Some thoughts about Anthony V. Rawlings and hydration and barrier function of the skin.

Anthony V. Rawlings has had 30+ years of experience in the general area of skin science. He has many scientific publications, and his work has been highly cited. He has made major contributions to our understanding of skin physiology, including xerosis and hydration, barrier function, desquamation, the corneocyte envelope, physical chemistry of stratum corneum lipids, photodamage and ethnic variation. He has held management positions with several companies in the US and UK, established AVR Consulting in 2002 and maintained a long-standing relationship with colleagues at University College London. His time as the Editor in Chief of the International Journal of Cosmetic Science was pivotal in the development of the journal. He worked hard and succeeded in getting the IJCS included in the PubMed database.

Anthony V. Rawlings a plus de 30 ans d'expérience dans le domaine général de la science de la peau. Il est l'auteur d'un grand nombre de publications scientifiques, et ses travaux ont été largement cités. Il a beaucoup contribué à notre compréhension de la physiologie de la peau, notamment la xérose et l'hydratation, la fonction de barrière, la desquamation, l'enveloppe des cornéocytes, la chimie physique des lipides de la couche cornée, le photodommage et les variations ethniques. Il a occupé des postes de direction dans plusieurs entreprises aux États­Unis et au Royaume­Uni, a créé AVR Consulting en 2002 et entretient une relation de longue date avec ses collègues de l'University College de Londres. Le temps qu'il a passé comme rédacteur en chef de l'International Journal of Cosmetic Science a été déterminant dans le développement de la revue. Il a travaillé dur et a réussi à faire inclure l'IJCS dans la base de données PubMed.

The role of ceramides in skin barrier function and the importance of their correct formulation for skincare applications.

Ceramides are a family of lipids constituted by a sphingoid base and a fatty acid. In the skin, they are mainly present in the stratum corneum where, with cholesterol and free fatty acids, they constitute the inter-corneocyte lipids. With the other lipid groups, they play a key role in the formation of dense lamellar structures between adjacent corneocytes, collectively ensuring the vital efficient barrier to water evaporation and protection from foreign agents´ penetration. Changes in ceramide level and relative composition, with potential impairment of lipid arrangement, have been evidenced in different skin conditions and skin diseases. Therefore, use of suitably formulated ceramides has been proposed for topical treatment to help re-structure damaged lipid arrangement and repair impaired skin barrier function. Nonetheless, the formulation of ceramides in products necessitates specific processes such as heating to high temperature before their introduction in the final formula. In this review on the structure, the role and the potential of ceramides for skincare, we point out the necessity of rigorous process when formulating ceramides into the final product. We demonstrate the counterproductive effects of undissolved ceramides on skin barrier repair capacity of the formulas, when assessed in different in vitro models of disrupted skin barrier.

Les céramides sont une famille de lipides constituée d'une base sphingoïde et d'un acide gras. Dans la peau, ils sont principalement présents dans la couche cornée où, avec le cholestérol et les acides gras libres, ils constituent les lipides inter­cornéocytes. Avec les autres groupes de lipides, ils jouent un rôle clé dans la formation de structures lamellaires denses entre les cornéocytes adjacents, assurant collectivement la barrière efficace vitale contre l'évaporation de l'eau et la protection contre la pénétration des agents étrangers. Des modifications du taux de céramides et de la composition relative, avec une altération potentielle de l'arrangement lipidique, ont été observées dans différentes affections cutanées et maladies cutanées. Par conséquent, l'utilisation de céramides formulés de manière appropriée a été proposée pour un traitement topique afin d'aider à restructurer la disposition des lipides endommagés et à réparer la fonction de barrière cutanée altérée. Néanmoins, la formulation des céramides dans les produits nécessite des processus spécifiques tels que le chauffage à température élevée avant leur introduction dans la formule finale. Dans cette revue sur la structure, le rôle et le potentiel des céramides pour les soins de la peau, nous soulignons la nécessité d'un processus rigoureux lors de la formulation des céramides dans le produit final. Nous démontrons les effets contre­productifs des céramides non dissous sur la capacité de réparation de la barrière cutanée des formules, lorsqu'ils sont évalués dans différents modèles in vitro de barrière cutanée perturbée.

Hematopoietic stem cell transplantation leads to biochemical and functional correction in two mouse models of acid ceramidase deficiency.

Farber disease (FD) and spinal muscular atrophy with progressive myoclonic epilepsy (SMA-PME) are ultra-rare lysosomal storage disorders caused by deficient acid ceramidase (ACDase) activity. Although both conditions are caused by mutations in the ASAH1 gene, clinical presentations differ considerably. FD patients usually die in childhood while SMA-PME patients can live until adulthood. There is no treatment for FD or SMA-PME. Hematopoietic stem cell transplantation (HSCT) and gene therapy strategies for the treatment of ACDase deficiency are being investigated. We have previously generated and characterized mouse models of both FD and SMA-PME that recapitulate the symptoms described in patients. Here, we show that HSCT improves lifespan, behavior, hematopoietic system anomalies, plasma cytokine levels, and significantly reduces histiocytic infiltration and ceramide accumulation throughout the tissues investigated, including the CNS, in both models of ACDase deficient mice. HSCT was also successful in preventing lesion development and significant demyelination of the spinal cord seen in SMA-PME mice. Importantly, we note that only early and generally pre-symptomatic treatment was effective and kidney impairment was not improved in either model.

Targeted metabolomics identifies accurate CSF metabolite biomarkers for the differentiation between COVID-19 with neurological involvement and CNS infections with neurotropic viral pathogens.

BACKGROUND: COVID-19 is primarily considered a respiratory tract infection, but it can also affect the central nervous system (CNS), which can result in long-term sequelae. In contrast to CNS infections by classic neurotropic viruses, SARS-CoV-2 is usually not detected in cerebrospinal fluid (CSF) from patients with COVID-19 with neurological involvement (neuro-COVID), suggesting fundamental differences in pathogenesis. METHODS: To assess differences in CNS metabolism in neuro-COVID compared to CNS infections with classic neurotropic viruses, we applied a targeted metabolomic analysis of 630 metabolites to CSF from patients with (i) COVID-19 with neurological involvement [n = 16, comprising acute (n = 13) and post-COVID-19 (n = 3)], (ii) viral meningitis, encephalitis, or myelitis (n = 10) due to herpes simplex virus (n = 2), varicella zoster virus (n = 6), enterovirus (n = 1) and tick-borne encephalitis virus (n = 1), and (iii) aseptic neuroinflammation (meningitis, encephalitis, or myelitis) of unknown etiology (n = 21) as additional disease controls. RESULTS: Standard CSF parameters indicated absent or low neuroinflammation in neuro-COVID. Indeed, CSF cell count was low in neuro-COVID (median 1 cell/µL, range 0-12) and discriminated it accurately from viral CNS infections (AUC = 0.99) and aseptic neuroinflammation (AUC = 0.98). 32 CSF metabolites passed quality assessment and were included in the analysis. Concentrations of differentially abundant (fold change ≥|1.5|, FDR ≤ 0.05) metabolites were both higher (9 and 5 metabolites) and lower (2 metabolites) in neuro-COVID than in the other two groups. Concentrations of citrulline, ceramide (d18:1/18:0), and methionine were most significantly elevated in neuro-COVID. Remarkably, triglyceride TG(20:1_32:3) was much lower (mean fold change = 0.09 and 0.11) in neuro-COVID than in all viral CNS infections and most aseptic neuroinflammation samples, identifying it as highly accurate biomarker with AUC = 1 and 0.93, respectively. Across all samples, TG(20:1_32:3) concentration correlated only moderately with CSF cell count (ρ = 0.65), protein concentration (ρ = 0.64), and Q-albumin (ρ = 0.48), suggesting that its low levels in neuro-COVID CSF are only partially explained by less pronounced neuroinflammation. CONCLUSIONS: The results suggest that CNS metabolite responses in neuro-COVID differ fundamentally from viral CNS infections and aseptic neuroinflammation and may be used to discover accurate diagnostic biomarkers in CSF and to gain insights into differences in pathophysiology between neuro-COVID, viral CNS infections and aseptic neuroinflammation.

Ceramides in the central control of metabolism.

Central ceramides regulate energy metabolism by impacting hypothalamic neurons. This allows ceramides to integrate endocrine signals - such as leptin, ghrelin, thyroid hormones, or estradiol - and to modulate the central control of puberty. In this forum article we discuss recent evidence suggesting that specific ceramide species and neuronal populations are involved in these effects.

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

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

Deletion of Sphingosine Kinase 2 Attenuates Acute Kidney Injury in Mice with Hemolytic-Uremic Syndrome.

Typical hemolytic uremic syndrome (HUS) can occur as a severe systemic complication of infections with Shiga toxin (Stx)-producing Escherichia coli. Its pathology can be induced by Stx types, resulting in toxin-mediated damage to renal barriers, inflammation, and the development of acute kidney injury (AKI). Two sphingosine kinase (SphK) isozymes, SphK1 and SphK2, have been shown to be involved in barrier maintenance and renal inflammatory diseases. Therefore, we sought to determine their role in the pathogenesis of HUS. Experimental HUS was induced by the repeated administration of Stx2 in wild-type (WT) and SphK1 (SphK1-/-) or SphK2 (SphK2-/-) null mutant mice. Disease severity was evaluated by assessing clinical symptoms, renal injury and dysfunction, inflammatory status and sphingolipid levels on day 5 of HUS development. Renal inflammation and injury were found to be attenuated in the SphK2-/- mice, but exacerbated in the SphK1-/- mice compared to the WT mice. The divergent outcome appeared to be associated with oppositely altered sphingolipid levels. This study represents the first description of the distinct roles of SphK1-/- and SphK2-/- in the pathogenesis of HUS. The identification of sphingolipid metabolism as a potential target for HUS therapy represents a significant advance in the field of HUS research.

An exploratory study on lipidomic profiles in a cohort of individuals with posttraumatic stress disorder.

Posttraumatic stress disorder (PTSD) can develop after trauma exposure. Some studies report that women develop PTSD at twice the rate of men, despite greater trauma exposure in men. Lipids and their metabolites (lipidome) regulate a myriad of key biological processes and pathways such as membrane integrity, oxidative stress, and neuroinflammation in the brain by maintaining neuronal connectivity and homeostasis. In this study, we analyzed the lipidome of 40 adults with PTSD and 40 trauma-exposed non-PTSD individuals (n = 20/sex/condition; 19-39 years old). Plasma samples were analyzed for lipidomics using Quadrupole Time-of-Flight (QToF) mass spectrometry. Additionally, ~ 90 measures were collected, on sleep, and mental and physical health indices. Poorer sleep quality was associated with greater PTSD severity in both sexes. The lipidomics analysis identified a total of 348 quantifiable known lipid metabolites and 1951 lipid metabolites that are yet unknown; known metabolites were part of 13 lipid subclasses. After adjusting for BMI and sleep quality, in women with PTSD, only one lipid subclass, phosphatidylethanolamine (PE) was altered, whereas, in men with PTSD, 9 out of 13 subclasses were altered compared to non-PTSD women and men, respectively. Severe PTSD was associated with 22% and 5% of altered lipid metabolites in men and women, respectively. Of the changed metabolites, only 0.5% measures (2 PEs and cholesterol) were common between women and men with PTSD. Several sphingomyelins, PEs, ceramides, and triglycerides were increased in men with severe PTSD. The correlations between triglycerides and ceramide metabolites with cholesterol metabolites and systolic blood pressure were dependent upon sex and PTSD status. Alterations in triglycerides and ceramides are linked with cardiac health and metabolic function in humans. Thus, disturbed sleep and higher body mass may have contributed to changes in the lipidome found in PTSD.

Analysis and Quantification of the Mitochondrial-ER Lipidome.

Mitochondria are vital organelles essential for cellular functions, but their lipid composition and response to stressors are not fully understood. Recent advancements in lipidomics reveal insights into lipid functions, especially their roles in metabolic perturbations and diseases. Previous methods have focused on the protein composition of mitochondria and mitochondrial-associated membranes. The advantage of our technique is that it combines organelle isolation with targeted lipidomics, offering new insights into the composition and dynamics of these organelles in pathological conditions. We developed a mitochondria isolation protocol for L6 myotubes, enabling lipidomics analysis of specific organelles without interference from other cellular compartments. This approach offers a unique opportunity to dissect lipid dynamics within mitochondria and their associated ER compartments under cellular stress. Key features • Analysis and quantification of lipids in mitochondria-ER fraction through liquid chromatography-tandem mass spectrometry-based lipidomics (LC-MS/MS lipidomics). • LC-MS/MS lipidomics provide precise and unbiased information on the lipid composition in in vitro systems. • LC-MS/MS lipidomics facilitates the identification of lipid signatures in mammalian cells.

Hyphenation of supercritical fluid chromatography and trapped ion mobility-mass spectrometry for quantitative lipidomics.

BACKGROUND: Lipidomics studies require rapid separations with accurate and reliable quantification results to further elucidate the role of lipids in biological processes and their biological functions. Supercritical fluid chromatography (SFC), in particular, can provide this rapid and high-resolution separation. The combination with trapped ion mobility spectrometry (TIMS) has not yet been applied, although the post-ionization separation method in combination with liquid chromatography or imaging techniques has already proven itself in resolving isomeric and isobaric lipids and preventing false identifications. However, a multidimensional separation method should not only allow confident identification but also provide quantitative results to substantiate studies with absolute concentrations. RESULTS: A SFC method was developed and the hyphenation of SFC and TIMS was further explored towards the separation of different isobaric overlaps. Furthermore, lipid identification was performed using mass spectrometry (MS) and parallel accumulation serial fragmentation (PASEF) MS/MS experiments in addition to retention time and collision cross section (CCS). Quantification was further investigated with short TIMS ramps and performed based on the ion mobility signal of lipids, since TIMS increases the sensitivity by noise filtering. The final method was, as an exemplary study, applied to investigate the function of different ceramide synthases (CerS) in the nematode and model organism Caenorhabditis elegans (C. elegans). Loss of three known CerS hyl-1, hyl-2 and lagr-1 demonstrated different influences on and alterations in the sphingolipidome. SIGNIFICANCE: This method describes for the first time the combination of SFC and TIMS-MS/MS, which enables a fast and sensitive quantification of lipids. The results of the application to C. elegans samples prove the functionality of the method and support research on the metabolism of sphingolipids in nematodes.

Novel insights into the modulation of the voltage-gated potassium channel KV1.3 activation gating by membrane ceramides.

Membrane lipids extensively modulate the activation gating of voltage-gated potassium channels (KV), however, much less is known about the mechanisms of ceramide and glucosylceramide actions including which structural element is the main intramolecular target and whether there is any contribution of indirect, membrane biophysics-related mechanisms to their actions. We used two-electrode voltage-clamp fluorometry capable of recording currents and fluorescence signals to simultaneously monitor movements of the pore domain (PD) and the voltage sensor domain (VSD) of the KV1.3 ion channel after attaching an MTS-TAMRA fluorophore to a cysteine introduced into the extracellular S3-S4 loop of the VSD. We observed rightward shifts in the conductance-voltage (G-V) relationship, slower current activation kinetics, and reduced current amplitudes in response to loading the membrane with C16-ceramide (Cer) or C16-glucosylceramide (GlcCer). When analyzing VSD movements, only Cer induced a rightward shift in the fluorescence signal-voltage (F-V) relationship and slowed fluorescence activation kinetics, whereas GlcCer exerted no such effects. These results point at a distinctive mechanism of action with Cer primarily targeting the VSD, while GlcCer only the PD of KV1.3. Using environment-sensitive probes and fluorescence-based approaches, we show that Cer and GlcCer similarly increase molecular order in the inner, hydrophobic regions of bilayers, however, Cer induces a robust molecular reorganization at the membrane-water interface. We propose that this unique ordering effect in the outermost membrane layer in which the main VSD rearrangement involving an outward sliding of the top of S4 occurs can explain the VSD targeting mechanism of Cer, which is unavailable for GlcCer.

Guselkumab treatment normalizes the stratum corneum ceramide profile and alleviates barrier dysfunction in psoriasis: results of a randomized controlled trial.

The epidermal inflammation associated with psoriasis drives skin barrier perturbations. The skin barrier is primarily located in stratum corneum (SC). Its function depends on the SC lipid matrix of which ceramides constitute important components. Changes in the ceramide profile directly correlate to barrier function. In this study, we characterized the dynamics of the barrier function and ceramide profile of psoriatic skin during anti-Interleukin-23 therapy with guselkumab. We conducted a double-blind, randomized controlled trial in which 26 mild-to-severe plaque psoriasis patients were randomization 3:1-100 mg guselkumab or placebo for 16 weeks and barrier dynamics monitored throughout. Barrier function was measured by trans-epidermal water loss measurements. Untargeted ceramide profiling was performed using liquid chromatography-mass spectrometry after SC was harvested using tape-stripping. The barrier function and ceramide profile of lesional skin normalized to that of controls during treatment with guselkumab, but not placebo. This resulted in significant differences compared to placebo at the end of the treatment. Changes in the lesional ceramide profile during treatment correlated with barrier function and target lesion severity. Nonlesional skin remained similar throughout treatment. Guselkumab therapy restored the skin barrier in psoriasis. Concomitant correlations between skin barrier function, the ceramide profile, and disease severity demonstrate their interdependency.

Efficacy and Safety of Oral Administration of Wine Lees Extract (WLE)-Derived Ceramides and Glucosylceramides in Enhancing Skin Barrier Function: A Randomized, Double-Blind, Placebo-Controlled Study.

BACKGROUND: Our search for plant-derived ceramides from sustainable sources led to the discovery of ceramides and glucosylceramides in wine lees. OBJECTIVE: This study evaluated the efficacy and safety of wine lees extract (WLE)-derived ceramides and glucosylceramides in enhancing skin barrier function. METHODS: A randomized, double-blind, placebo-controlled study was conducted with 30 healthy Japanese subjects aged 20-64. Subjects were allocated to receive either the WLE-derived ceramides and glucosylceramides (test group) or placebo for 12 weeks. The primary outcome was transepidermal water loss (TEWL), and secondary outcomes included skin hydration, visual analog scale (VAS) of itching sensation, and the Japanese Skindex-29. RESULTS: One participant withdrew for personal reasons, resulting in 29 subjects for data analysis (placebo n = 15; test n = 14). The test group showed a tendency of lower TEWL compared to the placebo after 8 weeks (p = 0.07). Furthermore, after 12 weeks of administration, the test group had significantly lower TEWL than the placebo (p = 0.04). On the other hand, no significant differences were observed in the secondary outcome parameters. No adverse events related to the supplements were reported. CONCLUSIONS: Oral supplementation of WLE-derived ceramides and glucosylceramides is a prominent and safe approach to enhancing skin barrier function and health. TRIAL REGISTRATION: (UMIN000050422).

Oxidative stress and plasma ceramides in broiler chickens.

The selection for rapid growth in chickens has rendered meat-type (broiler) chickens susceptible to develop metabolic syndrome and thus inflammation. The sphingolipid ceramide has been linked as a marker of oxidative stress in mammals, however, the relationship between sphingolipid ceramide supply and oxidative stress in broiler chickens has not been investigated. Therefore, we employed a lipidomic approach to investigate the changes in circulating sphingolipid ceramides in context of allopurinol-induced oxidative stress in birds. Day zero hatched chicks (n = 60) were equally divided into six groups; an unsupplemented control, an allopurinol group (25 mg/kg body weight), a conjugated linoleic acid (CLA) group where half of the oil used in the control diet was substituted for a CLA oil mixture, a CLA and an allopurinol group utilizing the same dose of CLA and allopurinol, a berberine (BRB) group consisting of berberine supplementation (200 mg/kg feed), and a BRB and allopurinol group, utilizing the same dose of BRB and allopurinol. Conjugated linoleic acid and berberine were utilized to potentially enhance antioxidant activity and suppress the oxidative stress induced by allopurinol treatment. Body weight, plasma uric acid, nonesterified fatty acids (NEFA) and sphingolipid ceramides were quantified. Allopurinol induced an inflammatory state as measured by a significant reduction in plasma uric acid - an antioxidant in birds as well as a metabolic waste product. Results showed that both total and saturated sphingolipid ceramides declined (p < 0.05) with age in unsupplemented chicks, although plasma ceramides C16:0 and 18:0 increased in concentration over the study period. Simple total and saturated sphingolipid ceremide's were further decreased (p < 0.05) with allopurinol supplementation, however, this may be an indirect consequence of inducing an inflammatory state. Neither CLA or BRB were able to significantly attenuate the decline. The administration of allopurinol specifically targets the liver which in birds, is the primary organ for fatty acids synthesis. For this reason, sphingolipid ceramide production might have been unwittingly affected by the addition of allopurinol.

ER stress inhibition enhances formation of triacylglcerols and protects endothelial cells from lipotoxicity.

Elevated concentrations of palmitate in serum of obese individuals can impair endothelial function, contributing to development of cardiovascular disease. Although several molecular mechanisms of palmitate-induced endothelial dysfunction have been proposed, there is no consensus on what signaling event is the initial trigger of detrimental palmitate effects. Here we report that inhibitors of ER stress or ceramid synthesis can rescue palmitate-induced autophagy impairment in macro- and microvascular endothelial cells. Furthermore, palmitate-induced cholesterol synthesis was reverted using these inhibitors. Similar to cell culture data, autophagy markers were increased in serum of obese individuals. Subsequent lipidomic analysis revealed that palmitate changed the composition of membrane phospholipids in endothelial cells and that these effects were not reverted upon application of above-mentioned inhibitors. However, ER stress inhibition in palmitate-treated cells enhanced the synthesis of trilglycerides and restored ceramide levels to control condition. Our results suggest that palmitate induces ER-stress presumably by shift in membrane architecture, leading to impaired synthesis of triglycerides and enhanced production of ceramides and cholesterol, which altogether enhances lipotoxicity of palmitate in endothelial cells.

Circulating Sphingolipids and All-Cause Mortality: The Strong Heart Family Study.

BACKGROUND: A growing body of research indicates that associations of ceramides and sphingomyelins with mortality depend on the chain length of the fatty acid acylated to the backbone sphingoid base. We examined associations of 8 ceramide and sphingomyelin species with mortality among an American Indian population. METHODS AND RESULTS: The analysis comprised 2688 participants from the SHFS (Strong Heart Family Study). Plasma ceramide and sphingomyelin species carrying long-chain (ie, 16:0) and very-long-chain (ie, 20:0, 22:0, 24:0) saturated fatty acids were measured by sequential liquid chromatography and mass spectroscopy using samples from 2001 to 2003. Participants were followed for 18.8 years (2001-2020). Associations of ceramides and sphingomyelins with mortality were assessed using Cox models. The mean age of participants was 40.8 years. There were 574 deaths during a median 17.4-year follow-up. Ceramides and sphingomyelins carrying fatty acid 16:0 were positively associated with mortality. Ceramides and sphingomyelins carrying longer fatty acids were inversely associated with mortality. Per SD difference in each ceramide and sphingomyelin species, hazard ratios for death were: 1.68 (95% CI, 1.44-1.96) for ceramide-16 (Cer-16), 0.82 (95% CI, 0.71-0.95) for Cer-20, 0.60 (95% CI, 0.51-0.70) for Cer-22, 0.67 (95% CI, 0.56-0.79) for Cer-24, 1.80 (95% CI-1.57, 2.05) for sphingomyelin-16 (SM-16), 0.54 (95% CI, 0.47-0.62) for SM-20, 0.50 (95% CI, 0.44-0.57) for SM-22, and 0.59 (95% CI, 0.52-0.67) for SM-24. CONCLUSIONS: The direction/magnitude of associations of ceramides and sphingomyelins with mortality differs according to the length of the fatty acid acylated to the backbone sphingoid base. REGISTRATION: URL: https://www.clinicatrials.gov; Unique identifier: NCT00005134.

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.

N-Acetylcysteine Alleviates Impaired Muscular Function Resulting from Sphingosine Phosphate Lyase Functional Deficiency-Induced Sphingoid Base and Ceramide Accumulation in Caenorhabditis elegans.

Sphingosine-1-phosphate lyase (SPL) resides at the endpoint of the sphingolipid metabolic pathway, catalyzing the irreversible breakdown of sphingosine-1-phosphate. Depletion of SPL precipitates compromised muscle morphology and function; nevertheless, the precise mechanistic underpinnings remain elusive. Here, we elucidate a model of SPL functional deficiency in Caenorhabditis elegans using spl-1 RNA interference. Within these SPL-deficient nematodes, we observed diminished motility and perturbed muscle fiber organization, correlated with the accumulation of sphingoid bases, their phosphorylated forms, and ceramides (collectively referred to as the "sphingolipid rheostat"). The disturbance in mitochondrial morphology was also notable, as SPL functional loss resulted in heightened levels of reactive oxygen species. Remarkably, the administration of the antioxidant N-acetylcysteine (NAC) ameliorates locomotor impairment and rectifies muscle fiber disarray, underscoring its therapeutic promise for ceramide-accumulation-related muscle disorders. Our findings emphasize the pivotal role of SPL in preserving muscle integrity and advocate for exploring antioxidant interventions, such as NAC supplementation, as prospective therapeutic strategies for addressing muscle function decline associated with sphingolipid/ceramide metabolism disruption.

Proteomics and lipidomic analysis reveal dysregulated pathways associated with loss of sacsin.

Introduction: Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is a rare incurable neurodegenerative disease caused by mutations in the SACS gene, which codes for sacsin, a large protein involved in protein homeostasis, mitochondrial function, cytoskeletal dynamics, autophagy, cell adhesion and vesicle trafficking. However, the pathogenic mechanisms underlying sacsin dysfunction are still largely uncharacterized, and so attempts to develop therapies are still in the early stages. Methods: To achieve further understanding of how processes are altered by loss of sacsin, we used untargeted proteomics to compare protein profiles in ARSACS fibroblasts versus controls. Results: Our analyses confirmed the involvement of known biological pathways and also implicated calcium and lipid homeostasis in ARSACS skin fibroblasts, a finding further verified in SH-SY5Y SACS -/- cells. Validation through mass spectrometry-based analysis and comparative quantification of lipids by LC-MS in fibroblasts revealed increased levels of ceramides coupled with a reduction of diacylglycerols. Discussion: In addition to confirming aberrant Ca2+ homeostasis in ARSACS, this study described abnormal lipid levels associated with loss of sacsin.

Intramuscular diacylglycerol accumulates with acute hyperinsulinemia in insulin-resistant phenotypes.

Elevated skeletal muscle diacylglycerols (DAGs) and ceramides can impair insulin signaling, and acylcarnitines (acylCNs) reflect impaired mitochondrial fatty acid oxidation, thus, the intramuscular lipid profile is indicative of insulin resistance. Acute (i.e., postprandial) hyperinsulinemia has been shown to elevate lipid concentrations in healthy muscle and is an independent risk factor for type 2 diabetes (T2D). However, it is unclear how the relationship between acute hyperinsulinemia and the muscle lipidome interacts across metabolic phenotypes, thus contributing to or exacerbating insulin resistance. We therefore investigated the impact of acute hyperinsulinemia on the skeletal muscle lipid profile to help characterize the physiological basis in which hyperinsulinemia elevates T2D risk. In a cross-sectional comparison, endurance athletes (n = 12), sedentary lean adults (n = 12), and individuals with obesity (n = 13) and T2D (n = 7) underwent a hyperinsulinemic-euglycemic clamp with muscle biopsies. Although there were no significant differences in total 1,2-DAG fluctuations, there was a 2% decrease in athletes versus a 53% increase in T2D during acute hyperinsulinemia (P = 0.087). Moreover, C18 1,2-DAG species increased during the clamp with T2D only, which negatively correlated with insulin sensitivity (P < 0.050). Basal muscle C18:0 total ceramides were elevated with T2D (P = 0.029), but not altered by clamp. Acylcarnitines were universally lowered during hyperinsulinemia, with more robust reductions of 80% in athletes compared with only 46% with T2D (albeit not statistically significant, main effect of group, P = 0.624). Similar fluctuations with acute hyperinsulinemia increasing 1,2 DAGs in insulin-resistant phenotypes and universally lowering acylcarnitines were observed in male mice. In conclusion, acute hyperinsulinemia elevates muscle 1,2-DAG levels with insulin-resistant phenotypes. This suggests a possible dysregulation of intramuscular lipid metabolism in the fed state in individuals with low insulin sensitivity, which may exacerbate insulin resistance.NEW & NOTEWORTHY Postprandial hyperinsulinemia is a risk factor for type 2 diabetes and may increase muscle lipids. However, it is unclear how the relationship between acute hyperinsulinemia and the muscle lipidome interacts across metabolic phenotypes, thus contributing to insulin resistance. We observed that acute hyperinsulinemia elevates muscle 1,2-DAGs in insulin-resistant phenotypes, whereas ceramides were unaltered. Insulin-mediated acylcarnitine reductions are also hindered with high-fat feeding. The postprandial period may exacerbate insulin resistance in metabolically unhealthy phenotypes.