INTERACTIONS OF PENTOSAN POLYSULFATE WITH CARTILAGE MATRIX PROTEINS AND SYNOVIAL FIBROBLASTS DERIVED FROM PATIENTS WITH OSTEOARTHRITIS

Pentosan polysulfate (PPS) has been shown to improve symptoms of patie nts with osteoarthritis (OA) when studied under double-blinded conditi ons. Laboratory studies indicated that this drug exhibits multiple act ions, including the preservation of articular cartilage (AC) proteogly cans in animal models of OA and the stimulation of hyaluronan synthesi s by synovial fibroblasts in vitro and in vivo. As PPS is strongly ani onic and has a molecular weight of similar to 5700 Da its ability to e nter connective tissues rich in proteoglycans and interact with the re sident cells has been questioned. In the present studies, experiments were undertaken to isolate and characterize proteins in human AC which have the potential to bind PPS. Thrombospondin was identified in 4.0 M GuHCl extracts of human AC as a PPS-binding protein. Furthermore, sy novial fibroblasts derived from OA joints were shown to secrete thromb ospondin and also bind PPS. Using bovine erythrocytes conjugated with PPS a resetting of the synovial fibroblast could be demonstrated. The level of resetting was not affected by pre-incubating cultures with th rombospondin antibody suggesting that PPS was interacting directly wit h the cells. Kinetic studies of H-3-PPS uptake by synovial fibroblasts showed saturation of binding sites within 30 min when cells were main tained at 4 degrees C but preservation of drug uptake for up to 120 mi n when cells were cultured at 37 degrees C. These data, together with the finding that cells labeled with drug at 37 degrees C showed higher incorporation, than at 4 degrees C after trypsin digestion suggests t hat PPS first binds to the cell membrane then at 37 degrees C is inter nalized, possibly by pinocytosis.