Increased scratching counts depend on a decrease in ability of cutaneous prostaglandin D2 biosynthesis in NC/Nga mice with atopic dermatitis

Dihomo-γ-linolenic acid prevents the development of atopic dermatitis through prostaglandin D1 production in NC/Tnd mice

BACKGROUND

Atopic dermatitis (AD) is a chronic and relapsing skin disorder with pruritic skin symptoms. We previously reported that dihomo-γ-linolenic acid (DGLA) prevented the development of AD in NC/Tnd mice, though the mechanism remained unclear.

OBJECTIVE

We attempted to investigate the mechanism of preventive effect of DGLA on AD development in NC/Tnd mice.

METHODS

The clinical outcomes of NC/Tnd mice that were given diets containing DGLA, arachidonic acid, or eicosapentaenoic acid were compared. Lipid mediator contents in the skin in each group were also quantified. In addition, release of lipid mediators from RBL-2H3 mast cells treated with either DGLA or prostaglandin D1 (PGD1) was measured. Furthermore, effect of PGD1 on gene expression of thymic stromal lymphopoietin (TSLP) in PAM212 keratinocyte cells was determined.

RESULTS

Only DGLA containing diet suppressed the development of dermatitis in vivo. By quantifying the 20-carbon fatty acid-derived eicosanoids in the skin, the application of DGLA was found to upregulate PGD1, which correlated with a better outcome in NC/Tnd mice. Moreover, we confirmed that mast cells produced PGD1 after DGLA exposure, thereby exerting a suppressive effect on immunoglobulin E-mediated degranulation. PGD1 also suppressed gene expression of TSLP in keratinocytes.

CONCLUSION

These results suggest that oral administration of DGLA causes preventive effects on AD development in NC/Tnd mice by regulating the PGD1 supply.

Signaling by IL-31 and functional consequences

Cytokines are key to control cellular communication. Interleukin-31 (IL-31) was recently discovered as a new member of the IL-6 family of cytokines. IL-31 signals through a heterodimeric receptor composed of OSMR and IL-31RA, a complex that stimulates the JAK-STAT, the RAS/ERK and the PI3K/AKT signal transduction pathways. The available data suggests that IL-31 is important for both innate and adaptive immunity in tissues that are in close contact with the environment, i.e. the skin, the airways and the lung, and the lining of the intestine. Enhanced expression of IL-31 is associated with a number of diseases, including pruritic diseases such as atopic dermatitis, but also in allergy and inflammatory bowel disease. In these tissues IL-31 coordinates the interaction of different immune cells, including T-cells, mast cells, and eosinophils, with epithelial cells. In this review we have summarized the available data on IL-31 and its receptor, their expression pattern and how they are regulated. We describe the current state of knowledge of the involvement of IL-31 in diseases, both in humans and in mouse models. From these studies it is becoming clear that IL-31 plays an important role in the proper functioning of the skin and of airway and intestinal epithelia. The findings available suggest that IL-31 might be an interesting target for directed drug therapy.

Pivotal role of mast cells in pruritogenesis in patients with myeloproliferative disorders

Pruritus is a common symptom in patients with Philadelphia chromosome-negative myeloproliferative disorders (MPDs). The pathophysiology of MPD-associated pruritus is unclear. We have demonstrated that MPD mast cells (MCs) are involved by the malignant process. In the present study, we explored the hypothesis that MCs play an important role in the development of pruritogenesis in MPDs. We found that MPD MCs released significantly greater amounts of pruritogenic factors, including histamine, leukotrienes, and interleukin-31 (IL-31) than normal MCs. Elevated levels of IL-31 were also observed in MPD CD3(+) cell-conditioned media. MPD MCs exhibited increased migratory behavior in response to stem cell factor or interleukin-8, which was associated with increased filamentous-actin content. Furthermore, the presence of pruritus in MPDs was statistically correlated with a greater number of MCs being generated by CD34(+) cells, a greater number of MC colonies being formed by CD34(+) cells, decreased apoptosis and prostaglandin D(2) release by cultured MCs, and higher plasma levels of IL-31. These data demonstrate that functional abnormalities of MPD MCs probably lead to pruritogenesis in patients with MPDs. These studies provide cellular and molecular targets for the development of antipruritus drugs for patients with MPDs.

Mediators of pruritus in psoriasis

The pathogenesis of pruritus in psoriasis remains unclear. Many possible mediators were implicated to transmit or modulate this sensation in psoriasis, but none has been clearly proven to be a causative agent of itching. The most often discussed theory mentioned the importance of impaired innervations and neuropeptides imbalance in psoriatic skin. Other possible causes of itching might be increased expression of interleukin 2 or vascular abnormalities. Recent data indicated that pruritus could be also evoked by opioid system, prostanoids, interleukin 31, serotonin, or proteases. Whether these mechanisms are also involved in pruritus accompanying psoriasis requires further investigation. Limited knowledge of pruritus origin in psoriasis is responsible for the lack of the effective antipruritic treatments for psoriatics. Here, we summarize the current knowledge about the pathogenesis of pruritus in psoriasis and point out possible directions of future studies aiming the pathogenesis of this symptom in psoriasis.

Role of prostaglandins on mechanical scratching-induced cutaneous barrier disruption in mice

The role of prostaglandins (PGs) on mechanical scratching-induced cutaneous barrier disruption in mice was investigated by comparing the observed effects of arachidonic acid (AA) application. Scratching of the mouse skin with a stainless-steel wire brush (mechanical scratching) was associated with significant, scratch-count-dependent elevation of the transepidermal water loss (TEWL) and skin PG levels (especially PGD(2) and PGE(2)). Histological evidence of inflammation (crusta, acanthosis and neutrophilic infiltration) in the skin also became evident 24 h after mechanical scratching. On the other hand, while topical application of 0.1% AA to the mouse skin also increased the skin PG levels, but did not produce any increase of TEWL or histological evidence of inflammation in the skin. Topical application of cyclooxygenase inhibitors (indomethacin, piroxicam, aspirin, diclofenac and ketoprofen) decreased the spontaneous recovery rates from cutaneous barrier disruption. These results suggest that the elevation of cutaneous PG production induced by mechanical scratching is involved in the repair of the skin damage caused by the scratching.

Detection of down-regulated acetaldehyde dehydrogenase 1 in atopic dermatitis patients by two-dimensional electrophoresis

We conducted the proteomic studies to detect the dysregulated proteins in the atopic dermatitis (AD) proteome obtained from the patient-derived primary cultured fibroblasts. Acetaldehyde dehydrogenase 1 (ALDH1) was detected as being significantly down-regulated at the pH ranges of 6-9 and 4-7. The transcriptional levels of ALDH1, as detected by RT-PCR and real-time PCR, further confirmed the down-regulated phenomena for all the AD-fibroblasts (n = 20). The expression levels of ALDH1 in the whole skin tissue samples were further supported by the results of the primary cultured samples. These findings clearly demonstrate that ALDH1 can be a dermal biomarker for AD disease.

Role of scratch-induced cutaneous prostaglandin D2production on atopic-like scratching behaviour in mice

NC/Nga mice are known to develop scratching dermatitis akin to atopic dermatitis, under conventional (Conv), but not under the specific-pathogen-free (SPF) condition. In this study, we examined the effects of mechanical-scratching on the spontaneous scratching counts (sign of itching), in relation to the cutaneous prostaglandin D2 (PGD2) levels in NC/Nga or BALB/c mice. Mechanical-scratching increased the cutaneous barrier damage and PGD2 levels in both strain mice under the SPF condition. By 4 weeks of cohabitation with the skin-lesioned NC/Nga mice, both the increase in the spontaneous scratching and development of dermatitis score were higher in the Conv-NC/Nga than in the Conv-BALB/c mice. At this time-point, the cutaneous PGD2 level induced by mechanical-scratching was significantly lower in the Conv-NC/Nga when compared with that in the SPF-NC/Nga mice, and that in the Conv-BALB/c was almost equal to that in the SPF-BALB/c mice. With mechanical scratches, the cohabitation-induced scratching was suppressed in the Conv-BALB/c, but not in the Conv-NC/Nga mice. These results suggest that the scratch-induced cutaneous PGD2 inhibits scratching and the subsequent development of dermatitis in BALB/c, while the impaired scratch-induced cutaneous PGD2 production in the NC/Nga mice resulted in no suppression of scratching, and aggravated the dermatitis.

The anti-pruritic efficacy of TS-022, a prostanoid DP1 receptor agonist, is dependent on the endogenous prostaglandin D2 level in the skin of NC/Nga mice

TS-022 is a prostanoid DP(1) receptor agonist, originally developed as a novel anti-pruritic drug for atopic dermatitis. The drug has been shown to suppress scratching and improve the skin inflammation in the NC/Nga (NC) mouse, a model of atopic dermatitis. Corticosteroids are commonly used as effective agents for the treatment of atopic dermatitis. We examined the anti-pruritic efficacy of TS-022 in NC mice cohabited with skin-lesioned NC mice, which showed spontaneous scratching without skin lesions in the early phase and chronic itching with severe dermatitis in the late phase, in comparison with that of dexamethasone. We have previously reported that prostaglandin D(2) might have a physiological role in the inhibition of pruritus. While after 2 weeks of cohabitation with skin-lesioned NC mice (early phase of dermatitis, characterized by the appearance of spontaneous scratching), topically applied TS-022 exhibited a weak anti-pruritic effect in the NC mice, after 6 weeks of cohabitation (late phase, characterized by both chronic scratching and dermatitis), the drug exerted potent anti-pruritic activity. In contrast, dexamethasone exerted potent anti-pruritic effect in both the early and late phases. Indomethacin aggravated the scratching in the early phase, but had no effect in the late phase. The skin prostaglandin D(2) level was significantly increased in the early phase, to subsequently declined and return to the basal level in the late phase. The cutaneous ability for prostaglandin D(2) production following topical application of arachidonic acid or mechanical scratching was decreased in the late phase. Moreover, the expression level of the prostanoid DP(1) receptor in the skin was increased in the late phase. These findings suggest that the potent anti-pruritic activity of TS-022 in the late phase might be attributable to the decrease of endogenous prostaglandin D(2) production and increase of prostanoid DP(1) receptor expression.

Effects of TS-022, a newly developed prostanoid DP1 receptor agonist, on experimental pruritus, cutaneous barrier disruptions and atopic dermatitis in mice

TS-022, {4-[(1R, 2S, 3R, 5R)-5-Chloro-2-((S)-3-cyclohexyl-3-hydroxyprop-1-ynyl)-3-hydroxycyclopentyl] butylthio} acetic acid monohydrate, inhibits ADP-induced platelet aggregation, an effect significantly antagonized, as in the case of prostaglandin D(2) by the prostanoid DP(1) receptor antagonist (BW A868C). TS-022 is a prostanoid DP(1) receptor agonist, originally developed as a novel anti-pruritic drug for patients with atopic dermatitis. We examined the effects of TS-022 on experimental pruritus, cutaneous barrier disruption, and atopic dermatitis and in in vitro immune function tests. Topically applied TS-022 significantly suppressed scratching in skin-lesioned NC/Nga mice from a concentration of 2.5 nM, and this scratch-suppressive activity was significantly antagonized by BW A868C. Tacrolimus (FK-506) and dexamethasone, used as reference drugs for atopic dermatitis, also exhibited suppressive effects against scratching, but only at concentrations of 125 and 25,000 microM. TS-022 applied topically, once a day for 2 days, significantly accelerated repair of the cutaneous barrier disruption caused by mechanical scratching, from concentrations of 2.5 nM. This acceleration of repair of the disrupted cutaneous barrier by this drug was also significantly antagonized by BW A868C. FK-506 and dexamethasone showed no beneficial effects on the repair of the disrupted cutaneous barrier. Repeated topical application of 2.5 microM of TS-022 and 12.5 microM of FK-506 once a day for 6 weeks significantly improved the skin inflammation scores in the NC/Nga mice. In regard to the effects of TS-022 in vitro, the inhibitory activity of TS-022 against concanavalin A-induced cytokine production by splenocytes was marginal as compared with that of FK-506 or dexamethasone. These results suggest that the beneficial therapeutic effects of TS-022 in NC/Nga mice with atopic dermatitis are mediated by its suppressive effect on scratching and its effect of accelerating repair of the disrupted cutaneous barrier, both effects being attributable to its prostanoid DP(1) receptor agonistic activity.

Putative mechanism of the itch-scratch circle: repeated scratching decreases the cutaneous level of prostaglandin D2, a mediator that inhibits itching

In atopic dermatitis, scratching of the skin as a reaction to itching causes injury to the skin, which, in turn, further increases the itching resulting in the establishment of the so-called itch-scratch circle. We have shown that prostaglandin (PG) D2 plays an inhibitory role against pruritus in mice with atopic-like dermatitis; therefore, we examined the relationship between scratching and the cutaneous PGD2 level using an artificial scratching model with a wire brush. Mechanical scratching induced a temporary increase of the skin PGs levels (PGE2, PGD2, 6-ketoPGF1alpha, PGF2alpha). The skin PGD2 level and the ability of PGD2 production decreased at 48 h after repeated scratch, compared to that of normal skin, not so after single scratch. Immunohistochemical analysis and Western blotting revealed a decrease in the levels of cyclooxygenase-1 (COX-1) and hematopoietic PGD synthase in mechanically scratched skin. The reduced ability of the skin for PGD2 production following mechanical scratching could be caused by this decrease in the expression levels of COX-1 and PGD2 synthase. The results suggest that repeated scratching in mice decreases the ability of the skin to produce PGD2, which is an endogenous mediator that inhibits pruritus, resulting in the establishment of the itch-scratch circle.

Time course changes of scratching counts, dermatitis symptoms, and levels of cutaneous prostaglandins in NC/Nga mice

NC/Nga (NC) mice are known to develop dermatitis resembling atopic dermatitis (AD) in conventional (Conv) conditions, but not in specific pathogen-free (SPF) conditions. We reported that the ability of skin prostaglandin D(2) (PGD(2)) production, which might be the endogenous inhibitor of itching, was attenuated in skin-lesioned Conv-NC mice. We examined the age-related change in scratching, dermatitis symptoms, and skin PGs of SPF- and Conv-NC mice. In Conv-NC, PGD(2) increased at 7 weeks, at which scratching counts increased, but dermatitis did not develop. PGE(2), PGI(2) and PGF(2alpha) increased at 10 and 13 weeks, at which dermatitis developed. The ability to produce skin PGs was examined by measuring PGs after application of arachidonic acid or after mechanical scratching using a wire brush. In Conv-NC, PGD(2) production at 13 weeks was lower than at 7 weeks. In Conv-NC, hematopoietic PGD synthase (hPGDS) expression in the skin at 13 weeks was lower than at 7 weeks by Western blotting and immunohistochemical analysis. The increase of skin PGD(2) level in the early phase of the development of dermatitis is due to the stress of extensive scratching, but did not increase in spite of the stress of extensive scratching in the late phase, due to decreasing capacity of PGD(2) production attributable to decreasing hPGDS expression in Conv-NC mice. These results suggest that a decreased ability to produce skin PGD(2) production could enhance scratching and aggravate dermatitis in Conv-NC mice.

COX-1 inhibition enhances scratching behaviour in NC/Nga mice with atopic dermatitis

NC/Nga (NC) mice, spontaneously develop an eczematous atopic dermatitis (AD)-like skin lesion when kept under conventional condition (Conv), but not under specific pathogen-free (SPF) conditions, have been thought to be an animal model of AD. We have previously shown that PGD(2) and arachidonic acid inhibited the scratching behaviour of NC mice, while indomethacin enhanced it. This study was designed to assess the role of cyclooxygenase (COX)-1 and COX-2 in the itch-related scratching behaviour of NC mice. We examined the expression of COX in the skin using real-time PCR and Western blotting and the effects of SC-560 (a COX-1 selective inhibitor) or NS-398 (a COX-2 selective inhibitor) on scratching behaviour in relation to skin prostaglandin (PG) levels in NC mice. COX-1 mRNA expression was unchanged and protein expression decreased in Conv NC mice compared with that of SPF mice. By contrast, COX-2 mRNA and protein expression increased in Conv NC mice. SC-560 increased scratching behaviour and significantly reduced skin PGD(2), PGE(2) and PGF(2alpha) levels, but NS-398 did not have effects on scratching and skin PG level. Moreover, the topical application of PGD(2), which might be the endogenous inhibitor of itching, suppressed the SC-560-induced enhancement of scratching behaviour by NC mice. These results suggest COX-1-coupled skin PGD(2) biosynthesis plays a physiological role in inhibiting regulation of pruritus in NC mice with AD.

Role of COX-1 and COX-2 on skin PGs biosynthesis by mechanical scratching in mice

We examined the involvement of cyclooxygenase (COX)-1 and COX-2 on mechanical scratching-induced prostaglandins (PGs) production in the skin of mice. The dorsal regions of mice were scratched using a stainless brush. COXs expressions in the skin were analyzed using real-time PCR and Western blotting. The effect of acetylsalicylic acid (ASA) on the ability of PGs production were determined based on skin PGs level induced by arachidonic acid (AA) application. Mechanical scratching increased PGD2, PGE2, PGI2 and PGF(2 alpha). COX-1 was constitutively expressed and COX-2 expression was enhanced by scratching. Intravenous administration of ASA inhibited PGs biosynthesis in the normal skin. PGs levels of the skin 6h after ASA administration (ASA 6 h) were almost equal to those of the skin 10 min after ASA administration (ASA 10 min). In the scratched skin, AA-induced PGE2 and PGI2 of ASA 6 h were significantly higher than those of ASA 10 min. The skin PGD2 and PGF(2 alpha) of ASA 10 min were almost same to those of ASA 6 h. In the normal skin of COX-1-deficient mice, skin PGD2 level was lower than that of wild-type mice, although PGE2, PGI2 and PGF(2 alpha) levels were almost equal to those of wild type. In the scratched skin of COX-1-deficient mice, PGD2, PGE2, PGI2 and PGF(2 alpha) levels were lower than those of wild-type mice. These results suggested that cutaneous PGD2 could be mainly produced by COX-1, and PGE2 and PGI2 could be produced by COX-1 and COX-2, respectively, in mice.