N-Acyl ethanolamide and eicosanoid involvement in irritant dermatitis

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

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

Comparative Study of Healthy Older and Younger Adults Shows They Have the Same Skin Concentration of Vitamin D3 Precursor, 7-Dehydrocholesterol, and Similar Response to UVR

Vitamin D3 synthesis in human skin is initiated by solar ultraviolet radiation (UVR) exposure of precursor 7-dehydrocholesterol (7DHC), but influence of age on the early stage of vitamin D3 metabolism is uncertain. We performed a prospective standardised study in healthy ambulant adults aged ≥65 and ≤40 years examining (1) if baseline skin 7DHC concentration differs between younger and older adults and (2) the impact of older age on serum vitamin D3 response to solar simulated UVR. Eleven younger (18-40 years) and 10 older (65-89 years) adults, phototype I-III, received low-dose UVR (95% UVA, 5% UVB, 1.3 SED) to ~35% of the body surface area. Biopsies were taken for 7DHC assay from unexposed skin, skin immediately and 24 h post-UVR, and blood sampled at baseline, 24 h and 7 d post-UVR for vitamin D3 assay. Samples were analysed by HPLC-MS/MS. Baseline skin 7DHC (mean ± SD) was 0.22 ± 0.07 and 0.25 ± 0.08 µg/mg in younger versus older adults (no significant difference). Baseline serum vitamin D3 concentration was 1.5 ± 1.5 and 1.5 ± 1.7 nmol/L in younger versus older adults, respectively, and showed a significant increase in both groups post-UVR (no significant differences between age groups). Thus, skin 7DHC concentration was not a limiting factor for vitamin D3 production in older relative to younger adults. This information assists public health guidance on sun exposure/vitamin D nutrition, with particular relevance to the growing populations of healthy ambulant adults ≥65 years.

Dietary Supplementation with Nervonic Acid Ameliorates Cerebral Ischemia-Reperfusion Injury by Modulating of Gut Microbiota Composition-Fecal Metabolites Interaction

SCOPE

Cerebral ischemia-reperfusion (IR) injury stands as a prominent global contributor to disability and mortality. Nervonic acid (NA), a bioactive elongated monounsaturated fatty acid, holds pivotal significance in human physiological well-being. This research aims to explore the prophylactic effects and fundamental mechanisms of NA in a rat model of cerebral IR injury.

METHODS AND RESULTS

Through the induction of middle cerebral artery occlusion, this study establishes a rat model of cerebral IR injury and comprehensively assesses the pharmacodynamic impacts of NA pretreatment. This evaluation involves behavioral analyses, histopathological examinations, and quantification of serum markers. Detailed mechanisms of nervonic acid's prophylactic effects are revealed through fecal metabolomics and 16S rRNA sequencing analyses. Our findings robustly support nervonic acid's capacity to ameliorate neurological impairments in rats afflicted with cerebral IR injury. Beyond its neurological benefits, NA demonstrates its potential by rectifying metabolic perturbations across diverse pathways, particularly those pertinent to unsaturated fatty acid metabolism. Additionally, NA emerges as a modulator of gut microbiota composition, notably by selectively enhancing vital genera like Lactobacillus.

CONCLUSION

These comprehensive findings highlight the potential of incorporating NA as a functional component in dietary interventions aimed at targeting cerebral IR injury.

Diseases from the Spectrum of Dermatitis and Eczema: Can "Omics" Sciences Help with Better Systematics and More Accurate Differential Diagnosis?

Researchers active in the field of inflammatory skin diseases from the spectrum of dermatitis and eczema are well aware of a considerable overlap in the clinical pictures and proposed sets of diagnostic criteria for these diseases, which can hardly be overcome through the clinical or epidemiological research. In effect, patients are included in studies based on vague and overlapping criteria, while heterogeneous study populations may, in turn, lead to non-representative outcomes and continued confusion. In this narrative review, a systematics of diseases from the spectrum of dermatitis and eczema is proposed based on the origins of causative factors and the pathomechanisms involved. Difficulties in differentiating between these diseases are discussed, and the extent to which advances in the "omics" sciences might help to overcome them is considered. Of all the "omics" research in this field, more than 90% of the published papers were devoted to atopic dermatitis, with a striking underrepresentation of other diseases from the spectrum of dermatitis and eczema, conditions which collectively exceed the rates of atopic dermatitis by far. A greater "omics" research effort is urgently needed to tackle other dermatitides, like allergic, irritant and protein contact dermatitis, as well as radiation, seborrheic, stasis or autoimmune dermatitis. Atopic dermatitis findings should be validated not only against healthy donors but also other dermatitides. A clinic-oriented approach is proposed for future "omics" studies in the field of dermatitis and eczema.

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.

Segregated functions of two cytosolic phospholipase A2 isoforms (cPLA2α and cPLA2ε) in lipid mediator generation

Among the phospholipase A₂ (PLA₂) superfamily, group IVA cytosolic PLA₂ (cPLA₂α) is currently attracting much attention as a central regulator of arachidonic acid (AA) metabolism linked to eicosanoid biosynthesis. Following cell activation, cPLA₂α selectively releases AA, a precursor of a variety of eicosanoids, from phospholipids in perinuclear membrane compartments. cPLA₂α-null mice display various phenotypes that could be largely explained by reduced eicosanoid signaling. In contrast, group IVE cPLA₂ε, another member of the cPLA₂ family, acts as a Ca²⁺-dependent N-acyltransferase rather than a PLA₂, thereby regulating the biosynthesis of N-acylethanolamines (NAEs), a unique class of lipid mediators with an anti-inflammatory effect. In response to Ca²⁺ signaling, cPLA₂ε translocates to phosphatidylserine-rich organelle membranes in the endocytic/recycling pathway. In vivo, cPLA₂ε is induced in keratinocytes of psoriatic skin, and its genetic deletion exacerbates psoriatic inflammation due to a marked reduction of NAE-related lipids. cPLA₂ε also contributes to NAE generation in several if not all mouse tissues. Thus, the two members of the cPLA₂ family, cPLA₂α and cPLA₂ε, catalyze distinct enzymatic reactions to mobilize distinct sets of lipid mediators, thereby differently regulating pathophysiological events in health and disease. Such segregation of the cPLA₂α-eicosanoid and cPLA₂ε-NAE pathways represents a new paradigm of research on PLA₂s and lipid mediators.

Group IVE cytosolic phospholipase A2 limits psoriatic inflammation by mobilizing the anti-inflammatory lipid N-acylethanolamine

Psoriasis is an inflammatory disorder characterized by keratinocyte hyper-proliferation and Th17-type immune responses. However, the roles of bioactive lipids and the regulation of their biosynthesis in this chronic skin disease are not fully understood. Herein, we show that group IVE cytosolic phospholipase A₂ (cPLA₂ ε/PLA2G4E) plays a counterregulatory role against psoriatic inflammation by producing the anti-inflammatory lipid N-acylethanolamine (NAE). Lipidomics analysis of mouse skin revealed that NAE species and their precursors (N-acyl-phosphatidylethanolamine and glycerophospho-N-acylethanolamine) were robustly increased in parallel with the ongoing process of imiquimod (IMQ)-induced psoriasis, accompanied by a marked upregulation of cPLA₂ ε in epidermal keratinocytes. Genetic deletion of cPLA₂ ε exacerbated IMQ-induced ear swelling and psoriatic marker expression, with a dramatic reduction of NAE-related lipids in IMQ-treated, and even normal, skin. Stimulation of cultured human keratinocytes with psoriatic cytokines concomitantly increased PLA2G4E expression and NAE production, and supplementation with NAEs significantly attenuated the cytokine-induced upregulation of the psoriatic marker S100A9. Increased expression of cPLA₂ ε was also evident in the epidermis of psoriatic patients. These findings reveal for the first time the in vivo role of cPLA₂ ε, which is highly induced in the keratinocytes of the psoriatic skin, promotes the biosynthesis of NAE-related lipids, and contributes to limiting psoriatic inflammation.

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.

Contact dermatitis

Contact dermatitis (CD) is among the most common inflammatory dermatological conditions and includes allergic CD, photoallergic CD, irritant CD, photoirritant CD (also called phototoxic CD) and protein CD. Occupational CD can be of any type and is the most prevalent occupational skin disease. Each CD type is characterized by different immunological mechanisms and/or requisite exposures. Clinical manifestations of CD vary widely and multiple subtypes may occur simultaneously. The diagnosis relies on clinical presentation, thorough exposure assessment and evaluation with techniques such as patch testing and skin-prick testing. Management is based on patient education, avoidance strategies of specific substances, and topical treatments; in severe or recalcitrant cases, which can negatively affect the quality of life of patients, systemic medications may be needed.

Cannabinoid type-2 receptor agonist, inverse agonist, and anandamide regulation of inflammatory responses in IL-1β stimulated primary human periodontal ligament fibroblasts

OBJECTIVE

The aim of this study is to understand the role of cannabinoid type 2 receptor (CB2R) during periodontal inflammation and to identify anti-inflammatory agents for the development of drugs to treat periodontitis (PD).

BACKGROUND

Cannabinoid type 2 receptor is found in periodontal tissue at sites of inflammation/infection. Our previous study demonstrated anti-inflammatory responses in human periodontal ligament fibroblasts (hPDLFs) via CB2R ligands.

METHODS

Anandamide (AEA), HU-308 (agonist), and SMM-189 (inverse agonist) were tested for effects on IL-1β-stimulated cytokines, chemokines, and angiogenic and vascular markers expressed by hPDLFs using Mesoscale Discovery V-Plex Kits. Signal transduction pathways (p-c-Jun, p-ERK, p-p-38, p-JNK, p-CREB, and p-NF-kB) were investigated using Cisbio HTRF kits. ACTOne and Tango™ -BLA functional assays were used to measure cyclic AMP (cAMP) and β-arrestin activity.

RESULTS

IL-1β stimulated hPDLF production of 18/39 analytes, which were downregulated by the CB2R agonist and the inverse agonist. AEA exhibited pro-inflammatory and anti-inflammatory effects. IL-1β increased phosphoproteins within the first hour except p-JNK. CB2R ligands attenuated p-p38 and p-NFĸB, but a late rise in p-38 was seen with HU-308. As p-ERK levels declined, a significant increase in p-ERK was observed later in the time course by synthetic CB2R ligands. P-JNK was significantly affected by SMM-189 only, while p-CREB was elevated significantly by CB2R ligands at 180 minutes. HU-308 affected both cAMP and β-arrestin pathway. SMM-189 only stimulated cAMP.

CONCLUSION

The findings that CB2R agonist and inverse agonist may potentially regulate inflammation suggest that development of CB2R therapeutics could improve on current treatments for PD and other oral inflammatory pathologies.

Cannabidiol Effects on Phospholipid Metabolism in Keratinocytes from Patients with Psoriasis Vulgaris

Psoriasis is a chronic inflammatory skin disease characterized by dysregulated keratinocyte differentiation, but oxidative stress also plays an important role in the pathogenesis of this disease. Here, we examined the effect of cannabidiol (CBD), a phytocannabinoid with antioxidant and anti-inflammatory properties, on the redox balance and phospholipid metabolism in UVA/UVB-irradiated keratinocytes isolated from the skin of psoriatic patients or healthy volunteers. CBD accumulates mainly in membrane keratinocytes, especially from patients with psoriasis. This phytocannabinoid reduces the redox imbalance observed in the UV-irradiated keratinocytes of healthy subjects. It does so by decreasing reactive oxygen species (ROS) generation, increasing the Trx-dependent system efficiency, and increasing vitamin A and E levels. Consequently, a reduction in lipid peroxidation products, such as 8-isoprostanes and 4-hydroxynonenal, was also observed. Moreover, CBD modifies redox balance and lipid peroxidation in psoriatic patient keratinocytes following UV-irradiation. Interestingly, these changes are largely in the opposite direction to the case of keratinocytes from healthy subjects. CBD also regulates metabolic changes by modulating the endocannabinoid system that is disturbed by psoriasis development and UV irradiation. We observed a decrease in anandamide level in the UV-irradiated keratinocytes of healthy controls following CBD treatment, while in keratinocytes from patients treated with CBD, anandamide level was increased. However, the level of palmitoylethanolamide (PEA) was decreased in both groups treated with CBD. We further demonstrate that CBD increases CB1 receptor expression, primarily in the keratinocytes of patients, and increases CB2 receptor expression in both the psoriatic and control groups. However, CBD decreases CB2 receptor expression in UV-irradiated keratinocytes taken from patients. The UV- and psoriasis-induced activity of transmembrane transporters (Multidrug-Resistance (MDR) and breast cancer resistance protein (BCRP)) is normalized after CBD treatment. We conclude that CBD partially reduces oxidative stress in the keratinocytes of healthy individuals, while showing a tendency to increase the oxidative and inflammatory state in the keratinocytes of patients with psoriasis, especially following UV-irradiation.

Dynamics of the human skin mediator lipidome in response to dietary ω-3 fatty acid supplementation

Nutritional supplementation with fish oil or ω-3 (n-3) polyunsaturated fatty acids (PUFAs) has potential benefits for skin inflammation. Although the differential metabolism of the main n-3PUFA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) could lead to distinct activities, there are no clinical studies comparing their relative efficacy in human skin. Following a 10-wk oral supplementation of healthy volunteers and using mass spectrometry-based lipidomics, we found that n-3PUFA mainly affected the epidermal mediator lipidome. EPA was more efficient than DHA in reducing production of arachidonic acid–derived lipids, and both n-3PUFA lowered N-acyl ethanolamines. In UV radiation–challenged skin (3 times the minimum erythemal dose), EPA attenuated the production of proinflammatory lipids, whereas DHA abrogated the migration of Langerhans cells, as assessed by immunohistochemistry. Interestingly, n-3PUFA increased the infiltration of CD4⁺ and CD8⁺ T cells but did not alter the erythemal response, either the sunburn threshold or the resolution of erythema, as assessed by spectrophotometric hemoglobin index readings. As EPA and DHA differentially impact cutaneous inflammation through changes in the network of epidermal lipids and dendritic and infiltrating immune cells, they should be considered separately when designing interventions for cutaneous disease.—Kendall, A. C., Pilkington, S. M., Murphy, S. A., Del Carratore, F., Sunarwidhi, A. L., Kiezel-Tsugunova, M., Urquhart, P., Watson, R. E. B., Breitling, R., Rhodes, L. E., Nicolaou, A. Dynamics of the human skin mediator lipidome in response to dietary ω-3 fatty acid supplementation.

Cannabinoid Signaling in the Skin: Therapeutic Potential of the "C(ut)annabinoid" System

The endocannabinoid system (ECS) has lately been proven to be an important, multifaceted homeostatic regulator, which influences a wide-variety of physiological processes all over the body. Its members, the endocannabinoids (eCBs; e.g., anandamide), the eCB-responsive receptors (e.g., CB₁, CB₂), as well as the complex enzyme and transporter apparatus involved in the metabolism of the ligands were shown to be expressed in several tissues, including the skin. Although the best studied functions over the ECS are related to the central nervous system and to immune processes, experimental efforts over the last two decades have unambiguously confirmed that cutaneous cannabinoid ("c[ut]annabinoid") signaling is deeply involved in the maintenance of skin homeostasis, barrier formation and regeneration, and its dysregulation was implicated to contribute to several highly prevalent diseases and disorders, e.g., atopic dermatitis, psoriasis, scleroderma, acne, hair growth and pigmentation disorders, keratin diseases, various tumors, and itch. The current review aims to give an overview of the available skin-relevant endo- and phytocannabinoid literature with a special emphasis on the putative translational potential, and to highlight promising future research directions as well as existing challenges.

The Endocannabinoid System and Its Role in Eczematous Dermatoses

The skin serves as the foremost barrier between the internal body and the external world, providing crucial protection against pathogens and chemical, mechanical, and ultraviolet damages. The skin is a central player in the intricate network of immune, neurologic, and endocrine systems. The endocannabinoid system (ECS) includes an extensive network of bioactive lipid mediators and their receptors, functions to modulate appetite, pain, mood, and memory, and has recently been implicated in skin homeostasis. Disruption of ECS homeostasis is implicated in the pathogenesis of several prevalent skin conditions. In this review, we highlight the role of endocannabinoids in maintaining skin health and homeostasis and discuss evidence on the role of ECS in several eczematous dermatoses including atopic dermatitis, asteatotic eczema, irritant contact dermatitis, allergic contact dermatitis, and chronic pruritus. The compilation of evidence may spark directions for future investigations on how the ECS may be a therapeutic target for dermatologic conditions.

Noninvasive profiling of sweat-derived lipid mediators for cutaneous research

BACKGROUND AND OBJECTIVE

Recent increases in the use of noninvasive matrices for biomedical analysis has led to interest in the evaluation of sweat for both clinical and research applications. However, despite being one of the two main cutaneous secretions, until very recently, only one study actually analyzed sweat in the context of cutaneous disease. This review attempts to make the case for increased use of sweat in cutaneous research, and discusses lipid mediators as potential analytical targets in sweat.

METHODS

Sweat composition and its relationship with the skin and systemic circulation are discussed, as are practical considerations for sweat sampling and analysis. Previous analyses of lipid mediators in skin biopsies are provided to show that lipid mediators can regulate cutaneous processes and disease pathways. Summaries of recent studies involving the analysis of sweat lipid mediators are provided to demonstrate the utility of sweat lipid mediator testing to support future cutaneous research studies.

RESULTS

Sweat has the potential to reflect both local and systemic biochemical changes in response to disease or intervention, and two recent studies of sweat lipid mediators confirm this ability. Additionally, sweat lipid mediators appear to be temporally stable with individual variability comparable to other matrices, suggesting that these analytes could be useful biomarkers.

CONCLUSIONS

Sweat metabolites may be capable of reporting changes in cutaneous biochemical pathways, thereby providing insight into the immunomodulatory biochemistry of the skin. Lipid mediator analysis of sweat appears to be a non invasive approach that could enhance existing cutaneous research and diagnostic methodologies.

Serum endocannabinoids and N-acyl ethanolamines and the influence of simulated solar UVR exposure in humans in vivo

Solar ultraviolet radiation (UVR) exposure of human skin has beneficial and harmful effects on health, including impact on immune function, inflammation and reportedly mood, but these are not fully elucidated. Since the endocannabinoid system is implicated in many activities including mood alteration, our objective was to (i) determine and quantify circulating levels of a wide range of endocannabinoid and N-acyl ethanolamine (NAE) species (ii) evaluate whether these are modulated by cutaneous UVR exposures, as attained through repeated low level summer sunlight exposure. Wearing goggles to prevent eye exposure, 16 healthy volunteers (23-59 y; 10 light skin, phototype II, and 6 dark skin, phototype V) received the same UVR exposures (1.3 SED, 95% UVA/5% UVB) thrice weekly for 6 weeks, whilst casually dressed to expose ∼35% skin surface area. Blood samples were taken at baseline, days 1, 3 and 5 of week one, then at weekly intervals, and analysed by LC-MS/MS. Eleven endocannabinoids and NAEs were detected and quantified at baseline, with N-palmitoyl ethanolamine the most abundant (30% of total). Levels did not vary according to phototype (p > 0.05), except for the NAE docosapentaenoyl ethanolamide, which was higher in phototype II than V (p = 0.0002). Level of the endocannabinoid, 2-AG, was elevated during the UVR exposure course (p < 0.05 vs. baseline for all subjects; p < 0.01 for each phototype group), with maximum levels reached by week 2-3, while NAE species did not significantly alter. These findings suggest differential involvement of the cutaneous endocannabinoid system in low dose solar UVR responses in humans.

Fatty acids and related lipid mediators in the regulation of cutaneous inflammation

Human skin has a distinct profile of fatty acids and related bioactive lipid mediators that regulate many aspects of epidermal and dermal homeostasis, including immune and inflammatory reactions. Sebum lipids act as effective antimicrobial agents, shape immune cell communications and contribute to the epidermal lipidome. The essential fatty acid linoleic acid is crucial for the structure of the epidermal barrier, while polyunsaturated fatty acids act as precursors to eicosanoids, octadecanoids and docosanoids through cyclooxygenase, lipoxygenase and cytochrome P450 monooxygenase-mediated reactions, and endocannabinoids and N-acyl ethanolamines. Cross-communication between these families of bioactive lipids suggests that their cutaneous activities should be considered as part of a wider metabolic network that can be targeted to maintain skin health, control inflammation and improve skin pathologies.

Lipid functions in skin: Differential effects of n-3 polyunsaturated fatty acids on cutaneous ceramides, in a human skin organ culture model

Ceramides are important for skin health, with a multitude of species found in both dermis and epidermis. The epidermis contains linoleic acid-Ester-linked Omega-hydroxylated ceramides of 6-Hydroxy-sphingosine, Sphingosine and Phytosphingosine bases (CER[EOH], CER[EOS] and CER[EOP], respectively), that are crucial for the formation of the epidermal barrier, conferring protection from environmental factors and preventing trans-epidermal water loss. Furthermore, a large number of ceramides, derivatives of the same sphingoid bases and various fatty acids, are produced by dermal and epidermal cells and perform signalling roles in cell functions ranging from differentiation to apoptosis.

Supplementation with the n-3 polyunsaturated fatty acids (PUFA) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have shown promise as therapeutic agents in a number of inflammatory skin conditions, altering the lipid profile of the skin and production of bioactive lipids such as the eicosanoids, docosanoids and endocannabinoids. In this study we wished to investigate whether EPA and DHA could also affect the ceramide profile in epidermis and dermis, and, in this way, contribute to formation of a robust lipid barrier and ceramide-mediated regulation of skin functions.

Ex vivo skin explants were cultured for 6 days, and supplemented with EPA or DHA (50 μM). Liquid chromatography coupled to tandem mass spectrometry with electrospray ionisation was used to assess the prevalence of 321 individual ceramide species, and a number of sphingoid bases, phosphorylated sphingoid bases, and phosphorylated ceramides, within the dermis and epidermis.

EPA augmented dermal production of members of the ceramide families containing Non-hydroxy fatty acids and Sphingosine or Dihydrosphingosine bases (CER[NS] and CER[NDS], respectively), while epidermal CER[EOH], CER[EOS] and CER[EOP] ceramides were not affected. DHA did not significantly affect ceramide production. Ceramide-1-phosphate levels in the epidermis, but not the dermis, increased in response to EPA, but not DHA.

This ex vivo study shows that dietary supplementation with EPA has the potential to alter the ceramide profile of the skin, and this may contribute to its anti-inflammatory profile. This has implications for formation of the epidermal lipid barrier, and signalling pathways within the skin mediated by ceramides and other sphingolipid species. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

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Omega-3 fatty acid supplementation alters ex vivo skin ceramide profiles

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Eicosapentaenoic acid (EPA) increases dermal ceramides with non-hydroxy fatty acids (CER[NS] and CER[NDS])

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EPA increases ceramide-1-phosphate (C1P) in the epidermis but not dermis

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Long-chain linoleic-acid-containing ceramides were unaltered by EPA or docosahexaenoic acid (DHA)