Cryotherapy is often applied after injuries of synovial joints. Although positive clinical effects on periarticular swelling and pain are well known, the effects on molecular processes of cartilage and synovial cells remained largely unknown so far. Therefore, the hypothesis was tested that hypothermia alleviates the synovial reaction and prevents chondrocyte death as well as cartilage destructive processes after blunt trauma.

Human articular cartilage and synovial tissue was obtained with informed consent from patients undergoing knee joint replacement. Cartilage explants from macroscopically intact cartilage were impacted by a drop-tower apparatus with defined energy (0.59J) and cultivated for 24h or 7d at following temperature conditions: 2h, 16h or throughout at 27°C and afterwards or throughout at 37°C. Furthermore, human fibroblast-like synoviocytes (FLS) were stimulated with conditioned medium from traumatized cartilage (t-CM) and cultivated as indicated above up to 4d. Effects of hypothermia were evaluated by live/dead assay, gene expression (RQ-PCR), and type II collagen synthesis/cleavage as well as release of MMP-2, MMP-13 and IL-6 on protein level (ELISA, gelatin zymography). Statistical analysis was performed by 2-way ANOVA. The experimental study was performed in the research laboratory of the Orthopedic Department, University Hospital Ulm, Germany.

Hypothermic treatment significantly improved chondrocyte viability 7d after blunt cartilage trauma (2h: p=0.016; 16h: p=0.036; throughout: p=0.039). 2h posttraumatic hypothermia attenuated expression of MMP-13 (m-RNA: p=0.012; protein: p=0.024). While type II collagen synthesis was significantly increased after 16h hypothermia, MMP-13 expression (mRNA: p=0.003; protein: p<0.001) and subsequent cleavage of type II collagen (p=0.049) were inhibited. Continuous hypothermia for 7d further significantly suppressed MMP release (proMMP-2, active MMP-2 and MMP-13) and type II collagen breakdown. On day 4 t-CM stimulated FLS revealed significantly suppressed gene expression of matrix-destructive enzymes (16h: ADAMTS-4; throughout: ADAMTS-4, MMP-3, MMP-13) and by trend reduced IL-6 expression in case of 16h or continuous hypothermia.

Overall, hypothermia for only 2h and/or 16h after blunt cartilage trauma exhibited significant cell- and matrix-protective effects and promoted anabolic activity of surviving chondrocytes. Expression of matrix-destructive enzymes by FLS stimulated with Danger Associated Molecular Patterns (DAMPs) released from traumatized cartilage was attenuated by more prolonged hypothermia. These findings suggest that an optimized cryotherapy management after cartilage trauma might have the potential to ameliorate early molecular processes usually associated with the pathogenesis of posttraumatic osteoarthritis.

Cartilage injury is generally associated with cytokine release and accumulation of reactive oxygen species. These mediators trigger pathologic behaviour of the surviving chondrocytes, which respond by excessive expression of catabolic enzymes, such as matrix metalloproteinase 13 (MMP-13), reduced synthesis of type II collagen (COL2A1) and apoptosis. In the long run, these pathologic conditions can cause a posttraumatic osteoarthritis. With the objective to attenuate the progressive degradation of the extracellular matrix and, what is more, promote chondroanabolic processes, a multidirectional treatment of trauma-induced pathogenesis was tested for the first time. Therefore, we evaluated the combinations of one anabolic growth factor (IGF-1, FGF18 or BMP7) with the antioxidant N-acetyl cysteine (NAC) in a human ex vivo cartilage trauma model and compared the findings with the corresponding monotherapy. Human cartilage tissue was obtained with informed consent from donors undergoing knee joint replacement (n=24). Only macroscopically intact tissue was used to prepare explants. Cartilage explants were subjected to a blunt impact (0.59 J) by a drop-tower and treated by IGF-1 [100 ng/mL], FGF18 [200 ng/mL] or BMP7 [100 ng/mL] and/or NAC [2 mM] for 7 days. Following parameters were analysed: cell viability (live/dead staining), gene expression (qRT-PCR) as well as biosynthesis (ELISA) of type II collagen and MMP-13. For statistical analysisKruskal-Wallis or One-way ANOVA was used. All data were collected in the orthopedic research laboratory of the University of Ulm, Germany.

Trauma-induced cell death was completely prevented by NAC treatment and FGF18 or BMP7 to a large extent, respectively (p<0.0001). IGF-1 exhibited only poor cell protection. Combination of NAC and FGF18 or BMP7 did not result in enhanced effectiveness; however, IGF-1 significantly reduced NAC-mediated cell protection. While IGF-1 or BMP7 induced collagen type II gene expression (p=0.0069 and p<0.0001, respectively) and its biosynthesis (p<0.0001 and p=0.0131, respectively), NAC or FGF18 caused significant suppression of this matrix component (each p<0.001). Although COL2A1 mRNA was significantly increased by NAC plus IGF-1 (p<0.0001), biosynthesis of collagen type II was generally abolished after multidirectional treatment. Except for IGF-1, all tested therapeutics exhibited chondroprotective qualities, as demonstrated by attenuated MMP-13 expression and breakdown of type II collagen. In combination with IGF-1, NAC-mediated chondroprotection was reduced.

Overall, both chondroanabolic and antioxidative therapy had individual advantages. Since adverse interactions were found by simultaneous application of the therapeutics, a sequential approach might improve the efficacy. In support of this strategy current experiments showed that though cell and chondroprotective effects of NAC were maintained after withdrawal of the antioxidant, type II collagen expression recovered by time.