N-acetyl cysteine protects function of TMJ chondrocytes from oxidative stress

Dental treatment often requires management of inflammation. For instance, arthrocentesis of the temporomandibular joint (TMJ) has been suggested for treatment of a variety of TMJ disorders. The inflammation is closely associated with oxidative stress which hinders and delays the healing process. However, therapeutic approach focused on controlling oxidative stress in dental treatment is seldom found. Objectives: This study tested the protective potential of an anti-oxidant, amino-acid derivative, N-acetyl cysteine (NAC) in controlling the oxidative stress against TMJ chondrocytes. Methods: Chondrocytes were extracted from the rat cartilage formed on TMJ condylar bone. The inflammatory condition was simulated by adding 100 µM hydrogen peroxide (H2O2) to TMJ-derived chondrocyte cultures. Some of the cultures were co-treated with H2O2　and NAC in a concentration of 2.5mM, 5mM or 10mM. Apoptotic cells were detected by flow cytometry analysis. Cell proliferation was evaluated by cell counting and BrdU incorporation. The chondrogenc phenotypes were assessed by reverse transcriptase-polymerase chain reaction for collagen I, II, and aggrecan gene expressions. Matrix synthesis was assessed by glycosaminoglycan deposition using alcian blue stain. Intracellular ROS level and glutathione redox status of the cells were also measured. Results: Exposure to H2O2 decreased the cell population by half within 2 days as a result of induced apoptosis and reduced proliferation. Gene expression of aggrecan and collagen II, as well as glycosaminoglycan production, were reduced by more than 70%. These compromised chondrocyte viability and function were fully restored by the addition of NAC into the cultures. NAC reduced the H2O2-elevated intracellular ROS to the normal level and increased the cellular glutathione reserves. Conclusion: Oxidative stress-induced by H2O2 could be devastating for chondrocytes. However, more importantly, the addition of NAC into the damaged culture restores their proliferative and differentiation capacities even under oxidative stress.