Platelet dependent thrombosis, blood thrombogenicity and response to antiplatelet therapy in health, ageing and type 2 diabetes mellitus

Abstract

Elderly and type 2 diabetes mellitus (T2DM) patients with stable coronary artery disease (CAD) have increased risk of atherothrombotic events despite recommended secondary prevention therapy. High platelet reactivity drives this risk. Novel approaches to antiplatelet therapy are needed. Objectives: To:  determine the effect of age and T2DM on blood thrombogenicity and response to dual antiplatelet therapy in stable CAD  assess the effect of changes in platelet count on thrombus quantity and quality with Rafigrelide Methods: Study 1: Patients with stable CAD, 4 groups: age<75 non-DM, age≥75 T2DM, age≥75 non-DM and age<75 T2DM studied at baseline and one week after clopidogrel. I performed Badimon chamber study, thromboelastography, VerifyNow® and Multiplate® aggregometry, coagulation and inflammatory biomarkers and scanning electron microscopy. Study 2: Twelve volunteers took Rafigrelide (novel platelet lowering agent) singly and then with aspirin. I performed Badimon chamber study and thromboelastography at pre-defined intervals. Results: Study 1: At baseline and after clopidogrel therapy, there was no difference in thrombus area between the four groups. Serum TNFα levels were higher in elderly T2DM patients. Other coagulation and inflammatory markers were similar between the groups. Clopidogrel reduced thrombus area, lowered platelet content of thrombus and increased fibrin diameter and density in all four groups. Elderly and T2DM patients demonstrated high platelet reactivity and hyporesponsiveness to clopidogrel. Significant reduction in thrombus area was demonstrated both in good- and hypo-responders to clopidogrel. Point of care tests and thrombus area showed no correlation. Post chamber blood confirmed release of P selectin, CD40 ligand and PAI-1 from activated platelets. ii Study 2: Rafigrelide reduced platelet count and thrombus area, delayed initiation of clot formation and reduced over all clot strength. Platelet count positively correlated with thrombus area. Conclusion: Elderly and T2DM patients had similar over all blood thrombogenicity but higher platelet reactivity when compared to young and non-diabetic patients. Addition of clopidogrel reduced thrombus area with ultrastructural changes in fibrin favouring fibrinolysis. Reduction in platelet count with Rafigrelide reduced thrombus formation and lowered viscoelastic strength. Dual antiplatelet therapy and novel therapeutic strategies may reduce future thrombotic risk in these high risk populations.