Local Administration of Simvastatin Stimulates Healing of an Avascular Meniscus in a Rabbit Model of a Meniscal Defect

Abstract

Background: Repair of an avascular meniscus is challenging because of its low capacity for healing. Several reports have shown that simvastatin stimulates the anabolic activity of intervertebral fibrochondrocytes, suggesting that simvastatin may be used for the treatment of meniscal defects. Purpose: To test whether the local administration of simvastatin stimulates healing of an avascular meniscus in rabbits. Study Design: Controlled laboratory study. Methods: In 30 Japanese White rabbits, a cylindrical defect (1.5-mm diameter) was introduced into the avascular zone of the anterior part of the medial meniscus in bilateral knees. Either a gelatin hydrogel (control group) or simvastatin-conjugated gelatin hydrogel (simvastatin group) was implanted into the defect. Histological assessments were performed using qualitative scoring systems, and immunohistochemical analysis was performed at 12 weeks after surgery. The occupation ratio (OR) and safranin O staining occupation ratio (SOR) were evaluated quantitatively at each time point. Stiffness of the regenerated tissue was analyzed biomechanically at 12 weeks after surgery. Rabbit meniscal cells were cultured in the presence or absence of 0.5 μM simvastatin, and then real-time polymerase chain reaction was performed to evaluate gene expression. Results: The qualitative score was significantly higher in the simvastatin group after 8 and 12 weeks (P = .031 and .035, respectively). The mean OR and SOR were also significantly higher in the simvastatin group (OR at 8 weeks: 0.396 ± 0.019 [control] vs 0.564 ± 0.123 [simvastatin], P = .008; OR at 12 weeks: 0.451 ± 0.864 [control] vs 0.864 ± 0.035 [simvastatin], P = .001; SOR at 8 weeks: 0.071 ± 0.211 [control] vs 0.487 ± 0.430 [simvastatin], P = .009; SOR at 12 weeks: 0.093 ± 0.088 [control] vs 0.821 ± 0.051 [simvastatin], P = .006). Immunohistochemical analysis showed that at 12 weeks, the reparative tissue was more strongly positive for type I collagen (COL1), type II collagen (COL2), bone morphogenetic protein 2 (BMP-2), and BMP-7 in the simvastatin group than in the control group. Biomechanical analysis showed significantly higher stiffness in the simvastatin group (2.417 ± 1.593 N/ms [control] vs 5.172 ± 1.078 N/ms [simvastatin]; P = .005). In rabbit meniscal cells, BMP-2 and BMP-7 were upregulated after 4 and 8 hours and after 7 and 14 days, whereas COL1A1 and COL2A1 were significantly upregulated by simvastatin after 7 and 14 days. Conclusion: The local administration of simvastatin promotes the regeneration of an avascular meniscus in the rabbit model of a meniscal defect. The mechanism may involve the upregulation of BMPs and the subsequent upregulation of COL1 and COL2. Clinical Relevance: This study suggests that simvastatin stimulated intrinsic healing of an avascular meniscus. The local administration of simvastatin is safe and inexpensive and seems to be a promising treatment of meniscal injuries.