Work

Altered composition of epidermal lipids correlates with Staphylococcus aureus colonization status in atopic dermatitis

Year: 2017

Type: article

Abstract: Dear Editor, Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by disrupted epidermal barrier functions.1 The stratum corneum (SC) consists of corneocytes and a lipid‐rich extracellular matrix, which plays a key role in epidermal permeability barrier functions.2,3 Major lipid constituents of the SC are ceramides, free fatty acids (FFAs), cholesterol and triglycerides.2,3,Staphylococcus aureus colonization is an important trigger of AD.4 Comprehensive profiling of SC lipids using S. aureus colonization status, and association between S. aureus colonization and skin lipid composition have never been documented. In our study cohort, 27 patients with AD and 15 healthy individuals with no history of skin disorders (age ≥ 18 years) were enrolled under an institutional review board‐approved protocol. All participants with AD had elevated transepidermal water loss (TEWL), thymus and activation‐regulated chemokine (TARC)/CCL17, total serum IgE levels and eosinophil counts (clinical markers of AD severity)5 compared with nonatopic participants before and after adjustment for age and sex (Fig. 1). We extracted SC lipids using a high‐yield, one‐step, modified Bligh and Dyer method,6 and all major SC lipids were analysed by liquid chromatography–tandem mass spectroscopy. Hypothetical model of altered lipid distribution in skin of participants with atopic dermatitis (AD) with or without Staphylococcus aureus colonization (S. aureus− and S. aureus+, respectively). Basal transepidermal water loss (TEWL), serum IgE, serum thymus and activation‐regulated chemokine (TARC/CCL17) and eosinophils are significantly elevated in S. aureus− and S. aureus+ patients with AD compared with nonatopic participants (green arrows). The levels of ceramides CER[AH]C48, CER[EOH]C66, CER[EOH]C68 and CER[EOS]C70; free fatty acids FFA16:1 and FFA18:1; and triglycerides TG46:2, TG48:2, TG50:2 and TG50:3 are significantly downregulated in S. aureus+ patients with AD compared with S. aureus− patients (red arrows). The level of cholesterol‐3‐sulfate is significantly increased in patients with AD both with and without S. aureus colonization compared with nonatopic individuals (green arrows). Ceramides are the most abundant lipid class in human SC (50%) and are divided into 12 subclasses.3 Consequently, the profile of SC lipids was compared between patients with AD with S. aureus colonization (S. aureus+, n =15), patients with AD without S. aureus colonization (S. aureus−, n =12) and nonatopic participants without S. aureus (n =15). Certain short‐chain ceramides, such as CER[AH]C34 and CER[AP]C34 (both 34 carbons in length), were significantly more abundant in patients with AD than in nonatopic participants, as reported previously.3 Specific ceramides, belonging to four of the 12 subclasses, differed between patients with AD with and without S. aureus. The levels of CER[AH] (44, 48, 50 and 52 carbons), CER[AP] (40 carbons) and very‐long‐chain ceramides – including CER[EOH] (66, 68 and 70 carbons) and CER[EOS] (70 carbons) – were significantly lower in S. aureus+ patients with AD than S. aureus− patients (Fig. 1). After age and sex adjustment, levels of CER[AH]C38, CER[AH]C48, CER[AP]C40, CER[EOH]C66, CER[EOH]C68 and CER[EOS]C70 were significantly lower in S. aureus+ patients with AD (Table S1; see Supporting Information). Basal TEWL negatively correlated with levels of certain ceramides, including CER[AH]C48, CER[AH]C50, CER[AP]C36, CER[EOH]C66, CER[EOH]C68, CER[EOS]C70, CER[NDS]C52 and CER[NDS]C54. Interestingly, CER[NDS]C52 and CER[NDS]C54 were significantly lower in S. aureus+ patients with AD than in nonatopic participants, but were comparable between S. aureus+ and S. aureus− participants with AD, suggesting that this subgroup of lipids might be involved only in epidermal permeability barrier homeostasis. However, CER[AH]C38 and CER[AP]C40 were significantly lower only in S. aureus+ patients with AD than in S. aureus− patients with AD, and no correlation with TEWL values was observed. This suggests that those ceramides might exhibit only antimicrobial activities or provide a survival advantage for S. aureus. The levels of very‐long‐chain ceramides – such as CER[EOH]C66, CER[EOH]C68 and CER[EOS]C70 – were significantly decreased in S. aureus+ patients with AD compared with S. aureus− patients, and negatively correlated with TEWL (Table S1). Cholesterol and cholesterol‐3‐sulfate are abundant in human epidermis. Here, the level of cholesterol was comparable among all groups as reported previously.7 Interestingly, compared with nonatopic participants, patients with AD showed significantly increased cholesterol‐3‐sulfate, irrespective of S. aureus colonization, age and sex (Fig. 1, Table S1). Increased cholesterol‐3‐sulfate was also associated with increased basal TEWL (Table S1), suggesting that increased cholesterol‐3‐sulfate level may be a risk factor for AD in general, and a possible contributor to barrier disruptions. A recent study indicated that cholesterol‐3‐sulfate cycle disruption accounts for epidermal permeability barrier abnormality in X‐linked ichthyosis.8 FFAs are crucial for barrier functions,2 and FFA chain length has been reported to be altered in AD skin.3 We found that levels of two unsaturated FFAs, FFA16:1 and FFA18:1, were significantly lower in S. aureus+ patients with AD than in S. aureus− patients, but were comparable between S. aureus− patients and nonatopic participants, regardless of age and sex adjustment (Table S1). There was no evidence of an association between basal TEWL and FFAs, suggesting that dysregulation of FFAs is more likely responsible for skin antimicrobial defence and not barrier function. Consistently with this theory, exogenous FFA16:1 has been reported as a potent bacterial growth inhibitor.9 Triglycerides that are broken down to FFAs play a critical role in epidermal permeability barrier maintenance.2,3 Notably, the levels of a group of triglycerides (e.g. TG46:1, TG48:1, TG48:2, TG50:1, TG50:2 and TG50:3) were significantly lower in S. aureus+ patients with AD and independent of age and sex adjustment. However, TG46:2 and TG56:2 were significantly reduced in S. aureus+ patients with AD after adjusting for age and sex. Increased basal TEWL was associated only with decreased TG46:2. These results suggest a potential role for triglycerides in cutaneous antimicrobial defence. Altogether, our work suggests that some lipids associate with bacterial colonization and others with physiological evidence of barrier dysfunction. Staphylococcus aureus colonization might be a confounder for disease severity in relation to lipid composition. A recent report identified 2430 differentially expressed genes in AD skin, with those involved in lipid metabolism and biosynthesis among the top Gene Ontology terms that were enriched, indicating the importance of lipid metabolism in atopic skin.10 The present study characterizes the unique lipid profile observed in AD and well‐recognized AD subphenotypes. The conclusions that can be made about cause and effect are limited from our cross‐sectional study design, but the ability to evaluate lipid composition in a fast, reliable and noninvasive way makes it feasible to perform a longitudinal study. The present results may be important for therapeutic applications that could reverse S. aureus colonization and improve skin barrier function in patients with AD. We gratefully acknowledge Dr Taifo Mahmud and Khaled Almabruk for help with performing the MIC assay. We thank Dr Fred Steven from the OSU Mass Spectrometry Facility for advice on mass spectrometry analyses. We also thank Dr Mark Zabriskie and Dr Theresa Filtz of the OSU College of Pharmacy for their continuous support and encouragement. Funding sources: this project has been funded in whole or in part by the National Institutes of Health (NIH)/National Institute of Allergy and Infectious Diseases Atopic Dermatitis Research Network contracts HHSN272201000020C and HHSN272201000017C, grants U19 AI117673‐01 and UM2AI117870, and ONAMI pre‐GAP Funding. The Clinical Trial Research Centers were supported in part by the Colorado Clinical and Translational Science Award/Colorado Clinical and Translational Sciences Institute grant UL1 RR025780 from the National Center for Research Resources/NIH and from the NIH/National Center for Advancing Translational Sciences (grant UL1 TR000154). Conflicts of interest: none declared. Table S1. Changes in stratum corneum lipid profile related to Staphylococcus aureus status in patients with atopic dermatitis.

Source: British Journal of Dermatology

DOI: 10.1111/bjd.15409