Inhibition of Inducible Nitric Oxide Synthase Prevents IL-1β-Induced Mitochondrial Dysfunction in Human Chondrocytes

Interleukin (IL)-1 beta is an important pro-inflammatory cytokine in the progression of osteoarthritis (OA), which impairs mitochondrial function and induces the production of nitric oxide (NO) in chondrocytes. The aim was to investigate if blockade of NO production prevents IL-1 beta-induced mitochondrial dysfunction in chondrocytes and whether cAMP and AMP-activated protein kinase (AMPK) affects NO production and mitochondrial function. Isolated human OA chondrocytes were stimulated with IL-1 beta in combination with/without forskolin, L-NIL, AMPK activator or inhibitor. The release of NO, IL-6, PGE(2), MMP3, and the expression of iNOS were measured by ELISA or Western blot. Parameters of mitochondrial respiration were measured using a seahorse analyzer. IL-1 beta significantly induced NO release and mitochondrial dysfunction. Inhibition of iNOS by L-NIL prevented IL-1 beta-induced NO release and mitochondrial dysfunction but not IL-1 beta-induced release of IL-6, PGE(2), and MMP3. Enhancement of cAMP by forskolin reduced IL-1 beta-induced NO release and prevented IL-1 beta-induced mitochondrial impairment. Activation of AMPK increased IL-1 beta-induced NO production and the negative impact of IL-1 beta on mitochondrial respiration, whereas inhibition of AMPK had the opposite effects. NO is critically involved in the IL-1 beta-induced impairment of mitochondrial respiration in human OA chondrocytes. Increased intracellular cAMP or inhibition of AMPK prevented both IL-1 beta-induced NO release and mitochondrial dysfunction.