Effect of Phenol Antioxidants on Cytokine Secretion in Oral Epithelium

Objectives: To determine if gallic acid, epicatechin, and ellagic acid, three phenol antioxidants found in multiple dietary sources, have an effect on the secretion of inflammatory cytokines and chemokines in TNFα-stimulated human oral epithelial cells. Methods: Commercially available human oral epithelial cells (ScienCell, Carlsbad, CA) were cultured in wells of a 24 well plate to confluence. Cells were pre-treated for 2 hours with 0, 1, 5, 10, 25, or 50 mM gallic acid, epicatechin, or ellagic acid. Cells were then stimulated with 10 μg/ml TNFα for 30 minutes. Culture medium samples were assayed for a panel of cytokine/chemokine expression including IL-1α, IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-17A, IFNγ, and GM-CSF (Multi-analyte profiler ELISArray Kit, SABiosciences, Frederick, MD). Expression levels were expressed as OD450nm values corrected for total cell number based on crystal violet blue staining. Values were compared between and within treatments to screen for changes in cytokine/chemokine expression. Results: IL-2, IL-10, IL-12, 1L-17A and IFNγ were not detected in control or TNFα-treated cells. Of the remaining cytokines/chemokines, IL-1α, IL-6, and IL-8 demonstrated increased secretion from the cells as a result of TNFα stimulation. None of the phenol antioxidants studied had an effect on TNFα-induced IL-1α secretion. Epicatechin suppressed TNFα-induced IL-6 and IL-8 secretion, but stimulated the secretion of IL-10. Gallic acid had a minor effect on suppressing TNFα-induced IL-8 secretion. Conclusions: We have previously shown that epigallocatechin gallate (EGCG), a major catechin component of green tea, suppresses TNFα-induced interleukin secretion in human oral epithelial cells. We have extended this observation to show that other phenol antioxidants, especially epicatechin, have similar functions. This study provides support for the potential use of catechins found in green tea as suppressors of oral inflammation.