Interaction of heparinoids with platelets: comparison with heparin and low molecular weight heparins

Heparin interacts with platelets to impair collagen-induced aggregation and adhesion to collagen. Low molecular weight heparin and heparinoids have little or no inhibitory activity in these platelet-collagen interactions. Thrombin-induced aggregation of platelets is inhibited by any of the glycosaminoglycans that will block the action of thrombin on fibrinogen. However, heparin is a much more potent inhibitor than low molecular weight heparins or heparinoids at equigravimetric concentrations in these reactions. The inhibition of ristocetin or asialo-von Willebrand factor aggregation of platelets is partially blocked by high dose heparin but not by low molecular weight heparin or heparinoids. The heparin-induced IgG antibody, produced to a heparin-platelet complex, aggregates platelets strongly in the presence of heparin, less strongly in the presence of low molecular weight heparins and pentosan polysulfate and not at all with dermatan sulfate or the pentasaccharide. Heparan sulfate does interact with platelets and this antibody, which is of interest because of the heparan sulfate on endothelial cells. Clinical information to date suggests a low incidence of heparin antibodies in patients receiving only low molecular weight heparin of the depolymerized type. Whether long-term clinical use of low molecular weight heparins, heparan sulfate, and dermatan sulfate will give rise to specific antibodies that would cause a similar problem as heparin remains to be seen.