Arecoline activates latent transforming growth factor β1 via mitochondrial reactive oxygen species in buccal fibroblasts: Suppression by epigallocatechin-3-gallate

Abstract

Background/Purpose: Oral submucous fibrosis (OSF) is a premalignant condition caused by the chewing of areca nut (AN). Transforming growth factor β (TGFβ) plays a central role in the pathogenesis of OSF. Connective tissue growth factor (CTGF or CCN2) and early growth response-1 (Egr-1) are important mediators in the fibrotic response to TGFβ in several fibrotic disorders including OSF. Arecoline, a major AN alkaloid, induced the synthesis of CCN2 and Egr-1 in human buccal mucosal fibroblast (BMFs). The aims of this study were to investigate whether arecoline-induced CCN2 and Egr-1 syntheses are mediated through TGFβ1 signaling and to inspect the detailed mechanisms involved. Methods: Western blot and TGFβ1 Emax® ImmunoAssay were used to measure the effect of arecoline on the TGFβ signaling pathways. 2′,7′-dichlorodihydrofluorescein diacetate and MitoSOX™ Red were used to measure the effect of arecoline on the cellular and mitochondrial reactive oxygen species (ROS). Results: Arecoline induced latent TGFβ1 activation, Smad2 phosphorylation, and mitochondrial and total cellular ROS in BMFs. TGFβ-neutralizing antibody completely inhibited the arecoline-induced synthesis of CCN2 and Egr-1. Mito-TEMPO, a mitochondria-targeted antioxidant, completely suppressed arecoline-induced latent TGFβ1 activation and mitochondrial and total cellular ROS. Epigallocatechin-3-gallate (EGCG) dose-dependently inhibited arecoline-induced TGFβ1 activation and mitochondrial ROS in BMFs. Conclusion: Our results indicated that arecoline-induced mitochondrial ROS plays pivotal roles in the activation of latent TGFβ1 leading to the initiation of TGFβ1 signaling and subsequent increase in the synthesis of CCN2 and Egr-1. EGCG can be a useful agent in the chemoprevention and treatment of OSF. Keywords: Areca nut chewing, EGCG, Fibroblast, TGFβ, Oral submucous fibrosis