EFFECT OF REACTIVE OXYGEN SPECIES ON THE BIOSYNTHESIS AND STRUCTURE OF NEWLY SYNTHESIZED PROTEOGLYCANS

The effect of reactive oxygen species (ROS) generated by a xanthine ox idase hypoxanthine system (mainly H2O2) on proteoglycan (PG) metabolis m and structure was investigated in vitro, using cell monolayers of cu ltured rabbit articular chondrocytes and purified resident and newly s ynthesized proteoglycans. It was shown that ROS generated in this syst em frequently stimulate (at low concentrations), and consistently inhi bit (at higher concentrations), the incorporation of (SO4)-S-35 and H- 3-glucosamine into PG molecules synthesized by cultured chondrocytes. The inhibition of isotopes' incorporation at higher enzyme concentrati ons was suppressed completely by heating xanthine oxidase and allopuri nol with superoxide dismutase (SOD) and catalase. ROS at high concentr ation also inhibited H-3-uridine incorporation but had no effect on (S O4)-S-35 and H-3-uridine uptake by the cells. They also alter hyaluron an (HA) and PG monomers by fragmenting the core protein moiety and des troying the hyaluronic acid binding region. Altered PG monomers do not interact with HA to form complexes, but fragmented HA still retain a significant PG monomer-binding capacity. PG-HA complexes are easily an d irreversibly destroyed by ROS. These results suggest that ROS may at low fluxes stimulate PG-synthesis under physiological conditions and alter cartilage metabolism and structure in conditions where they are overproduced, such as in rheumatoid arthritis, and in hemochromatosis and other iron storage diseases.