Uremic patients have decreased shear-induced platelet aggregation mediated by decreased availability of glycoprotein IIb-IIIa receptors

Abstract

Bleeding and platelet dysfunction are prominent features of uremia. Shear-induced platelet aggregation (SIPA) involves the interaction of von Willebrand factor (vWF) with platelet membrane glycoproteins (GP) Ib and IIb-IIIa, the same receptor-ligand pair involved in in vivo adhesion and aggregation of platelets in the arterial circulation. We have used a modified rotational cone-plate viscometer to measure SIPA and calcium flux in platelets. Flow cytometric analysis of the surface expression of GP Ib and IIb-IIIa was performed using fluorescein isothiocyanate-conjugated monoclonal antibodies CD42b and CD41a, respectively. Uremic patients showed decreased SIPA (controls, 43% ± 2% [mean ± SEM]; chronic renal failure patients, 36% ± 3%; chronic hemodialysis patients, 26% ± 2%; P < 0.0001) along with a decrease in GP IIb-IIIa (controls, chronic renal failure patients, and chronic hemodialysis patients, 840 ± 25, 649 ± 42, 661 ± 38 mean fluorescence intensity, respectively; P < 0.0001). Glycoprotein Ib in uremic patients was not significantly different from normal. Chronic hemodialysis patients also demonstrated increased platelet-bound fibrinogen ( P < 0.0001) and platelet-bound vWF ( P = 0.01). Calcium flux and thromboxane B 2 generation during SIPA of uremic platelets were normal. However, uremic plasma showed twice the normal concentration of vWF ( P < 0.0001) and sodium dodecyl sulfate agarose gel electrophoresis revealed the presence of fibrinogen fragments. Mixing experiments demonstrated an inhibitory effect of uremic plasma on SIPA of normal platelets (decreased from 39% ± 3% at baseline to 31% ± 3% after incubation in uremic plasma) along with an activation-independent increase in platelet-bound fibrinogen and platelet-bound vWF. When uremic platelets were incubated in normal plasma, their SIPA increased (from 12% ± 5% at baseline to 18% ± 4% after incubation in normal plasma; P = 0.002), although it did not return to normal. These results suggest that the uremic platelet dysfunction results from decreased GP IIb-IIIa availability due to receptor occupancy by fibrinogen fragments (and possibly vWF fragments).