Increased Melatonin in Oral Mucosal Tissue of Oral Lichen Planus (OLP) Patients: A Possible Link between Melatonin and Its Role in Oral Mucosal Inflammation

Abstract

The existence of extra-pineal melatonin has been observed in various tissues. No prior studies of melatonin in human oral mucosal tissue under the condition of chronic inflammation have been reported. The aim of this study was to investigate the presence of melatonin in oral mucosal tissue of patients with oral lichen planus (OLP) which was considered as a chronic inflammatory immunemediated disease causing oral mucosal damage and ulcerations. Materials and methods: Sections from formalin-fixed and paraffin-embedded oral mucosal tissue of OLP patients (n = 30), and control subjects (n = 30) were used in this study. Immunohistochemical staining was performed and the semiquantitative scoring system was used to assess the levels of arylalkylamine N-acetyltransferase (AANAT: a rate-limiting enzyme in the biosynthesis pathway of melatonin), melatonin, and melatonin receptor 1 (MT1) in oral mucosa of OLP patients and normal oral mucosa of control subjects. Results: AANAT, melatonin, and MT1were detected in oral mucosal tissue of OLP patients and control subjects. Immunostaining scores of AANAT, melatonin, and MT1 in oral mucosal tissue of OLP patients were significantly higher than those in control subjects (p = 0.002, p < 0.001, and p = 0.031, respectively). Conclusions: Increased levels of AANAT, melatonin, and MT1 in the inflamed oral mucosal tissue of OLP patients imply that chronic inflammation may induce the local biosynthesis of melatonin via AANAT, and may enhance the action of melatonin via MT1.