In 41 diabetics (27 type I, 14 type 11) and in 23 healthy controls the number of glycoprotein (GP)

Increased functional properties of diabetic platelets might be already conditioned during thrombopoiesis in the stem cell system. This hypothesis was studied by recording the distribution characteristics of the peripheral platelet pool in 218 diabetic patients versus 51 controls. Furthermore, platelet membrane coating with the stem cell marker glycoprotein IB was analyzed in 41 diabetic subjects and compared to 23 healthy volunteers. A consistent, significant shift of the volume distribution to larger platelets was found in diabetics: Mean platelet volume (MPV) - 7.9 +/- 0.9 versus 7.2 +/- 0.8 [fl]; Megathrombocyte index (MTI) - 20.4 +/- 2.8 versus 18.1 +/- 2.5 [fl]. These deviations were present in all patient subsets, however did not correlate to parameters of glucose metabolism. Whole blood platelet count was increased in the patient group; 195.0 +/- 59.5 versus 184.0 +/- 37.5 x 10(3) plts/ul. Coating with glycoprotein IB receptors correlated significantly to platelet size in platelets of both controls and diabetics (r normal = 0.52 +/- 0.07; r diabetic = 0.46 +/- 0.1). The quantitative expression of glycoprotein IB was significantly enhanced in the diabetic group: 54,500 x 1.28 +/- 1 versus 39,100 x 1.3 +/- 1 molecules per platelet. In conclusion, these findings strongly support the assumption of diabetic stem cell dysfunction of the megakaryocytic series and progenitor cells resulting in platelets with primarily increased potency to adhere and aggregate in diabetes mellitus.

Adhesion molecules such as P-selectin (CD 62), glycoprotein (CP) 53 (CD63) and thrombospondin play a decisive role in the thrombogenic transformation of platelets. Here we present evidence obtained using flow cytometric analysis that the PGI(2)-mimetics iloprost and taprostene, and an NO (EDRF)donor (SIN-1) are able to inhibit the expression of P-selectin, GP 53 and thrombospondin on human platelets activated by submaximal concentrations of thrombin. Since the half-maximal concentrations for inhibition of antigen expression (0.15 nM for iloprost, 3.0-5.3 nM for taprostene) are much lower than for activation of adenylate cyclase (1.4 nM for iloprost and 29.4 nM for taprostene) our data suggest that the occupation of a small number of PGI(2)-receptors is sufficient to inhibit the thrombogenic transformation and that spare PGI(2)-receptors are present on human platelets. In diabetes, the EC(50) for inhibition of expression of platelet antigens is shifted to higher concentrations suggesting that platelets from type 1 diabetic patients are partly resistant to PGI(2). Since the dose dependent increase in c-AMP by iloprost is not changed and intraplatelet c-AMP is elevated in platelets of diabetic patients, we assume that steps in the activation cascade subsequent to activation of adenylate cyclase are disturbed in diabetes.

Formation of a hemostatic plug is triggered by platelets. Platelet function (e.g. adhesion, aggregation) depends essentially on membrane bound receptor proteins. Conventional chromatographic analysis of these glycoprotein macromolecules is difficult and not appropriate for diagnostic routine. In combination of cytoflowmetric single cell analysis with monoclonal staining we developed a bio-assay for qualitative and semi-quantitative analysis of glycoprotein IB and IIB/IIIA on vital fixed platelets. The expression of these molecules was evaluated in 20 healthy volunteers. The assay offers for the first time the possibility of screening the expression of receptor proteins on platelet membranes, which are related to indicate either a functional lack in bleeding disorders or a prethrombotic state due to an enhanced functional potential in high risk patients.