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

Abstract

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 days in Dulbecco's modified Eagle's medium supplemented with 1) 1-13C-labeled GlcN, 2) 1-13C-labeled glucose (Glc), or 3) no labeling. Every 3-4 days, samples were removed and frozen in liquid nitrogen for carbon-13 magnetic resonance spectroscopic (MRS) analysis. The metabolic products of the labeled 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 glycosaminoglycan chains of articular cartilage proteoglycan. The data also demonstrated 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 proteoglycan components that are synthesized through the hexosamine biochemical pathway.