Novel high-throughput 'omics based approaches like proteomics have been underutilized globally in comprehending human hair morphology and its evolving use as a diagnostic testing substrate in the era of precision medicine. There is paucity of scientific evidence that evaluates the difference in drug incorporation into hair based on lipid content, and very few studies have addressed hair growth rates, hair forms, and the biological consequences of hair grooming or bleaching. It is apparent that protein-based identification using the human hair proteome would play a major role in understanding these parameters akin to DNA single nucleotide polymorphism profiling, up to single amino acid polymorphism resolution. Hence, this work seeks to identify and discuss the progress made thus far in the field of molecular hair testing using proteomic approaches, and identify ways in which proteomics would improve the field of hair research, considering that the human hair is mostly composed of proteins. Gaps in hair proteomics research are identified and the potential of hair proteomics in establishing a historic medical repository of normal and disease-specific proteome is also discussed.

Transcription Factor CTIP1/ BCL11A Regulates Epidermal Differentiation and Lipid Metabolism During Skin Development

The epidermal permeability barrier (EPB) prevents organisms from dehydration and infection. The transcriptional regulation of EPB development is poorly understood. We demonstrate here that transcription factor COUP-TF-interacting protein 1 (CTIP1/BCL11A; hereafter CTIP1) is highly expressed in the developing murine epidermis. Germline deletion of Ctip1 (Ctip1^−/−) results in EPB defects accompanied by compromised epidermal differentiation, drastic reduction in profilaggrin processing, reduced lamellar bodies in granular layers and significantly altered lipid composition. Transcriptional profiling of Ctip1^−/− embryonic skin identified altered expression of genes encoding lipid-metabolism enzymes, skin barrier-associated transcription factors and junctional proteins. CTIP1 was observed to interact with genomic elements within the regulatory region of the gene encoding the differentiation-associated gene, Fos-related antigen2 (Fosl2) and lipid-metabolism-related gene, Fatty acid elongase 4 (Elvol4), and the expression of both was altered in Ctip1^−/− mice. CTIP1 appears to play a role in EPB establishment of via direct or indirect regulation of a subset of genes encoding proteins involved in epidermal differentiation and lipid metabolism. These results identify potential, CTIP1-regulated avenues for treatment of skin disorders involving EBP defects.

Lipidomics profiling reveals the role of glycerophospholipid metabolism in psoriasis

Psoriasis is a common and chronic inflammatory skin disease that is complicated by gene-environment interactions. Although genomic, transcriptomic, and proteomic analyses have been performed to investigate the pathogenesis of psoriasis, the role of metabolites in psoriasis, particularly of lipids, remains unclear. Lipids not only comprise the bulk of the cellular membrane bilayers but also regulate a variety of biological processes such as cell proliferation, apoptosis, immunity, angiogenesis, and inflammation. In this study, an untargeted lipidomics approach was used to study the lipid profiles in psoriasis and to identify lipid metabolite signatures for psoriasis through ultra-performance liquid chromatography-tandem quadrupole mass spectrometry. Plasma samples from 90 participants (45 healthy and 45 psoriasis patients) were collected and analyzed. Statistical analysis was applied to find different metabolites between the disease and healthy groups. In addition, enzyme-linked immunosorbent assay was performed to validate differentially expressed lipids in psoriatic patient plasma. Finally, we identified differential expression of several lipids including lysophosphatidic acid (LPA), lysophosphatidylcholine (LysoPC), phosphatidylinositol (PI), phosphatidylcholine (PC), and phosphatidic acid (PA); among these metabolites, LPA, LysoPC, and PA were significantly increased, while PC and PI were down-regulated in psoriasis patients. We found that elements of glycerophospholipid metabolism such as LPA, LysoPC, PA, PI, and PC were significantly altered in the plasma of psoriatic patients; this study characterizes the circulating lipids in psoriatic patients and provides novel insight into the role of lipids in psoriasis.

Analytical Techniques in Lipidomics: State of the Art

Current studies related to lipid identification and determination, or lipidomics in biological samples, are one of the most important issues in modern bioanalytical chemistry. There are many articles dedicated to specific analytical strategies used in lipidomics in various kinds of biological samples. However, in such literature, there is a lack of articles dedicated to a comprehensive review of the actual analytical methodologies used in lipidomics. The aim of this article is to characterize the lipidomics methods used in modern bioanalysis according to the methodological point of view: (1) chromatography/separation methods, (2) spectroscopic methods and (3) mass spectrometry and also hyphenated methods. In the first part, we discussed thin layer chromatography (TLC), high-pressure liquid chromatography (HPLC), gas chromatography (GC) and capillary electrophoresis (CE). The second part includes spectroscopic techniques such as Raman spectroscopy (RS), Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR). The third part is a synthetic review of mass spectrometry, matrix-assisted laser desorption/ionization (MALDI), hyphenated methods, which include liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS) and also multidimensional techniques. Other aspects are the possibilities of the application of the described methods in lipidomics studies. Due to the fact that the exploration of new methods of lipidomics analysis and their applications in clinical and medical studies are still challenging for researchers working in life science, we hope that this review article will be very useful for readers.

Plasma Lipid Profiling of Patients with Chronic Ocular Complications Caused by Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis

Stevens-Johnson syndrome (SJS) and its severe variant, toxic epidermal necrolysis (TEN), are drug-induced acute inflammatory vesiculobullous reactions of the skin and mucous membranes, including the ocular surface. Even after recovery from skin symptoms, some SJS/TEN patients continue to suffer with severe ocular complications (SOCs). Therefore, this study aims to understand the pathophysiology of chronic SOCs. Because plasma lipid profiling has emerged as a useful tool to understand pathophysiological alterations in the body, we performed plasma lipid profiling of 17 patients who suffered from SJS/TEN-associated chronic SOCs. A lipidomics approach yielded 386 lipid molecules and demonstrated that plasma levels of inflammatory oxylipins increased in patients with SJS/TEN-associated chronic SOCs. In addition, oxidized phosphatidylcholines and ether-type diacylglycerols increased in the patients with chronic SOCs, while phosphoglycerolipids decreased. When we compared these lipidomic profiles with those of patients with atopic dermatitis, we found that patients with chronic SOCs, specifically, had decreased levels of ether-type phosphatidylcholines (ePCs) containing arachidonic acid (AA), such as PC(18:0e/20:4) and PC(20:0e/20:4). To confirm our finding, we recruited additional patients, who suffered from SOC associated with SJS/TEN (up to 51 patients), and validated the decreased plasma levels of AA-containing ePCs. Our study provides insight into the alterations of plasma lipidomic profiles in chronic SOCs and into the pathophysiology of SJS/TEN-associated chronic SOCs.

The 'omics' revolution: redefining the understanding and treatment of allergic skin diseases

PURPOSE OF REVIEW

To evaluate how the genomic, transcriptomic, and proteomic profiles of allergic skin diseases, like atopic dermatitis and allergic contact dermatitis, contribute to their understanding and promote their therapeutic development.

RECENT FINDINGS

The '-omics' revolution has facilitated the quantification of inflammatory skin diseases at the molecular level, expanding our understanding of disease pathogenesis. It has also greatly expanded once-limited treatment options and improved the ability to define posttreatment improvements, beyond clinical scores. The findings on the genomic/transcriptomic level are also complemented by proteomic data, contributing to the understanding of the later changes taking place in the final stages of protein formation. Atopic dermatitis is defined as a Th2/Th22 polarized disease with some contributions of Th17 and Th1 pathways. In atopic dermatitis, studies of biologics and small molecules, targeting specific pathways upregulated in atopic dermatitis, seem to provide well tolerated alternatives to conventional immunosuppressive therapies (i.e. corticosteroids and cyclosporine A), particularly for severe patients. Allergic contact dermatitis is defined as having Th1/Th17-centered inflammation, especially with nickel-induced disease, but additional pathways, including Th2 and Th22, are upregulated with other allergens (i.e. fragrance).

SUMMARY

Supplementing studies of allergic skin diseases with '-omics' approaches are transforming the pathogenic understanding, diagnosis and, perhaps, also the treatment of these diseases.

Lipidomics: Techniques, Applications, and Outcomes Related to Biomedical Sciences

Lipidomics is a newly emerged discipline that studies cellular lipids on a large scale based on analytical chemistry principles and technological tools, particularly mass spectrometry. Recently, techniques have greatly advanced and novel applications of lipidomics in the biomedical sciences have emerged. This review provides a timely update on these aspects. After briefly introducing the lipidomics discipline, we compare mass spectrometry-based techniques for analysis of lipids and summarize very recent applications of lipidomics in health and disease. Finally, we discuss the status of the field, future directions, and advantages and limitations of the field.