Serum keratan sulfate transiently increases in the early stage of osteoarthritis during strenuous running of rats: protective effect of intraarticular hyaluronan injection

INTRODUCTION Osteoarthritis is influenced by genetic and environment factors, including mechanical stress; however, the relationship between running and the development of osteoarthritis remains a matter of controversy. We investigated whether osteoarthritic change could be obtained in a rat strenuous running model, whether serum keratan sulfate in rats could be detected by HPLC and was associated with onset or progression of osteoarthritis, and whether hyaluronan injection suppressed development of osteoarthritis and elevation of serum keratan sulfate. METHODS Wistar rats were forced to run 30 km in 6 weeks on a treadmill machine. Articular cartilage of the knees was evaluated macroscopically and immunohistologically. Serum keratan sulfate was examined every week by HPLC. The effect of weekly knee injection of hyaluronan was also investigated. RESULTS Cartilage surfaces stained with India ink became irregular, metachromasia by safranin-O staining appeared to be almost lost, and Mankin's score significantly worsened after 30 km of running. Serum keratan sulfate in rats was detected by HPLC and transiently increased (peaked at 3 to 4 weeks) along with depletion of keratan sulfate in cartilage tissue. Hyaluronan treatment suppressed morphological progression of osteoarthritis and elevation of serum keratan sulfate. CONCLUSION Rat strenuous running induced osteoarthritis. Serum keratan sulfate was associated with progression of osteoarthritis. Weekly intraarticular injection of hyaluronan controlled the development of osteoarthritis, and the effect was reflected by serum keratan sulfate.