GLYCOSPHINGOLIPID INHIBITION OF THE ADHESION OF THROMBIN-ACTIVATED PLATELETS TO SURFACES IS POTENTIATED BY ALBUMIN

Previous studies have shown that exogenous glycosphingolipids (GSLs) i nhibit the adhesion of thrombin-activated platelets (TAP) to polystyre ne plates coated with various RGD-ligands (where RGD is the peptide se quence Arg-Gly-Asp), suggesting that GSLs can modulate the platelet in tegrin receptor glycoprotein IIb-IIIa. However, albumin was always use d as a plastic surface-blocking agent in these studies. In order to ev aluate the role of albumin in these experiments, we studied the effect of various GSLs and albumin on the interaction between TAP and hydrop hobic surfaces in a solid-phase assay using indium-111-labelled platel ets and polystyrene plates. TAP (10(8) platelets/ml) adhered to polyst yrene (half-saturation time 40 +/- 3 min) with a maximal adhesion dens ity of 56 +/-1 x 10(3) platelets/mm2. Platelet adhesion was only sligh tly affected (< 11% inhibition) by immobilized bovine serum albumin, i mmobilized mixed bovine brain gangliosides (MBG) or fluid-phase MBG. I n contrast, fluid-phase MBG was an effective inhibitor of platelet adh esion to polystyrene (> 46% inhibition), but only after albumin was fi rst immobilized to the plate. Covering albumin-coated polystyrene with MBG, followed by washing, was as effective as fluid-phase MBG at inhi biting platelet adhesion, thus indicating that a ganglioside-albumin i nteraction at the polystyrene surface was responsible for effective in hibition. When purified GSLs were substituted for MBG, it was found th at all those tested (GT1b, GD1a, GM1, asialo GM1 and globoside) had si milar inhibitory activity. Thus, GSLs non-specifically inhibit the pla telet-polystyrene interaction after albumin potentiation, in which it appears there is formation of GSL-albumin complexes on plastic surface s. These findings provide a better basis on which the results of any c ellular adherence study involving GSLs, albumin and hydrophobic surfac es may be properly interpreted.