gms | German Medical Science

Objectives: Mitochondrial dysfunction and subsequent oxidative stress play a crucial role in the pathogenesis of osteoarthritis (OA). Previously, we described cell- and chondroprotective effects of the antioxidant N-acetyl cysteine (NAC) after cartilage injury. However, NAC also exhibited adverse effects regarding chondroanabolism. Therefore, we compared a new mitoprotective therapy using Elamipretide (SS-31) with the gold standard of antioxidative therapy, NAC, in the context of pathophysiologic and regenerative processes in cartilage.

Methods: Porcine knee joints (n ≥ 4) were obtained from a slaughter house and used for chondrocyte isolation or cartilage culture. Chondrocytes were exposed to 100 µM H2O2, treated with SS-31 (1 µM – 10 µM) for 24 h, and analyzed by an alamarBlue assay. Cartilage explants were traumatized (energy: 0,47 J) using a drop tower device and treated with SS-31 (10 µM) or NAC (2 mM). After 7 days, cell viability (live dead assay), cartilage integrity (safranin-O staining), as well as NO release (griess assay) were determined. Human chondrocytes or murine ATDC5 chondroprogenitor cells were stimulated with chondrogenic differentiation (CD) medium in pellet culture for 28 days and monolayer for 7 days, respectively. Afterwards, CD was assessed by proteoglycan (PG) and collagen II expression. Statistical analysis was performed by one-way ANOVA.

Results and conclusion: H2O2-treatment decreased the metabolic activity of human chondrocytes (-25%), which was completely restored by addition of SS-31 in a concentration-dependent manner (10 µM: p<0.01). Cartilage trauma lowered the cell viability by 16%. While SS-31 had moderate cell protective effects (+8%, P=0.08), NAC prevented chondrocyte death as expected (+16%, P<0.01). Moreover, the griess assay revealed that only NAC clearly reduced NO release (-60%, p=0.05). However, trauma-related loss of proteoglycans was less pronounced in SS-31-treated cartilage as demonstrated by safranin-O staining. In contrast to NAC, which suppressed the CD of human chondrocytes as well as ATDC5 cells, SS-31 had no impairing effect on PG and collagen II production.

SS-31 specifically stabilizes the inner membrane of mitochondria, thus reducing the generation of harmful reactive oxygen species. In comparison to NAC, this approach seems to be beneficial in terms of anabolic processes but might be less effective regarding cell protection after trauma. The beneficial effects of SS-31 on mitochondrial integrity will be evaluated in future experiments.