Preferential incorporation of glucosamine into the galactosamine moieties of chondroitin sulfates in articular cartilage explants

Objective. To determine the metabolic fate of glucosamine (GlcN) in intact articular cartilage tissue. Methods. Intact articular cartilage explants were cultured for up to 13 day s in Dulbecco's modified Eagle's medium supplemented with 1) 1-C-13-labeled GlcN, 2) 1-C-13-labeled glucose (Glc), or 3) no labeling. Every 3-4 days, samples were removed and frozen in liquid nitrogen for carbon-13 magnetic r esonance spectroscopic (MRS) analysis. The metabolic products of the labele d precursors were determined from the MRS data based on resonance positions and comparison with known standards and published values. Results. GlcN was taken up by the chondrocytes and incorporated selectively into the hexosamine, but not the hexuronic acid, components of the glycosa minoglycan chains of articular cartilage proteoglycan. The data also demons trated that GlcN is the substrate of choice for the galactosamine moieties of the chondroitin sulfates, incorporating at levels 300% higher than with an equivalent amount of labeled Glc. Conclusion. The results indicate that GlcN facilitates the production of pr oteoglycan components that are synthesized through the hexosamine biochemic al pathway.