Objective - To characterize potential mechanisms of action of glucosamine inhibition of matrix metalloproteinase (MMP) expression and activity in lipopolysaccharide (LPS)-stimulated equine chondrocytes. Sample Population - Chondrocytes cultured from samples of metacarpophalangeal articular cartilage collected from cadaveric limbs of horses. Procedure - The effect of glucosamine on MMP activity in conditioned medium from LPS-stimulated cartilage explants was determined by a colorimetric assay with azocoll substrate. Treatments consisted of negative and positive controls, glucose (50mM), and glucosamine (50, 25, 6.25, 3, and 1.5mM), The influence of glucosamine on MMP synthesis was determined in chondrocytes in pellet culture incubated with LPS (20 μg/mL). Concentration of MMP-13 was quantified in spent medium via ELISA; nonspecific MMP activity was determined via azocoll digestion in organomercurial-activated medium. Effects of glucosamine on MMP mRNA concentration in similarly treated chondrocytes were determined by northern blot hybridization with MMP-1, -3, and -13 probes. Statistical analyses were performed with 2-way ANOVA. Results - Glucosamine had no effect on activated MMP activity but inhibited MMP protein expression, as determined by azocoll digestion (glucosamine, 3 to 50mM) and MMP-13 ELISA (glucosamine, 1.5 to 50mM). Resting mRNA concentrations for MMP-1, -3, and -13 mRNA were significantly lower in cultures exposed to glucosamine at concentrations of 50 and 25mM than those of positive controls. Conclusions and Clinical Relevance - Glucosamine appears capable of pretranslational, and possibly also translational, regulation of MMP expression; data suggest a potential mechanism of action for chondroprotective effects of this aminomonsaccharide.