UDP-D-Xylose : Proteoglycan Core Protein β-D-Xylosyltransferase: A New Marker of Cartilage Destruction in Chronic Joint Diseases

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Abstract
We investigated the diagnostic significance of UDP-D-xylose:proteoglycan core protein .beta.-D-xylosyltransferase (EC 2.4.2.26) in different chronic joint diseases. This enzyme is located almost exclusively within chondrocytes, where it initiates the formation of chrondroitin sulphate during the biosynthesis of proteoglycans and from which it is easily released after damage of articular cartilage. Xylosyltransferase activity was determined in synovial fluid and serum by a radiochemical method, based on the incorporation of [14C]xylose from UDP-[14C]xylose into an exogenous acceptor protein. Serum has been shown to be the appropriate material for the determination of xylosyltransferase activity in blood, since in plasma fibrinogen causes an inhibition of enzyme activity of about 50%. The catalytic concentrations of xylosyltransferase in synovial fluids and sera of patients with chronic joint diseases (n = 131) ranged from 0.5 to 22.0 mU/l and from 0.8 to 5.6 mU/l, respectively. On most cases we found higher xylosyltransferase activities in synovial fluids than in the corresponding sera. The highest catalytic concentrations of the enzyme were observed in the synovial fluids of patients suffering from rheumatoid arthritis (median value: 5.56 mU/l, 90%-range: 3.2-22.0 mU/l). Synovial fluids of patients with arthritis urica, however, showing a comparable high degree of inflammation, contained lower enzyme catalytic concentration (median value: 2.38 mU/l, 90%-range: 0.7-5.2 mU/l), which were in the range of those in osteoarthrosis (median value: 2.50 mU/l, 90%-range: 0.8-4.8 mU/l). The higher xylosyltransferase activities in rheumatoid synovial fluids seem to be attributed to an increased cartilage destruction during the course of this disease. Our results demonstrate that xylosyltransferase activity in the synovial fluid represents an appropriate clinical chemical parameter, indicating the degree of cartilage destruction in chronic joint diseases. The serum xylosyltransferase activities of patients with various chronic joint diseases, however, showed no significant differences.

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