Profile of glycosaminoglycan-degrading glycosidases and glycoside sulfatases secreted by human articular chondrocytes in homeostasis and inflammation

Objective. To determine enzymatic activities of the 8 key glycosaminoglycan -degrading glycosidases and glycoside sulfatases in cultured human articula r chondrocytes and in synovial fluid from patients with osteoarthritis. Methods. The following enzymes were analyzed: hexosaminidase and its isoenz yme A, N-acetyl-alpha-D-glucosaminidase, beta-galactosidase, beta-glucuroni dase, alpha-L-iduronidase, aryl sulfatase, and galactose-6-sulfate sulfatas e. Activity of the selected enzymes was analyzed by fluorometry with the ai d of 4-methylumbelliferryl derivatives of the appropriate monosaccharides. Results. Hexosaminidase was found to be the dominant enzyme released by cho ndrocytes into the extracellular compartment. Stimulation of chondrocytes w ith interleukin-1 beta resulted in a selective increase of the extracellula r hexosaminidase activity and, to a lesser degree, of the extracellular bet a-galactosidase activity, without significant changes in the activity of th e other studied enzymes. Analysis of the pH dependency of the enzymatic act ivities revealed that even at neutral pH, hexosaminidase expressed a measur able activity, much higher than the activity of the other studied enzymes. Chondrocyte apoptosis did not result in increased extracellular glycosidase activities, including hexosaminidase activity. The spectrum of glycosidase and glycoside sulfatase activities in the synovial fluid from patients wit h osteoarthritis was similar to that in cultured human articular chondrocyt es. Conclusion. These data support the concept that lysosomal glycosidases, in particular hexosaminidase, represent a distinct subset of cartilage matrix- degrading enzymes that are activated by proinflammatory stimuli.