The emerging role of peptides and lipids as antimicrobial epidermal barriers and modulators of local inflammation

Insights of early feeding regime supplemented with glutamine and various levels of omega-3 in broiler chickens: growth performance, muscle building, antioxidant capacity, intestinal barriers health and defense against mixed Eimeria spp infection

Early nutritional management approach greatly impacts broilers' performance and resistance against coccidiosis. The current study explored the impact of post-hatch feeding with a combination of glutamine (Glut) and different levels of omega-3 on broiler chickens' growth performance, muscle building, intestinal barrier, antioxidant ability and protection against avian coccidiosis. A total of six hundred Cobb 500 was divided into six groups: first group (fed basal diet and unchallenged (control) and challenged (negative control, NC) groups were fed a basal diet without additives, and the other groups were infected with Eimeria spp and supplemented with 1.5% Glut alone or with three different levels of omega-3 (0.25, 0.5 and 1%) during the starter period. Notable improvement in body weight gain was observed in the group which fed basal diet supplemented with glut and 1% omega 3 even after coccidia infection (increased by 25% compared challenged group) while feed conversion ratio was restored to control. Myogeneis was enhanced in the group supplemented with Glut and omega-3 (upregulation of myogenin, MyoD, mechanistic target of rapamycin kinase and insulin like growth factor-1 and downregulating of myostatin genes). Groups supplemented with Glut and higher levels of omega-3 highly expressed occluding, mucin-2, junctional Adhesion Molecule 2, b-defensin-1 and cathelicidins-2 genes. Group fed 1% Glut + omega-3 showed an increased total antioxidant capacity and glutathione peroxidase and super oxide dismutase enzymes activities with reduced levels of malondialdehyde, reactive oxygen species and H2O2. Post-infection, dietary Glut and 1% omega-3 increased intestinal interleukin-10 (IL) and secretory immunoglobulin-A and serum lysozyme, while decreased the elevated inflammatory mediators comprising interleukin IL-6, tumor necrosis factor-alpha, nitric oxide (NO) and inducible NO synthase. Fecal oocyst excretion and lesions score severity were lowered in the group fed 1% Glut and omega 3. Based on these findings, dietary Glut and omega-3 supplementation augmented restored overall broilers' performance after coccidial challenge.

Thymic stromal lymphopoietin induces IL-4/IL-13 from T cells to promote sebum secretion and adipose loss

BACKGROUND

The cytokine TSLP promotes type 2 immune responses and can induce adipose loss by stimulating lipid loss from the skin through sebum secretion by sebaceous glands, which enhances the skin barrier. However, the mechanism by which TSLP upregulates sebaceous gland function is unknown.

OBJECTIVES

This study investigated the mechanism by which TSLP stimulates sebum secretion and adipose loss.

METHODS

RNA-sequencing analysis was performed on sebaceous glands isolated by laser capture microdissection and single-cell RNA-sequencing analysis was performed on sorted skin T cells. Sebocyte function was analyzed by histological analysis and sebum secretion in vivo and by measuring lipogenesis and proliferation in vitro.

RESULTS

This study found that TSLP sequentially stimulated the expression of lipogenesis genes followed by cell death genes in sebaceous glands to induce holocrine secretion of sebum. TSLP did not affect sebaceous gland activity directly. Rather, single-cell RNA-sequencing revealed that TSLP recruited distinct T-cell clusters that produce IL-4 and IL-13, which were necessary for TSLP-induced adipose loss and sebum secretion. Moreover, IL-13 was sufficient to cause sebum secretion and adipose loss in vivo and to induce lipogenesis and proliferation of a human sebocyte cell line in vitro.

CONCLUSIONS

This study proposes that TSLP stimulates T cells to deliver IL-4 and IL-13 to sebaceous glands, which enhances sebaceous gland function, turnover, and subsequent adipose loss.

Sphingolipid-Induced Bone Regulation and Its Emerging Role in Dysfunction Due to Disease and Infection

The human skeleton is a metabolically active system that is constantly regenerating via the tightly regulated and highly coordinated processes of bone resorption and formation. Emerging evidence reveals fascinating new insights into the role of sphingolipids, including sphingomyelin, sphingosine, ceramide, and sphingosine-1-phosphate, in bone homeostasis. Sphingolipids are a major class of highly bioactive lipids able to activate distinct protein targets including, lipases, phosphatases, and kinases, thereby conferring distinct cellular functions beyond energy metabolism. Lipids are known to contribute to the progression of chronic inflammation, and notably, an increase in bone marrow adiposity parallel to elevated bone loss is observed in most pathological bone conditions, including aging, rheumatoid arthritis, osteoarthritis, and osteomyelitis. Of the numerous classes of lipids that form, sphingolipids are considered among the most deleterious. This review highlights the important primary role of sphingolipids in bone homeostasis and how dysregulation of these bioactive metabolites appears central to many chronic bone-related diseases. Further, their contribution to the invasion, virulence, and colonization of both viral and bacterial host cell infections is also discussed. Many unmet clinical needs remain, and data to date suggest the future use of sphingolipid-targeted therapy to regulate bone dysfunction due to a variety of diseases or infection are highly promising. However, deciphering the biochemical and molecular mechanisms of this diverse and extremely complex sphingolipidome, both in terms of bone health and disease, is considered the next frontier in the field.

Interaction between the microbiota and the skin barrier in aging skin: a comprehensive review

The interplay between the microbes and the skin barrier holds pivotal significance in skin health and aging. The skin and gut, both of which are critical immune and neuroendocrine system, harbor microbes that are kept in balance. Microbial shifts are seen with aging and may accelerate age-related skin changes. This comprehensive review investigates the intricate connection between microbe dynamics, skin barrier, and the aging process. The gut microbe plays essential roles in the human body, safeguarding the host, modulating metabolism, and shaping immunity. Aging can perturb the gut microbiome which in turn accentuates inflammaging by further promoting senescent cell accumulation and compromising the host's immune response. Skin microbiota diligently upholds the epidermal barrier, adeptly fending off pathogens. The aging skin encompasses alterations in the stratum corneum structure and lipid content, which negatively impact the skin's barrier function with decreased moisture retention and increased vulnerability to infection. Efficacious restoration of the skin barrier and dysbiosis with strategic integration of acidic cleansers, emollients with optimal lipid composition, antioxidants, and judicious photoprotection may be a proactive approach to aging. Furthermore, modulation of the gut-skin axis through probiotics, prebiotics, and postbiotics emerges as a promising avenue to enhance skin health as studies have substantiated their efficacy in enhancing hydration, reducing wrinkles, and fortifying barrier integrity. In summary, the intricate interplay between microbes and skin barrier function is intrinsically woven into the tapestry of aging. Sound understanding of these interactions, coupled with strategic interventions aimed at recalibrating the microbiota and barrier equilibrium, holds the potential to ameliorate skin aging. Further in-depth studies are necessary to better understand skin-aging and develop targeted strategies for successful aging.

The Skin and Lewy Body Disease

This manuscript reviews the significant skin manifestations of Lewy body disease, including Parkinson's disease and dementia with Lewy bodies, and the diagnostic utility of skin biopsy. Besides classic motor and cognitive symptoms, non-motor manifestations, particularly dermatologic disorders, can play a crucial role in disease presentation and diagnosis. This review explores the intricate relationship between the skin and Lewy body disease. Seborrheic dermatitis, autoimmune blistering diseases (bullous pemphigoid and pemphigus), rosacea, and melanoma are scrutinized for their unique associations with Parkinson's disease, revealing potential links through shared pathophysiological mechanisms. Advances in diagnostic techniques allow the identification of promising biomarkers such as α-synuclein in samples obtained by skin punch biopsy. Understanding the dermatologic aspects of Lewy body disease not only contributes to its holistic characterization but also holds implications for innovative diagnostic approaches.

Association Between Skin Acid Mantle, Natural Moisturizing Factors, and Antibacterial Activity Against S. aureus in the Stratum Corneum

Purpose

The skin has evolved a system to prevent pathogenic microorganism colonization and infection. This study examined the role of natural moisturizing factors (NMFs) and skin pH on Staphylococcus aureus (S. aureus) growth and colonization on the human stratum corneum (SC).

Study Population and Methods

A survey study with 82 female participants was performed. Participants maintained their daily hygiene routine, except for refraining from using leave-on products on their forearms on the day of the test. Skin sampling was performed using adhesive tapes. An ex vivo method was developed to study the viability and growth of S. aureus on human SC sampled from normal skin. NMFs, including pyrrolidone carboxylic acid (PCA), urocanic acid (UCA), histidine, and proline in SC samples, were measured by liquid chromatography with tandem mass spectrometry. The impact of PCA and UCA on S. aureus growth and metabolic activity was measured by optical density and isothermal microcalorimetry, respectively.

Results

Heterogeneity of S. aureus viability on human SC samples was observed. Skin pH showed a significant negative association (p<0.05) with SC antibacterial activity in the ex vivo assay. One unit of skin pH decrease corresponded to 68.1% of S. aureus cell death. The levels of PCA and histidine were significantly negatively associated (p<0.05) with skin pH. The addition of 5 mM and 10 mM PCA significantly inhibited S. aureus growth by approximately 25% at 20 hours and reduced its metabolic activity in vitro.

Conclusion

The results indicate that PCA, one of the NMFs in human skin, plays an important role in regulating the human skin acid mantle in vivo and contributes to antibacterial activity against S. aureus.

Induction of Endogenous Antimicrobial Peptides to Prevent or Treat Oral Infection and Inflammation

Antibiotics are often used to treat oral infections. Unfortunately, excessive antibiotic use can adversely alter oral microbiomes and promote the development of antibiotic-resistant microorganisms, which can be difficult to treat. An alternate approach could be to induce the local transcription and expression of endogenous oral antimicrobial peptides (AMPs). To assess the feasibility and benefits of this approach, we conducted literature searches to identify (i) the AMPs expressed in the oral cavity; (ii) the methods used to induce endogenous AMP expression; and (iii) the roles that expressed AMPs may have in regulating oral inflammation, immunity, healing, and pain. Search results identified human neutrophil peptides (HNP), human beta defensins (HBD), and cathelicidin AMP (CAMP) gene product LL-37 as prominent AMPs expressed by oral cells and tissues. HNP, HBD, and LL-37 expression can be induced by micronutrients (trace elements, elements, and vitamins), nutrients, macronutrients (mono-, di-, and polysaccharides, amino acids, pyropeptides, proteins, and fatty acids), proinflammatory agonists, thyroid hormones, and exposure to ultraviolet (UV) irradiation, red light, or near infrared radiation (NIR). Localized AMP expression can help reduce infection, inflammation, and pain and help oral tissues heal. The use of a specific inducer depends upon the overall objective. Inducing the expression of AMPs through beneficial foods would be suitable for long-term health protection. Additionally, the specialized metabolites or concentrated extracts that are utilized as dosage forms would maintain the oral and intestinal microbiome composition and control oral and intestinal infections. Inducing AMP expression using irradiation methodologies would be applicable to a specific oral treatment area in addition to controlling local infections while regulating inflammatory and healing processes.

Saprophytic bacteria and fungi colonize stearoyl coenzyme-A desaturase-1 knockout skin

Lipids synthesized on the skin are critical to the antimicrobial barrier. Skin lipids also facilitate survival of lipophilic skin commensals in an otherwise dry and acidic ecological landscape. Thus, skin-specific stearoyl-coenzyme A desaturase 1 knockout mice (Scd1^ΔK14 ) with sebocyte atrophy and decreased synthesis of monounsaturated fatty acids, triglycerides and wax diesters have dry, inflamed skin. Here, we used 16S rRNA (V1-V2 and V1-V9) and internal transcribed spacer 1 (ITS1) amplicon sequencing to compare bacterial and fungal skin microbiomes between Scd1^ΔK14 mice and wildtype control mice (Scd1^fl/fl ) in a barrier facility. Saprophytic bacteria including Sporosarcina spp. and Staphylococcus lentus and saprophytic fungi including Alternaria infectoria were found in higher relative abundance in the Scd1^ΔK14 group (ANCOM). Analysis of community diversity (Shannon index) revealed greater fungal alpha diversity in the Scd1^ΔK14 group (p = 0.009, Kruskal-Wallis). Principal coordinates analysis (Bray-Curtis dissimilarity) showed that both bacterial (p = 0.002, PERMANOVA) and fungal communities (p = 0.006, PERMANOVA) of the Scd1^ΔK14 group were unique from the wildtype group. Altogether, these results suggest that sebaceous gland-derived lipids normally restrict the skin microbiome, and in the absence of these lipids, a greater diversity of opportunistic organisms are able to colonize the surface of skin.

IL-38 orchestrates proliferation and differentiation in human keratinocytes

Interleukin (IL)-38 is a member of the IL-1 cytokine family with reported anti-inflammatory activity. The highest constitutive IL-38 expression is detected in the skin, where it is mainly produced by differentiating keratinocytes. However, little data are available regarding its biological functions. In this study, we investigated the role of IL-38 in skin physiology. We demonstrate here that dermal fibroblasts and epithelial cells of skin appendages, such as eccrine sweat glands and sebaceous glands, also express IL-38. Next, using two- and three-dimensional cell cultures, we show that endogenous expression of IL-38 correlates with keratinocyte differentiation and its ectopic overexpression inhibits keratinocyte proliferation and enhances differentiation. Accordingly, immunohistochemical analysis revealed downregulation of IL-38 in skin pathologies characterized by keratinocyte hyperproliferation, such as psoriasis and basal or squamous cell carcinoma. Finally, intracellular IL-38 can shuttle between the nucleus and the cytoplasm and its overexpression modulates the activity of the transcription regulators YAP and ID1. Our results indicate that IL-38 can act independently from immune system activation and suggest that it may affect the epidermis directly by decreasing proliferation and promoting differentiation of keratinocytes. These data suggest an important role of keratinocyte-derived IL-38 in skin homeostasis and pathologies characterized by epidermal alterations.

The family of kallikrein-related peptidases and kinin peptides as modulators of epidermal homeostasis

The epidermis is the outermost skin layer and is part of one of the largest organs in the body; it is supported by the dermis, a network of fibrils, blood vessels, pilosebaceous units, sweat glands, nerves, and cells. The skin as a whole is a protective shield against numerous noxious agents, including microorganisms and chemical and physical factors. These functions rely on the activity of multiple growth factors, peptide hormones, proteases, and specific signaling pathways that are triggered by the activation of distinct types of receptors sited in the cell membranes of the various cell types present in the skin. The human kallikrein family comprises a large group of 15 serine proteases synthesized and secreted by different types of epithelial cells throughout the body, including the skin. At this site, they initiate a proteolytic cascade that generates the active forms of the proteases, some of which regulate skin desquamation, activation of cytokines, and antimicrobial peptides. Kinin peptides are formed by the action of plasma and tissue kallikreins on kininogens, two plasma proteins produced in the liver and other organs. Although kinins are well known for their proinflammatory abilities, in the skin they are also considered important modulators of keratinocyte differentiation. In this review, we summarize the contributions of the kallikreins and kallikrein-related peptidases family and those of kinins and their receptors in skin homeostasis, with special emphasis on their pathophysiological role.

Lichen Planopilaris: The first biopsy layer microbiota inspection

Lichen Planopilaris (LPP) is a lymphatic disease affecting the scalp that is characterized by a chronic and destructive inflammation process, named as ‘cicatricial alopecia’ in which the hair follicles are targeted and may involve predominantly lymphocytes or neutrophils. Scalp and biopsy layers have never been used to investigate microbial community composition and its relative taxa abundances in LPP. We sought to examine the significant taxa of this chronic relapsing inflammatory skin disease, together with inspect the existing connections with metabolic pathways featuring this microbial community. We used a multilevel analysis based on 16S rRNA marker sequencing in order to detect OTU abundances in pathologic/healthy samples, real time PCR for measuring the levels of IL-23 interleukin expression and urinary metabolomics to find out volatile organic metabolites (VOMs). By using a linear regression model, we described peculiar taxa that significantly differentiated LPP and healthy samples. We inspected taxa abundances and interleukin mRNA levels and the Microbacteriaceae family resulted negatively correlated with the IL-23 expression. Moreover, starting from 16S taxa abundances, we predicted the metabolic pathways featuring this microbial community. By inspecting microbial composition, sample richness, metabolomics profiles and the relative metabolic pathways in a cohort of LPP and healthy samples we deepened the contribution of significant taxa that are connected to inflammation maintenance and microbiota plasticity in LPP pathology.

The Penis, the Vagina and HIV Risk: Key Differences (Aside from the Obvious)

Globally, most Human Immunodeficiency Virus type 1 (HIV) transmission occurs through vaginal–penile sex (heterosexual transmission). The local immune environment at the site of HIV exposure is an important determinant of whether exposure during sex will lead to productive infection, and the vaginal and penile immune milieus are each critically shaped by the local microbiome. However, there are key differences in the microbial drivers of inflammation and immune quiescence at these tissue sites. In both, a high abundance of anaerobic taxa (e.g., Prevotella) is associated with an increased local density of HIV target cells and an increased risk of acquiring HIV through sex. However, the taxa that have been associated to date with increased risk in the vagina and penis are not identical. Just as importantly, the microbiota associated with comparatively less inflammation and HIV risk—i.e., the optimal microbiota—are very different at the two sites. In the vagina, Lactobacillus spp. are immunoregulatory and may protect against HIV acquisition, whereas on the penis, “skin type” flora such as Corynebacterium are associated with reduced inflammation. Compared to its vaginal counterpart, much less is known about the dynamics of the penile microbiome, the ability of clinical interventions to alter the penile microbiome, or the impact of natural/induced microbiome alterations on penile immunology and HIV risk.

Functionalization of Nanomaterials for Skin Cancer Theranostics

Skin cancer has drawn attention for the increasing incident rates and high morbidity worldwide. Timely diagnosis and efficient treatment are of paramount importance for prompt and effective therapy. Thus, the development of novel skin cancer diagnosis and treatment strategies is of great significance for both fundamental research and clinical practice. Recently, the emerging field of nanotechnology has profoundly impact on early diagnosis and better treatment planning of skin cancer. In this review, we will discuss the current encouraging advances in functional nanomaterials for skin cancer theranostics. Challenges in the field and safety concerns of nanomaterials will also be discussed.

Antimicrobial Tear Lipids in the Ocular Surface Defense

The concept of antimicrobial lipids as effectors of innate host defense is an emerging field. There is limited knowledge on the antimicrobial role of lipids in the ocular environment. Tears act as first line of defense to protect the ocular surface from infections. Antimicrobial effects of tear lipids have been demonstrated using meibomian lipids that are the source of majority of lipids in tears. This article describes the knowledge available on the antimicrobial role of tear lipids at the ocular surface and the antimicrobial potential of various lipid classes present in tears that can contribute to antimicrobial protection of the eye. Like other mucosal secretions, tears contain many proteins and lipids with known antimicrobial effects. The antimicrobial defense of tears is far stronger than can be demonstrated by the effects of individual compounds many of which are present in low concentrations but synergistic and additive interactions between them provide substantial antimicrobial protection to the ocular surface. It is inferred that antimicrobial lipids play important role in innate defense of tears, and cooperative interactions between various antimicrobial lipids and proteins in tears provide a potent host defense mechanism that is effective against a broad spectrum of pathogens and renders self-sterilizing properties to tears for keeping the microbial load low at the ocular surface.

Antibacterial Copolypeptoids with Potent Activity against Drug Resistant Bacteria and Biofilms, Excellent Stability, and Recycling Property

The preparation of a type of innovative cationic copolypeptoid antimicrobials containing various hydrophobic moieties that resemble both structure and membrane-lytic antibacterial mechanism of natural antimicrobial peptides (AMPs) is reported. By finely tuning the hydrophilic/hydrophobic balance, the polypeptoids exhibit a wide spectrum of antibacterial activity against both Gram-positive bacteria and Gram-negative bacteria with the lowest minimum inhibitory concentration (MIC) at only 2 µg mL^-1 , whereas they also show low haemolytic properties. In particular, high selectivity (>128) is achieved from the polymers with butyl moieties. Moreover, the polypeptoids can readily inhibit the formation of biofilms and effectively eradicate the bacteria embedded in the mature biofilms, which is superior to many natural AMPs and vancomycin. Unlike conventional antibiotics, the polypeptoids possess potent activity against drug-resistant bacteria without visible resistance development after repeated usage. Notably, the polypeptoid antimicrobials not only have inherently fast bactericidal properties and excellent stability against incubation with human plasma, but also show excellent in vivo antibacterial effect. The prepared antimicrobials, coated onto magnetic nanospheres show recycling properties and enhanced antibacterial activity as combined with near-infrared (NIR)-induced photothermal antibacterial therapy.

Mammalian Epidermis: A Compendium of Lipid Functionality

Mammalian epidermis is a striking example of the role of lipids in tissue biology. In this stratified epithelium, highly specialized structures are formed that leverage the hydrophobic properties of lipids to form an impermeable barrier and protect the humid internal environment of the body from the dry outside. This is achieved through tightly regulated lipid synthesis that generates the molecular species unique to the tissue. Beyond their fundamental structural role, lipids are involved in the active protection of the body from external insults. Lipid species present on the surface of the body possess antimicrobial activity and directly contribute to shaping the commensal microbiota. Lipids belonging to a variety of classes are also involved in the signaling events that modulate the immune responses to environmental stress as well as differentiation of the epidermal keratinocytes themselves. Recently, high-resolution methods are beginning to provide evidence for the involvement of newly identified specific lipid molecules in the regulation of epidermal homeostasis. In this review we give an overview of the wide range of biological functions of mammalian epidermal lipids.

Aging Associated Changes in the Adult Human Skin Microbiome and the Host Factors That Affect Skin Microbiome Composition

Understanding changes in the skin microbiome and their relationship to host skin factors during aging remains largely unknown. To better understand this phenomenon, we collected samples for metagenomic and host skin factor analyses from forearm, buttock, and facial skin from 158 Caucasian females at 20-24, 30-34, 40-44, 50-54, 60-64, and 70-74 years of age. Metagenomics analysis was performed using 16S rRNA gene sequencing, while host sebocyte gland area, skin lipids, natural moisturizing factors (NMFs) and anti-microbial peptides (AMPs) measurements were also performed. These analyses demonstrated that skin bacterial diversity increased at all the skin sites with increasing age. Of the bacterial genera with average relative abundance of >1%, only Lactobacillus and Cutibacterium demonstrated a significant change (decrease) in abundance at all sampled skin sites with increasing age. Additional bacterial genera demonstrated significant age and site-specific changes in abundance. Analysis of sebocyte area, NMFs, lipids and AMPs demonstrated an age-related decrease in sebocyte area and increases in NMFs/AMPs/skin lipids, all which correlated with changes in specific bacterial genera. In conclusion, the human skin microbiome undergoes age-associated alterations that may reflect underlying age-related changes in cutaneous biology.

Topical Probiotics Do Not Satisfy New Criteria for Effective Use Due to Insufficient Skin Microbiome Knowledge

We propose a set of criteria for topical probiotics to adhere to for safe and effective use for the skin microbiome. To form the basis of the criteria, we redefine the term “probiotics” and discuss successful and unsuccessful high-profile examples of the artificial addition of organisms to ecosystems in nature to understand what worked and what did not. Probiotics are often immediately assumed to have health benefits. However, as ecologists are aware, interfering with ecosystems is potentially catastrophic. The addition or removal of just one organism can significantly upset the delicate ecosystem balance. If our criteria are not met, we argue that topical probiotics could also cause damage and will not be beneficial. Due to the large intra- and inter-personal variation of the skin microbiome, our current knowledge of a healthy skin microbiome composition is not complete enough to fully satisfy the criteria. In follow-up work, we will investigate whether current topical probiotics research and commercial products meet our new criteria. We will also discuss problems with how to measure their effectiveness and suggest alternative solutions to replacing the lost biodiversity of the skin microbiome that was stripped away by environmental factors in the Western world.

Thymic stromal lymphopoietin induces adipose loss through sebum hypersecretion

Emerging studies indicate that the immune system can regulate systemic metabolism. Here, we show that thymic stromal lymphopoietin (TSLP) stimulates T cells to induce selective white adipose loss, which protects against obesity, improves glucose metabolism, and mitigates nonalcoholic steatohepatitis. Unexpectedly, adipose loss was not caused by alterations in food intake, absorption, or energy expenditure. Rather, it was induced by the excessive loss of lipids through the skin as sebum. TSLP and T cells regulated sebum release and sebum-associated antimicrobial peptide expression in the steady state. In human skin, TSLP expression correlated directly with sebum-associated gene expression. Thus, we establish a paradigm in which adipose loss can be achieved by means of sebum hypersecretion and uncover a role for adaptive immunity in skin barrier function through sebum secretion.

Extraction of natural moisturizing factor from the stratum corneum and its implication on skin molecular mobility

The natural moisturizing factor (NMF) is a mixture of small water-soluble compounds present in the upper layer of the skin, stratum corneum (SC). Soaking of SC in water leads to extraction of the NMF molecules, which may influence the SC molecular properties and lead to brittle and dry skin. In this study, we investigate how the molecular dynamics in SC lipid and protein components are affected by the removal of the NMF compounds. We then explore whether the changes in SC components caused by NMF removal can be reversed by a subsequent addition of one single NMF component: urea, pyrrolidone carboxylic acid (PCA) or potassium lactate. Samples of intact SC were investigated using NMR, X-ray diffraction, infrared spectroscopy and sorption microbalance. It is shown that the removal of NMF leads to reduced molecular mobility in keratin filaments and SC lipids compared to untreated SC. When the complex NMF mixture is replaced by one single NMF component, the molecular mobility in both keratin filaments and lipids is regained. From this we propose a general relation between the molecular mobility in SC and the amount of polar solutes which does not appear specific to the precise chemical identify of the NMF compounds.

Nano-fats for bugs: the benefits of lipid nanoparticles for antimicrobial therapy

Bacterial infections are an imminent global healthcare threat evolving from rapidly advancing bacterial defence mechanisms that antibiotics fail to overcome. Antibiotics have been designed for systemic administration to target planktonic bacteria, leading to difficulties in reaching the site of localized bacterial infection and an inability to overcome the biological, chemical and physical barriers of bacteria, including biofilms, intracellular infections and antimicrobial resistance. The amphiphilic, biomimetic and antimicrobial properties of lipids provide a promising toolbox to innovate and advance antimicrobial therapies, overcoming the barriers presented by bacteria in order to directly and effectively treat recalcitrant infections. Nanoparticulate lipid-based drug delivery systems can enhance antibiotic permeation through the chemical and physical barriers of bacterial infections, as well as fuse with bacterial cell membranes, release antibiotics in response to bacteria and act synergistically with loaded antibiotics to enhance the total antimicrobial efficacy. This review explores the barriers presented by bacterial infections that pose bio-pharmaceutical challenges to antibiotics and how different structural and functional mechanisms of lipids can enhance antimicrobial therapies. Different nanoparticulate lipid-based systems are presented as valuable drug delivery systems to advance the efficacy of antibiotics, including liposomes, liquid crystalline nanoparticles, solid lipid nanoparticles, nanostructured lipid carriers and lipid nanocarriers. In summary, liquid crystalline nanoparticles are emerging with the greatest potential for clinical applications and commercial success as an "all-rounder" advanced lipid-based antimicrobial therapy that overcomes the multiple biological, chemical and physical barriers of bacteria.

Recent advances in the development of anti-infective peptoids

This feature article highlights the progress that has been made towards the development of novel anti-infective peptoids and the key areas for future development within this field.

Scalp bacterial shift in Alopecia areata

The role of microbial dysbiosis in scalp disease has been recently hypothesized. However, little information is available with regards to the association between microbial population on the scalp and hair diseases related to hair growth. Here we investigated bacterial communities in healthy and Alopecia areata (AA) subjects. The analysis of bacterial distribution at the genus level highlighted an increase of Propionibacterium in AA subjects alongside a general decrease of Staphylococcus. Analysis of log Relative abundance of main bacterial species inhabiting the scalp showed a significant increase of Propionibacterium acnes in AA subjects compared to control ones. AA scalp condition is also associated with a significant decrease of Staphylococcus epidermidis relative abundance. No significant changes were found for Staphylococcus aureus. Therefore, data from sequencing profiling of the bacterial population strongly support a different microbial composition of the different area surrounded hair follicle from the epidermis to hypodermis, highlighting differences between normal and AA affected the scalp. Our results highlight, for the first time, the presence of a microbial shift on the scalp of patients suffering from AA and gives the basis for a larger and more complete study of microbial population involvement in hair disorders.

Potential of short-wave infrared spectroscopy for quantitative depth profiling of stratum corneum lipids and water in dermatology

We demonstrate the feasibility of short wave infrared (SWIR) spectroscopy combined with tape stripping for depth profiling of lipids and water in the stratum corneum of human skin. The proposed spectroscopic technique relies on differential detection at three wavelengths of 1720, 1750, and 1770 nm, with varying ratio of the lipid-to-water absorption coefficient and an 'isosbestic point'. Comparison of the data acquired using SWIR spectroscopy with that obtained by a gold standard for non-invasive quantitative molecular-specific skin measurements, namely confocal Raman spectroscopy (CRS), revealed specificity of the proposed modality for water and lipid quantification. At the same time, we provide evidence showing aberrant sensitivity of Corneometer hydration read-outs to the presence of skin surface lipids, and a lack of sensitivity of the Sebumeter when attempting to measure the lipids of the cornified lipid envelope and intracellular lipid layers. We conclude that a spectroscopic SWIR-based spectroscopic method combined with tape stripping has the potential for depth profiling of the stratum corneum water and lipids, due to superior measurement sensitivity and specificity compared to the Corneometer and Sebumeter.

Immunotopographical Differences of Human Skin

The immunological barrier of the healthy skin is considered to be unified on the whole body surface—however, recent indirect findings have challenged this dogma since microbial and chemical milieu (e.g., sebum, sweat, and pH) exhibit remarkable differences on topographically distinct skin areas. Therefore, in the present study, we performed whole transcriptomic and subsequent pathway analyses to assess differences between sebaceous gland rich (SGR) and sebaceous gland poor (SGP) regions. Here, we provide the first evidence that different skin regions exhibit a characteristic innate and adaptive immune and barrier milieu as we could detect significantly increased chemokine (CCL2, 3, 19, 20, 23, 24) and antimicrobial peptide (S100A7, A8, A9, lipocalin, β-defensin-2) expression, altered barrier (keratin 17, 79) functions, and a non-inflammatory Th17/IL-17 dominance in SGR skin compared to SGP. Regarding pro-inflammatory molecules (IL-1α, IL-6, IL-8, IL-33, TNF-α), similarly low levels were detected in both regions. Our data may explain the characteristic topographical localization of some immune-mediated and autoimmune skin disorders and we also propose that the term “healthy skin control sample,” widely used in experimental Dermatology, should only be accepted if researchers carefully specify the exact region of the healthy skin (along with the site of the diseased sample).

Measurements of AMPs in stratum corneum of atopic dermatitis and healthy skin-tape stripping technique

Decreased levels of antimicrobial peptides (AMPs) in atopic dermatitis (AD) have previously been reported and have been linked to the increased susceptibility to skin infections found in AD patients. This study intents to identify AMPs: hBD-2, hBD-3, RNase7, psoriasin and LL-37 in AD patients and healthy controls, and determine concentrations in consecutive depths of the outer most skin layers. Tape stripping was used on lesional and non-lesional skin. From each skin site, 35 consecutive tape strips were collected and pooled in groups of 5. Commercially available ELISA kits were used to determine AMP concentration in stratum corneum samples. hBD-2, hBD-3, RNase7 and psoriasin were identified in stratum corneum samples. hBD-3-level was markedly higher in AD non-lesional skin compared to healthy controls, and a similar trend was observed for RNase7. Most AMPs were distributed evenly through 35 tape strips, implying a homogeneous distribution of antimicrobial defense in the outer most skin layers. The findings indicate that AD patients may not suffer from a general baseline deficiency in AMPs, and that the innate immune defense is present throughout the stratum corneum, both insights of importance for understanding the role of AMPs in AD.

Antibacterial Effect of Eicosapentaenoic Acid against Bacillus cereus and Staphylococcus aureus: Killing Kinetics, Selection for Resistance, and Potential Cellular Target

Polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA; C20:5n-3), are attracting interest as possible new topical antibacterial agents, particularly due to their potency and perceived safety. However, relatively little is known of the underlying mechanism of antibacterial action of EPA or whether bacteria can develop resistance quickly against this or similar compounds. Therefore, the aim of this present study was to determine the mechanism of antibacterial action of EPA and investigate whether bacteria could develop reduced susceptibility to this fatty acid upon repeated exposure. Against two common Gram-positive human pathogens, Bacillus cereus and Staphylococcus aureus, EPA inhibited bacterial growth with a minimum inhibitory concentration of 64 mg/L, while minimum bactericidal concentrations were 64 mg/L and 128 mg/L for B. cereus and S. aureus, respectively. Both species were killed completely in EPA at 128 mg/L within 15 min at 37 °C, while reduced bacterial viability was associated with increased release of 260-nm-absorbing material from the bacterial cells. Taken together, these observations suggest that EPA likely kills B. cereus and S. aureus by disrupting the cell membrane, ultimately leading to cell lysis. Serial passage of the strains in the presence of sub-inhibitory concentrations of EPA did not lead to the emergence or selection of strains with reduced susceptibility to EPA during 13 passages. This present study provides data that may support the development of EPA and other fatty acids as antibacterial agents for cosmetic and pharmaceutical applications.

Functional Regulation of the Plasma Protein Histidine-Rich Glycoprotein by Zn2+ in Settings of Tissue Injury

Divalent metal ions are essential nutrients for all living organisms and are commonly protein-bound where they perform important roles in protein structure and function. This regulatory control from metals is observed in the relatively abundant plasma protein histidine-rich glycoprotein (HRG), which displays preferential binding to the second most abundant transition element in human systems, Zinc (Zn²⁺). HRG has been proposed to interact with a large number of protein ligands and has been implicated in the regulation of various physiological and pathological processes including the formation of immune complexes, apoptotic/necrotic and pathogen clearance, cell adhesion, antimicrobial activity, angiogenesis, coagulation and fibrinolysis. Interestingly, these processes are often associated with sites of tissue injury or tumour growth, where the concentration and distribution of Zn²⁺ is known to vary. Changes in Zn²⁺ levels have been shown to modify HRG function by altering its affinity for certain ligands and/or providing protection against proteolytic disassembly by serine proteases. This review focuses on the molecular interplay between HRG and Zn²⁺, and how Zn²⁺ binding modifies HRG-ligand interactions to regulate function in different settings of tissue injury.

pH Dependent Antimicrobial Peptides and Proteins, Their Mechanisms of Action and Potential as Therapeutic Agents

Antimicrobial peptides (AMPs) are potent antibiotics of the innate immune system that have been extensively investigated as a potential solution to the global problem of infectious diseases caused by pathogenic microbes. A group of AMPs that are increasingly being reported are those that utilise pH dependent antimicrobial mechanisms, and here we review research into this area. This review shows that these antimicrobial molecules are produced by a diverse spectrum of creatures, including vertebrates and invertebrates, and are primarily cationic, although a number of anionic examples are known. Some of these molecules exhibit high pH optima for their antimicrobial activity but in most cases, these AMPs show activity against microbes that present low pH optima, which reflects the acidic pH generally found at their sites of action, particularly the skin. The modes of action used by these molecules are based on a number of major structure/function relationships, which include metal ion binding, changes to net charge and conformational plasticity, and primarily involve the protonation of histidine, aspartic acid and glutamic acid residues at low pH. The pH dependent activity of pore forming antimicrobial proteins involves mechanisms that generally differ fundamentally to those used by pH dependent AMPs, which can be described by the carpet, toroidal pore and barrel-stave pore models of membrane interaction. A number of pH dependent AMPs and antimicrobial proteins have been developed for medical purposes and have successfully completed clinical trials, including kappacins, LL-37, histatins and lactoferrin, along with a number of their derivatives. Major examples of the therapeutic application of these antimicrobial molecules include wound healing as well as the treatment of multiple cancers and infections due to viruses, bacteria and fungi. In general, these applications involve topical administration, such as the use of mouth washes, cream formulations and hydrogel delivery systems. Nonetheless, many pH dependent AMPs and antimicrobial proteins have yet to be fully characterized and these molecules, as a whole, represent an untapped source of novel biologically active agents that could aid fulfillment of the urgent need for alternatives to conventional antibiotics, helping to avert a return to the pre-antibiotic era.

Lrig1 Expression in Human Sebaceous Gland Tumors

Background

Sebaceous glands contribute significantly to the barrier functions of the skin. However, little is known about their homeostasis and tumorigenesis. Recently, increased expression of stem cell marker Lrig1 has been reported in sebaceous carcinoma-like tumors of K14ΔNLef1 transgenic mice. In this study, we analyzed the Lrig1 expression in human sebaceous tumors.

Methods

Twenty-eight formalin-fixed paraffin-embedded sebaceous tumor specimens (7 sebaceous hyperplasias, 7 sebaceous adenomas, 10 sebaceomas and 4 sebaceous carcinomas) were stained with anti-Lrig1, anti-CD44v3 and anti-Ki67 antibody.

Results

Four (100%) sebaceous carcinomas, 8 (80%) sebaceomas, 3 (43%) sebaceous adenomas and no sebaceous hyperplasia showed Lrig1 overexpression.

Discussion and Conclusion

Lrig1 is a known tumor suppressor gene and is usually considered to be an indicator of poorly aggressive tumors. In human sebaceous tumors, the stronger Lrig1 staining in sebaceous carcinoma compared to other sebaceous tumors might be a feature of an advanced stage in tumorigenesis and a bad prognosis. In our study, 100% of sebaceous carcinomas revealed Lrig1 overexpression. We propose that Lrig1 may be used as a possible new marker of poorly differentiated sebaceous carcinoma.

Antimicrobial Activity of Chemokine CXCL10 for Dermal and Oral Microorganisms

CXCL10 (IP-10) is a small 10 kDa chemokine with antimicrobial activity. It is induced by IFN-γ, chemoattracts mononuclear cells, and promotes adhesion of T cells. Recently, we detected CXCL10 on the surface of the skin and in the oral cavity. In the current study, we used broth microdilution and radial diffusion assays to show that CXCL10 inhibits the growth of Escherichia coli, Staphylococcus aureus, Corynebacterium jeikeium, Corynebacterium striatum, and Candida albicans HMV4C, but not Corynebacterium bovis, Streptococcus mutans, Streptococcus mitis, Streptococcus sanguinis, Fusobacterium nucleatum, Aggregatibacter actinomycetemcomitans, Poryphromonas gingivalis, or C. albicans ATCC 64124. The reason for the selective antimicrobial activity is not yet known. However, antimicrobial activity of CXCL10 may be related to its composition and structure, as a cationic 98 amino acid residue molecule with 10 lysine residues, 7 arginine residues, a total net charge of +11, and a theoretical pI of 9.93. Modeling studies revealed that CXCL10 contains an α-helix at the N-terminal, three anti-parallel β-strands in the middle, and an α-helix at the C-terminal. Thus, CXCL10, when produced on the surface of the skin or in the oral cavity, likely has antimicrobial activity and may enhance innate antimicrobial and cellular responses to the presence of select commensal or opportunistic microorganisms.

Antimicrobial peptides and wound healing: biological and therapeutic considerations

Repair of tissue wounds is a fundamental process to re-establish tissue integrity and regular function. Importantly, infection is a major factor that hinders wound healing. Multicellular organisms have evolved an arsenal of host-defense molecules, including antimicrobial peptides (AMPs), aimed at controlling microbial proliferation and at modulating the host's immune response to a variety of biological or physical insults. In this brief review, we provide the evidence for a role of AMPs as endogenous mediators of wound healing and their promising therapeutic potential for the treatment of non-life-threatening skin and other epithelial injuries.

Exploration of scalp surface lipids reveals squalene peroxide as a potential actor in dandruff condition

Dandruff is a common but complex disorder with three major contributing factors: (1) individual predisposition, (2) scalp sebum and (3) Malassezia yeast colonization. To obtain further insights into the role of sebum in dandruff biogenesis, we analyzed scalp lipid species in a cohort of ten dandruff-free (control) and ten dandruff-afflicted volunteers by gas chromatography coupled to mass spectrometry. Lipid peroxidation levels and biochemical markers of oxidative stress were also assessed. Squalene, a major sebum component, was significantly more peroxidized in dandruff-affected scalps, resulting in significantly higher ratios of squalene monohydroperoxide (SQOOH)/squalene. This was observed when comparing dandruff-affected zones of dandruff subjects to both their non-affected zones and control subjects. In addition, other biomarkers such as malondialdehyde indicated that oxidative stress levels were raised on dandruff scalps. Surprisingly, differences regarding either free or bound fatty acids were fairly rare and minor. Certain novel findings, especially squalene peroxidation levels, were then confirmed in a validation cohort of 24 dandruff-affected subjects, by comparing dandruff-affected and non-dandruff zones from the same individuals. As SQOOH can induce both keratinocyte inflammatory responses and hyperproliferation in vitro, we hypothesized that increased SQOOH could be considered as a new etiological dandruff factor via its ability to impair scalp barrier function. Our results also indicated that Malassezia could be a major source of squalene peroxidation on the scalp.

Hybrid peptide ATCUN-sh-Buforin: Influence of the ATCUN charge and stereochemistry on antimicrobial activity

The emergence of antibiotic resistant strains of bacteria has resulted in the need to develop more potent antimicrobials that target microorganisms in a novel manner. Antimicrobial Peptides (AMPs) show great potential for drug development because of their broad activity and unique mechanism of action. Several AMPs contain an Amino Terminal Copper and Nickel (ATCUN) binding motif; however, its function has not yet been determined. We have previously demonstrated that the activity of a truncated version of Buforin II (sh-Buforin, RAGLQFPVGRVHRLLRK-NH2) increases by the addition of an ATCUN motif. We now focus our current studies on understanding the effect of: 1) a positively charged ATCUN sequence, and 2) l-to-d amino acid substitution on the hybrid peptides. We identified that the addition of a positively charged ATCUN motif increases the affinity of the ATCUN-AMP for DNA but does not always result in an enhanced antimicrobial activity over a neutral ATCUN motif. The all-d peptides exhibited up to a 32-fold increase in antimicrobial activity compared to the all-l peptides. The larger activity of the all-d peptides is the result of a larger DNA cleavage activity and higher stability towards proteolysis. Cytotoxicity assays determined that, at their MIC, these peptides caused less than 8% hemolysis and, at 128 μM, no toxicity to HeLa and HEK293 cell lines. These results indicate that the ATCUN-AMP hybrids are an attractive alternative for treating infectious diseases and provide key insights into the role of the ATCUN motif in naturally-occurring AMPs.

Residual antibiotics in decontaminated human cardiovascular tissues intended for transplantation and risk of falsely negative microbiological analyses

We investigated the presence of antibiotics in cryopreserved cardiovascular tissues and cryopreservation media, after tissue decontamination with antibiotic cocktails, and the impact of antibiotic residues on standard tissue bank microbiological analyses. Sixteen cardiovascular tissues were decontaminated with bank-prepared cocktails and cryopreserved by two different tissue banks according to their standard operating procedures. Before and after decontamination, samples underwent microbiological analysis by standard tissue bank methods. Cryopreserved samples were tested again with and without the removal of antibiotic residues using a RESEP tube, after thawing. Presence of antibiotics in tissue homogenates and processing liquids was determined by a modified agar diffusion test. All cryopreserved tissue homogenates and cryopreservation media induced important inhibition zones on both Staphylococcus aureus- and Pseudomonas aeruginosa-seeded plates, immediately after thawing and at the end of the sterility test. The RESEP tube treatment markedly reduced or totally eliminated the antimicrobial activity of tested tissues and media. Based on standard tissue bank analysis, 50% of tissues were found positive for bacteria and/or fungi, before decontamination and 2 out of 16 tested samples (13%) still contained microorganisms after decontamination. After thawing, none of the 16 cryopreserved samples resulted positive with direct inoculum method. When the same samples were tested after removal of antibiotic residues, 8 out of 16 (50%) were contaminated. Antibiotic residues present in tissue allografts and processing liquids after decontamination may mask microbial contamination during microbiological analysis performed with standard tissue bank methods, thus resulting in false negatives.

Ceramide synthase 4 deficiency in mice causes lipid alterations in sebum and results in alopecia

Five ceramide synthases (CerS2-CerS6) are expressed in mouse skin. Although CerS3 has been shown to fulfill an essential function during skin development, neither CerS6- nor CerS2-deficient mice show an obvious skin phenotype. In order to study the role of CerS4, we generated CerS4-deficient mice (Cers4-/-) and CerS4-specific antibodies. With these biological tools we analysed the tissue distribution and determined the cell-type specific expression of CerS4 in suprabasal epidermal layers of footpads as well as in sebaceous glands of the dorsal skin. Loss of CerS4 protein leads to an altered lipid composition of the sebum, which is more solidified and therefore might cause progressive hair loss due to physical blocking of the hair canal. We also noticed a strong decrease in C20 1,2-alkane diols consistent with the decrease of wax diesters in the sebum of Cers4-/- mice. Cers4-/- mice at 12 months old display additional epidermal tissue destruction due to dilated and obstructed pilary canals. Mass spectrometric analyses additionally show a strong decrease in C20-containing sphingolipids.

Alpha-melanocyte stimulating hormone: an emerging anti-inflammatory antimicrobial peptide

The alpha-melanocyte stimulating hormone (α-MSH) is a neuropeptide belonging to the melanocortin family. It is well known for its anti-inflammatory and antipyretic effects and shares several characteristics with antimicrobial peptides (AMPs). There have been some recent reports about the direct antimicrobial activity of α-MSH against various microbes belonging to both fungal and bacterial pathogens. Similar to α-MSH's anti-inflammatory properties, its C-terminal residues also exhibit antimicrobial activity parallel to that of the entire peptide. This review is focused on the current findings regarding the direct antimicrobial potential and immunomodulatory mechanism of α-MSH and its C-terminal fragments, with particular emphasis on the prospects of α-MSH based peptides as a strong anti-infective agent.

New strategies for preoperative skin antisepsis

During the past decades, encouraging progress has been made in the prevention of surgical site infections (SSI). However, as SSI still occur today, strategic prevention measures such as standardized skin antisepsis must be implemented and rigorously promoted. Recent discoveries in skin physiology necessitate the development of novel antiseptic agents and procedures in order to ameliorate their efficacy. In particular, alternate target structures in the skin need to be taken into consideration for the development of the next generation of antiseptics. Recent investigations have shown that a high number of microorganisms are located within and in the close vicinity of the hair follicles. This suggests that these structures are an important reservoir of bacterial growth and activity in human skin. To date, it has not been fully elucidated to what extent conventional liquid antiseptics sufficiently target the hair follicle-related microbial population. Modern technologies such as tissue-tolerable plasma (TTP) have been tested for their potential antiseptic efficiency by reducing the bacterial load in the skin and in the hair follicles. First experiments using liposomes to deliver antiseptics into the hair follicles have been evaluated for their potential clinical application. The present review evaluates these two innovative methods for their efficacy and applicability in preoperative skin antiseptics.

Epidermal growth factor receptor signalling in keratinocyte biology: implications for skin toxicity of tyrosine kinase inhibitors

The epidermal growth factor receptor (EGFR) and its ligands have been long recognized as centrally involved in the growth and repair process of epithelia, as well as in carcinogenesis. In addition, the EGFR has been demonstrated to be importantly involved in the control of inflammatory responses. During this last decade, a number of highly specific agents targeting this system have become an integral component of pharmacologic strategies against many solid malignancies. These drugs have led to increased patient survival and made therapy more tolerant when compared to conventional cytotoxic drugs. Nonetheless, their use is associated with a constellation of toxic effects on the skin, including follicular pustules, persistent inflammation, xerosis and pruritus, and enhanced susceptibility to infections. This dramatic impairment of skin homoeostasis underscores the centrality of the EGFR-ligand system in the whole skin immune system. So far, no mechanism-based approaches are available to specifically counteract the adverse effects of anti-EGFR drugs or any other class of tyrosine kinase inhibitors. Only the knowledge of the cellular and molecular events underlying these adverse effects in humans, combined with in vitro/in vivo models able to mimic these toxic responses, may guide the development of mechanism-based treatment or prevention strategies.

Antibacterial activity of long-chain polyunsaturated fatty acids against Propionibacterium acnes and Staphylococcus aureus

New compounds are needed to treat acne and superficial infections caused by Propionibacterium acnes and Staphylococcus aureus due to the reduced effectiveness of agents used at present. Long-chain polyunsaturated fatty acids (LC-PUFAs) are attracting attention as potential new topical treatments for Gram-positive infections due to their antimicrobial potency and anti-inflammatory properties. This present study aimed to investigate the antimicrobial effects of six LC-PUFAs against P. acnes and S. aureus to evaluate their potential to treat infections caused by these pathogens. Minimum inhibitory concentrations were determined against P. acnes and S. aureus, and the LC-PUFAs were found to inhibit bacterial growth at 32–1024 mg/L. Generally, P. acnes was more susceptible to the growth inhibitory actions of LC-PUFAs, but these compounds were bactericidal only for S. aureus. This is the first report of antibacterial activity attributed to 15-hydroxyeicosapentaenoic acid (15-OHEPA) and 15-hydroxyeicosatrienoic acid (HETrE), while the anti-P. acnes effects of the six LC-PUFAs used herein are novel observations. During exposure to the LC-PUFAs, S. aureus cells were killed within 15–30 min. Checkerboard assays demonstrated that the LC-PUFAs did not antagonise the antimicrobial potency of clinical agents used presently against P. acnes and S. aureus. However, importantly, synergistic interactions against S. aureus were detected for combinations of benzoyl peroxide with 15-OHEPA, dihomo-γ-linolenic acid (DGLA) and HETrE; and neomycin with 15-OHEPA, DGLA, eicosapentaenoic acid, γ-linolenic acid and HETrE. In conclusion, LC-PUFAs warrant further evaluation as possible new agents to treat skin infections caused by P. acnes and S. aureus, especially in synergistic combinations with antimicrobial agents already used clinically.

The roles of cutaneous lipids in host defense

Lauric acid (C12:0) and sapienic acid (C16:1Δ6) derived from human sebaceous triglycerides are potent antimicrobials found at the human skin surface. Long-chain bases (sphingosine, dihydrosphingosine and 6-hydroxysphingosine) are also potent and broad-acting antimicrobials normally present at the skin surface. These antimicrobials are generated through the action of ceramidases on ceramides from the stratum corneum. These natural antimicrobials are thought to be part of the innate immune system of the skin. Exogenously providing these lipids to the skin may provide a new therapeutic option, or could potentially provide prophylaxis in people at risk of infection. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Organization, barrier function and antimicrobial lipids of the oral mucosa

As one moves from the skin across the vermilion region of the lip and into the oral cavity, the oral mucosa is encountered. The oral mucosa consists of connective tissue known as the lamina propria covered by a stratified squamous epithelium. In the regions of the hard palate and gingiva, the epithelium is keratinized like the epidermis. In the buccal region, the floor of the mouth and the underside of the tongue, the epithelium is non-keratinized. The epithelium on the dorsum of the tongue is a specialized epithelium, but can be approximated as a mosaic of keratinized and non-keratinized epithelia. The non-keratinized epithelial regions do not produce a stratum corneum. Nuclei with intact DNA are retained in the superficial cells. In all regions, the outer portions of the epithelium provide a protective permeability barrier, which varies regionally. Antimicrobial lipids at the surfaces of the oral mucosa are an integral part of innate immunity.