Aim of the study was to correlate fibronectin (Fn) and von Villebrand factor (vWf) levels measured in plasma and in platelets with the progression of diabetic retinopathy. Patients were classified in five groups reflecting the progression of this microvascular complication, on the basis of fluorangiographic findings (0 = no microangiopathy; 1= simple microangiopathy; 2= oedematous retinopathy; 3= ischaemic retinopathy; 4= ischaemic proliferative retinopathy). 43 patients were studied, 22 suffering from type I diabetes and 21 from type II diabetes, according to the classification of National Diabetes Data Group. Fn and vWf were measured in plasma and in platelet samples using an original double-sandwich microELISA method and expressed as micrograms/ml or as micrograms/10* platelets. Platelets were counted and solubilized with 0.5% Triton × 100. Bleeding time and platelet adhesion to glass beads were also evaluated on every patient. Intraplatelet Fn levels were reduced in retinopathies and correlate with the severity of the microvascular alteration, being the difference significant between the two extreme groups (p<0.05). vWf intraplatelet levels were also significantly lower in patients with severe microvascular complications (p<0.05). No significant differences were detected for plasma Fn and vWf levels in the 5 groups. Intraplatelet Fn and vWf levels may therefore be considered as markers of the severity of diabetic retinopathy. The leakage of Fn and vWf from activated platelet and the incorporation of these glycoproteins in the subendothelial matrix may be responsible for the worsening of this microvascular complication.

We previously demonstrated that dexamethasone increases fibronectin (FN) expression by human umbilical vein endothelial cell (HUVEC) as well as its incorporation in the extracellular matrix (EM). FN is primarily involved in platelet/vessel wall interactions as well as in cell attachment to substrates. The in vivo anti-haemorragic effect of glucocorticoids could therefore be related either to a better spreading and attachment of endothelial monolayer to the basement membrane or to an increase of vessel wall reactivity to platelets. To further investigate this, we studied the effect of dexamethasone treatment on EM reactivity to platelets in an in vitro perfusion system. Second passage HUVEC were seeded on glass coverslips at a density of 105/cm2 and treated with dexamethasone 1.0 μM for 48 hours. EM were prepared by exposure to 0.1 M NH4OH for 30’. Coverslips carrying the EM were perfused with citrated whole blood in a flat perfusion chamber(*) at wall shear rates of 300 and 900 sec™1 for 5’. Platelet adhesion to EM was evaluated by a morphometric method. The number of platelet adhering to EM at both shear rates was significantly increased by dexamethasone treatment, (+51.9% at 300 sec™1 (p<0.001) and +24.3% at 900 sec™1 (p<0.01)). Our results demonstrate that dexamethasone increases endothelial EM reactivity to platelets possibly through an increase of FN deposition. This, together with FN effect on cell spreading and anchorage to EM, might be responsible for the antl-haemorrhagic action of glucocorticoids.(*) K. Sakanassen et al . , J . Lab. Cl in . Med. 102:522, 1983

Many different mechanisms are involved in thrombus formation. We compared the effects on haemostatic function of two drugs having different mechanism of action, the one interfering with arachidonic acid metabolic cascade (Indobufen) and the other (Ticlopidine) independent from it. 18 adult patients of both sexes suffering from cerebral Transient Ischaemic Attack (T.I.A.) or Reversible Ischaemic Neurologic Disability (R.I.N.D.) have been treated with Indobufen (400 mg daily) or Ticlopidine (500 mg daily) for three weeks. The effects on various haemostatic parameters including bleeding time, platelet adhesion to glass beads, platelet aggregation induced by ADP, collagen, platelet activating factor (PAF )f have been evaluated at the beginning and at the end of treatment. Both drugs prolonged the bleeding time, Ticlopidine being more effective than Indobufen. ADP-induced platelet aggregation was more effectively inhibited by Ticlopidine, while Indobufen was more effective on collagen-induced aggregation. PAF-induced platelet aggregation was inhibited by Ticlopidine, while Indobufen was ineffective. Platelet adhesion to glass beads was not influenced by treatment with either drugs. In conclusion, both drugs confirmed to be effective in inhibiting haemostatic function although with different mechanisms. Ticlopidine seems to be involved in more mechanisms, interfering with platelet aggregation induced by ADP, collagen, PAF and prolonging the bleeding time. Indobufen interferes with platelet aggregation induced by ADP and collagen, is less effective in prolonging the bleeding time, and does not affect PAF-induced platelet aggregation.