Hyaluronic acid is widely used in the treatment of osteoarthritis and exerts significant chondroprotective effects. The exact mechanisms of its chondroprotective action are not yet fully elucidated. Human articular chondrocytes actively produce reactive oxygen and nitrogen species capable of causing cellular dysfunction and death. A growing body of evidence indicates that mitochondrial dysfunction and mitochondrial DNA damage play a causal role in disorders linked to excessive generation of oxygen free radicals. We hypothesized that the chondroprotective effects of hyaluronic acid on oxidatively stressed chondrocytes are due to preservation of mitochondrial function and amelioration of mitochondria-driven apoptosis. When primary human chondrocyte cultures were exposed to reactive oxygen or nitrogen species generators, mitochondrial DNA damage along with mitochondrial dysfunction and mitochondria-driven apoptosis accumulated as a consequence. In addition, cytokine-treated primary human chondrocytes showed increased levels of mitochondrial DNA damage. Pretreatment of chondrocytes with hyaluronic acid caused a decrease of mitochondrial DNA damage, enhanced mitochondrial DNA repair capacity and cell viability, preservation of ATP levels, and amelioration of apoptosis. The results of these studies demonstrate that enhanced chondrocyte survival and improved mitochondrial function under conditions of oxidative injury are probably important therapeutic mechanisms for the actions of hyaluronic acid in osteoarthritis
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