Involvement of leukotriene B4 in spontaneous itch-related behaviour in NC mice with atopic dermatitis-like skin lesions

A Novel Recombinant Human Filaggrin Segment (rhFLA-10) Alleviated a Skin Lesion of Atopic Dermatitis

Atopic dermatitis (AD), a prevalent chronic inflammatory skin disorder, is marked by impaired skin barrier function and persistent pruritus. It significantly deteriorates patients' quality of life, making it one of the most burdensome non-lethal skin disorders. Filaggrin plays a crucial role in the pathophysiology of barrier disruption in AD, interacting with inflammatory mediators. It is an integral part of the extracellular matrix architecture, serving to protect the skin barrier and attenuate the inflammatory cascade. In this study, we engineered a novel recombinant human filaggrin (rhFLA-10) expression vector, which was subsequently synthesized and purified. In vitro and ex vivo efficacy experiments were conducted for AD. rhFLA-10, at low concentrations (5 to 20 μg/mL), was non-toxic to HACaT cells, significantly inhibited the degranulation of P815 mast cells, and was readily absorbed by cells, thereby exerting a soothing therapeutic effect. Furthermore, rhFLA-10 demonstrated anti-inflammatory properties (p < 0.05). In vivo, efficacy experiments further substantiated that rhFLA-10 could effectively ameliorate AD in mice and facilitate the repair of damaged skin (p < 0.001). These findings underscore the considerable potential of rhFLA-10 in the treatment of AD.

Boesenbergia rotunda and Its Pinostrobin for Atopic Dermatitis: Dual 5-Lipoxygenase and Cyclooxygenase-2 Inhibitor and Its Mechanistic Study through Steady-State Kinetics and Molecular Modeling

Human 5-lipoxygenase (5-LOX) and cyclooxygenase-2 (COX-2) are potential targets for suppressing pruritic skin inflammation in atopic dermatitis (AD). In addition, Staphylococcus aureus colonization and oxidative stress worsen AD skin conditions. We aimed to investigate anti-inflammatory activity, using 5-LOX and COX-2 inhibitions, and the anti-staphylococcal, and antioxidant potentials of several medicinal plants bio-prospected from traditional medicine related to AD pathogenesis. Essential oils and hexane fractions were prepared and analyzed using gas chromatography-mass spectrometry. Boesenbergia rotunda hexane extract displayed anti-Staphylococcus aureus (MIC = 10 µg/mL) and antioxidant activities (IC50 = 557.97 and 2651.67 µg/mL against DPPH and NO radicals, respectively). A major flavonoid, pinostrobin, was further nonchromatographically isolated. Pinostrobin was shown to be a potent 5-LOX inhibitor (IC50 = 0.499 µM) compared to nordihydroguaiaretic acid (NDGA; IC50 = 5.020 µM) and betamethasone dipropionate (BD; IC50 = 2.077 µM) as the first-line of AD treatment. Additionally, pinostrobin inhibited COX-2 (IC50 = 285.67 µM), which was as effective as diclofenac sodium (IC50 = 290.35 µM) and BD (IC50 = 240.09 µM). This kinetic study and molecular modeling showed the mixed-type inhibition of NDGA and pinostrobin against 5-LOX. This study suggests that B. rotunda and its bioactive pinostrobin have promising properties for AD therapy.

Critical Players and Therapeutic Targets in Chronic Itch

Chronic itch is one of the most prominent clinical characteristics of diverse systematic diseases. It is a devastating sensation in pathological diseases. Despite its importance, there are no FDA-labelled drugs specifically geared toward chronic itch. The associated complex pathogenesis and diverse causes escalate chronic itch to being one of the top challenges in healthcare. Humanized antibodies against IL-13, IL-4, and IL-31 proved effective in treatment of itch-associated atopic dermatitis but remain to be validated in chronic itch. There are still no satisfactory anti-itch therapeutics available toward itch-related neuropeptides including GRP, BNP, SST, CGRP, and SP. The newly identified potential itch targets including OSM, NMB, glutamate, periostin, and Serpin E1 have opened new avenues for therapeutic development. Proof-of-principle studies have been successfully performed on antagonists against these proteins and their receptors in itch treatment in animal models. Their translational interventions in humans need to be evaluated. It is of great importance to summarize and compare the newly emerging knowledge on chronic itch and its pathways to promote the development of novel anti-itch therapeutics. The goal of this review is to analyze the different physiologies and pathophysiologies of itch mediators, whilst assessing their suitability as new targets and discussing future therapeutic development.

Recent advances in function and structure of two leukotriene B4 receptors: BLT1 and BLT2

Leukotriene B₄ (LTB₄) is generated by the enzymatic oxidation of arachidonic acid, which is then released from the cell membrane and acts as a potent activator of leukocytes and other inflammatory cells. Numerous studies have demonstrated the physiological and pathophysiological significance of this lipid in various diseases. LTB₄ exerts its activities by binding to its specific G protein-coupled receptors (GPCRs): BLT1 and BLT2. In mouse disease models, treatment with BLT1 antagonists or BLT1 gene ablation attenuated various diseases, including bronchial asthma, arthritis, and psoriasis, whereas BLT2 deficiency exacerbated several diseases in the skin, cornea, and small intestine. Therefore, BLT1 inhibitors and BLT2 activators could be beneficial for the treatment of several inflammatory and immune disorders. As a result, attractive compounds targeting LTB₄ receptors have been developed by several pharmaceutical companies. This review aims to understand the potential of BLT1 and BLT2 as therapeutic targets for the treatment of various inflammatory diseases. In addition, recent topics are discussed with major focuses on the structure and post-translational modifications of BLT1 and BLT2. Collectively, current evidence on modulating LTB₄ receptor functions provides new strategies for the treatment of various diseases.

Montelukast, an Antagonist of Cysteinyl Leukotriene Signaling, Impairs Burn Wound Healing

BACKGROUND

Burns are severe injuries often associated with impaired wound healing. Impaired healing is caused by multiple factors, including dysregulated inflammatory responses at the wound site. Interestingly, montelukast, an antagonist for cysteinyl leukotrienes and U.S. Food and Drug Administration approved for treatment of asthma and allergy, was previously shown to enhance healing in excision wounds and to modulate local inflammation.

METHODS

In this study, the authors examined the effect of montelukast on wound healing in a mouse model of scald burn injury. Burn wound tissues isolated from montelukast- and vehicle-treated mice at various times after burn injury were analyzed for wound areas ( n = 34 to 36), reepithelialization ( n = 14), inflammation ( n = 8 to 9), and immune cell infiltration ( n = 3 to 6) and proliferation ( n = 7 to 8).

RESULTS

In contrast to previously described beneficial effects in excision wounds, this study shows that montelukast delays burn wound healing by impairing the proliferation of keratinocytes and endothelial cells. This occurs largely independently of inflammatory responses at the wound site, suggesting that montelukast impairs specifically the proliferative phase of wound healing in burns. Wound healing rates in mice in which leukotrienes are not produced were not affected by montelukast.

CONCLUSION

Montelukast delays wound healing mainly by reducing the proliferation of local cells after burn injury.

CLINICAL RELEVANCE STATEMENT

Although additional and clinical studies are necessary, our study suggests that burn patients who are on montelukast may exhibit delayed healing, necessitating extra observation.

Connections between Immune-Derived Mediators and Sensory Nerves for Itch Sensation

Although histamine is a well-known itch mediator, histamine H1-receptor blockers often lack efficacy in chronic itch. Recent molecular and cellular based studies have shown that non-histaminergic mediators, such as proteases, neuropeptides and cytokines, along with their cognate receptors, are involved in evocation and modulation of itch sensation. Many of these molecules are produced and secreted by immune cells, which act on sensory nerve fibers distributed in the skin to cause itching and sensitization. This understanding of the connections between immune cell-derived mediators and sensory nerve fibers has led to the development of new treatments for itch. This review summarizes current knowledge of immune cell-derived itch mediators and neuronal response mechanisms, and discusses therapeutic agents that target these systems.

Th2 Modulation of Transient Receptor Potential Channels: An Unmet Therapeutic Intervention for Atopic Dermatitis

Atopic dermatitis (AD) is a multifaceted, chronic relapsing inflammatory skin disease that affects people of all ages. It is characterized by chronic eczema, constant pruritus, and severe discomfort. AD often progresses from mild annoyance to intractable pruritic inflammatory lesions associated with exacerbated skin sensitivity. The T helper-2 (Th2) response is mainly linked to the acute and subacute phase, whereas Th1 response has been associated in addition with the chronic phase. IL-17, IL-22, TSLP, and IL-31 also play a role in AD. Transient receptor potential (TRP) cation channels play a significant role in neuroinflammation, itch and pain, indicating neuroimmune circuits in AD. However, the Th2-driven cutaneous sensitization of TRP channels is underappreciated. Emerging findings suggest that critical Th2-related cytokines cause potentiation of TRP channels, thereby exaggerating inflammation and itch sensation. Evidence involves the following: (i) IL-13 enhances TRPV1 and TRPA1 transcription levels; (ii) IL-31 sensitizes TRPV1 via transcriptional and channel modulation, and indirectly modulates TRPV3 in keratinocytes; (iii) The Th2-cytokine TSLP increases TRPA1 synthesis in sensory neurons. These changes could be further enhanced by other Th2 cytokines, including IL-4, IL-25, and IL-33, which are inducers for IL-13, IL-31, or TSLP in skin. Taken together, this review highlights that Th2 cytokines potentiate TRP channels through diverse mechanisms under different inflammatory and pruritic conditions, and link this effect to distinct signaling cascades in AD. This review strengthens the notion that interrupting Th2-driven modulation of TRP channels will inhibit transition from acute to chronic AD, thereby aiding the development of effective therapeutics and treatment optimization.

Intractable Itch in Atopic Dermatitis: Causes and Treatments

Itch or pruritus is the hallmark of atopic dermatitis and is defined as an unpleasant sensation that evokes the desire to scratch. It is also believed that itch is a signal of danger from various environmental factors or physiological abnormalities. Because histamine is a well-known substance inducing itch, H₁-antihistamines are the most frequently used drugs to treat pruritus. However, H₁-antihistamines are not fully effective against intractable itch in patients with atopic dermatitis. Given that intractable itch is a clinical problem that markedly decreases quality of life, its treatment in atopic dermatitis is of high importance. Histamine-independent itch may be elicited by various pruritogens, including proteases, cytokines, neuropeptides, lipids, and opioids, and their cognate receptors, such as protease-activated receptors, cytokine receptors, Mas-related G protein-coupled receptors, opioid receptors, and transient receptor potential channels. In addition, cutaneous hyperinnervation is partly involved in itch sensitization in the periphery. It is believed that dry skin is a key feature of intractable itch in atopic dermatitis. Treatment of the underlying conditions that cause itch is necessary to improve the quality of life of patients with atopic dermatitis. This review describes current insights into the pathophysiology of itch and its treatment in atopic dermatitis.

Berberine induces anti-atopic dermatitis effects through the downregulation of cutaneous EIF3F and MALT1 in NC/Nga mice with atopy-like dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease with severe pruritus. Berberine, a naturally occurring isoquinoline alkaloid, has anti-inflammatory effects. This study investigated the effects and molecular mechanisms of berberine on AD-like symptoms in mice. In this study, NC/Nga mice with atopy-like dermatitis (dermatitis mice), fibroblast and mast cells were used. In dermatitis mice, intermittent oral administrations of berberine 3 times a week for 12 days inhibited skin symptom, itching, cutaneous infiltration of eosinophils and mast cells, and the expression of cutaneous eotaxin, macrophage migration inhibitory factor (MIF) and IL-4. Berberine also attenuated IL-4/MIF-induced eotaxin in fibroblasts and allergen-induced MIF and IL-4 in mast cells. In mast cells, the GeneChip® microarray showed that antigen increased the expression of EIF3F and MALT1, inhibited by berberine. The siRNAs for them inhibited the expression of MIF and IL-4 in antigen-stimulated mast cells. These results suggest that berberine improves AD-like symptoms through the inhibition of the eotaxin and pro-inflammatory cytokine expression and the related inflammatory cell recruitment. It is also suggested that the downregulation of EIF3F and MALT1 by berberine is involved in suppressing the cytokine expression. Taken together, berberine or berberine-containing crude drugs are expected to contribute to the improvement of AD symptoms.

Lactobacillus paracasei KBL382 administration attenuates atopic dermatitis by modulating immune response and gut microbiota

Administration of probiotics has been linked to immune regulation and changes in gut microbiota composition, with effects on atopic dermatitis (AD). In this study, we investigated amelioration of the symptoms of AD using Lactobacillus paracasei KBL382 isolated from the feces of healthy Koreans. Mice with Dermatophagoides farinae extract (DFE)-induced AD were fed 1 × 10⁹ CFU d^-1 of L. paracasei KBL382 for 4 weeks. Oral administration of L. paracasei KBL382 significantly reduced AD-associated skin lesions, epidermal thickening, serum levels of immunoglobulin E, and immune cell infiltration. L. paracasei KBL382-treated mice showed decreased production of T helper (Th)1-, Th2-, and Th17-type cytokines, including thymic stromal lymphopoietin, thymus, and activation-regulated chemokine, and macrophage-derived chemokine, and increased production of the anti-inflammatory cytokine IL-10 and transforming growth factor-β in skin tissue. Intake of L. paracasei KBL382 also increased the proportion of CD4+ CD25+ Foxp3+ regulatory T cells in mesenteric lymph nodes. In addition, administration of L. paracasei KBL382 dramatically changed the composition of gut microbiota in AD mice. Administration of KBL382 significantly ameliorates AD-like symptoms by regulating the immune response and altering the composition of gut microbiota.

Lactobacillus paracasei KBL382 administration attenuates atopic dermatitis by modulating immune response and gut microbiota

Administration of probiotics has been linked to immune regulation and changes in gut microbiota composition, with effects on atopic dermatitis (AD). In this study, we investigated amelioration of the symptoms of AD using Lactobacillus paracasei KBL382 isolated from the feces of healthy Koreans. Mice with Dermatophagoides farinae extract (DFE)-induced AD were fed 1 × 10⁹ CFU d^-1 of L. paracasei KBL382 for 4 weeks. Oral administration of L. paracasei KBL382 significantly reduced AD-associated skin lesions, epidermal thickening, serum levels of immunoglobulin E, and immune cell infiltration. L. paracasei KBL382-treated mice showed decreased production of T helper (Th)1-, Th2-, and Th17-type cytokines, including thymic stromal lymphopoietin, thymus, and activation-regulated chemokine, and macrophage-derived chemokine, and increased production of the anti-inflammatory cytokine IL-10 and transforming growth factor-β in skin tissue. Intake of L. paracasei KBL382 also increased the proportion of CD4+ CD25+ Foxp3+ regulatory T cells in mesenteric lymph nodes. In addition, administration of L. paracasei KBL382 dramatically changed the composition of gut microbiota in AD mice. Administration of KBL382 significantly ameliorates AD-like symptoms by regulating the immune response and altering the composition of gut microbiota.

Advances in Understanding the Initial Steps of Pruritoceptive Itch: How the Itch Hits the Switch

Pruritoceptive (dermal) itch was long considered an accompanying symptom of diseases, a side effect of drug applications, or a temporary sensation induced by invading pruritogens, as produced by the stinging nettle. Due to extensive research in recent years, it was possible to provide detailed insights into the mechanism of itch mediation and modulation. Hence, it became apparent that pruritus is a complex symptom or disease in itself, which requires particular attention to improve patients’ health. Here, we summarize recent findings in pruritoceptive itch, including how this sensation is triggered and modulated by diverse endogenous and exogenous pruritogens and their receptors. A differentiation between mediating pruritogen and modulating pruritogen seems to be of great advantage to understand and decipher the molecular mechanism of itch perception. Only a comprehensive view on itch sensation will provide a solid basis for targeting this long-neglected adverse sensation accompanying numerous diseases and many drug side effects. Finally, we identify critical aspects of itch perception that require future investigation.

Transcriptomic and lipidomic profiling of eicosanoid/docosanoid signalling in affected and non-affected skin of human atopic dermatitis patients

Lipoxygenases (LOX) and cyclooxygenase (COX) are the main enzymes for PUFA metabolism to highly bio-active prostaglandins, leukotrienes, thromboxanes, lipoxins, resolvins and protectins. LOX and COX pathways are important for the regulation of pro-inflammatory or pro-resolving metabolite synthesis and metabolism for various inflammatory diseases such as atopic dermatitis (AD). In this study, we determined PUFAs and PUFA metabolites in serum as well as affected and non-affected skin samples from AD patients and the dermal expression of various enzymes, binding proteins and receptors involved in these LOX and COX pathways. Decreased EPA and DHA levels in serum and reduced EPA level in affected and non-affected skin were found; in addition, n3/n6-PUFA ratios were lower in affected and non-affected skin and serum. Mono-hydroxylated PUFA metabolites of AA, EPA, DHA and the sum of AA, EPA and DHA metabolites were increased in affected and non-affected skin. COX1 and ALOX12B expression, COX and 12/15-LOX metabolites as well as various lipids, which are known to induce itch (12-HETE, LTB4, TXB2, PGE2 and PGF2) and the ratio of pro-inflammatory vs pro-resolving lipid mediators in non-affected and affected skin as well as in the serum of AD patients were increased, while n3/n6-PUFAs and metabolite ratios were lower in non-affected and affected AD skin. Expression of COX1 and COX-metabolites was even higher in non-affected AD skin. To conclude, 12/15-LOX and COX pathways were mainly upregulated, while n3/n6-PUFA and metabolite ratios were lower in AD patients skin. All these parameters are a hallmark of a pro-inflammatory and non-resolving environment in affected and partly in non-affected skin of AD patients.

Prostanoids and leukotrienes in the pathophysiology of atopic dermatitis and psoriasis

Lipid mediators, such as prostanoids and leukotrienes (LTs), exert a range of actions through their own receptors on cell surfaces in various pathophysiological conditions. It has been reported that the production of prostanoids and LTs is significantly elevated in the skin lesions of some chronic inflammatory skin diseases, such as atopic dermatitis (AD) and psoriasis, showing the possible involvement of these lipid mediators in the development of those diseases. Although the actual significance of these lipid mediators in humans is still unclear, the findings from studies in mice suggest diverse roles of the lipid mediators in the progression or regulation of these diseases. For example, in a mouse AD model, prostaglandin D2 inhibits the induction of Th2 cells through DP receptor on Langerhans cells, while it promotes infiltration of Th2 cells through chemoattractant receptor-homologous molecule expressed on Th2 cells. In a psoriasis model, thromboxane A2-TP signaling promotes psoriatic dermatitis by facilitating IL-17 production from γδ T cells. In this short review, we summarize the current findings on the roles of prostanoids and LTs in AD and psoriasis as revealed by studies in mice, and discuss the potential of these lipid mediators as therapeutic targets in humans.

Role of Sphingosylphosphorylcholine in Tumor and Tumor Microenvironment

Sphingosylphosphorylcholine (SPC) is a unique type of lysosphingolipid found in some diseases, and has been studied in cardiovascular, neurological, and inflammatory phenomena. In particular, SPC’s studies on cancer have been conducted mainly in terms of effects on cancer cells, and relatively little consideration has been given to aspects of tumor microenvironment. This review summarizes the effects of SPC on cancer and tumor microenvironment, and presents the results and prospects of modulators that regulate the various actions of SPC.

Administration of Lactobacillus fermentum KBL375 Causes Taxonomic and Functional Changes in Gut Microbiota Leading to Improvement of Atopic Dermatitis

Gut microbiota play an important role in immune responses and energy metabolism. In this study, we evaluated whether administration of Lactobacillus fermentum (L. fermentum) KBL375 isolated from healthy Korean feces improves the atopic dermatitis using the house dust mite (Dermatophagoides farinae)-induced atopic dermatitis (AD) mouse model. Administration of L. fermentum KBL375 significantly decreased dermatitis score, ear and dorsal thickness, and serum immunoglobulin E level in AD-induced mice. Significant reductions in mast cells and eosinophils were discovered in skin tissues from L. fermentum KBL375-treated mice. T helper 2 cell-related cytokines interleukin (IL)-4, IL-5, IL-13, and IL-31 significantly decreased, and anti-inflammatory cytokine IL-10 or transforming growth factor-β increased in skin tissues from L. fermentum KBL375-treated mice. In addition to phenotypic changes in skin tissues, L. fermentum KBL375 treatment induced an increase in the CD4+CD25+Foxp3+ cell population in mesenteric lymph nodes. Taxonomic and functional analyses of gut microbiota showed significantly higher cecum bacterial diversities and abundances including genus Bilophila, Dorea, and Dehalobacterium in L. fermentum KBL375-treated mice. Metabolic analysis of the cecum also showed significant changes in the levels of various amino acids including methionine, phenylalanine, serine, and tyrosine, as well as short chain fatty acids such as acetate, butyrate, and propionate in AD-induced mice due to L. fermentum KBL375 treatment. These altered metabolites in AD-induced mice returned to the levels similar to those in control mice when treated with L. fermentum KBL375. Therefore, L. fermentum KBL375 could be useful for AD treatment by modulating the immune system and inducing various metabolites.

Flavonoid Composition of Salacia senegalensis (Lam.) DC. Leaves, Evaluation of Antidermatophytic Effects, and Potential Amelioration of the Associated Inflammatory Response

Predominantly spread in West Tropical Africa, the shrub Salacia senegalensis (Lam.) DC. is known because of its medicinal properties, the leaves being used in the treatment of skin diseases. Prompted by the ethnomedicinal use, a hydroethanolic extract obtained from the leaves of the plant was screened against a panel of microbial strains, the majority of which involved in superficial infections. The extract was found to be active against the dermatophytes Trichophyton rubrum and Epidermophyton floccosum. Notable results were also recorded regarding the attenuation of the inflammatory response, namely the inhibitory effects observed against soybean 5-lipoxygenase (IC₅₀ = 71.14 μg mL^-1), no interference being recorded in the cellular viability of RAW 264.7 macrophages and NO levels. Relevantly, the extract did not lead to detrimental effects against the keratinocyte cell line HaCaT, at concentrations displaying antidermatophytic and anti-inflammatory effects. Flavonoid profiling of S. senegalensis leaves was achieved for the first time, allowing the identification and quantitation of myricitrin, three 3-O-substituted quercetin derivatives, and three other flavonoid derivatives, which may contribute, at least partially, to the observed antidermatophytic and anti-inflammatory effects. In the current study, the plant S. senegalensis is assessed concerning its antidermatophytic and anti-inflammatory properties.

β2-Microglobulin elicits itch-related responses in mice through the direct activation of primary afferent neurons expressing transient receptor potential vanilloid 1

Uremic pruritus is an unpleasant symptom in patients undergoing hemodialysis, and the underlying mechanisms remain unclear. β2-Microglobulin (β2-MG) is well-known as an MHC class I molecule and its level is increased in the plasma of patients undergoing hemodialysis. In this study, we investigated whether β2-MG was a pruritogen in mice. Intradermal injections of β2-MG into the rostral back induced scratching in a dose-dependent manner. Intradermal injection of β2-MG into the cheek also elicited scratching, but not wiping. β2-MG-induced scratching was inhibited by the μ-opioid receptor antagonist naltrexone hydrochloride. β2-MG-induced scratching was not inhibited by antagonists of itch-related receptors (e.g., H₁ histamine receptor (terfenadine), TP thromboxane receptor (DCHCH), BLT1 leukotriene B₄ receptor (CMHVA), and proteinase-activated receptor 2 (FSLLRY-NH₂)). However, β2-MG-induced scratching was attenuated in mice desensitized by repeated application of capsaicin and also by a selective transient receptor potential vanilloid 1 (TRPV1) antagonist (BCTC). In addition, β2-MG induced phosphorylation of extracellular signal-regulated kinase (a marker of activated neurons) in primary culture of dorsal root ganglion neurons that expressed TRPV1. These results suggest that β2-MG is a pruritogen and elicits itch-related responses, at least in part, through TRPV1-expressing primary sensory neurons.

Treatment with DHA/EPA ameliorates atopic dermatitis-like skin disease by blocking LTB4 production

Atopic dermatitis (AD) is caused by both dysregulated immune responses and an impaired skin barrier. Although leukotriene B4 (LTB4) is involved in tissue inflammation that occurs in several disorders, including AD, therapeutic strategies based on LTB4 inhibition have not been explored. Here we demonstrate that progression of an AD-like skin disease in NC/Nga mice is inhibited when docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA) is administered together with FK506. Treatment with DHA/EPA and FK506 decreases the clinical score of dermatitis in NC/Nga mice and lowers local LTB4 concentrations. The treatment also suppressed the infiltration of T cells, B cells, eosinophils and neutrophils, and promoted reduced serum IgE levels. Secretion of IL-13 and IL-17A in CD4(+) T cells was lower in DHA/EPA- and FK506-treated mice than in mice treated with FK506 alone. The inhibition of disease progression induced by DHA/EPA was reversed by local injection of LTB4, suggesting that the therapeutic effect of DHA/EPA is LTB4-dependent. Our results demonstrate that treatment of AD with DHA/EPA is effective for allergic skin inflammation and acts by suppressing LTB4 production. J. Med. Invest. 63: 187-191, August, 2016.

Exacerbating factors of itch in atopic dermatitis

Atopic dermatitis (AD) displays different clinical symptoms, progress, and response to treatment during early infancy and after childhood. After the childhood period, itch appears first, followed by formation of well-circumscribed plaque or polymorphous dermatoses at the same site. When accompanied with dermatitis and dry skin, treatment of skin lesions should be prioritized. When itch appears first, disease history, such as causes and time of appearance of itch should be obtained by history taking. In many cases, itch increases in the evening when the sympathetic nerve activity decreased. Treatment is provided considering that hypersensitivity to various external stimulations can cause itch. Heat and sweating are thought to especially exacerbate itch. Factors causing itch, such as cytokines and chemical messengers, also induce itch mainly by stimulating the nerve. Scratching further aggravates dermatitis. Skin hypersensibility, where other non-itch senses, such as pain and heat, are felt as itch, sometimes occurs in AD. Abnormal elongation of the sensory nerve into the epidermis, as well as sensitizing of the peripheral/central nerve, are possible causes of hypersensitivity, leading to itch. To control itch induced by environmental factors such as heat, treatment for dermatitis is given priority. In the background of itch exacerbated by sweating, attention should be given to the negative impact of sweat on skin homeostasis due to 1) leaving excess sweat on the skin, and 2) heat retention due to insufficient sweating. Excess sweat on the skin should be properly wiped off, and dermatitis should be controlled so that appropriate amount of sweat can be produced. Not only stimulation from the skin surface, but also visual and auditory stimulation can induce new itch. This "contagious itch" can be notably observed in patients with AD. This article reviews and introduces causes of aggravation of itch and information regarding how to cope with such causes.

Differences in therapeutic effects of topically applied corticosteroid and tacrolimus on atopic dermatitis-like symptoms in NC/Nga mice

BACKGROUND

Topical corticosteroid and calcineurin inhibitor have similar therapeutic benefits in atopic dermatitis (AD), but the differences in therapeutic mechanisms of action of these agents against AD symptoms are not fully understood.

OBJECTIVE

This study was performed to examine the different effects of topical betamethasone valerate (BMV), clobetasol propionate (CBP), and tacrolimus (TAC) on itch-related behavior and dermatitis in NC/Nga mice with AD-like symptoms.

METHODS

AD-like dermatitis was induced in the dorsal skin of NC/Nga mice by repeated topical application of Dermatophagoides farinae body (Dfb) ointment twice weekly for three weeks. Mice with dermatitis scores over 5 were divided into five groups with equal dermatitis scores and treated with BMV, CBP, TAC, or Vaseline (Vas) once daily for two consecutive days, or were not treated (NT). Scratching behavior was analyzed using a SCLABA^®-Real system. Transepidermal water loss (TEWL) before and after treatment was measured using a Tewameter^® TM210. Skin collected from each group was analyzed histologically.

RESULTS

After the second treatment, dermatitis showed significantly greater improvement in the CBP and TAC-treated groups than in the Vas-treated and NT groups. The numbers of scratching bouts were significantly lower in CBP and TAC-treated mice than in Vas-treated mice. TEWL was significantly lower in TAC-, but not in CBP-, treated mice than in Vas-treated mice. Immunohistochemical examination showed that BMV, CBP and TAC did not reduce the increased densities of epidermal protein gene product 9.5- and substance P-immunoreactive fibers. The numbers of dermal CD4-immunoreactive T cells were significantly lower in BMV and CBP-treated mice than in Vas-treated and NT mice. The numbers of dermal eosinophils were significantly lower in BMV, CBP and TAC-treated mice than in Vas-treated and NT mice, with CBP showing the strongest effect. CBP significantly reduced epidermal thickness compared with Vas and NT. There were no significant differences in the numbers of interleukin-31-immunoreactive cells and mast cells, or in expression of epidermal thymic stromal lymphopoietin among all five groups.

CONCLUSION

The therapeutic potency of TAC against AD-like symptoms, including pruritus, is equal to that of the corticosteroid CBP. Epidermal innervation of sensory nerves itself might not be related to the therapeutic effects of topical tacrolimus and corticosteroids in its early phase.

Early Activation of Th2/Th22 Inflammatory and Pruritogenic Pathways in Acute Canine Atopic Dermatitis Skin Lesions

Determining inflammation and itch pathway activation in patients with atopic dermatitis (AD) is fraught with the inability to precisely assess the age of skin lesions, thus affecting the analysis of time-dependent mediators. To characterize inflammatory events occurring during early experimental acute AD lesions, biopsy samples were collected 6, 24, and 48 hours after epicutaneous application of Dermatophagoides farinae house dust mites to sensitized atopic dogs. The skin transcriptome was assessed using a dog-specific microarray and quantitative PCR. Acute canine AD skin lesions had a significant up-regulation of genes encoding T helper (Th) 2 (e.g., IL4, IL5, IL13, IL31, and IL33), Th9 (IL9), and Th22 (IL22) cytokines as well as Th2-promoting chemokines such as CCL5 and CCL17. Proinflammatory (e.g., IL6, LTB, and IL18) cytokines were also up-regulated. Other known pruritogenic pathways were also activated: there was significant up-regulation of genes encoding proteases cathepsin S (CTSS), mast cell chymase (CMA1), tryptase (TPS1) and mastin, neuromedin-B (NMB), nerve growth factor (NGF), and leukotriene-synthesis enzymes (ALOX5, ALOX5AP, and LTA4H). Experimental acute canine house dust mite-induced AD lesions exhibit an activation of innate and adaptive immune responses and pruritogenic pathways similar to those seen in humans with acute AD, thereby validating this model to test innovative therapeutics modalities for this disease.

Methods for preclinical assessment of antipruritic agents and itch mechanisms independent of mast-cell histamine

Itch is a sensation that provokes a desire to scratch. Mast-cell histamine was thought to be a key itch mediator. However, histamine and mast-cell degranulation were reported not to elicit scratching in animals. It was difficult to investigate the pathophysiology of itching and to evaluate the antipruritic efficacy of chemical agents in the early 1990 s. We showed that hind-paw scratching and biting were elicited by stimulation with pruritogenic agents in mice. Those results demonstrated for the first time that cutaneous itching could be evaluated behaviorally in animals. We established various animal models of pathological itch of the skin (dry skin, mosquito allergy, surfactant-induced pruritus, and herpes zoster) and mucus membranes (pollen allergy). Mast-cell histamine did not play a key role in itching in any animal model examined except for the pollen allergy model. Histamine is not an exclusive itch mediator of mast cells; tryptase and leukotriene B4 released from mast cells also act as itch mediators. Epidermal keratinocytes release several itch mediators, such as leukotriene B4, sphingosylphosphorylcholine, thromboxane A2, nociceptin, nitric oxide, and histamine, which may play important roles in pathological itching. Appropriate animal models of pathological itching are needed for pharmacological evaluation of the antipruritic efficacy of chemical agents.

Efficacy of Astaxanthin for the Treatment of Atopic Dermatitis in a Murine Model

Atopic dermatitis (AD) is a common chronic inflammatory skin disease associated with various factors, including immunological abnormalities and exposure to allergens. Astaxanthin (AST) is a xanthophyll carotenoid that has recently been demonstrated to have anti-inflammatory effects and to regulate the expression of inflammatory cytokines. Thus, we investigated whether AST could improve the dermatitis and pruritus in a murine model of AD using NC/Nga mice. In addition to a behavioral evaluation, the effects of AST on the AD were determined by the clinical skin severity score, serum IgE level, histological analyses of skin, and by reverse transcription-PCR and Western blotting analyses for the expression of inflammation-related factors. AST (100 mg/kg) or vehicle (olive oil) was orally administered once day and three times a week for 26 days. When compared with vehicle-treated group, the administration of AST significantly reduced the clinical skin severity score. In addition, the spontaneous scratching in AD model mice was reduced by AST administration. Moreover, the serum IgE level was markedly decreased by the oral administration of AST compared to that in vehicle-treated mice. The number of eosinophils, total and degranulated mast cells all significantly decreased in the skin of AST-treated mice compared with vehicle-treated mice. The mRNA and protein levels of eotaxin, MIF, IL-4, IL-5 and L-histidine decarboxylase were significantly decreased in the skin of AST-treated mice compared with vehicle-treated mice. These results suggest that AST improves the dermatitis and pruritus in AD via the regulation of the inflammatory effects and the expression of inflammatory cytokines.

The role of leukotrienes in allergic diseases

Leukotrienes (LTs), both LTB4 and the cysteinyl LTs (CysLTs) LTC4, LTD4 and LTE4, are implicated in a wide variety of inflammatory disorders. These lipid mediators are generated from arachidonic acid via multistep enzymatic reactions through which arachidonic acid is liberated from membrane phospholipids through the action of phospholipase A2. LTB4 and CysLTs exert their biological effects by binding to cognate receptors, which belong to the G protein-coupled receptor superfamily. LTB4 is widely considered to be a potent chemoattractant for most subsets of leukocytes, whereas CysLTs are potent bronchoconstrictors that have effects on airway remodeling. LTs play a central role in the pathogenesis of asthma and many other inflammatory diseases. This review will provide an update on the synthesis, biological function, and relevance of LTs to the pathobiology of allergic diseases, and examine the current and future therapeutic prospects of LT modifiers.

Two distinct leukotriene B4 receptors, BLT1 and BLT2

Leukotriene B4 (LTB4) is a potent inflammatory mediator derived from arachidonic acid. Two G protein-coupled receptors for LTB4 have been identified: a high-affinity receptor, BLT1, and a low-affinity receptor, BLT2. Both receptors mainly couple to pertussis toxin-sensitive Gi-like G proteins and induce cell migration. 12(S)-hydroxy-5Z,8E,10E-heptadecatrienoic acid (12-HHT) was identified to bind BLT2 with higher affinity than LTB4. Expression of BLT1 was confirmed in type 1 helper T cells, type 2 helper T cells, type 17 helper T cells, effector CD8(+) T cells, dendritic cells and osteoclasts in addition to granulocytes, eosinophils and macrophages, and BLT1-deficient mice showed greatly reduced phenotypes in models of various inflammatory diseases, such as peritonitis, bronchial asthma, rheumatoid arthritis, atherosclerosis and osteoporosis. In mice, BLT2 expression is restricted to intestinal epithelial cells and epidermal keratinocytes. BLT2-deficient mice showed enhanced colitis after administration of dextran sulfate, possibly due to reduced intestinal barrier function. An aspirin-dependent reduction in 12-HHT production was responsible for delayed skin wound healing, showing that the 12-HHT/BLT2 axis also plays an important role in skin biology. BLT1 and BLT2 are therefore potential targets for the development of novel drugs.

Antipruritic mechanisms of topical E6005, a phosphodiesterase 4 inhibitor: inhibition of responses to proteinase-activated receptor 2 stimulation mediated by increase in intracellular cyclic AMP

BACKGROUND

Phosphodiesterase 4 (PDE4), which catalyses the conversion of cyclic adenosine 3',5'-monophosphate (cAMP) to 5'-AMP, plays a critical role in the pathogenesis of inflammatory disorders. Pruritus is the main symptom of dermatitides, such as atopic dermatitis, and is very difficult to control. Recent studies have shown that the activation of proteinase-activated receptor 2 (PAR2) is involved in pruritus in dermatoses in humans and rodents.

OBJECTIVE

To investigate the inhibitory effect of E6005, a topically effective PDE4 inhibitor, on PAR2-associated itching in mice.

METHODS

Mice were given an intradermal injection of SLIGRL-NH2 (100 nmol/site), a PAR2 agonist peptide, into the rostral part of the back. E6005 and 8-bromo-cAMP were applied topically and injected intradermally, respectively, to the same site. Scratching bouts were observed as an itch-related behavior, and firing activity of the cutaneous nerve was electrophysiologically recorded. Keratinocytes were isolated from the skin of neonatal mice and cultured for in vitro experiments. The concentrations of cAMP and leukotriene B4 (LTB4) were measured by enzyme immunoassay. The distribution of PDE4 subtypes in the skin was investigated by immunostaining.

RESULTS

Topical E6005 and intradermal 8-bromo-cAMP significantly inhibited SLIGRL-NH2-induced scratching and cutaneous nerve firing. Topical E6005 increased cutaneous cAMP content. Topical E6005 and intradermal 8-bromo-cAMP inhibited cutaneous LTB4 production induced by SLIGRL-NH2, which has been shown to elicit LTB4-mediated scratching. E6005 and 8-bromo-cAMP inhibited SLIGRL-NH2-induced LTB4 production in the cultured murine keratinocytes also. PDE4 subtypes were mainly expressed in keratinocytes and mast cells in the skin.

CONCLUSIONS

The results suggest that topical E6005 treatment inhibits PAR2-associated itching. Inhibition of LTB4 production mediated by an increase in cAMP may be partly involved in the antipruritic action of E6005.

Leukotrienes orchestrating allergic skin inflammation

Leukotrienes constitute a group of lipid mediators, which may be subdivided into two groups, with leukotriene B4 on the one hand and cysteinyl leukotrienes on the other. Although leukotrienes are abundantly expressed in skin affected by diverse chronic inflammatory diseases, including atopic dermatitis, psoriasis, pemphigus vulgaris and bullous pemphigoid, their pathological roles in these diseases have remained elusive. Recent data now reveal that both leukotriene B4 and cysteinyl leukotrienes are indispensable in the pathogenesis of atopic dermatitis, with leukotriene B4 initiating the recruitment of inflammatory cells, particularly neutrophils and TH 2 cells into the skin, and cysteinyl leukotrienes later inducing characteristic structural alterations of chronically affected skin, specifically skin fibrosis and keratinocyte proliferation. Thus, these results reveal a sequential cooperation of LTB4 and cysteinyl leukotrienes to initiate and perpetuate allergic skin inflammation. These new insights highlight leukotrienes as promising therapeutic targets in allergic skin inflammation and should encourage more research into the role of leukotrienes in other inflammatory skin diseases.

Involvement of leukotriene B4 in dermatophyte-related itch in mice

BACKGROUND

Proteinase-activated receptor-2 (PAR2) is involved in dermatophyte-induced scratching and leukotriene B4 (LTB4) release from keratinocytes. We investigated whether PAR2-mediated LTB4 production is involved in dermatophyte-induced scratching.

METHODS

Dermatophyte extract was injected intradermally and scratching was observed in mice. LTB4 was determined by enzyme immunoassay.

RESULTS

Dermatophyte extract-induced scratching was inhibited by zileuton (5-lipoxygenase inhibitor), ONO-4057 (LTB4 antagonist), FSLLRY-NH2 (PAR2 antagonist), and anti-PAR2 antibody. Dermatophyte extract injection increased the cutaneous content of LTB4, which was inhibited by zileuton and FSLLRY-NH2.

CONCLUSION

These results suggest the involvement of LTB4 in dermatophyte-associated itch. LTB4 production might be due to PAR2 stimulation in the skin.

Neural processing of itch

While considerable effort has been made to investigate the neural mechanisms of pain, much less effort has been devoted to itch, at least until recently. However, itch is now gaining increasing recognition as a widespread and costly medical and socioeconomic issue. This is accompanied by increasing interest in the underlying neural mechanisms of itch, which has become a vibrant and rapidly-advancing field of research. The goal of the present forefront review is to describe the recent progress that has been made in our understanding of itch mechanisms.

An aberrant parasympathetic response: a new perspective linking chronic stress and itch

Perceived stress has long been known to alter the dynamic equilibrium established between the nervous, endocrine and immune system and is widely recognised to trigger or enhance pruritus. However, the exact mechanism of how the major stress response systems, such as the hypothalamus-pituitary adrenal (HPA) axis and the autonomic nervous system induce or aggravate chronic itch, has not been elucidated. The limbic regions of the brain such as the prefrontal cortex and hippocampus are deeply involved in the regulation of the stress response and intersect with circuits that are responsible for memory and reward. According to the 'Polyvagal Theory', certain limbic structures that serve as a 'higher brain equivalent of the parasympathetic nervous system' play a foremost role in maintaining body homoeostasis by functioning as an active vagal brake. In addition, the limbic system has been postulated to regulate two distinct, yet related aspects of itch: (i) the sensory-discriminative aspect; and (ii) the affective-cognitive aspect. Chronic stress-induced itch is hypothesised to be caused by stress-related changes in limbic structure with subsequent rewiring of both the peripheral and central pruriceptive circuits. Herein, we review data suggesting that a dysfunctional parasympathetic nervous system associated with chronic stress may play a critical role in the regulatory control of key candidate molecules, receptors and brain structures involved in chronic itch.

Eicosanoids in skin inflammation

Eicosanoids play an integral part in homeostatic mechanisms related to skin health and structural integrity. They also mediate inflammatory events developed in response to environmental factors, such as exposure to ultraviolet radiation, and inflammatory and allergic disorders, including psoriasis and atopic dermatitis. This review article discusses biochemical aspects related to cutaneous eicosanoid metabolism, the contribution of these potent autacoids to skin inflammation and related conditions, and considers the importance of nutritional supplementation with bioactives such as omega-3 and omega-6 polyunsaturated fatty acids and plant-derived antioxidants as means of addressing skin health issues.

Sphingolipids and inflammatory diseases of the skin

Mammalian skin protects our body against external assaults due to a well-organized skin barrier. The formation of the skin barrier is a complex process, in which basal keratinocytes lose their mitotic activity and differentiate to corneocytes. These corneocytes are embedded in intercellular lipid lamellae composed of ceramides, cholesterol, fatty acids, and cholesterol esters. Ceramides are the dominant lipid molecules and their reduction is connected with a transepidermal water loss and an epidermal barrier dysfunction resulting in inflammatory skin diseases. Moreover, bioactive sphingolipid metabolites like ceramide-1-phosphate, sphingosylphosphorylcholine, and sphingosine-1-phosphate are also involved in the biological modulation of keratinocytes and immune cells of the skin. Therefore, it is not astonishing that a dysregulation of sphingolipid metabolism has been identified in inflammatory skin diseases such as atopic dermatitis and psoriasis vulgaris. This chapter will describe not only the specific sphingolipid species and their skin functions but also the dysregulation of sphingolipid metabolism in inflammatory skin diseases.

Superoxide generation and leukocyte accumulation: key elements in the mediation of leukotriene B₄-induced itch by transient receptor potential ankyrin 1 and transient receptor potential vanilloid 1

The underlying mechanisms of itch are poorly understood. We have investigated a model involving the chemoattractant leukotriene B₄ (LTB₄) that is up-regulated in common skin diseases. Intradermal injection of LTB4 (0.1 nmol/site) into female CD1 mice induced significant scratching movements (used as an itch index) compared with vehicle-injected (0.1% bovine serum albumin-saline) mice. Intraperitoneal transient receptor potential (TRP) channel antagonist treatment significantly inhibited itch as follows: TRP vanilloid 1 (TRPV1) antagonist SB366791 (0.5 mg/kg, by 97%) and the TRP ankyrin 1 (TRPA1) antagonists TCS 5861528 (10 mg/kg; 82%) and HC-030031 (100 mg/kg; 76%). Leukotriene B₄ receptor 2 antagonism by LY255283 (5 mg/kg i.p.; 62%) reduced itch. Neither TRPV1-knockout (TRPV1-KO) nor TRPA1-knockout (TRPA1-KO mice exhibited LTB₄-induced itch compared with their wild-type counterparts. The reactive oxygen species scavengers N-acetylcysteine (NAC; 204 mg/kg i.p.; 86%) or superoxide dismutase (SOD; 10 mg/kg i.p.; 83%) also inhibited itch. LTB4-induced superoxide release was attenuated by TCS 5861528 (56%) and HC-030031 (66%), NAC (58%), SOD (50%), and LY255283 (59%) but not by the leukotriene B4 receptor 1 antagonist U-75302 (9 nmol/site) or SB366791. Itch, superoxide, and myeloperoxidase generation were inhibited by the leukocyte migration inhibitor fucoidan (10 mg/kg i.v.) by 80, 61, and 34%, respectively. Myeloperoxidase activity was also reduced by SB366791 (35%) and SOD (28%). TRPV1-KO mice showed impaired myeloperoxidase release, whereas TRPA1-KO mice exhibited diminished production of superoxide. This result provides novel evidence that TRPA1 and TRPV1 contribute to itch via distinct mechanisms.

Anti pruritic effects of topical crotamiton, capsaicin, and a corticosteroid on pruritogen-induced scratching behavior

Itch accompanies various skin diseases. As a number of mediators other than histamine can be involved in the itch sensation, H1 receptor antagonists are not necessarily effective in treating itch. External application of antipruritic drugs is occasionally used as an alternative therapy for pruritic skin conditions, such as pruritus on primary non-diseased, non-inflamed skin. Even so, the actual effects of these drugs on the itch sensation have yet to be studied in detail. To verify the antipruritic effects of crotamiton, capsaicin, and a corticosteroid on the itch sensation, we examined the inhibitory effects of these drugs on various pruritogen-induced scratching behaviors in mice. Topical application of 10% crotamiton moderately inhibited histamine-, serotonin-, and PAR-2 agonist-induced scratching behaviors. Topical capsaicin (0.025%) also exerted a moderate suppressive effect on histamine-, substance P-, and PAR-2 agonist-induced itch responses. Notably, topical corticosteroid (0.05% clobetasol propionate) remarkably inhibited the scratching behaviors induced by all of the pruritogenic agents tested. Therapeutic effects of capsaicin on substance P-induced pruritus did not seem to be mediated by desensitization of the TRPV1 (+) C fibers and/or by altered responsiveness of the mast cells. In addition, the antipruritic effects of crotamiton and corticosteroid appear to be, at least partly, associated with a TRPV1-independent pathway. This study examined the itch responses to pruritogens and demonstrated the mode of action of the externally applied antipruritic drugs.

Involvement of leukotriene B4 in itching in a mouse model of ocular allergy

Itching of ocular allergy is alleviated but not completely relieved by H(1) histamine receptor antagonists, suggesting that histamine is not the sole itch mediator in ocular allergy. We investigated whether leukotriene B(4) (LTB(4)), a mediator of cutaneous itch, is involved in the itch of ocular allergy in mice. Mice were immunized by the repeated subcutaneous injections of ragweed pollen and alum into the caudal back, and given a subconjunctival injection of ragweed pollen extract into the palpebra for allergic challenge. Challenge with ragweed pollen extract markedly elicited ocular scratching in sensitized mice. The scratching was almost abolished by mast cell deficiency. The H(1) antagonist terfenadine partially inhibited scratching at a dose that almost completely suppressed plasma extravasation. Scratching was inhibited by the glucocorticoid betamethasone and the 5-lipoxygenase inhibitor zileuton at doses that inhibited the challenge-induced production of LTB(4). A subconjunctival injection of LTB(4) at doses 1/10,000 or less than that required for histamine elicited ocular scratching in naïve mice. The LTB(4) receptor antagonist ONO-4057 inhibited the ragweed pollen challenge-induced ocular scratching at doses that suppressed LTB(4)-induced ocular scratching. In addition to histamine, LTB(4) is involved in the ocular itching of pollen allergy. H(1) receptor antagonists with an inhibitory effect on the action and/or production of LTB(4) may have more potent anti-pruritic activity than selective H(1) antagonists.