Effects of anti-nerve growth factor antibody on symptoms in the NC/Nga mouse, an atopic dermatitis model

PL-ReliefTMplus Alleviates Atopic Dermatitis and Regulates Inflammatory Responses via Inhibiting NF-κB Signaling Pathway

BACKGROUND

Atopic dermatitis (AD) has various detrimental effects on individuals with limited drug cure rates which necessitate the development of new treatment methods. PL-ReliefTMplus (PLR) is composed of SupraOlive, Crocus Sativus extracts and Citrus reticulata extracts. The effect of PLR on AD remains to be explored.

METHODS

2,4-dinitrofluorobenzene-induced AD model mice were involved and the histopathology of the skin lesions was observed along with the levels of inflammatory chemokines levels were measured. To further validate the molecular mechanism of PLR, RNA-seq was performed in HaCaT cells. Western blotting and immunofluorescence were performed to investigate NF-κB signaling pathways response in AD.

RESULTS

Due to PLR treatment, the thickening of the epidermis and dermis was inhibited and the number of eosinophils, mast cells, and CD4+ T cells in the skin lesion was decreased. In addition, the levels of inflammatory cytokines were decreased in dorsal skin tissues and LPS-stimulated HaCat cells. Furthermore, KEGG pathway analysis suggested that most identified downstream biological functions were associated with inflammatory response. PLR inhibited NF-κB signaling in AD mice and HaCaT cells.

CONCLUSIONS

These results indicate that PLR is a potent therapeutic agent for attenuating symptoms of AD.

Chronic Nodular Prurigo: An Update on the Pathogenesis and Treatment

Chronic nodular prurigo (CNPG) is a recalcitrant chronic itchy disorder that affects the quality of life. It can be triggered by multiple etiologies, such as atopic dermatitis, diabetes, and chronic renal diseases. The mechanisms of CNPG are complicated and involved the interaction of the cutaneous, immune, and nervous systems. Diverse immune cells, including eosinophils, neutrophils, T cells, macrophages, and mast cells infiltrated the lesional skin of CNPG, which initiated the inflammatory cytokines and pruritogens release. In addition, the interaction between the immune cells and activated peripheral sensory nerve fibers by neurotransmitters caused neuroinflammation in the skin and intractable itch. This itch-scratch vicious cycle of CNPG results in disease exacerbation. CNPG is difficult to treat with traditional therapies. Recently, great advances have been made in the pathophysiology of both inflammation and pruritus transmission in CNPG. In this review, we summarize the updated mechanisms and novel therapies for CNPG.

Involvement of Neuro-Immune Interactions in Pruritus With Special Focus on Receptor Expressions

Pruritus is a common, but very challenging symptom with a wide diversity of underlying causes like dermatological, systemic, neurological and psychiatric diseases. In dermatology, pruritus is the most frequent symptom both in its acute and chronic form (over 6 weeks in duration). Treatment of chronic pruritus often remains challenging. Affected patients who suffer from moderate to severe pruritus have a significantly reduced quality of life. The underlying physiology of pruritus is very complex, involving a diverse network of components in the skin including resident cells such as keratinocytes and sensory neurons as well as transiently infiltrating cells such as certain immune cells. Previous research has established that there is a significant crosstalk among the stratum corneum, nerve fibers and various immune cells, such as keratinocytes, T cells, basophils, eosinophils and mast cells. In this regard, interactions between receptors on cutaneous and spinal neurons or on different immune cells play an important role in the processing of signals which are important for the transmission of pruritus. In this review, we discuss the role of various receptors involved in pruritus and inflammation, such as TRPV1 and TRPA1, IL-31RA and OSMR, TSLPR, PAR-2, NK1R, H1R and H4R, MRGPRs as well as TrkA, with a focus on interaction between nerve fibers and different immune cells. Emerging evidence shows that neuro-immune interactions play a pivotal role in mediating pruritus-associated inflammatory skin diseases such as atopic dermatitis, psoriasis or chronic spontaneous urticaria. Targeting these bidirectional neuro-immune interactions and the involved pruritus-specific receptors is likely to contribute to novel insights into the underlying pathogenesis and targeted treatment options of pruritus.

Mouse models of atopic dermatitis: a critical reappraisal

Mouse models for atopic dermatitis (AD) are an indispensable preclinical research tool for testing new candidate AD therapeutics and for interrogating AD pathobiology in vivo. In this Viewpoint, we delineate why, unfortunately, none of the currently available so-called "AD" mouse models satisfactorily reflect the clinical complexity of human AD, but imitate more "allergic" or "irriant" contact dermatitis conditions. This limits the predictive value of AD models for clinical outcomes of new tested candidate AD therapeutics and the instructiveness of mouse models for human AD pathophysiology research. Here, we propose to initiate a rational debate on the minimal criteria that a mouse model should meet in order to be considered relevant for human AD. We suggest that valid AD models should at least meet the following criteria: (a) an AD-like epidermal barrier defect with reduced filaggrin expression along with hyperproliferation, hyperplasia; (b) increased epidermal expression of thymic stromal lymphopoietin (TSLP), periostin and/or chemokines such as TARC (CCL17); (c) a characteristic dermal immune cell infiltrate with overexpression of some key cytokines such as IL-4, IL-13, IL-31 and IL-33; (d) distinctive "neurodermatitis" features (sensory skin hyperinnervation, defective beta-adrenergic signalling, neurogenic skin inflammation and triggering or aggravation of AD-like skin lesions by perceived stress); and (e) response of experimentally induced skin lesions to standard AD therapy. Finally, we delineate why humanized AD mouse models (human skin xenotransplants on SCID mice) offer a particularly promising preclinical research alternative to the currently available "AD" mouse models.

Contribution of nerves within osteochondral channels to osteoarthritis knee pain in humans and rats

OBJECTIVES

Subchondral bone may contribute to knee osteoarthritis (OA) pain. Nerve growth factor (NGF) can stimulate nerve growth through TrkA. We aimed to identify how sensory nerve growth at the osteochondral junction in human and rat knees associates with OA pain.

METHODS

Eleven symptomatic chondropathy cases were selected from people undergoing total knee replacement for OA. Twelve asymptomatic chondropathy cases who had not presented with knee pain were selected post-mortem. OA was induced in rat knees by meniscal transection (MNX) and sham-operated rats were used as controls. Twice-daily oral doses (30 mg/kg) of TrkA inhibitor (AR786) or vehicle were administered from before and up to 28 days after OA induction. Joints were analysed for macroscopic appearances of articular surfaces, OA histopathology and calcitonin gene-related peptide-immunoreactive (CGRP-IR) sensory nerves in medial tibial plateaux, and rats were assessed for pain behaviors.

RESULTS

The percentage of osteochondral channels containing CGRP-IR nerves in symptomatic chondropathy was higher than in asymptomatic chondropathy (difference: 2.5% [95% CI: 1.1-3.7]), and in MNX-than in sham-operated rat knees (difference: 7.8% [95%CI: 1.7-15.0]). Osteochondral CGRP-IR innervation was significantly associated with pain behavior in rats. Treatment with AR786 prevented the increase in CGRP-IR nerves in osteochondral channels and reduced pain behavior in MNX-operated rats. Structural OA was not significantly affected by AR786 treatment.

CONCLUSIONS

CGRP-IR sensory nerves within osteochondral channels are associated with pain in human and rat knee OA. Reduced pathological innervation of the osteochondral junction might contribute to analgesic effects of reduced NGF activity achieved by blocking TrkA.

Enhanced Thermal Sensitivity of TRPV3 in Keratinocytes Underlies Heat-Induced Pruritogen Release and Pruritus in Atopic Dermatitis

Itch in atopic dermatitis (AD) is aggravated under warm conditions. Transient receptor potential vanilloid (TRPV) 3, a member of the thermosensitive transient receptor potential channels, is activated by innocuous heat and is abundantly expressed in keratinocytes. The potential role of TRPV3 in itch is illustrated in TRPV3 channelopathies of humans and mice. However, the role of TRPV3 in heat-induced itch in AD and the underlying mechanisms are unclear. Here we showed that keratinocytes isolated from patients with AD exhibit enhanced expression and heat sensitivity with hyperactive channel function of TRPV3. Heat stimulus induced enhanced secretion of thymic stromal lymphopoietin, nerve growth factor, and prostaglandin E₂ by keratinocytes from patients with AD through TRPV3 activation. TRPV3 agonists increased thymic stromal lymphopoietin, nerve growth factor, prostaglandin E₂, and IL-33 production in human keratinocytes and induced scratching behavior upon intradermal injection in mice. TRPV3 was upregulated in the skin of MC903-induced AD mouse model. Heat stimulation to MC903-treated mice increased scratching behavior and produced higher levels of thymic stromal lymphopoietin, nerve growth factor, prostaglandin E₂, and IL-33 from the epidermis, which were attenuated by pharmacologic inhibition of TRPV3. Moreover, neutralization of thymic stromal lymphopoietin reduced heat-evoked scratching in MC903-challenged mice. These results suggest that TRPV3 is a potential therapeutic target for heat-induced itch in AD.

Emerging Treatments and Novel Pathways in Pruritus

Itch treatment is a major challenge in the dermatologist’s practice. We encounter patients suffering from pruritus on a regular basis, and often lack diverse treatment options to adequately respond to the patients’ needs. In the last 20 years, novel pathways have been investigated that were beyond the scope of histamine. Although most did not result in a molecule available on the Canadian market, it is interesting and important as health care providers to stay up to date with new neuronal pathways involved in itch transmission and potential new therapeutic options. In this review, we will discuss pathways targeted in new topical treatments such as antagonist of proteinase-activated receptor-2, the endocannabinoid system, neurotrophins and tropomyosin-related kinase A receptor, the transient receptor potential-vanilloid or transient receptor potential-melastatine ion channels. New systemic therapies are now focusing on antagonizing the neurokinin receptor, modulating the opioidergic system, or targeting itch cytokines such as interleukin-31.

[Treatment of chronic pruritus-what is new?]

Chronic pruritus is one of the most common and stressful symptoms in medicine. Therapy remains a great challenge because of the lack of approved therapies. In the recent past a greater understanding of the pathogenesis has enabled the results to be translated into new forms of therapy. The various therapies target a wide range of points in the pruritic cascade-from blockade of intracellular and intercellular signaling pathways in the skin to the modulation of neurotransmission. This article provides a summary of current therapeutic options based on the current S2K guideline and gives an overview about recent developments in antipruritic treatments.

Neuro-immune interactions in allergic diseases: novel targets for therapeutics

Recent studies have highlighted an emerging role for neuro-immune interactions in mediating allergic diseases. Allergies are caused by an overactive immune response to a foreign antigen. The peripheral sensory and autonomic nervous system densely innervates mucosal barrier tissues including the skin, respiratory tract and gastrointestinal (GI) tract that are exposed to allergens. It is increasingly clear that neurons actively communicate with and regulate the function of mast cells, dendritic cells, eosinophils, Th2 cells and type 2 innate lymphoid cells in allergic inflammation. Several mechanisms of cross-talk between the two systems have been uncovered, with potential anatomical specificity. Immune cells release inflammatory mediators including histamine, cytokines or neurotrophins that directly activate sensory neurons to mediate itch in the skin, cough/sneezing and bronchoconstriction in the respiratory tract and motility in the GI tract. Upon activation, these peripheral neurons release neurotransmitters and neuropeptides that directly act on immune cells to modulate their function. Somatosensory and visceral afferent neurons release neuropeptides including calcitonin gene-related peptide, substance P and vasoactive intestinal peptide, which can act on type 2 immune cells to drive allergic inflammation. Autonomic neurons release neurotransmitters including acetylcholine and noradrenaline that signal to both innate and adaptive immune cells. Neuro-immune signaling may play a central role in the physiopathology of allergic diseases including atopic dermatitis, asthma and food allergies. Therefore, getting a better understanding of these cellular and molecular neuro-immune interactions could lead to novel therapeutic approaches to treat allergic diseases.

[Neurophysiology of atopic pruritus]

Pruritus is one of the major symptoms of inflammatory skin diseases and strongly affects the quality of life in patients. Although the perception of pruritus and pain are closely intertwined, pruritus represents a distinct sensation, which is also significantly different to pain at a neurophysiological level. The pathophysiological basis of chronic and acute pruritus is not fully understood. Besides histamine, a plethora of different neuromediators of itch, including neurotrophins, neuropeptides and their corresponding receptors, have been identified. In atopic dermatitis the release of these mediators leads to an activation of immune cells, such as mast cells and eosinophilic granulocytes, which in turn release neuromediators and cytokines that activate peripheral neurons. This review focuses on the neurophysiological interactions which regulate pruritus and summarizes the function of neurological and inflammatory mediators in atopic pruritus.

Nerve growth factor: a neuroimmune crosstalk mediator for all seasons

Neurotrophic factors comprise a broad family of biomolecules - most of which are peptides or small proteins - that support the growth, survival and differentiation of both developing and mature neurons. The prototypical example and best-characterized neurotrophic factor is nerve growth factor (NGF), which is widely recognized as a target-derived factor responsible for the survival and maintenance of the phenotype of specific subsets of peripheral neurons and basal forebrain cholinergic nuclei during development and maturation. In addition to being active in a wide array of non-nervous system cells, NGF is also synthesized by a range of cell types not considered as classical targets for innervation by NGF-dependent neurons; these include cells of the immune-haematopoietic lineage and populations in the brain involved in neuroendocrine functions. NGF concentrations are elevated in numerous inflammatory and autoimmune states such as multiple sclerosis, chronic arthritis, systemic lupus erythematosus and mastocytosis, in conjunction with increased accumulation of mast cells. Intriguingly, NGF seems to be linked also with diabetic pathology and insulin homeostasis. Mast cells and NGF appear involved in neuroimmune interactions and tissue inflammation. As mast cells are capable of producing and responding to NGF, this suggests that alterations in mast cell behaviour could provoke maladaptive neuroimmune tissue responses, including those of an autoimmune nature. Moreover, NGF exerts a modulatory role on sensory nociceptive nerve physiology in the adult, which appears to correlate with hyperalgesic phenomena occurring in tissue inflammation. NGF can therefore be viewed as a multifactorial modulator of neuro-immune-endocrine functions.

Evaluation of intraepidermal nerve fibres in the skin of normal and atopic dogs

BACKGROUND

Interest in intraepidermal nerve fibres (IENFs) is rising in human medicine, because variations in fibre density occur in some diseases and these neurites might contribute to disease pathogenesis. An increase in IENF density is seen in human atopic dermatitis (AD); there are no such data in atopic dogs.

OBJECTIVES

To compare the prevalence of IENFs in normal and atopic canine skin.

METHODS

Eight millimetre skin punch biopsies were taken from six sites of 25 healthy dogs without dermatitis and compared to lesional and nonlesional skin samples of dogs with AD (23 and 14 dogs, respectively). Thirty micrometre-thick paraffin-embedded sections were stained by indirect immunofluorescence for neuronal beta-3 tubulin. Only sections with detectable dermal nerves were then screened for the presence of IENFs.

RESULTS

IENFs were identified in all 25 normal nasal planum sections, but in only one biopsy collected from each of the normal canine haired skin (NCHS) sites. As there was no significant difference in IENF prevalence between NCHS areas, they were grouped together. The rate of detection of IENFs was significantly higher (one-tailed Fisher's test, P = 0.004) in lesional AD specimens (18 of 23; 78%) than in nonlesional AD (four of 14; 29%) and NCHS specimens (four of 111; 4%, P < 0.0001). The prevalence of IENF detection in nonlesional AD samples was significantly higher than in normal canine skin (P = 0.006).

CONCLUSIONS AND CLINICAL IMPORTANCE

IENFs are detected more commonly in canine AD than in normal haired skin; these results are comparable to those seen for human AD.

Chronic Pruritus in the Absence of Skin Disease: Pathophysiology, Diagnosis and Treatment

Chronic pruritus arises not only from dermatoses, but also, in up to half of cases, from extracutaneous origins. A multitude of systemic, neurological, psychiatric, and somatoform conditions are associated with pruritus in the absence of skin disease. Moreover, pruritus is a frequently observed side effect of many drugs. It is therefore difficult for physicians to make a correct diagnosis. Chronic pruritus patients frequently present to the dermatologist with skin lesions secondary to a long-lasting scratching behavior, such as lichenification and prurigo nodularis. A structured clinical history and physical examination are essential in order to evaluate the pruritus, along with systematic, medical history-adapted laboratory and radiological tests carried out according to the differential diagnosis. For therapeutic reasons, a symptomatic therapy should be promptly initiated parallel to the diagnostic procedures. Once the underlying factor(s) leading to the pruritus are identified, a targeted therapy should be implemented. Importantly, the treatment of accompanying disorders such as sleep disturbances or mental symptoms should be taken into consideration. Even after successful treatment of the underlying cause, pruritus may persist, likely due to chronicity processes including peripheral and central sensitization or impaired inhibition at spinal level. A vast arsenal of topical and systemic agents targeting these pathophysiological mechanisms has been used to deter further chronicity. The therapeutic options currently available are, however, still insufficient for many patients. Thus, future studies aiming to unveil the complex mechanisms underlying chronic pruritus and develop new therapeutic agents are urgently needed.

Atopic dermatitis: allergic dermatitis or neuroimmune dermatitis?

Advances in knowledge of neurocellulars relations have provided new directions in the understanding and treatment of numerous conditions, including atopic dermatitis. It is known that emotional, physical, chemical or biological stimuli can generate more accentuated responses in atopic patients than in non-atopic individuals; however, the complex network of control covered by these influences, especially by neuropeptides and neurotrophins, and their genetic relations, still keep secrets to be revealed. Itching and airway hyperresponsiveness, the main aspects of atopy, are associated with disruption of the neurosensory network activity. Increased epidermal innervation and production of neurotrophins, neuropeptides, cytokines and proteases, in addition to their relations with the sensory receptors in an epidermis with poor lipid mantle, are the aspects currently covered for understanding atopic dermatitis.

STAT3-dependent reactive astrogliosis in the spinal dorsal horn underlies chronic itch

Chronic itch is an intractable symptom of inflammatory skin diseases, such as atopic and contact dermatitis. Recent studies have revealed neuronal pathways selective for itch, but the mechanisms by which itch turns into a pathological chronic state are poorly understood. Using mouse models of atopic and contact dermatitis, we demonstrate a long-term reactive state of astrocytes in the dorsal horn of the spinal segments that corresponds to lesioned, itchy skin. We found that reactive astrogliosis depended on the activation of signal transducer and activator of transcription 3 (STAT3). Conditional disruption of astrocytic STAT3 suppressed chronic itch, and pharmacological inhibition of spinal STAT3 ameliorated the fully developed chronic itch. Mice with atopic dermatitis exhibited an increase in scratching elicited by intrathecal administration of the itch-inducer gastrin-releasing peptide (GRP), and this enhancement was normalized by suppressing STAT3-mediated reactive astrogliosis. Moreover, we identified lipocalin-2 (LCN2) as an astrocytic STAT3-dependent upregulated factor that was crucial for chronic itch, and we demonstrated that intrathecal administration of LCN2 to normal mice increased spinal GRP-evoked scratching. Our findings indicate that STAT3-dependent reactive astrocytes act as critical amplifiers of itching through a mechanism involving the enhancement of spinal itch signals by LCN2, thereby providing a previously unrecognized target for treating chronic itch.

The excimer lamp induces cutaneous nerve degeneration and reduces scratching in a dry-skin mouse model

Epidermal hyperinnervation, which is thought to underlie intractable pruritus, has been observed in patients with atopic dermatitis (AD). The epidermal expression of axonal guidance molecules has been reported to regulate epidermal hyperinnervation. Previously, we showed that the excimer lamp has antihyperinnervative effects in nonpruritic dry-skin model mice, although epidermal expression of axonal guidance molecules was unchanged. Therefore, we investigated the antipruritic effects of excimer lamp irradiation and its mechanism of action. A single irradiation of AD model mice significantly inhibited itch-related behavior 1 day later, following improvement in the dermatitis score. In addition, irradiation of nerve fibers formed by cultured dorsal root ganglion neurons increased bleb formation and decreased nerve fiber expression of nicotinamide mononucleotide adenylyl transferase 2, suggesting degenerative changes in these fibers. We also analyzed whether attaching a cutoff excimer filter (COF) to the lamp, thus decreasing cytotoxic wavelengths, altered hyperinnervation and the production of cyclobutane pyrimidine dimer (CPD), a DNA damage marker, in dry-skin model mice. Irradiation with COF decreased CPD production in keratinocytes, as well as having an antihyperinnervative effect, indicating that the antipruritic effects of excimer lamp irradiation with COF are due to induction of epidermal nerve degeneration and reduced DNA damage.

Effects of magnesium deficiency--more than skin deep

Dead Sea and magnesium salt therapy are two of the oldest forms of treatment for skin disease and several other disorders, supported by a body of largely anecdotal evidence. In this paper we review possible pathways for penetration of magnesium ions through the epidermis to reach the circulation, in turn replenishing cellular magnesium levels. We also discuss mechanisms for intercellular movement of magnesium ions and possible mechanisms for the interaction between magnesium ions and inflammatory mediators. Upon addition of magnesium ions in vitro, the expression of inflammatory mediators such as tumour necrosis factor α (TNFα) and nuclear factor κβ (NFκβ) is down regulated. Dysregulation of these and other inflammatory mediators has been linked to several inflammatory disorders, including asthma, arthritis, atherosclerosis and neuroinflammation.

Itch mechanisms and circuits

The itch-scratch reflex serves as a protective mechanism in everyday life. However, chronic persistent itching can be devastating. Despite the clinical importance of the itch sensation, its mechanism remains elusive. In the past decade, substantial progress has been made to uncover the mystery of itching. Here, we review the molecules, cells, and circuits known to mediate the itch sensation, which, coupled with advances in understanding the pathophysiology of chronic itching conditions, will hopefully contribute to the development of new anti-itch therapies.

The kinin B1 receptor mediates alloknesis in a murine model of inflammation

Noxious stimuli and non-noxious mechanical stimuli elicit itch (alloknesis) instead of pain on skin lesions of patients with atopic dermatitis. We previously found that bradykinin evokes an itch-related scratching response through activation of kinin B1 receptor in skin inflamed using complete Freund's adjuvant. In this study we investigated whether alloknesis is evoked in CFA-inflamed skin and the involvement of kinin receptors. In our results, alloknesis was elicited four days after CFA-inflammation. Furthermore, pretreatment with a B1 receptor antagonist or μ-opioid receptor antagonist significantly reduced alloknesis. In contrast, treatment with a B2 receptor antagonist significantly increased alloknesis. These results suggest that the alloknesis response is mediated by the activation of kinin B1 receptor but antagonized by the B2 receptor in CFA-inflamed mice.

Suppressive effect of mangosteen rind extract on the spontaneous development of atopic dermatitis in NC/Tnd mice

Atopic dermatitis (AD) is a chronic and relapsing skin disorder characterized by pruritic and dry skin lesions with allergic inflammation. Recent studies have revealed anti-inflammatory and anti-allergic effects of xanthones in mangosteen through regulation of the nuclear factor (NF)-κB signaling pathway. Activation of NF-κB signals is responsible for allergic inflammation in AD. To develop a new preventive therapy for AD, we examined the effects of the natural medicine, mangosteen rind extract (ME), on AD in a murine model. ME (250 mg/kg per day) was administrated to NC/Tnd mice, a model for human AD, for 6 weeks to evaluate its preventive effects on AD. We also confirmed the effects of ME on various immune cell functions. Oral administration of ME prevented the increase of clinical skin severity scores, plasma total immunoglobulin E levels, scratching behavior, transepidermal water loss and epidermal hyperplasia in NC/Tnd mice; moreover, no adverse effects were noted. We demonstrated that ME suppressed thymic stromal lymphopoietin and interferon-γ mRNA expression both in vitro and in vivo. Not only immunoglobulin E production from splenic B cells but also immunoglobulin E-mediated degranulation of bone marrow-derived cultured mast cells was significantly reduced by the addition of ME to the culture. In addition, mRNA expression levels of nerve growth factor were decreased in ME-administrated NC/Tnd mice compared with those of controls. Keratinocyte proliferation was well-controlled by ME application. Oral administration of ME exhibited its suppressive potential on the early development of AD by controlling inflammation, itch and epidermal barrier function.

Chronically relapsing pruritic dermatitis in the rats treated as neonate with capsaicin; a potential rat model of human atopic dermatitis

BACKGROUND

The pathophysiological mechanisms underlying chronic pruritic skin diseases, e.g. atopic dermatitis (AD), and effective therapies remain elusive due to the paucity of animal models. Recently, we rediscovered that injection of capsaicin into rat pups resulted in vigorous scratching behavior and chronically relapsing AD-like cutaneous lesions well into adulthood.

OBJECTIVES

To characterize the chronic pruritic dermatitis induced by neonatal capsaicin treatment.

METHODS

Capsaicin (50mg/kg) was given to rat pups subcutaneously within 48 h after birth, and then scratching behavior, dermatitis and pathophysiological changes of rat skin were investigated chronologically.

RESULTS

Neonatal capsaicin treatment led to not only severe scratching and cutaneous lesions but also a large number of pathophysiological changes in the skin, such as histopathological changes including the deficiency of epidermal filaggrin expression, increases in the number of mast cells, levels of tissue NGF and Th2 cytokine mRNA, impaired skin barrier function and colonization with S. aureus. In addition, we observed the hyperproduction of serum IgE, which is clinically similar to the pathophysiology seen in the patients with atopic dermatitis. During the follow-up observation, the rats showed the alternative periods of relapsing and remitting skin lesions.

CONCLUSION

Injection of capsaicin into rat pups results in chronically relapsing pruritic dermatitis, similar to human AD. Therefore, we think neonatal capsaicin treatment could be a useful model for studying human AD and for the development of novel therapeutic drugs.

The itchy scalp--scratching for an explanation

Scalp pruritus is a common complaint that is considered a diagnostically and therapeutically challenging situation. Scalp skin has a unique neural structure that contains densely innervated hair follicles and dermal vasculature. In spite of the recent advances in our understanding of itch pathophysiology, scalp itching has not been studied as yet. In this review, we summarize the current knowledge on the neurobiology of scalp and hair follicles as well as itch mediators and provide a putative mechanism for scalp itch with special emphasis on neuroanatomy and pathophysiology.

Red ginseng inhibits scratching behavior associated with atopic dermatitis in experimental animal models

Pruritus is a severe symptom that is difficult to treat in atopic dermatitis patients. Red ginseng (RG), a natural medicine, has various biological activities such as anti-inflammatory effects. In this study, we examined the efficacy of RG extract (RGE) and its mechanism on experimental atopic dermatitis in mice. The effects of RGE on vascular permeability and itching were first evaluated. Histamine-induced permeability and itching were significantly inhibited by embrocation with RGE as well as diphenhydramine, an antihistamine drug. Next, we assessed the therapeutic effect of topical RGE in a mouse model of atopic dermatitis. Dermatitis was induced by repeated application of 2,4-dinitrofluorobenzene (DNFB) acetone solution to the mouse ear. The effects of tacrolimus (a calcineurin blocker), dexamethasone (a corticosteroid), and RGE on dermatitis and associated scratching behavior were compared. Repeated DNFB application caused frequent scratching behaviors and ear swelling. Topical treatment with tacrolimus, dexamethasone, and RGE for 8 days before the final challenge with DNFB significantly inhibited ear swelling. Tacrolimus and RGE significantly inhibited scratching behavior, whereas dexamethasone failed to do so. DNFB-induced nerve growth factor expression and nerve fiber extension were significantly attenuated by tacrolimus and RGE, but not by dexamethasone. RGE may have the potential for treatment of atopic dermatitis.

A study of serum concentrations and dermal levels of NGF in atopic dermatitis and healthy subjects

Nerve growth factor (NGF) was reported to be increased in the serum and skin of atopic dermatitis (AD) patients, to the extent that serum nerve growth factor levels were proposed to serve as a marker of disease severity. We studied NGF levels in the serum and dermis using skin microdialysis and attempted to correlate them with disease severity. We also examined if potential differences between morning and evening levels of NGF can explain the phenomenon of nocturnal itch. In addition, neurogenic inflammation and itch were induced using histamine iontophoresis in lesional and non-lesional skin and the effect of experimental itch on dermal NGF concentration was examined. We found that systemic (serum) and eczematous skin levels of NGF in AD are significantly lower in comparison to healthy controls. Serum NGF decreases from morning to late afternoon in both groups. Interestingly, serum NGF levels were correlated to disease severity in the morning in AD, although the NGF concentration in AD were significantly lower than in the healthy group. The local itch and neurogenic inflammation induction via experimental histamine reduced local NGF levels in the eczema and non-lesional skin in atopics, but not in the healthy controls, where it was slightly increased. The higher the clinical severity of the eczema, a significantly less pronounced effect of neurogenic inflammation on the local levels of NGF was found. The availability of measurable NGF might be reduced by a higher expression of NGF receptors. The fluctuations of NGF levels during the day suggest a complex modulation of this neurotrophin, potentially linked to stress or to an altered neurophysiological mechanism.

Matrix metalloproteinase-8 is involved in dermal nerve growth: implications for possible application to pruritus from in vitro models

Cutaneous nerve density is related to abnormal itch perception in dermatoses, such as atopic dermatitis and xerosis. However, the mechanisms underlying the elongation of dermal nerve fibers within the interstitial collagen (CoL) matrix are poorly understood. In this study, a culture system of rat dorsal root ganglion neurons consisting of type I CoL and a Boyden chamber containing a nerve growth factor (NGF) concentration gradient was used. Nerve fibers penetrating into type I CoL gel were observed in the presence of the NGF concentration gradient. Levels of matrix metalloproteinase-8 (MMP-8) mRNA and protein were increased in the cultured neurons and the conditioned medium, respectively. The nerve fiber penetration was dose dependently inhibited by MMP-8 blockers. Moreover, MMP-8 immunoreactivity was partially localized at growth cones in NGF-responsive nerve fibers. Semaphorin 3A stimulation also showed the opposite effects on these NGF-dependent events. Intriguingly, MMP-8 expression was upregulated by type I and III CoLs, which are substrates for this enzyme. These results suggested that MMP-8 is involved in sensory nerve growth within the interstitial CoL matrix through modulation by the axonal guidance molecules and/or extracellular matrix components. These findings provide insight into the development of pruritus involving skin nerve density.

Characterization of skin inflammation induced by repeated exposure of toluene, xylene, and formaldehyde in mice

Volatile organic compounds (VOCs) are considered the main cause of sick building syndrome and they are likely to irritate the skin, eyes, and mucous membrane; however, the toxic threshold and the mechanisms of cutaneous reaction induced by long-time VOC exposure have not been clarified. In the present study, we investigated the effect of repeated painting of VOCs onto mouse skin. Various concentrations of toluene, xylene, and formaldehyde (FA) were applied once a week for 5 weeks. While FA solution (2-10%) induced remarkable ear swelling and caused evident infiltration of inflammatory cells, high concentrations of toluene and xylene (50 or 100%) evoked mild ear swelling and marginal inflammatory cell invasion. In addition, FA exposure markedly increased the expression of interleukin-4 (IL-4), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and transient receptor potential vanilloid-1 (TRPV-1) mRNAs in the ears and IL-4 and NT-3 mRNAs in the cervical lymph nodes. Furthermore, capsazepine, a TRPV-1 antagonist, significantly suppressed ear swelling caused by repeated painting of 5% FA. These findings demonstrate that FA has more potent irritancy against skin than toluene or xylene and suggest that the Th2 response, neurotrophins and TRPV-1 play important roles in FA-induced skin inflammation.

Targeted treatment of pruritus: a look into the future

Recent advances in pruritus research have elucidated mediators and neuronal pathways involved in itch transmission, and this fast emerging knowledge may possibly be translated into new therapies in the near future. In the skin and peripheral nerves, potential mediator and receptor therapeutic targets include the H4 histamine receptor, protease-activated receptor 2, serine proteases, cathepsin S, peripheral mu- and kappa-opioid receptors, interleukin-31, transient receptor potential vanilloid 1 and 3, fatty acid amide hydrolase, nerve growth factor and its receptor, acetylcholine, and the Mas-related G protein-coupled receptors. In the spinal cord, gastrin-related peptide and its receptor, as well as substance P and its receptor neurokinin receptor-1 serve as potential therapeutic targets. In the brain, reduction of itch perception and modulation of emotions may possibly be achieved through drugs acting on the anterior cingulate cortex. Clinically, management of pruritus should be instituted early and should address the skin pathology, peripheral neuropathy, central sensitization, and the cognito-affective aspects of the disease.

Targeted treatment of pruritus: a look into the future

Recent advances in pruritus research have elucidated mediators and neuronal pathways involved in itch transmission, and this fast emerging knowledge may possibly be translated into new therapies in the near future. In the skin and peripheral nerves, potential mediator and receptor therapeutic targets include the H4 histamine receptor, protease-activated receptor 2, serine proteases, cathepsin S, peripheral mu- and kappa-opioid receptors, interleukin-31, transient receptor potential vanilloid 1 and 3, fatty acid amide hydrolase, nerve growth factor and its receptor, acetylcholine, and the Mas-related G protein-coupled receptors. In the spinal cord, gastrin-related peptide and its receptor, as well as substance P and its receptor neurokinin receptor-1 serve as potential therapeutic targets. In the brain, reduction of itch perception and modulation of emotions may possibly be achieved through drugs acting on the anterior cingulate cortex. Clinically, management of pruritus should be instituted early and should address the skin pathology, peripheral neuropathy, central sensitization, and the cognito-affective aspects of the disease.

CFTR-deficiency renders mice highly susceptible to cutaneous symptoms during mite infestation

Pruritus, also known as itch, is a sensation that causes a desire to scratch. Prolonged scratching exacerbates skin lesions in several skin diseases such as atopic dermatitis. Here, we identify the cystic fibrosis transmembrane conductance regulator (CFTR/Cftr), an integral membrane protein that mediates transepithelial chloride transport, as a determinant factor in mice for the susceptibility to several cutaneous symptoms during mite infestation. Mice that endogenously express dysfunctional Cftr (Cftr(ΔF508/ΔF508)) show significant increase of scratching behavior and skin fibrosis after mite exposure. These phenotypes were due to the increased expression of nerve growth factor (NGF) that augments the sensitization of peripheral nerve fibers. Moreover, protein gene product 9.5 (PGP9.5)-positive neurites were abundant in the epidermis of mite-infested Cftr(ΔF508/ΔF508) mice. Furthermore, mite-infested Cftr(+/+) mice orally administered with a chloride channel inhibitor glibenclamide had higher scratching count and increased level of NGF than vehicle-treated mice. Consistently, mite extract-exposed primary and transformed human keratinocytes, treated with CFTR inhibitor, had significantly higher level of NGF mRNA compared with vehicle-treated, mite extract-exposed cells. These results reveal that CFTR in keratinocytes plays a critical role for the regulation of peripheral nerve function and pruritus sensation, and suggest that Cftr(ΔF508/ΔF508) mice may serve as a novel mouse model that represents NGF-dependent generation of pruritus.

A Role of Staphyococcus aureus, Interleukin-18, Nerve Growth Factor and Semaphorin 3A, an Axon Guidance Molecule, in Pathogenesis and Treatment of Atopic Dermatitis

Staphylococcus aureus (SA) is usually present not only in the skin lesions of atopic dermatitis (AD) but also in the atopic dry skin. SA discharges various toxins and enzymes that injure the skin, results in activation of epidermal keratinocytes, which produce and release IL-18. IL-18 that induces the super Th1 cells secreting IFN-γ and IL-13 is supposed to be involved in development of AD and its pathogenesis. Indeed, the number of SA colonies on the skin surface and the serum IL-18 levels in patients with AD significantly correlated with the skin scores of AD lesions. Also, there is strong positive correlation between the skin scores and serum IL-18 levels in DS-Nh mice (P<0.0001, r=0.64), which develop considerable AD-like legions when they are housed under conventional conditions, but develop skin legions with less severity and less frequency under specific pathogens free (SPF) conditions. Therefore, they are well-known as model mice of AD, in which SA is presumed to be critical factor for the development of AD lesions. Also, theses DS-Nh mice pretreated with Cy developed more remarkable AD-like lesions in comparison with non-treated ones. The levels of INF-r and IL-13 in the supernatants of the lymph node cell cultures stimulated with staphylococcal enterotoxin B (SEB) or ConA were increased in the Cy-treated mice, although the serum levels of total IgE were not. In this experiment, we revealed that Cy-treated mice, to which CD25 +CD4 + reguratory T cells taken from non-treated ones had been transferred, developed the AD-like legions with less severity and less number of SA colonies on the skin surface. Therefore, it is presumed that CD25 +CD4 + reguratory T cells might be involved in the suppression of super Th1 cells which are induced by IL-18 and are involved in the development of AD-like lesions rather than IgE production. The efficient induction of CD25 +CD4 + reguratory T cells is expected for the new type of treatment of AD. We also found that farnesol (F) and xylitol (X) synergistically inhibited biofilm formation by SA, and indeed the ratio of SA in total bacteria at sites to which the FX cream containing F and X had been applied was significantly decreased 1 week later, accompanied with improvement of AD, when compared with that before application and at placebo sites. Therefore, the FX cream is a useful skin-care agent for atopic dry skin colonized by SA. The nerve growth factor (NGF) in the horny layer (the horn NGF) of skin lesions on the cubital fossa was collected by tape stripping and measured using ELISA in AD patients before and after 2 and 4 weeks treatments. Simultaneously, the itch and eruptions on the whole body and on the lesions, in which the horn NGF was measured, were recorded, and also the peripheral blood eosinophil count, serum LDH level and serum total IgE level were examined. The level of NGF was significantly higher in AD patients than in healthy controls, correlated with the severity of itch, erythema, scale/xerosis, the eosinophil count and LDH level, and also significantly decreased after treatments with olopatadine and/or steroid ointment for 2 and 4 weeks. Therefore, the measurement of the NGF by this harmless method seems to be useful to assess the severity of AD and the therapeutic effects on AD. In AD patients, C-fiber in the epidermis increase and sprout, inducing hypersensitivity, which is considered to aggravate the disease. Semaphorin 3A (Sema3A), an axon guidance molecule, is a potent inhibitor of neurite outgrowth of sensory neurons. We administered recombinant Sema3A intracutaneously into the skin lesions of NC/Nga mice, an animal model of AD, and investigated the effect of Sema3A on the skin lesions and their itch. Sema3A dose-dependently improved skin lesions and attenuated the scratching behavior in NC/Nga mice. Histological examinations revealed a decrease in the epidermal thickness, the density of invasive nerve fibers in the epidermis, inflammatory infiltrate including mast cells and CD4 +T cells, and the production of IL-4 in the Sema3A-treated lesions. Because the interruption of the itch-scratch cycle likely contributes to the improvement of the AD-like lesions, Sema3A is expected to become a promising treatment of patients with refractory AD.

Scratching behavior does not necessarily correlate with epidermal nerve fiber sprouting or inflammatory cell infiltration

BACKGROUND

Increased sprouting of epidermal nerve fibers of lesional skin are thought to be associated with persistent pruritus in chronic inflammatory dermatitis such as atopic dermatitis as supported by a murine study using tacrolimus (or FK506: FK) which was shown to inhibit both epidermal sprouting of nerves and scratching behavior or by immunohistochemical observations of lesional skin in the patients with atopic dermatitis or prurigo, etc.

OBJECTIVES

To examine a mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1/2 (MEK1/2) inhibitor (CX-659S: CX) for a possible anti-pruritic property in vivo since some MEK1/2 inhibitors have been reported to inhibit neurite growth in vitro.

METHODS

CX, FK and corticosteroids (betamethasone valerate: BV) were topically applied on inflamed skin in a mouse model of chronic dermatitis using repetitive hapten painting to examine anti-pruritic property and anti-inflammatory effects. Scratching behaviors were assessed using MicroAct automatic measuring system, and epidermal sprouting of nerves and skin inflammation was assessed histologically.

RESULTS

FK significantly decrease scratching behavior, but CX and BV failed to do so despite of their ability to significantly inhibit epidermal nerve fiber sprouting and skin inflammation, respectively. In addition, CX+BV mixture synergistically inhibited epidermal nerve fiber sprouting and skin inflammation even more potently than FK without decreasing scratching behavior.

CONCLUSIONS

These findings suggest that the scratching behavior does not necessarily correlate with epidermal nerve fiber sprouting or inflammatory cell infiltration.

Neurotropin inhibits both capsaicin-induced substance P release and nerve growth factor-induced neurite outgrowth in cultured rat dorsal root ganglion neurones

BACKGROUND

Neurotropin (NTP), a biological extract from rabbit skin inoculated with vaccinia virus, is an effective analgesic and anti-allergic agent, and has antipruritic effects in various dermatoses including eczema, dermatitis and urticaria. In patients receiving haemodialysis who have pruritus, NTP appears to exert its antipruritic effect by lowering the plasma levels of substance P (SP), but its underlying mechanisms are not fully understood.

AIM

To investigate the antipruritic mechanisms of NTP.

METHODS

The effects of NTP on capsaicin-induced SP release from neonatal rat dorsal root ganglion (DRG) neurones were assessed by measuring SP concentrations in culture media by a competitive ELISA. The effects of NTP on nerve growth factor (NGF)-induced neurite outgrowth were assessed by measuring the length of the longest process of cultured DRG neurones. The neuronal cytotoxicity of NTP was determined using a methylthiazole tetrazolium cytotoxicity assay.

RESULTS

NTP dose-dependently inhibited capsaicin-induced release of SP from cultured DRG neurones, whereas NTP alone had no effect on SP release. Moreover, NTP dose-dependently inhibited NGF-induced neurite outgrowth in cultured DRG neurones. NTP had no observable cytotoxicity.

CONCLUSIONS

These results suggest that NTP exerts its antipruritic effects by inhibiting both SP release and neurite outgrowth of cutaneous sensory nerves.

Analysis of the mechanism for the development of allergic skin inflammation and the application for its treatment: mechanisms and management of itch in atopic dermatitis

Although the identification of neural pathways for histamine-induced itch was a breakthrough in itch research, other pathways also seem to be involved in itch. In regard to itch of atopic dermatitis, neural sensitization complicates its mechanisms. Inflammatory mediators such as bradykinin that, normally, do not induce itch can function as pruritogens under neural sensitization, which also affects the treatment to a considerable extent. Complete inhibition of skin inflammation is, for now, the most effective way to suppress itching in atopic dermatitis, since there might be countless potential mediators inducing itch. Centrally acting anti-pruritic drugs as well as drugs against neural sensitization are prospective treatments for itch of atopic dermatitis.