Using a novel hydrogen peroxide heating method, we synthesized milky white, water-soluble polyhydroxylated fullerenes (fullerenols) with 36-40 hydroxyl groups (estimated average) along with 8-9 secondary bound water molecules. The fullerenols exhibited high water solubility up to 58.9 mg/mL in a neutral (pH = 7) condition. Dynamic light scattering analysis showed a high dispersion property, to give a narrow particle size distribution within 0.7-2.0 nm.

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Objective. Studies have shown the roles of oxidative stress in the pathogenesis of osteoarthritis (OA) and induction of chondrocyte senescence during OA progression. The aim of this study was to examine the potential of a strong free-radical scavenger, watersoluble fullerene (C60), as a protective agent against catabolic stress-induced degeneration of articular cartilage in OA, both in vitro and in vivo.Methods. In the presence or absence of C60 (100 M), human chondrocytes were incubated with interleukin-1␤ (10 ng/ml) or H 2 O 2 (100 M), and chondrocyte activity was analyzed. An animal model of OA was produced in rabbits by resection of the medial meniscus and medial collateral ligament. Rabbits were divided into 5 subgroups: sham operation or treatment with C60 at 0.1 M, 1 M, 10 M, or 40 M. The left knee joint was injected intraarticularly with watersoluble C60 (2 ml), while, as a control, the right knee joint received 50% polyethylene glycol (2 ml), once weekly for 4 weeks or 8 weeks. Knee bone and cartilage tissue were prepared for histologic analysis. In addition, in the OA rabbit model, the effect of C60 (10 M) on degeneration of articular cartilage was compared with that of sodium hyaluronate (HA) (5 mg/ml).Results. C60 (100 M) inhibited the catabolic stress-induced production of matrix-degrading enzymes (matrix metalloproteinases 1, 3, and 13), downregulation of matrix production, and apoptosis and premature senescence in human chondrocytes in vitro.In rabbits with OA, treatment with water-soluble C60 significantly reduced articular cartilage degeneration, whereas control knee joints showed progression of cartilage degeneration with time. This inhibitory effect was dose dependent, and was superior to that of HA. Combined treatment with C60 and HA yielded a significant reduction in cartilage degeneration compared with either treatment alone. Conclusion.The results indicate that C60 fullerene is a potential therapeutic agent for the protection of articular cartilage against progression of OA.During the development of osteoarthritis (OA), mechanical and chemical stresses on articular cartilage change the stable cellular activities of chondrocytes and stimulate the production of growth factors and matrix proteins as well as inflammation mediators (1-4). It is well known that catabolic-stressed chondrocytes produce excess amounts of reactive oxygen species (ROS) (superoxide, nitric oxide, hydrogen peroxide, and peroxynitrite) as well as proinflammatory cytokines and chemokines (4-9).Studies have provided ample confirmation of the generation of ROS and the depletion of cellular antioxidants in degenerated articular cartilage (8-10). Numerous reports have indicated that the degeneration of articular cartilage is partially mediated by oxygenderived free radicals (8-12). Kurz et al reported that the extent of mechanical stress on articular cartilage is sufficient to stimulate an excess production of ROS from chondrocytes, leading to depolymerization of hyaluronic acid and chondrocyte death (11,12). Similarly, Gree...