Relationship of ceramide-, and free fatty acid-cholesterol ratios in the stratum corneum with skin barrier function of normal, atopic dermatitis lesional and non-lesional skins

Association of the skin microbiome with the biomechanical scar properties in patients with burns

BACKGROUND AND OBJECTIVES

Skin microbiome dysbiosis can cause skin barrier dysfunction and stimulate scar property change. Skin barrier disruption post-burn injury leads to an imbalance in skin microbe diversity and distribution. We aimed to examine the changes in the skin microbiome of re-epithelialized burn scars.

MATERIAL AND METHODS

Twenty three patients were enrolled between January 2020 and July 2022. Twenty-six (13 Scar 1, immediately after complete wound healing; and 13 Scar 2, 3 months after complete wound healing) of seventy-eight scar skin samples (39 Scar 1 and 39 scar 2) qualified for analysis. Microbial community analysis was performed. Biomechanical scar properties of each patient and their correlation with skin microbiome were investigated.

RESULTS

The α-diversity of the scarred skin microbiome increased with time (Shannon's index, p = 0.029; Simpson's index, p = 0.009). The linear discriminant analysis effect size results showed that Bacteroides abundance decreased in scars after 3 months, whereas Campylobacter and Cutibacterium abundance increased. Campylobacter and Cutibacterium negatively and positively correlated with the final distensibility gross and biological elasticity, respectively. These results were consistent with the changes in the biomechanical properties of scars.

CONCLUSION

The scar skin microbial communities in patients with burns changed with biomechanical scar properties over time, and specific skin microorganisms correlated with biomechanical scar dynamics at the genus level.

Improving Sensitive Skin Diagnosis by Integrating Diagnostic Questionnaires, Lactic Acid Sting Test, and Lipid Profiling

BACKGROUND

Sensitive skin (SS) is characterized by subjective symptoms, including burning, stinging, and itching, which occur with the use of cosmetics. Over 40% of the population experiences skin sensitivity, yet no clear standards for evaluating SS have been established.

AIM

To diagnose SS by combining lactic acid sting test (LAST), skin irritation tests, and biophysical measurements with a developed questionnaire, validating the characteristics through quantitative analysis of natural moisturizing factors (NMF) and lipid profiles.

METHODS

The diagnostic questionnaires were administered to 975 healthy women from Beijing and Shanghai to evaluate their skin sensitivity. Among these, 154 participants from Beijing and 153 from Shanghai underwent physiological testing, which included a patch test, LAST, and biophysical assessments. For stratum corneum (SC) sampling, D-squame tape was used, and the levels of NMFs and lipids were quantitatively analyzed using UPLC-MS/MS.

RESULTS

The diagnostic questionnaires, especially when combined with LAST, improved sensitivity and reduced false negatives for identifying SS. The SS group exhibited notable differences compared to the NS group, including higher hydration and lower pH on the forehead, reduced ceramide and fatty acid levels, and fewer amino acids in the stratum corneum, although skin irritation scores were not significantly different.

CONCLUSIONS

The combination of our diagnostic questionnaire with LAST was found to effectively distinguish key characteristics of SS. This methodology offers a valuable approach for enhancing the diagnosis and assessment of SS, which could, in turn, aid in the development of more targeted products for SS.

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.

Skin Lipid Barrier: Structure, Function and Metabolism

Lipids are important skin components that provide, together with proteins, barrier function of the skin. Keratinocyte terminal differentiation launches unique metabolic changes to lipid metabolism that result in the predominance of ceramides within lipids of the stratum corneum (SC)-the very top portion of the skin. Differentiating keratinocytes form unique ceramides that can be found only in the skin, and generate specialized extracellular structures known as lamellae. Lamellae establish tight hydrophobic layers between dying keratinocytes to protect the body from water loss and also from penetration of allergens and bacteria. Genetic and immunological factors may lead to the failure of keratinocyte terminal differentiation and significantly alter the proportion between SC components. The consequence of such changes is loss or deterioration of skin barrier function that can lead to pathological changes in the skin. This review summarizes our current understanding of the role of lipids in skin barrier function. It also draws attention to the utility of testing SC for lipid and protein biomarkers to predict future onset of allergic skin diseases.

Skin hydration modulatory activities of Ficus deltoidea extract

Ficus deltoidea was known for its potent antioxidant, anti-melanogenic and photoprotective skin barrier activities. These properties are contributed by its biomarkers which are vitexin and isovitexin. This study aims to optimize the yield of methanolic extraction of Ficus deltoidea leaves (EFD) and evaluate their effects on skin barrier function and hydration. For optimization, Box-Behnken design was utilized to investigate the effects of methanol concentration, sonication time, and solvent-to-sample ratio on the yields of vitexin and isovitexin in EFD. The optimal yields obtained were 32.29 mg/g for vitexin and 35.87 mg/g for isovitexin. The optimum extraction conditions were 77.66% methanol concentration, 20.03 min sonication time, and 19.88 mL/g solvent-to-sample ratio. The quantitative real-time polymerase chain reaction was utilized to measure variant marker genes of transglutaminase-1, caspase 14, ceramide synthase 3, involucrin, and filaggrin of EFD-induced keratinocyte differentiation by in vitro study. Exposure to EFD has elevated the mRNA levels of all tested marker genes by 0.7-9.2 folds. Then, in vivo efficacy study was conducted on 20 female subjects for 14 days to evaluate skin biophysical assessment of hydration. EFD topical formulation treatment successfully increased skin hydration on day 7 (43.74%) and day 14 (47.23%). In silico study by molecular docking was performed to identify intermolecular binding interactions of vitexin and isovitexin with the interested proteins of tested marker genes. The result of molecular docking to the interested proteins revealed a similar trend with real-time PCR data. In conclusion, EFD potentially enhanced the skin barrier function and hydration of human skin cells.

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.

Diagnosing Atopic Dermatitis in Skin of Color

Atopic dermatitis (AD) is a pruritic inflammatory skin disease that disproportionately affects skin of color patients. African American, Asian, and Hispanic patients carry disproportionate disease burdens, with increased prevalence, disease severity, and health care utilization. AD has a unique clinical presentation in skin of color patients, often with greater extensor involvement, dyspigmentation, and papular and lichenified presentations. Erythema is also more difficult to appreciate and can result in an underappreciation of disease severity in skin of color patients. In this review, we highlight the important manifestations of AD across all skin types, including nuances in treatment.

Elucidating collective translocation of nanoparticles across the skin lipid matrix: a molecular dynamics study

The top layer of skin, the stratum corneum, provides a formidable barrier to the skin. Nanoparticles are utilized and further explored for personal and health care applications related to the skin. In the past few years, several researchers have studied the translocation and permeation of nanoparticles of various shapes, sizes, and surface chemistry through cell membranes. Most of these studies focused on a single nanoparticle and a simple bilayer system, whereas skin has a highly complex lipid membrane architecture. Moreover, it is highly unlikely that a nanoparticle formulation applied on the skin will not have multiple nanoparticle-nanoparticle and skin-nanoparticle interactions. In this study, we have utilized coarse-grained MARTINI molecular dynamics simulations to assess the interactions of two types (bare and dodecane-thiol coated) of nanoparticles with two models (single bilayer and double bilayer) of skin lipid membranes. The nanoparticles were found to be partitioned from the water layer to the lipid membrane as an individual entity as well as in the cluster form. It was discovered that each nanoparticle reached the interior of both single bilayer and double bilayer membranes irrespective of the nanoparticle type and concentration, though coated particles were observed to efficiently traverse across the bilayer when compared with bare particles. The coated nanoparticles also created a single large cluster inside the membrane, whereas the bare nanoparticles were found in small clusters. Both the nanoparticles exhibited preferential interactions with cholesterol molecules present in the lipid membrane as compared to other lipid components of the membrane. We have also observed that the single membrane model exhibited unrealistic instability at moderate to higher concentrations of nanoparticles, and hence for translocation study, a minimum double bilayer model should be employed.

Investigating the nanostructure of a CER[NP]/CER[AP]-based stratum corneum lipid matrix model: A combined neutron diffraction & molecular dynamics simulations approach

The human skin provides a physiochemical and biological protective barrier due to the unique structure of its outermost layer known as the Stratum corneum. This layer consists of corneocytes and a multi-lamellar lipid matrix forming a composite, which is a major determining factor for the barrier function of the Stratum corneum. A substantiated understanding of this barrier is necessary, as controlled breaching or modulation of the same is also essential for various health and personal care applications such as topical drug delivery and cosmetics to a name few. In this study, we discuss the state-of-the-art of neutron diffraction techniques, using specifically deuterated lipids, combined with the information obtained from molecular models using molecular dynamics simulations, to understand the structure and barrier function of the Stratum corneum lipid matrix. As an example, the effect of ceramide concentration on a lipid lamella system consisting of CER[NP]/CER[AP]/Cholesterol/free fatty acid (deprotonated) is studied. This study demonstrates the usefulness of the combined approach of neutron diffraction and molecular dynamics simulations for effective analysis of the model systems created for the Stratum corneum lipid matrix. The optimization of force fields by comparison with experimental data is furthermore an important step in the direction of providing a predictive quality.

Current knowledge of the implication of lipid mediators in psoriasis

The skin is an organ involved in several biological processes essential to the proper functioning of the organism. One of these essential biological functions of the skin is its barrier function, mediated notably by the lipids of the stratum corneum, and which prevents both penetration from external aggression, and transepidermal water loss. Bioactive lipid mediators derived from polyunsaturated fatty acids (PUFAs) constitute a complex bioactive lipid network greatly involved in skin homeostasis. Bioactive lipid mediators derived from n-3 and n-6 PUFAs have well-documented anti- and pro-inflammatory properties and are recognized as playing numerous and complex roles in the behavior of diverse skin diseases, including psoriasis. Psoriasis is an inflammatory autoimmune disease with many comorbidities and is associated with enhanced levels of pro-inflammatory lipid mediators. Studies have shown that a high intake of n-3 PUFAs can influence the development and progression of psoriasis, mainly by reducing the severity and frequency of psoriatic plaques. Herein, we provide an overview of the differential effects of n-3 and n-6 PUFA lipid mediators, including prostanoids, hydroxy-fatty acids, leukotrienes, specialized pro-resolving mediators, N-acylethanolamines, monoacylglycerols and endocannabinoids. This review summarizes current findings on lipid mediators playing a role in the skin and their potential as therapeutic targets for psoriatic patients.

Adiponectin receptor agonist ameliorates cardiac lipotoxicity via enhancing ceramide metabolism in type 2 diabetic mice

Accumulation of lipids and their metabolites induces lipotoxicity in diabetic cardiomyopathy. Lowering ceramide concentration could reduce the impact of metabolic damage to target organs. Adiponectin improves lipotoxicity through its receptors (AdiopRs), which have sequence homology with ceramidase enzymes. Therefore, cardioprotective role of AdipoR agonism by AdipoRon was investigated. Sixteen-week-old male db/m and db/db mice were fed a diet containing AdipoRon for four weeks. Phenotypic and metabolic profiles with associated cellular signaling pathways involved in lipid metabolism were investigated in the mice heart and human cardiomyocytes to establish treatment effect of AdipoRon. AdipoRon ameliorated insulin resistance, fibrosis, M1-dominant inflammation, and apoptosis in association with reduced accumulations of free fatty acid, triglycerides, and TLR4-related ceramide in the heart. This resulted in overall reduction in the level of oxidative stress which ameliorated cardiac hypertrophy and its function. AdipoRon increased the expression of AdipoR1 and AdipoR2 via pAMPK/FoxO1-induced Akt phosphorylation resulting from a decrease in PP2A level. It also increased acid ceramidase activity which reduced ceramide and increased sphingosine-1 phosphate levels in the heart of db/db mice and cultured human cardiomyocytes. Consistent upregulation of AdipoRs and their downstream regulatory pathways involving pAMPK/PPARα/PGC-1α levels led to lipid metabolism enhancement, thereby improving lipotoxicity-induced peroxisome biogenesis and oxidative stress. AdipoRon might control oxidative stress, inflammation, and apoptosis in the heart through increased AdipoR expression, acid ceramidase activity, and activation of AMPK-PPARα/PGC-1α and related downstream pathways, collectively improving cardiac lipid metabolism, hypertrophy, and functional parameters.

Research Techniques Made Simple: Lipidomic Analysis in Skin Research

Although lipids are crucial molecules for cell structure, metabolism, and signaling in most organs, they have additional specific functions in the skin. Lipids are required for the maintenance and regulation of the epidermal barrier, physical properties of the skin, and defense against microbes. Analysis of the lipidome-the totality of lipids-is of similar complexity to those of proteomics or other omics, with lipid structures ranging from simple, linear, to highly complex structures. In addition, the ordering and chemical modifications of lipids have consequences on their biological function, especially in the skin. Recent advances in analytic capability (usually with mass spectrometry), bioinformatic processing, and integration with other dermatological big data have allowed researchers to increasingly understand the roles of specific lipid species in skin biology. In this paper, we review the techniques used to analyze skin lipidomics and epilipidomics.

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.

The Pathogenic and Therapeutic Implications of Ceramide Abnormalities in Atopic Dermatitis

Ceramides play an essential role in forming a permeability barrier in the skin. Atopic dermatitis (AD) is a common chronic skin disease associated with skin barrier dysfunction and immunological abnormalities. In patients with AD, the amount and composition of ceramides in the stratum corneum are altered. This suggests that ceramide abnormalities are involved in the pathogenesis of AD. The mechanism underlying lipid abnormalities in AD has not yet been fully elucidated, but the involvement of Th2 and Th1 cytokines is implicated. Ceramide-dominant emollients have beneficial effects on skin barrier function; thus, they have been approved as an adjunctive barrier repair agent for AD. This review summarizes the current understanding of the mechanisms of ceramide abnormalities in AD. Furthermore, the potential therapeutic approaches for correcting ceramide abnormalities in AD are discussed.

Development of a non-invasive method for skin cholesterol detection: pre-clinical assessment in atherosclerosis screening

BACKGROUND

Establishing a high-accuracy and non-invasive method is essential for evaluating cardiovascular disease. Skin cholesterol is a novel marker for assessing the risk of atherosclerosis and can be used as an independent risk factor of early assessment of atherosclerotic risk.

METHODS

We propose a non-invasive skin cholesterol detection method based on absorption spectroscopy. Detection reagents specifically bind to skin cholesterol and react with indicator to produce colored products, the skin cholesterol content can be obtained through absorption spectrum information on colored products detected by non-invasive technology. Gas chromatography is used to measure cholesterol extracted from the skin to verify the accuracy and reliability of the non-invasive test method. A total of 342 subjects were divided into normal group (n = 115), disease group (n = 110) and risk group (n = 117). All subjects underwent non-invasive skin cholesterol test. The diagnostic accuracy of the measured value was analyzed by receiver-operating characteristic (ROC) curve.

RESULTS

The proposed method is able to identify porcine skin containing gradient concentration of cholesterol. The values measured by non-invasive detection method were significantly correlated with gas chromatography measured results (r = 0.9074, n = 73, p < 0.001). Bland-Altman bias was - 72.78 ± 20.03 with 95% limits of agreement - 112.05 to - 33.51, falling within the prespecified clinically non-significant range. We further evaluated the method of patients with atherosclerosis and risk population as well as normal group, patients and risk atherosclerosis group exhibited higher skin cholesterol content than normal group (all P < 0.001). The area under the ROC curve for distinguishing Normal/Disease group was 0.8642 (95% confidence interval, 0.8138 to 0.9146), meanwhile, the area under the ROC curve for distinguishing Normal/Risk group was 0.8534 (95% confidence interval, 0.8034 to 0.9034).

CONCLUSIONS

The method demonstrated its capability of detecting different concentration of skin cholesterol. This non-invasive skin cholesterol detection system may potentially be used as a risk assessment tool for atherosclerosis screening, especially for a large population.

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.

The ceramide [NP]/[NS] ratio in the stratum corneum is a potential marker for skin properties and epidermal differentiation

BACKGROUND

Specific species of ceramides (Cer), major constituents of lipids in the stratum corneum (SC), are decreased and are correlated with SC barrier and water-holding functions in the skin of patients with atopic dermatitis (AD) or psoriasis (Pso). However, possible correlations between Cer subclass ratios and skin properties in barrier-disrupted skin and in healthy skin remain unclear. The objective of this study was to identify a new marker to evaluate skin properties and epidermal differentiation in SC not only in barrier-disrupted skin but also in healthy skin.

METHODS

The Cer subclass ratios in the SC of healthy control subjects and in patients with AD or Pso were evaluated. Correlations with candidate markers and facial skin features of healthy Japanese females (20-74 years old, n = 210) were investigated. Variations of markers during epidermal differentiation were studied in human epidermis and in cultured keratinocytes.

RESULTS

The ratios of Cer [NP]/[NS], Cer [NH]/[NS], Cer [NP]/[AS], Cer [NH]/[NS], Cer [NDS]/[AS], Cer [AH]/[AS] and Cer [EOP]/[AS] showed significant differences between non-lesional skin of AD patients and normal skin of healthy control subjects, as well as Pso patients and their healthy control subjects. The Cer [NP]/[NS] ratio was correlated with SC functional parameters (transepidermal water loss and capacitance) and with skin appearance (texture, scaling and color) even in the cheek skin of healthy female subjects. The Cer [NP]/[NS] ratio in the SC was approximately 18-times higher than in living keratinocytes, and it increased as they differentiated.

CONCLUSIONS

The Cer [NP]/[NS] ratio in the SC is a potential marker for skin properties and epidermal differentiation in barrier-disrupted skin as well as in healthy skin.

Lipidomic Profiling of the Epidermis in a Mouse Model of Dermatitis Reveals Sexual Dimorphism and Changes in Lipid Composition before the Onset of Clinical Disease

Atopic dermatitis (AD) is a multifactorial disease associated with alterations in lipid composition and organization in the epidermis. Multiple variants of AD exist with different outcomes in response to therapies. The evaluation of disease progression and response to treatment are observational assessments with poor inter-observer agreement highlighting the need for molecular markers. SHARPIN-deficient mice (Sharpin^cpdm) spontaneously develop chronic proliferative dermatitis with features similar to AD in humans. To study the changes in the epidermal lipid-content during disease progression, we tested 72 epidermis samples from three groups (5-, 7-, and 10-weeks old) of cpdm mice and their WT littermates. An agnostic mass-spectrometry strategy for biomarker discovery termed multiple-reaction monitoring (MRM)-profiling was used to detect and monitor 1,030 lipid ions present in the epidermis samples. In order to select the most relevant ions, we utilized a two-tiered filter/wrapper feature-selection strategy. Lipid categories were compressed, and an elastic-net classifier was used to rank and identify the most predictive lipid categories for sex, phenotype, and disease stages of cpdm mice. The model accurately classified the samples based on phospholipids, cholesteryl esters, acylcarnitines, and sphingolipids, demonstrating that disease progression cannot be defined by one single lipid or lipid category.

Pharmacological management of atopic dermatitis in the elderly

INTRODUCTION

The prevalence of atopic dermatitis (AD) in geriatric populations of industrialized countries is currently estimated at 3-4% and continues to increase. AD is associated with significant morbidity, increased susceptibility to infection, and symptoms of pruritus and pain. Treatments may negatively affect elderly patients; thus, plans should be optimized for this population.

AREAS COVERED

This review summarizes treatment options for AD in the elderly. A systematic review of the literature was conducted using the key terms atopic dermatitis, elderly, geriatric, systemic therapy, therapy, and topical therapy in PubMed. Searches yielded articles on skincare management and topical and systemic pharmacotherapies.

EXPERT OPINION

Proper use of moisturizer is crucial in all patients with AD. Topical corticosteroids are commonly prescribed; however, they carry an increased risk of adverse events such as skin atrophy. Systemic corticosteroids should be avoided in elderly patients due to questionable efficacy and increased adverse events. Topical calcineurin inhibitors and crisaborole are similarly efficacious with an excellent safety profile. Cyclosporine, azathioprine, methotrexate, and mycophenolate mofetil are systemic agents available for the treatment of refractory AD; however, insufficient data exist to indicate the superiority of any one agent. Dupilumab is a safe and efficacious injectable therapy in elderly patients.

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.

Rab25 Deficiency Perturbs Epidermal Differentiation and Skin Barrier Function in Mice

Rab25, a member of the Rab11 small GTPase family, is central to achieving cellular polarity in epithelial tissues. Rab25 is highly expressed in epithelial cells of various tissues including breast, vagina, cervix, the gastrointestinal tract, and skin. Rab25 plays key roles in tumorigenesis, mainly by regulating epithelial differentiation and proliferation. However, its role in skin physiology is relatively unknown. In this study, we demonstrated that Rab25 knock-out (KO) mice show a skin barrier dysfunction with high trans-epidermal water loss and low cutaneous hydration. To examine this observation, we investigated the histology and epidermal differentiation markers of the skin in Rab25 KO mice. Rab25 KO increased cell proliferation at the basal layer of epidermis, whereas the supra-basal layer remained unaffected. Ceramide, which is a critical lipid component for skin barrier function, was not altered by Rab25 KO in its distribution or amount, as determined by immunohistochemistry. Notably, levels of epidermal differentiation markers, including loricrin, involucrin, and keratins (5, 14, 1, and 10) increased prominently in Rab25 KO mice. In line with this, depletion of Rab25 with single hairpin RNA increased the expression of differentiation markers in a human keratinocyte cell line, HaCaT. Transcriptomic analysis of the skin revealed increased expression of genes associated with skin development, epidermal development, and keratinocyte differentiation in Rab25 KO mice. Collectively, these results suggested that Rab25 is involved in the regulation of epidermal differentiation and proliferation.

Lysates of a Probiotic, Lactobacillus rhamnosus, Can Improve Skin Barrier Function in a Reconstructed Human Epidermis Model

The main function of the skin is to protect the body from the external environment. The barrier function of the skin is mainly provided by the stratum corneum, which consists of corneocytes bound with the corneodesmosomes and lamellar lipids. Skin barrier proteins like loricrin and filaggrin also contribute to the skin barrier function. In various skin diseases, skin barrier dysfunction is a common symptom, and skin irritants like detergents or surfactants could also perturb skin barrier function. Many efforts have been made to develop strategies to improve skin barrier function. Here, we investigated whether the microfluidized lysates of Lactobacillus rhamnosus (LR), one of the most widely used probiotic species for various health benefits, may improve the skin barrier function in a reconstructed human epidermis, Keraskin™. Application of LR lysate on Keraskin™ increased the expression of tight junction proteins; claudin 1 and occludin as determined by immunofluorescence analysis, and skin barrier proteins; loricrin and filaggrin as determined by immunohistochemistry and immunofluorescence analysis and qPCR. Also, the cytotoxicity of a skin irritant, sodium lauryl sulfate (SLS), was alleviated by the pretreatment of LR lysate. The skin barrier protective effects of LR lysate could be further demonstrated by the attenuation of SLS-enhanced dye-penetration. LR lysate also attenuated the destruction of desmosomes after SLS treatment. Collectively, we demonstrated that LR lysate has protective effects on the skin barrier, which could expand the utility of probiotics to skin-moisturization ingredients.

Breaking the Itch-Scratch Cycle: Topical Options for the Management of Chronic Cutaneous Itch in Atopic Dermatitis

Chronic itch is an unpleasant sensation that triggers a desire to scratch that lasts for six weeks or more. It is a major diagnostic symptom of myriad diseases, including atopic dermatitis for which it is the most prominent feature. Chronic itch can be hugely debilitating for the sufferer, damaging in terms of both the monetary cost of treatment and its socioeconomic effects, and few treatment options exist that can adequately control it. Corticosteroids remain the first line treatment strategy for atopic dermatitis, but due to the risks associated with long-term use of corticosteroids, and the drawbacks of other topical options such as topical calcineurin inhibitors and capsaicin, topical options for itch management that are efficacious and can be used indefinitely are needed. In this review, we detail the pathophysiology of chronic pruritus, its key features, and the disease most commonly associated with it. We also assess the role of the skin and its components in maintaining a healthy barrier function, thus reducing dryness and the itch sensation. Lastly, we briefly detail examples of topical options for the management of chronic pruritus that can be used indefinitely, overcoming the risk associated with long-term use of corticosteroids.

Effect of Ceramide Tail Length on the Structure of Model Stratum Corneum Lipid Bilayers

Lipid bilayers composed of non-hydroxy sphingosine ceramide (CER NS), cholesterol (CHOL), and free fatty acids (FFAs), which are components of the human skin barrier, are studied via molecular dynamics simulations. Since mixtures of these lipids exist in dense gel phases with little molecular mobility at physiological conditions, care must be taken to ensure that the simulations become decorrelated from the initial conditions. Thus, we propose and validate an equilibration protocol based on simulated tempering, in which the simulation takes a random walk through temperature space, allowing the system to break out of metastable configurations and hence become decorrelated from its initial configuration. After validating the equilibration protocol, which we refer to as random-walk molecular dynamics, the effects of the lipid composition and ceramide tail length on bilayer properties are studied. Systems containing pure CER NS, CER NS + CHOL, and CER NS + CHOL + FFA, with the CER NS fatty acid tail length varied within each CER NS-CHOL-FFA composition, are simulated. The bilayer thickness is found to depend on the structure of the center of the bilayer, which arises as a result of the tail-length asymmetry between the lipids studied. The hydrogen bonding between the lipid headgroups and with water is found to change with the overall lipid composition, but is mostly independent of the CER fatty acid tail length. Subtle differences in the lateral packing of the lipid tails are also found as a function of CER tail length. Overall, these results provide insight into the experimentally observed trend of altered barrier properties in skin systems where there are more CERs with shorter tails present.

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.

IFN-γ Reduces Epidermal Barrier Function by Affecting Fatty Acid Composition of Ceramide in a Mouse Atopic Dermatitis Model

IFN-γ is detected in chronic lesions of atopic dermatitis (AD); however, its specific role remains to be elucidated. An impaired stratum corneum barrier function is a hallmark of AD, and it is associated with a reduction in ceramides with long-chain fatty acids (FAs) in the stratum corneum. FA elongases, ELOVL1 and ELOVL4, are essential for the synthesis of these ceramides, together with ceramide synthase 3 (CerS3). We have previously shown that IFN-γ, but not other cytokines, induced the downregulation of these enzymes in cultured keratinocytes. Our aim was to investigate the in vivo role of IFN-γ in the lesional skin of AD by analyzing mouse dermatitis models. The local mRNA expression of IFN-γ increased in mite fecal antigen-induced AD-like dermatitis in NC/Nga mice but not in imiquimod-induced psoriasis-like dermatitis in BALB/c mice. The mRNA expression of ELOVL1 and ELOVL4 significantly decreased in AD-like dermatitis, whereas ELOVL1 increased in psoriasis-like dermatitis. The expression of CerS3 increased slightly in AD-like dermatitis, but it increased by 4.6-fold in psoriasis-like dermatitis. Consistently, the relative amount of ceramides with long-chain FAs decreased in AD-like dermatitis but not in psoriasis-like dermatitis. These results suggest that IFN-γ in the lesional skin may reduce ceramides with long-chain FAs by decreasing the expression of ELOVL. Thus, IFN-γ may contribute to the chronicity of AD by impairing barrier function.

Influence of Oral Administration of Lactic Acid Bacteria Metabolites on Skin Barrier Function and Water Content in a Murine Model of Atopic Dermatitis

The effects of orally administered lactic acid bacteria metabolites on skin were studied using an atopic dermatitis-like murine model generated by feeding HR-AD to mice. Lactic acid bacteria metabolites were obtained by inoculating and culturing soy milk with 35 strains of 16 species of lactic acid bacteria. The atopic dermatitis-like murine model was generated by feeding HR-AD to HR-1 mice for 40 days. The skin condition of HR-AD-fed mice worsened compared with normal mice, showing reduced water content in the stratum corneum, increased transepidermal water loss (TEWL), reduced ceramide AP content in the stratum corneum, and increased epidermis thickness. When HR-AD-fed mice were orally administered a raw liquid containing lactic acid bacteria metabolites, water content in the stratum corneum, TEWL, ceramide AP content in the stratum corneum, and epidermis thickness improved. To determine the active components responsible for these effects, filtrate, residue, and lipid components extracted from the raw liquid containing lactic acid bacteria metabolites were examined. While water-soluble components and residue obtained after filtration had no effects, the lipid fraction showed similar effects to the raw liquid. These findings suggest that lactic acid bacteria metabolites improve skin injury in an atopic dermatitis-like murine model.

Skin Ceramide Profile in Children With Atopic Dermatitis

BACKGROUND

Atopic dermatitis (AD) is a common disease, which involves a disruption of the skin barrier function. Skin ceramide (CER) composition, which plays crucial roles in maintaining the barrier function of the stratum corneum, is changed in patients with AD.

OBJECTIVE

The aim of this study was to identify and quantify skin CER subclasses in association with disease severity in pediatric patients with AD.

METHODS

Two hundred thirteen patients were entered into the observational study. We compared their CER profiles using normal-phase high-performance liquid chromatography coupled with dynamic multiple reaction monitoring mass spectrometry.

RESULTS

In total, 12 subclasses of CERs were identified. We found that 2 subclasses, that is, CER[AS] and CER[NS], were elevated (P = 0.007 and 0.012, respectively) and correlated with Severity Scoring of Atopic Dermatitis (P = 0.004 and 0.004, respectively).

CONCLUSIONS

Skin CER abundances are changed in children with AD compared with control subjects.

State of the art in Stratum Corneum research: The biophysical properties of ceramides

This review is summarizing an important part of the state of the art in stratum corneum research. A complete overview on discoveries about the general biophysical and physicochemical properties of the known ceramide species' is provided. The ceramides are one of the three major components of the lipid matrix and mainly govern its properties and structure. They are shown to exhibit very little redundancy, despite the minor differences in their chemical structure. The results are discussed, compared to each other as well as the current base of knowledge. New interesting aspects and concepts are concluded or suggested. A novel interpretation of the 3-dimensional structure of the lipid matrix and its influence on the barrier function will be discussed. The most important conclusion is the presentation of a new and up to date theoretical model of the nanostructure of the short periodicity phase. The model suggests three perpendicular layers: The rigid head group region, the rigid chain region and, a liquid-like overlapping middle layer. The general principle of the skin barrier function is highlighted in regard to this structure and the ceramides biophysical and physicochemical properties. As a result of these considerations, the entropy vs. enthalpy principle is introduced, shedding light on the function as well as the effectiveness of the skin barrier. Additionally, general ideas to effectively overcome this barrier principle for dermal and transdermal delivery of actives or how to use it for specific targeting of the stratum corneum are proposed.

Adiponectin receptor agonist AdipoRon decreased ceramide, and lipotoxicity, and ameliorated diabetic nephropathy

BACKGROUND

Adiponectin is known to take part in the regulation of energy metabolism. AdipoRon, an orally-active synthetic adiponectin agonist, binds to both adiponectin receptors (AdipoR)1/R2 and ameliorates diabetic complications. Among the lipid metabolites, the ceramide subspecies of sphingolipids have been linked to features of lipotoxicity, including inflammation, cell death, and insulin resistance. We investigated the role of AdipoRon in the prevention and development of type 2 diabetic nephropathy.

METHODS

AdipoRon (30 mg/kg) was mixed into the standard chow diet and provided to db/db mice (db + AdipoRon, n = 8) and age-matched male db/m mice (dm + AdipoRon, n = 8) from 17 weeks of age for 4 weeks. Control db/db (db cont, n = 8) and db/m mice (dm cont, n = 8) were fed a normal diet of mouse chow.

RESULTS

AdipoRon-fed db/db mice showed a decreased amount of albuminuria and lipid accumulation in the kidney with no significant changes in serum adiponectin, glucose, and body weight. Restoring expression of adiponectin receptor-1 and -2 in the renal cortex was observed in db/db mice with AdipoRon administration. Consistent up-regulation of phospho-Thr¹⁷² AMP-dependent kinase (AMPK), peroxisome proliferative-activated receptor α (PPARα), phospho-Thr⁴⁷³ Akt, phospho-Ser⁷⁹Acetyl-CoA carboxylase (ACC), and phospho-Ser¹¹⁷⁷ endothelial NO synthase (eNOS), and down-regulation of protein phosphatase 2A (PP2A), sterol regulatory element-binding protein-1c (SREBP-1c), and inducible nitric oxide synthase (iNOS) were associated within the same group. AdipoRon lowered cellular ceramide levels by activation of acid ceramidase, which normalized ceramide to sphingosine-1 phosphate (S1P) ratio. In glomerular endothelial cells (GECs) and podocytes, AdipoRon treatment markedly decreased palmitate-induced lipotoxicity, which ultimately ameliorated oxidative stress and apoptosis.

CONCLUSIONS

AdipoRon may prevent lipotoxicity in the kidney particularly in both GECs and podocytes through an improvement in lipid metabolism, as shown by the ratio of ceramide to sphingosines, and further contribute to prevent deterioration of renal function, independent of the systemic effects of adiponectin. The reduction in oxidative stress and apoptosis by AdipoRon provides protection against renal damage, thereby ameliorating endothelial dysfunction in type 2 diabetic nephropathy.

Impact of the ceramide subspecies on the nanostructure of stratum corneum lipids using neutron scattering and molecular dynamics simulations. Part I: impact of CER[NS]

For this study mixtures based on the ceramides [NS] (NS = non-hydroxy-sphingosine) and [AP] (AP = α-hydroxy-phytosphingosine) in a 2:1 and 1:2 ratio, together with cholesterol and lignoceric acid, were investigated. These mixtures are modelling the uppermost skin layer, the stratum corneum. Neutron diffraction, utilizing specifically deuterated ceramide molecules, was used to obtain a maximum amount of experimental detail. Highly detailed molecular dynamics simulations were used to generate even more information from the experimental data. It was possible to observe a single lamellar phase for both systems. They had a lamellar repeat distance of 5.43 ± 0.05 nm for the [NS]/[AP] 2:1 and a slightly shorter one of 5.34 ± 0.05 nm for the 1:2 system. The structure and water content was uninfluenced by excess humidity. Both the experimental and simulation data indicated slightly tilted ceramides, with their C24 chains overlapping in the lamellar mid-plane. This arrangement is well comparable to systems investigated before. The structure of both systems, except for the differing repeat distance, looks similar at first. However, on a smaller scale there were various distinct differences, demonstrating only low redundancy between the different ceramide species, despite only minor chemical differences. The mainly ceramide [AP] determined 1:2 system has a slightly smaller repeat distance. This is a result of a tighter arrangement of the lipids chain along the bilayer normal and increased overlapping of the long chains in the lamellar middle. For the CER[NS] some novel features could be shown, despite it being the overall most investigated ceramide. These include the low adaptability to changed lateral interactions, leading to an increased chain opening. This effect could explain its low miscibility with other lipids. The investigated model systems allows it to directly compare results from the literature which have used ceramide [NS] to the most recent studies using the phytosphingosine ceramides such as ceramide [AP].

Investigation of a CER[NP]- and [AP]-Based Stratum Corneum Modeling Membrane System: Using Specifically Deuterated CER Together with a Neutron Diffraction Approach

Neutron diffraction was used as a tool to investigate the lamellar as well as molecular nanostructure of ceramide-[NP]/ceramide-[AP]/cholesterol/lignoceric acid model systems with a nativelike 2:1 ratio and a 1:2 ratio to study the influence of the ceramide-[AP]. By using mixtures together with cholesterol and free fatty acids as well as a humidity and temperature chamber while measuring, natural conditions were simulated as closely as possible. Despite its simplicity, the system simulated the native stratum corneum lipid matrix fairly closely, showing a similar lamellar thickness with a repeat distance of 5.45 ± 0.1 nm and a similar arrangement with overlapping long C24 chains. Furthermore, despite the very minor chemical difference between ceramide-[NP] and ceramide-[AP], which is only a single OH group, it was possible to demonstrate substantial differences between the structural influence of the two ceramides. Ceramide-[AP] could be concluded to be arranged in such a way that its C24 chain in both ratios is somehow shorter than that of ceramide-[NP], not overlapping as much with the opposite lamellar leaflet. Furthermore, in the unnatural 1:2 ratio, the higher ceramide-[AP] content causes an increased tilt of the ceramide acyl chains. This leads to even less overlapping within the lamellar midplane, whereas the repeat distance stays the same as for the ceramide-[NP]-rich system. In this nativelike 2:1 ratio, the chains are arranged mostly straight, and the long C24 chains show a broad overlapping region in the lamellar midplane.

Determination of the influence of C24 D/(2R)- and L/(2S)-isomers of the CER[AP] on the lamellar structure of stratum corneum model systems using neutron diffraction

This study was able to investigate the different influence of the d- and l-ceramide [AP] on the lamellar as well as molecular nanostructure of stratum corneum simulating lipid model mixtures. In this case, neutron diffraction together with specifically deuterated ceramide was used as an effective tool to investigate the lamellar and the molecular nanostructure of the mixtures. It could clearly be demonstrated, that both isomers show distinctly different characteristics, even though the variation between both is only a single differently arranged OH-group. The l-ceramide [AP] promotes a crystalline like phase behaviour even if mixed with ceramide [NP], cholesterol and free fatty acids. The d-ceramide [AP] only shows crystalline-like features if mixed only with cholesterol and free fatty acids but adopts a native-like behaviour if additionally mixed with ceramide [NP]. It furthermore demonstrates that the l-ceramide [AP] should not be used for any applications concerning ceramide substitution. It could however possibly serve its own purpose, if this crystalline like behaviour has some kind of positive influence on the SC or can be utilized for any practical applications. The results obtained in this study demonstrate that the diastereomers of ceramide [AP] are an attractive target for further research because their influence on the lamellar as well as the nanostructure is exceptionally strong. Additionally, the results furthermore show a very strong influence on hydration of the model membrane. With these properties, the d-ceramide [AP] could be effectively used to simulate native like behaviour even in very simple mixtures and could also have a strong impact on the native stratum corneum as well as high relevance for dermal ceramide substitution. The unnatural l-ceramide [AP] on the other hand should be investigated further, to assess its applicability.

Etiology of epithelial barrier dysfunction in patients with type 2 inflammatory diseases

Epithelial barriers of the skin, gastrointestinal tract, and airway serve common critical functions, such as maintaining a physical barrier against environmental insults and allergens and providing a tissue interface balancing the communication between the internal and external environments. We now understand that in patients with allergic disease, regardless of tissue location, the homeostatic balance of the epithelial barrier is skewed toward loss of differentiation, reduced junctional integrity, and impaired innate defense. Importantly, epithelial dysfunction characterized by these traits appears to pre-date atopy and development of allergic disease. Despite our growing appreciation of the centrality of barrier dysfunction in initiation of allergic disease, many important questions remain to be answered regarding mechanisms disrupting normal barrier function. Although our external environment (proteases, allergens, and injury) is classically thought of as a principal contributor to barrier disruption associated with allergic sensitization, there is a need to better understand contributions of the internal environment (hormones, diet, and circadian clock). Systemic drivers of disease, such as alterations of the endocrine system, metabolism, and aberrant control of developmental signaling, are emerging as new players in driving epithelial dysfunction and allergic predisposition at various barrier sites. Identifying such central mediators of epithelial dysfunction using both systems biology tools and causality-driven laboratory experimentation will be essential in building new strategic interventions to prevent or reverse the process of barrier loss in allergic patients.

Clinical categories of exaggerated skin reactions to mosquito bites and their pathophysiology

Mosquito bites are skin irritating reactions, which usually resolve spontaneously without intensive medical care. However, in certain situations, mosquito bites may form a more vicious reaction, sometimes accompanying fever and systemic symptoms. In such cases, the presence of rare hematological disorders, abnormalities in eosinophils and/or association with Epstein-Barr virus (EBV) may underlie. Importantly, hypersensitivity to mosquito bites (HMB), which is characterized by necrotic skin reactions to mosquito bites with various systemic symptoms, is often observed in association with EBV infection and natural killer (NK) cell lymphoproliferative disorder. Exaggerated skin reaction to mosquito bites is also seen in Wells' syndrome. While strong Th2-skewing immune dysregulation is apparent in the patients, they also show robust CD4(+) T cell proliferation in response to mosquito salivary gland extracts, indicating close association between Wells' syndrome and mosquito bites. Similar skin reaction to mosquito bites is also noticed in certain types of B cell neoplasm, although the role of B cells in this peculiar reaction to mosquito bites is yet to be elucidated. In this review, we will discuss the current knowledge of exaggerated reaction toward mosquito bites seen in conjunction with these unique hematological disorders, and examine the scientific studies and observations reported in previous literatures to organize our current understanding of the pathogenesis of this distinct disorder.

Chain Length of Free Fatty Acids Influences the Phase Behavior of Stratum Corneum Model Membranes

The skin, the largest organ of the human body, forms a flexible interface between our internal and external environment that protects our organism from exogenous compounds as well as excessive water loss. The stratum corneum (SC), the outermost layer of mammal epidermis, is mainly responsible for the skin impermeability. The SC is formed by corneocytes embedded in a lipid matrix, which is mostly constituted of ceramides (Cer), free fatty acids (FFA), and cholesterol (Chol), organized in two coexisting crystalline lamellar phases. This arrangement of lipids is crucial to skin barrier function. The aim of this paper is to determine the impact of FFA chain length on the phase behavior of SC model lipid membranes using solid-state deuterium NMR and IR spectroscopy. We studied ternary mixtures of N-lignoceroyl-d-erythro-sphingosine (Cer24), cholesterol, and palmitic (FFA16) or lignoceric (FFA24) acid in an equimolar ratio. This proportion replicates the lipid composition found in the SC lipid matrix. Our studies revealed that the phase behavior of Cer24/FFA/Chol ternary mixtures is strongly affected by the length of the FFA. We found the formation of phase-separated crystalline lipid domains when using palmitic acid whereas the use of lignoceric acid results in a more homogeneous mixture. In addition, it was observed that mixtures with lignoceric acid form a gel phase, a very unusual feature for SC model mixtures.