Scratching behavior in NC/Nga mice with dermatitis: Involvement of histamine-induced itching

Analyzing the Antinociceptive Effect of Interleukin-31 in Mice

The theory that an itch inhibits pain has been refuted; however, previous research did not investigate this theory for an interleukin-31 (IL-31)-induced itch. Previously, we have found that morphine-induced antinociception was partially reduced in IL-31 receptor A (IL-31RA)-deficient (IL-31RAKI) mice, indicating that IL-31RA may play an important role in morphine-induced peripheral antinociception. In the present study, we evaluated the effect of IL-31-induced analgesia on a 2,4,6-trinitrochlorobenzene (TNCB)-sensitized mice using a hot-plate test. This test evaluated the antinociceptive activity of morphine and non-steroidal anti-inflammatory drugs (NSAIDs). Repeated pretreatment with IL-31 showed significant antinociceptive action. Furthermore, its combination with morphine, but not with NSAIDs, increased the analgesic action. In contrast, treatment with TNCB and capsaicin decreased antinociception. Moreover, TNCB increased IL-31RA expression in the dorsal root ganglia at 24 h, whereas capsaicin inhibited it. The comparative action of several analgesics on TNCB or capsaicin was evaluated using a hot-plate test, which revealed that the antinociceptive activity was decreased or disappeared in response to capsaicin-induced pain in IL-31RAKI mice. These results indicate that the analgesic action of IL-31 involves the peripheral nervous system, which affects sensory nerves. These results provide a basis for developing novel analgesics using this mechanism.

Intractable Itch in Atopic Dermatitis: Causes and Treatments

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

Anti-inflammatory effects of natural flavonoid diosmetin in IL-4 and LPS-induced macrophage activation and atopic dermatitis model

Diosmetin, a citrus flavonoid, has a variety of therapeutic properties such as antibacterial, anti-inflammatory and antioxidant effects. However, the effect of diosmetin on atopic dermatitis (AD) development has not been reported. This study thus aims to investigate whether diosmetin possesses inhibitory effects on AD development. A dinitrochlorobenzene (DNCB)-induced AD mouse model was used to evaluate the effects of diosmetin on AD development. Treatment with diosmetin significantly reduced the dermatitis score, thickness of epidermis and dermis and number of mast cells in comparison with the untreated group. Furthermore, immunohistochemical analysis using an anti-F4/80 antibody demonstrated that diosmetin significantly suppressed macrophage infiltration into the AD lesion. It was observed that the levels of pro-inflammatory cytokines (TNF-α, IL-4 and IL-1β) in skin lesion decreased in response to treatment with diosmetin. In addition, the anti-inflammatory effect of diosmetin was evaluated in LPS- or IL-4-induced a mouse macrophage cell line (raw 264.7). Diosmetin inhibited the production of nitric oxide and decreased the expression of inducible nitric oxide synthase (iNOS). Diosmetin not only suppressed the phosphorylation of MAP kinase (ERK 1/2, p38 and JNK) but the activation of JAK/STAT signaling. The mRNA analysis demonstrated that diosmetin also reduced the level of inflammatory cytokines such as IL-1β and IL-6. Collectively, these results demonstrate that diosmetin exhibits the inhibitory effect on AD, suggesting that diosmetin may be a potential therapeutic agent for this atopic disorder.

Lipopolysaccharide promotes and augments metal allergies in mice, dependent on innate immunity and histidine decarboxylase

BACKGROUND

Few adequate murine models exist for metal allergies, it being especially difficult to induce Ni allergy in mice.

OBJECTIVE

We examined the effect of lipopolysaccharide (LPS) on allergies to Ni and other metals in mice.

METHODS

Ten days after sensitization with a metal salt and LPS, the ears were challenged with the same metal salt.

RESULTS

LPS+NiCl(2) (1 mM) was effective at sensitizing mice to Ni, LPS being effective at very low concentrations whether injected intradermally or intraperitoneally. The ear-swelling response to Ni was more severe and more rapid in C57BL/6 mice than in BALB/c mice. In mast-cell-deficient mice, TNF-alpha-deficient mice, and interestingly even in nude (T cell deficient) mice, NiCl(2)+LPS induced a Ni allergy similar in degree to that in the respective control mice, but it induced Ni allergy only weakly in TLR4-mutant mice, macrophage-depleted mice, and IL-1-deficient mice. The activity of the histamine-forming enzyme histidine decarboxylase (HDC) in the ears increased in parallel with ear swelling, and HDC-deficient mice were resistant to ear swelling. Challenge with NiCl(2)+LPS augmented ear swelling (vs. NiCl(2) alone). LPS induced effective sensitization to other metals (Cr, Co, Pd, or Ag).

CONCLUSIONS

These results indicate that in mice, LPS is a very important inducer of metal allergies, and potently promotes them (dependent on both innate immunity and HDC induction in cells other than mast cells). We discussed the idea that the bacterial environment is important for the establishment of metal allergies and for their provocation, and that the current thinking (including the contribution of T cells) should be reappraised in future studies.

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.

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.

Involvement of IL-31 on scratching behavior in NC/Nga mice with atopic-like dermatitis

Pruritus is an important symptom in atopic dermatitis (AD), but the major pruritogen has not been identified. NC/Nga mice, spontaneously develop an eczematous AD-like skin lesion when kept under conventional conditions, but not under specific pathogen-free (SPF) conditions, have been thought to be an animal model for AD. In this study, to determine whether newly identified cytokine, IL-31, may be involved in pruritus of AD, we examined the IL-31 expression in spontaneous dermatitis model which showed itch-associated long-lasting (over 1.5 s duration) scratching behavior and compared with that of hapten-induced contact dermatitis model without itch-associated long-lasting scratching behavior, using NC/Nga mice. In NC/Nga mice cohabited with NC/Nga mice which developed severe dermatitis for 2 weeks (conventional NC/Nga mice), the numbers of long-lasting scratching counts were significantly increased. Yet in 2,4,6-trinitrochlorobenzene (TNCB)-sensitized and challenged mice (TNCB-applied NC/Nga mice), no significant increase in long-lasting scratching counts was observed. In conventional NC/Nga mice with long-lasting scratching behavior, expression of IL-31 mRNA was increased, while in TNCB-applied NC/Nga mice without long-lasting scratching behavior, the expression of IL-31 mRNA were unchanged. There was a good correlation between the scratching counts and expression of IL-31 mRNA in conventional NC/Nga mice, but not so in TNCB-applied NC/Nga mice. These results suggest that IL-31 causes the itch-associated scratching behavior in conventional NC/Nga mice, an experimental animal model for AD.

Scratching behavior in spontaneous- or allergic contact-induced dermatitis in NC/Nga mice

NC/Nga mice have pathological and behavioral features similar to those seen in human atopic dermatitis. There are two known dermatitis models in NC/Nga mice, one being spontaneous-induced dermatitis under conventional conditions and the other 2,4,6-trinitrochlorobenzene (TNCB)-induced allergic contact dermatitis. However, there are significant differences in time course on development of dermatitis. We studied the role of scratching behavior (sign of itch) on the development of dermatitis on spontaneous- and TNCB-induced dermatitis. We measured scratching counts, transepidermal water loss (TEWL), and skin inflammation score, under conventional conditions or by applying 5% TNCB once a week for 6 weeks in NC/Nga mice. In spontaneous-induced dermatitis, scratching counts increased with the passage of time. The scratching counts were significantly increased only 1 week after housing the mice under conventional conditions, but no changes were observed in cases of TNCB-induced dermatitis. In spontaneous-induced dermatitis, TEWL and skin-inflammation score were gradually increased, time-dependently. On the other hand, in TNCB-induced dermatitis, these dependent values rapidly increased and reached a maximum only after 24 h TNCB application. These data suggest that pathogenesis of spontaneous- and allergic contact-induced dermatitis was clearly different. It will be of major interest to identify the pruritic mediators causing profound scratching behavior and scratching-induced aggravation of inflammation in the spontaneous-induced dermatitis, as opposed to the inflammatory mediators that cause contact allergic dermatitis without major scratching.

Expression of IL-31 gene transcripts in NC/Nga mice with atopic dermatitis

To search for the pruritogen of atopic dermatitis, a characteristic symptom in atopic dermatitis patients, we examined interleukin-31 (IL-31) mRNA expression in NC/Nga mice as an animal model of atopic dermatitis. The expression of IL-31 mRNA in the skin of NC/Nga mice with scratching behavior was significantly higher than that in NC/Nga mice without scratching behavior. Our findings suggest that IL-31 may participate in the cause of itch sensation and promote scratching behavior in NC/Nga mice with atopic dermatitis.