Involvement of leukotriene B(4) in substance P-induced itch-associated response in mice

Glycyrrhetinic acid prevents cutaneous scratching behavior in mice elicited by substance P or PAR-2 agonist

Although glycyrrhetinic acid (GA) has been used for the prevention of itch in chronic dermatitis, the mechanism underlying the antipruritic effects of GA is still unclear. Recently, several mediators other than histamine, such as substance P and tryptase, were found to participate in chronic itch. Here, we investigated the effect of GA on pruritus induced by various pruritic agents including histamine in mice. We also determined the level of leukotriene (LT)B(4) in mouse skin injected with substance P in an effort to uncover part of the antipruritic mechanism of GA. Scratching events were counted for 10 min after intradermal injection of histamine, substance P (100 nmol per site each), protease-activated receptor-2 (PAR-2) agonistic peptide (50 nmol per site), or LTB(4) (0.03 nmol per site) with or without GA (4 nmol per site) into male ICR mice. Levels of LTB(4) in the skin after injection of substance P were determined by ELISA. GA did not suppress scratching behavior induced by histamine and LTB(4), but markedly and dose-dependently suppressed that induced by substance P and PAR-2 agonistic peptide. LTB(4) levels in skin elevated by substance P were lowered by GA. These data support the efficacy of GA in counteracting itch in chronic dermatitis because GA reduced scratching behavior induced by substance P and PAR-2 agonistic peptide. GA may exert antipruritic effects via inhibition of LTB(4) production in skin.

Basic mechanisms of itch

Chronic itch represents a burdensome clinical problem that can originate from a variety of aetiologies. Pruriceptive itch originates following the activation of peripheral sensory nerve endings following damage or exposure to inflammatory mediators and ascends to the brain through the spinal thalamic tract. Much insight has been gained into the understanding of the mechanisms underlying pruriceptive itch through studies using humans and experimental animals. More than one sensory nerve subtype is thought to subserve pruriceptive itch which includes both unmyelinated C-fibres and thinly myelinated Aδ nerve fibres. There are a myriad of mediators capable of stimulating these afferent nerves leading to itch, including biogenic amines, proteases, cytokines, and peptides. Some of these mediators can also evoke sensations of pain and the sensory processing underlying both sensations overlaps in complex ways. Studies have demonstrated that both peripheral and central sensitization to pruritogenic stimuli occur during chronic itch.

The role of fatty aldehyde dehydrogenase in epidermal structure and function

The epidermal water barrier resides in the stratum corneum (SC) and is dependent on a highly organized network of multi-lamellar membranes comprised of a critical lipid composition. The SC membranes are formed from precursor membranes packaged in cytoplasmic lamellar bodies in the stratum granulosum and delivered to the SC by exocytosis. An abnormal lipid composition of the SC membranes often results in a disrupted water barrier and the clinical appearance of ichthyosis. This cutaneous feature is characteristic of Sjögren-Larsson syndrome (SLS), an inborn error of lipid metabolism caused by deficiency of fatty aldehyde dehydrogenase (FALDH). The contribution of FALDH to normal epidermal function has become increasingly evident with the recognition that this enzyme has an essential role in metabolism of several lipids, including fatty aldehydes and alcohols, ether glycerolipids, isoprenoid alcohols and certain lipids that undergo ω-oxidation, such as leukotriene B4 and very long-chain fatty acids. In the absence of FALDH, the skin produces lamellar bodies that are empty, lack their surrounding vesicle membranes or contain granular contents rather then the usual cargo membranes. These defective organelles also have impaired exocytosis, which results in structurally abnormal, deficient multi-lamellar membranes in the SC and a leaky water barrier. Although the exact biochemical mechanism for the cutaneous pathology is still unclear, studies in SLS demonstrate the critical importance of FALDH for normal epidermal structure and function.

Topical cholecystokinin depresses itch-associated scratching behavior in mice

Cholecystokinin (CCK) serves as a gastrointestinal hormone and also functions as a neuropeptide in the central nervous system (CNS). CCK may be a downregulator in the CNS, as represented by its anti-opioid properties. The existence of CCK in the peripheral nervous system has also been reported. We investigated the suppressive effects of various CCKs on peripheral pruritus in mice. The clipped backs of ICR mice were painted with CCK synthetic peptides and injected intradermally with substance P (SP). The frequency of SP-induced scratching was reduced significantly by topical application of sulfated CCK8 (CCK8S) and CCK7 (CCK7S), but not by nonsulfated CCK8, CCK7, or CCK6. Dermal injection of CCK8S also suppressed the scratching frequency, suggesting that dermal cells as well as epidermal keratinocytes (KCs) are the targets of CCKs. As determined using real-time PCR, mRNA for CCK2R, one of the two types of CCK receptors, was expressed highly in mouse fetal skin-derived mast cells (FSMCs) and moderately in ICR mouse KCs. CCK8S decreased in vitro compound 48/80-promoted degranulation of FSMCs with a transient elevation of the intracellular calcium concentration. These findings suggest that CCK may exert an antipruritic effect via mast cells and that topical CCK may be clinically useful for pruritic skin disorders.

Pruritus: an overview of current concepts

Pruritus is an integral part of the patient's symptoms in numerous dermatological and systemic diseases in humans and animals. Comparable to chronic pain, pruritus can have a dramatic impact on the quality of life of the patient. In recent years, pruritus has been defined as an autonomous, pain-independent sensation, and itch-specific neurons, mediators, spinal neurons and cortical areas have been identified. These observations have not only improved our understanding of the neurobiology of itch but will also lead to improved diagnosis and to the development of new and more efficient therapeutic options. This article reviews the role of itch fibres and their response to various mediators of pruritus including histamine, vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), and substance P (SP), and opioids. Substances that may be involved in the induction or modulation of itch may be termed pruritogenic mediators and examples discussed include proteases, lipid mediators, neuropeptides, opioids and various cytokines. There is no single, generally accepted clinical classification of chronic pruritus. In the past pruritus has been classified on the basis of the neuroanatomical origin and on the potential underlying disease. Therapeutic options for the management of pruritus are discussed including topical and systemic therapies, assuming that trigger factors have been eliminated where possible. Topical agents may include capsaicin, the calcineurin inhibitors tacrolimus and pimecrolimus, and cannabinoid agonists such as N-palmitoyl ethanolamine. Systemic therapies may include antihistamines, anticonvulsants, opiate receptor antagonist or agonists, antidepressants, ciclosporin, and UV light.

Inhibitory effect of methanol extract of Ganoderma lucidum on acute itch-associated responses in mice

In this study, the antipruritic effect of the methanol extract of Ganoderma lucidum (MEGL) was studied in mice. Oral administration of MEGL (10-1000 mg/kg) produced a dose-dependent inhibition of scratching, an itch-related response, induced by intradermal 5-hydroxytryptamine (5-HT) (100 nmol/site), alpha-methyl-5-HT (100 nmol/site), and proteinase-activated receptor-2 (PAR(2))-activating peptide SLIGRL-NH(2) (50 nmol/site). However, MEGL (100-1000 mg/kg) did not inhibit the scratching induced by histamine (100 nmol/site), substance P (100 nmol/site), and compound 48/80 (10 microg/site). These results raise the possibility that MEGL is effective against pruritus mediated by proteinases and 5-HT and that primary afferents expressing PAR(2) and 5-HT(2A) receptors are the sites of its action.

Inhibitory effects of the methanol extract of Ganoderma lucidum on mosquito allergy-induced itch-associated responses in mice

Recently, we showed that a methanol extract of Ganoderma lucidum inhibits scratching, an itch-related response, induced by intradermal injections of some pruritogens in mice. The present study investigated whether G. lucidum extract would inhibit allergic itch. In mice sensitized with an extract of salivary gland of mosquito (ESGM), an intradermal injection of ESGM elicited scratching, which was suppressed by oral administration of G. lucidum extract (100 and 300 mg/kg). The scratching was inhibited by the H₁ histamine-receptor antagonist azelastine, but not by the peripherally acting H₁-antagonist terfenadine, at the oral dose of 30 mg/kg. In sensitized mice, ESGM increased the activity of cutaneous nerve, which was suppressed by G. lucidum extract (300 mg/kg). Although terfenadine (30 mg/kg) inhibited plasma extravasation induced by ESGM in the sensitized mice, G. lucidum extract (300 mg/kg) was without effect. These results suggest that G. lucidum extract relieves allergic itch through a peripheral action. The results support the idea that mast cells and H₁ histamine receptors are not the primary sites of the antipruritic action of G. lucidum extract.

Diclofenac: an update on its mechanism of action and safety profile

BACKGROUND

Diclofenac is a proven, commonly prescribed nonsteroidal anti-inflammatory drug (NSAID) that has analgesic, anti-inflammatory, and antipyretic properties, and has been shown to be effective in treating a variety of acute and chronic pain and inflammatory conditions. As with all NSAIDs, diclofenac exerts its action via inhibition of prostaglandin synthesis by inhibiting cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) with relative equipotency. However, extensive research shows the pharmacologic activity of diclofenac goes beyond COX inhibition, and includes multimodal and, in some instances, novel mechanisms of action (MOA).

DATA SOURCES

Literature retrieval was performed through PubMed/MEDLINE (through May 2009) using combinations of the terms diclofenac, NSAID, mechanism of action, COX-1, COX-2, and pharmacology. Reference citations resulting from publications identified in the literature search were reviewed when appropriate.

METHODS

This article reviews the established, putative, and emerging MOAs of diclofenac; compares the drug's pharmacologic and pharmacodynamic properties with other NSAIDs to delineate its potentially unique qualities; hypothesizes why it has been chosen for further recent formulation enhancement; and evaluates the potential effect of its MOA characteristics on safety.

DISCUSSION

Research suggests diclofenac can inhibit the thromboxane-prostanoid receptor, affect arachidonic acid release and uptake, inhibit lipoxygenase enzymes, and activate the nitric oxide-cGMP antinociceptive pathway. Other novel MOAs may include the inhibition of substrate P, inhibition of peroxisome proliferator activated receptor gamma (PPARgamma), blockage of acid-sensing ion channels, alteration of interleukin-6 production, and inhibition of N-methyl-D-aspartate (NMDA) receptor hyperalgesia. The review was not designed to compare MOAs of diclofenac with other NSAIDs. Additionally, as the highlighted putative and emerging MOAs do not have clinical data to demonstrate that these models are correct, further research is necessary to ascertain if the proposed pathways will translate into clinical benefits. The diversity in diclofenac's MOA may suggest the potential for a relatively more favorable profile compared with other NSAIDs.

Pharmacological characterization of itch-associated response induced by repeated application of oxazolone in mice

We investigated pharmacological characteristics of the itch-associated response to chronic dermatitis induced by 4-ethoxymethylene-2-phenyl-2-oxazolin-5-one (oxazolone) repeated application in mice. Application of an oxazolone challenge to mice with oxazolone-induced chronic dermatitis evoked severe and transient scratching behavior for up to 1h. Thereafter, mild and continuous scratching behavior was observed for at least 8 h. Both severe and continuous scratching behaviors were suppressed by the opioid-receptor antagonist naltrexone, but not by the H(1) histamine-receptor antagonist fexofenadine, 5-hydroxytryptamine-2 (5-HT(2))-receptor antagonist methysergide, NK(1)-receptor antagonist LY303870, cyclooxygenase inhibitor indomethacin, or the platelet-activating factor-receptor antagonist YM264. The severe scratching behavior was suppressed by the 5-lipoxygenase inhibitor zileuton and leukotriene B(4)-receptor antagonist ONO-4057, but not by the cysteinyl leukotriene-receptor antagonist montelukast. The continuous scratching behavior was suppressed by pretreatment with the non-selective muscarinic acetylcholine-receptor antagonist atropine and M(3) muscarinic acetylcholine-receptor antagonist darifenacin. These results suggest that leukotriene B(4) receptor and M(3) muscarinic acetylcholine receptor are involved in the itch-associated response induced by repeated application of oxazolone in mice.

Effect of epinastine hydrochloride on murine self-scratching behavior after skin-scratching stimulation

The itch-scratch cycle aggravates chronic inflammatory skin diseases. We have previously reported that mice begin to scratch themselves within several minutes after skin-scratching stimulation. This is associated with an increase in release of substance P (SP) from sensory nerve fibers in the skin, and the self-scratching behavior is suppressed by neurokinin-1 receptor (NK-1R) antagonist. Thus, SP may play a pivotal role in self-scratching behavior. The purpose of this study was to investigate the effect of second-generation histamine H(1)-receptor antagonists on self-scratching behavior in mice. After oral administration of epinastine hydrochloride (epinastine) (total dose 50 +/- 5 mg/kg for 7 days) or the vehicle only to ICR mice for 7 days, skin-scratching stimulation was administered to the dorsal skin for 10 min. Self-scratching behavior was recorded by video camera for 10 min. Twenty-four hours later, skin tissue was harvested and stained with toluidine blue. Immunohistochemical staining for SP was performed, and SP and nerve growth factor (NGF) concentrations were measured by enzyme-linked immunosorbent assay. Self-scratching behavior, mast cell degranulation, and NGF concentration decreased, and the length of SP-positive nerve fibers and SP concentrations increased significantly in the epinastine-treated group, when compared with the vehicle control group. We conclude that epinastine inhibits mast cell degranulation by attenuating SP release from sensory nerve fibers, which results in inhibition of self-scratching behavior. These results suggest that second-generation histamine H(1)-receptor antagonists might efficaciously control itch-scratch cycle-related skin diseases.

Expression of histamine H4 receptor in human epidermal tissues and attenuation of experimental pruritus using H4 receptor antagonist

Many medicines exist which can cause pruritus (itching) as "serious adverse events." Many severe pruritic conditions respond poorly to histamine H1 receptor antagonists; there is no generally accepted antipruritic treatment. Recently described histamine H4 receptors are expressed in haematopoietic cells and have been linked to the pathology of allergy and asthma. We previously reported their expression in human dermal fibroblasts; in this study we have investigated H4 receptor expression in human epidermal tissue and found it to be greater in keratinocytes in the epidermal upper layer than in the lower layer. We have also investigated the effect of histamine H4 receptor antagonists on histamine H1 receptor antagonist-resistant pruritus using a mouse model. Scratching behavior was induced by histamine (300 nmol) or substance P (100 nmol) injected intradermally into the rostral part of the back of each mouse. Fexofenadine, a histamine H1 receptor antagonist, reduced scratching induced by histamine but not by substance P, whereas JNJ7777120, a histamine H4 receptor antagonist, significantly reduced both histamine- and substance P-induced scratching. These results suggest that H4 receptor antagonists may be useful for treatment of H1 receptor antagonist-resistant pruritus.

Induction of leukotriene B(4) and prostaglandin E(2) release from keratinocytes by protease-activated receptor-2-activating peptide in ICR mice

Protease-activated receptor-2 (PAR2) has been shown to play a key role in the pathophysiology of itch. However, the precise mechanism of PAR2-mediated itch remains largely unknown. In the present study, we investigated the effects of several agents on the scratching behavior induced by PAR2-activating peptide (SLIGRL-NH2). Pretreatment of experimental animals with tacrolimus or the 5-lipoxygenase inhibitor zileuton significantly reduced SLIGRL-NH2-induced scratching behavior, whereas histamine H(1) receptor antagonist cetirizine or the cyclooxygenase inhibitor indomethacin had little effect. Furthermore, intradermal injection of SLIGRL-NH2 increased cutaneous levels of LTB(4) and PGE(2). In vitro, SLIGRL-NH2 treatment enhanced LTB(4) and PGE(2) release from primary keratinocytes in a concentration-dependent manner. Preincubation of keratinocytes with zileuton resulted in a significant decrease of LTB(4) release and treatment of indomethacin led to a significant decrease of PGE(2) in response to SLIGRL-NH2 stimulation. In addition, SLIGRL-NH2-induced secretion of LTB(4) and PGE(2) was significantly inhibited by tacrolimus, whereas cetirizine had no effect. These results indicate that SLIGRL-NH2 stimulates LTB(4) and PGE(2) release from mouse keratinocytes and that enhancement of LTB(4) and PGE(2) secretion contributes to SLIGRL-NH2-induced scratching behavior in ICR mice.

Leukotriene B(4) mediates sphingosylphosphorylcholine-induced itch-associated responses in mouse skin

In atopic dermatitis, the concentration in the skin of sphingosylphosphorylcholine (SPC), which is produced from sphingomyelin by sphingomyelin deacylase, is increased. In the present study, we investigated the itch-eliciting activity of SPC and related substances and the mechanisms of SPC action in mice. An intradermal injection of SPC, but not sphingomyelin and sphingosine, induced scratching, an itch-associated response, which was not suppressed by a deficiency in mast cells or the H(1) histamine receptor antagonist terfenadine. The action of SPC was inhibited by the mu-opioid receptor antagonist naltrexone. SPC action also was inhibited by the 5-lipoxygenase inhibitor zileuton and the leukotriene B(4) antagonist ONO-4057, but not by the cyclooxygenase inhibitor indomethacin. Moreover, SPC action was inhibited by the antiallergic agent azelastine, which suppresses the action and production of leukotriene B(4). Administration of SPC to the skin and to primary cultures of keratinocytes increased leukotriene B(4) production. SPC increased intracellular Ca(2+) ion concentration in primary cultures of dorsal root ganglion neurons and keratinocytes. These results suggest that SPC induces itching through a direct action on primary afferents and leukotriene B(4) production of keratinocytes. Sphingomyelin deacylase and SPC receptors may be previously unreported targets for antipruritic drugs.

Activation of proteinase-activated receptors induces itch-associated response through histamine-dependent and -independent pathways in mice

Proteinase-activated receptor-2 (PAR2) participates in itch, but the role of the other subtypes of this receptor remain unknown. To investigate this issue, scratching, an itch-related behavior, was observed following intradermal injections of the activating peptides of PAR1-4 in mice. Activating peptides of PAR1, PAR2, and PAR4, but not PAR3, induced scratching. The antihistamine terfenadine suppressed scratching elicited by activating peptides of PAR1 and PAR4, but not PAR2. These results suggest that PAR1, PAR2, and PAR4 are involved in itch and that histamine is a cause of itch related to PAR1 and PAR4, but not PAR2.

Involvement of the BLT2 receptor in the itch-associated scratching induced by 12-(S)-lipoxygenase products in ICR mice

BACKGROUND AND PURPOSE

Recently, we reported that 12(S)-HPETE (12(S)-hydroperoxyeicosa-5Z,8Z,10E,14Z-tetraenoic acid) induces scratching in ICR mice. We hypothesized that 12(S)-HPETE might act as an agonist of the low-affinity leukotriene B4 receptor BLT2. To confirm the involvement of the BLT2 receptor in 12(S)-HPETE-induced scratching, we studied the scratch response using the BLT2 receptor agonists compound A (4'-[[pentanoyl (phenyl) amino]methyl]-1,1'-biphenyl-2-carboxylic acid) and 12(S)-HETE (12(S)-hydroxyeicosa-5Z,8Z,10E,14Z-tetraenoic acid).

EXPERIMENTAL APPROACH

A video recording was used to determine whether the BLT2 receptor agonists caused itch-associated scratching in ICR mice. Selective antagonists and several chemicals were used.

KEY RESULTS

Both 12(S)-HETE and compound A dose dependently induced scratching in the ICR mice. The dose-response curve for compound A showed peaks at around 0.005-0.015 nmol per site. Compound A- and 12(S)-HETE-induced scratching was suppressed by capsaicin and naltrexon. We examined the suppressive effects of U75302 (6-[6-(3-hydroxy-1E,5Z-undecadienyl)-2-pyridinyl]-1,5-hexanediol, the BLT1 receptor antagonist) and LY255283 (1-[5-ethyl-2-hydroxy-4-[[6-methyl-6-(1H-tetrazol-5-yl)heptyl]oxy]phenyl]-ethanone, the BLT2 receptor antagonist) on the BLT2 agonist-induced scratching. LY255283 suppressed compound A- and 12(S)-HETE-induced scratching, but U75302 did not. LY255283 required a higher dose to suppress the compound A-induced scratching than it did to suppress the 12(S)-HETE-induced scratching. One of the BLT(2) receptor agonists, 12(R)-HETE (12(R)-hydroxyeicosa-5Z,8Z,10E,14Z-tetraenoic acid), also induced scratching in the ICR mice.

CONCLUSIONS AND IMPLICATIONS

Our present results corroborate the hypothesis that the BLT2 receptor is involved in 12(S)-lipoxygenase-product-induced scratching in ICR mice. We also confirmed that this animal model could be a valuable means of evaluating the effects of BLT2 receptor antagonists.

Effects of topical application of tacrolimus on acute itch-associated responses in mice

Using mice, we examined whether the topical application of tacrolimus would produce an acute anti-pruritic effect. An itch-related response, scratching, was elicited by intradermal injections of mosquito allergen (10 microg/site) in sensitized mice and SLIGRL-NH2 (protease-activated receptor-2 agonist, 50 nmol/site), histamine (100 nmol/site), serotonin (100 nmol/site) and substance P (100 nmol/site) in naive ones. Topical application of 1%, but neither 0.1% nor 0.3%, tacrolimus to the skin 1 h before injection inhibited scratching induced by mosquito allergen and SLIGRL-NH2, without effects on scratching induced by histamine, serotonin, and substance P. Topical tacrolimus also inhibited licking induced by an intraplantar injection of capsaicin (0.1 microg/site). These results suggest that topical tacrolimus exerts acute inhibitory effects on allergic and protease-activated receptor-2-mediated itching. Though precise mechanisms remain unclear, the action on sensory neurons expressing protease-activated receptor-2 and transient receptor potential vanilloid-1 capsaicin receptor may be involved in the inhibitory effects of tacrolimus.

Psychological stress can trigger atopic dermatitis in NC/Nga mice: an inhibitory effect of corticotropin-releasing factor

Atopic dermatitis (AD) is one of the most common inflammatory diseases of the skin and is usually associated with a family history of atopic diathesis. It has been well established that many environmental or psychological factors aggravate AD. However, it is not clear whether psychological stress by itself can trigger AD. We examined the effect of psychological stress on the onset of AD, using an animal model, the NC/Nga mouse. The animals were exposed to the water avoidance stress (WAS) test to induce psychological stress. Additionally, we examined how corticotropin-releasing factor (CRF) affected the development of AD induced by psychological stress. Under specific pathogen-free (SPF) conditions, NC/Nga mice did not develop AD-like skin lesions. In contrast, NC/Nga mice exposed to psychological stress developed AD-like skin lesions along with elevated levels of serum immunoglobulin E even when kept under SPF conditions. The AD-like skin lesions induced by WAS were completely blocked by pretreating the animals with CRF. Our data indicate that a psychological factor is capable of eliciting AD-like skin lesions in NC/Nga mice. It is possible that the inhibitory effect of CRF may be mediated by the functional modification of various cells that have CRF receptors.

Pathophysiology of nocturnal scratching in childhood atopic dermatitis: the role of brain-derived neurotrophic factor and substance P

BACKGROUND

Childhood atopic dermatitis (AD) is a distressing disease associated with pruritus and sleep disturbance. The pathophysiology of pruritus is complex and various neuropeptides may be involved.

OBJECTIVE

To evaluate whether or not brain-derived neurotrophic factor (BDNF) and substance P are associated with disease severity, quality of life and nocturnal scratching in AD.

METHODS

Patients with AD aged under 18 years were recruited. Disease severity was assessed with the SCORing Atopic Dermatitis (SCORAD) index, and quality of life with the Children's Dermatology Life Quality Index (CDLQI). Concentrations of plasma BDNF, substance P, AD-associated chemokines [cutaneous T-cell attracting cytokine (CTACK), thymus and activation regulated chemokine (TARC)], serum total IgE and eosinophil counts were measured in these patients. All children were instructed to wear the DigiTrac monitor on their dominant wrist while sleeping. The monitor was programmed to record limb motion between 22.00 and 08.00 h the following morning.

RESULTS

Twenty-eight children with AD [mean (SD) age 11.1 (3.3) years] were recruited. The mean (SD) SCORAD was 48.1 (21.5) and CDLQI was 8.7 (5.4) in the patients with AD. Their mean (SD) plasma concentrations of BDNF, substance P, CTACK and TARC were 1798 (935), 94 (42), 1424 (719) and 824 (1000) pg mL(-1), respectively. BDNF was significantly correlated with SCORAD (r = 0.478, P = 0.010) and CDLQI (r = 0.522, P = 0.004), whereas substance P showed significant correlation only with CDLQI (r = 0.441, P = 0.019). BDNF and substance P were also significantly correlated with the average (r = 0.905, P < 0.001 and r = 0.925, P < 0.001) and frequency-specific (r = 0.826, P < 0.001 and r = 0.870, P < 0.001) nocturnal wrist activities measured by DigiTrac. However, there was no correlation between BDNF or substance P and the subjective symptoms of pruritus or sleep-loss scores as reported by the parents in the SCORAD. In contrast, serum total IgE levels showed significant correlations with the subjective symptoms of pruritus (r = 0.576, P = 0.001) and sleep loss (r = 0.419, P = 0.027).

CONCLUSIONS

Serum levels of BDNF and substance P correlate with the clinical score and quality of life score in patients with AD. The strong correlations with nocturnal wrist movements suggest that they may be the pathogenic factors of the annoying symptoms of scratching.

Possible involvement of 5-lipoxygenase metabolite in itch-associated response of mosquito allergy in mice

This study investigated endogenous mediators involved in mosquito allergy-associated itching in mice. An intradermal injection of an extract of mosquito salivary gland elicited marked scratching in sensitized mice. The 5-lipoxygenase inhibitor zileuton (100 mg/kg), the 5-lipoxygenase activating peptide inhibitor MK-886 (10 mg/kg), and the glucocorticoid betamethasone 17-valerate (3 mg/kg) inhibited the scratching. The scratching was not affected by the cyclooxygenase inhibitors indomethacin and ketoprofen, the TP prostanoid receptor antagonist SQ-29548, the leukotriene B(4) antagonist ONO-4057, the cysteinyl leukotriene antagonist pranlucast, the leukotriene D(4) antagonist MK-571, the platelet-activating factor antagonist CV-3988, the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester, the H(2) histamine-receptor antagonist cimetidine, the H(1) histamine-receptor antagonist terfenadine plus cimetidine, and cypoheptadine that blocks the 5-HT(1/2) serotonin receptors. Zileuton (100 mg/kg) inhibited the increased activity of the cutaneous nerve branch induced by an intradermal injection of the extract, suggesting the peripheral action. Zileuton and MK-886 (10 and 100 microM) did not affect high K(+)-induced increase in intracellular Ca(2+) concentration in cultured dorsal root ganglion neurons. The results suggest that 5-lipoxygenase metabolite(s) other than leukotriene B(4) and cysteinyl leukotrienes are involved in mosquito allergy-associated itching.

A transient unresponsive state of self-scratching behaviour is induced in mice by skin-scratching stimulation

When mice were scratched with brushes on their dorsal skins, they began to scratch themselves with their hind paws. Thus, self-scratching behaviour was induced in mice in response to skin-scratching stimulation. If the second skin-scratching stimulation was given within a few days, the induction of the second self-scratching behaviour was significantly suppressed compared with the first one. Thereafter, mice gradually recovered from this unresponsive state within a week. Thus, a transient unresponsive state of self-scratching behaviour is induced by skin-scratching stimulation. Pretreatment with a tachykinin receptor NK-1R antagonist L-703606 or capsaicin significantly suppressed self-scratching behaviour, while pretreatment with a neutral endopeptidase inhibitor phosphoramidon significantly enhanced it. Pretreatment with a calcitonin gene-related peptide (CGRP) receptor antagonist CGRP(8-37) did not affect the following self-scratching behaviour. From these results, it is suggested that substance P (SP) signalling through its receptor NK-1R at least in part mediates the induction of self-scratching behaviour. After skin-scratching stimulation, immunoreactivity of SP both in the peripheral nerve fibres and in the dorsal root ganglion (DRG) neurons was significantly decreased and was well-correlated with suppression of self-scratching behaviour. From these findings, it is suggested that the induction of unresponsive states of self-scratching behaviour may be at least in part caused by the depleted states of SP in peripheral nerve fibres and/or in DRG neurons. The induction of a transient unresponsive state after skin-scratching may possibly happen also in patients with pruritus. Thus, further studies to elucidate the precise mechanisms are required.

TRP channels as novel players in the pathogenesis and therapy of itch

Itch (pruritus) is a sensory phenomenon characterized by a (usually) negative affective component and the initiation of a special behavioral act, i.e. scratching. Older studies predominantly have interpreted itch as a type of pain. Recent neurophysiological findings, however, have provided compelling evidence that itch (although it indeed has intimate connections to pain) rather needs to be understood as a separate sensory modality. Therefore, a novel pruriceptive system has been proposed, within which itch-inducing peripheral mediators (pruritogens), itch-selective receptors (pruriceptors), sensory afferents and spinal cord neurons, and defined, itch-processing central nervous system regions display complex, layered responses to itch. In this review, we begin with a current overview on the neurophysiology of pruritus, and distinguish it from that of pain. We then focus on the functional characteristics of the large family of transient receptor potential (TRP) channels in skin-coupled sensory mechanisms, including itch and pain. In particular, we argue that - due to their expression patterns, activation mechanisms, regulatory roles, and pharmacological sensitivities - certain thermosensitive TRP channels are key players in pruritus pathogenesis. We close by proposing a novel, TRP-centered concept of pruritus pathogenesis and sketch important future experimental directions towards the therapeutic targeting of TRP channels in the clinical management of itch.

Thromboxane A2 induces itch-associated responses through TP receptors in the skin in mice

Thromboxane A2 (TXA2), a metabolite of arachidonic acid produced by cyclooxygenase and thromboxane synthase, is thought to participate in chronic dermatitis. This study investigated the involvement of TXA2 in cutaneous itch. An intradermal injection of U-46619, a stable analogue of TXA2, elicited scratching, an itch-associated response, in mice. Dose-response curve was bell shaped with a maximum effect at 10 nmol per site. The action of U-46619 was inhibited by a coinjection of the TP antagonist ONO-3708 and was abolished by TP receptor deficiency. TP receptor was mainly expressed in nerve fiber in the skin and keratinocytes. Thromboxane synthase was also expressed in keratinocytes. U-46619 increased intracellular Ca2+ ion concentration in primary cultures of dorsal root ganglion neurons and keratinocytes. The results suggest that TXA2 synthesized by keratinocytes acts as an itch mediator. It may elicit itch through the activation of TP receptors on primary afferents and keratinocytes; keratinocytes may produce itch mediators including TXA2. Thus, thromboxane synthase inhibitor and TP receptor antagonists will be candidates for antipruritic medicines.

12(S)-HPETE induces itch-associated scratchings in mice

The itch-associated responses evoked by intradermal injection of 12(S)-HPETE and leukotriene B4 were compared in ICR-mice. 12(S)-HPETE and leukotriene B4 (0.01-0.2 nmol/site) induced scratching of the injected site, respectively; the dose-responses were a peak at 0.05 nmol/site (12(S)-HPETE) or 0.03 nmol/site (leukotriene B4). The scratching response by 12(S)-HPETE (0.05 nmol/site) started within 1 min, peaked in the first 10 min period, had almost subsided by 25 min whereas the effect of leukotriene B4 peaked in the second 10 min. The effect of leukotriene B4 is slightly stronger than that of 12(S)-HPETE in 40 min of count. The scratching induced by 12(S)-HPETE was inhibited by capsaicin, naltrexon, and LY255283. These results suggest the possibility that 12-lipoxygenase product can be added to a new member of an endogenous itch mediator in the skin.

Sjögren-Larsson syndrome: molecular genetics and biochemical pathogenesis of fatty aldehyde dehydrogenase deficiency

Sjögren-Larsson syndrome (SLS) is an inherited neurocutaneous disorder caused by mutations in the ALDH3A2 gene that encodes fatty aldehyde dehydrogenase (FALDH), an enzyme that catalyzes the oxidation of fatty aldehyde to fatty acid. Affected patients display ichthyosis, mental retardation and spastic diplegia. More than 70 mutations in ALDH3A2 have been discovered in SLS patients including amino acid substitutions, deletions, insertions and splicing errors. Most mutations are private, but several common mutations reflect founder effects, consanguinity or recurrent mutational events. FALDH oxidizes fatty aldehyde substrates arising from metabolism of fatty alcohols, leukotriene B4, ether glycerolipids and other potential sources such as sphingolipids. The pathogenesis of the cutaneous and neurologic symptoms is thought to result from abnormal lipid accumulation in the membranes of skin and brain; the formation of aldehyde Schiff base adducts with amine-containing lipids or proteins; or defective eicosanoid metabolism. Therapeutic approaches are being developed to target specific metabolic defects associated with FALDH deficiency or to correct the genetic defect by gene transfer.

Suppression by bepotastine besilate of substance P-induced itch-associated responses through the inhibition of the leukotriene B4 action in mice

Anti-pruritic effects of the antihistamine bepotastine besilate were studied in mice. Bepotastine besilate (10 mg/kg) inhibited scratching induced by an intradermal injection of histamine (100 nmol/site), but not serotonin (100 nmol/site). Bepotastine besilate (1-10 mg/kg, oral) dose-dependently suppressed scratching induced by substance P (100 nmol/site) and leukotriene B(4) (0.03 nmol/site). An intradermal injection of substance P (100 nmol/site) increased the cutaneous concentration of leukotriene B(4), which was not affected by bepotastine besilate (10 mg/kg, oral). Leukotriene B(4) increased Ca(2+) concentration in cultured neutrophils, which was suppressed by bepotastine besilate (1-100 microM). Leukotriene B(4) increased Ca(2+) concentration in cultured dorsal root ganglion neurons, which was also suppressed by bepotastine besilate (100 microM). The results suggest that the inhibition of the actions of leukotriene B(4) as well as histamine is involved in the anti-pruritic effect of bepotastine besilate.

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.

[Importance of epidermal keratinocytes in itching]

Itch, a skin sensation that provokes a desire to scratch, is a common complaint. Severe itch accompanying various skin diseases such as atopic dermatitis is an important issue related to the quality of life. Although histamine from mast cells has been thought to play an essential role in itch, many severe pruritic diseases respond poorly to the H(1) histamine receptor antagonists. Therefore the precise mechanisms and mediators of itch in most pruritic diseases are unclear. To investigate the detailed mechanisms of the induction of itch, we have developed a mouse model. Studies using this model have demonstrated that keratinocytes play an important role in the induction of itch. The identification of keratinocyte stimulus factors and of products in keratinocytes could lead to developing new antipruritic medicines.

Enhancement of the release of inflammatory mediators by substance P in rat basophilic leukemia RBL-2H3 cells

Substance P (SP), a neurotransmitter, may play an important role in neurogenic inflammation. Ginseng has been used extensively in traditional medicine; however, few studies were focused on their anti-allergic effect. Therefore, the effect and mechanism of ginsenoside Rb1 on the SP enhancement of allergic mediators were explored. In this study, SP and dinitrophenyl-bovine serum albumin (DNP-BSA) were used to activate rat basophilic leukemia (RBL)-2H3 cells. The cultured supernatants were assayed for histamine, leukotriene C(4)(LTC(4)) and interleulin-4 (IL-4) production. The mitogen-activated protein kinases (MAPKs) signaling pathway was determined by Western blotting analysis. We found that IgE/DNP-BSA, SP, ginsenoside Rb1, or MAPK specific inhibitors had no effect on cell viability and cytotoxicity. SP (30 microM) alone, did not induce histamine and LTC(4) release, but it enhanced allergen-induced histamine and LTC(4) release. In addition, SP significantly induced and enhanced allergen-activated IL-4. Ginsenoside Rb1 dose-dependently inhibited these effects. SP enhanced the allergen-activated ERK pathway in RBL-2H3 cells, and Rb1 effectively inhibited the ERK pathway activation. Although MAPK specific inhibitors suppressed LTC(4) and IL-4, only U0126 inhibited the SP enhanced histamine release. These results demonstrate that Rb1 dose-dependently inhibited SP enhanced allergen-induced mediator release and its mechanism was through the inhibition of the ERK pathway.

A new chronic itch model accompanied by skin lesions in hairless mice

The present study was performed to develop a new chronic itch model accompanied by skin lesions using hairless mice. The effects of some drugs on the itch response in this model were also studied. 2,4,6-Trinitrochlorobenzene (TNCB) was applied repeatedly on the rostral back of sensitized hairless mice every 2 days for 54 days, and the scratching behavior was observed on day 0, 18, 36 and 54. The skin symptoms and total IgE level were also observed. The number of scratches observed at 24 and 48 h after TNCB challenge was increased gradually from day 18 to day 54. An intimate relationship was observed between the number of scratches and the skin score at 48 h after TNCB on day 54. The skin symptoms and total IgE levels were also elevated gradually from day 18 to day 54. Chlorpheniramine, cyproheptadine and methysergide caused no effect on the scratching behavior accompanied by skin lesions at 48 h after TNCB challenge, even at a high dose. On the other hand, L-733,060, naloxone, naltrexone, prednisolone and dexamethasone caused a significant inhibition of the scratching behavior induced by TNCB. Therefore, this model may be useful to evaluate the effects of drugs on the itch response accompanied by skin lesions, such as atopic dermatitis.

How important are NK1 receptors for influencing microvascular inflammation and itch in the skin? Studies using Phoneutria nigriventer venom

Pain and itch sensations are induced by depolarization of C-fibre nerves and possibly other types of fibres. We have evidence from several species, including mice, that skin plasma extravasation induced by the Phoneutria nigriventer spider venom (PNV) is dependent on tachykinin NK(1) receptors. We have now investigated the itching measured as bouts of scratching in response to intradermal (i.d.) PNV in wildtype (NK(1)(+/+)) and NK(1) receptor knockout (NK(1)(-/-)) mice. Mice, either NK(1)(+/+) or NK(1)(-/-), were given a single i.d. injection (0.05 ml) of test agent or vehicle into the shaved dorsal skin, in the intercostal region, in a randomized way. The bouts of scratching were recorded in a blinded manner for 60 min. Oedema formation was concomitantly assessed by the extravascular accumulation of i.v. injected (125)I-albumin. The i.d. injection of either substance P (at a high dose of 100 nmol/site), or PNV (0.3-10 microg/site) induced oedema formation in NK(1)(+/+) but substantially less was observed in NK(1)(-/-) mice, as previously reported. PNV also induced scratching, but significantly less scratching was observed in NK(1)(-/-) compared with NK(1)(+/+) mice. In contrast, SP did not induce significant scratching at amounts up to 100 nmol in NK(1)(+/+) mice. Experiments with an NK(1) receptor antagonist SR140333 (at doses that blocked PNV-induced oedema) revealed that whilst a local co-injection i.d. (1 nmol) in NK(1)(+/+) mice had no effect on PNV (3 microg/site)-induced scratching (18.5+/-3.7 vs. 14.4+/-3.5 bouts, mean+/-S.E.M., n=5-7), systemic treatment with SR140333 (120 nmol/kg, i.v.) significantly inhibited scratching (14+/-3.5 vs. 3.1+/-1.2 bouts, n=4-6; P<0.05). These results indicate that NK(1) receptors are involved in mediating PNV-induced scratching and that the location of the receptors is unlikely to be skin. Thus, a distinct separation between endogenous microvascular and PNV nociceptive NK(1)-dependent effects is suggested.

Potent pruritogenic action of tryptase mediated by PAR-2 receptor and its involvement in anti-pruritic effect of nafamostat mesilate in mice

The pruritogenic potency of tryptase and its involvement in anti-pruritic effect of intravenous nafamostat mesilate (NFM) were studied in mice. An intradermal injection of tryptase (0.05-1 ng/site) elicited scratching in ICR mice, while chymase was without effects at doses of 0.05-50 ng/site. The dose-response curve of tryptase action was bell-shaped and the effect peaked at 0.1 ng/site (approximately 0.7 fmol/site). NFM (10 mg/kg) inhibited scratching induced by tryptase but not by histamine and serotonin. NFM (1-10 mg/kg) produced the dose-dependent inhibition of scratching induced by intradermal compound 48/80 (10 microg/site). The inhibition by NFM (10 mg/kg) was abolished in mast cell-deficient (WBB6F1 W/W(V)) mice, but not in wild-type (WBB6F1 +/+) mice. NFM (10 mg/kg) suppressed tryptase activity in the mouse skin. Proteinase-activated receptor-2 (PAR-2) neutralizing antibody (0.1 and 1 microg/site) and the PAR-2 antagonist FSLLRY (10 and 100 microg/site) inhibited scratching induced by tryptase (0.1 ng/site) and compound 48/80 (10 microg/site). These results suggest that mast cell tryptase elicits itch through PAR-2 receptor and that NFM inhibits itch-associated responses mainly through the inhibition of mast cell tryptase.

Antipruritic effect of ginsenoside rb1 and compound k in scratching behavior mouse models

The antipruritic and vascular permeability-inhibitory effects of ginsenoside Rb1, a main component of ginseng frequently used as a traditional medicine in Asian countries, and its metabolite compound K by intestinal microflora were investigated in scratching behavior animal models induced by compound 48/80, substance P, and histamine. Ginsenoside Rb1 and compound K orally administered 1 and 6 h before the treatment of compound 48/80 showed antipruritic effect. These ginsenosides administered at a dose of 50 mg/kg 6 h before the treatment of compound 48/80 inhibited scratching behaviors by 51% and 64%, respectively, compared with that of the control. These ginsenosides also inhibited the vascular permeability of skin. Compound K intraperitoneally administered 1 h before the treatment of compound 48/80 potently inhibited the scratching behaviors induced by compound 48/80. However, intraperitoneally administered ginsenoside Rb1 did not inhibit scratching behaviors. Compound K inhibited compound 48/80-, substance P-, and histamine-induced scratching behaviors, with 50% inhibitory doses of 4.2, 5.9, and 3.8 mg/kg, respectively, and vascular permeability, with 50% inhibitory doses of 5.8, 6.8, and 4.1 mg/kg, respectively. These results suggest that ginsenoside Rb1 and its metabolite compound K by intestinal microflora can improve scratching behaviors.

Cutaneous manifestations of neurological diseases: review of neuro-pathophysiology and diseases causing pruritus

Pruritus does not always originate from stimulation to the skin associated with primary dermatological disorders. It may be caused by neurological or behavioural disorders. The essential role of the nervous system in the control (enhancement and inhibition) of pruritus and its pathophysiology are presented. In order to allow differentiation between dermatological and neurological disorders, inherited or acquired peripheral neuropathies and central nervous disorders (Arnold-Chiari syndrome, seizure-related disorders, central nervous system tumours) that may induce itch are discussed.

Characterization of a Mouse Second Leukotriene B4 Receptor, mBLT2

Leukotriene B4 (LTB4) is a potent chemoattractant and activator for granulocytes and macrophages and is considered to be an inflammatory mediator. Two G-protein-coupled receptors for LTB4, BLT1 and BLT2, have been cloned from human and shown to be high and low affinity LTB4 receptors, respectively. To reveal the biological roles of BLT2 using mouse disease models, we cloned and characterized mouse BLT2. Chinese hamster ovary cells stably expressing mouse BLT2 exhibited specific binding to LTB4, LTB4-induced calcium mobilization, inhibition of adenylyl cyclase, and phosphorylation of extracellular signal-regulated kinase. We found that Compound A (4'-{[pentanoyl (phenyl) amino] methyl}-1, 1'-biphenyl-2-carboxylic acid) was a BLT2-selective agonist and induced Ca(2+) mobilization and phosphorylation of extracellular signal-regulated kinase through BLT2, whereas it had no effect on BLT1. 12-epi LTB4 exhibited a partial agonistic activity against mBLT1 and mBLT2, whereas 6-trans-12-epi LTB4 did not. Northern blot analysis showed that mouse BLT2 is expressed highly in small intestine and skin in contrast to the ubiquitous expression of human BLT2. By in situ hybridization and the reverse transcriptase polymerase chain reaction, we demonstrated that mouse BLT2 is expressed in follicular and interfollicular keratinocytes. Compound A, LTB4, and 12-epi LTB4 all induced phosphorylation of extracellular signal-regulated kinase in primary mouse keratinocytes. Furthermore, Compound A and LTB4 induced chemotaxis in primary mouse keratinocytes. These data suggest the presence of functional BLT2 in primary keratinocytes.

Involvement of substance P in scratching behaviour in an atopic dermatitis model

Substance P is speculated to be a key mediator of itching in atopic dermatitis, possibly acting via the tachykinin NK1 receptor. Thus, we examined the effect of a tachykinin NK1 antagonist, BIIF 1149 CL, on scratching behaviour in a picrylchloride-induced dermatitis model in NC/Nga mice. BIIF 1149 CL ((S)-N-[2-[3,5-bis(trifluoromethyl) phenyl]ethyl]-4-(cyclopropylmethyl)-N-methyl-alpha-phenyl-1-piperazineacetamide, monohydrochloride, monohydrate) at a dose of 100 mg/kg, p.o., significantly inhibited scratching behaviour immediately after administration, and the effect continued up to 6 h. The results suggest that clinical trials of tachykinin NK1 antagonists for the treatment of itching in atopic dermatitis patients would be warranted.

Intradermal nociceptin elicits itch-associated responses through leukotriene B(4) in mice

Nociceptin, the endogenous peptide ligand for opioid receptor like-1 (ORL1) receptor, has been implicated in the inflammation and pain in the skin. We examined whether nociceptin is a pruritogen in mice. Intradermal injections of nociceptin (1-100 nmol per site) concentration dependently increased scratching in ICR mice; the effect started within 1 min, peaked at 10-20 min, and almost subsided by 30 min. The nociceptin action was absent in ORL1 receptor-deficient (ORL1(-/-)) mice. Systemic, but not local, treatment with naloxone significantly inhibited scratching induced by nociceptin. The action of nociceptin was inhibited by the leukotriene B(4) receptor antagonist ONO-4057 and azelastine, which inhibits the action and production of leukotriene B(4) in the skin. Prepronociceptin and ORL1 receptor mRNAs were substantially expressed in the skin, whereas their expression levels were very low in the dorsal root ganglia. In the skin, nociceptin- and ORL1 receptor-like immunoreactivities were localized in the epidermis. Administration of nociceptin to primary cultures of keratinocytes from ICR and C57BL/6 (ORL1(+/+)) mice, but not ORL1(-/-) mice, produced leukotriene B(4). The results suggest that nociceptin acts on ORL1 receptor on the keratinocytes to produce leukotriene B(4), which induces itch-associated responses in mice.

Role of Substance P in an NC/Nga Mouse Model of Atopic Dermatitis-Like Disease

BACKGROUND

Atopic dermatitis (AD) can be exacerbated or induced in genetically predisposed individuals by psychological stress, which causes the release of substance P (SP). Therefore, SP may play an etiological role in the mechanisms underlying AD.

METHODS

Changes in the number of mast cells and SP-containing mast cells in lesional skin, and the serum concentrations of SP and IgE during the development of AD-like disease up to 8 weeks after the start of picryl chloride (PiCl) induction in NC/Nga mice were examined.

RESULTS

Clinical signs and symptoms seen in PiCl-treated NC/Nga mice as a model of AD-like disease began with erythema and haemorrhage, followed by oedema, superficial erosion, deep excoriation, scaling and dryness of the skin, as well as retarded growth, and the changes were exacerbated with an increase in the number of PiCl applications. An increase in the number of mast cells and eosinophil infiltration was observed in the lesional skin. The increase in SP-positive mast cells in the dermis in this model was significant from 1 week after the start of induction treatment, compared with intact mice, and SP-positive nerve fibres were observed in the dermis.

CONCLUSION

SP is a crucial mediator of both dermatitis and scratching behaviour in this model.

Repeated treatment with the traditional medicine Unsei-in inhibits substance P-induced itch-associated responses through downregulation of the expression of nitric oxide synthase 1 in mice

Unsei-in inhibits substance P (SP)-induced scratching of mice after repeated administration. The involvement of cutaneous nitric oxide (NO) in the SP-induced scratching led us to investigate the effects of Unsei-in on the cutaneous NO system in mice. Seven-day oral administration of Unsei-in (300, but not 100, mg/kg daily) significantly inhibited scratching and the increase of cutaneous NO after intradermal SP injection. The NO synthase 1 (NOS1) inhibitor 7-nitroindazole (1 nmol/site) decreased SP-induced scratching and NO production. Repeated administration of Unsei-in (300 mg/kg) reduced the cutaneous NOS1 level. The results suggest that the inhibition of cutaneous NOS1 expression and NO production participates in the antipruritic action of Unsei-in.

Pruritogenic mediators in psoriasis vulgaris: comparative evaluation of itch-associated cutaneous factors

BACKGROUND

Although some patients with psoriasis vulgaris also complain of severe pruritus, the data available regarding pruritus in psoriasis are sparse.

OBJECTIVES

To clarify the mechanism and mediators involved in the pruritus of psoriasis vulgaris, we compared itch-associated factors in lesional skin from psoriatic patients vs. skin without pruritus quantitatively using a panel of histological and immunohistological parameters.

PATIENTS AND METHODS

Biopsied specimens were obtained from 38 patients with psoriasis vulgaris who were divided into two groups according to the presence or absence of pruritus.

RESULTS

When compared with psoriatic patients devoid of pruritus, lesional skin from patients with pruritus showed the following characteristic features: (i) a rich innervation both in the epidermis and in the papillary dermis; (ii) an increase in neuropeptide substance P-containing nerve fibres in perivascular areas; (iii) decreased expression of neutral endopeptidase in the epidermal basal layer as well as in the endothelia of blood vessels; (iv) many mast cells showing degranulating processes in the papillary dermis; (v) a strong immunoreactivity for nerve growth factor (NGF) throughout the entire epidermis and an increased NGF content in lesional skin homogenates; (vi) an increase in the expression of high-affinity receptors for NGF (Trk A) in basal keratinocytes and in dermal nerves; (vii) an increased population of interleukin-2-immunoreactive lymphocytes; and (viii) a strong expression of E-selectin on vascular endothelial cells. A significant correlation was observed between the severity of pruritus and protein gene product 9.5-immunoreactive intraepidermal nerve fibres, NGF-immunoreactive keratinocytes, expression of Trk A in the epidermis and the density of immunoreactive vessels for E-selectin. These findings indicate that possible pruritogenic mediators in psoriatic lesional skin are neurogenic factors including innervation, neuropeptide substance P, neuropeptide-degrading enzymes and NGF, activated mast cells, one or more cytokines and endothelial-leucocyte adhesion molecules.

CONCLUSIONS

These data document for the first time itch-related local markers in psoriasis, and suggest complex and multifactorial mechanisms of pruritus in the disease. These results provide the groundwork for further studies to evaluate the efficacy of antipruritic treatment for psoriatic patients.

Inhibitory effect of the repeated treatment with Unsei-in on substance P-induced itch-associated responses through the downregulation of the expression of NK(1) tachykinin receptor in mice

Unsei-in, a traditional medicine, is prescribed against pruritic cutaneous diseases, but the mechanisms of antipruritic action are still unknown. In the present study, we examined the antipruritic effects of Unsei-in in mice. Single administration of Unsei-in did not inhibit substance P-induced itch-associated response (scratching) in mice. However, repeated treatment with Unsei-in for 7 d significantly inhibited substance P-induced scratching. The same repeated treatment with Unsei-in suppressed the expression of NK(1) tachykinin receptors in the skin. These results suggest that Unsei-in inhibits substance P-associated itching and that the inhibition is at least partly due to the suppression of the expression of NK(1) tachykinin receptors in the skin.

A tale of two neurons in the upper airways: pain versus itch

Pain and itch sensations are induced by depolarization of distinct populations of unmyelinated type C, and possibly other, neurons. Both sets of neurons and sensations serve critical protective mechanisms that maintain the integrity and patency of the upper airways. When noxious or pruritic stimuli are applied on the afferent nerve ending, pain and itch are appreciated at the thalamic and parietal cortex. In the mucosa, this neuronal depolarization spreads via the peripheral efferent axon response mechanism. Neuropeptides such as substance P and calcitonin gene-related peptide are released from neurosecretory varicosities on the nociceptive C fibers. The exact functions of axon responses differ between humans and rodents, and in health and disease. Separate itch- and pain-specific peripheral type C fibers, secondary relay interneurons in the spinal cord dorsal horn, anatomical locations in the lateral spinothalamic tract, and thalamic nuclei demonstrate that all nociceptive nerves are not the same. Other types of irritant-sensitive trigeminal neurons might be discovered that could mediate other unique sensations, specific axon responses, or central nervous system functions.

Antipruritic effects of Sophora flavescens on acute and chronic itch-related responses in mice

To find new antipruritic herbal medicines for pruritus, we screened the methanol extracts of seven herbal medicines which have been used to treat dermatologic diseases, testing them on mouse models of acute and chronic itch. When administrated perorally (p.o.) at a dose of 200 mg/kg, methanol extracts of Sophora flavescens and Cnidium monnieri, but not the others, significantly inhibited a serotonin (5-HT)-induced itch-related response (scratching) and the spontaneous scratching of NC mice, a mouse model of atopic dermatitis. The inhibitory effect of Sophora flavescens was stronger than that of Cnidium monnieri. The methanol extract from Sophora flavescens (50-200 mg/kg) inhibited 5-HT-induced scratching in a dose-dependent manner, without any effects on the locomotor activity. These results suggest that Sophora flavescens and its constituents widely affect acute and chronic pruritus, and are possible as new antipruritic agents.

Inhibitory effect of azelastine on allergic itch-associated response in mice sensitized with mosquito salivary glands extract

We examined whether azelastine would inhibit itch-associated responses of mice to mosquito allergy. Repeated injections of mosquito salivary gland extract increased scratching and sensory nerve activity. Azelastine inhibited the increased scratching and nerve activity, while terfenadine was without effects. Dexamethasone did not affect the increased scratching. Azelastine suppressed high K(+)-induced increase in intracellular free Ca(2+) in primary cultures of mouse sensory neurons. Direct inhibition by azelastine of sensory neurons may be at least involved in the anti-pruritic effect of azelastine. Histamine, substance P, and leukotriene B(4) may not play a key role in the itching of mosquito allergy.