Summary

Protease nexin-1 (PN-1) is a non-circulating pericellular serpinexpressed by vascular cells.PN-1 inhibits different proteases butwhen associated with glycosaminoglycans, its activity is mainlydirected towards thrombin. Fucoidans are sulphated polysaccharideswhich can interact with several serpins and have antithromboticand anticoagulant properties in vivo with a lowerhemorrhagic risk than heparin.The purpose of this study was tocompare the effects of low (LMW) or high molecular weight(HMW) fucoidans to those of standard heparin and LMW heparinon PN-1 properties. Using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOFMS) and affinity coelectrophoresis, we observed that polysaccharidesbound to thrombin,PN-1 and the thrombin/PN-1 complex.Progress curve kinetics showed that LMW and HMW fucoidansaccelerate thrombin inhibition by PN-1 (111 and 402 fold, respectively) whereas the acceleration by LMW heparinand standard heparin was only of 36– and of 307-fold, respectively.Moreover, the formation of PN-1/125I-thrombin complexwas increased in the presence of heparin, HMW and LMW fucoidans,but barely by LMW heparin. The dose response followeda bell shape curve, again suggesting the formation of ternarycomplexes between thrombin, PN-1 and polysaccharides.We also investigated the ability of polysaccharides to removePN-1 bound to the cell membrane of smooth muscle cells in culture.PN-1 was detached by fucoidans and heparins and was stillable to inhibit thrombin. In conclusion, fucoidans reduce cell-associatedPN-1 and thrombin/PN-1 complexes and increase theantithrombin activity of PN-1.The capacity of PN-1 to regulatethe pericellular activity of thrombin amongst other proteasesreinforces the therapeutical interest of f