Skin levels of vasoactive intestinal polypeptide in atopic dermatitis

IL-20 promotes cutaneous inflammation and peripheral itch sensation in atopic dermatitis

Atopic dermatitis (AD) is a chronic skin disease, which is associated with intense itch, skin barrier dysfunction and eczematous lesions. Aberrant IL‐20 expression has been implicated in numerous inflammatory diseases, including psoriasis. However, the role of IL‐20 in AD remains unknown. Here, RNA‐seq, Q‐PCR, and immunocytochemistry were utilized to examine disease‐driven changes of IL‐20 and its cognate receptor subunits in skin from healthy human subjects, AD patients and murine AD‐models. Calcium imaging, knockdown and cytokine array were used to investigate IL‐20‐evoked responses in keratinocytes and sensory neurons. The murine cheek model and behavioral scoring were employed to evaluate IL‐20‐elicited sensations in vivo. We found that transcripts and protein of IL‐20 were upregulated in skin from human AD and murine AD‐like models. Topical MC903 treatment in mice ear enhanced IL‐20R1 expression in the trigeminal sensory ganglia, suggesting a lesion‐associated and epidermal‐driven mechanism for sensitization of sensory IL‐20 signaling. IL‐20 triggered calcium influx in both keratinocytes and sensory neurons, and promoted their AD‐related molecule release and transcription of itch‐related genes. In sensory neurons, IL‐20 application increased TLR2 transcripts, implicating a link between innate immune response and IL‐20. In a murine cheek model of acute itch, intradermal injection IL‐20 and IL‐13 elicited significant itch‐like behavior, though only when co‐injected. Our findings provide novel insights into IL‐20 function in peripheral (skin‐derived) itch and clinically relevant intercellular neuron‐epidermal communication, highlighting a role of IL‐20 signaling in the pathophysiology of AD, thus forming a new basis for the development of a novel antipruritic strategy via interrupting IL‐20 epidermal pathways.

Mas-related G protein-coupled receptor X2 and its activators in dermatologic allergies

The Mas-related G protein-coupled receptor X2 (MRGPRX2) is a multiligand receptor responding to various exogenous and endogenous stimuli. Being highly expressed on skin mast cells, MRGPRX2 triggers their degranulation and release of proinflammatory mediators, and it promotes multicellular signaling cascades, such as itch induction and transmission in sensory neurons. The expression of MRGPRX2 by skin mast cells and the levels of the MRGPRX2 agonists (eg, substance P, major basic protein, eosinophil peroxidase) are upregulated in the serum and/or skin of patients with inflammatory and pruritic skin diseases, such as chronic spontaneous urticaria or atopic dermatitis. Therefore, MRGPRX2 and its agonists might be potential biomarkers for the progression of cutaneous inflammatory diseases and the response to treatment. In addition, they may represent promising targets for prevention and treatment of signs and symptoms in patients with skin diseases or drug reactions. To assess this possibility, this review explores the role and relevance of MRGPRX2 and its activators in cutaneous inflammatory disorders and chronic pruritus.

Role of parasympathetic nerves and muscarinic receptors in allergy and asthma

Parasympathetic nerves control the symptoms and inflammation of allergic diseases primarily by signaling through peripheral muscarinic receptors. Parasympathetic signaling targets classic effector tissues such as airway smooth muscle and secretory glands and mediates acute symptoms of allergic disease such as airway narrowing and increased mucus secretion. In addition, parasympathetic signaling modulates inflammatory cells and non-neuronal resident cell types such as fibroblasts and smooth muscle contributing to chronic allergic inflammation and tissue remodeling. Importantly, muscarinic antagonists are experiencing a rebirth for the treatment of asthma and may be useful for treating other allergic diseases.

Pathophysiology and therapy of pruritus in allergic and atopic diseases

Pruritus (itch) is a major characteristic and one of the most debilitating symptoms in allergic and atopic diseases and the diagnostic hallmark of atopic dermatitis. Pruritus is regularly defined as an unpleasant sensation provoking the desire to scratch. Although we achieved rather good knowledge about certain inducers of itch such as neuropeptides, amines, mu-opioids, cytokines and proteases, for example, less is known about the pathophysiological specifities among the different diseases, and the therapeutic consequences which may derive thereoff. This review dissects the role of mediators, receptors and itch inhibitors on peripheral nerve endings, dorsal root ganglia, the spinal cord and the CNS leading to the amplification or - vice versa - suppression of pruritus. As the treatment of pruritus in allergic and atopic skin disease is still not satisfactory, knowing these pathways and mechanisms may lead to novel therapeutic approaches against this frequently encountered skin symptom.

Neuroanatomy and neurophysiology of itch

The specific pathway of "pure," histaminergic itch is traced from the mechano-insensitive nerve fibers in the skin to their central cortical projections. Neuropathic itch created at different levels of this anatomical pathway is reviewed. In this review the present author discusses damage to pruritoceptors in the skin, entrapment syndromes, damage to spinal ganglia, nerve root impingement, injury of the spinal cord, and cerebral damage in the distribution of the middle cerebral artery, capsula interna, or thalamus. Itch in inflamed skin resulting from interactions between nerve transmitters and other mediators of inflammation is described.

Down-regulation of vasoactive intestinal polypeptide receptor expression in atopic dermatitis

BACKGROUND

Receptors for vasoactive intestinal polypeptide (VIP) have recently been suggested to play a key role in immunomodulation with genetically modified mice. However, it is not known whether changes in receptor gene regulation are involved in the pathogenesis of human immune disorders.

OBJECTIVE

We studied the expression of VPAC(2) in acute lesions of the human immune disease atopic dermatitis.

METHODS

By using nonradioactive in situ hybridization, quantitative immunohistochemistry, RT-PCR, and gene array studies, the expression status of VPAC(2) was assessed in atopic dermatitis and control tissues and in the human mast cell line HMC-1.

RESULTS

In situ hybridization and immunohistochemistry demonstrated VPAC(2) mRNA and protein expression in human mast cells surrounded by VIP positive nerve fibers. Gene array experiments and RT-PCR studies showed high levels of VPAC(2) mRNA expression in mast cells that were increased compared to other receptors such as VPAC(1) or VIP in the human mast cell line HMC-1. Stimulation of HMC-1 cells led to a downregulation of VPAC(2). Similarly, quantitative immunohistochemistry for VPAC(2) in acute atopic dermatitis lesions showed a significantly decreased VPAC(2) immunoreactivity in mast cells.

CONCLUSION

The downregulation of VPAC(2) in human mast cells in acute lesions of atopic dermatitis suggests a role of this G-protein;coupled receptor in the pathophysiology of the disease.

Serum levels of vasoactive intestinal peptide are elevated in patients with atopic dermatitis

Vasoactive intestinal peptide (VIP) has been suggested to play some roles in atopic dermatitis. Tissue of VIP levels has been reported to increase in chronic lichenified lesions of atopic dermatitis (AD). To analyze whether serum levels of VIP in AD patients are elevated compared with normal controls and correlated with the disease severity, we measured serum levels of VIP using enzyme-linked immunosorbent assay in 53 patients with AD and 21 healthy individuals. The results showed that serum levels of VIP in AD patients (345.8+/-71.5 microg/ml) were significantly higher than those in healthy individuals (307.1+/-42.6 microg/ml). However, a correlation was not found between serum VIP levels and disease severity, other markers including serum LDH levels, total serum IgE levels, and peripheral blood eosinophil counts in patients with AD. This indicates that VIP levels in AD patients were elevated not only in the skin but also in the serum, suggesting that increased serum VIP levels in the patients with AD might be involved in its pathogenesis.

Vasoactive intestinal peptide and cytokines enhance stem cell factor production from epidermal keratinocytes DJM-1

Stem cell factor can induce mast cell proliferation and melanocyte activation. Vasoactive intestinal peptide has been suggested to play a part in inflammatory dermatoses, such as atopic dermatitis. The aim of this study was to investigate the possible role of stem cell factor in atopic dermatitis by analyzing epidermal stem cell factor production induced by vasoactive intestinal peptide and cytokines. Full-length type stem cell factor transcript was detected in normal human epidermal keratinocytes, and a human epidermal keratinocyte cell line DJM-1, as well as normal human dermal fibroblasts, using reverse transcription-polymerase chain reaction. Spliced-type stem cell factor transcript was detected in both DJM-1 cells and normal human epidermal keratinocytes. Western blot analysis with stem cell factor antibody revealed a protein of the known molecular size of membrane-bound stem cell factor in the lysates of all three cell types. Stem cell factor immunoreactivity was found in the cytoplasm and the membrane of both DJM-1 cells and normal human epidermal keratinocytes using confocal laser scanning microscope. We examined the effects of vasoactive intestinal peptide and cytokines on stem cell factor production of DJM-1 cells using enzyme-linked immunosorbent assays. Stem cell factor contents significantly increased in culture supernatants of DJM-1 cells treated with 1000 nm vasoactive intestinal peptide and/or cytokines, including interleukins 4 and 13, tumor necrosis factor-alpha, and interferon-gamma. Overall, these results suggest that several inflammatory cytokines (T helper 1 and 2) and vasoactive intestinal peptide from mast cells and nerve endings are capable of inducing stem cell factor production from epidermal keratinocytes in atopic dermatitis.

Pathophysiology of pruritus in atopic dermatitis: an overview

Pruritus is an essential feature of atopic dermatitis (AD) and the diagnosis of active AD cannot be made without the history of itching. Because of the high impact on life quality, most of the patients measure the severity of eczema by the intensity of pruritus rather than appearance of skin lesions. However, although pruritus is a cardinal symptom of AD, its mechanism and association with the cutaneous nervous system is not completely understood. Recently, a considerable progress has been achieved in clarifying the complex pathophysiology of pruritus in AD. As a cutaneous sensory perception, itch requires excitation of neuropeptide-containing free nerve endings of unmyelinated nociceptor fibers. It is well known that histamine and acetylcholine provoke itch by direct binding to 'itch receptors' and several mediators such as neuropeptides, proteases or cytokines indirectly via histamine release. Interestingly, some variations of these complex mechanisms could be demonstrated in patients with AD. This review highlights the recent knowledge of different mechanisms which may be involved in regulating pruritus in patients with AD potentially leading to new therapeutic applications for the treatment of itch in AD.

Vasoactive intestinal peptide regulates its receptor expression and functions of human keratinocytes via type I vasoactive intestinal peptide receptors

Vasoactive intestinal peptide has been suggested to play some roles in inflammatory dermatoses such as atopic dermatitis and psoriasis. The aim of this study is to clarify the precise mechanisms of how vasoactive intestinal peptide is implicated in the pathogenesis of these disorders. We investigated the expression of vasoactive intestinal peptide and its receptors in normal human fibroblasts and keratinocytes, as well as in a human epidermal keratinocyte cell line DJM-1, using reverse transcription polymerase chain reaction and northern blotting. Type I VIP receptor mRNA was expressed in normal human keratinocytes and DJM-1 cells, and the latter also expressed type II receptor in lesser amounts. Neither type I nor type II VIP receptor mRNA was detected in fibroblasts, and vasoactive intestinal peptide transcript was not found in any cells examined. Type I VIP receptor mRNA was upregulated by Th1 cytokines (interferon-gamma), Th2 cytokines (interleukin-4), and tumor necrosis factor alpha, as well as vasoactive intestinal peptide itself, suggesting the presence of an autoregulatory loop. Vasoactive intestinal peptide increased cAMP production and cell proliferation of DJM-1 cells, and also induced the production of inflammatory cytokines such as interleukin-6, interleukin-8, and RANTES. The production of cAMP and cytokines was abrogated by a type I VIP receptor selective antagonist, indicating that type I receptor mediates these effects. Overall, these results suggest that upregulation of vasoactive intestinal peptide receptors by cytokines from inflammatory cells in the dermis enhances the proliferation and cytokine production of keratinocytes in response to vasoactive intestinal peptide from nerve endings. This cytokine network around keratinocytes may be involved in the pathogenesis of inflammatory dermatoses.

Administration of acetylcholine and vasoactive intestinal polypeptide to atopic eczema patients

Responses to acetylcholine (ACh) and vasoactive intestinal polypeptide (VIP) were investigated in atopic eczema (AE) patients. To elucidate the involvement of histamine to ACh-provoked vasoreactions and sensations, we applied a selective H1-antagonist (cetirizine) 3 h prior to the ACh-administration. Solutions of acetylcholine (ACh, 0.55 M) and vasoactive intestinal polypeptide (VIP, 1.5x 10(-5) M) were injected (10 microl) intracutaneously into the volar forearm of 14 healthy subjects and 14 atopic eczema (AE) patients. The substances were applied as single stimulus as well as in combination. Sensations evoked by the stimulation were recorded using 2 visual analog scales (VAS). Vasoreactions were analyzed with the new technique of computer assisted video image analysis. With this method we measured the dynamics of the flare development and the extension of the final flare size independent of the observer's assessment. In control subjects the development and extension of the final flare size was almost similar, regardless whether ACh and VIP were applied in combination or separately. Compared to healthy controls, after injection of ACh, VIP and the combination of VIP and ACh smaller flare sizes were recorded in AE patients. After VIP was given, the control subjects reported pruritus, which was significantly augmented compared to AE patients. In contrast, controls reported a burning pain after the injection of ACh, whereas AE patients felt predominantly pruritus. Itch sensation after the combined application of VIP and ACh was significantly elevated in AE patients. Consequently, we assume that mediators of sudomotor neurons, i.e., VIP and ACh meet in AE patients apparently sensitized nociceptive primary afferents and induce exaggerated itch, pain and flare responses. When pretreated with the selective H1-antagonist cetirizine before ACh was injected, pain and erythema due to ACh was diminished in healthy controls. In contrast, cetirizine did not influence the size of erythema and the magnitude of sensation in AE patients. We conclude, that the release of histamine is not involved in ACh-induced erythema and pruritus in AE. These data provide evidence that pruritus can be elicited in atopic eczema by a cholinergic, histamine independent mechanism.

Neuropeptides in the skin of patients with atopic dermatitis

There is increasing evidence that neuropeptides may be involved in the pathogenesis of atopic dermatitis (AD). This study examines whether neuropeptide distribution in the skin of patients with AD differs from normal controls. The distribution and density of several neuropeptides were examined in lesional and non-lesional skin of AD patients (n = 5) and in normal controls (n = 4) using indirect immunofluorescence and image analysis. Cholinergic innervation was studied using cholinesterase histochemistry. Staining with the general neuronal marker protein gene product 9 x 5 showed a subepidermal network of nerves with fibres penetrating the epidermis, and nerves around blood vessels, sweat glands and hair follicles. Image analysis of nerves around sweat glands showed a significantly higher nerve density in non-lesional compared with both normal controls and lesional skin (P < 0.05); lesional compared with control skin showed no significant difference. In the epidermis the density of nerves was not significantly greater in non-lesional compared with lesional skin and controls. Calcitonin gene-related peptide immunoreactivity was similar in all subjects except in three of the AD patients, where more nerves appeared to penetrate the epidermis. Substance P immunoreactivity in the papillary dermis was seen in all AD patients but no controls. Vasoactive intestinal polypeptide and neuropeptide Y staining were similar in all groups. Acetylcholinesterase-positive nerves were found around sweat glands in all subjects, the staining being greatest in non-lesional and least in lesional skin. Occasional nerves were seen in the papillary dermis in lesional skin of two out of the four patients. We have demonstrated quantitative differences in nerve growth in clinically normal skin of AD patients, and altered cutaneous neuropeptide expression in these patients which may contribute to the pathogenesis of AD. The cause of atopic dermatitis (AD) has not been fully established but it is believed that there is a complex interaction between genetic susceptibility, precipitating environmental factors and disordered immune responsiveness. There is increasing evidence that neuropeptides may be involved in the pathogenesis of AD. Exacerbations of the disease can be provoked by stress, scratching and sweating which may be the result of neurogenic inflammation. One of the first features of an exacerbation is flushing of the affected skin and pruritus. Several neuropeptides that have been identified in human skin are potent inducers of vasodilation and may induce pruritus. Substance P (SP), calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) all cause vasodilation when injected intradermally, and SP and CGRP have been shown to be mediators of the weal and flare reaction. Spantide, a competitive antagonist of SP, has been shown to inhibit immediate and delayed-type hypersensitivity reactions. Part of these responses may be due to release of histamine and indeed elevated concentrations of histamine have been found in vivo in the skin and plasma of patients with AD. In this study the distribution and density of several neuropeptides were examined in lesional and nonlesional skin of AD patients and in normal controls using indirect immunofluorescence and image analysis. Cholinergic innervation was studied using cholinesterase histochemistry. Because many afferent fibres do not express CGRP or SP, the general neuronal marker protein gene product (PGP 9 x 5) was used to assess the overall nerve supply to the skin.

Atopic dermatitis: recent trends in pathogenesis and therapy

Emerging concepts in the areas related to the pathogenesis and treatment of atopic dermatitis are reviewed. In particular, recent findings have revealed several key steps in the maintenance of a vicious circle of spongiotic dermatitis associated with elevated T-lymphocyte activation, hyperstimulatory Langerhans cells, defective cell-mediated immunity, and B-cell IgE overproduction. The discovery of specific IgE-binding structures on Langerhans cells provides a mechanism for Langerhans cells to capture and present IgE-targeted allergens to allergen-specific T cells. Furthermore, certain microbial allergens that tend to preferentially elicit IgE-type responses also elicit a T-cell response dominated by the IgE-inducing lymphokine interleukin 4. Repeated stimulation by activated Langerhans cells appears to induce just such a response. Abnormal biochemical responsiveness and mediator release by AD monocytes, mast cells, and eosinophils also participate in the sustainment or initiation of such a vicious circle, and contribute directly to the dermatitis as well. Developments in the areas of neuropeptides, genetics, microbial superantigens, and cytokine networks in the skin also appear to have promise in providing a rational link between immune defects and the inflammatory events in AD. Conventional therapy remains the mainstay of atopic dermatitis management; however, new therapies based upon the above concepts are being tested in clinical trials. Although the difficulty of objectively grading AD lesional activity and the high placebo response of AD patients hampers the interpretation of many reports, several types of approaches are coming into focus. The effectiveness of cyclosporin A, which targets T-cell activation and antigen presentation, indicates that additional agents with such activity should be effective, and verifies the criticality of these cells in AD pathogenesis. Therapy with biologic response modifiers, such as interferon gamma or thymopentin, is oriented toward normalization of imbalanced immune responsiveness, rather than direct suppression of the immune system. The mechanism of action of and toxicities of Chinese herbal mixtures require further investigation, but may reveal hitherto unconsidered avenues. Other recent therapeutic trials have focused on reduction of trigger factors, such as house dust mite exposure, foods, and the abnormal epidermal lipid barrier to irritation.

Glutamate- and aspartate-like immunoreactivities in human normal and inflamed skin

The presence of glutamate/aspartate-like immunoreactivity was studied in normal human skin and in skin with gold-induced inflammation. In normal skin all epithelial cells were glutamate and, apparently more weakly, aspartate immunoreactive. Both glutamate and aspartate immunoreactivities were also found in macrophage-like, HLA-DR positive cells in the dermis and in the epidermis. The intensity of glutamate and especially aspartate-like immunoreactivities seemed to be increased in the epidermis and dermis of the inflamed as compared to the normal skin, and this increase was particularly pronounced in the HLA-DR positive (dendritic) cells in the epidermis. Numerous cells, often of the mononuclear type, in the superficial dermis expressed glutamate- and aspartate-like immunoreactivities in the inflamed skin and many of these were HLA-DR positive. The functional role of glutamate and aspartate in normal skin, and the significance of the increase in the levels of these amino acids in several cell populations in the inflammatory skin is not known, but modulatory or protective roles may be considered. High concentrations of these amino acids could also induce cell damage. Moreover, the macrophage-like cells in the human skin may have a role in the processing of glutamate and aspartate on a recycling basis.

Plasma concentrations and urinary excretion of regulatory peptides in patients with urticaria pigmentosa

Patients with urticaria pigmentosa were investigated during symptom-free interval regarding plasma concentrations and urinary excretion of immunoreactive regulatory peptides: calcitonin gene-related peptide (CGRP), gastrin, neurokinin A (NKA), neuropeptide Y (NPY), somatostatin (SOM), substance P (SP) and vasoactive intestinal peptide (VIP). The plasma concentrations of these peptides, except for CGRP, were below the detection limit. The urinary excretion of the regulatory peptides were not higher in the patient group than in the controls, but in individual patients there was high urinary excretion of SP and VIP. A lower urinary excretion of CGRP was found in the patient group in addition to a tendency to a lower plasma concentration.

Substance P levels are decreased in lesional skin of atopic dermatitis

There is increasing evidence that neuropeptides (NP) such as substance P (SP) and vasoactive intestinal polypeptide (VIP) are involved in the pathogenesis of atopic dermatitis (AD). Vasoactive intestinal polypeptide levels were found to be significantly elevated in lesional skin of AD as compared to controls. We evaluated by radioimmunoassay the SP content in whole skin homogenates from chronic lichenified lesions of patients with AD. The levels of SP were significantly decreased in lesional skin from AD patients as compared to control skin (0.25 +/- 0.03 vs. 0.97 +/- 0.24 pmol/g tissue, p < 0.01). The diminished SP levels as opposed to increased VIP concentrations could be consistent with different roles of these NP as modulatory agents in the mechanisms associated with AD.

Substance P Is Diminished and Vasoactive Intestinal Peptide Is Augmented in Psoriatic Lesions and These Peptides Exert Disparate Effects on the Proliferation of Cultured Human Keratinocytes

An involvement of neurogenic components in the pathogenesis of psoriatic lesions has been suggested and neuropeptides are thought to play a modulatory role in cutaneous inflammation. In this study, we evaluated the immunoreactivity of the neuropeptides vasoactive intestinal polypeptide (VIP) and substance P (SP) in the skin of patients with chronic plaque psoriasis, by immunohistochemistry and radioimmunoassay. No differences were observed, by immunohistochemistry, in the expression and localization of VIP and SP between psoriatic and normal skin. Using the radioimmunologic technique on whole skin homogenates, VIP levels were significantly increased in psoriatic lesions as compared to normal skin. By contrast, SP levels were significantly lower in lesional and non-lesional psoriatic skin than in normal skin. In addition, we examined the effect of VIP and SP on the proliferation of cultured normal human keratinocytes. VIP (1-28) (1 nM-1 microM) as well as VIP fragments (10-28) (1 nM-1 microM) and (22-28) (1 nM-1 microM) stimulated the proliferation of keratinocytes in a dose-dependent manner, whereas the VIP fragment (1-12) (1 nM-1 microM) was ineffective. The VIP antagonist (N-Ac-Tyr1, D-Phe2)-GRF (1-29)-NH2 (0.1 microM) significantly inhibited the VIP effect on keratinocytes. On the other hand, SP (0.1 microM) not only failed to stimulate keratinocyte growth, but also blocked the VIP-induced stimulation of these cells. The imbalance of cutaneous VIP and SP and their disparate effects on the proliferation of normal human keratinocytes in culture would suggest that these peptides are involved in the pathogenesis of psoriasis and may exert different modulatory activities in the mechanisms underlying the psoriatic lesion.