Thromboxane A2 is Involved in Itch-associated Responses in Mice with Atopic Dermatitis-like Skin Lesions

To investigate the mechanisms underlying itching in atopic dermatitis, we examined whether thromboxane (TX) A(2), an arachidonic acid metabolite, is involved in spontaneous scratching, an itch-related response, in NC mice with atopic dermatitis-like skin lesions. The TXA(2) receptor (TP) antagonist ONO-3708 inhibited the spontaneous scratching. The mRNA expression of TX synthase (TXSyn) distributed mainly in epidermis and the concentration of TXB2, a metabolite of TXA(2), were increased in lesional skin. Scratching caused by the PAR2 agonist SLIGRL-NH2 was suppressed by ONO-3708. SLIGRL-NH2-induced scratching decreased approximately 75% in TP-deficient mice, compared to wild-type mice. In primary cultures of mouse keratinocytes, SLIGRL-NH2 induced the production of TXA(2), as evidenced by the increased TXB2, which was inhibited by the TXSyn inhibitor sodium ozagrel and a PAR2-neutralizing antibody. Taken together, these results suggest that epidermal TXA(2), which may be produced via PAR2 activation, is involved in itching in atopic dermatitis.