Nuclear factor erythroid 2–related factor 2 (Nrf2)/antioxidant response element (ARE) pathway is key in maintaining redox homeostasis and the pathogenesis of osteoarthritis (OA) involves oxidative distress. We thus investigated whether Nrf2/ARE signaling may control expression of key chondrogenic differentiation and hyaline cartilage maintenance factor SOX9.

In human C-28/I2 chondrocytes SOX9 expression was measured by RT–qPCR after shRNA-mediated knockdown of Nrf2 or its antagonist the Kelch-like erythroid cell-derived protein with cap “n” collar homology-associated protein 1 (Keap1). Putative ARE-binding sites in the proximal SOX9 promoter region were inactivated, cloned into pGL3, and co-transfected with phRL–TK for dual-luciferase assays to verify whether Nrf2 transcriptionally regulates SOX9. SOX9 promoter activity without and with Nrf2-inducer methysticin were analyzed. Sox9 expression in articular chondrocytes was correlated to cartilage thickness and degeneration in wild-type (WT) and Nrf2-knockout mice. Data were analyzed by one-way ANOVA, a Student's t-test, or Wilcoxon rank-sum test, according to the normal distribution. Statistical significance was set to p < 0.05.

While Keap1-specific RNAi increased SOX9 expression, Nrf2-specific RNAi significantly decreased it. Putative ARE sites (ARE₁, ARE₂) were identified in the SOX9 promoter region. ARE₂ mutagenesis significantly reduced SOX9 promoter activity, while truncation of ARE₁ did not. A functional ARE₂ site was thus essential for methysticin-mediated induction of SOX9 promoter activity. Knee cartilage of young Nrf2-knockout mice further revealed significantly fewer Sox9-positive chondrocytes as compared to old Nrf2-knockout animals, which further showed thinner cartilage and more severe cartilage erosion.

Our data suggest that SOX9 expression in articular cartilage is directly Nrf2-dependent and that pharmacological Nrf2 activation may hold potential to diminish age-dependent osteoarthritic changes in knee cartilage through improving protective SOX9 expression.

In two-stage revision surgery of infected joint prosthesis, temporary bone cement spacers have been used for several years. By adding antibiotics to the cement, high local antibiotic concentrations that exceed the minimum inhibiting and bactericidal concentration of the respective pathogen during the first days after surgery, are achieved. Currently, aminoglycosides (e.g. gentamicin and tobramycin), as well as glycopetides (e.g vancomycin) are used as antibiotic agents and mixed into the acrylic cement. In order to increase the quantity of active antibiotic substances, we established a novel surgical technique of additional superficial vancomycin coating (SVC) of temporary bone cement spacer. The aim of this study was to analyze the safety of this method by measuring postoperative joint and serum vancomycin concentrations, as well as the creatinine levels.

We reviewed prospectively collected data on all patients, which were treated by explanting the prosthetic components, following temporary spacer implantation and SVC between 05/2013 and 04/2015 at the Department of Orthopedic Surgery, Medical University of Graz. In total 13 patients were treated by addition SVC during the study period. Before hardening, vancomycin powder (2 grams) was pressed manually onto the surface of the bone cement. Vancomycin levels were obtained from drains and blood samples on postoperative days 1 to 5. Forty-six blood serum samples and 52 drain fluid samples were available for further

On postoperative day one to five, a median serum vancomycin level of < 2.0 μg/mL was present (range <2.0 – 3.9). The highest median vancomycin level from the drain was documented on postoperative day 1 with a value of 388.0 μg/mL (range 44.4–1650.0), continually decreasing until postoperative day 4. After SVC, neither an anaphylactic reaction nor side effects such as a red man syndrome, fever and chills were observed. Furthermore, no patient complained about subjective hearing loss. No serum creatinine increase of 0.5 mg/dL from creatinine baseline value or a ≥50% increase from baseline was detected. After a median of 64 days (range 18–82), the temporary cement spacer was explanted followed by prosthesis implantation. During this time no reinfection occurred. One patient suffered from a dislocation of the spacer with a distal femur fracture and was therefore re-operated after 18 days.

Powdered vancomycin as an additional superficial coating of bone cement spacer results in much higher local antibiotic concentrations than in conventional spacers. The newly introduced method is feasible, safe and promising to enhance local inhibiting concentrations of vancomycin.