Selenomethionine inhibits IL-1β inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX2) expression in primary human chondrocytes

Objective: Several lines of evidence show that selenium (Se) has potential protective effects in osteoarthritis (OA), however the exact mechanism is still unclear. As interleukin-1 beta (IL-1 beta) is one of the key proinflammatoiy cytokines contributing to the progression in OA, we investigated the effect of Se in neutralizing the inflammatory effects of IL-1 beta on nitric oxide (NO) and prostaglandin E-2 (PGE(2)) production, and the signaling pathways involved. Methods: Isolated primary human chondrocytes were pretreated with selenomethionine (SeMet) (0.5 mu M SeMet) for 24 h then co-treated without or with IL-1 beta (10 pg/ml or 50 pg/ml) for another 24 h followed by RNA isolation. Gene expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX2) was determined by quantitative Real Time-Polymerase Chain Reaction. Culture media concentrations of NO and PGE2 were determined by nitrite (NO2-) assay and immunoassay respectively. For analysis of cell signaling pathways, chondrocytes were pretreated with SeMet then stimulated with IL-1 beta for 0-45 min. The activity of IL-1 beta signaling pathways was determined by Western blot screening of phosphorylation states of signal transduction proteins. Results: SeMet inhibited chondrocyte gene expression of IL-1 beta induced iNOS (31-54%, P = 0.031) and COX2 (50-65%, P = 0.031) with corresponding reductions in both NO (19-47%, P = 0.031) and PGE2 (24 -32%, P = 0.031) production. Pretreatment with SeMet attenuated IL-1 beta induced activation of p38 MAPK (39%, P = 0.039) but not the extracellular signal-regulated kinase pathways (ERIC) 1/2, c-Jun N-terminal kinases (JNK) or nuclear factor kappa B (NF kappa B). Conclusions: This study elucidates one potential protective mechanism of Se, namely through the alteration of cell signaling and downstream transcription of pro-inflammatory effects of IL-1 beta. (C) 2010 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.