Effect of oral glucosamine on cartilage and meniscus in normal and chymopapain-injected knees of young rabbits

Objective. To determine if oral glucosamine (GlcN) improves joint biology after acute damage by a protease. Methods. The effect of 8 weeks of dietary GlcN (20 or 100 mg/kg/day) on knee joint cartilage was evaluated in 2.2-kg male NZW rabbits with and without damage introduced by intraarticular injection of chymopapain (CP). Cartilage was evaluated histologically and scored according to the Mankin scale. Analyses of total hydroxyproline and glycosaminoglycan (GAG) contents and reverse transcription-polymerase chain reaction (RT-PCR) analysis of selected genes were performed. Results. After 8 weeks, there was no effect of GlcN on the GAG content of normal cartilage. Both levels of GlcN treatment significantly increased the sulfated GAG content in the cartilage of the medial femoral condyle in damaged and contralateral knees, but did not change the collagen content. In CP-injected knees, there was still some loss of surface proteoglycan (PG) that was not completely corrected by dietary GlcN. Even after 8 weeks, levels of messenger RNA (mRNA) detected by RT-PCR showed changes indicative of damage and repair, such as elevated type II collagen mRNA, and these levels were not influenced by GlcN treatment. Meniscal GAG content was increased in the contralateral knee of rabbits receiving high-dose, GlcN, but was decreased in those receiving no GlcN or low-dose GlcN. Neither diet nor treatment affected the meniscal collagen content. Conclusion. These results suggest that oral GlcN treatment might be useful in a situation where GlcN is limiting, such as where there is a rapid replacement of cartilage PG.