Dietary deficiencies of unsaturated fatty acids and starch cause atopic dermatitis-like pruritus in hairless mice

Protective effects of extracts from Acer truncatum leaves on SLS-induced HaCaT cells

Introduction:A. truncatum Bunge (Sapindaceae or formerly Aceraceae) is a tall deciduous tree native to China. Traditionally, the leaves of A. truncatum are decocted and used by Chinese Mongolians, Koreans, and Tibetans to treat skin itching, dry cracks, and other skin ailments, which indicates A. truncatum leaves may have a potential inhibitory effect on various skin inflammations.

Methods: To examine the protective effect against skin inflammations of A. truncatum leaf extract (ATLE), an in vitro dermatitis model was established using sodium dodecyl sulfate (SLS)-induced HaCaT cells. The anti-inflammatory effect of ATLE was evaluated by analyzing cell viability, apoptosis, reactive oxygen species (ROS), interleukin 6 (IL-6), and prostaglandin E2 (PGE2) levels.

Results: Orthogonal experiments showed that the pretreatment with ATLE can reduce the IL-6 levels, PGE2 levels, and apoptosis increased in SLS-stimulated HaCaT cells, which indicates that ATLE has positive efficacy for dermatitis. Furthermore, three flavonoid compounds kaempferol-3-O-α-L-rhamnoside, quercetin-3-O-α-L-rhamnopyranoside, kaempferol-3,7-di-O-α-L-rhamnoside, and 1,2,3,4,6-Penta-O-galloyl-β-D-glucopyranose (PGG) were isolated and identified. Among them, kaempferol-3,7-di-O-α-L-rhamnoside was isolated from this plant for the first time. These compounds have been proven to have an anti-inflammatory effect. They may contribute to the efficacy of A. truncatumin treating skin inflammation.

Discussion: The results revealed that ATLE has the potential to be used as an additive in various skin care products to prevent skin inflammations and may be incorporated in formulations for topical application as a therapeutic approach against dermatitis.

Integrated transcriptomic and metabolomic analyses of DNCB-induced atopic dermatitis in mice

AIMS

Atopic dermatitis (AD) is a common chronic inflammatory skin disorder that affects up to 20 % of children and 10 % of adults worldwide; however, the exact molecular mechanisms remain largely unknown.

MATERIALS AND METHODS

In this study, we used integrated transcriptomic and metabolomic analyses to study the potential mechanisms of 1-chloro-2,4-dinitrobenzene (DNCB)-induced AD-like skin lesions.

KEY FINDINGS

We found that DNCB induced AD-like skin lesions, including phenotypical and histomorphological alterations and transcriptional and metabolic alterations in mice. A total of 3413 differentially expressed metabolites were detected between DNCB-induced AD-like mice and healthy controls, which includes metabolites in taurine and hypotaurine metabolism, phenylalanine metabolism, biosynthesis of unsaturated fatty acids, tryptophan metabolism, arachidonic acid metabolism, pantothenate and CoA biosynthesis, pyrimidine metabolism, and glycerophospholipid metabolism pathways. Furthermore, the differentially expressed genes associated (DEGs) with these metabolic pathways were analyzed using RNA sequencing (RNA-seq), and we found that the expression of pyrimidine metabolism-associated genes was significantly increased. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the glycolysis/gluconeogenesis, glucagon signaling pathway and pentose phosphate pathway-associated metabolic genes were dramatically altered.

SIGNIFICANCE

Our results explain the possible mechanism of AD at the gene and metabolite levels and provide potential targets for the development of clinical drugs for AD.

The contribution of mouse models to understanding atopic dermatitis

Atopic dermatitis (AD) is a dermatological disease accompanied by dry and cracked skin with severe pruritus. Although various therapeutic strategies have been introduced to alleviate AD, it remains challenging to cure the disorder. To achieve such a goal, understanding the pathophysiological mechanisms of AD is a prerequisite, requiring mouse models that properly reflect the AD phenotypes. Currently, numerous AD mouse models have been established, but each model has its own advantages and weaknesses. In this review, we categorized and summarized mouse models of AD and described their characteristics from a researcher's perspective.

The Pathogenic and Therapeutic Implications of Ceramide Abnormalities in Atopic Dermatitis

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

Novel mechanisms of microbial crosstalk with skin innate immunity

Skin is an organ with a dynamic ecosystem that harbours pathogenic and commensal microbes, which constantly communicate amongst each other and with the host immune system. Evolutionarily, skin and its microbiota have evolved to remain in homeostasis. However, frequently this homeostatic relationship is disturbed by a variety of factors such as environmental stress, diet, genetic mutations, and the microbiome itself. Commensal microbes also play a major role in the maintenance of microbial homeostasis. In addition to their ability to limit pathogens, many skin commensals such as Staphylococcus epidermidis and Cutibacterium acnes have recently been implicated in disease pathogenesis either by directly modulating the host immune components or by supporting the expansion of other pathogenic microbes. Likewise, opportunistic skin pathogens such as Staphylococcus aureus and Staphylococcus lugdunensis are able to breach the skin and cause disease. Though much has been established about the microbiota's function in skin immunity, we are in a time where newer mechanistic insights rapidly redefine our understanding of the host/microbial interface in the skin. In this review, we provide a concise summary of recent advances in our understanding of the interplay between host defense strategies and the skin microbiota.

Diet-Induced Mouse Model of Atopic Dermatitis

Atopic dermatitis (AD) is a common skin disease characterized by chronic inflammation and itchiness. Although skin barrier dysfunction and immune abnormalities are thought to contribute to the development of AD, the precise pathogenic mechanism remains to be elucidated. We have developed a unique, diet-induced AD mouse model based on the findings that deficiencies of certain polyunsaturated fatty acids and starches cause AD-like symptoms in hairless mice. Here, we present a protocol and tips for establishing an AD mouse model using a custom diet modified from a widely used standard diet (AIN-76A Rodent Diet). We also describe methods for evaluating skin barrier dysfunction and analyzing itch-related scratching behavior. This model can be used not only to investigate the complex pathogenic mechanism of human AD but also to study the puzzling relationship between nutrition and AD development.

Brain allopregnanolone induces marked scratching behaviour in diet-induced atopic dermatitis mouse model

Allopregnanolone (ALLO) is a neurosteroid produced in the brain, but so far, no study has explored its link with itching. Herein, we used a diet-induced atopic dermatitis mouse model to examine whether exogenously administered and endogenously produced ALLO contribute to inducing scratching. Systemic administration of ALLO elicited robust scratching in the atopic dermatitis model, while it did not affect spontaneous and pruritogen-induced scratching in normal mice. ALLO caused scratching when administered intracisternally, but not when administered intrathecally or intradermally, suggesting the involvement of supraspinal mechanisms. Pharmacological analyses suggested that both γ-aminobutyric acid type A receptor activation and serotonin type 3 receptor inhibition were involved in ALLO-induced scratching. We next examined whether endogenously produced ALLO is involved in ethanol-induced scratching in atopic dermatitis mice, because ethanol administration increases ALLO in rodent brain. Acute ethanol administration increased brain ALLO levels, which coincided with increased scratching. Pre-treatment with finasteride, a synthetic ALLO inhibitor, suppressed ethanol-induced scratching and ALLO production in the brain. Collectively, our results demonstrated for the first time that ALLO administration caused marked scratching in atopic dermatitis mice, and ethanol-induced scratching may be mediated through endogenously produced brain ALLO.

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

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

Barbiturates enhance itch-associated scratching in atopic dermatitis mice: A possible clue to understanding nocturnal pruritus in atopic dermatitis

In chronic pruritic diseases such as atopic dermatitis, pruritus is exacerbated during nocturnal sleep; however, the underlying mechanism remains unclear. We previously demonstrated that acute administration of the sedative-hypnotics ethanol markedly enhanced itch-associated spontaneous scratching in a diet-induced mouse model of atopic dermatitis. In the present study, to expand our previous finding and provide a general mechanism for the central modulation of chronic itch, we examined whether other hypnotic drugs, such as barbiturates and benzodiazepines, also enhance scratching, and further investigated the underlying mechanism. Barbiturates markedly enhanced spontaneous scratching in the atopic dermatitis model but not controls. However, unexpectedly, benzodiazepines only slightly increased scratching, and the selective γ-aminobutyric acid type A (GABA_A) receptor agonist, muscimol, had no effect. Local injection studies have demonstrated that barbiturates act at the supraspinal level to enhance scratching. Barbiturate-induced scratching was inhibited not only by GABA_A receptor antagonists but also by an L-type voltage-dependent calcium channel (L-VDCC) agonist and an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptor agonist. An intracisternally injected AMPA receptor antagonist alone or in combination with an L-VDCC antagonist sufficiently enhanced scratching. Barbiturate-induced scratching enhancement was observed in another atopic dermatitis model, NC/Nga, but not in histamine-induced acute itch model in normal healthy mice. Overall, our results suggest that a synergistic effect among AMPA receptor inhibition, GABA_A receptor activation, and L-VDCC inhibition in the brain mediates barbiturate-induced scratching in atopic dermatitis mice. This observation may provide a novel clue to understanding a supraspinal itch mechanism in chronic diseases such as atopic dermatitis.

High-Fat Diet and Alcohol Intake Promotes Inflammation and Impairs Skin Wound Healing in Wistar Rats

The wound-healing process is complex and remains a challenging process under the influence of several factors, including eating habits. As improper diets may lead to disorders such as dyslipidemia, insulin resistance, and chronic inflammation, potentially affecting the tissue ability to heal, we decided to investigate the effect of a high-fat diet and alcohol intake on the inflammatory process and skin wound healing in Wistar rats. Male rats (n = 30) were individually housed in cages with food and water ad libitum (registration number 213/2014). After anesthesia, at day 40, three circular wounds (12 mm diameter) were made on the back of each animal, which were then randomly assorted into five treatment groups: C1 (control 1)-water via gavage and standard chow diet; C2 (control 2)-water (no gavage) and standard chow diet; AL (alcohol)-water (no gavage) and alcohol (40%) via gavage and standard chow diet; HF (high fat)-water (no gavage) and high-fat diet (50%); and HF + AL (alcohol/high fat)-water (no gavage), alcohol (40%) via gavage, and high-fat diet. Animals were treated for 61 days. Every seven days, the area and the rate of wound contraction were evaluated. Tissue samples were removed for histopathological analysis and biochemical analyses. Our results showed that wound contraction was not complete in the HF + AL rats. Two specific indices of wound-healing impairment (total cell number and levels of the inflammatory cytokine TGF-β) were increased in the HF + AL rats. We also observed decreased type I and III collagen fibers in the HF, AL, and HF + AL groups and increased oxidative stress markers in the same groups. We suggest that a high-fat diet combined with alcohol intake contributed to delayed skin wound healing through increase of the inflammatory phase and promoting oxidative stress, which may have led to morphological alterations and impaired matrix remodeling.

Anti-Inflammatory and Skin Barrier Repair Effects of Topical Application of Some Plant Oils

Plant oils have been utilized for a variety of purposes throughout history, with their integration into foods, cosmetics, and pharmaceutical products. They are now being increasingly recognized for their effects on both skin diseases and the restoration of cutaneous homeostasis. This article briefly reviews the available data on biological influences of topical skin applications of some plant oils (olive oil, olive pomace oil, sunflower seed oil, coconut oil, safflower seed oil, argan oil, soybean oil, peanut oil, sesame oil, avocado oil, borage oil, jojoba oil, oat oil, pomegranate seed oil, almond oil, bitter apricot oil, rose hip oil, German chamomile oil, and shea butter). Thus, it focuses on the therapeutic benefits of these plant oils according to their anti-inflammatory and antioxidant effects on the skin, promotion of wound healing and repair of skin barrier.

Oral administration of β-carotene or lycopene prevents atopic dermatitis-like dermatitis in HR-1 mice

Atopic dermatitis (AD) is a chronic relapsing eczematous skin disease. Certain populations of patients are resistant to standard therapies with topical steroids and/or calcineurin inhibitors, and require systemic medication, such as immunosuppressants. Recently, several reports have shed light on the anti-allergic effects of carotenoids. Therefore, we investigated the effect of p.o. administration of β-carotene or lycopene on AD-like symptoms of HR-1 hairless mice fed with a low zinc/magnesium diet. Mice were divided into four groups: (i) fed with a standard diet (Co group); (ii) low zinc/magnesium diet (HR group); (iii) low zinc/magnesium and β-carotene diet (HR-C group); and (iv) low zinc/magnesium and lycopene diet (HR-L group). They were then fed these diets for 8 weeks. Severities of dermatitis were assessed by their appearance, and histopathological and hematological observations. Mice in the HR group developed AD-like dermatitis both clinically and histologically. HR-C and HR-L group mice also developed xerosis and wrinkle-like skin changes, but they were milder than those of HR group mice. Histological analysis revealed that epidermis thickening and inflammatory cell infiltration in the skin of the HR-C and HR-L groups were both statistically less than those of the HR group. The concentration of thymus and activation regulated chemokine in the skin of the HR-L group and the concentration of CCL27 in the skin of the HR-C group were significantly lower than those of the HR group, respectively. In conclusion, p.o. administration of β-carotene or lycopene prevents AD-like symptoms in association with a suppression of T-helper 2 chemokines in a murine model. Ingestion of carotenoids may be beneficial for patients with AD.

Need for Animal Models of Meibomian Gland Dysfunction

Evaporative dry eye has gained increasing interest in recent years in academia, pharmaceutical, and medical device industries. The main cause of this type of dry eye is attributed to meibomian gland dysfunction (MGD). MGD is a diffuse abnormality of the meibomian glands characterised by terminal duct obstruction and eventually leading to signs and symptoms of dry eye. There have been only a few reported animal models of MGD, but recent advances are likely to lead to new models and better ways to assess the pathology in these animals. Recent models reported include one based on cautery of the meibomian glands in mice and another based on aggravated allergy in mice. These developments will enable better pre-clinical assessment of novel therapies in the future.