BACKGROUND AND OBJECTIVE: In periodontitis, gingival epithelial cells can produce interleukin (IL)-6, a regulator of osteoclastic bone resorption, in response to IL-1beta. IL-1beta regulates cytokine expression via signaling pathways, including nuclear factor (NF)-B and mitogen activated protein kinase (MAPK)/activator protein (AP)-1. Cranberry proanthocyanidins (PACs) inhibit IL-1beta-stimulated IL-6 production, but specific mechanisms are unclear. The objectives of this study were to determine effects of cranberry PACs on NF-B and MAPK/AP-1 activation of IL-1beta-stimulated IL-6 production in gingival epithelial cells.

MATERIAL AND METHODS: Cranberry high molecular weight non-dialyzable material (NDM), rich in PACs, was derived from cranberry juice. Human gingival epithelial cells [Smulow-Glickman (S-G)] were incubated with IL-1beta in the presence or absence of NDM or inhibitors of NF-B, [nemo-binding domain (NBD) peptide] or AP-1 (SP600125), and IL-6 levels were measured by ELISA. Effects of NDM on IL-1beta-activated NF-B and AP-1 and phosphorylated intermediates in both pathways were measured in cell extracts via binding to specific oligonucleotides and specific sandwich ELISAs, respectively. Data were analyzed using ANOVA and Scheffe's F procedure for post hoc comparisons.

RESULTS: IL-1beta (> 0.1 nm) caused a time- and dose-dependent stimulation of S-G epithelial cell IL-6 production (p 0.005). This was significantly decreased in a dose-dependent manner by NBD peptide or SP600125 [maximum inhibition ~30-40% (p 0.02)], and together, the two inhibitors decreased IL-6 by ~80%, similar to the inhibition caused by NDM (p 0.001). IL-1beta stimulated NF-B and AP-1 activation (p 0.003), which was inhibited by NDM (p 0.0001). NDM did not significantly affect IL-1beta-stimulated levels of phosphorylated intermediates in the NF-B pathway (IBalpha) or the AP-1 pathway (c-Jun, ERK1/2).

CONCLUSION: In S-G epithelial cells, IL-1beta appeared to upregulate IL-6 production via activation of both NF-B and MAPK/AP-1 signaling pathways because cranberry NDM decreased nuclear levels of IL-1beta-activated NF-B (p65) and AP-1 (phospho-c-Jun) and strongly inhibited IL-6 production. Lack of inhibition of phosphorylation of IBalpha, c-Jun or ERK1/2 suggested that NDM might affect both pathways downstream from those points in S-G cells, such as ubiquitination and proteosomal degradation of IBalpha, or inhibition of nuclear activity of c-Jun and/or ERK1/2. Defining these points of inhibition precisely may help identify molecular targets of cranberry polyphenols. 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.