Increased expression of interleukin-6 (IL-6) gene transcript in relation to IL-6 promoter hypomethylation in gingival tissue from patients with chronic periodontitis

•We evaluated interleukin-6 (IL-6) promoter methylation in chronic periodontitis (CP).•The overall methylation rates decreased in gingiva relative to blood in CP.•The overall methylation rates were similar in gingiva and blood in the control.•IL-6 mRNA ratio of gingiva relative to blood increased in CP than in the control.

ObjectiveDNA methylation of the cytokine genes may play a role in the pathogenesis of periodontitis. The aim of this study is to evaluate whether the alteration of interleukin-6 (IL-6) gene promoter methylation in the gingival tissue (GT) and peripheral blood (PB) is unique to chronic periodontitis (CP).DesignDNA isolated from the GT and PB of 25 patients with (CP) and 20 healthy controls (H) was modified with sodium bisulfite and analyzed for IL-6 promoter methylation with direct sequencing. The levels of IL-6 mRNA and serum IL-6 protein were evaluated by a quantitative reverse transcription polymerase chain reaction and an enzyme-linked immunosorbent assay.ResultsThe CP group showed that the overall methylation rates of IL-6 promoter that contained 19 cytosine-guanine dinucleotide (CpG) motifs were significantly decreased in GT in comparison to PB (p < 0.001), which was significantly negatively correlated with the probing depth (p = 0.003). The GT and PB of the H group displayed similar overall methylation rates. No significant difference was observed in the methylation rates at each CpG in GT in comparison to the PB in both groups. The levels of IL-6 mRNA in the GT and PB and serum IL-6 of the two groups were comparable. The ratio of IL-6 mRNA in the GT relative to the PB was significantly higher in the CP group than in the H group (p = 0.03).ConclusionThe increased expression of IL-6 gene transcription may be related to IL-6 promoter hypomethylation in the GT from CP patients.