Hemostasis and microvascular function in type 1 diabetes : effects of treatment with statin and aspirin

Abstract: Background Patients with type 1 diabetes often develop microvascular complications and are at increased risk of premature cardiovascular disease. Women with type 1 diabetes lack the normal female protection against cardiovascular disease and may even be at higher risk compared with men with type 1 diabetes. Development of vascular complications may in part be explained by changes in hemostatic function in type 1 diabetes. Formation of a fibrin clot is the last step of the coagulation cascade and the structure of the formed clot reflects the environment in which it is formed. Tighter and less permeable fibrin clots are more resistant against degradation and are associated with cardiovascular risk factors and disease. Aims The aims of this work were to investigate in vitro fibrin clot properties in adult patients with type 1 diabetes in relation to sex and microvascular complications (Paper I); treatment effects of high-dose atorvastatin on fibrin clot properties (Paper II) and skin microvascular reactivity (Paper III); and effects of aspirin on fibrin clot properties (Paper IV). Methods The results are based on three studies: Paper I, a descriptive study involving 236 patients (107 females) with type 1 diabetes; Papers II and III, a randomized double- blind cross-over study in which 20 patients (10 females) with type 1 diabetes and dyslipidemia were treated daily with atorvastatin 80mg/day or placebo for two months; and Paper IV, a randomized cross-over study in which 24 patients (12 women) with good glycemic control and 24 patients (12 women) with poor glycemic control were treated with low (75 mg) and high (320 mg) doses of aspirin. Fibrin clot properties were assessed by determination of the permeability coefficient (Ks) and by turbidimetric clotting and lysis assays. Thrombin generation was investigated by assessment of plasma levels of prothrombin fragment 1+2 and tissue factor-induced thrombin formation in vitro. Plasma fibrinogen concentrations were measured by means of the Clauss method. Circulating levels of platelet and endothelial microparticles were investigated by flow cytometry. In Paper III, the effect of atorvastatin treatment on forearm skin microcirculation was investigated by way of laser Doppler perfusion imaging during iontophoresis of acetylcholine and sodium nitroprusside to assess endothelium-dependent and endothelium-independent microvascular reactivity. Various biochemical markers of endothelial function were also analyzed in this study. Results Paper I. Fibrin clot properties in vitro did not differ between men and women with type 1 diabetes. Women had worse glycemic control and higher thrombin generation. In women, fibrinogen concentration was the only determinant of fibrin clot permeability, while age and glycemic control also influenced clot permeability in men. Females younger than 30 years had less permeable fibrin clots and prolonged lysis time compared with age-matched men. Tighter and less permeable fibrin clots were also found in patients with poor glycemic control and in patients with microvascular complications. Associations between fibrin clot properties and microvascular complications were independent of glycemic control. Paper II. Treatment with high-dose atorvastatin (80 mg daily) was associated with increased fibrin clot permeability and reduced thrombin generation potential. In addition, reduced platelet microparticle concentrations and expression of prothrombotic antigens of platelet microparticles were found during atorvastatin therapy, indicating reduced platelet activation. These effects were independent of the lipid-lowering effects of atorvastatin. Paper III. Impaired endothelial-dependent skin microvascular reactivity and glycemic control was observed during atorvastatin treatment, concomitantly with a tendency towards increased levels of circulating endothelial microparticles. Paper IV. Treatment with aspirin at 75 mg daily had no effect on fibrin clot permeability, clot density or lysis time, while treatment with aspirin at 320 mg daily increased fibrin clot permeability and lag time in the turbidimetric clotting analyses. The beneficial effects of aspirin at 320 mg daily were more pronounced in patients with poor glycemic control. Conclusions Men and women with type 1 diabetes and no history of macrovascular disease have similar fibrin clot properties in vitro. Microvascular complications in type 1 diabetes are associated with formation of more prothrombotic fibrin clots. High-dose (80 mg/day) atorvastatin treatment in patients with type 1 diabetes and dyslipidemia induces positive effects on hemostatic function, while the endothelial-dependent skin microvascular function and glycemic control were impaired. Treatment with high-dose (320 mg/day) aspirin affects fibrin polymerization and increases fibrin clot permeability, whereas treatment with low-dose (75 mg/day) aspirin has no effect on fibrin clot characteristics in patients with type 1 diabetes.