Roles of keratinocyte inflammation in oral cancer: regulating the prostaglandin E ₂ , interleukin-6 and TNF-α production of oral epithelial cells by areca nut extract and arecoline

Abstract

Betel quid (BQ) chewing is an etiologic factor of oral cancer and submucus fibrosis (OSF). Keratinocyte inflammation is crucial for the pathogenesis of cancer and tissue fibrosis. We found that areca nut (AN) extract (100–400 µg/ml) induced PGE ₂ production by KB cells by 2.34- to 23.1-fold and also TNF-α production by gingival keratinocytes (GK). Arecoline (0.2–1.2 mM) elevated PGE ₂ production by KB cells by 2.5- to 6.1-fold. AN extract (200–400 µg/ml) also induced IL-6 production by GK (7.5- to 8.4-fold) and KB cells. In contrast, arecoline (0.1–1.2 mM) suppressed IL-6 production by GK and KB cells, with 42–81 and 41–63% inhibition, respectively. A 48 h exposure of GK to 800–1200 µg/ml AN extract led to 37–69% cell death. Arecoline cytotoxicity to GK was noted at concentrations of 0.8–1.2 mM, which led to 28–38% cell death. AN extract (400–800 µg/ml) induced Cox-2 and IL-6 mRNA expression and also COX-2 protein production by KB cells. IL-6 (5–100 ng/ml) suppressed GK growth by 20–33%, but enhanced oral fibroblast (OMF) and KB cell growth. PGE ₂ (0.05–5 µg/ml) and anti-IL-6 antibody (ab) (50–1000 ng/ml) showed little effect on GK and KB cell growth. Incubation of GK and KB cells with aspirin, anti-IL-6 ab and anti-TNF-α ab showed little effect on arecoline- and AN-induced cytotoxicity, cell cycle arrest and apoptosis. Exposure to anti-TNF-α ab slightly affected arecoline- and AN-modulated PGE ₂ and IL-6 production by GK and KB cells. Arecoline- and AN-conditioned medium decreased phytohemagglutinin-mediated CD4 ⁺ and CD8 ⁺ T cell activation. These results indicate that BQ chewing contributes to the pathogenesis of cancer and OSF by impairing T cell activation and by induction of PGE ₂ , TNF-α and IL-6 production, which affect oral mucosal inflammation and growth of OMF and oral epithelial cells.

AN, areca nut, ab, antibody, BQ, betel quid, DMEM, Dulbecco's modified Eagle's medium, FCS, fetal calf serum, GK, gingival keratinocyte, HNSCC, head and neck squamous cell carcinoma, IL-6, interleukin-6, KGM-SFM, keratinocyte growth medium, MAPK, mitogen-activated protein kinase, MTT, 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide, OMF, oral mucosal fibroblasts, OSF, oral submucous fibrosis, PBMC, peripheral blood mononuclear cells, PBS, phosphate-buffered saline, PG, prostaglandin, PHA, phytohemagglutinin, ROS, reactive oxygen species, RT, reverse transcription, TNF-α, tumor necrosis factor α