Transient Receptor Potential Vanilloid 1 — a Polymodal Nociceptive Receptor — Plays a Crucial Role in Formaldehyde-Induced Skin Inflammation in Mice

Abstract

Formaldehyde (FA) is irritating to the skin and is the main cause of sick building syndrome. However, the cutaneous reaction induced by long-term FA exposure has not been fully investigated. In our previous study, we demonstrated that repeated painting of 2% – 10% FA on mouse ears caused marked ear swelling and increased mRNA expression of transient receptor potential vanilloid 1 (TRPV1) and neurotrophins in the ear. TRPV1 is reported to be involved in neurogenic inflammation; therefore, in the present study, we investigated the role of TRPV1 in FA-induced skin inflammation using TRPV1 gene–knockout mice. Mice were painted with 5% FA once a week for 5 weeks, and ear swelling and mRNA expression were investigated. Ear swelling and increased expression of neurotrophins mRNA by FA provocation in wild-type mice were attenuated by disruption of the TRPV1 gene. Furthermore, painting with a threshold dose of capsaicin, which does not induce ear swelling in intact mice, caused marked ear swelling after painting the ear 5 times with FA, indicating that inflamed tissues after FA application are hyper-sensitive to various ligands of TRPV1 in mice. These results demonstrated that neurogenic inflammation via TRPV1 and neurotrophins could be involved in FA-induced dermatitis. Keywords:: ear swelling, formaldehyde, neurotrophin, transient receptor potential vanilloid 1