Effect of interleukin 1 on histone H3 lysine 9 methylation, lysine-specific demethylase 1 recruitment and flavin adenine dinucleotide levels in normal and osteoarthritis chondrocytes. Normal (A) and (C) and osteoarthritis (OA) (B) and (D) chondrocytes were treated with 100 pg/ml interleukin 1β (IL-1β) for the indicated time periods. Chromatin immunoprecipitation (ChIP) assays, coupled with real-time PCR, were performed using antibodies specific to mono-, di- and trimethylated histone H3 lysine 9 (H3K9) (A) and (B) and lysine-specific demethylase 1 (LSD1) (C) and (D). The results are expressed as percentages of control values (that is, untreated cells) or fold changes, and the data are the mean ± SD of three independent experiments using cells from three different donors. *P < 0.05 compared with unstimulated cells. Normal (E) and OA (F) chondrocytes were treated as indicated, and the levels of flavin adenine dinucleotide (FAD) were determined using a FAD assay kit. The results are expressed in picomolar units per 106 cells, and the data are the mean ± SD of three independent experiments using cells from three different donors. me1, Monomethylation; me2, Dimethylation; me3, Trimethylation.