Histamine Released from Epidermal Keratinocytes Plays a Role in a-MelanocyteeStimulating Hormone-Induced Itching in Mice

Histamine Released from Epidermal Keratinocytes Plays a Role in α-Melanocyte–Stimulating Hormone-Induced Itching in Mice

Kyoko Shimizu,* Tsugunobu Andoh,y Yoko Yoshihisa,* and Tadamichi Shimizu*
From the Departments of Dermatology* and Applied Pharmacology,y Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan
Accepted for publication July 14, 2015.
Address correspondence to Tadamichi Shimizu, Depart- ment of Dermatology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama, Japan. E-mail: shimizut@med.u- toyama.ac.jp.

Sunburn, wound repair, and chronic renal failure with hemodialysis are usually accompanied by both pigmentation and itching. Proopiomelanocortin-derived a-melanocyteestimulating hormone (a-MSH) is produced in response to external stimuli, such as UV irradiation, and is involved in cutaneous pigmen- tation. However, it is unclear whether a-MSH is also involved in the itching. We therefore investigated whether a-MSH elicited itch-related responses in mice. We found that an intradermal injection of a-MSH induced hind-paw scratching, an itch-related response, in mice. The a-MSHeinduced scratching was inhibited by the m-opioid receptor antagonist naltrexone and the H1 histamine receptor antagonist terfenadine. In mast cell-deficient mice, a-MSH also elicited scratching, which was inhibited by terfe- nadine. The immunoreactivity for L-histidine decarboxylase, a key enzyme required for the production of histamine, histamine, and the melanocortin 1 and 5 receptors were shown in not only mast cells but also keratinocytes in murine skin. In addition to the expression of L-histidine decarboxylase and melanocortin 1 and 5 receptors, the mouse keratinocyte cell lines (Pam212) also showed immunoreactivity for L-his- tidine decarboxylase, histamine, and melanocortin 1 and 5 receptors. The application of a-MSH induced the release of histamine from Pam212 cells. These findings indicate that a-MSH may play an important role in the itching associated with pigmented cutaneous lesions and that the histamine released from keratinocytes is involved in this a-MSHeinduced itching. (Am J Pathol 2015, -: 1e8; http://dx.doi.org/ 10.1016/j.ajpath.2015.07.015)

Antipruritic mechanisms of topical E6005, a phosphodiesterase
4 inhibitor: Inhibition of responses to proteinase-activated receptor 2 stimulation mediated by increase in intracellular cyclic AMP
Tsugunobu Andoh, Yasushi Kuraishi *
Department of Applied Pharmacology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama 930-0194, Japan

1-s2.0-S0923181114002497-main

ABSTRACT
Background: Phosphodiesterase 4 (PDE4), which catalyses the conversion of cyclic adenosine 30,50- monophosphate (cAMP) to 50-AMP, plays a critical role in the pathogenesis of inflammatory disorders. Pruritus is the main symptom of dermatitides, such as atopic dermatitis, and is very difficult to control. Recent studies have shown that the activation of proteinase-activated receptor 2 (PAR2) is involved in pruritus in dermatoses in humans and rodents.
Objective: To investigate the inhibitory effect of E6005, a topically effective PDE4 inhibitor, on PAR2-associated itching in mice.
Methods: Mice were given an intradermal injection of SLIGRL-NH2 (100 nmol/site), a PAR2 agonist peptide, into the rostral part of the back. E6005 and 8-bromo-cAMP were applied topically and injected intradermally, respectively, to the same site. Scratching bouts were observed as an itch-related behavior, and firing activity of the cutaneous nerve was electrophysiologically recorded. Keratinocytes were isolated from the skin of neonatal mice and cultured for in vitro experiments. The concentrations of cAMP and leukotriene B4 (LTB4) were measured by enzyme immunoassay. The distribution of PDE4 subtypes in the skin was investigated by immunostaining.
Results: Topical E6005 and intradermal 8-bromo-cAMP significantly inhibited SLIGRL-NH2-induced scratching and cutaneous nerve firing. Topical E6005 increased cutaneous cAMP content. Topical E6005 and intradermal 8-bromo-cAMP inhibited cutaneous LTB4 production induced by SLIGRL-NH2, which has been shown to elicit LTB4-mediated scratching. E6005 and 8-bromo-cAMP inhibited SLIGRL-NH2- induced LTB4 production in the cultured murine keratinocytes also. PDE4 subtypes were mainly expressed in keratinocytes and mast cells in the skin.
Conclusions: The results suggest that topical E6005 treatment inhibits PAR2-associated itching. Inhibition of LTB4 production mediated by an increase in cAMP may be partly involved in the antipruritic action of E6005.
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